Adnan PhD Thesis.pdf - Pakistan Research Repository

STUDIES ON IMPREGNATED CATALYSTS FOR

CONVERSION OF WASTE EXPANDED

POLYSTYRENE INTO VALUE ADDED

HYDROCARBONS

Ph.D Thesis

By

ADNAN

INSTITUTE OF CHEMICAL SCIENCES

UNIVERSITY OF PESHAWAR

PAKISTAN

MAY 2014

STUDIES ON IMPREGNATED CATALYSTS FOR

CONVERSION OF WASTE EXPANDED

POLYSTYRENE INTO VALUE ADDED

HYDROCARBONS

By

ADNAN

DISSERTATION

SUBMITTED TO THE UNIVERSITY OF PESHAWAR IN

PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR

THE DEGREE OF DOCTOR OF PHILOSOPHY

IN CHEMISTRY



PAKISTAN

MAY 2014



PAKISTAN

Certified that MR ADNAN S/O ABDUL RAUF has carried out his research and

experimental work on the topic entitled as “Studies on Impregnated Catalysts for

Conversion of Waste Expanded Polystyrene into Value Added Hydrocarbons” under

our guidance and supervision. His research work is original and his dissertation is worthy

of presentation to the University of Peshawar for the award of degree of Doctor of

Philosophy in Chemistry.

______________________ _______________________

SUPERVISOR CO-SUPERVISOR

Meritorious Prof. Dr. Jasmin Shah Prof. Emeritus Dr. Muhammad Rasul Jan

Institute of Chemical Sciences Institute of Chemical Sciences,

University of Peshawar, Pakistan, University of Peshawar, Pakistan

Khyber Pakhtunkhwa, Pakistan Vice Chancellor,

University of Peshawar, Peshawar,

Khyber Pakhtunkhwa, Pakistan

_____________________

EXTERNAL EXAMINER

In the name of ALLAH, the most Beneficent, the most Merciful.

Parents With Prayers and Love

To My

ACKNOWLEDGEMENTS

In the name of ALLAH, the most Gracious, the most Compassionate, Who is the Creator of

the heavens and the earth and He, Who guides us in oceans of darkness and difficulties. I

would like to express my gratitude to Allah for providing me the blessings to accomplish this

work. May Allah accept this work as Sadqa-e-Jaria for helping the environment and His

creation, and reward us the highest level in Jannah. During my PhD a number of people

contributed, to whom my words are insufficient to acknowledge.

First, I submit my highest appreciation to my primary supervisor, meritorious professor Dr.

Jasmin Shah, whose institution elevated me to the stature I am today, who have been my

parent, my mentor, my confidant, my colleague, and a never-ending fount of moral support.

Whose guidance, stimulation, valuable suggestions, constant encouragement and

affectionate behavior helped me to complete this work. She encouraged me to not only

grow as a researcher and as a chemist, but also as an instructor and an independent thinker.

She is an excellent example of a good and successful women chemist.

I am also obliged to my co-supervisor professor emeritus Dr. Muhammad Rasul Jan, whose

thought provoking attitude, skilled discussions, highly specialized guidance, constant

support and continuous feedback enabled me to complete this thesis. I am thankful to him

and acknowledge his devotion and precious time.

In fact, I am truly thankful to both of them and find myself lucky to have such teachers, who

cared so much about me and my work. I pray, may Allah shower His endless blessing upon

them and reward them according to His Generosity.

I would also like to mention my foreign advisor Ah-Hyung Alissa Park, Associate Professor,

Department of Earth and Environmental Engineering, Columbia University, New York, USA.

I am thankful to her for providing me the opportunity to work as a visiting researcher in her

lab. I learned much more from her company. I am also thankful to Greeshma Gadikota, post

doctorate researcher at Prof. Park Group for her help and guidance in writing skills.

I acknowledge the funding of Higher Education Commission of Pakistan under 5000 PhD

Indigenous Scholarship Program, Pin No. 106-1039-Ps6-033 and under International

Research Support Initiative Program (IRSIP), Pin No. IRSIP 24 PS 13. I am also thankful to the

Director and all the faculty of Institute of Chemical Sciences, University of Peshawar for

providing me help, facilities and encouragement in perusing my higher education in

chemistry.

After my teachers I would mention two of my friends because of whom inspiration I believe

I am here, Mr. Arif Khalil and Mr. Abdus Salam. Their constant support, unique guidance

towards getting knowledge heighted me in the skies.

Words cannot express the role of my uncle Dr. Abdul Ahad, who was a role example for me

and he was the one whose teachings led me here.

I am thankful to the teaching faculty of our section Assistant Prof. Dr. Kashif Gul, Dr.

Sajjadullah and Mrs. Saima Sohni.

I am obliged to Mr. Iftikhar Ahmad, Mr. Zia ur Rehman, Mr. Hamid Ali, Mr. Asmat Ali, Mr.

Zaheer ud Din, Mr. Muhammad Ali, other clerical and para teaching staff.

In my PhD lab. work, my lab. colleagues have a major role and they have to be mentioned

individually. I am thankful to Dr. Hussain Gulab for his true heartier suggestions, Dr. Atta ul

Haq for extreme sincerity, Dr. Mian Muhammad for his constant encouragement and boost

up, Dr. Behisht Ara for kind guide and gentle handling, Dr. Maria Sadia for creation of trust

and self-confidence, Dr. Inayatullah for his soft accent with kind heart, and a man of

principles, Dr. Sultan Shah for his wise talks, advises and sea of knowledge, Dr. Muhammad

Naeem for his friendly brother hood, moral support and working efficiency, Mr, Mansoor

Khan for his joyful discussions, enhancing personality and constant partnership, Ms. Salma

Amir for her companionship and enhancing quench of knowledge, Ms. Tasmia for her

believes and approach toward gaining knowledge, Mr. Aamir Iqbal for his good attitude

toward research and social work, Mr. Ibadat ur Rehman for his learning techniques Mr.

Muhammad Zada as co-worker. I would like to mention my other colleagues also Dr. Farhat

un Nissa, Dr. Sadaf Durani, Dr. Ubaid Khan, Mr. Aamir Javed, Mr. Sajjad Khan, Mr. Zeeshan

Khan, Ms. Mutaqia, Ms. Faiza Bakhtiar.

I have to mention the companionship and support of my roommates. Mr. Masaud Shah, Mr.

Gul Mar Jan, Mr. Rashid Khan, Mr. Naqeeb Ahmad Jan, Mr. Yahya Jamal, Mr. Ayaz Khan and

finally my US roommates Mr. Samiullah Khan and Mr.Muzafar Shah, who waited for me till

late nights and cared about me.

There are many people behind the screen, who encourage and support me during my PhD

studies. I would like to thank and acknowledge my friends of: PhD A1 Group; Dr. Faridoon,

Dr. Nasirullah, Dr. Muhammad Ikram, Dr. Waqas Ahmad, and Dr. Ihsan Ali. Swat A1 Group;

Mr. Zahid Ali, Mr. Mehboob Alam, Mr. Murad Alam, Mr. Iftikhar, Mr. Qayum, Mr. Kher

Muhamamd and Dr. Faiz Muhammad.

I cannot not forget the favors of my friends Mr. Shakil Khan, and my uncle Mr. Mehboob Ali,

Mr. Umer Farooq Khalil, Mr. Ikramullah, Mr. Nabiullah, Mr. Iqbal Yousaf, Mr. Shafiq Ahmad,

Mr. Afzal Khan, Mr. Hussain Ahmad, Mr. Salman Khan, Mr. Munir Khan, Mr. Shujaat Ali Khan,

Dr. Pervaiz Khan, Dr. Barkatullah and Mr. Arshad Khan. I would like to extend my words and

express my deepest gratitude and thanks to Mr. Umer Farooq Khalil.

I must acknowledge the help and support of Prof. Robert J. Farrauto (Bob Farrauto), Asst.

Prof. Junfeng Wang, Mr. Xiazhou (Hellius) Zhou, Ms. Sarah Frances Teevan, Mr. Kyle Fricker,

Shanxue Jiang and Dr. Ioannis Valsamakis, who all helped me in Lab. work during my stay at

Columbia University-in the City of New York, USA.

At the end, I have to mention my family; my father, my mother, my brothers, my sisters, my

late grandmother (May Allah keep her soul in rest and peace) and other relatives, whose

prayers and continuous moral support enabled me to achieve this hard task done.

ADNAN

University of Peshawar

May 2014

i

TABLE OF CONTENTS

S. No. Title Page No.

LIST OF FIGURES vi

LIST OF TABLES xiv

ABBREVIATIONS xix

SUMMARY xxxi

CHAPTER 1. INTRODUCTION

1.1 Catalysts and Catalysis 1

1.2 Classification of catalysts 1

1.2.1 Homogenous catalysts 1

1.2.2 Heterogeneous catalysts 2

1.3 Preparation of supported catalysts 5

1.3.1 Introduction of active phase 5

1.3.2 Drying and calcination 7

1.3.3 Reduction or activation 7

1.4 Catalyst performance parameters 7

1.4.1 Activity 7

1.4.2 Selectivity 7

1.4.3 Stability and regenerability 8

1.5 Plastics and its types 8

ii

1.6 Polystyrene and its applications 9

1.7 Environmental impact of polystyrene 9

1.8 Plastic waste management 10

1.9 Chemical recycling or tertiary recycling 11

1.9.1 Depolymerization 11

1.9.2 Partial oxidation 11

1.9.3 Degradation or cracking or pyrolysis 11

1.10 Polystyrene degradation mechanism 13

1.10.1 Thermal degradation (radical mechanism) 14

1.10.2 Catalytic degradation (ionic mechanism) 19

1.11 Aim of the present work 22

References 23

CHAPTER 2. LITERATURE REVIEW

2 Literature Review 32

References 42

CHAPTER 3. EXPERIMENTAL

3.1 Catalysts preparation 46

3.2 Characterization of catalysts 47

3.2.1 Surface area, pore volume and pore size analysis 47

3.2.2 SEM analysis 47

iii

3.2.3 XRD analysis 48

3.3 Thermogravimetric analysis (TGA) 48

3.3.1 TGA of waste expanded polystyrene (WEPS) 48

3.3.2 TGA of polystyrene (PS) and polyethylene terephthalate (PET) 48

3.4 Thermal and catalytic degradation of polymer samples 49

3.4.1 Thermal and catalytic degradation of WEPS 50

3.4.1.1 Reactor assembly 50

3.4.1.2 WEPS sample preparation 51

3.4.1.3 WEPS degradation 51

3.4.1.4 Liquid products collection in bulk 52

3.4.1.5 Fractional distillation 53

3.4.2 Thermal and catalytic degradation of polystyrene (PS) and

polyethylene terephthalate (PET)

54

3.4.1.1 Reactor assembly 54

3.4.1.2 PS and PET samples preparation 55

3.4.1.3 PS and PET degradation 56

3.5 Isolated liquid products characterization 56

3.5.1 Physiochemical properties 56

3.5.1.1 Determination of density (d) 56

3.5.1.2 Measurement of refractive index (η) 57

iv

3.5.2 Gas chromatography – mass spectrometry (GC-MS) analysis 58

CHAPTER 4. RESULTS AND DISCUSSIONS

Section 1: Characterization of impregnated catalysts 59

4.1 Metals impregnated catalysts over alumina (Al₂O₃) 59

4.2 Metals impregnated catalysts over montmorillonite (Mmn) 64

4.3 Metals impregnated catalysts over activated charcoal (AC) 69

Section 2: Catalytic activity, selectivity and recovery studies for the

degradation of waste expanded polystyrene (WEPS)

74

4.4 Thermogravimetric analysis (TGA) 74

4.4.1 TGA of WEPS 74

4.4.2 TGA of polystyrene (PS) and polyethylene terephthalate (PET) 75

4.5 Thermal degradation of WEPS 77

4.6 Catalytic degradation of WEPS using alumina (Al₂O₃),

montmorillonite (Mmn) and activated charcoal (AC) as catalysts

83

4.7 Catalytic degradation of WEPS using Mg, MgO and MgCO₃

catalysts

92

4.8 Catalytic degradation of WEPS using Mg impregnated catalysts 101

4.9 Catalytic degradation of WEPS using Zn, ZnO and ZnCl₂ catalysts 109

4.10 Catalytic degradation of WEPS using Zn impregnated catalysts 121

4.11 Catalytic degradation of WEPS using Al, Al₂O₃ and AlCl₃

catalysts

128

v

4.12 Catalytic degradation of WEPS using Al impregnated catalysts 139

4.13 Catalytic degradation of WEPS using Cu, CuO and CuCl₂

catalysts

146

4.14 Catalytic degradation of WEPS using Cu impregnated catalysts 156

4.15 Catalytic degradation of WEPS using Fe, Fe₂O₃ and FeCl₃

catalysts

163

4.16 Catalytic degradation of WEPS using Fe impregnated catalysts 174

4.17 Effect of polyethylene terephthalate (PET) on the catalytic

degradation of polystyrene (PS)

180

References 195

Conclusions 203

List of publications 209

vi

LIST OF FIGURES

Fig. No. Caption Page No.

1.1 Diagrammatic representation of the steps involves in

heterogeneous catalysis

3

3.1 Process Flow for the degradation of waste expanded polystyrene 49

3.2 Schematic flow sheet diagram of the reaction assembly used for

WEPS degradation

50

3.3 Schematic flow sheet diagram of fractional distillation assembly 54

3.4 Schematic flow sheet diagram of the reaction assembly used for

PS and PET degradation

55

4.1.1 SEM micrograph of (a) Al₂O₃ support, (b) 15% Mg-Al₂O₃, (c)

20% Zn-Al₂O₃, (d) 20% Al-Al₂O₃, (e) 20% Cu-Al₂O₃ and (f)

5% Fe-Al₂O₃

61

4.1.2 XRD diffractogram of (a) Al₂O₃ support, (b) 20% Mg-Al₂O₃, (c)

20% Zn-Al₂O₃, (d) 20% Al-Al₂O₃, (e) 20% Cu-Al₂O₃ and (f)

05% Fe-Al₂O₃

63

4.2.1 SEM micrograph of (a) Mmn support, (b) 20% Mg-Mmn, (c)

20% Zn-Mmn, (d) 05% Al-Mmn, (e) 15% Cu-Mmn and (f) 20%

Fe-Mmn

66

4.2.2 XRD diffractogram of (a) Mmn support, (b) 20% Mg-Mmn, (c)

20% Zn-Mmn, (d) 5% Al-Mmn, (e) 15% Cu-Mmn and (f) 20%

Fe-Mmn

68

4.3.1 SEM micrographs of (a) AC support, (b) 15% Mg-AC, (c) 20%

Zn-AC, (d) 20% Al-AC, (e) 20% Cu-AC and (f) 20% Fe-AC

71

vii

4.3.2 XRD diffractogram of (a) AC support, (b) 20% Mg-AC, (c) 20%

Zn-AC, (d) 20% Al-AC, (e) 20% Cu-AC and (f) 20% Fe-AC

73

4.4.1 TGA curves of WEPS in O2 and N₂ environment 75

4.4.2 TGA curves of PS and PET in N₂ environment 76

4.5.1 Effect of degradation temperature for thermal degradation of

WEPS

77

4.5.2 Effect of reaction time for thermal degradation of WEPS 78

4.5.3 Chromatogram of catalytically derived liquid products obtained

with thermal degradation at optimized conditions

80

4.6.1 Effect of degradation temperature and comparison of

catalytically derived liquid products obtained with Al₂O₃, Mmn

and AC as catalysts

84

4.6.2 Effect of reaction time and comparison of catalytically derived

liquid products obtained with Al₂O₃, Mmn and AC as catalysts

at optimum conditions

85

4.6.3 Effect of polymer to catalyst ratio and comparison of

catalytically derived liquid products obtained with Al₂O₃, Mmn

and AC as catalysts at optimum conditions

87


with Al₂O₃ catalyst at optimized conditions

90


with Mmn as catalyst at optimized conditions

90


with AC as catalyst at optimized conditions

91

viii


catalytically derived liquid products obtained with Mg, MgO and

MgCO₃ catalysts

92


liquid obtained with Mg, MgO and MgCO₃ catalysts at optimum

conditions

93


catalytically derived liquid products obtained with thermal

degradation, Mg, MgO and MgCO₃ catalysts at optimum

conditions

95


with Mg as catalyst at optimized conditions

97


with MgO as catalyst at optimized conditions

97


with MgCO₃ as catalyst at optimized conditions

98

4.8.1 Effect of percentage of impregnated precursor metal (Mg) over

Al₂O₃, Mmn and AC supports for maximum liquid products

102


with 15% Mg-Al₂O₃ catalyst at optimized conditions

106


with 20% Mg-Mmn catalyst at optimized conditions

106


with 20% Mg-AC catalyst at optimized conditions

107

ix

4.9.1 Effect of temperature and comparison of catalytically derived

liquid products obtained with Zn, ZnO and ZnCl₂ catalysts at

optimum conditions

110


liquid products obtained with Zn, ZnO and ZnCl₂ catalysts at

optimized conditions

111



degradation, Zn, ZnO and ZnCl₂ catalysts at optimized

conditions

114


with Zn catalyst at optimized conditions

116


with ZnO catalyst at optimized conditions

117


with ZnCl₂ catalyst at optimized conditions

117

4.10.1 Effect of percentage of impregnated precursor metal (Zn) over


123


with 20% Zn-Al₂O₃ catalyst at optimized conditions

126


with 20% Zn-Mmn catalyst at optimized conditions

126


with Zn-AC catalyst at optimized conditions

127

x

4.11.1 Effect of temperature and comparison of catalytically derived

liquid products obtained with Al, Al₂O₃ and AlCl₃ catalysts

129


liquid products obtained with Al, Al₂O₃ and AlCl₃ catalysts at


130



degradation, Al, Al₂O₃ and AlCl₃ catalysts at optimized

conditions

132


with Al catalyst at optimized conditions

135


with Al₂O₃ catalyst at optimized conditions

135


with AlCl₃ catalyst at optimized conditions

136

4.12.1 Effect of percentage of impregnated precursor metal (Al) over


140


with 20% Al-Al₂O₃ catalyst at optimized conditions

144


with 5% Al-Mmn catalyst at optimized conditions

144


with 20% Al-AC catalyst at optimized conditions

145

xi


catalytically derived liquid products obtained with Cu, CuO and

CuCl₂ catalysts

147


liquid products obtained with Cu, CuO and CuCl₂ catalysts at


148



degradation, Cu, CuO and CuCl₂ catalysts at optimized

conditions

149


with Cu catalyst at optimized conditions

152


with CuO catalyst at optimized conditions

152


with CuCl₂ catalyst at optimized conditions

153

4.14.1 Effect of percentage of impregnated precursor metal (Cu) over


157


with 20% Cu-Al₂O₃ catalyst at optimized conditions

161


with 20% Al-Mmn catalyst at optimized conditions

161


with 20% Al-AC catalyst at optimized conditions

162

xii


catalytically derived liquid products obtained with Fe, Fe₂O₃ and

FeCl₃ catalyst

164


liquid products obtained with Fe, Fe₂O₃ and FeCl₃ catalysts at


165



degradation, Fe, Fe₂O₃ and FeCl₃ catalysts at optimized

conditions

166


with Fe as catalyst at optimized conditions

170


with Fe₂O₃ catalyst at optimized conditions

170


with FeCl₃ catalyst at optimized conditions

171

4.16.1 Effect of percentage of impregnated precursor metal (Fe) over


175

4.16.2 Chromatogram of catalytically derived liquid products using 5%

Fe-Al₂O₃ catalyst at optimized conditions

178

4.16.3 Chromatogram of catalytically derived liquid products using

20% Fe-Mmn catalyst at optimized conditions

178

4.16.4 Chromatogram of catalytically derived liquid products using

20% Fe-AC catalyst at optimized conditions

179

xiii

4.17.1 Effect of degradation temperature on the yield of catalytically

derived products (liquids and gases) for the degradation of PS,

10PET+PS, 20PET+PS and 30PET+PS

182

4.17.2 Effect of reaction time on the yield of catalytically derived

products (liquid and gases) for the degradation of PS,

10PET+PS, 20PET+PS and 30PET+PS at optimized conditions

184

4.17.3 Effect of polymer to catalyst ratio of the yield of catalytically

derived products (liquid and gases) for the degradation of PS,

10PET+PS, 20PET+PS and 30PET+PS at optimized conditions

187

xiv

LIST OF TABLES

Table No. Caption Page No.

3.1 Percentage (%) of active metal and their calculated weight

impregnated over 5 g of each support i.e. Al2O3, Mmn and

AC.

47

4.1 Surface area, pore size and pore volume analysis of

impregnated catalysts over Al₂O₃ support

59


impregnated catalysts over Mmn support

64


impregnated catalysts over AC support

69

4.5.1 Products formed by thermal degradation of WEPS at


79

4.5.2 Physiochemical parameters of the fractions obtained using

fractional distillation of the liquid derived from the thermal

degradation of WEPS

81

4.5.3 Physiochemical parameters of standards compounds. 82

4.6.1 Optimum reaction conditions and contents of products using

Al₂O₃, Mmn and AC as catalysts

86

4.6.2 Products formed by the catalytic degradation of WEPS

using Al₂O₃, Mmn and AC as catalysts at optimized

conditions.

89


Mg, MgO and MgCO₃ catalysts

94

xv


using Mg, MgO and MgCO₃ catalysts at optimized

conditions

96

4.7.3 Physical parameters of the fractions obtained using

fractional distillation of the liquid derived from the

degradation of WEPS using Mg, MgO and MgCO₃ catalysts

100

4.8.1 Optimum reaction conditions and contents of product using

15% Mg-Al₂O₃, 20% Mg-Mmn and 20% Mg-AC catalysts

102


using 15% Mg-Al₂O₃, 20% Mg-Mmn and 20% Mg-AC

catalysts at optimized conditions

105

4.8.3 Comparison of liquid products and their contents with

literature reported methods along with their reaction

conditions

108


Zn, ZnO and ZnCl₂ catalysts

113


using Zn, ZnO and ZnCl₂ catalysts at optimized condition

116



degradation of WEPS using Zn, ZnO and ZnCl₂ catalysts

120

4.10.1 Optimum reaction conditions and contents of product 20%

Zn-Al₂O₃, 20% Zn-Mmn and 20% Zn-AC catalysts

122

xvi


using 20% Zn-Al₂O₃, 20% Zn-Mmn and 20% Zn-AC

catalysts

125


Al, Al₂O₃ and AlCl₃ catalysts

131


using Al, Al₂O₃ and AlCl₃ catalysts at optimized conditions

134



degradation of WEPS using Al, Al₂O₃ and AlCl₃ catalysts

138


20% Al-Al₂O₃, 5% Al-Mmn and 20% Al-AC catalysts

140

4.12.2 Products formed by WEPS degradation using Al

impregnated catalysts at optimized conditions

143

4.13.1 Optimum reaction conditions and contents of the products

obtained with Cu, CuO and CuCl₂ catalysts

150


using Cu, CuO and CuCl₂ catalysts at optimized conditions

151

4.13.3 Physical parameters of the fractions obtained using


degradation of WEPS using Cu, CuO and CuCl₂ catalysts

155

4.14.1 Comparison of reaction conditions and contents of products

using 20% Cu-Al₂O₃, 15% Cu-Mmn and 20% Cu-AC

catalysts

157

xvii

4.14.2 Products formed by WEPS degradation using 20% Cu-

Al₂O₃, 15% Cu-Mmn and 20% Cu-AC catalysts at


160

4.15.1 Optimum reaction conditions and contents of the product

using Fe, Fe₂O₃ and FeCl₃ catalysts

167


using thermal degradation, Fe, Fe₂O₃ and FeCl₃ catalysts at


169



degradation of WEPS using Fe, Fe₂O₃ and FeCl₃ catalysts

173

4.16.1 Comparison of reaction conditions and products

components using 5% Fe-Al₂O₃, 20% Fe-Mmn and 20%

Fe-AC catalysts

175

4.16.2 Products formed by WEPS degradation using Fe and its

impregnated catalysts at optimized conditions

177

4.17.1 Optimum reaction conditions and the yield of catalytically

derived products for the degradation of PS, 10PET+PS,

20PET+PS and 30PET+PS

186

4.17.2 Fractions of interest identified by GC-MS in the

catalytically derived liquid products obtained from the

degradation of PS, 10PET+PS, 20PET+PS and 30PET+PS

at optimized conditions

189

4.17.3 Depolymerization products identified by GC-MS in the

catalytically derived liquid products obtained from the

190

xviii

degradation of PS, 10PET+PS, 20PET+PS and 30PET+PS

at optimized conditions

4.17.4 Products obtained from the degradation of PS, 10PET+PS,

20PET+PS and 30PET+PS at optimized conditions

193

xix

ABBREVIATIONS

Abbreviation Full name

% Percent

AC Activated charcoal

(CaO2(Al,Mg)Si4O10(OH)2) montmorillonite-15A

(Mg,Fe)Al2SiO5(OH)2 Chloritoid

°C/min Degree Celsius per min

µL Micro liter

µm Micrometer

⁰ Degree

10PET+PS 10% PET mixture with 90% PS

15% Cu-Mmn 15 percent copper over montmorillonite

15% Mg-Al₂O₃ 15 percent magnesium over alumina

20% Al-AC 20 percent aluminium over activated charcoal

20% Al-Al₂O₃ 20 percent aluminium over alumina

20% Cu-AC 20 percent copper over activate charcoal

20% Cu-Al₂O₃ 20 percent copper over alumina

20% Fe-AC 20 percent iron over activated charcoal

20% Fe-Mmn 20 percent iron over montmorillonite

20% Mg-AC 20 percent magnesium over activated charcoal

xx

20% Mg-Mmn 20 percent magnesium over montmorillonite

20% Zn-AC 20 percent zinc over activated charcoal

20% Zn-Al₂O₃ 20 percent zinc over alumina

20% Zn-Mmn 20 percent zinc over montmorillonite



5% Al-Mmn 5 percent aluminium over montmorillonite

5% Fe-Al₂O₃ 5 percent iron over alumina

Å Angstrom

Al Aluminium

Al10Cl3(OH)27. 13H2O Aluminum chloride hydroxide hydrate

Al2.892Cu6.1808 Aluminium copper alloy

Al2CuMg Aluminium copper magnesium alloy

Al₂O₃-KOH-K Alumina-potassium hydroxide-potassium

Al3+ Aluminium (III) ion

AlCl₃ Aluminium Chloride

AlCl₃. 6H2O Aluminium chloride hexa hydrated or

Chloraluminite

BaO Barium oxide

BET Brunauer, Emmett and Teller method

xxi

BF3 Boron triflouride

BJH Barrett, Joyner and Halenda method

C10-C18 Hydrocarbons range having 10 carbons to 18

carbons


carbons


carbons

C6-C9 Hydrocarbons range having 6 carbons to 9 carbons

Ca14Mg2(SiO4)8 Bredigite

Ca2.8(Na,K)0.9Al6.5Si11.5O36.5H2O Sodium or potassium form calcium alumino

silicate hydrate

Ca2Al2O5 Dicalcium aluminate

Ca2CuO2Cl2 Oxychloride cuprate

Ca4Al8Si8O32.8H2O Calcium aluminum silicate hydrate

CaO Calcium oxide

C-C Carbon-carbon bond

C-C bond Carbon-carbon bond

cc/g Cubic centimeter per gram (unit of pore volume)

Cl Chlorine atom

Cm Centi meter (unit of length)

xxii

Co Cobalt

C-O Carbon oxygen bond

COx Carbon oxide - represent CO and CO₂

CrO3 Chromium trioxide or Chromium(VI) oxide

CsNaY Cesium and sodium zeolite Y

Cu Copper metal

Cu(ClO4)2 Copper(II) perchlorate

Cu2O Copper(I) oxide

CuAl2O4 Copper aluminate

CuCl₂ Copper chloride

CuCl3 Copper(III) chloride

CuO Copper oxide

Cu-Zn oxide/Al₂O₃ Copper and zinc oxide over alumina

Cx Carbon number, where x stands for 1,2,3,4…

d25 Density at 25 ºC

DTA Differential thermal analysis

EPS Expanded polystyrene

EPSW Expanded polystyrene wastes

eV Electron volt

FCC Spent FCC

xxiii

Fe Iron metal

Fe2O3 Ferric oxide or Iron(III) oxide

FeCl3 Ferric chloride or Iron (III) chloride

Fe-K/Al₂O₃ Iron potassium over alumina

Fig. Figure

FTIR Fourier Transform Infrared spectroscopy

g Gram (unit of mass)

g/ml Gram per micro liter (unit of density)

g/mol Gram per mole (unit of molar mass)

GC-MS Gas chromatography-mass spectrometry

GPPS General purpose polystyrene

H Hydrogen

h Height

h Hour

H‾ Hydride ion

H+ Hydrogen ion

H2SO4 Sulfuric acid

HDPE High density polyethylene

He Helium

HFC's Hydrofluorocarbons

xxiv

HIPS High impact polystyrene

HMCM-41 Hydrogen form of Mobil Composition of Matter-

41

HMOR Hydrogen form of mordenite zeolite

HMS Hexagonal mesoporous silica

HNZ Natural clinoptilolite zeolite

HUSY Hydrogen form of ultra-stable zeolite Y

HY Hydrogen form of zeolites Y

HY-700 Hydrogen form of zeolites Y No.700

HZSM-5 Hydrogen form of zeolite socony mobil-5

I.D Internal diameter

ICDD International committee for diffraction data

IEPC Isoelectric point charge

JCPDS Joint committee on powder diffraction standards

K Kelvin

K2O Potassium oxide

K2O/Si-MCM-41 Potassium oxide over silica modified MCM-41

KCaAl2F9 Elpasolite mineral

KCaCl3 Chlorocalcite

Kcal/mol Kilo calorie per mole (unit of energy per number

of molecules, atoms, or other similar particles)

xxv

KCrF4 A magnetic mineral of potassium chromium and

fluoride

Kg/h Kilo gram per hour (unit of mass flow rate)

KJ/mol Kilo joule per mol (Unit of energy per amount of

material)

KNO₃ Potassium nitrate

KV Kilo volt (major unit of electric potential)

LDPE Low density polyethylene

m/s meter per second (unit of velocity)

m2/g Meter square per gram (unit of surface area)

mA Milli ampere (sub unit of electric current)

MCM-41 Mobile composition of matter no.41

MCM-41 Mobile composition of matter-41

Mg Magnesium metal

Mg(OH)2 Magnesium hydroxide

Mg3Al2(SiO4)3 Magnesium aluminium silicate

MgAl₂O₃ Magnesium aluminium oxide

MgAl2O4 Magnesium aluminium oxide or spinel mineral

MgCl2. 6H2O Magnesium chloride hexa hydrate

MgCO3 Magnesium carbonate

MgO Magnesium oxide

xxvi

MgO-Al₂O₃ Magnesium oxide over alumina

min Minute

MIP Molecular impregnated polymers

ml Milli Liter (sub unit of volume commonly used for

liquids measurement)

mm Millimeter (sub unit of length measurement)

Mmn Montmorillonite

Mo2N Molybdenum nitride

MOF5 Metal organic framework 5

mol Mole (unit for the expression of amounts of a

chemical substance)

Mw Molecular weight

MWD Molecular weight distribution

N₂ Nitrogen

Na1.15Al1.15Si0.85O4 Sodium aluminum silicate - a type of mineral

Na10Zn4O9 Sodium zinc oxide (Oxozincate) - a type of

mineral

Na2Al2Si2.5O9.6.2H2O Sodium aluminum silicate hydrate - a type of

mineral

Na2Ca4Mg2Si4O15 Sodium magnesium silicate - a type of mineral

Na2Mg3Zn2Si12O30 Sodium magnesium zinc silicate - a type of

mineral

xxvii

Na2MgSiO4 Sodium magnesium silicate - a type of mineral

Na2ZnSiO4 Sodium zinc silicate

Na3Mg3Ca5Al19Si117O272 Gottardiite mineral

Na4(Si8Al4)O24·11H2O Gmelinite-Na

Na96Al96Si96O384.216H2O Sodium alumino silicate (zeolite A)

NaOH Sodium hydroxide

Ni/Al₂O₃ Nickel over alumina

NiO Nickel oxide

NiO2 Nickel oxide

nm Nano meter (sub unit of length)

NOx Nitrogen oxide - representation NO, NO2 and N2O

O(Et)2 Diethyl ether

O₂ Oxygen

ºC Degree Celsius

PE Polyethylene

PET Polyethylene terephthalate

pH Negative log of hydrogen concentration

PONA Paraffins (P), olefins (O), naphthenes (N) and

aromatics content

PP Polypropylene

xxviii

PS Polystyrene

Pt Platinum

Pt/γ-Al₂O₃ Platinum over gamma alumina

Pt-Cl/γ-Al₂O₃ Platinum and chlorine over gamma alumina

Pt-Rh Platinum-rhodium alloy

PVC Polyvinylchloride

PZC Zero point of charge

R1 Radical 1

R2 Radical 2

SA Silica-alumina

SAA Surface area analysis

SD Standard deviation

SEM Scanning electron microscopy

Si/Al Ratio determination for SiO₂ and Al₂O₃

Si/Al Silicalite - a type of mineral

Si34O68 Silicon oxide

SiO₂-Al₂O₃ Silica-alumina

SnCl4 Tin(VI) chloride

SOx Sulfur oxide - represent SO, SO2, SO3, S7O2, S6O2,

S2O2

xxix

Tab. Table

TEM Transmission Electron Microscopy

TG Thermogravimetry

TiO2 Titinia

USA United States of America

V Volume

V2O3 Vanadium(III) oxide

WC Tungsten carbide

WEPS Waste expanded polystyrene

WEPS Waste expanded polystyrene

wt.% Weight percent

xPET+PS x amount of PET mixture with x amount of PS

XRD X-ray diffraction

Zn Zinc

Zn3Al94O144 Zinc aluminum oxide

Zn4O6+ Zinc oxide cluster

ZnCl2 Zinc chloride

ZnO Zinc oxide

ZrO₂-KOH Zirconia-potassium hydroxide

ZSM-5 Zeolite Socony Mobile-5

xxx

α Alpha

β Beta

γ Specific refraction

γ-Al₂O₃ Gamma alumina

γM Molar refraction

θ Theta

λ Lambda

π Pie

σ Sigma

Refractive index

Refractive index at 20 ºC using sodium lamp

Density

Summary

xxxi

SUMMARY

The ongoing growth of population and rapid industrialization causes daily refusal of huge

quantities of solid waste especially of plastics. Polystyrene (PS) being an important

commodity is present in large quantities among the discarded plastic wastes in the form of

waste expanded polystyrene (WEPS) and represents a valuable source of chemical products

like styrene monomer and other valuable aromatic hydrocarbons. Waste management of

polymer via conversion into valuable hydrocarbons is a best solution for the problem. The

aim of the current study was the development of novel high activity impregnated catalysts

for the low cost thermo-catalytic degradation of WEPS into selective valuable products

and their separation via fractional distillation followed by physiochemical and GC-MS

characterization.

The first chapter of this dissertation based on brief introduction to catalysts, catalysis,

classification of catalysts, preparation of catalysts (impregnated catalysts) and catalyst

performance parameters. Along with catalysis it included introduction to plastics, types of

plastics with special context of polystyrene (PS), applications of PS and its impact on the

environment when discarded. Waste management and various ways to recycling of plastic

wastes including thermal and catalytic degradation methods which are the main focus of

this thesis are described. Mechanism involved in the processes using either thermal process

or various kinds of catalysts are also included in first chapter.

The second chapter covers a thorough review of relevant literature reported for the thermal

and thermo-catalytic degradation of PS. The literature included catalytic conversion of PS

and some other plastics to their monomer like styrene and other value added hydrocarbons

using various types of bulk and supported catalysts. The literature highlighted different

types of catalysts, reactor types, additives, solvents, effective parameters and impact of

other plastics on the yield of liquid products.

Third chapter comprise of preparation of supported catalysts, catalyst characterization

procedures and different instruments used during preparation and characterization of

catalysts. It include experimental methods applied for thermal and catalytic degradation of

WEPS. This chapter also include discussion of pyrolysis reactors used in the study and

Summary

xxxii

different equipments used in characterization and analysis of liquid products. It also include

the fractionation procedure of parent liquid products, their identification and analysis using

physiochemical parameters and GC-MS analysis.

In the fourth and last chapter results of the experimental findings were discussed. The

Section 1 of the thesis have characterization of the impregnated catalysts using N₂

adsorption and desorption, SEM and XRD analysis in comparison with their supporting

materials. The Section 2 based on characterization of WEPS using TGA, and thermal &

thermo-catalytic degradation of WEPS using several bulk and impregnated catalysts. The

bulk catalysts consist of Mg, MgO, MgCO₃, Zn, ZnO, ZnCl₂, Al, Al₂O₃, AlCl₃, Cu, CuO,

CuCl₂, Fe, Fe₂O₃, FeCl₃, montmorillonite (Mmn) and activated charcoal (AC). Whereas,

impregnated catalysts like Mg-Al₂O₃, Zn-Al₂O₃, Al-Al₂O₃, Cu-Al₂O₃, Fe-Al₂O₃, Mg-

Mmn, Zn-Mmn, Al-Mmn, Cu-Mmn, Fe-Mmn, Mg-AC, Zn-AC, Al-AC, Cu-AC and Fe-

AC. For maximum yield of liquid products different parameters and operation conditions

were optimized. The WEPS was degraded with and without catalysts using different

temperature like 250 ºC, 300 ºC, 350 ºC, 400 ºC, 450 ºC and 500 ºC, different reaction time

like 30 min, 60 min, 90 min, 120 min and 150 min, and different polymer to catalysts ratio

like 1:0.05, 1:0.1, 1:0.2, 1:0.3, 1:0.4 and 1:0.5. The degradation of WEPS were explored

with the effect of polyethylenterephthalat (PET) addition on the yield of component

products of liquid.

Part 1 of the section 2 describes the characterization of WEPS using thermogravimetric

analysis (TGA) in O₂ and N₂ environments. The onset and endset temperature in case of

N₂ environment was 300.98 °C and 409.85 °C, respectively. While the onset and endset

temperature in the case of O₂ environment was 292.50 °C and 407.79 °C, respectively. In

the case of O₂ environment, about 100 wt.% changes were observed and further

degradations of WEPS were carried out at ambient conditions.

In part 2 of the section, thermal degradation of WEPS without the use of any catalysts was

discussed. The maximum yield of liquid products was (78.07 ± 0.64 wt.%) achieved with

500 ºC degradation temperature and 150 min reaction time. Products analysis shows non-

significant yield of value added hydrocarbons and high concentration of high molecular

Summary

xxxiii

weight aromatic hydrocarbons. The yield of different components like toluene,

ethylbenzene, styrene monomer α-methylstyrene, benzene, 3-butynyl and 1,2-propanediol,

3-benzyloxy-1,2-diacetyl was 2.06 wt.%, 0.85 wt.%, 39.31 wt.%, 1.33 wt.%, 17.56 wt.%

and 10.10 wt.%, respectively. The recovery of component products were different than the

composition shown by GC-MS analysis that is attributed to the further degradation of the

products. Benzene, ethylbenzene and 1,2-propanediol, 3-benzyloxy-1,2-diacetyl were

recovered in small quantities. Where the abundant products recovered during the fractional

distillation were toluene (51.0 wt.%), styrene monomer (35.0 wt.%), and about 6.0 wt.%

phenanthrene.

Part 3 of the section describes the comparative degradation of WEPS using different

supporting as catalysts i.e., Al₂O₃, Mmn and AC. Degradation temperature, reaction time

and polymer to catalyst ratio were optimized for maximum liquid products. Mmn catalyst

was found with good catalytic activity having a maximum liquid product yield of 92.40 ±

0.87 wt.%. A significant amount of valuable products were produced with all the three

materials. AC catalysts was found to possess highly active sites that caused to yield mostly

low molecular weight aromatic hydrocarbons abundant with toluene (6.96 wt.%) and

ethylbenzene (6.55 wt.%). However, the yield of styrene monomer was 45.65 wt.% and

45.42 wt.% maximum with Al₂O₃ and AC catalyst.

Investigation on catalytic degradation of WEPS using Mg bulk catalysts were included in

Part 4 of the section 2. The current method i.e. using Mg bulk catalysts, gave more selective

products with significant yield. The yield of low molecular weight aromatic compounds

were in high quantities with selective production of aromatic hydrocarbons. Maximum

recovery of styrene (43.0 wt.%) was achieved with Mg metal catalyst. MgO catalyst

yielded 23.8 wt.% styrene and 35.0 wt.% ethylbenzene while MgCO₃ catalysts yielded

51.87 wt.% styrene and 15.81 wt.% toluene.

In Part 5 of this section thermo-catalytic degradation of WEPS using Mg impregnated

catalysts over Al₂O₃, Mmn and AC supports were explained. The catalytic degradation of

WEPS in the presence of 15% Mg-Al₂O₃ led to narrow range of hydrocarbons with higher

concentration as compared to Mg metal, 20% Mg-Mmn and 20% Mg-AC catalysts. The

Summary

xxxiv

yield of low molecular weight aromatic hydrocarbons like benzene, toluene, ethylbenzene,

styrene, α-methylstyrene and many other valuable hydrocarbons was maximum with 20%

Al-Al₂O₃ catalyst. The catalytic activity and yield of component products were compared

to literature reported methods and current method was found significant for low cost

conversion into valuable products.

Zn-bulk catalysts for thermo-catalytic degradation of WEPS were also described in Part 6

of this section. The catalytic activity and selectivity revealed that zinc bulk catalysts

enhanced the yield of liquid products and affected the formation of component products as

compared to thermal pyrolysis, particularly with Zn metal as catalysts. The catalysts

decreased pyrolysis temperature and heating time as compared to thermal degradation

while on the other hand it increased the yield of liquid products from 78.07 ± 0.64 wt.% to

96.73 ± 0.12 wt.%. The catalysts not only enhances the yield of liquid products, but also

increased value added compounds including toluene, ethylbenzene and styrene. Overall,

the zinc bulk catalysts enhanced both the activity and selectivity of products. During

fraction distillation in addition to thermal pyrolysis, cyclization and recombination

reactions were also observed.

Part 7 of the section describes zinc supported catalysts i.e. Zn-Al₂O₃, Zn-Mmn and Zn-AC

for thermo-catalytic degradation of WEPS. It was found that with zinc impregnated

catalysts the activity and selectivity were better than Zn bulk catalysts. Among the Zn

supported catalysts 20% Zn-Al₂O₃ was found with better catalytic performance, which

yielded 90.20 ± 0.35 wt.% liquid products that were less than the Zn metal catalyst (96.07

± 0.31), but the selectivity of products was good in case of 20% Zn-Al₂O₃ as maximum

valuable aromatic hydrocarbons were formed. The composition of styrene, toluene,

ethylbenzene and α-methylstyrene with 20% Zn-Al₂O₃ were 62.08%, 11.79%, 7.35% and

4.58%, respectively.

Part 8 of section 2 include discussion on the investigation of aluminium bulk catalysts i.e.

(Al metal, Al₂O₃ and AlCl₃) for the degradation of WEPS. Al bulk catalysts were found

with high activity comparable with thermal degradation. The catalyst yielded selective and

desirable hydrocarbons which more specifically in the case of Lewis acid catalysts i.e.

Summary

xxxv

AlCl₃. The yield of styrene monomer in case of AlCl₃ catalyst was 46 wt.%. The separation

of liquid products for the recovery of value added products were also studied in Part 8.

AlCl₃ catalyst was found with maximum recovery of toluene and ethylbenzene. Maximum

recovery of styrene was 50 wt.% and 51 wt.% and α-methylstyrene recovery was 13 wt.%

and 9 wt.% with Al and Al₂O₃ catalysts, respectively.

Part 9 (section 2) of chapter 4 describes aluminium impregnated catalysts over Al2O3, Mmn

and AC supports for thermo-catalytic degradation of WEPS. The results of liquid product

yield and GC-MS characterization revealed that the catalytic activity of 20% Al-Al2O3

catalyst was good producing 91.20 ± 0.35 wt.% liquid products with selective

hydrocarbons. The amount of light weight aromatics were higher in the case of 20% Al-

Al₂O₃ as compared to other catalysts used, which consist major fraction of styrene

monomer i.e. 56.52%.

Comparative degradation of WEPS using Cu, CuO and CuCl₂ bulk catalysts for the

recovery of valuable hydrocarbon have been described in Part 10 of Section 2. Copper bulk

catalysts were found more effective for catalytic activity and selectivity. The majority of

low molecular weight aromatic hydrocarbons were formed with a very small amount of

residue, gases and unwanted high molecular weight aromatic hydrocarbons. Cu metal was

found the best catalyst among the used catalysts with a liquid product yield of 93.93 wt.%

having styrene selectivity of 55.14 wt.% and styrene monomer recovery of 60 wt.%.

In Part 11 of the section discussed, the catalytic activity and selectivity of Cu impregnated

catalysts over Al2O3, Mmn and AC for the degradation of WEPS. It was found that the

yield of liquid products with Cu impregnated catalysts was moderate, but with high

selectivity toward low molecular weight aromatic hydrocarbons. Among the impregnated

catalysts, 20% Cu-Al₂O₃, 15% Cu-Mmn and 20% Cu-AC showed high activities, however,

the selectivity was good only with the 20% Cu-Al₂O₃ catalyst for styrene monomers. For

the selectivity of toluene and ethylbenzene, 15% Cu-Mmn and 20% Cu-AC were found

selective catalysts.

Summary

xxxvi

Part 12 of the section explains the catalytic degradation of WEPS using Fe, Fe₂O₃ and

FeCl₃ bulk catalysts. Fe bulk catalysts were found to increase the yield of liquid product

and selectivity as compared to thermal degradation. Fe and Fe₂O₃ were having more

selectivity for low molecular weight aromatic hydrocarbons. Where the recovery of styrene

monomer was high with Fe metal as catalyst. After Fe metal, FeCl₃ (Lewis acid) was found

with good recovery of toluene, ethylbenzene and styrene monomer.

Investigation and discussion on Fe impregnated catalysts for the degradation of WEPS was

described in Part 13 of this chapter. The catalysts were investigated for the activities of

liquid product and selectivity of component products. 5% Fe-Al₂O₃ and 20% Fe-Mmn was

found with good catalytic activity and selectivity of products. The yield of liquid products

with 5% Fe-Al₂O₃ and 20% Fe-Mmn was 89.27 ± 0.31 wt.% and 88.87 ± 0.42 wt.%,

respectively. The yield of component products like toluene, ethylene and styrene monomer

was almost the same with 5% Fe-Al₂O₃ and 20% Fe-Mmn catalysts. Overall, the yield of

liquid products was less than Fe metal catalysts, but the selectivity of products enhanced

with Fe impregnated catalysts.

The effect of PET on the degradation of PS was discussed in Part 14 of the section 2 in

chapter 4. In the presence of 20% Al-Al₂O₃ catalyst, the degradation of PS, 10PET+PS,

20PET+PS and 30PET+PS started at a lower temperature than the TG pyrolysis of PS and

PET. Degradation temperature, reaction time and feed to catalyst ratio affected the yield of

liquid products and gases. The yield of liquid products was maximum at 500 ºC, 60 min

reaction time and 1:0.2 polymer to catalyst ratio in the cases of PS and 10PET+PS, it was

maximum at 450 ºC, 60 min reaction time and 1:0.2 polymer to catalyst ratio in the case of

20PET+PS whereas it was maximum at 450 ºC, 90 min reaction time and 1:0.2 polymer to

catalyst ratio in the case of 30PET+PS. Generally, the yield of liquid products decreased

and gases increased with the increase of PET percentage. GC-MS analysis showed the

formation of single ring aromatic hydrocarbons (C6-C9 fraction) in bulk. Styrene monomer

was found dominant in the pyrolysis of all materials. The formation of many new and

oxygenated hydrocarbons is attributed to the addition of PET which increased with the

increase of PET percentage. The yield of styrene dimers, styrene oligomers and oxygen

Summary

xxxvii

containing compounds increased with the increase of PET percentage. 10% PET was found

to have good interaction with PS with the yield of maximum liquid and component

products after PS.

INTRODUCTION

Introduction

1

Chapter 1

INTRODUCTION

1.1. Catalysts and catalysis

The catalyst is a substance that increases the rate of a chemical reaction without being

consumed itself or changed chemically and recovered (recycled) at the end of a chemical

reaction for further use in next reaction. The phenomenon of a catalyst to accelerate a

chemical reaction is called catalysis. Catalyst work by binding itself with reactant species

and lower its activation block (rate-limiting free energy of activation or simply activation

energy) for the rapid transformation into products, by providing a new reaction mechanism.

The catalyst may increase the rate of a reaction, decrease the required temperature and may

enhance selectivity [1, 2].

1.2. Classification of catalysts

Catalysts vary from atoms and molecules to large structure like enzymes and zeolites.

Catalysts can be classified using criteria’s like structure, composition, area of application,

catalyst properties, or state of aggregation. Commonly they are classified as acid catalysts

and base catalysts. Here they are classified on the basis of state of aggregation according

to which catalyst has two large divisions i.e. homogeneous catalysts and heterogeneous

catalysts [3].

1.2.1. Homogenous catalysts

A homogenous catalyst is a substance that is in the same phase as the reactants.

Homogenous catalysts are typically dissolved in a solvent with the substrate. The reaction

of chlorine atoms to decompose ozone in the atmosphere is the example of homogenous

catalyst in this reaction. Ozone decomposes spontaneously and also with lightening, but

chlorine (Cl) atoms accelerate the reaction to form oxygen (O2) tremendously [1].

Introduction

2

or overall reaction is

Similarly, another example of homogeneous catalysts is the effect of H+ on carboxylic acid

esterification like the reaction of acetic acid and methanol to form methyl acetate [4].

1.2.2. Heterogeneous catalysts

A heterogeneous catalyst is a substance that is in a different phase from the reactant phase.

Most of heterogeneous catalysts are in solid form which act on the substrate in liquid or

gaseous reaction mixture. For example, Fe in the Haber process for the production of

ammonia [5].

And Co catalysed Fischer–Tropsch synthesis [6].

The heterogeneous catalysis involve three steps as shown in Fig. 1.1, i.e. adsorption,

reaction and desorption. In adsorption step reactants are bonded to catalyst active centers

on its surface, either by Langmuir-Hinshelwood, Eley-Rideal or Mars-van Krevelen

adsorption mechanisms and or their reverse or combination [7] while in second step when

the molecules get oriented, reaction takes place. In the last step the products are released

from catalyst surface and make it available for the next reaction [8].

http://en.wikipedia.org/wiki/Hydrogen

http://en.wikipedia.org/wiki/Reactions_on_surfaces#Langmuir-Hinshelwood_mechanism

http://en.wikipedia.org/wiki/Reactions_on_surfaces#Eley-Rideal_mechanism

Introduction

3

Figure 1.1 Diagrammatic representation of the steps involves in heterogeneous catalysis.

Heterogeneous catalysts have specific features that depend upon the morphology of

catalysts. They are preferred over homogenous catalysts because they are cheap, easily

regenerated and stable within a wide range of temperature and pressure. They can be stored

for a long time and could be easily handled. Due to non-toxic nature their disposal is easy

and safe. They present multiple active centres and avoid the formation of inorganic salts

[3]. The most important aspect of a catalyst is its total surface area, the smaller the particle

size of a catalyst will have the larger the surface area, facilitating the adsorption of reactant

molecules [9]. Thus the activity of a catalyst is the function of chemisorption, unsaturation

(uneven geometry of the surface of catalyst), acidity and electronic properties [10].

Heterogeneous catalysts have been classified on the basis of various properties. On the

basis of application, catalysts have been categorized as hydrogenation catalysts, oxidation

catalysts, dehydration catalysts, cracking catalysts and so on [11]. Other classification is

given below:

i. Solid acid and base catalysts

Solid acid catalysts exhibit acidity at elevated temperatures while solid base catalysts show

basic characters in their reactions. They are characterized by their Brønsted and/or Lewis

acidity and by the number and strength of their sites. Examples of solid acid catalysts are

MCM-41, mesoporous molecular sieves (HMS), AlCl3, FeCl3, montmorillonite (Mmn),

Introduction

4

sulfated zirconia and other ion exchange resins. Examples of solid base catalysts are oxides

(MgO, CaO, NiO, ZnO), modified oxides (Al2O3-KOH-K, ZrO2-KOH, MgO-Al2O3,

hydrotalcites) and zeolites (CsNaY, microporous titanosilicates) [12-15].

ii. Conductor, semiconductor and insulator catalysts

On the basis of electronic mobilities catalysts have been classified into conductors,

semiconductors and insulators. The majority of the conductor catalyst are metals like iron,

vanadium, silver and platinum. These catalysts have chemisorption by electron transfer

mechanism. Semiconductors are oxides, like NiO, ZnO and Cu2O. When sufficient energy

is provided in a compound they interchange electrons from the filled valence band. Where

insulators catalysts are a wide range of substances, like silica gel, alumina and activated

charcoal. These catalysts have no electronic movements and are often strong acids. Their

activity mechanism is known to be due to the carbonium ion generation at the acid site on

the surface of catalyst [10, 11, 16].

iii. Unsupported (bulk) and supported catalysts

a. Unsupported or bulk catalysts

Simple, solid heterogeneous catalysts are known as unsupported or bulk catalysts and they

have only active species. For example, metals and metals alloys (Fe, Pt, Mg, Cu, Pt-Rh,

etc.), metal oxides (TiO2, ZnO, NiO2 etc.), simple binary oxides (Al2O3, V2O3, CrO3 etc.),

complex multi component oxides (SiO2-Al2O3, zeolites, hydrotalcites, montmorillonite

etc.), carbides and nitrides (WC, Mo2N etc.), carbons (activated carbons, carbon nanotubes

and graphene etc.), ion-exchange resins and ionomers (polymers matrix, Nafion etc.),

molecularly imprinted catalysts (MIP of Al3+ doped silica gel and cross-link polymers etc.),

metal-organic frameworks (MOF-5 consist of Zn4O6+) and metal salts (ZnCl2, CuCl3,

FeCl3) [3, 17]. Most of the oxides of bulk catalysts can also be used as supports like Al2O3,

activated charcoal (AC), silica (SiO2), zirconia (ZrO2) and titania (TiO2) [18-23] etc.

b. Supported catalysts

When catalytically active components are dispersed on a porous support with large specific

surface area for the effectiveness or minimized cost, they are known as supported catalysts.

Introduction

5

In supported catalyst the active phase is in small quantity and in a sufficiently dispersed

form over a support to achieve large specific surface area and maximum specific activity.

Supported catalysts are prepared with the aim to achieve maximum activity, selectivity and

stability. In order to achieve the said objective the active metal phase is deposited over a

support – usually highly thermostable and porous material having a large surface area and

suitable mechanical strength to longer catalyst life [24, 25].

1.3. Preparation of supported catalysts

The preparation of supported catalyst involves three steps i.e. the introduction of active

phase or component, drying & calcination and reduction or activation, details are followed

below;

1.3.1. Introduction of active phase

The active metal precursor is introduced over porous support by four principle techniques.

i. Ion-exchange

Aqueous solution of suspended supports like Al2O3, TiO2, SiO2, MgO etc. tend to

polarize and surface changed, controlled by the pH of the solution according to the

following schematic equations:

1.1

1.2

In acidic media Eq. 1.1, the surface sites are positively charged and will be covered by

anions while in basic media Eq. 1.2, the acidic surface sites are negatively charged and

covered by cations. For these supports, the pH at which the surface become neutral called

isoelectric point charge (IEPC) or zero point of charge (PZC). For instance, γ-Al2O3 (PZC

8) will attract cations in a solution of pH above its PZC and will attract cations below its

PZC e.g. Pt/γ-Al2O3 is obtained in a solution with a pH above it PZC value and or Pt-Cl/γ-

Al2O3 by reverse pH. Instead of proton the surface could have ionic species to exchange

[24].

Introduction

6

ii. Precipitation or co-precipitation

This technique involves the precipitation or co-precipitation of the metal salt and support

(salt of a compound) under stirring with a base in the form of hydroxides and or carbonates

which after washing is transformed into refractory oxides support. The active metal is

dispersed by calcination e.g. Ni/Al2O3 and Cu-Zn oxide/Al2O3 prepared by co-precipitation

method [24, 26, 27].

iii. Deposition

This technique is identical to the co-precipitations and involve the precipitation of a metal

sol (containing active metal precursor in the form of hydroxide or carbonate) onto a

suspended support. For example phosphine stabilized gold cluster deposition onto TiO2

[24, 28].

iv. Impregnation

It is the most common method to prepare supported or impregnated catalysts. In

impregnation method the support is kept in contact with the solution of precursor metal salt

to achieve pore filling or saturation of pores of support followed by drying and calcination.

On the basis of amount of solution used there are two types of impregnation i.e. (a) dry

impregnation and (b) wet impregnation.

a. Dry impregnation

Its other names are incipient wetness or dry or capillary impregnation. In dry impregnation

the support is sprayed with impregnation or active component solution without the use of

excess solution.

b. Wet impregnation

Wet impregnation is also known as soaking or dipping impregnation. By this method the

catalyst is prepared by adding excess amount of the solution with respect to the pore

volume of the support, kept for a period of time under continuing stirring, filtered and dried.

Introduction

7

1.3.2. Drying and calcination

In order to evaporate the used solvent the material is heated at a temperature of 80-200 ºC,

under a specific atmosphere for a certain period of time depending on the nature of solvent

and materials used. After drying the material is usually heated at high or a little higher than

drying temperature in the presence of atmospheric oxygen or oxygenated environment. In

calcination the metal precursor is decomposed by the formation of oxide (sintering step) as

well as the removal of gases like water, carbon dioxide, the cations, the anions or other

residues [24, 29].

1.3.3. Reduction or activation

Reduction is the process in which the oxides or precursor metal compounds are converted

into metal by thermal treatment in the presence of hydrogen or solution of hydrazine or

formaldehyde [24].

1.4. Catalyst performance parameters

1.4.1. Activity

The action of a catalyst in terms of increasing the reaction rate is known as catalytic

activity. Activity is an important performance parameter for the evaluation of a catalyst.

Activity is increased by maximizing both the availability and dispersion of active phase

and it is expressed in terms of reaction rates normalized for the active phase surface area.

The catalytic activity is measured in terms of turnover frequency or measured readily by

space-time yield expressed in units of the amount of products formed in the reactor per unit

reactor volume and per unit time [7, 30].

1.4.2. Selectivity

The ability of a catalyst to convert reactants into desirable products per amount of

consumed reactants is selectivity. The selectivity of the products could be altered with

physical or chemical properties of catalysts, including diffusivity, pore-size distributions

and location of active ingredients as well as mass transport through the pore structure. For

selectivity the most important property is nature of the active phase of a catalyst [7, 30].

Introduction

8

1.4.3. Stability and regenerability

Stability means the loss of activity of a catalyst with the passage of time either out of the

reaction mixture (Environment) or in the reaction mixture. This might be caused by

polluting the catalyst surface, by sintering of the active phase, poising of active surface

with feed impurities or due to the clogging of pores in catalyst support. Regenerability

mean the regeneration of catalyst either by only washing, calcination in oxidative

environment or often accompanied by the re-dispersion of the active phase onto the surface

of the catalyst [30].

1.5. Plastics and its types

Plastics are man-made polymers or synthetic polymers that are moldable into any shape.

The examples of plastics are polyethylene (PE), polystyrene (PS) and polyvinylchloride

(PVC) etc. Plastics are made of petrochemicals like crude oil, coal or gas under the

application of pressure and heat. They can be classified on the basis of chemical structure

of their polymer backbone as well as side chains, they can also be classified by their

synthetic chemical process like condensation, polyaddition and cross-linking. On the basis

of processibility plastics have two main types i.e. one which gets soft with heating and hard

with cooling are thermoplastics, and those which get hard by heating and soft by cooling

are thermosetting [31].

The production of man-made polymers (plastics) has accelerated human society towards

success. Plastics have been produced in various forms because of their unique properties;

they tolerate a wide temperature range, resist chemicals and light, having good mechanical

strength and are easily moldable at high temperature. Human has started working with

plastics since 1600 BC while the plastic production on an industrial scale has started around

the 1940s and 1950s, since then its production and demand is increasing day by day.

Worldwide production of plastics in 2011 was 280 million tons with annual increases of

4% since 2010 and this is expected to grow till 2016 with a rate of about 5% per year.

Plastics have thousands of types, but low cost commodity plastics that are used on a large

scale are polyethylene terephthalate (PET), high-density polyethylene (HDPE),

polyvinylchloride (PVC), low-density polyethylene (LDPE), polypropylene (PP) and

Introduction

9

polystyrene (PS). According to a survey the global demand of categories of plastics i.e.

PET, PVC, PS, (expanded polystyrene) EPS and polyolefins is more than 90%. Among the

total plastics, the demand of PE, PP, PVC, PS and PET is 37%, 19%, 19%, 6% and 6%,

respectively [32-34]. These plastics have thousands of indoor and outdoor applications and

had made our society resourceful regarding human health and environment. Plastics have

dominated our lives, life without plastics is hard to consider, we use plastics extensively,

they are everywhere, from a writing pen to large bodies, including packing material, water

supplies, water storages, insulating materials, body organs, solar panels and in light aircraft

bodies [34].

1.6. Polystyrene and its applications

Polystyrene (PS) is a petroleum derived aromatic polymer of styrene monomer. PS was

discovered by Eduard Simon in 1839 while its commercial production started in 1930s.

Polystyrene is available in three forms: general purpose polystyrene (GPPS), high impact

polystyrene (HIPS) and expanded polystyrene (EPS) [34]. PS is a widely used commodity

thermoplastic, in 2004 the total world production of EPS was 5 million tons, the average

annual growth is expected to be 2.5% per annum through 2010 and according to an

expectation its total amount will be double, within 25 years.

EPS rank fourth in the world consumption of polymers due to its unique physical and

chemical properties like rigidity, light weight, resistant to chemicals and moisture, hygienic

character, thermal insulation, shock proof nature, cost effective production and durability.

EPS has a wide range of uses, it is used in packaging of breakable supplies or expensive

goods, as insulation material in buildings and in air-conditioning while for domestic

purpose EPS is commonly used in drinking cups, trays, hairdryers and kitchen appliances.

It is also used for making toys and molded parts inside of cars [35-40].

1.7. Environmental impact of polystyrene

The increasing demands of plastics and its growing industry is facilitating human beings

while on the other hand its increasing demands also leads its disposal into the environment

causing serious pollution [37, 41]. Most of the plastics are disposed in open space after its

use where PS comprise 9% of the total municipal solid waste. Statistical calculations per

Introduction

10

2010 reports the annual growth of EPS is 2.5 % per year that is expected to be doubled by

the year 2025 [38, 42]. Disposing plastics are unwise because they are produced from

limited petrochemical resources. The use of PS in furniture and upholstery is reported

highly flammable causing fire in commercial and domestic buildings. They are

environmentally stable and are non-biodegradable materials remaining unchanged for

hundreds of years, limiting landfill space while roads and buildings build over land filled

with EPS could crack and be crashed. EPS because of its light weight and moisture resistant

nature can easily float in the air and water bodies creating an unpleasant look affecting the

beauty of nature. According to an approximation, about 46,000 pieces of plastics are

floating in each square mile of the oceans and its wastes has killed millions seabirds, more

than hundred thousand mammals and countless fish each year [43]. EPS production is

energy demanding process producing greenhouse gases during its production. In spite the

claims of industries, EPS is produced with the use of hydrofluorocarbons (HFC’s) that are

3-5 time more dangerous than the original for the depletion of ozone layer [44]. Moreover,

incineration of EPS is also dangerous for health, it produces toxic gases like light

hydrocarbons, nitrous oxides and sulfur oxides, dioxins and other toxins and cause

associated diseases. Styrene has been reported to leach into food and into human tissues

from polystyrene food wares and has reported in occupational exposure with lung tumor,

leukemia, lymphoma and high rate of neurotoxicological effects (balance effect, spatial

orientation, hearing problems, decreased color judgment and concentration problems etc.)

and carcinogenic effects (Urinary bladder cancer, prostate cancer, colorectal cancer and

pancreatic cancer) [38, 45].

1.8. Plastic waste management

The excellent desirable properties of plastics and its numerous applications in diverse fields

is increasing its demand day by day. The increase in production and use of plastics with

special concern of PS throughout the world increasing its wastes too and it often disposed

directly to the open space or water flowing bodies. Plastics are recovered and managed

using five different ways i.e. disposing by landfill, mechanical recycling, biological

recycling, thermal incineration and chemical recycling. EPS disposal has become a threat

to the environment and its disposal by landfill is prohibited while due to the production of

Introduction

11

toxic and carcinogenic gases its incineration practice has also stopped. Mechanical

recycling is expensive and often full of impurities while biological recycling is much slow

process and it is only practiced for degradable plastics. All the above mentioned methods

are not suitable for waste management. The only way is chemical recycling or tertiary

recycling to get maximum benefit of the plastics waste and convert it into valuable

hydrocarbons [46].

1.9. Chemical recycling or tertiary recycling

Chemical recycling is also known as tertiary recycling, which refers to the recovery of

hydrocarbons or value added compounds. Polymers are considered to be the richest sources

of valuable hydrocarbons. Synthetic polymers, i.e. plastics are produced from

petrochemicals and waste plastics can be converted back into liquid fuels or other important

and useful compounds including its monomer [47]. Chemical recycling is achieved by three

different means:

1.9.1. Depolymerization

Depolymerization refers to reverse synthesis of condensation polymers like polyamides

and nylon to initial diacids and diamines etc. Hydrolysis, alcoholysis and glycolysis are the

typical examples of depolymerization. This method cannot be applied to more than 70% of

municipal solid wastes [47].

1.9.2. Partial oxidation

Partial oxidation (use of steam and/or oxygen) is the direct combustion of polymer waste

with high calorific value for energy recovery. Partial oxidation also produces NOx, SOx and

COx including some light hydrocarbons and thus is not an environmental friendly process.

This method has reported with 60% to 70% hydrogen production [47].

1.9.3. Degradation or cracking or pyrolysis

Degradation is the process of chemical conversion of polymers into its monomer or other

compounds due to secondary reactions taking place. It’s the breakdown of polymer chain

Introduction

12

into useful low molecular weight hydrocarbons in liquid forms that can be utilized as

chemicals or fuels for combustion. It has further subdivided into the following types:

i. Thermal degradation

Thermal degradation is a type of tertiary recycling, which is achieved with

elevated temperature (i.e., from 250 °C to 1200 °C or may vary with polymer

nature) in the absence of any other compounds like catalyst, solvent and oxygen.

Thermal degradation often requires high temperature and produce more gaseous

products. The liquid products produced are often in a broad range with no

selectivity and in much longer time [37, 47, 48].

ii. Catalytic degradation

In catalytic degradation the plastic wastes are broken down into chemical products in the

presence of a suitable cracking catalyst. The liquid products produced during the

degradation process can be used as a fuel or raw material like styrene, toluene and

ethylbenzene to produce either new polymers or other substances in case of PS degradation

[49-53]. Catalyst increases the rate of reaction by decreasing activation energy with

ultimate decrease of final degradation temperature and reaction time with selective and

desirable products yield in narrow ranges. This method is the best way to waste plastic

recycling that is cost effective and largely practiced throughout the world [47].

The catalytic or thermal degradation can also be carried out using special conditions like

in the presence of hydrogen (hydrocracking), oxygen and inert gas like nitrogen. Many

researchers have carried out the degradation of plastics in different solvents or other

compounds. The degradation of plastics may also be affected by different parameters like

degradation temperature, reaction time and polymer to catalyst ratio. Proper selection of

catalyst and reactor design can also decrease temperature for catalytic degradation as well

as an increase in selectivity of products [54-56].

iii. Photodegradation

The process of breakdown of large molecules of a polymer into small molecules by

irradiation with ultraviolet (UV) or visible light.

Introduction

13

iv. Biodegradation

The breakdown of polymer molecules into small fragment by the help of micro-organism

such as bacteria, which divide the polymer into fragments by the release of enzymes and

eat.

There are some other types of degradation but they have no importance to the context of

this study, therefore, not included. However, our field of interest is thermal and catalytic

degradation, therefor, they are given in details.

1.10. Polystyrene degradation mechanism

The degradation of polymers is a complex phenomenon to understand because thousands

of species are generating and interacting with each other at a single time, therefore, it is

hard to divine a specific mechanism but there are a few agreements using different natures

of catalysts. Generally the depolymerization and or degradation of polymers occur in three

stages:

i. Initiation

ii. Propagation

iii. Termination

The scission or degradation of PS polymer backbone is proposed by Cullis and Hirchler

[57] with four common proposed mechanisms i.e. (i) end-chain scission or unzipping –

where degradation is targeted at the chain ends and successively production of monomer

resulting decrease in the length of polymer, (ii) random-chain scission – in random

fragmentation of polymer result the formation of both monomers and oligomers, (iii) chain-

stripping - side chain reactions involving substituents on the polymer chain, (iv) cross-

linking reactions - two adjacent polymer chains can form a bond resulting in a higher

molecular weight species or even within the same polymer some cross-linking reactions

take place. There are various types of degradation with different mechanisms. It has been

proved that the degradation of PS is accompanied by thermal transformations along with

catalytic transformation in thermal assisted pyrolysis. Therefore, it is often termed as

Introduction

14

thermo-catalytic degradation [58] and the subject of our concern therefore, for ease of

understanding they are described separately.

1.10.1. Thermal degradation (radical mechanism)

The degradation of PS into its monomer, dimer, oligomers or associated degraded

compounds is caused by chemical bond scission reaction of the polymer backbone of

macromolecules [48]. Thermal or heat assisted degradation of PS follow chain mechanism

and initiate with the formation of polymer radicals, followed by propagation, transfer and

termination steps [59-68]. PS initiate thermal degradation via C-C bond rupture of the

polymer chain to form two radicals: a primary radical (R1) and a secondary radical (R₂).

The formation of radicals are followed by propagation step by continuous

depolymerization (β-scission) to form a series of R1 and R2 radicals with the formation of

styrene monomer. Some primary and secondary radicals also transformed to tertiary

radicals by the intramolecular H-abstraction, which lead the formation of α-methylstyrene

and dimers shown in Scheme 1.

Introduction

15

Some of the radicals along with α-methylstyrene and dimers undergo transfer or

recombination reaction of low activation energy [66, 67] shown in scheme 2. The formation

of head to head structure and some R1 and R2 root products were formed. The

recombination reactions followed by intermolecular H-abstraction and or

disproportionation reaction then lead to the formation of wide range of products. Extensive

random chain scission cause to form composite radicals of R1 and R2 in combination with

C-C bond linkage of phenyl rings in order to form phenyl radicals and these radicals are

then transformed into head-to-head structure by the abstraction of intermolecular hydrogen

(H) or disproportionation reactions. Scheme 2 represent the routes to many products

formed by this mechanism, which include toluene; ethylbenzene; Benzene, (1-

Introduction

16

methylethyl); diphenylmethane; benzene, 1,1'-ethylidenebis; ethylene, 1,1-diphenyl;

benzene, 1,1'-(1,2-ethanediyl)bis; 1,2-diphenylethylene; benzene, 1,1'-(1-methyl-1,2-

ethanediyl)bis; benzene, 1,1'-(1-butene-1,4-diyl)bis; benzene, 1,1'-(1,3-propanediyl)bis;

benzene, 1,1'-(3-methyl-1-propene-1,3-diyl)bis; benzene, 1,1'-(1-methyl-1,3-

propanediyl)bis; benzene, 1,1'-(1-butenylidene)bis; benzene, 1,1'-(1,5-hexadiene-1,6-

diyl)bis; benzene, 1,1'-(1,4-butanediyl)bis; benzene, 1,1'-(3-methyl-1-propene-1,3-

diyl)bis; 1,4-diphenyl-1,3-butadiene; benzene, 1,1'-(2-methyl-1-propenylidene)bis; 2,5-

diphenyl-1,5-hexadiene; 1-pentene, 1,5-diphenyl; 1-(4-methylphenyl)-4-phenylbuta-1,3-

diene; 1,5-diphenyl-1,5-hexadiene; benzene, 1,1'-(2-pentene-1,5-diyl)bis etc.

Scheme 3 & 4 shows that some of the radical composites also go through the random chains

scission and forming condensed aromatic compounds by intramolecular cyclization and

dehydrogenation of the alkyl moiety that lead to the formation of condensed products such

as 2-phenylnaphthalene; indene; 1,2-diphenylcyclopropane; 2-phenyl-1H-indene; 3-

phenyl-1Hindene; 1,2-dihydro-1-phenylnaphthalene; naphthalene, 1,2-dihydro-4-phenyl;

naphthalene, 1-phenyl and benzene, 1,3,5-triphenyl [68]. Apart from these they may also

form 1H-indene, 2-methyl-3-phenyl; p-terphenyl; m-terphenyl and similar products.

The formation of some condensed products like naphthalene; naphthalene, 1-methyl; and

naphthalene, 1-benzyl with their possible routes [69] have been presented in Scheme 5.

Where the formation mechanism of arenes from toluene with the production of anthracene

; anthracene, 9,10-dihydro and 9,10-dimethylanthracene [69] have given in Scheme 6.

These are mechanism for common products, there may occur hundreds of other reactions

producing numerous compounds depending upon the product of initiation and its

interacting species.

Introduction

17

Introduction

18

Introduction

19

1.10.2. Catalytic degradation (ionic mechanism)

1.10.2.1. Acidic catalysts (cationic mechanism)

Acidic catalysts initiate the degradation of PS with the attack of a proton associated with a

Brönsted acid site to the phenyl ring of the PS polymer backbone. The resulting carbocation

(carbenium) undergo β-scission followed by a hydrogen transfer.

The mechanism to the production of major and important compounds is described by

Audisio et al. [70]. The hydrogen of acidic catalysts attack the branched aromatic ring

giving rise to primary cation Type I of π-complex, which upon β-scission convert to σ-

complex (secondary cation) and release benzene, shown in scheme 1.

The secondary cation produce during the β-scission of type I primary cation undergo

catalytic cyclization and produce indane and or its derivatives [70, 71], the mechanism is

shown in scheme 2.

The same way the hydrogen of acidic catalysts attack the branched phenyl group of PS and

produce primary cation Type II, which upon β-scission give rise to a polymer ion (A)

having positive charge on the last carbon atom of the chain and also produce a cyclodiene

substituted polymer chain (B) as shown in scheme 3. The ion A further undergo β-scission

and yield styrene monomer and secondary ions of A. Therefore, high amount of styrene is

produced. The primary or secondary ion A also undergo hydride ion rearrangement

followed by β-scission to produce α-methylstyrene [70, 71].

Introduction

20

Scheme 4 shows the cyclodiene substituted polymer chain (B) rearrangement, which is

attacked by a proton and forms another cation. The cation then undergo β-scission

producing a toluene and a secondary ions.

Some intermolecular hydrogen transfer also takes place, which results in the formation of

ethylbenzene and benzene, (1-methylethyl). The mechanism is given in scheme 5.

Introduction

21

Lewis acids catalyze degradation of PS initiate with an elimination of hydrogen atom from

the benzyl carbon of the aliphatic chain in polymer backbone (dealkylation reaction)

forming a polycation [72, 73] shown in scheme 6. The polycation produced by the

elimination of hydride then undergo cationic transformations as shown in scheme 1-5.

Benzene, toluene and ethylbenzene can also be formed by further degradation and

hydrogenation of styrene [55, 74]. Whereas, the dispersion of Lewis acid over acidic

support results in the formation of both Brönsted and Lewis acidic sites for the degradation

of PS [75]. Beside these, some interaction between the pre-formed molecules also take

place and some cross-linking reactions among the adjacent polymeric chains or even inside

the same polymer take place [76]. The formation of residue is due to the secondary cross-

linking reactions [71, 77].

1.10.2.2. Basic catalysts (anionic mechanism)

The catalytic degradation of PS with basic catalyst initiate through deprotonation and

formation of carboanion. The resulting carboanion undergo β-scission of the C-C bond on

the aliphatic chain [71]. The formation route of styrene, dimers and many other compounds

with anionic mechanism is identical with thermal degradation.

Introduction

22

The later compounds upon isomerization and decomposition form other cracking products

such benzene; toluene; ethylbenzene; styrene; α-methylstyrene; benzene, (1-methylethyl);

indane; indene; naphthalene and others [58].

1.11. Aim of the Present Work

The aim of present work is the exploration of new bulk catalysts and preparation of novel

impregnated catalysts followed by characterization using N2 adsorption/desorption, SEM

and XRD techniques for the degradation of WEPS with high activity and selectivity of the

yielded products for desirable and valuable compounds obtained from degradation

reaction. After degradation of WEPS with high activity and selectivity bulk liquid products

will be collected and then its separation by fractional distillation followed by the

characterization of parent liquid products and fractionates by physiochemical techniques

and GC-MS studies.

Introduction

23

References

[1] I. Chorkendorff, J. W. Niemantsverdriet, "Concepts of Modern Catalysis and

Kinetics", Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, pp. 457

(2007).

[2] A. J. B. Robertson, "Catalysis of Gas Reactions by Metals", Logos Press Ltd.,

London, UK (1970).

[3] J. Hagen, "Introduction" in Industrial Catalysis: A practical approach, Wiley-VCH

Verlag GmbH & Co. KGaA, Weinheim, Germany, pp. 1-14 (2006).

[4] A. Behr, "Organometallic Compounds and Homogeneous Catalysis" in Ullmann's

Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH & Co. KGaA,

Weinheim, Germany, (2000).

[5] M. D. Fryzuk, Inorganic chemistry: Ammonia transformed, Nature 427 (6974) 498-

499 (2004).

[6] K. Pansanga, N. Lohitharn, A. C. Y. Chien, E. Lotero, J. Panpranot, P. Praserthdam,

J. G. Goodwin Jr, Copper-modified alumina as a support for iron Fischer–Tropsch

synthesis catalysts, Applied Catalysis A: General 332 (1) 130-137 (2007).

[7] H. Knözinger, K. Kochloefl, "Heterogeneous Catalysis and Solid Catalysts" in

Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH & Co.

KGaA, Weinheim, Germany, (2000).

[8] J. M. Thomas, W. J. Thomas, "Principles and Practice of Heterogeneous

Catalysis", VCH, Weinheim Germany, pp. 464 (1997).

[9] Y. Zhang, Y. Yoneyama, K. Fujimoto, N. Tsubaki, A new preparation method of

bimodal catalyst support and its application in Fischer–Tropsch Synthesis, Topics

in Catalysis 26 (1-4) 129-137 (2003).

[10] J. M. Smith, "Chemical engineering kinetics", McGraw-Hill Kogakusha Ltd.,

Tokoyo, Japan, pp. 612 (1970).

Introduction

24

[11] M. V. C. Sastri, V. Srinivasan, B. Viswanathan, "Electrical Properties of Solid

Catalysts" in Modern Aspects of Solid State Chemistry, C. N. R. Rao (Ed.), Springer

US, pp. 425-445 (1988).

[12] K. Wilson, J. H. Clark, Solid acids and their use as environmentally friendly

catalysts in organic synthesis, Pure and Applied Chemistry 72 (7) 1313-1319

(2000).

[13] M. A. Harmer, Q. Sun, Solid acid catalysis using ion-exchange resins, Applied

Catalysis A: General 221 (1–2) 45-62 (2001).

[14] M. H. Valkenberg, C. deCastro, W. F. Hölderich, Friedel-Crafts acylation of

aromatics catalysed by supported ionic liquids, Applied Catalysis A: General 215

(1–2) 185-190 (2001).

[15] K. Tanabe, W. F. Hölderich, Industrial application of solid acid–base catalysts,

Applied Catalysis A: General 181 (2) 399-434 (1999).

[16] A. Ozaki, K. Kimura, The effective site on acid catalysts revealed in n-butene

isomerization, Journal of Catalysis 3 (5) 395-405 (1964).

[17] O. Deutschmann, H. Knözinger, K. Kochloefl, T. Turek, "Heterogeneous Catalysis

and Solid Catalysts" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-

VCH Verlag GmbH & Co. KGaA, (2000).

[18] P. Gayán, M. A. Pans, M. Ortiz, A. Abad, L. F. de Diego, F. García-Labiano, J.

Adánez, Testing of a highly reactive impregnated Fe2O3/Al2O3 oxygen carrier for

a SR–CLC system in a continuous CLC unit, Fuel Processing Technology 96 (0)

37-47 (2012).

[19] Y. Lu, S. Li, L. Guo, Hydrogen production by supercritical water gasification of

glucose with Ni/CeO2/Al2O3: Effect of Ce loading, Fuel 103 (0) 193-199 (2013).

[20] A. Romero-Pérez, A. Infantes-Molina, A. Jiménez-López, E. R. Jalil, K. Sapag, E.

Rodríguez-Castellón, Al-pillared montmorillonite as a support for catalysts based

on ruthenium sulfide in HDS reactions, Catalysis Today 187 (1) 88-96 (2012).

Introduction

25

[21] J. Taghavimoghaddam, G. P. Knowles, A. L. Chaffee, Preparation and

characterization of mesoporous silica supported cobalt oxide as a catalyst for the

oxidation of cyclohexanol, Journal of Molecular Catalysis A: Chemical 358 (0) 79-

88 (2012).

[22] A. Machocki, A. Denis, W. Grzegorczyk, W. Gac, Nano- and micro-powder of

zirconia and ceria-supported cobalt catalysts for the steam reforming of bio-

ethanol, Applied Surface Science 256 (17) 5551-5558 (2010).

[23] J. Ludvíková, K. Jirátová, J. Klempa, V. Boehmová, L. Obalová, Titania supported

Co–Mn–Al oxide catalysts in total oxidation of ethanol, Catalysis Today 179 (1)

164-169 (2012).

[24] F. Pinna, Supported metal catalysts preparation, Catalysis Today 41 (1–3) 129-137

(1998).

[25] A. A. Adesina, Hydrocarbon synthesis via Fischer-Tropsch reaction: travails and

triumphs, Applied Catalysis A: General 138 (2) 345-367 (1996).

[26] G. Li, L. Hu, J. M. Hill, Comparison of reducibility and stability of alumina-

supported Ni catalysts prepared by impregnation and co-precipitation, Applied

Catalysis A: General 301 (1) 16-24 (2006).

[27] S. Wang, H. Liu, Selective hydrogenolysis of glycerol to propylene glycol on Cu–

ZnO catalysts, Catalysis Letters 117 (1-2) 62-67 (2007).

[28] C. C. Chusuei, X. Lai, K. A. Davis, E. K. Bowers, J. P. Fackler, D. W. Goodman,

A nanoscale model catalyst preparation: Solution deposition of phosphine-

stabilized gold clusters onto a planar TiO2 (110) support, Langmuir 17 (13) 4113-

4117 (2001).

[29] M. A. Vicente, C. Belver, R. Trujillano, M. A. Bañares-Muñoz, V. Rives, S. A.

Korili, A. Gil, L. M. Gandı́a, J. F. Lambert, Preparation and characterisation of

vanadium catalysts supported over alumina-pillared clays, Catalysis Today 78 (1–

4) 181-190 (2003).

Introduction

26

[30] G. J. K. Acres, A. J. Bird, J. W. Jenkins, F. King, "The design and preparation of

supported catalysts" in Catalysis, C. Kemball, D. A. Dowden (Eds.), The Royal

Society of Chemistry, pp. 1-30 (1981).

[31] L. Li, N. Zhao, W. Wei, Y. Sun, A review of research progress on CO2 capture,

storage, and utilization in Chinese Academy of Sciences, Fuel 108 (0) 112-130

(2013).

[32] A. Brems, J. Baeyens, J. Beerlandt, R. Dewil, Thermogravimetric pyrolysis of

waste polyethylene-terephthalate and polystyrene: A critical assessment of kinetics

modelling, Resources, Conservation and Recycling 55 (8) 772-781 (2011).

[33] B. Dutcher, M. Fan, S. Cui, X.-D. Shen, Y. Kong, A. G. Russell, P. McCurdy, M.

Giotto, Characterization and stability of a new, high-capacity amine-functionalized

CO2 sorbent, International Journal of Greenhouse Gas Control 18 (0) 51-56

(2013).

[34] A. L. Andrady, M. A. Neal, Applications and societal benefits of plastics,

Philosophical Transactions of the Royal Society B: Biological Sciences 364 (1526)

1977-1984 (2009).

[35] Z. Ahmad, F. Al-Sagheer, N. A. Al-Awadi, Pyro-GC/MS and thermal degradation

studies in polystyrene-poly(vinyl chloride) blends, Journal of Analytical and

Applied Pyrolysis 87 (1) 99-107 (2010).

[36] J. M. Arandes, J. Ereña, M. J. Azkoiti, M. Olazar, J. Bilbao, Thermal recycling of

polystyrene and polystyrene-butadiene dissolved in a light cycle oil, Journal of

Analytical and Applied Pyrolysis 70 (2) 747-760 (2003).

[37] Z. Hussain, K. M. Khan, K. Hussain, Microwave-metal interaction pyrolysis of

polystyrene, Journal of Analytical and Applied Pyrolysis 89 (1) 39-43 (2010).

[38] R. S. Chauhan, S. Gopinath, P. Razdan, C. Delattre, G. S. Nirmala, R. Natarajan,

Thermal decomposition of expanded polystyrene in a pebble bed reactor to get

Introduction

27

higher liquid fraction yield at low temperatures, Waste Management 28 (11) 2140-

2145 (2008).

[39] V. R. Chumbhale, J. S. Kim, S. B. Lee, M. J. Choi, Catalytic degradation of

expandable polystyrene waste (EPSW) over mordenite and modified mordenites,

Journal of Molecular Catalysis A: Chemical 222 (1–2) 133-141 (2004).

[40] H.-Y. Shin, S.-Y. Bae, Thermal decomposition of polystyrene in supercritical

methanol, Journal of Applied Polymer Science 108 (6) 3467-3472 (2008).

[41] M. R. Islam, M. Parveen, H. Haniu, M. R. Islam, Innovation in pyrolysis technology

for management of scrap tire: a Solution of energy and environment, International

Journal of Environmental Science and Development 1 (1) 89-96 (2010).

[42] S. E. Levine, L. J. Broadbelt, Reaction pathways to dimer in polystyrene pyrolysis:

A mechanistic modeling study, Polymer Degradation and Stability 93 (5) 941-951

(2008).

[43] Marine Litter: A Global Challenge, Available from:

http://www.unep.org/publications/search/pub_details_s.asp?ID=4021 (Accessed:

12th July, 2013)

[44] Polystyrene Foam Report, Available from:

http://www.earthresource.org/campaigns/capp/capp-styrofoam.html (Accessed: 12

July, 2013)

[45] Eliminate the Use of Polystyrene, Available from:

http://www.ejnet.org/plastics/polystyrene/nader.html (Accessed: 12th July, 2013)

[46] N. Miskolczi, L. Bartha, A. Angyal, High Energy Containing Fractions from Plastic

Wastes by Their Chemical Recycling, Macromolecular Symposia 245-246 (1) 599-

606 (2006).

[47] A. K. Panda, R. K. Singh, D. K. Mishra, Thermolysis of waste plastics to liquid

fuel: A suitable method for plastic waste management and manufacture of value

http://www.unep.org/publications/search/pub_details_s.asp?ID=4021

http://www.earthresource.org/campaigns/capp/capp-styrofoam.html

http://www.ejnet.org/plastics/polystyrene/nader.html

Introduction

28

added products-A world prospective, Renewable and Sustainable Energy Reviews

14 (1) 233-248 (2010).

[48] C. L. Beyler, M. M. Hirschler, "ASTM E 176, "Standard Terminology of Fire

Standards"" in Annual Book of ASTM Standards, American Society for Testing and

Materials, West Conshohocken, PA, USA,

[49] M. Blazsó, Recent trends in analytical and applied pyrolysis of polymers, Journal

of Analytical and Applied Pyrolysis 39 (1) 1-25 (1997).

[50] K. Huang, L. H. Tang, Z. B. Zhu, W. Y. Ying, Continuous distribution kinetics for

degradation of polystyrene in sub and supercritical toluene, Journal of Analytical

and Applied Pyrolysis 76 (1–2) 186-190 (2006).

[51] N. Kiran, E. Ekinci, C. E. Snape, Recyling of plastic wastes via pyrolysis,

Resources, Conservation and Recycling 29 (4) 273-283 (2000).

[52] P. Layman, Germany's big chemical firms cut dividends, Chemical and

Engineering News, 1993, pp. 4–5

[53] Z. Zhibo, S. Nishio, Y. Morioka, A. Ueno, H. Ohkita, Y. Tochihara, T. Mizushima,

N. Kakuta, Thermal and chemical recycle of waste polymers, Catalysis Today 29

(1-4) 303-308 (1996).

[54] K. H. Lee, Composition of aromatic products in the catalytic degradation of the

mixture of waste polystyrene and high-density polyethylene using spent FCC

catalyst, Polymer Degradation and Stability 93 (7) 1284-1289 (2008).

[55] S.-Y. Lee, J.-H. Yoon, J.-R. Kim, D.-W. Park, Degradation of polystyrene using

clinoptilolite catalysts, Journal of Analytical and Applied Pyrolysis 64 (1) 71-83

(2002).

[56] A. Marcilla, J. C. García-Quesada, S. Sánchez, R. Ruiz, Study of the catalytic

pyrolysis behaviour of polyethylene-polypropylene mixtures, Journal of Analytical

and Applied Pyrolysis 74 (1-2) 387-392 (2005).

Introduction

29

[57] C. F. Cullis, M. M. Hirschler, "The combustion of organic polymers", Clarendon

Press ; Oxford University Press, Oxford, New York (1981).

[58] M. Marczewski, E. Kamińska, H. Marczewska, M. Godek, G. Rokicki, J.

Sokołowski, Catalytic decomposition of polystyrene. The role of acid and basic

active centers, Applied Catalysis B: Environmental 129 (0) 236-246 (2013).

[59] H. H. G. Jellinek, Thermal degradation of polystyrene and polyethylene. Part III,

Journal of Polymer Science 4 (1) 13-36 (1949).

[60] S. L. Madorsky, S. Straus, D. Thompson, L. Williamson, Pyrolysis of

polyisobutene (vistanex), polyisoprene, polybutadiene, GR-S, and polyethylene in

a high vacuum, Journal of Polymer Science 4 (5) 639-664 (1949).

[61] T. Faravelli, M. Pinciroli, F. Pisano, G. Bozzano, M. Dente, E. Ranzi, Thermal

degradation of polystyrene, Journal of Analytical and Applied Pyrolysis 60 (1) 103-

121 (2001).

[62] J.-S. Kim, W.-Y. Lee, S.-B. Lee, S.-B. Kim, M.-J. Choi, Degradation of polystyrene

waste over base promoted Fe catalysts, Catalysis Today 87 (1–4) 59-68 (2003).

[63] Y. Hu, S. Li, The effects of magnesium hydroxide on flash pyrolysis of polystyrene,

Journal of Analytical and Applied Pyrolysis 78 (1) 32-39 (2007).

[64] T. M. Kruse, O. S. Woo, H.-W. Wong, S. S. Khan, L. J. Broadbelt, Mechanistic

modeling of polymer degradation: A comprehensive study of polystyrene,

Macromolecules 35 (20) 7830-7844 (2002).

[65] B. N. Jang, C. A. Wilkie, The thermal degradation of polystyrene nanocomposite,

Polymer 46 (9) 2933-2942 (2005).

[66] T. M. Kruse, S. E. Levine, H.-W. Wong, E. Duoss, A. H. Lebovitz, J. M. Torkelson,

L. J. Broadbelt, Binary mixture pyrolysis of polypropylene and polystyrene: A

modeling and experimental study, Journal of Analytical and Applied Pyrolysis 73

(2) 342-354 (2005).

Introduction

30

[67] T. M. Kruse, O. Sang Woo, L. J. Broadbelt, Detailed mechanistic modeling of

polymer degradation: application to polystyrene, Chemical Engineering Science 56

(3) 971-979 (2001).

[68] I. C. McNeill, M. Zulfiqar, T. Kousar, A detailed investigation of the products of

the thermal degradation of polystyrene, Polymer Degradation and Stability 28 (2)

131-151 (1990).

[69] C. D. Hurd, A. R. Macon, J. I. Simon, R. V. Levetan, Pyrolytic formation of arenes.

I. Survey of general principles and findings, Journal of the American Chemical

Society 84 (23) 4509-4515 (1962).

[70] G. Audisio, F. Bertini, P. L. Beltrame, P. Carniti, Catalytic degradation of

polymers: Part III—Degradation of polystyrene, Polymer Degradation and

Stability 29 (2) 191-200 (1990).

[71] H. Ukei, T. Hirose, S. Horikawa, Y. Takai, M. Taka, N. Azuma, A. Ueno, Catalytic

degradation of polystyrene into styrene and a design of recyclable polystyrene with

dispersed catalysts, Catalysis Today 62 (1) 67-75 (2000).

[72] V. Karmore, G. Madras, Thermal degradation of polystyrene by Lewis acids in

solution, Industrial & Engineering Chemistry Research 41 (4) 657-660 (2002).

[73] R. Lin, R. L. White, Acid-catalyzed cracking of polystyrene, Journal of Applied

Polymer Science 63 (10) 1287-1298 (1997).

[74] S. Y. Lee, J. H. Yoon, J. R. Kim, D. W. Park, Catalytic degradation of polystyrene

over natural clinoptilolite zeolite, Polymer Degradation and Stability 74 (2) 297-

305 (2001).

[75] X. S. Zhao, M. G. Q. Lu, C. Song, Immobilization of aluminum chloride on MCM-

41 as a new catalyst system for liquid-phase isopropylation of naphthalene, Journal

of Molecular Catalysis A: Chemical 191 (1) 67-74 (2003).

Introduction

31

[76] H. Nanbu, Y. Sakuma, Y. Ishihara, T. Takesue, T. Ikemura, Catalytic degradation

of polystyrene in the presence of aluminum chloride catalyst, Polymer Degradation

and Stability 19 (1) 61-76 (1987).

[77] C. Xie, F. Liu, S. Yu, F. Xie, L. Li, S. Zhang, J. Yang, Study on catalytic pyrolysis

of polystyrene over base modified silicon mesoporous molecular sieve, Catalysis

Communications 9 (6) 1132-1136 (2008).

LITERATURE REVIEW

Literature Review

32

Serrano et al., [1] reported the degradation of PS at 375 ºC using amorphous SiO2-Al2O3,

HMCM-41 and HZSM-5 zeolite as catalyst. Amorphous SiO2-Al2O3 and HZSM-5 catalyst

was reported with similar or lower conversion into products in comparison with thermal

degradation while HMCM-41 showed increased catalytic activity. This behavior of the

catalyst was explained by cross-linking competitive reaction supported by the strength and

Brönsted nature of the zeolite acid sites. Styrene was obtained as a major product

approximately 50 wt.% with thermal degradation and catalytic degradation using HZSM-

5 as a catalyst while using HMCM-41 and SiO2-Al2O3 as catalysts; benzene, ethylbenzene

and cumene were the major products but with less than 20 wt.%. The catalytic behavior of

HZSM-5 zeolite regarding its results was credited to of its microporous structure and acidic

character. The catalytic degradation of PS was explained that practically external acid sites

are active for degradation reactions, but the polymer is bulky to enter the micropores.

HMCM-41 was marked the best catalyst for the degradation of PS because of its moderate

acidic strength and mesoporous structure.

Ukei et al., [2] investigated a number of solid acid and solid base catalysts for the catalytic

cracking of PS into styrene monomer and dimer. Solid base catalysts were found with good

catalytic activity as compared to solid acid catalyst on the bases of the degradation

mechanism. BaO was as having better with best catalytic activity among solid bases. When

PS was thermally degraded in a mixture with BaO powder at 350 ºC, 90 wt.% styrene

produced. A model recyclable plastic was prepared with the help of a twin - roller at 120

ºC by dispersing 1 wt.% BaO powder in PS to produce PS films. The films were also

expanded into styrofoam along with dispersed BaO powder by using a gas absorption and

evolution method. More than 85 wt.% of the BaO dispersed PS films were converted into

the styrene at 350 ºC without the use of any other catalyst.

Lee et al., [3] reported the degradation of PS with natural clinoptilolite zeolite (HNZ) at

400 ºC. The pyrolysis studied were conducted to compare the catalytic performance of

HNZ catalyst with thermal degradation, HZSM-5 and silica-alumina catalysts and found

HNZ was as effective as HZSM-5 for liquid product yield with carbon numbers C5-C12

range. Styrene was the major product over both non-catalytic and catalytic degradation of

PS. Silica-alumina because of their mesoporous structure produced maximum

Literature Review

33

ethylbenzene with the concomitant decrease of styrene monomer. Using HNZ the

selectivity of ethylbenzene and propylbenzene was increased with increase in degradation

temperature while the selectivity for styrene monomer decreased styrene dimers. Kinetic

studies were also carried out by thermogravimetric analysis using a dynamic model which

showed reliable kinetic parameters for the degradation of PS using HNZ as catalyst.

Activation energy, calculated was 360 KJ/mol with first order kinetics.

Lee et al., [4] studied a number of solid acid i.e. silica-alumina, HY, HZSM-5, clinoptilolite

(both natural and synthetic) and mordenite for the degradation PS. They reported

clinoptilolites with good catalytic activity and yielded highly selective aromatic products

for the degradation of PS. The degradation behavior of the distribution of aromatic products

was discussed with the effect of catalyst acidity, degradation temperature and reaction time.

They found ethylbenzene was increased with the increase of reaction time and surface

acidity of the catalyst where styrene monomer was increased with increase of degradation

temperature.

Lee et al., [5] reported catalytic cracking of PS in fluidized bed reactor. Two types of PS;

general purpose polystyrene (GPPS) and expanded polystyrene wastes (EPSW) was used

while N2 was used as fluidized gas and silica sand was used as bed material. The study was

conducted with BaO, powder Fe2O3 and HZSM-5 (Si/Al=30) catalysts. The pyrolysis of

polymer was carried out uisng temperature ranging from 400 ºC to 550 ºC, gas velocity

from 0.3 m/s to 0.6 m/s and amount of catalyst (Fe2O3) for maximum yield of liquid

products and styrene monomer in comparison with thermal degradation. It was found that

catalysts yielded maximum liquids and styrene monomer as compared to thermal

degradation using the fluidized bed catalytic reactor. The catalytic activity of Fe₂O₃ was

found to be higher than BaO and HZSM-5 with the following descending order Fe2O3 >

BaO > HZSM-5. The amount of Fe2O3 was optimized with 5 wt.%. The amount of catalyst

using degradation temperature 450 ºC and gas velocity of 0.5 m/s.

Karmore and Madras [6] investigated Lewis acids such as AlCl3, FeCl3, BF3. O(Et)2 and

SnCl4 in the temperature ranging from 75 ºC to 125 ºC for the degradation of PS.

Continuous distribution kinetics and stoichiometry kernel for random chain scission was

used to model the evolution of molecular weight distribution (MWD). It was found that the

Literature Review

34

degradation rate was high with AlCl3 catalyst. The studies were also conducted with

varying amount of AlCl3 catalyst revealing that the rate of degradation was proportional to

the fourth power of the Lewis acid concentration. In the presence of AlCl3 catalyst, the

activation energy for the degradation of PS was found to be 7.7 Kcal/mol calculated from

the temperature dependence of the degradation rate coefficient.

Lee et al., [7] studied the degradation of waste PS for the recovery of styrene monomer and

value added products using swirling fluidized bed reactor with 5.8 cm I.D and 150 cm H

to control the residence time of feeds with the enhancement of temperature distribution

uniformity within the reactor. BaO, Fe2O3 and HZSM-5 (Si/Al=30) was used as catalysts

for maximum selective degradation of PS into styrene monomer. PS degradation was

investigated with respect to degradation temperature, reacting time, volume flow rate of

gas and the ratio of swirling gas to the amount of primary fluidizing gas. The effect of

operating variables on distribution of temperature and their variation in radial and axial

directions for the degradation of PS waste in swirling fluidized bed reactor was also

studied. It was found that with the addition of a catalyst. The reaction time and degradation

temperature decreased intensely. The cause of periodic and persistent temperature variation

was described by the mode of swirling fluidization which increased temperature

distribution uniformity by reducing the temperature gradient in the reactor. It was also

found that with the increase of swirling gas (V2/V1) the yield of liquid as well as styrene

monomer have increased, but their maximum values were achieved by increasing the

volume flow rate of gas.

Hu and Li [8] reported the pyrolysis of pure and flame-retarded PS composite with

Mg(OH)2 in off-line furnace for 10 min at 700 ºC degradation temperature. Cambridge pad

was used for collection of liquid and tar products and were analyzed both qualitatively and

quantitatively by GC-MS with significant results on flash pyrolysis of PS degradation with

Mg(OH)2. It was found that composite of PS and Mg(OH)2 does not produce new

compounds, but the quantity of resulting products was different from the that of pure PS

degradation. It was revealed that some head to head structures and condensed products

increased with the associated and prominent decrease of styrene monomer.

Literature Review

35

Rahul Kumar Balakrishnan and Chandan Guria [9] reported the pyrolysis of PS using

Fe2O3 catalyst, benzene solvent and hydrogen gas at low degradation temperature of 170

ºC to 240 ºC. The various factors affecting the degradation of PS like temperature, the

amount of catalyst and polymer in hydrogen atmosphere were investigated. The

degradation studies were also concluded at differing initial hydrogen partial pressure where

the time dependent molecular weight was calculated with viscosity average technique and

found that degradation was enhanced in the presence of hydrogen gas which followed

random chain scission degradation mechanism. Kelen- random degradation kinetic model

was used for the estimation of degradation rate constant and proposed empirical

correlations for the effect of amount of catalyst and initial hydrogen partial pressure in the

pyrolysis reaction. These proposed models were used to calculate true thermal degradation

rate constants at a given amount of catalyst and initial hydrogen partial pressure at changing

temperature. Arrhenius equation was used for the calculation of activation energy and

frequency factor considering the true thermal degradation rate constant.

Chauhan et al., [10] investigated the degradation of expanded PS into a maximum yield of

into liquid styrene monomer in a designed bench scale reactor for the recycling of styrene

and other value added hydrocarbons under oxidative (O2) environment and vacuum from

300 ºC to 500 ºC. Vacuum condition was found the best for degradation reaction with

heating temperature of 500 ºC, at these conditions 91.7 wt.% liquid products were obtained

with 85.5% of styrene. The products were characterized using distillation and IR

spectroscopy and the remaining products of degradation reactions were found to be

benzene, ethylbenzene, styrene monomer and styrene dimers.

Hussain et al., [11] developed a novel method for the degradation of PS waste using

microwave metal interaction at high temperature. The degradation may be catalyzed by the

interaction of metal and altering components of products was explained. A batch reactor

having a cylindrical mesh of iron was used in the study and it was observed that PS

degraded rapidly by heating in microwave. The temperature produced by iron mesh was

measured 1100 ºC to 1200 ºC producing 80% liquid and 15% gaseous products with small

amount of char residue (5%). The products were condensed by cooling and analyzed by

GC-MS. The results showed that the products contain styrene monomer and other aromatic

Literature Review

36

hydrocarbons i.e. polycyclic condensed ring aromatic and polycyclic aromatic as the

product of degradation. The formation of different products have also been explained.

Jin et al., [12] prepared mesoporous MCM-41 sepiolite percolation and sequent

hydrothermal preparation in NaOH solution in combination with

hexedecyltrimethylammonium bromide as template. The resulting products were

characterized by SEM, TEM and BET surface area. It was found to increase with increase

in crystallization time, ratios of surfactant to silica and decreases the Mg content increased

the pore size and crystallinity of MCM-41. The degradation of PS revealed MCM-41 with

MgO from natural sepiolite had high catalytic with good selectivity for the production of

styrene monomer using polymer to catalyst ratio 200. The side reactions of PS degradation

yield ethylbenzene, isopropylbenzene, isopropenylbenzene where side, cross linking

reactions were controlled by the basic character of the MgO in MCM-41 catalyst.

Lin and Sharratt [13] investigated catalytic degradation of pure plastics (high density

polyethylene, polypropylene, polystyrene and polyvinyl chloride) and waste plastics with

the aim to reduce net disposal cost. Acidic zeolitic catalysts (HMOR, HUSY and HZM-5),

non-zeolitic catalyst (SiO2-Al2O3) and silicalite (Si/Al) were used for the degradation

reactions in a designed fluidized bed reactor. It was observed that using catalysts in the

reactor reduce degradation temperature, enhanced aromatic products and product

distribution selectivity was also enhanced. To predict the production rates and selectivity a

kinetic/mechanistic model was presented. Product distributions have been discussed in

terms of catalyst structures, feedstock and preliminary process model.

Kim et al., [14] reported catalytic pyrolysis of mixture polypropylene (PP) and PS using

semi-batch reactor. The effect of degradation temperature and nature of catalyst was

investigated on the products. It was observed that liquid products were maximum products

of the degradation reactions mainly in the gasoline range. SiO2-Al2O3 (SA) and natural

clinoptilolite (HNZ) was found with similar catalytic activity for the degradation of plastic

mixture where HZSM-5 was marked to produce highest amount of gases. It was observed

that the amount of ethylbenzene and propylbenzene decreased by increasing pyrolysis

temperature with parallel increase of styrene monomer. Thermogravimetric analysis

revealed an interaction between PP and PS in the thermocatalytic pyrolysis.

Literature Review

37

Lee et al., [15] investigated the pyrolysis of mixture of high-density polyethylene (HDPE)

and PS with different proportions using spent FCC as catalyst in a stirred semi-batch

reactor at 400 ºC. The role of time or mixing proportion of mixing reactants were taken

into account for the determination of the rate of degradation into liquid products, aggregate

amount, distribution, the carbon number distribution, and the paraffin, naphthene, olefin

and aromatic (PONA) distribution of the resulting liquid products. The aggregated amount

distributed was found to depend on the mixing ratio of HDPE and PS, and the initial

degradation rate was ramped exponentially with PS contents while for the final degradation

rate ramped with HDPE contents. Increase in the gasoline fraction 85 wt.% to 100 wt.%

was observed with the increase of PS contents from 0 wt.% to 100 wt.%, respectively.

Liquid PONA product distribution was reported with the interaction of degraded

components of HDPE and PS. It was also observed that increasing PS components more

than 60 wt.% increased the production of aromatic components (mono-cycling) and the

selectivity toward aromatic products like ethylbenzene and styrene.

Ciliz et al., [16] investigated slow degradation of pure polypropylene (PP) and in mixture

with polyethylene (PE) and PS under identical conditions. The impact of waste on products

composition as well as different mixing ratios were investigated. They also conducted

thermogravimetric analysis of the plastics and because of impurities found differences from

the weight loss curves for the derivatives of pure PP and waste PP were observed. The

distribution of liquid yield regarding aliphatic, mono-aromatic and poly-aromatic

compounds varied with an increase in the ratio of PP in mixture. The variation of

alkene/alkane ratio of gas products with a mixing ratio of waste was also explained.

Miskolczi et al., [17] reported thermocatalytic degradation technique of plastics into liquid

hydrocarbon. Degradation of waste plastic mixture of polyethylene (PE) and PS was

carried out in batch reactor over equilibrium FCC, ZSM-5 and natural clinoptilolite zeolite

(HNZ) catalysts. The mixture of PE and PS was degraded from 410 ºC to 450 ºC

temperatures. The effect of catalyst and their average particle size have been investigated

on the yield of major degradation products i.e. gasoline, diesel oil and gases. Equilibrium

FCC and HNZ catalysts were founded with good catalytic activity to produce low

molecular weight hydrocarbons and ZSM-5 was found to yield the highest amount of

Literature Review

38

gaseous products. Gas chromatography was used for the characterization of resulting liquid

and gas products. The hydrocarbon distribution was broad from C5 to C28 carbon number

range depending upon degradation parameters. The degradation of polyethylene yielded

linear, non-branched compounds and the degradation of PS yielded benzene, toluene,

ethylbenzene and styrene like aromatic products. It was observed that with the increase in

pyrolysis temperature the concentration of volatile products increased, whereas the yield

of unsaturated component decreased. Infrared technique was used for the measurement of

olefin contents which was reported from 50% to 60%. On the basis of volatile products

composition, activation energies were calculated to be decreased. Carbon-chain and double

bond isomerization were reported due to catalyst.

Lee [18] used spent FCC catalyst because of its environmental favored and economical

aspect for thermocatalytic degradation of HDPE and PS mixture. The effect of reaction

time and the ratio of HDPE and PS mixture was investigated for liquid products and their

aromatic product distribution in comparative studies. It was found that light hydrocarbons

in the gasoline range were the major products in initial reaction time where the yield of

aromatics like ethylbenzene and styrene monomer were dependent on reaction time and

the ratio of HDPE and PS in mixture. The results revealed C9 to C12 alkylaromatic product

distribution as by-products where methylstyrene (C1-styrene) and isopropylbenzene (C3-

benzene) were the major products formed by β-scission mechanism and hydrogen transfer

mechanism. Other alkylaromatics were found in the range of 1% or less.

Murata et al., [19] degraded polyethylene (PE), polypropylene (PP) and PS in a mixture

with 1-2 wt.% polyvinylchloride (PVC) in a continuous flow reactor using a feed rate of

0-1.5 Kg/h under atmospheric pressure. The degradation was carried out in a temperature

range of 360 ºC to 440 ºC depending on the nature of feed material. The degradation

behavior and the resulting product and its properties were studied and explained as a

function of amount of PVC, degradation temperature and SiO2-Al2O3 catalyst. The study

was conducted for binary mixtures of PE/PVC, PP/PVC and PS/PVC as well as a complex

mixture of PE/PP/PS/PV and an interaction was found between PVC and each polyolefin.

It was observed that SiO2-Al2O3 catalyst decreased the concentration of Chloride contents

Literature Review

39

in liquid products but produces high amounts of organo-chlorine compounds in gaseous

products.

Huang et al., [20] reported the pyrolysis of polymer waste (LDPE/HDPE/PP/PS) of

hospital i.e. low-density polyethylene (LDPE), high-density polyethylene (HDPE),

polypropylene (PP) and PS. The degradation was carried out in isothermal fluidized-bed

reactor at ambient pressure over a different catalyst both zeolitic and non-zeolitic catalysts.

It was observed that zeolitic catalysts yielded a higher amount of volatile hydrocarbons

than non-zeolitic catalysts. The order of zeolitic catalysts in term of activity is ZSM-5 >

MOR > USY and non-zeolitic catalysts MCM-41 > ASA. A wide carbon number

distribution olefinic product mixture was yielded with MCM-41 because of large

mesopores. Catalyst ASA has weaker acidic sites on the other hand lead to the formation

of larger amount of saturated product mixture with wide carbon number distribution while

coke was produced using USY catalyst. The result of the study indicated the uses of catalyst

lead to better activity and increasing product selectivity. Based on kinetic and mechanistic

consideration a novel model was developed to investigate chemical reactions and

deactivation of catalysts for the degradation of mixture of polymer waste. The model

represented benefits of product selectivity like alkane, alkenes, aromatics and coke in

relation with nature and particle size of the catalyst.

Hussain et al., [21] reported co-degradation of PS and coal using microwave copper

interaction producing high temperature where copper antenna acts as catalyst too. It was

found that the degradation was occurring with the combine action of microwave

interaction, high temperature and the active species produced during degradation reactions.

The microwave metal interaction rapidly degraded the mixture giving 66%, 6% and 18%

liquids, gases and residue, respectively. It was observed that 10% of the liquids was

composed of sulfides where the GC-MS analysis of products reveal that it contain major

aromatic products in narrow ranges.

Kim et al., [22] investigated the degradation of waste expanded PS (WEPS) with low

temperature over modified Fe-base catalyst. It was found that the increase of degradation

temperature and Fe-based catalysts increased the yield of liquids and styrene monomer.

The selectivity toward styrene monomer was credited to carboanions. The degradation of

Literature Review

40

WEPS lead to the formation of 92.2 wt.% liquid products and 65.8 wt.% styrene monomer

at 400 ºC using Fe-K/Al2O3 catalyst. The activation energies calculated for thermal and

catalytic degradation are 194 KJ/mol and 138 KJ/mol, respectively.

Chumbhale et al., [23] reported the degradation of expanded PS waste (EPSW) over

modified mordenite zeolites. EPSW were degraded in a temperature range of 360 to 400

ºC using batch reactor. The study was aimed to understand the role of H-mordenite catalyst

followed by the effect of its modification weather through metal impregnation or

dealumination. It was found that dealuminated mordenite with silica-alumina ratio of 86

increased the styrene to styrene dimer molar ratios at 360 ºC and styrene to ethylbenzene

molar ratio at 400 ºC because of acidic strength generation. The metal impregnation of H-

mordenite with phosphorous loadings alter the acidic and catalytic properties of EPSW

degradation and improved the yield of styrene monomer with higher selectivity than

thermal degradation.

Tae et al., [24] reported the catalytic cracking of PS over acid-treated halloysite catalysts

using a semi-batch reactor. The cracking reactions of PS were carried out in the temperature

range of 400 to 450 ºC. Experiments were conducted to find out the effect of acidity of

catalyst, degradation temperature and reaction time on the yield of aromatic products. It

was found that acid-treated halloysite catalysts have higher catalytic activity and good

selectivity towards aromatic compounds. Increase in contact time and surface acidity

increased the production of ethylbenzene where increasing temperature enhanced the yield

of styrene.

Chumbhale et al., [25] investigated the degradation of expanded polystyrene waste (EPSW)

over HY and modified HY zeolites. HY zeolites were dealuminated by controlled steaming

with the application of heat. The study compared and discussed the yield of liquids, gases

and residues as well as boiling point distribution of liquid products with thermal

degradation without the use of any catalyst. It was found that the presence of HY catalyst

enhanced liquid product and decreased gases and residue while HY-700 catalyst showed

an enhancement in styrene monomer/styrene dimer as compared to the thermal

degradation. A correlation was also established between Al (nf/f), acidity (B/L) and styrene

monomer/styrene dimer (mole ratio).

Literature Review

41

Xie et al., [26] studied the degradation of polystyrene (PS) using impregnated catalyst.

Molecular sieve impregnated catalyst K2O/Si-MCM-41 was prepared by saturating Si-

MCM-41 with KNO3 and was characterized by N2 adsorption/desorption, FTIR, XRD and

TEM. It was observed from the results that K2O/Si-MCM-41 was mesoporous where K2O

decreased the long range order of the catalyst while KNO3 decomposed completely to K2O

at 600 ºC. Effect of K2O percentage, degradation temperature, catalyst to polymer ratio and

reaction time were investigated. The activity of the catalyst was determined for the

degradation of PS in comparison with CaO, Si-MCM-41 and Al-MCM-41 catalysts. The

results show that 9% K2O, 400 ºC temperature, 0.02 catalyst to polymer ratio and 30 min

heating time yielded 85.67% liquids with 69.02% styrene monomer.

Marczewski et al., [27]investigated acidic and basic catalysts for the degradation of PS, for

conversion into selective products. Treated SiO2-Al2O3 (45%) with 1-20 wt.% NaOH and

treated γ-Al2O3 with 1-8 wt.% NaOH or H2SO4 were initially tested for cumene and

diacetone degradation and then for PS degradation. It was found that thermal

transformation consists of gradual depolymerization to styrene monomer and further

cracking lead to the formation of dimers, trimmers or other oligomers where catalytic

transformation includes the conversion of oligomers. Toluene, ethylbenzene, styrene, α-

methylstyrene was formed also by the cracking linear styrene dimers activated by Brønsted

acid sites with simultaneous production of hydrogen (H+ and H‾) and coke where the

hydrogenation of styrene produced ethylbenzene. Acidic catalysts were found isomerize

linear dimers into cyclic products, followed by dealkylation leads to benzene and

methylindane, the later produces methylindene and naphthalene by isomerization and

hydrogen transfer reactions.

Literature Review

42

References

[1] D. P. Serrano, J. Aguado, J. M. Escola, Catalytic conversion of polystyrene over

HMCM-41, HZSM-5 and amorphous SiO2–Al2O3: comparison with thermal

cracking, Applied Catalysis B: Environmental 25 (2–3) 181-189 (2000).






305 (2001).



(2002).

[5] C. G. Lee, J. S. Kim, P. S. Song, Y. J. Cho, Y. Kang, M. J. Choi, Effects of catalyst

on the pyrolysis of polystyrene wastes in a fluidized bed catalytic reactor, Hwahak

Konghak 40 (4) 445-449 (2002).



[7] C.-G. Lee, Y.-J. Cho, P.-S. Song, Y. Kang, J.-S. Kim, M.-J. Choi, Effects of

temperature distribution on the catalytic pyrolysis of polystyrene waste in a swirling

fluidized-bed reactor, Catalysis Today 79–80 (0) 453-464 (2003).



[9] R. K. Balakrishnan, C. Guria, Thermal degradation of polystyrene in the presence

of hydrogen by catalyst in solution, Polymer Degradation and Stability 92 (8) 1583-

1591 (2007).

Literature Review

43




2145 (2008).



[12] S. Jin, K. Cui, H. Guan, M. Yang, L. Liu, C. Lan, Preparation of mesoporous MCM-

41 from natural sepiolite and its catalytic activity of cracking waste polystyrene

plastics, Applied Clay Science 56 (0) 1-6 (2012).

[13] Y.-H. Lin, P. N. Sharratt, Conversion of waste plastics to hydrocarbons by catalytic

zeolited pyrolysis, Journal of the Chinese Institute of Environmental Engineering

10 (4) 271-277 (2000).

[14] J.-R. Kim, J.-H. Yoon, D.-W. Park, Catalytic recycling of the mixture of

polypropylene and polystyrene, Polymer Degradation and Stability 76 (1) 61-67

(2002).

[15] K.-H. Lee, D.-H. Shin, Y.-H. Seo, Liquid-phase catalytic degradation of mixtures

of waste high-density polyethylene and polystyrene over spent FCC catalyst. Effect

of mixing proportions of reactants, Polymer Degradation and Stability 84 (1) 123-

127 (2004).

[16] N. Kiran Ciliz, E. Ekinci, C. E. Snape, Pyrolysis of virgin and waste polypropylene

and its mixtures with waste polyethylene and polystyrene, Waste Management 24

(2) 173-181 (2004).

[17] N. Miskolczi, L. Bartha, G. Deák, Thermal degradation of polyethylene and

polystyrene from the packaging industry over different catalysts into fuel-like feed

stocks, Polymer Degradation and Stability 91 (3) 517-526 (2006).

Literature Review

44




[19] K. Murata, M. Brebu, Y. Sakata, The effect of PVC on thermal and catalytic

degradation of polyethylene, polypropylene and polystyrene by a continuous flow

reactor, Journal of Analytical and Applied Pyrolysis 86 (1) 33-38 (2009).

[20] W.-C. Huang, M.-S. Huang, C.-F. Huang, C.-C. Chen, K.-L. Ou, Thermochemical

conversion of polymer wastes into hydrocarbon fuels over various fluidizing

cracking catalysts, Fuel 89 (9) 2305-2316 (2010).

[21] Z. Hussain, K. M. Khan, N. Basheer, K. Hussain, Co-liquefaction of Makarwal coal

and waste polystyrene by microwave–metal interaction pyrolysis in copper coil




[23] V. R. Chumbhale, J. S. Kim, S. B. Lee, M. J. Choi, Catalytic degradation of



[24] J.-W. Tae, B.-S. Jang, J.-R. Kim, I. Kim, D.-W. Park, Catalytic degradation of

polystyrene using acid-treated halloysite clays, Solid State Ionics 172 (1–4) 129-

133 (2004).

[25] V. R. Chumbhale, J. S. Kim, W. Y. Lee, S. H. Song, S. B. Lee, M. J. Choi, Catalytic

degradation of expandable polystyrene waste (EPSW) over HY and modified HY

zeolites, Journal of Industrial and Engineering Chemistry 11 (2) 253-260 (2005).



Communications 9 (6) 1132-1136 (2008).

Literature Review

45




EXPERIMENTAL

Experimental

46

3.1. Catalyst Preparation

i. Materials

Powder of Mg, MgCl2. 6H2O, ZnO, ZnCl2, Al, Al2O3, AlCl3. 6H2O, CuCl₂.

2H2O, MgO, MgCO₃, CuO, Fe₂O₃ and FeCl₃. 6H2O, granular Zn and metal

turnings of Cu and Fe were used.

ii. Catalyst preparation

The catalytic degradation of polystyrene (PS) was followed by two types of

catalysts i.e. bulk catalysts and impregnated catalysts. The bulk catalysts like

Mg, MgO, MgCO₃, Zn, ZnO, ZnCl₂, Al, Al₂O₃, AlCl₃ 6H2O, Cu, CuO, CuCl₂

2H2O, Fe, Fe₂O₃ and FeCl₃. 6H2O were grounded with the help of pestle and

mortar and screened to uniform size followed by drying in an oven at 120 ºC for

3 h.

A series of impregnated catalyst were prepared using the wet impregnation

method. Five different active central metals i.e. Mg, Zn, Al, Cu and Fe in the

form of their chloride salts were impregnated over three different supporting

materials i.e. alumina (Al₂O₃), montmorillonite clay (Mmn) and activated

charcoal (AC). The salts of Mg, Zn, Al, Cu and Fe was calculated 5%, 10%,

15%, 20% and 25% on the basis of metal weight for a known weight of support

i.e. for 5 g of each support the weight of Mg, Zn, Al, Cu and Fe are given in

table 1. The precursor metal salts were dissolved in appropriate amount of water

and were added to the slurry of supporting material. The mixture was stirred at

60 ºC for 1 h followed by drying in oven at 110 ºC for 6 h. The sample was

calcined at 300 ºC for 4 h and then brought to mesh size <445 µm.

Experimental

47

Table 3.1 Percentage (%) of active metal and their calculated weight

impregnated over 5 g of each support (Al2O3, Mmn and AC).

Percentage

(%)

Weight of metal loading (g)

Mg Zn Al Cu Fe

05 2.092 0.525 2.235 0.671 1.210

10 4.185 1.050 4.470 1.342 2.421

15 6.280 1.575 6.705 2.013 3.631

20 8.370 2.100 8.940 2.684 4.841

25 10.463 2.625 11.175 3.355 6.100

3.2. Characterization of catalysts

The prepared impregnated catalysts were characterized using N2 adsorption/desorption,

scanning electron microscopy (SEM) and X-ray diffraction (XRD).

3.2.1 Surface area, pore volume and pore size analysis

The surface area, pore volume and pore size of impregnated catalysts and supports was

determined using a Surface Area Analyzer “NOVA2200e Quantachrome, USA” using

nitrogen adsorption/desorption at 77.4 K. The surface area was determined using Brunauer-

Emmett-Teller (BET) method and Barrett-Joyner-Halenda (BJH) method, while the pore

volume and pore size were also measured by the BJH method. Prior to analysis the samples

were outgassed for 2 h at 100 ºC in vacuum to remove all adsorbed moisture from the

catalyst surface and pores and subjected to analysis.

3.2.2. SEM analysis

The surface morphology and particle size of the supports i.e. Al2O3, Mmn and AC before

and after impregnation were evaluated by 30 KV Scanning Electron Microscope (SEM)

(JSM5910, JEOL, Japan). The samples were prepared using conventional methods, the

powdered samples were mounted on standard specimen stubs with double adhesive carbon

tape.

Experimental

48

3.2.3. XRD analysis

X-ray diffraction (XRD) patterns were taken using a JDX-3532 JEOL (Japan) diffractmeter

with monochromatic Cu-Kα radiation (λ=1.5418Å) at 40 KV and 30 mA in the 2θ range

of 10-80⁰ with 1.03⁰ per minute.

3.3. Thermogravimetric analysis (TGA)

3.3.1. TGA of waste expanded polystyrene (WEPS)

i. Instrument

Perkin – Elmer TG/DTA Diamond series (USA)

ii. Material

Waste expanded polystyrene samples

iii. Procedure

Perkin-Elmer TG/DTA Diamond Series (USA) instrument was used for thermogravimetric

analysis of the WEPS sample, pieces of WEPS sample (7 Mg) was heated with the increase

of temperature from 40 °C to a final temperature 1000 °C at a rate of 10 °C/min. The

temperature of the sample was measured with a thermocouple attached directly at the

crucible very close to the sample. The weight loss verses temperature curve for thermal

decomposition of WEPS under a linear heating rate of oxidative (O2) and inert (N2)

atmosphere was recorded.

3.3.2. TGA of polystyrene (PS) and polyethylene terephthalate (PET)

iv. Instrument

Rigaku TAS 100 Data Station

v. Material

Virgin polystyrene (PS) and polyethylene terephthalate

Experimental

49

vi. Procedure

PS and PET samples were monitored by Thermogravimetric Analyzer (TGA) using Rigaku

TAS 100 Data Station. Approximately, 10 mg samples were heated. The temperature was

maintained for 10 min at ambient temperature (30 ºC) and then linearly increased from 30

ºC to 1000 ºC at the rate of 10 ºC/min in a nitrogen (N₂) flow rate of 20 ml/min.

3.4. Thermal and catalytic degradation of polymer samples

The flow process thermal and catalytic degradation of WEPS is given in Fig. 3.1.

Figure 3.1 Process flow for the degradation of waste expanded polystyrene.

Experimental

50

3.4.1. Thermal and catalytic degradation of WEPS

4.4.1.1. Reactor assembly

WEPS degradation studies were carried out using self-designed Pyrex glass reactor with

internal diameter 7 cm, height 22 cm and wall thickness 2.4 mm having a quick fit led,

inserted in an indigenously designed vertical heating furnace fitted with digital temperature

controller and attached thermocouple located in the center of furnace that can operate up

to 1000 ºC. The basic component of the reactor was fitted in steel assembly with power

on/off button. The outlet of the Pyrex glass reactor was connected with condenser and a

supply line of cold water. Cold traps was connected to the assembly for liquid product

collection as well as a sidewise outlet for gas collection. Schematic flow sheet diagram of

the assembly is given in Fig. 3.2.

1

49

7

6

8

1. Reactor2. Air tight lid3. Feed material + catalyst4. Electric furnace5. Temperature controller6. Water condenser7. Liquid products receiver8. Gas collection cylinder9. Ice cold trap

3

2

0450 ºC

ON

OFF

5

Figure 3.2 Schematic flow sheet diagram of the reaction assembly used for WEPS

degradation

Experimental

51

3.4.1.2. WEPS sample preparation

i. Instrument

Oven

ii. Materials

WEPS samples

iii. Procedure

WEPS samples were collected from refrigeration industry used for packing of

refrigerators and freezers; WEPS beads are manufactured with an average

molecular weight between (Mw) 160,000 and 260,000 g/mol. WEPS slabs and

large pieces were chopped into small granules and heated at 150 ºC for 20 min

to reduce its volume 20 times.

3.4.1.3. WEPS degradation

WEPS samples were degraded using thermal and thermocatalytic degradation.

Thermocatalytic degradation was carried out using two types of catalyst i.e.

simple and impregnated catalysts. The WEPS were degraded with metals and

their salts as a catalyst in a first step and then were degraded with impregnated

catalysts. Weighted sample of WEPS was taken in the center of the Pyrex glass

reactor without the use of any catalyst while in thermocatalytic degradation

WEPS in a mixture with corresponding amount of catalyst was loaded into the

reactor, a solid-solid blend without the use of any solvent and other chemicals.

For optimum reaction conditions of WEPS 5 g sample (each) was taken. The

effect of degradation temperature (250 ºC to 500 ºC) for constant reaction time

and polymer to catalyst ratio was investigated. For the effect of reaction time the

WEPS samples were degraded from 30 min to 150 min reaction time keeping

constant optimum temperature and polymer to catalyst ratio. In the last step for

the effect of polymer to catalyst ratio (only in thermocatalytic degradation)

WEPS sample in a mixture with corresponding catalyst from 1:0.1 to 1:0.5

Experimental

52

polymer to catalyst keeping optimum degradation temperature and optimum

reaction time was investigated. In impregnated catalysts, the percentage of

precursor active metal center with respect to its supporting material were

optimized from 5% to 25% using optimized condition for respective simple

metal catalyst. The reaction products were cooled by the condenser and liquid

product were collected in attached bottle. All experiments were carried out using

triplicate analysis, the results of the experiments are consistent and within the

statistical acceptable range. The degradation of WEPS products obtained were

liquids, gases and residues (the carbonaceous compounds stuck to the reactor

wall). The yield of liquids, gases and residue were reported in weight percent

(wt.%) of WEPS sample employed.

For wt.% and material balance calculations the following formula were used

given in Eqs. 3.1-3.3:

𝐿𝑖𝑞𝑢𝑖𝑑 𝑦𝑖𝑒𝑙𝑑 (𝑤𝑡. %) = 𝑊𝑡. 𝑜𝑓 𝐿𝑖𝑞𝑢𝑖𝑑 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑

𝑊𝑡. 𝑜𝑓 𝐹𝑒𝑒𝑑 × 100 3.1

𝐺𝑎𝑠 𝑦𝑖𝑒𝑙𝑑(𝑤𝑡. %) = 𝑊𝑡. 𝑜𝑓 𝐹𝑒𝑒𝑑−(𝑊𝑡. 𝑜𝑓 𝐿𝑖𝑞𝑢𝑖𝑑 + 𝑊𝑡. 𝑜𝑓 𝑅𝑒𝑠𝑖𝑑𝑢𝑒)

𝑊𝑡. 𝑜𝑓 𝐹𝑒𝑒𝑑 × 100 3.2

𝑇𝑜𝑡𝑎𝑙 𝑐𝑜𝑛𝑣𝑒𝑟𝑠𝑖𝑜𝑛 (𝑤𝑡. %) = (𝑊𝑡.𝑜𝑓 𝐹𝑒𝑒𝑑−𝑊𝑡.𝑜𝑓 𝑅𝑒𝑠𝑖𝑑𝑢𝑒)

𝑊𝑡.𝑜𝑓 𝐹𝑒𝑒𝑑 × 100 3.3

3.4.1.4. Liquid products collection in bulk

Liquid product was collected in bulk from the degradation of thermal and thermocatalytic

degradation experiments. WEPS sample (100 g) was degraded in each experiment in a

mixture using optimized parameters, and the liquid products were collected in a 500 mL

capacity flask.

Experimental

53

3.4.1.5. Fractional distillation

i. Instrument

The liquid product derived in bulk both of thermal and thermocatalytic degradation

reactions were subjected for fractional distillation. The same heating assembly was used in

fractional distillation as for degradation experiments. For fractional distillation, a Pyrex

glass tube was designed having internal diameter 7 cm, height 22 cm and wall thickness

2.4 mm with an outlet with thermometer as shown in Fig. 3.2. The fractionating outlet was

attached to condenser for collection of separated products.

ii. Procedure

The liquid products obtained with both thermal and thermocatalytic degradation (simple

and impregnated catalyst) were subjected to fractional distillation for the separation of

compounds. Liquid product (300 mL) was taken in the Pyrex glass tube and inserted in the

vertical furnace of the heating assembly, quick fitted with fractionating column, equipped

with a thermometer and condenser as shown in Fig. 3.3. The assembly was heated with a

rate of 10 ºC/min, the liquid components were vaporized according to their boiling point,

and the fractionating column separated liquids accordingly. The temperature of the

attached thermometer was observed continuously for the collection of different fractions

reaching at different temperatures. The liquid products collected were in the range of 80

ºC to 300 ºC.

Experimental

54

1

3

9

8

7

10

1. Reactor2. Feed material + catalyst3. Electric furnace4. Temperature controller5. Fractionating column6. Thermometer7. Water condenser8. Liquid products receiver9. Gas collection cylinder10. Ice cold trap

20450 ºC

ON

OFF

4

5

6

Figure 3.3 Schematic flow sheet diagram of fractional distillation assembly

3.4.2. Thermal and catalytic degradation of polystyrene (PS) and polyethylene

terephthalate (PET)

4.4.2.1. Reactor assembly

The degradation experiments were carried out in a quartz tube reactor having height 30 cm

and internal diameter 2.5 cm with steel fittings led with immersed thermocouple. The tube

reactor was set in a furnace operated at ambient conditions and temperature was controlled

by a digital temperature controller. The outlet of the quartz reactor was connected with

Schlenk-type Liebig condenser and a supply line of cold water, the condenser was

connected with round bottom flask receiver with the help of an adapter which also have

outlet for gas collection. The schematic of the experimental setup is shown in Fig. 3.4.

Experimental

55

1

48

6

5

7

1. Reactor2. Air tight lid3. Feed material + catalyst4. Electric furnace5. Water condenser6. Liquid products receiver7. Gas collection cylinder8. Ice cold trap

3

2

Figure 3.4 Schematic flow sheet diagram of the reaction assembly used for PS and PET

degradation

3.4.2.2. PS and PET sample preparation

i. Materials

Virgin polystyrene (PS) and polyethylene terephthalate samples

ii. Procedure

Virgin polystyrene (PS) were purchased from Sigma-Aldrich and Polyethylene

terephthalate (PET) was supplied by DuPont Teijin film with average molecular

weights (MW) ~192,000 and ~24,900, respectively. The compositions of PET

and PS were used in the mixture as feed material were denoted as xPET+PS,

where x represents the wt.% of PET with respect to PS. Three different varieties

of PET and PS were prepared and studied are: 10PET+PS, 20PET+PS and

30PET+PS.

Experimental

56

3.4.2.3. PS and PET degradation

The PS and PET samples were also degraded using thermal and thermocatalytic

degradation like the degradation of WEPS. For thermocatalytic degradation of PS and PET

mixture only 20% Al-Al₂O₃ catalysts was used. Known amount of sample (5 g) was loaded

into the reactor with a specified amount of catalyst in mixture with the feed material. The

reactor was heated to a desired temperature at 25 ºC/min rate for the rest of analysis and

the final temperature was held constant for specified durations of time. Like the

degradation of WEPS, the mixture of PS and PET was also optimized with the effect of

degradation temperature (250-500 ºC), reaction time (20-90 min) and polymer to catalysts

ratio (1:0.05-1:0.3). For the collection of products the same procedure was used as used for

WEPS and the yield was calculated according to equation 1-3 of section 3.4.1.3.

3.5. Isolated liquid products characterization

The WEPS degraded parent liquid product and fractionated products obtained both from

thermal and thermocatalytic degradation (i.e. with simple catalysts and impregnated

catalysts) were characterized using physiochemical tests and GC-MS analysis.

3.5.1. Physiochemical properties

3.5.1.1. Determination of density (d)

i. Instrument

Specific gravity bottle

ii. Materials

The parent liquid product obtained with thermal and thermocatalytic degradation and their

fractions obtained at a different temperature from the fractional distillation.

iii. Procedure

Density of both parent liquid products and fractionates was measured by standard method

using a pycnometer. For this first empty pycnometer was weighted followed by filling a

pycnometer with liquid products at 20 ºC. The following relation of Eq. 3.4 was used to

calculate the density of the liquid products.

Experimental

57

Density (d) =mass

volume 3.4

3.5.1.2. Measurement of Refractive index (η)

i. Instrument

Abbe’s Refractometer (ATAGO DTM-1 Japan)

ii. Procedure

The refractive index of the liquid product samples was measured at 20 ºC. For this purpose,

the sample holder or prism of the Refractometer was cleaned with acetone damped cotton

piece before measurement. After drying the instrument was calibrated with distilled water

by putting 2-3 drops of distilled water on the prism box and fixed the above prism on lower

prism in such a way that no air bubbles were left. Mirror position was adjusted for

maximum illumination and fine adjustment knob was used to focus the field front in such

a way that dark and bright half circles were touching each other in the center clearly. Using

other eye piece the reading was taken up to four decimal points. The refractive index (𝛈𝑫𝟐𝟎)

for water is 1.3330. The same procedure was repeated for parent liquid products and

fractions obtained by fractional distillation. Using refractive index (𝛈𝑫𝟐𝟎), density (d) and

molecular weight of the component compound, the specific refraction (r) and molar

refraction of the liquid products were calculated using the following Eqs. 3.5 and 3.6:

Specific Refraction (γ):

γ =(η2−1)

(η2+2)⋅

1

d 3.5

Molar Refraction (γM)

γM =(η2−1)

(η2+2)⋅

M

d 3.6

Experimental

58

3.5.1.3. GC-MS analysis

i. Instrument

GC-MS Shimadzu QP2010 Plus was used for both thermal and thermo-catalytically

derived liquid products, and their fractions obtained by fractional distillation. The

instrument has a stationary phase of 95% dimethylpolysiloxane with 5% polyphenyl fitted

with a DB-5MS (J&W Scientific) fused silica capillary column (30 m × 0.25 mm ID, 0.25

μm film thickness). 99.99% helium (He) was used as a carrier gas.

ii. Materials

Acetone, thermally and catalytically derived liquid products, and their fractions obtained

by fractional distillation at different temperatures.

iii. Procedure

A known amount (0.2 µL) of both parent liquid products and fractions obtained at different

temperatures were dissolved in 5 mL of acetone. The samples were taken in sample vials

and were placed in automatic sample analyzer of GC-MS. The volume of injection was 1

µL with injector temperature maintained at 300 ºC. The injector port was provided with

split mode 1:50. He flow rate was 1.5 mL/min. The oven temperature programing was as

follows; the oven was held at 35 ºC for 5 min, then increased to 100 ºC at the rate of 5

ºC/min, held for 1 min at 100 ºC then the temperature was increased to 150 ºC at the rate

of 10 ºC/min, held for 10 min at 150 ºC and then the temperature was increased to 290 ºC

at 2.5 ºC/min which was held for 10 min at 290 ºC. The mass ionization energy was 35 eV.

The ion source temperatures were 280 ºC and the interface temperature was 290 ºC. The

GC-MS chromatograms were obtained for all the samples, each peak in the chromatogram

was searched in digital updated library only those peaks were attributed name which have

matching more than 90% and the whole peaks were interpreted for a given sample. The

quantitative analysis of each identified component was done by the peak area normalization

method (calculation based on the peak area) and were expressed in terms of wt.% of WEPS

sample degraded. All the samples were analyzed by this procedure.

RESULTS & DISCUSSION

Results and Discussion

59

Section 1

Characterization of impregnated catalysts

4.1. Metals impregnated catalysts over alumina (Al₂O₃)

i. Surface area, pore size and pore volume analysis

BET and BJH surface area, BJH pore size and pore volume of the Al₂O₃ support and its

impregnated catalysts were determined, and the results are presented in Table 4.1. The

surface area of the impregnated catalysts as compared to Al₂O₃ support had increased. The

order of BET surface area for impregnated catalysts was 05% Fe-Al₂O₃ > 20% Zn-Al₂O₃

> 20% Cu-Al₂O₃ > 15% Mg-Al₂O₃ > 20% Al-Al₂O₃ > Al₂O₃.

Table 4.1 Surface area, pore size and pore volume analysis of impregnated catalysts

over Al₂O₃ support

Catalysts Al₂O₃ 15% Mg-

Al₂O₃

20% Zn-

Al₂O₃

20% Al-

Al₂O₃

20% Cu-

Al₂O₃

05% Fe-

Al₂O₃

BET surface area

( m2/g) 68.31 72.62 77.38 70.16 73.99 109.12

BJH surface area

( m2/g) 137.14 162.75 120.56 67.68 153.02 400.53

Pore volume (cc/g) 0.38 0.33 0.20 0.10 0.51 1.22

Pore size (Å) 119.91 100.45 103.12 79.30 133.78 121.38


60

ii. SEM analysis

SEM analysis was performed in order to study the morphology of the impregnated catalysts

prepared with maximum catalytic activity and its comparison to Al₂O₃ support. Fig.

4.1.1(a) shows the morphology of Al₂O₃ support, the micrograph of the sample depicts

oval discs particles, the particles are with smooth evident edges looks like flattened beans

having a relative particle size of 2-3 µm. Fig. 4.1.1(b) represent the morphology of 15%

Mg-Al₂O₃ catalyst. The SEM photograph of 15% Mg-Al₂O₃ clearly shows changes in the

morphology of support, the catalyst has a large particle size with rough surface, large

cracks and pores opening paths to the active metal centers (i.e., Mg) through micropores.

Where in the case of 20% Zn-Al₂O₃ shown in Fig. 4.1.1(c), the micrograph shows slabs of

the catalyst with varying shape and size ranging from 1 µm to 6 µm. Fig. 4.1.1(d) depicts

20% Al-Al₂O₃ which exhibiting rough surface with evident macro and micro cracks, the

micro cracks are formed due to accumulation of nano-crystalline structures with crystal

size 300-500 nm. In contrast, the Fig. 4.1.1(e) of 20% Cu-Al₂O₃ shows irregular shape and

rough surface. The particles are bright, clear with white shape, confirming the presence of

Cu loadings. The catalyst has particle size 2-5 µm in separated aggregation throughout the

micrograph with adequate dispersion of Cu on Al₂O₃ aggregation providing more reaction

site for the degradation reaction. The last micrograph in Fig. 4.1.1(f) represents 5% Fe-

Al₂O₃ catalyst with large particles, each particle is 5-13 µm in size with dense black

structure and evident emerging bodies.


61

Figure 4.1.1 SEM micrograph of (a) Al₂O₃ support, (b) 15% Mg-Al₂O₃, (c) 20% Zn-

Al₂O₃, (d) 20% Al-Al₂O₃, (e) 20% Cu-Al₂O₃ and (f) 5% Fe-Al₂O₃


62

iii. XRD analysis

The XRD diffraction patterns of both supports and impregnated catalysts were taken. It can

be seen from Fig. 4.1.2 that the composition of Al₂O₃ has changed after impregnation of

precursor active metals.

The diffraction patterns in Fig. 4.1.2(a) indicate that all the major peaks of Al₂O₃ at 25.5⁰,

35.2⁰, 37.8⁰, 43.5⁰, 52.2⁰, 61.4⁰, 66.7⁰, 76.9⁰ and 77.2⁰ of 2θ (ICDD Card No. 46212 and

520803). The XRD patterns for 15% Mg-Al₂O₃ catalyst are shown in Fig. 4. 1.2(b), the

major diffraction peaks at 31.3⁰ and 68.7⁰ of 2θ shows MgAl2O4, spinel mineral with major

peaks which indicates the solid-solid interaction between MgCl2 and Al₂O₃ (ICDD Card

No. 211152) in addition to residue peaks of Gmelinite-Na, KCrF4, KCaCl₃ (Chlorocalcite)

and KCaAl2F9 (elpasolite) according to ICDD Card No. 380435, 401001, 211170 and

441359, respectively. According to JCPDS card No. 21-1152, the spinel has cubic

structure.

In Fig. 4.1.2(c), the XRD patterns of 20% Zn-Al₂O₃ shows major peaks for Al₂O₃ at

25.48⁰, 35.08⁰, 37.72⁰, 43.27⁰, 52.51⁰, 57.46⁰, 61.00⁰, 66.43⁰, 68.11⁰ and 77.08⁰ (ICDD

Card No. 461212) and zinc aluminum oxide (Zn3Al94O144) at 30.31⁰, 35.08⁰, 37.72⁰,

43.27⁰, 57.46⁰, 61.00⁰, 66.43⁰ and 68.11⁰ (ICDD Card No. 231490) along with secondary

phases ZnCl2 and AlCl₃ (ICDD Card No. 160851 and 220010). The patterns show Al₂O₃

with rhombohedral geometry (JCPDS Card No. 46-1212) and Zn3Al94O144 with monoclinic

geometry (JCPDS Card No.23-1490).

The XRD patterns of 20% Al-Al₂O₃ catalyst are shown in Fig. 4.1.2(d). The patterns show

major peaks of chloraluminite (AlCl₃. 6H2O) according to ICDD Card No. 441473 at

15.07⁰, 27.19⁰, 27.52⁰, 35.05⁰, 39.01⁰, 41.38⁰, 43.33⁰, 51.94⁰ and 68.35⁰ with

rhombohedral geometry (JCPDS Card No. 44-1473) along with the peaks of aluminum

chloride hydroxide hydrate (Al10Cl3(OH)27. 13H2O) at 27.19, 39.01, 52.63 and 57.67

(ICDD Card No. 270009) having a monoclinic system according to JCPDS Card No. 27-

0009.


63

Where Fig. 4.1.2(e) corresponds to 20% Cu-Al₂O₃, according to ICDD Card No. 330448,

it shows CuAl2O4 at peaks 44.80⁰ and 77.23⁰ with cubic structure and according to ICDD

Card No. 110661, 11243, and 160394 it shows Al₂O₃ at 16.24⁰, 22.00⁰, 25.63⁰, 32.80⁰,

35.20⁰, 37.87⁰, 43.42⁰, 52.60⁰, 57.46⁰, 66.52⁰ and 68.29⁰ with Cu(ClO4)2 and

Al2.892Cu6.1808 according to ICDD Cards No. 320448 and 190010, respectively.

The Fig. 4.1.2(f) represent 05% Fe-Al₂O₃, there is no pattern for this catalyst suggesting

that the catalyst is amorphous.

Figure 4.1.2 XRD diffractogram of (a) Al₂O₃ support, (b) 20% Mg-Al₂O₃, (c) 20% Zn-

Al₂O₃, (d) 20% Al-Al₂O₃, (e) 20% Cu-Al₂O₃ and (f) 05% Fe-Al₂O₃


64

4.2. Metals impregnated catalysts over montmorillonite (Mmn)


Mmn support with 116.21 m2/g BET surface area was impregnated with 20% Mg, 20% Zn,

5% Al, 15% Cu and 20% Fe in the form of their respective salts. BET and BJH surface

area, BJH pore size and pore volume of the Mmn support and its impregnated catalysts are

given in Table 4.2. The surface area of the impregnated catalysts over Mmn support

decreased as compared to Mmn support. The order of BET surface area for impregnated

catalysts was Mmn>5% Al-Mmn>20% Mg-Mmn>20% Zn-Mmn>20% Fe-Mmn>15% Cu-

Mmn.


over Mmn support

Catalysts Mmn 20% Mg-

Mmn

20% Zn-

Mmn

5% Al-

Mmn

15% Cu-

Mmn

20% Fe-

Mmn

BET surface area

( m2/g) 116.21 96.14 78.25 102.2 49.86 69.53

BJH surface area

( m2/g) 489.23 412.08 297.60 264.56 54.60 77.53

Pore volume (cc/g) 1.25 1.26 0.68 1.23 0.09 0.13

Pore size (Å) 115.39 121.84 102.38 118.96 78.73 77.72

ii. SEM analysis

The SEM image of Mmn is depicted in Fig. 4.2.1(a) showing a highly porous structure

with uniform particle size of 10-30 µm. Fig. 4.2.1(b) presents the morphology of 20% Mg-

Mmn, the high magnification of the image reveal a huge condense structure presenting

valley model, the surface seems to have brailed bodies and pores throughout the whole


65

structure. The surface structure of 20% Zn-Mmn is shown in Fig. 4.2.1(c), the Zn-Mmn

particles are 2-3 µm in size having smooth surface area. The image shows clear

impregnation of Zn salt on Mmn support, the bright edges confirm successful impregnation

of zinc. Fig. 4.2.1(d) indicates 5% Al-Mmn catalyst with irregular shape particles having

size 1-4 µm, the bright metallic view of the particles indicate successful impregnation of

the precursor component. Fig. 4.2.1 (e) presents the morphology of 15% Cu-Mmn catalyst

which indicate agglomerated particles with smaller size than Mmn support. The picture

shows 0.6 µm (600 nm) to 5 µm particles with good dispersion of Cu active center. Fig.

4.2.1(f) corresponds to 20% Fe-Mmn, the surface of the catalysts also presents the

agglomerates in stack forms with irregular particles having porous channels throughout the

surface of the catalyst.


66

Figure 4.2.1 SEM micrograph of (a) Mmn support, (b) 20% Mg-Mmn, (c) 20% Zn-

Mmn, (d) 05% Al-Mmn, (e) 15% Cu-Mmn and (f) 20% Fe-Mmn


67

XRD analysis

Impregnated catalysts using XRD spectrum for montmorillonite support are shown in Fig.

4.2.2(a), the diffractogram for Mmn at 19.51⁰, 25.24⁰, 26.29⁰, 29.41⁰, 47.38⁰ and 57.07⁰

indicates bredigite (Ca14Mg2(SiO4)8 according to ICDD Card No. 360399, the patterns at

20.62⁰, 25.24⁰ and 57.07⁰ also shows sodium magnesium silicate (Na2MgSiO4) (ICDD

Card No. 471499). The structures of both minerals are orthorhombic according to JCPDS

Card No. 36-0399 and 47-1499, respectively, along with peaks at 19.51⁰, 23.77⁰ and 29.41⁰

shows montmorillonite-15A (CaO2(Al,Mg)Si4O10(OH)2) (ICDD Card No. 130135) having

hexagonal geometry (JCPDS Card No. 13-0135).

The XRD diffraction patterns for 20% Mg-Mmn are shown in Fig. 4.2.2(b). The major

diffraction peaks at 21.58⁰, 29.63⁰ and 31.87⁰ indicate Na3Mg3Ca5Al19Si117O272 according

to ICDD Card No. 491831 having orthorhombic geometry (JCPDS Card No.49-1831) and,

at 20.95⁰, 22.48⁰, 31.03⁰, 42.19⁰ and 49.42⁰ shows Na2Al2Si2.5O9.6.2H2O (ICDD Card No.

380237) with cubic system (JCPDS Card No. 38-237), it also indicates some relevant

materials i.e., (Mg,Fe)Al2SiO5(OH)2, Na2Ca4Mg2Si4O15, Na2Ca4Mg2Si4O15,

Na96Al96Si96O384.216H2O, Ca2.8(Na,K)0.9Al6.5Si11.5O36. 5H2O and Ca4Al8Si8O32.8H2O

according to ICDD Card Nos. 441427, 421484, 400064, 390222, 461263 and 460341,

respectively.

Fig. 4.2.2(c) shows XRD patterns for 20% Zn-Mmn, it indicates sodium zinc oxide

(Na10Zn4O9) at 22.03⁰, 32.38⁰ and 34.93⁰ according to ICDD Card No. 520058 with

rhombohedral system (JCPDS Card No. 52-0058), the pattern also shows sodium zinc

silicate (Na2ZnSiO4) at 19.87⁰ and 26.71⁰ (ICDD Card No. 370407) with orthorhombic

system according to JCPDS Card No. 37-0407. The XRD diffractogram also indicates

sodium magnesium zinc silicate (Na2Mg3Zn2Si12O30) at 29.50⁰, 32.38⁰ and 63.46⁰

according to ICDD Card No. 480418 having hexagonal geometry (JCPDS Card No. 48-

0418).

The XRD patterns for 5% Al-Mmn catalyst is shown in Fig. 4.2.2(d), it shows the major

peaks for silicon oxide (Si34O68) at 26.65⁰, 27.64⁰, 35.17⁰ and 45.40⁰ (ICDD Card No.

520144) that is in the hexagonal system according to JCPDS Card No. 52-0144. The


68

patterns also shows at 31.75⁰ and 62.02⁰ sodium aluminum silicate (Na1.15Al1.15Si0.85O4

and Na1.75Al1.75Si0.25O4) according to ICDD Card Nos. 490007 and 490004, respectively,

both with orthorhombic geometry. The catalyst also contain a small amount of magnesium

aluminum oxide (MgAl₂O₃) and magnesium aluminum silicate (Mg3Al2(SiO4)3 according

to ICDD Card No. 211152 and 150742. The presence of these substances indicates

interaction of Al with Mmn support.

Fig. 4.2.2(e) corresponds to 15% Cu-Mmn and its pattern shows Ca2CuO2Cl2 according to

ICDD Card No. 480319 at peaks 29.02⁰, 32.62⁰ and 61.63⁰, the patterns shows Al2CuMg

at 45.34⁰, 54.76⁰ and 61.63⁰ according to ICDD Card No. 280014, it shows Ca2Al2O5

according to ICDD Card No. 521722 at peaks 26.62⁰, 34.09⁰, 61.63⁰, it also shows

monoclinic CaCu at peaks 16.24⁰, 32.62⁰, 34.09⁰, 45.34⁰ and 57.55⁰ with ICDD Card No.

411276 and monoclinic CuCl₂ with ICDD Card No. 10185.

The XRD pattern indicates that 20% Fe-Mmn is amorphous as shown in Fig. 4.2.2(f)

Figure 4.2.2 XRD diffractogram of (a) Mmn support, (b) 20% Mg-Mmn, (c) 20% Zn-

Mmn, (d) 5% Al-Mmn, (e) 15% Cu-Mmn and (f) 20% Fe-Mmn


69

4.3. Metals impregnated catalysts over activated charcoal (AC)


The BET and BJH surface area, BJH pore size and pore volume for AC support and its

impregnated catalysts are given in Table 4.3. The surface area decreased remarkably after

impregnation with selected catalysts. The order of BET surface area for impregnated

catalysts was AC > 20% Zn-AC > 20% Cu-AC > 20% Mg-AC > 20% Fe-AC > 20% Al-

AC.


over AC support

Catalysts AC 20% Mg-

AC

20% Zn-

AC

20% Al-

AC

20% Cu-

AC

20% Fe-

AC

BET surface area

( m2/g) 335.24 116.50 141.60 66.31 120.44 71.00

BJH surface area

( m2/g) 106.15 241.75 69.04 47.66 47.40 64.77

Pore volume (cc/g) 0.11 1.00 0.10 0.06 0.04 0.09

Pore size (Å) 23.17 165.60 35.31 34.45 23.37 34.55

ii. SEM analysis

SEM was used to investigate the morphology of selected impregnated catalysts over AC in

comparison with AC support. Fig. 4.3.1(a) depicts the morphology of AC support, the

structure exhibits dense, smooth surface having pores and few particles emerging the

structural body. Like AC surface 20% Mg-AC catalysts (Fig. 4.3.1(b)) also exhibits dense

but highly rough structure having brailed slabs with ups and down having cracks with

evident shapes and the catalyst shows well-developed macropores system throughout the


70

body. Fig. 4.3.1(c) represent the morphology of 20% Zn-AC, which as compared to its

support shows great morphological changes, the catalyst structure consists of solid particles

with irregular and variable particle having 0.5-10 µm particle size. The SEM image of 20%

Al-AC catalyst is shown in Fig. 4.3.1(d), confirming the successful impregnation of

precursor forming large blocks like particles with smooth surfaces having a particle size

from 0.5-30 µm. Modified 20% Cu-AC catalysts (Fig. 4.3.1(e)) exhibits different

morphology in comparison with its AC support, but having a similar morphology with that

of 20% Zn-AC catalyst. It also shows agglomerates of varying size that range from 0.2 µm

(200 nm) to 5 µm particle size. Fig. 4.3.1(f) represents 20% Fe-AC impregnated catalyst

with very fine rice like uniform particles having particle size 1-3 µm with porous surfaces.


71

Figure 4.3.1 SEM micrographs of (a) AC support, (b) 15% Mg-AC, (c) 20% Zn-AC, (d)

20% Al-AC, (e) 20% Cu-AC and (f) 20% Fe-AC


72

iii. XRD analysis

The XRD diffraction patterns for activated charcoal (AC) is shown in Fig. 4.3.2(a), it

clearly indicates charcoal at 26.59⁰ (ICDD Card No. 261076) with hexagonal geometry

(JCPDS Card No. 26-1076). Where the XRD patterns of 20% Mg-AC and 20% Zn-AC are

shown in Fig. 4.3.2(b) and Fig. 4.3.2(c), respectively. It depicts that the precursor active

center is fully dispersed in the pores of AC with the amorphous nature of catalysts.

The Fig. 4.3.2(d) shows diffractogram aluminum chloride (AlCl₃) with maximum major

peaks at 17.26⁰, 26.62⁰, 30.31⁰, 36.55⁰, 62.59⁰, 66.34⁰, 73.57⁰ having monoclinic structure

(JCPDS Card No. 22-0010) and carbon (charcoal) with major peaks at 44.17⁰, 46.69⁰ and

70.96⁰ according to ICDD Card Nos. 220010 and 501086, respectively having

rhombohedral structure (JCPDS Card No. 50-1086).

Figs. 4.3.2(e) and 4.3.2(f) also shows that for 20% Cu-AC and 20% Fe-AC catalysts no

patter were observed and it was revealed that the catalysts are amorphous in nature.


73

Figure 4.3.2 XRD diffractogram of (a) AC support, (b) 20% Mg-AC, (c) 20% Zn-Ac,

(d) 20% Al-AC, (e) 20% Cu-AC and (f) 20% Fe-AC


74

Section 2

Catalytic activity, selectivity and recovery studies for the degradation of

waste expanded polystyrene (WEPS)

4.4. Thermogravimetric analysis (TGA)

4.4.1. TGA of WEPS

The weight loss verses temperature curves for thermal decomposition of WEPS

under a linear heating rate in the inert (N2) and oxidative (O2) environment was

carried out and the results are shown in Fig. 4.4.1. It can be seen from the figure

that the decomposition is a single step process with the onset and end temperature

of 300.98 °C and 409.85 °C, respectively in the case of N2 environment and 292.50

°C and 407.79 °C, respectively for oxidative environment. The curve shows that

maximum weight loss related to volatilization of hydrocarbons occurred at 369.28

°C in inert atmosphere and 364.68 °C in the case of oxidative atmosphere. In inert

atmosphere 99.57% change occurred from 300.98 °C to 409.85 °C. In the case of

oxidative environment 100% weight changes occurred from 292.50 °C to 407.79

°C. At these temperatures with the volatilization process, other reactions like

cracking of side chain from aromatic rings, isomerization and poly condensation

also takes place. Therefore, one might think that all the volatile matter of WEPS

has been decomposed to volatile hydrocarbons.


75

Figure 4.4.1 TGA curves of WEPS in O2 and N₂ environment

4.4.2. TGA of polystyrene (PS) and polyethylene terephthalate (PET)

The TGA results of virgin PS and PET are shown in Fig. 4.4.2. The initial thermal

decomposition of both PS and PET was endothermic due to C-C and C-O (for PET

only) bond rupture. The weight loss versus temperature curves of both, PS and

PET shows single step pyrolysis in a N₂ [1]. It shows the onset temperature of

290.2 ºC, 378.0 ºC, and end set temperature of 431.3 ºC and 479.8 ºC for PS and

PET, respectively. The curve shows 100 wt.% loss in the case of PS and 83.7 wt.%

loss in the case of PET at their respective end set temperatures. PET in the process

of thermal pyrolysis left carbonaceous material as a solid residue that did not

decompose at 1000 ºC. This phenomenon is supported by several studies of PET

pyrolysis in the N₂ environment at high temperature. The residue left even at a

high temperature in the case of PET is attributed to the interlinking reaction

between the decomposed products of PET forming stabilized products [2]. The TG


76

curves show almost complete conversion of PS where PET shows incomplete

conversion which was also reported in other studies [3].

Figure 4.4.2. TGA curves of PS and PET in N₂ environment


77

4.5. Thermal degradation of WEPS

i. Effect of temperature

The effect of temperature on the thermal degradation of WEPS was studied in the range of

250 ºC to 500 ºC, the results are shown in Fig. 4.5.1. Most of the previous studies have

reported the degradation of WEPS with fixed temperature [4, 5] or with the lower limit of

the reactor temperature, for example, most of autoclaves can be operated up to a certain

temperature like 250 °C and 427 °C [6, 7]. In the current method, thermal degradation was

carried out in 120 min reaction time. The amount of liquid products increased with increase

of temperature and maximum yield of liquid products were obtained at 500 ºC. The

maximum amount of liquid was 74.13 ± 4.05 wt.% with 95.87% total conversion. Further

increase in temperature did not show any significant increase in the yield of liquid products.

Figure 4.5.1 Effect of degradation temperature for thermal degradation of WEPS


78

ii. Effect of time

The Effect of reaction time on the thermal degradation of WEPS was studied from 30 min

to 150 min at optimum temperature i.e., 500 ºC, the results of the study are shown in Fig.

4.5.2. The effect of time has not been studied in most of the studies and the degradation of

WEPS has been carried out for a fixed reaction time [5, 7]. The effect of reaction time has

a profound effect on the degradation of WEPS and the reaction products or liquid products.

In the current study, the effect of time was checked for the degradation of WEPS at a fix

optimized temperature.

It was observed that the liquid product yield increased with the increase of time from 30

min to 150 min. The yield of liquid products was maximum with a 150 min reaction time.

This time was considered sufficient and beyond this time the degradation of WEPS will be

considered not economical. The maximum liquid products obtained at optimized

conditions was 78.07 ± 0.64 wt.% with 98.47% total percent conversion.

Figure 4.5.2 Effect of reaction time for thermal degradation of WEPS


79

iii. Composition of derived liquid products

The liquid products obtained were analyzed for their chemical composition using GC-MS.

The results of the analysis are given in Table 4.5.1 in terms of wt.% of WEPS degraded

and GC-MS spectra for thermal degradation is shown in Fig. 4.5.3. It was observed that

the liquid products consisted of eight major components, mostly of aromatic hydrocarbons.

These hydrocarbons included major products toluene, styrene, α-methylstyrene and

benzene, 3-butynyl etc. The percent composition of liquid showed that styrene monomer

is the predominant compound in the liquid products obtained with thermal degradation.

The yield of toluene; ethylbenzene; styrene; α-methylstyrene; benzene, 3-butynyl; 1,2-

propanediol, 3-benzyloxy-1,2-diacetyl was 2.06 wt.%, 0.85 wt.%, 39.31 wt.%, 1.33 wt.%,

17.56 wt.% and 10.10 wt.%, respectively. Thermal degradation of WEPS start with a

random initiation mechanism that ultimately form free radicals, which undergo β-scission

producing styrene monomer while during the depolymerization reaction the secondary

radicals, or tertiary radicals (formed by H-abstraction) produce α-methylstyrene and/or

dimers [8, 9]. The presence of oxygenated derivatives of aromatic hydrocarbons is believed

to be due to reaction between atmospheric oxygen and degraded products [10]. Toluene

and ethylbenzene are formed by further degradation of styrene monomer [11].

Table 4.5.1 Products formed by thermal degradation of WEPS at optimized conditions.

S.No. Products Composition (wt.%)

1 Toluene 2.06

2 Ethylbenzene 0.85

3 Styrene 39.31

4 α-Methylstyrene 1.33

5 Benzene, 1,1'-(1,3-propanediyl)bis 1.97

6 Benzene, 3-butynyl 17.56

7 Benzene, (1-methyl-3-butenyl) 1.16

8 1,2-propanediol, 3-benzyloxy-1,2-diacetyl 10.10

Other hydrocarbons 3.72

Gases (wt.%) 20.40

Residue (wt.%) 1.53


80

Figure 4.5.3 Chromatogram of catalytically derived liquid products obtained with

thermal degradation at optimized conditions

iii. Separation of the products using fractional distillation

After GC-MS characterization of the parent liquid products, the liquid was separated into

different fractions using fractional distillation to recover the hydrocarbons selectively.

Fractions obtained by the fractional distillation of parent liquids derived from the

degradation of WEPS, were characterized for different parameters like density (d25),

refractive index (𝜂𝐷25), and molar refraction (γM). The results of the study are given in

Table 4.5.3. As can be seen from the table that during fractional distillation the residence

time of liquid increased and further degradation occurs in the liquid with the decrease in

percentage of styrene from 39.31 wt.% to 35.0 wt.%, α-methylstyrene; benzene, 1,1'-(1,3-

propanediyl)bis; benzene, 3-butynyl and benzene, (1-methyl-3-butenyl) were totally

disappeared by further degradation where conversion to benzene took place and the yield

of toluene increased markedly from 2.06 wt.% to 51 wt.%. Phenanthrene was also formed

during the fractional distillation process and was isolated, which may have formed by the

intramolecular cyclization/dehydrogenation process [12, 13]. Beside these some other

hydrocarbons were also detected by GC-MS analysis in negligible quantity where open


81

chain hydrocarbons or gaseous products were also formed during the fractional distillation

process.

Refractive index and density of each fraction from fractional distillation was measured for

calculation of molar refraction (Table 4.5.2). The molar refraction values of standard

compounds used for comparison are given in Table 4.5.3. The molar refraction values of

aromatic compounds from different catalytic degradation of WEPS are in close agreement

with the standard compounds which confirm these compounds.

Table 4.5.2 Physiochemical parameters of the fractions obtained using fractional

distillation of the liquid derived from the thermal degradation of WEPS

Compounds

Thermal

%age d25 (g/ml) 𝜼𝑫𝟐𝟓 γM

Benzene 1.0 0.8770 1.5223 27.18

Toluene 51.0 0.9293 1.5363 30.93

Ethylbenzene 2.0 0.8731 1.5051 36.07

Styrene 35.0 0.9115 1.5510 36.45

Phenanthrene 6.0 0.9910 1.5999 61.52

1,2-propanediol, 3-benzyloxy-1,2-diacetyl 3.0 0.9320 1.5273 87.88

Where %age (Percentage of the Fraction), d25 (g/ml) (density), 𝜂𝐷25 (Refractive

Index using Na lamp at 25 ºC), and γM (Molar Refraction)


82

Table 4.5.3 Physiochemical parameters of standards compounds

Compound Density (d)

g/ml

Refractive

Index (η)

Molar

Refraction

(γM)

Benzene 0.873 1.5010 26.253

Toluene 0.872 1.4967 31.078

2-Phenone, 4-hydroxy-4-methyl 0.868 1.4970 35.802

Ethylbenzene 0.868 1.4970 35.802

Styrene 0.903 1.5460 37.177

Benzene, (1-methylethyl) or Cumene 0.862 1.4910 40.438

Benzaldehyde 1.050 1.5450 33.006

α-Methylstyrene 0.872 1.5450 42.002

Benzene, 1,1'-(1,3-propanediyl)bis 0.984 1.5600 64.922

Phenanthrene 1.130 1.7150 61.938

Benzene, 3-butynyl 0.936 1.5290 42.896

2-Phenylnaphthalene 1.082 1.6480 68.687

Benzene, (1-methyl-3-butynyl) 0.872 1.5020 49.429

1,2-propanediol, 3-benzyloxy-1,2-diacetyl 1.225 1.5420 68.393

1,1':3,1"-Terphenyl, 5'-phenyl 1.074 1.6190 100.290


83

4.6. Catalytic degradation of WEPS using alumina (Al₂O₃),

montmorillonite (Mmn) and activated charcoal (AC) as catalysts


The effect of temperature on the catalytic degradation of WEPS was monitored in the range

of 250 ºC to 500 ºC keeping optimum reaction time (30 min) and polymer to catalysts ratio

(1:0.2) using Al₂O₃, Mmn and AC as catalyst. The results are shown in Fig. 4.6.1. The

yield of liquid products increased with increase of temperature in the case of all catalysts

i.e., Al₂O₃, Mmn and AC. The degradation at 250 ºC yielded only gaseous products in the

case of Al₂O₃ and Mmn catalysts, while in case of AC a small liquid products was also

observed. At 450 ºC maximum liquid products that is 80.20 ± 1.91 wt.% and 89.93 ± 0.31

wt.% were observed in the case of Al₂O₃ and Mmn catalysts, respectively, with 100% total

conversion. The maximum yield of liquid products in case of AC was 83.80 ± 0.20 wt.%

at 500 ºC with 100% total conversion. The yield of liquid products was not affected with

further increase of temperature above optimized degradation temperature.


84

Figure 4.6.1 Effect of degradation temperature and comparison of catalytically derived

liquid products obtained with Al₂O₃, Mmn and AC as catalysts

ii. Effect of time

The effect of reaction time was followed in the range of 30 to 150 min for obtaining

maximum liquid products for the degradation of WESP at an optimized degradation

temperature (450 ºC for Al₂O₃ and Mmn, and 500 ºC for AC) and 1:0.2 polymer to catalyst

ratio (Fig. 4.6.2). Maximum liquid products was obtained at 60 min reaction time. There

was not much effect of reaction time on the liquid product. A slight decrease in reaction

products was observed with increase of reaction time that is due to high residence time of

the product in degradation reactor causing further cracking of the products to low molecular

weight hydrocarbons. The yield of liquid was 87.00 ± 0.80 wt.% and 91.33 ± 0.31 wt.%

with 100% total conversion using Al₂O₃ and Mmn catalysts, respectively. The yield of


85

liquid products was 83.80 ± 0.20 wt.% maximum with 30 min reaction time and 100% total

conversion using AC as catalyst.

Figure 4.6.2 Effect of reaction time and comparison of catalytically derived liquid

products obtained with Al₂O₃, Mmn and AC as catalysts at optimized

conditions

iii. Effect of polymer to catalyst ratio

WEPS degradation was also optimized for the effect of polymer to catalyst ratio using

Al₂O₃, Mmn and AC catalysts (Fig. 4.6.3), using 450 ºC degradation temperature with 60

min reaction time for Al₂O₃ and Mmn and 30 min reaction time for AC catalyst at 500 ºC.

The polymer to catalyst ratio was varied form 1:0.1 to 1:0.5. In the case of Al₂O₃ and Mmn

catalysts, the yield of liquid products was small with 1:0.1 polymer to catalyst ratio as

compared to the yield of 1:0.2 polymer to catalyst ratio. The yield of liquid products

decreased with the increase of catalyst. The increase of catalyst provided more surface area


86

in turn providing more reaction sites for degradation reaction ultimately leading to side

chain reactions, forming more gaseous products leading to decrease in the yield of liquid

products. The maximum liquid products obtained were 87.00 ± 0.80 wt.% and 92.40 ± 0.87

wt.% with 1:0.2 polymer to catalyst ratio with 100% total conversion for both Al₂O₃ and

Mmn catalysts. In the case of AC maximum yield was 84.47 ± 0.12 wt.% (100% total

conversion) with 1:0.1 polymer to catalyst ratio. The results are given in Table 4.6.1.

Table 4.6.1 Optimum reaction conditions and contents of products using Al₂O₃, Mmn

and AC catalysts

Al₂O₃ Mmn AC

Reaction conditions

Temperature (°C) 450 450 500

Time (min) 60 60 30

Polymer to catalyst ratio 1:0.2 1:0.2 1:0.1

Content of products (wt.%)

Liquids 87.00 ± 0.80 92.40 ± 0.87 84.47 ± 0.12

Gases 13.00 ± 0.80 7.60 ± 0.87 15.53 ± 0.12

Residue 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00

Total percent conversion 100.00 100.00 100.00


87

Figure 4.6.3 Effect of polymer to catalyst ratio and comparison of catalytically derived

liquid products obtained with Al₂O₃, Mmn and AC as catalysts at optimized

conditions

i. Composition of derived liquid products and selectivity of its components

The parent liquid products obtained from the catalytic degradation of WEPS using Al₂O₃,

Mmn and AC catalyst were analyzed by GC-MS for its chemical composition. The results

of the analysis are given in Table 4.6.2 expressed in terms of weight percent of the WEPS

sample degraded and GC-MS chromatograms are shown in Figs. 4.6.4-4.6.6 for Al₂O₃,

Mmn and AC catalysts, respectively.

The percentage composition of the analysis was correlated in 100%, according to the

following formula (Eq. 4.6.1) for all three catalysts i.e., Al₂O₃, Mmn and AC.

𝐶𝑜𝑟𝑟𝑒𝑙𝑎𝑡𝑖𝑜𝑛 %𝑎𝑔𝑒 = 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝑙𝑖𝑞𝑢𝑖𝑑

100 × %𝑎𝑔𝑒 𝑜𝑓 𝑐𝑜𝑚𝑝𝑜𝑛𝑒𝑛𝑡 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 4.6.1


88

Sixteen major chemical products were detected where styrene monomer was the dominant

product in the catalytic degradation similar to the data reported in the literature [10, 14].

The other important hydrocarbons included toluene, ethylbenzene, α-methylstyrene and

benzene, 1,1'-(1,3-propanediyl)bis. The selectivity of products formed, highly depend on

surface area, nature and active sites of the catalysts used. The nature of Al₂O₃, Mmn and

AC catalysts have been reported as heterogeneous solid acids, with a demerit of soon

deactivation than transition metal oxides and also impregnated catalysts [15, 16], however,

mechanism for the degradation described using acidic catalysts have been described in

many papers to be of carbonium nature followed by β-scission of C-C bond [17, 18].

GC-MS analysis revealed that AC catalyst formed the maximum number of products which

were mostly desirable and low molecular weight aromatic hydrocarbons while on the other

hand Mmn catalyst yielded a minimum number of products but with a high amount of

undesirable and high molecular weight aromatic hydrocarbons. The yield of styrene

monomer was approximately the same i.e., 45.65 wt.%, 45.42 wt.% and 43.61 wt.% with

Al₂O₃, Mmn and AC catalysts, respectively. Therefore, yield of toluene (6.96 wt.%),

ethylbenzene (6.55 wt.%) and α-methylstyrene (2.262 wt.%) were maximum with the AC

catalyst. AC catalyst has a porous internal microstructure with high surface area (335.24

m2/g) and the active sites present over charcoal showing high activity [19] which causes

further cracking of high molecular weight aromatic hydrocarbons to produce toluene and

ethylbenzene and/or α-methylstyrene like compounds by the acidic sites (of AC catalyst),

reported by Audisio et al. [17, 18]. Another dominant product after styrene monomer was

benzene, 3-butynyl with all the catalysts where 1,2-propanediol, 3-benzyloxy-1,2-diacetyl

was also dominant in the case of Al₂O₃ and Mmn catalysts. The presence of 1,2-

propanediol, 3-benzyloxy-1,2-diacetyl like oxygenated compounds have its origin with the

reaction with atmospheric oxygen or other possible residue present in the WEPS samples.


89

Table 4.6.2 Products formed by the catalytic degradation of WEPS using Al₂O₃, Mmn

and AC as catalysts at optimized conditions.


Al₂O₃ Mmn AC

1 Toluene 2.58 1.59 6.96

2 Ethylbenzene 1.40 0.49 6.55

3 Styrene 45.65 45.42 43.61

4 α-Methylstyrene 1.11 0.70 2.62

5 Benzene, 1,1'-(1,2-ethanediyl)bis 0.94 0.75 4.29

6 Benzene, 1,1'-(1-methyl-1,2-ethanediyl)bis 0.47 0.31 1.89

7 Benzene, 1,1'-(1-butene-1,4-diyl)bis-, (Z) 0.05 0.06 0.67

8 Benzene, 1,1'-(1,3-propanediyl)bis 0.98 0.81 0.00

9 Phenanthrene 0.09 0.07 0.53

10 Benzene, 3-butynyl 14.29 18.35 6.87

11 Benzene, (1-methyl-3-butenyl) 0.72 0.72 0.64

12 Benzene, (1-ethyl-2-propenyl) 0.39 0.51 0.11

13 2-Phenylnaphthalene 0.45 0.10 1.57

14 2-pentenal, 5-phenyl 0.11 0.13 0.52

15 1,2-propanediol, 3-benzyloxy-1,2-diacetyl 13.75 19.00 0.00

16 1,1':3,1''-Terphenyl, 5'-phenyl 0.36 0.30 0.67

17 Other hydrocarbons 3.67 3.09 6.98

Gases (Wt.%) 13.00 7.60 15.53

Residue (Wt.%) 0.00 0.00 0.00


90

Figure 4.6.4 Chromatogram of catalytically derived liquid products obtained with Al₂O₃

catalyst at optimized conditions

Figure 4.6.5 Chromatogram of catalytically derived liquid products obtained with Mmn

as catalyst at optimized conditions


91

Figure 4.6.6 Chromatogram of catalytically derived liquid products obtained with AC as



92

4.7. Catalytic degradation of WEPS using Mg, MgO and MgCO₃ catalysts

ii. Effect of temperature

The effect of temperature on thermal and catalytic degradation of WEPS using Mg, MgO

and MgCO₃ as a catalysts was studied in the range of 250 ºC to 500 ºC, keeping reaction

time (60 min) and polymer to catalyst ratio (1:0.3), the results are shown in Fig. 4.7.1. The

amount of liquid increased with increase of degradation temperature and maximum yield

of liquid products 76.87 ± 1.50 wt.% were obtained at 450 ºC with Mg as catalyst with

99.40% total conversion. The maximum amount of liquid 57.80 ± 0.53 wt.% and 43.27 ±

0.42 wt.% was obtained at 400 ºC with 79.27% and 60.47% total conversion in the case of

MgO and MgCO₃ catalysts, respectively. Further increase in temperature did not show any

increase in the yield of liquid, but the amount of residue was decreased with the increase

of gases in the case of Mg and MgO catalysts.


liquid products obtained with Mg, MgO and MgCO₃ catalysts


93

iii. Effect of time

The effect of reaction time on thermal and catalytic degradation of WEPS was studied from

30 min to 150 min at optimum temperature (Fig. 4.7.2) keeping polymer to catalyst ratio

1:0.3. Only in the case of Mg as a catalyst the yield of liquid was 82.20 ± 3.80 wt.% with

30 min reaction time, while with MgO and MgCO₃ catalysts maximum liquid obtained was

91.60 ± 0.20 wt.% and 81.80 ± 0.53 wt.% for 120 min reaction time. Negligible amount of

residue 0.60 ± 0.40 wt.% was obtained using Mg catalyst with 99.40 wt.% total conversion.

The yield of liquid products were high with minimum reaction time with all catalysts as

compared to previous studies. H. Ukei et al. [11] reported catalytic degradation of WEPS

with maximum liquid yield 93.4 wt.% producing 76.4 wt.% styrene at 450 °C for 180 min

and Lee et al. [20] found SiO2/Al₂O₃ catalyst with maximum 83.5 wt.% of liquid products

at 400 °C for 120 min.


obtained with Mg, MgO and MgCO₃ catalysts at optimized conditions


94

iv. Effect of polymer to catalyst ratio

Polymer to catalyst ratio was optimized from 1:0.1 to 1:0.5 using Mg, MgO and MgCO₃

as catalyst keeping optimum temperature and reaction time. The results are shown in Fig.

4.7.3. It is evident from the previous studies that catalyst selection has a profound role in

the degradation of polymer and as well as the selectivity of products. Many researchers

have reported the impact of polymer to catalyst ratio on the degradation of WEPS [6, 21].

In our study the effect of polymer to catalyst ratio was evaluated for the degradation of

WEPS. For all catalysts the liquid yield was increased with increase in feed ratio from 1:0.1

to 1:0.3 and a small decrease was observed with further increase. Therefore, a polymer to

catalyst ratio of 1:0.3 was taken as optimum and was used in the further degradation

process. At optimum conditions maximum liquid yield and gas was obtained with

minimum residue using all the three catalysts. The total percent conversion at optimum

conditions was 99.40 wt.%, 98.60 wt.% and 94.87 wt.% with Mg, MgO and MgCO₃

catalysts, respectively. Among the used catalysts Mg was found with high activity. The

comparative reaction conditions and contents of products are given in Table 4.7.1.

Table 4.7.1 Optimum reaction conditions and contents of products using Mg, MgO and

MgCO₃ catalysts

Mg MgO MgCO₃

Reaction conditions

Temperature (ºC) 450 400 400

Time (min) 30 120 120


Contents of product (wt.%)

Liquids 82.20 ± 3.80 91.60 ± 0.20 81.80 ± 0.53

Gases 17.20 ± 3.40 7.00 ± 0.20 13.07 ± 0.23

Residue 0.60 ± 0.40 1.40 ± 0.20 5.13 ± 0.31

Total conversion 99.40 98.60 94.97


95


liquid products obtained with thermal degradation, Mg, MgO and MgCO₃


v. Composition of derived liquid products and selectivity of its components

The liquid products obtained from catalytic degradation at optimum conditions were

dissolved in acetone and analyzed for their chemical composition by GC-MS. The results

of the analysis are given in Table 4.7.2 and GC-MS spectra’s are shown in Figs 4.7.4-4.7.6

for Mg, MgO and MgCO₃ catalysts, respectively. The liquid products consisted of ten

major components entirely of aromatic hydrocarbons. These hydrocarbons included

toluene, ethylbenzene, styrene, α-methylstyrene and benzene, 1,1'-(1,3-propanediyl)bis.

Catalysts with basic nature like BaO have been reported having good selectivity for styrene

monomer [11] where metal catalysts have also been reported for the efficient, rapid

degradation of polystyrene [10, 22]. It was observed that Mg catalysts act as synergist as

well as a catalyst with its basic compounds i.e., MgO and MgCO₃ using indigenously


96

designed glass reactor and heating assembly in order to compare the composition of liquid

products. Percent composition of liquid products showed that styrene monomer is the

predominant compound in the liquid obtained from catalytic degradation. Maximum

amount of styrene (54.71 wt.%) was obtained with Mg catalytic degradation while the yield

of styrene with MgO and MgCO₃ catalysts were 49.95 wt.% and 45.17 wt.%, respectively.

The presence of high molecular weight aromatic hydrocarbons like benzene, 3-butynyl in

the case of base catalysts indicate that along with depolymerization processes; ring

opening, dehydrogenation, hydrogenation and cyclization processes were also taking place

[11, 23]. The presence of oxygen containing compounds might be due to the reaction of

atmospheric oxygen and any residue present in the WEPS samples [10].

Table 4.7.2 Products formed by the catalytic degradation of WEPS using Mg, MgO and

MgCO₃ catalysts at optimized conditions


Mg MgO MgCO₃

1 Toluene 2.24 3.71 5.13


3 Styrene 54.71 49.95 45.17

4 Benzene, (1-methylethyl) 0.34 0.15 1.28



7 Benzene, 3-butynyl 0.00 15.67 7.03


9 Benzene, 1,1'-(2-methyl-1-

propenylidene)bis 0.08 0.49 0.58

10 1,2-propanediol, 3-benzyloxy-1,2-diacetyl 15.74 4.61 2.10

Other hydrocarbons 4.23 4.75 4.92

Gases (wt.%) 17.20 7.00 13.07

Residue (wt.%) 0.60 1.40 5.13


97

Figure 4.7.4 Chromatogram of catalytically derived liquid products obtained with Mg as


Figure 4.7.5 Chromatogram of catalytically derived liquid products obtained with MgO

as catalyst at optimized conditions


98

Figure 4.7.6 Chromatogram of catalytically derived liquid products obtained with

MgCO₃ as catalyst at optimized conditions

vi. Separation of the products using fractional distillation

After the characterization data of GC-MS, the liquid products obtained with Mg, MgO and

MgCO₃ catalytic degradation were separated into different fractions using fractional

distillation to recover the hydrocarbons selectively. Fractions obtained by the fractional

distillation of parent liquids derived from the catalytic degradation of WEPS were

characterized by different physiochemical parameters like density (d25), refractive index

(𝜂𝐷25), and molar refraction (γM) for the identification of different fractions (Table 4.7.3).

The separated component products were also confirmed individually by GC-MS analysis.

As can be seen from the data, during the fractional distillation increase in residence time

of liquid products caused further degradation of liquid products with the decrease of styrene

monomer percentage from 54.71 wt.% to 43.0 wt.% and 49.95 wt.% to 23.0 wt.% in the

case of liquid obtained with Mg and MgO catalysts, respectively, with the concurrent

increase of toluene, α-methylstyrene; benzene, 3-butynyl and 1,2-propanediol, 3-

benzyloxy-1,2-diacetyl in the case of liquid products obtained with Mg as a catalyst, where

with MgO catalyst, low molecular weight aromatic hydrocarbons were formed with high


99

amount and high molecular weight hydrocarbons disappeared. The decrease of styrene

monomer in the case of Mg catalyst might be due to the repolymerization of styrene and/or

condensation and degradation of new high molecular weight aromatic hydrocarbons [24]

while the formation of toluene and ethylbenzene in the case of liquids obtained with Mg,

MgO and MgCO₃ catalysts is because of further cracking of styrene or dimers [11, 17].

The yield of styrene increased with more basic catalyst relatively with low yields of toluene

and ethylbenzene with the disappearance of high molecular weight aromatic hydrocarbons.

Catalytic degradation of WEPS using MgCO₃ catalyst could be selectively used for the

recovery of toluene (15.8 wt.%) and styrene monomer (51.9 wt.%) where MgO could be

used for the selective recovery of ethylbenzene (35 wt.%). MgO catalyst could be used for

selective recovery of toluene (11.5 wt.%), ethylbenzene (35.0 wt.%), styrene monomer

(23.8 wt.%) and α.-methylstyrene (11.0 wt.%) while Mg catalyst could be used for the

recovery of toluene (9.0 wt.%), styrene monomer (43.0 wt.%), α-methylstyrene (4.0 wt.%)

and 1,2-propanediol, 3-benzyloxy-1,2-diacetyl (18 wt.%).

Refractive index and density of each fraction from fractional distillation was measured for

calculation of molar refraction (Table 4.7.3). The molar refraction values of standard

compounds used for comparison are given in Table 4.5.3 in section 4.5 (Page 82). The

molar refraction values of aromatic compounds from different catalytic degradation of

WEPS are in close agreement with the standard compounds molar refraction values which

confirm the product component.


100

Table 4.7.3 Physiochemical parameters of the fractions obtained using fractional distillation of the liquid derived from the

degradation of WEPS using Mg, MgO and MgCO₃ catalysts

Compound

Mg MgO MgCO₃

%age d25

(g/ml) 𝜼𝑫

𝟐𝟓 γM %age d25

(g/ml) 𝜼𝑫


(g/ml) 𝜼𝑫

𝟐𝟓 γM

2-Phenone, 4-hydroxy-4-

methyl - - - - - - - - 9.0 1.0033 1.4620 31.83

Toluene 9.0 0.9020 1.5334 31.72 11.5 0.8768 1.5086 31.36 15.8 0.9005 1.5097 30.59

Ethylbenzene 35.0 0.8909 1.5084 35.55 5.9 0.8684 1.5050 36.26

Styrene 43.0 0.9165 1.5421 35.77 23.8 0.9082 1.5470 36.37 51.9 0.9013 1.5463 36.60

Benzene, (1-methylethyl) - - - - 6.0 0.8802 1.5102 40.85 - - - -

Benzaldehyde -- - - - 1.5 0.8802 1.5455 38.15 - - - -

α.-Methylstyrene 4.0 0.9004 1.5496 41.79 11.0 0.9037 1.5329 40.58 3.0 0.9166 1.5347 40.12

Benzene, 1,1'-(1,3-

propanediyl)bis - - - - - - - - 6.0 0.9612 1.5497 65.03

Phenanthrene - - - - - - - - - - -

Benzene, 3-butynyl - - - -- - - - - 5.5 0.9035 1.5174 43.62

Benzene, (1-methyl-3-butynyl) 14.0 0.9022 1.5285 49.95 - - - - - - -

1,2-propanediol, 3-benzyloxy-

1,2-diacetyl 18.0 1.2095 1.5396 69.04 - - - - - - - -

Where %age (Percentage of the Fraction), d25 (g/ml) (density), 𝜂𝐷25 (Refractive Index), and γM (Molar Refraction)


101

4.8. Catalytic degradation of WEPS using Mg impregnated catalysts

i. Effect of percentage of precursor active metal center

WEPS samples were degraded with Mg impregnated catalysts (Mg-Al₂O₃, Mg-Mmn and

Mg-AC) and the percentage of impregnated metal (Mg) over different supports was

optimized using optimum conditions of Mg catalyst i.e., 450 ºC degradation temperature,

30 min reaction time and 1:0.3 polymer to catalyst ratio. WEPS was degraded using

impregnated catalysts having 5%, 10%, 15%, 20% and 25% precursor active center over

Al₂O₃, Mmn and AC supports (Fig. 4.8.1). The yield of liquid products was increased with

the increase of percentage of impregnated active center (Mg). The yield of liquid products

was lower in the case of 5% Mg-Al₂O₃ and it increases with the increase of percent Mg

impregnation. The low yield of liquid products in the case of 5% Mg-Al₂O₃ may be

attributed due to its acidic character and high reactivity of Al₂O₃ support for the

degradation of WEPS that transform it into gaseous products [25]. The yield of liquid

products was maximum in the case of 15% Mg-Al₂O₃ catalyst having maximum liquid

products 95.47 ± 0.12 wt.% and a further increase in the percentage of the impregnated

active center did not affect the yield of liquid products. The yield of liquid products was

88.87 ± 0.42 wt.% and 87.47 ± 0.12 wt.%, respectively, maximum with 20% Mg-Mmn and

20% Mg-AC catalysts. The increase of percent Mg impregnation increase the liquid

products are due to the blocking of support active site with the help of precursor active

center molecules, which cause to increase the selectivity of the catalyst. Comparative

reaction conditions and contents of products of 15% Mg-Al₂O₃, 20% Mg-Mmn and 20%

Mg-AC catalysts are given in Table 4.8.1. The order of activity of Mg impregnated

catalysts and Mg catalyst is 20% Mg-Mmn ≥ 15% Mg-Al₂O₃ > 20% Mg-AC > Mg. WEPS

was degraded with impregnated catalysts (Mg-Al₂O₃, Mg-Mmn and Mg-AC) and the

percentage of impregnated metal (Mg) over different supports was optimized using

optimum conditions of Mg catalyst i.e., 450 ºC degradation temperature, 30 min reaction

time and 1:0.3 polymer to catalyst ratio. The degradation data of impregnated catalysts i.e.

15% Mg-Al₂O₃, 20% Mg-Mmn and 20% Mg-AC were compared in terms of activity of

catalysts and selectivity of aromatic products.


102

Table 4.8.1 Optimum reaction conditions and contents of product using 15% Mg-

Al₂O₃, 20% Mg-Mmn and 20% Mg-AC catalysts

15% Mg-

Al₂O₃

20% Mg-

Mmn

20% Mg-

AC

Reaction conditions

Temperature (⁰C) 450 450 450

Time (min) 30 30 30



Liquids 95.47 ± 0.12 88.87 ± 0.42 87.47 ± 0.12

Gases 4.53 ± 0.12 11.20 ± 0.42 12.50 ± 0.12

Residue 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00

Total conversion 100 100 100

Figure 4.8.1 Effect of percentage of impregnated precursor metal (Mg) over Al₂O₃,

Mmn and AC supports for maximum liquid products


103

ii. Composition of derived liquid products and selectivity of its components

The liquid obtained with the degradation of WEPS using Mg, 15% Mg-Al₂O₃, 20% Mg-

Mmn and 20% Mg-AC catalyst was analyzed by GC-MS for identification of component

products. The results of GC-MS analysis represented in terms of weight percent of the

WEPS sample degraded and are given in Table 4.8.2. GC-MS chromatograms are shown

in Figs 4.8.2-4.8.4. The analysis showed that the degraded products of WEPS yielded 20

major components comprising toluene, ethyl benzene and styrene monomer in higher

percentages.

Acidic catalysts initiate the degradation of PS with the attack of a proton associated with a

Brönsted acid site to the phenyl ring of the PS polymer backbone. The resulting carbocation

(carbenium) undergo β-scission followed by a hydrogen transfer [18]. The hydrogen of

acidic catalysts attacks the branched aromatic ring giving rise to primary cation Type I of

π-complex, the same way the hydrogen of acidic catalysts attacks the branched phenyl

group of PS and produce primary cation Type II. The Type I cation upon β-scission convert

to σ-complex (secondary cation) and release benzene, shown in scheme 1 of section

1.10.2.1. Where cation Type II upon β-scission give rise to a polymer ion (A) and also

produce a cyclodiene substituted polymer chain (B) as shown in scheme 3 of section

1.10.2.1. The ion A further undergo β-scission and yield styrene monomer and secondary

ions of A. Therefore, styrene monomer was the major component with all the catalysts,

maximum with 15% Mg-Al₂O₃ (56.20 wt.%) and it was 46.62 wt.% and 44.41 wt.% with

20% Mg-Mmn and 20% Mg-AC catalysts, respectively. The primary or secondary ion A

also undergoes hydride ion rearrangement followed by β-scission to produce α-

methylstyrene [11, 18]. However, the formation of benzene and its hydrogenation to form

toluene and ethylbenzene or the formation of other products decreased the yield of styrene

monomer [11, 20]. The hydrogenation of styrene and production of benzene, (1-

methylethyl) by intermolecular H transfer are shown in scheme 5 section 1.10.2.1, where

the formation of toluene is shown in Scheme 4 of section 1.10.2.1. Toluene (13.10 wt.%)

and ethyl benzene (8.93 wt.%) were maximum with 15% Mg-Al₂O₃ catalyst as compared

to 20% Mg-Mmn and 20% Mg-AC catalysts. The production of toluene and the formation

of ethylbenzene from the hydrogenation of styrene is shown in Scheme 4 and Scheme 1,


104

respectively. The highly acidic support Al₂O₃ with 15% Mg impregnation was proved to

be the best activity and high selectivity catalysts. The activity of Mg impregnated catalysts

over Al₂O₃ and Mmn supports was almost the same, but selectivity was found to increase

with the increase of acidity of supporting material. The order of selectivity of valuable

hydrocarbons was 15% Mg-Al₂O₃ > 20% Mg-Mmn > 20% Mg-AC.

Catalysts like 15% Mg-Al₂O₃, 20% Mg-Mmn and 20% Mg-AC is having both Lewis acid

sites and Brönsted acid sites, does not seem to promote cross-linking reactions instead

accelerated hydrogenation reactions that’s why the yield of ethylbenzene is greater with

these catalysts. Along with aromatic products some open chain ketones were also formed

using impregnated catalysts. The presence of these ketones and other oxygenated products

might be due to the reaction of atmospheric oxygen [10]. The products obtained with 20%

Mg-AC catalyst including some open chain and other aromatic products were in a broad

range with relatively lower concentration as compared to the other two catalysts. The

catalytic activity as well as the selectivity of styrene and other aromatic hydrocarbons of

15% Mg-Al₂O₃ were better than the 20% Mg-Mmn and 20% Mg-AC catalysts. The high

yield of low molecular weight aromatic hydrocarbons in the presence of acidic catalyst has

already been reported and it was suggested that it is due to the acidic catalyst that led the

reaction through an end-chain scission pathway without promoting thermal cracking [26,

27]. The degradation of WEPS using 15% Mg-Al₂O₃, 20% Mg-Mmn and 20% Mg-AC

catalysts were compared with other literature reported methods, in terms of weight percent

of the WEPS degraded, which is different from their reported method, the comparison are

given in Table 4.8.3. The activity of Mg impregnated catalysts was (95.47 wt.%) better as

compared to the methods reported by Xie et al. [5], Chumbhale et al. [21], Tae et al. [28],

Chumbhale et al. [29], Lee et al. [30]. However, the selectivity of styrene was less than Fe-

K/Al₂O₃ [5] catalyst and 9% K2O/Si-MCM-41 [30] but the current catalysts are more

economic than all the reported catalysts, they are easy to prepare and can be recycled easily.

This method also gives more selective and high amount of low molecular weight aromatic

hydrocarbons in major with environmental friendly method as compared to the degradation

products by other researchers [7, 10, 31].


105

Table 4.8.2 Products formed by the catalytic degradation of WEPS using 15% Mg-

Al₂O₃, 20% Mg-Mmn and 20% Mg-AC catalysts at optimized conditions

S. No. Products

Composition (wt.%)

15% Mg-

Al₂O₃

20% Mg-

Mmn

20% Mg-

AC

1 Benzene 1.36 0.36 0.66

2 Toluene 13.10 5.90 6.38

3 3-Hexen-2-one 4.72 0.00 0.00

4 3-Penten-2-one, 4-methyl 0.00 0.00 8.83

5 2-Pentanone, 4-hydroxy-4-methyl- 1.53 3.84 3.82


7 5-Hexene-2-one 3.88 0.00 0.00

8 Styrene 56.20 46.62 44.41


10 Azulene 0.71 0.00 0.00

11 Undecane, 3,8-dimethyl 0.00 0.04 1.01

12 3-Ethyl-3-methylheptane 0.00 0.30 1.95


14 Benzene, 1,1'-(1-methyl-1,2-

ethanediyl)bis

0.00 1.38 0.78


16 Benzene, 3-butynyl 0.00 4.86 2.39



19 1,2-propanediol, 3-benzyloxy-1,2-

diacetyl

0.00 0.92 0.27



Gases (wt.%) 4.53 17.04 12.50

Residue (wt.%) 0.00 0.00 0.00


106

Figure 4.8.2 Chromatogram of catalytically derived liquid products obtained with 15%

Mg-Al₂O₃ catalyst at optimized conditions


Mg-Mmn catalyst at optimized conditions


107


Mg-AC catalyst at optimized conditions


108

Table 4.8.3 Comparison of liquid products and their contents with literature reported methods along with their reaction

conditions

Current Methods Literature Methods

15% Mg-

Al₂O₃

20%

Mg-

Mmn

20%

Mg-AC

9% K2O/Si-

MCM-41a HY-700b HHc

HDM

(147)d Fe-K/Al₂O₃e

Reaction conditions

Temperature (°C) 450 450 450 400 375 450 360 400

Time (min) 30 30 30 30 90 120 90 90

Pol. to cat. ratio 1:0.3 1:0.3 1:0.3 2:1 1:0.01 - 1:0.01 1:0.01

Content of products (wt.%)

Yield oil 95.47 95.47 87.50 85.67 68.00 90.20 59.00 92.20

Yield gas 4.53 4.50 12.50 4.86 18.80 4.80 22.70 6.40

Residue 0.00 0.00 0.00 9.47 13.20 5.00 18.30 1.40

Contents of liquid (wt.%)

Benzene 1.36 0.36 0.66 NRf 0.20 0.23 0.04 0.09

Toluene 13.10 5.90 6.38 NRf 4.90 6.44 3.37 5.72

Ethylbenzene 8.93 5.48 7.00 NRf 4.90 7.54 2.50 1.84

Styrene 56.20 46.62 44.41 59.13 45.29 53.06 39.95 65.83

Isopropyl benzene 0.00 0.00 0.40 NRf 0.68 1.02 0.35 0.37

a-Methylstyrene 3.05 2.22 2.00 NRf 6.32 6.49 6.80 7.74

1,3-diphenyl-propane 0.00 0.00 0.50 NRf 0.48 0.00 1.53 3.50

Other 17.36 39.42 22.80 7.70 5.13 15.42 4.54 28.56 a [5], b [21], c [28], d [29], e [30]

f Not Report


109

4.9. Catalytic degradation of WEPS using Zn, ZnO and ZnCl₂ catalysts

i. Effect of degradation temperature

The effect of pyrolysis temperature on thermo-catalytic pyrolysis of WEPS was

investigated in the temperature range of 250 ºC to 500 ºC for all the three catalysts at

optimum conditions using 60 min reaction time and 1:0.2 feed to catalyst ratio. The results

for the effect of pyrolysis temperature are shown in Fig. 4.9.1. Most of the reported work

has been carried out at fixed temperature either because of the limitation of reactor

(autoclave etc.) or heating assembly [4-7]. On the other hand 500 ºC is the adequate

maximum temperature for conversion into liquid products, which has been reported by

various researchers [17, 21, 28, 32]. The yield of liquid products at 250 ºC was 0% with

the formation of small amounts of gaseous products. The yield of liquid products started at

350 ºC in the case of Zn and ZnO catalysts where it was 0 wt.% in the case of ZnCl₂

catalysts at this temperature. However, the yield of gaseous product at this temperature was

more than Zn and ZnO catalysts. It is because of the moderate Lewis character of ZnCl₂,

which catalyze the polymer to yield only gaseous products (volatile light hydrocarbons). It

was confirmed by performing some additional experiments with 10 g of feed material (feed

to catalyst ratio of 1:0.05), the amount of gaseous products were almost the same with the

additional collection of 5.87 ± 1.39 wt.% liquid products. It was assumed that only ZnCl₂

surrounded polymer molecules are converted to gaseous products while the remaining are

converting due to thermal effects. The yield of liquid products increased with the increase

of degradation temperature using constant reaction time and feed to catalyst ratio for all

the three catalysts. The liquid product yield reached to a maximum of 82.93 ± 2.00 wt.%

and 84.73 ± 2.31 wt.% at 450 ºC for the Zn and ZnO catalysts, respectively, and no


110

significant increase was observed after 450 ºC. The yield of liquid products was 79.40 ±

0.72 wt.% for ZnCl2 catalyst at 500 ºC. For all the three catalysts the total yield was 100%.

Figure 4.9.1 Effect of temperature and comparison of catalytically derived liquid

products obtained with Zn, ZnO and ZnCl₂ catalysts at optimized contions

ii. Effect of reaction time

The effect of reaction time on the degradation of WEPS is shown in Fig. 4.9.2. The

degradation experiment was carried out in 30, 60, 90, 120 and 150 min reaction time at

their respective optimized conditions i.e. 450 ºC pyrolysis temperature and 1:0.2 feed to

catalyst ratio for Zn and ZnO catalysts, and 500 ºC pyrolysis temperature and 1:0.2 feed to

catalyst ratio for ZnCl2 catalyst. The effect of reaction time changes the amount of products

formed as well as alter component products because of changing residence reaction time.

The yield of the liquid products increased with increase of reaction time for all the three

catalysts and then with further increase it either remain constant or start decreasing. The


111

decrease of liquid products is due to the increase in residence time in the reactor, which

leads to inter-product's interaction and the formation of gaseous products. The second

cause is the escape of volatile products from the liquid products receiver through the gas

outlet at a much longer time. In the case of Zn catalyst, the yield of liquid products

increased from 30 min to 120 min, where it was maximum i.e., 96.73 ± 0.12 wt.% with

100% total yield. The yield of liquid products was maximum that is 84.73 ± 2.31 wt.% and

79.40 ± 0.72 wt.% with 60 min reaction time in the case of ZnO and ZnCl2 catalysts,

respectively. The total yield in case of Zn and ZnCl2 was 100%.


products obtained with Zn, ZnO and ZnCl₂ catalysts at optimized conditions


The degradation of WEPS was carried out using polymer to catalyst ratio in the range of

1:0.1 to 1:0.5, while keeping other reaction conditions as follow: for Zn catalyst; 120 min


112

reaction time and 450 ºC pyrolysis temperature, for ZnO catalyst; 60 min reaction time and

450 ºC pyrolysis temperature, and for ZnCl2 catalysts; 60 min reaction time and 500 ºC

pyrolysis temperature. The results of the experiments are shown in Fig. 4.9.3. Changing

the polymer to catalyst ratio in the case of Zn catalyst from 1:0.2 to 1:0.1, the yield of

liquids was 96.07 ± 0.31 wt.% - the same as with 1:0.2 feed to catalyst ratio. Further no

significant impact was recorded on the yield of liquid products above 1:0.2 feed to catalyst

ratio. Therefore, 1:0.2 was chosen optimum polymer to catalyst ratio. In the case of ZnO

catalyst, the yield of liquid products was 84.73 ± 2.31 wt.% maximum with 1:0.2 and then

a slight decrease was observed with increase of catalyst amount. In the case of ZnCl2

catalyst, the yield was maximum with 1:0.1 polymer to catalyst ratio (79.60 ± 4.20 wt.%).

The total yield was 100% at optimum conditions for all the three catalysts. The effect of

degradation temperature, reaction time and polymer to catalyst ratio were determined for

all the used catalysts for maximum conversion of WEPS into liquid products. The

maximum yield of liquids was 96.07 ± 0.31 wt.%, 84.73 ± 2.31 wt.% and 79.60 ± 4.20

wt.% using Zn, ZnO and ZnCl2 catalysts, respectively, at their respective optimized

conditions. Among the used catalysts, the yield of liquids was the highest in the case of Zn

as catalyst. A comparative study describing reaction conditions and contents of products

are given in Table 4.9.1 using thermal degradation and zinc bulk catalysts. The degradation

of WEPS using Zn catalyst without the use of any solvent was found better than using

benzene solvent as reported by Guoxi et al., [33]. The yield of liquid products of Zn catalyst

was more than reported by Ukei et al., [11] using BaO catalyst (93.4 wt.%) at 600 ºC for 3

hours and ZnO and ZnCl₂ catalyst were also good from his reported acid and base catalysts

due to low degradation temperature and small reaction time.


113

Table 4.9.1 Optimum reaction conditions and contents of product using Zn, ZnO and

ZnCl₂ catalysts

Zn ZnO ZnCl₂

Reaction conditions


Time (min) 120 60 60



Liquids 96.73 ± 0.12 84.73 ± 2.31 79.60 ± 4.20

Gases 3.27 ± 0.12 15.27 ± 2.31 20.40 ± 4.20

Residue 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00



114


liquid products obtained with thermal degradation, Zn, ZnO and ZnCl₂


iv. Composition of derived liquid products and selectivity of its components

The degraded liquid products of WEPS were analyzed by GC-MS. The results of the

analysis are given in Table 4.9.2. The analysis revealed that the products obtained with all

the three catalysts yielded nine major aromatic hydrocarbons among which toluene; styrene

monomer; α-methylstyrene; benzene, 3-butynyl: benzene, 1,1'-(1,3-propanediyl) bis and

1,2-propanediol, 3-benzyloxy-1,2-diacetyl were the major components. Like other

literature reported methods, styrene monomer in this study was also the major products

with thermal pyrolysis and as well as with zinc bulk catalysts [11, 16, 20]. The yield of all

the reported products was higher with Zn catalyst, as compared to thermal, ZnO and ZnCl₂

catalysts, except for 1,2-propanediol, 3-benzyloxy-1,2-diacetyl, the composition of which


115

was high with ZnO catalyst (13.91 wt.%). The yield of styrene monomer was 39.31 wt.%,

47.96 wt.%, 41.45 wt.% and 40.88 wt.% with thermal, Zn, ZnO and ZnCl₂ catalysts,

respectively. The yield of major products was maximum with Zn catalyst with 2.47 wt.%

toluene, 47.96 wt.% styrene, 1.90 wt.% α-methylstyrene, 2.98 wt.% benzene, 1,1'-(1,3-

propanediyl)bis, 21.53 wt.% benzene, 3-butynyl and 12.29 wt.% 1,2-propanediol, 3-

benzyloxy-1,2-diacetyl. In the current study, Zn as a catalyst was found with high activity

for the production of liquid products yielding minimum gases and residue (Table 4.9.1)

with 100% total yield as well as with high selectivity for aromatic hydrocarbons as

compared to the other catalysts used in this study. Thermo-catalytic degradation of

polymers leads to numerous species involving hundreds of interactions, therefore, it is hard

to devise a specific mechanism but there are a few agreements using different types of

catalysts. A Lewis acid such as ZnCl₂ catalyst detach a hydride anion from the benzylic

position in PS reported by Karmore et al [34] and basic catalysts like ZnO, activates PS

through deprotonating with subsequent β-scission of the polymer backbone [14]. The low

yield of styrene monomer with ZnCl₂ as compared to solid basic catalysts (ZnO and Zn

catalysts) is due to the numerous active Lewis acidic sites causing further cracking of the

styrene monomer and hydrogenation with a competitive crosslinking reaction or side

reaction which ultimately increase the yield of gases with the concomitant decrease of

liquid product yield [5, 11, 20]. As a whole the selectivity of low molecular weight aromatic

hydrocarbons was better with zinc bulk catalyst with small duration of reaction time and

degradation temperature without using any additive and solvent than reported by literature

[20, 35], but the selectivity of styrene was smaller than that of reported by Ukei et al. [11]

and Guoxi et al. [33]. This was because of their wt.% calculation method, high residence

time, degradation temperature and use of additives or solvent, which ultimately cause high

production cost. Zn was found with higher activity and selectivity for the production of

low molecular weight aromatic hydrocarbons, especially for styrene monomer with a cost

effective method.


116

Table 4.9.2 Products formed by the catalytic degradation of WEPS using Zn, ZnO and

ZnCl₂ catalysts at optimized condition


Zn ZnO ZnCl₂

1 Toluene 2.47 1.80 2.11


3 Styrene 47.96 41.45 40.88


5 Benzene, 1,1'-(1,3-

propanediyl)bis 2.98 1.70 1.16

6 Benzene, 3-butynyl 21.53 19.57 12.94


8 1,2-propanediol, 3-benzyloxy-

1,2-diacetyl 12.29 13.91 12.54



Gases (Wt.%) 3.27 15.27 20.40

Residue (Wt.%) 0.00 0.00 0.00

Figure 4.9.4 Chromatogram of catalytically derived liquid products obtained with Zn



117

Figure 4.9.5 Chromatogram of catalytically derived liquid products obtained with ZnO


Figure 4.9.6 Chromatogram of catalytically derived liquid products obtained with ZnCl₂



118

v. Separation of the products using fractional distillation

Catalytic degradation significantly increased the yield of liquid products as compared to

thermal cracking. Among the catalysts zinc bulk catalyst was found with amazing

selectivity for desirable aromatic hydrocarbons. The effective degradation of WEPS was

followed by the separation of component products of bulk liquids using fractional

distillation assembly. Fractions were collected at various boiling points ranges and were

characterized using physiochemical techniques like density (d20), refractive index (𝜂𝐷20),

molar refraction (γM) and as well as GC-MS analysis in order to identify different fractions

obtained. The results of the analysis are given in Table 4.9.3. It was observed that during

the fractional distillation further cracking of huge molecules took place in addition with

cyclization and recombination reactions [12, 13, 36] in the heating reactor and major

variation in the products were observed.

Each fraction separated was confirmed by the GC-MS analysis. Each fraction was found

with the contamination of other aromatic hydrocarbons in small percentage. The yield of

styrene remained almost constant, where benzene, 1,1’-(1,3-propanediyl)bis decreased

using the liquid products obtained with Zn and ZnO catalysts. For the liquid obtained with

ZnCl₂ catalyst the yield of styrene monomer increased from 40.88 wt.% to 48 wt.% and

the yield of benzene, 1,1’-(1,3-propanediyl)bis increased from 1.16 wt.% to 9.0 wt.%. The

yield of toluene, ethylbenzene and α-methylstyrene increased for all the liquid products.

The increase in the yield of these components may be attributed to further thermal pyrolysis

of higher molecular weight aromatic hydrocarbons. During fractional distillation, The last

products obtained was 1,1':3,1"-terphenyl, 5'-phenyl with apparent increase for all the three

liquids. The increase was from 0.71 wt.% to 10 wt.%, 0.34 wt.% to 6 wt.% and 0.35 wt.%

to 6 wt.% using liquid products obtained with Zn, ZnO and ZnCl₂ catalysts, respectively.

Increase in the yield of this component and the formation of 2-phenylnaphthalene using

liquid products obtained with ZnCl₂ catalysts might be due the dehydrogenation/

cyclization reaction [24]. From the separation studies it is concluded that the Zn containing

catalysts can be selectively used for the recovery of toluene, ethylbenzene, styrene

monomer and α-methylstyrene. Molar refraction of each component was calculated from


119

the measured refractive index and density as shown in Table 4.9.3. The data were compared

with the molar refraction of standards (Table 4.5.3 in section 4.5 (Page 82)) and found in

close agreement with that of the standards.


120


degradation of WEPS using Zn, ZnO and ZnCl₂ catalysts

Compound

Zn ZnO ZnCl₂

%age d25

(g/ml) 𝜼𝑫


(g/ml) 𝜼𝑫


(g/ml) 𝜼𝑫

𝟐𝟓 γM

Toluene 11.0 0.8740 1.5013 26.3434 7.0 0.8930 1.5109 30.9053 6.0 0.9387 1.5370 30.6545

Ethylbenzene 6.0 0.8710 1.4970 35.6689 9.0 0.8890 1.5069 35.5349 4.0 0.8720 1.4967 35.6097

Styrene 47.0 0.9128 1.5478 36.2280 42.0 0.9144 1.5463 36.0817 48.0 0.9103 1.5439 36.1155

α.-Methylstyrene 12.0 1.0337 1.5523 32.8176 9.0 0.9034 1.5435 41.2620 12.0 0.8974 1.5481 41.8319

Benzene, 1,1'-(1,3-

propanediyl)bis 0.0 - - - 7.0 0.9905 1.5670 64.7377 9.0 0.9835 1.5611 64.6428

Benzene, 3-butynyl 14.0 0.9457 1.5327 42.7045 17.0 0.9792 1.5585 42.8979 10.0 0.9421 1.5309 42.7477

2-Phenylnaphthalene 0.0 - - - 3.0 1.0870 1.6530 68.7928 5.0 1.0790 1.6409 68.2836

1,1':3,1"-Terphenyl, 5'-

phenyl 10.0 1.0730 1.6190 100.1761 6.0 1.0710 1.6150 99.8418 6.0 1.0690 1.6151 100.0417



121

4.10. Catalytic degradation of WEPS using Zn impregnated catalysts


The degradation of WEPS was carried out using Zn impregnated catalysts i.e., Zn-Al₂O₃,

Zn-Mmn and Zn-AC. The degradation experiments were conducted with the optimized

parameters for Zn catalyst i.e., 450 ºC degradation temperature, 120 min reaction time and

1:0.3 polymer to catalyst ratio. WEPS were degraded by 5%, 10%, 15%, 20%, and 25% of

Zn impregnation as precursor metal over Al₂O₃, Mmn and AC supports. The results of the

analysis are shown in Fig. 4.10.1. The yield of liquid products increased with the increase

of impregnated metal (Zn) percentage. The high activity of supported catalyst is due to the

availability of more reaction site for the degradation of WEPS into liquid products [16].

The yield of liquid products was maximum with 20% of the impregnated Zn catalysts for

all the three supports. The maximum yield of liquid products was 90.20 ± 0.35 wt.%, 84.53

± 0.12 wt.% and 84.13 ± 0.23 wt.% using Zn-Al₂O₃, Zn-Mmn and Zn-AC catalysts

respectively, with 100% total yield in all cases.

The maximum yield of liquid products at optimized conditions of temperature, time and

feed to catalysts ratio was 96.97 ± 0.42 wt.%, 90.20 ± 0.35 wt.%, 84.53 ± 0.12 wt.% and

84.13 ± 0.23 wt.% with Zn, 20% Zn-Al₂O₃, 20% Zn-Mmn and 20% Zn-AC catalysts,

respectively, with 100% total conversion in all cases. Comparison of optimum reaction

conditions and yield of products is given in Table 4.10.1. The activity of catalysts for

maximum yield of liquid products was in the order, Zn > 20% Zn-Al₂O₃ > 20% Zn-Mmn

> 20% Zn-AC. The activity of Zn catalysts was higher than reported by Ukei et al., [11]

with BaO catalyst and the activity of supported catalysts was also more than of their

reported catalysts, not only on the basis of products yield but also on the basis of

degradation temperature and reaction time. Moreover, the current degradation of WEPS

was carried out without the use of any solvent, which has been used in literature which also

increase the cost of the method [33]. Among the used catalysts, the activity of liquid


122

products was higher with Zn catalysts but the aim of the study was not only activity but

also selectivity with ultimate aim of low cost method.

Table 4.10.1 Optimum reaction conditions and contents of product 20% Zn-Al₂O₃, 20%

Zn-Mmn and 20% Zn-AC catalysts

20% Zn-Al₂O₃ 20% Zn-Mmn 20% Zn-AC

Reaction conditions


Time (min) 120 120 120



Liquids 90.20 ± 0.35 84.53 ± 0.12 84.13 ± 0.23

Gases 9.70 ± 0.35 15.40 ± 0.12 15.80 ± 0.23

Residue 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00



123

Figure 4.10.1 Effect of percentage of impregnated precursor metal (Zn) over Al₂O₃, Mmn

and AC supports for maximum liquid products


Highly dispersed Zn supported catalysts showed high activity than simple bulk catalysts

for the pyrolysis of PS. Acidic supports with Lewis acids have been reported with both

Lewis and Brönsted acidic sites active for pyrolysis [37]. ZnCl₂ dispersion over different

supports also results in the formation of acidic catalysts. The cracking of WEPS with acidic

catalysts is of carbonium nature involve with the attack of proton associated with a

Brönsted acid site to rings of PS [17, 18]. The reaction is followed by β-scission and a

hydrogen transfer to form styrene or lower aromatic fragments, the possible reaction

pathways toward most of the component products have been reported in the literature [14].

The GC-MS analysis of liquid products (WEPS degraded products) was carried out to

identify the component compounds. The GC-MS analysis results are given in Table 4.10.2,

while the GC-MS chromatograms are shown in Figs. 4.10.2-4.10.4 for 20% Zn-Al₂O₃,


124

20% Zn-Mmn and 20% Zn-AC catalysts, respectively. Styrene, ethylbenzene, toluene,

benzene, 1,1'-(1,3-propanediyl)bis, benzene, 3-butynyl were the major products along with

some other products. The data reveal that styrene monomer was the major component with

all the catalysts i.e. 62.88 wt.%, 46.16 wt.% and 42.72 wt.% with 20% Zn-Al₂O₃, 20% Zn-

Mmn, 20% Zn-AC, respectively. The compositions of benzene, toluene, styrene and α-

methylstyrene were maximum with 20% Zn-Al₂O₃ catalyst i.e. 0.72 wt.%, 11.79 wt.%,

7.35 wt.%, 62.88 wt.% and 4.58 wt.%, respectively, with small range of products. The yield

of these low molecular weight aromatic hydrocarbons using 20% Zn-Al₂O₃ catalyst is due

the successful depolymerization of WEPS into styrene monomer but the high activity of

the catalysts also cause further cracking of styrene monomer leading to production of

benzene & toluene, and upon hydrogenation of leads to the formation of ethylbenzene [11,

17].

Dimeric species like benzene, 1,1'-(1,2-ethanediyl)bis, benzene, 1,1'-(1-methyl-1,2-

ethanediyl)bis were formed with 20% Zn-Mmn, 20 % Zn-AC catalysts maximum with

20% Zn-Mmn catalyst. The formation of dimeric species with supported catalyst may be

attributed to the combination of thermal transformation, which not only produce styrene

monomer but also produce styrene dimers [11] and also other oligomers [23, 38, 39].

Benzene was maximum with 20% Zn-Al₂O₃ catalyst, ethylbenzene was maximum with

20% Zn-AC catalyst where high molecular weight aromatic hydrocarbons like benzene, 3-

butynyl; benzene, (1-methyl-3-butenyl) and 1,2-propanediol, 3-benzyloxy-1,2-diacetyl

were maximum with 20% Zn-Mmn and 20% Zn-AC catalysts. The presence of oxygenated

aromatic products is attributed to the presence of contamination in WEPS sample or might

be produced due to the reaction of products with atmospheric oxygen at elevated

temperature [10]. Among the Zn impregnated catalysts 20% Zn-Al₂O₃ was found with

better selectivity of component products. The selectivity and yield of component products

were compared with literature reported methods. The selectivity of low molecular weight

aromatic hydrocarbons such as benzene, toluene and ethylbenzene increased, especially in

the case of 20% Zn-Al₂O₃ catalysts. The selectivity of styrene monomer was higher than

reported literature methods using cost effective conditions and materials [11, 33].


125

Table 4.10.2 Products formed by the catalytic degradation of WEPS using 20% Zn-

Al₂O₃, 20% Zn-Mmn and 20% Zn-AC catalysts

S.No. Products

Composition (wt.%)

20% Zn-

Al₂O₃

20% Zn-

Mmn

20% Zn-

AC

1 Benzene 0.72 0.55 0.54

2 Toluene 11.79 7.16 7.79



5 Styrene 62.88 46.16 42.72

6 .α.-Methylstyrene 4.58 0.00 3.55

7 Naphthalene 0.82 0.72 0.00



ethanediyl)bis 0.00 2.06 1.27



12 Benzene, 3-butynyl 0.00 7.87 5.00


14 Anthracene 0.00 0.61 0.60



diacetyl 0.00 0.62 0.95



Gases (Wt.%) 9.70 18.13 14.03

Residue (Wt.%) 0.00 0.00 0.00


126


Zn-Al₂O₃ catalyst at optimized conditions


Zn-Mmn catalyst at optimized conditions


127

Figure 4.10.4 Chromatogram of catalytically derived liquid products obtained with Zn-

AC catalyst at optimized conditions


128

4.11. Catalytic degradation of WEPS using Al, Al₂O₃ and AlCl₃ catalysts


WEPS samples were degraded in the temperature range varies from 250 ºC to 500 ºC, and

the results are shown in Fig. 4.11.1. During optimization of temperature other reaction

conditions were as follow: for Al catalyst; reaction time 60 min, polymer to catalyst ratio

1:0.2, for Al₂O₃ and for AlCl₃ catalysts; reaction time 30 min, polymer to catalyst ratio

1:0.2. The results show that as the temperature was increased from 250 ºC to 500 ºC the

yield of liquid products also increased from 0.00 to 91.53 ± 2.27 wt.% in the case of Al

catalyst, from 0.00 to 80.20 ± 1.91 wt.% in the case of Al₂O₃ catalyst and from 0.00 to

93.47 ± 0.50 wt.% in the case of AlCl₃ catalyst with associated decrease of gases. The

maximum yield of liquid products in the case of Al catalyst was 91.53 ± 2.27 wt.% (100%

total conversion) at 500 ºC, while the maximum yield of liquid products in the case of

Al₂O₃ and AlCl₃ was 80.20 ± 1.19 wt.% (100% total conversion) and 93.47 ± 0.50 wt.%

(100% total conversion), respectively at 450 ºC. Among the three catalysts, the yield of

liquid products was high using AlCl₃ with relatively low degradation temperature.


129

Figure 4.11.1 Effect of temperature and comparison of catalytically derived liquid

products obtained with Al, Al₂O₃ and AlCl₃ catalysts

ii. Effect of time

WEPS samples were degraded using time intervals of 30 min, 60 min, 90 min, 120 min

and 150 min keeping other parameters constant. For Al catalyst the degradation

temperature was 500 ºC and polymer to catalyst ratio 1:0.2 while for Al₂O₃ and AlCl₃

catalysts; degradation temperature 450 ºC and polymer to catalyst ratio 1:0.2 were used.

The results of these experiments are shown in Fig. 4.11.2. The results shows that increasing

reaction time from 30 min to 60 min, the yield of liquid products increased in the case of

Al catalyst from 85.07 ± 2.58 wt.% to 91.53 ± 2.27 wt.% and in the case of Al₂O₃ from

80.20 ± 1.91 wt.% to 87.00 ± 0.80 wt.% where beyond 60 min no change in liquid products

was observed or a decrease occurred because of large residence time causing further

cracking of the products to gaseous compounds. The maximum yield of liquid products


130

was achieved with a 60 min reaction time in the case of Al (91.53 ± 2.27 wt.%) and Al₂O₃

(87.00 ± 0.80 wt.%) catalysts with 100% total conversion. For AlCl₃ catalyst maximum

liquid product was (93.47 ± 0.50 wt.%) achieved in 30 min reaction time with 100% total

conversion. Among the catalysts maximum liquid was achieved with AlCl₃ catalyst.


products obtained with Al, Al₂O₃ and AlCl₃ catalysts at optimized

conditions


The effect of polymer to catalysts ratio was investigated for the degradation of WEPS. The

catalysts were used in mixture of polymer to catalyst ratio of 1:0.1 to 1:0.5 using optimized

degradation temperature and reaction time for each catalyst. The results are shown in Fig.

4.11.3. It was observed that the change in polymer to catalyst ratio does not increase the

liquid products substantially, however an increase in the yield of liquid products was


131

observed up to 1:0.2 for all the catalysts. Decreasing/increasing the polymer to catalyst

ratio from 1:0.2 decreased the product in the case of Al₂O₃ and AlCl₃ catalysts. The yield

of liquid products was 90.13 ± 1.45 wt.%, 87.00 ± 0.80 wt.% and 93.47 ± 0.50 wt.% using

Al, Al₂O₃ and AlCl₃ catalysts, respectively. In the case of Al catalyst, 1:0.1 was taken

optimum viewing the cost of the method where in the case of Al₂O₃ and AlCl₃ 1:0.2

polymer to catalyst ratio was taken optimum. A comparison of reaction conditions and

contents of products using Al, Al₂O₃ and AlCl₃ catalysts are given in Table 4.11.1.

Table 4.11.1 Optimum reaction conditions and contents of products using Al, Al₂O₃ and

AlCl₃ catalysts

Catalysts Al Al₂O₃ AlCl₃

Reaction conditions


Time (min) 60 60 30


Contents of products (wt.%)

Liquids 91.53 ± 2.27 87.00 ± 0.80 93.47 ± 0.50

Gases 8.47 ± 22.7 13.00 ± 0.80 6.53 ± 0.50

Residue 0.00 ± 0.00 0.00 ± 0.00 0.00 ± 0.00

Total percent conversion 100 100 100


132


liquid products obtained with thermal degradation, Al, Al₂O₃ and AlCl₃



GC-MS was used for the identification of component products of the derived liquid

obtained from degradation of WEPS using Al, Al₂O₃ and AlCl₃ catalysts. The analysis in

term of weight percent of the WEPS degraded is given in Table 4.11.2 and GC-MS

chromatograms are shown in Figs. 4.11.4-4.11.6. The data obtained shows 16 different

compounds with toluene; ethylbenzene; styrene; α-methylstyrene; benzene, 3-butynyl and

1,2-propanediol, 3-benzyloxy-1,2-diacetyl as major components along with trace

compounds, which were entirely aromatic hydrocarbons.

Al and AlCl₃ catalysts were found with higher selectivity than Al₂O₃. The use of these

catalysts decreased the yield of gases and high molecular weight aromatic hydrocarbons to


133

desirable and low molecular weight aromatic hydrocarbons like benzene, toluene,

ethylbenzene, styrene and α-methylstyrene. Al and AlCl₃ act as heterogeneous acid and

had higher selectivity than acidic Al₂O₃. It was observed that catalyst nature and properties

have an important role in the selectivity of products, where literature has reported the role

of catalyst in the degradation of WEPS and selectivity of products [6, 21].

Heterogeneous acidic catalysts initiate the process of degradation production of carbonium

ion. This resulting ion may further undergo β-scission followed by a hydrogen transfer,

toward different possible products. The reaction mechanism is reported by Audisio et al.

[17, 18] for Lewis acid catalyst like AlCl₃. The degradation of PS starts with the

elimination of the proton, which depend on the strength and electronegativity of the Lewis

acid, followed by β-cleavage of C-C bond [34]. The yield of styrene monomer was 47.89

wt.% with Al catalyst and was 45.65 wt.% and 46.58 wt.% with Al₂O₃ and AlCl₃ catalysts,

the yield of styrene monomer was much higher than thermal degradation. Also other light

weight aromatic hydrocarbons like toluene (4.36 wt.%) and ethylbenzene (7.01 wt.%) were

maximum with AlCl₃. The higher amount of toluene and ethylbenzene are due to the

further degradation of styrene monomer and into other light weight aromatic hydrocarbons.

However, AlCl₃ was found to have high activity for the production of liquid products and

selectivity of desirable product, decreasing the yield of gases to 6.53 wt.%.


134

Table 4.11.2 Products formed by the catalytic degradation of WEPS using Al, Al₂O₃ and

AlCl₃ catalysts at optimized conditions


Al Al₂O₃ AlCl₃

1 Toluene 3.23 2.58 4.36


3 Styrene 47.89 45.65 46.58

4 Benzene, (1-methylethyl)- 0.04 0.03 1.07


6 α-Chloro-o-xylene 0.00 0.00 4.70

7 Benzene,1,1'-(1,1,2,2-tetramethyl-

1,2-ethanediyl)bis 0.00 0.00 3.75



10 Benzene, 3-butynyl 14.64 14.29 3.81


12 Tetracyclo[4,2,1,0(3,7),0(2,9)]non-4-

ene, 4-phenyl 0.20 0.00 0.76


propenylidene)bis 0.11 0.00 1.24



diacetyl 14.57 13.75 7.68

16 1-Propene, 3-(2-cyclopentenyl)-2-

methyl-1,1-diphenyl 0.04 0.00 1.61


Gases (Wt.%) 8.47 13.00 6.53

Residue (Wt.%) 0.00 0.00 0.00


135

Figure 4.11.4 Chromatogram of catalytically derived liquid products obtained with Al


Figure 4.11.5 Chromatogram of catalytically derived liquid products obtained with Al₂O₃



136

Figure 4.11.6 Chromatogram of catalytically derived liquid products obtained with AlCl₃



The liquid products obtained under optimized condition were collected in bulk for all

catalysts and were separated on the basis of boiling point using fractional distillation.

Fractional distillation was carried out in the same heating assembly with slight

modification in the reactor with top quick fit beads condenser and fitted thermometer.

Different fractions obtained at different temperature were characterized using

physiochemical parameter like density (d25), refractive index (𝜂𝐷25), and molar refraction

(γM) for the identification of fractions or component products, the result of the analysis are

given in Table 4.11.3. The components of product were identified by GC-MS analysis.

Physiochemical and GC-MS characterization data of component products suggest that

further cracking of high molecular weight aromatic hydrocarbons and/or condensation

followed by conversion to other products. The yield of toluene, ethylbenzene and α-

methylstyrene were observed to increase for all liquid products. The yield of these

components along with benzene that is only formed with the liquid product obtained with


137

AlCl₃ catalyst is believed to be due to further cracking of high molecular weight aromatic

hydrocarbons [14]. The yield of styrene increased from 47 wt.% to 50 wt.% and form 45

wt.% to 51 wt.% in the case of liquid product of Al and Al₂O₃ catalysts, respectively, where

the yield of styrene monomer decreased from 46.48 wt.% to 28 wt.% for liquid product

with strong Lewis acid i.e., AlCl₃ catalyst, in the case of this liquid product the yield of

1,1’-(1,3-propanediyl)bis (styrene dimer) increased and it might be because of the

condensation or polymerization followed by degradation into dimer. 2-Phenylnaphthalene

and 1,1':3,1"-Terphenyl, 5'-phenyl were formed and separated with all the liquid products

obtained with all the three catalysts. The yield of these products is believed to be due to the

cyclization/dehydrogenation reaction of the radicals formed, the same is also reported by

McNeil et al. [24, 40]. The formation of these head to head compounds and condense

aromatic hydrocarbons is believed due to their low activation energies [12, 13, 24]. Among

the used catalysts Al powder and Al₂O₃ was found good for the recovery of toluene,

ethylbenzene, styrene and α-methylstyrene like products. Where AlCl₃ catalyst is suitable

for the maximum recovery of benzene, toluene and ethylbenzene only.

Density and refractive index of the fractions obtained from the fractional distillation of

liquid products derived from catalytic degradation of WEPS were measured, their molar

refractions were calculated and the results are given in Table 4.11.3. The data of molar

refraction was compared with that of standard compounds and found in close agreement

(Table 4.5.3 in section 4.5 (Page 82)).


138


degradation of WEPS using Al, Al₂O₃ and AlCl₃ catalysts

Compound

Al Al₂O₃ AlCl₃

%age d25

(g/ml) 𝜼𝑫


(g/ml) 𝜼𝑫


(g/ml) 𝜼𝑫

𝟐𝟓 γM

Benzene 0.00 - - - - - - - 6.0 0.9023 1.5158 26.1386

Toluene 14.00 0.875 1.4970 30.8138 13.0 0.9266 1.5299 30.7117 17.0 0.9214 1.5239 30.5920

Ethylbenzene 8.00 0.833 1.4790 36.1427 4.0 0.8730 1.4983 35.6661 26.0 0.9001 1.5299 36.4300

Styrene 50.00 0.90722 1.5452 36.3072 51.0 0.8994 1.5400 36.3323 28.0 0.9032 1.5416 36.2686

α-Methylstyrene 13.00 0.9069 1.5321 40.3865 9.0 0.9307 1.5479 40.3237 - - - -

Benzene, 1,1'-(1,3-

propanediyl)bis 0.00 - - - - - - - 7.0 0.9844 1.5594 64.4190

Benzene, 3-butynyl 0.00 - - - 12.0 0.9354 1.5259 42.7145 - - - -

2-Phenylnaphthalene 7.0 1.0800 1.6389 68.0511 4.0 1.0820 1.6476 68.6583 7.0 1.1008 1.6623 68.6919

1,1':3,1"-Terphenyl, 5'-

phenyl 8.0 1.0740 1.5921 96.5550 7.0 1.0800 1.6201 99.6687 9.0 1.0803 1.5930 96.1105



139

4.12. Catalytic degradation of WEPS using Al impregnated catalysts

i. Effect of percent of precursor active metal center

The degradation of WEPS was carried out using Al impregnated catalysts i.e. Al-Al₂O₃,

Al-Mmn and Al-AC catalysts. The degradation experiments of WEPS samples were

carried out using optimized parameters of Al as catalyst (500 ºC degradation temperature,

120 min reaction time and 1:0.2 polymer to catalyst ratio). The effect of the impregnation

percentage of the precursor metal (Al) was optimized over Al₂O₃, Mmn and AC supports.

Al impregnated catalyst (5% to 25%) over Al₂O₃, Mmn and AC were applied for the

degradation of WEPS, the results are shown in Fig. 4.12.1.

In the case of Al-Al₂O₃ and Al-AC catalysts the yield of liquid products increased with the

increase of percentage of precursor metal (Al) and reached to maximum with the use of

20% of Al with further increase no significant changes in liquid product was observed. The

yield of liquid products with 20% Al-Al₂O₃ catalysts was 91.20 ± 0.35 wt.% and with 20%

Al-AC catalysts were 88.87 ± 0.81%. Using Al-Mmn catalyst, the yield of liquid products

was 89.60 ± 0.20 wt.% maximum with 5% Al-Mmn catalysts and does not changed with

the increase of Al percentage over Mmn support. The maximum yield of liquid products

was 91.20 ± 0.35 wt.%, 89.60 ± 0.20 wt.% and 88.87 ± 0.81 wt.% with 100%, 92% and

100% total conversion using 20% Al-Al₂O₃, 5% Al-Mmn and 20% Al-AC catalysts,

respectively. A comparison of optimum reaction conditions and yield of products is given

in Table 4.12.1.


140

Table 4.12.1 Optimum reaction conditions and contents of product using 20% Al-Al₂O₃,

5% Al-Mmn and 20% Al-AC catalysts

20% Al-Al₂O₃ 5% Al-Mmn 20% Al-AC

Reaction conditions


Time (min) 60 60 60



Liquids 91.20 ± 0.35 89.60 ± 0.20 88.87 ± 0.81

Gases 8.70 ± 0.35 2.40 ± 0.00 10.70 ± 0.81

Residue 0.00 ± 0.00 8.00 ± 0.20 0.00 ± 0.00

Total conversion 100.00 92.00 100.00

Figure 4.12.1 Effect of percentage of impregnated precursor metal (Al) over Al₂O₃, Mmn



141


The maximum liquid products obtained with 20% Al-Al₂O₃, 5% Al-Mmn and 20% Al-AC

was subjected to GC-MS analysis. The data obtained from the analysis was compared with

spectral libraries to identify the components of liquid products. The yield of compounds

was expressed in terms of wt.% of WEPS employed instead of wt.% of the oil. For the

calculation of yield in wt.% Eq. 4.6.1 of section 4.6 (Page 87) was used. The results of the

analysis are tabulated in Table 4.12.2 and GC-MS chromatograms for each liquid are given

in Fig. 4.12.2-4.12.4 for 20% Al-Al₂O₃, 5% Al-Mmn and 20% Al-AC catalysts,

respectively. The yield of lower molecular weight aromatic hydrocarbons was maximum

with impregnated catalysts. Toluene, ethylbenzene, styrene, α-methylstyrene, benzene,

1,1’(1,1,2,2-tetramethyl-1,2-ethanediyl)bis, benzene, 3-butynyl and 1,2-propanediol, 3-

benzyloxy-1,2-diacetyl were the major and prominent constituents with almost all the

catalysts used in the experiments. The yield of benzene was very small with Al impregnated

catalysts i.e., 1.13 wt.%, 0.81 wt.% and 1.42 wt.% with 20% Al-Al₂O₃, 5% Al-Mmn and

20% Al-AC catalysts, respectively. The yield of toluene was highest with 20% Al-Al₂O₃

(9.47 wt.%) where ethylbenzene was 8.90 wt.% maximum with 20% Al-AC. Styrene

monomer was the major component of the degradation products as it was 56.52 wt.%,

49.28 wt.% and 47.29 wt.% with 20% Al-Al₂O₃, 5% Al-Mmn and 20% Al-AC catalysts,

respectively. Styrene monomer was maximum (56.52 wt.%) with 20% Al-Al₂O₃. The yield

of benzene, 3-butynyl was 0 wt.%, 5.58 wt.% and 4.94 wt.%, 1,2-propanediol, 3-

benzyloxy-1,2-diacetyl was 0 wt.%, 0 wt.% and 1.55 wt.% with 20% Al-Al₂O₃, 5% Al-

Mmn and 20% Al-AC catalysts, respectively. The percent composition of α-methylstyrene

was 1.72 wt.%, 2.80 wt.% and 1.38 wt.% and the percent composition of benzene,

1,1,’(1,2-ethanediyl)bis was 0 wt.%, 3.56 wt.% and 1.35 wt.% with 20% Al-Al₂O₃, 5%

Al-Mmn and 20% Al-AC catalysts, respectively. Beside these, many other compounds

were formed by the degradation of WEPS using Al impregnated catalysts. Lewis acid

supported catalyst like AlCl₃ act as a heterogeneous solid super acid in reactions [41, 42],

where the acidic supports with Lewis acid have also been reported with both Lewis acid

and Brönsted sites [37]. Highly dispersed Al catalyst over different support actively

degrade PS depending on their acidic strength and nature of the sites. The yield of styrene,


142

toluene, ethylbenzene and α-methylstyrene with different routes have been reported by

many researchers [11, 17, 18, 43].

Nano-crystalline 20% Al-Al₂O₃ catalyst have exposed active center for resulting in the

formation of products in low molecular weight aromatic hydrocarbon region with high

contents of styrene, toluene, and ethylbenzene like components. The presence of oxygen

containing compounds may have sources of atmospheric oxygen action with reaction

products or due to any residue present in the PS samples.

The results of degradation of WEPS were compared with that of Table 4.8.3, the data in

the table are converted by the formula given in Eq. 4.6.1 of section 4.6 (Page 87).

According to the findings the yield of benzene and toluene was higher by 20% Al-Al₂O₃

than the reported catalysts, where the yield of styrene monomer was approximately the

same with 9% K2O/Si-MCM-41 [5] it was less than that of Fe-K/Al₂O₃ [16] and so for α-

methylstyrene. The yield of low molecular weight aromatic hydrocarbons was greater

using 20% Al-Al₂O₃ as compared to the reported catalysts by literature [5, 16].


143

Table 4.12.2 Products formed by WEPS degradation using Al impregnated catalysts at


S. No. Products

Composition (wt.%)

20% Al-

Al₂O₃

5% Al-

Mmn

20% Al-

AC

1 Benzene 1.13 0.81 1.42

2 Toluene 9.47 8.49 8.49

3 3-Hexen-2-one 6.10 0.00 0.00



6 5-Hexene-2-one 5.12 0.00 0.00

7 Styrene 56.32 49.28 47.29


9 .α.-Methylstyrene 1.71 2.80 1.38

10 Indene 0.71 0.00 0.00

11 .α.-Chloro-o-xylene 0.74 0.00 1.86


1,2-ethanediyl)bis

1.94 0.20 1.27

13 Naphthalene 0.74 0.62 0.44



ethanediyl)bis

0.00 1.69 0.97

16 Benzene, 3-butynyl 0.00 5.58 4.94


18 Anthracene 0.00 0.60 0.30



diacetyl

0.00 0.00 1.55


Gases (Wt.%) 8.70 2.40 10.70

Residue (Wt.%) 0.00 8.00 0.00


144


Al-Al₂O₃ catalyst at optimized conditions


Al-Mmn catalyst at optimized conditions


145


Al-AC catalyst at optimized conditions


146

4.13. Catalytic degradation of WEPS using Cu, CuO and CuCl₂ catalysts


Many of the previous reported methods have the limitation of fixed temperature [4-7]. The

current study was conducted using Cu, CuO and CuCl₂ as catalysts for the catalytic

degradation of WEPS in the range of 250 ºC to 500 ºC (Fig. 4.13.1) keeping 30 min reaction

time and 1:0.2 polymer to catalyst ratio. The degradation reaction started at 245 ºC with

the production of small amounts of gases, but the collection of liquid products started at

300 ºC in the case of CuO catalyst and started at 350 ºC in the case of Cu & CuCl₂ catalysts.

It was observed that with the increase of degradation temperature up to 450 ºC, the yield

of liquid products increased and beyond this temperature no significant change in the yield

of liquid product was observed. At 450 ºC the yield of liquid products was 91.53 ± 0.83

wt.% (97.53% total conversion), 90.27 ± 0.50 wt.% (98.07% total conversion) and 91.40

± 2.99 wt.% (91.40% total conversion) for Cu, CuO and CuCl₂ catalysts, respectively.


147


liquid products obtained with Cu, CuO and CuCl₂ catalysts

ii. Effect of time

Time is another parameter which affects the yield of liquid products, where most of the

work related to WEPS degradation has been carried out with fix reaction time while in

some methods time has no effect on the yield of liquid products [5, 7]. The Effect of

reaction time was optimized for the catalytic degradation of WEPS from 30 min to 150 min

at an optimum degradation temperature (450 ºC) using 1:0.2 polymer to catalyst ratio. The

results of the analysis are depicted in Fig. 4.13.2. As can be seen from the result that the

yield of liquid products was not affected with the increase of reaction time from 30 min to

150 min. The yield of liquid products was 91.53 ± 0.83 wt.% (97.53% total conversion),

90.27 ± 0.50 wt.% (98.07% total conversion) and 91.40 ± 2.99 wt.% (100% total

conversion) with Cu, CuO and CuCl₂ catalysts, respectively. As compared to previous


148

methods the degradation of WEPS was low cost and the yield of products were high in

relatively small reaction time [11, 20].


products obtained with Cu, CuO and CuCl₂ catalysts at optimized

conditions


The economical recycling of WEPS is of global interest and for this purpose its degradation

has been carried out with a number of heterogeneous acid and base catalysts. Catalyst

selection play a major role on the activity and selectivity of the products [6, 21]. For

effective conversion catalyst to polymer ratio was varied from 1:0.1 to 1:0.5 using optimum

temperature (450 ºC) & reaction time (30 min) and the results are shown in Fig. 4.13.3. At

optimum degradation temperature and reaction time, the yield of liquid products increased

with the increase of catalyst amount in polymer to catalyst ratio. However, the yield was


149

decreased using 1:0.1 polymer to catalyst as compared to 1:0.2 polymer to catalyst ratio.

The yield of liquid products was maximum with 1:0.2 polymer to catalysts ratio and no

further increase was observed when the amount of catalysts was increased in polymer to

catalyst ratio in the case of the CuO and CuCl₂ catalysts. The yield of liquid products was

increased in the case of Cu catalyst with the increase of amount of catalyst in polymer to

catalyst ratio up to 1:0.3. The maximum yield of liquid products was 90.27 ± 0.50 wt.%

(98.07% total conversion) and 91.40 ± 2.99 wt.% (100% total conversion) with 1:0.2

polymer to catalyst ratio using CuO and CuCl₂ catalysts, respectively. The maximum yield

of liquid products was 93.93 ± 2.69 wt.% (100% total conversion) with Cu catalyst beyond

this polymer to catalyst ratio no change in the yield of liquid products was observed.

Comparison reaction conditions and contents of products using Cu, CuO and CuCl₂

catalysts is given in Table 4.13.1.


liquid products obtained with thermal degradation, Cu, CuO and CuCl₂



150

Table 4.13.1 Optimum reaction conditions and contents of the products obtained with

Cu, CuO and CuCl₂ catalysts

Cu CuO CuCl₂

Reaction conditions


Time (min) 30 30 30



Liquids 93.93 ± 2.69 90.27 ± 0.50 91.40 ± 2.99

Gases 6.07 ± 2.60 7.80 ± 1.11 8.60 ± 2.99

Residue 0.00 ± 0.00 1.93 ± 0.61 0.00 ± 0.00

Total percent conversion 100 98.07 100


Parent liquid products obtained from the degradation of WEPS using Cu, CuO and CuCl₂

catalysts was analyzed using GC-MS (Fig. 4.13.4-4.13.6). The results reveal the presence

of 14 major components where styrene monomer was predominant specie along with

benzene, 3-butynyl and 1,2-propanediol, 3-benzyloxy-1,2-diacetyl. The results of the

analysis and its comparison with thermal degradation are shown in Table 4.13.2 in terms

of weight percent of the liquid applied. The yield of styrene was maximum in all the three

catalytically derived liquid as compared to thermal degradation, where the yield of styrene

monomer was 55.14 wt.% and 55.53 wt.% maximum with acidic catalysts i.e., Cu and

CuCl₂, respectively. The yield of styrene monomer was lower with basic catalyst (CuO).

CuCl₂ is a Lewis acid that initiates the degradation of WEPS with elimination of proton

from benzyl position and the reaction further proceed via β-cleavage of the polymer

backbone [14, 34]. Among the used catalysts, high acidic catalyst CuCl₂ was found with

good selectivity toward light weight aromatic hydrocarbons. The yield of toluene (4.87

wt.%), ethylbenzene (6.31 wt.%) was maximum with CuCl₂ catalyst having negligible

amount of other high molecular weight aromatic hydrocarbons. The production of styrene

and its dimer with acidic catalysts is due to the β-scission of C-C bonds or simple


151

depolymerization [11]. The high amount of toluene and ethylbenzene is believed to be

formed by further cracking of styrene monomer and hydrogenation [17, 20]. The yield of

oxygenated products may be due to the reaction carried out in atmospheric oxygen [10].

The yield of liquid products was almost the same with a Cu group of catalysts with benefits

of low reaction time and present a cost effective method having better selectivity for styrene

monomer than reported by Ukie et al [11].

Table 4.13.2 Products formed by the catalytic degradation of WEPS using Cu, CuO and

CuCl₂ catalysts at optimized conditions


Cu CuO CuCl₂

1 Toluene 0.00 1.81 4.87


3 Styrene 55.14 52.37 55.53



1,2-ethanediyl)bis

0.00 0.00 1.67


7 Benzene, 3-butynyl 17.07 11.54 2.65


9 Tetracyclo[4,2,1,0(3,7),0(2,9)]non-4-

ene, 4-phenyl

0.19 0.50 1.03



methyl-1,1-diphenyl

0.00 0.00 1.00


diacetyl

16.81 15.38 0.03


methyl-1,1-diphenyl

0.03 0.06 2.44



Gases (wt.%) 6.07 7.80 8.60

Residue (wt.%) 0.00 1.93 0.00


152

Figure 4.13.4 Chromatogram of catalytically derived liquid products obtained with Cu


Figure 4.13.5 Chromatogram of catalytically derived liquid products obtained with CuO



153

Figure 4.13.6 Chromatogram of catalytically derived liquid products obtained with CuCl₂



For isolation and identification of components the liquid obtained was fractionated by

fractional distillation. The separated fractions were characterized by different

physiochemical parameters like density (d25), refractive index (𝜂𝐷25), molar refraction (γM)

and GC-MS. Physiochemical characterization of the fractions with wt.% recovery are given

in the Table 4.13.3. The data suggest that during fractional distillation condensation,

polymerization and re-degradation processes has taken place with high variation in the

component products yield and recovery.

Toluene was formed or increased for all liquids obtained by catalytic degradation, where

ethylbenzene was only increased in the liquid obtained with CuCl₂ catalyst and α-

methylstyrene form during fractional distillation in the case of liquid obtained with Cu as

a catalyst. Formation or increase in the yield of these products is due to further dissociation

of high molecular weight aromatic hydrocarbons like styrene [17, 20]. It was observed that

these products were formed or increased with associated decrease of 1,1’-(1,3-


154

propanediyl)bis; benzene, 3-butynyl and 1,2-propanediol, 3-benzyloxy-1,2-diacetyl for

liquid products of all catalysts. Styrene monomer increased for liquid product obtained

with Cu catalyst, where it decreased for liquid obtained with CuO and CuCl₂ catalysts.

This was caused by further hydrogenation of styrene into toluene or polymerization

followed by dehydrogenation/cyclization to form head to head products like, 2-

phenylnaphthalene and 1,1':3,1"-Terphenyl, 5'-phenyl [11, 24]. The yield of 2-phenone, 4-

hydroxy-4-methyl may be due to the reaction of low molecular weight open chain

hydrocarbons with atmospheric oxygen [10]. The maximum recovery of toluene was 13

wt.%, 20 wt.% and 12 wt.% with liquid product obtained with Cu, CuO and CuCl₂

catalysts, respectively. Maximum recovery of styrene monomer (60 wt.%) was achieved

from the liquid products obtained with Cu catalyst where the recovery of styrene monomer

with CuO and CuCl₂ catalysts were 47 wt.% and 52 wt.%. The Cu catalyst was found more

selective for the recovery of styrene where CuO was good for the recovery of toluene.

Refractive index and density of each fraction separated was measured for the calculation

of molar refraction and are given in Table 4.13.3. The molar refraction of fractions obtained

was compared with that of the standards compounds molar refractions (Table 4.5.3 in

section 4.5 (Page 82)) and found the results in close agreement with each other.


155


degradation of WEPS using Cu, CuO and CuCl₂ catalysts

Compound

Cu CuO CuCl₂

%age d25

(g/ml) 𝜼𝑫


(g/ml) 𝜼𝑫


(g/ml) 𝜼𝑫

𝟐𝟓 γM


methyl - - - - 8.0 0.9472 1.4280 31.5510 - - - -

Toluene 13.0 0.8910 1.5104 30.9496 20.0 0.8830 1.5083 31.1210 12.0 0.9176 1.5320 31.1156

Ethylbenzene - - - - - - - - 11.0 0.8730 1.4879 35.0293

Styrene 60.0 0.9038 1.5539 36.9258 47.0 0.9112 1.5469 36.2422 52.0 0.9054 1.5443 37.0175

α.-Methylstyrene 4.0 0.8820 1.5140 40.3389 - - - - - - - -

Benzene, 1,1'-(1,3-

propanediyl)bis - - - - - - - - 7.0 0.9860 1.5635 64.7027

Benzene, 3-butynyl 8.0 0.9306 1.5226 42.7089 11.0 0.9779 1.5558 42.7815 - - - -

2-Phenylnaphthalene - - - - - - - - 12.0 1.0810 1.6480 68.7554

1,1':3,1"-Terphenyl, 5'-

phenyl 15.0 1.0750 1.6189 99.9768 14.0 1.0800 1.6220 99.9135 6.0 1.0810 1.6239 100.0653



156

4.14. Catalytic degradation of WEPS using Cu impregnated catalysts


WEPS samples were degraded using Cu impregnated catalysts i.e., Cu-Al₂O₃, Cu-Mmn

and Cu-AC at optimum parameters like 450 ºC degradation temperature, 30 min reaction

time and 1:0.2 polymer to catalyst ratio. The catalytic activities of differing percentage of

Cu (5-25%) supported on Al₂O₃, Mmn and AC was optimized for maximum yield of liquid

products, the results of the experiments are shown in Fig. 4.14.1. The yield of liquid

products as compared to pure Cu was drastically decreased in the case of Cu impregnated

catalyst over different supports. However, the yield of liquid products increased with the

increase of impregnated precursor copper on all the three supports. In the case of Cu-Al₂O₃

and Cu-AC the yield of liquid products was maximum with 20% Cu impregnation i.e.,

86.87 ± 0.23 wt.% and 83.47 ± 0.12 wt.%, respectively with 100% total conversion. In the

case of Cu-Mmn, the maximum yield of liquids was obtained with 15% Cu impregnation

having 98.20% total conversion. Up to reaching a maximum the yield of liquid products

decreased with further increase of precursor copper impregnation. The maximum yield of

liquid products was obtained with 20% Cu-Al₂O₃, 15% Cu-Mmn and 20% Al-C catalysts

producing liquid products 86.87 ± 0.23 wt.%, 89.20 ± 0.20 wt.% and 83.47 ± 0.12 wt.%

with 100%, 98.20% and 100% total conversion, respectively.

A comparison of reaction conditions and product components using 20% Cu-Al₂O₃, 15%

Cu-Mmn and 20% Cu-AC catalysts are presented in Table 4.14.1. Thermal degradation of

WEPS was not only time and energy consuming (150 min reaction time) but also yield

small amount of liquid products. The yield of liquid products was high using Al₂O₃ (450

ºC, reaction time 60 min, Polymer to catalyst ratio1: 0.2), Mmn (450 ºC, reaction 60 min,

polymer to catalyst ratio 1:0.2) and AC (500 ºC, 30 min, polymer to catalyst ratio 1:0.1) as

a catalyst but was more expensive for its more time and energy consumption than 20% Cu-

Al₂O₃, as mentioned in section 4.6 (page 94). The yield of liquid product is important, but

the focus of the study is the maximum liquid product with selectivity in products.


157

Table 4.14.1 Comparison of reaction conditions and contents of products using 20% Cu-

Al₂O₃, 15% Cu-Mmn and 20% Cu-AC catalysts

20% Cu-Al₂O₃ 15% Cu-Mmn 20% Cu-AC

Reaction conditions


Time (min) 30 30 30



Liquids 86.87 ± 0.23 89.20 ± 0.20 83.47 ± 0.12

Gases 13.00 ± 0.23 9.07 ± 0.12 16.50 ± 0.12

Residue 0.00 ± 0.00 1.73 ± 0.12 0.00 ± 0.00

Total conversion 100 98.27 100

Figure 4.14.1 Effect of percentage of impregnated precursor metal (Cu) over Al₂O₃, Mmn



158


GC-MS analysis of the liquid products obtained with 20% Cu-Al₂O₃ 15% Cu-Mmn and

20% Cu-AC shows more than 20 major compounds. The yield of compounds is expressed

in terms of wt.% of WEPS. The compounds are listed in Table 4.14.2 and their respective

GC-MS chromatograms are shown in Figs. 4.14.2-4.14.4. The table shows compounds

distribution from low to high molecular weight aromatic hydrocarbons. The selectivity of

20% Cu-Al₂O₃ was better than with 15% Cu-Mmn and 20% Cu-AC. Lewis acidic catalysts

over acidic supports bear Lewis acidic sites and some Brönsted sites too [16]. Cu

impregnated catalysts prepared by wet impregnation of active precursor Cu in the form of

CuCl₂ salt over different supports has been reported with good catalytic activities and

selectivity of products [44, 45]. Lewis acid catalysts like CuCl₂ initiate the degradation of

WEPS with the elimination of a proton from PS ring, where Brönsted acidic catalysts

initiate the degradation of WEPS by the attack of proton to generate a carbenium ion with

subsequent β-scission of C-C bonds [11]. The degradation of WEPS with Cu impregnated

catalysts is of acidic nature. The yield of styrene monomer and associated degraded

compounds like benzene, toluene, ethylbenzene and α-methylstyrene has been discussed

with possible routes and mechanism in literature [11, 17, 20]. Styrene monomer was the

maximum product with all the catalysts investigated, it was 60.48 wt.%, 48.46 wt.% and

39.39 wt.% with 20% Cu-Al₂O₃, 15% Cu-Mmn and 20% Cu-AC. 20% Cu-Al₂O₃ yielded

low molecular weight hydrocarbons and with very low selectivity of compounds with 15%

Cu-Mmn and 20% Cu-AC. Toluene was the second major compound (10.98 wt.%) with

20% Cu-Al₂O₃, while it was 9.76 wt.% and 6.55 wt.% with 15% Cu-Mmn and 20% Cu-

AC catalysts, respectively. The yield of ethylbenzene was maximum (12.92 wt.%) with

20% Cu-Mmn and it was 8.92 wt.% and 6.61 wt.% with 20% Cu-Al₂O₃ and 15% Cu-Mmn

catalysts, respectively. α-Methylstyrene was also the major product (3.66 wt.%) with 20%

Cu-Al₂O₃ and with 15% Cu-Mmn and 20% Cu-AC it was 2.75 wt.% and 2.20 wt.%,

respectively. The source of oxygenated compound is believed to be due to the reaction of

product with atmospheric oxygen or of other possible impurities present in WEPS samples.


159

20% Cu-Al₂O₃ produced mostly low molecular weight aromatic hydrocarbons in

maximum quantity with compared to the reported methods in literature (Table 4.8.3).


160

Table 4.14.2 Products formed by WEPS degradation using 20% Cu-Al₂O₃, 15% Cu-

Mmn and 20% Cu-AC catalysts at optimized conditions


20% Cu-Al₂O₃ 15% Cu-Mmn 20% Cu-AC

1 Benzene 0.00 0.82 0.82

2 Toluene 10.98 9.76 6.55

3 2-Pentanone, 4-hydroxy-4-

methyl-

0.66 1.59 0.12


5 Styrene 60.48 48.46 39.39


7 α.-Methylstyrene 3.66 2.75 2.20

8 Benzene,1,1'-(1,1,2,2-

tetramethyl-1,2-ethanediyl)bis

0.00 0.10 0.83

9 Octane, 2,3,3-trimethyl 0.00 0.90 0.02

10 Naphthalene 0.75 0.00 0.21

11 3-Ethyl-3-methylheptane 0.00 1.48 0.30



ethanediyl)bis

0.00 1.12 0.73

14 Benzene, 1,1'-(1,3-

propanediyl)bis

0.00 0.32 1.23


16 Benzene, 3-butynyl 0.00 2.68 2.89

17 Anthracene 0.00 0.75 0.14


propenylidene)bis

0.00 0.19 1.24


20 p-Terphenyl 0.00 0.51 0.18

21 1,2-propanediol, 3-benzyloxy-

1,2-diacetyl

0.00 0.16 1.50

22 1-Propene, 3-(2-cyclopentenyl)-

2-methyl-1,1-diphenyl

0.00 0.00 0.92



Gases (wt.%) 13.00 9.07 16.50

Residue (wt.%) 0.00 1.73 0.00


161


Cu-Al₂O₃ catalyst at optimized conditions


Al-Mmn catalyst at optimized conditions


162


Al-AC catalyst at optimized conditions


163

4.15. Catalytic degradation of WEPS using Fe, Fe₂O₃ and FeCl₃

catalysts


Temperature effect was investigated in the range of 250 ºC to 500 ºC for catalytic

degradation of WEPS using Fe, Fe₂O₃ and FeCl₃ catalysts (Fig. 4.15.1) keeping 30 min

reaction time and 1:0.2 polymer to catalyst ratio. The degradation of WEPS started with Fe

catalysts with the collection of liquid product at 250 ºC where the collection of liquid in

the case of Fe₂O₃ and FeCl₃ started at 350 ºC and 400 ºC, respectively. The yield of liquid

products increased with the increase of temperature and maximum liquid products were

88.07 ± 1.01 wt.% obtained at 450 ºC using Fe as a catalyst. The maximum yield of liquid

products was 86.27 ± 2.20 wt.% at 400 ºC in the case of Fe₂O₃ catalyst and 84.07 ± 0.46

wt.% at 500 ºC in the case of FeCl₃ catalysts. Further increase in temperature beyond

optimum did not affect the yield of liquid products and thus 450 ºC and 400 ºC was taken

optimum for Fe and Fe₂O₃ catalysts, respectively. At optimum temperatures the total

conversion was 93.33%, 96.20% and 100% for Fe, Fe₂O₃ and FeCl₃ catalysts, respectively.


164


liquid products obtained with Fe, Fe₂O₃ and FeCl₃ catalyst

ii. Effect of time

Reaction time on the degradation of WEPS was optimized in the range of 30 min to 150

min reaction time (Fig. 4.15.2) using 1:0.2 polymer to catalyst ratio and optimum

degradation temperature for each catalyst. Similar studies have been reported on the

degradation and collection of liquid products [5, 7]. The yield of liquid products was

independent of reaction time in the case of Fe and FeCl₃ catalysts and maximum liquid

was achieved at 30 min reaction time i.e., 99.07 ± 1.01 wt.% and 84.07 ± 0.46 wt.%,

respectively. The yield of liquid products increased with reaction time in the case of Fe₂O₃

catalyst and maximum liquid was achieved with 90 min reaction time. Further increase has


165

no effect on the quantity of liquid products. At optimized time the total conversion was

93.33%, 100% and 100% in the case of Fe, Fe₂O₃ and FeCl₃ catalysts, respectively.


products obtained with Fe, Fe₂O₃ and FeCl₃ catalysts at optimized

conditions


WEPS catalytic degradation was also optimized for the polymer to catalyst ratio in the

range of 1:0.1 to 1:0.5 for Fe, Fe₂O₃ and FeCl₃ catalysts using optimum temperature and

time for each catalysts .The results of the experiments are shown in Fig. 4.15.3. The yield

of liquid products decreased when the amount of catalyst was decrease in polymer to

catalyst ratio from 1:0.2 to 1:0.1 in the case of Fe and FeCl₃ catalysts. The yield of liquid

products was maximum with 1:0.1 polymer to catalyst ratio in the case of Fe₂O₃ catalysts.

The maximum yield liquid products were 88.07 ± 1.01 wt.% (97.40% total conversion),


166

91.60 ± 1.51 wt.% (100% total conversion) and 84.07 ± 0.46 wt.% (100% total conversion)

with Fe, Fe₂O₃ and FeCl₃ catalysts, respectively. Beyond the optimized value no change

in the yield of liquid products was observed.

A comparison of optimized reaction condition and maximum component products like

liquid and gas as well as residue left and total percent conversion of Fe, Fe₂O₃ and FeCl₃

catalysts are given in Table 4.15.1.


liquid products obtained with thermal degradation, Fe, Fe₂O₃ and FeCl₃



167

Table 4.15.1 Optimum reaction conditions and contents of the product using Fe, Fe₂O₃

and FeCl₃ catalysts

Fe Fe₂O₃ FeCl₃

Reaction conditions


Time (min) 30 90 30



Liquids 88.07 ± 1.01 91.60 ± 1.51 84.07 ± 0.46

Gases 9.33 ± 1.55 8.40 ± 1.51 15.93 ± 0.46

Residue 2.60 ± 0.72 0.00 ± 0.00 0.00 ± 0.00

Total percent conversion 97.40 100 100


The parent liquid products obtained with Fe, Fe₂O₃ and FeCl₃ catalysts were analyzed for

component products using GC-MS. The result of the study in comparison with each other

are given in Table 4.15.2 in terms of weight percent of the WEPS degraded. The conversion

to weight percent was made using formula given in Eq. 4.6.1 of section 4.6 (Page 87) and

the GC-MS chromatograms are given in Figs. 4.15.4-4.15.6. The analysis revealed that the

yield of liquid products has up to 15 major components with maximum amount of styrene

monomer and other major amongst these 15 components were benzene, 3-butynyl and 1,2-

propanediol, 3-benzyloxy-1,2-diacetyl in all the cases.

The degradation was carried out with Fe and Fe containing catalysts in order to find

similarities of the component products, Fe and FeCl₃ with acidic nature and Fe₂O₃ with

basic nature. Fe₂O₃ with high pH was found the best catalysts for the degradation of WEPS

and production of styrene monomer where FeCl₃ with low pH (high acidity) was found to

yield maximum quantity of low molecular weight aromatic hydrocarbons. The yield of

styrene monomer was maximum 62.76 wt.% with Fe₂O₃ catalyst, where the yield of

styrene monomer was 59.78 wt.% and 49.43 wt.% with Fe and FeCl₃ catalysts,


168

respectively. The yield of toluene and ethylbenzene was maximum with FeCl₃ catalysts.

The degradation of WEPS is initiated with elimination of proton followed by subsequent

β-scission of the C-C bond [14, 34]. The low yield of styrene monomer in the case of FeCl₃

catalyst is may be due the further cracking and hydrogenation of styrene monomer into

toluene and ethylbenzene [20]. Moreover, numerous Lewis acidic sites of FeCl₃ undergo

secondary competitive reactions, producing low molecular weight and high amount of

gaseous products, decreasing the ultimate yield of styrene monomer [5, 11, 18]. On the

other hand the catalytic degradation on solid bases is initiated with the formation of

carboanions due to the elimination of a hydrogen atom of WEPS [11]. In comparison with

solid base catalysts solid acid catalysts degrade WEPS on routes identical to thermal

degradation where solid basic catalysts have been found to have greater selectivity toward

styrene monomer than solid acid catalysts [11]. In the case of the basic catalysts the yield

of toluene and ethylbenzene may be due to the carboanions formation followed by β-

scission of C-C bond and due to the formation of resulting radicals and cations [50]. Among

the used catalysts both Fe and Fe₂O₃ were found with high activity and selectivity toward

value added products.


169

Table 4.15.2 Products formed by the catalytic degradation of WEPS using thermal

degradation, Fe, Fe₂O₃ and FeCl₃ catalysts at optimized conditions



1 Toluene 4.09 3.44 5.24


3 Styrene 59.78 62.76 49.43




ethanediyl)bis

0.86 0.43 0.28


8 Benzene, 3-butynyl 11.55 11.67 3.31


10 Tetracyclo[4,2,1,0(3,7),0(2,9)]non-

4-ene, 4-phenyl

0.00 0.57 0.57


propenylidene)bis

0.00 0.35 0.77



diacetyl

0.00 0.11 5.78


methyl-1,1-diphenyl

0.00 0.29 0.95



Gases (wt.%) 9.33 8.40 15.93

Residue (wt.%) 2.60 0.00 0.00


170

Figure 4.15.4 Chromatogram of catalytically derived liquid products obtained with Fe as


Figure 4.15.5 Chromatogram of catalytically derived liquid products obtained with Fe₂O₃



171

Figure 4.15.6 Chromatogram of catalytically derived liquid products obtained with FeCl₃



Catalytic degradation of WEPS with high selectivity has been reported in literature with

large number of catalysts [5, 10, 11, 16, 31, 46]. The separation or recovery of these

products is a big challenge and no study has been reported for the separation of the

products. After successful characterization the bulk liquid products were separated using

fractional distillation and the fractions were characterized by physiochemical parameter

i.e., density (d25), refractive index (𝜂𝐷25), and molar refraction (γM) with subsequent

identification by GC-MS analysis. The results of the analysis are given in Table 4.15.3

which suggests that further component polymerization, condensation or degradation to new

products lead to change the existing products. The yield of toluene, ethylbenzene, styrene

and α-methylstyrene were increased for liquid products of all catalysts except the yield of

styrene monomer decreased with liquid products of the Fe₂O₃ catalyst with the concurrent

formation of 2-pentanone, 4-hydroxy-4-methyl. It is because due to further degradation of

styrene or other high molecular weight aromatic hydrocarbons and their reaction with


172

atmospheric oxygen [10]. The yield of high molecular weight aromatic hydrocarbons

decreased due to further degradation except in the case of liquid products with Fe catalysts.

Maximum recovery of toluene was 12 wt.%, 15 wt.% and 18 wt.% for liquid products with

Fe, Fe₂O₃ and FeCl₃ catalysts, respectively. Maximum recovery for ethylbenzene was 5

wt.%, 6 wt.% and 20 wt.% where the recovery of styrene monomer was 60 wt.%, 36 wt.%

and 53 wt.% for liquid products with Fe, Fe₂O₃ and FeCl₃ catalysts, respectively. Styrene

monomer recovery was maximum (60 wt.%) for Fe catalyst along with toluene,

ethylbenzene and α-methylstyrene.

Density and refractive index measurement were used for the calculation of molar refraction

of each fraction collected, the results are given in Table 4.15.3 and the data was compared

with that of the molar refraction of standard compounds and found in close agreement

(Table 4.5.3 in section 4.5 (Page 82)).


173


degradation of WEPS using Fe, Fe₂O₃ and FeCl₃ catalysts

Compound


%age d25

(g/ml) 𝜼𝑫


(g/ml) 𝜼𝑫


(g/ml) 𝜼𝑫

𝟐𝟓 γM


methyl - - - - 17.0 0.9502 1.4241 31.2007 - - - -

Toluene 12.0 0.8892 1.4997 30.4613 15.0 0.8901 1.5089 30.9036 18.0 0.8750 1.4997 30.9557

Ethylbenzene 5.0 0.8770 1.4986 35.5215 6.0 0.8390 1.4895 36.5540 20.0 0.9337 1.5380 35.5664

Styrene 60.0 0.9018 1.5484 36.7032 36.0 0.9039 1.5478 36.5847 53.0 0.9088 1.5620 37.1654

α.-Methylstyrene 4.0 0.9279 1.5420 40.0835 9.0 0.9087 1.5370 40.6159 9.0 0.9534 1.5592 40.0339

Benzene, 1,1'-(1,3-

propanediyl)bis 6.0 0.9843 1.5637 64.8334 7.0 0.9675 1.5533 64.9533 - - - -

Benzene, 3-butynyl - - - - 10.0 0.9369 1.5333 43.1472 - - - -

2-Phenylnaphthalene 5.0 1.0840 1.6484 68.5986 - - - - - - - -

1,1':3,1"-Terphenyl, 5'-

phenyl 8.0 1.0600 1.6091 100.0979 - - - - - - - -

Where %age (Percentage of the Fraction), d25 (g/ml) (density), 𝜂𝐷25 (Refractive Index), and γM (Molar Refraction


174

4.16. Catalytic degradation of WEPS using Fe impregnated catalysts

i. Effect percentage of precursor active metal center

The degradation of WEPS was carried out with Fe impregnated catalysts i.e. Fe-Al₂O₃, Fe-

Mmn and Fe-AC catalysts. WEPS sample was degraded using Fe impregnated catalyst

using optimum parameter for Fe catalyst i.e., 450 ºC degradation temperature, 30 min

reaction time and 1:0.2 polymer to catalyst ratio. The percentage of impregnated Fe on

different support was varied from 5% to 25% for impregnation of Fe over Al₂O₃, and AC

supports and the result are shown in Fig. 4.16.1. The yield of liquid products was maximum

89.27 ± 0.31 wt.% for 5% Fe-Al₂O₃, the yield of liquids decreased with 10% Fe-Al₂O₃

and then the yield of liquid products remain the same with further increase of Fe

impregnation. In the case of Fe-Mmn and Fe-AC catalysts the yield of liquid products

increased with the increase of iron impregnation over respective supports. The yield of

liquid reached to a maximum of 88.87 ± 0.42 wt.% and 84.47 ± 0.42 wt.% with 20% Fe-

Mmn and 20% Fe-AC catalysts, respectively. With further increase of impregnated Fe

percentage the yield of liquid products decreased in the case of Fe-Mmn catalysts where

the yield of liquids remains constant in the case of Fe-AC catalysts. The maximum yield

of liquids was 89.27 ± 0.31 wt.%, 88.87 ± 0.42 wt.% and 84.47 ± 0.50 wt.% having 94.27%,

100% and 100% total conversion with 5% Fe-Al₂O₃, 20% Fe-Mmn and 20% Fe-C,

respectively. A comparison of reaction conditions and contents of the product are given in

Table 4.16.1.


175

Table 4.16.1 Comparison of reaction conditions and products components using 5% Fe-

Al₂O₃, 20% Fe-Mmn and 20% Fe-AC catalysts

5% Fe-Al₂O₃ 20% Fe-Mmn 20% Fe-AC

Reaction conditions


Time (min) 30 30 30



Liquids 89.27 ± 0.31 88.87 ± 0.42 84.47 ± 0.50

Gases 5.00 ± 0.53 11.20 ± 0.42 15.30 ± 0.50

Residue 5.73 ± 0.31 0.00 ± 0.00 0.00 ± 0.00

Total conversion 94.27 100 100

Figure 4.16.1 Effect of percentage of impregnated precursor metal (Fe) over Al₂O₃, Mmn



176


The composition of liquid products was recorded from GC-MS results for maximum liquid

products obtained with 5% Fe-Al₂O₃, 20% Fe-Mmn and 20% Fe-AC catalysts. The results

of the analysis are given in Table 4.16.2 and are expressed in terms of weight percent of

WEPS samples taken. The GC-MS analysis chromatograms are also shown in Figs. 4.16.2-

4.16.4 for liquid products obtained with 5% Fe-Al₂O₃, 20% Fe-Mmn and 20% Fe-AC

catalysts, respectively. The selectivity of product was founded related with the nature of

catalyst used. The use of FeCl₃ catalysts for different product as Lewis acid has good

activity and selectivity of products [47, 48] on the other hand impregnated catalysts shows

better activity and selectivity than bulk catalysts [49, 50]. The dispersion of Lewis acid

catalysts over acidic support result super heterogeneous solid acid with both Lewis and

Brönsted sites [37, 41, 42]. Acid catalysts have a well-established mechanism and have

routes to different products with the initiation of a carbonium ion generation where Lewis

acidic catalysts start depolymerization with the elimination of hydrogen, in both cases

followed by C-C bond scission [17, 18]. Using Fe impregnated catalysts, the composition

of liquid products were compared for the employed catalysts with the desired selectivity of

styrene monomer and other low molecular weight aromatic hydrocarbons. 20% Fe-Mmn

was the best selective catalyst for the production of low molecular weight aromatic

hydrocarbons. The yield of styrene monomer in comparison with Fe impregnated catalysts

was 51.68 wt.%, 50.93 wt.% and 46.31 wt.% with 5% Fe-Al₂O₃, 20% Fe-Mmn and 20%

Fe-AC catalysts, respectively. The yield of toluene (10.15 wt.%) was the highest with 20%

Fe-Mmn as compared to the other catalysts and the yield of α-methylstyrene was 2.31 wt.%

reasonable with 20% Fe-Mmn. The low yield of styrene with Fe impregnated catalysts was

because of their strong acidic sites responsible for further degradation of high molecular

weight aromatic hydrocarbons, which reduce styrene monomer with the production of

toluene, ethylbenzene and α-methylstyrene [17, 20]. The degradation of WEPS in

comparison with thermal degradation, and the supports used for the loading of Fe i.e.,

Al₂O₃, Mmn and AC were better. The efficient selective degradation was obtained with

20% Fe-Mmn yielding 88.87 wt.% liquid in comparison with literature reported method of

modified or impregnated catalysts [5, 21, 28-30]. It was found that the component products


177

of the degradation were having more tendency toward low molecular weight aromatic

hydrocarbons i.e., the yield of benzene, toluene, ethylbenzene and styrene were high.

Table 4.16.2 Products formed by WEPS degradation using Fe and its impregnated


S.No. Products

Composition (wt.%)

5% Fe-

Al₂O₃

20% Fe-

Mmn

20% Fe-

AC

1 Benzene 0.00 0.79 0.64

2 Toluene 7.50 10.15 6.34


4 Styrene 51.68 50.93 46.31

5 α.-Methylstyrene 2.71 2.31 1.97

6 Benzene,1,1'-(1,1,2,2-tetramethyl-1,2-

ethanediyl)bis

0.00 0.73 0.54

7 Naphthalene 0.00 0.67 0.00



ethanediyl)bis

1.54 1.14 1.11


11 Benzene, 3-butynyl 4.76 2.60 5.95


13 Anthracene 0.50 0.62 0.00


propenylidene)bis

0.00 0.00 0.85


16 p-Terphenyl 0.00 0.63 0.00


diacetyl

0.00 0.00 1.77



Gases (wt.%) 5.00 11.20 15.30

Residue (wt.%) 5.73 0.00 0.00


178

Figure 4.16.2 Chromatogram of catalytically derived liquid products using 5% Fe-Al₂O₃


Figure 4.16.3 Chromatogram of catalytically derived liquid products using 20% Fe-Mmn



179

Figure 4.16.4 Chromatogram of catalytically derived liquid products using 20% Fe-AC



180

4.17. Effect of polyethylene terephthalate (PET) on the catalytic

degradation of polystyrene (PS)

The complete conversion of WEPS into useful products is a challenge and it was decided

to explore the possibility of significant interaction of co-processing it with PET for the said

purpose. Thus, catalytic degradation reaction containing binary combination of PET and

PS were studied. The amount of PET was varied to understand and explore its role and

reactivity on the degradation of PS. The degradation products were liquids, gases, and solid

residue in the case of PS, 10PET+PS, 20PET+PS and 30PET+PS. The effect of

degradation temperature, reaction time and polymer to catalyst ratio on thermo-catalytic

degradation of PS, 10PET+PS, 20PET+PS and 30PET+PS were investigated to determine

the conditions that favor the formation of maximum liquid products and to compare the

products and product compositions formed at the optimized reaction conditions.

i. Effect of degradation temperature

The process of degrading PS or mixture of polystyrene with other plastic has been mostly

investigated at a constant temperature [27, 51] or within a small range such as 430-440 ºC

or 440-450 ºC [3, 52]. In the present work, the effect of degradation temperature over a

wide range of 250 ºC to 500 ºC at a reaction time of 30 min, and polymer to catalyst ratio

of 1:0.05 on the distribution of liquids and gases was studied (Fig. 4.17.1). Among the

impregnated catalysts, supported catalyst over Al₂O₃ support were found to have better

activity and selectivity, where 15% Mg-Al₂O₃ and 20% Al-Al₂O₃ were found to have the

higher activity and selectivity. However, the N₂ adsorption/desorption studies and SEM

images revealed 20% Al-Al₂O₃ to be the best as a future catalyst. Therefore, 20% Al-Al₂O₃

was constantly used throughout the study. This temperature range was selected because the

decomposition of PS and PET occurred after 250 ºC as shown by the TGA (Fig. 4.4.2) and

a temperature range of 400 ºC to 500 ºC was reported to achieve a maximum yield of liquid

products [14, 28, 51-53]. For liquid products, the yield increased linearly with the increase

in temperature reaching its maximum of 82.4 wt.% and 67.3 wt.% at 500 ºC in the case of


181

PS and 10PET+PS, respectively. In the case of 20PET+PS and 30PET+PS, the yield

initially increased up to a maximum of 37.3 wt.% and 19.2 at 450 ºC, respectively but

further increase in the degradation temperature slightly reduced the yield. For gases, the

maximum yield was achieved at 250 ºC and it decreased with the rise in temperature in the

degradation of PS and 10PET+PS. In the case of 20PET+PS, however, the yield of gases

increased initially with the rise in temperature reaching its upper limit at 300 ºC and then

decreased with further increase. In the case of 30PET+PS, the yield of gases increased up

to 350 ºC then decreased a little and eventually increased up to its upper limit at 500 ºC.

The maximum total yields in the cases of PS, 10PET+PS, 20PET+PS and 30PET+PS was

98.4 wt.% at 500 ºC, 98.4 wt.% at 450 ºC, 95.9 wt.% at 450 ºC and 96.7 wt.% at 500 ºC,

respectively. In the presence of 20% Al-Al₂O₃ the production of gases at 250 ºC in the case

of all materials indicates that the decomposition process started before 250 ºC instead of

290.2 ºC or 378.0 ºC for PS and PET, respectively as identified by the TGA (Fig. 4.4.2).

Interestingly, the increase of PET percentage dramatically reduced the yield of liquid

products with the concomitant increase of gases. At higher temperature, the decrease in the

liquid products and increase in gases produced might be due to the further cracking of the

preformed products, the same observations were also reported by Vasile et al., [52]. PET

has been reported to produce more gases and residue compared to liquid products and some

studies have reported the formation of negligible amount of liquid products [2]. In some

plastic mixtures, PET was also reported to increase the carbon residue by up to 25 wt.%

[54].


182

Figure 4.17.1 Effect of degradation temperature on the yield of catalytically derived

products (liquids and gases) for the degradation of PS, 10PET+PS,

20PET+PS and 30PET+PS

ii. Effect of reaction time

The effect of the reaction time on the degradation of virgin PS and mixed plastics

(xPET+PS) was investigated. Experiments were performed at reaction times varying from

20 to 90 min, at an optimized degradation temperature of 500 ºC for PS and 10PET+PS,

and 450 ºC for 20PET+PS and 30PET+PS, and a polymer to catalyst ratio of 1:0.05 (Fig.

4.17.2). It was observed that the liquid yield increased significantly when the reaction time

was increased from 20 min to 60 min in the cases of PS, 10PET+PS and 20PET+PS. In the

case of 30PET+PS however, a very small increase was observed when the reaction time

was increased to 90 min. The maximum yield was 86.3 wt.%, 70.0 wt.% and 40.6 wt.% in

60 min in the cases of PS, 10PET+PS and 20PET+PS, respectively. In the case of


183

30PET+PS, the maximum yield was 21.1 wt.% in 90 min. The maximum total yield in the

cases of PS, 10PET+PS, 20PET+PS and 30PET+PS was 99.3 wt.%, 97.7 wt.%, 95.4 wt.%

and 93.5 wt.%, respectively at optimum reaction conditions (degradation temperature 500

ºC for PS and 10PET+PS, and 450 ºC for 20PET+PS and 30PET+PS; reaction time 60 min

for PS, 10PET+PS and 20PET+PS and 90 min for 30PET+PS).

Beyond the described optimum time, a further increase in reaction time showed no apparent

change in the yield of liquid products. The yield of gases was observed to increase initially

up to 30 min and then decreases, it is suggested to be due the interaction of gaseous

products with other compounds which ultimately form high molecular weight aromatic

hydrocarbons. However, in some cases the yield of gases also increased beyond the

optimized time, which resulted in an increase in the total yield. The increase in the liquid

product in cases of longer reaction times indicates the completion of the degradation

reaction, whereas an increase in the yield of gases with further increase in reaction time

may be due to the further degradation of some pre-formed products or the decomposition

of some part of the residue.


184

Figure 4.17.2 Effect of reaction time on the yield of catalytically derived products (liquid

and gases) for the degradation of PS, 10PET+PS, 20PET+PS and

30PET+PS at optimized conditions


The influence of feed to catalyst ratio was investigated in 1:0 (without catalysts or thermal

degradation only), 1:0.05, 1:0.1, 1:0.2 and 1:0.3 feed to catalyst ratio at optimized

degradation temperature and reaction time, the results are shown in Fig. 4.17.3. A

significant increase was observed in the yield of liquid products when the catalyst was

added using the same reaction conditions as compared to thermal degradation without the

use of catalyst. The liquid products was increases from 78.1 to 86.3 wt.% in the case of PS,

from 56.2 to 70.0 wt.% in the case of 10PET+PS, from 21.6 to 40.60 wt.% in the case of

20PET+PS and from 6.3 to 21.1 wt.% in the case of 30PET+PS. In the presence of 20%

Al-Al₂O₃ catalysts, the yield of liquid products increased significantly when the polymer


185

to catalyst ratio was increased and a maximum was achieved with a feed to catalyst ratio

of 1:0.2 in all cases. The yield was increased significantly from 86.3 wt.% to 92.5 wt.% in

the case of PS and from 70.0 wt.% to 76.5 wt.% in the case of 10PET+PS. The conversion

of PS into liquid products was practically the same as those obtained with 20% Al-Al₂O₃

in our previous method [55]. The yield was increased slightly from 40.6 wt.% to 42.7 wt.%

in the case of 20PET+PS and it increased from 21.1 wt.% to 22.7 wt.% in the case of

30PET+PS.

The yield of gases was also affected by the increase in the polymer to catalyst ratio. Unlike

in the case of PS and 10PET+PS degradation when the yield of gases decreased with an

increase in the polymer to catalyst ratio. The yield, first decreased and then increased with

associated increase in liquid products in the cases of 20PET+PS and 30PET+PS. The feed

to catalyst ratio also raised the total yield, which was 100.00 wt.%, 97.7 wt.%, 95.1 wt.%

and 88.9 wt.% maximum with 1:0.2 polymer to catalyst ratio in the cases of PS, 10PET+PS,

20PET+PS and 30PET+PS. A further increase in the polymer to catalyst ratio of 1:0.2

reduced the yield of liquid products. It is suggested that this may be due to the availability

of more reaction sites due to an increase in the amount of acidic catalysts, which impacts

the reaction mechanism leading to the production of more gaseous products [17].

Collectively, the addition of PET resulted in a significant decrease in the yield of liquid

products, and a small decrease in the total percent conversion with concomitant increase in

the yield of gases.

The maximum yield of products and total yield along with the optimized conditions for the

degradation of PS, 10PET+PS, 20PET+PS and 30PET+PS using 20% Al-Al₂O₃ catalyst is

given in Table 4.17.1. The increase in gases with associated decrease in the liquid products

is attributed to the presence of PET and an increase in the amount of high activity catalysts,

which bear a large number of Brönsted acid sites [27]. The degradation of pure PET has

been reported to produce high amount of char and residue [2]. Therefore, the increase in

PET content during the degradation of xPET+PS produced more residue which may cause

deactivation of the catalyst, thus promoting thermal degradation.


186

Table 4.17.1 Optimum reaction conditions and the yield of catalytically derived products

for the degradation of PS, 10PET+PS, 20PET+PS and 30PET+PS

PS 10PET+PS 20PET+PS 30PET+PS

Reaction conditions

Degradation temperature

(ºC) 500 500 450 450

Reaction time (min) 60 60 60 90

Feed to catalyst ratio 1:0.2 1:0.2 1:0.2 1:0.2

Contents of products

(wt.%)

Liquid yield 92.69 76.40 44.60 22.50

Gas yield 7.31 21.30 50.51 71.80

Residue left - 2.30 03.89 05.70

Total conversion 100.00 97.70 95.11 88.90


187

Figure 4.17.3 Effect of polymer to catalyst ratio of the yield of catalytically derived

products (liquid and gases) for the degradation of PS, 10PET+PS,

20PET+PS and 30PET+PS at optimized conditions


The products obtained from the degradation of PS and xPET+PS were identified by GC-

MS and classified in three different ways i.e., classification on the basis of (i) carbon

number, (ii) depolymerization, and (iii) identified component products. The distribution of

liquid products obtained from the degradation of PS, 10PET+PS, 20PET+PS and

30PET+PS at optimized conditions are represented in Tables 4.17.2-4.17.4 and expressed

in terms of wt.% of the liquids. The liquid products derived from the degradation of virgin

PS and xPET+PS gave almost exclusively substituted aromatic hydrocarbons. Generally

the degradation of polymers due to their poly-disperse nature and high molecular weight

lead to reactions with thousands of species, which often result in the formation of a wide


188

spectrum of compounds. Furthermore, the catalytic degradation of polymers is also

accompanied by thermal processes, which result in more complex mechanisms [14]. As

discussed in the earlier section, increasing the concentration of PET increases the amount

of residue left, which in turn results in the deactivation of catalysts and leads to thermal

transformation.

Table 4.17.2 shows classification on the basis of the carbon number and the distribution of

aromatic and non-aromatic hydrocarbons in the range of C6-C24 which are grouped in three

categories: C6-C9, C10-C18, and C19-C24 fractions. As can be seen in Table 4.17.2, the yield

of C6-C9 non-aromatic fraction was 12.0 wt.%, 0.3 wt.%, 0.5 wt.% and 0.6 wt.%, where

the yield of C6-C9 aromatic fractions was 85.0 wt.%, 56.8 wt.%, 71.9 wt.% and 74.3 wt.%

in the cases of PS, 10PET+PS, 20PET+PS and 30PET+PS, respectively. Consequently, the

yield of C10-C18 fraction was 3.0 wt.%, 40.6 wt.%, 22.4 wt.% and 22.3 wt.% in the cases

of PS, 10PET+PS, 20PET+PS and 30PET+PS, respectively. Concerning the degradation

of PS, C21-C24 fraction did not form at all and it was 2.4 wt. %, 5.2 wt.% and 2.8 wt.% in

the cases of 10PET+PS, 20PET+PS and 30PET+PS, respectively. The C6-C9 fraction was

the main fraction and mostly comprised of aromatic hydrocarbons, more specifically single

ring aromatic hydrocarbons. However, the addition of PET caused an increase in the yield

of C10-C18 and C21-C24 fractions, which comprise double ring, triple ring and quartet ring

products. The yield of non-aromatic hydrocarbons in the C6-C9 fraction has also been

reported by Lopez-Urionabarrenechea et al. [27]. The high yield of low molecular weight

aromatic hydrocarbons in the presence of acidic catalyst has been reported and it was

suggested that it is due to the acidic catalyst that led the reaction through an end-chain

scission pathway without promoting thermal cracking [26, 27]. The results indicate the

formation of higher fraction in the case of PET addition. This is attributed to the

deactivation of the catalyst due to deposition of cracked and melted fragments of polymer

that ultimately promoted thermal degradation that resulted in the formation of a large

number of aromatic hydrocarbons with a random scission mechanism. Similarly, Carniti et

al., [56] suggested that the formation of aromatic hydrocarbons from the degradation of

polyolefins is due to the saturation of aromatic compounds at ethylenic double bonds which

leads to the formation of a large number of aromatic compounds.


189

Table 4.17.2 Fractions of interest identified by GC-MS in the catalytically derived liquid

products obtained from the degradation of PS, 10PET+PS, 20PET+PS and


Carbon No. Type PS 10PET+PS 20PET+PS 30PET+PS

C6-C9 Non-aromatic 12.00 0.28 0.54 0.61

Aromatic 85.01 56.75 71.93 74.32

C10-C18 Aromatic 2.99 40.59 22.37 22.27

C21-C24 Aromatic 0.00 2.38 5.16 2.80

The classification of component products based on the depolymerization of PS is shown in

Table 4.17.3. The main families identified were single styrene monomeric products,

styrene dimeric products, styrene oligomers, naphthalenes and naphthalene derivatives,

anthracene, and anthracene derivatives. Styrene monomeric products were abundant in all

the degradation liquids. Their compositions were 84.2 wt.%, 65.8 wt.%, 78.1 wt.% and

80.6 wt.% in the cases of PS, 10PET+PS, 20PET+PS and 30PET+PS, respectively. Among

the monomeric products, benzene, toluene, ethylbenzene, styrene, benzaldehyde, α-

methylstyrene, α-ethylstyrene and benzene, 3-butenyl were the dominant compounds. The

depolymerization of PS is of carbonium nature which involves the attack of a proton to the

aromatic rings of PS. The resulting carbenium species undergo continuous decomposition

followed by a hydrogen transfer. Therefore, styrene monomer was abundant in all the liquid

products [17, 18]. The formation of benzene and its hydrogenation to form toluene and

ethylbenzene or the formation of other products decreased the yield of styrene monomer

[11, 20]. The preformed compounds upon isomerization and further decomposition can

form final products such as benzene, toluene, ethylbenzene, α-methylstyrene, benzene, (1-

methylethyl), naphthalene, and others have been discussed in several studies using acidic

catalysts [14, 24]. The higher content of styrene monomeric products in the liquid products

derived from the degradation of xPET+PS as suggested by Serrano et al. [26] is due the


190

catalyst has lost its activity. Terepthalic acid is also reported as a rich source of aromatic

hydrocarbons like benzene, toluene, biphenyls, naphthalene and their derivatives [2, 3, 57].

The cracking PET on its ester bond results in the formation of terephthalic acid, which on

decarboxylation produces benzoic acid, and then benzene. These products are the sources

of aromatic hydrocarbons.

Table 4.17.3 Depolymerization products identified by GC-MS in the catalytically

derived liquid products obtained from the degradation of PS, 10PET+PS, 20PET+PS and


Products PS 10PET+PS 20PET+PS 30PET+PS

Styrene monomeric products 84.24 65.77 78.06 80.60

Styrene dimeric products 2.94 18.52 12.19 13.07

Styrene oligomers 0.00 5.11 4.51 1.80

Naphthalene and its derivatives 0.82 8.36 0.60 0.95

Anthracene and its derivatives 0.00 2.47 2.76 2.98

Other components 12.00 0.77 1.88 0.60

The highest compositions of styrene dimers, oligomers, naphthalenes, naphthalene

derivatives and some other products were noted in the case of 10PET+PS. These

compositions were lower in the case of 20PET+PS and 30PET+PS. The dominant dimeric

products detected were: benzene,1,1'-(1,1,2,2-tetramethyl-1,2-ethanediyl)bis; benzene,

1,1'-(1-methyl-1,2-ethanediyl)bis; benzene, 1,1'-(1,3-propanediyl)bis; benzene, 1,1'-(3-

methyl-1-propene-1,3-diyl)bis and benzene, 1,1'-(2-methyl-1-propenylidene)bis. The

formation of some styrene oligomers (trimers and tetramers) was also noted. Their

compositions were the highest (5.1 wt.%) in the case of liquid products with the

degradation of 10PET+PS. The highest yield of naphthalene and its derivatives were also

achieved in the case of liquid products obtained from the degradation of 10PET+PS. The

production of a considerable amount of naphthalene and naphthalene derivatives have also


191

been reported by Vasile et al. [52] during the degradation of mixed plastics. The formation

of products like benzene, naphthalene, indane and indene, and diphenyl derivatives have

been reported during the degradation of virgin PS over acidic catalysts [14]. The

depolymerization of PS in the presence of PET is again attributed to the loss of activity of

catalyst that resulted in the formation of dimers, trimers and oligomers with prolonged

heating in thermal degradation [58]. The yield of important compounds in the case of

10PET+PS in significant amounts is due to degradation at a sufficiently high temperature

of 500 ºC for a sufficient amount of time reaction time (60 min). The yield of anthracene

and its derivatives slightly increased with the increase in PET percentage. This might be

due to the interaction of styrene oligomers with the reactive groups of PET products or

further competitive interactions between the pyrolyzed products.

The main identified components of the degradation liquids are shown in Table 4.17.4. This

table shows that a small number of hydrocarbons were formed in the case of PS degradation

i.e. only C6-C18 fraction was formed. The addition of PET resulted in the production of

higher fractions i.e., C10-C24. The production of a wide spectrum of hydrocarbons with the

addition of PET on the catalytic degradation of PS resembles the thermal degradation of

PS. The yield of styrene monomer was dominant in all the liquids. These yields were 62.5

wt.%, 47.0 wt.%, 59.86 wt.% and 64.31 wt.% in the cases of PS, 10PET+PS, 20PET+PS

and 30PET+PS, respectively.

Other studies have also reported the formation of styrene as a major product during the

degradation of mixed plastics [27]. The addition of PET reduced the yield of benzene,

toluene and ethylbenzene, which was slightly increased with the further addition of PET

among the liquid products. High concentrations of ethylbenzene in all the liquid products

formed in the presence of acidic catalysts as a result of degradation of styrene oligomers,

which was also reported by Marczewski et al. [14] who studied the degradation of PS. The

insignificant yield of liquid in the addition of PET is due to the formation of large amount

of gaseous (COx and aliphatic) products. On the other hand, the competing reaction

between cross-linking of polymers (PS and PET) and cracking at elevated temperature

might be the cause of residue. The yield of aromatic hydrocarbons particularly benzene,


192

toluene, ethylbenzene, styrene, α-methylstyrene, naphthalene and anthracene represent a

potentially significant route from waste plastics as an alternative source of useful

hydrocarbons, which deliver a variety of industrial applications in the production of

dyestuffs, surfactants, pharmaceutical products, pesticides and as solvents [27]. Siddiqui

and Redhwi [3] proposed the same conclusion for the primary production of aromatic

hydrocarbons from the degradation of mixed plastics.

It can be seen that the component products of liquid derived from the degradation of virgin

PS are different from those derived with the addition PET (xPET+PS). The results of Table

4.17.2-4.17.4 indicate significant interactions between PET and PS materials that

contributed to the formation of new and important organic compounds. These compounds

include acetophenone, 2-buten-1-one, 1-phenyl; diphenylmethane; ethylene, 1,1-diphenyl;

biphenyl; 1,2-diphenylethylene; benzene, 1,1'-(1-methyl-1,2-ethanediyl)bis; benzene, 1,1'-

(1,3-propanediyl)bis; phenanthrene; benzene, 3-butynyl; benzene, (1-methyl-3-butenyl);

anthracene; benzene, 1,1'-(3-methyl-1-propene-1,3-diyl)bis; 1-methylanthracene; benzene,

1,1'-(2-methyl-1-propenylidene)bis; 2-phenylnaphthalene; p-terphenyl; di-n-octyl

phthalate; 1,1':2',1'':2''.1'''-quaterphenyl, and 1,1':3,1''-terphenyl, 5'-phenyl. In addition,

oxygen containing compounds were also formed [2]. In most cases, the yield of these

compounds increased with the increase in the composition of PET. Among the detected

compounds, many of them are reported with quite similar results either with the

degradation of PS or PET or PET+PS like acetophenone; diphenylmethane; ethylene, 1,1-

diphenyl; biphenyl; anthracene; terphenyl; di-n-octyl phthalate; 1,1': 2', 1'': 2''. 1'''-

quaterphenyl 7 and 1,1': 3,1''-terphenyl, 5'-phenyl [2, 3, 27, 57]. The formation of new

products suggests that during the degradation experiments, the rearrangement of the

reactant polymer structures via various reaction pathways led to the formation of new

degradation products.


193

Table 4.17.4 Products obtained from the degradation of PS, 10PET+PS, 20PET+PS and


S. No. Products Composition (wt.%)

PS 10PET+PS 20PET+PS 30PET+PS

1 Benzene 1.26 0.98 1.73 1.07

2 Toluene 10.51 0.06 1.28 1.49

3 3-Hexen-2-one 6.69 0.00 0.00 0.00

4 2-Pentanone, 4-hydroxy-4-methyl- 0.00 0.28 0.54 0.69

5 Ethylbenzene 7.17 1.58 3.01 3.30

6 Styrene 62.54 46.97 59.86 64.31

7 Benzaldehyde 0.00 1.44 1.09 0.29

8 α-Methylstyrene 1.90 3.50 2.48 1.65

9 Methyl-styrene 0.30 0.61 0.41 0.10

10 Indene 0.79 0.54 0.54 0.55

12 α-Ethylstyrene 0.02 0.06 2.97 3.84

13 Benzenemethanol, α, α-dimethyl 0.00 0.00 0.21 0.17

14 Acetophenone 0.00 0.71 0.77 0.87


1,2-ethanediyl)bis 2.15 0.65 0.76 0.84

16 Naphthalene 0.82 1.88 0.21 0.16

17 2-Butanone, 4-phenyl 0.00 0.00 0.18 0.23

18 2-Buten-1-one, 1-phenyl 0.00 0.35 0.58 1.08

19 Diphenylmethane 0.00 0.52 3.00 3.89

20 Ethylene, 1,1-diphenyl 0.00 0.39 0.00 1.14

21 Biphenyl 0.00 6.64 0.17 0.00

22 1,2-Diphenylethylene 0.00 0.16 1.75 2.22


ethanediyl)bis 0.00 3.89 0.59 0.00

24 Benzene, 1,1'-(1,3-propanediyl)bis 0.00 1.11 0.35 0.29

25 1,2-Diphenylcyclopropane 0.00 0.18 0.00 0.00


propene-1,3-diyl)bis 0.00 0.49 0.55 0.57

27 Phenanthrene 0.00 1.11 0.42 0.10

29 Benzene, 3-butynyl 0.00 4.39 0.00 0.00

30 Benzene, (1-methyl-3-butenyl) 0.00 1.21 0.32 0.05

31 Anthracene 0.00 0.13 0.96 1.39


194


propene-1,3-diyl)bis 0.00 0.18 1.07 1.18

33 1-Methylanthracene 0.00 0.02 1.08 1.38


propenylidene)bis 0.00 1.87 0.18 0.02

35 Benzene, (1-ethyl-2-propenyl) 0.00 0.46 0.47 0.96

36 Anthracene, 9-ethenyl- 0.00 0.87 0.12 0.09

37 o-Terphenyl 0.00 0.36 0.26 0.15

38 Naphthalene, 1,2-dihydro-4-phenyl 0.00 0.31 0.14 0.07

39 Anthracene, 9-methyl 0.00 0.31 0.13 0.02

40 2-Phenylnaphthalene 0.00 5.68 0.07 0.57

41 1-(4-Methylphenyl)-4-phenylbuta-

1,3-diene 0.00 0.24 0.43 0.74

42 9-Phenyl-5H-benzocycloheptene 0.00 0.60 0.61 0.63

43 p-Terphenyl 0.00 1.35 0.27 0.15

44 m-Terphenyl 0.00 0.65 0.00 0.00


diacetyl 0.00 2.31 0.63 0.00

46 Di-n-octyl phthalate 0.00 0.52 0.96 1.08

47 1,1':2',1'':2''.1'''-Quaterphenyl 0.00 0.13 1.48 1.59

48 1,1':3,1''-Terphenyl, 5'-phenyl 0.00 1.33 2.31 0.00

Other aromatic hydrocarbons 5.84 3.00 5.08 1.08


195

References

[1] Y. Cai, H. Ke, L. Lin, X. Fei, Q. Wei, L. Song, Y. Hu, H. Fong, Preparation,

morphology and thermal properties of electrospun fatty acid eutectics/polyethylene

terephthalate form-stable phase change ultrafine composite fibers for thermal

energy storage, Energy Conversion and Management 64 (0) 245-255 (2012).

[2] T. Yoshioka, G. Grause, C. Eger, W. Kaminsky, A. Okuwaki, Pyrolysis of

poly(ethylene terephthalate) in a fluidised bed plant, Polymer Degradation and

Stability 86 (3) 499-504 (2004).

[3] M. N. Siddiqui, H. H. Redhwi, Pyrolysis of mixed plastics for the recovery of useful

products, Fuel Processing Technology 90 (4) 545-552 (2009).

[4] J. Kronholm, P. Vastamäki, R. Räsänen, A. Ahonen, K. Hartonen, M.-L. Riekkola,

Thermal field-flow fractionation and gas chromatography−mass spectrometry in

determination of decomposition products of expandable polystyrene after reactions

in pressurized hot water and supercritical water, Industrial & Engineering

Chemistry Research 45 (9) 3029-3035 (2006).



Communications 9 (6) 1132-1136 (2008).

[6] H. Y. Shin, S. Y. Bae, Thermal decomposition of polystyrene in supercritical

methanol, Journal of Applied Polymer Science 108 (6) 3467-3472 (2008).

[7] P. Tiwary, C. Guria, Effect of Metal Oxide Catalysts on Degradation of Waste

Polystyrene in Hydrogen at Elevated Temperature and Pressure in Benzene

Solution, Journal of Polymers and the Environment 18 (3) 298-307 (2010 ).


196

[8] K. Murata, M. Brebu, Y. Sakata, The effect of PVC on thermal and catalytic

degradation of polyethylene, polypropylene and polystyrene by a continuous flow


[9] K. Murata, Y. Hirano, Y. Sakata, M. A. Uddin, Basic study on a continuous flow

reactor for thermal degradation of polymers, Journal of Analytical and Applied

Pyrolysis 65 (1) 71-90 (2002).






[12] T. M. Kruse, O. S. Woo, H.-W. Wong, S. S. Khan, L. J. Broadbelt, Mechanistic

modeling of polymer degradation: A comprehensive study of polystyrene,

Macromolecules 35 (20) 7830-7844 (2002).

[13] T. M. Kruse, O. S. Woo, L. J. Broadbelt, Detailed mechanistic modeling of polymer

degradation: application to polystyrene, Chemical Engineering Science 56 (3) 971-

979 (2001).




[15] Z. Zhang, T. Hirose, S. Nishio, Y. Morioka, N. Azuma, A. Ueno, H. Ohkita, M.

Okada, Chemical recycling of waste polystyrene into styrene over solid acids and

bases, Industrial & Engineering Chemistry Research 34 (12) 4514-4519 (1995).


197





305 (2001).


polymers: Part III—Degradation of polystyrene, Polymer Degradation and

Stability 29 (2) 191-200 (1990).

[19] A. Mukherjee, L. B. Alemany, R. Thaner, W. H. Guo, W. E. Billups, Soluble

activated charcoal, Carbon 47 (14) 3145-3150 (2009).



(2002).

[21] V. R. Chumbhale, J. S. Kim, W. Y. Lee, S. H. Song, S. B. Lee, M. J. Choi, Catalytic

degradation of expandable polystyrene waste (EPSW) over HY and modified HY

zeolites, Journal of Industrial and Engineering Chemistry 11 (2) 253-260 (2005).

[22] Z. Hussain, K. M. Khan, N. Basheer, K. Hussain, Co-liquefaction of Makarwal coal

and waste polystyrene by microwave–metal interaction pyrolysis in copper coil


[23] O. S. Woo, N. Ayala, L. J. Broadbelt, Mechanistic interpretation of base-catalyzed

depolymerization of polystyrene, Catalysis Today 55 (1-2) 161-171 (2000).




198

[25] D. P. Serrano, J. Aguado, J. M. Escola, Catalytic conversion of polystyrene over

HMCM-41, HZSM-5 and amorphous SiO2–Al2O3: comparison with thermal

cracking, Applied Catalysis B: Environmental 25 (2–3) 181-189 (2000).

[26] D. P. Serrano, J. Aguado, J. M. Escola, J. M. Rodríguez, Influence of

nanocrystalline HZSM-5 external surface on the catalytic cracking of polyolefins,

Journal of Analytical and Applied Pyrolysis 74 (1–2) 353-360 (2005).

[27] A. Lopez-Urionabarrenechea, I. de Marco, B. M. Caballero, M. F. Laresgoiti, A.

Adrados, Catalytic stepwise pyrolysis of packaging plastic waste, Journal of

Analytical and Applied Pyrolysis 96 (0) 54-62 (2012).

[28] J.-W. Tae, B.-S. Jang, J.-R. Kim, I. Kim, D.-W. Park, Catalytic degradation of

polystyrene using acid-treated halloysite clays, Solid State Ionics 172 (1–4) 129-

133 (2004).

[29] V. R. Chumbhale, J.-S. Kim, S.-B. Lee, M.-J. Choi, Catalytic degradation of



[30] C.-G. Lee, J.-S. Kim, P.-S. Song, G.-S. Choi, Y. Kang, M.-J. Choi, Decomposition

characteristics of residue from the pyrolysis of polystyrene waste in a fluidized-bed

reactor, Korean Journal of Chemical Engineering 20 (1) 133-137 (2003).





199

[32] A. Karaduman, E. H. Şimşek, B. Çiçek, A. Y. Bilgesü, Flash pyrolysis of

polystyrene wastes in a free-fall reactor under vacuum, Journal of Analytical and

Applied Pyrolysis 60 (2) 179-186 (2001).

[33] X. Guoxi, L. Rui, T. Qinhu, L. Jinghua, Mechanism studies on the catalytic

degradation of waste polystyrene into styrene in the presence of metal powders,

Journal of Applied Polymer Science 73 (7) 1139-1143 (1999).




polymers: Part III--Degradation of polystyrene, Polymer Degradation and Stability

29 (2) 191-200 (1990).

[36] C. D. Hurd, A. R. Macon, J. I. Simon, R. V. Levetan, Pyrolytic formation of arenes.

I. Survey of general principles and findings, Journal of the American Chemical

Society 84 (23) 4509-4515 (1962).

[37] X. S. Zhao, M. G. Q. Lu, C. Song, Immobilization of aluminum chloride on MCM-

41 as a new catalyst system for liquid-phase isopropylation of naphthalene, Journal

of Molecular Catalysis A: Chemical 191 (1) 67-74 (2003).

[38] R. Lin, R. L. White, Acid-catalyzed cracking of polystyrene, Journal of Applied

Polymer Science 63 (10) 1287-1298 (1997).

[39] T. Faravelli, M. Pinciroli, F. Pisano, G. Bozzano, M. Dente, E. Ranzi, Thermal

degradation of polystyrene, Journal of Analytical and Applied Pyrolysis 60 (1) 103-

121 (2001).


200

[40] I. C. McNeill, M. Zulfiqar, T. Kousar, A detailed investigation of the products of

the thermal degradation of polystyrene, Polymer Degradation and Stability 28 (2)

131-151 (1990).

[41] T. Xu, N. Kob, R. S. Drago, J. B. Nicholas, J. F. Haw, A solid acid catalyst at the

threshold of superacid strength: NMR, calorimetry, and density functional theory

studies of silica-supported aluminum chloride, Journal of the American Chemical

Society 119 (50) 12231-12239 (1997).

[42] Z. Li, X. Ma, J. Liu, X. Feng, G. Tian, A. Zhu, Silica-supported aluminum chloride:

A recyclable and reusable catalyst for one-pot three-component Mannich-type

reactions, Journal of Molecular Catalysis A: Chemical 272 (1–2) 132-135 (2007).

[43] A. Corma, V. Fornes, M. T. Navarro, J. Perezpariente, Acidity and Stability of

MCM-41 Crystalline Aluminosilicates, Journal of Catalysis 148 (2) 569-574

(1994).

[44] D. Gianolio, N. B. Muddada, U. Olsbye, C. Lamberti, Doped-CuCl2/Al2O3 catalysts

for ethylene oxychlorination: Influence of additives on the nature of active phase

and reducibility, Nuclear Instruments and Methods in Physics Research Section B:

Beam Interactions with Materials and Atoms 284 (0) 53-57 (2012).

[45] K. Tomishige, T. Sakaihori, S.-I. Sakai, K. Fujimoto, Dimethyl carbonate synthesis

by oxidative carbonylation on activated carbon supported CuCl2 catalysts: catalytic

properties and structural change, Applied Catalysis A: General 181 (1) 95-102

(1999).

[46] W.-L. Fanchiang, Y.-C. Lin, Catalytic fast pyrolysis of furfural over H-ZSM-5 and

Zn/H-ZSM-5 catalysts, Applied Catalysis A: General 419–420 (0) 102-110 (2012).


201

[47] R. Das, D. Chakraborty, I2-TEMPO as an efficient oxidizing agent for the one-pot

conversion of alcohol to amide using FeCl3 as the catalyst, Catalysis

Communications 26 (0) 48-53 (2012).

[48] Z. X. Li, Z. Duan, Y. J. Wu, FeCl3 catalyzed diarylmethanes formations, Chinese

Chemical Letters 20 (5) 511-513 (2009).

[49] M. Salavati-Niasari, J. Hasanalian, H. Najafian, Alumina-supported FeCl3, MnCl2,

CoCl2, NiCl2, CuCl2, and ZnCl2 as catalysts for the benzylation of benzene by

benzyl chloride, Journal of Molecular Catalysis A: Chemical 209 (1–2) 209-214

(2004).

[50] G.-F. Chen, H.-M. Jia, L.-Y. Zhang, B.-H. Chen, J.-T. Li, An efficient synthesis of

2-substituted benzothiazoles in the presence of FeCl3/Montmorillonite K-10 under

ultrasound irradiation, Ultrasonics Sonochemistry 20 (2) 627-632 (2013).

[51] P. T. Williams, E. Slaney, Analysis of products from the pyrolysis and liquefaction

of single plastics and waste plastic mixtures, Resources, Conservation and

Recycling 51 (4) 754-769 (2007).

[52] C. Vasile, H. Pakdel, B. Mihai, P. Onu, H. Darie, S. Ciocâlteu, Thermal and

catalytic decomposition of mixed plastics, Journal of Analytical and Applied

Pyrolysis 57 (2) 287-303 (2001).




2145 (2008).


202

[54] T. Bhaskar, J. Kaneko, A. Muto, Y. Sakata, E. Jakab, T. Matsui, M. A. Uddin,

Pyrolysis studies of PP/PE/PS/PVC/HIPS-Br plastics mixed with PET and

dehalogenation (Br, Cl) of the liquid products, Journal of Analytical and Applied

Pyrolysis 72 (1) 27-33 (2004).

[55] J. Shah, M. R. Jan, Adnan, Catalytic activity of metal impregnated catalysts for

degradation of waste polystyrene, Journal of Industrial and Engineering Chemistry

0) (2014). http://dx.doi.org/10.1016/j.jiec.2013.12.055 (

[56] P. Carniti, P. L. Beltrame, M. Armada, A. Gervasini, G. Audisio, Polystyrene

thermodegradation. 2. Kinetics of formation of volatile products, Industrial &

Engineering Chemistry Research 30 (7) 1624-1629 (1991).

[57] T. Yoshioka, T. Handa, G. Grause, Z. Lei, H. Inomata, T. Mizoguchi, Effects of

metal oxides on the pyrolysis of poly(ethylene terephthalate), Journal of Analytical

and Applied Pyrolysis 73 (1) 139-144 (2005).

[58] G. Xi, M. Lu, C. Sun, Study on depolymerization of waste polyethylene

terephthalate into monomer of bis(2-hydroxyethyl terephthalate), Polymer

Degradation and Stability 87 (1) 117-120 (2005).

http://dx.doi.org/10.1016/j.jiec.2013.12.055

Conclusions

203

CONCLUSIONS

The aim of this study was the development of novel high activity impregnated catalysts for

the low cost thermo-catalytic degradation of WEPS into selective valuable products and

their separation via fractional distillation followed by physiochemical and GC-MS

characterization. The degradation of WEPS was carried out using various groups of bulk

catalyst (i.e. metals, metal oxides and metal salts) and the metals were also impregnated in

the form of their salts over Al₂O₃, Mmn and AC supports. The impregnated catalyst 20%

Al-Al₂O₃ was also used for the degradation of PS with the effect of PET and was

investigated for activity and selectivity of products and as well as the novelty of the

products. PEI impregnated zeolite Y was also investigated for the capture of CO₂. The

supporting materials and catalysts were synthesized with wet impregnation and

characterized using N₂ adsorption/desorption, SEM and XRD analysis.

The WEPS was characterized using thermogravimetric analysis (TGA) in both O₂ and N₂

environments. In the case of O₂ environment, 100 wt.% changes were observed. Therefore,

the degradation of WEPS was carried out at ambient conditions.

The WEPS were also degraded using thermal degradation (without catalyst). The

maximum yield of liquid products was achieved with 500 ºC degradation temperature and

150 min reaction time. At optimum condition the yield of liquid products was 78.0.7 ± 0.64

wt.% and the total conversion was 98.47 ± 0.61 wt.%.

The GC-MS analysis of parent liquid products shows non-significant amount of valuable

material and the yield of products was major in high molecular weight aromatic

hydrocarbons. The yield of toluene was 2.06 wt.%, ethylbenzene was 0.85 wt.% and

styrene monomer was 39.31 wt.%, α-methylstyrene was 1.33 wt.%, benzene, 3-butynyl

was 17.56 wt.% and 1,2-propanediol, 3-benzyloxy-1,2-diacetyl was 10.10 wt.%.

However, during recovery the products further degraded into smaller products and the

small amount of benzene, ethylbenzene and 1,2-propanediol, 3-benzyloxy-1,2-diacetyl was

recovered. Toluene was abundant in the recovery with 51.0 wt.% styrene was the second

35.0 wt.% and small amount of phenanthrene (6.0 wt.%) was also found.

Conclusions

204

The comparative degradation of WEPS was carried out using different supporting materials

for the impregnation of metals i.e., Al₂O₃, Mmn and AC. The catalytic degradation was

optimized for degradation temperature, reaction time and polymer to catalyst ratio for

maximum liquid products. Mmn was found with good catalytic activity with a maximum

liquid product yield of 92.40 ± 0.87 wt.%. All the three materials yielded a significant

amount of valuable products. AC was found to possess acidic sites of high activity that

caused to yield mostly low molecular weight aromatic hydrocarbons abundant with toluene

(6.96) and ethylbenzene (6.55). However, the yield of styrene monomer was 45.65 wt.%

and 45.42 wt.% maximum with Al₂O₃ and AC catalyst

The catalytic degradation of WEPS investigated using Mg-bulk catalysts and compared.

The present method gave more selective products with significant yield. The majority of

low molecular weight aromatic compounds were in high quantities indicating the method

is environment friendly. The degradation process resulted in the selective production of

aromatic hydrocarbons. Maximum recovery of styrene (43.0 wt.%) could be achieved with

Mg (metal) catalyst, styrene (23.8 wt.%) and ethylbenzene (35.0 wt.%) with MgO catalyst,

while styrene (51.87 wt.%) and toluene (15.81 wt.%) with MgCO₃ catalyst.

Mg impregnated catalysts over different supports were used for thermo-catalytic

degradation of WEPS. The catalytic degradation of WEPS in the presence of 15% Mg-

Al₂O₃ led to a smaller number of hydrocarbons with higher concentration as compared to

Mg metal, 20% Mg-Mmn and 20% Mg-AC catalysts. The yield of benzene, toluene,

ethylbenzene, styrene, α-methylstyrene and many other valuable compounds was

maximum with 20% Al-Al₂O₃ catalyst. The catalytic activity and yield of component

products were compared to reported methods and current method was found significant for

low cost conversion into valuable products.

The catalytic pyrolysis of WEPS was carried out using zinc bulk catalysts. It was found

from the catalytic activity and selectivity data that zinc bulk catalysts enhanced the yield

of liquid products and affected the formation of component products as compared to

thermal degradation, particularly with Zn metal as a catalyst. In comparison to thermal

degradation, the catalysts decreased degradation temperature and heating time while on the

Conclusions

205

other hand it increased the yield of liquid products from 78.07 ± 0.64 wt.% to 96.73 ± 0.12

wt.%. The catalysts, not only enhanced liquid products, but also increased value added

components of the liquid products including toluene, ethylbenzene and styrene. Overall,

the zinc bulk catalysts enhanced both the activity and selectivity of products. During

fractional distillation variation in products was observed due to cyclization and re-

combination along with thermal degradation. The fractions were analyzed using

physiochemical methods as well as GC-MS characterization.

Zn-Al₂O₃, Zn-Mmn and Zn-AC impregnated catalysts were prepared by impregnating zinc

in the form of its salt over Al₂O₃, Mmn and AC supports. The catalysts were characterized

by SAA, SEM and XRD. The activity and selectivity of liquid products and its components

were better than Zn bulk catalysts. Among the Zn supported catalysts 20% Zn-Al₂O₃ was

having better catalytic performance with 90.20 ± 0.35 wt.% liquid products that are less

than the Zn (96.07 ± 0.31) but the selectivity of the products was good in case of 20% Zn-

Al₂O₃ having maximum valuable aromatic hydrocarbons. The composition of styrene,

toluene, ethylbenzene and α-methylstyrene with 20% Zn-Al₂O₃ were 62.08%, 11.79%,

7.35% and 4.58%, respectively.

Aluminum bulk catalysts i.e. (Al metal, Al₂O₃ and AlCl₃) were found with high activity

for the degradation of WEPS comparable with thermal degradation. The catalytic

degradation was selective with the production of desirable low molecular weight aromatic

hydrocarbons more specifically in the case of Lewis acid catalysts i.e. AlCl₃. The yield of

styrene monomer in case of AlCl₃ catalyst was 46 wt.%. The liquid product was also

separated for the recovery of value added products, AlCl₃ catalyst was found with

maximum recovery of toluene and ethylbenzene. Maximum recovery of styrene was 50

wt.% and 51 wt.% and α-methylstyrene recovery was 13 wt.% and 9 wt.% with Al and

Al₂O₃ catalysts, respectively.

Al and its impregnated catalysts using Al2O3, Mmn and AC as supports were prepared. The

prepared catalysts were characterized using surface area, SEM and XRD. The results of

liquid product yield and GC-MS characterization revealed that 20% Al-Al2O3 with good

catalytic activity producing 91.20 ± 0.35 wt. % liquid products with low molecular weight

Conclusions

206

hydrocarbons. The amount of light weight aromatic was higher as compared to other

catalysts used with a major fraction of styrene monomer i.e. 56.52%.

Cu, CuO and CuCl₂ bulk catalysts were compared for thermo-catalytic degradation of

WEPS for the recovery of valuable products. Cu bulk catalysts were found more effective

for catalytic activity and selectivity. The majority of low molecular weight aromatic

hydrocarbons was formed with a very small amount of residue, gases and unwanted high

molecular weight aromatic hydrocarbons. Cu metal was found the best catalyst among the

used catalysts with a liquid product yield of 93.93 wt.%, styrene selectivity of 55.14 wt.%

and styrene monomer recovery of 60 wt.%.

The catalytic activity and selectivity of Cu impregnated catalysts over Al2O3, Mmn and

AC were investigated for the degradation of WEPS. The BET surface area of 20% Cu-

Al₂O₃ was increased to 73.99m2/g as compared to Al₂O₃ (68.31 m2/g) with particle size 2-

5 μm and adequate dispersion of precursor active centers, which in turn provides more

reaction sites. It was found that the yield of liquid products with Cu impregnated catalysts

was moderate, but with high selectivity toward low molecular weight aromatic

hydrocarbons. Among the impregnated catalysts, 20% Cu-Al₂O₃, 15% Cu-Mmn and 20%

Cu-AC showed high activities, however, the selectivity was good only with the 20% Cu-

Al₂O₃ catalyst for styrene monomers. For the selectivity of toluene and ethylbenzene, 15%

Cu-Mmn and 20% Cu-AC were found good selective catalysts.

Catalytic degradation of WEPS was carried out using Fe, Fe₂O₃ and FeCl₃ bulk catalysts,

and found to increase the yield of liquid products with high selectivity as compared to

thermal degradation. Fe and Fe₂O₃ were having more selectivity for low molecular weight

aromatic hydrocarbons. Where the recovery of styrene monomer was high for liquid

product obtained with Fe metal as catalyst. FeCl₃ (Lewis acid) was found moderate

catalysts with good recovery of toluene, ethylbenzene and styrene monomer.

Fe impregnated catalysts were investigated for the degradation of WEPS. The

activities of liquid product and selectivity of component products were

determined. The BET surface area of 5% Fe-Al₂O₃ was increased to 109.12

m2/g as compared to Al₂O₃ (68.31 m2/g) with high pore volume and sized

Conclusions

207

throughout the catalysts body. 5% Fe-Al₂O₃ and 20% Fe-Mmn was found with

good catalytic activity and selectivity of products. The yield of liquid products

using 5% Fe-Al₂O₃ and 20% Fe-Mmn was 89.27 ± 0.31 wt.% and 88.87 ± 0.42

wt.%, respectively. The yield of component products like toluene, ethylene and

styrene monomer was almost the same with 5% Fe-Al₂O₃ and 20% Fe-Mmn

catalysts. Overall, the yield of liquid products was less than Fe metal, but the

selectivity of products enhanced with Fe impregnated catalysts.

In the presence of catalysts, the pyrolysis of PS, 10PET+PS, 20PET+PS and

30PET+PS started at a lower temperature than the TG pyrolysis. Pyrolysis

temperature, reaction time and feed to catalyst ratio affected the yield of liquid

products and gases. The yield of liquid products was maximum at 500 ºC, 60

min reaction time and 1:0.2 feed to catalyst ratio in the cases of PS and

10PET+PS, it was maximum at 450 ºC, 60 min reaction time and 1:0.2 feed to

catalyst ratio in the case of 20PET+PS while it was maximum at 450 ºC, 90 min

reaction time and 1:0.2 feed to catalyst ratio in the case of 30PET+PS.

Generally, the yield of liquid products decreased and gases increased with the

increase of PET percentage. GC-MS analysis showed the formation of single

ring aromatic hydrocarbons (C6-C9 fraction) in bulk. Styrene monomer was

found dominant in the pyrolysis of all materials. The formation of many new

and oxygenated hydrocarbons is attributed to the addition of PET which

increased with the increase of PET percentage. The yield of styrene dimers,

styrene oligomers and oxygen containing compounds increased with the

increase of PET percentage. 10% PET was found to have good interaction with

PS with the yield of maximum liquid and component products after PS.

Thermo-catalytic degradation of WEPS using bulk and impregnated catalysts significantly

enhanced the yield of liquid products and improved the selectivity of component products.

In most cases along with products enhancement it showed marked reduction in the

degradation temperature and reaction. More basic catalyst (like MgO, MgCO₃ and Fe₂O₃)

yielded maximum liquid products comparatively at low temperature i.e. 400 ⁰C and greater

time. High temperature (500 ⁰C) requires a relatively small amount of catalyst where the

Conclusions

208

yield of desirable products decreases with the increase of degradation temperature. Low

molecular weight aromatic hydrocarbons are favored by moderate temperature (450 ⁰C)

with maximum total percent conversion. In most cases, more reaction time favors the yield

of selective and desirable products with the decrease of non-desirable products.

Impregnated catalysts increased the selectivity of products and decreased the yield of high

molecular weight aromatic hydrocarbons to almost zero in most cases. Impregnation over

Al₂O₃ support gives greater activity and selectivity of products. Metals not only catalyzed

the reaction, but also acted as synergist with low degradation temperature and time. The

low yield of styrene monomer with acidic catalysts is due to the further degradation into

benzene, toluene and ethylbenzene like products. The impact of PET on the yield of liquid

products was observed with significant interactions. The addition of PET caused to yield

gases in the majority. GC-MS analysis of liquid products showed many novel compounds

and mostly oxygenated aromatic hydrocarbons.

List of Publications

209


1. Jasmin Shah, M. Rasul Jan, Adnan, “Catalytic activity of metal impregnated

catalysts for degradation of waste polystyrene”, Journal of Industrial and

Engineering Chemistry 20 (5) 3604-3611 (2014). IF = 2.063

2. Jasmin Shah, M. Rasul Jan, Adnan, “Conversion of waste polystyrene through

catalytic degradation into valuable products”, Korean Journal of Chemical

Engineering 31(8), 1389-1398 (2014). IF = 1.241

3. Adnan, Jasmin Shah, M. Rasul Jan, “Thermo-catalytic pyrolysis of polystyrene in

the presence of zinc bulk catalysts”, Journal of the Taiwan Institute of Chemical

Engineers 45 (2014) 2494–2500. IF = 2.637

4. Jasmin Shah, M. Rasul Jan, Adnan, “Catalytic Activity of Aluminum Impregnated

Catalysts for the Degradation of Waste Polystyrene”, International Journal of

Chemical, Nuclear, Metallurgical and Materials Engineering 8(4) 83-89 (2014).

5. Adnan, Jasmin Shah, M. Rasul Jan, “Polystyrene Degradation Studies using Cu

Supported Catalysts”, Journal Analytical and Applied Pyrolysis 109, 196–204

(2014). IF = 3.070

6. Adnan, Jasmin Shah, M. Rasul Jan, “Effect of polyethylene terephthalate on the

catalytic pyrolysis of polystyrene: Investigation of the liquid products”, Journal of

the Taiwan Institute of Chemical Engineers. (Accepted)

7. Adnan, Jasmin Shah, M. Rasul Jan, “Zinc supported catalysts for tertiary recycling

of polystyrene into desirable hydrocarbons”, Canadian Journal of Chemical

Engineering. (Submitted)

8. Jasmin Shah, M. Rasul Jan, Adnan, “Degradation of Polystyrene over Impregnated

Catalysts using Montmorillonite Clay as Supporting Material”, Applied Clay

Sciences. (Submitted)

9. Jasmin Shah, M. Rasul Jan, Adnan, “Thermo-catalytic degradation of polystyrene

using magnesium Impregnated catalysts”, Journal of Analytical and Applied

Pyrolysis. (Submitted)

10. Jasmin Shah, M. Rasul Jan, Adnan, “Cracking of Waste Expanded Polystyrene

using Supported Fe Catalysts”. (In the process of submission)


210

11. Jasmin Shah, M. Rasul Jan, Adnan, “Chemical Recycling of Waste Expanded

Polystyrene in the Presence of Impregnated Catalysts over Activated Charcoal”. (In

the process of submission)

12. Jasmin Shah, M. Rasul Jan, Adnan, “Thermo-Catalytic Decomposition of Waste

Polystyrene Plastic using Aluminum bulk catalyst”. (In the process of submission)

13. Jasmin Shah, M. Rasul Jan, Adnan, “Catalytic Degradation of Waste Expanded

Polystyrene Using Cu, CuO and CuCl₂ catalysts”. (In the process of submission)

14. Jasmin Shah, M. Rasul Jan, Adnan, “Study of Expanded Polystyrene Pyrolysis

using Iron Bulk Catalysts”. (In the process of submission)


211


212


213


214


215

Adnan PhD Thesis.pdf - Pakistan Research Repository

Documents

Transcript of Adnan PhD Thesis.pdf - Pakistan Research Repository