i

A Thesis

Entitled

Chemical Recycling of Poly (Ethylene Terephthalate) and its Co-polyesters with 2, 5-

Furandicarboxylic Acid using Alkaline Hydrolysis

by

Keerthi Vinnakota

Submitted to the Graduate Faculty as partial fulfillment of the requirements for the

Master of Science Degree in

Chemical Engineering

________________________________________ Dr. Maria Coleman, Committee Chair ________________________________________ Dr. Joseph Lawrence, Committee Member ________________________________________ Dr. Sridhar Viamajala, Committee Member ________________________________________

Dr. Amanda Bryant-Friedrich, Dean

College of Graduate Studies

The University of Toledo

August 2018

ii

Copyright 2108, Keerthi Vinnakota

This document is copyrighted material. Under copyright law, no parts of this document may be reproduced without the expressed permission of the author.

iii

An Abstract of

Chemical Recycling of Poly (Ethylene Terephthalate) and its Co-polyesters with 2, 5-

Furandicarboxylic Acid using Alkaline Hydrolysis

by

Keerthi Vinnakota

Submitted to the Graduate Faculty as partial fulfillment of the requirements for the

Master of Science Degree in Chemical Engineering

The University of Toledo

August 2018

The large increase in the generation of post-consumer plastic in past few decades

has led to an increased interest in eco-friendly recycling technologies. Polyethylene

terephthalate (PET) is a highly valued packaging material with broad applications because

it is strong, lightweight, non-reactive, non-toxic and shatterproof. To extend its

applications, the packaging industry adds co-monomers, additives, multilayered structures

and forms polymer blends to improve the mechanical and barrier properties of the base

polyester. These additives can pose challenges to the mechanical recycling methods that

are commonly used in the industry. While mechanical recycling is economical and broadly

commercially used, the recycled PET (RPET) tends to have reduced molecular weight and

can degrade in the presence of impurities (i.e. polyvinyl chloride (PVC)). Chemical

recycling is an attractive alternative approach that results in recovery of monomers and

other chemical constituents that can be used as precursors for new polymers. Several

chemical recycling methods were reported in literature to address the end-of-life PET

iv

waste, but little work was done on co-polyesters that are of interest to the packaging

industry. The focus of this thesis is to investigate alkaline hydrolysis of traditional PET

and a co-polyester (will be referred to as PETF20) containing ethylene glycol, 80%

terephthalic acid (TPA) and 20% 2,5-furan dicarboxylic acid (FDCA). Studies on

chemical/mechanical recycling of PETF20 were not reported in the literature.

Alkaline hydrolysis of PET and PETF20 was investigated at atmospheric pressure

and a range of temperatures (≤ 150℃) using sodium hydroxide solution (1.1 M) to recover

TPA and FDCA. The impact of time, temperature, co-solvent (i.e. γ- Valero lactone) and

impurity (i.e. PVC) on conversion of PET was investigated at ≤ 150℃, rate of

depolymerization and impact of co-solvents (γ-Valero lactone, γ- butyral lactone, ethylene

glycol diacetate, propylene glycol diacetate and triglycerol) on PET and PETF20 were

studied at 90℃. The chemical structure of the products was confirmed via FTIR and NMR.

The conversion of PET obtained at 150℃ and 180 min with and without impurity

(PVC) is approximately 81%. PETF20 flakes exhibited high conversions of 88% compared

to PET i.e. 42% at 90℃. Addition of triglycerol to PET flakes resulted in high TPA yields

of 63% while the other co-solvents resulted in either lower or same yields as that of base

NaOH solution. PETF20 with and without co-solvents resulted in the same yields.

Research was extended to separate TPA from FDCA using precipitation, 20 wt.% water in

DMSO solution exhibited promising results with 68.3% recovery of diacid from 20:80

molar fraction of TPA and FDCA.

Keywords: Alkaline hydrolysis, Co-polyesters of PET with FDCA, Co-solvents, Co-

monomer separation

v

To the memory of my brother Sarath Kumar Vinnakota, this is for you.

March 1995 – September 2016

&

To my parents for encouraging me and being my biggest strength.

vi

Acknowledgements

Firstly, I would like to express my sincere gratitude to my advisors Dr. Maria R

Coleman and Dr. Joseph Lawrence for the continuous support in my research and my life,

for the motivation, immense knowledge and encouragement. Their guidance helped me in

all the times of research and writing the thesis and gave me the chance to gain new

experiences during my education.

Besides my advisors, I would like to express my special thanks to Dr. Constance

Schall for rendering her help during the initial stages of my research and allowing me to

use the reactor setup throughout my research. I am also grateful to my committee member

Dr. Sridhar Viamajala for his invaluable comments and support.

I am thankful to Anup Joshi and Elizabeth Heil for their help and contribution to

my research. I am thankful to Niloofar Aliporaisabi and Chinedu Okeke for their constant

support. I thank my fellow lab mates for all the fun we had and the memories we have

created in the last two years.

Last but not the least; I would like to thank my family: my parents, my brother,

Abhishek Varma Pachunuri and friends for supporting me throughout my life in general.

vii

Table of Contents

Abstract ........................................................................................................................ iii - iv

Acknowledgements ............................................................................................................ vi

Table of Contents ........................................................................................................ vii - ix

List of Tables ......................................................................................................................x

List of Figures ............................................................................................................ xi - xiv

List of Abbreviations .........................................................................................................xv

List of Symbols ................................................................................................................ xvi

1 Introduction .................................................................................................... 1 - 8

1.1 Recycling methods ....................................................................................... 3 - 8

2 Chemical depolymerization methods ............................................................... 9 - 37

2.1 Background on synthesis of PET and copolymers/ renewable polyesters .........9

2.1.1 Synthesis of PET ........................................................................ 9 - 12

2.1.2 Commercial o-monomers .......................................................... 13 - 15

2.1.3 Renewable polyesters................................................................ 15 - 17

2.2 Recycling methods .................................................................................. 17 - 37

2.2.1 Methanolysis ............................................................................. 19 - 22

2.2.2 Glycolysis ................................................................................. 23 - 26

2.2.3 Hydrolysis ................................................................................ 27 - 34

viii

2.2.4 Ammonolysis ...................................................................................36

2.2.5 Aminolysis .......................................................................................36

3 Experimental section ...................................................................................... 38 - 52

3.1 Materials ................................................................................................ 39 - 40

3.1.a Polyethylene terephthalate powder and flakes .................................39

3.1.b 20% co-polyester of PET and PEF flakes (PETF20) .......................40

3.2 Methods ................................................................................................ 40 - 48

3.2.1 Experimental setup for chemical recycling of PET and PETF20 flakes

.......................................................................................................41

3.2.2 Procedure for alkaline hydrolysis of PET ................................ 42 - 48

3.2.2.a PET powder .......................................................................43

3.2.2.b PET Flakes ........................................................................44

3.2.2.c Impact of impurities-PVC ......................................... 44 - 45

3.2.2.d Impact of co-solvents ................................................ 45 - 48

3.3 Analysis of results ................................................................................... 49 - 52

3.3.1 Quantitative analysis ........................................................................49

3.3.2 Confirmation of structure of products ...................................... 50 - 52

4 Results and discussion .................................................................................. 53-102

4.0 Reaction mechanism of alkaline hydrolysis of PET with NaOH ..... 54 - 55

4.1 Hydrolysis of Polyethylene terephthalate ......................................... 56 - 81

4.1.1 Effect of time ........................................................................ 56 - 58

4.1.2 Impact of temperature on hydrolysis ..................................... 59 - 61

4.1.3 Kinetic model ........................................................................ 62 - 66

ix

4.1.4 Effect of impurities ................................................................ 67 - 69

4.1.5 Effect of green solvents (γ-Valero Lactone) .......................... 70 - 73

4.1.6 Characterization of monomer TPA .......................................... 74-81

4.1.6.a FTIR spectroscopy .................................................... 74 - 75

4.1.6.b Solution Nuclear Magnetic Resonance Spectroscopy

................................................................................................ 76 - 81

4.2 Hydrolysis of co - polyester of PET and PEF ................................... 81 - 97

4.2.1 PET vs PETF20 flakes .......................................................... 80 - 83

4.2.2 Impact of co-solvents on PET and PETF20 flakes ................ 84 - 87

4.2.3 Characterization .................................................................... 87 - 90

4.2.3.a FTIR spectroscopy ..................................................... 87 - 88

4.2.3.b Solution Nuclear Magnetic Resonance Spectroscopy

................................................................................................ 89 - 91

4.2.3.c Thermal transition and crystallinity of residue polymer flake

using DSC ................................................................... 91 - 97

4.3 Separation of TPA and FDCA .............................................................. 97 - 102

4.3.a Solubility of TPA and FDCA in DMSO water system . 97 - 98

4.3.b Recovery of TPA from FDCA in DMSO water system

.............................................................................................. 99 - 102

5 Conclusions and future work .................................................................... 103 - 105

References .............................................................................................................. 106 - 111

A Miscellaneous data .................................................................................... 112 - 115

x

List of Tables

2.1 List of commercial co-monomers used in PET synthesis ......................................14

3.1 Reaction conditions for alkaline hydrolysis of PET in Parr system ......................43

3.2 Reaction conditions for alkaline hydrolysis of PET flake/PVC in Parr system ....45

3.3 Co-solvents used for alkaline hydrolysis of PET and PETF20 ..............................47

3.4 Reaction conditions for alkaline hydrolysis of PET and PETF20 in oil bath .......48

3.5 FTIR data of monomers obtained from hydrolysis of PET and PETF20 .............51

3.6 NMR data of monomers obtained from hydrolysis of PET and PETF20 .............52

4.1 Reaction rate constants of PET flakes, depolymerization in1.1M NaOH ............65

4.2 Data of hydrolysis reaction using GVL as co-solvent at 150℃ and 90 min in NaOH

solution. .................................................................................................................74

4.3 Data of hydrolysis reaction using co-solvent at 90℃ and 3 days in 1.1 M NaOH

solution ...................................................................................................................95

xi

List of Figures

1 - 1 Schematic for mechanical recycling of post consumer PET waste ........................4

2 - 1 Synthesis of PET using TPA and EG route ..........................................................11

2 - 2 Synthesis of PET using DMT and EG route ..........................................................12

2 - 3 Reaction mechanism for polymerization of PEF ...................................................16

2 - 4 Reaction mechanism for copolymerization of PET with PEF ...............................17

2 - 5 Reaction mechanism for methanolysis of PET using excess methanol .................20

2 - 6 Schematic of methanolysis process .......................................................................21

2 - 7 Reaction mechanism for glycolysis of PET using excess EG ...............................24

2 - 8 Reaction mechanism for alkaline hydrolysis of PET using NaOH........................28

2 - 9 Reaction mechanism for acid hydrolysis of PET using sulphuric acid .................32

2 - 10 Reaction mechanism for neutral hydrolysis of PET using water ...........................34

2 - 11 Reaction mechanism for ammonolysis of PET using ammonia ............................35

2 - 12 Reaction mechanism for aminolysis of PET using amines ....................................36

3 - 1 Randcastle microtruder # RC - 0250 ....................................................................39

3 - 2 Structure of polyethylene terephthalte (PET) .......................................................40

3 - 3 Structure of co-polyester of PET and PEF (PETF) ...............................................40

3 - 4 Parr bench top reactor ............................................................................................41

xii

3 - 5 Reaction setup using oil bath @ 90°C ...................................................................41

3 - 6 Sketch on surface reaction of PET with NaOH and solvent ..................................46

4 - 1 Reaction mechanism of alkaline hydrolysis of PET with NaOH solution ............55

4 - 2 Effect of time on PET hydrolysis at 150°C in 1.1M sodium hydroxide solution

.......................................................................................................57

4 - 3 Unconverted residue (from left) A) 90min, B) 120min, c) 150min, D) 180min, E)

240min, F) 300min.................................................................................................58

4 - 4 Effect of temperature and time on hydrolysis of PET powder @ 120℃, 150℃ for

30, 60 and 90 minutes in Parr reactor A) % PET conversion, B) % TPA yield ....59

4 - 5 Effect of temperature and time on hydrolysis of PET flakes @ 90℃, 120℃ and

150℃ for 30, 60 and 90 minutes in Parr reactor A) % PET conversion, B) % TPA

yield ........................................................................................................60

4 - 6 Effect of temperature and time on hydrolysis of PET powder and flakes @ 90℃,

120℃ and 150℃ for 30, 60 and 90 minutes in Parr reactor .................................61

4 - 7 Plot of ln(1-X) vs t for data of PET flakes in 1.1M NaOH solution at 90℃, 120℃

and 150℃ at a time range of 0-90 minutes ...........................................................65

4 - 8 Arrhenius plot of the apparent kinetic rate constant for the aqueous sodium

hydroxide solution ................................................................................................66

4 - 9 Effect of PVC on PET hydrolysis at 150°C for 180℃ minutes, % TPA yield, %

PET conversion in Parr reactor .............................................................................69

4 - 10 Comparison of percentage yield of PET flakes vs PET flakes+5 wt.% PVC at 150°C

at different times ranging from 30 – 180 min in Parr reactor ...............................70

xiii

4 - 11 Hydrolysis of PET flakes with GVL at different molar compositions (0.5-10

mole%) at 150°C and 90min .................................................................................72

4 - 12 Infrared spectroscopy of precipitate monomer TPA and IPA ..............................75

4 - 13.a Proton NMR spectrum of recovered TPA from hydrolysis at 150°C, 90min in 1.1M

NaOH ........................................................................................................77

4 - 13.b 13 C NMR of precipitate from hydrolysis using I)1.1.25 M NaOH solution,

II) 5 wt.% PVC as impurity in 1.1 M NaOH solution, III) 1 mole% GVL in 1.1 M

NaOH solution ......................................................................................................78

4 - 13.c Possibility of spin-spin splitting of neighboring protons .....................................79

4 - 14 Percentage conversion and diacid yield of PET vs PETF20 flake after alkaline

hydrolysis with 1.1M NaOH solution for 3 days at 90℃ .....................................83

4 - 15 A) PET flakes residue from Parr reactor B) Fresh PET flake vs flake residue from

oil bath C) Fresh PETF20 flake vs flake residue from oil bath. ...........................84

4 - 16 Percentage yield of PET flake after alkaline hydrolysis in the presence of 1 mole%

co-solvents for 3 days at 90℃ at 13 pH.................................................................86

4 - 17 Percentage yield of PETF20 flake after alkaline hydrolysis in the presence of 1

mole% co-solvents for 3 days at 90℃ at 13 pH ....................................................87

4 - 18 Infrared spectroscopy of precipitate from PET and PETF20 alkaline hydrolysis in

NaOH solution for 3 days and 90℃ .....................................................................89

4 - 19a. 1H NMR of recovered TPA and FDCA from PETF20 flakes .............................90

4 - 19b. 13C NMR of recovered TPA and FDCA from PETF20 flakes .............................91

4 - 20.a. DSC curve of fresh PET flakes and PET flakes residue following reaction in 0-10

mole% GVL in NaOH solution at 150℃ and 90 minutes ....................................93

xiv

4 - 20.b. DCS curves of PET flake after hydrolysis using different co-solvents (1 mole%)

for 3 days at 90°C in NaOH solution ....................................................................94

4 - 20.c DSC curve of PETF20 flake after hydrolysis using different co-solvents (1

mole

%) for 3 days at 90°C in NaOH solution ..............................................................96

4 - 21 Schematics of alkaline hydrolysis of PETF20 using NaOH solution ...................97

4 - 22 Solubility of TPA and FDCA in DMSO water system at various wt - % water....99

4 - 23 Proposed separation method for recovery of TPA from FDCA using DMSO and

water system ......................................................................................................100

4 - 24 TPA percentage recovery vs water added in weight percentage for A) 20:80, B)

10:90, C) 5:95, D) 0: 100 molar ratios of FDCA to TPA solutions in DMSO ....101

4 - 25 Infrared spectroscopy of precipitate (TPA + FDCA) from 20:80 molar ratio of

FDCA and TPA in DMSO solution using 20 wt.% water. .................................102

A - 1 US waste generation by category .........................................................................112

A - 2 RPET used by product category in 2016 (MMlbs) as per NAPCOR report

.....................................................................................................113

A - 3 PET material flow in US(MMlbs) as per NAPCOR 2016 report

.....................................................................................................113

A - 4 Proton NMR spectrum of Pure TPA ....................................................................114

A - 5 Carbon NMR spectrum of Pure TPA ...................................................................114

A - 6 Proton NMR spectrum of Pure FDCA .................................................................115

A - 7 Carbon NMR spectrum of Pure FDCA ................................................................115

xv

List of Abbreviations

BHET .........................Bis (2-Hydroxyethyl Terephthalate) CHDM .......................Cyclo Hexane Di Methanol DEG ..........................Di Ethylene Glycol DSC ............................Differential Scanning Calorimetry DMT ..........................Dimethyl Terephthalate DMSO ........................Dimethyl Sulfoxide EG ..............................Ethylene Glycol EGDA ........................Ethylene Glycol Diacetate FDCA .........................Furan Dicarboxylic Acid FTIR ...........................Fourier Transformation Infra-Red spectroscopy GVL ...........................Gamma Valero Lactone GBL............................Gamma Butyral Lactone IPA .............................Iso Phthalic Acid NAPCOR ..................National Association for PET Container Resources NMR ..........................Nuclear Magnetic Resonance PET ............................Poly (Ethylene Terephthalate) PEF .............................Poly Ethylene Furanoate PVC ............................Poly Vinyl Chloride PETF20 .....................20% co-polyester of PET with PEF PGDA .........................Propylene Glycol Diacetate RPET ..........................Recycled Polyethylene Terephthalate TPA ...........................Terephthalic Acid USEPA ......................United States Environmental Protection Agency

xvi

List of Symbols

℃ ...............................Degree centigrade % ................................Percentage K .................................Degrees kelvin M ................................Molarity μ .................................Micron ρ..................................Density t ..................................Reaction time b..................................Constant δ ..................................Solubility parameter Ø .................................Diameter K1 ...............................Rate constant Ea ................................Activation energy R .................................Universal gas constant A .................................Frequency factor T .................................Absolute temperature in Kelvin X .................................Conversion g..................................Gram m ................................Meter cm ...............................Centi meter mm .............................Milli meter ml ...............................Milli liter atm..............................Atmospheric pressure ∆Hm ............................Enthalpy of melting

∆Hc ............................Enthalpy of crystallization

∆H°m...........................Enthalpy of fusion NA ...............................Number of moles of reactant

NAo .............................Initial number of moles of reactant CA ...............................Alkali concentration of ester CB ...............................Alkali concentration of solution V0 ...............................Volume of solution As ................................Surface area of flake A0 ...............................Initial surface area of flake

1

Chapter - 1

Introduction

The global market for polyethylene terephthalate (PET) has expanded and demand

has increased in sectors like food and beverage, health care, textiles, cosmetics, housing,

and other consumer products [1] because of the ability to offer light weight options and

unique container designs as a semi crystalline polymer [2]. PET characteristics such as high

clarity, medium rigidity, food contact safety, chemical resistance, gas and moisture barrier,

temperature resistance and high impact strength [3] have allowed a wide range of

applications boosting the growth of this polymer in the packaging industry. Further,

because of its contamination resistance properties, PET is extensively used in the food and

beverage industry.

With the growing demand for carbonated soft drinks, bottled water and other light

weight packaging, the global production of PET is growing. Production was 50 MMT in

2016 and is estimated to reach 88.16 MMT in 2022 at a compounded annual growth rate

of 9.17% [4]. The packaging industry continues to seek improvements in the barrier

properties of PET to provide longer shelf life for the packaged products [5]. Further,

manufacturers expect faster production rates and material designs that favor higher speed

production without compromising PET quality. To meet the industry needs and

2

specifications, formulators use various compatibilizers like co-monomers and small

molecule additives [5]. While the additives and co-monomers can improve the properties,

the more complex PET formulations pose challenges to polymer recycling, especially when

using traditional mechanical recycle processes.

According to a 2016 report from the United States Environmental Protection

Agency (EPA) [6], plastic waste is typically a mixture of PET, high-density polyethylene,

low-density polyethylene, polypropylene, polystyrene, poly vinyl chloride, acrylonitrile

butyl styrene, nylon, Teflon and fiber reinforced plastic. The primary interest of this work

is to develop methods to recycle packaging materials with comonomers. Extensive

research continues in our lab (the Polymer Institute at the University of Toledo) to improve

the properties of PET, and recently we have focused on using various bio-based co-

monomers for PET. Therefore, focus of this work is to recycle the PET and its co-

polyesters. Although, PET is the most recycled polymer with plastic resin identification

code number one, its recycling rates are still low (< 30%) because of a) disposal of post-

consumer waste after first use due to lack of awareness, b) costs associated with recycling,

c) limitations of mechanical recycling methods for co-monomers and additives which

affect the properties of recycled material.

The recycling rate of PET in United States according to the National Association

for PET Container Resource (NAPCOR) (refer appendix A) report from 2016 [7] was

28.4%, while the rest was disposed. Around 6,172 MMlbs of PET bottles were sold out of

which 1,753 MMlbs were collected for recycling. Of these recycled PET, 1,526 MMlbs

were purchased by US reclaimers for mechanical recycling and 379 MMlbs were exported.

3

Most of the post-consumer waste was exported to China for recycling, but the recent ban

by China on several recycle imports [8] and more stringent contamination standards (< 1.5

% impurities) on allowed imports could further restrict the extent of PET recycling [9].

This adds to the unrecycled post-consumer PET waste. Therefore, developing recycling

methods to handle impurity-containing heterogeneous waste is an imminent need in the

PET industry [9].

The broad focus of this thesis is to investigate chemical recycling methods which

can handle co-polyesters with high co-monomer concentrations and impurities and

ultimately recover the feedstock monomers to allow reuse in the production of the base

polymer. If successful, this approach would decrease waste disposal into landfills and

oceans and also lower petroleum consumption to produce new feed stock material. Several

recycling methods are described in detail and a method that meets the above requirements

was selected for use with co-polyester feed.

1.1 Recycling Methods

The following three primary methods of recycling can be used to manage PET

waste 1) mechanical recycling 2) chemical recycling and 3) pyrolysis to produce fuel oil

[10]. Incineration of PET waste is also possible for energy recovery, but with possible risks

of release of air-born toxins.

Mechanical recycling was commercialized during the 1970’s [11] to produce

pellets for reuse; it is relatively a cheap and simple method. Mechanical recycling of a

4

homo-polymer results in similar grade PET pellets as that of virgin PET and can be easily

re-used in manufacturing processes. Post-consumer waste undergoes several steps during

mechanical recycling [11] as listed below:

Cutting/shredding - Large-sized plastics are chopped into small flakes

Contaminant’s separation - Impurities are separated using a cyclone separator

Floating – Plastic flakes are separated in floating tank depending on variation in density

Milling - Similar-density polymers are milled together

Washing and drying – Chemical washing is used to remove the glue from plastic flake

Agglomeration - Product is stored, mixed with additives or sent for further processing

Extrusion/pelletizing; Plastic is extruded into strands and made into pellets before it is

sold to market. By doing so, a clear grade PET of high quality is produced which can

compete with virgin PET. In some cases, solid stating is used to upgrade the molecular

weight of the recycled PET pellets.

Fig 1-1. Schematic for mechanical recycling of post consumer PET waste

Post- consumer PET waste

Cutting and

shredding

Sorting (PVC &

other waste)

Floating

Extrusion /pelletizing

(Re-use)

Agglomeration

Chemical washing &

drying

Milling

5

While, mechanical recycling is economical and produces high quality polymer, increasing

heterogeneity of the plastic waste, as described earlier in this chapter, has become a major

issue for the mechanical recycling industry. For example, blending the polyamide MXD6

with PET increases the shelf-life of the container, but on mechanical recycling the result is

lower molecular weight polymer and an undesirable yellow color. The presence of

impurities, particularly PVC at as little as 50 ppm concentration in a post-consumer PET

stream has negative impacts on mechanical recycling leading to reduction in molecular

weight and color generation as discussed later in chapter-2 [12]. Employment of heat

during the process results in photo-oxidation and mechanical stresses, which deteriorates

the product properties and leads to undesirable yellowness in the product that increases in

intensity with each recycle [13]. This ultimately results in a low grade polymer with

degraded properties that can end up in landfills [14]. Overall, mechanical recycling offers

PET pellets that can potentially be applied directly in polymer processing, but the products

may have limitations on color, transparency and intrinsic viscosity that restrict the

applicability.

The combined effect of mechanical recycling on PET color and properties together

with the increasing use of copolymer or blended polymer products has prompted interest

in alternative recycling methods. Hence, chemical recycling became the subject of interest

to recycle contaminated or waste streams with end product recovered monomer or value

added compounds [14].

Chemical recycling is a process, which either totally decomposes the

polymer using chemical reagents and catalysts to obtain the original monomers or partially

6

decomposes the polymer to form oligomers and other industrial chemicals. Products are

formed with potential high value applications such as chemicals, monomers and new

polymers. Chemical recycling is broadly categorized into methanolysis, glycolysis,

hydrolysis, amminolysis and ammonolysis based on the chemical reagents used to

depolymerize the polymer. As PET is a polyester, chain scission occurs when in contact

with reagents like water, alcohol, acids, glycols and amines. PET is formed by an

equilibrium limited poly-condensation reaction discussed in chapter 2, which means if

reaction is pushed to the opposite direction by addition of a condensation product,

monomers and oligomers are expected to be formed. These chemical recycling methods

will be discussed in more detail in chapter 2.

Pyrolysis can convert plastic waste into fuels and other organic chemicals.

This process accepts almost any type of plastic waste including thermosets like natural

rubbers. The product obtained is liquid oil with high calorific value compared to

commercial oils [10].

As we compare these recycling methods, mechanical recycling is

inexpensive and an industrially popular process. Pyrolysis recovers oils which could serve

as feedstock for monomer synthesis, but not monomers. Considering the drawbacks of

pyrolysis and mechanical recycling in delivering low quality product with undesirable

color on increase in heterogeneity of waste, a viable option was to use chemical recycling

methods as it produces the raw material that PET is originated from.

This work addresses the issues of chemical recycling of co-polyesters by

selecting a process which uses low reaction times, temperatures and minimal amount of

7

catalyst to recover industrially used feed stock material for PET synthesis. Methanolysis

and glycolysis processes are industrially well established. These two processes were not

used in the study because the monomer dimethyl terephthalate produced from methanolysis

is currently not of industrial interest and glycolysis leads to production of oligomers which

will not isolate comonomers. Therefore, alkaline hydrolysis process was selected as model

system for chemically recycling PET from copolymers and contaminated waste streams.

In a broad sense this method can be applied to recycle nylons and mixed waste streams to

selectively recover monomers with some development.

Objectives of this work were to:

1) Study the effects of the presence of co-monomer furan dicarboxylic acid (FDCA) on the

rate of depolymerization of a 20% co-polyester of PET and polyethylene furanoate (PEF)

using alkaline hydrolysis and examine the possibility of selective recovery of the co-

monomers.

2) Assess the improvement of monomer yield after alkaline hydrolysis of PET or 20% co-

polyester in the presence of co-solvents.

3) Investigate the impact of the presence of PVC (up to 5 wt.% relative to PET) on the

hydrolysis of PET.

A simple method to recycle PET using 1.1M NaOH solution was selected

from the literature and the reactions were performed over a range of temperatures (90℃ -

150℃) [15]. Phase-I of the research was focused on studying the impact of reaction

parameters and the presence of PVC up to 5 wt% at 150℃ to make sure the results agree

with previous literature. After analyzing the results, it was understood that it took 5 h for

8

the PET flake to completely depolymerize during the reaction. The hypothesis was that by

adding a co-solvent to the NaOH solution, it swells the polymer matrix and there would be

an increase in the rate of conversion of PET. Therefore, a co-solvent, γ- valero lactone

(GVL) at molar compositions of 1-10 mole% relative to the NaOH solution was studied on

PET flakes at 150℃ and 90 min to improve the yield of the monomer terepthalic acid

(TPA) which was not reported in the literature. Also, research on co-polyesters using

alkaline hydrolysis was not reported in the literature.

Therefore, using the same method phase-II of the research was focused on

comparing alkaline hydrolysis of 20% co-polyester flakes of PET and PEF (PETF20)

relative to PET-only flake at 90℃ using a simple reaction system. Based on the outcomes

of PET flakes at 150℃ and 90 min with GVL as co-solvent, a 1.0 mole% of co-solvent

relative to NaOH solution was used to study the impact of other co-solvents i.e. GVL, γ-

butyral lactone, ethylene glycol diacetate, propylene glycol diacetate and triglycerol on

both PETF20 and PET flakes. PETF20 was expected to react faster than PET flake because

of the affinity of the furan towards water resulting in higher yields. Co-solvents were

expected to improve the yields of both PET and PETF20 flakes.

Study on selective recovery of monomers TPA and FDCA obtained from

hydrolysis of PETF20 was done using DMSO/water system to selectively precipitate

monomer components. Based on the solubility limits reported in the literature, TPA and

FDCA were expected to be selectively recovered by varying the composition of water from

0-20 wt.% in the DMSO solution containing TPA and FDCA at different molar ratios.

9

Chapter - 2

Chemical Depolymerization methods

2.1 Background on synthesis of PET and its copolymers / renewable polymers

The focus of this thesis is to investigate chemical depolymerization of polyester

with emphasis on PET based co-polyesters. Therefore, the synthesis of PET is discussed in

detail to highlight the reactions of interest to depolymerization. Also, the synthesis method

for the renewable polyethylene furanoate (PEF) polymer, which has gained the attention

of the packaging industry, is explained. Finally, industrially used co-monomers and the

properties that they impart to the final copolymer are discussed in detail. A renewable co-

monomer FDCA, which is used in the production of polyethylene furanoate (PEF) is the

subject of interest to this work. Therefore, synthesis of 20% co-polyesters of PET and PEF

(PETF20) is discussed in this section.

10

2.1.1 Synthesis of PET

Polyethylene terephthalate shown in Fig 2.1 is produced by either esterification or

transesterification reactions. Esterification reaction uses ethylene glycol and terephthalic

acid as raw materials and are conducted at moderate pressures between 2.7 – 5.5 bar and

high temperatures of 220-260℃ [16, 17]. In the first step bis (2-hydroxyethyl terephthalate)

(BHET) ester is formed in the presence of excess ethylene glycol (EG). The repeating unit

of this ester results in the formation of polyethylene terephthalate. The water formed during

this reaction and excess EG are eliminated continuously by vacuum distillation [16]. The

reaction is shown in Fig 2-1.

Transesterification reaction uses dimethyl terephthalate and excess ethylene glycol

along with basic catalyst as raw materials for production of PET as shown in Fig 2-2. First

step of the reaction is between 150 - 200℃, to drive the reaction forward methanol is

removed by distillation and excess ethylene glycol is distilled off at higher temperature

under vacuum. Poly-condensation step takes place at 270 - 280℃ with continuous

distillation of ethylene glycol [16, 18, 19]. The monomer bis (2-hydroxyethyl)

terephthalate is the intermediate product formed during both esterification and

transesterification reactions after the removal of water in former and methanol in the later

reactions. This monomer is condensed to form the polymer PET with EG as by product.

11

Fig 2-1. Synthesis of PET using TPA and EG route.

12

Fig 2-2. Synthesis of PET using DMT and EG route.

13

2.1.2 Commercial Co-monomers

The commercial co-monomers which are of interest to the packaging industry are

discussed in detail in this section. The nature of these monomers is of interest to recycling

because their presence can affect the properties of the final recycled materials.

Additionally, many of these co-monomers are of higher cost that TPA and their selective

recovery may be economically attractive. By adding these co-monomers to PET, the final

co-polyester of PET exhibits improved properties including controlled crystallization rate,

increase in glass transition temperature (Tg), low melting point and improved barrier

properties [20]. This increases the range of commercial applications of PET in packaging

markets. Table.2.1 provides the structure and advantages of each co-monomer when added

to PET homopolymer.

14

Table. 2.1. List of commercial co-monomers used in PET synthesis.

Co-monomer Advantage

Cyclohexane dimethanol (CHDM)

Lowers melting temperature

Isophthalic acid (IPA)

Disturbs crystallinity and reduces rate,

improve Barrier

Diethylene Glycol (DEG)

Disturbs crystallinity and reduces rate and lower

melting point

2,5-Furan dicarboxylic acid (FDCA)

Enhances barrier properties and increase

Tg

15

IPA improves the barrier properties which increases the shelf-life of the packaging

container. CHDM and DEG interfere with crystallization and lower polymer melting

temperature which helps in reducing processing temperatures. If only small amounts of co-

monomer is used, crystallization is slowed but not prevented entirely. As a result, bottles

that are both clear and crystalline enough to be an adequate barrier to aromas and even

gases, such as carbon dioxide in carbonated beverages can be obtained via stretch blow

molding "SBM", [3]. As will be discussed in section 2.1.3, mechanical recycling is limited

to pure PET or co-polyesters of PET with no more than 10% co-monomers because of the

deficiencies such as low molecular weight, low crystallinity of the products obtained after

mechanical recycling with high compositions of co-monomers [21]. This limits the range

of properties achievable through copolymerization of PET with high value co-monomers.

As a co-polyester of PET and PEF was synthesized in-house to improve the properties of

PET, the effect of co-monomer FDCA on the rate of depolymerization of PET using

chemical recycling methods was studied in this work.

2.1.3 Renewable polyesters

Polyethylene furanoate (PEF), a renewable polyester has attracted the attention of

the packaging industry, it is formed by polymerization of 2,5-Furandicarboxylic acid

(FDCA) and EG as shown in Fig 2-3. Though it is expensive to make, PEF is of interest

as replacement for PET because of better properties. PEF exhibits a tenfold improvement

in O2 and fivefold increase in CO2 barrier relative to PET [22]. This would allow longer

16

lasting packaging of carbonated drinks and shelf life for O2 sensitive products. PEF has

high glass transition temperature, which gives opportunity to extend temperature range of

operation and low melting temperature for easy processing. Economic production of FDCA

would make PEF a promising option to petroleum based TPA. Given the economic

challenges in replacing TPA with FDCA and limited availability of FDCA, one approach

that is being pursued by our group is copolymerizing PET and PEF.

Fig 2-3. Reaction mechanism for polymerization of PEF

Also for packaging application, bio-based FDCA was proven to be a major potential

feedstock monomer and bio based compounds are of interest for copolymers [20].

Therefore, a copolymer of PET and PEF was synthesized in-house by Anup Joshi, a PhD

candidate from University of Toledo [20], was used in this research to extend recycling

process for pure PET. This work explored the utility of chemical recycling to selectively

17

recover monomers from co-polyesters. A 20% co-polyester of PET/PEF flake was used for

the research as shown in Fig 2-4.

Fig 2-4. Reaction mechanism for copolymerization of PET with PEF

2.2 Recycling methods

Mechanical recycling is commonly used commercially to recycle PET and produce

pellets for further processing. Because of high temperature and sheer of mechanical

recycling, there is degradation of polymers structure and loss of molecular weight.

Additionally, it is hard to isolate value added monomers and additives during this process.

18

Moreover, impurities present in the post-consumer waste make it difficult to recycle

PET using mechanical recycling methods. Major impurities that can affect the recycling

efficiency are [23]: 1) polymer cross contamination i.e. PVC, 2) additives, and 3) non-

polymer impurities such as metal caps, labels etc., will have negative impacts on

mechanical recycling. PVC is of specific concern because as little as 50 ppm of PVC in

PET recycling stream can lead to degradation during mechanical recycling. PVC enters the

waste stream of PET in four different ways: a) PVC bottles (hard to identify and separate

from the PET bottles, trained individuals are required for manual separation of PVC bottles

from PET bottles), b) PVC used as lining for bottle labels, c) PVC present as liner for bottle

caps and 4) safety seals for bottles. PVC present in the waste stream forms acids that break

down PET resin both physically and chemically causing the PET plastic to become brittle

and yellowish in color. In addition, density of PVC is close to PET, which makes it hard to

separate using density flotation techniques. Similar problem would be encountered while

sorting PEF from the PET waste stream. Density follows the order PET < Poly vinyl

chloride (PVC) < Polyethylene furanoate (PEF) i.e. 1.38 < 1.39 < 1.43 g/cm3 [3, 24, 25].

Therefore, trace PVC present in PET/PEF mixed streams would be difficult to separate

using conventional mechanical recycling techniques.

To overcome these problems, this study focuses on selecting a recycling method to

treat contaminants and heterogeneous plastic waste. A chemical recycling method to

handle contamination through impurities (up to 5% PVC) and more than 10% co-monomer

is investigated which will be discussed in detail in chapter-4. Chemical recycling results in

depolymerization which can be used to selectively recover monomers for polymerization

19

to reproduce virgin polymer. Chemical recycling process has the advantage of recovering

monomers which can be used to manufacture synthetic chemicals or reproduce polymers.

While it is a technically feasible process, it has not gained much economic interest in the

industry because the cost of recycled monomer is higher than the cost of petrochemical

feed stock. However, use of recycled feedstock contributes in reducing the use of fossil

fuels and potentially the volume of polymers in landfill and environment.

The initial step for this work was to select a method out of the available methods,

develop a feasible process at low temperatures, atmospheric pressures and uses

environmentally beneficial solvents for de-polymerization. As a first step a literature

survey was conducted of the following five chemical recycling methods: 1) methanolysis,

2) glycolysis, 3) hydrolysis, 4) ammonolysis and 5) amminolysis. These classifications are

based on the type of reagent used for depolymerization. Each of the processes are described

in detail describing various methods reported in literature. Finally, a feasible process which

resulted in TPA and EG, handle co-polyesters and PVC was selected.

2.2.1 Methanolysis

Methanolysis was first reported in the patents of the late 1950’s. This process was

industrially established by the prime manufacturers of PET including Hoechst, Eastman-

Kodak, DuPont and other small companies. Methanol was used as a reagent for solvolysis

of post-consumer PET waste at high temperatures and pressure with addition of catalyst in

an autoclave as shown in Fig 2.5. The products are two raw materials that were used in

20

synthesis of PET i.e. dimethyl terephthalate and ethylene glycol [26]. Note that current

commercial PET processes do not use DMT because of issue with color in resulting

polymer. Therefore, DMT must be converted to TPA using hydrolysis reaction which adds

cost to the process.

Fig 2.5. Reaction mechanism for methanolysis of PET using excess methanol

Methanolysis was performed at temperatures from 160-300℃ and pressure up to 7

MPa, typical transesterification catalysts like zinc acetate, magnesium acetate, cobalt

acetate were used along with arylsulfonic acid salts for degradation. However, the catalyst

21

must be deactivated after completion of reaction; otherwise, it results in loss of DMT with

possible transesterification with EG. Reaction mixture obtained was cooled and DMT was

precipitated and optionally distilled [26].

Fig 2-6. Schematic of methanolysis process

The flow chart of a typical methanolysis process is shown in Fig 2-6 which was

reported by Spychaj et al [26]. Both continuous and batch processes were feasible except

the fact that cost associated with continuous process are higher because raw materials must

be continuously supplied into a pressurized reactor. The same steps can be used for both

processes i.e. autoclave, crystallizer, centrifuge and distillation system to obtain DMT.

Reaction products of methanolysis are a complex mixture of glycol, alcohols and phthalate

derivatives because of which the conversion was limited to 90%. Substantial amounts of

22

ethylene glycol formed during degradation can be distilled and fed back to the system to

produce PET [26].

Methanolysis is an expensive process that tolerates higher levels of contamination

so that higher chemical processing costs are offset by low feed stock costs [26]. It is rather

sensitive to the presence of water and causes problems associated with catalyst poisoning

and formation of azeotropes. Usually costs of DMT recovery are higher than virgin DMT

[26].

New technologies developed by Eastman-Kodak and DuPont were economically

more advantageous than the conventional processes [26]. Process used by industries were

well established with around 99% conversion rates. For example, in 2003 Mitsubishi

Heavy Industries Ltd [27] was issued a patent that used supercritical and subcritical

methanolysis. A high reaction velocity PET depolymerization process was developed for

use with existing DMT hydrolysis technique for converting PET into TPA. Supercritical

methanolysis was conducted at a temperature of 300℃, pressure of 15 MPa with a reaction

time of 10 min. Subcritical methanolysis was conducted at a temperature of 230℃,

pressure of 6.5 MPa with a reaction time of 5 h. Neither process required use of catalyst.

Therefore, reaction was simplified and the separation of catalyst was not necessary [27].

After the depolymerization, the mixture of DMT, EG and excess methanol were sent to

lower boiling product separation and separated into DMT and EG/excess methanol, which

in turn were sent to further purification section to recover purified EG and methanol by

distillation. Purified DMT monomer was converted to TPA in the hydrolysis section. EG

was purified from EG/excess in a purification section. Finally, purified TPA and EG were

23

then delivered into existing PET resin production plants to form an ideal recycling system.

Purity of DMT was around 99.9% and EG was 99.0% [28]. Methanolysis process

recovered DMT which was hydrolyzed to produce TPA (Yields were not reported).

2.2.2 Glycolysis

Glycolysis is a de-polymerization process that occurs via transesterification

between PET ester groups and a diol, in the presence of a transesterification catalyst.

Typically, EG is used in excess to obtain monomer BHET as shown in Fig 2-7. In this

process ester linkages are broken to form hydroxyl terminals. Glycolysis process cannot

achieve complete de-polymerization of PET to BHET. With time, in addition to the

monomer, oligomers were also formed which makes recovery of BHET difficult [26].

Glycolysis was first reported in 1965 by MacDowell et al [29], from then it has

been the subject of interest for various researchers of PET to improve process that

minimizes use of catalyst, requires less amount of glycol and optimizes reaction parameters

such as time, temperature, PET/catalyst ratio or PET/glycol ratio [30]. Variables affecting

glycolysis were studied in detail and reported by Vaidya et al [30].

Frequently used glycols were ethylene glycol, propylene glycol, diethylene glycol,

di-propylene glycol, 1-4 butane diol etc. Typical catalysts used in glycolysis were

hydrotalcites, ionic liquids, enzyme’s, amines, alkoxides and metal salts of acetic acid.

Reaction proceeds under normal or high pressures at 180 - 250℃ in the presence of catalyst

for 3 – 8 hours depending on the glycol used. Reaction should be carried out under nitrogen

24

purge to avoid the degradation of polyols [26]. Reaction mechanism along with formation

of side products are shown in Fig 2-7.

Fig 2-7. Reaction mechanism for glycolysis of PET using excess ethylene glycol

25

BHET is a solid that cannot be easily purified using conventional process.

According to the report of Scheirset et al, it is purified using melt filtration under pressure

[31]. Recovered BHET can be easily mixed with the fresh BHET used in PET production

plants.

Glycolysis process can be characterized as: 1) solvent assisted glycolysis, 2) super

critical glycolysis, 3) Microwave-irradiated glycolysis, and 4) catalyzed glycolysis. Many

industries use glycolysis process to recycle the PET from in plant scrap according to

Simonaitis et al [32] as it provides BHET for mixing with fresh BHET in PET synthesis.

Glycolysis process [33] using sub and supercritical ethylene glycol produce high

yields of BHET from PET flake in less time; super critical reaction was performed at 450℃

and 15.3 MPa while subcritical reactions were carried out at 350℃ and 2.49 MPa or 300℃

and 11 MPa. Monomer yield in the form of BHET was observed to be high i.e. 94% for

the subcritical conditions. According to Imran et al this method is useful for processes

requiring high throughput for short reaction times [33]. Note that operating at elevated

temperatures and pressures increases operating costs and may not be feasible for thermally

sensitive compounds including FDCA.

Microwave irradiation assisted glycolysis was invented to effectively

recycle PET in short times [34, 35]. Microwave irradiation was used at various controlled

temperatures, 2 MPa pressure, 90 – 120 min reaction time and catalyst to obtain BHET

monomer and ethylene glycol as products along with diethylene glycol as degradation

products. Pingale et al says that the microwaves couples with molecules and promote rapid

but controllable rise of temperature based on two fundamental mechanisms i.e. dipole

26

rotation and ionic conduction. Comparing the results, the time required for the reaction is

reduced drastically but there was no change in the yield. Pingale et al. reported that the rate

of de-polymerization of amorphous PET was high compared to the crystalline PET[34].

Many catalysts like hydrotalcites, ionic liquids, enzymes, amines,

alkoxides, metal salts of acetic acid, zeolites, metal oxides impregnated on different forms

of silica nano and micro particles were studied by Al-sabagh et al [28]. The key challenge

according to Al-sabagh et al was to use these catalysts, as it is a difficult process to recover

the catalyst from oligomers/BHET mixture after depolymerization. Most used metal

catalyst was zinc acetate but because of toxic nature it is not preferred. Use of eco-friendly

metal catalysts such as sodium carbonate, sodium bicarbonate will be more acceptable

industrially, but the PET/catalyst ratio required during the reaction will be higher compared

to zinc acetate.

An interesting hybrid process using simultaneous glycolysis with EG and

hydrolysis with water in the presence of xylene and an emulsifier was reported by Guclu

et al [36]. Guclu et al carried the reactions between 170 and 190℃ and lower pressures

compared to usual methods. Xylene and ethylene glycol were immiscible solvents which

make this process unique, reaction products after extraction with boiling water yields water

soluble crystallizable fraction (WSCF) which has the product BHET and mono

hydroxyethyl terephthalate (MHT) and water insoluble fraction (WIF) has dimer. With an

increase in water content formation of MHT was increased to 47%. The product was

characterized by determining the acid value (AV) and hydroxyl value (HV). Based on the

literature reported methods, it seems that it’s better to use green solvents to reduce the

27

harmful effect on environment. Glycolysis method used several catalysts and high

temperature (>170℃ - 450℃) and pressures (2- 15.3 MPa) and recovers BHET which

should be hydrolyzed to recover TPA.

2.2.3 Hydrolysis

Hydrolysis process uses aqueous reaction medium that can be alkaline, acid

or neutral without use of catalyst or neutralizers [37-41]. This process was reported in

patents during the period of 1959-1962. Each bond cleavage of polymer chain in hydrolysis

process consumes one water molecule to form the carboxylic and hydroxyl functional

groups. The reaction operates at moderate temperatures and pressures to obtain terephthalic

acid and ethylene glycol monomers. Reaction time usually takes less than 30 minutes at

elevated temperatures and pressures. This method has not been broadly applied industrially

compared to glycolysis and methanolysis because of the high costs associated with

purification of TPA. However, majority of the industries are using the monomer TPA as

raw material for synthesis of PET because of its commercial availability. For this reason,

now-a-days hydrolysis has gained importance over other chemical recycling methods.

Alkaline hydrolysis was carried out using alkaline solutions like sodium

hydroxide, potassium hydroxide and ammonium hydroxide solutions. This process can

recycle highly contaminated PET waste stream. The reaction is shown in Fig 2-8, reactions

with sodium hydroxide solution as reaction medium were run at temperatures of 100-

250℃, 1-2 MPa pressure and 3-20 wt.% alkaline concentrations. Various catalysts were

used in this process to promote the rate of reaction [26]. TPA showed good solubility with

28

alkaline hydroxides, because it forms a salt i.e. TPA-Na+2 in NaOH solution. Addition of

a mineral acid reproduces the TPA as precipitate, which is shown in Fig 2-8.

Fig 2-8. Reaction mechanism for alkaline hydrolysis of PET using NaOH.

29

Patent for 18-wt% solution of NaOH to recycle PET was reported [42]. This method

uses PET/NaOH weight ratio of 1:20 at 100℃ for about 2 hours. Reaction mixture

undergoes acidification with a mineral acid to precipitate TPA from the solution.

Recovered TPA was filtered, rinsed and dried for further use. The filtrate containing

ethylene glycol is sent back to the process as reaction medium with addition of NaOH.

When EG concentration in the solution increases, vacuum distillation can be done for its

recovery.

A process to recover monomers from PET/Polyamide-6 blend was studied

by Lazarus et al [43] using sodium hydroxide and potassium hydroxide solutions.

Monomer yield for this process was studied for temperature range from 180-320℃ and

pressures of 150-350 PSI. It takes about 3-5 hours if the reaction proceeds with hydroxide

solutions of 3-10 wt.% for the reaction to complete. PET/alkaline weight ratios of 1:2 or

1:3 were described to be the most feasible on an industrial scale. Quantity of alkaline

solution depends on the number of polyester blends present in the PET waste. Final product

i.e. dicarboxylic acid was precipitated out by acidification. Caprolactam and EG obtained

were distilled or salted out using NaCl.

Commercial process to recover highly contaminated PET was used in USA

under the trade name UnPETTM, in France under trade name RECOPETTM. This process

uses a rotary kiln, condenser and a centrifuge which is a low capital investment process

compared to established processes like glycolysis and methanolysis. Reaction mixture

containing TPA and EG was allowed to heat up to 340℃ to distill off the EG, later TPA

30

was purified under normal pressures at 100℃. Impure organic compounds were converted

into CO2 and water [26].

Many interesting approaches to use alkaline hydrolysis for PET recycling

were studied [15, 37, 38, 44, 45]. PET which was pre-heated at elevated temperatures in

methyl benzoate, undergoes alkaline metal hydroxide (2 - 7 wt.%) hydrolysis for 30 min at

100℃ to yield TPA and benzoic acid. Another approach to convert green color PET to

colorless TPA and oxalic acid was reported [46]. This process uses high molar (27M)

NaOH solution, elevated temperatures of 250℃ and oxygen partial pressure as 5 MPa. A

process using dioxane as co-solvent in alcohol to recycle PET accelerated the reaction [47].

With the addition of dioxane reaction time was 40 min at 60℃ whereas without dioxane

reaction completes in 7 hours. Study on depolymerization using mixer-extruder at 100-

200℃ was reported with a conversion of 97% [48]. This process uses solid NaOH to

recycle PET and the EG formed was distilled off under reduced pressure eliminating the

cost to separate EG and water. Salt of TPA was obtained in powder form.

From the processes described above alkaline hydrolysis can be done at

temperatures below 100℃ and atmospheric pressure. Using this process polymer blends

were recycled. Therefore, this process can handle contaminated post-consumer PET waste

stream. This can be a simple and cost-effective process compared to methanolysis and

glycolysis [15].

Acid hydrolysis was carried out using sulfuric acid, nitric acid and

phosphoric acid [15, 46, 49]. Among these, H2SO4 was of interest because it facilitated

31

reaction at low temperatures and pressures. Chemical reaction is shown in Fig 2-9.

Reaction can be carried with <100℃ or without external heating supply. If 87 wt.% of

H2SO4 was added into the PET waste reaction takes place below 100℃ under atmospheric

pressure for about 30 minutes, post reaction mixture contains sodium salt of TPA and

ethylene glycol in viscous form. It is neutralized to pH~7 using a base mostly NaOH

solution. This neutral mixture contains EG, sodium hydroxide, TPA as sodium salt, sodium

sulphate and insoluble impurities which undergo first filtration to remove the impurities

[50]. Color in the filtrate can be removed using ion-exchange method. Later, filtrate was

acidified to a range of pH (0-3, 2.5-3, 6-6.5) using H2SO4 or HCl to re-precipitate TPA

with >99% purity followed by filtration, washing with water and drying. EG can be

recovered either by extraction [51] with organic solvents or by salting-out.

The drawbacks of high corrosivity and inorganic salt formation were tried

to minimize by Yoshika T et al using low concentration H2SO4 at 150℃ with use of dilute

solution of sulphuric acid ( <67 wt.%) [49]. In this process sulphuric acid can be recovered

and reused. 5 M NH4OH was used to neutralize post-reaction mixture and PET and TPA

salt were filtered off. Recovered sulphuric acid was used to precipitate out TPA. This

process requires large reactor volumes because of dilute solution which was not cost

effective. However, it reduces the corrosive effect, waste inorganic salts and aqueous

wastes. Another process was studied to obtain oxalic acid with 40% yield after 72 h [46]

which was more expensive than TPA and EG. Separation of EG from acid and corrosion

of the equipment were the two main drawbacks of acidic hydrolysis as mentioned [26].

32

Fig 2-9. Reaction mechanism for acid hydrolysis of PET using sulphuric acid

33

Neutral hydrolysis has gained prominence over the other two hydrolysis methods

over the last two decades[40, 41]. It lacks the primary draw backs of alkaline and acid

hydrolysis i.e. formation of organic salts and alkaline or acid waste, corrosion problems,

also it is environmentally beneficial. Chemical reaction was shown in Fig 2-10. Neutral

hydrolysis takes place at elevated temperatures of 200-300℃ and neutral pH. After the

reaction, pH will be 3.5-4.0 because of the formation of TPA monoglycol ester. PET in

molten state depolymerizes faster than the one in solid state. Hence, reaction temperature

of more than 245℃ would be more advantageous [52]. Commercial PET was made using

catalysts like zinc acetate, manganese acetate, calcium acetate and antimony oxide. The

presence of these catalysts increased the rate constant about 20% relative to the base system

and favors the neutral hydrolysis process [53].

A mono ester of glycol and terephthalic acid was formed between 95-100℃

which was soluble in the reaction mixture at this temperature. TPA was practically

insoluble at this temperature and can be separated easily. Monoester formation can be

controlled through adjusting process parameters. A five-step process was reported by

Tustin et al. to recover TPA and EG from PET. Initially PET was heated at 200-280℃,

post reaction mixture was cooled to 70-100℃, solid product was dried at 25-199℃. Dried

product was heated with water at 310-370℃ to obtain TPA, yield as not reported. Ethylene

glycol obtained from the first step was recovered using two stage distillation process [54].

Though the neutral hydrolysis lacks in primary drawbacks of the alkaline

and acid hydrolysis, main drawback is the mechanical impurities present in PET are left in

34

TPA which needs a sophisticated purification process to recover the pure TPA.

Fig 2-10. Reaction mechanism for neutral hydrolysis of PET using water

35

2.2.4 Ammonolysis

Ammonolysis process uses anhydrous ammonia to depolymerize PET and

form terephthalamide [26]. This was converted to terephthalic acid nitrile and further to

para-xylene diamine or 1,4- bis aminomethyl cyclohexane. Chemical reaction is shown in

Fig 2-11. Reaction was carried at about 1 MPa pressures and 120-180℃ temperature for

1-7 hours. Post-reaction mixture was filtered to collect the amide product, washed and dried

at 80℃. High yields ~90% are observed for the mentioned reaction conditions with 99%

purity. A low-pressure degradation method of ammonia in ethylene glycol medium was

reported.

Fig 2-11. Reaction mechanism for ammonolysis of PET using ammonia[26].

36

2.2.5 Amminolysis

Amminolysis process uses primary amines in aqueous phase, gaseous phase

for partial surface modification of PET fiber [26]. Amminolytic surface modification was

a selective degradation process which allows to control fiber morphology. Chemical

reaction is shown in Fig 2-12. In this process amorphous region in a semi crystalline

polymer was rapidly degraded whereas crystalline regions are stable to amines. Typical

amines used in amminolysis process were methylamine, ethylamine, butylamine,

ethanolamine, ethylene diamine, triethylene tetra amine. This process improves the dye

ability and other end use properties of the fibers.

Fig 2-12. Reaction mechanism for amminolysis of PET using amines[26].

37

From all these processes, methanolysis and glycolysis are used on commercial

scale, former process recovers the monomer DMT and the later process recovers BHET.

As TPA has become the common raw material in the production of PET, the monomer

formed after methanolysis and glycolysis must be hydrolyzed to recover TPA monomer.

This becomes a problem when co-polyesters are recycled, both the processes cannot

recover the required co-monomers without using hydrolysis as final step. Ammonolysis

and amminolysis processes have not gained much industrial interest because of the

products recovered after recycling i.e. monomers of amides and imides. Therefore, as

hydrolysis recovers TPA and EG from PET, considering all the drawbacks of other

processes alkaline hydrolysis was selected to perform the experiments throughout the

research and it is expected to selectively recover the co-monomers present in PETF20 i.e.

TPA and FDCA.

38

Chapter - 3

Experimental section

As discussed in chapter-2, several methods have been developed for chemical

recycling of PET waste. Hydrolysis is the most feasible method to recover the co-

monomers for co-polyesters [26]. The focus of the research was to screen hydrolysis

reaction of pure PET considering economic and environmental factors. To choose a better

process among alkaline, acid and neutral hydrolysis, based on the data provided on

hydrolysis in chapter-2, considering the drawbacks of all the three processes, alkaline

hydrolysis was selected. A method used by Karayiannis’s et al. was selected to perform

further reactions as it is a simple method and uses 1.1 M NaOH solution, temperatures

below 150℃ which is low compared to other methods which are reported in chapter-2.

PET flakes with PVC, co-monomers were hydrolyzed individually using this method to

precipitate the respective monomers and study their effect on PET conversion. This method

was extended to use with a model co-polyester of PET and PEF.

39

Materials and methods

3.1 Materials

Sodium hydroxide pellets (CAS grade), H2SO4 (certified, 72% (w/w), 24.0N, ±0.1N

(12M)), Whatman ™ filter paper (4, Qualitative, circles, 55mm Ø) were supplied by Fisher

Scientific. Sigma Aldrich supplied other materials and solvents. Distilled water was used

for reactions and washings.

3.1.a Poly (ethylene terephthalate) powder and flakes

Polyethylene terephthalate (Fig 3-2) pellets containing 2.5% IPA (LASER+® from

DAK Americas) were ground into powder (<250μm) using cryogenic grinder (IKA A10).

The PET powder was vacuum dried at 110⁰C to remove any

moisture present in the sample which can degrade the polymer

while extrusion. Films were processed from PET powder

using a single screw extruder (Randcastle, RC-0250

microtruder shown in Fig 3-1). The films were chopped into

6mm X 6mm flakes, washed with isopropyl alcohol followed

by water and dried under vacuum @ 80⁰C overnight. PET

powder and flakes were used to screen hydrolysis process.

Fig. 3-1. Randcastle microtruder # RC-0250

40

Fig 3-2. Structure of polyethylene terephthalate (PET)

3.1.b 20% Co-polyesters of poly (ethylene terephthalate) and poly (ethylene

furanoate) (PETF20) flakes

Lower molecular weight, 20% co-polyester (Fig 3-3) of PET with FDCA was

prepared in-house [20] was grounded into powder using a cryogenic grinder. The co-

polyester powder was solid stated (a method to increase molecular weight of the polymer)

in a vacuum oven at 210℃ to increase the molecular weight of PETF20 for 24 h. Solid

stated powder of PETF20 was processed into films using a microtruder shown in Fig 3-1.

The films were chopped into 6mm X 6mm flakes, washed with isopropyl alcohol followed

by water and dried under vacuum @ 80⁰C overnight.

Fig 3-3. Structure of Co-polyester of PET and PEF (PETF)

41

3.2 Methods

3.2.1 Experimental setup for chemical recycling of PET and PETF20 flakes

Parr bench top pressure reactor (100mL) shown in Fig 3-4 was used for high

temperature hydrolysis reactions of PET up to 150℃. The Parr reactor is equipped with a

mixer to ensure mixing in the solution.

Reactions at low temperatures (90℃) were performed in sealed glass vials to screen

the impact of reaction conditions on depolymerization of PETF20 and PET. Glass oil bath

shown in Fig 3-5 with a thermometer to measure the temperature of the oil, glass vials with

lid to hold the reaction mixture were used. Note that reaction mixture was not stirred in

glass vials.

Fig. 3-4. Parr bench top reactor

Fig. 3-5. Reaction setup using oil bath @ 90℃

42

3.2.2 Procedure for alkaline hydrolysis of PET

Hydrolysis of PET flakes and powder was conducted at 120⁰C and 150⁰C in the

Parr reactor using method reported in the literature by Karayiannis’s et al. [15]. NaOH

solution of 1.1 M was prepared by dissolving (0.033mol, 1.35g) NaOH pellets into 30ml

water. NaOH solution (30 mL) and PET powder/flakes (3 g, 0.0156mol) were added to the

reaction vessel and heated to reaction temperature of 120℃ or 150℃. The system pressure

was recorded from the reading of pressure gauge present on the reactor which changes

according to the vapor pressure of NaOH solution at reaction temperature (120℃ ~ 2.5 bar,

150℃~5 bar). Hydrolysis of PET was run for up to three hours. The TPA-Na+2 product

formed is soluble in NaOH solution with the EG. After a specified reaction time, the

reaction vessel was separated from the setup and allowed to cool for 5 min under running

water. Once the reaction mixture reached room temperature, it was neutralized to pH~6.5

with H2SO4 and vacuum filtered to remove unreacted PET solids. The resulting filtrate was

precipitated to form TPA and Na2SO4 salt by acidification with H2SO4 to a pH of 2.5.

Acidified mixture was vacuum filtered using Whatman ™ filter paper to recover monomer

TPA, with the ethylene glycol remaining in aqueous solution. TPA was washed with

methanol to remove any impurities, salts and trace amounts of EG. Solid TPA was dried

under vacuum at 80⁰C, weighed on an analytical balance to estimate the monomer molar

yield as shown in eq.3.3.1. The structure of the product was confirmed using NMR and

FTIR as discussed in section.3.3 [15]. Experiments were performed for time intervals from

43

0.5 minutes to 5 hours at temperatures from 90⁰C, 120⁰C and 150⁰C, as outlined in

Table.3.1.

Table 3.1: Reaction conditions for alkaline hydrolysis of PET in Parr system

Parameters Units Powder Flakes

Temperature °C 120, 150 90, 120, 150

Pressure Atm VP of solution @ reaction temperature

VP of solution @ reaction temperature

Reaction time Min 30-90 30-300

Polymer g 3 3

NaOH solution ml 30 30

3.2.2.a PET powder

Initial experiments were performed using powder form of PET to observe the

reaction kinetics as a function of particle size. Since polymer chain scission is dependent

on surface area, the particle size and shape play an important role during depolymerization.

According to this hypothesis, powder should take less time to depolymerize than polymer

flakes. The powder was hydrolyzed at 150⁰C for reaction times ranging from 0.5 to 1.5

hours at 30-minute intervals. Reactions were performed on the PET powder with respect

to the reaction conditions provided in Table 3.1.

44

3.2.2.b PET Flakes

Flakes are typically available form of PET used in recycling. Therefore, the bulk of

hydrolysis experiments used PET, PETF20 flakes. Typical industrial flake size ranges

from 4-18mm. Therefore, a representative size of 6mm X 6mm was used for conducting

the experiments. Since rate of depolymerization is dependent on particle size and flake

thickness (0.03-0.09 mm), the reaction conditions chosen range from 0.5 to 5 hours at

varying time intervals as shown in Table 3.1.

3.2.2.c Impact of impurities -PVC

To study the impact of major impurity which is PVC on PET depolymerization,

hydrolysis experiments were conducted at reaction conditions shown in Table.3.2 for times

ranging from 0.5 to 3 hours at 150°C and system pressure of 5 bar. In mechanical recycling,

as little as 50 ppm of PVC can cause damage to the recycled PET and degrades the RPET

properties [12]. Keeping this in mind to test the impact of PVC on chemical recycling of

PET, up to 5 wt.% PVC was added along with PET during hydrolysis. At elevated

temperatures and long times, PVC degrades and reacts with PET, our hypothesis was that

PVC would not have a major effect on PET recycling at low reaction times and

temperatures i.e. 150℃ and 180 min.

45

Table 3.2: Reaction conditions for alkaline hydrolysis of PET flake/PVC in Parr system

Parameters Units Conditions

Temperature °C 150

Pressure Atm 5 bar

Reaction time min 30-180

PET flake g 3

NaOH solution ml 30

PVC wt.% PVC /wt.% PET 1,3,5

3.2.2.d Impact of co-solvents

Reports and literature indicated that it takes 5 h to completely depolymerize PET

flakes at 150℃, which is energy consuming. Therefore, impact of co-solvents was

investigated to improve the rate of reaction. For the reaction to occur faster within the

polymer matrix, a co-solvent is required to penetrate into the matrix, swell the polymer and

facilitate chain scission of PET (see Fig 3-6). Solvent with Hansen solubility parameters

(δ) close to PET (20.5 MPa1/2) would be acceptable. A green solvent γ-Valero lactone

shown in Table. 3.3, with Hansen solubility parameters , δ=23.1 MPa1/2 [55] was selected

as a model co-solvent. This is because compounds with similar Hansen solubility

parameters are miscible with one another.

46

As discussed in Chapter-2, swelling of PET matrix is mass transfer limited, the

initial trials were conducted on PET flakes using co-solvent γ- Valero lactone which was

screened at reaction time 1.5 h for varying the mole% in a Parr stainless steel isolated

system at 150°C and 5 bar. Molar compositions were selected based on the outcomes of

GVL and used to screen other co-solvents with Hansen solubility parameters close to PET.

The effect of co-solvent on alkaline hydrolysis at 90℃ was studied for both PET and PETF

20 flakes using five co-solvents shown in Table. 3.3.

Fig 3-6. Sketch on surface reaction of PET with NaOH and solvent.

47

Table 3.3: co-solvents used for alkaline hydrolysis of PET and PETF 20

Solvent Structure Parameters Solubility

Gamma

Valero

Lactone

ρ – 1.0465 g/ml

BP – 270°C

δ-23.1 MPa1/2 [55]

38%

Gamma

Butyral

lactone

ρ – 1.13 g/ml

BP – 270°C

δ-26.2MPa1/2 [56]

60-70%

Ethylene

Glycol

Diacetate

ρ – 1.104 g/ml

BP – 187.2°C

δ-23.3MPa1/2 [56]

18-20%

Propylene

Glycol

diacetate

ρ – 1.05 g/ml

BP – 191°C

δ-18.4 MPa1/2 [57]

5-7%

Triglycerol

ρ – 1.3 g/ml

δp<18.3 MPa1/2

3-4%

48

Table 3.4: Reaction conditions for alkaline hydrolysis of PET and PETF 20 in oil bath

Parameters Units Conditions

Temperature °C 90

Pressure Atm Atmospheric pressure

Reaction time Days 3 days

PET flake g 1

NaOH solution ml 10

Co-solvent Mole % 1

It is not possible to observe the ongoing reaction in the stainless-steel Parr reactor.

Therefore, a simple system was set up using glass oil bath with a thermometer to measure

the temperature of the oil, a glass vial with lid. Considering the boiling point of water, a

reaction temperature of 90℃ was selected to eliminate the possibility of pressure buildup

in the vial. PET flakes and PETF 20 copolymer flakes were screened at 90℃ using sodium

hydroxide solutions and co-solvents were shown in Table.3.3 at conditions listed in

Table.3.4.

49

3.3 Analysis of results

3.3.a Quantitative analysis

The extent of reaction was quantitatively analyzed using % yield of TPA and conversion

of PET. The yield of TPA was determined by weighing the dry TPA obtained following

precipitation of filtrate a shown in Eq.3.3.1. Percentage conversion of PET flakes was

calculated using the flakes collected and dried after the reaction is complete. Yield

percentage and PET conversion were calculated using the equations [15].

TPA molar yield percent (Y%) =

ⅹ 100 (3.3.1)

% conversion of PET =

ⅹ 100 (3.3.2)

50

3.3.b Confirmation of Structure of products

Chemical structure of the monomers obtained from hydrolysis of PET and PETF20

flakes i.e. TPA and FDCA were analyzed. FTIR spectroscopy was used to give the

information based on the vibrational states of the specific bond C-O, C=O, C=C and –OH

stretching’s as shown in Table.3.5, spectrum will be discussed in detail in chapter-4 (FTS

4000 FTIR with microscope model UMA 600, Digi lab Excalibur series). 1H NMR and 13C

NMR (Table.3.6) (Bruker Avance III 600Mhz spectrometer with Cryoprobe and a Z

gradient) was used to determine the molecular structures of TPA as discussed in section-

4.1.6. The proton and carbon spectrum of the monomer mixture obtained after hydrolysis

of PETF20 was used to confirm the presence of both pure TPA and FDCA as discussed in

section-4.2.3. To check if the PET flake is crystallizing during the reaction, DSC (DSC

Equipment, Perkin-Elmer Diamond DSC) was used for thermal analysis where, PET flakes

were heated to 300℃ at a heating rate of 10℃/min. first heating ramp was used to calculate

the crystallinity of the flake. The DSC curves will be discussed in section-4.2.3

51

Table: 3.5. FTIR data of monomers obtained from hydrolysis of PET and PETF20

Polymer Structure Peak (cm-1) Assignment

Terephthalic acid

3065 C-H st

1280 C-O st

1676 C=O st

1136-1020 C-C st

Isophthalic Acid

2300-3300 Carboxyl acid

1698 C=O

1486, 1612 C=C

1287 C-O

720 Oop meta

subst

2,5-Furan

dicarboxylic acid

3120 C-H st

1580 C=C st

52

Table: 3.6. NMR data of the monomers obtained from hydrolysis of PET and PETF20.

Structures Proton peaks (ppm) Carbon peaks (ppm)

Terephthalic Acid (TPA)

8.03

Aromatic ring 129.5

C-C

attachment 134.8

-COOH 166.7

Isophthalic acid (IPA)

Protons of meta

connected benzene

ring: 8.47, 8.16, 7.63

-COOH 166.58

Aromatic ring

[58]

133.32

131.28

130.02

129.02

2,5-furan dicarboxylic acid (FDCA)

7.2

Furan ring 118.48

C-C

attachment 147.07

-COOH 158.9

53

Chapter - 4

Results and discussion

The focus of this thesis was to perform alkaline hydrolysis of a co-polyester of 80%

PET and 20% PEF (PETF20). Alkaline hydrolysis reaction was chosen for

depolymerization of PET and its co-polyesters because it can tolerate highly contaminated

waste [15] and can handle major impurities in the PET waste stream including PVC [59].

Sodium hydroxide solution was used as reaction medium to perform depolymerization

reactions. As described in chapter -2, alkaline hydrolysis results in formation of TPA and

EG which can be converted back to PET. This is of interest to our work, as it allows the

potential to isolate co-monomers or value-added compounds from co-polyesters.

Phase-I of the work focused on the hydrolysis of PET flake at 120℃ and 150℃

using 1.1 M NaOH solution. Several experiments were performed to evaluate the impact

of time, temperature and PVC on PET to confirm that our results were in reasonable

agreement with the literature. The impact of a green co-solvent (γ-Valero lactone (GVL))

on the conversion of PET flakes was studied.

Phase two of the project focused on alkaline hydrolysis of PETF20 co-polyester

using the same method to potentially prove that chemical recycling can selectively recover

54

co-monomers. In addition, effect of several co-solvents on alkaline hydrolysis of both PET

and PETF20 flakes was studied to improve the yield of the monomer. All the experiments

were replicated at least twice.

4.0 Reaction mechanism of alkaline hydrolysis of PET with NaOH

Chemical degradation of PET typically starts with scission of polymer chains,

which are subsequently depolymerized to oligomers and further to monomers. This

requires that reactants access the polymer chain, therefore both surface area of the polymer

and reaction kinetics affect the rate of conversion. Since the polymer is insoluble in the

reaction media, the reaction occurs in the near surface layer and surface area is critical to

determining reaction rate as shown in chapter 3, Fig 3-6. Swelling of the polymer matrix

is a slow process as the alkaline solution has limited solubility in PET. In the reaction, the

metal catalyst (in this case sodium cation) activates the carbonyl group and forms a

coordination complex, this reduces the electron density and facilitates the nucleophilic

attack of hydroxyl group (OH-) on positively polarized carbon atoms. This results in the

cleavage of the polymer chains, which gives rise to the disodium salt of monomer TPA as

shown in Fig 4.1. PET samples with greater surface area per volume react faster with the

aqueous reaction medium. Disodium salt of monomer formed would be dissolved in the

aqueous reaction medium to which sulphuric acid was added. The H+ ions react with the

carbonyl oxygen and the SO42- reacts with the sodium attached to the carbonyl oxygen to

produce terephthalic acid (TPA) and the sodium sulphate. Precipitated TPA can be

recovered via filtration. The residual sodium sulphate was dissolved in the filtrate. In case

55

of co-polyesters, the diacids formed can be selectively recovered from solution and

purified.

Fig 4.1: Reaction mechanism of alkaline hydrolysis of PET with NaOH solution.

56

4.1 Hydrolysis of Polyethylene terephthalate (PET)

4.1.1 Effect of time

Initial studies focused on investigation of the conversion of PET flakes during

alkaline hydrolysis as a function of time. Separate reactions were conducted at each time

interval i.e. 15 min, 30 min, 60 min, 90 min, 120 min, 150 min, 180 min, 240 min and 300

min) to observe the reaction kinetics of PET in 1.1 M NaOH solution at 150℃. After each

experiment, the reaction mixture was precipitated using known amounts of sulphuric acid

to recover the monomer TPA. As the PET used for this work was copolymer with 2.5%

isophthalic acid (IPA), it was expected that the recovered monomer would contain trace

amounts of IPA.

A plot of percentage yield of TPA and conversion of PET flakes during alkaline

hydrolysis as function of time up to 300 minutes is shown in Fig 4-2. The yield of TPA is

the ratio of TPA recovered to mass of TPA available at complete conversion of PET. The

yields of TPA and conversions of PET were calculated using the equations 3.3.1 and 3.3.2.

Yield % of TPA were approximately equal to the PET conversion which is consistent with

expectations for case with limited secondary reactions. Percentage yield increased with

increasing reaction time from 15 min to 300 min i.e. 40% to 89.9% which is the same case

with conversions of PET. Due to the solubility limitation of water in PET, the conversion

of PET flake in the first 10 min was very low as there is not enough time for the alkaline

medium to swell the surface of PET flake. But the bulk of conversion of PET to TPA and

EG occurred within the first 30 minutes, with slight increase at longer reaction times. The

57

% crystallinity of the flakes before and after alkaline hydrolysis reactions were measured

using differential scanning calorimetry which will be discussed in section 4.2.2. There is a

scope of improving the rate of conversion of PET flake by reducing the crystallinity of the

flake during the reaction. Reasonable conversions were observed between 60 – 180

minutes. Based on this data, further experiments to study the impact of temperature and

impurities were conducted in this time range.

Fig 4-2. Effect of time on PET hydrolysis of flakes at 150°C in 1.1M sodium hydroxide

solution, where ♦ is % TPA yield and ■ % PET conversion.

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300

Perc

enta

ge (%

)

Reaction time (minutes)

58

Fig 4-3. Unconverted residue (from left) A) 90min, B) 120min, C) 150min, D) 180min, E)

240min and F) 300min.

The experiments performed to study the impact of time exhibited similar results

observed in the literature [15] where PET conversion increased up to 89% with increasing

reaction time up to 6 hours at 150°C.

Fig 4-3 shows the PET residue following reaction for 90 min, 120 min, 150 min,

180 min and monomer at 240 min and 300 min from left to right at 150°C. Reaction at 90,

120, 150 and 180 minutes resulted in conversions below 79.4% as shown in Fig 4-2, the

disodium salt of monomer formed was dissolved in the solution, unreacted PET was ] in

the flake form. Unreacted PET was collected and dried below 80℃ to determine the %

conversion and % crystallinity. Reactions conducted for more than 240 minutes resulted in

complete depolymerization of PET flakes and the product formed was dissolved in the

solution which was precipitated to recover the monomer as shown in the Fig 4-3.

A B C D E F

59

4.1.2 Impact of temperature on alkaline hydrolysis of PET

PET Powders

PET in powder form of 250μm diameter was hydrolyzed using sodium hydroxide solution

at temperatures 120℃ and 150℃ for 30, 60 and 90 minutes. As expected, the PET

conversion was low at 120℃ compared to the conversion at 150℃ over full time range.

PET powder exhibited interesting results with a conversion of 98% for 90 minutes at 150℃

as shown in Fig 4-4.

Fig 4-4. Effect of temperature and time on hydrolysis of PET powder @ ■ 120℃, ♦ 150℃

for 30, 60 and 90 minutes in Parr reactor. a) % PET conversion, b) % TPA yield.

0

20

40

60

80

100

0 50 100

% P

ET

Con

vers

ion

Time (min)

0

20

40

60

80

100

0 50 100

% T

PA y

ield

Time (min)

60

PET Flakes (6mm X 6mm)

PET in flake form was hydrolyzed at 90℃, 120℃ for up to 90 minutes and 150℃

for a time range of 30 – 300 minutes to study the kinetics as shown in Fig 4-5 and Fig 4-2.

Rate of depolymerization was very slow at 90℃, a conversion of 21% was observed at

120℃ and 90 minutes. However, reaction at 150℃ exhibited good results within 30

minutes. The rate of de-polymerization increased with increase in temperature as shown in

Fig 4-4 and Fig 4-5

Fig 4-5 Effect of temperature and time on hydrolysis of PET flake @ ♦ 90℃, ■ 120℃ and

▲ 150℃ for 30, 60 and 90 minutes in Parr reactor. A) % PET conversion, b) % TPA yield.

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90

% C

onve

rsio

n

Time (min)

0102030405060708090

100

0 10 20 30 40 50 60 70 80 90

% T

PA Y

ield

Time (min)

61

Fig 4-6 Effect of temperature and time on hydrolysis of ■ PET powder and ♦ PET flakes

at 90℃, 120℃ and 150℃ for 30, 60 and 90 minutes in the Parr reactor.

Hydrolysis of PET powder exhibited higher conversions i.e. around 98 % when

compared to PET flakes i.e. 72 % at 90 minutes as shown in Fig 4-6. This confirms the

importance of particle size, shape and surface area per volume during the depolymerization

process. As discussed in detail below, the much smaller spherical powder exhibited much

faster kinetics than the PET flakes which is consistent with surface dependent reaction.

The reaction is dependent on surface area and temperature. To discuss the surface

area dependency on the reaction, surface area to volume ratio of powder with < 0.25 μm Ø

and flakes with length*width*height of 6mm*6mm*0.09mm were estimated. Depending

on the shape of the material, the surface area to volume ratio of powder was 38:1 and flake

is 23:1. Based on the theory, small particles with larger surface area exhibit improved

reaction kinetics. Therefore, PET powder exhibited high conversions compared to flakes.

0

20

40

60

80

100

0 50 100

% P

ET

Con

vers

ion

Time (minutes)

0

20

40

60

80

100

0 50 100

% T

PA Y

ield

Time (minutes)

62

Though the powder was crystallized during the reaction like flakes, powder exhibited high

conversion because of its large surface area and the fact that the surface area was increasing

as the reaction progressed. Therefore, it is confirmed that size and shape of PET affect

reaction kinetics along with temperature and reaction time.

To confirm the chemical structure of the recovered monomer and its purity, 1H NMR

and 13C NMR were performed. Proton and carbon spectrum confirmed the recovered

monomer has TPA and IPA. These results will be discussed in more detail in section 4.1.6.

4.1.3 Kinetic model

A simple model derived by Karayiannis’s et al. [15] was modified to predict the

conversion of PET and determine the rate constant. As the monomer TPA formed during

the reaction was dissolved in the solution, reaction was considered irreversible. Since mass

transfer into the polyester matrix must occur prior to the chemical reaction, derivation of

the mathematical model was complicated. If the reaction takes place in the swollen near

surface of the PET flake and alkaline hydrolysis of esters can be considered first order in

the ester and alkaline concentration, a surface reaction model was derived using method

developed by Karayiannis’s et al.

The reaction rate equation can be expressed as:

= -kAsCACB ............................................................................................................ (4.2)

63

Where k is the rate constant ((dm3)/(mol.cm2.min), NA is the number of moles of ester

bonds remaining after reaction (mol/dm3), t is the reaction time (min), As is the surface area

of the PET flake (cm2), and CA and CB are the ester and alkali concentrations in solution

(mol/dm3).

On the assumption that reaction takes place on the surface of the flake, CA can be

considered constant for certain period. CB0 is considered as the initial concentration of the

alkaline solution, which is constant because excess OH- ions are present during reaction.

The number of moles of reactant (NA) and conversion (X) are defined below:

NA = NA0 (1-X) ............................................................................................................... (4.3)

X= .................................................................................................................... (4.4)

The rate expression can be expressed in terms of conversion combining eq.4.2-4.4.

= CB0 (1-X) ......................................................................................................... (4.5)

The model assumes that the concentration of active ester groups is proportional to area.

therefore, the surface area is (As) is directly proportional to the degree of unreacted PET.

Therefore, As = A0(1-X)b, where b is a constant (0 ≤ b ≤ 1) [15]. If the surface area of the

PET flake is constant during the reaction and PET depolymerization is lamellar, then b =

0. For these experiments, the PET flakes of even size with dimensions 6mm*6mm*0.09mm

64

were used, the surface area will not change in a substantive with conversion as shown in

Fig 3-6. Therefore, b=0 was considered as a best fit for flakes.

= k CB0 (1-X)(b+1) = = k CB0 (1-X) ............................................................... (4.6)

Integrating the equation (4.6) with limits X=0 and t=0:

Ln (1-X) = k1 t .............................................................................................................. (4.7)

Where

k1 = k CB0 ................................................................................................................... (4.8)

A plot of ln(1-X) vs t would be linear if surface area was independent of conversion as

expected for the PET flakes. The reaction kinetics for PET in NaOH solution as shown in

Fig 4-5 are plotted in terms of % conversion using eq-4.7 in Fig 4-7. Note that the data at

low times for conversions were very low and are within measurement error as shown in

Fig 4-5. Therefore, model was fit to the data in the linear region to find k. Rate constants

(k1) were calculated for each temperature (90, 120 and 150℃) using the slopes of each line

from the Fig 4-5. The model fit is linear for all temperatures and the experimental values

are in good agreement with the theory from Fig 4-5 and Fig 4-7.

65

Table.4.1: Reaction rate constants of PET flakes when depolymerized in 1.1M NaOH

Temperature (℃) Rate constant (K) [*10-5 ((dm3)/(mol.cm2.min)]

90 4.3

120 13.6

150 25.9

Fig 4-7. Plot of ln(1-X) vs t for data of PET flakes in 1.M NaOH solution at ♦ 150℃, ▲

120℃ and ■ 90℃ at a time range of 0-90 minutes.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0 20 40 60 80 100

-LN

(1-X

)

TIME (MIN)

150 120 90

66

Arrhenius equation is expressed as;

K = A * e(-Ea/RT) ............................................................................................................ (4.9)

Where K is the rate coefficient, A is Arrhenius constant, Ea is the activation energy, R is

the universal gas constant and T is the temperature in kelvin.

Fig 4-8 Arrhenius plot of the apparent kinetic rate constant for the aqueous sodium

hydroxide solution.

1/T (K-1)

67

The rate constants were fit to Arrhenius equation and plotted as apparent rate constants

(K1) vs 1/T as shown in Fig 4-8. The rate constants fall into a straight line and their value

increases with increase in temperate as shown in Table 4.1, which agree with the Arrhenius

equation 4.9, the calculated activation energy (Ea) was 40.16 KJ/ mol. k. As the temperature

chosen were 90℃, 120℃ and 150℃ and molarity of NaOH solution is 1.1M, the activation

energies were slightly lower than the reported activation energies i.e. 69 KJ/mol for

hydrolysis reactions at 120℃, 140℃ and 160℃ in 1-4 M KOH solution [60], 75.4 – 92.1

KJ/mol [39] in a hydrochloric acid solution at 150℃, 170℃ and 190℃.

68

4.1.4 Effect of impurities

After studying and understanding the impact of temperature and time on PET flakes, focus

was shifted to the impact of a common impurity that is a challenge for mechanical

recycling. The presence of as little as 50 ppm of polyvinyl chloride (PVC) in a PET waste

stream is a major concern as it can damage the recycled stream. PVC can form hydrochloric

acid that break down the PET resin both physically and chemically causing the PET to

become brittle and yellowish in color. Also, PVC when present in PET stream is hard to

separate using density flotation techniques because of similar densities of these polymers.

Alkaline hydrolysis of PET flakes was performed in the presence of PVC at 1, 3 and 5

wt.% relative to wt.% of PET at 150℃ for 180 minutes. The results for PET conversion

and yield of TPA during alkaline hydrolysis in the presence of PVC confirmed that the

PVC as impurity up to 5% did not affect PET de-polymerization (see Fig 4-9). It did not

show any effect on kinetics of alkaline hydrolysis of PET and no by products were formed

because of de-chlorination. As discussed in section 4.1.6 the TPA and EG were recovered

with trace amounts of IPA with no byproducts or PVC degradation products.

69

Fig 4-9. Effect of PVC on PET hydrolysis at 150°C for 180 minutes, ♦ % TPA yield, ■ % PET conversion in Parr reactor.

A similar study was done by Kumagai et al. [59] using PVC coated PET

fiber to recover PVC and monomers simultaneously using alkaline hydrolysis. According

to his report, TPA and EG were recovered and PVC was separated as residue along with

unconverted PET. With increase in reaction time de-chlorination had a noticeable effect in

the method used by Kumagai et al. It requires 48 h to obtain 1% de-chlorination rate at

120℃ and 24 h to obtain 9% de-chlorination rate at 150℃.

50556065707580859095

100

0 1 2 3 4 5

Per

cen

tage

(%

)

% PVC

70

Fig 4-10. Comparison of percentage yield of TPA from ♦ PET flakes vs ■ PET flake+5%

PVC at 150°C at different times ranging from 30 min-180 min in Parr reactor.

Present experiment at 150℃ for 180 min did not have de-chlorination as the reaction time

was less. It requires some time for hydroxide ion (OH-) to penetrate into the PVC matrix

and diffuse chloride ion (Cl-) from the bulk PVC [59]. As the reaction time was short, OH-

did not degrade PVC significantly and had no effect on rate of PET depolymerization. The

reaction of PET flakes in the presence of 5 wt.% PVC was performed for the times from

30 min to 180 min at 150℃ and the kinetics are plotted in Fig 4-10. It shows the comparison

of percentage yield of PET flakes and PET flakes + 5 wt.% PVC impurity. Observed

percentage yield was consistent for both PET flakes and PET flakes with 5 wt.% PVC

impurity because of less reaction times and temperatures as opposed to the high reaction

conditions used in literature [59]. No trace of PVC was identified in the recovered

0102030405060708090

100

0 50 100 150 200

% T

PA Y

ield

Time (min)

71

monomer, which was confirmed by FTIR and NMR analysis which will be discussed later

in section 4.1.6

4.1.5 Effect of green solvent γ-Valero Lactone (GVL)

Based on the kinetic study of PET flakes using NaOH solution as the reaction

medium and literature reports indicate that diffusion of reaction medium into the flake is

important rate limiting step to hydrolysis of PET to TPA and EG. A key goal of this work

was to investigate the use of co-solvents on reaction rate. Co-solvent may accelerate the

diffusion rate or expand layer in which reaction occurs by swelling the polymer and allow

the sodium hydroxide solution to break the bonds. To study the impact of a co-solvent on

the depolymerization process, a model green solvent γ-Valero lactone (GVL), was selected

because it has been identified as good solvent for polymers [61]. The effect of GVL on the

alkaline hydrolysis of PET was investigated for concentrations from 0.5 to 10 mole% GVL

relative to NaOH solution. The reaction conditions used for this screening were 150℃ and

90 min.

Eq-4.1

72

Addition of GVL at concentrations from 0.5 – 2.5 mole% resulted in an increase in

the monomer yield compared to the base NaOH solution. Further increasing GVL

concentration in the NaOH solution resulted in lower monomer yields compared to the base

NaOH solution as shown in Fig 4-11.

Fig 4-11. Hydrolysis of PET Flakes with GVL at different molar compositions (0.5-10

mole%) at 150℃ and 90 min.

The increase in PET conversion and yield of TPA might be because of two reasons:

1) pH of the solution remained constant up to addition of 2.5 mole% as the ability of the

buffer to resist changes to the addition of acid or alkali was not crossed. 2) GVL increased

swelling of the PET matrix, which was offset by the crystallization of PET.

0

10

20

30

40

50

60

70

80

90

100

0 0.5 1 2.5 5 10

% T

PA Y

ield

Mole % GVL in NaOH solution

73

When 5-mole% GVL was added, the pH dropped to 12, while 10- mole% GVL

resulted in a pH drop to 7.5 as shown in Table.4.2. The GVL at 10 mole% composition

reacted with NaOH solution resulting in formation of a white substance in noticeable

quantity according to eq.4-1 [62]. According to Wong et al the white substance formed was

the salt of 4-hydroxyvalarate (4-HVA) because of the ring opening reaction of GVL with

NaOH [62]. The OH- and Na+2 ions present in the solution reacts with the GVL resulting

in the ring opening and reduces the concentration of the NaOH solution by forming the salt

of 4-HVA [62]. Because of this the pH of the NaOH solution was reduced from 13 – 7.5.

This solution was added as reaction medium to the PET flakes, reaction mixture after the

reaction at 150℃ for 90 min was observed to have opaque PET flakes resulting in 0.04%

TPA yield. The rate of hydrolysis is proportional to the concentration of alkaline solution.

Addition of 10 mole% GVL to the NaOH solution reduced the concentration of the OH-

ions in the solution which, resulted in lower conversions of PET flakes. The pH remained

constant at low concentration of GVL from a range of 0.5 – 2.5 mole%, as these

compositions are below the buffer strength limit of the NaOH solution. This avoided the

formation of secondary products like 4-HVA and improved the swelling of polymer matrix

resulting in high yields compared to base NaOH solution.

Exposure of PET to co-solvent can result in solvent induced crystallization at

surface [63]. This crystallization may reduce swelling and negatively affect the surface

reaction if it is excessive. Therefore, the % crystallinity of PET residue (taken after 90

minutes from each reaction media) was determined by differential scanning calorimetry

which is discussed in detail in section 4.2.2. Percentage crystallinity of PET flakes after

74

hydrolysis reaction with and without addition of GVL are shown in the Table 4.2. This

indicates that PET flakes taken from reactions after addition of GVL ≤ 2.5 mole% have

low crystallinity compared to the flake taken from the reaction medium of the base NaOH

solution. Therefore, adding GVL increased the swelling of PET matrix improving the rate

of depolymerization of the PET flake. Whereas, GVL ≥ 5 mole% there was an increase in

the crystallinity of PET flake during the reaction due to surface induced crystallization and

resists depolymerization rate.

Table 4.2. Data of hydrolysis reaction using GVL as co-solvent at 150℃ and 90 min in

NaOH solution.

Mole% GVL in

NaOH solution

pH of the

solution

% TPA Yield % conversion

of PET

% crystallinity

of PET flake

after reaction

0 13 73 71 26.8

0.5 13 92.9 85.67 19.02

1.0 13 88.0 77 20.21

2.5 13 80.2 69 26.00

5.0 12-13 54.7 49.33 38.05

10 7.5 1.5 0 47.01

Crystallinity of fresh PET flake before reaction was 6.5%

75

Observed percentage yield at 0.5, 1 mole% of GVL as shown in Fig 4-11 was 92% and

87% respectively which was 21% greater than the yield of TPA obtained from base NaOH

solution i.e. 71%.

4.1.6 Characterization of monomer TPA

FTIR and NMR was used to analyze the precipitated product following filtration

of reaction mixture. FTIR confirmed the presence of functional groups consistent with

TPA and IPA. In addition, traces of BHET, which is an intermediate degradation

product, were not observed. NMR was used to qualitatively confirm the presence of co-

monomer and potential TPA vs BHET.

4.1.6.a FTIR spectroscopy

Fig 4-12. Infrared spectroscopy of precipitate monomer TPA (- - -) and IPA (-----).

76

The FTIR spectra of the precipitate is shown in Fig 4-12. The absorptions at 3065, 1676,

1280 cm-1 are typical for aromatic dicarboxylic acids (C-H, C=O, C-O). The vibrations

specific to 1,4-distributed benzene ring are at 1136, 1020 cm-1. The absorptions at 2300-

3300 are typical for carboxylic acid, 1698, 1486 and 1612, 1287, 720 cm-1 are related to

the co-polymer Isophthalic acid (IPA) [58]. The absorptions peaks for IPA and TPA are

similar because of the similarity in the structure. Absorption related to BHET oligomer

(3400, 3000-2800, 1750 and 1100 cm-1 indicates the –OH, C-H, C=O and C-O

stretching’s) and PVC (1720 cm-1, 1190 cm-1 indicating C=O, C-O) were not present in

the precipitate. FTIR gives the qualitative proof that the recovered precipitate has TPA and

IPA monomers.

77

4.1.6.b. Solution Nuclear Magnetic Resonance Spectroscopy

a) 1H NMR of precipitate from hydrolysis of PET at 150℃ and 90 min in 1.1M NaOH.

78

b) 13 C NMR of precipitate from hydrolysis using I)1.1.25 M NaOH solution, II)5% PVC

as impurity in 1.1 M NaOH solution and III) 1 mole% GVL in 1.1 M NaOH solution.

Fig 4-13. Nuclear Magnetic resonance analysis of recovered monomer from PET flakes

and PET flakes+5%PVC impurity at 180 minutes and 150°C using methyl sulfoxide

99.5% purity with d6.

The composition of precipitate obtained from hydrolysis of PET flake, PET flake+PVC

and PET flake in presence of co-solvents were analyzed using 1H NMR and 13 C NMR to

79

detect the presence of impurities in the product. NMR of the precipitate are consistent with

NMR for reference TPA spectrum (Appendix-A). 1H NMR for hydrolysis product for pure

PET at 150℃ is illustrated in the Fig 4-13.a. The signal at 8.03 ppm (s, 4H) (peak a)

indicates the presence of four phenyl protons. The signal at 8.47 ppm (peak b), 8.16 ppm

(peak c) and 7.63 ppm (peak d) indicates the presence of protons of meta connected

benzene ring of IPA, which was used as a co-monomer along with TPA during the

production of PET (2.5% IPA/97.5% TPA). Triplets at 7.6 ppm (peak d) corresponds to

the spin-spin splitting of the protons [64]. Consider a proton which has two neighboring

protons, if the magnetic field of the neighboring protons was in the direction or opposite to

the external magnetic field, depending on the energy difference between the external and

effective magnetic fields, chemical shift of the proton will either increase, decrease or

remains same appearing as the split peaks in the spectrum.

Fig 4-13.c. Possibility of spin- spin splitting of neighboring protons.

80

There are three possibilities for the alignment of neighboring protons with the external

magnetic field. From Fig 4-13.c, first possibility illustrates that both the neighboring

protons would be in the direction of external magnetic field, this adds up energy to the

external magnetic field increasing the effective magnetic field because of the energy

difference and results in increase in the chemical shift of the proton. The second possibility

illustrates that the two neighboring protons may align in different directions, which makes

external magnetic field equal to the effective magnetic field and the chemical shift stays in

the expected position. Third possibility illustrates that the protons would be in opposite

direction to the external magnetic field, which decreases the effective magnetic field

resulting in lower energy difference causing decrease in the chemical shift. Overall, triplets

are formed one for each spin [64]. Therefore, the H NMR is consistent with presence of

both IPA and TPA in the polymer and the much larger concentration of the TPA.

13 C NMR spectrum for the products are illustrated in Fig 4-13.b. The peaks at 129.5

ppm (peak e) indicate the presence of unsubstituted carbons of the aromatic ring, peak at

134.8 ppm (peak f) indicates the presence of the carbons of the aromatic ring to which the

carbonyl groups are attached, signal at 166.7 ppm (peak g) represents the carbonyl

resonances (COOH group). This was same for both IPA and TPA. Examining the NMR

spectrum, the presence of PVC (peaks at 3.34 ppm, 4.4 ppm, 47 ppm, 57 ppm) or impurities

formed because of the presence of co-solvent were not observed and there is no noticeable

change to TPA structure. This confirms that PVC was not present in the recovered

monomer and conversion of PET was not affected with presence of PVC. BHET was not

present in the precipitate as the peaks corresponding to BHET were not present in the

81

proton (8.12 ppm, 4.3 ppm, 3.7 ppm, 4.9 ppm) or carbon NMR (58.9 ppm, 67.06 ppm,

129.5 ppm, 133.7 ppm and 165.1 ppm). Impurities were not observed in either FTIR or

NMR analysis of the precipitate obtained from experiments conducted at reaction

temperatures 90°C, 120℃ and 150°C.

Therefore, alkaline hydrolysis in the presence of co-solvents was successfully applied to

depolymerization of PET. The conversion of PET at 150℃ and 300 min was 89.9% and

there was no PVC/co-solvent present in the TPA product. The next section will focus on

applying alkaline hydrolysis to co-polyester of PET/PEF with emphasis on screening co-

solvents.

4.2 Hydrolysis of co-polyesters of PET and PEF

4.2.1 PET vs PETF20 flakes

There is increasing interest in incorporating co-monomers in PET to moderate the

overall properties. For example, FDCA is a bio-based monomer that can be used as diacid

in production of furan analogue of PET known as PEF. The PEF exhibits a 10-fold lower

oxygen permeability than PET which is attractive for packaging applications but is

available in limited volumes at high cost. Copolymer of PET and PEF would provide a

bridge to transition to bio-sourced polyester. While copolymers exhibit improved

properties relative to the pure PET, mechanical recycling is limited to copolymers of PET

with less than 10% co-monomers [65, 66].

82

The alkaline hydrolysis of model co-polyester of 20% FDCA and 80% TPA

(PETF20) was investigated using the same experimental conditions for PET. Alkaline

hydrolysis of co-polyesters of PET and PEF have not been reported in the literature. Since

a 20% co-polyester was used, both the diacids TPA and FDCA were expected to be present

in the precipitated monomer. A modified reaction system was used for screening the

available samples and observation of polymer flakes during the experiment. This allowed

observation of transition from clear to opaque films that indicate the onset of solvent

induced crystallization. The simple system discussed in chapter-3 consisting of oil bath,

glass vails, holder and thermometer was used for reactions performed at 90℃ to avoid high

pressure in vials.

PETF20 flakes were subjected to alkaline hydrolysis at 90°C for 3 days using 1.1

M NaOH solution in a simple oil bath setup shown in Fig 3-5. After 3 days the conversion

of PET flakes and PETF20 flakes and the yield of diacid (TPA+FDCA) as shown in Fig 4-

14 were 42% and 88% respectively indicating a large difference in reactions of the co-

polyesters.

83

Fig 4-14. % Conversion ■ and % diacid Yield ▲ of PET vs PETF20 flake after alkaline

hydrolysis with 1.1M NaOH solution for 3 days at 90℃.

The conversion of PETF20 flake is higher than PET flake in NaOH solution. % conversion

and yield of PET and PETF20 are shown in Fig 4-14. Possible reasons for the high

conversions of PETF20 are: 1) PET has a benzene ring and PETF20 has both benzene and

furan rings, presence of oxygen in the structure of furan increases the solubility of PETF20

in ethylene glycol and water relative to the benzene of TPA. 2) PETF20 has low %

crystallinity (fresh flake - 4.5 %, reacted flake – 24.3) than the PET flake (fresh flake - 6.5

%, reacted flake – 26.8) which will be discussed in detail in section 4.2.3. 3) Glass

transition temperature of PETF20 is 77.7℃ which is lower than the PET flake Tg= 87.2℃,

0

10

20

30

40

50

60

70

80

90

100

PET PETF 20

Per

ecnt

age

(%)

Polymers

84

which means PETF20 will be in rubbery state and PET will be in the glassy state. This

allows the reaction medium to react fast with PETF20 than PET. PET flakes before and

after the reaction were collected, which were shown in Fig 4-15. Surface of PET flakes

after reaction at 90℃, 120℃ and 150℃ in NaOH solution, with 5% and 10% GVL in

NaOH solution at 150℃ are shown in Fig 4-15A. Comparison of surface area of fresh PET

flake with flakes in 1.0 mole% EGDA, PGDA, GVL, GBL and triglycerol in NaOH

solution for 3 days at 90℃ is shown in Fig 4-15B. Comparison of surface area of fresh

PETF20 flake in 1.0 mole% GVL, GBL and triglycerol in NaOH solution for 3 days at

90℃ is shown in Fig.4-15C. It can be understood that PET has the same surface area after

reaction but PETF20 almost degraded after 3 days at 90℃. All these factors favored the

high conversions of PETF20 at 90℃.

Fig: 4-15. A) PET flakes residue from Parr reactor B) Fresh PET flake vs flake residue

from oil bath C) Fresh PETF20 flake vs flake residue from oil bath.

A B C

85

4.2.2 Impact of co-solvents on PET vs PETF20 flakes

After studying the effect of GVL co-solvent on PET flakes at 150℃ and 90

minutes, a series of co-solvents with Hansen solubility parameters (HSP) close to PET were

selected to screen PET and PETF20. Generally, HSP’s are used to determine solvent-

polymer interactions. Based on the idea that like dissolves like, two compounds with

similar solubility parameters dissolve in one another and form a solution[56]. As shown in

Table 3.4 solvents used for this study were, Gamma butyral lactone (GBL), ethylene glycol

diacetate(EGDA); propylene glycol diacetate (PGDA) and triglycerol. For each case 1.0

mole% co-solvent in 1.1 M NaOH solution at 90℃ were used for hydrolysis experiments.

Reactions were conducted using the modified system to study the effect of co-solvents and

to observe the onset of solvent induced crystallization specifically.

Reactions were conducted in the oil bath by placing 5 glass vials, charged with 1.0

mole% of co-solvent relative to NaOH solution, 1.0 gm of PET flakes and 1.1M NaOH

solution. Reaction took place for 3 days since depolymerization of PET takes longer

reaction times at low temperatures. The yield of TPA for PET flakes following hydrolysis

at 90℃ in presence of co-solvents are shown in Fig 4-16. The results at 90℃ for

degradation of PET in 1.1M NaOH was compared for Parr reactor and glass vials. The

decrease in degradation after 3 days in glass vial is likely due to lack of mixing in the

system. Interestingly adding GVL did not improve the reaction kinetics at 90℃ in a way

that it did at 150℃. The GVL and GBL systems exhibited a similar rate of

depolymerization with 42% yield of TPA. The addition of PGDA and EGDA sharply

86

reduced the depolymerization rate relative to base NaOH solution. Triglycerol gave good

results with 63% yield at 90℃.

Fig 4-16. % yield of PET flake after alkaline hydrolysis in the presence of 1 mole% co-

solvents for 3 days at 90℃ at 13 pH.

It is interesting to note that at 90℃ from Fig 4-16, the compounds of similar structure had

similar outcomes. A) EGDA and PGDA had relatively low kinetics, b) GVL and GBL

exhibited similar intermediate effect, c) Triglycerol exhibited the highest yield of TPA.

Similarly, PETF20 was subjected to hydrolysis using co-solvents to test the effect

on the depolymerization rate of co-polyester. The co-solvents were selected based on the

0

10

20

30

40

50

60

70

80

90

100%

TPA

Yie

ld

1.0 mole % Co-solvents in NaOH solution

87

outcomes of hydrolysis of PET flakes. The PGDA and EGDA were not used for co-

polyesters because of poor results for PET flake.

Fig 4-17. % Yield of PETF20 flake after alkaline hydrolysis with 1 mole% co-solvents in

NaOH solution for 3 days at 90℃ at 13 pH.

Results from Fig 4-16 suggest that co-solvents GVL, GBL and triglycerol exhibited good

results when used for PET flakes at 90℃ relative to base NaOH. In the case of PET flakes,

selecting a proper solvent with suitable composition helps to facilitate depolymerization of

the PET flake with high yields. Interestingly these co-solvents did not facilitate hydrolysis

of the PEFT-20. In the case of co-polyesters, the experiments with co-solvents should be

conducted at shorter times to better understand the impact. As discussed in section 4.2.1,

0102030405060708090

100

No-solvent GVL Triglycerol GBL

% (T

PA+F

DCA

) Yie

ld

1 mole % co-solvents in NaOH solution

88

because of the oxygen present in the furan ring, PETF20 reacted faster than PET flake and

exhibited high conversions even in the absence of co-solvents in 3 days. It is possible that

the longer times used for this experiment mask any impact of the co-solvents. It is

recommended that future studies expand to kinetics of PETF20 in presence of co-solvents

at short times to study their impact.

4.2.3 Characterization

The precipitated product was analyzed by FTIR and proton and carbon NMR. The

FTIR confirmed the presence of functional groups consistent with TPA and FDCA. NMR

was used to qualitatively confirm the presence of co-monomers TPA and FDCA.

The PET and co-polyester flakes turned from clear to opaque after the reaction in

NaOH solution with and without use of co-solvents. The surface area of the flakes remained

constant, but the thickness has reduced with time as shown in Fig 4-15 indicating that the

surface reaction was occurring during hydrolysis as discussed in section.3.3. To study the

behavior of the flakes, PET and PETF20 flakes in the residue following the reaction were

washed and dried under vacuum below 80℃ to avoid crystallization while drying.

Differential scanning calorimetry was used for the analysis with heating rates of 10℃/min

up to 300℃ and immediate quenching to 40℃ at 20℃/min. The DSC scans were analyzed

to understand how the reaction is occurring.

89

4.2.3.a FTIR Spectroscopy

Fig 4-18. Infrared spectroscopy of precipitate (TPA - - -, FDCA ) from a) PETF20 and

b) PET alkaline hydrolysis in NaOH solution for 3 days and 90℃.

90

The FTIR spectra for dried precipitate of PET and PETF20 following alkaline hydrolysis

are compared in Fig 4-18a. The absorptions at 3120, 1580 cm-1 are specific to C-H, C=C

stretch of furan ring present in the structure of 2,5-furan dicarboxylic acid (FDCA). The

characteristic bands obtained specific to TPA were same as shown in the Fig 4-18b. This

confirms that the recovered monomer from alkaline hydrolysis of PETF20 has both TPA

and FDCA.

4.2.3.b Nuclear Magnetic Resonance Spectroscopy

a) 1H NMR of recovered TPA and FDCA from PETF20 flakes

91

b) 13C NMR of recovered TPA and FDCA from PETF20 flakes

Fig 4-19. Nuclear Magnetic resonance analysis of recovered monomer (TPA+FDCA)

from PETF20 flakes at 90°C and 3days using methyl sulfoxide 99.5% purity with d6

solvent.

The diacid precipitate obtained from PETF20 hydrolysis was analyzed using 1H

NMR and 13C NMR to detect the presence of oligomers and confirm the presence of both

TPA and FDCA (Refer appendix-A for NMR of pure compounds). Figure 4-19a shows

that the 1H NMR has signal at 8.03 ppm (peak a) that indicate the presence of four phenyl

92

protons of TPA, signal at 7.2 ppm (peak h) that indicates the presence of protons associated

with the furan ring of FDCA. The co-polyester was 20% FDCA and 80% TPA. From the

calculation of area under the curve of the carbonyl peaks (peak ‘g’ and peak ‘k’) of the

NMR spectrum, recovered precipitate has 17.6% FDCA and remaining TPA as monomers.

1H NMR spectrum of recovered mixture of TPA and FDCA resembles with the reference

spectrum of TPA and FDCA. Fig 4-19b shows 13 C NMR spectrum. The signal at 129.5

ppm (peak e), 134.8 ppm (peak f) and 166.7 ppm (peak g) indicates the presence of carbons

associated with the chemical structure of TPA. The signal at 118.48 ppm (peak I) indicates

the carbon on the furan ring, signal at 147.07 ppm (peak J) indicates the carbon present in

the furan ring attached to carbonyl group, signal at 158.9 ppm (peak K) indicates the carbon

in the carboxyl group. Both proton and carbon spectrum confirmed the presence of TPA

and FDCA in the recovered monomer.

4.2.3.a Thermal transition and crystallinity of residue polymer flake using DSC.

To observe the behavior of both PET and PETF20, dried flakes before and after the

reaction were thermally analyzed using DSC. Fig 4-20. a illustrates the first heating ramp

of DSC scans of PET and PETF20 flakes before and after reaction. Glass transition

temperature (87℃), crystalline temperature (156℃), melting temperature (246℃) were

observed for raw PET flake.

93

Fig 4-20. a DSC curves of fresh PET flakes and PET flakes residue following reaction in

0 – 10 mole% GVL in NaOH solution at 150℃ and 90 minutes.

The PET flake which was recovered after reaction in 1.12M NaOH solution did not

exhibit glass transition or crystallization peak but had a melting peak at 246℃. This

indicates that samples were all semi crystalline. The % crystallinity was calculated from

the first heating ramp using the enthalpy of melting (ΔHm), enthalpy of crystallization

(ΔHc) and enthalpy of fusion (ΔH⁰m=84.9 joules/gm) per gram of a perfect crystal of PET

of infinite size [67].

% crystallinity =

⁰∗ 100

94

The % crystallinity of PET before reaction was 6.5 and after reaction was 26.8 in NaOH

solution. This confirms significant crystallization of PET flake during the reaction. Similar

results were observed for all co-solvents at 90℃ following 3 days reaction as shown in Fig

20.b.

Fig 4-20. b DSC curves of PET flake after hydrolysis using different co-solvents (1

mole%) for 3 days at 90℃ in NaOH solution.

The % crystallinity of PET and PETF20 flakes following hydrolysis reaction for 3

days and 90℃ in the presence of 0-1.0 mole% of co-solvents are shown in Table 4.3. Fresh

95

flakes have <7% crystallinity, whereas the crystallinity increased following the reaction in

NaOH solution.

Table.4.3. Data of hydrolysis reaction using co-solvent at 90℃ and 3 days in 1.12M NaOH

solution.

Co-solvent in 1.12M NaOH solution pH of the solution % crystallinity of flakes

PET PETF20

Reference flake -- 6.54 4.5

NaOH solution 13 26.8 24.3

1 mole% EGDA 13 37.2 --

1 mole% PGDA 13 31.9 --

1 mole% GVL 13 32.2 27.4

1 mole% GBL 13 39.5 22.4

1 mole% Triglycerol 13 30.9 24.6

The glass transition temperature (77℃), crystalline temperature (153℃), melting

temperature (214℃) observed for raw PETF20 flake is shown in Fig 4-20. c. PETF20 flake

following hydrolysis in 1.12M NaOH solution were crystallized during the reaction as

shown in Table 4.3, melting peak at 212℃ was observed for all the residue flakes. Flakes

following reaction in co-solvent/NaOH solution exhibited a second melting peak at 128℃

indicating that the polymer is converting to oligomer and then monomer with time. %

96

crystallinity of PETF20 before reaction was 4.5 and was 24.6 following reaction in NaOH

solution. This confirms the significant crystallization of PET flake during the reaction.

Fig 4-20.c DSC curve of PETF20 flake after hydrolysis using different co-solvents (1

mole%) for 3 days at 90℃ in NaOH solution.

DSC scan curves from Fig 4-20. b confirms that PET flake was crystallized even after

adding co-solvent to the reaction medium for the co-solvents depending on the

concentration. From this DSC scans it was evident that addition of co-solvents clearly did

not affect significantly the rate of crystallization during reaction. The % crystallinity was

calculated for the unreacted PET and PETF20 flakes. Average value of % crystallinity of

PET and PETF20 flakes were 30 % and 24.6 % after the reaction. The lower level of

97

crystallinity of PETf20 is consistent with decreased crystallization of co-polyester relative

to homopolymer. Crystallization of the PET and PETF20 flakes in presence of alkaline

solution will reduce rate of diffusion into the matrix and swelling which may decrease the

thickness of reaction zone. The lower crystallization of the PETF20 may contribute to large

conversions relative to PET flake. The high values of crystallization could be because the

reaction took place for 3 days and PETF20 flakes were exposed to alkaline medium for a

long period giving enough time for the flakes to crystallize.

4.3 Separation of TPA from FDCA

A key challenge to hydrolysis of co-polyesters will be selective recovery of the

monomers. Studies on separation of TPA from FDCA were conducted with the help of an

undergraduate student Elizabeth Heil. The focus of this section is a brief discussion of

selective recovery of TPA from FDCA. In this case, the FDCA-Na+2 and TPA-Na+2 were

dissolved in the alkaline solution upon hydrolysis of PETF20 as shown in Fig 4-21. The

salts are precipitated upon addition of H2SO4.

Fig 4-21. Schematics of alkaline hydrolysis of PETF20 using NaOH solution.

98

The solubilities of these two monomers were tested in multiple solvents and co-

solvents, to explore relative solubilities as mentioned in monomer separation. Solvents

tested in this study include, water, sodium hydroxide solution, ethylene glycol, and

dimethyl sulfoxide (DMSO). The behavior of pure components in each solvent was

evaluated to determine the ability of the solvent to selectively dissolve and precipitate the

two components. Dissolving a mixture of TPA and FDCA in DMSO followed by

precipitation of TPA using water was determined to be the viable option for separating

TPA from FDCA.

4.3. a Solubility of TPA and FDCA in DMSO water system

The solvent system that showed promise for the separation of TPA from FDCA was water

and DMSO system. From literature, solubility limits of FDCA and TPA were reported as

55 wt.% [68] and 19 wt.% in DMSO [69]. Because of the potential to selectively dissolve

FDCA in the presence of TPA using DMSO, the behavior of TPA and FDCA with varying

weight percentages of water in DMSO from 0-20 wt.% water was investigated in

collaboration with Elizabeth Heil.

To determine the solubility of TPA in DMSO, known amounts of TPA was placed

in a vial at room temperature. A water and DMSO solution was prepared and weighed.

DMSO solution with up to 20% water was added drop wise to the vial containing TPA,

after each drop the vial was capped and stirred well. This process was repeated until the

TPA completely dissolved. The remaining solution of water and DMSO was weighed, final

99

weight was subtracted from the initial weight to determine the mass of co-solvent added to

the TPA. To determine the solubility limit of the solution in weight percentage, mass of

TPA was divided by mass of co-solvent added to TPA. The same method was repeated to

determine the solubility of FDCA in DMSO water system.

The experimental solubility’s of TPA i.e. 18 wt.% and FDCA i.e. 45 wt.% were

close to the values reported in the literature[68]. Solubility limit for TPA and FDCA

decreased with increasing water content as shown in Fig 4-22. Interestingly at all water

concentrations the FDCA exhibited much better solubility than TPA. Therefore, it is

possible to use these differences in solubility to design process to selectively recover the

TPA and FDCA.

Fig 4-22 Solubility of TPA and FDCA in DMSO water system at various wt.% water. ■

TPA, literature, ● FDCA, literature, ▲ TPA, ■ FDCA.

100

4.3. b Recovery of TPA from FDCA in DMSO water system

DMSO dissolves the monomers TPA and FDCA but addition of water can be used

to selectively precipitate TPA. Considering the solubility limits i.e.19% and 55% in pure

DMSO, water has a large effect on TPA than FDCA due to initial higher solubility of

FDCA in DMSO. Combining the solubility effects of water and DMSO, a method to

precipitate out TPA while leaving FDCA in the solution was proposed as shown in Fig 4-

23.

Solutions of four possible product mixtures i.e., 20:80, 10:90, 5:95, and 0:100

molar ratios of FDCA to TPA were analyzed. Initially, TPA, DMSO, and FDCA were

placed in vials. To be consistent 1.00 g of TPA was added to the vial containing DMSO,

appropriate weights of FDCA was added depending on the molar ratios of the batch. All

four vials were capped, shaken well and allowed to sit for 24 hours to allow complete

dissolution of products.

Fig 4-23. Proposed separation method for recovery of TPA from FDCA using DMSO and

water system.

101

Fig 4-24. TPA percentage recovery vs water added in weight percentage for A) 20:80, B)

10:90, C) 5:95, D) 0:100 molar ratio of FCDA to TPA solutions in DMSO.

Water was added to each vial to make solutions that were 5-20 weight% water. All

the vials were capped, stirred well and allowed to sit for 24 hours to allow contact time for

the solution to reach equilibrium. Later, samples were filtered using gravimetric filtration.

Solid collected on the filter paper was dried at 80℃ and 30-psig vacuum for 24 hours.

Percentage diacid recovery was calculated by dividing dried solid collected on filter paper

by the initial mass of diacid. From Fig 4-24, maximum TPA product recovery of 68.3%

was observed for the reaction mixture of 20:80 molar fraction of FDCA to TPA where 20

wt.% water was added to the solution. FTIR analysis was done on the samples of 0:100

102

and 20:80 molar fraction of TPA and FDCA as there is highest chance of precipitating

FDCA along with TPA in 20:80 molar fraction. The results indicated that the absorption

spectrum of the 0:100 molar fraction of TPA and FDCA was like the FTIR spectrum of the

precipitate obtained following alkaline hydrolysis of PET i.e. TPA as shown in Fig 4-25.

The absorption spectrum of 20:80 molar fraction of TPA and FDCA was similar to the

FTIR spectrum of the precipitate obtained following hydrolysis of PETF20 i.e. TPA and

FDCA. This indicates that some amount of FDCA was precipitated along with TPA. To

separate TPA from FDCA further work should be done to explore a best method to

precipitate TPA leaving FDCA in the solution. Therefore, future work should include

further analysis of the solid product.

Fig 4-25. Infrared spectroscopy of precipitate (TPA - - -, FDCA ) from 20:80 molar

ratio of FDCA and TPA in DMSO solution using 20 wt.% water.

103

Chapter - 5

Conclusions and future work

Chemical recycling of PET flakes and co-polyesters (PETF20) was carried out by

alkaline hydrolysis using 1.1 M NaOH solution to selectively recover the monomers. The

effect of operational parameters such as time, temperature, presence of PVC and co-

solvents on the hydrolysis of PET flakes were investigated. Results indicated that PET

conversion increased with increase in reaction time and temperature. Moderate conversions

of 71 % were observed at 150℃ and 90 min which increased to 89.8 % by 300 min.

Alkaline hydrolysis of PET flakes was not affected by up to 5 wt.% PVC/wt.% PET. There

was no dichlorination of PVC or effect0020on the PET conversion at 150℃ and 180 min.

Modeling results are consistent with a reaction on surface or a thin swollen region

near surface. Therefore, co-solvents were used to improve swelling of polymer matrix to

increase degradation rates. Studies using GVL and PET are similar, studies using GVL as

co-solvent to increase the rate of depolymerization of PET have not been reported in the

literature. Therefore, the effect of GVL at 0-10 mole% in NaOH solution on hydrolysis

was investigated at 150℃ and 90 min. Presence of 1 mole% GVL resulted in a conversion

of 85.7%, with a percentage increase of 20.7 compared to the conversion of base NaOH

solution i.e. 71%.

104

Chemical recycling of co-polyesters of PET and PEF was investigated for the first

time using alkaline hydrolysis. Experiments on PET flakes and PETF20 flakes at 90℃ for

3 days were compared. PETF20 flakes exhibited 88% conversion, which is higher than the

conversion of PET flakes i.e. 42%. Impact of various co-solvents including gamma butyral

lactone, ethylene glycol diacetate, propylene glycol diacetate and triglycerol along with

GVL were studied at 1mole% composition in NaOH solution. In the case of PET flakes,

triglycerol exhibited a TPA yield of 63% while the other co-solvents resulted in either

lower or same yields as that of base NaOH solution. Ethylene glycol diacetate and

propylene glycol diacetate were excluded in the reactions of PETF20 flakes because of the

low reaction rate observed during the reactions of PET flakes. None of the selected solvents

improved the conversions of PETF20 flakes which may be because the long reaction times

used masked the effect of co-solvents.

FTIR and NMR analysis confirmed the presence of TPA, IPA and FDCA in the

precipitates, confirming that the precipitate obtained from hydrolysis of PETF20 flakes has

17.6% FDCA and PET flakes has 2.5% IPA along with TPA. Therefore, monomers can be

selectively recovered from polyesters and co-polyesters using alkaline hydrolysis process.

This potentially addresses the problem of recycling PET with impurities, co-polyesters,

polymer blends, complex layered material and contributes to the plastic waste problem

resulting in the monomer TPA which is used in industrial production of PET.

Finally, separation of TPA from FDCA was studied using DMSO water system. A

method to dissolve TPA and FDCA in DMSO followed by addition of water to selectively

precipitate TPA while leaving the FDCA in the solution resulted in highest recovery of

105

68.3% diacid. DSC scans confirmed the crystallization of residue of PET and PETF20

flakes. This residue can be melted and made into pellets which can be reused on

commercial scale in PET synthesis. The major by product, sodium sulphate formed can be

sold separately [15].

For future work, studying the effect of temperature on PET conversion using

triglycerol as co-solvent at various compositions is an interesting topic. Study on

crystallinity of PET flakes and its effects on the rate of depolymerization would help in

understanding the reason for crystallization of PET flakes during reaction with sodium

hydroxide solution. Also, GVL and GBL resisted the rate of depolymerization at low

temperatures by crystallizing the polymer which is an interesting work to be looked at.

Effect of co-solvents on PETF20 should be investigated at shorter time intervals and

different temperature ranges. In addition, a method for recovering 100% FDCA and TPA

should be investigated. As solubility is temperature dependent, investigating DMSO water

system at increasing temperatures could be valuable. Analysis of the components present

in the filtrate of hydrolysis would be an interesting work to be done.

106

References

1. Nester, R., Global Polyethylene Terephthalate (PET) market analysis & opportunity outlook 2021. 2018.

2. Schloss, F., Amber PET bottles: recycling challenges and opportunities. 2017,

Plastics today. 3. Wikipedia, Polyethylene terephthalate. 4. Woods, L., Global Polyethylene Terephtalate Market Report 2017 - By End-Use

Industries, Products & Regions - Research and Markets. 2017: business wire. 5. Larsen, D.Å., Extended shelf-life biopolymers for sustainable and multifunctional

food packaging solutions. 2016. 6. USEPA, Advancing sustainable materials management: 2014 fact sheet, EPA,

Editor. 2016, EPA: online. 7. NAPCOR, NAPCOR-APR-2016 rate report. 2016. 8. Staff, r.t., Two dozen types of scrap imports banned by China in 2018, in

recycling today. 2017. 9. O'Sullivan, M., China trash ban creates crisis for us recyclers, in. 2018. 10. Anuar Sharuddin, S.D., et al., A review on pyrolysis of plastic wastes. Energy

Conversion and Management, 2016. 115: p. 308-326. 11. Al-Salem, S.M., P. Lettieri, and J. Baeyens, Recycling and recovery routes of

plastic solid waste (PSW): a review. Waste Management, 2009. 29(10): p. 2625-43.

12. Machine, P.r., PVC in PET bottle recycling. 13. Kim*, S.H.P.a.S.H., Poly (ethylene terephthalate) recycling for highvalue added

textiles. 2014.

107

14. Aguado, A., et al., Chemical depolymerisation of PET complex waste: hydrolysis vs. glycolysis. Journal of Material Cycles and Waste Management, 2013. 16(2): p. 201-210.

15. Karayannidis, G.P., Chatziavgoustis, A. P., Achilias, D. S., Poly (ethylene

terephthalate) recycling and recovery of pure terephthalic acid by alkaline hydrolysis. Advances in Polymer Technology, 2002. 21(4): p. 250-259.

16. Kaminsky, H.K.M.S.W.B.J.R.W., Polyesters. Wiley Online Library, 15 June

2000. 17. Karayannidis, G.P., Roupakias, C. P., Bikiaris, D. N., Achilias, D. S., Study of

various catalysts in the synthesis of poly (propylene terephthalate) and mathematical modeling of the esterification reaction. Polymer, 2003. 44(4): p. 931-942.

18. Logakis, E., Pissis, Polycarpos, Pospiech, Doris, Korwitz, Andreas, Krause,

Beate, Reuter, Uta, Pötschke, Petra, Low electrical percolation threshold in poly (ethylene terephthalate)/multi-walled carbon nanotube nanocomposites. European Polymer Journal, 2010. 46(5): p. 928-936.

19. Di Serio, M., Tesser, R., Ferrara, A., Santacesaria, E., Heterogeneous basic

catalysts for the transesterification and the polycondensation reactions in PET production from DMT. Journal of Molecular Catalysis, 2004. 212(1): p. 251-257.

20. Joshi, A.S., Coleman, Maria R, Lawrence, Joseph G, Co-polyesters of

polyethylene terephthalate and polyethylene 2, 5-furandicarboxylate. 21. Seymour, T.J.P.J.M.L.W., Process for the preparation of polyesters with high

recycle content. 2013. 22. Pierce, L.M., PEF will not oust PET for beverage bottles anytime soon. 2014:

Packaging digest. 23. Zhao, M., PVC in PET Bottle Recycling till date: plastic recyling machine. 24. Wikipedia, Polyethylene 2,5-furandicarboxylate. 25. box, T.e.t., Densities of common solids. 26. T.Spychaj, Chemical recycling of PET: methods and products. 2002.

108

27. Minoru Genta, F.Y., Yuichi Kondo, Wataru Matsubara, Setsuo Oomoto, Development of chemical recycling process for post-consumer PET bottles by methanolysis in supercritical methanol. 2003.

28. Al-Sabagh, A.M., et al., Greener routes for recycling of polyethylene

terephthalate. Egyptian Journal of Petroleum, 2016. 25(1): p. 53-64. 29. J.T. MacDowell, N.C.K., US Patent 3,222,999. 1965. 30. U.R. Vaidya, V.M.N., J. Appl. Polym. Sci. 35 Polyester polyols for polyurethanes

from pet waste: Kinetics of polycondensation. 1988. 31. Scheirs, R., Recycling of PET, in Polymer Recycling: Science, Technology and

Application. J Wiley &; Sons, Chichester, 1998. pp. 119-182. 32. Simonaitis.T, B., R., Jankauskaitė, V., Adhesive composition with poly (ethylene

terephthalate) waste. 2005. 33. Imran, M., Kim, Bo-Kyung, Han, Myungwan, Cho, Bong Gyoo, Kim, Do Hyun,

Sub- and supercritical glycolysis of polyethylene terephthalate (PET) into the monomer bis(2-hydroxyethyl) terephthalate (BHET). Polymer Degradation and Stability, 2010. 95(9): p. 1686-1693.

34. Pingale, N.D., Shukla, S. R., Microwave assisted ecofriendly recycling of poly

(ethylene terephthalate) bottle waste. European Polymer Journal, 2008. 44(12): p. 4151-4156.

35. Nazari, M.M.A.N.F., Microwave‐assisted depolymerization of poly (ethylene

terephthalate) [PET] at atmospheric pressure. 2007. 24(4). 36. Güçlü, G., et al., Simultaneous glycolysis and hydrolysis of polyethylene

terephthalate and characterization of products by differential scanning calorimetry. Polymer, 2003. 44(25): p. 7609-7616.

37. J Dasa, A.B.H., Alkaline hydrolysis of poly (ethylene terephthalate) in presence

of a phase transfer catalyst. Indian Journal of Chemical Technology, 2007. 14. 38. Abdelaal, M.Y., T.R. Sobahi, and M.S.I. Makki, Chemical Degradation of Poly

(Ethylene Terephthalate). International Journal of Polymeric Materials, 2008. 57(1): p. 73-80.

39. Yoshioka, T., Kinetics of Hydrolysis of PET Powder in Nitric Acid by a Modified

Shrinking-Core Model. 1998.

109

40. Santos, A.S., Agnelli, J. A., Manrich, S., Evaluation of sub-critical water as an extraction fluid for model contaminants from recycled PET for reuse as food packaging material. 2010. 27(4): p. 567-73.

41. Cata, A., Chemical recycling of polyethylene terephthalate (pet) waste using sub-

and supercritical water. 2015. 42. J. Pitat, V.H., M. Bacak, A method of processing waste of polyethylene

terephthalate by hydrolysis. 1959. 43. S.D. Lazarus, J.C.T., O.E. Snider, US Patent 3,317,519. 1967. 44. Kozlow, N., Korotusko, GP, Kashinskii, AV, Gavrilenco, ND, Preparation of

terephthalic and benzoic acid by simultaneous alkaline hydrolysis of wastes from PET and methyl benzoate. Vesti Acad Nauk BSSR, Ser Khim Nauk, 1984. 5: p. 91-93.

45. A.Liarou, environmentally friendly chemical recycling of polyesters (pet, ppt)

using alkaline hydrolysis under microwave irradiation. 46. Yoshioka T, O.N.a.O.A., Simultaneous hydrolysisoxidation mechanism of waste

PET powder in nitric acid solutions. 1996. 47. Oku, A., Hu, L.-C., Yamada, E. J Applied Polymer Science 1997, 63, 595. 1997. 48. Benzaria J, D.-V.B., Dawans F and Gaillard J B Process for recovery of alkali

metal or alkali earth metal terephthalate and alkylene glycol from alkylene polyterephthalates, EP 597 751. 1994.

49. Yoshioka T, S.T.a.O.A., Hydrolysis of waste PET by sulfuric acid at 15O0C for a

chemical recycling, J Appl Polym Sei 52:1353-1355. 1994. 50. F, P.S., Method for recovery of terephthalic acid from polyester scrap, US Patent

4,355,175. 1982. 51. C, B.G.B.J.a.O.B.R., Method for recovering terephthalic acid and ethylene glycol

from polyester materials, US Patent 3,952,053. 1976. 52. A, M., Poly (ethylene terephthalate) waste utilization by hydrolysis in neutral

environment, Ekoplast 2:52-59. 1993. 53. Campanelli J R, K.M.R.a.C.D.G., A kinetic study of the degradation of poly

(ethylene terephthalate) at high temperatures, J Appl Polym Sd 48:443-451. 1993.

110

54. Tustin G C, P.T.M.J., Jenkins U A and Jernigan M T, recovery and purification of terephthalic acid and ethylene glycol from poly(ethylene terephthalate), US Patent 5,413,681. 1995.

55. Le, H.Q., Solubility of organosolv lignin in γ-valerolactone/water binary

mixtures. 2016. 56. Halterman, D., Hansen Solubility Parameters (Esters and Derivatives). 57. Dow, Dowanol™ PGDA Propylen glycol diacetate 58. Spectrum 1: Isophthalic acid (R2, C1). 59. Kumagai, S., et al., Alkaline hydrolysis of PVC-coated PET fibers for

simultaneous recycling of PET and PVC. Journal of Material Cycles and Waste Management, 2018. 20(1): p. 439-449.

60. Ben-Zu Wan, †, Kinetics of Depolymerization of Poly (ethylene terephthalate) in

a Potassium Hydroxide Solution. 2001. 61. Wong, C.Y.Y., Choi, Alex Wing-Tat, Lui, Matthew Y., Fridrich, Bálint, Horváth,

Attila K., Mika, László T., Horváth, István T., Stability of gamma-valerolactone under neutral, acidic, and basic conditions. Structural Chemistry, 2016. 28(2): p. 423-429.

62. Wong, C.Y.Y., Choi, Alex Wing-Tat, Lui, Matthew Y., Fridrich, Bálint, Horváth,

Attila K., Mika, László T., Horváth, István T., Stability of gamma-valerolactone under neutral, acidic, and basic conditions. Structural Chemistry, 2017. 28(2): p. 423-429.

63. J. G. Poulakis, C.D.P., Dissolution/reprecipitation: A model process for pet bottle

recycling. 2000. 64. Libre. Spin-spin splitting in ¹H NMR spectra. 2016. 65. Holger, A.B.F.K.O.K.D.K., Use of biaxially stretched film comprising polyester,

whose diol component is cyclohexanedimethanol and dicarboxylic acid component is benzene- and/or naphthalene dicarboxylic acid, as electrical insulating filler. 2011.

66. Kasai, T.T., Polyester resin copolymerized with isosorbide and 1,4- cyclohexane

dimethanol and preparing method. 2002.

111

67. Luboš Běhálek, M.M., Petr Lenfeld, Jiří Habr, Jiří Bobek, Martin Seidl, Study of crystallization of polylactic acid composites and nanocomposites with natural fibres by DSC method. 2013.

68. Gajula, S., 2017. Fructose dehydration to 5-hydroxymethylfurfural: Remarkable solvent influence on recyclability of Amberlyst-15 catalyst and regeneration studies, Elsevier, Volume -37, Pg. 41-44.

69. National Center for Biotechnology Information, U.S.N.L.o.M., Terephthalic Acid.

112

Appendix - A

Miscellaneous data

Fig. A-1. US Waste Generation by category.

113

Fig. A-2. RPET used by product category in 2016 (MMlbs) as per NAPCOR report.

Fig. A-3. PET material flow in US(MMlbs) as per NAPCOR 2016 report.

114

Fig A-4. Proton NMR spectrum of Pure TPA.

Fig A-5. Carbon NMR spectrum of Pure TPA.

115

Fig A-6. Proton NMR spectrum of Pure FDCA.

Fig A-7. Carbon NMR spectrum of Pure FDCA.