Thermo-Catalytic Versus Thermo-Chemical Recycling of Polystyrene Waste

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Waste and Biomass Valorization ISSN 1877-2641Volume 4Number 1 Waste Biomass Valor (2013) 4:37-46DOI 10.1007/s12649-012-9136-4

Thermo-Catalytic Versus Thermo-Chemical Recycling of Polystyrene Waste

Manar El-Sayed Abdel-Raouf, AbdelRaheim Mahmoud Abdel-Raheim &Shimaa Mohamed El-Saeed

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ORIGINAL PAPER

Thermo-Catalytic Versus Thermo-Chemical Recyclingof Polystyrene Waste

Manar El-Sayed Abdel-Raouf •

Abdel Raheim Mahmoud Abdel-Raheim •

Shimaa Mohamed El-Saeed

Received: 27 January 2012 / Accepted: 5 June 2012 / Published online: 22 June 2012

� Springer Science+Business Media B.V. 2012

Abstract Degradation of polystyrene was carried out

thermally and thermo-chemically in order to compare

between the conversion of polystyrene in both cases. The

catalyzed thermal degradation was achieved without sol-

vents in an autoclave at pressure range 20–50 bar and tem-

perature range 300–400 �C in presence of 1 % Al2O3 as a

catalyst. The thermo-chemical degradation was achieved by

two solvents namely, supercritical cyclohexane and super-

critical ethyl cyclohexane under the same reaction condi-

tions. It was found that conversion of polystyrene increased

in the thermo-chemical process than in thermal process.

Furthermore, it was found that the conversion process

increases with rising temperature and pressure. It also was

found that high molecular-weight compounds decreased but

oligomers and monomers increased with rising temperature.

Polystyrene rapidly degraded after reaching a prescribed

temperature of 400 �C, the degree of degradation was nearly

about 95 % after 1 h in presence of ethyl cyclohexane, 89 %

in presence of cyclohexane and about 81 % only in absence

of the solvent (thermal degradation).

Keywords Thermal � Thermo-chemical � Degradation �Polystyrene � Aluminum oxide

Abbreviations

MSW Municipal solid waste

SCF Supercritical fluids

PET Poly (ethylene Terephthalate)

PS Polystyrene

PE Polyethylene

PP Polypropylene

Introduction

As the consumption of polymeric materials increases

around the world every year, plastic waste disposal has

been recognized as a serious environmental problem

worldwide. The three basic methods of managing MSW

are: landfilling, incineration, and recycling. The landfilling

will be hindered in the near future due to their disadvan-

tages. Furthermore, the deficiency of landfill site or the air

pollution by toxic gases generated from incineration pro-

cesses will hinder these two options Ambrose et al. [2],

Boettcher [4] and EAP [7]. The common methods for

plastic waste management are provided in Fig. 1.

Therefore, in recent years, increased attention has been

paid to the recycling or degradation of synthetic polymer

waste. This can contribute to solving pollution problems

and the reuse of cheap and abundant waste products.

Degradation of polymers is a very important reaction in the

chemistry of high molecular mass compounds. It occurs

under the action of chemical agents, thermal effects or

as a result of physical influences Flynn and Florin [8] and

Kaminsky [16].

Among the advantages of pyrolysis as one of the most

promising alternatives to the landfill and/or incineration for

recycling of plastic wastes is that pyrolysis can convert

wasted plastics into valuable raw materials or fuels without

generating toxic gaseous emissions from the process itself

unlike the incineration Andrews and Subramanian [3].

Unfortunately, commercial application of plastics pyrolysis

M. E.-S. Abdel-Raouf (&) � A. R. Mahmoud Abdel-Raheim �S. M. El-Saeed

Petroleum Application Department, Egyptian Petroleum

Research Institute, 1 Ahmed El-zomor street, Nasr City,

Cairo 11727, Egypt

e-mail: [email protected]

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Waste Biomass Valor (2013) 4:37–46

DOI 10.1007/s12649-012-9136-4

Author's personal copy

is being hindered not only by the lack of sufficient eco-

nomic incentives, but also by various operational difficul-

ties such as low heat transfer coefficient and poor mixing.

Beside, this method still has problems such as high tem-

perature conditions (at least 600 �C), excessively long

degradation time, secondary pollution due to incomplete

combustion and byproduct like char Shah et al. [23]. The

chemical recycling of waste plastic (polymers) has an

advantage of converting into reusable materials like

monomer or raw material of the petrochemical industry or

fuel Wang et al. [24] and William and Brindle [25].

However, Supercritical fluids (SCF) have recently been

used in the treatment of waste plastic to solve the problems

induced in pyrolysis of waste plastics. Kim et al. [18] used

supercritical methanol to depolymerize PET. Model [22]

developed a process in which supercritical water was used

to degrade organic materials. Dhawan et al. [6] decom-

posed polyisoprene and waste rubber using super critical

toluene; Kocher et al. [19] decomposed poly (vinyl chlo-

ride) using super critical water. Super critical water was

also used to recover terephthalic acid from PET waste

Adschiri et al. [1]. Tyre and other wastes were depoly-

merized using some super critical fluids. This accounts for

most waste plastics, the experimental temperature ranged

from 400 to 450 �C. It was found that the supercritical fluid

method produced hydrocarbon products of shorter carbon

chain and a higher ratio of l-alkene/n-alkane than those

yielded through general thermolysis Chen et al. [5]. Joung

et al. [14, 15] reported seven types of solvents like toluene

and cyclohexane as the most appropriate to waste tyre

processing. At the conditions of 300 �C and 10 MPa and a

reaction time of 1 h, cyclohexane decomposed waste tyres

into lower molecular weight substances. Supercritical tol-

uene also gave a similar result. Hwang et al. [12] used

supercritical acetone in the degradation of PE, PP and their

mixture. Lee et al. [20] used supercritical tetrahydrofuran

in decomposing cis-polyisoprene rubber and got products

of narrow distribution. In case of thermolysis of PS, Hwang

et al. [11] used supercritical acetone in decomposing waste

PS. The total conversion of PS waste, composition of the

decomposed products and the yield of monomer were

determined. Gyou-Cheol et al. [10] studied the degradation

of waste polystyrene in super criticaJ n-hexane that has

relatively lower critical pressure and temperature. The

conversion of polystyrene molecular- weight distribution of

products and residual elements were measured to under-

stand the degradation mechanism.

The focus of this study is the tertiary recycling (chem-

ical recycling) of polystyrene waste, that is, conversion of

plastics waste into higher value products. More specifi-

cally, the objective is to recover styrene and other valuable

aromatics by the thermo-catalytic and thermo-chemical

treatment of polystyrene at moderate temperatures. The

thermo-catalytic conversion of polystyrene was achieved

without solvents in an autoclave at pressure range

20–50 bar and temperature range 300–400 �C in presence

of 1 % Al2O3 as a catalyst. The thermo-chemical degra-

dation was achieved by two solvents (supercritical cyclo-

hexane and supercritical ethyl cyclohexane) under the same

pressure and temperature conditions. The efficiency of both

methods was compared and related to the composition of

the products.

Experimental

Materials and Methodology

Plastic cups made of Polystyrene waste were used

throughout this study. They were washed and left in the air

to dry then they were chopped into smaller segments and

grinded to pieces of 20–40 mm in size. The data obtained

from GPC revealed that its number average molecular

weight (Mn) and its polydispersity index (Mw/Mn) were

122,000 and 1.4, respectively.

The other chemicals used such as Al2O3 (as powder),

ethyl cyclohexane and cyclohexane were all first grade

chemicals supplied from Sigma–Aldrich Company and

used as received with no further processing.

Instrumentation

Qualitative and quantitative analyses of the gas and liquid

type product after the reaction were made by using gas

chromatography (GC 22A, Shimadzu, Japan). Gel perme-

ation chromatography (GPC Perkin-Elmer) was used for

identifying solid residual substances in order to find out the

molecular weight distribution and the degree of PS reaction

plastic wastes

Reuse of Materials

Collection

Segregation

Incineration

Energy recovery

Volume reduction

Landfilling

Recycling

Mixed plastic waste recycling

Chemical recycling

Solvent thermolysis

Hydrolysis

pyrolysis

Hydrocracking

Fig. 1 Plastic waste management

38 Waste Biomass Valor (2013) 4:37–46

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completion. The standard sample was polystyrene, the

mobile phase was tetrahydrofuran (THF) and the fluid flow

was fixed at 1.0 ml/min.

Pyrolysis Experiments (Thermo-Catalytic Degradation)

Pyrolysis experiments were carried out in a thermostated

stainless steel high pressure reactor of 500 ml capacity

with two thermocouples, an external heating coil and a

stirrer. The permissible reactor conditions are 500 �C and

400 bars. A water-cooling system is also installed inside

the reactor in order to prevent any temperature change

during the recovery of the products. Since the test is done

under high pressure, a safety valve, outside of the reactor;

with a rupture disc was used that can work at up to 400 bar.

A spiral condenser is mounted on a special opening in the

reactor lid and directly connected to trap for collecting gas

samples.

The reactants (50 g PS ? 0.5 g Al2O3) were charged

directly into the container then the container was closed,

blushed by nitrogen for 10 min. to expel air and to make

the reaction environment inert then placed in the thermo-

stated heater which was adjusted to the desired tempera-

ture. About 1 ml of gas was drawn from the trap with 1 ml

syringe each 15 min. and sent for analysis on gas chro-

matography instrument. At the end of reaction, i.e. after an

hour, a gas sample was drawn by a syringe for analysis and

the system is disconnected and cooled, the liquids left were

separated and weighed and the solids left in the reaction

container were collected and weighed. The conditions of

the pyrolysis reaction experiments together with the codes

given to the batches are provided in Table 1. It is worthy to

mention that the notification system used throughout this

work is as follows: PSA for thermal degradation, PSB for

degradation in supercritical cyclohexane and PSC for

degradation in supercritical ethyl cyclohexane. The num-

bers 1–3 are given for the temperatures 300, 350 and

400 �C respectively. The small letters a–d are given for the

pressure 20, 30, 40 and 50 bar respectively.

Thermo-Chemical Experiments

The same procedure was applied in absence of catalyst.

Instead, the solvent, either cyclohexane or ethyl cyclo-

hexane, was fed into the reactor. The heating rate was

10 �C/min until the temperature was reached a prescribed

level. The stirring speed was adjusted at 400 rpm. The

reaction pressure was controlled through the increase of the

solvent volume fed into the reactor. When reaching the

reaction conditions, the reaction was continued for an hour.

Then the temperature of the reactor after the reaction was

lowered to room temperature. The discharging products

from the reactor were recovered. The products were only

liquids and solids. The liquids were decanted off whereas

the solid residual was dissolved in acetone, recovered, and

then oven-dried to remove the solvent.

Results and Discussion

Thermal Degradation of Polystyrene

Effect of Reaction Temperature

Polymer degradation involves bond scission that occurs in

the macromolecule and caused by chemical reactions.

Various modes of degradation are found, for example,

thermoplastic polymers undergo oxidative degradation

during processing which involves the combined actions of

heat, mechanical forces, and oxygen. Thermal degradation

involves chemical changes for the polymer chains at ele-

vated temperatures in presence or absence of catalyst.

To find out the effect of reaction temperature on the PS

disintegration pattern, tests were made at the following

conditions: the temperature at the starting point was 300 �C

a relatively low temperature. Then, it went up to 350 then

finally to 400 �C. The reaction time was an hour but the

products of the reaction were monitored every 15 min. The

reaction pressure also varied from 20–50 bars, but the

provided data were obtained at fixed pressure (50 bars).

The catalyst was 1 %Al2O3 according to our previous work

Abdel-Raouf et al. [21]. Time 0 min. means the beginning

point after the temperature and pressure reached the preset

values.The PS conversion was calculated from the fol-

lowing equation:

PS Conversion wt%½ � ¼ Ws

Wi� 100; ð1Þ

where Ws refer to the residual solid after the reaction in

grams and Wi refer to the weight of the initial sample of PS

(50 g).The yield was calculated from the following

equation:

Product yield ¼ Wsp

Wtp� 100; ð2Þ

where Wp refer to the weight of the single product in grams

and Wtp refer to the weight of the total product, i.e. gas or

oil or solid.As seen in Fig. 2a, the PS conversion increases

at higher temperatures. The PS conversion started at the

early stage of the reaction, i.e., within 15 min. At tem-

perature of 400 �C, there appeared almost little change in

the conversion after 45 min elapsed, which means the

reaction is about to reach its end or it reached a kind of

equilibrium. Furthermore, the data in Fig. 2a reveal that oil

constitutes the highest yield among the products. The oil

production increases dramatically by temperature whereas

Waste Biomass Valor (2013) 4:37–46 39

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the solids left decrease at higher temperature. The gases

produced from the reaction slightly increase. Our finding

runs parallel to Gyou-Cheol et al. [10] and Kaminsky [16].

Upon analyzing the gaseous products (Table 2), it was

found that ethane, ethylene, butane and butylenes were the

most abundant gases. The first two gases increase by

increasing temperature from 300 to 400 whereas the last

two decrease by increasing the temperature. GC analysis

was performed for the oil products; the data are mentioned

in Table 3. It is clear that styrene constitutes the major

component among the produced liquids. Its percentage

increased from 66.8 at 300 �C to 81.1 at 400 �C (Fig. 3).

GPC analysis of the solid products reveal that Mn of the

residual solid PS decreased by temperature as given in

Table 4. This may be due to that the degradation reaction is

enhanced by temperature so that some of solid residue is

converted into liquid and gases. These findings are very

close to those obtained by Jong-Ryeol et al. [13]. The

Table 1 Different reaction conditions and codes given to the batches

PS Designation Reaction conditions

Temperature (�C) Pressure (bar) Catalyst Solvent

PSA PSA1a 300 20 (1 % A l2O3) –

PSA1b 30 (1 % A l2O3)

PSA1c 40 (1 % A l2O3)

PSA1d 50 (1 % A l2O3)

PSA2a 350 20 (1 % A l2O3) –

PSA2b 30 (1 % A l2O3)

PSA2c 40 (1 % A l2O3)

PSA2d 50 (1 % A l2O3)

PSA3a 400 20 (1 % A l2O3) –

PSA3b 30 (1 % A l2O3)

PSA3c 40 (1 % A l2O3)

PSA3d 50 (1 % A l2O3)

PSB PSB1a 300 20 – Super critical cyclohexane

PSB1b 30 Super critical cyclohexane

PSB1c 40 Super critical cyclohexane

PSB1d 50 Super critical cyclohexane

PSB2a 350 20 – Super critical cyclohexane




PSB3a 400 20 – Super critical cyclohexane




PSC PSC1a 300 20 – Super critical ethyl cyclohexane

PSC1b 30 Super critical ethyl cyclohexane

PSC1c 40 Super critical ethyl cyclohexane

PSC1d 50 Super critical ethyl cyclohexane

PSC2a 350 20 – Super critical ethyl cyclohexane




PSC3a 400 20 – Super critical ethyl cyclohexane





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residue of one batch is analyzed by IR spectroscopy in

order to confirm that the residue is non-degraded poly

styrene. For brevity, the IR spectrum of PSA1d is provided

in Fig. 2b.

Effect of Reaction Time

The pyrolysis rate versus time is shown in Fig. 4 expressed

as % of conversion of PS. The maximum pyrolysis rate was

observed approximately at the end of reaction, i.e. after

60 min. of heating in the isothermal pyrolysis conditions.

The conversion increased from 58 % at 300 �C to 81 % at

400 �C. The data are mentioned in Table 5. Furthermore,

the yield of styrene produced from the thermal degradation

of styrene is given in Fig. 3. It is clear that also % of

styrene increased by time under any of the applied tem-

peratures. The data of styrene production from polystyrene

degradation is listed in Table 6.

Effect of the Applied Pressure

The pressure was changed from 20 to 50 bars. The tem-

perature was ranged from 300 to 400 �C and the reaction

time was set at 60 min in order to investigate the PS

Yie

ldBatch code: PSA

Temp

1d

perature (°C

PSA2d

C)

PSA3

Gas yield (wt%)

Oil Yield (wt %)

Solid Yield (wt%)

d

(a)

(b)

Fig. 2 a Yields of PS pyrolysis

products versus temperature.

b FT-IR spectrum of PSA1d

Table 2 Composition of gaseous products in PS isothermal pyrolysis

at different reaction temperatures (at 50 bars and after an hour)

Batch code PSA1d PSA2d PSA3d

Compound Temperature (�C)

300 350 400

Methane 4.6 5.9 7.8

Ethane 11.3 20.8 24.5

Ethylene 22.7 28.9 31.7

Butane 25.6 17.8 14.4

Butene 28.9 20.1 16.8

Isobutene 6.9 6.5 4.8


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conversion pattern according to the pressure change. The

relationships between the PS conversion and the applied

pressure at different temperatures are shown in Fig. 5. The

percentage of conversion varies from 44 to 58 at 300 �C

when the pressure increased from 20 to 50 bars. This

implies that the pressure has a smaller influence on the PS

conversion than do the reaction time/temperature. In other

words, the pressure increase is less obvious than the tem-

perature increase for the PS degradation. This may be due

to that the starting reactants are solids and the increase in

pressure has neither effect on the collision between reac-

tants nor degradation reaction. Our finding agrees with

Kaminsky [16]. Also there was little effect for the change

of the applied pressure on the yield of styrene produced

from degradation process. All the data are collected in

Table 7.

Thermo-Chemical Degradation of PS

The thermo-chemical reaction was performed by using two

solvents, namely, cyclohexane and ethyl cyclohexane -

under critical conditions- in order to compare the priority

of thermal to thermo-chemical degradation or vice versa.

The products of the thermo-chemical reaction were com-

pared to those produced from thermal degradation under

the same reaction conditions.

Effect of Reaction Temperature

The conversion of poly styrene in thermo-chemical deg-

radation is depicted in Fig. 6. It is obvious that the con-

version increases by temperature to reach about 95 % in

presence of ethyl cyclohexane and about 89 % in presence

of cyclohexane.

Careful inspection to the data listed in Table 8, one can

conclude the following:

• Only gas and liquid products are produced from

thermo-chemical recycling of polystyrene.

• The oil yield decreases and the gas yield increase by

raising the reaction temperature.

• The % of conversion in case of degradation by ethyl

cyclohexane is much greater than that produced in case

of cyclohexane.

Analysis of the gaseous products from thermo-chemical

degradation is given in Table 9. The data reveal that the

most abundant gases are ethane, propane, ethylene, butane

and butane. They increase by temperature except butane

which increases by temperature in case of presence of

cyclohexane but it decreases by temperature in case of

ethyl cyclohexane. Furthermore, the gases propane, ethyl-

ene and butane produced from degradation by ethyl

cyclohexane are much more those produced in case of

Table 3 Yields of oil products in PS isothermal pyrolysis at different

reaction temperatures (at 50 bars and after an hour)


Compound Temperature (�C)

300 350 400

Toluene 3.2 4.1 4.5

Benzene 5.7 3.8 2.6

Styrene 66.8 76.4 81.1

Ethyl cyclohexane 12.2 11.4 7.4

1,3 diphenyl propane 3.1 2.7 1.3

1,2 diphenyl propane 2.5 1.1 1.9

1,4 diphenyl butane 1.7 0.5 0.4

1,3 diphenyl butane 1.9 0 0.6

1,3 diphenyl butene 2.1 0 0.2

% Y

ield

of

styr

ene

Time (min.)

Fig. 3 Yield of styrene produced from PS isothermal pyrolysis at

different time intervals

Table 4 Characterization of residual solid products in PS isothermal

pyrolysis at different reaction temperatures

Batch code Temperature (�C) Mn (g/mol) Mw (g/mol) PD

PSA1d 300 71,000 95.140 1.34

PSA2d 350 62,000 77.500 1.25

PSA3d 400 49,000 92.610 1.89

% c

onve

rsio

n

Time (min.)

Fig. 4 % Conversion of polystyrene in isothermal pyrolysis at

different time intervals


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degradation by cyclohexane. This observation may reflect

the efficiency of ethyl cyclohexane in converting polysty-

rene into smaller molecular weight gaseous hydrocarbons

than does cyclohexane and it also may be due to the sim-

ilarity of chemical structure between the ethyl cyclohexane

and polystyrene. Chen et al. [5] reported that the effect of

supercritical fluids in depolymerization of natural rubber

depends mainly on the compatibility of the solvent with the

polymer.

GC analysis data of the oil products produced from

thermo-chemical degradation are provided in Table 10. As

expected, styrene was the predominant liquid and its yield

increases by temperature to reach about 88.1 and 95.7 for

degradation in cyclohexane and ethyl cyclohexane

respectively. One can observe that the oil products in case

of ethyl cyclohexane were only styrene and ethyl cyclo-

hexane. Our findings are very close to those obtained by

Gyou-Cheol et al. [10].

Effect of Reaction Time

Yield of styrene produced from PS thermo-chemical deg-

radation at different time intervals is illustrated in Fig. 7. It

is clear that styrene yield was over than 95 % at the end of

thermo-chemical degradation by ethyl cyclohexane (i.e.

after an hour). It was 88.4 % in presence of cyclohexane.

This reveals that ethyl cyclohexane is more efficient than

cyclohexane in PS thermo-chemical recycling under the

same conditions. Gyou-Gyou-Cheol et al. [10] used

n-hexane for PS thermo-chemical degradation at tempera-

ture range (330–390 �C). They found that about 87 % of

the PS was converted at 390 �C after 90 min.

Effect of Pressure

Figure 8 shows the effect of the applied pressure on the %

of conversion of PS under thermo-chemical degradation

conditions in presence of ethyl cyclohexane and

Table 5 Characterization of residual solid products in PS isothermal

pyrolysis at different reaction temperatures

Batch

code

Temperature

(�C)

% Of conversion at different time

intervals

15 min 30 min 45 min 60 min

PSA1d 300 12 18 45 58

PSA2d 350 30 42 51 70

PSA3d 400 41 53 62 81

Table 6 % of Conversion in PS isothermal pyrolysis at different

reaction conditions (at 50 bars)


Time (min.) Temperature (�C)

300 350 400

15 31.1 42.8 51.5

30 45.3 55.9 64.7

45 61.6 72.4 72.9

60 66.8 76.4 81.1

% c

onve

rsio

n

pressure (bars)

Fig. 5 Effect of the applied pressure on the % of conversion of PS at

different temperatures

Table 7 Yield of styrene produced from PS isothermal pyrolysis at

different reaction conditions (at 50 bars)

Designation Pressure (bar) % Conversion Yield of styrene

PSA1a 20 44 51.4

PSA1b 30 50 58.3

PSA1c 40 56 61.2

PSA1d 50 58 66.8

PSA2a 20 57 65.7

PSA2b 30 64 71.3

PSA2c 40 68 75.2

PSA2d 50 70 76.4

PSA3a 20 69 67.9

PSA3b 30 75 72.5

PSA3c 40 79 77.9

PSA3d 50 81 81.1

% C

onve

rsio

n

Time(min.)

Fig. 6 % Conversion of polystyrene in thermo-chemical degradation

at different time intervals


123


cyclohexane. The applied pressure ranged between 20 and

50 bars. It is obvious that increasing the pressure had slight

effect on PS conversion. This runs parallel to the effect of

pressure in thermal degradation.

Comparison with the General Thermolysis

The conversions of the general thermal degradation and the

supercritical solvents (ethyl cyclohexane and cyclohexane)

degradation are shown in Fig. 9. The test conditions were

the same for both reactions, temperature of 300–400 �C at

15 min. interval for an hour, a pressure of 50 bars. In case

of the general thermolysis, the recorded conversion was

about 50 % at 300 �C at the end of reaction but it was

about 77 % and 62 % in a supercritical ethyl cyclohexane

and cyclohexane respectively. This means that the degra-

dation reaction takes place rapidly even at relatively low

temperature and pressure, if supercritical fluid is used. The

general thermal degradation test showed that about 81 %

conversion was attained only at 400 �C and higher. It

should be noted that under supercritical fluid conditions

(cyclohexane and ethyl cyclohexane), more than 88 and

96 % conversion have been attained at the same tempera-

ture. Our findings run parallel to those obtained by Gent

et al. [9] and Kanji et al. [17].

Analysis of Products

The variations of product composition under the various

temperatures and reaction times are thoroughly studied.

The products from thermal degradation of styrene are

Table 8 Effect of pressure on % of conversion and yield of styrene

produced from PS isothermal pyrolysis

Code Reaction temperature (�C) Yield (wt. %)

Gas Oil

PSB1d 300 3.4 96.6

PSB2d 350 5.7 94.3

PSB3d 400 6.2 93.8

PSC1d 300 4.7 95.3

PSC2d 350 6.8 93.2

PSC3d 400 9.1 91.9

Table 9 Yields of different products in PS thermo- chemical degradation at different reaction temperatures (at 50 bars and after an hour)

Batch code PSB1d PSB2d PSB3d PSC1d PSC2d PSC3d

Temperature (�C)

Compound 300 350 400 300 350 400

Methane – – – – – –

Ethane 5.7 6.3 7.1 3.4 6.9 7.8

Propane 20.1 18.9 16.4 15.4 16.9 18.2

Ethylene 24.2 26.2 30.2 27.2 30.8 32.4

Butane 34.4 30.2 27.4 35.2 37.3 38.6

Butene 15.6 17.8 18.3 11.9 3.6 1.7

Isobutene – 0.6 0.6 6.9 4.5 1.3

Table 10 Yields of oil products in PS thermo-chemical degradation at different reaction temperatures under the reaction conditions

Batch code PSB1d PSB2d PSB3d PSC1d PSC2d PSC3d

Temperature (�C)

Compound 300 350 400 300 350 400

Toluene 0.3 0.7 1.1 1.1 1.4 –

Benzene 0.4 0.9 1.4 – 0.5 –

Styrene 70.2 74.3 88.1 75.2 77.8 95.7

Ethyl cyclohexane 10.1 11.4 5.1 11.4 13.1 4.3

1,3 diphenyl propane 5.4 2.2 1.7 2.1 2.6 –

1,2 diphenyl propane 3.6 1.4 0.9 0.9 1.3 –

1,4 diphenyl butane 2.1 3.7 1.1 3.1 2.4 –

1,3 diphenyl butane 1.4 1.6 0.6 2.1 0.5 –

1,3 diphenyl butene 3.5 2.7 – 3.7 0.4 –

1,5-diphenyl 1,3-pentadiene 3.0 1.1 – 0.4 – –


123


provided in Tables (2, 3, 4) and those for thermo-chemical

recycling of polystyrene in Tables 8 and 9. Careful

inspection to the data listed in these tables, the following

outcomes can be abstracted:

• Thermal degradation produced gas, oil and solid

products whereas the thermo-chemical degradation

produced only gas and oil products.

• In both reactions, the % conversion of polystyrene

increases by temperature, time and pressure.

• The styrene yield produced from degradation under

ethyl cyclohexane is the highest among the other

reactions.

• The rate of degradation by ethyl cyclohexane is faster

than the other two types.

Conclusions

The degradation of PS was performed under thermal and

thermo-chemical conditions. The degradation reaction was

conducted at various combinations of conditions: temper-

ature 300–400 �C, pressure 20–50 bar and reaction time

0–60 min. It was shown that the decomposition started at an

early stage within 15 min and the conversion increased

drastically at the end of the reaction. The increase in tem-

perature or pressure of the reaction led to the enhancement

of the degradation reaction but the pressure variation had a

smaller effect on PS conversion than did the temperature

variation. Furthermore, it was found that the thermo-

chemical degradation is more effective than the thermal

degradation under the same conditions.

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% Y

ield

of

styr

ene

Time (min.)

Fig. 7 Yield of styrene produced from PS thermo-chemical degra-

dation at different time intervals

% C

onve

rsio

n

Pressure (bars)

Fig. 8 Effect of the applied pressure on the % of conversion of PS

under thermo-chemical degradation conditions

% c

onve

rsio

n

Time (min.)

Fig. 9 Comparison between thermal and thermo-chemical degrada-

tion of PS


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Thermo-Catalytic Versus Thermo-Chemical Recycling of Polystyrene Waste

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