KINETIC STUDY OF

CATALYTIC GLYCOLYSIS OF PET WASTES

WITH ZINC ACETATE

CHAN WEI TATT

UNIVERSITI MALAYSIA PAHANG

KINETIC STUDY OF

CATALYTIC GLYCOLYSIS OF PET WASTES

WITH ZINC ACETATE

CHAN WEI TATT

A thesis submitted in fulfillment of the requirements

for the degree of

Bachelor of Chemical Engineering

Faculty of Chemical and Natural Resources Engineering

University Malaysia Pahang

February 2013

vi

TABLE OF CONTENTS

TITLE

PAGE

SUPERVISOR’S ENDORSEMENT ii

DECLARATION iii

DEDICATION iv

ACKNOWLEDGEMENT v

ABSTRACT ix

ABSTRAK x

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF ABBREVIATIONS xv

LIST OF SYMBOLS xvi

LIST OF APPENDIX xvii

CHAPTER 1 - INTRODUCTION

1.1 Introduction 1

1.2 Problem statement 3

1.3 Research objectives 4

1.4 Research scopes 5

1.5 Expected outcomes 6

1.6 Significance of research 6

1.7 Summary of chapter 7

CHAPTER 2 – LITERATURE REVIEW

2.1 Introduction 8

2.2 Polyethylene Terephthalate(PET) 9

2.3 Synthesis of PET 11

2.4 Recycling of PET

2.4.1 Mechanical recycling

14

15

vii

2.4.2 Chemical recycling 16

2.5 Glycolysis

2.5.1 Glycolysis used in glycolysis

2.5.1.1 Di-ethylene glycol (DEG)

2.5.2 Catalyst used in glycolysis

2.5.2.1 Zinc Acetate

18

21

22

23

24

2.6 Optimization using Response Surface Methodology(RSM) 26

2.7 Kinetic study of glycolysis reaction 29

CHAPTER 3 - METHODOLOGY

3.1 Introduction 31

3.2 Materials, glassware and apparatus

3.2.1 Materials

3.2.2 Glassware and apparatus

32

32

32

3.3 Preparation of PET flakes 33

3.4 Glycolysis of PET 34

3.5 Characterization of glycolyzed PET waste 36

3.6 Optimization 37

CHAPTER 4 - RESULT AND DISCUSSION

4.1 Characterization of glycolyed PET 39

4.2 Thermal analysis of glycolyzed PET 42

4.3 Influence of reaction conditions

4.3.1 Influence of the glycolysis time

4.3.2 Influence of reaction temperature

4.3.3 Influence of the amount of catalyst

4.3.4 Influence of the amount of DEG

44

44

46

49

50

4.4 Optimization

4.4.1 Glycolysis conversion percentage

4.4.2 Optimization of glycolysis reaction

52

55

59

4.5 Kinetic study of glycolysis reaction 60

viii

CHAPTER 5 - CONCLUSION AND RECOMMENDATION

5.1 Conclusion 67

5.2 Recommendation 68

REFERENCES 69

APPENDICES 75

ix

KINETIC STUDY OF CATALYTIC GLYCOLYSIS OF PET WASTES WITH

ZINC ACETATE

ABSTRACT

Poly(ethylene terephthalate) (PET) was depolymerized by di-ethylene glycol

(DEG) in the presence of zinc acetate. Qualitative analysis showed that the main product

from glycolysis was bis(hydroxylethyl) terephthalate. Fourier Transform infra-red (FTIR)

was used for characterization of product while thermo-gravimetry analysis (TGA) and

differential scanning calorimetry (DSC) were used for thermal analysis. The respond

surface methodology (RSM) was used to predict the optimum conditions of reaction

which includes time, temperature, amount of catalyst and amount of DEG. Besides that,

the analysis of variance (ANOVA) was employed to evaluate the validity of the

developed model. The maximum conversion obtained from RSM was 99.79%, The

optimum temperature, time, amount of catalyst and amount of DEG were 183.37 °C,

0.82 hour, 0.09 g and 10.33 g respectively. Lastly, a simple theoretical power-law model

was developed to predict the time evolution of conversion. This kinetic model was found

to be consistent with the experimental data. From the study, activation energy and

enthalpy of reaction of 38.24 kJ/mol and 14.87kJ/mol were obtained, respectively.

x

KAJIAN KINETIC TERHADAP PEMANGKINAN GLIKOLISIS BAHAN

BUANGAN PET DENGAN ASETAT ZINC

ABSTRAK

PET diuraikan dengan menggunakan di-ethylene glycol (DEG) dengan kehadiran

zinc acetate sebagai pemangkin. Produk yang dihasilkan daripada glikolisis adalah

BHET telah dipastikan melalui analisis kualitatif. FTIR telah digunakan untuk pencirian

manakala TGA dan DSC telah digunakakn untuk melaksanakan analisis haba.

Sementara itu, RSM telah digunakan untuk mendapatkan keadaan optima untuk tindak

balas glikolisis seperti masa, suhu, jumlah pemangkin dan juga jumlah DEG. Selain itu,

ANOVA telah digunakan untuk mengesahkan model yang dicadangkan oleh RSM. Pada

keadaan optima, penukaran setinggi 99.79% telah direkodkan. Keaddan optima untuk

tindak balas glikolisis adalah pada 183.37oC, 0.82 jam, 0.09g zinc asetat dan 10.33g

DEG. Daripada pengajian tersebut, tenaga pengaktifan dan entalpi tindak balas yang

ditentukan adalah 38.24 kJ/mold dan 14.87 kJ/mol masing-masing.

xi

LIST OF TABLES

TITLE Page

Table 2.1 Catalyst studied in PET glycolysis 25

Table 4.1 Detected functional groups on FTIR 40

Table 4.2 Conversion of PET and selectivity of product at

different reaction time

44

Table 4.3 Conversion of PET and selectivity of product at

different reaction temperature

47

Table 4.4 Conversion of PET and selectivity of BHET at

different amount of catalyst

49

Table 4.5 Conversion of PET and selectivity of product at

different amount of catalyst.

50

Table 4.6 ANOVA for response quadratic model for

conversion percentage

53

Table 4.7 Model Validation 53

Table 4.8 Optimum parameters for glycolysis reaction of PET 60

Table 4.9 Kinetic parameters of the catalytic glycolysis of PET

at different temperatures and varying zinc acetate

concentration

66

xii

LIST OF FIGURES

TITLE Page

Figure 2.1 Formation of commercial PET 9

Figure 2.2 Macromolecular formula of PET 11

Figure 2.3 PET synthesis from DMT and EG 13

Figure 2.4 Direct esterification of EG with TPA in PET

synthesis

14

Figure 2.5 (a) Reaction mechanism of uncatalyzed PET

glycolysis

(b) Reaction mechanism of catalyzed PET

glycolysis

18

18

Figure 2.6 Response surface plot 28

Figure 3.1 Setup for glycolysis reaction 35

Figure 3.2 Overview of methodology 38

Figure 4.1 (a) Proposed structure of glycolyzed product 40

Figure 4.1 (b) FTIR spectra of raw materials 41

Figure 4.1 (c) FTIR spectra of DEG and glycolyzed PET 41

Figure 4.2 DSC scans of glycolyzed PET 43

Figure 4.3 TGA curves of glycolyzed PET 43

Figure 4.4 Effect of reaction time on the conversion of PET

and selectivity of glycolyzed product

45

Figure 4.5 Effect of reaction time on products distribution 46

Figure 4.6 Effect of reaction temperature on the conversion

of PET and selectivity of glycolyzed product

47

Figure 4.7 Effect of reaction temperature on products

distribution

48

Figure 4.8 Effect of amount of catalyst on the conversion of

PET and selectivity of product

49

xiii

Figure 4.9 Effect of molar ratio of DEG: EPT on the

conversion of PET and selectivity of product

50

Figure 4.10 Linear correlation plots between actual and

predicted response for conversion percentage

54

Figure 4.11 (a) Surface plot (3D) showing variation in glycolysis

conversion percentage with glycolysis time and

temperature

55

Figure 4.11(b) Surface plot (3D) showing variation in glycolysis

conversion percentage with amount of catalyst and

temperature

56

Figure 4.11 (c) Surface plot (3D) showing variation in glycolysis

conversion percentage with weight of DEG and

temperature

57

Figure 4.11(d) Surface plot (3D) showing variation in glycolysis

conversion percentage with weight of catalyst and

time

58

Figure 4.11(e) Surface plot (3D) showing variation in glycolysis

conversion percentage with weight of DEG and

time

58

Figure 4.11(f) Surface plot (3D) showing variation in glycolysis

conversion percentage with weight of DEG and

weight of catalyst

59

Figure 4.12(a) Fitting of kinetic data according to Eq. (13) at

different temperature and varying amount of

catalyst

64

Figure 4.12(b) Effect of reaction time, temperature, and amount

of catalyst on yield (according to Eq. (14))

64

Figure 4.12(c) Plot of the kinetic rate constant k1’ as a function of

catalyst concentration

65

xiv

Figure 4.12(d) Arrhenius plot of pseudo first order rate constant

k1 for the direct reaction of PET glycolysis in the

presence of zinc acetate

65

Figure 4.12(e) Van’t Hoff plot of the equilibrium constant of

PET glycolysis

66

xv

LIST OF ABBREVIATIONS

ANOVA - Analysis of variance

BHET - bis(2-hydroxyethylene) terephthalate

CV - Coefficient of variance

DEG - Di-ethylene Glycol

DMT - Dimethyl terephthalate

DSC - Differential Scanning Calorimetry

EG - Ethylene glycol

FTIR - Fourier Transform Infra-Red

n. d. - no date

PE - Polyester

PEG - Polyethylene glycol

PET - Polyethylene terephthalate

PP - Polypropyl

R2 - Correlation coefficient value

R2

adj - Adjusted correlation coefficient value

RSM - Response Surface Methodology

TGA - Thermo-Gravimetry Analaysis

TPA - Terephthalic acid

UF - Urea formaldehyde

UV - Ultraviolet

xvi

LIST OF SYMBOLS

% - percent

atm - atmosphere

C - concentration

cm - centimetre

g - gram

h - hour

Hg - mercury

K - Kelvin

kg - Kilogram

kJ - kilojoule

L - litre

m - meter

mL - mililitre

mm - milimeter

oC - degree celcius

t - time

xvii

LIST OF APPENDICES

Page

APPENDIX A Gantt Chart for URP I and II 75

APPENDIX B FTIR Spectra 77

APPENDIX C Thermographs of DSC and TGA 78

APPENDIX D Results of Optimization 79

1

CHAPTER 1

INTRODUCTION

1.1 Background of research

The usage of industrial synthesized polymer are widely discovered in many

consumer end products, especially the polyethylene terephthalate (PET), being one of

the most popular in the polyester families. According to a reported technical paper, PET

consumption was approximately 15.3 million tons in 2009 (GBI, 2010). As the

population increases from year to year, the usage of PET may be doubled, and most

likely will be tripled in the future. PET is characterized by its high strength, low density,

low gas permeability and good aesthetic appearance (Liu, Wang, and Pan, 2011). The

products of PET cover a wide range of application, which includes plastic drinking

bottles, plastic bags, food containers, and even toys for kids. Indeed, the invention and

commercial application of PET has brought a lot of benefits and conveniences to

mankind in the aspect of improvement on the standard of life; however, the excess usage

of PET has also caused a lot of serious environmental issues. These environmental

2

issues can be reviewed from various aspects, such as recycling, landfill disposal,

incineration as well as marine pollution. Out of the issues arisen, the disposal of PET

products can be considered as a very critical issue and needed to be solved as soon as

possible. PET can be classified into two categories, namely biodegradable and non-

biodegradable PET. Due to the economical factor, majority of the PET produced are

non-biodegradable, as they are much cheaper in the production cost. Actually, the

biodegradable PET has been existed for a long time, but the high expense has never

made it become a commercial option (Chong and Kim, 2007). When the amount of

produced PET increases from years to years and yet no better alternatives to deal with

the environmental issues arisen, it will eventually lead to serious environmental

problems. For an example, the villagers in the rural areas disposed the PET products

such as bottles and plastic bags by open burning, which is a very unwise decision and

action since the toxic fumes are released to the air and it will harm both the environment

and mankind significantly.

The productions of PET are most probably encouraged by the economic factor,

which is a critical and vital aspect to be considered in any production processes. The low

manufacturing and processing costs of PET is definitely an important factor behind the

progressive development of PET usages. When the amount of PET increases, the

problems of PET wastes disposal are created. Among all the alternatives available,

recycling is the most well-known, commercial and common solution. Since most of the

PET products are non-biodegradable, it is always a wise decision to recycle or reuse the

PET products (waste to wealth). More and more researches are currently directed

towards the recycling of PET waste, and they are mainly encouraged and motivated by

3

both the environmental and economic reasons. The recycling of plastic became popular

in the era of 1990s. Two classes of plastics are thermosetting and thermoplastics. For

thermoplastics, they were melted and remoulded to form new products; for

thermosetting plastics, they were normally ground up and used as filler.

In this research, the collected PET waste will be recycled using glycolysis

process, in which the di-ethylene glycol (DEG) is used as the main glycol chemical and

zinc acetate is used as trans-esterification agent (catalyst).

1.2 Problem statement

The varieties of PET products seem to be an endless list as they can be found

commonly all around the world. Most of the manufacturers will choose to produce non-

biodegradable PET rather than those with biodegradable one since the cost of production

between these two PETs is considerably huge in their difference. As the production of

PET products give a profitable return to the country, however, when the amount of PETs

produced are growing more rapidly than the amount of PETs disposed or recycled, it

started to create environmental problems.

Malaysia is one of the countries that facing this problem. A clear indication can

be observed that the PET products such as plastic bottles and containers occupy the

majority quantities of the trash collected. There are many alternatives available

nowadays to deal with the PET waste, utilizes them by turning them from waste to

4

wealth being the wisest choice. However, before they can be integrated into particular

product, it is necessary to go through the characterization process so that their chemical

and physical properties can be determined. It helps the experts to decide whether they

can be integrated into which products by looking at the characterization results.

1.3 Research objectives

Based on the problem statement that had been identified, the following

objectives are proposed:

i. To carry out the glycolysis process using the DEG as glycol and zinc

acetate as trans-esterification agent.

ii. To investigate the impacts of reaction parameters on the glycolysis

process of PET.

iii. To carry out the optimization of parameters for the glycolysis process.

iv. To perform the kinetics study of glycolysis process.

5

1.4 Research scopes

By identifying the scopes of the study, it provides a guideline in conducting the

experiment. The study concentrates on the scopes as listed as below in order to achieve

the objectives stated above.

i. The glycolysis process will be conducted using di-ethylene glycol (DEG),

and zinc acetate as trans-esterification agent (catalyst).

ii. Fourier Transform Infrared Spectrometry (FTIR), Thermogravimetry analysis

(TGA) and Differential Scanning Calorimetry (DSC) will be used for

characterization of glycolyzed PET.

iii. The Response Surface Methodology (RSM) will be used to perform the

optimization for glycolysis reaction.

iv. The kinetic study of glycolysis was developed using a simple theoretical

power-law model.

6

1.5 Expected outcomes

By doing this research, the following expected outcomes are formulated:

i. It is expected that the glycolysis of PET wastes can be carried out successfully.

ii. It is expected that the characterization of PET waste can be done so that it can

provide useful information about the glycolysis process.

iii. It is expected that the optimization of reaction variables can be performed so that

optimum glycolysis reaction can be achieved.

iv. It is expected the kinetics study can be developed to provide insight into the

glycolysis reaction.

1.6 Significance of research

This research is able to provide information about the changes to PET waste in

glycolysis process. The qualitative and quantitative analysis of the chemical process will

also provide useful information about the PET waste and optimum temperature and time

can be obtained. The optimization carried out will help researchers to perform the same

experiment more effectively. Furthermore, the kinetics study is able to provide useful

information that will help people to understand more about the glycolysis reaction.

7

1.7 Summary of chapter

Overall, this chapter gives explanation and elaboration about the research that is

going to be conducted. In early stage, there are some descriptions on the background of

the problem that exists currently. This includes the environmental issues brought upon

the vast usage of PET products. After all the problems had been clarified, the next step is

to set the expected outcomes to achieve the objectives within the scopes of research.

Finally in this chapter is the significance of the research, which provides explanation on

the importance of conducting this research to provide useful information about the

glycolysis process.

8

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

Literature review is a preliminary study for related topics before developing a

research, in this case. It is one of the important techniques used in gathering data and

information, as well as facts in a research development. Literature review can be done

through researching and study of previous and similar researches. Study on the previous

researches will help to generate solutions for improving or create new innovative ideas

in the functions of the research, and hence new implementation can be done for the

benefits of mankind.

9

2.2 Polyethylene Terephthalate (PET)

Polyethylene Terephthalate (PET) is one of the members from the polyester

family, which is also an industrially important thermoplastic resin. PET is mainly

formed from terephthalic acid (HOOC-C6H4-COOH) and ethylene glycol (HO-C2H4-

OH), in which both were the derivatives of oil feed stocks. The formation of PET can be

illustrated by the figure shown below. The average molecular weight for commercial

PET (bottle grade) is 192 g mol-1

(López-Fonseca et al, 2011).

Figure 2.1 Formation of commercial PET

(Source: Vedula, 2005)

10

PET is a semi-crystalline polymer composed of both crystalline and amorphous

regions, as well as a versatile engineering plastics material with excellent thermal and

chemical resistance and mechanical performance (Vedula, 2005). Due to its properties of

chemically flexible nature which can be modified and applied commercially, the PETs

have been studied extensively since a long time ago. It has a high melting point of 250oC

and glass transition temperature of 80oC, PETs can still retain its excellent mechanical

properties up to 175 - 180oC. Because PET exists as a semi crystallizer, its crystallinity

varies from amorphous to fairly high crystalline degree. It can be highly transparent and

colourless, but thicker samples are usually opaque and off-white. Overalls, PET is a hard,

stiff, strong, dimensionally stable material that absorb very little amount of water.

Furthermore, it has good barrier properties and has good chemical resistance except to

alkalis, which it can be recycled chemically using alkaline hydrolysis process (Vedula,

2005).

The application of PET can be found almost everywhere. Its product varies from

the manufacture of video and audio tapes, X-ray films, high strength fibres, food

packaging, especially of soft-drink bottles (Joshi, 2011; Kao, Cheng, and Wan, 1996).

Typical applications of PET include in the automotive, electrical, and packaging fields.

For the automotive field, PET is applied in the production of sunroof rails and wiper

blade supports. For the electrical field, PET is produced as computer fans, fuse holder

and insulated housings. On the other hands, PET is used a soft drink container and

packaged food containers. Generally, the usage of PET almost can be seen everywhere

surrounding the mankind.