A Thesis Entitled Chemical Recycling of Poly (Ethylene Terephthalate)
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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 i 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. ii 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 iii 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 iv 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. v 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. vi 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 vii 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