Assessment of PET Depolymerization Processes for Circular Economy. 1. Thermodynamics, Chemistry, Purification, and Process Design

Abstract

Poly(ethylene terephthalate) (PET) is the most widely produced thermoplastic and is used in drink bottles, packaging, and textiles. Chemical depolymerization represents a way to recycle PET that is robust to the low purity and quality of some waste PET sources. This work investigates the three primary routes to depolymerize PET into feedstocks used to produce the PET polymer: methanolysis, glycolysis, and hydrolysis. This work is unique in providing a thorough review of the depolymerization thermodynamics, chemistry, purification strategies, and design of PET depolymerization processes from an industrial perspective. This work provides detailed descriptions of different variants of PET depolymerization processes. We summarize available data necessary to design a PET depolymerization process and indicate where gaps in data exist. We demonstrate the importance of separation and purification sections of the process, which are rarely addressed in academic literature. We also demonstrate different designs and strategies that industrial technologies employ to address challenges.

Assessment of PET Depolymerization Processes for Circular Economy. 2. Process Design Options and Process Modeling Evaluation for Methanolysis, Glycolysis, and Hydrolysis

“…The PET in the model represents both the polymer and lower-molecular-weight oligomers. We provide an example of the operation of the rectifier with the vapor methanolysis reactor in our associated work …”

“…We use the same reaction conditions described in our associated work . The reaction temperature is 260 °C, the reaction pressure is 300 kPa, and the methanol-to-PET ratio is 4 by mass.…”

“…Patent literature review demonstrates two types of purification for glycolysis with relatively substantial differences. One type, used by IFPEN and JEPLAN, utilizes short-path distillation (SPD) to separate heavies and solids from BHET product . We have discussed SPD in some detail in our associated work .…”

“…This forces reclaimers to extensively sort waste PET to create bales of clear or lightly colored bottles. Colored bottles and PET packaging are typically recycled to low-value products . More importantly, mechanical recycling of PET is almost entirely limited to bottles, which only represent ∼30% of PET end use.…”

“…We refer the reader to Table S1 in the Supporting Information that presents the chemical formulas and molecular structures of reactants, products, and byproducts relevant to PET depolymerization. In our associated work, we provide a comprehensive literature review of these depolymerization routes, along with purification techniques, and commercial technologies being developed.…”