Catalytic Upcycling of PET: From Waste to Chemicals and Degradable Polymers

ConspectusThe global plastic waste crisis, driven by exponential growth in plastic production, has necessitated the development of innovative approaches for recycling and upcycling. Poly(ethylene terephthalate) (PET), one of the most widely used polyesters, poses significant environmental challenges due to its chemical stability and non-degradable nature. While existing methodologies have made significant contributions to the recycling of PET waste through mechanical or chemical processes, an emerging strategy of upcycling PET into high-value products may offer greater potential to present significant advantages in economic feasibility and long-term sustainability. Over the past ten years, hundreds of publications have explored the upcycling of PET in the laboratory through catalytic reactions with various co-reactants, primarily water, hydroxides, alcohols, and amines. In this Account, we summarize our contributions on the design of novel catalytic strategies for the upcycling of PET along with other problematic wastes and H2. For instance, we explored the co-upcycling of PET with other plastics such as poly(vinyl chloride) (PVC) and polyoxymethylene (POM), demonstrating how the chlorine from PVC could be utilized to depolymerize PET into terephthalic acid (TPA) and 1,2-dichloroethane (EDC) and how the formaldehyde derived from POM could be converted into 1,3-dioxolane through the condensation reaction with ethylene glycol (EG) derived from PET. We also developed a one-pot catalytic system that simultaneously hydrogenated PET and CO2 into high-value chemicals, leveraging a dual-promotion effect on both CO2 hydrogenation and PET methanolysis and achieving high yields of EG, dimethyl cyclohexanedicarboxylate (DMCD) and p-xylene (PX). A H2-free, one-pot, two-step catalytic process was further presented to upcycle PET with CO2, yielding formic acid (FA) and TPA. Moreover, we demonstrated a direct hydrogenation strategy to convert PET into a degradable polyester, poly(ethylene terephthalate)-poly(ethylene-1,4-cyclohexanedicarboxylate) (PET-PECHD), through controlled hydrogenation of its aromatic rings, which preserved the polymer's mechanical and thermal properties while introducing degradability, offering a sustainable alternative for packaging materials.Our research highlights the importance of catalyst design, reaction engineering, and process optimization in achieving efficient and scalable PET upcycling processes. By integrating multiple catalytic steps and leveraging waste-derived resources, we outline a roadmap for the near future of PET upcycling, aiming to enable breakthroughs in real-life plastic upcycling.