Depolymerization of PET by glycolysis

Abstract

The chemical depolymerization of poly(ethylene terephthalate) or PET has led to various opportunities to recycle polyester feedstock and convert them into high-value products. PET’s monomer BHET and its oligomers obtained from these processes can be used as a component in polymer composites or be converted to various materials such as polyesters, polyurethane resins, and ester plasticizers. The monomer BHET is obtained by the glycolysis of PET, whose kinetics and catalysis are investigated in this study. Although glycolysis has been commonly modeled as a second-order reaction, the generalized kinetics approach applied in this study reveals that a nucleation-based kinetic behavior can be observed. Such nucleation-based kinetics affects the depolymerization in terms of an induction period and scission-induced chain reorganization. Moreover, the application of non-conventional glycolysis catalysts based on magnetically recoverable iron oxide nanoparticles is studied. Instead of the co-precipitation method previously developed to fabricate the iron oxide nanocatalyst, a single-step, surfactant-free synthesis using supercritical ethanol produced efficient nanocatalysts. Using the supercritical synthesis approach, a much simpler synthesis method is developed while also being able to easily fabricate mixed-metal nanocatalysts such as iron oxide spinels. The contribution of this study to the fundamental understanding of the glycolysis kinetics and to development of depolymerization catalysts is expected to further improve existing polymer recycling processes for PET.