Integrated Conversion of Polyesters, CO2, and Glycerol via Ethylene Oxide-Mediated Tandem Process.

The co-conversion of poly(ethylene terephthalate) (PET), CO2, and renewable carbon resources offers a sustainable strategy for reducing plastic waste and carbon emissions, but remains challenging. Here, we develop a one-pot cycloaddition-transesterification-glycolysis (CTG) tandem process to efficiently convert PET, CO2, and glycerol into bis-hydroxyethyl terephthalate (BHET) and glycerol carbonate, achieving yields of 92% and 99%, respectively. The process begins with the cycloaddition of ethylene oxide and CO2 in an ionic liquid, followed by transesterification with glycerol to produce glycerol carbonate and ethylene glycol. The in situ-generated ethylene glycol participates in PET glycolysis to yield BHET catalyzed by zinc acetate. Kinetic studies, isotope labelling, and theoretical calculations reveal that ethylene oxide serves two functions: (i) swelling the PET matrix to enhance mass transfer and (ii) providing ethylene glycol. The synchronized kinetics of cycloaddition, transesterification, and glycolysis enable ethylene oxide to play both roles effectively, significantly accelerating PET depolymerization at mild temperatures.