Enhanced polyethylene terephthalate (PET) glycolysis with biochar-supported organic ionic liquid-based catalysts

Glycolysis of polyethylene terephthalate (PET) is a promising chemical recycling approach that converts PET waste into its monomer, bis(hydroxyethyl)terephthalate (BHET). Ionic liquids (ILs) have emerged as promising catalysts; however, key research gaps remain in limited comparisons between metal-based and organic-based ILs, inadequate understanding of the roles of cations and anions, and insufficient assessing catalyst supports such as biochar. In this study, Density Functional Theory screening identified [Ch][OAc] and [bmim]2[CoCl4] as the most effective catalysts, with experimental validation confirming that superior BHET yield of [bmim]2[CoCl4]. Mechanistic insights reveal that IL anions can play a bifunctional catalytic role, whereas the cation contribution may be limited, challenging the established IL-catalysed mechanism. The biochar-supported [Ch][OAc] system increased BHET yield from 46% to 79% with 99% PET conversion, outperforming the corresponding metal-based biochar catalyst. These results advance understanding of IL-catalysed PET glycolysis and demonstrate the potential of biochar-supported organic ILs for plastic waste valorisation.