Depolymerization mechanisms and closed-loop assessment in polyester waste recycling

Abstract Alcoholysis of poly(ethylene terephthalate) (PET) waste to produce monomers, including methanolysis to yield dimethyl terephthalate (DMT) and glycolysis to generate bis-2-hydroxyethyl terephthalate (BHET), is a promising strategy in PET waste management. Here, we introduce an efficient PET-alcoholysis approach utilizing an oxygen-vacancy ( V o )-rich catalyst under air, achieving space time yield (STY) of 505.2 g DMT ·g cat −1 ·h −1 and 957.1 g BHET ·g cat −1 ·h −1 , these results represent 51-fold and 28-fold performance enhancements compared to reactions conducted under N 2 . In situ spectroscopy, in combination with density functional theory calculations, elucidates the reaction pathways of PET depolymerization. The process involves O 2 -assisted activation of CH 3 OH to form CH 3 OH * and OOH * species at V o -Zn 2+ –O–Fe 3+ sites, highlighting the critical role of V o -Zn 2+ –O–Fe 3+ sites in ester bond activation and C–O bond cleavage. Moreover, a life cycle assessment demonstrates the viability of our approach in closed-loop recycling, achieving 56.0% energy savings and 44.5% reduction in greenhouse-gas emissions. Notably, utilizing PET textile scrap further leads to 58.4% reduction in initial total operating costs. This research offers a sustainable solution to the challenge of PET waste accumulation.