Depolymerization mechanisms and closed-loop assessment in polyester waste recycling

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 N₂. In situ spectroscopy, in combination with density functional theory calculations, elucidates the reaction pathways of PET depolymerization. The process involves O₂-assisted activation of CH₃OH to form CH₃OH^* and OOH^* species at V_o-Zn²⁺-O-Fe³⁺ sites, highlighting the critical role of V_o-Zn²⁺-O-Fe³⁺ 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.