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 (Vo)-rich catalyst under air, achieving space time yield (STY) of 505.2 gDMT<middle dot>gcat-1<middle dot>h-1 and 957.1 gBHET<middle dot>gcat-1<middle dot>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 Vo-Zn2+-O-Fe3+ sites, highlighting the critical role of Vo-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. Polyester waste is increasingly accumulating in the environment, and alcoholysis recycling offers a sustainable management solution. This study demonstrates the use of an oxygen vacancy-rich catalyst to transform waste blended polyester/textiles into high-value monomers.