Highly Efficient Glycolysis of Polybutylene Terephthalate to Value-Added Monomers Catalyzed by 1,4-Butanediol Dispersions of Ultrasmall Zinc Oxide Nanoparticles

The escalating global demand for poly(butylene terephthalate) (PBT), as one of the five major engineering plastics, has led to severe ecological crises and significant resource consumption. In this work, we employ 1,4-butanediol dispersions of ultrasmall zinc oxide nanoparticles (ZnO NPs) with an average size of 2.8 nm and excellent dispersity as catalysts for the highly efficient glycolysis of PBT using 1,4-butanediol. Specifically, complete depolymerization of PBT and approximately 98% yield of bis(4-hydroxybutyl) terephthalate (BHBT) are achieved within 45 min at 200 °C by only a minimal amount of ZnO NPs (0.1 wt %). More importantly, 95% PBT conversion can still remain after five cycles, exhibiting high recyclability of ZnO NPs. The possible reaction mechanism for glycolysis of PBT in 1,4-butanediol over ZnO NPs is proposed, and the reaction kinetics is also studied with an activation energy of 149.7 kJ/mol. Furthermore, ZnO NPs also show outstanding catalytic activity in the methanolysis of PBT, reaching over 97% yield of dimethyl terephthalate (DMT) within 60 min at 160 °C. This work provides a sustainable pathway for efficient recycling and reuse of PBT and broadens its market prospect.