Synergistic Catalysis Driven by Solvent Effect: Efficient Glycolysis of Polyethylene Terephthalate (PET) by the Zn(OAc)₂/DBU-DMSO System

The widespread use of poly(ethylene terephthalate) (PET) has led to severe environmental pollution and significant resource depletion. The depolymerization of waste PET into bis(2-hydroxyethyl) terephthalate (BHET) offers considerable potential for chemical recycling. Although conventional glycolysis faces challenges such as low degradation efficiency and high energy requirements, an efficient catalytic method was developed herein to convert postconsumer PET into BHET under milder conditions. The incorporation of the cosolvent dimethyl sulfoxide (DMSO) into the reaction system reduced the degradation temperature to 150 °C, significantly lower than the temperature observed without cosolvents, which exceeded 190 °C. Under optimized conditions, the combination of a metal catalyst and the organic nitrogen heterocycle 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) enabled complete depolymerization of PET within 90 min, yielding BHET at 80.11%. In addition, the recrystallized product was repolymerized into PET, enabling closed-loop resource recycling. Life cycle assessment (LCA) indicates that this closed-loop approach is not only technically feasible but also environmentally beneficial, reducing energy consumption by approximately 64.54% and greenhouse gas emissions by 37.32%. This strategy offers a practical low-carbon solution for the sustainable recycling of waste PET.