Efficient Glycolysis of Polyethylene Terephthalate (PET) Catalyzed by Cyclic(alkyl)(amino)carbene Copper Complexes

Polyethylene terephthalate (PET) is widely used, yet the accumulation of its waste poses serious environmental challenges, making efficient recycling essential. PET glycolysis using EG as a solvent has emerged as a green recycling strategy. In this study, a cyclic alkylamino carbene copper (CAAC-Cu) complex was prepared as a catalyst for PET glycolysis. Under optimized conditions (160 °C, 90 min, catalyst amount 3 wt%, and PET/EG = 1:4.), PET conversion reached 98.2%, the selectivity toward BHET was 88.1%, and the yield was 86.5%. Kinetic analysis indicated that the glycolysis follows first-order kinetics with an activation energy of 98.7 kJ mol−1. In addition, the catalyst can be recovered together with excess EG, and after multiple recycles, PET degradation remained above 95% and BHET yield remained above 80%. A possible mechanism has also been proposed: Cu acts as a Lewis acid coordinating to the carbonyl oxygen of PET, facilitating ester bond activation, while the amino-carbene forms hydrogen bonds with EG, assisting bond cleavage in a Brønsted-base manner. This catalytic system provides a novel and efficient approach for the green, high-performance glycolysis of PET.