Lewis Acid–Base Synergistic Catalysis for Polyethylene Terephthalate Degradation by 1,3-Dimethylurea/Zn(OAc)2 Deep Eutectic Solvent

Deep eutectic solvents (DESs) become more attractive in the catalytic field due to their biodegradation, low toxicity, and designability. This study focused on the active sites and influencing factors of 1,3-dimethylurea (1,3-DMU) based DESs in the polyethylene terephthalate (PET) glycolysis process. It is found that the active site of urea derivatives is the amino group, and the basicity and steric hindrance of the amino group affect its catalytic activity. Additionally, the mechanism of PET glycolysis reaction catalyzed by DES was investigated. The outstanding catalytic activity of DES can be attributed to the synergistic effect of acid and base formed between metal salts and 1,3-DMU. Under the optimization conditions, PET (5.0 g), ethylene glycol (20.0 g), and catalyst (n(1,3-DMU)/n(Zn(OAc)2) 4/1, 0.25 g) at 190 °C for 20 min, the PET conversion is up to 100%, and the yield of bis(hydroxyalkyl) terephthalate (BHET) is 82%. Furthermore, the kinetic research shows that the glycolysis of PET follows the shrink-core model, and the apparent activity energy is 148.89 kJ/mol.