Synergistic catalysis of ionic liquids and metal salts for facile PET glycolysis

Polyethylene terephthalate (PET), a thermoplastic engineering polyester, is one of the most widely used polymers today. However, PET can be recycled and difficult to degrade under atmospheric conditions due to high chemical stability, causing problems such as environmental pollution and waste of resources. Through comparative experiments, it was found that protic ionic liquids (PIL) and transition metal salts have a synergistic catalytic effect, under optimal reaction conditions, PET was subjected to glycolysis at 180 °C for 20 min by using PIL-Zn(OAc)2 as a catalyst, PET was almost completely converted and the yield of monomeric BHET reached a peak of 91.25 %, this is much higher than the yield using ionic liquids or metal salts alone. In this paper, protic ionic liquids were synthesized and compounded with transition metal salts as catalysts for PET glycolysis. Through FT-IR, NMR, TG and SEM analysis of the experimental product, it can be determined that the target product is bis-hydroxyethyl terephthalate (BHET). The composite catalyst still exhibited excellent catalytic activity after 8 cycles. Further, this study explored the reaction kinetics of PIL-Zn(OAc)2 catalyzed PET glycolysis to obtain an apparent activation energy Ea = 120.59 kJ/mol of the reaction. Finally, this paper also discussed the possible reaction pathway of the composite catalyst, hoping this composite catalyst can provide a reference for the industrialization of PET recycling.