Effect of anion structure on the ethanolysis of poly(ethylene terephthalate) in imidazolium-based ionic liquids

Depolymerizing waste poly(ethylene terephthalate) (PET) in ionic liquids (ILs) offers an efficient and sustainable route for chemical recycling. In this study, PET was depolymerized using imidazolium-based ILs containing various anions, including acetate, chloride, dimethyl phosphate, methyl sulfate, and nitrate, to elucidate the role of anion structure in depolymerization. Among them, 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]) exhibited remarkable catalytic activity, achieving complete PET conversion and a diethyl terephthalate (DET) yield of 67 % under optimized conditions, with over 95 % IL recovery after three reuse cycles. The catalytic behavior was rationalized by density functional theory (DFT) and COSMO-RS calculations, which revealed that anion-dependent O–H bond activation and hydrogen-bonding strength strongly influence PET depolymerization. These findings highlight the critical role of IL anion design in promoting efficient and recyclable PET ethanolysis systems. • PET was depolymerized in imidazolium-based ionic liquids containing various anions. • Only [EMIM][OAc] exhibited significant depolymerization activity. • A PET conversion of 100 % was obtained under the optimal ethanolysis conditions. • The ionic liquid was recovered in >95 % yield over three consecutive cycles of use. • The nature of the anion in the IL affects the extent of PET depolymerization.