Structure Designed Methylpiperidine Ionic Liquids for Efficient and Recyclable PET Glycolysis

Developing efficient and recyclable catalysts is crucial for advancing the chemical recycling of polyethylene terephthalate (PET). In this study, a series of ionic liquids derived from methylpiperidine (MP) with adjustable structures were constructed, and their application in PET glycolysis was evaluated. By adjusting the substitution positions on the MP framework, introducing alkyl chains, and changing the coordinating metal center, the catalytic system was optimized to enhance reaction activity and durability. The optimized catalyst (1-C 6 -2MP/Zn(OAc) 3 ) enabled PET to degrade rapidly, achieving a BHET yield of 93.27% within 60 min at 185°C using 4 wt% catalyst. Moreover, this system demonstrated excellent reusability, maintaining a BHET yield above 90% after 10 consecutive cycles. Kinetic analysis indicated that the reaction followed a pseudo-first-order model, with an apparent activation energy of 79.59 kJ mol −1 , suggesting a relatively low energy barrier. The catalyst also showed good applicability in commercial PET glycolysis. Overall, this study revealed clear structure-performance relationships and provided guidance for the rational design of robust ionic liquid catalysts for sustainable PET recycling. Highlights MP-based ionic liquids were rationally designed for PET glycolysis. Optimized 1-C 6 -2MP/Zn(OAc) 3 achieved a 93.27% BHET yield. BHET yields remained > 90% after 10 recycling cycles. First-order kinetics with a low activation energy of 79.59 kJ·mol −1 . DFT reveals the catalyst effectively activated EG.