The upcycling of polyethylene terephthalate using protic ionic liquids as catalyst

•A series of protic ionic liquids were synthesized to catalyze PET glycolysis. These ionic liquids were characterized by FT-IR. 1H MNR and ESI-MS.•The influence of different anion of ionic liquid and experimental parameters on PET glycolysis was investigated and it found that PIL3 has excellent catalytic performance. PET conversion was 100% and BHET yield reached 87.3% at 190 °C for 30 min with PIL3 as catalyst.•1H NMR and DFT calculation were performed to study mechanism of PET glycolysis catalyzed by protic ionic liquids and it found that there is process of hydrogen transfer in PET glycolysis. The possible mechanism was proposed.•The shrink-core model was applied to kinetic of PET glycolysis catalyzed by protic ionic liquids and apparent activation energy is 162.82 kJ/mol.•The main product of PET glycolysis was characterized by ESI-MS, NMR, FT-IR and UPLC and confirmed to be bis(hydroxyethyl) terephthalate (BHET).