Multiscale mechanisms elucidation and kinetic modeling for polyethylene terephthalate separation pathways: A combined computational-experimental perspective on pyrolysis, hydrolysis, and alcoholysis processes

• Mechanism of PET pyrolysis , hydrolysis, and alcoholysis was studied in combination with theory and experiment. • Action mechanism of water (alcohol) as reactant and catalyst was investigated. • The mechanism of action of alcohol is superior to that of water. • To explore the effect of temperature on PET decomposition process. Pyrolysis, hydrolysis, and alcoholysis are regarded as effective methods for processing waste plastics and obtaining high-value products. Herein, we aimed to elucidate the thermochemical transformation behaviors of polyethylene terephthalate (PET) by examining the mechanisms of pyrolysis, hydrolysis, and alcoholysis using density functional theory in conjunction with Py-GCMS. The results show that the main experimental products (terephthalic acid, methyl terephthalate, etc.) are consistent with those predicted by the designed reaction pathways. Notably, compared with the pyrolysis of PET dimer (263.0 kJ/mol), hydrolysis and alcoholysis reactions exhibit significantly reduced activation energies (169.0 kJ/mol and 156.0 kJ/mol, respectively). Moreover, water/methanol molecules can facilitate PET dimer depolymerization through hydrogen transfer, with activation energies for these assisted processes (102.0 kJ/mol and 96.0 kJ/mol, respectively) being significantly lower than direct hydrolysis/alcoholysis. Specifically, methanol-assisted alcoholysis demonstrates the lowest activation energy (96.0 kJ/mol). These findings indicate that incorporating appropriate amounts of water/methanol during thermochemical recycling of PET waste can enhance decomposition efficiency. This research provides critical insights into energy conversion processes for PET and other polyester materials.