Mechanistic investigation on hydrolysis, alcoholysis, and ammonolysis of polyethylene terephthalate initiated by participation of calcium ions

Alkali Ca2+ ion plays a crucial role in the chemical depolymerization of plastics. To investigate the catalytic effects of Ca2+ on the hydrolysis, alcoholysis, and ammonolysis mechanisms of polyethylene terephthalate (PET) plastic waste, the density functional theory (DFT) method using B3P86/6-31++G(d,p) was employed. This study focused on the catalytic reactions of Ca2+ with a PET dimer. The calculations show that Ca2+ interacts with the oxygen-containing functional groups in the PET dimer, leading to a reduction in the Gibbs free energy of the PET model compound. During the depolymerization of the Ca2+-catalyzed PET dimer, the energy barriers for the primary reaction steps are approximately 183.0 kJ/mol (hydrolysis), 175.0 kJ/mol (alcoholysis), and 153.0 kJ/mol (ammonolysis), respectively. Additionally, the study explores the impact of temperature on reaction rates and branching ratios during the Ca2+ ion catalytic initial hydrolysis, alcoholysis, and ammonolysis of the PET dimer. It also elucidates the product yield in the co-treatment of PET with Ca2+ ion under varying temperatures. This work enhances the current knowledge of Ca2+ catalyzing the hydrolysis, alcoholysis, and ammonolysis of plastic waste, offering theoretical insights for minimizing pollutant emissions in the thermal treatment and sustainable conversion of PET-containing waste.