Reaction kinetic model of glycolysis of polyethylene terephthalate

The reaction kinetics of the glycolysis of polyethylene terephthalate (PET) in ethylene glycol (EG) solvent using zinc acetate as a catalyst were investigated. The experimental results show that stirring rate, EG/PET mass ratio, and catalyst dosage all influence the glycolysis rate. The reaction temperature has a decisive effect on the glycolysis rate and the yield of the target product, bis(2-hydroxyethyl) terephthalate (BHET). By tracking the distribution of PET repeat units in the products and combining the heterogeneous shrinking core model and homogeneous reaction model, a reaction kinetic model for PET glycolysis was developed. The model accurately predicts the equilibrium product distribution at high temperature and the reaction behavior of large PET particles. The activation energy for the depolymerization of PET to oligomers is 172.71 kJ/mol, making it the ratedetermining step of the entire reaction network. The standard reaction enthalpy and entropy change for this step are 22.58 kJ/mol and 16.46 J/mol & sdot;K, respectively, indicating that PET glycolysis is an entropy-driven process that requires high temperatures. Increasing the reaction temperature significantly reduces the sensitivity of the reaction rate to PET particle diameter. When conducting PET glycolysis in a series of continuous stirred tank reactors, it is necessary to use both high temperatures and small PET particle sizes to minimize reactor volume and reduce the number of reactors in series.