Studies on hydrolysis/alcoholysis/ammonolysis mechanisms of ethylene terephthalate dimer using DFT method

Abstract

Hydrolysis/alcoholysis/ammonolysis are considered as viable routes for efficient degradation and recycling of polyethylene terephthalate waste plastic. The possible hydrolysis/alcoholysis/ammonolysis pathways for the degradation of ethylene terephthalate dimer were investigated by the density functional theory (DFT) method M06/cc-pVDZ. The geometric structure optimization and frequency calculation of various intermediates, transition states and products involved in the reaction were carried out to obtain thermodynamic and kinetic parameter values. The results show that the reaction energy barrier of the cracking process of ethylene terephthalate dimer can be reduced under the conditions of hydrolysis/alcoholysis/ammonolysis, which makes the reaction easier. Additionally, at 298 K and 1 atm, the total rate constants of hydrolysis/alcoholysis/ammonolysis are 1.51 × 10-43 cm3 molecular-1s−1, 1.86 × 10-41 cm3 molecular-1s−1, and 2.82 × 10-40 cm3 molecular-1s−1, respectively. The hydrolysis products of ethylene terephthalate dimer are mainly terephthalic acid and ethylene glycol; the alcoholysis products of ethylene terephthalate dimer are dimethyl terephthalate and ethylene glycol; and ammonolysis products mainly include terephthalamide and ethylene glycol. Furthermore, this study shows that the Gibbs free energy change of hydrolysis/alcoholysis/ammonolysis is negatively correlated with temperature and an increase in temperature enhance the spontaneity of the reaction.