Kinetics of catalytic glycolysis of PET wastes with sodium carbonate

The kinetics of glycolysis of poly(ethylene terephthalate) wastes with ethylene glycol to give highly pure bis(2-hydroxyethyl terephthalate) was examined in a batch reactor. An excess of ethylene glycol (EG:PET molar ratio of 7.6:1) was used and the reaction was carried out in the presence of sodium carbonate as active catalyst. The influence of several operating conditions covering temperature (165–196 °C), mean particle size (0.14–3 mm), stirring rate (50–800 rpm), reaction time (0–10 h), and catalyst type and concentration was analysed. The selected PET particle size and stirring rate for kinetic calculations were 0.25 mm and 600 rpm, respectively. Using a PET:catalyst molar ratio of 100:1 about 80% BHET yield was attained at 196 °C after 1 h. A simple theoretical power-law model was developed to predict the time evolution of conversion. This kinetic model was found to be consistent with experimental data. The rate constants for both direct and reverse reactions were estimated. Also the values of the activation energy (185 kJ mol−1) and enthalpy of reaction (12 kJ mol−1) were derived.