Kinetic and thermodynamic study of methanolysis of poly(ethylene terephthalate) waste powder

Depolymerization of poly(ethylene terephthalate) waste (PETW) was carried out by methanolysis using zinc acetate in the presence of lead acetate as the catalyst at 120-140degreesC in a closed batch reactor. The particle size ranging from 50 to 512.5 mum and the reaction time 60 to 150 min required for methanolysis of PETW were optimized. Optimal percentage conversion of PETW into dimethyl terephthalate (DMT) and ethylene glycol (EG) was 97.8% (at 120degreesC) and 100% (at 130 and 140degreesC) for the optimal reaction time of 120min. Yields of DMT and EG were almost equal to PET conversion. EG and DMT were analyzed qualitatively and quantitatively. To avoid oxidation/carbonization during the reaction, methanolysis reactions were carried out below 150degreesC. A kinetic model is developed and the experimental data show good agreement with the kinetic model. Rate constants, equilibrium constant, Gibbs free energy, enthalpy and entropy of reaction are also evaluated at 120, 130 and 140degreesC. The methanolysis rate constant of the reaction at 140degreesC (10.3 atm) was 1.4 x 10(-3)g PET mol(-1) min(-1). The activation energy and the frequency factor for methanolysis of PETW were 95.31 kJ mol(-1) and 107.1g PET mol(-1) min, respectively. (C) 2003 Society of Chemical Industry.