Chemical Recycling, Kinetics, and Thermodynamics of Hydrolysis of Poly(ethylene terephthalate) Waste with Nonaqueous Potassium Hydroxide Solution

Abstract

Poly(ethylene terephthalate) (PET) waste was reacted in a batch process with KOH in nonaqueous ehtylene glycol (EG) solution at 100–180°C for 5–140 min to convert them quantitatively into dipotassium terephthalate (K2-TPA) and EG. Particle size of PET, mol/L of KOH, and reaction time required for depolymerization of complete PET were optimized. Dipotassium terephthalate was precipitated into terephthalic acid (TPA) using HCl from the reaction mixture and separated readily. Other product EG, being the same component as nonaqueous solvent (EG) remains in liquid phase. The EG was recovered completely by using the salting-out method. Rate of hydrolysis was significantly accelerated by addition of another additional solvent, tetrahydrofurane (THF) to EG in the atmosphere of cyclohexylamine (CHA). Moreover, to improve the hydrolysis rate, TPA salt deposited from the unreacted PET surface was removed by introduction of dimethylsulfoxide (DMSO). Analyses of monomers (TPA and EG) and PET were undertaken. Yields of monomers were almost equal to PET conversion. The kinetic model was developed and experimental data were fitted with it. The model showed a good consistency with experimental data. Thermodynamics were also undertaken by determination of activation energy, Arrhenius constant, equilibrium constant, Gibbs free energy, enthalpy, and entropy. The dependence of the rate constant on the reaction temperature was correlated by Arrhenius plot, which shows activation energy of 24.2 kJ/mol and Arrhenius constant of 199.3 min−1.