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.

Keywords:

• Poly(ethylene terephthalate)
• Hydrolysis
• Recycling
• Kinetics
• Recovery
• Thermodynamics

Acknowledgments

Author (A. S. Goje) gratefully acknowledges the financial support given by the Honorable Chairman Chhatrapati Rajarshi Shri. Shahu Maharaj and secretary Shri B. Y. Tekawadeji of All India Shree Shivaji Memorial Society, Pune-411 005, M.S., (India). The authors also sincerely give thanks for the technological support for analyses purpose given by Dr. (Prof.) S. P. Kallurkar, Principal of All India Shree Shivaji Memorial Society's College of Engineering, Near R.T.O. Office, Pune - 411 001, M.S., (India). Authors gratefully acknowledge the technical support given by the Hon. Dr. B. D. Kulkarni, Head of Chemical Engineering Division, National Chemical Laboratory, Pune, M.S., (India). Authors gratefully acknowledge the process technology support given by Dr. M. S. Pradhan, and Dr. S. Bapat, Head, Chemical Engineering Department, Vishwakarma Institute Of Technology, Pune, M.S., (India). The authors also sincerely give thanks for the economical support for literature survey given by Dr. Ramdasraoji Ambulgekar, Government Medical College, Aurangabad, M.S., (India).