Chemical Recycling, Kinetics, and Thermodynamics of Alkaline Depolymerization of Waste Poly (Ethylene Terephthalate) (PET)

Abstract

Depolymerization of PET in aqueous sodium hydroxide solution was undertaken in a batch process at 90–150°C and 1 atm by varying PET particle size in the range of 50–512.5 µm. Reaction time was also varied from 10–110 min to explore effect of particle size of PET and reaction time on batch reactor performance. Particle size of PET and reaction time required were optimized. Disodium terephthalate (TPA salt) and ethylene glycol (EG) remain in liquid phase. EG was recovered by salting‐out technique. Disodium terephthalate was separated by acidification to obtain solid terephthalic acid (TPA). Produced TPA and EG were analyzed qualitatively and quantitatively. Yields of TPA and EG were almost equal to PET conversion. Depolymerization reaction rate was first order to PET concentration as well as first order to sodium hydroxide concentration. Acid value of TPA changes with reaction time. This indicates that PET molecule gets fragmented and hydrolyzes simultaneously with aqueous sodium hydroxide to produce EG and disodium terephthalate. Thermodynamics was also undertaken by determination of activation energy, Arrhenius constant, equilibrium constant, Gibbs free energy, enthalpy and entropy. Dependence of hydrolysis rate constant on reaction temperature was correlated by Arrhenius plot, which shows activation energy of 26.3 kJ/mol and Arrhenius constant of 427.2 L/min/cm2.