Microkinetics and Mass Transfer Study of Treatment of Aqueous and Alcoholic Potassium Hydroxide on Poly (Ethylene Terephthalate) Waste

Abstract

The depolymerization reactions of poly (ethylene terephthalate) (PET) waste with aqueous as well as alcoholic (methanolic and ethanolic) solutions of potassium hydroxide was studied in a batch reactor at atmospheric pressure and at various temperatures (35–98°C) for different time periods (0.5–60 min). Methanolic alkaline solution was shown to have a greater reaction effect compared to that of aqueous as well as ethanolic solutions. The products of the reaction were found to be ethylene glycol (EG) and dipotasium terephthalate salt (K2-TPA) in liquid phase. The K2-TPA was converted into terephthalic acid (TPA) by using HCl. The EG, TPA, and PET wastes were analyzed and confirmed. Acid value as well as carboxyl-group concentrations of TPA significantly increases with reaction time. Kinetic analysis was undertaken. A microkinetic-mass transport model was developed, and simulated data was compared with experimental data. The model showed good agreement with the experimental data. The model prediction was undertaken by using our own laboratory data. The mass transport was described by using a classical diffusion equation according to Fick's law and a modified Wilke-Chang diffusion model. Diffusion coefficient and mass transfer coefficient were calculated at different temperatures as a function of operation time to understand the process phenomena. Thermodynamics was undertaken. Activation energy for methanolic KOH hydrolysis of PET, calculated from an Arrhenius plot, was 24 kJ/mol, and the Arrhenius constant was recorded as 76,326 L/min/cm2.