Chemical Recycling, Kinetics, and Thermodynamics of Poly (Ethylene Terephthalate) (PET) Waste Powder by Nitric Acid Hydrolysis

Hydrolysis reaction of PET waste powder in HNO3 was undertaken in batch process at 88–120°C temperature and 1 atm pressures. Particle size ranging from 50–512.5 μm and reaction time 30–200 min required for hydrolysis of PET were optimized. Terephthalic acid (TPA) and ethylene glycol (EG) remain in liquid phase and were separated out by using NaOH solution and then acidification. EG was recovered during hydrolysis by salting‐out technique. Oxidation of EG was avoided by introduction of sodium sulphate into reaction mixture. Produced TPA and EG were analyzed qualitatively and quantitatively. Yields of TPA and EG were almost equal to PET conversion. Results of kinetic analysis showed that the depolymerization reaction in nitric acid could be explored by a modified shrinking‐core model, in which effective surface area is proportional to degree of unreacted PET (1‐X). Effect of particle size of PET showed that weight (%) loss of PET was inversely proportional to particle size. Thermodynamics was also undertaken by determination of activation energy, Arrhenius constant, equilibrium constant, Gibbs free energy, enthalpy and entropy. Dependence of rate constant on reaction temperature was correlated by Arrhenius plot, which shows an activation energy of 88.3 kJ/mol and Arrhenius constant of 659 L/min/cm2.