Alkaline Hydrolysis of Waste Poly(Ethylene Terephthalate): A Modified Shrinking Core Model

Hydrolytic decomposition of waste poly(ethylene terephthalate) (PET) is studied in the presence of an aqueous potassium hydroxide solution. A modified shrinking core model with a depleting product layer of waste PET is developed under finite solution volume conditions. An analytical solution is obtained for the model based on average molar distribution coefficient of aqueous potassium hydroxide solution. This model assumes the first order depolymerization kinetics with respect to the concentration of potassium hydroxide solution. The convrsion of the waste PET is determined after filtration of the unreacted PET left after depolymerization. The conversion of PET is also compared with the amount of terephthalic acid obtained after acidification of the filtrate. Infra red (IR) spectroscopy studies of unreacted PET samples at different hydrolysis time intervals are carried out. It is observed that the transmittance at ∼1700 cm−1 decreases gradually with reaction time, which confirms the increased concentration of carbonyl group generated from aryl carboxylic acid group and the major reaction is occurring on the polymer chain end on the solid PET surface. Average molar distribution coefficient of aqueous potassium hydroxide solution, intrinsic PET depolymerization rate constant, frequency factor and activation energy of PET depolymerization are estimated based on the modified shrinking core model.