Kinetics of Hydrolysis of PET Powder in Nitric Acid by a Modified Shrinking-Core Model

Poly(ethylene terephthalate) (PET) powder from waste bottles was degraded at atmospheric pressure in 7−13 M nitric acid at 70−100 °C for 72 h, to clarify the mechanism of a feed stock recycling process. Terephthalic acid (TPA) and ethylene glycol (EG) were produced by the acid-catalyzed heterogeneous hydrolysis of PET in nitric acid, and the resulting EG was simultaneously oxidized to oxalic acid. The kinetics of the hydrolysis of PET in nitric acid could be explained by a modified shrinking core model of chemical reaction control, in which the effective surface area is proportional to the degree of unreacted PET, (1 − X ), affected by the deposition of the product TPA. The apparent rate constant was inversely proportional to particle size and to the concentration of the nitric acid. The activation energy of the reaction was 101.3 kJ/mol.