Kinetics of depolymerization of poly(ethylene terephthalate) in a potassium hydroxide solution

The depolymerization of poly(ethylene terephthalate) (PET) flakes in a pota ssium hydroxide solution was carried out in a stirred batch reactor at 120, 140, and 160 degreesC, below its melting point and under pressures of abou t 1.7, 2.9, and 4.6 atm, respectively. After the reactions, the residual so lids almost remained in flake shape and their molecular weights were close to that of PET before the reaction. The products composed of ethylene glyco l and terephthalic potassium salt were in the liquid phase. They were separ ated by acidification (to obtain solid terephthalic acid) and filtration pr ocesses and subsequently were analyzed quantitatively by potentiometric tit ration, elementary analysis, and gas chromatography. The results of kinetic analysis showed that the depolymerization reaction rate was first order to potassium hydroxide and first order to the PET concentration. This indicat es that the ester linkages on the surface of the solid PET flakes sequentia lly reacted with potassium hydroxide in the solution to produce ethylene gl ycol and terephthalic potassium salt. A mechanism for the major reaction oc curring on the polymer chain end section on the solid PET surface was propo sed in this research. The dependence of the rate constant on the reaction t emperature was correlated by the Arrhenius plot, which shows an activation energy of 69 kJ/mol and an Arrhenius constant of 419 L/min/cm(2).