Kinetics of glycolysis of polyethylene terephthalate with zinc catalyst

The glycolysis reaction of poly(ethylene terephthalate) (PET) melts with ethylene glycol has been examined in a pressurized reactor. The kinetics of the glycolysis reaction are studied. The rate constants for glycolysis without addition of catalyst are calculated at four different temperatures, yielding an activation energy of 108kJ mol^-1. By comparison, the rate constants for glycolysis with addition of zinc acetate are also calculated at four different temperatures, yielding an activation energy of 85kJ mol^-1. It is found that the activation energy of glycolysis with addition of zinc acetate is lower than that of glycolysis without addition of catalyst. Therefore, zinc acetate has a catalytic effect on PET glycolysis at temperatures between 235 and 275°C. The effect of catalyst concentration on reaction rate constants is also discussed. Below a critical catalyst concentration, the rate constant for glycolysis is linearly dependent on catalyst concentration. © 1999 Society of Chemical Industry.