Kinetic study on depolymerization of poly(ethylene terephthalate) with methanol at high temperature and pressure

The rate constants of the decomposition of poly(ethylene terephthalate) (PET) with methanol were determined from 453 to 623 K. The temperature mainly influenced the reactivity of methanol at 488 similar to 623 K. The Arrhenius plot of the rate constants below and above the critical temperature of methanol was the same straight line. On the other hand, the rate constant at 453 K, in which the conventional depolymerization of PET is carried out using liquid methanol, was very small because the vapor pressure of methanol (2.7 MPa) was small. Furthermore, PET existed as a solid, so its concentration and the contact area with methanol were limited. Investigating the structure of the oligomers produced together with the monomers, we found that PET could be decomposed to the oligomers with the degree of polymerization of around 3 above 573 K, at 11 MPa and 30 min of the reaction time.