Abstract
The kinetics of polyethylene terephthalate (PET) depolymerization in supercritical methanol was investigated to develop a chemical recycling process for post-consumer PET bottles. PET with a high molecular weight of IV 0.84 was depolymerized in a batch reactor at temperatures between 553 and 593 K under estimated pressures of 13 - 15 MPa. In addition to PET with high molecular weight, PET with low molecular weight, such as its oligomer, bis-hydroxyethyl terephthalate (BHET) and methyl-(2-hydroxyethyl) terephthalate (MHET) was used as a model reactant to clarify the depolymerization scheme of polyethylene terephthalate in supercritical methanol. The reaction products were analyzed with size exclusion chromatography, high performance liquid chromatography, and high performance liquid chromatography-mass spectrometry. The main products of each reaction were the monomers, dimethyl terephthalate (DMT) and ethylene glycol (EG). The depolymerization of high molecular weight PET to its oligomer was faster than that of oligomer to its monomer. PET was depolymerized into DMT and EG through MHET. The molecular-weight distribution showed that the depolymerization of PET proceed consecutively where the step of the oligomer to its monomer would be a rate-determining step. MHET is a relatively stable intermediate in the depolymerization. The rate constants were estimated with simple reaction models.
