CO₂-enhanced PET depolymerization by catalyst free methanolysis

Depolymerization shows promise as a strategy for converting waste plastic into monomers that can be used for repolymerization. However, catalytic approaches would be more complex and expensive due to catalyst separation, recovery, and recycling. Here, we present a CO2-enhanced subcritical methanolysis method without catalyst that can generate monomer from poly(ethylene terephthalate)(PET). The synergistic effect of CO2 on the subcritical methanolysis process for PET depolymerization was investigated including the CO2 initial pressure, reaction temperature and reaction time. Under subcritical conditions, the optimal reaction parameters with PET conversion ratio of 100% and DMT yield of 79.1% are as follows: temperature of 220degree celsius, methanol to PET mass ratio of 6:1 and reaction time of 50 min. Moreover, through the analysis of experimental data, it was concluded that the depolymerization reaction follows a first-order kinetics, with the reaction rate being 2-3 times faster than the traditional process. However, the apparent activation energy for both reactions is found to be similar, with values of 135.1 kJ center dot mol- 1 and 146.2 kJ center dot mol- 1, respectively.