Mechanistic Insights of Cosolvent Efficient Enhancement of PET Methanol Alcohololysis

The recycling of poly(ethylene terephthalate) (PET) is an important issue for environmental protection and resource conservation. Methanol alcoholysis is the main chemical method commonly used today to degrade PET into high-value monomers. However, conventional methanolysis of poly(ethylene terephthalate) (PET) has problems such as high temperature and high pressure. To further reduce the temperature of methanolysis, in this work, cosolvent-enhanced methanol alcoholysis of PET polyesters was employed and systematically compared with the common methanol alcoholysis process. The results showed that the addition of a cosolvent could significantly lower the reaction temperature and shorten the reaction time compared with conventional methanol alcoholysis. The 100% conversion of PET can be achieved at 120 °C and 2 h. Meanwhile, the mechanisms for choosing acetonitrile as the best cosolvent for the reaction were investigated by combining experimental characterization and DFT simulation calculations and proposed the relevant basis for selecting a cosolvent. The experimental results showed that the addition of the cosolvent could increase the specific surface area of PET, which increased the mass transfer coefficient of methanol and enhanced the mass transfer process of the reaction, thus promoting the contact between methanol and PET and making the reaction easier. In addition, the kinetic study revealed that the addition of the cosolvent acetonitrile reduced the activation energy of the reaction from 106.9 to 90.3 kJ/mol, thus making the reaction easier to proceed. This paper provides a new method for achieving efficient methanolysis of PET.