Carbon Dioxide Synergistic Enhancement of Supercritical Methanol on PET Depolymerization for Chemical Recovery

Poly(ethylene terephthalate) (PET) is an important polyester material widely used in beverage bottles, fibers, engineering plastics, and film fields. The typical method of waste recycling is to use supercritical methanol to depolymerize PET into monomers such as dimethyl terephthalate (DMT) and ethylene glycol (EG). However, the supercritical methanol alcoholysis process of PET usually faces the problems of high temperature and pressure and high energy consumption. To further enhance the alcoholysis efficiency, CO2-enhanced supercritical methanol alcoholysis of PET polyester is used in this work, and the general supercritical methanol alcoholysis process is systematically compared. The research results revealed that the DMT yield of PET polyester by CO2-enhanced supercritical methanol alcoholysis was maximized under the same reaction conditions, up to 95%. Combined with the p-x,y phase diagram, the mechanism of carbon dioxide intensification is discussed, which can provide guidance for the industrial large-scale recycling of PET.