Study of polyester degradation by sub/supercritical ethanol and enhancement of carbon dioxide

The harmless treatment of solid wastes such as polyethylene terephthalate (PET) and polycarbonate (PC) is an inevitable requirement of green development. In this paper, sub/supercritical ethanol was used to degrade this type of polyester, and carbon dioxide was used as a cooperative medium to obtain high depolymerization rate and high value depolymerization products by regulating reaction conditions. PC and PET polyester was alcoholized under less toxic and milder reaction conditions (200 and 270 ℃). Under optimal conditions, the yield of BPA and DET reached 87.5% and 90%, respectively. The results show that carbon dioxide enhances depolymerization by reducing the interaction between molecular chains and providing a weak acidic environment in depolymerization process with ethanol as main solvent, while this enhancement can only be achieved if ethanol dominates the depolymerization process. More moderate depolymerization conditions were explored and more than 90% solvent recovery can be achieved, which realized the resource utilization of polyester and significantly reduced the consumption of polymer solvent.