Depolymerization of polycarbonate by methanol under pressurized microwave irradiation

Depolymerization of polycarbonate (PC) waste by methanolysis without catalyst under pressurized microwave irradiation was proposed in order to get bisphenol A (BPA). The depolymerized products were identified by NMR and FTIR spectroscopy. A maximum BPA yield of 94% was achieved at a reaction temperature and pressure of 190°C and 3 MPa for 3 hours. On the other hand, dimethyl carbonate could not be detected by FTIR analysis. In order to clarify the reaction mechanism, benzyl alcohol was used instead of methanol under the similar condition. Dibenzyl ether was found to be directly produced by the simultaneous reactions of transesterification and decarbonation during the microwave irradiation. The proton ratio of dibenzyl carbonate:dibenzyl ether = 11.2:88.8 was determined from the ¹H-NMR chemical shifts of the reaction mixture. Therefore, dimethyl carbonate in the case of the methanolysis was converted to dimethyl ether, which vaporized at atmospheric pressure after the reaction under pressurized microwave irradiation. The proposed methanolysis method of waste PC can achieved the high efficient recovery of BPA without catalyst use and avoid the need for a further separation process of dimethyl carbonate.