Degradation of polycarbonate to produce bisphenol A catalyzed by imidazolium-based DESs under metal-and solvent-free conditions

Abstract

Bisphenol A (BPA) is an important chemical raw material, but the traditional preparation process of BPA is costly and complicated, so it is necessary to find an efficient and environmentally friendly method for the production of BPA. Deep eutectic solvents (DESs) have attracted widespread attention due to their low cost, low toxicity, low melting point, non-volatilization, easy preparation, recyclablility and biodegradability. In this work, a series of imidazolium-based DESs were synthesized and used for the degradation of polycarbonate (PC), and BPA was obtained from the methanolysis of PC catalyzed by DESs under metal- and solvent-free conditions. It was found that imidazolium-based DES [EmimOH]Cl-2Urea showed excellent catalytic activity and reusability. Under the optimized reaction conditions (the mass ratio of DES to PC is 0.1 : 1, the molar ratio of CH₃OH to PC is 5 : 1, 120 °C, reaction time 2 h), the PC conversion and BPA yield were almost 100% and 98%, respectively. Moreover, the kinetics of methanolysis catalyzed by [EmimOH]Cl-2Urea was investigated in the temperature range 100–120 °C, and the results indicated that it is a pseudo-first order reaction with an activation energy of 133.59 kJ mol⁻¹. In addition, a possible catalytic mechanism of PC methanolysis is proposed.