Methanolysis of polycarbonate into valuable product bisphenol A using choline chloride-based deep eutectic solvents as highly active catalysts

Compared with ionic liquids, deep eutectic solvents (DESs) show many special physical and chemical characteristics, such as low cost, easy synthesis, low toxicity, good biological degradability and compatibility. In this work, a series of DESs based on choline chloride (ChCl) were synthesized and used for the methanolysis of polycarbonate (PC) to obtain the valuable product Bisphenol A (BPA). The most effective DES was ChCl-2Urea which was formed between ChCl and Urea in the molar ratio of 1:2. Using ChCl-2Urea as catalyst, PC conversion was nearly 100% at 130 ℃ and 2.5 h, under this mild reaction condition, BPA yield was over 99%. More importantly, BPA could be easily separated from this reaction system by simple filtration and extraction. DES was recycled and reused without obvious loss of its catalytic activity. In other words, it described a simple, cheap, highly efficient catalytic and environmentally friendly method for PC methanolysis into the valuable product. In addition, this mechanism of PC methanolysis was proposed through experiments and DFT calculations. The kinetics of the reaction was also investigated, indicating that PC methanolysis was a pseudo-first order reaction with an activation energy of 141.47 kJ mol−1.