Highly efficient application of Mg/Al layered double oxides catalysts in the methanolysis of polycarbonate

Polycarbonate (PC) is a very versatile material widely used in industry, agriculture and packaging, etc. The global production of PC generates several million tons of non-biodegradable wastes. In this work, chemical recycling of bisphenol A (BPA) from the PC methanolysis was explored, by using Mg/Al layered double hydroxides (LDHs) and their corresponding layered double oxides (LDOs) as heterogeneous catalysts. Mg/Al-LDHs with different molar ratios were prepared, and their hydrotalcite structures were confirmed by powder X-ray diffraction (XRD). Compared with Mg/Al-LDHs, Mg/Al-LDOs exhibited better catalytic activity for the PC methanolysis. Using Mg3Al-LDO as a catalyst, the PC conversion was 100% and the BPA yield exceeded 98% at 110 °C and 1.0 h. Namely, this method not only significantly reduces the reaction temperature, but also shortens the reaction time, and the solid catalyst Mg3Al-LDO can be easily separated and reused after calcinations again. The effects of experimental parameters on the PC conversion and the BPA yield were investigated. Moreover, the mechanism was described by infrared spectroscopy (IR), gel permeation chromatography (GPC), and scanning electron microscope (SEM). The kinetics of PC methanolysis was also studied, and the results indicated that this process is a pseudo-first-order reaction with an activation energy of 92.41 kJ/mol.