Enhanced cleavage of C-C bonds in polycarbonate plastic wastes to valuable phenolics over potassium modified triazine-based strong base catalyst

Abstract

The recycling and upgrading of polycarbonate (PC) plastic wastes has attracted worldwide attention, while the selective cleavage of inert C-C bonds remains the key challenge. Herein, the noble metal-free potassium-modified covalent triazine-based framework (K-CTF) as the strong base catalyst could efficiently catalyze the cleavage of C-C bonds in various PC plastic wastes to achieve valuable phenolics. Compared with other alkali and alkaline earth species (Na, Mg, Ca) modified catalysts, K-CTF showed the optimal catalytic performance due to its strong basicity. The total yield of acquired phenolic monomers reached up to 98.1%. The reaction pathway investigation displayed that PC plastic firstly underwent methanolysis to form bisphenol A (BPA) intermediate. The catalytic amount of strong basic sites then promoted the cleavage of C-C bonds to form phenol and 4-isopropenylphenol (IPP) by deprotonation activation of the phenolic hydroxyl group in BPA. Thereinto, methanol and H2O played a crucial part in the PC plastic alcoholysis and C-C bonds cleavage, respectively, which acted synergistically for the high-efficiency conversion of PC plastic to monophenols. This work opened new opportunities for the efficient utilization of PC plastic wastes.