Metal-free carbocatalysts for the selective production of ethylbenzene and cumene from mixed plastic waste

Abstract

Conventional production of ethylbenzene and cumene relies on fossil fuels and results in significant CO2 emissions. As a sustainable alternative, plastic waste can be used to produce high-value aromatics via catalytic fast pyrolysis (CFP). However, the existing CFP approaches for plastics to aromatics offer low selectivity of these two products, or require high-pressure hydrogen that is detrimental to the process cost-competitiveness. In this study, we demonstrate a one-pot CFP approach based on the use of mixed plastic waste, mild conditions (i.e., 550 oC, atmospheric pressure and no H2) and most importantly, a metal-free carbocatalyst derived from tire char, another otherwise polymer waste causing a significant environmental concern. This approach has been proven to achieve two high-purity products, ethylbenzene and cumene, while reducing CO2 emissions by 80% compared to conventional processes. It could also be highly cost-competitive as opposed to the virgin products from naphtha. Intensive characterization and density functional theory calculations further reveal that, the defect-rich amorphous carbon in the tire-derived carbocatalyst created by chemical etching plays a dual role in abstracting and transferring hydrogen, enhancing the in-situ interactive synergy between individual plastics that simultaneously promotes both the hydrogenation of monomers/radicals from polystyrene (PS) and the aromatization of short-chain aliphatics from low-density polyethylene (LDPE) and polypropylene (PP).