Recycling benzene and ethylbenzene from in-situ catalytic fast pyrolysis of plastic wastes

Recovering waste plastics by catalytic fast pyrolysis to selectively generate aromatic hydrocarbons is a promising approach to dispose of solid wastes. In the present work, catalytic conversion of polystyrene over ultra-stable Y zeolites (USY) was conducted to directionally produce benzene and ethylbenzene. Experimental results indicated that catalyst type considerably affected the distribution of aromatic hydrocarbons, and USY with high surface area (734 m²/g), large pore size (5.6 nm), and an abundant amount of strong acid sites (1.21 mmol/g) exhibited the most effective shape selectivity for ethylbenzene and benzene generation as the yield enhanced rate reached 401.8% and 61.1%, respectively. Plastic type also played a vital role in the formation of desirable aromatic hydrocarbons, and polystyrene was more beneficial to the production of ethylbenzene as a 54-fold increase was obtained compared to polycarbonate in the catalytic degradation process. Concerning reaction conditions to maximize the formation of benzene and ethylbenzene in the catalytic decomposition of polystyrene, the catalyst/feedstock mass ratio, Si/Al mole ratio in USY, and catalytic conversion temperature could be optimized at 1.5, 5.3, and 650 °C, respectively.