Resource recovery via catalytic fast pyrolysis of polystyrene using zeolites

This study focuses on selective production of valuable chemicals from polystyrene (PS) via catalytic fast pyrolysis using micropyrolyzer-GC/MS set-up. Catalytic fast pyrolysis of PS was performed using eight different zeolites belonging to ZSM-5, zeolite-β, and zeolite-Y families. The catalysts were characterized for the strength of Brønsted acid sites and pore size distribution. The composition of PS:catalyst was optimized at 1:2.3 ± 0.2 wt./wt. to enhance the yield of benzene, at the same time reduce the yield of condensed ring fragments like indene and indane derivatives. The yields of various products correlated well with specific properties of zeolites like relative strength of Brønsted acid sites, specific surface area, and pore volume. Importantly, the yield of benzene increased, while that of styrene, α-methyl styrene, and dimers decreased with Brønsted acidity. Zeolite-β hydrogen and zeolite-Y ammonia catalysts resulted in the formation of up to 50 wt.% of benzene. High temperatures led to a reduction in benzene yield and promoted the formation of styrene, α-methyl styrene, and ethyl benzene. The observed product distribution with different zeolites and at different temperatures was corroborated using the relative importance of the primary protonation pathways involved in catalytic fast pyrolysis of PS.