Maximizing light olefin production via one-pot catalytic cracking of crude waste plastic pyrolysis oil

Abstract

Energy-efficient processes for converting polyolefinic waste plastics into light olefins are critical for mitigating environmental pollution and reducing carbon emissions. In this study, an alternative recycling scheme, the catalytic cracking of crude waste plastic pyrolysis oil (WPPO) over microspherical P-modified steam-treated ZSM-5 (ms-P-HZSM5-S), was demonstrated and compared to a state-of-the-art commercial scheme, the thermal cracking of a hydrotreated naphtha range of WPPO. The C2–C4 olefins yield achieved by the catalytic WPPO cracking (56.6 wt%) exceeded those achieved by the thermal WPPO cracking (36.1 wt%), thermal naphtha cracking (23.1 wt%), and catalytic naphtha cracking (29.7 wt%), which indicated the superiority of WPPO over naphtha as a feedstock. However, during a deactivation test over ms-P-HZSM5-S, coke accumulation resulted in a rapid decline in the yields of ethylene (from 17.2 to 14.6 wt%), propylene (from 25.8 to 23.6 wt%), and benzene, toluene, and xylenes (from 16.1 to 13.4 wt%) after a reaction time of 810 s (temperature = 680 °C, weight hourly space velocity = 16 h−1). Nevertheless, the catalytic performance was fully restored through regeneration in air at 730 °C, which confirmed the viability of continuous operation involving successive reaction–regeneration cycles. These findings can be leveraged to devise a new approach, the catalytic cracking of WPPO integrated with a continuous regeneration (e.g., circulating fluidized bed reactor) system, which could offer several advantages over the commercial strategy, including the posttreatment-free utilization of the entire WPPO range, higher light olefins yields, continuous coke removal, reduced energy consumption, and non-necessity of H2.