Catalytic and thermal fast pyrolysis of agricultural plastic waste: Comparison of BTEX and steam cracker feed production in a bubbling fluidized bed reactor

Thermal and catalytic fast pyrolysis of agricultural waste plastic was studied in industrially relevant bubbling fluidized bed reactor. In thermal pyrolysis, yield of middle distillates (BP < 350 °C) suitable for steam cracker was maximized. In catalytic pyrolysis, target was to maximize yield of BTEX by utilizing highly acidic zeolite catalyst. Residence time and temperature were varied in 2^2 factorial experimental design, complemented by the centre point runs. In thermal operation, lower temperature resulted in higher total condensable yield but the share of hydrocarbons boiling above 350 °C was higher. In higher temperature, product spectra shifted towards gases and lower boiling hydrocarbons and the combination of higher temperature and longer residence was found to be favorable when production of lower boiling hydrocarbons is optimized. In catalytic operation, higher temperature and longer residence times were found to decrease the quantity of unsaturated gas components and to increase the liquid yield, which indicates that more severe conditions enhanced the conversion of gases into aromatic hydrocarbons. No rapid catalyst deactivation was observed, but inorganic impurities from feedstock were found to deposit on the catalyst surface which can be an issue in long term processing. The liquid produced from the catalytic pyrolysis was further distilled to demonstrate the separation of the BTEX components. Results clarify the combinatory effects of temperature and residence time in different operation modes. Fluidized bed fast pyrolysis could provide a scalable approach for chemical plastic recycling, but gas utilization needs more attention when more severe pyrolysis conditions are used.