Microwave-assisted catalytic pyrolysis of waste cooking oil into hydrocarbon-rich bio-oil: Optimization of dual-stage catalysis and techno-economic assessment

This study addresses the need for sustainable waste cooking oil valorization by developing a continuous catalytic pyrolysis system to produce hydrocarbon-rich bio-oil. The research focuses on optimizing both the pyrolysis process and catalytic upgrading to maximize bio-oil yield and hydrocarbon content while ensuring process stability. The pyrolysis system demonstrated excellent thermal stability across the pyrolysis process at all bed heights, with a maximum heating rate of 224.0 °C/min. The maximum catalytic bed heating rate was 322.5 °C/min. Temperature overshooting was observed when the CaMg-to-CS ratio reached 1.4 mol/20 g. Average bio-oil yield reached its peak yield of 63.23 wt% at a CaMg-to-CS ratio of 1.0 mol/20 g. Significantly, the hydrocarbon content in bio-oil peaked at 91.37 % when using a ratio of 0.6 mol/20 g. Comparative analysis revealed distinct performance characteristics between single-stage and dual-stage catalysis. While HZSM-5-CS single-stage catalysis showed higher initial activity, but the catalyst deactivated more quickly. In contrast, the dual-stage catalysis demonstrated superior initial activity and more stable catalytic performance. Catalyst characterization showed that the dual-stage catalysis helps mitigate coke-induced deactivation of the HZSM-5-CS catalyst. Microwave radiation had a positive effect on promoting deoxygenation of pyrolysis vapors and aromatization. Catalyst characterization showed that microwave radiation slowed the deactivation of the catalytic bed by reducing coke deposition. Aspen Plus simulate results showed that producing hydrocarbon-rich bio-oil through catalytic pyrolysis of waste cooking oil, especially bio-oil with high benzene, toluene, and xylene content and low oxygen-containing compounds content, is economically feasible.