In Situ Catalytic Fast Pyrolysis Using Red Mud Catalyst: Impact of Catalytic Fast Pyrolysis Temperature and Biomass Feedstocks

Catalytic fast pyrolysis (CFP) has been considered as a very promising approach for converting lignocellulosic biomass into higher-quality bio-oils followed by hydrotreating to produce fuel-range products. A reactive, robust, and low-cost catalyst is required to drive the CFP process. Red mud, a side-product produced during the refining of bauxite to alumina, appears to be an effective catalyst for in situ CFP of biomass. In this paper, we report the impact of CFP reaction temperature on the conversion of a pinyon juniper feedstock to bio-oils using red mud as the catalyst and then to fuel-range hydrocarbons by hydrotreating of the produced bio-oil. The yield and quality of the CFP bio-oil produced and the yield and quality of hydrotreated final products were determined. When the CFP process temperature was lowered from 450 to 400 °C, the bio-oil yield increased with minimal differences in the oxygen content, hydrogen-to-carbon ratio, water content, etc. In addition, CFP bio-oils at both temperatures were processed in a single-stage continuous hydrotreater without reactor plugging during the testing period (i.e., ∼100 h on stream). The yield of hydrocarbon fuel from CFP bio-oil produced at 400 °C was lower than that of at 450 °C. However, the overall yield, from biomass to hydrocarbon fuel, was still higher for CFP processing at 400 °C than for processing at 450 °C. This indicates such a low-cost catalyst can enable production of bio-oil with much improved stability and consequently enable hydrotreating with a much simplified process and the potential for enhancing overall carbon efficiency by further tuning the CFP parameters. Detailed analysis of bio-oil and hydrotreated products showed a lower content of lignin-derived species in both samples from lower CFP temperature, suggesting more cellulose derived products staying in bio-oil which led to a higher bio-oil yield. Furthermore, CFP processing of three different biomass feedstocks corroborated red mud catalyst development for producing improved quality bio-oil and, when combined with hydrotreating, for the production of fuel range hydrocarbons.