Olefin Production by Catalytic Transformation of Crude Bio-Oil in a Two-Step Process

Abstract

The valorization of crude bio-oil by catalytic transformation into hydrocarbons has been carried out in an online two-step (thermal-catalytic) process. The deposition of pyrolytic lignin, formed by polymerization of biomass-derived products, is enhanced in the thermal step. Volatiles are processed in a fluidized bed reactor with a catalyst that is hydrothermally stable and selective for olefin production, which has been based on a HZSM-5 zeolite. A study has been made of the effect of operating conditions (methanol content in the feed of bio-oil/methanol, temperature, space time, and time on stream) on bio-oil conversion, product lump yields and the selectivity of each individual C2−C4 olefin. These conditions also have a significant effect on deactivation, which is attributed to coke deposited on the catalyst. The TPO curves of coke combustion identify two fractions: one of thermal origin (pyrolytic lignin) and the other of catalytic origin, whose formation depends on the concentration of oxygenates in the reaction medium. A feed with 50 wt % of methanol, at 500 °C, with space time of 0.371 (g of catalyst) h (g of methanol)−1 allows a 94 wt % conversion of the bio-oil in the feed, with a selectivity of C2−C4 olefins of 48 wt % (50 wt % is propene) and low yields of CO and CO2 (its formation is attenuated by cofeeding methanol).