Selective Production of Aromatics by Crude Bio-oil Valorization with a Nickel-Modified HZSM-5 Zeolite Catalyst

Abstract

The transformation of crude bio-oil to hydrocarbons has been studied in an online thermal catalytic process that is comprised of two steps: the thermal treatment reactor, followed by the catalytic reactor. The deposition of pyrolytic lignin formed by the 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 aromatic production, which is based on a HZSM-5 zeolite modified by the incorporation of 1 wt % of nickel. The effect of operating conditions (temperature, space time, and time-on-stream), as well as feedstock ratio, on bio-oil conversion, product lump yields, and the selectivity of aromatics has been studied. These conditions also have a significant effect on deactivation, which is attributed to coke deposit on the catalyst. The temperature-programmed oxidation (TPO) curves of coke combustion allow the identification of two fractions: one of thermal origin (pyrolytic lignin) and the other of catalytic origin, whose formation is dependent on the concentration of oxygenates in the reaction medium. A feed with 60 wt % methanol, at 450 °C, with a space time of 0.371 (g of catalyst) h (g of oxygenates)−1 allows one to obtain 90 wt % conversion of the bio-oil in the feed in the catalytic transformation step, with a selectivity of aromatics of 0.4 (benzene, toluene, xylenes (BTX) selectivity of 0.25). These results remain almost constant in the first hour of reaction. The yields of CO and CO2 are low, because their formation is attenuated by co-feeding methanol.