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 CO 2 are low, because their formation is attenuated by co-feeding methanol.