Operating Strategies for the Oxidative Steam Reforming (OSR) of Raw Bio-oil in a Continuous Two-step System

Abstract

This work aimed to establish a suitable O₂ feeding strategy for the hydrogen production by oxidative steam reforming (OSR) of raw bio-oil in a reaction system with two-steps: thermal treatment (at 500 °C, for the controlled deposition of pyrolytic lignin) followed by the reforming of the volatile stream in a fluidized bed reactor. Specifically, the effect of co-feeding O₂ before or after the thermal step was analyzed for oxygen-to- carbon molar ratio (O/C) in the 0.34-0.67 range. The catalytic step was kept at 700 °C, steam-to-carbon molar ratio (S/C) = 6.0, and space-time = 0.6 g_catalyst h(g_bio-oil)^-1. When O₂ is co-fed before the thermal step, there is a partial combustion of both, pyrolytic lignin and oxygenates, thus resulting a lower amount of oxygenated compounds entering the reforming reactor, although the composition of these oxygenates is not affected by the presence of O₂ in the thermal step. As a result, a noticeable lower H₂ yield was obtained when O₂ is fed before the thermal treatment, although catalyst deactivation rate was similar to that obtained when co-feeding O₂ after thermal treatment. Consequently, in the OSR of bio-oil in a two-step system, O₂ must be co-fed after the thermal treatment step; in order to avoid bio-oil oxygenates oxidation prior to the reforming reaction.