Effect of mixing bio-oil aqueous phase model compounds on hydrogen production in non-catalytic supercritical reforming

Bio-oil derived from biomass fast pyrolysis can be processed into fuel or some chemical products, but it has a waste aqueous phase that, however, may be valorized. Supercritical reforming of this stream, simulated using mixtures of model compounds (acetic acid, acetol, 1-butanol and glucose), was experimentally studied in a tubular reactor without using a catalyst. The effect of mixing the model compounds at different operating parameters (temperature, feed composition, and residence time) on the process performance was investigated, thus addressing an important chemical aspect of biomass-based renewable energy. The experimental dry gas composition consisted of H-2, CO2, CO and CH4, although the gas yields were far from equilibrium. Hydrogen yields were normally less than 2.0 moles of H-2 per mole of organic feed, which are lower than those obtained for pure compounds with the same concentration. Based on the analyzed liquid samples, a series of probable reaction pathways were proposed to explain the experimental results by considering the interactions among the compounds and their formed intermediates. Thus, under tested supercritical conditions, the residence time was insufficient to reform the formed methane into hydrogen, thus leading to lower hydrogen production.