Use of heavy fraction of bio-oil as fuel for hydrogen production in iron-based chemical looping process

Chemical looping hydrogen (CLH) process with renewable energy sources as fuel shows the potential of producing pure hydrogen with inherent capture of CO₂ in a low-cost and sustainable way. The heavy fraction (HF) of bio-oil, derived from the fast pyrolysis of biomass and characterized as an energy carrier with difficulty in upgrading itself to bio-fuel or chemicals, was used in this study to generate H₂. Four low-cost iron-based oxygen carriers including an ilmenite and three iron ores were initially evaluated with respect to their reducibility and the ability to minimize carbon or iron carbide (Fe₃C) formation in a thermogravimetric analyzer (TGA). The reactivity and cyclic performance of the selected best candidate was then assessed in a laboratory scale fixed-bed reactor with HF bio-oil as fuel. The screening test in TGA showed that ilmenite was superior over the three iron ores in terms of promoting CO conversion and minimizing carbon or Fe₃C formation. Ilmenite could maintain its increasing reducibility with the increase of surrounding CO concentration, in contrast with the iron ores that were deactivated seriously by the formed carbon or Fe₃C. Subsequent CLH test with ilmenite and HF bio-oil showed that the reducibility and H₂ production capacity of ilmenite were strongly dependent on the operating temperature. The steam oxidation step at 950 °C yielded H₂ concentration and hydrogen yield exceeding all of those observed at the other investigated temperatures because of the deepest reduction degree of ilmenite at 950 °C. The decrease in the reducibility and H₂ production capacity of ilmenite in the cyclic test could be ascribed to the poorer physical structure of ilmenite with cycles.