Synthesis, Characterization and Evaluation of Iron-Molybdenum Oxide Catalyst for the Hydrothermal Liquefaction of Wastewater to Bio-oil

Abstract

Handling of ever increasing municipal sewage containing organics has become a challenge in one hand whereas getting the supply of cheaper and assured supply of biomass to produce biofuels, a replacement for fossil fuels is a challenge on the other hand. Thus developing suitable technologies to process municipal sewage to biofuels is of huge interest to address both the UN sustainable development goals (SDG) 11.6 and 7. Hydrothermal liquefaction (HTL) is the only thermochemical conversion that can process the municipal liquid sewage to bio-oil, which upon hydrotreating could be the substitute for gasoline, kerosene and diesel. The development of appropriate recyclable heterogeneous catalyst with high deoxygenation activity is crucial for increasing the yield and quality of bio-oil to make the process commercially viable. Iron-molybdenum oxide was prepared from iron and molybdenum precursors of Mo/Fe mole ratio 1.5 and 2.2 by co-precipitation method, calcined, characterized by XRD and FTIR. The XRD and FTIR characteristics indicated the presence of Fe (III) molybdate and molybdenum oxide (MoO3) phases in both the Fe–Mo Oxide (1.5) and (2.2) catalysts but the Fe (III) molybdate phase was the predominant phase in the former, since the Mo/Fe mole ratio of Fe (III) molybdate phase is also1.5. The catalysts were evaluated for hydrothermal liquefaction of synthetic wastewater to bio-oil under subcritical conditions and Fe–Mo Oxide (1.5) gave Total Oil Yield of 36.5%, which was more than double that of Fe–Mo Oxide (2.2). The higher bio-oil yield of Fe–Mo Oxide (1.5) was attributed to the deep deoxygenation activity of Fe (III) molybdate phase predominantly present.