Promotion effects of metallic iron on hydrothermal liquefaction of cornstalk in ethanol-water mixed solvents for the production of biocrude oil

In this article, effects of metallic Fe on biocrude oil production from cornstalk via hydrothermal liquefaction (HTL) in ethanol–water mixed solvents were investigated under various conditions. Experiments were conducted in single solvent of water or ethanol using Fe₃O₄ catalyst to explore the role of metallic Fe in the liquefaction process. The physiochemical properties of the liquefaction products were comprehensively characterized by elemental analysis, GC–MS, FT-IR and XRD. The results showed that the maximum biocrude oil yield (approx. 50 wt%) and higher heating value (HHV) of 30.86 MJ/kg were obtained in ethanol–water mixed solvents (50/50, v/v) at 300 °C for 30 min with 10 wt% Fe loading. It was found that the presence of Fe also promoted the hydrogenation and deoxygenation of liquid products, obtaining biocrude oils mainly consisted of phenolic, ester and hydrocarbon compounds. The positive role of metallic Fe in HTL of biomass in ethanol–water mixed solvents, simultaneously improving the yield and quality of biocrude oil, was believed to be due to in-situ hydrogen formed from the reaction of metallic Fe and water, while the generated Fe₃O₄ exhibited negligible catalytic effect in the process.