Enhanced bio-crude yield and quality by reductive hydrothermal liquefaction of oak wood biomass: Effect of iron addition

Hydrothermal liquefaction (HTL) is a promising technology for the production of high quality bio- crude. Aim of this study is to investigate the effect of the addition of iron powder into the HTL process of oak wood biomass. Fe in HTL conditions should be oxidized by water into Fe3O4 producing H-2 in situ which is responsible for the increase of bio-crude yield. Furthermore, the presence of Fe contributes to enhance bio-crude quality due to the presence of Fe3O4 which is recognized to have catalytic activity in hydrogenation reactions. Tests in presence of oxides containing Fe in higher oxidation number such as Fe3O4 and Fe3O3 were performed. The tests were conducted with water to biomass ratio of 5, in a range of temperature of 260-320 degrees C, the reaction time was set to 15 min and the catalysts were added in an amount of 10% with respect to the biomass weight. Highest bio-crude yields of about 40% were reached using zerovalent Fe. Tests performed in presence of Fe3O4 gave intermediate behaviour while no improvements were registered adding Fe3O3. These results confirmed the positive dual effect of Fe addition. In fact, the H/C ratio in the bio-oil increases of about 15% with respect to the reaction conducted without iron-based compounds and Gas Chromatography-Mass Spectrometry analyses showed that the presence of aliphatic compounds is improved.