Hydrothermal Catalytic Deoxygenation of Fatty Acid and Bio-oil with In Situ H₂

Fatty acid and its derivatives have recently received considerable interest as a possible precursor for producing renewable hydrocarbon. Compared to the traditional hydrotreating method that consumes a significant amount of H₂, this study developed a hydrothermal catalytic deoxygenation approach that produced hydrocarbon from fatty acids and bio-oil with in situ self-sustaining H₂. The presence of H₂O played a critical role in the generation of in situ H₂ via enhancing water–gas shift and reforming reactions, thus promoting fatty acid decarbonylation and increased paraffin yields. Both saturated and unsaturated fatty acids (stearic acid (SA) and oleic acid (OA)) were employed as model compounds, where 100% conversion was achieved with 63.59% paraffin yield from SA and 47% <i>n</i>-paraffin yield from OA. By investigating the reaction pathway, fatty acid and glycerol reforming, and water–gas shift reactions, were determined to be the major reactions for the in situ H₂ generation. Decarbonylation was found as the major route for fatty acid and bio-oil deoxygenation. Fatty acid reforming and hydrogenoloysis reactions were found as the major reactions for producing short-chain hydrocarbons (C8–C16). We previously developed a sequential hydrothermal liquefaction method to produce bio-oil from yeast biomass. In this study, the produced bio-oil was also tested, where 100 wt % bio-oil conversion and 55.17 wt % of liquid <i>n</i>-paraffin yield were achieved at 320 °C. This study demonstrates that this hydrothermal catalytic process is a promising approach for producing liquid paraffin (C8–C15) from fatty acid and bio-oil under the conditions of no H₂ supply