(449f) Hydrothermal Deoxygenation of Fatty Acid

Fatty acid alkyl esters are renewable liquid biodiesel fuel, but the high oxygen content limits their application. As a better alternate, low-oxygen content hydrocarbon has received increased interest. The deoxygenation of fatty acid via hydrodeoxygenation however, requires a large amount of H₂, which significantly limits the commercialization of this process. Decarbonylation is another pathway to remove oxygen with the formation of CO. Water-gas shift reaction can be a potential way to produce H₂ from H₂O and CO. Therefore, we proposed to combine the decarbonylation with water-gas shift reaction to produce in-situ H₂, which will accelerate the deoxygenation of fatty acid.

Our lab has been working on employing hydrothermal deoxygenation reaction in aqueous media for this application. We aimed at removing oxygen in the form of DeCOx without or with a little amount usage of H₂. We use fatty acid as model compounds to screen several transition metal catalysts on different support and found Ni/ZrO₂ to be promising. The catalyst showed great selectivity for converting palmitic acid to pentadecane in aqueous phase. Without hydrogen usage, 50% conversion of palmitic acid was achieved at 300C and the selectivity to linear paraffin was 70%. Under hydrogen and palmitic acid molar ratio at 1:2, 82% conversion was achieved with the selectivity to linear paraffin at 50%. Three other fatty acids, stearic, oleic, and linoleic acid were also compared to illustrate the effect of fatty acid saturation on the conversion rate and products selectivity. Saturated fatty acid was observed to be more effectively deoxygenated to hydrocarbon than unsaturated fatty acid. The main organic product was the paraffin with one carbon less than the precursor fatty acid. The results provide another possible pathway: to conduct deoxygenation of fatty acid in subcritical water phase. The lower H₂ consumption in this process will reduce the cost for the production of oxygen-free bio-fuels.