Hydrothermal catalytic deoxygenation of palmitic acid over nickel catalyst

Abstract

Fatty acid has recently received considerable interest as a possible precursor for producing renewable hydrocarbon. In this study, we investigated hydrothermal catalytic deoxygenation of palmitic acid to produce paraffin over a Ni/ZrO2 catalyst with no or low-pressure (100 psi) external supply of H2. The results show that the presence of water greatly improved conversion of palmitic acid and paraffin yield. Significant improvement was attributed to the formation of in-situ H2. Without an external H2 supply, a 64.2 C% conversion of palmitic acid was achieved in the presence of water, while only a 17.2 C% conversion was achieved without water. The results also show that the presence of water suppressed the side reactions of palmitic acid, specifically ketonization and esterification. We concluded that, compared with decarboxylation and hydrodeoxygenation, decarbonylation was the major route for palmitic acid deoxygenation catalyzed by Ni/ZrO2. Varieties of shorter-chain paraffin (C8-C14) were formed through hydrogenolysis, which also produced a considerable amount of CH4. A viable reaction pathway for hydrothermal catalytic deoxygenation of palmitic acid in the presence of Ni/ZrO2 was suggested. The results show that hydrogenolysis and decarbonylation were the major reactions that occurred. This study demonstrates that this hydrothermal catalytic process is a promising approach for producing liquid paraffin (C8-C15) from fatty acids under no or low-pressure H2.