Catalytic deoxygenation of triglycerides to hydrocarbons over supported nickel catalysts

The deoxygenation of triolein and soybean oil under nitrogen atmosphere was investigated over Ni-Al, Ni-Mg-Al and Mg-Al layered double hydroxides, as well as 20 wt.% Ni/Al2O3. Deoxygenation was found to proceed via removal of the carboxyl group in the fatty acid structure as CO2 and CO, while additional cracking of the fatty acid chains resulted in the formation of mainly liquid (C5–C17) hydrocarbons. In comparison with triolein, the greater unsaturation of soybean oil resulted in increased cracking, leading to the formation of lighter hydrocarbons and higher amounts of coke deposits. According to 13C NMR measurements, one of the pathways for hydrocarbon formation involves a β-hydrogen elimination in the triglyceride to produce a fatty acid, the decarboxylation of which yields a linear hydrocarbon. The formation of coke was consistently observed in these reactions and was found to limit catalyst activity.

► Layered double hydroxides catalyze triglyceride deoxygenation to hydrocarbons. ► Reactions involved in this transformation occur over reduced Ni and basic MgO sites. ► Fatty acid intermediates are produced from triglycerides. ► Subsequent fatty acid deoxygenation proceeds via decarboxylation/decarbonylation. ► Unsaturated feeds favor both cracking and coke formation as side reactions.