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Analysis and Properties of the Decarboxylation Products of Oleic Acid by Catalytic Triruthenium Dodecacarbonyl

Moser Bryan R., Knothe Gerhard, Walter Erin L., Murray Rex E., Dunn Robert O., Doll Kenneth M.
Energy & Fuels 2016 v.30 no.9 pp. 7443-7451
benzene, biodiesel, chemical analysis, chemical composition, decarboxylation, dehydrogenation, diesel fuel, dimethyl disulfide, gas chromatography-mass spectrometry, hydrogen, hydrogenation, isomers, oleic acid, oxidative stability, petroleum, ruthenium
Recently, ruthenium-catalyzed isomerization–decarboxylation of fatty acids to give alkene mixtures was reported. When the substrate was oleic acid, the reaction yielded a mixture consisting of heptadecene isomers. In this work, we report the compositional analysis of the mixture obtained by triruthenium dodecacarbonyl catalyzed decarboxylation of oleic acid. Surprisingly, the most prominent single compound identified was heptadecane at approximately 18 wt %. A mixture of heptadecene isomers constituted the greatest percentage of the product (>75%), where all positional isomers were confirmed by GC–MS analysis of dimethyl disulfide derivatives of the product. Besides these components, minor amounts of alkyl aromatics, each with a total of 17 carbons atoms, among them undecyl benzene, were observed. Minor amounts of other compounds, such as shorter-chain hydrocarbons and polyunsaturated C17 compounds, were also observed. A reaction pathway to explain the existence of these products is proposed. Heptadecenes first cyclize to the observed alkyl aromatics under liberation of hydrogen with the formed hydrogen, then in turn hydrogenating some heptadecenes to heptadecane. Thus, triruthenium dodecacarbonyl is suggested to also promote dehydrogenation, aromatization, and hydrogenation under the present conditions. Since the product mixture consisted mainly of long-chain hydrocarbons, its properties regarding diesel fuel application were studied and compared to biodiesel and petroleum diesel. The cetane number (86.9) was high, but oxidative stability (3.4 h; EN 15751) and cold flow (cloud point −1 °C) would require improvement to meet fuel specifications. All other fuel properties were within the limits prescribed in the petrodiesel standards.