Analysis and properties of the decarboxylation products of oleic acid by catalytic triruthenium dodecacarbonyl

Authors: Moser, Bryan; Knothe, Gerhard; Walter, Erin; Murray, Rex; Dunn, Robert - Bob; Doll, Kenneth - Ken

Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2016
Publication Date: 9/15/2016
Publication URL: http://handle.nal.usda.gov/10113/5510199
Citation: Moser, B.R., Knothe, G., Walter, E.L., Murray, R.E., Dunn, R.O., Doll, K.M. 2016. Analysis and properties of the decarboxylation products of oleic acid by catalytic triruthenium dodecacarbonyl. Energy and Fuels. 30(9):7443-7451.

Interpretive Summary: This research reveals that fatty acids derived from vegetable oils may be directly converted into hydrocarbons that are suitable as alternative renewable diesel fuels. The primary objective of this study was to prepare and measure the composition and fuel properties of the hydrocarbon mixture and compare those results to conventional petroleum diesel (petrodiesel) fuel as well to internationally recognized petrodiesel fuel standards. The results indicated that most of the fuel properties were within the specifications listed in the petrodiesel standards, but oxidative stability and cold flow would require improvement. Otherwise, the newly reported alternative fuel has excellent energy content, viscosity, lubricity, and cetane number. These results will be important to the agricultural sector as well as to petroleum companies and manufacturers of diesel engines because a new renewable diesel fuel was described that is similar to petrodiesel and derived from fatty acids. This research may ultimately improve market penetration, availability, and public perception of domestically produced agricultural fuels and chemicals, thus affording greater national independence from imported petroleum and its consequent environmental impact.

Technical Abstract: 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 carbon 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 deg. C) would require improvement to meet fuel specifications. All other fuel properties were within the limits prescribed in the petrodiesel standards.