(434d) Cracking of Lipid Molecules by a Superacid

The U.S. dependence on foreign oil and the recent increased in crude oil prices have spurred the exploration for new strategies for the application and development of biofuels from lipids and fatty acids. Lipids are produced by plants, animals, and microorganisms for energy storage and cell membrane components. Municipal sewage sludge and cultivated algae are just two lipid sources that could be used to produce green diesel. These lipids (i.e., glycolipids, phospholipids, sphingolipids, etc.) could be cracked with superacids to produce diesel range organics that could be burned in compression ignition engines. Furthermore, the fuels generated from this research could be directly burned or blended with #2 diesel currently being used in the automotive industry. One cracking mechanism proposed in the literature for olefinic compounds is the protonation and generation of relatively stable carbenium ions. In superacid media, protonation occurs at the C-C or C-H bonding to form a 2-electron, 3-center carbenium ion. Superacids, formed by combining Lewis acids with Bronsted acids, offer greater control of reaction conditions (i.e. temperature and pressure) and selectivities. For alkanes, once the protonation induces the carbenium ion, the molecule will generally undergo β-scission to form an alkene and another carbenium ion. Alkylation, the opposite of β-scission, will form an alkane from alkene groups such as those found in unsaturated fatty acids. Much work has been done to determine reaction mechanisms for straight chain and aromatic hydrocarbons; however, little work has been reported for superacid reactions of lipid and fatty acid molecules. This work focuses on the reaction mechanism of model lipid compounds such as palmitic acid, oleic acid, monoglycerides, and tripalmitin. Initial studies were performed using triflic acid to elucidate the cracking mechanism and key products. These results, along with AM1 calculations, will be used to select and synthesize heterogeneous catalysts.