Converting Algal Triglycerides to Distillate Fuels: Converting Algal Alkanes to Diesel and Jet Fuels

摘要

Conversion of renewable triglycerides to liquid distillate fuels requires a number of chemical transformations. First, the triglycerides must be converted to normal alkanes. Next, the normal alkanes must be catalytically isomerized and hydrocracked to a distribution of alkane isomers and the fractions appropriate for diesel and aviation fuel recovered. The composition of the n-alkanes derived from a single algal source will depend on the distribution of fatty acids comprising the triglycerides and the chemistry of converting the triglycerides to n-alkanes. Fatty acids can yield n-alkanes conserving the starting carbon number as well as those with one fewer carbon atom. Generally, the range of fatty acid carbon numbers is quite restricted, with the most likely carbon numbers being 16 and 18. Hydrocarbons of this size are well within the typical span of diesel fuels. However, since these n-alkanes would gel and solidify not much below typical room temperature, some hydroisomerization is required to improve cold flow properties. In contrast, aviation kerosene has C_(15+) in rapidly diminishing abundance in order to meet the much more rigorous low temperature flow requirements. Consequently, C_(14+) n-alkanes require catalytic hydrocracking in order to produce HEFA (hydrotreated esters and fatty acids) blendstock for mixing with a petroleum fuel.