Middle Distillate Transportation Fuels Research Articles

Triacylglyceride Thermal Cracking: Pathways to Cyclic Hydrocarbons

Thermal cracking of triacylglyceride (TG) oils results in complex mixtures, containing nearly 20% cyclic hydrocarbons, which can be further processed into middle-distillate transportation fuels and byproduct chemicals. The occurrence patterns of cyclic products obtained via the thermal cracking of several TG feedstocks, such as canola and soybean oils, as well as triolein and tristearin (conducted at 430–440 °C in the absence of catalysts under vacuum), were investigated to probe possible formation mechanisms. Detailed gas chromatographic characterization furnished full molar homology/molecular size and partial isomeric profiles for cyclopentanes, cyclopentenes, cyclohexanes, cyclohexenes, aromatics, and polycyclic aromatic hydrocarbons (PAHs). It was found that the data were inconsistent with previously proposed mechanisms involving the Diels–Alder reaction as a single pathway. An alternate mechanism was proposed and supported with experimental evidence based on the intramolecular cyclization of alkenyl and alkadienyl radicals formed as a result of TG cracking. The product homology profiles corroborate the proposed mechanism and show the depletion of medium-size alkenes coupled with the accumulation of corresponding monocyclic hydrocarbons (those with the matching number of carbon atoms). Similarly, the product mixtures were depleted of long-chain alkyl-substituted monocyclic hydrocarbons because of the formation of the corresponding PAHs as long as sufficient time is available. Entropy appears to determine the type and size of cyclic hydrocarbons formed.

Recycled Soybean Derived Cooking Oils as Blending Stocks for Middle Distillate Transportation Fuels

It has been proposed that biodiesel liquids be used as blending stocks for middle distillate ground transportation fuels by the Department of Defense. The U.S. Navy is considering allowing up to 20% biodiesel to be added as a blending stock to petroleum diesel fuels. It is important for operational consideration to look at the many problems this could present. Among the more important considerations are storage stability, filterability, fuel solubility, oxidative stability and induced instability reactions. This article reports on the use of recycled soybean derived fuel liquids. The fuel liquid was derived from recycled restaurant cooking oil with no added antioxidant after reprocessing. We compare this biodiesel in blends of both 10% and 20% with stable and unstable middle distillate fuels for storage stability, oxidative stability, solubility, and chemical instability results.