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 degrees 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 PAH-Is as long as sufficient time is available. Entropy appears to determine the type and size of cyclic hydrocarbons formed.

Triacylglycerols (TGs) are naturally occurring oils abundant in many crops. A series of batch uncatalyzed thermal decomposition experiments were performed using canola and soybean oils to explore pathways of TG cracking. A detailed gas chromatographic protocol based on mass spectrometric identification and flame ionization quantification was applied to the organic liquid product generated upon cracking. Reaction conditions were identified that resulted in a novel organic liquid product (OLP) composition compared to previously reported work. Under these conditions (temperatures within a 420-440 degrees C range) a new route for TG thermolysis was discovered in which cracking reactions of original TG-bound fatty acids were nearly complete and led to the formation of 15-25 wt.% C-2-C-10 linear saturated monocarboxylic acids and ca. 30% linear alkanes. Less than 2 wt.% C-16-C-18 fatty acids which were originally present in the feedstocks as glycerol triesters were found in the OLP. These reactions appear to be kinetically controlled due to abundant hydrogen formation. This route provides a significant enrichment of low-MW compounds in the OLP (65-70 wt.% being <C-11) and thus may be considered as a new option for the production of replacement products for petroleum-based fuels and chemicals. (C) 2011 Elsevier Ltd. All rights reserved.

Triacyl glycerides (TGs) are naturally occurring oils produced by a significant variety of crops, microorganisms (bacteria and algae), and animals (certain fats). The diversity and prevalence of the sources of these compounds suggest that they may serve as an attractive alternative to crude oil as the feedstock for the production of transportation fuels and certain industrial chemicals — organic compounds with carbon chain lengths in the range of C7 to C15. In the present study a series of batch thermal cracking reactions was performed using soybean oil and canola oil under reaction conditions leading towards attractive yields of potentially valuable (as fuels and/or chemicals) shorter chain products. An attractive yield of alkanes and fatty acids (from oil cracking) or esters (from biodiesel) was obtained. From a parametric study reaction temperature, followed by residence time, was found to have the most significant effect. Significantly, cracking under increased pressures in a hydrogen atmosphere did not improve the yields of desirable species.

A study was performed to evaluate the use of thermal cracking to overcome cold flow and stability limitations of current biodiesel. Experiments were conducted in a batch cracking reactor system using soy methyl ester and canola methyl ester feedstocks. The amount of high-MW C16–C24 FAMEs was reduced from nearly 100% in the original feedstock by an order of magnitude. Yields of desirable cracking product ranged from 70 to 85% while cloud and pour points decreased around 20°C and 15°C, respectively. The stability of the fuel was improved by converting all of the unsaturated esters into lower-MW saturated esters. This method may lead to an attractive process to produce an improved biodiesel that is more conductive to cold temperature utilization and more stable during storage.