Degradation of Biodiesel as a Function of Feedstock, Blend Level, and Environmental Conditions

In recent years, many nations have moved towards the use of alternative fuel sources such as biodiesel, a biofuel synthesized from plant and animal feedstocks. Biodiesel is commonly mixed with petroleum diesel to form blends, notated by their ratio of biodiesel to diesel (e.g., B20 = 20% v/v biodiesel). As the use of biodiesel fuels increases, the likelihood of spills during manufacture, transportation, and consumption also rises. Although biodiesel spills may be less critical than those of petroleum-based fuels, it is important to understand their total environmental impact.
The objective in this work is to identify biodiesel degradation products and to model changes in the kinetic rate of degradation as a function of feedstock, blend level, and environmental conditions. Biodiesels were synthesized from different feedstocks (canola oil, soybean oil, and waste cooking oil) and blended at different levels with petroleum diesel (B0, B5, B20, B100). Aliquots of each biodiesel blend were allowed to degrade for 600 h under different environmental conditions including different atmospheric gas compositions (oxygen deficient, oxygen rich), humidity levels, and environmental substrates (sand, soil). At selected times during degradation, biodiesels were extracted from the substrate and analyzed by gas chromatography-mass spectrometry (GC-MS).
The total ion chromatograms were evaluated to identify degradation products under the different environmental and substrate conditions. Normalized abundances of compounds were plotted as a function of degradation time and were fit to kinetic decay curves to define the degradation rate constants. Initial results demonstrate that degradation of petroleum diesel compounds is more rapid in soybean biodiesel as blend level increases in an oxygen-rich and humid environment. Differences in degradation products and rates across feedstocks, blend levels, and environmental conditions will be discussed in more detail in this presentation.