Previous research studies have implicated polar organic nitrogen compounds in fuel instability. Twenty-one middle distillate fuels were investigated for their organic nitrogen content and to determine if any specific organic nitrogen compound might be linked to fuel instability. The organic nitrogen compounds were isolated by mild acid extraction followed by silica gel adsorption. Three extracts were obtained from each fuel sample: a basic nitrogen extract in methylene chloride (BNC), a nonbasic nitrogen extract in methylene chloride (NBNC), and a nonbasic nitrogen extract in methanol (NBNC). The major constituents of each extract were determined by high-resolution gas chromatography/mass spectrometry (GC/MS). After the compounds were identified for each fuel, the fuels were grouped by ASTM stability values to determine if there was significantly more or less of one type of organic nitrogen compound present that could cause instability. The results of this study showed that there was not a specific organic nitrogen compound responsible for instability, but probably an imbalance in either the basic or nonbasic organic nitrogen compounds that caused a shift in equilibrium resulting in sediment or gum formation. This is important to the military because military fuels can remain in storage tanks for 1 or more years. As fuels are drawn from these tanks, the tanks are subsequently topped off with more recently purchased fuels. In many cases, the mixed fuels are not compatible, resulting in sediment and sludge formation.
The purpose of this investigation was to remove the organic nitrogen compounds from petroleum-derived diesel fuels. These nitrogen compounds can cause environmental problems, as well as fuel instability problems that can degrade fuels and affect engine performance. Fuels were treated with two different filtering media, activated clay and silica tel. The methylene chloride extracts from both the activated clay and silica gel were subjected to GC/MS analysis. Close to 99% of the total organic nitrogen compounds were removed. About 60% of the nitrogen compounds identified consisted of pyridines, quinolines and tetra-hydroquinolines made up 26%, while indoles and carbazoles about 10% of the total nitrogen compounds. Of the nitrogen heterocyclics identified, indoles and carbazoles were linked to fuel instability reactions. The proposed method was tested on diesels fuels from a variety of countries and found to remove between 97.8 and 99.9% of the N-compounds. The results of this study showed that both of these filtering materials were effective in removing the organic nitrogen compounds and resulted in fuels that exhibited excellent storage stability. These simple filtering methods can be independent of the refining process and do result in an environmentally cleaner burning fuel.
The Department of Defense is the largest consumer of middle distillate fuels. It has been recommended that alternative fuel sources be considered as replacements or blending stocks for middle distillate ground transportation and marine fuels. Therefore, the search for suitable replacements or blending stocks is earnestly continuing. Renewable agricultural crops such as soybeans and others are now in the forefront. Nonrenewable synthetic fuels such as those produced by Fischer−Tropsch, FT, synthesis from coal and natural gas have been suggested. It is probable that several of these substitutes would be simultaneously blended into a middle distillate petroleum based diesel fuel. Care must be employed when blending fuels so that fuel specifications and storage stability are not decreased. This paper compares the storage stability of a three-part mixture consisting of Fischer−Tropsch diesel, a petroleum diesel, and a 5% and 10% soy biodiesel under ambient conditions.
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