Evaluation of the effect of biodiesel content in diesel/biodiesel fuel blends on sediments and gums formation during storage

The oxidation process of fuels during storage affects their quality and has been a recurring problem in the use of neat biodiesel or diesel/biodiesel blends. One of the most significant and undesirable change that occurs due to deterioration is the formation of sediments and gums (SG's). SG's are degradation products resulting from oxidation process of fuels and have a negative effect on the fuel atomization process, reducing its calorific value and ignition quality (cetane number). Diesel fuel sold in Brazil is a diesel/biodiesel blend containing 14% by volume of biodiesel (B14), which increases fuel degradation during storage time. The main aim of this study was to evaluate the effect of the biodiesel content in diesel/biodiesel fuel blends on the SG content formed after storage period using thermogravimetric analysis (TGA). Blends were prepared using methyl soybean biodiesel (B100) and S10 diesel with different volumetric biodiesel percentage, from 10% (B10) to 50% (B50). The samples were stored in amber glass bottles (similar to ASTM D4625), at room temperature and protected from light. Every 30 days, bottles of each mixture were opened and a sample collected for analysis. This procedure was repeated for six consecutive months. Blends oxidized and not oxidized (immediate age) were analyzed using thermogravimetry (TG) and derivative thermogravimetry (DTG). The physicochemical properties of blends were also evaluated, such oxidation stability, kinematic viscosity at 40 degrees C and specific mass a 20 degrees C. Size exclusion chromatography analyses (SEC) were also performed. Thermogravimetry shows that, as the B100 content increases regarding diesel, the interactions between the two fuels are distinct, which result in changes in the TG/DTG curve profile. It is also observed that the increase in B100 promotes the retardation of the mass loss steps of the blends to higher temperatures. The final (Tendset) and the maximum (Tonset) degradation temperatures are affected as well. The TG/DTG curves of the sample showed that increasing biodiesel content in the blend, the percentage of SG formed for the same aging age increases. Moreover, the formation of SG is correlated with the proportion of the blend constituents. The profiles of TG/DTG curves for each blend are a function of the added percentages of biodiesel in the mixture. The experimental results obtained showed that the degradation products formed during the storage of fuels, sediments/gums (SG's), can be quantified using thermogravimetric techniques.