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Biodiesel, an alternative diesel fuel that may be derived from soybean oil, is composed of long-chain saturatedand unsaturated fatty acid alkyl esters. Extensive oxidative degradation can compromise viscosity, acid value, peroxidevalue, and other parameters in the current ASTM biodiesel fuel guideline. This work examines pressurized-differentialscanning calorimetry (P-DSC) for analysis of oxidative stability of biodiesel. Heating scans were conducted under staticair-atmosphere with 5C/min ramping. Increasing pressure from 1000 to 5000 kPa did not significantly affect results and2000 kPa was selected for the remainder of this study. Curves were analyzed for oxidation temperature (OT) of methylsoyate samples from four separate sources. With respect to unmodified methyl soyate, addition of antioxidants increasedOT from 108.4-127.2C to 137.2-163.4C. Mixtures with added tert.-butylhydroquinone consistently gave higher OTvalues than those with -tocopherol; therefore, P-DSC may be useful for screening antioxidants. Although P-DSCresults were consistent with corresponding oil stability index (OSI) data measured at 50C, no correlation for predictingOSI directly from OT results was evident, with the possible exception of unmodified methyl soyate. This work establishesP-DSC as an analytical tool in evaluating the oxidative stability of biodiesel with and without antioxidants.
Robert O. Dunn (Sat,) studied this question.