Submitted to: Annual Meeting and Expo of the American Oil Chemists' Society
Publication Type: Abstract Only
Publication Acceptance Date: May 12, 1999
Publication Date: N/A
Technical Abstract: Biodiesel, an alternative diesel fuel that may be derived from soybean oil, is composed of saturated and unsaturated long-chain fatty acid alkyl esters. When exposed to air during long-term storage, biodiesel undergoes oxidative degradation. Extensive degradation compromises overall fuel quality by adversely affecting kinematic viscosity, acid value, peroxide value, and other properties. Although addition of tert.- butylhydroquinone (TBHQ) can significantly bolster resistance to oxidation of neat biodiesel, treatment of biodiesel/No. 2 diesel fuel blends with TBHQ results in formation of insoluble solids. This work examines four other antioxidants, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate (PrG), and alpha- tocopherol in comparison with TBHQ. Relative effects on resistance to oxidation are analyzed by measuring oxidation temperature by pressurized-differential scanning calorimetry (P-DSC) operating at 2 MPa and in static mode (closed system). Results showed that PrG and BHA were most effective in increasing the resistance for neat biodiesel. Optimum loadings ranged from 2,000 ppm for alpha-tocopherol to 5,000 ppm for BHA. Tests with mixed antioxidants showed that binary mixtures produced a synergistic effect on resistance to oxidation. The most effective binary mixtures were BHA/TBHQ and BHA/PrG, with respect to increasing resistance of neat biodiesel. Materials compatibility tests showed that splash-blending biodiesel-antioxidant with No. 2 diesel fuel was not recommended for either BHT or PrG with respect to their optimum loadings.