Submitted to: Annual Meeting and Expo of the American Oil Chemists' Society
Publication Type: Abstract Only
Publication Acceptance Date: March 15, 2004
Publication Date: May 15, 2004
Citation: Dunn, R.O. 2004. Effect of mixed antioxidants on oxidative stability of biodiesel [abstract]. Annual Meeting and Expo of the American Oil Chemists' Society. p. 77. Technical Abstract: Biodiesel is a mixture of fatty acid alkyl esters with a relatively high concentration of unsaturated (low-melting point) esters to promote better cold flow properties and performance in blends with conventional diesel fuels. For example, methyl soyate (SME) has 80-85 wt% total unsaturated fatty acid methyl esters (oleic, linoleic and linolenic). As a consequence, biodiesel is very prone to oxidative degradation when placed into contact with ambient air during storage. To maintain good fuel quality, many fuel producers treat biodiesel with antioxidants such as tert-butylhydroquinone (TBHQ) or butylated hydroxytolune (BHT). Antioxidants add cost and can diminish economic advantages of biodiesel with respect to alternative fuels. Some antioxidants such as TBHQ are also known to decrease significantly in potency with time. This work investigates the use of binary antioxidant mixtures to more effectively promote resistance to oxidation. Binary antioxidants are typically composed of a primary antioxidant that seeks and quenches free radicals formed during the initiation step of the oxidation reaction and a secondary antioxidant whose role is to replace the proton donated by the primary antioxidant to quench the radicals. In this work, oil stability index (OSI) at 90ºC analyses were employed to measure the effectiveness of several antioxidant mixtures in solution with SME. Results showed that 50/50 (w/w) mixtures of propyl gallate (PrG)/butylated hydroxyanisole (BHA), TBHQ/BHA, TBHQ/BHT and TBHQ/alpha-tocopherol exhibited synergistic effects with respect to data for corresponding individual antioxidants in SME. No synergistic effects were noted for similar mixtures of BHA, BHT and PrG with alpha-tocopherol.