Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/19/2002
Publication Date: 9/20/2002
Citation: DUNN, R.O. EFFECT OF OXIDATION UNDER ACCELERATED CONDITIONS ON FUEL PROPERTIES OF METHYL SOYATE (BIODIESEL). JOURNAL OF THE AMERICAN OIL CHEMISTS' SOCIETY. 2002. Interpretive Summary: Biodiesel made soybean oil and methanol (methyl soyate) is attractive as an alternative fuel for combustion in compression ignition (diesel) type engines. During storage, reaction with oxygen in ambient air (oxidation) may degrade the fuel quality of biodiesel, particularly if the fuel is stored above room temperature. This study examines effects of oxidation on properties that determine the quality of biodiesel fuels. Methyl soyate biodiesel samples from four separate producers with varying histories were collected and oxidized under controlled conditions. Fuel properties were measured before and after oxidation of each sample. Two easy-to-measure properties, viscosity and acid value, were identified as suitable for monitoring biodiesel fuel quality during storage. Also, two readily available oxidation inhibitors were effective in protecting biodiesel from oxidative degradation under most conditions studied. These findings are important because biodiesel production and distribution industries will need accurate, timely approaches for monitoring and protecting biodiesel fuel quality during long term storage.
Technical Abstract: Biodiesel derived from transesterification of soybean oil and methanol is an attractive alternative fuel for combustion in direct-injection compression ignition (diesel) engines. During long term storage, oxidation due to contact with air (autoxidation) presents a legitimate concern with respect to maintaining fuel quality of biodiesel. This work examines the effects of oxidation under controlled accelerated conditions on fuel properties of methyl soyate (SME). SME samples from four separate sources with varying storage histories were oxidized at elevated temperature under a 0.5 SCCM air purge and with continuous stirring. Results showed that reaction time significantly affect kinematic viscosity (v, at 40C). With respect to increasing reaction temperature, v, acid value (AV), peroxide value (PV), and specific gravity (SG) increased significantly, while cold flow properties were minimally affected for temperatures up to 150C. Both v and AV were identified as the most suitable properties for rapid and easy monitoring biodiesel fuel quality during storage. Treatment with antioxidants tert-butylhydroquinone (TBHQ) and alpha-tocopherol showed beneficial effects on retarding oxidative degradation of SME.