Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/11/2005
Publication Date: 5/29/2005
Citation: Dunn, R.O. 2005. Oxidative stability of soybean oil fatty acid methyl esters by oil stability index (osi). Journal of the American Oil Chemists' Society. 82(5):381-387. Interpretive Summary: Biodiesel, an alternative diesel fuel made from vegetable oils or animal fats, is very reactive to oxygen when placed in contact with air. Detecting the effects of oxidative degradation during storage presents a legitimate concern for those seeking the widespread commercialization of biodiesel. This work examines the application of the oil stability index (OSI) as a parameter for monitoring fuel quality with respect to oxidative stability of biodiesel made from soybean oil (methyl soyate). Methyl soyate samples from five separate fuel producers were analyzed for OSI and discrepancies in relative stability were observed. This work showed that OSI is a suitable parameter for measuring relative resistance of methyl soyate to oxidation during storage in terms of detecting the effects degradation or the presence of oxidation inhibitors in untreated samples. Results will benefit biodiesel fuel producers, distributors and customers by providing a user-friendly (automated) method to monitor fuel quality during long-term storage.
Technical Abstract: Biodiesel, an alternative diesel fuel derived from transesterification of vegetable oils or animal fats, is composed of saturated and unsaturated long-chain fatty acid alkyl esters. During long term storage, oxidation caused by contact with air (autoxidation) present a legitimate concern with respect to monitoring and maintaining fuel quality. Extensive oxidative degradation may compromise quality by adversely affecting kinematic viscosity, acid value or peroxide value. This work examines the oil stability index (OSI) as a parameter for monitoring the oxidative stability of methyl soyate (SME). SME samples from five separate sources and with varying storage and handling histories were anlyzed for OSI at 60 deg C using an oxidative stability instrument. Results showed that OSI may be employed to measure relative oxidative stability of SME samples as well as differentiating between samples from different producers. Although addition of alpha-tocopherol or tert-butylhydroquinone (TBHQ) increased OSI, responses to these antioxidants varied with respect to SME sample. Variations in response to added antioxidant were attributed to aging and other effects that may cause oxidative degradation in samples prior to acquisition for this study. Results showed that OSI was more sensitive than iodine value (IV) in detecting the affects of oxidative degradation in its early stages when monitoring SME during storage.