International specifications for biodiesel include a test of oxidative stability (EN14112 Rancimat test) in which conductivity is measured in a tube containing 50 mL of DI water downstream of 3 g of biodiesel exposed to 10 L/h of air at 110� C. The biodiesel fuel is deemed acceptable if an increase in conductivity is detected only after 3 hours(ASTM D6751) or after 6 hours (EN14214). While this test is used worldwide, there is virtually no information on the oxidation products that are responsible for the increase in conductivity. We have carried out Rancimat tests with a soy biodiesel and analyzed by ion chromatography the contents of the tube used to monitor conductivity. Products identified include the carboxylic acids formic acid, acetic acid and propionic acid, along with smaller amounts of butyric acid and lactic acid. Formation rates of these acids have been calculated. Inorganic ions have also been measured, and an attempt was made to estimate the contribution of each ion to the measured conductivity. Some of the carboxylic acids were also present in the biodiesel sample at the end of the test. Implications with respect to engine corrosion by carboxylic acids will be discussed.

Ion chromatography study of the reaction products of soy biodiesel in the EN14112 (Rancimat) oxidative stability test

245th National Meeting (2013)

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