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Quantitation of Aging Products Formed in Biodiesel during the Rancimat Accelerated Oxidation Test

Flitsch, Stephanie, Neu, Philipp Marco, Schober, Sigurd, Kienzl, Norbert, Ullmann, Jörg, Mittelbach, Martin
Energy & Fuels 2014 v.28 no.9 pp. 5849-5856
acetic acid, air flow, biodiesel, chemical elements, epoxides, fatty acid composition, fatty acid methyl esters, gas chromatography-mass spectrometry, ion exchange chromatography, ionization, linoleic acid, linolenic acid, oleic acid, oxidation, rapeseed oil, stearic acid, temperature
Biodiesel (rapeseed oil methyl ester) was aged in a Rancimat device at a temperature of 110 °C and an air flow of 10 L/h. Time-resolved analyses applying gas chromatography–flame ionization detection, gas chromatography–mass spectrometry, and ion-exchange chromatography on the formation of aging products were performed. Formic and acetic acid, fatty acids with chain lengths from 5 to 18 carbon atoms, fatty acid methyl esters, and epoxides were quantified. After 12 h of aging, the concentrations of formic and acetic acid were 5600 ± 80 and 1360 ± 80 mg/kg, respectively. Fatty acid concentrations were in the range of <18–4200 mg/kg after 18 h of aging. Linoleic acid methyl ester and linolenic acid methyl ester (19 and 9.1 mass % of the non-aged fuel) were shown to be fully decomposed after 24 and 18 h of aging, respectively. After 51 h of aging, the concentration of oleic acid methyl ester (63 mass % of the non-aged fuel) decreased to 2.2 mass % and trans-epoxy stearic acid methyl ester and cis-epoxy stearic acid methyl ester reached concetrations of 5.9 and 0.7 mass %, respectively. The fuel composition shows only minor changes in early stages of aging, and a strong timely correlation of the formation of aging products with the end of the induction period of fuel was observed.