Experimental study of the factors affecting the oxidation stability of biodiesel FAME fuels

• Established the effect of biodiesel composition on its oxidative stability.
• FAME main components were Palmitate, Stearate, Oleate,Linoleate, and Linolenate
• No correlation between the compositions stability indices and Rancimat OS index.
• All FAME biodiesels failed to meet EN 14214 requirement on OS (> 6 h)
• Rancimat OS exhibited Arrhenius temperature dependence.
• Extrapolation of Rancimat OS to estimate storage life predicted poor estimate.

Oxidative stability of fatty acid alkyl esters or biodiesel during storage is very important as it yields products that degrade biodiesel quality and consequently affect engine performance. Accurate measurement, prediction and control of the oxidative stability of biodiesel from different feedstocks remain a challenging problem in biodiesel research. The current study relates to the investigation of the impacts of variation in feedstock on the oxidative stability of biodiesel, efficacy of various stability models (APE, BAPE, and OX) at predicting biodiesel oxidative stability, and the impacts of antioxidant loads in controlling oxidative instability of biodiesel. Firstly, oxidation stability for twelve different fatty acid methyl ester (FAME) biodiesels was measured to establish the effects of feedstock type on it. Then, fatty acid compositions were measured to establish the efficacy of the various models known as APE, BAPE, and OX proposed for characterizing the susceptibility of FAME to oxidation. Results showed oxidative stability and stability indices did not correlate well indicating that these models are inaccurate indicator for biodiesel stability. The response of the four biodiesel (Palm, Olive, Soyabean, and Jatropha) to the loading of the antioxidant (tertiary butyl-hydroquinone, TBHQ) was investigated to establish antioxidant threshold loading for delaying needed to delay oxidative degradation. It was found that biodiesel with high polyunsaturated fatty acids showed little improvement in oxidative stability to the same antioxidant dose. Finally, the efficacy of Rancimat methods in predicting the storage life of biodiesel was carried out by developing and extrapolating the oxidative stability Arrhenius temperature curves. The results for Sesame and Rapeseed FAME kept at 40 °C showed under prediction of the storage life by the Rancimat method than obtained in real conditions.