Biodiesel oxidative stability from Rancimat data

• Sunflower biodiesel was stabilized with a hindered phenol antioxidant.
• Oxidative stability is defined by the length of the Rancimat induction period (IP).
• A novel Rancimat response function allows automated IP determination.
• IP follows an Arrhenius temperature dependence.
• IP increased linearly with antioxidant concentration.

It is conventional to quantify the oxidative stability of oils and biodiesel through an induction time determined by a Rancimat instrument. European Standard EN 14112 for the Rancimat method describes two procedures for determining this induction period. The automated method relies on finding the position of the peak in the second derivative of the conductivity vs. time curve. The manual method is based on the intersection of two tangents lines. It is shown that this method can also be automated by a curve fitting approach based on a novel Rancimat response function. This analysis demonstrates that the induction period values determined by the two methods differ with the second derivative method returning slightly higher estimates for the induction period.Biodiesel was prepared using base-catalysed methanolysis of sunflower oil. It was stabilized using the hindered phenol antioxidant tetrakis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]methane. It was found that stability increases linearly with stabiliser concentration and that the effect of the measurement temperature follows Arrhenius kinetics. The effectiveness of the antioxidant stabiliser diminished with increasing temperature.

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