Biodiesel oxidative stability from Rancimat data

Abstract

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