Kinetics on the oxidation of biodiesel stabilized with antioxidant

Oxidation stability of safflower biodiesel stabilized with propyl gallate whose concentration spreads from 0 to 5000 ppm was studied by Rancimat method at temperatures from 100 °C to 120 °C. It was consequently demonstrated that the induction period of biodiesel increases with the increase of antioxidant concentration and decreases with increase of temperature. Kinetics on its oxidation was described by the first order rate law with an accuracy higher than 0.98. The reaction rate of propyl gallate consumed in safflower biodiesel obtained from the experiment fits well with Arrhenius equation and the activation energy obtained from Arrhenius equation was 97.02 kJ/mol. Logarithm of induction periods determined by Rancimat method with various antioxidant concentrations shows a linear relation with temperatures. It was, consequently, found that the Rancimat method for the oxidation stability determination shows an approximate correlation between storage stability and Rancimat induction period. The Rancimat method cannot directly measure the overall storage stability of fuels, since other conditions such as presence of water, microbial contamination and storage conditions would affect fuel quality during storage.