Determination of antioxidant depletion kinetics using ASTMD 7545 as the accelerated oxidation method

The oxidation stability of biodiesels obtained from the transesterification of sunflower and soybean refined oils was studied using a method of accelerated oxidation (under 700 kPa oxygen atmosphere), the so-called PetrOXY method. The antioxidant Ionol BF 200 was used in a concentration range from 0 to 5000 ppm, and the experiments were carried out with temperatures varying from 130 to 145 °C. Oxidation kinetics could be described with a good precision, considering that correlation coefficients were above 0.99, obeying a first-order reaction kinetics in relation to the concentration of antioxidant for soybean biodiesel and an apparently zero-order kinetics for sunflower biodiesel (which was the result of mathematical approximations derived from a more chemically appropriated first-order kinetics). Reaction specific velocities were determined and enthalpies of activation for antioxidant oxidation were determined from Arrhenius plots. All the results indicated that, for the same inhibitor concentration, sunflower-derived biodiesel was less stable towards oxidation than the soybean one.