Sunflower biodiesel Use of P-DSC in the evaluation of antioxidant efficiency

The higher is the degree of unsaturation in ester chain of a biodiesel, the smaller is its oxidation stability. Sunflower biodiesel obtained by the ethyl route possesses a high amount of unsaturated fatty acids, mainly oleic acid (C18:1) and linoleic acid (C18:2), thus being more prone to the oxidation process. In Brazil, with the purpose of meeting the specifications of the Brazilian National Agency of Petroleum, Natural Gas and Biofuels (ANP), antioxidant additives, from synthetic and natural origins, have been added to the biofuel. Antioxidants are an alternative to prevent the oxidative deterioration of the fatty acid derivatives, as they are substances able to reduce the oxidation rate. In this study, the oxidative stability of sunflower biodiesel, obtained by the ethyl route and additivated with different concentrations of the antioxidants butylated hydroxytoluene (BHT) and t-butylhydroquinone (TBHQ), was evaluated by means of Pressure differential scanning calorimetry (P-DSC) and the Accelerated oxidative stability test (Rancimat, Method EN 14112). The results obtained by the two techniques showed the same oxidation tendency. Thus, P-DSC can be used as an alternative to determine the oxidative stability of biodiesel. The antioxidant TBHQ, added to biodiesel at the concentrations of 2000 and 2500 mg kg(-1), raised the oxidation induction time to a value higher than 6 h, the limit established by the Resolution ANP number 7/2008, thus being the best alternative among the studied antioxidants.