Cottonseed biodiesel oxidative stability in mixture with natural antioxidants

We evaluated the antioxidant power of the natural extracts catechin, curcumin and quercetin on the oxidative stability of methylic cottonseed oil biodiesel by applying the simplex-centroid augmented mixture experimental design, in addition to verifying the existence and the type of synergy among the extracts. The oxidative stability was measured using Rancimat method (EN 14112) for biodiesel added with 1,000, 2,000 and 3,000 ppm of additives, and compared with the commercial synthetic antioxidant butyl hydroxyanisole at the same concentrations. All additives had a positive effect on biodiesel oxidative stability; in addition, catechin and quercetin proved to be more efficient than the synthetic antioxidant, whereas curcumin showed similar results. The results also revealed that the interactions among the extracts varied not only with the proportion in which they were added to the biodiesel, but also with the total concentration, so that the increase in concentration reduced the magnitude of the synergistic effect.