Effect of Natural Antioxidants on Oxidative Stability of Biodiesel from Soybean Oil. Applying Simplex-Centroid Design

Oxidation stability is a parameter of great importance for biodiesel quality control to both producers and future consumers. Keeping the quality of biodiesel, currently the most effective and economical method is the addition of antioxidants. Natural antioxidants can be an alternative to prevent or retard the degradation of biofuels from vegetable oils. In this study, it was evaluated the oxidative stability of B100 biodiesel from soybean oil in the presence of alcoholic extracts of rosemary, oregano and basil. The results suggested that the induction period, which precedes the oxidation process, was delayed in the presence of antioxidants, compared with the control, in all cases studied. The joint optimization, for all essay temperatures, demonstrated that a mixture containing 25% of rosemary ethanolic extract and 75% of oregano ethanolic extract is the most effective to retard the oxidation process. This simplex-centroid mixture experimental design shows viability to be applied in the biodiesel, oils and fats industry to evaluate the oxidation stability and the occurrence of synergism between different mixtures of synthetic or natural antioxidants. Besides, the results showed that the B100 biodiesel containing extract of oregano can provides, at 25 degrees C, a storage period seven times higher than the estimated for pure B100.