The effect of synthetic antioxidants such as BHT (butyl-hydroxytoluene), BHA (butyl-hydroxyanisol) and TBHQ (t-butyl-hydroxyquinone) was evaluated on the induction time of soybean oil ethyl esters with low oxidation stability, employing the Rancimat method (EN14112). Interaction effects were also investigated by employing a 2³ factorial design, which had as minimum and maximum levels the concentrations of zero and 1500 ppm of each antioxidant. Among the synthetic antioxidants evaluated, BHT displayed the highest effectiveness in the concentration range from 200 to 7000 ppm. TBHQ displayed a greater stabilizing potential when used at higher concentrations (8000 ppm), while BHA was found to provide no noticeable increase in the induction time at concentrations greater than 2000 ppm. The combined use of these antioxidants, at the levels tested in this study, yielded no evidence of any positive synergic effect that would justify their use in binary or ternary mixtures.
biodiesel; ethyl esters; antioxidants; oxidation stability; Rancimat method
