Comparative study of biodiesel oxidation stability using Rancimat, PetroOXY, and low P-DSC

Abstract

Oxidation stability of biodiesel is one of the most important factors used to evaluate its quality, allowing its commercialization and ensuring its shelf life. In this context, several accelerated methods have been used to measure oxidative stability to predict the maximum storage time at which biodiesel can be submitted without compromising its quality. In the present study, the oxidation stability of two commercial biodiesel and of their blends with two antioxidants was evaluated using the standard methods described in the EN 14214 norm (Rancimat Method) and in ASTM D7545 (PetroOXY method), as well as by low pressurized differential scanning calorimetry (low P-DSC). Both biodiesel were obtained from soybean oil, produced by methylic and ethylic route. The antioxidants, which were used in different concentrations, have the following active components: bisphenol and phenol. The three assessed methodologies can be used to determine the effect of the commercial antioxidants on the oxidative stability of the studied biodiesel. As each method is based on the measurement of different parameters to obtain the respective oxidation induction time, their results cannot be compared directly. But when the results are expressed in terms of the percentage change of the respective oxidation induction times, there is a higher correlation between those obtained by Rancimat and PetroOXY methods than when compared with the results obtained by low P-DSC. Because of their characteristics, the bisphenolic antioxidant is more effective than the phenolic one and, at a same antioxidant concentration, the oxidation stability of the ethylic biodiesel is higher than that of the methylic one. Considering analysis time and sensitivity, the low P-DSC method is the one that better attends both parameters among the applied methods.