Evaluation of the oxidation stability of biodiesel stabilized with antioxidants using the Rancimat and PDSC methods

In this study, both the standardized Rancimat and thermoanalytical pressure differential scanning calorimetry (PDSC) methods were employed to investigate the effects of antioxidants on the oxidation stability of biodiesel. The differences in the antioxidant effectiveness between these phenolic compounds could be clearly distinguished by both methods. Results revealed that the efficiency of antioxidant was highly dependent on the test conditions used in each method. Among the five antioxidants investigated, tert-butylhydroquinone (TBHQ) showed the highest sensitivity to different conditions between two methods: the highest oxidation stability in Rancimat vs. the lowest efficiency in PDSC. Butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) acted more efficiently in PDSC than in Rancimat due to lower volatilization losses, but not as well as pyrogallol (PY) and propyl gallate (PG) in increasing the oxidation stability of biodiesel. Results from isothermal and nonisothermal PDSC methods were basically consistent with each other with respect to the antioxidant efficiency: PY > PG > BHA, BHT > TBHQ. A positive linear relationship between results obtained from both methods could be observed within each type of antioxidant, but the overall correlation for the entire data set between Rancimat and PDSC was not as strong as that between isothermal and nonisothermal PDSC methods.