Effect of Metal Contaminants and Antioxidants on the Oxidation Stability of the Methyl Ester of Pongamia

According to the proposed National Mission on biodiesel in India, we have undertaken studies on the stability of biodiesel from tree-borne non-edible oil seeds like Pongamia pinnata. Neat Pongamia methyl ester (PoME) exhibited an oxidation stability (OS) of 2.54 h and research was conducted to investigate the effect of the presence of transition metals likely to be present in the metallurgy of storage tanks and barrels, on the OS of PoME. It was found that the influence of metal was detrimental to OS and was catalytic, as even small concentrations of metal contaminants showed nearly the same influence on OS as large amounts. Copper showed the strongest detrimental and catalytic effect on OS. The OS of metal-contaminated PoME was found to increase with an increase in the dosage of antioxidant but the dosage required for copper-contaminated PoME became approximately four times than required for neat PoME. The dependence of the OS on the type of metal showed that long-term storage tests in different types of metal containers for examining the influence of container material on OS of biodiesel may be replaced by the significantly faster Rancimat test serving as an accelerated storage test.