Effects of antioxidants on oxidation and storage stability of Croton megalocarpus biodiesel

The effects of antioxidants and storage on oxidation stability of croton biodiesel and its blends with petro-diesel were determined using PetroOxy equipment. The biodiesel and blends were kept in Pyrex reagent bottles and stored in a metallic locker at room temperature for 8 weeks, a condition that imitated ordinary storage environment in tanks before use. The oxidation stability indices of the biodiesel and blends were determined by measuring Rancimat induction periods for 8 weeks at intervals of 2 weeks. Although the Rancimat induction period for freshly prepared biodiesel of 4 h was higher than the commonly used American standard (ASTM D6751) limit of 3 h, it was lower than the European standard (EN 14214) of 6 h. The induction periods of B50 and lower blends were, however, equal to or greater than 6 h. The Rancimat induction periods for biodiesel with 100 ppm antioxidants were 5.6, 6.8 and 7.8 h for Butylated hydroxyanisol (BHA), Propyl gallate (PRG) and Pyrogallol (PYG), respectively, while the Rancimat induction periods for biodiesel with 1000 ppm antioxidants were 6.8, 8.2 and 10 h for BHA, PRG and PYG, respectively. The oxidation stability index for neat biodiesel decreased by 45 % while that for biodiesel with 1000 ppm antioxidants depreciated by 16, 12.2 and 20.59 % for PYG, PRG and BHA, respectively, during the 8-week storage period. A more rapid decline in oxidation stability was observed in the biodiesel and blends without antioxidants than those with antioxidants. The results from this study showed that the use of appropriate concentrations of suitable antioxidants can greatly improve the oxidation stability of biodiesel and blends which can therefore be stored over longer periods of time before use without undergoing extensive and deleterious oxidative deterioration.