Comparison of Synthetic and Plant Extract Antioxidant Additives on Biodiesel Stability

Oxidation stability is a critical parameter on biodiesel quality. Relates to The Indonesian Government policy to increase the percentage of biodiesel in diesel fuel blends, it is necessary to improve biodiesel quality so the diesel blends can meet the specification. This research focus on the effects of antioxidant additive to biodiesel quality, especially on oxidation stability characteristics, represented by Acid value, kinematic viscosity and induction period. Three additives used on this study were synthetic antioxidant additives tert-Butylhydroquinone (TBHQ), Propyl Gallate (PG) and a natural based antioxidant from Mango leaves extract prepared at LEMIGAS laboratory. Palm Oil based biodiesel is added with these three additives. A sample which is biodiesel without any additive was used for reference. All samples stored at an open glass tin for 12 weeks period. The Acid value, kinematic viscosity and induction period were measured for each 2 weeks. The result shows that additive TBHQ gives better performance in terms of Acid value, where sample containing TBHQ increase only 2.86% compare to PG and mango leaves extract that increase 11.43% and 22.22% respectively during 12 weeks storage. In terms of kinematic viscosity, these three additives shows similar result where the increasing of viscosity isn't significant during test period. From the oxidation stability which is measured by induction period, PG additive show the lowest decreasing with only 1.96% lower from its initial value compare to TBHQ and mango leaves extract which decrease 5.03% and 18.76% respectively. From the result we conclude that the synthetic additives give better performance on biodiesel oxidation stability that the natural based additive.