Long term storage stability of biodiesel: Influence of feedstock, commercial additives and purification step

In the present work, the effect of four commercial additives, three synthetic (AO1, AO2 and AO3) and one natural based antioxidant (AO4), on the oxidation stability of biodiesel after six months of storage was investigated. Biodiesel fuel was obtained from different vegetable oils: Soybean, rapeseed, high oleic sunflower and palm methyl ester (SBME, RME, HOSME and PME, respectively). The influence of the washing agent used in the purification step (distilled water or a citric acid solution) was also studied. Samples were stored for a 6 month period at room temperature and not exposed to day light. Propyl gallate based antioxidant was found to provide the best oxidative stability after the storage period. Biodiesel obtained from low unsaturated feedstocks, such as palm oil, presented more oxidative stability than higher unsaturated oils, such as soybean oil. By purifying methyl ester phase with citric acid, the washing agent volume required resulted reduced. The antioxidant characteristic of citric acid enhanced the IP values of the samples, retarding the oxidation process.