Influence of stainless steel corrosion on biodiesel oxidative stability during storage

Biodiesel degradation is the modification of its original composition and properties as a result of fuel aging and metal corrosion during the storage process. This study examines the linkage between biodiesel degradation and the corrosion of stainless steel used to store the biodiesel. First, biodiesel was synthesized from soybean oil via methanolysis and ethanolysis homogeneous base-catalyzed transesterification routes. Next, immersion tests were carried out at room temperature, with little air turnover and in the dark. AISI 316 coupons were used to evaluate the corrosion of metal surfaces after contact with the biofuel. Changes in fuel composition were studied using FTIR and gas chromatography analysis, and the oxidative stability was analyzed by Rancimat and the peroxide index. The corrosion was evaluated by the gravimetric and SEM/EDS microscopy techniques and XRF analysis. Results revealed little influence of methyl and ethyl esters on metal degradation, indicating that routes have no importance on corrosion, since a low corrosion rate was observed for both esters, albeit with some surface micropitting. On the other hand, the presence of a small amount of metal ions released from the stainless steel surface during its corrosion promoted oxidation of the biodiesel, changing fuel composition and quality, as well as reducing its oxidative stability generally.