The impact of antioxidants on biodiesel oxidation stability

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Abstract
The potential of 11 different synthetic phenolic antioxidants to improve the oxidation stability of biodiesel prepared from different feedstocks was investigated. Measurements of oxidation stability were carried out according to the European biodiesel specifications with a Rancimat instrument at 110 °C. At antioxidant concentrations of 1000 mg/kg, an improvement in oxidation stability could be achieved with all antioxidants tested. Especially the antioxidants DTBHQ, IONOX 220, Vulkanox ZKF, Vulkanox BKF, and Baynox were able to significantly improve the oxidation stability, leading to stabilization factors between 1.89 and 13.07. Variation of antioxidant concentrations between 100 and 1000 mg/kg showed that the efficiency of the antioxidants varied depending on the different types of biodiesel. When used as additives, Baynox showed good effects on rapeseed oil methyl ester (RME) stability, DBHQ on recycled cooking oil methyl ester (RCOME) stability, Vulkanox BKF on distilled RCOME (DRCOME) stability, and IONOX 220 on tallow methyl ester (TME) stability. Evaluation of the influence of the antioxidants on critical biodiesel fuel parameters showed no negative impacts on viscosities, densities, carbon residues, CFPP, and sulphated ash contents of the different biodiesel samples. However, in terms of acid values, a noticeable increase could be observed at antioxidant levels of 1000 mg/kg. At lower antioxidant concentrations, this increase was much lower and the values remained within the required limits.