Effect of Antioxidants on the Oxidative Stability of Waste Cooking Oil Based Biodiesel under Different Storage Conditions

Abstract

In this study, the effects of antioxidant on biodiesel degradation characteristics with and without antioxidant under different storage temperatures were investigated. The oxidation stability of waste cooking oil methyl ester (WCOME) originated from soybean and canola oil was studied using different concentrations, ranging from 0 to 600 ppm, of BHT and BPH antioxidants. All mixtures were stored in glass containers at 20 and 40 oC storage temperatures for the testing period of 3 months. The samples were monitored in terms of oxidation stability, peroxide value, acid value, kinematic viscosity and water content. The results showed that both BHT and BPH could increase the oxidation resistance of biodiesel, especially at higher concentrations. The optimum concentration of both BHT and BPH antioxidants were 300 ppm in order to meet the requirement of European standard of oxidation stability, i.e., 6 hours. Due to their different chemical structure, BPH was more effective than BHT, while comparing at the same antioxidant concentration. The results also suggested that biodiesel degradation rate could become faster at higher storage temperature as detected by significant changes in oxidation stability, peroxide value and acid value. Consequently, the fuel quality could be worsened. Furthermore, the high level of unsaturated fatty acid methyl ester in WCOME composition was another factor that could contribute to higher rate of degradation.