Long-term storage stability of biodiesel and biodiesel blends

Longer-term storage stability of biodiesel and blends was studied in experiments simulating up to one year for 100% biodiesel (B100) and three years for blends. Aging was simulated by holding samples at 43 °C to accelerate oxidation (ASTM D4625). Biodiesels were treated with antioxidants before and after aging, with continued aging after antioxidant treatment. Treating aged biodiesel was effective at restoring stability; however, antioxidant effectiveness was decreased relative to fresh biodiesel. Blends were prepared at B5 (5 vol.%) and B20 (20 vol.%) with biodiesel having either 3- or 6-hour Rancimat induction time and low or high polyunsaturated ester content with two diesels produced from hydrocracked or hydrotreated feedstocks. All B5s were stable for the entire storage time regardless of B100 induction time. B20s were unstable if prepared from high polyunsaturated ester biodiesel with a 3-hour induction time. Base diesel stability had considerable effect on blend stability. All but the lowest-stability B20s remained within specification, indicating that long-term storage of biodiesel blends is possible if the biodiesel has high oxidative stability and storage conditions are clean. Induction time decreases indicated loss of stability (consumption of antioxidant) prior to blend degradation; therefore, induction time monitoring is recommended for predicting quality changes during storage.