Effect of Antioxidants on the Storage Stability of Soybean-Oil-Based Biodiesel

Biodiesel is composed of the monoalkyl esters produced from a variety of animal fats or vegetable oils, which can be used in blends with conventional petroleum diesel in existing diesel engines. While having many desirable properties, poor oxidative and storage stabilities are a source of considerable concern. This paper presents results of studies on the effectiveness of various individual and binary antioxidants [(alpha-tocopherol (alpha-T), butylated hydroxyanisole (BHA), butyl-4-methylphenol (BHT), t-butylhydroquinone (TBHQ), 2,5-ditert-butyl-hydroquinone (DTBHQ), ionol BF200 (IB), propylgallate (PG), and pyrogallol (PY)] to improve the storage stability of soybean oil (SBO)- and distilled SBO-based biodiesel. Results indicate that the induction period (IP) of untreated SBO-based biodiesel significantly decreased with the increasing storage time, while the IP values with adding TBHQ to SBO-based biodiesel remained constant for up to 30 months. Moreover, the binary antioxidant formulations of THBQ/BHA maintained the IP of distilled SBO-based biodiesel stable over a 6 month period. TBHQ is the most effective antioxidant to improve the storage stability of SBO-based biodiesel.