Optimization of soybean oil transesterification using an ionic liquid and methanol for biodiesel synthesis

Fatty acid methyl esters (FAME) were synthesized through the transesterification of soybean oil with methanol using an ionic liquid as a catalyst. The ionic liquid 3-(N, N-dimethyldocecyl ammonium) propane sulfonic acid p-toluene sulfonate ([DDPA] [Tos]) was synthesized, characterized and used for the transesterification of soybean oil for biodiesel synthesis. Factors affecting the reaction, including the soybean-oil-to-methanol ratio (1:2 v/v), the ionic liquid catalyst concentration of 8.0 %w/v, the reaction time of 4 h, the agitation speed of 300 rpm, and the constant refluxing reaction temperature were optimized. A 75 % yield of biodiesel was obtained under the optimized conditions. The biodiesel was purified using an ion exchange resin and then the analyzed by GC–MS. The properties of the biodiesel such as kinematic viscosity at 40 ºC, the density at 25 ºC, the cloud point and pour points were also determined. The biodiesel met the quality standard defined under ASTM D6751-02. In this research study, a novel method for biodiesel synthesis under mild conditions using methanol and an ionic liquid was developed.