Effect of Ultrasonication on Droplet Size in Biodiesel Mixtures

Biodiesel fuels have become more attractive recently because of their environmental benefits and cost competitiveness compared to diesel fuel. Many processing improvements have been proposed to increase the conversion rates and the yields of vegetable oil in order to lower production costs and improve biodiesel product quality. In conventional biodiesel production chemistries, alkaline transesterifications of alcohol/oil dispersions should occur primarily near the interface. Ultrasonic mixing has already been shown to increase overall conversion rates for alcohol/vegetable oil mixtures. Our data show that ultrasonic mixing produced smaller droplet sizes than conventional agitation, leading to more interfacial area for the reaction to occur. Droplet size distributions have been measured for conventional impeller and ultrasonic mixing systems using methanol/soybean oil as a model system. The dispersions were stabilized by surfactant in order to obtain droplet size distribution for mixture samples. Ultrasonic mixing produced dispersions with average droplet sizes 42% smaller than those generated using standard impellers.