Optimization studies for the alkaline transesterification biodiesel reaction using ultrasound mixing

The feasibility of using ultrasound mixing to obtain the displacement of the equilibrium biodiesel reaction to the products has been established. In particular, the alkaline transesterification reaction was studied at three levels of temperature and alcohol to oil ratio. The results have determined that the optimum conditions for the reaction are a constant temperature of 40°C, ultrasonic agitation, and a molar ratio 6:1 methanol/oil. The production of biodiesel was complete (>99.4% conversion) after about 15 minutes at these conditions. For a 6:1 methanol to oil ratio and 25 to 60°C temperature range a pseudo-second order kinetic model was confirmed for the di- and tri-glycerides hydrolysis reaction. Reaction rate constants were higher by an enhancement factor of 3 to 5 than the reported in the literature for mechanical agitation. The mass transfer and kinetics rates enhancements observed were due to the increase in interfacial area and activity of the microscopic and macroscopic bubbles formed when ultrasonic waves of 20kHz are applied to the immiscible reactant. The Rayleigh-Plesset bubble dynamics model was used to describe the ultrasonic effect in the reactive medium.