Application of ultrasonication in transesterification processes for biodiesel production

Abstract

In biodiesel production, adequate mixing is required to create sufficient contact between the vegetable oil or animal fat and alcohol, especially at the beginning of the reaction. Application of ultrasonication provides sufficient mixing and energy so that the transesterification can proceed at a faster rate due to two effects. First, ultrasonic cavitation and microbubble formation, which are caused by the ultrasonic energy introduced by the sonotrode, greatly improve the interfacial contact between the immiscible methanol and plant oil/animal fat mixture, thus increasing the reaction rate. Second, the formation and bursting of microbubbles caused by ultrasonic cavitation intensifies the local energy transfer and energizes the reactant molecules, thus enhancing the overall reaction rate. The other possible beneficial aspect of ultrasonication may be ultrasonic energy-induced free radical formation, which initiates chain reactions, as has been observed in other organic systems, although it is not fully understood in transesterification yet.