Synergy of Microwave and Ultrasound for Intensification of Biodiesel Synthesis

Biodiesel synthesis from sustainable feedstock is gaining importance in depleting crude oil feedstock and addressing greenhouse emission challenges. A developing country like India has planned to reduce its 10% dependency on crude oil by 2022. Synthesis of biodiesel from sustainable edible feedstock has been a concern for energy vs. food issues. Non-edible feedstock such as Calophyllum innophyllum Linn, Karanja, Jatropha, Waste Cooking oil, waste engine oil, etc., is gaining importance. However, biodiesel synthesis from these feedstocks requires higher processing due to higher initial free fatty content. Intensified techniques can overcome the shortcoming of higher processing requirements. Spectacular effects associated with ultrasound and microwave are beneficial for enhancing the rate of processing. Individual results of microwave and ultrasound have certain limitations. The intensification of biodiesel synthesis is dependent on the removal of heat/mass barriers in the transesterification process. Microwave interaction with polar molecules present in the system enhances the temperature of the reaction at a very intense rate. Microemulsification and the high speed of micro-streaming velocities produced from the ultrasound during interaction with the aqueous phase are incredibly useful for reducing the mass transfer barrier in heterogeneous phases. The synergy of microwave and ultrasound may help enhance the processing rate on a multi-fold basis. The present chapter has presented an overview of microwave and ultrasound energy effects for biodiesel synthesis. Process economics has been discussed for future development in biodiesel synthesis.