State of the art review on development of ultrasound-assisted catalytic transesterification process for biodiesel production

Abstract

Excessive utilization of petroleum diesel has led to severe environmental pollution. Biodiesel, which is greener and renewable, can be a potential alternative fuel. Biodiesel is produced through transesterification reaction between vegetable oil, animal fat or even waste cooking oil (WCO) and alcohol in the presence of catalyst. Under process intensification, ultrasonic irradiation is employed in the transesterification reaction to enhance the agitation between immiscible reactants. Besides providing intensive mixing, it also offers uniform heating due to the localized temperature increase and formation of micro jets from the transient collapse of cavitation bubbles, thus reducing the energy consumption. The focus of this paper is to review the recent research progress on the ultrasound-assisted catalytic transesterification of non-edible vegetable oils using homogeneous and heterogeneous catalysts. The primary factors that affect the operation and efficiency of ultrasound-assisted transesterification such as alcohol to oil molar ratio, catalyst loading, reaction time, reaction temperature, energy consumption, phase separation time, ultrasonic pulse mode and biodiesel conversion or yield have been reviewed. The highlights of this review paper are the provisions on the mechanism of ultrasonic reactive extraction (RE) in the biodiesel production, kinetic study and the existing pilot reactors on the ultrasound-assisted transesterification which are still rarely reviewed in the current literature. Lastly, the challenges and feasibility for future development in the process intensification of biodiesel production are also addressed.