Intensification of Biodiesel Production Process using Acoustic and Hydrodynamic Cavitation

Biodiesel is an alternative to conventional fossil fuels. It has several advantages over conventional fuels. It is non-toxic, renewable, and biodegradable with no sulfur content. Researchers have used different techniques to produce biodiesel from various edible and non-edible oil sources in the last many years, but these technologies have several disadvantages. They are highly energy-intensive, have high operating costs, low volume throughput, and require high investment costs that make them uneconomical for large-scale operations. In recent years, sonochemical reactors such as ultrasonication or acoustic cavitation (AC) and hydrodynamic cavitation (HC) have been considered promising, efficient, and environmentally acceptable techniques for synthesizing biodiesel. These techniques work on the principle of generation, growth, and collapse of cavities due to pressure variation within the solution. The cavity collapse releases a tremendous amount of energy within a short period, typically within a microsecond at multiple locations within the solution. The release of such immense power generates local hot spots and highly disruptive pressure shock waves, which help in increasing the mass transfer rate and thereby causing improved transesterification reactions. This book chapter reviews the primary mechanism of intensified approaches using cavitation, fundamentals of acoustic and hydrodynamic cavitation reactors, basic designs, and operational guidelines for obtaining the maximum biodiesel yields. This chapter discusses the effect of various operating parameters of AC and HC on biodiesel yield. In the case of HC, details of different cavitating devices and the impact of geometrical and operating parameters that affect the cavitation conditions and biodiesel yield are discussed.