Abstract
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.