Process Intensification: An Overview of Principles and Practice - Process Intensification for Green Chemistry - page 13

Figure 1.6

Generation and collapse of an acoustic cavitation bubble. Reprinted from [ref 29]

# 2010, with permission from Elsevier.

referred to as 'sonolysis') under the very intense local temperatures attained in the bubble
cavities. The literature has many documented examples of sonolysis [26,30,31]. Such
chemical effects are usually reflected in changes in mechanisms and product distributions
[32]. The well-documented influence of ultrasound on crystallization processes illustrates
the latter effect most appropriately [33].
In summary, ultrasonic processing for intensification of chemical processes is associated
with the following benefits, all of which have wider implications for greener processing
[26,29]:
Increases in both reaction speed and yield in an extensive range of heterogeneous and
homogeneous systems, as highlighted by Thompson and Doirasawmy [28].
Waste minimization through increased selectivity.
Changes in and simplification of reaction pathways, which can lead to milder processing
conditions (e.g. ambient temperatures and pressures, reduced solvent use) and higher
energy efficiency.
The use of environmentally benign reactants and solvents while retaining or even
enhancing the reaction rate under ultrasonication.
Chapter 7 explores these concepts in more detail.

Electric Fields. High-intensity electrical fields have long been known to have a
destabilizing effect on dispersed systems containing polar molecules, such as water,
and to enhance mass-transfer processes via promoted coalescence of the dispersed
phase. The removal of dust from air in the Cottrell precipitator [34] and the dehydration
of crude oil emulsion in oilfields were among the first industrial processes developed
almost a century ago to harness the beneficial effects of electric fields in such phase