Sonochemical Activation in Flow Systems

The use of sonication combined with continuous-flow processes has gained increasing attention in recent years and will hopefully continue in future pursuits. The chemo-mechanical activation by ultrasound hinges on the cavitational implosion of bubbles, thus creating an elongational field through the liquid. Actually, ultrasonic agitation provides local microflows hosting extreme, yet transient, conditions that facilitate mixing and reactivity. The bath-to-continuous transition in sonochemical processes establishes new conditions that improve production. By positioning the ultrasonic transducer(s) and adjusting the irradiation time in a continuous flow-device through which the reagents are passed, clear advantages in terms of simplification and safety are achieved, while eliminating the need to resize the reactor. Technical hurdles are unavoidable, nevertheless, and ultrasound-flow modules often require ad hoc designs and operational control to ensure reproducibility and scalability. This concise chapter gives some fundamentals of ultrasonic activation in the context of flow chemistry and provides a glimpse on technical implementations and representative examples, which illustrate the benefits of flow sonoreactors as a greener way of chemical production, or degradation, than in conventional bench processes.