A multi-frequency sonochemical reactor utilizing a cylindrically focused acoustic wavefield for improved sonochemical efficiency

Sonochemistry involves several steps. First, an acoustic wave must be generated with sufficient energy to nucleate cavitation. This cavitation event must then be energetic enough to produce radicals through the sonolysis of the gas or vapor molecules in the bubble. Finally, these radical species must survive long enough to react with other chemical species to yield the desired product. The sonochemical efficiency (SE) is thus defined as the ratio of the product yield to the input acoustic power. Here, we put forward a novel approach to enhancing the SE by designing a multi-frequency (0.25 to 1MHz) sonochemical reactor that reflects a cylindrically spreading acoustic wave 180°. The reflected wave converges to cylindrically shaped high-intensity “hot zone” positioned along the axis of the reaction vessel. At modest power input, we detected noise with a passive cavitation detector in air-saturated water, suggesting the direct nucleation of cavitation. Using the Weissler reaction to determine the production of hydroxyl radicals, we determined the SE of our sonochemical reactor at various operation conditions. We also compared these values to conventional bath, horn, and plate sonochemical reactors. The comparison suggested that our reactor design had a better sonochemical efficiency for the Weissler reaction.