(680f) The Effects of Solvent Properties on Radical Formation from Ultrasound-Driven Inertial Cavitation for Sono-Chemical Process Intensification.

Ultrasound waves propagating through aqueous media induce the inertial cavitation of suspended cavities driving homolysis of di- or poly-atomic species to form radical fragments (e.g. H• and •OH). The radical products dissolve into solution where they initiate aqueous reactions of organic substrates. Such ultrasound processes require only a piezoelectric material, electricity, and use water as the solvent presenting a promising route for sustainable chemical synthesis. The properties of the solvent (e.g. density, surface tension, viscosity) influence the rates of momentum transfer between the gas and liquid thus affecting cavitation dynamics and amounts of radicals formed. The sensitivity of radical yield and thermodynamic efficiency of inertial cavitation processes to solvent properties were investigated by solving mass, energy, and momentum balance laws that simulate the dynamics of isolated O₂/Ar bubbles evolving in a H₂O bath with ultrasound irradiation. Figure 1 shows the change in the formation rate of free radicals during cavitation upon small increases (1%) in the values of experimental conditions, physical parameters of the solvent, and acoustic parameters. Radical formation rates decreased as values of solvent properties increased, and became more sensitive to changes to the solvent as the acoustic frequency increased. These solvent parameters also affected rates within the same order of magnitude as acoustic parameters, indicating that decreasing their values (by, for instance, diluting H₂O with lower-density solvents or adding surfactants to lower the surface tension) can influence radical formation to a similar extent. The effects of solvent properties on radical formation rates elucidate the influence of dissolved organics in aqueous solution on cavitation properties with implications for chemical synthesis in ultrasound reactors. These trends moreover inform design strategies that leverage solvent properties to maximize radical yield from cavitation.