Sonochemical efficiency dependence on liquid height and frequency in an improved sonochemical reactor

The aim of this study was to evaluate the effects of liquid height and frequency on sonochemical efficiency of a cup-horn sonoreactor. The selected frequencies (22, 371, 504 kHz) and liquid height (29–348 mm) were applied while measuring acoustic yield, I3- formation rate and the resulting sonochemical efficiency. The frequency effect was shown to be coupled to liquid height effect. Indeed, acoustic zones (i.e. Fresnel and Fraunhöfer zones), which limits depends on both transducer diameter and frequency, significantly determine the production of radicalar species quantified by I3- formation rate. An increase of ultrasonic frequency results in lower acoustic yield and higher sonochemical efficiency. Theoretical physical and chemical effects attributed to collapsing bubbles were considered. Sonochemical efficiencies obtained at 500 kHz were similar or higher than those at 371 kHz, depending on liquid height. The effect of reactor configuration was further investigated as an hypothesis to explain unsignificant effect of standing waves in our study. Therefore, the dependence of sonochemical efficiency with liquid height might be firstly attributed to reactor configuration prior to frequency effects.

► Sonochemical efficiency is lower at 20 kHz but similar at 371 and 500 kHz.
► Frequency increase results in lower acoustic yield.
► The sonochemical efficiency mainly depends on liquid height.
► Fresnel and Fraunhöfer zones determine the production of hydroxyl radicals.
► The reactor configuration is more influent than the frequency variation above 300 kHz.