Effect of violent mixing on sonochemical oxidation activity under various geometric conditions in 28-kHz sonoreactor

Abstract

The effects of violent mixing and reactor geometric conditions were investigated using the overhead stirrer and high-speed homogenizer in 28-kHz sonoreactors. The sonochemical oxidation activity was quantified using the KI dosimetry method, and the sonochemical active zone was visually observed using the luminol method. Higher mixing rates resulted in a significant enhancement of the sonochemical oxidation activity, primarily due to a significant change in the sonochemical active zone. When using the overhead stirrer (0-2,000 rpm), the highest activity for 2 lambda and 3 lambda occurred at 500 rpm, whereas the highest activity for 4 lambda was obtained at 250 rpm. For the high-speed homogenizer (0-12,000 rpm), the highest activity was consistently obtained at 3,500 rpm across all liquid height conditions. The impact of mixing position (Top, Mid, and Bot positions) on sonochemical activity was analyzed. The results revealed that the lowest activity was obtained for the bottom position, likely attributed to significant ultrasound attenuation. The reactor size effect was investigated using the high-speed homogenizer in five cylindrical sonoreactors with different diameters (12-27 cm). It was found that very low activity could be observed due to unexpected geometric conditions, and the application of mixing (3,500 rpm in this study) could result in high sonochemical activity regardless of geometric conditions.