Comparative study of sonochemical reactors with different geometry using thermal and chemical probes

Laboratory scale 20 kHz sonochemical reactors with different geometries have been tested using thermal probes, the kinetics of H2O2 formation, and the kinetics of diphenylmethane (DPhM) sonochemical darkening. Results revealed that the overall sonochemical reaction rates in H2O and DPhM are driven by the total absorbed acoustic energy and roughly independent the geometry of the studied reactors. However, the sonochemical efficiency, defined as η = VG/S, where G is a sonochemical yield of H2O2, V is a volume of sonicated liquid, and S is a surface of the sonotrode, was proved to increase with the decrease of S. This phenomenon was explained by growing of the maximum cavitating bubble size with ultrasonic intensity and its independence towards the specific absorbed acoustic power. For the cleaning bath reactor the kinetics of the sonochemical reactions in H2O and DPhM depends strongly on the reaction vessel materials: the reaction rates decreased with the increase of the materials elasticity. Kinetic study of H2SO4 sonolysis using a sonoreactor without direct contact with titanium sonotrode showed that sulphate anion is an effective scavenger of OH radicals formed during water sonolysis.