High-frequency, high-power ultrasonic chemical reactors

Abstract

A novel high-frequency (612 kHz), high-power (4 kW), pilot-plant scale sonochemical reactor was developed and used to study the degradation of organic chemical pollutants in aqueous solutions. The degradation rates of trichloroethylene, dichloromethane, and phenol were found to exceed those of similar frequency, small-scale bench reactors by factors ranging from 2.5 to 7. In addition, there is linear dependence between the observed sonolytic rate constants and the applied power density. The addition of ozone during sonication did not affect the first-order degradation rate constants for phenol degradation compared to the linear combination of sonication and ozonation. However, enhancement in the degradation rates of the total organic carbon (TOC) were observed. The enhanced reactivity of sonolysis coupled with ozonation is due to the sonolytic formation of hydrogen peroxide in water, which in turn reacts with ozone to form a highly reactive ozonide intermediate, dihydrogen trioxide, that reacts in a similar fashion to hydroxyl radical. However, its lifetime in aqueous solution is found to be substantially longer, and thus it is more likely to react with refractory organic compound fragments.