Chapter 13 - Ultrasonic destruction of CCl4: A microscopic-scale analysis

Abstract

Sonication using high-frequency ultrasound can destruct volatile contaminate, like CCl4, via pyrolysis within the acoustic microbubbles (i.e., the sonomicroreactors); the known sonochemistry technique. The influence of ultrasound frequency (213–1000kHz) and acoustic intensity on the microprocess of CCl4 breakdown within the cavitation bubble is studied in the present work. A pyrolytic reaction scheme for CCl4 was associated with a single bubble oscillation dynamics model in an aqueous CCl4 medium. CCl4 pyrolysis within the bubble reduces the bubble temperature but increases the molar yield of oxidants generation at the collapse. OH radicals and reactive chlorinated species (Reactive chlorine species: Cl, CCl3, :CCl2, HOCl and Cl2) are the main reactive species produced from the CCl4 acoustic-pyrolysis. For the frequencies 213 and 355kHz ([CCl4]=0.01–1mM), the elimination of CCl4 is ∼100%, and is independent of its concentration in the solution. Conversely, for the higher frequencies {355kHz ([CCl4]>1mM) to 1000kHz}, the maximal conversion yield of CCl4 depends on its concentration in the liquid phase. Higher conversion rate were associated to higher acoustic intensity. The conjunction of these results with the effect of frequency on the number of active cavities indicates that an optimum frequency for CCl4 sonobreakdown is more probable to be existing at 355kHz.