Sonication of aqueous solutions of chlorobenzene

Abstract

Sonication at two frequencies (20 and 900 kHz) was carried out on dilute (220 ppm) aqueous solutions of chlorobenzene. The formation of chloride ions was followed using ion chromatography. The solutions became more colored with time; the absorbance maximum was around 270 nm. Some of the compounds remaining in the solution could be identified; they were chlorinated phenols, chloronaphthalene, mono and dichlorobiphenyls, etc. At the same acoustic power, the rate of chloride formation with 20 kHz ultrasound was greater when a probe with a larger tip area was used, but significantly less than the rate with 900 kHz. The use of ultrasound for conversion of chlorine in organic compounds in water to chloride can thus be performed more efficiently using a higher frequency and with a lower intensity (power per area). There is, however, a possibility that the toxicity of the aqueous solution is increased by such treatment.

Sonochemical Treatment of Water Polluted by Chlorinated Organocompounds. A Review

“…This saturation has been observed in several systems [87,88,89]. Other authors have pointed out that lower intensities are more effective than higher intensities at the same total power, not only in experiments on water sonolysis [90] but also in degradation process of chlorinated organocompounds [45].…”

“…Some controversy is again found in the literature. An increase of the rate of degradation with frequency has been routinely reported for the degradation of volatile compounds such as CCl 4 [34], trichloroethylene [38] and chlorobenzene [45]. However, if the range of studied frequencies reaches values higher than 1 MHz, some authors have detected a maximum around ranging 350-850 kHz [30,36] while other authors have reported a continuous increase [35].…”

“…Kruus et al [45] suggested that, at the same total power, a lower intensity is more effective than higher intensity in the sonication of chlorobenzene in water. Yiang et al [49] reported that the rate constant of the degradation of 1,4-dichlorobenzene and 1-chloronaphthalene at 500 kHz linearly increases with increasing ultrasonic intensity, advising that the ultrasound power used was too low to find the saturation effect reported previously.…”

“…Hydrophobic and volatile chlorinated organocompounds such as CCl 4 [13,30,31], chloroform [13], trihalomethanes [43] chlorobenzene [45,46,47,49,50,51] and trichloroethylene [38,50,51] have been subject to kinetic analysis and their degradation has been used to develop simulation models of kinetics for compounds which are degraded in the interior of cavitation bubbles by thermolysis (pyrolysis) and, in presence of oxygen, by oxidation reactions. Pyrolysis reactions are expected to follow simple first-order kinetics [44].…”

“…From the previous section, we can realize that a vast number of academic studies have been focused on kinetic and mechanistic aspects of the sonochemical degradation of chlorinated compounds, but there are few authors who comment on the mass balance, due to the difficulty to close it [45,52,54]. Looking at the literature, the sonochemical degradation of other compounds, even with a volatile behavior, can yield a totally closed mass balance [65] but, as we have noticed in the previous section analyzing the mechanisms, the complexity of the process involves a wide range of intermediates, and therefore a wide speciation.…”