Sonochemistry : the mechanism and the application

Citation

Hung, Hui-Ming (2000) Sonochemistry : the mechanism and the application. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/e2xw-jv23. https://resolver.caltech.edu/CaltechETD:etd-09062005-085408

Abstract

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The ultrasonic irradiation of chlorinated hydrocarbon and iodide in aqueous solution is studied under various physical conditions. The observed sonochemical rate constants can be analyzed to yield information about the nature of the bubbles which exist during acoustic cavitation and to determine which parameters are significant for enhancing cavitation chemistry.

A significant feature of the sonolytic decomposition of chlorinated hydrocarbon is the dependence on Henry's law constant, [...]. First-order degradation rate constants, [...], for a series of chlorinated hydrocarbons vary as [...] at all frequencies ([...]), change with [...] by less than a factor of two in this range, and peak near 600 kHz for all species. The non-linear dependence of the observed rate constants on [...] indicates that rate constants are not solely determined by equilibrium parameters. Rectified diffusion contributes significantly to the composition of the vapor phase of a cavitation bubble before collapse, particularly for the less volatile substrates.

The maximum [...] production rates measured by iodine dosimetry depend on frequency, [...], and acoustic intensity in a concerted manner, e.g., the optimal frequency is 358 kHz at 83 W/L, and 205 kHz at 33 W/L. The zero-order production rate of [...] radical increases with acoustic intensity up to 248 W/L before leveling off. A temperature range of 3900 to 4300 K inside the cavitation bubble is estimated from the power dependence data at 205 and 358 kHz.

The combination of ultrasound and iron metal was used to study the degradation of carbon tetrachloride and nitrobenzene. In the coupled ultrasound and iron system, the contribution to the overall degradation rate of carbon tetrachloride by direct reaction with [...] results in an apparent rate enhancement by a factor of 40. A comparison of the first order degradation rate constants for carbon tetrachloride and nitrobenzene by [...] reduction with/without sonication revealed that the observed enhancement upon the combination of ultrasound and [...] is attributed 1) to the continuous cleaning and chemical activation of the [...] surface by the combined chemical and physical effects of acoustic cavitation, and 2) to accelerated mass transport rates of reactants to the [...] surfaces.

In addition, a new advanced oxidation process, combination of ultrasound and ozone, was developed to investigate the decomposition of methyl tert-butyl ether (MTBE). The faster rates of MTBE degradation in actual groundwaters by ultrasound/O3 systems are most likely due to the fact that ozone is more effectively converted to hydroxyl radical in high alkalinity groundwater, and that the carbonate radical anion, which is formed from the oxidation of bicarbonate by hydroxyl radical, reacts further with MTBE by a hydrogen-atom abstraction pathway.

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