Degradation of organic compounds by acoustic cavitation and pulsed-power discharges

Citation

Hochemer, Ralf H. (1996) Degradation of organic compounds by acoustic cavitation and pulsed-power discharges. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/3tyz-e528. https://resolver.caltech.edu/CaltechETD:etd-06262006-111213

Abstract

The exposure of organic chemical compounds to acoustically induced cavitation under various conditions in aqueous solution is studied. Emphasis is given to the degradation of undesired chemical compounds present at relatively low concentration.

The hydrolysis rate of p-nitrophenylacetate is enhanced in sonicated solution when compared to the reaction under ambient conditions. This rate enhancement is ascribed to the transient existence of supercritical water in sonicated aqueous solutions.

The degradation rate of 2,4,6-trinitrotoluene is shown to depend on the ultrasonic frequency and the nature of the background gas. Degradation products include nitrite, nitrate, carbon dioxide, and short-chain organic acids.

Ultrasonic irradiation of a mixture of nitro- and aminoaromatic compounds leads to competition of the substrates for reactive sites and rates of degradation scale with the electron density of the aromatic ring.

The near-field parallel-plate acoustical processor is investigated as an example of large-scale treatment a of dilute waste stream. Energy density and intensity have a pronounced effect on the overall degradation rate of p-nitrophenol. Most notably, the maximum reaction rate is found to be at an energy intensity of 1.2 W cm-2. Higher intensities decrease the rate due to decoupling of the reaction mixture from the vibrating surface.

Electrical underwater discharges at relatively low electrical field strengths exhibit two distinct phases: the pre-breakdown, or initiation period, and the actual discharge itself. The length of the initiation period, the slope of the voltage transient, and the absolute and relative energy losses during initiation are investigated as a function of the electrical conductivity and temperature under various circuit parameters.

The temperature of the plasma-arc occurring during an electrical underwater discharge is estimated to be (9000 ± 300) K.

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