Plasma-catalyst interactions in treatment of gas phase contaminants and in electrical discharge in water.

摘要

Pulsed gas phase corona discharge was studied as a possible new technology for the removal of nitrogen oxides and volatile organic compounds from contaminated gases. The combination of pulsed positive streamer corona discharge with a platinum-rhodium catalyst was investigated for removal of toluene, acetonitrile, and nitrogen oxides. The reactors that were used consisted of two parallel disks made from reticulated vitreous carbon, with the downstream disk coated with platinum and rhodium for catalyst experiments. Removal of contaminants was measured with and without plasma over a range of temperatures, and several interesting phenomena were observed which differed between the three species. Results indicate that the catalyst is capable of both reduction of nitrogen oxides and oxidation of hydrocarbons. In addition, the combination of the active catalyst with the plasma discharge was found to either enhance or interrupt catalyst activity depending on which contaminant was considered and the catalyst temperature.; High voltage electrical discharges in water are of increasing interest for the degradation of organic compounds and destruction of biological species. Previous work has demonstrated the importance of the formation of hydroxyl radicals and hydrogen peroxide by high voltage pulsed electrical discharge in water and the utility of these species for the degradation of a number of organic compounds including phenol, chlorophenol, nitrobenzene, and trichloroethylene and the destruction of various bacteria, yeast, viruses and multicellular organisms. The present study reports measurements of the rates of molecular hydrogen, molecular oxygen, and hydrogen peroxide formation in a pulsed positive needle-plane electrical discharge in water. In experiments for various solution conductivity, applied voltage, and discharge power, the ratio of the molar rate of production of hydrogen : hydrogen peroxide : oxygen was approximately 4:2:1. A global reaction is proposed to add to existing kinetic models for the simulation of reactive species production in electrical discharge in water. The use of platinum metal as discharge electrode was found to affect the production of all three species mentioned above. The net rate of hydrogen, hydrogen peroxide, and oxygen was lower with a platinum high voltage needle electrode than with a nickel-chromium electrode. Heterogeneous reactions are proposed to account for the reduction in the overall production rate of these species.; Emissions spectroscopy was used to investigate two different types of gas phase electrical discharge near a water surface and electrical discharge in water. The results of this work showed that there are distinct differences between a gas phase discharge created by a pulsed high voltage electrode in the gas, and the discharge formed when the pulsed high voltage discharge electrode is in the water, but the grounded electrode is suspended above the water surface. The results indicate higher local temperatures and higher amounts of radical species such as oxygen radical, hydrogen radical, and hydroxyl radical in the latter type of discharge.; Another type of gas phase discharge, a 'gliding arc' discharge, was studied with a new reactor design with a water spray present in the discharge region. Production of hydrogen was found when no oxygen was present in the gas, and nitrite, nitrate, hydrogen peroxide, and ozone were found in the water after being sprayed through the discharge.