Corona Electric Discharge as a Source of Chemically Active Species

Abstract

The yields of oxidation of substances in aqueous solutions under the action of a corona electric discharge were studied. The possibilities of reducing the energy consumption for the oxidation of organic compounds by hydroxyl radicals by initiating and maintaining chain reactions are considered. Hydroxyl radicals were generated in a corona electric discharge on a point solid electrode located above the surface of an aqueous solution. Under the experimental conditions, an ozone-hydroxyl mixture is formed, in which the lifetime of hydroxyl radicals increases to 0.2 s. The conditions for the development of a chain reaction were analysed. Experiments were carried out for aqueous solutions of phenol with COD values from 710 to 2900 mg O/L, oxalic acid with a COD of 2000 mg O/L and 0.1 M solution KI for treated liquid volumes from 2.5 to 35 L. Oxalic acid was used as a detector of hydroxyl radicals, KI solution – detector OH^• + O₃. At a low concentration of dissolved organic substances (COD ~ 700 mgO/L), initiation of a chain reaction is impossible. It is shown that there are conditions, when take place the inhibition of chain oxidative reactions of phenol. The reasons for inhibition are a decrease in the pH of the medium, the transformation of primary radicals into inactive secondary ones, and the occurrence of reverse reactions. The yield of hydroxyl radicals is ~ 0.2 (100 eV)⁻¹, while the oxidation yield reaches ~ 7.5 (100 eV)⁻¹ and increases with an increase in the volume of the treated liquid.