Electro-catalytic Oxidative Degradation Of Aniline At RuO_x-PdO_y/Ti Electrode

Aniline is a important chemical intermediate wildly used in the chemical industry, however, it has serious toxic effects on health of people and induced abnormality, cancer, chromosomal mutation. It is also a bio-refractory organic in wastewater. It was estimated that more than 30 million kilograms of aniline were released to the environment in the effluents and exhaust gases, and damaged the environment. For these reason, there have been numerous studies devoted to the development of effective procedures for the treatment of aniline-containing wastewater.Titanium supported ruthenium-palladium binary oxides electrode was prepared by coatation of the corresponding metal chlorides on titanium substrates and followed by thermal decomposition. The electrode was used for the electro-catalytic oxidative degradation of aniline in the presence of NaCl electrolyte, and the effects of current density, initial pH, electrolyte concentration and initial concentration of aniline on aniline conversion were investigated. The bulk electrolysis was performed under the constant current operation. A gradual decrease in chemical oxygen demand (COD) and concentration of aniline for various concentration of NaCl solutions with electrolysis time was always found, and the removal rate of aniline and COD was 99.4% and 84.0% respectively at the very electrode after lh electrolysis under the following conditions: NaCl, 1g L~-1; pH, 5; current density, 20 mA cm~-2; initial concentration of aniline 640 mg L~-1The main intermediate species of aniline degradation such as m-chloroaniline, p-chloroaniline, 2,4-dichloroaniIine, 3,5-dichloroaniline, 2,4,5-trichloroaniline and benzoquinone etc were detected by GC-MS, and some of the intermediates wasconverted into solid polymeric compounds, finally, the insoluble materials was disappeared completely within 60 mins After the electro-catalytic oxidative degradation process, the brown-yellow wastewater was changed into colourless. The final degradation product was found to be carbon dioxide, and organochlorinated compounds were not detected in the solution after 60 mins It was indicated that the process could reach the mineralization of the aniline and it's degradative intermediates using the electrode prepared in the present work. A general pathway of aniline degradation was proposed according to this results.The removal of aniline was found to be related intimately to indirect oxidation by in situ produced active chlorine species to a series of chloroanilines, and the removal of intermediates could be attributed to the synergic effect of direct oxidation by electrolysis and indirect oxidation.The electro-catalytic oxidation degradation activity of the RuOx-PdOy/Ti electrode in terms of the removal rate of aniline and COD kept nearly constant until it was used for 120 times. The characteristic of electrode was characterized by means of XPS, XRD, SEM. It was found that the RuCl? and PdCl2 become a series of oxides aftee thermal decomposition, and become dense crystallites finally in the preparation processes, while the concentration of Ru and Pd decreased, the anode losses activity, the valence of the Ru and Pd were to be found increased also. The loss of anode activity may be related to the loss of Ru and Pd as well as the increase of the valence of Ru and Pd, and the crystallite may be the activity phase for of the electro-catalystic oxidation degradation.