Oxidation Of NO In Flue Gas By ClO₂ Produced By Electrolytic

In this paper, the processes of catalytic electrolysis of sodium chlorate to produce of chlorine dioxide and gas-phase oxidation of NO and SO₂ with ClO₂ were investigated with the purpose of pre-oxidation desulfurization and denitration. In the study of electrochemical generation of ClO₂, four kinds of catalytic electrodes with content of Pt-Ru-Pd supported on titanium plate were prepared. The electrodes were tested to produce ClO₂ in both undivided electrolytic cell and diaphragm cell. Sulfuric acid concentration, sodium chlorate concentration, current density, temperature were chosen as parameters to study their effects on the catalytic electrolysis process. In the study of gas-phase oxidation of ClO₂ on NO and SO₂, oxidation mechanism was discussed, and mixture condition, temperature, residence time and flue gas composition, etc, were investigated to optimize reaction conditions of chlorine dioxide oxidation of NO.In the study of catalytic electrolysis generation of ClO₂, ClO₃^-?ClO₂ is not completely controlled by electrode current. The electrode reaction and catalytic recation both contribute to the overall yield of ClO₂. In undivided electrolytic cells, the catalytic reaction has greater contribution, but in the diaphragm cells, the electrolysis process has greater contribution. ClO₂+e ? ClO₂^- is a key step for the reaction, so a certain content of ClO₂ must be kept in the electrolyte solution to ensure the reaction to continue. From the performance analysis of the four catalysts in undivided electrolysis, the Ti/Ru-Pt catalyst shows a high activity. For undivided electrolysis, increasing concentration of H2SO4 and NaClO3 could improve the yield of ClO₂, and the effect of current density is not significant. From the analysis of the four catalysts in diaphragm cell, the Ti/Ru-Pt catalyst shows a high activity, and the effect of current density is significant. For the diaphragm cell low mass transfer ability of diaphragm becomes the main factor, which results a lower yield of ClO₂ in diaphragm cell. But the purity of ClO₂ in diaphragm cell is relatively high.The properties of gas-phase oxidation of ClO₂ on NO and SO₂ are investigated. In the dry gas, NO can quickly be oxidized by ClO₂, but SO₂ is hardly to be oxidized. When the H2O content in gas phase is more than 0.45%, the gas-phase oxidation mechanism of ClO₂ on NO and SO₂ will change, and SO₂ will be preferentially oxidized. The increased temperature is disadvantageous to the oxidation reaction and it has great influence on oxidation of SO₂ and simultaneous oxidizing NO and SO₂. The high oxygen content in gas phase has a negative impact on SO₂ oxidation efficiency, but not significant on NO.