Mechanism of nitric acid generation on Ag-X Zeolite

When Ag-X Zeolite is used for the removal of iodine from the off gas streams of nuclear facilities, it is possible that nitric acid is formed on Ag-X Zeolite from co-existing nitrogen dioxide and water vapor. If nitric acid is formed on the surface of Ag-X zeolite, Ag-X zeolite is damaged and is not able to operate for a long time. When Ag-X zeolite is used in NO2-O2-H2O mixture, the nitric acid generation reaction is varied, depending upon the reaction temperature, and concentration of NO2 and H2O. At a temperature of more than 40 deg. C, however, only the surface reaction will be progressed on the zeolite surface. The generation of nitric acid solution on the zeolite can be forecasted through the relationship between the concentration of nitric acid solution, equilibrium vapor pressure of H2O, and equilibrium vapor pressure of HNO3. Concerning the surface reaction caused on the zeolite, the adsorption water reacts on NO2, and the resulting HNO3 is adsorbed firmly by the zeolite, which is thought to interfere with the surface reaction for generation of the HNO3. When the adsorption bed is long, the time required for adsorbed HNO3 to saturate is increased in proportion to the bed length