Modeling of NO<i>_x</i> Absorption into Nitric Acid Solutions Containing Hydrogen Peroxide

Abstract

A mathematical model was developed for the isothermal absorption of nitrogen oxides into nitric acid solutions containing hydrogen peroxide. This model, based on the two-film theory of absorption with chemical reactions, includes diffusive transport and equilibrium between species in the gas phase and simultaneous absorption of the NO x components with fast irreversible reactions in the liquid phase. Kinetic parameters relative to the absorption of the different NO x species were determined at increasing acidities and for a low concentration of H 2 O 2 from test runs performed in a small packed column at 20 °C and atmospheric pressure for various NO x partial pressures up to 500 Pa and the whole range of NO x oxidation ratios. Only the parameter relative to trivalent NO x was found to increase with the HNO 3 molarity, the other ones remaining constant. Interpretation of the experimental results according to the model showed that the hydrolysis is the main controlling step for tetravalent nitrogen oxides and that among the trivalent components nitrous acid is likely to be a major transporting species.