The oxidation and absorption of nitrogen oxides in nitric acid in relation to the tail gas problem of nitric acid plants

It has been suggested that concentrated nitric acid absorbs NO 2 very well. In this work it is demonstrated that concentrated nitric acid can also be used for the oxidation of NO to NO 2, thus making an efficient removal of nitrogen oxides from tail gases in nitric acid plants possible. It is shown that the oxidation of NO takes place in the gas phase on a reaction plane parallel to the gas-liquid interface and that Danckwerts' solution for instantaneous irreversible reactions in the liquid phase can also be applied to gas phase reactions. The NO 2 and N 2O 4 produced, which are in continuous equilibrium with each other, diffuse from the reaction plane to the gas bulk and to the gas-liquid interface. At the gas-liquid interface only N 2O 4 dissolves physically into the concentrated nitric acid. The mathematical model to describe these diffusion processes agrees very well with the experiments.