Absorption of nitrogen oxides into aqueous sodium hydroxide solutions

The scrubbing of dilute gaseous nitrogen oxides into aqueous sodium hydroxide solutions has been studied using a pilot plant featuring an absorber packed with 1/2" Intalox saddles. The scrubbing efficiencies for dilute mixtures of NO and NO₂ were observed to dramatically increase when caustic solutions were used as the absorbent.

Three absorption models were tested in an attempt to explain the absorption of mixtures of dilute nitrogen oxides into caustic solutions in an absorber packed with 13-mm Intalox saddles. These models were first tested by finding values of (√Dk/H)_N2O4 and (√Dk/H)_N2O3 that allowed the three models to best fit the data.

The second phase of testing involved using each of the models to predict scrubbing efficiencies. Predictions from a model based on the absorption/hydrolysis of N₂O₄ and N₂O₃ agree well with experimental data.