Unified model for NO_X absorption in aqueous alkaline and dilute acidic solutions

Abstract

The absorption of NO_X gases in water and alkalies [NaOH, NH₄OH, Ca(OH)₂] provides commercially important products nitric acid and salts (nitrates and nitrites), respectively. This complex phenomena of mass transfer with chemical reactions is described quantitatively in terms of [H√ (kD)]_Jvalues for J = N₂O₃, N₂O₄. However, the reported value of H√(kD) for N₂O₃ absorption in strong alkaline solution was 50 times its value in water. For the intermediate case of NO_X absorption in weak alkali Ca(OH)₂, it was necessary to have a mathematical model which incorporated the HNO₂ decomposition, as well as neutralization by alkali. This led to a unified model for NO_X absorption, which can be used for predicting point rates of NO_X absorption as well as selectivity, for various gas compositions and liquid-phase pH. Parametric sensitivity has been reported. A comparison of the model predictions with data from patent on Ca(NO₂)₂ manufacture has been made to test the model validity.