20 Absorption of nitrogen oxides into water

Abstract

Absorption of NO 2 and NONO 2 mixture into weak alkaline solutions are studied. Emphasis is put on the concentration level ranging from 5000 down to 5 ppm. The absorption rates and the stoichiometric relations are determined by simultaneously measuring the gas and liquid phase compositions. Flat-liquid-level absorber and bubbling type absorber are employed for testing the effects of mass transfer coefficient. The absorption rates of NO 2 depend on the concentration of NO 2 in second order at the concentrations above around 800 ppm. At the lower concentrations, the rate dependency changes to 1 1/2 order in NO 2 and, in the case of rather large mass transfer coefficients, it further changes to 1'st order. The absorption rates from NO and NO 2 mixtures change in 3/4 order with respect to the product of NO and NO 2. A model is constructed by postulating the equilibrations between NO, NO 2, N 2O 3 and N 2O 4 and the hydration reactions of N 2O 3 and N 2O 4 in the liquid film. The computational results based on the model agree well with the all present experiments as well as those in literature. The parameters required for predicting the absorption, including the solubilities of NO 2 and N 2O 4, the hydration rates of N 2O 3 and N 2O 4 and the equilibrium constants, have been established.