Absorption of nitrogen oxides in alkaline solutions: selective manufacture of sodium nitrite

Abstract

Absorption of nitrogen oxides was studied in a pilot-scale 150-mm-i.d., 3000-mm-long packed column. An aqueous solution of sodium hydroxide (5% w/w) was used as a solvent. Superficial liquid velocity was varied in the range 2.0-7.0 mm/s, and the inlet solvent temperature was varied in the range 50-90°C. The conversion of NaOH, the selectivity of sodium nitrite, and the temperature were monitored along the length of the column. A mathematical model has been developed for an adiabatic operation. The gas-phase reactions and equilibra, gas-phase mass transfer, interface equilibria, and liquid-phase reactions were included in the mathematical model. The parametric sensitivity was investigated. The gas-phase mass-transfer coefficient was found to play a significant role on the selectivity in addition to the temperature, the total partial pressure of NO_x, and the radio of divalent to tetravalent nitrogen oxides. A comparison has been presented between the model predictions and the experimental observations.