Absorption of NO in aqueous solutions of Fe(II)EDTA: determination of the equilibrium constant

Valid alternatives to the selective catalytic reduction (SCR) process for the removal of nitrogen oxides from waste gases (denoxing) may be found in wet scrubbing processes where the low solubility of NO in aqueous media is enhanced by the application of chelate complexes. The most widely used complex for this purpose is Fe II EDTA (iron II ethylenediaminetetra-acetic acid). Iron II nitrilotriacetic acid (Fe II NTA) might be another candidate, with similar chemical properties as Fe II EDTA but available industrially at a considerably lower price. For the development of technical processes, a knowledge of the equilibrium data over a range of temperature is of prime importance. Therefore experimental investigations were carried out concerning the chemical equilibrium of the reaction:NO + Fe II NTA ⇌ Fe II NTA · NO The equilibrium constant was determined in the temperature range 22–80 °C. All experimental data fit the equilibrium constant equation well: K p = 3.05 x 10 -8 exp(7332/T) (bar -1 ) The equilibrium constant for Fe II NTA is approximately 25% lower than the constant for Fe II EDTA. However, considering the price difference between the two complexants, Fe II NTA is an interesting alternative to Fe II EDTA.