Experimental determination of equilibrium constant for the complexing reaction of nitric oxide with hexamminecobalt(II) in aqueous solution.

Ammonia solution can be used to scrub NO from the flue gases by adding soluble cobalt(II) salts into the aqueous ammonia solutions. The hexamminecobalt(II), Co(NH3)62+, formed by ammonia binding with Co2+ is the active constituent of eliminating NO from the flue gas streams. The hexamminecobalt(II) can combine with NO to form a complex. For the development of this process, the data of the equilibrium constants for the coordination between NO and Co(NH3)62+over a range of temperature is very important. Therefore, a series of experiments were performed in a bubble column to investigate the chemical equilibrium. The equilibrium constant was determined in the temperature range of 30.0–80.0°C under atmospheric pressure at pH 9.14. All experimental data fit the following equation well:Kp=(1.9051±0.124)×10−6exp5359.25±280.13T(bar−1)where the enthalpy and entropy are ΔH°=−(44.559±2.329)kJmol−1 and ΔS°=−(109.50±7.126)JK−1mol−1, respectively.