Nitric oxide removal by combined urea and FeIIEDTA reaction systems

- FeIIEDTA was firstly added to (NH2)2CO solution to improve the NO removal.
- The synergistic mechanism of (NH2)2CO and FeIIEDTA on NO removal was discussed.
- Urea could react with FeIIEDTA-NO to produce FeIIEDTA, N2, and CO2.
- Urea could hinder oxidation of FeIIEDTA.
- FeIIEDTA-NO reduction by urea was a first-order reaction concerning FeIIEDTA-NO.

(NH2)2CO as well as FeIIEDTA is an absorbent for simultaneous desulfurization and denitrification. However, they have their own drawbacks, like the oxidation of FeIIEDTA and the low solubility of NO in urea solution. To overcome these defects, A mixed absorbent containing both (NH2)2CO and FeIIEDTA was employed. The effects of various operating parameters (urea and FeIIEDTA concentration, temperature, inlet oxygen concentration, pH value) on NO removal were examined in the packed tower. The results indicated that the NO removal efficiency increased with the decrease of oxygen concentration as well as the increase of FeIIEDTA concentration. The NO removal efficiency had little change with a range of 25-45 °C, and sharply decreased at the temperature of above 55 °C. The NO removal efficiency initially increases up to the maximum value and then decreases with the increase of pH value as well as the raise of urea concentration. In addition, the synergistic mechanism of (NH2)2CO and FeIIEDTA on NO removal was investigated. Results showed that urea could react with FeIIEDTA-NO to produce FeIIEDTA, N2, and CO2, and hinder oxidation of FeIIEDTA. Finally, to evaluate the effect of SO32− on NO removal, a mixed absorbent containing FeIIEDTA, urea, and Na2SO3 was employed to absorb NO. The mixed absorbent could maintain more than 78% for 80 min at 25 °C, pH = 7.0, (NH2)2CO concentration of 5 wt%, FeIIEDTA concentration of 0.02 M, O2 concentration of 7% (v/v), and Na2SO3 concentration of 0.2 M.