Absorption of Lean NO_x in Aqueous Solutions of NaClO₂ and NaOH

Abstract

The absorption of such lean NO, as encountered in flue gases in aqueous mixed solutions of NaCI02 and NaOH was carried out using a stirred vessel with a plane interface at 25 °C and atmospheric pressure. The rate of N02 absorption was analyzed by the chemical absorption theory under the fast-reaction regime. The reaction which prevailed was found to be the parallel reactions involving oxidation and hydrolysis, and to be second order with respect to N02. The second-order rate constant for the hydrolysis was evaluated as 3.09 X 108 L/mol s. The order of reaction relative to CI02' was derived as unity for chlorite concentrations greater than 1.0 M. The third-order rate constant for the oxidation was derived as 7.32 X 10® (L/mol)2/s at [NaOH] = 0.20 M. For the absorption of NO, there appears to be a gradual jump in absorption rate at the interfacial concentration of NO ranging from 5 X 10"7 to 2 X 10"® mol/L. Above this transition region, the order of reaction in NO approaches 2, whereas below the transition region, the order of reaction becomes unity.

Absorption of NO in an Aqueous Solution of NaClO2

“…Figure 12 shows how the absorption rate varies with the interfacial concentration of NO at a pH of 10 and chlorite concentrations of 0.2 and 1.0 kmol/m 3 , respectively. These curves should be compared with the absorption rates measured by Sada et al [6] at a hydroxide concentration of 0.1 kmol/m 3 . At 250 ppm the interfacial concentration of NO is approximately 5 10 ±4 mol/m 3 when the gas-phase resistance is 5%.…”

“…The absorption of NO x in a solution of sodium chlorite was studied in the late seventies by Sada et al [5,6] They measured the absorption rate of NO and NO 2 using a stirred vessel with a plane interface. The overall reaction between NO and ClO 2 ± was considered to be:…”

“…. Later Sada et al [7] performed experiments with absorption of NO in an aqueous slurry of NaClO 2 /Ca(OH) 2 and NaClO 2 /Mg(OH) 2 . Due to the lower solubility of alkaline-earth hydroxides, chlorine dioxide was formed in the liquid through decomposition of NaClO 2 .…”

Absorption of NO in Aqueous NaClO2/Na2CO3 Solutions

“…One possible option is to have an absorption solution with a high concentration of hydroxide ions. Therefore, NaOH as an alkaline additive had been widely used in the application of NaClO 2 solution [16][17][18][19][20]. However, the pH of the absorption solution is seen to increase greatly and the ability of sodium chlorite to act as an oxidizer decreases sharply after the addition of NaOH [21].…”

“…However, the pH of the absorption solution is seen to increase greatly and the ability of sodium chlorite to act as an oxidizer decreases sharply after the addition of NaOH [21]. Sada et al also performed experiments for the absorption of NO in an aqueous slurry of NaClO 2 /Ca(OH) 2 and NaClO 2 / Mg(OH) 2 [22]. Due to the lower solubility of alkaline-earth hydroxides, chlorine dioxide was also formed in the liquid.…”