Nitrogen Dioxide Absorption and Sulfite Oxidation in Aqueous Sulfite

Abstract

Removal of NO from flue gas may be achieved by its oxidation to NO 2 followed by absorption in sulfite solution in existing scrubbers for desulfurization. Rates of NO 2 absorption and sulfite oxidation were measured in a highly characterized stirred-cell contactor. The results were interpreted by the theory of mass transfer with fast reaction in the boundary layer. The reactions between NO 2 and sulfite (SO 3 2-), bisulfite (HSO 3 -), and thiosulfate (S 2 O 3 2-) were first order in NO 2 concentration, and their respective rate constants at 55°C were 11.2 × 10 5 , 2.8 × 10 4 , and 5.4 × 10 3 M -1 s -1 . The NO 2 hydrolysis reaction was second order in NO 2 concentration, with a rate constant of 1.6 × 10 7 M -1 s -1 at 55°C. NO 2 absorption initiates sulfite oxidation in the presence of oxygen, and this study quantified the effect of sulfite and oxygen concentration, the rate of NO 2 absorption, and the presence of thiosulfate and gasphase SO 2 on the rate of sulfite oxidation. With typical conditions for limestone slurry, 10 mM total dissolved S(IV) and pH 4-5, the estimated NO 2 removal was less than 50%. Therefore, an acceptable level of NO 2 removal by a conventional limestone slurry scrubber is not probable. However, NO 2 absorption is feasible in sodium sulfite inhibited by thiosulfate. NO 2 may also be an effective catalyst for sulfite oxidation in limestone slurry scrubbing.

Isotopic constraints on heterogeneous sulfate production in Beijing haze

“…S(IV) oxidation by H 2 O 2 and O 3 leads to 17 O(SO 2− 4 ) = 0.7 and 6.5 ‰, respectively, on the basis of 17 O(H 2 O 2 ) = 1.4 ‰ (Savarino and Thiemens, 1999) and assuming 17 O(O 3 ) = 26 ‰ (Vicars and Savarino, 2014;Ishino et al, 2017 (Dubey et al, 1997;Luz and Barkan, 2005;Lee et al, 2002;Bao et al, 2000). Sulfate produced by NO 2 oxidation is suggested to occur either via a radical chain mechanism (Shen and Rochelle, 1998), via oxygen-atom transfer from OH − (Clifton et al, 1988), or from O 2 based on experimental results of He et al (2014) (Fu, 2014). In the present study, H 2 O 2 mole fraction was estimated from our measured T with the empirical equation above.…”

Nitrogen Dioxide Absorption and Sulfide Oxidation in Aqueous Sulfide

“…5 However, in the presence of oxygen, NO 2␣ initiates the oxidation of sulfite, requiring 5-100 mols of sulfite per mol of NO 2 removed. 6 Commercial technology is available for aqueous scrubbing of NO 2 by sodium sulfide (Na 2 S) solution. 4,7 The relative economics of sulfite and sulfide scrubbing will depend on their local availability.…”

“…This same reactor was used in studying the absorption of NO 2 into sulfite solutions. 6,8 This design was based upon similar gas-liquid contactor devices for which mass transfer properties have been determined by several previous investigators. [9][10][11][12][13] The cylindrical reactor had a 4-in.…”

The Chemical Behaviors of Nitrogen Dioxide Absorption in Sulfite Solution

“…As shown in Figure 3, NO3 − , NO2 − , and SO4 2− concentrations in absorption solution increase as the absorption proceeds. Compared with NO2 − , more NO3 − was formed at the same absorption time, which can be ascribed to the oxidation of NO2 − and the decomposition of unstable HNO2 [22,28]. After the absorption time of about 300 min, NO2 − concentration is almost unchanged although NO3 − ions still increase, which is attributed to the fact that nitrite ions are further oxidized into nitrate ions.…”

“…For NO2 absorption in sulfite solution, the sulfate is formed through the reaction between NO2 or O2 and sulfite (R1) [29]. [22,28]. After the absorption time of about 300 min, NO 2 − concentration is almost unchanged although NO 3 − ions still increase, which is attributed to the fact that nitrite ions are further oxidized into nitrate ions.…”