Coexistence Of SO2 Research Articles

SO and NO selective adsorption properties of coal-based activated carbons

Abstract The aim of this paper is to study binary gas adsorption on the activated carbon in the fixed-bed reactor. Coal-based granular activated carbons can selectively adsorb SO2 and NO. Physically adsorbed NO is replaced and desorbed by SO2. Chemically adsorbed NO can promote the absorption of SO2. The presence of SO2 and NO can enhance the chemical adsorption of NO and SO2, respectively. When the diameter of granular activated carbon decreases and the specific surface area increases, both the penetration time of the activated carbon bed and SO2 removal efficiency increase. The whole removal efficiency of SO2 is more than 99% in the penetration time, but the whole removal efficiency of NO is only 55% in the coexistence of SO2 and NO. SO2 adsorption capacity of HNO3 dipped granular activated carbon is higher than that of non-treated one. The two experimental results are agree with each other.

Characteristics of Raindrop Acidification by Co-Washout of SO2(G)-H2O2(G)-HNO3(G)

In order to investigate the acid rain formation under the coexistence of SO2(g), H2O2(g), and HNO3(g) in the air, a mathematical model has been built and some numerical simulations have been carried out with use of the model. The simulation reveals that SO2(g) absorbed into a raindrop is released and then re-absorbed as the fall distance increases. The desorption and re-absorption processes of SO2(g) are caused by: (1) the fact that the equilibrium concentration of H2O2(aq) and HNO3(aq) in raindrops are much higher than that of SO2(aq), and (2) the fact that the oxidation reaction rate of HSO3− with H2O2(aq) increases with H+ concentration in raindrops. The degree of acidification of the rainwater has been estimated by introducing a raindrop size distribution. The acidification is mainly caused by the adsorption of SO2(g) in the usual case where the atmospheric concentration of SO2(g) is much higher than that of HNO3(g). With the increase in the atmospheric concentration of HNO3(g), the concentration of H+ generated from SO2(g) decreases and the contribution of HNO3(g) to the generation of H+ becomes dominant.

Thermostable Molecular Sieves, Silicoaluminophosphate (SAPO)-34, for the Removal of NOX with C3H6 in the Coexistence of O2, H2O, and SO2

Selective reduction of NO with C3H6 under an oxidizing atmosphere was studied over various Cu ion-exchanged molecular sieves. All examined Cu ion-exchanged catalysts are active for NO reduction with C3H6 in a large excess of O2; however, the temperature at the maximum NO conversion depends on the kind of molecular sieves. In particular, it was found that Cu-SAPO-34 is sometimes more active than Cu-ZSM-5. Thermal stability of SAPO-34 was extremely high, and consequently, decrease in the activity to NO selective reduction on Cu-SAPO-34 was negligible over 60 h at 673 K in an atmosphere containing 15 vol % H2O. After thermal treatment at 1073 K in a humidified atmosphere, decrease in the activity to NO reduction was also small. Although the activity of Cu-SAPO-34 to NO reduction was decreased slightly with the coexistence of SO2, it is expected that the activity of Cu-SAPO-34 is sustained over a long period.

低温乾式同時脱硫・脱硝触媒の開発 Ｃｒ２Ｏ３‐ＴｉＯ２共沈酸化物

Catalysts for the low-temperature dry-type simultaneous removal of sulfur oxides (SOx) and nitrogen oxides (NOx) were investigated, and Cr2O3-TiO2 prepared by the coprecipitation method was found as a superior catalyst.In this process, SO2 was catalytically oxidized to SO3, then deposited onto catalyst surface as ammonium sulfates by the reaction with H2O and NH3, and NOx were reduced to N2 with NH3 over the same catalyst at low temperature (ca. 130°C).The experiments were carried out using a flow type packed bed reactor under atmospheric pressure at 110-150°C. Inlet gases were SO2 (mainly 250ppm), NO (250ppm), NH3 (500-750ppm), O2 (5%), H2O (10%) and N2 (balance gas).The main results obtained are as follows:1) 10-30mol%Cr2O3-90-70mol%TiO2 gave the higer activity than the other composition oxides for the simultaneous removal of SOx, and NOx.2) The salts deposited on Cr2O3-TiO2 were amorphous form of NH4HSO4 and (NH4) 2SO4.3) The used catalyst could be regenerated by heating at 500°C in N2 stream, and then treating with O2 (5%)-N2 mixture at 500°C.4) The active oxygen of Cr2O3-TiO2 gave the high activity for not only the denitrification (NOx removal), but the oxidation of NO to NO2. When the active oxygen was consumed, the addition rate of the oxygen from the gas phase was promoted by the coexistence of SO2.5) The almost complete removal of SOx, and NOx without the leak of NH3 could be done by controling the quantity of NH3 supplied over Cr2O3-TiO2.

Single and simultaneous absorptions of lean SO2 and NO2 into aqueous slurries of Ca(OH)2 or Mg(OH)2 particles.

The absorption rate of lean SO2 and/or NO2 into aqueous slurries of fine Ca(OH)2 or Mg(OH)2 particles was measured using a stirred vessel with a plain gas-liquid interface at 25°C and 1 atm. The absorption process of lean SO2 into Ca(OH)2 slurries was found to be almost gas-film controlled under the partial pressures considered here. On the other hand, for SO2-Mg(OH)2 slurry system, the diffusion of the reactant across the liquid film was significant and the absorption rate was increased with solid concentration. The observed enhancement factors were compared with the theoretical prediction according to the previously proposed model to estimate the dimensionless parameter concerning solid dissolution. For NO2-slurry system, the reaction between NO2 and the aqueous slurry may satisfactorily be considered the reaction between NO2 and water. The hydrolysis was found to be second-order in NO2 and the secondorder rate constant was derived as 5.0×107 l/mol•sec. The absorption rate of NO2 with coexistence of SO2 into aqueous slurries of Mg(OH)2 greatly exceeded that of NO2 alone into clear solutions with the same sulfite concentrations, which may be due to the solid-surface reaction in a region from the interface to the reaction plane.