Absence Of SO2 Research Articles

Selective autocatalytic reduction of NO from sintering flue gas by the hot sintered ore in the presence of NH3

In this paper, the selective autocatalytic reduction of NO by NH3 combined with multi-metal oxides in the hot sintered ore was studied, and the catalytic activity of the hot sintered ore was investigated as a function of temperature, NH3/NO ratio, O2 content, H2O and SO2. The experimental results indicated that the hot sintered ore, when combined with NH3, had a maximum denitration efficiency of 37.67% at 450 °C, 3000 h−1 gas hourly space velocity (GHSV) and a NH3/NO ratio of 0.4/1. Additionally, it was found that O2 played an important role in removing NOx. However, high O2 content had a negative effect on NO reduction. H2O was found to promote the denitration efficiency in the absence of SO2, while SO2 inhibited the catalytic activity of the sintered ore. In the presence of H2O and SO2, the catalytic activity of the sintered ore was dramatically suppressed.

Complex refractive index of secondary organic aerosol generated from isoprene/NOx photooxidation in the presence and absence of SO2

AbstractWe report the first measurements of the complex refractive index (RI) at 375, 405, 532, and 781 nm for secondary organic aerosol (SOA) generated from isoprene/NOx photooxidation. At all wavelengths studied, slightly greater real components of the RI were observed for the SOA generated in the absence of SO2 compared with those generated in its presence. Considering the chemical properties, the differences in the oxidation state and/or ratio of particle density to molecular weight of compounds in the SOA are considered to be the main factors determining the real components. The imaginary components at ≤532 nm were found to increase with increasing initial SO2 concentration. The highly conjugated oligomers are suggested to be plausible chromophore candidates. This study suggests that when large amounts of SOA are generated after mixing of isoprene with NOx and SOx, light absorption of these SOAs may compete with that of black carbon, especially at ultraviolet wavelengths.

Location and Influence of Added Block Copolymers on the Droplet Size in Oil-in-Oil Emulsions.

We have investigated the effect of added polystyrene-b-poly(ethylene oxide) (SO) copolymer on the stability of oil-in-oil (O/O) emulsions containing polystyrene (PS) and poly(ethylene glycol) (PEG) in chloroform (CHCl3) and directly visualized the location of SO in the emulsions by using dye-labeled SO (SO*) with confocal laser scanning microscopy (CLSM). The emulsion formed by PS/PEG/CHCl3 = 14/6/80 (wt %) consisted of a droplet phase of PS in CHCl3 and a continuous phase containing PEG in CHCl3. SO*s with various molecular weights (Mn,SO) and volume fractions of the PS block in SO (fPS) were prepared via living anionic polymerization and subsequent end-esterification. The effect of SO on the droplet size in the emulsions was investigated as a function of both Mn,SO and fPS. Increasing Mn,SO and decreasing fPS were effective at reducing the droplet size down to less than 1 μm, which is 100 times smaller than in the absence of SO. The location of SO*s in the O/O emulsions was further investigated by CLSM. We found that the location of SO*s changed from the droplet interior to the liquid-liquid interface and then to the continuous phase with decreasing fPS. We discuss the possible mechanism in terms of the relation of SO* location to the droplet size.

Corrosion of Fe–9Cr–(Mn, Si) alloys in CO2–H2O–SO2 gases

Model alloys, Fe–9Cr, Fe–9Cr–2Mn and Fe–9Cr–0.5Si (wt%) were exposed to Ar–20%CO2–20%H2O–(0, 0.1, 0.5 and 1.0%)SO2 gases at 650°C. In the absence of SO2, all alloys grew thick iron-rich oxide scales. Adding SO2 led to partial passivation by chromia formation on Fe–9Cr and Fe–9Cr–0.5Si, but not the Fe–9Cr–2Mn. Alloy carburisation was extensive in sulphur-free gas, but substantially suppressed by SO2. Internal sulphidation and oxidation were also observed. A silica layer formed beneath the chromia scale on Fe–9Cr–0.5Si in SO2-bearing gas, but not in sulphur-free gas. Reaction morphologies are discussed in terms of oxide grain boundary diffusion, as affected by sulphur uptake.

The influence of SO2 on the tolerable water content to avoid pipeline corrosion during the transportation of supercritical CO2

A systematic study is undertaken to establish the influence of sulfur dioxide (SO2) concentration on the critical water content required to avoid substantial levels of internal corrosion during the transport of supercritical CO2 for carbon capture and storage (CCS) applications. Corrosion experiments were performed on X65 carbon steel in autoclaves containing supercritical CO2 at 80bar and 35°C in the presence of 0, 50, and 100ppm (mole) SO2. General and localized corrosion rates were determined over a period of 48h through the implementation of gravimetric analysis and surface profilometry, respectively. Analysis of corrosions products formed on the steel surface was performed using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The results indicate that the presence of SO2 reduces the critical water content required to maintain a general corrosion rate below 0.1mm/year. Furthermore, the water content required to avoid excessive localized corrosion is far less than that to prevent significant general corrosion. Localized corrosion rates close to 1mm/year were observed in the absence of SO2 when the CO2 system was water-saturated, but below water contents of ∼1800ppm (mole) and ∼500ppm, general and localized corrosion rates (respectfully) were found to be below 0.1mm/year even in the presence of 100ppm SO2. The research presented highlights that reducing water content is a more favorable option compared to reducing SO2 content to minimize internal pipeline corrosion during transportation. Consideration is also afforded to the consumption of impurities in the closed system experiments.

Sulfur-Tolerant Mn-Ce-Ti Sorbents for Elemental Mercury Removal from Flue Gas: Mechanistic Investigation by XPS

The influence of structural interaction between Mn, Ce, and Ti on the elemental mercury adsorption properties of Mn-Ce-Ti sorbents has been investigated. For this purpose, Mn-Ce-Ti sorbents have been synthesized by coprecipitation, codeposition-precipitation, coimpregnation, sequential impregnation, and deposition-impregnation to get different structural properties. All the sorbents were evaluated for elemental mercury capture in the absence and presence of SO2. Among the sorbents tested, the Mn-Ce-Ti sorbent synthesized by coimpregnation exhibits better sulfur resistance. X-ray diffraction measurements show that the samples prepared using impregnation methods exhibit intense reflections due to the cubic fluorite structure of cerium. Temperature-programmed desorption measurements reveal that the type and strength of acid sites depend on the synthesis method. Temperature-programmed reduction measurements suggest that precipitating Mn and Ce together over the surface of titania promotes surface ceria and manganese oxide reduction. However, the simultaneous precipitation of Mn, Ce, and Ti inhibits surface ceria and manganese oxide reduction. X-ray photoelectron spectroscopy (XPS) measurements suggest that the mechanism for Hg adsorption over Mn-Ce-Ti sorbents is the same regardless of the presence or absence of SO2. The Ce 3d XPS spectra show that all the samples exhibit peaks due to both Ce4+ and Ce3+ oxidation states. Surface atomic ratios determined from XPS measurements show that the sorbent synthesized by coimpregnation yields a higher concentration of cerium atoms on the surface and exhibits better sulfur resistance than the other sorbents. The sorbent synthesized by coprecipitation yields more titanium atoms on the surface and exhibits the least sulfur resistance.

Effects of flue gas components on the oxidation of gaseous Hg0 by dielectric barrier discharge plasma

This study investigated the effects of gas components on the oxidation of Hg0 by dielectric barrier discharge (DBD) non-thermal plasma (NTP) technology. The findings indicated that reactive species such as O and Cl generated by ionization of O2 and HCl played dominant roles during oxidation processes. The presence of 50ppm of HCl in N2/O2 atmosphere enhanced the Hg0 oxidation, the complete oxidation of Hg0 was observed by 6kV of applied voltage. The presence of NO in the reactor decreased the Hg0 oxidation efficiency due to the interference by NO reaction with O and O3. The addition of 310ppm of NO into the flue gas remained in 55% of Hg0 oxidation efficiency. Water vapor inhibited Hg0 oxidation, which was attributed to the consumption of reactive species and decomposition of HgOH. SO2 had a slight promoting effect on Hg0 oxidation, compared with the absence of SO2, the oxidation efficiency increased by 2–8% with the addition of 100–200ppm of SO2. This study leads to starting the development of a novel promising environmental technology for Hg removal in the flue gas.

Pt-Rh/CeO2-Al2O3 for Controlling Emissions from Natural Gas Engines: Three-Way Catalytic Activity at Low Temperatures and Effects of SO2 Aging

The three-way catalytic activity of Pt-Rh/CeO2-Al2O3 was examined at temperatures below 500 °C under conditions simulating gas engine exhaust, and the results were compared with those of O2-CH4, NO-O2-CH4, and NO-CH4 model reactions. The catalyst exhibited sufficient three-way catalytic activity, even at 400 °C, in the absence of SO2. After SO2 aging, the activity under stoichiometric conditions remarkably decreased. In addition, methane conversion under rich (reducing) conditions severely decreased after SO2 aging due to the suppression of steam methane reforming by sulfur poisoning.

Nanostructured MnOx catalysts for low-temperature NOx SCR

Manganese oxides with different structures and morphologies have been investigated as catalysts for low temperature SCR by preparing a series of samples by both SCS (Solution Combustion Synthesis) and co-precipitation methods. The samples have been characterized by XRD, BET, H2-TPR, NH3-TPD, FESEM and their catalytic activity tested for NOx removal in the range of temperature of interest (120–350°C) both in the presence and in the absence of SO2, and after catalyst regeneration from sulphur deactivation. The different preparation procedures allowed to obtain MnOx systems with variable average oxidation state (measured through H2-TPR) that can be put in correlation with the porosity and the morphology measured by the other techniques, and the resulting catalytic performances in the SCR. The presence of Mn3O4 in the resulting material with low degree of crystallinity seemed to be the key factor to get the best catalyst among those prepared, being this phase not only active, but very selective towards the production of N2. Finally, the presence of a relatively high amount of SO2 among reactants (100ppm) drastically reduces the activity of all samples, but regeneration of catalyst for 2h at 400°C almost completely restores the catalytic performances.

Significant catalytic effects induced by the electronic interactions between carboxyl and hydroxyl group modified carbon nanotube supports and vanadium species for NO reduction with NH3 at low temperature

The relative content of carboxyl and hydroxyl groups on carbon nanotubes (CNTs) was tuned through a controlled reduction process. It was found that the CNTs decorated by varying ratio of carboxyl and hydroxyl groups can obviously enhance the catalytic activity of supported vanadium oxide catalysts for selective catalytic reduction (SCR) of NO with NH3. The improvement effects induced by carboxyl and hydroxyl groups depend significantly on the reacting feedstock with and without SO2 and H2O. In the absence of SO2 and H2O, hydroxyl-modified CNT supported vanadium oxide (Vx+yO2−z (x ⩽ 4)/CNTs-OH) shows more significant improvement on SCR activity, while more obviously promoting effect was observed over carboxyl-modified CNT supported vanadium oxide (Vx+yO2−z (x ⩽ 5)/CNTs-COOH) catalyst in the presence of SO2. The variation in oxidation states of active vanadium species (V5+, V4+ and V3+) originated from the electronic interactions between carboxyl and hydroxyl modified CNTs and vanadium precursors are indicated to be the main reason for the very different SCR performances over the two Vx+yO2−z/CNTs catalysts. Low valence V4+ and V3+ species show much higher SCR activity in the absence of SO2 and H2O, while the high valence V5+ species are very beneficial to NO reduction in the presence of SO2. The V5+ species have an excellent catalytic ability of oxidizing SO2 to SO3, leading to the in situ formation of ammonium sulfate, and are capable of catalyzing the reaction between the sulfate salts and NO. Furthermore, both of the Vx+yO2−z/CNTs catalysts are very stable for SCR of NO even in the presence of SO2 and H2O. These findings give some insight into the mechanisms behind the SCR reaction over CNT supported vanadium oxides, which would be beneficial to the design and synthesis of more efficient and much stable SCR catalysts.

Mitigation of Fireside Corrosion of Stainless Steel in Power Plants: A Laboratory Study of the Influences of SO2 and KCl on Initial Stages of Corrosion

The effect of SO2(g) on the initial oxidation of the stainless-steel 304L, sprayed with 0.1 mg/cm2 KCl and exposed in 5% O2 and 40% H2O at 600 °C, was investigated. In the absence of SO2(g), KCl accelerates the corrosion attack by the formation of K2CrO4. The reaction with KCl depletes the oxide in chromium and converts it into an iron-rich, poorly protective oxide. When SO2(g) was introduced to the gas flow, KCl rapidly transformed into K2SO4. In contrast to KCl, K2SO4 does not form K2CrO4. Hence, it does not accelerate the corrosion rate. Although the conversion of KCl to K2SO4 is fast, the corrosion rate of KCl samples exposed in the presence of SO2(g) is higher than samples exposed in the presence of K2SO4. It is therefore suggested that small amounts of unreacted KCl react initially with the protective oxide, forming K2CrO4, which depletes the oxide in chromium. However, because of the presence of SO2(g), K2CrO4 immediately reacts with SO2(g) to form K2SO4. This study shows that the initial stages of...

Sulfur Tolerance of CaxMn1–yMyO3−δ (M = Mg, Ti) Perovskite-Type Oxygen Carriers in Chemical-Looping with Oxygen Uncoupling (CLOU)

Perovskite-structured oxygen carriers of the type CaxMn1–yMyO3−δ (M = Mg, Ti) have been investigated for the CLOU process. The oxygen carrier particles were produced by spray-drying and were calcined at 1300 °C for 4 h. A batch fluidized-bed reactor was used to investigate the chemical-looping characteristics of the materials. The effect of calcium content, dopants (Mg and Ti), and operating temperature (900, 950, 1000, and 1050 °C) on the oxygen uncoupling property and the reactivity with CH4 in the presence and absence of SO2 was evaluated. In addition, the attrition resistance and mechanical integrity of the oxygen carriers were examined in a jet-cup attrition rig. All of the investigated perovskite-type materials were able to release gas phase oxygen in inert atmosphere. Their reactivity with methane was high and increased with temperature and calcium content, approaching complete gas yield at 1000 °C. The reactivity decreased in the presence of SO2 for all of the investigated oxygen carriers. Decreasing the calcium content resulted in a less severe decrease in reactivity in the presence of SO2, with the exception of materials doped with both Mg and Ti, for which a higher resistance to sulfur deactivation could be maintained even at higher calcium contents. The drop in reactivity in the presence of SO2 also decreased at higher temperatures, and at 1050 °C, the decrease in the reactivity of the Mg- and Ti-doped material was minimal. Sulfur balance over the reactor system indicated that the fraction of the introduced SO2 that passed through the reactor increased with temperature. It was shown that it is possible to regenerate the oxygen carriers during reduction in the absence of SO2. Most of the materials also showed relatively low attrition rates. The results indicate that it is possible to modify the operating conditions and properties of perovskite-type oxygen carriers to decrease or avoid their deactivation by sulfur.

Sulfur Deposition and Poisoning of La0.6Sr0.4Co0.2Fe0.8O3-δ Cathode Materials of Solid Oxide Fuel Cells

Sulfur in the air stream is one of the major contaminants affecting the performance stability of cathodes of solid oxide fuel cells (SOFCs) such as La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) perovskite. Here sulfur deposition and poisoning was investigated on LSCF bar samples in the presence of 20 ppm SO2 and temperature range of 400–900°C, using scanning electron microscopy, confocal laser Raman spectroscopy and electrical conductivity relaxation (ECR) methods. Sulfur (SO2) reacts with LSCF, primarily forming SrSO4 at high temperatures (i.e., ≥ 700°C) and SrS at low temperatures (i.e. <700°C). Surface segregated SrO plays an important role in the sulfur deposition. The most important observation of this study is that sulfur deposition shows a distinct volcano-type dependency on the heat-treatment temperature and is most pronounced at temperatures around 700°C, indicating that the reaction rate between the segregated SrO and SO2 is highest at ∼700°C. The ECR results indicate that the surface exchange coefficient of LSCF after the exposure to 20 ppm SO2 at 700, 800 and 900°C for 48 h is two orders of magnitude lower than that of the sample tested in the absence of SO2, indicating that sulfur poisoning deteriorates significantly the surface exchange and diffusion processes for the O2 reduction reaction on LSCF electrodes.

Effect of SO2 on the chain reaction of hydrogen oxidation: Intermittent flames

The effect of SO2 on the chain reaction of hydrogen oxidation in the autoignition region (T = 470–510°C and p < 200 torr) is studied. In the absence of SO2 under flow conditions, the process occurs in a low-temperature flame mode with a characteristic pale blue glow. With the addition of sulfur dioxide, SO2 is transformed to elemental sulfur and a new phenomenon is observed. At a small contact time (less than 4–5 s), the process enters the mode of intermittent flames. Dependences of the rate and intensity of light flashes on pressure, temperature, and contact time are studied. An interpretation of the observed phenomenon is given.

Post-flame gas-phase sulfation of potassium chloride

The sulfation of KCl during biomass combustion has implications for operation and emissions: it reduces the rates of deposition and corrosion, it increases the formation of aerosols, and it leads to higher concentrations of HCl and lower concentrations of SO2 in the gas phase. Rigorously homogeneous systems are required to characterize the gas-phase formation of alkali sulfates. We have measured the temperature and gas-phase concentrations of KCl and HCl, and detected the presence of aerosols in the post-flame region of a range of hydrocarbon flames seeded with KCl, with and without the addition of SO2. Dilution of the flame products with different amounts of N2 ensured post-flame temperatures in the range 950–1400K. In the absence of SO2, KCl levels were constant in the post-flame zone and no aerosols were formed, even at the lowest temperatures. In the presence of SO2, KCl was consumed and HCl and aerosols formed, most pronounced in flames with the lowest post-flame temperatures. This shows that KCl is sulfated in the gas phase to K2SO4, and this is followed by homogeneous nucleation of K2SO4 to form aerosols. Predictions from a kinetic model of the S/Cl/K chemistry agreed well with the experimental results. The model showed that the rate-limiting steps in the sulfation process are the oxidation of SO2 to SO3 and the homogeneous nucleation of K2SO4.

Deactivation Mechanism of SCR Catalyst Based on Nano-ZrO&lt;sub&gt;2&lt;/sub&gt;

A catalyst, 8%Fe-10%MnOx-CeO2/ZrO2, was prepared and applied for selective catalytic reduction of NO with NH3 at low temperature. The effects of SO2 and H2O on the catalyst were studied. The results showed that in the absence of SO2 and H2O, the catalyst 8%Fe-10%MnOx-CeO2/ZrO2 has good activity and stability. The presence of SO2 and H2O make the catalyst deactivate, and the activity can be recovered mostly by heating at 400°C. Properties of the catalyst on different reaction stages were characterized by FT-IR to study the inactivation mechanism of the catalyst. The results showed that the catalyst deactivation is due to the deposition of ammonium sulfate on the catalyst and the sulphation of the metal oxides of the catalyst.

Development of Iridium Catalysts for Selective Reduction of NO with CO

The development of Ir/SiO2-based catalysts for the selective reduction of NO with CO in the presence of O2 is described in this review paper. The catalytic activity of Ir/SiO2 was promoted considerably by addition of Nb2O5 and WO3. These promoted catalysts showed NO reduction activity even in the absence of SO2, in contrast to Ir/SiO2 catalyst. The addition of Nb2O5 was found to stabilize Ir metal as the active species for NO reduction. Also in the case of WO3, it was concluded that Ir metal interacting strongly with WO3 (denoted as Ir–WO3) is the catalytic active species. High temperature calcination created preferentially the Ir–WO3 species. The catalytic activity and durability of Ir/WO3/SiO2 was further promoted by addition of Ba. The developed Ba/Ir/WO3/SiO2 catalyst in monolithic form showed good performance for NO reduction for actual diesel exhaust.

Yield of HO2 Radicals in the OH-Initiated Oxidation of SO2

Abstract The HO2 radical yield in the OH initiated oxidation of SO2 has been determined by direct observation of HO2 concentration time profiles following the 248 nm photolysis of H2O2/SO2/O2 mixtures. Initial OH radical concentrations have been deduced from a fit of the absolute HO2 concentration time profiles after 248 nm photolysis of H2O2 in the absence of SO2, an increase in the HO2 concentration upon addition of SO2 to this reaction mixture is observed and can be explained by a decrease of HO x -radical losses due to a faster decay of OH radicals in the presence of SO2. Simulations of theses profiles using recommended rate constants in a simple model are in agreement with an HO2-yield of 1.0 ± 0.1 from the OH initiated oxidation of SO2.

The influence of sulfur dioxide and water on the performance of a marine SCR catalyst

This study investigates how sulfur affects the NOx reduction activity over a commercial vanadium based urea-SCR catalyst for marine applications, especially at low temperatures, and in combination with H2O. The addition of SO2 in the absence of H2O promotes the NOx reduction at 350°C, while the addition of H2O, in the absence of SO2, gives rise to a decrease in the NOx reduction and also an inhibition of the N2O formation. The same trends are observed at transient temperatures, but no promotional effect by SO2 is seen at temperatures below 230°C. Further, long term effects of SO2 and H2O were investigated and the NOx reduction remains stable, also after long term exposure of SO2. The ammonia desorption is investigated using temperature programmed desorption (TPD) experiments, both in the presence and in the absence of SO2. In general in the presence of both H2O and SO2 the catalyst does not show any sign of deactivation at temperatures above 300°C and fairly low space velocities (below 12,200h−1). However, at lower temperatures (250°C) and/or higher space velocities the catalytic performance for NOx reduction decreases with time.

Influence of the Concentration of CO2 and SO2 on the Absorption of CO2 by a Lithium Orthosilicate-Based Absorbent

A novel, high temperature solid absorbent based on lithium orthosilicate (Li(4)SiO(4)) has shown promise for postcombustion CO(2) capture. Previous studies utilizing a clean, synthetic flue gas have shown that the absorbent has a high CO(2) capacity, >25 wt %, along with high absorption rates, lower heat of absorption and lower regeneration temperature than other solids such as calcium oxide. The current effort was aimed at evaluating the Li(4)SiO(4) based absorbent in the presence of contaminants found in typical flue gas, specifically SO(2), by cyclic exposure to gas mixtures containing CO(2), H(2)O (up to 25 vol. %), and SO(2) (up to 0.95 vol. %). In the absence of SO(2), a stable CO(2) capacity of ∼ 25 wt % over 25 cycles at 550 °C was achieved. The presence of SO(2), even at concentrations as low as 0.002 vol. %, resulted in an irreversible reaction with the absorbent and a decrease in CO(2) capacity. Analysis of SO(2)-exposed samples revealed that the absorbent reacted chemically and irreversibly with SO(2) at 550 °C forming Li(2)SO(4). Thus, industrial application would require desulfurization of flue gas prior to contacting the absorbent. Reactivity with SO(2) is not unique to the lithium orthosilicate material, so similar steps would be required for other absorbents that chemically react with SO(2).