Presence Of SO2 Research Articles

Promotion of the performance of Cu-SSZ-13 for selective catalytic reduction of NOx by ammonia in the presence of SO2 during high temperature hydrothermal aging

The influence of SO2 presence during high temperature hydrothermal aging (600, 700, and 800 °C) on the performance of Cu-SSZ-13 prepared by the conventional ion-exchange method for selective catalytic reduction of NOx by NH3 (NH3-SCR) was studied. The high-temperature activity of Cu-SSZ-13 is obviously enhanced by the SO2 presence for the 700 and 800 °C-aged samples and is not hampered for the 600 °C-aged sample. The presence of SO2 during hydrothermal aging has no influence on the framework Al. The interaction of Cu2+ with SO2 results in the formation of ZCuHSO4, which helps suppress the aggregation of Cu2+ into CuO and maintain more isolated Cu2+, leading to higher activity at high temperatures. The low Cu content yields higher relative population of Cu2+ species at more stable sites. The low-temperature (≤350 °C) activity is slightly lowered for the 600 and 700 °C-aged samples.

Analysis of dynamic CO2 capture over 13X zeolite monoliths in the presence of SOx, NOx and humidity

AbstractIn this investigation, the CO2 capture performances of zeolite 13X monoliths with 600 and 800 cells per square inch (cpsi) in the presence of SO2/NO impurities under dry and humid conditions were evaluated and compared with that of 13X beads. Dynamic breakthrough tests demonstrated a drastic reduction in CO2 capture capacity and deterioration of kinetics under dry‐clean conditions, whereas, upon switching the feed from a clean gas to contaminated gas which contained SO2 and NO, different adsorption performance was observed. Specifically, in dry‐contaminated mode, the adsorbents retained their capture capacities with comparable kinetics to that of dry‐clean feed conditions, however, in humid‐contaminated mode, the adsorbents experienced improved CO2 uptake and CO2/N2 selectivity, albeit at the expense of deteriorated kinetics. These findings indicate that the presence of SO2 and NO contaminants, especially SO2 contaminants, lead to dramatic changes in the adsorption performance of zeolite 13X monoliths, indicating the importance of evaluating adsorbent materials under realistic conditions.

Synergetic catalytic removal of chlorobenzene and NOx from waste incineration exhaust over MnNb0.4Ce0.2Ox catalysts: Performance and mechanism study

Nb doped MnCe0.2Ox complex oxides catalysts prepared via a homogeneous precipitation method were investigated for synergistic catalytic removal of NOx and chlorobenzene (CB) at low temperatures. The MnNb0.4Ce0.2Ox catalyst with a molar ratio of Nb/Mn = 0.4 exhibits excellent activity and the NOx and CB removal efficiency reaches 94.5% and 96% at 220 °C, respectively. Furthermore, the NOx and CB removal efficiency of MnNb0.4Ce0.2Ox still remains above 80% after injecting 300 ppm SO2 and 7 vol% H2O for 36 h. In addition, the presence of CB and NOx + NH3 can improve the NOx and CB removal efficiency of MnNb0.4Ce0.2Ox, respectively. The analysis results from N2-BET, Py-IR, H2-TPR and NH3-TPD reveal that the introduction of Nb increases the average pore size, pore volume and surface area, promoted the growth of Lewis acid amount obviously, and enhances redox ability of MnCe0.2Ox at 100–250 °C. Moreover, the molecular migration process of NOx, NH3, CB and SO2 in NH3-SCR and CB oxidation reaction over MnNb0.4Ce0.2Ox catalysts were systematically studied. In situ DRIFTS, FT-IR and XPS also confirm that the adsorption of sulfate species and SO2 on the surface of MnNb0.4Ce0.2Ox is inhibited effectively by the introduction of Nb in the presence of SO2 and H2O. Moreover, Nb additives also enhance the structural stability of MnNb0.4Ce0.2Ox, due to the interactions among Mn, Nb and Ce. The NH3-TPD, H2-TPR and in situ DRIFTS results also confirm that the MnNb0.4Ce0.2Ox still retains abundant acid sites and high redox ability in the presence of SO2 and H2O. In summary, MnNb0.4Ce0.2Ox catalysts represent a promising and effective candidate for controlling NOx and CB at low temperatures.

Phase Equilibria of Ferrous-Calcium Silicate Slags in the Liquid/Spinel/White Metal/Gas System for the Copper Converting Process

Ferrous calcium silicate (FCS) slags are reported to have high potential for use in the copper converting process. However, no phase equilibrium study has been carried out under a simulated converting gas atmosphere in the presence of SO2. In this study, under accurately controlled P(SO2) 0.4 atm and P(O2) 10−6 atm, the phase equilibria of FCS slags in a liquid/spinel/white metal/gas system were investigated for the copper converting process. The liquidus temperatures of slags in the Fe-Ca-Cu-Si-S-O system were quantified as well as the solid solubilities of Cu2O in the spinel phase. The experimental results were compared with the FactSage predictions, which provided clues for further improvement of the thermodynamic modelling. The applications of the FCS slags were further discussed and compared with iron silicate slags. The results obtained will contribute to slag development for converting operations and thermodynamic calculations.

Impact fragmentation of limestone-based sorbents for calcium looping: The effect of steam and sulphur dioxide

Calcium Looping (CaL) for CO2 capture and utilisation is affected by the presence of SO2 and/or H2O in the flue gases that are processed in the carbonator. The influence regards both the course of carbonation as well as the mechanisms and extent of attrition and fragmentation phenomena to which sorbent particles are exposed in Dual Interconnected Fluidised Beds (DIFB) that are commonly used for this process. Fragmentation by impact has been comparatively less investigated with reference to operating conditions entailing the presence of SO2 and/or H2O. In this study, two high-calcium commercial limestones, similar in chemical composition but different in reactivity, have been subjected to CaL tests in a lab-scale DIFB apparatus in presence of sulphur dioxide and/or steam. Calcination was carried out at 940 °C in an atmosphere containing 70% CO2. Carbonation was carried out at 650 °C in an atmosphere containing 15% CO2. The effect of SO2 and/or H2O was assessed with reference to six carbonation atmospheres, with different concentrations of steam (0 and 10%v) and sulphur dioxide (0, 75 and 1500 ppmv). After ten CaL cycles, the particles were tested ex-situ in an impact test rig, consisting of a duct where samples were entrained in a gas stream at a controlled velocity and impacted against a target. The apparatus was operated at room temperature at various impact velocities (six values from 10 to 45 m/s). The extent and pattern of impact fragmentation was assessed by characterising the particle size distribution of the debris and the fractional mass of generated fragments. Results are discussed in the light of the different sorbent nature and of the CaL FB operating conditions.

Synthesis of highly oriented WO3 nanowire bundles decorated with Au for gas sensing application

This study demonstrates the synthesis of self-assembled hexagonal WO3 nanowire bundles, with both ordered and random structures in the presence of SO42− ions, by a simple but efficient solvent-thermal method. The as-synthesized products are composed of hierarchical bundles with assembled ultrathin nanowire subunits. The growth and assembly mechanisms, regarding WO3 nanowire bundles, may be elucidated through oriented attachment or Ostwald ripening growth, based on a synergistic effect from both oxalic acid and ethylene glycol in dehydrating WO3·xH2O to WO3 nanocrystals and in controlling segregation behavior, along with high surface areas (18.4 m2 g-1 for ordered structures while 11.6 m2 g-1 disordered ones), which makes WO3 bundles great potential for gas sensing. To further enhance gas sensing, gold nanoparticles were chosen to deposit on the surface of WO3 nanowire bundles by acting with amino groups linked with WO3 bundles in the HAuCl4 solution with further oxidation. The Au-WO3 composites were examined towards various reducing gases, with exemplary sensitivities of (S = 127, 82), (S = 72, 52) towards n-butanol and acetone, respectively. The sensing mechanisms of such WO3 bundle structures are further understood in detail. This work will make the unique WO3 bundle nanostructures highly potential for gas sensing applications.

Efficient separation of Zn(Ⅱ) from Cd(Ⅱ) in sulfate solution by mechanochemically activated serpentine

Clay minerals are widely used to treat sewage containing heavy metals such as zinc and cadmium. In this study, the chemical reactivity of natural serpentine was signally improved through mechanochemical activation, achieving the efficient separation of Zn(Ⅱ) and Cd(Ⅱ) ions in a mixed solution. The activated serpentine would release a large amount of Mg2+ and OH− and thereby selectively precipitate Zn(Ⅱ) ions as an uncommon metamorphic zinc mineral, bechererite, in the presence of SO42−. By adjusting the parameters including grinding intensity, reaction temperature, serpentine dosage and salt species, the optimum conditions were determined and a 92% separation rate of Zn(Ⅱ) and Cd(Ⅱ) ions was achieved. The mechanochemical activation of natural clay minerals expresses a great potential for purification of heavy metal contaminated sewage, as well as the simultaneous separation and recovery of multi-metal secondary resources.

The emission characteristic of particulate matter in the spray-and-scattered-bubble process during ammonia desulfurization: Experiments, mechanisms and prospects

Given the positive effects of jet bubble reactors as particulate matter (PM) traps, a new integrated technology was investigated, termed here the spray-and-scattered-bubble process. The main goal was to demonstrate that it can satisfy ultra-low emission limits for the ammonia-based desulfurization process, where the aerosol generated by the spraying droplets is further removed by the bubbling step in one device. Compared with the conventional spray-only method, this new technology generates a lower particulate level based on the same desulfurization efficiency, and the particulate size has an effectively unimodal distribution with a main size range from 0.156 μm to 1.64 μm. The removal mechanism under the new technology is further explored by density functional theory (DFT) and a large adsorption energy between was found to exist between the sulfites and (NH4)2SO4 particles. The process parameters that affect the particulate emission were studied using lab-scale tests, by changing the SO2 concentration, the immersion depth and the liquid/gas ratio. The results indicated that the amount of particulate matter significantly increases in the presence of SO2 in the flue gas and was positively correlated with the SO2 concentration. The liquid/gas ratio showed a positive correlation with the particulate matter emissions, while the immersion depth is closely tied to the inhibition effect. To further verify its potential, long-term experiments with actual flue gas were performed in a 5000 Nm3/h pilot platform. The “daily mean results” showed that the PM emission concentration was 5 mg/m3, which is far below the ultra-low limits now proposed in China.

Mechanochemical redox-based synthesis of highly porous CoxMn1-xOy catalysts for total oxidation

A mechanochemical redox reaction between KMnO4 and CoCl2 was developed to obtain a CoxMn1–xOy catalyst with a specific surface area of 479 m2 g−1, which was higher than that obtained using a co-precipitation (CP) method (34 m2 g−1), sol-gel (SG) method (72 m2 g−1), or solution redox process (131 m2 g−1). During catalytic combustion, this CoxMn1–xOy catalyst exhibited better activity (T100 for propylene = ~200 °C) than the control catalysts obtained using the SG (325 °C) or CP (450 °C) methods. The mechanical action, mainly in the form of kinetic energy and frictional heating, may generate a high degree of interstitial porosity, while the redox reaction could contribute to good dispersion of cobalt and manganese species. Moreover, the as-prepared CoxMn1–xOy catalyst worked well in the presence of water vapor (H2O 4.2%, >60 h) or SO2 (100 ppm) and at high temperature (400 °C, > 60 h). The structure MnO2·(CoOOH)2.93 was suggested for the current CoxMn1–xOy catalyst. This catalyst could be extended to the total oxidation of other typical hydrocarbons (T90 = 150 °C for ethanol, T90 = 225 °C for acetone, T90 = 250 °C for toluene, T90 = 120 °C for CO, and T90 = 540 °C for CH4). Scale-up of the synthesis of CoxMn1–xOy catalyst (1 kg) can be achieved via ball milling, which may provide a potential strategy for real world catalysis.

A MnOx@Eu-CeOx nanorod catalyst with multiple protective effects: Strong SO2-tolerance for low temperature DeNOx processes

A novel MnOx@Eu-CeOx catalyst with multiple protective attributes was designed and fabricated using a chemical precipitation method and tested for its low temperature SCR activity. The subject MnOx@Eu-CeOx nanorod catalyst exhibited superior SCR performance and strong SO2-tolerance. The formation of the composite-shell structure enhanced the catalysts' surface acidity and redox performance, which resulted in excellent SCR performance. Moreover, the TG results suggested that the protective effect of the EuOx-CeOx composite-shell effectively reduced the deposition of the surface sulphates. The XPS, XRD analysis results of the subject catalyst together with theoretical calculations provided strong evidence that there was a strong interaction between Mn and Ce in the MnOx@Eu-CeOx. This significant interaction could provide maximum protection to the core from the effect of SO2, which also contributed to the high SO2 resistance of the catalyst. In situ FT-IR results also indicated that the chemisorbed species on MnOx@Eu-CeOx were much more stable in the presence of SO2 compared to Eu-CeOx/MnOx, which resulted in the deposition of significantly less sulphates. This low temperature SCR catalyst with multiple protective attributes, including composite shell, strong interaction and core-shell structure, is the key to long-term resistance to SO2.

Sulfur poisoning and regeneration of Rh-ZSM-5 catalysts for total oxidation of methane

The activity of Rh/ZSM-5 catalysts for methane oxidation was investigated under conditions simulating the exhaust from lean burning, natural gas fueled engines to evaluate the influence of reaction atmosphere on catalytic activity. The Rh-catalysts yield high methane conversion at conditions achievable in real exhaust systems, despite the inhibiting effects of H2O and SO2. The influence of temperature and SO2 concentration (1−20 ppm) on the activity were studied. The deactivation caused by SO2 was intensified with decreasing temperature and increasing SO2 concentration, and the SO2-poisoning could be modeled as the occupation of active sites following a Temkin adsorption isotherm. At 400 °C essentially full coverage of S-species was reached with 1−2 ppm of SO2, but at 500 °C the coverage had decreased significantly, and considerable catalytic activity was preserved in the presence of SO2. Significant activity was regenerated in SO2-free gas, but the nature of the SO2-free regeneration atmosphere was unimportant.

Role of acid gases in Hg0 removal from flue gas over a novel cobalt-containing biochar prepared from harvested cobalt-enriched phytoremediation plant

A novel biochar containing highly-dispersed cobalt oxides was prepared by one-step pyrolysis using Co-enriched Siberian Iris as the raw material, and it was used for elemental mercury removal from flue gas. The presence of NO or HCl could approximately keep Hg0 removal efficiency over 85%, while the presence of SO2 suppressed Hg0 removal. The role of aforementioned acid gases in Hg0 removal over such biochar was systematically studied. The surface active oxygen species derived from the reversible conversion between Co3+ and Co2+ could activate the adsorbed NO (HCl) to produce active nitrogenous (chlorine) species, which functioned as active site for Hg0 oxidation removal. The reaction between NO (HCl) and Hg0 occurred mainly through the Eley-Rideal mechanism. SO2 consumed active oxygen and reacted with active Co3+ to generate Co2+ bonded with SO42−, resulting in irreversible damage on the biochar. The formation of active nitrogenous (chlorine) species as well as its reaction with Hg0 would be hampered by the generation of sulfate. This study can give some basic insights into the application of such heavy metal enriched phytoremediation plants for elemental mercury removal from flue gas.

SO2-tolerant NOx reduction over ceria-based catalysts: Shielding effects of hollandite Mn-Ti oxides

Ceria-based catalysts are well-established alternative to commercial V-based catalysts for NOx removal via selective catalytic reduction (SCR). However, their poor SO2 tolerance prevents their practical application to NOx removal from SO2-containing flue gas. It is desirable and challenging to develop a catalytic system in which the Ce-based catalyst is protected from SO2 inactivation (especially below 300 °C, because it is difficult to decompose the sulfate product at low temperatures). In this work, we unraveled the shielding effects of hollandite Mn-Ti oxides (HMT) from SO2 poisoning, and demonstrated that HMT modified CeW (HMT/CeW) catalysts showed excellent catalytic activity and admirable SO2-tolerance at 270 °C. Interestingly, HMT inhibited the formation of sulfate and facilitated the decomposition of sulfates, thereby enabling the high reactivity of the HMT/CeW catalysts in the presence of SO2. This work provides an innovative pathway for the protection of Ce-based catalysts from SO2 poisoning and is beneficial for both academic and practical applications.

Facile synthesis of porous anatase TiO2 nanomaterials with the assistance of biomass resource for lithium ion batteries with high-rate performance

Porous TiO2 nanomaterials assembled by anatase TiO2 nanoparticles are successfully synthesized via a simple method with the assistance of an easily accessed biomass-sodium alginate. The alginate is favorable for the formation of small TiO2 nanoparticles and the presence of SO42- in the precursors could prevent crystal phase transformation from anatase to rutile to a certain extent during high-temperature calcination process. The pyrolysis product of alginate ions could also prevent the formation of large TiO2 nanoparticles. The reactant concentrations and the ratio of sodium alginate and Ti(SO4)2 play important roles in the surface area and pore volume of porous TiO2 nanomaterials. The porous TiO2 nanomaterials are used as anode materials for lithium ion batteries and possess a reversible capacity of 223 mAh g−1 at 1C after 20 cycles. Further increasing the cycling rates, the relatively large reversible capacities still maintain. The efficient nanostructures and good crystallinity of porous TiO2 nanomaterials result in their superior electrochemical behavior.

A highly dispersed mesoporous zeolite@TiO2 – supported Pt for enhanced sulfur-resistance catalytic CO oxidation

A novel mesoporous zeolite Beta@TiOx with core-shell structure and highly dispersed Pt species was designed and synthesized by a facile photochemical reduction route. The obtained Pt/m-Beta@TiO2 catalyst exhibited oxygen vacancy defects and showed excellent catalytic activity for CO oxidation. Especially, the optimal sample Pt/m-Beta@TiO2-3 exhibited an improved sulfur-resistance, where CO complete conversion at as low as 105 °C in the presence of H2O and SO2 was achieved due to the highly dispersed Pt species and the protective TiO2-shell.

Fluoride removal from aqueous solution by municipal solid waste compost ash: kinetics, and isotherms studies

ABSTRACTFluoride (F–) is one of the common water pollutants, which causes severe diseases if be present over 1.5 mg/L suggested by WHO for drinking water. There is essential to find a simple and cost-effective method for excess F– removal from contaminated water. In this study, municipal solid waste compost ash (MSWCA) was used to remove F– from aqueous solution. The effect of operational variables such as adsorbent calcination temperature (550–900°C), adsorbent dose (0.25–1.5 g/L), pH (2–12), occurrence of competing anions (HCO3−, CO32−, Cl−, NO3 − and SO42−), adsorption temperature (20–50°C) and mixing time (15–120 min) were investigated. F–adsorption was highest when compost ash calcinated at 550°C. F– removal increased from 42.6 to 87.7% by increasing adsorbent dose from 0.25 to 1.5 g/L. The removal also increased 4.4% when the temperature of solutions increased from 20 to 50°C, an indicative of endothermic process. Furthermore, adsorption increased by increasing pH from 4 to 10 and then decreased with pH up to 12. F− removal reduced about 10% in the presence of SO42−. Based on pseudo- second-order kinetic model, it was found that the process was controlled by chemisorption. The equilibrium data were well fitted with Langmuir model, which implied the F−ions doesn’t interact and adsorbed in monolayer onto MSWA. The Langmuir maximum adsorption capacity was 30.56 mg F/g MSWCA. Due to excellent adsorptive properties, MSWCA presents as a promising material for F− adsorption from wastewaters or landfill leachates.

Simultaneous removal of SO2, NO and Hg0 using an enhanced gas phase UV-AOP method

The core for simultaneous removal of SO2, NO and Hg0 is the oxidation of NO and Hg0. Radical induced oxidation of NO and Hg0 is considered to be the most efficient method. We develop a novel gas phase advanced oxidation process (AOP) of UV-Heat/H2O2-NaClO2 to simultaneously remove SO2, NO and Hg0 due to a great synergism between H2O2 and NaClO2 under thermal and ultraviolet (UV) co-catalysis. The results indicated that the SO2 removal was always good, while the removal of NO and Hg0 was affected by NaClO2 and UV. Higher catalytic temperature and longer flue gas residence time favored the removal of NO and Hg0. The presence of SO2 and NO facilitated Hg0 removal. Kinetics analyses were conducted to provide the reaction rate of removal of NO and Hg0 under different conditions. X-ray photoelectron spectroscopy (XPS) revealed the product composition as Cl−, Hg2+, NO3− and SO42−. Electron spin resonance (ESR) tests confirmed the generation of HO. Cost analyses demonstrated the better cost performance of the proposed method compared to SCR-ACI combined method. HO and ClO2 were proved to be the main oxidant. The reaction mechanism for removal of NO and Hg0 by using UV-Heat/H2O2-NaClO2 were proposed finally.

Effects of NOx and SO2 on the secondary organic aerosol formation from the photooxidation of 1,3,5-trimethylbenzene: A new source of organosulfates

1,3,5-Trimethylbeneze (TMB) is an important constituent of anthropogenic volatile organic compounds that contributes to the formation of secondary organic aerosol (SOA). A series of chamber experiments were performed to probe the effects of NOx and SO2 on SOA formation from TMB photooxidation. The molecular composition of TMB SOA was investigated by ultra-high performance liquid chromatography/electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (UPLC/ESI-HR-Q-TOFMS). We found that the SOA yield increases notably with elevated NOx concentrations under low-NOx condition ([TMB]0/[NOx]0 > 10 ppbC ppb−1), while an opposite trend is observed in high-NOx experiments ([TMB]0/[NOx]0 < 10 ppbC ppb−1). The increase in SOA yield in low-NOx regime is attributed to the increase of NOx-induced OH concentrations. The formation of low-volatility species might be suppressed, thereby leading to a lower SOA yield in high-NOx conditions. Moreover, SOA formation was promoted in experiment with SO2 addition. Multifunctional products containing carbonyl, acid, alcohol, and nitrate functional groups were characterized in TMB/NOx photooxidation, whereas several organosulfates (OSs) and nitrooxy organosulfates were identified in TMB/NOx/SO2 photooxidation based on HR-Q-TOFMS analysis. The formation mechanism relevant to the detected compounds in SOA were proposed. Based on our measurements, the photooxidation of TMB in the presence of SO2 may be a new source of OSs in the atmosphere. The results presented here also deepen the understanding of SOA formation under relatively complex polluted environments.

Capture of arsenic in coal combustion flue gas at high temperature in the presence of CaSiO3 with good anti-sintering

Arsenic with high volatility and toxicity is usually generated during coal combustion and the capture of arsenic is restrained at high temperature since the sintering of adsorbents. Therefore, it is necessary to develop an adsorbent with sintering resistance for the arsenic removal at high temperature. In the study, the arsenic vapor capture by CaSiO3, CaO and SiO2 was carried out in the flue gas with/without SO2 and NO at high temperatures from 1000 °C to 1200 °C. The results showed that CaSiO3 exhibited excellent arsenic capture with the capacity of 4.98 mg/g and the capture efficiency was increased with the temperature increasing. The effect of acid gases was also considered. A certain amount of CaSO4 with poor capture performance was formed on CaSiO3 surface in the presence of SO2, leading to the decrease of the amount of arsenic captured. On the other hand, the effect of NO was not obvious as SO2. Although arsenic capture was suppressed when introduced SO2 and NO, it still remained considerable arsenic capture for the CaSiO3 adsorbent. Additionally, the pivotal role of O2 was also studied. Taking into account the high capture capacity and excellent anti-sintering property, CaSiO3 was a good adsorbent suitable for the removal of arsenic from coal combustion flue gas.

Effects of Sulfates on Corrosion of 430 Ferritic Steel in CO2-Saturated Water Containing Oxygen

Aqueous corrosion can be an issue for structural materials in direct supercritical CO2 power cycles, especially in low temperature components such as water separators and coolers where aqueous condensation appears as supercritical CO2 working fluid containing impurities (SOx, O2, H2O) cools down. This study aims at testing 430 ferritic steel as a material of construction for the low temperature components. Immersion experiments were carried out in an aqueous solution with and without H2SO4 (pH was 3 and 4, respectively) in an autoclave pressurized to 8 MPa with 99% CO2 and 1% O2 gas mixture. Temperature of each solution was 50°C. Immersion tests lasted up to 500 hours. Post-corrosion surface characterization techniques included X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The characterization indicated that general corrosion took place in both cases with and without H2SO4. The corrosion rate of samples was calculated based on the mass loss. The corrosion rate values for 430 steel in solutions with and without H2SO4 were very low and similar after 96 hours of immersion. These initial results indicated that the presence of SO4 2- in CO2 -saturated water containing O2 did not have a detrimental effect on the corrosion resistance of 430 steel.