Reduction of Fe(II)EDTA‐NO using Paracoccus denitrificans and changes of Fe(II)EDTA in the system

BACKGROUND: In the BioDeNO_X technology for NO_X removal from flue gas, bioreduction of Fe(II)EDTA‐NO and Fe(III)EDTA are core processes. In this study, a newly isolated strain, Paracoccus denitrificans, was used to reduce Fe(II)EDTA‐NO with glucose and Fe(II)EDTA as donor electrons. To better understand the change law of Fe(II)EDTA, the process of Fe(II)EDTA‐NO reduction by P. denitrificans with glucose and Fe(II)EDTA as electron donors was investigated, and the factors that might affect Fe(II)EDTA concentration were studied. RESULTS: For the bioreduction process of Fe(II)EDTA‐NO, P. denitrificans could use glucose and Fe(II)EDTA as electron donors. At different stages, primary electron donors were different, thereby affecting the concentration of Fe(II)EDTA in the system. It was also proved that this strain not only reduced Fe(III)EDTA with glucose as the electron donor but also secreted several substances that reacted with Fe(III)EDTA, resulting in increased Fe(II)EDTA concentration in the solution. CONCLUSIONS: This work has shown that P. denitrificans can reduce Fe(II)EDTA‐NO and Fe(III)EDTA simultaneously to regenerate NO_X absorption solution. © 2012 Society of Chemical Industry     

Denitrification in aqueous FeEDTA solutions

The biological reduction of nitric oxide (NO) in aqueous solutions of FeEDTA is an important key reaction within the BioDeNOx process, a combined physico‐chemical and biological technique for the removal of NO_x from industrial flue gasses. To explore the reduction of nitrogen oxide analogues, this study investigated the full denitrification pathway in aqueous FeEDTA solutions, ie the reduction of NO₃^?, NO₂^?, NO via N₂O to N₂ in this unusual medium. This was done in batch experiments at 30 °C with 25 mmol dm^?3 FeEDTA solutions (pH 7.2 ± 0.2). Also Ca²⁺ (2 and 10 mmol dm^?3) and Mg²⁺ (2 mmol dm^?3) were added in excess to prevent free, uncomplexed EDTA. Nitrate reduction in aqueous solutions of Fe(III)EDTA is accompanied by the biological reduction of Fe(III) to Fe(II), for which ethanol, methanol and also acetate are suitable electron donors. Fe(II)EDTA can serve as electron donor for the biological reduction of nitrate to nitrite, with the concomitant oxidation of Fe(II)EDTA to Fe(III)EDTA. Moreover, Fe(II)EDTA can also serve as electron donor for the chemical reduction of nitrite to NO, with the concomitant formation of the nitrosyl‐complex Fe(II)EDTA–NO. The reduction of NO in Fe(II)EDTA was found to be catalysed biologically and occurred about three times faster at 55 °C than NO reduction at 30 °C. This study showed that the nitrogen and iron cycles are strongly coupled and that FeEDTA has an electron‐mediating role during the subsequent reduction of nitrate, nitrite, nitric oxide and nitrous oxide to dinitrogen gas. Copyright © 2004 Society of Chemical Industry     

Removal of NOx from wet flue gas by corona discharge

This paper researches on the reduction of NO_x (DeNO_x) from wet flue gas by a DC corona radical shower system. The experimental results show that the water vapor in the flue gas not only reduces the corona but also reduces the discharge current. The DeNO_x efficiency and the quantity of NO_x removal per unit energy can be enhanced by raising the concentration of water vapor in the flue gas properly and the maximum quantity of NO_x removal per unit energy is more than 25.5 g as the humidity of the flue gas ranges from 10 to 12%. The longer the flue gas resides in the reactor, the higher the DeNO_x efficiency is and the lesser NO_x will be reduced by per unit power.     

Simultanabsorption von schwefeldioxid und stickstoffmonoxid in wässrigen Lösungen von eisenchelat-komplexenSimultaneous absorption of sulfur dioxide and nitrogen monoxide in aqueous solutions of iron chelate complexes

Since about ten years — especially in Japan — processes for simultaneous wet removal of SO₂ and NO_x from waste gases of power plants and industrial combustions are in development or even in practice. During the absorption of SO₂ in alkaline solutions sulfite ions are formed which can be used for NO_x reduction. Whereas nitrogen dioxide is chemisorbed in appreciable amounts, nitrogen monoxide is merely physically absorbed in low quantities. To enhance the effectiveness of NO absorption, chelate complexes are added to the absorbent. The present work gives a survey on the chemistry of this simultaneous NO/SO₂ process of the absorption/reduction type. The experiments were performed in a laboratory setup with a jet tube reactor characterised by a large gas/liquid interfacial area. The main parameters influencing the NO/SO₂ absorption in Fe(II)EDTA-containing solutions were studied.     

Nitrosylmetallochelates—III. Rotating ring disk electrode study of redox reaction of Fe(II)EDTA with NO−2

The oxidation process of the nitrosyliron(II)EDTA complex which was produced by the reaction of Fe(II)EDTA and NO^?₂ has been studied by the rotating disk electrode and the spectroscopic methods. The oxidation of Fe(II)(NO)_xEDTA proceeds via two steps occurring at different potentials. The first step is the oxidation of Fe(II)EDTA to Fe(III)EDTA which is limited by the rate of chemical reaction, and the second is oxidation of NO to NO^?₃ which corresponds to surface controlled process. This result suggests the possibility that the noxious species can be transferred to the innocuous ion.     

Removal of so x and NO x from flue gas with ceria

Ceria (CeO₂) is considered as one of materials for the simultaneous removal of SO_x and NO_x from flue gas. Ceria was coated on honeycomb and tested for adsorption of SO₂ and reduction of NO with ammonia. Experimental results showed the characteristics similar to copper oxide but reactivity for NO reduction was higher in broader temperature range compared with the latter.     

Experimental study of the influence of sodium salts as additive to NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>OUT process

An experimental study of the SNCR process with urea as reducing agent and sodium salts as additive has been carried out, and detailed analysis of the reaction mechanism has been given here. In the temperature range of 800–975 °C, NO concentration decreases at first and then increases while the concentration of N₂O increases at first and then decreases with the increasing of temperature, and the turning point is 900 °C. With increasing of normalized stoichiometric ratio of reduction nitrogen to NO _x (NSR), NO removal efficiency increases, while the concentration of N₂O also increases, which decreases overall NO _x removal efficiency. With sodium salts as additive, the concentration of N₂O decreases with increasing of sodium salts addition at all temperatures, while the concentration of NO decreases at first and then increases at low-temperature side of the temperature window and increases at high-temperature side with additional increasing, whose changing extent is smaller than N₂O. Since sodium salts as additive can remove N₂O effectively and have no large influence on the removal of NO, the effect of sodium salts as additive is the combined effect of the production of active radicals and the removal of HNCO produced by the decomposition of urea through neutralization reactions, which is more important. To achieve the same effect under each condition, the needed addition of NaOH and CH₃COONa is less than that of Na₂CO₃ counting as Na atom. For the decomposition of CH₃COONa can produce CH₃COO, its addition can promote the reduction of NO more obviously at the lower temperature than Na₂CO₃ or NaOH. Overall NO _x removal efficiency at 900 ‡C with NSR=1.5 had been improved from about 30% to 70.45% through the addition of sodium salts. Sodium salts as additive caused the flue gas to become alkaline gas, but it was not serious for sodium salts existing as NaNCO.     

Removal of NOx with radical injection caused by corona discharge

Removal of NO_x (namely DeNO_x) from simulated flue gas with direct current (d.c.) corona radical shower system was investigated. Steady streamer coronas occur when the flow rates of the fed gases are adjusted properly. The experimental results show that both the composition and the flow rate of the gas fed into the nozzles influence the V-I characteristic of corona discharge. The vapor in the flue gas restrains the discharge, reduces the discharge current, but enhances the DeNO_x efficiency. Furthermore, removal of NO_x from flue gas by radical injection associated with alkali solution (26% by weight of NaOH in water) scrubbing was carried out. Oxygen together with water vapor is fed into the nozzle electrode and the oxygen and water molecules are decomposed in the corona zone. It is found that NO and NO₂ can be converted into HNO₂ and HNO₃, respectively, by radicals formed during the discharge process and the conversion efficiency of NO_x in the plasma reactor is more than 60%. The overall DeNO_x efficiency of the system reaches 81.7% after the flue gas was scrubbed by the NaOH solution.     

Removal of nitric oxide and sulfur dioxide from flue gases using a FeII-ethylenediamineteraacetate solution

The combined absorption of NO and SO₂ into the Fe(II)-ethylenediamineteraacetate(EDTA) solution has been realized. Activated carbon is used to catalyze the reduction of Fe^III-EDTA to Fe^II-EDTA to maintain the ability to remove NO with the Fe-EDTA solution. The reductant is the sulfite/bisulfite ions produced by SO₂ dissolved into the aqueous solution. Experiments have been performed to determine the effects of activated carbon of coconut shell, pH value, temperature of absorption and regeneration, O₂ partial pressure, sulfite/bisulfite and chloride concentration on the combined elimination of NO and SO₂ with Fe^II-EDTA solution coupled with the Fe^II-EDTA regeneration catalyzed by activated carbon. The experimental results indicate that NO removal efficiency increases with activated carbon mass. There is an optimum pH of 7.5 for this process. The NO removal efficiency increases with the liquid flow rate but it is not necessary to increase the liquid flow rate beyond 25 ml min^?1. The NO removal efficiency decreases with the absorption temperature as the temperature is over 35 °C. The Fe²⁺ regeneration rate may be speeded up with temperature. The NO removal efficiency decreases with O₂ partial pressure in the gas streams. The NO removal efficiency is enhanced with the sulfite/bisulfite concentration. Chloride does not affect the NO removal. Ca(OH)₂ and MgO slurries have little influence on NO removal. High NO and SO₂ removal efficiencies can be maintained at a high level for a long period of time with this heterogeneous catalytic process.     

UV/H2O2氧化联合Ca(OH)2吸收同时脱硫脱硝

在小型紫外光-鼓泡床反应器中,对UV/H₂O₂氧化联合Ca(OH)₂吸收同时脱除燃煤烟气中NO与SO₂的主要影响因素[H₂O₂浓度、紫外光辐射强度、Ca(OH)₂浓度、NO浓度、溶液温度、烟气流量以及SO₂浓度]进行了考察。采用烟气分析仪和离子色谱仪分别对尾气中的NO₂和液相阴离子作了检测分析。结果显示:在本文所有实验条件下,SO₂均能实现完全脱除。随着H₂O₂浓度、紫外光辐射强度和Ca(OH)₂浓度的增加,NO的脱除效率均呈现先大幅度增加后轻微变化的趋势。NO脱除效率随烟气流量和NO浓度的增加均有大幅度下降。随着溶液温度和SO₂浓度的增加,NO脱除效率仅有微小的下降。离子色谱分析表明,反应产物主要是SO₄^2-和NO₃^-,同时有少量的NO₂^-产生。尾气中未能检测到有害气体NO₂。     

Nitric oxide enhanced reduction in a rotating drum biofilter coupled with absorption by FeII(EDTA)

BACKGROUND: The ongoing emission of nitric oxide (NO) is a serious persistent environmental problem, because it contributes to atmospheric ozone destruction and global warming. A novel and effective system was developed for the complete treatment of NO from flue gases. The system features NO absorption by Fe^II(EDTA) and biological denitrification in a rotating drum biofilter (RDB). RESULTS: After 100 mg L^?1 Fe^II(EDTA) was added to the nutrient solution, the results show that the NO removal efficiency was improved from 70.56% to 80.15%, the optimal temperature improved from 32.5 °C to 40.5 °C, and the pH improved from 7.5 to 8.0–8.3. A maximum NO removal efficiency of 96.5% was achieved when 500 mg L^?1 Fe^II(EDTA) was used in the nutrient solution. CONCLUSION: This experiment demonstrates that Fe^II(EDTA) could not only improve the mass transfer efficiency of NO from gas to liquid, but also serve as an electron donor for the biological reduction of NO to N₂. The new integrated treatment system seemed to be a promising alternative for the complete treatment of NO from flue gases. © 2012 Society of Chemical Industry     

NOx Abatement by Catalytic Traps: On the Mechanism of NOx Trapping Under Automotive Conditions

NO _x adsorption was measured with a barium based NO_x storage catalyst at an engine bench equipped with a lean burn gasoline direct injection engine (GDI). In order to study the influence of gas phase NO₂ on the NO_x storage efficiency two different pre-catalysts were used: One with excellent NO oxidation activity to produce a high NO₂ concentration and another pre-catalyst without NO oxidation activity and therefore high NO concentration at the NO _x storage catalyst inlet. Both pre-catalyst had excellent HC and CO conversion efficiency and therefore the CO and HC concentration at the NO _x storage catalyst inlet was practically zero. No lean NO _x reduction was observed. Under that conditions, experiments with NO _x storage catalysts of different length show that a high NO₂ inlet concentration did not enhance the NO _x storage efficiency. Moreover, we observed reduction of NO₂ to NO over the NO_x storage catalyst. However, in presence of a high NO inlet concentration NO₂ formation was observed which may proceed parallel to NO _x storage.     

A sustainable mediated electrochemical process for the abatement of NOx from simulated flue gas by using Ag(I)/Ag(II) redox mediators

Electrochemical removal of NO and NO₂ by using Ag(I)/Ag(II) redox mediator system in nitric acid medium by two-stage scrubbing process was investigated. Experiments were carried out for the complete removal of NO and NO₂ from the stimulated flue gas at room temperature and atmospheric pressure. The process parameters like current density, Ag(I) concentration, HNO₃ concentration, initial concentration of NO, Ag(I) concentration and temperature were studied and optimized. A removal efficiency of >99% was achieved using this sustainable redox process. Ag(II)/Ag(I) can be regenerated and reused for the scrubbing of waste gases continuously and there is no other gases emission during scrubbing.     

A novel continuous reactor for catalytic reduction of NOx—fixed bed simulations

A novel dual‐zone fluidized bed reactor was proposed for the continuous adsorption and reduction of NO_x from combustion flue gases. The adsorption and reaction behaviour of such a reactor has been simulated in a fixed bed reactor using Fe/ZSM‐5 catalyst and propylene reductant with model flue gases. Fe/ZSM‐5 exhibited acceptable activity at T = 350°C and GHSV = 5000 h^?1 when O₂ concentration was controlled at levels lower than 1% with a HC to NO molar ratio of about 2:1. XPS and BET surface area measurement revealed the nature of the deactivation of the catalyst. Those performance data demonstrated the feasibility of a continuous dual‐zone fluidized bed reactor for catalytic reduction of NO_x under lean operating conditions.     

Simultaneous removal of SO2, NO and particulate by pilot-scale scrubber system

SO _x and NO _x have both previously been identified as primary precursors of acid rain, and thus the abatement of SO _x and NO _x emissions constitutes a major target in the field of air pollution control. In this study, the efficacy of a pilot-scale scrubber was evaluated with regard to the simultaneous removal of SO₂, NO and particulate with wet catalysts. The removal efficiencies of particulate were measured to be 83, 92 and 97% with catalyst flux of 0.5, 0.8 and 1.5 L/min, respectively. The average removal efficiencies of particulate with different nozzles were approximately 94 and 90% with FF6.5 (5/8 in.) and 14 W (1.0 in.) nozzles, respectively. At least 96–98% of particulate and SO₂ were removed, regardless of the stage number of reactor. In a one-stage scrubber, 83.3% removal efficiency of NO was achieved after 48 hours; however, the two-stage scrubber achieved an NO removal efficiency of 95.7%. Regardless of the liquid-gas ratio, SO₂ and particulate were removed effectively, whereas NO was removed about 84% and 74% under liquid-gas ratio conditions of 39.32 L/m³ and 27.52 L/m³, respectively. In experiments using STS and P.P. pall ring as packing material, particulate and SO₂ removal efficiency values in excess of 98% were achieved; however, NO removal was correlated with the different packing materials tested in this study. With the above optimum operation conditions, even after 20 hours, the removal efficiency for NO stayed at 95% or higher, the removal efficiency for SO₂ stayed at 97% or higher, and the removal efficiency for particulate stayed at 92% or higher. In accordance, then, with the above results, it appears that this process might be utilized in scrubber systems, as well as systems designed to simultaneously remove particulate, SO₂ and NO from flue gas.     

IR and UV gas absorption measurements during NOx reduction on an industrial natural gas fired power plant

NO_x reduction of flue gas by plasma-generated ozone was investigated in pilot test experiments on an industrial power plant running on natural gas. Reduction rates higher than 95% have been achieved for a molar ratio O₃:NO_x slightly below two. Fourier transform infrared and ultraviolet absorption spectroscopy were used for spatial measurements of stable molecules and radicals along the reduction reactor. Reactions of O₃ injected in the flue gas in the reduction reactor were also modeled. Experiments are in good agreement with numerical simulations. The operation costs for NO_x reduction were estimated based on field tests measurements.     

介质阻挡放电中气体成分对NOx脱除的影响

利用介质阻挡放电(DBD)产生低温等离子体进行烟气的脱硝实验,研究了在乙烯存在的条件下,温度和其他烟气成分对NO_x脱除率的影响。结果表明:随着温度的升高,NO脱除速率增快;模拟烟气中加入CO₂,在能量密度较低时,CO₂作为电负性分子会降低自由基的生成,导致NO的脱除率降低,随着能量密度的升高,CO₂对NO脱除的影响减小;模拟烟气中加入水后可以产生更多的OH、HO₂等自由基,促进NO的氧化;SO₂的加入会与自由基O反应,使初始反应中O与C₂H₄的反应速率减弱,从而影响了NO的氧化速率,但O₃、HO₂等强氧化自由基会优先与NO反应,因此SO₂的加入不会影响NO最终的脱除率。     

Simultaneous Removal of NOx and SOx from Flue Gas of a Glass Melting Furnace using a Combined Ozone Injection and Semi-dry Chemical Process

In this study, we propose a plasma-chemical hybrid NO_x removal process using nonthermal plasma for the treatment of flue gases emitted from glass melting furnaces; the process is demonstrated through a laboratory-scale model experiment conducted using a semi-dry desulfurization apparatus. The performance of the system for simultaneous removal of SO₂ and NO_x is investigated. As a result, NO is effectively oxidized to NO₂ by injecting ozone into the spray region and the removal efficiencies of 90% and 50% were obtained for NO and NO_x, respectively. In addition, the SO₂ removal efficiency of 84% was achieved.     

Simultaneous removal of SO2 and NO by low cost sorbent-catalysts prepared by lime, fly ash and industrial waste materials

The potential of the sorbent-catalysts prepared from three low cost materials, i.e., the lime, fly ash and some industrial waste material containing iron oxide, have been investigated for simultaneous removal of SO₂ and NO _x from flue gas in the temperature range 700–850 °C. NH₃ was chosen as the reducing agent for NO reduction in this study. Experimental results showed that SO₂ and NO could be simultaneously removed efficiently in the absence of O₂ at the temperature window of 700–800 °C. The effect of product layer generated from SO₂ removal on NO removal was not obvious. NO removal efficiency was strongly inhibited by O₂, which was attributed to the partial oxidation of NH₃ to NO over the sorbent-catalysts in the presence of oxygen. Neither NO₂ nor N₂O by-product was detected both in the absence and presence of O₂. Three routes were suggested to overcome the negative effect of O₂. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

Microwave catalytic NOx and SO2 removal using FeCu/zeolite as catalyst

Non-thermal plasma technology is a promising process for flue gas treatment. Microwave catalytic NO_x and SO₂ removal simultaneously has been investigated using FeCu/zeolite as catalyst. The experimental results showed that a microwave reactor with FeCu/zeolite only could be used to microwave catalytic oxidative 91.7% NO_x to nitrates and 79.6% SO₂ to sulfate; the reaction efficiencies of microwave catalytic reduction of NO_x and SO₂ in a microwave reactor with FeCu/zeolite and ammonium bicarbonate (NH₄HCO₃) as a reducing agent could be up to 95.8% and 93.4% respectively. Microwave irradiation accentuates catalytic reduction of SO₂ and NO_x treatment, and microwave addition can increases SO₂ removal efficiency from 14.5% to 18.7%, and NO_x removal efficiency from 13.4% to 18.7%, separately. FeCu/zeolite catalyst was characterized by X-ray diffraction (XRD), X-ray photoelectron spectrum analysis (XPS), scanning electron microscopy (SEM) and the Brunauer Emmett Teller (BET) method. Microwave catalytic NO_x and SO₂ removal follows Langmuir-Hinshelwood (L-H) kinetics.