Nitric oxide removal by combined urea and FeIIEDTA reaction systems

Reaction Mechanism for the Removal of NOx by Wet Scrubbing Using Urea Solution: Determination of Main and Side Reaction Paths

Secondary problems, such as the occurrence of side reactions and the accumulation of by-products, are a major challenge in the application of wet denitrification technology through urea solution. We revealed the formation mechanism of urea nitrate and clarified the main and side reaction paths and key intermediates of denitrification. Urea nitrate would be separated from urea absorption solution only when the concentration product of [urea], [H⁺] and [NO₃^-] was greater than 0.87~1.22 mol³/L³. The effects of the urea concentration (5-20%) and reaction temperature (30-70 °C) on the denitrification efficiency could be ignored. Improving the oxidation degree of the flue gas promoted the removal of nitrogen oxides. The alkaline condition was beneficial to the dissolution process, while the acidic condition was beneficial to the reaction process. As a whole, the alkaline condition was the preferred process parameter. The research results could guide the optimization of process conditions in theory, improve the operation efficiency of the denitrification reactor and avoid the occurrence of side reactions.

Sustainable NO removal and its sensitive monitoring at room temperature by electrogenerated Ni (I) electron mediator

Online monitoring of gas pollutants in the gas phase at room temperature using an electrochemical macro gas flow sensor is challenging and important for the pollutant treatment process. In this work, for the first time, we tried to explore the homogeneous and heterogeneous application of Ni(II) (CN)₄^2- in the KOH environment for the removal and monitoring of toxic nitric oxide gas. The homogeneous electrogenerated Ni(I) (CN)₄^3- was effectively removing the toxic nitric oxide gas by electro scrubbing method and the novel Ni(II) (CN)₄^2- and KOH modified electrode used for heterogeneous sensor application with high sensitivity, and reliability toward Nitric oxide gas. The sensor showed enhanced gas diffusion and high sensitivity. Scanning electron microscopy and X-ray diffraction confirmed the modification of the carbon felt electrode. In a high concentrated KOH environment, the active mediator stabilized the sensor for a long time compared to the neutral environment. The Ni(II) (CN)₄^2- fabricated carbon felt was used to monitor the concentration of nitric oxide gas pollutant; the calculated sensitivity was approximately -0.33 mA ppm^-1 cm^-2. The current increased linearly with increasing nitric oxide concentration up to 12 ppm and was validated by online gas chromatography. The developed electrochemical gas flow sensor successfully monitored the unremoved nitric oxide gas at the exit from the MER electro-scrubbing process; the concentration was calculated using a calibration plot.

Highly efficient absorption of nitric oxide by RuIII(edta) aqueous solutions at low concentrations

In this paper, Ru^III(edta) was used as a highly efficient absorbent for the removal of NO due to its desirable properties of high NO affinity and oxygen insensitivity. The effects of the Ru^III(edta) concentration, reaction temperature, initial solution pH, oxygen concentration, inlet NO concentration, and liquid-to-gas ratio on denitration performance were examined. The results indicated that Ru^III(edta) showed excellent denitration performance at low concentrations and that an increase in the concentration of Ru^III(edta) resulted in an increase in NO removal efficiency. In addition, NO removal efficiency increased to its optimum value at first and then declined as both the reaction temperature and initial solution pH rose. The optimal reaction temperature and ideal initial solution pH were determined to be 45°C and 5.0 respectively. The suitable liquid-to-gas ratio was found to be 51.5 L/m³. NO removal efficiency was less affected by the oxygen concentration in the range of 0-12% due to a superior anti-oxidation performance at pH = 5.0. Furthermore, the NO removal efficiency decreased significantly as the inlet NO concentration increased. The addition of 5 wt% urea to an aqueous solution of Ru^III(edta) enhanced denitration performance, and an Ru^III(edta) and urea mixed solution were able to exceed 65.07% NO removal efficiency within 30 min under optimal experimental conditions. This work proposed an alternative absorbent for NO removal and provided fundamental data for industrial denitration with Ru^III(edta) absorbents.

Theoretical study on simultaneous removal of SO2, NO, and Hg0 over graphene: competitive adsorption and adsorption type change

In this work, the influence of competitive adsorption and the change of charge transfer for simultaneous adsorption removal of SO₂, NO, and Hg⁰ over graphene were investigated using density functional theory method. The results showed that all the adsorptive effect of SO₂, NO, and Hg⁰ were caused by physical interaction. The adsorptive energy of SO₂ was the highest, and the adsorptive energy of Hg⁰ was the lowest. SO₂ could be preferentially adsorbed and removed. NO/SO₂ and Hg⁰ had the mutual promotion effect for simultaneous adsorption over graphene surface. SO₂ and NO had the mutual inhibition effect for simultaneous adsorption over graphene surface. Compared with single molecular adsorption, the adsorption type of bi-molecular adsorption did not change. However, the simultaneous adsorption changed the adsorption type of Hg⁰ + SO₂ + NO to chemical adsorption due to the interaction among Hg⁰, SO₂, and NO. As such, this study provides a theoretical insight for future application and development. Graphical abstractNO/SO₂ and Hg⁰ had the mutual promotion effect for simultaneous adsorption. SO₂ and NO had the mutual inhibition effect for simultaneous adsorption.

Simultaneous removal of SO2 and NOx from flue gas by wet scrubbing using a urea solution

Nitrogen oxides (NO_x) and sulfur dioxide (SO₂) are major air pollutants, so simultaneously removing them from gases emitted during fossil fuel combustion in stationary systems is important. Wet denitrification using urea is used for a wide range of systems. Additives have strong effects on wet denitrification using urea, and different mechanisms are involved and different effects found using different additives. In this study, the effects of different additives, initial urea concentrations, reaction temperatures, initial pH values, gas flow rates, and reaction times on the simultaneous desulfurization and denitrification efficiencies achieved using wet denitrification using urea were studied in single factor experiment. The optimum reaction conditions for desulfurization and denitrification were found. Desulfurization and denitrification efficiencies of 97.5% and 96.3%, respectively, were achieved at a KMnO₄ concentration 5 mmol/L, a reaction temperature of 70°C, initial urea solution pH 8, a urea concentration of 9%, and a gas flow rate of 40 L/h. The concentrations of the desulfurization and denitrification reaction products in the solution were determined. NO_x was mainly transformed into N₂, and the NO3- and NO2- concentrations in the solution became very low. The reactions involved in SO₂ and NO_x removal using urea were analyzed from the thermodynamic viewpoint. Increasing the temperature was not conducive to the reactions but increased the rate constant, so an optimum temperature was determined. The simultaneous desulfurization and denitrification kinetics were calculated. The urea consumption and NO2- , NO3- , and SO42- generation reactions were all zero order. The NO3- generation rate was greater than the NO2- generation rate. The simultaneous desulfurization and denitrification process and mechanism were studied. The results provide reference data for performing flue gas desulfurization and denitrification in factories.

Use of cobalt(II) chelates of monothiol-containing ligands for the removal of nitric oxide

It is first reported herein that cobalt(II) complexes solution of monothiol-containing multidentate ligands are used to remove low concentration of nitric oxide (NO). These chelating ligands are water-soluble amines, alcohols or acids which containing at least one -SH group, include those of cysteine, mercaptosuccinic acid, mercaptoethanesulfonate, mercaptopropionic acid and the like. These -SH compounds when coordinated with cobalt ions, forming complexes are very effective for NO removal. The results indicate that the side group (methyl, carboxyl, carboxymethyl) on α-carbon atom of ligands contribute to the denitration of the chelate solution, whereas the substituents on sulfur atom of ligands deactivate the complexation system. In addition, we have found that several monothiol compounds with simple molecule structure and low cost exhibit good performance in denitration, and some of cobalt thiol complexes are more valuable in removing NO than ferrous thiol complexes.

NO Removal with Efficient Recovery of N2O by Using Recyclable Fe3O4@EDTA@Fe(II) Complex: A Novel Approach toward Resource Recovery from Flue Gas

Traditional technologies for handling nitrogen oxides (NO _x) from flue gas commonly entail the formation of harmless nitrogen gas (N₂), while less effort has been made to recover the N-containing chemicals produced. In this work, we developed a novel nanomagnetic adsorbent, Fe₃O₄@EDTA@Fe(II) (MEFe(II)), for NO removal. The NO adsorbed by MEFe(II) was then selectively converted to N₂O, a valuable compound in many industries, by using sulfite (a product from desulfurization in flue gas treatment) as the reductant for the regeneration of MEFe(II). Because of the magnetic and solid properties of MEFe(II), the processes of NO adsorption and N₂O recovery can be readily carried out under their optimal pH conditions in separate systems. In addition, the produced N₂O is easily handled without unwanted release to the atmosphere. At the optimal pH (7.5 and 8.0 for NO adsorption and N₂O recovery, respectively), the maximum NO adsorption capacity of MEFe(II) was measured as 0.303 ± 0.037 mmol·g^-1, over 90% of which was converted to N₂O during the recovery process. Moreover, MEFe(II) exhibited good five consecutive cycles. All of above reactions were performed at room temperature. These findings indicate MEFe(II) may hold great potential for application to NO removal from flue gas with the benefits of resource recovery, decreased chemical use, and low energy consumption.

Evaluation of Fe(iii)EDTA reduction with ascorbic acid in a wet denitrification system

The reduction of Fe(iii)EDTA to Fe(ii)EDTA is the core process in a wet flue gas system with simultaneous desulfurization and denitrification. Herein, at first, the reductant ascorbic acid (VC) was used for reducing Fe(iii)EDTA. The feasibility of Fe(iii)EDTA reduction with ascorbic acid was investigated at different Fe(iii)EDTA concentrations, various pH values, diverse temperatures, and different molar ratios of VC to Fe(iii)EDTA. The results showed that the Fe(ii)EDTA concentration increased with an increase in the initial Fe(iii)EDTA concentration. Furthermore, the reduction efficiency increased as the mole ratio of VC to Fe(iii)EDTA was increased, and all the Fe(iii)EDTA reduction efficiencies were close to 100% when the mole ratio was more than 0.5. On the other hand, an alkaline environment did not favor the conversion of Fe(iii)EDTA by VC. The Fe(iii)EDTA conversion slightly increased as the temperature was increased. Moreover, compared with other reduction systems, ascorbic acid (VC) was found to be more powerful in reducing Fe(iii)EDTA, especially in air. In addition, VC only exhibited powerful ability in the conversion of Fe(iii)EDTA to Fe(ii)EDTA and hardly reduced Fe(ii)EDTA–NO. Finally, the stoichiometry of Fe(iii)EDTA reduction by ascorbic acid was derived. Thus, our study would offer a bridge between foundational research and industrial denitration using the combination of Fe(ii)EDTA and VC.

Color change during Fe(iii)EDTA reduction by VC ((A) Fe(iii)EDTA color; (B) color of Fe(iii)EDTA solution after reduction by VC; (C) Fe(ii)EDTA-NO color; (D) color of Fe(ii)EDTA-NO solution after reduction by VC).

Fe containing MoO3 nanowires grown along the [110] direction and their fast selective adsorption of quasi-phenothiazine dyes

Herein, MoO₃ nanowires (Fe–MoO₃ NWs) along the [110] direction were successfully synthesized in the presence of Fe³⁺ cations.

The inhibition effect and deactivation mechanism of H2O and SO2 on selective catalytic oxidation of NO over the Mn–Ca–Ox–(CO3)y catalyst

H₂O and SO₂ had an inhibition effect on NO oxidation. SO₂ increased the particle size of the catalyst. H₂O decreased the particle size of the catalyst.

Simultaneous absorption of NO and SO2 by combined urea and FeIIEDTA reaction systems

SO₂ and NO emitted from coal-fired power plants have caused serious air pollution in China. In this work, a novel mixed absorbent, Fe^IIEDTA/urea, was employed for simultaneous removal of SO₂ and NO in a packed tower, with a corresponding optimal ratio of 0.014 mol L⁻¹ : 5%. The effects of various factors, such as mixed absorbent constitutions, reaction temperature, pH, O₂ concentration, as well as concentrations of SO₂ and NO, on simultaneous removal were investigated. The desulfurization efficiency was 95–99% in all tests, whereas denitrification was affected significantly by various conditions. NO removal efficiency decreased increasing oxygen concentration as well as increasing NO concentration. With an increase in temperature, pH, or SO₂ concentration, NO removal efficiency increased first and then decreased. Under optimal conditions, SO₂ removal efficiency was 100% and NO removal efficiency could exceed 91% within 80 min. The reaction mechanism was speculated according to relevant literature.

SO₂ and NO emitted from coal-fired power plants have caused serious air pollution in China.

Oxidation Removal of Nitric Oxide from Flue Gas Using UV Photolysis of Aqueous Hypochlorite

The oxidation removal of nitric oxide (NO) from flue gas using UV photolysis of aqueous hypochlorite (Ca(ClO)₂ and NaClO) in a photochemical spraying reactor was studied. The key parameters (e.g., light intensity, hypochlorite concentration, solution temperature, solution pH, and concentration of NO, SO₂, O₂, and CO₂), mechanism and kinetics of NO oxidation removal were investigated. The results demonstrate that UV and hypochlorite have a significant synergistic role for promoting the production of hydroxyl radicals (·OH) and enhancing NO removal. NO removal was enhanced with the increase of light intensity, hypochlorite concentration, or O₂ concentration but was inhibited with the increase of NO or CO₂ concentration. Solution temperature, solution pH, and SO₂ concentration have double the effect on NO removal. NO is oxidized by ·OH and hypochlorite, and ·OH plays a key role in NO oxidation removal. The rate equation and kinetic parameters of NO oxidation removal were also obtained, which can provide an important theoretical basis for studying the numerical simulation of NO absorption process and the amplification design of the reactor.