Applied Kinetics Aspects of Ferric EDTA Complex Reduction with Metal Powder

Postsynthetic Modification of Amine-Functionalized MIL-101(Cr) Metal-Organic Frameworks with an EDTA-Zn(II) Complex as an Effective Heterogeneous Catalyst for Hantzsch Synthesis of Polyhydroquinolines

The present work aims at preparing the EDTA-Zn(II) complex-supported on the amine-functionalized MIL-101(Cr) MOF-as a new and effective heterogenized catalyst. The optimization of the hydrothermal process shows that 120 °C is the best condition to grow the MIL-101(Cr)-NH2 MOF crystals. Moreover, regarding the use of the postsynthetic modification (PSM) method, hexadentate EDTA was grafted on this support via a simple aminolysis process before further coordinating it with Zn ions to create the corresponding Zn(II) catalytic complex. The catalytic activity of this compound was then investigated in the context of a one-pot synthesis of polyhydroquinolines. This approach has a number of advantages including the following: the use of a solvent that is not hazardous, applying a porous catalyst that is inexpensive, secure, and recyclable; rapid reaction times, high levels of efficiency, and the simplicity of MOF catalyst separation. Accordingly, the process in question can be given the label of "green chemistry".

Purification Technologies for NOx Removal from Flue Gas: A Review

Nitrogen oxide (NOx) is a major gaseous pollutant in flue gases from power plants, industrial processes, and waste incineration that can have adverse impacts on the environment and human health. Many denitrification (de-NOx) technologies have been developed to reduce NOx emissions in the past several decades. This paper provides a review of the recent literature on NOx post-combustion purification methods with different reagents. From the perspective of changes in the valence of nitrogen (N), purification technologies against NOx in flue gas are classified into three approaches: oxidation, reduction, and adsorption/absorption. The removal processes, mechanisms, and influencing factors of each method are systematically reviewed. In addition, the main challenges and potential breakthroughs of each method are discussed in detail and possible directions for future research activities are proposed. This review provides a fundamental and systematic understanding of the mechanisms of denitrification from flue gas and can help researchers select high-performance and cost-effective methods.

Study on NO Removal Characteristics of the Fe(II)EDTA and Fe(II)PBTCA Composite System

Fe²⁺ complexation wet denitrification technology has become a research hotspot. It is very important to achieve efficient regeneration of the absorbent and increase NO absorption in the Fe²⁺ complexation system. They are the key to the industrial application of the Fe²⁺ complexation absorption process. In this paper, 2-phosphonate-butane-1,2,4-tricarboxylic acid and ethylenediamine tetraacetic acid were used as ligands to prepare a composite system for the first time. The characteristics of NO removal were investigated under different temperatures, pHs, Fe²⁺ concentrations, O₂ contents, NO concentrations, CO₂ contents, and SO₂ concentrations. Compared with the single ligand, the results show that the denitrification performance of the solution with a complex ligand is significantly improved. In this system, pH 9, 40 °C temperature, and 20 mmol/L Fe²⁺ concentration are the economic ideal conditions for NO removal. The system can realize simultaneous removal of NO and SO₂, but SO₂ in flue gas has a dual effect on the NO removal reaction.

Simultaneous removal of NOX and SO2 from flue gas in an integrated FGD-CABR system by sulfur cycling-mediated Fe(II)EDTA regeneration

Chemical absorption-biological reduction (CABR) process is an attractive method for NO_X removal and Fe(II)EDTA regeneration is important to sustain high NO_X removal. In this study a sustainable and eco-friendly sulfur cycling-mediated Fe(II)EDTA regeneration method was incorporated in the integrated biological flue gas desulfurization (FGD)-CABR system. Here, we investigated the NO_X and SO₂ removal efficiency of the system under three different flue gas flows (100 mL/min, 500 mL/min, and 1000 mL/min) and evaluated the feasibility of chemical Fe(III)EDTA reduction by sulfide in series of batch tests. Our results showed that complete SO₂ removal was achieved at all the tested scenarios with sulfide, thiosulfate and S⁰ accumulation in the solution. Meanwhile, the total removal efficiency of NO_X achieved ∼100% in the system, of which 3.2%-23.3% was removed in spray scrubber and 76.7%-96.5% in EGSB reactor along with no N₂O emission. The optimal pH and S^2-/Fe(III)EDTA for Fe(II)EDTA regeneration and S⁰ recovery was 8.0 and 1:2. The microbial community analysis results showed that the cooperation of heterotrophic denitrifier (Saprospiraceae_uncultured and Dechloromonas) and iron-reducing bacteria (Klebsiella and Petrimonas) in EGSB reactor and sulfide-oxidizing, nitrate-reducing bacteria (Azoarcus and Pseudarcobacter) in spray scrubber contributed to the efficient removal of NO_X in flue gas.

Nitrogen oxide gas purification using carbon in water as reducing reagent with the aid of microbial fuel cell

Microbial Fuel Cell (MFC) can degrade the organic matter (OM) in wastewater at the anode and transfer electrons to the cathode. In this work, the harmful NO_X gas was used as electron acceptor in MFC and converted to harmless N₂. The OM in water was indirectly used as a zero-cost reducing agent for NOx removal. More than 80% of NO_X was removed continuously by MFC at room temperature. The NO_X was directly reduced to N₂ at MFC cathode and the cathode activity played a key role on enhancing the NO_X removal. The NO_X removal efficiency by the cathode of high potential was 1.37 times that by the cathode of low potential. When O₂ coexisting with NO as the electron acceptor, not only the NO_X removal but also the power output of MFC was improved greatly. The presence of NO_X did not decrease the power generation of MFC under the same O₂ concentration. The MFCs showed good stability for NO_X treatment and power output. Moreover, the possible pathways and advantages of NO_X removal by MFC were discussed in detail. These results indicated that the MFC system has the potential to treat wastewater, purify flue gas and recover energy simultaneously.

A novel method of pH-buffered NaClO2-NaCl system for NO removal from marine diesel engine

Marine diesel engines produce a lot of exhaust gas (NO, SO₂). Based on the situation that wet scrubbing methods have been already applied to ship desulfurization and seawater is easily accessible around the ships, this paper proposed a novel AOP (advanced oxidation process) of NaClO₂ (sodium chlorite) with Cl^- (abundant Cl^- exist in seawater) to remove NO from the flue gases of marine engines. The buffer capacity of NaAC (sodium acetate), the effect of Cl^- concentration, and Cl^- promotion mechanism on NO removal were investigated. The result showed that the existence of NaAC in solution could inhibit the rapid decline of the solution pH. The addition of Cl^- achieved a remarkable promotion to NO removal at lower NaClO₂ concentration, which was due to the fast generation of ClO₂ from the promotion decomposition of NaClO₂ by Cl^- in acidic condition. Then, the thermodynamic and dynamic mechanism of the generation of ClO₂ was intensively analyzed. And the mechanism of NO removal was discussed finally.

Reduction of FeII(EDTA)-NO by Mn powder in wet flue gas denitrification technology: stoichiometry, kinetics, and thermodynamics

Conversion of Fe^II(EDTA)-NO or Fe^III(EDTA) into Fe^II(EDTA) is a key process in a wet flue gas denitrification technology with Fe^II(EDTA) solution. In this work, the stoichiometry, kinetics, and thermodynamics of Fe^II(EDTA)-NO reduction by Mn powder were investigated. We first studied the Fe^II(EDTA)-NO reduction and product distribution to speculate a possible stoichiometry of Fe^II(EDTA)-NO reduction by Mn powder. Then, the effects of major influencing factors, such as pH value, temperature, and Mn concentration, were studied. The pseudo-second-order model was established to describe the Fe^II(EDTA)-NO reduction. Simultaneously, according to Arrhenius and Eyring-Polanyi equations, the reaction activation energy (E_a), enthalpy of activation (∆H^‡), and entropy of activation (∆S^‡) were calculated as 23.68 kJ/mol, 21.148 kJ/mol, and - 149.728 J/(k mol), respectively. Additionally, simultaneous reduction of Fe^III(EDTA) and Fe^II(EDTA)-NO was investigated to better study the mechanism of Fe^II(EDTA) regeneration, suggesting that there was a competition between the two reduction processes. Finally, a simple schematic mechanism of NO absorption by Fe^II(EDTA) combined with regeneration of manganese ion and ammonium was proposed. These fundamental researches could offer a valuable guidance for wet flue gas denitrification technology with Fe^II(EDTA) solution.

Promoting Effect of H+ and Other Factors on NO Removal by Using Acidic NaClO2 Solution

In this study, NaClO2 was selected as a denitration oxidant. In order to clarify the mechanism of NaClO2 as an oxidation agent for NO removal efficiency, the effects of H+ and other factors (NaClO2 concentration, temperature, and the other gas) on the NO removal efficiency were investigated. NaClO2 showed a promotional ability on NO removal, whose efficiency increased with the increase of NaClO2 concentration. One hundred percent removal efficiency of NO could be achieved when the NaClO2 concentration was 0.014 mol/L. Furthermore, raising the reaction temperature benefited the removal of NO. The lower the pH, the better the NO removal efficiency. The promoting effect of H+ on the NO removal was studied by the Nernst equation, ionic polarization, and the generation of ClO2. Under the optimal conditions, the best removal efficiency of NO was 100%. Based on the experimental results, the reaction mechanism was finally speculated.

Simultaneous Biological and Chemical Removal of Sulfate and Fe(II)EDTA-NO in Anaerobic Conditions and Regulation of Sulfate Reduction Products

In the simultaneous flue gas desulfurization and denitrification by biological combined with chelating absorption technology, SO2 and NO are converted into sulfate and Fe(II)EDTA-NO which need to be reduced in biological reactor. Increasing the removal loads of sulfate and Fe(II)EDTA-NO and converting sulfate to elemental sulfur will benefit the application of this process. A moving-bed biofilm reactor was adopted for sulfate and Fe(II)EDTA-NO biological reduction. The removal efficiencies of the sulfate and Fe(II)EDTA-NO were 96% and 92% with the influent loads of 2.88 kg SO42−·m−3·d−1 and 0.48 kg NO·m−3·d−1. The sulfide produced by sulfate reduction could be reduced by increasing the concentrations of Fe(II)EDTA-NO and Fe(III)EDTA. The main reduction products of sulfate and Fe(II)EDTA-NO were elemental sulfur and N2. It was found that the dominant strain of sulfate reducing bacteria in the system was Desulfomicrobium. Pseudomonas, Sulfurovum and Arcobacter were involved in the reduction of Fe(II)EDTA-NO.

The regeneration of Fe-EDTA denitration solutions by nanoscale zero-valent iron

Fe(ii) ethylenediaminetetraacetate (EDTA) chelate solution is generally considered to be an effective nitric oxide (NO) absorbent. However, since the ferrous active site is occupied by nitric oxide and the ferrous chelate is oxidized to ferric chelate by oxygen in air, its absorption capacity will gradually decrease with the NO absorption process. Here, we propose a method for regenerating the NO-attenuated Fe(ii)EDTA solution by adding nanoscale zero-valent iron (NZVI) under three different pH conditions. Furthermore, compared with the commercially available iron powder, NZVI was also found to be effective not only for the regeneration of expired Fe-EDTA solution but also for the reduction of Fe(iii) EDTA solution. According to the results obtained herein, different acidity levels of solution, from weakly acidic to near neutral, are all suitable for the regeneration–absorption process.

NZVI is very effective for the regeneration of the inactive Fe chelate solution in the NO absorption process.

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).

Nitric oxide removal by combined urea and FeIIEDTA reaction systems

(NH₂)₂CO as well as Fe^IIEDTA is an absorbent for simultaneous desulfurization and denitrification. However, they have their own drawbacks, like the oxidation of Fe^IIEDTA and the low solubility of NO in urea solution. To overcome these defects, A mixed absorbent containing both (NH₂)₂CO and Fe^IIEDTA was employed. The effects of various operating parameters (urea and Fe^IIEDTA concentration, temperature, inlet oxygen concentration, pH value) on NO removal were examined in the packed tower. The results indicated that the NO removal efficiency increased with the decrease of oxygen concentration as well as the increase of Fe^IIEDTA concentration. The NO removal efficiency had little change with a range of 25-45 °C, and sharply decreased at the temperature of above 55 °C. The NO removal efficiency initially increases up to the maximum value and then decreases with the increase of pH value as well as the raise of urea concentration. In addition, the synergistic mechanism of (NH₂)₂CO and Fe^IIEDTA on NO removal was investigated. Results showed that urea could react with Fe^IIEDTA-NO to produce Fe^IIEDTA, N₂, and CO₂, and hinder oxidation of Fe^IIEDTA. Finally, to evaluate the effect of SO₃^2- on NO removal, a mixed absorbent containing Fe^IIEDTA, urea, and Na₂SO₃ was employed to absorb NO. The mixed absorbent could maintain more than 78% for 80 min at 25 °C, pH = 7.0, (NH₂)₂CO concentration of 5 wt%, Fe^IIEDTA concentration of 0.02 M, O₂ concentration of 7% (v/v), and Na₂SO₃ concentration of 0.2 M.

Reactivity of nano-size zinc powder in the aqueous solution of [FeIII(edta)(H2O)]. ENVIRONMENTAL TECHNOLOGY 2017;38:103-107. [PMID: 27227652 DOI: 10.1080/09593330.2016.1186745]

Nitrogen mono-oxide and sulfur dioxide can be removed by simultaneous absorption into aqueous mixed solutions of sulfite and [Fe^II(edta)]H₂O)]^2-, ferrous ion coordinated to an anion of ethylene-diaminetetraacetic acid (EDTA or edta). In the industrial system with coexisting oxygen in the gas phase, [Fe^II(edta)](H₂O)]^2- complex is oxidized to [Fe^III(edta)](H₂O)]^- by molecular oxygen. Because the ferric complex has no capability for reaction with NO, the suppression of this undesired oxidation process is a very important technological problem to be overcome. In our preceding work, we discussed the reduction kinetics of ferric ion by metal powder on the basis of the kinetic data regarding the ferric ion reduction in aqueous solutions of [Fe^III(edta)](H₂O)]^- containing aluminum, tin or zinc powders. Zinc powder of normal size was recognized as an effective reducing agent. In the present work, augmentation of reducing capability of zinc powder was examined more. The rate of reduction of nano-size zinc powder was found to be about 11 times higher than that of normal-size zinc one.

Kinetics of FeIIIEDTA complex reduction with iron powder under aerobic conditions

The kinetic model of Fe^IIIEDTA complex reduction with iron powder under aerobic condition is deduced and validated. It was .