A method for regenerating ferrous chelated denitration absorbent by using anode assisted reduction of Fe(III)

Abstract

The application discloses a method for regenerating ferrous complex de-NOx absorbent by anode-assisted reduction of Fe(III), and belongs to the field of industrial flue gas de-NOx. The electrolytic device of the application is a non-uniformly coupled double-chamber electrolytic cell, which is composed of a cathode chamber and an anode chamber, and a cloth is arranged between the two chambers. Fe(III) in the complex absorbent is efficiently reduced by the anode-assisted cathode in the electrolytic cell. When the absorbent loses iron species, reverse electrolysis is performed to supplement the iron species, and a reducing agent is added to the cathode chamber to assist electrochemical reduction. The application is designed by using a large cathode and a small anode and using cloth as a diaphragm, so that the anode provides an acidic environment for the cathode through OER, assists the efficient reduction of Fe(III) in the cathode, and reduces the oxidation of the reduction product Fe(II) by the anode. The cathode area is increased, and more active sites are provided for the reaction. The reverse electrolysis for supplementing the iron species maintains good iron circulation in the system, and ensures the continuous and stable operation of the system.

Description

Technical Field

[0001] This invention belongs to the field of industrial flue gas denitrification, specifically relating to a method for regenerating ferrous complex denitrification absorbent by anodic-assisted reduction of Fe(III). Background Technology

[0002] Nitrogen oxides (NO) X Nitrogen monoxide (NO) is one of the most typical air pollutants, accounting for a significant portion of NO emissions. X Approximately 95% of NOx emissions will cause a series of environmental pollution problems, including acid rain, photochemical smog, and ozone layer depletion. With increasing societal emphasis on environmental protection, the country is taking NOx very seriously. X Increasingly stringent emission standards have been established for emission concentrations. Beijing, Xi'an, and Zhengzhou have set NOx emission standards for... X Emission concentration has dropped to as low as 30 mg / Nm³ 3 Therefore, efficient NO removal has become an urgent problem to be solved in the environmental protection field.

[0003] Currently, the mainstream NO removal technologies are selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). SCR reduces NO to N2 using the synergistic effect of NH3 and the catalyst at a reaction temperature of 300-450℃, but it can only remove NO to a concentration of 100 mg / m³. 3 However, this method suffers from problems such as ammonia slip, catalyst layer wear, and deactivation. The SNCR method uses a reducing agent at 850-1150℃ without a catalyst to remove NO from flue gas. Compared to the SCR method, the SNCR method has the advantages of lower investment and shorter cycle time, but its denitrification efficiency is not high (emission concentration 200 mg / m³). 3 However, it also suffers from the problem of ammonia escape. Complexation absorption utilizes the coordination of transition metals in the complexing agent with NO to increase the solubility of NO in water. Compared to SCR and SNCR methods, NO can be removed up to 10 mg / m³. 3 The reaction can proceed at room temperature. However, during the complexation and absorption of NO, Fe(II) is easily oxidized to Fe(III) by O2 and loses its ability to complex NO. Therefore, achieving the reduction of Fe(III) is key to maintaining an efficient denitrification process. Currently, the main methods for Fe(III) reduction include chemical, biological, catalytic, and electrochemical methods.

[0004] Chemical methods primarily utilize sulfur-containing compounds such as sulfites, bisulfites, sodium dithionite, hydrogen sulfide, reducing metal powders such as iron powder and zinc powder, and organic substances to reduce Fe(III). CN202011458873.9 discloses a method for reducing Fe(III) using reducing agents such as sodium sulfite, sodium sulfide, oxalic acid, and urea. However, chemical methods consume large amounts of reducing agents, and the byproducts are difficult to recover, easily causing secondary pollution. Biological methods utilize denitrifying bacteria to reduce Fe(III), and on this basis, combine it with electrochemical methods to form a biofilm electrode reactor, using electrochemical methods to assist biological methods in enhancing the reduction of Fe(III). CN200710156368.7 discloses a method for reducing Fe(III) using an iron-reducing bacteria electrode, involving the attachment and acclimatization of iron-reducing bacteria on a porous carbon electrode. However, the reducing bacteria have high environmental requirements, long acclimatization periods, and are difficult to cultivate, which limits their widespread application. In addition, catalytic reduction is another method for regenerating Fe(II). It uses sulfites as reducing agents and activated carbon or selenium as catalysts to accelerate the reduction of Fe(III). However, this method suffers from continuous consumption of reducing agents and secondary pollution. Electrochemical reduction utilizes renewable electricity to reduce Fe(III). This process mainly involves donating electrons to Fe(III) at the cathode, offering advantages such as simple process, single reaction product, and low theoretical overpotential. CN201510759472.X and CN201510755953.3 both disclose methods for converting Fe(III) to Fe(II) in a single-chamber electrochemical reactor. However, the reduction product Fe(II) easily diffuses to the anode and is re-oxidized to Fe(III), resulting in low overall Fe(III) reduction efficiency. Furthermore, dual-chamber electrolyzers have also been used for the reduction of Fe(III). These typically utilize membranes to separate the anodic and cathode regions. The membranes effectively prevent the diffusion of Fe(II) to the anode, ensuring the concentration of Fe(II) in the cathode region. However, the presence of the membrane inevitably increases the resistance of the reaction system. Simultaneously, the introduction of membrane devices and membrane fouling caused by metal ions increase investment and operating costs. Moreover, for purely electrochemical systems dominated by electroreduction, the anode is usually used to form a complete electrical circuit, and its value is rarely explored in depth.

[0005] In summary, among existing electrochemical reactors, although single-chamber electrolyzers have a simple structure and low reaction resistance, they reduce the reduction efficiency and current efficiency for the re-oxidation of Fe(II). While double-chamber electrolyzers effectively prevent the diffusion of Fe(II) to the anode and ensure the concentration of Fe(II) in the cathode region, they have higher resistance and the introduction of membrane devices increases investment and operating costs. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method for regenerating ferrous complex denitrification absorbent by anodic-assisted reduction of Fe(III), which solves the problem of easy oxidation of complex denitrification absorbent and achieves efficient reduction of Fe(III).

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a method for regenerating ferrous complex denitrification absorbent by anodic-assisted reduction of Fe(III), using a non-uniformly coupled dual-chamber electrolytic cell as the electrolytic device, the electrolytic device including a cathode chamber and an anode chamber, with a cloth as a diaphragm between the cathode chamber and the anode chamber; the cathode chamber includes a first cathode and a second cathode, and the anode chamber includes an anode;

[0009] The method includes a reduction process and a reverse electrolysis. The reduction process involves using the anode to assist the cathode in reducing the oxidized Fe(III) in the ferrous complex denitrification absorbent in the electrolysis device. The reverse electrolysis involves replenishing the iron species when there is iron loss in the ferrous complex denitrification absorbent, while adding a reducing agent to the cathode chamber to assist electrochemical reduction.

[0010] During the reduction process, the anode is connected to the positive terminal of the power supply, and the first cathode is connected to the negative terminal of the power supply.

[0011] During the reverse electrolysis, the second cathode is connected to the negative terminal of the power supply, and the first cathode is connected to the positive terminal of the power supply.

[0012] This invention comprehensively considers the shortcomings of existing Fe(III) electrochemical reduction reactors and improves upon existing electrochemical reduction devices by designing a non-uniformly coupled dual-chamber electrolytic cell. This utilizes the anode to assist the cathode in the efficient reduction of Fe(III) in the complexed absorbent. Furthermore, in actual industrial denitrification processes, flue gas causes the loss of iron species in the absorbent; therefore, reverse electrolysis is considered to replenish the iron species. To ensure the reduction effect of Fe(III), a small amount of reducing agent is added to the cathode chamber to assist the electrochemical reduction when necessary. The aforementioned anode assistance is based on the pH-dependent behavior of the Fe(III) reduction potential. Specifically, the Fe(III) reduction potential decreases with increasing pH when pH > 6.8 and pH < 3.8, and remains relatively stable within the pH range of 3.8 to 6.8. The higher the Fe(III) reduction potential, the easier the Fe(III) reduction; therefore, acidic conditions are more favorable for Fe(III) reduction than neutral and alkaline conditions. The oxygen evolution reaction (OER) at the anode generates a large number of hydrogen ions, which may provide an acidic environment for the reduction of Fe(III)EDTA in the cathode region. Therefore, using a mature oxygen evolution anode DSA to produce hydrogen ions, and improving the anode potential through a large cathode and small anode design, further ensures hydrogen ion generation while reducing the cost of the DSA anode. A larger cathode area also provides more active sites for the reaction, which is beneficial to improving the reduction effect of Fe(III). In addition, compared with membranes, the thickness or number of layers of cloth can be changed, thus providing flexible and adjustable material permeability, which is a feasible and low-cost strategy more suitable for practical industrial applications. A reasonable design of the number or thickness of cloth layers facilitates the rapid migration of hydrogen ions from the anode to the cathode region; on the other hand, it can slow down the migration rate of Fe(II) to the anode region, ensuring the reduction effect of Fe(III). Reverse electrolysis of the cathode can supplement iron species to achieve good iron circulation in the system. If necessary, the addition of reducing agent in the cathode chamber can further ensure the reduction effect of Fe(III). In this invention, the Fe(II) generation rate is 1.4 times and 6 times that of electrochemical reduction and iron powder reduction in the same device system, respectively, and the reduction efficiency can be maintained at over 90% for 24 hours. Furthermore, the cost of generating 1 mol of Fe(II) in this invention is 27.8 yuan, which is much lower than the current mainstream sodium dithionite reduction cost of 69 yuan and zinc powder reduction cost of 469.4 yuan. Therefore, this invention has significant advantages in Fe(III) reduction capacity and economy.

[0013] Furthermore, in the above technical solution, the ferrous complex denitrification absorbent includes ferrous ions, ferrous complexing ligands, and complexation regulators.

[0014] Furthermore, in the above technical solution, preferably, the ferrous complexing agent ligand includes one or a mixture of two or more of ethylenediaminetetraacetic acid (EDTA), citric acid (Cit), nitrotriacetic acid (NTA), or triethanolamine (TEA).

[0015] Furthermore, in the above technical solution, preferably, the complexing regulator is an organophosphorus chelating agent, including one or more of aminotrimethylene phosphate (ATMP), diethylenetriaminepentamethylene phosphate (HTPMP), or triethylenetetraminehexamethylene phosphate (TETHMP).

[0016] Furthermore, in the above technical solution, preferably, the volume ratio of the cathode chamber to the anode chamber is 2:1 to 100:1, and the ratio of the sum of the first cathode and the second cathode to the area of ​​the anode is 4:1 to 100:1.

[0017] Furthermore, in the above technical solution, preferably, the anode chamber includes an anode, the anode is covered with an anode porous tube, there is a certain gap between the anode porous tube and the anode, and the anode porous tube is covered with at least one layer of cloth.

[0018] The anode porous tube has uniform equal-diameter holes on its tube wall. The anode is a DSA anode with a titanium surface coated with a metal oxide. The potential of the anode is set to 0.9–3.0V vs. SCE.

[0019] Furthermore, in the above technical solution, preferably, both the first cathode and the second cathode are stainless steel mesh cathodes or electrodes containing elemental iron.

[0020] During the reduction process, the potential of the first cathode is set to (-0.1) to (-2.5) V vs. SCE.

[0021] During the reverse electrolysis, the potential of the first cathode is set to 0.1–1.0 V vs. SCE.

[0022] Furthermore, in the above technical solution, preferably, the reducing agent is one or more of iron powder, zinc powder, sodium sulfite, sodium dithionite, or ascorbic acid. The molar ratio of the reducing agent to the ferrous complex denitrification absorbent is 0 to 20:1.

[0023] Secondly, the present invention provides the application of the above method in the removal of nitric oxide, wherein a gas containing nitric oxide is introduced into the ferrous complex denitrification absorbent, and after a period of time, the anode of the electrolysis device is connected to the positive terminal of the power supply and the first cathode is connected to the negative terminal of the power supply to carry out the reduction process, thereby reducing the oxidized Fe(III) to Fe(II).

[0024] When iron species are lost in the ferrous complex denitrification absorbent, the second cathode is connected to the negative terminal of the power supply and the first cathode is connected to the positive terminal of the power supply to perform reverse electrolysis to replenish the iron species. At the same time, a reducing agent is added to the cathode chamber to assist electrochemical reduction.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) Exploring the value of the anode, achieving efficient reduction of Fe(III) assisted by the anode.

[0027] In electrochemical systems primarily driven by electroreduction, the anode is typically used to form a complete electrical circuit, and its value is rarely explored in depth. This invention, through a design of a large cathode and a small anode, and using cloth as a diaphragm, allows the anode to provide an acidic environment to the cathode via the OER (electrocatalytic oxygen evolution reaction), facilitating the efficient reduction of Fe(III) at the cathode. Simultaneously, it reduces the oxidation of the reduction product Fe(II) by the anode, transforming the anode, which is inherently detrimental to Fe(III) reduction, into a reducing aid, thus ensuring the reduction effect.

[0028] (2) Fe(III) has high reduction efficiency

[0029] This invention not only utilizes the anode to facilitate the electroreduction of Fe(III), but also increases the cathode area through a large cathode and small anode design, providing more active sites for the reaction. Simultaneously, the anode's design reduces the oxidation of the reduction product Fe(II). The addition of a reducing agent, if necessary, also accelerates the reduction rate. These design elements collectively ensure the efficient reduction of Fe(III). The Fe(II) formation rate of this invention is 1.4 times and 6 times that of separate electrochemical reduction and separate iron powder reduction in the same apparatus system, respectively, and the reduction efficiency can be maintained above 90% for 24 hours.

[0030] (3) Low cost

[0031] On the one hand, using inexpensive fabric instead of expensive membranes not only directly reduces investment costs but also further reduces operating costs by avoiding high energy consumption caused by mold resistance. On the other hand, the small anode design reduces anode costs, further lowering investment costs. The cost required to generate 1 mol of Fe(II)EDTA in this invention is only 27.8 yuan, far lower than the current mainstream costs of 69 yuan for sodium dithionite reduction and 469.4 yuan for zinc powder reduction, demonstrating higher economic efficiency.

[0032] (4) Maintained good iron circulation in the system.

[0033] In practical industrial applications, the loss of iron species caused by iron carry-out from flue gas is not conducive to maintaining the denitrification effect for a long time. This invention replenishes iron species through reverse electrolysis to maintain good iron circulation in the system and ensures the continuous and stable operation of the system. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of a non-uniformly coupled dual-chamber electrolytic cell structure for anodic-assisted efficient reduction of Fe(III) to regenerate ferrous complex denitrification absorbent, according to the present invention.

[0035] In the diagram: 1. Power source; 2. Anode; 3. Electrolytic cell; 4. First cathode; 5. Second cathode; 6. Complexing absorbent containing Fe(III); 7. Porous tube for anode; 8. Cloth.

[0036] Figure 2 This diagram illustrates the changes in Fe(II) concentration in an electrochemical method for efficient reduction with anodic assistance, a conventional electrochemical reduction, and an iron powder reduction system.

[0037] Figure 3 A schematic diagram illustrating the reduction effect of an electrochemical method that uses an anode to facilitate efficient reduction.

[0038] Figure 4 A schematic diagram illustrating the long-term reduction effect of an electrochemical method that uses the anode to facilitate efficient reduction at different temperatures.

[0039] Figure 5 A schematic diagram illustrating the reduction effect of an electrochemical method for efficient reduction with the anode at different amounts of reducing agent.

[0040] Figure 6 A schematic diagram illustrating the reduction effect of an electrochemical method that facilitates efficient reduction with the anode at different anode-cathode area ratios.

[0041] Figure 7 A schematic diagram illustrating the changes in iron concentration and electrode mass during the reduction and reverse electrolysis processes in an electrochemical method that uses the anode to facilitate efficient reduction.

[0042] Figure 8 A schematic diagram showing the changes in NO removal rate and Fe(II) concentration before and after reduction using an electrochemical method with anode-assisted efficient reduction. Detailed Implementation

[0043] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below. It should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the invention to those skilled in the art.

[0045] Example 1: Comparison of the effects of an anode-assisted high-efficiency reduction electrochemical method, conventional electrochemical reduction, and iron powder reduction system on the generation of Fe(II)EDTA.

[0046] The electrochemical device for anode-assisted high-efficiency reduction in this embodiment is as follows: Figure 1As shown, the electrolytic cell 3 includes an anode chamber at its center, comprising an anode 2. An anode porous tube 7 is fitted over the anode 2, and a cloth 8 is fitted over the anode porous tube 7, with a certain gap between the anode 2 and the anode porous tube 7. A cathode chamber is fitted over the anode chamber, comprising a first cathode 4 and a second cathode 5, with a certain gap between the first cathode 4 and the second cathode 5. The gap within the electrolytic cell 3 is filled with a complexing absorbent 6 containing Fe(III). The electrochemical device also includes a power source 1. During the electrochemical reduction reaction, the positive terminal of the power source 1 is connected to the anode 2, and the negative terminal of the power source 1 is connected to the first cathode 4. During reverse electrolysis, the positive terminal of the power source 1 is connected to the first cathode 4, and the negative terminal of the power source 1 is connected to the second cathode 5.

[0047] The porous anode tube 7 has uniformly distributed equal-diameter holes on its wall. In this embodiment, the holes are arranged in a single layer.

[0048] The electrolysis device of the present invention is a non-uniformly coupled dual-chamber electrolytic cell, which consists of a cathode chamber and an anode chamber, with a cloth between the two chambers. In the non-uniformly coupled dual-chamber electrolytic cell, the anode assists the cathode in the efficient reduction of Fe(III) in the complex absorbent containing Fe(III). When the complex absorbent containing Fe(III) experiences iron species loss, reverse electrolysis is performed to replenish the iron species (iron powder), and at the same time, a reducing agent is added to the cathode chamber to assist electrochemical reduction.

[0049] In the electrolytic cell of this embodiment, the volume ratio of the cathode chamber to the anode chamber is 10:1, and the ratio of the sum of the areas of the first cathode and the second cathode to the area of ​​the anode is 50:1.

[0050] The preparation method of the Fe(III)-containing complex absorbent selected in this embodiment is as follows: Oxygen is introduced into a solution of 100 mM FeSO4, 150 mM Na2EDTA (80 mL solution volume, pH = 7, temperature 298 K) to completely oxidize it, resulting in a 100 mM Fe(III)EDTA solution. 4.48 g of iron powder (molar ratio of iron powder to Fe(III)EDTA is 10:1) is added to the 100 mM Fe(III)EDTA (80 mL), pH = 7, temperature 25 °C, and nitrogen gas is bubbled into the reduction device at a rate of 0.4 L / min as a disturbance. In the above electrolysis device, the reference electrode is a saturated calomel electrode; the anode material is a Ti / IrO2-Ta2O5 anode strip with a potential set to 1.5 V vs. SCE; the cathode material is a stainless steel mesh with a potential set to -1.5 V vs. SCE, and the cathode area is 100 cm². 2 The current was 400 mA; the electrolysis time was 60 min. The total iron ion concentration and ferrous ion concentration were measured by spectrophotometry every 10 minutes to calculate the formation rate of Fe(II)EDTA.

[0051] Ordinary electrochemical reduction to Figure 1 The cathode chamber in the device contains only one cathode and does not perform reverse electrolysis or add a reducing agent.

[0052] The iron powder reduction system directly uses iron powder to reduce Fe(III)EDTA.

[0053] like Figure 2 By the 30-minute mark, the concentrations of Fe(II)EDTA in the anodic-assisted high-efficiency reduction electrochemical method, the electrochemical reduction system, and the iron powder reduction system were 87.306 mM, 40.196 mM, and 10.413 mM, respectively. By the 60-minute mark, the concentrations of Fe(II)EDTA in the three reduction systems were 102.739 mM, 74.852 mM, and 17.182 mM, respectively. This demonstrates that the anodic-assisted high-efficiency reduction electrochemical method consistently exhibits the highest Fe(II)EDTA concentration. Calculations showed that the Fe(II)EDTA formation rates in the anodic-assisted high-efficiency reduction electrochemical method, the conventional electrochemical reduction system, and the iron powder reduction system were 1.712 mM / min, 1.248 mM / min, and 0.286 mM / min, respectively. The anodic-assisted high-efficiency reduction electrochemical method significantly increased the Fe(II)EDTA formation rate. Therefore, the anodic-assisted high-efficiency reduction electrochemical reduction system is more favorable for the reduction of Fe(III)EDTA.

[0054] Example 2: Effect of Fe(II)EDTA generation in an anode-assisted high-efficiency reduction electrochemical reduction system

[0055] Using the apparatus of Example 1, in this embodiment, the volume ratio of the cathode chamber to the anode chamber in the electrolytic cell is 100:1, and the area ratio of the sum of the first and second cathodes to the anode is 60:1. The preparation method of the Fe(III)-containing complex absorbent selected in this embodiment is as follows: Oxygen is introduced into a solution of 100mM FeSO4, 150mM Na2EDTA (80mL solution volume, pH=4, temperature 298K) to completely oxidize it and obtain a 100mM Fe(III)EDTA solution. Then, 4.48g of iron powder (molar ratio of iron powder to Fe(III)EDTA is 10:1) is added to the 100mM Fe(III)EDTA (80mL), pH=4, temperature 25℃, and nitrogen gas is bubbled into the reduction device at a rate of 0.4L / min as a disturbance. In the above electrolysis apparatus, the reference electrode is a saturated calomel electrode; the anode material is a Ti / IrO2-Ta2O5 anode bar; and the cathode material is a stainless steel mesh with a cathode area of ​​100 cm². 2 The current was 400 mA; the electrolysis time was 60 min. The total iron ion concentration and ferrous ion concentration were measured by spectrophotometry every 10 minutes to calculate the formation rate of Fe(II)EDTA.

[0056] The curve showing the change in Fe(II)EDTA concentration over time during reduction in the aforementioned reduction apparatus is shown below. Figure 3 As shown. By Figure 3 It can be seen that after 10 minutes of reaction, the concentration of Fe(II)EDTA produced by the system remained above 100 mM. As the reaction proceeded, the concentration of Fe(II)EDTA gradually increased, indicating that the anolyte-assisted high-efficiency reduction electrochemical system has a good reduction effect on Fe(III)EDTA. Furthermore, a long-term effect experiment on the reduction of Fe(III)EDTA was conducted. The curve of Fe(II)EDTA concentration changing with time is shown below. Figure 4 As shown, the concentration of Fe(II)EDTA rapidly increased to over 100 mM in the first 1 hour of reduction. As the reaction proceeded, the concentration of Fe(II)EDTA fluctuated over the next 23 hours, but remained above 100 mM. This indicates that the reduction method of Fe(III)EDTA can maintain a high reduction efficiency for a relatively long period. In summary, the anodic-assisted high-efficiency electrochemical reduction exhibits long-lasting effectiveness.

[0057] Example 3: Effect of Anodic-Assisted High-Efficiency Reduction of Fe(III) to Regenerate Ferrous Complex Denitrification Absorbent under Different Reduction Conditions

[0058] Using the apparatus of Example 1, in this embodiment, the volume ratio of the cathode chamber to the anode chamber in the electrolytic cell is 10:1, and the ratio of the sum of the areas of the first cathode and the second cathode to the anode area is 50:1. The preparation method of the Fe(III)-containing complexing absorbent selected in this embodiment is as follows: Oxygen is introduced into a solution of 100mM FeSO4, 150mM Na2EDTA (80mL solution volume), pH=7, and temperature 298K, to completely oxidize it and obtain a 100mM Fe(III)EDTA solution. Different proportions of iron powder are added to 100mM Fe(III)EDTA (80mL), pH=7, temperature 25℃, and nitrogen gas is bubbled into the reduction device at a rate of 0.4L / min as a disturbance. In the above electrolysis apparatus, the reference electrode is a saturated calomel electrode; the anode material is a Ti / IrO2-Ta2O5 anode bar; the cathode material is a stainless steel mesh cathode, with different anode and cathode area ratios; the current is 400mA; and the electrolysis time is 60min.

[0059] This embodiment investigated the effects of different iron powder addition amounts and anode-cathode surface ratios on the reduction effect. The molar ratios of iron powder to Fe(III)EDTA were set to 0, 1:1, 5:1, and 10:1, and the anode-cathode surface ratios were set to 15:1, 20:1, 25:1, and 30:1. The total iron ion concentration and ferrous ion concentration were measured spectrophotometrically every 10 minutes to calculate the Fe(II)EDTA formation rate.

[0060] Under different iron powder addition conditions, the electrochemical reduction effect of anodic-assisted efficient reduction of Fe(III) is as follows: Figure 5 As shown, the addition of iron powder is beneficial to the reduction of Fe(III)EDTA. With the increase of the amount of iron powder added, the amount of Fe(II)EDTA generated also increases. When the molar ratio of iron powder to Fe(III)EDTA is 10:1, the concentration of Fe(II)EDTA is 110.32 mM at 60 min.

[0061] Under different anode-cathode area ratios, the electrochemical reduction effect of anode-assisted efficient reduction of Fe(III) is as follows: Figure 6 As shown, it can be seen that increasing the anode-cathode area ratio is beneficial to the reduction of Fe(III)EDTA. The increased anode-cathode area ratio provides more active sites for the reaction and promotes the formation of Fe(II)EDTA.

[0062] Example 4: Maintaining good iron circulation in the reverse electrolysis system

[0063] Using the apparatus of Example 1, in this embodiment, the volume ratio of the cathode chamber to the anode chamber in the electrolytic cell is 10:1, and the ratio of the sum of the areas of the first cathode and the second cathode to the anode area is 100:1. The preparation method of the Fe(III)-containing complexing absorbent selected in this embodiment is as follows: A solution of 100mM FeSO4, 150mM Na2EDTA (80mL solution volume, pH=7, temperature 298K) is oxidized completely by passing oxygen through it to obtain a 100mM Fe(III)EDTA solution. Then, 4.48g of iron powder (molar ratio of iron powder to Fe(III)EDTA is 10:1) is added to the 100mM Fe(III)EDTA (80mL), pH=7, temperature 25℃, and nitrogen gas is bubbled into the reduction device at a rate of 0.4L / min as a disturbance. In the above electrolysis apparatus, the reference electrode is a saturated calomel electrode; the anode material is a Ti / IrO2-Ta2O5 anode strip; the first and second cathode materials are stainless steel meshes, with a cathode area of ​​100 cm2; during reduction, the Ti / IrO2-Ta2O5 anode strip serves as the anode, and the first cathode serves as the cathode; during reverse electrolysis, the first cathode serves as the anode, and the second cathode serves as the cathode. The reduction time is 18 h; the reverse electrolysis time is 1 h. The total iron ion concentration and ferrous ion concentration are detected by spectrophotometry; the change in electrode mass before and after reverse electrolysis is measured by an analytical balance.

[0064] Changes in iron concentration and electrode mass during the anode-assisted high-efficiency reduction process and reverse electrolysis are as follows: Figure 7As shown in the figure, after 18 hours of electrolysis, the amount of iron in the solution is 127.106 mM, and the mass of the stainless steel mesh electrode increases from 4.930 g to 5.275 g. Then, reverse electrolysis is performed. After 1 hour, the total amount of iron increases from 127.106 mM to 142.268 mM, while the mass of the stainless steel electrode decreases to 5.068 g. The changes in electrode mass and the amount of iron ions in the solution are 0.207 g and 15.162 mM, respectively. Calculations show that reverse electrolysis releases 3.696 mmol of iron from the electrode into the solution, and the amount of iron added to the solution is 3.791 mmol. These two values ​​are essentially equal, and the error may be due to a small amount of Fe(II)EDTA generated during reverse electrolysis. The experimental results indicate that reverse electrolysis can release iron deposited on the cathode into the solution, achieving good circulation of iron powder in the system.

[0065] Example 5: Absorption of NO by the complex solution after electrochemical reduction of Fe(III) with anodic assistance for high-efficiency reduction.

[0066] This embodiment investigates the absorption of NO by the complex solution following the electrochemical reduction of Fe(III) with anodic assistance. The apparatus of Example 1 was used. In this embodiment, the volume ratio of the cathode chamber to the anode chamber in the electrolytic cell was 10:1, and the ratio of the sum of the areas of the first and second cathodes to the anode area was 100:1. The parameters of the selected complexing absorbent were: 100 mM FeSO4, 150 mM Na2EDTA, solution volume 130 mL, pH = 7, temperature 298 K, and 7.28 g of iron powder added (molar ratio of iron powder to Fe(III)EDTA was 10:1). The simulated flue gas parameters used in this embodiment were: NO concentration 1000 mg / m³. 3 The gas flow rate was 0.4 L / min, and the oxygen content in the simulated flue gas was 10% (by volume). The electrolysis parameters were: a saturated calomel electrode as the reference electrode; a Ti / IrO2-Ta2O5 anode as the anode material; and a stainless steel mesh cathode with a cathode area of ​​100 cm². 2 During reduction, the Ti / IrO2-Ta2O5 anode strip serves as the anode, and the first cathode serves as the cathode; during reverse electrolysis, the first cathode serves as the anode, and the second cathode serves as the cathode. The reduction time is 30 min; the reverse electrolysis time is 10 min. The absorption time is 100 min, with reduction starting at 60 min. The concentration of ferrous ions is detected by spectrophotometry, and the inlet and outlet concentrations of NO are determined using a flue gas analyzer (KANE905, UK).

[0067] The NO removal rate before and after the electrochemical reduction of Fe(III) with anodic assistance and high efficiency is related to the Fe(II) concentration as follows: Figure 8 As shown. By Figure 8It can be seen that before 50 minutes, the change in NO removal rate was consistent with the change in Fe(II)EDTA concentration. Oxygen in the NO gas oxidized Fe(II)EDTA, causing its concentration to decrease, which in turn led to a decrease in the NO removal rate from 97.98% to 94.35%. After 10 minutes of electrochemical synergistic iron powder reduction, the Fe(II)EDTA concentration increased from 59.184 mM to 83.245 mM, and the NO removal rate also increased to 98.31%. The NO removal rate remained above 95% for 30 minutes, higher than the denitrification rate before reduction. At this time, reverse electrolysis was performed, and after 10 minutes, the Fe(II)EDTA concentration increased to 89.303 mM, and the NO removal rate increased to 96.37%. The experimental results show that the complexed denitrification solution after electrochemical reduction of Fe(III) with anodic assistance has a good NO removal effect.

[0068] The embodiments described above are only used to illustrate the technical solutions of the present invention and do not limit the technical scope of the present invention in any way. Any modifications, alterations, improvements, and evolutions made by researchers in the art using the disclosed technical content without departing from the essential scope of the present invention are equivalent embodiments of the present invention and are considered to be within the protection scope of the present invention.

Claims

1. A method for regenerating ferrous complex denitrification absorbent by anodic-assisted reduction of Fe(III), characterized in that: A cloth-coupled dual-chamber electrolytic cell is used as the electrolysis device. The electrolysis device includes a cathode chamber and an anode chamber, and a cloth is provided between the cathode chamber and the anode chamber as a diaphragm. The cathode chamber includes a first cathode and a second cathode, and the anode chamber includes an anode. The method includes a reduction process and a reverse electrolysis. The reduction process involves using the anode to assist the cathode in reducing the oxidized Fe(III) in the ferrous complex denitrification absorbent in the electrolysis device. The reverse electrolysis involves replenishing the iron species when there is iron loss in the ferrous complex denitrification absorbent, while adding a reducing agent to the cathode chamber to assist electrochemical reduction. During the reduction process, the anode is connected to the positive terminal of the power supply, and the first cathode is connected to the negative terminal of the power supply. During the reverse electrolysis, the second cathode is connected to the negative terminal of the power supply, and the first cathode is connected to the positive terminal of the power supply. The volume ratio of the cathode chamber to the anode chamber is 2:1 to 100:1, and the ratio of the sum of the areas of the first cathode and the second cathode to the area of ​​the anode is 4:1 to 100:

1. The anode is fitted with a porous anode tube, and there is a certain gap between the porous anode tube and the anode. The porous anode tube is fitted with at least one layer of cloth. The anode porous tube has uniform equal-diameter holes on its tube wall. The anode is a DSA anode with a titanium surface coated with a metal oxide. The potential of the anode is set to 0.9~3.0 V vs. SCE.

2. The method for regenerating ferrous complex denitrification absorbent by anodic-assisted reduction of Fe(III) according to claim 1, characterized in that: The ferrous complex denitrification absorbent includes ferrous ions, ferrous complexing ligands, and complexation modifiers.

3. The method for regenerating ferrous complex denitrification absorbent by anodic-assisted reduction of Fe(III) according to claim 2, characterized in that: The ferrous complexing agent ligand includes one or a mixture of two or more of ethylenediaminetetraacetic acid, citric acid, hypozinotriacetic acid, or triethanolamine.

4. The method for regenerating ferrous complex denitrification absorbent by anodic-assisted reduction of Fe(III) according to claim 2, characterized in that: The complexing regulator is an organophosphorus chelating agent, including one or more of aminotrimethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, or triethylenetetraminehexamethylenephosphonic acid.

5. The method for regenerating ferrous complex denitrification absorbent by anodic-assisted reduction of Fe(III) according to claim 1, characterized in that: Both the first cathode and the second cathode are stainless steel mesh cathodes or electrodes containing elemental iron. During the reduction process, the potential of the first cathode is set to (-0.1)~(-2.5) V vs. SCE; During the reverse electrolysis, the potential of the first cathode is set to 0.1~1.0 V vs. SCE.

6. The method for regenerating ferrous complex denitrification absorbent by anodic-assisted reduction of Fe(III) according to claim 1, characterized in that: The reducing agent is one or more of iron powder, zinc powder, sodium sulfite, sodium dithionite, or ascorbic acid; the molar ratio of the reducing agent to the ferrous complex denitrification absorbent is (0~20):

1.

7. The application of the method according to any one of claims 1-6 in the removal of nitric oxide, characterized in that: Nitric oxide gas is passed into the ferrous complex denitrification absorbent. After a period of time, the anode of the electrolysis device is connected to the positive terminal of the power supply, and the first cathode is connected to the negative terminal of the power supply to carry out the reduction process, reducing the oxidized Fe(III) to Fe(II). When iron species are lost in the ferrous complex denitrification absorbent, the second cathode is connected to the negative terminal of the power supply and the first cathode is connected to the positive terminal of the power supply to perform reverse electrolysis to replenish the iron species. At the same time, a reducing agent is added to the cathode chamber to assist electrochemical reduction.

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