An anthraquinone / quinone-mediated iron-based complexing denitrifying agent and its application in flue gas denitrification.

Abstract

This invention discloses an anthraquinone / quinone-mediated iron-based complex denitrification agent and its application in flue gas denitrification, belonging to the field of flue gas denitrification technology. The iron-based complex denitrification agent comprises Fe(II) complexes and anthraquinone compounds. This agent utilizes anthraquinone compounds as redox mediators to construct a synergistic redox cycle system of anthraquinone / quinone and Fe(III) / Fe(II). Furthermore, by optimizing the molecular structure of the anthraquinone compounds (including the number of phenolic hydroxyl groups, spatial symmetry, substituent types and positions), it achieves better inhibition of direct oxidation of the ferrous complex by oxygen and maintains the long-term stable activity of the denitrification agent. This denitrification agent maintains a denitrification efficiency of over 80% for flue gas containing O2, SO2, and NO for over 95 hours, significantly reducing the consumption of reducing agents and operating costs.

Description

Technical Field

[0001] This invention relates to an iron-based complexing denitrification agent, particularly to an anthraquinone / quinone-mediated iron-based complexing denitrification agent, and also to the application of an anthraquinone / quinone-mediated iron-based complexing denitrification agent in flue gas denitrification, belonging to the field of flue gas denitrification technology. Background Technology

[0002] Nitrogen oxides (NO) x NO is one of the main pollutants causing air pollution, primarily originating from emissions from coal-fired power plants, industrial boilers, and vehicle exhaust. x Not only does it damage the human respiratory system, but it also causes environmental problems such as acid rain, photochemical smog, and fine particulate matter (PM2.5) pollution. Therefore, the development and application of flue gas denitrification technology is of great significance for improving air quality and protecting the ecological environment.

[0003] Currently, widely used flue gas denitrification technologies in industry include selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). However, both methods suffer from high investment costs, narrow operating temperature windows, and secondary pollution from ammonia escape. Wet complexation denitrification technology, as a low-temperature flue gas denitrification method, has received widespread attention in recent years due to its ability to achieve efficient NO removal at room temperature or lower, and its advantages such as simple equipment and flexible operation.

[0004] The basic principle of wet complexation denitrification is to utilize Fe(II) to form a stable complex, Fe(II)L, with a soluble complexing agent (such as EDTA, NTA, etc.). This complex can complex with NO in the flue gas to generate Fe(II)L(NO), thereby transferring NO from the gas phase to the liquid phase and achieving efficient denitrification. However, actual flue gas usually contains a high concentration of oxygen (O2), which is often much higher than the NO concentration. The complexed ferrous ions are easily oxidized by oxygen to Fe(III), and the Fe(III) complex has almost no complexing ability for NO, causing the denitrification agent to quickly become ineffective.

[0005] To restore the activity of denitrification agents, existing technologies typically employ the addition of reducing agents to reduce Fe(III) to Fe(II). Commonly used reducing agents include dithionite (sodium hydrosulfite), citric acid, ascorbic acid, and iron powder. However, since the concentration of O2 in flue gas is usually tens or even hundreds of times higher than that of NO, the vast majority of the added reducing agent is consumed by oxygen, with only a very small portion used for the reduction and regeneration of Fe(III). This results in enormous consumption of reducing agents, high reagent costs, and poor economic efficiency, severely restricting the industrial application of wet complexation denitrification technology.

[0006] In recent years, literature has reported the introduction of hydroquinone as an adjuvant into iron-based complex denitrification systems to extend the stable working time of iron-based complex denitrification agents. For example, Chinese patent application (CN112717668A) discloses the addition of additives, auxiliaries, nano-reagents, and dispersants to a denitrification agent mainly composed of Fe(II)EDTA. This improves the denitrification agent's ability to complex NO while also enhancing its antioxidant capacity, thereby increasing its absorption capacity and stability. Experimental results show that the initial denitrification rate is 96%, and the denitrification agent's failure time is extended from the existing 60 min to 270 min. However, its ability to improve the stability of the denitrification agent is limited. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the first objective of this invention is to provide an anthraquinone / quinone-mediated iron-based complex denitrification agent. This agent utilizes anthraquinone compounds to construct a synergistic redox cycle system of anthraquinone / quinone and Fe(III) / Fe(II) to effectively maintain the long-term activity of the iron-based complex denitrification agent. This solves the technical problems in existing technologies, such as the high concentration and large amount of O2 in actual flue gas, which leads to the rapid oxidation and failure of the iron-based complex denitrification agent, large consumption of reducing agent, and high operating costs.

[0008] The second objective of this invention is to provide an anthraquinone / quinone-mediated iron-based complex denitrification agent for use in flue gas denitrification. This iron-based complex denitrification agent, when used for flue gas denitrification, not only exhibits a denitrification efficiency of over 95%, but also provides a continuous and stable denitrification time of over 95 hours, which is significantly better than the prior art. Furthermore, it can greatly reduce the consumption of reducing agent and operating costs.

[0009] To achieve the above-mentioned technical objectives, the present invention provides an anthraquinone / quinone-mediated iron-based complexing denitrifier, which comprises an Fe(II) complex and anthraquinone compounds;

[0010] The anthraquinone compounds have the following molecular structures: R1 and R2 are independently selected from hydrogen, hydroxyl, C1-C5 alkyl, C1-C5 alkoxy or sulfonic acid groups.

[0011] The key to the iron-based complex denitrification agent of this invention lies in the introduction of anthraquinone compounds as redox mediators. By constructing a synergistic redox cycle system of anthraquinone and Fe(III) / Fe(II), the long-term denitrification activity of the iron-based complex denitrification agent is effectively maintained. Specifically, anthraquinone compounds (taking 1-anthraquinone sulfonic acid as an example) can reduce Fe(III) complexes to Fe(II) complexes, while simultaneously being oxidized to free radical intermediates. The generated free radical intermediates have appropriate reduction potentials, enabling them to reduce Fe(III) oxidized by oxygen in the denitrification solution back to Fe(II), while simultaneously reducing themselves back to the anthraquinone structure. Meanwhile, in this denitrification solution, the presence of anthraquinone compounds allows them to play an electron transfer role in the Fe(III) / Fe(II) redox cycle, significantly inhibiting the rate of direct O2 oxidation of Fe(II) complexes. Conversely, the electron transfer rate between the free radical intermediate and Fe(III) is relatively fast, thus forming two synergistic redox cycles: anthraquinone and Fe(III) / Fe(II). This effectively maintains the long-term activity of the denitrification agent. (See [link to principle]). Figure 1 .

[0012] As a preferred embodiment, in the molecular structure of the anthraquinone compound, at least one of R1 and R2 is a sulfonic acid group or a hydroxyl group. The anthraquinone compound includes at least one of 1-anthraquinone sulfonic acid, anthraquinone-1,5-disulfonic acid, and 1,2,3-trihydroxyanthraquinone. By introducing electron-donating groups, such as phenolic hydroxyl, alkoxy, or alkyl groups, onto the anthraquinone, the redox activity of the anthraquinone can be improved, which is beneficial for its electron transfer role in the Fe(III) / Fe(II) redox cycle and avoids the direct oxidation of Fe(II) complexes by O2. Alternatively, introducing a sulfonic acid group onto the anthraquinone can simultaneously affect its redox activity through steric hindrance and electronic effects, achieving a similar effect. The most preferred anthraquinone compound is 1,2,3-trihydroxyanthraquinone.

[0013] As a preferred embodiment, the Fe(II) complex is a complex formed by ferrous ions with at least one of ethylenediaminetetraacetic acid, hypozinotriacetic acid, or citric acid. These Fe(II) complexes are all common active ingredients in iron-based complexing denitrification agents in the prior art.

[0014] As a preferred embodiment, the iron-based complexing denitrification agent comprises Fe(II) complex, anthraquinone compounds, and water; the concentration of the Fe(II) complex in water is 0.005M to 0.05M; the concentration of the anthraquinone compounds in water is 1 mmol / L to 100 mmol / L. The concentration of the Fe(II) complex in water is further preferably 0.01M to 0.05M. The concentration of the anthraquinone compounds in water is 5 mmol / L to 20 mmol / L. If the concentration of the anthraquinone compounds is too high, crystallization is likely; if the concentration is too low, it cannot effectively construct the synergistic redox cycle system of anthraquinone / quinone and Fe(III) / Fe(II).

[0015] As a preferred embodiment, the pH of the iron-based complexing denitrifying agent is 5-9. More preferably, the pH of the iron-based complexing denitrifying agent is 6-8. Under these preferred pH conditions, the redox activity and electron transfer properties of anthraquinone compounds are more effectively utilized.

[0016] The present invention also provides another application of anthraquinone / quinone-mediated iron-based complex denitrification agent, wherein flue gas is passed into the anthraquinone / quinone-mediated iron-based complex denitrification agent to carry out a denitrification reaction.

[0017] As a preferred embodiment, the volume fraction of O2 in the flue gas is 1%~20%, the volume concentration of SO2 is 500ppm~10000ppm, and the volume concentration of NO is 200ppm~1000ppm. Generally, O2 in flue gas is a detrimental factor that leads to the failure of Fe(II) complexes and increases the consumption of reducing agents. The higher the oxygen concentration, the more detrimental it is to the denitrification effect of the iron-based complex denitrification agent. However, the iron-based complex denitrification agent of this invention can tolerate a maximum oxygen volume concentration of 20% in the flue gas, and exhibits a good denitrification effect when the volume fraction of O2 in the flue gas is 5%~15%. Since most flue gas contains SO2, which can act as a reducing agent, an appropriate SO2 concentration is beneficial to the denitrification effect of the iron-based complex denitrification agent.

[0018] As a preferred embodiment, the temperature of the denitrification reaction is 15℃~60℃.

[0019] The method for using the iron-based complexing denitrification agent of the present invention for flue gas denitrification:

[0020] (1) Preparation of iron-based complexing denitrification agent solution: Dissolve ferrous salt and complexing agent in water to prepare a denitrification agent solution containing Fe(II) complex; wherein, the complexing agent is ethylenediaminetetraacetic acid (EDTA), nitric acid (NTA), citric acid or a mixture thereof; the concentration of the Fe(II) complex is 0.005 M to 0.05 M;

[0021] (2) Add anthraquinone compounds: Add anthraquinone compounds to the above iron-based complexing denitrification agent solution to make its concentration in the iron-based complexing denitrification agent solution 1 mmol / L~100 mmol / L; (3) Adjust pH value: Use acid-base adjuster to control the pH value of the solution in the range of 5 to 9;

[0022] (4) Flue gas denitrification treatment: The prepared iron-based complex denitrification agent solution is placed in the absorption device, so that the flue gas containing NO and O2 comes into contact with the iron-based complex denitrification agent solution to carry out the denitrification reaction; the volume fraction of O2 in the flue gas is 1%~20%, the concentration of SO2 is 500ppm~10000ppm, and the concentration of NO is 200ppm~1000ppm; the absorption device is a bubbling absorption tower, a spray tower, or a packed tower.

[0023] The ferrous salt involved in this invention is preferably ferrous sulfate, ferrous chloride, or ferrous acetate.

[0024] The acid-base regulators involved in this invention are preferably sodium hydroxide, sulfuric acid, hydrochloric acid, or calcium hydroxide.

[0025] Compared with the prior art, the technical solution of the present invention has the following significant advantages:

[0026] (1) The iron-based complex denitrification agent of the present invention can significantly extend the stable working time of flue gas denitrification, especially under flue gas conditions with high oxygen content (e.g., oxygen content of 10%), the stable denitrification time of traditional Fe(II)EDTA denitrification agent is less than 3 hours; while the iron-based complex denitrification agent of the present invention, after adding a trace amount of anthraquinone compounds, can maintain a stable denitrification time of more than 95 hours with a denitrification efficiency of more than 85%, and the denitrification stability is improved by at least 25 times.

[0027] (2) The iron-based complex denitrification agent of the present invention is used for flue gas denitrification, which can significantly reduce the consumption of reducing agent and operating costs. Since the anthraquinone / quinone mediator in the iron-based denitrification agent forms an efficient electron transfer cycle system between Fe(III) / Fe(II), it effectively inhibits the direct oxidation of Fe(II) by O2. Therefore, the amount of reducing agent required for subsequent Fe(III) reduction and regeneration is greatly reduced, which can reduce the consumption of reducing agent by more than 80%, and significantly reduce the operating cost of the complex denitrification system.

[0028] (3) The iron-based complexing denitrification agent of the present invention only requires trace amounts of anthraquinone compounds, which has low reagent cost, stable chemical properties, and is easy to store and transport, making it suitable for industrial application.

[0029] (4) The iron-based complex denitrification agent of the present invention is applicable to a wide range of flue gas conditions and can operate stably under complex flue gas composition conditions such as O2 volume fraction of 1%~20%, SO2 concentration of 500ppm~10000ppm and NO concentration of 200ppm~1000ppm, and has strong adaptability to working conditions.

[0030] (5) The iron-based complex denitrification agent of the present invention can be used in the flue gas denitrification process with conventional absorption tower equipment, without the need for large-scale modification of existing wet desulfurization and denitrification equipment. The project is simple to implement and the investment cost is low. Attached Figure Description

[0031] Figure 1 A schematic diagram illustrating the antioxidant mechanism of anthraquinone / quinone-mediated iron-based complex denitrifying agents. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the content of this invention and are not intended to limit the scope of protection of the claims of this invention.

[0033] Comparative Example 1

[0034] No anthraquinone compounds added:

[0035] (1) Preparation of denitrification agent solution: Accurately weigh ferrous sulfate heptahydrate (FeSO4·7H2O) and disodium ethylenediaminetetraacetate (Na2EDTA), dissolve them in 100mL of deionized water, and prepare a denitrification agent solution with a Fe(II)EDTA concentration of 0.02 M. Transfer the above solution to a bubbling absorption bottle.

[0036] (2) Preparation and introduction of simulated flue gas: High-purity nitrogen, high-purity oxygen, NO standard gas (concentration of 10000ppm, with nitrogen as the balance gas), and SO2 standard gas (concentration of 10000ppm, with nitrogen as the balance gas) are mixed in proportion using a mass flow controller to prepare simulated flue gas. The composition of the simulated flue gas is: O2 volume fraction of 10%, SO2 concentration of 1000ppm, NO concentration of 500ppm, and the remainder being nitrogen. The total flue gas flow rate is adjusted to 1L / min, and the simulated flue gas is introduced into the denitrification agent solution from the bottom of the bubbling absorption bottle through the sand core aerator.

[0037] (3) pH control: Install an automatic liquid addition device in the bubbling absorption bottle, and use 0.1 mol / L NaOH solution and 0.1 mol / L H2SO4 solution to automatically adjust and maintain the pH value of the denitrification agent solution at 6 ± 0.2.

[0038] (4) Denitrification performance test: The NO concentration in the flue gas at the outlet of the bubbling absorption bottle was continuously measured using a flue gas analyzer, and the denitrification efficiency was recorded over time. The denitrification efficiency was calculated using the following formula:

[0039] η=(C in -C out ) / C in ×100%;

[0040] In the formula, η is the denitrification efficiency (%), and C in The concentration of imported NO (ppm), C out The NO concentration at the export site is expressed in ppm.

[0041] (5) Experimental Results: During the experiment, the NO concentration in the tail gas remained below 100 ppm for the first 30 minutes, corresponding to a denitrification efficiency of over 80% (a denitrification efficiency of 80% is sufficient to meet emission requirements). However, as the reaction proceeded, the denitrification efficiency rapidly decreased, and after 3 hours, the outlet NO concentration approached the inlet concentration, indicating that the denitrification agent almost completely lost its denitrification effect. This suggests that under oxygen-containing flue gas conditions, Fe(II)EDTA is rapidly oxidized to Fe(III)EDTA by O2, leading to the failure of the denitrification function.

[0042] Comparative Example 2

[0043] Add hydroquinone (1,4-hydroquinone):

[0044] (1) Preparation of denitrification agent solution: Accurately weigh ferrous sulfate heptahydrate (FeSO4·7H2O) and disodium ethylenediaminetetraacetate (Na2EDTA), dissolve them in 90 mL of deionized water to prepare a denitrification agent solution with a Fe(II)EDTA concentration of 0.02 M. Separately weigh 1,4-hydroquinone and dissolve it in 10 mL of deionized water to prepare a 1,4-hydroquinone solution with a 100 mmol / L concentration. Mix the two solutions and transfer them to a bubbling absorption bottle. After mixing, the concentration of Fe(II)EDTA in the solution is 0.018 M and the concentration of 1,4-hydroquinone is 10 mmol / L.

[0045] (2) Preparation and introduction of simulated flue gas: The simulated flue gas was prepared in the same way as in Example 1. The composition was 10% O2 volume fraction, 1000ppm SO2 concentration, 500ppm NO concentration, and the remainder was nitrogen. The total flue gas flow rate was 1L / min, and it was introduced from the bottom of the bubbling absorption bottle.

[0046] (3) pH control: The same automatic liquid addition device as in Example 1 was used to maintain the pH value of the solution at 6±0.2 using 0.1mol / L NaOH solution and 0.1mol / L H2SO4 solution.

[0047] (4) Denitrification performance test: The NO concentration in the outlet flue gas was continuously measured using a flue gas analyzer, and the denitrification efficiency was recorded over time.

[0048] (5) Experimental results: During the 3-hour continuous experiment, the NO tail gas concentration remained below 100 ppm, and the corresponding denitrification efficiency remained above 80%. No obvious precipitation occurred in the denitrification agent solution throughout the experiment. This is in stark contrast to the result of complete failure within 3 hours in Comparative Example 1, proving that quinone compounds have a certain effect on inhibiting the oxidative failure of complexed denitrification agents, but it is not significant.

[0049] Example 1

[0050] Add anthraquinone-1,5-disulfonic acid:

[0051] (1) Following the method of Comparative Example 2, anthraquinone-1,5-disulfonic acid was used to replace 1,4-hydroquinone to prepare a denitrification agent solution with a Fe(II)EDTA concentration of 0.02 mol / L and anthraquinone-1,5-disulfonic acid concentration of 10 mmol / L.

[0052] (2) Denitrification performance test: Denitrification experiment was conducted under the same general simulated flue gas conditions as Comparative Example 1.

[0053] (3) Experimental results: During the 95-hour continuous experiment, the NO tail gas concentration remained below 100 ppm, and the denitrification efficiency remained above 80% (of which, the NO removal rate was above 95% for 31 hours, the NO removal rate was above 90% for 76 hours, and the NO removal rate was above 85% for 86 hours).

[0054] Example 2

[0055] Add 1-anthraquinone sulfonic acid:

[0056] (1) Following the method of Comparative Example 2, 1-anthraquinone sulfonic acid was used to replace 1,4-hydroquinone to prepare a denitrification agent solution with a Fe(II)EDTA concentration of 0.02 mol / L and a 1-anthraquinone sulfonic acid concentration of 10 mmol / L.

[0057] (2) Denitrification performance test: Denitrification experiment was conducted under the same general simulated flue gas conditions as Comparative Example 1.

[0058] (3) Experimental results: During the 118-hour continuous experiment, the NO tail gas concentration remained below 100 ppm, and the denitrification efficiency remained above 80% (of which, the NO removal rate was above 95% for 38 hours, the NO removal rate was above 90% for 81 hours, and the NO removal rate was above 85% for 107 hours).

[0059] Example 3

[0060] Add 1,2,3-trihydroxyanthraquinone:

[0061] (1) Following the method of Comparative Example 2, 1,2,3-trihydroxyanthraquinone was used to replace 1,4-hydroquinone to prepare a denitrification agent solution with a Fe(II)EDTA concentration of 0.02 mol / L and a 1,2,3-trihydroxyanthraquinone concentration of 10 mmol / L.

[0062] (2) Denitrification performance test: Denitrification experiment was conducted under the same general simulated flue gas conditions as Comparative Example 1.

[0063] (3) Experimental results: During the 155-hour continuous experiment, the NO tail gas concentration remained below 100 ppm, and the denitrification efficiency remained above 80% (of which, the NO removal rate was above 95% for 51 hours, the NO removal rate was above 90% for 105 hours, and the NO removal rate was above 85% for 138 hours).

[0064] The above results indicate that by systematically regulating the number, symmetry, and substituent types of phenolic hydroxyl groups in quinone compounds, the antioxidant protection effect of hydroquinone compounds against ferrous ions can be significantly optimized by utilizing the synergistic effect of electronic and steric effects, thereby achieving more durable flue gas denitrification stability.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the scope of the present invention should be included within the protection scope of the present invention.

Claims

1. An anthraquinone / quinone-mediated iron-based complexing denitrifying agent, characterized in that: It contains Fe(II) complexes and anthraquinone compounds; The anthraquinone compounds have the following molecular structures: R1 and R2 are independently selected from hydrogen, hydroxyl, C1-C5 alkyl, C1-C5 alkoxy or sulfonic acid groups.

2. The anthraquinone / quinone-mediated iron-based complexing denitrifier according to claim 1, characterized in that: In the anthraquinone compounds, at least one of R1 and R2 is a sulfonic acid group or a hydroxyl group.

3. An anthraquinone / quinone-mediated iron-based complexing denitrifying agent according to claim 1 or 2, characterized in that: The anthraquinone compounds include at least one of 1-anthraquinone sulfonic acid, anthraquinone-1,5-disulfonic acid, and 1,2,3-trihydroxyanthraquinone.

4. The anthraquinone / quinone-mediated iron-based complexing denitrifier according to claim 1, characterized in that: The Fe(II) complex is a complex formed by ferrous ions with at least one of ethylenediaminetetraacetic acid, hypozinotriacetic acid, or citric acid.

5. An anthraquinone / quinone-mediated iron-based complexing denitrifying agent according to claim 1, 2, or 4, characterized in that: It contains Fe(II) complexes, anthraquinone compounds, and water; The concentration of the Fe(II) complex in water is 0.005 M to 0.05 M; The concentration of the anthraquinone compound in water is 1 mmol / L to 100 mmol / L.

6. The anthraquinone / quinone-mediated iron-based complexing denitrifier according to claim 5, characterized in that: Its pH is 5-9.

7. The application of the anthraquinone / quinone-mediated iron-based complexing denitrifying agent according to any one of claims 1 to 6, characterized in that: The flue gas is passed into the anthraquinone / quinone-mediated iron-based complex denitrification agent to carry out the denitrification reaction.

8. The application of the anthraquinone / quinone-mediated iron-based complexing denitrifier according to claim 7, characterized in that: The volume fraction of O2 in the flue gas is 1% to 20%, the volume concentration of SO2 is 500 ppm to 10000 ppm, and the volume concentration of NO is 200 ppm to 1000 ppm.

9. The application of an anthraquinone / quinone-mediated iron-based complexing denitrifier according to claim 7 or 8, characterized in that: The temperature of the denitrification reaction is 15℃~60℃.

Images