Multi-characterization modification method of fly ash catalyst for tail gas after-treatment

Abstract

The invention discloses a fly ash catalyst multi-characterization modification method for tail gas aftertreatment, and relates to the technical field of denitration catalyst preparation. Through the method, various abundant defects are formed on the surface of the material, so that the catalyst obtains high catalytic activity; magnetic substances in the fly ash base material are effectively separated out, and impurities contained in the fly ash base material are effectively removed, so that the iron content of the material is improved, and the oxidation-reduction property of the catalyst is improved. In the ball milling process, surface oxygen vacancies are activated and generated through collision and friction among material particles, multiple surface point defects and line defects are obtained, the specific surface area of the catalyst is increased, and the oxidation-reduction performance of the material is further improved. Finally, plasma discharge modification is carried out in an oxygen atmosphere, more active oxygen vacancies are created through plasma discharge treatment, and the chemical reaction process of the surface of the catalyst is promoted. The electron mobility of the catalyst is improved, and the catalytic activity of the material is further excited.

Description

Technical Field

[0001] The invention relates to the technical field of denitration catalyst preparation, and in particular to a multi-characterization modification method for a fly ash catalyst used for tail gas post-treatment. Background Art

[0002] Nitrogen oxides (NOx), a major atmospheric pollutant, not only harm human health but also cause environmental problems such as acid rain and photochemical smog. Selective catalytic reduction (SCR) technology can effectively reduce NOx emissions. Its key lies in selecting the right catalyst to reduce NOx to nitrogen and water. Traditional vanadium-based catalysts suffer from a narrow active temperature window and high cost. While molecular sieve catalysts broaden the active window, they suffer from poor sulfur resistance and complex preparation processes, hindering large-scale application.

[0003] Fly ash, a widely available and low-cost industrial waste, can be significantly enhanced through modification, achieving efficient resource utilization and maximizing economic benefits. Compared to other catalysts, nanoscale fly ash catalysts are more affordable to prepare, helping to reduce overall production costs. However, fly ash itself faces three major technical bottlenecks: low redox activity, poor mass transfer efficiency, and insufficient electron mobility. A single modification method is unlikely to synergistically enhance its catalytic performance.

[0004] Existing fly ash modification technologies (such as patent CN202410587684.3) process the mixture through processes such as ball milling, drying, and screening. While this improves the specific surface area and active component content, resulting in good catalytic performance, there is still room for improvement. For example, screening treatment results in poor redox performance of the material. Furthermore, existing technologies have not considered further improving the reaction rate by enhancing the catalyst's electron mobility, a key factor that significantly impacts catalytic efficiency. Summary of the Invention

[0005] The purpose of the present invention is to provide a multi-characterization modification method for fly ash catalysts used for exhaust gas post-treatment, which significantly improves the denitrification activity by synergistically optimizing the redox properties, specific surface area and electron mobility of the catalytic material, so that the denitrification efficiency of the modified catalyst is more than doubled compared with the original ash.

[0006] To achieve the above objectives, the technical solution of the present application is: a multi-characterization modification method for fly ash catalyst for tail gas post-treatment, comprising:

[0007] Use high-intensity magnetic separation equipment to carry out wet magnetic separation of fly ash raw ash to improve redox properties;

[0008] The powder after magnetic separation is subjected to ball milling activation treatment in an oxygen-rich environment in the presence of hydrogen peroxide solution to improve the specific surface area;

[0009] The iron-based powder after ball milling is modified by plasma discharge in an oxygen atmosphere to improve electron mobility.

[0010] As a preferred solution of the present invention, the high-intensity magnetic separation device is a magnetic separation rod with a magnetic strength of 10000G.

[0011] As a preferred solution of the present invention, a high-intensity magnetic separation device is used to perform wet magnetic separation on the fly ash raw ash, specifically:

[0012] Mixing raw fly ash with deionized water to form a slurry;

[0013] Add 2-5wt% anhydrous ethanol as a dispersant to the mortar and stir it with an electronic stirrer to effectively prevent particles from agglomerating;

[0014] Immerse a magnetic separation rod with a magnetic strength of 10,000 G into the slurry and stir continuously;

[0015] Use a plastic scraper to collect the magnetic mixture adsorbed on the surface of the magnetic separation rod;

[0016] The obtained magnetic mixture was placed in a drying oven and dried for several hours to a constant weight.

[0017] As a preferred embodiment of the present invention, the powder after magnetic separation is subjected to an oxygen-rich environment ball milling activation treatment in the presence of a hydrogen peroxide solution, specifically:

[0018] The fly ash raw materials after magnetic separation are placed in a planetary ball mill;

[0019] adding hydrogen peroxide solution as a ball milling aid and ball milling coolant;

[0020] Set the ball mill speed and ball milling time;

[0021] The ball-milled material and the ball mill jar are placed in a drying oven and dried to powder form. The surface of the grinding balls is brushed and the final product is sieved and collected.

[0022] As a preferred embodiment of the present invention, the mass percentage of the hydrogen peroxide solution used is 5.7%-8.7wt%.

[0023] As a preferred solution of the present invention, the grinding balls are made of zirconium oxide and have radii of 4 mm, 6 mm, 10 mm and 20 mm, respectively, with a mass ratio of 2:3:3:2; and a filling rate of 0.25-0.35.

[0024] As a preferred embodiment of the present invention, when performing plasma discharge modification, the discharge spacing, discharge length and discharge power are first set, the iron-based powder after ball milling is evenly spread in the discharge area, the gas atmosphere is selected as an oxygen atmosphere, and the modification is carried out for several minutes.

[0025] As a preferred solution of the present invention, the discharge power is 120-150W.

[0026] As a preferred embodiment of the present invention, a device for achieving plasma discharge includes a high-voltage electrode, a ground electrode, a nylon fixing member, and a transparent quartz tube. The two ends of the transparent quartz tube are connected to nylon fixing members, one of the nylon fixing members is provided with an air inlet, and the other nylon fixing member is provided with an air outlet. The high-voltage electrode passes through the two nylon fixing members and is placed in the transparent quartz tube. The ground electrode is sleeved on the outside of the transparent quartz tube.

[0027] As a preferred solution of the present invention, the iron-based powder after ball milling is placed in the discharge area of a transparent quartz tube.

[0028] By adopting the above technical solution, the present invention can achieve the following technical effects:

[0029] 1) Raw material advantages: fly ash, which is widely available and low-cost, is used as the base material, and has the potential for large-scale industrial application;

[0030] 2) Process advantages: The processing method adopted requires a wide range of precision, is easy to operate, and can be produced in large quantities and in a streamlined process;

[0031] 3) Environmental benefits: Using solid waste from thermal power plants as raw materials to prepare diesel engine denitrification catalysts has achieved a "waste-to-waste" circular economy model;

[0032] 4) Technological Innovation: Through a gradient-controlled process involving wet magnetic separation, oxygen-enriched ball milling, and plasma modification, we achieve synergistic optimization of the material's redox properties, specific surface area, and electron mobility. This technology approach can be expanded to enhance the performance of other catalytic materials.

[0033] 5) Environmental friendliness: The entire process adopts green processing technology, without the emission of toxic and harmful substances;

[0034] 6) Mechanism innovation: Based on the research on the catalytic mechanism, the fly ash catalyst performance was systematically improved by wet magnetic separation to enhance redox activity, high-energy ball milling to increase specific surface area, and plasma treatment to improve electron mobility.

[0035] The present invention solves the three major technical bottlenecks of low redox activity of fly ash catalyst, poor mass transfer efficiency and insufficient electron mobility through a multi-scale control strategy. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0037] Figure 1 This is a schematic diagram of the wet slag magnetic separation operation process of the present invention;

[0038] Figure 2 Schematic diagram of the oxygen-enriched ball milling operation process of the present invention;

[0039] Figure 3 Schematic diagram of the structure of the plasma reaction device of the present invention;

[0040] Figure 4 Schematic diagram comparing the denitration rate of the final fly ash catalyst sample of the present invention with the denitration rate of the original fly ash;

[0041] Figure 5 These are the XRD patterns of the different modification stages of the present invention, where FA, MSFA, BMFA, and PFA represent the original ash, samples after magnetic separation, after ball milling, and after plasma treatment, respectively.

[0042] Explanation of the numbers in the figure: 1-air outlet, 2-discharge area, 3-transparent quartz tube, 4-high voltage electrode, 5-air inlet, 6-ground electrode, 7-iron-based powder. DETAILED DESCRIPTION

[0043] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, this application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0044] In order to make the purpose, technical solutions and advantages of this application more clearly understood, this application is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application. That is, the embodiments described are only part of the embodiments of this application, not all of them.

[0045] The present invention primarily aims to provide a method for modifying fly ash catalysts for exhaust gas post-treatment. The method presented in this example maximizes the denitrification efficiency of fly ash-based catalysts. This method can achieve the highest denitrification efficiency in the final catalytic sample. If this result is not a consideration, parameters can be adjusted during the actual preparation process.

[0046] A multi-characterization modification method for a fly ash catalyst for tail gas post-treatment according to this embodiment specifically includes:

[0047] 1) A high-intensity magnetic separation device is used to perform wet magnetic separation on the fly ash to improve the redox property; wherein the high-intensity magnetic separation device is preferably a magnetic separation rod with a magnetic strength of 10000G.

[0048] like Figure 1 As shown in , a certain amount of fly ash raw ash is weighed and placed in a mixing container, and deionized water is added at a water-to-material ratio of 4:1 to prepare a slurry; in order to avoid the coating phenomenon caused by agglomeration between material particles, 2-5wt% anhydrous ethanol is added as a dispersant to increase the dispersibility of the particles in the slurry, and an electronic stirrer or a glass rod is used to stir at a constant rate for 3-5 minutes to ensure the formation of a uniform and stable suspended slurry; while the slurry remains suspended, a magnetic separation rod is inserted for circular stirring for 60±5 seconds; a plastic scraper is used to collect the magnetic mixture adsorbed on the surface of the magnetic separation rod, and the magnetic mixture is transferred to a drying container, and dried at a constant temperature of 40°C-48°C for 5-7 hours to constant weight to obtain a fly ash sample after magnetic separation enrichment.

[0049] 2) The powder after magnetic separation is subjected to ball milling activation treatment in an oxygen-rich environment in the presence of a hydrogen peroxide solution to improve the specific surface area;

[0050] like Figure 2 As shown, a planetary ball mill with model KE-0.4L is used for oxygen-enriched high-energy ball milling. Zirconia grinding balls with diameters of 4mm, 6mm, 10mm, and 20mm are selected and mixed in a mass ratio of 2:3:3:2. The ball mill filling rate is selected to be 0.25-0.35. 23.6g of fly ash raw material after magnetic separation is weighed and put into a ball mill jar. 10ml of 5.7%-8.7wt% laboratory hydrogen peroxide solution is added to each ball mill jar, which can be used as an oxygen-enriched ball milling aid and ball milling coolant. After addition, the slurry in the ball mill jar becomes paste-like. The ball mill speed is set to 550r / min, and the ball milling time is continuous for 8h. The equipment status should be observed in the middle, and the ball mill jar should be opened at an appropriate time to release the pressure and continue ball milling. After the ball milling is completed, the ball mill jar with slurry is blown dry in a drying oven at 45°C for about 8 hours until the slurry is completely dry and powdery. Then, the surface of the grinding balls is scrubbed with a brush. After sieving through a filter, the oxygen-enriched ball-milled sample and the zirconia grinding balls are separated. The powder after separation is dark brown.

[0051] 3) The iron-based powder after ball milling is subjected to plasma discharge modification in an oxygen atmosphere to improve electron mobility;

[0052] like Figure 3As shown, a plasma discharge apparatus was constructed; a discharge gap of 3 mm and a discharge length of 200 mm were selected, and 5 g of the sample, after oxygen-enriched ball milling, was evenly spread within the discharge area. The voltage and current of the plasma generator power supply were adjusted, and the discharge apparatus power was set to 120-150 W. Discharge modification was performed in an oxygen atmosphere for 20 minutes to obtain a nanoscale fly ash catalyst sample modified by plasma discharge. Table 1 shows the BET analysis data of the present invention at different modification stages.

[0053] Table 1

[0054]

[0055] The gas composition of the dynamic gas distribution system is as follows: NO concentration is 0.1%, O2 concentration is 5%, NH3 concentration is 1%, N2 is used as the balance gas, and the gas input space velocity is 15000h -1 The final multi-characterized modified fly ash catalyst produced at 350°C had a denitration rate of 87.29%, a significant improvement over the 74.19% denitration rate achieved with magnetic separation and ball milling alone, and the 58.10% denitration rate achieved with ball milling and plasma treatment alone. The denitration rate of the original fly ash, which was approximately 43.5%, was more than doubled.

[0056] The multi-characterized modified nanoscale fly ash catalyst prepared by this invention further improves the surface defect level of the material, increasing the average pore size to 12 nm, the resistivity to 33 MΩ·cm, and the oxygen vacancy concentration to 80%. This provides more oxygen vacancy active sites, thereby accelerating the selective catalytic reduction process during denitrification. This catalyst has a wide temperature window and achieves better exhaust gas treatment results. Furthermore, utilizing these characteristic properties to improve denitrification catalysts provides new insights into catalyst design. Fly ash is a widely generated industrial waste with low disposal costs and wide availability, thus enabling full resource utilization. The significance of modifying fly ash lies in improving its application performance, thereby maximizing resource utilization and economic benefits. Compared to other catalysts, the cost of preparing the multi-characterized modified nanoscale fly ash catalyst is relatively low, effectively reducing catalyst production costs. Based on a 10,000-ton / year production capacity, the production cost of the catalyst presented in this invention is 23% of that of conventional V2O5-WO3 / TiO2 catalysts, and the use of toxic vanadium compounds is avoided.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A multi-characterization modification method for fly ash catalyst for tail gas post-treatment, characterized in that: include: Use high-intensity magnetic separation equipment to carry out wet magnetic separation of fly ash raw ash to improve redox properties; The powder after magnetic separation is subjected to ball milling activation treatment in an oxygen-rich environment in the presence of hydrogen peroxide solution to improve the specific surface area; The iron-based powder after ball milling is modified by plasma discharge in an oxygen atmosphere to improve electron mobility.

2. The method for multi-characterization modification of fly ash catalyst for exhaust gas post-treatment according to claim 1, characterized in that: The high-intensity magnetic separation device is a magnetic separation rod with a magnetic strength of 10000G.

3. The method for multi-characterization modification of fly ash catalyst for exhaust gas post-treatment according to claim 2, characterized in that: High-intensity magnetic separation equipment is used to carry out wet magnetic separation of fly ash raw ash, specifically: Mixing raw fly ash with deionized water to form a slurry; Add 2-5wt% anhydrous ethanol as a dispersant to the mortar and stir it with an electronic stirrer to effectively prevent particles from agglomerating; Immerse a magnetic separation rod with a magnetic strength of 10,000 G into the slurry and stir continuously; Use a plastic scraper to collect the magnetic mixture adsorbed on the surface of the magnetic separation rod; The obtained magnetic mixture was placed in a drying oven and dried for several hours to a constant weight.

4. The method for multi-characterization modification of fly ash catalyst for exhaust gas post-treatment according to claim 1, characterized in that: The powder after magnetic separation is subjected to ball milling activation treatment in an oxygen-rich environment in the presence of hydrogen peroxide solution, specifically: The fly ash raw materials after magnetic separation are placed in a planetary ball mill; adding hydrogen peroxide solution as a ball milling aid and ball milling coolant; Set the ball mill speed and ball milling time; The ball-milled material and the ball mill jar are placed in a drying oven and dried to powder form. The surface of the grinding balls is brushed and the final product is sieved and collected.

5. A multi-characterization modification method for fly ash catalyst for tail gas post-treatment according to claim 1 or 4, characterized in that: The mass percentage of the hydrogen peroxide solution used is 5.7%-8.7wt%.

6. The method for multi-characterization modification of fly ash catalyst for exhaust gas post-treatment according to claim 4, characterized in that: The grinding balls are made of zirconium oxide and have four radii: 4 mm, 6 mm, 10 mm, and 20 mm, with a mass ratio of 2:3:3:2 and a filling rate of 0.25-0.

35.

7. The method for multi-characterization modification of fly ash catalyst for exhaust gas post-treatment according to claim 1, characterized in that: When performing plasma discharge modification, first set the discharge spacing, discharge length and discharge power, evenly spread the ball-milled iron-based powder in the discharge area, select oxygen atmosphere as the gas atmosphere, and modify for several minutes.

8. The method for multi-characterization modification of fly ash catalyst for exhaust gas post-treatment according to claim 7, characterized in that: The discharge power is 120-150W.

9. The method for multi-characterization modification of fly ash catalyst for exhaust gas post-treatment according to claim 1, characterized in that: The device for achieving plasma discharge includes a high-voltage electrode, a grounding electrode, a nylon fixing piece and a transparent quartz tube. The two ends of the transparent quartz tube are connected to the nylon fixing pieces, one of the nylon fixing pieces is provided with an air inlet, and the other nylon fixing piece is provided with an air outlet. The high-voltage electrode passes through the two nylon fixing pieces and is placed in the transparent quartz tube. The grounding electrode is sleeved on the outside of the transparent quartz tube.

10. The method for multi-characterization modification of fly ash catalyst for exhaust gas post-treatment according to claim 9, characterized in that: The ball-milled iron-based powder is placed in the discharge area of a transparent quartz tube.

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