Catalyst for flue gas purification and process for its production

Abstract

The application discloses a kind of catalysts for flue gas purification and its production process, belong to denitration catalyst technical field.The catalysts for flue gas purification, including by outer to inside sequentially coated manganese shell, carrier and iron core;The manganese shell, carrier and iron core;Preparation method includes the following steps: butyl titanate is dispersed in anhydrous ethanol, add urea and tourmaline, after filtration precipitation deionized water washing dry, obtain tourmaline modified nano TiO2;Tourmaline modified nano TiO2 is immersed in iron precursor solution, rotary evaporation is calcined to obtain intermediate;Intermediate is immersed in manganese precursor solution, add KMnO4 stationary reaction, suction filtration wash dry obtained catalyst is a three-layer coated core-shell structure, with high denitration activity and excellent sulfur poisoning resistance at low temperature (100-200 DEG C).

Description

Technical Field

[0001] This invention belongs to the field of denitrification catalyst technology, specifically relating to a catalyst for flue gas purification and its production process. Background Technology

[0002] The combustion of fossil fuels inevitably produces harmful substances. Because vehicle exhaust and industrial emissions are located close to densely populated areas and tend to accumulate, they cause severe environmental damage, leading to various environmental problems including acid rain, photochemical smog, and ozone depletion. These problems have long had a significant impact on human survival and development. Such environmental pollution issues have long been a concern for researchers worldwide. Nitrogen oxides (NOx) are a major pollutant. x Nitrogen oxides pose a serious threat in terms of both composition and hazard, therefore, the treatment of both stationary and mobile sources must be thoroughly implemented. Although denitrification technology has achieved some results and accumulated some experience in related technologies in the past, selective catalytic reduction (SCR) technology is still considered the most economical and effective treatment method for nitrogen oxides.

[0003] Currently, NO x There are many emission reduction methods, but the most widely used in industry is ammonia selective catalytic reduction (NH3-SCR). SCR technology involves adding NH3 as a reducing agent at a flue gas temperature of 300-400℃, and under the action of a catalyst, reducing NO2... x Converting to nitrogen and water, the denitrification efficiency can reach over 90%. Currently, the commercially available catalyst is V2O5-WO3 / TiO2, with an activity temperature window of 300-400℃. Industrially, SCR reactors are mainly placed before dust removal and desulfurization units. However, the high content of fly ash and sulfur dioxide in the flue gas easily causes catalyst blockage and poisoning, resulting in a significant reduction in catalyst lifespan. From this perspective, the SCR reactor should be placed after dust removal and desulfurization units for low-temperature, low-dust operation. However, the flue gas temperature after dust removal and desulfurization is relatively low (<200℃). The flue gas temperature emitted from pollution sources such as cement kilns, industrial kilns, coking furnaces, and waste incineration plants is below 250℃, which does not reach the effective temperature of the V2O5-WO3 / TiO2 catalyst system, resulting in a significant reduction in denitrification efficiency. Furthermore, the main active substance of the catalyst, V2O5, is a highly toxic substance, and catalyst waste causes serious secondary pollution to the environment. Therefore, a low-temperature denitrification catalyst for flue gas purification is urgently needed to solve these problems. Summary of the Invention

[0004] The purpose of this invention is to provide a catalyst for flue gas purification and its production process, so as to solve the problems of low denitrification efficiency and poor resistance to SO2 poisoning of existing denitrification catalysts in the low temperature range of 120-200℃.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A process for producing a catalyst for flue gas purification includes the following steps:

[0007] S1. Add ferric nitrate to oxalic acid solution and stir at room temperature (25-30℃) until the solution turns yellow-green to obtain an iron precursor solution;

[0008] S2. Tetrabutyl titanate was dispersed in anhydrous ethanol, urea was added and mixed evenly, then tourmaline was added, and the mixture was stirred at 40-50℃ for 20-30 h. The precipitate was filtered, washed with deionized water and dried to obtain tourmaline-modified nano-TiO2.

[0009] S3. Tourmaline-modified nano-TiO2 was impregnated in an iron precursor solution, stirred at room temperature for 2-4 hours, the solid was collected by rotary evaporation, dried at 90-120℃ for 10-15 hours, and then calcined at 450-500℃ for 4-5 hours to obtain an intermediate.

[0010] S4. In-situ growth preparation of manganese shell: Manganese acetate was dissolved in deionized water as a precursor solution for manganese. The intermediate was immersed in the manganese precursor solution and allowed to stand for 12-16 h. KMnO4 solution was added and stirred until homogeneous. After standing for another 12-16 h, the mixture was filtered and washed until the filtrate was clear. The filtrate was dried at 90-120℃ for 15-20 h to prepare a catalyst for flue gas purification, denoted as Mn@TiO2 / Fe-T catalyst.

[0011] As a further aspect of the present invention, the concentration of oxalic acid solution in S1 is 10%.

[0012] As a further embodiment of the present invention, the stirring speed in S1 is 250-350 rpm.

[0013] As a further embodiment of the present invention, the ratio of tetrabutyl titanate, anhydrous ethanol and urea in S2 is 1-2 mL: 20 mL: 0.4-0.8 g.

[0014] As a further embodiment of the present invention, the stirring speed in S2 is 300-400 rpm.

[0015] As a further embodiment of the present invention, the stirring speed in S3 is 300-400 rpm.

[0016] As a further embodiment of the present invention, the ratio of tourmaline-modified nano-TiO2 to iron precursor solution in S3 is 1-2g:20mL.

[0017] As a further embodiment of the present invention, the ratio of manganese precursor solution to intermediate in S4 is 20 mL: 1-2 g.

[0018] As a further embodiment of the present invention, the stirring speed in S4 is 400-500 rpm.

[0019] As a further aspect of the present invention, the molar ratio of manganese to iron in the Mn@TiO2 / Fe-T catalyst is 4:6.

[0020] As a further aspect of the present invention, the amount of tourmaline added is 2% of the mass of the Mn@TiO2 / Fe-T catalyst.

[0021] A catalyst for flue gas purification is prepared by the above-mentioned method, comprising a manganese shell, a support, and an iron core; the manganese shell, the support, and the iron core are sequentially coated from the outside to the inside; the support is tourmaline-modified nano-TiO2.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. This invention provides a catalyst for flue gas purification, which is a three-layer coated core-shell structure catalyst that exhibits high denitrification activity and excellent resistance to sulfur poisoning at low temperatures.

[0024] 2. This invention provides a production process for a catalyst for flue gas purification. By using a combined impregnation-in-situ growth method, on the one hand, the carrier gas stone is modified with nano-TiO2 to protect the internal active materials from sulfation; on the other hand, the Mn active component grown in situ on the carrier surface is uniformly dispersed on the carrier surface, which can easily participate in the SCR reaction, thus improving the low-temperature denitrification performance of the catalyst.

[0025] 3. In this invention, manganese active material forms a manganese shell on the surface of the support through an in-situ growth method of redox reaction, accumulating on the support surface. Due to mass transfer resistance, the mixed gas first contacts the manganese active material on the surface and participates in the SCR reaction. After the manganese active material is activated, the mixed gas further enters the interior of the support, thereby reacting with the iron active material. Therefore, the prepared catalyst can effectively cope with gases to be purified at different flow rates: when the flow rate of the mixed gas is low, it mainly reacts immediately with the manganese active material on the surface, effectively extending the service life of the catalyst; when the flow rate of the mixed gas is high, the active material of the manganese shell on the surface and the iron core inside play a common role, increasing the catalytic efficiency. Attached Figure Description

[0026] The present invention will now be further described with reference to the accompanying drawings.

[0027] Figure 1 This is a schematic diagram of the cross-sectional structure of the Mn@TiO2 / Fe-T catalyst prepared in this invention;

[0028] Figure 2 This is a line graph showing the test results of the denitrification efficiency of the catalysts for flue gas purification prepared in Example 1 and Comparative Examples 1-4 of this invention.

[0029] Figure 3 This is a line graph showing the low-temperature denitrification capacity test results of the Mn@TiO2 / Fe-T catalyst prepared in Example 1 of this invention under different space velocities;

[0030] Figure 4 This is a line graph showing the test results of the sulfur poisoning resistance of the Mn@TiO2 / Fe-T catalyst prepared in Example 1 of this invention.

[0031] In the diagram: 1. Manganese shell; 2. Carrier; 3. Iron core. Detailed Implementation

[0032] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] A process for producing a catalyst for flue gas purification includes the following steps:

[0034] S1. Ferric nitrate is added to a 10% oxalic acid solution and stirred at 250-350 rpm at room temperature until the solution turns yellow-green to obtain an iron precursor solution.

[0035] S2. Disperse tetrabutyl titanate in anhydrous ethanol, add urea and mix well, then add tourmaline, stir at 300-400 rpm for 20-30 h at 40-50℃, filter the precipitate, wash with deionized water and dry to obtain tourmaline-modified nano TiO2; the ratio of tetrabutyl titanate, anhydrous ethanol and urea is 1-2 mL: 20 mL: 0.4-0.8 g;

[0036] S3. Tourmaline-modified nano-TiO2 was impregnated in an iron precursor solution, stirred at 300-400 rpm for 2-4 h at room temperature, the solid was collected by rotary evaporation, dried at 90-120℃ for 10-15 h, and then calcined at 450-500℃ for 4-5 h to obtain an intermediate; the ratio of tourmaline-modified nano-TiO2 to iron precursor solution was 1-2 g: 20 mL.

[0037] S4. Dissolve manganese acetate in deionized water to obtain a manganese precursor solution. Immerse the intermediate in the manganese precursor solution and let it stand for 12-16 hours. Then add KMnO4 solution and stir at 400-500 rpm until homogeneous. Let it stand again for 12-16 hours, filter and wash until the filtrate is clear. Dry at 90-120℃ for 15-20 hours to prepare a catalyst for flue gas purification, denoted as Mn@TiO2 / Fe-T catalyst. The ratio of manganese precursor solution to intermediate is 20 mL: 1-2 g. The molar ratio of manganese to iron in the Mn@TiO2 / Fe-T catalyst is 4:6. The amount of tourmaline added is 2% of the mass of the Mn@TiO2 / Fe-T catalyst.

[0038] A schematic diagram of the cross-sectional structure of the Mn@TiO2 / Fe-T catalyst is shown below. Figure 1 As shown, 1 is a manganese shell, 2 is a carrier, and 3 is an iron core; the carrier 2 is tourmaline-modified nano-TiO2 that coats the iron core 3 to form an intermediate, and the manganese shell 1 is grown in situ on the surface of the intermediate through oxidation-reduction.

[0039] Example 1

[0040] A process for producing a catalyst for flue gas purification includes the following steps:

[0041] S1. Ferric nitrate was added to a 10% oxalic acid solution and stirred at 300 rpm at room temperature until the solution turned yellow-green to obtain an iron precursor solution.

[0042] S2. Tetrabutyl titanate was dispersed in anhydrous ethanol, urea was added and mixed evenly, then tourmaline was added, and the mixture was stirred at 350 rpm for 25 h at 45 °C. The precipitate was filtered, washed with deionized water and dried to obtain tourmaline-modified nano-TiO2. The ratio of tetrabutyl titanate, anhydrous ethanol and urea was 1.5 mL: 20 mL: 0.6 g.

[0043] S3. Tourmaline-modified nano-TiO2 was immersed in an iron precursor solution, stirred at 350 rpm for 3 h at room temperature, the solid was collected by rotary evaporation, dried at 100 °C for 12 h, and then calcined at 480 °C for 4 h to obtain an intermediate; the ratio of tourmaline-modified nano-TiO2 to iron precursor solution was 1.5 g: 20 mL.

[0044] S4. In-situ growth method: Manganese acetate was dissolved in deionized water as a manganese precursor solution. The intermediate was immersed in the manganese precursor solution and allowed to stand for 14 h. KMnO4 solution was then added, and the mixture was stirred at 450 rpm until homogeneous. After standing for another 15 h, the mixture was filtered and washed until the filtrate was clear. It was then dried at 100 °C for 18 h to prepare a catalyst for flue gas purification, denoted as Mn@TiO2 / Fe-T catalyst. The ratio of manganese precursor solution to intermediate was 20 mL:1.5 g. The molar ratio of manganese to iron in the Mn@TiO2 / Fe-T catalyst was 4:6. The amount of tourmaline added was 2% of the mass of the Mn@TiO2 / Fe-T catalyst.

[0045] A schematic diagram of the cross-sectional structure of the Mn@TiO2 / Fe-T catalyst is shown below. Figure 1 As shown, 1 is a manganese shell, 2 is a carrier, and 3 is an iron core; the carrier 2 (tourmaline-modified nano-TiO2) coats the iron core 3 to form an intermediate, and then the manganese shell 1 is grown in situ on the surface of the intermediate through oxidation-reduction.

[0046] Comparative Example 1

[0047] A process for producing a catalyst for flue gas purification includes the following steps:

[0048] S1. Ferric nitrate was added to a 10% oxalic acid solution and stirred at 300 rpm at room temperature until the solution turned yellow-green to obtain an iron precursor solution.

[0049] S2. Tetrabutyl titanate was dispersed in anhydrous ethanol, urea was added and mixed evenly, then tourmaline was added, and the mixture was stirred at 350 rpm for 25 h at 45 °C. The precipitate was filtered, washed with deionized water and dried to obtain tourmaline-modified nano-TiO2. The ratio of tetrabutyl titanate, anhydrous ethanol and urea was 1.5 mL: 20 mL: 0.6 g.

[0050] S3. Tourmaline-modified nano-TiO2 was immersed in an iron precursor solution, stirred at 350 rpm for 3 h at room temperature, the solid was collected by rotary evaporation, dried at 100 °C for 12 h, and then calcined at 480 °C for 4 h to obtain an intermediate; the ratio of tourmaline-modified nano-TiO2 to iron precursor solution was 1.5 g: 20 mL.

[0051] S4. Impregnation method: Manganese acetate was dissolved in deionized water as a manganese precursor solution. The intermediate was impregnated in the manganese precursor solution, allowed to stand for 25 h, dried at 100 °C for 20 h, and then calcined at 480 °C for 3 h. The resulting catalyst for flue gas purification was designated as Mn-TiO2 / Fe-T catalyst. The ratio of manganese precursor solution to intermediate was 20 mL: 1.5 g. The molar ratio of manganese to iron in the Mn-TiO2 / Fe-T catalyst was 4:6. The amount of tourmaline added was 2% of the mass of the Mn-TiO2 / Fe-T catalyst.

[0052] Comparative Example 2

[0053] A process for producing a catalyst for flue gas purification includes the following steps:

[0054] S1. Ferric nitrate was added to a 10% oxalic acid solution and stirred at 300 rpm at room temperature until the solution turned yellow-green to obtain an iron precursor solution.

[0055] S2. Using P25 nano-TiO2: P25 nano-TiO2 and tourmaline were impregnated together in an iron precursor solution. After stirring at 350 rpm for 3 h at room temperature, the solid was collected by rotary evaporation, dried at 100 °C for 12 h, and then calcined at 480 °C for 4 h to obtain an intermediate. The ratio of P25 nano-TiO2 to iron precursor solution was 1.5 g: 20 mL.

[0056] S3. In-situ growth method: Manganese acetate was dissolved in deionized water as a manganese precursor solution. The intermediate was immersed in the manganese precursor solution and allowed to stand for 14 h. KMnO4 solution was added and stirred at 450 rpm until homogeneous. After standing for another 15 h, the mixture was filtered and washed until the filtrate was clear. It was then dried at 100℃ for 18 h to prepare a catalyst for flue gas purification, denoted as Mn@TiO2-Fe-T catalyst. The ratio of manganese precursor solution to intermediate was 20 mL:1.5 g. The molar ratio of manganese to iron in the Mn@TiO2-Fe-T catalyst was 4:6. The amount of tourmaline added was 2% of the mass of the Mn@TiO2-Fe-T catalyst.

[0057] Comparative Example 3

[0058] A process for producing a catalyst for flue gas purification includes the following steps:

[0059] S1. Ferric nitrate was added to a 10% oxalic acid solution and stirred at 300 rpm at room temperature until the solution turned yellow-green to obtain an iron precursor solution; manganese acetate was dissolved in deionized water to obtain a manganese precursor solution; the iron precursor solution and the manganese precursor solution were mixed evenly at a molar ratio of manganese to iron of 6:4 to obtain a manganese-iron precursor solution.

[0060] S2. Tetrabutyl titanate was dispersed in anhydrous ethanol, urea was added and mixed evenly, then tourmaline was added, and the mixture was stirred at 350 rpm for 25 h at 45 °C. The precipitate was filtered, washed with deionized water and dried to obtain tourmaline-modified nano-TiO2. The ratio of tetrabutyl titanate, anhydrous ethanol and urea was 1.5 mL: 20 mL: 0.6 g.

[0061] S3. Tourmaline-modified nano-TiO2 was impregnated in a manganese-iron precursor solution, stirred at 350 rpm for 5 h at room temperature, the solid was collected by rotary evaporation, dried at 100℃ for 12 h, and then calcined at 480℃ for 5 h to obtain a catalyst for flue gas purification, denoted as TiO2@MnFe-T catalyst; the ratio of tourmaline-modified nano-TiO2 to manganese-iron precursor solution was 1.5 g: 20 mL; the amount of tourmaline added was 2% of the mass of TiO2@MnFe-T catalyst.

[0062] Comparative Example 4

[0063] A production process for a catalyst for flue gas purification is the same as that in Example 1, except that tourmaline is not added in S2. The resulting catalyst for flue gas purification is denoted as Mn@TiO2 / Fe catalyst.

[0064] Performance testing:

[0065] (1) Catalytic activity test:

[0066] The catalytic activity of the flue gas purification catalysts prepared in Example 1 and Comparative Examples 1-4 was tested. The denitrification activity of the catalysts was tested using a fixed-bed SCR reactor, and the composition of the tail gas was determined using a flue gas analyzer (model KM940). The catalysts were ground into 40-60 mesh particles, and 0.5 mL was used in a quartz tube reactor for reaction testing. The reaction gases were: equilibrium gases N2, NO and NH3 at 500 ppm each, and O2 at 5 vol.%, with a total flow rate of 100 mL / min and a space velocity of 10000 h⁻¹. -1 The test temperature range was 120-250℃, and the exhaust gas values ​​were measured every 25℃.

[0067] The formula for calculating NOx conversion rate is shown in Equation A:

[0068]

[0069] In the formula, n represents the NOx conversion rate, NOx includes NO and NO2, (NOx)in is the maximum concentration of NOx entering the reactor, and (NOx)out is the concentration of flue gas measured after passing through the catalyst;

[0070] Test results are as follows Figure 2 As shown, by Figure 2 It can be seen that the Mn@TiO / Fe-T prepared in Example 1 exhibits the best catalytic activity under low-temperature conditions, with a conversion rate exceeding 95% between 100-200℃. In Comparative Example 1, the manganese acetate was decomposed by calcination through impregnation. Part of the manganese active material was loaded on the surface, while the other part migrated to the support and iron core, resulting in less manganese active component on the surface. In Comparative Example 2, nano-TiO2 and tourmaline were directly mixed and impregnated. Tourmaline did not effectively promote the growth of nano-TiO2, and the effective loading surface area of ​​the support was relatively small, resulting in lower catalytic efficiency. In Comparative Example 3, the active material was encapsulated on the support, resulting in weak surface catalytic ability. However, the catalytic performance improved with increasing temperature. In Comparative Example 4, no tourmaline was added. The addition of tourmaline promoted the growth of TiO2, resulting in finer grains, effectively protecting the internal structure of the catalyst, and further improving the denitrification performance.

[0071] (2) Airspeed condition test:

[0072] The low-temperature denitrification capacity of the Mn@TiO2 / Fe-T catalyst prepared in Example 1 was tested under different space velocities. The test results are as follows: Figure 3 As shown, by Figure 3 It can be seen that space velocity reflects the duration of contact between the gas and the catalyst. A higher space velocity means a larger gas flow rate on the same cross-section, thus placing higher demands on the catalyst performance. The Mn@TiO2 / Fe-T catalyst prepared in Example 1 exhibits higher denitration catalytic efficiency under higher space velocity conditions. This is because the tourmaline-modified TiO2 support layer protects the iron core active material, extending the catalyst's lifespan.

[0073] (3) Sulfur poisoning resistance test:

[0074] The sulfur poisoning resistance of the flue gas purification catalysts prepared in Example 1 and Comparative Examples 1-4 was tested using a denitrification activity testing device: first, the temperature was raised to 150°C and held for 2 hours, then 250 and 500 mg·m³ of sulfur were introduced. -3 SO2 was removed, and the process was stopped after 10 hours; during this period, the denitrification efficiency of the catalyst was recorded. The sulfur poisoning resistance of the catalyst prepared in Example 1 was as follows. Figure 4 As shown in Table 1, the test results of the sulfur poisoning resistance of the catalysts in Example 1 and Comparative Examples 1-4 are shown in Table 1.

[0075] Table 1

[0076]

[0077] Depend on Figure 4 As shown in Table 1, the catalyst for flue gas purification prepared in this invention has a performance of 250 mg·m³. -3At SO2 concentrations, the desulfurization efficiency hardly decreased, indicating that the catalyst has excellent sulfur resistance at this concentration; when the SO2 concentration increased to 500 mg·m³, the desulfurization efficiency remained almost unchanged. -3 At that time, the desulfurization efficiency dropped to 78.2% after 10 hours, but it still had a good denitrification effect.

[0078] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0079] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A production process for a catalyst for flue gas purification, characterized in that, Includes the following steps: S1. Ferric nitrate is added to oxalic acid solution and stirred at room temperature until the solution turns yellow-green to obtain an iron precursor solution; S2. Tetrabutyl titanate was dispersed in anhydrous ethanol, urea was added and mixed evenly, then tourmaline was added, and the mixture was stirred at 40-50℃ for 20-30 h. The precipitate was filtered, washed with deionized water and dried to obtain tourmaline-modified nano-TiO2. S3. Tourmaline-modified nano-TiO2 was impregnated in an iron precursor solution, stirred at room temperature for 2-4 hours, the solid was collected by rotary evaporation, dried at 90-120℃ for 10-15 hours, and then calcined at 450-500℃ for 4-5 hours to obtain an intermediate. S4. Dissolve manganese acetate in deionized water as a manganese precursor solution. Immerse the intermediate in the manganese precursor solution. After standing for 12-16 hours, add KMnO4 solution and stir to mix evenly. After standing for another 12-16 hours, filter and wash until the filtrate is clear. Dry at 90-120℃ for 15-20 hours to prepare a catalyst for flue gas purification. In S3, the ratio of tourmaline-modified nano-TiO2 to iron precursor solution is 1-2g:20mL; The molar ratio of manganese to iron in the catalyst for flue gas purification is 4:

6. The amount of tourmaline added is 2% of the mass of the catalyst used for flue gas purification.

2. The production process of a catalyst for flue gas purification according to claim 1, characterized in that, The concentration of oxalic acid solution in S1 is 10%.

3. The production process of a catalyst for flue gas purification according to claim 1, characterized in that, The ratio of tetrabutyl titanate, anhydrous ethanol, and urea in S2 is 1-2 mL: 20 mL: 0.4-0.8 g.

4. The production process of a catalyst for flue gas purification according to claim 1, characterized in that, The ratio of manganese precursor solution to intermediate in S4 is 20 mL: 1-2 g.

5. The production process of a catalyst for flue gas purification according to claim 1, characterized in that, The stirring speed in S1 is 250-350 rpm; the stirring speed in S2 is 300-400 rpm; the stirring speed in S3 is 300-400 rpm; and the stirring speed in S4 is 400-500 rpm.

6. A catalyst for flue gas purification, characterized in that, It is produced by the production process described in any one of claims 1-5.

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