Ceramic filter tube for dry flue gas removal and method for producing the same

Abstract

The application discloses a ceramic filter tube for dry flue gas removal and a preparation method thereof. The filter tube comprises a support body, a ceramic fiber layer and a catalytic layer, the ceramic fiber layer is located between the support body and the catalytic layer, the catalytic layer is prepared after catalyst slurry is dried and calcined, and the catalyst slurry comprises vanadyl oxalate solution, nano titanium dioxide powder and nitrogen-containing metal organic framework. x The application also adds a self-made pore-forming agent in the process of preparing the support body, so that the filter tube material has stable removal effect on NOx, the removal effect changes little with the increase of flue gas flow rate, and the catalytic effect is high.

Description

Technical Field

[0001] This invention belongs to the field of flue gas treatment technology, specifically relating to a ceramic filter tube for dry flue gas removal and its preparation method. Background Technology

[0002] Ceramic filter tubes are prepared by vacuum filtration using a support, ceramic fibers, and a binder, and then loaded with a denitrification catalyst to form ceramic fiber catalytic filter tubes. These can be applied to "dry desulfurization, defluorination, denitrification, and dust removal technology"—ceramic filter tube denitrification and dust removal combined with two-stage series desulfurization treatment. Ceramic fibers are inert, corrosion-resistant, and high-temperature resistant, and do not readily react with chemicals. In the field of flue gas treatment, ceramic filter tubes have a longer service life than traditional filter bags.

[0003] In the water catalytic layer of ceramic filter tubes, increasing the catalyst loading rate can promote catalytic activity and improve the NO emission of the catalytic filter tube. x Conversion rate and N2O generation. However, the higher the catalyst loading rate, the easier it is for catalyst particles to clog the internal pores of the filter tube, leading to an increase in pressure drop; some fine dust may firmly adhere to the surface of the ceramic fiber catalytic filter tube or penetrate into the interior of the filter tube, affecting catalytic and flue gas treatment efficiency. Furthermore, traditional catalyst impregnation processes are insufficient in terms of catalyst uniformity for large-sized ceramic fiber filter tubes, resulting in lower catalytic efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide a ceramic filter tube for dry flue gas removal and its preparation method, so as to solve the problem of low catalytic efficiency of ceramic fiber catalytic filter tubes.

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

[0006] A ceramic filter tube for dry flue gas removal includes a support, a ceramic fiber layer, and a catalyst layer. The ceramic fiber layer is located between the support and the catalyst layer. The catalyst layer is prepared by drying and calcining a catalyst slurry. The catalyst slurry includes a vanadium oxalate solution, nano-titanium dioxide powder, and a nitrogen-containing metal-organic framework. Ammonium metavanadate and oxalic acid are mixed in water at a molar ratio of 1:2 to obtain a vanadium oxalate solution. Then, nano-titanium dioxide and a nitrogen-containing metal-organic framework are added to prepare a catalyst slurry with a solid content of 3%-6%.

[0007] Furthermore, the nitrogen-containing metal-organic framework is synthesized with organic ligands centered on metal Zr ions, wherein the organic ligands are pyridine-2,6-dicarboxylic acid and 2-aminoterephthalic acid.

[0008] Furthermore, the thickness of the ceramic fiber layer is 1.5-2 mm.

[0009] A method for preparing a ceramic filter tube for dry flue gas removal includes the following steps:

[0010] Step 1: Mix 70-80 parts cordierite aggregate, 20-30 parts binder and 5-7 parts pore-forming agent by weight, and heat-cast the mixture with vibration to obtain a green body. The green body is then sintered to obtain a support body. The pore-forming agent is a graphene-POSS composite material.

[0011] The second step is to place the support into the fiber suspension slurry, filter and shape it, and then fire it to obtain a ceramic fiber layer.

[0012] The third step involves coating the surface of the fiber layer with a catalyst slurry at room temperature, followed by drying and calcination to obtain a ceramic filter tube for dry flue gas removal.

[0013] Furthermore, the fiber suspension slurry is prepared by mixing ceramic fibers, cordierite aggregate, and binder in a mass ratio of 4:3:3 to form a slurry with a mass fraction of 15%-30%. Carboxymethyl cellulose is added at a mass ratio of 0.3% of the slurry, and the mixture is ball-milled. The ceramic fibers have a length of 100-300 μm and a fiber aspect ratio of 15-20. The cordierite aggregate has a particle size of 80-150 μm.

[0014] Furthermore, in the first step, the temperature control during the sintering process is as follows:

[0015] 100-700℃, heating rate is 10℃ / h; 700-1340℃, heating rate is 15℃ / h; hold at 1340℃ for sintering for 2-3 hours, and cool with the furnace after sintering.

[0016] Furthermore, in the second step, the temperature control during the firing process is as follows:

[0017] The heating rate is 40℃ / h, the temperature is raised to 1220-1260℃, and held for 2-3 hours. After firing, the furnace is cooled.

[0018] Furthermore, the temperature control in the third step is as follows:

[0019] The product is dried at 105℃ for 12 hours and calcined at 500℃ for 5 hours.

[0020] Furthermore, the pore-forming agent is prepared by the following steps:

[0021] NH2-POSS, graphene oxide aqueous dispersion, anhydrous ethanol and water were mixed, the pH was adjusted to 9, and the mixture was stirred for 8 hours at 80℃. After the reaction was completed, the mixture was centrifuged, washed with ethanol and dried to obtain the pore-forming agent. The mass ratio of NH2-POSS to graphene oxide was 1:1.

[0022] Furthermore, the NH2-POSS is synthesized by the hydrolytic condensation reaction of γ-aminopropyltriethoxysilane.

[0023] The beneficial effects of this invention are:

[0024] 1. This invention prepares a ceramic filter tube for dry flue gas removal. The ceramic filter tube includes a support, a ceramic fiber layer, and a catalyst layer. The catalyst layer is prepared by drying and calcining a catalyst slurry. The catalyst slurry includes vanadium oxalate solution, nano-titanium dioxide powder, and a nitrogen-containing metal-organic framework. The added nitrogen-containing metal-organic framework provides alkaline adsorption sites, improving the selective adsorption of acidic gases containing nitrogen pollutants by the catalyst layer. This catalyst layer has strong adsorption affinity and oxidation catalytic activity. The prepared filter tube material is effective against NO. x The removal effect is stable, and the removal effect changes little with the increase of flue gas velocity, resulting in a high catalytic effect.

[0025] 2. The support provides mechanical performance assurance for the application of ceramic membranes and is the foundation for the use of the entire membrane. In addition, the present invention adds a self-made pore-forming agent in the preparation of the support to ensure high porosity, appropriate pore size and distribution, and certain mechanical strength. The pore-forming agent is a graphene-POSS composite material, in which organic-inorganic hybrid particles (POSS) with good dispersibility are loaded on the surface of graphene oxide to improve the uniformity of pore size distribution. The gas generated by the carbothermic reaction of the pore-forming agent forms micropores in the green body, which is beneficial to improving the porosity of the support and increasing the firing temperature. The sintering residue is mainly composed of silicon compounds including SiO2, SiC and SiCO, which have high heat resistance and mechanical strength, which is beneficial to improving the strength and porosity of the support. Detailed Implementation

[0026] 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.

[0027] Example 1

[0028] Preparation of the support:

[0029] Measure 11 mL of deionized water, 5 mL of propanol, 1 mL of acetonitrile and 200 mL of tetraethylammonium hydroxide into a three-necked flask, mix thoroughly at room temperature, slowly add 25 g of γ-aminopropyltriethoxysilane, stir vigorously for 10 min, then stir magnetically at 60 °C for 24 h, cool to room temperature, place the product in tetrahydrofuran cooled to 0 °C and keep it at a constant temperature until a large amount of white solid precipitates, filter, precipitate with tetrahydrofuran, and dry under vacuum at 35 °C to constant weight to obtain NH2-POSS product;

[0030] Mix 0.5 g NH2-POSS, 50 mL 10 g / L graphene oxide aqueous dispersion, 60 g anhydrous ethanol, and 20 g water. Adjust the pH to 9 and react at 80 °C for 8 h. After the reaction, centrifuge, wash with ethanol, and dry to obtain the pore-forming agent. The mass ratio of NH2-POSS to graphene oxide is 1:1.

[0031] By weight, 70 parts cordierite aggregate, 20 parts binder, and 5 parts pore-forming agent were mixed and vibratory hot casting was performed to obtain a green body. The green body was then sintered to obtain a support body. The pore-forming agent was a graphene-POSS composite material. The temperature control during the sintering process was as follows: 100-700℃, heating rate of 10℃ / h; 700-1340℃, heating rate of 15℃ / h; sintering at 1340℃ for 2 hours; after sintering, the material was cooled in the furnace to obtain the support body.

[0032] Example 2

[0033] Preparation of the support:

[0034] Compared with Example 1, this embodiment, by weight, uses 80 parts cordierite aggregate, 30 parts binder, and 7 parts pore-forming agent prepared in Example 1. The remaining raw materials and preparation process are the same as in the example.

[0035] Comparative Example 1

[0036] Compared with Example 1, the pore-forming agent in this comparative example is replaced with graphene treated with conventional silane coupling agent, while the other raw materials and preparation process remain the same as in Example 1.

[0037] The samples prepared in Examples 1-2 and Comparative Example 1 were tested. The bending strength of the porous support material was tested using the three-point bending method, and the test method was in accordance with GBT1965-1996.

[0038] Porosity: refers to the percentage of open pore volume in the total volume of a product. It is tested using the vacuum method. The sample used is Φ40×10×40mm, and the testing standard is GB1966-1996. The results are shown in Table 1 below.

[0039] Table 1

[0040] project Example 1 Example 2 Comparative Example 1 Porosity / % 31 33 25 Flexural strength / MPa 27.2 26.5 24.8

[0041] In Example 1, the amount of pore-forming agent added was approximately 5%, and in Example 2, it was approximately 6%. Within a certain range, as the amount of pore-forming agent increases, the porosity increases, but the corresponding flexural strength decreases. However, the support prepared in this invention can maintain high compressive strength while ensuring good porosity, better meeting the application requirements of the support as a ceramic filter tube. In Comparative Example 1, graphene treated with conventional silane coupling agents was used. Silane coupling agents can improve the dispersibility of graphene, but during processing, there are hydrolysis and condensation reactions between silane coupling agent molecules. This not only fails to reduce the overlap between layers but also leads to the inhomogeneity of the overall structure, thereby causing a decrease in the overall performance of the support.

[0042] Example 3

[0043] Preparation of catalyst slurry:

[0044] 0.7 g of pyridine-2,6-dicarboxylic acid and 1.4 g of zirconium oxychloride octahydrate were added to 50 mL of formic acid, followed by 1 L of water. The mixture was refluxed at 120 °C for 3 h. After centrifugation, washing with ethanol, and vacuum drying at 55 °C, a nitrogen-containing metal-organic framework was obtained.

[0045] Ammonium metavanadate and oxalic acid were mixed in water at a molar ratio of 1:2 to obtain a vanadium oxalate oxychloride solution. Then, nano-titanium dioxide and a nitrogen-containing metal-organic framework were added to prepare a catalyst slurry with a solid content of 3%. The mass ratio of ammonium metavanadate, nano-titanium dioxide, and the nitrogen-containing metal-organic framework was 1:18:1.

[0046] Example 4

[0047] Preparation of catalyst slurry:

[0048] 0.7g of 2-amino-1,4-phthalic acid, 1g of zirconium chloride and 1 drop of DMF (N,N-dimethylformamide) were added to 30mL of glacial acetic acid, stirred and dissolved, and then added to 5mL of water. The mixture was heated to 120℃ and reacted for 2h. After centrifugation, washing with ethanol and vacuum drying at 55℃, a nitrogen-containing metal-organic framework was obtained.

[0049] Ammonium metavanadate and oxalic acid were mixed in water at a molar ratio of 1:2 to obtain a vanadium oxalate oxychloride solution. Then, nano-titanium dioxide and a nitrogen-containing metal-organic framework were added to prepare a catalyst slurry with a solid content of 5%. The mass ratio of ammonium metavanadate, nano-titanium dioxide, and the nitrogen-containing metal-organic framework was 1:18:1.

[0050] Comparative Example 2

[0051] Compared with Example 4, this comparative example replaces the nitrogen-containing metal-organic framework with nano-titanium dioxide, while the other raw materials and preparation process remain the same as in Example 4.

[0052] Example 5

[0053] This embodiment provides a ceramic filter tube for dry flue gas removal, comprising a support, a ceramic fiber layer and a catalyst layer, wherein the ceramic fiber layer is located between the support and the catalyst layer, and the catalyst layer is obtained by drying and calcining a catalyst slurry.

[0054] A method for preparing a ceramic filter tube for dry flue gas removal includes the following steps:

[0055] Step 1: Use the support prepared in Example 1;

[0056] The second step involves placing the support in a fiber suspension slurry, filtering and molding it, and then firing it to obtain a ceramic fiber layer. The fiber suspension slurry is made by mixing ceramic fibers (containing zirconium aluminosilicate fibers), cordierite aggregate, and binder (clay, feldspar, talc, spodumene, and zinc oxide in a mass ratio of 2:1:1:0.5) in a mass ratio of 4:3:3 to form a slurry with a mass fraction of 15%. Carboxymethyl cellulose is added at a mass fraction of 0.3% of the slurry, and the mixture is ball-milled for 60 minutes. The length of the ceramic fibers is 100-300 μm, and the aspect ratio is 15-20. The particle size of the cordierite aggregate is 80-150 μm. The temperature control during the firing process is as follows: the heating rate is 40℃ / h, the temperature is raised to 1220-1260℃, and the temperature is held for 2-3 hours. After firing, the mixture is cooled in the furnace.

[0057] The third step involves coating the surface of the fiber layer with the catalyst slurry prepared according to the proportions in Example 3 at room temperature, followed by drying at 105°C for 12 hours and calcining at 500°C for 5 hours, to produce a ceramic filter tube for dry flue gas removal. The catalyst loading is 10% (based on solid content); the thickness of the ceramic fiber layer is 1.5-2 mm.

[0058] Example 6

[0059] This embodiment provides a ceramic filter tube for dry flue gas removal, comprising a support, a ceramic fiber layer and a catalyst layer, wherein the ceramic fiber layer is located between the support and the catalyst layer, and the catalyst layer is obtained by drying and calcining a catalyst slurry.

[0060] A method for preparing a ceramic filter tube for dry flue gas removal includes the following steps:

[0061] Step 1: Use the support prepared in Example 1;

[0062] The second step involves placing the support in a fiber suspension slurry, filtering and molding it, and then firing it to obtain a ceramic fiber layer. The fiber suspension slurry is made by mixing ceramic fibers (containing zirconium aluminosilicate fibers), cordierite aggregate, and binder (clay, feldspar, talc, spodumene, and zinc oxide in a mass ratio of 2:1:1:0.5) in a mass ratio of 4:3:3 to form a slurry with a mass fraction of 30%. Carboxymethyl cellulose is added at a mass fraction of 0.3% of the slurry, and the mixture is ball-milled for 60 minutes. The length of the ceramic fibers is 100-300 μm, and the aspect ratio is 15-20. The particle size of the cordierite aggregate is 80-150 μm. The temperature control during the firing process is as follows: the heating rate is 40℃ / h, the temperature is raised to 1220-1260℃, and the temperature is held for 2-3 hours. After firing, the mixture is cooled with the furnace.

[0063] The third step involves coating the surface of the fiber layer with the catalyst slurry prepared according to the proportions in Example 4 at room temperature, followed by drying at 105°C for 12 hours and calcining at 500°C for 5 hours, to produce a ceramic filter tube for dry flue gas removal. The catalyst loading is 10% (based on solid content); the thickness of the ceramic fiber layer is 1.5-2 mm.

[0064] Comparative Example 3

[0065] Compared with Example 5, this embodiment uses the catalyst slurry prepared in Comparative Example 2 instead.

[0066] Performance tests were conducted on Examples 5-6 and Comparative Example 3, and the NO removal rate was recorded at different flue gas velocities. Evaluation experiments were performed using simulated flue gas without considering the influence of fly ash particles.

[0067] Evaluation experiments were conducted using simulated flue gas without considering the influence of fly ash particles. Typical experimental conditions were: N2 as the equilibrium gas, O2 volume fraction of 4%, temperature of 340-350℃, and NO... x The mass concentration is 750-1100 mg / m³ 3 The NH3 mass concentration is 430 mg / m³. 3 By changing the flue gas velocity to vary the surface velocity between 1-6 cm / s, the removal rate / % = (C 进 -C 出 ) / C 进 ×100%; (where C is a percentage of 100%) 进 For imported NO x Mass concentration, C 出 For imported NO x The results (mass concentration) are shown in Table 2:

[0068] Table 2

[0069]

[0070] As can be seen from Table 2, the filter tube material prepared in this invention is effective against NO.x The removal effect is stable, and the removal effect changes little with the increase of flue gas velocity, resulting in a high catalytic effect.

[0071] 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.

[0072] 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 ceramic filter tube for dry flue gas removal, characterized in that, The catalyst comprises a support, a ceramic fiber layer, and a catalyst layer, wherein the ceramic fiber layer is located between the support and the catalyst layer. The catalyst layer is prepared by drying and calcining a catalyst slurry, and the catalyst slurry comprises vanadium oxalate solution, nano-titanium dioxide powder, and a nitrogen-containing metal-organic framework; the solid content of the catalyst slurry is 3%-6%; the support is prepared by the following steps: 70-80 parts cordierite aggregate, 20-30 parts binder, and 5-7 parts pore-forming agent are mixed and then vibrated and hot-cast to obtain a green body. The green body is then sintered to obtain a support. The pore-forming agent is prepared by the following steps: NH2-POSS, graphene oxide aqueous dispersion, anhydrous ethanol, and water are mixed and the pH value is adjusted to 9. The mixture is stirred and reacted at 80°C. After centrifugation, washing with ethanol, and drying, the pore-forming agent is obtained. The mass ratio of NH2-POSS to graphene oxide is 1:

1. The NH2-POSS is synthesized by the hydrolysis and condensation reaction of γ-aminopropyltriethoxysilane.

2. The ceramic filter tube for dry flue gas removal according to claim 1, characterized in that, The nitrogen-containing metal-organic framework is synthesized with organic ligands centered on the metal Zr ion, wherein the organic ligands are pyridine-2,6-dicarboxylic acid and 2-aminoterephthalic acid.

3. The ceramic filter tube for dry flue gas removal according to claim 1, characterized in that, The thickness of the ceramic fiber layer is 1.5-2 mm.

4. A method for preparing a ceramic filter tube for dry flue gas removal according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Mix 70-80 parts cordierite aggregate, 20-30 parts binder and 5-7 parts pore-forming agent by weight, and heat-cast the mixture with vibration to obtain a green body. The green body is then sintered to obtain a support body. The pore-forming agent is a graphene-POSS composite material. The second step is to place the support into the fiber suspension slurry, filter and shape it, and then fire it to obtain a ceramic fiber layer. The third step involves coating the surface of the fiber layer with a catalyst slurry at room temperature, followed by drying and calcination to obtain a ceramic filter tube for dry flue gas removal.

5. The method for preparing a ceramic filter tube for dry flue gas removal according to claim 4, characterized in that, The fiber suspension slurry is made by mixing ceramic fibers, cordierite aggregate, and binder in a mass ratio of 4:3:3 to form a slurry with a mass fraction of 15%-30%. Carboxymethyl cellulose is added at a mass ratio of 0.3% of the slurry and then ball-milled. The ceramic fibers have a length of 100-300μm and a fiber aspect ratio of 15-20. The cordierite aggregate has a particle size of 80-150μm.

6. The method for preparing a ceramic filter tube for dry flue gas removal according to claim 4, characterized in that, In the first step, the temperature is controlled as follows during the sintering process: 100-700℃, heating rate is 10℃ / h; 700-1340℃, heating rate is 15℃ / h; hold at 1340℃ for sintering for 2-3 hours, and cool with the furnace after sintering.

7. The method for preparing a ceramic filter tube for dry flue gas removal according to claim 4, characterized in that, In the second step, the temperature control during the firing process is as follows: The heating rate is 40℃ / h, the temperature is raised to 1220-1260℃, and held for 2-3 hours. After firing, the furnace is cooled.

8. The method for preparing a ceramic filter tube for dry flue gas removal according to claim 4, characterized in that, The temperature control in the third step is as follows: The product is dried at 105℃ for 12 hours and calcined at 500℃ for 5 hours.

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