Preparation method and application of multifunctional dedusting and denitration filter material with PTFE (Polytetrafluoroethylene) foam coating

Abstract

The invention provides a PTFE foam coating multifunctional dedusting and denitration filter material and a preparation method thereof, and the technology is realized through the following steps: firstly preparing an efficient denitration catalyst, then preparing a dedusting filter material taking double base cloth as a substrate, and enhancing the structural stability through a special process. Then, the catalyst powder is uniformly impregnated in the substrate layer and dried to ensure the maximization of the catalytic activity. Then, a PTFE foaming coating is prepared, the surface of the needled felt is accurately coated with the PTFE foaming coating, the uniformity of the coating and the strong adhesive force of the coating and the base material are ensured through a gradient drying technology, and preparation of the multifunctional dust removal and denitration filter material is completed. According to the filter material, the PTFE foam coating and the efficient catalyst are combined, the integrated removal efficiency of various pollutants in industrial flue gas is effectively improved, the filter material is suitable for large-scale production, the cost effectiveness is optimized, the filter material has obvious advantages in economical efficiency and market application, and an efficient and economical solution is provided for industrial flue gas purification.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial flue gas purification, and in particular provides a method for preparing a composite filter material integrating high temperature resistance, high-efficiency dust removal and denitration functions, and application thereof. Background Art

[0002] With the acceleration of industrialization, flue gas generated by coal-fired power plants, cement manufacturing, steel industry and other fields has become one of the main sources of air pollution. These flue gases contain a large amount of dust, nitrogen oxides, dioxins and other harmful substances, which have a serious impact on human health and the ecological environment. In order to meet increasingly stringent environmental protection standards, industrial flue gas treatment technology continues to improve, among which dust removal and denitrification technology are particularly critical.

[0003] Traditional dust removal technologies, such as bag filters and electrostatic precipitators, have achieved certain results in removing dust, but have limitations in removing nitrogen oxides. At the same time, denitrification technologies, such as selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR), can effectively reduce NOx emissions, but often require high operating costs and complex equipment maintenance. Therefore, the development of an efficient and low-cost filter material that integrates dust removal and denitrification has become an urgent need in the field of industrial flue gas treatment.

[0004] In the field of industrial coal-fired flue gas purification, Chinese Patent No. 202011057270.8 proposes an innovative process for preparing mercury removal filter bags. This technology prepares catalyst composite powders by impregnation and mixes them with polytetrafluoroethylene PTFE powders. After ball milling, aging, extrusion, calendering and film cracking processes, mercury removal filter bags with high mercury oxidation ability, low filtration resistance and high strength bonding are finally made. However, although the mercury removal filter bag performs well in the removal of mercury, it is limited in the removal of other pollutants such as nitrogen oxides and sulfides and the efficiency of dust removal. Furthermore, Chinese Patent No. 202310199154.7 proposes a catalytic filter bag of modified molecular sieve catalyst, which achieves efficient removal of dust and nitrogen oxides by fixing the modified molecular sieve catalyst on the surface of the flexible filter bag substrate. Its denitrification performance is good under low temperature conditions, but it will affect its performance in high temperature environment or complex environment, and the preparation process is relatively complicated. In practical applications, it needs to be further optimized to improve its stability and durability. Summary of the invention

[0005] In view of the limitations of existing industrial flue gas purification technologies, such as single pollutant removal efficiency, limited adaptability to the use environment, and challenges in cost, process and space occupation, this invention proposes an innovative PTFE foam coating catalytic filter material preparation technology. This technology not only significantly improves the removal efficiency of dust and nitrogen oxides in industrial flue gas, but also realizes the simultaneous and efficient removal of multiple pollutants by applying PTFE foam coating on the surface of traditional filter materials and cleverly integrating the catalyst impregnation process.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A preparation method and application of a PTFE foam coating multifunctional dust removal and denitrification filter material, comprising the following steps:

[0008] (1) Catalyst preparation: Cobalt chloride hexahydrate (CoCl2·6H20), cerium chloride heptahydrate (CeCl3·7H20), manganese chloride tetrahydrate (MnCl2·4H20), ferric chloride hexahydrate (FeCl3·6H20) and 1-methyl-2-pyrrolidone (C5H9NO) are mixed to form a catalytically active metal salt solution with a certain concentration;

[0009] (2) Preparation of needle felt base fabric: PPS is mixed with high-performance fibers, and a uniform fiber web layer is formed after opening and combing. Multiple layers of fiber webs and mesh base fabrics are stacked in a specific order, and pre-needled and needled through a needle loom to connect the fibers in the longitudinal and transverse directions to form a three-dimensional structure of the needle felt.

[0010] (3) Preparation of catalytic layer: first, the surface of the needle-punched felt in step (2) is activated for 1-2 hours, then immersed in an active salt solution, and stirred for 4-6 hours. The impregnated filter material is dried at 60-100° C. to constant weight for subsequent use;

[0011] (4) Preparation of PTFE foaming liquid: PTFE emulsion and foaming agent are mixed in proportion, deionized water is added to prepare foaming liquid, and then a foam stabilizer, a thickener and a cell opening agent are added to prepare a foaming coating foam for use;

[0012] (5) Preparation of multifunctional dust removal and denitrification filter material: The surface of the dried filter material is uniformly coated with a foaming coating foam, and after gradient drying and cooling, a PTFE foam coating multifunctional dust removal and denitrification filter material is finally obtained.

[0013] Preferably, the step (1) involves accurately weighing the corresponding chloride salt according to the molar ratio of Mn, Ce, Fe and Co of 4:5:0.7:0.3, and preparing a catalytically active salt solution of a specific concentration.

[0014] Preferably, in step (2), PPS is mixed with high-performance fiber to form a fiber mesh layer, and PPS and high-performance fiber mesh layers and glass fiber mesh base cloth are stacked in sequence, and this structure is repeated, and then fed into a needling machine, the needling frequency of pre-needling is 80 punctures / min; the needling frequency of main needling is 120 punctures / min, the number of needling passes is 2, and the needling depth is 5 mm.

[0015] Preferably, the high-performance fiber in step (2) is any one of polytetrafluoroethylene, polyetheretherketone, and polyimide fibers.

[0016] Preferably, the activation treatment of the needle felt in step (3) comprises immersing it in a 3-8% dilute nitric acid solution for 10-30 minutes for activation. Subsequently, the needle felt is thoroughly washed with deionized water to remove residual nitric acid, and finally dried for subsequent use.

[0017] Preferably, the foaming liquid formula in step (4) comprises: 60% PTFE emulsion with a solid content of 60%, 1%-2% foaming agent, 2%-4% foam stabilizer, 4%-6% thickener, 0.1%-1% pore opening regulator, and the balance is water.

[0018] Preferably, the foaming agent in step (4) is any one of betaine, methyl laurate soap, sodium lauryl sulfate or alkyl glycoside foaming agent.

[0019] Preferably, the foam stabilizer in step (4) is one of Tween 80 and polyol nonionic surfactant.

[0020] Preferably, the thickener in step (4) is one or more of methyl cellulose, acrylic resin, and nonionic polyacrylamide (NPAM).

[0021] Preferably, the pore opening agent in step (4) is one of polyoxyethylene (20E0) oleyl alcohol ether, polyoxyethylene monooleate, and polyoxyethylene cetyl alcohol.

[0022] Preferably, the rotation speed of the foaming machine in step (4) should be controlled at 500-3000 r / min, and the duration of the foaming process should be set at 15-60 min to ensure that the generated foam is fine and uniform.

[0023] Preferably, the thickness of the PTFE foam scraped by the scraper in step (5) is precisely controlled to be 0.1-5 mm, and after pre-drying at 80°C-120°C and calcining and curing at 140°C-260°C, a uniform foaming coating is formed to obtain a finished filter material.

[0024] Compared with the prior art, the present invention has the following beneficial technical effects:

[0025] Excellent mechanical strength: Compared with general dust removal filter bags, the filter material of the present invention is reinforced with double base cloth, which can maintain high strength and excellent acid resistance even in high temperature and corrosive flue gas environment above 250°C, ensuring stability and reliability during long-term use.

[0026] Fine pore design: By precisely adjusting the foaming formula, the PTFE foam coating creates an optimized pore structure for the filter material, which not only improves the filtration efficiency, but also effectively reduces the pressure drop during operation and improves energy efficiency.

[0027] Integrated multifunctional catalysis: By impregnating the Mn-Ce-Fe-Co-Ox catalyst on the inner and outer surfaces of the needle-punched felt and combining it with the coating technology of the PTFE foam coating, the present invention realizes a high-efficiency catalytic function integrating dust removal and denitrification, while overcoming the problems of easy shedding and insufficient catalytic activity of traditional catalysts, solving the limitations of mercury removal filter bags in the removal efficiency of other pollutants, and broadening the application range of filter materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the double-base cloth needle felt structure.

[0029] Figure 2 This is the surface morphology of PTFE foam coating.

[0030] Figure 1 Middle: 1-PTFE foam coating; 2-high performance fiber mixed fiber mesh layer; 3-glass fiber mesh base cloth. DETAILED DESCRIPTION

[0031] The present invention is described in detail below in conjunction with the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0032] Example 1

[0033] A preparation method and application of a PTFE foam coating multifunctional dust removal and denitrification filter material, characterized in that it comprises the following steps:

[0034] (1) Catalyst preparation: Cobalt chloride hexahydrate (CoCl2·6H20), cerium chloride heptahydrate (CeCl3·7H20), manganese chloride tetrahydrate (MnCl2·4H20), ferric chloride hexahydrate (FeCl3·6H20) and 1-methyl-2-pyrrolidone (C5H9NO) are mixed to form a catalytically active metal salt solution with a certain concentration;

[0035] (2) Preparation of needle-punched felt base fabric: PPS is mixed with high-performance fibers, and after being opened and combed, a uniform fiber web layer is formed, which is then stacked in the order of fiber web layer / grid base fabric / fiber web layer / grid base fabric / fiber web layer. Pre-needling and needle-punching are performed by a needle-punching machine to connect the fibers in the longitudinal and transverse directions to form a three-dimensional needle-punched felt.

[0036] (3) Preparation of catalytic layer: First, the surface of the needle-punched felt in step (2) was activated for 2 hours, then immersed in an active salt solution, and stirred for 4 hours. The impregnated filter material was dried at 70° C. to constant weight for subsequent use;

[0037] (4) Preparation of PTFE foaming liquid: PTFE emulsion and foaming agent are mixed in proportion, deionized water is added to prepare foaming liquid, and then a foam stabilizer, a thickener and a cell opening agent are added to prepare a foaming coating foam for use;

[0038] (5) Preparation of multifunctional dust removal and denitrification filter material: The surface of the dried filter material is uniformly coated with a foaming coating foam, and after gradient drying and cooling, a PTFE foam coating multifunctional dust removal and denitrification filter material is finally obtained.

[0039] Preferably, the step (1) involves accurately weighing the corresponding chloride salt according to the molar ratio of Mn, Ce, Fe and Co of 4:5:0.7:0.3, and preparing a catalytically active salt solution of a specific concentration.

[0040] Preferably, the frequency of pre-acupuncture in step (2) is 80 punctures / min; the frequency of main acupuncture is 120 punctures / min, the number of acupuncture paths is 2, and the acupuncture depth is 5 mm.

[0041] Preferably, the high-performance fiber in step (2) is polytetrafluoroethylene fiber.

[0042] Preferably, the activation treatment of the needle felt in step (3) comprises immersing it in a 3% dilute nitric acid solution for 20 minutes for activation, then thoroughly washing the needle felt with deionized water to remove residual nitric acid, and finally drying it for subsequent use.

[0043] Preferably, the foaming liquid formula in step (4) comprises: 60% PTFE emulsion with a solid content of 60%, 1% foaming agent, 2% foam stabilizer, 4% thickener, 0.2% pore opening regulator, and the balance is water.

[0044] Preferably, the foaming agent in step (4) is betaine.

[0045] Preferably, the foam stabilizer in step (4) is Tween 80.

[0046] Preferably, the thickener in step (4) is a mixture of methyl cellulose and acrylic resin.

[0047] Preferably, the pore opening agent in step (4) is polyoxyethylene (20E0) oleyl alcohol ether.

[0048] Preferably, the rotation speed of the foaming machine in step (4) should be controlled at 800 r / min, and the duration of the foaming process should be set at 30 min to ensure that the generated foam is fine and uniform.

[0049] Preferably, in step (5), the thickness of the PTFE foam scraped by a scraper is precisely controlled at 0.2 mm, and after pre-drying at 100° C. and calcining and curing at 160° C., a uniform foaming coating is formed to obtain a finished filter material.

[0050] The PTFE foam coating multifunctional dust removal and denitrification filter material prepared by the present invention exhibits a PM2.5 filtration efficiency of 96.4%, and this high efficiency is attributed to the significant refinement of the pores of the needle felt by the PTFE foam coating. In addition, the NOx reduction efficiency of the filter material treated with catalyst impregnation reaches an optimal state of up to 82% at an operating temperature of 170°C. This shows that the filter material of the present invention has excellent denitrification performance while achieving efficient dust removal, fully proving its application potential in the field of industrial flue gas purification.

[0051] Example 2

[0052] A preparation method and application of a PTFE foam coating multifunctional dust removal and denitrification filter material, characterized in that it comprises the following steps:

[0053] (1) Catalyst preparation: Cobalt chloride hexahydrate (CoCl2·6H20), cerium chloride heptahydrate (CeCl3·7H20), manganese chloride tetrahydrate (MnCl2·4H20), ferric chloride hexahydrate (FeCl3·6H20) and 1-methyl-2-pyrrolidone (C5H9NO) are mixed to form a catalytically active metal salt solution with a certain concentration;

[0054] (2) Preparation of needle-punched felt base fabric: PPS is mixed with high-performance fibers, and after being opened and combed, a uniform fiber web layer is formed, which is then stacked in the order of fiber web layer / grid base fabric / fiber web layer / grid base fabric / fiber web layer. Pre-needling and needle-punching are performed by a needle-punching machine to connect the fibers in the longitudinal and transverse directions to form a three-dimensional needle-punched felt.

[0055] (3) Preparation of catalytic layer: First, the surface of the needle-punched felt in step (2) was activated for 1.5 hours, then immersed in an active salt solution, and stirred for 5 hours. The impregnated filter material was dried at 80° C. to constant weight for subsequent use;

[0056] (4) Preparation of PTFE foaming liquid: PTFE emulsion and foaming agent are mixed in proportion, deionized water is added to prepare foaming liquid, and then a foam stabilizer, a thickener and a cell opening agent are added to prepare a foaming coating foam for use;

[0057] (5) Preparation of multifunctional dust removal and denitrification filter material: The surface of the dried filter material is uniformly coated with a foaming coating foam, and after gradient drying and cooling, a PTFE foam coating multifunctional dust removal and denitrification filter material is finally obtained.

[0058] Preferably, step (1) involves accurately weighing the corresponding chloride salt according to the molar ratio of Mn, Ce, Fe and Co of 5:7:0.3:0.7, and preparing a catalytically active salt solution of a specific concentration.

[0059] Preferably, the frequency of pre-acupuncture in step (2) is 80 punctures / min; the frequency of main acupuncture is 120 punctures / min, the number of acupuncture paths is 2, and the acupuncture depth is 5 mm.

[0060] Preferably, the high-performance fiber in step (2) is polyetheretherketone fiber.

[0061] Preferably, the activation treatment of the needle felt in step (3) comprises immersing it in a 4% dilute nitric acid solution for 30 minutes for activation. Subsequently, the needle felt is thoroughly washed with deionized water to remove residual nitric acid, and finally dried for subsequent use.

[0062] Preferably, the foaming liquid formula in step (4) comprises: 70% PTFE emulsion with a solid content of 60%, 2% foaming agent, 3% foam stabilizer, 5% thickener, 0.4% pore opening regulator, and the balance is water.

[0063] Preferably, the foaming agent in step (4) is lauric acid methyl soap.

[0064] Preferably, the foam stabilizer in step (4) is a polyol nonionic surfactant.

[0065] Preferably, the thickener in step (4) is acrylic resin.

[0066] Preferably, the pore opening agent in step (4) is polyoxyethylene monooleate.

[0067] Preferably, the rotation speed of the foaming machine in step (4) should be controlled at 1300 r / min, and the duration of the foaming process should be set at 20 min to ensure that the generated foam is fine and uniform.

[0068] Preferably, the thickness of the PTFE foam scraped by a scraper in step (5) is precisely controlled to be 0.3 mm, and after pre-drying at 120° C. and calcining and curing at 180° C., a uniform foaming coating is formed to obtain a finished filter material.

[0069] The PTFE foam coating multifunctional dust removal and denitrification filter material successfully developed by the present invention has achieved a PM2.5 filtration efficiency of 93%, thanks to the optimization adjustment of the pores of the needle-punched felt by the PTFE foam coating. At the same time, after the filter material is treated with catalyst impregnation at 170°C, the NOx reduction efficiency can reach a peak value of 83%.

[0070] Example 3

[0071] A preparation method and application of a PTFE foam coating multifunctional dust removal and denitrification filter material, comprising the following steps:

[0072] (1) Catalyst preparation: Cobalt chloride hexahydrate (CoCl2·6H20), cerium chloride heptahydrate (CeCl3·7H20), manganese chloride tetrahydrate (MnCl2·4H20), ferric chloride hexahydrate (FeCl3·6H20) and 1-methyl-2-pyrrolidone (C5H9NO) are mixed to form a catalytically active metal salt solution with a certain concentration;

[0073] (2) Preparation of needle-punched felt base fabric: PPS is mixed with high-performance fibers, and after being opened and combed, a uniform fiber web layer is formed, which is then stacked in the order of fiber web layer / grid base fabric / fiber web layer / grid base fabric / fiber web layer. Pre-needling and needle-punching are performed by a needle-punching machine to connect the fibers in the longitudinal and transverse directions to form a three-dimensional needle-punched felt.

[0074] (3) Preparation of catalytic layer: First, the surface of the needle-punched felt in step (2) was activated for 2 hours, then immersed in an active salt solution, and stirred for 6 hours. The impregnated filter material was dried at 100° C. to constant weight for subsequent use;

[0075] (4) Preparation of PTFE foaming liquid: PTFE emulsion and foaming agent are mixed in proportion, deionized water is added to prepare foaming liquid, and then a foam stabilizer, a thickener and a cell opening agent are added to prepare a foaming coating foam for use;

[0076] (5) Preparation of multifunctional dust removal and denitrification filter material: The surface of the dried filter material is uniformly coated with a foaming coating foam, and after gradient drying and cooling, a PTFE foam coating multifunctional dust removal and denitrification filter material is finally obtained.

[0077] Preferably, step (1) involves accurately weighing the corresponding chloride salt according to the molar ratio of Mn, Ce, Fe and Co of 6:4:0.5:0.5, and preparing a catalytically active salt solution of a specific concentration.

[0078] Preferably, the frequency of pre-acupuncture in step (2) is 80 punctures / min; the frequency of main acupuncture is 120 punctures / min, the number of acupuncture paths is 2, and the acupuncture depth is 5 mm.

[0079] Preferably, the high-performance fiber in step (2) is polyimide fiber.

[0080] Preferably, the activation treatment of the needle felt in step (3) comprises immersing it in a 5% dilute nitric acid solution for 15 minutes for activation. Subsequently, the needle felt is thoroughly washed with deionized water to remove residual nitric acid, and finally dried for subsequent use.

[0081] Preferably, the foaming liquid formula in step (4) comprises: 80% PTFE emulsion with a solid content of 60%, 2% foaming agent, 4% foam stabilizer, 6% thickener, 0.6% pore opening regulator, and the balance is water.

[0082] Preferably, the foaming agent in step (4) is sodium dodecyl sulfate.

[0083] Preferably, the foam stabilizer in step (4) is Tween 80.

[0084] Preferably, the thickener in step (4) is non-ionic polyacrylamide (NPAM).

[0085] Preferably, the pore opening agent in step (4) is polyoxyethylene cetyl alcohol.

[0086] Preferably, the rotation speed of the foaming machine in step (4) should be controlled at 1800 r / min, and the duration of the foaming process should be set at 15 min to ensure that the generated foam is fine and uniform.

[0087] Preferably, the thickness of the PTFE foam scraped by a scraper in step (5) is precisely controlled to be 0.5 mm, and after pre-drying at 80° C. and calcining and curing at 220° C., a uniform foaming coating is formed to obtain a finished filter material.

[0088] The PTFE foam coating dust removal and denitrification filter material developed by the present invention, with its 96% PM2.5 filtration efficiency, highlights the superb technology in optimizing the pore structure of needle felt. After the filter material is treated with a catalyst impregnation at 170°C, the NOx reduction efficiency is significantly increased to 85%. This catalytic filter material not only has high dust removal efficiency and good denitrification performance, but also has significant cost-effectiveness and is easy to industrialize, providing an innovative solution for industrial flue gas treatment.

[0089] The above is only a specific embodiment of the present invention, but the technical features of the present invention are not limited thereto. Any changes and modifications to the present invention, as long as they do not change its basic functions and scope, are equivalent alternatives of the present invention and are included in the protection scope of the present invention.

Claims

1. A preparation method and application of a PTFE foam coating multifunctional dust removal and denitrification filter material, characterized in that: The following steps are involved: (1) Catalyst preparation: Cobalt chloride hexahydrate (CoCl2·6H20), cerium chloride heptahydrate (CeCl3·7H20), manganese chloride tetrahydrate (MnCl2·4H20), ferric chloride hexahydrate (FeCl3·6H20) and 1-methyl-2-pyrrolidone (C5H9NO) are mixed to form a catalytically active metal salt solution with a certain concentration; (2) Preparation of needle-punched felt base fabric: polyphenylene sulfide (PPS) is mixed with high-performance fibers, and a uniform fiber web layer is formed after opening and combing. Multiple layers of fiber webs and glass mesh base fabrics are stacked in a specific order, and pre-needled and needle-punched by a needle-punching machine to connect the fibers in the longitudinal and transverse directions to form a three-dimensional needle-punched felt; (3) Preparation of catalytic layer: first, the surface of the needle-punched felt in step (2) is activated for 1-2 hours, then immersed in an active salt solution, and stirred for 4-6 hours. The impregnated filter material is dried at 60-100° C. to constant weight for subsequent use; (4) Preparation of PTFE foaming liquid: PTFE emulsion and foaming agent are mixed in proportion, deionized water is added to prepare foaming liquid, and then a foam stabilizer, a thickener and a cell opening agent are added to prepare a foaming coating foam for use; (5) Preparation of multifunctional dust removal and denitrification filter material: The surface of the dried filter material is uniformly coated with a foaming coating foam, and after gradient drying and cooling, a PTFE foam coating multifunctional dust removal and denitrification filter material is finally obtained.

2. The preparation method and application of a PTFE foam coating multifunctional dust removal and denitrification filter material according to claim 1, characterized in that: In the step (1), a certain amount of chloride salt is weighed according to the molar ratio of Mn, Ce, Fe and Co being 4:5:0.7:0.3 to prepare a catalytically active salt solution of a certain concentration.

3. The preparation method and application of a PTFE foam coating multifunctional dust removal and denitrification filter material according to claim 1, characterized in that: In the step (2), PPS is mixed with high-performance fiber to form a fiber mesh layer, and PPS and high-performance fiber fiber mesh layer and glass fiber mesh base cloth are stacked in sequence. This structure is repeated and then fed into a needle loom. The needling frequency of pre-needling is 80 punctures / min; the needling frequency of main needling is 120 punctures / min, the number of needling paths is 2, and the needling depth is 5 mm.

4. The preparation method and application of a PTFE foam coating multifunctional dust removal and denitrification filter material according to claim 1, characterized in that: The foaming liquid formula in step (4) includes: 60% PTFE emulsion with a solid content of 60%, 1%-2% foaming agent, 2%-4% foam stabilizer, 4%-6% thickener, 0.1%-1% pore opening regulator, and the balance is water.

5. The preparation method and application of a PTFE foam coating multifunctional dust removal and denitrification filter material according to claim 1, characterized in that: In the step (4), the rotation speed of the foaming machine should be precisely controlled at 500-3000 r / min, and the duration of the foaming process should be set at 15-60 min to ensure that the generated foam has a fine and uniform texture.

6. The preparation method and application of a PTFE foam coating multifunctional dust removal and denitrification filter material according to claim 1, characterized in that: In step (5), the thickness of the PTFE foam on the surface of the catalytic needle felt is precisely controlled to be 1-5 mm by a scraper. After pre-drying at 80°C-120°C and calcining and curing at 140°C-260°C, a uniform foaming coating is formed to obtain a finished filter material.

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