A whole extrusion type methanol-SCR denitration catalyst based on molecular sieve, a preparation method and application thereof

Abstract

The application discloses a whole extrusion type molecular sieve based methanol-SCR denitration catalyst and a preparation method and application thereof, and belongs to the field of gas purification. The denitration catalyst takes a molecular sieve based honeycomb ceramic as a matrix, and comprises a nitrogen oxide reduction zone and a CO oxidation zone; and a transition metal composite oxide is loaded on the matrix in the CO oxidation zone. The catalyst has high denitration activity when methanol is used as a reducing agent, and the removal efficiency of NO reaches 100% at most, and meanwhile, the generation of CO in the reduction process can be greatly reduced.

Description

Technical Field

[0001] This invention relates to a catalyst for removing nitrogen oxides from exhaust gases and its preparation method, belonging to the field of gas purification. Background Technology

[0002] The combustion of fossil fuels emits large amounts of NOx, causing severe environmental pollution. Among various methods for removing nitrogen oxides, selective catalytic reduction (SCR) technology is the most important and industrially valuable method for removing NOx from various exhaust gases. This method involves adding a reducing agent to the flue gas under the action of a catalyst to reduce NOx to N2 before it is released into the atmosphere. Currently, NH3 is the main reducing agent used. The NH3-SCR method has high catalytic activity and good selectivity, and various developed catalytic systems have different temperature windows, making them suitable for different applications. However, a problem exists: when the flue gas temperature is below 280℃, SO2 in the flue gas reacts with NH3 to form ammonium bisulfate, which blocks the pores of the catalyst, causing catalyst deactivation. Ammonium bisulfate can also clog pipes and valves, affecting the stable operation of the system. Another problem with using ammonia as a reducing agent is that in actual denitrification processes, operators may over-spray ammonia to meet denitrification requirements, causing a lot of unreacted NH3 to escape into the air. This NH3 can react with acidic substances to form ammonium salt particles, affecting the atmospheric environment.

[0003] The SCR method using methanol as a reducing agent has attracted considerable attention in recent years. Using methanol instead of NH3 as the reducing agent can completely solve the problems of ammonium sulfate formation and ammonia escape. Molecular sieves are excellent catalytic materials in the methanol-SCR method, exhibiting good denitrification activity; however, to meet the requirements of industrial applications, the molecular sieve powder needs to be integrally extruded. Integral extrusion-type full-component honeycomb ceramic catalysts have many advantages, such as low pressure drop, strong resistance to airflow erosion, good stability, and low cost, and have been widely used in industrial flue gas treatment, proving to be the optimal catalyst configuration for treating large volumes of industrial flue gas.

[0004] As a type of rigid material, molecular sieves are difficult to extrude integrally, hindering their industrial application. The extrusion process often requires the addition of large amounts of adhesives and binders, resulting in a reduction of the effective components in the integrally formed catalyst. To achieve the desired removal effect, the catalyst loading must be increased, leading to bulky equipment and increased investment. Drying the molecular sieve after molding is also a technical challenge. For example, the integrally extruded molecular sieve honeycomb ceramic structure reported in Chinese invention patent CN105618159B requires strict control of drying conditions: temperature at 30±5℃, humidity maintained at 75%–80%, and water loss rate controlled at 0.2%–1% per day. The entire drying process lasts for more than a week, impacting production efficiency.

[0005] Another problem with using methanol as a reducing agent is the generation of a significant amount of carbon monoxide (CO) during the reaction. CO is a toxic gas to humans and animals and also affects the atmospheric environment. Domestic regulations and standards already restrict CO emissions, and CO generation should be minimized during the methanol-SCR process. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an integrally extruded molecular sieve-based methanol-SCR denitration catalyst and its preparation method, the resulting catalyst exhibiting excellent performance.

[0007] According to one aspect of the present invention, a denitrification catalyst is provided, wherein the denitrification catalyst is based on a molecular sieve-based honeycomb ceramic matrix, the matrix comprising a nitrogen oxide reduction zone and a CO oxidation zone; the CO oxidation zone is located at one end of the matrix; the CO oxidation zone is loaded with a transition metal composite oxide.

[0008] The components of the molecular sieve-based honeycomb ceramic include FER-type molecular sieves.

[0009] Optionally, the molecular sieve-based honeycomb ceramic has a plurality of parallel channels, the pore diameter of which is 2 to 8 mm and the wall thickness of which is 0.5 to 1 mm.

[0010] The matrix comprises, by mass of the denitrification catalyst, 85%–90% FER-type molecular sieve, 10%–20% SiO2, and 5%–10% glass fiber.

[0011] Optionally, the transition metal in the transition metal composite oxide is selected from at least two of copper, cerium, manganese, and iron; the atomic molar ratio of any two transition metals in the transition metal composite oxide is 1:4 to 1:1; and the loading of the transition metal composite oxide accounts for 1% to 15% of the mass of the denitrification catalyst.

[0012] The loading of the transition metal composite oxide is 1% to 15% of the mass of the denitration catalyst.

[0013] Optionally, the CO oxidation zone accounts for 15% to 35% of the total length of the denitrification catalyst, with the remainder being a nitrogen oxide reduction zone.

[0014] According to one aspect of the present invention, a method for preparing the above-mentioned denitrification catalyst is provided, comprising the following steps:

[0015] a) Mix and knead the raw materials containing FER molecular sieve, plasticizer, deionized water, silicone resin emulsion, palm oil, and glycerin; add glass fiber after kneading, seal and age to obtain molecular sieve catalyst slurry.

[0016] b) The molecular sieve catalyst sludge is vacuum-kneaded and repeated 5 to 10 times to form a catalyst sludge segment with a smooth surface and good viscosity. Then it is sealed and aged to obtain the molecular sieve catalyst sludge segment. The molecular sieve catalyst sludge segment is extruded, microwaved, dried and calcined to obtain the molecular sieve catalyst.

[0017] c) Immerse one end of the molecular sieve catalyst in a mixed solution containing at least two transition metal precursors, and then dry and calcine it to obtain the denitration catalyst.

[0018] Optionally, in step a), the plasticizer is selected from one of methylcellulose, carboxymethylcellulose, and hydroxypropyl methylcellulose;

[0019] The kneading time for the mixture is 3 to 6 hours;

[0020] The aging time for the aging process is 24 to 48 hours.

[0021] Optionally, in step a), the kneading time for mixing and kneading is selected from 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, or any value between any two of the above.

[0022] The aging time is selected from 28 hours, 30 hours, 32 hours, 35 hours, 37 hours, 40 hours, 42 hours, 44 hours, 45 hours, 46 hours, or any value between any two of the above.

[0023] Optionally, based on the mass of the FER molecular sieve, the amount of plasticizer added is 2% to 6%, the amount of silicone resin emulsion added is 10% to 20%, the amount of glass fiber added is 2% to 6%, the amount of palm oil added is 2% to 6%, the amount of glycerol added is 1% to 3%, and the amount of deionized water added is 30% to 50%.

[0024] The moisture content of the molecular sieve catalyst slurry is 25% to 30%.

[0025] Optionally, in step b), the vacuum degree of the vacuum plowing is -0.08 to -0.095 MPa;

[0026] The aging time for the aging product is 24 to 48 hours;

[0027] The diameter of the molecular sieve catalyst sludge segment is 50 mm.

[0028] Optionally, in step b), the aging time is selected from 28 hours, 30 hours, 32 hours, 35 hours, 37 hours, 40 hours, 42 hours, 44 hours, 45 hours, 46 hours, or any value between any two of the above.

[0029] Optionally, in step b), the extruder used for extrusion is selected from one of a plunger extruder, a continuous screw extruder, or a twin-screw extruder;

[0030] The microwave power is 500W to 1000W, and the microwave duration is 3 to 5 minutes.

[0031] The drying temperature is 100-120℃, and the drying time is 8-12 hours;

[0032] The roasting temperature is 500-700℃, and the roasting time is 4-6 hours.

[0033] Optionally, in step b), the microwave power is selected from 500W to 1000W, or any value between any two of the above points; the microwave duration is selected from 3.5 minutes, 3.8 minutes, 4 minutes, 4.2 minutes, 4.5 minutes, 4.8 minutes, or any value between any two of the above points.

[0034] The roasting temperature is selected from 520℃, 550℃, 570℃, 580℃, 600℃, 620℃, 650℃, 670℃, 690℃, or any value between any two of the above points; the roasting time is selected from 4.2 hours, 4.5 hours, 4.7 hours, 4.9 hours, 5 hours, 5.3 hours, 5.5 hours, 5.8 hours, or any value between any two of the above points.

[0035] Optionally, in step c), the impregnation height is 15% to 35% of the total length of the molecular sieve catalyst, and the impregnation time is 1 minute to 5 minutes;

[0036] The roasting temperature is 500℃ and the roasting time is 2 to 4 hours.

[0037] Optionally, in step c), the roasting temperature is selected from 2.2 hours, 2.5 hours, 2.8 hours, 3 hours, 3.2 hours, 3.5 hours, 3.8 hours, or any value between any two of the above points; the roasting time is selected from 2.2 hours, 2.5 hours, 2.8 hours, 3 hours, 3.2 hours, 3.5 hours, 3.8 hours, or any value between any two of the above points.

[0038] Optionally, the transition metal precursor is selected from at least one of the nitrates and acetates of transition metals; the concentration of the metal cation in the mixed solution is 1 mol / L to 5 mol / L.

[0039] According to one aspect of the present invention, the application of the above-described denitrification catalyst and the denitrification catalyst prepared by the above-described preparation method in the selective reduction of nitrogen oxides by methanol is provided.

[0040] Optionally, a mixture of nitrogen oxides and methanol is passed into a reactor containing the denitrification catalyst for reaction; the reaction conditions are: a volume hourly space velocity (VHSV) of 2000–12000 h⁻¹. -1 The temperature ranges from 150 to 500℃.

[0041] Optionally, the volumetric space velocity is 4000–6000 h⁻¹. -1 The temperature is 200-300℃.

[0042] Optionally, the volumetric hourly space velocity is selected from 2500 h⁻¹. -1 3000h -1 3500h -1 5000h -1 5500h -1 6500h -1 7000h -1 7500h -1 8000h -1 8500h -1 9000h -1 9500h -1 The temperature is selected from 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, or any value between any two of the above points; the temperature is selected from 200℃, 250℃, 300℃, 350℃, 400℃, 450℃, or any value between any two of the above points.

[0043] As one embodiment of this application, a method for preparing a denitrification catalyst is provided, comprising the following steps:

[0044] a) After dry mixing FER type molecular sieve and plasticizer, add deionized water, organosilicon resin emulsion, palm oil, glycerin and glass fiber to mix and knead; after kneading, seal and age to obtain molecular sieve catalyst sludge;

[0045] b) Vacuum kneading of molecular sieve catalyst sludge is repeated 5 to 10 times and then sealed and aged to obtain molecular sieve catalyst sludge segments; the molecular sieve catalyst sludge segments are extruded, microwaved, dried and calcined to obtain molecular sieve catalyst.

[0046] c) Immerse one end of the molecular sieve catalyst in a mixed solution containing at least two transition metal precursors, and then dry and calcine it to obtain the denitration catalyst.

[0047] The present invention has the following beneficial effects:

[0048] The molecular sieve extrusion structure of this invention has a molecular sieve content of up to 80% or more, which has high denitrification activity; microwave drying is used, the dried green body is free of defects and cracks, the drying speed is accelerated, the production speed is improved and the energy consumption is reduced; the end is loaded with a transition metal, which greatly eliminates the CO generated during the reduction process.

[0049] The integral extrusion molecular sieve-based methanol-SCR catalyst provided by this invention has high denitrification activity when methanol is used as a reducing agent. Within a certain temperature range, the NO removal efficiency can reach 90-100%, while greatly reducing the CO generation during the reduction process. Detailed Implementation Plan

[0050] The present invention will be described in detail below. The following are only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention.

[0051] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased commercially. Unless otherwise specified, all testing methods were conventional methods, and all instrument settings were as recommended by the manufacturer.

[0052] The FER molecular sieve was purchased from Nankai University in Tianjin; the methyl silicone resin emulsion was purchased from Sihai Chemical Plant in Hubei.

[0053] Example 1

[0054] Weigh 800g of FER type molecular sieve and 32g of hydroxypropyl methylcellulose and add them to a kneader for dry mixing. After 30 minutes, add 160g of methyl silicone resin emulsion, 32g of palm oil, 16g of glycerol, 32g of glass fiber, and 400g of deionized water. Knead for 2 hours until the material is homogeneous, obtaining a molecular sieve catalyst slurry with a moisture content of 30%. After aging this molecular sieve catalyst slurry for 24 hours, begin vacuum kneading at a vacuum degree of -0.09Mpa. After kneading, let the slurry sit for 24 hours and then extrude it through a porous die using a hydraulic piston extruder to form a honeycomb structure. The die specifications are as follows: After letting the kneaded slurry sit for 24 hours, cut a section of the aged molecular sieve catalyst slurry and place it into a hydraulic piston extruder to extrude it through a porous die to form a honeycomb structure. The die specifications are as follows:

[0055] <![CDATA[Cross-sectional dimensions (mm 2 )]]> Number of holes Hole width (mm) Inner wall thickness (mm) Outer wall thickness (mm) 22.3×22.3 5×5 3.3 0.9 1.1

[0056] The extruded honeycomb structure was quickly shaped by drying in a microwave oven at 750w for 5 minutes, then transferred to a drying oven and dried at 100℃ for 12 hours to obtain a dried green body. It was then cut into small segments with a length of 4.5cm and calcined in a muffle furnace at 500℃ for 4 hours to obtain a molecular sieve-based honeycomb ceramic structure.

[0057] Weigh 20g Cu(NO3)2·3H2O and 35.9g Ce(NO3)3·6H2O, add 30g deionized water to prepare a mixed solution. Add the above solution to a small beaker, control the liquid level so that the height of the metal-impregnated honeycomb structure is 0.8cm. Then, immerse one end of the sintered molecular sieve-based honeycomb ceramic structure in the solution for 5 seconds, remove it, quickly dry it with hot air, and calcine it in a muffle furnace at 500℃ for 2 hours to obtain a molecular sieve-based methanol-SCR denitration catalyst.

[0058] Example 2

[0059] The preparation of the catalyst is basically the same as in Example 1, except that the die specifications used in the extrusion process are as follows:

[0060] <![CDATA[Cross-sectional dimensions (mm 2 )]]> Number of holes Hole width (mm) Inner wall thickness (mm) Outer wall thickness (mm) 21.2×21.2 3×3 5.7 0.9 1.15

[0061] Example 3

[0062] The preparation of the catalyst is basically the same as in Example 1, except that the die specifications used in the extrusion process are as follows:

[0063] <![CDATA[Cross-sectional dimensions (mm 2 )]]> Number of holes Hole width (mm) Inner wall thickness (mm) Outer wall thickness (mm) 21.4×21.4 9×9 1.8 0.45 0.8

[0064] Example 4

[0065] The preparation of the catalyst is basically the same as in Example 1, except that in the step of impregnating the mixed solution of copper nitrate and cerium nitrate, the liquid level is controlled so that the height of the honeycomb impregnated with metal is 1.5 cm.

[0066] Example 5

[0067] The preparation of the catalyst is basically the same as in Example 1, except that in the step of impregnating the mixed solution of copper nitrate and cerium nitrate, the liquid level is controlled so that the height of the honeycomb impregnated with metal is 0.4 cm.

[0068] Comparative Example 1

[0069] The catalyst was prepared in the same way as in Example 1, except that the tail end was not impregnated with a mixed solution of copper nitrate and cerium nitrate.

[0070] Test Example 6

[0071] The catalysts prepared in Examples 1-5 and Comparative Example 1 were evaluated for activity. The catalyst denitrification activity test method was as follows: The prepared monolithic honeycomb catalyst was placed in a fixed-bed reactor. A methanol-water solution of a certain concentration was prepared and pumped into an evaporator for evaporation. After evaporation, the solution was mixed with other component gases. The pump flow rate was controlled to maintain a water vapor concentration of 5% and a methanol concentration of 1000 ppm. The final feed gas composition was: 500 ppm NO + 1000 ppm CH3OH + 6% O2 + 5% H2O + N2 equilibrium, with a flow rate of 1.5 L / min. The NO concentration at the inlet and outlet was measured respectively, and the NO conversion rate was calculated to obtain the catalyst denitrification efficiency X. NO Simultaneously, the CO concentration at the reaction outlet was also measured. Appendix Table 1 shows the denitrification efficiency and CO generation of several catalysts in the 200–300℃ range.

[0072] Appendix Table 1. Denitrification efficiency of each catalyst and CO concentration at the reaction outlet

[0073]

[0074]

[0075] As can be seen from the data in Appendix 1, the catalyst prepared by the present invention has good denitrification activity and also greatly reduces the generation of CO. When the conversion rate of NO is 100%, the concentration of CO generated by the reaction can be controlled to be less than 20 ppm.

[0076] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A denitrification catalyst, characterized in that, The denitration catalyst uses molecular sieve-based honeycomb ceramic as a matrix, which includes a nitrogen oxide reduction zone and a CO oxidation zone; the CO oxidation zone is located at one end of the matrix; the CO oxidation zone is supported on a copper and cerium transition metal composite oxide. The CO oxidation zone accounts for 15% to 35% of the total length of the denitrification catalyst, and the remainder is the nitrogen oxide reduction zone. The molecular sieve-based honeycomb ceramic has several parallel channels with a pore diameter of 2-8 mm and a wall thickness of 0.5-1 mm. The matrix, by mass of the denitrification catalyst, comprises 85% to 90% FER-type molecular sieve, 10% to 20% SiO2, and 5% to 10% glass fiber. The FER type molecular sieve has a silica-to-alumina ratio of 2 to 500.

2. The denitrification catalyst according to claim 1, characterized in that, The molar ratio of any two transition metal atoms in the transition metal composite oxide is 1:4 to 1:1; The loading of the transition metal composite oxide accounts for 1% to 15% of the mass of the denitrification catalyst.

3. A method for preparing the denitrification catalyst according to any one of claims 1 to 2, characterized in that, Includes the following steps: a) Mix and knead the raw materials containing FER molecular sieve, plasticizer, deionized water, silicone resin emulsion, palm oil, and glycerin; add glass fiber after kneading, seal and age to obtain molecular sieve catalyst slurry. The plasticizer is selected from one of methylcellulose, carboxymethylcellulose, and hydroxypropyl methylcellulose; b) Vacuum kneading of molecular sieve catalyst sludge, sealing and aging to obtain molecular sieve catalyst sludge segments; extrusion, microwave, drying and calcination of molecular sieve catalyst sludge segments to obtain molecular sieve catalyst. c) Immerse one end of the molecular sieve catalyst in a mixed solution containing two transition metal precursors, and then dry and calcine it to obtain the denitration catalyst, wherein the transition metals are copper and cerium.

4. The preparation method according to claim 3, characterized in that, In step a), The kneading time for the mixture is 3 to 6 hours; The aging time for the aging process is 24 to 48 hours.

5. The preparation method according to claim 3, characterized in that, In step a), Based on the mass of FER molecular sieve, the amount of plasticizer added is 2%~6%, the amount of silicone resin emulsion added is 10%~20%, the amount of glass fiber added is 2%~6%, the amount of palm oil added is 2%~6%, the amount of glycerin added is 1%~3%, and the amount of deionized water added is 30%~50%. The moisture content of the molecular sieve catalyst slurry is 25% to 30%.

6. The preparation method according to claim 3, characterized in that, In step b), the vacuum degree of the vacuum plowing is -0.08 to -0.095 MPa; The aging time for the aging product is 24 to 48 hours; The diameter of the molecular sieve catalyst sludge segment is 50 mm.

7. The preparation method according to claim 3, characterized in that, In step b), the extruder used for extrusion is selected from one of a plunger extruder, a continuous screw extruder, or a twin-screw extruder; The microwave power is 500W~1000W, and the microwave duration is 3~5 minutes; The drying temperature is 100~120℃, and the drying time is 8~12 hours; The roasting temperature is 500-700℃, and the roasting time is 4-6 hours.

8. The preparation method according to claim 3, characterized in that, In step c), the impregnation height is 15% to 35% of the total length of the molecular sieve catalyst, and the impregnation time is 1 minute to 5 minutes; The roasting temperature is 500℃ and the roasting time is 2 to 4 hours.

9. The preparation method according to claim 3, characterized in that, In step c), the transition metal precursor is selected from at least one of the transition metal nitrates and acetates; the concentration of the metal cation in the mixed solution is 1 mol / L to 5 mol / L.

10. The application of the denitrification catalyst according to any one of claims 1 to 2, or the denitrification catalyst prepared by the preparation method according to any one of claims 3 to 9, in the selective reduction of nitrogen oxides by methanol; A mixture of gas containing nitrogen oxides and methanol is passed into a reactor containing the aforementioned denitrification catalyst for reaction; the reaction conditions are: volume hourly space velocity (VHSV) of 2000–12000 h⁻¹. -1 The temperature is 150~500℃.

11. The application according to claim 10, characterized in that, Volumetric hourly space velocity (VHSV) is 4000~6000 h⁻¹ -1 The temperature is 200~300℃.

Images