Denitration catalyst, preparation method thereof and application of denitration catalyst in cement kiln flue gas denitration

Abstract

The invention belongs to the technical field of flue gas denitration, and particularly relates to a denitration catalyst, a preparation method thereof and application of the denitration catalyst in flue gas denitration of a cement kiln. The denitration catalyst provided by the invention is prepared from the following raw materials: 5 to 10 parts of montmorillonite powder, 60 to 85 parts of titanium dioxide, 1 to 2 parts of stearic acid, 4 to 6 parts of metavanadate, 2 to 4 parts of glass fiber, 3 to 5 parts of niobium phosphate, 1 to 3 parts of carboxymethylcellulose and 1 to 3 parts of polyoxyethylene. When the denitration catalyst provided by the invention is applied to cement kiln flue gas denitration, the main active component vanadium poisoning of the catalyst can be effectively avoided, and the denitration activity of the catalyst is further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of flue gas denitration, and in particular relates to a denitration catalyst and a preparation method thereof, and application thereof in denitration of cement kiln flue gas. Background Art

[0002] Nitrogen oxides, a major source of atmospheric pollution, include N2O, NO, N2O2, N2O3, NO2, N2O4, and N2O5. NO and NO2 are the most serious contributors to atmospheric pollution. Nitrogen oxide emissions exacerbate environmental degradation. Under certain conditions, nitrogen oxides react with hydrocarbons to form photochemical smog, damaging the atmospheric environment and endangering human health. Furthermore, nitrogen oxides are a major cause of acid rain.

[0003] In fact, most of the nitrogen oxides emitted by humans come from the combustion process of fossil fuels. Thermal power generation, steel sintering, waste incineration, glass kilns, cement kilns, etc. are all major sources of nitrogen oxides.

[0004] At present, SNCR or SCR are generally used for flue gas denitrification. SCR denitrification technology is a selective catalytic reduction technology. An amino reducing agent is injected into the flue gas upstream of the catalyst to reduce NO in the flue gas through the catalyst. x Converted into nitrogen and water. Research on the reaction mechanism of vanadium-based catalysts has always been one of the important areas of SCR research. The SCR denitrification catalysts currently used in industry are mainly V2O5 / TiO2, V2O5-WO3 / TiO2 and other catalysts. The main structural component is TiO2, with a content of more than 75wt%. Researchers have conducted extensive research on the SCR denitrification reaction mechanism of this type of catalyst. The SCR denitrification reaction proceeds according to the Eley-Rideal mechanism, that is, adsorbed NH3 reacts with gaseous or weakly adsorbed NO on the catalyst surface. The working principle of the denitrification catalyst is as follows:

[0005] Main reaction equation:

[0006] 4NH3+4NO+O2→4N2+6H2O (1.1);

[0007] 4NH3+2NO+2O2→3N2+6H2O (1.2);

[0008] 4NH3+6NO→5N2+6H2O (1.3);

[0009] 8NH3+6NO→7N2+12H2O (1.4).

[0010] With increasingly stringent environmental protection requirements, the demand for flue gas denitrification in industrial sectors such as the cement industry continues to increase. However, currently widely used denitrification catalysts are susceptible to poisoning and inactivation by the heavy metal thallium present in flue gas from specific operating conditions, such as cement kilns. Thallium is a highly toxic and dispersed element, present in certain amounts in cement production raw materials such as pyrite. During the cement production process, thallium from the raw materials evaporates into the flue gas. When the flue gas containing thallium comes into contact with the denitrification catalyst, the thallium reacts with the active ingredients in the catalyst, causing catalyst poisoning.

[0011] After thallium enters the catalyst, it first interacts with the Ti-(OH)-Ti on the catalyst surface, then forms a thallium oxide coating on the catalyst surface. As the amount of thallium deposition continues to increase, the thallium oxide completely covers the active component V element, occupying and destroying the active sites of the catalyst. At the same time, because thallium is a sulfur-loving element, it reacts with SO2 in the flue gas to form Tl2SO4, which further covers the Tl2O3 layer on the catalyst surface. This thallium coating on the catalyst surface not only completely depletes the oxidizing ability of the active sites, leading to catalyst deactivation, micropore clogging, and a reduction in specific surface area, which fails to effectively improve the SCR reaction efficiency, but also increases N2O production and causes large-scale greenhouse gas emissions.

[0012] When a denitrification catalyst is mildly poisoned by thallium, its catalytic activity is low; when it is severely poisoned, the catalyst is completely deactivated. While most other poisoning substances, such as alkali metals and sulfur, can be effectively removed through conventional regeneration techniques, there is currently little research on the regeneration of thallium-poisoned catalysts. While existing technologies include some denitrification catalyst preparation methods and regeneration technologies, these are not ideal for addressing thallium poisoning and cannot meet the requirements for high catalyst activity, high stability, and resistance to thallium poisoning in industrial production. Summary of the Invention

[0013] The purpose of the present invention is to provide a denitration catalyst, a preparation method thereof and application in denitration of cement kiln flue gas. When the denitration catalyst provided by the present invention is applied to denitration of cement kiln flue gas, it can effectively avoid vanadium poisoning, the main active component of the catalyst, and further improve the denitration activity of the catalyst.

[0014] In order to achieve the above object, the present invention provides the following technical solutions:

[0015] The present invention provides a denitration catalyst comprising the following raw materials in parts by weight:

[0016] 5-10 parts of montmorillonite powder, 60-85 parts of titanium dioxide, 1-2 parts of stearic acid, 4-6 parts of metavanadate, 2-4 parts of glass fiber, 3-5 parts of niobium phosphate, 1-3 parts of carboxymethyl cellulose, and 1-3 parts of polyoxyethylene.

[0017] Preferably, the preparation raw materials further include molybdate, and the mass fraction of the molybdate is 1 to 3 parts.

[0018] Preferably, the titanium dioxide is anatase titanium dioxide, and the specific surface area of ​​the titanium dioxide is 90 to 110 m 2 / g, the particle size D of the titanium dioxide 50 0.8~1.2μm.

[0019] Preferably, the components of the montmorillonite powder include SiO2, Al2O3 and MgO, and the specific surface area of ​​the montmorillonite powder is 40 to 60 m 2 / g, the particle size D of the montmorillonite powder 90 <18μm; the metavanadate is ammonium metavanadate; the components of the glass fiber include SiO2, Al2O3, CaO, B2O3, MgO and Na2O; the viscosity of the carboxymethyl cellulose is 100~200mPa·s; the viscosity of the polyoxyethylene is 250~350mPa·s.

[0020] Preferably, the molybdate is ammonium heptamolybdate.

[0021] Preferably, the preparation method of niobium phosphate comprises the following steps:

[0022] Ammonium phosphate, niobium oxalate and water are mixed for hydrothermal reaction to obtain the niobium phosphate; the mass ratio of the ammonium phosphate to the niobium oxalate is 1:1, the temperature of the hydrothermal reaction is 170-180° C., and the time is 3-4 hours.

[0023] The present invention provides a method for preparing the denitration catalyst described in the above technical solution, comprising the following steps:

[0024] Mixing the raw materials for preparing the denitration catalyst, water and a pH regulator to obtain an alkaline sludge;

[0025] Aging the alkaline mud to obtain aged mud;

[0026] shaping the aged clay material to obtain a shaped body;

[0027] The molded body is calcined to obtain the denitration catalyst.

[0028] Preferably, the mixing comprises the following steps:

[0029] Mixing montmorillonite powder, titanium dioxide, stearic acid, metavanadate, glass fiber and water to obtain a first slurry, wherein the temperature of the first mixing is 50 to 70° C. and the water content of the first slurry is 40 to 50 wt %;

[0030] performing a second mixing of the first slurry and niobium phosphate to obtain a second slurry, wherein the temperature of the second mixing is 50 to 70° C.;

[0031] The second mud, carboxymethyl cellulose, polyoxyethylene and pH regulator are mixed for the third time to obtain an initial alkaline mud material, wherein the temperature of the third mixing is 50 to 70° C. and the pH value of the initial alkaline mud material is 7 to 8;

[0032] The initial alkaline mud is heated and stirred to obtain the alkaline mud, the heating and stirring temperature is ≥50° C., and the water content of the alkaline mud is 23-28wt%.

[0033] Preferably, the forming comprises the following steps:

[0034] Pre-extruding the stale clay material to obtain strip-shaped clay material;

[0035] Extruding the strip-shaped mud material in an extrusion die to obtain a molded body, wherein the extrusion die is a honeycomb mold, and the molded body is a honeycomb catalyst molded body;

[0036] The calcination further includes drying the shaped body to obtain a dried shaped body, wherein the water content of the dried shaped body is less than 5 wt %;

[0037] The calcination temperature is 500-550° C., and the calcination time is 28-32 hours.

[0038] The present invention provides the use of the denitration catalyst described in the above technical solution or the denitration catalyst prepared by the preparation method described in the above technical solution in denitration of cement kiln flue gas.

[0039] The present invention provides a denitration catalyst comprising the following raw materials in parts by weight: 5-10 parts montmorillonite powder, 60-85 parts titanium dioxide, 1-2 parts stearic acid, 4-6 parts metavanadate, 2-4 parts glass fiber, 3-5 parts niobium phosphate, 1-3 parts carboxymethyl cellulose, and 1-3 parts polyethylene oxide. The present invention introduces niobium phosphate into the denitration catalyst. Niobium phosphate has abundant acidic sites (Bronsted acidic sites and Lewis acidic sites). The introduction of niobium phosphate increases the specific surface area and surface acidity of the denitration catalyst, thereby enriching the active sites on the surface of the denitration catalyst. When the denitration catalyst contacts thallium, it can avoid poisoning by vanadium, the main active element of the denitration catalyst. Even after the denitration catalyst is poisoned and enriched with thallium, the denitration catalyst can still maintain a high denitration activity.

[0040] Furthermore, in the present invention, the raw materials for preparation also include molybdate, with the mass fraction of molybdate being 1 to 3 parts. The present invention introduces molybdate into the denitration catalyst, with molybdenum acting as a co-catalyst, which can further enhance the denitration activity of the denitration catalyst. In summary, the denitration catalyst provided by the present invention can effectively prevent vanadium poisoning, the main active component of the catalyst, and further enhance the denitration activity of the catalyst.

[0041] The present invention provides a method for preparing a denitration catalyst according to the above technical solution, comprising the following steps: mixing raw materials for preparing the denitration catalyst, water, and a pH adjuster to obtain an alkaline sludge; aging the alkaline sludge to obtain an aged sludge; shaping the aged sludge to obtain a formed body; and calcining the formed body to obtain the denitration catalyst. The preparation method provided herein directly utilizes niobium phosphate as the raw material. Compared with other methods of doping niobium (e.g., in-situ synthesis), the preparation method provided herein significantly preserves the activity of niobium phosphate in the resulting denitration catalyst, resulting in a significant resistance to thallium poisoning.

[0042] The present invention provides the use of the denitration catalyst described in the above technical solution, or the denitration catalyst prepared by the preparation method described in the above technical solution, in denitrification of cement kiln flue gas. Thallium in cement kiln flue gas originates from the ash produced by cement production. The denitration catalyst provided by the present invention has significant resistance to thallium poisoning and is well suited for denitrification of cement kiln flue gas. DETAILED DESCRIPTION

[0043] The present invention provides a denitration catalyst comprising the following raw materials in parts by weight:

[0044] 5-10 parts of montmorillonite powder, 60-85 parts of titanium dioxide, 1-2 parts of stearic acid, 4-6 parts of metavanadate, 2-4 parts of glass fiber, 3-5 parts of niobium phosphate, 1-3 parts of carboxymethyl cellulose, and 1-3 parts of polyoxyethylene.

[0045] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0046] The raw materials for preparing the denitration catalyst provided by the present invention include 5 to 10 parts by mass of montmorillonite powder, which may be 10 parts, 7.5 parts or 5 parts in the embodiment. In the present invention, the components of the montmorillonite powder preferably include SiO2, Al2O3 and MgO. The specific surface area of ​​the montmorillonite powder is preferably 40 to 60 m 2 / g. The particle size D of the montmorillonite powder 90In the present invention, the main function of the montmorillonite powder is to form the main structure of the denitration catalyst. The montmorillonite powder has a large specific surface area, a low thermal expansion coefficient, high stability, and good thermal shock resistance, which can improve the denitration catalyst's anti-sintering ability in a high-temperature environment.

[0047] Based on the mass fraction of the montmorillonite powder, the raw material for preparing the denitration catalyst provided by the present invention includes 60 to 85 parts of titanium dioxide, and in the embodiment, it can be 64 parts, 72.5 parts or 82 parts. In the present invention, the titanium dioxide is preferably anatase titanium dioxide (TiO2). The specific surface area of ​​the titanium dioxide is preferably 90 to 110 m 2 / g. The particle size D of the titanium dioxide 50 Preferably, it is 0.8 to 1.2 μm. In the present invention, the main function of the titanium dioxide is to form the main structure of the denitration catalyst. The titanium dioxide has a large specific surface area and serves as a carrier of the active component elements of the denitration catalyst.

[0048] The raw materials for preparing the denitration catalyst provided by the present invention include 1 to 2 parts of stearic acid, based on the mass fraction of the montmorillonite powder, and in embodiments, may be 2 parts, 1.5 parts, or 1 part. In the present invention, the stearic acid can reduce friction during mixing of the raw materials during the preparation process of the denitration catalyst and also facilitate extrusion demolding.

[0049] Based on the mass fraction of the montmorillonite powder, the raw material for preparing the denitration catalyst provided by the present invention preferably further comprises 1 to 3 parts of molybdate, and in the embodiment, it may be 3 parts, 2.5 parts or 1 part. In the present invention, the molybdate is preferably ammonium heptamolybdate ((NH4)6Mo7O 24 In the present invention, the ammonium heptamolybdate provides molybdenum element for the denitration catalyst, and the molybdenum element serves as a promoter element to improve the catalyst activity.

[0050] The raw materials for preparing the denitration catalyst provided by the present invention include 4 to 6 parts of metavanadate, based on the mass fraction of the montmorillonite powder, and in the embodiments, the amount can be 6 parts, 5 parts, or 4 parts. In the present invention, the metavanadate is preferably ammonium metavanadate (NH4VO3). In the present invention, the vanadium element provided by the ammonium metavanadate is the main active element of the denitration catalyst.

[0051] The raw materials for preparing the denitration catalyst provided by the present invention include 2-4 parts of glass fiber, based on the mass fraction of the montmorillonite powder, and in embodiments, the amount can be 4 parts, 3 parts, or 2 parts. In the present invention, the glass fiber preferably comprises SiO2, Al2O3, CaO, B2O3, MgO, and Na2O. In the present invention, the glass fiber acts as a skeleton in the denitration catalyst, enhancing its structural strength.

[0052] Based on the mass fraction of the montmorillonite powder, the raw materials for preparing the denitration catalyst provided by the present invention include 3 to 5 parts of niobium phosphate, and in the embodiment, it can be 5 parts, 4 parts or 3 parts.

[0053] In the present invention, the method for preparing niobium phosphate preferably includes the following steps: mixing ammonium phosphate, niobium oxalate, and water to undergo a hydrothermal reaction to obtain the niobium phosphate. In the present invention, the water is preferably deionized water. The mass ratio of ammonium phosphate to niobium oxalate is preferably 1:1. The mass ratio of water to ammonium phosphate is 10:1. The temperature of the hydrothermal reaction is preferably 170-180°C, and the reaction time is preferably 3-4 hours. After the hydrothermal reaction, a hydrothermal reaction liquid is obtained. In the present invention, the hydrothermal reaction liquid is preferably subjected to solid-liquid separation to obtain a precipitate; and the precipitate is dried to obtain the niobium phosphate. The solid-liquid separation is preferably centrifugal separation. The drying is preferably performed in an oven, and the drying temperature is preferably 55-60°C.

[0054] The raw materials for preparing the denitration catalyst provided by the present invention include 1 to 3 parts of carboxymethyl cellulose (CMC), based on the mass fraction of the montmorillonite powder. In the embodiments, the amount can be 3 parts, 2 parts, or 1 part. In the present invention, the viscosity of the carboxymethyl cellulose is preferably 100 to 200 mPa·s. In the present invention, the CMC acts as a pore-forming agent and can also improve the water absorption and water retention of the slurry obtained after mixing the raw materials, thereby improving the plasticity of the slurry and facilitating extrusion molding.

[0055] The raw materials for preparing the denitration catalyst provided by the present invention include 1 to 3 parts of polyoxyethylene (PEO), based on the mass fraction of the montmorillonite powder. In the embodiments, the amount can be 3 parts, 2 parts, or 1 part. In the present invention, the viscosity of the polyoxyethylene is preferably 250 to 350 mPa·s. In the present invention, the PEO acts as a thickener, flocculant, and lubricant to improve the plasticity of the sludge.

[0056] The raw materials for preparing the denitration catalyst provided by the present invention preferably also include water and a pH regulator. The present invention has no special requirements for the amount of the water and pH regulator, which are determined according to the water content and pH value during the preparation of the denitration catalyst.

[0057] The specific surface area of ​​the denitration catalyst provided by the present invention is preferably 65 to 70 m 2 / g.

[0058] The pore volume of the denitration catalyst provided by the present invention is preferably 0.28 to 0.3 m 2 / g.

[0059] The axial compressive strength of the denitration catalyst provided by the present invention is preferably 2.5 to 2.8 MPa.

[0060] The radial compressive strength of the denitration catalyst provided by the present invention is preferably 0.5 to 0.54 m 2 / g.

[0061] The present invention provides a method for preparing the denitration catalyst described in the above technical solution, comprising the following steps:

[0062] Mixing the raw materials for preparing the denitration catalyst, water and a pH regulator to obtain an alkaline sludge;

[0063] Aging the alkaline mud to obtain aged mud;

[0064] shaping the aged clay material to obtain a shaped body;

[0065] The molded body is calcined to obtain the denitration catalyst.

[0066] In the present invention, the raw materials for preparing the denitration catalyst, water, and a pH adjuster are mixed to produce an alkaline sludge. In the present invention, the water is preferably deionized water. The pH adjuster is preferably aqueous ammonia. The present invention has no particular requirements for the concentration of the aqueous ammonia. The mixing is preferably performed in a kneader. The mixing is preferably performed under stirring.

[0067] In the present invention, the mixing preferably comprises the following steps:

[0068] In the present invention, montmorillonite powder, titanium dioxide, stearic acid, metavanadate, glass fiber, and water are first mixed to produce a first slurry. In the present invention, when the raw materials for preparing the denitration catalyst preferably also include molybdate, the raw materials for the first mixing preferably also include the molybdate. The temperature of the first mixing is preferably 50-70°C. The first mixing time is preferably 1.5-2 hours. The water content of the first slurry is preferably 40-50 wt%.

[0069] After obtaining the first slurry, the present invention performs a second mixing of the first slurry and niobium phosphate to obtain a second slurry. In the present invention, the temperature of the second mixing is preferably 50-70°C.

[0070] After obtaining the second slurry, the present invention further comprises a third mixing step of the second slurry, carboxymethyl cellulose, polyethylene oxide, and a pH adjuster to obtain an initial alkaline slurry. In the present invention, the temperature of the third mixing step is preferably 50 to 70° C. The pH value of the initial alkaline slurry is preferably 7 to 8.

[0071] After obtaining the initial alkaline mud, the present invention heats and stirs the initial alkaline mud to obtain the alkaline mud. The temperature of the heating and stirring is preferably ≥50°C, more preferably 50-60°C. The present invention controls the moisture content of the alkaline mud by heating and stirring. The water content of the alkaline mud is preferably 23-28wt%.

[0072] After obtaining the alkaline clay, the present invention ages the alkaline clay to obtain aged clay. In the present invention, the aging is preferably performed under sealed conditions. In the present invention, the alkaline clay is preferably sealed with plastic wrap before aging. In the present invention, the aging temperature is preferably room temperature (20-30° C.). The aging time is preferably 10-12 hours.

[0073] After obtaining the aged clay material, the present invention shapes the aged clay material to obtain a molded body. In the present invention, the shaping preferably includes the following steps:

[0074] The present invention pre-extrudes the stale clay material to obtain strip-shaped clay material. In the present invention, the pre-extruded material is preferably carried out in an extruder.

[0075] After obtaining the strip-shaped clay material, the present invention extrudes the strip-shaped clay material through an extrusion die to obtain a molded body. In the present invention, the extrusion die is preferably a honeycomb mold. The inner wall thickness of the honeycomb mold is preferably 1.3 mm, the outer wall thickness is preferably 1.5 mm, and the number of holes in the honeycomb mold is preferably 13. The molded body is preferably a honeycomb catalyst molded body. The inner wall thickness of the honeycomb catalyst molded body is preferably 1.3 mm, the outer wall thickness is preferably 1.5 mm, and the number of holes is preferably 13.

[0076] After obtaining the shaped body, the present invention calcines the shaped body to obtain the denitration catalyst. In the present invention, the shaped body is preferably dried prior to calcination to obtain a dried shaped body. The dried shaped body preferably has a water content of less than 5 wt%. The present invention preferably calcines the dried shaped body. The calcination temperature is preferably 500-550°C, and the calcination time is preferably 28-32 hours. The calcination is preferably performed in a mesh belt kiln.

[0077] The present invention provides the use of the denitration catalyst described in the above technical solution or the denitration catalyst prepared by the preparation method described in the above technical solution in denitration of cement kiln flue gas.

[0078] The present invention provides the use of the denitration catalyst described in the above technical solution or the denitration catalyst prepared by the preparation method described in the above technical solution in flue gas denitration, wherein the flue gas contains thallium.

[0079] In the present invention, the application conditions include: the temperature of the cement kiln flue gas (ie flue gas) is preferably 280-300° C. The composition of the cement kiln flue gas preferably includes: NO X Preferably 500mg / Nm 3 , O2 is preferably 5v%, SO2 is preferably 20mg / Nm 3 The molar ratio of ammonia to nitrogen is preferably 1. The space velocity of the denitration catalyst is preferably 2500h -1 .

[0080] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0081] The niobium phosphate used in the following examples and comparative examples was prepared by a hydrothermal method. The specific preparation method is as follows:

[0082] Ammonium phosphate and niobium oxalate were added to deionized water and stirred uniformly. The mass ratio of ammonium phosphate to niobium oxalate was 1:1, and the mass ratio of deionized water to niobium oxalate was 10:1. After uniform stirring, the mixed solution was poured into a polytetrafluoroethylene-lined container, which was then placed in a Teflon reactor. The reactor was then heated in an oven at 180°C for 3 hours. After cooling, the precipitate was collected by centrifugation and dried in an oven at 60°C to obtain niobium phosphate powder.

[0083] Examples 1 to 4:

[0084] The raw materials used in the preparation of the denitration catalysts provided in Examples 1 to 4 and their mass fractions are shown in Table 1.

[0085] Table 1 Mass fractions of various raw materials used in the denitration catalysts provided in the examples and comparative examples

[0086] name Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Titanium dioxide 64 72.5 82 64 72.5 72.5 Montmorillonite 10 7.5 5 10 7.5 7.5 Ammonium metavanadate 6 5 4 6 5 5 Ammonium heptamolybdate 3 2.5 1 0 2.5 2.5 stearic acid 2 1.5 1 2 1.5 1.5 fiberglass 4 3 2 4 3 3 CMC 3 2 1 3 2 2 PEO 3 2 1 3 2 2 Niobium phosphate 5 4 3 5 0 0 Niobium acetate 0 0 0 0 0 4

[0087] The preparation methods of the denitration catalysts provided in Examples 1 to 3 are as follows:

[0088] (1) Montmorillonite powder, anatase titanium dioxide, stearic acid, ammonium heptamolybdate, ammonium metavanadate, glass fiber and deionized water were added to a kneader according to the mass fractions of each raw material given in Table 1. The mixture was heated to 70°C and stirred for 2 hours until the mud was uniform to obtain a first mud. The water content of the first mud was 50 wt%.

[0089] (2) Niobium phosphate powder is added to the first slurry, and the mixture is heated in a kneader at 70°C and stirred to obtain a second slurry. Carboxymethyl cellulose and polyethylene oxide are added to the second slurry at 70°C, and then ammonia water is added to adjust the pH value to 7-8. The mixture is then stirred in a kneader under heating (50°C) until the water content of the obtained alkaline slurry reaches 28wt%. The alkaline slurry is taken out and sealed with plastic wrap, and aged at room temperature for 12 hours to obtain aged slurry.

[0090] (3) The stale clay material is squeezed into a strip-shaped clay material through a pre-extruder, and the strip-shaped clay material is placed in an extruder and extruded using a honeycomb mold to form a honeycomb catalyst molded body. The honeycomb mold is a 13-hole honeycomb mold with an inner wall thickness of 1.3 mm and an outer wall thickness of 1.5 mm. The extruded honeycomb catalyst molded body is placed in a drying oven for dehydration drying until the water content of the dried honeycomb catalyst molded body is less than 5wt%. Finally, it is placed in a mesh belt kiln for calcination at a calcination temperature of 550°C and a calcination time of 32 hours. Finally, a honeycomb denitrification catalyst is obtained.

[0091] Example 4 and Comparative Examples 1-2:

[0092] The raw materials used in the preparation of the denitration catalysts provided in Example 4 and Comparative Examples 1-2 and their mass fractions are shown in Table 1.

[0093] The preparation methods of the denitration catalysts provided in Example 4 and Comparative Example 1 are the same as those in Examples 1 to 3, except that the preparations are carried out according to the raw materials given in Table 1, and niobium acetate is used in place of niobium phosphate in Examples 1 to 3 during the preparation of Comparative Example 2.

[0094] Test example:

[0095] (1) The components (mass content) of the denitration catalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were tested by XRF spectroscopy. The results are shown in Table 2. Table 2 lists the main components of the denitration catalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 2, and non-important components are not listed.

[0096] Table 2 Main components of catalysts in Examples and Comparative Examples

[0097]

[0098] As can be seen from Table 2, the main components of the denitration catalysts prepared in the examples and comparative examples vary with the type and weight fraction of the raw materials used, and there are no other abnormalities.

[0099] (2) Specific surface area and pore volume data

[0100] The specific surface areas and pore volume data of the denitration catalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 2 are shown in Table 3.

[0101] Table 3 Specific surface area and pore volume data of the denitration catalysts prepared in Examples 1 to 4 and Comparative Example 1

[0102]

[0103] As can be seen from Table 3: By comparing Examples 1 to 4 with Comparative Examples 1 to 2, it can be found that the addition of niobium phosphate is beneficial to the increase of specific surface area. Comparison between Example 2 and Comparative Example 1 shows that hydrothermally synthesized niobium phosphate has a certain ability to improve the specific surface area of ​​the denitration catalyst. It should be noted that after calcination, niobium phosphate is converted into niobium phosphate of different crystal forms, and partially decomposes to form oxides of phosphorus and niobium. However, because the honeycomb denitration catalyst needs to have a certain strength, the calcination process is inevitable. The present invention preferentially synthesizes niobium phosphate through a hydrothermal method. Unlike the method of directly doping niobium elements in Comparative Example 2, the embodiment of the present invention uses hydrothermally synthesized niobium phosphate as a raw material for the preparation of the denitration catalyst, which greatly preserves the activity of niobium phosphate and improves the anti-thallium poisoning activity of the denitration catalyst.

[0104] (3) Compressive strength test data

[0105] The mechanical property data of the denitration catalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 2 are shown in Table 4.

[0106] Table 4 Mechanical properties data of catalysts prepared in Examples and Comparative Examples

[0107]

[0108] As can be seen from Table 4, for the denitration catalysts prepared in Examples 1 to 4, the addition of niobium phosphate has no significant effect on the compressive strength of the denitration catalysts.

[0109] (4) Denitrification efficiency (temperature range 280~300℃)

[0110] The denitration catalysts prepared in Examples 1 to 4 and Comparative Examples 1 to 2 work at a flue gas temperature of 280 to 300°C. The temperature of the medium-temperature cement kiln is generally within this temperature range. X 500mg / Nm 3 , 5v% O2, 20mg / Nm 3 The molar ratio of SO2 and ammonia nitrogen is 1, and the space velocity is 2500h -1Under this condition, the denitrification efficiency can reach more than 80%. The test conditions are based on the GBT31587-2015 honeycomb flue gas denitrification catalyst, the aging time is 30 hours, and the gas composition and content are tested every 1 hour. The number of holes in the honeycomb catalyst is 13, the inner wall thickness is 1.3mm, and the outer wall thickness is 1.50mm. The test equipment used is the SCR flue gas denitrification test device produced by Tianjin Aozhan Technology Co., Ltd. After on-site application in the cement kiln (operating cycle 2.5 years), the denitrification efficiency of the embodiment and the comparative example after thallium poisoning was tested respectively.

[0111] Table 5 Denitration efficiency of denitration catalyst samples prepared in Examples and Comparative Examples before thallium poisoning

[0112]

[0113] Table 6 Denitrification efficiency of denitrification catalyst samples prepared in Examples and Comparative Examples after thallium poisoning

[0114]

[0115] The denitration efficiencies in Tables 5 and 6 indicate that increasing V2O5 content increases the denitration capacity of the denitration catalyst, as vanadium is the primary active component in denitration. It should be noted that the denitration efficiencies of Example 4 and Example 1, and Comparative Example 1 and Example 2, respectively, are slightly lower due to the lack of molybdenum and niobium phosphate. This is because these two materials (molybdenum and niobium phosphate) act as co-catalysts, which promote denitration efficiency.

[0116] After the cement kiln's operating cycle, the present invention discovered that all denitration catalysts suffer from thallium poisoning. Comparative Example 1, which does not contain niobium phosphate, exhibits the most significant reduction in denitration efficiency. This is because thallium accumulates on the surface of the denitration catalyst, reducing the acidic sites on the surface and affecting the capture and catalytic decomposition of nitrogen oxides by the denitration catalyst. Niobium phosphate has a high surface area and abundant acidic sites, which enrich the active sites on the surface of the denitration catalyst. Under the same conditions of thallium enrichment and poisoning, the addition of niobium phosphate in the present invention protects the denitration activity of the denitration catalyst. In contrast, Comparative Example 2, in which niobium acetate is directly used as the raw material for preparing the denitration catalyst, plays a minimal role in protecting the catalyst during the denitration reaction. Comparative Example 2: Compared with Example 2, Example 2 uses a hydrothermal method to synthesize niobium phosphate as a raw material for the preparation of the catalyst. Unlike Comparative Example 2, which directly introduces niobium acetate as a raw material, after the calcination of the niobium phosphate in Example 2, the niobium phosphate in the denitration catalyst retains more acidic sites because the hydrothermally prepared niobium phosphate has a stable structure. Secondly, because the niobium phosphate structure is stable during the calcination process, it does not convert excessively into niobium oxide, thereby not significantly reducing the number of acidic sites. In contrast, Comparative Example 2 directly uses niobium oxalate as a raw material for the preparation of the denitration catalyst. During the calcination process, niobium oxalate generates a large amount of niobium oxide from the raw material for the preparation of the denitration catalyst. The conversion to niobium oxide reduces the number of acidic sites. Niobium oxide is speculated to have a practical effect similar to tungsten oxide (a commonly used co-catalyst, mainly for anti-sintering), and has almost no effect in providing acidic sites. Therefore, the catalyst prepared in Comparative Example 2 has poor resistance to thallium poisoning.

[0117] From the above examples, it can be seen that the present invention introduces niobium phosphate raw material into the denitration catalyst. Niobium phosphate has abundant acid sites (Bronsted acid sites and Lewis acid sites). After the introduction of niobium phosphate, the specific surface area and surface acidity of the denitration catalyst are improved, thereby enriching the active sites on the surface of the denitration catalyst. When the denitration catalyst contacts the thallium element, it can avoid poisoning by the main active element of the denitration catalyst, vanadium, and can maintain a high denitration activity of the denitration catalyst after the denitration catalyst is poisoned and enriched by thallium. At the same time, the present invention introduces molybdate into the denitration catalyst, and the molybdenum element serves as a co-catalyst, which can further improve the denitration activity of the denitration catalyst. In the preparation method of the denitration catalyst, the preparation method provided by the present invention uses niobium phosphate as a raw material, and greatly preserves the activity of niobium phosphate in the prepared denitration catalyst.

[0118] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A denitration catalyst, characterized in that: The preparation comprises the following raw materials in parts by weight: 5-10 parts of montmorillonite powder, 60-85 parts of titanium dioxide, 1-2 parts of stearic acid, 4-6 parts of metavanadate, 2-4 parts of glass fiber, 3-5 parts of niobium phosphate, 1-3 parts of carboxymethyl cellulose, and 1-3 parts of polyoxyethylene.

2. The denitration catalyst according to claim 1, characterized in that The raw materials for preparation further include molybdate, and the mass fraction of the molybdate is 1 to 3 parts.

3. The denitration catalyst according to claim 1 or 2, characterized in that: The titanium dioxide is anatase titanium dioxide with a specific surface area of ​​90 to 110 m 2 / g, the particle size D of the titanium dioxide 50 0.8~1.2μm.

4. The denitration catalyst according to claim 1 or 2, characterized in that The components of the montmorillonite powder include SiO2, Al2O3 and MgO, and the specific surface area of ​​the montmorillonite powder is 40 to 60 m 2 / g, the particle size D of the montmorillonite powder 90 <18μm; the metavanadate is ammonium metavanadate; the components of the glass fiber include SiO2, Al2O3, CaO, B2O3, MgO and Na2O; the viscosity of the carboxymethyl cellulose is 100~200mPa·s; the viscosity of the polyoxyethylene is 250~350mPa·s.

5. The denitration catalyst according to claim 2, characterized in that The molybdate is ammonium heptamolybdate.

6. The denitration catalyst according to claim 1, characterized in that The preparation method of niobium phosphate comprises the following steps: Ammonium phosphate, niobium oxalate and water are mixed for hydrothermal reaction to obtain the niobium phosphate; the mass ratio of the ammonium phosphate to the niobium oxalate is 1:1, the temperature of the hydrothermal reaction is 170-180° C., and the time is 3-4 hours.

7. The method for preparing the denitration catalyst according to any one of claims 1 to 6, characterized in that: The following steps are involved: Mixing the raw materials for preparing the denitration catalyst, water and a pH regulator to obtain an alkaline sludge; Aging the alkaline mud to obtain aged mud; shaping the aged clay material to obtain a shaped body; The molded body is calcined to obtain the denitration catalyst.

8. The preparation method according to claim 7, characterized in that The mixing comprises the following steps: Mixing montmorillonite powder, titanium dioxide, stearic acid, metavanadate, glass fiber and water to obtain a first slurry, wherein the temperature of the first mixing is 50 to 70° C. and the water content of the first slurry is 40 to 50 wt %; performing a second mixing of the first slurry and niobium phosphate to obtain a second slurry, wherein the temperature of the second mixing is 50 to 70° C.; The second mud, carboxymethyl cellulose, polyoxyethylene and pH regulator are mixed for the third time to obtain an initial alkaline mud material, wherein the temperature of the third mixing is 50 to 70° C. and the pH value of the initial alkaline mud material is 7 to 8; The initial alkaline mud is heated and stirred to obtain the alkaline mud, the heating and stirring temperature is ≥50° C., and the water content of the alkaline mud is 23-28wt%.

9. The preparation method according to claim 7, characterized in that The molding comprises the following steps: Pre-extruding the stale clay material to obtain strip-shaped clay material; Extruding the strip-shaped mud material in an extrusion die to obtain a molded body, wherein the extrusion die is a honeycomb mold, and the molded body is a honeycomb catalyst molded body; The calcination further includes drying the shaped body to obtain a dried shaped body, wherein the water content of the dried shaped body is less than 5 wt %; The calcination temperature is 500-550° C., and the calcination time is 28-32 hours.

10. Use of the denitration catalyst according to any one of claims 1 to 6 or the denitration catalyst prepared by the preparation method according to any one of claims 7 to 9 in denitration of cement kiln flue gas.

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