Ammonia oxidation catalyst, method for producing the same, and use thereof
By designing and preparing a three-layer catalyst, the problem of easy sublimation of ammonia oxidation catalysts at high temperatures was solved, achieving the goal of efficient preparation of nitrile compounds, extending the catalyst's lifespan, and improving reaction efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- WANHUA CHEM GRP CO LTD
- Filing Date
- 2024-01-15
- Publication Date
- 2026-07-10
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalyst preparation, specifically relating to an ammonia oxidation catalyst for preparing nitrile compounds from hydrocarbons or alcohols, its preparation method, and its application. Background Technology
[0002] Nitriles are important basic organic chemical raw materials, playing a crucial role in adjusting the future energy structure and developing the chemical industry. In modern industrial nitrile production, gas-phase ammonia oxidation is a significant process. For example, hydrogen cyanide can be produced by methanol or methane ammonia oxidation, propylene ammonia oxidation produces acrylonitrile, and xylene ammonia oxidation produces phthalonitrile, etc.
[0003] In ammonia oxidation processes, tubular reactors are generally used to produce nitrile compounds. A typical tubular reactor consists of tens of thousands of metal tubes filled with solid particulate catalyst of a specific morphology and cooled by oil or molten salt as the heat transfer fluid. Because the reaction is highly exothermic, it is difficult to achieve a uniform bed temperature distribution; generally, hot spots form in the reaction zone. To eliminate these hot spots, fluidized bed ammonia oxidation processes are also used to produce nitrile products, such as the ammonia oxidation of propylene to acrylonitrile and the ammonia oxidation of xylene to phthalonitrile. Ammonia oxidation is a complex process, involving many side reactions in addition to the main reaction. To control the amount of side reactions, catalyst development requires high precision, demanding not only high activity but also excellent selectivity. Therefore, the catalyst support, active components, and preparation methods significantly influence catalyst performance.
[0004] Currently, the catalysts used in ammonia oxidation processes are mainly molybdenum-based catalysts. For example, the hydrogen cyanide catalyst is a mixture of iron molybdate (Fe2(MoO4)3) and molybdenum trioxide (MoO3), and both acrylonitrile catalysts and aromatic hydrocarbon ammonia oxidation catalysts contain molybdenum. The addition of the active component molybdenum results in satisfactory catalytic performance; the product yield is high (generally above 90%), and due to the low toxicity of molybdenum, its impact on the environment and human health is limited.
[0005] Since oxidation reactions typically occur at temperatures above 300°C, molybdenum will sublimate and be lost from the catalyst, leading to catalyst deactivation. Sublimated molybdenum forms needle-like MoO3 crystals at the reactor outlet. As a result of molybdenum sublimation and concentration / decomposition, catalytic activity and main product selectivity decrease, and the pressure drop in the reactor increases. Therefore, the catalyst needs to be replaced approximately every 1-2 years, or less than 1 year, depending on production economics.
[0006] In summary, developing a new catalyst and its preparation method that can not only improve the yield of nitrile products but also has good thermal conductivity and lifespan is a challenging technical problem in the process of preparing nitrile compounds from hydrocarbons or alcohols. Summary of the Invention
[0007] To address the aforementioned problems, this invention provides an ammonia oxidation catalyst, its preparation method, and its applications. The prepared catalyst exhibits high activity and high thermal conductivity. When applied to the gas-phase ammonia oxidation of hydrocarbons or alcohols to prepare nitrile compounds, it achieves a conversion rate greater than 99% for hydrocarbons with fewer than 8 Cs, an effective selectivity for nitrile compounds greater than 81%, and a yield exceeding 80%. This catalyst is suitable for large-scale industrial applications in nitrile compound production.
[0008] To achieve the objectives of this invention, this application provides the following technical solution:
[0009] An ammonia oxidation catalyst includes an outer layer structure, an intermediate layer structure, and an inner layer structure, wherein the outer layer structure includes Mo, V, Co, optional metal Bi, and metal A, wherein metal A is selected from one or more of Cs, K, and Cu.
[0010] The intermediate layer structure includes Mo, Cr, optional Sb, optional W and element X, wherein element X is selected from one or more of Fe, P, Na and Mg;
[0011] The inner structure includes Mo, Al, Si and optional metal Y, with element Y selected from one or more of Sb, Sr, Ru, B and Ce.
[0012] Preferably, the elements in the catalyst exist mainly in the form of oxides.
[0013] Preferably, the molar ratio of Mo, Bi, V, Co, and A in the outer layer structure of the catalyst is 12:0-10:0.1-100:0.001-10:0.001-5, and more preferably 12:0-8:5-95:0.05-10:0.1-4.
[0014] Preferably, the molar ratio of Mo, Sb, Cr, W, and X in the intermediate layer structure of the catalyst is 0.006-15:0-1:0.1-110:0-5:0.01-5, more preferably 5-12:0-0.98:50-110:3-5:1-5.
[0015] Preferably, the molar ratio of Mo, Al, Si, and Y in the inner layer structure of the catalyst is 0.001-3:5-200:3-700:0-50, more preferably 0.1-1:5-100:3-50:0.1-40.
[0016] Preferably, the outer layer structure of the catalyst is Mo. 12 Bi b V c Co d A e O x Where b = 0-10, c = 0.1-100, d = 0.001-10, e = 0.001-5, preferably b = 0-8, c = 5-95, d = 0.05-10, e = 0.1-4, x is the sum of the oxidation state values of the other elements; A is one or more elements among K, Cs, and Cu;
[0017] Preferably, the intermediate layer structure of the catalyst is: Mo a1 Sb f Cr g W h X i O y a1 = 0.006-15, f = 0-1, g = 0.1-110, h = 0-5, i = 0.01-5, preferably a1 = 5-12, f = 0-0.98, g = 50-110, h = 3-5, i = 1-5, y is the sum of the oxidation state values of the other elements, and X is one or more elements among Fe, P, Na, and Mg;
[0018] Preferably, the inner layer structure of the catalyst is: Mo a2 Al j Si k Y l O z a2 = 0.001-3, j = 5-200, k = 3-700, l = 0-50, preferably a2 = 0.1-1, j = 5-100, k = 3-50, l = 0.1-40. z is the sum of the oxidation state values of all other elements, and Y is one or more elements among Sb, Sr, Ru, B, and Ce.
[0019] Preferably, the mass ratio of the outer layer, the middle layer, and the inner layer is 1:0.2-1.2:0.8-4.
[0020] The present invention also provides a method for preparing the catalyst, wherein an inner layer structure catalyst, an intermediate layer structure catalyst and an outer layer structure catalyst are prepared respectively, and then the intermediate layer structure and the outer layer are respectively coated on the inner layer structure to obtain a three-layer structure catalyst.
[0021] Preferably, the preparation methods of the inner layer catalyst, outer layer catalyst, and intermediate layer catalyst can be known methods in the prior art, such as co-precipitation method, direct mixing and kneading, etc., and the preparation methods of the three layers may be the same or different.
[0022] Preferably, the catalyst is prepared by: preparing metal or non-metal precursors into solutions, then performing co-precipitation reactions, followed by aging, drying and calcining to obtain inner-layer structure catalysts, intermediate-layer structure catalysts and outer-layer structure catalysts respectively.
[0023] Preferably, the precursor of the metal or non-metal element is prepared into a solution using water or dilute acid. After the solution is mixed evenly, the pH is adjusted to 0.5-5 with ammonia, preferably 1.5-4. The solution is then stirred and matured at 30-100°C for 1-12 hours, dried at 70-260°C, and then calcined at 260-1500°C for 1-10 hours.
[0024] The resulting catalyst is formed in three steps from the inner layer to the outer layer. The final morphology of the catalyst is one of the following: powder, sphere, strip, cylinder, multi-channel, and honeycomb. The catalyst can be subjected to irregular shape treatment, among which spherical, hollow cylindrical, and honeycomb catalysts are preferred.
[0025] Preferably, the precursors for each component element of the catalyst can be selected according to those known in the art. For example, the silicon and aluminum sources for the inner catalyst include commercial silica sol, chromatographic silica gel, Cab-O-Sil, SBA-1, SBA-15, MCM-41, MCM-48, silicon carbide, titanium dioxide, bauxite, kaolin, boehmite, α-alumina powder, etc.; the precursors for the copper of the outer catalyst include copper oxide, copper nitrate, copper chloride, copper acetate, cuprous chloride, copper acetylacetone, etc. Copper oxalate, basic copper carbonate, etc., with copper nitrate, copper chloride, and copper acetate being particularly preferred; cesium precursors include cesium acetate, carbonate, halide, oxide, nitrate, and sulfate, with cesium carbonate and cesium nitrate being preferred; potassium precursors include potassium carbonate, potassium nitrate, potassium chloride, carnallite (KCl·MgCl2·6H2O), heterohalite (2CaSO4·K2SO4·2H2O), potassium feldspar K[AlSi3O8], mica, etc., with potassium carbonate and potassium nitrate being preferred. Molybdenum precursors include ammonium polymolybdate, molybdenum trioxide, molybdic acid, molybdenum disulfide, etc. The selection of metal precursors is well known in the art and will not be listed here.
[0026] After each catalyst layer is prepared, the inner catalyst layer is shaped to prepare the core, and then the middle catalyst layer and the outer catalyst layer are coated onto the core. The shaping method can be a method known in the art, such as kneading together with an adhesive.
[0027] The shaped and coated catalyst is dried and calcined to obtain a three-layer catalyst.
[0028] Preferably, the calcination temperature is 400-650℃.
[0029] Preferably, the intermediate catalyst and the outer catalyst are prepared by co-precipitation.
[0030] The present invention also provides the application of the catalyst in the ammoxidation of hydrocarbons or alcohols to prepare nitrile compounds.
[0031] A method for preparing nitrile compounds involves reacting hydrocarbons or alcohols with oxygen, ammonia, or liquid ammonia under the catalysis of the catalyst described in this invention to undergo an ammonia oxidation reaction.
[0032] Preferably, the catalyst needs to be activated before use. The activation method is to activate the catalyst in an oxygen-containing atmosphere at 200-500°C for 60-200 minutes.
[0033] Preferably, the flow rate of the oxygen-containing atmosphere used for activating each gram of catalyst is 100–1000 ml / min. -1 .
[0034] Preferably, the oxygen-containing atmosphere can be air or a mixture of oxygen and nitrogen.
[0035] Preferably, during activation, the temperature is increased from room temperature by no more than 20°C per minute. -1 The temperature is increased to 200-500℃ at a heating rate.
[0036] Preferably, after activation, the flow rate is 100–1000 ml / min. -1 Purge with nitrogen for 60–200 min;
[0037] Preferably, the ammonia oxidation reaction temperature is 350–500°C, more preferably 400–450°C; the absolute pressure is 0.04–0.3 MPa, more preferably 0.05–0.15 MPa.
[0038] Preferably, the ammonia oxidation reaction is a gas-phase reaction, with all feedstocks being gases, and the total volume hourly space velocity (VHSV) of the feedstock gases being 500–2500 h⁻¹. -1 Preferred operating time: 1000-2000h -1 .
[0039] Preferably, the feed gas contains a diluent gas, and the molar ratio of the diluent gas to hydrocarbons or alcohols is 5–45, preferably 7–45.
[0040] Preferably, the molar ratio of oxygen to hydrocarbons or alcohols is 1 to 10, more preferably 4 to 9.
[0041] Preferably, the molar ratio of ammonia to hydrocarbons or alcohols is 0.5-15, more preferably 1-10.
[0042] The diluent gas can be one or a mixture of N2, H2O, He, and Ne, and the oxygen can come from pure oxygen or air.
[0043] The catalyst bed is segmented and filled with catalyst and inert filler, wherein the volume ratio of catalyst to inert filler is 1.5 to 4.5, preferably 2.5 to 3.5. In a preferred embodiment of the invention, the catalyst bed is filled from top to bottom in the following order: inert filler layer, pure catalyst layer, and inert filler layer. The inert filler is one or a mixture of various materials selected from quartz sand, gravel, inert alumina balls, silicon carbide, glass beads, graphite, and ceramic beads in any proportion.
[0044] The calculation methods for hydrocarbon or alcohol conversion rates and the selectivity of any product (represented as product X in the formula) mentioned in the embodiments of the present invention are described as follows:
[0045]
[0046]
[0047] Compared with existing catalysts, this application has the following advantages:
[0048] 1. The catalyst is prepared with a three-layer structure. The outer layer contains two or more elements from Mo, Bi, V, Co, Cs, K, Cu, and O; the middle layer contains two or more elements from Mo, Sb, Cr, W, Fe, P, Na, Mg, and O; and the inner layer contains two or more elements from Mo, Al, Si, Sb, Sr, Ru, B, Ce, and O. This layered structure fully follows the typical "redox" mechanism of gas-phase ammonia oxidation. Lattice oxygen participates in the oxidation reaction, and after being consumed by the reduction reaction, it is replenished through the adsorption and dissociation of gas-phase oxygen molecules at oxygen vacancies. During ammonia oxidation, ammonia also needs to be adsorbed and activated to participate in the reaction. Therefore, a V-Co-Mo catalyst is placed in the outer layer to form a bifunctional catalyst capable of simultaneously adsorbing and activating both ammonia and oxygen molecules. A Cr-Mo catalyst is placed in the middle layer to maintain the charge balance of the outer V-Co-Mo catalyst. A Mo-Al-Si core is placed in the inner layer to ensure the structural strength of the catalyst. The multilayer catalyst formed can effectively promote the activation of aromatics and the ammonia oxidation reaction. In addition, during the high-temperature reaction, the outer layer of Mo will be lost and depleted. The Mo element can gradually migrate from the inner layer to the middle layer and then to the outer layer to replenish it, thereby extending the service life of the catalyst.
[0049] 2. The catalyst is uniformly coated and wrapped from the inside out, and the layers are interconnected by channels with a diameter of 50 to 200 μm, which also connects to the surface, thus ensuring the free migration of elements from the inner layer to the outer surface of the catalyst.
[0050] 3. The catalyst prepared by this technology has distinct layers, and the temperature range corresponding to the acid content from the inside to the outside is regular. Under the same acid content as normal commercial catalysts, the reaction temperature is reduced by 30℃-200℃. The reduction in reaction temperature can effectively slow down the loss of active components. Detailed Implementation
[0051] The present invention will be further illustrated by the following embodiments, but the present invention is not limited to the following embodiments.
[0052] Example 1
[0053] Catalyst preparation
[0054] Preparation of outer catalyst powder: 100g of ammonium heptamolybdate was dissolved in 1L of pure water at 50℃, and solution A was obtained after complete dissolution. 5g of bismuth nitrate, 800g of vanadium pentoxide, 1g of cobalt nitrate, and 10g of potassium nitrate were added to 1kg of dilute nitric acid (13wt%) aqueous solution, and slurry B was obtained after partial dissolution. While maintaining the solution temperature at 65℃, solution B was added dropwise to solution A with stirring. The pH was adjusted to 2.4 using ammonia water during the addition process. After adjustment, the solution was stirred and matured for 4 hours, spray-dried at 280℃, and pre-calcined at 400℃ for 3 hours to obtain a powdered catalyst.
[0055] Preparation of intermediate layer catalyst powder: At 80℃, 30g of ammonium heptamolybdate and 10g of molybdenum trioxide (MoO3) were dissolved in 300g of pure water to form solution C. 3g of antimony trioxide, 400g of chromium trioxide, 15g of 85wt% phosphoric acid, 10g of 30% silica sol, and 3g of magnesium acetate were dissolved in 1kg of water to form slurry D. D was slowly added dropwise to C while stirring. During the addition process, the pH was adjusted to 1.9 with ammonia water. After adjustment, the mixture was stirred and matured for 2h. After spray drying at 250℃ and pre-calcining at 410℃ for 3h, the intermediate layer catalyst powder was obtained.
[0056] Preparation of the inner catalyst: 40g of wood fiber was acid-washed and then mechanically mixed with 35g of polyethylene (particle size 100-250μm), followed by microwave drying at 120℃ for 10h. A mixture of wood fiber and polypropylene was mechanically mixed with 600g of bauxite, 50g of molybdenum trioxide, 100g of kaolin, 0.2kg of guar gum powder, and 4kg of feldspar powder. 2kg of sodium lignosulfonate aqueous solution (sodium lignosulfonate mass fraction 3%) was added to the mixture, and then transferred to a kneader for thorough kneading. The mixture was then pelletized into 3mm diameter spheres using a pelletizing machine. 10g of highly pulverized wood chips were embedded into the surface of the spheres using a coating machine. The spheres were then microwave-dried at 75℃ for 0.5h, dried in an oven at 120℃ for 3h, and calcined at 1400℃ for 4h to obtain the inner spherical catalyst.
[0057] The intermediate and outer catalyst layers were sequentially coated using a spray coating method. A commercially available binder containing 20%–40% silica sol was used to coat the inner catalyst layer, with the mass ratio of outer catalyst: intermediate catalyst: inner catalyst = 1:0.4:1.8. The coated catalyst was dried at 65℃ for 5 hours and then calcined at 550℃ for 5 hours to obtain spherical catalysts with a diameter of 4.5 mm. The pore size distribution, acid content characterization temperature, and other parameters of the catalyst are shown in Table 2.
[0058] Evaluation of oxidation experiments
[0059] 100g of catalyst was loaded into a 0.5m long reactor, with the reaction tube being a Ф25mm stainless steel tube. After catalyst pretreatment, the reaction mixture was prepared at a xylene:oxygen:nitrogen:ammonia ratio of 1:9:38:9 (molar ratio) and a volume hourly space velocity of 800 h⁻¹. -1 The oxidation reaction was carried out under standard conditions and atmospheric pressure. Results: At a medium temperature of 370℃, the initial xylene conversion rate was 99.4%, and the phthalonitrile selectivity was 83%. After 5000 hours of operation, the xylene conversion rate was 99.2%, and the phthalonitrile selectivity was 82%. The catalyst hotspot temperature was 420℃. After in-situ catalyst treatment to migrate the inner and middle Mo layers to the outer catalyst layer, the xylene conversion rate was 99.5%, and the phthalonitrile selectivity was 82.5%. The catalyst activity trend reflects that after 7 years of catalyst use, the xylene conversion rate was 99%, and the phthalonitrile selectivity was 81.5%.
[0060] Example 2
[0061] Catalyst preparation
[0062] Preparation of outer catalyst powder: 100g of ammonium heptamolybdate was dissolved in 1L of pure water at 50℃. After complete dissolution, solution A was obtained. 500g of vanadium pentoxide and 5g of potassium nitrate were added to 1kg of dilute nitric acid (13wt%) aqueous solution. After partial dissolution, slurry B was obtained. The solution temperature was maintained at 65℃. B was added dropwise to A while stirring. During the addition process, the pH was adjusted to 2 with ammonia water. After adjustment, the mixture was stirred and matured for 5h, spray-dried at 300℃, and pre-calcined at 440℃ for 3h to obtain powdered catalyst.
[0063] Preparation of intermediate layer catalyst powder: At 80℃, 30g of ammonium heptamolybdate was dissolved in 300g of pure water to form solution C. 2g of antimony trioxide, 100g of chromium trioxide, 6g of ferric nitrate nonahydrate, 5g of 85wt% phosphoric acid, and 2g of 30% silica sol were dissolved in 1kg of water to form slurry D. D was slowly added dropwise to C while stirring. During the addition process, the pH was adjusted to 1.8 with ammonia water. After adjustment, the mixture was stirred and matured for 3h. After spray drying at 260℃ and pre-calcining at 420℃ for 3h, the intermediate layer catalyst powder was obtained.
[0064] Preparation of the inner catalyst: 40g of wood fiber was acid-washed and then mechanically mixed with 35g of polyethylene (particle size 100-250μm), followed by microwave drying at 120℃ for 10h. The mixture of wood fiber and polypropylene was then mechanically mixed with 300g of bauxite, 3g of molybdenum trioxide, 200g of kaolin, 0.2kg of guar gum powder, 20g of antimony trioxide, and 100g of boric acid until homogeneous. 1.5kg of sodium lignosulfonate aqueous solution (sodium lignosulfonate mass fraction 3%) was added to the mixture, and then transferred to a kneader for thorough kneading. The mixture was then pelletized into 2.8mm diameter spheres using a pelletizing machine. 5g of highly pulverized wood chips were embedded into the surface of the spheres using a coating machine. The spheres were then microwave-dried at 85℃ for 0.5h, dried in an oven at 125℃ for 3h, and calcined at 1450℃ for 5h to obtain the inner spherical catalyst.
[0065] The intermediate and outer catalyst layers were sequentially coated using a spray coating method. A commercially available binder containing 20%–40% silica sol was used to coat the inner catalyst layer, with the mass ratio of outer catalyst: intermediate catalyst: inner catalyst = 1:0.5:1.9. The coated catalyst was dried at 75℃ for 6 hours and then calcined at 680℃ for 3 hours to obtain spherical catalysts with a diameter of 3.5 mm. The pore size distribution, acid content characterization temperature, and other parameters of the catalyst are shown in Table 2.
[0066] Evaluation of oxidation experiments
[0067] 100g of catalyst was loaded into a 0.5m long reactor, with the reaction tube being a Ф25mm stainless steel tube. After catalyst pretreatment, the reaction mixture was prepared at a xylene:oxygen:nitrogen:ammonia ratio of 1:9:38:9 (molar ratio) and a volume hourly space velocity of 800 h⁻¹. -1 The oxidation reaction was carried out under standard conditions and atmospheric pressure. Results: At a medium temperature of 370℃, the initial xylene conversion rate was 99.2%, and the phthalonitrile selectivity was 81.5%. After 5000 hours of operation, the xylene conversion rate was 99.1%, and the phthalonitrile selectivity was 81.2%. The catalyst hotspot temperature was 418℃. After in-situ catalyst treatment to migrate the inner and middle Mo layers to the outer catalyst layer, the xylene conversion rate was 99.3%, and the phthalonitrile selectivity was 81.6%. The catalyst activity trend reflects that after 7 years of catalyst use, the xylene conversion rate was 99%, and the phthalonitrile selectivity was 81.1%.
[0068] Example 3
[0069] Catalyst preparation
[0070] Preparation of outer catalyst powder: 100g of ammonium heptamolybdate was dissolved in 1L of pure water at 50℃, and solution A was obtained after complete dissolution. 200g of bismuth nitrate, 300g of vanadium pentoxide, 10g of cobalt nitrate, and 30g of cesium carbonate were added to 1kg of dilute nitric acid (13wt%) aqueous solution, and slurry B was obtained after partial dissolution. While maintaining the solution temperature at 70℃, B was added dropwise to A with stirring. The pH was adjusted to 2.05 using ammonia water during the addition process. After adjustment, the mixture was stirred and matured for 4 hours, spray-dried at 280℃, and pre-calcined at 430℃ for 3 hours to obtain a powdered catalyst.
[0071] Preparation of intermediate layer catalyst powder: At 80℃, 30g of ammonium heptamolybdate and 15g of molybdenum trioxide were dissolved in 300g of pure water to form solution C. 45g of silicotungstic acid (H4[Si(W3O)) was then added... 10 )4]·xH2O), 3g of ferric nitrate nonahydrate, and 5g of 30% silica sol were dissolved in 1kg of water to form slurry D. D was slowly added to C while stirring. The pH was adjusted to 1.9 with ammonia water during the addition process. After adjustment, the mixture was stirred and matured for 3h. After spray drying at 280℃ and pre-calcining at 420℃ for 3h, the intermediate layer catalyst powder was obtained.
[0072] Preparation of the inner catalyst: 40g of wood fiber was acid-washed and then mechanically mixed with 35g of polyethylene (particle size 100-250μm), followed by microwave drying at 120℃ for 10h. The mixture of wood fiber and polypropylene was then mechanically mixed with 800g of bauxite, 800g of kaolin, 20g of molybdenum trioxide, 200g of kaolin, 30g of strontium nitrate, 20g of ruthenium chloride, and 0.1kg of guar gum powder. 1.8kg of sodium lignosulfonate aqueous solution (sodium lignosulfonate mass fraction 3%) was added to the mixture, and then transferred to a kneader for thorough kneading. The mixture was then pelletized into 4mm diameter spheres using a pelletizing machine. 7g of highly pulverized wood chips were embedded into the surface of the spheres using a coating machine. The spheres were then microwave-dried at 80℃ for 1h, dried in an oven at 115℃ for 8h, and calcined at 1450℃ for 4h to obtain the inner spherical catalyst.
[0073] The intermediate and outer catalyst layers were sequentially coated using a spray coating method. A commercially available binder containing 20%–40% silica sol was used to coat the inner catalyst layer, with the mass ratio of outer catalyst: intermediate catalyst: inner catalyst = 1:0.6:2.2. The coated catalyst was dried at 80℃ for 5 hours and then calcined at 500℃ for 5 hours to obtain spherical catalysts with a diameter of 4.5 mm. The pore size distribution, acid content characterization temperature, and other parameters of the catalyst are shown in Table 2.
[0074] Evaluation of oxidation experiments
[0075] 50g of catalyst was loaded into a 0.5m long reactor, with the reaction tube being a Ф25mm stainless steel tube. After catalyst pretreatment, the reaction mixture was prepared with a propylene:oxygen:nitrogen:ammonia ratio of 1:1.8:8.7:1.5 (molar ratio) and a volume hourly space velocity (VHSV) of 1100 h⁻¹. -1 The oxidation reaction was carried out under standard conditions and atmospheric pressure. Results: At a salt bath temperature of 320℃, the initial propylene conversion rate was 99.4%, and the effective selectivity for acrylonitrile was 95.3%. After 5000 hours of operation, the propylene conversion rate was 99.2%, and the effective selectivity for acrylonitrile was 95.1%. The catalyst hotspot temperature was 370℃. After in-situ catalyst regeneration to migrate Mo from the inner and middle catalyst layers to the outer catalyst layer, the propylene conversion rate was 99.3%, and the effective selectivity for acrylonitrile was 95.2%. The catalyst activity trend indicates that the catalyst can be used for approximately 7 years.
[0076] Example 4
[0077] Preparation of the outer catalyst: At 50℃, 400g of ammonium heptamolybdate was added to 1L of pure water and completely dissolved to obtain solution A. 690g of bismuth nitrate, 55g of cobalt nitrate, 300g of vanadium pentoxide, 2g of potassium nitrate, and 5.6g of copper nitrate were added to 1kg of dilute nitric acid (15wt%) aqueous solution and completely dissolved to obtain solution B. While maintaining the solution temperature at 80℃, solution B was added to solution A with stirring. The pH was then adjusted to 2.5 with ammonia. After adjustment, the solution was stirred and matured for 5-6 hours, dried at 250℃, spray-dried at 220℃, and pre-calcined at 390℃ for 3 hours to obtain the outer catalyst powder.
[0078] Preparation of intermediate layer catalyst powder: At 80℃, 400g ammonium molybdate and 10g molybdenum trioxide were dissolved in 2kg pure water to form solution C. 30.5g ferric nitrate, 2g phosphoric acid, and 4g magnesium acetate were dissolved in 10kg water to form solution D. Solution D was slowly added dropwise to solution C while stirring. After the solution was completely added, 1.1kg tungstic acid was added, and the final solution pH was 2.6. The solution was stirred and matured for 4h, then spray-dried at 220℃ and pre-calcined at 390℃ for 3h to obtain intermediate layer catalyst powder.
[0079] Preparation of the inner catalyst: 20g of wood fiber was acid-washed and then mechanically mixed with 20g of polyethylene (particle size 50-500μm), and microwave-dried at 130℃ for 12h. The mixture of wood fiber and polypropylene was mechanically mixed with 500g of bauxite, 20g of molybdenum trioxide, 300g of kaolin, 50g of silicon carbide powder, 20g of guar gum powder, 100g of feldspar powder, 8.9g of antimony trioxide, and 26.5g of cerium nitrate until homogeneous. 500g of sodium lignosulfonate aqueous solution (sodium lignosulfonate mass fraction 3%) was added to the mixture, and then transferred to a kneader for thorough kneading. The mixture was pelletized into 4mm diameter spheres using a pelletizing machine. 20g of highly pulverized wood chips were embedded into the surface of the spheres using a coating machine. The spheres were then microwave-dried at 75℃ for 1h, dried in an oven at 120℃ for 4h, and calcined at 1300℃ for 4h to obtain the inner spherical catalyst.
[0080] The intermediate and outer catalyst layers were sequentially coated using a spray coating method. A 20% silica sol binder was used to coat the inner catalyst layer, with the mass ratio of outer catalyst: intermediate catalyst: inner catalyst = 1:0.2:3.3. The coated catalyst was dried at 75℃ for 4 hours and then calcined at 550℃ for 6 hours to obtain spherical catalysts with a diameter of 4.5 mm. The pore size distribution, acid content characterization temperature, and other parameters of the catalyst are shown in Table 2.
[0081] Evaluation of oxidation experiments
[0082] 50g of catalyst was loaded into a 0.5m long reactor, with the reaction tube being a Ф25mm stainless steel tube. After catalyst pretreatment, the reaction mixture was prepared with a propylene:oxygen:nitrogen:ammonia ratio of 1:1.8:8.7:1.5 (molar ratio) and a volume hourly space velocity (VHSV) of 1100 h⁻¹. -1 The oxidation reaction was carried out under standard conditions and atmospheric pressure. Results: At a salt bath temperature of 320℃, the initial propylene conversion rate was 99.3%, and the effective selectivity for acrylonitrile was 95.4%. After 5000 hours of operation, the propylene conversion rate was 99.2%, and the effective selectivity for acrylonitrile was 95.2%. The catalyst hotspot temperature was 390℃. After in-situ catalyst regeneration to migrate Mo from the inner and middle catalyst layers to the outer catalyst layer, the propylene conversion rate was 99.2%, and the effective selectivity for acrylonitrile was 95.3%. The catalyst activity trend indicates that the catalyst can be used for approximately 7 years.
[0083] Example 5
[0084] Preparation of the outer catalyst: At 50℃, 30g of ammonium heptamolybdate was added to 1L of pure water and completely dissolved to obtain solution A. 39g of cobalt nitrate, 3.1g of cesium carbonate, and 5.6g of copper nitrate were added to 1kg of dilute nitric acid (15wt%) aqueous solution and completely dissolved to obtain solution B. While maintaining the solution temperature at 75℃, solution B was added to solution A with stirring, and then the pH was adjusted to 4 with ammonia. After adjustment, the solution was stirred and matured for 5-6 hours, dried at 100℃, ground, and pre-calcined at 350℃ for 4 hours to obtain the outer powder catalyst.
[0085] Preparation of intermediate layer catalyst powder: At 90℃, 310g of ammonium molybdate was dissolved in 5kg of pure water to form solution C. 120g of ferric nitrate and 4g of magnesium acetate were dissolved in 200g of water to form solution D. Solution D was slowly added dropwise to solution C while stirring. The pH was adjusted to 1.7 with ammonia water during the addition process. After adjustment, the mixture was stirred and matured for 3h. After spray drying at 200℃ and pre-calcining at 390℃ for 3h, the intermediate layer catalyst powder was obtained.
[0086] Preparation of the inner catalyst: 20g of wood fiber was acid-washed and then mechanically mixed with 20g of polyethylene (particle size 50-500μm), and microwave-dried at 130℃ for 12h. A mixture of wood fiber and polypropylene was mechanically mixed with 500g of bauxite, 35g of molybdenum trioxide, 53g of cerium nitrate, 300g of kaolin, 50g of silicon carbide powder, 20g of guar gum powder, and 100g of feldspar powder. 500g of sodium lignosulfonate aqueous solution (sodium lignosulfonate mass fraction 3%) was added to the mixture, and then transferred to a kneader for thorough kneading. The mixture was pelletized into 4.2mm diameter spheres using a pelletizing machine. 10g of highly pulverized wood chips were embedded into the surface of the spheres using a coating machine. The spheres were then microwave-dried at 72℃ for 1h, dried in an oven at 120℃ for 4h, and calcined at 1350℃ for 4h to obtain the inner spherical catalyst.
[0087] The intermediate and outer catalyst layers were sequentially coated using a spray coating method. A binder consisting of 20%–40% silica sol was applied to the inner catalyst layer, with the mass ratio of outer catalyst: intermediate catalyst: inner catalyst = 1:0.3:2.5. The coated catalyst was dried at 90℃ for 5 hours and then calcined at 560℃ for 5 hours to obtain spherical catalysts with a diameter of 4.6 mm. The pore size distribution, acid content characterization temperature, and other parameters of the catalyst are shown in Table 2.
[0088] Evaluation of oxidation experiments
[0089] 50g of catalyst was loaded into a 0.5m long reactor, with the reaction tube being a Ф25mm stainless steel tube. After catalyst pretreatment, the reaction mixture was prepared at a methanol:oxygen:nitrogen:ammonia ratio of 1:19:72:1.25 (molar ratio) and a volume hourly space velocity (VHSV) of 4000 h⁻¹.-1 The oxidation reaction was carried out under standard conditions and atmospheric pressure. Results: At a salt bath temperature of 320℃, the initial methanol conversion rate was 99.5%, and the HCN selectivity was 91%. After 5000 hours of operation, the methanol conversion rate was 99.3%, the HCN selectivity was 90.2%, and the catalyst hotspot temperature was 490℃. After in-situ catalyst regeneration to migrate Mo from the inner and middle catalyst layers to the outer catalyst layer, the methanol conversion rate reached 99.3%, and the effective HCN selectivity was 90.4%. The catalyst activity trend indicates that the catalyst can be used for approximately 5 years.
[0090] Comparative Example 1
[0091] Catalyst preparation
[0092] Preparation of the outer catalyst: 100g of ammonium heptamolybdate was dissolved in 1L of pure water at 50℃, and solution A was obtained after complete dissolution. 200g of bismuth nitrate, 300g of vanadium pentoxide, 10g of cobalt nitrate, and 30g of cesium carbonate were added to 1kg of dilute nitric acid (13wt%) aqueous solution, and slurry B was obtained after partial dissolution. While maintaining the solution temperature at 70℃, B was added dropwise to A with stirring. The pH was adjusted to 2.05 using ammonia water during the addition process. After adjustment, the solution was stirred and matured for 4 hours, spray-dried at 280℃, and pre-calcined at 430℃ for 3 hours to obtain a powdered catalyst.
[0093] Preparation of the inner catalyst: 40g of wood fiber was acid-washed and then mechanically mixed with 35g of polyethylene (particle size 100-250μm), followed by microwave drying at 120℃ for 10h. The mixture of wood fiber and polypropylene was then mechanically mixed with 800g of bauxite, 800g of kaolin, 20g of molybdenum trioxide, 200g of kaolin, 30g of strontium nitrate, 20g of ruthenium chloride, and 0.1kg of guar gum powder. 1.8kg of sodium lignosulfonate aqueous solution (sodium lignosulfonate mass fraction 3%) was added to the mixture, and then transferred to a kneader for thorough kneading. The mixture was then pelletized into 4mm diameter spheres using a pelletizing machine. 7g of highly pulverized wood chips were embedded into the surface of the spheres using a coating machine. The spheres were then microwave-dried at 80℃ for 1h, dried in an oven at 115℃ for 8h, and calcined at 1450℃ for 4h to obtain the inner spherical catalyst.
[0094] The outer catalyst layer was coated using a spray coating method, with 20%–40% silica sol, a commercially available binder, applied to the inner catalyst layer. The mass ratio of the outer catalyst to the inner catalyst layer was 1:2.2. After coating, the catalyst was dried at 80℃ for 5 hours and then calcined at 500℃ for 5 hours to obtain spherical catalysts with a diameter of 4.2 mm. The pore size distribution, acid content characterization temperature, and other parameters of the catalyst are shown in Table 2.
[0095] Evaluation of oxidation experiments
[0096] 50g of catalyst was loaded into a 0.5m long reactor, with the reaction tube being a Ф25mm stainless steel tube. After catalyst pretreatment, the reaction mixture was prepared with a propylene:oxygen:nitrogen:ammonia ratio of 1:1.8:8.7:1.5 (molar ratio) and a volume hourly space velocity (VHSV) of 1100 h⁻¹. -1 The oxidation reaction was carried out under standard conditions and atmospheric pressure. Results: At a salt bath temperature of 320℃, the initial propylene conversion rate was 99%, and the effective selectivity for acrylonitrile was 93%. After 5000 hours of operation, the propylene conversion rate was 98.5%, the effective selectivity for acrylonitrile was 91%, and the catalyst hotspot temperature was 420℃. The catalyst activity trend indicates that the catalyst can be used for approximately 4 years.
[0097] Comparative Example 2
[0098] Preparation of the outer catalyst: At 50℃, 30g of ammonium heptamolybdate was added to 1L of pure water and completely dissolved to obtain solution A. 39g of cobalt nitrate, 3.1g of cesium carbonate, and 5.6g of copper nitrate were added to 1kg of dilute nitric acid (15wt%) aqueous solution and completely dissolved to obtain solution B. While maintaining the solution temperature at 75℃, solution B was added to solution A with stirring, and then the pH was adjusted to 4 with ammonia. After adjustment, the solution was stirred and matured for 5-6 hours, dried at 100℃, ground, and pre-calcined at 350℃ for 4 hours to obtain the outer powder catalyst.
[0099] Preparation of the inner catalyst: 20g of wood fiber was acid-washed and then mechanically mixed with 20g of polyethylene (particle size 50-500μm), and microwave-dried at 130℃ for 12h. A mixture of wood fiber and polypropylene was mechanically mixed with 500g of bauxite, 35g of molybdenum trioxide, 53g of cerium nitrate, 300g of kaolin, 50g of silicon carbide powder, 20g of guar gum powder, and 100g of feldspar powder. 500g of sodium lignosulfonate aqueous solution (sodium lignosulfonate mass fraction 3%) was added to the mixture, and then transferred to a kneader for thorough kneading. The mixture was pelletized into 4.2mm diameter spheres using a pelletizing machine. 10g of highly pulverized wood chips were embedded into the surface of the spheres using a coating machine. The spheres were then microwave-dried at 72℃ for 1h, dried in an oven at 120℃ for 4h, and calcined at 1350℃ for 4h to obtain the inner spherical catalyst.
[0100] The outer catalyst layer was coated using a spray coating method, with a binder of 20%–40% silica sol applied to the inner catalyst layer. The mass ratio of the outer catalyst to the inner catalyst layer was 1:2.5. After coating, the catalyst was dried at 90℃ for 5 hours and then calcined at 560℃ for 5 hours to obtain spherical catalysts with a diameter of 4.3 mm. The pore size distribution, acid content characterization temperature, and other parameters of the catalyst are shown in Table 2.
[0101] Evaluation of oxidation experiments
[0102] 50g of catalyst was loaded into a 0.5m long reactor, with a Ф25mm stainless steel reaction tube. The reaction was carried out at a methanol:oxygen:nitrogen:ammonia ratio of 1:19:72:1.25 and a volume hourly space velocity of 4000 h⁻¹. -1 The oxidation reaction was carried out under standard conditions and atmospheric pressure. Results: At a salt bath temperature of 320℃, the initial methanol conversion rate was 99%, and the HCN selectivity was 80%. After 5000 hours of operation, the methanol conversion rate was 97.5%, the HCN selectivity was 76%, and the catalyst hotspot temperature was 510℃. The catalyst activity trend indicates that the catalyst can be used for approximately 3 years.
[0103] Comparative Example 3
[0104] Catalyst preparation
[0105] Preparation of outer catalyst powder: 100g of ammonium heptamolybdate was dissolved in 1L of pure water at 50℃, and solution A was obtained after complete dissolution. 5g of bismuth nitrate, 800g of vanadium pentoxide, 1g of cobalt nitrate, and 10g of potassium nitrate were added to 1kg of dilute nitric acid (13wt%) aqueous solution, and slurry B was obtained after partial dissolution. While maintaining the solution temperature at 65℃, solution B was added dropwise to solution A with stirring. The pH was adjusted to 2.4 using ammonia water during the addition process. After adjustment, the solution was stirred and matured for 4 hours, spray-dried at 280℃, and pre-calcined at 400℃ for 3 hours to obtain a powdered catalyst.
[0106] Preparation of the inner catalyst: 40g of wood fiber was acid-washed and then mechanically mixed with 35g of polyethylene (particle size 100-250μm), followed by microwave drying at 120℃ for 10h. A mixture of wood fiber and polypropylene was mechanically mixed with 600g of bauxite, 50g of molybdenum trioxide, 100g of kaolin, 0.2kg of guar gum powder, and 4kg of feldspar powder. 2kg of sodium lignosulfonate aqueous solution (sodium lignosulfonate mass fraction 3%) was added to the mixture, and then transferred to a kneader for thorough kneading. The mixture was then pelletized into 3mm diameter spheres using a pelletizing machine. 10g of highly pulverized wood chips were embedded into the surface of the spheres using a coating machine. The spheres were then microwave-dried at 75℃ for 0.5h, dried in an oven at 120℃ for 3h, and calcined at 1400℃ for 4h to obtain the inner spherical catalyst.
[0107] The outer catalyst layer was coated using a spray coating method, employing a commercially available binder of 20%–40% silica sol to coat the inner catalyst layer. The mass ratio of the outer catalyst to the inner catalyst layer was 1:1.8. After coating, the catalyst was dried at 65℃ for 5 hours and then calcined at 550℃ for 5 hours to obtain spherical catalysts with a diameter of 4.1 mm. The pore size distribution, acid content characterization temperature, and other parameters of the catalyst are shown in Table 2.
[0108] Evaluation of oxidation experiments
[0109] 100g of catalyst was loaded into a 0.5m long reactor, with the reaction tube being a Ф25mm stainless steel tube. After catalyst pretreatment, the reaction mixture was prepared at a xylene:oxygen:nitrogen:ammonia ratio of 1:9:38:9 (molar ratio) and a volume hourly space velocity of 800 h⁻¹. -1 The oxidation reaction was carried out under standard conditions and atmospheric pressure. Results: At a salt bath temperature of 370℃, the initial xylene conversion rate was 98.5%, and the effective selectivity for phthalonitrile was 79%. After 5000 hours of operation, the xylene conversion rate was 97.5%, and the effective selectivity for phthalonitrile was 73%. The catalyst activity trend indicates that the catalyst can be used for approximately 3 years.
[0110] Table 1. Catalyst elemental composition
[0111]
[0112] Table 2 Catalyst Parameters
[0113]
[0114]
Claims
1. An ammonia oxidation catalyst, characterized in that, It includes an outer layer structure, a middle layer structure and an inner layer structure, wherein the outer layer structure includes Mo, V, Co, optional metal Bi and metal A, wherein metal A is selected from one or more of Cs, K and Cu; The intermediate layer structure includes Mo, Cr, optional Sb, optional W and element X, wherein element X is selected from one or more of Fe, P, Na and Mg; The inner structure includes Mo, Al, Si and optional element Y, which is selected from one or more of Sb, Sr, Ru, B and Ce.
2. The catalyst according to claim 1, characterized in that, The elements in the catalyst exist in the form of oxides.
3. The catalyst according to claim 1, characterized in that, The molar ratio of Mo, Bi, V, Co, and A in the outer layer structure of the catalyst is 12:0-10:0.1-100:0.001-10:0.001-5.
4. The catalyst according to claim 3, characterized in that, The molar ratio of Mo, Bi, V, Co, and A in the outer layer structure of the catalyst is 12:0-8:5-95:0.05-10:0.1-4.
5. The catalyst according to claim 1, characterized in that, The molar ratio of Mo, Sb, Cr, W, and X in the intermediate layer structure of the catalyst is 0.006-15:0-1:0.1-110:0-5:0.01-5.
6. The catalyst according to claim 5, characterized in that, The molar ratio of Mo, Sb, Cr, W, and X in the intermediate layer structure of the catalyst is 5-12:0-0.98:50-110:3-5:1-5.
7. The catalyst according to claim 1, characterized in that, The molar ratio of Mo, Al, Si, and Y in the inner layer structure of the catalyst is 0.001-3:5-200:3-700:0-50.
8. The catalyst according to claim 7, characterized in that, The molar ratio of Mo, Al, Si, and Y in the inner layer structure of the catalyst is 0.1-1:5-100:3-50:0.1-40.
9. The catalyst according to claim 1, characterized in that, The outer layer structure of the catalyst is Mo. 12 Bi b V c Co d A e O x Where b = 0-10, c = 0.1-100, d = 0.001-10, e = 0.001-5, x is the sum of the oxidation state values of the other elements; A is one or more elements among K, Cs, and Cu.
10. The catalyst according to claim 9, characterized in that, b=0-8, c=5-95, d=0.05-10, e=0.1-4.
11. The catalyst according to claim 1, characterized in that, The intermediate layer structure of the catalyst is: Mo a1 Sb f Cr g W h X i O y a1=0.006-15, f=0-1, g=0.1-110, h=0-5, i=0.01-5, y is the sum of the oxidation state values of the other elements, and X is one or more elements among Fe, P, Na, and Mg.
12. The catalyst according to claim 11, characterized in that, a1=5-12, f=0-0.98, g=50-110, h=3-5, i=1-5.
13. The catalyst according to claim 1, characterized in that, The inner layer structure of the catalyst is: Mo a2 Al j Si k Y l O z a2=0.001-3, j=5-200, k=3-700, l=0-50, z is the sum of the oxidation state values of the other elements, and Y is one or more elements among Sb, Sr, Ru, B, and Ce.
14. The catalyst according to claim 13, characterized in that, a2=0.1-1, j=5-100, k=3-50, l=0.1-40.
15. The catalyst according to claim 1, characterized in that, The mass ratio of the outer layer, middle layer, and inner layer is 1:0.2-1.2:0.8-4.
16. The method for preparing the catalyst according to claim 1, characterized in that, Inner-layer catalyst, middle-layer catalyst, and outer-layer catalyst were prepared separately. Then, the middle-layer structure was coated onto the inner-layer structure, and the outer-layer structure was coated onto the middle-layer structure to obtain a three-layer catalyst.
17. The use of the catalyst according to any one of claims 1-15 in the ammoxidation of hydrocarbons or alcohols to prepare nitrile compounds.
18. A method for preparing a nitrile compound, characterized in that, Hydrocarbons or alcohols are reacted with oxygen and ammonia under the catalysis of the catalyst described in any one of claims 1-15 to undergo an ammonia oxidation reaction.
19. The preparation method according to claim 18, characterized in that, The catalyst needs to be activated before use. The activation method is to activate the catalyst in an oxygen-containing atmosphere at 200~500℃ for 60~200min.
20. The preparation method according to claim 19, characterized in that, The oxygen-containing atmosphere used for activation per gram of catalyst is at a flow rate of 100~1000 ml / min. -1 .
21. The preparation method according to claim 19, characterized in that, The oxygen-containing atmosphere is air or a mixture of oxygen and nitrogen.
22. The preparation method according to claim 19, characterized in that, During activation, the temperature is increased from room temperature at a rate not exceeding 20°C / min. -1 The temperature is increased to 200~500℃ at a heating rate.
23. The preparation method according to claim 19, characterized in that, After activation, use at a flow rate of 100~1000 ml / min. -1 Purge with nitrogen for 60-200 minutes.
24. The preparation method according to claim 18, characterized in that, The ammonia oxidation reaction temperature is 350~500℃; the absolute pressure is 0.04~0.3MPa.
25. The preparation method according to claim 24, characterized in that, The ammonia oxidation reaction temperature is 400~450℃; Absolute pressure 0.05~0.15MPa.
26. The preparation method according to claim 18, characterized in that, The ammonia oxidation reaction is a gas-phase reaction, with all feedstocks being gases, and the total volume hourly space velocity (VHSV) of the feedstock gases is 500–2500 h⁻¹. -1 .
27. The preparation method according to claim 26, characterized in that, The total volumetric space velocity of the feed gas is 1000~2000 h⁻¹ -1 .
28. The preparation method according to claim 18, characterized in that, The feed gas contains diluent gas, and the molar ratio of diluent gas to hydrocarbons or alcohols is 5 to 45.
29. The preparation method according to claim 28, characterized in that, The feed gas contains diluent gas, and the molar ratio of diluent gas to hydrocarbons or alcohols is 7~45.
30. The preparation method according to claim 18, characterized in that, The molar ratio of oxygen to hydrocarbons or alcohols is 1 to 10.
31. The preparation method according to claim 30, characterized in that, The molar ratio of oxygen to hydrocarbons or alcohols is 4 to 9.
32. The preparation method according to claim 18, characterized in that, The molar ratio of ammonia to hydrocarbons or alcohols is 0.5-15.
33. The preparation method according to claim 32, characterized in that, The molar ratio of ammonia to hydrocarbons or alcohols is 1-10.
34. The preparation method according to claim 28, characterized in that, The diluent gas is one or a mixture of N2, H2O, He, and Ne.
35. The preparation method according to any one of claims 18-34, characterized in that, The catalyst bed is filled in sections with catalyst and inert packer, and the volume ratio of catalyst to inert packer is 1.5 to 4.
5.
36. The preparation method according to claim 35, characterized in that, The catalyst bed is filled in sections with catalyst and inert packer, wherein the volume ratio of catalyst to inert packer is 2.5 to 3.5.