A modified catalyst and its preparation method and application

Abstract

The present application provides a modified catalyst and its preparation method and application. The modified catalyst comprises a composite carrier and an active component; the composite carrier comprises silicon dioxide, white carbon black, aluminum oxide, molecular sieve and / or kaolin; the chemical formula of the active component is: A 0.01～5 B 1～15 C 0.01～2 Fe 0.1～10 Bi 0.1～5 Mo 30 O x A comprises at least one of Li, Na, K, Rb, and Cs; B is selected from at least one of Ca, Ba, Mn, Co, Ni, Mg, Cr, W, P, and Nb; and C is selected from at least one of Ce, Pr, Nd, La, and Sm. x represents the total number of oxygen atoms required to satisfy the valences of each element in the catalyst. This application improves the active component and composite support separately to promote interaction between the active component and composite support, thereby enhancing the redox performance of the catalyst. Furthermore, the catalyst structure is improved to enhance its stability, thereby increasing the selectivity for acrylonitrile and further improving the yield of acrylonitrile.

Description

Technical Field

[0001] The present application relates to the field of catalyst technology, and in particular to a modified catalyst and a preparation method and application thereof. Background Art

[0002] Currently, the industrial production of unsaturated nitriles by olefin ammoxidation still generally relies on the fluidized bed ammoxidation process. Catalysts are a core technology, and therefore crucial. Currently, two main types of catalysts are used in the industrial ammoxidation of propylene to acrylonitrile: Mo-Bi and Sb. Mo-Bi catalysts are the mainstream, with a market share exceeding 90%, and the majority of research efforts focus on Mo-Bi catalysts.

[0003] The Mo-Bi catalysts proposed in patents CN1210033A, CN1285238A, CN1294942A, and CN1751790A are suitable for use under conditions of relatively high reaction pressures and high propylene loadings, while still maintaining high acrylonitrile yields. In all of these patents, the oxide catalyst is supported on a silica carrier, and the preparation methods for these oxidation catalysts all use silica sol as the silica source. However, none of these patents mention the influencing factors of silica sol.

[0004] Patent CN1129408A proposes regulating the aluminum content of silica sol added during catalyst preparation to improve acrylonitrile selectivity. However, the preparation method in this patent is relatively complex, making it difficult to control the aluminum content to a low level, making it unsuitable for large-scale industrial production.

[0005] Patent CN1744949A proposes controlling the pore size distribution of the catalyst by varying the initial particle size of the silica feedstock. This patent requires precise control of the silica's fine structure, with the content of particles smaller than 80 angstroms and larger than 1000 angstroms not exceeding 20%. This requires a more complex preparation process, further increasing the difficulty of industrial production.

[0006] Therefore, it is necessary to develop a catalyst that is simple to prepare, easy to industrially produce, and can improve the selectivity and yield of acrylonitrile. Summary of the Invention

[0007] In response to the above-mentioned problems, the present application provides a modified catalyst, a preparation method thereof, and an application thereof; by separately improving the active component and the composite support, the mutual coordination between the active component and the composite support is promoted, and the oxidation-reduction performance of the catalyst is enhanced; the structure of the catalyst is improved and its stability is increased, thereby improving the selectivity of acrylonitrile and further improving the yield of acrylonitrile, thereby overcoming the deficiencies and defects mentioned in the background technology.

[0008] To achieve the above objectives, this application adopts the following technical solutions:

[0009] The invention of this application is to provide a modified catalyst, comprising a composite carrier and an active component; the composite carrier comprises silicon dioxide, white carbon black, alumina, molecular sieve and / or kaolin; the chemical formula of the active component is: 0.01～ 5B 1～15 C 0.01～2 Fe 0.1～10 Bi 0.1～5 Mo 30 O x ; A includes at least one of Li, Na, K, Rb, and Cs; B is selected from at least one of Ca, Ba, Mn, Co, Ni, Mg, Cr, W, P, and Nb; C is selected from at least one of Ce, Pr, Nd, La, and Sm; x is the total number of oxygen atoms required to satisfy the valence of each element in the catalyst.

[0010] Optionally, the mass content of the composite carrier in the modified catalyst is 10 to 70%, preferably 30 to 70%.

[0011] At this carrier content, the carrier can cooperate better with the active components, so that the active components are mostly located on the surface of the carrier, avoiding entering the interior of the carrier, causing problems such as a decrease in catalyst performance, the occurrence of side reactions, and a decrease in yield.

[0012] Optionally, the composite carrier comprises a carrier and a carrier modifier; the carrier is silica; and the carrier modifier comprises white carbon black, alumina, molecular sieves and / or kaolin.

[0013] Optionally, the mass content of the support modifier in the composite support is 0.1 to 30 wt %, preferably 1 to 10 wt %.

[0014] Optionally, in the carrier modifier, the mass ratio of alumina, kaolin and / or molecular sieve, and white carbon black is: (1-3): (1-5): (1-3).

[0015] The ratio of white carbon black mass to the sum of alumina and kaolin mass is: 1:(0.5~2)

[0016] Optionally, the chemical formula of the active component is: A 0.1～1 B 1～5 C 0.5～2 Fe 0.1～1 Bi 0.1～1 Mo 30 O x .

[0017] Optionally, A includes at least two of Li, Na, K, Rb, and Cs, preferably K and Rb.

[0018] Optionally, B is selected from at least three of Ca, Ba, Mn, Co, Ni, Mg, Cr, W, P and Nb; preferably Ni, Cr, Mg.

[0019] Optionally, C is selected from at least three of Ce, Pr, Nd, La and Sm; preferably Ce, Pr and Nd.

[0020] Optionally, the general chemical formula of the active component is:

[0021] K 0.1 Rb 0.5～0.9 Ni 0.2～0.5 Cr 0.7 Mg 0.1～0.3 Ce 0.1～0.5 Pr 0.3～0.6 Nd 0.1～0.5 Fe 0.1～1 Bi 0.1～1 Mo 30 O x .

[0022] Another invention of the present application is to provide a method for preparing any of the modified catalysts described above.

[0023] Optionally, the method includes: (1) dissolving source A, source B, source C, Fe source and Bi source to obtain a mixed solution I; dissolving the molybdenum source and adding the composite carrier raw material to obtain a mixed solution II; (2) mixing the mixed solution I and the mixed solution II to obtain a slurry; (3) granulating the slurry and then calcining it to obtain a modified catalyst.

[0024] The A source, B source, C source, Fe source, Bi source and molybdenum source include A, B, C, Fe, Bi and molybdenum in the form of oxides, salts, bases or acids.

[0025] The salt is a soluble salt, preferably a nitrate, sulfate, carbonate, sulfite, phosphate, phosphite, or the like.

[0026] The molybdenum source is preferably molybdate and molybdenum trioxide, and the molybdate is preferably ammonium molybdate.

[0027] The composite carrier raw material includes silica, white carbon black, alumina, molecular sieve and / or kaolin.

[0028] The composite support source includes a support source and a support modifier source.

[0029] The carrier is silicon dioxide, which is added in the form of silica sol.

[0030] The support modifier is selected from white carbon black, aluminum oxide, molecular sieve and / or kaolin, preferably white carbon black, aluminum oxide, molecular sieve and / or kaolin. The support modifier is added in the form of powder with a particle size of 10 to 100 μm, preferably 20 to 50 μm.

[0031] When the particle size of the support modifier does not meet the above range, the particle size can be reduced by grinding or other operations to meet the above range.

[0032] Optionally, in step (2), stirring and mixing are performed.

[0033] The mixing conditions are: pH 1 to 7, preferably 1 to 5; temperature 40 to 100°C, preferably 60 to 90°C.

[0034] Under acidic conditions, precipitation of various substances can be avoided. When the temperature is slightly higher than room temperature, the fluidity of various substances can be increased and the mixing can be more uniform.

[0035] The slurry is then granulated, preferably spray-dried, to form microspheres.

[0036] The microspheres are calcined in a calcining furnace to obtain a modified catalyst.

[0037] Optionally, the calcination conditions are: temperature of 500-750° C., preferably 550-700° C.; time of 1-6 h, preferably 2-4 h.

[0038] Another invention of the present application is to provide a use of any of the above modified catalysts in the preparation of acrylonitrile from propylene.

[0039] The method for preparing acrylonitrile from propylene comprises: subjecting propylene to ammoxidation in the presence of a catalyst to prepare acrylonitrile; the catalyst comprises any of the modified catalysts described above.

[0040] That is, after ammonia, air and propylene are mixed, they react under the catalytic action of a modified catalyst to produce acrylonitrile.

[0041] Optionally, the molar ratio of propylene, ammonia, and air is: 1:(1.05-1.25):(9.1-9.8); the reaction temperature is 400-460°C; the reaction pressure is 0.06-0.14 MPa; and the propylene load WWH of the catalyst is 0.06-0.12 h -1 .

[0042] Compared with the prior art, this application has the following advantages:

[0043] (1) By improving the support, this application can increase the specific surface area and pore volume of the catalyst, which is beneficial to improving the dispersion of the metal. At the same time, by combining different supports, the pore distribution of the catalyst is enriched, which is beneficial to the rapid diffusion of reactants and products and reduces the occurrence of side reactions. In addition, the modification can increase the acidity of the catalyst and enrich the distribution of acidic sites. This not only promotes the dispersion of the metal, but also improves the adsorption performance of the reactants.

[0044] (2) The method of the present application is simple and convenient, easy to carry out industrial production, and can reduce costs and improve production efficiency. DETAILED DESCRIPTION

[0045] To make the purpose, technical solutions and advantages of this application more clear, this application is further described in detail below. However, it should be understood that the description herein is only used to explain this application and is not intended to limit the scope of this application.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are intended solely for the purpose of describing specific embodiments and are not intended to limit this application. The reagents and instruments used herein are commercially available, and the characterization methods involved can be found in the relevant descriptions in the prior art and will not be further elaborated herein.

[0047] In order to further understand the present application, the present application is further described in detail below in conjunction with the best embodiment.

[0048] The activity of the catalyst of the present invention was evaluated in a fluidized bed reactor with an inner diameter of 38 mm. The catalyst loading was 500 g, the reaction temperature was 420°C, the molar ratio of propylene, ammonia, and air was 1:1.1:9.5, the reaction pressure was 0.08 MPa, and the reaction load was 0.08 h. -1 Run for 2000h under the conditions of

[0049] In the present invention, the definitions of propylene conversion, acrylonitrile selectivity and single-pass yield are as follows:

[0050]

[0051]

[0052]

[0053] Example 1

[0054] (1) 73.27 g of Bi(NO3)3·5H2O, 26.73 g of RbNO3, 81.09 g of Mn(NO3)2, 39.35 g of Ce(NO3)3·6H2O, 39.73 g of Nd(NO3)3·6H2O, 17.57 g of Ni(NO3)2·6H2O, 61.02 g of Fe(NO3)3·9H2O, 61.97 g of Mg(NO3)2·6H2O, 1.69 g of KOH, 65.7 g of Pr(NO3)3·6H2O and 60.44 g of Cr(NO3)3·9H2O were dissolved in 160 g of water by heating to obtain solution I. 1600.0 g of (NH4)6Mo7O 24 4H2O was dissolved in 1000 g of water, and 1500 g of silica sol with a weight concentration of 40% was added, and a carrier modifier (60 g of white carbon black, 20 g of alumina and 40 g of kaolin) was added to obtain a mixed solution II.

[0055] (2) Solution I and mixed solution II were mixed and stirred at a pH of 2 and a temperature of 80° C. to obtain a slurry.

[0056] (3) The prepared slurry was formed into microspheres in a spray dryer and finally calcined in a rotary calciner at 600°C for 4 hours to prepare a modified catalyst, wherein the active component is K 0.1 Ce 0.3 Rb 0.6 Ni 0.2 Cr 0.7 Mg 0.1 Pr 0.5 Nd 0.3 Fe 0.5 Bi 0.5 Mo 30 .

[0057] Examples 2 to 11

[0058] Same as Example 1, except that the mass of the support modifier was changed, as shown in Table 1.

[0059] Table 1

[0060]

[0061] Comparative Example 1

[0062] The same as Example 1, except that the support modifier is changed to 60 grams of white carbon black, 20 grams of alumina and 40 grams of montmorillonite.

[0063] Comparative Example 2

[0064] The same as Example 1, except that the support modifier was changed to 60 g of diatomaceous earth, 20 g of alumina and 40 g of kaolin.

[0065] Comparative Example 3

[0066] The same as Example 1, except that the support modifier was changed to 60 g of diatomaceous earth, 20 g of alumina and 40 g of montmorillonite.

[0067] Compared with the test examples of the present application and comparative examples 1 to 3, the composite carrier of the present application enriches the pore distribution of the catalyst, which is beneficial to the rapid diffusion of reactants and products; at the same time, the carrier can improve the acidity of the catalyst after compounding and enrich the distribution of acidic sites; on the one hand, it is beneficial to the dispersion of the metal, and on the other hand, it can also improve the adsorption performance of the reactants.

[0068] As shown in Table 1, when alumina, kaolin, and white carbon black are present simultaneously, selectivity for acrylonitrile is higher, and yield is higher, both exceeding 85%. When any one of these is missing, the selectivity drops below 85%. When the ratio of white carbon black to the sum of the mass of alumina and kaolin is 1:(0.5-2), even better selectivity and yield are achieved.

[0069] Comparative Example 4

[0070] Same as Example 1, except that the active ingredient is changed to K 0.1 Rb 0.5 Ni2Cr 0.5 Mg 0.1 Ce 0.5 Fe2Bi3Mo 12 (SiO250%).

[0071] This catalyst is a common industrial catalyst. After it is compounded with a composite carrier, the activity of the resulting composite catalyst is significantly lower than that of the catalyst in Example 1. This is mainly because the active component of the present application has more oxygen vacancies and more active sites than the catalyst in Comparative Example 4; and has more acidic sites on the surface; combined with the effect of the composite carrier, it can further promote the distribution and adsorption performance of active sites; in active components with a larger number of lattice oxygen, it can further improve the diffusion of reactants and products, and has a better improvement effect than general active components.

[0072] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements or improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A modified catalyst, characterized in that comprising a composite carrier and an active component; The active ingredient is K 0.1 Ce 0.3 Rb 0.6 Ni 0.2 Cr 0.7 Mg 0.1 Pr 0.5 Nd 0.3 Fe 0.5 Bi 0.5 Mo 30 O x ; x is the total number of oxygen atoms required to satisfy the valence of each element in the active component; The composite carrier comprises a carrier and a carrier modifier; the carrier is silicon dioxide; the carrier modifier comprises white carbon black, alumina and kaolin; the mass ratio of alumina, kaolin and white carbon black in the carrier modifier is: (1-3): (1-5): (1-3); the mass content of the composite carrier in the modified catalyst is 10-70%; the mass content of the carrier modifier in the composite carrier is 0.1-30%; The preparation method of the modified catalyst comprises: (1) dissolving source A, source B, source C, source Fe and source Bi to obtain a mixed solution I; dissolving a molybdenum source and adding a composite carrier raw material to obtain a mixed solution II; (2) mixing the mixed solution I and the mixed solution II to obtain a slurry; (3) granulating the slurry and then calcining to obtain a modified catalyst; wherein A is K and Rb; B is Ni, Mg and Cr; and C is Ce, Pr and Nd.

2. The modified catalyst according to claim 1, characterized in that The mass content of the composite carrier in the modified catalyst is 30-70%.

3. The modified catalyst according to claim 1, characterized in that The mass content of the support modifier in the composite support is 1-10%.

4. The modified catalyst according to claim 1, characterized in that In the carrier modifier, the ratio of the mass of the white carbon black to the sum of the mass of the alumina and the kaolin is: 1: (1-2).

5. A method for preparing a modified catalyst according to any one of claims 1 to 4, characterized in that: include: (1) Dissolving source A, source B, source C, Fe source, and Bi source to obtain a mixed solution I; The molybdenum source is dissolved and then added to the composite carrier raw material to obtain a mixed solution II; wherein A is K and Rb; B is Ni, Mg and Cr; C is Ce, Pr and Nd; (2) Mixing the mixed solution I and the mixed solution II to obtain a slurry; (3) calcining the slurry to obtain a modified catalyst; In step (2), the mixing conditions are: pH 1-5; temperature 40-100°C; In step (3), the calcination conditions are: temperature 500~750℃; time 1~6h.

6. Use of the modified catalyst according to any one of claims 1 to 4 in the preparation of acrylonitrile by ammoxidation of propylene.

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