Ammonia oxidation catalyst, preparation method and application thereof, and acrylonitrile preparation method

Abstract

The invention relates to the field of catalysts, and discloses an ammoxidation catalyst and a preparation method and application thereof and a preparation method of acrylonitrile, the catalyst comprises an active component and a carrier, the active component has the following general formula FedBieMofAaBbCcOx, the value range of a is 0-1, the value range of b is 0-12.5, the value range of c is 0-3, and the value range of d is 0.1-4, the value range of e is 0.01-3, the value range of f is 9-16, and x is the total number of oxygen atoms required by valence of each element in the active component; the catalyst comprises microspheres with a hollow structure and a partial hollow sphere structure, and the hollow rate of the catalyst is 10-30%. The catalyst not only has relatively high propylene ammoxidation activity and acrylonitrile selectivity in propylene ammoxidation reaction, but also has relatively high acrylonitrile single-pass yield under a high-load condition.

Description

Technical Field

[0001] The invention relates to the field of catalysts, and in particular to an ammonia oxidation catalyst with a hollow structure, a preparation method and application thereof, and a preparation method of acrylonitrile. Background Art

[0002] Acrylonitrile, as an important organic chemical raw material, is an important monomer for synthesizing synthetic materials such as acrylic fiber, ABS, SAN and carbon fiber. It can also be used as an intermediate to prepare chemicals such as adiponitrile and acrylamide. At present, fluidized bed ammoxidation process is widely used for production, in which catalyst is one of the core technologies of this process, and research and improvement on it have never stopped. Developing acrylonitrile synthesis catalysts that can be used for high catalyst loads, that is, increasing the number of tons of propylene that can be processed per ton of catalyst per hour, is an important trend in the development of acrylonitrile catalysts. However, with the increase of catalyst load, the feed amount of the reactor increases, the corresponding contact time between the catalyst and the raw material will also be shortened, and higher requirements are also placed on the catalytic performance of the catalyst itself. Due to the limited utilization rate of its own active components, the existing catalysts cannot fully meet the requirements under high load conditions. When used under high load conditions, it is very easy to produce problems such as low acrylonitrile yield and poor stability.

[0003] In order to ensure a good fluidization effect, the acrylonitrile catalyst using the fluidized bed process uses a spherical catalyst with a certain size distribution, and its average particle size is generally 50μm. Under high load conditions, due to the short contact time between the catalyst and the raw material, the inner area of ​​the catalyst particles is affected by the mass transfer diffusion rate, and it is often difficult to achieve effective contact with the raw material. The active components of the catalyst that can be effectively utilized are mainly concentrated in the outer area of ​​the catalyst particles. The effective utilization rate of the active components in the catalyst is lower under low load, which leads to a more obvious decrease in the activity of the catalyst under high load conditions.

[0004] CN111744493A discloses an acrylonitrile catalyst, which can improve the stability of the catalyst during long-term operation by controlling the relative size of the Mo / Bi element molar ratio on the surface of the catalyst particles and the Mo / Bi element molar ratio in the bulk phase, but the load used in the catalyst evaluation is relatively low.

[0005] CN107282063B, CN107282060B, CN107282065B and CN107282094B disclose that adding a certain amount of zirconium oxide, titanium oxide, diatomaceous earth and ZSM-5 molecular sieve as carrier modifiers during the catalyst preparation process can improve the selectivity and stability of the catalyst in the propylene ammoxidation reaction, but the catalyst evaluation is also carried out under relatively low load conditions.

[0006] The above methods show that although the performance of the catalyst can be improved to a certain extent by controlling the spatial distribution of the elements in the catalyst or adding appropriate carrier modifiers, it still cannot solve the problem of low acrylonitrile yield and poor stability of the current propylene ammoxidation catalyst under high load conditions.

[0007] How to obtain a catalyst that has good selectivity, high conversion rate, high single-pass yield and good stability under high load has always been an important research direction in the field of ammonia oxidation catalysts. Summary of the invention

[0008] The purpose of the present invention is to overcome the problem that the catalyst used for ammoxidation reaction in the prior art has a low yield of the target product under high load conditions, and to provide an ammoxidation catalyst and a preparation method and application thereof, as well as a method for preparing acrylonitrile. The catalyst has not only high propylene ammoxidation activity and acrylonitrile selectivity in the propylene ammoxidation reaction, but also a high acrylonitrile per-pass yield under high load conditions.

[0009] The first aspect of the present invention provides an ammonia oxidation catalyst, wherein the catalyst comprises an active component and a carrier, and the active component has the following general formula Fe d Bi e Mo f A a B b C c O x ;

[0010] Wherein, A is at least one of alkali metal elements, B is at least one of alkaline earth metal elements, transition metal elements, Group IIIA metal elements, antimony and tellurium, and C is a rare earth element;

[0011] a is in the range of 0-1, b is in the range of 0-12.5, c is in the range of 0-3, d is in the range of 0.1-4, e is in the range of 0.01-3, f is in the range of 9-16, and x is the total number of oxygen atoms required to satisfy the valence of each element in the above active component;

[0012] The catalyst includes microspheres with partially hollow spherical structures having a hollow structure, and the hollow ratio of the catalyst is 10-30%. The hollow ratio refers to the percentage of microspheres with a hollow structure in the catalyst microspheres to the total number of catalyst microspheres. The microspheres with a hollow structure refer to the catalyst particles whose maximum diameter of the hollow structure exceeds 25% of the maximum diameter of the catalyst particles.

[0013] A second aspect of the present invention provides a method for preparing an ammonia oxidation catalyst, the method comprising the following steps:

[0014] (a) providing a solution I containing a Mo precursor;

[0015] (b) providing a solution containing an Fe precursor, a Bi precursor, an optional precursor of an A element, an optional precursor of an B element, an optional precursor of an C element, and a polycarboxylic acid, and then aging to obtain a solution II;

[0016] (c) mixing the solution I obtained in step (a), fumed silica and optionally a solvent to obtain a slurry I;

[0017] (d) mixing the slurry I obtained in step (c) with a silicon dioxide precursor to obtain slurry II;

[0018] (e) mixing the slurry II obtained in step (d) and the solution II obtained in step (b) to obtain slurry III;

[0019] (f) boiling the slurry III obtained in step (e);

[0020] (g) drying and calcining the slurry obtained in step (f);

[0021] Among them, A is at least one of alkali metal elements, B is at least one of alkaline earth metal elements, transition metal elements, Group IIIA metal elements, antimony and tellurium, and C is a rare earth element.

[0022] The third aspect of the present invention provides a catalyst prepared by the method described in the second aspect.

[0023] The fourth aspect of the present invention provides an application of the catalyst described in the first aspect or the third aspect in an ammoxidation reaction, preferably in an olefin ammoxidation reaction, and more preferably in the preparation of acrylonitrile by ammoxidation of propylene.

[0024] The fifth aspect of the present invention provides a method for preparing acrylonitrile, which comprises: in the presence of the catalyst described in the first aspect or the third aspect, propylene, an ammonia source and an oxygen source are contacted and reacted.

[0025] The inventors of the present invention found in the research process that by optimizing the components of the catalyst, adding polycarboxylic acid as a pore-forming agent, and using fumed silica and a silica precursor in the preparation process, the catalyst obtained is a partially hollow sphere structure with a spherical hollow structure. The active components in the catalyst are more concentrated in the outer area of ​​the catalyst particles, which can improve the effective utilization rate of the active components of the catalyst. When the hollow rate is 10-30%, the catalytic performance of the catalyst under high load conditions can be effectively improved, and the catalyst has good stability and can maintain a high single-pass yield of acrylonitrile for a long time, thereby greatly improving the efficiency and economy of acrylonitrile production. Specifically, compared with the prior art, the present invention has the following advantages:

[0026] (1) The catalyst of the present invention includes microspheres with a partially hollow spherical structure and a hollow ratio of 10-30%. The active components in the catalyst are more concentrated in the outer region of the catalyst particles, which can improve the effective utilization rate of the active components of the catalyst.

[0027] (2) The catalyst has good stability and can maintain a high acrylonitrile single-pass yield for a long time, thereby greatly improving the efficiency and economy of acrylonitrile production.

[0028] (3) The propylene conversion rate can reach up to 99% or more, and the acrylonitrile single-pass yield can reach up to 84% or more. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is the 2D plane imaging of the catalyst along the Z-axis direction. DETAILED DESCRIPTION

[0030] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0031] The first aspect of the present invention provides an ammonia oxidation catalyst, wherein the catalyst comprises an active component and a carrier, and the active component has the following general formula Fe d Bi e Mo f A a B b C c O x ;

[0032] Wherein, A is at least one of alkali metal elements, B is at least one of alkaline earth metal elements, transition metal elements, Group IIIA metal elements, antimony and tellurium, and C is a rare earth element;

[0033] a is in the range of 0-1, b is in the range of 0-12.5, c is in the range of 0-3, d is in the range of 0.1-4, e is in the range of 0.01-3, f is in the range of 9-16, and x is the total number of oxygen atoms required to satisfy the valence of each element in the above active component;

[0034] The catalyst includes microspheres with partially hollow spherical structures having a hollow structure, and the hollow ratio of the catalyst is 10-30%. The hollow ratio refers to the percentage of microspheres with a hollow structure in the catalyst microspheres to the total number of catalyst microspheres. The microspheres with a hollow structure refer to the catalyst particles whose maximum diameter of the hollow structure exceeds 25% of the maximum diameter of the catalyst particles.

[0035] In the present invention, the hollow structure is spherical or quasi-spherical.

[0036] In the present invention, the hollow ratio refers to the percentage of the number of microspheres with hollow structures in the catalyst microspheres to the number of all catalyst microspheres. Specifically, hollow ratio (%) = number of catalyst particles with hollow structures / total number of catalyst particles counted × 100%. In the present invention, the hollow ratio is obtained by counting more than 200 (preferably not less than 250) complete catalyst particles.

[0037] In the present invention, the maximum diameter of the hollow structure of the catalyst particles exceeds 25% of the maximum diameter of the catalyst particles, and is defined as a microsphere with a hollow structure. The hollowness of the catalyst can be measured by micron-scale X-ray computed tomography, using the Xraida 400Versa 3D X-ray microscope of Zeiss. The catalyst sample is loaded into a sample tube with a diameter of 1 mm and a length of about 1 cm, and placed vertically in a micron CT scanning device. The single exposure time is set to 5 s, the scanning voltage is 60 kV, and the test temperature is 20°C. The scanning obtains 2D plane imaging (about 2048 images) along the Z-axis direction for statistical calculation of the hollowness of the catalyst. Typical 2D plane imaging is as follows: Figure 1 As shown, the high contrast area is the active components and carrier contained in the catalyst, and the low contrast area is the gap between the catalysts or the cavity in the catalyst particles.

[0038] According to a preferred embodiment of the present invention, the hollow ratio of the catalyst is 10-22.5%, for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21% or 22.5%.

[0039] The catalyst has a partially hollow sphere structure with a spherical hollow structure, which can concentrate the active components in the catalyst more in the outer area of ​​the catalyst particles, thereby improving the effective utilization rate of the active components of the catalyst, thereby greatly improving the efficiency and economy of acrylonitrile production.

[0040] It should be noted that, in the present invention, "Fe d Bi e Mo f A a B b C c Ox The general formula of " merely represents the individual elements and molar contents of the active components in the catalyst, and does not mean that the active components of the catalyst in the present invention exist as molecules of the general formula.

[0041] According to a preferred embodiment of the present invention, the alkali metal element is selected from at least one of Na, K, Rb and Cs.

[0042] According to a preferred embodiment of the present invention, the alkaline earth metal element is selected from at least one of Mg, Ca, Ba and Sr.

[0043] According to a preferred embodiment of the present invention, the transition metal element is selected from at least one of Mn, Co, Ni, Zn, Cr, Zr, Ti, Nb and W, preferably at least one of Ni, Co and Mn, more preferably at least two of Ni, Co and Mn, and most preferably Ni, Co and Mn. When two or three of Ni, Co and Mn are combined, the present invention has no particular limitation on their ratio. For example, the molar ratio of Ni, Co and Mn is 1:0.1-2.5:0.1-2.5.

[0044] According to a preferred embodiment of the present invention, the Group IIIA metal element is selected from at least one of Al, Ga and In.

[0045] According to a preferred embodiment of the present invention, the rare earth element is selected from at least one of Ce, Pr, Nd and Sm.

[0046] The use of the above-mentioned types of active components is more conducive to further improving the ammoxidation reaction performance of the catalyst.

[0047] In the present invention, components A, B, and C may or may not be contained, but are preferably contained. When contained, the content thereof can be selected within a wide range.

[0048] According to a preferred embodiment of the present invention, the value range of a is 0.05-0.5 (for example, 0.05, 0.1, 0.3, 0.4 or 0.5), the value range of b is 1-10 (for example, 1, 2, 4, 5, 7, 8, 9 or 10), and the value range of c is 0.01-2 (for example, 0.01, 0.03, 0.05, 0.06, 0.07, 0.1, 0.2, 0.5, 1, 1.5 or 2), d is in the range of 0.5-4 (e.g. 0.5, 1, 1.5, 2, 2.5, 3, 4), e is in the range of 0.01-1.5 (e.g. 0.01, 0.03, 0.05, 0.06, 0.07, 0.1, 0.2, 0.5, 1 or 1.5), and f is in the range of 10-15 (e.g. 10, 11, 12, 13, 14 or 15). The above-mentioned embodiment can better increase the catalytic performance of the catalyst when used for ammoxidation reaction.

[0049] Preferably, e / f is 0.005-0.5, preferably 0.01-0.25 (e.g. 0.01, 0.03, 0.05, 0.06, 0.07, 0.1, 0.2 or 0.25).

[0050] Preferably, d / f is 0.02-1.25, preferably 0.1-1 (e.g. 0.1, 0.3, 0.5, 0.6, 0.7, 0.8, 0.9 or 1).

[0051] Adopting a specific e / f or d / f ratio is more conducive to improving the catalytic performance of the catalyst when used in ammonia oxidation reaction.

[0052] According to a preferred embodiment of the present invention, the carrier is silicon dioxide.

[0053] According to the present invention, preferably, based on the total amount of the catalyst, the content of the carrier is 30-70wt%, and the content of the active component in terms of oxide is 30-70wt%; more preferably, based on the total amount of the catalyst, the content of the carrier is 40-60wt%, and the content of the active component in terms of oxide is 40-60wt%. The above-mentioned implementation can better improve the activity of the catalyst.

[0054] According to the present invention, preferably, the specific surface area of ​​the catalyst is 30-45 m 2 / g, preferably 35-45m 2 / g, more preferably 38-45m 2 / g, and the average pore size is 6-15nm, preferably 9-15nm.

[0055] A second aspect of the present invention provides a method for preparing an ammonia oxidation catalyst, the method comprising the following steps:

[0056] (a) providing a solution I containing a Mo precursor;

[0057] (b) providing a solution containing an Fe precursor, a Bi precursor, an optional precursor of an A element, an optional precursor of an B element, an optional precursor of an C element, and a polycarboxylic acid, and then aging to obtain a solution II;

[0058] (c) mixing the solution I obtained in step (a), fumed silica and optionally a solvent to obtain a slurry I;

[0059] (d) mixing the slurry I obtained in step (c) with a silicon dioxide precursor to obtain slurry II;

[0060] (e) mixing the slurry II obtained in step (d) and the solution II obtained in step (b) to obtain slurry III;

[0061] (f) boiling the slurry III obtained in step (e);

[0062] (g) drying and calcining the slurry obtained in step (f);

[0063] Among them, A is at least one of alkali metal elements, B is at least one of alkaline earth metal elements, transition metal elements, Group IIIA metal elements, antimony and tellurium, and C is a rare earth element.

[0064] According to a preferred embodiment of the present invention, the average particle size of the fumed silica particles is 5-30 nm, preferably 5-15 nm, and the specific surface area is 200-500 m 2 / g, preferably 300-450m 2 / g. The use of fumed silica having the above characteristics is more conducive to improving the ammonia oxidation reaction performance of the prepared catalyst. The average particle size of the fumed silica particles can be obtained by a nano-force potential analyzer test, and the specific surface area can be obtained by a BET method test.

[0065] The present invention has no particular limitation on the source of the fumed silica, which can be prepared by existing methods or purchased commercially.

[0066] Preferably, the silicon dioxide precursor is selected from at least one of silica sol, water glass, inorganic silica gel and silicate, more preferably silica sol.

[0067] According to the present invention, preferably, the solid content of the silica sol is 20-50 wt % calculated as silicon dioxide.

[0068] According to the present invention, preferably, calculated on the basis of silicon dioxide, the mass ratio of the fumed silicon dioxide to the silicon dioxide precursor is 1:1-1:20, preferably 1:2-20, for example, 1:2, 1:3, 1:2, 1:3, 1:4, 1:6, 1:8, 1:10, 1:10, 1:12, 1:14, 1:16, 1:18 or 1:20, preferably 1:2-5.

[0069] The catalyst of the present invention is a partially hollow sphere structure of a spherical hollow structure obtained by using fumed silica and a silica precursor. Wherein, when the mass ratio of the fumed silica to the silicon contained in the silica precursor in terms of silica is 1:1-1:20, preferably 1:2-20, it is conducive to forming a uniformly dispersed slurry, the average particle size of the fumed silica is smaller and has a higher specific surface area, which can increase the specific surface area of ​​the catalyst to a certain extent, and the thixotropy and reinforcement characteristics of the fumed silica are conducive to the stable formation of the hollow structure of the catalyst, thereby improving the catalytic performance and stability of the catalyst under high load conditions.

[0070] According to the method provided by the present invention, the selection range of the types of each metal active component can be the same as the selection range described in the first aspect above, and the present invention will not be repeated here.

[0071] According to a specific embodiment of the present invention, the precursors of Fe, Bi, Mo, A, B, and C can be soluble compounds of the corresponding elements. The specific type of the precursor of the present invention is not particularly limited, as long as it can be converted into the oxides corresponding to each component through subsequent calcination.

[0072] According to a preferred embodiment of the present invention, the molar ratio of Fe, Bi, Mo, A, B and C is 0.1-4: 0.01-3: 9-16: 0-1: 0-12.5: 0-3, preferably 0.5-3: 0.01-1.5: 10-15: 0.05-0.5: 1-10: 0.01-2.

[0073] According to the present invention, preferably, the molar ratio of Bi to Mo is 0.005-0.5, more preferably 0.01-0.25.

[0074] According to the present invention, preferably, the molar ratio of Fe to Mo is 0.02-1.25, preferably 0.1-1.

[0075] According to a preferred embodiment of the present invention, the Fe precursor, the Bi precursor, the optional precursor of the A element, the optional precursor of the B element, the optional precursor of the C element, the fumed silica, and the silica precursor are used in such an amount that the prepared catalyst has a content of Fe, Bi, Mo, A, B and C in terms of oxides of 30-70wt%, preferably 40-60wt%, based on the total amount of the catalyst, and a content of silica of 30-70wt%, preferably 40-60wt%.

[0076] The present invention has no particular limitation on the method for providing the solution. The type of solvent in the solution and the concentration of the solution can be selected in a wide range as long as a mixing environment can be provided. Preferably, the solvent is water.

[0077] The present invention has no particular limitation on the provision mode of solution II in step (b). The Fe precursor, Bi precursor, optional precursor of element A, optional precursor of element B, optional precursor of element C and polycarboxylic acid can be added to the solvent in sequence or simultaneously for mixed contact. It is also possible to first mix part of the precursor or polycarboxylic acid by solvent and then mix with the remaining part of the precursor. Preferably, the polycarboxylic acid is added after the Fe precursor, Bi precursor, optional precursor of element A, optional precursor of element B and optional precursor of element C are mixed. In order to make the mixing more uniform, the mixing can be carried out under heating and / or stirring conditions, for example, heating and stirring for 10-30min at a temperature of 40-120°C and a stirring speed of 100-500 rpm.

[0078] According to a preferred embodiment of the present invention, in step (b), the polycarboxylic acid is selected from at least one of citric acid, oxalic acid, tartaric acid, and ethylenediaminetetraacetic acid, preferably citric acid.

[0079] According to a preferred embodiment of the present invention, the molar ratio of the added amount of the polycarboxylic acid to the total molar number of Fe, Bi and Mo is 0.01-0.5:1, for example, 0.01, 0.03, 0.05, 0.06, 0.07, 0.1, 0.2 or 0.5, preferably 0.1-0.3:1.

[0080] According to a preferred embodiment of the present invention, the aging conditions include: a temperature of 40-80°C and a time of 0.1-0.5h. Preferably, the aging is carried out under stirring conditions, and preferably the stirring speed is 200-1000rpm.

[0081] In the present invention, the polycarboxylic acid is used as a pore-forming agent, which can generate gas during the calcination process, making the catalyst more likely to have a hollow structure, and the hollow ratio of the catalyst can be further adjusted by selecting the appropriate type and amount of the polycarboxylic acid.

[0082] The mixing in step (c) of the present invention may or may not contain a solvent, and the present invention has no particular limitation on this. Preferably, the solvent is water.

[0083] According to a preferred embodiment of the present invention, the mixing in step (d) is performed under stirring conditions. The present invention has no particular limitation on the stirring speed, which is based on the speed that is more conducive to uniform mixing.

[0084] According to a preferred embodiment of the present invention, in step (f), the conditions for cooking the slurry include: a temperature of 80-175°C, a time of 0.1-3h, and a stirring speed of 200-1000rpm. This preferred embodiment is more conducive to achieving uniform dispersion of fumed silica in the slurry and more easily forming a uniform hollow structure.

[0085] Preferably, in step (g), the drying method is spray drying. The present invention has a wide range of spray drying conditions. Preferably, the spray drying conditions include: a drying temperature of 250-400°C, a drying time of 0.5-3h, and an average diameter of the spray droplets of 40-200μm.

[0086] Preferably, in step (g), the calcination conditions include: in an oxygen-containing atmosphere, the calcination temperature is 200-750° C., and the calcination time is 1-8 h. Preferably, the calcination temperature is 400-650° C., and the calcination time is 1-6 h.

[0087] The third aspect of the present invention provides a catalyst prepared by the method described in the second aspect.

[0088] The fourth aspect of the present invention provides an application of the catalyst described in the first aspect or the third aspect in an ammoxidation reaction, preferably in an olefin ammoxidation reaction, and more preferably in the preparation of acrylonitrile by propylene ammoxidation. The catalyst of the present invention not only has good catalyst activity in the olefin ammoxidation reaction, but also can maintain a high single-pass yield of nitrile compounds after long-term operation.

[0089] The fifth aspect of the present invention provides a method for preparing acrylonitrile, which comprises: in the presence of the catalyst described in the first aspect or the third aspect, propylene, an ammonia source and an oxygen source are contacted and reacted.

[0090] Preferably, the contact reaction conditions include: the molar ratio of propylene: ammonia source (in terms of ammonia gas): oxygen source is 1:1-1.5:8-10.5, preferably 1:1-1.3:8.8-10; and / or, the reaction temperature is 400-470°C, preferably 410-450°C; and / or, the reaction pressure (gauge pressure) is 0.03-0.15 MPa, preferably 0.06-0.14 MPa; and / or, the reaction load WWH is 0.045-0.15 h -1 , preferably 0.06-0.12h -1 .

[0091] The present invention will be described in detail below by way of examples. In the following examples and comparative examples:

[0092] The specific surface area and pore size were measured using a TriStar II physical adsorption instrument. Before the sample was tested, it was necessary to heat and vacuum degas. The porosity of the sample was measured at 77K, and the specific surface area was calculated using the Brunauer-Emmett-Teller (BET) method. The pore size distribution and pore volume can be calculated from the isothermal adsorption branch using the Barrettner-Joyner-Halenda (BJH) model.

[0093] The definition and test method of hollow rate are as described above and will not be repeated here.

[0094] The activity of the catalyst was evaluated in a fluidized bed reactor with an inner diameter of 38 mm. The catalyst loading was 400 g, the reaction temperature was 430 ° C, the molar ratio of raw materials propylene: ammonia: air was 1: 1.25: 9.7, the reaction pressure (gauge pressure) was 0.085 MPa, and the reaction load (WWH) was 0.095 h -1 .

[0095] The conversion rate of propylene, selectivity of acrylonitrile and single-pass yield are used as indicators for evaluating catalyst performance, and their definitions are as follows:

[0096] Propylene conversion (%) = (moles of propylene consumed in the reaction / moles of propylene fed) × 100%

[0097] Acrylonitrile selectivity (%) = (moles of acrylonitrile produced / moles of propylene consumed in the reaction) × 100%

[0098] Acrylonitrile single-pass yield (%) = (moles of acrylonitrile produced / moles of propylene fed) × 100%

[0099] Example 1

[0100] 860.7 g (NH4)6Mo7O 24·4H2O was dissolved in 1000mL of water to obtain a mixed solution I. 173.9g of Bi(NO3)3·5H2O, 469.1g of Ni(NO3)2·6H2O, 104.3g of Co(NO3)2·6H2O, 434.4g of Fe(NO3)3·9H2O, 42.3g of Ca(NO3)2·4H2O, 6.0g of KOH, 93.4g of Ce(NO3)3·6H2O and 128.29g of 50% Mn(NO3)2 aqueous solution were dissolved in 200mL of water, and 81.9g of citric acid was added, the molar ratio of the amount of citric acid added to the total molar number of Mo, Bi and Fe elements was 0.2:1, and the mixture was aged at 60°C with a stirring speed of 400rpm for 0.25h to obtain a mixed solution II. Then 270g of quartz with an average particle size of 7nm and a specific surface area of ​​380m 2 / g of fumed silica and 800g of water are added to the mixed solution I to obtain slurry I.

[0101] Under stirring conditions, 1575 grams of silica sol with a mass concentration of 40wt% was added to slurry I to obtain slurry II, and then slurry II and mixed solution II were mixed to obtain slurry III and stirred and boiled at a temperature of 160°C at a stirring speed of 300rpm for 0.75h, and then spray-dried at a drying temperature of 325°C, a drying time of 1h, and an average diameter of the spray droplets of 120μm to obtain particles. Finally, the obtained particles were calcined at 580°C for 1h in an oxygen-containing atmosphere (oxygen volume fraction 21%) to obtain a catalyst.

[0102] Example 2

[0103] The catalyst preparation steps are the same as in Example 1, except that:

[0104] The raw material is 957.3 g (NH4)6Mo7O 24 ·4H2O, 193.4 g Bi(NO3)3·5H2O, 521.8 g Ni(NO3)2·6H2O, 94.2 g Ca(NO3)2·4H2O, 116.0 g Co(NO3)2·6H2O, 483.2 g Fe(NO3)3·9H2O, 6.7 g KOH, 103.9 g Ce(NO3)3·6H2O;

[0105] The molar ratio of the amount of citric acid added to the total molar number of Mo, Bi, and Fe elements was changed to 0.15:1;

[0106] Add 240 grams of average particle size of 7nm and specific surface area of ​​380m 2 / g of fumed silica and 700g of water are added to a mixed solution I to obtain a slurry I;

[0107] 1400 g of silica sol having a mass concentration of 40 wt % was added to slurry I to obtain slurry II.

[0108] Example 3

[0109] The catalyst preparation steps are the same as in Example 1, except that:

[0110] The average particle size of the added fumed silica is 15 nm and the specific surface area is 340 m 2 / g.

[0111] Example 4

[0112] The catalyst preparation steps are the same as in Example 1, except that:

[0113] The raw material is 762.2 g (NH4)6Mo7O 24 ·4H2O, 231.0 grams Bi(NO3)3·5H2O, 419.7 grams Ni(NO3)2·6H2O, 138.6 grams Co(NO3)2·6H2O, 259.1 grams Fe(NO3)3·9H2O, 122.1 grams Mg(NO3)2·6H2O, 9.23 grams CsNO3, and 103.4 grams Ce(NO3)3·6H2O.

[0114] Example 5

[0115] The catalyst preparation steps are the same as in Example 1, except that:

[0116] The raw material is 867.6 g (NH4)6Mo7O 24 ·4H2O, 131.4 grams Bi(NO3)3·5H2O, 530.8 grams Ni(NO3)2·6H2O, 128.0 grams Ca(NO3)2·4H2O, 589.9 grams Fe(NO3)3·9H2O, 92.7 grams Mg(NO3)2·6H2O, 13.3 grams Rb(NO3)2, and 93.8 grams Pr(NO3)3·6H2O.

[0117] Example 6

[0118] The steps for preparing the catalyst are the same as those in Example 1, except that citric acid is replaced by oxalic acid, and the molar ratio of the added amount of oxalic acid to the total molar number of Mo, Bi, and Fe elements is 0.2:1.

[0119] Example 7

[0120] The catalyst preparation steps are the same as in Example 1, except that:

[0121] The spray drying conditions were as follows: drying temperature of 350°C, drying time of 1 h, and average diameter of spray droplets of 100 μm.

[0122] Example 8

[0123] The catalyst preparation steps are the same as in Example 1, except that:

[0124] The calcination conditions are: calcination at 640° C. for 0.5 h in an oxygen-containing atmosphere (oxygen volume fraction 21%).

[0125] Example 9

[0126] The catalyst preparation steps are the same as in Example 1, except that:

[0127] Add 150g of average particle size of 7nm and specific surface area of ​​380m 2 / g of fumed silica and 400g of water are added to a mixed solution I to obtain a slurry I;

[0128] 1875 g of silica sol having a mass concentration of 40 wt % was added to slurry I to obtain slurry II.

[0129] Comparative Example 1

[0130] The catalyst preparation steps are the same as in Example 1, except that:

[0131] No fumed silica was added, and only silica sol with a weight concentration of 40 wt % was used as a carrier precursor.

[0132] Comparative Example 2

[0133] The catalyst preparation steps are the same as in Example 1, except that:

[0134] No silica sol with a weight concentration of 40 wt % was added, and only fumed silica was used as a carrier.

[0135] Comparative Example 3

[0136] The catalyst preparation steps are the same as in Example 1, except that:

[0137] The citric acid was replaced by acetic acid, and the molar ratio of the added amount of acetic acid to the total molar number of Mo, Bi and Fe elements was 0.2:1.

[0138] The catalyst related data and evaluation data of the above examples and comparative examples are shown in Table 1 and Table 2, respectively.

[0139] Table 1

[0140]

[0141]

[0142] Table 2

[0143]

[0144] It can be seen from Table 1 and Table 2 that the ammoxidation catalyst prepared by the method of the present invention has a hollow rate of 10%-30%, and has high propylene ammoxidation activity and acrylonitrile selectivity, and can also maintain a high acrylonitrile single-pass yield for a long time under high load conditions.

[0145] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. An ammonia oxidation catalyst, characterized in that The catalyst comprises an active component and a carrier, wherein the active component has the following general formula Fe d Bi e Mo f A a B b C c O x ; Wherein, A is at least one of alkali metal elements, B is at least one of alkaline earth metal elements, transition metal elements, Group IIIA metal elements, antimony and tellurium, and C is a rare earth element; a is in the range of 0-1, b is in the range of 0-12.5, c is in the range of 0-3, d is in the range of 0.1-4, e is in the range of 0.01-3, f is in the range of 9-16, and x is the total number of oxygen atoms required to satisfy the valence of each element in the above active component; The catalyst comprises microspheres with partially hollow spherical structures having hollow structures, and the hollow ratio of the catalyst is 10-30%, preferably 10-22.5%. The hollow ratio refers to the percentage of microspheres with hollow structures in the catalyst microspheres to the total number of catalyst microspheres. Microspheres with hollow structures refer to catalyst particles whose maximum diameter of the hollow structure exceeds 25% of the maximum diameter of the catalyst particles.

2. The catalyst according to claim 1, wherein The alkali metal element is selected from at least one of Na, K, Rb and Cs; And / or, the alkaline earth metal element is selected from at least one of Mg, Ca, Ba and Sr; and / or, the transition metal element is selected from at least one of Mn, Co, Ni, Zn, Cr, Zr, Ti, Nb and W, preferably at least one of Ni, Co and Mn; and / or, the Group IIIA metal element is at least one selected from Al, Ga and In; And / or, the rare earth element is selected from at least one of Ce, Pr, Nd and Sm; and / or, a is in the range of 0.05-0.5, b is in the range of 1-10, c is in the range of 0.01-2, d is in the range of 0.5-4, e is in the range of 0.01-1.5, and f is in the range of 10-15; Preferably, e / f is 0.005-0.5, preferably 0.01-0.25; Preferably, d / f is 0.02-1.25, preferably 0.1-1.

3. The catalyst according to claim 1, wherein The carrier is silicon dioxide; Preferably, based on the total amount of the catalyst, the content of the carrier is 30-70wt%, and the content of the active component in terms of oxide is 30-70wt%; More preferably, based on the total amount of the catalyst, the content of the carrier is 40-60wt%, and the content of the active component in terms of oxide is 40-60wt%; Preferably, the catalyst has a specific surface area of ​​30-45 m 2 / g, and the average pore size is 6-15nm.

4. A method for preparing an ammonia oxidation catalyst, characterized in that: The method comprises the following steps: (a) providing a solution I containing a Mo precursor; (b) providing a solution containing an Fe precursor, a Bi precursor, an optional precursor of an A element, an optional precursor of an B element, an optional precursor of an C element, and a polycarboxylic acid, and then aging to obtain a solution II; (c) mixing the solution I obtained in step (a), fumed silica and optionally a solvent to obtain a slurry I; (d) mixing the slurry I obtained in step (c) with a silicon dioxide precursor to obtain slurry II; (e) mixing the slurry II obtained in step (d) and the solution II obtained in step (b) to obtain slurry III; (f) boiling the slurry III obtained in step (e); (g) drying and calcining the slurry obtained in step (f); Among them, A is at least one of alkali metal elements, B is at least one of alkaline earth metal elements, transition metal elements, Group IIIA metal elements, antimony and tellurium, and C is a rare earth element.

5. The preparation method according to claim 4, wherein The average particle size of the fumed silica particles is 5-30 nm, preferably 5-15 nm, and the specific surface area is 200-500 m 2 / g, preferably 300-450m 2 / g; Preferably, the silicon dioxide precursor is selected from at least one of silica sol, water glass, inorganic silica gel and silicate, preferably silica sol; Preferably, the solid content of the silica sol is 20-50 wt % calculated as silicon dioxide; Preferably, based on silicon dioxide, the mass ratio of the fumed silicon dioxide to the silicon dioxide precursor is 1:1-20, preferably 1:2-20.

6. The preparation method according to claim 4 or 5, wherein: The alkali metal element is selected from at least one of Na, K, Rb and Cs; And / or, the alkaline earth metal element is selected from at least one of Mg, Ca, Ba and Sr; And / or, the transition metal element is at least one selected from Mn, Co, Ni, Zn, Cr, Zr, Ti, Nb and W, preferably at least one selected from Ni, Co and Mn; and / or, the Group IIIA metal element is at least one selected from Al, Ga and In; And / or, the rare earth element is selected from at least one of Ce, Pr, Nd and Sm; Preferably, the precursors of Fe, Bi, Mo, A, B, and C are soluble compounds of the corresponding elements.

7. The preparation method according to any one of claims 4 to 6, wherein: The molar ratio of Fe, Bi, Mo, A, B and C is 0.1-4: 0.01-3: 9-16: 0-1: 0-12.5: 0-3, preferably 0.5-3: 0.01-1.5: 10-15: 0.05-0.5: 1-10: 0.01-2; Preferably, the molar ratio of Bi to Mo is 0.005-0.5, preferably 0.01-0.25; Preferably, the molar ratio of Fe to Mo is 0.02-1.25, preferably 0.1-1; Preferably, the Fe precursor, the Bi precursor, the optional precursor of the A element, the optional precursor of the B element, the optional precursor of the C element, and the fumed silica and the silica precursor are used in such an amount that the content of Fe, Bi, Mo, A, B and C in terms of oxides in the prepared catalyst is 30-70wt%, preferably 40-60wt%, based on the total amount of the catalyst, and the content of silica is 30-70wt%, preferably 40-60wt%.

8. The preparation method according to any one of claims 4 to 7, wherein: In step (b), the polycarboxylic acid is selected from at least one of citric acid, oxalic acid, tartaric acid, and ethylenediaminetetraacetic acid, preferably citric acid; Preferably, the molar ratio of the amount of the polycarboxylic acid added to the total molar number of Fe, Bi and Mo is 0.01-0.5:1; Preferably, the polycarboxylic acid is added after the Fe precursor, the Bi precursor, the optional precursor of the A element, the optional precursor of the B element and the optional precursor of the C element are mixed; Preferably, the aging conditions include: temperature of 40-80° C., time of 0.1-0.5 h, and stirring speed of 200-1000 rpm.

9. The preparation method according to any one of claims 4 to 8, wherein: In step (f), the conditions for cooking the slurry include: a temperature of 80-175° C., a time of 0.1-3 h, and a stirring speed of 200-1000 rpm; Preferably, in step (g), the drying method is spray drying, and the conditions of spray drying include: drying temperature of 250-400°C, drying time of 0.5-3h, and average diameter of spray droplets of 40-200 μm; Preferably, in step (g), the calcination conditions include: in an oxygen-containing atmosphere, a calcination temperature of 200-750° C., and a calcination time of 1-8 h.

10. An ammonia oxidation catalyst prepared by the method according to any one of claims 4 to 9.

11. Use of the catalyst according to any one of claims 1 to 3 and 10 in an ammoxidation reaction, preferably in an olefin ammoxidation reaction, more preferably in the preparation of acrylonitrile by ammoxidation of propylene.

12. A method for preparing acrylonitrile, characterized in that: The method comprises: in the presence of the catalyst described in any one of claims 1 to 3 and 10, contacting and reacting propylene, an ammonia source and an oxygen source; Preferably, the contact reaction conditions include: the molar ratio of propylene: ammonia source as ammonia: oxygen source is 1:1-1.5:8-10.5, preferably 1:1-1.3:8.8-10; and / or, the reaction temperature is 400-470°C, preferably 410-450°C; and / or, the reaction pressure is 0.03-0.15 MPa, preferably 0.06-0.14 MPa; and / or, reaction load WWH is 0.045-0.15h -1 , preferably 0.06-0.12h -1 .

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