Flaky MFI molecular sieve, preparation method thereof and catalyst

Abstract

The invention provides a flaky MFI molecular sieve, a preparation method thereof and a catalyst. The preparation method comprises the following steps: mixing a silicon source, an additive, a template agent and water to form a reaction system, and crystallizing and roasting the reaction system to obtain the flaky MFI molecular sieve, wherein the additive comprises tetramethyl guanidine; the silicon source is metered by silicon dioxide, and the molar ratio of the silicon source to the additive is 1: z, 0lt; and z < = 0.5. The invention further provides the flaky MFI molecular sieve obtained by the preparation method and a catalyst containing the flaky MFI molecular sieve. Compared with a conventional MFI molecular sieve, the sheet-shaped MFI molecular sieve provided by the invention has a shorter b axis, and the diffusion efficiency of molecules in the molecular sieve can be improved, so that the catalytic activity of the molecular sieve is improved.

Description

Technical Field

[0001] The invention relates to the technical field of molecular sieve synthesis, and in particular to a sheet-like MFI molecular sieve and a preparation method and a catalyst thereof. Background Art

[0002] Zeolite molecular sieve is a crystalline inorganic aluminosilicate framework material, which is typically characterized by micropores with uniform pore size and neatly arranged holes in the crystal structure. MFI zeolite molecular sieve is one of the most important catalytic materials in the petroleum industry due to its developed pore structure, good thermal stability, suitable adjustable acid center density and excellent shape-selective catalysis. It is widely used in petrochemical, coal chemical and fine chemical industries. MFI zeolite is a mesoporous material with 10-membered ring channels. Due to its small pore size, the diffusion of larger reactants in its pores is hindered during the catalytic reaction, thereby reducing the catalytic reaction efficiency to a certain extent.

[0003] There are currently three main solutions to the problem of hindered diffusion of molecules in MFI zeolite. The first is to introduce larger mesopores (2-50nm) into the MFI zeolite crystals to form hierarchical pore materials, which can significantly reduce the diffusion path of reactants in the MFI zeolite crystals. The second is to reduce the crystal size of the MFI zeolite to the nanoscale, so that the material has a higher specific surface area and utilization efficiency of the catalytic active sites in the crystal. It is well known that the MFI zeolite structure has the structural characteristics of straight channels along the b axis and Z-shaped channels in the a and c axis directions, and the diffusion rate of molecules in straight channels is higher than that in Z-shaped channels. Therefore, the third solution is to regulate the morphology of the MFI zeolite according to the pore structure characteristics of the zeolite to obtain a catalyst with a flake morphology with a shorter b-axis length, which can exhibit excellent catalytic performance and anti-carbon deposition ability, and extend the service life of the catalyst.

[0004] In the prior art, the synthesis method of sheet-like MFI molecular sieve has the following problems:

[0005] 1. Requires complex organic templates, such as diquaternary ammonium salt C 22 -6-6Br 2 , bispiperidone alkylene cation, etc.;

[0006] 2. Fluorine-containing substances are usually used as mineralizers, but fluorine-containing substances are highly corrosive and toxic, causing serious environmental pollution and safety issues, thus greatly limiting the application prospects of this method;

[0007] 3. The synthesis time is long, usually several days or more than ten days.

[0008] In summary, synthesizing highly crystalline and high-yield flaky MFI zeolite molecular sieves using simple organic templating agents and under fluoride-free conditions is a challenging task. Summary of the Invention

[0009] To solve the above problems, the object of the present invention is to provide a flaky MFI molecular sieve, its preparation method, and a catalyst. Compared with conventional MFI molecular sieves, the flaky MFI molecular sieve provided by the present invention has a shorter b-axis, which can improve the diffusion efficiency of molecules in the molecular sieve, thereby enhancing the catalytic activity of the molecular sieve.

[0010] To achieve the above object, the present invention provides a preparation method of a flaky MFI molecular sieve, which includes: mixing a silicon source, an additive, a templating agent, and water to form a reaction system, and subjecting the reaction system to crystallization and calcination to obtain the flaky MFI molecular sieve; wherein, the additive includes tetramethylguanidine; the silicon source is calculated as silicon dioxide, and the molar ratio of the silicon source to the additive is 1:z, where 0 < z ≤ 0.5.

[0011] In the above preparation method, by using additives such as tetramethylguanidine, flaky MFI molecular sieves with a shorter b-axis can be obtained. The MFI zeolite structure has straight channels along the b-axis direction and zigzag channels along the a-axis and c-axis directions. Compared with shortening the a-axis and c-axis, shortening the b-axis is more conducive to shortening the diffusion path of molecules in the MFI molecular sieve and improving the diffusion efficiency of molecules. Therefore, the above preparation method provided by the present invention can improve the specific surface area and catalytic activity of the molecular sieve product, and improve the carbon deposition situation in the molecular sieve, thereby enhancing the catalytic activity of the molecular sieve and extending its service life.

[0012] In the above preparation method, the silicon source is calculated as silicon dioxide, and the molar ratio of the silicon source to the additive is 1:z, where 0 < z ≤ 0.5. Specifically, z can be specific values such as 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, etc., and ranges with any two of the above specific values as endpoints. In some specific embodiments, z can further be 0 < z ≤ 0.4.

[0013] In the above preparation method, the silicon source can include one or more combinations of tetraethyl orthosilicate, silica sol, sodium silicate, and fumed silica. In some specific embodiments, the silicon source can include tetraethyl orthosilicate and / or silica sol.

[0014] In the above preparation method, the silicon source is calculated as silicon dioxide, and the molar ratio of the silicon source to the template agent is 1:y, where y is 0.01 - 0.36. In some specific embodiments, y can be specific values such as 0.01, 0.02, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.36, etc., and ranges with any two of the above specific values as endpoints.

[0015] In the above preparation method, the template agent can include one or a combination of two or more of tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and ethylenediamine.

[0016] In the above preparation method, a pure silica MFI zeolite can be obtained using the silicon source; the reaction system can further include a metal source to obtain a silica-alumina zeolite and / or a silica-gallium zeolite, etc. Specifically, the metal source includes an aluminum-containing compound and / or a gallium-containing compound.

[0017] In the above preparation method, the aluminum-containing compound can include aluminum hydroxide and / or an aluminum salt. The aluminum salt can include one or a combination of two or more of aluminum sulfate, aluminum nitrate, aluminum sulfate, sodium metaaluminate, and aluminum isopropoxide.

[0018] In the above preparation method, the gallium-containing compound can include a gallium salt. The gallium salt can include gallium nitrate, etc.

[0019] In the above preparation method, the silicon source is calculated as silicon dioxide, the metal source is calculated as metal oxide, and the molar ratio of the silicon source to the metal source is 1:x, where 0 < x ≤ 0.025. In some specific embodiments, x can be specific values such as 0.01, 0.015, 0.02, 0.025, etc., and ranges with any two of the above specific values as endpoints.

[0020] In the above preparation method, the metal source is calculated as metal oxide, and the molar ratio of the metal source to the template agent can be 0.01 - 0.07:1, specifically 0.01:1, 0.02:1, 0.025:1, 0.027:1, 0.028:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, etc., and ranges with any two of the above specific values as endpoints.

[0021] In the above preparation method, by controlling the amount of water in the reaction system, the concentration of the reaction system and the crystallization time of the zeolite can be controlled, thereby adjusting the morphology and the length of the b-axis of the zeolite. The amount of water added to the reaction system can be adjusted according to the types of framework elements of the zeolite, that is, the types of elements of the zeolite precursor.

[0022] Specifically, when the reaction system only includes a silicon source and does not include a metal source, the silicon source is calculated as silica, and the molar ratio of the silicon source to water is 1:m, where m is 5 - 30. In some specific embodiments, m can be specific values such as 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, etc., and ranges with any two of the above specific values as endpoints. m can be further controlled to be 8 - 30, and even further controlled to be 8 - 15.

[0023] When the reaction system includes a silicon source and a metal source, the silicon source is calculated as silica, and the molar ratio of the silicon source to water is 1:m, where 10 ≤ m < 30. In some specific embodiments, m can be specific values such as 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, etc., and ranges with any two of the above specific values as endpoints. m can be further controlled to be 10 - 15.

[0024] In the above preparation method, the reaction system is formed by mixing a silicon source or a combination of a silicon source and a metal source, an additive, a template agent, and water;

[0025] wherein, the silicon source is calculated as silica, the metal source is calculated as metal oxide, and the chemical composition of the reaction system can satisfy the following molar ratios: SiO2: metal oxide: template agent: additive: water = 1:x:y:m,

[0026] 0 ≤ x ≤ 0.025;

[0027] y = 0.01 - 0.36;

[0028] 0 < z ≤ 0.5;

[0029] When x = 0, m = 5 - 30; when 0 < x ≤ 0.025, 10 ≤ m < 30.

[0030] In the above preparation method, the crystallization temperature is 120 - 180 °C, specifically, it can be specific values such as 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C, 180 °C, etc., and ranges with any two of the above specific values as endpoints.

[0031] In the above preparation method, the crystallization time is 3 hours to 7 days, specifically, it can be specific values such as 3h, 6h, 12h, 20h, 24h, 1d, 3d, 5d, 7d, etc., and ranges with any two of the above specific values as endpoints. In some specific embodiments, the crystallization time can be 3 hours to 5 days.

[0032] In the above preparation method, the calcination temperature is 450-600° C. In some specific embodiments, the calcination temperature can be 450° C., 500° C., 550° C., 600° C., and other specific values, as well as a range with any two of the above specific values ​​as endpoints. The calcination time can be adjusted accordingly according to the calcination temperature.

[0033] According to a specific embodiment of the present invention, when the reaction system does not include a metal source, the additive can be added before the silicon source is hydrolyzed. For example, the preparation method can include mixing the additive with the template and the silicon source, and then adding water and crystallizing. Alternatively, the additive can also be added after the silicon source is hydrolyzed. In this case, the preparation method can include mixing the additive with the silicon source, hydrolyzing, adding water and the additive in sequence, and crystallizing.

[0034] According to a specific embodiment of the present invention, when the reaction system includes a metal source, the preparation method may include mixing the metal source with a template, and then sequentially adding an additive, a silicon source, water, and crystallizing.

[0035] The present invention also provides a sheet-like MFI molecular sieve, which is obtained by the above preparation method.

[0036] According to a specific embodiment of the present invention, the b-axis length of the above-mentioned flaky MFI molecular sieve is 50-600nm. In some specific embodiments, the length of the b-axis can be 50nm, 70nm, 100nm, 150nm, 180nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm and other specific values ​​and the scope with any two of the above specific values ​​as endpoints.

[0037] According to a specific embodiment of the present invention, the a-axis length of the above-mentioned flaky MFI molecular sieve is 0.14-2.9 μm, for example 0.5-2.9 μm. In some specific embodiments, the a-axis length of the flaky MFI molecular sieve can be 0.14 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, 2.8 μm, 2.9 μm and other specific values ​​and the range with any two of the above specific values ​​as endpoints.

[0038] According to a specific embodiment of the present invention, the c-axis length of the above-mentioned flaky MFI molecular sieve is 1.3-35 μm, for example, it can be 1.3 μm, 1.5 μm, 2.0 μm, 2.5 μm, 2.8 μm, 3.0 μm, 3.3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 7 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm and other specific values ​​and the range with any two of the above specific values ​​as endpoints. The c-axis length of the flaky MFI molecular sieve can further be 1.5-35 μm.

[0039] According to a specific embodiment of the present invention, the relationship between the dimensions of the a-axis, the b-axis and the c-axis in the above-mentioned sheet-like MFI molecular sieve can be: b-axis < a-axis < c-axis.

[0040] According to a specific embodiment of the present invention, the MFI molecular sieve includes one or a combination of two or more of pure silicon Silicalite-1 molecular sieve, aluminum-containing ZSM-5 molecular sieve, and gallium-containing MFI molecular sieve. For example, when the reaction system only includes a silicon source and does not include a metal source, the prepared MFI molecular sieve can be a pure silicon Silicalite-1 molecular sieve; when the reaction system includes a silicon source and also includes a metal source such as an aluminum source and a gallium source, the MFI molecular sieve can also be an aluminum-containing ZSM-5 molecular sieve, a gallium-containing MFI molecular sieve, and the like.

[0041] The present invention also provides a catalyst, which includes the above-mentioned flaky MFI molecular sieve or is made of the above-mentioned flaky MFI molecular sieve. Compared with conventional MFI molecular sieves, the flaky MFI molecular sieve provided by the present invention has a shorter b-axis, which can significantly shorten the diffusion path of molecules in the molecular sieve, improve diffusion efficiency, and have higher catalytic activity.

[0042] The beneficial effects of the present invention include:

[0043] 1. The preparation method provided by the present invention can effectively adjust the morphology of the molecular sieve and the size of the molecular sieve in different crystal axis directions by adding an additive including tetramethylguanidine in the molecular sieve synthesis process without using a complex organic template or fluoride, thereby obtaining a sheet-like MFI molecular sieve. Compared with conventional MFI molecular sieves, the sheet-like MFI molecular sieve of the present invention has a shorter b-axis, uniform sheet thickness, and regular morphology, which can significantly shorten the diffusion path of molecules in the molecular sieve, improve the diffusion efficiency, and thus improve the catalytic activity of the molecular sieve.

[0044] 2. The method provided by the present invention is time-saving and has a high yield, and is suitable for preparing various molecular sieves such as pure silicon molecular sieves, silicon aluminum molecular sieves, silicon gallium molecular sieves, etc.; it is low in cost and has high parallelism, operational repeatability, universality, simplicity, and practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 These are the XRD and SEM images of the molecular sieve prepared in Example 1.

[0046] Figure 2 These are the XRD and SEM images of the molecular sieve prepared in Example 2.

[0047] Figure 3 These are the XRD and SEM images of the molecular sieve prepared in Example 3.

[0048] Figure 4 These are the XRD and SEM images of the molecular sieve prepared in Example 4.

[0049] Figure 5 These are the XRD and SEM images of the molecular sieve prepared in Example 5.

[0050] Figure 6 These are the XRD and SEM images of the molecular sieve prepared in Example 6.

[0051] Figure 7 These are the XRD and SEM images of the molecular sieve prepared in Example 7.

[0052] Figure 8 These are the XRD and SEM images of the molecular sieve prepared in Example 8.

[0053] Fig. 9 These are the XRD and SEM images of the molecular sieve prepared in Example 9.

[0054] Fig.10 These are the XRD and SEM images of the molecular sieve prepared in Example 10.

[0055] Fig.11 The XRD and SEM images of the molecular sieve prepared in Comparative Example 1 are shown.

[0056] Fig.12 The XRD and SEM images of the molecular sieve prepared in Comparative Example 2 are shown.

[0057] Fig.13 The XRD and SEM images of the molecular sieve prepared in Comparative Example 3 are shown.

[0058] Fig.14 The XRD and SEM images of the molecular sieve prepared in Comparative Example 4 are shown. DETAILED DESCRIPTION

[0059] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be construed as limiting the applicable scope of the present invention.

[0060] Example 1

[0061] This embodiment provides a flake MFI zeolite molecular sieve, and the preparation method thereof specifically comprises the following steps:

[0062] (1) adding tetramethylguanidine to a tetrapropylammonium hydroxide solution having a concentration of 1 mol / L and mixing to form a uniform solution, wherein the molar ratio of tetramethylguanidine to tetrapropylammonium hydroxide is 1:1.2;

[0063] (2) adding tetraethyl orthosilicate to the solution of step (1), wherein the molar ratio of tetraethyl orthosilicate (calculated as silicon dioxide) to tetrapropylammonium hydroxide is 1:0.36;

[0064] (3) adding a certain amount of water to the solution obtained in step (2) so that the molar ratio of water to tetraethyl orthosilicate (calculated as silicon dioxide) in the solution is finally controlled to be 30, thereby obtaining a reaction system;

[0065] (4) moving the reaction system obtained in step (3) to a reaction kettle and crystallizing at 170° C. for 24 hours;

[0066] (5) The crystallized product is taken out from the reactor, separated by centrifugation or filtration, fully washed with deionized water until neutral, and dried to obtain a flaky pure silicon Silicalite-1 zeolite molecular sieve.

[0067] The XRD data of the molecular sieve prepared in this example are as follows Figure 1 As shown in a in FIG. 1 . From the XRD data, it can be seen that the molecular sieve has an MFI zeolite structure and has a high degree of crystallinity. The morphology and structure of the molecular sieve of this embodiment are shown in FIG. Figure 1 As shown in b, it can be seen that the molecular sieve is flaky, and the b-axis (thickness) size of the molecule is concentrated in the range of 200-300nm; the a-axis size of the molecular sieve is 2.5-2.9μm, and the c-axis size is 30-35μm.

[0068] Example 2

[0069] This embodiment provides a flake MFI zeolite molecular sieve, and the preparation method thereof specifically comprises the following steps:

[0070] (1) adding tetramethylguanidine to a tetrapropylammonium hydroxide solution having a concentration of 1 mol / L and mixing to form a uniform solution, wherein the molar ratio of tetramethylguanidine to tetrapropylammonium hydroxide is 1:1.2;

[0071] (2) adding tetraethyl orthosilicate to the solution of step (1) to prepare a uniform sol or gel; the molar ratio of tetraethyl orthosilicate (calculated as silicon dioxide) to the template is 1:0.36;

[0072] (3) volatilizing a certain amount of water from the solution obtained in step (2) at room temperature until the molar ratio of water to tetraethyl orthosilicate (calculated as silicon dioxide) in the solution is finally controlled to be 15, thereby obtaining a reaction system;

[0073] (4) moving the reaction system obtained in step (3) to a reaction kettle and crystallizing at 170° C. for 12 hours;

[0074] (5) The sample reactor obtained in step (4) is taken out, centrifuged or filtered, washed with deionized water until neutral, and dried to obtain a flaky MFI zeolite molecular sieve.

[0075] The XRD data of the molecular sieve prepared in this example are as follows Figure 2 As shown in a in FIG. 1 , it can be seen from the XRD data that the molecular sieve has an MFI zeolite structure and has a high degree of crystallinity. The morphology and structure of the molecular sieve of this embodiment are shown in FIG. Figure 2 As shown in b, it can be seen that the molecular sieve is in the form of a sheet, and the b-axis (thickness) size of the molecular sieve is concentrated in the range of 180-250 nm; the a-axis size of the molecular sieve is 500-600 nm, and the c-axis size is 5-6 μm.

[0076] Example 3

[0077] This embodiment provides a flake MFI zeolite molecular sieve, and the preparation method thereof specifically comprises the following steps:

[0078] (1) adding tetraethyl orthosilicate to a tetrapropylammonium hydroxide solution having a concentration of 1 mol / L and mixing to form a uniform solution; the molar ratio of tetraethyl orthosilicate (based on silicon dioxide) to the template is 1:0.2;

[0079] (2) stirring the solution obtained in step (1) at room temperature, and after the hydrolysis of tetraethyl orthosilicate is completed, adding a certain amount of water until the molar ratio of water to tetraethyl orthosilicate (calculated as silicon dioxide) in the solution is finally controlled to be 15, thereby obtaining a reaction system;

[0080] (3) adding a certain amount of tetramethylguanidine to the gel of step (2); the molar ratio of tetraethyl orthosilicate (calculated as silicon dioxide) to the additive is 1:0.2;

[0081] (4) moving the reaction system obtained in step (3) to a reaction kettle and crystallizing at 170° C. for 12 hours;

[0082] (5) The sample reactor obtained in step (4) is taken out, centrifuged or filtered, washed with deionized water until neutral, and dried to obtain a flaky MFI zeolite molecular sieve.

[0083] The XRD data of the molecular sieve prepared in this example are as follows Figure 3As shown in a in FIG. 1 , it can be seen from the XRD data that the molecular sieve has an MFI zeolite structure and has a high degree of crystallinity. The morphology and structure of the molecular sieve of this embodiment are shown in FIG. Figure 3 As shown in b, it can be seen that the molecular sieve is in the form of a sheet, and the b-axis (thickness) size of the molecular sieve is concentrated in the range of 150-200 nm; the a-axis size of the molecular sieve is 500-600 nm, and the c-axis size is 2.5-3 μm.

[0084] Example 4

[0085] This embodiment provides a flake MFI zeolite molecular sieve, and the preparation method thereof specifically comprises the following steps:

[0086] (1) adding silica sol having a mass concentration of 40% to a tetrapropylammonium hydroxide solution having a concentration of 1 mol / L to form a uniform solution; the molar ratio of silica sol (calculated as silicon dioxide) to the template is 1:0.36;

[0087] (2) stirring the solution obtained in step (1) at room temperature, adding a certain amount of water until the molar ratio of water to silica sol (calculated as silicon dioxide) in the solution is finally controlled to be 15, thereby obtaining a reaction system;

[0088] (3) adding a certain amount of tetramethylguanidine to the gel in step (2); the molar ratio of silica sol (calculated as silicon dioxide) to the additive is 1:0.3;

[0089] (4) moving the reaction system obtained in step (3) to a reaction kettle and crystallizing at 170° C. for 24 hours;

[0090] (5) The sample reactor obtained in step (4) is taken out, centrifuged or filtered, washed with deionized water until neutral, and dried to obtain a flaky MFI zeolite molecular sieve.

[0091] The XRD data of the molecular sieve prepared in this example are as follows Figure 4 As shown in a in FIG. 1 , it can be seen from the XRD data that the molecular sieve has an MFI zeolite structure and has a high degree of crystallinity. The morphology and structure of the molecular sieve of this embodiment are shown in FIG. Figure 4 As shown in b, it can be seen that the molecular sieve is in the form of a sheet, and the b-axis (thickness) size of the molecular sieve is concentrated in the range of 300-350 nm; the a-axis size of the molecular sieve is 1-1.2 μm, and the c-axis size is 3-3.5 μm.

[0092] Example 5

[0093] This embodiment provides a flake MFI zeolite molecular sieve, and the preparation method thereof specifically comprises the following steps:

[0094] (1) adding tetramethylguanidine to a tetrapropylammonium hydroxide solution having a concentration of 1 mol / L to prepare a uniform solution; the molar ratio of tetramethylguanidine to tetrapropylammonium hydroxide is 1:1.2;

[0095] (2) adding tetraethyl orthosilicate to the solution of step (1), wherein the molar ratio of tetraethyl orthosilicate (calculated as silicon dioxide) to tetrapropylammonium hydroxide is 1:0.36;

[0096] (3) volatilizing a certain amount of water from the solution obtained in step (2) at room temperature so that the molar ratio of water to tetraethyl orthosilicate (calculated as silicon dioxide) is finally controlled to be 8, thereby obtaining a reaction system;

[0097] (4) transferring the reaction system obtained in step (3) to a reaction kettle and crystallizing at 170° C. for 3 hours;

[0098] (5) The crystallized product of step (4) is taken out from the reactor, separated by centrifugation or filtration, washed thoroughly with deionized water until neutral, and dried to obtain a flaky MFI zeolite molecular sieve.

[0099] The XRD data of the molecular sieve prepared in this example are as follows Figure 5 As shown in a in FIG. 1 . From the XRD data, it can be seen that the molecular sieve has an MFI zeolite structure and has a high degree of crystallinity. The morphology and structure of the molecular sieve of this embodiment are shown in FIG. Figure 5 As shown in b, it can be seen that the molecular sieve is in the form of a sheet, and the b-axis size of the molecular sieve is concentrated in the range of 50-70 nm; the a-axis size of the molecular sieve is 0.14-0.2 μm, and the c-axis size is 1.5-2.0 μm.

[0100] Example 6

[0101] This embodiment provides a flake MFI zeolite molecular sieve, and the preparation method thereof specifically comprises the following steps:

[0102] (1) adding aluminum sulfate into a tetrapropylammonium hydroxide solution as a template to dissolve the aluminum sulfate and obtain a uniform solution;

[0103] (2) adding tetramethylguanidine as an additive to the solution of step (1) to prepare a uniform solution;

[0104] (3) adding tetraethyl orthosilicate as a silicon source to the solution of step (2) to prepare a uniform intermediate system (which may be a sol or a gel);

[0105] (4) The stoichiometric ratio of each component in the intermediate system is as follows: tetraethyl orthosilicate is calculated as silicon dioxide, and aluminum sulfate is calculated as aluminum oxide: SiO 2 :Al 2 O 3: Template: Additive = 1: 0.01: 0.36: 0.3;

[0106] (5) volatilizing a certain amount of water from the solution obtained in step (3) at 45° C. so that the molar ratio of water to tetraethyl orthosilicate is finally controlled to be 15, thereby obtaining a reaction system;

[0107] (6) transferring the reaction system obtained in step (5) to a reaction kettle and crystallizing at 170° C. for 24 hours;

[0108] (7) The crystallized product of step (6) is taken out from the reactor, separated by centrifugation or filtration, washed thoroughly with deionized water until neutral, and dried to obtain a flaky ZSM-5 zeolite molecular sieve.

[0109] The XRD data of the molecular sieve prepared in this example are as follows Figure 6 As shown in a in FIG. 1 . From the XRD data, it can be seen that the molecular sieve has an MFI zeolite structure and has a high degree of crystallinity. The morphology and structure of the molecular sieve of this embodiment are shown in FIG. Figure 6 As shown in b, it can be seen that the molecular sieve is flaky, and the b-axis size is concentrated in the range of 500-600nm; the a-axis size of the molecular sieve is 1.5-1.8μm, and the c-axis size is 6-7μm.

[0110] Example 7

[0111] This embodiment provides a flake MFI zeolite molecular sieve, and the preparation method thereof specifically comprises the following steps:

[0112] (1) adding aluminum sulfate into a tetrapropylammonium hydroxide solution as a template to dissolve the aluminum sulfate and obtain a uniform solution;

[0113] (2) adding tetramethylguanidine as an additive to the solution of step (1) to prepare a uniform solution;

[0114] (3) adding tetraethyl orthosilicate as a silicon source to the solution of step (2) to prepare a uniform intermediate system (specifically, a sol or a gel);

[0115] (4) Tetraethyl orthosilicate is calculated as silicon dioxide, and aluminum sulfate is calculated as aluminum oxide. The synthetic ratio of the intermediate system obtained in step (3) is in the following molar ratio: SiO 2 :Al 2 O 3 : Template: Additive = 1: 0.01: 0.36: 0.3;

[0116] (5) volatilizing a certain amount of water from the solution obtained in step (3) at 45° C. so that the molar ratio of water to tetraethyl orthosilicate (calculated as silicon dioxide) is finally controlled to be 10, thereby obtaining a reaction system;

[0117] (6) transferring the reaction system obtained in step (5) to a reaction kettle and crystallizing at 170° C. for 20 hours;

[0118] (7) The crystallized product of step (6) is taken out from the reactor, separated by centrifugation or filtration, washed thoroughly with deionized water until neutral, and dried to obtain a flaky ZSM-5 zeolite molecular sieve.

[0119] The XRD data of the molecular sieve prepared in this example are as follows Figure 7 As shown in a in FIG. 1 . From the XRD data, it can be seen that the molecular sieve has an MFI zeolite structure and has a high degree of crystallinity. The morphology and structure of the molecular sieve of this embodiment are shown in FIG. Figure 7 As shown in b, it can be seen that the molecular sieve is in the form of a sheet, and its b-axis size is concentrated in the range of 150-250nm; the a-axis size of the molecular sieve is 0.6-0.8μm, and the c-axis size is 1.3-1.5μm.

[0120] Example 8

[0121] This embodiment provides a flake MFI zeolite molecular sieve, and the preparation method thereof specifically comprises the following steps:

[0122] (1) adding aluminum nitrate into a tetrapropylammonium hydroxide solution as a template to dissolve the aluminum nitrate and obtain a uniform solution;

[0123] (2) adding tetramethylguanidine as an additive to the solution of step (1) to prepare a uniform solution;

[0124] (3) adding tetraethyl orthosilicate as a silicon source to the solution of step (2) to prepare a uniform intermediate system (specifically, a sol or a gel);

[0125] (4) Tetraethyl orthosilicate is calculated as silicon dioxide, and aluminum sulfate is calculated as aluminum oxide. The synthetic ratio of the intermediate system obtained in step (3) is in the following molar ratio: SiO 2 :Al 2 O 3 : Template: Additive = 1: 0.01: 0.36: 0.3;

[0126] (5) volatilizing a certain amount of water from the solution obtained in step (3) at 45° C. so that the molar ratio of water to tetraethyl orthosilicate (calculated as silicon dioxide) is finally controlled to be 10, thereby obtaining a reaction system;

[0127] (6) transferring the reaction system obtained in step (5) to a reaction kettle and crystallizing at 170° C. for 24 hours;

[0128] (7) The crystallized product of step (6) is taken out from the reactor, separated by centrifugation or filtration, washed thoroughly with deionized water until neutral, and dried to obtain a flaky ZSM-5 zeolite molecular sieve.

[0129] The XRD data of the molecular sieve prepared in this example are as follows Figure 8 As shown in a in FIG. 1 , it can be seen from the XRD data that the molecular sieve has an MFI zeolite structure and has a high degree of crystallinity. The morphology and structure of the molecular sieve of this embodiment are shown in FIG. Figure 8 As shown in b, it can be seen that the molecular sieve is in the form of a sheet, and its b-axis size is concentrated in the range of 200-250nm; the a-axis size of the molecular sieve is 0.8-0.9μm, and the c-axis size is 2.8-3.3μm.

[0130] Example 9

[0131] This embodiment provides a flake MFI zeolite molecular sieve, and the preparation method thereof specifically comprises the following steps:

[0132] (1) adding aluminum sulfate into a tetrapropylammonium hydroxide solution as a template to dissolve the aluminum sulfate and obtain a uniform solution;

[0133] (2) adding tetramethylguanidine as an additive to the solution of step (1) to prepare a uniform solution;

[0134] (3) adding silica sol as a silicon source to the solution of step (2) to prepare a uniform intermediate system (specifically, a sol or a gel);

[0135] (4) The silica sol is calculated as silicon dioxide, and the aluminum sulfate is calculated as aluminum oxide. The synthesis ratio of the intermediate system obtained in step (3) is in the following molar ratio: SiO 2 :Al 2 O 3 : Template: Additive = 1: 0.025: 0.36: 0.3;

[0136] (5) volatilizing a certain amount of water from the solution obtained in step (3) at 45° C. so that the molar ratio of water to silica sol (calculated as silicon dioxide) is finally controlled to be 10, thereby obtaining a reaction system;

[0137] (6) transferring the reaction system obtained in step (5) to a reaction kettle and crystallizing at 170° C. for 5 days;

[0138] (7) The crystallized product of step (6) is taken out from the reactor, separated by centrifugation or filtration, washed thoroughly with deionized water until neutral, and dried to obtain a flaky ZSM-5 zeolite molecular sieve.

[0139] The XRD data of the molecular sieve prepared in this example are as follows Fig. 9 As shown in a in FIG. 1 , it can be seen from the XRD data that the molecular sieve has an MFI zeolite structure and has a high degree of crystallinity. The morphology and structure of the molecular sieve of this embodiment are shown in FIG. Fig. 9As shown in b, it can be seen that the molecular sieve is in the form of a sheet, and its b-axis size is concentrated in the range of 180-230 nm; the a-axis size of the molecular sieve is 0.55-0.65 μm, and the c-axis size is 1.5-2 μm.

[0140] Example 10

[0141] This embodiment provides a flaky Ga-MFI zeolite molecular sieve, and the preparation method thereof specifically comprises the following steps:

[0142] (1) adding gallium nitrate into a tetrapropylammonium hydroxide solution as a template to dissolve and obtain a uniform solution;

[0143] (2) adding tetramethylguanidine as an additive to the solution of step (1) to prepare a uniform solution;

[0144] (3) adding tetraethyl orthosilicate as a silicon source to the solution of step (2) to prepare a uniform intermediate system (which may be a sol or a gel);

[0145] Tetraethyl orthosilicate is calculated as silicon dioxide, and gallium nitrate is calculated as gallium trioxide. The synthesis ratio of the intermediate system is in the following molar ratio:

[0146] SiO 2 :Ga 2 O 3 : Template: Additive = 1: 0.01: 0.36: 0.3;

[0147] (4) volatilizing a certain amount of water from the solution obtained in step (3) at 45° C. so that the molar ratio of water to tetraethyl orthosilicate is finally controlled to be 15, thereby obtaining a reaction system;

[0148] (5) transferring the reaction system obtained in step (4) to a reaction kettle and crystallizing at 170° C. for 20 hours;

[0149] (6) The crystallized product obtained in step (5) is taken out from the reactor, separated by centrifugation or filtration, washed thoroughly with deionized water until neutral, and dried to obtain a flaky Ga-MFI zeolite molecular sieve.

[0150] The XRD data of the molecular sieve prepared in this example are as follows Fig.10 As shown in a in FIG. 1 . From the XRD data, it can be seen that the molecular sieve has an MFI zeolite structure and has a high degree of crystallinity. The morphology and structure of the molecular sieve of this embodiment are shown in FIG. Fig.10 As shown in b, it can be seen that the molecular sieve is in the form of a sheet, and its b-axis size is concentrated in the range of 500-600nm; the a-axis size of the molecular sieve is 2.4-2.6μm, and the c-axis size is 6-7μm.

[0151] Comparative Example 1

[0152] This comparative example provides a hexagonal Silicalite-1 zeolite molecular sieve without tetramethylguanidine, and the preparation method thereof specifically comprises the following steps:

[0153] (1) tetraethyl orthosilicate is added to a tetrapropylammonium hydroxide solution having a concentration of 1 mol / L to prepare a uniform sol or gel; the molar ratio of tetraethyl orthosilicate (based on silicon dioxide) to the template is 1:0.36;

[0154] (2) volatilizing a certain amount of water from the solution obtained in step (1) at room temperature until the molar ratio of water to tetraethyl orthosilicate (calculated as silicon dioxide) in the solution is finally controlled to be 10, thereby obtaining a reaction system;

[0155] (3) moving the reaction system obtained in step (2) to a reaction kettle and crystallizing at 170° C. for 6 hours;

[0156] (4) The sample reactor obtained in step (3) is taken out, centrifuged or filtered, washed thoroughly with deionized water until neutral, and dried to obtain Silicalite-1 type MFI zeolite molecular sieve.

[0157] The XRD data of the molecular sieve prepared in this example are as follows Fig.11 As shown in a in FIG. 1 . From the XRD data, it can be seen that the molecular sieve has an MFI zeolite structure. The morphology and structure of the molecular sieve of this embodiment are shown in FIG. Fig.11 As shown in b, it can be seen that the molecular sieve crystal is in the shape of a hexagonal prism, and its three-dimensional size is about 100 nm.

[0158] Comparative Example 2

[0159] This comparative example provides a ZSM-5 zeolite molecular sieve, and its preparation method specifically comprises the following steps:

[0160] (1) adding aluminum sulfate into a tetrapropylammonium hydroxide solution as a template to dissolve the aluminum sulfate and obtain a uniform solution;

[0161] (2) adding tetramethylguanidine as an additive to the solution of step (1) to prepare a uniform solution;

[0162] (3) adding tetraethyl orthosilicate as a silicon source to the solution of step (2) to prepare a uniform intermediate system (which may be a sol or a gel); tetraethyl orthosilicate is calculated as silicon dioxide, and aluminum sulfate is calculated as aluminum oxide. The stoichiometric ratio of the components in the intermediate system is the following molar ratio:

[0163] SiO 2 :Al 2 O 3 : Template: Additive = 1: 0.01: 0.36: 0.3;

[0164] (4) adding a certain amount of water to the solution obtained in step (3) so that the molar ratio of water to tetraethyl orthosilicate (calculated as silicon dioxide) is finally controlled to be 30, thereby obtaining a reaction system;

[0165] (5) transferring the reaction system obtained in step (4) to a reaction kettle and crystallizing at 170° C. for 24 hours;

[0166] (6) The crystallized product of step (5) is taken out from the reactor, separated by centrifugation or filtration, washed thoroughly with deionized water until neutral, and dried to obtain a flaky ZSM-5 zeolite molecular sieve.

[0167] The XRD data of the molecular sieve prepared in this example are as follows Fig.12 As shown in a in FIG. 1 . From the XRD data, it can be seen that the molecular sieve has an MFI zeolite structure. The morphology and structure of the molecular sieve of this embodiment are shown in FIG. Fig.12 As shown in b, it can be seen that the b-axis size of the molecular sieve is concentrated in the range of 1.4-1.9 μm, which is larger than the b-axis size of the molecular sieve in the above embodiment; the a-axis size of the molecular sieve is 2.5-3.0 μm, and the c-axis size is 10-12 μm. In addition, amorphous SiO 2 Particles having a crystallinity of less than 80%.

[0168] Comparative Example 3

[0169] This comparative example provides a Ga-MFI zeolite molecular sieve, and its preparation method specifically comprises the following steps:

[0170] (1) adding gallium nitrate into a tetrapropylammonium hydroxide solution as a template to dissolve and obtain a uniform solution;

[0171] (2) adding tetramethylguanidine as an additive to the solution of step (1) to prepare a uniform solution;

[0172] (3) adding tetraethyl orthosilicate as a silicon source to the solution of step (2) to prepare a uniform intermediate system (which may be a sol or a gel);

[0173] Tetraethyl orthosilicate is calculated as silicon dioxide, and gallium nitrate is calculated as gallium trioxide. The synthesis ratio of the intermediate system is in the following molar ratio:

[0174] SiO 2 :Ga 2 O 3 : Template: Additive = 1: 0.01: 0.36: 0.3;

[0175] (4) adding a certain amount of water to the solution obtained in step (3) so that the molar ratio of water to tetraethyl orthosilicate is finally controlled to be 30, thereby obtaining a reaction system;

[0176] (5) transferring the reaction system obtained in step (4) to a reaction kettle and crystallizing at 170° C. for 24 hours;

[0177] (6) The crystallized product obtained in step (5) is taken out from the reactor, separated by centrifugation or filtration, washed thoroughly with deionized water until neutral, and dried to obtain Ga-MFI zeolite molecular sieve.

[0178] The XRD data of the molecular sieve prepared in this example are as follows Fig.13 As shown in a in FIG. 1 . From the XRD data, it can be seen that the molecular sieve has an MFI zeolite structure. The morphology and structure of the molecular sieve of this embodiment are shown in FIG. Fig.13 As shown in b, it can be seen that the b-axis size of the molecular sieve is concentrated in the range of 2.0-2.5 μm, which is larger than the b-axis size of the molecular sieve in the above embodiment; the a-axis size of the molecular sieve is 6-7 μm, and the c-axis size is 14-16 μm.

[0179] Comparative Example 4

[0180] This comparative example provides an ellipsoidal ZSM-5 zeolite molecular sieve, and its preparation method specifically comprises the following steps:

[0181] (1) adding gallium nitrate into a tetrapropylammonium hydroxide solution as a template to dissolve and obtain a uniform solution;

[0182] (2) adding tetramethylguanidine as an additive to the solution of step (1) to prepare a uniform solution;

[0183] (3) adding tetraethyl orthosilicate as a silicon source to the solution of step (2) to prepare a uniform intermediate system (which may be a sol or a gel);

[0184] Tetraethyl orthosilicate is calculated as silicon dioxide, and gallium nitrate is calculated as gallium trioxide. The synthesis ratio of the intermediate system is in the following molar ratio:

[0185] SiO 2 :Ga 2 O 3 : Template: Additive = 1: 0.01: 0.36: 0.3;

[0186] (4) volatilizing a certain amount of water from the solution obtained in step (3) at 45° C. so that the molar ratio of water to tetraethyl orthosilicate is finally controlled to be 8, thereby obtaining a reaction system;

[0187] (5) transferring the reaction system obtained in step (4) to a reaction kettle and crystallizing at 170° C. for 20 hours;

[0188] (6) The crystallized product obtained in step (5) is taken out from the reactor, separated by centrifugation or filtration, washed thoroughly with deionized water until neutral, and dried to obtain a flaky MFI zeolite molecular sieve.

[0189] The XRD data of the molecular sieve prepared in this example are as follows Fig.14 As shown in a in FIG. 1 . From the XRD data, it can be seen that the molecular sieve has an MFI zeolite structure. The morphology and structure of the molecular sieve of this embodiment are shown in FIG. Fig.14 As shown in b, it can be seen that the morphology of the molecular sieve has already fallen into the category of ellipsoidal crystals, and the size of the b axis is similar to that of the a axis and the c axis. Specifically, the size of the b axis is concentrated in the range of 300-400nm; the size of the a axis of the molecular sieve is 0.5-0.6μm, and the size of the c axis is 0.6-0.7μm.

[0190] Table 1 shows the molecular sieve structural parameters of the above embodiments and comparative examples.

[0191] The calculation formula of crystallinity is: crystallinity = sample diffraction peak area / standard sample diffraction peak area × 100%.

[0192] Table 1

[0193]

[0194] Comparing Comparative Example 1 with the examples, it can be seen that by using tetramethylguanidine as an additive, a sheet-like molecular sieve with a shortened b-axis can be obtained.

[0195] Comparing Comparative Examples 2-4 with Examples 6-10, it can be seen that if the molar amount m of water relative to the silicon source is too high (more than 30), the b-axis will be too large and the molecular diffusion efficiency will be reduced; if the molar amount m of water relative to the silicon source is too low (less than 10), it will result in the inability to form a sheet-like molecular sieve. The present invention controls the amount of water added to the reaction system within a certain range (m=5-30 when the raw material does not contain a metal source, and 10≤m<30 when the raw material contains a metal source), thereby controlling the concentration of the reaction system and the crystallization time of the molecular sieve, thereby adjusting the morphology of the molecular sieve and the length of the b-axis, and obtaining a sheet-like MFI molecular sieve with a short b-axis.

Claims

1. A method for preparing a flaky MFI molecular sieve, the method comprising mixing a silicon source, an additive, a template and water to form a reaction system, crystallizing and calcining the reaction system to obtain the flaky MFI molecular sieve; wherein: The additive includes tetramethylguanidine; the silicon source is calculated as silicon dioxide, and the molar ratio of the silicon source to the additive is 1:z,0 <z≤0.5。 2. The preparation method according to claim 1, wherein The silicon source is calculated as silicon dioxide, and the molar ratio of the silicon source to the additive is 1:z,0 <z≤0.4。 3. The preparation method according to claim 1, wherein The silicon source includes one or a combination of two or more of tetraethyl orthosilicate, silica sol, sodium silicate and white carbon black.

4. The preparation method according to claim 1, wherein The template agent includes one or a combination of two or more of tetraethylammonium hydroxide, tetrapropylammonium hydroxide and ethylenediamine.

5. The preparation method according to any one of claims 1 to 4, wherein: The reaction system further comprises a metal source, wherein the metal source comprises an aluminum-containing compound and / or a gallium-containing compound; Preferably, the aluminum-containing compound includes aluminum hydroxide and / or aluminum salt, and the aluminum salt preferably includes one or a combination of two or more of aluminum sulfate, aluminum nitrate, aluminum sulfate, sodium metaaluminate, and aluminum isopropoxide; Preferably, the gallium-containing compound comprises a gallium salt, and the gallium salt preferably comprises gallium nitrate.

6. The preparation method according to claim 5, wherein: The silicon source is calculated as silicon dioxide, the metal source is calculated as metal oxide, and the molar ratio of the silicon source to the metal source is 1:x, wherein 0 <x≤0.025。 7. The preparation method according to claim 5, wherein: The metal source is calculated as metal oxide, and the molar ratio of the metal source to the template is 0.01-0.07:

1.

8. The preparation method according to claim 5, wherein: The silicon source is calculated as silicon dioxide, and the molar ratio of the silicon source to water is 1:m. When the reaction system does not include the metal source, m is 5-30; when the reaction system includes the metal source, 10≤m<30.

9. The preparation method according to claim 1, wherein The crystallization temperature is 120-180° C., and the crystallization time is 3 hours to 7 days.

10. A sheet-like MFI molecular sieve obtained by the preparation method according to any one of claims 1 to 9.

11. The sheet-like MFI molecular sieve according to claim 10, wherein: The b-axis length of the flaky MFI molecular sieve is 50-600 nm; Preferably, the a-axis length of the flaky MFI molecular sieve is 0.14-2.9 μm, and the c-axis length is 1.3-35 μm.

12. The sheet-like MFI molecular sieve according to claim 10 or 11, wherein: The MFI molecular sieve includes one or a combination of two or more of pure silicon Silicalite-1 molecular sieve, aluminum-containing ZSM-5 molecular sieve, and gallium-containing MFI molecular sieve.

13. A catalyst comprising the flaky MFI molecular sieve according to any one of claims 10 to 12 or made from the flaky MFI molecular sieve.

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