Zsm-5 molecular sieve, method for preparing the same and use thereof

Abstract

The application relates to the field of silicon-aluminum molecular sieve preparation, and discloses a ZSM-5 molecular sieve and a preparation method and application thereof. The molecular sieve has a cage-shaped structure formed by stacking sheet-shaped primary crystal grains. The ZSM-5 molecular sieve provided by the application has high catalytic activity.

Description

Technical Field

[0001] This invention relates to the field of silicon-aluminum molecular sieve preparation, specifically to a ZSM-5 molecular sieve, its preparation method, and its application. Background Technology

[0002] In 1972, Mobil Corporation in the United States synthesized ZSM-5 molecular sieve. It is a five-membered ring zeolite, with its basic structural unit consisting of eight five-membered rings linked by oxygen bridges to form a chain-like structure, which then encloses the zeolite framework, exhibiting a two-dimensional 10×10 ring pore structure (0.56nm×0.53nm and 0.55nm×0.51nm). Since its introduction, ZSM-5 molecular sieve has been widely used in catalysis fields such as petroleum processing, petrochemicals, coal chemicals, and fine chemicals due to its unique pore structure and excellent catalytic performance, and is currently one of the most important molecular sieve catalytic materials.

[0003] CN115818663B employs a two-stage crystallization combined with silicon supplementation method to prepare amine-free high-silica ZSM-5 molecular sieves. Specifically, the process includes: S1, mixing a first silicon source, an aluminum source, a first alkali source, water, and a first seed crystal, and then subjecting the resulting mixture to a first hydrothermal reaction to obtain a first hydrothermal reaction product; S2, mixing the first hydrothermal reaction product with a second silicon source, a second alkali source, water, and a second seed crystal, and then subjecting the resulting mixture to a second hydrothermal reaction. The resulting amine-free high-silica ZSM-5 molecular sieve, when applied to the catalytic cracking reaction of light hydrocarbons, exhibits superior low-carbon olefin yields, particularly favoring the production of propylene. However, the combined yields of ethylene and propylene are less than 30%. Therefore, it is necessary to develop a ZSM-5 molecular sieve with even better catalytic performance. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems existing in the prior art and provide a ZSM-5 molecular sieve, its preparation method, and its applications. The ZSM-5 molecular sieve provided by this invention exhibits high catalytic activity. When applied to the catalytic cracking reaction of olefins, it achieves a high diene yield.

[0005] To achieve the above objectives, the first aspect of the present invention provides a ZSM-5 molecular sieve, wherein the molecular sieve has a cage-like structure formed by stacking plate-like primary crystals.

[0006] A second aspect of this invention provides a method for preparing ZSM-5 molecular sieve, the method comprising the following steps:

[0007] (1) Aluminum source, silicon source, alkali source, structure directing agent, fluoride and water are gelled to obtain a colloidal solution; the molar ratio of silicon source to alkali source is 1:0.2-0.9, and the molar ratio of silicon source to fluoride is 1:0.08-0.3, wherein the silicon source is calculated as SiO2;

[0008] (2) The colloidal solution is dynamically crystallized, and then dried and calcined.

[0009] The third aspect of this invention provides the application of the ZSM-5 molecular sieve described in the first aspect or prepared by the method described in the second aspect in catalytic cracking reactions.

[0010] The beneficial effects of the present invention through the above technical solution include:

[0011] The ZSM-5 molecular sieve with a specific morphology described in this invention has high catalytic performance, and its application in the field of catalytic cracking exhibits high reaction performance.

[0012] The method for preparing ZSM-5 molecular sieves provided by this invention involves adding a structure-directing agent, an alkali source, and a fluoride to the system without the need for seed crystals. A single dynamic crystallization step yields the ZSM-5 molecular sieve with a specific morphology described in this invention. The process is simple. The ZSM-5 molecular sieves prepared using this method exhibit high yield, high crystallinity, and uniform particle size. Attached Figure Description

[0013] Figure 1 This is the XRD pattern of the ZSM-5 molecular sieve prepared in Example 1 of this invention;

[0014] Figure 2 This is a SEM image of the ZSM-5 molecular sieve prepared in Example 1 of this invention;

[0015] Figure 3 This is a SEM image of the ZSM-5 molecular sieve prepared in Example 2 of this invention;

[0016] Figure 4 This is a SEM image of the ZSM-5 molecular sieve prepared in Comparative Example 1 of this invention.

[0017] Figure 5 This is a SEM image of the ZSM-5 molecular sieve prepared in Comparative Example 2 of this invention;

[0018] Figure 6 This is a SEM image of the ZSM-5 molecular sieve prepared in Comparative Example 3 of this invention.

[0019] Figure 7 This is a SEM image of the ZSM-5 molecular sieve prepared in Comparative Example 4 of this invention.

[0020] Figure 8 This is a SEM image of the ZSM-5 molecular sieve prepared in Comparative Example 5 of this invention. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] The first aspect of the present invention provides a ZSM-5 molecular sieve, wherein the molecular sieve has a cage-like structure formed by stacking plate-like primary crystals.

[0023] The morphology of the molecular sieve described in this invention was measured using SEM. The overall morphology of the molecular sieve resembles a lantern with internal cavities, hence it is termed a cage-like structure. This cage-like structure is formed by the stacking of layered primary crystals, as can be seen from [reference needed]. Figure 1 The ZSM-5 molecular sieve with the structure described in this invention exhibits high reaction performance when applied to the field of catalytic cracking.

[0024] The cage-like structure described in this invention can be regular or not completely regular, both of which are within the protection scope of this invention.

[0025] The size of the plate-shaped primary grains of the present invention is relatively small. Preferably, the average size of the plate-shaped primary grains is (40-170)×(20-100)×(30-100)nm, and more preferably (100-140)×(40-70)×(30-50)nm.

[0026] In this invention, the average size of the primary grain is given in the form of length × width × height.

[0027] The method for testing the average size of the lamellar primary grains of the present invention includes: measuring the length, width and height of 20-40 primary grains in the SEM image using a NanoMeasurer and taking the average value.

[0028] The molecular sieve of this invention has a high specific surface area, which is beneficial for increasing the reaction contact area. Preferably, the specific surface area of ​​the ZSM-5 molecular sieve is 300-500 m² / g. 2 / g, preferably 300-400m 2 / g.

[0029] According to the present invention, preferably, the ratio of the external specific surface area of ​​the ZSM-5 molecular sieve to its total surface area is 30-55%, specifically 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, and any two of these values, preferably 35-50%. This preferred embodiment provides more active centers, promotes chemical reactions, and improves reaction efficiency.

[0030] It is understood that in this invention, the specific surface area is the sum of the external specific surface area and the internal specific surface area.

[0031] The specific surface area parameter of the molecular sieve described in this invention was measured by the BET method.

[0032] According to the present invention, preferably, the SiO2 / Al2O3 molar ratio of the ZSM-5 molecular sieve is 15-50, more preferably 20-40.

[0033] The SiO2 / Al2O3 molar ratio of the molecular sieve described in this invention was measured by inductively coupled plasma atomic emission spectrometry (ICP).

[0034] A second aspect of this invention provides a method for preparing ZSM-5 molecular sieve, the method comprising the following steps:

[0035] (1) Aluminum source, silicon source, alkali source, structure directing agent, fluoride and water are gelled to obtain a colloidal solution; the molar ratio of silicon source to alkali source is 1:0.2-0.9, and the molar ratio of silicon source to fluoride is 1:0.08-0.3, wherein the silicon source is calculated as SiO2;

[0036] (2) The colloidal solution is dynamically crystallized, and then dried and calcined.

[0037] The method for preparing ZSM-5 molecular sieve provided by this invention involves adding a structure-directing agent, an alkali source, and a fluoride to the system without adding seed crystals, followed by a one-step dynamic crystallization process to obtain the ZSM-5 molecular sieve described in the first aspect of this invention. The ZSM-5 molecular sieve prepared using the method described in this invention exhibits high yield, high crystallinity, and uniform particle size.

[0038] According to the present invention, the molar ratio of silicon source to alkali source is 1:0.2-0.9, specifically 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, and any two of these values ​​within a range, preferably 1:0.3-0.7, wherein the silicon source is SiO2. In the present invention, controlling the amount of alkali source within the above-mentioned preferred range is beneficial for inducing the formation of the molecular sieve with the structure described in the first aspect.

[0039] According to the present invention, the molar ratio of silicon source to fluoride is 1:0.08-0.3, specifically 1:0.08, 1:0.09, 1:0.1, 1:0.11, 1:0.12, 1:0.13, 1:0.14, 1:0.15, 1:0.16, 1:0.17, 1:0.18, 1:0.19, 1:0.2, 1:0.21, 1:0.22, 1:0.23, 1:0.24, 1:0.25, 1:0.26, 1:0.27, 1:0.28, 1:0.29, 1:0.3, and any two of these values ​​forming a range, preferably 1:0.08-0.24, wherein the silicon source is SiO2. In the present invention, controlling the amount of fluoride within the above-mentioned preferred range is beneficial for forming a specific zeolite framework structure.

[0040] According to the present invention, preferably, the molar ratio of silicon source, aluminum source and water is 1:0.01-0.07:50-80, more preferably 1:0.02-0.06:50-75, wherein the silicon source is calculated as SiO2 and the aluminum source is calculated as Al2O3.

[0041] According to the present invention, preferably, the molar ratio of silicon source to structure directing agent is 1:0.3-0.8, more preferably 1:0.4-0.7, wherein the silicon source is SiO2.

[0042] The present invention does not impose any particular limitation on the type of aluminum source, and any conventional choice in the art can be made. Preferably, the aluminum source is selected from at least one of sodium aluminate, aluminum sulfate, aluminum powder, and boehmite.

[0043] The present invention does not impose any particular limitation on the type of silicon source, and any conventional choice in the art can be used. Preferably, the silicon source is selected from at least one of silicic acid, silica sol, silica fume, and water glass.

[0044] The present invention does not impose any particular limitation on the type of alkali source, and any conventional choice in the art can be made. Preferably, the alkali source is selected from at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, and ammonia water.

[0045] The present invention has a wide range of choices for the type of structure directing agent. Preferably, the structure directing agent is selected from at least one of ethylenediamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide and hexadecyltrimethylammonium bromide.

[0046] The present invention has a wide range of choices for the types of fluorides. Preferably, the fluorides are selected from at least one of sodium fluoride, potassium fluoride, calcium fluoride and magnesium fluoride.

[0047] According to the present invention, preferably, the gelation conditions in step (1) include: a gelation temperature of 10-60°C, preferably 20-50°C; and a gelation time of 2-10 h, preferably 3-8 h.

[0048] The present invention does not impose any particular limitation on the order of adding the aluminum source, silicon source, alkali source, structure directing agent, fluoride, and water in step (1), and can make appropriate adjustments according to the actual situation. Moreover, during the addition of the above substances, conventional operations such as stirring or ultrasonication can be performed to achieve uniform mixing. According to a preferred embodiment of the present invention, step (1) includes: first adding the aluminum source aqueous solution to the aqueous solution containing the silicon source and alkali source, then adding the fluoride aqueous solution, and finally adding the structure directing agent aqueous solution.

[0049] According to a particularly preferred embodiment of the present invention, step (1) includes: first, adding an aqueous solution of aluminum source dropwise to an aqueous solution containing silicon source and alkali source, stirring for 20-40 min, then adding an aqueous solution of fluoride, stirring for 60-120 min, and finally adding an aqueous solution of structure guiding agent, stirring for 3-6 h to obtain a colloidal solution.

[0050] The dynamic crystallization process described in this invention does not require temperature-variable crystallization and has a short crystallization time. Preferably, the conditions for dynamic crystallization in step (2) include: a crystallization temperature of 150-220℃ and a crystallization time of 18-40h.

[0051] The present invention does not particularly limit the method of achieving dynamic crystallization, and conventional methods in the art can be used. Preferably, the dynamic crystallization in step (2) is carried out under stirring conditions.

[0052] Preferably, the stirring speed is 1-60 r / min, more preferably 10-40 r / min. This preferred embodiment facilitates gel conversion and crystallization, and also helps to obtain small-diameter primary crystals.

[0053] The present invention does not have any particular limitation on the drying conditions described in step (2), and can be carried out with reference to conventional methods in the art.

[0054] According to the present invention, preferably, the calcination conditions in step (2) include: a calcination temperature of 300-700℃, preferably 350-600℃; and a calcination time of 2-10h, preferably 3-8h.

[0055] Preferably, the method further includes: performing solid-liquid separation and washing before drying the dynamic crystallization product described in step (2).

[0056] The present invention does not particularly limit the method of solid-liquid separation, and conventional technical means in the art can be used.

[0057] The present invention does not have any particular limitation on the washing method, and conventional methods in the art can be used.

[0058] The third aspect of this invention provides the application of the ZSM-5 molecular sieve described in the first aspect or prepared by the method described in the second aspect in catalytic cracking reactions.

[0059] The present invention will be described in detail below through embodiments.

[0060] In the following examples, the specific surface area of ​​the molecular sieve was measured using the nitrogen physical adsorption-desorption (BET) method: the nitrogen physical adsorption-desorption isotherm of the molecular sieve was measured using a Micromeretic ASAP2020M physical adsorption instrument, and then calculated using the BET equation and t-plot equation. The experimental conditions for this molecular sieve were: measurement temperature -196℃, and before measurement, the molecular sieve was heat-treated at 550℃ in air for 6 hours, followed by vacuum pretreatment at 350℃ for 4 hours.

[0061] The content of each element in the molecular sieve was determined by inductively coupled plasma atomic emission spectrometry (ICP) using a Varian 725-ES instrument. The sample was dissolved in hydrofluoric acid before testing, and the content was expressed in moles.

[0062] Example 1

[0063] Solution A is prepared by mixing sodium hydroxide, silica sol (containing 40% by weight of SiO2), and deionized water; solution B is prepared by mixing aluminum sulfate octadechydrate and deionized water; solution C is prepared by mixing potassium fluoride dihydrate and deionized water; and solution D is prepared by mixing tetraethylammonium hydroxide and deionized water.

[0064] While stirring, solution B was added dropwise to solution A, and the mixture was stirred at room temperature for 30 minutes. Then solution C was added, and the mixture was stirred at room temperature for 80 minutes. Finally, solution D was added to the above solutions, and the mixture was stirred at 30°C for 5 hours to obtain a mixed solution. The final material ratio (molar ratio) is:

[0065] SiO2 / Al2O3 = 33.28;

[0066] NaOH / SiO2 = 0.67;

[0067] Structure directing agent / SiO2 = 0.5;

[0068] Fluoride / SiO2 = 0.22;

[0069] H2O(total) / SiO2 = 56.29.

[0070] The above mixed solution was placed in a stainless steel reactor and crystallized at 190°C with a stirring speed of 20 rpm for 26 hours. After crystallization, the crystallized product was filtered, washed with deionized water, dried overnight in an oven at 105°C, and calcined in air at 550°C for 6 hours to obtain ZSM-5 molecular sieve. The yield of the molecular sieve was 95 wt%.

[0071] The XRD pattern of the molecular sieve prepared in Example 1 is shown below. Figure 1 As shown. (Through) Figure 1 It can be seen that the characteristic diffraction peaks of the typical MFI-type framework structure appear at 2θ = 7.9°, 8.8°, 23.1°, 23.8° and 24.3°, and there are no other impurity phase peaks, indicating that the synthesized ZSM-5 molecular sieve is a pure phase with high crystallinity.

[0072] An exemplary SEM image of the molecular sieve prepared in Example 1 is shown below. Figure 2 As shown. (Through) Figure 2 As can be seen, the molecular sieve of the present invention has an overall cage-like structure, and the molecular sieve is composed of multiple plate-like primary crystals stacked together.

[0073] Example 2

[0074] Solution A is prepared by mixing sodium hydroxide, silica sol (containing 40% by weight of SiO2), and deionized water; solution B is prepared by mixing aluminum sulfate octadechydrate and deionized water; solution C is prepared by mixing sodium fluoride and deionized water; and solution D is prepared by mixing tetraethylammonium hydroxide and deionized water.

[0075] While stirring, solution B was added dropwise to solution A, and the mixture was stirred at room temperature for 30 minutes. Then, solution C was added, and the mixture was stirred at room temperature for 90 minutes. Finally, solution D was added to the above solutions, and the mixture was stirred at 40°C for 4 hours to obtain a mixed solution. The final material ratio (molar ratio) is:

[0076] SiO2 / Al2O3 = 22.18;

[0077] NaOH / SiO2 = 0.56;

[0078] Structure directing agent / SiO2 = 0.62;

[0079] Fluoride / SiO2 = 0.16;

[0080] H2O(total) / SiO2 = 71.11.

[0081] The above mixed solution was placed in a stainless steel reactor and crystallized at 200°C with a stirring speed of 18 rpm for 24 hours. After crystallization, the crystallization product was filtered, washed with deionized water, dried overnight in an oven at 110°C, and calcined in air at 550°C for 6 hours to obtain ZSM-5 molecular sieve. The yield of the molecular sieve was 94.8 wt%.

[0082] An exemplary SEM image of the molecular sieve prepared in Example 2 is shown below. Figure 3 As shown. (Through) Figure 3 As can be seen, the molecular sieve of the present invention has an overall cage-like structure, and the molecular sieve is composed of multiple plate-like primary crystals stacked together.

[0083] Example 3

[0084] Solution A is prepared by mixing sodium hydroxide, silica sol (containing 40% by weight of SiO2), and deionized water; solution B is prepared by mixing aluminum sulfate octadechydrate and deionized water; solution C is prepared by mixing potassium fluoride dihydrate and deionized water; and solution D is prepared by mixing tetraethylammonium hydroxide and deionized water.

[0085] While stirring, solution B was added dropwise to solution A, and the mixture was stirred at room temperature for 30 minutes. Then, solution C was added, and the mixture was stirred at room temperature for 100 minutes. Finally, solution D was added to the above solutions, and the mixture was stirred at 36°C for 5 hours to obtain a mixed solution. The final material ratio (molar ratio) is:

[0086] SiO2 / Al2O3 = 26.10;

[0087] NaOH / SiO2 = 0.47;

[0088] Structure directing agent / SiO2 = 0.55;

[0089] Fluoride / SiO2 = 0.21;

[0090] H2O(total) / SiO2 = 69.48.

[0091] The above mixed solution was placed in a stainless steel reactor and crystallized at 170°C with a stirring speed of 30 rpm for 30 hours. After crystallization, the crystallization product was filtered, washed with deionized water, dried overnight in an oven at 100°C, and calcined in air at 550°C for 6 hours to obtain ZSM-5 molecular sieve. The yield of the molecular sieve was 94.9 wt%.

[0092] The SEM images of the molecular sieves prepared in Example 3 are similar to those in Example 1.

[0093] Example 4

[0094] Solution A is prepared by mixing sodium hydroxide, silica sol (containing 40% by weight of SiO2), and deionized water; solution B is prepared by mixing aluminum sulfate octadechydrate and deionized water; solution C is prepared by mixing magnesium fluoride and deionized water; and solution D is prepared by mixing tetraethylammonium hydroxide and deionized water.

[0095] While stirring, add solution B dropwise to solution A and stir at room temperature for 30 minutes. Then add solution C and stir at room temperature for 80 minutes. Finally, add solution D to the above solutions and stir at 22°C for 5 hours to obtain a mixed solution. The final material ratio (molar ratio) is:

[0096] SiO2 / Al2O3 = 29.58;

[0097] NaOH / SiO2 = 0.39;

[0098] Structure directing agent / SiO2 = 0.54;

[0099] Fluoride / SiO2 = 0.12;

[0100] H2O(total) / SiO2 = 68.71.

[0101] The above mixed solution was placed in a stainless steel reactor and crystallized at 180°C with a stirring speed of 12 rpm for 28 hours. After crystallization, the crystallization product was filtered, washed with deionized water, dried overnight in an oven at 110°C, and calcined in air at 550°C for 6 hours to obtain ZSM-5 molecular sieve. The yield of the molecular sieve was 94.9 wt%.

[0102] The SEM image of the molecular sieve prepared in Example 4 is similar to that in Example 1.

[0103] Example 5

[0104] Solution A is prepared by mixing sodium hydroxide, silica sol (containing 40% by weight of SiO2), and deionized water; solution B is prepared by mixing aluminum sulfate octadechydrate and deionized water; solution C is prepared by mixing sodium fluoride and deionized water; and solution D is prepared by mixing tetraethylammonium hydroxide and deionized water.

[0105] While stirring, solution B was added dropwise to solution A, and the mixture was stirred at room temperature for 30 minutes. Then, solution C was added, and the mixture was stirred at room temperature for 100 minutes. Finally, solution D was added to the above solutions, and the mixture was stirred at 28°C for 4 hours to obtain a mixed solution. The final material ratio (molar ratio) is:

[0106] SiO2 / Al2O3 = 28.99;

[0107] NaOH / SiO2 = 0.32;

[0108] Structure directing agent / SiO2 = 0.47;

[0109] Fluoride / SiO2 = 0.13;

[0110] H2O(total) / SiO2 = 61.55.

[0111] The above mixed solution was placed in a stainless steel reactor and crystallized at 160°C with a stirring speed of 35 rpm for 38 hours. After crystallization, the crystallization product was filtered, washed with deionized water, dried overnight in an oven at 100°C, and calcined in air at 550°C for 6 hours to obtain ZSM-5 molecular sieve. The yield of the molecular sieve was 95.3 wt%.

[0112] The SEM image of the molecular sieve prepared in Example 5 is similar to that in Example 1.

[0113] Example 6

[0114] Solution A is prepared by mixing sodium hydroxide, silica sol (containing 40.0% by weight of SiO2), and deionized water; solution B is prepared by mixing aluminum sulfate octadechydrate and deionized water; solution C is prepared by mixing calcium fluoride and deionized water; and solution D is prepared by mixing tetraethylammonium hydroxide and deionized water.

[0115] While stirring, add solution B dropwise to solution A, and stir at room temperature for 30 minutes. Then add solution C, stir at room temperature for 100 minutes, and then add solution D to the above solutions. Stir at 42°C for 3 hours to obtain a mixed solution. The final material ratio (molar ratio) is:

[0116] SiO2 / Al2O3 = 28;

[0117] NaOH / SiO2 = 0.42;

[0118] Structure directing agent / SiO2 = 0.49;

[0119] Fluoride / SiO2 = 0.11;

[0120] H2O (total) / SiO2 = 66.95.

[0121] The above mixed solution was placed in a stainless steel reactor and crystallized at 210°C with a stirring speed of 32 rpm for 20 hours. After crystallization, the crystallized product was filtered, washed with deionized water, dried overnight in an oven at 120°C, and calcined in air at 550°C for 6 hours to obtain ZSM-5 molecular sieve. The yield of the molecular sieve was 96.8 wt%.

[0122] The SEM image of the molecular sieve prepared in Example 6 is similar to that in Example 1.

[0123] Example 7

[0124] Solution A is prepared by mixing sodium hydroxide, silica sol (containing 40% by weight of SiO2), and deionized water; solution B is prepared by mixing aluminum sulfate octadechydrate and deionized water; solution C is prepared by mixing sodium fluoride and deionized water; and solution D is prepared by mixing tetraethylammonium hydroxide and deionized water.

[0125] While stirring, solution B was added dropwise to solution A, and the mixture was stirred at room temperature for 30 minutes. Then, solution C was added, and the mixture was stirred at room temperature for 100 minutes. Finally, solution D was added to the above solutions, and the mixture was stirred at 45°C for 3 hours to obtain a mixed solution. The final material ratio (molar ratio) is:

[0126] SiO2 / Al2O3 = 26.90;

[0127] NaOH / SiO2 = 0.42;

[0128] Structure directing agent / SiO2 = 0.54;

[0129] Fluoride / SiO2 = 0.10;

[0130] H2O (total) / SiO2 = 72.10.

[0131] The above mixed solution was placed in a stainless steel reactor and crystallized at 180°C with a stirring speed of 26 rpm for 26 hours. After crystallization, the crystallization product was filtered, washed with deionized water, dried overnight in an oven at 115°C, and calcined in air at 550°C for 6 hours to obtain ZSM-5 molecular sieve. The yield of the molecular sieve was 96.7 wt%.

[0132] The SEM image of the molecular sieve prepared in Example 7 is similar to that in Example 1.

[0133] Comparative Example 1

[0134] Sodium hydroxide, silica sol (containing 40% by weight of SiO2), and deionized water were prepared to form solution A; aluminum sulfate octadecylhydrate was prepared to form solution B; and tetraethylammonium hydroxide and deionized water were prepared to form solution C.

[0135] While stirring, solution B was added dropwise to solution A. The mixture was stirred at room temperature for 30 minutes. Then, solution C was added to the above solution, and the mixture was stirred at 38°C for 2 hours to obtain a mixed solution. The final material ratio (molar ratio) is:

[0136] SiO2 / Al2O3 = 22.18;

[0137] NaOH / SiO2 = 0.56;

[0138] Structure directing agent / SiO2 = 0.62;

[0139] Fluoride / SiO2 = 0;

[0140] H2O(total) / SiO2 = 71.11.

[0141] The above mixed solution was placed in a stainless steel reactor and crystallized at 200°C with a stirring speed of 18 rpm for 24 hours. After crystallization, the crystallization product was filtered, washed with deionized water, dried overnight in an oven at 110°C, and calcined in air at 550°C for 6 hours to obtain ZSM-5 molecular sieve. The yield of the molecular sieve was 96.7 wt%.

[0142] SEM image of the molecular sieve prepared in Comparative Example 1 is shown below. Figure 4 As shown. (Through) Figure 4 It can be seen that the molecular sieve described in this invention is a spherical structure formed by primary crystal stacking, rather than a cage-like structure.

[0143] Comparative Example 2

[0144] The method of Example 3 was followed, except that no stirring was performed during crystallization. ZSM-5 molecular sieve was obtained with a yield of 94.8 wt%.

[0145] SEM image of the molecular sieve prepared in Comparative Example 2 is shown below. Figure 5 As shown. (Through) Figure 5 As can be seen, the molecular sieve of the present invention has a flat spherical structure, not a cage-like structure, and has no primary crystals.

[0146] Comparative Example 3

[0147] Solution A is prepared by mixing sodium hydroxide, silica sol (containing 40% by weight of SiO2), and deionized water; solution B is prepared by mixing aluminum sulfate octadechydrate and deionized water; solution C is prepared by mixing magnesium fluoride and deionized water; and solution D is prepared by mixing deionized water.

[0148] While stirring, add solution B dropwise to solution A and stir at room temperature for 30 minutes. Then add solution C and stir at room temperature for 100 minutes. Finally, add solution D to the above solutions and stir at 51°C for 4 hours to obtain a mixed solution. The final material ratio (molar ratio) is:

[0149] SiO2 / Al2O3 = 29.58;

[0150] NaOH / SiO2 = 0.39;

[0151] Structure directing agent / SiO2 = 0;

[0152] Fluoride / SiO2 = 0.12;

[0153] H2O(total) / SiO2 = 68.71.

[0154] The above mixed solution was placed in a stainless steel reactor and crystallized at 180°C with a stirring speed of 8 rpm for 28 hours. After crystallization, the crystallized product was filtered, washed with deionized water, dried in an oven at 110°C overnight, and calcined in air at 550°C for 6 hours to obtain an amorphous structure.

[0155] SEM image of the molecular sieve prepared in Comparative Example 3 is shown below. Figure 6 As shown. (Through) Figure 6 It can be seen that the substance described in this invention has an amorphous structure.

[0156] Comparative Example 4

[0157] Solution A is prepared by mixing sodium hydroxide, silica sol (containing 40% by weight of SiO2), and deionized water; solution B is prepared by mixing aluminum sulfate octadechydrate and deionized water; solution C is prepared by mixing potassium fluoride dihydrate and deionized water; and solution D is prepared by mixing tetraethylammonium hydroxide and deionized water.

[0158] While stirring, solution B was added dropwise to solution A, and the mixture was stirred at room temperature for 30 minutes. Then, solution C was added, and the mixture was stirred at room temperature for 100 minutes. Finally, solution D was added to the above solutions, and the mixture was stirred at 30°C for 5 hours to obtain a mixed solution. The final material ratio (molar ratio) is:

[0159] SiO2 / Al2O3 = 33.28;

[0160] NaOH / SiO2 = 0.67;

[0161] Structure directing agent / SiO2 = 0.5;

[0162] Fluoride / SiO2 = 0.02;

[0163] H2O(total) / SiO2 = 56.29.

[0164] The above mixed solution was placed in a stainless steel reactor and crystallized at 190°C with a stirring speed of 20 rpm for 26 hours. After crystallization, the crystallized product was filtered, washed with deionized water, dried overnight in an oven at 105°C, and calcined in air at 550°C for 6 hours to obtain ZSM-5 molecular sieve. The yield of the molecular sieve was 95.6 wt%.

[0165] SEM image of the molecular sieve prepared in Comparative Example 4 is shown below. Figure 7 As shown. (Through) Figure 7 It can be seen that the molecular sieve is basically a spherical shape formed by the stacking of primary crystal grains, with only the central 80nm being hollow and not a cage-like structure.

[0166] Comparative Example 5

[0167] The procedure was carried out according to Example 1, except that the amount of sodium hydroxide was adjusted so that the NaOH / SiO2 molar ratio in the resulting mixed solution was 0.95. ZSM-5 molecular sieve was obtained with a yield of 93.2 wt%.

[0168] SEM image of the molecular sieve prepared in Comparative Example 5 is shown below. Figure 8 As shown. (Through) Figure 8 It can be seen that the molecular sieve is formed by stacking primary crystals. Many primary crystals have grown in the original cage-like structure, filling the hollow structure, and it is no longer a cage-like structure.

[0169] Table 1

[0170]

[0171]

[0172] Test Example 1

[0173] The catalytic cracking performance of n-octane was evaluated using a laboratory fixed-bed microreactor. Hydrogen-form ZSM-5 molecular sieves prepared in the examples and comparative examples were pressed into tablets and sieved to form 40–60 mesh particles. Before the reaction, the catalyst was activated at 500°C for 2 h under nitrogen purging. Nitrogen was used as the dilution gas at a flow rate of 400 mL / min, the reaction temperature was 620°C, the catalyst mass was 0.5 g, the n-octane feed rate was 2 mL / h, and the hydrogen-to-oil volume ratio was 1200. The results after 20 h of reaction are detailed in Table 2.

[0174] Table 2

[0175]

[0176]

[0177] As can be seen from the results in Table 2, the ZSM-5 molecular sieve provided by the present invention has a high n-octane conversion rate and diene yield, which indicates that the ZSM-5 molecular sieve of the present invention has excellent catalytic performance.

[0178] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A ZSM-5 molecular sieve, characterized in that, The molecular sieve has a cage-like structure formed by stacked plate-like primary crystals.

2. The molecular sieve according to claim 1, wherein, The average size of the plate-like primary grains is (40-170)×(20-100)×(30-100)nm, preferably (100-140)×(40-70)×(30-50)nm.

3. The molecular sieve according to claim 1 or 2, wherein, The specific surface area of ​​the ZSM-5 molecular sieve is 300-500 m². 2 / g, preferably 300-400m 2 / g; Preferably, the ratio of the external specific surface area of ​​the ZSM-5 molecular sieve to the total surface area is 30-55%, more preferably 35-50%. Preferably, the SiO2 / Al2O3 molar ratio of the ZSM-5 molecular sieve is 15-50, more preferably 20-40.

4. A method for preparing ZSM-5 molecular sieve, characterized in that, The preparation method includes the following steps: (1) Aluminum source, silicon source, alkali source, structure directing agent, fluoride and water are gelled to obtain a colloidal solution; the molar ratio of silicon source to alkali source is 1:0.2-0.9, and the molar ratio of silicon source to fluoride is 1:0.08-0.3, wherein the silicon source is calculated as SiO2; (2) The colloidal solution is dynamically crystallized, and then dried and calcined.

5. The method according to claim 4, wherein, The molar ratio of silicon source to alkali source is 1:0.3-0.7, where the silicon source is SiO2. Preferably, the molar ratio of silicon source to fluoride is 1:0.08-0.24, wherein the silicon source is SiO2. Preferably, the molar ratio of silicon source, aluminum source and water is 1:0.01-0.07:50-80, more preferably 1:0.02-0.06:50-75, wherein the silicon source is calculated as SiO2 and the aluminum source is calculated as Al2O3; Preferably, the molar ratio of silicon source to structure directing agent is 1:0.3-0.8, more preferably 1:0.4-0.7, wherein the silicon source is SiO2.

6. The method according to claim 4 or 5, wherein, The aluminum source is selected from at least one of sodium aluminate, aluminum sulfate, aluminum powder, and boehmite. Preferably, the silicon source is selected from at least one of silicic acid, silica sol, silica fume, and water glass; Preferably, the alkali source is selected from at least one of sodium hydroxide, potassium hydroxide, sodium carbonate, and ammonia water; Preferably, the structure-directing agent is selected from at least one of ethylenediamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, and hexadecyltrimethylammonium bromide; Preferably, the fluoride is selected from at least one of sodium fluoride, potassium fluoride, calcium fluoride, and magnesium fluoride.

7. The method according to any one of claims 4-6, wherein, The gelation conditions in step (1) include: a gelation temperature of 10-60℃, preferably 20-50℃; and a gelation time of 2-10h, preferably 3-8h.

8. The method according to any one of claims 4-7, wherein, The conditions for dynamic crystallization in step (2) include: crystallization temperature of 150-220℃ and crystallization time of 18-40h; Preferably, the dynamic crystallization in step (2) is carried out under stirring conditions, and the stirring speed is 1-60 r / min, preferably 10-40 r / min.

9. The method according to any one of claims 4-8, wherein, The roasting conditions in step (2) include: a roasting temperature of 300-700℃, preferably 350-600℃; and a roasting time of 2-10h, preferably 3-8h.

10. The application of a ZSM-5 molecular sieve according to any one of claims 1-3 or a ZSM-5 molecular sieve prepared by any one of claims 4-9 in a catalytic cracking reaction.

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