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

Abstract

This invention relates to the field of catalysts, and discloses a ZSM-5 molecular sieve, its preparation method, and its applications. The ZSM-5 molecular sieve has a spindle-shaped particle morphology; the aspect ratio of the molecular sieve is 1-3.5, and the height is 0.5-10 micrometers. The ZSM-5 molecular sieve of this invention is a hierarchical porous ZSM-5 molecular sieve with a spindle-shaped morphology, which, when applied to the reaction of oxygen-containing compounds to olefins, exhibits high reactant conversion and product selectivity.

Description

Technical Field

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

[0002] In 1972, Mobil first reported the synthesis of a zeolite, named ZSM-5 (Zeolite SoconyMobil-five) (Argauer R J. Crystalline Zeolite ZSM-5 and Method of Preparing the Same. US Patent 3,702,886,1972). Subsequently, Kokotailo et al. determined that the crystal structure of ZSM-5 is an MFI type crystal structure (Kokotailo GT, Lawton SL, Olson DH, et al. Structure of Synthetic Zeolite ZSM-5[J]. Nature,1978,272(5652):437-438).

[0003] The ZSM-5 molecular sieve framework contains two different sets of 10-membered ring channels, namely straight channels along the b-axis, with a pore size of [missing information]. And a sinusoidal channel along the a-axis, with a diameter of... The two sets of pore sizes are basically the same. The two sets of 10-membered ring channels are interconnected in the MFI structure, thus giving MFI a three-dimensional pore network system. The cell parameters of MFI-type zeolite are... The MFI framework belongs to the orthorhombic crystal system, with space group Pnma (Zampieri A. Development of MFI-type Zeolite Coatings on SiSiCCeramic Monoliths for Catalytic Applications[D].PhD thesis,University ofErlangen-Nuremberg,2007).

[0004] The synthesis of ZSM-5 molecular sieves generally uses organic amines or quaternary ammonium salts as structure directing agents, such as propylamine, ethylenediamine, hexamethylenediamine, ethanolamine, and tetrapropylamine. Among these structure directing agents, tetrapropylamine (TPA) has the best spatial matching between its molecular configuration and the pore structure of MFI-type zeolites. MFI-type zeolite materials prepared with TPA as a structure directing agent have advantages such as high crystallinity, uniform morphology, and good thermal stability (Cundy CS, Cox P A. The Hydrothermal Synthesis of Zeolites: Precursors, Intermediates and Reaction Mechanism[J]. Microporous and Mesoporous Materials, 2005, 82(1-2):1-78). The synthesis conditions for zeolites are relatively broad. MFI-type zeolites can still be formed by adjusting the basicity, template concentration, reaction time, type of template, and reaction temperature to a certain extent. However, the morphology of the zeolite and the growth of different crystal faces will be affected (Bonilla G, Díaz I, Tsapatsis M, et al. Zeolite (MFI) Crystal Morphology Control Using Organic Structure-Directing Agents[J]. Chemistry of Materials, 2004, 16(26): 5697-5705). In recent years, many green methods for synthesizing zeolites have been developed, such as template-free and solvent-free methods (Meng X, Xiao FS. Green Routes for Synthesis of Zeolites[J]. Chemical Reviews, 2013, 114(2): 1521-1543). The development of these methods provides favorable conditions for the better industrial application of MFI zeolites.

[0005] ZSM-5 molecular sieves, as an important heterogeneous catalyst, have been widely used in industrial refining for xylene isomerization, catalytic cracking, toluene disproportionation, methanol-to-gasoline conversion, lubricating oil dewaxing, methanol-to-propylene, and methanol-to-aromatics processes. In the fine chemical industry, they have achieved excellent catalytic effects in reactions such as the synthesis of methyl tert-butyl ether from methanol and isobutylene, and the synthesis of 1,4-dioxane from diethylene glycol. When other metal atoms are added to the zeolite framework, zeolites also exhibit excellent catalytic effects in other areas. For example, TS-1 with a titanium-silicon framework has achieved large-scale industrial application in reactions such as the ammonium oximeation of cyclohexanone and the hydroxylation of phenol.

[0006] Currently, many scientists have adopted novel template-guided synthesis of ZSM-5 molecular sieves, but the variety of morphologies obtained is still limited and the cost of the products is relatively high. Therefore, it is still necessary to design and study new synthetic strategies. Summary of the Invention

[0007] 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 application. This ZSM-5 molecular sieve is a hierarchical porous ZSM-5 molecular sieve with a spindle-shaped morphology, which, when applied to the olefin production reaction of oxygen-containing compounds, exhibits high reactant conversion and product selectivity.

[0008] To achieve the above objectives, the present invention provides a ZSM-5 molecular sieve, wherein the molecular sieve has a morphology of spindle-shaped particles;

[0009] The molecular sieve has an aspect ratio of 1-3.5 and a height of 0.5-10 micrometers.

[0010] A second aspect of this invention provides a method for preparing ZSM-5 molecular sieves, the method comprising the following steps:

[0011] A mixture containing an aluminum source, an alkali source, a silicon source, water, and a structure-directing agent is crystallized.

[0012] The structure-directing agent has the structure shown in formula (1), (CH3)2N-(CH2)6-[N + (CH3)2(CH2)6] n N(CH3)2[Br - ] n Equation (1), where 1≤n≤4.

[0013] In existing technologies, traditional ZSM-5 molecular sieves are typically coffin-shaped particles with large sizes and no hierarchical pores, resulting in significant mass transfer resistance in catalytic reactions and hindering the transport and diffusion of substances. This invention synthesizes a hierarchical ZSM-5 molecular sieve with a spindle-shaped morphology using a specific structure-directing agent. This sieve is applied to the production of olefins from oxygen-containing compounds, particularly in the selective production of propylene from methanol, exhibiting high reactant conversion rates and product (propylene) selectivity.

[0014] 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 the reaction of oxygen-containing compounds to olefins.

[0015] The beneficial effects of the present invention through the above technical solution include:

[0016] 1. The spindle-shaped ZSM-5 molecular sieve provided by the present invention is suitable for the reaction of oxygen-containing compounds to olefins, especially for the selective production of propylene from methanol, and has high reactant conversion rate and product (propylene) selectivity.

[0017] 2. The ZSM-5 molecular sieve preparation method of this invention utilizes a novel structure-directing agent to obtain a hierarchical porous ZSM-5 molecular sieve with a spindle-shaped morphology. Furthermore, the preparation method of the ZSM-5 molecular sieve described in this invention is simple, requires minimal equipment, and has excellent prospects for industrial application. Attached Figure Description

[0018] Figure 1 These are the XRD patterns of the ZSM-5 molecular sieves prepared in Examples 1-4;

[0019] Figure 2 The XRD pattern of the ZSM-5 molecular sieve prepared in Comparative Example 1 is shown.

[0020] Figure 3 The XRD pattern of the ZSM-5 molecular sieve prepared in Comparative Example 2 is shown below.

[0021] Figure 4-9 These are scanning electron microscope images of the ZSM-5 molecular sieves prepared in the examples and comparative examples. Detailed Implementation

[0022] 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.

[0023] In one aspect, the present invention provides a ZSM-5 molecular sieve, wherein the molecular sieve has a morphology of spindle-shaped particles;

[0024] The molecular sieve has an aspect ratio of 1-3.5 and a height of 0.5-10 micrometers.

[0025] According to the present invention, preferably, the molecular sieve has an aspect ratio of 1.5-3 and a height of 1.5-6 micrometers.

[0026] The aspect ratio and height of the molecular sieve described in this invention were obtained by scanning electron microscopy.

[0027] The secondary particles of the molecular sieve described in this invention are formed by the stacking of primary particles. Preferably, the molecular sieve is formed by the stacking of nanocrystals aligned along a spindle-shaped axis.

[0028] Preferably, the average particle size of the nanocrystals is less than 100 nm, and more preferably 40-80 nm.

[0029] The average particle size of the nanocrystals described in this invention was determined by scanning electron microscopy.

[0030] According to the present invention, preferably, the micropore volume of the molecular sieve is 0.1-0.25 cm³. 3 / g, preferably 0.1-0.16cm 3 / g; mesoporous pore volume is 0.1-0.3cm³ 3 / g, preferably 0.15-0.25cm 3 / g.

[0031] The micropore volume and mesopore volume of the molecular sieve described in this invention were determined by nitrogen adsorption-desorption method.

[0032] According to the present invention, preferably, the specific surface area of ​​the molecular sieve is 450-600 m². 2 / g, preferably 500-540m 2 / g.

[0033] The specific surface area of ​​the molecular sieve described in this invention was determined by nitrogen adsorption-desorption method.

[0034] According to the present invention, preferably, the SiO2 / Al2O3 molar ratio of the molecular sieve is 20-300:1, more preferably 40-200:1.

[0035] The SiO2 / Al2O3 molar ratio of the molecular sieve described in this invention is determined by the feeding ratio method.

[0036] A second aspect of this invention provides a method for preparing ZSM-5 molecular sieves, the method comprising the following steps:

[0037] A mixture containing an aluminum source, an alkali source, a silicon source, water, and a structure-directing agent is crystallized.

[0038] The structure-directing agent has the structure shown in formula (1), (CH3)2N-(CH2)6-[N + (CH3)2(CH2)6] n N(CH3)2[Br - ] n Equation (1), where 1≤n≤4.

[0039] According to the present invention, preferably, 1 ≤ n ≤ 4, and more preferably, 2 ≤ n ≤ 4. For example, 1, 2, 3, 4. When n is greater than 4, the system has higher capability, and the structure directing agent is difficult to direct to the synthesis of molecular sieves.

[0040] According to the present invention, preferably, the molar ratio of aluminum source, alkali source, silicon source and water is (0.005-0.05):(0.3-0.6):(0.07-2):(40-80), more preferably (0.01-0.03):(0.3-0.5):(0.8-1.5):(50-70), wherein the aluminum source is calculated as Al2O3 and the silicon source is calculated as SiO2. This preferred embodiment facilitates the directed synthesis of ZSM-5 molecular sieves with a spindle-shaped morphology using the structure-directing agent described in this invention.

[0041] According to the present invention, preferably, the mass ratio of the structure-directing agent to the silicon source is 0.5-2:1, more preferably 0.7-1.2:1, wherein the silicon source is SiO2. When the amount of structure-directing agent is below the specified range, the ZSM-5 molecular sieve is not fully formed, and it is also not conducive to the formation of mesopores. When the amount of structure-directing agent is above the specified range, the concentration of structure-directing agent is too high, which is not conducive to the large-scale aggregation of inorganic precursors around the template agent ammonium ions, and is not conducive to the formation of micropores.

[0042] According to the present invention, preferably, the crystallization conditions include: a temperature of 120-200℃, more preferably 140-180℃; and a time of 20-100 hours, more preferably 48-72 hours. Using this preferred embodiment, the relatively high temperature allows the molecular sieve to crystallize more quickly, shortening the crystallization time and reducing the waste of time and electricity, while avoiding the disadvantage of low crystallinity of the molecular sieve.

[0043] According to the present invention, preferably, the crystallization is carried out under stirring conditions.

[0044] The present invention does not impose any particular limitation on the stirring conditions, which can be appropriately selected according to specific circumstances. Preferably, the stirring speed is 5-50 rpm.

[0045] The present invention allows for a wide range of aluminum sources, as long as aluminum can be provided. Preferably, the aluminum source is selected from at least one of boehmite, aluminum isopropoxide, and sodium aluminate.

[0046] The present invention allows for a wide range of silicon sources, which can be various silicon sources conventionally used in the art. Specifically, the silicon source is an organosilicon source and / or an inorganic silicon source. Preferably, the silicon source is selected from at least one of silica sol, silica fume, and tetraethyl orthosilicate.

[0047] The present invention allows for a wide range of alkaline sources, including various alkaline sources commonly used in the art. NaOH is used as an example in this embodiment.

[0048] In this invention, there is no particular limitation on the order in which the aluminum source, alkali source, silicon source, water, and structure directing agent are added; they can be added together or separately. To enhance mixing uniformity, preferably, the aluminum source, alkali source, water, and structure directing agent are mixed first, and then the silicon source is added.

[0049] According to the present invention, preferably, the method further includes: subjecting the crystallized product to a first drying to obtain ZSM-5 molecular sieve.

[0050] According to the present invention, preferably, the conditions for the first drying include: a temperature of 40-150°C, preferably 60-100°C; and a time of 8-30 hours, preferably 10-20 hours.

[0051] Preferably, the method further includes: performing solid-liquid separation and a first washing before the crystallized product is first dried.

[0052] The present invention does not have any particular limitations on the solid-liquid separation and the first washing, which can be carried out in accordance with conventional technical means in the field, and will not be described in detail here.

[0053] Preferably, a method for preparing ZSM-5 molecular sieve includes the following steps:

[0054] A mixture containing an aluminum source, an alkali source, a silicon source, water, and a structure-directing agent is crystallized.

[0055] The structure-directing agent is obtained by reacting 1,6-dibromohexane with N,N,N',N'-tetramethyl-1,6-hexanediamine. The conditions and specific procedures for the reaction of 1,6-dibromohexane with N,N,N',N'-tetramethyl-1,6-hexanediamine are described below.

[0056] According to the present invention, preferably, the method for preparing the structure-directing agent includes: reacting 1,6-dibromohexane with N,N,N',N'-tetramethyl-1,6-hexanediamine in the presence of a solvent to obtain a solid product, and then washing and drying the solid product.

[0057] In this invention, obtaining the solid product is considered to have synthesized the structure-directing agent of this invention.

[0058] According to the present invention, preferably, the reaction conditions include: a temperature of 70-100°C, more preferably 80-90°C; and a time of 10-20 hours, more preferably 10-15 hours.

[0059] According to the present invention, preferably, the reaction is carried out under stirring conditions.

[0060] The present invention does not impose any particular limitation on the stirring speed and time, which can be appropriately selected according to the specific circumstances, as long as the purpose of achieving a full reaction can be achieved.

[0061] According to the present invention, preferably, the molar ratio of 1,6-dibromohexane and N,N,N',N'-tetramethyl-1,6-hexanediamine is 1:1.1-3, more preferably 1:1.2-2. This preferred embodiment allows the two organic molecules to react fully, thereby forming a multi-quaternary ammonium salt compound. Simultaneously, the slight excess of N,N,N',N'-tetramethyl-1,6-hexanediamine ensures that the final product has tertiary amines at both ends, avoiding bromine atoms, which is more conducive to guiding the synthesis of hierarchical porous ZSM-5 molecular sieves in subsequent work.

[0062] According to the present invention, preferably, the mass ratio of the total mass of the reactants and solvent to the mass of 1,6-dibromohexane is 2-10:1, more preferably 3-6:1.

[0063] The present invention allows for a wide range of solvent selection; any solvent that does not react with 1,6-dibromohexane and N,N,N',N'-tetramethyl-1,6-hexanediamine can be used. Preferably, the solvent is acetonitrile and / or toluene.

[0064] More preferably, the solvent is acetonitrile and toluene.

[0065] Preferably, the volume ratio of acetonitrile to toluene is 0.5-2:1.

[0066] Preferably, the method further includes: performing solid-liquid separation on the reaction products to obtain solid products.

[0067] This invention does not particularly limit the method of solid-liquid separation, and commonly used techniques in the art can be employed. Preferred methods are rotary evaporation or filtration.

[0068] The present invention does not impose any particular limitations on the conditions for rotary evaporation or filtration, and can refer to the methods commonly used in the art. The present invention will not elaborate further here.

[0069] Preferably, the washing process of the present invention uses anhydrous diethyl ether as the washing agent, and the washing conditions are such that there are essentially no unreacted reactants in the washing agent.

[0070] The present invention does not particularly limit the conditions for the second drying; simply drying the material after the second washing is sufficient. Preferably, the conditions for the second drying include: a temperature of 50-70°C and a time of 3-6 hours.

[0071] In this invention, the terms "first" and "second" do not limit the operations, but are only used to distinguish operations performed at different stages.

[0072] The ZSM-5 molecular sieve provided by this invention has a wide range of applications, including heterogeneous catalysis, adsorption, separation, and ion exchange. The inventors have discovered that it exhibits significantly better performance in the production of olefins from oxygen-containing compounds, hence the third aspect of this invention.

[0073] 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 the reaction of oxygen-containing compounds to olefins, preferably in the selective reaction of methanol to propylene.

[0074] According to the present invention, preferably, the reaction conditions include: a temperature of 300-600°C, more preferably 450-500°C; a pressure of 0.01-0.06 MPa, more preferably 0.02-0.04 MPa; and a weight hourly space velocity of 1-7 h⁻¹. -1 Preferably 2-5h -1 .

[0075] The reaction described in this invention can be a gas-phase reaction or a liquid-phase reaction. Preferably, the reaction described in this invention is a liquid-phase reaction.

[0076] Preferably, the reactants of the reaction are a mixture of methanol and water.

[0077] Preferably, the mass ratio of methanol to water is 1:0.5-3, and more preferably 1:0.8-2.

[0078] In a preferred embodiment, the ZSM-5 molecular sieve is first converted into an H-type before use.

[0079] The present invention does not specifically limit the method for converting the molecular sieve into the H-type; methods commonly used in the field can be referred to.

[0080] According to a specific embodiment of the present invention, ZSM-5 molecular sieve is reacted with ammonium chloride solution, and then solid-liquid separation, drying and calcination are performed to obtain H-ZSM-5 molecular sieve.

[0081] The present invention does not have a particular limitation on the number of times the above-mentioned reaction, solid-liquid separation, drying and calcination operations are performed. They can be performed once or multiple times, as long as the sodium ion content in the molecular sieve is less than 5 wt%.

[0082] The present invention does not particularly limit the method of solid-liquid separation, and it can be carried out in accordance with conventional technical means in the field, which will not be described in detail here.

[0083] The present invention does not impose any particular limitation on the drying conditions, which can be carried out in accordance with conventional methods in the art, and will not be described in detail here.

[0084] The present invention does not particularly limit the calcination conditions, and can be carried out according to conventional methods in the art. Preferably, the calcination conditions include: a temperature of 450-650℃ and a time of 4-10 hours.

[0085] The present invention does not impose a particular limitation on the particle size of the H-ZSM-5 molecular sieve, which can be appropriately selected according to the reaction system. Preferably, the particle size of the H-ZSM-5 molecular sieve is 20-40 mesh.

[0086] The present invention does not particularly limit the method for obtaining the H-ZSM-5 molecular sieve with the specified particle size, and conventional techniques in the art can be used. Preferably, the present invention employs a tableting and sieving method.

[0087] The present invention will be described in detail below through embodiments.

[0088] In the method of this invention, XRD data were obtained using a Bruker AXS D8 Advance X-ray diffractometer (Germany). The test conditions were as follows: voltage 40 kV, current 80 mA, CuKα target, and scanning speed 15° / min. -1 The scanning range 2θ is 5-50°.

[0089] In the method of this invention, the scanning electron microscope (SEM) image was obtained by a HITACHI S4800 field emission scanning electron microscope from Japan, and the test conditions were as follows: voltage 3kV, current 50mA.

[0090] In the method of this invention, the nitrogen adsorption-desorption test was measured on a Micromeritics TriStar3000 instrument, using liquid nitrogen to cool to 75K, and degassing at 200℃ for 3 hours before analysis at a pressure of 0.67Pa.

[0091] The reagents used in the following examples are commercially available and of analytical grade.

[0092] Preparation Example 1

[0093] Preparation of the structure-directing agent described in this invention

[0094] 1,6-dibromohexane and N,N,N ’ N'-Tetramethyl-1,6-hexanediamine was added to a mixed solution of acetonitrile / toluene at a molar ratio of 1:1.2 and a volume ratio of 1:1,6-dibromohexane at a mass ratio of 4.5:1. The mixture was stirred at 82°C for 12 hours. After the reaction system cooled, a white solid was obtained by rotary evaporation or filtration. The solid was washed three times with anhydrous diethyl ether and dried at 60°C for 5 hours to obtain the structure-directing agent. The structural formula is: (CH3)2N-(CH2)6-[N + (CH3)2(CH2)6]n N(CH3)2[Br - ] n , 1≤n≤4.

[0095] Example 1

[0096] Boehmite (70 wt% Al2O3), sodium hydroxide, and the structure-directing agent prepared in Preparation Example 1 were added to water and stirred for 1.5 hours; then silica sol (40 wt% SiO2) was added dropwise and stirred for 2 hours to obtain a gel mixture. The boehmite was calculated as Al2O3, the silica sol as SiO2, the molar ratio of Al2O3:NaOH:SiO2:H2O was 0.01:0.4:1:50, and the mass ratio of the structure-directing agent to SiO2 was 1:1.1.

[0097] The gel mixture obtained above was subjected to crystallization treatment with a stirring speed of 20 rpm. The crystallization temperature was 170℃, and the crystallization time was 60 hours. The crystallized product was centrifuged, washed, and dried at 90℃ for 12 hours. This yielded the ZSM-5 molecular sieve with a spindle-shaped morphology as described in this invention. The composition and characteristic parameters of the ZSM-5 molecular sieve are shown in Table 1.

[0098] The XRD pattern of ZSM-5 molecular sieve is as follows: Figure 1 As shown, from Figure 1 As can be seen, characteristic diffraction peaks of ZSM-5 appeared at 7.9°, 8.9°, 23.4°, and 24.2°, proving that the synthesized material is a ZSM-5 molecular sieve. The synthesized silica-alumina molecular sieve has the peak shape of ZSM-5 molecular sieve, with relatively sharp and significant diffraction peaks.

[0099] Figure 4 This is a scanning electron microscope image of ZSM-5 molecular sieve. Figure 4 As shown, the molecular sieve particles are spindle-shaped particles, formed by crystals with an average particle size of 50 nanometers arranged and stacked along the spindle axis.

[0100] Example 2

[0101] Boehmite (70 wt% Al2O3), sodium hydroxide, and the structure-directing agent prepared in Preparation Example 1 were added to water and stirred for 1.5 hours; then silica sol (40 wt% SiO2) was added dropwise and stirred for 2 hours to obtain a gel mixture. The boehmite was calculated as Al2O3, the silica sol as SiO2, the molar ratio of Al2O3:NaOH:SiO2:H2O was 0.01:0.5:1:70, and the mass ratio of the structure-directing agent to SiO2 was 1:1.

[0102] The gel mixture obtained above was subjected to crystallization treatment with a stirring speed of 20 rpm. The crystallization temperature was 150℃, and the crystallization time was 72 hours. The crystallized product was centrifuged, washed, and dried at 100℃ for 10 hours. This yielded the ZSM-5 molecular sieve with a spindle-shaped morphology as described in this invention. The composition and characteristic parameters of the ZSM-5 molecular sieve are shown in Table 1.

[0103] The XRD pattern of ZSM-5 molecular sieve is as follows: Figure 1 As shown, from Figure 1 As can be seen, characteristic diffraction peaks of ZSM-5 appeared at 7.9°, 8.9°, 23.4°, and 24.2°, proving that the synthesized material is a ZSM-5 molecular sieve. The synthesized silica-alumina molecular sieve has the peak shape of ZSM-5 molecular sieve, with relatively sharp and significant diffraction peaks.

[0104] Figure 5 This is a scanning electron microscope image of ZSM-5 molecular sieve. Figure 5 As shown, the molecular sieve particles are spindle-shaped particles, formed by crystals with an average particle size of 80 nanometers arranged and stacked along the spindle axis.

[0105] Example 3

[0106] Boehmite (70 wt% Al2O3), sodium hydroxide, and the structure-directing agent prepared in Preparation Example 1 were added to water and stirred for 1.5 hours; then silica sol (40 wt% SiO2) was added dropwise and stirred for 2 hours to obtain a gel mixture. The boehmite was calculated as Al2O3, the silica sol as SiO2, the molar ratio of Al2O3:NaOH:SiO2:H2O was 0.01:0.4:1.5:60, and the mass ratio of the structure-directing agent to SiO2 was 1:1.4.

[0107] The gel mixture obtained above was subjected to crystallization treatment with a stirring speed of 20 rpm. The crystallization temperature was 150℃, and the crystallization time was 72 hours. The crystallized product was centrifuged, washed, and dried at 100℃ for 10 hours. This yielded the ZSM-5 molecular sieve with a spindle-shaped morphology as described in this invention. The composition and characteristic parameters of the ZSM-5 molecular sieve are shown in Table 1.

[0108] The XRD pattern of ZSM-5 molecular sieve is as follows: Figure 1 As shown, from Figure 1 As can be seen, characteristic diffraction peaks of ZSM-5 appeared at 7.9°, 8.9°, 23.4°, and 24.2°, proving that the synthesized material is a ZSM-5 molecular sieve. The synthesized silica-alumina molecular sieve has the peak shape of ZSM-5 molecular sieve, with relatively sharp and significant diffraction peaks.

[0109] Figure 6This is a scanning electron microscope image of ZSM-5 molecular sieve. Figure 6 As shown, the molecular sieve particles are spindle-shaped particles, formed by crystals with an average particle size of 80 nanometers arranged and stacked along the spindle axis.

[0110] Example 4

[0111] Boehmite (70% by weight Al2O3), sodium hydroxide, and the structure-directing agent prepared in Preparation Example 1 were added to water and stirred for 1.5 hours. Then, silica sol (containing 40% by weight SiO2) was added dropwise and stirred for 2 hours to obtain a gel mixture. The boehmite was calculated as Al2O3, the silica sol as SiO2, the molar ratio of Al2O3:NaOH:SiO2:H2O was 0.03:0.4:1.2:60, and the mass ratio of the structure-directing agent to SiO2 was 1:1.2.

[0112] The gel mixture obtained above was subjected to crystallization treatment with a stirring speed of 20 rpm. The crystallization temperature was 150℃, and the crystallization time was 72 hours. The crystallized product was centrifuged, washed, and dried at 100℃ for 10 hours. This yielded the ZSM-5 molecular sieve with a spindle-shaped morphology as described in this invention. The composition and characteristic parameters of the ZSM-5 molecular sieve are shown in Table 1.

[0113] The XRD pattern of ZSM-5 molecular sieve is as follows: Figure 1 As shown, from Figure 1 As can be seen, characteristic diffraction peaks of ZSM-5 appeared at 7.9°, 8.9°, 23.4°, and 24.2°, proving that the synthesized material is a ZSM-5 molecular sieve. The synthesized silica-alumina molecular sieve has the peak shape of ZSM-5 molecular sieve, with relatively sharp and significant diffraction peaks.

[0114] Figure 7 This is a scanning electron microscope image of ZSM-5 molecular sieve. Figure 7 As shown, the molecular sieve particles are spindle-shaped particles, formed by crystals with an average particle size of 80 nanometers arranged and stacked along the spindle axis.

[0115] Comparative Example 1

[0116] The procedure is carried out according to the method of Example 1, except that...

[0117] The molar ratio of pseudoboehmite:NaOH:silica sol:H2O was 0.01:0.4:1:33, and the mass ratio of structure-directing agent to silica sol was 1:1.1. The resulting product, its composition and characteristic parameters are shown in Table 1.

[0118] The XRD pattern of the product is as follows Figure 2 As shown, from Figure 2As can be seen, the XRD pattern shows only a relatively wide bulge, without the diffraction peaks corresponding to ZSM-5 crystals, indicating that it is not a ZSM-5 molecular sieve.

[0119] Figure 8 This is a scanning electron microscope image of Comparative Example 1. Figure 8 As shown, the product is amorphous particles.

[0120] This product is not a molecular sieve and does not possess catalytic properties.

[0121] Comparative Example 2

[0122] Boehmite (70% by weight Al2O3), sodium hydroxide, and tetrapropylammonium hydroxide (TPAOH, 40% by weight aqueous solution) were added to water and stirred for 1.5 hours. Then, silica sol (containing 40% by weight SiO2) was added dropwise and stirred for 2 hours to obtain a gel mixture. The molar ratio of Al2O3:TPAOH:NaOH:SiO2:H2O was 0.03:0.4:1.2:60, where the boehmite was calculated as Al2O3, the silica sol as SiO2, and the total molar ratio was 0.03:0.4:1.2:60.

[0123] The gel mixture obtained above was subjected to crystallization treatment with a stirring speed of 20 rpm. The crystallization temperature was 150℃, and the crystallization time was 72 hours. The crystallized product was centrifuged, washed, and dried at 100℃ for 10 hours. This yielded the ZSM-5 molecular sieve with a spindle-shaped morphology as described in this invention. The composition and characteristic parameters of the ZSM-5 molecular sieve are shown in Table 1.

[0124] The XRD pattern of ZSM-5 molecular sieve is as follows: Figure 3 As shown, from Figure 3 It can be seen that the synthesized silica-alumina molecular sieve has the peak shape of ZSM-5 molecular sieve, with relatively sharp and obvious diffraction peaks. Characteristic diffraction peaks of ZSM-5 appeared at 7.9°, 8.9°, 23.4°, and 24.2°, proving that the synthesized material is ZSM-5 molecular sieve.

[0125] Figure 9 This is a scanning electron microscope image of ZSM-5 molecular sieve. Figure 9 As shown, the molecular sieve particles are coffin-shaped with an average particle size of 20 micrometers.

[0126] Table 1

[0127]

[0128] Test Example 1

[0129] The ZSM-5 molecular sieves from Examples 1 and 2 (Comparative Example 2) were used as catalysts in the methanol-to-propylene reaction. Before the reaction, they were first converted to the H-form. The molecular sieve powders obtained from Examples 1 and 2 (Comparative Example 2) were reacted with ammonium chloride solution (1 mol / L concentration) (solid-liquid mass ratio 1:30) at 60°C with stirring for 2 hours. After solid-liquid separation, the mixture was dried at 80°C for 6 hours and calcined at 550°C for 6 hours. This process of reaction, solid-liquid separation, drying, and calcination was repeated three times to obtain solid H-ZSM-5 molecular sieves. The H-ZSM-5 molecular sieves were then pressed into tablets and sieved to 20-40 mesh.

[0130] The evaluation was conducted in a fixed-bed reactor using a mixture of methanol and water at a molar ratio of 1:2. The reaction temperature in the ZSM-5 molecular sieve bed was 500℃, the reaction pressure was 0.02 MPa, and the methanol liquid hourly space velocity was 4 h⁻¹. -1 The raw materials were passed through an H-ZSM-5 molecular sieve bed to react and produce propylene. Specific results are shown in Table 2. In Table 2, the propylene yield and methanol conversion rate refer to the propylene yield and methanol conversion rate at the points where the propylene yield was at its maximum during the reaction process.

[0131] Table 2

[0132] catalyst Methanol conversion rate, wt% Propylene yield, wt% Example 1 99 46.81 Example 2 99 47.05 Example 3 99 47.65 Example 4 98 43.36 Comparative Example 2 99 42.38

[0133] As can be seen from the results in Table 2, applying the ZSM-5 molecular sieve of the present invention to the selective methanol-to-propylene reaction results in significantly higher methanol conversion and propylene selectivity.

[0134] 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 combining the 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 the morphology of spindle-shaped particles; The molecular sieve has an aspect ratio of 1-3.5 and a height of 0.5-10 micrometers; The preparation method of the ZSM-5 molecular sieve includes the following steps: crystallizing a mixture containing an aluminum source, an alkali source, a silicon source, water and a structure directing agent; The structure-directing agent has the structure shown in formula (1), (CH3)2N-(CH2)6-[N + (CH3)2(CH2)6] n N(CH3)2[Br - ] n Equation (1), where 1≤n≤4.

2. The molecular sieve according to claim 1, wherein, The molecular sieve has an aspect ratio of 1.5-3 and a height of 1.5-6 micrometers.

3. The molecular sieve according to claim 1, wherein, The molecular sieve is formed by stacking nanocrystals arranged along a spindle-shaped axis; The average particle size of the nanocrystals is less than 100 nm.

4. The molecular sieve according to claim 3, wherein, The average particle size of the nanocrystals is 40-80 nm.

5. The molecular sieve according to any one of claims 1-4, wherein, The molecular sieve has a micropore volume of 0.1-0.25 cm³. 3 / g; mesoporous pore volume is 0.1-0.3cm³ 3 / g.

6. The molecular sieve according to claim 5, wherein, The molecular sieve has a micropore volume of 0.1-0.16 cm³. 3 / g; mesoporous pore volume is 0.15-0.25cm³ 3 / g.

7. The molecular sieve according to any one of claims 1-4, wherein, The specific surface area of ​​the molecular sieve is 450-600 m². 2 / g.

8. The molecular sieve according to claim 7, wherein, The specific surface area of ​​the molecular sieve is 500-540 m². 2 / g.

9. The molecular sieve according to any one of claims 1-4, wherein, The SiO2 / Al2O3 molar ratio of the molecular sieve is 20-300:

1.

10. The molecular sieve according to claim 9, wherein, The SiO2 / Al2O3 molar ratio of the molecular sieve is 40-200:

1.

11. A method for preparing ZSM-5 molecular sieve, the method comprising the following steps: A mixture containing an aluminum source, an alkali source, a silicon source, water, and a structure-directing agent is crystallized. The structure-directing agent has the structure shown in formula (1), (CH3)2N-(CH2)6-[N + (CH3)2(CH2)6] n N(CH3)2[Br - ] n Equation (1), where 1≤n≤4.

12. The method according to claim 11, wherein, The molar ratio of aluminum source, alkali source, silicon source and water is (0.005-0.05):(0.3-0.6):(0.07-2):(40-80), wherein the aluminum source is calculated as Al2O3 and the silicon source is calculated as SiO2.

13. The method according to claim 12, wherein, The molar ratio of aluminum source, alkali source, silicon source and water is (0.01-0.03):(0.3-0.5):(0.8-1.5):(50-70), wherein the aluminum source is calculated as Al2O3 and the silicon source is calculated as SiO2.

14. The method according to claim 11, wherein, The mass ratio of the structure directing agent to the silicon source is 0.5-2:1, and the silicon source is SiO2.

15. The method according to claim 14, wherein, The mass ratio of the structure directing agent to the silicon source is 0.7-1.2:1, and the silicon source is SiO2.

16. The method according to claim 11, wherein, The crystallization conditions include: a temperature of 120-200℃ and a time of 20-100 hours.

17. The method according to claim 16, wherein, The crystallization conditions include: a temperature of 140-180℃ and a time of 48-72 hours.

18. The method according to claim 11, wherein, The crystallization is carried out under stirring conditions; The stirring speed is 5-50 rpm.

19. The method according to any one of claims 11-18, wherein, The aluminum source is selected from at least one of boehmite, aluminum isopropoxide and sodium aluminate; The silicon source is selected from at least one of silica sol, silica, and tetraethyl orthosilicate.

20. The method according to any one of claims 11-18, wherein, The method also includes: subjecting the crystallized product to a first drying process to obtain ZSM-5 molecular sieve; The first drying conditions include: a temperature of 40-150℃ and a time of 8-30 hours.

21. The method according to any one of claims 11-18, wherein, The method for preparing the structure-directing agent includes: reacting 1,6-dibromohexane with N,N,N',N'-tetramethyl-1,6-hexanediamine in the presence of a solvent to obtain a solid product, and then washing and drying the solid product.

22. The method according to claim 21, wherein, The reaction conditions include: a temperature of 70-100℃ and a time of 10-20 hours.

23. The method according to claim 22, wherein, The reaction conditions include: a temperature of 80-90℃ and a time of 10-15 hours.

24. The method according to claim 21, wherein, The reaction was carried out under stirring.

25. The method according to claim 21, wherein, The molar ratio of 1,6-dibromohexane to N,N,N',N'-tetramethyl-1,6-hexanediamine is 1:1.1-3.

26. The method of claim 25, wherein, The molar ratio of 1,6-dibromohexane to N,N,N',N'-tetramethyl-1,6-hexanediamine is 1:1.2-2.

27. The method according to claim 21, wherein, The total mass ratio of reactants and solvent to 1,6-dibromohexane is 2-10:

1.

28. The method according to claim 27, wherein, The total mass ratio of reactants and solvent to 1,6-dibromohexane is 3-6:

1.

29. The method according to claim 21, wherein, The solvent is acetonitrile and / or toluene.

30. The method according to claim 21, wherein, The second drying conditions include a temperature of 50-70°C and a time of 3-6 hours.

31. The use of the ZSM-5 molecular sieve according to any one of claims 1-10 or the ZSM-5 molecular sieve prepared by the preparation method according to any one of claims 11-30 in the reaction of oxygen-containing compounds to olefins.

32. The application according to claim 31, wherein, Application of the ZSM-5 molecular sieve in the selective production of propylene from methanol.

33. The application according to claim 31, wherein, The reaction conditions include: a temperature of 300-600℃; a pressure of 0.01-0.06 MPa; and a mass hourly space velocity of 1-7 h⁻¹. -1 .

34. The application according to claim 33, wherein, The reaction conditions include: a temperature of 450-500℃; a pressure of 0.02-0.04 MPa; and a mass hourly space velocity of 2-5 h⁻¹. -1 .

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