A ZSM-5 molecular sieve, its preparation method and application

Abstract

This invention discloses a ZSM-5 molecular sieve, its preparation method, and its applications. The molecular sieve has a morphology consisting of particles formed by perpendicularly intersecting elliptical cylinders, with a particle size of 1.2–8.0 μm. The preparation method of the ZSM-5 molecular sieve includes the following steps: crystallizing a mixture of an aluminum source, a silicon source, water, an alkali source, and a structure-directing agent; wherein the structure-directing agent is a quaternary ammonium salt dimer. This molecular sieve is suitable for heterogeneous catalysis, adsorption, separation, and ion exchange, and is particularly suitable for methanol-to-aromatics reactions, exhibiting high conversion rates and target product selectivity.

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 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 was 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 SiSiC Ceramic Monoliths for Catalytic Applications[D].PhD thesis, University of Erlangen-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 F-S. 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] Regarding the formation mechanism of ZSM-5 molecular sieves, the generally accepted process is that the template agent first guides nucleation, and then the crystal nuclei aggregate and grow into macroscopic crystals. Chang et al. believe that in the early stage of MFI-type zeolite crystallization, TPA hydrated spheres are formed first, and then the silica in the gel isomorphically replaces the water molecules in the hydrated spheres. Under alkaline conditions, nucleation is achieved through continuous formation and dissociation of Si-O-Si (Chang CD, Bell A T. Studies on the Mechanism of ZSM-5 Formation[J]. Catalysis Letters, 1991, 8(5-6): 305-316). Subsequently, Burkett et al. used techniques such as 29SiMAS NMR to prove the existence of TPA hydrated spheres and further refined this mechanism (Burkett SL, Davis ME. Mechanisms of Structure Direction in the Synthesis of Pure-SilicaZeolites.1. Synthesis of TPA / Si-ZSM-5[J]. Chemistry of Materials, 1995, 7(5): 920-928). Under the action of van der Waals forces and hydrogen bonds, the hydrated spheres continuously overlap and release water molecules, and then the TPA-SiO2 composite structure is formed. These composite structures aggregate and nucleate each other in the solution. As the crystallization time increases, the crystal nuclei continuously grow to form large crystals.

[0006] ZSM-5 molecular sieve, as an important heterogeneous catalyst, has been widely used in the industrial refining field for xylene isomerization, catalytic cracking, toluene disproportionation, methanol-to-gasoline conversion, lubricating oil dewaxing, and methanol-to-aromatics. In the fine chemical field, it has achieved good 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 good catalytic effects in other aspects. For example, TS-1 with added titanium-silicon framework has achieved large-scale industrial application in reactions such as cyclohexanone ammonium oximeation and phenol hydroxylation. Summary of the Invention

[0007] The technical problem to be solved by this invention is to provide a novel ZSM-5 molecular sieve, its preparation method, and its applications. This ZSM-5 molecular sieve is used in the methanol-to-aromatics reaction, exhibiting high conversion rate and selectivity for the target product (aromatics).

[0008] The first aspect of the present invention provides a ZSM-5 molecular sieve, which has a morphology of particles formed by perpendicularly intersecting elliptical cylinders, and the particle size is 1.2 to 8.0 μm, preferably 1.3 to 5.5 μm.

[0009] Furthermore, the ZSM-5 molecular sieve particles contain a main elliptical cylinder, which is the elliptical cylinder with the maximum height.

[0010] Furthermore, in the ZSM-5 molecular sieve particles, the height of the main elliptical cylinder is 1.2–8.0 μm, the major axis of the ellipse is 0.5–6.0 μm, and the minor axis is 0.3–4.0 μm. Preferably, the height of the main elliptical cylinder is 1.3–2.5 μm, the major axis of the ellipse is 0.8–2.0 μm, and the minor axis is 0.4–1.0 μm.

[0011] Furthermore, in the ZSM-5 molecular sieve particles, the height of the elliptical cylinders other than the main elliptical cylinder is 0.5–7.0 μm, the major axis is 0.1–5.0 μm, and the minor axis is 50–3000 nm. Preferably, the height of the other elliptical cylinders is 0.5–2.0 μm, the major axis is 0.1–2.0 μm, and the minor axis is 80–1000 nm.

[0012] Furthermore, in the ZSM-5 molecular sieve particles, in addition to the main elliptical cylinder, there can be multiple other elliptical cylinders or quasi-elliptical cylinders, which are perpendicular to the main elliptical cylinder.

[0013] A second aspect of this invention provides a method for preparing ZSM-5 molecular sieves, comprising the following steps:

[0014] A mixture of aluminum source, alkali source, silicon source, water and structure guiding agent is subjected to crystallization treatment;

[0015] The structure-directing agent is a dimer tetraethyl quaternary ammonium salt with the molecular formula: [(CH3CH2)3N + -(CH2)6-N + (CH2CH3)3][Br - ]2.

[0016] Furthermore, the preparation method of the ZSM-5 molecular sieve is as follows: aluminum source, alkali source, structure directing agent and water are mixed evenly; then silicon source is added dropwise and mixed evenly to obtain a gel mixture; the mixture is crystallized to obtain the ZSM-5 molecular sieve.

[0017] Furthermore, the aluminum source is one or more of boehmite, aluminum isopropoxide, and sodium aluminate. The silicon source is one or more of silica sol, silica fume, and tetraethyl orthosilicate. The alkali source is sodium hydroxide.

[0018] Further, in the gel mixture, the aluminum source is calculated as Al2O3, the silicon source as SiO2, and the alkali source as NaOH. The molar ratio of Al2O3:NaOH:structure directing agent:SiO2:H2O is (0.02-0.08):(1.5-3.0):(0.7-2.0):(5-12):(200-500), preferably (0.02-0.05):(1.5-2.5):(0.7-1.5):(5-8):(300-400). H2O represents the total water content in the preparation method.

[0019] Furthermore, the crystallization conditions are as follows: crystallization temperature is 120–200°C, and crystallization time is 20–100 hours.

[0020] Furthermore, the crystallization is dynamic crystallization, carried out under stirring conditions, wherein the rotation speed is 5 to 50 rpm.

[0021] Furthermore, after the crystallization process, the solid, namely the ZSM-5 molecular sieve, can be separated from the obtained mixture using any conventionally known solid-liquid separation method. After solid-liquid separation, washing and drying can be performed. The solid-liquid separation, washing, and drying can be carried out in any manner conventionally known in the art. Specifically, the solid-liquid separation can be performed, for example, by centrifugation. The washing can be performed, for example, using deionized water. The drying temperature is 40–150°C, preferably 60–100°C, and the drying time is 8–30 hours, preferably 10–20 hours.

[0022] The third aspect of the present invention provides a ZSM-5 molecular sieve obtained by the preparation method of the second aspect.

[0023] Furthermore, the ZSM-5 molecular sieve has a morphology of particles formed by perpendicularly intersecting elliptical cylinders, with a particle size of 1.2–8.0 μm, preferably 1.3–5.5 μm.

[0024] Furthermore, the ZSM-5 molecular sieve particles contain a main elliptical cylinder, which is the tallest elliptical cylinder.

[0025] Furthermore, in the ZSM-5 molecular sieve particles, the height of the main elliptical cylinder is 1.2–8.0 μm, the major axis of the ellipse is 0.5–6.0 μm, and the minor axis is 0.3–4.0 μm. Preferably, the height of the main elliptical cylinder is 1.3–2.5 μm, the major axis of the ellipse is 0.8–2.0 μm, and the minor axis is 0.4–1.0 μm.

[0026] Furthermore, in the ZSM-5 molecular sieve particles, the height of the elliptical cylinders other than the main elliptical cylinder is 0.5–7.0 μm, the major axis is 0.1–5.0 μm, and the minor axis is 50–3000 nm. Preferably, the height of the other elliptical cylinders is 0.5–2.0 μm, the major axis is 0.1–2.0 μm, and the minor axis is 80–1000 nm.

[0027] Furthermore, in the ZSM-5 molecular sieve particles, in addition to the main elliptical cylinder, there can be multiple other elliptical cylinders or quasi-elliptical cylinders, which are perpendicular to the main elliptical cylinder.

[0028] The fourth aspect of the present invention provides a ZSM-5 molecular sieve, as described in either the first or third aspect, for use in heterogeneous catalysis, adsorption, separation, and ion exchange, particularly suitable for methanol-to-aromatics reactions, with aromatics as the main target product.

[0029] Furthermore, the ZSM-5 molecular sieve is first converted to the H-form using ammonium chloride solution before use. ZSM-5 molecular sieve powder is mixed with ammonium chloride solution (concentration 0.2–2 mol / L) (solid-liquid mass ratio 1:10–1:100) and stirred at 40–80°C for 2–6 hours. After solid-liquid separation, solid ZSM-5 molecular sieve is obtained. This process is repeated 1–4 times to obtain the H-form ZSM-5 molecular sieve.

[0030] Furthermore, the H-type ZSM-5 molecular sieve is used in the methanol-to-aromatics reaction.

[0031] Furthermore, the application involves reacting the H-type ZSM-5 molecular sieve with the reactants in the presence of the sieve.

[0032] Furthermore, the H-type ZSM-5 molecular sieve is diluted with quartz sand at a weight ratio of 1:5 before the reaction.

[0033] Furthermore, the reaction conditions are as follows: reaction temperature of 300–500°C and volume hourly space velocity of 2–5 h⁻¹. -1 The process is carried out under normal pressure.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] 1. The ZSM-5 molecular sieve provided by the present invention has a novel morphology, with particles formed by the perpendicular intersection of elliptical cylinders.

[0036] 2. In the preparation method of ZSM-5 molecular sieve of the present invention, a specific structure directing agent, tetraethyl quaternary ammonium salt of dimer, is used to obtain ZSM-5 molecular sieve with a novel morphology. The preparation method of ZSM-5 molecular sieve of the present invention is simple, requires low equipment, and yields high product output; therefore, the present invention has good prospects for industrial application.

[0037] 3. The ZSM-5 molecular sieve provided by this invention is suitable for heterogeneous catalysis, adsorption, separation and ion exchange, and is particularly suitable for methanol to aromatics reaction, with high conversion rate and selectivity for target product (aromatics). Attached Figure Description

[0038] Figure 1 These are the XRD patterns of the ZSM-5 molecular sieves obtained in Examples 1-5 of this invention;

[0039] Figure 2 This is a scanning electron microscope (SEM) image of the ZSM-5 molecular sieve obtained in Example 1 of the present invention;

[0040] Figure 3 This is the XRD pattern of the material obtained in Comparative Example 1 of this invention;

[0041] Figure 4 This is a scanning electron microscope (SEM) image of the material obtained in Comparative Example 1 of the present invention;

[0042] Figure 5 This is a scanning electron microscope (SEM) image of the material obtained in Comparative Example 2 of the present invention. Detailed Implementation

[0043] The technical solution of the present invention will be further illustrated below with reference to the embodiments, but it is not limited to the following embodiments.

[0044] In the method of this invention, XRD data were obtained using a Bruker AXS D8 Advance X-ray diffractometer (Germany), under the following conditions: voltage 40 kV, current 80 mA, CuKα target, and scanning speed 15° / min. -1 The scanning range 2θ is 5–50°.

[0045] In the method of this invention, scanning electron microscope (SEM) images were obtained by a Zeiss Gemini 2 field emission scanning electron microscope from Germany, under the following test conditions: voltage 1.5kV, current 30mA, and by a HITACHI S4800 field emission scanning electron microscope from Japan, under the following test conditions: voltage 3.0kV, current 50mA.

[0046] Example 1

[0047] Boehmite (containing 70% by mass Al2O3), sodium hydroxide, and structure-directing agent ([(CH3CH2)3N)) were added. + -(CH2)6-N + (CH2CH3)3][Br -2) Add to water and stir for 1.5 hours; then add silica sol (containing 40% by weight SiO2) dropwise to the mixture obtained above, stir for 2 hours to obtain a gel mixture; wherein, in the mixture, the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, the alkali source is calculated as NaOH, and the molar ratio of Al2O3∶NaOH∶structure directing agent∶SiO2∶H2O is 0.04∶2.2∶1.0∶7.5∶350.

[0048] The resulting gel mixture was subjected to dynamic crystallization treatment with a stirring speed of 20 rpm. The resulting sample was centrifuged, washed, and dried at 100°C for 10 hours. The crystallization temperature was 150°C, and the crystallization time was 72 hours. This yielded the ZSM-5 molecular sieve with the morphology (perpendicularly intersecting elliptical cylinders) described in this invention.

[0049] The XRD pattern of ZSM-5 molecular sieve is as follows: Figure 1 As shown, from Figure 1 It can be seen that the synthesized silica-alumina molecular sieve has the peak shape of ZSM-5 molecular sieve, with relatively sharp diffraction peaks and obvious intensity.

[0050] Figure 2 This is a scanning electron microscope image of the product. For example... Figure 2 As shown, the molecular sieve particles are formed by perpendicularly intersecting elliptical cylinders, with a particle size of 1.6–1.9 μm. The main elliptical cylinder is the tallest elliptical cylinder, with a major axis of 1.2–1.6 μm, a minor axis of 0.5–0.8 μm, and a height of 1.6–1.9 μm. The other ellipses in the ZSM-5 molecular sieve particles have a height of 1.2–1.7 μm, a major axis of 0.1–1.3 μm, and a minor axis of 100–900 nm. In the ZSM-5 molecular sieve particles, except for the main elliptical cylinder, the other elliptical cylinders or quasi-elliptical cylinders are perpendicular to the main elliptical cylinder.

[0051] Example 2

[0052] Boehmite (containing 70% by mass Al2O3), sodium hydroxide, and structure-directing agent ([(CH3CH2)3N)) were added. + -(CH2)6-N + (CH2CH3)3][Br - ]2) Add to water and stir for 1.5 hours; then add fumed silica to the mixture obtained above and stir for 2 hours to obtain a gel mixture; wherein, in the mixture, the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, the alkali source is calculated as NaOH, and the molar ratio of Al2O3∶NaOH∶structure directing agent∶SiO2∶H2O is 0.04∶2.2∶1.0∶7.5∶350.

[0053] The resulting gel mixture was subjected to dynamic crystallization treatment with a stirring speed of 20 rpm. The resulting sample was centrifuged, washed, and dried at 100°C for 10 hours. The crystallization temperature was 150°C, and the crystallization time was 72 hours. This yielded the ZSM-5 molecular sieve with the morphology (perpendicularly intersecting elliptical cylinders) described in this invention.

[0054] The XRD pattern of ZSM-5 molecular sieve is as follows: Figure 1 As shown, from Figure 1 It can be seen that the synthesized silica-alumina molecular sieve has the peak shape of ZSM-5 molecular sieve, with relatively sharp diffraction peaks and obvious intensity.

[0055] The SEM image of the molecular sieve and Figure 2 Similarly, the molecular sieve particles are formed by perpendicularly intersecting elliptical cylinders, with a particle size of 1.3–1.8 μm. The main elliptical cylinder is the tallest elliptical cylinder, with a major axis of 0.8–1.5 μm, a minor axis of 0.4–0.7 μm, and a height of 1.3–1.8 μm. The other ellipses in the ZSM-5 molecular sieve particles have a height of 0.7–1.7 μm, a major axis of 0.1–1.3 μm, and a minor axis of 80–800 nm. Except for the main elliptical cylinder, the other elliptical cylinders or quasi-elliptical cylinders in the ZSM-5 molecular sieve particles are perpendicular to the main elliptical cylinder.

[0056] Example 3

[0057] Boehmite (containing 70% by mass Al2O3), sodium hydroxide, and structure-directing agent ([(CH3CH2)3N)) were added. + -(CH2)6-N + (CH2CH3)3][Br - ]2) Add to water and stir for 1.5 hours; then add fumed silica to the mixture obtained above and stir for 2 hours to obtain a gel mixture; wherein, in the mixture, the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, the alkali source is calculated as NaOH, and the molar ratio of Al2O3∶NaOH∶structure directing agent∶SiO2∶H2O is 0.04∶2.2∶1.0∶7.5∶450.

[0058] The resulting gel mixture was subjected to dynamic crystallization treatment with a stirring speed of 20 rpm. The resulting sample was centrifuged, washed, and dried at 100°C for 10 hours. The crystallization temperature was 150°C, and the crystallization time was 72 hours. This yielded the ZSM-5 molecular sieve with the morphology (perpendicularly intersecting elliptical cylinders) described in this invention.

[0059] The XRD pattern of ZSM-5 molecular sieve is as follows: Figure 1 As shown, from Figure 1It can be seen that the synthesized silica-alumina molecular sieve has the peak shape of ZSM-5 molecular sieve, with relatively sharp diffraction peaks and obvious intensity.

[0060] The SEM image of the molecular sieve and Figure 2 Similarly, the molecular sieve particles are formed by perpendicularly intersecting elliptical cylinders, with a particle size of 4.5–5.5 μm. The main elliptical cylinder is the tallest elliptical cylinder, with a major axis of 3.5–4.5 μm, a minor axis of 2.0–3.0 μm, and a height of 4.5–5.5 μm. Other ellipses in the ZSM-5 molecular sieve particles have a height of 2.0–3.0 μm, a major axis of 0.8–3.0 μm, and a minor axis of 500–1200 nm. Except for the main elliptical cylinder, the other elliptical cylinders or quasi-elliptical cylinders in the ZSM-5 molecular sieve particles are perpendicular to the main elliptical cylinder.

[0061] Example 4

[0062] Boehmite (containing 70% by mass Al2O3), sodium hydroxide, and structure-directing agent ([(CH3CH2)3N)) were added. + -(CH2)6-N + (CH2CH3)3][Br - 2) Add to water and stir for 1.5 hours; then add silica sol (containing 40% by weight SiO2) dropwise to the mixture obtained above, stir for 2 hours to obtain a gel mixture; wherein, in the mixture, the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, the alkali source is calculated as NaOH, and the molar ratio of Al2O3∶NaOH∶structure directing agent∶SiO2∶H2O is 0.04∶3.0∶1.0∶11∶450.

[0063] The resulting gel mixture was subjected to dynamic crystallization treatment with a stirring speed of 20 rpm. The resulting sample was centrifuged, washed, and dried at 100°C for 10 hours. The crystallization temperature was 150°C, and the crystallization time was 72 hours. This yielded the ZSM-5 molecular sieve with the morphology (perpendicularly intersecting elliptical cylinders) described in this invention.

[0064] The XRD pattern of ZSM-5 molecular sieve is as follows: Figure 1 As shown, from Figure 1 It can be seen that the synthesized silica-alumina molecular sieve has the peak shape of ZSM-5 molecular sieve, with relatively sharp diffraction peaks and obvious intensity.

[0065] The molecular sieve particles are formed by perpendicularly intersecting elliptical cylinders, with a particle size of 5.0–6.0 μm. The main elliptical cylinder is the tallest, with a major axis of 4.4–5.0 μm, a minor axis of 1.8–2.5 μm, and a height of 5.0–6.0 μm. Other ellipses in the ZSM-5 molecular sieve particles have a height of 5.0–6.0 μm, a major axis of 4.4–5.0 μm, and a minor axis of 1.8–2.5 μm. Besides the main elliptical cylinder, there are few other perpendicular elliptical or elliptical-like cylinders in the ZSM-5 molecular sieve particles, and the particle surface contains numerous nanoparticles with a size of 20–50 nm.

[0066] Example 5

[0067] Boehmite (containing 70% by mass Al2O3), sodium hydroxide, and structure-directing agent ([(CH3CH2)3N)) were added. + -(CH2)6-N + (CH2CH3)3][Br - ]2) Add to water and stir for 1.5 hours; then add silica sol (containing 40% by weight SiO2) dropwise to the mixture obtained above and stir for 2 hours to obtain a gel mixture; wherein, in the mixture, the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, the alkali source is calculated as NaOH, and the molar ratio of Al2O3∶NaOH∶structure directing agent∶SiO2∶H2O is 0.08∶2.2∶1.0∶10∶400.

[0068] The resulting gel mixture was subjected to dynamic crystallization treatment with a stirring speed of 20 rpm. The resulting sample was centrifuged, washed, and dried at 100°C for 10 hours. The crystallization temperature was 150°C, and the crystallization time was 72 hours. This yielded the ZSM-5 molecular sieve with the morphology (perpendicularly intersecting elliptical cylinders) described in this invention.

[0069] The XRD pattern of ZSM-5 molecular sieve is as follows: Figure 1 As shown, from Figure 1 It can be seen that the synthesized silica-alumina molecular sieve has the peak shape of ZSM-5 molecular sieve, with relatively sharp diffraction peaks and obvious intensity.

[0070] The molecular sieve particles are formed by perpendicularly intersecting elliptical cylinders, with a particle size of 7.0–8.0 μm. The main elliptical cylinder is the largest elliptical cylinder, with a major axis of 5.0–6.0 μm, a minor axis of 3.0–4.0 μm, and a height of 7.0–8.0 μm. Other ellipses in the ZSM-5 molecular sieve particles have a height of 3.0–7.0 μm, a major axis of 0.5–4.0 μm, and a minor axis of 0.3–3.0 μm. Besides the main elliptical cylinder, there are relatively few other perpendicular elliptical cylinders or quasi-elliptical cylinders in the ZSM-5 molecular sieve particles, and the particle surface contains numerous nanoparticles with a size of 20–50 nm.

[0071] Comparative Example 1

[0072] Boehmite (containing 70% by mass Al2O3), sodium hydroxide, and structure-directing agent ([(CH3CH2)3N)) were added. + -(CH2)6-N + (CH2CH3)3][Br - ]2) Add to water and stir for 1.5 hours; then add silica sol (containing 40% by weight SiO2) dropwise to the mixture obtained above and stir for 2 hours to obtain a gel mixture; wherein, in the mixture, the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, the alkali source is calculated as NaOH, and the molar ratio of Al2O3∶NaOH∶structure directing agent∶SiO2∶H2O is 0.1∶1.1∶1.0∶7.5∶350.

[0073] The resulting gel mixture was subjected to dynamic crystallization treatment with a stirring speed of 20 rpm. The resulting sample was centrifuged, washed, and dried at 100°C for 10 hours. The crystallization temperature was 150°C, and the crystallization time was 72 hours. This yielded the silica-alumina molecular sieve.

[0074] The XRD pattern of the molecular sieve is as follows: Figure 3 As shown, from Figure 3 It can be seen that the synthesized silica-alumina molecular sieve has a poor ZSM-5 peak shape, weak diffraction peak intensity, and incomplete characteristic peaks.

[0075] Figure 4 This is a scanning electron microscope image of the product. For example... Figure 4 As shown, the molecular sieve has three types of particle morphologies: sheet-like nanosheets, nanospheres, and cubically stacked particles.

[0076] Comparative Example 2

[0077] Boehmite (containing 70% by mass Al2O3), sodium hydroxide, and structure-directing agent ([(CH3CH2)3N)) were added. + -(CH2)6-N +(CH2CH3)3][Br - ]2) Add to water and stir for 1.5 hours; then add fumed silica to the mixture obtained above and stir for 2 hours to obtain a gel mixture; wherein, in the mixture, the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, the alkali source is calculated as NaOH, and the molar ratio of Al2O3∶NaOH∶structure directing agent∶SiO2∶H2O is 0.06∶1.4∶1.0∶15∶180.

[0078] The resulting gel mixture was subjected to dynamic crystallization treatment with a stirring speed of 20 rpm. The resulting sample was centrifuged, washed, and dried at 100°C for 10 hours. The crystallization temperature was 150°C, and the crystallization time was 72 hours. This yielded the silica-alumina molecular sieve.

[0079] The XRD pattern of this molecular sieve is similar to Figure 3 Similarly, the synthesized silica-alumina molecular sieves exhibited poor ZSM-5 peak shape, weak diffraction peak intensity, and incomplete characteristic peaks.

[0080] Figure 5 This is a scanning electron microscope image of the product. For example... Figure 5 As shown, the molecular sieve particles consist of a large number of nanosheets and nanoparticles, as well as a small number of spindle-shaped particles.

[0081] Example 6

[0082] The molecular sieves obtained in Examples 1-5 and Comparative Examples 1-2 were used as catalysts for the methanol-to-aromatics reaction. Before the reaction, they were converted to the H-form. The molecular sieve powders obtained in Examples 1-5 and Comparative Examples 1-2 were stirred with ammonium chloride solution (concentration 1 mol / L) (solid-liquid mass ratio 1:30) at 60°C for 2 hours. After solid-liquid separation, solid ZSM-5 molecular sieves were obtained. This process was repeated 3 times.

[0083] The reaction apparatus is a fixed-bed reactor. High-purity nitrogen gas, the raw material, enters the preheater via a pressure reducing valve and a quality controller. Methanol is pumped into the preheater by a horizontal flow pump. In the preheater, the liquid vaporizes, mixes with nitrogen, and is superheated to 300°C before entering the reactor. The gas exiting the reactor is controlled by a needle valve; a small amount enters the chromatograph for online analysis, while the remainder is discharged after gas-liquid separation.

[0084] The reactor is a U-shaped tube reactor with an inner diameter of 6 mm and a length of 1000 mm. During the catalytic process, the catalyst powder is diluted to 5 ml with quartz sand and filled into the middle section of the straight tube near the outlet. The remaining space is filled with quartz sand to ensure the isothermal effect of the reactor. The salt bath is prepared by melting a mixture of 50% KNO3 and 50% NaNO3, with a melting temperature of approximately 230℃ and a maximum operating temperature of approximately 550℃, which meets the experimental requirements. The catalyst evaluation temperature is 480℃, the reaction pressure is atmospheric pressure, and the methanol feed weight hourly space velocity (WHSV) is 4.7 h⁻¹. -1 The reaction apparatus was coupled to a GC9560 gas chromatograph using an HP-PLOTQ capillary column (30m × 0.32mm × 20μm).

[0085] Table 1. Results of methanol-to-aromatics reaction using molecular sieves from Examples 1-5 and materials from Comparative Examples 1-2 as catalysts.

[0086] catalyst Methanol conversion rate, wt% Aromatics, wt% Olefins, wt% Alkanes, wt% Example 1 99 22.14 52.21 25.65 Example 2 99 22.86 52.02 25.12 Example 3 99 19.67 56.57 23.76 Example 4 99 18.17 55.99 26.84 Example 5 98 17.04 55.84 27.12 Comparative Example 1 96 10.29 36.11 53.6 Comparative Example 2 95 8.42 34.24 57.34

[0087] The embodiments described above are merely detailed descriptions of the technical solutions of the present invention, but the present invention is not limited to the above embodiments; that is, the present invention does not depend on the steps described in the above embodiments for implementation. In summary, any improvements made to the present invention by those skilled in the art, including substitutions for the raw materials and additives described in the present invention, and selections of specific implementation methods, all fall within the protection and disclosure scope of the present invention.

Claims

1. A ZSM-5 molecular sieve, comprising particles formed by perpendicularly intersecting elliptical cylinders, with a particle size of 1.2~8.0 μm, wherein the ZSM-5 molecular sieve particles contain a main elliptical cylinder, which is the tallest elliptical cylinder; the height of the main elliptical cylinder is 1.2~8.0 μm, the major axis is 0.5~6.0 μm, and the minor axis is 0.3~4.0 μm; and the height of the other elliptical cylinders in the ZSM-5 molecular sieve particles, excluding the main elliptical cylinder, is 0.5~7.0 μm, the major axis is 0.1~5.0 μm, and the minor axis is 50~3000 nm.

2. The molecular sieve according to claim 1, characterized in that, The ZSM-5 molecular sieve has a particle size of 1.3~5.5μm.

3. The molecular sieve according to claim 1, characterized in that, In the ZSM-5 molecular sieve particles, the height of the main elliptical cylinder is 1.3~2.5μm, the major axis of the ellipse is 0.8~2.0μm, and the minor axis is 0.4~1.0μm.

4. The molecular sieve according to claim 1, characterized in that, In the ZSM-5 molecular sieve particles, the height of the other elliptical cylinders, excluding the main elliptical cylinder, is 0.5~2.0μm, the major axis is 0.1~2.0μm, and the minor axis is 80~1000nm.

5. The method for preparing the ZSM-5 molecular sieve according to any one of claims 1-4, characterized in that, The method includes the following steps: A mixture of aluminum source, alkali source, silicon source, water and structure guiding agent is subjected to crystallization treatment; The structure-directing agent is a dimer tetraethyl quaternary ammonium salt with the molecular formula: [(CH3CH2)3N + -(CH2)6-N + (CH2CH3)3][Br - ]2.

6. The preparation method according to claim 5, characterized in that, The aluminum source is one or more of boehmite, aluminum isopropoxide, and sodium aluminate.

7. The preparation method according to claim 5, characterized in that, The silicon source is one or more of silica sol, silica fume, and tetraethyl orthosilicate; the alkali source is sodium hydroxide.

8. The preparation method according to claim 5, characterized in that, In the gel mixture, the aluminum source is calculated as Al2O3, the silicon source as SiO2, and the alkali source as NaOH. The molar ratio of Al2O3:NaOH:structure directing agent:SiO2:H2O is (0.02~0.08):(1.5~3.0):(0.7~2.0):(5~12):(200~500).

9. The preparation method according to claim 8, characterized in that, In the gel mixture, the aluminum source is calculated as Al2O3, the silicon source is calculated as SiO2, the alkali source is calculated as NaOH, and the molar ratio of Al2O3:NaOH:structure directing agent:SiO2:H2O is (0.02~0.05):(1.5~2.5):(0.7~1.5):(5~8):(300~450).

10. The preparation method according to claim 5, characterized in that, The crystallization conditions are as follows: crystallization temperature is 120~200℃, and crystallization time is 20~100 hours.

11. The preparation method according to claim 5, characterized in that, The crystallization is dynamic crystallization, carried out under stirring conditions, with a rotation speed of 5~50 rpm.

12. The application of the ZSM-5 molecular sieve according to any one of claims 1-4 in the methanol-to-aromatics reaction.

13. The application according to claim 12, characterized in that, The reaction conditions were: reaction temperature 300-500℃, volume hourly space velocity 2-5 h⁻¹. -1 The process is carried out under normal pressure.

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