SAPO-11 molecular sieve, method for preparing same, and use thereof

Abstract

This invention relates to the field of molecular sieve synthesis, specifically to a SAPO-11 molecular sieve, its preparation method, and its applications. This molecular sieve is a spherical aggregate with a diameter of 2-50 μm, composed of primary nanosheet crystals with a thickness of 15-50 nm. The median pore size of the molecular sieve is 1550-1700 nm. The SAPO-11 molecular sieve of this invention has a small crystal size and a long service life.

Description

Technical Field

[0001] This invention relates to the field of molecular sieve synthesis, specifically to a SAPO-11 molecular sieve, its preparation method, and its applications. Background Technology

[0002] Molecular sieves are a class of substances with uniform micropores, the size of which is comparable to that of ordinary molecules. They are widely used in petrochemicals, agriculture, animal husbandry, environmental protection, and high-tech fields. Because molecular sieves have uniform and regular channels, and the channel size is on the same order of magnitude as small organic molecules, molecules entering the molecular sieve can be "sieved" according to their spatial size during chemical reactions, thus achieving selective adsorption and catalytic shape-selective effects. The framework of molecular sieves is usually composed of coordination tetrahedra (TO4) connected by shared vertices (usually oxygen atoms). For conventional zeolite molecular sieves, the tetrahedra in the framework are mainly silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra. These two types of tetrahedra can also be replaced by other tetrahedra, thus forming many different framework structures or molecular sieves composed of various frameworks.

[0003] In 1971, Flanigen et al. reported the synthesis of aluminosilicate zeolites (Molecular Sieve Zeolites-I, ACS, Washingtom DC), which can be understood as the replacement of silicon-oxygen tetrahedra with phosphorus-oxygen tetrahedra in zeolite zeolites to form a zeolite. The framework of this type of zeolite is mediated by AlO4. - and PO4 +The molecular sieve framework is electrically neutral, formed by the bonding of co-oxygen atoms. Similar to zeolite molecular sieves, the aluminum-oxygen tetrahedra or phosphorus-oxygen tetrahedra in aluminum phosphate molecular sieves can be replaced by other tetrahedra, most commonly silicon-oxygen tetrahedra and zinc-oxygen tetrahedra. The introduction of these tetrahedra endows aluminum phosphate molecular sieves with new properties. Compared to zeolite molecular sieves, the artificial synthesis of aluminum phosphate molecular sieves is relatively recent. Under hydrothermal synthesis conditions, oxides of aluminum, silicon, and phosphorus were mixed to obtain silicon-phosphorus-aluminum molecular sieves with the same crystal structure as analcime, chabazite, Phillipsite-harmotome, L-type molecular sieves, A-type molecular sieves, and B-type molecular sieves, with a phosphorus content of 5%–25% (calculated as P2O5). However, no molecular sieves with structures different from known zeolite molecular sieves were found. US patent 4310440 describes the hydrothermal synthesis of a series of aluminum phosphate molecular sieves using organic amines or quaternary ammonium compounds as template agents. These include AlPO4-5, AlPO4-8, AlPO4-9, AlPO4-11, AlPO4-12, AlPO4-14, AlPO4-16, AlPO4-17, AlPO4-18, AlPO4-20, AlPO4-21, AlPO4-22, AlPO4-23, AlPO4-25, AlPO4-26, AlPO4-28, and AlPO4-31. With a deeper understanding of the structure, properties, synthesis methods, and conditions of molecular sieves, and with continuous advancements in synthesis technology, new molecular sieve structures are constantly being synthesized. With the development of industrial applications and the need for controlled growth of small crystallites and crystal faces, the type of organic template agent is one of the key factors determining the structure of aluminum phosphate molecular sieves. To date, organic amines remain the most widely used template agents in the synthesis of aluminum phosphate molecular sieves. Compared to silica-alumina zeolite molecular sieves, phosphorus-alumina molecular sieves are not widely used in industry. Currently, only a few molecular sieves have achieved practical industrial applications, such as SAPO-34 and SAPO-11 molecular sieves.

[0004] In addition, in practical applications, it is precisely because of this "sieving" function of molecular sieves that the mass transfer and heat transfer performance of the reaction is often limited, which in turn affects the activity and lifespan of the catalyst. This deficiency can be further overcome by reducing the crystal size and modifying the crystal pore structure. Therefore, the synthesis of nanocrystals, nanocrystalline sheets and the introduction of mesopores to synthesize hierarchical porous crystals have aroused great interest among researchers.

[0005] CN108996518A describes the preparation of SAPO-11 molecular sieves with hierarchical pores by post-treating them with solid acids under different conditions. CN109896531A describes the preparation of nanorod-shaped SAPO-11 molecular sieves by using diethylamine and diisopropylamine as mixed template agents and pretreating the crystallization solution using a microwave reactor. The master's thesis, "Preparation and Isomerization Performance Study of Ultrafine SAPO-11 Molecular Sieves" (China University of Petroleum, Han Lei, 2013.5), describes the preparation of ultrafine SAPO-11 molecular sieves with a size of 200 nm by optimizing the synthesis conditions using hexadecyltrimethylammonium bromide (CTAB) and hydrofluoric acid (HF) as additives.

[0006] In existing technologies and research, commonly used template agents are diethylamine, dipropylamine, or diisopropylamine. To reduce crystal size, expensive surfactants (such as hexadecyltrimethylammonium bromide) and special additives such as HF(aq) are usually added, which is not conducive to industrial scale-up. Although the microwave method has a significant advantage in terms of time cost, it is prone to crystal transformation during crystallization, generating AlPO-5 or CFSAPO-1(C) impurities, which is not conducive to the preparation of pure-phase SAPO-11 molecular sieves. At the same time, the microwave method is not suitable for large-scale industrial production.

[0007] In view of the shortcomings of existing technologies, this invention aims to propose a preparation method that is not covered by existing technologies, requires no additional surfactants, and does not use environmentally harmful substances. The raw materials are inexpensive and readily available, the operation is simple, the reproducibility is good, and it is easy to scale up for industrial production. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems of large size and high preparation cost of SAPO-11 molecular sieves in the prior art, and to provide a SAPO-11 molecular sieve, its preparation method and application, which has the characteristics of small size and low preparation cost.

[0009] To achieve the above objectives, the first aspect of the present invention provides a SAPO-11 molecular sieve, which is a spherical aggregate with a diameter of 2-50 μm formed by the aggregation of primary nanosheet crystals with a thickness of 15-60 nm, and the median pore size of the molecular sieve is 1550-1700 nm.

[0010] A second aspect of the present invention provides a method for preparing the molecular sieve described herein. The method includes preparing a hydrothermal reaction mixture using a phosphorus source, an aluminum source, a silicon source, a structure directing agent R1, and an additive R2. The reaction mixture is then aged and crystallized. The molar ratio of each substance is: (0.01-0.5)SiO2:(0.8-1.2)Al2O3:1P2O5:(0.1-0.5)R1:(0.3-1.0)R2:(40-90)H2O. The structure directing agent R1 is selected from N,N,N',N'-tetramethylhexanediamine and / or N,N,N',N'-tetramethylpentanediamine. The additive R2 is an imidazole compound.

[0011] A third aspect of the present invention provides an application of the molecular sieve described herein in catalyst preparation.

[0012] Through the above technical solution, the present invention has the following beneficial effects:

[0013] This invention provides a SAPO-11 molecular sieve with small crystal size and long service life.

[0014] The catalyst described in this invention is prepared using a method that eliminates the need for ultrasonic or microwave treatment during synthesis, and avoids the addition of complex organic surfactants and environmentally harmful substances such as HF, making the preparation process simple, economical, and environmentally friendly. The raw materials are inexpensive and readily available, offering significant advantages in practical industrial applications.

[0015] Using the molecular sieve described in this invention for catalyst preparation can significantly improve the catalyst's lifespan. Attached Figure Description

[0016] Figure 1 The XRD pattern of the molecular sieve in Example 1;

[0017] Figure 2 This is a SEM image of the molecular sieve from Example 1, magnified 40,000 times.

[0018] Figure 3 This is a 2,000x magnified SEM image of the molecular sieve from Example 1.

[0019] Figure 4 The XRD pattern of the molecular sieve in Example 6;

[0020] Figure 5 This is a SEM image of the molecular sieve from Example 6, magnified 20,000 times.

[0021] Figure 6 This is a SEM image of the molecular sieve from Example 6, magnified 10,000 times.

[0022] Figure 7 The XRD pattern of the molecular sieve in Comparative Example 1 is shown.

[0023] Figure 8 The image shows the SEM image of the molecular sieve in Comparative Example 1.

[0024] Figure 9 The image shows the XRD pattern of the molecular sieve in Comparative Example 2. Detailed Implementation

[0025] 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.

[0026] The first aspect of the present invention provides a SAPO-11 molecular sieve, which is a spherical aggregate with a diameter of 2-50 μm formed by the aggregation of primary nanosheet crystals with a thickness of 15-60 nm, and the median pore size of the molecular sieve is 1550-1700 nm.

[0027] This invention provides a SAPO-11 molecular sieve with small crystal size and long service life.

[0028] According to a preferred embodiment of the present invention, the molecular sieve is a spherical aggregate with a diameter of 20-40 μm formed by the aggregation of primary nanosheet crystals with a thickness of 20-45 nm, and the median pore size of the molecular sieve is 1600-1650 nm.

[0029] Molecular sieves possessing the aforementioned features of this invention can all achieve the objectives of this invention, and there are no special requirements for their preparation methods. In view of this invention, a method for preparing the molecular sieve described in this invention is provided. This method includes preparing a hydrothermal reaction mixture using a phosphorus source, an aluminum source, a silicon source, a structure-directing agent R1, and an additive R2. The reaction mixture is then aged and crystallized. The molar ratio of each substance is: (0.01-0.5)SiO2:(0.8-1.2)Al2O3:1P2O5:(0.1-0.5)R1:(0.3-1.0)R2:(40-90)H2O; the structure-directing agent R1 is selected from N,N,N',N'-tetramethylhexanediamine and / or N,N,N',N'-tetramethylpentanediamine; and the additive R2 is an imidazole compound.

[0030] According to a preferred embodiment of the present invention, the molar ratio of each substance in the reaction mixture is: (0.05-0.3)SiO2:(0.8-1.0)Al2O3:1P2O5:(0.2-0.5)R1:(0.3-1.0)R2:(50-75)H2O.

[0031] In this invention, the silicon source can be a silicon-containing compound commonly used in the art. According to a preferred embodiment of this invention, the silicon source is selected from one or a mixture of silica sol, fumed silica, or the like.

[0032] In this invention, the aluminum source can be a common aluminum-containing compound in the art. According to a preferred embodiment of this invention, the aluminum source is selected from at least one of boehmite, aluminum isopropoxide, aluminum sulfate, aluminum chloride, and aluminum hydroxide.

[0033] In this invention, the phosphorus source can be a phosphorus-containing compound commonly used in the art. According to a preferred embodiment of this invention, the phosphorus source is selected from at least one of phosphoric acid, phosphorous acid, ammonium hydrogen phosphate, and ammonium dihydrogen phosphate.

[0034] According to a preferred embodiment of the present invention, the imidazole compound is selected from at least one of imidazole, 1-methylimidazolium, 1-ethylimidazolium, 1-propylimidazolium, 1-butylimidazolium, 1-(2-aminoethyl)imidazolium and 1-(3-aminopropyl)imidazolium.

[0035] In this invention, the preparation steps of the hydrothermal reaction mixture can be conventional choices in the art. According to a preferred embodiment of this invention, the preparation steps of the hydrothermal reaction mixture are as follows:

[0036] 1) Dissolve the aluminum source and phosphorus source in water to obtain mixed solution I;

[0037] 2) Add a mixture of template agent R1, additive R2 and water to mixture I to obtain mixture II;

[0038] 3) Add a silicon source to mixture II to obtain a hydrothermal reaction mixture.

[0039] In this invention, the aging conditions can be conventionally selected in the art. According to a preferred embodiment of this invention, the aging conditions include: an aging temperature of 20-40°C and an aging time of 2-15 hours.

[0040] In this invention, the crystallization conditions can be conventionally selected in the art. According to a preferred embodiment of this invention, the crystallization conditions include: a crystallization temperature of 180-210℃, preferably 190-205℃; and / or a crystallization time of 2-36h, preferably 4-24h.

[0041] According to a preferred embodiment of the present invention, the aging and crystallization can be carried out in a crystallization kettle lined with polytetrafluoroethylene, preferably using dynamic aging and crystallization, and more preferably aging and crystallization under stirring conditions.

[0042] According to a preferred embodiment of the present invention, the method further includes cooling, separating, washing, drying and calcining the crystallized product.

[0043] In this invention, the cooling, separation, and washing processes can all be conventional choices in the field, as long as they can achieve the purpose of this invention.

[0044] In this invention, the drying conditions can be conventionally selected in the art. According to a preferred embodiment of the invention, the drying conditions include: a drying temperature of 50-200°C, preferably 80-120°C, and / or a drying time of 5-30 hours, preferably 8-15 hours.

[0045] In this invention, the calcination conditions can be conventionally selected in the art. According to a preferred embodiment of this invention, the calcination conditions include: a calcination temperature of 350-700℃, preferably 450-600℃; and / or a calcination time of 1-15h, preferably 5-8h.

[0046] A third aspect of the present invention provides an application of the molecular sieve described herein in catalyst preparation.

[0047] Using the molecular sieve described in this invention for catalyst preparation can significantly improve the catalyst's lifespan.

[0048] The present invention will be described in detail below through embodiments. In the following embodiments, the structure of the molecular sieve is determined by X-ray diffraction (XRD), which is measured by X-ray powder diffraction (XRD) using a Cu-Kα ray source with a Kα1 wavelength λ = 1.5405980 angstroms. A nickel filter was used, operating at 40 kV and 40 mA, with a scanning range of 3–50°. Product morphology was captured using a Japanese emission scanning electron microscope (Fe-SEM). Median pore size was determined using a mercury porosimeter, with the following specifications: Pascal 140 low-pressure mercury porosimeter: pore size: 116–3.8 μm, pressure range: 0.1–400 kPa; Pascal 240 high-pressure mercury porosimeter: pore size: 15–0.0074 μm, maximum pressure: 200 MPa.

[0049] The raw materials, including phosphoric acid (85%), phosphorous acid, and ammonium hydrogen phosphate (Shanghai Test), as well as N,N,N',N'-tetramethylhexanediamine and / or N,N,N',N'-tetramethylpentanediamine (Wokai), aluminum isopropoxide (Shanghai Test), and nano silica (Wokai), are commercially available products from Sinopharm Chemical Reagent Co., Ltd.; the imidazole chemically pure raw materials are commercially available products from Aladdin Reagent Co., Ltd.; boehmite (alumina content 70% on a dry basis) is a commercially available product from Jiangsu Sanji Industrial Co., Ltd.; and the silicon source, HS Ludox-40%, is from Sigama-Aldrich.

[0050] Example 1

[0051] Weigh 2.56 g of pseudoboehmite (70% dry basis, the same below), add 13 g of water, then add 4.6 g of 85% phosphoric acid, stir at room temperature for 2 h to obtain mixture I; then add a mixture of 1.76 g of 1-(3-aminopropyl)imidazolium and 5 g of water, and a mixture of 0.68 g of N,N,N',N'-tetramethylhexanediamine and 5 g of water to mixture I, stir at room temperature for 3 h to obtain mixture II; then add 0.12 g of nano-silica to mixture II, stir overnight at 30 °C. Crystallize at 200 °C for 6 h. Cool to room temperature, centrifuge, and wash. The obtained solid material is dried at 110 °C overnight and calcined at 550 °C for 5 h to obtain molecular sieve. Figure 1 The XRD pattern of the obtained molecular sieve shows that it is SAPO-11 molecular sieve. Figure 2 (Magnified 40,000 times) Figure 3 (SEM images of the molecular sieve obtained at different magnifications, magnified 2000x) show that the molecular sieve is composed of spheroidal aggregates formed by nanosheets. The high-magnification SEM images reveal that the thickness of the nanosheets ranges from 20-45 nm, and the diameter of the spheroidal aggregates ranges from 5-20 μm. Mercury intrusion porosimetry (MIP) analysis determined the median pore size of the molecular sieve to be 1639.93 nm.

[0052] Example 2

[0053] Weigh 2.56 g of boehmite, add 13 g of water, then add 4.6 g of 85% phosphoric acid, and stir at room temperature for 2 h to obtain mixture I. Then add a mixture of 1.24 g imidazole and 5 g water, and a mixture of 1.37 g N,N,N',N'-tetramethylhexanediamine and 5 g water to mixture I, and stir at room temperature for 3 h to obtain mixture II. Then add 0.12 g of nano-silica to mixture II, and stir overnight at 30 °C. Crystallize at 200 °C for 6 h. Cool to room temperature, centrifuge, and wash. The resulting solid is dried overnight at 110 °C and calcined at 550 °C for 6 h to obtain spherical SAPO-11 molecular sieves aggregated from nanosheets. High-magnification scanning electron microscopy shows that the thickness of the nanosheets is in the range of 20-45 nm, and the diameter of the spherical aggregates is in the range of 5-20 μm. The median pore size of the molecular sieve was determined to be 1637.89 nm using a mercury porosimetry pore size analyzer.

[0054] Example 3

[0055] 2.91 g of boehmite was weighed, 23 g of water was added, and then 4.6 g of 85% phosphoric acid was added. The mixture was stirred at room temperature for 2 h to obtain mixture I. Then, a mixture of 1.76 g of 1-(3-aminopropyl)imidazolium and 10 g of water, and a mixture of 0.68 g of N,N,N',N'-tetramethylhexanediamine and 5 g of water were added to mixture I. The mixture was stirred at room temperature for 3 h to obtain mixture II. Then, 0.48 g of nano-silica was added to mixture II, and the mixture was stirred overnight at 30 °C. Crystallization was carried out at 200 °C for 6 h. After cooling to room temperature, the mixture was centrifuged and washed. The resulting solid was dried overnight at 110 °C and calcined at 520 °C for 10 h to obtain spherical SAPO-11 molecular sieves aggregated into nanosheets. High-magnification scanning electron microscopy showed that the thickness of the nanosheets ranged from 20 to 45 nm, and the diameter of the spherical aggregates ranged from 5 to 20 μm. The median pore size of the molecular sieve was determined to be 1643.73 nm using a mercury porosimetry pore size analyzer.

[0056] Example 4

[0057] Weigh 2.56 g of boehmite, add 13 g of water, then add 4.6 g of 85% phosphoric acid, and stir at room temperature for 2 h to obtain mixture I. Then add a mixture of 1.76 g of 1-(3-aminopropyl)imidazolium and 5 g of water, and a mixture of 0.68 g of N,N,N',N'-tetramethylhexanediamine and 5 g of water to mixture I, and stir at room temperature for 3 h to obtain mixture II. Then add 0.3 g of 40% silica sol (Ludox-40%) to mixture II, and stir overnight at 30 °C. Crystallize at 185 °C for 16 h. Cool to room temperature, centrifuge, and wash. The resulting solid is dried overnight at 110 °C and calcined at 550 °C for 5 h to obtain spherical SAPO-11 molecular sieves aggregated into nanosheets. High-magnification scanning electron microscopy shows that the thickness of the nanosheets is in the range of 20-45 nm, and the diameter of the spherical aggregates is in the range of 5-20 μm. The median pore size of the molecular sieve was determined to be 1641.37 nm using a mercury porosimetry pore size analyzer.

[0058] Example 5

[0059] Weigh 3.2 g of boehmite, add 22 g of water, then add 4.6 g of 85% phosphoric acid, and stir at room temperature for 2 h to obtain mixture I. Then add a mixture of 1.76 g of 1-(3-aminopropyl)imidazolium and 5 g of water, and a mixture of 1.3 g of N,N,N',N'-tetramethylpentanediamine and 5 g of water to mixture I, and stir at room temperature for 4 h to obtain mixture II. Then add 0.3 g of 40% silica sol (Ludox-40%) to mixture II, and stir overnight at 30 °C. Crystallize at 205 °C for 4 h. Cool to room temperature, centrifuge, and wash. The resulting solid is dried overnight at 110 °C and calcined at 600 °C for 2 h to obtain spherical SAPO-11 molecular sieves aggregated into nanosheets. High-magnification scanning electron microscopy shows that the thickness of the nanosheets is in the range of 20-45 nm, and the diameter of the spherical aggregates is in the range of 5-20 μm. The median pore size of the molecular sieve was determined to be 1642.61 nm using a mercury porosimetry pore size analyzer.

[0060] Example 6

[0061] Weigh 2.56 g of boehmite, add 6 g of water, then add 4.6 g of 85% phosphoric acid, and stir at room temperature for 2 h to obtain mixture I. Then add a mixture of 0.76 g of 1-(3-aminopropyl)imidazolium and 5 g of water, and a mixture of 0.78 g of N,N,N',N'-tetramethylpentanediamine and 5 g of water to mixture I, and stir at room temperature for 3 h to obtain mixture II. Then add 0.12 g of nano-silica to mixture II, and stir overnight at 30 °C. Crystallize at 190 °C for 12 h. Cool to room temperature, centrifuge, and wash. The resulting solid is dried overnight at 110 °C and calcined at 550 °C for 5 h to obtain a molecular sieve. Figure 4The XRD pattern of the obtained molecular sieve shows that it is SAPO-11 molecular sieve. Figure 5 (Magnified 20,000 times) Figure 6 (SEM images of the molecular sieve obtained at different magnifications, magnified 10,000 times) show that the molecular sieve is composed of spherical aggregates formed by nanosheets. The high-magnification SEM images reveal that the thickness of the nanosheets ranges from 20 to 45 nm, and the diameter of the spherical aggregates ranges from 5 to 20 μm. Mercury intrusion porosimetry (MIMO) analysis determined the median pore size of the molecular sieve to be 1639.67 nm.

[0062] Example 7

[0063] Weigh 7.2 g of aluminum isopropoxide (100% purity), add 13 g of water, stir at room temperature for 2 h to fully hydrolyze, then add 4.6 g of 85% phosphoric acid, stir at room temperature for another 2 h to obtain mixture I; then add a mixture of 1.76 g of 1-(3-aminopropyl)imidazolium and 5 g of water, and a mixture of 0.68 g of N,N,N',N'-tetramethylhexanediamine and 5 g of water to mixture I, stir at room temperature for 3 h to obtain mixture II; then add 0.36 g of nano-silica to mixture II, stir overnight at 30 °C. Crystallize at 200 °C for 6 h. Cool to room temperature, centrifuge, and wash. The obtained solid material is dried at 110 °C overnight and calcined at 550 °C for 5 h to obtain spherical SAPO-11 molecular sieves aggregated into nanosheets. High-magnification scanning electron microscopy revealed that the thickness of the nanosheets ranged from 20 to 45 nm, and the diameter of the spheroidal aggregates ranged from 5 to 20 μm. Mercury intrusion porosimetry determined the median pore size of the molecular sieve to be 1640.94 nm.

[0064] Example 8

[0065] Weigh 2.56 g of boehmite, add 13 g of water, then add 4.6 g of 85% phosphoric acid, and stir at room temperature for 2 h to obtain mixture I. Then add a mixture of 1.24 g of imidazole and 5 g of water, and a mixture of 0.68 g of N,N,N',N'-tetramethylhexanediamine and 5 g of water to mixture I, and stir at room temperature for 3 h to obtain mixture II. Then add 0.12 g of nano-silica to mixture II, and stir overnight at 30 °C. Crystallize at 200 °C for 6 h. Cool to room temperature, centrifuge, and wash. The obtained solid material is dried overnight at 110 °C and calcined at 550 °C for 5 h to obtain spherical SAPO-11 molecular sieves aggregated into nanosheets. High-magnification scanning electron microscopy shows that the thickness of the nanosheets is in the range of 20-45 nm, and the diameter of the spherical aggregates is in the range of 5-20 μm. The median pore size of the molecular sieve was determined to be 1644.13 nm using a mercury porosimetry pore size analyzer.

[0066] Example 9

[0067] Weigh 2.56 g of boehmite, add 13 g of water, then add 4.6 g of 85% phosphoric acid, and stir at room temperature for 2 h to obtain mixture I. Then add a mixture of 2 g of 1-propylimidazolium and 5 g of water, and a mixture of 0.68 g of N,N,N',N'-tetramethylhexanediamine and 5 g of water to mixture I, and stir at room temperature for 3 h to obtain mixture II. Then add 0.12 g of nano-silica to mixture II, and stir overnight at 30 °C. Crystallize at 200 °C for 6 h. Cool to room temperature, centrifuge, and wash. The resulting solid material is dried overnight at 110 °C and calcined at 550 °C for 5 h to obtain spherical SAPO-11 molecular sieves aggregated from nanosheets. High-magnification scanning electron microscopy shows that the thickness of the nanosheets is in the range of 20-45 nm, and the diameter of the spherical aggregates is in the range of 5-20 μm. The median pore size of the molecular sieve was determined to be 1644.73 nm using a mercury porosimetry pore size analyzer.

[0068] Example 10

[0069] Weigh 2.56 g of boehmite, add 13 g of water, then add 4.6 g of 85% phosphoric acid, and stir at room temperature for 2 h to obtain mixture I. Then add a mixture of 1.49 g of 1-methylimidazole and 5 g of water, and a mixture of 0.68 g of N,N,N',N'-tetramethylhexanediamine and 5 g of water to mixture I, and stir at room temperature for 3 h to obtain mixture II. Then add 0.12 g of nano-silica to mixture II, and stir overnight at 30 °C. Crystallize at 200 °C for 6 h. Cool to room temperature, centrifuge, and wash. The resulting solid is dried overnight at 110 °C and calcined at 550 °C for 5 h to obtain spherical SAPO-11 molecular sieves aggregated from nanosheets. High-magnification scanning electron microscopy shows that the thickness of the nanosheets is in the range of 20-45 nm, and the diameter of the spherical aggregates is in the range of 5-20 μm. The median pore size of the molecular sieve was determined to be 1645.03 nm using a mercury porosimetry pore size analyzer.

[0070] Comparative Example 1

[0071] Weigh 2.56 g of boehmite, add 13 g of water, then add 4.6 g of 85% phosphoric acid, and stir at room temperature for 2 h to obtain mixture I. Then add a mixture of 0.68 g of N,N,N',N'-tetramethylhexanediamine and 5 g of water to mixture I, and stir at room temperature for 3 h to obtain mixture II. Then add 0.12 g of aerosol to mixture II and stir overnight. Crystallize at 200 °C for 6 h. Cool to room temperature, centrifuge, and wash. The obtained solid is dried at 110 °C overnight and calcined at 550 °C for 5 h to obtain a molecular sieve. Figure 7 The XRD pattern of the obtained molecular sieve shows that it is SAPO-11 molecular sieve. Figure 8The image shows a SEM image of the molecular sieve obtained by scanning electron microscopy. It can be seen that the molecular sieve is a non-spherical aggregate formed by non-plate-like crystals containing slightly impurities.

[0072] Comparative Example 2

[0073] Weigh 2.56 g of boehmite, add 12.8 g of water, then add 4.6 g of 85% phosphoric acid, and stir at room temperature for 2 h to obtain mixture I; then add a mixture of 1.76 g of aminopropylimidazol and 10 g of water to mixture I, and stir at room temperature for 3 h to obtain mixture II; then add 0.12 g of aerosol to mixture II and stir overnight. Crystallize at 200 °C for 6 h. Cool to room temperature, centrifuge, and wash. The obtained solid material is dried at 110 °C overnight to obtain a molecular sieve. Figure 9 The XRD pattern of the obtained molecular sieve shows that the molecular sieve is not SAPO-11 molecular sieve.

[0074] As can be seen from the results of the embodiments, the molecular sieve of the present invention is a spherical aggregate with a diameter of 2-50 μm, which is composed of primary nanosheet crystals with a thickness of 15-50 nm. The molecular sieve has a small size.

[0075] 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 SAPO-11 molecular sieve, characterized in that, The molecular sieve is a spherical aggregate with a diameter of 2-50 μm, which is composed of primary nanosheet crystals with a thickness of 15-60 nm. The median pore size of the molecular sieve, as determined by a mercury porosimetry pore size analyzer, is 1550-1700 nm. The preparation method of this molecular sieve includes preparing a hydrothermal reaction mixture using a phosphorus source, an aluminum source, a silicon source, a structure directing agent R1, and an additive R2. The reaction mixture is then aged and crystallized. The molar ratio of each substance is: (0.01-0.5) SiO2:(0.8-1.2)Al2O3:1P2O5:(0.1-0.5)R1:(0.3-1.0)R2:(40-90)H2O. The structure directing agent R1 is selected from N,N,N',N'-tetramethylhexanediamine and / or N,N,N',N'-tetramethylpentanediamine. The additive R2 is an imidazole compound.

2. The molecular sieve according to claim 1, wherein, The molecular sieve is a spherical aggregate with a diameter of 20-40 μm, consisting of primary nanosheet crystals with a thickness of 20-45 nm. The median pore size of the molecular sieve, as measured by a mercury porosimetry pore size analyzer, is 1600-1650 nm.

3. The molecular sieve according to claim 1, wherein, The molar ratio of each substance in the reaction mixture is: (0.05-0.3) SiO2:(0.8-1.0)Al2O3:1P2O5:(0.2-0.5)R1:(0.3-1.0)R2:(50-75)H2O.

4. The molecular sieve according to claim 1, wherein, The imidazole compounds are selected from at least one of imidazole, 1-methylimidazolium, 1-ethylimidazolium, 1-propylimidazolium, 1-butylimidazolium, 1-(2-aminoethyl)imidazolium, and 1-(3-aminopropyl)imidazolium.

5. The molecular sieve according to claim 1, wherein, The preparation steps of the hydrothermal reaction mixture are as follows: 1) Dissolve the aluminum source and phosphorus source in water to obtain mixed solution I; 2) Add a mixture of template agent R1, additive R2 and water to mixture I to obtain mixture II; 3) Add a silicon source to mixture II to obtain a hydrothermal reaction mixture.

6. The molecular sieve according to claim 1, wherein, The aging conditions include: an aging temperature of 20-40℃ and an aging time of 2-15 hours; and / or The crystallization conditions include: a crystallization temperature of 180-210℃; and / or a crystallization time of 2-36h.

7. The molecular sieve according to claim 6, wherein, The crystallization conditions include: a crystallization temperature of 190-205℃; and / or a crystallization time of 4-24h.

8. The molecular sieve according to claim 1, wherein, The method also includes cooling, separating, washing, drying and calcining the crystallized product.

9. The molecular sieve according to claim 8, wherein, The drying conditions include: a drying temperature of 50-200℃, and / or a drying time of 5-30 hours; and / or The calcination conditions include: a calcination temperature of 350-700℃; and / or a calcination time of 1-15h.

10. The molecular sieve according to claim 9, wherein, The drying conditions include: a drying temperature of 80-120℃, and / or a drying time of 8-15 hours; and / or The calcination conditions include: a calcination temperature of 450-600℃; and / or a calcination time of 5-8 hours.

11. The application of the molecular sieve according to claim 1 or 2 in catalyst preparation.

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