A nanoscale SAPO-34 molecular sieve with a large amount of mesopores and a preparation method thereof

Abstract

The application discloses a kind of more mesoporous sheet-like nanoscale SAPO-34 molecular sieve and its preparation method, the SAPO-34 molecular sieve, with nanoscale sheet-like crystal grain, mesoporous volume accounts for more than 10% of total pore volume.Its synthesis method includes: aluminum source, template agent I and water are mixed, stirring, then a certain proportion of template agent II is added;Phosphorus source and silicon source are added, hydrothermal dynamic crystallization, separation, washing, drying, calcination.The SAPO-34 molecular sieve contains more mesoporous in the case of having sheet-like nanoscale crystal grain, and can be used for macromolecular conversion or the reaction of forming macromolecule.

Description

Technical Field

[0001] This invention belongs to the field of molecular sieve synthesis technology, specifically relating to a layered nanoscale SAPO-34 molecular sieve containing numerous mesopores and its preparation method. Background Technology

[0002] In the early 1980s, Union Carbide Corporation of the United States successfully developed a novel molecular sieve system—the silica-alumina (SAPO-n) series of molecular sieves. These sieves consist of a three-dimensional framework structure composed of phosphorus-oxygen tetrahedra (PO4), aluminum-oxygen tetrahedra (AlO4), and silicon-oxygen tetrahedra (SiO4). After 40 years of development, the structural types of silica-alumina molecular sieves have reached more than 60, and they are widely used in C1 chemistry, environmental protection and emission reduction, and oil refining and chemical industries, providing material support for technologies such as comprehensive carbon resource utilization, clean environmental protection, and the transformation of oil refining into chemical engineering.

[0003] SAPO-34 molecular sieve is a silica-alumina phosphate molecular sieve with a chalcogenide (CHA) topology. Its framework structure consists of parallel double six-membered rings stacked in an ABC configuration. SAPO-34 molecular sieve has eight-membered ring pores and a three-dimensional intersecting channel structure. The pore size is 0.38 nm × 0.38 nm, and an ellipsoidal CHA cage with a size of 1.0 nm × 0.67 nm × 0.67 nm is formed at the intersection of the eight-membered ring channels. Due to its suitable acid strength, unique channel structure, good stability, and hydrothermal stability, SAPO-34 molecular sieve has wide applications in methanol-to-olefins (MTO), selective reduction of nitrogen oxides, CO2 hydrogenation to olefins, and CO2 adsorption and separation.

[0004] The small pore size of SAPO-34 molecular sieves provides a unique confinement effect for reactions, but these narrow channels also introduce significant mass transfer resistance, adversely affecting the catalyst's reactivity and lifespan. Studies have shown that synthesizing small-crystal, lamellar SAPO-34 nanoscale molecular sieves can not only shorten the residence time of reactant and product molecules within the pores and improve intracrystalline diffusion efficiency, but also enhance the connectivity between the pores and the outer surface, thereby increasing the utilization rate of active sites.

[0005] The commonly used synthesis method for SAPO-34 molecular sieve is hydrothermal synthesis, using water as a solvent. Commonly used organic template agents include tetraethylammonium hydroxide, triethylammonium, diethylammonium, morpholine, and isopropylammonium. The synthesized samples usually appear as cubic crystals.

[0006] CN102616810A uses tetraethylammonium hydroxide as a template agent, mixes it with aluminum, silicon and phosphorus sources, and controls the gel concentration by adding a specific solvent. It then obtains SAPO-34 molecular sieves with a size range of 20-300 nm and cubic or flake morphology by conventional hydrothermal or microwave heating.

[0007] CN103641131 A discloses a method for preparing thin-film nano-SAPO-34 molecular sieves with low silicon content. Using tetraethylammonium hydroxide as a template agent, thin-film nano-SAPO-34 molecular sieves with an average crystal particle size of 50-250 nm and a thickness of 50-100 nm are synthesized by conventional hydrothermal or solvothermal synthesis methods.

[0008] CN104192860A describes the preparation of SAPO-34 molecular sieves with a thin-layer morphology by adding a bis-headed amine cationic surfactant to a hydrothermal synthesis system. However, the thin-layer SAPO-34 molecular sieves prepared by this method suffer from a decrease in specific surface area due to the use of the bis-headed amine cationic surfactant during synthesis. This surfactant is difficult to remove during calcination, leading to pore blockage.

[0009] CN106044794A describes a method that first prepares a accelerator solution, then adds it to an initial gel, and obtains a lamellar SAPO-34 molecular sieve via hydrothermal crystallization. This sieve is then applied to the methanol-to-olefins reaction. However, this method requires the prior preparation of the accelerator solution, increasing energy consumption and production costs, making it unsuitable for industrial applications.

[0010] The nanosheet SAPO-34 molecular sieves synthesized by the above-mentioned existing technologies all have low mesopore content, which will affect the diffusion of larger reactant and product molecules. Summary of the Invention

[0011] The technical problem to be solved by the present invention is to provide a nanoscale layered SAPO-34 molecular sieve having a large number of mesoporous structures. Another technical problem to be solved by the present invention is to provide a method for synthesizing the aforementioned nanoscale layered SAPO-34 molecular sieve with numerous mesopores.

[0012] The term "nanoscale" in this invention refers to the thickness of the SAPO-34 molecular sieve crystals being less than 200 nm.

[0013] In this invention, the crystal size and thickness are determined by scanning electron microscopy (SEM). The measurement method is as follows: 50 crystals are randomly selected, and the crystal size and thickness are measured by measurement software. The minimum and maximum values ​​of the crystal size and thickness are taken as their respective size ranges.

[0014] In this invention, mesopore volume refers to the volume of pores with a diameter in the range of 2 to 50 nm, and total pore volume refers to the volume of pores with a diameter in the range of 0 to 100 nm. The pore volume is measured by the low-temperature nitrogen physical adsorption BET method, see standard GB T 21650.2-2008.

[0015] The present invention provides a SAPO-34 molecular sieve with a nanoscale lamellar crystal structure. The SAPO-34 molecular sieve also has a large number of mesoporous structures, wherein the presence of a large number of mesoporous structures means that the mesoporous volume accounts for more than 10% of the total pore volume, for example, 13-17%.

[0016] According to the present invention, preferably, the APO-34 molecular sieve has a grain thickness of less than 200 nm and a grain size of less than 1 micrometer. The grain thickness refers to the size of the grain in this dimension being smaller than the dimensions of the other two dimensions perpendicular to it in three-dimensional space. The grain size refers to the length of the longest side of the grain surface perpendicular to the grain thickness direction.

[0017] According to the present invention, in one embodiment of the SAPO-34 molecular sieve, the surface of the lamellar crystals perpendicular to the thickness direction is rectangular. The thickness of the crystal is smaller than the side length of the shortest side of the surface perpendicular to the thickness direction.

[0018] According to the SAPO-34 molecular sieve of the present invention, preferably, the SAPO-34 molecular sieve has a crystal thickness of 20-200 nm and a crystal size of 90-980 nm. Preferably, the thickness does not exceed 40% of the crystal size, for example, 3-35%. The present invention also provides a method for synthesizing the SAPO-34 molecular sieve, comprising the following steps:

[0019] (1) Mix aluminum source, template agent I and water, stir for 0 to 30 minutes, then add template agent II and mix evenly to obtain mixture A; the even mixing is, for example, stirred at room temperature for 1 to 10 hours, the room temperature being 20 to 30°C;

[0020] The ratio of template agent I to template agent II and the total amount of template agent I and template agent II are controlled within a certain range; the ratio of template agent I to template agent II is 0.25-4:1 molar ratio, and the ratio of the total amount of template agent I and template agent II to the aluminum source based on alumina is 1-4:1 molar ratio.

[0021] Template agent I is a template agent that has the function of forming CHA cages and filling microporous structures, and template agent II is a template agent that is easily adsorbed on the crystal surface of the grain and has the function of inhibiting crystal surface growth;

[0022] (2) Add phosphorus source to mixture A and stir evenly, for example, stir at room temperature for 1 to 10 hours to obtain mixture B;

[0023] (3) Add silicon source to mixture B and stir evenly, for example, stir for more than 0.5 hours, for example, stir for 0.5-10 hours, to obtain mixture C;

[0024] (4) Mixture C is hydrothermally dynamically crystallized at 150-220℃ for 12-120h;

[0025] (5) Separate, wash, and dry to obtain a solid product;

[0026] (6) Roasting.

[0027] According to the SAPO-34 molecular sieve synthesis method of the present invention, in step (1), the aluminum source, template agent I and water are mixed and stirred for 0-30 minutes, and then template agent II is added. In one embodiment, after the aluminum source and template agent I are mixed, the mixture is stirred for 0-30 minutes, for example, 5-20 minutes, and then template agent II is added. The water can be added before the aluminum source and template agent I, or simultaneously with the aluminum source and template agent I, or after the aluminum source and template agent I.

[0028] According to one embodiment of the SAPO-34 molecular sieve synthesis method of the present invention, the silicon source is selected from one or more of silica sol, silica, or silicone grease such as tetraethyl orthosilicate.

[0029] According to one embodiment of the SAPO-34 molecular sieve synthesis method of the present invention, the aluminum source is selected from one or more of boehmite, pseudoboehmite, alumina, aluminum hydroxide, or aluminum isopropoxide.

[0030] According to one embodiment of the SAPO-34 molecular sieve synthesis method of the present invention, the phosphorus source is one or more of phosphoric acid, phosphorous acid, ammonium dihydrogen phosphate or diammonium hydrogen phosphate, preferably phosphoric acid.

[0031] According to the SAPO-34 molecular sieve synthesis method of the present invention, in one embodiment, the template agent I is selected from one or more of tetraethylammonium hydroxide, tetraethylammonium chloride, or tetraethylammonium bromide; and the template agent II is selected from one or more of diethylamine, triethylamine, morpholine, or isopropylamine.

[0032] According to the SAPO-34 molecular sieve synthesis method of the present invention, the mixture C (also referred to as the initial gel mixture) has the following molar ratio:

[0033] The SiO2:Al2O3 ratio is 0.2–1.2, for example, 0.4–1.

[0034] P2O5:Al2O3 = 0.8–1.2;

[0035] Template agent I: Al2O3 = 0.2–1.8;

[0036] Template agent II: Al2O3 = 0.2–1.8;

[0037] H2O:Al2O3 = 20-100:1, for example 40-80:1.

[0038] According to the SAPO-34 molecular sieve synthesis method of the present invention, preferably, the ratio of (template agent I + template agent II):Al2O3 is 1 to 2. Template agent I:Al2O3 is preferably 0.2 to 0.8, and template agent II:Al2O3 is preferably 0.4 to 1.2. All ratios are molar ratios.

[0039] According to the SAPO-34 molecular sieve synthesis method of the present invention, preferably, the molar ratio of template agent I to template agent II is 0.25 to 2.5:1.

[0040] According to the SAPO-34 molecular sieve synthesis method of the present invention, the hydrothermal dynamic crystallization in step (4) is an existing technology, for example, crystallization can be carried out by stirring at 150-220°C for 12-120 hours.

[0041] According to the SAPO-34 molecular sieve synthesis method of the present invention, the separation, washing, and drying in step (5) can be performed using existing separation, washing, and drying methods. For example, centrifugation or filtration can be used for separation, deionized water or distilled water can be used for washing, and drying can be performed using drying, airflow drying, or flash drying methods.

[0042] According to the SAPO-34 molecular sieve synthesis method of the present invention, in step (6), the calcination can be carried out at 450-600°C for 2-8 hours.

[0043] The SAPO-34 molecular sieve provided by the present invention can be used for macromolecular conversion reactions or for reactions that form macromolecules. The macromolecular conversion reaction is, for example, the 1-butene cracking reaction, and the reactions that form macromolecules are, for example, the methanol conversion to olefins and the carbon dioxide hydrogenation to gasoline.

[0044] The SAPO-34 molecular sieve synthesis method provided by this invention employs a traditional hydrothermal synthesis method, using two template agents. By controlling the order of addition and synthesis conditions, as well as the ratio and other characteristics of the two template agents, a SAPO-34 molecular sieve with a large number of mesopores and a nanoscale lamellar morphology is obtained. The molecular sieve synthesis method provided by this invention has at least one of the following beneficial effects, preferably multiple or all of them:

[0045] 1. Capable of synthesizing nanoscale layered SAPO-34 molecular sieve materials with a thickness of no more than 200 nm and a grain size of less than 1 micrometer.

[0046] 2. The synthesized SAPO-34 molecular sieve material has a large number of mesoporous structures, in which the mesoporous volume accounts for more than 10% of the total pore volume.

[0047] 3. By using inexpensive organic templates as the second template, and in combination with other features, nanosheet SAPO-34 molecular sieves can be synthesized with a lower amount of expensive first organic template, for example, template I: Al2O3 less than 0.4, for example, 0.2 to 0.4. This eliminates the need to use large amounts of the relatively expensive first organic template, resulting in lower production costs.

[0048] 4. The synthesis is carried out by a one-step crystallization method, which is simple and efficient.

[0049] 5. The hydrothermal synthesis method is used, and no solvent other than water needs to be added, resulting in lower subsequent separation costs.

[0050] 6. It does not require the use of crystal morphology modifiers, surfactants, specific solvents or other additives, nor does it require special equipment such as ultrasound, making it economical and environmentally friendly. Attached Figure Description

[0051] Figure 1 The image shows the XRD pattern of the nanoscale layered SAPO-34 molecular sieve prepared in Example 1.

[0052] Figure 2 The XRD pattern of SAPO-34 molecular sieve prepared for Comparative Example 1.

[0053] Figure 3 SEM images of the nanoscale layered SAPO-34 molecular sieve prepared in Example 1: (a) scale bar 2 μm (b) scale bar 500 nm.

[0054] Figure 4 This is a TEM image of the nanoscale layered SAPO-34 molecular sieve prepared in Example 1.

[0055] Figure 5 The image shows the SEM pattern of the SAPO-34 molecular sieve prepared in Comparative Example 1.

[0056] Figure 6 SEM image of SAPO-34 molecular sieve prepared for Comparative Example 2

[0057] Figure 7 The N2 physical adsorption-desorption curve of the nanoscale layered SAPO-34 molecular sieve prepared in Example 1 is shown.

[0058] Figure 8 The N2 physical adsorption-desorption curve of SAPO-34 molecular sieve prepared in Comparative Example 1 is shown. Detailed Implementation

[0059] One embodiment of the SAPO-34 molecular sieve synthesis method of the present invention includes the following steps:

[0060] a) At room temperature, add aluminum source and template agent I to water. After adding all aluminum source and template agent I, stir at room temperature (e.g., 25°C) for 0-30 minutes (e.g., 5-20 minutes). Then add template agent II and stir at room temperature (e.g., 25°C) for 1-10 hours to obtain mixture A. The ratio of template agent I to template agent II is 0.25-4:1 molar ratio, and the total amount of template agent I and template agent II is 1-4:1 molar ratio to the aluminum source (calculated as alumina).

[0061] b) Add a phosphorus source to mixture A and stir at room temperature for 1–10 h to obtain mixture B;

[0062] c) Add a silicon source to mixture B and stir for 1–10 h to obtain mixture C; the molar ratio of each component in mixture C (initial gel mixture) is: SiO2:Al2O3 = 0.2–0.8, P2O5:Al2O3 = 0.8–1.2, template agent I:Al2O3 = 0.2–1.8, template agent II:Al2O3 = 0.2–1.8, H2O:Al2O3 = 20–100;

[0063] d) The mixture C is hydrothermally and dynamically crystallized at 150-220°C for 12-120 hours. The hydrothermal and dynamic crystallization can be carried out under stirring. In one embodiment, the stirring speed is in the range of 5-50 r / min. The synthesis liquid can be stirred by mechanical stirring or by rotating the crystallization vessel. After crystallization, the mixture is centrifuged, washed, and dried to obtain a solid product, namely molecular sieve powder.

[0064] e) The molecular sieve powder is calcined in air at 450-600℃ for 2-8 hours to remove the template agent, thereby obtaining mesoporous nanoscale lamellar SAPO-34 molecular sieve.

[0065] The method described above for synthesizing SAPO-34 molecular sieve yields mesoporous, layered nano-SAPO-34 molecular sieve crystals. The crystal thickness is preferably no more than 200 nm, and the length and width of the rectangular surface perpendicular to the thickness are both less than 1 micrometer.

[0066] The following examples will further illustrate the present invention and are intended to help readers better understand the essence of the present invention and its beneficial effects, but should not be construed as limiting the scope of the present invention.

[0067] In the embodiments, the measurement of total pore volume and mesopore volume refers to standard GB / T 21650.2-2008.

[0068] Boehmite, Shanxi New Materials Co., Ltd. of China Aluminum Corporation, with an Al2O3 content of 72.6% by weight.

[0069] Triethylamine, Beijing Inokai Technology Co., Ltd., purity 99.5%.

[0070] Isopropylamine, Beijing Inokai Technology Co., Ltd., 99% purity.

[0071] Tetraethylammonium hydroxide solution, Beijing Inokai Technology Co., Ltd., content 25% by weight

[0072] Phosphoric acid solution, Tianjin Damao Chemical Reagent Factory, phosphoric acid content 85% by weight

[0073] Silica sol, Qingdao Jiyida Silica Reagent Co., Ltd., SiO2 content 40% by weight

[0074] Fumed silica, Maclean's Bioreactors Ltd., specific surface area 200 μm 2 / g

[0075] Alumina, Beijing Innocare Technology Co., Ltd., 99.9% purity.

[0076] Morpholine, Maclean's Biological Reagents Co., Ltd., 99% purity

[0077] Diethylamine, Beijing Inokai Technology Co., Ltd., 99% purity.

[0078] Aluminum isopropoxide, Shanghai Aladdin Biochemical Technology Co., Ltd., 98% purity.

[0079] Tetraethylammonium bromide, TISA (Shanghai) Chemical Industry Development Co., Ltd., 98% purity.

[0080] Tetraethylammonium chloride, Beijing Inokai Technology Co., Ltd., 98% purity.

[0081] Example 1

[0082] 13.00 g of boehmite and 76.20 g of tetraethylammonium hydroxide solution were added to 26.97 g of deionized water and mixed. The mixture was stirred at 25 °C for 10 min, followed by the addition of 5.61 g of triethylamine. The mixture was stirred for another 2 h to obtain a homogeneous solution, A. 21.35 g of phosphoric acid solution was added to solution A and stirred at 25 °C for 2 h to obtain solution B. 6.87 g of silica sol was added to solution B and stirred for 2 h to obtain solution C. Solution C was crystallized at 200 °C for 48 h at a crystallization vessel speed of 10 r / min. After crystallization, the solution was centrifuged, washed, and dried to obtain a solid product, namely the molecular sieve powder. The molecular sieve powder was then calcined in air at 550 °C for 5 h to remove the template agent, yielding nanoscale layered SAPO-34 molecular sieve, labeled as sample A. Sample A has layered crystals with rectangular surfaces.

[0083] Example 2

[0084] 12.78 g of boehmite and 43.58 g of tetraethylammonium hydroxide solution were added to 47.29 g of deionized water and stirred at 25 °C for 10 min. Then, 9.19 g of triethylamine was added, and stirring continued for 1 h to obtain a homogeneous mixture A. 25.18 g of phosphoric acid solution was added to mixture A, and stirring was continued at 25 °C for 1 h to obtain mixture B. 9.36 g of silica sol was added to mixture B, and stirring was continued for 2 h to obtain mixture C. Mixture C was crystallized at 190 °C for 24 h at a crystallization vessel speed of 15 r / min. After crystallization, the mixture was centrifuged, washed, and dried to obtain a solid product, namely the molecular sieve raw powder. The molecular sieve raw powder was then calcined in air at 550 °C for 4 h to remove the template agent, yielding nanoscale layered SAPO-34 molecular sieve, labeled as sample B. Sample B has layered crystals with rectangular surfaces.

[0085] Example 3

[0086] 14.16 g of boehmite and 23.72 g of tetraethylammonium hydroxide solution were added to 79.20 g of deionized water and mixed. The mixture was stirred at 25 °C for 10 min, followed by the addition of 7.15 g of isopropylamine. The mixture was stirred for another 1 h to obtain a homogeneous solution, A. 20.93 g of phosphoric acid solution was added to solution A and stirred at 25 °C for 1 h to obtain solution B. 4.45 g of fumed silica was added to solution B and stirred for 2 h to obtain solution C. Solution C was crystallized at 190 °C for 24 h at a crystallization vessel speed of 15 r / min. After crystallization, the solution was centrifuged, washed, and dried to obtain a solid product, namely the molecular sieve powder. The molecular sieve powder was then calcined in air at 550 °C for 4 h to remove the template agent, yielding nanoscale layered SAPO-34 molecular sieve, which was labeled as sample C. Sample C has layered crystals with rectangular surfaces.

[0087] Example 4

[0088] 11.47 g of alumina and 11.91 g of tetraethylammonium hydroxide solution were added to 84.03 g of deionized water and mixed. The mixture was stirred at 25 °C for 10 min, followed by the addition of 7.06 g of morpholine and stirring for another 1 h to obtain mixture A. 28.02 g of phosphoric acid solution was added to mixture A and stirred at room temperature for 1 h to obtain mixture B. 7.51 g of silica sol was added to mixture B and stirred for 2 h to obtain mixture C. Mixture C was crystallized at 210 °C for 24 h at a crystallization vessel speed of 15 r / min. After crystallization, the mixture was centrifuged, washed, and dried to obtain a solid product, namely the molecular sieve powder. The molecular sieve powder was then calcined in air at 550 °C for 4 h to remove the template agent, yielding nanoscale layered SAPO-34 molecular sieve, labeled as sample D. Sample D has layered crystals with rectangular surfaces.

[0089] Example 5

[0090] 32.39 g of aluminum isopropoxide and 9.9 g of tetraethylammonium bromide were added to 73.58 g of deionized water and mixed. The mixture was stirred at 25 °C for 10 min, and then 3.41 g of diethylamine was added. The mixture was stirred for another 1 h to obtain a homogeneous solution, A. 21.50 g of phosphoric acid solution was added to solution A and stirred at 25 °C for 1 h to obtain solution B. 9.22 g of silica sol was added to solution B and stirred for 2 h to obtain solution C. Solution C was crystallized at 190 °C for 72 h at a crystallization vessel speed of 15 r / min. After crystallization, the solution was centrifuged, washed, and dried to obtain a solid product, namely the molecular sieve powder. Subsequently, the molecular sieve powder was calcined in air at 550 °C for 4 h to remove the template agent, yielding nanoscale layered SAPO-34 molecular sieve, which was labeled as sample E. Sample E has layered crystals with rectangular surfaces.

[0091] Example 6

[0092] 13.11 g of boehmite and 15.79 g of tetraethylammonium chloride were added to 87.01 g of deionized water and stirred at 25 °C for 10 min. Then, 3.77 g of triethylamine was added, and stirring continued for 1 h to obtain a homogeneous mixture A. 25.84 g of phosphoric acid solution was added to mixture A, and stirring was continued at 25 °C for 1 h to obtain mixture B. 4.48 g of fumed SiO2 was added to mixture B, and stirring was continued for 2 h to obtain mixture C. Mixture C was crystallized at 190 °C for 72 h at a crystallization vessel speed of 30 r / min. After crystallization, the mixture was centrifuged, washed, and dried to obtain a solid product, namely the molecular sieve powder. The molecular sieve powder was then calcined in air at 550 °C for 4 h to remove the template agent, yielding nanoscale layered SAPO-34 molecular sieve, labeled as sample F. Sample F has layered crystals with rectangular surfaces.

[0093] Comparative Example 1

[0094] 13.54 g of boehmite and 19.47 g of triethylamine were added to 87.61 g of deionized water and mixed. The mixture was stirred at 25 °C for 2 h until homogeneous, yielding mixture A. 22.23 g of phosphoric acid solution was added to mixture A and stirred at 25 °C for 1 h, yielding mixture B. 7.15 g of silica sol was added to mixture B and stirred for 2 h, yielding mixture C. Mixture C was crystallized at 200 °C for 24 h at a crystallization vessel speed of 10 r / min. After crystallization, the mixture was centrifuged, washed, and dried to obtain a solid product, namely the molecular sieve powder. The molecular sieve powder was then calcined in air at 550 °C for 5 h to remove the template agent, yielding SAPO-34 molecular sieve, which was labeled as sample G. Sample G has cubic crystals.

[0095] Comparative Example 2

[0096] 12.50 g of boehmite, 30.1 g of tetraethylammonium hydroxide, and 80.21 g of deionized water were mixed and stirred at 25 °C for 2 h until homogeneous, yielding mixture A. 20.52 g of phosphoric acid solution was added to mixture A, and the mixture was stirred at 25 °C for 1 h to obtain mixture B. 6.67 g of silica sol was added to mixture B, and the mixture was stirred for 2 h to obtain mixture C. Mixture C was crystallized at 200 °C for 24 h at a crystallization vessel speed of 10 r / min. After crystallization, the mixture was centrifuged, washed, and dried to obtain a solid product, namely the molecular sieve powder. Subsequently, the molecular sieve powder was calcined in air at 550 °C for 5 h to remove the template agent, yielding SAPO-34 molecular sieve, which was labeled as sample H. Sample H has cubic crystal grains.

[0097] Comparative Example 3

[0098] 13.00 g of boehmite, 5.61 g of triethylamine, and 26.97 g of deionized water were mixed and stirred at 25 °C for 10 min. Then, 76.20 g of tetraethylammonium hydroxide solution was added, and stirring continued for 2 h to obtain a homogeneous mixture A. 21.35 g of phosphoric acid solution was added to mixture A, and stirring was continued at 25 °C for 2 h to obtain mixture B. 6.87 g of silica sol was added to mixture B, and stirring was continued for 2 h to obtain mixture C. Mixture C was crystallized at 200 °C for 48 h at a crystallization vessel speed of 10 r / min. After crystallization, the mixture was centrifuged, washed, and dried to obtain a solid product, namely the molecular sieve powder. The molecular sieve powder was then calcined in air at 550 °C for 5 h to remove the template agent, yielding SAPO-34 molecular sieve, which was labeled as sample I. Sample I has cubic crystals.

[0099] Comparative Example 4

[0100] 10.61 g of boehmite and 24.47 g of tetraethylammonium hydroxide solution were added to 76.10 g of deionized water and mixed. The mixture was stirred at 25 °C for 10 min, followed by the addition of 3.04 g of triethylamine. The mixture was stirred for another 2 h to obtain a homogeneous solution, A. 23.99 g of phosphoric acid solution was added to solution A and stirred at 25 °C for 2 h to obtain solution B. 7.80 g of silica sol was added to solution B and stirred for 2 h to obtain solution C. Solution C was crystallized at 200 °C for 48 h at a crystallization vessel speed of 10 r / min. After crystallization, the solution was centrifuged, washed, and dried to obtain a solid product, namely the molecular sieve powder. The molecular sieve powder was then calcined in air at 550 °C for 5 h to remove the template agent, yielding SAPO-34 molecular sieve, which was labeled as sample J. Sample J has rod-shaped crystals.

[0101] Table 1 lists the measured grain size and mesopore volume of the samples synthesized in each embodiment and comparative example. As can be seen from the table, the SAPO-34 molecular sieve products synthesized using the method in this patent all have a lamellar structure and have a larger mesopore volume compared to SAPO-34 molecular sieves synthesized by traditional methods.

[0102] Table 1. Grain size and mesopore volume of each embodiment and comparative sample.

[0103]

[0104] Table 1 shows the percentage of mesopore volume in the total pore volume.

[0105] Table 2 shows the proportions of each embodiment and comparative example mixture C.

[0106] Example 1 1.0 1.0 0.5 1.4 0.6 60.0 Example 2 1.0 1.2 0.8 0.8 1.0 60.0 Example 3 1.0 0.9 0.8 0.4 1.2 60.0 Example 4 1.0 1.2 0.5 0.2 0.8 60.0 Example 5 1.0 1.2 0.8 0.6 0.6 80.0 Example 6 1.0 1.2 0.8 1.0 0.4 60.0 Comparative Example 1 1.0 1.0 0.5 0.0 2.0 60.0 Comparative Example 2 1.0 1.0 0.5 2.0 0.0 60.0 Comparative Example 3 1.0 1.0 0.5 1.4 0.6 60.0 Comparative Example 4 1.0 1.0 0.5 0.4 0.4 60.0

Claims

1. A method for synthesizing SAPO-34 molecular sieve, comprising the following steps: (1) Mix the aluminum source, template agent I and water, stir for 0~30 min, then add template agent II and mix evenly to obtain mixture A; in, The molar ratio of template agent I to template agent II is 0.25 to 4:1, and the molar ratio of the total amount of template agent I and template agent II to the aluminum source calculated as Al2O3 is 1 to 4:

1. Template agent I is a template agent that forms CHA cages and fills microporous structures, and template agent II is a template agent that is easily adsorbed onto the crystal face and inhibits crystal face growth; template agent I is selected from one or more of tetraethylammonium hydroxide, tetraethylammonium chloride, or tetraethylammonium bromide; template agent II is selected from one or more of diethylamine, triethylamine, morpholine, or isopropylamine; (2) Add phosphorus source to mixture A and stir evenly to obtain mixture B; (3) Add silicon source to mixture B and stir until homogeneous to obtain mixture C; (4) Mixture C is subjected to hydrothermal dynamic crystallization at 150~220℃ for 12~120 h; (5) Separate, wash, and dry to obtain a solid product; (6) Roasting; The SAPO-34 molecular sieve has nanoscale lamellar crystals, and the mesopore volume of the SAPO-34 molecular sieve accounts for more than 10% of the total pore volume; the SAPO-34 molecular sieve crystal thickness is 20-200 nm, and the crystal size is 90-980 nm.

2. The method according to claim 1, characterized in that, The silicon source is selected from one or more of silica sol, silicon dioxide, and silicone grease; The aluminum source is selected from one or more of boehmite, pseudoboehmite, alumina, aluminum hydroxide, or aluminum isopropoxide; The phosphorus source is one or more of phosphoric acid, phosphorous acid, ammonium dihydrogen phosphate, or diammonium hydrogen phosphate.

3. The method according to claim 1, characterized in that, Mixture C has the following molar ratio: SiO2:Al2O3 = 0.2~1.2; P2O5:Al2O3 = 0.8~1.2; Template agent I: Al2O3 = 0.2~1.8; Template agent II: Al2O3 = 0.2~1.8; H2O:Al2O3 = 20 ~ 100.

4. The method according to claim 3, characterized in that, Template agent I:Al2O3 is 0.2~0.8, template agent II:Al2O3 is 0.4~1.2; all the above ratios are molar ratios.

5. The method according to claim 3, characterized in that, (Template agent I + template agent II): Al2O3 = 1~2; the above ratio is a molar ratio.

6. The method according to any one of claims 1 to 5, characterized in that, The molar ratio of template agent I to template agent II is 0.25~2.5:

1.

7. The method according to claim 1, characterized in that, In step (6), the roasting is carried out at 450~600℃ for 2~8 h.

8. The method according to claim 1, characterized in that, After mixing the aluminum source and template agent I, stir for 0-30 minutes, then add template agent II; water can be added before the aluminum source and template agent, simultaneously with the aluminum source and template agent I, or after the aluminum source and template agent I.

9. The method according to claim 1, characterized in that, In step (1), the mixing is uniform, which means stirring at room temperature for 1 to 10 hours, where room temperature is 20 to 30°C; in step (2), the mixing is uniform, which means stirring at room temperature for 1 to 10 hours; in step (3), the mixing is uniform, which means stirring for more than 0.5 hours.

10. The method according to claim 8, characterized in that, After mixing the aluminum source and template agent I, stir for 5-20 minutes.

11. The SAPO-34 molecular sieve obtained by any one of the synthesis methods according to claims 1 to 10.

12. The SAPO-34 molecular sieve according to claim 11, characterized in that, The surface of the SAPO-34 molecular sieve crystals perpendicular to the thickness direction is rectangular, and the mesopore volume accounts for 13-17% of the total pore volume.

13. The SAPO-34 molecular sieve according to claim 11, characterized in that, The thickness dimension shall not exceed 40% of the grain size.

14. The application of the SAPO-34 molecular sieve according to any one of claims 11 to 13 in reactions involving macromolecular conversion or macromolecular formation, wherein the macromolecular conversion reaction is a 1-butene cracking reaction, and the macromolecular formation reaction is methanol conversion to olefins or carbon dioxide hydrogenation to gasoline.

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