A sa po-34 molecular sieve with a hollow structure and a preparation method and application thereof

Abstract

The application provides a kind of hollow SAPO-34 molecular sieve prepared by using aluminum phosphate with kanemite structure and its preparation method and application, characterized by using aluminum phosphate with kanemite structure as aluminum source and phosphorus source, and grinding and mixing with silicon source, template agent and a small amount of water, then adding into hydrothermal kettle to synthesize SAPO-34 molecular sieve with hollow structure. The synthesis method of the hollow SAPO-34 molecular sieve of the application can form hollow structure without acid-base post-treatment process or adding mesoporous template agent, the process is simple, which is beneficial to industrial scale production; and the formation of hollow structure is beneficial to diffusion mass transfer and heat conduction in methanol to olefin reaction. The SAPO-34 molecular sieve prepared by the method has a selectivity of ethylene and propylene as high as 85% in methanol to olefin reaction, and the service life reaches more than 400 minutes, which is beneficial to industrial application.

Description

Technical Field

[0001] This application relates to a SAPO-34 molecular sieve with a hollow structure, its preparation method and application, belonging to the field of molecular sieve synthesis. Background Technology

[0002] Low-carbon olefins (especially ethylene and propylene) are fundamental raw materials for modern chemical industry. They can be used to prepare various plastics and rubbers through self-polymerization or copolymerization reactions, and can also be used to generate important chemical intermediates through various conversion reactions. Currently, the production of low-carbon olefins mainly follows two technical routes: the traditional petrochemical route and the coal-based chemical route. my country has relatively scarce petroleum resources, but abundant coal reserves and a relatively mature coal chemical technology system. Therefore, the process route of producing low-carbon olefins from methanol using coal as a raw material is more in line with my country's national conditions.

[0003] Currently, upstream processes such as coal gasification, syngas purification, and methanol synthesis are quite mature. Therefore, the key technological link in the coal-to-olefins route lies in the methanol to olefins (MTO) process. Among these processes, the catalyst, as the core of the MTO process, is crucial for mastering and developing complete methanol-to-olefins technologies. Developing MTO catalysts with high selectivity and stability is of great significance for improving process economics.

[0004] SAPO-34 molecular sieve, with its CHA topology, exhibits excellent catalytic performance in MTO reactions due to its eight-membered ring open channels, suitable cage size, and tunable acidic sites: methanol conversion can reach 100%, C2-C4 low-carbon olefin selectivity is as high as about 90%, and almost no C5 or higher byproducts are generated (Applied Catalysis, 1990, 64: 31). However, the small-sized eight-membered ring pores of SAPO-34 also lead to significant diffusion limitations. Larger carbon deposits generated in the reaction are difficult to diffuse out of the cage, which not only exacerbates side reactions but also easily causes pore blockage, leading to rapid catalyst deactivation.

[0005] Studies have shown that constructing hollow structures within molecular sieve crystals can effectively improve their MTO catalytic performance. On one hand, SAPO-34 molecular sieves with hollow structures can be obtained through acid-base post-treatment (Chem. Commun., 2016, 52, 5718; Micro. Meso. Mater., 2022, 341, 112100; CN 106892439 B), which facilitates the diffusion of reactants and products and can improve the activity and selectivity of the molecular sieve for low-carbon olefins. However, the post-treatment method is cumbersome, generates significant pollution, and easily damages the molecular sieve framework, resulting in low yields. On the other hand, SAPO-34 molecular sieves with hollow structures can also be obtained by introducing metals, seed crystals, or auxiliaries during conventional molecular sieve synthesis. Patent CN105858684A reports a method for synthesizing hollow hierarchical SAPO-34 molecular sieves using seed-assisted crystal synthesis; patent CN110002462A reports a method for preparing hollow SAPO-34 molecular sieves by adding a crystallization aid to the synthesis system. Patent CN114890435B reports a method for preparing hollow SAPO-34 molecular sieves using spent MTO catalyst, a method that does not require the introduction of a special template agent or acid / base post-treatment.

[0006] In summary, the research and development of a simple and effective method for in-situ synthesis of SAPO-34 molecular sieves with hollow structures without the addition of other auxiliaries has significant industrial application value and prospects. Summary of the Invention

[0007] The purpose of this invention is to provide a novel method for preparing SAPO-34 molecular sieves with a hollow structure and its application in methanol-to-olefins conversion and various hydrocarbon conversions, in order to solve the problems in the prior art.

[0008] The SAPO-34 molecular sieve prepared by this invention has a hollow structure and a large specific surface area and mesoporous pore volume. As a catalyst for methanol-to-olefins reaction, it can greatly improve diffusion restriction, slow down the formation of carbon deposits, thereby prolonging the catalyst's catalytic life and improving the selectivity of low-carbon olefins.

[0009] This invention utilizes layered aluminum phosphate with a kanemite structure as a phosphorus and aluminum source, and synthesizes SAPO-34 molecular sieve with a hollow structure using a solid-phase grinding method.

[0010] The synthesis method of this invention is simple, requiring no acid-base post-treatment or addition of additives to form a hollow structure; the process is simple, requiring only about 20 minutes of grinding to obtain the gel precursor, eliminating the need for long-term stirring and mixing and subsequent aging processes required in the preparation of gel precursors in molecular sieve hydrothermal synthesis; the synthesis system uses less water, greatly reducing the waste liquid generated during synthesis; and the formation of the hollow structure is beneficial for diffusion mass transfer and heat conduction in the methanol-to-olefins reaction, achieving a selectivity of over 85% for ethylene and propylene in the methanol-to-olefins reaction.

[0011] This invention provides a method for preparing SAPO-34 molecular sieve with a hollow structure, characterized in that SAPO-34 molecular sieve with a hollow structure is synthesized by solid-phase grinding using layered aluminum phosphate with a kanemite structure.

[0012] The method for preparing SAPO-34 molecular sieve with a hollow structure according to the present invention is characterized by the following synthesis steps:

[0013] a) Layered aluminum phosphate with a kanemite structure is ground and mixed with a silicon source, then water and an organic template agent are added. After grinding for a certain period of time, a gel precursor is obtained. In the precursor, the molar ratio of each component oxide is (0.5~4.0) R:1 Al2O3:1 P2O5:(0.05~3.0) SiO2:(2~25) H2O, where R is an organic template agent. Preferably, the molar ratio of each component oxide is (0.5~3.0):1 Al2O3:1 P2O5:(0.2~1.0) SiO2:(8~20) H2O.

[0014] b) The gel precursor obtained in step a) is placed in a high-pressure reactor and crystallized at an isothermal temperature under autogenous pressure. After crystallization, the solid product is centrifuged and washed with deionized water until neutral. It is then dried in air at 80~120℃ to obtain SAPO-34 molecular sieve raw powder.

[0015] c) The SAPO-34 molecular sieve raw powder is calcined at high temperature to remove the template agent, thereby obtaining SAPO-34 molecular sieve with a hollow structure.

[0016] In the above steps, the preparation process of layered aluminum phosphate with a kanemite structure in step a) is as follows: Boehmite and water are mixed, stirred evenly, and then phosphoric acid is added. After stirring for a certain period of time, organic template agent T is added. The molar ratio of the oxides used in each component is (1.5~2): T: 1 Al2O3: 1 P2O5: (20~80) H2O, where T is any one or more linear aliphatic amines [NH2(CH2)]. nCH3], n=4~12; the resulting mixture was placed in a high-pressure reactor and heated in an oven at 180~200℃ for 24~72 hours. The solid product was then centrifuged and washed with deionized water until neutral. After drying, layered aluminum phosphate with kanemite structure was obtained.

[0017] In the above steps, the silicon source used in step a) is selected from at least one of silica sol, activated silica, fumed silica, sodium silicate or tetraethyl orthosilicate, and the organic template agent used is selected from at least one of diethylamine, triethylamine, morpholine, diisopropylamine, di-n-propylamine, diethanolamine, triethanolamine, tetraethylammonium hydroxide.

[0018] In the above steps, step a) involves grinding and mixing layered aluminum phosphate with a kanemite structure and a silicon source, which means grinding for 10 to 30 minutes at room temperature; after adding water and an organic template agent, grinding for another 10 to 30 minutes to obtain a gel precursor.

[0019] In the above steps, step b) isothermal crystallization refers to placing the reactor in an oven under autogenous pressure for isothermal crystallization at a temperature of 140~230℃ and a crystallization time of 10~72 hours. Preferably, the crystallization temperature is 180~200℃ and the crystallization time is 24~48 hours.

[0020] In the above steps, the calcination temperature in step c) is 500~700℃, and the calcination time is 2~10 hours. Preferably, the calcination temperature is 550~600℃, and the calcination time is 6~10 hours.

[0021] The present invention also provides a hollow SAPO-34 molecular sieve prepared using layered aluminum phosphate with a kanemite structure, especially prepared by the above-described preparation method.

[0022] According to an embodiment of the present invention, the hollow SAPO-34 molecular sieve has an average particle size of 1-4 μm and a wall thickness of 40-800 nm. Preferably, the hollow SAPO-34 molecular sieve has an average particle size of 1-2 μm and a wall thickness of 40-100 nm.

[0023] According to an embodiment of the present invention, the hollow SAPO-34 molecular sieve has a mesoporous structure with a mesoporous size of 30~80 nm.

[0024] The present invention also provides an application of the above-mentioned hollow SAPO-34 molecular sieve prepared using layered aluminum phosphate with a kanemite structure as a catalyst in methanol-to-olefins.

[0025] In the above applications, the hollow SAPO-34 molecular sieve, as a catalyst, has a catalytic lifetime of over 400 minutes in the methanol-to-olefins reaction, and the selectivity for ethylene and propylene is over 85%.

[0026] The beneficial effects of this application include, but are not limited to:

[0027] (1) Using layered aluminum phosphate with kanemite structure as raw material, SAPO-34 molecular sieve with hollow structure can be prepared without the need for additional additives or post-processing. It is simple and effective and conducive to its industrial application.

[0028] (2) The process is simple, requiring only about 20 minutes of grinding to obtain the gel precursor. The synthesis system uses less water, which greatly reduces the waste liquid generated during synthesis.

[0029] (3) By changing the gel ratio, the wall thickness or mesopore size of SAPO-34 molecular sieve with hollow structure can be effectively controlled;

[0030] (4) The prepared SAPO-34 molecular sieve with hollow structure has a significantly increased lifetime in the reaction of methanol or dimethyl ether to low carbon olefins compared with conventional SAPO-34, and the total selectivity of ethylene and propylene can be as high as 85% or more. Attached Figure Description

[0031] Figure 1 The image shows the X-ray diffraction pattern of layered aluminum phosphate with a kanemite structure in Example 1.

[0032] Figure 2 The image shows the X-ray diffraction pattern of amorphous aluminum phosphate in Comparative Example 2.

[0033] Figure 3 The X-ray diffraction patterns are of Examples 1 to 3 and Comparative Examples 1 and 2.

[0034] Figure 4 This is a transmission electron microscope image of Example 1.

[0035] Figure 5 The diagram shows the physical adsorption of nitrogen in Examples 1 to 3.

[0036] Figure 6 This is a transmission electron microscope image of Example 2.

[0037] Figure 7 This is a transmission electron microscope image of Example 3.

[0038] Figure 8 This is a transmission electron microscope image of Comparative Example 1.

[0039] Figure 9This is a transmission electron microscope image of Comparative Example 2. Detailed Implementation

[0040] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise specified, the raw materials used in this application are all purchased commercially and used directly without special treatment.

[0041] Unless otherwise specified, the test conditions for this application are as follows:

[0042] X-ray powder diffraction (XRD) phase analysis was performed using an X'Pert PRO X-ray diffractometer from PANalytical, Netherlands, with a Cu target, a Kα radiation source (λ=0.15418 nm), a voltage of 40 kV, and a current of 40 mA.

[0043] The morphology of the samples was analyzed using a Tecnai G2 F20 S-TWIN TMP transmission electron microscope (TEM).

[0044] The specific surface area and pore size of the samples were determined using an ASAP 2420-4 Micron adsorption analyzer.

[0045] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments; the terminology used in the embodiments is for describing specific implementations and is not intended to limit the scope of protection of the present invention; unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art. In addition to the specific methods, devices, and materials used in the embodiments, those skilled in the art, based on their mastery of the prior art and the description of the present invention, may also use any prior art methods, devices, and materials similar to or equivalent to those described, used, and materials in the embodiments of the present invention to implement the present invention.

[0046] Example 1

[0047] Preparation of layered aluminum phosphate with a kanemite structure: 54.9 g of deionized water and 10 g of boehmite were added to a beaker and stirred continuously for 30 minutes to ensure thorough dispersion. Then, 15.4 g of 85% phosphoric acid was slowly added dropwise to the mixture, and stirring continued for 2 hours. Next, 9.8 g of n-butylamine was added, and stirring continued for 1 hour until homogeneous. The mixture was transferred to a high-pressure reactor and crystallized at 200 °C for 24 hours. After the reaction, the solid product was removed, centrifuged at high speed, washed three times with deionized water, and finally dried in an oven at 100 °C to obtain AlPO-kanemite. This product exhibits a layered morphology with a layer thickness of approximately 100 nm.

[0048] The prepared layered aluminum phosphate and silica were mixed and ground in a mortar for 20 minutes. A 35% tetraethylammonium hydroxide aqueous solution was added, and grinding was continued for a certain time to obtain a gel precursor. The molar ratio of the oxide components in the precursor was 1.5 tetraethylammonium hydroxide: 1 Al₂O₃: 1 P₂O₅: 0.4 SiO₂: 22H₂O. The obtained gel precursor was placed in a high-pressure reactor and crystallized at 200°C in an oven for 48 hours. After crystallization, the solid product was centrifuged and washed with deionized water until neutral. It was then dried in air at 100°C to obtain SAPO-34 molecular sieve powder. The SAPO-34 molecular sieve powder was calcined at 550°C with air for 6 hours to remove the template agent, thus obtaining a SAPO-34 molecular sieve with a hollow structure, designated as Example 1. Based on the mass of the molecular sieve sample obtained after calcination, the yield of the hollow SAPO-34 molecular sieve in this example was calculated to be 83%.

[0049] Example 1: The sample was characterized by XRD, SEM, and nitrogen physisorption. The results are shown in the figure below. Figure 3 , Figure 4 and Figure 5 The results showed that the synthesized product was a SAPO-34 molecular sieve with a CHA structure, which had a hollow structure, an average crystal particle size of 1-2 μm, a wall thickness of 400-600 nm, and a crystal mesopore size of 40-60 nm.

[0050] The obtained sample was calcined at 550℃ with air for 4 hours, then tableted and crushed to 40-60 mesh. 1.0 g of sample was weighed and loaded into a fixed-bed reactor for MTO reaction evaluation. Nitrogen gas was introduced at 550℃ for 1 hour for activation, then the temperature was lowered to the reaction temperature of 450℃. The nitrogen gas was then turned off, and a 40 wt% methanol-water solution was fed using a plunger pump at a methanol weight hourly space velocity (MHSV) of 2.0 h⁻¹. -1 The reaction products were analyzed by online gas chromatography, and the results are shown in Table 1.

[0051] Comparative Example 1

[0052] At room temperature, the prepared layered aluminum phosphate with a kanemite structure, silica, water, and a 35% tetraethylammonium hydroxide aqueous solution were added sequentially to a beaker. After stirring to ensure thorough mixing, an initial gel mixture of SAPO-34 molecular sieve was obtained. The molar ratio of each component in the mixture was: 1.5 tetraethylammonium hydroxide: 1 Al₂O₃: 1 P₂O₅: 0.4 SiO₂: 50 H₂O. After stirring, the gel mixture was placed in a stainless steel reactor and crystallized at 200℃ for 48 hours. After washing and drying, a control sample was obtained, designated as Control Sample 1. Control Sample 1 is a SAPO-34 molecular sieve with a CHA structure, and its crystals have a cubic morphology and lack a hollow structure. The XRD pattern is shown below. Figure 3 As shown, the SEM image is as follows Figure 8 As shown in Table 1.

[0053] Comparative Example 2

[0054] The ingredient ratio and process were the same as in Example 1, but the difference was that amorphous aluminum phosphate without a layered structure was used as the raw material. After washing and drying the crystallized product, Comparative Sample 2 was obtained. Comparative Sample 2 was a SAPO-34 molecular sieve with a CHA structure; its crystals had a cubic morphology and lacked a hollow structure. SEM images are shown below. Figure 9 As shown in Table 1.

[0055] Example 2

[0056] Preparation of layered aluminum phosphate with a kanemite structure: 32.9 g of deionized water and 10 g of boehmite were added to a beaker and stirred continuously for 30 minutes to ensure thorough dispersion. Then, 15.4 g of 85% phosphoric acid was slowly added dropwise to the mixture, and stirring continued for 2 hours. Next, 15.5 g of n-octylamine was added, and stirring continued for 1 hour until homogeneous. The mixture was transferred to a high-pressure reactor and crystallized at 190 °C for 60 hours. After the reaction, the solid product was removed, centrifuged at high speed, washed three times with deionized water, and finally dried in an oven at 100 °C to obtain AlPO-kanemite. This product exhibits a layered morphology with a layer thickness of approximately 150 nm.

[0057] The prepared layered aluminum phosphate and tetraethyl orthosilicate were mixed and ground in a mortar for 10 minutes. A small amount of water and triethylamine were added, and after grinding for a certain period of time, a gel precursor was obtained. The molar ratio of the oxides in the precursor was 3 triethylamine: 1 Al₂O₃: 1 P₂O₅: 0.8 SiO₂: 11 H₂O. The obtained gel precursor was placed in a high-pressure reactor and crystallized at 180°C in an oven for 48 hours. After crystallization, the solid product was centrifuged and washed with deionized water until neutral. It was then stored in air at 80°C.

[0058] The SAPO-34 molecular sieve raw powder was obtained by drying. The SAPO-34 molecular sieve raw powder was then calcined at 500°C with air for 10 hours to remove the template agent, thereby obtaining a SAPO-34 molecular sieve with a hollow structure, designated as Example 2. Based on the mass of the molecular sieve sample obtained after calcination, the yield of the hollow SAPO-34 molecular sieve in this example was calculated to be 86%.

[0059] Example 2: The sample was characterized by XRD, SEM, and nitrogen physisorption. The results are shown in the figure below. Figure 3 , Figure 5 and Figure 6 The results showed that the synthesized product was a SAPO-34 molecular sieve with a CHA structure, which had a hollow structure, an average crystal particle size of 1-2 μm, a wall thickness of 100-200 nm, and a crystal mesopore size of 10-20 nm.

[0060] The obtained sample was calcined at 550℃ with air for 4 hours, then tableted and crushed to 40-60 mesh. 1.0 g of sample was weighed and loaded into a fixed-bed reactor for MTO reaction evaluation. Nitrogen gas was introduced at 550℃ for 1 hour for activation, then the temperature was lowered to the reaction temperature of 450℃. The nitrogen gas was then turned off, and a 40 wt% methanol-water solution was fed using a plunger pump at a methanol weight hourly space velocity (MHSV) of 2.0 h⁻¹. -1 The reaction products were analyzed by online gas chromatography, and the results are shown in Table 1.

[0061] Example 3

[0062] Preparation of layered aluminum phosphate with a kanemite structure: 90.6 g of deionized water and 10 g of boehmite were added to a beaker and stirred continuously for 30 minutes to ensure thorough dispersion. Then, 15.4 g of 85% phosphoric acid was slowly added dropwise to the mixture, and stirring continued for 2 hours. Next, 18.5 g of n-dodecylamine was added, and stirring continued for 1 hour until homogeneous. The mixture was transferred to a high-pressure reactor and crystallized at 180 °C for 72 hours. After the reaction, the solid product was removed, centrifuged at high speed, washed three times with deionized water, and finally dried in an oven at 100 °C to obtain AlPO-kanemite. This product exhibits a layered morphology with a layer thickness of approximately 180 nm.

[0063] The prepared layered aluminum phosphate and silica sol were mixed and ground in a mortar for 10 minutes. Diethylamine was added, and after grinding for a certain time, a gel precursor was obtained. In the precursor, the molar ratio of the oxide components was 2 diethylamine: 1 Al₂O₃: 3 P₂O₅: 1 SiO₂: 7.8 H₂O. The obtained gel precursor was placed in a high-pressure reactor and crystallized at 170°C in an oven for 72 hours. After crystallization, the solid product was centrifuged and washed with deionized water until neutral. It was then dried in air at 120°C to obtain SAPO-34 molecular sieve powder. The SAPO-34 molecular sieve powder was calcined at 650°C with air for 4 hours to remove the template agent, thereby obtaining SAPO-34 molecular sieve with a hollow structure, which is recorded as Example 3. Based on the mass of the molecular sieve sample obtained after calcination, the yield of the hollow SAPO-34 molecular sieve in this example was calculated to be 85%.

[0064] Example 3: The sample was characterized by XRD, SEM, and nitrogen physisorption. The results are shown in the figure below. Figure 3 , Figure 5 and Figure 7 The results showed that the synthesized product was a SAPO-34 molecular sieve with a CHA structure, which had a hollow structure, an average crystal particle size of 2-3 μm, a wall thickness of 50-100 nm, and a crystal mesopore size of 20-50 nm.

[0065] The obtained sample was calcined at 550℃ with air for 4 hours, then tableted and crushed to 40-60 mesh. 1.0 g of sample was weighed and loaded into a fixed-bed reactor for MTO reaction evaluation. Nitrogen gas was introduced at 550℃ for 1 hour for activation, then the temperature was lowered to the reaction temperature of 450℃. The nitrogen gas was then turned off, and a 40 wt% methanol-water solution was fed using a plunger pump at a methanol weight hourly space velocity (MHSV) of 2.0 h⁻¹. -1 The reaction products were analyzed by online gas chromatography, and the results are shown in Table 1.

[0066] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

[0067] Table 1. Results of methanol-to-olefins reaction for samples prepared in each example and comparative example*

[0068]

[0069] *Lifetime refers to the period during which the methanol conversion rate remains above 99%.

[0070] Selectivity refers to the highest selectivity when the methanol conversion rate is maintained above 99%.

Claims

1. A method for preparing SAPO-34 molecular sieve with a hollow structure, characterized in that, SAPO-34 molecular sieve with a hollow structure was hydrothermally synthesized by using aluminum phosphate with a kanemite structure as both an aluminum and phosphorus source, mixed with a silicon source, an organic template agent, and water.

2. The method for preparing SAPO-34 molecular sieve with a hollow structure according to claim 1, characterized in that, The synthesis steps are as follows: a) After grinding and mixing aluminum phosphate with a kanemite structure and a silicon source, water and an organic template agent are added. After grinding for a certain period of time, a gel precursor is obtained. In the precursor, the molar ratio of each component oxide is (0.5~4.0) R: 1 Al2O3:1 P2O5: (0.05~3.0) SiO2: (2~25) H2O, where R is an organic template agent. Preferably, the molar ratio of each component oxide is (0.5~3.0): 1 Al2O3: 1 P2O5: (0.2~1.0) SiO2: (8~20) H2O. b) The gel precursor obtained in step a) is placed in a high-pressure reactor and crystallized at an isothermal temperature under autogenous pressure. After crystallization, the solid product is centrifuged and washed with deionized water until neutral. It is then dried in air at 80~120℃ to obtain SAPO-34 molecular sieve raw powder. c) The SAPO-34 molecular sieve raw powder is calcined at high temperature to remove the template agent, thereby obtaining SAPO-34 molecular sieve with a hollow structure.

3. The method for preparing SAPO-34 molecular sieve with a hollow structure according to claim 2, characterized in that: The aluminum phosphate with the kanemite structure in step a) is prepared by the following steps: Mix boehmite and water, stir evenly, add phosphoric acid, continue stirring for a certain time, then add organic template agent T. The molar ratio of the oxides of each component is (1.5~2) T: 1 Al2O3: 1 P2O5: (20~80) H2O, where T is any one or more straight-chain aliphatic amines [NH2(CH2)]. n [CH3], n=4~12; the resulting mixture was placed in a high-pressure reactor and heated in an oven at 180~200 ℃ for 24~72 h. The solid product was then centrifuged and washed with deionized water until neutral. After drying, aluminum phosphate with a kanemite structure was obtained.

4. The method for preparing SAPO-34 molecular sieve with a hollow structure according to claim 2, characterized in that: The silicon source is selected from at least one of silica sol, activated silica, silica fume, sodium silicate, or tetraethyl orthosilicate; the organic template agent is selected from at least one of diethylamine, triethylamine, morpholine, diisopropylamine, di-n-propylamine, diethanolamine, triethanolamine, or tetraethylammonium hydroxide.

5. The method for preparing SAPO-34 molecular sieve with a hollow structure according to claim 2, characterized in that: In step a), grinding and mixing aluminum phosphate with a kanemite structure and a silicon source means grinding for 10 to 40 minutes at room temperature; after adding water and an organic template agent, grinding for 0.2 to 0.5 hours to obtain a gel precursor.

6. The method for preparing SAPO-34 molecular sieve with a hollow structure according to claim 2, characterized in that: The isothermal crystallization in step b) refers to placing the reactor in an oven under autogenous pressure for isothermal crystallization, with a crystallization temperature of 140~230℃ and a crystallization time of 10~72 hours.

7. The method for preparing SAPO-34 molecular sieve with a hollow structure according to claim 2, characterized in that: The calcination temperature is 500~700℃, and the calcination time is 2~10 hours.

8. A SAPO-34 molecular sieve with a hollow structure, which is prepared by the method according to any one of claims 1-7.

9. The hollow SAPO-34 molecular sieve according to claim 8, wherein the average particle size of the hollow SAPO-34 molecular sieve is 1~4μm and the wall thickness is 40~800nm.

10. The application of the hollow SAPO-34 molecular sieve of claim 8 or 9 as a catalyst in the methanol-to-olefins reaction.

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