SAPO-34 molecular sieve, preparation method thereof and application of SAPO-34 molecular sieve in methanol-to-olefin process

Abstract

The invention relates to the technical field of preparation of olefin by methanol conversion, and discloses an SAPO-34 molecular sieve, a preparation method thereof and application of the SAPO-34 molecular sieve in a methanol-to-olefin process. The method comprises the following steps: (1) mixing melamine with water to obtain a mixed solution of melamine and water, and then mixing the mixed solution of melamine and water with an aluminum source, a silicon source, a phosphorus source, a template agent and water to obtain a mixture; and (2) mixing the mixture obtained in the step (1) with polyoxyethylene sorbitan fatty acid ester, carrying out hydrothermal crystallization reaction, and then sequentially separating, drying and roasting the obtained molecular sieve stock solution. The prepared SAPO-34 molecular sieve can improve the catalytic activity and selectivity to low-carbon olefins in a methanol-to-olefin reaction, can accommodate more carbon deposits, can effectively delay the deactivation speed caused by the carbon deposits, and further significantly prolongs the service life of a catalyst, and the method has the advantages of simple process, mild reaction conditions and low cost, and is suitable for industrial production. The method has obvious economic value and wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of methanol-to-olefins technology, specifically to a SAPO-34 molecular sieve, its preparation method, and its application in the methanol-to-olefins process. Background Technology

[0002] SAPO-34 molecular sieves are a class of silica-alumina phosphate materials with a well-defined crystal structure. Their unique framework consists of a stable three-dimensional network formed by oxygen atoms bridging three tetrahedral units: PO4, AlO4, and SiO4. In this architecture, the eight-membered rings composed of oxygen atoms not only construct a regular ellipsoidal cage-like space but also extend into an interconnected three-dimensional pore system. The pore size of this pore structure is highly matched to the kinetic diameter of low-carbon olefin molecules, providing a natural advantage for molecular recognition and shape-selective catalysis in the reaction. Due to these properties, SAPO-34 molecular sieves have become a core choice for the development of methanol-to-olefins (MTO) reaction catalysts. Industrial catalysts prepared using SAPO-34 as the active component have been successfully applied in multiple large-scale MTO production plants both domestically and internationally, supporting the large-scale synthesis of low-carbon olefins.

[0003] However, due to the spatial constraints of its eight-membered ring micropore structure, SAPO-34 molecular sieves face a severe problem of carbon deposition and deactivation during long-term reactions: the large molecular hydrocarbon intermediates generated in the reaction are easily retained in the pores and gradually polymerize to form coke, blocking active sites and diffusion channels, leading to a rapid decline in catalyst activity. Therefore, how to improve its selectivity for low-carbon olefins and extend the catalyst's single-pass life and regeneration cycle by inhibiting coke formation or promoting coke desorption remains a key direction that urgently needs to be addressed in the current research field of SAPO-34 molecular sieves. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of low selectivity for low-carbon olefins and easy carbon deposition and deactivation of existing SAPO-34 molecular sieves in the catalytic methanol-to-olefins process. This invention provides a SAPO-34 molecular sieve, its preparation method, and its application in the methanol-to-olefins process. The SAPO-34 molecular sieve prepared by this method has the characteristics of uniform distribution of acidic sites, high pore volume, excellent catalytic activity, and long service life. In the methanol-to-olefins reaction, it can improve catalytic activity and selectivity for low-carbon olefins while accommodating more carbon deposits, effectively delaying the deactivation rate caused by carbon deposition, and thus significantly extending the catalyst's service life. Furthermore, the method described in this invention is simple, the reaction conditions are mild, and it highly meets the needs of large-scale industrial production, demonstrating significant economic value and broad industrial application prospects.

[0005] To achieve the above objectives, the present invention provides a method for preparing SAPO-34 molecular sieve, the method comprising the following steps:

[0006] (1) Melamine is mixed with water to obtain a melamine-water mixture, and then the melamine-water mixture is mixed with an aluminum source, a silicon source, a phosphorus source, a template agent and water to obtain a mixture.

[0007] (2) The mixture obtained in step (1) is mixed with polyoxyethylene dehydrated sorbitan fatty acid ester and subjected to hydrothermal crystallization reaction. Then the resulting molecular sieve stock solution is separated, dried and calcined in sequence.

[0008] Preferably, in step (1), the weight ratio of the aluminum source to the melamine is 100:0.5-10, more preferably 100:1-8.

[0009] Preferably, in the mixture of melamine and water, the content of melamine is 0.5-35 wt%, more preferably 0.7-30 wt%.

[0010] Preferably, the aluminum source is selected from at least one of crystalline aluminum chloride, boehmite, and aluminum isopropoxide.

[0011] Preferably, the weight ratio of the aluminum source to the polyoxyethylene sorbitan fatty acid ester is 100:0.5-25, and more preferably 100:1-20.

[0012] Preferably, in step (1), the aluminum source is calculated as Al2O3, the phosphorus source is calculated as P2O5, the silicon source is calculated as SiO2, and the molar ratio of the aluminum source, the phosphorus source, the silicon source, the template agent and water is 1:(0.1-1):(0.8-2):(1-6):(20-80).

[0013] Preferably, the phosphorus source is selected from at least one of phosphoric acid, ammonium phosphate, diammonium hydrogen phosphate, ammonium hydrogen phosphate, potassium phosphate, dipotassium hydrogen phosphate, potassium hydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, and sodium hydrogen phosphate.

[0014] Preferably, the silicon source is selected from at least one of silica, silica sol, tetraethyl orthosilicate, type A molecular sieve, type X molecular sieve, and type Y molecular sieve.

[0015] Preferably, the template agent is selected from at least one of morpholine, N,N-dimethyl-diisopropylethylamine, N,N,N',N'-tetramethyl-1,3-propanediamine, diethylamine, hexamethylenediamine, triethylamine, tetraethylammonium chloride, and tetraethylammonium hydroxide.

[0016] Preferably, in step (2), the conditions for the hydrothermal crystallization reaction include: a temperature of 120-220°C and a time of 20-80 h.

[0017] Preferably, in step (2), the drying conditions include: a temperature of 100-150°C and a time of 10-30 hours.

[0018] Preferably, in step (2), the calcination conditions include: a temperature of 450-650℃ and a time of 4-10h.

[0019] A second aspect of the present invention provides a SAPO-34 molecular sieve prepared by the above method.

[0020] The third aspect of this invention provides the application of the above-mentioned SAPO-34 molecular sieve in the methanol-to-olefins process.

[0021] The method described in this invention introduces polyoxyethylene sorbitan fatty acid ester, which highly disperses the silicon source. The resulting molecular sieve, when combined with the aluminum source, exhibits a uniform distribution of acidic sites, effectively controlling acid density. Applying the prepared SAPO-34 molecular sieve to the methanol-to-olefins reaction further enhances the catalyst's catalytic activity and selectivity for low-carbon olefins. The introduction of melamine, after calcination, leaves pores, increasing the pore volume of the molecular sieve. This allows for greater carbon deposition in the methanol-to-olefins reaction, effectively delaying catalyst deactivation caused by carbon buildup and significantly extending catalyst lifespan. Therefore, the SAPO-34 molecular sieve prepared by this method possesses characteristics such as uniform acidic site distribution, high pore volume, excellent catalytic activity, and long lifespan. In the methanol-to-olefins reaction, it improves catalytic activity and selectivity for low-carbon olefins while accommodating more carbon deposits, effectively slowing down the deactivation rate caused by carbon buildup and significantly extending catalyst lifespan. Furthermore, the method described in this invention is simple, with mild reaction conditions, highly suitable for large-scale industrial production, demonstrating significant economic value and broad industrial application prospects. Attached Figure Description

[0022] Figure 1 This is a morphology diagram of SAPO-34 molecular sieve S1 prepared in Example 1 of the present invention;

[0023] Figure 2 This is the XRD pattern of SAPO-34 molecular sieve S1 prepared in Example 1 of this invention;

[0024] Figure 3 These are NH3-TPD diagrams of the SAPO-34 molecular sieves prepared in Examples 1-3 and Comparative Example 1 of this invention. Detailed Implementation

[0025] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0026] 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.

[0027] The preparation method of SAPO-34 molecular sieve according to the present invention includes the following steps:

[0028] (1) Melamine is mixed with water to obtain a melamine-water mixture, and then the melamine-water mixture is mixed with an aluminum source, a silicon source, a phosphorus source, a template agent and water to obtain a mixture.

[0029] (2) The mixture obtained in step (1) is mixed with polyoxyethylene dehydrated sorbitan fatty acid ester and subjected to hydrothermal crystallization reaction. Then the resulting molecular sieve stock solution is separated, dried and calcined in sequence.

[0030] In some embodiments, in step (1), in order to further improve the pore volume of the SAPO-34 and thus significantly extend the service life of the SAPO-34 molecular sieve, it is necessary to limit the content of melamine in the melamine-water mixture. Specifically, in the melamine-water mixture, the content of melamine is preferably 0.5-35 wt%, more preferably 0.7-30 wt%, and even more preferably 0.9-25 wt%. As a specific example, in the melamine-water mixture, the content of melamine can be 0.9 wt%, 1 wt%, 2 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, or 25 wt%.

[0031] In the method described in this invention, the addition of melamine leaves pores in the prepared molecular sieve after calcination, which increases the pore volume of the molecular sieve. This allows it to accommodate more carbon deposits in the methanol-to-olefins reaction, effectively slowing down the catalyst deactivation rate caused by carbon deposits and thus significantly extending the catalyst's lifespan. In this invention, the melamine can be a commercially available product or prepared using conventional methods in the art.

[0032] In some embodiments, in step (1), in order to further improve the pore volume of the SAPO-34 and thus significantly extend the service life of the SAPO-34 molecular sieve, it is necessary to limit the weight ratio of the aluminum source to the melamine. Specifically, the weight ratio of the aluminum source to the melamine is preferably 100:0.5-10, more preferably 100:1-8, and even more preferably 100:3-6. As a specific example, the weight ratio of the aluminum source to the melamine can be 100:3, 100:4, 100:5, or 100:6.

[0033] In the method described in this invention, the type of aluminum source is not limited, and various aluminum sources commonly used in the art can be used. Preferably, the aluminum source is selected from at least one of crystalline aluminum chloride, boehmite, and aluminum isopropoxide. In a further preferred embodiment, the aluminum source is boehmite.

[0034] In some embodiments, in step (1), the aluminum source is calculated as Al2O3, the phosphorus source as P2O5, and the silicon source as SiO2, and the molar ratio of the aluminum source, the phosphorus source, the silicon source, the template agent, and water can be 1:(0.1-1):(0.8-2):(1-6):(20-80). Preferably, the aluminum source is calculated as Al2O3, the phosphorus source as P2O5, and the silicon source as SiO2, and the molar ratio of the aluminum source, the phosphorus source, the silicon source, the template agent, and water can be 1:(0.2-0.95):(0.9-1.8):(1.5-5):(25-70). In a further preferred embodiment, the aluminum source is calculated as Al2O3, the phosphorus source as P2O5, the silicon source as SiO2, and the molar ratio of the aluminum source, the phosphorus source, the silicon source, the template agent, and water can be 1:(0.4-0.9):(1-1.5):(2-4):(30-60).

[0035] In the method described in this invention, the type of phosphorus source is not limited, and various phosphorus sources commonly used in the art can be used. Preferably, the phosphorus source is selected from at least one of phosphoric acid, ammonium phosphate, diammonium hydrogen phosphate, ammonium hydrogen phosphate, potassium phosphate, dipotassium hydrogen phosphate, potassium hydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, and sodium hydrogen phosphate. In a further preferred embodiment, the phosphorus source is phosphoric acid.

[0036] In the method described in this invention, the type of silicon source is not limited, and various silicon sources commonly used in the art can be used. Preferably, the silicon source is selected from at least one of silica, silica sol, tetraethyl orthosilicate, type A molecular sieve, type X molecular sieve, and type Y molecular sieve. In a further preferred embodiment, the silicon source is silica sol.

[0037] In the method described in this invention, there is no limitation on the type of template agent; various template agents commonly used in the art can be used. Preferably, the template agent is selected from at least one of morpholine, N,N-dimethyl-diisopropylethylamine, N,N,N',N'-tetramethyl-1,3-propanediamine, diethylamine, hexamethylenediamine, triethylamine, tetraethylammonium chloride, and tetraethylammonium hydroxide. In a further preferred embodiment, the template agent is tetraethylammonium hydroxide.

[0038] In some embodiments, in step (2), in order to ensure that the silicon source is highly dispersed and the acidic sites of the molecular sieve formed after combining with the aluminum source are uniformly distributed, and to effectively control the acid density, so that the prepared SAPO-34 molecular sieve can further improve the catalytic activity and selectivity for low-carbon olefins in the methanol-to-olefins reaction, it is necessary to limit the weight ratio of the aluminum source to the polyoxyethylene sorbitan fatty acid ester. Specifically, the weight ratio of the aluminum source to the polyoxyethylene sorbitan fatty acid ester is preferably 100:0.5-25, more preferably 100:1-20, and even more preferably 100:5-18. As a specific example, the weight ratio of the aluminum source to the polyoxyethylene sorbitan fatty acid ester can be 100:5, 100:7, 100:9, 100:10, 100:12, 100:14, 100:15, 100:16, or 100:18.

[0039] In this invention, the polyoxyethylene sorbitan fatty acid ester can be a commercially available product or prepared using methods conventional in the art. In some embodiments, the polyoxyethylene sorbitan fatty acid ester can be polyoxyethylene sorbitan laurate (Tween 20), polyoxyethylene sorbitan palmitate (Tween 40), or polyoxyethylene sorbitan oleate (Tween 80).

[0040] In some specific embodiments, in step (2), the specific process of mixing the mixture obtained in step (1) with the polyoxyethylene sorbitan fatty acid ester and carrying out a hydrothermal crystallization reaction includes: rapidly adding the polyoxyethylene sorbitan fatty acid ester to the mixture obtained in step (1), and quickly stirring and mixing, and then carrying out a hydrothermal crystallization reaction after uniform mixing. In this invention, the purpose of emphasizing rapid stirring and mixing is: to enable the polyoxyethylene sorbitan fatty acid ester to be quickly and uniformly dispersed in the mixture to form a stable system; to accelerate the transfer of the polyoxyethylene sorbitan fatty acid ester in the mixture and promote uniform heat distribution through the turbulence and shear force generated by stirring; and to enable the polyoxyethylene sorbitan fatty acid ester to be rapidly dispersed in the mixture by means of external forces such as stirring, thereby increasing the contact area and avoiding incomplete reaction caused by stratification.

[0041] In some specific embodiments, in step (2), the conditions for the hydrothermal crystallization reaction include: a temperature of 120-220℃, preferably 140-205℃; and a time of 20-80h, preferably 24-72h. Specifically, the temperature of the hydrothermal crystallization reaction can be 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, or 205℃; and the time of the hydrothermal crystallization reaction can be 24h, 25h, 30h, 35h, 40h, 45h, 50h, 55h, 60h, 65h, 70h, or 72h.

[0042] In some specific embodiments, the specific process of separating, drying and calcining the obtained molecular sieve stock solution in step (2) includes: filtering the molecular sieve stock solution, drying the obtained solid product, and then calcining the dried solid product.

[0043] In some specific embodiments, in step (2), the drying conditions include: a temperature of 100-150°C, preferably 110-120°C; and a time of 10-30 hours, preferably 12-24 hours.

[0044] In some specific embodiments, in step (2), the calcination conditions include: a temperature of 450-650℃, preferably 500-600℃; and a time of 4-10h, preferably 6-8h.

[0045] The present invention also provides a SAPO-34 molecular sieve prepared by the above method. The SAPO-34 molecular sieve has the characteristics of uniform distribution of acidic sites, high pore volume, excellent catalytic activity and long service life. In the methanol-to-olefins reaction, it can improve catalytic activity and selectivity for low carbon olefins, while accommodating more carbon deposits, effectively delaying the deactivation rate caused by carbon deposits, and thus significantly extending the service life of the catalyst.

[0046] This invention further provides the application of the above-mentioned SAPO-34 molecular sieve in the methanol-to-olefins process. Because the SAPO-34 molecular sieve prepared by the method of this invention has the characteristics of uniform distribution of acidic sites, high pore volume, excellent catalytic activity and long service life, it can improve catalytic activity and selectivity for low carbon olefins in the methanol-to-olefins reaction, while accommodating more carbon deposits, effectively delaying the deactivation rate caused by carbon deposits, and thus significantly extending the service life of the catalyst. Moreover, the method is simple, the reaction conditions are mild, and it is highly compatible with the needs of large-scale industrial production, showing significant economic value and broad industrial application prospects.

[0047] The following examples further illustrate the SAPO-34 molecular sieve, its preparation method, and its application in the methanol-to-olefins process of the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0048] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0049] In the following examples and comparative examples, melamine was purchased from Guangdong Shengke Biochemical Technology Co., Ltd.

[0050] The polyoxyethylene sorbitan fatty acid esters, including polyoxyethylene sorbitan lauryl ester, polyoxyethylene sorbitan palmitate ester and polyoxyethylene sorbitan oleate ester, are all purchased from Jinan Shouyue Chemical Technology Co., Ltd. as 99% industrial grade reagents.

[0051] Boehmite and aluminum isopropoxide with A l2 O3 is calculated as SiO2, silica sol and tetraethyl orthosilicate as SiO2, and phosphoric acid, ammonium phosphate and diammonium hydrogen phosphate as P2O5.

[0052] Example 1

[0053] (1) Dissolve 1g of melamine in 100mL of water to obtain a mixture of melamine and water. Then add boehmite, silica sol, phosphoric acid, tetraethylammonium hydroxide and water to the mixture of melamine and water, and stir until uniform to obtain a mixture. The weight ratio of boehmite to melamine is 100:3, and the molar ratio of boehmite, silica sol, phosphoric acid, tetraethylammonium hydroxide and water is 1:0.6:1.2:3:50.

[0054] (2) Polyoxyethylene sorbitan laurate was rapidly added to the mixture obtained in step (1), and the mixture was stirred rapidly until homogeneous. After homogeneity, the mixture was subjected to hydrothermal crystallization at 180°C for 48 hours. After the reaction was completed, the resulting molecular sieve stock solution was separated, and the resulting solid product was dried at 115°C for 15 hours. The dried solid product was then calcined at 550°C for 7 hours to obtain SAPO-34 molecular sieve S1. The weight ratio of boehmite to polyoxyethylene sorbitan laurate was 100:10. Figure 1 The morphology of SAPO-34 molecular sieve S1 is shown. The results show that the prepared SAPO-34 molecular sieve has a regular crystal structure, a cubic structure, a smooth surface, and most of the particles are between 2 and 4 μm in size.

[0055] Example 2

[0056] (1) Dissolve 3g of melamine in 50mL of water to obtain a mixture of melamine and water. Then add boehmite, silica sol, phosphoric acid, tetraethylammonium hydroxide and water to the mixture of melamine and water, and stir until uniform to obtain a mixture. The weight ratio of boehmite to melamine is 100:4, and the molar ratio of boehmite, silica sol, phosphoric acid, tetraethylammonium hydroxide and water is 1:0.4:1:2:30.

[0057] (2) Polyoxyethylene sorbitan palmitate was rapidly added to the mixture obtained in step (1), and the mixture was stirred rapidly until homogeneous. After homogeneity, the mixture was subjected to hydrothermal crystallization at 140°C for 72 hours. After the reaction was completed, the resulting molecular sieve stock solution was separated, and the resulting solid product was dried at 110°C for 24 hours. The dried solid product was then calcined at 500°C for 8 hours to obtain SAPO-34 molecular sieve S2. The weight ratio of boehmite to polyoxyethylene sorbitan palmitate was 100:5.

[0058] Example 3

[0059] (1) Dissolve 8g of melamine in 25mL of water to obtain a mixture of melamine and water. Then add boehmite, silica sol, phosphoric acid, tetraethylammonium hydroxide and water to the mixture of melamine and water, and stir until uniform to obtain a mixture. The weight ratio of boehmite to melamine is 100:6, and the molar ratio of boehmite, silica sol, phosphoric acid, tetraethylammonium hydroxide and water is 1:0.9:1.5:4:60.

[0060] (2) Polyoxyethylene sorbitan oleate was rapidly added to the mixture obtained in step (1) and stirred rapidly until homogeneous. After homogeneity, the mixture was subjected to hydrothermal crystallization at 205°C for 24 hours. After the reaction was completed, the resulting molecular sieve stock solution was separated. The resulting solid product was then dried at 120°C for 12 hours, and then calcined at 600°C for 6 hours to obtain SAPO-34 molecular sieve S3. The weight ratio of boehmite to polyoxyethylene sorbitan oleate was 100:18.

[0061] Example 4

[0062] The method described in Example 1 was implemented, except that in step (1), the amount of melamine used was 0.133g, so that the weight ratio of boehmite to melamine was 100:0.4, and SAPO-34 molecular sieve S4 was finally obtained.

[0063] Example 5

[0064] The method described in Example 1 was implemented, except that in step (1), the amount of melamine used was 5g, so that the weight ratio of boehmite to melamine was 100:15, and SAPO-34 molecular sieve S5 was finally obtained.

[0065] Example 6

[0066] The method described in Example 1 was carried out, except that in step (2), the weight ratio of boehmite to polyoxyethylene sorbitan laurate was 100:0.1, and SAPO-34 molecular sieve S6 was finally obtained.

[0067] Example 7

[0068] The method described in Example 1 was carried out, except that in step (2), the weight ratio of boehmite to polyoxyethylene sorbitan laurate was 100:30, and SAPO-34 molecular sieve S7 was finally obtained.

[0069] Example 8

[0070] (1) Dissolve 1g of melamine in 100mL of water to obtain a mixture of melamine and water. Then add boehmite, silica sol, phosphoric acid, tetraethylammonium hydroxide and water to the mixture of melamine and water, and stir until uniform to obtain a mixture. The weight ratio of boehmite to melamine is 100:3, and the molar ratio of boehmite, silica sol, phosphoric acid, tetraethylammonium hydroxide and water is 1:0.6:1.2:3:50.

[0071] (2) Polyoxyethylene sorbitan laurate was rapidly added to the mixture obtained in step (1), and the mixture was stirred rapidly until homogeneous. After homogeneity, the mixture was subjected to hydrothermal crystallization at 180°C for 48 hours. After the reaction was completed, the resulting molecular sieve stock solution was separated, and the resulting solid product was dried at 110°C for 12 hours. The dried solid product was then calcined at 550°C for 6 hours to obtain SAPO-34 molecular sieve S8. The weight ratio of boehmite to polyoxyethylene sorbitan laurate was 100:5.

[0072] Example 9

[0073] (1) Dissolve 3g of melamine in 50mL of water to obtain a mixture of melamine and water. Then add boehmite, silica sol, phosphoric acid, ethylenediamine and water to the mixture of melamine and water and stir until uniform to obtain a mixture. The weight ratio of boehmite to melamine is 100:4, and the molar ratio of boehmite, silica sol, phosphoric acid, ethylenediamine and water is 1:0.8:1:2.5:40.

[0074] (2) Polyoxyethylene sorbitan laurate was rapidly added to the mixture obtained in step (1), and the mixture was stirred rapidly until homogeneous. After homogeneity, the mixture was subjected to hydrothermal crystallization at 190°C for 60 hours. After the reaction was completed, the resulting molecular sieve stock solution was separated, and the resulting solid product was dried at 110°C for 12 hours. The dried solid product was then calcined at 550°C for 6 hours to obtain SAPO-34 molecular sieve S9. The weight ratio of boehmite to polyoxyethylene sorbitan laurate was 100:10.

[0075] Example 10

[0076] (1) Dissolve 8g of melamine in 25mL of water to obtain a mixture of melamine and water. Then add boehmite, tetraethyl orthosilicate, ammonium phosphate, ethylenediamine and water to the mixture of melamine and water and stir until homogeneous to obtain a mixture. The weight ratio of boehmite to melamine is 100:6, and the molar ratio of boehmite, tetraethyl orthosilicate, ammonium phosphate, ethylenediamine and water is 1:1:0.8:2:35.

[0077] (2) Polyoxyethylene sorbitan laurate was rapidly added to the mixture obtained in step (1), and the mixture was stirred rapidly until homogeneous. After homogeneity, the mixture was subjected to hydrothermal crystallization at 200°C for 72 hours. After the reaction was completed, the resulting molecular sieve stock solution was separated, and the resulting solid product was dried at 110°C for 12 hours. The dried solid product was then calcined at 550°C for 6 hours to obtain SAPO-34 molecular sieve S10. The weight ratio of boehmite to polyoxyethylene sorbitan laurate was 100:15.

[0078] Example 11

[0079] (1) Dissolve 1.6g of melamine in 50mL of water to obtain a mixture of melamine and water. Then add boehmite, silica sol, diamine hydrogen phosphate, tetraethylammonium hydroxide and water to the mixture of melamine and water, and stir until uniform to obtain a mixture. The weight ratio of boehmite to melamine is 100:4.5, and the molar ratio of boehmite, silica sol, diamine hydrogen phosphate, tetraethylammonium hydroxide and water is 1:0.5:1.5:3.5:60.

[0080] (2) Polyoxyethylene sorbitan laurate was rapidly added to the mixture obtained in step (1), and the mixture was stirred rapidly until homogeneous. After homogeneity, the mixture was subjected to hydrothermal crystallization at 170°C for 50 hours. After the reaction was completed, the resulting molecular sieve stock solution was separated, and the resulting solid product was dried at 110°C for 12 hours. The dried solid product was then calcined at 550°C for 6 hours to obtain SAPO-34 molecular sieve S11. The weight ratio of boehmite to polyoxyethylene sorbitan laurate was 100:8.

[0081] Example 12

[0082] (1) Dissolve 2.5g of melamine in 100mL of water to obtain a mixture of melamine and water. Then add boehmite, silica sol, phosphoric acid, tetraethylammonium hydroxide and water to the mixture of melamine and water, and stir until uniform to obtain a mixture. The weight ratio of boehmite to melamine is 100:8, and the molar ratio of boehmite, tetraethyl orthosilicate, phosphoric acid, tetraethylammonium hydroxide and water is 1:0.7:1.1:4:45.

[0083] (2) Polyoxyethylene sorbitan laurate was rapidly added to the mixture obtained in step (1), and the mixture was stirred rapidly until homogeneous. After homogeneity, the mixture was subjected to hydrothermal crystallization at 185°C for 65 hours. After the reaction was completed, the resulting molecular sieve stock solution was separated, and the resulting solid product was dried at 110°C for 12 hours. The dried solid product was then calcined at 550°C for 6 hours to obtain SAPO-34 molecular sieve S12. The weight ratio of boehmite to polyoxyethylene sorbitan laurate was 100:12.

[0084] Example 13

[0085] (1) Dissolve 1g of melamine in 100mL of water to obtain a mixture of melamine and water. Then add boehmite, silica sol, diamine hydrogen phosphate, tetraethylammonium hydroxide and water to the mixture of melamine and water, and stir until uniform to obtain a mixture. The weight ratio of boehmite to melamine is 100:0.1, and the molar ratio of boehmite, tetraethyl orthosilicate, diamine hydrogen phosphate, tetraethylammonium hydroxide and water is 1:0.9:1.3:2.2:55.

[0086] (2) Polyoxyethylene sorbitan laurate was rapidly added to the mixture obtained in step (1), and the mixture was stirred rapidly until homogeneous. After homogeneity, the mixture was subjected to hydrothermal crystallization at 195°C for 55 h. After the reaction was completed, the resulting molecular sieve stock solution was separated, and the resulting solid product was dried at 110°C for 12 h. The dried solid product was then calcined at 550°C for 6 h to obtain SAPO-34 molecular sieve S13. The weight ratio of boehmite to polyoxyethylene sorbitan laurate was 100:18.

[0087] Example 14

[0088] (1) Dissolve 1.5g of melamine in 100mL of water to obtain a mixture of melamine and water. Then add aluminum isopropoxide, silica sol, phosphoric acid, tetraethylammonium hydroxide and water to the mixture of melamine and water, and stir until uniform to obtain a mixture. The weight ratio of boehmite to melamine is 100:30, and the molar ratio of aluminum isopropoxide, tetraethyl orthosilicate, phosphoric acid, tetraethylammonium hydroxide and water is 1:0.65:1.4:3.8:50.

[0089] (2) Polyoxyethylene sorbitan laurate was rapidly added to the mixture obtained in step (1), and the mixture was stirred rapidly until homogeneous. After homogeneity, the mixture was subjected to hydrothermal crystallization at 205°C for 45 hours. After the reaction was completed, the resulting molecular sieve stock solution was separated, and the resulting solid product was dried at 110°C for 12 hours. The dried solid product was then calcined at 550°C for 6 hours to obtain SAPO-34 molecular sieve S14. The weight ratio of boehmite to polyoxyethylene sorbitan laurate was 100:12.

[0090] Comparative Example 1

[0091] The method described in Example 1 was carried out, except that melamine was not added in step (1), and SAPO-34 molecular sieve D1 was finally obtained.

[0092] Comparative Example 2

[0093] The method described in Example 1 was carried out, except that in step (2), polyoxyethylene sorbitan fatty acid ester was not added, and SAPO-34 molecular sieve D2 was finally obtained.

[0094] Test case

[0095] (1) The present invention uses X-ray diffraction to analyze SAPO-34 molecular sieve S1 prepared in Example 1. Figure 2The XRD pattern of SAPO-34 molecular sieve S1 is shown. The results show that the sample has strong CHA diffraction peaks at 2θ of 9.48°, 15.99°, 20.55°, 26.55° and 31°, indicating that the sample has a typical CHA topology and is a high-purity SAPO-34 molecular sieve.

[0096] (2) The specific surface area, total pore volume and average pore size of the SAPO-34 molecular sieve prepared in the examples and comparative examples were tested by N2 adsorption-desorption method. The results are shown in Table 1.

[0097] (3) The acidity of the SAPO-34 molecular sieve prepared in the examples and comparative examples was tested by the NH3-TPD method in this invention. Figure 3 The NH3-TPD curves of SAPO-34 molecular sieves prepared in Examples 1, 2, 3 and Comparative Example 1 are shown. The results show that the NH3-TPD curves of all samples have two NH3 desorption peaks, with the centers of the desorption peaks near 200℃ and 450℃, respectively. These two desorption peaks correspond to the weak acid and strong acid of the molecular sieve, respectively.

[0098] (4) In this invention, the SAPO-34 molecular sieve prepared according to the examples and comparative examples is applied to the process of methane to olefins. The reactor is a fixed fluidized bed, and the reaction products are analyzed online by gas chromatography (Agilent GC 7890N), quantitatively detected by a flame ionization (FID) detector, using an HP-Plot / Q capillary column. The normalization method is used for calculation. In the conversion calculation, dimethyl ether is used as a reactant. The calculation methods for methanol conversion (E, %) and diene selectivity (Y, %) are as follows:

[0099] E = (1 - ω1 - ω2) × 100%

[0100]

[0101] Wherein, ω1 is the mass fraction of methanol in the product, %; ω2 is the mass fraction of dimethyl ether in the product, %; ω x The mass fraction of diene (ethylene + propylene) in the product, %.

[0102] The results are shown in Table 1.

[0103] (5) In this invention, the SAPO-34 molecular sieve prepared according to the examples and comparative examples is applied to the process of methane to olefins. The catalytic activity of the SAPO-34 molecular sieve is evaluated in a fixed fluidized bed with a catalyst loading of 50g, the reaction temperature is 480℃, the pressure is atmospheric pressure, and the mass hourly space velocity is 0.5h. -1 The service life of the SAPO-34 molecular sieve was tested, and the results are shown in Table 1.

[0104] Table 1

[0105]

[0106]

[0107] As shown in Table 1, the method described in this invention, by introducing polyoxyethylene sorbitan fatty acid ester, achieves high dispersion of the silicon source. This results in a uniform distribution of acidic sites in the molecular sieve formed after combining with the aluminum source, effectively controlling the acid density. Furthermore, the introduction of melamine increases the pore volume of the molecular sieve, effectively slowing down the deactivation rate caused by carbon deposition, thereby significantly extending the catalyst's lifespan. In addition, the method described in this invention features a simple process, mild reaction conditions, and is highly suitable for large-scale industrial production, demonstrating significant economic value and broad industrial application prospects.

[0108] 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 method for preparing SAPO-34 molecular sieve, characterized in that, The method includes the following steps: (1) Melamine is mixed with water to obtain a melamine-water mixture, and then the melamine-water mixture is mixed with an aluminum source, a silicon source, a phosphorus source, a template agent and water to obtain a mixture. (2) The mixture obtained in step (1) is mixed with polyoxyethylene dehydrated sorbitan fatty acid ester and subjected to hydrothermal crystallization reaction. Then the resulting molecular sieve stock solution is separated, dried and calcined in sequence.

2. The method according to claim 1, characterized in that, In step (1), the weight ratio of the aluminum source to the melamine is 100:0.5-10, preferably 100:1-8; and / or In the melamine-water mixture, the melamine content is 0.5-35 wt%, preferably 0.7-30 wt%. Preferably, the aluminum source is selected from at least one of crystalline aluminum chloride, boehmite, and aluminum isopropoxide.

3. The method according to claim 1 or 2, characterized in that, The weight ratio of the aluminum source to the polyoxyethylene sorbitan fatty acid ester is 100:0.5-25, preferably 100:1-20.

4. The method according to any one of claims 1-3, characterized in that, In step (1), the aluminum source is calculated as Al2O3, the phosphorus source is calculated as P2O5, the silicon source is calculated as SiO2, and the molar ratio of the aluminum source, the phosphorus source, the silicon source, the template agent and water is 1:(0.1-1):(0.8-2):(1-6):(20-80).

5. The method according to claim 1 or 4, characterized in that, The phosphorus source is selected from at least one of phosphoric acid, ammonium phosphate, diammonium hydrogen phosphate, ammonium hydrogen phosphate, potassium phosphate, dipotassium hydrogen phosphate, potassium hydrogen phosphate, sodium phosphate, disodium hydrogen phosphate, and sodium hydrogen phosphate; and / or The silicon source is selected from at least one of silica, silica sol, tetraethyl orthosilicate, type A molecular sieve, type X molecular sieve, and type Y molecular sieve; and / or The template agent is selected from at least one of morpholine, N,N-dimethyl-diisopropylethylamine, N,N,N',N'-tetramethyl-1,3-propanediamine, diethylamine, hexamethylenediamine, triethylamine, tetraethylammonium chloride, and tetraethylammonium hydroxide.

6. The method according to claim 1 or 3, characterized in that, In step (2), the conditions for the hydrothermal crystallization reaction include: a temperature of 120-220℃ and a time of 20-80h.

7. The method according to claim 1 or 3, characterized in that, In step (2), the drying conditions include a temperature of 100-150°C and a time of 10-30 hours.

8. The method according to claim 1 or 3, characterized in that, In step (2), the calcination conditions include a temperature of 450-650℃ and a time of 4-10h.

9. SAPO-34 molecular sieve prepared by the method according to any one of claims 1-8.

10. The application of the SAPO-34 molecular sieve according to claim 9 in the methanol-to-olefins process.

Images