Synthesis method of hexagonal-prism-shaped SAPO-5 molecular sieve with high length-diameter ratio

Abstract

The invention belongs to the technical field of synthesis of molecular sieve materials, and relates to a synthesis method of a hexagonal-prism-shaped SAPO-5 molecular sieve with a high length-diameter ratio, and the method comprises the following steps: forming initial gel from an aluminum source and a template agent, adding a phosphorus source, adding sulfate radicals, then adding a silicon source to form a crystallization mixed solution with a certain ratio, crystallizing, filtering, washing, drying and roasting. According to the method, the hexagonal-prism-shaped SAPO-5 molecular sieve with the high length-diameter ratio can be obtained, and the synthesis method is simple. The SAPO-5 molecular sieve has a hexagonal prism shape and a high length-diameter ratio.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieve synthesis, and particularly relates to a method for synthesizing a high aspect ratio hexagonal SAPO-5 molecular sieve. Background Art

[0002] In the early 1980s, Union Carbide Corporation (UCC) successfully developed a new molecular sieve system—the silicoaluminophosphate (SAPO-n) series of molecular sieves. These molecular sieves feature a three-dimensional framework composed of phosphorus oxide tetrahedrons (PO4), aluminum oxide tetrahedrons (AlO4), and silicon oxide tetrahedrons (SiO4). After 40 years of development, the number of structural variations of silicoaluminophosphate molecular sieves has grown to over 60. These sieves are widely used in carbon-to-chemicals, environmental emission reduction, and petroleum refining and chemical industries, providing material support for technologies such as the comprehensive utilization of carbon resources, clean environmental protection, and the transition from petroleum refining to chemical industries.

[0003] SAPO-5 molecular sieve features a twelve-membered, one-dimensional straight pore structure composed of SiO₄, PO₄, and AlO₄ tetrahedral units, alternating between two six-membered and two four-membered rings. The pore diameter is approximately 0.73 nm, making it a large-pore silicon-aluminum-phosphorus molecular sieve. Its framework is AFI-type, belonging to the hexagonal crystal system, with unit cell parameters a = b = 1.3827 nm, c = 0.858 nm; α = β = 90.000°, γ = 120.000°. SAPO-5 molecular sieve exhibits excellent thermal and hydrothermal stability, as well as suitable acidity. It is currently widely used in acid-catalyzed reactions such as hydroisomerization, xylene isomerization, propylene polymerization, and alkane cracking.

[0004] The morphology of SAPO-5 molecular sieves significantly affects their performance in applications, with rod-shaped SAPO-5 molecular sieves often exhibiting superior performance. Rod-shaped SAPO-5 molecular sieves are generally hexagonal in shape, and aspect ratio is a very important parameter in their morphology. Rod-shaped SAPO-5 molecular sieves with high aspect ratios generally exhibit better diffusion properties.

[0005] SAPO-5 molecular sieves are commonly synthesized hydrothermally, using water as the solvent and commonly used organic templates such as diethylammonium, triethylammonium, tetrapropylammonium hydroxide, and mixtures thereof. Synthesizing high aspect ratio SAPO-5 molecular sieves using simple methods remains a major challenge.

[0006] CN 110040745 A discloses a preparation method for synthesizing nano-rod-shaped SAPO-5 molecular sieves. First, a silicon source, an aluminum source, a phosphorus source and water are mixed, and then a preliminary hydrothermal crystallization is performed. After that, an organic amine template is added and high-temperature hydrothermal crystallization is performed again. After the hydrothermal crystallization reaction is completed, tap water is used to rapidly cool the reaction vessel. Finally, after centrifugation, washing and drying, the SAPO-5 molecular sieve raw powder can be obtained. Further, nano-rod-shaped SAPO-5 molecular sieves can be obtained after high-temperature calcination. The SAPO-5 molecular sieve prepared by this method has excellent crystallinity and regular morphology and size. It has shown performance superior to spherical and sheet-like SAPO-5 molecular sieves in the methanol to olefins reaction. However, the synthetic method disclosed in the document requires two-step crystallization. After the crystallization is completed, a large amount of water needs to be used for rapid cooling, and the operation is not simple enough. In addition, the obtained rod-shaped SAPO-5 molecular sieve does not have the structure of a regular hexagonal prism, and the utilization rate and stability of the material are not as good as those of a hexagonal prism structure molecular sieve.

[0007] In a paper published in the journal Microporous & Mesoporous Materials, Utchariyajit K et al. synthesized short hexagonal SAPO-5 molecular sieves by prolonging the aging time. However, further extension of the aging time resulted in the appearance of SAPO-34 molecular sieve impurity crystals. Furthermore, the synthesized SAPO-5 molecular sieve had a low aspect ratio, with excessive radial length impeding the diffusion of reactants and products, and resulting in low utilization of active sites. Summary of the Invention

[0008] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a high aspect ratio hexagonal SAPO-5 molecular sieve and a preparation method thereof.

[0009] The grain length and diameter are determined by scanning electron micrograph (SEM) measurement. The measurement method is as follows: 50 grains are randomly selected, and the grain length and diameter are measured by measurement software. The arithmetic mean of the grain length and diameter is used as the average length and average diameter of the sample. The ratio of the average length to the average diameter is calculated to obtain the aspect ratio of the molecular sieve grains. The grain length refers to the length of the side edge of the regular hexagonal prism grain, and the grain diameter refers to the diameter of the circumscribed circle of the regular hexagonal bottom surface of the prism, such as Figure 1 shown.

[0010] The present invention provides a method for synthesizing a high aspect ratio hexagonal SAPO-5 molecular sieve, which comprises the following steps:

[0011] a) mixing an aluminum source, an organic template, and water, and stirring at room temperature, for example, for 1 to 10 hours, to obtain a SAPO-5 molecular sieve initial gel mixture A (also referred to as mixed solution A); wherein the molar ratio of the organic template to the aluminum source is 0.1 to 0.6, calculated as Al2O3;

[0012] b) adding a phosphorus source to the SAPO-5 molecular sieve initial gel mixture A, and stirring at room temperature, for example, for 1 to 10 hours, to obtain a mixture B;

[0013] c) adding sulfate to the mixed solution B and stirring at room temperature, for example, for 1 to 10 hours, to obtain a mixed solution C; wherein the sulfate is SO4 2- : Aluminum source calculated as Al2O3 = 0.02 to 0.18 molar ratio;

[0014] d) adding a silicon source to the mixed solution C and stirring, for example, for 1 to 10 hours, to obtain a mixed solution D;

[0015] e) subjecting the mixed solution D to hydrothermal dynamic crystallization at 150-220° C. for a preferably 12-120 h. After completion of the crystallization, separation, such as by filtration or centrifugation, washing, and drying to obtain a solid product, i.e., molecular sieve raw powder;

[0016] f) calcining the molecular sieve raw powder to remove the template agent to obtain a hexagonal SAPO-5 molecular sieve, wherein the calcination is carried out, for example, at 450-600° C. in air for 2-8 hours.

[0017] The room temperature of the present invention may be 20-30°C.

[0018] According to the method for synthesizing SAPO-5 molecular sieve of the present invention, the silicon source may be selected from one or more of silica sol, silicon dioxide or tetraethyl orthosilicate.

[0019] The aluminum source is a solid aluminum source or an organic aluminum source that can be hydrolyzed to form a solid, for example, one or more selected from boehmite, pseudo-boehmite, alumina, aluminum hydroxide or aluminum isopropoxide.

[0020] The phosphorus source may be selected from one or more of orthophosphoric acid, phosphorous acid, ammonium dihydrogen phosphate or diammonium hydrogen phosphate.

[0021] The water is, for example, deionized water or distilled water.

[0022] The organic template can be selected from tetraethylammonium hydroxide, tetraethylammonium chloride or tetraethylammonium bromide.

[0023] The sulfate may be one or more of sodium sulfate and potassium sulfate.

[0024] According to the SAPO-5 molecular sieve synthesis method of the present invention, preferably, the molar ratio of phosphorus source calculated as P2O5: aluminum source calculated as Al2O3 is 0.6 to 1.2, for example, 0.9 to 1.1.

[0025] According to the SAPO-5 molecular sieve synthesis method of the present invention, preferably, the molar ratio of H2O in the mixed solution D to the aluminum source calculated as Al2O3 is 20 to 100, for example, 40 to 80.

[0026] According to the SAPO-5 molecular sieve synthesis method of the present invention, preferably, the molar ratio of silicon source calculated as SiO2: aluminum source calculated as Al2O3 is 0.1 to 1.0, for example, 0.3 to 0.8.

[0027] According to the method for synthesizing SAPO-5 molecular sieve of the present invention, preferably, the molar ratio of organic template: aluminum source calculated as Al2O3 is 0.1 to 0.4.

[0028] According to the SAPO-5 molecular sieve synthesis method of the present invention, preferably, sulfate is SO4 2- Calculation: Aluminum source = 0.05 to 0.15 molar ratio based on Al2O3.

[0029] According to the method for synthesizing SAPO-5 molecular sieve of the present invention, in one embodiment, the mixed solution D has the following molar composition:

[0030] SiO2:Al2O3=0.1~1.0, for example, 0.3~0.8;

[0031] P2O5:Al2O3=0.6~1.2, for example 0.9~1.1;

[0032] Organic template: Al2O3 = 0.1-0.6, for example, 0.1-0.5 or 0.1-0.4;

[0033] H2O:Al2O3=20-100, for example, 40-80;

[0034] and SO4 2- :Al2O3=0.01~0.15, for example 0.05~0.1.

[0035] The dynamic crystallization can be carried out under stirring or under rotation of the crystallization kettle. For example, the crystallization can be carried out with the rotation speed of the crystallization kettle within the range of 5-50 r / min.

[0036] The washing in step e can be performed with water, for example, to remove the residual unreacted silicon source, aluminum source, phosphorus source or organic template in the molecular sieve.

[0037] The drying in step e can be carried out by conventional drying methods, such as oven drying, air flow drying or flash drying.

[0038] The present invention provides a SAPO-5 molecular sieve having a hexagonal prism-shaped grain structure and an average aspect ratio of greater than 10.

[0039] In one embodiment, the average diameter of the SAPO-5 molecular sieve is 0.55 to 0.75 microns.

[0040] In one embodiment, the average length of the SAPO-5 molecular sieve is 8 to 13 microns.

[0041] Compared with the prior art, the SAPO-5 molecular sieve synthesis method provided by the present invention has one or more of the following beneficial effects, preferably all of the following beneficial effects:

[0042] 1. The synthesis method of the high aspect ratio hexagonal SAPO-5 molecular sieve provided by the present invention adopts a hydrothermal synthesis method, which does not require the addition of solvents other than water, reduces subsequent separation costs, and facilitates the industrial production of molecular sieves;

[0043] 2. The synthesis method of the high aspect ratio hexagonal SAPO-5 molecular sieve provided by the present invention adopts a one-step synthesis method, by adjusting the ratio of the organic template and adding a small amount of SO4 during the synthesis process. 2- Dynamic crystallization accelerates the axial growth rate of grains and can synthesize SAPO-5 molecular sieves with high aspect ratio. The synthesis process is simple and efficient.

[0044] 3. The method for synthesizing a high aspect ratio hexagonal SAPO-5 molecular sieve provided by the present invention can easily adjust the aspect ratio of the obtained hexagonal SAPO-5 molecular sieve, and the average aspect ratio of the prepared hexagonal SAPO-5 molecular sieve is greater than 10;

[0045] 4. The synthesis method of the high aspect ratio hexagonal SAPO-5 molecular sieve provided by the present invention uses a low amount of organic template, which can significantly reduce the amount of organic template used and reduce production costs;

[0046] 5. The high aspect ratio hexagonal SAPO-5 molecular sieve prepared by the synthesis method of the present invention has a small diameter and a thin thickness, and has better diffusion performance.

[0047] The SAPO-5 molecular sieve provided by the present invention has crystal grains with a hexagonal prism morphology, a high aspect ratio and good diffusion performance.

[0048] The SAPO-5 molecular sieve provided by the present invention can be used for hydrocarbon conversion reactions, such as alkylation, isomerization, and cracking reactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram of the measurement method for the length and diameter of regular hexagonal prism grains

[0050] Figure 2 This is the XRD spectrum of the high aspect ratio hexagonal SAPO-5 molecular sieve prepared in Example 1.

[0051] Figure 3 This is the XRD spectrum of the low aspect ratio hexagonal SAPO-5 molecular sieve prepared in Comparative Example 1.

[0052] Figure 4 This is an SEM image of the high aspect ratio hexagonal SAPO-5 molecular sieve prepared in Example 1.

[0053] Figure 5 This is the SEM spectrum of the low aspect ratio hexagonal SAPO-5 molecular sieve prepared in Comparative Example 1. DETAILED DESCRIPTION

[0054] The following examples will further illustrate the present invention and are intended to help readers better understand the essence of the present invention and the beneficial effects it brings, but should not be construed as any limitation on the scope of the present invention.

[0055] The drug information used in the examples is as follows:

[0056] Pseudo-boehmite, China Aluminum Shanxi New Materials Co., Ltd., with an Al2O3 content of 72.6% by weight.

[0057] Tetraethylammonium hydroxide solution, Beijing Yinuokai Technology Co., Ltd., content 25% by weight

[0058] Phosphoric acid solution, Tianjin Damao Chemical Reagent Factory, phosphoric acid content 85% by weight

[0059] Silica sol, Qingdao Jiyida Silica Gel Reagent Co., Ltd., SiO2 content 40% by weight, pH = 10.0

[0060] Fumed silica, MacLean Biological Reagent Co., Ltd., surface area 200 m 2 / g

[0061] Alumina, Beijing Yinuokai Technology Co., Ltd., purity 99.9%

[0062] Aluminum isopropoxide, Shanghai Aladdin Biochemical Technology Co., Ltd., purity 98%

[0063] Tetraethylammonium bromide, Tokyo Chemical Industry Development Co., Ltd. (Shanghai), purity 98%

[0064] Tetraethylammonium chloride, Beijing Yinuokai Technology Co., Ltd., purity 98%

[0065] Sodium sulfate, Beijing Yinuokai Technology Co., Ltd., purity 99%

[0066] Potassium sulfate, Beijing Yinuokai Technology Co., Ltd., purity 99%

[0067] Example 1

[0068] 14.86 g of pseudo-boehmite, 24.89 g of tetraethylammonium hydroxide and 77.25 g of deionized water were mixed and stirred at room temperature for 2 h to obtain a SAPO-5 molecular sieve initial gel mixture A; 24.40 g of phosphoric acid solution was added to the mixture A and stirred at room temperature for 2 h to obtain a mixture B; 0.75 g of sodium sulfate was added to the mixture B and stirred for 1 h to obtain a mixture C; 7.85 g of silica sol was added to the mixture C and stirred for 2 h to obtain a mixture D; the mixture D was crystallized at 190° C. for 24 h with a crystallization kettle speed of 15 r / min. After the crystallization was completed, the mixture was centrifuged, washed and dried to obtain a solid product, i.e., the molecular sieve raw powder; the molecular sieve raw powder was then calcined in air at 550° C. for 5 h to remove the template agent to obtain a high aspect ratio regular hexagonal SAPO-5 molecular sieve, which was marked as sample A.

[0069] Example 2

[0070] 14.81 g of pseudo-boehmite, 24.32 g of tetraethylammonium hydroxide and 76.66 g of deionized water were mixed and stirred at room temperature for 2 h to obtain a SAPO-5 molecular sieve initial gel mixture A; 24.32 g of phosphoric acid solution was added to the mixture A and stirred at room temperature for 2 h to obtain a mixture B; 1.50 g of sodium sulfate was added to the mixture B and stirred for 1 h to obtain a mixture C; 7.91 g of silica sol was added to the mixture C and stirred for 2 h to obtain a mixture D; the mixture D was crystallized at 190° C. for 24 h with a crystallization kettle speed of 15 r / min. After the crystallization was completed, the mixture was centrifuged, washed and dried to obtain a solid product, i.e., the molecular sieve raw powder; the molecular sieve raw powder was then calcined in air at 550° C. for 5 h to remove the template agent to obtain a high aspect ratio regular hexagonal SAPO-5 molecular sieve, which was marked as sample B.

[0071] Example 3

[0072] 14.76 g of pseudo-boehmite, 24.24 g of tetraethylammonium hydroxide and 76.16 g of deionized water were mixed and stirred at room temperature for 2 h to obtain a SAPO-5 molecular sieve initial gel mixture A; 24.24 g of phosphoric acid solution was added to the mixture A and stirred at room temperature for 2 h to obtain a mixture B; 2.24 g of sodium sulfate was added to the mixture B and stirred for 1 h to obtain a mixture C; 7.88 g of silica sol was added to the mixture C and stirred for 2 h to obtain a mixture D; the mixture D was crystallized at 190° C. for 24 h with a crystallization kettle speed of 15 r / min. After the crystallization was completed, the mixture was centrifuged, washed and dried to obtain a solid product, i.e., the molecular sieve raw powder; the molecular sieve raw powder was then calcined in air at 550° C. for 5 h to remove the template agent to obtain a high aspect ratio regular hexagonal SAPO-5 molecular sieve, which was marked as sample C.

[0073] Example 4

[0074] 11.99 g of aluminum oxide, 24.89 g of tetraethylammonium hydroxide and 80.12 g of deionized water were mixed and stirred at room temperature for 1 hour to obtain a SAPO-5 molecular sieve initial gel mixture A; 24.40 g of phosphoric acid solution was added to the mixture A and stirred at room temperature for 2 hours to obtain a mixture B; 0.75 g of sodium sulfate was added to the mixture B and stirred for 1 hour to obtain a mixture C; 7.85 g of silica sol was added to the mixture C and stirred for 2 hours to obtain a mixture D; the mixture D was crystallized at 190°C for 24 hours with a crystallization kettle speed of 15 r / min. After the crystallization was completed, the mixture was centrifuged, washed and dried to obtain a solid product, i.e., the molecular sieve raw powder; the molecular sieve raw powder was then calcined in air at 550°C for 5 hours to remove the template agent to obtain a high aspect ratio regular hexagonal SAPO-5 molecular sieve, which was marked as sample D.

[0075] Example 5

[0076] 44.63 g of aluminum isopropoxide, 4.55 g of tetraethylammonium bromide and 67.43 g of deionized water were mixed and stirred at room temperature for 1 hour to obtain a SAPO-5 molecular sieve initial gel mixture A; 24.69 g of phosphoric acid solution was added to the mixture A and stirred at room temperature for 2 hours to obtain a mixture B; 0.76 g of sodium sulfate was added to the mixture B and stirred for 1 hour to obtain a mixture C; 7.94 g of silica sol was added to the mixture C and stirred for 2 hours to obtain a mixture D; the mixture D was crystallized at 190° C. for 24 hours with a crystallization kettle speed of 15 r / min. After the crystallization was completed, the mixture was centrifuged, washed and dried to obtain a solid product, i.e., the molecular sieve raw powder; the molecular sieve raw powder was then calcined in air at 550° C. for 5 hours to remove the template agent to obtain a high aspect ratio regular hexagonal SAPO-5 molecular sieve, which was marked as sample E.

[0077] Example 6

[0078] 15.32g of pseudo-boehmite, 1.84g of tetraethylammonium chloride and 103.65g of deionized water were mixed, stirred at room temperature for 1h, and mixed evenly to obtain SAPO-5 molecular sieve initial gel mixture A; 25.15g of phosphoric acid solution was added to mixture A, and stirred at room temperature for 2h to obtain mixture B; 0.77g of sodium sulfate was added to mixture B, and stirred for 1h to obtain mixture C; 7.94g of gas-phase SiO2 was added to mixture C, and stirred for 2h to obtain mixture D; mixture D was crystallized at 190°C for 24h, with the crystallization kettle speed of 15r / min. After the crystallization, the mixture was centrifuged, washed, and dried to obtain a solid product, i.e., molecular sieve raw powder; the molecular sieve raw powder was then calcined in air at 550°C for 5h to remove the template agent, to obtain a high aspect ratio regular hexagonal SAPO-5 molecular sieve, which was marked as sample F.

[0079] Comparative Example 1

[0080] 14.83 g of pseudo-boehmite, 20.50 g of tetraethylammonium hydroxide and 95.75 g of deionized water were mixed, stirred at room temperature for 2 h, and mixed evenly to obtain SAPO-5 molecular sieve initial gel mixture A; 24.35 g of phosphoric acid solution was added to the mixture A, and stirred at room temperature for 2 h to obtain mixture B; 7.92 g of silica sol was added to the mixture B, and stirred for 2 h to obtain mixture D; the mixture D was crystallized at 190° C. for 24 h, with the crystallization kettle speed being 15 r / min. After the crystallization, the mixture was centrifuged, washed, and dried to obtain a solid product, i.e., molecular sieve raw powder; the molecular sieve raw powder was then calcined in air at 550° C. for 5 h to remove the template agent, to obtain a low aspect ratio regular hexagonal SAPO-5 molecular sieve, which was marked as sample G.

[0081] Comparative Example 2

[0082] 13.43 g of pseudo-boehmite, 20.50 g of tetraethylammonium bromide and 86.18 g of deionized water were mixed and stirred at room temperature for 1 hour to obtain a SAPO-5 molecular sieve initial gel mixture A; 22.05 g of phosphoric acid solution was added to the mixture A and stirred at room temperature for 1 hour to obtain a mixture B; 0.68 g of sodium sulfate was added to the mixture B and stirred for 1 hour to obtain a mixture C; 7.17 g of silica sol was added to the mixture C and stirred for 2 hours to obtain a mixture D; the mixture D was crystallized at 190°C for 24 hours with a crystallization kettle speed of 15 r / min. After the crystallization, the mixture was centrifuged, washed and dried to obtain a solid product, i.e., the original molecular sieve powder; the original molecular sieve powder was then calcined in air at 550°C for 4 hours to remove the template agent to obtain a low aspect ratio regular hexagonal SAPO-5 molecular sieve, which was labeled as sample H.

[0083] Comparative Example 3

[0084] 14.86 g of pseudo-boehmite, 24.89 g of tetraethylammonium hydroxide and 77.25 g of deionized water were mixed and stirred at room temperature for 2 h to obtain a SAPO-5 molecular sieve initial gel mixture A; 0.75 g of sodium sulfate was added to the mixture A and stirred for 1 h to obtain a mixture B; 24.40 g of phosphoric acid solution was added to the mixture B and stirred at room temperature for 2 h to obtain a mixture C; 7.85 g of silica sol was added to the mixture C and stirred for 2 h to obtain a mixture D; the mixture D was crystallized at 190° C. for 24 h with a crystallization kettle speed of 15 r / min. After the crystallization was completed, the mixture was centrifuged, washed and dried to obtain a solid product, i.e., the molecular sieve raw powder; the molecular sieve raw powder was then calcined in air at 550° C. for 5 h to remove the template agent to obtain a low aspect ratio regular hexagonal SAPO-5 molecular sieve, which was marked as sample I.

[0085] Table 1 Proportions of mixed solutions of various embodiments and comparative examples

[0086] sample <![CDATA[n(Al2O3)]]> <![CDATA[n(P2O5)]]> <![CDATA[n(SiO2)]]> n(template) <![CDATA[n(SO4 2- )]]> <![CDATA[n(H2O)]]> Example 1 1.0 1.0 0.5 0.4 0.05 60.0 Example 2 1.0 1.0 0.5 0.4 0.10 60.0 Example 3 1.0 1.0 0.5 0.4 0.15 60.0 Example 4 1.0 1.0 0.5 0.4 0.05 60.0 Example 5 1.0 1.0 0.5 0.2 0.05 60.0 Example 6 1.0 1.0 0.5 0.1 0.05 60.0 Comparative Example 1 1.0 1.0 0.5 0.4 0.00 60.0 Comparative Example 2 1.0 1.0 0.5 1.0 0.05 60.0 Comparative Example 3 1.0 1.0 0.5 0.4 0.05 60.0

[0087] Table 2 Grain size and mesopore volume of samples in various embodiments and comparative examples

[0088] sample Average length (μm) Average diameter (μm) Aspect ratio Example 1 9.21 0.72 12.8 Example 2 11.38 0.70 16.3 Example 3 12.53 0.68 18.4 Example 4 8.82 0.65 13.6 Example 5 10.23 0.62 16.5 Example 6 11.36 0.60 18.9 Comparative Example 1 0.51 1.44 0.35 Comparative Example 2 0.35 1.28 0.27 Comparative Example 3 0.63 1.56 0.40

Claims

1. A method for synthesizing a high aspect ratio hexagonal SAPO-5 molecular sieve, comprising: a) mixing an aluminum source, an organic template, and water, and stirring at room temperature to obtain a mixed solution A; wherein the molar ratio of the organic template to the aluminum source calculated as Al2O3 is 0.1 to 0.6; b) adding a phosphorus source to the mixed solution A and stirring at room temperature to obtain a mixed solution B; c) Add sulfate to mixed solution B and stir at room temperature to obtain mixed solution C; wherein SO4 2- : Aluminum source calculated as Al2O3 = 0.02 to 0.18 molar ratio; d) adding a silicon source to the mixed solution C and stirring, for example, for 1 to 10 hours, to obtain a mixed solution D; e) dynamically crystallizing the mixed solution D at 150-220° C., separating, washing, and drying to obtain molecular sieve raw powder after the crystallization is completed; f) calcining the molecular sieve raw powder to remove the template to obtain a hexagonal SAPO-5 molecular sieve.

2. The method for synthesizing the SAPO-5 molecular sieve according to claim 1, wherein The crystallization time is 12 to 120 hours; the calcination is, for example, calcined in air at 450 to 600° C. for 2 to 8 hours.

3. The method for synthesizing the SAPO-5 molecular sieve according to claim 1, wherein In step a, the stirring time is 1 to 10 hours; in step b, the stirring time is 1 to 10 hours; in step c, the stirring time is 1 to 10 hours.

4. The method for synthesizing the SAPO-5 molecular sieve according to claim 1, wherein The silicon source is selected from one or more of silica sol, silicon dioxide or tetraethyl orthosilicate; the aluminum source is selected from one or more of boehmite, pseudo-boehmite, alumina, aluminum hydroxide or aluminum isopropoxide; the phosphorus source is selected from one or more of phosphoric acid; the organic template is selected from one of tetraethylammonium hydroxide, tetraethylammonium chloride or tetraethylammonium bromide; and the sulfate is one or more of sodium sulfate and potassium sulfate.

5. The method for synthesizing the SAPO-5 molecular sieve according to claim 1, wherein Phosphorus source calculated as P2O5: The molar ratio of the aluminum source calculated as Al2O3 is 0.6 to 1.2, the molar ratio of H2O in the mixed solution D: the aluminum source calculated as Al2O3 is 20 to 100, and the molar ratio of the silicon source calculated as SiO2: the aluminum source calculated as Al2O3 is 0.1 to 1.

0.

6. The method for synthesizing the SAPO-5 molecular sieve according to claim 1, wherein: Phosphorus source calculated as P2O5: The molar ratio of aluminum source calculated on the basis of Al2O3 is 0.9-1.

1. The molar ratio of H2O in the mixed solution D to aluminum source calculated on the basis of Al2O3 is 40-80. The molar ratio of silicon source calculated on the basis of SiO2 to aluminum source calculated on the basis of Al2O3 is 0.3-0.

8. The molar ratio of organic template to aluminum source calculated on the basis of Al2O3 is 0.1-0.

4. SO4 2- : Aluminum source = 0.05 to 0.15 molar ratio based on Al2O3.

7. A SAPO-5 molecular sieve, wherein the SAPO-5 molecular sieve has a hexagonal prism-shaped grain structure and an average aspect ratio of greater than 10.

8. The SAPO-5 molecular sieve according to claim 7, characterized in that The average diameter of the SAPO-5 molecular sieve is 0.55 to 0.75 microns.

9. The SAPO-5 molecular sieve according to claim 7, characterized in that The average length of the SAPO-5 molecular sieve is 8 to 13 microns.

10. Use of the SAPO-5 molecular sieve according to claim 7 in hydrocarbon conversion.

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