Spherical SAPO-44 molecular sieve as well as preparation method and application thereof

Abstract

The invention belongs to the field of catalysts, and provides a spherical SAPO-44 molecular sieve, which comprises irregular spherical particles, and the irregular spherical particles are formed by aggregation of cubic units in a mortise and tenon connection mode. In addition, the invention also provides a preparation method and application of the spherical SAPO-44 molecular sieve. The spherical SAPO-44 molecular sieve provided by the invention has relatively long catalytic life.

Description

Technical Field

[0001] The invention belongs to the field of catalysts and relates to the field of silicoaluminophosphate molecular sieves, and specifically relates to a spherical SAPO-44 molecular sieve and a preparation method and application thereof. Background Art

[0002] In 1982, the Union Carbide Corporation (UCC) of the United States first introduced AlPO4 molecular sieves. The framework of this type of molecular sieve is neutral, without exchangeable cations, lacking the proton acid required for the catalytic activity of positive carbon ions, and exhibiting weak acid catalytic performance. In 1984, Lok et al. introduced Si into the AlPO4 series of molecular sieves and synthesized a series of [SiO2], [AlO2] － and [PO2] + Alumino-silicophosphate (SAPO) molecular sieve with small, medium or large pores composed of tetrahedral units. The pore structure of SAPO molecular sieves ranges from six-membered rings to twelve-membered rings, with pore diameters between 0.3 and 0.8 nm, and has different acidity strengths, which can meet the requirements of adsorption, diffusion and reaction of molecules of different sizes.

[0003] In the face of my country's growing demand for low-carbon olefins, combined with my country's structural characteristics of rich coal, less gas and poor oil, methanol to olefins has important national strategic significance. The industrial development of MTO and the diversification of low-carbon olefin production raw materials represented by ethylene and propylene are the most effective ways to solve my country's oil resource shortage and promote the rapid development of low-carbon olefin industrialization in my country. Among the many zeolite catalysts, the most studied and widely used catalyst is the small-pore SAPO-34 molecular sieve, whose crystal structure is similar to chabazite (CHA). The SAPO-44 molecular sieve has a CHA structure similar to that of the SAPO-34 molecular sieve, with a three-dimensional structure and a pore size of 0.43nm. Its basic structural unit is a double six-membered ring, which is connected by some four-membered rings to form a three-dimensional channel structure with a maximum of eight-membered rings. This type of molecular sieve has high shape selectivity and outstanding thermal stability and wet-heat stability. In the methanol conversion to light olefins (MTO) process, due to its pore size of about 0.43nm, it is shape-selective only for C1-C4 hydrocarbons. Using it as a catalyst can make the vast majority of the products of methanol conversion light olefins, without the generation of aromatic compounds and branched isomers, thereby improving the conversion rate and yield of the MTO process.

[0004] CN 201410411909.6 discloses a SAPO-44 molecular sieve, the anhydrous chemical composition of which is: BTA+·(Si x Al y P z)O2, wherein BTA+ is benzyltrimethylammonium cation, distributed in the molecular sieve cage and pores; m is the molar number of benzyltrimethylammonium cation per mole of (SixAlyPz)O2, m=0.01~0.15; x, y, z represent the molar fractions of Si, Al, and P, respectively, and their ranges are x=0.01~0.28, y=0.40~0.60, z=0.25~0.50, and x+y+z=1, and the synthesized molecular sieve has a cubic structure.

[0005] CN 201210363833.5 discloses a SAPO-44 molecular sieve and a synthesis method thereof. The molecular sieve micropores contain a template agent hexamethyleneimine, the molecular sieve crystal surface is slightly silicon-rich, the ratio of the silicon content on the outer surface to the silicon content in the bulk phase of the crystal is 1.50-1.01, and the molecular sieve has a cubic structure.

[0006] CN 201310499121.0 discloses a Si(4Al)-rich SAPO-44 molecular sieve with multi-level pores and a preparation method thereof. The raw materials used to prepare the molecular sieve satisfy the following ratio: the molar ratio of Al2O3:P2O5:SiO2:R:H2O is 1:(0.7-1.3):(0.1-0.2):(2.5-3.0):(30-80), wherein R is a composite template agent. The above raw material mixture is subjected to a secondary crystallization synthesis reaction to obtain the molecular sieve, and the morphology of the molecular sieve is a cubic structure containing multi-level pores.

[0007] SAPO-44 molecular sieve generally has a cubic structure, and carbon deposits are easily generated in the pores due to internal and external diffusion resistance. In addition, the strong exothermic characteristics of the methanol to olefins reaction itself lead to rapid deactivation of the catalyst and a very short single-pass life. Therefore, the market has a demand for SAPO-44 molecular sieves with long catalytic life, and how to extend the catalyst life is one of the directions that R&D personnel focus on. Summary of the invention

[0008] In order to overcome the problems existing in the prior art, the present invention provides a spherical SAPO-44 molecular sieve, wherein the spherical particles of the spherical SAPO-44 molecular sieve are aggregated by cubic units connected by mortise and tenon joints. This SAPO-44 molecular sieve with a special morphology can effectively improve the catalyst active center and anti-coking ability, accelerate the removal of reaction heat, increase the catalyst reaction activity and extend the catalyst life.

[0009] In a first aspect, the present invention provides a spherical SAPO-44 molecular sieve, the spherical SAPO-44 molecular sieve comprising irregular spherical particles formed by aggregating cubic units through mortise and tenon joints. The inventors of the present application have found that the spherical molecular sieve formed by aggregating cubic units through mortise and tenon joints can effectively improve the catalyst active center and anti-coking ability, and the catalyst has a relatively long one-way life.

[0010] In some embodiments of the present invention, the diameter of the spherical particles is about 30-100 μm.

[0011] In some embodiments of the present invention, the side length of the cubic unit is about 1.5-3.0 μm.

[0012] In some embodiments of the present invention, the raw materials for preparing the spherical SAPO-44 molecular sieve include an aluminum source, a phosphorus source, a silicon source, a template and water, wherein the template includes an organic amine and an inorganic ammonium salt.

[0013] In some embodiments of the present invention, the molar ratio of the organic amine to the inorganic ammonium salt is (0.5-15.0):1, for example, 0.5:1, 1.0:1, 1.5:1, 2.0:1, 2.5:1, 3.0:1, 3.5:1, 4.0:1, 4.5:1, 5.0:1, 5.5:1, 6.0:1, 6.5:1, 7.0:1, 7.5:1, 8.0:1, 8.5:1, 9.0:1, 9.5:1, 10.0:1, 10.5:1, 11:1, 12:1, 13:1 or 14:1. In some preferred embodiments of the present invention, the molar ratio of the organic amine to the inorganic ammonium salt is (0.5-10):1.

[0014] In some embodiments of the SAPO-44 molecular sieve of the present invention, the organic amine is a cycloalkylamine having 5 to 7 carbon atoms, preferably cyclohexylamine.

[0015] In some embodiments of the SAPO-44 molecular sieve of the present invention, the inorganic ammonium salt includes one or more of ammonium chloride, ammonium bromide, ammonium iodide, ammonium sulfate, ammonium carbonate, ammonium nitrate, ammonium bisulfate, and ammonium bicarbonate.

[0016] In some embodiments of the SAPO-44 molecular sieve of the present invention, the inorganic ammonium salt includes one or more of ammonium chloride, ammonium bromide, ammonium bisulfate, ammonium sulfate, ammonium nitrate or ammonium bicarbonate.

[0017] In some embodiments of the SAPO-44 molecular sieve of the present invention, the inorganic ammonium salt includes one or two of ammonium chloride, ammonium bisulfate, ammonium sulfate, ammonium nitrate or ammonium bicarbonate.

[0018] In some embodiments of the SAPO-44 molecular sieve of the present invention, the molar ratio of the aluminum source, the phosphorus source, the silicon source, the template and water is 1:(0.5-1.5):(0.1-1):(0.35-4):(10-120).

[0019] In some embodiments of the SAPO-44 molecular sieve of the present invention, the molar ratio of the aluminum source, phosphorus source, silicon source, template and water is 1:(0.8-1):(0.1-0.5):(1.5-2.2):(30-60).

[0020] In some embodiments of the SAPO-44 molecular sieve of the present invention, the molar ratio of the aluminum source, phosphorus source, silicon source, organic amine, inorganic ammonium salt and water is 1:(0.8-1):(0.1-0.5):(0.5-1.2):(0.5-1):(30-60).

[0021] In some embodiments of the SAPO-44 molecular sieve of the present invention, the molar ratio of the aluminum source, phosphorus source, silicon source, organic amine, inorganic ammonium salt and water is 1:(0.9-1):(0.2-0.3):(0.5-1.2):(0.5-1):(40-60).

[0022] In a second aspect, the present invention also provides a method for preparing a spherical SAPO-44 molecular sieve, the method comprising crystallizing a mixture containing an aluminum source, a phosphorus source, a silicon source, a template and water; wherein the template comprises an organic amine and an inorganic ammonium salt. The preparation method of the present invention can prepare a spherical SAPO-44 molecular sieve formed by aggregating cubic units through mortise and tenon joints by using a mixed template comprising an organic amine and an inorganic ammonium salt.

[0023] In some embodiments of the preparation method of the present invention, the crystallization is a one-stage crystallization or a two-stage crystallization.

[0024] In some embodiments of the preparation method of the present invention, the temperature of the one-stage crystallization is 170-200°C.

[0025] In some embodiments of the preparation method of the present invention, the one-stage crystallization time is 12 to 120 hours.

[0026] In some embodiments of the preparation method of the present invention, the two-stage crystallization includes a first-stage crystallization and a second-stage crystallization. Preferably, the temperature of the first-stage crystallization is 20-100°C higher than the temperature of the second-stage crystallization, and more preferably, the temperature of the first-stage crystallization is 30-80°C higher than the temperature of the second-stage crystallization (e.g., 30°C, 40°C, 50°C, 60°C, or 70°C higher).

[0027] In some embodiments of the preparation method of the present invention, the crystallization temperature of the first stage crystallization is 100-160° C., for example, 100° C., 110° C., 120° C., 125° C., 130° C., 135° C., 140° C., 145° C., 150° C., 155° C. or 160° C. In some preferred embodiments of the preparation method of the present invention, the crystallization temperature of the first stage crystallization is 140-160° C., for example, 140° C., 145° C., 150° C., 155° C. or 160° C.

[0028] In some embodiments of the preparation method of the present invention, the crystallization time of the first stage crystallization is 2 to 48 hours, preferably, the crystallization time of the first stage crystallization is 12 to 24 hours.

[0029] In some embodiments of the preparation method of the present invention, the crystallization temperature of the second stage crystallization is 170-200° C., for example, 170° C., 175° C., 180° C., 185° C., 190° C., 195° C. or 200° C. In some preferred embodiments of the preparation method of the present invention, the crystallization temperature of the second stage crystallization is 190-200° C.

[0030] In some embodiments of the preparation method of the present invention, the crystallization time of the second stage crystallization is 2 to 96 hours, for example, 3 hours, 5 hours, 10 hours, 15 hours, 20 hours, 25 hours, 30 hours, 35 hours, 40 hours, 50 hours or 60 hours. In some preferred embodiments of the preparation method of the present invention, the crystallization time of the second stage crystallization is 24 to 36 hours.

[0031] In some embodiments of the preparation method of the present invention, the method further comprises drying and calcining the crystallized product; preferably, the drying temperature is 40 to 150° C.; preferably 60 to 100° C. Preferably, the calcining temperature is 500 to 600° C. Preferably, the calcining time is 5 to 10 hours.

[0032] The preparation method of the spherical SAPO-44 molecular sieve provided by the present invention has simple process, high conversion rate, low cost, and good industrial application prospect; and can obtain the spherical SAPO-44 molecular sieve as described in the first aspect of the present invention.

[0033] On the other hand, the present invention also provides the use of the spherical SAPO-44 molecular sieve described in the first aspect or the spherical SAPO-44 molecular sieve prepared by the preparation method described in the second aspect as a catalyst in a process for converting methanol to light olefins.

[0034] On the other hand, the present invention also provides a method for preparing low-carbon olefins, which comprises using the spherical SAPO-44 molecular sieve described in the first aspect of the present invention or the spherical SAPO-44 molecular sieve prepared by the preparation method described in the second aspect as a catalyst to contact with methanol for reaction.

[0035] Preferably, the contact conditions include: temperature 350-500°C (e.g., 380°C, 400°C, 450°C, 170°C), pressure no greater than 1MPa (e.g., 0.05MPa, 0.1MPa, 0.2MPa, 0.3MPa, 0.5MPa, 0.8MPa), weight space velocity 1-6h -1 .

[0036] By using the spherical SAPO-44 molecular sieve provided by the present invention to catalyze the preparation of light olefins from methanol, higher stability is achieved and process costs are reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings are used to provide further understanding of the present application and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present application, but do not constitute a limitation to the present application.

[0038] Figure 1 is a scanning electron microscope photograph of the molecular sieve prepared in Example 1.

[0039] Figure 2 This is an enlarged view of the scanning electron microscope photograph of the molecular sieve prepared in Example 1.

[0040] Figure 3 This is a scanning electron microscope photograph of the molecular sieve prepared in Comparative Example 1. DETAILED DESCRIPTION

[0041] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0042] Examples and drawings are provided below to help understand the present invention. However, it should be understood that these examples and drawings are only used to illustrate the present invention, but do not constitute any limitation. The actual protection scope of the present invention is set forth in the claims. It should be understood that any modifications and changes can be made without departing from the spirit of the present invention.

[0043] The present invention will be described in detail below through examples.

[0044] In the method of the present invention, the morphology of the molecular sieve product is determined by scanning electron microscopy (SEM). The scanning electron microscopy (SEM) photo of the molecular sieve is measured by a Nova NanoSEM 450 scanning electron microscope. The sample is first ground into a powder of 200-400 mesh, fixed with double-sided conductive adhesive, and tested under high vacuum, with the microscope emission voltage of 200kV.

[0045] The reagents used in the following examples are commercially available and of analytical grade.

[0046] Example 1

[0047] Cyclohexylamine and ammonium chloride are used as templates, and pseudo-boehmite, phosphoric acid, silica sol, cyclohexylamine (R1), ammonium chloride (R2) and water are weighed in a molar ratio of Al2O3:P2O5:SiO2:R1:R2:H2O=1.0:1.0:0.25:1.2:0.5:40. The specific operation is as follows: first, mix pseudo-boehmite and deionized water evenly, then add phosphoric acid and stir for 2 hours, then add silica sol and stir for 2 hours, and finally add cyclohexylamine and ammonium chloride and stir evenly; the above reaction mixture is charged into a crystallization kettle with a polytetrafluoroethylene liner, first crystallized at 150°C under autogenous pressure for 18 hours, and then crystallized at 195°C under autogenous pressure for 24 hours, the crystallized product is washed with deionized water until neutral, the separated solid is dried in an oven at 100°C, and calcined in a muffle furnace at 550°C for 6 hours to obtain SAPO-44 molecular sieve, denoted as S1.

[0048] Scanning electron microscope photos Figure 1 and Figure 2 As shown, it is an irregular spherical crystal morphology, each spheroid is composed of cubic units connected by mortise and tenon joints. The diameter of the spherical particles is about 30 to 100 μm; the side length of the cube is about 1.5 to 3.0 μm.

[0049] Example 2

[0050] Cyclohexylamine and ammonium bicarbonate are used as templates, and aluminum isopropoxide, metaphosphoric acid, methyl orthosilicate, cyclohexylamine (R1), ammonium bicarbonate (R2) and water are weighed in a molar ratio of Al2O3:P2O5:SiO2:R1:R2:H2O=1.0:0.8:0.22:1.0:0.5:55. The specific operation is as follows: first, aluminum isopropoxide and deionized water are mixed evenly, then metaphosphoric acid is added and stirred for 2 hours, then methyl orthosilicate is added and stirred for 2 hours, and finally cyclohexylamine and ammonium bicarbonate are added and stirred evenly; the above reaction mixture is charged into a crystallization kettle with a polytetrafluoroethylene liner, firstly crystallized at 145°C under autogenous pressure for 20 hours, and then crystallized at 200°C under autogenous pressure for a second time for 24 hours, the crystallized product is washed with deionized water until neutral, the separated solid is dried in an oven at 100°C, and calcined in a muffle furnace at 550°C for 6 hours to obtain SAPO-44 molecular sieve, recorded as S2.

[0051] Scanning electron microscope photos have the following features: Figure 1 , Figure 2 Similar photos show irregular spherical crystals, each sphere is composed of cubic units connected by mortise and tenon joints.

[0052] Example 3

[0053] The difference between this embodiment and embodiment 1 is that the ratio of R1:R2 is adjusted from 1.2:0.5 to 0.5:1, and a SAPO-44 molecular sieve is obtained, which is recorded as S3.

[0054] Example 4

[0055] The difference between this embodiment and embodiment 1 is that the ratio of R1:R2 is adjusted from 1.2:0.5 to 1:1, and a SAPO-44 molecular sieve is obtained, which is recorded as S4.

[0056] Example 5

[0057] The difference between this embodiment and embodiment 1 is that the ratio of R1:R2 is adjusted from 1.2:0.5 to 5:1, and a SAPO-44 molecular sieve is obtained, which is recorded as S5.

[0058] Example 6

[0059] The difference between this embodiment and embodiment 1 is that the ratio of R1:R2 is adjusted from 1.2:0.5 to 10:1, and a SAPO-44 molecular sieve is obtained, which is recorded as S6.

[0060] Example 7

[0061] The only difference from Example 1 is that R2 is replaced by ammonium bisulfate to obtain SAPO-44 molecular sieve, which is denoted as S7.

[0062] Example 8

[0063] The only difference from Example 1 is that R2 is replaced by ammonium sulfate to obtain SAPO-44 molecular sieve, which is denoted as S8.

[0064] Example 9

[0065] The only difference from Example 1 is that R2 is replaced by ammonium nitrate to obtain SAPO-44 molecular sieve, which is denoted as S9.

[0066] The scanning electron microscope photos of the molecular sieve SAPO-44 prepared in Examples 3-9 are similar to Figure 1 , Figure 2 Similar to the above, it has an irregular spherical crystal morphology, and each sphere is composed of cubic units connected by mortise and tenon joints.

[0067] Example 10

[0068] The only difference from Example 1 is that the crystallization treatment is changed from "first crystallization at 150°C under autogenous pressure for 18 hours, then second crystallization at 195°C under autogenous pressure for 24 hours" to "crystallization at 170°C under autogenous pressure for 48 hours". The obtained molecular sieve is recorded as S10.

[0069] Embodiment 11

[0070] The only difference from Example 1 is that the crystallization treatment is changed from "first crystallization at 150°C under autogenous pressure for 18 hours, then second crystallization at 195°C under autogenous pressure for 24 hours" to "crystallization at 200°C under autogenous pressure for 36 hours". The obtained molecular sieve is recorded as S11.

[0071] Comparative Example 1

[0072] Preparation of conventional SAPO-44 molecular sieve:

[0073] Pseudo-boehmite, phosphoric acid, silica sol, and cyclohexylamine are aluminum source, phosphorus source, silicon source, and template (R) respectively, and the molar ratio is Al2O3: P2O5: SiO2: R: H2O = 1.0: 1.0: 0.25: 1.2: 40. The specific preparation process is as follows: after pseudo-boehmite and deionized water are mixed evenly, phosphoric acid is added and stirred for 2 hours, then silica sol is added and stirred for 2 hours, and finally cyclohexylamine is added and stirred evenly, the above reaction mixture is placed in a crystallization kettle with a polytetrafluoroethylene liner, crystallized at 195°C under autogenous pressure for 24 hours, the crystallized product is washed with deionized water until neutral, the separated solid is dried in an oven at 100°C, and calcined in a muffle furnace at 550°C for 6 hours to obtain SAPO-44 molecular sieve, which is recorded as B1.

[0074] Scanning electron microscope photos Figure 3 As shown, it is a cubic crystal morphology.

[0075] Comparative Example 2

[0076] The difference from Example 1 is that R2 is replaced by triethylamine, which is denoted as B2.

[0077] Comparative Example 3

[0078] The only difference from Example 1 is that R2 is replaced by tetraethylammonium hydroxide, which is denoted as B3.

[0079] The SAPO-44 molecular sieves prepared in Comparative Examples 2-3 all have a cubic crystalline morphology.

[0080] Test Example 1

[0081] Catalyst evaluation experiment

[0082] The samples obtained in the comparative example and the example were tableted and crushed, and then the particle size of 20-40 mesh was screened. A fixed bed catalytic reaction device was used to conduct catalyst evaluation experiments. The experimental conditions were: catalyst loading of 2.0g, reaction temperature of 470℃, reaction pressure of 0.1MPa, reaction raw material of 80% methanol aqueous solution, methanol weight space velocity of 4h -1 The results are shown in Table 1. Compared with the comparative example samples, the catalyst of the present invention has longer reaction stability and higher olefin selectivity.

[0083] Table 1

[0084]

[0085] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A spherical SAPO-44 molecular sieve, comprising irregular spherical particles, wherein the irregular spherical particles are aggregated by cubic units connected by mortise and tenon joints; Preferably, the diameter of the spherical particles is about 30 to 100 μm; Preferably, the side length of the cubic unit is about 1.5-3.0 μm.

2. The spherical SAPO-44 molecular sieve according to claim 1, wherein: The raw materials for preparing the spherical SAPO-44 molecular sieve include an aluminum source, a phosphorus source, a silicon source, a template and water, and the template includes an organic amine and an inorganic ammonium salt; Preferably, the molar ratio of the organic amine to the inorganic ammonium salt is (0.5-15.0):1, preferably (0.5-10):

1.

3. The spherical SAPO-44 molecular sieve according to claim 2, wherein: The organic amine is a cycloalkylamine having 5 to 7 carbon atoms, preferably cyclohexylamine.

4. The spherical SAPO-44 molecular sieve according to claim 2 or 3, wherein: The inorganic ammonium salt includes one or more of ammonium chloride, ammonium bromide, ammonium iodide, ammonium sulfate, ammonium nitrate, ammonium carbonate, ammonium bisulfate, and ammonium bicarbonate; Preferably, the inorganic ammonium salt includes one or more of ammonium chloride, ammonium bromide, ammonium bisulfate, ammonium sulfate, ammonium nitrate or ammonium bicarbonate.

5. The spherical SAPO-44 molecular sieve according to any one of claims 2 to 4, wherein: The molar ratio of aluminum source, phosphorus source, silicon source, template and water is 1:(0.5-1.5):(0.1-1):(0.35-4):(10-120); Preferably, the molar ratio of the aluminum source, phosphorus source, silicon source, template and water is 1:(0.8-1):(0.1-0.5):(1.5-2.2):(30-60).

6. A method for preparing a spherical SAPO-44 molecular sieve, comprising crystallizing a mixture containing an aluminum source, a phosphorus source, a silicon source, a template and water, wherein: The template includes organic amines and inorganic ammonium salts.

7. The preparation method according to claim 6, wherein The crystallization is one-stage crystallization or two-stage crystallization, Preferably, the temperature of the one-stage crystallization is 170 to 200° C. and / or the time of the one-stage crystallization is 12 to 120 hours; Preferably, the two-stage crystallization includes a first-stage crystallization and a second-stage crystallization, wherein the temperature of the first-stage crystallization is 20-100° C. higher than the temperature of the second-stage crystallization, and preferably the temperature of the first-stage crystallization is 30-80° C. higher than the temperature of the second-stage crystallization; Preferably, the crystallization temperature of the first stage crystallization is 100-160° C., and / or the crystallization time of the first stage crystallization is 2-48 hours; and / or the crystallization temperature of the second stage crystallization is 170-200° C., and / or the crystallization time of the second stage crystallization is 2-96 hours; Preferably, the crystallization temperature of the first stage crystallization is 140-160° C., and / or the crystallization time of the first stage crystallization is 12-24 hours; Preferably, the crystallization temperature of the second stage crystallization is 190-200° C., and / or the crystallization time of the second stage crystallization is 24-36 hours.

8. The preparation method according to claim 6 or 7, wherein: The process also includes drying and calcining the crystallized product; Preferably, the drying temperature is 40 to 150° C.; preferably 60 to 100° C.; and / or Preferably, the calcination temperature is 500-600°C; and / or Preferably, the calcination time is 5 to 10 hours.

9. Use of the spherical SAPO-44 molecular sieve according to any one of claims 1 to 5 or the spherical SAPO-44 molecular sieve prepared by the preparation method according to any one of claims 6 to 8 as a catalyst in a process for converting methanol to light olefins.

10. A method for preparing low-carbon olefins, comprising using the spherical SAPO-44 molecular sieve according to any one of claims 1 to 5 or the spherical SAPO-44 molecular sieve prepared by the preparation method according to any one of claims 6 to 8 as a catalyst in contact with methanol for reaction; Preferably, the contact conditions include: Temperature 350~500℃, pressure no more than 1MPa, weight space velocity 1~6h -1 .

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