Small-grain SAPO-34 molecular sieve as well as preparation method and application thereof

Abstract

The invention relates to the field of molecular sieves, in particular to a small-grain SAPO-34 molecular sieve as well as a preparation method and application thereof. The method comprises the following steps: (1) carrying out first mixing on a first template agent, a first silicon source, a first aluminum source, a first phosphorus source and first water to obtain a mixed solution A; (2) performing first aging and first crystallization treatment on the mixed solution A to obtain a mixed solution I; (3) performing second mixing on a second template agent, a second silicon source, a second aluminum source, a second phosphorus source and second water to obtain a mixed solution B; (4) performing first aging and first crystallization treatment on the mixed solution B to obtain a mixed solution J; (5) carrying out third mixing on the mixed solution I and the mixed solution J, and then carrying out second aging and second crystallization treatment to obtain a mixed solution K; (6) removing the residual template agent from the mixed solution K, and drying to obtain SAPO-34 raw powder; and (7) roasting the SAPO-34 raw powder to obtain the SAPO-34 molecular sieve. The SAPO-34 molecular sieve provided by the invention is small in crystal grain and unique in pore structure, and has the advantages of high activity, long service life and high low-carbon olefin selectivity in catalytic MTO reaction.

Description

Technical Field

[0001] This invention relates to the field of molecular sieves, specifically to a small-crystal SAPO-34 molecular sieve, its preparation method, and its applications. Background Technology

[0002] SAPO-34 molecular sieve, as a key catalyst in methanol-to-olefins (MTO) technology, is the industry's first choice due to its excellent proton acidity, pore structure, small pore size, large specific surface area, good adsorption performance, and thermal and hydrothermal stability. However, MTO, as a typical gas-solid heterogeneous reaction, faces challenges such as easy carbon deposition within the pores of SAPO-34 molecular sieve and rapid catalyst deactivation caused by strong exothermic reactions, which significantly limits the catalyst's single-pass lifetime.

[0003] To overcome these challenges, researchers have found that reducing the particle size of SAPO-34 molecular sieves and forming a hierarchical porous structure can effectively improve catalyst performance. Specifically, reducing the particle size increases the specific surface area of ​​the catalyst, thus providing more active sites; while the hierarchical porous structure helps reduce diffusion limitations, improves the mass transfer efficiency of the catalyst, and thus enhances its resistance to coking. Furthermore, the hierarchical porous structure also helps accelerate the removal of reaction heat, avoiding localized overheating, thereby further improving the catalyst's reactivity and extending its lifespan. Therefore, reducing the molecular sieve grain size and forming a hierarchical porous structure can improve the activity of SAPO-34 molecular sieves, thereby enhancing the activity of MTO catalysts.

[0004] CN102464338B discloses a method for preparing small-crystal SAPO-34 molecular sieves. This method is a two-step synthesis of molecular sieves. First, a first hydrothermal crystallization is performed to obtain a solution containing microcrystals. Then, using this solution as a crystallization directing agent, a second hydrothermal crystallization is performed with the same mixture in a certain proportion. Finally, the molecular sieve is obtained after washing and filtration. However, in this method, the solution containing microcrystals obtained from the first hydrothermal crystallization is in dynamic equilibrium, and these microcrystals have a tendency to dissolve. This causes the amount of these microcrystals in the solution to change over time, making it difficult to control the crystal form and size of the molecular sieve prepared using this microcrystal-containing solution as a directing agent. Furthermore, the solution containing microcrystals contains residual template agent, which can also have environmental impacts during the mixing process.

[0005] CN101555020B discloses a method for synthesizing SAPO molecular sieves. The method includes: a) mixing a template agent, a silicon source, an aluminum source, a phosphorus source, and water to form a solution, and then crystallizing the solution to form a seed crystal; b) mixing the aluminum source, phosphorus source, silicon source, and water to form a solution, adding the seed crystal, and then performing a crystallization reaction; c) filtering, washing, and drying the crystallized mixed solution to obtain SAPO molecular sieve powder. This method significantly reduces the amount of template agent used in the synthesis of SAPO molecular sieves in existing technologies, reducing costs and mitigating pollution. However, this method also faces the disadvantage that the seed crystal changes over time, making it difficult to control the crystal form and size of the resulting molecular sieve. Furthermore, the solution containing the seed crystal contains residual template agent, and the mixing process can also impact the environment. Summary of the Invention

[0006] The purpose of this invention is to solve the problems encountered in the prior art, thereby providing a small-crystal SAPO-34 molecular sieve, which has the characteristics of high activity, long catalytic lifetime and high selectivity for low-carbon olefins when catalyzing methanol to olefins.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for preparing SAPO-34 molecular sieve, the method comprising the following steps:

[0008] (1) The first template agent, the first silicon source, the first aluminum source, the first phosphorus source and the first water are mixed to obtain a mixture A;

[0009] (2) The mixture A is subjected to a first aging and a first crystallization treatment to obtain mixture I;

[0010] (3) The second template agent, the second silicon source, the second aluminum source, the second phosphorus source, and the second water are mixed to obtain a mixture B;

[0011] (4) The mixture B is subjected to a first aging and a first crystallization treatment to obtain the mixture J;

[0012] (5) Mix the mixture I and J for the third time, and subject the resulting mixture C to a second aging and second crystallization treatment to obtain mixture K;

[0013] (6) After removing the residual template agent from the mixture II, it is dried to obtain SAPO-34 raw powder;

[0014] (7) The SAPO-34 raw powder is calcined to obtain the SAPO-34 molecular sieve.

[0015] A second aspect of the present invention provides a SAPO-34 molecular sieve obtained by the above preparation method, wherein,

[0016] The average particle size of the SAPO-34 molecular sieve is 0.5-1 μm;

[0017] The specific surface area of ​​the SAPO-34 molecular sieve is 500-700 m². 2 / g;

[0018] The SAPO-34 molecular sieve has a pore volume of 0.25-0.4 cm³. 3 / g; of which, the volume content of micropores is 60-85%, and the volume content of mesopores and macropores is 15-40%.

[0019] A third aspect of the present invention provides the use of the above-mentioned SAPO-34 molecular sieve in methanol-to-olefins technology.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] I. This invention utilizes two different template agents (a first template agent and a second template agent) to induce the formation of primary crystal solutions with different crystal sizes. These solutions are then mixed and subjected to secondary crystallization. By utilizing the differences in structure and crystal growth rate of these primary crystals, an overall crystal structure with hierarchical structure is formed, which promotes the formation of small-crystal molecular sieves. This results in higher selectivity for low-carbon olefins and a longer catalytic lifetime when catalyzing methanol to olefins.

[0022] Second, in the preparation of small-crystal SAPO-34 molecular sieves, this invention uses vacuum distillation to remove residual template agent, thus the molecular sieve synthesis process will not have any environmental impact. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the process for preparing SAPO-34 molecular sieves according to an embodiment of the present invention.

[0024] Figure 2 This is a schematic diagram of the process for preparing SAPO-34 molecular sieves in a comparative manner according to the present invention.

[0025] Figure 3 The images show the X-ray powder diffraction (XRD) patterns of the samples prepared in the embodiments and comparative examples of this invention.

[0026] Figures 4a-4d Here is a scanning electron microscope (SEM) image of the SAPO-34 molecular sieve prepared according to an embodiment of the present invention; wherein,

[0027] 4a) is a SEM image of the sample prepared in Example 1, 4b) is a SEM image of the sample prepared in Example 2, 4c) is a SEM image of the sample prepared in Example 3, and 4d) is a SEM image of the sample prepared in Example 4.

[0028] Figures 5a-5cHere is a scanning electron microscope (SEM) image of the SAPO-34 molecular sieve prepared in the comparative example of this invention; wherein,

[0029] 5a) is the SEM image of the sample prepared in Comparative Example 1, 5b) is the SEM image of the sample prepared in Comparative Example 2, and 5c) is the SEM image of the sample prepared in Comparative Example 3. Detailed Implementation

[0030] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not imply that the scope of the invention is limited thereto.

[0031] The first aspect of this invention provides a method for preparing SAPO-34 molecular sieve, the method comprising the following steps:

[0032] (1) The first template agent, the first silicon source, the first aluminum source, the first phosphorus source and the first water are mixed to obtain a mixture A;

[0033] (2) The mixture A is subjected to a first aging and a first crystallization treatment to obtain mixture I;

[0034] (3) The second template agent, the second silicon source, the second aluminum source, the second phosphorus source, and the second water are mixed to obtain a mixture B;

[0035] (4) The mixture B is subjected to a first aging and a first crystallization treatment to obtain the mixture J;

[0036] (5) Mix the mixture I and J for the third time, and subject the resulting mixture C to a second aging and second crystallization treatment to obtain mixture K;

[0037] (6) After removing the residual template agent from the mixture K, it is dried to obtain SAPO-34 raw powder;

[0038] (7) The SAPO-34 raw powder is calcined to obtain the SAPO-34 molecular sieve.

[0039] In some embodiments, in step (1), the first template agent is selected from one or more of tetraethylammonium hydroxide, triethylamine, diethylamine, morpholine, aniline, n-propylamine, diisopropylamine, and n-butylamine;

[0040] The first silicon source is selected from one or more of silica sol, silicic acid, silicon dioxide, silica, water glass, and tetraethyl orthosilicate;

[0041] The first aluminum source is selected from one or more of boehmite, alumina, aluminum isopropoxide, and aluminum hydroxide;

[0042] The first phosphorus source is selected from one or more of orthophosphoric acid, ammonium phosphate, ammonium hydrogen phosphate, diammonium hydrogen phosphate, and aluminum phosphate.

[0043] In some embodiments, in step (1), the molar ratio of the first template agent, the first silicon source, the first aluminum source, the first phosphorus source and the first water is: first template agent: first silicon source (as SiO2): first aluminum source (as Al2O3): first phosphorus source (as P2O5): first water = (1-5): (0.1-0.8): 1: (0.5-1.5): (20-200).

[0044] In some implementations, in step (1), the conditions for the first mixing include a temperature of 20-80°C and a time of 1-10 hours.

[0045] Furthermore, the pH value of the mixture A obtained from the first mixing is 3-10.

[0046] In some implementations, in step (2), the conditions for the first aging include: a temperature of 20-80°C and a time of 1-24 hours;

[0047] The conditions for the first crystallization include: a temperature of 120-250℃ and a time of 10-120h.

[0048] In some embodiments, in step (3), the second template agent is preferably different from the first template agent.

[0049] Furthermore, the second template agent and the first template agent are independently selected from one or more of tetraethylammonium hydroxide, triethylamine, diethylamine, morpholine, aniline, n-propylamine, diisopropylamine, and n-butylamine;

[0050] The second silicon source and the first silicon source may be the same or different, and are independently selected from one or more of silica sol, silicic acid, silicon dioxide, silica, water glass and tetraethyl orthosilicate;

[0051] The second aluminum source and the first aluminum source may be the same or different, and are independently selected from one or more of boehmite, alumina, aluminum isopropoxide and aluminum hydroxide;

[0052] The second phosphorus source and the first phosphorus source may be the same or different, and are independently selected from one or more of orthophosphoric acid, ammonium phosphate, ammonium hydrogen phosphate, diammonium hydrogen phosphate, and aluminum phosphate.

[0053] In some embodiments, in step (3), the molar ratio of the second template agent, the second silicon source, the second aluminum source, the second phosphorus source, and the second water is: second template agent: second silicon source (as SiO2): second aluminum source (as Al2O3): second phosphorus source (as P2O5): second water = (0.2-7): (0.1-1): 1: (0-1.5): (20-200).

[0054] In some embodiments, in step (3), the conditions for the second mixing include a temperature of 20-80°C and a time of 1-10 hours.

[0055] Furthermore, the pH value of the mixture B obtained by the second mixing is 5-9.

[0056] In some embodiments, in step (4), the conditions for the first aging include: a temperature of 20-80°C and a time of 1-24 hours;

[0057] The conditions for the first crystallization include: a temperature of 120-250℃ and a time of 10-120h.

[0058] In some implementations, the conditions for the third mixing in step (5) include a temperature of 20-80°C and a time of 1-10 hours.

[0059] In some embodiments, in step (5), the conditions for the second aging include: a temperature of 20-80°C and a time of 1-24 hours;

[0060] The conditions for the second crystallization include a temperature of 150-250℃ and a time of 10-72h.

[0061] In some implementations, the residual template agent is removed in step (6) by means of flash evaporation or vacuum distillation.

[0062] In some embodiments, the drying method in step (6) can be any method conventional in the art, such as static drying by heating, spray drying of crystallization solution, etc.

[0063] Furthermore, the drying conditions include a temperature of 100-150°C and a time of 2-24 hours.

[0064] In some embodiments, the roasting method in step (7) can be conventional in the art, such as roasting in a muffle furnace or rotary kiln.

[0065] Furthermore, the calcination conditions include: a temperature of 500-700℃ and a time of 1-10h.

[0066] In the preparation method of this invention, firstly, two different template agents are used to induce the formation of primary crystal solutions with different crystallite sizes under hydrothermal crystallization conditions. Subsequently, these two primary crystal solutions undergo secondary crystallization. Due to the structural differences between the two primary crystals and the different crystal growth rates during the second hydrothermal crystallization, they compete for growth, resulting in a hierarchical crystal structure. Particularly noteworthy is that during the second hydrothermal crystallization, the dissolution rate of different primary crystals forms new crystal nuclei at a rate higher than the crystal growth rate; this characteristic promotes the formation of small-grained molecular sieves. This hierarchical small-grained SAPO-34 molecular sieve exhibits higher selectivity for low-carbon olefins and a longer catalytic lifetime compared to molecular sieves prepared by conventional methods.

[0067] A second aspect of the present invention provides a SAPO-34 molecular sieve obtained by the above preparation method, wherein,

[0068] The average particle size of the SAPO-34 molecular sieve is 0.5-1 μm;

[0069] The specific surface area of ​​the SAPO-34 molecular sieve is 500-700 m². 2 / g;

[0070] The SAPO-34 molecular sieve has a pore volume of 0.25-0.4 cm³. 3 / g; of which, the volume content of micropores is 60-85%, and the volume content of mesopores and macropores is 15-40%.

[0071] A third aspect of the present invention provides the use of the above-described SAPO-34 molecular sieve in methanol-to-olefins technology.

[0072] The preparation method of SAPO-34 molecular sieve provided by the present invention is further described in detail below, but the present invention is not limited thereto. Examples 1-4 are prepared according to... Figure 1 Comparative Examples 1-3 Figure 2 The preparation was carried out according to the process shown. In the following examples and comparative examples:

[0073] The surface morphology of SAPO-34 molecular sieve was characterized using a Nova Nano SEM 450 scanning electron microscope (SEM).

[0074] The crystal phase structure of SAPO-34 molecular sieve was characterized using a Bruker D8A X-ray powder diffractometer (XRD).

[0075] The specific surface area and pore volume of SAPO-34 molecular sieve were determined using Micrometitics ASAP 2020.

[0076] All raw materials used can be purchased commercially, including:

[0077] The aluminum source has an Al2O3 content of 65 wt% after conversion from boehmite.

[0078] The phosphorus source contains 85 wt% H3PO4 in phosphoric acid.

[0079] In the silicon source, the SiO2 content after conversion from silica sol is 30 wt%; the SiO2 content after conversion from tetraethyl orthosilicate is 28 wt%.

[0080] Example 1 (A1)

[0081] (1) The first template agent, the first silicon source, the first aluminum source, the first phosphorus source, and the first water are mixed according to... Figure 1 The process involves a first mixing to obtain mixture A; wherein...

[0082] The first template agent is 100g triethylamine, the first silicon source is 13g silica sol, the first aluminum source is 45g boehmite, the first phosphorus source is 65g phosphoric acid, and the first water is 200g deionized water.

[0083] The deionized water is used to prepare the aluminum source, phosphorus source and silicon source into a solution, thereby allowing the mixing to take place in the form of a liquid mixture;

[0084] The first mixing results in a molar ratio of triethylamine:SiO2:Al2O3:P2O5:H2O = 3.45:0.23:1:0.98:45 for each component in mixture A.

[0085] (2) Mixture A is subjected to first aging and first crystallization treatment to obtain mixture I.

[0086] (3) The second template agent, the second silicon source, the second aluminum source, the second phosphorus source, and the second water are mixed according to... Figure 1 The process involves a second mixing to obtain mixture B; wherein...

[0087] The second template agent is 20g diethylamine, the second silicon source is 3g silica sol, the second aluminum source is 12g boehmite, the second phosphorus source is 17g, and the second water is 60g deionized water;

[0088] The deionized water is used to prepare the aluminum source, phosphorus source and silicon source into a solution, thereby allowing the mixing to take place in the form of a liquid mixture;

[0089] The second mixing results in a molar ratio of diethylamine:SiO2:Al2O3:P2O5:H2O = 3.58:0.20:1:0.96:50 for each component in mixture B.

[0090] (4) The mixture B is subjected to the first aging and first crystallization treatment to obtain the mixture J.

[0091] (5) Mix the mixture I and J for the third time, and then perform a second aging and second crystallization treatment on the resulting mixture C to obtain mixture K.

[0092] (6) The template agent in mixture K was removed by vacuum distillation, followed by static drying to obtain SAPO-34 raw powder; wherein...

[0093] The vacuum degree of the distillation is -0.65 MPa and the temperature is 75°C.

[0094] (7) The SAPO-34 raw powder was calcined in a muffle furnace to obtain a SAPO-34 molecular sieve sample; wherein...

[0095] In step (1), the conditions for the first mixing include: a temperature of 25°C and a time of 2 hours.

[0096] In step (2), the conditions for the first aging include: a temperature of 25°C and a time of 2 hours; the conditions for the first crystallization include: a temperature of 150°C and a time of 24 hours.

[0097] In step (3), the conditions for the second mixing include: a temperature of 25°C and a time of 2 hours.

[0098] In step (4), the conditions for the first aging include: a temperature of 25°C and a time of 2 hours; the conditions for the first crystallization include: a temperature of 150°C and a time of 24 hours.

[0099] In step (5), the conditions for the third mixing include: a temperature of 25°C and a time of 2 hours.

[0100] In step (5), the conditions for the second aging include a temperature of 25°C and a time of 2 hours; the conditions for the second crystallization include a temperature of 200°C and a time of 24 hours.

[0101] In step (6), the drying conditions include a temperature of 120°C and a time of 24 hours.

[0102] In step (7), the calcination conditions include a temperature of 650°C and a time of 5 hours.

[0103] Example 2 (A2)

[0104] The procedure is the same as in Example 1, except that:

[0105] In step (2), the conditions for the first aging include: constant temperature and 3 hours; the conditions for the first crystallization include: constant temperature and constant time.

[0106] In step (3), the second silicon source is 3.12g of tetraethyl orthosilicate; the second mixing makes the molar ratio of each component in the mixture B be diethylamine:SiO2:Al2O3:P2O5:H2O=3.58:0.19:1:0.96:50, and the rest remain unchanged.

[0107] In step (4), the conditions for the first aging include: constant temperature and 3 hours; the conditions for the first crystallization include: constant temperature and constant time.

[0108] In step (5), the conditions for the second aging include: constant temperature and 3 hours.

[0109] In step (7), the calcination conditions include a temperature of 550°C and a time of 6 hours.

[0110] Example 3 (A3)

[0111] The procedure is the same as in Example 1, except that:

[0112] In step (1), the aluminum source is 57g of boehmite; the first template agent is diisopropylamine;

[0113] The first mixing results in a molar ratio of diisopropylamine:SiO2:Al2O3:P2O5:H2O = 4.20:0.28:1:1.20:55 for each component in mixture A, with the rest remaining unchanged.

[0114] In step (2), the conditions for the first aging include: constant temperature and 3 hours; the conditions for the first crystallization include: temperature of 120°C and 16 hours.

[0115] In step (3), the second template agent is 30g diethylamine, the second silicon source is 3.12g tetraethyl orthosilicate, and the aluminum source is 10g boehmite; the second mixing makes the molar ratio of each component in the mixture B be diethylamine:SiO2:Al2O3:P2O5:H2O=6.45:0.23:1:1.16:60, and the rest remain unchanged.

[0116] In step (4), the conditions for the first aging include: constant temperature and 3 hours; the conditions for the first crystallization include: temperature of 120°C and 16 hours.

[0117] In step (5), the conditions for the second aging include: constant temperature and 3 hours.

[0118] In step (7), the calcination conditions include a temperature of 600°C and a time of 6 hours.

[0119] Example 4 (A4)

[0120] The procedure is the same as in Example 1, except that:

[0121] In step (2), the conditions for the first aging include: constant temperature and 3 hours; the conditions for the first crystallization include: temperature of 200°C and 8 hours.

[0122] In step (3), the second template agent is 40g diethylamine, the second silicon source is 5g silica sol, the second aluminum source is 20g boehmite, the second phosphorus source is 15g phosphoric acid, and the second water is 80g deionized water; the second mixing makes the molar ratio of each component in the mixture B be diethylamine:SiO2:Al2O3:P2O5:H2O=4.30:0.20:1:0.51:40, and the rest remain unchanged.

[0123] In step (4), the conditions for the first aging include: constant temperature and 3 hours; the conditions for the first crystallization include: constant temperature and 20 hours.

[0124] In step (5), the conditions for the second aging include: constant temperature and 3 hours; the conditions for the second crystallization include: constant temperature and 12 hours.

[0125] In step (7), the calcination conditions include a temperature of 600°C and a time of 6 hours.

[0126] Comparative Example 1 (D1)

[0127] (1) The template agent, silicon source, aluminum source, phosphorus source and water are mixed in the first step to obtain a mixture M; wherein,

[0128] The template agent is 220g triethylamine and 4.4g diethylamine, the silicon source is 10g silica sol, the aluminum source is 12g boehmite, the phosphorus source is 18g phosphoric acid, and the water is 60g deionized water.

[0129] The deionized water is used to prepare the aluminum source, phosphorus source and silicon source into a solution, thereby allowing the mixing to take place in the form of a liquid mixture;

[0130] The conditions for the first mixing include: a temperature of 25°C and a time of 2 hours;

[0131] The first mixing results in a molar ratio of triethylamine: diethylamine: SiO2: Al2O3: P2O5: H2O of 2.85: 0.79: 0.65: 1: 1.02: 54 for each component in the mixture M.

[0132] (2) The mixture M is subjected to aging and crystallization treatment to obtain the mixture N; wherein,

[0133] The aging conditions include: a temperature of 25°C and a time of 2 hours;

[0134] The crystallization conditions include a temperature of 200°C and a time of 24 hours.

[0135] (3) The mixture N is washed, filtered, and then dried to obtain SAPO-34 raw powder; wherein,

[0136] The drying conditions include a temperature of 120°C and a time of 24 hours.

[0137] (4) The SAPO-34 raw powder was calcined in a muffle furnace to obtain a SAPO-34 molecular sieve sample; wherein...

[0138] The roasting conditions include a temperature of 550°C and a time of 6 hours.

[0139] Comparative Example 2 (D2)

[0140] Refer to Comparative Example 1, the only difference being:

[0141] In step (1), the template agent is only 30g of triethylamine and the silicon source is 3g of silica sol;

[0142] The first mixing results in a molar ratio of triethylamine:SiO2:Al2O3:P2O5:H2O = 3.88:0.20:1:1.02:50 for each component in the mixture M, with the rest remaining unchanged.

[0143] Comparative Example 3 (D3)

[0144] Refer to Comparative Example 1, the only difference being:

[0145] In step (1), the silicon source is 3g of silica sol;

[0146] The first mixing results in a molar ratio of triethylamine: diethylamine: SiO2: Al2O3: P2O5: H2O of 2.85: 0.79: 0.20: 1: 1.02: 50 for each component in the mixture M.

[0147] In step (2), the aging conditions include: constant temperature and 3 hours; the crystallization conditions include: constant temperature and 18 hours.

[0148] In step (4), the calcination conditions include a temperature of 650°C and a time of 5 hours.

[0149] The SAPO-34 molecular sieves obtained in Examples 1-4 and Comparative Examples 1-3 were characterized, and the results are shown in the appendix. Figure 3 -5 and as shown in Table 1 below.

[0150] Table 1:

[0151]

[0152]

[0153] Depend on Figure 3 It can be seen that the characteristic diffraction peaks of SAPO-34 appear in the XRD spectra of each embodiment and comparative example, proving that the samples prepared are all SAPO-34 molecular sieves.

[0154] As shown in Figures 4 and 5, the SAPO-34 molecular sieve prepared by this invention has a small crystal size (0.5-1 μm) and a visible hollow structure. This hollow structure reveals that the molecular sieve has a hierarchical pore morphology, which suggests that it has a high specific surface area and pore volume. When used as an active component of a catalyst, it exhibits high activity and reaction lifetime in the MTO reaction. When mixed with additives, binders, etc., it exhibits high strength. In contrast, the SAPO-34 molecular sieve obtained by conventional one-step hydrothermal crystallization has a crystal size of 3-10 μm, a relatively smooth crystal surface, and does not exhibit a hollow hierarchical pore structure. Consequently, it has a relatively low specific surface area and pore volume, resulting in lower activity and reaction lifetime when used as a catalyst. Furthermore, it exhibits lower strength when mixed with additives, binders, and other auxiliaries.

[0155] Test case

[0156] The catalytic performance of samples A1-A4 and D1-D3 in the MTO reaction was evaluated using a fixed-bed reactor, as follows:

[0157] 0.8 g of sample was weighed and placed in the reactor. Activation was performed at 500 °C with nitrogen for 0.5 h, followed by cooling to 450 °C. The raw methanol solution, after being transported by a metering pump and carried by a carrier gas (nitrogen, flow rate 14 mL / min), was mixed and fed into a preheating furnace. In the preheating furnace, the methanol vaporized into a gas, which then entered the reactor for reaction (methanol space velocity 1.68 h⁻¹). -1 The reaction products were analyzed online using an Agilent 7890B chromatograph. Table 2 below shows the experimental results, in which...

[0158] When the methanol conversion rate in the tested component is below 99%, it is considered that the catalyst is deactivated, that is, the catalyst lifetime is the time that the methanol conversion rate is above 99%.

[0159] Table 2:

[0160]

[0161]

[0162] As can be seen from the results in Table 2, the SAPO-34 molecular sieve prepared by the method of the present invention has a selectivity of more than 85% for low carbon olefins (C2H4 and C3H6) and a catalytic lifetime of more than 210 min in the MTO reaction, which is significantly higher than that of SAPO-34 molecular sieve obtained by one-step hydrothermal crystallization method in the prior art.

[0163] As can be seen from the results in Table 2, compared with the molecular sieve induced by a single template agent (Comparative Example 2), the molecular sieve induced by two different template agents (Comparative Example 3) has higher selectivity for low carbon olefins and a longer lifetime.

Claims

1. A method for preparing a SAPO-34 molecular sieve, characterized in that, The method comprises the following steps: (1) first mixing a first template agent, a first silicon source, a first aluminum source, a first phosphorus source and first water to obtain a mixed solution A; (2) performing first aging and first crystallization treatment on the mixed solution A to obtain a mixed solution I; (3) second mixing a second template agent, a second silicon source, a second aluminum source, a second phosphorus source and second water to obtain a mixed solution B; (4) performing first aging and first crystallization treatment on the mixed solution B to obtain a mixed solution J; (5) third mixing the mixed solution I and the mixed solution J, and performing second aging and second crystallization treatment on the obtained mixed solution C to obtain a mixed solution K; (6) drying the mixed solution K after removing residual template agent to obtain SAPO-34 raw powder; (7) performing calcination treatment on the SAPO-34 raw powder to obtain the SAPO-34 molecular sieve.

2. The production method according to claim 1, characterized by, In step (1), the molar ratio of the use amount of the first template agent, the first silicon source, the first aluminum source, the first phosphorus source and the first water is: first template agent: first silicon source (calculated as SiO2): first aluminum source (calculated as Al2O3): first phosphorus source (calculated as P2O5): first water = (1-5):(0.1-0.8):1:(0.5-1.5):(20-200).

3. The production method according to claim 1 or 2, characterized by, In step (3), the molar ratio of the use amount of the second template agent, the second silicon source, the second aluminum source, the second phosphorus source and the second water is: second template agent: second silicon source (calculated as SiO2): second aluminum source (calculated as Al2O3): second phosphorus source (calculated as P2O5): second water = (0.2-7):(0.1-1):1:(0-1.5):(20-200).

4. The production method according to any one of claims 1 to 3, characterized by, In step (1), the conditions of the first mixing include: temperature 20-80℃, time 1-10h; In step (3), the conditions of the second mixing include: temperature 20-80℃, time 1-10h; In step (5), the conditions of the third mixing include: temperature 20-80℃, time 1-10h.

5. The production method according to any one of claims 1 to 4, characterized by, In step (2), the conditions of the first aging include: temperature 20-80℃, time 1-24h; the conditions of the first crystallization include: temperature 120-250℃, time 10-120h; In step (4), the conditions of the first aging include: temperature 20-80℃, time 1-24h; the conditions of the first crystallization include: temperature 120-250℃, time 10-120h.

6. The production method according to any one of claims 1 to 5, characterized by, In step (5), the conditions of the second aging include: temperature 20-80℃, time 1-24h; the conditions of the second crystallization include: temperature 150-250℃, time 10-72h.

7. The production method according to any one of claims 1 to 6, characterized by, In step (6), the conditions of the drying include: temperature 100-150℃, time 2-24h; In step (6), the way of removing residual template agent is reduced pressure distillation or flash evaporation; In step (7), the conditions of the calcination include: temperature 500-700℃, time 1-10h.

8. The production method according to any one of claims 1 to 7, characterized by, The first and second template agents are independently selected from one or more of tetraethylammonium hydroxide, triethylamine, diethylamine, morpholine, aniline, n-propylamine, diisopropylamine, and n-butylamine; preferably the first and second template agents are different; The first and second silicon sources are independently selected from one or more of silica sol, silicic acid, silica, white carbon black, water glass, and tetraethyl orthosilicate; The first and second aluminum sources are independently selected from one or more of pseudoboehmite, aluminum oxide, aluminum isopropoxide, and aluminum hydroxide; The first and second phosphorus sources are independently selected from one or more of orthophosphoric acid, ammonium phosphate, ammonium hydrogen phosphate, diammonium hydrogen phosphate, and aluminum phosphate.

9. A SAPO-34 molecular sieve obtained by the preparation method of any one of claims 1 to 8; wherein, The average particle size of the SAPO-34 molecular sieve is 0.5 to 1 μm; The SAPO-34 molecular sieve has a specific surface area of 500-700 m 2 / g. The SAPO-34 molecular sieve has a pore volume of 0.25-0.4 cm 3 / g; wherein the volume content of micropores is 60-85%, and the volume content of mesopores and macropores is 15-40%.

10. Use of the SAPO-34 molecular sieve of any one of claims 1 to 9 in a methanol-to-olefins technology.

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