Catalyst for converting methanol to olefins and its preparation method and application

Abstract

The application discloses a methanol conversion to olefin catalyst and a preparation method and application thereof. The preparation method of the catalyst comprises the following steps: mixing a silicon source, an alkali source, a solvent and a template R to prepare a shell growth solution; adding a core phase SAPO molecular sieve into the shell growth solution, stirring at a certain temperature, and roasting to obtain the methanol conversion to olefin catalyst. The catalyst prepared by the method has a core-shell structure of SAPO@mesosilica molecular sieve, has a large specific surface area, a proper micropore / mesopore ratio, and can significantly improve the reaction activity of methanol conversion to olefin.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation, specifically relating to a methanol-to-olefins catalyst, its preparation method, and its application. Background Technology

[0002] Ethylene and propylene are important organic chemical raw materials in modern chemical industry. Currently, methanol or dimethyl ether is often used as a raw material to catalyze the production of low-carbon olefins (MTO or DTO). Researchers have explored using various molecular sieves as catalysts for methanol-to-olefins (MTO), with SAPO molecular sieves being the most widely used. SAPO molecular sieves were first synthesized and discovered by Union Carbide Corporation in the United States. By introducing silicon atoms into a novel aluminum phosphate framework, the molecular sieve framework becomes negatively charged, possessing both Lewis (L) and Beta (B) acid properties. SAPO-34 molecular sieve exhibits the best selectivity for low-carbon olefins in methanol-to-olefins reactions to date. Other suitable molecular sieves include SAPO-18, SAPO-17, SAPO-44, SAPO-47, and SAPO-56.

[0003] CN201410305293.4 discloses a method for synthesizing SAPO-18 molecular sieves with an AEI-type structure. This method uses a combination of template agents, which shortens the reaction time. The synthesized molecular sieve has a plate-like structure and can be applied in MTO reactions. CN99126306.5 discloses a method for preparing SAPO-17 and SAPO-44 molecular sieves. By controlling the ratio of silicon source to phosphorus source, SAPO-17, SAPO-44, and symbiotic mixtures with different ratios can be formed.

[0004] With the research on core-shell molecular sieve catalysts, it has been found that the core-shell structure can effectively improve the pore structure on the outer surface of the core-phase molecular sieve, thereby improving the catalytic performance of the catalyst. CN201710532100.2 discloses a method for preparing a core-shell molecular sieve SAPO-34@Silicite-1, which prepares a core-shell catalyst suitable for MTO reaction with SAPO-34 molecular sieve as the core phase and Silicite-1 as the shell phase. In the preparation process, it is necessary to pretreat the core-phase SAPO-34 molecular sieve with a polycationic reagent, and then perform Silicite-1 seed adsorption and secondary seed growth. However, the preparation process of this method is relatively complicated and the selectivity for low-carbon olefins is low. Summary of the Invention

[0005] To address the problems of poor reaction stability and low selectivity for low-carbon olefins in existing catalysts used in the methanol-to-olefins process, this invention provides a methanol-to-olefins catalyst, its preparation method, and its application. The catalyst prepared by this invention exhibits high catalytic activity and good reaction stability when used in the methanol-to-olefins reaction.

[0006] The first aspect of this invention provides a method for preparing a methanol-to-olefins catalyst, comprising the following steps:

[0007] (1) Mix silicon source, alkali source, solvent and template agent R to obtain shell growth solution;

[0008] (2) The core phase SAPO molecular sieve is added to the shell growth solution obtained in step (1), stirred and calcined at a certain temperature to obtain the methanol-to-olefins catalyst.

[0009] Further, in step (1), the silicon source in the shell growth solution is SiO2, and the molar ratio of each component is as follows: R: SiO2: Alkali source: Organic solvent: H2O = 0.01~0.2: 0.01~0.3: 0.2~1.2: 5~50: 20~105.

[0010] The solvent is a mixture of an organic solvent and water, wherein the organic solvent is selected from at least one of diethyl ether, ethanol, and cyclohexane.

[0011] Furthermore, the silicon source is selected from at least one of sodium silicate, methyl orthosilicate, ethyl orthosilicate, and silica sol; the alkali source is selected from at least one of tetraethylammonium hydroxide aqueous solution, ammonia, sodium hydroxide, and urea; and the template agent is selected from at least one of hexadecyltrimethylammonium bromide (CTAB), hexadecylpyridine bromide, and hexadecyltoluenesulfonate.

[0012] Further, in step (2), the core phase SAPO-molecule is selected from at least one of SAPO-34, SAPO-17, SAPO-18, SAPO-44, SAPO-47 or SAPO-56 molecular sieves, preferably SAPO-34 and / or SAPO-18 molecular sieves.

[0013] Furthermore, the SiO2 / Al2O3 molar ratio of the core phase SAPO molecular sieve is 0.10 to 1.2.

[0014] Furthermore, the specific surface area of ​​the core-phase SAPO molecular sieve is 300–580 m². 2 / g.

[0015] Further, in step (2), the mass ratio of the silicon source in the shell growth solution (calculated as SiO2) to the core phase SAPO molecular sieve is 1:1 to 1:100, preferably 1:5 to 1:50.

[0016] Further, in step (2), the stirring conditions are as follows: stirring temperature 50-100℃, stirring time 3-48h.

[0017] Further, in step (2), the calcination conditions are as follows: the calcination temperature is 480-700℃, the calcination time is 3-48h, and the calcination atmosphere is a mixture of air and nitrogen, wherein the volume ratio of air to nitrogen is 1.0-6.0.

[0018] Furthermore, after stirring, the intermediate crystalline material product can be separated from the obtained mixture by any conventionally known separation method, such as filtration, washing, and drying. Here, the filtration, washing, and drying can be carried out in any manner conventionally known in the art. The drying temperature is optionally 80–160°C, preferably 100–150°C; the drying time is 4–48 hours, preferably 6–24 hours. The drying can be carried out under normal pressure or under reduced pressure; to save energy, normal pressure is usually chosen.

[0019] Furthermore, the nucleated SAPO molecular sieve can be prepared according to conventional methods in the art.

[0020] A second aspect of the present invention provides a catalyst for methanol-to-olefins conversion prepared according to the above preparation method.

[0021] Furthermore, the catalyst is a core-shell structured SAPO@mesosilica molecular sieve, with SAPO molecular sieve as the core phase and mesosilica (mesoporous silica) as the shell.

[0022] Furthermore, the specific surface area of ​​the SAPO@mesosilica molecular sieve is 600–820 m². 2 / g, preferably 610-800m 2 / g.

[0023] Furthermore, the SAPO@mesosilica molecular sieve has a microporous-mesoporous composite pore structure, wherein the micropore volume is 0.05–0.35 cm³. 3 / g, pore size 0.1–1.5 nm; mesopore volume 0.1–0.4 cm³ 3 / g, pore size is 2-50nm; micropore / mesopore ratio is 0.5-2.5.

[0024] Furthermore, the shell coverage of the SAPO@mesosilica molecular sieve is 50% to 98%.

[0025] A third aspect of the present invention provides a method for converting methanol to low-carbon olefins, comprising: reacting the above-mentioned catalyst with methanol feedstock to obtain low-carbon olefins.

[0026] Furthermore, the methanol feedstock can be pure methanol, crude methanol containing water (water content 60-85%), or methanol containing inert gas (inert gas volume fraction 10%-20%).

[0027] Furthermore, the reactor can be a fixed-bed or fluidized-bed reactor. The preferred reaction conditions are as follows: reaction temperature 350–500°C, reaction pressure 0–1 MPa, and weight hourly space velocity 1–6 h⁻¹. -1 .

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] This invention uses SAPO molecular sieves as the core phase and, by controlling the proportion of the added shell growth liquid and calcining in an air / nitrogen mixed atmosphere, produces a methanol-to-olefins catalyst with a significantly increased specific surface area and an optimal micropore / mesopore ratio. When applied to the methanol-to-olefins reaction, this catalyst can significantly improve product diffusion, reduce mass transfer resistance, and delay the formation of reaction carbon deposits, thereby enhancing the catalytic activity, especially the stability, of the methanol-to-olefins reaction.

[0030] The catalyst provided by this invention is a core-shell structured SAPO@mesosilica molecular sieve, with SAPO molecular sieve as the core phase and mesosilica as the shell. This catalyst has a large specific surface area and a suitable micropore / mesopore ratio, which can significantly improve the reactivity of methanol to olefins conversion. Attached Figure Description

[0031] Figure 1 To compare the small-angle and wide-angle XRD patterns of the SAPO-18 molecular sieve obtained in Example 1;

[0032] Figure 2 To compare the small-angle and wide-angle XRD patterns of the SAPO-34 molecular sieve obtained in Example 2;

[0033] Figure 3 To compare the small-angle and wide-angle XRD patterns of the SAPO-18 / SAPO-34 molecular sieve obtained in Example 3;

[0034] Figure 4 To compare the small-angle and wide-angle XRD patterns of the SAPO-18@mesosilica molecular sieve obtained in Example 4;

[0035] Figure 5 To compare the small-angle and wide-angle XRD patterns of the SAPO-18@mesosilica molecular sieve obtained in Example 5;

[0036] Figure 6 The XRD small-angle and wide-angle diffraction patterns of the SAPO-18@mesosilica molecular sieve obtained in Example 1 are shown below.

[0037] Figure 7 The XRD small-angle and wide-angle diffraction patterns of the SAPO-34@mesosilica molecular sieve obtained in Example 2 are shown below.

[0038] Figure 8 The XRD small-angle and wide-angle diffraction patterns of the SAPO-18 / SAPO-34@mesosilica molecular sieve obtained in Example 3 are shown below.

[0039] Figure 9 The XRD small-angle and wide-angle diffraction patterns of the SAPO-44@mesosilica molecular sieve obtained in Example 9 are shown below.

[0040] Figure 10 SEM images of SAPO-18 molecular sieve obtained in Comparative Example 1;

[0041] Figure 11 SEM images of SAPO-34 molecular sieve obtained in Comparative Example 2;

[0042] Figure 12 SEM images of SAPO-18@mesosilica molecular sieve obtained in Comparative Example 4;

[0043] Figure 13 This is a SEM image of the SAPO-18@mesosilica molecular sieve obtained in Example 1. Detailed Implementation

[0044] The present invention will be further illustrated below through embodiments, but the scope of protection of the present invention is not limited to the embodiments.

[0045] The molecular sieves prepared in this invention are characterized using the following equipment. The same characterization equipment and testing methods are used in the following examples and comparative examples.

[0046] In this invention, the morphology of the molecular sieve product is determined by scanning electron microscopy (SEM). The SEM images of the molecular sieve are obtained using a Nova NanoSEM 450 scanning electron microscope. Before testing, the sample is ground into a powder of 200-400 mesh, fixed with double-sided conductive adhesive, and tested under high vacuum conditions with a microscope emission voltage of 200 kV.

[0047] In this invention, the crystal form of the molecular sieve product is determined by X-ray diffraction (XRD). A Bruker D8 Advance diffractometer is used, employing a Cu-Kα ray source with an operating voltage of 40 kV, a current of 200 mA, a scanning range of 0-50°, a scanning step size of 0.02°, and a scanning speed of 4° / min. The characteristic peak of SiO2 appears at 2θ = 2.2 ± 0.2° in the small-angle diffraction pattern.

[0048] In this invention, the specific surface area of ​​the molecular sieve was measured on a Micromeritics TriStar 3000 adsorption instrument. The calcined sample was processed under vacuum at 300°C. The specific surface area of ​​the sample was calculated using the BET formula, the pore volume was calculated using the t-plot method, and the pore size distribution was calculated using the BJH or DFT method. The shell coverage of the sample was calculated based on the specific surface area, which is (1 - specific surface area of ​​uncalcined core-shell molecular sieve / specific surface area of ​​molecular sieve core) × 100%.

[0049] In the embodiments and comparative examples of this invention, during the methanol-to-olefins reaction: a small fixed-bed device is used, the methanol feed pump is turned on, the methanol flow rate is set, the feed valve is opened, and methanol enters the reactor to start the reaction. The reaction product is taken after a certain reaction time, and samples are taken once at regular intervals. The samples are analyzed using an Agilent 7890 gas chromatograph.

[0050] The distribution of hydrocarbon products (wt%) was quantitatively detected by the FID detector of the chromatography and calculated using the correction normalization method.

[0051]

Comparative Example 1

[0052] Alumina, phosphoric acid, silica sol, and N,N-diisopropylethylamine were weighed and mixed in a molar ratio of Al₂O₃:P₂O₅:SiO₂:R:H₂O = 1.0:1.0:0.25:2.0:45. The mixture was then placed in a crystallization vessel lined with polytetrafluoroethylene (PTFE) and crystallized at 195°C under autogenous pressure for 24 hours. The crystallized product was washed with deionized water until neutral, and the solid was separated and dried in an oven at 100°C. The solid was then calcined in a muffle furnace at 550°C for 6 hours to obtain SAPO-18 molecular sieve, denoted as B1. The specific surface area of ​​B1 is 483.19 m². 2 / g, the molar ratio of SiO2 / Al2O3 is 0.21. The XRD pattern of B1 is shown below. Figure 1 As shown, Figure (a) is the XRD small-angle diffraction pattern, and Figure (b) is the XRD wide-angle diffraction pattern; the SEM image is shown below. Figure 10 As shown.

[0053] [Comparative Example 2]

[0054] Using pseudoboehmite, phosphoric acid, silica sol, and tetraethylammonium hydroxide as the aluminum source, phosphorus source, silicon source, and template agent (R), respectively, the ingredients were weighed and mixed in a molar ratio of Al₂O₃:P₂O₅:SiO₂:R:H₂O = 0.8:1.0:0.2:2.0:50. The mixture was then placed in a crystallization vessel lined with polytetrafluoroethylene (PTFE) and crystallized at 150°C for 24 hours. The temperature was then raised to 200°C and crystallized for another 24 hours. The crystallized product was washed with deionized water until neutral, and the solid was separated and dried in an oven at 100°C for 12 hours. It was then calcined in a muffle furnace at 550°C for 3 hours to obtain SAPO-34 molecular sieve, denoted as B2. The specific surface area was 506.73 m². 2 / g, the molar ratio of SiO2 / Al2O3 is 0.18. The XRD pattern of B2 is shown below. Figure 2 As shown, Figure (a) is the XRD small-angle diffraction pattern, and Figure (b) is the XRD wide-angle diffraction pattern; the SEM image is shown below. Figure 11 As shown.

[0055] [Comparative Example 3]

[0056] Using pseudoboehmite, phosphoric acid, silica sol, and tetraethylammonium hydroxide as the aluminum source, phosphorus source, silicon source, and template agent (R), respectively, the ingredients were weighed and mixed in a molar ratio of Al2O3:P2O5:SiO2:R:H2O = 0.8:1.0:0.2:2.0:50. The mixture was then added to the SAPO-18 molecular sieve obtained in Comparative Example 1. The reaction mixture was placed in a crystallization vessel lined with polytetrafluoroethylene and crystallized at 200°C under autogenous pressure for 4 hours. The crystallized product was washed with deionized water until neutral, and the solid was separated and dried in an oven at 100°C. It was then calcined in a muffle furnace at 550°C for 6 hours. The resulting SAPO18 / SAPO-34 mixed molecular sieve was designated B3. The specific surface area of ​​B3 was 496.57 m². 2 / g, the molar ratio of SiO2 / Al2O3 is 0.28. The XRD pattern of B3 is shown below. Figure 3 As shown, Figure (a) is the XRD small-angle diffraction pattern, and Figure (b) is the XRD wide-angle diffraction pattern.

[0057] [Comparative Example 4]

[0058] (1) Using hexadecyltrimethylammonium bromide (CTAB) as a template agent, tetraethyl orthosilicate (TEOS) as a silicon source, and ethanol and water as solvents, a shell growth solution was prepared according to the ratio of CTAB:SiO2:C2H5OH:NH3·H2O:H2O = 0.02:0.05:25:0.7:100;

[0059] (2) The SAPO-18 molecular sieve obtained in Comparative Example 1, as the core-phase molecular sieve, was added to the above-mentioned shell growth solution, wherein the mass ratio of tetraethyl orthosilicate (SiO2) to SAPO-18 was 1:30. The mixture was stirred at 80°C for 16 hours, centrifuged, washed with deionized water until neutral, dried in an oven at 100°C for 12 hours, and calcined in a muffle furnace with pure air at 550°C for 3 hours to obtain the SAPO-18@mesosilica molecular sieve, denoted as B4. The specific surface area of ​​B4 was 580.25 m². 2 The XRD pattern of / g. B4 is as follows: Figure 4 As shown in the figure, Figure (a) is the small-angle diffraction pattern and Figure (b) is the wide-angle diffraction pattern. Figure (a) shows a characteristic peak of SiO2 at 2θ = 2.2°. The SEM image is shown below. Figure 12 As shown.

[0060] [Comparative Example 5]

[0061] (1) Using hexadecyltrimethylammonium bromide (CTAB) as a template agent and tetraethyl orthosilicate (TEOS) as a silicon source, a shell growth solution was prepared according to the ratio of CTAB:SiO2:C2H5OH:NH3·H2O:H2O = 0.02:0.05:25:0.7:100;

[0062] (2) The SAPO-18 molecular sieve obtained in Comparative Example 1, as the core-phase molecular sieve, was added to the above-mentioned shell growth solution, wherein the mass ratio of tetraethyl orthosilicate (SiO2) to SAPO-18 was 1:30. The mixture was stirred at 80°C for 16 hours, centrifuged, washed with deionized water until neutral, dried in an oven at 100°C for 12 hours, and calcined in a tube furnace at 550°C with pure nitrogen for 3 hours to obtain SAPO-18@mesosilica molecular sieve, denoted as B5. The specific surface area of ​​B5 was 511.86 m². 2 The XRD pattern of / g. B5 is as follows: Figure 5 As shown, Figure (a) is the small-angle diffraction pattern, and Figure (b) is the wide-angle diffraction pattern. Figure (a) shows a characteristic peak of SiO2 at 2θ = 2.2°. The SEM image is similar to... Figure 12 .

[0063] [Comparative Example 6]

[0064] (1) Using hexadecyltrimethylammonium bromide (CTAB) as a template agent and tetraethyl orthosilicate (TEOS) as a silicon source, a shell growth solution was prepared according to the ratio of CTAB:SiO2:C2H5OH:NH3·H2O:H2O = 0.02:0.05:25:0.7:100;

[0065] (2) The SAPO-18 molecular sieve obtained in Comparative Example 1, as the core-phase molecular sieve, was added to the above-mentioned shell growth solution, wherein the mass ratio of tetraethyl orthosilicate (SiO2) to SAPO-18 was 1:110. The mixture was stirred at 80°C for 16 hours, centrifuged, washed with deionized water until neutral, dried in an oven at 100°C for 12 hours, and calcined in a tube furnace at 550°C with pure nitrogen for 3 hours to obtain SAPO-18@mesosilica molecular sieve, denoted as B6. The specific surface area of ​​B6 was 503.17 m². 2 / g. The XRD pattern of B6 is similar to Figure 5 SEM images are similar to Figure 12 .

[0066]

Example 1

[0067] (1) Using hexadecyltrimethylammonium bromide (CTAB) as a template agent, tetraethyl orthosilicate (TEOS) as a silicon source, and ethanol and water as solvents, a shell growth solution was prepared according to the ratio of CTAB:SiO2:C2H5OH:NH3·H2O:H2O = 0.02:0.05:25:0.7:100;

[0068] (2) The SAPO-18 molecular sieve obtained in Comparative Example 1, as the core-phase molecular sieve, was added to the above-mentioned shell growth solution, wherein the mass ratio of tetraethyl orthosilicate (SiO2) to SAPO-18 was 1:30. The mixture was stirred at 80°C for 16 hours, centrifuged, washed with deionized water until neutral, dried in an oven at 100°C for 12 hours, and calcined in a tube furnace at 550°C for 3 hours with an air / nitrogen volume ratio of 2:1 to obtain the SAPO-18@mesosilica molecular sieve, denoted as S1. The specific surface area of ​​S1 was 613.25 m². 2 / g. The XRD pattern of S1 is as follows Figure 6 As shown in the figure, Figure (a) is the small-angle diffraction pattern and Figure (b) is the wide-angle diffraction pattern. Figure (a) shows a characteristic peak of SiO2 at 2θ = 2.2°. The SEM image is shown below. Figure 13 As shown.

[0069]

Example 2

[0070] (1) Using hexadecyltrimethylammonium bromide (CTAB) as a template agent, tetraethyl orthosilicate (TEOS) as a silicon source, and ethanol and water as solvents, a shell growth solution was prepared according to the ratio of CTAB:SiO2:C2H5OH:NH3·H2O:H2O = 0.02:0.05:25:0.7:100;

[0071] (2) The SAPO-34 molecular sieve obtained in Comparative Example 2, as the core-phase molecular sieve, was added to the above-mentioned shell growth solution, wherein the mass ratio of tetraethyl orthosilicate (SiO2) to SAPO-34 was 1:25. The mixture was stirred at 80°C for 16 hours, centrifuged, washed with deionized water until neutral, dried in an oven at 100°C for 12 hours, and calcined in a tube furnace at 550°C for 3 hours with an air / nitrogen volume ratio of 2:1 to obtain the SAPO-34@mesosilica molecular sieve, denoted as S2. The specific surface area of ​​S2 was 650.34 m². 2 / g. The XRD pattern of S2 is as follows Figure 7 As shown, Figure (a) is the small-angle diffraction pattern, and Figure (b) is the wide-angle diffraction pattern. Figure (a) shows a characteristic peak of SiO2 at 2θ = 2.4°. The SEM image is similar to... Figure 13 .

[0072]

Example 3

[0073] (1) Using hexadecyltrimethylammonium bromide (CTAB) as a template agent, tetraethyl orthosilicate (TEOS) as a silicon source, and ethanol and water as solvents, a shell growth solution was prepared according to the ratio of CTAB:SiO2:C2H5OH:NH3·H2O:H2O = 0.02:0.05:25:0.7:100;

[0074] (2) The SAPO-18 / SAPO-34 mixed molecular sieve obtained in Comparative Example 3 was added to the above-mentioned shell growth solution, wherein the mass ratio of tetraethyl orthosilicate (SiO2) to the SAPO-18 / SAPO-34 mixed molecular sieve was 1:8. The mixture was stirred at 80°C for 16 h, centrifuged, washed with deionized water until neutral, dried in an oven at 100°C for 12 h, and calcined in a tube furnace at 550°C for 3 h with an air / nitrogen volume ratio of 2:1 to obtain the SAPO-18 / SAPO-34@mesosilica molecular sieve, denoted as S3. The specific surface area of ​​S3 was 690.76 m². 2 / g. The XRD pattern of S3 is as follows Figure 8 As shown, Figure (a) is the small-angle diffraction pattern, and Figure (b) is the wide-angle diffraction pattern. Figure (a) shows a characteristic peak of SiO2 at 2θ = 2.4°. The SEM image is similar to... Figure 13 .

[0075]

Example 4

[0076] (1) A shell growth solution was prepared using hexadecylpyridine bromide as template agent R, silica sol as silicon source, tetraethylammonium hydroxide as alkali source, and diethyl ether and water as solvents, according to the ratio R:SiO2:(C2H5)2O:TEAOH:H2O = 0.03:0.06:30:0.5:60;

[0077] (2) The SAPO-18 molecular sieve obtained in Comparative Example 1, as the core-phase molecular sieve, was added to the above-mentioned shell growth solution, wherein the mass ratio of silica sol (SiO2) to SAPO-18 was 1:10. The mixture was stirred at 80°C for 16 hours, centrifuged, washed with deionized water until neutral, dried in an oven at 100°C for 12 hours, and calcined in a tube furnace at 550°C for 3 hours with an air / nitrogen volume ratio of 2:1 to obtain SAPO-18@mesosilica molecular sieve, denoted as S4. The specific surface area of ​​S4 was 699.78 m². 2 The XRD pattern of / g. S4 is similar to Figure 6 SEM images are similar to Figure 13 .

[0078]

Example 5

[0079] (1) A shell growth solution was prepared using hexadecylpyridine bromide as template agent R, silica sol as silicon source, tetraethylammonium hydroxide as alkali source, and diethyl ether and water as solvents, according to the ratio R:SiO2:(C2H5)2O:TEAOH:H2O = 0.03:0.06:30:0.5:60;

[0080] (2) The SAPO-34 molecular sieve obtained in Comparative Example 2, as the core-phase molecular sieve, was added to the above-mentioned shell growth solution, wherein the mass ratio of silica sol (SiO2) to SAPO-34 was 1:13. The mixture was stirred at 80°C for 16 hours, centrifuged, washed with deionized water until neutral, dried in an oven at 100°C for 12 hours, and calcined in a tube furnace at 550°C for 3 hours with an air / nitrogen volume ratio of 2:1 to obtain the SAPO-34@mesosilica molecular sieve, denoted as S5. The specific surface area of ​​S5 was 725.39 m². 2 / g. The XRD pattern of S5 is similar to Figure 7 SEM images are similar to Figure 13 .

[0081]

Example 6

[0082] (1) A shell growth solution was prepared using hexadecylpyridine bromide as template agent R, silica sol as silicon source, tetraethylammonium hydroxide as alkali source, and diethyl ether and water as solvents, according to the ratio R:SiO2:(C2H5)2O:TEAOH:H2O = 0.03:0.06:30:0.5:60;

[0083] (2) The SAPO-18 / SAPO-34 mixed molecular sieve obtained in Comparative Example 3 was added to the above-mentioned shell growth solution, wherein the mass ratio of silica sol (SiO2) to SAPO-18 / SAPO-34 mixed molecular sieve was 1:6. The mixture was stirred at 80°C for 16 hours, centrifuged, washed with deionized water until neutral, dried in an oven at 100°C for 12 hours, and calcined in a tube furnace at 550°C for 3 hours with an air / nitrogen volume ratio of 2:1 to obtain SAPO-18 / SAPO-34@mesosilica molecular sieve, denoted as S6. The specific surface area of ​​S6 was 756.15 m². 2 The XRD pattern of / g. S6 is similar to Figure 8 SEM images are similar to Figure 13 .

[0084]

Example 7

[0085] Compared to Example 5, the difference lies in that after the sample was dried in an oven, it was calcined in a tube furnace at 550°C for 3 hours with an air / nitrogen volume ratio of 3:1 to obtain SAPO-34@mesosilica molecular sieve, denoted as S7. S7 has a specific surface area of ​​799.98 m². 2 / g. The XRD pattern of S8 is similar to Figure 7 SEM images are similar to Figure 13 .

[0086]

Example 8

[0087] Compared to Example 6, the difference lies in that after the sample was dried in an oven, it was calcined in a tube furnace at 550°C for 3 hours with an air / nitrogen volume ratio of 5:1 to obtain SAPO-18 / SAPO-34@mesosilica molecular sieve, denoted as S8. S8 has a specific surface area of ​​706.27 m². 2 / g. The XRD pattern of S8 is similar to Figure 8 SEM images are similar to Figure 13 .

[0088]

Example 9

[0089] (1) Using ammonium hexadecyl toluenesulfonate as template agent R, methyl orthosilicate as silicon source, urea as alkali source, and cyclohexane and water as solvents, according to the formula R:SiO2:C6H 12 A shell growth solution was prepared using a ratio of CO(NH2)2:H2O of 0.05:0.10:35:0.3:75.

[0090] (2) SAPO-44 molecular sieve (specific surface area of ​​560.79 m²) 2A core-phase molecular sieve (with a SiO2 / Al2O3 molar ratio of 0.28) was added to the above-mentioned shell growth solution, wherein the mass ratio of silica sol (SiO2 to SAPO-44) was 1:3. The mixture was stirred at 80℃ for 16 h, centrifuged, washed with deionized water until neutral, dried in an oven at 100℃ for 12 h, and calcined in a tube furnace at 550℃ for 3 h with an air / nitrogen volume ratio of 2:1 to obtain SAPO-44@mesosilica molecular sieve, denoted as S9. The specific surface area of ​​S9 is 817.65 m² / g. 2 / g. The XRD pattern of S9 is as follows Figure 9 As shown in the figure, Figure (a) is the small-angle diffraction pattern and Figure (b) is the wide-angle diffraction pattern. It can be seen from Figure (a) that the characteristic peak of SiO2 appears at 2θ=2.4°.

[0091]

Example 10

[0092] (1) Using ammonium hexadecyl toluenesulfonate as template agent R, methyl orthosilicate as silicon source, urea as alkali source, and cyclohexane and water as solvents, according to the formula R:SiO2:C6H 12 A shell growth solution was prepared using a ratio of CO(NH2)2:H2O of 0.05:0.10:35:0.3:75.

[0093] (2) SAPO-47 molecular sieve (specific surface area of ​​550.24 m²) 2 A core-phase molecular sieve (SiO2 / Al2O3 molar ratio of 0.3) was added to the above-mentioned shell growth solution, wherein the mass ratio of silica sol (SiO2 to SAPO-47) was 1:55. The mixture was stirred at 80℃ for 16 h, centrifuged, washed with deionized water until neutral, dried in an oven at 100℃ for 12 h, and calcined in a tube furnace at 550℃ for 3 h with an air / nitrogen volume ratio of 2:1 to obtain SAPO-47@mesosilica molecular sieve, denoted as S10. The specific surface area of ​​S10 is 600.78 m² / g. 2 / g.

[0094] Catalyst evaluation experiment

[0095] Samples B1-B6 and S1-S10 obtained from Comparative Examples 1-6 and Examples 1-10 were tableted, crushed, and sieved to obtain particles of 20-40 mesh size. Catalyst evaluation experiments were conducted using a fixed-bed catalytic reactor. The experimental conditions were: catalyst loading of 2.0 g, reaction temperature of 460 °C, reaction pressure of 0.1 MPa, reactant of 90% methanol, and weight hourly space velocity of 4 h⁻¹. -1 The evaluation results are shown in Table 2.

[0096] Table 1. Physicochemical properties of the (core-shell) molecular sieves obtained in each example.

[0097]

[0098] Table 2

[0099]

[0100] The embodiments described above are merely detailed descriptions of the technical solutions of the present invention, but the present invention is not limited to the above embodiments, that is, the present invention does not depend on the steps described in the above embodiments to be implemented. In summary, any improvements made to the present invention by those skilled in the art, including the substitution of the raw materials and additives described in the present invention, the selection of specific implementation methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a catalyst for methanol-to-olefins conversion, wherein the catalyst is a core-shell structured SAPO@mesosilica, with SAPO molecular sieve as the core phase and mesosilica as the shell, and the method for preparing the catalyst includes the following steps: (1) Mix the silicon source, alkali source, solvent and template agent R to obtain the shell growth solution; (2) Add the core phase SAPO molecular sieve to the shell growth solution obtained in step (1), stir and calcine at a certain temperature to obtain the methanol-to-olefins catalyst. In step (2), the mass ratio of the silicon source in the shell growth solution (calculated as SiO2) to the core phase SAPO molecular sieve is 1:1 to 1:

100. In step (2), the stirring conditions are as follows: stirring temperature 50~100℃, stirring time 3~48h; the calcination atmosphere is a mixture of air and nitrogen, wherein the volume ratio of air to nitrogen is 1.0~6.

0.

2. The preparation method according to claim 1, characterized in that, The solvent is a mixture of an organic solvent and water, wherein the organic solvent is selected from at least one of diethyl ether, ethanol, and cyclohexane; the silicon source is selected from at least one of sodium silicate, methyl orthosilicate, ethyl orthosilicate, and silica sol; the alkali source is selected from at least one of tetraethylammonium hydroxide aqueous solution, ammonia, sodium hydroxide, and urea; and the template agent R is selected from at least one of hexadecyltrimethylammonium bromide, hexadecylpyridine bromide, and hexadecyltoluenesulfonate.

3. The preparation method according to claim 2, characterized in that, In the shell growth solution, the silicon source is SiO2, and the molar ratio of each component is as follows: template agent R: SiO2: alkali source: organic solvent: H2O = 0.01~0.2: 0.01~0.3: 0.2~1.2: 5~50: 20~105.

4. The preparation method according to claim 1, characterized in that, The nucleus-phase SAPO molecular sieve is selected from at least one of SAPO-34, SAPO-17, SAPO-18, SAPO-44, SAPO-47 or SAPO-56 molecular sieves.

5. The preparation method according to claim 4, characterized in that, The nucleus phase SAPO-molecular sieve is SAPO-34 and / or SAPO-18 molecular sieve.

6. The preparation method according to claim 1 or 4, characterized in that, The SiO2 / Al2O3 molar ratio of the core-phase SAPO molecular sieve is 0.10~1.2; and / or, the specific surface area of ​​the core-phase SAPO molecular sieve is 300~580 m². 2 / g.

7. The preparation method according to claim 1, characterized in that, The mass ratio of the silicon source (SiO2) in the shell growth solution to the core phase SAPO molecular sieve is 1:5 to 1:

50.

8. The preparation method according to claim 1, characterized in that, The calcination conditions are as follows: calcination temperature is 480~700℃, and calcination time is 3~48h.

9. A catalyst for methanol-to-olefins conversion prepared by any one of the preparation methods according to claims 1-8.

10. The catalyst according to claim 9, characterized in that, The specific surface area of ​​the SAPO@mesosilica is 600~820m². 2 / g.

11. The catalyst according to claim 10, characterized in that, The specific surface area of ​​the SAPO@mesosilica is 610~800 m². 2 / g.

12. The catalyst according to claim 10, characterized in that, The SAPO@mesosilica has a microporous-mesoporous composite pore structure, wherein the micropore volume is 0.05~0.35 cm³. 3 / g, micropore size is 0.1~1.5nm; mesopore volume is 0.1~0.4cm³. 3 / g, mesopore size is 2~50nm; micropore / mesopore ratio is 0.5~2.

5.

13. A method for converting methanol to low-carbon olefins, comprising: The catalyst according to any one of claims 9-12 reacts with methanol feedstock to obtain low-carbon olefins.

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