Ultra-small nano SAPO-34 molecular sieve, preparation method and application thereof

Abstract

The present application relates to the technical fields of molecular sieve preparation, in particular to a kind of ultra-small nano SAPO-34 molecular sieve and its preparation method and application, comprising the following steps: aluminum source, silicon source, phosphorus source, structure directing agent and growth inhibitor and distilled water are mixed, stirred uniformly, and initial gel is obtained;Initial gel is placed in high-pressure reaction kettle and subjected to microwave crystallization treatment;The product after crystallization treatment is sequentially subjected to centrifugation, washing, drying and calcination, and ultra-small nano SAPO-34 molecular sieve is obtained;Wherein, the growth inhibitor is silane-based high molecular copolymer, and the volume ratio of silane-based high molecular copolymer to distilled water is (0.01-0.11):1.The ultra-small nano SAPO-34 molecular sieve prepared in the present application contains abundant intercrystalline mesopores, while also retaining the integrity of microporous structure, and exhibits excellent catalytic performance in methanol to olefin reaction, and the catalytic life and olefin selectivity are greatly improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of molecular sieve preparation, in particular to a kind of ultra-small nano SAPO-34 molecular sieve and its preparation method and application. BACKGROUND

[0002] SAPO-34 molecular sieve is one of the important members in SAPO series, SAPO-34 has CHA topology structure, it is three-dimensional pore structure microporous zeolite molecular sieve formed by SiO 4, AlO 4 And PO 4 Tetrahedron is connected by oxygen bridge key each other, its pore size is about 0.38nm. Because it has unique microporous structure, high thermal stability and hydrothermal stability and chemical stability, make it have wide application in adsorption, separation and methanol to olefin (MTO) reaction. A large number of studies show that the pure microporous structure of SAPO-34 seriously hinders the transmission and diffusion of guest molecules. Therefore, how to improve the mass transfer efficiency of reactant molecules in SAPO-34 molecular sieve has become the focus of continuous attention in the field of molecular sieve research.

[0003] To solve the above problems, at present, the most effective method is to construct hierarchical pore structure in zeolite crystal, its main method includes hard template method, soft template method and post-processing method. Hard template method and soft template method need to occupy a certain space in the process of zeolite crystallization, so that the silicon source, aluminum source and phosphorus source in the gel grow around the hard (soft) template, and then the template is removed by calcination treatment to obtain hierarchical pore molecular sieve with intracrystalline mesopore or macropore. Post-processing method refers to (acid or alkali) treatment of the synthesized zeolite to remove the framework elements of the zeolite to form secondary pore structure.

[0004] The above treatment methods will inevitably cause the collapse of zeolite framework and reduce the crystallinity of zeolite. Therefore, no matter which method is used, there are problems such as complicated synthesis steps, high cost and large time consumption, which seriously limit the industrial application.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] The purpose of the present application is to provide a preparation method of ultra-small nano SAPO-34 molecular sieve, the ultra-small nano SAPO-34 molecular sieve prepared by the present application contains rich intercrystalline mesopore, and the integrity of microporous structure is also retained.

[0007] In the first aspect, the present application provides a preparation method of ultra-small nano SAPO-34 molecular sieve, comprising the following steps:

[0008] S1, the aluminum source, silicon source, phosphorus source, structure directing agent and growth inhibitor are mixed with distilled water, and stirred uniformly to obtain initial gel;

[0009] S2, the initial gel is placed in a high-pressure reactor for microwave crystallization treatment;

[0010] S3, the product after crystallization treatment is sequentially subjected to centrifugation, washing, drying and calcination to obtain the ultra-small nano SAPO-34 molecular sieve;

[0011] The growth inhibitor is a silane-based high molecular copolymer, and the volume ratio of the silane-based high molecular copolymer to distilled water is (0.01-0.11):1.

[0012] The present application first proposes to use a silane-based high molecular polymer as a growth inhibitor, which not only does not inhibit the nucleation of zeolite, but also plays a role of "bond breaking" during the growth of zeolite, thereby replacing the construction of the zeolite framework by silicon and aluminum species in the solution, further inhibiting the continuous growth of the zeolite crystal, to obtain an ultra-small nano SAPO-34 molecular sieve. In addition, the introduction of the silane-based high molecular polymer also provides a part of the silicon source for the surface growth of SAPO-34, and through this synthesis method, the chemical composition of the surface of SAPO-34 and the coordination state of silicon atoms can be flexibly adjusted.

[0013] Therefore, the ultra-small nano SAPO-34 molecular sieve prepared by the present application is accumulated by ultra-small SAPO-34 nanocrystals with a size of 10-20 nm, contains abundant intercrystalline mesopores, and retains the integrity of the internal micropore structure of the crystal, shortens the diffusion path of the reactants and products, and exhibits excellent catalytic performance in the methanol-to-olefin reaction, with a significantly improved catalytic life and selectivity of olefin (ethylene and propylene) products. The preparation method of the present application is simple and easy to operate, and is suitable for large-scale industrial production.

[0014] Specifically, in use, the amount of the silane-based high molecular copolymer is (0.01-0.11):1 in volume ratio to distilled water in the preparation process of the initial gel.

[0015] As preferred in the technical solution, the silane-based high molecular copolymer used in the present application is a copolymer of a silane-based compound and a methyl ester compound, wherein the silane-based compound includes any one or more of vinyltrimethoxysilane and propenyltrimethoxysilane, and the methyl ester compound includes any one or more of methyl methacrylate, ethyl methacrylate and butyl methacrylate, so that the monomer mixture for preparing the silane-based high molecular copolymer can be any one of vinyltrimethoxysilane and methyl methacrylate, propenyltrimethoxysilane and methyl methacrylate, vinyltrimethoxysilane and butyl methacrylate, and vinyltrimethoxysilane and ethyl methacrylate.

[0016] As the preferred technical solution, the preparation method of the silane-based high molecular copolymer specifically comprises the following steps:

[0017] First, the emulsifier and ammonia are added to distilled water, and after uniform mixing, the silane-based compound and the methyl ester compound are added, the temperature is raised to 55-80 DEG C, then the initiator is added, and the reaction is carried out for 2-4 hours to prepare the silane-based high molecular copolymer by emulsion polymerization.

[0018] The emulsion polymerization method can prepare a large amount of high molecular material in a short time, and the entire polymerization process is carried out in an aqueous phase, and the formed high molecular material has the advantages of low viscosity and high quality, so the obtained silane-based high molecular copolymer emulsion can be directly used as a growth inhibitor to prepare an initial gel.

[0019] Specifically, in the emulsion polymerization process, the mass ratio of the silane-based compound, the methyl ester compound, the emulsifier, the initiator, the ammonia and the distilled water is (2.23-30.56):(50.25-150.78):(0.12-0.98):(2.56-18.24):(0.15-4.52):(50.45-400.51), and the mass ratio of the silane-based compound, the methyl ester compound, the emulsifier, the initiator, the ammonia and the distilled water is preferably 5.68:70.32:0.57:10.36:3.54:200.35;

[0020] The emulsifier includes any one of DNS-13, DNS-268 and DNS-86; and the initiator is any one of ammonium persulfate, azobisisobutyronitrile, potassium persulfate and sodium persulfate.

[0021] As the preferred technical solution, the molar ratio of the aluminum source, the structure directing agent, the silicon source, the phosphorus source and the distilled water in the initial gel is (0.52-2.05):(0.4-10.50):(0.2-2.36):(0.52-2.37):(60.57-600.30), and is preferably 1.54:6.17:2.12:1.37:121.45;

[0022] The aluminum source includes any one of aluminum isopropoxide, aluminum sec-butoxide, aluminum oxide and pseudo-boehmite; the silicon source includes any one of tetraethyl orthosilicate, fumed silica and silica sol; the structure directing agent includes any one of tetraethylammonium hydroxide, n-propylamine, diethylamine and triethylamine, and is preferably tetraethylammonium hydroxide; and the phosphorus source includes any one of phosphoric acid, ammonium dihydrogen phosphate, ammonium hydrogen phosphate and ammonium phosphate.

[0023] As the preferred technical solution, in step S2, the microwave crystallization method can effectively promote the formation of a large number of crystal nuclei in the initial growth stage of the zeolite, thereby facilitating the bonding with the silane-based high molecular copolymer, and obtaining SAPO-34 nanocrystals with smaller crystal grain size. Specifically, during the microwave crystallization treatment, the temperature needs to be controlled at 160-220 DEG C, and the time needs to be controlled at 2-7 hours.

[0024] As the preferred technical solution, in step S3, the present application does not make strict limitations on the drying conditions, and the temperature can be controlled at 80-110 DEG C, and the time can be controlled at 24-48 hours.

[0025] As the preferred technical solution, in step S3, during the calcination, the temperature needs to be controlled at 550-650 DEG C, and the time needs to be controlled at 4-12 hours.

[0026] In the second aspect, the present application also provides the ultra-small nano SAPO-34 molecular sieve prepared by the above preparation method, wherein the size of the primary nanoparticle in the ultra-small nano SAPO-34 molecular sieve is 10-20 nm.

[0027] In the third aspect, the application of the above-mentioned ultra-small nano SAPO-34 molecular sieve in the methanol-to-olefin reaction also belongs to the protection scope of the present application. Research shows that the ultra-small nano SAPO-34 molecular sieve prepared by the present application can exhibit excellent catalytic performance in the methanol-to-olefin reaction, and the catalytic life and the selectivity of the olefin are greatly improved.

[0028] The preparation method of the ultra-small nano SAPO-34 molecular sieve has at least the following beneficial effects:

[0029] 1. The present application adds a silane-based high molecular copolymer as a growth inhibitor for synthesizing ultra-small nano SAPO-34, which does not affect the nucleation of the zeolite, and in the growth process of the zeolite, the silane group in the silane-based high molecular copolymer bonds with the silicon hydroxyl group on the surface of the zeolite crystal, replacing the construction of the zeolite framework by the silicon species and aluminum species in the solution, thereby inhibiting the continuous growth of the zeolite crystal; at the same time, by adopting the microwave crystallization method, a large number of crystal nuclei can be effectively promoted in the initial growth stage of the zeolite, thereby facilitating the bonding with the silane-based high molecular copolymer, and obtaining SAPO-34 nanocrystals with smaller crystal grain size;

[0030] 2. The preparation method of the present application has relatively mild reaction conditions and simple process, and can realize industrial application, thereby effectively overcoming the problem that the existing technology inevitably causes the collapse of the zeolite framework by adding a mesoporous directing agent or performing acid or alkali treatment on the synthesized zeolite to reduce the crystallinity of the zeolite;

[0031] 3. The prepared ultra-small nanometer SAPO-34 molecular sieve contains abundant intercrystalline mesopores, meanwhile, the integrity of microporous structure is retained, and the molecular sieve exhibits excellent catalytic performance in the methanol to olefin reaction, and the catalytic life and the selectivity of olefin are greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the specific embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0033] Figure 1 XRD spectrum of the molecular sieve obtained in Example 1 and Comparative Example 1 of the present application;

[0034] Figure 2 SEM image of the molecular sieve obtained in Example 1 of the present application;

[0035] Figure 3 N2 adsorption-desorption isotherm and pore size distribution graph of the molecular sieve obtained in Example 1 of the present application;

[0036] Figure 4 SEM image of the molecular sieve obtained in Comparative Example 1 of the present application;

[0037] Figure 5 SEM image of the molecular sieve obtained in Comparative Example 2 of the present application;

[0038] Figure 6 SEM image of the molecular sieve obtained in Comparative Example 3 of the present application;

[0039] Figure 7 SEM image of the molecular sieve obtained in Comparative Example 4 of the present application. DETAILED DESCRIPTION

[0040] It should be noted that the following detailed description is illustrative only and is intended to provide further description of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0041] It should be noted that the terms used herein are only intended to describe specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form also includes the plural form unless the context clearly indicates otherwise, and it should also be understood that when the terms "comprise" and / or "include" are used in the specification, there is a presence of the features, steps, operations, devices, components and / or combinations thereof.

[0042] The technical solutions of the present application will be described clearly and completely in combination with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0043] Embodiment 1

[0044] Preparation of silane-based high molecular copolymer

[0045] The emulsifier DNS-268, ammonia water were sequentially added into a four-necked flask containing distilled water, and stirred for 2 h at room temperature; then the monomer mixture (mass ratio of methyl methacrylate to vinyl trimethoxysilane was about 9:1) was added into the four-necked flask, and then the temperature was raised to 55℃, and ammonium persulfate was added, and the reaction was continued for 2.5 h under stirring, to obtain a silane-based high molecular copolymer emulsion; wherein the mass ratio of vinyl trimethoxysilane, methyl methacrylate, emulsifier DNS-268, ammonium persulfate, ammonia water, distilled water was 2.25:50.25:0.33:2.56:0.20:62.13.

[0046] Preparation of ultra-small nano SAPO-34 molecular sieve

[0047] S1. 5.36 g of aluminum isopropoxide was dissolved in a solution of 32.8 mL of distilled water and 26.3 tetraethylammonium hydroxide, and a clear solution was obtained after stirring, then 4.5 mL of ethyl silicate, 5 mL of silane-based high molecular copolymer and 4 mL of phosphoric acid were sequentially added, and after stirring uniformly, an initial gel was obtained;

[0048] S2. The initial gel was transferred to a 100 ml polytetrafluoroethylene reaction tube and crystallized by microwave, and the reaction temperature was 180℃, and the time was 4 h;

[0049] S3. The product after crystallization was centrifuged, washed to neutral, dried at 80℃ for 24 h, and then calcined at 550℃ for 6 h, to obtain an ultra-small nano SAPO-34 molecular sieve.

[0050] Embodiment 2

[0051] Preparation of silane-based high molecular copolymer

[0052] The four-necked flask is sequentially added with emulsifier DNS-13, ammonia water into distilled water at room temperature, and stirred for 2 hours; then a monomer mixture (mass ratio of butyl methyl acrylate to vinyl trimethoxysilane is about 7:1) is added into the four-necked flask, and then the temperature is raised to 60°C, sodium persulfate is added, and the reaction is continuously stirred for 3 hours to obtain a silane-based polymer copolymer emulsion; wherein the mass ratio of vinyl trimethoxysilane, butyl methyl acrylate, emulsifier DNS-13, sodium persulfate, ammonia water, distilled water is 5.06:100.45:0.33:0.45:3.03:0.17:150.56.

[0053] Preparation of ultra-small nano SAPO-34 molecular sieve

[0054] S1. 4.70 g of aluminum isopropoxide is dissolved in a solution of 28.8 mL of distilled water and 26.3 tetraethylammonium hydroxide, and after stirring to obtain a clear solution, 4.5 mL of ethyl silicate, 3.5 mL of silane-based polymer copolymer and 4 mL of phosphoric acid are sequentially added, and after stirring uniformly, an initial gel is obtained;

[0055] S2. The initial gel is moved to a 100 ml polytetrafluoroethylene reaction tube and microwave crystallized, the reaction temperature is 170°C, and the time is 5 hours;

[0056] S3. The product after crystallization is centrifuged, washed to neutral, dried at 90°C for 30 hours, and then calcined at 580°C for 6 hours to obtain an ultra-small nano SAPO-34 molecular sieve.

[0057] Example 3

[0058] Preparation of silane-based polymer copolymer

[0059] The four-necked flask is sequentially added with emulsifier DNS-86, ammonia water into distilled water at room temperature, and stirred for 2 hours; then a monomer mixture (mass ratio of butyl methyl acrylate to vinyl trimethoxysilane is about 7:1) is added into the four-necked flask, and then the temperature is raised to 60°C, sodium persulfate is added, and the reaction is continuously stirred for 3 hours to obtain a silane-based polymer copolymer emulsion; wherein the mass ratio of vinyl trimethoxysilane, butyl methyl acrylate, emulsifier DNS-86, sodium persulfate, ammonia water, distilled water is 5.06:100.45:0.33:0.45:3.03:0.17:150.56.

[0060] Preparation of ultra-small nano SAPO-34 molecular sieve

[0061] S1. 5.08 pseudo-boehmite was dissolved in a solution of 28.8 mL distilled water and 8 ml triethylamine, after stirring to get a clear solution, 3.7 mL of silica sol, 3.8 mL of silane-based copolymer and 4 mL of phosphoric acid were added in turn, after stirring evenly, the initial gel was obtained;

[0062] S2. The initial gel was moved to a 100 ml polytetrafluoroethylene reaction tube and microwave crystallization, the reaction temperature was 200℃, the time was 3.5h;

[0063] S3. The product after crystallization was centrifuged, washed to neutral, dried at 85℃ for 36h, then calcined at 600℃ for 4h, to obtain ultra-small nano SAPO-34 molecular sieve.

[0064] Example 4

[0065] The emulsifier DNS-86 in example 3 was replaced by DNS-268;

[0066] Other steps and parameters were basically the same as example 3.

[0067] Example 5

[0068] 4 mL of phosphoric acid in example 3 was replaced by 6.28 g of sodium dihydrogen phosphate;

[0069] Other steps and parameters were basically the same as example 3.

[0070] Example 6

[0071] Preparation of silane-based copolymer

[0072] The emulsifier DNS-13, ammonia water was added to distilled water in a four-necked flask at room temperature, stirring for 2h; then the monomer mixture (mass ratio of ethyl methacrylate to vinyl trimethoxysilane was about 6.5:1) was added to the four-necked flask, then the temperature was raised to 65℃, and azobisisobutyronitrile was added, and the stirring reaction was continued for 3h, to obtain a silane-based copolymer emulsion; wherein the mass ratio of vinyl trimethoxysilane, ethyl methacrylate, emulsifier DNS-13, azobisisobutyronitrile, ammonia water, distilled water was 14.5:50.70:0.45:2.58:0.36:330.35.

[0073] Preparation of ultra-small nano SAPO-34 molecular sieve

[0074] S1. 5.08 pseudo-boehmite was dissolved in a solution of 28.8 mL distilled water and 8 ml triethylamine, after stirring to get a clear solution, 3.7 mL of silica sol, 3.8 mL of silane-based copolymer and 4 mL of phosphoric acid were added in turn, after stirring evenly, the initial gel was obtained;

[0075] S2. The initial gel was placed in a 100ml polytetrafluoroethylene reaction tube and crystallized by microwave, the reaction temperature was 190℃, and the time was 3.5h;

[0076] S3. The product after crystallization was centrifuged, washed to neutral, dried at 80℃ for 48h, and then calcined at 560℃ for 6h to obtain the ultra-small nano SAPO-34 molecular sieve.

[0077] Example 7

[0078] Preparation of silane-based high molecular copolymer

[0079] The emulsifier DNS-268, ammonia water were sequentially added to a four-necked flask, stirred for 2h; then the monomer mixture (the mass ratio of ethyl methacrylate to vinyl trimethoxysilane was about 10:1) was added to the four-necked flask, then the temperature was raised to 75℃, and azobisisobutyronitrile was added, and the reaction was continued for 3.5h to obtain a silane-based high molecular copolymer emulsion; wherein the mass ratio of vinyl trimethoxysilane, ethyl methacrylate, emulsifier DNS-268, azobisisobutyronitrile, ammonia water, distilled water was 15.5:50.13:0.57:2.58:0.36:340.25.

[0080] Preparation of ultra-small nano SAPO-34 molecular sieve

[0081] S1. 5.00 aluminum sec-butoxide was dissolved in a solution of 32.8mL distilled water and 8ml diethylamine, a clear solution was obtained after stirring, and then 3.2mL silica sol, 3.8mL silane-based high molecular copolymer and 3.9mL phosphoric acid were sequentially added, and stirred uniformly to obtain an initial gel;

[0082] S2. The initial gel was placed in a 100ml polytetrafluoroethylene reaction tube and crystallized by microwave, the reaction temperature was 180℃, and the time was 3.5h;

[0083] S3. The product after crystallization was centrifuged, washed to neutral, dried at 95℃ for 48h, and then calcined at 560℃ for 6h to obtain the ultra-small nano SAPO-34 molecular sieve.

[0084] Example 8

[0085] In example 7, S2 step, 3.9 phosphoric acid was replaced by 7.58g sodium monohydrogen phosphate;

[0086] The other steps and parameters were basically the same as those in example 7.

[0087] Example 9

[0088] In Example 7, Step S1, 8 mL of diethylamine was replaced by 10.3 mL of n-propylamine; in S2, the reaction temperature was 180°C and the time was 3.5 h, which was replaced by a reaction temperature of 190°C and a time of 3 h;

[0089] The other steps and parameters were basically the same as in Example 7.

[0090] Comparative Example 1

[0091] No high molecular copolymer was added;

[0092] The other steps and parameters were basically the same as in Example 1.

[0093] Comparative Example 2

[0094] The high molecular copolymer was replaced by vinyltrimethoxysilane monomer;

[0095] The other steps and parameters were basically the same as in Example 1.

[0096] Comparative Example 3

[0097] The high molecular copolymer was replaced by SAPO-34 seed crystals;

[0098] The other steps and parameters were basically the same as in Example 1.

[0099] Comparative Example 4

[0100] The high molecular copolymer was replaced by small molecule ethanol;

[0101] The other steps and parameters were basically the same as in Example 1.

[0102] Figure 1 The X-ray diffraction pattern (XRD) of the ultrasmall nanometer SAPO-34 molecular sieve prepared in Example 1 of the application is shown in FIG. 1. Figure 1 It can be seen that the material prepared belongs to a typical SAPO-34 molecular sieve. Compared with the SAPO-34 prepared without adding silane-based high molecular copolymer (Comparative Example 1), the characteristic diffraction peak of the SAPO-34 appears obvious broadening phenomenon, indicating that the addition of silane-based high molecular copolymer can prepare SAPO-34 molecular sieve with relatively small crystal size. Further, from the SEM (FIG. 2), Figure 2 ), the size of the primary crystal grains of the SAPO-34 molecular sieve prepared by adding silane-based high molecular copolymer is rapidly reduced to the nanometer level, and the crystal size thereof is mainly concentrated at about 19 nm.

[0103] Figure 3The N2 adsorption-desorption isotherm and pore size distribution graph of the super-small nanometer SAPO-34 molecular sieve of the embodiment 1 of the present application are shown in the figure. It can be seen from the figure that the super-small nanometer SAPO-34 molecular sieve prepared by adding the silane-based high molecular copolymer presents an I+IV type isotherm, indicating that the sample has a typical mesoporous material, and the pore size distribution is mainly concentrated in 2-10 nm.

[0104] Figure 4 The SEM graph of the SAPO-34 molecular sieve prepared without adding the silane-based high molecular copolymer of the comparative example 1 is shown in the figure. Figure 4 It can be seen that the SAPO-34 molecular sieve is a spherical aggregate formed by stacking of primary cubic blocks with a size of about 700 nm. In addition, the morphology of the SAPO-34 synthesized by replacing the high molecular copolymer with a vinyl trimethoxysilane monomer is basically the same as that of the comparative example 1 Figure 5 ), indicating that the added vinyl trimethoxysilane monomer cannot play a "bond blocking" role in the growth of the zeolite. Similarly, the addition of SAPO-34 crystal seeds or a small molecule ethanol cannot inhibit the growth of the zeolite Figure 6 and Figure 7 ), so that a relatively large grain size is obtained.

[0105] The present application further uses the above-prepared sample as a catalyst for a methanol-to-light olefin reaction, and investigates the catalytic performance of the catalyst. The test results are shown in Table 1.

[0106] The specific experimental method is as follows:

[0107] The reaction is carried out in a normal-pressure micro fixed-bed reactor, and 0.40 g of the catalyst is loaded in the reactor. N2 is first introduced into the reactor at a flow rate of 50 mL / min, and the temperature is raised from room temperature to the reaction temperature (550℃) at a temperature raising rate of 5℃ / min, and the activation time is 1 h, and then the temperature is lowered to 400℃; then a trace metering pump is used to introduce methanol, and the feed amount is controlled to be 0.5 mL / h, and the space velocity is maintained at 1 h -1 The products after the reaction are analyzed on a gas chromatograph equipped with a hydrogen flame ionization detector (FID).

[0108] Table 1: Catalytic performance data

[0109]

[0110] It can be seen from Table 1 that the super-small SAPO-6 molecular sieves prepared in the embodiments 1-9 of the present application have excellent methanol catalytic activity, stability and light olefin selectivity.

[0111] The SAPO-34 molecular sieve prepared by not adding the silane-based high molecular copolymer in the comparative example 1 shows poor methanol activity and low selectivity of the low carbon olefin, and the main reason is that the crystal grain size is large, which seriously hinders the mass transfer and diffusion of the reactants and products, increases the probability of secondary reaction of the olefin, and is not conducive to the catalytic reaction.

[0112] The comparative example 2 uses vinyl trimethoxysilane monomer as a growth inhibitor, and because the size of the vinyl trimethoxysilane monomer segment is short, the growth of the crystal nucleus cannot be effectively prevented, resulting in that the crystal grain size of the prepared molecular sieve is large.

[0113] The SAPO-34 crystal seed is used as a growth inhibitor in the comparative example 3, which can reduce the crystal grain size of the zeolite to a certain extent, but the effect is not obvious, and the crystal grain cannot be reduced to nanoscale.

[0114] In the comparative example 4, the small molecule ethanol is used as a growth inhibitor, and has no inhibitory effect on the growth of the zeolite, and the crystal grain size is large.

[0115] In summary, the application first proposes to use a high molecular copolymer with a silane group as a growth inhibitor for synthesizing ultra-small nano SAPO-34, which not only does not affect the nucleation of the zeolite, but also can replace the silicon species and aluminum species in the solution to construct the zeolite framework, thereby inhibiting the growth of the zeolite crystal. At the same time, the introduction of the high molecular copolymer can also flexibly adjust the chemical components on the surface of the molecular sieve and the coordination state of the silicon atoms. Therefore, the ultra-small nano SAPO-34 molecular sieve prepared by the application not only contains abundant intercrystalline mesopores, but also retains the integrity of the microporous structure, and shows excellent catalytic performance in the methanol to olefin reaction, and the catalytic life and the selectivity of the olefin are greatly improved.

[0116] Finally, it should be pointed out that: the above examples are only used to illustrate the technical solutions of the application, and not to limit them; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can modify the technical solutions described in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the application.

Claims

1. A method for preparing ultra-small nano-SAPO-34 molecular sieves, characterized in that, Includes the following steps: S1. Mix the aluminum source, silicon source, phosphorus source, structure guiding agent, growth inhibitor and distilled water, stir evenly to obtain the initial gel; S2. Place the initial gel in a high-pressure reactor for microwave crystallization treatment; S3. The crystallized product is centrifuged, washed, dried and calcined in sequence to obtain ultra-small nano SAPO-34 molecular sieve; The growth inhibitor is a silane polymer copolymer, and the volume ratio of the silane polymer copolymer to distilled water is (0.01-0.11):

1. The preparation method of the silane polymer copolymer includes the following steps: Emulsifier and ammonia are added to distilled water and mixed evenly. Then, silane compounds and methyl ester compounds are added. The mixture is heated to 55-80℃ and an initiator is added. The reaction is carried out for 2-4 hours to obtain a silane polymer copolymer.

2. The preparation method according to claim 1, characterized in that, The silane compound includes any one or more of vinyltrimethoxysilane and propenyltrimethoxysilane. The methyl ester compounds include any one or more of methyl methacrylate, methyl ethyl acrylate, and methyl butyl acrylate.

3. The preparation method according to claim 1, characterized in that, The mass ratio of silane compounds, methyl ester compounds, emulsifiers, initiators, ammonia, and distilled water is (2.23-30.56): (50.25-150.78): (0.12-0.98): (2.56-18.24): (0.15-4.52): (50.45-400.51). The emulsifier includes any one of DNS-13, DNS-268, and DNS-86; The initiator is any one of ammonium persulfate, azobisisobutyronitrile, potassium persulfate, and sodium persulfate.

4. The preparation method according to claim 1, characterized in that, In the initial gel, the molar ratio of aluminum source, structure-directing agent, silicon source, phosphorus source and distilled water is (0.52-2.05): (0.4-10.50): (0.2-2.36): (0.52-2.37): (60.57-600.30). The aluminum source includes any one of aluminum isopropoxide, aluminum sec-butoxide, alumina, and boehmite. The silicon source includes any one of tetraethyl orthosilicate, fumed silica, and silica sol; The structure-directing agent includes any one of tetraethylammonium hydroxide, n-propylamine, diethylamine, and triethylamine; The phosphorus source includes any one of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

5. The preparation method according to claim 1, characterized in that, In step S2, the microwave crystallization process is carried out at a temperature of 160-220°C for 2-7 hours.

6. The preparation method according to claim 1, characterized in that, In step S3, during the drying process, the temperature is controlled at 80-110℃ and the time is 24-48h.

7. The preparation method according to claim 1, characterized in that, In step S3, the roasting temperature is controlled at 550-650℃ and the time is 4-12h.

8. A type of ultra-small nano-SAPO-34 molecular sieve, characterized in that, The primary nanoparticles in the ultrasmall nano SAPO-34 molecular sieve prepared according to any one of claims 1-7 have a size of 10-20 nm.

9. The application of the ultra-small nano SAPO-34 molecular sieve prepared by the preparation method according to any one of claims 1-7 or the ultra-small nano SAPO-34 molecular sieve according to claim 8 in the methanol-to-olefins reaction.

Images