Lamellar SAPO-34 molecular sieve, its synthesis method and application

Abstract

The present application discloses a lamellar SAPO-34 molecular sieve. The crystals of the SAPO-34 molecular sieve have a lamellar structure arranged radially, with nanosheets arranged radially. The thickness of the nanosheets is 10-40 nm. The present application also discloses a synthesis method and applications of the molecular sieve. The crystals of the SAPO-34 molecular sieve as a whole have a wrinkled shape like mushroom gills, and the single-layer nanosheets are in an irregular wavy shape and lean against each other. The nanosheets are arranged radially and connected at the roots, which can increase the total amount of lamellae of a single molecular sieve particle, thereby increasing the specific surface area of each molecular sieve particle. Since the molecular sieve has a lamellar structure, this morphology is beneficial to increasing the specific surface area, shortening the length of the microporous channels, and significantly increasing the number of pore mouths. This not only facilitates the rapid diffusion of reactants and products, but also facilitates the escape of carbon deposition precursors from the microporous channels, avoiding the rapid deactivation of the molecular sieve, prolonging the service life of the molecular sieve, and increasing the selectivity and yield of ethylene and propylene.

Description

Technical Field

[0001] The present application relates to a lamellar SAPO-34 molecular sieve and a synthesis method and application thereof. Background Art

[0002] Low-carbon olefins, especially ethylene and propylene, are important raw materials for synthetic plastics, fibers and various chemical materials, and play a very important role in the modern chemical industry. In traditional petrochemical production, ethylene and propylene are mainly obtained by petroleum cracking. However, with the increase in global energy demand and the decrease in crude oil reserves, the cost of preparing light olefins through traditional petroleum routes is getting higher and higher. Therefore, in recent years, countries around the world have begun to research and develop technologies for preparing low-carbon olefins through non-petrochemical routes. Since methanol has a wide range of sources and can be prepared using coal or natural gas, the technology of preparing olefins from methanol is currently attracting more and more attention from people around the world. In the methanol to olefins (MTO) process, the catalyst plays a vital role, so the synthesis and modification of the catalyst is a key step in the MTO process.

[0003] SAPO-34 molecular sieve has moderate acidity, good hydrothermal stability and special pore structure, and has a specific selectivity for product molecules. It is used in the methanol to olefins process, and has high selectivity for low-carbon olefins, showing excellent catalytic performance. However, the microporous structure of SAPO-34 makes it very easy for some macromolecular substances to be difficult to diffuse out and deposit inside the molecular sieve, which can easily cause the molecular sieve to be deactivated due to carbon deposition.

[0004] At present, in order to improve the catalytic performance and prepare SAPO-34 with high crystallinity, uniform structure and high performance, the main research direction of researchers is to reduce the particle size of molecular sieve crystals and synthesize molecular sieves with special crystal morphology. CN113493212B discloses a method for preparing a novel morphological SAPO-34 molecular sieve, wherein the outer surface of the prepared molecular sieve is distributed with protruding nanosheets, which are hexagonal or quasi-hexagonal, and show good catalytic effect in catalyzing methanol to olefins, and the yield of ethylene and propylene can reach 85%, but the life span is short. CN107915237B synthesizes a twin SAPO-34 molecular sieve crystal morphology as a cube with a triangular pyramid at the center of each of the six faces by a two-step crystallization method, which has good selectivity for low-carbon olefins in the methanol conversion to low-carbon olefins reaction, but the synthesis process requires secondary crystallization, the synthesis process is relatively complicated, and the pyrrolidine template agent used has certain toxicity, requiring strong production safety measures and environmental safety measures.

[0005] In view of this, it is still of great significance to develop SAPO-34 molecular sieves with different morphologies to improve the yield of light olefins in methanol to olefins. Summary of the invention

[0006] In order to develop a SAPO-34 molecular sieve with a new morphology to improve the yield of light olefins in methanol to olefins, the present application first proposes a lamellar SAPO-34 molecular sieve, the crystals of which are in a radially arranged lamellar structure, with radially arranged nanosheets, and the thickness of the nanosheets is 10-40nm. The crystals of the SAPO-34 molecular sieve are in the shape of mushroom folds as a whole, and the single-layer nanosheets are in an irregular wavy shape and abut against each other, and the nanosheets are arranged radially and connected at the roots.

[0007] The particle size of the lamellar SAPO-34 molecular sieve in this application is 3-12 μm, the mesopore diameter is 15-40 nm, and the specific surface area is 650-750 m 2 / g. The SAPO-34 molecular sieve has a large number of folded and mutually abutting lamellae structures. Due to the folded shape, the lamellae structures abutting against each other will not block the channels on the molecular sieve lamellae, but can increase the total amount of lamellae of a single molecular sieve particle, thereby increasing the specific surface area of ​​each molecular sieve particle. Since the molecular sieve is a lamellae structure, this morphology is conducive to increasing the specific surface area, shortening the length of the microporous channels and significantly increasing the number of pores, which is not only conducive to the rapid diffusion of reactants and products, but also conducive to the escape of carbon deposit precursors from the microporous channels, avoiding rapid deactivation of the molecular sieve, thereby extending the service life of the molecular sieve and improving the selectivity and yield of ethylene and propylene.

[0008] The molecular sieve can be used in the methanol to olefin (MTO) process and has good selectivity for low-carbon olefins of ethylene and propylene. The SAPO-34 molecular sieve has a catalytic life of more than 540 minutes in the MTO reaction and a total yield of ethylene and propylene of more than 89 wt%.

[0009] Secondly, the present application also proposes a method for synthesizing the lamellar SAPO-34 molecular sieve, the specific steps of which are as follows:

[0010] (1) dissolving a betaine-type surfactant in isooctane to form a reverse micelle system;

[0011] (2) adding an aluminum source aqueous solution dropwise to the reverse micelle system to form a mixed solution;

[0012] (3) adding a phosphorus source to the mixed solution and stirring to form a mixed material;

[0013] (4) adding a silicon source, tetraethylammonium hydroxide and triethylamine to the mixture in sequence, mixing them evenly to obtain a precursor solution;

[0014] (5) The precursor solution is subjected to a hydrothermal reaction. After the reaction is completed and cooled, the reaction materials are filtered, and then the obtained solid is washed, dried, ground and calcined to obtain a lamellar SAPO-34 molecular sieve catalyst.

[0015] In step (4), when the silicon source, tetraethylammonium hydroxide (TEAOH) and triethylamine (TEA) are added to the mixture in sequence, it is best to leave an interval of 10-20 minutes in between so that the first added materials can be first dispersed into the mixture, that is, after adding the silicon source, continue stirring for 10-20 minutes, then add TEAOH, stir for another 10-20 minutes, and finally add TEA to stir all the components evenly.

[0016] When synthesizing molecular sieves, if water is first added to the reverse micelle system, the surfactant and isooctane will form micelles under the action of water. As the amount of water increases, the surfactant concentration decreases, the micelle size becomes larger, the interface strength decreases, and the spatial confinement effect weakens, which is not conducive to the synthesis of lamellar morphology. In this application, the aluminum source is first dissolved in water, and after mixing evenly, the water molecules are uniformly attached to the surface of the aluminum source through van der Waals forces to form a metastable sol system, and then the sol system is added dropwise to the reverse micelle solution. The oxygen atoms in betaine are combined with the hydroxyl groups on the surface of the aluminum source layer and the water molecules through hydrogen bonds, resulting in a steric hindrance effect, which weakens the mutual bonding between the particles of the aluminum source. There is a large amount of [AlO 4 ] - Tetrahedral nucleation sites. Then, a phosphorus source is added, and the negatively charged [AlO 4 ] - and positively charged [PO 4 ] + Charge interaction occurs to form an aluminum phosphate framework structure. Since silicon atoms are mainly embedded in the framework structure by replacing phosphorus in the aluminum phosphate framework structure, when the silicon content is large, adjacent phosphorus and aluminum atoms in the aluminum phosphate framework will be replaced at the same time to form a silicon-rich area. The excessive acidity of the molecular sieve reduces the selectivity of low-carbon olefins. Therefore, the present application adds a silicon source and a template agent after the aluminum phosphate structure is formed by phosphorus aluminum oxygen to promote the formation of a pure phase SAPO-34 molecular sieve with suitable acidity.

[0017] In the early stage of crystallization, the aluminum source, phosphorus source and silicon source interact with each other to form amorphous precursor nanoparticles, after which the nanoparticles spontaneously align and combine with each other, reducing the interfacial energy of the system and forming a lamellar structure. Triethylamine has the specificity of binding to the crystal surface and acts as a growth regulator to promote the directional growth of crystals. The anion part of the betaine surfactant combines with the quaternary ammonium cation of tetraethylammonium hydroxide in the form of an ionic bond to form a structure-directing agent containing two quaternary ammonium groups, which then bonds with the precursor nanoparticles in the form of a covalent bond, inhibiting the directional attachment of the generated precursor nanoparticles along the c-axis, causing the nanoparticles to aggregate along the a-axis or b-axis. At the same time, isooctane is selectively adsorbed on the

[001] surface of the nanoparticles, controlling and limiting the growth rate of the nanoparticles along the

[001] direction, forming a lamellar structure. During the crystallization process, a pair of adjacent layers grow into a thick layer, and a thick layer formed by numerous adjacent layers is generated, and the thick layer recrystallizes into a thin nanosheet. Finally, the nanosheets are further assembled into an ordered fan-shaped structure through the interaction of the alkyl hydrophobic chains between the tails of the betaine surfactant located on the outside of the nanosheets, so that the formed nanosheet layers are arranged radially.

[0018] The lamellar SAPO-34 molecular sieve prepared by the present application has the following advantages: (1) The obtained SAPO-34 molecular sieve is in the form of lamellar micron particles, and the molecular sieve crystals are composed of nanosheets, which are in the form of folded lamellar sheets and abut against each other. Since the nanosheets are in the form of folds, there are many gaps between the nanosheets, and there are more acid sites. (2) Triethylamine is added as a mixed template agent on the basis of a small amount of tetraethylammonium hydroxide for synthesis, which greatly reduces the amount of tetraethylammonium hydroxide used, which not only controls the cost, but also reduces the particle size of the molecular sieve and prolongs the catalytic life of the molecular sieve.

[0019] Specifically, the molar ratio of raw materials for preparing the precursor solution is: (3.8-7)H: (0.2-0.7)S: (75-105)H 2 O: (0.9-1.7)Al 2 O 3 :(0.8-1.4)P 2 O 5 :(0.3-0.8)SiO 2 :(0.1-0.5)TEAOH:(1.5-2.0)TEA, where H represents isooctane and S represents betaine type surfactant. The silicon source is converted to SiO 2 , aluminum source is converted to Al 2 O 3 , phosphorus source is converted to P 2 O 5 .

[0020] When the content of betaine-type surfactant is high, the cationic quaternary ammonium group in the surfactant will compete with the TEA cation (i.e., template agent) for interaction with the negatively charged skeleton, affecting the template-guiding effect of the TEA cation and thus reducing the crystallinity of the product; when the content of betaine-type surfactant is low, due to the lack of protection of the betaine surfactant, the precursor nanoparticles will aggregate and cannot form a lamellar morphology.

[0021] When the isooctane content is high, some unprotonated triethylamine will be distributed from the water phase to the oil phase, resulting in a decrease in the content of triethylamine in the water phase, resulting in insufficient structure directing agent, and no formation of CHA-structured SAPO-34 crystals; when the isooctane content is low, the proportion of the water phase increases, the stability of the precursor solution deteriorates, the nanoparticles are easy to agglomerate, the dispersibility of the nanoparticles is reduced, the number of acidic sites is reduced, and the catalytic activity of SAPO-34 is reduced.

[0022] In order to ensure the total amount of the template, the total molar ratio of TEAOH to TEA is 1.9-2.1.

[0023] When the water content is too low, the aluminum source is not fully hydrolyzed, resulting in the inability to fully dissolve the raw materials, and obvious impurity crystals will appear. The particle size of the molecular sieve will also increase with the decrease in water content. If the water content is too high, the precursor solution will be unstable, thus affecting the effective crystallization of the SAPO-34 molecular sieve.

[0024] If the amount of silicon added is too low, the silicon element substitution ability is poor, and the resulting CHA structure SAPO-34 molecular sieve framework structure is unstable and is easily converted into the crystal form of the AFI structure SAPO-5 molecular sieve. If the amount of silicon source added is too high, silicon itself will agglomerate to form silicon dioxide.

[0025] The low content of phosphorus source leads to too high pH value of the initial solution, which cannot provide a pH environment suitable for the formation of SAPO-34, resulting in the final formation of amorphous matter. Excessive phosphorus source easily leads to the formation of dense phase or agglomerates, and the ability of silicon source, aluminum source, phosphorus source and template agent to enter the SAPO-34 molecular sieve framework is weakened, resulting in a decrease in the crystallinity of the molecular sieve.

[0026] When triethylamine is used as a template, the synthesized SAPO-34 has large grains, low crystallinity, strong acidity, and large particle size. When tetraethylammonium hydroxide is used as a template, the synthesized SAPO-34 has small grains, low acidity, and high cost. In the present application, tetraethylammonium hydroxide is first added, and tetraethylammonium hydroxide has good dispersibility in a hydrothermal system, so a large number of crystal nuclei can be formed in the early stage of crystallization, and then triethylamine is added. Triethylamine has a strong guiding effect that makes the silicon source and the aluminum source more easily adsorbed into the crystal nucleus, thereby accelerating the growth of the crystal nucleus. The interaction between the templates reduces the space filling around the molecular template, thereby generating more small seeds in the nucleation process, and the grain size becomes smaller.

[0027] When the amount of triethylamine is too small, it is not enough to induce the formation of the target product structure, and it is easier to self-polymerize and induce the formation of AFI structure, so the pure phase SAPO-34 molecular sieve cannot be obtained. When the amount of template agent is too large, its normal structure-guiding effect is disturbed, which is not conducive to synthesis and leads to a decrease in the crystallinity of the target product. When the amount of tetraethylammonium hydroxide is small, it cannot promote the effective substitution of silicon atoms into the AlPO skeleton, and the acidity is reduced. When the amount of tetraethylammonium hydroxide is large, the initial sol system of the reaction is strongly alkaline, resulting in the agglomeration of SAPO-34 molecular sieve or the appearance of irregular crystals.

[0028] Specifically, the required betaine-type surfactant is one or both of dodecyl dimethyl betaine and dodecyl dimethyl hydroxypropyl sulfonyl betaine; the aluminum source is one or both of aluminum isopropoxide and pseudo-boehmite; the phosphorus source is phosphoric acid; and the silicon source is one or both of silica sol and ethyl orthosilicate.

[0029] In step (4), the stirring time is preferably 6-12h. If the stirring time is too short, the components in the gel are not mixed evenly, and SAPO-5 is easily generated. Prolonging the stirring time is conducive to forming more primary structural units, thereby forming more crystal nuclei, so that the crystallinity of the final product is improved. However, if the stirring time is too long, the crystal nuclei that have been generated will be redissolved, so that the final product becomes an amorphous substance. Under the above stirring speed, the components can be evenly dispersed, agglomeration can be avoided, and damage to the shape of the crystal nuclei can be avoided. In order to maintain a certain stirring intensity so that the materials can be smoothly mixed evenly, in step (4), the stirring speed is 450-550rpm.

[0030] Furthermore, in order to allow the aluminum source to be smoothly mixed with the reverse micelle system and to adsorb betaine around the aluminum source to form micelles, in step (2), the aluminum source aqueous solution is ultrasonically treated for 15-30 minutes. The aluminum source has a higher dispersion in the aqueous solution, which prevents the aluminum source particles from agglomerating, improves the activity of the aluminum source, and shortens the stirring time.

[0031] Further, in step (5), a hydrothermal reaction is carried out in a homogeneous reactor at 60 rpm, the reaction temperature is 180-230°C, and the reaction time is 36-54h. If the reaction temperature is low or the time is too short, the SAPO-34 molecular sieve cannot be completely crystallized, and SAPO-5 molecular sieve impurities are prone to appear during the crystallization process. The stability of SAPO-5 molecular sieve is lower than that of SAPO-34 molecular sieve, and the solubility is higher than that of SAPO-34 molecular sieve. By increasing the crystallization temperature and extending the crystallization time, the SAPO-5 molecular sieve gradually degrades, and the SAPO-34 molecular sieve is transformed into a crystallization, and the high temperature is conducive to the nucleation and crystal growth of the SAPO-34 molecular sieve. If the crystallization temperature is too high, the grain size increases and the lifespan decreases. If the crystallization time is too long, more Si atoms will enter the molecular sieve framework, forming larger silicon islands, reducing the surface acidity of the molecular sieve, and when used as an MTO catalyst, the selectivity of (ethylene + propylene) will decrease.

[0032] The use of a homogeneous reactor allows the components to react more evenly, with a faster reaction speed and a more thorough reaction, which is beneficial to the nucleation of the crystallization solution and the growth of crystals, thereby improving the crystallinity of the sample.

[0033] Furthermore, in order to obtain a molecular sieve catalyst with a more uniform structure, after the hydrothermal reaction is completed, the temperature of the reaction material is lowered to 60-90° C. and aged for 10-15 hours to allow solids to precipitate and reduce the adsorption of impurities on the solid surface.

[0034] Furthermore, in step (5), the drying temperature is 80-120°C and the time is 5h-12h; the calcination temperature is 450-650°C and the time is 3h-7h. If the drying temperature is too low and the time is too short, the moisture inside the molecular sieve cannot be completely removed. If the temperature is too high, the moisture inside the molecular sieve evaporates and vaporizes, resulting in a large amount of water vapor escaping, destroying the internal structure of the molecular sieve. If the calcination temperature is too low and the time is too short, the organic components in the SAPO-34 pores cannot be completely removed, covering the catalytic active centers. If the calcination temperature is too high and the time is too long, exceeding the temperature that the molecular sieve can withstand, the structure is severely damaged, the catalyst activity is reduced to a certain extent, and the energy consumption is increased.

[0035] Again, the present application also provides the use of the above-mentioned SAPO-34 molecular sieve in the methanol to olefins reaction.

[0036] Specifically, the reaction conditions of the methanol to olefins reaction are: activation temperature of 500-600°C, activation time of 0.8-1.2h; reaction temperature of 430-470°C, raw material methanol concentration of 40-45wt%, methanol feed weight space velocity of 3.5-4.5h -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1This is the XRD pattern of the lamellar SAPO-34 molecular sieve sample obtained in Example 1.

[0038] Figure 2 This is a SEM image of the lamellar SAPO-34 molecular sieve sample obtained in Example 1, wherein Figure 2 (a) is a SEM image of the sample of Example 1, Figure 2 (b) is another SEM image of the sample of Example 1.

[0039] Figure 3 This is the SEM image of the lamellar SAPO-34 molecular sieve sample obtained in Example 2.

[0040] Figure 4 This is the SEM image of the lamellar SAPO-34 molecular sieve sample obtained in Example 3.

[0041] Figure 5 This is the SEM image of the lamellar SAPO-34 molecular sieve sample obtained in Example 4.

[0042] Figure 6 This is the SEM image of the lamellar SAPO-34 molecular sieve sample obtained in Comparative Example 1.

[0043] Figure 7 This is the SEM image of the SAPO-34 molecular sieve sample obtained in Comparative Example 2.

[0044] Figure 8 This is the SEM image of the SAPO-34 molecular sieve sample obtained in Comparative Example 3.

[0045] Fig. 9 This is the SEM image of the SAPO-34 molecular sieve sample obtained in Comparative Example 4.

[0046] Fig.10 This is the SEM image of the SAPO-34 molecular sieve sample obtained in Comparative Example 5.

[0047] Fig.11 This is the SEM image of the SAPO-34 molecular sieve sample obtained in Comparative Example 6.

[0048] Fig.12 This is the SEM image of the SAPO-34 molecular sieve sample obtained in Comparative Example 7.

[0049] Fig.13 This is the SEM image of the SAPO-34 molecular sieve sample obtained in Comparative Example 8.

[0050] Fig.14 The methanol conversion curves of SAPO-34 molecular sieves prepared in Examples and Comparative Examples are shown in FIG.

[0051] Fig.15The selectivity curves of SAPO-34 molecular sieves prepared in Examples and Comparative Examples are for light olefins. DETAILED DESCRIPTION

[0052] The following will illustrate the implementation of the present invention through specific implementation examples and drawings. However, the following implementation examples are only used to clearly illustrate the technical solutions used in the present invention, and cannot be used to limit the scope of protection of the present invention. The experimental methods for specific conditions not indicated in the following implementation examples are generally implemented under conventional conditions or according to the recommended conditions of the corresponding standards.

[0053] The characterization instruments used in the embodiment of the present invention are: X-ray diffraction uses Japan Rigaku MiniFlex600 X-ray diffractometer, Cu target, tube voltage 40KV, tube current 15mA, scanning speed 10° / min, scanning angle 5-50°. Scanning electron microscope (SEM) uses Japan Hitachi S4800 model. The sample preparation process is to apply a small amount of the dried molecular sieve sample on the conductive glue, blow off the unfixed sample with an ear cleaning bulb, and then perform gold spraying for 40s to complete the sample preparation.

[0054] In the following examples and comparative examples, for ease of calculation, the molecular weight of dodecyl dimethyl hydroxypropyl sulfobetaine is calculated according to the molecular weight of tridecyl dimethyl hydroxypropyl sulfobetaine. In the following examples and comparative examples, the hydrothermal reaction is carried out in a homogeneous reactor at 60 rpm.

[0055] Example 1

[0056] (1) 10.12 g of dodecyl dimethyl betaine (30 wt%) was added to 10.37 g of isooctane to prepare a reverse micelle system B;

[0057] (2) At room temperature, 3.38 g of pseudo-boehmite (86 wt% Al 2 O 3 ) was dissolved in 22.09 g of deionized water, stirred and mixed evenly to form an aluminum source aqueous solution A; the aluminum source aqueous solution A was ultrasonically treated for 20 minutes, and then the aluminum source aqueous solution A was added to the reverse micelle system B to form a mixed solution C.

[0058] (3) 4.96 g phosphoric acid (85 wt % H 3 PO 4 ) is added into mixed solution C and stirred evenly to form a mixed material.

[0059] (4) Weigh 2.58 g of silica sol (30 wt% SiO 2), 2.53g tetraethylammonium hydroxide (25wt%) and 3.96g triethylamine were added to the above mixture in sequence, stirred for 12h, and after uniform mixing, a precursor solution was obtained; the stirring speed was 550 rpm. After adding the silica sol, it was stirred for 15 minutes, then tetraethylammonium hydroxide was added, and after stirring for another 15 minutes, triethylamine was finally added. This addition method was adopted in the following embodiments and will not be repeated.

[0060] In the precursor solution, the molar ratio of each material is: 4.15H:0.44S:89H 2 O:1.30Al 2 O 3 :0.98P 2 O 5 :0.59SiO 2 : 0.20TEAOH: 1.79TEA, wherein H represents isooctane and S represents dodecyl dimethyl betaine.

[0061] (5) The precursor solution is placed in a reactor for a hydrothermal reaction at a temperature of 200° C. for 48 hours.

[0062] After the hydrothermal reaction is completed, the temperature of the reaction materials in the reactor is first reduced to 80°C. After aging for 10 hours, the reaction materials are cooled to room temperature, the reaction materials are filtered, and the solid product obtained is washed with deionized water until neutral. After washing, the solid product is dried at 110°C for 6 hours, ground, and finally calcined at 550°C in a programmed temperature muffle furnace for 5 hours to obtain 1# SAPO-34 molecular sieve.

[0063] The 1# SAPO-34 molecular sieve obtained in this example was scanned to obtain Figure 1 The XRD pattern shown is the same as the standard pattern of SAPO-34 molecular sieve. Figure 2 It can be seen that SAPO-34 has a fan-shaped morphology and presents nanosheets perpendicular to the edge. There are gaps between the sheets, and some of the middle parts have not completely transformed into sheets. The thickness of the sheets is 10-30nm, the mesopore diameter is 30-40nm, and the specific surface area is 717.8m 2 / g, which can make the molecular sieve have more active sites and short diffusion paths, thus helping to improve the catalytic performance of the MTO reaction.

[0064] Example 2

[0065] (1) 5.74 g of dodecanediyl dimethyl hydroxypropyl sulfobetaine (45 wt%) was added to 12.40 g of isooctane to form a reverse micelle system B;

[0066] (2) At room temperature, 3.37 g of pseudo-boehmite (86 wt% Al 2 O 3 ) was dissolved in 25.53 g of deionized water, stirred and mixed evenly to form an aluminum source aqueous solution A; the aluminum source aqueous solution A was ultrasonically treated for 25 minutes, and then the aluminum source aqueous solution A was added to the reverse micelle system B to form a mixed solution C.

[0067] (3) 5.49 g phosphoric acid (85 wt % H 3 PO 4 ) is added into mixed solution C and stirred evenly to form a mixed material.

[0068] (4) Weigh 1.43 g of silica sol (30 wt% SiO 2 ), 1.40g tetraethylammonium hydroxide (25wt%) and 4.63g triethylamine were added to the above mixture in sequence, stirred for 10h, and after mixing evenly, a precursor solution was obtained; the stirring speed was 500 rpm. In the precursor solution, the molar ratio of each material was: 4.59H:0.30S:78H 2 O:1.20Al 2 O 3 :1.00P 2 O 5 :0.30SiO 2 : 0.10TEAOH: 1.94TEA, wherein H represents isooctane and S represents dodecyl dimethyl hydroxypropyl sulfobetaine.

[0069] (5) The precursor solution is placed in a reactor for a hydrothermal reaction at a temperature of 210° C. for 48 hours.

[0070] After the hydrothermal reaction is completed, the temperature of the reaction materials in the reactor is first reduced to 60°C. After aging for 15 hours, the reaction materials are cooled to room temperature, the reaction materials are filtered, and the obtained solid product is washed with deionized water until neutral. After washing, the solid product is dried at 100°C for 10 hours, ground, and finally calcined at 500°C in a programmed temperature muffle furnace for 6 hours to obtain 2# SAPO-34 molecular sieve.

[0071] The 2# SAPO-34 molecular sieve obtained in this example was scanned. Figure 3 As shown, the SAPO-34 molecular sieve has radially arranged nanosheets with a sheet thickness of 20-40 nm, a mesopore diameter of 35-40 nm, and a specific surface area of ​​685.4 m 2 / g.

[0072] Example 3

[0073] (1) 8.25 g of dodecanediyl dimethyl hydroxypropyl sulfobetaine (45 wt%) was added to 15.54 g of isooctane to form a reverse micelle system B;

[0074] (2) At room temperature, 4.17 g of pseudo-boehmite (86 wt% Al 2 O 3 ) was dissolved in 15.26 g of deionized water, stirred and mixed evenly to form an aluminum source aqueous solution A; the aluminum source aqueous solution A was ultrasonically treated for 15 minutes, and then the aluminum source aqueous solution A was added to the reverse micelle system B to form a mixed solution C.

[0075] (3) 5.18 g phosphoric acid (85 wt % H 3 PO 4 ) is added into mixed solution C and stirred evenly to form a mixed material.

[0076] (4) Weigh 2.45 g of silica sol (30 wt% SiO 2 ), 6.01g tetraethylammonium hydroxide (25wt%) and 3.13g triethylamine were added to the above mixture in sequence, stirred for 7h, and after mixing evenly, a precursor solution was obtained; the stirring speed was 450 rpm. In the precursor solution, the molar ratio of each material was: 6.59H:0.49S:77H 2 O:1.70Al 2 O 3 :1.09P 2 O 5 :0.59SiO 2 : 0.50TEAOH: 1.50TEA, wherein H represents isooctane and S represents dodecyl dimethyl hydroxypropyl sulfobetaine.

[0077] (5) The precursor solution is placed in a reactor for a hydrothermal reaction at a temperature of 180° C. for 54 hours.

[0078] After the hydrothermal reaction is completed, the temperature of the reaction materials in the reactor is first reduced to 90°C. After aging for 12 hours, the reaction materials are cooled to room temperature, the reaction materials are filtered, and the solid product obtained is washed with deionized water until neutral. After washing, the solid product is dried at 80°C for 12 hours, ground, and finally calcined at 450°C in a programmed temperature muffle furnace for 7 hours to obtain 3# SAPO-34 molecular sieve.

[0079] The 3# SAPO-34 molecular sieve obtained in this example was scanned. Figure 4 As shown in Figure 1, the SAPO-34 molecular sieve is composed of nanosheets that bend outward from one end. The thickness of the sheet is 20-40nm, the mesopore diameter is 24-33nm, and the specific surface area is 682.6m2 / g.

[0080] Example 4

[0081] (1) 10.15 g of dodecyl dimethyl betaine (30 wt%) was added to 12.81 g of isooctane to form a reverse micelle system B;

[0082] (2) At room temperature, 3.23 g of pseudo-boehmite (86 wt% Al 2 O 3 ) was dissolved in 20.39 g of deionized water, stirred and mixed evenly to form an aluminum source aqueous solution A; the aluminum source aqueous solution A was ultrasonically treated for 30 minutes, and then the aluminum source aqueous solution A was added to the reverse micelle system B to form a mixed solution C.

[0083] (3) 3.88 g phosphoric acid (85 wt % H 3 PO 4 ) is added into mixed solution C and stirred evenly to form a mixed material.

[0084] (4) Weigh 2.99 g of silica sol (30 wt% SiO 2 ), 3.30g tetraethylammonium hydroxide (25wt%) and 3.25g triethylamine were added to the above mixture in sequence, stirred for 6h, and after mixing evenly, a precursor solution was obtained; the stirring speed was 520 rpm. In the precursor solution, the molar ratio of each material was: 6.02H:0.52S:101H 2 O:1.46Al 2 O 3 :0.90P 2 O 5 :0.80SiO 2 : 0.30TEAOH: 1.73TEA, wherein H represents isooctane and S represents dodecyl dimethyl betaine.

[0085] (5) The precursor solution is placed in a reactor for a hydrothermal reaction at a temperature of 230° C. for 36 hours.

[0086] After the hydrothermal reaction is completed, the temperature of the reaction materials in the reactor is first reduced to 70°C. After aging for 14 hours, the reaction materials are cooled to room temperature, the reaction materials are filtered, and the solid product obtained is washed with deionized water until neutral. After washing, the solid product is dried at 120°C for 5 hours, ground, and finally calcined at 650°C in a programmed temperature muffle furnace for 3 hours to obtain 4# SAPO-34 molecular sieve.

[0087] The 4# SAPO-34 molecular sieve obtained in this example was scanned. Figure 5As shown in Figure 2, the SAPO-34 molecular sieve is completely transformed into nanosheets, with a sheet thickness of 10-30 nm, a mesopore diameter of 18-35 nm, and a specific surface area of ​​656.4 m 2 / g.

[0088] Comparative Example 1

[0089] The difference between this comparative example and Example 1 is that no dodecyl dimethyl betaine and isooctane solution are added, that is, no reverse micelle system is used.

[0090] The 5# SAPO-34 molecular sieve obtained in this example was scanned to obtain Figure 6 The SEM images shown. Figure 6 It can be seen that the shape of SAPO-34 without the addition of the reverse micelle solution is lamellar, and no flakes appear.

[0091] Comparative Example 2

[0092] (1) 10.12 g of dodecyl dimethyl betaine (30 wt%) was added to 10.37 g of isooctane to form a reverse micelle system B;

[0093] (2) At room temperature, 3.38 g of pseudo-boehmite (86 wt% Al 2 O 3 ) was dissolved in 23.99 g of deionized water, stirred and mixed evenly to form an aluminum source aqueous solution A; the aluminum source aqueous solution A was ultrasonically treated for 20 minutes, and then the aluminum source aqueous solution A was added to the reverse micelle system B to form a mixed solution C.

[0094] (3) 4.96 g phosphoric acid (85 wt % H 3 PO 4 ) is added into mixed solution C and stirred evenly to form a mixed material.

[0095] (4) Weigh 2.58 g of silica sol (30 wt% SiO 2 ) and 4.41g triethylamine were added to the above mixture in sequence, stirred for 12h, and after mixing evenly, a precursor solution was obtained; the stirring speed was 550 rpm. In the precursor solution, the molar ratio of each material was: 4.15H:0.44S:89H 2 O:1.30Al 2 O 3 :0.98P 2 O 5 :0.59SiO 2 : 1.99TEA, where H represents isooctane and S represents dodecyl dimethyl betaine.

[0096] (5) The precursor solution is placed in a reactor for a hydrothermal reaction at a temperature of 200° C. for 48 hours.

[0097] After the hydrothermal reaction is completed, the temperature of the reaction materials in the reactor is first reduced to 80°C. After aging for 10 hours, the reaction materials are cooled to room temperature, the reaction materials are filtered, and the solid product obtained is washed with deionized water until neutral. After washing, the solid product is dried at 110°C for 6 hours, ground, and finally calcined at 550°C in a programmed temperature muffle furnace for 5 hours to obtain 6# SAPO-34 molecular sieve.

[0098] The 6# SAPO-34 molecular sieve obtained in this example was scanned to obtain Figure 7 The SEM images shown. Figure 7 It can be seen that in the reverse micelle system, SAPO-34 synthesized using only triethylamine template appears in lamellar form, but many crystals are not transformed.

[0099] Comparative Example 3

[0100] (1) 10.12 g of dodecyl dimethyl betaine (30 wt%) was added to 10.37 g of isooctane to form a reverse micelle system B;

[0101] (2) At room temperature, 3.38 g of pseudo-boehmite (86 wt% Al 2 O 3 ) was dissolved in 10.09 g of deionized water, stirred and mixed evenly to form an aluminum source aqueous solution A; the aluminum source aqueous solution A was ultrasonically treated for 20 minutes, and then the aluminum source aqueous solution A was added to the reverse micelle system B to form a mixed solution C.

[0102] (3) 4.96 g phosphoric acid (85 wt % H 3 PO 4 ) is added into mixed solution C and stirred evenly to form a mixed material.

[0103] (4) Weigh 2.58 g of silica sol (30 wt% SiO 2 ) and 25.58g tetraethylammonium hydroxide (25wt%) were added to the above mixture in sequence and stirred for 12h. After mixing evenly, a precursor solution was obtained; the stirring speed was 550 rpm. The molar ratio of each material in the precursor solution was: 4.15H:0.44S:103H 2 O:1.30Al 2 O 3 :0.98P 2 O 5 :0.59SiO 2 : 1.98TEAOH, wherein H represents isooctane and S represents dodecyl dimethyl betaine.

[0104] (5) The precursor solution is placed in a reactor for a hydrothermal reaction at a temperature of 200° C. for 48 hours.

[0105] After the hydrothermal reaction is completed, the temperature of the reaction materials in the reactor is first reduced to 80°C. After aging for 10 hours, the reaction materials are cooled to room temperature, the reaction materials are filtered, and the solid product obtained is washed with deionized water until neutral. After washing, the solid product is dried at 110°C for 6 hours, ground, and finally calcined at 550°C in a programmed temperature muffle furnace for 5 hours to obtain 7# SAPO-34 molecular sieve.

[0106] The 7# SAPO-34 molecular sieve obtained in this example was scanned to obtain Figure 8 The SEM images shown. Figure 8 It can be seen that in the reverse micelle system, SAPO-34 synthesized using only tetraethylammonium hydroxide template agent does not appear in lamellar form and the cubic morphology is destroyed.

[0107] Comparative Example 4

[0108] (1) At room temperature, 3.38 g of pseudo-boehmite (86 wt% Al 2 O 3 ) was dissolved in 22.09 g of deionized water, stirred and mixed evenly to form an aluminum source aqueous solution A; the aluminum source aqueous solution A was added into a beaker containing 10.12 g of dodecyl dimethyl betaine (30 wt %) to form a mixed solution B.

[0109] (2) 4.96 g phosphoric acid (85 wt % H 3 PO 4 ) is added into mixed solution B, stirred evenly to form a mixed material.

[0110] (3) Weigh 2.58 g of silica sol (30 wt% SiO 2 ), 2.53g tetraethylammonium hydroxide (25wt%) and 3.96g triethylamine were added to the above mixture in sequence, stirred for 12h, and after mixing evenly, a precursor solution was obtained; the stirring speed was 550 rpm. In the precursor solution, the molar ratio of each material was: 0.44S:89H 2 O:1.30Al 2 O 3 :0.98P 2 O 5 :0.59SiO 2 : 0.20TEAOH: 1.79TEA, wherein S represents dodecyl dimethyl betaine.

[0111] (4) The precursor solution is placed in a reactor for a hydrothermal reaction at a temperature of 200° C. for 48 hours.

[0112] After the hydrothermal reaction is completed, the temperature of the reaction materials in the reactor is first reduced to 80°C. After aging for 10 hours, the reaction materials are cooled to room temperature, the reaction materials are filtered, and the solid product obtained is washed with deionized water until neutral. After washing, the solid product is dried at 110°C for 6 hours, ground, and finally calcined at 550°C in a programmed temperature muffle furnace for 5 hours to obtain 8# SAPO-34 molecular sieve.

[0113] The 8# SAPO-34 molecular sieve obtained in this example was scanned to obtain Fig. 9 The SEM images shown. Fig. 9 It can be seen that the addition of betaine surfactant alone cannot form a reverse micelle system and the synthesized SAPO-34 particles are not completely separated.

[0114] Comparative Example 5

[0115] The difference between this comparative example and Example 1 is that the surfactant used is hexadecyltrimethylammonium bromide to replace dodecyldimethylbetaine, and the molar numbers of hexadecyltrimethylammonium bromide and dodecyldimethylbetaine are the same.

[0116] The 9# SAPO-34 molecular sieve obtained in this example was scanned to obtain Fig.10 As shown in the SEM image, the cationic surfactant cannot be evenly dispersed in the oil phase, the interfacial tension is large, the diffusion of the particles of each component is hindered, and amorphous SAPO-34 is formed.

[0117] Comparative Example 6

[0118] The difference between this comparative example and Example 1 is that the surfactant used is glycine to replace dodecyl dimethyl betaine, and the molar number of glycine and dodecyl dimethyl betaine is the same.

[0119] The 10# SAPO-34 molecular sieve obtained in this example was scanned to obtain Fig.11 As shown in the SEM image, the cubic structure of SAPO-34 is destroyed. The precursor solution of SAPO-34 is weakly alkaline and cannot cause the carboxyl group in glycine to lose hydrogen ions and become negatively charged, thus exerting its effect.

[0120] Comparative Example 7

[0121] The difference between this comparative example and Example 1 is that the organic solvent used is cyclohexane to replace isooctane, and the molar numbers of cyclohexane and isooctane are the same.

[0122] The 11# SAPO-34 molecular sieve obtained in this example was scanned to obtain Fig.12 The SEM image shown shows that there is basically no lamellar appearance. Compared with isooctane, cyclohexane has a ring structure and is not easy to insert into the tail end of the micelle to form a reverse micelle system.

[0123] Comparative Example 8

[0124] At room temperature, 10.12 g of dodecyl dimethyl betaine (30 wt%) was added to a beaker containing 10.37 g of isooctane to prepare a reverse micelle solution. The solution was stirred at a constant speed on a magnetic stirrer, and 22.09 g of deionized water, 4.96 g of phosphoric acid (85 wt% H 3 PO 4 )、2.58g silica sol (30wt%SiO 2 ), 2.53 g tetraethylammonium hydroxide (25 wt %), 3.96 g triethylamine and 3.38 g pseudo-boehmite (86 wt % Al 2 O 3 ), stirred for 12 hours, and after mixing evenly, a precursor solution was obtained; the stirring speed was 550 rpm. In the precursor solution, the molar ratio of each material was: 4.15H:0.44S:89H 2 O:1.30Al 2 O 3 :0.98P 2 O 5 :0.59SiO 2 :0.20TEAOH:1.79TEA, where H represents isooctane and S represents dodecyl dimethyl betaine. The precursor solution is placed in a reactor for a hydrothermal reaction. The temperature of the hydrothermal reaction is 200°C and the reaction time is 48 hours. After the hydrothermal reaction is completed, the temperature of the reaction material in the reactor is first reduced to 80°C. After aging for 10 hours, the reaction material is cooled to room temperature, the reaction material is filtered, and the obtained solid product is washed with deionized water until neutral. After washing, the solid product is dried at 110°C for 6 hours and ground. Finally, it is calcined at 550°C for 5 hours in a programmed temperature muffle furnace to obtain 12# SAPO-34 molecular sieve.

[0125] The 12# SAPO-34 molecular sieve obtained in this example was scanned to obtain Fig.13 As shown in the SEM images, by changing the order of adding the aluminum source, the properties of the reverse micelle solution and the pH of the crystallization solution changed, the synthesized SAPO-34 was amorphous and no lamellar structure appeared.

[0126] The molecular sieves prepared in the above embodiments and comparative examples were tested.

[0127] Conversion rate and selectivity of light olefins of SAPO-34 molecular sieve: The catalyst was tested for methanol to olefins (MTO) reaction performance in a fixed bed reactor customized by Beijing Kemenuo Company. During the performance test reaction, the activation temperature was 550℃, the activation time was 1h; the reaction temperature was 450℃, the reaction pressure was 1.5MPa, the raw methanol concentration was 40wt%, and the methanol feed mass space velocity was 4h -1 , Performance Test The products obtained from the reaction were detected by gas chromatograph (GC 2014, Shimadzu), and the conversion rate and selectivity were calculated based on the detection results.

[0128] Each test data is made Fig.14 and Fig.15 , and are listed in Table 1.

[0129] Fig.15 In each group of bar graphs, from left to right are Examples 1, 2, 3, 4, and Comparative Examples 1, 2, 3, 4, 5, 6, 7, 8.

[0130] Fig.14 It is shown that when the methanol conversion rate is 100%, due to the appearance of the flaky structure, the SAPO-34 molecular sieve can have more active sites, thereby improving the selectivity of light olefins. At the same time, the thickness of the sample lamellae is reduced, and the intermediate products are more quickly derived from the reaction system, thereby reducing the rate of coking and carbon deposition of the molecular sieve. As a result, the catalytic life of the molecular sieves of Examples 1, 2, 3, and 4 is significantly longer than that of Comparative Examples 1, 2, 3, 4, 5, 6, 7, and 8.

[0131] like Fig.15 As shown, the selectivity of light olefins of Examples 1, 2, 3, 4 and Comparative Examples 1, 2, 3, 4, 5, 6, 7, 8 are 90.45wt%, 89.27wt%, 88.68wt%, 89.70wt%, 85.70wt%, 84.49wt%, 80.27wt%, 81.62wt%, 84.29wt%, 82.21wt1%, 82.64wt%, 83.56wt%, respectively. Compared with the comparative example, the selectivity of the examples is significantly improved, proving that the SAPO-34 synthesized by the present invention not only has a novel morphology and structure, but also can improve the diene yield in the methanol to olefin reaction and prolong the catalyst life.

[0132] Table 1 Catalytic results of the samples prepared in various embodiments and comparative examples in methanol to olefins.

[0133]

[0134]

[0135] It can be seen from Table 1 that the molecular sieve prepared by the present application can effectively improve the service life of the molecular sieve and the total selectivity of dienes in the MTO reaction. The improvement of the total selectivity of dienes is mainly reflected in ethylene. After the molecular sieve of the present application is used, the selectivity of ethylene can be increased by about 5-6wt%, while the selectivity of propylene can only be increased by about 1-2wt%, so that the average total selectivity of dienes in the embodiments and comparative examples of the present application is increased by 7.1wt% compared with the comparative example. Since the conversion rate of methanol in the MTO reaction is 100%, the above selectivity can be used as the yield of each product.

Claims

1. A method for synthesizing a lamellar SAPO-34 molecular sieve, characterized in that: The crystals of the SAPO-34 molecular sieve are in a radially arranged lamellar structure, and have radially arranged nanosheets, the thickness of the nanosheets being 10-40 nm. The steps of the synthesis method of the lamellar SAPO-34 molecular sieve are as follows: (1) Dissolving a betaine-type surfactant in isooctane to form a reverse micelle system; (2) adding an aluminum source aqueous solution dropwise into the reverse micelle system to form a mixed solution; (3) adding the phosphorus source to the mixed solution and stirring evenly to form a mixed material; (4) Adding a silicon source, tetraethylammonium hydroxide and triethylamine to the above mixture in sequence, mixing them evenly, to obtain a precursor solution; The molar ratio of raw materials for preparing the precursor solution is: (3.8-7)H: (0.2-0.7)S: (75-105)H2O: (0.9-1.7)Al2O3: (0.8-1.4)P2O5: (0.3-0.8)SiO2: (0.1-0.5)TEAOH: (1.5-2.0)TEA, wherein H represents isooctane and S represents a betaine-type surfactant; (5) The precursor solution is subjected to a hydrothermal reaction. After the reaction is completed and cooled, the reaction materials are filtered, and then the obtained solid is washed, dried, ground and calcined to obtain a lamellar SAPO-34 molecular sieve catalyst.

2. The method for synthesizing the lamellar SAPO-34 molecular sieve according to claim 1, characterized in that: In the precursor solution, the total molar ratio of TEAOH to TEA is 1.9-2.

1.

3. The method for synthesizing the lamellar SAPO-34 molecular sieve according to claim 1, characterized in that: The betaine-type surfactant is one or both of dodecyl dimethyl betaine and dodecyl dimethyl hydroxypropyl sulfobetaine; the aluminum source is one or both of aluminum isopropoxide and pseudoboehmite; the phosphorus source is phosphoric acid; and the silicon source is one or both of silica sol and ethyl orthosilicate.

4. The method for synthesizing the lamellar SAPO-34 molecular sieve according to claim 1, characterized in that: In step (2), the aluminum source aqueous solution is ultrasonically treated for 15-30 minutes.

5. The method for synthesizing the lamellar SAPO-34 molecular sieve according to claim 1, characterized in that: In step (5), a hydrothermal reaction is carried out in a homogeneous reactor at 60 rpm, the reaction temperature is 180-230° C., and the reaction time is 36-54 h.

6. The method for synthesizing the lamellar SAPO-34 molecular sieve according to claim 5, characterized in that: After the hydrothermal reaction is completed, the temperature of the reaction material is lowered to 60-90°C and aged for 10-15 h.

7. The method for synthesizing the lamellar SAPO-34 molecular sieve according to claim 1, characterized in that: In step (5), the drying temperature is 80-120°C, and the drying time is 5-12 hours; the roasting temperature is 450-650°C, and the roasting time is 3-7 hours.

8. Use of the lamellar SAPO-34 molecular sieve according to claim 1 in the methanol to olefins reaction.

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