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

Abstract

The invention relates to the technical field of molecular sieves, and discloses an SAPO-34 molecular sieve and a preparation method and application thereof, the SAPO-34 molecular sieve has a cube-like blocky morphology, each surface of a cube is provided with an etching structure with the width not smaller than 50 nm, and the side length of the cube is 1-5 [mu] m. The SAPO-34 molecular sieve is complete in crystal structure and high in crystallinity, has a relatively large specific surface area, a relatively large micropore area and a relatively large micropore volume under a preferable condition, can be used for gas adsorption separation, can also be used for a reaction for preparing low-carbon olefin by converting an oxygen-containing compound, and has a good industrial application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of molecular sieves, and in particular to a SAPO-34 molecular sieve and a preparation method and application thereof. Background Art

[0002] SAPO-34 molecular sieve is a silicon-phosphorus-aluminum molecular sieve (US4440871A1) developed by UCC in the United States in 1984. Due to the advantages of suitable pore size, pore structure, acid strength, good thermal stability and hydrothermal stability, SAPO-34 molecular sieve has good application properties in the fields of gas adsorption separation and various hydrocarbon conversion catalysis, especially in the methanol conversion to light olefins (MTO), it has high selectivity for ethylene and propylene and shows excellent catalytic performance.

[0003] CN103011188A discloses the use of tetraethylammonium hydroxide as a template, microwave heating, and control of microwave synthesis conditions to synthesize SAPO-34 molecular sieves with nano-spherical and lamellar morphologies. CN104986780A discloses the use of triethylamine as a first template and hexadecyltrimethylammonium bromide as a second template to synthesize SAPO-34 molecular sieves with nano-lamellar morphologies. The method uses a hydrothermal synthesis method to synthesize nano-lamellar crystals under the conditions of a crystallization temperature of 200°C and a crystallization time of 50h. CN103936027A discloses a method for synthesizing a flower-like SAPO-34 molecular sieve using triethylamine as a template. The method adds a biomass suspension during the crystallization process, and synthesizes a flower-like microsphere-shaped SAPO-34 molecular sieve under the conditions of a crystallization temperature of 200°C and a crystallization time of 72h.

[0004] SAPO-34 molecular sieve is prone to carbon deposition and deactivation due to its small pore size, and has a short lifespan. The formation of carbon deposition is related to factors such as the silicon-aluminum ratio of SAPO-34 molecular sieve, the strength and number of acid centers, and the grain morphology will also affect the diffusion process of raw materials and product molecules in the pores, thereby affecting the formation of carbon deposition. Therefore, the regulation of the micromorphology of SAPO-34 molecular sieve has an extremely important influence on optimizing the catalytic performance in the reaction. In view of this, it is of great significance to develop a preparation route for synthesizing SAPO-34 molecular sieves with special morphology. Summary of the invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a SAPO-34 molecular sieve and its preparation method and application. The SAPO-34 molecular sieve has a complete grain structure and a special surface etching structure, which is conducive to optimizing the diffusion process of molecules in the pores.

[0006] In order to achieve the above objectives, the present invention provides a SAPO-34 molecular sieve having a cubic block morphology, each surface of the cube having an etched structure not less than 50 nm wide, and a side length of the cube being 1-5 μm.

[0007] The second aspect of the present invention provides a method for preparing SAPO-34 molecular sieve, comprising:

[0008] (1) performing a first mixing of a phosphorus source, an aluminum source, a silicon source and water to obtain a mixed solution; the first mixing temperature is 70-100° C. and the time is 6-12 hours;

[0009] (2) mixing the mixed solution with 4-dimethylaminopyridine and performing hydrothermal crystallization at 180-200° C. for 72-120 h;

[0010] The phosphorus and aluminum in the phosphorus source and aluminum source are calculated as P2O5 and Al2O3 respectively, the silicon source is calculated as SiO2, and the molar ratio of P2O5, Al2O3, SiO2, 4-dimethylaminopyridine and water is 0.8-1.2:1:0.5-1:2-10:10-100.

[0011] The third aspect of the present invention provides the SAPO-34 molecular sieve prepared by the above preparation method.

[0012] The fourth aspect of the present invention provides use of the SAPO-34 molecular sieve described in the first aspect or the third aspect in gas adsorption separation.

[0013] The fifth aspect of the present invention provides the use of the SAPO-34 molecular sieve described in the first aspect or the third aspect in the reaction of converting oxygen-containing compounds to produce light olefins.

[0014] The SAPO-34 molecular sieve provided by the present invention has a special cubic-like etching morphology, the cubic-like size is 2-3 μm, and each surface of the cube is composed of an etching morphology that can be as small as 50 nm wide. The SAPO-34 molecular sieve has a complete crystal structure and high crystallinity. In a preferred case, it has a large specific surface area, micropore area and micropore volume, can be used for gas adsorption separation, and can also be used for oxygen-containing compound conversion to produce low-carbon olefins, and has good industrial application prospects. The present invention adopts conventional hydrothermal synthesis or aluminum phosphate liquid phase conversion method to synthesize the SAPO-34 molecular sieve with the above-mentioned special morphology, the preparation method is simple, and the morphology is controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is the XRD spectrum of the molecular sieve raw powder sample prepared in Example 1 of the present invention;

[0016] Figure 2is a SEM photograph of the molecular sieve raw powder sample prepared in Example 1 of the present invention;

[0017] Figure 3 is a SEM photograph of the molecular sieve raw powder sample prepared in Example 2 of the present invention;

[0018] Figure 4 is the XRD spectrum of the molecular sieve raw powder sample prepared in Example 3 of the present invention;

[0019] Figure 5 is a SEM photograph of the molecular sieve raw powder sample prepared in Example 3 of the present invention;

[0020] Figure 6 is the XRD spectrum of the molecular sieve raw powder sample prepared in Example 4 of the present invention;

[0021] Figure 7 This is a SEM photograph of the molecular sieve raw powder sample prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0022] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0023] In the present invention, the "raw molecular sieve powder" refers to the molecular sieve that has only been dried before calcination.

[0024] In a first aspect, the present invention provides a SAPO-34 molecular sieve having a cubic block morphology, each surface of the cubic block having an etched structure with a width of not less than 50 nm, and a side length of the cubic block being 1-5 μm.

[0025] In the present invention, the SAPO-34 molecular sieve refers to a molecular sieve with a chabazite-type (CHA) topological structure. The typical crystal morphology of the SAPO-34 molecular sieve is a cubic morphology, and there are also reports of SAPO-34 molecular sieves with special morphologies such as flake morphology and spherical morphology, but the grain surface of the SAPO-34 molecular sieve prepared in the prior art is relatively regular and smooth. The inventors of the present invention have found in their research that the block-shaped SAPO-34 molecular sieve with a surface having a cubic shape composed of an etched structure not less than 50 nm wide is conducive to obtaining a larger specific surface area, micropore area and micropore volume, which is conducive to having good industrial application prospects in gas adsorption separation or oxygen-containing compound conversion to light olefins.

[0026] In the present invention, the “cubic block morphology” refers to the outer contour of the SAPO-34 molecular sieve grains being in the shape of a cube as a whole, such as Figure 3 The “side length of the cube-like structure” refers to the side length of each face in the outer contour of the SAPO-34 molecular sieve crystal. The side length of the cube-like structure is 1-5 μm, preferably 2-3 μm.

[0027] In the present invention, each surface of the cube-like crystal grains of the SAPO-34 molecular sieve has an etched structure with a width of not less than 50 nm. The "etched structure" refers to the structure in which the originally smooth and complete cubic surface of the SAPO-34 molecular sieve is etched into many protrusions and grooves. This patent defines this as an etched structure. The size of the etched structure refers to the width of the small protrusions, such as Figure 3 As shown, each surface of the cube-like crystal grains of the SAPO-34 molecular sieve is stacked by etching structures. Preferably, the width of the etching structure is 50-1200nm, more preferably 50-500nm. The inventors of the present invention have found that the SAPO-34 molecular sieve having the above preferred morphology structure is conducive to optimizing the diffusion process of molecules in the pores.

[0028] In the present invention, the grain morphology of the SAPO-34 molecular sieve is obtained by scanning electron microscopy (SEM) testing. The scanning electron microscopy morphology analysis (SEM) adopts a Japanese Hitachi S4800 scanning electron microscope. Test conditions: After the sample is dried and ground, it is glued on a conductive adhesive. The acceleration voltage of the analytical electron microscope is 5.0 kV, and the magnification is 20-800000 times.

[0029] According to the present invention, the cube-like block morphology of the SAPO-34 molecular sieve with an etched structure having a surface width of not less than 50 nm is conducive to obtaining a larger specific surface area, micropore area and micropore volume, thereby facilitating the molecular sieve to have a good application effect in gas adsorption separation, or the conversion of oxygen-containing compounds to light olefins.

[0030] Preferably, the total specific surface area of ​​the SAPO-34 molecular sieve is 420-500m 2 / g, preferably 430-490m 2 The total specific surface area of ​​the SAPO-34 molecular sieve includes the matrix area and the micropore area. In a further preferred embodiment, the micropore area of ​​the SAPO-34 molecular sieve is 410-480 m 2 / g, preferably 412-470m 2 / g.

[0031] In the present invention, the SAPO-34 molecular sieve has a large total pore volume. Preferably, the total pore volume of the SAPO-34 molecular sieve is 0.18-0.25 cm 3 / g, preferably 0.185-0.24cm 3 / g.

[0032] Further preferably, the micropore volume accounts for a higher proportion of the total pore volume of the SAPO-34 molecular sieve. Preferably, the micropore volume of the SAPO-34 molecular sieve is 0.17-0.24 cm 3 / g, more preferably 0.172-0.23cm 3 / g.

[0033] According to some preferred embodiments of the present invention, the anhydrous chemical composition of the SAPO-34 molecular sieve is expressed as: mR·(Si x Al y P z )O2, wherein R is 4-dimethylaminopyridine, and m is per mole (Si x Al y P z )O2 corresponding to the mole number of 4-dimethylaminopyridine, m = 0.15-0.34. x, y, z represent the mole fractions of Si, Al, and P based on the total mole number of Si, Al, and P, respectively, wherein x = 0.1-0.25, y = 0.4-0.55, z = 0.3-0.52, and x + y + z = 1. In the present invention, the anhydrous chemical composition of the SAPO-34 molecular sieve refers to the chemical composition of the original molecular sieve powder without calculating water.

[0034] Preferably, per mole (Si x Al y P z )The molar number m of 4-dimethylaminopyridine corresponding to )O2 is 0.16-0.3.

[0035] Preferably, x=0.11-0.22, y=0.41-0.54, z=0.31-0.49, and x+y+z=1.

[0036] The second aspect of the present invention provides a method for preparing SAPO-34 molecular sieve, comprising:

[0037] (1) first mixing a combination of a phosphorus source and an aluminum source and / or a phosphorus aluminum source with a silicon source and water to obtain a mixed solution; the first mixing temperature is 70-100° C. and the time is 6-12 hours;

[0038] (2) mixing the mixed solution with 4-dimethylaminopyridine and performing hydrothermal crystallization at 180-200° C. for 72-120 h;

[0039] Wherein, the combination of the phosphorus source and the aluminum source and / or the phosphorus and aluminum in the phosphorus and aluminum source are calculated as P2O5 and Al2O3 respectively, the silicon source is calculated as SiO2, and the molar ratio of P2O5, Al2O3, SiO2, 4-dimethylaminopyridine and water is 0.8-1.2:1:0.5-1:2-10:10-100.

[0040] According to the preparation method of the present invention, 4-dimethylaminopyridine is used as a template, and the SAPO-34 molecular sieve with the above special morphology is synthesized by conventional hydrothermal synthesis method or aluminum phosphate liquid phase conversion method. The preparation method is simple and the morphology is controllable.

[0041] In the present invention, the phosphorus source and the aluminum source can be provided by a phosphorus-containing substance and an aluminum-containing substance, respectively, or by the same substance (i.e., a substance containing both phosphorus and aluminum) such as a phosphorus-aluminum source, and the present invention has no particular limitation on this. The present invention has a wide selection range for the phosphorus source, and any conventional phosphorus-containing compound that can be used for the preparation of molecular sieves in the art can be used in the present invention as long as the phosphorus element can be provided. Preferably, the phosphorus source is selected from at least one of orthophosphoric acid, phosphorous acid, ammonium hydrogen phosphate, ammonium dihydrogen phosphate and an organic phosphide, and the organic phosphide is preferably trimethyl phosphide and / or triethyl phosphide.

[0042] The present invention has no special requirements for the selection of the aluminum source, as long as it can provide aluminum elements, and those skilled in the art can select it according to actual needs. Preferably, the aluminum source is selected from at least one of aluminum salts, pseudo-boehmite, aluminum isopropoxide, aluminum hydroxide dry gel and activated alumina, and the aluminum salt can be, for example, aluminum chloride and / or aluminum sulfate.

[0043] In some preferred embodiments of the present invention, phosphorus and aluminum are provided by a phosphorus-aluminum source. The molar ratio of P in terms of P2O5 to Al in terms of Al2O3 in the phosphorus-aluminum source is 0.8-1.2, and the phosphorus-aluminum source has a phosphorus-aluminum crystal skeleton structure. Preferably, the phosphorus-aluminum source is aluminum phosphate, preferably crystalline aluminum phosphate. The present invention has no special requirements for the source of the crystalline aluminum phosphate, which can be obtained from commercial purchase or prepared by methods known in the art. Preferably, the crystalline aluminum phosphate is prepared according to the method disclosed in Example 2 of patent CN111422843B. Using the phosphorus-aluminum complex as a phosphorus source and an aluminum source to synthesize the molecular sieve of the present invention can be more conducive to shortening the feeding time and mixing time of the synthesis, and has low cost, good repeatability, high crystallinity of the molecular sieve product, and can be synthesized under a lower water-aluminum ratio, which improves the problems of low single-pot yield and high wastewater discharge caused by the high water-aluminum ratio in traditional hydrothermal synthesis.

[0044] The present invention has a wide range of choices for the silicon source, and can be any conventional choice in the art, as long as it can provide silicon. Preferably, the silicon source is selected from at least one of silica sol, active silica, solid silica gel, a silicon-containing organic compound (silicate) shown in formula I, and white carbon black.

[0045]

[0046] In formula I, R1, R2, R3 and R4 are each independently a C1-C4 alkyl group.

[0047] The silicon-containing organic compound may be, for example, tetraethyl orthosilicate, methyl orthosilicate, propyl orthosilicate, butyl orthosilicate, etc. Preferably, the silicon-containing organic compound is tetraethyl orthosilicate.

[0048] In the preparation method of the present invention, the phosphorus source, aluminum source, silicon source and water are first mixed under heating conditions, and then a template is added for hydrothermal crystallization, which helps to form the special crystal structure and grain morphology of the SAPO-34 molecular sieve. The reason may be that the pretreatment under heating conditions can affect the depolymerization rate of silicon, aluminum and phosphorus raw materials, and on this basis, the structural guidance, space filling and charge balance of the molecular sieve are further affected under the action of the template, thereby guiding a new crystal structure. Preferably, the temperature of the first mixing is 70-90°C and the time is 6-10h. Under the above preferred conditions, it is conducive to further synthesizing the SAPO-34 molecular sieve with an etched structure.

[0049] According to some preferred embodiments of the present invention, the first mixing is performed under stirring conditions. The present invention has no particular requirements for the stirring conditions, and conventional operating conditions in the art can be used as long as they are conducive to uniform mixing of the reaction raw materials.

[0050] In the present invention, 4-dimethylaminopyridine is used as a template, and the hydrothermal crystallization conditions are further controlled to facilitate the structural guidance of 4-dimethylaminopyridine. Preferably, the hydrothermal crystallization conditions include: hydrothermal crystallization at 180-190° C. for 72-96 hours. The above preferred hydrothermal crystallization conditions are used to facilitate the synthesis of SAPO-34 molecular sieves with etched structures.

[0051] The hydrothermal crystallization can be carried out in a conventional container in the art, such as a closed polytetrafluoroethylene container, and the pressure during the reaction is autogenous pressure.

[0052] In the present invention, the hydrothermal crystallization can be static crystallization or dynamic crystallization, preferably dynamic crystallization. As a condition for dynamic crystallization, the preferred rotation speed is 15-40r / min. Dynamic crystallization can be carried out in a conventional device in the art, for example, a closed polytetrafluoroethylene container can be placed in a rotary convection oven to carry out the dynamic crystallization.

[0053] In the present invention, the temperature of the first mixing can be directly raised to the hydrothermal crystallization temperature for the hydrothermal crystallization, or the mixed solution can be cooled after the first mixing, and then mixed with 4-dimethylaminopyridine, and then heated to the hydrothermal crystallization temperature. Preferably, the mixed solution is cooled to room temperature (25±5°C) after the first mixing, and then mixed with 4-dimethylaminopyridine, and then heated to the hydrothermal crystallization temperature for the hydrothermal crystallization. The above preferred embodiment is conducive to guiding the synthesis of the SAPO-34 molecular sieve topology.

[0054] According to the present invention, the phosphorus and aluminum in the phosphorus source and aluminum source are calculated as P2O5 and Al2O3 respectively, the silicon source is calculated as SiO2, and the molar ratio of P2O5, Al2O3, SiO2, 4-dimethylaminopyridine and water is 0.8-1.2:1:0.5-1:2-10:10-100, preferably 0.9-1.1:1:0.55-0.9:2.5-5:25-70.

[0055] According to the present invention, preferably, the preparation method further comprises: subjecting the hydrothermal crystallization product to solid-liquid separation, washing and drying.

[0056] The present invention has no particular requirements for the solid-liquid separation and washing methods, and can be carried out by conventional methods in the art, subject to removing unreacted raw materials in the hydrothermal crystallization product. For example, the solid-liquid separation can be filtration or centrifugation. The present invention has no particular requirements for the number of washings, and is also subject to removing unreacted raw materials in the hydrothermal crystallization product. The washing detergent can be, for example, water.

[0057] The present invention has no special requirements for the drying conditions, which are based on the drying of the molecular sieve sample, and those skilled in the art can make the selection according to actual needs.

[0058] The third aspect of the present invention provides the SAPO-34 molecular sieve prepared by the above preparation method.

[0059] The SAPO-34 molecular sieve prepared by the above method has a cubic block morphology, each surface of the cubic block has an etched structure with a width of not less than 50 nm, and the side length of the cubic block is 1-5 μm.

[0060] The fourth aspect of the present invention provides use of the SAPO-34 molecular sieve described in the first aspect or the third aspect in gas adsorption separation.

[0061] The fifth aspect of the present invention provides the use of the SAPO-34 molecular sieve described in the first aspect or the third aspect in the reaction of converting oxygen-containing compounds to produce light olefins.

[0062] The SAPO-34 molecular sieve has a special cubic etching morphology, a complete crystal structure, high crystallinity, a large specific surface area, a micropore area and a micropore volume. It can be used for gas adsorption separation and for the conversion of oxygen-containing compounds to produce light olefins, and has good industrial application prospects.

[0063] The present invention will be described in detail below through examples.

[0064] In the following examples and comparative examples, X-ray powder diffraction phase analysis (XRD) was performed using a PANalytical Empyrean diffractometer equipped with a PIXcel 3D Detector. Test conditions: Cu target, Kα radiation, Ni filter, tube voltage 40kV, tube current 40mA, scanning range 5°-50°.

[0065] In the following examples and comparative examples, scanning electron microscope (SEM) morphology analysis was performed using a Japanese Hitachi S4800 scanning electron microscope. Test conditions: After the sample was dried and ground, it was glued on a conductive adhesive. The acceleration voltage of the analysis electron microscope was 5.0 kV, and the magnification was 20-800000 times.

[0066] In the following examples and comparative examples, the contents of Si, P and Al in the prepared molecular sieve raw powder were determined by a Philips MagiX fluorescence spectrometer, and the contents of C, H and N in the prepared molecular sieve raw powder were determined by an Elementar vario EL CUBE elemental analyzer.

[0067] In the following examples, the testing instrument for BET analysis is Micromeritics ASAP 2010 adsorption instrument. Test conditions: The weighed sample is vacuumed to 1.33×10 -2 Pa, constant temperature and pressure for 15h, sample pretreatment. At liquid nitrogen temperature -196℃, the adsorption and desorption of nitrogen by the sample under different pressure ratios p / p0 were measured to obtain nitrogen adsorption-desorption isotherms. The BET specific surface area was calculated using the BET formula, and the micropore specific surface area and micropore volume of the sample were calculated using the t-plot method. The total pore volume was calculated using the adsorption at P / P0 = 0.98.

[0068] The crystalline aluminum phosphate used in the following examples and comparative examples was prepared according to the method described in Example 2 of patent CN111422843B, with a solid content of 100% and a molar ratio of P2O5 / Al2O3 of 0.99.

[0069] Example 1

[0070] Take deionized water and add it to the polytetrafluoroethylene liner, add crystalline aluminum phosphate, and then add solid silica gel (SiO2 mass fraction 90%), mix well, preheat at 80 ° C and continue stirring for 7 h, and then add 4-dimethylaminopyridine (C7H 10 N2 mass fraction 99%), stirred and mixed evenly. The added molar ratio of each component is: P2O5 / Al2O3=0.99, SiO2 / Al2O3=0.8, R / Al2O3=3, H2O / Al2O3=40.

[0071] The polytetrafluoroethylene liner containing the above reaction mixture was covered, placed in a stainless steel autoclave, sealed, and placed in a rotary convection oven with a rotation speed set to 20 r / min. Crystallization was carried out under autogenous pressure: crystallization at 180°C for 72 hours. After the crystallization was completed, the temperature was lowered to room temperature, the product was taken out, filtered, washed, and dried at 110°C for 12 hours to obtain SAPO-34 molecular sieve raw powder.

[0072] The XRD spectrum of SAPO-34 molecular sieve raw powder is shown in Figure 1 , which is a pure phase SAPO-34 molecular sieve. SEM photos are shown in Figure 2 The morphology of the sample was confirmed to be a cubic etched morphology. Each surface of the cube consisted of an etched structure with a width of 70-280 nm, and the side length of the cube was about 1.9-3 μm.

[0073] The obtained SAPO-34 molecular sieve raw powder was subjected to XRF and CHN element analysis, and its chemical composition was determined to be 0.18R·(Si 0.195 Al 0.454 P 0.351 )O2, R is 4-dimethylaminopyridine.

[0074] The obtained SAPO-34 molecular sieve raw powder was calcined at 550°C for 3h and then subjected to BET analysis. The results of its surface area and pore volume are shown in Table 1. The obtained SAPO-34 has good micropore area and micropore volume, indicating that its crystal structure is complete and its crystallinity is high.

[0075] Example 2

[0076] Take deionized water and add it to the polytetrafluoroethylene liner, add crystalline aluminum phosphate (solid content 100%, P2O5 / Al2O3=0.99), then add solid silica gel (SiO2 mass fraction 90%), mix well, preheat at 70°C and continue stirring for 10h, cool to room temperature, and then add 4-dimethylaminopyridine (C7H 10 N2 mass fraction 99%), stirred and mixed evenly. The added molar ratio of each component is: P2O5 / Al2O3=0.99, SiO2 / Al2O3=0.7, R / Al2O3=4, H2O / Al2O3=40.

[0077] The polytetrafluoroethylene liner containing the above reaction mixture was covered, placed in a stainless steel autoclave, sealed, and placed in a rotary convection oven with a rotation speed set to 20 r / min. Crystallization was carried out under autogenous pressure: crystallization at 185°C for 80 hours. After the crystallization was completed, the temperature was lowered to room temperature, the product was taken out, filtered, washed, and dried at 110°C for 12 hours to obtain SAPO-34 molecular sieve raw powder.

[0078] XRD analysis of the SAPO-34 molecular sieve powder confirmed that it was pure phase SAPO-34 molecular sieve. SEM photos are shown in Figure 3 The morphology of the cube is confirmed to be a cubic etched morphology. Each surface of the cube is composed of an etched structure with a width of 50-300 nm, and the side length of the cube is about 2-2.3 μm.

[0079] The obtained SAPO-34 molecular sieve raw powder was subjected to XRF and CHN element analysis, and its chemical composition was 0.23R·(Si 0.173 Al 0.49 P 0.337 )O2, R is 4-dimethylaminopyridine.

[0080] The obtained SAPO-34 molecular sieve raw powder was calcined at 550°C for 3h and then subjected to BET analysis. The results of its surface area and pore volume are shown in Table 1. The obtained SAPO-34 has good micropore area and micropore volume, indicating that its crystal structure is complete and its crystallinity is high.

[0081] Example 3

[0082] Take deionized water and add it to the polytetrafluoroethylene liner, add crystalline aluminum phosphate, then add silica sol (SiO2 mass fraction 30%), mix well, preheat at 80 ° C and continue stirring for 9 h, then add 4-dimethylaminopyridine (C7H 10 N2 mass fraction 99%), stirred and mixed evenly. The added molar ratio of each component is: P2O5 / Al2O3=0.99, SiO2 / Al2O3=0.6, R / Al2O3=5, H2O / Al2O3=40.

[0083] The polytetrafluoroethylene liner containing the above reaction mixture was covered, placed in a stainless steel autoclave, sealed, and placed in a rotary convection oven with a rotation speed set to 20 r / min. Crystallization was carried out under autogenous pressure: crystallization at 190°C for 85 hours. After the crystallization was completed, the temperature was lowered to room temperature, the product was taken out, filtered, washed, and dried at 110°C for 12 hours to obtain SAPO-34 molecular sieve raw powder.

[0084] The XRD spectrum of SAPO-34 molecular sieve raw powder is shown in Figure 4 , which is a pure phase SAPO-34 molecular sieve. SEM photos are shown in Figure 5 The morphology of the cube is confirmed to be a cubic etched morphology. Each surface of the cube is composed of an etched structure with a width of 200-1200 nm, and the side length of the cube is about 3-3.4 μm.

[0085] The obtained SAPO-34 molecular sieve raw powder was subjected to XRF and CHN element analysis, and its chemical composition was 0.25R·(Si 0.158 Al 0.521 P 0.321 )O2, R is 4-dimethylaminopyridine.

[0086] The obtained SAPO-34 molecular sieve raw powder was calcined at 550°C for 3h and subjected to BET analysis. The results of its surface area and pore volume are shown in Table 1. The obtained SAPO-34 has good micropore area and micropore volume, indicating that its crystal structure is complete and its crystallinity is high.

[0087] Example 4

[0088] Take deionized water and add it to the polytetrafluoroethylene liner, add crystalline aluminum phosphate (solid content 100%, P2O5 / Al2O3=0.99), then add silica sol (SiO2 mass fraction 30%), mix well, preheat at 90℃ and continue stirring for 6h, cool to room temperature, and then add 4-dimethylaminopyridine (C7H 10 N2 mass fraction 99%), stirred and mixed evenly. The added molar ratio of each component is: P2O5 / Al2O3=0.99, SiO2 / Al2O3=0.9, R / Al2O3=4, H2O / Al2O3=40.

[0089] The polytetrafluoroethylene liner containing the above reaction mixture was covered, placed in a stainless steel autoclave, sealed, and placed in a rotary convection oven with a rotation speed set to 20 r / min. Crystallization was carried out under autogenous pressure: crystallization at 190°C for 80 hours. After the crystallization was completed, the temperature was lowered to room temperature, the product was taken out, filtered, washed, and dried at 110°C for 12 hours to obtain SAPO-34 molecular sieve raw powder.

[0090] The XRD spectrum of SAPO-34 molecular sieve raw powder is shown in Figure 6 , which is a pure phase SAPO-34 molecular sieve. SEM photos are shown in Figure 7 The morphology of the cube is confirmed to be a cubic etched morphology. Each surface of the cube is composed of an etched structure with a width of 50-1000 nm, and the side length of the cube is about 2.9-3.9 μm.

[0091] The obtained SAPO-34 molecular sieve raw powder was subjected to XRF and CHN element analysis, and its chemical composition was 0.25R·(Si 0.201 Al 0.443 P 0.356 )O2, R is 4-dimethylaminopyridine.

[0092] The SAPO-34 molecular sieve raw powder was calcined at 550°C for 3h and then subjected to BET analysis. The results of its surface area and pore volume are shown in Table 1. The obtained SAPO-34 has good micropore area and micropore volume, indicating that its crystal structure is complete and the crystallinity is high.

[0093] Comparative Example 1

[0094] The molecular sieve was synthesized according to the method of Example 3, except that the SiO2 / Al2O3 ratio in this comparative example was 0.3 and the preheating and stirring step was not performed.

[0095] Deionized water was added to the polytetrafluoroethylene liner, followed by crystalline aluminum phosphate (solid content 100%, P2O5 / Al2O3=0.99), silica sol (SiO2 mass fraction 30%), and 4-dimethylaminopyridine (C7H 10 N2 mass fraction 99%), stirred and mixed evenly. The added molar ratio of each component is: P2O5 / Al2O3=0.99, SiO2 / Al2O3=0.3, R / Al2O3=5, H2O / Al2O3=40.

[0096] The polytetrafluoroethylene liner containing the above reaction mixture was covered, placed in a stainless steel autoclave, sealed, and placed in a rotary convection oven with a rotation speed set to 20 r / min. Crystallization was carried out under autogenous pressure: crystallization at 190°C for 85 hours. After the crystallization was completed, the temperature was lowered to room temperature, the product was taken out, filtered, washed, and dried at 110°C for 12 hours to obtain a solid sample.

[0097] XRD analysis of the obtained solid sample confirmed that it was a mixed crystal phase of other molecular sieve structures and that a pure phase SAPO-34 molecular sieve could not be synthesized.

[0098] Comparative Example 2

[0099] The SAPO-34 molecular sieve was synthesized according to Example 1 in patent CN109467100B. The synthesized SAPO-34 molecular sieve had a cubic structure, a smooth surface, and no etched structure.

[0100] Table 1

[0101]

[0102]

[0103] It can be seen from the above examples and comparative examples that the SAPO-34 molecular sieve prepared in the examples of the present invention has a special cubic-like etching morphology, the cubic-like size is 2-3 μm, and each surface of the cube is composed of an etching morphology with a minimum width of 50 nm. The SAPO-34 molecular sieve has a complete crystal structure, high crystallinity, a large specific surface area, micropore area and micropore volume, can be used for gas adsorption separation, and can also be used for the conversion of oxygen-containing compounds to light olefins, and has good industrial application prospects.

[0104] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A SAPO-34 molecular sieve, characterized in that: The SAPO-34 molecular sieve has a cubic block morphology, each surface of the cubic block has an etched structure with a width of no less than 50 nm, and the side length of the cubic block is 1-5 μm.

2. The SAPO-34 molecular sieve according to claim 1, wherein The side length of the cube-like structure is 2-3 μm; Preferably, each surface of the cube-like structure has an etched structure with a width of 50-1200 nm.

3. The SAPO-34 molecular sieve according to claim 1 or 2, wherein: The total specific surface area of ​​the SAPO-34 molecular sieve is 420-500m 2 / g; Preferably, the micropore area of ​​the SAPO-34 molecular sieve is 410-480 m 2 / g; Preferably, the total pore volume of the SAPO-34 molecular sieve is 0.18-0.25 cm 3 / g; Preferably, the micropore volume of the SAPO-34 molecular sieve is 0.17-0.24 cm 3 / g.

4. The SAPO-34 molecular sieve according to any one of claims 1 to 3, wherein: The anhydrous chemical composition of the SAPO-34 molecular sieve is expressed as: mR·(Si x Al y P z )O2, Wherein, R is 4-dimethylaminopyridine, m is per mole (Si x Al y P z ) The number of moles of 4-dimethylaminopyridine corresponding to O2, m = 0.15-0.34; x, y, z represent the molar fractions of Si, Al, and P based on the total molar number of Si, Al, and P, respectively, wherein x=0.1-0.25, y=0.4-0.55, z=0.3-0.52, and x+y+z=1.

5. A method for preparing SAPO-34 molecular sieve, comprising: (1) a phosphorus source, an aluminum source, a silicon source and water are first mixed to obtain a mixed solution; the first mixing temperature is 70-100° C. and the time is 6-12 hours; (2) mixing the mixed solution with 4-dimethylaminopyridine and performing hydrothermal crystallization at 180-200° C. for 72-120 h; The phosphorus and aluminum in the phosphorus source and aluminum source are calculated as P2O5 and Al2O3 respectively, and the silicon source is calculated as SiO2. The amounts of the phosphorus source, aluminum source and silicon source are such that the molar ratio of P2O5, Al2O3, SiO2, 4-dimethylaminopyridine and water is 0.8-1.2:1:0.5-1:2-10:10-100.

6. The preparation method according to claim 5, wherein: The phosphorus source is selected from at least one of orthophosphoric acid, phosphorous acid, ammonium hydrogen phosphate, ammonium dihydrogen phosphate and an organic phosphide, and the organic phosphide is preferably trimethyl phosphide and / or triethyl phosphide; and / or, The aluminum source is selected from at least one of aluminum salts, pseudo-boehmite, aluminum isopropoxide, aluminum hydroxide and anhydrous aluminum oxide, and the aluminum salt is preferably aluminum chloride and / or aluminum sulfate; and / or, The phosphorus source and the aluminum source are provided by a phosphorus-aluminum source, and the phosphorus-aluminum source is preferably crystalline aluminum phosphate; and / or, The silicon source is selected from at least one of silica sol, silicon dioxide, silica gel, a silicon-containing organic compound shown in formula I, and white carbon black. In formula I, R1, R2, R3 and R4 are each independently a C1-C4 alkyl group, Preferably, the silicon-containing organic compound is tetraethyl orthosilicate.

7. The preparation method according to claim 5 or 6, wherein: The first mixing is performed under stirring conditions; Preferably, the temperature of the first mixing is 70-90°C and the time is 6-10h; Preferably, the hydrothermal crystallization conditions include: hydrothermal crystallization at 180-190° C. for 72-90 h.

8. The preparation method according to any one of claims 5 to 7, wherein: The amounts of the phosphorus source, aluminum source and silicon source are such that the molar ratio of P2O5, Al2O3, SiO2, 4-dimethylaminopyridine and water is 0.9-1.1:1:0.55-0.9:2.5-5:25-70.

9. SAPO-34 molecular sieve prepared by the preparation method according to any one of claims 5 to 8.

10. Use of the SAPO-34 molecular sieve according to any one of claims 1 to 4 and 9 in gas adsorption separation.

11. Use of the SAPO-34 molecular sieve according to any one of claims 1 to 4 and 9 in the reaction of converting oxygen-containing compounds to light olefins.

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