CN108217686B - Synthesis method of SAPO-34 molecular sieve with surface defects - Google Patents
Synthesis method of SAPO-34 molecular sieve with surface defects Download PDFInfo
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- 239000002808 molecular sieve Substances 0.000 title claims abstract description 106
- URGAHOPLAPQHLN-UHFFFAOYSA-N sodium aluminosilicate Chemical compound [Na+].[Al+3].[O-][Si]([O-])=O.[O-][Si]([O-])=O URGAHOPLAPQHLN-UHFFFAOYSA-N 0.000 title claims abstract description 106
- 230000007547 defect Effects 0.000 title claims abstract description 34
- 238000001308 synthesis method Methods 0.000 title description 4
- 238000000034 method Methods 0.000 claims abstract description 48
- 238000005216 hydrothermal crystallization Methods 0.000 claims abstract description 30
- 239000003795 chemical substances by application Substances 0.000 claims abstract description 17
- 229910001868 water Inorganic materials 0.000 claims abstract description 15
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 13
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 13
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims abstract description 13
- 229910052782 aluminium Inorganic materials 0.000 claims abstract description 13
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 13
- 239000011574 phosphorus Substances 0.000 claims abstract description 13
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 13
- 239000010703 silicon Substances 0.000 claims abstract description 13
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 13
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims abstract description 9
- 229910052593 corundum Inorganic materials 0.000 claims abstract description 7
- 229910001845 yogo sapphire Inorganic materials 0.000 claims abstract description 7
- 230000002194 synthesizing effect Effects 0.000 claims abstract description 4
- 238000002425 crystallisation Methods 0.000 claims description 37
- 230000008025 crystallization Effects 0.000 claims description 37
- 238000006243 chemical reaction Methods 0.000 claims description 36
- ZMANZCXQSJIPKH-UHFFFAOYSA-N Triethylamine Chemical compound CCN(CC)CC ZMANZCXQSJIPKH-UHFFFAOYSA-N 0.000 claims description 33
- 239000013078 crystal Substances 0.000 claims description 24
- 230000015572 biosynthetic process Effects 0.000 claims description 14
- 238000003786 synthesis reaction Methods 0.000 claims description 14
- 229940073455 tetraethylammonium hydroxide Drugs 0.000 claims description 11
- LRGJRHZIDJQFCL-UHFFFAOYSA-M tetraethylazanium;hydroxide Chemical compound [OH-].CC[N+](CC)(CC)CC LRGJRHZIDJQFCL-UHFFFAOYSA-M 0.000 claims description 11
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 6
- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 claims description 5
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 4
- 239000000126 substance Substances 0.000 claims description 4
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 3
- VXAUWWUXCIMFIM-UHFFFAOYSA-M aluminum;oxygen(2-);hydroxide Chemical compound [OH-].[O-2].[Al+3] VXAUWWUXCIMFIM-UHFFFAOYSA-M 0.000 claims description 3
- 229910052681 coesite Inorganic materials 0.000 claims description 2
- 229910052906 cristobalite Inorganic materials 0.000 claims description 2
- 239000000377 silicon dioxide Substances 0.000 claims description 2
- 229910052682 stishovite Inorganic materials 0.000 claims description 2
- 229910052905 tridymite Inorganic materials 0.000 claims description 2
- 238000002156 mixing Methods 0.000 claims 2
- 230000003197 catalytic effect Effects 0.000 abstract description 11
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 36
- 239000000047 product Substances 0.000 description 15
- 229910052799 carbon Inorganic materials 0.000 description 12
- 230000000052 comparative effect Effects 0.000 description 12
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 9
- 239000005977 Ethylene Substances 0.000 description 9
- 238000001878 scanning electron micrograph Methods 0.000 description 9
- JRZJOMJEPLMPRA-UHFFFAOYSA-N olefin Natural products CCCCCCCC=C JRZJOMJEPLMPRA-UHFFFAOYSA-N 0.000 description 8
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 7
- 239000000203 mixture Substances 0.000 description 7
- 239000011148 porous material Substances 0.000 description 7
- 238000005406 washing Methods 0.000 description 6
- 238000001035 drying Methods 0.000 description 5
- 238000002360 preparation method Methods 0.000 description 5
- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 description 5
- 125000004805 propylene group Chemical group [H]C([H])([H])C([H])([*:1])C([H])([H])[*:2] 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- 150000001336 alkenes Chemical class 0.000 description 4
- 239000003054 catalyst Substances 0.000 description 4
- 239000003245 coal Substances 0.000 description 3
- 238000001816 cooling Methods 0.000 description 3
- 239000003208 petroleum Substances 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 239000007795 chemical reaction product Substances 0.000 description 2
- 230000008021 deposition Effects 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000035484 reaction time Effects 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 238000000547 structure data Methods 0.000 description 2
- 230000001133 acceleration Effects 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 150000001993 dienes Chemical class 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000005008 domestic process Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 239000011737 fluorine Substances 0.000 description 1
- 229910052731 fluorine Inorganic materials 0.000 description 1
- -1 fluorine ions Chemical class 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 230000000877 morphologic effect Effects 0.000 description 1
- 239000003345 natural gas Substances 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 239000004033 plastic Substances 0.000 description 1
- 229920003023 plastic Polymers 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B39/00—Compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites; Their preparation; After-treatment, e.g. ion-exchange or dealumination
- C01B39/54—Phosphates, e.g. APO or SAPO compounds
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J29/00—Catalysts comprising molecular sieves
- B01J29/82—Phosphates
- B01J29/84—Aluminophosphates containing other elements, e.g. metals, boron
- B01J29/85—Silicoaluminophosphates (SAPO compounds)
-
- B01J35/613—
-
- B01J35/617—
-
- B01J35/633—
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B37/00—Compounds having molecular sieve properties but not having base-exchange properties
- C01B37/06—Aluminophosphates containing other elements, e.g. metals, boron
- C01B37/08—Silicoaluminophosphates (SAPO compounds), e.g. CoSAPO
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C1/00—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon
- C07C1/20—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon starting from organic compounds containing only oxygen atoms as heteroatoms
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/01—Particle morphology depicted by an image
- C01P2004/03—Particle morphology depicted by an image obtained by SEM
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/12—Surface area
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C2529/00—Catalysts comprising molecular sieves
- C07C2529/82—Phosphates
- C07C2529/84—Aluminophosphates containing other elements, e.g. metals, boron
- C07C2529/85—Silicoaluminophosphates (SAPO compounds)
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P30/00—Technologies relating to oil refining and petrochemical industry
- Y02P30/20—Technologies relating to oil refining and petrochemical industry using bio-feedstock
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P30/00—Technologies relating to oil refining and petrochemical industry
- Y02P30/40—Ethylene production
Abstract
The invention provides a method for synthesizing an SAPO-34 molecular sieve with surface defects. The method comprises the following steps: silicon source, aluminum source, phosphorus source, template agent and water are SiO according to the molar ratio2：Al2O3：P2O5：R：H2O ═ 0.5 to 0.8: 1: (0.8-1.2): (1-3): (40-80), and then carrying out dynamic hydrothermal crystallization at the low temperature of 190 ℃ at 170 ℃ for 2-15h to obtain the cubic SAPO-34 molecular sieve with surface defects. The SAPO-34 molecular sieve product obtained according to the technical scheme provided by the invention has surface defects and excellent methanol-to-olefin catalytic performance.
Description
Technical Field
The invention relates to a synthesis method of a cubic SAPO-34 molecular sieve with surface defects, belonging to the technical field of catalyst preparation.
Background
Ethylene and propylene as basic organic raw materials in modern chemical industry can be used for producing various chemical products such as plastics and the like, and the demand of the ethylene and the propylene is increasing. The traditional diene production process is characterized by being excessively dependent on petroleum resources, and the development of a novel process route for preparing ethylene and propylene becomes a research focus under the background that the supply of the petroleum resources is unstable and the price is continuously increased at present. The energy structure of China is 'rich in coal, short of oil and less in gas', and the domestic process for preparing methanol from coal is very mature, so that the process for preparing low-carbon olefin from methanol has important significance for reducing the dependence on petroleum and maintaining the energy safety of China. The methanol-to-olefin process generally refers to a process technology for producing low-carbon olefins such as ethylene and propylene by using methanol produced from natural gas or coal under the action of a catalyst.
So far, the molecular sieve frequently used in the process of preparing olefin from methanol is a silicoaluminophosphate molecular sieve (SAPO-n), in particular an SAPO-34 molecular sieve, which is widely applied to a reaction process of preparing olefin from methanol due to a series of characteristics of moderate-strength acidity, small air-interface diameter, good selection effect, ethylene and propylene as main reaction products, high conversion rate of raw material methanol and the like.
However, at present, scholars at home and abroad usually introduce a macromolecular template agent and fluorine ions into a synthesis system or prepare the SAPO-34 molecular sieve by adopting an in-situ crystallization mode when preparing the SAPO-34. When a series of SAPO-34 molecular sieves with different crystal grain morphologies need to be obtained in the preparation process, the SAPO-34 molecular sieve synthesis template agent needs to be changed, and the feeding silica-alumina ratio needs to be changed or post-treatment modification and other ways need to be realized. Therefore, the existing methods for preparing the SAPO-34 molecular sieve at home and abroad generally have the defects of high cost, complex process and the like, and the catalytic performance of the SAPO-34 molecular sieve prepared by the method, such as the ethylene selectivity, the reaction life and the carbon content of the SAPO-34 molecular sieve in the MTO reaction, is not excellent. In addition, if a series of SAPO-34 molecular sieves with different crystal grain morphologies need to be prepared, a mode of changing the template agent and feeding silica-alumina ratio of SAPO-34 molecular sieve synthesis or a mode of carrying out aftertreatment modification is needed to obtain a series of SAPO-34 molecular sieves with different crystal grain morphologies, and the modulation process is complicated and is not easy to operate.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a method for synthesizing a cubic SAPO-34 molecular sieve with surface defects. The SAPO-34 molecular sieve product synthesized by the method has specific morphological characteristics and excellent catalytic performance for preparing olefin from methanol.
In order to achieve the purpose, the invention provides a method for synthesizing a cubic SAPO-34 molecular sieve with surface defects, which comprises the following steps:
silicon source, aluminum source, phosphorus source, template agent and water are SiO according to the molar ratio2：Al2O3：P2O5：R：H2O ═ 0.5 to 0.8: 1: (0.8-1.2): (1-3): (40-80) after the mixture is mixed, dynamic hydrothermal crystallization is carried out at the low temperature of 190 ℃ for 2-15h to obtain the cubic morphology with surface defectsSAPO-34 molecular sieve. In the technical scheme provided by the invention, the dynamic crystallization process needs to have the characteristics of low crystallization temperature and short crystallization time at the same time.
In the above method, preferably, the crystallization temperature is controlled to be 175-185 ℃ and the crystallization time is controlled to be 3-8h when the dynamic hydrothermal crystallization is performed.
The research of the invention finds that: the grain morphology of the SAPO-34 molecular sieve has an important influence on the catalytic performance of the SAPO-34 molecular sieve. The SAPO-34 molecular sieve prepared by the synthesis method provided by the invention has the advantages that the crystal grains are mainly in a cubic shape, and the surface of the cubic shape is not smooth but has surface defects. Such as SAPO-34 molecular sieves shown in figures 2-4. Compared with the smooth surface morphology of the common SAPO-34 molecular sieve, the crystal grain morphology with surface defects can increase the mesoporous volume and the large pore volume of the molecular sieve, is favorable for improving the carbon capacity of the SAPO-34 molecular sieve in the reaction process, and can further prolong the reaction life. In addition, the crystal morphology with surface defects can also effectively improve the catalytic performance of the SAPO-34 molecular sieve, for example, the selectivity, the reaction life and the carbon capacity of the SAPO-34 molecular sieve for low-carbon olefin in the MTO reaction can be improved.
In the above method, preferably, the method further comprises: in the synthesis process, keeping the mole ratio of the silicon source, the aluminum source, the phosphorus source, the template agent and the water unchanged, and only adjusting the condition of the dynamic hydrothermal crystallization to obtain SAPO-34 molecular sieves with different crystal grain morphologies; wherein the conditions of the dynamic hydrothermal crystallization comprise crystallization temperature and crystallization time.
By adopting the technical scheme provided by the invention, in the synthesis process, SAPO-34 molecular sieve products with different crystal grain appearances and/or pore structure properties can be obtained by only adjusting the conditions of dynamic hydrothermal crystallization without changing the material ratio of an SAPO-34 molecular sieve synthesis system and adding other additives. When the conditions of the dynamic hydrothermal crystallization are changed, the morphology of the surface defects of the SAPO-34 molecular sieve can be changed. For example, when the crystallization temperature is 175 ℃ and the crystallization time is 8 hours, the surface defects can be uniformly distributed on the surfaces of the SAPO-34 molecular sieve grains. When the crystallization temperature is 180 ℃ and the crystallization time is 6h, the surface defects are mainly and intensively distributed in the opposite triangular regions of the surfaces of the SAPO-34 molecular sieve grains (as shown in figure 3). The crystallization temperature is 185 ℃, and the crystallization time is 3 hours, the surface defects are mainly concave in an hourglass shape. When a series of SAPO-34 molecular sieve products with different morphologies and/or pore structure properties need to be prepared, the technical scheme provided by the invention only needs to modulate the condition of dynamic hydrothermal crystallization, and the operation process is simple and convenient.
In the above method, preferably, the method further comprises: and in the synthesis process, keeping the mole ratio of the silicon source, the aluminum source, the phosphorus source, the template agent and the water unchanged, and obtaining the SAPO-34 molecular sieves with different crystal grain shapes only by adjusting the crystallization temperature and the crystallization time of the dynamic hydrothermal crystallization.
According to the technical scheme provided by the invention, when SAPO-34 molecular sieves with different crystal grain morphologies are required to be prepared, under the condition of the same proportioning of a feeding system, the crystal grain morphology of a synthesized SAPO-34 molecular sieve product can be modulated only by changing the condition of dynamic hydrothermal crystallization, so that the SAPO-34 molecular sieves with different crystal grain morphologies can be obtained. The purpose of modulating the molecular sieve pore structure can be realized by modulating the crystal grain morphology, and the MTO catalytic reaction performance of the molecular sieve can be finally improved. After the crystal grain morphology of the SAPO-34 molecular sieve is changed, the external specific surface area, the meso/macroporous volume and the MTO reaction performance of the molecular sieve can be correspondingly changed.
In the above method, the dynamic hydrothermal crystallization is usually carried out by raising the temperature from room temperature to a predetermined crystallization temperature.
The method of dynamic hydrothermal crystallization according to the present invention is not particularly limited, and for example, dynamic hydrothermal crystallization may be performed using a rotary reactor or a stirred reactor, but is not limited thereto.
In the above method, preferably, the silicon source includes silica sol. The silica sol may be an alkaline silica sol.
In the above method, preferably, the aluminum source comprises pseudoboehmite.
In the above method, preferably, the phosphorus source comprises phosphoric acid.
In the above method, preferably, the template includes triethylamine and tetraethylammonium hydroxide.
In the above method, preferably, in the template, the molar ratio of the triethylamine to the tetraethylammonium hydroxide is (1-70): 1; more preferably 50: 1.
In the above method, preferably, the method further comprises the steps of cooling, washing and drying the product after the dynamic hydrothermal crystallization is finished.
In the above method, preferably, when the product is cooled, the product is left at room temperature for natural cooling.
In the above method, preferably, when the product is washed, the washing is performed by a pouring method.
In the above method, preferably, the method comprises the steps of:
the silicon source, the aluminum source, the phosphorus source, the template agent and the water are SiO according to the molar ratio2：Al2O3：P2O5：R：H2O ═ 0.5 to 0.8: 1: (0.8-1.2): (1-3): (40-80), and then carrying out dynamic hydrothermal crystallization, cooling, washing and drying to obtain the SAPO-34 molecular sieve; wherein the content of the first and second substances,
the silicon source, the aluminum source and the phosphorus source are respectively made of SiO2、Al2O3、P2O5The template agent comprises triethylamine and tetraethyl ammonium hydroxide, and the molar ratio of the triethylamine to the tetraethyl ammonium hydroxide is (1-70): 1;
when the dynamic hydrothermal crystallization is carried out, the crystallization temperature is controlled to be 175-185 ℃, and the crystallization time is controlled to be 3-8 h.
The invention also provides a cubic SAPO-34 molecular sieve with surface defects, which is prepared by the method.
The invention also provides application of the cubic SAPO-34 molecular sieve with the surface defects in a methanol-to-olefin reaction.
The invention has the beneficial effects that:
1) according to the technical scheme provided by the invention, the proportion of a synthesis system is not required to be changed in the synthesis process, and the crystal grain appearance of the synthesized SAPO-34 molecular sieve product can be modulated only by changing the condition of dynamic hydrothermal crystallization, so that a series of SAPO-34 molecular sieves with different crystal grain appearances can be obtained; correspondingly, the external specific surface area, the meso/macroporous volume and the MTO reaction performance of the SAPO-34 molecular sieve can be changed.
2) The SAPO-34 molecular sieve product synthesized according to the technical scheme provided by the invention has surface defects and excellent catalytic performance.
3) The SAPO-34 molecular sieve product synthesized according to the technical scheme provided by the invention can be used as a catalyst for preparing low-carbon olefin through methanol catalytic conversion, and has longer reaction life and low-carbon olefin selectivity compared with the ordinary commercially available SAPO-34 molecular sieve.
Drawings
FIG. 1 is an XRD pattern of different SAPO-34 molecular sieve samples;
FIG. 2 is a SEM image of SAPO-34 molecular sieve provided in example 1;
FIG. 3 is a SEM image of SAPO-34 molecular sieve provided in example 2;
FIG. 4 is a SEM image of SAPO-34 molecular sieve provided in example 3;
FIG. 5 is a SEM image of the SAPO-34 molecular sieve obtained after prolonging the crystallization time of example 2 to 24 hours;
FIG. 6 is a SEM image of the SAPO-34 molecular sieve provided by comparative example 1;
FIG. 7 is a graph of MTO reaction methanol conversion versus reaction time for different SAPO-34 molecular sieves.
Detailed Description
The technical solutions of the present invention will be described in detail below in order to clearly understand the technical features, objects, and advantages of the present invention, but the present invention is not limited to the practical scope of the present invention.
The apparatus used in the following embodiments is as follows:
1) the model of an X-ray diffractometer used for measuring the phase and relative crystallinity of the SAPO-34 molecular sieve is a Panalytical X' Pert Powder diffractometer, the test voltage is 40kV, the test current is 40mA, and the test range is 5-50 degrees.
2) The shape analysis of the SAPO-34 molecular sieve crystal grains adopts the types of a Scanning Electron Microscope (SEM): the Quanta 200F field emission scanning electron microscope has the acceleration voltage of 200V-30kV, the resolution of 1.2nm and the magnification of 25-200K.
3) SAPO-34 molecular sieve meso/macroporous structure analysis was performed using TriStarII3020 adsorber and AUTOPORE IV9500 (Micromeritics, USA), respectively, manufactured by Micromeritics, USA.
4) The MTO reaction performance of the SAPO-34 molecular sieve can be evaluated by adopting a fixed bed micro-reverse evaluation device commonly used in the field. The reaction products can be analyzed in real time and the methanol conversion and product selectivity calculated. The carbon deposition amount of the catalyst can be analyzed by a thermogravimetric method.
Example 1
This example provides a SAPO-34 molecular sieve with excellent catalytic properties. The synthesis of the SAPO-34 molecular sieve provided in this example comprises the following steps:
1) preparation of the reaction System
42.75g of pseudo-boehmite was added to 300g of deionized water, and the mixture was dispersed with stirring in a water bath at 30 ℃. Then 65.56g of phosphoric acid is slowly added into the mixture, and the mixture is stirred for 30min to form gel. Further, 33.24g of silica sol was added thereto, and the mixture was stirred for 1 hour. Finally, 85.89g of mixed template agent (the used mixed template agent is a mixture of triethylamine and tetraethylammonium hydroxide, wherein the molar ratio of the triethylamine to the tetraethylammonium hydroxide is 50:1) is added, and the mixture is stirred for 1.5h to obtain a reaction system.
2) Putting the reaction system into a pressure-resistant reaction kettle for dynamic hydrothermal crystallization
When dynamic hydrothermal crystallization is carried out, the temperature of the dynamic hydrothermal crystallization is 175 ℃, and the crystallization time is 8 h.
3) After crystallization, the SAPO-34 molecular sieve is obtained after washing, drying and roasting.
Example 2
This example provides a SAPO-34 molecular sieve with excellent catalytic properties. The synthesis of the SAPO-34 molecular sieve provided in this example comprises the following steps:
1) preparation of the reaction System
The reaction system in this example was prepared in the same manner as in example 1, that is, the raw materials and the feed ratio used in this example were the same as in example 1.
2) Putting the reaction system into a pressure-resistant reaction kettle for dynamic hydrothermal crystallization
When the dynamic hydrothermal crystallization is carried out, the temperature of the dynamic hydrothermal crystallization is 180 ℃, and the crystallization time is 6 hours.
3) After crystallization, the SAPO-34 molecular sieve is obtained after washing, drying and roasting.
Example 3
This example provides a SAPO-34 molecular sieve with excellent catalytic properties. The synthesis of the SAPO-34 molecular sieve provided in this example comprises the following steps:
1) preparation of the reaction System
The reaction system in this example was prepared as in example 1.
2) Putting the reaction system into a pressure-resistant reaction kettle for dynamic hydrothermal crystallization
When the dynamic hydrothermal crystallization is carried out, the temperature of the dynamic hydrothermal crystallization is 185 ℃, and the crystallization time is 3 hours.
3) After crystallization, the SAPO-34 molecular sieve is obtained after washing, drying and roasting.
The results of testing the SAPO-34 molecular sieves provided in examples 1-3 are shown in tables 1 and 2, figures 2 to 4. From the examples 1 to 3, it can be seen that the technical scheme provided by the invention can obtain SAPO-34 molecular sieve products with different crystal grain morphologies and pore structure properties by changing the dynamic hydrothermal crystallization conditions without changing the material ratio of the synthesis system of the SAPO-34 molecular sieve (i.e. the molar ratio of the silicon source, the aluminum source, the phosphorus source, the template and the water is constant).
The crystallization time in example 2 was extended to 24 hours to obtain a SAPO-34 molecular sieve having a different surface morphology than in examples 1-3 (see figure 5 of the scanning electron micrograph).
Comparative example 1
This comparative example provides a sample of a conventional commercially available SAPO-34 molecular sieve purchased from boen scientific ltd, beijing.
The SAPO-34 molecular sieve samples provided in examples 1-3 and comparative example 1 above were subjected to the relevant tests and characterizations, respectively, and the results are shown in table 1, table 2 and fig. 1-4, 6 and 7.
TABLE 1 pore Structure data for different SAPO-34 molecular sieve samples
As can be seen from the pore structure data shown in table 1: examples 1-3 provide SAPO-34 molecular sieves with surface defect sites having higher external specific surface area, mesoporous volume, and macroporous volume than SAPO-34 molecular sieves of conventional commercial morphology (comparative example 1).
TABLE 2 ethylene selectivity and carbon deposition data for different SAPO-34 molecular sieve MTO reactions
| Ethylene selectivity, wt. -%) | Reaction Life, min | The carbon content% | |
| Example 1 | 49.96 | 850 | 18.79 |
| Example 2 | 52.62 | 1095 | 20.39 |
| Example 3 | 52.86 | 1335 | 21.75 |
| Comparative example 1 | 47.14 | 720 | 17.64 |
From the results of Methanol To Olefin (MTO) reaction evaluations (as shown in table 2 and fig. 7, fig. 7 is a graph of MTO reaction methanol conversion versus reaction time for SAPO-34 molecular sieve samples provided in examples 1-3 and comparative example 1): compared with the SAPO-34 molecular sieve with the conventional commercially available morphology (comparative example 1), the SAPO-34 molecular sieve with the surface defect sites provided by the above examples 1-3 has the advantages of obviously prolonged reaction life, improved carbon-containing capacity, improved selectivity of the main product ethylene and excellent catalytic performance.
FIG. 1 is an XRD pattern of the SAPO-34 molecular sieves provided in examples 1-3 and comparative example 1, from which it can be seen that the SAPO-34 molecular sieves provided in examples 1-3 and comparative example 1 are both phase pure SAPO-34 molecular sieves.
FIGS. 2-4 are scanning electron micrographs of SAPO-34 molecular sieves provided in examples 1-3. FIG. 5 is a scanning electron micrograph of the SAPO-34 molecular sieve obtained by prolonging the crystallization time of example 2 to 24 hours. FIG. 6 is a scanning electron micrograph of the SAPO-34 molecular sieve provided in comparative example 1. As can be seen from fig. 2-4: the SAPO-34 molecular sieve obtained in the example 1 is basically in a cubic shape, but crystal grains have a plurality of surface defects, the surfaces of the crystal grains are rough, and meanwhile, the surface defects are uniformly distributed on the surfaces of the crystal grains; the SAPO-34 molecular sieve obtained in example 2 has obvious surface defect distribution rules, on one hand, defect sites are uniformly distributed on two opposite crystal faces, and on the other hand, the defect sites are mainly concentrated in a triangular region (as shown in FIG. 3); the surface of the crystal grains of the SAPO-34 molecular sieve obtained in example 3 has hourglass-shaped hollow defects (as shown in FIG. 4). As can be seen from fig. 5 and 6: the SAPO-34 molecular sieve finally obtained when the crystallization time is not in the range required by the technical scheme of the invention and the conventional commercially available SAPO-34 molecular sieve (comparative example 1) have a cubic shape with smooth grain surfaces.
Claims (7)
1. A method for synthesizing a cubic SAPO-34 molecular sieve with surface defects comprises the following steps:
silicon source, aluminum source, phosphorus source, template agent and water are SiO according to the molar ratio2：Al2O3：P2O5：R：H2O ═ 0.5 to 0.8: 1: (0.8-1.2): (1-3): (40-80) mixing in proportion, and then carrying out dynamic hydrothermal crystallization to obtain the cubic SAPO-34 molecular sieve with surface defects;
in the synthesis process, keeping the mole ratio of the silicon source, the aluminum source, the phosphorus source, the template agent and the water unchanged, adjusting the crystallization temperature to be 175 ℃, and when the crystallization time is 8 hours, uniformly distributing the obtained surface defects on the surfaces of the SAPO-34 molecular sieve grains;
adjusting the crystallization temperature to 180 ℃ and the crystallization time to 6h, wherein the obtained surface defects are distributed in a triangular region on the surface of the SAPO-34 molecular sieve crystal grains;
the crystallization temperature is adjusted to 185 ℃, and the crystallization time is adjusted to 3 hours, so that the obtained surface defects are sunken in an hourglass shape.
2. The method of claim 1, wherein,
the silicon source comprises silica sol;
the aluminum source comprises pseudoboehmite;
the phosphorus source comprises phosphoric acid;
the template agent comprises triethylamine and tetraethyl ammonium hydroxide.
3. The method of claim 2, wherein the molar ratio of triethylamine to tetraethylammonium hydroxide in the templating agent is (1-70): 1.
4. The process of claim 3, wherein the molar ratio of triethylamine to tetraethylammonium hydroxide is 50: 1.
5. The method of claim 1, wherein the method comprises the steps of:
the silicon source, the aluminum source, the phosphorus source, the template agent and the water are SiO according to the molar ratio2：Al2O3：P2O5：R：H2O ═ 0.5 to 0.8: 1: (0.8-1.2): (1-3): (40-80) mixing in proportion, and then carrying out dynamic hydrothermal crystallization to obtain the cubic SAPO-34 molecular sieve with surface defects; wherein the content of the first and second substances,
the silicon source, the aluminum source and the phosphorus source are respectively made of SiO2、Al2O3And P2O5The template agent comprises triethylamine and tetraethyl ammonium hydroxide, and the molar ratio of the triethylamine to the tetraethyl ammonium hydroxide is (1-70): 1;
when the dynamic hydrothermal crystallization is carried out, the crystallization temperature is controlled to be 175-185 ℃, and the crystallization time is controlled to be 3-8 h.
6. A cubic SAPO-34 molecular sieve having surface defects, prepared by the method of any one of claims 1-5.
7. The use of the surface-defected, cubic-morphology SAPO-34 molecular sieve of claim 6 in methanol-to-olefin reactions.
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