A method for preparing nano-flaky AFN structure molecular sieve

Abstract

This invention discloses a method for preparing nanosheet-like AFN structured molecular sieves. An aluminum source is added to water, along with a phosphorus source, a template agent, and a silicon source. The mixture is then dried and milled to obtain a SAPO-14 molecular sieve dry gel precursor. Alternatively, an aluminum source is added to water and mixed thoroughly, followed by the addition of a phosphorus source and a template agent. This mixture is then dried and milled to obtain an AlPO-14 molecular sieve dry gel precursor. The SAPO-14 or AlPO-14 molecular sieve dry gel precursor is placed in a reactor with water added, isolating the dry gel precursor from the water, and maintained at 150-180°C for 4-8 hours to obtain a nanosheet-like AFN structured molecular sieve. In this invention, the precursor is in a dry gel form before crystallization in the reactor, with extremely low solvent content, which facilitates close contact between different components and results in a rapid nucleation rate. Therefore, the synthesis time is significantly shortened, although there are slight differences in crystallinity, which increases with time.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieve preparation, and relates to a method for preparing a nano-flaky AFN structure molecular sieve. Background Art

[0002] As an important chemical raw material, propylene is widely used in modern petrochemical and fine chemical fields. It plays a pivotal role in the chemical industry and is an important raw material for the production of chemicals such as polypropylene, acrylonitrile and propylene oxide. At present, the production processes of propylene in my country mainly include catalytic cracking, steam cracking, coal / methanol to olefins (CTO / MTO), and propane dehydrogenation to olefins (PDH).

[0003] Crude oil catalytic cracking and naphtha steam cracking are traditional propylene production routes, but in these two routes, propylene is only a by-product with low yield and low purity. Propane dehydrogenation uses propane as raw material and obtains propylene through dehydrogenation. This route has the characteristics of low investment, high yield, short process flow, high purity of obtained propylene, and few by-products. However, the economic efficiency of the propane dehydrogenation process mainly depends on the price difference between the raw materials propane and propylene and the stable acquisition of propane. The supply of propane raw materials is uncertain. In addition, the production capacity will explode in the future, and the economic efficiency of the propane dehydrogenation process is subject to certain risks. Coal-to-olefins mainly uses coal as raw material to synthesize methanol, and then produces ethylene, propylene and other olefins from methanol. At the same time, the methanol-to-olefins reaction has the advantages of high methanol conversion rate and high selectivity for low-carbon olefins. The coal-to-methanol technology is mature, and the market situation of methanol oversupply, the MTO reaction has broad development prospects and huge application space.

[0004] The research and development of high-performance catalysts is the core of controlling the methanol to olefins reaction. Molecular sieves have uniform pore structure, good hydrothermal stability, controllable acid properties and unique shape selectivity, and are the main catalysts for the methanol to olefins reaction. At present, the common methanol to olefins catalysts are mainly ZSM-5 and SAPO-34 molecular sieves. ZSM-5 is a silicon aluminum molecular sieve with MFI topology. Due to its special pore structure, this molecular sieve has excellent anti-carbon deposition performance. It deactivates slowly in the MTO (Methanol to Olefins) reaction and can maintain long-term catalysis. At the same time, due to its strong acidity, it has more advantages in product selectivity for propylene and aromatics. SAPO-34 is a silicon aluminum phosphorus molecular sieve with CHA topology. It is the most widely used catalyst for the current MTO reaction. Due to the pore size formed by its special pore structure and the appropriate acidity, it has the advantage of high total olefin selectivity in the MTO reaction, but the product selectivity of the MTO reaction catalyzed by SAPO-34 molecular sieve is difficult to control, and the propylene / ethylene ratio is relatively low.

[0005] Patent CN108147423 discloses a method for synthesizing AFN structure silicon-aluminum-phosphorus SAPO-14 molecular sieve, using 1-isopropyl-4-piperidone as a template agent. It includes preparing AFN structure silicon-aluminum-phosphorus molecular sieve by hydrothermal method: subjecting a mixed solution containing a phosphorus source, an aluminum source, a silicon source, a template agent R and water to hydrothermal crystallization, followed by solid-liquid separation and drying; and preparing AFN structure silicon-phosphorus-aluminum molecular sieve by phosphorus-aluminum dry gel liquid phase conversion method, subjecting a mixed solution A containing a phosphorus source, an aluminum source and water to aging, followed by drying, to obtain phosphorus-aluminum dry gel, and subjecting a raw material mixture B containing phosphorus-aluminum dry gel, a silicon source, a template agent R and water to hydrothermal crystallization, followed by solid-liquid separation and drying.

[0006] In the literature (Yang M, Li B, Gao M, et al. High propylene selectivity in methanol conversion over a small-pore SAPO molecular sieve with ultra-small cage [J]. ACS Catalysis, 2020, 10 (6): 3741-3749.), the SAPO-14 molecular sieve was prepared by hydrothermal synthesis with pseudo-boehmite, phosphoric acid, TEOS, isopropylamine and water as raw materials and rotary hydrothermal crystallization at 200 ° C for 48 hours. It was then used in the MTO reaction, and the highest diene selectivity could reach 87.5%, of which the propylene selectivity could reach up to 77.3%, which is the highest record of single-pass propylene selectivity reported in the literature so far.

[0007] The literature (Zhou Y, Zhang J, Ma W, et al. Small pore SAPO-14-based zeolites with improved propylene selectivity in the methanol to olefins process [J]. Inorganic Chemistry Frontiers, 2022, 9 (8): 1752-1760.) also used the hydrothermal synthesis method to prepare SAPO-14 molecular sieve with pseudo-boehmite, phosphoric acid, TEOS, isopropylamine and water as raw materials and crystallized at 200 ° C for 24 hours.

[0008] In summary, the current synthesis method of AFN structured molecular sieves is relatively simple, mainly based on hydrothermal synthesis, and the crystallization temperature is high and the crystallization time is long, usually crystallizing at 200°C for more than 24 hours. In addition, the hydrothermal synthesis of AFN molecular sieves also has the disadvantages of low raw material utilization and complex subsequent product separation procedures.

[0009] Therefore, it is urgent to develop a simple, green, economical and efficient AFN structure molecular sieve synthesis technology. Summary of the invention

[0010] In order to overcome the problems in the prior art, the purpose of the present invention is to provide a method for preparing nano-sheet AFN structure molecular sieves, which has low reaction temperature, short preparation time, high raw material utilization rate and simple subsequent separation process.

[0011] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0012] 1) adding an aluminum source to water, mixing evenly, adding a phosphorus source and a template agent, mixing evenly, adding a silicon source, then mixing evenly, drying, and grinding to obtain a SAPO-14 molecular sieve dry gel precursor; adding an aluminum source to water, mixing evenly, adding a phosphorus source and a template agent, mixing evenly, then drying, and grinding to obtain an AlPO-14 molecular sieve dry gel precursor;

[0013] 2) Add water to the SAPO-14 molecular sieve dry gel precursor or AlPO-14 molecular sieve dry gel precursor reactor, isolate the dry gel precursor from the water, and then maintain it at 150-180° C. for 4-8 hours. After quenching, remove the template agent to obtain a molecular sieve with a nano-sheet AFN structure.

[0014] Furthermore, the silicon source is tetraethoxysilane, silica sol Ludox-40, silicon powder or hydrated silicic acid.

[0015] Furthermore, the template agent is isopropylamine.

[0016] Furthermore, the aluminum source is pseudo-boehmite or aluminum isopropoxide.

[0017] Furthermore, the phosphorus source is phosphoric acid.

[0018] Furthermore, the SAPO-14 molecular sieve dry gel precursor is calculated according to the molar ratio of SiO2 in the silicon source, Al2O3 in the aluminum source, P2O5 in the phosphorus source, isopropylamine and water, (0.1-1.5)SiO2:(0.4-3)Al2O3:1P2O5:(1.5-3)IPA:(20-50)H2O; the AlPO-14 molecular sieve dry gel precursor is calculated according to the molar ratio of Al2O3 in the aluminum source, P2O5 in the phosphorus source, isopropylamine and water, (0.4-3)Al2O3:1P2O5:(1.5-3)IPA:(20-50)H2O.

[0019] Furthermore, in step 2), the ratio of the SAPO-14 molecular sieve dry gel precursor or the AlPO-14 molecular sieve dry gel precursor to water is 1:0.5-24 g.

[0020] Furthermore, the temperature for removing the template is 550-650°C.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention adopts a combination of dry gel method and steam-assisted crystallization technology to efficiently prepare nano-sheet AFN structure molecular sieve phosphorus aluminum AlPO-14 molecular sieve and silicon aluminum phosphorus SAPO-14 molecular sieve, the molecular sieve has good crystallinity, good hydrothermal stability, and a nano-sheet particle morphology, and the silicon aluminum phosphorus SAPO-14 molecular sieve has moderate acid strength and adjustable acid amount. In the present invention, the SAPO-14 molecular sieve dry gel precursor and the AlPO-14 molecular sieve dry gel precursor are in the form of dry gel before entering the kettle for crystallization, and the solvent content is extremely low, which is conducive to close contact between different component materials and a fast nucleation rate, so the synthesis time is greatly shortened, the crystallization time is 4-8h, and the crystallinity is slightly different. The crystallinity increases with time, overcoming the problem that the hydrothermal preparation technology in the prior art requires the materials to interact under the self-pressure of the solvent, and the nucleation rate is slow. The synthesis temperature in the present invention is low, and crystallization can be performed at 150-180°C, which is easy to operate.

[0023] Furthermore, when the SAPO-14 molecular sieve of the present invention is used in the MTP reaction, the selectivity of dienes (ethylene, propylene) is as high as 86.57%, among which the selectivity of propylene is as high as 79.98%, and the P / E is as high as 9.08.

[0024] Furthermore, the silicon and aluminum sources of the present invention have a wide range of sources. The silicon source can be TEOS, Ludox-40, Fumedsilica, and hydrated silicate, and the aluminum source can be pseudo-boehmite and aluminum isopropoxide.

[0025] Furthermore, the dry gel is put into a kettle for crystallization, the amount of solvent used is small, and the product is easy to separate. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The X-ray diffraction patterns of Comparative Example 1 and Example 1 are shown.

[0027] Figure 2 This is a scanning electron microscope image of Comparative Example 1.

[0028] Figure 3 This is a scanning electron microscope image of Example 1.

[0029] Figure 4 NH3-TPD spectra of Comparative Example 1 and Example 1. DETAILED DESCRIPTION

[0030] The present invention is described in detail below with reference to specific embodiments.

[0031] The present invention adopts a method combining a dry gel method and a steam-assisted crystallization technology to efficiently prepare a silicon-aluminum-phosphorus molecular sieve SAPO-14 and a phosphorus-aluminum molecular sieve AlPO-14 with a nano-sheet AFN structure, and the preparation process is as follows:

[0032] 1) Raw materials: silicon source (TEOS (tetraethoxysilane, Tetraethoxysilane,), Ludox-40 (i.e. silica sol), Fumesilica (i.e. silicon powder) or hydrated silicic acid), template (isopropylamine, IPA), aluminum source (pseudoboehmite or aluminum isopropoxide), phosphorus source (phosphoric acid) and water.

[0033] 2) Synthesis ratio: SAPO-14 molecular sieve is calculated based on the molar ratio of SiO2 in the silicon source, Al2O3 in the aluminum source, P2O5 in the phosphorus source, isopropylamine and water; AlPO-14 molecular sieve is calculated based on the molar ratio of Al2O3 in the aluminum source, P2O5 in the phosphorus source, isopropylamine and water, as follows:

[0034] SAPO-14 molecular sieve: (0.1-1.5)SiO2: (0.4-3)Al2O3: 1P2O5: (1.5-3)IPA: (20-50)H2O.

[0035] AlPO-14 molecular sieve: (0.4-3)Al2O3:1P2O5:(1.5-3)IPA:(20-50)H2O.

[0036] 3) Preparation steps

[0037] Preparation of SAPO-14 molecular sieve dry gel: take aluminum source according to the synthesis ratio and add it to water, and stir evenly for 1 hour; then add phosphorus source and template agent in sequence, and stir evenly for 1 hour; finally add silicon source to obtain solvent, transfer the solution to a shaker, shake until the solution is uniform and there is no stratification, transfer the solution to an evaporating dish, dry it at 60-80°C to obtain dry gel, and then crush the hard cake-like dry gel into powder to obtain SAPO-14 molecular sieve dry gel precursor.

[0038] Preparation of AlPO-14 molecular sieve dry gel: take aluminum source according to the synthesis ratio and add it into water, and stir evenly for 1 hour; then add phosphorus source and template agent in sequence, stir evenly for 1 hour to obtain solvent, and then transfer the solution to an evaporating dish, dry it at 80°C to obtain dry gel, and then crush the hard cake-like dry gel into powder to obtain AlPO-14 molecular sieve dry gel precursor.

[0039] Steam assisted conversion (SAC): 1g of the prepared SAPO-14 molecular sieve dry gel precursor or AlPO-14 molecular sieve dry gel precursor is placed in a glass container, 0.5-24g of water is added to the polytetrafluoroethylene lining of a stainless steel autoclave, and then the glass container is placed in the lining so that the dry gel precursor cannot directly contact with liquid water, and then the autoclave is sealed and transferred to an oven preheated to 150-180°C. After keeping for 4-8 hours, the autoclave is quenched with tap water. Due to the high temperature adsorption of water and the condensation of steam during quenching, the product in the glass container is in a paste state. The sample is recovered by centrifugation, washing, and drying, and the template is removed by calcination at 550-650°C to obtain a silicon aluminum phosphorus molecular sieve SAPO-14 or a phosphorus aluminum molecular sieve AlPO-14 with a nano-sheet AFN structure.

[0040] 4) Application of SAPO-14 molecular sieve in MTP (Methanol To Propylene) reaction: The MTP catalytic reaction experiment was carried out on a two-stage fixed bed reactor. The device was divided into a preheating section and a reaction section. The preheating section preheated the reaction material to 150°C, and the reaction section was filled with 0.25g SAPO-14 molecular sieve. The entire device used argon as the carrier gas, and the flow rate was controlled at 30mL / min. The catalyst was first activated at 600°C for 2h, and then the temperature of the reaction section was maintained at 400°C. The device was intermittently injected, and samples were collected at 2 minutes, 6 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 40 minutes, and 50 minutes of the reaction, and the product components were detected by online chromatography.

[0041] Among them, the raw material components and dosage are as follows:

[0042] Silicon source (TEOS, Ludox-40, hydrated silicate, Fumedsilica), aluminum source (pseudo-boehmite), phosphorus source (phosphoric acid), template (isopropylamine) and deionized water, wherein the silicon source is calculated as SiO2, the aluminum source is calculated as Al2O3, the phosphorus source is calculated as P2O5, and the molar ratio of each material of SAPO-14 molecular sieve is: aSiO2: bAl2O3: cP2O5: dIPA: eH2O, wherein a: b: c: d: e = 0.1-1.5: 0.4-3: 1: 1.5-3: 20-50; the molar ratio of each material of AlPO-14 molecular sieve is: aAl2O3: bP2O5: cIPA: dH2O, wherein a: b: c: d = 0.4-3: 1: 1.5-3: 20-50.

[0043] The molecular sieve prepared by the present invention has good crystallinity, good hydrothermal stability, and a nano-flaky particle morphology. The acid property of SAPO-14 molecular sieve is moderate in acid strength and the acid amount is adjustable. AlPO-14 molecular sieve has no acid property because it does not contain silicon.

[0044] Comparative Example 1 (Synthesis of SAPO-14 by Hydrothermal Method)

[0045] (1) Under stirring conditions, 1.70 g of pseudo-boehmite was added to 11.26 g of deionized water and stirred for 1 h to form a uniform solution A;

[0046] (2) Under stirring conditions, 2.88 g of phosphoric acid and 2.22 g of isopropylamine were slowly added to solution A in sequence and stirred for another 1 h;

[0047] (3) Slowly add 0.26 g of TEOS to the solution in step (2), transfer the solution to a shaker, and shake until the solution is uniform and there is no stratification;

[0048] (4) The solution obtained in step (3) is placed in a polytetrafluoroethylene liner of a stainless steel autoclave, and then the autoclave is sealed and transferred to an oven preheated to 200° C., and after being kept for 24 hours, the autoclave is quenched with tap water, and the sample is recovered by centrifugation, washing, and drying, and then calcined at 650° C. for 12 hours to remove the template to obtain the final product.

[0049] Example 1 (TEOS, 0.8SiO2, 8H-SAPO-14)

[0050] (1) Under stirring conditions, 1.70 g of pseudo-boehmite was added to 11.26 g of deionized water and stirred for 1 h to form a uniform solution A;

[0051] (2) Under stirring conditions, 2.88 g of phosphoric acid and 2.22 g of isopropylamine were slowly added to solution A in sequence and stirred for another 1 h;

[0052] (3) Slowly add 2.08 g of TEOS to the solution in step (2), transfer the solution to a shaker, and shake until the solution is uniform and there is no stratification;

[0053] (4) The solution of step (3) was transferred to an evaporating dish, dried at 80° C. for 5 h, and then ground into powder to obtain a solid precursor.

[0054] (5) 1 g of the solid precursor obtained in step (4) was placed in a glass bottle, 4 g of deionized water was added to the polytetrafluoroethylene liner of a stainless steel autoclave, and a glass container was placed in the liner to prevent the dry gel from directly contacting the liquid water, and then the autoclave was sealed;

[0055] (6) The autoclave was transferred to an oven preheated to 180°C and kept for 8 h. The autoclave was quenched with tap water, and the sample was recovered by centrifugation, washing, and drying. The sample was then calcined at 650°C for 12 h to remove the template and obtain the final product.

[0056] Example 2 (AlPO-14)

[0057] (1) Under stirring conditions, 1.70 g of pseudo-boehmite was added to 11.26 g of deionized water and stirred for 1 h to form a uniform solution A;

[0058] (2) Under stirring conditions, 2.88 g of phosphoric acid and 2.22 g of isopropylamine were slowly added to solution A in sequence, and stirred for 1 h to obtain a solution;

[0059] (3) The solution of step (2) was transferred to an evaporating dish, dried at 80° C. for 5 h, and then ground into powder to obtain a solid precursor.

[0060] (4) 1 g of the solid precursor obtained in step (3) was placed in a glass bottle, 4 g of deionized water was added to the polytetrafluoroethylene liner of a stainless steel autoclave, and a glass container was placed in the liner to prevent the dry gel from directly contacting the liquid water, and then the autoclave was sealed;

[0061] (5) The autoclave was transferred to an oven preheated to 180°C and kept for 8 h. The autoclave was quenched with tap water. The sample was recovered by centrifugation, washing, and drying. The sample was then calcined at 650°C for 12 h to remove the template and obtain the final product.

[0062] Example 3 (3Al2O3, 1.5SiO2-SAPO-14)

[0063] (1) Under stirring conditions, 5.10 g of pseudo-boehmite was added to 11.26 g of deionized water and stirred for 1 h to form a uniform solution A;

[0064] (2) Under stirring conditions, 2.88 g of phosphoric acid and 2.22 g of isopropylamine were slowly added to solution A in sequence and stirred for another 1 h;

[0065] (3) Slowly add 3.91 g of TEOS to the solution in step (2), transfer the solution to a shaker, and shake until the solution is uniform and there is no stratification;

[0066] (4) The solution of step (3) was transferred to an evaporating dish, dried at 60° C. for 5 h, and then ground into powder to obtain a solid precursor.

[0067] (5) 1 g of the solid precursor obtained in step (4) was placed in a glass bottle, 4 g of deionized water was added to the polytetrafluoroethylene liner of a stainless steel autoclave, and a glass container was placed in the liner to prevent the dry gel from directly contacting the liquid water, and then the autoclave was sealed;

[0068] (6) The autoclave was transferred to an oven preheated to 180°C and kept for 4 h. The autoclave was quenched with tap water, and the sample was recovered by centrifugation, washing, and drying. The sample was then calcined at 550°C for 12 h to remove the template and obtain the final product.

[0069] Example 4 (0.4Al2O3, 1SiO2-SAPO-14)

[0070] (1) Under stirring conditions, 0.68 g of pseudo-boehmite was added to 11.26 g of deionized water and stirred for 1 h to form a uniform solution A;

[0071] (2) Under stirring conditions, 2.88 g of phosphoric acid and 2.22 g of isopropylamine were slowly added to solution A in sequence and stirred for another 1 h;

[0072] (3) Slowly add 2.60 g of TEOS to the solution in step (2), transfer the solution to a shaker, and shake until the solution is uniform and there is no stratification;

[0073] (4) The solution of step (3) was transferred to an evaporating dish, dried at 70° C. for 5 h, and then ground into powder to obtain a solid precursor.

[0074] (5) 1 g of the solid precursor obtained in step (4) was placed in a glass bottle, 4 g of deionized water was added to the polytetrafluoroethylene liner of a stainless steel autoclave, and a glass container was placed in the liner to prevent the dry gel from directly contacting the liquid water, and then the autoclave was sealed;

[0075] (6) The autoclave was transferred to an oven preheated to 180°C and kept for 6 h. The autoclave was quenched with tap water, and the sample was recovered by centrifugation, washing, and drying. The sample was then calcined at 600°C for 12 h to remove the template to obtain the final product.

[0076] Example 5 (1.5SDA-SAPO-14)

[0077] (1) Under stirring conditions, 1.70 g of pseudo-boehmite was added to 11.26 g of deionized water and stirred for 1 h to form a uniform solution A;

[0078] (2) Under stirring conditions, 2.88 g of phosphoric acid and 1.11 g of isopropylamine were slowly added to solution A in sequence, and stirred for another 1 h;

[0079] (3) Slowly add 1.04 g of TEOS to the solution in step (2), transfer the solution to a shaker, and shake until the solution is uniform and there is no stratification;

[0080] (4) The solution of step (3) was transferred to an evaporating dish, dried at 80° C. for 5 h, and then ground into powder to obtain a solid precursor.

[0081] (5) 1 g of the solid precursor obtained in step (4) was placed in a glass bottle, 4 g of deionized water was added to the polytetrafluoroethylene liner of a stainless steel autoclave, and a glass container was placed in the liner to prevent the dry gel from directly contacting the liquid water, and then the autoclave was sealed;

[0082] (6) The autoclave was transferred to an oven preheated to 160°C and kept for 8 h. The autoclave was quenched with tap water, and the sample was recovered by centrifugation, washing, and drying. The sample was then calcined at 650°C for 12 h to remove the template and obtain the final product.

[0083] Example 6 (Ludox-40-SAPO-14)

[0084] (1) Under stirring conditions, 1.70 g of pseudo-boehmite was added to 11.26 g of deionized water and stirred for 1 h to form a uniform solution A;

[0085] (2) Under stirring conditions, 2.88 g of phosphoric acid and 2.22 g of isopropylamine were slowly added to solution A in sequence and stirred for another 1 h;

[0086] (3) Slowly add 0.75 g of Ludox-40 to the solution in step (2), transfer the solution to a shaker, and shake until the solution is uniform and there is no stratification;

[0087] (4) The solution of step (3) was transferred to an evaporating dish, dried at 80° C. for 5 h, and then ground into powder to obtain a solid precursor.

[0088] (5) 1 g of the solid precursor obtained in step (4) was placed in a glass bottle, 4 g of deionized water was added to the polytetrafluoroethylene liner of a stainless steel autoclave, and a glass container was placed in the liner to prevent the dry gel from directly contacting the liquid water, and then the autoclave was sealed;

[0089] (6) The autoclave was transferred to an oven preheated to 180°C and kept for 8 h. The autoclave was quenched with tap water, and the sample was recovered by centrifugation, washing, and drying. The sample was then calcined at 650°C for 12 h to remove the template and obtain the final product.

[0090] Example 7 (Fumedsilica-SAPO-14)

[0091] (1) Under stirring conditions, 1.70 g of pseudo-boehmite was added to 11.26 g of deionized water and stirred for 1 h to form a uniform solution A;

[0092] (2) Under stirring conditions, 2.88 g of phosphoric acid and 2.22 g of isopropylamine were slowly added to solution A in sequence and stirred for another 1 h;

[0093] (3) Add 0.30 g of Fumedsilica to the solution in step (2), transfer the solution to a shaker, and shake until the solution is uniform and there is no stratification;

[0094] (4) The solution of step (3) was transferred to an evaporating dish, dried at 80° C. for 5 h, and then ground into powder to obtain a solid precursor.

[0095] (5) 1 g of the solid precursor obtained in step (4) was placed in a glass bottle, 4 g of deionized water was added to the polytetrafluoroethylene liner of a stainless steel autoclave, and a glass container was placed in the liner to prevent the dry gel from directly contacting the liquid water, and then the autoclave was sealed;

[0096] (6) The autoclave was transferred to an oven preheated to 180°C and kept for 8 h. The autoclave was quenched with tap water, and the sample was recovered by centrifugation, washing, and drying. The sample was then calcined at 650°C for 12 h to remove the template and obtain the final product.

[0097] Example 8 (Hydrated Silicic Acid-SAPO-14)

[0098] (1) Under stirring conditions, 1.70 g of pseudo-boehmite was added to 11.26 g of deionized water and stirred for 1 h to form a uniform solution A;

[0099] (2) Under stirring conditions, 2.88 g of phosphoric acid and 2.22 g of isopropylamine were slowly added to solution A in sequence and stirred for another 1 h;

[0100] (3) Add 0.075 g of hydrated silicic acid to the solution of step (2), transfer the solution to a shaker, and shake until the solution is uniform and there is no stratification;

[0101] (4) The solution of step (3) was transferred to an evaporating dish, dried at 80° C. for 5 h, and then ground into powder to obtain a solid precursor.

[0102] (5) 1 g of the solid precursor obtained in step (4) was placed in a glass bottle, 4 g of deionized water was added to the polytetrafluoroethylene liner of a stainless steel autoclave, and a glass container was placed in the liner to prevent the dry gel from directly contacting the liquid water, and then the autoclave was sealed;

[0103] (6) The autoclave was transferred to an oven preheated to 180°C and kept for 8 h. The autoclave was quenched with tap water, and the sample was recovered by centrifugation, washing, and drying. The sample was then calcined at 650°C for 12 h to remove the template and obtain the final product.

[0104] Example 9

[0105] 1) Add aluminum source to water, mix well, add phosphorus source and template agent in turn, mix well, add silicon source, shake on a shaker until the solution is uniform and there is no stratification, dry to obtain dry gel, and then crush and grind the dry gel into powder to obtain SAPO-14 molecular sieve dry gel precursor; the silicon source is silicon powder, the template agent is isopropylamine, the aluminum source is pseudo-boehmite, and the phosphorus source is phosphoric acid. The SAPO-14 molecular sieve dry gel precursor is calculated according to the molar ratio of SiO2 in the silicon source, Al2O3 in the aluminum source, P2O5 in the phosphorus source, isopropylamine and water, aSiO2:bAl2O3:cP2O5:dIPA:eH2O, where a:b:c:d:e=0.1:3:1:3:20;

[0106] 2) Put the SAPO-14 molecular sieve dry gel precursor into a glass container, add water to the polytetrafluoroethylene lining of the stainless steel autoclave, and then put the glass container into the lining to isolate the dry gel precursor from the water, and then keep it at 170°C for 5 hours, quench it, and calcine it at 580°C for 12 hours to remove the template agent to obtain a molecular sieve with a nano-sheet AFN structure. The dosage ratio of SAPO-14 molecular sieve dry gel precursor to water is 1:0.5g.

[0107] Example 10

[0108] 1) Add aluminum source to water, mix well, add phosphorus source and template agent in turn, mix well, add silicon source, shake on a shaker until the solution is uniform and there is no stratification, dry to obtain dry gel, and then crush and grind the dry gel into powder to obtain SAPO-14 molecular sieve dry gel precursor; the silicon source is silicon powder, the template agent is isopropylamine, the aluminum source is pseudo-boehmite, and the phosphorus source is phosphoric acid. The SAPO-14 molecular sieve dry gel precursor is calculated according to the molar ratio of SiO2 in the silicon source, Al2O3 in the aluminum source, P2O5 in the phosphorus source, isopropylamine and water, aSiO2:bAl2O3:cP2O5:dIPA:eH2O, where a:b:c:d:e=1.5:0.4:1:1.5:50;

[0109] 2) Put the SAPO-14 molecular sieve dry gel precursor into a glass container, add water to the polytetrafluoroethylene lining of the stainless steel autoclave, and then put the glass container into the lining to isolate the dry gel precursor from the water, and then keep it at 170°C for 5 hours, quench it, and calcine it at 620°C for 12 hours to remove the template agent to obtain a molecular sieve with a nano-sheet AFN structure. The dosage ratio of SAPO-14 molecular sieve dry gel precursor to water is 1:24g.

[0110] Embodiment 11

[0111] 1) adding an aluminum source to water and mixing evenly, adding a phosphorus source and a template agent in turn, mixing evenly, and then drying to obtain a dry gel, crushing and grinding the dry gel into powder to obtain an AlPO-14 molecular sieve dry gel precursor; the silicon source is a silica sol Ludox-40, the template agent is isopropylamine, the aluminum source is aluminum isopropoxide, and the phosphorus source is phosphoric acid.

[0112] The AlPO-14 molecular sieve dry gel precursor is calculated according to the molar ratio of Al2O3 in the aluminum source, P2O5 in the phosphorus source, isopropylamine and water, aAl2O3:bP2O5:cIPA:dH2O, wherein a:b:c:d=1:1:2:30.

[0113] 2) The AlPO-14 molecular sieve dry gel precursor was placed in a glass container, water was added to the polytetrafluoroethylene lining of the stainless steel autoclave, and the glass container was placed in the lining to isolate the dry gel precursor from the water, and then kept at 150°C for 8 hours, quenched, and calcined at 600°C for 12 hours to remove the template agent, thereby obtaining a molecular sieve with a nano-sheet AFN structure. The dosage ratio of the AlPO-14 molecular sieve dry gel precursor to water was 1:15g.

[0114] Example 12

[0115] 1) adding an aluminum source to water and mixing evenly, adding a phosphorus source and a template agent in turn, mixing evenly, and then drying to obtain a dry gel, crushing and grinding the dry gel into powder to obtain an AlPO-14 molecular sieve dry gel precursor; the silicon source is a silica sol Ludox-40, the template agent is isopropylamine, the aluminum source is aluminum isopropoxide, and the phosphorus source is phosphoric acid.

[0116] The AlPO-14 molecular sieve dry gel precursor is calculated according to the molar ratio of Al2O3 in the aluminum source, P2O5 in the phosphorus source, isopropylamine and water, aAl2O3:bP2O5:cIPA:dH2O, wherein a:b:c:d=2:1:2.5:40.

[0117] 2) The AlPO-14 molecular sieve dry gel precursor was placed in a glass container, water was added to the polytetrafluoroethylene lining of the stainless steel autoclave, and the glass container was placed in the lining to isolate the dry gel precursor from the water, and then kept at 165°C for 5 hours, quenched and calcined at 550°C for 12 hours to remove the template agent, and a molecular sieve with a nano-sheet AFN structure was obtained. The ratio of the AlPO-14 molecular sieve dry gel precursor to water was 1:5g.

[0118] Application of SAPO-14 prepared by dry gel method in MTP reaction:

[0119] Application of SAPO-14 molecular sieve in MTP reaction: The MTP catalytic reaction experiment was carried out on a two-stage fixed bed reactor. The device was divided into a preheating section and a reaction section. The preheating section preheated the reaction material to 150°C, and the reaction section was filled with 0.25g of the SAPO-14 molecular sieve of Comparative Example 1 or Example 1. The entire device used argon as the carrier gas, and the flow rate was controlled to be 30mL / min. The catalyst was first activated at 600°C for 2h, and then the temperature of the reaction section was maintained at 400°C. The device was sampled intermittently, and samples were collected at 2 minutes, 6 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 40 minutes, and 50 minutes of the reaction, and the product components were detected by online chromatography. The highest propylene selectivity is shown in Table 1.

[0120] Table 1 Data summary of comparative example 1 and embodiment 1

[0121]

[0122] See also Figure 1 As shown in Table 1, compared with the products of Comparative Example 1 and Example 1, the crystallinity and yield of the product of Example 1 are greatly improved.

[0123] See also Figure 2 and Figure 3 It can be seen that the products of Comparative Example 1 and Example 1 have similar particle morphologies, both of which are nano-flake particle morphologies.

[0124] See also Figure 4 It can be seen that compared with the products of Comparative Example 1 and Example 1, when the total acid amount is similar, the weak acid content of the product of Example 1 is higher, so that the propylene selectivity of the product of Example 1 is improved when it is applied to the MTP reaction.

Claims

1. A method for preparing a nano-flaky AFN structured molecular sieve, characterized in that: The following steps are involved: 1) Adding an aluminum source to water, mixing evenly, adding a phosphorus source and a template agent, mixing evenly, adding a silicon source, then mixing evenly, drying, and grinding to obtain a SAPO-14 molecular sieve dry gel precursor; Adding an aluminum source to water, mixing evenly, adding a phosphorus source and a template agent, mixing evenly, then drying, and grinding to obtain an AlPO-14 molecular sieve dry gel precursor; The template agent is isopropylamine; The synthesis ratio of SAPO-14 molecular sieve dry gel precursor and AlPO-14 molecular sieve dry gel precursor is: SAPO-14 molecular sieve is calculated based on the molar ratio of SiO2 in silicon source, Al2O3 in aluminum source, P2O5 in phosphorus source, isopropylamine and water; AlPO-14 molecular sieve is calculated based on the molar ratio of Al2O3 in aluminum source, P2O5 in phosphorus source, isopropylamine and water, specifically as follows: SAPO-14 molecular sieve: (0.1-1.5)SiO2: (0.4-3)Al2O3: 1P2O5: (1.5-3)IPA: (20-50)H2O; AlPO-14 molecular sieve: (0.4-3)Al2O3:1P2O5:(1.5-3)IPA:(20-50)H2O; 2) Add water to the SAPO-14 molecular sieve dry gel precursor or AlPO-14 molecular sieve dry gel precursor reactor, isolate the dry gel precursor from the water, and then keep it at 150-180° C. for 4-8 hours. After quenching, remove the template agent to obtain a molecular sieve with a nano-sheet AFN structure.

2. The method for preparing a nano-sheet AFN structure molecular sieve according to claim 1, characterized in that: The silicon source is tetraethoxysilane, silica sol Ludox-40, silicon powder or hydrated silicic acid.

3. The method for preparing a nano-sheet AFN structure molecular sieve according to claim 1, characterized in that: The aluminum source is pseudoboehmite or aluminum isopropoxide.

4. The method for preparing a nano-sheet AFN structure molecular sieve according to claim 1, characterized in that: The phosphorus source is phosphoric acid.

5. The method for preparing a nano-sheet AFN structure molecular sieve according to claim 1, characterized in that: In step 2), the dosage ratio of SAPO-14 molecular sieve dry gel precursor or AlPO-14 molecular sieve dry gel precursor to water is 1:0.5g-24g.

6. The method for preparing a nano-sheet AFN structure molecular sieve according to claim 1, characterized in that: The temperature for removing the template is 550-650°C.

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