Silicophosphoaluminic molecular sieve with afn structure, synthesis method and application thereof

Abstract

The application relates to the field of catalytic material synthesis, and particularly discloses an AFN structure silicon-phosphorus-aluminum molecular sieve as well as a synthesis method and application thereof. Silicon-aluminum species in the AFN structure silicon-phosphorus-aluminum molecular sieve are in a form of four-coordination Si(4Al). The AFN structure silicon-phosphorus-aluminum molecular sieve is applied to gas adsorption separation and / or oxygen-containing compound conversion low-carbon olefin, in particular, to a methanol-to-olefin reaction, and has good MTO catalytic activity, a longer catalytic life, and higher ethylene selectivity and propylene selectivity.

Description

Technical Field

[0001] This invention relates to the field of catalytic material synthesis, specifically to AFN-structured silica-phosphorus-aluminum molecular sieves, their synthesis methods, and applications. Background Technology

[0002] Phosphorus aluminum molecular sieves are an important class of porous materials, widely used in adsorption, separation, catalysis, and ion exchange. In 1982, Union Carbide Corporation (UCC) first developed a series of phosphorus aluminum molecular sieves, AlPO4-n (where n represents the structural model). Subsequently, researchers successfully synthesized over 60 different structural types of phosphorus aluminum molecular sieves using hydrothermal synthesis, solvothermal synthesis, and dry gel synthesis methods, with organic compounds from different systems as templates or structure-directing agents. A typical phosphorus aluminum molecular sieve framework is electrically neutral, with a P / Al ratio of 1, and is composed of strictly alternating PO4 tetrahedra and AlO4 tetrahedra connected by oxygen bridges. Later, some metallic and non-metallic elements were introduced into the phosphorus aluminum molecular sieve framework, partially replacing P and Al in the framework, forming heteroatom phosphorus aluminum molecular sieves (such as MeAPO-n and SAPO-n), enriching the framework composition, expanding the structural types of molecular sieves, and broadening the applications of phosphorus aluminum molecular sieves in catalysis, magnetism, electronics, and optics.

[0003] AlPO-14 molecular sieve is a phosphorus-aluminum molecular sieve developed by UCC in 1982. The International Zygotes Association (IZA) designates its structural code as AFN. Its chemical formula is Al8P8O. 32 It belongs to the triclinic crystal system, space group P-1, and cell parameters are... α = 77.81°, β = 77.50°, γ = 87.69°, with a three-dimensional eight-membered ring pore structure. The pore size of the eight-membered ring along the

[100] direction is 0.19 × 0.46 nm, along the

[010] direction is 0.21 × 0.49 nm, and along the

[001] direction is 0.33 × 0.40 nm, belonging to small-pore molecular sieves.

[0004] In 1982, USP4310440 first disclosed two methods for synthesizing AlPO-14. Method one involves crystallization at 150°C for 96 hours under hydrothermal conditions, using phosphoric acid as the phosphorus source, boehmite as the aluminum source, and tert-butylamine (t-BuNH2) as the template agent. The synthesis process follows a molar ratio of 1.0t-BuNH2:Al2O3:P2O5:40H2O. Method two involves crystallization at 200°C for 24 hours under hydrothermal conditions, using phosphoric acid as the phosphorus source, hydrated alumina as the aluminum source, and isopropylamine (iPrNH2) as the template agent. The synthesis process follows a molar ratio of 1.0iPrNH2:Al2O3:P2O5:40H2O.

[0005] In 2016, a paper (The Journal of Physical Chemistry C, 2016, 120(22): 11854-11863) synthesized ULM-6 aluminum phosphate molecular sieve using triisopropanolamine and acrylurea as template agents and HF mineralizing agent. In-situ temperature-variable XRD results showed that when the temperature was increased to 330-360℃, the ULM-6 molecular sieve transformed into AlPO-14 molecular sieve. Compared with conventionally synthesized AlPO-14 molecular sieve, the structure of ULM-6 molecular sieve was more distorted, but it still belonged to the AFN topology. Based on this, the paper added silicon source to the synthesis system to try to synthesize AFN-structured silicon-aluminum phosphate molecular sieve, but... 29 The Si NMR spectrum characterization results showed that Si did not enter the molecular sieve framework, but only promoted the synthesis of pure phase ULM-6 phosphorus aluminum molecular sieve.

[0006] In 2016, CN108147423A reported a method for synthesizing SAPO-14, an AFN-structured molecular sieve composed of silicon, phosphorus, and aluminum. This molecular sieve uses 1-isopropyl-4-piperidinone as a template agent and is prepared via a phosphorus-aluminum dry gel liquid-phase inversion method or a hydrothermal method. Example 1 uses aluminum hydroxide dry gel, orthophosphoric acid, and solid silica gel as raw materials. The molar ratio in the synthesis process is: 1.0P₂O₅:1.0Al₂O₃:0.15SiO₂:2.0R:20H₂O. Crystallization is carried out at 150°C for 36 hours under hydrothermal conditions, followed by a second crystallization at 180°C for 45 hours. Furthermore, from this patent... 29 The Si NMR spectrum shows that the synthesized SAPO-14 molecular sieve sample has peaks at -90ppm and -95ppm, corresponding to Si(4Al) and Si(3Al), respectively, indicating that it has multiple silicon coordination environments.

[0007] The synthesis of the AFN-structured silica-phosphorus-aluminum molecular sieve is difficult due to its demanding conditions. Currently, only 1-isopropyl-4-piperidinone has been used as a template agent to synthesize the silica-phosphorus-aluminum molecular sieve SAPO-14, but it does not have a single Si(4Al) coordination structure, and the template agent is expensive.

[0008] This invention uses inexpensive isopropylamine as a template agent to synthesize AFN-structured silica-alumina molecular sieves via a dry gel-liquid phase inversion method. Furthermore, in the synthesized silica-alumina molecular sieve SAPO-14, Si exists in the molecular sieve framework in a single Si(4Al) coordination structure. Summary of the Invention

[0009] The purpose of this invention is to provide an AFN-structured silicon-phosphorus-aluminum molecular sieve with silicon-phosphorus-aluminum as its framework element, its preparation method and application, and the AFN-structured silicon-phosphorus-aluminum molecular sieve synthesized by this invention has a single Si(4Al) coordination structure.

[0010] According to existing technology, there are no reports of synthesizing SAPO-14 molecular sieves with a single Si(4Al) coordination structure using isopropylamine as a template agent.

[0011] This invention uses inexpensive isopropylamine as a template agent to synthesize AFN-structured silica-alumina molecular sieves via a dry gel-liquid phase inversion method. Furthermore, in the synthesized silica-alumina molecular sieve SAPO-14, Si exists in the molecular sieve framework in a single Si(4Al) coordination structure.

[0012] To achieve the above objectives, according to a first aspect of the present invention, the present invention provides an AFN-structured silicon-phosphorus-aluminum molecular sieve, wherein the silicon and aluminum species in the AFN-structured silicon-phosphorus-aluminum molecular sieve are all present in the tetracoordinate form of Si(4Al).

[0013] Preferably, the XRD pattern of the AFN-structured aluminosilicate phosphorus molecular sieve powder contains at least the diffraction peaks shown in Table 1 below.

[0014] Table 1

[0015] 2θ(deg) <![CDATA[Relative intensity (100×I / I0)]]> 9.020 100 9.506 13.12 11.158 23.24 13.075 26.01 13.390 11.75 15.823 14.43 15.954 15.82 18.011 10.22 21.814 12.73 22.246 11.92 22.699 22.89 22.824 18.36 29.591 12.51 30.839 13.43

[0016] The table above mainly lists the XRD diffraction peak data for relative intensities of 100×I / I0>10.

[0017] According to a second aspect of the present invention, the present invention provides a method for synthesizing AFN-structured silica-phosphorus-aluminum molecular sieves, wherein the synthesis method comprises:

[0018] An initial gel mixture is provided, the initial gel mixture containing aluminum phosphide dry gel, a silicon source, a template agent, and water;

[0019] The initial gel mixture is crystallized;

[0020] The crystallized product is subjected to solid-liquid separation, and the resulting solid phase is washed, dried, and optionally calcined.

[0021] The template agent is isopropylamine.

[0022] According to a third aspect of the present invention, the present invention provides the application of the AFN structured silica-phosphorus-aluminum molecular sieve in gas adsorption separation and / or conversion of oxygen-containing compounds into low-carbon olefins.

[0023] Preferably, the application of the AFN-structured silica-phosphorus-aluminum molecular sieve in the conversion of oxygen-containing compounds into low-carbon olefins is a method for methanol-to-olefins, the method comprising: contacting methanol with the AFN-structured heteroatom molecular sieve under methanol-to-olefins reaction conditions.

[0024] This invention provides an AFN-structured silicon-phosphorus-aluminum molecular sieve synthesized using inexpensive isopropylamine as a template agent and a phosphorus-aluminum dry gel liquid-phase inversion method. In the AFN-structured silicon-phosphorus-aluminum molecular sieve, Si exists in the molecular sieve framework in a single Si(4Al) coordination structure.

[0025] The AFN-structured silica-phosphorus-aluminum molecular sieve prepared by this invention can be used for gas separation and adsorption, as well as for the conversion of oxygen-containing compounds into low-carbon olefins. It has good application prospects, especially for the adsorption and separation of mixed gases such as C3H6 / C3H8, CO2 / CH4, and CO2 / N2, and for the conversion of methanol into low-carbon olefins. Attached Figure Description

[0026] Figure 1 The XRD pattern of the molecular sieve sample synthesized in Example 1;

[0027] Figure 2 SEM image of the molecular sieve sample synthesized in Example 1;

[0028] Figure 3 SEM images of the molecular sieve samples synthesized in Example 2;

[0029] Figure 4 The molecular sieve sample synthesized in Example 2 29 Si MAS NMR spectrum;

[0030] Figure 5 SEM image of the molecular sieve sample synthesized in Example 6;

[0031] Figure 6 The molecular sieve sample synthesized for Comparative Example 1 29 Si MAS NMR spectrum. Detailed Implementation

[0032] The endpoints and any values ​​of the ranges disclosed herein 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 the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0033] The technical terms used in this invention, where defined, shall be used according to their definitions, and where not defined, shall be understood according to their common meaning in the art.

[0034] The template agent in this invention is also known in the art as a structure-directing agent or an organic structure-directing agent.

[0035] According to a first aspect of the present invention, the present invention provides an AFN-structured silica-phosphorus-aluminum molecular sieve, wherein the silica-aluminum species in the AFN-structured silica-phosphorus-aluminum molecular sieve are all present in the tetracoordinate form of Si(4Al).

[0036] According to the present invention, the XRD pattern of the AFN-structured aluminosilicate phosphorus molecular sieve powder contains at least the diffraction peaks shown in Table 1 below.

[0037] Table 1

[0038] 2θ(deg) <![CDATA[Relative intensity (100×I / I0)]]> 9.020 100 9.506 13.12 11.158 23.24 13.075 26.01 13.390 11.75 15.823 14.43 15.954 15.82 18.011 10.22 21.814 12.73 22.246 11.92 22.699 22.89 22.824 18.36 29.591 12.51 30.839 13.43

[0039] The table above mainly lists the XRD diffraction peak data for relative intensities of 100×I / I0>10.

[0040] The diffraction peak data contained in the XRD pattern of the AFN-structured silicon-phosphorus-aluminum molecular sieve powder and the cell parameter data of the AFN-structured silicon-phosphorus-aluminum molecular sieve can prove that what was obtained is AFN silicon-phosphorus-aluminum molecular sieve.

[0041] pass 29 The Si MAS NMR spectrum proves that the silicon and aluminum species in the AFN structured silicon-phosphorus-aluminum molecular sieve all exist in the tetracoordinate form of Si(4Al).

[0042] The present invention provides a method for synthesizing AFN-structured silicon-phosphorus-aluminum molecular sieves by a phosphorus-aluminum dry gel liquid-phase inversion method, using isopropylamine as a template agent.

[0043] According to a second aspect of the present invention, the method for synthesizing the AFN-structured silica-phosphorus-aluminum molecular sieve includes:

[0044] An initial gel mixture is provided, the initial gel mixture containing aluminum phosphide dry gel, a silicon source, a template agent, and water;

[0045] The initial gel mixture is crystallized;

[0046] The crystallized product is subjected to solid-liquid separation, and the resulting solid phase is washed, dried, and optionally calcined.

[0047] According to a specific embodiment of the present invention, the phosphorus aluminum dry gel liquid-phase inversion method includes the following steps:

[0048] (1) Provide mixture A, said mixture A containing a phosphorus source, an aluminum source and water;

[0049] (2) The mixture A is aged and then dried to obtain aluminum phosphate dry glue;

[0050] (3) Provide an initial gel mixture B, wherein the initial gel mixture B contains the aluminum phosphide dry gel obtained in step (2), a silicon source, a template agent and water;

[0051] (4) Crystallize the initial gel mixture B;

[0052] (5) The crystallized product is subjected to solid-liquid separation, and the resulting solid phase is washed, dried and optionally calcined.

[0053] According to the above-described synthesis method of the present invention, the template agent is isopropylamine.

[0054] In this article, "at least one" means one or more.

[0055] According to the present invention, the molecular sieve of the present invention is synthesized by a phosphorus-aluminum dry gel liquid-phase inversion method. In preparing the mixture A, the mixture A contains a phosphorus source, an aluminum source, and water. The phosphorus source is calculated as P2O5, and the aluminum source is calculated as Al2O3. The molar ratio of the phosphorus source, aluminum source, and water is 0.6-1.2:1:30-70, preferably 0.8-1.2:1:35-65. In preparing the mixture A, the water refers to the total water volume, including, for example, added water, as well as water from the phosphorus source and aluminum source. In preparing the initial gel mixture B, the initial gel mixture B contains the aluminum phosphate dry gel obtained in step (2), a silicon source, a template agent, and water. The aluminum phosphate dry gel is calculated as Al2O3, the silicon source is calculated as SiO2, and the molar ratio of the aluminum phosphate dry gel, the silicon source, the template agent, and water is 1:0.1-0.8:1-3:10-200, preferably 1:0.15-0.6:1.5-2.5:20-120. In preparing the initial gel mixture B, the water refers to the total water volume, including, for example, the added water, as well as the water in the aluminum phosphate dry gel, the silicon source, and the template agent.

[0056] According to the present invention, the molecular sieve of the present invention is synthesized using the phosphorus aluminum dry gel liquid-phase inversion method. The phosphorus aluminum dry gel can be prepared using conventional methods, and the phosphorus aluminum dry gel, silicon source, template agent, and water are mixed to obtain the initial gel mixture B. Specifically, the aluminum source is mixed with water, and then the phosphorus source is added while stirring to obtain mixture A. Mixture A is aged under stirring at an aging temperature of 50-80°C, preferably 60-70°C, for 6-20 hours, preferably 10-18 hours. The aged mixture A is then dried at an aging temperature of 80-110°C, preferably 80-100°C, for 15-35 hours, preferably 20-30 hours, to obtain the phosphorus aluminum dry gel. The phosphorus aluminum dry gel, silicon source, water, and template agent are added sequentially and mixed evenly to obtain the initial gel mixture B.

[0057] This invention does not have any particular limitations on the types of phosphorus sources, silicon sources, and aluminum sources; conventional choices can be made.

[0058] Generally, the phosphorus source may be selected from at least one of orthophosphoric acid, phosphorous acid, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, and organophosphorus compounds.

[0059] Preferably, the organophosphorus compound is at least one of trimethylphosphorus and triethylphosphorus.

[0060] The aluminum source may be selected from at least one of aluminum salts, boehmite, aluminum isopropoxide, aluminum hydroxide gel, and activated alumina.

[0061] Preferably, the aluminum salt is at least one of aluminum chloride and aluminum sulfate.

[0062] The silicon source may be selected from at least one of silica sol, activated silica, solid silica gel, silicon-containing compounds of Formula I, and silica.

[0063]

[0064] In Formula I, R1, R2, R3 and R4 are each C1-C4 alkyl groups, such as methyl, ethyl, propyl and their isomers and butyl and their isomers.

[0065] Preferably, the silicon-containing compound is at least one selected from silica sol, activated silica, solid silica gel, tetraethyl orthosilicate, and fumed silica.

[0066] According to the present invention, the crystallization process can be carried out at a single temperature. Generally, the crystallization is carried out at autogenous pressure and 170-210°C for 30-92 hours; preferably, the crystallization is carried out at autogenous pressure and 170-200°C for 40-85 hours; more preferably, the crystallization is carried out at autogenous pressure and 180-190°C for 50-81 hours.

[0067] According to the present invention, in a preferred embodiment, the crystallization process employs a two-stage variable-temperature crystallization, namely, a first-stage crystallization and a second-stage crystallization. Typically, the crystallization temperature of the first stage is lower than that of the second stage. The crystallization conditions for each stage are independent: the first stage crystallization is carried out at autogenous pressure and 130-170°C for 25-45 hours, and the second stage crystallization is carried out at autogenous pressure and 170-200°C for 30-55 hours; preferably, the first stage crystallization is carried out at autogenous pressure and 135-165°C for 25-40 hours, and the second stage crystallization is carried out at autogenous pressure and 170-195°C for 35-50 hours; more preferably, the first stage crystallization is carried out at autogenous pressure and 140-160°C for 30-40 hours, and the second stage crystallization is carried out at autogenous pressure and 175-190°C for 40-50 hours.

[0068] According to the present invention, the solid phase obtained by solid-liquid separation and water washing of the mixture obtained by crystallization can be dried under conventional conditions and optionally calcined to obtain a molecular sieve. In this invention, "optional" means not necessary and can be understood as including or excluding. Specifically, the drying can be carried out at a temperature of 90-120°C, and the drying time can be selected according to the drying temperature, generally 6-14 hours. The purpose of calcination is mainly to remove the template agent remaining in the molecular sieve channels during the molecular sieve synthesis process, and whether or not to perform calcination can be determined according to specific application requirements. Calcination is preferably performed after drying. The calcination can be carried out at a temperature of 400-700°C, and the duration of calcination can be selected according to the calcination temperature, generally 3-6 hours. The calcination is generally carried out in an air atmosphere. Furthermore, the solid phase obtained by solid-liquid separation can be washed before drying; that is, the crystallization product obtained by hydrothermal crystallization can be subjected to solid-liquid separation, washing, and drying to obtain molecular sieve raw powder; or, the crystallization product obtained by hydrothermal crystallization can be subjected to solid-liquid separation, washing, drying, and calcination to obtain a calcined hydrogen-form molecular sieve. The washing method can be a conventional method, and to avoid introducing other impurities, it is preferable to wash with deionized water until neutral. The solid-liquid separation method can be a conventional method, such as filtration or centrifugation.

[0069] According to the present invention, there are no particular restrictions on the heating method of any step in the synthesis method of the AFN structured molecular sieve, and a programmed heating method can be adopted, for example, 0.5℃-5℃ / min.

[0070] According to the present invention, there is no particular limitation on the pressure of the crystallization process in the synthesis method of the AFN structured molecular sieve, and it can be the self-generated pressure of the crystallization system.

[0071] According to the present invention, the crystallization in the synthesis method of the AFN structured molecular sieve is carried out in a closed environment, and the reaction vessel for crystallization is a stainless steel reactor with a polytetrafluoroethylene liner.

[0072] According to a third aspect of the present invention, the present invention also provides the application of the AFN-structured silica-phosphorus-aluminum molecular sieve in gas adsorption separation and / or conversion of oxygen-containing compounds into low-carbon olefins, especially in the adsorption separation of mixed gases such as C3H6 / C3H8, CO2 / CH4, and CO2 / N2, as well as in the reaction of methanol conversion to low-carbon olefins, all of which have good application prospects.

[0073] According to a specific embodiment of the present invention, the application of the AFN-structured silica-phosphorus-aluminum molecular sieve in the conversion of oxygen-containing compounds into low-carbon olefins is a method for methanol-to-olefins, the method comprising: contacting methanol with the AFN-structured silica-phosphorus-aluminum molecular sieve of the present invention under methanol-to-olefins reaction conditions.

[0074] According to the present invention, the methanol-to-olefins reaction can be carried out under conventional methanol-to-olefins reaction conditions, provided that the AFN-structured aluminosilicate molecular sieve provided by the present invention is used. Generally, methanol can be contacted with the AFN-structured aluminosilicate molecular sieve of the present invention at a temperature of 400-500°C. The weight hourly space velocity (WHSV) of methanol is generally 1-9 h⁻¹. -1 .

[0075] The present invention will be described in detail below through embodiments.

[0076] In the following embodiments, X-ray powder diffraction phase analysis (XRD) was performed using a Panaco Empyrean diffractometer from the Netherlands, which is equipped with a PIXcel. 3D Detector. Test conditions: Cu target, Kα radiation, Ni filter, tube voltage 40kV, tube current 40mA, scan range 5°-50°.

[0077] In the following examples, scanning electron microscopy (SEM) morphology analysis was performed using a Hitachi S4800 SEM. Test conditions: After drying and grinding, the samples were adhered to conductive adhesive. The accelerating voltage of the analytical electron microscope was 5.0 kV, and the magnification ranged from 20 to 800,000 times.

[0078] In the following embodiments, 29 The instrument used for Si MAS NMR analysis was a Bruker Avance III 500MHz nuclear magnetic resonance spectrometer. Test conditions: 7mm dual resonance probe; resonance frequency 99.28MHz; sampling time 17.3ms; delay time 4s; pulse width 2.1μs; 5000 samples; rotation speed 5000Hz.

[0079] In the following examples, R represents the template agent, which is isopropylamine.

[0080] In the experimental example, the catalytic lifetime of the molecular sieve is defined as the duration of the catalytic reaction from the start of the reaction until the CH3OH conversion rate is higher than 99%.

[0081] Examples 1-6 illustrate the synthesis of the AFN-structured silicon-phosphorus-aluminum molecular sieve of the present invention using the phosphorus-aluminum dry gel liquid-phase inversion method.

[0082] Example 1

[0083] 4.91 g of boehmite (Al₂O₃, 83% by mass) was mixed with 33.81 g of deionized water until homogeneous. Then, 9.22 g of orthophosphoric acid (H₃PO₄, 85% by mass) was slowly added in a thin stream while stirring. The mixture was stirred thoroughly at 70°C and aged for 12 hours to obtain mixture A. Mixture A was poured into a tray and dried at 80°C for 24 hours to obtain aluminum phosphate gel.

[0084] Take 5.72 g of the prepared aluminum phosphate dry adhesive (solid content 85.22%) and add it to the polytetrafluoroethylene liner. Then add 0.19 g of solid silica gel (SiO2 mass fraction 93%), 6.32 g of deionized water, and 2.39 g of isopropylamine (C3H9N mass fraction 99%) in sequence. Stir well. The molar ratio of each component is: P2O5 / Al2O3 = 1.0, SiO2 / Al2O3 = 0.15, R / Al2O3 = 2.0, H2O / Al2O3 = 20.

[0085] The polytetrafluoroethylene liner containing the above reaction mixture was sealed in a stainless steel autoclave. The autoclave was then placed in a rotating convection oven at a speed of 20 r / min for the first stage of crystallization under autogenous pressure: crystallization at 150°C for 36 hours. The temperature was then raised to 180°C for the second stage of crystallization: crystallization at 180°C for 45 hours. Once crystallization was complete and the autoclave temperature had dropped to room temperature, the crystallized product was removed. After filtration or centrifugation, the obtained solid phase was washed with deionized water until neutral and dried at 110°C for 12 hours to obtain the molecular sieve powder.

[0086] The obtained molecular sieve was subjected to X-ray diffraction analysis; the XRD pattern is shown below. Figure 1 It was confirmed to be a pure-phase AFN-structured silica-phosphorus-aluminum molecular sieve. The morphology of the molecular sieve was observed using SEM; SEM images are shown below. Figure 2 It has a sheet-like appearance.

[0087] Example 2

[0088] 5.44 g of aluminum hydroxide dry adhesive (75% Al2O3 by mass) was mixed with 26.15 g of deionized water until homogeneous. While stirring, 8.76 g of orthophosphoric acid (85% H3PO4 by mass) was slowly added in a thin stream. The mixture was stirred thoroughly at 70°C and aged for 10 hours to obtain mixture A. Mixture A was poured into a tray and dried at 80°C for 28 hours to obtain aluminum phosphate dry adhesive.

[0089] Take 5.68 g of the prepared aluminum phosphate dry adhesive (solid content 83.40%) and add it to the polytetrafluoroethylene liner. Then add 1.20 g of silica sol (SiO2 mass fraction 30%), 12.60 g of deionized water, and 2.99 g of isopropylamine (C3H9N mass fraction 99%) in sequence and stir evenly. The molar ratio of each component is: P2O5 / Al2O3 = 0.95, SiO2 / Al2O3 = 0.3, R / Al2O3 = 2.5, H2O / Al2O3 = 40.

[0090] The polytetrafluoroethylene liner containing the above reaction mixture was sealed in a stainless steel autoclave. The autoclave was then placed in a rotating convection oven at a speed of 20 r / min for the first stage of crystallization under autogenous pressure: crystallization at 150°C for 40 hours. The temperature was then raised to 180°C for the second stage of crystallization: crystallization at 180°C for 50 hours. Once crystallization was complete and the autoclave temperature had dropped to room temperature, the crystallized product was removed. After filtration or centrifugation, the obtained solid phase was washed with deionized water until neutral and dried at 110°C for 12 hours to obtain the molecular sieve powder.

[0091] X-ray diffraction analysis confirmed that the obtained molecular sieve was a pure-phase AFN-structured silica-phosphorus-aluminum molecular sieve. SEM was used to observe the morphology of the molecular sieve; SEM images are shown below. Figure 3 It exhibits a sheet-like morphology. And it is produced using a solid-state... 29 Si MAS NMR was used to investigate the silicon coordination environment of the sample, such as Figure 4 As shown, the sample exhibits a resonance signal peak at a chemical shift of -90.70, whereas SAPO molecular sieves typically... 29 The Si MAS NMR signal peaks are assigned to: -92~Si(4Al), -95~Si(3Al), -100~Si(2Al), -105~Si(1Al), and -110~Si(0Al), respectively. Based on the signal peaks, Si in the synthesized SAPO-14 molecular sieve exists in the form of a single Si(4Al) coordination.

[0092] Example 3

[0093] 4.91 g of boehmite (83% Al2O3 by mass) was mixed with 27.76 g of deionized water until homogeneous. Then, 11.32 g of ammonium hydrogen phosphate (98% (NH4)2HPO4 by mass) was slowly added while stirring. The mixture was stirred thoroughly at 60°C and aged for 18 hours to obtain mixture A. Mixture A was poured into a tray and dried at 100°C for 21 hours to obtain aluminum phosphate dry gel.

[0094] Take 6.09 g of the prepared aluminum phosphate dry adhesive (solid content 82.35%) and add it to the polytetrafluoroethylene liner. Then add 0.65 g of solid silica gel (SiO2 mass fraction 93%), 16.88 g of deionized water, and 1.79 g of isopropylamine (C3H9N mass fraction 99%) in sequence and stir evenly. The molar ratio of each component is: P2O5 / Al2O3 = 1.05, SiO2 / Al2O3 = 0.5, R / Al2O3 = 1.5, H2O / Al2O3 = 50.

[0095] The polytetrafluoroethylene liner containing the above reaction mixture was sealed in a stainless steel autoclave. The autoclave was then placed in a rotating convection oven at a speed of 20 r / min for the first stage of crystallization under autogenous pressure: crystallization at 160℃ for 35 hours. The temperature was then raised to 175℃ for the second stage of crystallization: crystallization at 175℃ for 45 hours. Once crystallization was complete and the autoclave temperature had dropped to room temperature, the crystallized product was removed. After filtration or centrifugation, the obtained solid phase was washed with deionized water until neutral and dried at 110℃ for 12 hours to obtain the molecular sieve powder.

[0096] The obtained molecular sieve was subjected to X-ray diffraction analysis and its morphology was observed using SEM. The characterization results showed that the sample was a pure-phase AFN structure silicon-phosphorus-aluminum molecular sieve with a plate-like morphology.

[0097] Example 4

[0098] 4.16 g of activated alumina (Al₂O₃, 98% by mass) was mixed with 23.62 g of deionized water until homogeneous. While stirring, 10.15 g of orthophosphoric acid (H₃PO₄, 85% by mass) was slowly added in a thin stream. The mixture was stirred thoroughly at 75°C and aged for 15 hours to obtain mixture A. Mixture A was poured into a tray and dried at 100°C for 18 hours to obtain aluminum phosphate gel.

[0099] Take 5.98 grams of the prepared aluminum phosphate dry adhesive (solid content 86.35%) and add it to the polytetrafluoroethylene liner. Then add 0.38 grams of active silica (SiO2 mass fraction 95%), 27.97 grams of deionized water, and 2.39 grams of isopropylamine (C3H9N mass fraction 99%) in sequence and stir evenly. The molar ratios of each component are: P2O5 / Al2O3 = 1.1, SiO2 / Al2O3 = 0.3, R / Al2O3 = 2.0, and H2O / Al2O3 = 80.

[0100] The polytetrafluoroethylene liner containing the above reaction mixture was sealed in a stainless steel autoclave. The autoclave was then placed in a rotating convection oven at a speed of 20 r / min for the first stage of crystallization under autogenous pressure: crystallization at 170°C for 28 hours. The temperature was then raised to 190°C for the second stage of crystallization: crystallization at 190°C for 40 hours. Once crystallization was complete and the autoclave temperature had dropped to room temperature, the crystallized product was removed. After filtration or centrifugation, the obtained solid phase was washed with deionized water until neutral and dried at 110°C for 12 hours to obtain the molecular sieve powder.

[0101] The obtained molecular sieve was subjected to X-ray diffraction analysis and its morphology was observed using SEM. The characterization results showed that the sample was a pure-phase AFN structure silicon-phosphorus-aluminum molecular sieve with a plate-like morphology.

[0102] Example 5

[0103] 16.67 aluminum isopropoxide (C9H) 21 AlO3 (98% by mass) was mixed with 50.03 g of deionized water until homogeneous. Then, 7.44 g of ammonium dihydrogen phosphate (NH4H2PO4, 99% by mass) was slowly added while stirring. The mixture was stirred thoroughly at 65°C and aged for 18 hours to obtain mixture A. Mixture A was poured into a tray and dried at 90°C for 22 hours to obtain aluminum phosphate dry gel.

[0104] Take 5.31 grams of the prepared aluminum phosphate dry adhesive (solid content 81.11%) and add it to the polytetrafluoroethylene liner, then add 3.37 grams of tetraethyl orthosilicate (C8H2O) sequentially. 20 42.19 g of deionized water and 1.19 g of isopropylamine (C3H9N, 99% mass fraction) were stirred until homogeneous. The molar ratios of the components were: P2O5 / Al2O3 = 0.8, SiO2 / Al2O3 = 0.8, R / Al2O3 = 1.0, and H2O / Al2O3 = 120.

[0105] The polytetrafluoroethylene liner containing the above reaction mixture was capped and placed in a stainless steel autoclave for sealing. The autoclave was then placed in a rotating convection oven with a rotation speed of 20 r / min for single-stage crystallization under autogenous pressure: crystallization at 180℃ for 81 hours. After crystallization was completed and the autoclave temperature dropped to room temperature, the crystallized product was removed, filtered or centrifuged, and the obtained solid phase was washed with deionized water until neutral. The solid phase was then dried at 110℃ for 12 hours to obtain the molecular sieve powder.

[0106] The obtained molecular sieve was subjected to X-ray diffraction analysis and its morphology was observed using SEM. The characterization results showed that the sample was a pure-phase AFN structure silicon-phosphorus-aluminum molecular sieve with a blocky morphology.

[0107] Example 6

[0108] 10.78 g of aluminum chloride (AlCl3, 99% by mass) was mixed with 36.90 g of deionized water until homogeneous. While stirring, 12.47 g of phosphorous acid (H3PO3, 50% by mass) was slowly added in a thin stream. The mixture was stirred thoroughly at 55°C and aged for 20 hours to obtain mixture A. Mixture A was poured into a tray and dried at 85°C for 25 hours to obtain aluminum phosphate gel.

[0109] Take 5.67 g of the prepared aluminum phosphate dry adhesive (solid content 83.45%) and add it to the polytetrafluoroethylene liner. Then add 0.74 g of silica (SiO2 mass fraction 98%), 35.04 g of deionized water, and 3.58 g of isopropylamine (C3H9N mass fraction 99%) in sequence and stir evenly. The molar ratio of each component is: P2O5 / Al2O3 = 0.95, SiO2 / Al2O3 = 0.6, R / Al2O3 = 3, H2O / Al2O3 = 100.

[0110] The polytetrafluoroethylene liner containing the above reaction mixture was capped and placed in a stainless steel autoclave and sealed. The autoclave was then placed in a rotating convection oven with a rotation speed of 20 r / min and subjected to single-stage crystallization under autogenous pressure: crystallization at 200℃ for 50 hours. After crystallization was completed, the crystallized product was removed when the autoclave temperature dropped to room temperature. After filtration or centrifugation, the obtained solid phase was washed with deionized water until neutral and dried at 110℃ for 12 hours to obtain molecular sieve powder.

[0111] X-ray diffraction analysis confirmed that the obtained molecular sieve was a pure-phase AFN-structured silica-phosphorus-aluminum molecular sieve. SEM was used to observe the morphology of the molecular sieve; SEM images are shown below. Figure 5 It exhibits a blocky morphology.

[0112] Comparative Example 1

[0113] Molecular sieves were synthesized according to the method in Example 2, except that 1-isopropyl-4-piperidinone was used as a template agent in this comparative example.

[0114] 5.44 g of aluminum hydroxide dry adhesive (75% Al2O3 by mass) was mixed with 26.15 g of deionized water until homogeneous. While stirring, 8.76 g of orthophosphoric acid (85% H3PO4 by mass) was slowly added in a thin stream. The mixture was stirred thoroughly at 70°C and aged for 10 hours to obtain mixture A. Mixture A was poured into a tray and dried at 80°C for 28 hours to obtain aluminum phosphate dry adhesive.

[0115] Take 5.68 g of the prepared aluminum phosphide dry adhesive (solid content 83.40%) and add it to the polytetrafluoroethylene liner, followed by 1.20 g of silica sol (SiO2 mass fraction 30%), 12.48 g of deionized water, and 7.20 g of 1-isopropyl-4-piperidinone (C8H12H2O). 16 NO mass fraction 98%, stir evenly, the molar ratio of each component added is: P2O5 / Al2O3=0.95, SiO2 / Al2O3=0.3, R / Al2O3=2.5, H2O / Al2O3=40.

[0116] The polytetrafluoroethylene liner containing the above reaction mixture was sealed in a stainless steel autoclave. The autoclave was then placed in a rotating convection oven at a speed of 20 r / min for the first stage of crystallization under autogenous pressure: crystallization at 150°C for 40 hours. The temperature was then raised to 180°C for the second stage of crystallization: crystallization at 180°C for 50 hours. Once crystallization was complete and the autoclave temperature had dropped to room temperature, the crystallized product was removed. After filtration or centrifugation, the obtained solid phase was washed with deionized water until neutral and dried at 110°C for 12 hours to obtain the molecular sieve powder.

[0117] X-ray diffraction analysis of the obtained molecular sieve confirmed it to be a pure-phase AFN-structured silica-phosphorus-aluminum molecular sieve. Solid-state... 29 Si MAS NMR was used to investigate the silicon coordination environment of the sample, such as Figure 6 As shown, the sample exhibits a major resonance peak at chemical shift -91, belonging to the Si(4Al) structure, while weaker resonance peaks exist at chemical shifts of -100, -104, and -112, corresponding to the Si(2Al), Si(1Al), and Si(0Al) structures, respectively. Therefore, the Si coordination mode in the SAPO-14 molecular sieve synthesized using 1-isopropyl-4-piperidinone as a template agent is quite complex.

[0118] Comparative Example 2

[0119] Molecular sieves were synthesized according to the method in Example 1, except that this comparative example uses a hydrothermal synthesis method.

[0120] 2.46 g of boehmite (Al2O3 mass fraction 83%), 6.06 g of deionized water, 4.61 g of orthophosphoric acid (H3PO4 mass fraction 85%), 0.19 g of solid silica gel (SiO2 mass fraction 93%), and 2.39 g of isopropylamine (C3H9N mass fraction 99%) were sequentially added to a polytetrafluoroethylene liner and stirred until homogeneous. The molar ratios of the components added were: P2O5 / Al2O3 = 1.0, SiO2 / Al2O3 = 0.15, R / Al2O3 = 2.0, and H2O / Al2O3 = 20.

[0121] The polytetrafluoroethylene liner containing the above reaction mixture was sealed in a stainless steel autoclave. The autoclave was then placed in a rotating convection oven at a speed of 20 r / min for the first stage of crystallization under autogenous pressure: crystallization at 150°C for 36 hours. The temperature was then raised to 180°C for the second stage of crystallization: crystallization at 180°C for 45 hours. Once crystallization was complete and the autoclave temperature had dropped to room temperature, the crystallized product was removed. After filtration or centrifugation, the obtained solid phase was washed with deionized water until neutral and dried at 110°C for 12 hours to obtain the molecular sieve powder.

[0122] X-ray diffraction analysis of the obtained solid confirmed that it was an amorphous phase, thus indicating that the AFN-structured aluminosilicate molecular sieve cannot be synthesized by hydrothermal synthesis.

[0123] Experimental Example 1

[0124] This experimental example illustrates the catalytic performance of the AFN-structured silica-phosphorus-aluminum molecular sieve synthesized in Example 2 in the methanol-to-olefins reaction.

[0125] The SAPO-14 molecular sieve powder obtained in Example 2 was placed in a muffle furnace and heated to 550°C for 3 hours to obtain the calcined sample. After pressing and sieving, the 20-40 mesh sample was selected and labeled as S-1.

[0126] The evaluation apparatus was a fixed-bed reactor, and the evaluation conditions were: catalyst loading of 3g, reactant of pure methanol, and mass hourly space velocity (WHSV) of 1h. -1 The carrier gas was nitrogen, with a flow rate of 350 mL / min. The reaction temperature was 450 °C, and the reaction pressure was 0.1 MPa. Ethylene and propylene were the target products. The reaction products were analyzed online using an Agilent GC7890A gas chromatograph. The MTO catalytic performance results are shown in Table 2.

[0127] Comparative Experiment Example 1

[0128] This comparative experiment is used to illustrate the catalytic performance of the AFN-structured silica-phosphorus-aluminum molecular sieve synthesized in Comparative Example 1 in the methanol-to-olefins reaction.

[0129] The methanol-to-olefins (MTO) reaction was carried out according to the method of Experimental Example 1, except that the catalyst used was an AFN-structured silica-phosphorus-aluminum molecular sieve synthesized in Comparative Example 1, labeled D-1. Ethylene and propylene were the target products. The reaction products were analyzed online by an Agilent GC7890A gas chromatograph, and the MTO catalytic performance results are shown in Table 2.

[0130] Table 2

[0131]

[0132] As shown in Table 2, the AFN-structured silica-phosphorus-aluminum molecular sieve product prepared by this invention exhibits excellent MTO catalytic activity, with a longer catalytic lifetime (130 min) and higher ethylene selectivity (38.45%) and propylene selectivity (42.77%). This indicates that the Si in the AFN-structured silica-phosphorus-aluminum molecular sieve provided by this invention exists in a single Si(4Al) coordination form, serving as a medium-strong acidic center, which is not prone to coking and deactivation, thus exhibiting excellent catalytic performance in the MTO reaction.

[0133] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0134] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0135] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for synthesizing AFN-structured silica-alumina molecular sieves, characterized in that, The synthesis method includes the following steps: (1) providing a mixture A, wherein the mixture A contains a phosphorus source, an aluminum source and water; (2) The mixture A is aged and then dried to obtain aluminum phosphate dry adhesive; (3) Provide an initial gel mixture B, which contains the aluminum phosphide dry gel obtained in step (2), a silicon source, a template agent and water; (4) Crystallize the initial gel mixture B; (5) The crystallized product is subjected to solid-liquid separation, and the resulting solid phase is washed, dried and optionally calcined. Wherein, the phosphorus source is calculated as P2O5, the aluminum source is calculated as Al2O3, and the molar ratio of phosphorus source, aluminum source and water in mixture A is 0.6-1.2 : 1 : 30-70; In the initial gel mixture B, the molar ratio of aluminum phosphate dry adhesive (calculated as Al2O3), silicon source (calculated as SiO2), aluminum phosphate dry adhesive, silicon source, template agent, and water is 1:0.1-0.8:1-3:10-200. The template agent is isopropylamine.

2. The synthesis method according to claim 1, wherein, The phosphorus source is calculated as P2O5, the aluminum source is calculated as Al2O3, and the molar ratio of phosphorus source, aluminum source and water in mixture A is 0.8-1.2 : 1 : 35-65; The phosphorus aluminum dry adhesive is calculated as Al2O3, the silicon source is calculated as SiO2, and the molar ratio of phosphorus aluminum dry adhesive, silicon source, template agent and water in the initial gel mixture B is 1 : 0.15-0.6 : 1.5-2.5 : 20-120.

3. The synthesis method according to claim 1, wherein, The crystallization process consists of two stages, including a first stage of crystallization and a second stage of crystallization, with the first stage crystallization temperature being lower than the second stage crystallization temperature. The first stage of crystallization involves crystallization at autogenous pressure and 130-170℃ for 25-45 hours, while the second stage involves crystallization at autogenous pressure and 170-200℃ for 30-55 hours.

4. The synthesis method according to claim 3, wherein, The first stage of crystallization involves crystallization at autogenous pressure and 135-165℃ for 25-40 hours, while the second stage involves crystallization at autogenous pressure and 170-195℃ for 35-50 hours.

5. The synthesis method according to claim 4, wherein, The first stage of crystallization involves crystallization at autogenous pressure and 140-160℃ for 30-40 hours, while the second stage involves crystallization at autogenous pressure and 175-190℃ for 40-50 hours.

6. The synthesis method according to claim 1 or 2, wherein, The crystallization is a single-stage crystallization process, which is carried out under autogenous pressure and at 170-210°C for 30-92 hours.

7. The synthesis method according to claim 6, wherein, The crystallization process involves crystallization under autogenous pressure and at 170-200°C for 40-85 hours.

8. The synthesis method according to claim 7, wherein, The crystallization is carried out under autogenous pressure and at 180-190°C for 50-81 hours.

9. The synthesis method according to claim 1 or 2, wherein, The phosphorus source is selected from at least one of orthophosphoric acid, phosphorous acid, ammonium hydrogen phosphate, ammonium dihydrogen phosphate, and organophosphorus compounds.

10. The synthesis method according to claim 9, wherein, The organophosphorus compound is trimethylphosphorus and / or triethylphosphorus.

11. The synthesis method according to claim 1 or 2, wherein, The aluminum source is selected from at least one of aluminum salts, boehmite, aluminum isopropoxide, aluminum hydroxide gel, and activated alumina.

12. The synthesis method according to claim 11, wherein, The aluminum salt is aluminum chloride and / or aluminum sulfate.

13. The synthesis method according to claim 1 or 2, wherein, The silicon source is selected from at least one of silica sol, activated silica, solid silica gel, and silicon-containing compounds represented by Formula I. (Equation I) In Formula I, R1, R2, R3 and R4 are each C1-C4 alkyl groups.

14. The synthesis method according to claim 13, wherein, The silicon-containing compound is tetraethyl orthosilicate.

15. The synthesis method according to claim 1 or 2, wherein, The silicon source is silica.

16. The synthesis method according to claim 1, wherein, In step (2), mixture A is aged under stirring at a temperature of 50-80°C for 6-20 hours and at a temperature of 80-110°C for 15-35 hours.

17. The synthesis method according to claim 16, wherein, In step (2), mixture A is aged under stirring at a temperature of 60-70°C for 10-18 hours; the drying temperature is 80-100°C for 20-30 hours.

18. The synthesis method according to claim 1, wherein, The obtained solid phase is dried at a temperature of 90-120℃ and calcined at a temperature of 400-700℃.

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