Supported MFI molecular sieve membrane as well as preparation method and application thereof

Abstract

The invention provides a supported MFI molecular sieve membrane as well as a preparation method and application thereof. The preparation method of the supported MFI molecular sieve membrane comprises the following steps: carrying out silane coupling agent modification treatment on a carrier loaded with an oxide coating to obtain a modified carrier; growing a single-layer MFI molecular sieve nanosheet dispersion liquid containing a structure-directing agent on the surface of the modified carrier to obtain the supported MFI molecular sieve membrane, wherein the structure-directing agent comprises a hydrophilic group and a hydrophobic chain. According to the preparation method disclosed by the invention, the carrier is subjected to surface modification, and the molecular sieve nanosheet is loaded on the surface of the modified carrier, so that the ultrathin continuous supported MFI molecular sieve membrane is formed.

Description

Technical Field

[0001] This application relates to the field of molecular sieve membranes, and more particularly to a supported MFI molecular sieve membrane, its preparation method, and its application. Background Technology

[0002] MFI-type molecular sieve membranes, due to their unique two-dimensional zigzag pore structure and acidic surface properties, are widely used in gas separation (such as olefin / alkane separation), pervaporation (organic solvent dehydration), and membrane catalysis (such as olefin isomerization and aromatization). Thicker membrane layers increase mass transfer resistance, lengthen molecular diffusion paths, and lead to reduced conversion and selectivity in catalytic reactions. Therefore, reducing membrane thickness is one of the key approaches to improving its catalytic performance, effectively shortening diffusion paths and enhancing mass transfer processes.

[0003] Traditional hydrothermal in-situ synthesis methods for preparing MFI molecular sieve membranes suffer from poor controllability and insufficient precision in film thickness. To prepare ultrathin MFI molecular sieve membranes, a strategy of directly synthesizing molecular sieve crystals on a support surface is often employed. However, this method places extremely high demands on the smoothness and thermal expansion coefficient of the support surface, and is currently only applicable to two-dimensional planar supports, such as polished single-crystal silicon wafers or alumina plates. However, these supports cannot meet the high-throughput requirements of industrial-grade reactors, and the mismatch in thermal expansion coefficients between the support and the membrane layer can easily lead to membrane cracking during calcination or operation, shortening membrane life.

[0004] Existing research largely focuses on optimizing two-dimensional supports, such as inducing b-axis oriented films through spin-coating nanocrystal seeds and secondary growth methods. However, these methods are difficult to extend to three-dimensional supports and are highly sensitive to the shape, size, and surface roughness of the support, making it difficult to control the film thickness and achieve ultrathin films (<500 nm). Therefore, developing a method for preparing ultrathin continuous MFI molecular sieve films suitable for three-dimensional supports is key to overcoming support limitations and obtaining high-performance films. Summary of the Invention

[0005] This application provides a supported MFI molecular sieve membrane, its preparation method, and its application. By modifying the support, a single layer of MFI molecular sieve nanosheets is grown on the surface of the modified support, thereby forming an ultrathin and continuous molecular sieve membrane. At the same time, it can induce the molecular sieve membrane to be oriented along the b-axis, thus solving the problem of limited support when preparing high-performance molecular sieve membranes, thereby broadening the application scenarios of MFI molecular sieve membranes.

[0006] In a first aspect, this application provides a method for preparing a supported MFI molecular sieve membrane, comprising the following steps:

[0007] A carrier loaded with an oxide coating is modified with a silane coupling agent to obtain a modified carrier; a single-layer MFI molecular sieve nanosheet dispersion including a structure-directing agent is grown on the surface of the modified carrier to obtain the supported MFI molecular sieve membrane; wherein the structure-directing agent includes hydrophilic groups and hydrophobic chains.

[0008] In one possible embodiment, the oxide coating comprises at least one of TiO2, SiO2, and ZrO2; and / or, the silane coupling agent comprises at least one of (3-aminopropyl)triethylsilane, (3-aminopropyl)trimethoxysilane, 3-aminopropylmethyldiethoxysilane, and N-ethyl-3-aminopropyltrimethoxysilane; and / or, the hydrophilic group comprises n quaternary ammonium salt cations, wherein 1 ≤ n ≤ 4, and the hydrophobic chain comprises a long-chain alkyl group, wherein the long-chain alkyl group has ≥ 12 carbon atoms; and / or, the carrier comprises at least one of glass slides, silicon wafers, sodium carbonate tubes, hollow fiber ceramics, silicon carbide, stainless steel, commercial glass spheres, alumina spheres, silica spheres, mixed oxide carriers, zirconia spheres, quartz sand, and titanium dioxide spheres.

[0009] In one possible embodiment, the single-layer MFI molecular sieve nanosheet dispersion is prepared by a method comprising the following steps: mixing multilayer MFI molecular sieve nanosheets including a structure-directing agent with an organic base solution; performing a first exfoliation treatment on the mixture to obtain an exfoliation intermediate; and performing a second exfoliation treatment on the mixed solution including the exfoliation intermediate to obtain the single-layer MFI molecular sieve nanosheet dispersion; wherein the mass-to-volume ratio of the multilayer MFI molecular sieve nanosheets to the organic base solution is 0.01-10 g / ml.

[0010] In one possible implementation, the organic base includes at least one of tetrabutylammonium hydroxide, tetraethylammonium hydroxide, hexadecyltrimethylammonium hydroxide, benzyltrimethylammonium hydroxide, tetramethylammonium hydroxide, and tetrapropylammonium hydroxide; and / or, the pressure of the first stripping treatment is 5000-15000 psi, and the number of cycles is 3-10; the pressure of the second stripping treatment is 2000-8000 psi, and the number of cycles is 1-5.

[0011] In one possible embodiment, the carrier loaded with the oxide coating is prepared by the following process: stirring a mixed solution including coating raw materials for 0.5-2 hours to obtain an oxide coating sol; coating the oxide coating sol onto the surface of the carrier; and then drying and calcining to obtain the carrier loaded with the oxide coating; wherein the carrier loaded with the oxide coating comprises a carrier substrate and a coating on the carrier surface, and wherein the coating thickness is 10-1000 nm.

[0012] In one possible implementation, the drying process is carried out at a temperature of 80-120°C for 3-12 hours; and / or the calcination process is carried out at a heating rate of 0.5-4°C / min, at a temperature of 350-550°C for 4-10 hours.

[0013] In one possible embodiment, the silane coupling agent modification treatment of the oxide-coated support includes: heating and refluxing a mixed solution comprising the oxide-coated support and the silane coupling agent to obtain the modified support, wherein the heating and refluxing temperature is 60-110°C and the time is 1-12 h; the mass ratio of the silane coupling agent to the oxide-coated support is (0.01-2):(0.01-4).

[0014] In one possible implementation, the calcination process is followed by irradiation of the carrier loaded with the oxide coating with ultraviolet light; wherein the irradiation time is 3-24 hours.

[0015] Secondly, this application provides a supported MFI molecular sieve membrane, which is prepared by the method described in any one of the preceding claims.

[0016] Thirdly, this application provides a catalytic reaction carried out using the supported MFI molecular sieve membrane described in the second aspect.

[0017] This application provides a method for preparing a supported MFI molecular sieve membrane. The method involves sequentially modifying a support with an oxide coating and then with a silane coupling agent to obtain a modified support. A monolayer of MFI molecular sieve nanosheets, including a structure-directing agent, is then grown on the surface of the modified support. Therefore, this method can stably prepare ultrathin, continuous MFI molecular sieve membranes and is applicable to various supports. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0019] Figure 1 This is a SEM image of the supported molecular sieve membrane prepared in Example 1 of this application;

[0020] Figure 2 This is a SEM image of the supported molecular sieve membrane prepared in Example 2 of this application;

[0021] Figure 3 This is a SEM image of the supported molecular sieve membrane prepared in Example 3 of this application;

[0022] Figure 4This is a SEM image of the supported molecular sieve membrane prepared in Example 4 of this application;

[0023] Figure 5 This is a SEM image of the supported molecular sieve membrane prepared in Example 5 of this application;

[0024] Figure 6 This is a SEM image of the cross-section of the supported molecular sieve membrane prepared in Example 1 of this application;

[0025] Figure 7 This is a graph showing the change in catalytic performance over time in Example 2 of this application.

[0026] Figure 8 This is a graph showing the change in catalytic performance of Comparative Example 1 of this application over time. Detailed Implementation

[0027] To enable those skilled in the art to better understand the solutions of this application, a further detailed description of this application is provided below. The specific embodiments listed below are merely descriptions of the principles and features of this application; the examples are only for explaining this application and are not intended to limit its scope. Based on this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0028] To prepare supported ultrathin MFI molecular sieve membranes adaptable to various carriers, the inventors investigated the preparation method and found that three-dimensional carrier MFI molecular sieve membranes have significant advantages over two-dimensional carrier MFI molecular sieve membranes, exhibiting exponential growth in membrane area and significantly improved mechanical stability. However, extending membrane formation technology from planar to three-dimensional carriers faces significant challenges. Three-dimensional carriers have rough and curved surfaces with complex internal pore structures, making them prone to pore blockage by reagents during pretreatment, affecting permeability. Different carrier materials, such as metals, polymers, and ceramics, exhibit significant differences in thermal expansion coefficients, surface energy, and chemical stability, necessitating the development of universal pretreatment methods. Furthermore, the large difference in thermal expansion coefficients between MFI molecular sieve membranes and three-dimensional carriers like metals and ceramics exacerbates stress concentration during high-temperature treatment, easily leading to cracking at joints or membrane delamination. The synthesis solution struggles to uniformly wet and diffuse within the complex three-dimensional pores, resulting in uneven membrane growth rate and thickness distribution, impacting membrane quality. Therefore, it is necessary to develop a method for preparing MFI molecular sieve membranes that effectively overcomes these shortcomings.

[0029] Based on this, the first aspect of this application provides a method for preparing a supported MFI molecular sieve membrane, comprising the following steps:

[0030] The carrier loaded with oxide coating is modified with silane coupling agent to obtain a modified carrier;

[0031] A supported MFI molecular sieve membrane was obtained by growing a dispersion of monolayer MFI molecular sieve nanosheets containing a structure-directing agent on the surface of a modified support.

[0032] Structure directing agents include hydrophilic groups and hydrophobic chains.

[0033] First, this application uses a silane coupling agent to modify the support loaded with an oxide coating. In this process, one end of the silane coupling agent hydrolyzes to produce silanol groups, which condense with the hydroxyl groups on the surface of the support loaded with the oxide coating to form stable covalent bonds. The organic functional groups at the other end then bind to the organic polymer through a specific chemical reaction. This mechanism of the silane coupling agent forming chemical bonds with different phases at both ends effectively improves interfacial compatibility and adhesion strength, thereby modifying the support loaded with the oxide coating to obtain a modified support.

[0034] Subsequently, a dispersion of monolayer MFI molecular sieve nanosheets including a structure-directing agent is grown on a support surface modified with a coupling agent. At this time, the monolayer MFI molecular sieve nanosheets including the structure-directing agent form chemical bonds with the modified support, thereby forming a supported MFI molecular sieve membrane.

[0035] Structure-directing agents achieve precise control over the b-axis orientation of MFI molecular sieves through their amphiphilic molecular structure. Hydrophilic groups selectively adsorb onto the (100) / (001) crystal planes along the a / c axis, occupying surface nucleation sites through electrostatic and hydrogen bonding interactions, forming a molecular barrier to block precursor deposition. Hydrophobic chains extend outwards from the adsorption layer, constructing spatial barriers that further hinder the precursor from approaching the crystal planes, while simultaneously altering its diffusion path in solution, driving it to migrate towards the exposed b-axis (010) crystal plane. The synergistic effect of hydrophilic adsorption and hydrophobic shielding suppresses a / c axis growth, making the b-axis the dominant growth direction, ultimately inducing the formation of b-axis oriented MFI molecular sieve nanosheet structures.

[0036] Therefore, this invention modifies the carrier surface by coating it with a smooth oxide layer to eliminate the influence of surface properties such as carrier roughness, shape, and size on membrane growth. Stable loading of ultrathin MFI molecular sieve nanosheets on the three-dimensional carrier surface is achieved through chemical bond anchoring. The b-axis orientation of the molecular sieve nanosheets on the carrier surface is anchored, thus significantly reducing the thickness while forming a b-axis oriented molecular sieve membrane. The single-layer molecular sieve nanosheets have smaller grain sizes, allowing for better adhesion to carriers of different shapes and sizes. Therefore, this method reduces the influence of carrier roughness, shape, and size on the orientation, thickness, and density of the molecular sieve membrane, thereby solving the problem of limited carrier selection when obtaining qualified molecular sieve membranes.

[0037] In the specific preparation process, this application uses a coating raw material comprising a coating modifier, an inorganic acid, and an aqueous precursor solution of ethanol as a carrier for preparing the oxide coating. The selection of the coating modifier and the inorganic acid can be the same as conventional selections in the art. For example, the coating modifier includes at least one of tetrabutyl titanate, tetraethyl titanate, tetraisostearate titanate, and (isopropoxy)tris(isostearyl)titanate, preferably tetrabutyl titanate; the inorganic acid includes at least one of nitric acid, hydrochloric acid, phosphoric acid, sulfuric acid, and boric acid, preferably sulfuric acid.

[0038] Specifically, an oxide coating sol is obtained by mixing a mixed solution containing deionized water, inorganic acid, and ethanol with a solution containing a modifier. The solution containing the coating modifier includes the coating modifier and ethanol, with a molar ratio of coating modifier to ethanol of 1:(2-1000); the molar ratio of deionized water, inorganic acid, and ethanol is (1-5):(0.01-10):(1-19).

[0039] In this application, the carrier loaded with oxide coating includes oxide coating and carrier. This application does not limit the cleaning method of carrier, as long as the carrier surface can be effectively cleaned and the organic matter, inorganic salts and dust impurities attached to its surface can be removed, so as to provide a clean and activated substrate for subsequent processing.

[0040] As described above, in one specific embodiment, multilayer MFI molecular sieve nanosheets including a structure-directing agent can be prepared by the following method: a solution containing haloalkanes is slowly added dropwise to a solution containing amines to form a mixed solution; the mixed solution is heated under inert gas protection at 60-110°C for 10-24 hours, preferably at 70°C for 10 hours, and then post-processed including cooling, centrifugation, washing, and drying to obtain a structure-directing agent intermediate; a solution containing a structure-directing agent is mixed with a solution containing haloalkanes to obtain a mixed solution; the mixed solution is heated under inert gas protection at 60-110°C for 10-24 hours, preferably at 70°C for 10 hours, and then post-processed including cooling, centrifugation, washing, and drying to obtain the structure-directing agent of this application. Among them, the halogenated long-chain alkane can be 1-bromodocosahexadecane with a concentration of 0.2 mmol / L; the amine can be N,N,N,N'-tetramethyl-1,6-hexanediamine with a concentration of 2 mmol / L; the concentration of the structure-directing agent intermediate is 0.67 mmol / L; and the halogenated alkane can be 1-bromohexane with a concentration of 1.33 mmol / L.

[0041] It should be noted that in the preparation of the structure-directing agent, this application controls the number of carbon atoms in the above-mentioned haloalkanes to be in the range of 12-25 to provide a suitable carbon chain length. The carbon chain length within this range is beneficial for controlling the thickness of the subsequent supported MFI molecular sieve membrane.

[0042] This application does not limit the specific choice of solvent, as long as it can ensure that all components are fully dissolved and refluxed; this application does not limit the specific conditions of post-treatment, including cooling, centrifugation, washing, and drying, which can be the same as conventional operations in the field. For example, the washing solvent can be diethyl ether, the number of washings is 4-5 times, preferably 4 times, the drying temperature is 20-30°C, preferably 25°C, and the drying time is 24-48 hours, preferably 24 hours.

[0043] Furthermore, this application uses a precursor sol comprising an alkali source, an aluminum source, an inorganic acid, and the structure-directing agent of this application as a raw material for preparing multilayer MFI molecular sieve nanosheets including the structure-directing agent. The selection of the alkali source, aluminum source, and inorganic acid can be the same as conventional selections in the art. For example, the alkali source can be sodium hydroxide, the aluminum source can be aluminum sulfate octadecahydrate, the silicon source can be tetraethyl silicate, and the inorganic acid can be sulfuric acid, wherein the mass concentration of sulfuric acid can be 10-30 wt%, preferably 10 wt%.

[0044] Specifically, a mixed solution containing an alkali source, deionized water, and the above-mentioned structure-directing agent is mixed with a mixed solution containing an aluminum source and an inorganic acid. A silicon source is added to the mixed solution and stirred at 50-100°C for 0.5-4 hours, preferably at 60°C for 1 hour, to obtain a precursor gel. The precursor gel is transferred to a stainless steel reactor with a polytetrafluoroethylene liner and crystallized in a rotary oven at 120-200°C for 1-5 days, preferably at 150°C for 5 days, at a rotation speed of 60-100 rpm, preferably 60 rpm. Post-treatment, including washing, filtration, and drying, is then performed.

[0045] The molar ratio of the alkali source, aluminum source, silicon source, inorganic acid, deionized water, and structure directing agent can be (10-50): (1-5): (50-200): (10-100): (1000-8000): (5-20), where the silicon source is calculated as SiO2, the alkali source as Na2O, and the aluminum source as Al2O3.

[0046] It should be noted that this application does not limit the specific conditions for washing, filtering, and drying, and can be the same as conventional operations in the field. For example, the drying temperature is 60-150℃, preferably 120℃, and the drying time is 12-24h, preferably 12h.

[0047] Furthermore, to facilitate the subsequent exfoliation process, before mixing the multilayer MFI molecular sieve nanosheets containing the structure-directing agent with the organic alkaline solution, the multilayer MFI molecular sieve nanosheets containing the structure-directing agent can be pyrolyzed. The heating rate is 0.5-4℃ / min, preferably 0.5℃ / min, and the pyrolysis is carried out at 300-400℃ for 4-12 hours, preferably at 350℃ for 10 hours. Finally, the multilayer MFI molecular sieve nanosheets containing the structure-directing agent of this application are obtained. The high temperature causes the interlayer template agent to decompose and escape, forming through channels and interlayer gaps, which is beneficial to the subsequent exfoliation and improves the exfoliation efficiency.

[0048] The stripping process also includes centrifuging the system after each stripping process. The centrifugation speed can be 5000-12000 rpm, preferably 10000 rpm, and the centrifugation time can be 0.5-4 h, preferably 0.5 h.

[0049] As mentioned above, this application uses a dispersion of monolayer MFI molecular sieve nanosheets including a structure-directing agent to grow on the surface of a modified support. In one specific embodiment, the surface growth can be prepared by a one-step hydrothermal method.

[0050] First, a dispersion of monolayer MFI molecular sieve nanosheets including a structure-directing agent is mixed with deionized water to obtain a mixed solution. The modified support is placed in the mixed solution and placed in a crystallization kettle for hydrothermal crystallization. Dynamic crystallization is carried out at 60-150℃ for 12-24 hours, preferably at 60℃ for 12 hours, with a reaction speed of 30-90 rpm, preferably 60 rpm. After drying, ammonium exchange, and calcination, the supported MFI molecular sieve membrane of this application is obtained.

[0051] For example, the volume ratio of the structure-directing agent-containing monolayer MFI molecular sieve nanosheet dispersion to deionized water can be (0.2-1):1, preferably 0.2:1; the solid-liquid ratio of the modified carrier to the structure-directing agent-containing monolayer MFI molecular sieve nanosheet dispersion is 0.05-0.2 g / ml, preferably 0.1 g / ml; the solid-liquid ratio of the carrier to the exchange liquid is 0.1-0.3 g / ml, preferably 0.1 g / ml; the ammonium exchange temperature is 60-120℃, preferably 80℃; the exchange rotation speed is 30-120 rpm, preferably 60 rpm; the exchange time is 1-6 h, preferably 2 h; the number of exchanges is 1-5 times, preferably 3 times; the calcination temperature is 500-600℃, preferably 550℃; the time is 4-8 h, preferably 4 h; and the heating rate is 0.5-4℃ / min, preferably 4℃ / min.

[0052] In one specific embodiment, in order to eliminate the influence of the roughness of the carrier surface on the film growth, the oxide coating can be selected to include at least one of TiO2, SiO2, and ZrO2. The inventors have found that, on the one hand, a smooth oxide layer covering the carrier surface reduces the heterogeneity of crystal nucleus growth and improves the uniformity of the film; on the other hand, the oxide coating provides active sites for subsequent coupling agent modification and promotes the anchoring of chemical bonds.

[0053] Furthermore, the silane coupling agent may include at least one of (3-aminopropyl)triethylsilane, (3-aminopropyl)trimethoxysilane, 3-aminopropylmethyldiethoxysilane, and N-ethyl-3-aminopropyltrimethoxysilane.

[0054] The structure-directing agent of this application comprises n quaternary ammonium salt cations in its hydrophilic group, where 1 ≤ n ≤ 4, and a hydrophobic chain comprising a long-chain alkyl group, wherein the long-chain alkyl group has ≥ 12 carbon atoms. The inventors have discovered that controlling the number of quaternary ammonium salt cations in the hydrophilic group and the number of carbon atoms in the long-chain alkane in the hydrophobic chain can induce the oriented growth of MFI molecular sieve nanosheets along the b-axis, thereby improving the mass transfer efficiency of the MFI molecular sieve membrane.

[0055] This application may select at least one of the following: glass slide, silicon wafer, sodium carbonate tube, hollow fiber ceramic, silicon carbide, stainless steel, commercial glass sphere, alumina sphere, silica sphere, mixed oxide carrier, zirconia sphere, quartz sand, and titanium dioxide sphere.

[0056] In one specific embodiment, a single-layer MFI molecular sieve nanosheet dispersion is prepared by a method comprising the following steps: mixing multilayer MFI molecular sieve nanosheets including a structure-directing agent with an organic base solution; subjecting the mixture to a first exfoliation treatment to obtain an exfoliation intermediate; and subjecting the mixture including the exfoliation intermediate to a second exfoliation treatment to obtain the single-layer MFI molecular sieve nanosheet dispersion; wherein the mass-to-volume ratio of the multilayer MFI molecular sieve nanosheets to the organic base solution is 0.01-10 g / ml. The inventors have discovered that by controlling this ratio, it is possible to ensure that the organic base fully penetrates the interlayer spaces of the nanosheets, and combined with the shear force of high-pressure homogenization, to achieve an expansion of the interlayer distance, thereby improving the efficiency of the exfoliation treatment.

[0057] It should be noted that, in one specific embodiment, the multilayer MFI molecular sieve nanosheets including the structure-directing agent are stirred and mixed with an organic base solution for 0.5-24 hours, preferably 2 hours; the concentration of the organic base solution is in the range of 10-30 wt%, preferably 10 wt%.

[0058] In one specific embodiment, the organic base includes at least one of tetrabutylammonium hydroxide, tetraethylammonium hydroxide, hexadecyltrimethylammonium hydroxide, benzyltrimethylammonium hydroxide, tetramethylammonium hydroxide, and tetrapropylammonium hydroxide.

[0059] Furthermore, by using a high-pressure homogenizer to perform stepwise exfoliation of multilayer MFI molecular sieve nanosheets, the inventors discovered that controlling the pressure of the first exfoliation treatment to 5000-15000 psi and the number of cycles to 3-10, and the pressure of the second exfoliation treatment to 2000-8000 psi and the number of cycles to 1-5, can, on the one hand, avoid excessive shearing and preserve the crystal integrity of the nanosheets; on the other hand, it can ensure a higher proportion of monolayer MFI molecular sieve nanosheets in the dispersion, ensuring that the thickness of the subsequent MFI molecular sieve membrane layer is controllable.

[0060] In one specific embodiment, the carrier loaded with oxide coating is prepared by the following process: a mixed solution including coating raw materials is stirred for 0.5-2 hours to obtain an oxide coating sol; the oxide coating sol is coated onto the surface of the carrier; and then dried and calcined to obtain the carrier loaded with oxide coating.

[0061] It should be noted that this application does not limit the specific method of coating, and can be completed by dip coating; this application does not limit the treatment method after each dip coating, for example, drying treatment can be performed after each dip coating.

[0062] In one specific embodiment, the carrier loaded with the oxide coating includes a carrier substrate and a coating on the carrier surface, wherein the coating thickness is 10-1000 nm. The inventors have found that controlling the above-mentioned coating thickness can ensure that the film layer has good stability. On the one hand, insufficient thickness will lead to defects in the coating, poor adhesion, weakened protective effect and insufficient active sites; on the other hand, excessive thickness will cause an increase in internal stress, resulting in cracking and peeling of the coating.

[0063] In one specific embodiment, during the preparation of the carrier loaded with the oxide coating, the drying treatment is carried out at a temperature of 80-120°C for 3-12 hours; the calcination treatment involves a heating rate of 0.5-4°C / min, preferably 0.5°C / min, a temperature of 350-550°C, preferably 450°C, and a time of 4-10 hours, preferably 4 hours. This combination of parameters, through thermodynamic control, avoids cracking caused by excessively rapid water loss of the sol, while ensuring that the grain size of the oxide coating is controlled within a suitable range, providing high-density reaction sites for subsequent hydroxylation.

[0064] In one specific embodiment, the silane coupling agent modification treatment of the support loaded with oxide coating includes: heating and refluxing a mixed solution comprising the support loaded with oxide coating and silane coupling agent under inert gas protection to obtain a coupling agent-modified support loaded with oxide coating. The heating and reflux temperature is 60-110°C, preferably 70°C, and the time is 1-12 hours, preferably 10 hours. The mass ratio of silane coupling agent to the support loaded with oxide coating is (0.01-2):(0.01-4). The inventors have found that controlling the above mass ratio can ensure the coverage of the coupling agent on the support, guarantee the amino density on the modified support surface, thereby improving the anchoring efficiency of MFI molecular sieve nanosheets; at the same time, it avoids excessive waste of coupling agent and increased preparation costs.

[0065] This application does not limit the specific solvent used for the heating and reflux process, as long as it ensures the silane coupling agent is fully dissolved and the system is fully refluxed; for example, toluene may be used. This application does not limit the specific choice of the inert gas; for example, nitrogen or helium may be used. Furthermore, the concentration of the coupling agent is 10-50 mmol / L, preferably 20 mmol / L.

[0066] In one specific embodiment, the calcination process further includes irradiating the support loaded with the oxide coating with ultraviolet light; wherein the irradiation time is 3-24 hours. The inventors discovered that, upon irradiation, the TiO2 coating on the support surface undergoes a photocatalytic reaction. Photogenerated holes interact with water molecules to generate hydroxyl groups (-OH), and photogenerated free radicals oxidize organic matter into carboxyl groups (-COOH). These two processes synergistically increase surface energy and interfacial bonding density, promoting the uniform and dense spreading of the silane layer, strengthening the stability of the organic-inorganic interface, and improving the density of the MFI molecular sieve membrane. Controlling the irradiation time range allows for precise regulation of the generation and distribution of the two types of functional groups, avoiding insufficient activity due to too short an irradiation time or structural damage caused by too long an irradiation time, thus ensuring stable and consistent membrane performance.

[0067] The second aspect of this application provides a supported ultrathin MFI molecular sieve membrane, which is prepared by the above method.

[0068] In one specific embodiment, the thickness of the supported MFI molecular sieve membrane prepared by the above method is in the range of 50-100 nm.

[0069] A third aspect of this application provides a catalytic reaction using the aforementioned supported ultrathin MFI molecular sieve membrane.

[0070] Specifically, the supported molecular sieve membrane of this application is used for the isomerization reaction of olefins. The reactants are C4-C8 olefins by mass fraction, and the reaction conditions are: reaction temperature of 230-310℃ and feed volume hourly space velocity of 1-7 h⁻¹. -1The reaction pressure is 1-3 MPa, and the hydrogen flow rate is 50 mL / min.

[0071] The preparation method of this application will be described in detail below through specific embodiments.

[0072] Example 1

[0073] (1) Use 7ml of methanol, 14ml of ethanol and 24ml of deionized water to ultrasonically clean the glass slide, and then dry it.

[0074] A mixed solution containing deionized water, sulfuric acid, and ethanol was mixed with a solution containing tetrabutyl titanate and stirred for 30 min to obtain TiO2 sol; wherein the molar ratio of tetrabutyl titanate to ethanol was 1:54; and the molar ratio of deionized water, nitric acid, and ethanol was 1:0.01:19.

[0075] TiO2 sol was dip-coated onto the surface of the above-mentioned carrier. After each dip-coating, the substrate was dried at 60°C for 4 hours and then calcined at 450°C for 4 hours, with a heating rate of 0.5°C / min. After calcination, the substrate was irradiated under ultraviolet light for 12 hours to obtain a glass slide loaded with a TiO2 coating. The thickness of the TiO2 coating was 1000 nm.

[0076] 0.221 g of (3-aminopropyl)triethylsilane was dissolved in 50 ml of toluene, and then a TiO2-coated glass slide was added. The mixture was heated under reflux at 110 °C for 1 h, washed repeatedly four times with ethanol and deionized water, and dried at 120 °C for 12 h to obtain the modified glass slide. The mass ratio of (3-aminopropyl)triethylsilane to the TiO2-coated glass slide was 0.01:0.1.

[0077] (2) Dissolve 3.9 g of 1-bromodocosahexadecane in 50 ml of toluene to form solution A; dissolve 17.2 g (0.1 mol) of N,N,N',N'-tetramethyl-1,6-hexanediamine in 50 ml of acetonitrile to form solution B; slowly add solution A dropwise to solution B to form solution C, and reflux at 70 °C for 10 h. Cool the solution to room temperature, centrifuge to obtain a white product, and wash repeatedly with cold ether 4-5 times; dry the product at 30 °C for 24 h to obtain C. 22-6 Br2; Take 5.62g of C 22-6 Br2 was dissolved in 15 ml of acetonitrile to form solution D; 2.46 g of 1-bromohexane was dissolved in 15 ml of acetonitrile to form solution E; solutions D and E were mixed to form solution F, and the mixture was refluxed at 70 °C for 10 h. After cooling the solution to room temperature, the product was centrifuged to obtain a white product, which was then washed repeatedly with cold ether 4-5 times; the product was dried at 30 °C for 24 h to obtain the structure-directing agent C of this application. 22-6-6 Br2.

[0078] Dissolve 1.80g of NaOH in 42.10g of deionized water, and add 5.02g of C... 22-6-6 Br2 was dissolved in the above solution and stirred at room temperature to form solution A; 0.50 g of aluminum sulfate octahydrate was dissolved in 13.23 g of 10 wt% dilute sulfuric acid and stirred at room temperature for 10 min to form solution B; solution B was added to solution A, and the mixture was stirred at 60 °C for 1 h. After cooling to room temperature, 15.63 g of tetraethyl orthosilicate was added, and the mixture was stirred at 60 °C for another 1 h. The final precursor gel was formed with the following ratio: Na2O:Al2O3:SiO2:H2SO4:H2O:C 22-6-6 The Br2 ratio was 30:1:100:18:4000:10. The above gel was placed in a crystallization vessel and crystallized at 60 rpm and 150 °C for 5 days. After crystallization, the product was washed and filtered, and then dried at 120 °C for 12 h to obtain multilayer MFI molecular sieve nanosheets containing structure-directing agents.

[0079] The multilayer MFI molecular sieve nanosheets containing the structure-directing agent were pyrolyzed and calcined at 350°C for 10 h. 1 g of the pyrolyzed multilayer MFI molecular sieve nanosheets containing the structure-directing agent were stirred with 20 ml of 10 wt% tetrabutylammonium hydroxide for 2 h to obtain a mixture. The mixture was homogenized 7 times at 15000 psi using a high-pressure homogenizer and centrifuged at 10000 rpm for 30 min. The reddish-brown supernatant was discarded. The separated solid was mixed with 30 g of water and stirred for 6 h. The mixture was homogenized twice at 3000 psi using a high-pressure homogenizer and centrifuged at 10000 rpm for 30 min. About 25 ml of the supernatant was collected and stored. The remaining solid was mixed with water again and this step was repeated 3-4 times to obtain a single-layer MFI molecular sieve nanosheet dispersion.

[0080] (3) Take 5 ml of the above single-layer MFI molecular sieve nanosheet dispersion into 25 ml of deionized water and stir for 10 min. Take a piece of the above modified glass slide and place it in the above solution in the reaction vessel. Crystallize at 60°C for 12 h with a reaction speed of 60 rpm. Wash the product repeatedly with deionized water 4 times and dry at 120°C for 12 h.

[0081] The solid-liquid ratio of the modified glass slide to the single-layer MFI molecular sieve nanosheet dispersion was 0.1 g / ml.

[0082] The above product was subjected to ammonium exchange with a 1 mol / L ammonium chloride solution at 80 °C for 2 h at a rotation speed of 60 rpm for 3 times. After washing with deionized water, filtering, drying at 120 °C for 6 h, and calcining in a muffle furnace at 550 °C for 4 h at a heating rate of 4 °C / min, the supported MFI molecular sieve membrane was finally obtained.

[0083] Example 2

[0084] The preparation method of the supported molecular sieve in this embodiment is basically the same as that in Example 1, except that commercial glass beads are used as the carrier in step 1).

[0085] Example 3

[0086] The preparation method of the supported molecular sieve in this embodiment is basically the same as that in Example 1, except that alumina balls are used as the support in step 1).

[0087] Example 4

[0088] The preparation method of the supported molecular sieve in this embodiment is basically the same as that in Example 1, except that the support in step 1) is zirconium oxide spheres.

[0089] Example 5

[0090] The preparation method of the supported molecular sieve in this embodiment is basically the same as that in Example 1, except that titanium dioxide balls are used as the support in step 1).

[0091] Comparative Example 1

[0092] The preparation method of this comparative example is basically the same as that of Example 2. The difference is that the support is only modified with TiO2 coating in step 1), without any other subsequent modification process and molecular sieve membrane growth process.

[0093] Experimental Example 1

[0094] 1. The supported molecular sieve membrane in the examples was analyzed using SEM, and the results are as follows: Figures 1-6 See Table 1.

[0095] Figure 1 This is a SEM image of the supported molecular sieve membrane prepared in Example 1 of this application. Figure 2 This is a SEM image of the supported molecular sieve membrane prepared in Example 2 of this application. Figure 3 This is a SEM image of the supported molecular sieve membrane prepared in Example 3 of this application. Figure 4 This is a SEM image of the supported molecular sieve membrane prepared in Example 4 of this application. Figure 5 This is a SEM image of the supported molecular sieve membrane prepared in Example 5 of this application. Figure 6 This is a SEM image of the cross-section of the supported molecular sieve membrane prepared in Example 1 of this application. Figures 1-6 It can be seen that the supported MFI molecular sieves synthesized in Examples 1-5 of this application all exhibit good surface uniformity.

[0096] Table 1

[0097]

[0098] As shown in Table 1, the preparation method of this application helps to prepare ultrathin supported MFI molecular sieves.

[0099] Experimental Example 2

[0100] The supported MFI molecular sieve membranes of the examples and comparative examples were used in olefin isomerization experiments, specifically including the following steps:

[0101] The catalyst was packed in the isothermal zone of a reaction tube (13 mm inner diameter) with a loading volume of 5 ml, separated from the top and bottom by quartz wool and 2 ml of quartz sand. 1-Octenene was fully vaporized in a preheated furnace at 150 °C using a plunger pump, and then fed into the reaction tube, where it underwent three-stage condensation to obtain the reaction product. The reaction temperature was 270 °C, and the feed volume hourly space velocity (VHSV) was 4 h⁻¹. -1 The reaction pressure was 2 MPa, and the hydrogen flow rate was 50 ml / min. The reaction products were analyzed by gas chromatography, and the feed conversion rate and product yield were calculated using the following formula. Specific results are shown in Table 2. Figure 7 and Figure 8 .

[0102] Raw material conversion rate = (moles of raw material - moles of raw material in the product) / moles of raw material × 100%

[0103] Isomer selectivity = (Number of moles of target isomer) / (Number of moles of starting material - Number of moles of starting material in product) × 100%

[0104] Yield = Feed conversion rate × Heterogeneity selectivity

[0105] Table 2

[0106]

[0107] As shown in Table 2, the prepared supported MFI molecular sieve membrane can achieve an olefin conversion rate of approximately 95%, and its catalytic activity is much higher than that of blank TiO2. The supported MFI molecular sieve membrane prepared in this application has a significant catalytic effect on olefin isomerization reactions. However, Example 1, due to the use of a two-dimensional support, cannot be applied to a fixed bed for performance evaluation.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application.

Claims

1. A method for preparing a supported MFI molecular sieve membrane, characterized in that, Includes the following steps: The carrier loaded with oxide coating is modified with silane coupling agent to obtain a modified carrier; The supported MFI molecular sieve membrane was obtained by growing a dispersion of monolayer MFI molecular sieve nanosheets including a structure-directing agent on the surface of the modified support. The structure-directing agent includes hydrophilic groups and hydrophobic chains.

2. The method of claim 1, wherein, The oxide coating includes at least one of TiO2, SiO2, and ZrO2; and / or, The silane coupling agent comprises at least one of (3-aminopropyl)triethylsilane, (3-aminopropyl)trimethoxysilane, 3-aminopropylmethyldiethoxysilane, and N-ethyl-3-aminopropyltrimethoxysilane; and / or, The hydrophilic group comprises n quaternary ammonium salt cations, wherein 1 ≤ n ≤ 4, and the hydrophobic chain comprises a long-chain alkyl group, wherein the long-chain alkyl group has ≥ 12 carbon atoms; and / or, The carrier includes at least one of the following: glass slide, silicon wafer, sodium carbonate tube, hollow fiber ceramic, silicon carbide, stainless steel, commercial glass sphere, alumina sphere, silica sphere, mixed oxide carrier, zirconium oxide sphere, quartz sand, and titanium dioxide sphere.

3. The method according to claim 1 or 2, characterized in that, The single-layer MFI molecular sieve nanosheet dispersion was prepared by a method comprising the following steps: Multilayer MFI molecular sieve nanosheets including a structure-directing agent are mixed with an organic base solution. The mixture is subjected to a first exfoliation treatment to obtain an exfoliation intermediate. The mixed solution including the exfoliation intermediate is subjected to a second exfoliation treatment to obtain the single-layer MFI molecular sieve nanosheet dispersion. The mass-to-volume ratio of the multilayer MFI molecular sieve nanosheets to the organic alkali solution is 0.01-5 g / ml.

4. The method of claim 3, wherein, The organic base includes at least one selected from tetrabutylammonium hydroxide, tetraethylammonium hydroxide, hexadecyltrimethylammonium hydroxide, benzyltrimethylammonium hydroxide, tetramethylammonium hydroxide, and tetrapropylammonium hydroxide; and / or, The first stripping treatment is performed at a pressure of 5000-15000 psi, with 3-10 cycles; the second stripping treatment is performed at a pressure of 2000-8000 psi, with 1-5 cycles.

5. The method according to any one of claims 1 to 4, characterized in that, The support loaded with the oxide coating is prepared by the following process: The mixed solution containing the coating raw materials is stirred for 0.5-2 hours to obtain an oxide coating sol. The oxide coating sol is then coated onto the surface of the carrier, followed by drying and calcination to obtain the carrier loaded with the oxide coating. The carrier loaded with oxide coating includes a carrier substrate and a coating on the carrier surface, wherein the coating thickness is 10-1000 nm.

6. The method of claim 5, wherein, The drying process is carried out at a temperature of 80-120℃ for 3-12 hours; and / or, The calcination process involves a heating rate of 0.5-4℃ / min, a temperature of 350-550℃, and a time of 4-10h.

7. The method according to any one of claims 1 to 6, characterized in that, The modification treatment of the support loaded with oxide coating using a silane coupling agent includes: heating and refluxing a mixed solution comprising the support loaded with oxide coating and the silane coupling agent to obtain the modified support, wherein the heating and refluxing temperature is 60-110℃ and the time is 1-12h; and / or, The mass ratio of the silane coupling agent to the carrier loaded with the oxide coating is (0.01-2):(0.01-4).

8. The method according to claim 5 or 6, characterized in that, The roasting process is followed by irradiating the carrier loaded with oxide coating with ultraviolet light. The duration of ultraviolet lamp irradiation is 3-24 hours.

9. A supported MFI molecular sieve membrane, characterized in that, It is prepared by the method described in any one of claims 1-8.

10. A catalytic reaction, characterized in that, The supported MFI molecular sieve membrane as described in claim 9 is used.

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