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

Abstract

The invention provides a supported molecular sieve membrane as well as a preparation method and application thereof, and the preparation method of the supported molecular sieve membrane comprises the following steps: pretreating a carrier by adopting a piranha solution to obtain a pretreated carrier; carrying out first modification treatment on the pretreated carrier by adopting a silane coupling agent to obtain a coupling agent-carrier; carrying out second modification treatment on the coupling agent-carrier by adopting a structure-directing agent to obtain a directing agent-coupling agent-carrier; and growing a molecular sieve layer on the surface of the guiding agent-coupling agent-carrier to obtain the supported molecular sieve membrane, wherein the structure-directing agent comprises a hydrophilic group and a hydrophobic chain. According to the preparation method, the carrier is modified twice, and the ultrathin continuous molecular sieve membrane is prepared on the basis.

Description

Technical Field

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

[0002] Molecular sieve membranes, with their unique regular pore structure, precise molecular sieving ability, excellent thermal stability, and tunable surface chemistry, are considered the most promising membrane materials for industrial applications. To endow them with specific sieving capabilities and mechanical strength, molecular sieve membranes are currently optimized through two approaches: first, constructing supported molecular sieve membranes, such as preparing two-dimensional supported molecular sieve membranes with specific orientations using a secondary growth method on a two-dimensional planar support (such as a silicon wafer or glass slide); second, precisely controlling the membrane thickness, such as reducing the membrane thickness through seed coating or secondary hydrothermal synthesis, thereby reducing the mass transfer resistance of such membranes. These molecular sieve membranes are widely used in separation and catalysis fields, including energy gas separation (such as H2 / CO2, H2 / CH4), biofuel dehydration (such as bioethanol purification), organic solvent nanofiltration (OSN), and alkane isomerization. Their performance parameters directly determine the separation efficiency, product purity, and the economic feasibility of the entire process.

[0003] The selective separation capability and mechanical strength of molecular sieve membranes largely depend on key factors such as the complex geometry of the support, membrane thickness, and crystal orientation. Generally, loading ultrathin molecular sieve membranes onto three-dimensional supports can provide a larger effective contact area, higher mechanical strength, and lower mass transfer resistance, thus significantly improving separation efficiency. However, the complex structure of three-dimensional supports and the presence of more microscopic inhomogeneities on their surfaces make it difficult to directly apply mature film-forming processes from two-dimensional supports to three-dimensional supports. This results in the difficulty of achieving continuous, uniform, ultrathin, and defect-free molecular sieve membranes on three-dimensional support surfaces, a technological bottleneck that severely restricts the large-scale industrial application of this type of membrane material.

[0004] Therefore, under the premise of maintaining or even improving the selective separation capability and mechanical strength of molecular sieve membranes, how to break through the existing synthesis limitations and achieve the preparation of ultrathin, continuous, uniform and defect-free molecular sieve membranes on the surface of complex three-dimensional carrier structures, or to develop more advanced surface film formation processes to fundamentally solve the core problem of limited carrier selection, has become a key issue that urgently needs to be solved in this field. Summary of the Invention

[0005] This application provides a supported molecular sieve membrane, its preparation method, and its application. By pretreating and modifying the support separately, a molecular sieve membrane is grown on the surface of the modified support. This effectively solves the problem of limited support selection when preparing high-quality molecular sieve membranes and overcomes the core challenges of excessive membrane thickness and low support universality.

[0006] This application provides a method for preparing a supported molecular sieve membrane, comprising the following steps:

[0007] The carrier was pretreated with a piranha solution to obtain a pretreated carrier;

[0008] The pretreated support was first modified using a silane coupling agent to obtain a coupling agent-support.

[0009] A second modification treatment was performed on the coupling agent-carrier using a structure-directing agent to obtain a directing agent-coupling agent-carrier.

[0010] A molecular sieve layer is grown on the surface of the directing agent-coupling agent-carrier to obtain the supported molecular sieve membrane;

[0011] The structure-directing agent includes hydrophilic groups and hydrophobic chains.

[0012] The preparation method described above, wherein the pretreatment includes: immersing the carrier in the piranha solution, treating it under ultrasonic conditions for 1-4 hours, and then drying it to obtain the pretreated carrier; in the piranha solution, the volume ratio of concentrated sulfuric acid to hydrogen peroxide is (2:8)-(8:2); the water contact angle of the pretreated carrier is less than 10°.

[0013] The preparation method described above, wherein the silane coupling agent comprises at least one selected from 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, and 4-chlorobutyltrimethoxysilane; and / or,

[0014] The hydrophilic group comprises n amino groups, wherein 1 ≤ n ≤ 4; the hydrophobic chain comprises a long-chain alkyl group, wherein the long-chain alkyl group has ≥ 12 carbon atoms; and / or,

[0015] The carrier includes at least one of stainless steel, hollow fiber ceramic, glass slide, silicon wafer, glass sphere, alumina sphere, silica sphere, mixed oxide carrier, zirconia sphere, quartz sand, and silicon carbide.

[0016] The preparation method described above, wherein the structure-directing agent is prepared by a method comprising the following steps:

[0017] After subjecting a first mixed solution comprising long-chain haloalkanes and amine compounds to a first reflux treatment, the first reflux system is subjected to crystallization treatment to obtain a first intermediate.

[0018] After subjecting a second mixed solution comprising the first intermediate and haloalkanes to a second reflux treatment, the second reflux system is subjected to crystallization treatment to obtain the second intermediate;

[0019] After subjecting a third reflux treatment to a third mixed solution comprising the second intermediate and the amine compound, the third reflux system is subjected to crystallization treatment to obtain the structure directing agent;

[0020] The long-chain haloalkane includes at least one of 1-bromodocosahexadecane, 1-bromooctadecane, and 1-bromohexadecane;

[0021] The amine compound includes at least one of N,N,N',N'-tetramethyl-1,6-hexanediamine, N,N,N',N'-tetramethyl-1,3-propanediamine, and N,N,N',N'-tetramethyl-1,3-octanediamine;

[0022] The haloalkane includes at least one of 1,6-dibromohexane, 1,6-dibromobutane, and 1,6-dibromooctane.

[0023] In the preparation method described above, the molar ratio of the long-chain haloalkane to the amine compound is 1-3:1-15;

[0024] The molar ratio of the first intermediate to the haloalkane is 1-2:1-20;

[0025] The molar ratio of the second intermediate to the amine compound is 1-2:1-20.

[0026] The preparation method described above, wherein the first modification treatment includes: subjecting a mixed solution comprising the pretreated carrier and the silane coupling agent to a first heat treatment to obtain the coupling agent-carrier, wherein the temperature of the first heat treatment is 60-120°C and the time is 1-10 h; the mass ratio of the silane coupling agent to the pretreated carrier is 1-50:1-5.

[0027] The preparation method described above, wherein the second modification treatment includes: subjecting a mixed solution comprising the structure directing agent and the coupling agent-carrier to a second heat treatment to obtain the directing agent-coupling agent-carrier, wherein the temperature of the second heat treatment is 60-120°C and the time is 1-10h; the mass ratio of the structure directing agent to the coupling agent-carrier is 1-100:1-50.

[0028] The preparation method described above, wherein growing a molecular sieve layer on the surface of the directing agent-coupling agent-carrier comprises: dynamically crystallizing the directing agent-coupling agent-carrier and precursor sol at 100-180°C for 24-168 h.

[0029] This application provides a supported molecular sieve membrane, which is prepared by any of the methods described above.

[0030] This application provides an apparatus including the above-described supported molecular sieve membrane.

[0031] The method for preparing supported molecular sieve membranes provided in this application involves pretreating the support and performing two-step modification treatments. In the first modification treatment, a silane coupling agent is added to obtain a coupling agent-support. In the second modification treatment, a structure-directing agent is added to obtain a directing agent-coupling agent-support. A molecular sieve layer is then grown on the surface of the directing agent-coupling agent-support. Therefore, the preparation method of this application can stably prepare supported molecular sieve membranes with good support versatility and ultrathin, continuous structure. Attached Figure Description

[0032] 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.

[0033] Figure 1 The image shows the XRD pattern of the sol system during the dynamic crystallization process in Example 1 of this application.

[0034] Figure 2 This is a SEM image of the supported molecular sieve membrane of Example 1 of this application;

[0035] Figure 3 This is a SEM image of the supported molecular sieve membrane of Example 1 of this application;

[0036] Figure 4 This is a SEM image of the supported molecular sieve membrane of Example 2 of this application;

[0037] Figure 5 This is a SEM image of the supported molecular sieve membrane of Example 3 of this application;

[0038] Figure 6 This is a SEM image of the supported molecular sieve membrane of Example 3 of this application;

[0039] Figure 7 This is a SEM image of the supported molecular sieve membrane of Comparative Example 1 of this application. Detailed Implementation

[0040] 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.

[0041] To prepare ultrathin, continuous, supported molecular sieve membranes adaptable to various carriers, the inventors researched and discovered that traditional membrane preparation methods primarily rely on two-dimensional carriers for synthesis optimization. However, two-dimensional carriers have inherent limitations; their space utilization is far lower than that of three-dimensional carriers. Three-dimensional carriers themselves exhibit greater microscopic inhomogeneity, which, combined with the inhomogeneity of the film formation process, significantly increases the probability of defects such as pinholes and cracks. Achieving three-dimensional spatial uniformity in membrane thickness, crystal size, orientation, and density within complex geometries such as narrow channels, deep pores, and curved surfaces remains a significant challenge. Mature two-dimensional carrier processes are not applicable to three-dimensional carriers. Therefore, optimizing carrier surface modification and molecular sieve membrane growth processes is necessary to form ultrathin, continuous, uniform, and defect-free molecular sieve membranes on three-dimensional carriers. This would overcome the carrier limitations in high-performance molecular sieve membrane preparation and improve its versatility.

[0042] Based on this, the first aspect of this application provides a method for preparing a supported molecular sieve membrane, comprising the following steps:

[0043] The carrier was pretreated with a piranha solution to obtain a pretreated carrier;

[0044] The pretreated support was modified by using a silane coupling agent to obtain the coupling agent-support;

[0045] A second modification treatment was performed on the coupling agent-carrier using a structure-directing agent to obtain a directing agent-coupling agent-carrier.

[0046] A molecular sieve layer is grown on the surface of the directing agent-coupling agent-support to obtain a supported molecular sieve membrane;

[0047] Structure directing agents include hydrophilic groups and hydrophobic chains.

[0048] First, this application introduces a piranha solution to pretreat the carrier. Since the piranha solution includes concentrated sulfuric acid and hydrogen peroxide, this strong oxidizing environment can greatly enhance the hydrophilicity and hydroxyl density of the carrier surface, and provide uniform and abundant reaction sites for the subsequent hydrolysis and condensation of the silane coupling agent. This lays the foundation for the subsequent first and second modification treatments and provides more ideal anchoring sites for the modifier.

[0049] Subsequently, this application introduces a silane coupling agent to perform a first modification treatment on the support. The siloxane end is covalently bonded to the surface of the pretreated support through a bond (-Si-O-), and the active group at the other end replaces the original group on the surface of the support, thus obtaining the coupling agent-support.

[0050] After the first modification treatment, a structure-directing agent is introduced in the second modification treatment. The hydrophilic groups of the structure-directing agent are covalently anchored to the surface of the carrier with the active groups on the surface of the coupling agent-carrier. It predetermines the starting point and direction of the template at the molecular level. As a result, its hydrophobic chains are forced to arrange themselves in a specific way due to the hydrophobic effect and the spatial limitation of the anchoring point, thus forming an ordered and regular molecular template, resulting in the direction-coupling agent-carrier.

[0051] Finally, guided by the template anchored on the surface of the aforementioned directing agent, coupling agent, and support, the molecular sieve layer undergoes directional nucleation and confined growth. The specific spatial structure of the template causes the molecular sieve layer crystals to preferentially grow along the b-axis. These uniformly oriented nuclei gradually grow and fuse, eventually forming a dense molecular sieve membrane with a vertical b-axis and straight channels, ultimately achieving a support-adaptive, ultrathin, controllable, uniform, and continuous supported molecular sieve membrane.

[0052] This invention constructs a carrier with an ideal modified anchoring interface through pretreatment for both the first and second modification treatments. The first modification treatment enhances the compatibility between the carrier and the organic matrix, strengthens the interfacial bonding between the carrier and the coupling agent, and helps reduce interfacial defects, thereby significantly improving the mechanical properties of the final supported molecular sieve membrane. The second modification treatment enables the pre-design of the molecular sieve microstructure, laying the foundation for the subsequent orderly growth of the molecular sieve layer.

[0053] Therefore, in this invention, a silane coupling agent is used as a molecular bridge between the pretreated carrier and the structure-directing agent, constructing a stable connection through interfacial chemical interactions, providing a foundation for the precise anchoring of the directing agent. The structure-directing agent then performs a dual function after anchoring: firstly, it acts as a template to pre-define the pore structure; secondly, it inhibits subsequent disordered lateral crystal growth through its steric hindrance effect, driving the membrane towards ultrathinness. The molecular sieve layer growth process further ensures the orderly deposition of the molecular sieve layer raw materials under the action of the directing agent template, significantly improving the density and continuity of the molecular sieve membrane. Ultimately, through the synergistic effect of these steps, ultrathin, continuous, uniform, and defect-free molecular sieve membranes can be prepared on the surface of a complex three-dimensional carrier structure. The absence or weakening of any step will lead to a significant decrease in membrane performance.

[0054] During the preparation process, to facilitate the subsequent growth of a molecular sieve layer on the surface of the directing agent-coupling agent-carrier, the mixed solution after the first and second modification treatments can be filtered. The filtered solid (i.e., the coupling agent-carrier and the directing agent-coupling agent-carrier) is then washed and dried. The washing agent can be at least one of anhydrous ethanol, acetone, and methanol. Generally, it can be washed 2-5 times, followed by drying at 60-120℃ for 4-12 hours.

[0055] It should be noted that the specific solvents used in the first and second modification treatments in this application are not limited, for example, they can be toluene; this application does not limit the types of inert gases used in the two modification treatments, for example, they can be nitrogen or helium.

[0056] Further, the pretreatment includes: immersing the carrier in a piranha solution, treating it under ultrasonic conditions for 1-4 hours, and then drying it to obtain a pretreated carrier; the volume ratio of concentrated sulfuric acid to hydrogen peroxide in the piranha solution is (2:8)-(8:2); the water contact angle of the pretreated carrier is less than 10°. Under these conditions, pretreating the carrier with a piranha solution composed of a specific ratio of concentrated sulfuric acid and hydrogen peroxide significantly enhances its surface hydrophilicity and hydroxyl coverage. This enhancement effect mainly stems from the synergistic effect of ultrasonic cavitation and the strong oxidizing properties of the piranha solution. On the one hand, the high-temperature and high-pressure microjets generated locally on the carrier surface by ultrasonic cavitation can violently impact and clean the surface, effectively removing organic pollutants, while increasing its specific surface area and surface defects, providing more active sites for subsequent modification treatment. On the other hand, the specific ratio of acid and hydrogen peroxide ensures that while providing a strongly acidic environment, sulfuric acid can continuously and efficiently generate highly reactive peroxymonosulfuric acid with hydrogen peroxide, thereby efficiently introducing a large number of silanol groups on the new surface, ultimately forming a denser hydroxylation layer at the microscopic level, further enhancing the hydrophilicity of the carrier and making the water contact angle less than 10°.

[0057] Furthermore, the frequency of the ultrasound can be 20-100Hz, the drying can be air-cooled drying at 10-20℃, and the volume ratio of concentrated sulfuric acid to hydrogen peroxide is 3:7.

[0058] In one specific embodiment, in order to make the silane coupling agent more accurately match the carrier and the structure directing agent, this application introduces at least one of 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, and 4-chlorobutyltrimethoxysilane as a silane coupling agent during the first modification treatment stage.

[0059] The hydrophilic groups of the structure-directing agent used in this application include n amino groups, where 1 ≤ n ≤ 4, and the hydrophobic chain includes long-chain alkyl groups, where the number of carbon atoms in the long-chain alkyl group is ≥ 12. The inventors have discovered that when the number of amino groups and the number of carbon atoms in the long-chain alkane are controlled within the above ranges, excessive disordered growth of subsequent molecular sieve layers can be suppressed, thereby significantly improving the density, ultrathinness, and continuity of the molecular sieve membrane.

[0060] The carriers used in this application include at least one of stainless steel, hollow fiber ceramics, glass slides, silicon wafers, glass spheres, alumina spheres, silica spheres, mixed oxide carriers, zirconia spheres, quartz sand, and silicon carbide.

[0061] In one specific embodiment, the structure-directing agent of this application is prepared by a method comprising the following process:

[0062] After subjecting a first mixed solution comprising long-chain haloalkanes and amine compounds to a first reflux treatment, the first reflux system is subjected to crystallization treatment to obtain a first intermediate.

[0063] After subjecting a second mixed solution, including the first intermediate and the haloalkane, to a second reflux treatment, the second reflux system is crystallized to obtain the second intermediate.

[0064] After subjecting the third mixed solution, which includes the second intermediate and the amine compound, to a third reflux treatment, the third reflux system is subjected to crystallization treatment to obtain the structure-directing agent.

[0065] Specifically, in the first reflux process, a solution containing long-chain haloalkanes is added dropwise to a solution containing an amine compound and mixed thoroughly. After heating and refluxing under an inert atmosphere, a first intermediate is obtained. A solution containing the first intermediate is uniformly mixed with a solution containing haloalkanes and heated and refluxed under an inert atmosphere to obtain a second intermediate. A solution containing the second intermediate is uniformly mixed with a solution containing the same amine compound and heated and refluxed under an inert atmosphere to obtain the structure-directing agent of this application. It should be noted that in the process of preparing the structure-directing agent, the long-chain halogenated alkanes include at least one of 1-bromodocosahexadecane, 1-bromooctadecane, and 1-bromohexadecane; the amine compounds include at least one of N,N,N',N'-tetramethyl-1,6-hexanediamine, N,N,N',N'-tetramethyl-1,3-propanediamine, and N,N,N',N'-tetramethyl-1,3-octanediamine; and the halogenated alkanes include at least one of 1,6-dibromohexane, 1,6-dibromobutane, and 1,6-dibromooctane.

[0066] The inventors discovered that the choice of long-chain haloalkanes can further control the thickness of the supported molecular sieve membrane. Specifically, the longer the alkane chain of the long-chain haloalkanes, the thinner the supported molecular sieve membrane. That is, when the long-chain haloalkanes are 1-bromodocosahexadecane, 1-bromooctadecane, and 1-bromohexadecane, the prepared supported molecular sieve membrane is thicker.

[0067] It should be noted that in the process of preparing the structure-directing agent, the system after three reflux treatments also needs to undergo post-treatment including concentration and cooling, separation, washing, and drying to obtain the structure-directing agent of this application. Specifically, firstly, the refluxed liquid is concentrated using a rotary evaporator to remove most of the solvent. Secondly, cold diethyl ether is added and the system is placed in a refrigerator to cool and stand for several hours (generally more than 12 hours) until no more precipitate is formed. Then, the system is centrifuged after standing, and the precipitate after centrifugation is washed 1-5 times with cold diethyl ether. Finally, the obtained product is placed in an oven to dry for 4-12 hours.

[0068] Furthermore, this application does not limit the specific experimental apparatus for the three heating and reflux processes; for example, it can be a two-necked flask. This application does not limit the specific choice of solvent in the preparation process of the structure-directing agent, as long as it ensures sufficient dissolution of all components and adequate reflux; for example, it can be one of toluene, acetonitrile, or chloroform. This application does not limit the type of inert atmosphere used in the three heating processes; for example, it can be one of nitrogen or helium.

[0069] Furthermore, in the first reflux treatment, the solvent for the solution containing long-chain haloalkanes can be toluene, and the volume / molar ratio of toluene to long-chain haloalkanes is (20-100) ml: 0.01 mol; the solvent for the solution containing amine compounds can be acetonitrile, and the volume / molar ratio of acetonitrile to amine compounds is (30-100) ml: (0.1) mol. The temperature of the first reflux treatment can be 50-120℃, more preferably 50℃, and the time of the first reflux treatment can be 4-12 h, more preferably 10 h.

[0070] In the second reflux treatment, the solvent for the solution containing the first intermediate can be chloroform, and the volume / molar ratio of chloroform to the first intermediate is (8-30) ml:(0.01) mol. The solvent for the solution containing the haloalkane can be chloroform, and the volume / molar ratio of chloroform to the haloalkane is (1-15) ml:(0.1) mol. The temperature of the second reflux treatment can be 40-100℃, more preferably 50℃, and the time of the second reflux treatment can be 4-12 h, more preferably 10 h.

[0071] In the third reflux treatment, the solvent for the solution containing the second intermediate can be chloroform, and the volume / molar ratio of chloroform to the second intermediate is (10-50) ml:(0.01) mol. The solvent for the solution containing the amine compound can be chloroform, and the volume / molar ratio of chloroform to the amine compound is (2-20) ml:(0.01) mol. The temperature of the third reflux treatment can be 40-100℃, more preferably 50℃, and the time of the third reflux treatment can be 4-12 h, more preferably 10 h.

[0072] In one specific embodiment, during the preparation of the structure-directing agent, this application controls the molar ratio of long-chain haloalkanes to amine compounds to be 1-3:1-15, the molar ratio of the first intermediate to haloalkanes to be 1-2:1-20, and the molar ratio of the second intermediate to amine compounds to be 1-2:1-20. Controlling these molar ratios allows for precise regulation of the molecular configuration of the structure-directing agent. By altering the hydrophilic-hydrophobic balance and spatial arrangement of the molecules, the modification effect on the coupling agent-support is significantly improved.

[0073] In one specific embodiment, the first modification treatment includes: subjecting a mixed solution comprising a pretreated support and a silane coupling agent to a first heat treatment to obtain a coupling agent-support, wherein the temperature of the first heat treatment is 60-120°C and the time is 1-10 h; the mass ratio of the silane coupling agent to the pretreated support is 1-50:1-5. The inventors have discovered that within this heating temperature and time range, silane molecules can be fully and orderly bonded to the support surface, ultimately forming an ultrathin, uniform, and continuous interface layer, which lays the foundation for the directional and uniform growth of subsequent molecular sieve layers.

[0074] Meanwhile, in order to improve the modification effect of the silane coupling agent on the pretreated carrier, the mass ratio of the coupling agent to the pretreated carrier can be controlled to be 1-50:1-5.

[0075] Furthermore, in the mixed solution comprising the pretreated carrier and the silane coupling agent, the solvent may be toluene; the volume-to-mass ratio of the solvent to the pretreated carrier is 10-200 ml / g, and the first modification treatment described above is carried out in an inert atmosphere, such as nitrogen or helium.

[0076] Furthermore, the temperature of the first modification treatment was 110°C, and the time was 4 hours.

[0077] In one specific embodiment, the second modification treatment includes: subjecting a mixed solution comprising a structure-directing agent and a coupling agent-carrier to a second heat treatment to obtain a structure-directing agent-coupling agent-carrier, wherein the temperature of the second heat treatment is 60-120°C and the time is 1-10 hours; the mass ratio of the structure-directing agent to the coupling agent-carrier is 1-100:1-50. The inventors have discovered that within the above-mentioned heating temperature and time range, it is possible to promote the directional alignment of the structure-directing agent molecules and the active groups on the surface of the coupling agent-carrier at the interface, providing nucleation sites for subsequent molecular sieve growth, thereby achieving the directional growth of the molecular sieve layer.

[0078] To enhance the modification effect of the structure-directing agent on the coupling agent-carrier, the mass ratio of structure-directing agent to coupling agent-carrier can be controlled at 1-100:1-50. This interface layer can serve as a precise template to induce uniform nucleation and orientation of the molecular sieve precursor, while avoiding incomplete coverage and nucleation defects caused by an excessively low ratio. This fundamentally ensures the uniform, ultrathin, and defect-free growth of the subsequent molecular sieve membrane.

[0079] In one specific embodiment, growing a molecular sieve layer on the surface of the directing agent-coupling agent-support includes: dynamically crystallizing a precursor sol comprising the directing agent-coupling agent-support at a temperature of 100-180°C for 24-186 hours. This growth process significantly inhibits excessive crystal nucleus growth, thereby reducing the final molecular sieve membrane thickness and achieving the preparation of an ultrathin molecular sieve membrane.

[0080] Specifically, molecular sieve layers can be grown using a one-step hydrothermal method.

[0081] In detail, a silicon source, an aluminum source, an alkaline source, an inorganic acid, deionized water, and a directing agent-coupling agent-carrier are mixed and stirred to obtain a gel. The resulting gel is placed in a stainless steel reactor with a polytetrafluoroethylene liner, and the reactor is placed in a homogeneous reaction for crystallization treatment. Subsequently, post-processing including filtration, washing, and drying is performed to obtain the supported molecular sieve membrane of this application. It should be noted that the post-processing method in this application is basically the same as the post-processing methods currently used in the art.

[0082] For example, in the above-mentioned precursor sol, the molar ratio of alkali source, silicon source, aluminum source, inorganic acid, and deionized water is 10-60:40-100:0-1:2-18:1000-6000, wherein the silicon source is calculated as SiO2, the alkali source as Na2O, and the aluminum source as Al2O3. Further, the alkali source can be at least one of lithium hydroxide, sodium hydroxide, and potassium hydroxide; the aluminum source can be at least one of boehmite, aluminum isopropoxide, sodium aluminate, and aluminum sulfate octadechydrate; the silicon source can be at least one of tetraethyl orthosilicate, fumed silica, silica sol, methyl orthosilicate, and amorphous silica powder; and the inorganic acid can be at least one of nitric acid, sulfuric acid, and hydrochloric acid.

[0083] A second aspect of this application provides a supported molecular sieve membrane, prepared by any of the methods described above. This method can stably prepare ultrathin, controllable, uniform, and continuous supported molecular sieve membranes.

[0084] The molecular sieve membranes prepared by the above method in this application have a thickness range of 50-1000 nm.

[0085] A third aspect of this application provides an apparatus comprising the above-described supported molecular sieve membrane.

[0086] The device can be a separation device. The device in this application uses the aforementioned supported molecular sieve membrane. The molecular sieve membrane is firmly and uniformly grown on the surface of the carrier, and the device can achieve efficient and precise sieving of mixtures. Compared with traditional separation technologies, this device has significant advantages such as high separation efficiency, low energy consumption, good stability, and easy integration and scale-up, and is especially suitable for industrial fields such as gas separation (e.g., hydrogen purification, carbon dioxide capture) and liquid pervaporation.

[0087] Alternatively, the apparatus of this application can be a catalytic device, such as a fixed-bed reactor. The apparatus of this application employs the aforementioned supported molecular sieve membrane. This molecular sieve membrane is firmly and uniformly grown on the surface of a support. For example, in the catalytic alkane isomerization reaction, this molecular sieve membrane can serve as a support for a non-precious metal catalyst, providing acidic active centers, promoting the reaction, and significantly improving the yield and reaction efficiency of the target isomeric alkane.

[0088] The preparation method of this application will be described in detail below through specific embodiments.

[0089] Example 1

[0090] The preparation method of the supported molecular sieve membrane in this embodiment includes the following:

[0091] (1) Preparation of structure-directing agents:

[0092] For the first reflux treatment, 0.01 mol of a long-chain haloalkane (1-bromotetracosane) was dissolved in 50 ml of toluene to prepare solution A, and 0.1 mol of an amine compound (N,N,N',N'-tetramethyl-1,6-hexanediamine) was dissolved in 50 ml of acetonitrile to prepare solution B. Solution A was added dropwise to solution B, and the thoroughly mixed solution was added to a two-necked flask and placed in an oil bath. Under nitrogen protection, the mixture was heated at 60°C and refluxed for 12 h. After removing most of the solvent from the refluxed liquid using a rotary evaporator, cold diethyl ether was added, and the mixture was placed in a refrigerator to cool and stand for 12 h. The solution was centrifuged, and the precipitate was washed five times with cold diethyl ether. Finally, the obtained product was dried in a 100°C oven for 12 h to obtain the first intermediate C. 22-6 .

[0093] The second reflux treatment involves removing 0.02 mol of the first intermediate C. 22-6 Solution C was prepared by dissolving 0.2 mol of a haloalkane (1,6-dibromohexane) in 25 ml of chloroform. Solution D was prepared by dissolving solution C and solution D thoroughly. The mixture was heated under nitrogen protection and refluxed at 50 °C for 12 h. After removing most of the solvent from the refluxed liquid using a rotary evaporator, cold diethyl ether was added and the mixture was placed in a refrigerator to cool and stand for 12 h. The solution was centrifuged and the precipitate was washed five times with cold diethyl ether. Finally, the product was dried in a 100 °C oven for 12 h to obtain the second intermediate C. 22-6-6 .

[0094] The third reflux treatment removes 0.01 mol of the second intermediate C. 22-6-6Solution E was prepared by dissolving 0.01 mol of N,N,N',N'-tetramethyl-1,6-hexanediamine in 25 ml of chloroform. Solution F was prepared by dissolving N,N,N',N'-tetramethyl-1,6-hexanediamine in 25 ml of chloroform. Solution E and solution F were mixed thoroughly and heated under nitrogen protection at 50 °C for 10 h under reflux. After removing most of the solvent from the refluxed liquid using a rotary evaporator, cold diethyl ether was added and the mixture was placed in a refrigerator to cool and stand for 12 h. The solution was centrifuged and the precipitate was washed five times with cold diethyl ether. Finally, the obtained product was dried in a 100 °C oven for 12 h to obtain the structure-directing agent C of this application. 22-6-6-6 .

[0095] (2) Pretreatment: The slide was immersed in the piranha solution and treated under ultrasonic conditions for 4 hours. Finally, it was dried with cold air at 15°C to obtain the pretreated slide. The ultrasonic frequency was 80Hz, and the volume ratio of concentrated sulfuric acid to hydrogen peroxide in the piranha solution was 3:7. The water contact angle of the pretreated slide was measured to be 8.1°.

[0096] (3) First modification treatment: Place the pretreated slide into a special loader, dissolve 0.05 mol of 3-chloropropyltrimethoxysilane in 50 ml of toluene, stir until homogeneous, and pour the solution into a three-necked flask containing 70 ml of toluene; then place the loader containing the slide into the three-necked flask, and heat at 90°C for 3 h under nitrogen protection. Remove the slide, wash it 5 times with ethanol, and then dry it in a 100°C oven for 12 h to obtain the coupling agent-carrier.

[0097] The mass ratio of 3-chloropropyltrimethoxysilane to the pretreated glass slide is 10:1.

[0098] (4) Second modification treatment: The 0.01 mol structure-directing agent C synthesized above is subjected to a second modification treatment. 22-6-6-6 Dissolve the coupling agent in 50 ml of toluene and pour it into a three-necked flask. Add another 70 ml of toluene and place the coupling agent-carrier into the flask. Heat at 90°C for 3 hours under nitrogen protection. Remove the slide and wash it five times with ethanol. Then dry the slide in a 100°C oven for 12 hours to obtain the structure-directing agent-coupling agent-carrier.

[0099] Among them, structure-directing agent C 22-6-6-6 The mass ratio of the coupling agent to the carrier is 10:1.

[0100] (5) Dissolve 1.80g of solid NaOH in 41.84g of deionized water to form a NaOH solution; dissolve 1.32g of concentrated sulfuric acid in 11.88g of deionized water and stir until homogeneous to obtain a sulfuric acid solution; pour 0.50g of solid aluminum sulfate into the prepared sulfuric acid solution and stir with a magnetic stirrer at room temperature for 10min. Then, mix the solutions and stir at 25℃ for 1h. Add 15.25g of tetraethyl silicate to the beaker and stir with a magnetic stirrer at 25℃ for 1h to obtain the precursor sol.

[0101] The structure-directing agent, coupling agent, carrier, and precursor sol were placed in a stainless steel reactor with a polytetrafluoroethylene liner. The reactor was placed in a rotary oven and dynamically crystallized at 160°C for 120 hours. The resulting mixed solution was filtered, washed four times with deionized water, and then dried in an oven for 12 hours to obtain the supported molecular sieve membrane of this embodiment. Figure 1 This is an XRD pattern of the sol system during the dynamic crystallization process of Example 1 of this application. Figure 1 The XRD patterns of the sol system from day 1 to day 5 are shown, which show that the molecular sieve membrane gradually grows and takes shape.

[0102] Example 2

[0103] The preparation method of the supported molecular sieve in this embodiment is basically the same as that in Example 1, except that a silicon wafer is used as the support in step 2). The water contact angle of the pretreated silicon wafer was measured to be 7.2°.

[0104] Example 3

[0105] The preparation method of the supported molecular sieve in this embodiment is basically the same as that in Example 1, except that glass spheres are used as the support in step 2). The water contact angle of the pretreated glass spheres was measured to be 9.6°.

[0106] Example 4

[0107] The preparation method of the supported molecular sieve in this embodiment is basically the same as that in Example 1, except that silicon carbide is used as the support in step 2). The water contact angle of the pretreated silicon carbide was measured to be 8.5°.

[0108] Example 5

[0109] The preparation method of this embodiment is basically the same as that of Example 3, except that 1-bromodocosahexadecane in step 1) is replaced with 1-bromooctadecane.

[0110] Example 6

[0111] The preparation method of this embodiment is basically the same as that of Example 3, except that 1-bromodocosahexadecane in step 1) is replaced with 1-bromohexadecane.

[0112] Comparative Example 1

[0113] The preparation method of this comparative example is basically the same as that of Example 3, except that the support is directly subjected to the dynamic crystallization process in step 4.

[0114] Comparative Example 2

[0115] The preparation method of this comparative example is basically the same as that of Example 3, except that the pretreatment in step 2) is omitted. The water contact angle of the glass sphere used for the first modification treatment in step 3) of this comparative example was measured to be 25.7°.

[0116] Experimental Example 1

[0117] 1. The supported molecular sieve membranes in the examples and comparative examples were analyzed using SEM, and the results are shown in Table 1. Figures 2-7 .

[0118] Figure 2 This is a SEM image of the supported molecular sieve membrane of Example 1 of this application. Figure 3 This is a SEM image of the supported molecular sieve membrane of Example 1 of this application. Figure 4 This is a SEM image of the supported molecular sieve membrane of Example 2 of this application. Figure 5 This is a SEM image of the supported molecular sieve membrane of Example 3 of this application; Figure 6 This is a SEM image of the supported molecular sieve membrane of Example 3 of this application. Figure 7 This is a SEM image of the supported molecular sieve membrane of Comparative Example 1 of this application.

[0119] Table 1

[0120]

[0121] As shown in Table 1 and the figures, the method of this application can still grow uniform and thickness-adjustable molecular sieve membranes even on the surface of a three-dimensional support.

[0122] Experimental Example 2

[0123] The supported molecular sieve membranes of Examples 3, 4, 5, 6 and Comparative Examples 1, 2 were used in olefin isomerization experiments, specifically including the following steps: The supported molecular sieve membrane was packed into the isothermal zone of a reaction tube (inner diameter 13 mm), with a catalyst loading of 5 ml, separated from the top and bottom by quartz wool and 2 ml of quartz sand. 1-Octene was fully vaporized in a preheated furnace at 150°C using a plunger pump, and then entered the reaction tube, undergoing three-stage condensation to obtain the reaction product. The reaction temperature was 260°C, and the feed volume hourly space velocity (WHSV) was 6 h⁻¹. -1The 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 according to the following formula. Specific results are shown in Table 2 and... Figure 7 .

[0124] Raw material conversion rate = (moles of raw material - moles of raw material in the product) / moles of raw material × 100%

[0125] Isomer selectivity = (Number of moles of target isomer) / (Number of moles of starting material - Number of moles of starting material in product) × 100%

[0126] Yield = Feed conversion rate × Heterogeneity selectivity

[0127] Table 2

[0128]

[0129] As shown in Table 2, the supported molecular sieve membrane of this application exhibits excellent olefin isomerization catalytic performance. However, Examples 1 and 2, due to their use of two-dimensional supports, cannot be applied to fixed beds for performance evaluation.

[0130] 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 molecular sieve membrane, characterized in that, Includes the following steps: The carrier was pretreated with a piranha solution to obtain a pretreated carrier; The pretreated support was first modified using a silane coupling agent to obtain a coupling agent-support. A second modification treatment was performed on the coupling agent-carrier using a structure-directing agent to obtain a directing agent-coupling agent-carrier. A molecular sieve layer is grown on the surface of the directing agent-coupling agent-carrier to obtain the supported molecular sieve membrane; The structure-directing agent includes hydrophilic groups and hydrophobic chains.

2. The preparation method according to claim 1, characterized in that, The pretreatment includes: immersing the carrier in the piranha solution, treating it under ultrasonic conditions for 1-4 hours, and then drying it to obtain the pretreated carrier; in the piranha solution, the volume ratio of concentrated sulfuric acid to hydrogen peroxide is (2:8)-(8:2). The water contact angle of the pretreated carrier is less than 10°.

3. The method according to claim 1 or 2, characterized in that, The silane coupling agent comprises at least one selected from 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, and 4-chlorobutyltrimethoxysilane; and / or The hydrophilic group comprises n amino groups, wherein 1 ≤ n ≤ 4; 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 stainless steel, hollow fiber ceramic, glass slide, silicon wafer, glass sphere, alumina sphere, silica sphere, mixed oxide carrier, zirconia sphere, quartz sand, and silicon carbide.

4. The method according to any one of claims 1-3, characterized in that, The structure-directing agent is prepared by a method comprising the following process: After subjecting a first mixed solution comprising long-chain haloalkanes and amine compounds to a first reflux treatment, the first reflux system is subjected to crystallization treatment to obtain a first intermediate. After subjecting a second mixed solution comprising the first intermediate and haloalkanes to a second reflux treatment, the second reflux system is subjected to crystallization treatment to obtain the second intermediate; After subjecting a third reflux treatment to a third mixed solution comprising the second intermediate and the amine compound, the third reflux system is subjected to crystallization treatment to obtain the structure directing agent; The long-chain haloalkane includes at least one of 1-bromodocosahexadecane, 1-bromooctadecane, and 1-bromohexadecane; The amine compound includes at least one of N,N,N',N'-tetramethyl-1,6-hexanediamine, N,N,N',N'-tetramethyl-1,3-propanediamine, and N,N,N',N'-tetramethyl-1,3-octanediamine; The haloalkane includes at least one of 1,6-dibromohexane, 1,6-dibromobutane, and 1,6-dibromooctane.

5. The method according to claim 4, characterized in that, The molar ratio of the long-chain haloalkane to the amine compound is 1-3:1-15; The molar ratio of the first intermediate to the haloalkane is 1-2:1-20; The molar ratio of the second intermediate to the amine compound is 1-2:1-20.

6. The method according to any one of claims 1-5, characterized in that, The first modification treatment includes: subjecting a mixed solution comprising the pretreated carrier and the silane coupling agent to a first heat treatment to obtain the coupling agent-carrier, wherein the temperature of the first heat treatment is 60-120°C and the time is 1-10h; the mass ratio of the silane coupling agent to the pretreated carrier is 1-50:1-5.

7. The method according to any one of claims 1-6, characterized in that, The second modification treatment includes: subjecting a mixed solution comprising the structure directing agent and the coupling agent-carrier to a second heat treatment to obtain the directing agent-coupling agent-carrier, wherein the temperature of the second heat treatment is 60-120°C and the time is 1-10h; the mass ratio of the structure directing agent to the coupling agent-carrier is 1-100:1-50.

8. The method according to any one of claims 1-7, characterized in that, The growth of a molecular sieve layer on the surface of the directing agent-coupling agent-carrier includes: dynamically crystallizing the directing agent-coupling agent-carrier and precursor sol at 100-180°C for 24-168 hours.

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

10. An apparatus, characterized in that, Includes the supported molecular sieve membrane as described in claim 9.

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