Separation membranes, their preparation methods and applications

Abstract

This invention relates to the field of gas separation technology, and discloses a separation membrane, its preparation method, and its application. The preparation method includes the following steps: (1) mixing a first metal source, a first organic ligand, a first alkali source, a particle size regulator, and a first solvent, and performing a hydrothermal reaction to obtain seed crystals; the median particle size of the seed crystals is 0.1-8 μm; (2) preparing a dispersion containing the seed crystals; (3) coating the dispersion onto the surface of a support to obtain a separation membrane intermediate; (4) preparing a membrane synthesis mother liquor containing a second metal source, a second organic ligand, a second alkali source, and a second solvent, and then performing at least one hydrothermal growth on the surface of the separation membrane intermediate to form a membrane. The separation membrane prepared by this method has high gas flux and high selectivity, low cost, and high reliability, and has good application prospects.

Description

Technical Field

[0001] This invention relates to the field of gas separation technology, specifically to a separation membrane, its preparation method, and its application. Background Technology

[0002] Membrane separation technology, as a highly efficient and low-energy-consumption separation technique, is currently widely used in industrial processes such as water treatment and solvent recovery. In the field of gas separation, polycrystalline separation membranes composed of porous materials such as molecular sieve membranes and metal-organic framework membranes possess highly uniform pore structures, and can effectively separate and concentrate preferentially permeating gas molecules through the molecular sieving effect. However, the preparation and performance of existing porous membrane materials still have certain problems, including long preparation processes, high energy consumption, and insufficient membrane separation selectivity and gas flux.

[0003] 3,4,5-Trihydroxybenzoate-type (also known as gallic acid-type or M-Gallate) metal-organic frameworks are microporous materials developed in recent years, with the molecular formula M(C7O5H4)·2H2O. CN112156659A discloses a method for preparing such metal-organic frameworks using ball milling seeding and counter-diffusion methods; a research group at Dalian University of Technology reported a method for preparing such metal-organic frameworks using a freeze-diffusion method (DOI: 10.1021 / acsmaterialslett.2c01107). Although the above methods can realize the application of this type of metal-organic framework membrane in the ethylene / ethane membrane separation process, the preparation process of the above existing technologies is complex, requiring ball milling, freezing, and other methods, increasing additional energy consumption, making it difficult to control the membrane structure, and limiting the flexibility of membrane performance adjustment. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of complex preparation process, high cost, difficulty in controlling membrane structure, and unsatisfactory gas separation performance of existing metal-organic framework separation membranes. This invention provides a separation membrane, its preparation method, and its application. The preparation method has a simple route, strong process controllability, and the separation membrane obtained can be effectively applied to gas separation processes such as ethylene / ethane. The separation membrane obtained has high gas flux and high selectivity.

[0005] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a separation membrane, comprising the following steps:

[0006] (1) The first metal source, the first organic ligand, the first base source, the particle size regulator and the first solvent are mixed and subjected to a hydrothermal reaction to obtain seed crystals; the median particle size of the seed crystals is 0.1-8 μm;

[0007] (2) Prepare a dispersion containing the seed crystals;

[0008] (3) The dispersion is coated on the surface of the support to obtain a separation membrane intermediate;

[0009] (4) Prepare a membrane synthesis mother liquor containing a second metal source, a second organic ligand, a second alkali source and a second solvent, and then perform at least one hydrothermal growth on the surface of the separation membrane intermediate to form a membrane.

[0010] Preferably, the metal element in the first metal source includes Co and / or Mg; the metal element in the second metal source includes Mg, and optionally Co and / or Ni.

[0011] The second aspect of the present invention provides a separation membrane prepared by the above-described method.

[0012] A third aspect of the present invention provides the application of the above-described separation membrane in gas separation.

[0013] The separation membrane preparation method provided by this invention involves preparing seed crystals with a suitable median particle size via a one-step hydrothermal method, followed by hydrothermal growth to form a membrane. The preparation process is simple and controllable, requiring no additional steps such as ball milling or freezing. The separation membrane prepared by this method exhibits high gas flux and high selectivity, low cost, and high reliability, showing promising application prospects. In preferred cases, optimizing the composition of the seed crystals and the metals in the mother liquor can further improve the separation performance of the membrane. Detailed Implementation

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0015] The first aspect of this invention provides a method for preparing a separation membrane, comprising the following steps:

[0016] (1) The first metal source, the first organic ligand, the first base source, the particle size regulator and the first solvent are mixed and subjected to a hydrothermal reaction to obtain seed crystals; the median particle size of the seed crystals is 0.1-8 μm;

[0017] (2) Prepare a dispersion containing the seed crystals;

[0018] (3) The dispersion is coated on the surface of the support to obtain a separation membrane intermediate;

[0019] (4) Prepare a membrane synthesis mother liquor containing a second metal source, a second organic ligand, a second alkali source and a second solvent, and then perform at least one hydrothermal growth on the surface of the separation membrane intermediate to form a membrane.

[0020] In this invention, seed crystals with a suitable median particle size are prepared in a one-step process, and then a hydrothermal growth film is formed on the surface of the seed-coated separation membrane intermediate. This reduces the difficulty of metal-organic framework film formation and facilitates control of the membrane structure. The resulting separation membrane exhibits high gas flux and high selectivity.

[0021] Metal-organic frameworks (MOFs) are microporous materials that have emerged in recent years. However, due to the difficulty in forming MOF films, existing technologies for preparing MOF membranes are quite complex, typically employing ball milling seeding combined with back-diffusion or cryogenic back-diffusion, which are difficult to control, costly, and lack flexibility in membrane performance adjustment. The inventors of this invention have discovered that controlling the median particle size of the seed crystals within a suitable range facilitates the formation of a dense, continuous MOF membrane layer, resulting in a separation membrane with excellent separation performance.

[0022] In existing technologies, the median particle size of metal-organic framework seeds obtained by conventional hydrothermal crystallization is relatively large, generally above 25 μm. In this invention, by introducing a particle size modifier to control the hydrothermal reaction, the median particle size of the obtained seeds is 0.1-8 μm. If the seed particle size is too large, it may lead to difficulties in intergranular interaction and coexistence, increased defects, decreased selectivity, and increased film thickness with lower film flux. If the particle size is too small, the seed may enter the pores of the support layer, thus affecting the film flux.

[0023] According to some preferred embodiments of the present invention, the median particle size of the seed crystals is 0.2-1.2 μm, preferably 0.4-0.9 μm. In the above preferred cases, controlling the seed crystal particle size within the above suitable range is beneficial to the subsequent hydrothermal growth of the metal-organic framework into a film, and also facilitates the flexible adjustment of the film composition, which is beneficial to further improving the density and separation performance of the subsequent hydrothermal grown film.

[0024] In this invention, the term "median particle size" refers to the particle size corresponding to the cumulative particle size distribution percentage of a seed sample reaching 50%, and represents the average particle size in this invention.

[0025] In this invention, the median particle size of the seed crystals is obtained by dynamic light scattering laser particle size analyzer.

[0026] The present invention allows for a wide range of specific particle size modifiers, as long as they can adjust the median particle size of the seed crystals obtained from the hydrothermal reaction to be within the aforementioned range. Preferably, the particle size modifier is selected from at least one of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, octadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, sodium dodecyl sulfate, dodecanoic acid, polyvinylpyrrolidone, benzoic acid, formic acid, acetic acid, and triethylamine, and is more preferably hexadecyltrimethylammonium bromide.

[0027] In this invention, there are no special requirements for the mixing order of the first metal source, the first organic ligand, the first alkali source, the first solvent, and the particle size regulator; conventional operating methods in the art can be used. Preferably, the first alkali source and the first solvent are mixed first, then the first organic ligand is added, followed by the first metal source, and finally the particle size regulator is added. Using the above preferred embodiment facilitates the complete dissolution of each component, forming a homogeneous system or a uniformly dispersed system.

[0028] According to some preferred embodiments of the present invention, the molar ratio of the first metal source, the first organic ligand, the first base source, the particle size modifier and the solvent, calculated in terms of metal elements, satisfies the following: n(first metal source): n(first organic ligand): n(first base source): n(particle size modifier): n(first solvent) = 1: (1-5): (1-6): (0.01-1.8): (100-500), preferably 1: (1.8-3.5): (2-4): (0.14-0.9): (200-400).

[0029] In this invention, the terms "first" and "second" in "first metal source" and "second metal source", "first organic ligand" and "second organic ligand", "first alkali source" and "second alkali source", "first solvent" and "second solvent" are only used to distinguish the raw materials in different steps and do not limit the invention.

[0030] According to some preferred embodiments of the present invention, the metal elements in the first metal source and the second metal source are each independently selected from at least one of Co, Mg and Ni.

[0031] In this invention, the metal elements in the first metal source and the second metal source may be the same or different.

[0032] According to some preferred embodiments of the present invention, the metal element in the first metal source includes Co and / or Mg; preferably, the metal element in the first metal source includes Co, and optionally Mg.

[0033] Preferably, the metal elements of the first metal source include Co and Mg, and the molar ratio of Co to Mg is 1:0.05-20, preferably 1:0.1-10.

[0034] According to some preferred embodiments of the present invention, the metal element in the second metal source is selected from at least one of Co, Mg and Ni; preferably, the metal element in the second metal source includes Mg, and optionally Co and / or Ni.

[0035] Preferably, the second metal source comprises Mg, Co, and / or Ni, wherein the total molar ratio of Mg to Co and / or Ni is 1:0.05-20, more preferably 1:0.1-10, and even more preferably 1:0.2-0.5. In the above-mentioned preferred embodiments, it is advantageous to further improve the gas flux and selectivity of the separation membrane.

[0036] According to a particularly preferred embodiment of the present invention, the metal element in the first metal source includes Co, the metal element in the second metal source includes Mg, and Co and / or Ni. Using the above preferred embodiment, the resulting separation membrane can achieve both high gas flux and high selectivity.

[0037] According to some preferred embodiments of the present invention, the first metal source and the second metal source are soluble salts that can provide the aforementioned metal elements, such as at least one of chlorides, nitrates, and sulfates. The first metal source and the second metal source may also contain water of crystallization, as is well known to those skilled in the art.

[0038] According to some preferred embodiments of the present invention, the first organic ligand and the second organic ligand are 3,4,5-trihydroxybenzoic acid, also known as gallic acid. The gallic acid may also include water of crystallization. In the above case, the chemical composition of the seed crystal obtained in step (1) or the hydrothermal growth film formed in step (4) can be independently expressed as M(C7O5H4)·2H2O, wherein M is selected from at least one of Co, Mg and Ni, and more preferably M corresponds to the metal species in the above preferred embodiments.

[0039] According to some preferred embodiments of the present invention, the first alkali source and the second alkali source are each independently selected from at least one of potassium hydroxide, sodium hydroxide, and lithium hydroxide, preferably potassium hydroxide. The first alkali source and the second alkali source can be provided in the form of an aqueous solution of alkali.

[0040] According to some preferred embodiments of the present invention, the first solvent and the second solvent are each independently selected from at least one of water, methanol, ethanol, N,N-dimethylformamide and N,N-dimethylacetamide, preferably water.

[0041] According to some preferred embodiments of the present invention, in step (1), the conditions for the hydrothermal reaction include: a temperature of 50-200℃, preferably 70-140℃; and a time of 1-168h, preferably 8-48h. Under the above preferred reaction conditions, it is beneficial to shorten the preparation cycle and reduce energy consumption while generating qualified seed crystals that meet the particle size requirements.

[0042] In this invention, preferably, the method further includes: performing solid-liquid separation, washing, and drying on the product of the hydrothermal reaction to obtain the seed crystals. This invention does not impose special limitations on the specific methods and conditions for the solid-liquid separation, washing, and drying; conventional operating methods in the art can be used.

[0043] According to the present invention, in step (2), the seed crystals are dispersed in a solvent to obtain a dispersion containing the seed crystals, and then the coating described in step (3) is performed. The solvent is preferably water.

[0044] According to some preferred embodiments of the present invention, in step (2), the mass concentration of the dispersion is 0.01-5%, preferably 0.1-1.5%, and more preferably 0.2-0.5%.

[0045] In this invention, there are no particular limitations on the coating method described in step (3), and conventional methods and operating conditions in the art can be used. Preferably, the coating method is selected from room temperature dip coating, hot dip coating, or vacuum dip coating, and room temperature dip coating is preferred. The room temperature dip coating can be carried out at room temperature and pressure.

[0046] The present invention does not have any particular limitation on the coating thickness and coating amount of the seed crystals. In a preferred case, a single-layer dense coating is used. After coating, excess seed crystals can be gently wiped away so that the coating thickness of the seed crystals is basically consistent with the median grain size of the seed crystals.

[0047] In this invention, there is no particular limitation on the number of times the seed crystal is applied; multiple applications are permissible, an operation well known to those skilled in the art. Preferably, the number of applications is 1-20, more preferably 2-10, and even more preferably 3-6. A drying process is preferably included between any two applications. Preferably, the drying process is performed at a temperature of 20-150°C, more preferably 40-100°C.

[0048] In this invention, the seed crystals in the seed dispersion are any seed crystals that meet the particle size range mentioned above. They can be seed crystals with a single particle size distribution, seed crystals with different single particle size distributions used in multiple coating processes, or a direct mixture of seed crystals with multiple particle size distributions.

[0049] In this invention, the support can be an inorganic porous support, such as at least one of aluminum oxide, silicon oxide, titanium oxide, chromium oxide, iron oxide, zirconium oxide, yttrium oxide, copper oxide, phosphorus oxide, silicon carbide and elemental carbon.

[0050] The present invention does not have a particular limitation on the shape of the support, for example, the support can be in the form of a flat plate, a tube or a hollow fiber, preferably a tube support.

[0051] In this invention, the size and specifications of the support are not particularly limited, and supports with conventional length, thickness, diameter, pore size, and porosity in the art can be used. Preferably, the porosity of the support is 20-70%, more preferably 30-50%. Under these preferred conditions, it is beneficial to reduce the mass transfer resistance of the support while maintaining a certain mechanical strength.

[0052] According to some preferred embodiments of the present invention, the pore size of the support does not exceed twice the median grain size of the seed crystal; preferably, the pore size of the support is 0.05-1.8 μm. In the above preferred cases, it is advantageous to obtain a higher gas flux while ensuring membrane compactness. This is likely because, in these cases, the seed crystal can avoid entering the pores of the support through bridging; if the pore size of the support is too large, the probability of the seed crystal entering the pores may increase significantly, leading to pore blockage and thus affecting the gas flux.

[0053] According to some preferred embodiments of the present invention, the molar ratio of the second metal source, the second organic ligand, the second alkali source and the second solvent in the membrane synthesis mother liquor, calculated by metal element, satisfies n(second metal source):n(second organic ligand):n(second alkali source):n(second solvent) = 1:(1-5):(1-8):(200-20000), preferably 1:(1.8-2.2):(2-4):(800-4000).

[0054] The present invention does not impose any particular limitations on the specific operation and conditions for the hydrothermal growth film formation, and conventional methods in the art can be used, as long as the uniform film formation of the metal-organic framework membrane is satisfied. Preferably, in step (4), the hydrothermal growth film formation includes: immersing the separation membrane intermediate in the membrane synthesis mother liquor, performing a second hydrothermal reaction, washing, and drying.

[0055] Preferably, the conditions for the second hydrothermal reaction include: a temperature of 50-180℃, more preferably 60-120℃; and a time of 2-168h, more preferably 16-72h.

[0056] According to some preferred embodiments of the present invention, the reaction temperature of the second hydrothermal reaction is not higher than the reaction temperature of the hydrothermal reaction in step (1), and / or the reaction time of the second hydrothermal reaction is not less than the reaction time of the hydrothermal reaction in step (1). Preferably, the reaction temperature of the second hydrothermal reaction is lower than the reaction temperature of the hydrothermal reaction in step (1), and the reaction time of the second hydrothermal reaction is greater than the reaction time of the hydrothermal reaction in step (1).

[0057] The preferred embodiments described above are beneficial for improving the separation effect of the separation membrane. This is likely because, under the aforementioned conditions, the formation of metal-organic framework particles in the bulk phase can be reduced, allowing nutrients to be utilized by the metal-organic framework for membrane formation as much as possible. Furthermore, the longer reaction time helps to increase the density of the membrane layer, thereby enabling the separation membrane to have suitable gas flux and excellent selectivity.

[0058] Preferably, the thickness of the membrane layer obtained by hydrothermal growth is 50 nm-50 μm, more preferably 0.5-20 μm, and even more preferably 10-15 μm. With the above-mentioned preferred membrane layer thickness, it is beneficial to further improve the separation performance of the separation membrane.

[0059] In this invention, the film thickness is measured using a scanning electron microscope. The film thickness is measured in three different film regions, and the average value is taken.

[0060] Preferably, the hydrothermal growth film formation process is performed 1-20 times, more preferably 1-4 times, to meet the thickness requirements of the separation membrane.

[0061] A second aspect of the present invention provides a separation membrane prepared by the above-described preparation method.

[0062] According to the present invention, the separation membrane includes a support and a metal-organic framework membrane layer composited on the surface of the support.

[0063] Preferably, the chemical composition of the metal-organic framework film can be expressed as M(C7O5H4)·2H2O, wherein M is selected from at least one of Co, Mg and Ni.

[0064] A third aspect of the present invention provides the application of the above-described separation membrane in gas separation.

[0065] The present invention has a wide range of gas selection options, and the metal-organic framework membrane is suitable for the separation of any gas system in the art. Preferably, the gas separation includes ethane-ethylene separation, propylene-propane separation, or hydrogen-methane separation.

[0066] The present invention will be described in detail below through embodiments.

[0067] Unless otherwise specified, the raw materials used in the following examples and comparative examples are all commercially available.

[0068] In this invention, the gas permeability of the metal-organic framework membrane is measured using a membrane gas permeation device, and the specific operating conditions include:

[0069] The pressure difference method is used, where the feed side of the membrane contains a single gas at a certain pressure, while the permeate side contains another gas at a constant pressure, typically atmospheric pressure. The permeability of the single gas through the membrane is calculated by measuring the gas volumetric flow rate during stable permeation, using the following formula:

[0070]

[0071] GTR stands for gas transmission rate, measured in mol / (m³). 2 ·s·Pa) represents the number of moles of gas passing through a unit membrane area per unit pressure difference per unit time; Q is the volumetric flow rate of gas permeating the membrane, in m³ / s. 3 / s; R is the gas constant, with a value of 8.314 m. 3 ·Pa / (K·mol); T is the system temperature, in K; A is the effective film area, in m². 2 ;P feed and P perm These are the feed pressure and the permeation pressure, respectively, and their units are Pa.

[0072] By comparing the permeability of two arbitrary gases, the ideal gas selectivity of the membrane for that pair of gases can be obtained, as shown in the following formula:

[0073]

[0074] Where S is the ideal selectivity of the membrane for a pair of gases, with a dimension of 1; GTR1 and GTR2 are the gas permeability of gas 1 and gas 2 through the membrane, respectively.

[0075] The median particle size of the seed crystals was obtained by dynamic light scattering laser particle size analyzer.

[0076] Example 1

[0077] (1) Seed synthesis: The raw materials are cobalt chloride hexahydrate (2.618 g, 0.011 mol), gallic acid monohydrate (4.703 g, 0.025 mol), KOH (2.05 g, purity 85 wt%, 0.031 mol), hexadecyltrimethylammonium bromide (CTAB) (1.749 g, 0.0048 mol), and deionized water (60 mL, 3.333 mol). The reagents are added slowly while stirring in the following order: deionized water, KOH, gallic acid monohydrate, cobalt chloride hexahydrate, and CTAB. The reagents are completely dissolved before adding the next reagent. The mixture is sealed in a polytetrafluoroethylene-lined hydrothermal reactor and statically hydrothermally synthesized at 110 °C for 10 h. After washing with water and ethanol, the mixture is dried at 80 °C for 8 h to obtain seed crystals. The median particle size of the seed crystals is obtained by dynamic light scattering laser particle size analyzer, as shown in Table 1.

[0078] (2) Seed coating: The above-mentioned seed crystals were dispersed in deionized water to prepare a seed crystal dispersion with a concentration of 0.2 wt%. An alumina ceramic tube with a total length of 6.5 cm, a surface pore size of 0.5 μm, and an outer diameter of 12 mm was sealed at both ends and fixed in a vertical dip-pull machine. It was immersed in the seed crystal dispersion at a speed of 8000 μm / s, held for 1 min, and then pulled up at a speed of 1000 μm / s. The coating process was repeated 4 times, each time followed by drying at room temperature for 1 h and drying at 80 °C for 30 min. After the last coating, the drying time at 80 °C was increased to 12 h, and a single-layer coated alumina ceramic tube was prepared.

[0079] (3) Hydrothermal growth of the membrane: A membrane synthesis mother liquor containing magnesium chloride hexahydrate (2.8 mmol), gallic acid monohydrate (1.054 g, 5.6 mmol), KOH (0.462 g, purity 85 wt%, 7 mmol), and deionized water (140 mL, 7.77 mol) was prepared. The mother liquor was added in the following order: deionized water, KOH, gallic acid monohydrate, magnesium chloride hexahydrate, cobalt chloride hexahydrate, and nickel chloride hexahydrate. The addition was slow while stirring, ensuring each reagent was completely dissolved before adding the next. Then, the alumina-coated ceramic tube was sealed at both ends and inserted into a polytetrafluoroethylene (PTFE) liner. The above membrane synthesis mother liquor was slowly poured into the tube. The PTFE liner was then placed in a stainless steel hydrothermal reactor and hydrothermally synthesized at 80°C for 24 h. After washing with water and ethanol, the membrane was dried at 80°C for 8 h to obtain the metal-organic framework separation membrane. The resulting separation membrane includes a support layer and a metal-organic framework membrane composited on the support layer, the metal-organic framework membrane having a thickness of 14 μm.

[0080] The gas separation performance of the above-mentioned separation membranes was evaluated using a cross-flow membrane evaluation device.

[0081] The feed side gauge pressure was 0.3 MPa, the permeation side was at atmospheric pressure, and the test temperature was 25℃. The measured C2H4 transmittance (GTR) was 1.66 × 10⁻⁶. -8 mol / (m 2 The transmittance (GTR) of C2H6 (·s·Pa) is 2.1 × 10⁻⁶. -9 mol / (m 2 The ideal selectivity for C2H4 / C2H6 is 7.90 (·s·Pa).

[0082] Example 2

[0083] (1) Seed synthesis: The raw materials are cobalt chloride hexahydrate (2.618 g, 0.011 mol), gallic acid monohydrate (4.703 g, 0.025 mol), KOH (2.05 g, purity 85 wt%, 0.031 mol), hexadecyltrimethylammonium bromide (CTAB) (1.312 g, 0.0036 mol), and deionized water (60 mL, 3.333 mol). The reagents are added slowly while stirring in the following order: deionized water, KOH, gallic acid monohydrate, cobalt chloride hexahydrate, and CTAB. The reagents are completely dissolved before adding the next reagent. The mixture is sealed in a polytetrafluoroethylene-lined hydrothermal reactor and statically hydrothermally synthesized at 120 °C for 8 h. After washing with water and ethanol, the mixture is dried at 80 °C for 8 h to obtain seed crystals. The median particle size of the seed crystals is obtained by dynamic light scattering laser particle size analyzer, as shown in Table 1.

[0084] (2) Seed Coating: The above-mentioned seed crystals were dispersed in deionized water to prepare a seed crystal dispersion with a concentration of 0.2 wt%. An alumina ceramic tube with a total length of 6.5 cm, a surface pore size of 0.5 μm, and an outer diameter of 12 mm was sealed at both ends and fixed in a vertical dip-pull machine. It was immersed in the seed crystal dispersion at a speed of 8000 μm / s, held for 1 min, and then pulled up at a speed of 1000 μm / s. The coating process was repeated 4 times, each time followed by drying at room temperature for 1 h and drying at 80 °C for 30 min. After the last coating, the drying time at 80 °C was increased to 12 h, and a single-layer coated alumina ceramic tube was finally prepared.

[0085] (3) Hydrothermal membrane growth: A membrane synthesis mother liquor containing magnesium chloride hexahydrate (0.455 g, 2.24 mmol), cobalt chloride hexahydrate (0.133 g, 0.56 mmol), gallic acid monohydrate (1.129 g, 6.0 mmol), KOH (0.462 g, purity 85 wt%, 7 mmol), and deionized water (160 mL, 8.88 mol) was prepared. The solution was added in the following order: deionized water, KOH, gallic acid monohydrate, magnesium chloride hexahydrate, and cobalt chloride hexahydrate. The solution was added slowly while stirring, ensuring complete dissolution of each reagent before adding the next. The alumina-coated ceramic tube was then sealed at both ends and inserted into a polytetrafluoroethylene (PTFE) liner. The PTFE liner was then slowly poured into the membrane synthesis mother liquor. The PTFE liner was then placed in a stainless steel hydrothermal reactor and hydrothermally synthesized at 120 °C for 24 h. After washing with water and ethanol, the membrane was dried at 80 °C for 8 h to obtain a metal-organic framework separation membrane. The resulting separation membrane includes a support layer and a metal-organic framework membrane composited on the support layer, the metal-organic framework membrane having a thickness of 15 μm.

[0086] The composition of the prepared separation membrane is shown in Table 1.

[0087] The gas separation performance of the separation membrane was evaluated using the method of Example 1, and the results are shown in Table 1.

[0088] Example 3

[0089] (1) Seed synthesis: The raw materials are cobalt chloride hexahydrate (1.904 g, 0.008 mol), gallic acid monohydrate (5.267 g, 0.028 mol), KOH (1.918 g, purity 85 wt%, 0.029 mol), hexadecyltrimethylammonium bromide (CTAB) (2.187 g, 0.006 mol), and deionized water (60 mL, 3.333 mol). The reagents are added slowly while stirring in the following order: deionized water, KOH, gallic acid monohydrate, cobalt chloride hexahydrate, and CTAB. The reagents are added one at a time until they are completely dissolved. The mixture is sealed in a polytetrafluoroethylene-lined hydrothermal reactor and statically hydrothermally synthesized at 120 °C for 16 h. After washing with water and ethanol, the mixture is dried at 80 °C for 8 h to obtain seed crystals. The median particle size of the seed crystals is obtained by dynamic light scattering laser particle size analyzer, as shown in Table 1.

[0090] (2) Seed Coating: The above-mentioned seed crystals were dispersed in deionized water to prepare a seed crystal dispersion with a concentration of 0.2 wt%. An alumina ceramic tube with a total length of 6.5 cm, a surface pore size of 0.5 μm, and an outer diameter of 12 mm was sealed at both ends and fixed in a vertical dip-pull machine. It was immersed in the seed crystal dispersion at a speed of 8000 μm / s, held for 1 min, and then pulled up at a speed of 1000 μm / s. The coating process was repeated 4 times, each time followed by drying at room temperature for 1 h and drying at 80 °C for 30 min. After the last coating, the drying time at 80 °C was increased to 12 h, and a single-layer coated alumina ceramic tube was finally prepared.

[0091] (3) Hydrothermal membrane growth: Prepare a membrane synthesis mother liquor containing magnesium chloride hexahydrate (0.398 g, 1.96 mmol), cobalt chloride hexahydrate (0.133 g, 0.56 mmol), nickel chloride hexahydrate (0.067 g, 0.28 mmol), gallic acid monohydrate (1.318 g, 7.0 mmol), KOH (0.594 g, purity 85 wt%, 9 mmol), and deionized water (140 mL, 7.77 mol). Add the reagents in the following order: deionized water, KOH, gallic acid monohydrate, magnesium chloride hexahydrate, cobalt chloride hexahydrate, and nickel chloride hexahydrate. Add the reagents slowly while stirring, ensuring that each reagent is completely dissolved before adding the next. Then, seal both ends of the alumina-coated ceramic tube, insert a polytetrafluoroethylene liner, and slowly pour the above membrane synthesis mother liquor into it. Subsequently, the polytetrafluoroethylene liner was placed in a stainless steel hydrothermal reactor and hydrothermally synthesized at 120°C for 36 hours. After washing with water and ethanol, it was dried at 80°C for 8 hours to prepare a metal-organic framework (MOF) separation membrane. The prepared separation membrane includes a support layer and a MOF membrane composited on the support layer, and the thickness of the MOF membrane is 14.5 μm.

[0092] The composition of the prepared separation membrane is shown in Table 1.

[0093] The gas separation performance of the separation membrane was evaluated using the method of Example 1, and the results are shown in Table 1.

[0094] Example 4

[0095] The method of Example 1 was followed, except that in step (1), benzoic acid was used to replace CTAB in equal molar amounts; the median particle size of the seed crystals was obtained by dynamic light scattering laser particle size analyzer, as shown in Table 1. The composition of the membrane synthesis mother liquor in step (3) included: cobalt chloride hexahydrate (0.666 g, 2.8 mmol), gallic acid monohydrate (1.054 g, 5.6 mmol), KOH (0.462 g, purity 85 wt%, 7 mmol), and deionized water (140 mL, 7.77 mol). The composition of the obtained separation membrane is shown in Table 1.

[0096] The gas separation performance of the separation membrane was evaluated using the method of Example 1, and the results are shown in Table 1.

[0097] Example 5

[0098] The method was followed in Example 1, except that CTAB was replaced with an equimolar amount of dodecanoic acid. The median particle size of the resulting seed crystals and the composition of the separation membrane are shown in Table 1.

[0099] The gas separation performance of the separation membrane was evaluated using the method of Example 1, and the results are shown in Table 1.

[0100] Example 6

[0101] The method was followed in Example 1, except that in step (1), magnesium chloride hexahydrate (0.559 g, 2.75 mmol) and cobalt chloride hexahydrate (1.963 g, 8.25 mmol) were used instead of magnesium chloride hexahydrate in the seed crystal synthesis mother liquor, so that the molar ratio was n(Mg):n(Co) = 1:3. The median particle size of the seed crystals was obtained by dynamic light scattering laser particle size analyzer, as shown in Table 1. The composition of the prepared separation membrane is shown in Table 1.

[0102] The gas separation performance of the separation membrane was evaluated using the method of Example 1, and the results are shown in Table 1.

[0103] Example 7

[0104] The method of Example 2 is followed, except that the total molar amount of the second metal source remains unchanged, wherein the molar ratio of n(Mg):n(Co) is 1:30, and the composition of the resulting separation membrane is shown in Table 1.

[0105] The gas separation performance of the separation membrane was evaluated using the method of Example 1, and the results are shown in Table 1.

[0106] Comparative Example 1

[0107] The method of Example 4 was followed, except that no particle size modifier was introduced in step (1). The median particle size of the seed crystals was obtained by dynamic light scattering laser particle size analyzer, as shown in Table 1. The composition of the prepared separation membrane is shown in Table 1.

[0108] The gas separation performance of the above-mentioned separation membranes was evaluated using a cross-flow membrane evaluation device.

[0109] The feed side gauge pressure was 0.1 MPa, the permeation side was at atmospheric pressure, and the test temperature was 25℃. The measured C2H4 transmittance (GTR) was 5.20 × 10⁻⁶. -8 mol / (m 2 The transmittance (GTR) of C2H6 (·s·Pa) is 5.03 × 10⁻⁶. -8 mol / (m 2The ideal selectivity of C2H4 / C2H6 is 1.03 (·s·Pa). However, due to the excessively large seed crystal size, it is difficult to form a dense membrane layer, resulting in excessive membrane flux, significantly reduced selectivity, and poor separation performance.

[0110] Table 1

[0111]

[0112] As can be seen from the results in Table 1, in the embodiments of the present invention, seed crystals with suitable median particle size are prepared by a one-step hydrothermal method, and then hydrothermally grown into a membrane. The resulting separation membrane can achieve both high ethylene permeability and ethylene / ethane selectivity, exhibiting good separation performance. A comparison between Example 4 and Comparative Example 1 shows that when the median particle size of the seed crystals is too large, the membrane flux is too high, and the selectivity is significantly reduced. This is because excessively large seed crystal particles are difficult to form a dense membrane layer through hydrothermal growth, resulting in poor separation performance.

[0113] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a separation membrane, characterized in that, Includes the following steps: (1) A first metal source, a first organic ligand, a first alkali source, a particle size modifier and a first solvent are mixed and subjected to a hydrothermal reaction to obtain seed crystals; the median particle size of the seed crystals is 0.1-8 μm; The particle size modifier is selected from at least one of hexadecyltrimethylammonium bromide, hexadecyltrimethylammonium chloride, octadecyltrimethylammonium bromide, octadecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, sodium dodecyl sulfate, dodecanoic acid, polyvinylpyrrolidone, benzoic acid, formic acid, acetic acid, and triethylamine; (2) Prepare a dispersion containing the seed crystals; (3) The dispersion is coated on the surface of the support to obtain a separation membrane intermediate; (4) Prepare a membrane synthesis mother liquor containing a second metal source, a second organic ligand, a second alkali source and a second solvent, and then perform at least one hydrothermal growth on the surface of the separation membrane intermediate to form a membrane.

2. The preparation method according to claim 1, wherein, The median grain size of the seed crystals is 0.2-1.2 μm.

3. The preparation method according to claim 2, wherein, The median grain size of the seed crystals is 0.4-0.9 μm.

4. The preparation method according to claim 1, wherein, The particle size modifier is hexadecyltrimethylammonium bromide.

5. The preparation method according to claim 1, wherein, The molar ratio of the first metal source, the first organic ligand, the first base source, the particle size modifier, and the first solvent, calculated by metal element, satisfies the following: n(first metal source): n(first organic ligand): n(first base source): n(particle size modifier): n(first solvent) = 1: (1-5): (1-6): (0.01-1.8): (100-500).

6. The preparation method according to claim 5, wherein, The molar ratio of the first metal source, the first organic ligand, the first base source, the particle size modifier, and the first solvent, calculated by metal element, satisfies the following: n(first metal source): n(first organic ligand): n(first base source): n(particle size modifier): n(first solvent) = 1: (1.8-3.5): (2-4): (0.14-0.9): (200-400).

7. The preparation method according to claim 1, wherein, The metal elements in the first metal source and the second metal source are each independently selected from at least one of Co, Mg and Ni.

8. The preparation method according to claim 7, wherein, The metal elements in the first metal source include Co and / or Mg.

9. The preparation method according to claim 8, wherein, The metal element in the first metal source is Co.

10. The preparation method according to claim 7, wherein, The metal element in the second metal source includes Mg, and optionally Co and / or Ni.

11. The preparation method according to claim 10, wherein, The second metal source includes Mg, as well as Co and / or Ni, with the total molar ratio of Mg to Co and / or Ni being 1:0.05-20.

12. The preparation method according to claim 11, wherein, The second metal source includes Mg, as well as Co and / or Ni, with the total molar ratio of Mg to Co and / or Ni being 1:0.1-10.

13. The preparation method according to claim 1, wherein, The first organic ligand and the second organic ligand are 3,4,5-trihydroxybenzoic acid.

14. The preparation method according to claim 1, wherein, The first alkali source and the second alkali source are each independently selected from at least one of potassium hydroxide, sodium hydroxide and lithium hydroxide.

15. The preparation method according to claim 1, wherein, In step (1), the conditions for the hydrothermal reaction include: a temperature of 50-200℃ and a time of 1-168h.

16. The preparation method according to claim 15, wherein, In step (1), the conditions for the hydrothermal reaction include: a temperature of 70-140℃ and a time of 8-48h.

17. The preparation method according to claim 1, wherein, In step (2), the mass concentration of the dispersion is 0.01-5%.

18. The preparation method according to claim 17, wherein, In step (2), the mass concentration of the dispersion is 0.1-1.5%.

19. The preparation method according to claim 18, wherein, In step (2), the mass concentration of the dispersion is 0.2-0.5%.

20. The preparation method according to any one of claims 1-19, wherein, The coating method is selected from room temperature dip coating, hot dip coating, or vacuum dip coating.

21. The preparation method according to claim 20, wherein, The coating method is a room temperature dip coating method.

22. The preparation method according to any one of claims 1-19, wherein, The molar ratio of the second metal source, the second organic ligand, the second base source, and the second solvent in the membrane synthesis mother liquor, calculated by metal element, satisfies the following: n(second metal source):n(second organic ligand):n(second base source):n(second solvent) = 1:(1-5):(1-8):(200-20000).

23. The preparation method according to claim 22, wherein, The molar ratio of the second metal source, the second organic ligand, the second base source, and the second solvent in the membrane synthesis mother liquor, calculated by metal element, satisfies the following: n(second metal source):n(second organic ligand):n(second base source):n(second solvent) = 1:(1.8-2.2):(2-4):(800-4000).

24. The preparation method according to any one of claims 1-19, wherein, In step (4), the hydrothermal growth of the membrane includes: immersing the separation membrane intermediate in the membrane synthesis mother liquor, performing a second hydrothermal reaction, washing, and drying.

25. The preparation method according to claim 24, wherein, The conditions for the second hydrothermal reaction include: a temperature of 50-180℃ and a time of 2-168h.

26. The preparation method according to claim 25, wherein, The conditions for the second hydrothermal reaction include: a temperature of 60-120℃ and a time of 16-72h.

27. The preparation method according to claim 24, wherein, The reaction temperature of the second hydrothermal reaction is not higher than the reaction temperature of the hydrothermal reaction in step (1), and / or the reaction time of the second hydrothermal reaction is not less than the reaction time of the hydrothermal reaction in step (1).

28. The preparation method according to any one of claims 1-19, wherein, The thickness of the film obtained by hydrothermal growth is 50nm-50μm.

29. The preparation method according to claim 28, wherein, The thickness of the film obtained by hydrothermal growth is 0.5-20 μm.

30. The preparation method according to claim 29, wherein, The thickness of the film obtained by hydrothermal growth is 10-15 μm.

31. The separation membrane prepared by the method according to any one of claims 1-30.

32. The application of the separation membrane according to claim 31 in gas separation; The gas separation includes ethane-ethylene separation, propylene-propane separation, or hydrogen-methane separation.

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