Composite membrane as well as preparation method and application thereof

Abstract

The invention relates to the field of composite membranes, and discloses a composite membrane as well as a preparation method and application thereof. The composite membrane comprises 40-90% by mass of a polymer and 10-60% by mass of a molecular sieve, the molecular sieve is an FAU molecular sieve, and the average particle size of the FAU molecular sieve is 2-20 [mu] m. The composite membrane comprises the polymer and the FAU molecular sieve with the specific particle size, the composite membrane is used for mixed gas separation, high flux and permeation selectivity are achieved, and the interface defects of the polymer and the molecular sieve and plasticizing in the long-period using process are effectively inhibited.

Description

Technical Field

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

[0002] Propane and propylene are mainly separated by cryogenic distillation. In contrast, membrane separation is a simpler process that can significantly reduce energy consumption. The core of membrane separation technology is high-performance membrane materials. Single polymer membrane materials generally have low flux and permeate selectivity. Researchers have prepared composite membranes by introducing other components into the polymer to obtain higher separation performance.

[0003] CN104190270A discloses a mixed matrix membrane, its preparation method and its application. First, polyetherimide (PEI) is mixed with dichloromethane, then SAPO-34 is added. After vigorous stirring, ultrasonic treatment and static degassing, the membrane is formed. The prepared PEI / SAPO-34 mixed matrix membrane exhibits high CO2 / CH4 and H2 / CH4 permeation selectivity and flux.

[0004] CN105032216A discloses an attapulgite-polyether-b-polyamide mixed matrix membrane, its preparation and application. First, polyether-b-polyamide is dissolved in a solvent, then attapulgite is added, and it is dispersed in the polyether-b-polyamide solution by ultrasonic treatment. After degassing treatment, the membrane is formed. The prepared attapulgite-polyether-b-polyamide mixed matrix membrane not only significantly improves the CO2 permeability coefficient, but also improves the CO2 / CH4 and CO2 / N2 permeability selectivity.

[0005] CN106975372A discloses a mixed matrix membrane based on sheet material filling and its preparation method. First, a polyether-polyamide block copolymer is dissolved in an ethanol-water mixed solvent, then silver nanosheets are added, and then the mixture is cast into a membrane. The mixed matrix membrane is used to remove CO2 from natural gas, and high CO2 flux and CO2 / CH4 and CO2 / N2 permeability selectivity are obtained.

[0006] CN113385043A discloses a method for preparing and applying a mixed matrix membrane filled with bead-like material. Pebax is first dissolved in an ethanol-water mixed solution, then PSS-ZIF is added for physical blending, and then the mixture is cast into a film. The thickness of the resulting mixed matrix membrane is 100-130 μm. The mixed matrix membrane is used to remove CO2 from natural gas, and high CO2 flux and CO2 / CH4 and CO2 / N2 permeability selectivity are obtained.

[0007] Although the gas flux and permeation selectivity of the above-mentioned mixed matrix membranes are improved to varying degrees, this composite membrane still has some problems, such as plasticization during long-term contact with hydrocarbons leading to a decrease in permeation selectivity, and interfacial defects between the filler and the polymer. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems of plasticization during long-term contact with hydrocarbons and interfacial defects between the filler and the polymer in existing mixed-matrix membranes, and to provide a composite membrane, its preparation method, and its application. The composite membrane comprises a polymer and a FAU molecular sieve with a specific particle size. When used for mixed gas separation, this composite membrane exhibits high flux and permeation selectivity, effectively suppressing interfacial defects between the polymer and the molecular sieve and preventing plasticization during long-term use.

[0009] To achieve the above objectives, the first aspect of the present invention provides a composite membrane comprising 40-90% by mass of a polymer and 10-60% by mass of a molecular sieve, wherein the molecular sieve is a FAU molecular sieve and the average particle size of the FAU molecular sieve is 2-20 μm.

[0010] Preferably, the FAU molecular sieve contains cations, wherein the cations are monovalent metal ions with an atomic number ≥ 27.

[0011] A second aspect of the present invention provides a method for preparing a composite membrane, the method comprising the following steps:

[0012] (1) A composite membrane matrix material, molecular sieve and solvent are mixed to obtain a casting solution, and a polymer membrane is prepared;

[0013] (2) Stabilize the polymer film prepared in step (1);

[0014] (3) Crosslink the polymer film obtained by the stabilization treatment to obtain the composite film;

[0015] The molecular sieve is a FAU molecular sieve, and the average particle size of the FAU molecular sieve is 2-20 μm.

[0016] The third aspect of the present invention provides an application of the composite membrane described in the first aspect above or the composite membrane prepared by the method described in the second aspect above in gas separation, preferably in the separation of mixed gases of olefins and alkanes.

[0017] Through the above technical solution, the present invention has the following beneficial effects:

[0018] (1) The composite membrane provided by the present invention includes a polymer and FAU molecular sieves with a specific particle size. The introduction of the molecular sieve effectively shortens the diffusion distance of the permeating gas in the polymer, and improves the permeation flux and permeation selectivity of the gas to be separated. Furthermore, the polymer chains of the composite membrane are connected to form a stable three-dimensional network structure, thereby avoiding plasticization during long-term contact with hydrocarbon gases.

[0019] (2) In the preferred case, the cation of the FAU molecular sieve provided by the present invention is a monovalent metal ion with an atomic number of not less than 27, which effectively adjusts the micropore size and electrostatic field, thereby giving the FAU molecular sieve higher permeation selectivity for the gas to be separated.

[0020] (3) The method for preparing the composite membrane provided by the present invention involves stabilizing the polymer membrane to reduce interfacial defects between the polymer matrix and the FAU molecular sieve, and further crosslinking to connect the polymer chains, thereby effectively preventing the composite membrane from plasticizing during long-term contact with hydrocarbon gases and thus maintaining its long-term separation performance. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof.

[0022] Figure 1 This is a schematic diagram of the constant pressure gas permeation device described in this invention. Detailed Implementation

[0023] 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.

[0024] The first aspect of the present invention provides a composite membrane comprising 40-90% by mass of a polymer and 10-60% by mass of a molecular sieve, wherein the molecular sieve is a FAU molecular sieve and the average particle size of the FAU molecular sieve is 2-20 μm.

[0025] In this invention, the composite membrane comprises a polymer and FAU molecular sieves of a specific particle size. The introduction of the molecular sieve effectively shortens the diffusion distance of the permeating gas in the polymer. When the composite membrane is used for the separation of mixed gases, it has high permeation flux and permeation selectivity. Furthermore, the composite membrane avoids plasticization during long-term contact with hydrocarbon gases and has long-term separation performance.

[0026] In this invention, preferably, the polymer content in the composite membrane can be 40% by mass, 45% by mass, 50% by mass, 55% by mass, 60% by mass, 65% by mass, 70% by mass, 75% by mass, 80% by mass, 85% by mass, 90% by mass, or any value within the range of the two values ​​above; the molecular sieve content in the composite membrane can be 10% by mass, 15% by mass, 20% by mass, 25% by mass, 30% by mass, 35% by mass, 40% by mass, 45% by mass, 50% by mass, 55% by mass, 60% by mass, or any value within the range of the two values ​​above.

[0027] In this invention, controlling the content of polymer and molecular sieve in the composite membrane within the above-mentioned range is beneficial to enabling the composite membrane to have high flux and permeation selectivity in mixed gas separation.

[0028] Preferably, the composite membrane comprises 70-90% by mass of a polymer and 10-30% by mass of a molecular sieve.

[0029] In this invention, the content of polymer and molecular sieve in the composite membrane is determined according to the amount of feed.

[0030] In this invention, the average particle size of the FAU molecular sieve can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any value within the range of the two values ​​mentioned above. Unless otherwise specified, the average particle size of the FAU molecular sieve in this invention is obtained by scanning electron microscopy.

[0031] In this invention, controlling the average particle size of the FAU molecular sieve within the specified range is beneficial for shortening the diffusion distance of the permeating gas in the polymer and for ensuring uniform dispersion of the FAU molecular sieve in the polymer matrix, reducing interfacial defects, and improving the flux and permeation selectivity of the composite membrane. If the average particle size of the FAU molecular sieve is greater than 20 μm, it will lead to the formation of large voids or defects within the membrane, making it prone to breakage during use and resulting in uneven distribution of the molecular sieve within the membrane, forming non-selective permeation channels. If the average particle size of the FAU molecular sieve is less than 2 μm, the diffusion path of gas molecules within the membrane will be relatively long, increasing the time for gas to pass through the membrane, reducing flux, and making dispersion in the polymer matrix difficult, easily leading to an increase in interfacial defects between the molecular sieve and the polymer matrix, thus reducing the permeation selectivity of the membrane.

[0032] Preferably, the average particle size of the FAU molecular sieve is 5-15 μm.

[0033] In some embodiments of the present invention, preferably, the FAU molecular sieve contains cations, wherein the cations are monovalent metal ions with an atomic number ≥ 27.

[0034] In this invention, the cations in the FAU molecular sieve are beneficial for effectively adjusting the micropore size and electrostatic field of the FAU molecular sieve, thereby improving the permeation selectivity of the gas to be separated, and specific cations are beneficial for enhancing the interaction between the FAU molecular sieve and the polymer, reducing interface defects.

[0035] In this invention, the type of cation can be selected from a wide range, as long as it is a monovalent metal ion with an atomic number ≥ 27. Preferably, the cation is selected from Ag. + Cs + and Rb + At least one of them, preferably Ag + and / or Cs + In this invention, the cations are more advantageous in improving the permeation selectivity of the gases to be separated.

[0036] In this invention, the cation content in the FAU molecular sieve has a wide selection range. Preferably, based on the total amount of the FAU molecular sieve, the cation content, calculated as oxides, is 5-63% by weight, more preferably 10-55% by weight. In this invention, the cation content in the FAU molecular sieve is obtained by X-ray fluorescence spectrometry (XRF).

[0037] In this invention, the SiO2 / Al2O3 molar ratio of the FAU molecular sieve has a wide selection range. Preferably, the SiO2 / Al2O3 molar ratio of the FAU molecular sieve is 2-2.5, for example, it can be 2, 2.1, 2.2, 2.3, 2.4, 2.5, or any value within the range of the two values ​​above, preferably 2-2.2.

[0038] In this invention, controlling the SiO2 / Al2O3 molar ratio of the FAU molecular sieve within the above-mentioned range is beneficial to improving the structural stability of the FAU molecular sieve and optimizing the separation performance of the composite membrane for the gas to be separated.

[0039] In some embodiments of the present invention, preferably, the polymer is formed from a composite membrane matrix material through a crosslinking reaction.

[0040] In this invention, the type of composite membrane matrix material is not particularly limited and can be any of the polymer membrane matrix materials conventionally used in the art. Preferably, the composite membrane matrix material is selected from at least one of polyvinylidene fluoride, polyimide, cellulose acetate, ethyl cellulose, polyacrylonitrile, and polyetherimide, and more preferably from at least one of polyvinylidene fluoride, cellulose acetate, and polyimide.

[0041] In this invention, the composite membrane matrix material has excellent chemical stability and good mechanical properties, is easy to form a film, and as the matrix of the composite membrane, it can work synergistically with the FAU molecular sieve to improve the flux and permeation selectivity of the composite membrane.

[0042] In this invention, the molecular weight of the composite membrane matrix material has a wide selection range. Preferably, the weight-average molecular weight of the composite membrane matrix material is 60,000-200,000 g / mol, and more preferably 70,000-160,000 g / mol.

[0043] In this invention, the thickness of the composite film has a wide range of selectable values, which can be chosen by those skilled in the art according to actual needs. Preferably, the thickness of the composite film is 5-30 μm, for example, it can be 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or any value within the range of the two values ​​mentioned above, preferably 10-30 μm. In this invention, unless otherwise specified, the thickness of the composite film is obtained by measuring with a thickness gauge.

[0044] A second aspect of the present invention provides a method for preparing a composite membrane, the method comprising:

[0045] (1) A composite membrane matrix material, molecular sieve and solvent are mixed to obtain a casting solution, and a polymer membrane is prepared;

[0046] (2) Stabilize the polymer film prepared in step (1);

[0047] (3) Crosslink the polymer film obtained by the stabilization treatment to obtain the composite film;

[0048] The molecular sieve is an FAU molecular sieve with an average particle size of 2-20 μm.

[0049] In this invention, the polymer membrane is stabilized to reduce interfacial defects between the polymer matrix (composite membrane matrix material) and the FAU molecular sieve. Through further cross-linking treatment, the polymer (composite membrane matrix material) chains are linked together, effectively preventing plasticization of the composite membrane during long-term contact with hydrocarbon gases, thereby maintaining its long-term separation performance. When this composite membrane is used for mixed gas separation, it has high flux and permeation selectivity.

[0050] In some embodiments of the present invention, preferably, based on the total amount of the casting solution, the polymer content is 5-20% by mass, for example, it can be 5% by weight, 6% by weight, 8% by weight, 10% by weight, 12% by weight, 14% by weight, 16% by weight, 18% by weight, 20% by weight, and any value within the range of the two values ​​above; the molecular sieve content is 1-20% by mass, 1% by weight, 2% by weight, 4% by weight, 6% by weight, 8% by weight, 10% by weight, 12% by weight, 14% by weight, 16% by weight, 18% by weight, 20% by weight, and any value within the range of the two values ​​above; the solvent content is 60-94% by mass.

[0051] In this invention, the contents of the composite membrane matrix material, molecular sieve, and solvent are controlled within the above-mentioned range to ensure that the casting solution has good uniformity and stability, which is beneficial to subsequent film formation treatment, and to ensure that the prepared composite membrane has high flux and high permeation selectivity in mixed gas separation.

[0052] Preferably, based on the total amount of the casting solution, the content of the composite membrane matrix material is 8-18% by mass; the content of the molecular sieve is 2-7% by mass; and the content of the solvent is 75-90% by mass.

[0053] In this invention, the type of composite membrane matrix material is not particularly limited and can be any of the polymer membrane matrix materials conventionally used in the art. Preferably, the composite membrane matrix material is selected from at least one of polyvinylidene fluoride, polyimide, cellulose acetate, ethyl cellulose, polyacrylonitrile, and polyetherimide, and more preferably from at least one of polyvinylidene fluoride, cellulose acetate, and polyimide.

[0054] In some embodiments of the present invention, preferably, the FAU molecular sieve contains cations, wherein the cations are monovalent metal ions with an atomic number ≥ 27.

[0055] In this invention, the solvent has a wide range of selection, as long as it can dissolve the composite membrane matrix material and the molecular sieve. Preferably, the solvent is selected from at least one of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, chloroform, and N-methylpyrrolidone, and more preferably from at least one of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone. In this invention, the solvent has good solubility, ensuring that the composite membrane matrix material and the molecular sieve can be uniformly dispersed in the solvent to form a stable casting solution. The preferred solvent of this invention has better solubility for the composite membrane matrix material and the molecular sieve.

[0056] In this invention, the mixing conditions are not particularly limited, as long as a uniform and stable casting solution is formed. Preferably, the mixing conditions in step (1) include: a temperature of 30-60°C, preferably 30-50°C; a time of 1-10 hours, preferably 2-6 hours; and a rotation speed of 20-100 rpm. In this invention, controlling the mixing conditions within the above range ensures that the composite membrane matrix material, molecular sieve, and solvent are fully and uniformly mixed to form a stable casting solution.

[0057] In some embodiments of the present invention, preferably, the method in step (1) further includes: degassing the casting solution and then performing a film-forming treatment to obtain a polymer film.

[0058] In this invention, the degassing method and conditions are not particularly limited, and can be any of the methods and conditions conventionally used in the art for degassing casting solutions, as long as the air bubbles in the casting solution are removed. Preferably, the casting solution is allowed to stand at room temperature (20℃-30℃) for 12-24 hours.

[0059] In this invention, preferably, the casting solution obtained after degassing is subjected to a film-forming treatment. Preferably, the film-forming treatment method includes: pouring the casting solution onto a glass plate, scraping it with a doctor blade to form a polymer liquid film, then subjecting the polymer liquid film to a film-forming treatment, and obtaining a polymer film after the solvent evaporates.

[0060] In this invention, the conditions for the film-forming treatment are not particularly limited, as long as the solvent in the polymer liquid film evaporates to obtain the polymer film. Preferably, the conditions for the film-forming treatment include: a temperature of 20-50°C and a time of 6-48 hours.

[0061] In this invention, the specifications of the scraper are not particularly limited, and those skilled in the art can choose according to actual needs. For example, the specifications of the scraper can be 100μm, 150μm, 200μm, 250μm, 300μm, 350μm, or 400μm.

[0062] In some embodiments of the present invention, preferably, the stabilization treatment conditions include: a temperature of 60-150°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, and any value within the range of the two aforementioned values; and a time of 0.5-5 hours, for example, 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, and any value within the range of the two aforementioned values. In the present invention, the stabilization treatment is preferably carried out in an air atmosphere.

[0063] In this invention, controlling the stabilization treatment conditions within the above-mentioned range is beneficial for dispersing the FAU molecular sieve in the polymer matrix, thereby reducing voids and interface defects between the polymer and the FAU molecular sieve.

[0064] Preferably, the stabilization treatment conditions include: a temperature of 80-120℃ and a time of 1-4 hours.

[0065] In this invention, preferably, the polymer film obtained by the stabilization treatment is subjected to crosslinking treatment. This invention, through further crosslinking treatment, links the polymer chains together to form a more stable three-dimensional network structure, thereby preventing plasticization during long-term contact with hydrocarbon gases.

[0066] In this invention, preferably, the crosslinking liquid for crosslinking comprises a crosslinking agent, an inorganic base, and a dispersant. The content of the crosslinking agent, inorganic base, and dispersant in the crosslinking liquid for crosslinking has a wide selection range. Preferably, the crosslinking liquid for crosslinking comprises: 10-40% by mass of crosslinking agent, 5-30% by mass of inorganic base, and 30-85% by mass of dispersant. In this invention, the content of the crosslinking agent in the crosslinking liquid can be 10% by mass, 15% by mass, 20% by mass, 25% by mass, 30% by mass, 35% by mass, 40% by mass, or any value within the range of the two values ​​above; the content of the inorganic base in the crosslinking liquid can be 5% by mass, 10% by mass, 15% by mass, 20% by mass, 25% by mass, 30% by mass, or any value within the range of the two values ​​above; the content of the dispersant in the crosslinking liquid can be 30% by mass, 35% by mass, 40% by mass, 45% by mass, 50% by mass, 55% by mass, 60% by mass, 65% by mass, 70% by mass, 75% by mass, 80% by mass, 85% by mass, or any value within the range of the two values ​​above.

[0067] In this invention, the crosslinking liquid is beneficial for crosslinking the polymer molecular chains in the stabilized polymer film to form a more compact and stable network structure, thereby avoiding plasticization during long-term contact with hydrocarbon gases.

[0068] Preferably, the crosslinking liquid for crosslinking comprises: 10-30% by mass of a crosslinking agent, 5-20% by mass of an inorganic alkali, and 50-85% by mass of a dispersant.

[0069] In this invention, the type of crosslinking agent is not particularly limited and can be any crosslinking agent for polymer film crosslinking conventionally used in the art. Preferably, the crosslinking agent is selected from at least one of p-phenylenediamine, p-phenylenediamine, hexamethylenediamine, terephthalaldehyde, isophthalaldehyde, and hexamethylenedialdehyde, with p-phenylenediamine and / or terephthalaldehyde being more preferred. The crosslinking agent of this invention has high reactivity and selectivity, which is beneficial for effectively promoting the crosslinking reaction of polymer molecules. The preferred crosslinking agent of this invention has even better crosslinking effect.

[0070] In this invention, the type of inorganic base is not particularly limited, and various inorganic bases conventionally used in the art can be used in this invention. For example, the inorganic base can be selected from at least one of sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, and barium hydroxide. Preferably, the inorganic base is sodium hydroxide and / or potassium hydroxide. The inorganic base of this invention has high catalytic activity and stability, maintaining high catalytic efficiency during the crosslinking process.

[0071] In this invention, the type of dispersant is not particularly limited, as long as the crosslinking agent and inorganic base are uniformly dispersed in the solvent and fully contact and react with the polymer film. Preferably, the dispersant is an organic solvent, preferably selected from at least one of water, methanol, ethanol, ethylene glycol, and isopropanol. The dispersant of this invention effectively disperses the crosslinking agent and inorganic base during the crosslinking process and is removed by washing and drying after crosslinking is completed. The washing and drying methods and conditions can adopt conventional methods and conditions in the art.

[0072] In this invention, the mass ratio of the crosslinking liquid to the polymer membrane has a wide selection range. Preferably, the mass ratio of the crosslinking liquid to the polymer membrane is 5-20:1, for example, it can be 5:1, 6:1, 8:1, 10:1, 12:1, 14:1, 16:1, 18:1, 20:1, and any value within the range of the two values ​​above, preferably 8-16:1. In this invention, controlling the mass ratio of the crosslinking liquid to the polymer membrane within the above range helps to ensure sufficient crosslinking and reduce costs while ensuring the performance of the polymer membrane.

[0073] In this invention, the conditions for the crosslinking treatment are not particularly limited. Preferably, the conditions for the crosslinking treatment include: a temperature of 20-100°C and a time of 2-12 hours. In this invention, controlling the conditions of the crosslinking reaction within the above range ensures that the crosslinking reaction proceeds smoothly and completely, and that the performance of the polymer film is not impaired.

[0074] Preferably, the conditions for the crosslinking treatment include: a temperature of 30-80℃ and a time of 3-10h.

[0075] In a preferred embodiment of the present invention, the method for preparing the composite membrane includes the following steps:

[0076] (1) A composite membrane matrix material, molecular sieve and solvent are mixed to obtain a casting solution, and a polymer membrane is prepared;

[0077] (2) Stabilize the polymer film obtained in step (1) at a temperature of 60-150℃ for 0.5-5h;

[0078] (3) Crosslink the polymer film obtained by the stabilization treatment to obtain the composite film.

[0079] The molecular sieve is an FAU molecular sieve, and the average particle size of the FAU molecular sieve is 2-20 μm.

[0080] Based on the total amount of the casting solution, the polymer content is 5-20% by mass, the molecular sieve content is 1-20% by mass, and the solvent content is 60-94% by mass.

[0081] The crosslinking liquid for crosslinking comprises: 10-40% by mass of crosslinking agent, 5-30% by mass of inorganic alkali and 30-85% by mass of dispersant.

[0082] The third aspect of the present invention provides an application of the composite membrane described in the first aspect above or the composite membrane prepared by the method described in the second aspect above in gas separation, preferably in the separation of mixed gases of olefins and alkanes.

[0083] In this invention, the composite membrane is particularly suitable for separating olefin and alkane mixed gases, and has high propylene permeation flux, propane permeation flux and propylene / propane permeation selectivity, effectively suppressing interface defects between polymer and FAU molecular sieve and plasticization during long-term use.

[0084] The present invention will be described in detail below through embodiments.

[0085] Unless otherwise specified, all raw materials used in the following embodiments are commercially available products.

[0086] Unless otherwise specified, room temperature in this invention refers to 25±5℃.

[0087] In this invention, a constant pressure gas permeation device is used to determine the permeability of a single-component gas, with an operating pressure of 0.3 MPa and an operating temperature of 30°C.

[0088] A schematic diagram of the constant pressure gas permeation device of the present invention is shown below. Figure 1The device mainly consists of a membrane cell, pressure gauge A, and flow meter. The gas to be tested is introduced into the membrane cell, and the pressure on the gas inlet side is adjusted to 0.3 MPa. After 24 hours, the time t seconds required for 0.5 mL of gas to flow out on the permeate side is recorded. The effective membrane area is 8.04 cm². 2 The membrane thickness is 1 cm. The gas permeability P is calculated using the following formula, with units of barrers (1 barrer = 10⁻⁶). -10 cm 3 ·cm·cm -2 ·s -1 ·cmHg -1 ).

[0089]

[0090] In the formula, 3 represents the transmembrane pressure difference, in bar; 75 represents that 1 bar equals 75 cmHg.

[0091] Wherein, when the gas to be tested is propylene, P is the permeability of propylene; when the gas to be tested is propane, P is the permeability of propane.

[0092] In this invention, propylene / propane permeation selectivity = propylene permeability / propane permeability.

[0093] In this invention, the method for determining the thickness of the composite film is as follows: a thickness gauge is used to measure the thickness at the four right-angle vertices and the center of a square with a side length of 3cm at the center of the film, and then the average thickness of the film at the five locations is calculated.

[0094] In this invention, the average particle size of the FAU molecular sieve was measured using a scanning electron microscope.

[0095] Example 1

[0096] (1) Cellulose acetate (weight-average molecular weight of 73827 g / mol) and AgLSX molecular sieve (SiO2 / Al2O3 molar ratio of 2.0, average particle size of 6 μm, Ag2O calculated as Ag2O) were mixed. + The content of cellulose acetate (39.5 wt%) was added to the solvent N,N-dimethylacetamide and stirred at 30°C for 2 h to prepare a casting solution. The casting solution contained 8 wt% cellulose acetate and 2 wt% AgLSX molecular sieve. The casting solution was allowed to stand at 30°C for 12 h to degas. Then the casting solution was poured onto a glass plate and scraped with a 300 μm doctor blade to form a polymer liquid film. The liquid film was then treated at 35°C for 6 h to form a film.

[0097] (2) The polymer film obtained after the film-forming treatment is placed in air and stabilized at 100°C for 1.5 hours;

[0098] (3) Place 0.8g of the polymer membrane obtained after the stabilization treatment in 8g of crosslinking solution, wherein the crosslinking solution contains 0.8g of terephthalaldehyde, 0.5g of sodium hydroxide and 6.7g of water, stand at 60°C for 6h for crosslinking treatment, wash with water 3 times, and dry at 80°C for 12h to obtain composite membrane.

[0099] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this embodiment are shown in Table 1.

[0100] Example 2

[0101] (1) Polyvinylidene fluoride (weight-average molecular weight of 99738 g / mol) and CsLSX molecular sieve (SiO2 / Al2O3 molar ratio of 2.1, average particle size of 10 μm, Cs2O calculated as Cs2O) were mixed. + The content of the substance was 40.9 wt%. The substance was added to the solvent N,N-dimethylacetamide and stirred at 50°C for 6 h to prepare the casting solution. The casting solution contained 15% by mass of polyvinylidene fluoride and 5% by mass of CsLSX molecular sieve. The casting solution was allowed to stand at 30°C for 12 h to remove bubbles. Then the casting solution was poured onto a glass plate and scraped into a polymer liquid film with a 300 μm doctor blade. The liquid film was then treated at 35°C for 6 h to form a film.

[0102] (2) The polymer film obtained after the film-forming treatment is placed in air and stabilized at 120°C for 1 hour;

[0103] (3) Place 0.8g of the polymer membrane obtained after the stabilization treatment in 12g of crosslinking solution, wherein the crosslinking solution contains 3g of p-phenylenediamine, 2g of sodium hydroxide and 7g of methanol, stand at 60°C for 6 hours for crosslinking treatment, wash with water 3 times, and dry at 80°C for 12 hours to obtain a composite membrane.

[0104] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this embodiment are shown in Table 1.

[0105] Example 3

[0106] The method described in Example 1 is different except that in step (1), the content of cellulose acetate in the casting solution is 9% by mass and the content of AgLSX molecular sieve is 3.8% by mass; thus, a composite membrane is obtained.

[0107] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this embodiment are shown in Table 1.

[0108] Example 4

[0109] The method described in Example 1 is different except that in step (1), the content of cellulose acetate in the casting solution is 9% by mass and the content of AgLSX molecular sieve is 1% by mass; a composite membrane is obtained.

[0110] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this embodiment are shown in Table 1.

[0111] Example 5

[0112] The method described in Example 1 is different except that in step (1), the content of cellulose acetate in the casting solution is 10% by mass and the content of AgLSX molecular sieve is 2% by mass; a composite membrane is obtained.

[0113] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this embodiment are shown in Table 1.

[0114] Example 6

[0115] The method described in Example 1 is different except that in step (1), the average particle size of the AgLSX molecular sieve is 2 μm.

[0116] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this embodiment are shown in Table 1.

[0117] Example 7

[0118] The method described in Example 1 is different except that in step (1), AgLSX molecular sieve is replaced by an equal amount of CsLSX molecular sieve (SiO2 / Al2O3 molar ratio is 2.0, average particle size is 6μm, and Cs is calculated as Cs2O). + The content of the compound was 38.1 wt%; a composite membrane was obtained.

[0119] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this embodiment are shown in Table 1.

[0120] Example 8

[0121] The method described in Example 1 differs in that, in step (2), the polymer film obtained after the film-forming treatment is placed in air and stabilized at 120°C for 3 hours to obtain a composite film.

[0122] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this embodiment are shown in Table 1.

[0123] Example 9

[0124] The method described in Example 1 is different except that in step (3), the amount of terephthalaldehyde in the crosslinking solution is increased from 0.8g to 1.6g to obtain a composite membrane.

[0125] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this embodiment are shown in Table 1.

[0126] Example 10

[0127] The method described in Example 1 is different except that in step (1), AgLSX molecular sieve is replaced by an equal amount of RbLSX molecular sieve (SiO2 / Al2O3 molar ratio is 2.0, average particle size is 6μm, and Rb is calculated as Rb2O). + The content of the compound was 25.5 wt%; a composite membrane was obtained.

[0128] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this embodiment are shown in Table 1.

[0129] Example 11

[0130] The method described in Example 1 is different in that, in step (1), the content of cellulose acetate in the casting solution is 8% by mass and the content of AgLSX molecular sieve is 4.3% by mass; thus, a composite membrane is obtained.

[0131] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this embodiment are shown in Table 1.

[0132] Example 12

[0133] The method described in Example 1 differs in that, in step (2), the polymer film obtained after the film-forming treatment is placed in air and stabilized at 140°C for 1 hour to obtain a composite film.

[0134] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this embodiment are shown in Table 1.

[0135] Comparative Example 1

[0136] The method described in Example 1 is different except that AgLSX molecular sieve is not added in step (1).

[0137] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this comparative example are shown in Table 1.

[0138] Comparative Example 2

[0139] The method described in Example 1 is different except that the stabilization process described in step (2) is not performed.

[0140] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this comparative example are shown in Table 1.

[0141] Comparative Example 3

[0142] The method described in Example 1 is different except that the crosslinking treatment described in step (3) is not performed.

[0143] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this comparative example are shown in Table 1.

[0144] Comparative Example 4

[0145] The method described in Example 1 differs from that in step (1), the average particle size of the AgLSX molecular sieve is 30 μm.

[0146] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this comparative example are shown in Table 1.

[0147] Comparative Example 5

[0148] The method described in Example 1 differs in that, in step (1), the casting solution contains 9.5% by mass of cellulose acetate and 0.5% by mass of AgLSX molecular sieve.

[0149] The thickness, composition, propylene permeation flux, propane permeation flux, and permeation selectivity of the composite membrane prepared in this comparative example are shown in Table 1.

[0150] Table 1

[0151]

[0152]

[0153] As can be seen from the results in Table 1, the composite membrane prepared by the method provided in this invention has high propylene permeation flux, propane permeation flux, and propylene / propane permeation selectivity.

[0154] Based on Table 1, Example 1, and the comparative examples, it can be seen that compared with Example 1, Comparative Example 1 did not add FAU molecular sieve, and the resulting membrane had low permeation flux for both propylene and propane, and no permeation selectivity, thus failing to achieve propylene / propane separation. Comparative Example 2 was directly crosslinked without stabilization treatment, resulting in a composite membrane with low propylene / propane permeation selectivity, indicating that the composite membrane had many defects. In Comparative Example 3, the polymer membrane after stabilization treatment was not crosslinked, and the resulting composite membrane had low propylene / propane permeation selectivity, indicating that when the composite membrane was in contact with propylene or propane for a long time under high pressure, the polymer was prone to swelling, leading to an increase in both propylene and propane flux and a significant decrease in propylene / propane permeation selectivity. The AgLSX molecular sieve used in Comparative Example 4 had a particle size that was not within the range provided by this invention, resulting in many defects in the composite membrane. In Comparative Example 5, the polymer content and AgLSX molecular sieve content were not within the range provided by this invention, resulting in a membrane with low permeation flux for both propylene and propane, failing to achieve propylene / propane separation.

[0155] 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 composite membrane, characterized in that, The composite membrane comprises 40-90% by mass of a polymer and 10-60% by mass of a molecular sieve, wherein the molecular sieve is a FAU molecular sieve with an average particle size of 2-20 μm.

2. The composite membrane according to claim 1, wherein, The composite membrane comprises 70-90% by mass of a polymer and 10-30% by mass of a molecular sieve; Preferably, the average particle size of the FAU molecular sieve is 5-15 μm.

3. The composite membrane according to claim 1 or 2, wherein, The FAU molecular sieve contains cations, which are monovalent metal ions with an atomic number ≥ 27; Preferably, the cation is selected from Ag. + Cs + and Rb + At least one of them, preferably Ag + and / or Cs + ; Preferably, based on the total amount of the FAU molecular sieve, the content of the cation, calculated as oxides, is 5-63% by weight, preferably 10-55% by weight; Preferably, the SiO2 / Al2O3 molar ratio of the FAU molecular sieve is 2-2.5, more preferably 2-2.

2.

4. The composite membrane according to any one of claims 1-3, wherein, The polymer is formed from a composite membrane matrix material through a cross-linking reaction; Preferably, the composite membrane matrix material is selected from at least one of polyvinylidene fluoride, polyimide, cellulose acetate, ethyl cellulose, polyacrylonitrile, and polyetherimide, and more preferably from at least one of polyvinylidene fluoride, cellulose acetate, and polyimide; Preferably, the weight-average molecular weight of the composite membrane matrix material is 60,000-200,000 g / mol, and more preferably 70,000-160,000 g / mol.

5. The composite membrane according to any one of claims 1-4, wherein, The thickness of the composite film is 5-30 μm, preferably 10-30 μm.

6. A method for preparing a composite membrane, characterized in that, The method includes the following steps: (1) A composite membrane matrix material, molecular sieve and solvent are mixed to obtain a casting solution, and a polymer membrane is prepared; (2) Stabilize the polymer film prepared in step (1); (3) Crosslink the polymer film obtained by the stabilization treatment to obtain the composite film; The molecular sieve is an FAU molecular sieve with an average particle size of 2-20 μm.

7. The method according to claim 6, wherein, Based on the total amount of the casting solution, the content of the composite membrane matrix material is 5-20% by mass, preferably 8-18% by mass; the content of the molecular sieve is 1-20% by mass, preferably 2-7% by mass; and the content of the solvent is 60-94% by mass, preferably 75-90% by mass. Preferably, the composite membrane matrix material is selected from at least one of polyvinylidene fluoride, polyimide, cellulose acetate, ethyl cellulose, polyacrylonitrile, and polyetherimide, and more preferably from at least one of polyvinylidene fluoride, cellulose acetate, and polyimide; Preferably, the FAU molecular sieve contains cations, wherein the cations are monovalent metal ions with an atomic number ≥ 27; Preferably, the solvent is selected from at least one of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, chloroform and N-methylpyrrolidone, and more preferably from at least one of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone; Preferably, the mixing conditions in step (1) include: a temperature of 30-60°C, a time of 1-10 hours, and a rotation speed of 20-100 rpm; Preferably, the method in step (1) further includes: degassing the casting solution and then performing a film-forming treatment to obtain a polymer film; Preferably, the film-forming treatment conditions include: a temperature of 20-50°C and a time of 6-48 hours.

8. The method according to claim 6 or 7, wherein, The stabilization treatment conditions include: a temperature of 60-150℃, preferably 80-120℃; and a time of 0.5-5h, preferably 1-4h.

9. The method according to any one of claims 6-8, wherein, The crosslinking liquid for crosslinking comprises: 10-40% by mass of crosslinking agent, 5-30% by mass of inorganic alkali and 30-85% by mass of dispersant; Preferably, the crosslinking liquid for crosslinking comprises: 10-30% by mass of a crosslinking agent, 5-20% by mass of an inorganic alkali, and 50-85% by mass of a dispersant; Preferably, the crosslinking agent is selected from at least one of p-phenylenediamine, p-phenylenediamine, hexamethylenediamine, terephthalaldehyde, isophthalaldehyde and hexamethylenedialdehyde, and is more preferably p-phenylenediamine and / or terephthalaldehyde; Preferably, the inorganic base is sodium hydroxide and / or potassium hydroxide; Preferably, the dispersant is an organic solvent, preferably selected from at least one of water, methanol, ethanol, ethylene glycol, and isopropanol; Preferably, the mass ratio of the crosslinking liquid to the polymer film is 5-20:1, more preferably 8-16:1; Preferably, the conditions for the crosslinking treatment include: a temperature of 20-100℃, more preferably 30-80℃; and a time of 2-12h, more preferably 3-10h.

10. The application of the composite membrane according to any one of claims 1-5 or the composite membrane prepared by the method according to any one of claims 6-9 in gas separation, preferably in the separation of mixed gases of olefins and alkanes.

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