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

Abstract

The invention relates to the field of carbon molecular sieve membranes, and discloses a carbon molecular sieve membrane as well as a preparation method and application thereof. The method for preparing the carbon molecular sieve membrane comprises the following steps: (1) contacting a polymer membrane with a modifier solution for modification treatment, wherein the modifier contains an aldehyde group and a benzene ring; (2) contacting a product obtained by modification treatment with alkali liquor, and then carrying out stabilization treatment; and (3) carrying out carbonization treatment on a product obtained by stabilizing treatment under the pressure of 0.15-0.8 MPa to obtain the carbon molecular sieve membrane. The method effectively inhibits the formation of defects of the carbon molecular sieve membrane, keeps the membrane layer complete, and significantly improves the flux and permeation selectivity of the carbon molecular sieve membrane to the gas to be separated.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of carbon molecular sieve membrane, and in particular to a carbon molecular sieve membrane, a preparation method and application thereof. BACKGROUND

[0002] Carbon molecular sieve membrane has high thermal stability, chemical stability and permeation selectivity, and is widely concerned in the field of gas separation.

[0003] CN101277754A discloses a preparation process of carbon molecular sieve membrane, which comprises the following steps: first, treating a mixture of cellulose and hemicellulose with trifluoroacetic acid, and then adding metal salt to flow casting into a film; and then drying and carbonizing at 500-600 DEG C to prepare the carbon molecular sieve membrane, which exhibits good separation performance in CO2 / CH4 separation system and can be regenerated by applying current.

[0004] CN106823821A discloses a repairing method for defects of carbon molecular sieve membrane, which comprises the following steps: mixing silicon rubber with catalyst, crosslinking agent and organic solvent to prepare sol, and then coating the sol on the surface of the carbon molecular sieve membrane to form a film, and drying. The catalyst is preferably organic tin, the crosslinking agent is preferably tetraethyl orthosilicate, and the organic solvent is preferably isooctane. The method utilizes the good permeability of silicon rubber, which can penetrate into the interior of the carbon molecular sieve membrane, and the silicon rubber prepared by crosslinking of silicon rubber forms a film on the surface of the carbon molecular sieve membrane to fill the defects of the carbon molecular sieve membrane, thereby greatly improving the permeability of the carbon molecular sieve membrane.

[0005] CN108472595A discloses a preparation method of carbon molecular sieve membrane, which comprises the following steps: first, heating a polymer precursor to a temperature at which the precursor polymer undergoes pyrolysis to form a carbon molecular sieve membrane; then, cooling the carbon molecular sieve membrane to a temperature at which no further pyrolysis occurs; and finally, exposing the carbon molecular sieve membrane to a conditioning atmosphere composed of target permeating gas molecules, so as to realize a carbon molecular sieve membrane with improved combination of selectivity and permeability.

[0006] CN109070009A discloses an improved method for manufacturing carbon molecular sieve membrane, which comprises the following steps: pyrolyzing a polyimide precursor polymer to form a carbon molecular sieve membrane by heating the polyimide precursor polymer in a furnace to a final pyrolysis temperature of 600-700 DEG C, heating from 400 DEG C to the final pyrolysis temperature at a pyrolysis heating rate of 3-7 DEG C / min, and maintaining the final pyrolysis temperature in a non-oxidizing atmosphere for a pyrolysis time of up to 60 minutes, so as to realize a carbon molecular sieve membrane with improved selectivity and permeability.

[0007] In the process of high-temperature carbonization of organic polymers to generate carbon molecular sieve membranes, defects of carbon molecular sieve membranes are generated due to gas escaping, thereby affecting the permeability or selectivity of the carbon molecular sieve membranes. The prior art reduces the defects of carbon molecular sieve membranes by repairing or selecting special polymer precursor materials, but it is still difficult to effectively inhibit the formation of defects in the high-temperature pyrolysis process. SUMMARY

[0008] The present application aims to overcome the problem of defects of carbon molecular sieve membranes generated due to gas escaping in the process of high-temperature carbonization of organic polymers to generate carbon molecular sieve membranes, and provides a carbon molecular sieve membrane and a preparation method and application thereof. The method for preparing the carbon molecular sieve membrane of the present application inhibits the formation of defects of the carbon molecular sieve membrane, maintains the integrity of the membrane layer, and greatly improves the flux and permeation selectivity of the carbon molecular sieve membrane to the gas to be separated.

[0009] To achieve the above-mentioned object, the first aspect of the present application provides a method for preparing a carbon molecular sieve membrane, which comprises:

[0010] (1) contacting a polymer membrane with a modifier solution to perform modification treatment, wherein the modifier contains an aldehyde group and a benzene ring;

[0011] (2) contacting the product obtained by the modification treatment with an alkali solution, and then performing stabilization treatment;

[0012] (3) performing carbonization treatment on the product obtained by the stabilization treatment under a pressure of 0.15-0.8 MPa to obtain the carbon molecular sieve membrane.

[0013] Preferably, the modifier is at least one selected from 2,5-dihydroxyterephthaldehyde, 4-hydroxyisophthaldehyde, 2,6-dihydroxynaphthaldehyde and 2,3-dimethoxy-1,4-naphthaldehyde.

[0014] The second aspect of the present application provides a carbon molecular sieve membrane prepared by the method of the first aspect.

[0015] The third aspect of the present application provides an application of the carbon molecular sieve membrane prepared by the method of the first aspect or the carbon molecular sieve membrane of the second aspect in gas separation, preferably in the separation of a mixture of olefins and alkanes.

[0016] Through the above technical solution, the present application has the following beneficial effects:

[0017] The method for preparing carbon molecular sieve membrane provided by the application adopts a modifier solution to treat a polymer membrane, modifier molecules diffuse into the polymer membrane layer, the aldehyde groups contained in the modifier molecules condense with the hydroxyl groups on the long-chain polymers of the polymer membrane to form stable covalent bonds, meanwhile, the strong hydrogen bond interaction between the modifier molecules makes the long-chain polymer chains in the polymer membrane arrange more closely, thereby reducing the escape of the polar groups on the long-chain polymers of the polymer membrane in the high-temperature carbonization process and reducing the formation of defects of the carbon molecular sieve membrane; the modifier molecules contain benzene rings, which are easy to be converted into carbon molecular sieve in the high-temperature carbonization process, further reducing the defects of the carbon molecular sieve membrane. In addition, the carbonization process of the application is carried out under a higher pressure, which is conducive to converting more carbon-containing species into carbon molecular sieve and reducing the formation of gas, thereby significantly improving the flux and permeation selectivity of the carbon molecular sieve membrane to the gas to be separated.

[0018] Preferably, the stabilization treatment is first carried out at a lower temperature, a small amount of gas can escape under the condition of keeping the membrane layer intact, the small amount of gas is preferentially escaped, which avoids the problem that a large amount of gas produced by the decomposition of the polymer simultaneously escapes in the high-temperature carbonization process, is conducive to inhibiting the formation of defects of the carbon molecular sieve membrane and keeping the membrane layer intact, and then the carbonization treatment is carried out at a higher temperature and a higher pressure, which is conducive to reducing the escape of gas, inhibiting the formation of defects of the carbon molecular sieve membrane and keeping the membrane layer intact, and greatly improves the separation performance of the carbon molecular sieve membrane to the gas to be separated. BRIEF DESCRIPTION OF DRAWINGS

[0019] The accompanying drawings are included to provide a further understanding of the application, and are incorporated in and constitute a part of this specification, illustrate embodiments of the application, and together with the description serve to explain the principles of the application.

[0020] Figure 1 The schematic diagram of the constant-pressure gas permeation device described in the application. DETAILED DESCRIPTION

[0021] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges or values should be construed to be approximations that allow for significant variation. Various ranges of values that are explicitly delineated in the specification as supplied in the art and when all combining to yield one or more new ranges of values, the ranges of values should be considered as being specifically disclosed herein.

[0022] The first aspect of the application provides a method for preparing a carbon molecular sieve membrane, the method comprising:

[0023] (1) contacting a polymer membrane with a modifier solution for modification treatment, wherein the modifier contains aldehyde groups and benzene rings;

[0024] (2) contacting the product obtained by the modification treatment with an alkali solution, and then performing a stabilization treatment;

[0025] (3) performing a carbonization treatment on the product obtained by the stabilization treatment under a pressure of 0.15-0.8 MPa, to obtain the carbon molecular sieve membrane.

[0026] The method for preparing a carbon molecular sieve membrane provided by the present application uses a modifier solution to treat a polymer membrane, and the strong hydrogen bonding between the modifier molecules makes the polymer chains in the polymer membrane more closely arranged. The modifier molecules contain an aldehyde group and a benzene ring, which reduces the formation of gas from the polar groups on the long-chain polymers in the polymer membrane during the high-temperature carbonization process, and reduces the formation of defects in the carbon molecular sieve membrane. In addition, the carbonization process in the present application is performed under a relatively high pressure, which is conducive to the conversion of more carbon-containing species into carbon molecular sieves, reduces the formation of gas, and thus greatly improves the flux and permeation selectivity of the carbon molecular sieve membrane for the gas to be separated.

[0027] In some embodiments of the present application, preferably, the modifier is selected from at least one of 2,5-dihydroxyterephthaldehyde, 4-hydroxyisophthaldehyde, 2,6-dihydroxynaphthaldehyde and 2,3-dimethoxy-1,4-naphthaldehyde, and preferably at least one of 2,5-dihydroxyterephthaldehyde, 2,6-dihydroxynaphthaldehyde and 2,3-dimethoxy-1,4-naphthaldehyde. The source of the modifier in the present application is not particularly limited, and it can be commercially available or prepared by using the prior art.

[0028] In the present application, the modifier is conducive to effective chemical reaction with the polymer membrane, forms stable covalent bonds, and enhances the tightness of the membrane layer structure through the strong hydrogen bonding between the molecules. In addition, the benzene ring structure contained in the modifier is conducive to the formation of stable carbon molecular sieves during the high-temperature carbonization process, thereby reducing defects in the membrane layer and improving the performance of the carbon molecular sieve membrane. The preferred modifier in the present application has more excellent effects.

[0029] In the present application, the mass ratio of the polymer membrane and the modifier solution has a relatively wide selection range. Preferably, the mass ratio of the polymer membrane and the modifier solution is 1:10-100, for example, it can be 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:65, 1:70, 1:80, 1:90, 1:100, and any value in the range formed by the above two values, and preferably 1:20-65.

[0030] In the present application, the mass ratio of the polymer film and the modifier solution is controlled within the above range, which is advantageous to ensure that the modifier solvent sufficiently penetrates into the polymer film, reacts with the polymer chains in the film, forms stable covalent bonds, and enhances the close arrangement of the polymer chains in the film, thereby reducing the defects of the carbon molecular sieve membrane. The preferred range of the present application is more advantageous to effectively improve the performance of the polymer film while reducing the cost.

[0031] In the present application, the content of the modifier in the modifier solution has a wide selection range. Preferably, the content of the modifier in the modifier solution is 0.5-5 mass%, for example, it can be 0.5 mass%, 1 mass%, 1.5 mass%, 2 mass%, 2.5 mass%, 3 mass%, 3.5 mass%, 4 mass%, 4.5 mass%, 5 mass%, and any value within the range consisting of the above two values, preferably 1-4 mass%.

[0032] In the present application, the content of the modifier in the modifier solution is controlled within the above range, which has a good modification effect, reduces the gas escape during the high-temperature carbonization process, inhibits the formation of defects of the carbon molecular sieve membrane, and enhances the stability of the film layer, so that it can maintain good integrity during the subsequent high-temperature carbonization process. The preferred range of the present application is more advantageous to prepare a carbon molecular sieve membrane with excellent performance and stable structure.

[0033] In the present application, the type of the solvent in the modifier solvent is not particularly limited as long as it can dissolve the modifier. Preferably, the solvent in the modifier solution is selected from at least one of water, methanol and ethanol. In the present application, the solvent can penetrate into the polymer film, so that the modifier molecules can fully contact with the polymer chains in the film.

[0034] In the present application, the type of the polymer film is not particularly limited, which can be various polymer films commonly used in the art. Preferably, the polymer film is selected from at least one of cellulose acetate film, ethyl cellulose film, oligomeric cellulose film and polyacrylonitrile film, preferably at least one of cellulose acetate film, ethyl cellulose film and oligomeric cellulose film. The source of the polymer film in the present application is not particularly limited, which can be commercially available or prepared by the prior art.

[0035] In the present application, the thickness of the polymer film has a wide selection range. Preferably, the thickness of the polymer film is 50-150 μm. In the present application, the thickness of the polymer film is measured by a thickness gauge without special instructions.

[0036] In the present application, the method of the contacting in step (1) is not particularly limited, which can be contacting the polymer film in the modifier solution or contacting the polymer film by pouring the modifier solution on the polymer film. Preferably, the contacting in step (1) is contacting the polymer film in the modifier solution.

[0037] In some embodiments of the present application, preferably, the conditions of the modification treatment include: temperature of 40-100℃, preferably 60-90℃; time of 5-24h, preferably 6-12h.

[0038] In the present application, controlling the conditions of the modification treatment in the above range is advantageous to ensure the modifier to enter the polymer chains and contact the polymer sufficiently, to obtain a better modification effect and to ensure the smooth progress of the subsequent steps. The preferred range of the present application has a more excellent modification effect.

[0039] In some embodiments of the present application, preferably, the method of step (1) further comprises drying the product obtained by the modification treatment. In the present application, the solvent in the modification solution is removed by the drying treatment, which avoids the solvent affecting the performance of the film in the subsequent steps and fixes the position of the modifier on the film surface, thereby enhancing the modification effect.

[0040] In the present application, the conditions of the drying are not particularly limited. Preferably, the conditions of the drying include: temperature of 30-80℃, preferably 40-60℃; time of 2-12h, preferably 5-10h. In the present application, controlling the conditions of the drying in the above range is advantageous to remove the solvent in the modification solution effectively and to enhance the modification effect.

[0041] In the present application, preferably, the product obtained by the modification treatment is contacted with an alkali solution. In the present application, the aldehyde group of the modifier reacts with the hydroxyl group of the polymer to form a chemical bond by the contacting with the alkali solution, which makes the polymer chains closely connected and enhances the carbonization effect.

[0042] In the present application, the content of the alkali in the alkali solution has a wide selection range. Preferably, the concentration of OH - in the alkali solution is 0.1-1.5mol / L, for example, it can be 0.1mol / L, 0.2mol / L, 0.4mol / L, 0.6mol / L, 0.8mol / L, 1mol / L, 1.2mol / L, 1.4mol / L, 1.5mol / L, and any value in the range consisting of two of the above values, preferably 0.2-1mol / L.

[0043] In the present application, the product obtained by the modification treatment is contacted with the alkali solution. In the present application, the aldehyde group of the modifier reacts with the hydroxyl group of the polymer to form a chemical bond by the contacting with the alkali solution, which makes the polymer chains closely connected and enhances the carbonization effect. -The concentration of the product obtained by the contacting with the alkali solution is controlled within the above range, which ensures a moderate reaction rate, forms stable chemical bonds and structures, and is beneficial to improve the permeation flux and permeation selectivity of the carbon molecular sieve membrane to the gas to be separated.

[0044] In the present application, the conditions for the contacting with the alkali solution are not particularly limited. Preferably, the conditions for the contacting with the alkali solution include a temperature of 40-90°C, preferably 50-80°C, and a time of 1-10h, preferably 2-6h. In the present application, the conditions for the contacting with the alkali solution are controlled within the above range, which is beneficial to make the reaction proceed sufficiently, adjust the structure and properties of the membrane, and facilitate the subsequent stabilization treatment and carbonization treatment.

[0045] In some embodiments of the present application, preferably, the method further comprises drying the product obtained by the contacting with the alkali solution. In the present application, the residual moisture is removed by the drying treatment.

[0046] In the present application, the conditions for the drying are not particularly limited. Preferably, the conditions for the drying include a temperature of 30-80°C, preferably 40-60°C, and a time of 10-50h, preferably 20-40h. In the present application, the conditions for the drying are controlled within the above range, which is beneficial to ensure that the moisture in the membrane layer is sufficiently removed while maintaining the integrity and stability of the membrane layer.

[0047] In the present application, preferably, the product obtained by the contacting with the alkali solution is subjected to a stabilization treatment. In the present application, by the modification treatment and the stabilization treatment, a small amount of gas is preferentially released, which avoids the problem that a large amount of gas generated by the decomposition of the polymer is simultaneously released in the subsequent carbonization process, thereby effectively inhibiting the formation of defects in the carbon molecular sieve membrane.

[0048] In some embodiments of the present application, the conditions for the stabilization treatment include a temperature of 120-250°C, for example, 120°C, 140°C, 150°C, 160°C, 180°C, 200°C, 220°C, 240°C, 250°C, and any value within the range consisting of any two of the above values, preferably 150-220°C, and a time of 0.5-5h, for example, 0.5h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, and any value within the range consisting of any two of the above values, preferably 1-3h, under an air atmosphere.

[0049] In the present application, the conditions for the stabilization treatment are controlled within the above range, which is beneficial to sufficiently volatilize the volatile substances in the membrane while avoiding the destruction of the structure of the membrane and the resulting decline in the performance of the membrane. The preferred conditions of the present application have more excellent stabilization treatment effects.

[0050] In the present application, preferably, the product obtained by the stabilizing treatment is subjected to a carbonization treatment under a higher pressure. In the present application, by the aforementioned stabilizing treatment, a small amount of gas is allowed to escape while keeping the membrane layer intact, and then a high-temperature carbonization treatment is performed under a higher pressure, which is advantageous for converting a larger amount of carbon-containing species into carbon molecular sieve, reducing the escape of gas, and further inhibiting the formation of defects in the carbon molecular sieve membrane, keeping the membrane layer intact, thereby significantly improving the flux and permeation selectivity of the carbon molecular sieve membrane to the gas to be separated.

[0051] In some embodiments of the present application, preferably, the pressure of the carbonization treatment is 0.15-0.8 MPa, for example, can be 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa, 0.5 MPa, 0.55 MPa, 0.6 MPa, 0.65 MPa, 0.7 MPa, 0.75 MPa, 0.8 MPa, and any value in the range consisting of two of the aforementioned values, preferably 0.2-0.6 MPa.

[0052] In the present application, controlling the pressure of the carbonization treatment in the aforementioned range is advantageous for converting a larger amount of carbon-containing species into carbon molecular sieve and further reducing the defects in the carbon molecular sieve membrane layer caused by the formation of gas. The preferred pressure range has a more excellent effect.

[0053] In the present application, the conditions of the carbonization treatment are not particularly limited and can be the conditions of carbonization of a polymer membrane commonly used in the art, as long as the carbonization treatment is performed under the pressure described in the present application. Preferably, the conditions of the carbonization treatment further include: under an inert atmosphere, the temperature is 450-800°C, preferably 500-700°C; the time is 1-8 h, preferably 2-6 h; and the temperature rising rate is 0.5-5°C / min, preferably 0.8-3°C / min.

[0054] In the present application, controlling the conditions of the carbonization treatment in the aforementioned range ensures that the polymer membrane can be sufficiently carbonized to form a stable carbon molecular sieve structure and is advantageous for controlling the gas escape process and avoiding defects in the membrane layer caused by a large amount of gas escaping in a short time, thereby significantly improving the flux and permeation selectivity of the carbon molecular sieve membrane to the gas to be separated.

[0055] In the present application, the type of the inert gas is not particularly limited and various inert gases commonly used in the art can be used in the present application. Preferably, the inert atmosphere is selected from at least one of nitrogen, argon, and helium.

[0056] In a preferred embodiment of the present application, the method for preparing a carbon molecular sieve membrane comprises:

[0057] (1) modifying the polymer film by contacting it with a modifier solution, wherein the modifier contains an aldehyde group and a benzene ring;

[0058] (2) drying the product obtained in the modifying step and contacting it with an alkali solution;

[0059] (3) drying the product obtained in the contacting step with the alkali solution and stabilizing it at a temperature of 120-250℃ for 0.5-5h;

[0060] (4) carbonizing the product obtained in the stabilizing step at a pressure of 0.15-0.8MPa and a temperature of 450-800℃ to obtain the carbon molecular sieve membrane;

[0061] In the present application, the modifier is at least one selected from 2,5-dihydroxyterephthaldehyde, 4-hydroxyisophthaldehyde, 2,6-dihydroxynaphthaldehyde and 2,3-dimethoxy-1,4-naphthaldehyde.

[0062] The present application provides a carbon molecular sieve membrane prepared by the method of the first aspect.

[0063] In the present application, the carbon molecular sieve membrane prepared by the method has high gas permeability and selectivity, and the membrane layer is complete and the thickness is adjustable, thus having wide application prospect and market value.

[0064] In the present application, the thickness of the carbon molecular sieve membrane is not particularly limited and can be selected by those skilled in the art according to actual needs. Preferably, the thickness of the carbon molecular sieve membrane is 10-60μm, more preferably 20-50μm. In the present application, the thickness of the carbon molecular sieve membrane is measured by a thickness gauge unless otherwise specified.

[0065] The present application provides a carbon molecular sieve membrane prepared by the method of the first aspect or the carbon molecular sieve membrane of the second aspect for use in gas separation, preferably in the separation of a mixture of olefins and alkanes.

[0066] In the present application, the carbon molecular sieve membrane is particularly suitable for use in the separation of a mixture of olefins and alkanes, more preferably in the separation of a mixture of propylene and propane, and has high propylene permeation flux, propane permeation flux and propylene / propane permeation selectivity.

[0067] The present application will be described in detail by way of examples.

[0068] In the following examples, the raw materials used are all commercially available unless otherwise specified.

[0069] In the present application, room temperature refers to 25±5℃ unless otherwise specified.

[0070] 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.

[0071] A schematic diagram of the constant pressure gas permeation device of the present invention is shown below. Figure 1 The 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 ).

[0072]

[0073] In the formula, 3 represents the transmembrane pressure difference, in bar; 75 represents that 1 bar equals 75 cmHg.

[0074] 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.

[0075] In this invention, propylene / propane permeation selectivity = propylene permeability / propane permeability.

[0076] In this invention, the method for determining the thickness of the carbon molecular sieve membrane 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 membrane, and then the average thickness of the membrane at the five locations is calculated.

[0077] Example 1

[0078] (1) 0.82 g of cellulose acetate membrane was placed in 30 g of methanol solution of 2,5-dihydroxyterephthalaldehyde (2,5-dihydroxyterephthalaldehyde mass fraction was 1% by mass) and modified at 60 °C for 12 h, and then dried at 40 °C for 10 h.

[0079] (2) The product obtained from the modification treatment in step (1) is placed in an OH solution. - The sample was treated in a 0.3 mol / L sodium hydroxide aqueous solution at 50°C for 6 hours, and then dried at 40°C for 36 hours.

[0080] (3) Place the product obtained in step (2) in air and stabilize it at 180°C for 3 hours;

[0081] (4) The product obtained in step (3) is subjected to carbonization treatment under a nitrogen atmosphere, wherein the carbonization treatment pressure is 0.3 MPa, the temperature increasing rate is 1°C / min, the temperature is increased to 550°C for carbonization treatment for 4 h, and then decreased to room temperature (25°C) under a nitrogen atmosphere to obtain a carbon molecular sieve membrane.

[0082] The membrane thickness, propylene permeation flux, propane permeation flux, and propylene / propane permeation selectivity of the carbon molecular sieve membrane obtained in this example are shown in Table 1.

[0083] Example 2

[0084] (1) 0.82 g of a cellulose acetate membrane is placed in 50 g of a methanol solution of 2,6-dihydroxynaphthalene dialdehyde (mass fraction of 2,6-dihydroxynaphthalene dialdehyde is 3 mass %) for modification treatment at 80°C for 8 h, and then dried at 40°C for 10 h;

[0085] (2) The product obtained by modification treatment in step (1) is placed in an aqueous sodium hydroxide solution with a concentration of 0.3 mol / L of NaOH at 80°C for 2 h, and then dried at 40°C for 36 h; -

[0086] (3) The product obtained in step (2) is subjected to stabilization treatment in air at 220°C for 2 h;

[0087] (4) The product obtained in step (3) is subjected to carbonization treatment under a nitrogen atmosphere, wherein the carbonization treatment pressure is 0.5 MPa, the temperature increasing rate is 1°C / min, the temperature is increased to 600°C for carbonization treatment for 2 h, and then decreased to room temperature (25°C) under a nitrogen atmosphere to obtain a carbon molecular sieve membrane.

[0088] The membrane thickness, propylene permeation flux, propane permeation flux, and propylene / propane permeation selectivity of the carbon molecular sieve membrane obtained in this example are shown in Table 1.

[0089] Example 3

[0090] According to the method described in Example 1, except that in step (1), the mass fraction of 2,5-dihydroxyterephthalaldehyde is 4 mass %; a carbon molecular sieve membrane is obtained.

[0091] The membrane thickness, propylene, propane permeation flux, and propylene / propane permeation selectivity of the carbon molecular sieve membrane obtained in this example are shown in Table 1.

[0092] Example 4

[0093] According to the method described in Example 1, except that in step (1), 2,5-dihydroxyterephthalaldehyde is replaced by an equal amount of 2,3-dimethoxy-1,4-naphthalene dialdehyde; a carbon molecular sieve membrane is obtained.

[0094] ​The membrane thickness, propylene permeation flux, propane permeation flux and propylene / propane permeation selectivity of the carbon molecular sieve membrane prepared in this example are shown in Table 1.

[0095] Example 5

[0096] The method described in Example 1 was followed, except that in step (3), the product obtained in step (2) was placed in air and subjected to a stabilization treatment at 240°C for 3h; a carbon molecular sieve membrane was obtained.

[0097] The membrane thickness, propylene permeation flux, propane permeation flux and propylene / propane permeation selectivity of the carbon molecular sieve membrane prepared in this example are shown in Table 1.

[0098] Example 6

[0099] The method described in Example 1 was followed, except that in step (4), the product obtained in step (3) was subjected to a carbonization treatment in an argon atmosphere, wherein the carbonization treatment pressure was 0.5MPa, the heating rate was 2°C / min, the temperature was raised to 650°C and the carbonization treatment was carried out for 6h, and then the temperature was lowered to room temperature (25°C) in an argon atmosphere; a carbon molecular sieve membrane was obtained.

[0100] The membrane thickness, propylene permeation flux, propane permeation flux and propylene / propane permeation selectivity of the carbon molecular sieve membrane prepared in this example are shown in Table 1.

[0101] Example 7

[0102] The method described in Example 1 was followed, except that in step (2), the product obtained by the modification treatment in step (1) was placed in an aqueous sodium hydroxide solution with an OH - concentration of 1mol / L, and was treated at 80°C for 2h, and then was dried at 60°C for 20h; a carbon molecular sieve membrane was obtained.

[0103] The membrane thickness, propylene permeation flux, propane permeation flux and propylene / propane permeation selectivity of the carbon molecular sieve membrane prepared in this example are shown in Table 1.

[0104] Example 8

[0105] The method described in Example 1 was followed, except that in step (1), 2,5-dihydroxyterephthaldehyde was replaced by 4-hydroxyisophthaldehyde; a carbon molecular sieve membrane was obtained.

[0106] The membrane thickness, propylene permeation flux, propane permeation flux and propylene / propane permeation selectivity of the carbon molecular sieve membrane prepared in this example are shown in Table 1.

[0107] Example 9

[0108] The method described in Example 1 was followed, except that in step (4), the carbonization treatment pressure was increased to 0.15 MPa; a carbon molecular sieve membrane was obtained.

[0109] The membrane thickness, propylene permeation flux, propane permeation flux, and propylene / propane permeation selectivity of the carbon molecular sieve membrane obtained in this example are shown in Table 1.

[0110] Example 10

[0111] The method described in Example 1 was followed, except that in step (1), the mass fraction of 2,5-dihydroxyterephthaldehyde was 0.5 mass%; a carbon molecular sieve membrane was obtained.

[0112] The membrane thickness, propylene, propane permeation flux, and propylene / propane permeation selectivity of the carbon molecular sieve membrane obtained in this example are shown in Table 1.

[0113] Example 11

[0114] The method described in Example 1 was followed, except that in step (1), the modification treatment temperature was 50°C, and the modification treatment time was 20 h; a carbon molecular sieve membrane was obtained.

[0115] The membrane thickness, propylene, propane permeation flux, and propylene / propane permeation selectivity of the carbon molecular sieve membrane obtained in this example are shown in Table 1.

[0116] Comparative Example 1

[0117] The method described in Example 1 was followed, except that in step (1), 2,5-dihydroxyterephthaldehyde was replaced by an equivalent amount of adipaldehyde; a carbon molecular sieve membrane was obtained.

[0118] The carbon molecular sieve membrane obtained in this comparative example was easily broken and could not be evaluated.

[0119] Comparative Example 2

[0120] The method described in Example 1 was followed, except that step (1) was not performed; a carbon molecular sieve membrane was obtained.

[0121] The carbon molecular sieve membrane obtained in this comparative example was broken and could not be evaluated.

[0122] Comparative Example 3

[0123] The method described in Example 1 was followed, except that in step (4), the carbonization treatment pressure was atmospheric pressure (0.1 MPa); a carbon molecular sieve membrane was obtained.

[0124] The membrane thickness, propylene permeation flux, propane permeation flux, and propylene / propane permeation selectivity of the carbon molecular sieve membrane obtained in this comparative example are shown in Table 1.

[0125] Table 1

[0126]

[0127] As can be seen from the results of Table 1, the method for preparing carbon molecular sieve membrane provided by the present application inhibits the formation of defects of carbon molecular sieve membrane, maintains the integrity of the membrane layer, and significantly improves the flux and permeation selectivity of carbon molecular sieve membrane for propane and propylene mixed gas.

[0128] As can be seen from Table 1, Example 1 and Comparative Examples, compared with Example 1, the type of modifier added in Comparative Example 1 is not within the range defined by the present application, and the obtained carbon molecular sieve membrane has poor strength, and the permeation flux of propylene and propane cannot be measured; in Comparative Example 2, the cellulose acetate membrane is not subjected to modification treatment, and only subjected to low-temperature stabilization and high-temperature carbonization treatment, and thus an intact carbon molecular sieve membrane cannot be obtained, and thus the permeation flux of propylene and propane cannot be measured; in Comparative Example 3, carbonization treatment is performed at normal pressure, and the obtained carbon molecular sieve membrane has low thickness, and the propylene / propane permeation selectivity is low, indicating that the obtained carbon molecular sieve membrane has more defects.

[0129] The above describes the preferred embodiments of the present application, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as the disclosed content of the present application, and all fall within the protection scope of the present application.

Claims

1. A method for preparing carbon molecular sieve membranes, characterized in that, The method includes: (1) The polymer film is modified by contacting a modifying agent solution, wherein the modifying agent contains aldehyde group and benzene ring; (2) The product obtained by the modification treatment is contacted with an alkaline solution and then stabilized. (3) The product obtained by the stabilization treatment is carbonized under a pressure of 0.15-0.8 MPa to obtain the carbon molecular sieve membrane.

2. The method according to claim 1, wherein, The modifier is selected from at least one of 2,5-dihydroxyterephthalaldehyde, 4-hydroxyisophthalaldehyde, 2,6-dihydroxynaphthalenedialdehyde, and 2,3-dimethoxy-1,4-naphthalenedialdehyde; preferably selected from at least one of 2,5-dihydroxyterephthalaldehyde, 2,6-dihydroxynaphthalenedialdehyde, and 2,3-dimethoxy-1,4-naphthalenedialdehyde.

3. The method according to claim 1 or 2, wherein, The mass ratio of the polymer film to the modifier solution is 1:10-100, preferably 1:20-65; Preferably, the content of the modifier in the modifier solution is 0.5-5% by mass, and more preferably 1-4% by mass; Preferably, the solvent in the modifier solution is selected from at least one of water, methanol, and ethanol.

4. The method according to any one of claims 1-3, wherein, The polymer membrane is selected from at least one of cellulose acetate membrane, ethyl cellulose membrane, oligocellulose membrane and polyacrylonitrile membrane; Preferably, the thickness of the polymer film is 50-150 μm.

5. The method according to any one of claims 1-4, wherein, The conditions for the modification treatment include: a temperature of 40-100℃, preferably 60-90℃; and a time of 5-24h, preferably 6-12h. Preferably, the method in step (1) further includes drying the product obtained by the modification treatment; Preferably, the drying conditions include: a temperature of 30-80℃, more preferably 40-60℃; and a time of 2-12 hours, more preferably 5-10 hours.

6. The method according to any one of claims 1-5, wherein, OH in the alkaline solution - The concentration is 0.1-1.5 mol / L, preferably 0.2-1 mol / L; Preferably, the conditions for contact with the alkaline solution include: a temperature of 40-90℃, preferably 50-80℃; and a time of 1-10 hours, preferably 2-6 hours. Preferably, the method further includes drying the product obtained by contacting the alkaline solution; Preferably, the drying conditions include: a temperature of 30-80℃, more preferably 40-60℃; and a time of 10-50h, more preferably 20-40h.

7. The method according to any one of claims 1-6, wherein, The stabilization treatment conditions include: in an air atmosphere, a temperature of 120-250℃, preferably 150-220℃; and a time of 0.5-5h, preferably 1-3h.

8. The method according to any one of claims 1-7, wherein, The carbonization process is carried out at a pressure of 0.2-0.6 MPa. Preferably, the carbonization treatment conditions further include: under an inert atmosphere, a temperature of 450-800℃, preferably 500-700℃; a time of 1-8h, preferably 2-6h; and a heating rate of 0.5-5℃ / min, preferably 0.8-3℃ / min. Preferably, the inert atmosphere is selected from at least one of nitrogen, argon and helium.

9. The carbon molecular sieve membrane prepared by the method according to any one of claims 1-8; Preferably, the thickness of the carbon molecular sieve membrane is 10-60 μm, and more preferably 20-50 μm.

10. The application of the carbon molecular sieve membrane prepared by the method of any one of claims 1-8 or the carbon molecular sieve membrane of claim 9 in gas separation, preferably in the separation of mixed gases of olefins and alkanes.

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