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

Abstract

The invention relates to a preparation method of a carbon molecular sieve membrane, which comprises the following steps: (1) a polymer membrane is placed in a modification solution for modification treatment and then dried, and the modifier solution contains a modifier; (2) placing the product obtained in the step (1) in air for stabilizing treatment; and (3) carrying out carbonization treatment on the product obtained in the step (2) in an inert gas atmosphere, wherein the carbonization treatment pressure is 0.15-0.8 MPa. The method provided by the invention can reduce the escape of gas during carbonization treatment, inhibit the formation of defects of the carbon molecular sieve membrane, and well maintain the completeness of the carbon molecular sieve membrane layer, thereby significantly improving the permeation selectivity of the carbon molecular sieve membrane to propane / propylene.

Description

Technical Field

[0001] The invention relates to a carbon molecular sieve membrane and a preparation method and application thereof, in particular to a carbon molecular sieve membrane for separating olefins and alkanes and a preparation method and application thereof. Background Art

[0002] Carbon molecular sieve membranes have high thermal stability, chemical stability and permeation selectivity, and have received widespread attention in the field of gas separation.

[0003] CN101277754A discloses a process for preparing a carbon molecular sieve membrane, wherein a mixture of cellulose and hemicellulose is treated with trifluoroacetic acid, and then a metal salt is added to form a film by casting, and then the film is dried and carbonized at 500-600°C. The prepared carbon molecular sieve membrane is heated to CO 2 / CH 4 The separation system exhibits good separation performance and can be regenerated by applying electric current.

[0004] CN106823821A discloses a method for repairing defects of a carbon molecular sieve membrane, using silicone rubber as a raw material, mixing with a catalyst, a cross-linking agent and an organic solvent to react and prepare a sol, and then coating the sol on the surface of the carbon molecular sieve membrane to form a film, and drying, wherein the catalyst is preferably organic tin, the cross-linking agent is preferably ethyl orthosilicate, and the organic solvent is preferably isooctane. The method utilizes the good permeability of silicone rubber, which can penetrate into the interior of the carbon molecular sieve membrane, and the silicone rubber prepared by cross-linking silicone rubber is formed 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 method for preparing a carbon molecular sieve membrane, which comprises 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 regulated atmosphere composed of target permeating gas molecules, thereby achieving a carbon molecular sieve membrane with an improved combination of selectivity and permeability.

[0006] CN109070009A discloses an improved method for manufacturing a carbon molecular sieve membrane, wherein a polyimide precursor polymer is pyrolyzed to form a carbon molecular sieve membrane by: heating the polyimide precursor polymer in a furnace to a final pyrolysis temperature of 600°C to 700°C, heating from 400°C to the final pyrolysis temperature at a pyrolysis heating rate of 3 to 7°C / min, and maintaining the final pyrolysis temperature for a pyrolysis time of up to 60 minutes in a non-oxidizing atmosphere. This method can achieve a CMS with an improved combination of selectivity and permeability.

[0007] During the high-temperature carbonization of organic polymers to form carbon molecular sieve membranes, defects in the carbon molecular sieve membranes will occur due to gas escape, thereby affecting the permeability / selectivity of the carbon molecular sieve membranes. The existing technology reduces the defects of the carbon molecular sieve membranes by repairing or selecting special polymer precursor materials, but it is still difficult to effectively inhibit the formation of defects during high-temperature pyrolysis. Summary of the invention

[0008] One of the purposes of the present invention is to provide a method for preparing a carbon molecular sieve membrane, which can be used for propylene / propane separation and has high permeation selectivity.

[0009] The method for preparing the carbon molecular sieve membrane provided by the present invention comprises the following steps:

[0010] (1) placing the polymer film in a modification solution for modification treatment, and then drying, wherein the modification solution contains a modification agent;

[0011] (2) placing the product obtained in step (1) in air for stabilization treatment;

[0012] (3) The product obtained in step (2) is carbonized in an inert gas atmosphere, wherein the carbonization pressure is 0.15 to 0.8 MPa.

[0013] The second object of the present invention is to provide a carbon molecular sieve membrane prepared by the method of the present invention.

[0014] The third object of the present invention is to provide a method for separating a mixed gas of propylene and propane using the carbon molecular sieve membrane of the present invention or the carbon molecular sieve membrane prepared by the method of the present invention.

[0015] The present invention uses a solution containing a modifier to treat a polymer membrane, allowing the modifier molecules to enter the membrane layer, first performing a stabilization treatment at a relatively low temperature, allowing a small amount of gas to escape while maintaining the integrity of the membrane layer, and then performing a carbonization treatment at a relatively high temperature and a relatively high pressure, which can reduce gas escape and is beneficial for inhibiting the formation of carbon molecular sieve membrane defects and maintaining the integrity of the membrane layer, thereby significantly improving the carbon molecular sieve membrane's propane / propylene permeability selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of the permeability evaluation device. DETAILED DESCRIPTION

[0017] The present invention uses a solution containing a modifier to treat a polymer membrane, and the modifier molecules diffuse into the polymer membrane layer. The modifier molecules contain polar groups, which can form hydrogen bonds or covalent bonds with polar groups on long-chain polymers of the polymer membrane, thereby reducing the gas escape formed by polar groups on long-chain polymers of the polymer membrane during high-temperature carbonization, and reducing the formation of carbon molecular sieve membrane defects; in addition, the modifier molecules contain benzene rings, which are easily converted into carbon molecular sieves during high-temperature carbonization, and can further reduce the defects of the carbon molecular sieve membrane. After the polymer membrane is modified and stabilized at a relatively low temperature, a small amount of gas is preferentially escaped, which further avoids the problem of a large amount of gas generated by polymer decomposition escaping at the same time during high-temperature carbonization, thereby effectively inhibiting the formation of carbon molecular sieve membrane defects. In addition, the high-temperature carbonization process of the present invention is carried out under a relatively high pressure, which is conducive to converting more carbon-containing species into carbon molecular sieves, and further reducing the formation of gas. The carbon molecular sieve membrane prepared by the method of the present invention exhibits a relatively high propylene / propane separation performance.

[0018] The method for preparing the carbon molecular sieve membrane provided by the present invention comprises the following steps:

[0019] (1) placing the polymer film in a modifying agent solution for modification treatment, and then drying, wherein the modifying agent solution contains a modifying agent;

[0020] (2) placing the product obtained in step (1) in air for stabilization treatment;

[0021] (3) The product obtained in step (2) is carbonized in an inert gas atmosphere, wherein the carbonization pressure is 0.15 to 0.8 MPa.

[0022] In the method provided by the present invention, the mass ratio of the polymer film to the modifier solution in step (1) is 1:10-100, preferably 1:20-60; the polymer film is one of polyvinylidene fluoride film, cellulose acetate film, ethyl cellulose film, and polyacrylonitrile film, preferably polyvinylidene fluoride film; the modifier is an amino acid, preferably an amino acid containing a benzene ring, more preferably at least one of phenylalanine, tyrosine, and tryptophan; the solvent of the modifier solution is at least one of water, methanol, or ethanol; the OH in the modifier solution ... OH in the modifier solution is 1:10-100, preferably 1:20-60; the OH in the modifier solution is 1:10-100, preferably 1:20-60; the OH in the modifier solution is 1:10-100, preferably 1:20-60; the OH in the modifier solution is 1:10-100, preferably 1:20-60 - , the concentration is 0.1-1.5 mol / L; the mass fraction of the modifier in the modifier solution is 2-15% by mass, preferably 5-15% by mass. The treatment temperature of the modifier solution is 40-90°C, preferably 50-80°C, the treatment time is 6-24 hours, preferably 8-16 hours, and the drying temperature is 40-100°C, preferably 50-80°C.

[0023] In the method provided by the present invention, the stabilization treatment temperature in step (2) is 200-260° C., preferably 210-250° C., and the time is 0.5-5 hours, preferably 1-3 hours.

[0024] In the method provided by the present invention, the inert gas in step (3) is preferably at least one of nitrogen, argon and helium. The carbonization treatment pressure is preferably 0.2-0.6 MPa, the heating rate is 0.5-5°C / min, preferably 0.8-3°C / min, the carbonization treatment temperature is 450-700°C, preferably 480-650°C, preferably 480-650°C, and the time is 1-8 hours, preferably 2-6 hours.

[0025] The carbon molecular sieve membrane prepared by the method of the invention has a thickness of 20 to 40 microns.

[0026] The carbon molecular sieve membrane prepared by the method of the present invention is suitable for gas separation, such as propylene / propane. The permeability of a single component gas is measured using a constant pressure gas permeation device, with an operating pressure of 0.3 MPa and an operating temperature of 30°C. Figure 1 As shown in the figure, the device consists of a membrane pool, a pressure gauge A, a flow meter, etc. The gas to be tested is allowed to enter the membrane pool, and the pressure on the gas inlet side of the membrane pool is adjusted to 0.3 MPa. After 2 hours, the time t seconds required for the gas on the permeate side to flow out 0.5 mL is recorded. The effective membrane area is 8.04 cm 2 , the film thickness is 1 cm. The gas permeability P is calculated as follows, in barrer.

[0027]

[0028] In the formula, 3 represents the transmembrane pressure difference, the unit is bar, and 75 means that 1 bar is equal to 75 cmHg.

[0029] When the gas to be measured is propylene, P is the permeability of propylene; when the gas to be measured is propane, P is the permeability of propane.

[0030] The propylene / propane permeability selectivity is the ratio of the permeabilities of the two. The higher the permeability selectivity, the better the separation effect.

[0031] The method for measuring the thickness of the carbon molecular sieve membrane in the present invention is: using a thickness gauge to measure the thickness at the four right-angle vertices and the center of a square, and taking the average value of the membrane thickness at these five positions.

[0032] The present invention is further described below by way of examples, but the present invention is not limited thereto.

[0033] Example 1

[0034] (1) 0.66 g of polyvinylidene fluoride membrane was placed in 30 g of a modifier solution and treated at 50° C. for 12 hours, and then dried at 60° C. for 8 hours. The mass fraction of phenylalanine in the modifier solution was 6 mass %, the concentration of sodium hydroxide was 0.5 mol / L, and the solvent was a mixture of water and methanol, wherein the mass ratio of water to methanol was 1:1.

[0035] (2) The product obtained in step (1) was placed in air and stabilized at 220°C for 1.5 hours.

[0036] (3) The product obtained in step (2) is carbonized in a nitrogen atmosphere at a pressure of 0.3 MPa and a heating rate of 1°C / min. The temperature is raised to 500°C for carbonization for 4 hours and then cooled to room temperature in a nitrogen atmosphere to obtain a carbon molecular sieve membrane A.

[0037] The membrane thickness, propylene and propane permeation fluxes and propylene / propane permeation selectivity of carbon molecular sieve membrane A are shown in Table 1.

[0038] Example 2

[0039] A carbon molecular sieve membrane B was prepared according to the method of Example 1, except that the mass fraction of phenylalanine in the modifier solution in step (1) was 12 mass %.

[0040] The membrane thickness, propylene and propane permeation fluxes and propylene / propane permeation selectivity of carbon molecular sieve membrane B are shown in Table 1.

[0041] Example 3

[0042] A carbon molecular sieve membrane C was prepared according to the method of Example 1, except that the modifier in step (1) was tyrosine.

[0043] The membrane thickness, propylene and propane permeation fluxes and propylene / propane permeation selectivity of the carbon molecular sieve membrane C are shown in Table 1.

[0044] Example 4

[0045] A carbon molecular sieve membrane D was prepared according to the method of Example 1, except that in step (2), the product obtained in step (1) was stabilized at 240°C for 3 hours.

[0046] The membrane thickness, propylene and propane permeation fluxes and propylene / propane permeation selectivity of carbon molecular sieve membrane D are shown in Table 1.

[0047] Example 5

[0048] A carbon molecular sieve membrane E was prepared according to the method of Example 1, except that in step (3), the product obtained in step (2) was carbonized in an argon atmosphere at a carbonization pressure of 0.5 MPa. The temperature was increased to 550°C at a heating rate of 2°C / min for 6 hours and then cooled to room temperature in an argon atmosphere.

[0049] The membrane thickness, propylene and propane permeation fluxes and propylene / propane permeation selectivity of the carbon molecular sieve membrane E are shown in Table 1.

[0050] Example 6

[0051] The carbon molecular sieve membrane F was prepared according to the method of Example 1, except that the modifier solution in step (1) was water and the concentration of sodium hydroxide was 1.2 mol / L.

[0052] The membrane thickness, propylene and propane permeation fluxes and propylene / propane permeation selectivity of the carbon molecular sieve membrane F are shown in Table 1.

[0053] Comparative Example 1

[0054] The membrane thickness, propylene and propane permeation fluxes and propylene / propane permeation selectivity of the polyvinylidene fluoride membrane G are shown in Table 1.

[0055] Comparative Example 2

[0056] The carbon molecular sieve membrane H was prepared according to the method of Example 1, except that the polyvinylidene fluoride membrane was not treated in step (1). A complete carbon molecular sieve membrane could not be obtained.

[0057] Comparative Example 3

[0058] A carbon molecular sieve membrane I was prepared according to the method of Example 1, except that the modifier in step (1) was p-xylenediamine.

[0059] The membrane thickness, propylene and propane permeation fluxes and propylene / propane permeation selectivity of the carbon molecular sieve membrane I are shown in Table 1.

[0060] Comparative Example 4

[0061] A carbon molecular sieve membrane J was prepared according to the method of Example 1, except that the carbonization treatment in step (3) was carried out under normal pressure.

[0062] The membrane thickness, propylene and propane permeation fluxes and propylene / propane permeation selectivity of carbon molecular sieve membrane J are shown in Table 1.

[0063] Table 1

[0064]

[0065] As can be seen from Table 1, the polyvinylidene fluoride membrane described in Comparative Example 1 has low permeation fluxes for propylene and propane, has no permeation selectivity, and cannot achieve propylene / propane separation; the polyvinylidene fluoride membrane in Comparative Example 2 is not modified, and only undergoes low-temperature stabilization and high-temperature carbonization treatment, and a complete carbon molecular sieve membrane cannot be obtained, so the permeation fluxes of propylene and propane cannot be measured; the modifier used in Comparative Example 3 is p-xylene diamine, and the propylene / propane permeation selectivity of the obtained carbon molecular sieve membrane I is lower than that of Examples 1 to 6 of the present invention, indicating that there are more defects in the carbon molecular sieve membrane I; Comparative Example 4 is carbonized at normal pressure, and the obtained carbon molecular sieve membrane J has a low thickness, and its propylene / propane permeation selectivity is lower than that of Examples 1 to 6 of the present invention, indicating that there are more defects in the carbon molecular sieve membrane J.

Claims

1. A method for preparing a carbon molecular sieve membrane, comprising the following steps: (1) placing the polymer film in a modification solution for modification treatment, and then drying, wherein the modification solution contains a modification agent; (2) placing the product obtained in step (1) in air for stabilization treatment; (3) The product obtained in step (2) is carbonized in an inert gas atmosphere, wherein the carbonization pressure is 0.15 to 0.8 MPa.

2. The method according to claim 1, characterized in that In step (1), the mass ratio of the polymer film to the modifier solution is 1:10-100, preferably 1:20-60.

3. The method according to claim 1, characterized in that (1) The polymer membrane is one of polyvinylidene fluoride membrane, cellulose acetate membrane, ethyl cellulose membrane and polyacrylonitrile membrane.

4. The method according to claim 1, characterized in that The modifying agent in step (1) is an amino acid.

5. The method according to claim 1, characterized in that The mass fraction of the modifier in the modifier solution in step (1) is 2 to 15 mass %.

6. The method according to claim 4, characterized in that (1) The amino acid is at least one of phenylalanine, tyrosine and tryptophan.

7. The method according to claim 1, characterized in that The solvent in the modifier solution in step (1) is at least one of water, methanol or ethanol.

8. The method according to claim 1, characterized in that (1) The modifier solution contains OH - , concentration is 0.1~1.5mol / L.

9. The method according to claim 1, characterized in that The modification treatment temperature in step (1) is 40 to 90°C, preferably 50 to 80°C.

10. The method according to claim 1, characterized in that The modification treatment time in step (1) is 6 to 24 hours, preferably 8 to 16 hours.

11. The method according to claim 1, characterized in that The drying temperature in step (1) is 40 to 100°C, preferably 50 to 80°C.

12. The method according to claim 1, characterized in that The drying time in step (1) is 2 to 12 hours, preferably 5 to 10 hours.

13. The method according to claim 1, characterized in that (3) The inert gas is at least one of nitrogen, argon and helium.

14. The method according to claim 1, characterized in that The stabilization treatment temperature in step (2) is 200-260°C, preferably 210-250°C.

15. The method according to claim 1, characterized in that The stabilization treatment time in step (2) is 0.5 to 5 hours, preferably 1 to 3 hours.

16. The method according to claim 1, characterized in that The pressure in step (3) is 0.2-0.6 MPa.

17. The method according to claim 1, characterized in that The heating rate in step (3) is 0.5 to 5°C / min, preferably 0.8 to 3°C / min.

18. The method according to claim 1, characterized in that The carbonization treatment temperature in step (3) is 450-700°C, preferably 480-650°C.

19. The method according to claim 1, characterized in that The carbonization treatment time in step (3) is 1 to 8 hours, preferably 2 to 6 hours.

20. The method according to claim 1, characterized in that The thickness of the carbon molecular sieve membrane is 20 to 40 microns.

21. A carbon molecular sieve membrane prepared by the method according to any one of claims 1 to 20.

22. A method for separating a mixed gas of propylene and propane using the carbon molecular sieve membrane according to claim 21.

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