A carbon molecular sieve membrane, its preparation method and application

Abstract

A method for preparing a carbon molecular sieve membrane includes the following steps: (1) modifying a polymer membrane in a modification solution and then drying it, wherein the modification solution contains a modification agent; (2) stabilizing the product obtained in step (1) in air; and (3) carbonizing the product obtained in step (2) in an inert gas atmosphere at a pressure of 0.15–0.8 MPa. This method reduces gas escape during carbonization, inhibits the formation of defects in the carbon molecular sieve membrane, and better maintains the integrity of the carbon molecular sieve membrane layer, thereby significantly improving the permeation selectivity of the carbon molecular sieve membrane for propane / propylene.

Description

Technical Field

[0001] This invention relates to a carbon molecular sieve membrane, its preparation method, and its application; more specifically, it relates to a carbon molecular sieve membrane for the separation of olefins and alkanes, its preparation method, and its application. Background Technology

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

[0003] CN101277754A discloses a process for preparing a carbon molecular sieve membrane. First, a mixture of cellulose and hemicellulose is treated with trifluoroacetic acid, and then a metal salt is added before casting into a membrane. After drying, the membrane is carbonized at 500-600℃. The prepared carbon molecular sieve membrane exhibits good separation performance in a CO2 / CH4 separation system and can be regenerated by applying an electric current.

[0004] CN106823821A discloses a method for repairing defects in carbon molecular sieve membranes. The method uses silicone rubber as a raw material, which is mixed with a catalyst, a crosslinking agent, and an organic solvent to prepare a sol. The sol is then coated onto the surface of the carbon molecular sieve membrane to form a film, which is then dried. The catalyst is preferably organotin, the crosslinking agent is preferably tetraethyl orthosilicate, and the organic solvent is preferably isooctane. This method utilizes the excellent permeability of silicone rubber, allowing it to penetrate into the interior of the carbon molecular sieve membrane. The silicone rubber prepared by crosslinking is used to form a film on the surface of the carbon molecular sieve membrane to fill the defects, thereby significantly improving the permeability of the carbon molecular sieve membrane.

[0005] CN108472595A discloses a method for preparing a carbon molecular sieve membrane. First, a polymer precursor is heated to a temperature at which the precursor polymer undergoes pyrolysis to form a carbon molecular sieve membrane. Then, the carbon molecular sieve membrane is cooled to a temperature at which no further pyrolysis occurs. Finally, the carbon molecular sieve membrane is exposed to a conditioned atmosphere composed of target permeable gas molecules. This method can achieve a carbon molecular sieve membrane with an improved combination of selectivity and permeability.

[0006] CN109070009A discloses an improved method for manufacturing carbon molecular sieve membranes, wherein a carbon molecular sieve membrane is formed by pyrolyzing a polyimide precursor polymer: heating the polyimide precursor polymer in a furnace to a final pyrolysis temperature of 600°C to 700°C, heating it 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 at 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 produce carbon molecular sieve membranes, defects in the carbon molecular sieve membranes can be generated due to gas escape, thereby affecting the permeability / selectivity of the carbon molecular sieve membranes. Existing technologies reduce carbon molecular sieve membrane defects by repairing or selecting special polymer precursor materials, but it is still difficult to effectively suppress the formation of defects during high-temperature pyrolysis. Summary of the Invention

[0008] One of the objectives of this 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 carbon molecular sieve membranes provided by this invention includes the following steps:

[0010] (1) The polymer film is placed in a modification solution for modification treatment and then dried, wherein the modification solution contains a modifier;

[0011] (2) Stabilize the product obtained in step (1) in air;

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

[0013] A second objective of this invention is to provide a carbon molecular sieve membrane prepared using the method described herein.

[0014] A third objective of this invention is to provide a method for separating a mixture of propylene and propane gases using the carbon molecular sieve membrane described in this invention or a carbon molecular sieve membrane prepared using the method of this invention.

[0015] This invention employs a solution containing a modifier to treat the polymer membrane, allowing the modifier molecules to enter the membrane layer. A stabilization treatment is first performed at a lower temperature, allowing a small amount of gas to escape while maintaining the integrity of the membrane layer. Then, carbonization is performed at a higher temperature and pressure, which reduces gas escape and helps suppress the formation of defects in the carbon molecular sieve membrane, maintaining the integrity of the membrane layer and thus significantly improving the permeation selectivity of the carbon molecular sieve membrane for propane / propylene. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a permeability evaluation device. Detailed Implementation

[0017] This invention employs a solution containing a modifier to treat the polymer membrane. The modifier molecules diffuse into the polymer membrane layer. These modifier molecules contain polar groups that can form hydrogen bonds or covalent bonds with the polar groups on the long-chain polymer of the polymer membrane, thereby reducing the formation of gas escape from the long-chain polymer during high-temperature carbonization and minimizing defects in the carbon molecular sieve membrane. Furthermore, the modifier molecules contain benzene rings, which readily transform into carbon molecular sieves during high-temperature carbonization, further reducing defects in the carbon molecular sieve membrane. After modification and stabilization at lower temperatures, a small amount of gas preferentially escapes, further avoiding the simultaneous escape of large amounts of gas generated by polymer decomposition during high-temperature carbonization, thus effectively suppressing the formation of defects in the carbon molecular sieve membrane. Additionally, the high-temperature carbonization process of this invention is carried out under high pressure, which facilitates the transformation of more carbon-containing species into carbon molecular sieves, further reducing gas formation. The carbon molecular sieve membrane prepared using this method exhibits high propylene / propane separation performance.

[0018] The method for preparing carbon molecular sieve membranes provided by this invention includes the following steps:

[0019] (1) The polymer film is placed in a modifying agent solution for modification treatment, and then dried. The modifying agent solution contains a modifying agent.

[0020] (2) Stabilize the product obtained in step (1) in air;

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

[0022] In the method provided by this invention, in step (1), the mass ratio of the polymer membrane to the modifier solution is 1:10-100, preferably 1:20-60; the polymer membrane is one of polyvinylidene fluoride membrane, cellulose acetate membrane, ethyl cellulose membrane, and polyacrylonitrile membrane, preferably polyvinylidene fluoride membrane; 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 group in the modifier solution... - 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, and the treatment time is 6–24 hours, preferably 8–16 hours. 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 this 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 to 0.6 MPa, the heating rate is 0.5 to 5 °C / min, preferably 0.8 to 3 °C / min, the carbonization treatment temperature is 450 to 700 °C, preferably 480 to 650 °C, and the time is 1 to 8 hours, preferably 2 to 6 hours.

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

[0026] The carbon molecular sieve membrane prepared by the method of this invention is suitable for gas separation, such as propylene / propane. The permeability of a single-component gas was determined using a constant-pressure gas permeation apparatus at an operating pressure of 0.3 MPa and an operating temperature of 30°C. A schematic diagram of the constant-pressure gas permeation apparatus is shown below. Figure 1 As shown, the device consists of a membrane cell, pressure gauge A, flow meter, etc. 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 2 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, in barrers.

[0027]

[0028] In the formula, 3 represents the transmembrane pressure difference in bar, and 75 represents that 1 bar equals 75 cmHg.

[0029] 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.

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

[0031] The method for determining the thickness of the carbon molecular sieve membrane in this invention is as follows: a thickness gauge is used to measure the thickness at the four right-angle vertices and the center of a square, and the average value of the membrane thickness at these five locations is taken.

[0032] The invention is further illustrated by the following examples, but the invention is not limited thereto.

[0033] Example 1

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

[0035] (2) Place the product obtained in step (1) in air and stabilize it at 220°C for 1.5 hours.

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

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

[0038] Example 2

[0039] 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% by mass.

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

[0041] Example 3

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

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

[0044] Example 4

[0045] Carbon molecular sieve membrane D was prepared according to the method in 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 flux, and propylene / propane permeation selectivity of carbon molecular sieve membrane D are shown in Table 1.

[0047] Example 5

[0048] The carbon molecular sieve membrane E was prepared according to the method in 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 and at a heating rate of 2 °C / min, and then heated to 550 °C for 6 hours. The product was then cooled to room temperature in an argon atmosphere.

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

[0050] Example 6

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

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

[0053] Comparative Example 1

[0054] The membrane thickness, propylene and propane permeation flux, 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 in Example 1, except that the polyvinylidene fluoride membrane did not undergo step (1). A complete carbon molecular sieve membrane could not be obtained.

[0057] Comparative Example 3

[0058] 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 flux, and propylene / propane permeation selectivity of carbon molecular sieve membrane I are shown in Table 1.

[0060] Comparative Example 4

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

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

[0063] Table 1

[0064]

[0065] As shown in Table 1, the polyvinylidene fluoride membrane described in Comparative Example 1 has low permeation flux for both propylene and propane, exhibiting no permeation selectivity and thus failing to achieve propylene / propane separation. The polyvinylidene fluoride membrane in Comparative Example 2, without modification, only undergoes low-temperature stabilization and high-temperature carbonization, failing to yield a complete carbon molecular sieve membrane, therefore the permeation flux for propylene and propane cannot be measured. The modifier used in Comparative Example 3 is p-xylenediamine, and the resulting carbon molecular sieve membrane I exhibits lower propylene / propane permeation selectivity than Examples 1-6 of this invention, indicating numerous defects in carbon molecular sieve membrane I. Comparative Example 4, carbonized under normal pressure, yields a carbon molecular sieve membrane J with low thickness and lower propylene / propane permeation selectivity than Examples 1-6 of this invention, indicating numerous defects in carbon molecular sieve membrane J.

Claims

1. A method for preparing a carbon molecular sieve membrane, comprising the following steps: (1) The polymer film is placed in a modification solution for modification treatment, and then dried. The modification solution contains a modifier, which is an amino acid, and the modification solution contains OH-. - The concentration is 0.1–1.5 mol / L; (2) Stabilize the product obtained in step (1) in air; (3) The product obtained in step (2) is carbonized in an inert gas atmosphere, and the carbonization pressure is 0.15 to 0.8 MPa.

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

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

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

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

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

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

8. The method according to claim 1, characterized in that... (1) The modification treatment temperature is 40-90℃.

9. The method according to claim 1, characterized in that... (1) The modification treatment temperature is 50-80℃.

10. The method according to claim 1, characterized in that... (1) The modification process described in step 1 takes 6 to 24 hours.

11. The method according to claim 1, characterized in that... (1) The modification process described in step 1 takes 8 to 16 hours.

12. The method according to claim 1, characterized in that... (1) The drying temperature is 40-100℃.

13. The method according to claim 1, characterized in that... (1) The drying temperature is 50-80℃.

14. The method according to claim 1, characterized in that... (1) The drying time is 2 to 12 hours.

15. The method according to claim 1, characterized in that... (1) The drying time is 5 to 10 hours.

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

17. The method according to claim 1, characterized in that... (2) The stabilization treatment temperature in step 2 is 200-260℃.

18. The method according to claim 1, characterized in that... (2) The stabilization treatment temperature in step 2 is 210-250℃.

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

20. The method according to claim 1, characterized in that... (2) The stabilization process in step 1 takes 1 to 3 hours.

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

22. The method according to claim 1, characterized in that... (3) The heating rate of the carbonization process in step 3 is 0.5 to 5 °C / min.

23. The method according to claim 1, characterized in that... (3) The heating rate of the carbonization process in step 3 is 0.8 to 3 °C / min.

24. The method according to claim 1, characterized in that... (3) The carbonization temperature in step 3 is 450-700℃.

25. The method according to claim 1, characterized in that... (3) The carbonization temperature in step 3 is 480-650℃.

26. The method according to claim 1, characterized in that... (3) The carbonization process in step 3 takes 1 to 8 hours.

27. The method according to claim 1, characterized in that... (3) The carbonization process in step 3 takes 2 to 6 hours.

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

29. A carbon molecular sieve membrane prepared by the method according to any one of claims 1 to 28.

30. A method for separating a mixture of propylene and propane using the carbon molecular sieve membrane of claim 29.

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