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

Abstract

The carbon molecular sieve membrane comprises 40-90% by mass of a carbon material and 10-60% by mass of a molecular sieve, the carbon material is a polymer high-temperature carbonized product, the molecular sieve is a silicon-aluminum molecular sieve, a phosphorus-aluminum molecular sieve or a silicon-phosphorus-aluminum molecular sieve, and the thickness of the carbon molecular sieve membrane is 5-60 microns. The carbon molecular sieve membrane has high permeation selectivity and can be used for propylene / propane separation.

Description

Technical Field

[0001] The invention relates to a carbon molecular sieve membrane and a preparation method thereof, in particular to a carbon molecular sieve membrane used for separation of olefins and alkanes and a preparation method 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. A mixture of cellulose and hemicellulose is first treated with trifluoroacetic acid, and then a metal salt is added to form a film by casting. After drying, the film is carbonized at 500-600°C. 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 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, wherein a polymer precursor is first heated to a temperature where the precursor polymer undergoes pyrolysis to form a carbon molecular sieve membrane, the carbon molecular sieve membrane is then cooled to a temperature where no further pyrolysis occurs, and finally the carbon molecular sieve membrane is exposed to a regulated atmosphere composed of target permeating gas molecules, and a carbon molecular sieve membrane having an improved combination of selectivity and permeability can be achieved. 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 the final pyrolysis temperature is maintained in a non-oxidizing atmosphere for a pyrolysis time of up to 60 minutes, and the method can achieve a CMS having an improved combination of selectivity and permeability.

[0006] 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

[0007] One of the purposes of the present invention is to provide a carbon molecular sieve membrane, comprising 60-90 mass % of carbon material and 10-40 mass % of molecular sieve, wherein the carbon material is a polymer high temperature carbonization product, the molecular sieve is a silicon aluminum molecular sieve, a phosphorus aluminum molecular sieve or a silicon phosphorus aluminum molecular sieve, and the thickness of the carbon molecular sieve membrane is 5-60 microns. The carbon molecular sieve membrane can be used for propylene / propane separation and has a high permeation selectivity.

[0008] The second object of the present invention is to provide a method for preparing the above-mentioned carbon molecular sieve membrane, comprising the following steps:

[0009] (1) mixing a polymer, a molecular sieve and a solvent to obtain a casting solution, preparing a polymer membrane and performing a membrane forming treatment to obtain a polymer membrane;

[0010] (2) placing the polymer film obtained in step (1) in a cross-linking solution, performing a cross-linking treatment, washing, and drying to obtain a cross-linked polymer film;

[0011] (3) placing the cross-linked polymer film obtained in step (2) in air for stabilization treatment;

[0012] (4) The product obtained in step (3) is carbonized in an inert gas atmosphere, wherein the carbonization pressure is 0.15 to 0.8 MPa.

[0013] 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.

[0014] The present invention provides a method for preparing a carbon molecular sieve membrane. Molecular sieves are added to a casting solution. After film formation and cross-linking, carbonization treatment can be performed at a relatively low temperature and a certain pressure, which is beneficial to reducing gas escape and inhibiting the formation of carbon molecular sieve membrane defects. The carbon molecular membrane prepared by the method of the present invention is used for propylene / propane separation and has a relatively high propane / propylene permeation selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the permeability evaluation device. DETAILED DESCRIPTION

[0016] In the preparation of the carbon molecular sieve membrane, the molecular sieve is introduced into the casting liquid, and a polymer membrane containing the molecular sieve is formed after the film is formed. After the cross-linking treatment, due to the catalytic effect of the molecular sieve, the polymer can be converted into a carbon material at a lower temperature, reducing the gas emission during the carbonization process. At the same time, the carbonization treatment is carried out under a certain pressure, which can further reduce the gas emission during the carbonization process, thereby effectively inhibiting the formation of defects in the carbon molecular sieve membrane. The carbon molecular sieve membrane prepared by the method described in the present invention has a higher propylene / propane separation performance.

[0017] The carbon molecular sieve membrane provided by the present invention comprises 60-90% by mass of carbon material and 10-40% by mass of molecular sieve, preferably 70-80% by mass of carbon material and 20-30% by mass of molecular sieve, wherein the carbon material is a high-temperature carbonization product of a polymer, and the polymer is selected from polyvinylidene fluoride, polyimide, cellulose acetate, ethyl cellulose or polyacrylonitrile, preferably polyvinylidene fluoride; the molecular sieve is a silicon aluminum molecular sieve, a phosphorus aluminum molecular sieve or a silicon phosphorus aluminum molecular sieve, preferably a silicon aluminum molecular sieve, more preferably an A-type molecular sieve, and more preferably the cation of the A-type molecular sieve is Na + , K + , Ca 2+ ; The thickness of the carbon molecular sieve membrane is 5 to 60 microns, preferably 8 to 25 microns.

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

[0019] (1) mixing a polymer, a molecular sieve and a solvent to obtain a casting solution, preparing a polymer membrane and performing a membrane forming treatment to obtain a polymer membrane;

[0020] (2) placing the polymer film obtained in step (1) in a cross-linking solution, performing a cross-linking treatment, washing, and drying to obtain a cross-linked polymer film;

[0021] (3) placing the cross-linked polymer film obtained in step (2) in air for stabilization treatment;

[0022] (4) The product obtained in step (3) is carbonized in an inert gas atmosphere, wherein the carbonization pressure is 0.15 to 0.8 MPa.

[0023] The present invention provides a method for preparing a carbon molecular sieve membrane, wherein step (1) is a membrane forming step, wherein the casting solution comprises 5 to 20% by mass of a polymer and 3 to 10% by mass of a molecular sieve; the polymer is polyvinylidene fluoride, polyimide, cellulose acetate, ethyl cellulose or polyacrylonitrile, preferably polyvinylidene fluoride; the molecular sieve is a silicon aluminum molecular sieve, a phosphorus aluminum molecular sieve or a silicon phosphorus aluminum molecular sieve, preferably a silicon aluminum molecular sieve; the solvent is at least one of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide and chloroform; the membrane forming treatment temperature is 60 to 150°C and the time is 0.5 to 5 hours.

[0024] The preparation method of the carbon molecular sieve membrane provided by the present invention, step (2) is a cross-linking treatment step, wherein the cross-linking liquid comprises 10-40 mass % of a cross-linking agent, 5-30 mass % of an inorganic base and 30-85 mass % of a dispersant, the cross-linking agent is p-phenylenediamine, p-phenylenediamine, hexamethylenediamine, the inorganic base is sodium hydroxide or potassium hydroxide, and the dispersant is methanol or ethanol; the mass ratio of the cross-linking liquid to the polymer membrane is 5-20:1; the washing solvent is methanol or ethanol, preferably the same as the dispersant, and the number of washing times is 2-5 times; the cross-linking treatment temperature is 20-100°C, the time is 2-12 hours, and the drying treatment temperature is 50-100°C, and the time is 5-24 hours.

[0025] In the method for preparing the carbon molecular sieve membrane provided by the present invention, in step (3), the stabilization treatment temperature is 160-250° C. and the time is 0.5-5 hours.

[0026] The present invention provides a method for preparing a carbon molecular sieve membrane, wherein in step (4), the inert gas atmosphere is nitrogen, argon or helium; the heating rate is 0.5 to 5°C / min, preferably 0.8 to 3°C / min; the carbonization treatment temperature is 300 to 500°C, preferably 320 to 420°C, and the time is 1 to 8 hours.

[0027] The carbon molecular sieve membrane of the present invention or the carbon molecular sieve membrane prepared by the method of the present invention is suitable for gas separation, especially for propylene / propane separation. The permeability of a single component gas is measured by 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.

[0028]

[0029] In the formula, 3 represents the transmembrane pressure difference, the unit is bar, and 75 means that 1 bar is equal to 75 cmHg.

[0030] 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.

[0031] The propylene / propane permeability selectivity is the ratio of the permeabilities of the two. The higher the permeability selectivity, the better the separation effect.

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

[0033] 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.

[0034] The mass fractions of carbon material and molecular sieve in the carbon molecular sieve membrane of the present invention are calculated as follows: from the mass fraction a1 of the polymer in the casting solution in step (1), the mass fraction a2 of the molecular sieve and the mass m1 of the polymer membrane, it can be seen that the mass m2 of the molecular sieve in the polymer membrane is m1 x (a2 / (a1+a2)), the mass of the molecular sieve remains unchanged during the carbonization process, and the mass of the carbon molecular sieve membrane is m3. Then the mass fraction a3 of the molecular sieve in the obtained carbon molecular sieve membrane is m2 / m3, and the mass fraction a4 of the carbon material is (m3-m2) / m3.

[0035] The present invention is further described below by way of examples, but the present invention is not limited thereto.

[0036] Example 1

[0037] (1) Polyvinylidene fluoride and NaA molecular sieve are added to the solvent N,N-dimethylacetamide to prepare a casting solution, wherein the casting solution contains 15% by mass of polyvinylidene fluoride and 4.7% by mass of NaA molecular sieve. The casting solution is poured onto a glass plate, and a polymer film is scraped with a 300 μm scraper, and the film is treated at 80° C. for 3 hours.

[0038] (2) 0.8 g of the polymer film obtained in step (1) after the film-forming treatment was placed in a cross-linking solution prepared by 1.6 g of p-phenylenediamine, 1.5 g of sodium hydroxide, and 5 g of methanol, and allowed to stand at 40°C for 6 hours for cross-linking treatment. The film was then washed three times with methanol and dried at 80°C for 12 hours.

[0039] (3) The cross-linked polymer film obtained in step (2) was placed in air and stabilized at 190°C for 1.5 hours.

[0040] (4) The product obtained in step (3) was carbonized in a nitrogen atmosphere at a pressure of 0.3 MPa. The temperature was increased to 350°C for 6 hours at a heating rate of 0.5°C / min, and then cooled to room temperature in a nitrogen atmosphere to obtain a carbon molecular sieve membrane A.

[0041] The thickness, composition, propylene and propane permeation fluxes and permeation selectivity of carbon molecular sieve membrane A are shown in Table 1.

[0042] Example 2

[0043] Carbon molecular sieve membrane B was prepared according to the method of Example 1, except that the mass fraction of NaA molecular sieve in the casting solution in step (1) was 7.6 mass %.

[0044] The thickness, composition, propylene and propane permeation fluxes and permeation selectivity of carbon molecular sieve membrane B are shown in Table 1.

[0045] Example 3

[0046] A carbon molecular sieve membrane C was prepared according to the method of Example 1, except that the mass fraction of NaA molecular sieve in the casting solution in step (1) was 3.2 mass %.

[0047] The thickness, composition, propylene and propane permeation fluxes and permeation selectivity of the carbon molecular sieve membrane C are shown in Table 1.

[0048] Example 4

[0049] A carbon molecular sieve membrane D was prepared according to the method of Example 1, except that in the casting solution of step (1), the mass fraction of polyvinylidene fluoride was 11 mass % and the solvent was tetrahydrofuran.

[0050] The thickness, composition, propylene and propane permeation fluxes and permeation selectivity of carbon molecular sieve membrane D are shown in Table 1.

[0051] Example 5

[0052] A carbon molecular sieve membrane E was prepared according to the method of Example 1, except that the membrane forming treatment temperature in step (1) was 120°C, the carbonization treatment pressure in step (4) was 0.6 MPa, and the carbonization treatment temperature was 330°C.

[0053] The thickness, composition, propylene and propane permeation fluxes and permeation selectivity of the carbon molecular sieve membrane E are shown in Table 1.

[0054] Example 6

[0055] The carbon molecular sieve membrane F was prepared according to the method of Example 1, except that in step (4), the temperature was raised to 400° C. for carbonization treatment for 4.5 hours at a heating rate of 1.5° C. / min.

[0056] The thickness, composition, propylene and propane permeation fluxes and permeation selectivity of the carbon molecular sieve membrane F are shown in Table 1.

[0057] Example 7

[0058] Carbon molecular sieve membrane G was prepared according to the method of Example 1, except that the NaA molecular sieve in step (1) was replaced by KA molecular sieve, and the cross-linking agent in step (2) was p-phenylenediamine.

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

[0060] Example 8

[0061] Carbon molecular sieve membrane H was prepared according to the method of Example 1, except that the NaA molecular sieve in step (1) was replaced by CsX molecular sieve.

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

[0063] Comparative Example 1

[0064] Carbon molecular sieve membrane I was prepared according to the method of Example 1, except that no NaA molecular sieve was added to the casting solution in step (1).

[0065] The thickness, composition, propylene and propane permeation fluxes and permeation selectivity of the carbon molecular sieve membrane I are shown in Table 1.

[0066] Comparative Example 2

[0067] A carbon molecular sieve membrane J was prepared according to the method of Example 1, except that in step (4), the carbonization treatment temperature was 550°C.

[0068] The thickness, composition, propylene and propane permeation fluxes and permeation selectivity of carbon molecular sieve membrane J are shown in Table 1.

[0069] Comparative Example 3

[0070] The carbon molecular sieve membrane K was prepared according to the method of Example 1, except that in step (4), the carbonization treatment pressure was normal pressure.

[0071] The thickness, composition, propylene and propane permeation fluxes and permeation selectivity of the carbon molecular sieve membrane K are shown in Table 1.

[0072] Table 1

[0073]

[0074] It can be seen from Table 1 that when the carbon molecular sieve membrane I is prepared in Comparative Example 1, no molecular sieve is added to the casting liquid, the permeation fluxes for propylene and propane are low, there is no permeation selectivity, and the separation of propylene / propane cannot be achieved; when the carbon molecular sieve membrane J is prepared in Comparative Example 2, the carbonization treatment temperature is high, and the thickness, carbon material content and propylene / propane permeation selectivity of the obtained carbon molecular sieve membrane J are lower than those of the carbon molecular sieve membranes of Examples 1 to 8 of the present invention, indicating that more gas escapes during the carbonization process, resulting in more defects in the carbon molecular sieve membrane; when the carbon molecular sieve membrane K is prepared in Comparative Example 3, the carbonization treatment pressure is normal pressure, and the thickness, carbon material content and propylene / propane permeation selectivity of the obtained carbon molecular sieve membrane K are lower than those of the carbon molecular sieve membrane A of Example 1 of the present invention, indicating that more gas escapes during the normal pressure carbonization treatment than during the pressurized carbonization treatment, resulting in more defects in the carbon molecular sieve membrane.

Claims

1. A carbon molecular sieve membrane, comprising 60-90 mass % of carbon material and 10-40 mass % of molecular sieve, wherein the carbon material is a high-temperature carbonization product of a polymer, the molecular sieve is a silicon-aluminum molecular sieve, a phosphorus-aluminum molecular sieve or a silicon-phosphorus-aluminum molecular sieve, and the thickness of the carbon molecular sieve membrane is 5-60 microns.

2. The carbon molecular sieve membrane according to claim 1, characterized in that The polymer is polyvinylidene fluoride, polyimide, cellulose acetate, ethyl cellulose or polyacrylonitrile.

3. The carbon molecular sieve membrane according to claim 1, characterized in that The polymer is polyvinylidene fluoride.

4. The carbon molecular sieve membrane according to claim 1, characterized in that The molecular sieve is a silicon-aluminum molecular sieve.

5. The carbon molecular sieve membrane according to claim 4, characterized in that The silicon-aluminum molecular sieve is a type A molecular sieve.

6. The carbon molecular sieve membrane according to claim 5, characterized in that The cation of the A-type molecular sieve is Na + , K + , Ca 2+ .

7. The carbon molecular sieve membrane according to claim 1, characterized in that The carbon molecular sieve membrane has a thickness of 8 to 25 microns.

8. The method for preparing the carbon molecular sieve membrane according to claim 1, comprising the following steps: (1) mixing a polymer, a molecular sieve and a solvent to obtain a casting solution, preparing a polymer membrane and performing a membrane forming treatment to obtain a polymer membrane; (2) placing the polymer film obtained in step (1) in a cross-linking solution, performing a cross-linking treatment, washing, and drying to obtain a cross-linked polymer film; (3) placing the cross-linked polymer film obtained in step (2) in air for stabilization treatment; (4) The product obtained in step (3) is carbonized in an inert gas atmosphere, wherein the carbonization pressure is 0.15 to 0.8 MPa.

9. The method according to claim 8, characterized in that In step (1), the casting solution comprises 5 to 20% by mass of a polymer and 3 to 10% by mass of a molecular sieve.

10. The method according to claim 8, characterized in that In step (1), the polymer is polyvinylidene fluoride, polyimide, cellulose acetate, ethyl cellulose or polyacrylonitrile, preferably polyvinylidene fluoride; the molecular sieve is silica-alumina molecular sieve, phosphate-alumina molecular sieve or silicon-phosphate-alumina molecular sieve, preferably silica-alumina molecular sieve; and the solvent is at least one of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide and chloroform.

11. The method according to claim 8, characterized in that In step (1), the film forming treatment temperature is 60 to 150° C. and the time is 0.5 to 5 hours.

12. The method according to claim 8, characterized in that In step (2), the cross-linking liquid comprises 10 to 40% by mass of a cross-linking agent, 5 to 30% by mass of an inorganic base and 30 to 85% by mass of a dispersant, wherein the cross-linking agent is p-phenylenediamine, p-phenylenediamine or hexamethylenediamine, the inorganic base is sodium hydroxide or potassium hydroxide, and the dispersant is methanol or ethanol.

13. The method according to claim 8, characterized in that In step (2), the mass ratio of the cross-linking liquid to the polymer film is 5 to 20:

1.

14. The method according to claim 8, characterized in that In step (2), the washing solvent is methanol or ethanol, and the washing times are 2 to 5 times.

15. The method according to claim 8, characterized in that In step (2), the cross-linking treatment temperature is 20-100° C., the time is 2-12 hours, and the drying treatment temperature is 50-100° C., the time is 5-24 hours.

16. The method according to claim 8, characterized in that In step (3), the stabilization treatment temperature is 160-250° C. and the time is 0.5-5 hours.

17. The method according to claim 8, characterized in that In step (4), the inert gas atmosphere is nitrogen, argon or helium.

18. The method according to claim 8, characterized in that In step (4), the heating rate is 0.5 to 5°C / min, preferably 0.8 to 3°C / min.

19. The method according to claim 1, characterized in that In step (4), the carbonization treatment temperature is 300-500° C., preferably 320-420° C., and the time is 1-8 hours.

20. A method for separating a mixed gas of propylene and propane using the carbon molecular sieve membrane according to any one of claims 1 to 7 or the carbon molecular sieve membrane prepared by the method according to any one of claims 8 to 19.

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