Hollow fiber supported carbon molecular sieve composite membrane and preparation method thereof

Abstract

The invention relates to the technical field of gas separation, in particular to a hollow fiber supported carbon molecular sieve composite membrane and a preparation method thereof.The preparation method comprises the steps that firstly, a dianhydride-based polyimide dip-coating solution is prepared, then a balance weight is added to the tail end of a hollow carbon fiber base material, and the top end of the hollow carbon fiber base material is connected with dip-coating equipment; the hollow carbon fiber base material is kept vertical and slowly immersed in the dianhydride-based polyimide dip-coating solution, meanwhile, a protective cover is arranged between a container opening of the dianhydride-based polyimide dip-coating solution and the dip-coating equipment, then the hollow carbon fiber base material obtained after dip-coating is dried, and the balance weight is removed; the hollow fiber supported carbon molecular sieve composite membrane is obtained. The dianhydride-based polyimide dip-coating solution is uniformly distributed on the surface of the hollow fiber base material, and the carbon molecular sieve composite membrane is good in morphology, has excellent gas separation performance and has a wide application prospect in the field of gas separation.

Description

Technical Field

[0001] The invention relates to the technical field of gas separation, and in particular to a hollow fiber-supported carbon molecular sieve composite membrane and a preparation method thereof. Background Art

[0002] Carbon molecular sieve membrane is a commonly used membrane material for membrane gas separation. Carbon molecular sieve membrane is usually manufactured by pyrolysis of polymer precursors such as polyimide, resin, cellulose and polyetherimide. Pyrolysis reduces the precursor polymer to carbon, and some micropores are left in the product obtained by pyrolysis to ensure that it has a certain porosity. The carbon molecular sieve membrane thus formed can then be used for the separation of various gases. The carbon molecular sieve membrane can adjust the pore size to achieve highly selective separation of specific molecules, making it have higher efficiency and separation performance. The highly ordered pore structure of the carbon molecular sieve membrane, the rapid diffusion of molecules inside it shows high permeability, so that the carbon molecular sieve membrane can achieve a high-throughput separation process. The carbon molecular sieve membrane has high chemical stability and can withstand harsh conditions such as corrosion by various solvents and high temperature. Under the same separation conditions, the carbon molecular sieve membrane has a longer service life than other membrane materials.

[0003] The carbon molecular sieve membranes widely studied at present include self-supporting hollow fiber carbon molecular sieve membranes and supported carbon molecular sieve composite membranes. Among them, the self-supporting hollow fiber carbon molecular sieve membrane has the advantages of light weight, high surface area-volume ratio, and more compact equipment. It is the carbon molecular sieve membrane with the most potential for industrial application, but the membrane obtained by high temperature (>700℃) and long time (insulation time>1h) carbonization is brittle and not conducive to long-term recycling. Supported carbon molecular sieve composite membranes are prepared by coating precursor materials on tubular ceramic supports. They have good mechanical properties and can be recycled for a long time, but the support increases the mass transfer resistance of gas permeation.

[0004] Therefore, it is urgent to develop a supported hollow carbon fiber carbon molecular sieve membrane that not only has the advantages of light weight and high surface area-volume ratio of self-supporting hollow fiber carbon molecular sieve membrane, but also has the characteristics of good mechanical properties of supported carbon molecular sieve composite membrane. However, in the actual preparation process, when the membrane-forming raw material is coated on the hollow carbon fiber substrate according to the existing technical method, the coating is uneven, which affects the separation performance of the carbon molecular sieve membrane. Summary of the invention

[0005] In view of this, the present invention provides a hollow fiber supported carbon molecular sieve composite membrane and a preparation method thereof, so as to solve the technical problem in the prior art that when the membrane-forming raw material is coated on the hollow carbon fiber substrate, uneven coating occurs, thereby affecting the separation performance of the carbon molecular sieve membrane.

[0006] The technical solution of this application to solve the above technical problems is as follows:

[0007] A method for preparing a hollow fiber supported carbon molecular sieve composite membrane comprises the following steps:

[0008] S10. Prepare a dianhydride-based polyimide dip coating solution for standby use;

[0009] S20. Adding a counterweight at the end of the hollow carbon fiber substrate;

[0010] S30. A protective cover is provided between the dipping solution container port and the coating pulling device;

[0011] S40. adding the dianhydride-based polyimide dipping solution into the dipping solution container, connecting the top of the hollow carbon fiber substrate with the added counterweight to the pulling coating device so that it can move up and down inside the dipping solution container and the protective cover, keeping the hollow carbon fiber substrate with the added counterweight vertically and slowly dipping it into the dianhydride-based polyimide dipping solution, and after dipping for a predetermined time, slowly pulling it up, and then drying the hollow carbon fiber substrate after dipping and removing the counterweight to obtain a polyimide / hollow carbon fiber composite membrane;

[0012] S50. Preparing a hollow fiber supported carbon molecular sieve composite membrane: subjecting the polyimide / hollow carbon fiber composite membrane to pyrolysis and carbonization treatment under a protective gas to obtain the hollow fiber supported carbon molecular sieve composite membrane.

[0013] Preferably, in the above preparation method, in step S20, the "adding a counterweight to the end of the hollow carbon fiber substrate" is specifically: wrapping the end of the hollow carbon fiber substrate with a high temperature resistant tape, and then wrapping the epoxy resin AB glue on the outer surface of the high temperature resistant tape, and drying.

[0014] Preferably, in the above preparation method, in step S40, the predetermined dipping time is 30 to 90 seconds, and the rate of slow pulling up is 0.5 to 2 cm / min.

[0015] Preferably, in the above preparation method, in step S10, the "preparing a dianhydride-based polyimide dip-coating solution" comprises the following steps:

[0016] S11. The purified dianhydride and diamine after sublimation are added to a first organic solvent under anhydrous and protective gas to obtain a polyamic acid solution;

[0017] S12. The polyamic acid solution is chemically imidized to obtain a polyimide solution;

[0018] S13. The polyimide solution is precipitated in ethanol, then washed with ethanol and filtered, and then dried in vacuo to obtain the dianhydride-based polyimide powder;

[0019] S14. dissolving the dianhydride-based polyimide powder in a second organic solvent, stirring until the mixture is uniform, and then degassing to obtain a dianhydride-based polyimide dip coating solution.

[0020] Preferably, in the above preparation method, in step S11, the molar ratio of the dianhydride to the diamine is (1 to 1.05):1.

[0021] Preferably, in the above preparation method, in step S11, the dianhydride includes any one of hexafluorodianhydride, pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, monoether tetracarboxylic dianhydride and diether tetracarboxylic dianhydride; the diamine includes at least one of metaphenylenediamine, trimethyldiamine and 2,4,6-trimethylmetaphenylenediamine.

[0022] Preferably, in the above preparation method, the first organic solvent and the second organic solvent respectively include any one of tetrahydrofuran, N-methylpyrrolidone, and nitrogen-dimethylacetamide.

[0023] Preferably, in the above preparation method, in step S20, the mass fraction of the dianhydride-based polyimide dipping solution is 15 to 25 wt %.

[0024] Preferably, in the above preparation method, in step S40, the pyrolysis carbonization treatment conditions are controlled to be 500 to 700°C, a heating rate of 5 to 15°C / min, a heat preservation time of 0 to 2h, and a protective gas flow rate of 200 to 500mL / min.

[0025] A hollow fiber supported carbon molecular sieve composite membrane is prepared by adopting the above preparation method.

[0026] The above technical solution has at least the following advantages:

[0027] The preparation method of the hollow fiber supported carbon molecular sieve composite membrane (hereinafter referred to as carbon molecular sieve composite membrane) of the present application, first prepare a dianhydride polyimide dipping solution (hereinafter referred to as dipping solution), then add a counterweight to the end of the hollow carbon fiber substrate, connect the top end to the pulling coating device, keep the hollow carbon fiber substrate vertically and slowly immerse it in the dianhydride polyimide dipping solution, and at the same time, set a protective cover between the dianhydride polyimide dipping solution container port and the pulling coating device, and then remove the counterweight after drying the hollow carbon fiber substrate after dipping to obtain a polyimide / hollow carbon fiber composite membrane. The effect of increasing the counterweight can prevent the dipping solution from entering the interior of the hollow fiber substrate, and another method can increase the weight of the hollow fiber substrate to keep it in a vertical state in the dipping solution, so that the hollow fiber substrate can be prevented from deforming during the coating process, and keeping it vertical can prevent the hollow fiber substrate from floating on the dipping solution, so that the uneven coating caused affects the separation performance of the carbon molecular sieve membrane. The protective cover can isolate the hollow carbon fiber substrate from the air, further preventing it from producing uneven coating; in particular, the method is suitable for preparing membranes on small-sized supports, especially supports of 280 to 300 μm, and the prepared membranes have excellent surface morphology and excellent gas separation performance.

[0028] The hollow fiber supported carbon molecular sieve composite membrane of the present application has a dianhydride-based polyimide dipping solution evenly distributed on the surface of the hollow fiber substrate, the carbon molecular sieve composite membrane has a good morphology, has excellent gas separation performance, and has broad application prospects in the field of gas separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the X-ray photoelectron spectrum of 6FDA-based polyimide powder.

[0030] Figure 2 This is an electron microscope image of the cross-section of the hollow fiber substrate.

[0031] Figure 3 This is an electron microscope image of the hollow fiber supported carbon molecular sieve composite membrane in Experimental Example 1.

[0032] Figure 4 This is an electron microscope image of the carbon molecular sieve composite membrane supported by hollow fibers in Experimental Example 2.

[0033] Figure 5 The permeability and ideal selectivity diagram of the gas separation by the hollow fiber supported carbon molecular sieve composite membrane in Experimental Examples 2 and 3.

[0034] Figure 6 This is a schematic diagram of the protective cover installation.

[0035] In the figure: a dipping solution container 1, a protective cover 2, an elastic telescopic tube 3, a hollow carbon fiber substrate 4, and a pulling coating device 5. DETAILED DESCRIPTION

[0036] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. The technical solution of the present invention will be further described below in conjunction with the drawings of the embodiments of the present invention, and the present invention is not limited to the following specific implementation methods.

[0037] In one specific embodiment of the present application, a method for preparing a hollow fiber supported carbon molecular sieve composite membrane comprises the following steps:

[0038] S10. Prepare a dianhydride-based polyimide dip coating solution for standby use;

[0039] Wherein, the "preparation of dianhydride-based polyimide dip-coating solution" comprises the following steps:

[0040] S11. The purified dianhydride and diamine after sublimation are added to a first organic solvent under anhydrous and protective gas to obtain a polyamic acid solution;

[0041] S12. The polyamic acid solution is chemically imidized to obtain a polyimide solution;

[0042] S13. The polyimide solution is precipitated in ethanol, then washed with ethanol and filtered, and then dried in vacuo to obtain the dianhydride-based polyimide powder;

[0043] S14. dissolving the dianhydride-based polyimide powder in a second organic solvent, stirring until the mixture is uniform, and then degassing to obtain a dianhydride-based polyimide dip coating solution.

[0044] Dianhydride is an organic compound, which is an acid anhydride connected by two acetyl groups. Dianhydride is an important organic synthesis intermediate, commonly used in the synthesis of other compounds, and can be used as an acylating agent in organic synthesis for acylation and esterification. Preferably, the dianhydride includes any one of hexafluorodianhydride, pyromellitic anhydride, biphenyltetracarboxylic anhydride, monoether tetracarboxylic anhydride and diether tetracarboxylic anhydride. Among them, hexafluorodianhydride (also known as 4,4'-(hexafluoroisopropylidene) diphthalic anhydride, 6FDA) is one of the most widely used dianhydride monomers and is also the dianhydride monomer with the largest amount of use in colorless and transparent polyimide. Therefore, hexafluorodianhydride (6FDA) is preferred in this application. The diamine includes at least one of m-phenylenediamine, trimethyldiamine, and 2,4,6-trimethylm-phenylenediamine. The first organic solvent and the second organic solvent include any one of tetrahydrofuran, N-methylpyrrolidone, nitrogen, and nitrogen-dimethylacetamide. Among them, N-methylpyrrolidone is a polar solvent with strong selectivity and good stability, and has the advantages of low toxicity, high boiling point, strong solvency, non-flammability, biodegradability, recyclability, safety in use, and applicability to a variety of formulations, so the first organic solvent and the first organic solution in the present application are preferably N-methylpyrrolidone. The protective gas is one or more of nitrogen, argon and helium.

[0045] In a preferred embodiment, the molar ratio of the dianhydride to the diamine is (1 to 1.05):1.

[0046] Since the carbon molecular sieve composite membrane prepared by different mass fractions of dianhydride based polyimide dipping solution has different permeabilities for different gas separations, in a preferred embodiment, the mass fraction of the dianhydride based polyimide dipping solution is 5 to 25wt%, and further, the mass fraction of the dianhydride based polyimide dipping solution is 15 to 25wt%.

[0047] “Chemically imidizing the polyamic acid solution” specifically refers to adding a mixed solution of acetic acid and triethylamine into the polyamic acid solution for chemical imidization.

[0048] For example, "preparing a dianhydride-based polyimide dipping solution" specifically includes: first, subliming and purifying two monomers, dianhydride and diamine, and then, under anhydrous and protective gas conditions, mixing dianhydride and diamine in a molar ratio of (1 to 1.05):1, adding a certain amount of a first organic solvent in batches to make the polyimide reach 10wt%, and continuing to stir to obtain a polyamic acid solution; adding a mixed solution of acetic acid and triethylamine to the polyamic acid solution for chemical imidization; then precipitating the synthesized polyimide solution in ethanol, washing with ethanol and filtering under reduced pressure; finally, removing the residual ethanol in the dianhydride-based polyimide in a vacuum oven overnight to obtain a dianhydride-based polyimide powder; dissolving the dianhydride-based polyimide powder synthesized in the previous step in a second organic solvent, stirring until completely dissolved, and continuing to stir for 12 to 24 hours, degassing the evenly mixed dipping solution for 5 to 20 minutes, and obtaining a dianhydride-based polyimide dipping solution with a mass fraction of 5 to 25wt%.

[0049] S20. Adding a counterweight at the end of the hollow carbon fiber substrate;

[0050] Since the hollow carbon fiber substrate is very light, it is easy to deform or float on the dipping solution during the coating process, resulting in uneven coating, which affects the separation performance of the carbon molecular sieve membrane. Therefore, a counterweight can be added to the end of the hollow carbon fiber substrate so that it can remain vertical in the dipping solution instead of floating on the dipping solution. The specific method of adding the counterweight is: wrap the end of the hollow carbon fiber substrate with a high-temperature resistant tape, and then wrap the epoxy resin AB glue on the outer surface of the high-temperature resistant tape, and then dry it. The effect of adding the counterweight can prevent the dipping solution from entering the inner surface of the hollow fiber substrate. Another method is to increase the weight of the hollow fiber substrate to keep it in a vertical state in the dipping solution, so that the hollow fiber substrate can be prevented from contacting the container wall during the coating process, and keeping it vertical can prevent the hollow fiber substrate from floating on the dipping solution, thereby causing uneven coating to affect the separation performance of the carbon molecular sieve membrane.

[0051] However, during the experiment, it was found that although adding weights can prevent the hollow fiber substrate from contacting the container wall and improve the uneven coating phenomenon to a certain extent, surface defects still exist and the experimental plan needs to be further optimized.

[0052] See also Figure 6 In a preferred embodiment, that is, step S30, a protective cover 2 is set between the dipping solution container 1 and the film pulling device 5 to reduce the influence of air humidity on the morphology of the carbon molecular sieve composite film. The protective cover 2 can be used as long as it can isolate the hollow carbon fiber substrate 4 from the air. The specific shape and material are not limited. In this application, in order to facilitate the observation of the coating process and pulling trajectory of the hollow carbon fiber substrate 4, the protective cover 2 is preferably a tubular glass cover. Please refer to the setting of the protective cover 2 Figure 6 Since the hollow carbon fiber substrate 4 needs to be immersed downward in the dipping solution, and it needs to be pulled up after dipping, in order to keep the whole process isolated from the outside air, an elastic telescopic tube 3 is also arranged between the protective cover 2 and the film pulling device 5. The elastic telescopic tube 3 is compressed when the hollow carbon fiber substrate 4 is downward, and stretched when it is pulled upward, so that it can meet the up and down strokes during the dipping process and keep the hollow carbon fiber substrate 4 isolated from the outside air. This method is particularly suitable for preparing small-sized support-based membranes, especially 280-300μm supports, and the prepared membrane has excellent surface morphology and excellent gas separation performance.

[0053] S40. Add the dianhydride-based polyimide dipping solution into the dipping solution container 1, connect the top of the hollow carbon fiber substrate 4 with the added weight to the pulling coating device 5 so that it can move up and down inside the dipping solution container 1 and the protective cover 2, keep the hollow carbon fiber substrate 4 with the added weight vertically and slowly immerse it in the dianhydride-based polyimide dipping solution, and after dipping for a predetermined time, slowly pull it up, and then dry the dipped hollow carbon fiber substrate 4 and remove the weight to obtain a polyimide / hollow carbon fiber composite membrane; as described above, in order to make the coating uniform, during the coating process, keep the hollow carbon fiber substrate 4 vertically and slowly immerse it in the dianhydride-based polyimide dipping solution, the immersion time is 30 to 90s, and the pulling-up rate after the immersion is 0.5 to 2cm / min.

[0054] For example, step S30. The specific steps for preparing a polyimide / hollow carbon fiber composite membrane are as follows: wrap the end of a hollow carbon fiber substrate 4 having a diameter of 280 to 300 μm and a length of 8 to 11 cm with a high-temperature resistant tape, and then wrap the epoxy resin AB glue on the outer surface of the high-temperature resistant tape, dry for 1 to 2 hours, and connect the top of the hollow carbon fiber substrate 4 to the pulling coating device 5; connect a tubular glass cover between the bottle mouth of the dipping solution container 1 and the pulling ring of the pulling coating device 5; keep the hollow carbon fiber substrate 4 vertical Slowly immerse it in the dipping solution for 30 to 90 seconds, and then pull it up at a rate of 0.5 to 2 cm / min; move the hollow carbon fiber substrate 4 after dipping to a vacuum oven for drying, dry it at 50 to 80°C for 8 to 12 hours, then heat it to 150 to 200°C, and dry it for 15 to 20 hours, then remove the counterweight at the end of the dried hollow carbon fiber substrate 4, that is, the high temperature resistant tape and the AB glue on its outer surface (usually cut off the counterweight), to obtain a polyimide / hollow carbon fiber composite membrane.

[0055] S50. Preparing a hollow fiber supported carbon molecular sieve composite membrane: subjecting the polyimide / hollow carbon fiber composite membrane to pyrolysis and carbonization treatment under a protective gas to obtain the hollow fiber supported carbon molecular sieve composite membrane.

[0056] Specifically, the polyimide / hollow carbon fiber composite membrane is placed in a tubular furnace for pyrolysis and carbonization. The carbonization conditions are controlled at 500 to 700°C, a heating rate of 5 to 15°C / min, insulation for 0 to 2h, and a protective gas flow rate of 200 to 500mL / min. After carbonization, a hollow fiber-supported carbon molecular sieve composite membrane is obtained.

[0057] In another specific embodiment of the present invention, a hollow fiber supported carbon molecular sieve composite membrane is prepared by the method for preparing a hollow fiber supported carbon molecular sieve composite membrane as described above.

[0058] It is worth noting that the process temperature and process time involved in the above-mentioned embodiments are all temperatures or times used in the experimental process. Those skilled in the art can make reasonable adjustments within the error range based on the process temperature and process time provided by the present invention, which should be included in the protection scope of the present invention.

[0059] The technical solution and technical effects of the present invention are further illustrated below through specific experimental examples.

[0060] 1. Main reagents

[0061] It should be noted that in the examples of the present invention, all reagents and solvents are commercially available and can be used without further purification.

[0062] 2. Preparation of hollow fiber supported carbon molecular sieve composite membrane

[0063] Synthesis of dianhydride-based polyimide: First, 6FDA and diamine monomers are sublimated and purified, then 6FDA and diamine are mixed at a molar ratio of 1.03:1 under anhydrous and N2 protection conditions, N-methylpyrrolidone is added to make the polyimide reach 20wt%, and then N-methylpyrrolidone is added to make the polyimide reach 10wt%, and stirring is continued to obtain a polyamic acid solution; a mixed solution of acetic acid and triethylamine is added to the polyamic acid solution for chemical imidization; then the synthesized polyimide solution is precipitated in ethanol, washed with ethanol and filtered under reduced pressure; finally, the dianhydride-based polyimide, that is, the residual ethanol in the 6FDA-based polyimide is removed in a vacuum oven at 100°C overnight to obtain a dianhydride-based polyimide powder, that is, a 6FDA-based polyimide powder, and the X-ray photoelectron energy spectrum is shown in Figure 1 .

[0064] Preparation of 6FDA-based polyimide dip-coating solution: dissolve the 6FDA-based polyimide powder synthesized in the previous step in N-methylpyrrolidone, stir until completely dissolved, continue stirring for 18±1h, degas the evenly mixed solution for 15±5min, and obtain a dianhydride-based polyimide dip-coating solution with a mass fraction of 17wt%, i.e., a 6FDA-based polyimide dip-coating solution.

[0065] Preparation of polyimide / hollow carbon fiber composite membrane:

[0066] Comparative Example: A hollow carbon fiber substrate with a diameter of 290 μm and a length of 10 cm (see the cross-sectional view) Figure 2 ) was connected to the pulling coating equipment, slowly immersed in the dipping solution for 50 seconds, and then pulled up at a rate of 1 cm / min; the hollow fiber after dipping was moved to a vacuum oven for drying at 70°C for 10 hours, then heated to 180°C and dried for 17 hours.

[0067] Experimental Example 1: A hollow carbon fiber substrate with a diameter of 290 μm and a length of 10 cm (see the cross-sectional view) Figure 2 ) Wrap the end with a high-temperature resistant tape, and then wrap the epoxy resin AB glue on the outer surface of the high-temperature resistant tape, and dry it for 1.5 hours to prevent the dipping solution from entering the interior of the hollow fiber and increase the weight of the fiber substrate to keep it vertical in the dipping solution. Connect the top of the hollow fiber substrate to the pulling coating equipment; keep the hollow fiber vertical, slowly immerse it in the dipping solution, immerse it for 50 seconds, and then pull it up at a rate of 1cm / min; move the dipped hollow fiber to a vacuum oven for drying, dry it at 70°C for 10 hours, then heat it to 180°C and dry it for 17 hours.

[0068] Experimental Example 2: Different from the comparative example, a tubular glass cover is connected between the mouth of the dipping liquid bottle and the lifting ring of the film-lifting coating equipment to prevent the influence of humidity in the air on the film morphology; the other steps are the same as those of the experimental example.

[0069] Preparation of hollow fiber supported carbon molecular sieve composite membrane: The dried polyimide / hollow carbon fiber composite membrane of the comparative example and experimental example 1 was placed in a tubular furnace for pyrolysis and carbonization. The carbonization conditions were controlled at 600°C, a heating rate of 10°C / min, insulation for 1h, and a N2 flow rate of 300mL / min.

[0070] It was found in the experiment that the hollow carbon fiber substrate of the comparative example floated on the dipping solution, and its surface could not be completely dipped into the coating solution. The obtained carbon molecular sieve composite membrane had serious surface defects and could not be put into use.

[0071] The electron microscope images of the carbon molecular sieve composite membranes obtained in the above-mentioned Experimental Examples 1 and 2 are as follows: Figure 3 to Figure 4 As shown, from Figure 3It can be seen that the surface of the carbon molecular sieve composite membrane prepared in Experimental Example 1 is uneven and has many small holes. This surface morphology will have an adverse effect on the gas separation performance of the carbon molecular sieve composite membrane.

[0072] from Figure 4 It can be seen that the carbon molecular sieve composite membrane prepared in Experimental Example 2 has a smooth surface and no obvious appearance defects, and is a qualified target product.

[0073] Experimental Example 3: The difference from Experimental Example 2 is that in the process of "preparing 6FDA-based polyimide dipping solution", dianhydride-based polyimide dipping solutions with mass fractions of 5wt%, 10wt%, 15wt%, 20wt%, and 25wt%, i.e., 6FDA-based polyimide dipping solution, are obtained; the other steps are the same as in Experimental Example 2.

[0074] 3. Performance characterization of hollow fiber supported carbon molecular sieve composite membrane

[0075] Gas separation performance test: Permeability and selectivity are two important indicators for evaluating membrane gas separation performance, respectively using permeability and separation factor (α ij ) to characterize. The gas separation performance test of the carbon molecular sieve hollow fiber membrane uses a gas permeameter to test the gas separation performance of all sample membrane materials using the pressure difference method in accordance with the national standard GB / T1083, and the permeability and separation factor are calculated using the following formula:

[0076]

[0077] Where i and j are different gases, α represents the separation factor, Q (cm 3 (STP)s -1 ) represents the volume flow rate of the gas at the outlet, l is the thickness of the membrane (cm), and A represents the membrane area (cm 2 ), ΔP (cmHg) represents the pressure difference of the gas on both sides of the membrane. 1GPU = 3.35 × 10 -10 mol m -2 s -1 Pa -1 .

[0078] The separation performance of the carbon molecular sieve composite membranes of Experimental Examples 2 and 3 (the carbon molecular sieve composite membranes are marked as M-1, M-2, M-3, M-4, M-5, and M-6 according to the concentration of the 6FDA-based polyimide dipping solution from small to large) was measured using a self-made constant-volume variable-pressure single-component gas separation test device. The high-purity single-component gases used in the experiment include He, H2, CO2, O2, N2, CH4, C3H6, and C3H8. The test conditions are: temperature 25°C, and the pressure difference on both sides of the membrane is 1 bar. The test results are shown in Tables 1 and 2.

[0079] Table 1

[0080]

[0081] Table 2

[0082]

[0083] See Table 1 and Figure 5 Compared with other membranes, M-3 and M-4 can not only separate common single-component gases, but also propylene (C3H6), propane (C3H8) and other gases, and can be used in the fields of petroleum and chemical industry. M-5 has a high separation coefficient for a variety of gases and can be widely used in the field of gas separation, especially in the field of natural gas helium extraction.

[0084] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a hollow fiber supported carbon molecular sieve composite membrane, characterized in that: The following steps are involved: S10. Prepare a dianhydride-based polyimide dip coating solution for standby use; S20. Adding a counterweight at the end of the hollow carbon fiber substrate; S30. A protective cover is provided between the dipping solution container port and the coating pulling device; S40. adding the dianhydride-based polyimide dipping solution into the dipping solution container, connecting the top of the hollow carbon fiber substrate with the added counterweight to the pulling coating device so that it can move up and down inside the dipping solution container and the protective cover, keeping the hollow carbon fiber substrate with the added counterweight vertically and slowly dipping it into the dianhydride-based polyimide dipping solution, and after dipping for a predetermined time, slowly pulling it up, and then drying the hollow carbon fiber substrate after dipping and removing the counterweight to obtain a polyimide / hollow carbon fiber composite membrane; S50. Preparing a hollow fiber supported carbon molecular sieve composite membrane: subjecting the polyimide / hollow carbon fiber composite membrane to pyrolysis and carbonization treatment under a protective gas to obtain the hollow fiber supported carbon molecular sieve composite membrane.

2. The preparation method according to claim 1, characterized in that: In step S20, the "adding a counterweight to the end of the hollow carbon fiber substrate" is specifically: wrapping the end of the hollow carbon fiber substrate with a high-temperature resistant tape, and then wrapping the epoxy resin AB glue on the outer surface of the high-temperature resistant tape, and drying.

3. The preparation method according to claim 1, characterized in that: In step S40, the predetermined dipping time is 30 to 90 seconds, and the rate of slowly pulling up is 0.5 to 2 cm / min.

4. The preparation method according to claim 1, characterized in that: In step S10, the "preparation of a dianhydride-based polyimide dip-coating solution" comprises the following steps: S11. The purified dianhydride and diamine after sublimation are added to a first organic solvent under anhydrous and protective gas to obtain a polyamic acid solution; S12. The polyamic acid solution is chemically imidized to obtain a polyimide solution; S13. The polyimide solution is precipitated in ethanol, then washed with ethanol and filtered, and then dried in vacuo to obtain the dianhydride-based polyimide powder; S14. dissolving the dianhydride-based polyimide powder in a second organic solvent, stirring until the mixture is uniform, and then degassing to obtain a dianhydride-based polyimide dip coating solution.

5. The preparation method according to claim 4, characterized in that: In step S11, the molar ratio of the dianhydride to the diamine is (1 to 1.05):

1.

6. The preparation method according to claim 5, characterized in that: In step S11, the dianhydride includes any one of hexafluorodianhydride, pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, monoether tetracarboxylic dianhydride and diether tetracarboxylic dianhydride; the diamine includes at least one of metaphenylenediamine, trimethyldiamine and 2,4,6-trimethylmetaphenylenediamine.

7. The preparation method according to claim 1, characterized in that: The first organic solvent and the second organic solvent respectively include any one of tetrahydrofuran, N-methylpyrrolidone, and nitrogen-dimethylacetamide.

8. The preparation method according to claim 1, characterized in that: In step S20, the mass fraction of the dianhydride-based polyimide dipping solution is 15 to 25 wt%.

9. The preparation method according to claim 1, characterized in that: In step S40, the pyrolysis carbonization treatment conditions are controlled to be 500 to 700°C, a heating rate of 5 to 15°C / min, a heat preservation time of 0 to 2h, and a protective gas flow rate of 200 to 500mL / min.

10. A hollow fiber supported carbon molecular sieve composite membrane, characterized in that: The method is prepared according to any one of claims 1 to 9.

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