A hollow fiber supported carbon molecular sieve composite membrane and a method for preparing the same

Abstract

The present application 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, which comprises the following steps: first, preparing a dianhydride-based polyimide dip-coating solution; then, adding a counterweight to the end of a hollow carbon fiber substrate, connecting the top end of the substrate with a pulling film coating device, slowly immersing the substrate vertically into the dianhydride-based polyimide dip-coating solution, setting a protective cover between the mouth of the dianhydride-based polyimide dip-coating solution container and the pulling film coating device, and then removing the counterweight after drying the dip-coated hollow carbon fiber substrate to obtain the hollow fiber supported carbon molecular sieve composite membrane. The dianhydride-based polyimide dip-coating solution is uniformly distributed on the surface of the hollow fiber substrate, the carbon molecular sieve composite membrane has a good appearance, and has excellent gas separation performance, thus having a wide application prospect in the field of gas separation.

Description

TECHNICAL FIELD

[0001] The present application 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. BACKGROUND

[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 a certain porosity. The carbon molecular sieve membrane thus formed can then be applied to the separation of various gases. Carbon molecular sieve membrane can adjust the pore size to achieve high selective separation of specific molecules, making it have higher efficiency and separation performance. The highly ordered pore structure of carbon molecular sieve membrane enables rapid diffusion of molecules inside it, showing high permeability, so that carbon molecular sieve membrane can realize a high-throughput separation process. 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, carbon molecular sieve membrane has a longer service life than other membrane materials.

[0003] The widely studied carbon molecular sieve membranes include self-supporting hollow fiber carbon molecular sieve membranes and supported carbon molecular sieve composite membranes. The self-supporting hollow fiber carbon molecular sieve membrane has the advantages of light weight, high surface-to-volume ratio, and compact equipment, and is the most promising carbon molecular sieve membrane for industrial application. However, the membrane obtained by high-temperature (>700℃) and long-time (holding time >1h) carbonization is brittle, which is not conducive to long-term cyclic use. The supported carbon molecular sieve composite membrane is prepared by coating a precursor material on a tubular ceramic support body and has good mechanical properties, which can be used for long-term cyclic use. However, the support body 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-to-volume ratio of the self-supporting hollow fiber carbon molecular sieve membrane, but also has the characteristics of good mechanical properties of the supported carbon molecular sieve composite membrane. However, in the actual preparation process, when the film-forming raw material is coated on the hollow carbon fiber substrate according to the existing technology, uneven coating occurs, which affects the separation performance of the carbon molecular sieve membrane. SUMMARY

[0005] Therefore, the present application provides a hollow fiber supported carbon molecular sieve composite membrane and a preparation method thereof to solve the technical problem that the film-forming raw material is unevenly coated on the hollow carbon fiber substrate in the prior art, thereby affecting the separation performance of the carbon molecular sieve membrane.

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

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

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

[0009] S20. Adding a weight to the end of a hollow carbon fiber substrate;

[0010] S30. Setting a protective cover between the mouth of a dip-coating solution container and a pulling-coating device;

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

[0012] S50. Preparing a hollow fiber supported carbon molecular sieve composite membrane: pyrolytic carbonization treatment of the polyimide / hollow carbon fiber composite membrane 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 weight to the end of a hollow carbon fiber substrate" specifically refers to wrapping the end of the hollow carbon fiber substrate with a high-temperature-resistant adhesive tape, and then wrapping the outer surface of the high-temperature-resistant adhesive tape with epoxy AB glue, and drying.

[0014] Preferably, in the above preparation method, in step S40, the predetermined time of immersion is 30 to 90 s, 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. Adding sublimation-purified dianhydride and diamine into a first organic solvent under anhydrous and protective gas to obtain a polyamic acid solution;

[0017] S12. Chemically imidizing the polyamic acid solution to obtain a polyimide solution;

[0018] S13. Precipitating the polyimide solution in ethanol, then washing and filtering with ethanol, and vacuum drying to obtain the dianhydride-based polyimide powder;

[0019] S14. Dissolving the dianhydride-based polyimide powder in a second organic solvent, stirring until mixed evenly, and then defoaming treatment to obtain a dianhydride-based polyimide dip coating solution.

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

[0021] Preferably, in the above preparation method, in step S11, the dianhydride includes any one of hexafluorodiphthalic anhydride, pyromellitic dianhydride, biphenyl tetracarboxylic dianhydride, monoether tetracarboxylic dianhydride and bisether tetracarboxylic dianhydride; and the diamine includes at least one of m-phenylenediamine, trimethyl diamine and 2,4,6-trimethyl-m-phenylenediamine.

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

[0023] Preferably, in the above preparation method, in step S20, the mass fraction of the dianhydride-based polyimide dip coating 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℃, a temperature rising rate of 5 to 15℃ / min, a holding 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 the above preparation method.

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

[0027] The hollow fiber supported carbon molecular sieve composite membrane (hereinafter referred to as carbon molecular sieve composite membrane) of the present application is prepared by first preparing a dianhydride-based polyimide dip-coating solution (hereinafter referred to as dip-coating solution), then adding a weight to the end of a hollow carbon fiber substrate, connecting the top end of the hollow carbon fiber substrate to a pulling coating device, slowly immersing the hollow carbon fiber substrate vertically into the dianhydride-based polyimide dip-coating solution, while setting a protective cover between the mouth of the dianhydride-based polyimide dip-coating solution container and the pulling coating device, then drying the dip-coated hollow carbon fiber substrate and removing the weight to obtain a polyimide / hollow carbon fiber composite membrane. The weight added to the end of the hollow fiber substrate can prevent the dip-coating solution from entering the interior of the hollow fiber substrate, and can also increase the weight of the hollow fiber substrate to keep it in a vertical state in the dip-coating solution, thereby preventing deformation of the hollow fiber substrate during coating and keeping it vertical to avoid floating on the dip-coating solution and causing uneven coating and affecting the separation performance of the carbon molecular sieve membrane. The protective cover can isolate the hollow carbon fiber substrate from the air to further prevent uneven coating. In particular, the method is suitable for preparing membranes with small-sized supports, especially supports with a size of 280-300 μm, and the prepared membranes have excellent surface morphology and gas separation performance, and have a wide application prospect in the field of gas separation.

[0028] The hollow fiber supported carbon molecular sieve composite membrane of the present application has a uniform distribution of dianhydride-based polyimide dip-coating solution on the surface of the hollow fiber substrate, a good morphology of the carbon molecular sieve composite membrane, excellent gas separation performance, and a wide application prospect in the field of gas separation. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 X-ray photoelectron spectrogram of 6FDA-based polyimide powder.

[0030] Figure 2 Electron microscope graph of the cross-sectional view of the hollow fiber substrate.

[0031] Figure 3 Electron microscope graph of the hollow fiber supported carbon molecular sieve composite membrane in Experimental Example 1.

[0032] Figure 4 Electron microscope graph of the hollow fiber supported carbon molecular sieve composite membrane in Experimental Example 2.

[0033] Figure 5 Graph of the permeation rate and ideal selectivity of the hollow fiber supported carbon molecular sieve composite membrane in Experimental Example 2 and Experimental Example 3.

[0034] Figure 6 Schematic diagram of the installation of the protective cover.

[0035] In the figure: dip-coating solution container 1, protective cover 2, elastic expansion tube 3, hollow carbon fiber substrate 4, pulling coating device 5. DETAILED DESCRIPTION

[0036] It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict. The technical solutions of the present application will be further described below in conjunction with the drawings of the embodiments of the present application. The present application is not limited to the following specific embodiments.

[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;

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

[0040] S11. Sublimate the dianhydride and the diamine after purification, and add them into a first organic solvent under anhydrous and protective gas to obtain a polyamic acid solution;

[0041] S12. Perform chemical imidization on the polyamic acid solution to obtain a polyimide solution;

[0042] S13. Precipitate the polyimide solution in ethanol, then wash and filter it with ethanol, and vacuum dry it to obtain the dianhydride-based polyimide powder;

[0043] S14. Dissolve the dianhydride-based polyimide powder in a second organic solvent, stir until mixed uniformly, and then perform defoaming treatment to obtain a dianhydride-based polyimide dip coating solution.

[0044] Diacetic anhydride is an organic compound that is an anhydride of two acetyl groups. Diacetic anhydride is an important intermediate in organic synthesis, often used to synthesize other compounds, and can be used as an acylating agent in organic synthesis, for acylation and esterification reactions. As preferred, the diacetic anhydride includes any one of hexafluorodiacid anhydride, pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, monoether tetracarboxylic dianhydride and bisether tetracarboxylic dianhydride. Among them, hexafluorodiacid anhydride (i.e. 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 6FDA) is one of the most widely used diacid monomers, and is also the largest amount of diacid monomer used in the current colorless transparent polyimide, so the hexafluorodiacid anhydride (6FDA) is preferred in the present application. The diamine includes at least one of m-phenylenediamine, trimethyl diamine, 2,4,6-trimethyl-m-phenylenediamine. The first organic solvent and the second organic solvent include any one of tetrahydrofuran, N-methyl pyrrolidone, N,N-dimethylacetamide. Among them, N-methyl pyrrolidone is a polar solvent with high selectivity and good stability, which has the advantages of low toxicity, high boiling point, strong solubility, non-flammability, biodegradability, recyclability, safety in use and suitability for various formulations, etc. Therefore, the first organic solvent and the first organic solution are preferably N-methyl pyrrolidone in the present application. The protective gas is one or more of nitrogen, argon and helium.

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

[0046] Since the carbon molecular sieve composite membranes prepared by different mass fractions of diacid-based polyimide dip coating solution have different permeation rates for different gas separation, in a more preferred embodiment, the mass fraction of the diacid-based polyimide dip coating solution is 5 to 25 wt%, and further, the mass fraction of the diacid-based polyimide dip coating solution is 15 to 25 wt%.

[0047] The "chemical imidization of the polyamic acid solution" specifically refers to adding a mixed solution of acetic acid and triethylamine to the polyamic acid solution for chemical imidization.

[0048] For example, the "preparation of dianhydride-based polyimide dip coating solution" is specifically as follows: first, sublimation purification of dianhydride and diamine two monomers, then under the conditions of anhydrous and protective gas, mixing dianhydride and diamine in a molar ratio of (1 to 1.05):1, adding a certain amount of the first organic solvent to make the polyimide reach 10wt%, 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 performing vacuum filtration; finally, removing the residual ethanol in the dianhydride-based polyimide in the vacuum oven overnight to obtain dianhydride-based polyimide powder; dissolving the dianhydride-based polyimide powder synthesized in the above step in the second organic solvent, stirring until completely dissolved, then continuing to stir for 12 to 24 hours, and degassing the uniformly mixed dip coating solution for 5 to 20 minutes to obtain a dianhydride-based polyimide dip coating solution with a mass fraction of 5 to 25wt%.

[0049] S20. Adding weights to the ends of the hollow carbon fiber substrate;

[0050] Due to the very light weight of the hollow carbon fiber substrate, deformation or floating on the dip coating solution may occur during the coating process, resulting in uneven coating and affecting the separation performance of the carbon molecular sieve membrane. Therefore, the method of adding weights to the ends of the hollow carbon fiber substrate can be used to keep it vertical in the dip coating solution instead of floating on the dip coating solution. The specific method of adding weights is to wrap the ends of the hollow carbon fiber substrate with a high-temperature-resistant tape, and then wrap the outer surface of the high-temperature-resistant tape with epoxy AB glue, and dry it. The effect of adding weights is to prevent the dip coating solution from entering the inner surface of the hollow fiber substrate, and to increase the weight of the hollow fiber substrate to keep it vertical in the dip coating solution. This can prevent the hollow fiber substrate from contacting the container wall during the coating process, and keeping it vertical can avoid the hollow fiber substrate floating on the dip coating solution, thereby causing uneven coating and affecting the separation performance of the carbon molecular sieve membrane.

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

[0052] Please refer to Figure 6 In a preferred embodiment, that is, step S30. A protective cover 2 is arranged between the dip coating solution container 1 and the pull-coating device 5 to reduce the influence of air humidity on the morphology of the carbon molecular sieve composite membrane. The protective cover 2 only needs to isolate the hollow carbon fiber substrate 4 from the air, and the specific shape and material are not limited. In this application, in order to facilitate the observation of the coating process and the pulling track of the hollow carbon fiber substrate 4, the protective cover 2 is preferably a tubular glass cover. The arrangement of the protective cover 2 is shown inFigure 6 In order to keep the whole process from the immersion to the pulling-up process from the outside air, an elastic telescopic tube 3 is arranged between the protective cover 2 and the pulling-up coating device 5, which is compressed when the hollow carbon fiber substrate 4 is immersed and stretched when the hollow carbon fiber substrate 4 is pulled up, so that the up-and-down movement in the immersion process can be met and the hollow carbon fiber substrate 4 can be kept from the outside air. This method is especially suitable for the preparation of small size support film, especially the support of 280-300 μm, and the prepared film has excellent surface morphology and gas separation performance.

[0053] S40. The dianhydride-based polyimide immersion solution is added to the immersion solution container 1, the top end of the hollow carbon fiber substrate 4 with added weight is connected to the pulling-up coating device 5, which can move up and down inside the immersion solution container 1 and the protective cover 2, the hollow carbon fiber substrate 4 with added weight is slowly immersed in the dianhydride-based polyimide immersion solution vertically, after a predetermined time of immersion, the hollow carbon fiber substrate 4 after immersion is slowly pulled up, then the weight is removed after drying, and a polyimide / hollow carbon fiber composite membrane is obtained. In order to make the coating uniform, the hollow carbon fiber substrate 4 is slowly immersed in the dianhydride-based polyimide immersion solution vertically during the coating process, the immersion time is 30-90 s, and the pulling-up rate after immersion is 0.5-2 cm / min.

[0054] For example, the step S30. The preparation of polyimide / hollow carbon fiber composite membrane is specifically as follows: the end of the hollow carbon fiber substrate 4 with a diameter of 280-300 μm and a length of 8-11 cm is wrapped with a high-temperature resistant tape, then the epoxy resin AB glue is wrapped on the outer surface of the high-temperature resistant tape, and dried for 1-2 h, then the top end of the hollow carbon fiber substrate 4 is connected to the pulling-up coating device 5; a tubular glass cover is connected between the bottle opening of the immersion solution container 1 and the pulling-up ring of the pulling-up coating device 5; the hollow carbon fiber substrate 4 is slowly immersed in the immersion solution vertically, and the immersion time is 30-90 s, then the pulling-up rate is 0.5-2 cm / min; the hollow carbon fiber substrate 4 after immersion is moved to a vacuum oven for drying, dried at 50-80 °C for 8-12 h, then heated to 150-200 °C, and dried for 15-20 h, then the weight at the end of the dried hollow carbon fiber substrate 4, that is, the high-temperature resistant tape and the AB glue on the outer surface thereof, is removed (usually by cutting off the weight), and a polyimide / hollow carbon fiber composite membrane is obtained.

[0055] S50. Preparation of hollow fiber supported carbon molecular sieve composite membrane: the polyimide / hollow carbon fiber composite membrane is pyrolyzed and carbonized 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 pyrolyzed and carbonized in a tube furnace, and the carbonization conditions are controlled as follows: 500 to 700 ℃, 5 to 15 ℃ / min heating rate, 0 to 2 h holding time, and 200 to 500 mL / min flow rate of protective gas. After carbonization, a hollow fiber supported carbon molecular sieve composite membrane is obtained.

[0057] In still another specific embodiment of the present application, 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 should be noted that in the above embodiments, the process temperature and process time are a temperature or a time used in the experiment. Those skilled in the art can make reasonable adjustments within the error range on the basis of the process temperature and process time provided by the present application, which should be included in the protection scope of the present application.

[0059] The technical solutions and technical effects of the present application are further illustrated by specific experimental examples below.

[0060] 1. Main reagents

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

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

[0063] Synthesis of dianhydride-based polyimide: first, sublimate and purify the two monomers of 6FDA and diamine, then mix 6FDA and diamine in a molar ratio of 1.03:1 under anhydrous and N2 protection conditions, add N-methyl pyrrolidone to make the amount of polyimide reach 20 wt%, then add N-methyl pyrrolidone to make the amount of polyimide reach 10 wt%, continue to stir to obtain a polyamide acid solution; add a mixed solution of acetic acid and triethylamine to the polyamide acid solution for chemical imidization; then precipitate the synthesized polyimide solution in ethanol, wash with ethanol and perform reduced pressure filtration; finally, remove the residual ethanol in the dianhydride-based polyimide, i.e., 6FDA-based polyimide, in a 100 ℃ vacuum oven overnight to obtain dianhydride-based polyimide powder, i.e., 6FDA-based polyimide powder, and the X-ray photoelectron spectrogram is shown in Figure 1 .

[0064] Preparation of 6FDA-based polyimide dip coating solution: The 6FDA-based polyimide powder synthesized in the above step was dissolved in N-methyl pyrrolidone. After stirring until completely dissolved, the mixture was continuously stirred for 18±1 h. The uniformly mixed solution was degassed for 15±5 min to obtain a 17 wt% dianhydride-based polyimide dip coating solution, i.e., a 6FDA-based polyimide dip coating solution.

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

[0066] Comparative Example: Hollow carbon fiber substrates (cross-sectional view shown in FIG. 1) with a diameter of 290 μm and a length of 10 cm were connected to a pull-coating device, slowly immersed in the dip coating solution, immersed for 50 s, and then pulled up at a rate of 1 cm / min. The dipped hollow fibers were moved to a vacuum oven for drying, dried at 70°C for 10 h, and then heated to 180°C for drying for 17 h. Figure 2

[0067] Experimental Example 1: Hollow carbon fiber substrates (cross-sectional view shown in FIG. 1) with a diameter of 290 μm and a length of 10 cm were wrapped with high-temperature-resistant adhesive tape at the end, and then an epoxy AB glue was wrapped on the outer surface of the high-temperature-resistant adhesive tape and dried for 1.5 h to prevent the dip coating solution from entering the hollow fiber and to increase the weight of the fiber substrate to maintain the vertical state in the dip coating solution. The top end of the hollow fiber substrate was connected to a pull-coating device. The hollow fiber was kept vertical, slowly immersed in the dip coating solution, immersed for 50 s, and then pulled up at a rate of 1 cm / min. The dipped hollow fibers were moved to a vacuum oven for drying, dried at 70°C for 10 h, and then heated to 180°C for drying for 17 h. Figure 2

[0068] Experimental Example 2: Different from the comparative example, a tubular glass cover was connected between the bottle opening of the dip coating solution and the pull-coating device to prevent the influence of humidity in the air on the film morphology. The other steps were the same as those of Experimental Example 1.

[0069] Preparation of hollow fiber-supported carbon molecular sieve composite membrane: The dried polyimide / hollow carbon fiber composite membranes of the comparative example and Experimental Example 1 were pyrolyzed and carbonized in a tube furnace. The carbonization conditions were controlled at 600°C, a heating rate of 10°C / min, a holding time of 1 h, and a N2 flow rate of 300 mL / min.

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

[0071] The electron microscope images of the carbon molecular sieve composite membranes prepared in Experimental Example 1 and Experimental Example 2 are shown in FIG. 2. Figures 3 to 4 Figure 3 ​​​It can be seen that the carbon molecular sieve composite membrane prepared in Experimental Example One has uneven surface and many small holes, which will have adverse effects 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 Two has smooth surface and no obvious appearance defects, which is the target product.

[0073] Experimental Example Three: Different from Experimental Example Two, in the process of "preparing 6FDA-based polyimide dip coating solution", 6FDA-based polyimide dip coating solutions with mass fractions of 5wt%, 10wt%, 15wt%, 20wt%, and 25wt% of dianhydride-based polyimide dip coating solution are obtained; other steps are the same as those in Experimental Example Two.

[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 the gas separation performance of the membrane, and are respectively characterized by permeability and separation factor (α ij ). The gas separation performance test of the carbon molecular sieve hollow fiber membrane uses a gas permeation instrument to test the gas separation performance of all sample membrane materials by pressure difference method according to the national standard GB / T1083, and the permeability and separation factor are calculated by using the following formula:

[0076]

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

[0078] The self-made constant volume variable pressure single-component gas separation test device was used to determine the separation performance of the carbon molecular sieve composite membranes of Experimental Example Two and Experimental Example Three (the carbon molecular sieve composite membranes are respectively marked as M-1, M-2, M-3, M-4, M-5, and M-6 according to the concentration of the 6FDA-based polyimide dip coating solution from small to large). 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℃, 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 M-3 and M-4 can separate not only common single-component gases but also propylene (C3H6) and propane (C3H8) and can be used in the petroleum and chemical industries. M-5 has high separation coefficients for various 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 enable those of ordinary skill in the art to understand and use the invention. Those skilled in the art can easily make various modifications to the embodiments and apply the general principles described herein to other embodiments without creative effort, which should not be considered departing from the scope of the invention. Therefore, the 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 invention without departing from the scope of the invention should be within the scope of protection of the invention.

Claims

1. A method for producing a hollow-fiber-supported carbon molecular sieve composite membrane, characterized by, The method comprises the following steps: S10. Preparing a dianhydride-based polyimide dip-coating solution; S20. Adding weights to the ends of the hollow carbon fiber substrate; S30. Setting a protective cover between the mouth of the dip-coating solution container and the pull-coating device; S40. Adding the dianhydride-based polyimide dip-coating solution into the dip-coating solution container, connecting the top end of the hollow carbon fiber substrate with the added weights to the pull-coating device so that it can move up and down inside the dip-coating solution container and the protective cover, slowly immersing the hollow carbon fiber substrate with the added weights vertically into the dianhydride-based polyimide dip-coating solution, slowly pulling up after a predetermined time of dip-coating, and then removing the weights after drying the dip-coated hollow carbon fiber substrate to obtain a polyimide / hollow carbon fiber composite membrane; S50. Preparing a hollow fiber supported carbon molecular sieve composite membrane: pyrolytic carbonization treatment of the polyimide / hollow carbon fiber composite membrane under a protective gas to obtain the hollow fiber supported carbon molecular sieve composite membrane.

2. The production method according to claim 1, characterized by, In step S20, the "adding weights to the ends of the hollow carbon fiber substrate" specifically comprises: wrapping the ends of the hollow carbon fiber substrate with a high-temperature-resistant adhesive tape, and then wrapping epoxy AB glue on the outer surface of the high-temperature-resistant adhesive tape and drying.

3. The production method according to claim 1, characterized by, In step S40, the predetermined time of dip-coating is 30 to 90 s, and the rate of slow pulling up is 0.5 to 2 cm / min.

4. The method of claim 1, wherein, In step S10, the "preparing a dianhydride-based polyimide dip-coating solution" comprises the following steps: S11. Adding sublimation-purified dianhydride and diamine into a first organic solvent under anhydrous and protective gas to obtain a polyamic acid solution; S12. Chemically imidizing the polyamic acid solution to obtain a polyimide solution; S13. Precipitating the polyimide solution in ethanol, then washing and filtering with ethanol, and vacuum drying to obtain the dianhydride-based polyimide powder; S14. Dissolving the dianhydride-based polyimide powder in a second organic solvent, stirring until uniformly mixed, 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 amount-of-substance ratio of the dianhydride to the diamine is (1 to 1.05):

1.

6. The production method according to claim 5, wherein In step S11, the dianhydride includes any one of hexafluorodiphthalic anhydride, pyromellitic dianhydride, biphenyl tetracarboxylic dianhydride, mono-ether tetra-carboxylic dianhydride, and bis-ether tetra-carboxylic dianhydride; and the diamine includes at least one of m-phenylenediamine, trimethyl diamine, and 2,4,6-trimethyl-m-phenylenediamine.

7. The preparation method according to claim 4, characterized in that, The first organic solvent and the second organic solvent each include any one of tetrahydrofuran, N-methyl pyrrolidone, and N,N-dimethylacetamide.

8. The production method according to claim 1, characterized by, In step S20, the mass fraction of the dianhydride-based polyimide dip-coating solution is 15 to 25 wt%.

9. The production method according to claim 1, characterized by, In step S40, the pyrolytic carbonization treatment conditions are controlled to be 500 to 700 ℃, a temperature rising rate of 5 to 15 ℃ / min, a holding time of 0 to 2 h, and a protective gas flow rate of 200 to 500 mL / min.

Images