Polyimide gas separation membrane, method for preparing the same, and use thereof

Abstract

The application discloses a kind of polyimide gas separation membrane and its preparation method and application, belong to gas separation membrane technical field.The polyimide gas separation membrane includes base film and separation layer, the base film is the blending film of polyimide and polymer additive;The separation layer is composed of polyimide, after dissolving polyimide as separation layer material, it is evenly coated on polyimide base film, volatilizes part of solvent, immerses in water and separates phase, again by high-temperature water wash, the polymer additive in bottom film and the solvent of coating liquid are removed, i.e., the polyimide composite membrane of the present application can be obtained.The preparation method of the polyimide composite membrane of the present application is low in cost, and can be used for the separation of oxygen and nitrogen, hydrogen separation, CO2 and CH4 separation, natural gas helium extraction and gas dehumidification and other gas membrane separation processes, and has wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of separation membrane, and particularly relates to a polyimide gas separation membrane and a preparation method and application thereof. BACKGROUND

[0002] In 1979, the Prism membrane of Monsanto Company was applied to the recovery of hydrogen in synthetic ammonia, which began the industrial application of gas separation membrane. At present, the membrane materials for hydrogen recovery mainly include cellulose acetate, polysulfone, polyimide and polyaramid, among which polyimide is the most, which is related to the excellent properties of polyimide material itself. For example, polyimide has high thermal stability, high mechanical properties, excellent solvent resistance and chemical stability, excellent film-forming property and structural diversity.

[0003] The gas separation membranes actually applied are all asymmetric membranes, which are composed of a thin dense separation layer and a much thicker porous layer. The polyimide material must also be converted into the form of asymmetric membrane to have practical application value.

[0004] One method is to prepare by immersion gel phase inversion method, which is relatively simple, is a commonly used membrane preparation method, and is suitable for the case where the material cost is not high. This kind of membrane is also called integrated asymmetric membrane. Compared with the composite membrane, the phase inversion membrane has two characteristics: the skin layer and the support layer are the same material; the skin layer and the support layer are prepared and formed at the same time.

[0005] Another method is to prepare composite membranes by coating or double-layer spinning, which is suitable for materials that are expensive or limited by the material itself, and cannot be prepared into asymmetric membranes by the immersion gel phase inversion method. The polyimide materials with excellent performance and suitable for gas separation, especially the soluble materials, are often expensive and not suitable for the immersion gel phase inversion method. US 5,085,676A discloses a co-extrusion method for preparing double-layer asymmetric hollow fiber membranes using a three-channel nozzle, which is a novel composite membrane preparation technology. The advantage is that the support layer and the functional layer are prepared in one step, reducing the membrane preparation steps. However, there are some difficulties that cannot be overcome at present, one is the delamination problem between the two layers of the membrane, which destroys the integrity of the membrane and affects the operating pressure of the membrane; the second is the mass transfer resistance problem of the two layers of the membrane, which affects the improvement of the membrane flux. These limit the practical application of the co-extrusion method, and there is no industrial product using this preparation method at present. The traditional composite membrane preparation methods such as coating and interfacial polymerization are multi-step processes, and the support layer and the functional layer are prepared separately. Usually, a porous support layer is first prepared, and then a super-thin skin layer (i.e. separation layer) is prepared on the porous support layer (i.e. base membrane or bottom membrane) by various methods. The current problem of this method applied to polyimide membranes is that the solvent of the solution used for coating is often also the solvent of the base membrane, and the solvent will seriously damage the structure of the base membrane and the integrity of the base membrane skin layer during the coating process, resulting in that the polyimide asymmetric membrane with complete morphology and excellent performance cannot be obtained by coating method. SUMMARY

[0006] In view of the above problems in the preparation process of the existing polyimide gas separation membrane that the solvent seriously damages the base membrane and the polyimide asymmetric membrane with complete morphology and excellent performance cannot be obtained by the coating method, the purpose of the present application is to provide a method for preparing a polyimide gas separation membrane by coating, which can avoid the serious damage of the solvent to the base membrane, and at the same time, the base membrane and the separation layer are firmly combined, and the gas permeability and selectivity are very excellent.

[0007] To achieve the above purpose, the present application provides the following technical solutions:

[0008] A preparation method of a polyimide gas separation membrane, mainly comprising the following steps:

[0009] (1) Base membrane preparation: Dissolve polyimide A particles or powders as base membrane materials and high molecular additives in an organic solvent to prepare a casting solution with a polyimide A content of 5-30 wt.%, and after degassing, a blended base membrane of polyimide A and high molecular additives is prepared;

[0010] (2) Separation layer solution preparation: Dissolve polyimide B particles or powders as separation layer materials in an organic solvent to prepare a coating solution with a polyimide B content of 0.5-15 wt.%, and degas for standby;

[0011] (3) Composite membrane preparation: The coating liquid obtained in step (2) is coated on the base film obtained in step (1), and is left to dry at room temperature for 1-100 s, and is rinsed in deionized water at a temperature of 0-40℃ for 1-20 min; is soaked in deionized water at 50-100℃ for 1-24 h, to remove the high molecular additive in step (1) and the solvent in step (2), and is dried at 50-120℃ for 5-60 min, to obtain a polyimide gas separation membrane.

[0012] Based on the above technical solution, further, the polyimide A in step (1) is a high molecular material containing an imide ring in the structure, which is soluble in N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO) and the like.

[0013] Based on the above technical solution, further, the polyimide A in step (1) includes P84 and PEI.

[0014] Based on the above technical solution, further, the high molecular additive in step (1) is a water-soluble polymer with a molecular weight of 10000-200000, including but not limited to one or a combination of two or more of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), polyvinyl alcohol (PVA), and the like, and the addition amount is 1 / 6 to 1 / 1 of the mass of the polyimide A, preferably 1 / 3 to 5 / 6.

[0015] Based on the above technical solution, further, the organic solvent in step (1) is one or a mixture of two or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO).

[0016] Based on the above technical solution, further, the form of the blended base film in step (1) is a flat plate type or a hollow fiber type.

[0017] Based on the above technical solution, further, the preparation method of the blended base film in step (1) includes a gel immersion phase inversion method and a dry-wet spinning method.

[0018] Based on the above technical solution, further, the polyimide B in step (2) is a high molecular material containing an imide ring in the structure, which is soluble in N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO) and the like.

[0019] Based on the above technical scheme, further, the organic solvent in step (2) is one or more than two mixed solution of N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N-methyl pyrrolidone (NMP), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO).

[0020] Based on the above technical scheme, further, the polyimide B in step (2) includes Matrimid-5218, P84, Ultem-1000.

[0021] Based on the above technical scheme, further, in step (3), the soaking temperature is 70-99℃, the soaking time is 2-12h, the drying temperature is 70-99℃, and the drying time is 10-40min.

[0022] Another aspect of the present application provides a polyimide gas separation membrane prepared by the above preparation method.

[0023] Based on the above technical scheme, further, the polyimide gas separation membrane includes a base film and a separation layer, and the thickness of the separation layer is 0.01-2μm.

[0024] The present application also provides the application of the above polyimide gas separation membrane in gas separation and recovery.

[0025] Based on the above technical scheme, further, the application is specifically the separation and recovery of hydrogen, oxygen and nitrogen from hydrogen-containing mixed gas, the separation of CO2 and CH4, the extraction of helium from natural gas or the gas dehumidification.

[0026] Compared with the prior art, the present application has the following advantages:

[0027] 1. The present application overcomes the damage of the solvent of the coating solution to the base film which is also a polyimide material during the preparation of the polyimide composite membrane by the traditional dip coating method, and the traditional coating method can be used to prepare a polyimide composite membrane with high gas permeability and high selectivity.

[0028] 2. The preparation method of the polyimide composite membrane of the present application is low in cost and easy to control, and can be used in the process of gas separation and recovery, and has a wide application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present application, the drawings involved in the embodiments will be briefly introduced as follows.

[0030] Figure 1 The test device for the gas separation membrane. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0032] The permeation and separation performance of the gas separation membrane prepared in the embodiments of the present invention are characterized by the permeation rate J of pure gas and the separation coefficient α.

[0033] Test equipment such as Figure 1 As shown, gas cylinder 1 is connected to membrane evaluation tank 5 through pressure reducing valve 2. Pressure gauge 3 is also installed between pressure reducing valve 2 and membrane evaluation tank. Pressure gauge 4 is installed at the end of membrane evaluation tank 5 and then connected to soap bubble flow meter 7 through pipeline. Membrane evaluation tank 5 is also equipped with temperature control system 6. Membrane evaluation tank 5 contains test components or membranes.

[0034] The hollow fiber membrane testing assembly is constructed as follows: Take the hollow fiber membrane to be tested, approximately 150mm in length, bundle 10 strands together, cast the open end with epoxy resin onto an aluminum end cap, and seal the other end with epoxy resin. For example... Figure 1 As shown, the test assembly was fixed in a stainless steel membrane tank. The feed gas flowed out through the membrane, and the volumetric flow rate of the gas was measured using a soap bubble flow meter. The permeate-side pressure was maintained at atmospheric pressure, and the temperature of the test system was 35°C.

[0035] Before the experiment, the test system needs to be stabilized under the selected conditions for at least 2 hours before use. The gas flow rate is measured by a soap bubble flow meter, and the permeation rate (J) is calculated using Equation 1:

[0036]

[0037] In the formula:

[0038] V—Permeate gas flux under test conditions (cm³) 3 ),

[0039] A—Effective membrane area (cm²) 2 ),

[0040] Δp — membrane pressure difference (cm Hg)

[0041] T0,p0—Temperature (K) and pressure (cmHg) under the test conditions.

[0042] The ideal selectivity coefficient α of the membrane i / j Defined as the ratio of the permeation rates Ji and Jj of the two gases:

[0043]

[0044] Wherein, the subscripts i, j represent two different gases, respectively.

[0045] The raw material information involved in the following examples:

[0046] Polyetherimide (PEI): purchased from Sabic, model Ultem-1000; Polyimide (PI): Matrimid 5218 purchased from Huntsmann Corporation, P84 purchased from HP Polymer Corporation; PEG, PVP, analytical pure, Sigma; THF, DMF, DMAc analytical pure, Tianjin Kemio.

[0047] Comparative Example 1

[0048] This comparative example provides a polyimide gas separation membrane, which is prepared by the following steps:

[0049] (1) P84 is dissolved in DMF to form a mixed solution with a concentration of 20 wt.%, heated and stirred at 70°C. After vacuum degassing, dry-wet spinning process is used. The spinning solution is extruded from the nozzle, using a mixture of water and DMF (DMF / H2O=90 / 10) as the core solution. The nascent hollow fiber membrane passes through a 30mm air layer and enters a pure water gel bath. After being collected by a spinning reel, the residual solvent is removed in a water tank. After 2 days, it is taken out and ready for use.

[0050] (2) Separation layer solution preparation: Matrimid 5218 powder as the separation layer material is dissolved in a mixed solvent of THF and DMF (THF / DMF=1 / 1) to prepare a coating solution with a solid content of 5.0 wt.%, and degassed for use.

[0051] (3) Composite membrane preparation: The solution obtained in step (2) is coated on the base membrane obtained in step (1), and dried at room temperature for 10s and dried at 90°C for 30min to obtain a polyimide composite membrane.

[0052] In the process of preparing the polyimide composite membrane by the above method, it was found that when step (3) was performed, the polyimide base membrane of step (1) collapsed rapidly when it contacted the solution of step (2), and could not maintain its original shape, so that subsequent testing and evaluation could not be performed.

[0053] Comparative Example 2

[0054] This comparative example provides a polyimide gas separation membrane, which is prepared by the following steps:

[0055] (1) P84, PVP-k30 were dissolved in DMF, P84 concentration was 20 wt.%, PVP / P84 = 0.6, heated and stirred at 70°C to form a mixed solution, after vacuum degassing, dry-wet spinning process was used to spin. The spinning solution was extruded from the nozzle, using a mixture of water and DMF (DMF / H2O = 90 / 10) as the core solution, the nascent hollow fiber membrane passed through a 30 mm air layer and then entered a pure water gel bath. After collection with a spinning reel, residual solvents were removed in a water tank, and after 2 days, it was taken out and ready for use.

[0056] (2) Separation layer solution preparation: Matrimid5218 powder as the separation layer material was dissolved in a mixed solvent of THF and DMF (THF / DMF = 1 / 1) to prepare a coating solution with a solid content of 5.0 wt.%, and was degassed for standby.

[0057] (3) Composite membrane preparation: The solution obtained in step (2) was coated on the base membrane obtained in step (1), and was dried at room temperature for 10 s and dried at 90°C for 30 min to obtain a polyimide composite membrane.

[0058] During the preparation of the polyimide composite membrane by the above method, it was found that when step (1) of the polyimide base membrane contacted the solution of step (2), the basic morphology of the hollow fiber membrane was not destroyed. The test results of the obtained polyimide composite membrane were: J N2 = 0.32 GPU, J O2 = 1.2 GPU, a O2 / N2 = 3.9. The polyimide membrane obtained by this method has poor gas permeability, and the toughness of the hollow fiber membrane is poor, which is not resistant to bending, making it difficult to operate during subsequent assembly.

[0059] Comparative Example 3

[0060] This comparative example provides a polyimide gas separation membrane, which is prepared by the following steps:

[0061] (1) P84, PVP-k30 were dissolved in DMF, P84 concentration was 20 wt.%, PVP / P84 = 0.6, heated and stirred at 70°C to form a mixed solution, after vacuum degassing, dry-wet spinning process was used to spin. The spinning solution was extruded from the nozzle, using a mixture of water and DMF (DMF / H2O = 90 / 10) as the core solution, the nascent hollow fiber membrane passed through a 30 mm air layer and then entered a pure water gel bath. After collection with a spinning reel, residual solvents were removed in a water tank, and after 2 days, it was taken out and ready for use.

[0062] (2) Separation layer solution preparation: Matrimid 5218 powder as separation layer material was dissolved in a mixed solvent of THF and DMF (THF / DMF = 1 / 1), and a coating solution with a solid content of 5.0 wt.% was prepared, and defoaming was ready for use.

[0063] (3) Composite membrane preparation: The solution obtained in step (2) was coated on the base membrane obtained in step (1), and was air-dried at room temperature for 10 s, and then was rinsed in deionized water at a temperature of 20°C for 1 min; and was dried at 90°C for 30 min to obtain a polyimide composite membrane.

[0064] During the preparation of the polyimide composite membrane by the above method, it was found that when the polyimide base membrane of step (1) contacted the solution of step (2), the hollow fiber membrane was intact without any damage, and the separation layer formed in step (3) was smooth without any wrinkles. The test results of the polyimide composite membrane were as follows: J N2 = 0.85 GPU, J O2 = 4.2 GPU, a O2 / N2 = 4.9. The polyimide membrane obtained by this method has good toughness, good bending resistance, and is beneficial to the subsequent membrane module production, but has poor air permeability.

[0065] Example 1

[0066] This example provides a polyimide gas separation membrane, which is prepared by the following steps:

[0067] (1) P84 and PVP-k30 were dissolved in DMF, the concentration of P84 was 20 wt.%, and PVP / P84 = 0.6. The mixed solution was heated and stirred at 70°C, and then was spun by a dry-wet spinning process after vacuum defoaming. The spinning solution was extruded from a nozzle, and a mixed solution of water and DMF (DMF / H2O = 90 / 10) was used as a core solution. The nascent hollow fiber membrane passed through a 30 mm air layer and then entered a pure water gel bath. After being collected by a spinning reel, the residual solvent was removed in a water tank, and then the product was taken out after 2 days for standby.

[0068] (2) Separation layer solution preparation: Matrimid-5218 powder as separation layer material was dissolved in a mixed solvent of THF and DMF (THF / DMF = 1 / 1), and a coating solution with a solid content of 5.0 wt.% was prepared, and defoaming was ready for use.

[0069] (3) Composite membrane preparation: The solution obtained in step (2) was coated on the base membrane obtained in step (1), and was air-dried at room temperature for 10 s, and then was rinsed in deionized water at a temperature of 20°C for 1 min; and was dried at 90°C for 30 min to obtain a polyimide composite membrane.

[0070] The polyimide composite membrane prepared by the above method has complete morphology, the separation layer formed in step (3) is smooth and wrinkle-free, and has good toughness. Electron microscopy observation shows that the thickness of the separation layer is about 0.5 μm. The obtained polyimide composite membrane is tested, and the test results are: J N2 = 2.2 GPU, J O2 = 15.6 GPU, a O2 / N2 = 7.1. Compared with Comparative Example 3, the operation of soaking in deionized water at 80°C for 4h is added, and the PVP in the base membrane obtained in step (1) can be effectively removed in high-temperature water, so the gas permeability of the composite membrane is obviously improved. Further test the permeability of other gases, and the results are shown in Table 1.

[0071] Table 1 Permeability of the prepared polyimide composite membrane

[0072]

[0073] Example 2

[0074] The present example provides a polyimide composite membrane, which is prepared by the following steps:

[0075] (1) Dissolve PEI (Ultem-1000) and PEG-20000 in DMAc, PEG / PEI = 0.8, PEI concentration is 16 wt.%, heat and stir at 80°C to form a mixed solution, vacuum degassing, and then spin by dry-wet spinning process. The spinning solution is extruded from a nozzle, and a mixture of water and DMAc (DMAc / H2O = 90 / 10) is used as the core liquid. The nascent hollow fiber membrane passes through a 50 mm air layer and then enters a pure water gel bath. After collection by a winding wheel, it is rinsed in a water tank to remove residual solvent, taken out after 2 days, and prepared for use.

[0076] (2) Preparation of separation layer solution: Dissolve Matrimid-5218 powder as the separation layer material in THF to prepare a coating solution with a solid content of 8.0 wt.%, and degas for use.

[0077] (3) Preparation of composite membrane: coat the solution obtained in step (2) on the base membrane obtained in step (1), dry at room temperature for 10s, and then immerse in deionized water at a temperature of 20°C for 5min; soak in deionized water at 95°C for 10h, and dry at 90°C for 30min to obtain a polyimide composite membrane.

[0078] Similar to Example 1, the polyimide composite membrane prepared by the above method has complete morphology, the separation layer is smooth and wrinkle-free, and has good toughness. Electron microscopy observation shows that the thickness of the separation layer is about 0.9 μm. The obtained polyimide composite membrane is tested, and the test results are: J N2 = 1.9 GPU, J O2 = 12.4 GPU, J H2= 240.6 GPU, a O2 / N2 = 6.5, a H2 / N2 = 126.6, the specific results are shown in Table 2.

[0079] Table 2 Permeation properties of the prepared polyimide composite membrane

[0080]

[0081] Example 3

[0082] This example provides a method for recovering hydrogen from a hydrogen-containing gas mixture in a certain refinery, and the polyimide membrane prepared in Example 2 is used in this example.

[0083] The hydrogen-containing gas mixture has a pressure of 34.6 barG, a temperature of 25.2°C, and a gas amount of 42946.7 Nm 3 / hr, and the composition is shown in Table 3.

[0084] Table 3 Composition of the hydrogen-containing gas mixture

[0085] Name [H2] CH4 C2 C3 C4 C5 [N2] H2O CO CO2 Composition (%) 37.95 48.03 1.91 0.330 0.433 0.107 10.55 0.0289 0.622 0.033

[0086] The specific process is as follows: the mixed gas to be separated first enters a gas-liquid separator to remove liquid hydrocarbons, then passes through a coalescing filter to remove possible liquid droplets and dust, etc., and then enters a heater to be heated to 80°C, ensuring that the gas entering the membrane separator is far from the dew point to prevent liquid droplets from condensing on the membrane surface. The heated gas enters the membrane separator for hydrogen concentration. The membrane separator is filled with the polyimide membrane prepared by the method of Example 2. After passing through the membrane separator, hydrogen is enriched at a relatively fast rate through the membrane and is called product hydrogen. The purity of the product hydrogen is 90.3%, the hydrogen recovery is 83.3%, the pressure is 1.0 barG, and the gas amount is 15040.2 Nm 3 / hr, which can enter the PSA adsorption unit for further purification, and the specific composition is shown in Table 4.

[0087] Table 4 Composition of the permeated gas of the polyimide membrane

[0088]

[0089] Another gas is called tail gas or retentate gas, which has a hydrogen purity of 9.74%, a pressure of 34.6 barG, and a gas amount of 27906.5 Nm 3 / hr. It can enter the fuel gas pipeline network for use as fuel gas. The specific composition is shown in Table 5.

[0090] Table 5 Composition of the retentate gas after polyimide membrane separation

[0091] Name [H2] [CAT] C2 C3 C4 C5 [N2] H2O CO CO2 Composition (%) 9.74 69.91 2.87 0.498 0.657 0.163 15.3 0.00742 0.849 0.0292

[0092] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for producing a polyimide gas separation membrane, characterized by, The method comprises the following steps: (1) Base film preparation: polyimide A particles or powder as base film material and polymer additives are dissolved in an organic solvent to prepare a casting solution with a polyimide A content of 5-30 wt.%, and after degassing, a blended base film of polyimide A and polymer additives is prepared; (2) Separation layer solution preparation: polyimide B particles or powder as separation layer material are dissolved in an organic solvent to prepare a coating solution with a polyimide B content of 0.5-15 wt.%, and after degassing, the coating solution is prepared; (3) Composite film preparation: the coating solution obtained in step (2) is applied on the base film obtained in step (1), and after air drying at room temperature for 1-100 s, the composite film is rinsed in deionized water at a temperature of 0-40℃ for 1-20 min, immersed in deionized water at 50-100℃ for 1-24 h, and dried at 50-120℃ for 5-60 min to obtain a polyimide gas separation membrane; In step (1), the polyimide A is a high molecular material containing an imide ring in the structure; In step (1), the polymer additive is a water-soluble polymer with a molecular weight of 10,000-200,000, including one or a combination of two or more of polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), and polyvinyl alcohol (PVA); In step (2), the polyimide B is a high molecular material containing an imide ring in the structure; In step (1), the addition amount of the polymer additive is 1 / 6 to 1 / 1 of the mass of the polyimide A; and the preparation method of the blended base film includes the immersion gel phase inversion method and the dry-wet spinning method.

2. The production method according to claim 1, characterized by, In step (1), the addition amount of the polymer additive is 1 / 3 to 5 / 6 of the mass of the polyimide A.

3. The preparation method according to claim 1, characterized in that, In step (1), the blended base film is in the form of a flat plate or a hollow fiber.

4. The method of claim 1, wherein, In steps (1) and (2), the organic solvent is one or a mixture of two or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), tetrahydrofuran (THF), and dimethyl sulfoxide (DMSO).

5. The polyimide gas separation membrane prepared by the method of any one of claims 1-4.

6. The polyimide gas separation membrane according to claim 5, wherein The polyimide gas separation membrane comprises a base film and a separation layer, and the thickness of the separation layer is 0.01-2 μm.

7. The polyimide gas separation membrane of claim 5 or 6 for use in gas separation and recovery.

8. Use according to claim 7, characterized in that, The use is specifically for separating and recovering hydrogen, oxygen, and nitrogen from a hydrogen-containing mixed gas, separating CO2 and CH4, extracting helium from natural gas, or gas dehumidification.

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