Asymmetric structure metal organic framework mixed matrix gas separation membrane as well as preparation method and application thereof

Abstract

The invention discloses an asymmetric structure metal organic framework mixed matrix gas separation membrane and a preparation method and application thereof, and belongs to the technical field of gas separation membrane materials, the asymmetric structure metal organic framework mixed matrix gas separation membrane is composed of a commercial base membrane and an in-situ growth MOF layer, the MOF layer is only distributed in a near-surface area of the commercial base membrane, and other areas keep the original structure of the base membrane, so that an asymmetric structure is formed; the prepared asymmetric structure metal organic framework mixed matrix gas separation membrane has high gas separation selectivity and good mechanical strength, the asymmetric structure can generate a gas concentration gradient to promote a mass transfer process, and the problems of interface defects and mechanical strength reduction of a traditional mixed matrix membrane are avoided; the catalyst can be suitable for carbon dioxide capture, flue gas purification, air separation and oxygen enrichment, the preparation method is simple, and large-scale production can be achieved.

Description

Technical Field

[0001] This invention relates to the field of gas separation membrane materials technology, and in particular to an asymmetric structure metal-organic framework hybrid matrix gas separation membrane, its preparation method and application. Background Technology

[0002] Gas membrane separation refers to the process of separating components in a gas mixture by utilizing the different permeation rates of the components within a gas separation membrane under the driving force of a pressure difference. As an energy-efficient and highly effective separation technology, gas separation membranes have been widely used in natural gas purification, carbon dioxide capture, and hydrogen purification. Traditional polymer membranes possess good film-forming properties and mechanical strength, but their gas separation performance is limited, making it difficult to exceed the Robeson limit. Metal-organic frameworks (MOFs) are porous crystals formed by linking metal ions or metal clusters through organic ligands. They possess high specific surface area, regular channels, and tunable pore size, and are considered ideal functional materials for gas separation.

[0003] However, the high cost and low processability of pure MOF membranes limit their large-scale application in gas separation. To overcome this problem, researchers have attempted to directly blend MOF materials with polymer matrices to construct hybrid matrix membranes, aiming to combine the molecular sieving properties of MOFs with the processability of polymers. However, due to the poor interfacial compatibility between MOFs and polymer matrices, interfacial defects often occur, severely weakening gas selectivity. Furthermore, high proportions of MOF doping can disrupt the continuity and structural integrity of the base membrane, leading to decreased mechanical properties and insufficient membrane separation stability.

[0004] The aforementioned problems have become key bottlenecks limiting the practical application of hybrid matrix membranes. Therefore, how to effectively introduce MOF functional layers while maintaining the integrity of the membrane structure, and simultaneously considering gas separation performance and mechanical strength, has become a pressing technical challenge in this field. Thus, this invention proposes an asymmetric structure metal-organic framework hybrid matrix gas separation membrane, its preparation method, and its application to solve the problems existing in the prior art. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to propose an asymmetric structure metal-organic framework hybrid matrix gas separation membrane, its preparation method, and its application. This gas separation membrane balances gas separation performance and mechanical strength, overcoming the problems of high preparation cost and poor processability of existing pure MOF membranes, as well as insufficient interfacial compatibility, decreased mechanical properties, and reduced separation selectivity in traditional MOF / polymer hybrid matrix membranes.

[0006] To achieve the objectives of this invention, the invention is implemented through the following technical solution: an asymmetric structure metal-organic framework hybrid matrix gas separation membrane, comprising a commercially available base membrane and an in-situ grown MOF layer, wherein the MOF layer is distributed only in the near-surface region of the commercially available base membrane, and the other regions of the commercially available base membrane without the MOF layer maintaining the original structure of the commercially available base membrane, forming an asymmetric structure, thereby maintaining the mechanical strength of the base membrane while endowing it with high gas separation selectivity.

[0007] A further improvement is that the material type of the commercial base film is selected from at least one of polyethersulfone (PES), polyimide (PI), polysulfone (PSF), and cellulose acetate (CA).

[0008] A further improvement is that the geometry of the commercial base film is either a flat sheet film or a hollow fiber film, and the thickness is 50–200 μm.

[0009] A further improvement is that the MOF layer is selected from at least one of the following: IR series metal-organic frameworks, ZIF series metal-organic frameworks, CPL series metal-organic frameworks, MIL series metal-organic frameworks, PCN series metal-organic frameworks, and UiO series metal-organic frameworks, with a thickness of 1 to 5 µm.

[0010] A method for preparing an asymmetric metal-organic framework hybrid matrix gas separation membrane includes the following steps:

[0011] Step 1: Dissolve organic ligand A and metal salt solution B in organic solvent / water mixed solvent and water respectively to obtain two monomer solutions for MOF synthesis, namely precursor A monomer solution and metal salt B monomer solution.

[0012] Step 2: Immerse the pre-prepared commercial base film in the precursor A monomer solution from Step 1, allowing the commercial base film to adsorb organic ligand A during the micro-swelling process of the mixed polar solvent, followed by drying.

[0013] Step 3: Immerse the commercially available base membrane dried in Step 2 in the metal salt B monomer solution from Step 1 to allow MOF nucleation and in-situ growth on the commercially available base membrane. After washing and drying, an asymmetric metal-organic framework mixed matrix gas separation membrane is obtained.

[0014] A further improvement is that, in step one, the organic ligand A is selected from at least one of imidazole compounds, terephthalic acid and its amino-substituted derivatives, naphthalenedicarboxylic acid, pyridine carboxylic acid, or polycarboxylic acid aromatic compounds.

[0015] A further improvement is that, in step one, the metal salt monomer B is selected from at least one of zinc salt, cobalt salt, nickel salt, zirconium salt, iron salt, chromium salt, aluminum salt, copper salt, or cadmium salt.

[0016] A further improvement is that, in step one, the organic solvent is selected from at least one of methanol, ethanol, N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc), and the volume ratio of the organic solvent to water is 1:1 to 10.

[0017] Further improvements are made in that the in-situ growth conditions of the MOF include: a molar ratio of metal salt to organic ligand of 1:2 to 6, a reaction temperature of 20 to 100°C, a reaction time of 1 to 24 h, a contact time between the commercial base film and the two monomer solutions of 0.5 to 24 h, and after the reaction, the film is washed with solvent and dried to obtain a metal-organic framework layer distributed in the near-surface region of the commercial base film.

[0018] An application of an asymmetric structure metal-organic framework hybrid matrix gas separation membrane is disclosed. This membrane is used for carbon dioxide capture and flue gas purification, as well as air separation and oxygen enrichment. The asymmetric structure metal-organic framework hybrid matrix gas separation membrane exhibits the following performance in CO2 / O2 separation:

[0019] CO2 enrichment mode (25℃, 1 bar, dry state) CO2 / O2 selectivity ≥3, CO2 transmittance ≥150 GPU;

[0020] In O2 enrichment mode (25℃, 1 bar, dry state), O2 / CO2 selectivity ≥2 and O2 transmittance ≥120 GPU.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] Structurally, this invention grows MOF in situ in the near-surface region of the commercial base film, forming an asymmetric structure of "functional selection region / mechanical support region". The thickness of the functional region is controllable (1-5μm), which can achieve shortening of molecular sieving path and reconstruction of effective diffusion channel without sacrificing overall strength.

[0023] At the interface, MOFs nucleate and grow directly on the surface of the base membrane and in the pores. The interface is continuous and without obvious voids, which significantly reduces the particle aggregation and shedding problems of traditional mixed matrix membranes, suppresses bypass permeation and defect diffusion, and maintains more stable selectivity and flux in long-term operation.

[0024] In terms of performance, it can achieve higher apparent selectivity and permeability in CO2 / O2 separation scenarios, and balance strength, toughness and anti-attenuation performance in wet flue gas and other water-containing conditions. It is suitable for practical conditions such as oxygen-enriched combustion and oxygen-containing flue gas decarbonization.

[0025] In terms of process, this invention adopts a mild in-situ growth process with low equipment requirements and simple steps. Furthermore, by adjusting the ligand / metal salt molar ratio (1:2-6), temperature (20-100℃), and time (1-24h), the thickness of the MOF layer can be controlled, which is conducive to large-scale preparation and promotion of different configurations (flat sheet / hollow fiber). Attached Figure Description

[0026] Figure 1 This is a schematic diagram comparing the CO2 / O2 separation performance of the ZIF-8 / PES asymmetric membrane and the pure PES membrane in Application Example 1 of the present invention (25°C, 1 bar, dry state).

[0027] Figure 2 This is a schematic diagram showing the comparison of CO2 / O2 separation performance (30°C, 3 bar, dry / slightly wet) between the UiO-66-NH2 / PI asymmetric membrane and the pure PI membrane in Application Example 2 of the present invention.

[0028] Figure 3 This is a schematic diagram comparing the CO2 / O2 separation performance of the MIL-53(Fe) / PES asymmetric membrane and the pure PES membrane in Application Example 3 of the present invention (25°C, 1 bar, dry state). Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be noted that technical means not described in detail in the embodiments of the present invention can be implemented by conventional means and are not the key points of the invention, and will not be elaborated upon. Example 1

[0030] This embodiment provides a method for preparing an asymmetric structure metal-organic framework hybrid matrix gas separation membrane, including the following steps:

[0031] A 100 μm thick PES sheet membrane was used as the substrate, and 2-methylimidazole (concentration of 0.2–0.5 mol·L⁻¹) was then added. -1 In this embodiment, 0.3 mol·L⁻¹ is used. -1The PES sheet membrane was dissolved in methanol / water (1:1) to prepare a ligand solution. The membrane was then immersed in the prepared ligand solution and allowed to swell slightly at –40°C for 30–60 min (45 min in this example) to fully wet and swell the membrane and adsorb the ligand. After removal, the surface solution was gently wiped off and the membrane was briefly dried to obtain the precursor membrane. The precursor membrane was then transferred to a metal salt solution: Zn(NO3)2 (concentration 0.05–0.2 mol·L⁻¹). -1 In this embodiment, 0.1 mol·L⁻¹ is used. -1 The ZIF-8 / PES composite membrane was reacted with methanol at 60°C for 6 hours to allow ZIF-8 to nucleate and grow in situ near the membrane surface, forming a locally covered MOF functional layer. After the reaction, the membrane was washed with methanol at least 3 times (3 times in this example) to remove unreacted substances and mother liquor residue. Finally, it was vacuum dried at 50-60°C (55°C in this example) for 4-12 hours (8 hours in this example) to obtain an asymmetric ZIF-8 / PES composite membrane. Example 2

[0032] This embodiment provides a method for preparing an asymmetric structure metal-organic framework hybrid matrix gas separation membrane, including the following steps:

[0033] A 100 μm thick PI sheet film was used as the substrate, and phthalic acid (concentration of 0.2 mol·L⁻¹) was then used. -1 The PI sheet membrane was dissolved in DMF / water (1:10) to prepare a ligand solution. The membrane was then immersed in the prepared ligand solution and allowed to swell slightly at 80°C for 60 minutes to fully wet and adsorb the ligand. After removal, the surface solution was gently wiped off and the membrane was briefly dried to obtain the precursor membrane. The precursor membrane was then transferred to a metal salt solution: ZrCl4 (concentration 0.1 mol·L⁻¹). -1 The reaction was carried out at 80℃ for 8 hours with DMF to allow UiO-66-NH2 to nucleate and grow in situ near the membrane surface to form a locally covered MOF functional layer. After the reaction, the membrane was washed three times each with DMF and ethanol to remove unreacted substances and mother liquor residue. Finally, the membrane was vacuum dried at 60℃ for 12 hours to obtain an asymmetric UiO-66-NH2 / PI composite membrane. Example 3

[0034] This embodiment provides a method for preparing an asymmetric structure metal-organic framework hybrid matrix gas separation membrane, including the following steps:

[0035] A 100 μm thick PES sheet membrane was used as the substrate, and phthalic acid (concentration 0.2 mol·L⁻¹) was then used. -1The PI sheet membrane was dissolved in DMF / water (1:10) to prepare a ligand solution. The membrane was then immersed in the prepared ligand solution and allowed to swell slightly at 95°C for 60 minutes to fully wet and adsorb the ligand. After removal, the surface solution was gently wiped off and the membrane was briefly dried to obtain the precursor membrane. The precursor membrane was then transferred to a metal salt solution: FeCl3 (concentration 0.1 mol·L⁻¹). -1 MIL-53(Fe) was grown in situ by reacting MIL-53(Fe) / PES with DMF at 100℃ for 12 h. After the reaction, the membrane was washed three times each with DMF and ethanol to remove unreacted material and mother liquor residue. Finally, it was vacuum dried at 55℃ for 8 h to obtain an asymmetric structure MIL-53(Fe) / PES composite membrane. Example 4

[0036] This embodiment provides a method for preparing an asymmetric structure metal-organic framework hybrid matrix gas separation membrane, including the following steps:

[0037] A 100 μm thick PES sheet membrane was used as the substrate, with half of the area obscured. Tetraphenyltetracarboxylic acid (concentration 0.05–0.1 mol·L⁻¹) was then used. -1 In this embodiment, 0.08 mol·L⁻¹ is used. -1 Dissolve the tetraphenyltetracarboxylic acid ligand in DMF / water (1:10), and add 1-3 vol% acetic acid to adjust the nucleation rate (2 vol% is used in this example) to prepare a tetraphenyltetracarboxylic acid ligand solution. Then, immerse the PES flat sheet membrane in the prepared ligand solution and allow it to swell slightly at 90°C for 60 min, so that the PES flat sheet membrane is wetted and swollen to adsorb the ligand. After removal, gently wipe off the surface liquid and dry briefly to obtain the precursor membrane. Subsequently, the precursor membrane is transferred to a metal salt solution: Cu(NO3)2 (concentration of 0.05-0.1 mol·L⁻¹). -1 In this embodiment, 0.08 mol·L⁻¹ is used. -1 The reaction was carried out at 90℃ for 10 h to promote the local in-situ growth of PCN-222 on the membrane surface. After the reaction, the membrane was washed three times each with DMF and ethanol to remove unreacted substances and mother liquor residue. Finally, the membrane was vacuum dried at 60℃ for 12 h to obtain an asymmetric PCN-222 / PES composite membrane. Example 5

[0038] This embodiment provides a method for preparing an asymmetric structure metal-organic framework hybrid matrix gas separation membrane, including the following steps:

[0039] A 100 μm thick PES hollow membrane was used as the substrate, and pyridine-x-carboxylic acid (such as pyridine-3-carboxylic acid or pyridine-4-carboxylic acid, with a concentration of 0.10–0.30 mol·L⁻¹) was then used. -1 In this embodiment, 0.20 mol·L⁻¹ is used. -1The ligand solution was prepared by dissolving the PES hollow membrane in DMF / water (1:10). The membrane was then immersed in the prepared ligand solution and allowed to swell slightly at 80°C for 45–60 min (50°C in this example). This allowed the PES hollow membrane to wet and swell, adsorbing the ligand. After removal, the surface solution was gently wiped off and the membrane was briefly dried to obtain the precursor membrane. The precursor membrane was then transferred to a metal salt solution: Zn(NO3)2 (concentration 0.05–0.20 mol·L⁻¹). -1 In this embodiment, 0.10 mol·L⁻¹ is used. -1 The CPL series MOF was grown in situ on the membrane surface by reacting with DMF and ethanol at 80°C for 8 hours. After the reaction, the membrane was washed three times each with DMF and ethanol to remove unreacted substances and mother liquor residue. Finally, it was vacuum dried at 50-60°C for 4-12 hours (in this example, it was vacuum dried at 55°C for 8 hours) to obtain an asymmetric CPL / PES composite membrane. Application Example 1

[0040] See Figure 1 In this application example, the asymmetric ZIF-8 / PES composite membrane (membrane size 1cm × 1cm) prepared in Example 1 was installed in a flat sheet membrane testing device; the test was conducted at 25°C and 1 bar using a binary gas mixture with CO2 / O2 = 50 / 50 (volume fraction). Figure 1 The results showed that the membrane exhibited preferential permeation / adsorption behavior for CO2, achieving a CO2 enrichment operation mode. Compared with the unmodified PES-based membrane, the CO2 / O2 selectivity and apparent permeability were simultaneously improved, proving that the asymmetric structure of Example 1 can achieve effective molecular sieving and mass transfer amplification in the functionalized region while maintaining the strength of the mechanical support region. Application Example 2

[0041] See Figure 2 In this application example, the asymmetric UiO-66 / PI membrane prepared in Example 2 is used in a simulated oxygen-containing flue gas system (30°C, 3 bar) with CO2 / O2 = 30 / 70 (volume fraction). Figure 2 Test results show that the membrane maintains stable selectivity and improves flux for CO2, which is a significant advantage over the unmodified PI-based membrane, verifying the applicability of the membrane in the scenario of CO2 capture and residual oxygen (O2) separation and recovery of flue gas after oxygen-enriched combustion. Application Example 3

[0042] See Figure 3 In this application example, the asymmetric structure MIL-53(Fe) / PES membrane prepared in Example 3 was loaded into a flat sheet membrane module and continuously tested under humid conditions of 30°C and 5% (volume fraction) water vapor, using simulated flue gas with CO2 / O2 = 15 / 85 (volume fraction). Figure 3The results show that the membrane maintains stable CO2 / O2 selectivity and considerable flux under dry and slightly wet conditions, and its performance does not significantly decline after 72 hours of continuous operation, indicating that it has good operational stability and durability under the condition of capturing CO2 in humid flue gas. Comparative Example 1

[0043] This comparative example uses unmodified ZIF-8 powder blended with PES to prepare a mixed matrix membrane, and the test conditions are the same as in Application Example 1 (CO2 / O2 = 50 / 50, 25℃, 1 bar). The results show that the CO2 / O2 selectivity of the membrane is close to 1 and fluctuates significantly. This indicates that direct blending leads to interfacial incompatibility and an increase in defect channels, making it difficult to achieve stable and effective CO2 / O2 separation; while the asymmetric in-situ growth of this invention can significantly avoid this problem. Comparative Example 2

[0044] This comparative example uses a membrane prepared by blending unmodified UiO-66-NH2 powder with PES, applied to simulated oxygen-containing flue gas separation conditions with CO2 / O2 = 30 / 70. The results show that the membrane exhibits low CO2 / O2 selectivity and decreased mechanical strength during operation, with localized cracking and leakage risks. This comparative example further demonstrates that direct blending of powders weakens the overall performance and lifespan of the membrane, while the asymmetric local in-situ growth of this invention improves selectivity and flux while maintaining the strength and long-term stability of the mechanical support region.

[0045] As can be seen from the above application examples and comparative examples, the asymmetric structure metal-organic framework (MOF) mixed matrix gas separation membrane provided by this invention exhibits significant advantages in scenarios such as mixed gas separation and enrichment. Compared with mixed matrix membranes prepared by traditional direct mixing of powders, this invention significantly reduces defect permeation caused by interfacial voids and particle agglomeration by forming a dense and continuous MOF layer near the membrane surface, thus avoiding mechanical property degradation and flux-selectivity deterioration. This asymmetric structure membrane fabrication method has mild conditions, scalability, and adjustable coverage ratio and layer thickness, making it suitable for the on-demand selection and combination of multiple series of MOFs such as IR, ZIF, CPL, MIL, PCN, and UiO. It can achieve precise separation and enrichment of mixed gases in scenarios such as oxygen-enriched combustion and air-conditioning oxygen distribution, oxygen-containing flue gas decarbonization, life support and medical respiration, and food and cold chain modified atmosphere packaging, and has broad prospects for industrial application.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An asymmetric structure metal-organic framework hybrid matrix gas separation membrane, comprising a commercially available base membrane and an in-situ grown MOF layer, characterized in that: The MOF layer is distributed only in the near-surface region of the commercial base film, while other regions of the commercial base film where the MOF layer is not grown retain the original structure of the commercial base film, forming an asymmetric structure.

2. The asymmetric structure metal-organic framework hybrid matrix gas separation membrane according to claim 1, characterized in that: The commercially available base film is selected from at least one of polyethersulfone, polyimide, polysulfone, and cellulose acetate.

3. The asymmetric structure metal-organic framework hybrid matrix gas separation membrane according to claim 1, characterized in that: The commercially available base film is either a flat sheet film or a hollow fiber film, with a thickness of 50–200 μm.

4. The asymmetric structure metal-organic framework hybrid matrix gas separation membrane according to claim 1, characterized in that: The MOF layer is selected from at least one of the following: IR series metal-organic frameworks, ZIF series metal-organic frameworks, CPL series metal-organic frameworks, MIL series metal-organic frameworks, PCN series metal-organic frameworks, and UiO series metal-organic frameworks, with a thickness of 1 to 5 µm.

5. A method for preparing an asymmetric structure metal-organic framework hybrid matrix gas separation membrane, characterized in that, Includes the following steps: Step 1: Dissolve organic ligand A and metal salt solution B in organic solvent / water mixed solvent and water, respectively, to obtain two monomer solutions for MOF synthesis, namely precursor A monomer solution and metal salt B monomer solution. Step 2: Immerse the pre-prepared commercial base film in the precursor A monomer solution from Step 1, allowing the commercial base film to adsorb organic ligand A during the micro-swelling process of the mixed polar solvent, followed by drying. Step 3: Immerse the commercially available base membrane dried in Step 2 in the metal salt B monomer solution from Step 1 to allow MOF nucleation and in-situ growth on the commercially available base membrane. After washing and drying, an asymmetric metal-organic framework mixed matrix gas separation membrane is obtained.

6. The method for preparing an asymmetric structure metal-organic framework hybrid matrix gas separation membrane according to claim 5, characterized in that: In step one, the organic ligand A is selected from at least one of imidazole compounds, terephthalic acid and its amino-substituted derivatives, naphthalenedicarboxylic acid, pyridine carboxylic acid, or polycarboxylic acid aromatic compounds.

7. The method for preparing an asymmetric structure metal-organic framework hybrid matrix gas separation membrane according to claim 5, characterized in that: In step one, the metal salt monomer B is selected from at least one of zinc salt, cobalt salt, nickel salt, zirconium salt, iron salt, chromium salt, aluminum salt, copper salt, or cadmium salt.

8. The method for preparing an asymmetric structure metal-organic framework hybrid matrix gas separation membrane according to claim 5, characterized in that: In step one, the organic solvent is selected from at least one of methanol, ethanol, N,N-dimethylformamide, and N,N-dimethylacetamide, and the volume ratio of the organic solvent to water is 1:1 to 10.

9. The method for preparing an asymmetric structure metal-organic framework hybrid matrix gas separation membrane according to claim 5, characterized in that: The in-situ growth conditions of the MOF include: a molar ratio of metal salt to organic ligand of 1:2 to 6, a reaction temperature of 20 to 100°C, a reaction time of 1 to 24 h, a contact time between the commercial base film and the two monomer solutions of 0.5 to 24 h, and after the reaction, the film is washed with solvent and dried to obtain a metal-organic framework layer distributed in the near-surface region of the commercial base film.

10. An application of an asymmetric structure metal-organic framework hybrid matrix gas separation membrane, characterized in that: The asymmetric structure metal-organic framework hybrid matrix gas separation membrane is used for carbon dioxide capture and flue gas purification, as well as air separation and oxygen enrichment.

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