Preparation method and application of coordination polymer mixed matrix membrane

Abstract

The present invention belongs to the technical field of membrane-based materials, and specifically relates to a method for preparing and applying a coordination polymer mixed matrix membrane. The method first separately prepares a metal precursor solution containing metal clusters and a terephthalic acid ligand solution, then secures a polymer substrate in a reverse diffusion device, adds a metal cluster solution and a ligand solution to both sides of the polymer substrate, and finally, prepares a coordination polymer mixed matrix membrane after standing, soaking, and drying. The present invention utilizes a reverse diffusion method to in situ prepare a metal-organic framework-based mixed matrix membrane on a commercial polymer substrate. This method is simple to operate, does not require prior synthesis of MOF fillers, and has mild reaction conditions. The method is also applicable to other MOF and polymer materials. Furthermore, the mixed matrix membrane prepared by the present invention exhibits excellent gas separation performance and can be used for CO2 / CH4 separation.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane-based materials, and in particular relates to a preparation method and application of a coordination polymer mixed matrix membrane. Background Art

[0002] Excessive greenhouse gas emissions (especially CO₂) resulting from human economic and social activities have long been a serious environmental concern. Membrane-based materials have long been a focus of attention in the field of CO₂ separation, as membrane-based gas separations offer excellent selectivity, flexible processes, ease of operation, and scale-up. Polymer membranes are considered the most promising membrane materials for industrial applications due to their low cost, availability, flexibility, and ease of scale-up. However, due to their dense and amorphous structures, most polymer membranes often face a trade-off between permeability and selectivity during separations. This is often limited by the "trade-off" effect of the polymer material, making it difficult to break the Robeson upper limit. To address these issues, nanofillers are incorporated as dispersed phases into polymer matrices to prepare mixed matrix membranes (MMMs). This approach combines the advantages of inorganic fillers and polymer matrices to enhance the separation performance of membrane-based materials. However, the preparation of MMMs currently faces challenges such as insufficient compatibility between the filler and the polymer matrix, limited effective filler loading within the selective layer, interfacial solidification, and the presence of non-selective voids.

[0003] Coordination polymers (PCPs), also known as metal-organic frameworks (MOFs), are a class of crystalline materials assembled from metal ions and organic ligands. MOFs are considered attractive alternatives for advanced separations due to their high porosity, uniform and tunable pore size, well-defined pore structure, and tunable surface properties. Because MOFs are organic-inorganic hybrids, they exhibit improved compatibility with polymer matrices compared to pure inorganic fillers. Among them, [Zr6O4(OH)4(bdc)6] (bdc = 1,4-benzenedicarboxylic acid) is a thermally and chemically stable MOF composed of hexanuclear Zr6O4(OH)4 nodes as secondary building units (SBUs) coordinated to terephthalic acid. As one of the most attractive MOF materials, this coordination polymer exhibits excellent gas separation performance and has been widely used as a filler in mixed-matrix membranes.

[0004] In summary, if [Zr6O4(OH)4(bdc)6] can be used to develop a method to improve the compatibility and loading capacity of mixed matrix membranes to enhance their CO2 separation performance, it will undoubtedly have great potential application value. Summary of the Invention

[0005] To overcome the shortcomings of the aforementioned prior art, the present invention proposes a method for preparing a coordination polymer mixed matrix membrane, which is prepared at room temperature via an in-situ reverse diffusion method. Compared to existing methods, this method offers advantages such as easier operation, simpler equipment, and milder reaction conditions. The resulting coordination polymer mixed matrix membrane exhibits excellent CO2 / CH4 separation performance.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions:

[0007] A first aspect of the present invention provides a method for in-situ preparation of a coordination polymer mixed matrix membrane by reverse diffusion at room temperature, the method comprising the following steps:

[0008] S1. Adding N,N-dimethylformamide and acetic acid to the metal salt in sequence, mixing and heating to obtain a metal precursor solution containing metal clusters;

[0009] S2. Add N,N-dimethylformamide to the organic ligand and mix well to prepare a ligand solution;

[0010] S3. Fix the polymer substrate in the middle of the anti-diffusion device, then add the metal precursor solution of step S1 and the ligand solution of step S2 to both sides of the substrate respectively, and prepare the coordination polymer mixed matrix membrane after standing, soaking and drying.

[0011] The method of the present invention involves fixing a commercial polymer substrate in a reverse diffusion device and then, through reverse diffusion, in-situ filling the pores of the polymer substrate with MOF nanoparticles. This method successfully fabricates a mixed matrix membrane with excellent compatibility, high filler loading, and superior separation performance. The method is simple to operate, operates under mild reaction conditions, is easily reproducible, and is amenable to large-scale production.

[0012] Preferably, the metal salt includes but is not limited to zirconium n-propoxide. When the metal salt is zirconium n-propoxide, the prepared metal precursor solution contains Zr6O4(OH)4(OAc) 12 Metal precursor solutions of metal clusters.

[0013] Preferably, the organic ligand includes but is not limited to terephthalic acid. More preferably, the organic ligand is terephthalic acid.

[0014] Preferably, the polymer substrate comprises polypropylene, polysulfone, polyethersulfone, nylon, polyamide.

[0015] Preferably, in step S3, the standing is standing at room temperature, and the standing time is 24 to 96 hours.

[0016] Preferably, the molar ratio of the organic ligand to the metal salt is 1.4 to 3:1.

[0017] Preferably, in step S3, the concentrations of the organic ligand and the metal salt are 0.0274-0.1173 mol / L and 0.0195-0.0389 mol / L, respectively.

[0018] Preferably, in step S1, the heating is performed at 120-140° C. for 2-4 hours.

[0019] Preferably, the volume ratio of N,N-dimethylformamide to acetic acid is 15:8.

[0020] The second aspect of the present invention provides a coordination polymer mixed matrix membrane prepared by the method described in the first aspect.

[0021] The third aspect of the present invention provides use of the coordination polymer mixed matrix membrane described in the second aspect in gas separation.

[0022] Preferably, the gas is a CO2 / CH4 mixed gas.

[0023] The present invention fills nanofillers in a polymer matrix by in-situ growth, effectively improving the compatibility and loading capacity issues between the polymer matrix and the nanofillers, so that the prepared mixed matrix membrane exhibits excellent CO2 / CH4 separation performance, reaching 18.63.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention discloses a method for in situ preparation of a coordination polymer mixed matrix membrane by reverse diffusion at room temperature. The method comprises first preparing a metal precursor solution containing metal clusters and a terephthalic acid ligand solution, respectively. A polymer substrate is then fixed in a reverse diffusion device, and the metal cluster solution and ligand solution are added to both sides of the polymer substrate. Finally, the polymer substrate is allowed to stand, soaked, and dried to produce the coordination polymer mixed matrix membrane. The present invention utilizes a reverse diffusion method to in situ prepare a MOF-based mixed matrix membrane on a commercial polymer substrate. This method is simple to operate, does not require prior synthesis of MOF fillers, and operates under mild reaction conditions. The method is also applicable to other MOF and polymer materials. Furthermore, the filler in the prepared mixed matrix membrane is doped into the polymer substrate by filling its pores. This results in a more uniform filler dispersion, improved compatibility with the substrate, and reduced interfacial defects. Consequently, the prepared coordination polymer mixed matrix membrane exhibits excellent gas separation performance and can be used for CO2 / CH4 separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is an SEM image of the coordination polymer mixed matrix membrane of Example 1;

[0027] Figure 21 is the EDS image of the coordination polymer mixed matrix membrane of Example 1;

[0028] Figure 3 is the XRD spectrum of the coordination polymer mixed matrix membrane of Example 1;

[0029] Figure 4 This is a graph showing the gas separation performance of the coordination polymer mixed matrix membrane of Example 1. DETAILED DESCRIPTION

[0030] The following is a further description of specific embodiments of the present invention. It should be noted that the description of these embodiments is intended to facilitate understanding of the present invention and does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0031] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0032] Example 1 Method for in-situ preparation of coordination polymer mixed matrix membranes by reverse diffusion at room temperature

[0033] (1) 0.84 g zirconium n-propoxide was added to a screw-capped glass bottle, followed by 30 mL N,N-dimethylformamide and 16 mL acetic acid. The mixture was ultrasonicated for 10 min and then heated at 130 °C for 3 h to obtain a mixture containing Zr6O4(OH)4(OAc) 12 a metal precursor solution of the metal cluster;

[0034] (2) 0.42 g of terephthalic acid was added to a beaker, followed by 46 mL of N,N-dimethylformamide. The ligand solution was obtained after ultrasonication for 20 min.

[0035] (3) A polymer substrate (polypropylene, PP) was fixed in the middle of a reverse diffusion device (purchased from Jinan Beibo Instrument Equipment Co., Ltd., model: 30*100 mm), and then the metal precursor solution of step (1) and the ligand solution of step (2) were added to both sides of the substrate respectively. The mixture was allowed to stand at room temperature for 96 hours, and the obtained mixed matrix membrane was immersed in methanol. Finally, the coordination polymer mixed matrix membrane was obtained by vacuum drying.

[0036] like Figure 1 As shown in the SEM, the coordination polymer filler in the mixed matrix membrane is successfully filled into the pores of the substrate. The filler is evenly dispersed throughout the entire substrate without agglomeration, and is well compatible with the substrate. Figure 2EDS further demonstrated that the coordination polymer was uniformly dispersed throughout the matrix, and the zirconium content in the mixed matrix membrane was high, indicating a high filler loading. Figure 3 XRD results show that although the coordination polymer grows in the pores of the substrate by back diffusion, the coordination polymer still maintains the correct crystal structure and has good crystallinity.

[0037] Example 2 Method for in-situ preparation of coordination polymer mixed matrix membranes by reverse diffusion at room temperature

[0038] (1) 0.84 g zirconium n-propoxide was added to a screw-capped glass bottle, followed by 30 mL N,N-dimethylformamide and 16 mL acetic acid. The mixture was ultrasonicated for 10 min and then heated at 130 °C for 3 h to obtain a mixture containing Zr6O4(OH)4(OAc) 12 a metal precursor solution of the metal cluster;

[0039] (2) 0.42 g of terephthalic acid was added to a beaker, followed by 46 mL of N,N-dimethylformamide. The ligand solution was obtained after ultrasonication for 20 min.

[0040] (3) A polymer substrate (polypropylene, PP) was fixed in the middle of a counter-diffusion device (purchased from Jinan Beibo Instrument Equipment Co., Ltd., model: 30*100 mm), and then the metal precursor solution of step (1) and the ligand solution of step (2) were added to both sides of the substrate respectively. The mixture was allowed to stand at room temperature for 24 h. The obtained mixed matrix membrane was immersed in methanol for 24 h, and finally vacuum dried to obtain a coordination polymer mixed matrix membrane.

[0041] As in Example 1, the coordination polymer filler in the mixed matrix membrane was successfully filled into the pores of the substrate. The filler was evenly dispersed throughout the substrate without agglomeration, and was well compatible with the substrate. In addition, the zirconium content in the mixed matrix membrane was high, and the coordination polymer maintained the correct crystal structure and had good crystallinity.

[0042] Experimental Example 1 Determination of Gas Separation Performance of Coordination Polymer Mixed Matrix Membranes

[0043] Before conducting permeation tests of various gases or mixed gases, the coordination polymer mixed matrix membrane was activated at 60°C for 12 hours to remove various impurities adsorbed on the membrane and ensure the reliability of the permeation data obtained. To measure the permeability of single gases and the corresponding binary mixtures (CO2, CH4), the UiO-66 mixed matrix membrane prepared in Example 1 was sealed in a permeation module using an O-ring at room temperature. The feed side pressure was maintained at 1.4 bar, the permeate side pressure was maintained at 1 bar, and the total gas flow rate was controlled at 40 mL min. -1 Ar is used as a sweep gas on the permeate side to keep the concentration of the permeate gas at a low level, thereby providing a driving force for permeation.

[0044] In the permeation test of single-component gas, the permeability of the membrane (P i ) is defined as:

[0045]

[0046] Where Ni is the permeation rate of component i (mol·s -1 ), A is the effective area of the film being tested (m 2 ), and ΔP i is the transmembrane pressure (Pa).

[0047] The separation selectivity of the membrane is calculated from the permeability of a single component:

[0048]

[0049] Among them, α i,j represents the separation factor of component i to component j; P j represents the permeability of component j; i and j represent different components in gas separation.

[0050] In the separation selectivity test of a two-component gas mixture, the gas concentration on the permeate side is measured by a calibrated gas chromatograph (SHIMADZU GC-2014C). In this system, the gas separation factor is defined as:

[0051]

[0052] Among them, α i,j represents the separation factor of component i to component j; Yi(j) and Xi(j) represent the content of gas component i or j on the permeate side and feed side, respectively.

[0053] Depend on Figure 4 It can be seen that the mixed matrix membrane prepared in Example 1 exhibits excellent CO2 / CH4 separation performance, reaching 18.63, and maintains a high CO2 permeability. Similarly, the mixed matrix membrane prepared in Example 2 also has excellent CO2 / CH4 separation performance and high CO2 permeability.

[0054] In summary, the present invention synthesizes coordination polymer nanoparticles in situ in the pores of a polypropylene (PP) substrate by an in-situ diffusion method to fill the channels and obtains a good gas separation effect. Simultaneously, more coordination polymer nanoparticles can be in-situ filled in the polymer substrate by increasing the time of back diffusion. Since this method is to fill the nanofiller in the polymer matrix by in-situ growth, the compatibility and loading capacity problems between the polymer matrix and the nanofiller are effectively improved, so that the prepared mixed matrix membrane shows excellent CO2 / CH4 separation performance, reaching 18.63.

[0055] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. It is apparent to those skilled in the art that various changes, modifications, substitutions, and variations of these embodiments may be made without departing from the principles and spirit of the present invention, and the changes still fall within the scope of protection of the present invention.

Claims

1. A method for in situ preparation of a coordination polymer mixed matrix membrane by reverse diffusion at room temperature, characterized in that: The following steps are involved: S1. Add N,N-dimethylformamide and acetic acid to zirconium n-propoxide in sequence, mix well and heat to obtain Zr6O4(OH)4(OAc) 12 A metal precursor solution of a metal cluster; the heating temperature is 120-140°C; S2. Add N,N-dimethylformamide to the organic ligand and mix well to prepare a ligand solution; S3, fixing the polymer substrate in the middle of the counter-diffusion device, then adding the metal precursor solution of step S1 and the ligand solution of step S2 to both sides of the substrate respectively, and preparing a coordination polymer mixed matrix membrane after standing, soaking and drying; The volume ratio of N,N-dimethylformamide to acetic acid is 15:8; The polymer substrate includes at least one of polypropylene, polysulfone, polyethersulfone, and polyamide.

2. The method for in-situ preparation of a coordination polymer mixed matrix membrane by reverse diffusion at room temperature according to claim 1, characterized in that: In step S3, the standing is standing at room temperature for 24-96 hours.

3. The method for in-situ preparation of a coordination polymer mixed matrix membrane by reverse diffusion at room temperature according to claim 1, characterized in that: The molar ratio of the organic ligand to zirconium n-propoxide is 1.4-3:

1.

4. The method for in-situ preparation of a coordination polymer mixed matrix membrane by reverse diffusion at room temperature according to claim 1, characterized in that: In step S3, the concentrations of the organic ligand and zirconium n-propoxide are 0.0274-0.1173 mol / L and 0.0195-0.0389 mol / L, respectively.

5. The method for in-situ preparation of a coordination polymer mixed matrix membrane by reverse diffusion at room temperature according to claim 1, characterized in that: In step S1, the heating time is 2-4 hours.

6. A coordination polymer mixed matrix membrane prepared by the method according to any one of claims 1 to 5.

7. Use of the coordination polymer mixed matrix membrane according to claim 6 in gas separation.

8. The use according to claim 7, characterized in that The gas is a CO2 / CH4 mixed gas.

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