Polyimide mixed matrix gas separation membrane and preparation method thereof

Abstract

The invention discloses a polyimide mixed matrix gas separation membrane and a preparation method thereof. The preparation method comprises the following steps: step 1, preparing a polyimide glue solution; step 2, modifying the surface of the two-dimensional nanosheet; step 3, coating the two-dimensional nanosheet with the metal organic framework; step 4, preparing a polyimide glue solution containing the metal organic framework coated two-dimensional nanosheet; and 5, preparing the polyimide mixed matrix gas separation membrane. According to the preparation method, a metal organic framework is loaded on the surface of a two-dimensional nanosheet through an in-situ growth method, polyimide molding powder is dissolved in a solvent to serve as a polymer matrix, and the polyimide mixed matrix gas separation membrane with the two-dimensional nanosheet coated with the metal organic framework is prepared. Therefore, the gas permeability of the polyimide mixed matrix gas separation membrane is improved, and the gas selectivity of the polyimide mixed matrix gas separation membrane can be effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of gas separation membrane preparation, and in particular to a polyimide mixed matrix gas separation membrane and a preparation method thereof. Background Art

[0002] In the past few decades, separation and purification in the petrochemical industry is a key industrial process for separating the components of chemical mixtures, which accounts for about half of the industrial energy consumption. Compared with traditional separation processes such as cryogenic distillation and adsorption separation, membrane separation technology has the advantages of low energy consumption, small footprint, and convenient operation, making it a more energy-efficient option. Membrane separation technology has been widely used in gas separation, such as natural gas purification, air separation, and hydrogen purification. Polymer membranes are widely used in the field of membrane separation due to their advantages such as low cost and easy processing. However, most polymers are limited by the inherent trade-off between permeability and selectivity, which is called the "Robeson upper limit". Porous membranes prepared from carbon materials, zeolites or other crystalline microporous materials such as metal-organic frameworks usually have better separation performance, but their high cost, complex preparation process, and poor mechanical strength often hinder their industrial application. Mixed matrix membranes combine the advantages of polymers and fillers, and will be greatly optimized in terms of mechanical properties, processability, cost, permeability, and selectivity.

[0003] Polyimide (PI) is a class of polymer compounds containing imide groups in its molecular structure. The imide ring contained in the main chain of the molecule is formed by the condensation of compounds containing diamine and dianhydride in a non-protonic polar solvent. Polyimide materials have excellent thermal stability and good electrical insulation properties. They are called "problem solvers" and have been developed into a variety of application forms such as thin films, composite materials, special engineering plastics, fibers, photoresists, etc. They are widely used in aerospace, electronics, bioengineering and other fields. As selective materials for gas separation, two-dimensional nanomaterials with high aspect ratios are considered to have well-known advantages. However, in mixed matrix membranes, the high aspect ratio and high specific surface area of ​​two-dimensional fillers will increase the transmission resistance, thereby reducing the permeability of gas molecules. Therefore, it is necessary to develop an effective method for preparing a two-dimensional material and a metal organic framework composite filler for a mixed matrix membrane to construct a gas separation membrane with high permeability and selectivity. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems that the gas permeability and selectivity of polyimide mixed matrix gas separation membranes in the prior art are low and difficult to be applied to the needs of special gas separation, and to provide a method for preparing a polyimide mixed matrix gas separation membrane containing metal organic framework-coated two-dimensional nanosheets. The method is to in-situ grow a layer of metal organic framework particles on the surface of a high aspect ratio two-dimensional nanosheet to form a directional arrangement along the horizontal direction of the sheet layer, then add the metal organic framework-coated two-dimensional nanosheets to a polyimide glue solution, cast the film, and dry it to obtain a polyimide mixed matrix gas separation membrane containing metal organic framework-coated two-dimensional nanosheets.

[0005] The present invention is achieved through the following technical solutions.

[0006] A method for preparing a polyimide mixed matrix gas separation membrane comprises the following steps:

[0007] (1) Preparation of polyimide adhesive: The polyimide molding powder is uniformly mixed and defoamed in a non-protonic polar solvent to obtain a polyimide adhesive.

[0008] (2) Surface modification of two-dimensional nanosheets: The two-dimensional nanosheets are infiltrated and modified in an alcohol aqueous solution containing a surface modifier, dispersed, filtered, and dried to obtain surface-modified two-dimensional nanosheets.

[0009] (3) Metal-organic framework-coated two-dimensional nanosheets: The surface-modified two-dimensional nanosheets obtained in step (2) are ultrasonically dispersed in methanol for 1 hour; then a metal salt methanol solution is added, ultrasonically dispersed for 1 hour; then an organic framework methanol solution is added, ultrasonically dispersed and reacted for 3 hours to synthesize a metal-organic framework in situ on the surface of the two-dimensional nanosheets. After centrifugation, washing and drying, a metal-organic framework-coated two-dimensional nanosheet is obtained.

[0010] (4) Preparation of polyimide glue containing metal organic framework coated two-dimensional nanosheets: Add 5-40% by mass of the metal organic framework coated two-dimensional nanosheets obtained in step (3) to the polyimide glue obtained in step (1). After stirring, dispersing, filtering and vacuum degassing, a polyimide glue containing metal organic framework coated two-dimensional nanosheets is obtained.

[0011] (5) Preparation of polyimide mixed matrix gas separation membrane: The polyimide adhesive solution containing metal organic framework-coated two-dimensional nanosheets obtained in step (4) is coated on a smooth clean glass plate to form a film to obtain a polyimide adhesive film containing metal organic framework-coated two-dimensional nanosheets. The film is then dried in a vacuum drying oven at 60° C. for 12 hours to obtain a polyimide mixed matrix gas separation membrane containing metal organic framework-coated two-dimensional nanosheets.

[0012] Furthermore, in the preparation method, the polyimide molding powder in step (1) is any one of Vespel SP-1, Ultem1000, Torlon 4203, Upimol, and Aurum PL450c, or a combination thereof.

[0013] Furthermore, in the preparation method, the non-protonic polar solvent in step (1) is any one of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone, or a combination of solvents.

[0014] Furthermore, in the preparation method, the solid content of the polyimide glue in step (1) is 5-25%.

[0015] Furthermore, in the preparation method, the two-dimensional nanosheets in step (2) are any one or a combination of boron nitride nanosheets, aluminum oxide nanosheets, and graphene nanosheets.

[0016] Furthermore, in the preparation method, the surface modifier in step (2) is at least one of a phthalate coupling agent and an amino-functional silane coupling agent; wherein the phthalate coupling agent includes at least one of PN-130, PN-101, and PN-102, and the vinyl silane coupling agent includes at least one of KH-540, KH-550, KH-560, KH-570, and KH-602. Preferably, the amount of the coupling agent is 0.5-2% of the mass of the inorganic thermally conductive particles.

[0017] Furthermore, in the preparation method, the alcohol aqueous solution in step (2) is a mixture of water and low molecular alcohol. The mass ratio of water to low molecular alcohol is (0.5-2): (9.5-8). The low molecular alcohol is any one of methanol, ethanol, and isopropanol, or a combination thereof.

[0018] Furthermore, in the preparation method, the metal organic framework of step (3) is UiO-66, UiO-66-NH 2 , ZIF-8, ZIF-67, MIL-101(Fe), MIL-101(Cr), HKUST-1 or a combination thereof. The metal salt and organic framework material are conventional raw materials for preparing the corresponding metal organic framework.

[0019] Furthermore, in the preparation method, the mass ratio of the two-dimensional nanosheets, metal salt and organic framework in step (3) is (0.1-1):1:(1-5).

[0020] Furthermore, in the preparation method, the concentration of the metal salt methanol solution in step (3) is 0.1-4 mol / L.

[0021] Furthermore, in the preparation method, the concentration of the organic framework methanol solution in step (3) is 0.1-4 mol / L.

[0022] The present invention also provides a polyimide mixed matrix gas separation membrane, which is prepared by the above method.

[0023] The present invention is based on a large number of systematic experimental studies on the preparation of polyimide mixed matrix gas separation membranes by the inventors. At present, in order to meet the application requirements in the field of gas separation, inorganic materials are usually added to the polyimide matrix to prepare a mixed matrix membrane to improve its gas separation performance. Among many inorganic fillers, two-dimensional nanosheets are ideal fillers due to their high aspect ratio and high specific surface area. However, the high aspect ratio and high specific surface area of ​​the two-dimensional nanosheet filler will increase the transmission resistance. Too much filler will greatly reduce the permeability of gas molecules and have a negative impact on the performance of the film. Therefore, the present invention intends to load the metal organic framework onto the surface of the two-dimensional nanosheet by an in-situ growth method, and use polyimide molding powder dissolved in a solvent as a polymer matrix to prepare a polyimide mixed matrix gas separation membrane with a metal organic framework coated with two-dimensional nanosheets, thereby achieving the purpose of improving the gas permeability of the polyimide mixed matrix gas separation membrane while effectively improving its gas selectivity.

[0024] The beneficial effects of the present invention are:

[0025] (1) The metal-organic framework is composited with the two-dimensional nanosheet material through in-situ growth. It can take advantage of the high aspect ratio of the two-dimensional nanosheet to arrange the metal-organic framework in an orderly manner on the surface of the two-dimensional nanosheet to construct a gas transmission pathway, which can effectively reduce the transmission resistance and improve the gas permeability performance.

[0026] (2) Compared with one-dimensional nanowires, the random arrangement of two-dimensional nanosheets in the polyimide matrix acts as a barrier in the gas transmission path, providing a more complex gas transmission path, which is beneficial to improving gas selectivity.

[0027] (3) The metal organic framework particles are in situ grown on the surface of high aspect ratio two-dimensional nanosheets, and the interface bonding is strong. In the process of preparing polyimide mixed matrix gas separation membranes, it is not easy to block the gas transmission path due to particle shedding.

[0028] (4) The process of the present invention is simple and can be easily implemented on a large scale in industrial scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a SEM surface morphology image of the two-dimensional boron nitride nanosheets coated with the metal organic framework ZIF-67 according to Example 1 of the present invention.

[0030] Figure 2This is a SEM cross-sectional morphology of a polyimide mixed matrix gas separation membrane containing two-dimensional boron nitride nanosheets coated with metal organic framework ZIF-67 according to Example 1 of the present invention.

[0031] Figure 3 This is the SEM surface morphology of the two-dimensional boron nitride nanosheets of comparative example 5 of the present invention.

[0032] Figure 4 This is a SEM cross-sectional morphology of a polyimide gas separation membrane containing only two-dimensional boron nitride nanosheets according to comparative example 5 of the present invention. DETAILED DESCRIPTION

[0033] The invention is further described below in conjunction with specific examples. It should be noted that the following examples are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although the present invention has been described in detail in this specification with reference to the following examples, it should be understood by those skilled in the art that the present invention can still be modified or replaced by equivalents; and all technical solutions and improvements that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

[0034] Example 1.

[0035] This embodiment 1 provides a method for preparing a polyimide mixed matrix gas separation membrane, comprising the following steps:

[0036] (1) Preparation of polyimide adhesive: The polyimide molding powder Vespel SP-1 was uniformly mixed and defoamed in a non-protonic polar solvent N, N-dimethylformamide to prepare a polyimide adhesive with a solid content of 20%.

[0037] (2) The two-dimensional boron nitride nanosheets are infiltrated, modified, dispersed, filtered, and dried in an alcohol-water solution containing a KH-550 silane coupling agent (the mass ratio of water to ethanol is 1:9, and the amount of KH-550 silane coupling agent is 1.5% of the mass of the two-dimensional boron nitride nanosheets) to obtain surface-modified two-dimensional boron nitride nanosheets.

[0038] (3) Metal organic framework ZIF-67 coated two-dimensional boron nitride nanosheets: The surface modified two-dimensional boron nitride nanosheets obtained in step (2) were ultrasonically dispersed in methanol for 1 hour; then 1 mol / L Co(NO 3 ) 2 6H 2 O in methanol solution, ultrasonically disperse for 1 hour; then add a methanol solution containing 1.2 mol / L dimethylimidazole, ultrasonically disperse and react for 3 hours (two-dimensional boron nitride nanosheets, Co(NO 3 ) 2 6H 2O and dimethylimidazole (the mass ratio is 0.1:1:2), and a metal organic framework ZIF-67 is in situ synthesized on the surface of a two-dimensional boron nitride nanosheet. After centrifugation, washing, and drying, a metal organic framework ZIF-67 coated two-dimensional boron nitride nanosheet is obtained.

[0039] (4) Preparation of polyimide glue containing metal organic framework ZIF-67 coated two-dimensional boron nitride nanosheets: Add 10% by mass of the metal organic framework ZIF-67 coated two-dimensional boron nitride nanosheets obtained in step (3) to the polyimide glue obtained in step (1). After stirring and dispersing, filtering and vacuum degassing, a polyimide glue containing metal organic framework ZIF-67 coated two-dimensional boron nitride nanosheets is obtained.

[0040] (5) Preparation of polyimide mixed matrix gas separation membrane: The polyimide glue solution containing metal organic framework ZIF-67 coated with two-dimensional boron nitride nanosheets obtained in step (4) is coated on a smooth clean glass plate to form a film to obtain a polyimide glue film containing metal organic framework ZIF-67 coated with two-dimensional boron nitride nanosheets. Subsequently, the film is dried in a vacuum drying oven at 60° C. for 12 hours to obtain a polyimide mixed matrix gas separation membrane containing metal organic framework ZIF-67 coated with two-dimensional boron nitride nanosheets.

[0041] Figure 1 This is the SEM surface morphology of the metal-organic framework ZIF-67 coated with two-dimensional boron nitride nanosheets. Figure 2 This is the SEM cross-sectional morphology of a polyimide mixed matrix gas separation membrane containing metal organic framework ZIF-67 coated with two-dimensional boron nitride nanosheets.

[0042] Example 2.

[0043] This embodiment 2 provides a method for preparing a polyimide mixed matrix gas separation membrane, which is different from the embodiment 1 in that:

[0044] When executing step (4), the metal organic framework ZIF-67 coated two-dimensional boron nitride nanosheets obtained in step (3) are added to the polyimide glue obtained in step (1) at a mass fraction of 15%.

[0045] Example 3.

[0046] This embodiment 3 provides a method for preparing a polyimide mixed matrix gas separation membrane, which is different from the embodiment 1 in that:

[0047] When executing step (3), the two-dimensional boron nitride nanosheets, Co(NO 3 ) 2 6H 2 The mass ratio of O and dimethylimidazole is 0.2:1:2.

[0048] Example 4.

[0049] This embodiment 4 provides a method for preparing a polyimide mixed matrix gas separation membrane, which is different from the embodiment 1 in that:

[0050] When performing step (1), the polyimide molding powder Ultem 1000 is uniformly mixed and defoamed in the non-protonic polar solvent N,N-dimethylformamide to prepare a polyimide glue solution with a solid content of 20%.

[0051] Comparative example 5.

[0052] This comparative example 5 provides a method for preparing a polyimide mixed matrix gas separation membrane, which is different from Example 1 in that it has a polyimide mixed matrix gas separation membrane with a similar two-dimensional boron nitride nanosheet loading as Example 1, but does not contain the metal organic framework ZIF-67.

[0053] Step (3) is not performed. When step (4) is performed, the surface-modified two-dimensional boron nitride nanosheets are added to the polyimide glue obtained in step (1) at a mass fraction of 1.8%.

[0054] Figure 3 This is the SEM surface morphology of two-dimensional boron nitride nanosheets. Figure 4 This is the SEM cross-sectional morphology of a polyimide gas separation membrane containing only two-dimensional boron nitride nanosheets.

[0055] Comparative Example 6.

[0056] Comparative Example 6 provides a method for preparing a polyimide mixed matrix gas separation membrane, which is different from Example 1 in that a polyimide mixed matrix gas separation membrane having a metal organic framework ZIF-67 and two-dimensional boron nitride nanosheets with similar loading amounts to Example 1 is added respectively.

[0057] Step (3) is not performed. When step (4) is performed, the surface-modified two-dimensional boron nitride nanosheets and the metal organic framework are added to the polyimide glue obtained in step (1) at a mass fraction of 1.8% and 8.2%, respectively.

[0058] Gas separation and permeability performance:

[0059] The polyimide mixed matrix gas separation membrane containing metal organic framework ZIF-67 coated with two-dimensional boron nitride nanosheets prepared in Examples 1 to 4, the polyimide mixed matrix gas separation membrane containing only two-dimensional boron nitride nanosheets prepared in Comparative Example 5, and the polyimide mixed matrix gas separation membrane containing metal organic framework ZIF-67 and two-dimensional boron nitride nanosheets prepared in Comparative Example 6 were tested for gas separation and permeation performance, and the test was carried out in accordance with GB / T 1038-2000 standard. The test data are shown in Table 1.

[0060] Table 1

[0061]

[0062] Comparative Example 5 is a polyimide mixed matrix gas separation membrane having a similar loading amount of two-dimensional boron nitride nanosheets as in Example 1, but without the metal organic framework ZIF-67. Comparative Example 6 is a polyimide mixed matrix gas separation membrane having metal organic framework ZIF-67 and two-dimensional boron nitride nanosheets having similar loading amounts as in Example 1, respectively.

[0063] As can be seen from Table 1, compared with the polyimide mixed matrix gas separation membrane comparative example 5 having a similar two-dimensional boron nitride nanosheet loading as in Example 1 but without the metal organic framework ZIF-67, and the polyimide mixed matrix gas separation membrane comparative example 6 having a metal organic framework ZIF-67 and two-dimensional boron nitride nanosheet loading similar to that in Example 1, the polyimide mixed matrix gas separation membrane containing metal organic framework ZIF-67 coated with two-dimensional boron nitride nanosheets prepared in Examples 1 to 4 provided in the present application has a more excellent H 2 , CO 2 Permeability and H 2 / CO 2 Selectivity. This is mainly due to the following points: the metal organic framework particles are in-situ grown on the surface of high aspect ratio two-dimensional nanosheets, and are oriented in the horizontal direction of the sheet, which is more conducive to the construction of gas transmission channels in the direction outside the gas separation membrane surface and improves gas permeability; compared with one-dimensional nanowires, the random arrangement of two-dimensional nanosheets provides a longer gas transmission path, which is conducive to improving gas selectivity. In addition, the application of the in-situ growth method makes the metal organic framework and the two-dimensional nanosheet interface firmly bonded, and it is not easy for particles to fall off and block the gas transmission path.

[0064] As described above, the random arrangement of two-dimensional nanosheets of in-situ oriented metal-organic framework particles in the polyimide matrix not only makes it easier to construct gas transmission channels, but also lengthens the gas transmission path of the gas in the polyimide matrix. This provides feasibility for achieving high gas permeability and selectivity in the polyimide mixed matrix gas separation membrane containing metal-organic framework-coated two-dimensional nanosheets provided in the present application.

[0065] Although the embodiments of the present invention are described in detail above, it is obvious to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention as described in the claims. Moreover, the present invention described herein may have other embodiments and may be implemented or realized in a variety of ways.

Claims

1. A method for preparing a polyimide mixed matrix gas separation membrane, characterized in that: The steps include: Step 1, preparing polyimide glue solution: uniformly mixing and defoaming polyimide molding powder in a non-protonic polar solvent to prepare polyimide glue solution; Step 2, surface modification of two-dimensional nanosheets: infiltrating, modifying, dispersing, filtering and drying the two-dimensional nanosheets in an alcohol aqueous solution containing a surface modifier to obtain surface-modified two-dimensional nanosheets; Step 3, metal organic framework coated two-dimensional nanosheets: ultrasonically disperse the surface modified two-dimensional nanosheets obtained in step 2 in methanol for 1 hour; then add the metal salt methanol solution, ultrasonically disperse for 1 hour; then add the organic framework methanol solution, ultrasonically disperse and react for 3 hours, and in situ synthesize the metal organic framework on the surface of the two-dimensional nanosheet; after centrifugation, washing and drying, the metal organic framework coated two-dimensional nanosheets are obtained; Step 4, preparing a polyimide glue containing metal organic framework coated two-dimensional nanosheets: adding 5-40% by mass fraction of the metal organic framework coated two-dimensional nanosheets obtained in step 3 to the polyimide glue obtained in step 1; stirring, dispersing, filtering and vacuum degassing to obtain a polyimide glue containing metal organic framework coated two-dimensional nanosheets; Step 5, preparing a polyimide mixed matrix gas separation membrane: coating the polyimide adhesive solution containing metal organic framework-coated two-dimensional nanosheets obtained in step 4 on a smooth and clean glass plate to form a film to obtain a polyimide adhesive film containing metal organic framework-coated two-dimensional nanosheets; then drying it in a vacuum drying oven at 60°C for 12 hours to obtain a polyimide mixed matrix gas separation membrane containing metal organic framework-coated two-dimensional nanosheets.

2. The method for preparing a polyimide mixed matrix gas separation membrane according to claim 1, characterized in that: The polyimide molding powder in step 1 is any one or a combination of Vespel SP-1, Ultem 1000, Torlon 4203, Upimol, and Aurum PL450c, and the aprotic polar solvent in step 1 is any one or a combination of N,N-dimethylacetamide, N,N-dimethylformamide, and N-methylpyrrolidone.

3. The method for preparing a polyimide mixed matrix gas separation membrane according to claim 1, characterized in that: The solid content of the polyimide glue in step 1 is 5-25%.

4. The method for preparing a polyimide mixed matrix gas separation membrane according to claim 1, characterized in that: The two-dimensional nanosheets in step 2 are any one or a combination of boron nitride nanosheets, aluminum oxide nanosheets, and graphene nanosheets.

5. The method for preparing a polyimide mixed matrix gas separation membrane according to claim 1, characterized in that: The surface modifier in step 2 is at least one of a phthalate coupling agent and an amino-functional silane coupling agent; wherein the phthalate coupling agent includes at least one of PN-130, PN-101, and PN-102, and the vinyl silane coupling agent includes at least one of KH-540, KH-550, KH-560, KH-570, and KH-602.

6. The method for preparing a polyimide mixed matrix gas separation membrane according to claim 1, characterized in that: The alcohol aqueous solution in step 2 is a mixture of water and low molecular alcohol, the mass ratio of water to low molecular alcohol is (0.5-2):(9.5-8), and the low molecular alcohol is any one of methanol, ethanol, and isopropanol or a combination thereof.

7. The method for preparing a polyimide mixed matrix gas separation membrane according to claim 1, characterized in that: The metal organic framework in step 3 is any one or a combination of UiO-66, UiO-66-NH2, ZIF-8, ZIF-67, MIL-101(Fe), MIL-101(Cr), and HKUST-1.

8. The method for preparing a polyimide mixed matrix gas separation membrane according to claim 1, characterized in that: The mass ratio of the two-dimensional nanosheets, metal salt and organic framework in step 3 is (0.1-1):1:(1-5).

9. The method for preparing a polyimide mixed matrix gas separation membrane according to claim 1, characterized in that: The concentration of the metal salt methanol solution in step 3 is 0.1-4 mol / L, and the concentration of the organic framework methanol solution in step 3 is 0.1-4 mol / L.

10. A polyimide mixed matrix gas separation membrane, characterized in that: The preparation method is described in any one of claims 1 to 9.

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