Mixed matrix membrane for high-efficiency oxygen-nitrogen separation as well as preparation method and application of mixed matrix membrane

Abstract

The invention discloses a mixed matrix membrane for efficient oxygen and nitrogen separation and a preparation method and application thereof. The mixed matrix membrane comprises a polymer continuous phase and an MOF filler uniformly dispersed in the polymer continuous phase, the MOF filler can separate nitrogen and oxygen, and the surface of the MOF filler is modified by the silane coupling agent, so that the MOF filler is well compatible with a polymer, and the oxygen-nitrogen separation effect is improved. The polymer solution and the MOF filler dispersion liquid are mixed, the mixed matrix membrane is prepared through the non-solvent induced phase separation method, and the method has the advantages of being simple in reaction condition, high in efficiency, easy to amplify and the like and has wide engineering prospects.

Description

Technical Field

[0001] This invention relates to the fields of functional polymer materials and membrane separation technology, and in particular to a mixed matrix membrane for efficient oxygen and nitrogen separation, its preparation method, and its application. Background Technology

[0002] Air contains approximately 21% oxygen and 78% nitrogen by volume. Oxygen-enriched air refers to air enriched by separating nitrogen and oxygen, and it has wide applications in healthcare, high-temperature combustion, chemical oxidation, and aquaculture. Membrane gas separation technology has become an important air separation method due to its advantages such as low energy consumption, simple operation, and environmental friendliness. Currently, commercially available gas separation membranes mainly use polymer membranes, such as glassy polymer membranes like polyimide and polysulfone, which utilize the differences in gas permeability to separate nitrogen and oxygen.

[0003] However, traditional polymer membranes generally suffer from a trade-off known as the "Robson's upper limit," where permeability and selectivity are mutually constrained; high selectivity often comes at the cost of low permeability, and vice versa. This limits further improvements in separation efficiency. To overcome this limit, mixed matrix membranes have emerged. Mixed matrix membranes (MMMs) disperse inorganic fillers, such as zeolites, carbon molecular sieves, and metal-organic frameworks, into a polymer matrix, aiming to combine the excellent film-forming properties and processability of polymers with the superior sorting performance of inorganic fillers.

[0004] MOFs (metal-organic frameworks) are a class of crystalline porous materials with regular pore structures formed by the self-assembly of metal ions and organic ligands. Their pore sizes are tunable, and their specific surface areas are large, showing great potential for gas adsorption and separation. However, using MOF materials to prepare MMMs faces a key challenge: poor interfacial compatibility between MOF particles and the polymer matrix. Since MOF surfaces are typically inorganic while polymers are organic, non-selective voids (interfacial defects) easily form at the interface. These voids are usually much wider than the molecular diameter, allowing both oxygen and nitrogen to pass through, severely reducing the actual separation selectivity of the membrane. Furthermore, MOF particles readily aggregate in polymer solutions, leading to uneven dispersion and further deteriorating membrane performance.

[0005] Therefore, developing a high-performance oxygen-nitrogen separation mixed matrix membrane that can effectively solve the interfacial compatibility problem and fully utilize the sieving advantages of MOF packing has important scientific value and engineering significance. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the primary objective of this invention is to provide a hybrid matrix membrane in which modified MOF particles can be well dispersed and compatible within a polymer matrix, avoiding non-selective voids and thereby improving nitrogen and oxygen separation efficiency.

[0007] To achieve the above objectives, the present invention provides a mixed matrix membrane for efficient oxygen and nitrogen separation, comprising a polymer continuous phase and MOF packing uniformly dispersed in the polymer continuous phase; the MOF packing is capable of separating nitrogen and oxygen, and the surface of the MOF packing is modified by a silane coupling agent.

[0008] As a preferred technical solution, the MOF packing includes ZIF-8, and the pore opening size of the ZIF-8 is 0.35~0.38nm.

[0009] As a preferred technical solution, the continuous polymer phase is a glassy polymer, including one or more of polyimide, polysulfone, and polyethersulfone.

[0010] As a preferred technical solution, the silane coupling agent is 3-aminopropyltriethoxysilane.

[0011] As a preferred technical solution, the MOF filler has a mass fraction of 5% to 30% in the mixed matrix membrane.

[0012] As a preferred technical solution, the surface of the polymer continuous phase has a porous structure.

[0013] To address the shortcomings of existing technologies, a second objective of this invention is to provide a preparation method capable of producing a hybrid matrix membrane, comprising the following steps: S1, Surface modification of MOF filler: MOF filler is dispersed in a first organic solvent, and silane coupling agent is added and heated to react. After reaction, the filler is separated, washed and dried to obtain modified MOF filler. S2, Preparation of casting solution: Dissolve the glassy polymer in a second organic solvent to form a polymer solution; disperse the modified MOF filler in the second organic solvent to obtain a MOF filler dispersion; mix the polymer solution and the MOF filler dispersion, and stir to make them uniformly mixed to obtain the casting solution; S3, Film Formation: The casting liquid is scraped onto the substrate to form a liquid film, and then the substrate with the liquid film is immersed in a coagulation bath to form a solid film by a non-solvent-induced phase separation method. S4, Post-processing: The solid membrane is washed and dried to obtain the mixed matrix membrane.

[0014] As a preferred technical solution, the first organic solvent is one or a mixture of several of alcohols, benzenes, hydrocarbons, and esters.

[0015] As a preferred technical solution, the second organic solvent is N-methylpyrrolidone or N,N-dimethylformamide.

[0016] As a preferred technical solution, in step S3, the coagulation bath is water or a mixture of water and a second organic solvent.

[0017] To address the shortcomings of existing technologies, a third objective of this invention is to provide an application of a mixed matrix membrane in gas separation, wherein the gas separation is the separation of oxygen and nitrogen from air for the preparation of oxygen-enriched air.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention treats the surface of MOF packing material with a silane coupling agent. One end of the silane molecule is connected to the surface of the MOF packing material through a chemical bond, while the organic segment at the other end is compatible with the polymer. This eliminates the interfacial property differences between the MOF packing material and the polymer, making the MOF packing material and the polymer highly compatible. This avoids the formation of non-selective voids between the MOF packing material and the polymer, and improves the overall selective separation effect of nitrogen and oxygen in the mixed matrix membrane.

[0019] Secondly, after silanization modification, the organic segments on the MOF surface can reduce its surface energy and also hinder particle aggregation through steric hindrance, thus ensuring uniform dispersion in the polymer matrix. Improved dispersibility allows for sufficient contact between MOF particles and the polymer, preventing localized agglomeration and guaranteeing the compactness of the film structure.

[0020] 2. The MOF packing of the present invention includes ZIF-8, the pore opening size of which is 0.35~0.38 nm. The kinetic diameter of oxygen molecules is approximately 0.346 nm, and the kinetic diameter of nitrogen molecules is approximately 0.364 nm. The pore opening of ZIF-8 allows oxygen molecules to pass through smoothly, ensuring the oxygen transport rate. Simultaneously, because the kinetic diameter of nitrogen molecules is similar to that of the pore opening of ZIF-8, the transport rate of nitrogen is lower than that of oxygen, thus achieving nitrogen-oxygen separation. Oxygen can diffuse through the polymer continuous phase to reach the other side of the mixed matrix membrane, achieving nitrogen-oxygen separation. Furthermore, the silanized ZIF-8 is uniformly dispersed in the polymer continuous phase, and oxygen permeating in the polymer continuous phase can also diffuse through ZIF-8, thereby increasing the oxygen transport rate.

[0021] 3. This invention uses a solvent-inducible phase separation method for preparation, which is simple and has good prospects for engineering applications. Detailed Implementation

[0022] The following examples further illustrate the features and other related characteristics of the present invention in detail, to facilitate understanding by those skilled in the art: An embodiment of the present invention provides a mixed matrix membrane for efficient oxygen and nitrogen separation, comprising a polymer continuous phase and MOF packing uniformly dispersed in the polymer continuous phase; the MOF packing is capable of separating nitrogen and oxygen, and the surface of the MOF packing is modified by a silane coupling agent.

[0023] Since the kinetic diameter of oxygen molecules is approximately 0.346 nm and that of nitrogen molecules is approximately 0.364 nm, in some embodiments, the MOF packing includes ZIF-8, with a pore opening size of 0.35~0.38 nm. The pore openings of ZIF-8 allow oxygen molecules to pass through smoothly, ensuring the oxygen molecule transport rate. Simultaneously, because the kinetic diameter of nitrogen molecules is similar to that of the ZIF-8 pore openings, the nitrogen transport rate is lower than that of oxygen, thus achieving nitrogen-oxygen separation. Furthermore, oxygen can diffuse through the polymer continuous phase to reach the other side of the mixed matrix membrane, achieving nitrogen-oxygen separation. Simultaneously, the silanized ZIF-8 is uniformly dispersed in the polymer continuous phase, and oxygen permeating in the polymer continuous phase can also diffuse through ZIF-8, further increasing the oxygen transport rate.

[0024] In some embodiments, the continuous polymer phase is a glassy polymer, including one or more of polyimide, polysulfone, and polyethersulfone, which can provide necessary mechanical support for the mixed matrix membrane. At the same time, polyimide, polysulfone, and polyethersulfone are resistant to acids and alkalis, have strong anti-swelling ability, and maintain structural stability in a working environment of 10~60°C and a certain pressure.

[0025] In some embodiments, the polyimide is a 6FDA type polyimide or Matrimid® 5218.

[0026] In some embodiments, the silane coupling agent is 3-aminopropyltriethoxysilane, which contains amino groups that can bond with the continuous phase of polymers such as polyimide, polysulfone, and polyethersulfone. The triethoxysilane groups can bond with MOF fillers and are soluble in most organic solvents, which is beneficial for the preparation of mixed matrix membranes.

[0027] To balance the structural stability and oxygen-nitrogen separation efficiency of the mixed matrix membrane, in some embodiments, the mass fraction of the MOF filler in the mixed matrix membrane is 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%.

[0028] In some embodiments, the surface of the polymer continuous phase has a porous structure, which increases the surface area of ​​the polymer continuous phase and facilitates the diffusion of oxygen into the polymer continuous phase.

[0029] This invention also provides a method for preparing a hybrid matrix membrane, comprising the following steps: S1, Surface modification of MOF filler: The MOF filler is dispersed in a first organic solvent, and a silane coupling agent is added and heated to react. After the reaction, the filler is separated, washed, and dried to obtain the modified MOF filler. The first organic solvent is one or a mixture of several alcohols, benzenes, hydrocarbons, and esters, and will not react with the silane coupling agent.

[0030] S2, Preparation of casting solution: Dissolve the glassy polymer in a second organic solvent to form a polymer solution; disperse the modified MOF filler in the second organic solvent to obtain a MOF filler dispersion; mix the polymer solution and the MOF filler dispersion and stir to make them uniformly mixed to obtain a casting solution; the second organic solvent is N-methylpyrrolidone or N,N-dimethylformamide, which is miscible with water, glassy polymer and other organic solvents.

[0031] S3, Film Formation: The casting liquid is scraped onto the substrate to form a liquid film, and then the substrate with the liquid film is immersed in a coagulation bath to form a solid film by a non-solvent-induced phase separation method.

[0032] S4, Post-processing: The solid membrane is washed and dried to obtain the mixed matrix membrane.

[0033] Example 1 Example 1 of the present invention provides a hybrid matrix membrane, the preparation method of which includes the following steps: S1. Surface modification of ZIF-8: Weigh 1.0 g of ZIF-8A powder (pore opening size 0.35~0.4 nm, particle size range 200~500 nm) and place it in a 100 ml round-bottom flask. Add 50 mL of anhydrous toluene and ultrasonically disperse for 30 minutes. Under nitrogen protection, slowly add 1.0 mL of 3-aminopropyltriethoxysilane (APTES) dropwise to the round-bottom flask. Heat the system to 110 °C and reflux for 12 hours. After the reaction is complete, cool to room temperature and collect the solid product by centrifugation. Wash three times each with anhydrous toluene and anhydrous ethanol. Dry the product in a vacuum drying oven at 80 °C for 12 hours to obtain the surface-grafted aminopropyl modified ZIF-8 filler, denoted as APTES@ZIF-8a1.

[0034] S2, Preparation of casting solution: Weigh 0.9 g of Matrimid 5218 polymer and dissolve it in 18.1 g of N-methylpyrrolidone. Stir at 60°C for 6 hours to form a homogeneous and transparent 5 wt% polymer solution. Weigh 0.1 g of APTES@ZIF-8a1 and disperse it in 5 g of N-methylpyrrolidone. Sonicate the solution in an ice-water bath (400 W) for 30 minutes to obtain a uniform MOF dispersion. Pour the MOF dispersion into the polymer solution and mechanically stir for 24 hours to ensure uniform mixing. Allow to stand to remove bubbles to obtain the casting solution.

[0035] S3, Film Formation: Using a doctor blade, the casting solution is applied to a clean glass plate to form a liquid film. The substrate with the liquid film is then immersed in a deionized water coagulation bath. The film automatically peels off from the glass plate. The film is then cured in the coagulation bath for 24 hours, during which the water is changed three times to fully replace the solvent.

[0036] S4, Post-processing: Remove the membrane, sandwich it between two filter papers, and allow it to air dry at room temperature for 48 hours to obtain a mixed matrix membrane, labeled as 10 wt% APTES@ZIF-8A / Matrimid 5218.

[0037] Example 2 The difference between this embodiment and Embodiment 1 is that in S2, the amount of APTES@ZIF-8A added is 20% of the mixed matrix membrane, i.e., 0.8g of Matrimid 5218 and 0.2g of APTES@ZIF-8 are weighed out. The remaining steps and parameters are exactly the same as in Embodiment 1. The label is 20wt% APTES@ZIF-8A / Matrimid 5218.

[0038] Example 3 The difference between this embodiment and Example 1 is that the polymer used is 6FDA type polyimide. The remaining steps and parameters are exactly the same as in Example 1. (Note: 10wt% APTES@ZIF-8A / 6FDA)

[0039] Comparative Example 1 The difference between this comparative example and Example 1 is that APTES was not used to modify ZIF-8A; instead, the original ZIF-8 powder was used directly. The remaining steps and parameters were exactly the same as in Example 1, designated as 10 wt% ZIF-8A / Matrimid 5218.

[0040] Comparative Example 2 This comparative example prepared a pure Matrimid 5218 polymer membrane. No MOF filler was added; 1.0 g of Matrimid 5218 was dissolved in 19.0 g of N-methylpyrrolidone to form a casting solution. Subsequent film formation steps were the same as in Example 1. Matrimid 5218 and N-methylpyrrolidone are designated as such. Comparative Example 3 The difference between this comparative example and Example 1 is that ZIF-8B powder (pore opening size of 1~2nm, particle size range of 200~500nm) was used in S1, while the remaining steps and parameters were exactly the same as in Example 1. The designation is 10wt% APTES@ZIF-8B / Matrimid 5218.

[0041] Comparative Example 4 The difference between this comparative example and Example 1 is that in S2, the amount of APTES@ZIF-8A added is 35% of the mixed matrix membrane, i.e., 0.65g of Matrimid 5218 and 0.35g of APTES@ZIF-8 are weighed. The remaining steps and parameters are exactly the same as in Example 1. The sample number is 35wt% APTES@ZIF-8A / Matrimid 5218.

[0042] The aforementioned ZIF-8A and ZIF-8B powders were both custom-made by the applicant from Guangdong Carbon Language New Materials Co., Ltd.

[0043] Performance testing The membranes prepared in Examples 1-3 and Comparative Examples 1-4 were cut into circular samples with an effective area of ​​10 cm² and installed in a gas permeability testing device. The upstream pressure was set to 5 bar, and the downstream pressure was kept at atmospheric pressure. High-purity oxygen, nitrogen, and simulated air (78 parts by volume of nitrogen and 21 parts by volume of oxygen) were used, respectively. After the downstream gas flux stabilizes, the gas permeation rate is measured using a soap film flow meter.

[0044] Calculate the permeability coefficients of nitrogen and oxygen: P = (Q × L) / (A × Δp × t), where the unit of permeability coefficient P is Barrer and the unit of total gas permeation Q is cm³. 3 The unit for the mixed matrix membrane thickness L is cm, the unit for the effective permeation area A is cm², the unit for the pressure difference Δp across the membrane is cm (Hg), and the unit for the gas permeation time t is s. Nitrogen-oxygen separation rate = (volume fraction of oxygen in downstream simulated air) / (volume fraction of oxygen in upstream simulated air).

[0045] Table 1 shows the test results of Examples 1-3 and Comparative Examples 1-4. project Nitrogen permeability coefficient / Barrer Oxygen permeability coefficient / Barrer Oxygen / nitrogen selectivity Nitrogen-oxygen separation rate Example 1 2.7 22.5 8.2 3.25 Example 2 3.3 25.8 7.6 3.16 Example 3 3.1 25.3 8.1 3.23 Comparative Example 1 5.4 26.1 4.8 2.66 Comparative Example 2 1.1 9.2 8.5 3.28 Comparative Example 3 4.6 24.4 5.3 2.94 Comparative Example 4 3.9 28.3 7.2 3.11 (1) As can be seen from the comparison between Example 1 and Comparative Example 1, modifying ZIF-8 with a silane coupling agent can significantly improve the selectivity of oxygen / nitrogen. This is because the modified ZIF-8 is well compatible with the polymer, reducing the interfacial defects between ZIF-8 and the polymer. The gas needs to pass through the polymer or ZIF-8 for selection before it can pass through the mixed matrix membrane, thus achieving a good separation effect. However, the ZIF-8 in Comparative Example 1 was not modified with silane, and there were more interfacial defects between ZIF-8 and the polymer, which caused a large amount of nitrogen to pass through the mixed matrix membrane, thereby reducing the nitrogen-oxygen separation effect.

[0046] (2) As can be seen from the comparison between Example 1 and Comparative Example 2, the polymer mixed with ZIF-8 can significantly improve the oxygen permeability coefficient, thereby improving the nitrogen-oxygen separation efficiency, and can also maintain a good separation effect.

[0047] (3) As can be seen from Examples 1, 2 and Comparative Example 4, the higher the ZIF-8 content in the mixed matrix membrane, the higher the oxygen permeation coefficient, but the corresponding oxygen / nitrogen selectivity will decrease, and the polymer has a lower supporting and dispersing effect on ZIF-8. This is because the polymer has a higher selectivity for nitrogen and oxygen, but the polymer has a lower permeation effect on gases. Taking into account the nitrogen and oxygen separation efficiency and the mechanical strength of the mixed matrix membrane, the ZIF-8 content in the mixed matrix membrane is 10%~30%.

[0048] (4) Comparing Example 1 and Comparative Example 3, it can be seen that the ZIF-8 pore size is similar to the nitrogen molecule dynamic diameter, and the increased nitrogen flow rate leads to a significant decrease in selectivity. Although the oxygen permeability coefficient is high, the nitrogen-oxygen separation efficiency is reduced.

[0049] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A mixed matrix membrane for efficient oxygen / nitrogen separation, characterized in that, The mixed matrix membrane comprises a polymer continuous phase, and MOF fillers uniformly dispersed in the polymer continuous phase; the MOF fillers can separate nitrogen and oxygen, and the surface of the MOF fillers is modified by a silane coupling agent.

2. The mixed matrix membrane for efficient oxygen / nitrogen separation according to claim 1, wherein, The MOF fillers comprise ZIF-8, and the pore opening size of the ZIF-8 is 0.35-0.38 nm.

3. The mixed matrix membrane for efficient oxygen / nitrogen separation of claim 1, wherein, The polymer continuous phase is a glassy polymer, and comprises one or more of polyimide, polysulfone and polyethersulfone.

4. The mixed matrix membrane for efficient oxygen / nitrogen separation of claim 1, wherein, The silane coupling agent is 3-aminopropyltriethoxysilane.

5. The mixed matrix membrane for efficient oxygen / nitrogen separation of claim 1, wherein, The mass fraction of the MOF fillers in the mixed matrix membrane is 5%-30%.

6. The mixed matrix membrane for efficient oxygen / nitrogen separation of claim 1, wherein, The surface of the polymer continuous phase has a porous structure.

7. A method for producing a mixed matrix membrane according to any one of claims 1 to 6, characterized in that, The method comprises the following steps: S1, surface modification of the MOF fillers: dispersing the MOF fillers in a first organic solvent, adding a silane coupling agent and heating for reaction, and then separating, washing and drying to obtain modified MOF fillers; S2, preparation of a casting solution: dissolving a glassy polymer in a second organic solvent to form a polymer solution; dispersing the modified MOF fillers in the second organic solvent to obtain an MOF filler dispersion; mixing the polymer solution and the MOF filler dispersion, and stirring to uniformly mix them to obtain the casting solution; S3, film formation: coating the casting solution on a substrate to form a liquid film, and then immersing the substrate with the liquid film in a coagulation bath to form a solid film by a non-solvent induced phase separation method; S4, post-treatment: washing and drying the solid film to obtain the mixed matrix membrane.

8. The method of claim 7, wherein The first organic solvent is a mixture of one or more of alcohols, benzene, hydrocarbons and esters; the second organic solvent is N-methylpyrrolidone or N,N-dimethylformamide; in step S3, the coagulation bath is water or a mixed solution of water and the second organic solvent.

9. The method of claim 7, wherein In steps S1 and S2, the substances are dispersed by ultrasonic treatment of the liquids.

10. Use of a mixed matrix membrane according to claims 1 to 6 or a mixed matrix membrane prepared according to the method of claims 7 to 9 for gas separation. The gas separation is separation of oxygen and nitrogen from air for preparation of oxygen-enriched air.