Mixed matrix membrane with high filler loading capacity and preparation method thereof

Abstract

The invention relates to a membrane material, in particular to a mixed matrix membrane with high filler loading capacity and a preparation method thereof. According to the invention, the MOF particle modification layer polymer and the film-forming polymer both adopt PIM-1, so that the interface energy is reduced, and the compatibility between the filler and the film layer is improved, thereby greatly increasing the filler loading capacity in the film-forming polymer.

Description

TECHNICAL FIELD

[0001] The present application relates to a membrane material, in particular to a mixed matrix membrane with high filler loading and a preparation method thereof. BACKGROUND

[0002] Polymer intrinsic microporous material (PIM-1) as a new type of polymer separation membrane material, due to its unique rigid twisted chain segment structure and nanoscale microporous characteristics, shows significant advantages in the field of CO2 / CH4 separation. In order to improve the performance of PIM-1 separation membrane, dispersing porous fillers (such as metal-organic frameworks, MOFs) with ordered channels in PIM-1 polymer to form mixed matrix membranes (MMMs) is an effective strategy.

[0003] However, the full performance of MMMs depends on the uniform dispersion of fillers in the matrix and the good interfacial compatibility between the polymer matrix and the fillers. Insufficient interfacial compatibility will lead to the formation of non-selective defects at the interface, and gas molecules will transport through these defects, which will seriously damage the separation selectivity of the membrane. In order to solve the difference in chemical properties between the surface of MOFs and the polymer matrix, the strategy of organic surface modification of MOFs is often used to enhance the interfacial compatibility. Traditional organic modifiers (usually small molecules or non-gas permeable polymers) often form a dense coating layer on the surface of MOFs, which blocks the opening of the MOF channels and hinders gas transmission, thereby reducing the molecular sieving function of MOFs.

[0004] In the early work of the inventors, ZIF-NH2 was surface modified with acyl chloride functionalized PIM (PIM-COCl) and doped in 6FDA-DAM polymer to prepare defect-free MMMs, which achieved good results. However, the optimal loading of the fillers is only 20wt%, and with the continuous increase of the loading, the selectivity of the MMMs decreases significantly. Therefore, how to prepare a mixed matrix membrane with high filler loading to simultaneously improve its separation selectivity for CO2 / CH4 and CO2 permeability is a problem to be solved. SUMMARY

[0005] In view of the above problems, the present application uses PIM-1 as the modifier layer polymer of MOF particles and the film-forming polymer, which reduces the interfacial energy and improves the compatibility between the fillers and the membrane layer, thereby greatly increasing the filler loading in the film-forming polymer.

[0006] Specifically, the application provides a mixed matrix membrane with high filler loading, which comprises a PIM-1 polymer matrix and modified MOF composite particles, wherein the modified MOF composite particles are obtained by surface grafting of acyl chloride functionalized PIM-1 polymer on modified MOF nanoparticles, and the mass percentage of the modified MOF composite particles in the mixed matrix membrane is 5-45 wt%.

[0007] Preferably, the modified MOF nanoparticles are MOF nanoparticles with amino groups or hydroxyl groups on the surface.

[0008] Preferably, the modified MOF nanoparticles are selected from at least one of ZIF-8-NH2, ZIF-67-NH2 、 UiO-66-NH2, ZIF-8-OH, ZIF-67-OH and UiO-66-OH.

[0009] Preferably, in the modified MOF composite particles, the mass ratio of acyl chloride functionalized PIM-1 polymer to modified MOF nanoparticles is 1:1 to 1:4.

[0010] Preferably, the PIM-1 polymer matrix contains 1-5 wt% of PIM-COOH.

[0011] Preferably, the mass percentage of the modified MOF composite particles in the mixed matrix membrane is 20-45 wt%, more preferably 30-40 wt%, and most preferably 35 wt%, under which the performance of the mixed matrix membrane is optimal.

[0012] The application also provides a method for preparing the mixed matrix membrane based on the gradient bonding interface, which comprises the following steps: (1) preparing acyl chloride functionalized PIM-1 polymer; (2) preparing modified MOF composite particles: mixing MOF nanoparticles with amino groups or hydroxyl groups on the surface with acyl chloride functionalized intrinsic microporous polymer in an organic solvent, and performing amidation reaction at a certain temperature, then separating, washing and re-dispersing in chloroform to obtain a modified MOF composite particle dispersion; (3) preparing a casting solution: dissolving PIM-1 polymer matrix in chloroform, then adding the modified MOF composite particle dispersion obtained in step (2) and mixing uniformly to obtain a casting solution; (4) film forming: casting the casting solution into a film, and obtaining the mixed matrix membrane after drying.

[0013] Preferably, in step (1), the acyl chloride functionalized PIM-1 polymer is prepared by the following steps: PIM is oxidatively hydrolyzed in a mixture of sulfuric acid and acetic acid to obtain PIM-COOH, after purification, PIM-COOH is reacted with SOCl2 to obtain PIM-COCl, and PIM-COCl is separated and dried by solvent precipitation.

[0014] Preferably, in step (2), the temperature of the amidation reaction is 25-100℃, and the stirring time is 20-60 min.

[0015] The mixed matrix membrane provided by the application can be applied in separating a gas mixture, wherein the gas mixture is a CO2 / CH4 mixed gas, and the mixed matrix membrane is used for selectively permeating CO2.

[0016] Compared with the prior art, the application has the following advantages: Firstly, the modified polymer and the film-forming polymer both use PIM-1 in the application, which significantly reduces the interfacial energy, greatly improves the compatibility between the filler and the membrane layer, and enables the filler and the membrane layer to form a more compact and uniform combination, so that the filler loading in the film-forming polymer can be greatly increased. High filler loading not only enhances the separation selectivity of the membrane for CO2 / CH4, but also improves the CO2 permeability, effectively solving the problem of significant decrease in selectivity under high filler loading in the prior art, and providing a new idea and method for preparing a high-performance mixed matrix membrane.

[0017] Secondly, the application introduces a specific content of PIM-COOH into the PIM-1 polymer matrix, which further optimizes the performance of the mixed matrix membrane. The carboxyl group of PIM-COOH can react with the acyl chloride group on the surface of the modified MOF composite particles, which further enhances the interfacial bonding force between the filler and the polymer matrix, effectively inhibits the agglomeration of the filler under high filler loading, reduces the formation of non-selective defects, and makes the gas transmission channel more ordered, thereby improving the separation selectivity of the membrane for CO2 / CH4. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a FT-IR absorption spectrum of ZIF-NH2 and PZIF-CONH, which is a local amplification of the formation of covalent bonds between the amino functionalized ZIF and the acyl chloride modified PIM in Example 1; Figure 2 is a SEM image of the mixed matrix membrane sample prepared in Example 1; Figure 3 is a SEM image of the mixed matrix membrane sample prepared in Comparative Example 2. DETAILED DESCRIPTION

[0019] The technical solutions of the present application will be described in detail below with specific examples, so that those skilled in the art can better understand and implement the technical solutions of the present application, but the present application is not limited in the scope of the examples.

[0020] Example 1 This example provides an aluminum-based MOF mixed matrix membrane, and the preparation steps are as follows: Preparation of raw materials and intermediates: (1) Synthesis of amino-functionalized zeolitic imidazolate framework (ZIF-8-NH2): 0.3719 g (1.25 mmol) of zinc nitrate hexahydrate was dissolved in 25 mL of methanol. Separately, 0.6568 g (8 mmol) of 2-methylimidazole and 0.2663 g (2 mmol) of 2-aminobenzimidazole were dissolved in 25 mL of methanol and stirred for 2 h. The zinc salt solution was slowly added to the ligand solution under stirring, and the reaction was continued at room temperature for 12 h. The product was collected by centrifugation, washed with fresh methanol and tetrahydrofuran (THF) three times each, and finally dispersed in THF to obtain a ZIF-8-NH2 dispersion with a concentration of 10 mg / mL.

[0021] (2) Synthesis of acyl chloride-terminated intrinsic microporous polymer (PIM-COCl): First, PIM-1 was synthesized. 3.4 g (10 mmol) of TTSBI and 2 g (10 mmol) of TFTPN were added to 70 mL of anhydrous DMF and stirred at 65°C under argon until clear. 4.1 g of anhydrous K2CO3 was added and the reaction was stirred at 65°C for 72 h. The product was precipitated, filtered, and purified twice by dissolving in chloroform and precipitating in methanol, and then washed with 1,4-dioxane, acetone, water, and methanol, respectively, and dried at 120°C under vacuum to obtain PIM-1. 1 g of PIM-1 was added to a mixed acid composed of 60 mL of water, 60 mL of concentrated H2SO4, and 20 mL of acetic acid, and reacted at 150°C for 48 h to obtain PIM-COOH. 0.8 g of PIM-COOH was reacted with 30 mL of SOCI2 at 90°C for 24 h, and after evaporation, dissolution (chloroform), and precipitation (n-hexane), it was dried at 70°C under vacuum to obtain PIM-COCl with a yield of 89.7%. It was dissolved in THF to prepare a 10 mg / mL stock solution.

[0022] 2. Preparation of hybrid filler (PZIF): 10 g of the above THF solution of PIM-COCl (containing 100 mg of PIM-COCl) was mixed with 200 mg of ZIF-NH2 and stirred at room temperature for 30 min. After the reaction, the product was collected by centrifugation, washed with THF and chloroform three times each, and finally dispersed in chloroform to prepare a PZIF dispersion with a concentration of 88.71 mg / g.

[0023] 3. Preparation of PZIF / 6FDA-DAM mixed matrix membrane: 0.3 g PIM-1 polymer (containing 3 wt% of PIM-COOH) was dissolved in 6 mL chloroform and filtered. To prepare a membrane with a filler loading of 35 wt.%, 1.82 g PZIF was weighed and chloroform was added to make the total mass 4 g, and the above polymer solution was added. The mixture was roller mixed overnight, degassed for 30 min, and ultrasonicated for 5 min before being cast on a glass dish and left in a sealed bag for 2 days. The membrane was then vacuum dried at 120 °C for 12 h to obtain the membrane sample.

[0024] Example 2 The difference between this example and Example 1 is that the filler loading in the membrane sample is 25 wt%.

[0025] Example 3 The difference between this example and Example 1 is that the filler loading in the membrane sample is 45 wt%.

[0026] Comparative Example 1 This comparative example does not add any filler, and is a pure PIM-1 polymer membrane.

[0027] Comparative Example 2 The difference between this comparative example and Example 1 is that the PIM-1 polymer does not contain PIM-COOH in step 3.

[0028] Characterization Figure 1 is the FT-IR absorption spectrum of ZIF-NH2 and PZIF-CONH, which is a local amplification of the formation of covalent bonds between the amino-functionalized ZIF and the acyl chloride modified PIM in Example 1, Figure 2 is the SEM image of the mixed matrix membrane sample prepared in Example 1, from which it can be seen that the PZIF particles are uniformly dispersed in the polymer matrix without agglomeration, even at a filler loading of up to 35 wt%. Figure 3 is the SEM image of the mixed matrix membrane sample prepared in Comparative Example 2, from which it can be seen that there are defects between the filler and the polymer matrix.

[0029] The mixed matrix membrane samples obtained in Examples 1-3 and Comparative Examples 1-2 were tested for their permeability and selectivity for CO2 and CH4 at 2 bar, 298 K, and the results are shown in Table 1: Table 1 Permeation properties of CO2 / CH4 for the membrane samples of Examples 1-3 and Comparative Examples 1-2 The above examples are only for illustrating the technical concept and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and to implement it, and cannot limit the protection scope of the present application. Any equivalent changes or modifications made according to the spirit and essence of the present application shall be covered within the protection scope of the present application.

Claims

1. A hybrid matrix membrane with high filler loading, characterized in that: The hybrid matrix membrane comprises a PIM-1 polymer matrix and modified MOF composite particles. The modified MOF composite particles are obtained by surface grafting of modified MOF nanoparticles with acyl chloride-functionalized PIM-1 polymer, and the mass percentage of the modified MOF composite particles in the hybrid matrix membrane is 5-45 wt%.

2. The hybrid matrix membrane according to claim 1, characterized in that, The modified MOF nanoparticles are MOF nanoparticles with amino or hydroxyl groups on their surface.

3. The hybrid matrix membrane according to claim 2, characterized in that, The modified MOF nanoparticles are selected from ZIF-8-NH2 and ZIF-67-NH2. 、 UiO-66-NH2 or at least one of ZIF-8-OH, ZIF-67-OH, and UiO-66-OH.

4. The hybrid matrix membrane according to claim 1, characterized in that, In the modified MOF composite particles, the mass ratio of acyl chloride-functionalized PIM-1 polymer to modified MOF nanoparticles is 1:1 to 1:

4.

5. The hybrid matrix membrane according to claim 1, characterized in that, The PIM-1 polymer matrix contains 1-5 wt% PIM-COOH.

6. The hybrid matrix membrane according to claim 1, characterized in that, The modified MOF composite particles constitute 20-45 wt% of the mixed matrix membrane.

7. A method for preparing the hybrid matrix film based on gradient bonding interface as described in claim 1, characterized in that, Includes the following steps: (1) Preparation of acyl chloride-functionalized PIM-1 polymer; (2) Preparation of modified MOF composite particles: MOF nanoparticles with amino or hydroxyl groups on the surface are mixed with microporous polymers with acyl chloride in the structural unit in an organic solvent and subjected to an amidation reaction at a certain temperature. After separation and washing, the particles are redispersed in chloroform to obtain a dispersion of modified MOF composite particles. (3) Preparation of casting solution: Dissolve the PIM-1 polymer matrix in chloroform, then add the modified MOF composite particle dispersion obtained in step (2), mix evenly, and obtain the casting solution; (4) Film formation: The casting solution is cast into a film, and the mixed matrix film is obtained after drying.

8. The method according to claim 7, characterized in that: In step (1), the acyl chloride-functionalized PIM-1 polymer is prepared by the following steps: PIM is oxidized and hydrolyzed in a mixture of sulfuric acid and acetic acid to obtain PIM-COOH, which is then purified and reacted with SOCl2 to generate PIM-COCl, which is then separated by solvent precipitation and dried.

9. The method according to claim 7, characterized in that: In step (2), the temperature of the amidation reaction is 25°C to 100°C, and the reaction stirring time is 20 to 60 min.

10. The application of the mixed matrix membrane according to claim 1 in the separation of gas mixtures, characterized in that: The gas mixture is a CO2 / CH4 mixture, and the mixed matrix membrane is used for selective permeation of CO2.

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