Preparation method of fluorinated covalent organic framework / fluorine-containing polyimide mixed matrix membrane

Abstract

The invention discloses a preparation method of a fluorinated covalent organic framework / fluorine-containing polyimide mixed matrix membrane, which comprises the following steps: preparing a fluorinated covalent organic framework, preparing fluorine-containing polyimide and preparing a mixed matrix membrane, and relates to the technical field of mixed matrix membranes. The covalent organic framework material (COFs) can be promoted to be uniformly dispersed in a polymer matrix by utilizing the full-organic property of the COFs, non-selective pores generated due to interface defects in a mixed matrix membrane are reduced, the pore size of the COFs can be effectively improved by introducing fluorine atoms, adsorption sites interacting with gas can be provided, and the adsorption efficiency of the COFs is improved. The stability of a mixed structure can be greatly improved through the strong electrostatic interaction of fluorine atoms and the interaction of a C-F bond and a polymer matrix, and a fluorine-containing fragment is also introduced into the polymer matrix, so that the interaction with fluorine-containing COFs can be effectively enhanced, the overall stability of the material is improved, and the pore size is favorably maintained.

Description

Technical Field

[0001] The invention relates to the technical field of mixed matrix membranes, in particular to a method for preparing a fluorinated covalent organic framework / fluorinated polyimide mixed matrix membrane. Background Art

[0002] Helium is a rare gas that plays a key role in many areas of production and life. The importance of helium in production and life cannot be ignored. In the field of scientific research, it is a key medium for cooling superconducting magnets, enabling equipment such as magnetic resonance imaging (MRI) to work normally, and has greatly promoted the advancement of medical diagnostic technology. At the same time, in aerospace, helium is used to fill balloons and airships, and is also used as a protective gas for some space equipment to ensure the stable operation of equipment in a space environment. In industrial welding, helium can be used as a protective gas to prevent oxidation of welding parts and improve welding quality. In daily life, helium-filled balloons are deeply loved by people and are widely used in celebrations and other occasions. The stable supply of helium production is of far-reaching significance to the progress of science and technology and the normal development of social life. Increasing its production and ensuring its supply are issues that need to be focused on now and in the future. Helium needs to be separated using separation membranes during the production process.

[0003] However, the practical application and research of gas separation membrane technology in recent years have also exposed many problems, such as high temperature stability, chemical stability, defects and non-uniformity, fatigue resistance and other issues.

[0004] The present invention provides a method for preparing a fluorinated covalent organic framework / fluorinated polyimide mixed matrix membrane. Through the interaction between the set fluorinated covalent organic framework and the fluorinated polyimide, the stability of the mixed structure can be greatly improved, the overall stability of the material is improved, and the pore size is helped to be maintained. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a method for preparing a fluorinated covalent organic framework / fluorinated polyimide mixed matrix membrane, which solves the above problems.

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

[0007] The method for preparing a fluorinated covalent organic framework / fluorinated polyimide mixed matrix membrane comprises the following steps:

[0008] Step 1, preparation of fluorinated covalent organic framework:

[0009] Step 1.1: Add 2,4,6-triformylphloroglucinol, 2-trifluoromethyl-1,4-phenylenediamine, an appropriate amount of 1,3,5-trimethylbenzene and an appropriate amount of 1,4-dioxane into a Pyrex tube in sequence and mix;

[0010] Step 1.2: Use liquid nitrogen to freeze the Pyrex tube and remove the air, then thaw it at room temperature. Repeat this operation three times.

[0011] Step 1.3: Seal the tube tightly and place the Pyrex tube in an oil bath at 100-140°C until the reaction is complete. After the reaction is complete, cool to room temperature and collect the product by filtration;

[0012] Step 1.4: The collected product is stirred and washed three times with a DMF solution, and then purified. The purified product is dried in a vacuum oven to obtain an orange-red powdery fluorinated covalent organic framework sample, namely TpPa-CF3;

[0013] Step 2, preparing fluorinated polyimide:

[0014] Step 2.1: In a N2 atmosphere, add equal amounts of BASA, 6FDA and an appropriate amount of m-cresol to a three-necked flask equipped with mechanical stirring and condensation reflux, then raise the temperature to a medium temperature and wait for the reactants to be completely dissolved, then add 5 to 6 drops of isoquinoline and raise the temperature to 120-200°C for reaction for 6-12 hours;

[0015] Step 2.2: After the reaction is completed and cooled to room temperature, the polyimide solution is slowly poured into a large amount of industrial alcohol to draw a wire for precipitation, the product is collected by filtration, and dried in a vacuum oven;

[0016] Step 2.3: Use an appropriate amount of DMF to re-dissolve and perform secondary precipitation to remove residual impurities in the polyimide to obtain a fluorinated polyimide, namely BASA-6FDA;

[0017] Step 3, preparation of mixed matrix membrane:

[0018] Step 3.1: Weigh a certain amount of TpPa-CF3 powder and disperse it in DMF, sonicate and stir for a period of time to ensure that the TpPa-CF3 powder is evenly dispersed in the DMF solution;

[0019] Step 3.2: Weigh a certain amount of BASA-6FDA and dissolve it in an appropriate amount of DMF, and filter to remove impurities;

[0020] Step 3.3: Add the TpPa-CF3 dispersion dropwise into the BASA-6FDA solution and stir for a certain period of time until TpPa-CF3 and BASA-6FDA are fully mixed;

[0021] Step 3.4: Slowly cast the mixed solution onto a smooth glass plate, heat it to remove the solvent, and then remove the film in warm water after cooling to room temperature. Finally, dry it in a vacuum oven to remove the residual solvent molecules to prepare a TpPa-CF3 / BASA-6FDA mixed matrix membrane with a content of 3-9wt%.

[0022] Preferably, in step 1.1, the concentration of 2,4,6-triformylphloroglucinol is 0.2-0.5 mmol / L, and the concentration of 2-trifluoromethyl-1,4-phenylenediamine is 0.3-0.6 mmol / L.

[0023] Preferably, the mixing operation in step 1.1 is to uniformly disperse the mixture in the Pyrex tube by an ultrasonic oscillator, and add a certain amount of acetic acid solution.

[0024] Preferably, the purification operation in step 1.4 is performed by Soxhlet extraction, wherein the purification solvent is acetone.

[0025] Preferably, the method of filtering and removing impurities in step 3.2 is to use a nylon needle filter with a specification of 0.45 μm for filtering.

[0026] Beneficial Effects

[0027] The present invention provides a method for preparing a fluorinated covalent organic framework / fluorinated polyimide mixed matrix membrane. Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention utilizes the fully organic properties of covalent organic framework materials (COFs) to promote their uniform dispersion in the polymer matrix, reducing the non-selective pores generated by interface defects in the mixed matrix membrane. The introduction of fluorine atoms can effectively improve the pore size of COFs and provide adsorption sites for interaction with gases. The strong electrostatic effect of fluorine atoms and the C-F bonds can interact with the polymer matrix, which can greatly improve the stability of the mixed structure.

[0029] (2) The present invention also introduces fluorinated segments into the polymer matrix, which can effectively enhance the interaction with the fluorinated COFs, improve the overall stability of the material and help maintain the pore size. The mixed matrix membrane prepared by this method can effectively improve the flux and selectivity of helium. The present invention can provide a new reference solution for the field of helium separation.

[0030] (3) The introduction of the fluorinated organic framework in the present invention can significantly improve the selectivity and permeability of the flat membrane to helium, and the fluorinated polyimide can improve the plasticization resistance of the membrane. The preparation method is simple and low-cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the chemical reaction diagram for preparing the fluorine-containing polyimide of the present invention;

[0032] Figure 2 is a line graph of the anti-plasticization performance of the film prepared in Example 2 of the present invention;

[0033] Figure 3is a line graph of the anti-plasticization performance of the film prepared in Comparative Example 1 of the present invention;

[0034] Figure 4 It is a line graph of the anti-plasticization performance of the film prepared in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Embodiment 1:

[0037] The method for preparing a fluorinated covalent organic framework / fluorinated polyimide mixed matrix membrane comprises the following steps:

[0038] Step 1, preparation of fluorinated covalent organic framework:

[0039] Step 1.1: 0.2 mmol / L 2,4,6-triformylphloroglucinol, 0.3 mmol / L 2-trifluoromethyl-1,4-phenylenediamine, an appropriate amount of 1,3,5-trimethylbenzene and an appropriate amount of 1,4-dioxane are sequentially added into a Pyrex tube. In order to make the mixture uniformly dispersed, ultrasonic treatment is performed until it is completely dispersed, and then a certain amount of acetic acid solution is added;

[0040] Step 1.2: Use liquid nitrogen to freeze the Pyrex tube and remove the air, then thaw it at room temperature. Repeat this operation three times.

[0041] Step 1.3: Seal the tube tightly and place the Pyrex tube in an oil bath at 100°C until the reaction is complete. After the reaction is complete, cool it to room temperature and collect the product by filtration;

[0042] Step 1.4: The collected product was stirred and washed three times with a DMF solution, and then purified by Soxhlet extraction (with acetone as the purification solvent). The purified product was dried in a vacuum oven to obtain an orange-red powdery fluorinated covalent organic framework sample, namely TpPa-CF3;

[0043] Step 2, preparing fluorinated polyimide, such as Figure 1 As shown:

[0044] Step 2.1: In a N2 atmosphere, add equal amounts of BASA, 6FDA and an appropriate amount of m-cresol to a three-necked flask equipped with mechanical stirring and condensation reflux, then raise the temperature to a medium temperature and wait for the reactants to be completely dissolved, then add 5 to 6 drops of isoquinoline and raise the temperature to 120°C for 6 hours;

[0045] Step 2.2: After the reaction is completed and cooled to room temperature, the polyimide solution is slowly poured into a large amount of industrial alcohol to draw a wire for precipitation, the product is collected by filtration, and dried in a vacuum oven;

[0046] Step 2.3: Use an appropriate amount of DMF to re-dissolve and perform secondary precipitation to remove residual impurities in the polyimide to obtain a fluorinated polyimide, namely BASA-6FDA;

[0047] Step 3, preparation of mixed matrix membrane:

[0048] Step 3.1: Weigh a certain amount of TpPa-CF3 powder and disperse it in DMF, sonicate and stir for a period of time to ensure that the TpPa-CF3 powder is evenly dispersed in the DMF solution;

[0049] Step 3.2: Weigh a certain amount of BASA-6FDA and dissolve it in an appropriate amount of DMF, and filter it with a 0.45 μm nylon needle filter to remove impurities;

[0050] Step 3.3: Add the TpPa-CF3 dispersion dropwise into the BASA-6FDA solution and stir for a certain period of time until TpPa-CF3 and BASA-6FDA are fully mixed;

[0051] Step 3.4: Slowly cast the mixed solution onto a smooth and flat glass plate, heat it to remove the solvent, and then remove the film in warm water after cooling to room temperature. Finally, dry it in a vacuum oven to remove the residual solvent molecules to prepare a TpPa-CF3 / BASA-6FDA mixed matrix membrane with a content of 3wt%.

[0052] Embodiment 2:

[0053] The difference between this embodiment and embodiment 1 is that in step 1.1, the concentration of 2,4,6-triformylphloroglucinol is 0.3 mmol / L, the concentration of 2-trifluoromethyl-1,4-phenylenediamine is 0.45 mmol / L, the oil bath temperature of the Pyrex tube in step 1.3 is 120°C, and after adding dropwise isoquinoline in step 2.1, the temperature is raised to 160°C and reacted for 9 hours. The other methods remain unchanged, and a TpPa-CF3 / BASA-6FDA mixed matrix membrane with a content of 5 wt% is prepared.

[0054] Embodiment 3:

[0055] The difference between this embodiment and embodiment 1 is that in step 1.1, the concentration of 2,4,6-triformylphloroglucinol is 0.4 mmol / L, the concentration of 2-trifluoromethyl-1,4-phenylenediamine is 0.45 mmol / L, the oil bath temperature of the Pyrex tube in step 1.3 is 120°C, and after adding isoquinoline dropwise in step 2.1, the temperature is raised to 160°C and reacted for 9 hours. The other methods remain unchanged, and a TpPa-CF3 / BASA-6FDA mixed matrix membrane with a content of 7 wt% is prepared.

[0056] Embodiment 4:

[0057] The difference between this embodiment and embodiment 1 is that in step 1.1, the concentration of 2,4,6-triformylphloroglucinol is 0.5 mmol / L, the concentration of 2-trifluoromethyl-1,4-phenylenediamine is 0.6 mmol / L, the oil bath temperature of the Pyrex tube in step 1.3 is 140°C, and after adding dropwise isoquinoline in step 2.1, the temperature is raised to 200°C and reacted for 12 hours. The other methods remain unchanged, and a TpPa-CF3 / BASA-6FDA mixed matrix membrane with a content of 9wt% is prepared.

[0058] Comparative Example 1:

[0059] The difference between this comparative example and Example 2 is that no TpPa-CF3 is added, and a BASA-6FDA membrane is prepared.

[0060] Comparative Example 2:

[0061] The difference between this comparative example and Example 2 is that BASA-6FDA was not added, and a TpPa-CF3 membrane was prepared.

[0062] Performance Testing

[0063] The membranes prepared in Examples 1-4 and Comparative Examples 1-2 were tested for gas separation performance. The test method was to encapsulate the prepared membranes in a component and test their performance under conditions of a pressure of 1 MPa and a temperature of room temperature. The test gases included CH4, CO2, He, and N2. The test results are shown in Table 1.

[0064] Table 1 Gas separation performance test results of membranes prepared in Examples 1-4 and Comparative 12

[0065]

[0066] The films prepared in Example 2 and Comparative Examples 1-2 were tested for their anti-plasticization performance. The test conditions were that He / CO2 / CH4 ternary mixed gas was used as the feed gas and the feed pressure was controlled to test their anti-plasticization performance. The test results are shown in Figure 2. Figure 2-4 shown.

[0067] From the data in Table 1, it can be seen that the permeability and selectivity of pure TpPa-CF3 membrane and BASA-6FDA membrane for helium and other gases are not ideal, while the mixed matrix membrane prepared with TpPa-CF3 and BASA-6FDA has greatly improved helium flux and selectivity, with the maximum helium flux reaching 295GPU, and He / CH4, He / N2 and He / CO2 selectivities reaching 475, 453, 421 respectively. It can be concluded that the mixed matrix membrane prepared with TpPa-CF3 and BASA-6FDA can greatly improve the transfer efficiency and selectivity of flat membrane for helium, and can also collect other types of gases in the process. Figure 1-3 From the anti-plasticization performance test chart, it can be seen that with the continuous increase of the inlet pressure, the separation rate of pure TpPa-CF3 membrane and pure BASA-6FDA membrane decreases rapidly, indicating that the stability of this type of membrane is very low, while the gas separation efficiency of the mixed matrix membrane of TpPa-CF3 / BASA-6FDA is stable and its anti-plasticization performance is excellent.

[0068] Meanwhile, the contents not described in detail in this specification belong to the prior art known to those skilled in the art.

[0069] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0070] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a fluorinated covalent organic framework / fluorinated polyimide mixed matrix membrane, characterized in that: The following steps are involved: Step 1, preparation of fluorinated covalent organic framework: Step 1.1: Add 2,4,6-triformylphloroglucinol, 2-trifluoromethyl-1,4-phenylenediamine, an appropriate amount of 1,3,5-trimethylbenzene and an appropriate amount of 1,4-dioxane into a Pyrex tube in sequence and mix; Step 1.2: Use liquid nitrogen to freeze the Pyrex tube and remove the air, then thaw it at room temperature. Repeat this operation three times. Step 1.3: Seal the tube tightly and place the Pyrex tube in an oil bath at 100-140°C until the reaction is complete. After the reaction is complete, cool to room temperature and collect the product by filtration; Step 1.4: The collected product is stirred and washed three times with a DMF solution, and then purified. The purified product is dried in a vacuum oven to obtain an orange-red powdery fluorinated covalent organic framework sample, namely TpPa-CF3; Step 2, preparing fluorinated polyimide: Step 2.1: In a N2 atmosphere, add equal amounts of BASA, 6FDA and an appropriate amount of m-cresol to a three-necked flask equipped with mechanical stirring and condensation reflux, then raise the temperature to a medium temperature and wait for the reactants to be completely dissolved, then add 5 to 6 drops of isoquinoline and raise the temperature to 120-200°C for reaction for 6-12 hours; Step 2.2: After the reaction is completed and cooled to room temperature, the polyimide solution is slowly poured into a large amount of industrial alcohol to draw a wire for precipitation, the product is collected by filtration, and dried in a vacuum oven; Step 2.3: Use an appropriate amount of DMF to re-dissolve and perform secondary precipitation to remove residual impurities in the polyimide to obtain a fluorinated polyimide, namely BASA-6FDA; Step 3, preparation of mixed matrix membrane: Step 3.1: Weigh a certain amount of TpPa-CF3 powder and disperse it in DMF, sonicate and stir for a period of time to ensure that the TpPa-CF3 powder is evenly dispersed in the DMF solution; Step 3.2: Weigh a certain amount of BASA-6FDA and dissolve it in an appropriate amount of DMF, and filter to remove impurities; Step 3.3: Add the TpPa-CF3 dispersion dropwise into the BASA-6FDA solution and stir for a certain period of time until TpPa-CF3 and BASA-6FDA are fully mixed; Step 3.4: Slowly cast the mixed solution onto a smooth glass plate, heat it to remove the solvent, and then remove the film in warm water after cooling to room temperature. Finally, dry it in a vacuum oven to remove the residual solvent molecules to prepare a TpPa-CF3 / BASA-6FDA mixed matrix membrane with a content of 3-9wt%.

2. The method for preparing a fluorinated covalent organic framework / fluorinated polyimide mixed matrix membrane according to claim 1, characterized in that: In the step 1.1, the concentration of 2,4,6-triformylphloroglucinol is 0.2-0.5 mmol / L, and the concentration of 2-trifluoromethyl-1,4-phenylenediamine is 0.3-0.6 mmol / L.

3. The method for preparing a fluorinated covalent organic framework / fluorinated polyimide mixed matrix membrane according to claim 1, characterized in that: The mixing operation in step 1.1 is to uniformly disperse the mixture in the Pyrex tube by an ultrasonic oscillator, and add a certain amount of acetic acid solution.

4. The method for preparing a fluorinated covalent organic framework / fluorinated polyimide mixed matrix membrane according to claim 1, characterized in that: The purification operation in step 1.4 is performed by Soxhlet extraction, wherein the purification solvent is acetone.

5. The method for preparing a fluorinated covalent organic framework / fluorinated polyimide mixed matrix membrane according to claim 1, characterized in that: The method of filtering and removing impurities in step 3.2 is to use a 0.45 μm nylon needle filter for filtering.

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