Polyimide hollow fiber membrane with polyionic liquid side chain structure and preparation method and application thereof

Abstract

The application belongs to the field of gas separation membrane preparation, and discloses a polyimide hollow fiber membrane with a polyionic liquid side chain structure and a preparation method and application thereof. The polyimide hollow fiber membrane with the polyionic liquid side chain structure comprises an aromatic polyimide main chain containing alkyl and a vinyl polyionic liquid side chain. The polyionic liquid fragment is fixed on the aromatic polyimide main chain by using an atom transfer radical polymerization reaction, and the active H on the imidazole ring in the polyionic liquid has a strong interaction with CO2 and other polar gases, so that high selective and rapid transportation of CO2 can be realized, and the permeation performance of the membrane to CO2 and other polar gases is improved. The obtained hollow fiber membrane has good heat resistance and mechanical properties, can treat flue gas at a high temperature and a high pressure, and improves production efficiency.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of gas separation membrane preparation, and particularly relates to a polyimide hollow fiber membrane with a polyionic liquid side chain structure and a preparation method and application thereof. BACKGROUND

[0002] With the intensification of climate warming, extreme weather events are increasingly frequent worldwide. People are urgently seeking green technological innovation to achieve clean production, reduce greenhouse gas emissions, and alleviate global warming. Membrane separation technology is gradually becoming a research hotspot for CO2 separation because the separation process does not involve phase change and does not require the addition of a separation agent, thus having the characteristics of energy saving, high efficiency, no secondary pollution, simple operation, and low cost.

[0003] Ionic liquids, also known as room temperature ionic liquids, room temperature molten salts, or organic ionic liquids, are salts composed of organic cations and inorganic or organic anions that are in a liquid state at room temperature or near room temperature. Due to the Lewis acid / base complexation between ionic liquids and CO2, the solubility of CO2 in ionic liquids is high, and ionic liquids have been widely used in recent years for capturing CO2 in industrial tail gas and natural gas. Currently, gas separation membranes based on ionic liquids can be divided into polyionic liquid membranes and ionic liquid-polymer blend membranes. Polyionic liquid membranes are generally obtained by chemical reaction polymerization of vinyl-based ionic liquid monomers. Since polyionic liquids generally have an alkane backbone, they have poor heat resistance and a low thermal distortion temperature, making them difficult to apply in high-temperature flue gas and other practical scenarios. Moreover, such membranes are costly and are not suitable for large-scale applications. Ionic liquid-polymer blend membranes refer to the incorporation of a certain amount of ionic liquid into a polymer matrix material to improve the selectivity of the membrane for CO2. However, the presence of ionic liquids can plasticize the material, reducing the heat resistance and mechanical properties of the separation membrane. Moreover, when the content of ionic liquid is too high, the ionic liquid can easily agglomerate in the polymer matrix, hindering the transmission of CO2.

[0004] Aromatic polyimides generally have a high free volume fraction, excellent thermal stability, and chemical stability due to the presence of a large number of rigid benzene ring structures, making them one of the most promising gas separation membrane materials. However, current aromatic polyimide gas separation membranes still cannot simultaneously achieve high permeability and high selectivity.

[0005] In order to overcome the shortcomings and deficiencies of the prior art, the primary purpose of the present application is to provide a polyimide hollow fiber membrane with a polyionic liquid side chain structure.

[0006] The polyimide hollow fiber membrane with a polyionic liquid side chain structure obtained by the present application has excellent high permeability, high selectivity, and mechanical properties.

[0007] Another purpose of the present application is to provide a preparation method for the polyimide hollow fiber membrane with a polyionic liquid side chain structure as described above.

[0008] Another object of the present application is to provide the use of the polyimide hollow fiber membrane with polyionic liquid side chain structure in gas separation.

[0009] The object of the present application is achieved by the following solutions:

[0010] A polyimide hollow fiber membrane with polyionic liquid side chain structure, comprising a polyimide main chain containing an alkyl group, and a vinyl polyionic liquid side chain.

[0011] The preparation method of the polyimide hollow fiber membrane with polyionic liquid side chain structure comprises the following steps:

[0012] (1) Under the protection of inert atmosphere, polyimide resin containing alkyl structure, N-bromosuccinimide, azobisisobutyronitrile are dissolved in organic solvent, heated and stirred for reaction, after the reaction is completed, the solution is poured into methanol for precipitation, and the obtained solid is brominated polyimide resin;

[0013] (2) Under the protection of inert atmosphere, brominated polyimide resin, vinyl ionic liquid monomer, catalyst, ligand are dissolved in organic solvent, heated and stirred for reaction, after the reaction is completed, the solution is poured into methanol for precipitation, and the obtained solid is polyimide resin with polyionic liquid side chain structure;

[0014] (3) The polyimide resin with polyionic liquid side chain structure is dissolved in organic solvent, filtered, spun, soaked and dried to obtain a hollow fiber membrane.

[0015] The number average molecular weight of the polyimide resin containing alkyl structure in step (1) is 1000-500000.

[0016] The organic solvent in step (1) is one or more of chloroform, o-cresol, m-cresol, p-cresol, dimethyl sulfoxide, N-methyl pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide.

[0017] The mass ratio of the polyimide resin containing alkyl structure, N-bromosuccinimide and azobisisobutyronitrile in step (1) is 100:(0.2-50):(0.001-0.5); the usage ratio of the polyimide resin containing alkyl structure to the organic solvent is 1g:(1-50)mL.

[0018] The temperature of the reaction in step (1) is 30-70℃; the time is 12-48h.

[0019] The vinyl ionic liquid monomer in step (2) is at least one of the following compounds:

[0020]

[0021] wherein X is Cl, Br, I, COO, SCN, NO3, BF4 or PF6.

[0022] The catalyst in step (2) is a halide of a transition metal; preferably one of CuCl, CuBr, CuI.

[0023] The ligand in step (2) is one of the following compounds:

[0024]

[0025] The organic solvent in step (2) is one or more of dimethyl sulfoxide, N-methyl pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide.

[0026] The mass ratio of the brominated polyimide resin, the vinyl ionic liquid monomer, the catalyst, the ligand in step (2) is 100:(1-100):(0.01-0.5):(0.02-1); the ratio of the amount of the brominated polyimide resin to the organic solvent is 100 g:(100-5000) mL.

[0027] The temperature of the reaction in step (2) is 60-120℃; the time of the reaction is 12-36 h.

[0028] The number average molecular weight of the polyimide resin with poly(ionic liquid) side chain structure obtained in step (2) is 5000-1000000.

[0029] The organic solvent in step (3) is one or more of tetrahydrofuran, dimethyl sulfoxide, N-methyl pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide.

[0030] The amount of the organic solvent in step (3) satisfies: the concentration of the polyimide resin with poly(ionic liquid) side chain structure in the spinning solution is 10-45 wt.%.

[0031] The mesh number of the filter in step (3) is 300-500.

[0032] The feed solution for the spinning in step (3) is the polyimide resin solution obtained after the filtration, the flow rate is 1-15 mL / min; the core solution is a mixed solution of water and an organic solvent, the flow rate is 0.2-5 mL / min, wherein the mass ratio of water to the organic solvent is 50:50-10:90.

[0033] The coagulation bath for the spinning in step (3) is water.

[0034] The soaking in step (3) is soaking in methanol solution and n-hexane in sequence; wherein, the soaking time is 1-5h, and the concentration of methanol in the methanol solution is 70-90wt.%.

[0035] The hollow fiber membrane in step (3) has a fiber outer diameter of 200-500mu m, an inner diameter of 150-350mu m, and a membrane thickness of 40-100mu m.

[0036] The drying in step (3) is vacuum drying, the drying temperature is 100-150 DEG C, and the drying time is 12-48h.

[0037] The application of the polyimide hollow fiber membrane with polyionic liquid side chain structure in gas separation.

[0038] The gas separation is capturing carbon dioxide in air, industrial flue gas, natural gas or biogas.

[0039] The mechanism of the application is as follows:

[0040] The application provides a polyimide hollow fiber membrane with polyionic liquid side chain structure and a preparation method thereof.

[0041] Compared with the prior art, the application has the following advantages and beneficial effects:

[0042] 1. The ATRP reaction is used to construct polyionic liquid side chains on the aromatic polyimide main chain, the active H on the polyionic liquid has a strong interaction with CO2 and other polar gases, the solubility of the material to CO2 and other polar gases can be effectively enhanced, and high selective and rapid transport of CO2 can be realized.

[0043] 2. The aromatic polyimide main chain and the polyionic liquid side chain have a large difference in compatibility structure, the microphase separation structure can be formed in the film by preparing polyionic liquid side chains with appropriate length, and a rapid channel for gas molecule permeation can be constructed.

[0044] 3. The polyionic liquid segment and the aromatic polyimide main chain are connected through a chemical bond in the application, and the overflow of the ionic liquid due to high working pressure can be effectively avoided.

[0045] 4. The aromatic polyimide is used as the base material, the obtained hollow fiber membrane has good heat resistance and mechanical properties, the flue gas can be treated at a high temperature and a high pressure, and the production efficiency is improved.

[0046] 5、The present application has versatility, and the method is applicable to all aromatic polyimide resins containing alkyl groups in the structure, without the need to prepare special diamine or dianhydride monomers at high cost. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 The infrared spectra of the resins obtained in the comparative examples and the examples.

[0048] Figure 2 The separation performance of the hollow fiber membranes obtained in the comparative examples and the examples for the CO2 / N2 gas pair.

[0049] Figure 3 The separation performance of the hollow fiber membranes obtained in the comparative examples and the examples for the CO2 / CH4 gas pair.

[0050] Figure 4 The thermogravimetric curves of the hollow fiber membranes obtained in the comparative examples and the examples.

[0051] Figure 5 The mechanical tensile property diagrams of the hollow fiber membranes obtained in the comparative examples and the examples. DETAILED DESCRIPTION

[0052] The present application will be described in further detail below with reference to the examples and the accompanying drawings, but the embodiments of the present application are not limited thereto. In the examples, the specific conditions not mentioned are carried out according to the conventional conditions or the conditions recommended by the manufacturers. The reagents or instruments used are not mentioned by the manufacturers, and are all conventional products that can be purchased on the market.

[0053] The reagents used in the examples are all conventional products that can be purchased on the market, unless otherwise specified.

[0054] Polyimide resin (PI):

[0055]

[0056] a) In a 250 mL three-necked flask, 50 mL of m-cresol solvent, 25 mL of toluene, 4.4424 g (0.01 mol) of hexafluorodianhydride (6FDA), 1.5023 (0.01 mol) of 2,4,6-trimethyl-1,3-phenylenediamine and 0.1 g of isoquinoline were sequentially added, and after refluxing to remove water at 120°C for 6 h, the temperature was increased to 180°C for polycondensation for 12 h. The polycondensation process was carried out in a nitrogen atmosphere throughout.

[0057] b) After the polyimide solution was cooled to 80°C, it was slowly poured into anhydrous ethanol, and white fibrous polyimide was precipitated. After being washed with ethanol for multiple times, the polyimide resin (PI) material was dried.

[0058] 1 -vinyl-3 -methylimidazolium iodide:

[0059] wherein X is I;

[0060] Compound 1 :

[0061]

[0062] Example 1

[0063] (1) Under nitrogen protection, 150 mL of chloroform, 5.0 g of polyimide resin (PI), 0.65 g of N-bromosuccinimide (NBS), and 0.004 g of azobisisobutyronitrile (AIBN) were added into a 250 mL three-necked flask, stirred uniformly, and heated to 60°C for 24 h. After the reaction was completed, the system was cooled to room temperature and poured into methanol for precipitation. The precipitate was filtered and washed multiple times, and then dried to obtain the PI-Br resin.

[0064] (2) Under nitrogen protection, 150 mL of N-methylpyrrolidone (NMP), 5.0 g of PI-Br resin, 0.5 g of 1 -vinyl-3 -methylimidazolium iodide, 0.02 g of CuCl, and 0.03 g of Compound 1 were added into a 250 mL three-necked flask, stirred uniformly, and heated to 70°C for 20 h. After the reaction was completed, the system was cooled to room temperature and poured into methanol for precipitation. The precipitate was filtered and washed multiple times, and then dried to obtain the PI-PIL (10:1) resin.

[0065] (3) The dried PI-PIL (10:1) resin was uniformly mixed with NMP at room temperature to obtain a spinning solution with a polymer content of 30 wt.%, which was filtered through a metal screen (325 mesh) and poured into a feed tank. During spinning, the core solution flow rate was set to 1 mL / min, the feed solution flow rate was set to 3 mL / min, the core solution was a mixture solution of deionized water and NMP (15 / 85 wt.%), and the outer coagulation bath was deionized water. The spun hollow fiber membrane was soaked in 85 wt.% methanol for 30 min, repeated for 3 times, then moved into n-hexane for soaking for 30 min, repeated for 3 times, and finally dried in a vacuum oven at 120°C for 24 h to obtain the PI-PIL (10:1) hollow fiber membrane.

[0066] Example 2:

[0067] The difference from Example 1 is that the amount of 1 -vinyl-3 -methylimidazolium iodide added in step (2) is 1.0 g, and the PI-PIL (5:1) hollow fiber membrane is obtained.

[0068] Example 3:

[0069] The difference from Example 1 is that the amount of 1-vinyl-3-methylimidazolium iodide added in step (2) is 2.5 g, and a PI-PIL (2:1) hollow fiber membrane is obtained.

[0070] Comparative Example

[0071] The difference from Example 1 is that steps (1) and (2) are not performed, and the polymer in the spinning solution in step (3) is a polyimide resin (PI), and a PI hollow fiber membrane is obtained.

[0072] Test Example

[0073] (1) Infrared test of the resins obtained in the comparative example and the examples:

[0074] As Figure 1 , 1784 cm -1 , 1726 cm -1 , 1375 cm -1 , 1253 cm -1 are characteristic absorption peaks of imide rings, 1649 cm -1 is a stretching vibration peak of C=C on the imidazole ring of the polyionic liquid, and 1566 cm -1 is a stretching vibration peak of C=N on the imidazole ring of the polyionic liquid. It can be clearly seen that the intensities of these two absorption peaks increase significantly with the increase of the amount of 1-vinyl-3-methylimidazolium iodide.

[0075] (2) Determination of the molecular weight of the resins obtained in the examples and the comparative example:

[0076] Determination was performed using a gel permeation chromatograph, and DMF was used as the eluent at a flow rate of 1 mL / min.

[0077] Table 1 GPC test results of the resins obtained in the examples and the comparative example

[0078]

[0079] The results of the GPC test show that the GPC results increase with the increase of the amount of 1-vinyl-3-methylimidazolium iodide, which indicates that the molecular weight of the polyionic liquid side chain increases with the increase of the amount of the material.

[0080] (3) Inner and outer diameters of the hollow fiber membranes obtained in the examples and the comparative example:

[0081] Table 2 Comparison of the inner and outer diameters of the hollow fiber membranes obtained in the examples and the comparative example

[0082]

[0083] (4) Pure gas separation performance of the hollow fiber gas separation membranes obtained in the examples and the comparative example:

[0084] See Table 3, the test pressure is 0.5 MPa, and the test temperature is 35℃.

[0085] Table 3 Comparison of pure gas separation performance of hollow fiber membranes obtained in examples and comparative examples

[0086]

[0087] From the pure gas separation performance test results, it can be seen that in the case of similar inner and outer diameters of the hollow fiber, the polyimide gas separation membrane with polyionic liquid side chain structure has a great improvement in the selectivity to CO2 compared with the unmodified polyimide gas separation membrane. By comparing the three examples, it can be found that from PI-PIL(10:1) to PI-PIL(2:1), the permeability of the sample to CO2 gradually increases. This is because with the increase of the content of polyionic liquid, the microphase separation phenomenon of the material gradually becomes obvious, and the channels through which the gas can pass increase.

[0088] (5) Determination of thermal stability of the hollow fiber membrane:

[0089] Determination was performed using a thermogravimetric analyzer, under N2 atmosphere, with a heating rate of 10 K / min.

[0090] According to Figure 4 , the thermogravimetric test results show that the T d5％ of the samples before and after modification all exceeds 300℃, and has good thermal stability.

[0091] (6) Determination of tensile strength and elongation at break of the hollow fiber membrane:

[0092] Determination was performed using an electronic universal testing machine, with an effective length of the sample of 50 mm, and a tensile rate of 2 mm / min.

[0093] According to Figure 5 , the tensile test results show that the introduction of polyionic liquid side chain will lead to the decrease of the interaction force between polyimide molecular chains, and further lead to the decrease of the tensile strength, but the difference between the samples with different side chain lengths is not large, and all have a strength of about 20 MPa, which can meet the actual needs of gas separation.

[0094] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and all are included in the protection scope of the present application.

Claims

1. A polyimide hollow fiber membrane having a polyionic liquid side chain structure, characterized by: The polyimide backbone contains alkyl groups, and the polyionic liquid side chain contains vinyl groups. The preparation method of the polyimide hollow fiber membrane comprises the following steps: (1) under the protection of inert atmosphere, polyimide resin containing alkyl structure, N-bromosuccinimide, azobisisobutyronitrile are dissolved in organic solvent, heated and stirred, after the reaction, the solution is poured into methanol to precipitate, the obtained solid is brominated polyimide resin; (2) under the protection of inert atmosphere, brominated polyimide resin, vinyl ionic liquid monomer, catalyst, ligand are dissolved in organic solvent, heated and stirred, after the reaction, the solution is poured into methanol to precipitate, the obtained solid is polyimide resin with polyionic liquid side chain structure; (3) polyimide resin with polyionic liquid side chain structure is dissolved in organic solvent, filtered, spun, soaked and dried to obtain hollow fiber membrane.

2. The polyimide hollow fiber membrane with polyionic liquid side chain structure according to claim 1, wherein: the number average molecular weight of the polyimide resin containing alkyl structure in step (1) is 1000-500000; the organic solvent in step (1) is one or more of chloroform, o-cresol, m-cresol, p-cresol, dimethyl sulfoxide, N-methyl pyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide.

3. The polyimide hollow fiber membrane with polyionic liquid side chain structure according to claim 1, wherein: the mass ratio of the polyimide resin containing alkyl structure, N-bromosuccinimide and azobisisobutyronitrile in step (1) is 100: (0.2-50): (0.001-0.5); the dosage ratio of the polyimide resin containing alkyl structure and the organic solvent is 1g: (1-50)mL; the reaction temperature in step (1) is 30-70℃; the reaction time in step (1) is 12-48h.

4. The polyimide hollow fiber membrane with polyionic liquid side chain structure according to claim 1, wherein: the vinyl ionic liquid monomer in step (2) is at least one of the following compounds: wherein, X is Cl, Br, I, COO, SCN, NO3, BF4 or PF6; the catalyst in step (2) is halide of transition metal; the ligand in step (2) is one of the following compounds: the organic solvent in step (2) is one or more of dimethyl sulfoxide, N-methyl pyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide.

5. The polyimide hollow fiber membrane with polyionic liquid side chain structure according to claim 4, wherein: the catalyst in step (2) is one of CuCl, CuBr and CuI.

6. The polyimide hollow fiber membrane with polyionic liquid side chain structure according to claim 1, wherein: ​ ​ ​ 、 、 、 、 、 、 ​ ​ ​ 、 、 、 、 、 、 、 ； ​ ​ ​ ​ The mass ratio of the brominated polyimide resin, the vinyl ionic liquid monomer, the catalyst, and the ligand in step (2) is 100: (1-100): (0.01-0.5): (0.02-1); the ratio of the amount of the brominated polyimide resin to the organic solvent is 100 g: (100-5000) mL; The temperature of the reaction in step (2) is 60-120°C; the reaction time is 12-36 h; The number average molecular weight of the polyimide resin with a polyionic liquid side chain structure obtained in step (2) is 5000-1000000.

7. The polyimide hollow fiber membrane with a polyionic liquid side chain structure according to claim 1, characterized in that: The organic solvent in step (3) is one or more of tetrahydrofuran, dimethyl sulfoxide, N-methyl pyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; The amount of the organic solvent in step (3) satisfies: the concentration of the polyimide resin with a polyionic liquid side chain structure in the spinning solution is 10-45 wt.%; The mesh number of the filter in step (3) is 300-500.

8. The polyimide hollow fiber membrane with a polyionic liquid side chain structure according to claim 1, characterized in that: The feed solution for spinning in step (3) is the polyimide resin solution obtained after filtration, and the flow rate is 1-15 mL / min; the core solution is a mixed solution of water and an organic solvent, and the flow rate is 0.2-5 mL / min, wherein the mass ratio of water to the organic solvent is 50:50-10:90; The coagulation bath for spinning in step (3) is water; The fiber outer diameter of the hollow fiber membrane in step (3) is 200-500 μm, the inner diameter is 150-350 μm, and the membrane thickness is 40-100 μm.

9. The polyimide hollow fiber membrane with a polyionic liquid side chain structure according to claim 1 for use in gas separation.

10. Use of the polyimide hollow fiber membrane having a polyionic liquid side chain structure according to claim 9 in gas separation, characterized by: The gas separation is the capture of carbon dioxide in air, industrial flue gas, natural gas, or biogas.

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