Polyimide, separation membrane, and preparation method and application thereof

Abstract

The application relates to the technical field of polymer preparation, and discloses a polyimide, a separation membrane, and a preparation method and application thereof. The polyimide has a structure shown in formula (I); X is derived from a diamine containing an -O-A-A-A-O- structure, wherein O represents an oxygen atom, A represents an arbitrary atom, and A forms a ring with other atoms except the oxygen atom. The polyimide contains a specific diamine structure, so that the polyimide has good processing film-forming property and heat resistance. The separation membrane prepared from the polyimide has high selectivity, good heat resistance and mechanical strength when used for helium separation.

Description

Technical Field

[0001] This invention relates to the field of polymer preparation technology, specifically to a polyimide, a separation membrane, and its preparation method and application. Background Technology

[0002] Helium's light weight, low boiling point, and strong chemical inertness make it widely used in various technological industries, including military, medical, semiconductor, superconducting testing, metal manufacturing, deep-sea diving, and high-precision welding. Currently, extracting helium from natural gas is the only way to realize the resource utilization of helium. my country's helium reserves are low in both quantity and quality; my country accounts for less than 5% of the global helium production, and its helium concentration is generally less than 0.2%. Benefiting from the development of the military, aerospace, and other fields, my country has a high demand for helium and urgently needs to develop advanced natural gas helium extraction technologies for application in the helium production process.

[0003] Currently, the main technologies for helium extraction from natural gas include cryogenic extraction, pressure swing adsorption (PSA), absorption, and membrane separation. Cryogenic extraction is the primary method, although it can extract high-purity He from natural gas. However, due to the low He concentration in my country's natural gas, the cost of extracting He using cryogenic extraction is high, hindering the large-scale construction of helium extraction plants in my country. In recent years, with the development of membrane separation technology, it has shown great application potential in the field of helium enrichment. Polymer membranes have become the most attractive material in the gas separation membrane industry due to their diverse preparation materials, simple manufacturing methods, good processing performance, ease of scale-up production, and good mechanical stability. Currently, the most researched membrane materials for helium separation include cellulose acetate membranes, polysulfone membranes, polycarbonate membranes, polymethyl methacrylate membranes, and polyimide membranes.

[0004] Current helium separation membranes suffer from drawbacks such as poor selectivity, low separation efficiency, and susceptibility to aging. Therefore, there are currently no industrial applications that use gas separation membrane technology alone to separate helium and nitrogen. Industrially, it is still necessary to combine it with pressure swing adsorption (PSA) and cryogenic processes to achieve efficient helium extraction. However, these methods are energy-intensive and not economically efficient for natural gas helium extraction. Therefore, there is a need to develop a helium separation membrane with high selectivity and high separation efficiency to achieve low-energy, high-efficiency helium separation and enrichment. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of poor selectivity and low separation efficiency of existing helium separation membranes, and to provide a polyimide, a separation membrane, a preparation method thereof, and its application. The polyimide contains a specific diamine structure, which gives it good processability and heat resistance. The separation membrane made from this polyimide has high selectivity, good heat resistance, and mechanical strength when used for helium separation.

[0006] To achieve the above objectives, a first aspect of the present invention provides a polyimide having the structure shown in formula (I);

[0007]

[0008] Y comes from a diamine containing the -OAAAO- structure, where O represents an oxygen atom, A represents any atom, and A forms a ring with other atoms besides the oxygen atom.

[0009] A second aspect of the present invention provides a method for preparing the polyimide described in the first aspect of the present invention, wherein the preparation method includes:

[0010] (1) In the presence of a protective atmosphere, diamine monomer, dianhydride monomer and solvent are mixed and polycondensation reaction is carried out to obtain polyamic acid solution;

[0011] (2) The polyamic acid solution is imidized to obtain the polyimide;

[0012] The diamine monomer is a diamine monomer containing the -OAAAO- structure, where O represents an oxygen atom, A represents any atom, and A forms a ring with other atoms besides the oxygen atom.

[0013] A third aspect of the present invention provides a separation membrane, wherein the separation membrane is made of polyimide according to the first aspect of the present invention.

[0014] A fourth aspect of the present invention provides a method for preparing the separation membrane of the third aspect of the present invention, wherein the method comprises:

[0015] S1. Prepare a casting solution containing the polyimide described in the first aspect of the present invention;

[0016] S2. The casting solution is cast into a film and then dried to obtain the separation membrane.

[0017] The fifth aspect of the present invention provides an application of the polyimide described in the first aspect of the present invention or the separation membrane provided in the third aspect of the present invention in gas separation.

[0018] Through the above technical solutions, the polyimide, polyimide separation membrane, preparation method and application provided by the present invention achieve the following beneficial effects:

[0019] Compared with the prior art, the polyimide of the present invention contains a specific diamine structure, which not only gives the polyimide good processability and film-forming properties, but also, in particular, gives the separation membrane made from the polymer high helium selectivity, thermal stability, mechanical stability and chemical stability.

[0020] Specifically, some embodiments of the present invention provide polyimides that exhibit superior selectivity while maintaining existing levels of permeability. Attached Figure Description

[0021] Figure 1 This is the infrared spectrum of the polyimide prepared in Example 1;

[0022] Figure 2 This is the NMR spectrum of the polyimide prepared in Example 1;

[0023] Figure 3 This is the infrared spectrum of the polyimide prepared in Example 2. Detailed Implementation

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] A first aspect of the present invention provides a polyimide having the structure shown in formula (I);

[0026]

[0027] Y comes from a diamine containing the -OAAAO- structure, where O represents an oxygen atom, A represents any atom, and A forms a ring with other atoms besides the oxygen atom.

[0028] In this invention, the polyimide contains a specific diamine structure, which gives the polyimide good processability and film-forming properties. When the separation membrane made from the polyimide is used for helium separation, it has high selectivity, good heat resistance and mechanical strength.

[0029] In this invention, in the -OAAAO- structure, A represents only the atom that directly bonds with O. In addition to the oxygen atom, depending on the valence state of the atom, the A atom may contain substituents, and AAA may be linked with one or more atoms other than the oxygen atom to form a ring.

[0030] In this invention, n refers to the number of repeating units in the structure shown by formula (1) of polyimide. The number of repeating units can be calculated based on the weight-average molecular weight of polyimide.

[0031] In one specific embodiment of the present invention, A is at least one of carbon atom, nitrogen atom and silicon atom.

[0032] In a preferred embodiment of the present invention, A is a carbon atom, and AAA is connected to three carbon atoms to form a benzene ring.

[0033] In one specific embodiment of the present invention, Y comes from the structure shown in formula (1);

[0034] R1-R3 are each independently an H or C1-C3 alkyl group.

[0035] In one specific embodiment of the present invention, in formula (1), R1-R3 are all H.

[0036] According to the present invention, X comes from at least one of the following structures:

[0037]

[0038] In a preferred embodiment of the present invention, X is selected from at least one structure shown in the group consisting of:

[0039]

[0040] According to the present invention, the polyimide has a weight-average molecular weight of 1 × 10⁻⁶. 4 -100×10 4 g / mol.

[0041] According to the present invention, the polyimide has a molecular weight distribution of 1-5.

[0042] In this invention, when the weight-average molecular weight and / or molecular weight distribution of the polyimide meets the above-mentioned range, the polyimide has good film-forming properties, and the film made from the polyimide has good mechanical strength.

[0043] Furthermore, the polyimide has a weight-average molecular weight of 5 × 10⁻⁶. 4 -30×10 4 g / mol.

[0044] Furthermore, the polyimide has a molecular weight distribution of 1-3, preferably 1-2.5.

[0045] In this invention, when the polyimide is mixed with conventional solvents used in the art for forming casting solutions, such as NMP, DMAc, DMF, DMSO and THF, a uniform and stable solution can be formed and a homogeneous film can be prepared, indicating that the polyimide has excellent film-forming properties.

[0046] According to the present invention, the 5wt% thermogravimetric temperature T of the polyimide is d 5wt％ The temperature is 500-700℃.

[0047] Furthermore, the 5wt% thermal weight loss temperature T of the polyimide d 5wt％ The temperature is 520-600℃.

[0048] A second aspect of the present invention provides a method for preparing the polyimide described in the first aspect of the present invention, characterized in that the preparation method comprises:

[0049] (1) In the presence of a protective atmosphere, diamine monomer, dianhydride monomer and solvent are mixed and polycondensation reaction is carried out to obtain polyamic acid solution;

[0050] (2) The polyamic acid solution is imidized to obtain the polyimide;

[0051] The diamine monomer is a diamine monomer containing the -OAAAO- structure, where O represents an oxygen atom, A represents any atom, and A forms a ring with other atoms besides the oxygen atom.

[0052] In the second aspect of this invention, the definition of A is the same as that described in the first aspect of this invention, and will not be repeated here.

[0053] In one specific embodiment of the present invention, the diamine monomer has the structure shown in formula (1);

[0054] R1-R3 are each independently an H or C1-C3 alkyl group.

[0055] In a preferred embodiment of the present invention, in formula (1), R1-R3 are all H.

[0056] In this invention, the dianhydride monomer is selected from one of the following groups:

[0057]

[0058]

[0059] In this invention, there is no particular limitation on the amount of diamine monomer and dianhydride monomer used, and the amount can be in accordance with the conventional amount used in the art. Preferably, the molar ratio of the diamine monomer to the dianhydride monomer is 0.9:1-1.2:1, and more preferably 0.95:1-1.05:1.

[0060] In one specific embodiment of the present invention, the conditions for the polycondensation reaction include: a temperature of -20°C to 30°C and a time of 8-18 hours.

[0061] In this invention, to ensure the temperature controllability of the polycondensation reaction, preferably, the polycondensation reaction is carried out in stages. Specifically, the first polycondensation reaction is carried out at a low temperature, and the second polycondensation reaction is carried out at a high temperature. The low temperature refers to a polycondensation reaction temperature not exceeding 5°C, and the high temperature refers to a polycondensation reaction temperature greater than or equal to 5°C. In this invention, there is no particular limitation on the reaction time of the first and second polycondensation reactions, as long as the sum of the times of the first and second polycondensation reactions is 8-18 hours.

[0062] In this invention, there is no particular limitation on the type of protective atmosphere; commonly used inert protective gases in the art, such as N2, can be used.

[0063] In one specific embodiment of the present invention, the solvent is selected from at least one of NMP, DMF, DMAc and DMSO.

[0064] In this invention, the amount of solvent used is such that the concentration of the diamine monomer, dianhydride monomer, and solvent in the mixed system is 10-20 wt%.

[0065] In a preferred embodiment of the present invention, step (1) includes: mixing the diamine monomer with a solvent, then adding the dianhydride monomer, and finally adding a solvent so that the concentration of the mixed system meets the requirements of the present invention.

[0066] In one specific embodiment of the present invention, the imidization is carried out in the presence of a catalyst and a dehydrating agent.

[0067] According to the present invention, the catalyst is selected from at least one of isoquinoline, pyridine and 3-methylpyridine.

[0068] According to the present invention, the dehydrating agent is acetic anhydride.

[0069] In this invention, there is no particular limitation on the amount of the catalyst or the dehydrating agent, and conventional amounts in the art can be used. Preferably, the molar ratio of the catalyst to the dianhydride monomer is 2.5:1-5.5:1, more preferably 3.6:1-4.5:1; the molar ratio of the dehydrating agent to the dianhydride monomer is 2.5:1-6:1, more preferably 3.6:1-5:1.

[0070] In one specific embodiment of the present invention, the imidization conditions include: a temperature of 20-60°C and a time of 12-48 hours.

[0071] According to the present invention, the preparation method further includes: pouring the product obtained by imidization into a precipitant to precipitate, washing and drying to obtain the polyimide.

[0072] In this invention, there is no particular limitation on the type of precipitant, as long as it can cause polyimide to precipitate from the solution after the amidation reaction. For example, it can be at least one selected from methanol, ethanol, water and acetone.

[0073] In one specific embodiment of the present invention, the precipitant is a mixed solvent of ethanol and water, wherein the volume ratio of ethanol to water is 1:1 to 9:1.

[0074] In this invention, there are no particular limitations on the drying conditions, as long as the polyimide can be fully dried. In one specific embodiment of this invention, the drying is carried out under vacuum conditions at a temperature of 120-180°C.

[0075] A third aspect of the present invention provides a separation membrane, wherein the separation membrane is made from the polyimide described in the first aspect of the present invention.

[0076] In this invention, the polyimide with a specific structure described in the first aspect of the invention is used to prepare a separation membrane. Since the polyimide contains a specific diamine structure, it not only ensures that the polyimide has good film-forming properties, but also significantly improves the separation performance, heat resistance and mechanical properties of the separation membrane.

[0077] According to the present invention, the thickness of the separation membrane is 20-50 μm, preferably 20-30 μm.

[0078] A fourth aspect of the present invention provides a method for preparing the separation membrane of the third aspect of the present invention, wherein the method comprises:

[0079] S1. Prepare a casting solution containing the polyimide described in the first aspect of the present invention;

[0080] S2. The casting solution is cast into a film and then dried to obtain the separation membrane.

[0081] According to the present invention, the solid content of the casting solution is 3-20 wt%.

[0082] In this invention, there is no particular limitation on the type of organic solvent in the casting solution. It can be any conventional organic solvent in the art, as long as it can fully dissolve the polyimide to form a homogeneous solution. For example, the organic solvent is selected from at least one of THF, DMF, NMP, DMAc and DMSO.

[0083] In this invention, to improve the dissolution of polyimide in the organic solvent, it is preferable to mix the polyimide with the organic solvent under heating and stirring conditions. Specifically, the heating temperature is 50-80°C.

[0084] In this invention, there is no particular limitation on the method of casting film formation by casting liquid. Conventional film-forming methods in the art can be used. For example, after the casting liquid is allowed to stand and degas, it is coated onto the surface of a glass plate, dried, and then immersed in deionized water to remove the separation membrane from the glass plate to obtain the separation membrane.

[0085] In this invention, there are no particular limitations on the drying conditions, as long as the solvent in the casting solution can be fully removed.

[0086] The fifth aspect of the present invention provides an application of the polyimide described in the first aspect of the present invention or the separation membrane provided in the third aspect of the present invention in gas separation, preferably in helium separation.

[0087] The present invention will be described in detail below through embodiments. In the following embodiments,

[0088] The structure of polyimide was determined using Fourier transform infrared spectroscopy and nuclear magnetic infrared spectroscopy.

[0089] The weight-average molecular weight and molecular weight distribution of polyimide were determined using GPC.

[0090] T of polyimide 5wt％ Thermogravimetric analysis was performed, with test temperatures ranging from 30 to 800℃, a heating rate of 20℃ / min, and nitrogen protection.

[0091] The mechanical properties of the separation membrane were measured using a universal tensile tester. The test sample had dimensions of 4cm × 1cm × 30μm.

[0092] The thickness of the separation membrane was measured using a micrometer screw gauge.

[0093] All raw materials used in the examples and comparative examples are commercially available products.

[0094] Preparation Example 1

[0095] Step 1: Under nitrogen protection, 50 mL of anhydrous N-methylpyrrolidone and 1,3-bis(3-aminophenoxy)benzene (in formula (1), R1-R3 are all H) (2.9233 g, 0.01 mmol) were added sequentially to a 250 mL three-necked flask and stirred until the material was completely dissolved; 4,4'-(hexafluoroisopropene) phthalic anhydride (6FDA) (4.4424 g, 0.01 mmol) were added to the above system and subjected to polycondensation reaction at 0 °C and 300 r / min under mechanical stirring for 2 h, and the reaction was continued at room temperature for 14 h to obtain a material containing polyimide acid; wherein the molar ratio of diamine monomer to dianhydride monomer is 1:1.

[0096] Step 2: Add a mixture of acetic anhydride (3.6753 g, 0.036 mmol) and pyridine (2.8476 g, 0.036 mmol) to the polyimide material obtained in Step 1, and perform intramolecular dehydration at 30 °C for 24 h to obtain a polyimide-containing solution; wherein, the molar ratio of the catalyst pyridine to the dianhydride monomer is 3.6:1, and the molar ratio of the dehydrating agent acetic anhydride to the dianhydride monomer is 3.6:1.

[0097] Step 3: Pour the above solution into a mixed solvent of water and ethanol (500mL: 500mL) to precipitate polyimide and obtain filamentous polyimide. Then, soak and wash the polyimide in a mixed solution of water and ethanol (1500mL: 1500mL) at 50°C (3 times). After filtration and drying, polyimide is obtained and designated as PI-1. The infrared spectrometer shows that PI-1 has the structure shown in the figure below.

[0098]

[0099] The infrared spectrum of PI-1 is as follows Figure 1 As shown, at 1789cm -1 and 1725cm -1 At 1377 cm⁻¹, peaks representing both asymmetric vibrations of the C=O ring on the imide ring and symmetric tensile vibrations were observed. -1 A stretching vibration peak of CN appeared at 720 cm⁻¹. -1 A deformation vibration peak of the imine ring appeared at 1110 cm⁻¹. -1 A stretching vibration peak of the CF bond appeared at 1250 cm⁻¹. -1 The appearance of asymmetric stretching vibration peaks of aromatic ethers at 1680-1620 cm⁻¹ indicates the successful synthesis of PI-1. -1 The absence of characteristic peaks within the specified range indicates the absence of imide acid characteristic peaks in the polymer, confirming the complete imidization of the polyimide.

[0100] PI-1 1 H-NMR spectrum as shown Figure 2 As shown, 1 The presence of only characteristic peaks of the benzene ring in the H-NMR spectrum indicates that there is no active hydrogen in the prepared polymer, and that the prepared polymer is fully amidated.

[0101] Preparation Example 2

[0102] Step 1: Under nitrogen protection, 67 mL of anhydrous N-methylpyrrolidone and 1,3-bis(3-aminophenoxy)benzene (in formula (1), R1-R3 are all H) (5.8466 g, 0.02 mmol) were added sequentially to a 250 mL three-necked flask and stirred until the material was completely dissolved; 3,3,4,4-diphenylsulfone tetracarboxylic acid dianhydride (7.1656 g, 0.02 mmol) was added to the above system and polycondensation reaction was carried out at 0 °C and 300 r / min under mechanical stirring for 12 h to obtain a material containing polyimide acid;

[0103] Step 2: Add a mixture of acetic anhydride (7.3505 g, 0.072 mmol) and pyridine (5.6952 g, 0.072 mmol) to the polyimide material obtained in Step 1, and perform intramolecular dehydration at 30 °C for 24 h to obtain a polyimide-containing solution; wherein the molar ratio of acetic anhydride to dianhydride is 3.6:1, and the molar ratio of pyridine to dianhydride is 3.6:1.

[0104] Step 3: Pour the above solution into a mixed solvent of water and ethanol (500mL: 500mL) to precipitate polyimide and obtain filamentous polyimide. Then, soak and wash the polyimide in a mixed solution of water and ethanol (1500mL: 1500mL) at 50°C (3 times). After filtration and drying, polyimide is obtained and designated as PI-2. The infrared spectrometer shows that PI-2 has the structure shown in the figure below.

[0105]

[0106] The infrared spectrum of PI-2 is as follows Figure 3 As shown, at 1785cm -1 and 1725cm -1 At 1375 cm⁻¹, peaks representing both asymmetric vibrations of the C=O ring on the imide ring and symmetric tensile vibrations were observed. -1 A stretching vibration peak of CN appeared at 724 cm⁻¹. -1 A deformation vibration peak of the imine ring appeared at 1373 cm⁻¹. -1 and 1103cm -1 At 1259 cm⁻¹, asymmetric and symmetric stretching vibration peaks of the sulfone group S=O=S were observed. -1 The appearance of an asymmetric stretching vibration peak for aromatic ethers at 1680-1620 cm⁻¹ indicates the successful synthesis of PI-2. -1 The absence of characteristic peaks within the specified range indicates the absence of imide acid characteristic peaks in the polymer, confirming the complete imidization of the polyimide.

[0107] Preparation Example 3

[0108] Step 1: Under nitrogen protection, 39 mL of anhydrous N-methylpyrrolidone and 1,3-bis(3-aminophenoxy)benzene (in formula (1), R1-R3 are all H) (2.9233 g, 0.01 mmol) were added sequentially to a 250 mL three-necked flask and stirred until the material was completely dissolved; 9,9-bis(3,4-dicarboxyphenyl)fluorene dihydric anhydride (4.5842 g, 0.01 mmol) was added to the above system, and the polycondensation reaction was carried out at 0 °C and 300 r / min under mechanical stirring for 2 h, and the reaction was continued at room temperature for 14 h to obtain a material containing polyimide acid;

[0109] Step 2: Add a mixture of acetic anhydride (4.5941 g, 0.045 mmol) and pyridine (3.5595 g, 0.045 mmol) to the polyimide material obtained in step (1), and perform intramolecular dehydration at 20 °C for 24 h to obtain a solution containing polyimide; the molar ratio of acetic anhydride to dianhydride is 4.5:1, and the molar ratio of pyridine to dianhydride is 4.5:1.

[0110] Step 3: Pour the above solution into a mixed solvent of water and ethanol (500mL: 500mL) to precipitate polyimide and obtain filamentous polyimide. Then, soak and wash the polyimide in a mixed solution of water and ethanol (1500mL: 1500mL) at 50°C (3 times). After filtration and drying, polyimide is obtained and designated as PI-3. The infrared spectrometer shows that PI-3 has the structure shown in the figure below.

[0111]

[0112] Preparation Example 4

[0113] Step 1: Under nitrogen protection, 43 mL of anhydrous N-methylpyrrolidone and 1,3-bis(3-aminophenoxy)benzene (in formula (1), R1-R3 are all H) (5.8466 g, 0.02 mmol) were added sequentially to a 250 mL three-necked flask and stirred until the material was completely dissolved; 4,4'-biphenyl ether dianhydride (6.2042 g, 0.02 mmol) was added to the above system, and the polycondensation reaction was carried out at 0 °C and 300 r / min under mechanical stirring for 1 h, and the reaction was continued at room temperature for 8 h to obtain a material containing polyimide acid;

[0114] Step 2: Add a mixture of acetic anhydride (7.3505 g, 0.072 mmol) and pyridine (5.6952 g, 0.072 mmol) to the polyimide material obtained in step (1), and perform intramolecular dehydration for 24 h at room temperature to obtain a polyimide-containing solution.

[0115] Step 3: Pour the above solution into a mixed solvent of water and ethanol (500 mL: 500 mL) to precipitate polyimide and obtain filamentous polyimide. Then, soak and wash the polyimide in a mixed solution of water and ethanol (1500 mL: 1500 mL) at 50°C (3 times). After filtration and drying, polyimide is obtained and designated as PI-4. The infrared spectrometer shows that PI-4 has the structure shown in the figure below.

[0116]

[0117] Preparation Example 5

[0118] Step 1: Under nitrogen protection, 43 mL of anhydrous N-methylpyrrolidone and 1,3-bis(3-aminophenoxy)benzene (in formula (1), R1-R3 are all H) (3.5080 g, 0.012 mmol) were added sequentially to a 250 mL three-necked flask and stirred until the material was completely dissolved; 4,4'-terephthalodioxydiphthalic anhydride (4.8277 g, 0.012 mmol) was added to the above system, and the polycondensation reaction was carried out at 0 °C and 300 r / min under mechanical stirring for 1 h, and the reaction was continued at room temperature for 15 h to obtain a material containing polyimide acid;

[0119] Step 2: Add a mixture of acetic anhydride (5.5129 g, 0.054 mmol) and pyridine (4.2714 g, 0.054 mmol) to the polyimide material obtained in step (1), and perform intramolecular dehydration for 24 h at room temperature to obtain a polyimide-containing solution.

[0120] Step 3: Pour the above solution into a mixed solvent of water and ethanol (500mL:500mL) to precipitate polyimide and obtain filamentous polyimide. Then, soak and wash the polyimide in a mixed solution of water and ethanol (1500mL:1500mL) at 50°C (3 times). After filtration and drying, polyimide is obtained and designated as PI-5. The infrared spectrometer shows that PI-5 has the structure shown in the figure below.

[0121]

[0122] Comparative Preparation Example 1

[0123] Step 1: Under nitrogen protection, 85 mL of anhydrous N-methylpyrrolidone and 1,2-bis(4-aminophenoxy)ethane (a diamine monomer containing an -OAAO- structure and in a chain form) (4.8858 g, 0.02 mmol) were added sequentially to a 250 mL three-necked flask, and stirred until the material was completely dissolved; 4,4'-(hexafluoroisopropene)phthalic anhydride (6FDA) (8.8848 g, 0.02 mmol) was added to the above system, and the polycondensation reaction was carried out at 0 °C and 300 r / min under mechanical stirring for 6 h, and the reaction was continued at room temperature for 6 h to obtain a material containing polyimide acid;

[0124] Step 2: Add a mixture of acetic anhydride (7.3505 g, 0.072 mmol) and pyridine (5.6952 g, 0.072 mmol) to the polyimide material obtained in Step 1, and perform intramolecular dehydration at 30 °C for 24 h to obtain a solution containing polyimide.

[0125] Step 3: Pour the above solution into a mixed solvent of water and ethanol (500 mL: 500 mL) to precipitate polyimide and obtain filamentous polyimide. Then, soak and wash the polyimide in a mixed solution of water and ethanol (1500 mL: 1500 mL) at 50°C (3 times). After filtration and drying, polyimide is obtained and designated as PI-D1. The infrared spectrometer shows that PI-D1 has the structure shown in the figure below.

[0126]

[0127] The weight-average molecular weight, molecular weight distribution, and Tg of the polyimides prepared in the preparation examples and comparative preparation examples were compared. d5wt％ The test was conducted, and the results are shown in Table 1.

[0128] Table 1

[0129]

[0130]

[0131] As can be seen from Table 1, the polyimide provided by this invention has a high 5wt% thermogravimetric temperature Tw. d5wt％ All temperatures were above 520℃, indicating that polyimide possesses excellent heat resistance. Analysis of the weight-average molecular weight and molecular weight distribution showed that the molecular weights of the prepared polymers were all above 5 × 10⁻⁶. 4 The molecular weight distribution coefficient of g / mol is less than 3, indicating that the prepared polymer has a relatively uniform molecular weight distribution.

[0132] Example 1

[0133] The polyimide (PI-1) obtained in Preparation Example 1 was used to prepare a gas separation membrane:

[0134] PI-1 was added to NMP at a solid content of 8 wt%, and magnetically stirred on a flat plate heater at 50°C until PI-1 was completely dissolved, resulting in a uniform and stable casting solution. After cooling the casting solution to room temperature, it was filtered, allowed to stand, and then uniformly coated onto a clean glass plate surface. The solution was dried in a forced-air oven at 60°C for 6 hours to remove a large amount of solvent, and then transferred to a vacuum oven (dried at 150°C for 12 hours) to further remove the remaining solvent. After cooling to room temperature, the glass plate with the film was immersed in deionized water until the film detached from the glass plate surface, resulting in a gas separation membrane, denoted as S1.

[0135] Example 2

[0136] The polyimide (PI-2) obtained in Preparation Example 2 was used to prepare a gas separation membrane:

[0137] PI-2 was added to NMP at a solid content of 15 wt%, and magnetically stirred on a flat plate heater at 50°C until PI-2 was completely dissolved, resulting in a uniform and stable casting solution. After cooling the casting solution to room temperature, it was filtered, allowed to stand, and then uniformly coated onto a clean glass plate surface. The plate was dried in a forced-air oven at 60°C for 6 hours to remove a large amount of solvent, and then transferred to a vacuum oven (dried at 150°C for 12 hours) to further remove the remaining solvent. After cooling to room temperature, the glass plate with the film was immersed in deionized water until the film detached from the glass plate surface, resulting in a gas separation membrane, denoted as S2.

[0138] Example 3

[0139] The polyimide (PI-3) obtained in Preparation Example 3 was used to prepare a gas separation membrane:

[0140] PI-3 was added to NMP at a solid content of 8 wt%, and magnetically stirred on a flat plate heater at 50°C until PI-3 was completely dissolved, resulting in a uniform and stable casting solution. After cooling the casting solution to room temperature, it was filtered, allowed to stand, and then uniformly coated onto a clean glass plate surface. The plate was dried in a forced-air oven at 60°C for 6 hours to remove a large amount of solvent, and then transferred to a vacuum oven (dried at 150°C for 12 hours) to further remove the remaining solvent. After cooling to room temperature, the glass plate with the film was immersed in deionized water until the film detached from the glass plate surface, resulting in a gas separation membrane, designated as S3.

[0141] Example 4

[0142] The polyimide (PI-4) obtained in Preparation Example 4 was used to prepare a gas separation membrane:

[0143] PI-4 was added to NMP at a solid content of 8 wt%, and magnetically stirred on a flat plate heater at 50°C until PI-4 was completely dissolved, resulting in a uniform and stable casting solution. After cooling the casting solution to room temperature, it was filtered, allowed to stand, and then uniformly coated onto a clean glass plate surface. The solution was dried in a forced-air oven at 60°C for 6 hours to remove a large amount of solvent, and then transferred to a vacuum oven (dried at 150°C for 12 hours) to further remove the remaining solvent. After cooling to room temperature, the glass plate with the film was immersed in deionized water until the film detached from the glass plate surface, resulting in a gas separation membrane, designated as S4.

[0144] Example 5

[0145] The polyimide (PI-5) obtained in Preparation Example 5 was used to prepare a gas separation membrane:

[0146] PI-5 was added to NMP at a solid content of 5 wt%, and magnetically stirred on a flat plate heater at 50°C until PI-5 was completely dissolved, resulting in a uniform and stable casting solution. After cooling the casting solution to room temperature, it was filtered, allowed to stand, and then uniformly coated onto a clean glass plate surface. The solution was dried in a forced-air oven at 60°C for 6 hours to remove a large amount of solvent, and then transferred to a vacuum oven (dried at 150°C for 12 hours) to further remove the remaining solvent. After cooling to room temperature, the glass plate with the film was immersed in deionized water until the film detached from the glass plate surface, resulting in a gas separation membrane, designated as S5.

[0147] Comparative Example 1

[0148] The 6FDA-p-phenylenediamine (mPDA) gas separation membrane prepared in the literature “Gas separation performance of 6FDA-based polyimides with different chemical structures” is designated as DS1.

[0149] Comparative Example 2

[0150] Gas separation membranes were prepared using the polyimide (PI-D1) obtained in Comparative Preparation Example 1:

[0151] PI-D1 was added to NMP at a solid content of 8 wt%, and magnetically stirred on a flat plate heater at 50°C until PI-D1 was completely dissolved, resulting in a uniform and stable casting solution. After cooling the casting solution to room temperature, it was filtered, allowed to stand, and then uniformly coated onto a clean glass plate surface. The plate was dried in a forced-air oven at 60°C for 6 hours to remove a large amount of solvent, and then transferred to a vacuum oven (dried at 150°C for 12 hours) to further remove the remaining solvent. After cooling to room temperature, the glass plate with the film was immersed in deionized water until the film detached from the glass plate surface, resulting in a gas separation membrane, denoted as DS2.

[0152] Test case

[0153] The performance of the polyimide gas separation membranes obtained in the above examples and comparative examples was tested using the differential pressure method (referring to GB / T 1038-2000 Test Method for Gas Permeability of Plastic Films and Sheets):

[0154] The gas permeability coefficients of He, H2, Ne, N2, CH4, and CO2, as well as the selectivity of He / Ne, He / N2, and He / CH4, were tested at 35℃ and 100psi. The test results are shown in Table 2.

[0155] The thickness and mechanical properties of the polyimide gas separation membrane were tested, and the results are shown in Table 2.

[0156] Table 2

[0157]

[0158]

[0159] Table 2

[0160] Thickness / μm Fracture strength (MPa) Elongation at break (%) Example 1 30 122.8 5.0 Example 2 30 106.9 4.2 Example 3 30 154.3 5.5 Example 4 30 101.7 10.8 Example 5 30 128.2 12.5 Comparative Example 2 30 73.5 22.8

[0161] As shown in Table 2, the separation membrane prepared from the polyimide of this invention exhibits a high permeability coefficient and high selectivity for He, indicating that the separation membrane prepared from the polyimide provided by this invention has significantly improved separation performance when used for helium separation. Furthermore, the separation membrane prepared from the polyimide of this invention has high tensile strength, indicating that the separation membrane possesses both excellent separation performance and high mechanical properties.

[0162] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including 1240826.

[0163] Any combination of the various technical features in any other suitable manner, such simple variations and combinations, should also be considered as part of the disclosure of this invention and fall within the protection scope of this invention.

Claims

1. A polyimide, characterized in that, The polyimide has the structure shown in formula (I); Y comes from a diamine containing the -OAAAO- structure, where O represents an oxygen atom, A represents any atom, and A forms a ring with other atoms besides the oxygen atom.

2. The polyimide according to claim 1, wherein, A is at least one of carbon, nitrogen, and silicon atoms; Preferably, Y comes from the structure shown in equation (1); R1-R3 are each independently an H or C1-C3 alkyl group; Preferably, X is selected from at least one structure shown in the group consisting of; 3. The polyimide according to claim 1 or 2, wherein, The polyimide has a weight-average molecular weight of 1×10⁻⁶. 4 -100×10 4 g / mol, preferably 5×10 g / mol 4 -30×10 4 g / mol; Preferably, the polyimide has a molecular weight distribution of 1-5, more preferably 1-3; Preferably, the 5wt% thermogravimetric temperature T of the polyimide is... d5wt％ The temperature range is 500-700℃, preferably 520-600℃.

4. A method for preparing the polyimide according to any one of claims 1-3, characterized in that, The preparation method includes: (1) In the presence of a protective atmosphere, diamine monomer, dianhydride monomer and solvent are mixed and polycondensation reaction is carried out to obtain polyamic acid solution; (2) The polyamic acid solution is imidized to obtain the polyimide; The diamine monomer is a diamine monomer containing the -OAAAO- structure, where O represents an oxygen atom, A represents any atom, and A forms a ring with other atoms besides the oxygen atom.

5. The preparation method according to claim 4, wherein, The imidization is carried out in the presence of a catalyst and a dehydrating agent; Preferably, the catalyst is selected from at least one of isoquinoline, pyridine, and 3-methylpyridine; Preferably, the dehydrating agent is acetic anhydride; Preferably, the conditions for the polycondensation reaction include: a temperature of -20°C to 30°C and a time of 8-18 hours; Preferably, the imidization conditions include a temperature of 20-60°C and a time of 12-48 hours.

6. The preparation method according to claim 4 or 5, wherein, The preparation method further includes: pouring the product obtained by imidization into a precipitant to precipitate, washing and drying it to obtain the polyimide; Preferably, the precipitant is selected from at least one of methanol, ethanol, water, and acetone.

7. A separation membrane, characterized in that, The separation membrane is made from the polyimide according to any one of claims 1-3.

8. The separation membrane according to claim 7, wherein, The thickness of the separation membrane is 20-50 μm.

9. A method for preparing the separation membrane according to claim 7 or 8, characterized in that, The method includes: S1. Prepare a casting solution comprising the polyimide according to any one of claims 1-3; S2. The casting solution is cast into a film and then dried to obtain the separation membrane.

10. The method according to claim 9, wherein, The solid content of the casting solution is 3-20 wt%. Preferably, the organic solvent in the casting solution is selected from at least one of THF, DMF, NMP, DMAc and DMSO.

11. The application of the polyimide according to any one of claims 1-3 or the separation membrane according to claim 7 or 8 in gas separation, preferably in helium separation.

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