Polyimide for gas separation as well as preparation method and application thereof

Abstract

The invention provides polyimide for gas separation and a manufacturing method and application thereof, and relates to the technical field of high polymer materials, the polyimide comprises the following components by mass: 80%-99.5% of fluorine-containing polyimide, 0.5%-20% of polyimide containing unsaturated end groups and 0.05%-5% of a catalyst; according to the invention, fluorine-containing polyimide is compounded with unsaturated terminal group-containing polyimide with a specific structure and a catalyst, so that a novel polyimide material which can be processed in a solution and can be thermally crosslinked under a mild condition is successfully developed. The material keeps the inherent high heat resistance and mechanical properties of polyimide, and more importantly, the carbon dioxide plasticizing resistance is remarkably improved while good gas permeability is kept through molecular design. In addition, after being prepared into a gas separation membrane, the gas separation membrane shows excellent selective stability for a long time or in a high-pressure carbon dioxide environment.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a polyimide for gas separation, its manufacturing method, and its application. Background Technology

[0002] Membrane separation technology for gas mixtures utilizes the differences in permeability and selectivity of polymer membranes for different gas molecules to separate a target gas from a gas mixture. Examples include separating carbon dioxide and methane from biogas. Polyimide, due to its high heat resistance and excellent overall performance, is an ideal raw material for gas separation membranes. However, conventional polyimide resins are difficult to dissolve, do not melt, are difficult to process, and have low permeability, thus limiting their potential for widespread industrial application.

[0003] Commercially available polyimide resins for gas separation membranes commonly include Matrimid 5218 and P84. Matrimid 5218 is obtained by polymerizing 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) with 5(6)-amino-1-(4-aminophenyl)-1,3,3-trimethylindane (PIDA). P84 is prepared by co-condensation polymerization of three monomers: 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), diphenylmethane diisocyanate (MDI), and toluene diisocyanate (TDI). When used for carbon dioxide separation, these two commercially available polyimide gas separation membranes exhibit relatively limited selectivity and are prone to plasticization by carbon dioxide under prolonged or high-pressure conditions, resulting in decreased selectivity. Therefore, this invention proposes a polyimide for gas separation, its manufacturing method, and its application to address the problems existing in the prior art. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to provide a polyimide for gas separation, its manufacturing method, and its application. The present invention successfully prepares a gas separation membrane with excellent comprehensive performance by introducing a specific proportion of unsaturated end-group polyimide and a catalyst into a fluorinated polyimide matrix and then performing a controllable heat treatment crosslinking process.

[0005] To achieve the objectives of this invention, the invention is implemented through the following technical solution: a polyimide for gas separation, characterized in that it comprises the following components by mass percentage:

[0006] It contains 80%–99.5% fluorinated polyimide, 0.5%–20% polyimide with unsaturated end groups, and 0.05%–5% catalyst.

[0007] A further improvement lies in the following: the general structural formula of the fluorinated polyimide is as follows:

[0008] Ar is a bisphenol residue selected from one or more of the following structures:

[0009] R is a diamine residue, selected from one or more of the following structures: .

[0010] A further improvement lies in the following: the general structural formula of the polyimide containing unsaturated end groups is as follows:

[0011] Wherein R1 is a bisphenol residue, selected from one or more of the following structures:

[0012] R2 is a dianhydride residue selected from one or more of the following structures:

[0013] EG is an unsaturated monohydric anhydride or monoamine, selected from one or more of the following structures:

[0014] The n value of the molecular weight of the polyimide containing unsaturated end groups is controlled to be between 1 and 10.

[0015] A further improvement is that the catalyst is selected from one or more of the following categories:

[0016] Aliphatic tertiary amines, nucleophilic tertiary organophosphorus compounds, and nucleophilic heteroaryl compounds;

[0017] Aliphatic tertiary amines include 1,4-diazabicyclo[2.2.2]octane and triethylamine;

[0018] Nucleophilic tertiary organophosphorus compounds such as triphenylphosphine, organooxyphosphine, and triphenylphosphite;

[0019] Nucleophilic heteroaryl compounds such as benzimidazole, triazole, pyrazole, benzopyrazole, tetrazolium, pyridine, tetrazine, trizine, oxazole, isoxazole, 4-dimethylaminopyridine, and 1-methylimidazole are organic compounds that can lower the initiation temperature of chain extension and crosslinking of polyimides containing unsaturated terminal groups.

[0020] A further improvement is that the catalyst is preferably one or more of triphenylphosphine, benzimidazole, 1-methylimidazole, triethylamine, and 1,4-diazabicyclo[2.2.2]octane.

[0021] A method for preparing polyimide for gas separation includes the following steps:

[0022] Step 1: Preparation of fluorinated polyimide polymerization solution:

[0023]

[0024] X is a substituent, which can be a halogen substituent -F, -Cl, -Br, -I or a nitro substituent -NO2;

[0025] Under the protection of high-purity nitrogen, equimolar amounts of disubstituted imide, sodium bisphenolate, and anhydrous polar solvent are added to a reaction vessel and refluxed at 150℃~200℃ for 6~12 hours. After the reaction is completed, the inorganic salt is removed by filtration to obtain the first polymerization solution.

[0026] Step 2: Preparation of polyimide polymerization solution containing unsaturated end groups:

[0027] Under the protection of high-purity nitrogen, diamine, dianhydride and polar solvent are mixed and reacted at room temperature for 6 to 12 hours. Then, a capping agent is added and the reaction continues for 12 to 24 hours. Toluene is then added and the mixture is heated to 160°C to 200°C and refluxed for 8 to 12 hours to remove water. After imidization is completed, toluene is removed to obtain the second polymerization solution.

[0028] Step 3, Post-processing: Mix the first polymerization liquid and the second polymerization liquid according to the mass ratio so that the mass percentage of each component in the mixed composition is: 80% to 99.5% fluorinated polyimide, 0.5% to 20% unsaturated end-group polyimide, and 0.05% to 5% catalyst. Then add the catalyst and stir and mix at 80°C until uniform. After degassing, the polyimide composition is obtained.

[0029] An application of a polyimide for gas separation in a gas separation membrane, which is used in the field of carbon dioxide separation.

[0030] A further improvement is that the preparation step of the gas separation membrane includes the following steps:

[0031] Step S1: Coat the substrate (glass plate) with a 50µm polyimide scraper, immerse it in a 0-80℃ coagulation bath for 24-48 hours, and then dry it in a 30-100℃ forced-air oven for 1-8 hours;

[0032] Step S2: Perform heat treatment crosslinking under vacuum conditions, then immerse the heat-treated membrane in an ethanol bath for 24 hours to remove the crosslinking catalyst, and finally air dry to obtain a gas separation membrane.

[0033] A further improvement is that the coagulation bath is selected from one or a mixture of several of the following: water, tert-butanol, ethanol, acetone, glycerol, etc.

[0034] A further improvement is that the specific method of heat treatment crosslinking is: heat treatment at 100-400℃ for 1-3 hours in a vacuum oven.

[0035] The beneficial effects of this invention are as follows: By combining fluorinated polyimide with a polyimide containing unsaturated end groups of a specific structure and a catalyst, this invention successfully developed a novel polyimide material that is solution-processable and thermally crosslinkable under mild conditions. This material not only maintains the inherent high heat resistance and mechanical properties of polyimide, but more importantly, through molecular design, it significantly enhances resistance to carbon dioxide plasticization while maintaining good gas permeability. Furthermore, after being fabricated into a gas separation membrane, this invention exhibits excellent selectivity stability under prolonged or high-pressure carbon dioxide environments, effectively overcoming the inherent defect of decreased selectivity due to plasticization effects in traditional commercial polyimide membranes. Simultaneously, this invention employs a solution processing route, achieving crosslinking through subsequent controllable heat treatment, thus overcoming the difficulties of dissolving and processing conventional polyimide resins, and providing a practical material basis for the industrial preparation of high-performance gas separation membranes. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the polyimide preparation steps of the present invention. Detailed Implementation

[0037] To enhance understanding of the present invention, the present invention will be further described in detail below with reference to embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0038] The test methods for various properties of the polyimide film in the following examples and comparative examples are as follows:

[0039] Solvent resistance test:

[0040] After drying the polyimide film in a vacuum oven at 80°C for 1 hour, the thickness of the film at any 5 points was measured. Then, a 2 cm * 2 cm sample of the film was immersed in a 100 ml beaker containing 50 ml of 100% DMAc for 10 minutes, washed with water, dried in a vacuum oven at 80°C for 1 hour, and the thickness of the film at any 5 points was measured again. The solvent resistance index was then calculated according to the following formula.

[0041] The thickness of the film was measured using an Anritsu Electronic Micrometer, which has a deviation of less than ±0.5%.

[0042]

[0043] In the above formula, a is the thickness of the film before immersion in the solution, and b is the thickness of the film after immersion in the polar solvent for 10 minutes.

[0044] Viscosity: The polyimides prepared in each example and comparative example were measured at 30°C using N-methylpyrrolidone (NMP) as solvent in an Ubbelohde viscometer.

[0045] Gas permeability testing of membranes: Gas permeability is measured by the pressure rise method. A gas or gas mixture is applied to one side of a flat sheet membrane with a thickness of 10 to 70 μm; on the other side (the permeation side), a vacuum is created at the start of the experiment (approximately 10 μm). -2 (mbar). The osmotic pressure increases over time, and the data is recorded.

[0046] The permeability of polyimide membranes can be calculated using the following formula:

[0047]

[0048] P…with Barrer(10) -10 cm 3 (STP)cm / cm 2 Permeability in units of scmHg

[0049] V…in cm 3 permeable side volume

[0050] MW…molar mass of a gas in g / mol

[0051] ...thickness of the thin film layer in cm

[0052] ρ…in g / cm 3 gas density in units

[0053] R…in cm 3 .cmHg.K -1 .mol -1 gas constant in units

[0054] T… temperature in Kelvin

[0055] A… with cm 2 unit film area

[0056] …Pressure difference between the feed and permeate sides, expressed in cmHg dp / dt. Pressure rise per unit time on the permeate side, expressed in cmHg / s.

[0057] Example 1

[0058] according to Figure 1 As shown in the figure, this embodiment proposes a polyimide for gas separation, the composition of which and its preparation method are as follows:

[0059] Step 1: Under high-purity nitrogen protection, add 38.0200 g (0.1 mol) of dry bisphenol AF disodium salt, 61.642 g (0.1 mol) of 4,4-diamino-2,2-bis(trifluoromethyl)biphenyl difluoroimide monomer, and 896.9580 g of anhydrous N-methylpyrrolidone to a three-necked flask. Set the reaction temperature to 200℃ and react for 12 h, continuously monitoring the viscosity during the reaction. After the reaction is completed, cool to room temperature and filter out the inorganic salts in the reaction solution to obtain the first polymerization solution.

[0060] Step 2: Under high-purity nitrogen protection, add 4,4'-(9-fluoreneyl)diphenylamine (4.1814 g, 0.012 mol), hexafluoroisopropylphthalic anhydride (4.4424 g, 0.01 mol), and 87.5592 g NMP to a three-necked flask. Stir the reaction at room temperature for 8 h. After 8 h, add the end-capping agent PETA (1.105 g, 0.004 mol) and continue the reaction at room temperature for 12 h.

[0061] After 12 hours, 22g of toluene was added and the temperature was raised to 200℃ and refluxed to remove water. After 12 hours, the toluene was distilled off. Once all the toluene had distilled off, the second polymerization solution was obtained.

[0062] Step 3: Mix the first polymerization liquid and the second polymerization liquid by mechanical stirring at 80°C, and add the catalyst 1-methylimidazole (1g). Stir until no solids are visible to the naked eye; turn off the stirring and let it stand at 80°C for 12 hours to remove bubbles.

[0063] Step S1: Apply the coating to a glass plate using a 50µm scraper, immerse it in 60℃ water for 24 hours, and then dry it in a 60℃ forced-air oven for 4 hours.

[0064] Step S2: The obtained membrane sample is heat-treated and crosslinked at 190°C in a vacuum oven for 1.5 h. The heat-treated membrane is then immersed in an ethanol bath for 24 h to remove the crosslinking catalyst, and finally air-dried.

[0065] Step S3: Characterize the obtained membrane sample. The data are shown in Tables 1-3.

[0066] Example 2

[0067] This embodiment provides a polyimide for gas separation, the composition of which and its preparation method are shown below:

[0068] The preparation method of polyimide in this embodiment is the same as that in Example 1, except that the catalyst used is triphenylphosphine (1g). After the polyimide resin composition is prepared, it is then used to prepare a polyimide separation membrane using the method in Example 1, and characterized. The data are shown in Tables 1-3.

[0069] Example 3

[0070] This embodiment provides a polyimide for gas separation, the composition of which and its preparation method are shown below:

[0071] The preparation method of polyimide in this embodiment is the same as that in Example 1, except that the ratio of the formulation is different. After the polyimide resin composition is prepared, it is then used in Example 1 to prepare a polyimide separation membrane and characterized. The data are shown in Tables 1 to 3.

[0072] Example 4

[0073] This embodiment provides a polyimide for gas separation, the composition of which and its preparation method are shown below:

[0074] Preparation steps: Step 1: Under high-purity nitrogen protection, add dry disodium phenolphthalein (36.2290g, 0.1mol), 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether type difluoroimide monomer (63.2420g, 0.1mol), and anhydrous N-methylpyrrolidone (563.6690g) to a three-necked flask. Set the reaction temperature to 200℃ and react for 12h, continuously monitoring the viscosity during the reaction. After the reaction is completed, cool to room temperature and filter out the inorganic salts in the reaction solution to obtain the first polymerization solution.

[0075] Step 2: Under high-purity nitrogen protection, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (3.2279 g, 0.0096 mol), 2,3,3',4'-biphenyltetracarboxylic dianhydride (2.4714 g, 0.0084 mol), and 87.5592 g NMP were added to a three-necked flask. The mixture was stirred at room temperature for 8 h. After 8 h, PETA (0.6630 g, 0.0024 mol) was added, and the reaction was continued at room temperature for 12 h.

[0076] After 12 hours, 24 g of toluene was added and the temperature was raised to 200°C and refluxed to remove water. After 12 hours, the toluene was distilled off. Once all the toluene had distilled off, the second polymerization solution was obtained.

[0077] Step 3: Mix the first polymerization liquid and the second polymerization liquid by mechanical stirring at 80°C, and add the catalyst triphenylphosphine (2g). Stir until no solids are visible to the naked eye; turn off the stirring and let it stand at 80°C for 12 hours to remove bubbles.

[0078] Step S1: Apply the coating to a glass plate using a 50µm scraper, immerse it in 60℃ water for 24 hours, and then dry it in a 60℃ forced-air oven for 4 hours.

[0079] Step S2: The obtained membrane sample is heat-treated and crosslinked in a vacuum oven at 190°C for 2 hours. The heat-treated membrane is then immersed in an ethanol bath for 24 hours to remove the crosslinking catalyst, and finally air-dried.

[0080] Step S3: Characterize the obtained membrane sample. The data are shown in Tables 1-3.

[0081] Comparative Example 1

[0082] This comparative example provides a polyimide for gas separation, the composition of which and its preparation method are shown below:

[0083] The preparation method of polyimide in this comparative example is the same as that in Example 1, except that the formulation contains only 100% fluorinated polyimide. Polyimide separation membranes are prepared using the method in Example 1 and characterized. The data are shown in Tables 1-3.

[0084] Comparative Example 2

[0085] This comparative example provides a polyimide for gas separation, the composition of which and its preparation method are shown below:

[0086] The preparation method of polyimide in this comparative example is the same as that in Example 1. The only difference is that the formulation contains only 90% fluorinated polyimide and 10% polyimide with unsaturated functionalities. Polyimide separation membranes are prepared using the method in Example 1 and characterized. The data are shown in Tables 1-3.

[0087] Comparative Example 3

[0088] This comparative example provides a polyimide for gas separation, the composition of which and its preparation method are shown below:

[0089] The preparation method of polyimide in this comparative example is the same as that in Example 1, except that the formulation contains 70% fluorinated polyimide, 25% unsaturated functional polyimide, and 5% catalyst 1-methylimidazole. Polyimide separation membranes were prepared using the method in Example 1 and characterized. The data are shown in Tables 1-3.

[0090] Comparative Example 4

[0091] This comparative example provides a polyimide for gas separation, the composition of which and its preparation method are shown below:

[0092] The composition and preparation method of the polyimide in this comparative example are the same as those in Example 1. The only difference is that the thermal crosslinking treatment is performed by heat-treating the obtained membrane sample at 350°C in a vacuum oven for 10 hours. All other steps are the same as in Example 1. The polyimide separation membrane is prepared using the method in Example 1 and characterized. The data are shown in Tables 1-3.

[0093] The polyimide separation membranes prepared in each embodiment and comparative example were characterized. The viscosity results are shown in Table 1, the solvent resistance test results are shown in Table 2, and the permeability of single gases CO2 and N2 is shown in Table 3, as follows:

[0094]

[0095] Table 1 Viscosity results for examples and comparative examples.

[0096]

[0097] Table 2 Solvent resistance test results of the examples and comparative examples

[0098]

[0099] *The transmembrane pressure was tested at 5 bar.

[0100] Table 3. Gas permeability results of the examples and comparative examples

[0101] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the present invention without departing from its framework and scope of application, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A polyimide for gas separation, characterized in that: It includes the following components by mass percentage: It contains 80%–99.5% fluorinated polyimide, 0.5%–20% polyimide with unsaturated end groups, and 0.05%–5% catalyst.

2. The polyimide for gas separation according to claim 1, characterized in that: The general structural formula of the fluorinated polyimide is as follows: Ar is a bisphenol residue selected from one or more of the following structures: R is a diamine residue, selected from one or more of the following structures:

3. The polyimide for gas separation according to claim 1, characterized in that: The general structural formula of the polyimide containing unsaturated end groups is as follows: Wherein R1 is a bisphenol residue, selected from one or more of the following structures: R2 is a dianhydride residue selected from one or more of the following structures: EG is an unsaturated monohydric anhydride or monoamine, selected from one or more of the following structures:

4. The polyimide for gas separation according to claim 1, characterized in that: The catalyst is selected from one or more of the following categories: Aliphatic tertiary amines, nucleophilic tertiary organophosphorus compounds, and nucleophilic heteroaryl compounds.

5. A polyimide for gas separation according to claim 4, characterized in that: The catalyst is preferably one or more of triphenylphosphine, benzimidazole, 1-methylimidazole, triethylamine, and 1,4-diazabicyclo[2.2.2]octane.

6. The method for preparing polyimide for gas separation according to claim 1, characterized in that: Includes the following steps: Step 1: Preparation of fluorinated polyimide polymerization solution: Under the protection of high-purity nitrogen, equimolar amounts of disubstituted imide, sodium bisphenolate, and anhydrous polar solvent are added to a reaction vessel and refluxed at 150℃~200℃ for 6~12 hours. After the reaction is completed, the inorganic salt is removed by filtration to obtain the first polymerization solution. Step 2: Preparation of polyimide polymer solution with unsaturated end groups: Under the protection of high-purity nitrogen, diamine, dianhydride and polar solvent are mixed and reacted at room temperature for 6 to 12 hours. Then, end-capping agent is added and the reaction continues for 12 to 24 hours. Toluene is then added and the mixture is heated to 160℃ to 200℃ and refluxed for 8 to 12 hours to remove water. After imidization is completed, toluene is removed to obtain the second polymer solution. Step 3, Post-processing: Mix the first polymerization liquid and the second polymerization liquid according to the mass ratio so that the mass percentage of each component in the mixed composition is: 80% to 99.5% fluorinated polyimide, 0.5% to 20% unsaturated end-group polyimide, and 0.05% to 5% catalyst. Then add the catalyst and stir and mix at 80°C until uniform. After degassing, the polyimide composition is obtained.

7. The use of the polyimide for gas separation as described in claim 1 in a gas separation membrane.

8. The application of a polyimide for gas separation according to claim 7 in a gas separation membrane, characterized in that: The preparation steps of the gas separation membrane include the following steps: Step S1: Coat polyimide onto the substrate, immerse it in a coagulation bath at 0-80°C for 24-48 hours, and then dry it in a forced-air oven at 30-100°C for 1-8 hours; Step S2: Perform heat treatment crosslinking under vacuum conditions, then immerse the heat-treated membrane in an ethanol bath for 24 hours to remove the crosslinking catalyst, and finally air dry to obtain a gas separation membrane.

9. The application of a polyimide for gas separation according to claim 8 in a gas separation membrane, characterized in that: The coagulation bath is selected from one or a mixture of several of the following: water, tert-butanol, ethanol, acetone, and glycerol.

10. The application of a polyimide for gas separation according to claim 8 in a gas separation membrane, characterized in that: The specific method of heat treatment crosslinking is as follows: heat treatment at 100-400℃ for 1-3 hours in a vacuum oven.

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