Preparation method of anion exchange composite membrane

Abstract

The invention belongs to the technical field of functional polymer membrane materials, and discloses a method for improving the mechanical stability of an anion exchange membrane. According to the method, two-way stretched porous polytetrafluoroethylene is used as a supporting and reinforcing framework, interface compounding of polytetrafluoroethylene fibers and anion exchange resin is improved, and from OH <-> ion conduction, water diffusion and interface failure of a composite membrane, quaternization modification is carried out on perfluorinated sulfonic acid resin, so that the composite membrane is obtained. Performing impregnation regulation on the interface of the expanded polytetrafluoroethylene film; performing impregnation by using solvents with different proportions to regulate the shrinkage stress of the polytetrafluoroethylene microporous film; and adding a surfactant into anion exchange resin to enhance the wettability of the solution. The preparation of the perfluoro-structure composite reinforced membrane is realized, the mechanical stability of the anion exchange membrane for water electrolysis in a high-temperature and alkali application environment is effectively improved, and the service life of the anion exchange membrane in an alkaline electrolytic bath is prolonged.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer membrane materials technology, specifically relating to a method for preparing a composite membrane to improve the mechanical stability of anion exchange membranes. Background Technology

[0002] Anion exchange membranes (AEM) are key materials for OH- ion conduction and gas cross-contamination prevention in alkaline water electrolysis for hydrogen production. They combine the advantages of ALK and PEM membranes, enabling the use of non-precious metal catalysts in alkaline environments, reducing the high demands on components such as electrodes. They also feature rapid response and high current density, significantly improving electrolysis efficiency and minimizing the need for mechanical compression of stored hydrogen, effectively reducing operating costs. However, anion exchange membranes currently face severe challenges in mechanical and chemical stability during water electrolysis for hydrogen production.

[0003] In existing technologies, hydrocarbon-based main-chain structures are highly susceptible to main-chain degradation in strongly alkaline and high-temperature environments. Partially fluorinated anion exchange membranes also suffer from insufficient incubation, unsatisfactory long-term stability, weak interfacial bonding between the reinforcing framework and ion-conducting phases, and a tendency to delaminate. Therefore, most existing technologies still focus on preparing homogeneous membranes, which presents a significant challenge in balancing high conductivity and high mechanical stability during the membrane formation process.

[0004] Perfluorinated resins have excellent chemical corrosion resistance, and perfluorosulfonic acid resins have proven their ultra-long lifespan in proton exchange membranes. However, the application of perfluorinated resins in anion exchange membranes still faces challenges such as functionalization difficulties, low ionic conductivity, and low mechanical properties of flexible resins.

[0005] The network structure of the hydrophobic polytetrafluoroethylene porous membrane effectively limits the water absorption and swelling of the anion exchange resin, thereby limiting and reducing the swelling or shrinkage behavior of the anion exchange membrane under temperature and humidity cycling. Summary of the Invention

[0006] This invention discloses a method for preparing anion exchange composite membrane, which can overcome the above-mentioned shortcomings of the prior art.

[0007] The present invention adopts the following technical solution:

[0008] Quaternization modification of perfluorosulfonic acid resins

[0009] Perfluorosulfonic acid resins with an equivalent weight (EW) of 800-1500 are selected and converted to potassium salt form. Under nitrogen protection, they are reacted with a 20%-40% trimethylamine ethanol solution at 60-90℃ for 24-72 hours. Through nucleophilic substitution, the sulfonic acid groups are converted to quaternary ammonium sulfonamide groups, with the conversion rate controlled at 70-90%. Subsequent alkylation treatment yields a quaternary ammonium perfluoroanionic polymer, such as... Figure 7 As shown.

[0010] Interface immersion control for enhanced skeleton

[0011] Due to the incompatibility of the interface between hydrophobic polytetrafluoroethylene and hydrophilic perfluorinated anion exchange resin, the coating solution is difficult to completely penetrate the microporous structure of the porous polytetrafluoroethylene film during the film formation process, resulting in a large number of fine pores in the composite film structure, which reduces the ion conductivity.

[0012] S1) The shrinkage stress of the polytetrafluoroethylene microporous membrane is controlled by impregnation with solvents of different proportions, wherein the solvent is one or more of water, methanol, ethanol, n-propanol, isopropanol, toluene, formamide, DMF, and DMSO.

[0013] S2) A surfactant is added to the anion exchange resin to enhance the wettability of the solution; the surfactant is one or more of N-methylpyrrolidone, sodium perfluorononenylbenzenesulfonate, and perfluoropolyether carboxylic acid amine. High-temperature treatment improves the bonding force between the anion exchange resin and expanded polytetrafluoroethylene, increases the filling degree of the coating liquid in the expanded polytetrafluoroethylene to more than 90%, forms physical entanglement with polytetrafluoroethylene, and improves the compatibility of its interface.

[0014] Preparation of composite films with high mechanical stability

[0015] S1) Coating liquids with different solid contents

[0016] The successfully modified resin is dissolved in an organic solvent to obtain an organic resin solution, wherein the organic resin solution contains at least one of 20%, 30%, 40%, and 50% respectively. After dispersion, shearing, filtration, and defoaming, the solution is obtained as a coating liquid to be used.

[0017] S2) Support layers with different weights

[0018] Porous hydrophobic polytetrafluoroethylene films activated with different basis weights were used as support layers. The basis weights of the support layers were 2 g / m³. 2 4 g / m 2 6 g / m 2 9 g / m 2 12 g / m 2 At least one of them, with a porosity of 80-90%.

[0019] S3) Different number of coating liquid layers and support layers

[0020] Conductive layers are prepared using coating solutions of varying thicknesses, and microporous polytetrafluoroethylene (PTFE) films with different numbers of layers are used as the supporting framework. The coating solution is applied in at least one of one, two, or three layers, resulting in a conductive layer thickness of 10–30 μm. The supporting framework consists of one or more layers with a basis weight of 2–12 g / m².

[0021] Advantages of this invention:

[0022] In existing AEM membrane formation technologies, the coating solution is typically poured directly onto substrates such as glass plates, PET, and PI. However, these membranes lack a supporting framework and are prone to swelling and deformation in alkaline water electrolysis environments, resulting in irreversible mechanical damage. This invention addresses this issue by introducing a supporting framework (polytetrafluoroethylene microporous membrane) during the membrane formation process, constructing a microphase separation layer. This effectively solves the problem of mechanical damage caused by excessive swelling of anion exchange membranes in alkaline environments, leading to membrane deformation and performance degradation. Attached Figure Description

[0023] Figure 1 This is an electron microscope image of the AEM composite film in Example 1.

[0024] Figure 2 This is an electron microscope image of the AEM composite film in Example 2.

[0025] Figure 3 This is an electron microscope image of the AEM composite film in Example 1.

[0026] Figure 4 This is an electron microscope image of the AEM composite film in Example 1.

[0027] Figure 5 This is a photo of the AEM membrane in Comparative Example 1.

[0028] Figure 6 This is a photo of the AEM membrane in Comparative Example 2.

[0029] Figure 7 This is a reaction diagram of the quaternization modification of the perfluorosulfonic acid resin of the present invention. Detailed Implementation

[0030] A method for preparing anion exchange composite membrane includes the following steps:

[0031] S1) Select a perfluorosulfonic acid resin with an equivalent weight (EW) of 800-1500 and convert it to its potassium salt form. Under nitrogen protection, react with a 20% concentration of trimethylamine ethanol solution at 60-90℃ for 24 hours. Convert the sulfonic acid groups to quaternary ammonium sulfonamide groups via nucleophilic substitution, controlling the conversion rate at 70-90%. Subsequent alkylation treatment yields a quaternary ammonium perfluoroanionic polymer.

[0032] S2) The shrinkage stress of the polytetrafluoroethylene microporous membrane is controlled by impregnation with solvents of different proportions, wherein the solvent is one or more of water, methanol, ethanol, n-propanol, isopropanol, toluene, formamide, DMF, and DMSO.

[0033] S3) A surfactant is added to the anion exchange resin to enhance the wettability of the solution. The surfactant is one or more of N-methylpyrrolidone, sodium perfluorononenylbenzenesulfonate, and perfluoropolyether carboxylic acid amine. High-temperature treatment improves the bonding force between the anion exchange resin and expanded polytetrafluoroethylene (ePTFE). This increases the filling density of the coating solution in the ePTFE to over 90%, forming a physical entanglement with the ePTFE and improving its interfacial compatibility.

[0034] In the preparation method of the anion exchange composite membrane, the solid content of the coating liquid is 20%~50%.

[0035] In the preparation method of the anion exchange composite membrane, the basis weight of the supporting framework is 2~12g.

[0036] In the preparation method of the anion exchange composite membrane, the material of the supporting skeleton is expanded porous polytetrafluoroethylene film.

[0037] In the preparation method of the anion exchange composite membrane, the number of coating liquid layers is 1 to 3.

[0038] In the preparation method of the anion exchange composite membrane, the number of coating liquid layers is 1 to 3.

[0039] In the preparation method of the anion exchange composite membrane, the number of supporting framework layers is 1 to 3.

[0040] In the preparation method of the anion exchange composite membrane, the thickness of the composite membrane is 10~100μm.

[0041] Example 1

[0042] S1) Preparation of coating solution: Dissolve the modified solid organic polymer in a mixed solvent of water, ethanol, and DMF according to the mass ratio, wherein the solid polymer material accounts for 15% and the solvent accounts for 85%. Stir and mix, shear, crush, filter, defoam, and place in a beaker for later use.

[0043] S2) Support frame selection: Select a frame with a weight of 4g / m². 2 Expanded polytetrafluoroethylene film after impregnation and regulation.

[0044] S3) Composite membrane preparation: Coat with a layer of coating liquid, cover with a layer of expanded polytetrafluoroethylene film, wait 5-10 minutes until the coating liquid fully wets and fills the support skeleton, and then dry in an oven at 80~150℃.

[0045] Example 2

[0046] S1) Preparation of coating solution: Dissolve the modified solid organic polymer in a mixed solvent of water, isopropanol, and DMF according to the mass ratio, wherein the solid polymer material accounts for 20% and the solvent accounts for 80%. Stir and mix, shear, crush, filter, defoam, and place in a beaker for later use.

[0047] S2) Support frame selection: A frame with a weight of 9g / m² is selected. 2 Expanded polytetrafluoroethylene film after impregnation and regulation.

[0048] S3) Composite membrane preparation: Coat with a layer of coating liquid, cover with a layer of expanded polytetrafluoroethylene film, wait 5-10 minutes until the coating liquid fully wets and fills the support skeleton, and then dry in an oven at 80~150℃.

[0049] Example 3

[0050] S1) Preparation of coating solution: Dissolve the modified solid organic polymer in a mixed solvent of water, isopropanol, and DMF according to the mass ratio, wherein the solid polymer material accounts for 30% and the solvent accounts for 70%. Stir and mix, shear, crush, filter, defoam, and place in a beaker for later use.

[0051] S2) Support frame selection: Select a frame with a weight of 6g / m². 2 Expanded polytetrafluoroethylene film after impregnation and regulation.

[0052] S3) Composite membrane preparation: Coat with two layers of coating liquid, cover with two layers of expanded polytetrafluoroethylene film, wait 5-10 minutes until the coating liquid fully wets and fills the support skeleton, and then dry in an oven at 80~150℃.

[0053] Example 4

[0054] S1) Preparation of coating solution: Dissolve the modified solid organic polymer in a mixed solvent of water, isopropanol, and DMF according to the mass ratio, wherein the solid polymer material accounts for 30% and the solvent accounts for 70%. Stir and mix, shear, crush, filter, defoam, and place in a beaker for later use.

[0055] S2) Support frame selection: Select a frame with a weight of 6g / m². 2 Expanded polytetrafluoroethylene film after impregnation and regulation.

[0056] S3) Composite membrane preparation: Coat with three layers of coating liquid, cover with two layers of expanded polytetrafluoroethylene film, wait 5-10 minutes until the coating liquid fully wets and fills the support skeleton, and then dry in an oven at 80~150℃.

[0057] Comparative Example 1

[0058] S1) Preparation of coating solution: Dissolve the modified solid organic polymer in a mixed solvent of water, isopropanol, and DMF according to the mass ratio, wherein the solid polymer material accounts for 30% and the solvent accounts for 70%. Stir and mix, shear, crush, filter, defoam, and place in a beaker for later use.

[0059] S2) Film preparation: Coat a layer of coating solution, let stand for 5-10 minutes, and dry in an oven at 80~150℃.

[0060] Comparative Example 2

[0061] S1) Preparation of coating solution: Dissolve the modified solid organic polymer in a mixed solvent of water, isopropanol, and DMF according to the mass ratio, wherein the solid polymer material accounts for 30% and the solvent accounts for 70%. Stir and mix, shear, crush, filter, defoam, and place in a beaker for later use.

[0062] S2) Film preparation: Coat two layers of coating liquid, let stand for 5-10 minutes, and dry in an oven at 80~150℃.

[0063] Swelling and tensile strength tests in different alkaline solutions for AEM film formation

[0064] S1) Tensile strength (MPa): Tested according to (GB / T 20042.3-2009) at room temperature;

[0065] S2) Swelling rate %: Tested according to (GB / T 20042.3-2009), the test solution is 1M KOH, and the test temperature is room temperature.

[0066] S3) OH- conductivity mS / cm: Tested according to (GB / T 20042.3-2009) at a temperature of 80℃.

[0067] The test results are shown in Table 1.

[0068] Table 1

[0069] According to Table 1 and Figures 1-6 It can be known that:

[0070] S1) In alkaline electrolysis applications, introducing a supporting framework into the anion exchange membrane does not significantly affect the membrane's conductivity. Using the modified coating solution and the activated supporting framework layer to prepare a multilayer composite membrane results in a membrane with good interfacial composite, sufficient wetting and filling, and no pores.

[0071] S2) Compared with the comparative example, the swelling of the membrane prepared by the present invention is significantly improved in alkaline application environment.

[0072] S3) Compared with the comparative example, the mechanical properties of the membrane prepared by the present invention are significantly improved in alkaline application environments.

[0073] In summary, the test results in the table and figures show that the anion exchange membrane prepared by this invention for use in alkaline water electrolysis environments has advantages such as high conductivity, high strength, low swelling, and high production efficiency.

[0074] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing an anion exchange composite membrane, comprising the following steps: S1) Quaternization modification of perfluorosulfonic acid resin: Select perfluorosulfonic acid resin with an equivalent value (EW) of 800-1500 and convert it into potassium salt form. S2) Impregnation control of the interface for reinforcing the framework: The surface tension of the polytetrafluoroethylene microporous membrane was controlled by impregnation with solvents of different proportions, and surfactants were added to the anion exchange resin to enhance the wettability of the solution. S3) Preparation of high mechanical stability composite membranes: Coating liquids with different solid contents are matched, support layers with different basis weights are screened, and high mechanical stability composite membranes are prepared by using different numbers of coating liquid layers and support layers.

2. The method for preparing anion exchange composite membrane according to claim 1, characterized in that, The stress-regulating solvent is one or more of the following: water, methanol, ethanol, n-propanol, isopropanol, toluene, formamide, DMF, and DMSO.

3. The method for preparing anion exchange composite membrane according to claim 1, characterized in that, The modified surfactant is one or more of N-methylpyrrolidone, sodium perfluorononenylbenzenesulfonate, and perfluoropolyether carboxylic acid amine. High-temperature treatment improves the bonding force between the anion exchange resin and expanded polytetrafluoroethylene, increases the filling degree of the coating liquid in expanded polytetrafluoroethylene to more than 90%, forms physical entanglement with polytetrafluoroethylene, and improves the compatibility of its interface.

4. The method for preparing anion exchange composite membrane according to claim 1, characterized in that, The organic resin solution contains at least one of the following: 20%, 30%, 40%, and 50%. After dispersion, shearing, filtration, and defoaming, it becomes a coating solution ready for use.

5. The method for preparing an anion exchange composite membrane according to claim 1, characterized in that, The weight of the supporting skeleton layer is 2 g / m³. 2 4 g / m 2 6 g / m 2 9 g / m 2 12 g / m 2 At least one of them, with a porosity of 80-90%.

6. The method for preparing an anion exchange composite membrane according to claim 1, characterized in that, The coating liquid is applied in at least one of one, two, or three layers.

7. The method for preparing anion exchange composite membrane according to claim 1, characterized in that, The thickness of the conductive layer is 10~30μm.

8. The method for preparing an anion exchange composite membrane according to claim 1, characterized in that, The supporting frame has a weight of 2~12 g / m². 2 One or more layers in a structure.

9. The method for preparing an anion exchange composite membrane according to claim 1, characterized in that, The thickness of the composite membrane is 10~100μm.

10. The method for preparing an anion exchange composite membrane according to claim 1, characterized in that, Under nitrogen protection, the reaction is carried out with trimethylamine ethanol solution at 60-90℃ for 24-72 hours to convert sulfonic acid groups into quaternary ammonium sulfonamide groups through nucleophilic substitution reaction, with the conversion rate controlled at 70-90%. Then, alkylation treatment is performed to generate quaternary ammonium perfluoro anionic polymer.

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