Preparation method of cation exchange membrane with high alkali resistance

Abstract

The invention relates to the technical field of exchange membranes, in particular to a preparation method of a high-alkali-resistance cation exchange membrane, which comprises the following steps: (1) pretreating a base material; (2) in-situ cross-linking polymerization; (3) forming a film and curing; (4) alkali liquor activation treatment; according to the technical scheme, in the gradient heating thermal crosslinking process, the crosslinking reaction is slowly and uniformly carried out in a gradual heating manner, so that stress concentration and microcracks in the film caused by direct high temperature are avoided, and the regularity and compactness of a crosslinking network are ensured; the NaOH solution and the alkali liquor at 70 DEG C are used for activating treatment, so that ion exchange sites in the membrane can be activated, the membrane can adapt to a strong alkali environment in advance, and swelling deformation in actual use is reduced. The whole process chain forms an organic whole from pretreatment of the base material to in-situ cross-linking polymerization and then to film-forming curing and alkali liquor activation, and the problems that an existing cation exchange membrane is short in service life and poor in comprehensive performance in a strong alkaline environment are successfully solved.

Description

Technical Field

[0001] This invention relates to the field of exchange membrane technology, specifically to a method for preparing a highly alkali-resistant cation exchange membrane. Background Technology

[0002] In industrial production processes such as chlor-alkali manufacturing and alkaline electrolysis for hydrogen production, cation exchange membranes are core materials for achieving selective ion transport, ensuring product purity, and maintaining process efficiency. As these industries transition towards higher efficiency and cleaner processes, higher demands are placed on the long-term stable operation of cation exchange membranes in strongly alkaline and high-temperature environments. They not only need to maintain excellent ion conductivity but also possess good mechanical strength, dimensional stability, and resistance to alkali degradation.

[0003] Currently, cation exchange membranes on the market are mainly divided into two categories: perfluorinated and non-fluorinated. While perfluorinated membranes exhibit strong corrosion resistance, they suffer from high costs and reliance on imports. Furthermore, under prolonged immersion in strong alkalis, they still show a decrease in ion exchange capacity and an increase in swelling rate. Non-fluorinated membranes, such as polyethersulfone and polyarylether membranes, are lower in cost and easier to produce domestically, but their alkali resistance is insufficient. In concentrated alkali environments above 12 mol / L, the polymer backbone is prone to hydrolysis, and the cross-linked network is easily broken, leading to membrane structure damage and shortened service life. To improve alkali resistance, the industry has attempted modification by adding cross-linking agents and inorganic nanoparticles. However, many problems remain in practical applications: using conventional cross-linking agents alone is difficult to form a uniform and dense cross-linked network, easily resulting in defects within the membrane; nanoparticles have poor compatibility with the polymer matrix, easily agglomerating and causing blockage of ion transport channels; some modification schemes, while improving alkali resistance, sacrifice ion conduction efficiency or mechanical strength, making it difficult to achieve a balance of multiple performance characteristics.

[0004] Therefore, developing a method for preparing cation exchange membranes that can balance high alkali resistance, high ion conductivity, and excellent mechanical properties, while also having a controllable process, has become a pressing technical problem for the industry. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and propose a method for preparing a highly alkali-resistant cation exchange membrane.

[0006] The specific technical solution is as follows: A method for preparing a highly alkali-resistant cation exchange membrane, comprising the following steps:

[0007] (1) Substrate pretreatment: Take fluorinated polyethersulfone powder, add it to N-methylpyrrolidone solvent, stir and dissolve at 50-70℃; add 1-3wt% γ-aminopropyltriethoxysilane of fluorinated polyethersulfone to the solution, and ultrasonically disperse at 150-200W power and 50-60℃ for 30-40min to obtain a pretreated substrate solution with 15-25% fluorinated polyethersulfone mass fraction;

[0008] (2) In-situ crosslinking polymerization: Imidazole hybrid crosslinking system and hydroxylated graphene quantum dots are added to the pretreated substrate solution;

[0009] The amount of imidazole-based hybrid crosslinking system added is 3.0-3.5 wt% of the mass of fluorinated polyether sulfone; the hydroxylated graphene quantum dots have a particle size of 5-10 nm and a hydroxyl content of 10-15 wt%, and the amount added is 0.6-1.5 wt% of the mass of fluorinated polyether sulfone; under nitrogen protection at a flow rate of 0.8-1 L / min, the reaction is carried out at 80-100 °C for 2-4 h, and the mixture is stirred once every 30 min at a rate of 300-500 r / min to form a hybrid crosslinking precursor solution;

[0010] (3) Film formation and curing: The precursor solution is cast into a wet film with a thickness of 250-300 μm on a clean glass plate and vacuum dried for 12-16 h; then thermal crosslinking is carried out by gradient heating, and the film is removed after cooling.

[0011] (4) Alkali activation treatment: The membrane after stripping is immersed in NaOH solution for activation treatment, taken out and washed with deionized water until neutral, and dried to obtain a highly alkali-resistant cation exchange membrane.

[0012] As a further technical solution, in step (1), the number average molecular weight of the fluorinated polyethersulfone powder is 60,000-80,000 g / mol and the fluorine content is 30-35 wt%.

[0013] As a further technical solution, the imidazole-based hybrid crosslinking system in step (2) is made of imidazole monomer, amino-functionalized silica nanoparticles, and azobisisobutyronitrile in a mass ratio of 10:(2-5):(0.5-1).

[0014] As a further technical solution, the preparation steps of the amino-functionalized silica nanoparticles in step (2) are as follows: disperse silica nanoparticles in anhydrous ethanol, add 5% of 3-aminopropyltriethoxysilane by mass of silica nanoparticles, reflux at 50-60℃ for 4-6h, and then filter, wash and dry to obtain amino-functionalized silica nanoparticles.

[0015] As a further technical solution, the specific preparation steps of the imidazole hybrid crosslinking system in step (2) are as follows:

[0016] (1) Mix imidazole monomer with 37% formaldehyde aqueous solution at a mass ratio of 1:(0.8-1.2), adjust the pH to 8-9, and react at 40-50℃ for 1-2 hours;

[0017] (2) Add amino-functionalized silica nanoparticles, continue the reaction for 3-4 hours, remove water by vacuum distillation, and obtain amino-functionalized imidazole crosslinking agent;

[0018] (3) Dissolve the crosslinking agent in N-methylpyrrolidone to prepare a crosslinking agent solution with a mass fraction of 10-15%, and mix it evenly with hydroxylated graphene quantum dots to obtain the desired solution.

[0019] As a further technical solution, the hydroxylated graphene quantum dots in step (2) are prepared by the Hummers method and then modified by hydroxylation; the hydroxylation modification is carried out by a mixture of concentrated nitric acid and concentrated sulfuric acid with a volume ratio of 1:3, and treated at 80°C for 4 hours.

[0020] As a further technical solution, the vacuum drying conditions in step (3) are -0.08~-0.1MPa pressure and 60-80℃.

[0021] As a further technical solution, the gradient temperature thermal crosslinking in step (3) is: 120℃ for 1h, 130℃ for 1h, and 140℃ for 0.5-1h.

[0022] As a further technical solution, the conditions for alkaline activation treatment in step (4) are: 12 mol / L NaOH solution, soaking at 70℃ for 5 hours.

[0023] As a further technical solution, the drying temperature in step (4) is 60°C and the time is 3-4 hours.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] This invention addresses the interfacial bonding defects at their source through substrate pretreatment and optimization of functional components. The addition of γ-aminopropyltriethoxysilane during substrate pretreatment allows its amino groups to stabilize the fluorinated polyethersulfone, while the silanol groups generated from ethoxyl hydrolysis establish chemical bonds with active sites in the subsequent crosslinking system. This significantly improves the interfacial compatibility between the substrate and the crosslinking network, reducing the formation of micropores and interfacial gaps within the membrane. Furthermore, the fluorinated polyethersulfone substrate, with a number-average molecular weight of 60,000-80,000 g / mol and a fluorine content of 30-35 wt%, possesses excellent chemical stability. Combined with the silane coupling agent, this further enhances the substrate's resistance to strongly alkaline environments, thus resolving the core issues of interlayer delamination and rapid performance degradation in traditional membranes caused by weak interfacial bonding.

[0026] The synergistic effect of the imidazole-based hybrid crosslinking system and hydroxylated graphene quantum dots achieves a simultaneous improvement in alkali resistance and ion conduction efficiency. In the imidazole-based hybrid crosslinking system, the imidazole monomer provides abundant ion exchange sites, while the amino-functionalized silica nanoparticles form physical support points by dispersing in the crosslinking network. Together with azobisisobutyronitrile (AIBN), they promote the uniform crosslinking reaction, constructing a dense and tough crosslinking structure that effectively prevents alkali solutions from corroding the membrane interior. Meanwhile, the hydroxylated graphene quantum dots, with their 5-10 nm particle size and 10-15 wt% hydroxyl content, can not only uniformly disperse in the system to fill the tiny defects in the crosslinking network, but their high specific surface area and abundant hydroxyl groups can also adsorb and conduct ions, forming continuous ion transport channels.

[0027] The gradient heating thermal crosslinking process in this invention allows the crosslinking reaction to proceed slowly and uniformly by gradually increasing the temperature, avoiding stress concentration and microcracks inside the membrane caused by direct high temperatures, thus ensuring the regularity and density of the crosslinked network. The alkaline activation treatment with 12 mol / L NaOH solution at 70°C not only activates the ion exchange sites in the membrane but also allows the membrane to adapt to the strongly alkaline environment in advance, reducing swelling and deformation during actual use. From substrate pretreatment to in-situ crosslinking polymerization, and then to film formation, curing, and alkaline activation, the entire process chain forms an organic whole, successfully solving the problems of short service life and poor overall performance of existing cation exchange membranes in strongly alkaline environments, and meeting the industrial demand for high-performance, long-cycle membrane materials. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating a method for preparing a highly alkali-resistant cation exchange membrane. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] (1) Substrate pretreatment:

[0031] The fluorinated polyethersulfone powder used in this invention is preferably a product with a number average molecular weight of 60,000-80,000 g / mol and a fluorine content of 30-35 wt%, and commercially available conventional products are acceptable. The fluorinated polyethersulfone powder is added to an N-methylpyrrolidone solvent and stirred at 50-70°C to ensure complete dispersion of the powder without particles. γ-aminopropyltriethoxysilane is added to this solution at 1-3 wt% of the fluorinated polyethersulfone mass, followed by ultrasonic dispersion at 150-200 W power and 50-60°C for 30-40 min, finally obtaining a pretreated substrate solution with a fluorinated polyethersulfone mass fraction of 15-25%.

[0032] (2) In-situ crosslinking polymerization:

[0033] Amine-functionalized silica nanoparticles: Silica nanoparticles were dispersed in anhydrous ethanol, and 5% (by weight) of 3-aminopropyltriethoxysilane was added. The mixture was refluxed at 50-60°C for 4-6 hours. After filtration, washing three times with anhydrous ethanol, and vacuum drying at 60°C for 4 hours, amino-functionalized silica nanoparticles were obtained.

[0034] Imidazole-based hybrid crosslinking system: First, imidazole monomer and 37% formaldehyde aqueous solution are mixed at a mass ratio of 1:(0.8-1.2), and the pH is adjusted to 8-9 with 10% sodium carbonate solution. The reaction is carried out at 40-50℃ for 1-2 hours. Second, amino-functionalized silica nanoparticles are added, and the reaction continues at the same temperature for 3-4 hours. Water is then removed by distillation under reduced pressure of 0.08 MPa to obtain the amino-functionalized imidazole-based crosslinking agent. Third, this crosslinking agent is dissolved in N-methylpyrrolidone to prepare a 10-15% crosslinking agent solution, which is then mixed uniformly with hydroxylated graphene quantum dots to obtain the imidazole-based hybrid crosslinking system. The mass ratio of imidazole monomer, amino-functionalized silica nanoparticles, and azobisisobutyronitrile is 10:(2-5):(0.5-1).

[0035] Hydroxylated graphene quantum dots: After preparing graphene quantum dots by the Hummers method, they are hydroxylated by treating them with a mixture of concentrated nitric acid and concentrated sulfuric acid at a volume ratio of 1:3 at 80°C for 4 hours. The resulting quantum dots have a particle size of 5-10 nm and a hydroxyl content of 10-15 wt%. Commercially available products that meet these parameters can also be used directly.

[0036] The above-mentioned imidazole-based hybrid crosslinking system and hydroxylated graphene quantum dots were added to the pretreated substrate solution, wherein the amount of imidazole-based hybrid crosslinking system added was 3.0-3.5 wt% of the mass of fluorinated polyethersulfone, and the amount of hydroxylated graphene quantum dots added was 0.6-1.5 wt% of the mass of fluorinated polyethersulfone. Under nitrogen protection at a flow rate of 0.8-1 L / min, the system was heated to 80-100℃ and reacted for 2-4 h. During the reaction, the mixture was stirred at a rate of 300-500 r / min for 10 min every 30 min to finally form a hybrid crosslinking precursor solution.

[0037] (3) Film formation and curing:

[0038] The hybrid crosslinking precursor solution was poured onto a clean glass plate and a wet film of 250-300 μm thickness was prepared by casting. The film was then placed in a vacuum drying oven and dried at -0.08 to -0.1 MPa pressure and 60-80℃ for 12-16 hours. The dried film underwent a gradient temperature thermal crosslinking treatment: 120℃ for 1 hour, 130℃ for 1 hour, and 140℃ for 0.5-1 hour. After naturally cooling to room temperature, the film was soaked in deionized water for 1 hour to remove it.

[0039] (4) Alkali activation treatment:

[0040] The membrane after stripping was immersed in a 12 mol / L NaOH solution and activated at 70°C for 5 hours. After removal, it was repeatedly washed with deionized water until the pH of the washing solution reached 7. Finally, it was dried at 60°C for 3-4 hours to obtain a highly alkali-resistant cation exchange membrane.

[0041] This invention introduces a silane coupling agent through substrate pretreatment to enhance interfacial bonding, constructs a stable cross-linking network using an imidazole hybrid cross-linking system, and combines it with hydroxylated graphene quantum dots to enhance mechanical properties and ion conduction efficiency. After gradient cross-linking and alkaline activation, the membrane material can still maintain excellent comprehensive performance in a strongly alkaline environment, solving the problems of poor alkali resistance and short service life of traditional cation exchange membranes.

[0042] The following are specific examples:

[0043] Example 1:

[0044] Substrate pretreatment: Fluorinated polyethersulfone powder with a number average molecular weight of 70,000 g / mol and a fluorine content of 32 wt% was added to N-methylpyrrolidone solvent and stirred at 60 °C to dissolve. γ-aminopropyltriethoxysilane (2 wt% by mass) was added to the solution and ultrasonically dispersed at 180 W power and 55 °C for 35 min to obtain a pretreated substrate solution with a fluorinated polyethersulfone content of 20%.

[0045] Preparation of amino-functionalized silica nanoparticles: Silica nanoparticles were dispersed in anhydrous ethanol, and 3-aminopropyltriethoxysilane (5% by weight of silica nanoparticles) was added. The mixture was refluxed at 55°C for 5 h, filtered, washed three times with anhydrous ethanol, and dried under vacuum at 60°C for 4 h to obtain amino-functionalized silica nanoparticles.

[0046] Preparation of the imidazole-based hybrid crosslinking system: Imidazole monomer, amino-functionalized silica nanoparticles, and azobisisobutyronitrile were mixed at a mass ratio of 10:3:0.7. First, the imidazole monomer was mixed with a 37% formaldehyde aqueous solution at a mass ratio of 1:1, and the pH was adjusted to 8.5 with a 10% sodium carbonate solution. The mixture was reacted at 45°C for 1.5 h. Second, amino-functionalized silica nanoparticles were added, and the reaction continued at 45°C for 3.5 h. Water was removed by vacuum distillation at 0.08 MPa to obtain the amino-functionalized imidazole-based crosslinking agent. Third, the crosslinking agent was dissolved in N-methylpyrrolidone to prepare a 12% crosslinking agent solution, which was then mixed uniformly with hydroxylated graphene quantum dots to obtain the imidazole-based hybrid crosslinking system.

[0047] In-situ crosslinking polymerization: An imidazole-based hybrid crosslinking system and hydroxylated graphene quantum dots were added to the pretreated substrate solution. The amount of the imidazole-based hybrid crosslinking system added was 3.2 wt% of the mass of fluorinated polyethersulfone, and the amount of the hydroxylated graphene quantum dots was 1.0 wt% of the mass of fluorinated polyethersulfone with a particle size of 8 nm and a hydroxyl content of 12 wt%. The reaction was carried out at 90 °C for 3 h under nitrogen protection at a flow rate of 0.9 L / min, with stirring at a rate of 400 r / min for 10 min every 30 min during the reaction to form a hybrid crosslinking precursor solution.

[0048] Film formation and curing: The precursor solution was cast into a 280 μm thick wet film on a clean glass plate and placed in a vacuum drying oven to dry at -0.09 MPa pressure and 70 °C for 14 h. Subsequently, gradient temperature thermal crosslinking was performed, holding at 120 °C for 1 h, 130 °C for 1 h, and 140 °C for 0.8 h. After naturally cooling to room temperature, the film was removed by soaking in deionized water for 1 h.

[0049] Alkali activation treatment: The membrane after stripping is immersed in 12 mol / L NaOH solution and soaked at 70℃ for 5 h. After removal, it is washed with deionized water until neutral and dried at 60℃ for 3.5 h to obtain a highly alkali-resistant cation exchange membrane.

[0050] Example 2:

[0051] Substrate pretreatment: Fluorinated polyethersulfone powder with a number average molecular weight of 60,000 g / mol and a fluorine content of 30 wt% was added to N-methylpyrrolidone solvent and stirred at 50 °C to dissolve. γ-aminopropyltriethoxysilane (1 wt% by mass) was added to the solution and ultrasonically dispersed at 150 W power and 50 °C for 30 min to obtain a pretreated substrate solution with a fluorinated polyethersulfone content of 15%.

[0052] Preparation of amino-functionalized silica nanoparticles: Silica nanoparticles were dispersed in anhydrous ethanol, and 3-aminopropyltriethoxysilane (5% by weight of silica nanoparticles) was added. The mixture was refluxed at 50°C for 4 hours, filtered, washed three times with anhydrous ethanol, and dried under vacuum at 60°C for 4 hours to obtain amino-functionalized silica nanoparticles.

[0053] Preparation of the imidazole-based hybrid crosslinking system: Imidazole monomer, amino-functionalized silica nanoparticles, and azobisisobutyronitrile were mixed at a mass ratio of 10:2:0.5. First, the imidazole monomer was mixed with a 37% formaldehyde aqueous solution at a mass ratio of 1:0.8, and the pH was adjusted to 8 with a 10% sodium carbonate solution. The mixture was reacted at 40℃ for 1 hour. Second, amino-functionalized silica nanoparticles were added, and the reaction continued at 40℃ for 3 hours. Water was removed by vacuum distillation at 0.08 MPa to obtain the amino-functionalized imidazole-based crosslinking agent. Third, the crosslinking agent was dissolved in N-methylpyrrolidone to prepare a 10% crosslinking agent solution, which was then mixed uniformly with hydroxylated graphene quantum dots to obtain the imidazole-based hybrid crosslinking system.

[0054] In-situ crosslinking polymerization: An imidazole-based hybrid crosslinking system and hydroxylated graphene quantum dots were added to the pretreated substrate solution. The amount of the imidazole-based hybrid crosslinking system added was 3.0 wt% of the mass of fluorinated polyethersulfone, and the amount of the hydroxylated graphene quantum dots was 0.6 wt% of the mass of fluorinated polyethersulfone with a particle size of 5 nm and a hydroxyl content of 10 wt%. The reaction was carried out at 80 °C for 2 h under nitrogen protection at a flow rate of 0.8 L / min, with stirring at a rate of 300 r / min for 10 min every 30 min during the reaction to form a hybrid crosslinking precursor solution.

[0055] Film formation and curing: The precursor solution was cast into a 250 μm thick wet film on a clean glass plate and placed in a vacuum drying oven to dry at -0.08 MPa pressure and 60℃ for 12 h. Subsequently, gradient temperature thermal crosslinking was performed: holding at 120℃ for 1 h, 130℃ for 1 h, and 140℃ for 0.5 h. After naturally cooling to room temperature, the film was removed by soaking in deionized water for 1 h.

[0056] Alkali activation treatment: The membrane after stripping is immersed in 12 mol / L NaOH solution and soaked at 70℃ for 5 hours. After removal, it is washed with deionized water until neutral and dried at 60℃ for 3 hours to obtain a highly alkali-resistant cation exchange membrane.

[0057] Example 3:

[0058] Substrate pretreatment: Fluorinated polyethersulfone powder with a number average molecular weight of 80,000 g / mol and a fluorine content of 35 wt% was added to N-methylpyrrolidone solvent and stirred at 70 °C to dissolve. γ-aminopropyltriethoxysilane (3 wt% by mass) was added to the solution and ultrasonically dispersed at 200 W power and 60 °C for 40 min to obtain a pretreated substrate solution with a fluorinated polyethersulfone content of 25%.

[0059] Preparation of amino-functionalized silica nanoparticles: Silica nanoparticles were dispersed in anhydrous ethanol, and 5% (by weight) of 3-aminopropyltriethoxysilane was added. The mixture was refluxed at 60°C for 6 hours. After filtration, washing with anhydrous ethanol three times, and vacuum drying at 60°C for 4 hours, amino-functionalized silica nanoparticles were obtained.

[0060] Preparation of the imidazole-based hybrid crosslinking system: Imidazole monomer, amino-functionalized silica nanoparticles, and azobisisobutyronitrile were mixed at a mass ratio of 10:5:1. First, the imidazole monomer was mixed with a 37% formaldehyde aqueous solution at a mass ratio of 1:1.2, and the pH was adjusted to 9 with a 10% sodium carbonate solution. The mixture was reacted at 50°C for 2 hours. Second, amino-functionalized silica nanoparticles were added, and the reaction continued at 50°C for 4 hours. Water was removed by vacuum distillation at 0.08 MPa to obtain the amino-functionalized imidazole-based crosslinking agent. Third, the crosslinking agent was dissolved in N-methylpyrrolidone to prepare a 15% crosslinking agent solution, which was then mixed uniformly with hydroxylated graphene quantum dots to obtain the imidazole-based hybrid crosslinking system.

[0061] In-situ crosslinking polymerization: An imidazole-based hybrid crosslinking system and hydroxylated graphene quantum dots were added to the pretreated substrate solution. The amount of the imidazole-based hybrid crosslinking system added was 3.5 wt% of the mass of fluorinated polyethersulfone. The hydroxylated graphene quantum dots had a particle size of 10 nm, a hydroxyl content of 15 wt%, and were added at a rate of 1.5 wt% of the mass of fluorinated polyethersulfone. The reaction was carried out at 100 °C for 4 h under nitrogen protection at a flow rate of 1 L / min, with stirring at a rate of 500 r / min for 10 min every 30 min during the reaction to form a hybrid crosslinking precursor solution.

[0062] Film formation and curing: The precursor solution was cast into a 300 μm thick wet film on a clean glass plate and placed in a vacuum drying oven to dry at -0.1 MPa pressure and 80℃ for 16 h. Subsequently, gradient temperature thermal crosslinking was performed, holding at 120℃ for 1 h, 130℃ for 1 h, and 140℃ for 1 h. After naturally cooling to room temperature, the film was removed by soaking in deionized water for 1 h.

[0063] Alkali activation treatment: The membrane after stripping is immersed in 12 mol / L NaOH solution and soaked at 70℃ for 5 h. After removal, it is washed with deionized water until neutral and dried at 60℃ for 4 h to obtain a highly alkali-resistant cation exchange membrane.

[0064] Comparative Example 1:

[0065] The preparation method provided in Example 1 is used, except that: γ-aminopropyltriethoxysilane is not added during the substrate pretreatment process in step 1. Instead, fluorinated polyethersulfone powder is dissolved in N-methylpyrrolidone solvent, stirred and dissolved at 60°C, and then directly used in the subsequent in-situ crosslinking polymerization step. Other process parameters are completely consistent with those in Example 1.

[0066] Comparative Example 2:

[0067] The preparation method provided in Example 1 is used, except that: no hydroxylated graphene quantum dots are added during the in-situ crosslinking polymerization process in step 4, and only an imidazole hybrid crosslinking system is added to the pretreated substrate solution. Other process parameters are completely consistent with those in Example 1.

[0068] Comparative Example 3:

[0069] The preparation method provided in Example 1 is used, except that the imidazole-based hybrid crosslinking system in step 3 is replaced with a single imidazole monomer, that is, no amino-functionalized silica nanoparticles and azobisisobutyronitrile are added, and only the imidazole monomer is directly added to the pretreated substrate solution. The amount added is still 3.2 wt% of the mass of fluorinated polyethersulfone. Other process parameters are completely consistent with those in Example 1.

[0070] Comparative Example 4:

[0071] The preparation method provided in Example 1 is used, except that: in step 5, the gradient temperature thermal crosslinking is not performed during the film formation and curing process. Instead, the dried wet film is placed in an environment of 140°C for 2.5 hours. Other process parameters are completely consistent with those in Example 1.

[0072] test:

[0073] Experiment 1: Alkali resistance stability test;

[0074] The cation exchange membrane samples prepared in Examples 1-3 and Comparative Examples 1-4 were cut into strips of 2cm × 5cm and immersed in 12mol / L NaOH solution for 1000h at a constant temperature of 70℃. The ion exchange capacity of the membranes was determined by titration before immersion, after 500h of immersion, and after 1000h of immersion. The water absorption rate was determined by gravimetric method (water absorption rate = (mass after immersion - dry mass) / dry mass × 100%). The tensile strength and elongation at break were determined by universal testing machine (tensile rate 5mm / min). The retention rate of each property after 1000h was calculated (retention rate = property value after immersion / property value before immersion × 100%). The results are as follows:

[0075] Table 1

[0076] Sample Ion exchange capacity retention (%) Water absorption retention (%) Tensile strength retention (%) Elongation at break retention (%) Example 1 92.3 88.7 90.5 87.2 Example 2 89.1 85.3 87.8 84.5 Example 3 94.6 91.2 93.1 89.7 Comparative Example 1 72.5 65.8 68.3 62.1 Comparative Example 2 78.6 73.2 75.4 70.3 Comparative Example 3 69.8 62.5 65.7 59.8 Comparative Example 4 81.3 76.9 79.2 74.6

[0077] As can be seen from Table 1, the retention rates of various performance parameters in Examples 1-3 are significantly higher than those in Comparative Examples 1-4, indicating that the technical solution of the present invention can effectively improve the alkali resistance stability of the cation exchange membrane.

[0078] Experiment 2: Ion conduction performance test;

[0079] Initial ionic conductivity test: The AC impedance method was used, with a test frequency range of 1Hz-1MHz and a test temperature of 25℃. The membrane sample was clamped between two platinum electrodes, and the sheet resistance R of the membrane was measured. The ionic conductivity was calculated using the formula σ=L / (R×A) (where L is the average thickness of the membrane, and A is the effective contact area of ​​the electrodes).

[0080] Ion conductivity test after alkali resistance: The membrane sample was immersed in 12 mol / L NaOH solution at 70℃ for 1000 h, then washed until neutral and dried. The ion conductivity was measured using the same method as above, and the conductivity retention rate was calculated. The results are as follows:

[0081] Table 2

[0082] Sample Initial ion conductivity (S / cm) Alkali resistance after ion conductivity (S / cm) Conductivity retention (%) Example 1 0.089 0.082 92.1 Example 2 0.083 0.074 89.2 Example 3 0.094 0.088 93.6 Comparative Example 1 0.078 0.056 71.8 Comparative Example 2 0.081 0.063 77.8 Comparative Example 3 0.075 0.052 69.3 Comparative Example 4 0.085 0.065 76.5

[0083] As can be seen from Table 2, the initial ionic conductivity and the retention rate of conductivity after alkali resistance in Examples 1-3 are better than those in the comparative examples, indicating that the technical solution of the present invention can maintain long-term conductivity stability while ensuring high ionic conductivity efficiency.

[0084] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not describe all details exhaustively, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification.

Claims

1. A method for preparing a highly alkali-resistant cation exchange membrane, characterized in that, Includes the following steps: (1) Substrate pretreatment: Take fluorinated polyethersulfone powder, add it to N-methylpyrrolidone solvent, stir and dissolve at 50-70℃; add 1-3wt% γ-aminopropyltriethoxysilane of fluorinated polyethersulfone to the solution, and ultrasonically disperse at 150-200W power and 50-60℃ for 30-40min to obtain a pretreated substrate solution with 15-25% fluorinated polyethersulfone mass fraction; (2) In-situ crosslinking polymerization: Imidazole hybrid crosslinking system and hydroxylated graphene quantum dots are added to the pretreated substrate solution; The amount of imidazole-based hybrid crosslinking system added is 3.0-3.5 wt% of the mass of fluorinated polyether sulfone; the hydroxylated graphene quantum dots have a particle size of 5-10 nm and a hydroxyl content of 10-15 wt%, and the amount added is 0.6-1.5 wt% of the mass of fluorinated polyether sulfone; under nitrogen protection at a flow rate of 0.8-1 L / min, the reaction is carried out at 80-100 °C for 2-4 h, and the mixture is stirred once every 30 min at a rate of 300-500 r / min to form a hybrid crosslinking precursor solution; (3) Film formation and curing: The precursor solution is cast into a wet film with a thickness of 250-300 μm on a clean glass plate and vacuum dried for 12-16 h; then thermal crosslinking is carried out by gradient heating, and the film is removed after cooling. (4) Alkali activation treatment: The membrane after stripping is immersed in NaOH solution for activation treatment, taken out and washed with deionized water until neutral, and dried to obtain a highly alkali-resistant cation exchange membrane.

2. The preparation method according to claim 1, characterized in that, In step (1), the fluorinated polyethersulfone powder has a number average molecular weight of 60,000-80,000 g / mol and a fluorine content of 30-35 wt%.

3. The preparation method according to claim 1, characterized in that, The imidazole-based hybrid crosslinking system described in step (2) is made of imidazole monomer, amino-functionalized silica nanoparticles, and azobisisobutyronitrile in a mass ratio of 10:(2-5):(0.5-1).

4. The preparation method according to claim 3, characterized in that, The preparation steps of the amino-functionalized silica nanoparticles in step (2) are as follows: disperse silica nanoparticles in anhydrous ethanol, add 5% of 3-aminopropyltriethoxysilane by mass of silica nanoparticles, reflux at 50-60℃ for 4-6h, filter, wash and dry to obtain amino-functionalized silica nanoparticles.

5. The preparation method according to claim 4, characterized in that, The specific preparation steps of the imidazole hybrid crosslinking system described in step (2) are as follows: (1) Mix imidazole monomer with 37% formaldehyde aqueous solution at a mass ratio of 1:(0.8-1.2), adjust the pH to 8-9, and react at 40-50℃ for 1-2 hours; (2) Add amino-functionalized silica nanoparticles, continue the reaction for 3-4 hours, remove water by vacuum distillation, and obtain amino-functionalized imidazole crosslinking agent; (3) Dissolve the crosslinking agent in N-methylpyrrolidone to prepare a crosslinking agent solution with a mass fraction of 10-15%, and mix it evenly with hydroxylated graphene quantum dots to obtain the desired solution.

6. The preparation method according to claim 1, characterized in that, The hydroxylated graphene quantum dots in step (2) are obtained by hydroxylation modification after preparation by the Hummers method. The hydroxylation modification is carried out by treating a mixture of concentrated nitric acid and concentrated sulfuric acid with a volume ratio of 1:3 at 80°C for 4 hours.

7. The preparation method according to claim 1, characterized in that, The vacuum drying conditions in step (3) are -0.08~-0.1MPa pressure and 60-80℃.

8. The preparation method according to claim 1, characterized in that, The gradient temperature thermal crosslinking in step (3) is as follows: keep at 120℃ for 1 hour, keep at 130℃ for 1 hour, and keep at 140℃ for 0.5-1 hour.

9. The preparation method according to claim 1, characterized in that, The conditions for alkaline activation treatment in step (4) are: 12 mol / L NaOH solution, soaking at 70℃ for 5 hours.

10. The preparation method according to claim 1, characterized in that, In step (4), the drying temperature is 60℃ and the time is 3-4 hours.

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