Alkali-resistant high-conductivity anion exchange membrane based on biguanide salt cross-linked network

Abstract

The invention relates to the technical field of ion exchange membrane preparation, in particular to an alkali-resistant high-conductivity anion exchange membrane based on a biguanide salt cross-linked network, which is prepared from a biguanide salt monomer, a polymer matrix, a cross-linking agent and a solvent. The biguanide salt monomer comprises at least one of 1, 3-diphenyl biguanide hydrochloride and 1, 1-dimethyl biguanide sulfate; the polymer matrix comprises at least one of polyether sulfone and polyether-ether-ketone; the cross-linking agent is hexamethylene diisocyanate; the solvent is prepared from at least one of N, N-dimethyl formamide and N-methyl pyrrolidone. The membrane has relatively high ionic conductivity and stable temperature response, and the energy conversion efficiency of alkaline fuel cells and electrolysis equipment can be remarkably improved; the combined design of different types of biguanide salt monomers and polymer matrixes is introduced, so that the performance of the membrane can be flexibly regulated and controlled to adapt to different application scenes.

Description

Technical Field

[0001] The present invention relates to the technical field of ion exchange membrane preparation, in particular to an alkali-resistant high-conductivity anion exchange membrane based on a biguanidine salt cross-linked network. Background Art

[0002] Anion exchange membranes, as an important functional polymer material, are widely used in alkaline fuel cells, water treatment, electrolysis and other fields. However, traditional anion exchange membranes face many challenges in alkaline environments.

[0003] In alkaline fuel cells, traditional anion exchange membranes often have poor alkaline resistance, making their chemical structure susceptible to OH- attack and degradation, leading to a rapid decline in membrane performance and significantly shortening the fuel cell's service life. For example, some quaternary ammonium salt-based anion exchange membranes are susceptible to Hofmann elimination reactions in strong alkaline conditions, reducing the membrane's ion exchange capacity and ionic conductivity.

[0004] In the water treatment sector, the low conductivity of traditional anion exchange membranes hinders treatment efficiency. This low ionic conductivity slows ion migration within the membrane, reducing the ion exchange rate during the water treatment process and failing to meet the requirements for efficient treatment. Furthermore, some traditional membrane materials have poor mechanical properties, making them prone to breakage and swelling over long-term use, further limiting their application.

[0005] Therefore, developing an anion exchange membrane with excellent alkali resistance and high conductivity is of great practical significance. Summary of the Invention

[0006] The purpose of the present invention is to solve the shortcomings of the prior art and to propose an alkali-resistant high-conductivity anion exchange membrane based on a biguanide salt cross-linked network.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for preparing an alkali-resistant high-conductivity anion exchange membrane based on a biguanide salt cross-linked network, comprising the following steps:

[0008] (1) Raw material preparation: selecting a biguanidine salt monomer, a polymer matrix, a crosslinking agent, and a solvent; the biguanidine salt monomer includes at least one of 1,3-diphenylbiguanidine hydrochloride and 1,1-dimethylbiguanidine sulfate; the polymer matrix includes at least one of polyethersulfone and polyetheretherketone; the crosslinking agent is hexamethylene diisocyanate; the solvent includes at least one of N,N-dimethylformamide and N-methylpyrrolidone;

[0009] (2) Solution preparation: the biguanide salt monomer and the polymer matrix are added into the solvent according to the mass ratio of 1: (2-5), and stirred at 60-80°C for 2-4 hours to form a uniform mixed solution;

[0010] (3) Crosslinking reaction: the crosslinking agent is added to the above mixed solution, and the amount of the crosslinking agent is 5%-15% of the total mass of the biguanide salt monomer and the polymer matrix, and the reaction is carried out at 80-100°C for 4-8 hours under nitrogen protection;

[0011] (4) Film forming: the solution after crosslinking reaction is made into a film, and dried at 60-80°C for 12-24 hours to obtain an alkali-resistant high-conductivity anion exchange membrane based on a biguanide salt crosslinked network, wherein the structural formula of N, N-diphenyl guanidine hydrochloride is as follows:

[0012]

[0013] wherein the 1,1-dimethyl biguanide sulfate is as follows:

[0014]

[0015] Preferably, the purity of the biguanide salt monomer is not less than 98.5%.

[0016] Preferably, the number average molecular weight of the polymer matrix is 45,000-50,000.

[0017] Preferably, the solvent is anhydrous grade, and the moisture content is <0.01%.

[0018] Preferably, during the solution preparation process, the stirring speed is 250-350 r / min, and nitrogen is simultaneously introduced to remove oxygen, and the nitrogen flow is 0.5 L / min.

[0019] Preferably, during the crosslinking reaction process, online infrared monitoring or viscosity change is used to determine the reaction endpoint.

[0020] Preferably, during the film forming process, pre-drying is first carried out in a vacuum drying oven at 60°C for 2 hours, the vacuum degree is -0.09 MPa, and then the temperature is raised to 70°C for normal pressure drying.

[0021] An alkali-resistant high-conductivity anion exchange membrane based on a biguanide salt crosslinked network, wherein the ion exchange capacity retention rate of the anion exchange membrane is not less than 85% after being placed in a 6 mol / L KOH solution at 80°C for 1,000 hours; and the ion conductivity is not less than 0.07 S / cm at 25°C.

[0022] Preferably, the tensile strength of the anion exchange membrane is not less than 22 MPa, and the elongation at break is not less than 25%.

[0023] Preferably, after the anion exchange membrane is immersed in deionized water at 90° C. for 24 hours, the surface swelling rate is no higher than 8% and the thickness change rate is less than 3%.

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

[0025] 1. The anion exchange membrane of the present invention has excellent alkali resistance and can maintain a stable chemical structure and performance in a strong alkaline environment. The ion exchange capacity retention rate exceeds 85%, and the service life is extended by more than 3 times.

[0026] 2. The membrane has high ionic conductivity and stable temperature response, which can significantly improve the energy conversion efficiency of alkaline fuel cells and electrolysis equipment; the introduction of a combination design of different types of biguanidine salt monomers and polymer matrices can flexibly adjust the membrane performance to adapt to different application scenarios; the preparation process adopts a controllable cross-linking process and gradient drying technology, and the membrane product has good uniformity and high batch stability, making it suitable for large-scale industrial production.

[0027] 3. The membrane material has both good mechanical properties and dimensional stability, and can maintain reliable operation under complex working conditions, reducing equipment maintenance costs. DETAILED DESCRIPTION

[0028] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0029] Example 1

[0030] Raw material preparation: 1,3-diphenylbiguanidine hydrochloride as the biguanidine salt monomer, purified by recrystallization, with a purity of 99.2%; polyethersulfone as the polymer matrix, with a number average molecular weight of 50,000; hexamethylene diisocyanate as the cross-linking agent, which is industrial grade and purified by vacuum distillation; N,N-dimethylformamide as the solvent, which is anhydrous grade and has a moisture content of <0.01%.

[0031] Solution preparation: Weigh 10 g of 1,3-diphenylbiguanidine hydrochloride and 30 g of polyethersulfone, add them to 100 mL of N,N-dimethylformamide, and stir at 300 rpm at 70°C for 3 hours. Simultaneously, introduce nitrogen at a flow rate of 0.5 L / min to deoxygenate, forming a homogeneous, transparent mixed solution with a viscosity of 3500 mPa·s.

[0032] Crosslinking reaction: 6 g of hexamethylene diisocyanate, which is 15% of the total mass of the biguanide salt monomer and the polymer matrix, was added to the mixed solution, and the reaction was carried out at 90°C under 0.1 MPa pressure for 6 hours under nitrogen protection. Online infrared monitoring was used, and the isocyanate characteristic peak at 1650 cm -1 disappeared completely.

[0033] Film formation: The reacted solution was poured onto a glass plate treated with a silane coupling agent, and a precision scraper was used to scrape a wet film with a thickness of 50 um. First, it was pre-dried in a vacuum drying oven at 60°C under a vacuum degree of -0.09 MPa for 2 hours, and then it was dried at 70°C under normal pressure for 16 hours. An anion exchange membrane M1 was obtained, with a uniformity deviation of the membrane surface resistance of less than 3%.

[0034] Performance test of membrane M1:

[0035] Alkali resistance test: The membrane M1 was soaked in a 6 mol / L KOH solution and placed at 80°C for 1000 hours. The ion exchange capacity retention rate of the membrane was 92%, and the water absorption rate of the membrane only increased by 8%.

[0036] Ion conductivity test: At 25°C, the ion conductivity of membrane M1 was tested by AC impedance method with a frequency range of 1 Hz-1 MHz. The ion conductivity of membrane M1 was 0.085 S / cm, and it showed a linear temperature response in the range of -20-80°C, with a temperature coefficient of 0.002 S / (cm·℃).

[0037] Mechanical properties: Tensile strength 28 MPa, elongation at break 32%, no cracks after 100 bending tests.

[0038] Long-term operation: The membrane was assembled in a 50 cm 2 alkaline electrolytic cell, and continuously operated for 500 hours with a cell voltage fluctuation amplitude of less than 5 mV. The structure of 1,3-diphenyl biguanide hydrochloride is as follows:

[0039]

[0040] Hexamethylene diisocyanate is as follows:

[0041]

[0042] Example 2

[0043] Raw material preparation: 1,1-dimethyl biguanide sulfate as biguanide salt monomer, self-made with a purity of 98.5%; polyether sulfone as in Example 1; hexamethylene diisocyanate as in Example 1; N,N-dimethylformamide as in Example 1.

[0044] Solution preparation: Weigh 10 g of 1,1-dimethylbiguanidine sulfate and 50 g of polyethersulfone, add them to 150 mL of N,N-dimethylformamide, and stir at 250 r / min at 60°C for 4 hours to form a uniform mixed solution with a viscosity of 2800 mPa·s.

[0045] Cross-linking reaction: 3 g of hexamethylene diisocyanate (5% of the total mass of the biguanidine salt monomer and polymer matrix) was added to the mixed solution. The mixture was reacted at 80°C for 8 hours under nitrogen protection. Samples were taken every 2 hours to measure the gel content. The final gel content reached 82%.

[0046] Membrane formation: The reacted solution was poured onto a glass plate and scraped into a 60 μm thick film using a scraper. The film was then dried using a gradient temperature increase method, i.e., dried at 60°C for 4 hours and then at 70°C for 20 hours to obtain an anion exchange membrane M2.

[0047] Performance test of membrane M2:

[0048] Alkali resistance test: The membrane M2 was immersed in a 6 mol / L KOH solution and placed at 80°C for 1000 hours. The ion exchange capacity retention rate of the tested membrane was 88%, and the X-ray photoelectron spectroscopy showed no obvious attenuation of the guanidine characteristic peak.

[0049] Ionic conductivity test: At 25°C, the AC impedance method was used to test the ionic conductivity of membrane M2, which was 0.072 S / cm. The conductivity increased to 0.105 S / cm in a 3 mol / L KOH solution.

[0050] Anti-pollution: In the treatment of simulated wastewater containing 100 mg / L oil, the membrane flux attenuation rate was only 12% after 100 hours of continuous operation, and the recovery rate reached 95% after flushing with pure water.

[0051] Thermal stability: Thermogravimetric analysis shows that the 5% weight loss temperature is 285°C, which is better than the 220°C of traditional quaternary ammonium salt membranes. The structural formula of 1,1-dimethylbiguanidine sulfate is as follows:

[0052]

[0053] Example 3

[0054] Raw material preparation: 1,3-diphenylbiguanidine hydrochloride is the same as in Example 1; polyetheretherketone is used as the polymer matrix, with a number average molecular weight of 45,000; hexamethylene diisocyanate is the same as in Example 1; N-methylpyrrolidone is used as the solvent to replace N,N-dimethylformamide to improve high-temperature solubility.

[0055] Solution preparation: Weigh 10 g of 1,3-diphenylbiguanidine hydrochloride and 20 g of polyetheretherketone, add them to 80 mL of N-methylpyrrolidone, stir at 350 r / min at 80°C for 2 hours, and use ultrasonic assisted dispersion for 10 minutes to form a uniform mixed solution.

[0056] Cross-linking reaction: 4.5 g of hexamethylene diisocyanate (10% by weight of the total mass of the biguanidine salt monomer and polymer matrix) was added to the mixed solution. The mixture was reacted at 100°C under nitrogen for 4 hours. The endpoint of the reaction was determined by a sudden increase in viscosity from 2200 to 5800 mPa·s.

[0057] Membrane formation: The reacted solution was poured onto a glass plate and scraped into a 40 μm thick film using a scraper. The film was then dried in an oven at 80°C for 12 hours to obtain a high-temperature resistant anion exchange membrane M3.

[0058] Performance test of membrane M3:

[0059] Alkali resistance test: The membrane M3 was immersed in 6 mol / L KOH solution and placed at 80°C for 1000 hours. The ion exchange capacity retention rate of the tested membrane was 90%, and it still maintained 85% retention rate under strong alkaline conditions at 100°C.

[0060] Ionic conductivity test: At 25°C, the AC impedance method was used to test the ionic conductivity of membrane M3 to be 0.090 S / cm, and at 100°C it reached 0.15 S / cm.

[0061] Dimensional stability: After soaking in 90℃ deionized water for 24 hours, the surface swelling rate is only 5.2% and the thickness change rate is less than 3%.

[0062] Chemical compatibility: After immersion in an alkaline solution containing 5% hydrogen peroxide for 100 hours, the performance retention rate is 89%, demonstrating excellent antioxidant properties.

[0063] Comparative Example

[0064] Comparative Example 1

[0065] A traditional quaternary ammonium salt anion exchange membrane is used, specifically a commercial quaternized polyethersulfone anion exchange membrane C1.

[0066] Performance test of membrane C1:

[0067] Alkali resistance test: Membrane C1 was immersed in a 6 mol / L KOH solution and placed at 80°C for 1000 hours. The ion exchange capacity retention rate of the tested membrane was 45%, and the membrane showed obvious embrittlement.

[0068] Ionic conductivity test: At 25°C, the ionic conductivity of membrane C1 was tested using the AC impedance method. The ionic conductivity was 0.035 S / cm, which dropped to 0.012 S / cm after 500 hours of operation.

[0069] Comparative Example 2

[0070] The anion exchange membrane without a biguanide cross-linked network is prepared by the following steps:

[0071] Raw material preparation: polyethersulfone is the same as in Example 1; the quaternizing agent is trimethylchlorosilane; the cross-linking agent is hexamethylene diisocyanate; and N,N-dimethylformamide is the same as in Example 1.

[0072] Solution preparation: Weigh 50 g of polyethersulfone, add it to 150 mL of N,N-dimethylformamide, and stir at 70°C for 3 hours to form a homogeneous solution.

[0073] Quaternization and cross-linking reaction: add 10 g of trimethylsilyl chloride and 3 g of hexamethylene diisocyanate to the solution and react at 90° C. for 6 hours under nitrogen protection.

[0074] Membrane formation: The reacted solution was poured onto a glass plate and scraped into a 50 μm thick film using a scraper. The film was then dried in an oven at 70°C for 18 hours to obtain an anion exchange membrane C2.

[0075] Performance test of membrane C2:

[0076] Alkali resistance test: Membrane C2 was immersed in 6 mol / L KOH solution and placed at 80°C for 1000 hours. The ion exchange capacity retention rate of the tested membrane was 52%, and the infrared spectrum showed a characteristic peak of quaternary ammonium group (1480 cm -1 ) strength decreased by 40%.

[0077] Ionic conductivity test: At 25°C, the AC impedance method was used to test the ionic conductivity of membrane C2, which was 0.042 S / cm and showed a nonlinear decay with increasing temperature.

[0078] Comparative Analysis

[0079] By comparing the performance test results of Examples 1-3 and Comparative Examples 1-2, it can be seen that:

[0080] In terms of alkali resistance: after 1000 hours of strong alkali immersion, the ion exchange capacity retention rates of the anion exchange membranes M1, M2, and M3 in the examples were 92%, 88%, and 90%, respectively, which were much higher than 45% of membrane C1 and 52% of membrane C2 in the comparative example. In addition, the physical morphology of the example membranes was stable, without obvious embrittlement or excessive swelling, indicating that the biguanide salt cross-linked network can effectively resist OH- erosion.

[0081] In terms of ion conductivity: the ion conductivity of membranes M1, M2, and M3 in the examples are 0.085 S / cm, 0.072 S / cm, and 0.090 S / cm, respectively, which are significantly higher than 0.035 S / cm of membrane C1 and 0.042 S / cm of membrane C2 in the comparative example. In addition, the conductivity of the example membranes is more stable with temperature changes, reflecting the efficient ion transport characteristics of the biguanide group.

[0082] Comprehensive performance: The example membrane is superior to the comparative example in terms of mechanical strength, long-term stability, temperature resistance, etc., especially showing a lower performance attenuation rate in actual application scenarios, verifying the creative advantages of the biguanide salt cross-linked network design.

[0083] In summary, the alkali-resistant high-conductivity anion exchange membrane based on a biguanide salt cross-linked network of the present invention solves the problems of poor alkali resistance and low ion conductivity of traditional anion exchange membranes, and has significant creativity and superiority.

[0084] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to the specific embodiments described. Obviously, many modifications and variations are possible based on the content of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing an alkali-resistant high-conductivity anion exchange membrane based on a biguanide salt cross-linked network, characterized in that: The following steps are involved: (1) Raw material preparation: selecting a biguanidine salt monomer, a polymer matrix, a crosslinking agent, and a solvent; the biguanidine salt monomer includes at least one of 1,3-diphenylbiguanidine hydrochloride and 1,1-dimethylbiguanidine sulfate; the polymer matrix includes at least one of polyethersulfone and polyetheretherketone; the crosslinking agent is hexamethylene diisocyanate; the solvent includes at least one of N,N-dimethylformamide and N-methylpyrrolidone; (2) Solution preparation: add biguanidine salt monomer and polymer matrix into solvent in a mass ratio of 1:(2-5), stir at 60-80°C for 2-4 hours to form a uniform mixed solution; (3) Cross-linking reaction: adding a cross-linking agent to the above mixed solution, wherein the amount of the cross-linking agent added is 5%-15% of the total mass of the biguanidine salt monomer and the polymer matrix, and reacting at 80-100° C. for 4-8 hours under nitrogen protection; (4) Film formation: The cross-linked solution is formed into a thin film, and dried at 60-80° C. for 12-24 hours to obtain an alkali-resistant high-conductivity anion exchange membrane based on a biguanidine salt cross-linked network, wherein the structural formula of N,N-diphenylguanidine hydrochloride is as follows: Wherein 1,1-dimethylbiguanidine sulfate is as follows:

2. The preparation method according to claim 1, characterized in that The purity of the biguanidine salt monomer is not less than 98.5%.

3. The preparation method according to claim 1, characterized in that The number average molecular weight of the polymer matrix is ​​45,000-50,000.

4. The preparation method according to claim 1, characterized in that The solvent is anhydrous and has a moisture content of less than 0.01%.

5. The preparation method according to claim 1, characterized in that During the solution preparation process, the stirring speed was 250-350 r / min, and nitrogen was introduced simultaneously for deoxygenation, with a nitrogen flow rate of 0.5 L / min.

6. The preparation method according to claim 1, characterized in that During the cross-linking reaction, online infrared monitoring or viscosity change is used to determine the reaction endpoint.

7. The preparation method according to claim 1, characterized in that During the film forming process, the film was pre-baked in a vacuum drying oven at 60°C for 2 hours with a vacuum degree of -0.09MPa, and then heated to 70°C and dried at normal pressure.

8. An alkali-resistant high-conductivity anion exchange membrane based on a biguanide salt cross-linked network, characterized in that: The anion exchange membrane is prepared by the preparation method according to any one of claims 1 to 7, wherein the anion exchange membrane has an ion exchange capacity retention rate of not less than 85% after being placed in a 6 mol / L KOH solution at 80°C for 1000 hours; and an ion conductivity of not less than 0.07 S / cm at 25°C.

9. The anion exchange membrane according to claim 8, characterized in that The tensile strength of the anion exchange membrane is not less than 22 MPa, and the elongation at break is not less than 25%.

10. The anion exchange membrane according to claim 8, characterized in that After the anion exchange membrane is immersed in deionized water at 90° C. for 24 hours, the surface swelling rate is no higher than 8%, and the thickness change rate is less than 3%.

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