A composite cation exchange membrane, its preparation method and application

Abstract

The present invention relates to the technical field of membrane for water treatment, and particularly relates to a composite cation exchange membrane, a preparation method thereof and an application thereof. In the present invention, polyether ether ketone is used as a skeleton, and 98% concentrated sulfuric acid is used as a sulfonating agent to prepare sulfonated polyether ether ketone. Subsequently, the sulfonated polyether ether ketone is blended with polyvinylpyrrolidone with a hydrophilic-hydrophobic structure. The flexible polyvinylpyrrolidone and the sulfonated polyether ether ketone are used to form an interpenetrating three-dimensional crosslinked network to improve the water content and swelling ratio of the sulfonated polyether ether ketone. On this basis, polyaniline with conductive properties is introduced to react with the sulfonic acid groups on the sulfonated polyether ether ketone to generate a composite cation exchange membrane with a dense structure. The finally obtained composite cation exchange membrane has better water content, better swelling ratio, high mechanical strength and high conductivity, and can be used for electrodialysis water treatment. At the same time, it can recycle and reuse printing and dyeing wastewater, and realize the desalination of brackish water and salt concentration.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane technology for water treatment, and particularly relates to a composite cation exchange membrane, a preparation method thereof, and an application thereof. Background Art

[0002] Polyetheretherketone (PEEK) is a polymer composed of repeating units containing a ketone bond and two ether bonds in the main chain structure. The main chain has strong hydrophobicity and is a rigid polymer material with excellent corrosion resistance and anti-aging properties. It has been widely used in the field of preparing ion exchange membranes. Patent CN115260422B discloses using polyetheretherketone materials as raw materials for cation exchange membranes, and grafting sulfonic acid groups through sulfonation reactions to obtain sulfonated polyetheretherketone materials, which have good proton conductivity and hydrophilicity. It can be used to prepare filtration materials such as ultrafiltration, nanofiltration, reverse osmosis, and proton exchange membranes; in addition, it is also used in fuel cells, flow batteries, and biomedical materials. Patent CN102945972A discloses using sulfuric acid to sulfonate polyetheretherketone to obtain sulfonated polyetheretherketone (SPEEK) for cation membranes in flow batteries. Although the above-mentioned patents disclose the preparation methods of SPEEK, they do not pay attention to the characteristic performance indicators such as moisture content and swelling rate for electrodialysis applications, and the corresponding technical solutions are not suitable for the preparation of SPEEK for electrodialysis.

[0003] Sulfonation reactions can introduce sulfonic acid groups into polyetheretherketone polymer materials. Compared with cation exchange membranes prepared from traditional side-chain sulfonated materials, the preparation process of main-chain sulfonated polyetheretherketone materials has advantages such as simple and easy operation, easy control of sulfonation degree, and easy obtainment of sulfonated materials. However, while SPEEK cation exchange membranes have a high sulfonation degree and ion exchange capacity, their moisture content is too high, and they are extremely prone to water absorption and swelling during application, resulting in the destruction of ion exchange channels and the inability of ion membranes to function properly. To enable ion membranes to have a low moisture content, swelling rate, strong mechanical properties, and stability while having a high ion exchange capacity, more work needs to be done.

[0004] Polyvinylpyrrolidone (PVP) is a non-ionic water-soluble polymer material with many hydrophilic groups and a long molecular chain. When PVP is blended with SPEEK in an aqueous solvent, it exhibits good compatibility. The addition of PVP can improve the fluidity of the solution, enhance the fluidity and uniformity of the SPEEK solution, making it more suitable for coating and casting processes. This results in a denser and more uniform membrane, reducing the generation of pores and cracks. The addition of PVP can cause phase separation between SPEEK and PVP, forming an interpenetrating cross-linked structure, thereby reducing the water content and swelling rate of the membrane, improving the mechanical strength, durability, and service life of the membrane; at the same time, a microporous structure is formed inside the membrane, adjusting the pore size and porosity, and improving the selective permeability and permeability of the membrane.

[0005] Ion exchange membranes are a special type of functional material and one of the core components of electrodialysis technology. Electrodialysis is a process that uses the special functionality of ion exchange membranes under the action of an externally applied direct current electric field to achieve the separation and purification of solutions, and it has a wide range of applications in seawater desalination, wastewater treatment, the food industry, the pharmaceutical industry, and other fields. From the perspective of energy conservation and environmental protection, conductivity is an important parameter for evaluating the performance of ion exchange membranes. In order to save energy and make it consume less energy in practical applications, the most important thing is to improve the conductivity of composite ion exchange membranes. The low conductivity of the SPEEK / PVP composite ion exchange membrane will seriously affect the industrial application of ion membranes and even cause great energy loss. Therefore, improving the conductivity of the composite membrane is a problem that needs to be solved currently.

[0006] Polyaniline (CPAN) is a conductive polymer with good conductivity. When CPAN is mixed with SPEEK / PVP materials, mainly through physical dispersion, CPAN particles are evenly distributed in the SPEEK / PVP composite matrix, and there can also be hydrogen bonding or other interactions between the amino groups on CPAN and the sulfonic acid groups in the SPEEK material.

[0007] Patent CN107596932A discloses a method for surface modification of a SPEEK cation exchange membrane, that is, immersing the cured SPEEK cation exchange membrane in the prepared CPAN dispersion solution and then taking it out for drying to obtain a SPEEK cation exchange membrane with certain conductive properties. However, this method does not solve the problem of uniform dispersion of CPAN particles, and the CPAN fixed by the adhesive is not sufficiently combined with the SPEEK matrix, and the improvement of the conductive performance is not obvious for enhancing the electrodialysis effect.

[0008] Therefore, a new method for preparing a composite cation exchange membrane is needed to improve the CPAN dispersion degree and membrane structure and further enhance the electrodialysis application performance. Summary of the Invention

[0009] The present invention provides a composite cation exchange membrane, a preparation method thereof, and an application thereof. The composite cation exchange membrane has better water content, better swelling ratio, high mechanical strength and high conductivity, and can be used for electrodialysis water treatment. At the same time, it can recycle and reuse printing and dyeing wastewater, realizing the desalination of brackish water and salt concentration.

[0010] In order to achieve the above object, the present invention provides the following technical solutions:

[0011] The present invention provides a preparation method of a composite cation exchange membrane, comprising:

[0012] S1. Under an inert atmosphere, polyether ether ketone resin and 98% sulfuric acid are mixed for sulfonation reaction to obtain sulfonated polyether ether ketone;

[0013] S2. The sulfonated polyether ether ketone obtained in S1 is dispersed in a solvent, and then polyvinylpyrrolidone with a molecular weight of 100,000 g / mol to 500,000 g / mol is added, and the mixture is obtained to obtain a pre-dispersion liquid;

[0014] S3. Under an ultrasonic state, a solution containing polyaniline with a molecular weight of 20,000 g / mol to 50,000 g / mol is dropped into the pre-dispersion liquid obtained in S3, and an ionic liquid is prepared. The ionic liquid is spread on a glass plate by a casting method and dried to obtain a composite cation exchange membrane.

[0015] In this application, polyether ether ketone is used as the skeleton, and 98% concentrated sulfuric acid is used as the sulfonating agent to prepare sulfonated polyether ether ketone. Immediately afterwards, the sulfonated polyether ether ketone is blended with polyvinylpyrrolidone with a hydrophilic-hydrophobic structure. The flexible polyvinylpyrrolidone and the sulfonated polyether ether ketone form a cross-linked three-dimensional network to improve the water content and swelling ratio of the sulfonated polyether ether ketone. On this basis, polyaniline with conductive properties is introduced to react with the sulfonic acid groups on the sulfonated polyether ether ketone to generate a composite cation exchange membrane with a dense structure.

[0016] At the same time, the molecular weights of polyvinylpyrrolidone and polyaniline introduced are controlled to help improve the dispersion degree of polyaniline on the cross-linked three-dimensional network and improve the mechanical strength of the cation exchange membrane. And it is blended with the polyaniline solution in the form of a pre-dispersion liquid instead of the form of a SPEEK / PVP composite membrane to strengthen the interaction of polyaniline, polyvinylpyrrolidone, and sulfonated polyether ether ketone in a liquid form. Secondly, the uniform dispersion of polyaniline is further strengthened by slowly dropping polyaniline under ultrasonic conditions. Under the combined action of the above three dispersion means, this application can achieve the uniform dispersion of polyaniline in the composite cation exchange membrane while obtaining a composite cation exchange membrane with more excellent mechanical properties and conductivity.

[0017] In summary, the composite cation exchange membrane prepared in this application combines the functions of polyvinylpyrrolidone and polyaniline. On the one hand, it has a better moisture content and a better swelling rate. On the other hand, it has a higher mechanical strength and a higher conductivity, and is suitable for electrodialysis water treatment. It can recycle and reuse printing and dyeing wastewater, and realize the desalination of brackish water and the resource treatment of salt concentration.

[0018] Preferably, in S1, the inert atmosphere is a nitrogen atmosphere.

[0019] Preferably, in S1, the mass-volume ratio of the polyetheretherketone resin to the 98% sulfuric acid is 1 g:(5~25) mL.

[0020] More preferably, in S1, the mass-volume ratio of the polyetheretherketone resin to the 98% sulfuric acid is 1 g:(15~25) mL.

[0021] Preferably, in S1, the temperature of the sulfonation reaction is 20~80°C, the reaction time is 3~10 h, and the stirring speed of the sulfonation reaction is 300~800 r / min.

[0022] More preferably, in S1, the temperature of the sulfonation reaction is 40~60°C, the reaction time is 6 h, and the stirring speed of the sulfonation reaction is 500 r / min.

[0023] Preferably, in S2, the solvent is selected from at least one of water, absolute ethanol, dimethyl sulfoxide, N-methylpyrrolidone, and N,N-dimethylformamide.

[0024] More preferably, the solvent is dimethyl sulfoxide.

[0025] Preferably, in S2, the molecular weight of polyvinylpyrrolidone is 100,000 g / mol~300,000 g / mol.

[0026] Preferably, in S2, the molecular weight of polyvinylpyrrolidone is 200,000 g / mol~400,000 g / mol.

[0027] Preferably, in S3, the molecular weight of polyaniline is 20,000 g / mol~30,000 g / mol.

[0028] Preferably, in S3, the solvent in the solution containing polyaniline with a molecular weight of 20,000 g / mol~50,000 g / mol is absolute ethanol.

[0029] Any other solvent that can help the uniform dispersion of polyaniline is also acceptable.

[0030] Preferably, in S3, the polyaniline is selected from at least one of conductive polyaniline, intrinsic polyaniline, sulfonic acid-doped polyaniline, and emeraldine base polyaniline.

[0031] Preferably, the mass ratio among the polyaniline with a molecular weight of 20,000 g / mol to 50,000 g / mol, the polyvinylpyrrolidone with a molecular weight of 100,000 g / mol to 500,000 g / mol, and the sulfonated polyether ether ketone is (1 - 5):(20 - 40):100.

[0032] More preferably, the mass ratio among the polyaniline with a molecular weight of 20,000 g / mol to 50,000 g / mol, the polyvinylpyrrolidone with a molecular weight of 100,000 g / mol to 500,000 g / mol, and the sulfonated polyether ether ketone is 1:(20 - 40):100.

[0033] More preferably, the mass ratio among the polyaniline with a molecular weight of 20,000 g / mol to 50,000 g / mol, the polyvinylpyrrolidone with a molecular weight of 100,000 g / mol to 500,000 g / mol, and the sulfonated polyether ether ketone is 1:(30 - 35):100.

[0034] The addition of polyaniline materials can improve the conductivity of the composite cation exchange membrane, increase the fixed charge density in the composite cation exchange membrane, thereby improving the ion exchange capacity, and improving the selective permeability and ion transport rate of the membrane. The rigidity strength of polyaniline is relatively high. When blended with the pre-dispersion liquid (the main component is SPEEK / PVP), it can also improve the mechanical strength, durability, and thermal stability of the composite cation exchange membrane. If the amount of polyaniline used is too small, the improvement of the conductivity of the composite cation exchange membrane will not be obvious. If the amount of polyaniline used is too large, it will cause agglomeration in the blending solution, thus affecting the mechanical strength and conductivity of the composite cation exchange membrane.

[0035] Therefore, the selection of polyaniline specifications, the selection of the ratio among PVP, CPAN, and SPEEK, the selection of the polyaniline addition method, and the selection of preparation conditions of the composite cation exchange membrane such as the molecular weights of polyaniline and polyvinylpyrrolidone have a significant impact on the performance of the final composite cation exchange membrane.

[0036] Preferably, in S3, the power of the ultrasound is 100 - 200 W, the temperature of the ultrasound is 40 - 55 °C, and the dropping speed is 30 - 50 drops / min.

[0037] Further preferably, in S3, the solid-liquid ratio in the solution containing polyaniline with a molecular weight of 20,000 g / mol to 50,000 g / mol is 0.002 to 0.005 g / mL; the power of the ultrasonic wave is 200 W, the temperature of the ultrasonic wave is 55 °C, and the dropping speed is (0.8 to 1) mL / min.

[0038] Preferably, in S3, the mixing time is 1 to 48 h, and the mixing is completed at 25 to 80 °C.

[0039] Preferably, in S3, the drying temperature is 90 to 160 °C, and the drying time is at least 12 h.

[0040] The purpose of drying is to completely volatilize all solvents in the ionic liquid; the selection of temperature and time only needs to meet the requirement of completely volatilizing the solvent to obtain a dry composite cation exchange membrane. The temperature and time provided in this application are only the preferred ranges selected in the experiment. Other range selections outside this range, as long as they can achieve the complete volatilization of the solvent, are within the protection scope of this application.

[0041] The present invention also provides a composite cation exchange membrane prepared by the above preparation method.

[0042] The present invention also provides the application of the above composite cation exchange membrane in the recycling and reuse of printing and dyeing wastewater, the desalination of brackish water or the concentration of salt.

[0043] Therefore, the present invention has the following beneficial effects:

[0044] (1) The present invention uses the interpenetrating network structure between polyvinylpyrrolidone and sulfonated polyether ether ketone to help improve the water content and swelling ratio of sulfonated polyether ether ketone, and introduces polyaniline to solve the problem of poor conductivity of the SPEEK / PVP composite membrane. Finally, the obtained composite cation exchange membrane has better water content, better swelling ratio, high mechanical strength and high conductivity, and can be used for electrodialysis water treatment. At the same time, it can recycle and reuse printing and dyeing wastewater, and realize the desalination of brackish water and the concentration of salt.

[0045] (2) The present invention solves the dispersion problem of polyaniline by using three parallel means: First, using polyvinylpyrrolidone with a specific molecular weight and polyaniline with a specific molecular weight; Second, mixing with polyaniline in the form of a pre-dispersion liquid to avoid the problem of uneven dispersion often occurring in the mixing of polyaniline in the form of a membrane; Third, slowly dropping polyaniline under ultrasonic conditions, so that polyaniline can be evenly dispersed in the composite cation exchange membrane. Under the action of these three means, it helps polyaniline to be better dispersed in the interpenetrating network structure, and a composite cation exchange membrane with higher conductivity and mechanical strength is obtained. Description of the Drawings

[0046] Figure 1 1H NMR spectrum of the SPEEK membrane of Comparative Example 1;

[0047] Figure 2 is Figure 1 Partial enlarged view of the dashed part;

[0048] Figure 3 Infrared characteristic curve comparison chart;

[0049] Figure 4 SEM comparison chart, where a is the surface view of the SPEEK / PVP membrane of Comparative Example 2, b is the cross-sectional view of the SPEEK / PVP membrane of Comparative Example 2, c is the surface view of the SPEEK / PVP / CPAN membrane of Example 1, and d is the cross-sectional view of the SPEEK / PVP / CPAN membrane of Example 1;

[0050] Figure 5 Element distribution map of the SPEEK / PVP / CPAN composite membrane of Example 1, where a is the C element, b is the O element, and c is the S element;

[0051] Figure 6 TGA curve of the SPEEK / PVP / CPAN composite membrane of Example 1. Detailed implementation mode

[0052] The present invention will be further described below in conjunction with specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following descriptions are usually only a part of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work shall fall within the scope of protection of the present invention.

[0053] All reagents in this part were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and were used directly without further processing.

[0054]

Example

[0055] Example 1

[0056] S1. Under a nitrogen atmosphere, 10 g of polyetheretherketone resin and 150 mL of 98% sulfuric acid were added to a three-necked round-bottom flask. Stirring was carried out under a water bath heating condition of 55 °C, the stirring speed was 500 r / min, and after 6 h of sulfonation reaction, sulfonated polyetheretherketone (SPEEK) was obtained.

[0057] S2. Add 7.5 g of SPEEK and 50 mL of dimethyl sulfoxide to a three-necked round-bottom flask. Ultrasonically disperse for 30 min at 55 °C, then add 2.5 g of polyvinylpyrrolidone with a molecular weight of 200,000 g / mol and mix to obtain a pre-dispersed solution.

[0058] S3. The preparation method of the solution containing conductive polyaniline with a molecular weight of 20,000 g / mol is as follows: Add 0.075 g of conductive polyaniline with a molecular weight of 20,000 g / mol to 25 mL of absolute ethanol, ultrasonically treat for 30 min, and then ultrasonically treat for 1 h.

[0059] S4. Under an ultrasonic state of 200 W, drop all the amount of the solution containing conductive polyaniline with a molecular weight of 20,000 g / mol prepared in S3 into the pre-dispersed solution at a dropping rate of 1 mL / min. Ultrasonically mix at 55 °C for 3 h to obtain an ionic liquid. Cast the ionic liquid onto a glass plate by the casting method and dry it overnight (about 18 h) at 130 °C until the solvent in the ionic liquid completely volatilizes, obtaining a dense dark blue film, that is, a composite cation exchange membrane, denoted as SPEEK / PVP / CPAN.

[0060] Comparative Example 1

[0061] Under a nitrogen atmosphere, add 10 g of polyetheretherketone resin and 150 mL of 98% sulfuric acid to a three-necked round-bottom flask. Stir under a water bath heating condition of 55 °C with a stirring speed of 500 r / min. After a sulfonation reaction for 6 h, sulfonated polyetheretherketone is obtained, denoted as SPEEK.

[0062] Comparative Example 2

[0063] S1. Under a nitrogen atmosphere, add 10 g of polyetheretherketone resin and 150 mL of 98% sulfuric acid to a three-necked round-bottom flask. Stir under a water bath heating condition of 55 °C with a stirring speed of 500 r / min. After a sulfonation reaction for 6 h, sulfonated polyetheretherketone (SPEEK) is obtained.

[0064] S2. Add 7.5 g of SPEEK and 50 mL of dimethyl sulfoxide to a three-necked round-bottom flask. Ultrasonically disperse for 30 min at 55 °C, then add 2.5 g of polyvinylpyrrolidone with a molecular weight of 200,000 g / mol and mix to obtain an ionic liquid.

[0065] S3. Cast the ionic liquid onto a glass plate by the casting method and dry it overnight (about 18 h) at 130 °C until the solvent in the ionic liquid completely volatilizes, obtaining a composite cation exchange membrane, denoted as SPEEK / PVP.

[0066] Comparative Example 3

[0067] This comparative example is basically the same as Example 1, except that the molecular weight of polyvinylpyrrolidone is 58,000 g / mol.

[0068] Comparative Example 4

[0069] This comparative example is basically the same as Example 1, except that the molecular weight of polyvinylpyrrolidone is 600,000 g / mol.

[0070] Comparative Example 5

[0071] This comparative example is basically the same as Example 1, except that the molecular weight of conductive polyaniline is 10,000 g / mol.

[0072] Comparative Example 6

[0073] This comparative example is basically the same as Example 1, except that the molecular weight of conductive polyaniline is 60,000 g / mol.

[0074] Comparative Example 7

[0075] S1. Under a nitrogen atmosphere, 10 g of polyetheretherketone resin and 150 mL of 98% sulfuric acid were added to a three-necked round-bottom flask. Stirring was carried out under a water bath at 55 °C, with a stirring speed of 500 r / min. After a sulfonation reaction for 6 h, sulfonated polyetheretherketone (SPEEK) was obtained.

[0076] S2. 7.5 g of SPEEK and 50 mL of dimethyl sulfoxide were added to a three-necked round-bottom flask. Ultrasonic dispersion was carried out at 55 °C for 30 min, and then 2.5 g of polyvinylpyrrolidone with a molecular weight of 200,000 g / mol was added to obtain a pre-dispersion solution. The pre-dispersion solution was spread on a glass plate by the casting method and dried overnight at 130 °C (about 18 h) until the solvent in the pre-dispersion solution was completely volatilized, and a SPEEK / PVP composite membrane was prepared.

[0077] S3. The preparation method of the solution containing conductive polyaniline with a molecular weight of 20,000 g / mol was as follows: 0.075 g of conductive polyaniline with a molecular weight of 20,000 g / mol was added to 25 mL of absolute ethanol, and ultrasonic treatment was carried out for 30 min and then ultrasonic treatment was carried out for another 1 h.

[0078] S4. Under an ultrasonic state of 200 W, the SPEEK / PVP composite membrane was placed in the solution containing conductive polyaniline with a molecular weight of 20,000 g / mol in all the amounts in S3, and ultrasonic treatment was carried out at 55 °C for 3 h. Subsequently, it was dried overnight at 130 °C (about 18 h) until the solvent was completely volatilized to obtain a composite cation exchange membrane.

[0079] Comparative Example 8

[0080] This comparative example is substantially the same as Example 1, except that in S4, the solution containing conductive polyaniline with a molecular weight of 20,000 g / mol is added at once.

[0081] Comparative Example 9

[0082] This comparative example is substantially the same as Example 1, except that the conductive polyaniline with a molecular weight of 20,000 g / mol is replaced by poly(3-hexylthiophene-2,5-diyl).

[0083]

Performance test

[0084] The determination method in this section is:

[0085] ① Determination of moisture content and swelling rate

[0086] The water uptake of the membrane represents the mass of water absorbed by the unit mass of the dry membrane. The area swelling of the membrane refers to the change in the membrane area after the unit area of ​​the dry membrane absorbs water. When testing, the mass and related dimensions of the dry and wet membranes must be accurately measured first, and then the corresponding performance data is obtained through calculation. Before testing, the prepared ion exchange membrane is cut into 2 For samples of 2 cm in size, first place the membrane to be tested in a vacuum drying oven at 60°C for continuous drying to obtain the dry weight Wdry g and the size Ldry mm of the membrane. Then soak the dried membrane in deionized water and place it under different temperature conditions to allow it to fully absorb water and swell in the water. After taking it out, quickly wipe the moisture on the surface of the membrane with filter paper, weigh and record the wet weight Wwet g and the size Lwet mm of the membrane. Each measurement of the ion membrane is repeated three times, and the average value is finally taken (the error is required to be controlled within 5.0%). The moisture content and swelling rate of the membrane can be calculated according to the following formula:

[0087] (1-1);

[0088] (1-2);

[0089] In the above formula, WU is the moisture content, %; Wwet is the wet weight of the membrane, g; Wdry is the dry weight of the membrane, g; SR is the swelling ratio, %; Lwet is the size of the wet membrane, mm; Ldry is the size of the dry membrane, mm.

[0090] ②Methods for measuring mechanical properties

[0091] The prepared ion exchange membrane was cut into dumbbell-shaped membrane samples with a total length of 60 mm, a gauge length of 25 mm, and a narrow parallel part width of 4 mm, and dried in a vacuum drying oven at 60 °C. After 12 h, it was taken out, and the gauge, thickness, and width of the samples were measured respectively. The mechanical properties of the samples were tested on a biaxial tensile tester produced by Kato-Tech Co., Ltd. of Japan at room temperature. During the test, the tensile speed was controlled at 20.000 mm / min, and a 100.0 kg tensile sensor was selected. After the test was completed, data such as elongation at break and tensile strength were recorded.

[0092] 1. Structural Characterization

[0093] The sulfonated SPEEK was characterized by nuclear magnetic resonance hydrogen spectrum, and the sulfonation degree of SPEEK could be calculated to be about 62% according to the Figure 1 results, which proved that the method provided in this application successfully completed sulfonation. Furthermore, the surface and cross-section of the SPEEK / PVP and SPEEK / PVP / CPAN membranes were scanned by SEM to observe Figure 4 It can be seen that the cross-section of the prepared composite membrane is smooth and dense without cracks; and the porosity of the membrane increases after adding polyaniline. Figure 5 The elemental distribution results in Figure 6 showed that polyaniline was uniformly dispersed in the composite cation exchange membrane and formed a uniform dispersed phase.

[0094] 2. Performance Characterization

[0095] The water content, swelling ratio, elongation at break, breaking strength, ion exchange capacity, membrane surface resistance, and ion selectivity of the membranes prepared in Example 1 and Comparative Examples 1-8 were measured, and the results are shown in Table 1.

[0096] Table 1 Performance Comparison Table

[0097]

[0098] It can be seen from the data in Table 1 that the addition of PVP significantly reduces the water content and swelling ratio of the composite cation exchange membrane. The addition of CPAN, on the other hand, significantly reduces the membrane surface resistance of the composite cation exchange membrane. This is mainly because the addition of polyaniline forms a continuous conductive network within the membrane. These conductive paths can significantly increase the conductivity of the membrane, making it easier for ions to be transported through the membrane material, increasing the speed of ion transport, helping to increase the conductivity of the membrane, and reducing the membrane surface resistance. It should be noted that the choice of the molecular weight of CPAN, the choice of the molecular weight of PVP, and the differences in the membrane preparation method lead to poor dispersion of CPAN in the composite cation exchange membrane, which also results in a decrease in conductivity. Among them, the choice of the molecular weight of CPAN and the choice of the molecular weight of PVP are the most crucial for preparing a membrane with high mechanical strength.

Claims

1. A method for preparing a composite cation exchange membrane, characterized in that: include: S1. Under an inert atmosphere, a polyetheretherketone resin and 98% sulfuric acid were mixed for sulfonation to obtain a sulfonated polyetheretherketone; S2. The sulfonated polyetheretherketone of S1 is dispersed in a solvent, and then polyvinylpyrrolidone having a molecular weight of 100,000 g / mol to 500,000 g / mol is added, and the mixture is mixed to obtain a pre-dispersion; S3. Under ultrasonic conditions, a solution of polyaniline with a molecular weight of 20,000 g / mol to 50,000 g / mol is dropped into the pre-dispersed liquid of S2 to obtain an ionic liquid. The ionic liquid is spread onto a glass plate by a casting method and dried to obtain a composite cation exchange membrane.

2. The preparation method according to claim 1, characterized in that In S1, the inert atmosphere is a nitrogen atmosphere.

3. The preparation method according to claim 1, characterized in that: In S1, the mass volume ratio of the polyetheretherketone resin to the 98% sulfuric acid is 1 g:(5-25) mL.

4. The preparation method according to claim 1, characterized in that: In S1, the temperature of the sulfonation reaction is 20~80°C, the reaction time is 3~10 h, and the stirring speed of the sulfonation reaction is 300~800 r / min.

5. The preparation method according to claim 1, characterized in that: In S2, the solvent is selected from at least one of water, anhydrous ethanol, dimethyl sulfoxide, N-methylpyrrolidone and N,N-dimethylformamide.

6. The preparation method according to claim 1, characterized in that: In S3, the polyaniline is selected from at least one of conductive polyaniline and intrinsic polyaniline.

7. The preparation method according to claim 6, characterized in that: The conductive polyaniline is sulfonic acid-doped polyaniline.

8. The preparation method according to claim 1, 3 or 6, characterized in that: The mass ratio of the polyaniline with a molecular weight of 20,000 g / mol to 50,000 g / mol, the polyvinyl pyrrolidone with a molecular weight of 100,000 g / mol to 500,000 g / mol and the sulfonated polyetheretherketone is (1-5):(20-40):

100.

9. The preparation method according to claim 1, characterized in that: In S3, the solid-to-liquid ratio of the solution containing polyaniline with a molecular weight of 20,000 g / mol~50,000 g / mol is 0.002~0.005 g / mL; the power of the ultrasound is 100~200 W, the temperature of the ultrasound is 40~55° C., and the dripping speed is (0.8~1) mL / min.

10. The composite cation exchange membrane obtained by the preparation method according to any one of claims 1 to 9.

11. Use of the composite cation exchange membrane as claimed in claim 10 in the recycling and reuse of printing and dyeing wastewater, desalination of brackish water or concentration of salt.

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