Composite cation exchange membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of membranes for water treatment, in particular to a composite cation exchange membrane as well as a preparation method and application thereof. The sulfonated polyether-ether-ketone is prepared by taking polyether-ether-ketone as a framework and 98% concentrated sulfuric acid as a sulfonating agent. And then, blending the sulfonated polyether ether ketone with polyvinylpyrrolidone with a hydrophilic and hydrophobic structure. A cross-interpenetrating three-dimensional cross-linked network formed by flexible polyvinylpyrrolidone and sulfonated polyether-ether-ketone is used for improving the water content and swelling rate of sulfonated polyether-ether-ketone. On the basis, polyaniline with conductive characteristics is introduced to react with sulfonic acid groups on the sulfonated polyether-ether-ketone to generate the composite cation exchange membrane with a compact structure. The finally obtained composite cation exchange membrane has better water content, better swelling ratio, high mechanical strength and high conductivity, can be used for electrodialysis water treatment, can recycle printing and dyeing wastewater, and realizes brackish water desalination and salt concentration.

Description

Technical Field

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

[0002] Polyetheretherketone (PEEK) is a polymer composed of repeating units containing one 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 the use of polyetheretherketone material as a raw material for cation exchange membranes, and the use of sulfonation reaction to graft sulfonic acid groups to obtain sulfonated polyetheretherketone material, which has good proton conductivity and hydrophilicity. It can be used to prepare filter materials such as ultrafiltration, nanofiltration, reverse osmosis, and proton exchange membranes; in addition, it is also used in fuel cells, liquid flow batteries, and biomedical materials. Patent CN102945972A discloses the use of sulfuric acid to sulfonate polyetheretherketone to obtain sulfonated polyetheretherketone (SPEEK) for liquid flow battery cation membranes. Although the above-disclosed patents disclose the preparation method of SPEEK, they do not focus on the characteristic performance indicators of electrodialysis applications such as its water content and swelling rate. The corresponding technical solutions are not suitable for the preparation of SPEEK for electrodialysis.

[0003] Sulfonation reaction can introduce sulfonic acid groups into polyetheretherketone polymer materials. Compared with the cation exchange membrane prepared by traditional side chain sulfonated materials, the preparation process of main chain sulfonated polyetheretherketone materials has the advantages of simple and easy operation, easy control of sulfonation degree, and easy acquisition of sulfonated materials. However, while SPEEK cation exchange membrane has a high degree of sulfonation and ion exchange capacity, its water content is too high. It is very easy to absorb water and swell during use, and the ion exchange channel is destroyed, so the ion membrane cannot function normally. More work needs to be done to make the ion membrane have a low water content, swelling rate, strong mechanical properties and stability while having a high ion exchange capacity.

[0004] Polyvinylpyrrolidone (PVP) is a non-ionic water-soluble polymer material with more hydrophilic groups and longer molecular chains. PVP and SPEEK show good compatibility when blended in aqueous solvents. The addition of PVP can improve the fluidity of the solution, improve the fluidity and uniformity of the SPEEK solution, and make it more suitable for coating and casting processes. It makes the prepared membrane more dense and uniform, and reduces the generation of holes and cracks. The addition of PVP can cause phase separation between SPEEK and PVP, forming a cross-interpenetrating cross-linked structure, thereby reducing the water content and swelling rate of the membrane, and improving the mechanical strength, durability and service life of the membrane; at the same time, a microporous structure is formed inside the membrane, the pore size and porosity are adjusted, and the selective permeability and permeability of the membrane are improved.

[0005] Ion exchange membrane is a special 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 external DC electric field to achieve the purpose of solution separation and purification. It is widely used in seawater desalination, wastewater treatment, food industry, pharmaceutical industry and other fields. From the perspective of energy conservation and environmental protection, conductivity is an important parameter for judging the performance of ion exchange membranes. In order to save energy and make it produce less energy consumption in practical applications, the most important thing is to improve the conductivity of composite ion exchange membranes. The low conductivity of SPEEK / PVP composite ion exchange membranes will seriously affect the industrial application of ion membranes and even cause great loss of energy. Therefore, improving the conductivity of composite membranes is a difficult problem that needs to be overcome at present.

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

[0007] Patent CN107596932A discloses a surface modification method for a SPEEK cation exchange membrane, which involves immersing a solidified SPEEK cation exchange membrane in a prepared CPAN dispersion and then taking it out and drying it to obtain a SPEEK cation exchange membrane with certain conductivity. However, this method does not solve the problem of uniform dispersion of CPAN particles, and the CPAN fixed by the adhesive is not sufficiently bonded to the SPEEK body, and the improvement in conductivity does not significantly improve the electrodialysis effect.

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

[0009] The present invention provides a composite cation exchange membrane and its preparation method and application. The composite cation exchange membrane has a good water content, a good swelling rate, high mechanical strength and high conductivity, can be used for electrodialysis water treatment, and can also recycle and reuse printing and dyeing wastewater to achieve brackish water desalination and salt concentration.

[0010] In order to achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for preparing a composite cation exchange membrane, comprising: 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 500,000g / 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 S3 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.

[0011] The present application uses polyetheretherketone as a skeleton and 98% concentrated sulfuric acid as a sulfonating agent to prepare sulfonated polyetheretherketone. Then, the sulfonated polyetheretherketone is blended with polyvinylpyrrolidone with a hydrophilic and hydrophobic structure. Flexible polyvinylpyrrolidone and sulfonated polyetheretherketone are used to form a cross-interpenetrating three-dimensional cross-linked network to improve the water content and swelling rate of sulfonated polyetheretherketone. On this basis, polyaniline with conductive properties is introduced to react with the sulfonic acid group on the sulfonated polyetheretherketone to generate a dense composite cation exchange membrane.

[0012] At the same time, the molecular weight of polyvinyl pyrrolidone and polyaniline introduced is controlled to help improve the dispersion of polyaniline in the cross-interpenetrating three-dimensional cross-linked 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-dispersed liquid rather than a SPEEK / PVP composite membrane to strengthen the interaction between polyaniline, polyvinyl pyrrolidone, and sulfonated polyetheretherketone in liquid form. Secondly, the uniform dispersion of polyaniline is further enhanced by slowly dripping polyaniline under ultrasonic conditions. Under the joint action of the above three dispersion means, the present application can achieve a composite cation exchange membrane with better mechanical properties and conductivity while achieving uniform dispersion of polyaniline in the composite cation exchange membrane.

[0013] In summary, the composite cation exchange membrane prepared in the present application has the functions of both polyvinyl pyrrolidone and polyaniline. On the one hand, it has a better water content and a better swelling rate. On the other hand, it has higher mechanical strength and higher conductivity. It is suitable for electrodialysis water treatment, can recycle and reuse printing and dyeing wastewater, and realize the desalination of brackish water and the resource disposal of salt concentration.

[0014] Preferably, in S1, the inert atmosphere is a nitrogen atmosphere.

[0015] Preferably, in S1, the mass volume ratio of the polyetheretherketone resin to the 98% sulfuric acid is 1 g:(5~25) mL.

[0016] Further preferably, in S1, the mass volume ratio of the polyetheretherketone resin to the 98% sulfuric acid is 1 g:(15~25) mL.

[0017] 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.

[0018] Further 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.

[0019] Preferably, in S2, the solvent is selected from at least one of water, anhydrous ethanol, dimethyl sulfoxide, N-methylpyrrolidone and N,N-dimethylformamide.

[0020] More preferably, the solvent is dimethyl sulfoxide.

[0021] Preferably, in S2, the molecular weight of polyvinyl pyrrolidone is 100,000 g / mol to 300,000 g / mol.

[0022] Preferably, in S2, the molecular weight of polyvinyl pyrrolidone is 200,000 g / mol to 400,000 g / mol.

[0023] Preferably, in S3, the molecular weight of polyaniline is 20,000 g / mol to 30,000 g / mol.

[0024] Preferably, in S3, the solvent in the solution containing polyaniline having a molecular weight of 20,000 g / mol to 50,000 g / mol is anhydrous ethanol.

[0025] Other solvents that can help polyaniline to be evenly dispersed can be used.

[0026] Preferably, in S3, the polyaniline is selected from at least one of conductive polyaniline, intrinsic polyaniline, sulfonic acid-doped polyaniline and emeraldine-based polyaniline.

[0027] Preferably, 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.

[0028] More preferably, 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:(20-40):100.

[0029] More preferably, 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:(30-35):100.

[0030] The addition of polyaniline material can improve the conductivity of the composite cation exchange membrane, increase the fixed charge density in the composite cation exchange membrane, thereby increasing the ion exchange capacity, improving the membrane's selective permeability and ion transfer rate. Polyaniline has a relatively high rigidity strength, and when blended with the pre-dispersed liquid (mainly SPEEK / PVP), it can also improve the mechanical strength, durability and thermal stability of the composite cation exchange membrane. Too little polyaniline will not significantly improve the conductivity of the composite cation exchange membrane, while too much polyaniline will cause it to agglomerate in the blended solution, thereby affecting the mechanical strength and conductivity of the composite cation exchange membrane.

[0031] Therefore, the selection of polyaniline specifications, the ratio of PVP, CPAN and SPEEK, the method of adding polyaniline, the molecular weight of polyaniline and polyvinyl pyrrolidone and other preparation conditions of the composite cation exchange membrane have a significant impact on the performance of the final composite cation exchange membrane.

[0032] Preferably, in S3, the power of the ultrasound is 100-200 W, the temperature of the ultrasound is 40-55° C., and the dripping speed is 30-50 drops / min.

[0033] Further preferably, 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 200 W, the temperature of the ultrasound is 55°C, and the dripping speed is (0.8~1) mL / min.

[0034] Preferably, in S3, the mixing time is 1 to 48 hours, and the mixing is completed at 25 to 80°C.

[0035] Preferably, in S3, the drying temperature is 90-160° C., and the drying time is at least 12 h.

[0036] The purpose of drying is to completely volatilize all solvents in the ionic liquid; the temperature and time can be selected as long as the solvent can be completely volatilized 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, and other ranges outside this range are within the protection scope of this application as long as the solvent can be completely volatilized.

[0037] The invention also provides a composite cation exchange membrane prepared by the preparation method.

[0038] The present invention also provides the application of the composite cation exchange membrane in the recycling and reuse of printing and dyeing wastewater, the desalination of brackish water or the concentration of salt.

[0039] Therefore, the present invention has the following beneficial effects: (1) The present invention utilizes the cross-interpenetrating network structure between polyvinyl pyrrolidone and sulfonated polyetheretherketone to help improve the water content and swelling rate of sulfonated polyetheretherketone, and introduces polyaniline to solve the problem of poor conductivity of SPEEK / PVP composite membrane. The composite cation exchange membrane finally obtained has better water content, better swelling rate, 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 to achieve desalination of brackish water and salt concentration.

[0040] (2) The present invention solves the problem of polyaniline dispersion by adopting three parallel means: first, using polyvinyl pyrrolidone of a specific molecular weight and polyaniline of a specific molecular weight; second, mixing with polyaniline in the form of a pre-dispersed liquid, thereby avoiding the problem of uneven dispersion that often occurs when mixing with polyaniline in the form of a membrane; third, slowly dripping polyaniline under ultrasonic conditions, so that polyaniline can be evenly dispersed in the composite cation exchange membrane. The three means help polyaniline to be better dispersed in the cross-interpenetrating network structure, thereby obtaining a composite cation exchange membrane with higher conductivity and mechanical strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is the hydrogen nuclear magnetic resonance spectrum of the SPEEK film of Comparative Example 1; Figure 2 for Figure 1 A partial enlarged view of the dotted line portion; Figure 3 This is a comparison chart of infrared characteristic curves; Figure 4 are SEM comparison diagrams, wherein a is a surface diagram of the SPEEK / PVP membrane of Comparative Example 2, b is a cross-sectional diagram of the SPEEK / PVP membrane of Comparative Example 2, c is a surface diagram of the SPEEK / PVP / CPAN membrane of Example 1, and d is a cross-sectional diagram of the SPEEK / PVP / CPAN membrane of Example 1; Figure 5 Element distribution diagram of the SPEEK / PVP / CPAN composite membrane of Example 1, wherein a is the C element, b is the O element, and c is the S element; Figure 6 This is the TGA curve of the SPEEK / PVP / CPAN composite membrane of Example 1. DETAILED DESCRIPTION

[0042] The present invention is 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 description are generally only embodiments of a part of the present invention, rather than all embodiments. Therefore, based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work should fall within the scope of protection of the present invention.

[0043] All reagents in this section were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. and were used directly without further processing.

[0044] [Example] Example 1 S1. Under nitrogen atmosphere, 10 g of polyetheretherketone resin and 150 mL of 98% sulfuric acid were added to a three-necked round-bottom flask. The mixture was stirred in a 55°C water bath at a stirring speed of 500 r / min. After sulfonation reaction for 6 h, sulfonated polyetheretherketone (SPEEK) was obtained.

[0045] S2. Add 7.5 g of SPEEK and 50 mL of dimethyl sulfoxide into a three-necked round-bottom flask, disperse by ultrasonic at 55°C for 30 min, then add 2.5 g of polyvinyl pyrrolidone with a molecular weight of 200,000 g / mol, and mix to obtain a pre-dispersion solution.

[0046] S3. A solution containing conductive polyaniline with a molecular weight of 20,000 g / mol was prepared by adding 0.075 g of conductive polyaniline with a molecular weight of 20,000 g / mol to 25 mL of anhydrous ethanol, ultrasonically treating for 30 min and then ultrasonically treating for another 1 h.

[0047] S4. Under 200 W ultrasonic state, all the amount of the solution containing conductive polyaniline with a molecular weight of 20,000 g / mol in S3 was dripped into the pre-dispersed liquid at a dripping rate of 1 mL / min. The ionic liquid was ultrasonically mixed at 55°C for 3 h to obtain the ionic liquid. The ionic liquid was spread onto a glass plate by a casting method and dried at 130°C overnight (about 18 h) until the solvent in the ionic liquid was completely evaporated to obtain a dense dark blue film, i.e., a composite cation exchange membrane, denoted as SPEEK / PVP / CPAN.

[0048] Comparative Example 1 Under nitrogen atmosphere, 10 g of polyetheretherketone resin and 150 mL of 98% sulfuric acid were added to a three-necked round-bottom flask. The mixture was stirred in a 55°C water bath at a stirring speed of 500 r / min. After 6 h of sulfonation reaction, sulfonated polyetheretherketone was obtained, which was recorded as SPEEK.

[0049] Comparative Example 2 S1. Under nitrogen atmosphere, 10 g of polyetheretherketone resin and 150 mL of 98% sulfuric acid were added to a three-necked round-bottom flask. The mixture was stirred in a 55°C water bath at a stirring speed of 500 r / min. After sulfonation reaction for 6 h, sulfonated polyetheretherketone (SPEEK) was obtained.

[0050] S2. Add 7.5 g of SPEEK and 50 mL of dimethyl sulfoxide into a three-necked round-bottom flask, disperse ultrasonically at 55°C for 30 min, then add 2.5 g of polyvinyl pyrrolidone with a molecular weight of 200,000 g / mol, and mix to obtain an ionic liquid.

[0051] S3. Spread the ionic liquid onto a glass plate by a casting method and dry it at 130°C overnight (about 18 h) until the solvent in the ionic liquid is completely evaporated to obtain a composite cation exchange membrane, which is denoted as SPEEK / PVP.

[0052] Comparative Example 3 This comparative example is substantially the same as Example 1, except that the molecular weight of polyvinyl pyrrolidone is 58,000 g / mol.

[0053] Comparative Example 4 This comparative example is substantially the same as Example 1, except that the molecular weight of polyvinyl pyrrolidone is 600,000 g / mol.

[0054] Comparative Example 5 This comparative example is substantially the same as Example 1, except that the molecular weight of the conductive polyaniline is 10,000 g / mol.

[0055] Comparative Example 6 This comparative example is substantially the same as Example 1, except that the molecular weight of the conductive polyaniline is 60,000 g / mol.

[0056] Comparative Example 7 S1. Under nitrogen atmosphere, 10 g of polyetheretherketone resin and 150 mL of 98% sulfuric acid were added to a three-necked round-bottom flask. The mixture was stirred in a 55°C water bath at a stirring speed of 500 r / min. After sulfonation reaction for 6 h, sulfonated polyetheretherketone (SPEEK) was obtained.

[0057] S2. Add 7.5 g SPEEK and 50 mL dimethyl sulfoxide into a three-necked round-bottom flask, ultrasonically disperse at 55°C for 30 min, then add 2.5 g polyvinyl pyrrolidone with a molecular weight of 200,000 g / mol, and mix to obtain a pre-dispersion solution. Spread the pre-dispersion solution onto a glass plate by a casting method and dry it at 130°C overnight (about 18 h) until the solvent in the pre-dispersion solution is completely evaporated to obtain a SPEEK / PVP composite film.

[0058] S3. A solution containing conductive polyaniline with a molecular weight of 20,000 g / mol was prepared by adding 0.075 g of conductive polyaniline with a molecular weight of 20,000 g / mol to 25 mL of anhydrous ethanol, ultrasonically treating for 30 min and then ultrasonically treating for another 1 h.

[0059] S4. Under 200 W ultrasonic state, the SPEEK / PVP composite membrane was placed in the entire amount of the solution containing conductive polyaniline with a molecular weight of 20,000 g / mol in S3, and ultrasonicated at 55°C for 3 h. Then, it was dried at 130°C overnight (about 18 h) until the solvent was completely evaporated to obtain a composite cation exchange membrane.

[0060] Comparative Example 8 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.

[0061] Comparative Example 9 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).

[0062]

Performance test

[0063] ②Methods for measuring mechanical properties 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. The samples were dried in a vacuum drying oven at 60 ° C and taken out after 12 hours. The gauge length, thickness and width of the samples were measured respectively. The mechanical properties of the samples were tested at room temperature using a biaxial tensile tester produced by Kato-Tech Company of Japan. During the test, the tensile speed was controlled at 20.000 mm / min, and the tensile sensor was selected as 100.0 kg. After the test was completed, the elongation at break, tensile strength and other data were recorded.

[0064] 1. Structural Characterization The sulfonated SPEEK was characterized by hydrogen nuclear magnetic resonance spectroscopy. Figure 1 The results show that the sulfonation degree of SPEEK is about 62%, which proves that the method provided in this application successfully completes the sulfonation. Then, the surface and cross-section of 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 element distribution results show that polyaniline is uniformly dispersed in the composite cation exchange membrane and forms a uniform dispersed phase. Figure 6 Figure 3 is the thermal weight loss curve of SPEEK / PVP / CPAN composite membrane. It can be observed that the thermal weight loss of the composite membrane can be divided into several stages. The first stage is water and solvent, the second stage is the decomposition of sulfonic acid groups and polyaniline, and the third stage is the decomposition of the polymer main chain. Generally speaking, the composite membrane has good stability.

[0065] 2. Performance Characterization The water content, swelling ratio, elongation at break, breaking strength, ion exchange capacity, membrane surface resistance and ion selective permeability of the membranes prepared in Example 1 and Comparative Examples 1 to 8 were measured, and the results are shown in Table 1.

[0066] Table 1 Performance comparison table

[0067] Observing the data in Table 1, it can be seen that the addition of PVP significantly reduces the water content and swelling rate of the composite cation exchange membrane. The addition of CPAN 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 in the membrane. These conductive paths can significantly improve the conductivity of the membrane, making it easier for ions to be transmitted through the membrane material, increasing the speed of ion transmission, and helping to improve the conductivity of the membrane and reduce the surface resistance of the membrane. It is worth noting that the selection of CPAN molecular weight, the selection of PVP molecular weight, and the differences in membrane preparation methods lead to poor dispersibility of CPAN in the composite cation exchange membrane, which also leads to a decrease in conductivity. Among them, the selection of CPAN molecular weight and the selection of PVP molecular weight are the most critical for preparing membranes 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 S3 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, intrinsic polyaniline, sulfonic acid-doped polyaniline and emeraldine-based polyaniline.

7. 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.

8. 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.

9. The composite cation exchange membrane obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the composite cation exchange membrane as claimed in claim 9 in the recycling and reuse of printing and dyeing wastewater, desalination of brackish water or concentration of salt.

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