A polymer, a preparation method thereof, and a cation exchange membrane

Abstract

The present invention discloses a polymer, a preparation method thereof, and a cation exchange membrane, belonging to the technical field of ion exchange membranes. The structure of the polymer is shown in Formula 1, Formula 2 or Formula 3; wherein, m, n, x, y, a, b, c, d are degrees of polymerization; m is selected from 1, 1≤n≤5; x is selected from 1, y = 5; 0.4≤a≤1, 1≤b≤5, c is selected from 1 - a, d is selected from 5 - b. The cation exchange membrane prepared from the polymer is a homogeneous membrane, having a high cation flux, a low membrane resistance, and a long service life. The preparation method of the cation exchange membrane has a simple process, a short reaction period, mild conditions, and simple post-treatment, significantly reducing the production cost and being suitable for large-scale industrial production. #imgabs0#Formula 1#imgabs1#Formula 2#imgabs2#Formula 3.

Description

Technical Field

[0001] The present invention relates to the technical field of ion exchange membranes, and in particular to a polymer, a preparation method thereof, and a cation exchange membrane. Background Art

[0002] Electrodialysis technology is widely used in the fields of energy, chemical production, pharmaceutical purification, water treatment, etc. With an externally applied electric field as the driving force, ions migrate directionally and selectively pass through the ion exchange membrane to separate the solution electrolyte. Among them, the ion exchange membrane is an important membrane component device that determines the quality of electrodialysis separation performance. Currently, the common commercial cation exchange membranes for electrodialysis water treatment on the market mainly include perfluorosulfonic acid type, polysulfone type, polyether ketone type and other polymer membrane materials. They generally have problems such as high price, complex preparation process, and unsatisfactory dimensional stability, mechanical strength, and ion separation performance, which greatly limit their application in many important fields. Therefore, it is urgent for domestic and foreign researchers to explore the synthesis of cation exchange membranes with low cost, simple process, industrial production, good mechanical properties and ion separation performance.

[0003] The cation exchange membrane is composed of a polymer backbone, a negatively charged acidic active group, and a positively charged counter ion. It can be divided into main-chain type and side-chain type cation exchange membranes according to the connection mode between the active group and the polymer backbone. When the negatively charged functional group is directly linked to the main-chain structural unit, it is a main-chain type cation exchange membrane, which is the main membrane material in the initial stage of the development of homogeneous cation exchange membranes; when the negatively charged functional group is linked to the main-chain structural unit through a spacer group or the group exists in the graft chain, it is a side-chain type cation exchange membrane. In comparison, the side-chain type cation exchange membrane has a higher mobility of the active group, which is conducive to the aggregation of ionic groups, forms a microphase separation structure with the rigid hydrophobic main chain, constructs an interpenetrating ion channel, and has more efficient ion transport and current conduction capabilities. Such membrane materials can also further optimize the membrane performance through various modification methods such as regulating the side-chain length, distribution, and connection mode with the main chain, and have gradually become the research and development focus in the field of ion exchange membranes in recent years.

[0004] Patent CN113522043A discloses a homogeneous cation exchange membrane for anionic surfactants, which provides negatively charged functional groups through fatty anionic surfactants, forms a good homogeneous system with polymers under the action of solubilizers, and prepares cation exchange membranes through defoaming, constant temperature storage, scraping, drying, and peeling, and is applied to the field of electrodialysis concentration. Patent CN113426496A discloses a composite cation exchange membrane preparation process using polyvinylidene fluoride and phthalimide as precursors, preparing a blend membrane on a mesh cloth, and then sulfonating with 4,4'-diaminostilbene-2,2'-disulfonic acid. The ion channels constructed by adjacent sulfonated ion exchange resins are used to achieve ion transport, and the phase separation between the ion exchange functional material and the substrate is alleviated by blending the hydrophobic precursor and the binder, improving the electrochemical performance of the cation exchange membrane. Patent CN108067102A discloses a cation exchange membrane using a microporous membrane as a support material, blending and filling the pores with comonomers, crosslinking agents, and initiators, and polymerizing at high temperature. This membrane has a semi-interpenetrating network structure, promotes the selective transport of ions by filling functional polymers, and at the same time uses porous matrices to inhibit its water absorption and swelling, improving the dimensional stability and mechanical properties of the membrane material, and is suitable for electrodialysis. However, such preparation processes usually require a large amount of organic solvents, there are certain toxicity risks, the process is complex, the base membrane and polymer electrolyte need to be prepared step by step, and the operating energy consumption is high, which is not conducive to batch production.

[0005] Currently, cation exchange membranes mostly have problems such as poor stability, easy breakage, complex synthesis processes, and high costs, which are not conducive to industrial production applications. Therefore, it is of great significance to research and develop a side-chain sulfonic acid type cation exchange membrane material with good mechanical properties and ion separation properties, and low cost, low energy consumption, simple preparation process, and suitable for industrial production for electrodialysis desalination. Summary of the Invention

[0006] In view of this, the technical problem to be solved by the present invention is to provide a polymer, its preparation method, and a cation exchange membrane. The cation exchange membrane prepared from the polymer has a high cation flux, a low membrane resistance, as well as good mechanical properties, ion separation properties, and chemical stability.

[0007] To achieve the above objectives, the technical solutions adopted by the present invention are as follows:

[0008] The present invention provides a polymer, the structure of which is shown in Formula 1, Formula 2, or Formula 3:

[0009] Formula 1;

[0010] Formula 2;

[0011] Formula 3;

[0012] Among them, m, n, x, y, a, b, c, and d are degrees of polymerization;

[0013] Preferably, m is selected from 1, and 1 ≤ n ≤ 5;

[0014] Preferably, x is selected from 1, and y = 5;

[0015] Preferably, 0.4 ≤ a ≤ 1, 1 ≤ b ≤ 5, c is selected from 1 - a, and d is selected from 5 - b.

[0016] More preferably in the present invention, m is selected from 1, and 1 ≤ n ≤ 3;

[0017] More preferably, x is selected from 1, and y = 5;

[0018] More preferably, c is selected from 1 - a, d is selected from 5 - b, 0.6 ≤ a ≤ 1, and 3 ≤ b ≤ 5.

[0019] Further preferably in the present invention, the polymer has any one of the following structures:

[0020] 、

[0021] 、

[0022] 、

[0023] 、

[0024] 、

[0025] 、 、

[0026] 。

[0027] The present invention also provides a method for preparing the above polymer, including the following steps:

[0028] Mix 2,2 - bis(3 - sulfonatopropoxy)biphenyl disodium with biphenyl and trifluoroacetone, and carry out a polyhydroxyalkylation reaction under the catalysis of trifluoromethanesulfonic acid to prepare the polymer shown in Formula 1;

[0029] Alternatively, mix 2,2 - bis(3 - sulfonatopropoxy)biphenyl disodium with 2,2'-dihydroxybiphenyl and indole - 2,3 - dione, and carry out a polyhydroxyalkylation reaction under the action of trifluoroacetic acid and trifluoromethanesulfonic acid to prepare the polymer shown in Formula 2;

[0030] Alternatively, sodium 2,2-bis(3-sulfopropyl)biphenyl-4,4'-disulfonate, 2,2'-dihydroxybiphenyl, and indole-2,3-dione are mixed and subjected to a polyhydroxyalkylation reaction under the action of trifluoroacetic acid and trifluoromethanesulfonic acid to first obtain the polymer shown in Formula 2, and then the polymer shown in Formula 2 is mixed with sodium tert-butoxide and octanoyl chloride and heated to prepare the polymer shown in Formula 3.

[0031] The preparation methods of the above Formula 1, Formula 2, or Formula 3 use sodium 2,2-bis(3-sulfopropyl)biphenyl-4,4'-disulfonate (DSOBP) as a functional monomer, and biphenyl, trifluoroacetone, or 2,2'-dihydroxybiphenyl and indole-2,3-dione as comonomers. Based on the polyalkylation reaction mechanism under the catalysis of trifluoromethanesulfonic acid or the combined action of trifluoroacetic acid and trifluoromethanesulfonic acid, a strategy of sulfonation first and then polymerization is adopted. Trifluoromethanesulfonic acid is used to dissolve the functional monomer DSOBP, and at the same time, trifluoromethanesulfonic acid acts as an electrophilic activating reagent to catalyze the polyhydroxyalkylation reaction, so that the functional group (sulfonic acid group) is connected to the polymer backbone through a chemical bond and is not easily detached, and a side-chain sulfonic acid-type polymer is obtained.

[0032] The polymers shown in Formula 1, Formula 2, or Formula 3 use a hydrophobic aryl group as a supporting skeleton and self-assemble with hydrophilic sulfonic acid groups to form interpenetrating ion clusters, forming a microphase separation structure. Moreover, the preparation method uses DSOBP as a functional monomer (its structure is shown below), which overcomes the problems of complicated steps, high cost, and complex post-treatment in sulfonation after polymerization.

[0033] 。

[0034] In addition, the preparation method also realizes precise control of the relative position and content of the sulfonic acid groups in the polymers shown in Formula 1, Formula 2, or Formula 3 by designing the structure of the sulfonated monomer in the polymer and regulating the addition ratio of the sulfonated monomer, promoting the uniform dispersion of the negatively charged sulfonic acid groups on the polymer backbone.

[0035] Preferably, when preparing the polymer shown in Formula 1, the molar ratio of sodium 2,2-bis(3-sulfopropyl)biphenyl-4,4'-disulfonate to biphenyl is 1:(1.5 - 3); in some specific embodiments of the present invention, it is preferably 1:1.5.

[0036] Preferably, the molar ratio of the sum of the moles of sodium 2,2-bis(3-sulfopropyl)biphenyl-4,4'-disulfonate and biphenyl to the mole of trifluoroacetone is 1:(1.1 - 1.3); in some specific embodiments of the present invention, it is preferably 1:1.2.

[0037] Preferably, the dosage ratio of trifluoromethanesulfonic acid to sodium 2,2-bis(3-sulfopropyl)biphenyl-4,4'-disulfonate is (3.4 - 3.7) mL:1 mmol. In some specific embodiments of the present invention, it is preferably 3.54 mL:1 mmol.

[0038] Preferably, when preparing the polymer shown in Formula 2, the molar ratio of disodium 2,2-bis(3-sulfonatopropoxy)biphenyl to 2,2'-dihydroxybiphenyl is 1:(4 - 6); in some specific embodiments of the present invention, it is preferably 1:5.

[0039] Preferably, the molar ratio of disodium 2,2-bis(3-sulfonatopropoxy)biphenyl to indole-2,3-dione is 1:(6 - 7); in some specific embodiments of the present invention, it is preferably 1:6.6.

[0040] Preferably, the dosage ratio of trifluoromethanesulfonic acid to disodium 2,2-bis(3-sulfonatopropoxy)biphenyl is (4.4 - 4.6) mL:1 mmol. In some specific embodiments of the present invention, it is preferably 4.5 mL:1 mmol.

[0041] The polymer shown in Formula 2 introduces phenolic hydroxyl and secondary amine group active sites on the main chain. Based on the esterification reaction, the hydroxyl group on the main chain reacts with alkyl acyl chloride to obtain the polymer shown in Formula 3 with an alkyl side chain. The polymer shown in Formula 3 adjusts the hydrophilicity and hydrophobicity of the polymer by incorporating different contents of alkyl side chains.

[0042] In some specific embodiments of the present invention, the polymer shown in Formula 3 is prepared by reacting the main chain hydroxyl group of the polymer shown in Formula 2 with octanoyl chloride under alkaline conditions.

[0043] Preferably, when preparing the polymer shown in Formula 3, the molar ratio of the polymer shown in Formula 2 to octanoyl chloride is 1:(1.2 - 2.0). In some specific embodiments of the present invention, it is preferably 1:1.2.

[0044] Preferably, when preparing the polymer shown in Formula 3, the temperature of the heating reaction is 75°C - 85°C; more preferably 80°C.

[0045] Among them, the preparation of the polymer shown in Formula 1 is carried out in a mixed solution of trifluoromethanesulfonic acid and dichloromethane. Preferably, disodium 2,2-bis(3-sulfonatopropoxy)biphenyl and biphenyl are first dissolved in the mixed solution of trifluoromethanesulfonic acid and dichloromethane to obtain a mixed system S1, and then trifluoroacetone is dissolved in dichloromethane and the mixture of the two is added to the above mixed system S1 for polyhydroxyalkylation reaction.

[0046] Dissolving trifluoroacetone in dichloromethane aims to slow down the evaporation rate of trifluoroacetone and increase the solution viscosity to facilitate the control of the dropping rate.

[0047] The polymer shown in Formula 1 is a white fibrous polymer.

[0048] The preparation of the polymer shown in the above formula 2 is carried out in a mixed solution of trifluoromethanesulfonic acid, trifluoroacetic acid and dichloromethane. Preferably, first, disodium 2,2-bis(3-sulfonatopropoxy)biphenyl, 2,2'-dihydroxybiphenyl and indole-2,3-dione are dissolved in a mixed solution of trifluoroacetic acid and dichloromethane to obtain a mixed system S2, and then trifluoromethanesulfonic acid is added to the mixed system S2 for polyhydroxyalkylation reaction. The polymer shown in the formula 2 is a yellow fibrous polymer.

[0049] The addition of the above-mentioned mixture of trifluoroacetone and dichloromethane and trifluoromethanesulfonic acid is preferably carried out by dropwise addition under an ice bath condition.

[0050] The time of the dropwise addition is preferably 0.33 - 1 h. After the dropwise addition is completed, the reaction is carried out at room temperature, and the room temperature is preferably 10 - 30°C. The time of the reaction is preferably 0.25 - 4 h.

[0051] The preparation of the polymer shown in the above formula 3 is carried out by mixing with sodium tert-butoxide and octanoyl chloride on the basis of the polymer shown in the formula 2 and heating. The present invention also provides a cation exchange membrane, which is prepared by dissolving the above polymer or the polymer prepared by the above preparation method to obtain a membrane solution and then heating and shaping.

[0052] The functional groups (sulfonic acid groups) in the polymers shown in the above formula 1, formula 2 or formula 3 are connected to the polymer main chain through chemical bonds and are not easy to fall off, so that the prepared cation exchange membrane has a long service life.

[0053] The negatively charged sulfonic acid groups in the polymers shown in the formula 1, formula 2 or formula 3 are uniformly dispersed on the polymer main chain, so that the prepared cation exchange membrane has a homogeneous structure, and further makes the cation exchange membrane have a high cation flux and a low membrane resistance.

[0054] Moreover, the polymers shown in the formula 1, formula 2 or formula 3 form a hydrophilic-hydrophobic phase separation structure through chain segment self-assembly, thereby promoting the ion transmembrane transport of the cation exchange membrane prepared by the polymer, and realizing the low swelling and high proton conductivity of the cation exchange membrane. And, the polarity difference of the polymer promotes the negatively charged sulfonic acid groups to aggregate in the membrane of the cation exchange membrane to form ion clusters and highly hydrophilic continuous hydration channels, which promote the migration of cations in the aqueous solution and at the same time hinder the passage of anions, realizing the ion selective separation of the membrane material.

[0055] In addition, based on the difference in hydration energy between different ions, the polymer shown in the formula 3 can adjust the hydrophilic-hydrophobic property of the polymer by introducing different contents of alkyl side chains, further reducing the water content and swelling property of the prepared cation exchange membrane, promoting the formation of the microphase separation structure of the main side chain of the membrane material, improving the ion separation performance and dimensional stability of the cation exchange membrane, and further realizing more efficient ion separation.

[0056] In the cation exchange membrane of the present invention, the PDSB-x series cation exchange membranes are prepared from the polymer shown in Formula 1, and the SPB-x series cation exchange membranes are prepared from the polymer shown in Formula 2 or Formula 3.

[0057] Both the PDSB-x series and SPB-x series cation exchange membranes have a hydrophobic aromatic group as the polymer backbone, ensuring the stability of the structure of the cation exchange membrane prepared from the polymer, endowing it with good mechanical properties and chemical stability, and being suitable for long-term stable electrodialysis desalination operation.

[0058] Among them, x in the SPB-x series cation exchange membrane represents the theoretical grafting rate, that is, the percentage of the grafted hydroxyl group containing an alkyl side chain in all the hydroxyl groups on the main chain. In Formula 3 of the present invention, x is equal to b / (b + d).

[0059] Preferably, the thickness of the cation exchange membrane of the present invention is 40 - 300 μm.

[0060] Preferably, the concentration of the polymer shown in Formula 1, Formula 2 or Formula 3 in the membrane solution is 5 wt% - 10 wt%.

[0061] Preferably, the solvent of the membrane solution is selected from dimethyl sulfoxide or N,N-dimethylformamide.

[0062] Preferably, the temperature of the heat setting is 65°C - 75°C.

[0063] Preferably, the time of the heat setting is 3 - 6 h.

[0064] The above cation exchange membrane further includes post-treatment after heat setting.

[0065] The post-treatment is: removing the membrane after heat setting and storing it in pure water or sodium chloride solution to obtain the cation exchange membrane.

[0066] The concentration of the sodium chloride solution is preferably 0.1 mol·L -1 .

[0067] Compared with the prior art, the polymer provided by the present invention has a structure as shown in Formula 1, Formula 2 or Formula 3; wherein, m, n, x, y, a, b, c, d are degrees of polymerization; m is selected from 1, 1≤n≤5; x is selected from 1, y = 5; 0.4≤a≤1, 1≤b≤5, c is selected from 1 - a, d is selected from 5 - b. The cation exchange membrane prepared from the polymer is a homogeneous membrane, which has a high cation flux, a low membrane resistance and a long service life. The preparation method of the cation exchange membrane has a simple process flow, a short reaction period, mild conditions and simple post-treatment, significantly reducing the production cost and being suitable for large-scale industrial production. Description of the Drawings

[0068] Figure 1 are the appearance diagrams and internal structure schematic diagrams of the cation exchange membranes described in Example 1 (Figure a), Example 5 (Figure b), and Example 6 (Figure c);

[0069] Figure 2 are the 1 1H NMR spectra of PDSB-2.5 (Figure a) and DSOBP (Figure b) prepared in Example 3;

[0070] Figure 3 are the infrared characterization results of the cation exchange membranes prepared in Examples 1-4 respectively;

[0071] Figure 4 are the AFM diagrams of the cation exchange membranes PDSB-1.5, PDSB-2, PDSB-2.5, and PDSB-3 prepared in Examples 1-4 respectively;

[0072] Figure 5 is the comparative analysis of the NaCl salt concentration limit between the membrane (PDSB-2.5) prepared in Example 3 and the commercial CM-2 membrane. Figure a is the curve of conductivity changing with time, and Figure b is the curve of voltage changing during operation;

[0073] Figure 6 is the diagram of the desalination performance test device used for the cation exchange membranes prepared in Examples 1-4;

[0074] Figure 7 are the 1 1H NMR spectra of SPB-80% (Figure a) and SPB (Figure b) prepared in Example 7;

[0075] Figure 8 are the infrared characterization results of the cation exchange membranes prepared in Examples 5-8;

[0076] Figure 9 is the diagram of the desalination performance test device used for the membranes prepared in Examples 5-8. Detailed Embodiments

[0077] To further illustrate the present invention, the polymers provided by the present invention, their preparation methods, and cation exchange membranes will be described in detail below in conjunction with embodiments.

[0078] Example 1

[0079] The steps for preparing the cation exchange membrane are as follows:

[0080] (1) Preparation of PDSB-1.5: Weigh 7.52 g of the sulfonated diaryl monomer 2,2-bis(3-sulfonatopropoxy)biphenyl disodium (DSOBP) into a three-necked round-bottom flask, then add 56 mL of trifluoromethanesulfonic acid and 20 mL of dichloromethane. Insert an electric stirrer and start stirring at room temperature. After stirring until dissolved, add 3.60 g of biphenyl and continue stirring at room temperature until the solution is evenly mixed and there is no obvious layering. Place the three-necked flask in an ice bath. When the temperature stabilizes near 0 °C, slowly dropwise add a mixed solution of 5.32 g of trifluoroacetone and 20 mL of dichloromethane to the three-necked flask. After the addition is complete, remove the three-necked flask from the ice bath. After reacting at room temperature for 0.6 h, slowly drop the reaction solution into pure water, and a white fibrous product of PDSB-1.5 can be precipitated. Soak and rinse the product repeatedly with pure water to wash away the residual acid on the surface of the product. Take out the polymer, dry it, and obtain the polymer PDSB-1.5. Its structural formula is:

[0081] .

[0082] (2) Preparation of the membrane solution: Weigh 1.00 g of the polymer PDSB-1.5 into a 20 mL round-bottom flask, add 9.00 g of N,N-dimethylformamide to the flask, add a magnetic stir bar, and stir on a magnetic stirrer until dissolved to obtain the membrane solution.

[0083] (3) Preparation of the membrane: Take 5 mL of the membrane solution, evenly pour the membrane solution onto a glass plate, place the glass plate on a heating table, and heat-treat it at 70 °C for 3 h to form a membrane, thus obtaining the cation exchange membrane. Take out the membrane and place it in a 0.1 mol·L -1 sodium chloride solution for storage.

[0084] Example 2

[0085] The steps for preparing the cation exchange membrane are as follows:

[0086] (1) Preparation of PDSB-2: Use the same preparation method as in Example 1. The only difference is that the addition amounts of biphenyl and trifluoroacetone are adjusted to 4.80 g and 6.39 g, respectively.

[0087] The structural formula of PDSB-2 is:

[0088] .

[0089] (2) Preparation of the membrane solution and the membrane: The same preparation method as in Example 1 was used.

[0090] Example 3

[0091] The steps for preparing the cation exchange membrane are as follows:

[0092] (1) Preparation of PDSB-2.5: The same preparation method as in Example 1 was used. The only difference is that the addition amounts of biphenyl and trifluoroacetone were adjusted to 6.10 g and 7.45 g respectively.

[0093] (2) Preparation of the membrane solution and the membrane: The same preparation method as in Example 1 was used.

[0094] The structural formula of PDSB-2.5 is:

[0095] .

[0096] The salt concentration experiment was carried out using the membrane material prepared in Example 3 to verify the actual concentration effect of the membrane material. The experimental results are as Figure 5 shown. At the same time, the commercial membrane CM-2 was tested for comparison. After 100 min of electrodialysis experiment, the conductivity in the concentration chamber first increased linearly and then gradually stabilized, reaching the concentration limit, which was comparable to that of the commercial membrane CM-2. The salt concentration in the desalination chamber remained almost unchanged, the membrane stack resistance changed little during the electrodialysis operation, and the voltage tended to be stable. During the operation of the membrane stack, the volume of the concentration chamber gradually increased, and the growth rate of the salt concentration in the concentration chamber gradually decreased. This is because as the NaCl concentration in the concentration chamber continuously increased, the concentration difference between the concentration and desalination chambers increased, and the phenomena of forward osmosis of water molecules and reverse diffusion of ions were aggravated. When the electromigration of the target ions and the reverse diffusion reached equilibrium, the salt concentration in the concentration chamber remained unchanged and reached the concentration limit.

[0097] In addition, although PDSB-2.5 showed comparable concentration performance to the commercial membrane in the later stage of concentration, the overall operating voltage of the membrane material prepared in Example 3 was slightly lower than that of the CM-2 membrane. This means that the membrane material prepared in Example 3 will have lower energy consumption performance during actual operation.

[0098] Example 4

[0099] The steps for preparing the cation exchange membrane are as follows:

[0100] (1) Preparation of PDSB-3: The same preparation method as in Example 1 was used. The only difference is that the addition amounts of biphenyl and trifluoroacetone were adjusted to 7.30 g and 8.52 g respectively.

[0101] (2) Preparation of the membrane solution and the membrane: The same preparation method as in Example 1 was used.

[0102] The structural formula of PDSB-3 is as follows:

[0103] .

[0104] The membrane materials prepared in the above Examples 1-4 are cation exchange membranes. They were respectively tested for the desalination performance of the membrane materials under the test conditions as Figure 6 shown at a current density of 15 mA·cm -2 . The results are shown in Table 1. At the same time, the desalination performance of the commercial membrane CM-2 was tested by the same method for comparison. Moreover, the polymer PDSB-2.5 prepared in Example 3 was verified by nuclear magnetic resonance, and the results are as Figure 2 shown. In addition, the infrared spectra of the membrane materials prepared in the above Examples 1-4 were tested by a Fourier transform infrared spectrometer, and the results are as Figure 3 shown.

[0105] The above Figure 6 shown test conditions are specifically as follows:

[0106] Using an electrodialysis device, a desalination test was carried out on a 0.1 mol·L -2 NaCl solution at a current density of 15 mA·cm -1 for 25 min. The desalination performance of the PDSB-x series (x is 1.5 or 2 or 2.5 or 3) membrane materials was evaluated by comparing with the commercial membrane CM-2 in terms of desalination rate, salt flux, device energy consumption and current efficiency, where Figure 6 sodium sulfate in it is the electrode chamber solution and only serves to conduct the circuit.

[0107] Example 5

[0108] The steps for preparing the cation exchange membrane are as follows:

[0109] (1) Preparation of SPB: Weigh 4.74 g of the sulfonated diaryl monomer 2,2-bis(3-sulfonatopropoxy)biphenyl disodium (DSOBP) into a round-bottom three-necked flask, then add 45 mL of trifluoroacetic acid and 30 mL of dichloromethane. Insert an electric stirrer and start stirring at room temperature. After stirring until dissolved, add 9.31 g of 2,2'-dihydroxybiphenyl and 9.72 g of indole-2,3-dione, and continue stirring at room temperature until the solution is evenly mixed without obvious stratification. Place the three-necked flask in an ice bath. When the temperature is stable near 0 °C, slowly add 45 mL of trifluoromethanesulfonic acid to the three-necked flask. After the addition is completed, remove the three-necked flask from the ice bath. After reacting at room temperature for 0.25 h, slowly pour the reaction system into pure water, and a pale yellow fibrous product can be precipitated. The product was repeatedly soaked and rinsed with pure water to remove the residual acid and unreacted monomers on the surface of the product. Take out the polymer and dry it to obtain the polymer SPB, and its structural formula is:

[0110] 。

[0111] (2) Preparation of the membrane solution: Weigh 1.00 g of SPB into a 20 mL round-bottom flask, add 9.00 g of dimethyl sulfoxide to the flask, add a magnetic stir bar, and stir on a magnetic stirrer until dissolved to obtain the membrane solution.

[0112] (3) Preparation of the membrane: Take 5 mL of the membrane solution, pour the membrane solution evenly onto a glass plate, place the glass plate on a heating table, heat-treat at 65 °C for 3 h, then raise the temperature to 75 °C and heat for 3 h to obtain the cation exchange membrane. Take out the membrane and store it in a 0.1 mol·L -1 sodium chloride solution.

[0113] Example 6

[0114] The steps for preparing the cation exchange membrane are as follows:

[0115] (1) Preparation of SPB: Use the same preparation method as in Example 5.

[0116] (2) Preparation of SPB-60%: Weigh 4.55 g of SPB polymer into a round-bottom flask, add 60.45 g of dimethyl sulfoxide, insert an electric stirrer, start stirring at room temperature, wait until dissolved, add 1.57 g of sodium tert-butoxide, place the flask in a water bath, adjust the temperature to 80 °C, stir until there are no obvious solid particles, slowly drop 2.42 g of octanoyl chloride into the flask, and continue to react under the condition of heating in an 80 °C water bath for 24 h. After the reaction is completed, slowly pour the reaction solution into an aqueous hydrochloric acid solution to precipitate the white fibrous product of SPB-60%. Soak and rinse the product repeatedly with pure water to remove the acid, organic reagents and unreacted monomers remaining on the surface of the product. Take out the polymer and air-dry it at room temperature to remove the moisture to obtain the polymer SPB-60%, and its structural formula is:

[0117] 。

[0118] (3) Preparation of the membrane solution: Use the same preparation method as in Example 5.

[0119] (4) Preparation of the membrane: Take 5 mL of the membrane solution, pour the membrane solution evenly onto a polytetrafluoroethylene plate, set the heating table to heat at 65 °C for 4 h to obtain the cation exchange membrane. Take out the membrane and store it in a 0.1 mol·L -1 sodium chloride solution.

[0120] Figure 1Appearance diagrams and internal structure schematic diagrams of the cation exchange membranes described in Example 1 (Figure a), Example 5 (Figure b), and Example 6 (Figure c). The results show that the functional monomers in the membrane material are evenly distributed on the main chain, and the polymer chains form a comb-like structure, with a regular overall structure.

[0121] Example 7

[0122] The steps for preparing the cation exchange membrane are as follows:

[0123] (1) Preparation of SPB: The same preparation method as in Example 5 is used.

[0124] (2) Preparation of SPB-80%: The same preparation method as in Example 6 is used. The only difference is that 1.57 g of sodium tert-butoxide is replaced with 2.09 g of sodium tert-butoxide, and 2.42 g of octanoyl chloride is replaced with 3.22 g of octanoyl chloride.

[0125] (3) Preparation of the membrane solution: The same preparation method as in Example 5 is used.

[0126] (4) Preparation of the membrane: The same preparation method as in Example 6 is used.

[0127] The structural formula of SPB-80% is:

[0128] .

[0129] Example 8

[0130] The steps for preparing the cation exchange membrane are as follows:

[0131] (1) Preparation of SPB: The same preparation method as in Example 5 is used.

[0132] (2) Preparation of SPB-100%: The same preparation method as in Example 6 is used. The only difference is that 1.57 g of sodium tert-butoxide is replaced with 2.62 g of sodium tert-butoxide, and 2.42 g of octanoyl chloride is replaced with 4.03 g of octanoyl chloride.

[0133] (3) Preparation of the membrane solution: The same preparation method as in Example 5 is used.

[0134] (4) Preparation of the membrane: The same preparation method as in Example 6 is used.

[0135] The structural formula of SPB-100% is:

[0136] .

[0137] For the membrane materials, i.e., the cation exchange membranes, prepared in the above Examples 5 - 8, under the test conditions as shown in Figure 9 at 10 mA·cm -2The desalination performance of the membrane was tested at the current density, and the results are shown in Table 2. Meanwhile, the desalination performance of the commercial membrane CM-2 was tested by the same method for comparison. Moreover, the infrared spectrum of the membrane materials prepared in Examples 5-8 above was tested using a Fourier transform infrared spectrometer, as Figure 8 shown.

[0138] The above Figure 9 specific test conditions are as follows:

[0139] Using an electrodialysis device, a desalination test was carried out on a 0.1 mol·L -2 NaCl solution at a current density of 10 mA·cm -1 for 80 min. The desalination performance of the SPB and SPB-x series membrane materials was evaluated by comparing with the commercial membrane CM-2 in terms of desalination rate, salt flux, device energy consumption and current efficiency, where Figure 9 sodium sulfate in it is the anolyte and only serves to conduct the circuit.

[0140] Table 1 Test results of the desalination performance of the membrane materials prepared in Examples 1-4

[0141]

[0142] Note: The data obtained in Table 1 were measured under the following membrane stack conditions: the current density was 15 mA·cm -2 .

[0143] Rd (%) represents the desalination rate; J (mmol·m -2 ·s -1 ) represents the Na + flux; EC (kWh·kg -1 ) represents the energy consumption; η (%) represents the current efficiency.

[0144] Table 1 shows that by adjusting the contents of biphenyl and trifluoroacetone in the present invention, the relative content of the DSOBP monomer containing a sulfonic acid group in the polymer is changed, thereby changing the sulfonic acid group concentration. The membrane materials (cation exchange membranes) prepared in Examples 1-4 have a high desalination rate and Na + flux, as well as low energy consumption and current efficiency when the sulfonic acid group concentration is low. This is because the functional monomers in the membrane materials of the present invention are uniformly distributed on the main chain, and the polymer chains form a comb-like structure, and the overall structure is regular. Moreover, due to the formation of a microphase separation structure between the rigid aryl hydrophobic main chain (such as the benzene ring structure on the main chain) and the hydrophilic ion exchange group side chain (the side chain containing a sulfonic acid group), the construction of the ion transport membrane channels in the membrane is promoted, which is beneficial to ion transport. Furthermore, the desalination performance of the prepared PDSB-x series membrane materials is better than that of the commercial membrane CM-2, and the electrochemical performance is good, having certain industrial application value.

[0145] Table 2 Desalination performance test results of the membrane materials prepared in Examples 5 - 8

[0146]

[0147] Note: The membrane stack conditions for the data obtained in Table 2 are: current density is 10 mA·cm -2 。

[0148] Rd (%) represents the desalination rate; J (mmol·m -2 ·s -1 )represents the Na + flux; EC (kWh·kg -1 )represents the energy consumption; η (%) represents the current efficiency.

[0149] The results in Table 2 show that for the SPB - x series of membrane materials (Examples 6 - 8), the desalination rate increases with the increase of the octanoyl chloride grafting rate, the Na + flux is positively correlated with the octanoyl chloride grafting rate, and the current efficiency shows an upward trend with the increase of the octanoyl chloride grafting rate. This is because the graft modification of the hydrophobic alkyl side chain (alkyl side chain grafted through octanoyl chloride) reduces the water content, further promoting the microphase separation of the membrane material, constructing ion channels, and promoting cation transport. Among them, the SPB - 100% membrane has the most prominent electrodialysis desalination performance, with a desalination rate reaching 82.44%, while having a relatively high salt flux, low energy consumption (EC = 7.35 kWh·kg -1 ), and high current efficiency (η = 88.24%), all of which are superior to the commercial CM - 2 membrane, and have good application prospects in the field of electrodialysis seawater desalination and certain industrial application value. Although the membrane material prepared in Example 5 has a lower desalination rate and Na + flux than the commercial membrane CM - 2, its energy consumption and current efficiency are superior to those of the commercial membrane CM - 2. Therefore, the comprehensive advantages in various aspects indicate that the SPB - x series of cation exchange membranes prepared by the present invention have more excellent performance than the commercial membrane CM - 2.

[0150] The descriptions of the above embodiments are only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can still be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A polymer, characterized in that, The structure is as shown in Formula 2 or Formula 3: Formula 2; Formula 3; wherein, x, y, a, b, c, and d are the degree of polymerization; x is selected from 1 and y = 5; 0.4 ≤ a ≤ 1, 1 ≤ b ≤ 5, c is selected from 1 - a, and d is selected from 5 - b.

2. The polymer according to claim 1, characterized in that, Said x is selected from 1 and y = 5; Said c is selected from 1 - a, said d is selected from 5 - b, 0.6 ≤ a ≤ 1, and 3 ≤ b ≤ 5.

3. The polymer according to claim 1, wherein The polymer has any one of the following structures: 、 、 、 。 4. The preparation method of the polymer according to any one of claims 1 - 3, comprising the following steps: Mix sodium 2,2 - bis(3 - sulfopropoxy)biphenyl - 5,5'-disulfonate, 2,2'-dihydroxybiphenyl, and indole - 2,3 - dione, and carry out polyhydroxyalkylation reaction under the action of trifluoroacetic acid and trifluoromethanesulfonic acid to prepare the polymer shown in Formula 2; Alternatively, mix sodium 2,2 - bis(3 - sulfopropoxy)biphenyl - 5,5'-disulfonate, 2,2'-dihydroxybiphenyl, and indole - 2,3 - dione, and carry out polyhydroxyalkylation reaction under the action of trifluoroacetic acid and trifluoromethanesulfonic acid to first obtain the polymer shown in Formula 2, and then mix the polymer shown in Formula 2 with sodium tert - butoxide and octanoyl chloride, and carry out a heating reaction to prepare the polymer shown in Formula 3.

5. The preparation method according to claim 4, characterized in that, When preparing the polymer shown in Formula 2, the molar ratio of sodium 2,2 - bis(3 - sulfopropoxy)biphenyl - 5,5'-disulfonate to 2,2'-dihydroxybiphenyl is 1:5; The molar ratio of sodium 2,2 - bis(3 - sulfopropoxy)biphenyl - 5,5'-disulfonate to indole - 2,3 - dione is 1:(6 - 7); The dosage ratio of trifluoromethanesulfonic acid to sodium 2,2 - bis(3 - sulfopropoxy)biphenyl - 5,5'-disulfonate is (4.4 - 4.6) mL:1 mmol; When preparing the polymer shown in Formula 3, the molar ratio of the polymer shown in Formula 2 to octanoyl chloride is 1:(1.2 - 2).

6. The preparation method according to claim 4, characterized in that, When preparing the polymer shown in Formula 3, the temperature of the heating reaction is 75°C - 85°C.

7. A cation exchange membrane, characterized in that, The polymer prepared by the polymer according to any one of claims 1 - 3 or the preparation method according to any one of claims 4 - 6 is dissolved to obtain a membrane solution, and then prepared by heat setting.

8. The cation exchange membrane according to claim 7, characterized in that, The thickness of the cation exchange membrane is 40 - 300 μm.

9. The cation exchange membrane according to claim 7, wherein The concentration of the polymer shown in Formula 2 or Formula 3 in the membrane solution is 5 wt% - 10 wt%.

10. The cation exchange membrane according to claim 7, characterized in that, The solvent of the membrane solution is selected from dimethyl sulfoxide or N,N - dimethylformamide; The temperature of the heat setting is 65°C - 75°C.

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