A salt-splitting ion exchange membrane for electrodialysis and a method for preparing the same

Abstract

The application discloses a kind of salt ion exchange membrane for electrodialysis and preparation method thereof, cation exchange membrane is immersed in the buffer containing tannic acid and zwitterion diamine monomer, reaction is carried out at 0~60 ℃ for 0.5~60 h, obtain salt ion exchange membrane for electrodialysis.The application is formed by the Michael addition or Schiff base reaction between tannic acid molecule and zwitterion diamine monomer under weak alkaline condition, uniform, stable tannic acid / diamine zwitterion ultrathin coating is formed on the surface of cation exchange membrane.The application significantly improves Li + / Mg 2+ Selectivity. Preparation process is simple, environmental protection, strong universality, the modified cation exchange membrane prepared by the application has excellent Li + / Mg 2+ Selectivity, and can improve the anti-pollution of membrane, can be used for high magnesium lithium ratio brine electrodialysis method lithium extraction.

Description

Technical Field

[0001] This invention belongs to the field of selective electrodialysis and membrane technology, and relates to a salt-separating ion exchange membrane for electrodialysis and its preparation method. Background Technology

[0002] Mg 2+ With Li + Having similar atomic radii and chemical properties is the main difficulty and challenge in current lithium extraction technology from salt lakes.

[0003] Electrodialysis technology, with its advantages of convenient operation, high degree of continuity, and environmentally friendly process, has received widespread attention in lithium extraction from salt lakes in recent years. Its essence lies in using an electric field as a driving force to selectively pass ions through an exchange membrane, thereby achieving ion separation and enrichment. The ion exchange membrane is the core component of the electrodialysis device, and its performance directly determines the effectiveness of lithium extraction. However, the current manufacturing process of ion exchange membranes for lithium extraction via electrodialysis is complex, and their performance needs further improvement, which restricts the industrial application of lithium extraction via electrodialysis. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a salt-separating ion exchange membrane for electrodialysis and its preparation method, wherein the preparation method is simple and quick and the preparation process is green and environmentally friendly.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a salt-separating ion-exchange membrane for electrodialysis includes the following steps:

[0007] A cation exchange membrane is immersed in a buffer solution containing tannic acid and zwitterionic diamine monomer, and the reaction is carried out at 0–60 °C for 0.5–60 h to obtain a salt-separating ion exchange membrane for electrodialysis.

[0008] Furthermore, the zwitterionic diamine monomer is at least one of NO-containing zwitterionic diamine and N,N-bis(3-aminopropyl)methylamine propanesulfonic acid.

[0009] Furthermore, the structural formula of the NO compound zwitterionic diamine is as follows:

[0010]

[0011] Furthermore, the structural formula of N,N-bis(3-aminopropyl)methylamine propanesulfonic acid is as follows:

[0012]

[0013] Furthermore, the buffer solution containing tannic acid and zwitterionic diamine monomer is prepared by the following process:

[0014] Add tannic acid and zwitterionic diamine monomer to the buffer solution and mix thoroughly.

[0015] Furthermore, the buffer solution includes at least one of N,N-bis(2-hydroxyethyl)glycine buffer, tris(hydroxymethyl)aminomethane buffer, and phosphate buffer with a pH of 7 to 9.

[0016] Furthermore, by mass parts, the ratio of tannic acid, zwitterionic diamine monomer to buffer solution is 0.01–0.6 parts: 0.01–0.8 parts: 100 parts.

[0017] Furthermore, the reaction temperature is 25–50°C, and the time is 1–24 hours.

[0018] Furthermore, the cation exchange membrane can be a heterogeneous cation exchange membrane or a homogeneous cation exchange membrane.

[0019] A salt-separating ion exchange membrane for electrodialysis.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) In this invention, the co-deposition of tannic acid and zwitterionic diamine monomer is based on chemical covalent interaction. Compared with the surface modification process of polyelectrolyte layer self-assembly driven by electrostatic force, the coating obtained by this invention has better long-term stability.

[0022] (2) This invention utilizes the covalent deposition of tannic acid and zwitterionic diamine monomers to modify the surface of ion exchange membranes, which can form an ultra-thin coating with very low resistance on the surface of various membrane materials. It has the characteristics of universality and can be applied to the modification of various cation exchange membranes.

[0023] (3) The present invention introduces a zwitterionic structure with both cationic and anionic functional groups onto the surface of a cation exchange membrane. The zwitterionic modification can significantly improve the hydrophilicity of the membrane, block the direct contact between pollutants and the membrane surface, and improve the membrane’s antifouling properties.

[0024] (4) This invention uses water as a solvent, the materials used are safe and non-toxic, the preparation process is simple and environmentally friendly, and the resulting modified cation exchange membrane has good Li + / Mg 2+ It is selective and can be used for lithium extraction via electrodialysis from brines with a high magnesium-to-lithium ratio.

[0025] (5) This invention utilizes the Michael addition or Schiff base reaction between tannic acid molecules and zwitterionic diamine monomers under weakly alkaline conditions to form a uniform and stable ultrathin tannic acid / diamine zwitterionic coating on the surface of a conventional cation exchange membrane. This invention overcomes the limitations of existing commercially available cation exchange membranes and significantly improves the efficiency of Li...+ / Mg 2+ Selectivity. Furthermore, the preparation process is simple, environmentally friendly, and widely applicable. The modified cation exchange membrane obtained by this invention exhibits excellent Li... + / Mg 2+ It is selective and can improve the membrane's antifouling properties, making it suitable for lithium extraction via electrodialysis from brines with a high magnesium-to-lithium ratio. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0027] Figure 1 This is a schematic diagram of the composition of the tannic acid / zwitterionic diamine modified coating in this invention. Detailed Implementation

[0028] To enable those skilled in the art to better understand the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, not all embodiments, and are not intended to limit the scope of the present invention. Furthermore, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion regarding the concepts disclosed in the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0029] The present invention discloses a method for preparing a salt-separating ion exchange membrane for electrodialysis, comprising the following steps:

[0030] S1. Prepare a buffer solution with a pH of 6 to 10;

[0031] S2. Dissolve 0.01 to 0.6 parts of tannic acid and 0.01 to 0.8 parts of zwitterionic diamine monomer in the above buffer solution to obtain a buffer solution containing tannic acid and zwitterionic diamine monomer;

[0032] S3. Immerse the commercial cation exchange membrane in a buffer solution containing tannic acid and zwitterionic diamine monomer, and shake it at a constant speed in a water bath shaker at 0-60°C for 0.5-60 h; clean it with deionizer to obtain a salt-separating ion exchange membrane for electrodialysis, and store it for later use.

[0033] Preferably, the buffer solution in step (1) above includes at least one of N,N-bis(2-hydroxyethyl)glycine (Bicine) buffer, tris(hydroxymethyl)aminomethane (Tris) buffer, and phosphate buffer (PBS).

[0034] As a further preferred option, the pH of the buffer solution in step (1) above is 7 to 9.

[0035] Preferably, the buffer solution in step (2) above includes at least one of N,N-bis(2-hydroxyethyl)glycine (Bicine) buffer, Tris (Tris) buffer, and phosphate buffer (PBS).

[0036] As a further preferred embodiment, the amount of buffer solution used in step (1) above is 100 parts by mass, the amount of tannic acid is 0.05 to 0.4 parts, and the amount of zwitterionic diamine monomer is 0.05 to 0.6 parts.

[0037] Preferably, in step (3) above, the temperature of the shaking water bath is 25–50°C, and the reaction time is 1–24 h. A higher water bath temperature will help accelerate the reaction rate of tannic acid and zwitterionic diamine monomer, but will increase energy consumption; a longer reaction time will help increase the deposition of tannic acid and zwitterionic diamine monomer on the cation membrane surface, but will increase time costs.

[0038] As a further preferred option, the temperature of the shaking water bath in step (3) above is 30-40°C, and the reaction time is 12-24 hours.

[0039] The conventional cation exchange membrane can be a commercially available heterogeneous cation exchange membrane or a homogeneous cation exchange membrane.

[0040] The zwitterionic diamine monomer is at least one of NO-based zwitterionic diamine (DNMAO) and N,N-bis(3-aminopropyl)methylamine propane sulfonic acid (Z-DNMA).

[0041] The structural formula of the NO compound zwitterionic diamine (DNMAO) is as follows:

[0042]

[0043] The structural formula of N,N-bis(3-aminopropyl)methylaminopropanesulfonic acid (Z-DNMA) is as follows:

[0044]

[0045] The principle of this invention is as follows: Under neutral to weakly alkaline conditions, the numerous ortho-phenolic hydroxyl groups within the tannic acid molecule are oxidized to form an ortho-benzoquinone structure. Ortho-benzoquinone exhibits high chemical reactivity and readily undergoes Michael addition or Schiff base reactions with the amino groups in zwitterionic diamine monomers to form covalent bonds. This results in the formation of a uniform and stable tannic acid / diamine zwitterionic ultrathin coating on the surface of the cation exchange membrane substrate (see [link to tannic acid / zwitterionic diamine modified coating composition]). Figure 1 The positively charged functional groups in the zwitterionic structure can effectively repel divalent Mg. 2+ For monovalent Li + The impact is relatively small; meanwhile, the negatively charged functional groups in the zwitterionic structure can promote the growth of monovalent Li. + Transmembrane transport. Therefore, the modified cation exchange membrane exhibits good Li-related properties when applied in electrodialysis. + / Mg 2+ Selectivity. Therefore, this invention can effectively solve the problem of existing commercial cation exchange membranes for Li. + / Mg 2+ The problem of limited selectivity.

[0046] The following are specific examples.

[0047] Example 1

[0048] A type with good Li + / Mg 2+ A method for preparing an ion-exchange membrane for electrodialysis with high separation performance includes the following steps:

[0049] (1) Synthesis of the zwitterionic diamine monomer NO compound zwitterionic diamine (DNMAO): 10 g of N,N-bis(3-aminopropyl)methylamine (DNMA) was dissolved in 45 mL of deionized water. Then, 30 mL of 8% (w / w) H2O2 solution was added dropwise to the above DNMA aqueous solution under ice-water bath conditions with continuous stirring. The mixture after adding hydrogen peroxide was continuously stirred in air at room temperature for 12 h. Next, the solution was extracted three times with dichloromethane to remove residual DNMA. Finally, the resulting aqueous solution was freeze-dried to obtain a light yellow viscous liquid, which is the NO compound zwitterionic diamine (DNMAO) monomer, with the following molecular structure:

[0050]

[0051] (2) Prepare a 50 mmol / L N,N-diethanolamine (Bicine) buffer solution with a pH of 8;

[0052] (3) Dissolve 0.2 parts of tannic acid and 0.2 parts of NO-containing zwitterionic diamine (DNMAO) in 100 parts of the above Bicine buffer solution by mass to obtain a buffer solution containing tannic acid and DNMAO zwitterionic diamine monomer.

[0053] (4) The homogeneous cation exchange membrane of Shandong Tianwei Membrane Technology Co., Ltd. was immersed in a buffer solution containing tannic acid and DMNAO zwitterionic diamine monomer, and the mixture was shaken at a constant speed in a water bath at 40°C for 16 hours. The modified membrane was cleaned with deionizer to obtain a salt-separating ion exchange membrane for electrodialysis, which was then stored for later use.

[0054] Example 2

[0055] A type with good Li + / Mg 2+ A method for preparing an ion-exchange membrane for electrodialysis with high separation performance includes the following steps:

[0056] (1) Synthesis of the zwitterionic diamine monomer N,N-bis(3-aminopropyl)methylamine propanesulfonic acid (Z-DNMA): First, 5.8 g of N,N-bis(3-aminopropyl)methylamine (DNMA) was dissolved in 80 mL of dichloromethane, and then 80 mL of dichloromethane containing 19.2 g of ditert-butyl dicarbonate was added. The mixture was stirred at room temperature for 12 h to protect the amino group. After extraction with deionized water and evaporation to remove the dichloromethane, intermediate 1 (DNMA-Boc) was obtained. Then, 20 mL of chloroform solution containing 1.7 g of 1,3-propanesulfonyl lactone was added dropwise to 20 mL of chloroform solution containing 4.0 g of intermediate 1. The mixture was stirred at 40 °C for 10 h. Afterward, the product was washed with deionized water, and the chloroform was evaporated to obtain intermediate 2 (Z-DNMA-Boc). Finally, intermediate 2 was deprotected in 4.0 mol / L hydrochloric acid solution at room temperature. The product was washed with acetonitrile to remove impurities and then freeze-dried to obtain the final target compound N,N-bis(3-aminopropyl)methylamine propane sulfonic acid (Z-DNMA), with the following molecular structure:

[0057]

[0058] (2) Prepare phosphate-buffered saline (PBS) with a pH of 8.0;

[0059] (3) Dissolve 0.2 parts of tannic acid and 0.2 parts of N,N-bis(3-aminopropyl)methylamine propanesulfonic acid (Z-DNMA) in 100 parts of the above PBS buffer solution by mass to obtain a buffer solution containing tannic acid and Z-DNMA zwitterionic diamine monomer.

[0060] (4) The homogeneous cation exchange membrane of Shandong Tianwei Membrane Technology Co., Ltd. was immersed in a buffer solution containing tannic acid and Z-DNMA zwitterionic diamine monomer, and the mixture was shaken at a constant speed in a water bath at 40°C for 12 hours. The modified membrane was cleaned with deionizer to obtain a salt-separating ion exchange membrane for electrodialysis, which was then stored and prepared for use.

[0061] Example 3

[0062] A type with good Li + / Mg 2+ A method for preparing an ion-exchange membrane for electrodialysis with high separation performance includes the following steps:

[0063] (1) Synthesis of the zwitterionic diamine monomer N,N-bis(3-aminopropyl)methylamine propanesulfonic acid (Z-DNMA): First, 5.8 g of N,N-bis(3-aminopropyl)methylamine (DNMA) was dissolved in 80 mL of dichloromethane, and then 80 mL of dichloromethane containing 19.2 g of ditert-butyl dicarbonate was added. The mixture was stirred at room temperature for 12 h to protect the amino group. After extraction with deionized water and evaporation to remove the dichloromethane, intermediate 1 (DNMA-Boc) was obtained. Then, 20 mL of chloroform solution containing 1.7 g of 1,3-propanesulfonyl lactone was added dropwise to 20 mL of chloroform solution containing 4.0 g of intermediate 1. The mixture was stirred at 40 °C for 10 h. Afterward, the product was washed with deionized water, and the chloroform was evaporated to obtain intermediate 2 (Z-DNMA-Boc). Finally, intermediate 2 was deprotected in 4.0 mol / L hydrochloric acid aqueous solution at room temperature. The product was washed with acetonitrile to remove impurities and then freeze-dried to obtain the final target compound N,N-bis(3-aminopropyl)methylaminopropanesulfonic acid (Z-DNMA).

[0064] (2) Prepare a 10 mmol / L Tris buffer solution with a pH of 7;

[0065] (3) Dissolve 0.05 parts of tannic acid and 0.05 parts of N,N-bis(3-aminopropyl)methylamine propanesulfonic acid (Z-DNMA) in 100 parts of the above Tris buffer solution by mass to obtain a buffer solution containing tannic acid and Z-DNMA zwitterionic diamine monomer.

[0066] (4) Immerse the homogeneous cation exchange membrane of Shandong Tianwei Membrane Technology Co., Ltd. into a buffer solution containing tannic acid and Z-DNMA zwitterionic diamine monomer, and shake it at a constant speed in a water bath shaker at 60°C for 1 hour. Clean the modified membrane with deionizer to obtain a salt-separating ion exchange membrane for electrodialysis, and store it for later use.

[0067] Example 4

[0068] A type with good Li + / Mg 2+ A method for preparing an ion-exchange membrane for electrodialysis with high separation performance includes the following steps:

[0069] (1) Synthesis of the zwitterionic diamine monomer N,N-bis(3-aminopropyl)methylamine propanesulfonic acid (Z-DNMA): First, 5.8 g of N,N-bis(3-aminopropyl)methylamine (DNMA) was dissolved in 80 mL of dichloromethane, and then 80 mL of dichloromethane containing 19.2 g of ditert-butyl dicarbonate was added. The mixture was stirred at room temperature for 12 h to protect the amino group. After extraction with deionized water and evaporation to remove the dichloromethane, intermediate 1 (DNMA-Boc) was obtained. Then, 20 mL of chloroform solution containing 1.7 g of 1,3-propanesulfonyl lactone was added dropwise to 20 mL of chloroform solution containing 4.0 g of intermediate 1. The mixture was stirred at 40 °C for 10 h. Afterward, the product was washed with deionized water, and the chloroform was evaporated to obtain intermediate 2 (Z-DNMA-Boc). Finally, intermediate 2 was deprotected in 4.0 mol / L hydrochloric acid solution at room temperature. The product was washed with acetonitrile to remove impurities and then freeze-dried to obtain the final target compound N,N-bis(3-aminopropyl)methylaminopropanesulfonic acid (Z-DNMA).

[0070] (2) Prepare phosphate-buffered saline (PBS) with a pH of 8.0;

[0071] (3) Dissolve 0.4 parts of tannic acid and 0.6 parts of N,N-bis(3-aminopropyl)methylamine propanesulfonic acid (Z-DNMA) in 100 parts of the above PBS buffer solution by mass to obtain a buffer solution containing tannic acid and Z-DNMA zwitterionic diamine monomer.

[0072] (4) The homogeneous cation exchange membrane of Shandong Tianwei Membrane Technology Co., Ltd. was immersed in a buffer solution containing tannic acid and Z-DNMA zwitterionic diamine monomer, and the mixture was shaken at a constant speed in a water bath at 30°C for 24 hours. The modified membrane was cleaned with deionizer to obtain a salt-separating ion exchange membrane for electrodialysis, which was then stored and prepared for use.

[0073] Example 5

[0074] (1) Same as Example 1;

[0075] (2) Prepare phosphate-buffered saline (PBS) with a pH of 6.0;

[0076] (3) Dissolve 0.01 parts of tannic acid and 0.01 parts of NO-containing zwitterionic diamine (DNMAO) in 100 parts of the above phosphate buffer (PBS) by mass to obtain a buffer containing tannic acid and DNMAO zwitterionic diamine monomer.

[0077] (4) Immerse the homogeneous cation exchange membrane of Shandong Tianwei Membrane Technology Co., Ltd. into a buffer solution containing tannic acid and DMNAO zwitterionic diamine monomer, and shake it at a constant speed in a water bath shaker at 50°C for 0.5 h. Clean the modified membrane with deionizer to obtain a salt-separating ion exchange membrane for electrodialysis, and store it for later use.

[0078] Example 6

[0079] (1) Same as Example 1;

[0080] (2) Prepare a 50 mmol / L N,N-diethanolamine (Bicine) buffer solution with a pH of 10;

[0081] (3) Dissolve 0.6 parts of tannic acid and 0.8 parts of NO-containing zwitterionic diamine (DNMAO) in 100 parts of the above Bicine buffer solution by mass to obtain a buffer solution containing tannic acid and DNMAO zwitterionic diamine monomer.

[0082] (4) The homogeneous cation exchange membrane of Shandong Tianwei Membrane Technology Co., Ltd. was immersed in a buffer solution containing tannic acid and DMNAO zwitterionic diamine monomer, and the mixture was shaken at a constant speed in a water bath at 25°C for 60 hours. The modified membrane was cleaned with deionizer to obtain a salt-separating ion exchange membrane for electrodialysis, which was then stored for later use.

[0083] Example 7

[0084] (1) Same as Example 1;

[0085] (2) Prepare a 50 mmol / L N,N-diethanolamine (Bicine) buffer solution with a pH of 9;

[0086] (3) Dissolve 0.1 parts of tannic acid and 0.1 parts of NO-containing zwitterionic diamine (DNMAO) in 100 parts of the above Bicine buffer solution by mass to obtain a buffer solution containing tannic acid and DNMAO zwitterionic diamine monomer.

[0087] (4) Immerse the homogeneous cation exchange membrane of Shandong Tianwei Membrane Technology Co., Ltd. into a buffer solution containing tannic acid and DNMAO zwitterionic diamine monomer, and shake it at a constant speed in a water bath shaker at 0°C for 16 hours. Clean the modified membrane with deionizer to obtain a salt-separating ion exchange membrane for electrodialysis, and store it for later use.

[0088] Comparative Example 1

[0089] Commercially available homogeneous cation exchange membranes, without tannic acid / zwitterionic diamine coating modification.

[0090] The modified cation exchange membranes prepared in Examples 1 to 7 were subjected to an electrodialysis lithium extraction experiment together with Comparative Example 1. The tests were carried out under the conditions shown in Table 1 below, and the results are shown in Table 2.

[0091] Table 1

[0092]

[0093] Table 2

[0094]

[0095] Compared to Comparative Example 1, the Li cation exchange membrane modified with tannic acid / zwitterionic diamine coating... + The flux decreased slightly, Li + / Mg 2+ Selectivity was significantly improved in both cases. The original homogeneous cation exchange membrane in Comparative Example 1, with its high negative charge density and abundant pore structure, exhibited the highest Li... + Flux, but it cannot effectively suppress divalent Mg 2+ The penetration is limited, therefore the selectivity is only 2.16. Li in Examples 1 and 2 + / Mg 2+ The selectivity was improved to 12.74 and 14.35, respectively. When N-N-bis(3-aminopropyl)methylamine propanesulfonic acid (Z-DNMA) or N-N-bis(3-aminopropyl)methylamine propanesulfonic acid (Z-DNMA) was introduced onto the surface of the cation exchange membrane, the positively charged quaternary ammonium groups in the zwitterionic structural units led to a significant increase in the positive charge density on the separation layer surface, and its interaction with divalent Mg 2+ There is a relative Li + A stronger electrostatic repulsion effectively inhibits Mg 2+ The transmission enables Li + / Mg 2+ Selectivity was significantly improved. Meanwhile, the introduction of the tannic acid / zwitterionic diamine ultrathin coating resulted in a denser separation layer surface, thereby enabling Li... + The flux has decreased.

[0096] Comparing Examples 2, 3, and 4 illustrates the effect of the amount of tannic acid and zwitterionic diamine, and the reaction time on Li + / Mg 2+ Selectivity has a significant impact. Insufficient amounts of tannic acid and zwitterionic diamine, along with a short reaction time, make it difficult to form a uniform and effective zwitterionic coating on the cation exchange membrane surface. This affects the density and uniform distribution of positively charged quaternary ammonium groups on the separation layer surface, which is detrimental to Li + / Mg 2+ Fully utilize selectivity.

[0097] Comparing Examples 5, 6, and 7, it is shown that the amounts of tannic acid and zwitterionic diamine, as well as the reaction conditions, affect the Li + Flux and Li + / Mg 2+ Selectivity has a significant impact; choosing appropriate reactant amounts and reaction conditions is beneficial for simultaneously achieving a large Li content. + Flux and high Li + / Mg 2+ Selectivity.

[0098] In terms of overall performance, Example 2 is more ideal and has the best Li + / Mg 2+ Selective, and retaining a considerable degree of Li + Flux.

[0099] This invention utilizes a Michael addition or Schiff base reaction between tannic acid molecules and zwitterionic diamine monomers under weakly alkaline conditions to form a uniform and stable ultrathin tannic acid / diamine zwitterionic coating on the surface of a conventional cation exchange membrane. This invention overcomes the limitations of existing commercially available cation exchange membranes and significantly improves the efficiency of Li... + / Mg 2+ Selectivity. The preparation process is simple, environmentally friendly, and widely applicable. The modified cation exchange membrane prepared by this invention exhibits excellent Li... + / Mg 2+ It is selective and can improve the membrane's antifouling properties, making it suitable for lithium extraction via electrodialysis from brines with a high magnesium-to-lithium ratio.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for producing a fractionating ion exchange membrane for electrodialysis, characterized by, The method comprises the following steps: The cation exchange membrane is immersed in a buffer solution containing tannic acid and zwitterionic diamine monomers, and the reaction is carried out at 0-60 ℃ for 0.5-60 h to obtain a salt ion exchange membrane for electrodialysis. The zwitterionic diamine monomer is N-O compound zwitterionic diamine and N , N - at least one of bis(3-aminopropyl)methylamine propane sulfonic acid; The structure of the N-O compound zwitterionic diamine is as follows: ； N , N - The structural formula of bis(3-aminopropyl)methylamine propane sulfonic acid is as follows: 。 2. The method for producing a fractionation ion exchange membrane for electrodialysis according to claim 1, characterized by, The buffer solution containing tannic acid and zwitterionic diamine monomers is prepared by the following process: The tannic acid and zwitterionic diamine monomers are added to the buffer solution and uniformly mixed.

3. The method for producing a fractionation ion exchange membrane for electrodialysis according to claim 2, characterized by, The buffer solution includes at least one of a pH of 7 to 9 N , N - bis(2-hydroxyethyl)glycine buffer, tris-hydroxymethylaminomethane buffer, and phosphate buffer.

4. The method for producing a fractionation ion exchange membrane for electrodialysis according to claim 3, characterized by, The ratio of tannic acid, zwitterionic diamine monomers and buffer solution is 0.01-0.6 parts: 0.01-0.8 parts: 100 parts by mass.

5. The method for producing a fractionation ion exchange membrane for electrodialysis according to claim 1, characterized by, The reaction temperature is 25-50 ℃, and the reaction time is 1-24 h.

6. The method for producing a fractionation ion exchange membrane for electrodialysis according to claim 1, characterized by, The cation exchange membrane is a heterogeneous cation exchange membrane or a homogeneous cation exchange membrane.

7. A salt ion exchange membrane for electrodialysis prepared by the method according to any one of claims 1-6.

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