Preparation method of carboxylated cation selective separation membrane for acid recovery

Abstract

The invention discloses a preparation method of a carboxylated cation selective separation membrane for acid recovery, which comprises the following steps: grafting an acyl chloride-containing monomer onto a self-polymerized microporous polymer PN, hydrolyzing part of acyl chloride to generate a-COO-group as a polymer ion exchange group; the PNT polymer with strong Pi-Pi interaction and hydrogen bond self-assembly capability is obtained, the crosslinking degree of the PNT polymer and the number of ion exchange groups in the membrane are further regulated and controlled by regulating and controlling the equivalent weight of the acyl chloride-containing monomer, the prepared homogeneous membrane liquid is coated on the surface of a glass plate, and by regulating the drying temperature, the PNT polymer with high Pi-Pi interaction and hydrogen bond self-assembly capability is obtained. And an H < + > rapid transmission channel is constructed while a compact cross-linked network is formed by the membrane. The membrane material prepared by the invention shows excellent mechanical properties, and shows relatively high H < + > flux and cation selectivity in the electrodialysis process, so that the membrane material has wide application potential in industrial production and practical application.

Description

Technical Field

[0001] The present invention belongs to the field of membrane technology, and particularly relates to a method for preparing a carboxylated cation exchange membrane for acid recovery. Background Art

[0002] Acids play an important role in many industrial fields such as waste lithium recovery, steel pickling, rare earth ion separation, electroplating, and chemical engineering, and are widely used as cleaning agents, corrosion agents, and catalysts. However, during the recycling process, the continuous consumption of H + and the increase in impurities lead to a gradual decrease in the effectiveness of the acid, eventually forming a large amount of waste acid. Waste acid usually contains various corrosive and toxic heavy metal ions. Direct discharge of untreated waste acid will pose a serious threat to the ecological environment, pollute water sources and soil, and even endanger human health. The complex composition of waste acid is one of the main difficulties in industrial waste acid recovery, which is mainly reflected in the coexistence of various acids, the presence of heavy metal ions, the mixing of organic substances, and the change in acid concentration. These factors result in significant differences in the physicochemical properties of waste acid, increasing the difficulty of separation and purification. In addition, different components in waste acid may react with each other to form new compounds or precipitates. Therefore, precise separation of H + is the key to waste acid recovery. In industries such as waste lithium recovery, rare earth ion separation, electroplating, and metal processing, the main systems for acid recovery include H + / Fe 2+ 、H + / Li + and H + / Nd 3+ etc.

[0003] Currently, waste acid recovery technologies mainly include neutralization precipitation, crystallization, rectification, solvent extraction, membrane separation, etc. These methods all have obvious deficiencies. For example, the neutralization precipitation method may cause secondary pollution, the crystallization method has high energy consumption, the rectification method has high equipment investment and maintenance costs, and the solvent extraction method has high usage costs and operation complexity. In contrast, membrane separation technology shows significant advantages in waste acid recovery: it can efficiently separate ions and small molecules in waste acid, has high selectivity and separation efficiency, low energy consumption, simple operation, reduces the dependence on chemical reagents, and reduces the risk of secondary pollution. This technology has strong adaptability, is suitable for various types of waste acid, can achieve continuous operation, improve treatment efficiency, and recover high-purity acid to meet industrial requirements.

[0004] Currently, diffusion dialysis is mainly used in the membrane separation method for acid recovery. Its basic principle is that the concentration difference of acid in the waste acid solution drives anions to diffuse from the high-concentration area to the low-concentration area. The anion exchange membrane allows anions to pass through while hindering cations or molecules, thereby achieving the separation purpose. Under the action of the concentration difference, anions (such as Cl - 、NO3 - , SO 4 2- , etc.) are migrated to the low-concentration side to promote the recovery of acid. However, the diffusion dialysis treatment capacity is small, and the concentration of the recovered acid is limited by the concentration of acid in the wastewater. Compared with the diffusion dialysis method, the electrodialysis method utilizes the selective permeability of the ion exchange membrane to perform deacidification of the waste acid solution and concentration recovery of the acid under the action of an externally applied direct current electric field. The electrodialysis process is relatively simple, the product recovery rate is high, and there is no limit to the initial concentration of the waste acid. However, there are still problems such as the restrictive relationship between the ion exchange capacity and ion selectivity and low cation selectivity in the cation-selective separation membrane currently used for electrodialysis, resulting in a low purity of the recovered acid. To achieve high selectivity and high H + flux, there are mainly the following ways: 1) Adjust the microphase separation structure and the size of the ion transport channels. For example, in the modified cation-selective separation membrane mentioned in Patent CN118620152A, the regulation of the ion transport channels is achieved by adjusting the introduced side chains with carboxylic acid at the end, achieving the effect of simultaneously improving the H + flux and selectivity. 2) Increase the membrane crosslinking degree: Achieve high selectivity of ion separation through pore size sieving. For example, the hydrogen bond crosslinking structure formed by "A-T base pairs" reported in the Journal of Membrane Science (711, 123203) is beneficial for selective permeation. 3) Modify the membrane surface to change the membrane surface charge level. For example, in the modified cation-selective membrane mentioned in Patent CN117815915A, by coating a crosslinked anion exchange membrane on the membrane surface, the H + flux is ensured, and at the same time, other cations are effectively intercepted to improve its selectivity.

[0005] However, the adjustment of the microphase separation of the membrane may lead to a decrease in the mechanical strength of the membrane, affecting its stability and durability. Moreover, this adjustment method may require complex processes, increasing the production cost and technical difficulty. The increase in the membrane crosslinking degree is difficult to avoid the decrease in ion conductivity and the increase in energy consumption. When modifying the membrane surface, the modified layer is difficult to avoid peeling off during long-term operation. Therefore, it is necessary to develop a cation-selective separation membrane for acid recovery with excellent comprehensive performance that can meet commercial applications. Summary of the Invention

[0006] To overcome the deficiencies of the current technology, the present invention provides a method for preparing a carboxylated cation-selective separation membrane for acid recovery. Using a self-microporous polymer PN containing a large number of hydrogen bonds as a precursor, an ordered structure is spontaneously formed through non-covalent interactions between hydrogen bonds, thereby constructing a precisely controllable ion transport channel. At the same time, the polymer PN is grafted with an acyl chloride monomer to obtain an intermediate membrane with a cross-linked structure. The carboxylic acid groups generated by the hydrolysis of some unreacted acyl chloride groups can be used as ion exchange sites to prepare a cation-selective separation membrane. The preparation method of this acid recovery cation-selective separation membrane is simple, and as a homogeneous membrane, it is compatible with the existing membrane production process, having great potential for commercial application.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A preparation method for carboxylated cation-selective separation for acid recovery, comprising the following steps:

[0009] Step 1: Dissolve the self-microporous polymer PN shown in the structural formula (1) in an organic solvent to obtain a polymer PN solution;

[0010]

[0011] Step 2: Add an acyl chloride monomer to the polymer PN solution for grafting reaction to obtain a membrane solution containing polymer PNT;

[0012] Step 3: Coat the membrane solution containing polymer PNT on a substrate and dry it to obtain an intermediate membrane;

[0013] Step 4: Immerse the intermediate membrane in water to make it fall off from the substrate. At the same time, the unreacted acyl chloride groups in the membrane are rapidly hydrolyzed to generate carboxylic acid groups as ion exchange groups, obtaining a carboxylated cation-selective separation membrane for acid recovery.

[0014] Further, in Step 1, the degree of polymerization m of the polymer PN ranges from 10 2 –10 5 between.

[0015] Further, in formula (1), R is from a bisphenol monomer, and its specific structural formula is shown as any one of formula (2), where * is the connection position:

[0016]

[0017] Furthermore, the polymer PN used in the present invention is prepared by reacting a bisphenol monomer (such as 1,1-bi(2-naphthol), 2,2'-dihydroxybiphenyl, 3,3,3,3-tetramethyl-1,1-spirobi(indane)-6,6-diol) with a keto monomer (such as isatin). The specific reaction method can refer to the literature "One-step synthesis of hydroxyl-functionalized fully carbon main chain PIMs via a Friedel-Crafts reaction for efficient gas separation" (Separation and Purification Technology 262 (2021) 118313).

[0018] Furthermore, in step 1, the organic solvent includes one of common organic solvents such as tetrahydrofuran, dimethyl sulfoxide, N,N-dimethylformamide, N-methylpyrrolidone, etc. The mass concentration of PN in the polymer PN solution is 5-20%.

[0019] Furthermore, in step 2, the specific structural formula of the acyl chloride monomer is shown as any one of those in formula (3):

[0020]

[0021] Furthermore, in step 2, the reaction grafting site on the polymer PN is the -OH site, and the molar ratio of the polymer PN to the acyl chloride monomer is 1:0.1-2.

[0022] Furthermore, in step 2, the reaction temperature of the grafting reaction is 50°C - 120°C, and the reaction time is 12h - 48h.

[0023] Furthermore, in step 3, the drying temperature is 40°C - 100°C.

[0024] Furthermore, in step 4, the soaking time of the membrane is 1h - 3h.

[0025] The preparation method of the carboxylated cation selective separation membrane for acid recovery provided by the present invention adopts a homogeneous membrane casting process. The membrane has high uniformity and good mechanical properties. At the same time, the introduction of the surface modification layer is avoided, thereby significantly improving various performance indicators of the membrane. Its beneficial effects are specifically reflected in the following aspects:

[0026] (1) Different from traditional microporous materials, self-assembled microporous polymers are polymers with intrinsic porosity formed due to the ineffective stacking of rigid chain segments. The micropore size and shape of the self-assembled microporous polymer PN can be regulated, thus enabling the construction of more precise ion-selective transport channels. Specifically, the π-π stacking effect between benzene rings in the self-assembled microporous polymer PN drives the ordered assembly of molecules, forming nanostructures or supramolecular structures, enhancing the intermolecular forces between polymer chains, and then forming continuous ion transport channels. At the same time, the self-assembled microporous polymer PN has good mechanical strength and chemical stability, and can maintain the structural stability under complex working conditions. The pore size of its micropores is adjustable, providing a large specific surface area, thereby improving the ion transport efficiency. In addition, the polymer PN itself has an ether-free main chain structure, with good antioxidant and acid-base stability, ensuring the service life of the membrane.

[0027] (2) The polymer PN contains abundant -OH sites and -NH- sites, which can serve as modification sites, laying a foundation for improving the membrane separation performance. High-density hydrogen bonds can significantly enhance the intermolecular forces between polymer PN chains, driving the formation of stable structures during the self-assembly process of polymer chains, thus maintaining an ordered arrangement. At the same time, the structures formed by self-assembly often have specific functions, such as selective permeability. During the separation of H + from metal ions, the smaller-sized H + can easily pass through the ion transport channels formed by the self-assembly of polymer PN molecules, while the larger-sized metal ions are blocked by the size sieving mechanism and are difficult to undergo transmembrane transport, thereby achieving the selective separation of H + from metal ions.

[0028] (3) Traditional sulfonic acid groups, as ion exchange groups, although having excellent ion conductivity, also have some deficiencies. For example, their high dissociation in water may lead to excessive swelling of the membrane, and in a strong acid environment, it is easy to cause the degradation and failure of the groups. In addition, the sulfonic acid groups have low selectivity for specific ions, affecting the separation effect. To solve these problems, the present invention selects acyl chloride monomers to react with -OH sites. On the one hand, the structure and size of the pores in the membrane are precisely regulated through crosslinking, thereby enhancing the selective separation ability of the membrane; on the other hand, the unreacted acyl chloride groups are hydrolyzed to form carboxylic acid groups, forming new ion exchange sites, reducing the transmembrane energy barrier of ions, and thus reducing the membrane surface resistance and energy consumption. At the same time, the carboxylic acid groups can interact with specific cations through electrostatic and coordination interactions, further improving the selectivity for target ions. Selecting carboxylic acid groups as ion exchange sites, their weak acidic characteristics make them less dissociable under low pH conditions and difficult to carry out ion exchange. This property may cause metal ions to be difficult to effectively exchange through carboxylic acid groups, thereby hindering their transmembrane transport and improving the selectivity of the membrane. However, due to the microporous structure of the PNT membrane itself, and H+ is smaller in size, which can ensure the H + flux, thus achieving the precise separation of H + metal ions. In addition, the carboxylic acid group exhibits good stability in various chemical environments and can maintain its function under acidic and alkaline conditions.

[0029] (4) The preparation process of the ion exchange membrane of the present invention is the homogeneous membrane casting method, which is an efficient, flexible and simple membrane preparation technology that can achieve the uniformity and consistency of the membrane. During the preparation process, by precisely controlling the casting speed, coating thickness and drying conditions, the physical and chemical properties of the membrane can be accurately controlled. For example, by controlling the forming temperature of the PNT membrane material, the directional self-assembly of hydrogen bonds can be adjusted, thereby affecting the structure and performance of the membrane. In addition, the casting method supports large-scale production, is convenient for compatibility with existing processes, and can be post-treated to further improve the performance of the membrane. Description of the Drawings

[0030] Figure 1 is the H NMR result analysis of the polymer PN prepared in Example 1 of the present invention.

[0031] Figure 2 is a photo of the cation selective separation membrane prepared in Example 1 of the present invention.

[0032] Figure 3 is a diagram of the ion selective test device used in the examples of the present invention.

[0033] Figure 4 is the membrane surface resistance of the membrane materials prepared in Examples 1 to 4 of the present invention.

[0034] Figure 5 is the H + / Fe 2+ selectivity test results of the membrane materials prepared in Examples 1 to 4 of the present invention.

[0035] Figure 6 is the H + / Li + selectivity test results of the membrane materials prepared in Examples 1 to 4 of the present invention.

[0036] Figure 7 is the H + / Nd 3+ selectivity test results of the membrane materials prepared in Examples 1 to 4 of the present invention. Detailed Description of the Invention

[0037] The technical solutions of the present invention will be further described below through embodiments. These technical solutions are only to make the present invention easy to understand by researchers in the field and do not limit the protection scope of the present invention. All divergences and variations made using the present invention are within the protection scope of the present invention.

[0038] I. Preparation of carboxylated cation selective separation membrane

[0039] Example 1

[0040] The preparation steps of the carboxylated cation selective separation membrane for acid recovery provided in this example are as follows:

[0041] Preparation of polymer PN: Measure 28.6 g of 1,1 - bi(2 - naphthol) into a three - necked round - bottom flask, then add 150 mL of dichloromethane. Place the three - necked flask in an ice - bath circulation system, insert a stirring paddle, and start stirring until all the solids are dissolved. Add 18.6 g of isatin, then dropwise add 15 mL of trifluoroacetic acid, and continue stirring until isatin is completely dissolved to form a light - red homogeneous solution. Set the condensation circulation temperature to - 10°C. After the temperature stabilizes, slowly dropwise add 150 mL of trifluoromethanesulfonic acid to the three - necked flask. After reacting for 24 h, the viscosity of the system rises sharply. Slowly pour the reactant into pure water to obtain the crude product of PN. After drying this product, dissolve it with the organic solvent DMSO, pour the obtained solution into pure water again to precipitate, and repeat this operation three times. Then dry the precipitated polymer to obtain the final polymer PN: where the degree of polymerization m ranges from 10 2 –10 5 between.

[0042] Preparation of the membrane solution containing polymer PNT: Take 1 g of polymer PN and place it in a 20 - mL round - bottom flask. Add a magnetic stirrer to the round - bottom flask, put the round - bottom flask into an oil - bath pot, add 9 g of organic solvent (DMSO) to the flask, raise the temperature of the oil - bath pot to 80°C. Wait until polymer PN is completely dissolved, add 0.1 g of acyl chloride monomer (TMC), stop the reaction after reacting for 48 h and store it.

[0043] Obtain the membrane solution containing polymer PNT. The structure of polymer PNT is shown as follows, where y = 0.1.

[0044]

[0045] Preparation of the intermediate membrane: Take 3 mL of the membrane solution containing polymer PNT, pour it evenly on a glass plate, and dry it at 80°C for 12 h to form a film to obtain the intermediate membrane.

[0046] Hydrolysis: The intermediate membrane was immersed in water for 1 h to make it fall off the substrate. Meanwhile, the unreacted acyl chloride groups in the membrane were hydrolyzed to produce carboxylic acid groups as ion exchange groups, obtaining a carboxylated cation selective separation membrane for acid recovery. The photograph of the cation exchange membrane prepared in this example is as shown in Figure 1 shown.

[0047] Example 2

[0048] The preparation steps of the carboxylated cation selective separation membrane for acid recovery provided in this example are as follows:

[0049] Preparation of polymer PN: The same preparation method as in Example 1 was adopted.

[0050] Preparation of the membrane solution containing polymer PNT: The same preparation method as in Example 1 was adopted, except that the addition amount of the acyl chloride monomer was adjusted to 0.3 g

[0051] Preparation of the intermediate membrane: The same preparation method as in Example 1 was adopted.

[0052] Hydrolysis: The same preparation method as in Example 1 was adopted.

[0053] Example 3

[0054] The preparation steps of the carboxylated cation selective separation membrane for acid recovery provided in this example are as follows:

[0055] Preparation of polymer PN: The same preparation method as in Example 1 was adopted.

[0056] Preparation of the membrane solution containing polymer PNT: The same preparation method as in Example 1 was adopted, except that the addition amount of the acyl chloride monomer was adjusted to 0.5 g

[0057] Preparation of the intermediate membrane: The same preparation method as in Example 1 was adopted.

[0058] Hydrolysis: The same preparation method as in Example 1 was adopted.

[0059] Example 4

[0060] The preparation steps of the carboxylated cation selective separation membrane for acid recovery provided in this example are as follows:

[0061] Preparation of polymer PN: The same preparation method as in Example 1 was adopted.

[0062] Preparation of the membrane solution containing polymer PNT: The same preparation method as in Example 1 was adopted, except that the addition amount of the acyl chloride monomer was adjusted to 0.7 g

[0063] Preparation of the intermediate membrane: The same preparation method as in Example 1 was adopted.

[0064] Hydrolysis: The same preparation method as in Example 1 was adopted.

[0065] II. Membrane Flux and Ion Selectivity Tests

[0066] Using the device as Figure 3 shown, the H -2 / Fe + ion selectivity of the cation-selective separation membranes obtained in Examples 1-4 of the current density test (and using the commercial monovalent / divalent selective cation exchange membrane CIMS tested under the same conditions as a control), H 2+ / Li + ion selectivity, and H + / Nd + ion selectivity were tested. The specific method was as follows: Take 0.3M Na 3+ SO 2 , 0.01M HCl, and 1M HCl / 0.267M MCl 4 (where M is the corresponding metal for the ion selectivity test and x is the valence of the metal ion). The mixed solutions were placed in the anode chamber, the concentration chamber, and the dilution chamber respectively. After the water pump filled each chamber and there were no bubbles, a constant current density was applied across the membrane pair, and the start time of the power-on was recorded. The cations in the dilution chamber migrated from the dilution chamber to the concentration chamber under the action of the electric field. Due to the ion selectivity of the membrane, H X permeated through in large quantities while other ions permeated less. Finally, the H + concentration and the metal ion concentration in the concentration chamber were measured, and the ion flux was calculated based on the concentration:

[0067]

[0068] In the figure, C + is the ion concentration in the concentration chamber after running for t hours, C t is the initial ion concentration in the concentration chamber, A 0 is the effective area of the membrane in the test, t is the running time, and V is the final volume of the concentration chamber. Finally, the flux ratio of H m to the metal ion flux is the selectivity value. The H + / Fe + ion selectivity, H 2+ / Li + ion selectivity, and H + / Nd + ion selectivity test results of the cation-selective separation membranes obtained in Examples 1-4 are shown in 3+ , Figure 5 , Figure 6 , Figure 7 respectively.

[0069] Analysis of the nuclear magnetic resonance results of Example 1 and the membrane surface resistance test results of Examples 1-4 confirmed the successful synthesis of the proposed target membrane material structure and the effective introduction of carboxylic acid groups, verifying the feasibility of the route of the present invention. At the same time, the prepared membrane is a homogeneous membrane, avoiding the disadvantages of traditional surface-modified membranes and mixed matrix membranes such as high energy consumption, low stability, low flux, and short lifespan. The preparation method of this membrane is simple, the conditions are easy to control, and large-scale production has been successfully achieved. It has excellent mechanical properties and meets the requirements of industrial applications.

[0070] The structure and properties of the self-polymerized microporous polymer PN are stable. The π-π stacking between benzene rings enhances the intermolecular force between polymer PN chains, thereby improving the stability of its microporous structure and mechanical strength. In addition, the π-π stacking of benzene rings also promotes the self-assembly behavior of polymer PN, forming an ordered microporous structure, which is a prerequisite for realizing the selective separation function. Due to the abundant -OH sites on the main chain of polymer PN, by regulating the temperature during the film-forming process, the formation of hydrogen bonds in the polymer can be adjusted, enabling the polymer molecules to be further arranged in an orderly manner.

[0071] Polymer PN itself does not have ion-exchange groups for ions to cross the membrane, but ion-exchange groups can be introduced through the abundant -OH on the main chain. The acyl chloride monomer reacts with the hydroxyl sites, and the high-density hydroxyl environment promotes the formation of a cross-linked network, thereby making the spatial structure of the membrane denser and increasing the steric hindrance of ion transmembrane transport. During the acid recovery process, the steric hindrance has little effect on the smaller-sized H + , so the flux of H + can be guaranteed. At the same time, some of the acyl chloride groups that did not participate in the acylation reaction undergo hydrolysis to generate carboxyl groups, realizing the carboxylation of PN polymer and introducing carboxylic acid groups as ion-exchange groups. Since carboxylic acid is a weak acid and has weak dissociation under low pH conditions, during the acid recovery process, other metal cations are difficult to achieve ion exchange through carboxylic acid groups, further reducing the flux of metal cations and improving the selectivity.

[0072] Analysis of the membrane surface resistance of Examples 1-4 found that with the increase in the content of the acyl chloride monomer, the membrane surface resistance decreased significantly. This indicates that the more the amount of the acyl chloride monomer added, the more carboxyl groups are generated by hydrolysis, and the higher the degree of carboxylation of polymer PN, resulting in a decrease in the membrane surface resistance. Analysis of the separation experiments of H + and metal ions for Examples 1-4 and commercial membrane CIMS showed that with the increase in the addition amount of the acyl chloride monomer, the selectivity of H + and Li + decreased, and the selectivity of H + and Fe 2+ generally also showed a downward trend. The Nd 3+ of Examples 1-4The concentration is lower than the detection limit of the instrument and cannot be measured, but it is sufficient to prove its excellent selectivity. By comparing the selectivities of different metal ions, it is found that the larger the ionic hydration radius, the higher its selectivity, further proving the size screening effect of Examples 1-4. At the same time, the H + fluxes of different examples all remain at a high level, further proving the existence of the regular intrinsic micropores and hydrogen bond network of polymer PNT, which is helpful for the H + transmembrane transport.

[0073] The preparation method of the acid recovery cation selective separation membrane proposed by the present invention has a simple process and excellent performance, can be efficiently produced in a short time, and is convenient for industrialization and large-scale application. By comparing with the commercial cation membrane CIMS, this method not only effectively solves the precise separation of hydrogen and metal ions, but also replaces the introduction of sulfonic acid groups to achieve the goals of high selectivity and high flux. At the same time, this technology significantly improves the acid recovery efficiency, reduces energy consumption, promotes the efficient utilization of resources, has an important positive impact on environmental protection and resource recycling, and helps to achieve the sustainable development goal.

Claims

1. A method for preparing a carboxylated cation selective separation membrane for acid recovery, characterized in that: The steps include: Step 1: dissolving the self-microporous polymer PN having the structural formula shown in formula (1) in an organic solvent to obtain a polymer PN solution; Step 2: Adding an acyl chloride-containing monomer to the polymer PN solution for grafting reaction to obtain a membrane solution containing polymer PNT; Step 3: coating the film solution containing polymer PNT on the substrate and drying it to obtain an intermediate film; Step 4: Soak the intermediate membrane in water to make it fall off from the substrate, and at the same time, the acyl chloride groups that do not participate in the reaction in the membrane are hydrolyzed to produce carboxylic acid groups as ion exchange groups, thereby obtaining a carboxylated cation selective separation membrane for acid recovery.

2. The preparation method according to claim 1, characterized in that: In step 1, the degree of polymerization m of the polymer PN is in the range of 10 2 –10 5 between.

3. The preparation method according to claim 1, characterized in that: In formula (1), the structural formula of R is shown in any one of formulas (2), where * is the connection position:

4. The preparation method according to claim 1, characterized in that: In step 2, the specific structural formula of the acyl chloride-containing monomer is shown in any one of formulas (3):

5. The preparation method according to claim 1, characterized in that: In step 1, the mass concentration of PN in the polymer PN solution is 5-20%.

6. The preparation method according to claim 1, characterized in that: In step 2, the reaction grafting site on the polymer PN is the -OH site, and the molar ratio of the polymer PN to the acyl chloride-containing monomer is 1:0.1-2.

7. The preparation method according to claim 1, characterized in that: In step 2, the reaction temperature of the grafting reaction is 50° C.-120° C., and the reaction time is 12 h-48 h.

8. The preparation method according to claim 1, characterized in that: In step 3, the drying temperature is between 40°C and 100°C.

9. The preparation method according to claim 1, characterized in that: In step 4, the membrane is immersed for 1 h to 3 h.

10. A carboxylated cation selective separation membrane for acid recovery obtained by the preparation method according to any one of claims 1 to 9.

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