Preparation method of modified cation selective separation membrane containing ether side chain

Abstract

The invention discloses a preparation method of an ether-containing side chain modified cation selective separation membrane, which comprises the following steps: by taking an own microporous polymer as a precursor for preparing a membrane material, realizing an ion exchange function of the membrane material through grafting a sulfonated monomer; on the basis, the transmission difference of different ions in the membrane is further realized through grafting of ether-bond-containing micromolecular monomers, the ion selectivity is constructed, and the prepared membrane material has the ion separation performance superior to that of a current commercial cation selective separation membrane. The industrial production difficulty is remarkably reduced by the membrane synthesis preparation route of the solution grafting reaction, the large-scale production is easy to realize, and the prepared membrane material can reach the ion flux of industrial-grade electrodialysis and is expected to realize large-scale application.

Description

Technical Field

[0001] The invention belongs to the field of membrane technology, and in particular relates to a method for preparing a cationic selective separation membrane modified with an ether side chain. Background Art

[0002] Chemical separation technology plays an important role in the fields of seawater desalination, lithium extraction from salt lakes, and high-salt wastewater treatment. Among them, the application demand for precise separation of ions is urgently needed, especially the separation of ions with the same charge but different valence states, such as Li + / Mg 2+ 、Na + / Ca 2+ 、Na + / Mg 2+ Plasma system separation. Current traditional methods mainly focus on technical processes such as nanofiltration, solvent extraction, and chromatography. However, due to the technical limitations of these processes themselves, these processes have problems such as high investment costs, low recovery rates, and high energy consumption. In contrast, electrodialysis technology with ion-selective separation membranes as the core is constantly developing and maturing, and electrodialysis technology has the advantages of high separation efficiency, low equipment cost, and small footprint. It has great application demand in many chemical separation fields. With the continuous development of various industries, higher requirements are also placed on the performance of membrane materials, including cation-selective separation membranes, and the current commercial membranes still have problems such as low selectivity, poor membrane stability, and easy shedding. Therefore, further research and development of cation-selective separation membranes is needed, and new synthesis and preparation routes are developed to improve performance, meet application requirements in different scenarios, and control membrane production costs to achieve cost reduction and efficiency improvement.

[0003] Since ions of the same valence but different charges have similar intrinsic properties, their efficient separation has always been a problem. Based on the relevant information, it can be seen that the current research on cation selective separation membranes mainly focuses on: 1) achieving selectivity of ions of different ion sizes by increasing density and using pore size screening. For example, CN112546872B effectively increases the density of the membrane by polymerizing a layer of pyrrole-2-carboxylic acid polymer on the surface of the cation exchange base membrane. At the same time, due to the introduction of ion exchange groups, the ionic conductivity of the membrane itself is guaranteed, thereby achieving cation selectivity. 2) Construct selectivity through electrostatic repulsion. For example, CN114377731B uses Fe 3+Co-deposited with polyimide on the membrane surface, a monovalent selective cation selective separation membrane is prepared. However, the surface modification method often increases the membrane resistance, resulting in increased energy consumption during actual application. At the same time, the problem of surface layer shedding also significantly reduces the stability of the membrane during operation. 3) Some researchers have also constructed selectivity through the specific adsorption of ions and groups within the membrane. For example, CN1179919964A, crown ether nanomaterials are incorporated into the membrane liquid by blending to form a mixed matrix membrane. The specific interaction between crown ethers and monovalent ions is utilized to prepare the membrane by casting method, achieving monovalent / divalent ion selectivity. However, although this method of preparing a mixed matrix membrane by blending avoids the introduction of a surface modification layer, it increases the complexity of the process and is not compatible with the mature production process of the current membrane material production line, making it difficult to achieve large-scale preparation. In addition, current cation selective separation membranes still have problems such as poor selectivity, high membrane resistance, and poor stability. Currently, a more efficient and lower-cost cation selective separation membrane can meet the needs of industrial applications. Summary of the Invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the present invention is based on the excellent directional self-assembly ability of microporous polymers to obtain a polymer membrane with microporous channels after the polymer dissolved membrane-forming liquid is dried, and the secondary interactions between molecules are used to regulate the self-assembly of polymer molecules, and the discreteness of the micropore size after the polymer membrane is formed. At the same time, functional groups that have specific interactions with target ions are introduced to increase the target ion flux and construct ion selectivity. It provides a preparation method for a cation-selective separation membrane modified with ether side chains, which is homogeneous and stable, simple in preparation method, matches the current membrane production line production process, has high ion flux and excellent ion selectivity.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions:

[0006] The method for preparing the cation selective separation membrane modified with ether side chains of the present invention comprises the following steps:

[0007] Step 1: using a PN polymer having a structural formula as shown in formula (1) as a precursor for preparing a cation selective separation membrane;

[0008]

[0009] Step 2: reacting and grafting the PN polymer with the sulfonated monomer to prepare a polymer SPN with ion exchange groups;

[0010] Step 3: The polymer SPN with cation exchange groups is reacted and grafted with a small molecule monomer containing an ether bond to prepare an SPNO polymer.

[0011] Step 4: dissolving the SPNO polymer in an organic solvent to obtain a membrane solution, pouring the membrane solution into a mold and drying it to obtain a cation selective separation membrane.

[0012] Furthermore, in step 1, the molecular weight range of the PN polymer is m in the range of 10 2 -10 7 between.

[0013] Furthermore, in step 1, R is derived from a bisphenol monomer, and its specific structural formula is shown in any one of formula (2), where * represents the connection position:

[0014]

[0015] Furthermore, the PN polymer 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-spiro BI(indane)-6,6-diol) with a ketone monomer (such as isatin). The specific reaction method can be referred to the literature "One-step synthesis of hydroxyl-functionalized fully carbon main chain PIMs via a Friedel-Crafts reaction for efficient gasseparation" (Separation and Purification Technology 262(2021)118313).

[0016] Furthermore, in step 2, the sulfonated monomer that makes PN obtain ion exchange groups after the reaction is Wherein, x is any integer from 1 to 5.

[0017] Furthermore, in step 2, the sites of reactive grafting on the PN polymer are some -OH sites or -NH- sites, the molar ratio of the total number of reactive sites in the PN polymer (i.e., the total molar amount of -OH and -NH-) to the sulfonated monomer is 1:0.1-1, the reaction temperature is 50°C-120°C, the reaction time is 12h-48h, and a hydrogenation reagent (such as NaH, potassium carbonate, sodium tert-butoxide, etc.) is added during the reaction. The molar ratio of the amount of the hydrogenation reagent added to the total number of reactive sites in the PN polymer is 0.1-1:1.

[0018] Further, in step 3, the small molecule monomer containing an ether bond is Wherein, y is any integer between 1 and 10.

[0019] Furthermore, in step 3: the reaction grafting site on the SPN polymer is a -OH site or a -NH- site, and the molar ratio of the total number of reaction sites in SPN (i.e., the total molar amount of -OH and -NH-) to the small molecule containing an ether bond is 1:0.1~1; the temperature range of the reaction grafting is 50°C-120°C, the reaction time is 12h-48h, and a hydrogenation reagent (such as NaH, potassium carbonate, sodium tert-butoxide, etc.) is added during the reaction, and the molar ratio of the amount of the hydrogenation reagent added to the total number of reaction sites in the SPN polymer is 0.1~1:1.

[0020] Furthermore, in step 4, the drying temperature is between 30°C and 120°C.

[0021] The present invention provides a method for preparing a cation-selective separation membrane that matches existing homogeneous membrane casting processes and avoids the introduction of a surface modification layer, significantly improving the stability of the membrane material. Furthermore, by adjusting the pore size of the inherent micropores, the method further reduces the target ion transport resistance, increases ion flux, reduces membrane resistance, and achieves excellent ion selectivity. Its beneficial effects are specifically reflected in the following aspects:

[0022] (1) Based on the inherent microporous properties of PN polymers, sulfonated monomers and small molecule monomers containing ether bonds are confined to grow in the intrinsic micropores of the polymer. Selective ion transport channels are constructed using the inherent confined pores of the microporous polymer, avoiding the uncontrollable ion transport channel problem caused by the random distribution of ion exchange sites in traditional random polymers. Specifically, the grafted sulfonated monomers first form ion transport sites in the micropores, realizing the ion exchange function, ensuring the membrane material's ability to transport ions and the flux of target ions. Secondly, the grafting of small molecule monomers containing ether bonds forms transmission differences between different ions in the micropores, achieving ion separation performance. The combination of the two ultimately achieves the preparation of a high-performance cation selective separation membrane.

[0023] (2) Based on the grafting of small molecule monomer side chains containing ether bonds, the ether bonds and Li + , K + The specific interactions between ions significantly reduce the distribution energy barrier for monovalent cations entering the membrane from solution, making ion transport across the membrane more likely. Simultaneously, the charge compensation effect of the ether bond enhances the solvation capacity of monovalent cations within the membrane, facilitating their transport and increasing their diffusion rate. Ultimately, the total transmembrane energy barrier for monovalent ions is significantly lower than that for divalent ions, resulting in a membrane material with excellent cation selectivity.

[0024] (3) Using PN as the base polymer of the membrane material, the rigidity of its own structure also ensures excellent swelling resistance after the membrane is formed. At the same time, the π-π interaction and abundant hydrogen bonding sites brought about by the structural characteristics of the PN molecule itself promote hydrogen bond self-assembly, promote the formation of regular channels in the membrane, control the pore size distribution of the self-produced micropores within a limited range, avoid the random discrete pore size distribution, and effectively construct the ion transport channel in the membrane. The abundant -OH sites and -NH- sites in the PN structure itself provide convenience for subsequent modification and lay the foundation for the precise regulation of membrane material performance. Sulfonic acid monomers are used to modify and graft the PN functional sites, and ion exchange sites are added on the basis of ensuring that its main chain remains unchanged. Specifically, different amounts of sulfonic acid monomers are added to further regulate the microphase separation and microporous structure in the membrane, thereby changing the distribution and size of the free volume in the membrane, achieving separation performance between different cations, and ensuring high flux, high selectivity and low membrane resistance for target ions during the use of the membrane material.

[0025] (4) By utilizing the difference in the interaction force between different ions caused by the small molecule monomer, it is possible to achieve a gradient difference in the transmission of different ions, and to achieve a transmission difference between two different ions, thereby achieving ion separation performance. This method also avoids increasing the density of the membrane material, reduces the membrane resistance, and significantly reduces the energy consumption of the membrane material during the application of the membrane group device. The film formation method is simple, avoids the introduction of surface modification methods, and significantly improves the stability of the membrane material. Based on the interaction of the small molecule monomer containing an ether bond with the cation, the small molecule monomer is introduced through a grafting method to make it part of the polymer structure. The homogeneous membrane material finally prepared matches the roll-to-roll production process of the current industrial membrane material, and is easy to achieve industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a photograph of the cation selective separation membrane modified with ether side chains prepared in Example 1 of the present invention.

[0027] Figure 2 The NMR results of the SPNO polymer prepared in Example 1 of the present invention are analyzed.

[0028] Figure 3 These are the infrared spectroscopy characterization results of the SPNO polymers prepared in Examples 1-3 of the present invention.

[0029] Figure 4 These are the pore size analysis results of the carbon dioxide adsorption and desorption tests of the SPNO polymers and PN prepared in Examples 1-3 of the present invention.

[0030] Figure 5This is a diagram of the ion selectivity test device used in the present invention, where MCl&NCl2 are LiCl&MgCl2, NaCl&MgCl2, and NaCl&CaCl2 respectively.

[0031] Figure 6 It is a schematic diagram of the present invention for constructing an ion-selective membrane based on the regulation of ion channels by self-microporous polymers. DETAILED DESCRIPTION

[0032] The technical solutions of the present invention are further illustrated by examples below. These technical solutions are only intended to make the present invention easier to understand by researchers in the field, and are not intended to limit the scope of protection of the present invention. All variations and extensions made using the present invention are within the scope of protection of the present invention.

[0033] 1. Preparation of cation selective separation membrane

[0034] Example 1

[0035] The steps for preparing the cation selective separation membrane modified with ether side chains in this embodiment are as follows:

[0036] 1. Preparation of PN polymer:

[0037] Measure 28.6g of 1,1-bi(2-naphthol) in a round-bottom three-necked flask, then add 150mL of dichloromethane, place the three-necked flask in an ice bath circulation system, insert a stirring paddle, and start stirring until all the solid drugs are dissolved. Add 18.6g of indigo red, then add 15mL of trifluoroacetic acid dropwise, and continue stirring until all the indigo red is dissolved to form a light red uniform solution. Set the condensation circulation temperature to -10°C. After the temperature stabilizes, slowly add 150mL of trifluoromethanesulfonic acid dropwise to the three-necked flask. After reacting for 48 hours, the viscosity of the system rises sharply. Slowly pour the reactant into pure water to obtain a crude PN product. After drying this product, dissolve it in an organic solvent, DMSO, and pour the dissolved solution into pure water again to precipitate. Repeat this operation three times, and then dry the precipitated polymer to obtain the final polymer PN: where m is 10 2 -10 7 between.

[0038] 2. Preparation of SPN polymer:

[0039] Weigh 2.5g of PN polymer into a single-necked round-bottom flask, place the round-bottom flask in an oil bath, add a magnet, and add the organic solvent DMF to dissolve with stirring. After dissolution is complete, add 0.9g of propane sultone and 0.39g of NaH as a hydrogen extraction agent. Raise the oil bath temperature to 70°C and react for 12 hours. Then, precipitate the reactant and dry it to obtain a crude SPN product. Dissolve the crude SPN product in the organic solvent DMF and precipitate it again. Repeat this process three times to obtain a high-purity SPN polymer: Where y=0.5.

[0040] 3. Preparation of SPNO polymer:

[0041] Weigh 5g of SPN polymer and place it in a single-necked round-bottom flask. Place the round-bottom flask in an oil bath, add a magnetic rod to the round-bottom flask, add the organic solvent DMSO and stir to dissolve. After the dissolution is complete, add 0.4g of 1-bromo-2-(2-methoxyethoxy)ethane and 0.22g of NaH as a hydrogen extraction agent. Raise the oil bath temperature to 60°C and react for 12 hours. Then, precipitate the reactant and dry it to obtain a crude SPNO product. Dissolve the crude SPNO product in the organic solvent DMSO and precipitate it again. Repeat this three times to obtain a high-purity SPNO polymer:

[0042] Where p=0.5, q=0.3.

[0043] 4. Preparation of membrane:

[0044] Weigh 1 g of the SPN polymer prepared in Step 2 into a 20 mL round-bottom flask. Add 9 g of the organic solvent, DMF, to the flask. Stir on a magnetic stirrer until dissolved to obtain a membrane solution. Cast the membrane solution evenly onto a glass plate and dry at 90°C for 24 hours to obtain an SPN membrane, which serves as a control for side chain modification.

[0045] Weigh 1 g of the SPNO polymer prepared in Step 3 into a 20 mL round-bottom flask. Add 9 g of the organic solvent, DMF, and stir on a magnetic stirrer until dissolved to obtain a membrane solution. This membrane solution was evenly cast onto a glass plate and dried at 90°C for 24 hours to form a membrane. This resulted in a cation-selective membrane modified with ether side chains, designated SPNO-1.

[0046] The photo of the membrane material prepared in this example is as follows Figure 1 As shown. 1 The chemical structure of the SPNO polymer prepared in this example was characterized by HNMR. Figure 2 The infrared spectrum of the film material prepared in this embodiment was tested using a Fourier transform infrared spectrometer, as shown in FIG. Figure 3As shown in the figure, the significant ether bond peak in the infrared results proves the successful synthesis of SPNO polymer. The pore size distribution of SPNO-1 membrane calculated from the carbon dioxide adsorption and desorption test results is shown in the figure. Figure 4 shown.

[0047] Example 2

[0048] The steps for preparing the cation selective separation membrane modified with ether side chains in this embodiment are as follows:

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

[0050] Preparation of SPN polymer: The same preparation method as in Example 1 was used.

[0051] Preparation of SPNO polymer: The same preparation method as in Example 1 was used, except that the amount of 1-bromo-2-(2-methoxyethoxy)ethane added was adjusted to 0.75 g.

[0052] Preparation of membrane: The same preparation method as in Example 1 was used, and the obtained membrane was named SPNO-2.

[0053] The pore size distribution of the membrane obtained in this embodiment is calculated from the infrared spectrum and carbon dioxide adsorption and desorption test results. Figure 3 and Figure 4 The significant ether bond peak in the infrared results proves the successful synthesis of SPNO-2 polymer.

[0054] Example 3

[0055] The steps for preparing the cation selective separation membrane modified with ether side chains in this embodiment are as follows:

[0056] Preparation of PN polymer: The same preparation method as in Example 1 was used.

[0057] Preparation of SPN polymer: The same preparation method as in Example 1 was used.

[0058] Preparation of SPNO polymer: The same preparation method as in Example 1 was used, except that the amount of 1-bromo-2-(2-methoxyethoxy)ethane added was adjusted to 1.1 g.

[0059] Preparation of membrane: The same preparation method as in Example 1 was used, and the obtained membrane was named SPNO-3.

[0060] The infrared spectrum and pore size analysis results of the carbon dioxide adsorption and desorption tests of the membrane obtained in this example are as follows: Figure 3 and Figure 4 The significant ether bond peak in the infrared results proves the successful synthesis of SPNO-2 polymer.

[0061] 2. Membrane flux and ion selectivity test

[0062] Use Figure 5 The device shown in the figure tests the Li ion selective separation membrane obtained in each embodiment at different current densities. + / Mg 2+ 、Na + / Mg 2+ 、Na + / Ca 2+ Ion selectivity was determined using a commercial cation selective separation membrane CIMS and a membrane made directly from the SPN polymer synthesized in Example 1 as controls.

[0063] The interior of the device is divided into four chambers by three membranes: (cathode) pole chamber | concentration chamber | desalination chamber | pole chamber (anode). The membranes between the pole chamber and the concentration chamber, and between the pole chamber and the desalination chamber are commercial common anion exchange membranes AGU, whose main purpose is to separate the pole chamber solution from the internal chamber solution. The membrane to be tested is located between the desalination chamber and the concentration chamber. A 0.3M sodium sulfate solution circulates in the pole chamber, a 0.01M LiCl solution circulates in the concentration chamber, and a mixture of 0.1M MCl and 0.1M NCl2 (where M represents Li or Na, and N represents Mg or Ca) circulates in the desalination chamber. After the device circulates the corresponding solutions, voltage is applied on both sides. The cations in the desalination chamber migrate from the desalination chamber to the concentration chamber under the action of the electric field. Finally, the concentrations of different ions in the concentration chamber are measured, and the ion flux is calculated based on the concentration:

[0064]

[0065] Where: C t is the ion concentration after the concentration chamber has been running for t hours, C0 is the initial ion concentration of the concentration chamber, and A m is the effective area of the membrane in the test, t is the running time, V is the final volume of the concentration chamber, and the final selectivity P is calculated by the following formula:

[0066]

[0067] in, is the initial lithium ion or sodium ion concentration in the desalination chamber, is the initial concentration of magnesium ions or calcium ions in the desalination chamber.

[0068] The membranes obtained in Examples 1 to 3 were -2 , 5mAcm -2 、10mAcm -2 Li at current density + / Mg 2+ The selectivity test results are shown in Table 1, Table 2, and Table 3. -2Na at current density + / Mg 2+ 、Na + / Ca 2+ The ion selectivity test results are shown in Tables 4 and 5.

[0069] Table 1

[0070]

[0071] Table 2

[0072]

[0073] Table 3

[0074]

[0075] Table 4

[0076]

[0077]

[0078] Table 5

[0079]

[0080] From the selectivity test results of the SPNO membranes and SPN-based membranes obtained in Examples 1-3, it can be seen that the ion separation performance of SPN is significantly improved after the introduction of ether-containing side chains, which illustrates the effectiveness of the introduction of ether-containing side chains in the present invention. Compared with commercial membranes, the performance of the series of membrane materials prepared by the present invention at different current densities far exceeds that of commercial CIMS cation-selective membranes, and the selectivity under different ion systems is also better than that of commercial membranes. This is mainly due to the large number of ether bond units introduced into the self-microporous polymer membrane of the present invention. The interaction between the ether bond in the small molecule and the lithium and sodium ions promotes a significant reduction in the energy barrier when the ether bond enters the membrane from the solution, while the divalent ions enter the membrane relatively less due to the weaker interaction force. And due to its specific interaction force with monovalent cations such as lithium ions and sodium ions, it promotes the transmission of monovalent ions, and ultimately significantly increases the flux of monovalent ions, at 10 mA cm -2 The monovalent ion flux at the current density was greater than 3 mol m -2 h -1, far exceeding the monovalent ion flux of the commercial membrane CIMS, illustrating the effectiveness of the ether bond-containing small molecules introduced by the present invention in the selective construction of mono / divalent selective cation selective separation membranes. In contrast, the flux of divalent cations is much lower than that of the commercial membrane CIMS, which ultimately significantly increases the selectivity of the cation selective separation membrane provided by the present invention. This is based on the competitive relationship between ions. Under the action of ether bonds, monovalent cations have a higher affinity. Due to the limited binding sites in the membrane, more monovalent ions are bound into the membrane, reducing the amount of divalent cations entering. On the other hand, thanks to the inherent microporous characteristics of PN polymer, the pore size of PN is further reduced through the regulation of sulfonic acid monomers and ether bond small molecule monomers, which makes the size smaller. Based on the reaction grafting of sulfonated monomers of the basic self-microporous polymer PN, the prepared SPN polymer itself has sulfonate groups, which makes the polymer have ion exchange function. On this basis, additional small molecule monomers containing ether bonds are grafted, and the different forces between ether bonds and different ions are used to construct the transmission differences between ions. From the pore size analysis results, it can be seen that the introduction of small molecule monomers containing ether bonds can effectively regulate the original pore size of PN polymer, and the pore size distribution is narrower and the pore size is smaller (such as Figure 4 At the same time, as the amount of ether-containing small molecule monomers gradually increased, the selectivity of the SPNO membrane showed a gradual upward trend, which means that ether-containing small molecules play an important role in the process of constructing selectivity.

[0081] In summary, the preparation method of the cation-selective separation membrane containing ether side chains provided by the present invention has a simple process, excellent performance, and is extremely easy to achieve industrial preparation. It has great application potential in the fields of chemical precision separation, seawater desalination, energy, rare earth separation, etc.

Claims

1. A method for preparing a cation selective separation membrane modified with an ether side chain, characterized in that: The steps include: Step 1: using a PN polymer having a structural formula as shown in formula (1) as a precursor for preparing a cation selective separation membrane; Step 2: reacting and grafting the PN polymer with the sulfonated monomer to prepare a polymer SPN with ion exchange groups; Step 3: The polymer SPN with cation exchange groups is reacted and grafted with a small molecule monomer containing an ether bond to prepare an SPNO polymer; Step 4: dissolving the SPNO polymer in an organic solvent to obtain a membrane solution, pouring the membrane solution into a mold and drying it to obtain a cation selective separation membrane modified with an ether side chain.

2. The preparation method according to claim 1, wherein: In step 1, the molecular weight range of PN polymer is 10 2 -10 7 between.

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

4. The preparation method according to claim 1, wherein: In step 2, the sulfonated monomer is Wherein, x is any integer from 1 to 5.

5. The preparation method according to claim 1 or 4, characterized in that: In step 2, the reaction grafting site on the PN polymer is a -OH site or a -NH- site, the molar ratio of the total number of reaction sites of the PN polymer to the sulfonated monomer is 1:0.1-1, the reaction temperature is 50°C-120°C, the reaction time is 12h-48h, and a hydrogen extraction reagent is added during the reaction.

6. The preparation method according to claim 1, wherein: In step 3, the small molecule monomer containing an ether bond is Wherein, y is any integer between 1 and 10.

7. The preparation method according to claim 1 or 6, characterized in that: In step 3, the reaction grafting site on the SPN polymer is a -OH site or a -NH- site, the molar ratio of the total number of SPN reaction sites to the small molecule containing an ether bond is 1:0.1~1, the reaction grafting temperature range is 50°C-120°C, the reaction time is 12h-48h, and a hydrogen extraction reagent is added during the reaction.

8. The preparation method according to claim 1, wherein: In step 4, the drying temperature is between 30°C and 120°C.

9. A cation selective separation membrane modified with ether side chains obtained by the preparation method according to any one of claims 1 to 8.

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