A monovalent selective cation exchange membrane with crown ether encapsulated in the membrane and its preparation method

Abstract

The present invention belongs to the field of cation exchange membranes and discloses a monovalent selective cation exchange membrane with crown ether encapsulated within the membrane and a preparation method thereof. First, a sulfonated chloromethylated polymer is synthesized and the solvent is evaporated to form a membrane. The chemical reaction between the chloromethyl groups contained in the membrane and the amine groups provides growth sites for the covalent organic framework. Subsequently, the covalent organic framework is constructed within the membrane channel by an in situ growth method, and the crown ether nanomaterial is encapsulated within the membrane. The regular porous channels of the covalent organic framework and the sulfonic acid groups in the base membrane act synergistically to ensure good ion flux of monovalent ions. At the same time, the crown ether structure has a special recognition and complexing effect on alkali metal ions and has different affinities for different metal ions, thereby achieving selective separation of monovalent cations. The monovalent selective cation exchange membrane prepared by the present invention is suitable for electrodialysis processes.

Description

Technical Field

[0001] The invention belongs to the field of cation exchange membranes, and particularly relates to a monovalent selective cation exchange membrane with crown ether encapsulated in the membrane and a preparation method thereof. Background Art

[0002] Water, as an indispensable resource, is of paramount importance both in itself and for the valuable resources it contains. In numerous applications, such as lithium extraction from salt lakes, seawater desalination, and wastewater treatment, electrodialysis technology, centered around monovalent-selective cation exchange membranes, has demonstrated unique appeal due to its ease of operation, high energy efficiency, and low application requirements. Generally speaking, efficient monovalent-selective cation exchange membranes require high flux of monovalent ions and good selectivity between monovalent and polyvalent cations. Previously, researchers have successfully developed a series of cation exchange membranes with some success through various strategies, including cross-linking, surface modification, and polymer blending. However, while existing methods improve membrane selectivity, they often increase monovalent ion transport resistance, leading to increased membrane resistance and reduced cation flux. Furthermore, the commercialization of monovalent ion-selective membranes is severely hampered by poor separation structural stability. Therefore, there is an urgent need to develop novel membrane materials that can effectively address the trade-off between ion flux and selectivity while simultaneously improving separation structural stability.

[0003] Covalent organic frameworks (COFs) are a new type of crystalline porous polymers formed by covalent bonds. Their remarkable characteristics are regular pore structure, high porosity and excellent chemical stability. In many studies, due to the regular and orderly porous channels of COFs materials, they can exhibit low mass transfer resistance. This low mass transfer resistance is extremely beneficial for the transport of ions, and is therefore regarded as an effective way to resolve the trade-off between ion flux and selectivity. At present, the research progress of using COFs to prepare monovalent selective cation exchange membranes is still relatively slow. The main difficulty lies in the difficulty of constructing a defect-free COFs layer. In addition, the pore size of existing COFs materials is usually in the range of 1-5nm, which is relatively large compared to the hydration kinetic diameter of inorganic salt ions (less than 1nm), so it is difficult to achieve efficient ion screening effects. Therefore, by carefully designing and adapting COFs, COF is only used as a sealing network within the membrane, and it is not relied on to achieve ion screening. Instead, other compounds with specific functions are encapsulated inside the membrane through the sealing of the COF network, thereby achieving selective separation of ions. In this way, monovalent selective cation exchange membranes can be prepared, which can effectively avoid the above-mentioned defects while achieving precise and efficient separation of specific ions. This is of extremely critical significance and value for promoting technological development in related fields. Summary of the Invention

[0004] To address the aforementioned technical issues in the prior art, a method for preparing a monovalent selective cation exchange membrane for electrodialysis is needed. The method should ensure that the resulting cation exchange membrane exhibits good stability and monovalent and polyvalent cation selective permeability, while also being simple and easy to operate.

[0005] The present invention aims to produce a highly selective, high-throughput monovalent selective cation exchange membrane. A method for preparing a monovalent selective cation exchange membrane with crown ether encapsulation within the membrane is provided. The monovalent selective cation exchange membrane with crown ether encapsulation within the membrane utilizes an in-situ growth method to construct a covalent organic framework encapsulation network composed of aldehyde and amine monomers within a SPPSU-Cl membrane. This encapsulates the crown ether compound within the membrane. When ions pass through the membrane, the crown ether structure's specific ion recognition and complexing capabilities enable ion separation.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The present invention uses a very simple in-situ growth method to prepare a monovalent selective cation exchange membrane with a covalent organic framework structure and a crown ether structure. The covalent organic framework network is successfully constructed within the membrane while the crown ether is encapsulated within the membrane. The specific technical solution is as follows:

[0008] A method for preparing a monovalent selective cation exchange membrane with crown ether encapsulated in the membrane comprises the following steps:

[0009] Step 1: Weigh a certain amount of sulfonated polymer and dissolve it in N,N-dimethylacetamide, use a chloromethyl ether compound as a chloromethylation reagent, and use tin tetrachloride as a catalyst to prepare a sulfonated chloromethylated polymer;

[0010] Step 2: Weigh a certain amount of the sulfonated chloromethylated polymer prepared in step 1 and dissolve it in dimethyl sulfoxide to prepare a casting solution. Cast the casting solution on a glass plate and heat and dry it. After the solvent is completely evaporated, take out the film and store it in a wet state.

[0011] Step 3: Weigh a certain amount of aldehyde monomer and crown ether compound and add them to a certain amount of organic solvent to prepare an organic phase solution; weigh a certain amount of amino monomer and add it to a certain concentration of acetic acid aqueous solution to prepare an aqueous phase solution;

[0012] Step 4: Place the membrane prepared in step 2 in a diffusion cell, add the organic phase solution prepared in step 3 to one side, and add the aqueous phase solution prepared in step 3 to the other side, and react at a certain temperature for a period of time;

[0013] Step 5: Take out the membrane prepared in step 4, wash it in pure water and store it in a wet state.

[0014] Furthermore, in step one, the sulfonated polymer is one or more of sulfonated polyphenylsulfone, sulfonated polyetheretherketone, and sulfonated polyethersulfone.

[0015] Furthermore, the chloromethyl ether compound in step 1 is one of chloromethyl methyl ether and chloromethyl ethyl ether.

[0016] Furthermore, the aldehyde monomer in step three is one of trialdehyde phloroglucinol, trimesaldehyde, and 1,3,5-tris(4-aminophenyl)benzene.

[0017] Furthermore, the amino monomer in step three is one of trialdehyde p-phenylenediamine, benzidine, and 4,4'-diaminoterphenyl.

[0018] Furthermore, the crown ether compound in step three is one of dibenzo-12-crown-4, dibenzo-15-crown-5, dibenzo-18-crown-6, benzo-18-crown-6, and dibenzo-24-crown-8.

[0019] Furthermore, in step 3, the concentration of the organic phase is 0.1-2 mmol / L for the aldehyde monomer and the crown ether compound, and 0.15-3 mmol / L for the positively charged amino monomer.

[0020] A monovalent selective cation exchange membrane with crown ether encapsulated in the membrane is prepared by any one of the preparation methods described above.

[0021] Compared with the existing technology, the present invention has the following advantages: 1. The present invention adopts a very simple in-situ growth method to prepare a monovalent selective cation exchange membrane with crown ether encapsulated in the membrane, successfully constructs a covalent organic framework network in the membrane and encapsulates the crown ether in the membrane, which is simple and easy to operate. 2. The monovalent selective cation exchange membrane with crown ether encapsulated in the membrane prepared by the present invention has a covalent organic framework network and an internal encapsulated crown ether structure. The crown ether structure has different forces on alkali metal ions, thereby achieving Li + / Mg 2+ 、Na + / Mg 2+ and K + / Mg 2+ Selective separation, with separation performance higher than commercial membranes, can be applied to lithium extraction from salt lakes, crude salt refining, etc. 3. The covalent organic framework structure and crown ether structure introduced in the present invention are expected to alleviate the balance / trade-off effect between flux and selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a physical picture of the monovalent selective cation exchange membrane prepared in Example 1;

[0023] Figure 2a This is a scanning electron microscope plan view of the monovalent selective cation exchange membrane prepared in Example 1;

[0024] Figure 2b This is a transmission electron microscopy cross-sectional view of the monovalent selective cation exchange membrane prepared in Example 1;

[0025] Figure 3 Schematic diagram of the structure of the testing device of the present invention;

[0026] Reference numerals in the figure: 1-first electrode chamber, 2-dilute chamber, 3-concentrated chamber, 4-second electrode chamber, 5-first anion exchange membrane, 6-monovalent selective cation exchange membrane, 7-second anion exchange membrane, 8-anode, 9-cathode, 10-feed liquid port. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings.

[0028] The method for preparing a monovalent selective cation exchange membrane with crown ether encapsulated in the membrane of the present invention comprises the following steps:

[0029] Step 1: Weigh a certain amount of sulfonated polymer and dissolve it in N,N-dimethylacetamide, use a chloromethyl ether compound as a chloromethylation reagent, and use tin tetrachloride as a catalyst to prepare a sulfonated chloromethylated polymer;

[0030] Step 2: Weigh a certain amount of the sulfonated chloromethylated polymer prepared in step 1 and dissolve it in dimethyl sulfoxide to prepare a casting solution. Cast the casting solution on a glass plate and heat and dry it. After the solvent is completely evaporated, take out the film and store it in a wet state.

[0031] Step 3: Weigh a certain amount of aldehyde monomer and crown ether compound and add them to a certain amount of organic solvent to prepare an organic phase solution; weigh a certain amount of amino monomer and add it to a certain concentration of acetic acid aqueous solution to prepare an aqueous phase solution;

[0032] Step 4: Place the membrane prepared in step 2 in a diffusion cell, add the organic phase solution prepared in step 3 to one side, and add the aqueous phase solution prepared in step 3 to the other side, and react at a certain temperature for a period of time;

[0033] Step 5: Take out the membrane prepared in step 4, wash it in pure water and store it in a wet state.

[0034] Example 1

[0035] Monovalent selective cation exchange membranes based on different polymers were prepared by selecting different sulfonated polymers. 8.8 g of sulfonated polyphenylsulfone (SPPSU) was dissolved in 150 ml of dimethyl ether (DMCA), followed by the dropwise addition of 2 ml of chloromethyl ether and 2 ml of anhydrous tin tetrachloride. The reaction was carried out at 0°C for 48 h. The product was precipitated and dried in water to obtain sulfonated chloromethylated polyphenylsulfone (SPPSU-Cl). 0.784 g of SPPSU-Cl was added to 6.30 g of dimethyl sulfoxide to prepare a casting solution, which was then dried at 60°C for 12 h to obtain the SPPSU-Cl-based membrane. 0.05 mmol of trialdehyde phloroglucinol and 0.05 mmol of dibenzo-18-crown 6 were dissolved in 100 mL of n-heptane, and 0.075 mmol of benzidine was dissolved in 100 ml of 6 mol / L aqueous acetic acid. Both solutions were added to both sides of a diffusion cell sandwiching the SPPSU-Cl membrane. The solution was reacted at room temperature for 72 h. The membrane was removed, de-bubbled, and placed in a mixed salt solution, designated M-1.

[0036] Example 2

[0037] The difference from Example 1 is that in step 1, the sulfonated polyethersulfone is chloromethylated, and the degree of chloromethylation is the same. In step 2, 0.784 g of SPES-Cl is added to 6.30 g of dimethyl sulfoxide to prepare a casting solution. Other operations are the same as in Example 1. The membrane is named M-2.

[0038] Example 3

[0039] The difference from Example 1 is that in step 1, the sulfonated polyetheretherketone is chloromethylated, and the degree of sulfonation is the same as the degree of chloromethylation. In step 2, 0.784 g of SPEEK-Cl is added to 6.30 g of dimethyl sulfoxide to prepare a casting solution. Other operations are the same as in Example 1. The membrane is named M-3.

[0040] Example 4

[0041] This example prepares different monovalent selective cation exchange membranes by adjusting the type of amino monomer. The difference from Example 1 is that 0.075 mmol of p-phenylenediamine is used in step 3. Other operations are the same as Example 1. The membrane is named M-4.

[0042] Example 5

[0043] The difference from Example 1 is that 0.075 mmol of one of the 4,4'-diaminoterphenyls is used in step 3. Other operations are the same as in Example 1. The membrane is named M-5.

[0044]

[0045] Table 1: Separation performance of the cation exchange membranes prepared in Examples 1-5 for a 0.05 mol / L lithium-magnesium mixed solution.

[0046] Table 1 shows that regardless of the type of polymer, the monovalent selective cation exchange membrane obtained by the preparation method of the present invention has a good screening effect of monovalent and divalent cations. Example 1 is the membrane with the best lithium and magnesium selectivity, Li + / Mg 2+ The selectivity reached 22.290, and the flux of lithium ions was also high, reaching 1164.687 mmol m -2 h -1 Regardless of the type of amino monomer, a certain monovalent and divalent cation screening effect can be achieved.

[0047] Example 6

[0048] In this example, different monovalent selective cation exchange membranes were prepared by adjusting the type of crown ether compound. 0.784 g of SPPSU-Cl was added to 6.30 g of dimethyl sulfoxide to prepare a casting solution, which was then dried at 60°C for 12 hours to obtain the SPPSU-Cl-based membrane. 0.05 mmol of trialdehyde phloroglucinol and 0.05 mmol of dibenzo-12-crown-4 were dissolved in 100 mL of n-heptane, and 0.075 mmol of benzidine was dissolved in 100 mL of 6 mol / L aqueous acetic acid. Both solutions were added to both sides of a diffusion cell sandwiching an SPPSU-Cl membrane. The membrane was reacted at room temperature for 72 hours. The membrane was removed, defoamed, and placed in a mixed salt solution, designated M-6.

[0049] Example 7

[0050] The difference from Example 6 is that in step 3, 0.05 mmol of trialdehyde phloroglucinol and 0.05 mmol of dibenzo-15-crown-5 were dissolved in 100 mL of n-heptane. Other operations were the same as in Example 6, and the membrane was named M-7.

[0051] Example 8

[0052] The difference from Example 4 is that in step 3, 0.05 mmol of TP and 0.05 mmol of dibenzo-24-crown-8 were dissolved in 100 mL of n-heptane. Other operations were the same as in Example 6, and the membrane was named M-8.

[0053] Example 9

[0054] The difference from Example 4 is that in step 3, 0.05 mmol of TP and 0.05 mmol of benzo-18-crown 6 were dissolved in 100 mL of n-heptane. Other operations were the same as in Example 6, and the membrane was named M-9.

[0055]

[0056] Table 2: Separation performance of the cation exchange membranes prepared in Examples 6-9 for 0.05 mol / L lithium-magnesium mixed solution.

[0057] Table 2 shows that Example 7 is the membrane with the best lithium-magnesium selectivity, Li + / Mg 2+ The selectivity reached 68.489, and the flux of lithium ions was also high, reaching 1225.408 mmol m -2 h -1 The regular porous channels of the covalent organic framework and the sulfonic acid groups in the SPPSU-Cl membrane ensure good ion flux for monovalent ions. Different crown ether compounds exhibited certain lithium-magnesium selectivity, with dibenzo-15-crown-5 performing the best.

[0058] Application test experiment:

[0059] like Figure 3 As shown in the figure, this experiment uses a laboratory-made membrane stack to test the unit price selectivity of the membrane. First, 0.05 mol / L Na + / Mg 2+ 、Li + / Mg 2+ , K + / Mg 2+ The mixed solution was used as the test solution and 0.05 mol / L Na2SO4 solution was used as the circulating polar solution. The modified membrane was immersed in 0.05 mol / L Na + / Mg 2+ 、Li + / Mg 2+ , K + / Mg 2+ The mixed solution was equilibrated for 24 hours. Then the modified cation exchange membrane was fixed between two commercial anion membranes (blue, alloy membranes), with 100 mL of Na + / Mg 2+ 、Li + / Mg 2+ , K + / Mg 2+ Mixed solution, 500mL Na2SO4 solution circulates in the polar chambers on both sides of the anion membrane through a water pump. The modified membrane has an effective area of ​​7.065cm 2 Under the direct current, the constant current density is 5.0mA cm -2 , and the stable operation was carried out for 1 h. The ion concentration in the freshwater chamber before and after the operation was determined by a cation ion chromatograph (SH-CC-3L, Shenghan, China).

[0060] The monovalent selective cation exchange membrane was operated stably for 1 h, and the ion flux was calculated using the following equation:

[0061]

[0062] where c0 and c tis a monovalent ion M + (K + 、Na + He Li + ) or Mg 2+ The concentration is 0 and th is the concentration in the desalination chamber, V is the volume of the solution in the desalination chamber, A m Represents the effective test area of ​​the membrane (7.065 cm 2 ), t represents the test duration.

[0063] The selectivity calculation formula is as follows:

[0064]

[0065] Where: J represents the membrane ion flux, unit is mmol m -2 h -1 ; c0 represents the ion concentration before separation, in mol / L. Na+ and c Mg2+ Represents the monovalent ion M after separation + (K + 、Na + He Li + )Na + Mg 2+ Plasma concentration, in mol / L.

[0066] The above contents are only preferred embodiments of the present invention and are not intended to limit the implementation scheme of the present invention. Ordinary technicians in this field can easily make corresponding changes or modifications based on the main concepts and spirit of the present invention. Therefore, the scope of protection of the present invention shall be based on the scope of protection required by the claims.

Claims

1. A method for preparing a monovalent selective cation exchange membrane with crown ether encapsulated in the membrane, characterized in that The following steps are involved: Step 1: Weigh a certain amount of sulfonated polymer and dissolve it in N,N-dimethylacetamide, use a chloromethyl ether compound as a chloromethylation reagent, and use tin tetrachloride as a catalyst to prepare a sulfonated chloromethylated polymer; Step 2: Weigh a certain amount of the sulfonated chloromethylated polymer prepared in step 1 and dissolve it in dimethyl sulfoxide to prepare a casting solution. Cast the casting solution on a glass plate, heat and dry it. After the solvent is completely evaporated, take out the film and store it in a wet state. Step 3: Weigh a certain amount of aldehyde monomer and crown ether compound and add them to a certain amount of organic solvent to prepare an organic phase solution; weigh a certain amount of amino monomer and add them to a certain concentration of acetic acid aqueous solution to prepare an aqueous phase solution; Step 4: Place the membrane prepared in step 2 in a diffusion cell, add the organic phase solution prepared in step 3 to one side, and add the aqueous phase solution prepared in step 3 to the other side, and react at a certain temperature for a period of time; Step 5: Take out the membrane prepared in step 4, wash it in pure water and store it in a wet state.

2. The preparation method according to claim 1, wherein: In step 1, the sulfonated polymer is one or more of sulfonated polyphenylsulfone, sulfonated polyetheretherketone, and sulfonated polyethersulfone.

3. The preparation method according to claim 1, wherein: The chloromethyl ether compound in step 1 is one of chloromethyl methyl ether and chloromethyl ethyl ether.

4. The preparation method according to claim 1, wherein: The aldehyde monomer in step 3 is one of trialdehyde phloroglucinol, trimesaldehyde, and 1,3,5-tris(4-aminophenyl)benzene.

5. The preparation method according to claim 1, wherein: The amino monomer in step 3 is one of p-phenylenediamine, benzidine, and 4,4'-diaminoterphenyl.

6. The preparation method according to claim 1, wherein: The crown ether compound in step three is one of dibenzo-12-crown-4, dibenzo-15-crown-5, dibenzo-18-crown-6, benzo-18-crown-6, and dibenzo-24-crown-8.

7. The preparation method according to claim 1, wherein: The concentration of the organic phase solution in step 3 is 0.1-2 mmol / L for the aldehyde monomer and the crown ether compound, and 0.15-3 mmol / L for the positively charged amino monomer.

8. A monovalent selective cation exchange membrane with crown ether encapsulated in the membrane, characterized in that: The method is as described in any one of claims 1 to 7.

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