Monovalent selective cation exchange membrane with crown ether encapsulated therein and preparation method of monovalent selective cation exchange membrane

Abstract

The invention belongs to the field of cation exchange membranes, and discloses a monovalent selective cation exchange membrane with crown ether encapsulated in the membrane and a preparation method of the monovalent selective cation exchange membrane. Firstly, a sulfonated chloromethylated polymer is synthesized, a solvent is evaporated to form a membrane, and a chemical reaction of chloromethyl and amido contained in the membrane endows a growth site of a covalent organic framework. And then constructing a covalent organic framework in a membrane channel by an in-situ growth method, and packaging the crown ether nano material in the membrane. A regular porous channel of the covalent organic framework and a sulfonic acid group in the base membrane have a synergistic effect, so that good ion flux of monovalent ions is ensured. Meanwhile, the crown ether structure has a special recognition complexing effect on alkali metal ions and has different affinity to different metal ions, so that the monovalent cation selective separation is achieved, and the prepared monovalent selective cation exchange membrane is suitable for an electrodialysis process.

Description

Technical Field

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

[0002] As an indispensable resource, water itself and the precious resources contained in it are of great significance. In many fields such as lithium extraction from salt lakes, seawater desalination and wastewater treatment, electrodialysis technology with monovalent selective cation exchange membrane as the core has shown unique appeal due to its significant advantages of simple operation, high energy efficiency and low application requirements. Generally speaking, efficient monovalent selective cation exchange membranes often need to have high flux of monovalent ions and good selectivity between monovalent and multivalent cations. Previously, researchers have successfully developed a series of cation exchange membranes with certain results through various strategies such as cross-linking, surface modification and polymer mixing. However, while the existing methods improve membrane selectivity, they often lead to increased monovalent ion transmission resistance, which in turn increases membrane resistance and reduces cation flux. In addition, the poor stability of the separation structure has also seriously restricted the commercialization process of monovalent ion selective separation membranes. Therefore, there is an urgent need to develop new membrane materials to effectively solve the trade-off between ion flux and selectivity, and simultaneously improve the stability of the separation structure.

[0003] Covalent organic frameworks (COFs) are a new type of crystalline porous polymers formed by covalent bonds. Their remarkable features include regular pore structure, high porosity and excellent chemical stability. In many studies, COFs materials can exhibit low mass transfer resistance due to their regular and orderly porous channels. This low mass transfer resistance is extremely beneficial for the transport of ions, and is therefore seen as an effective way to resolve the trade-off between ion flux and selectivity. At present, the research progress on the use of 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 ion screening is not achieved by relying on it. 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] In order to solve the above technical problems existing in the prior art, a method for preparing a monovalent selective cation exchange membrane is required for the electrodialysis process. The method should enable the obtained cation exchange membrane to have good stability and monovalent and polyvalent cation selective permeability, and the preparation method should be simple and easy to operate.

[0005] The purpose of the present invention is to prepare a high-selectivity and high-flux monovalent selective cation exchange membrane, and to provide a method for preparing a monovalent selective cation exchange membrane with crown ether encapsulated in the membrane. The monovalent selective cation exchange membrane with crown ether encapsulated in the membrane is to construct an in-situ growth covalent organic framework encapsulation network of aldehyde monomers and amine monomers in SPPSU-Cl membrane by an in-situ growth method, and encapsulate the crown ether compound in the membrane. When ions pass through the membrane, due to the specific ion recognition and complexing ability of the crown ether structure, the purpose of ion separation is achieved.

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

[0007] The present invention adopts a very simple in-situ growth method to prepare a monovalent selective cation exchange membrane having a covalent organic framework structure and a crown ether structure, successfully constructs a covalent organic framework network in the membrane and encapsulates the crown ether in the membrane. The specific technical scheme 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, weighing a certain amount of sulfonated polymer and dissolving it in N,N-dimethylacetamide, using chloromethyl ether compounds as chloromethylation reagents, and using tin tetrachloride as a catalyst to prepare 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, heat and dry it, and after the solvent is completely evaporated, take out the film and store it in a wet state;

[0011] Step 3, weighing a certain amount of aldehyde monomer and crown ether compound and adding them to a certain amount of organic solvent to prepare an organic phase solution; weighing a certain amount of amine monomer and adding them to an acetic acid aqueous solution of a certain concentration 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 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 amine 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 prior art, 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 internally 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 A scanning electron microscope plan view of the monovalent selective cation exchange membrane prepared in Example 1;

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

[0025] Figure 3 It is a 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 inlet. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with 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, weighing a certain amount of sulfonated polymer and dissolving it in N,N-dimethylacetamide, using chloromethyl ether compounds as chloromethylation reagents, and using tin tetrachloride as a catalyst to prepare 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, heat and dry it, and after the solvent is completely evaporated, take out the film and store it in a wet state;

[0031] Step 3, weighing a certain amount of aldehyde monomer and crown ether compound and adding them to a certain amount of organic solvent to prepare an organic phase solution; weighing a certain amount of amine monomer and adding them to an acetic acid aqueous solution of a certain concentration 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 in step 4, wash it in pure water and store it in a wet state.

[0034] Example 1

[0035] Monovalent selective cation exchange membranes with different polymer substrates were prepared by selecting different sulfonated polymers. 8.8g of sulfonated polyphenylsulfone (SPPSU) was weighed and dissolved in 150ml DMAC, and 2ml of chloromethyl ether and 2ml of anhydrous tin tetrachloride were added dropwise in turn. The reaction was carried out at 0℃ for 48h. The product was precipitated and dried in water to obtain sulfonated chloromethylated polyphenylsulfone (SPPSU-Cl). 0.784g of SPPSU-Cl was weighed and added to 6.30g of dimethyl sulfoxide to prepare a casting solution, which was dried at 60℃ for 12 hours to obtain a SPPSU-Cl-based membrane. 0.05mmol of trialdehyde pyrogallol and 0.05mmol of dibenzo-18-crown 6 were dissolved in 100mL of n-heptane, and 0.075mmol of benzidine was dissolved in 100ml of 6mol / L acetic acid aqueous solution. The two solutions were added to both sides of the diffusion cell sandwiched with the SPPSU-Cl membrane, and reacted at room temperature for 72 hours. The membrane was taken out and defoamed in a mixed salt solution and named M-1.

[0036] Example 2

[0037] The difference from Example 1 is that the sulfonated polyethersulfone is chloromethylated in step 1, and the chloromethylation degree is the same. In step 2, 0.784 g of SPES-Cl is weighed and added to 6.30 g of dimethyl sulfoxide to prepare a casting solution, and the 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 the sulfonated polyetheretherketone is chloromethylated in step 1, and the degree of sulfonation is the same as the degree of chloromethylation. In step 2, 0.784 g of SPEEK-Cl is weighed and added to 6.30 g of dimethyl sulfoxide to prepare a casting solution. The other operations are the same as in Example 1, and the membrane is named M-3.

[0040] Example 4

[0041] This example prepares different monovalent selective cation exchange membranes by adjusting the type of amine monomer. The difference from Example 1 is that 0.075 mmol of p-phenylenediamine is used in step 3. The 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. The other operations are the same as in Example 1, and the membrane is named M-5.

[0044]

[0045] Table 1: Separation performance of the cation exchange membranes prepared in Examples 1-5 for 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 for 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 1164.687mmol 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] This example prepares different monovalent selective cation exchange membranes by adjusting the type of crown ether compound. Weigh 0.784g of SPPSU-Cl and add it to 6.30g of dimethyl sulfoxide to prepare a casting solution, and dry it at 60°C for 12 hours to obtain an SPPSU-Cl base membrane. 0.05mmol of trialdehyde pyrogallol and 0.05mmol of dibenzo-12-crown 4 are dissolved in 100mL of n-heptane, and 0.075mmol of benzidine is dissolved in 100ml of 6mol / L acetic acid aqueous solution. The two solutions are added to both sides of the diffusion cell sandwiched with the SPPSU-Cl membrane, reacted at room temperature for 72 hours, and the membrane is taken out to remove bubbles in a mixed salt solution and named M-6.

[0049] Example 7

[0050] The difference from Example 6 is that in step 3, 0.05 mmol of trialdehyde pyrogallol and 0.05 mmol of dibenzo-15-crown-5 are dissolved in 100 mL of n-heptane. Other operations are the same as those in Example 6, and the membrane is 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-2,4-crown-8 are dissolved in 100 mL of n-heptane. Other operations are the same as those in Example 6, and the membrane is 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 are dissolved in 100 mL of n-heptane. Other operations are the same as those in Example 6, and the membrane is 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 1225.408mmol 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 of monovalent ions. Different types of crown ether compounds all show certain lithium-magnesium selectivity, among which dibenzo-15-crown-5 has the best performance.

[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 The constant current density is 5.0 mA cm -2 , and the stable operation was carried out for 1 h. The ion concentration in the fresh water 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 tIt is a monovalent ion M + (K + 、Na + and Li + ) or Mg 2+ The concentration is 0 and th 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, in 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 + and 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. A person skilled in the art can easily make corresponding changes or modifications based on the main concept and spirit of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope 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, weighing a certain amount of sulfonated polymer and dissolving it in N,N-dimethylacetamide, using chloromethyl ether compounds as chloromethylation reagents, and using tin tetrachloride as a catalyst to prepare 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, and after the solvent is completely evaporated, take out the film and store it in a wet state; Step 3, weighing a certain amount of aldehyde monomer and crown ether compound and adding them to a certain amount of organic solvent to prepare an organic phase solution; weighing a certain amount of amine monomer and adding them to an acetic acid aqueous solution of a certain concentration 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 in step 4, wash it in pure water and store it in a wet state.

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

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

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

6. The preparation method according to claim 1, characterized in that: 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, characterized in that: In step 3, the concentration of the organic phase is 0.1-2 mmol / L for aldehyde monomers and crown ether compounds, and 0.15-3 mmol / L for positively charged amine monomers.

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

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