Monovalent selective cation exchange membrane with crown ether grafted in ion channel 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 grafted in an ion channel and a preparation method of the monovalent selective cation exchange membrane. The preparation method comprises the following steps: firstly, synthesizing a sulfonated chloromethylated polymer, evaporating a solvent to form a membrane, and then grafting a diaminodibenzo crown ether compound into an ion channel by adopting a simple and convenient hot soaking method and utilizing mutual reaction of amino and chloromethyl, so as to introduce a crown ether structure into the ion channel of the membrane. The crown ether structure has electrostatic interaction on alkali metal and also has different acting forces on different metals, 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 grafted in an ion channel and a preparation method thereof. Background Art

[0002] Electrodialysis technology has been developing rapidly in recent years and has been widely used in many fields such as seawater desalination, brackish water treatment, acid and alkali recovery, papermaking industry, electroplating industry and food industry. As society continues to move forward, the application scope of electrodialysis continues to expand, and the performance requirements for ion exchange membranes, the key components of electrodialysis, are also increasing. Especially in specific fields such as lithium extraction from salt lakes, crude salt refining, and waste acid and waste alkali recovery, the demand for ion exchange membranes with excellent performance and high selectivity is extremely urgent.

[0003] Biological ion channels have an angstrom scale, and the channels are lined with functional groups that have specific interactions with alkaline ions, thus achieving ultra-high ion selectivity. Crown ethers have become a popular choice for constructing ion-selective structures because of their special cavity structure and electron donor properties, which can efficiently complex and anchor cations. The method of introducing crown ethers into polymer materials is mainly to introduce them into the polymer backbone or side chain, and use the crown ether's ion complexing ability or synergistic effect with other groups to achieve selective extraction or adsorption of ions. The main disadvantage of these processes is that equal amounts of stripping agents and desorbing agents are required to further obtain specific cations. Few studies have been conducted on the selective screening of ions by regulating ion channels through crown ethers in the formed polymer membrane ion channels. If crown ethers and their derivatives are combined with ion exchange resins or membranes and fixed in the membrane ion channels, effective separation of specific ions can be achieved while overcoming these shortcomings.

[0004] Common fully oxygenated crown ethers include 15-crown-5, 18-crown-6, 24-crown-8, etc. When the diameter of the metal ion matches the size of the crown ether cavity, the two will form a 1:1 crown ether-ion complex. When the diameter of the metal ion is larger than the size of the crown ether cavity, a 2:1 "sandwich" structure can be formed between the crown ether and the metal ion, such as 15-crown-5 and K + Ions can form a 2:1 complex structure. Bhattacharyya found that Li + Effect of Nafion-117 membrane loaded with dibenzo-18-crown-6 on Li + The selectivity was increased by about 6 times (compared with the blank membrane). Zoetebier et al. confirmed that poly(aryletherketone) (PEAK) and sulfonated PEAK (SPEAK) containing dibenzo-18-crown-6 groups in the main chain had a significant effect on K +The diffusion rate is 1 / 4 of that of SPAEK ion exchange membrane. Studies have shown that crown ethers and their derivatives can achieve selective separation of certain cations by reducing the mobility of specific ions in solution or membrane matrix. Therefore, it is necessary to make the ion exchange membrane modified by crown ether provide new ion channels for specific cations, ensuring ion selectivity while having higher ion flux. Summary of the invention

[0005] 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.

[0006] 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 grafted in an ion channel. The crown ether-based cation exchange membrane is a simple hot soaking method that utilizes the mutual reaction of amino groups and chloromethyl groups to first graft a diaminodibenzo crown ether compound into the ion channel of a sulfonated chloromethylated polymer membrane, thereby introducing a crown ether structure into the membrane ion channel. The crown ether and the sulfonic acid group work together to promote K + 、Na + , Li + transmission, thereby achieving the purpose of ion separation.

[0007] The objective of the present invention is achieved through the following technical solutions:

[0008] The present invention adopts a very mature casting method and a simple hot soaking method to prepare a monovalent selective cation exchange membrane having a sulfonic acid group and a crown ether structure, and successfully introduces the crown ether structure into the membrane. The specific technical scheme is as follows:

[0009] A method for preparing a monovalent selective cation exchange membrane with a crown ether grafted in an ion channel comprises the following steps:

[0010] 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;

[0011] Step 2: Weigh a certain amount of sulfonated chloromethylated polymer 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 cation exchange membrane and store it in a wet state;

[0012] Step 3, weighing a certain amount of diaminodibenzocrown ether compound and dissolving it in water to prepare a crown ether modification solution;

[0013] Step 4, immersing the cation exchange membrane in step 2 in the crown ether modification solution in step 3, and adjusting the temperature of the modification solution;

[0014] Step 5: Take out the ion exchange membrane, wash it in pure water, dry it, and store it in a wet state after low-temperature drying.

[0015] Furthermore, the sulfonated polymer in step 1 is one or more of polyphenylsulfone (PPSU), polyetheretherketone (PEEK), and polyethersulfone (PES).

[0016] Furthermore, the chloromethyl ether compound in step 1 is one of chloromethyl methyl ether and chloromethyl ethyl ether.

[0017] Furthermore, the diaminodibenzo crown ether compound in step three is one of diaminodibenzo-18-crown-4 (A18C5), diaminodibenzo-18-crown-6 (A18C6), and diaminodibenzo-18-crown-8 (A18C8).

[0018] Furthermore, in step three, the concentration of the crown ether modified liquid is 0.17-1.03 g / L.

[0019] Furthermore, in step 4, the temperature of the modified liquid is regulated to be 30-90°C.

[0020] A monovalent selective cation exchange membrane with crown ether grafted in an ion channel is prepared by any of the above-mentioned preparation methods.

[0021] Compared with the prior art, the present invention has the following advantages: 1. The present invention adopts the very mature casting method and hot soaking method to prepare the membrane with sulfonic acid group and crown ether structure, successfully introduces the crown ether into the membrane, does not require the use of special equipment, and is simple and easy to operate. 2. The crown ether-based monovalent selective cation exchange membrane prepared by the present invention has the same + 、Na + , Li + The crown ether structure has a specific interaction with the alkali metal ions, which has different forces on the alkali metal ions, thus realizing 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 crown ether structure introduced in the present invention is 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 6;

[0023] Figure 2a A scanning electron microscope plan view of the monovalent selective cation exchange membrane prepared in Example 6;

[0024] Figure 2b A scanning electron microscope cross-sectional view of the monovalent selective cation exchange membrane prepared in Example 6;

[0025] Figure 3 It is the H NMR spectrum of sulfonated chloromethylated polyphenylsulfone, A18C5, A18C6, and A18C8;

[0026] Figure 4 It is the Fourier transform infrared spectra of A18C6, sulfonated chloromethylated polyphenylsulfone and Example 6;

[0027] Figure 5 It is a schematic diagram of the structure of the testing device of the present invention;

[0028] 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

[0029] The present invention will be further described below in conjunction with the accompanying drawings.

[0030] The preparation method of the monovalent selective cation exchange of the grafted crown ether in the ion channel of this embodiment comprises the following steps:

[0031] 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;

[0032] Step 2: Weigh a certain amount of sulfonated chloromethylated polymer 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 membrane and store it in a wet state.

[0033] Step 3, weigh a certain amount of diaminodibenzo crown ether compound (A18C5, A18C6 or A18C8) and dissolve it in water to prepare a crown ether modification solution, wherein the concentration of the crown ether modification solution is 0.17-1.03 g / L;

[0034] Step 4: soak the cation exchange membrane material in step 2 in the crown ether modification solution in step 3, and adjust the temperature of the modification solution to 30-90° C.;

[0035] Step 5: Take out the ion exchange membrane, wash it in pure water, dry it, and store it in a wet state after drying it at a low temperature (60° C.).

[0036] Example 1

[0037] 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 sequence. The reaction was carried out at 0℃ for 48h, and 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, and dried at 60℃ for 12 hours to obtain a SPPSU-Cl base membrane. 0.060g of A18C6 was weighed and added to 100ml of water, and the SPPSU-Cl base membrane was stirred and immersed in it at 60℃ for 6 hours to obtain a monovalent selective cation exchange membrane based on SPPSU-Cl. The membrane was taken out and soaked in a mixed salt solution, named SPPSU-18C6.

[0038] Example 2

[0039] The difference from Example 1 is that the sulfonated polyethersulfone is sulfonated and chloromethylated in step 1, and the degree of sulfonation is the same as the degree of chloromethylation. In step 3, 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 SPES-18C6.

[0040] Example 3

[0041] 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. Other operations are the same as in Example 1, and the membrane is named SPEEK-18C6.

[0042] Example 4

[0043] The difference from Example 1 is that in step 1, chloromethyl methyl ether is used to chloromethylate the sulfonated polyphenylsulfone, and the degree of sulfonation is the same as the degree of chloromethylation. In step 2, 0.784 g of SPPSU-Cl is weighed and added to 6.30 g of dimethyl sulfoxide to prepare a casting solution. Other operations are the same as in Example 1, and the membrane is named SPPSU / 2-18C6.

[0044]

[0045] Table 1: Separation performance of the cation exchange membranes prepared in Examples 1-4 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 prepared by chloromethylation of sulfonated polyphenylsulfone with chloromethyl ethyl ether is the membrane with the best lithium-magnesium selectivity, with a Li+ / Mg2+ selectivity of 7.730 and a high lithium ion flux of 1111.605 mmol m -2 h -1 .

[0047] Example 5

[0048] In this example, different monovalent selective cation exchange membranes were prepared by adjusting the amount of A18C6. 0.784 g of SPPSU-Cl was weighed and added to 6.30 g of dimethyl sulfoxide to prepare a casting solution, which was dried at 60°C for 12 hours to obtain a SPPSU-Cl base membrane. 0.017 g of A18C6 was weighed and added to 100 ml of water, and the SPPSU-Cl base membrane was stirred and immersed in the water at 60°C for 6 hours to obtain a monovalent selective cation exchange membrane based on SPPSU-Cl. The membrane was taken out and immersed in a mixed salt solution, named SPPSU-18C6 / 1.

[0049] Example 6

[0050] The difference from Example 4 is that in step 3, 0.060 g of A18C6 was weighed and added to the above water. Other operations were the same as in Example 4, and the membrane was named SPPSU-18C6 / 2.

[0051] Example 7

[0052] The difference from Example 4 is that in step 3, 0.103 g of A18C6 was weighed and added to the above water. Other operations were the same as in Example 4. The membrane was named SPPSU-18C6 / 3.

[0053] Example 8

[0054] This example prepares different monovalent selective cation exchange membranes by adjusting the crown ether modified liquid temperature. The difference from Example 6 is that in step 4, the SPPSU-Cl base membrane is stirred and soaked at 30°C for 6 hours. Other operations are the same as Example 6, and the membrane is named SPPSU-18C6 / 4.

[0055] Example 9

[0056] The difference from Example 6 is that in step 4, the SPPSU-Cl based membrane is stirred and immersed at 90° C. for 6 hours. Other operations are the same as in Example 4. The membrane is named SPPSU-18C6 / 5.

[0057] Example 10

[0058] This example prepares different monovalent selective cation exchange membranes by adjusting the type of diaminodibenzo 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 a SPPSU-Cl base membrane. Weigh 0.062g of A18C5 and add it to 100ml of water. Stir and soak the SPPSU-Cl base membrane at 60°C for 6 hours to obtain a monovalent selective cation exchange membrane based on SPPSU-Cl. Take out the membrane and soak it in a mixed salt solution, named SPPSU-18C5 / 2.

[0059] Embodiment 11

[0060] The difference from Example 9 is that in step 5, 0.108 g of A18C8 was weighed and added to the above water. Other operations were the same as in Example 9, and the membrane was named SPPSU-18C8 / 2.

[0061]

[0062] Table 2: Separation performance of the cation exchange membrane prepared in Examples 5-11 for 0.05 mol / L lithium-magnesium mixed solution.

[0063] Table 2 shows that Example 6 is the membrane with the best lithium-magnesium selectivity, Li + / Mg 2+ The selectivity reached 7.730, and the flux of lithium ions was also high, reaching 1111.605mmol m -2 h -1 , at this time, the specific recognition of crown ether plays a leading role. In Example 7, due to the introduction of too many crown ether structures, there are too many crown ether structures in the membrane channel, and the complexation of crown ether becomes the ion transmission resistance instead, the resistance of the membrane is also the largest, and the ion flux is also reduced. At the same time, the separation performance of the modified membrane in Example 8 under low temperature conditions is poor. Different types of crown ether compounds all show a certain lithium-magnesium selectivity, among which 18-crown 6 has the best performance.

[0064]

[0065]

[0066] Table 3: Separation performance of the cation exchange membrane prepared in Examples 5-11 for 0.05 mol / L sodium-magnesium mixed solution.

[0067] As shown in Table 3, the experimental results of Examples 5-11 show that Na + Flux changes with Li + The trend is similar, when Example 6 Na + / Mg 2+ The selectivity is the best, reaching 14.059.

[0068]

[0069] Table 4: Separation performance of the cation exchange membrane prepared in Examples 5-11 for 0.05 mol / L potassium-magnesium mixed solution.

[0070] As shown in Table 4, the cation exchange membranes prepared in Examples 5-11 have higher selectivity for potassium and magnesium than for sodium and magnesium and lithium and magnesium. + / Mg 2+ The separation performance is the best, with a selectivity of 37.560.

[0071] In summary, the SPPSU-Cl membrane modified with crown ether grafted into the ion channel prepared in this experiment has a good + / Mg 2+ 、Na + / Mg 2+ and K + / Mg 2+ The system shows that Li + 、Na + and K + The excellent selectivity can be inferred to be due to the crown ether compounds + 、Na + and K + The specific interaction is achieved under the synergistic effect of the external electric field, due to the water and radius Li + >Na + >K + , the electrostatic coupling force of crown ether compounds on ions Li + <Na + <K + , selective Li + / Mg 2+ <Na + / Mg 2+ <K + / Mg 2+ , and the best selectivities were 7.730, 14.059, and 37.560, respectively.

[0072] Application test experiment:

[0073] This experiment uses a laboratory-made membrane stack to test the unit price selectivity of the membrane, such as Figure 5 First, prepare 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).

[0074] The monovalent selective cation exchange membrane was operated stably for 1 h, and the ion flux was calculated using the following equation:

[0075]

[0076] where c0 and c t It 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.

[0077] The selectivity calculation formula is as follows:

[0078]

[0079] 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.

[0080] 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 a crown ether grafted into an ion channel, 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 a sulfonated chloromethylated polymer; Step 2: Weigh a certain amount of sulfonated chloromethylated polymer 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 cation exchange membrane and store it in a wet state; Step 3, weighing a certain amount of diaminodibenzocrown ether compound and dissolving it in water to prepare a crown ether modification solution; Step 4, immersing the cation exchange membrane in step 2 in the crown ether modification solution in step 3, and adjusting the temperature of the modification solution; Step 5: Take out the ion exchange membrane, wash it in pure water, dry it, and store it in a wet state after low-temperature drying.

2. The preparation method according to claim 1, characterized in that: The sulfonated polymer in step 1 is one or more of polyphenylsulfone (PPSU), polyetheretherketone (PEEK), and polyethersulfone (PES).

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 diaminodibenzo crown ether compound in step three is one of diaminodibenzo-18-crown-4 (A18C5), diaminodibenzo-18-crown-6 (A18C6), and diaminodibenzo-18-crown-8 (A18C8).

5. The preparation method according to claim 1, characterized in that: In step three, the concentration of the crown ether modified solution is 0.17-1.03 g / L.

6. The preparation method according to claim 1, characterized in that: In step 4, the temperature of the modified liquid is adjusted to 30-90°C.

7. A monovalent selective cation exchange membrane with crown ether grafted into an ion channel, characterized in that: The method is described in any one of claims 1 to 6.

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