A monovalent selective cation exchange membrane grafted with crown ether in ion channel and its preparation method

Abstract

The application belongs to the field of cation exchange membrane, and discloses a monovalent selective cation exchange membrane with ion channel grafting crown ether and a preparation method thereof. The preparation method comprises the following steps: firstly, synthesizing a sulfonated chloromethylated polymer and evaporating the solvent to form a film; and then, using a simple hot soaking method, grafting a diamino diphenyl crown ether compound into the ion channel by the mutual reaction of amino and chloromethyl, so as to introduce the crown ether structure into the ion channel of the membrane. The crown ether structure has electrostatic interaction with alkali metals, and the interaction force is different for different metals, so that monovalent cation selective separation is achieved. The monovalent selective cation exchange membrane prepared by the application is suitable for the electrodialysis process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of cation exchange membrane, and particularly relates to a monovalent selective cation exchange membrane with crown ether grafted in ion channel and a preparation method thereof. BACKGROUND

[0002] Electrodialysis technology has developed rapidly in recent years and has been widely used in many fields such as seawater desalination, brackish water treatment, acid and alkali recovery, paper industry, electroplating industry and food industry. With the continuous progress of society, the application range of electrodialysis is expanding, and the performance requirements of ion exchange membrane, the key component of electrodialysis, are also increasing. Especially in the fields of lithium extraction from salt lake, refined salt, waste acid and alkali recovery, the demand for ion exchange membranes with excellent performance and high selectivity is extremely urgent.

[0003] Biological ion channels have a scale of angstrom, and the functional groups in the channel have specific interactions with basic ions, thereby achieving ultra-high ion selectivity. Crown ether can efficiently complex and anchor cations due to its special cavity structure and electron donor properties, and has become a popular choice for constructing ion selective structures. The main method of introducing crown ether into polymer materials is to introduce it into the main chain or side chain of the polymer, and to realize the selective extraction or adsorption of ions by means of the ion complexing ability of crown ether or the synergistic effect with other groups. The main disadvantage of these processes is that an equal amount of stripping agent and desorbent is required to further obtain specific cations. Few studies have regulated ion channels by crown ether to achieve selective separation of ions in the ion channel of the formed polymer membrane. If crown ether and its derivatives are combined with ion exchange resins or membranes and fixed in the ion channel of the membrane, the disadvantages can be overcome while achieving effective separation of specific ions.

[0004] Common all-oxygen 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, a 1:1 complex of crown ether-ion is formed. 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 + A 2:1 complex structure can be formed between ions. Bhattacharyya found that Nafion-117 membrane loaded with Li + Formate supported dibenzo-18-crown-6 increased the selectivity of Li + about 6 times (compared with the blank membrane). Zoetebier et al. confirmed that polyaryletherketone (PEAK) and sulfonated PEAK (SPEAK) containing dibenzo-18-crown-6 groups in the main chain had high selectivity for K +The diffusion rate is 1 / 4 of the 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 a new ion channel for specific cations, ensure ion selectivity and have higher ion flux. SUMMARY

[0005] In order to solve the above technical problems existing in the prior art, a preparation method of monovalent selective cation exchange membrane is provided for electrodialysis process. The method should enable the obtained cation exchange membrane to have good stability and monovalent and multivalent cation selective permeability, and the preparation method is simple and easy to operate.

[0006] The purpose of the present application is to prepare a monovalent selective cation exchange membrane with high selectivity and high flux, and to provide a preparation method of monovalent selective cation exchange membrane with crown ether grafted in the ion channel. The crown ether-based cation exchange membrane is prepared by a simple hot soaking method, using the mutual reaction of amino and chloromethyl. The diamino dipyridine crown ether compound is grafted into the ion channel of the sulfonated chloromethylated polymer membrane, so as to introduce the crown ether structure into the membrane ion channel. The crown ether and the sulfonic acid group jointly promote the transmission of K + , Na + , Li + , so as to achieve the purpose of ion separation.

[0007] The purpose of the present application is achieved by the following technical scheme:

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

[0009] A preparation method of monovalent selective cation exchange membrane with crown ether grafted in the ion channel, comprising the following steps:

[0010] Step one, weigh a certain amount of sulfonated polymer and dissolve it in N,N-dimethylacetamide, chloromethyl ether compound as chloromethylation reagent, and tin tetrachloride as catalyst to prepare sulfonated chloromethylated polymer;

[0011] Step two, weigh a certain amount of sulfonated chloromethylated polymer and dissolve it in dimethyl sulfoxide to prepare casting solution, pour the casting solution on a glass plate, heat and dry, and after the solvent is completely volatilized, take out the cation exchange membrane and store it in wet state;

[0012] Step three, weigh a certain amount of diamino dipyridine crown ether compound and dissolve it in water to prepare crown ether modification solution;

[0013] Step four, the cation exchange membrane in step two is soaked in the crown ether modification solution in step three, and the modification solution temperature is controlled;

[0014] Step five, the ion exchange membrane is taken out and washed in pure water, dried, and then stored in a wet state after low-temperature drying.

[0015] Further, the sulfonated polymer in step one is one or more of polyphenylsulfone (PPSU), polyether ether ketone (PEEK), and polyether sulfone (PES).

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

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

[0018] Further, the concentration of the crown ether modification solution in step three is 0.17-1.03 g / L.

[0019] Further, the modification solution temperature in step four is controlled to be 30-90℃.

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

[0021] Compared with the prior art, the present application has the following advantages: 1. The present application uses the very mature flow casting method and hot soaking method to prepare a membrane with sulfonic acid groups and crown ether structures, successfully introducing crown ether into the membrane, without the need for special equipment, and is simple and easy to operate. 2. The crown ether-based monovalent selective cation exchange membrane prepared by the present application has specific interactions with K + , Na + , Li + , and the crown ether structure has different forces on alkali metal ions, thereby realizing Li + / Mg 2+ , Na + / Mg 2+ , and K + / Mg 2+ selective separation, with higher separation performance than commercial membranes, and can be applied to salt lake lithium extraction, crude salt refining, etc. 3. The crown ether structure introduced in the present application is expected to alleviate the balance / trade off effect between flux and selectivity. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 A physical map of the monovalent selective cation exchange membrane prepared for Example 6;

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

[0024] Figure 2b Scanning electron microscope section view of the monovalent selective cation exchange membrane prepared for Example 6;

[0025] Figure 3 NMR hydrogen spectrum of sulfonated chloromethylated polyphenylsulfone, A18C5, A18C6, A18C8;

[0026] Figure 4 Fourier infrared spectrum of A18C6, sulfonated chloromethylated polyphenylsulfone, Example 6;

[0027] Figure 5 Structure schematic diagram of the testing device of the application;

[0028] In the figure, the reference numerals are: 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-liquid inlet. DETAILED DESCRIPTION

[0029] The application will be further described below in combination with the drawings.

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

[0031] Step one, a certain amount of sulfonated polymer is dissolved in N,N-dimethylacetamide, chloromethyl ether compound is used as chloromethylation reagent, and tin tetrachloride is used as catalyst to prepare sulfonated chloromethylated polymer;

[0032] Step two, a certain amount of sulfonated chloromethylated polymer is dissolved in dimethyl sulfoxide to prepare casting solution, the casting solution is cast on a glass plate, heated and dried, after the solvent is completely volatilized, the membrane is taken out and stored in a wet state.

[0033] Step three, a certain amount of diamino dibenzo crown ether compound (A18C5, A18C6 or A18C8) is dissolved in water to prepare crown ether modification solution, and the concentration of the crown ether modification solution is 0.17-1.03 g / L;

[0034] Step four, the cation exchange membrane material in step two is soaked in the crown ether modification solution in step three, and the modification solution temperature is controlled at 30-90°C;

[0035] Step five, the ion exchange membrane is taken out, washed and dried in pure water, dried at low temperature (60°C), and stored in a wet state.

[0036] Example 1

[0037] A monovalent selective cation exchange membrane with different polymer matrix was prepared by choosing different sulfonated polymers. 8.8 g of sulfonated polyphenylsulfone (SPPSU) was dissolved in 150 ml DMAC, 2 ml of chloromethyl ether and 2 ml of anhydrous tin tetrachloride were added dropwise in turn, and the reaction was carried out at 0°C for 48 h. The product was precipitated in water and dried to obtain sulfonated chloromethylated polyphenylsulfone (SPPSU-Cl). 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 h to obtain a SPPSU-Cl-based membrane. 0.060 g of A18C6 was weighed and added to 100 ml of water. The SPPSU-Cl-based membrane was soaked in the water at 60°C for 6 h to obtain a monovalent selective cation exchange membrane with a SPPSU-Cl matrix, which was named SPPSU-18C6.

[0038] Example 2

[0039] Different from Example 1, the sulfonated polyether sulfone was sulfonated and chloromethylated in step one, and the degree of sulfonation and chloromethylation was the same. In step three, 0.784 g of SPES-Cl was weighed and added to 6.30 g of dimethyl sulfoxide to prepare a casting solution, and other operations were the same as in Example 1. The membrane was named SPES-18C6.

[0040] Example 3

[0041] Different from Example 1, the sulfonated polyether ketone was chloromethylated in step one, and the degree of sulfonation and chloromethylation was the same. In step two, 0.784 g of SPEEK-Cl was weighed and added to 6.30 g of dimethyl sulfoxide to prepare a casting solution, and other operations were the same as in Example 1. The membrane was named SPEEK-18C6.

[0042] Example 4

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

[0044]

[0045] Table 1: Separation performance of the cation exchange membranes prepared in Examples 1-4 on 0.05 mol / L lithium-magnesium mixed solution.

[0046] From Table 1, it can be seen that the monovalent selective cation exchange membranes prepared by the preparation method of the present application have good divalent cation screening effect regardless of the type of polymer. The lithium-magnesium selective membrane prepared by chloromethylation of sulfonated polyphenylsulfone with chloromethyl ethyl ether has the best lithium-magnesium selectivity, with Li+ / Mg2+selectivity of 7.730 and lithium ion flux of 1111.605 mmol m-2s-1. -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 into 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-based membrane. 0.017 g of A18C6 was weighed into 100 ml of water, and the SPPSU-Cl-based membrane was stirred and soaked in the water at 60°C for 6 hours to obtain a monovalent selective cation exchange membrane based on SPPSU-Cl, which was taken out and soaked in a mixed salt solution, and was named SPPSU-18C6 / 1.

[0049] Example 6

[0050] Different from Example 4, 0.060 g of A18C6 was weighed into the water in step three, and the other operations were the same as in Example 4, and the membrane was named SPPSU-18C6 / 2.

[0051] Example 7

[0052] Different from Example 4, 0.103 g of A18C6 was weighed into the water in step three, and the other operations were the same as in Example 4, and the membrane was named SPPSU-18C6 / 3.

[0053] Example 8

[0054] In this example, different monovalent selective cation exchange membranes were prepared by adjusting the temperature of the crown ether modification solution. Different from Example 6, the SPPSU-Cl-based membrane was stirred and soaked at 30°C for 6 hours in step four, and the other operations were the same as in Example 6, and the membrane was named SPPSU-18C6 / 4.

[0055] Example 9

[0056] Different from Example 6, the SPPSU-Cl-based membrane was stirred and soaked at 90°C for 6 hours in step four, and the other operations were the same as in Example 4, and the membrane was named SPPSU-18C6 / 5.

[0057] Example 10

[0058] The present example is to prepare different monovalent selective cation exchange membranes by adjusting the type of diamino-dibenzo-crown ether compound. 0.784 g of SPPSU-Cl was weighed into 6.30 g of dimethyl sulfoxide to prepare a casting solution, and dried at 60°C for 12 hours to obtain a SPPSU-Cl based membrane. 0.062 g of A18C5 was weighed into 100 ml of water, and the SPPSU-Cl based membrane was stirred and soaked at 60°C for 6 hours to obtain a monovalent selective cation exchange membrane based on SPPSU-Cl, which was taken out and soaked in a mixed salt solution, and named as SPPSU-18C5 / 2.

[0059] Example 11

[0060] Different from Example 9, 0.108 g of A18C8 was weighed into the above water in step five, and other operations were the same as in Example 9, and the membrane was named as SPPSU-18C8 / 2.

[0061]

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

[0063] As can be seen from Table 2, Example 6 is the best membrane for lithium-magnesium selectivity, Li + / Mg 2+ selectivity reaches 7.730, and the flux of lithium ions is also high, reaching 1111.605 mmol m -2 h -1 At this time, the specific recognition of crown ether plays a leading role. In Example 7, too many crown ether structures are introduced into the membrane channel, and the complexation of crown ether becomes an ion transmission resistance, the membrane resistance is also the largest, and the ion flux is also reduced. At the same time, the modified membrane in Example 8 performs poorly at low temperature. Different types of crown ether compounds all show certain lithium-magnesium selectivity, among which the performance of 18C6 is the best.

[0064]

[0065]

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

[0067] As can be seen from the experimental results of Examples 5-11 in Table 3, the flux of Na + changes similarly to the trend of Li + , and the Na + / Mg 2+ selectivity of Example 6 is the best, reaching 14.059.

[0068]

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

[0070] Table 4 shows that the cation exchange membranes prepared in Examples 5-11 have higher selectivity for potassium and magnesium than those for sodium and magnesium and lithium and magnesium. Example 7 shows higher selectivity for K... + / Mg 2+ It exhibits the best separation performance, with a selectivity of 37.560.

[0071] In summary, the SPPSU-Cl membrane with crown ether grafted into the ion channel prepared in this experiment exhibits good performance in Li... + / Mg 2+ Na + / Mg 2+ and K + / Mg 2+ The system exhibits Li + Na + and K + The excellent selectivity can be attributed to the effect of crown ether compounds on Li. + Na + and K + The specific interactions are achieved under the synergistic effect of an applied electric field, where the water content of the ions and the radius of Li are affected. + >Na + >K + The electrostatic coupling force of crown ether compounds to ions Li + <Na + <K + Selective Li in binary mixed solutions + / Mg 2+ <Na + / Mg 2+ <K + / Mg 2+ The optimal selectivity values ​​were 7.730, 14.059, and 37.560, respectively.

[0072] Application testing experiments:

[0073] This experiment used a laboratory-made membrane stack to test the unit valence selectivity of the membrane, such as... Figure 5 As shown. First, prepare 0.05 mol / L Na. + / Mg 2+ Li + / Mg 2+ K + / Mg 2+The mixed solution was used as the test solution. 0.05 mol / L Na2SO4 solution was used as the circulating electrolyte. The modified membrane was immersed in 0.05 mol / L Na + / Mg 2+ , Li + / Mg 2+ , K + / Mg 2+ mixed solution for 24 h for equilibrium. Then the modified cation exchange membrane was fixed between two commercial anion membranes (Bolan, alloy membrane), and 100 mL of Na + / Mg 2+ , Li + / Mg 2+ , K + / Mg 2+ mixed solution was placed on both sides of the anion membrane. 500 mL of Na2SO4 solution was circulated in the anode chamber by a water pump. The modified membrane was operated at a direct current of 7.065 cm 2 , a constant current density of 5.0 mA cm -2 , and a stable operation for 1 h. The ion concentration in the dilution chamber before and after operation was determined by using a cation ion chromatograph (SH-CC-3L, Shenghe, 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 c0and c t are the concentrations of monovalent ions M + (K + , Na + , and Li + ) or Mg 2+ at 0 and th in the dilution chamber, V is the volume of the solution in the dilution chamber, A m represents the effective test area of the membrane (7.065 cm 2 ), and t represents the test duration.

[0077] The calculation formula for selectivity is as follows:

[0078]

[0079] where J represents the ion flux of the membrane, mmol m -2 h -1 ; c0represents the ion concentration before separation, mol / L. c Na+ and c Mg2+ represent the concentrations of monovalent ions M + (K + , Na+ and Li + )Na + , Mg 2+ plasma concentration, unit: mol / L.

[0080] The above merely provides the preferred embodiments of the present application and is not intended to limit the implementation of the present application. Based on the main concept and spirit of the present application, the person skilled in the art can easily make corresponding modification or change, and the protection scope of the present application should be subject to the protection scope required by the claims.

Claims

1. A method for preparing a monovalent selective cation exchange membrane grafted with crown ethers within an ion channel, characterized in that... Includes the following steps: Step 1: Weigh a certain amount of sulfonated polymer and dissolve it in N,N-dimethylacetamide, using chloromethyl ether compounds as chloromethylating agents and tin tetrachloride as a catalyst to prepare 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 onto a glass plate, heat and dry it. After all the solvent has evaporated, take out the cation exchange membrane and store it in a wet state. Step 3: Weigh a certain amount of diaminodibenzocrown ether compound and dissolve it in water to prepare crown ether modified solution; Step 4: Immerse the cation exchange membrane from Step 2 in the crown ether modification solution from Step 3, and adjust the temperature of the modification solution. Step 5: Remove the ion exchange membrane, wash it in pure water, dry it, dry it at low temperature, and then store it in a humid state. The sulfonated polymer mentioned in step one is one or more of polyphenylene sulfone (PPSU), polyether ether ketone (PEEK), and polyether sulfone (PES); The chloromethyl ether compound mentioned in step one is one of chloromethyl methyl ether and chloromethyl ethyl ether; The diaminodibenzocrown ether compound mentioned in step three is one of diaminodibenzo-18-crown-4 (A18C5), diaminodibenzo-18-crown-6 (A18C6), and diaminodibenzo-18-crown-8 (A18C8).

2. 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.

3. The preparation method according to claim 1, characterized in that: In step four, the temperature of the modified liquid is adjusted to 30-90℃.

4. A monovalent selective cation exchange membrane with crown ether grafted into an ion channel, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 3.

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