Monovalent selective cation exchange membrane modification method and application

Abstract

The invention relates to a monovalent selective cation exchange membrane modification method and application, and belongs to the technical field of electrically driven membranes.The method comprises the steps that a triaminoguanidine hydrochloride solution is prepared, and one side of a cation exchange membrane is soaked in the triaminoguanidine hydrochloride solution for one day at the room temperature; then preparing a 2, 5-dihydroxy terephthalaldehyde solution, injecting the 2, 5-dihydroxy terephthalaldehyde solution into the triaminoguanidine hydrochloride solution, uniformly mixing the two solutions on the surface of the cation exchange membrane, continuously soaking the cation exchange membrane in the mixed solution at room temperature for three days, and growing a COFs layer on the soaked side of the cation exchange membrane in situ; and finally, fully washing the soaked cation exchange membrane with deionized water to obtain the modified monovalent selective cation exchange membrane. According to the invention, the migration of magnesium ions is hindered through the comprehensive action of electrostatic repulsion and chemical affinity, effective screening of sodium ions and magnesium ions is realized, and the monovalent selectivity of the cation exchange membrane is improved on the basis of maintaining the flux of sodium ions.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrically driven membranes, and particularly relates to a monovalent selective cation exchange membrane modification method and application. BACKGROUND

[0002] Ion separation is of great significance in resource recycling, product upgrading and ecological protection. Precise separation of Na + , Mg 2+ , Ca 2+ and other cations has become a core demand in many fields such as industrial manufacturing and chemical production.

[0003] Electrodialysis technology has significant advantages relying on the selective permeability of ion exchange membranes. However, traditional ion exchange membranes are limited by defects such as large pore flexibility, easy swelling and uneven distribution of functional groups, and cannot meet the precise screening needs of monovalent and divalent ion coexisting systems. Moreover, there is a "trade-off" effect between ion flux and selectivity, and there are problems such as single separation mechanism and insufficient structural stability, which restrict the industrial application of electrically driven membrane technology.

[0004] Covalent organic framework (COFs) materials provide a new direction for breaking through the bottleneck of traditional membrane technology due to their unique structure and performance. However, key problems such as efficient compounding of COFs with base membranes and precise regulation of interface structure have not been completely solved. Existing COFs modified membranes still cannot achieve precise screening of monovalent and divalent ions, and the stability of membrane layer combination needs to be optimized. Under this background, it is an urgent need for the industry to develop new ion separation membrane modification technology based on COFs, to realize efficient separation of monovalent and divalent ions through dual regulation of pore size and interface chemical environment, and to simultaneously improve selectivity and permeation flux.

[0005] To solve the above technical problems, a COFs structure and a cation exchange membrane are combined to introduce a COFs functional layer on the surface of the membrane, and a monovalent selective cation exchange membrane is modified, and the modified membrane is applied to an electrodialysis process, so as to realize efficient and precise screening of monovalent and divalent ions. SUMMARY

[0006] The technical problem to be solved by the application is to provide a monovalent selective cation exchange membrane modification method and application which can effectively reduce the trade-off effect between ion flux and selectivity in the cation exchange membrane and promote effective screening of sodium ions and magnesium ions.

[0007] To solve the above technical problems, the technical solution adopted by the application is as follows: a monovalent selective cation exchange membrane modification method, comprising the following steps:

[0008] S1, preparing triaminoguanidine hydrochloride (TG Cl) Solution: a certain amount of triaminoguanidine hydrochloride powder is dissolved in deionized water and ultrasonic dispersed to prepare a triaminoguanidine hydrochloride solution;

[0009] S2, fixing the cation exchange membrane, immersing one side of the cation exchange membrane in the triaminoguanidine hydrochloride solution at room temperature for one day;

[0010] S3, preparing a 2, 5-dihydroxyterephthalaldehyde (Da) solution: a certain amount of 2, 5-dihydroxyterephthalaldehyde powder is dissolved in 1, 4-dioxane and ultrasonic dispersed to prepare a 2, 5-dihydroxyterephthalaldehyde solution;

[0011] S4, injecting the 2, 5-dihydroxyterephthalaldehyde solution into the triaminoguanidine hydrochloride solution, slightly stirring and mixing the two solutions on the surface of the cation exchange membrane, and immersing the cation exchange membrane in the mixed solution at room temperature for three days, so that a COFs layer is prepared on one side of the cation exchange membrane by in-situ growth;

[0012] S5, washing the immersed cation exchange membrane with deionized water to obtain a modified monovalent selective cation exchange membrane.

[0013] Further, the cation exchange membrane can be any commercially available or self-made heterogeneous, homogeneous or semi-homogeneous cation exchange membrane. The manufacturers of commercially available cation exchange membranes include but are not limited to Lanlian, Tingrun, Shanghua, etc.

[0014] The present application is based on DaTG Cl The positive electrification of the COF structure and the high binding force with magnesium ions hinder the migration of magnesium ions through the comprehensive action of electrostatic repulsion and chemical affinity, improve the monovalent selectivity of the cation exchange membrane, and realize the effective screening of sodium ions and magnesium ions.

[0015] Further, in step S1, the triaminoguanidine hydrochloride solution is prepared as follows: a certain amount of triaminoguanidine hydrochloride powder is dissolved in 20 mL of deionized water and ultrasonic dispersed, so that the concentration of triaminoguanidine hydrochloride is 2.5-10 mmol / L.

[0016] Further, in step S3, the 2, 5-dihydroxyterephthalaldehyde solution is prepared as follows: a certain amount of 2, 5-dihydroxyterephthalaldehyde powder is dissolved in 20 mL of 1, 4-dioxane and ultrasonic dispersed, so that the concentration of 2, 5-dihydroxyterephthalaldehyde is 3.75-15 mmol / L.

[0017] Another object of the present application is to provide a monovalent selective cation exchange membrane prepared by a monovalent selective cation exchange membrane modification method.

[0018] Another object of the present application is the application of the monovalent selective cation exchange membrane prepared by the monovalent selective cation exchange membrane modification method in an electrodialysis device.

[0019] The electrodialysis device comprises an anode plate, a first anion exchange membrane, a monovalent selective cation exchange membrane, a second anion exchange membrane and a cathode plate arranged in sequence, an anode chamber is formed between the anode plate and the first anion exchange membrane, a dilution chamber is formed between the first anion exchange membrane and the monovalent selective cation exchange membrane, a concentration chamber is formed between the monovalent selective cation exchange membrane and the second anion exchange membrane, and a cathode chamber is formed between the second anion exchange membrane and the cathode plate.

[0020] The COFs layer of the monovalent selective cation exchange membrane is located on the dilution chamber side.

[0021] The specific method for ion sieving by using the electrodialysis device is that a mixed solution of sodium chloride and magnesium chloride is injected into the dilution chamber, a potassium chloride solution is injected into the concentration chamber, and a sodium sulfate solution is injected into the anode chamber and the cathode chamber. Under the action of a constant current, sodium ions in the dilution chamber enter the concentration chamber, and magnesium ions in the dilution chamber are intercepted.

[0022] Further, the concentration of sodium chloride in the dilution chamber is 0.05 mol / L, and the concentration of magnesium chloride is 0.05 mol / L; the concentration of potassium chloride in the concentration chamber is 0.05 mol / L; and the concentration of sodium sulfate in the cathode chamber and the anode chamber is 0.05 mol / L.

[0023] Further, the liquid inlet flow rate of the dilution chamber, the concentration chamber, the cathode chamber and the anode chamber is 60-100 mL / min, and the current density is 5-10 mA / cm 2 ; the volume of the dilution chamber and the concentration chamber is 200 mL, and the total volume of the cathode chamber and the anode chamber is 500 mL.

[0024] The cathode chamber and the anode chamber of the present application are connected in series, which ensures that the total volume of the cathode chamber and the anode chamber is 500 mL.

[0025] In summary, the beneficial effects of the present application are:

[0026] (1) The present application controls the pore by in-situ growth method. The triaminoguanidine hydrochloride monomer is positively charged. The cation exchange membrane with a negative surface is soaked in its solution for one day. The uniform adsorption of the monomer on the membrane surface can be achieved by electrostatic action to form a stable anchoring site. The base membrane with triaminoguanidine hydrochloride monomer as the anchoring site is soaked in two kinds of monomer solutions with a ratio of COFs topological structure for three days, which can help COFs to grow vertically on the membrane surface and retain the pore topological structure, and the precise control of COFs pore is realized by in-situ growth.

[0027] (2) The application focuses on the screening of sodium ions and magnesium ions, maintains the sodium ion flux, and improves the monovalent selectivity. The monovalent selective cation exchange membrane prepared by the modification method of the application can effectively reduce the trade-off effect between the cation flux and the selectivity, further hinder the migration of magnesium ions while maintaining the sodium ion flux. It can be seen that the application uses cation exchange membrane and COFs to modify cooperatively, which realizes the win-win effect of no reduction of sodium ion flux and significant improvement of magnesium ion retention rate for the first time. The anchoring growth process of the application makes the COFs layer thin and uniform, and takes into account the flux and selectivity.

[0028] (3) The modification condition of the application is mild, the whole process is at room temperature, and high pressure environment is not needed. The COFs functional layer is stably loaded by step-by-step soaking and in-situ polymerization. The process is simpler and the energy consumption is lower. The modified layer is more stable under the interaction of hydrogen bond and charge effect. BRIEF DESCRIPTION OF DRAWINGS

[0029] The advantages and implementation modes of the application will be more obvious by referring to the accompanying drawings and combining the examples, wherein the contents shown in the drawings are only used to explain and illustrate the application, and do not constitute any sense of limitation to the application. In the drawings:

[0030] Figure 1 It is a structural schematic diagram of the electrodialysis device of the application.

[0031] Figure 2 It is a structural schematic diagram of the electrodialysis device of the comparative example of the application.

[0032] Figure 3 It is a scanning electron microscope graph of the monovalent selective cation exchange membrane of Example 3 of the application, wherein a) is a scanning electron microscope graph of the surface of the monovalent selective cation exchange membrane, and b) is a scanning electron microscope graph of the cross-sectional morphology of the monovalent selective cation exchange membrane.

[0033] Figure 4 It is a comparative schematic diagram of the desalination performance of the monovalent selective cation exchange membrane of Example 3 of the application and the unmodified cation exchange membrane of the comparative example.

[0034] Figure 5 It is a comparative schematic diagram of the monovalent selectivity and ion flux of the monovalent selective cation exchange membrane of Example 3 of the application and the unmodified cation exchange membrane of the comparative example.

[0035] In the figure:

[0036] 1, anode plate; 2, first anion exchange membrane; 3, monovalent selective cation exchange membrane; 4, second anion exchange membrane; 5, cathode plate; 6, anode chamber; 7, dilution chamber; 8, concentration chamber; 9, cathode chamber; 10, cation exchange membrane. DETAILED DESCRIPTION

[0037] In order for those skilled in the art to better understand the technical solutions of the present application, the present application will be further described in detail below in combination with the best embodiments.

[0038] Embodiment 1:

[0039] A monovalent selective cation exchange membrane modification method, comprising the following steps:

[0040] S1, 7.0mg of triaminoguanidine hydrochloride powder is dissolved in 20ml of deionized water and ultrasonic dispersed to prepare a triaminoguanidine hydrochloride solution with a concentration of 2.5mmol / L;

[0041] S2, the cation exchange membrane is fixed, and one side of the cation exchange membrane is soaked in 20ml of triaminoguanidine hydrochloride solution at room temperature for one day;

[0042] S3, 12.5mg of 2,5-dihydroxy terephthaldehyde powder is dissolved in 20ml of 1,4-dioxane and ultrasonic dispersed to prepare a 2,5-dihydroxy terephthaldehyde solution with a concentration of 3.75mmol / L;

[0043] S4, 20ml of 2,5-dihydroxy terephthaldehyde solution is injected into the triaminoguanidine hydrochloride solution, and the two solutions are slightly stirred and mixed evenly on the surface of the cation exchange membrane, so that the cation exchange membrane continues to be soaked in the mixed solution at room temperature for three days, and the COFs layer is prepared on one side of the cation exchange membrane by in-situ growth;

[0044] S5, the soaked cation exchange membrane is washed with deionized water to obtain a modified monovalent selective cation exchange membrane.

[0045] Another object of the present application is to provide a monovalent selective cation exchange membrane prepared by the monovalent selective cation exchange membrane modification method.

[0046] Another object of the present application is the application of the monovalent selective cation exchange membrane prepared by the monovalent selective cation exchange membrane modification method in an electrodialysis device.

[0047] As shown in Figure 1 , the electrodialysis device comprises an anode plate 1, a first anion exchange membrane 2, a monovalent selective cation exchange membrane 3, a second anion exchange membrane 4 and a cathode plate 5 arranged in sequence, an anode chamber 6 is formed between the anode plate 1 and the first anion exchange membrane 2, a dilution chamber 7 is formed between the first anion exchange membrane 2 and the monovalent selective cation exchange membrane 3, a concentration chamber 8 is formed between the monovalent selective cation exchange membrane 3 and the second anion exchange membrane 4, and a cathode chamber 9 is formed between the second anion exchange membrane 4 and the cathode plate 5.

[0048] The COFs layer of the monovalent selective cation exchange membrane 3 is located on the side of the desalination chamber 7.

[0049] In this embodiment, the electrodialysis ion sieve application: the concentration of sodium chloride in the desalination chamber 7 is 0.05 mol / L, the concentration of magnesium chloride is 0.05 mol / L, the concentration of potassium chloride in the concentration chamber 8 is 0.05 mol / L, the volume of the desalination chamber 7 and the concentration chamber 8 is 200 mL; the concentration of sodium sulfate in the cathode chamber 9 and the anode chamber 6 is 0.05 mol / L, and the total volume is 500 mL. Under the driving of the peristaltic pump, a constant current circulation mode is used. The liquid flow rate of the desalination chamber 7, the concentration chamber 8, the cathode chamber 9 and the anode chamber 6 is 100 mL / min, and the current density is 5 mA / cm 2 .

[0050] Through the atomic absorption detection experiment result, according to formula (1) and formula (2) to calculate the monovalent selective cation exchange membrane 3 monovalent ion selectivity, The value of the monovalent selective cation exchange membrane 3 monovalent selectivity is positively correlated.

[0051] (1)

[0052] (2)

[0053] In the formula, J i represents the ion flux of the cation (mol·cm -2 ·s -1 ), v represents the volume of the circulating solution in the concentration chamber 8 (L), C i represents the concentration of sodium ions or magnesium ions in the concentration chamber 8 (mol / L), A represents the effective area of the monovalent selective cation exchange membrane 3 (cm 2 ), t represents the experimental time (s), represents the concentration of sodium ions in the concentration chamber 8 (mol / L), represents the concentration of magnesium ions in the concentration chamber 8 (mol / L), represents the ion flux of sodium ions (mol·cm -2 ·s -1 ), represents the ion flux of magnesium ions (mol·cm -2 ·s -1 ), represents the initial concentration of sodium ions in the concentration chamber 8 (mol / L), represents the initial concentration of magnesium ions in the concentration chamber 8 (mol / L).

[0054] It is tested that the monovalent selective cation exchange membrane 3 in this embodiment has a monovalent cation selectivity = 2.879.

[0055] Embodiment 2:

[0056] A monovalent selective cation exchange membrane modification method, comprising the following steps:

[0057] S1, 14.1mg of triaminoguanidine hydrochloride powder is dissolved in 20ml of deionized water and ultrasonic dispersed to prepare a triaminoguanidine hydrochloride solution with a concentration of 5mmol / L;

[0058] S2, the cation exchange membrane is fixed, and one side of the cation exchange membrane is soaked in 20ml of triaminoguanidine hydrochloride solution at room temperature for one day;

[0059] S3, 24.9mg of 2,5-dihydroxy terephthaldehyde powder is dissolved in 20ml of 1,4-dioxane and ultrasonic dispersed to prepare a 2,5-dihydroxy terephthaldehyde solution with a concentration of 7.5mmol / L;

[0060] S4, 20ml of 2,5-dihydroxy terephthaldehyde solution is injected into the triaminoguanidine hydrochloride solution, and the two solutions are slightly stirred and mixed uniformly on the surface of the cation exchange membrane, so that the cation exchange membrane continues to be soaked in the mixed solution at room temperature for three days, and the COFs layer is prepared on one side of the cation exchange membrane by in-situ growth;

[0061] S5, the soaked cation exchange membrane is washed with deionized water to obtain a modified monovalent selective cation exchange membrane.

[0062] Another object of the application is to provide a monovalent selective cation exchange membrane prepared by the monovalent selective cation exchange membrane modification method.

[0063] Another object of the application is the application of the monovalent selective cation exchange membrane prepared by the monovalent selective cation exchange membrane modification method in an electrodialysis device.

[0064] The structure of the electrodialysis device is the same as that of embodiment 1.

[0065] The application of the electrodialysis ion sieve is the same as that of embodiment 1.

[0066] The experimental results are detected by atomic absorption, and the monovalent cation selectivity of the monovalent selective cation exchange membrane 3 is calculated according to formula (1) and formula (2) in embodiment 1. = 5.338.

[0067] Embodiment 3:

[0068] A monovalent selective cation exchange membrane modification method, comprising the following steps:

[0069] S1, 21.1 mg of triaminoguanidine hydrochloride powder is weighed and dissolved in 20 mL of deionized water and ultrasonic dispersed to prepare a triaminoguanidine hydrochloride solution with a concentration of 7.5 mmol / L;

[0070] S2, the cation exchange membrane is fixed, and one side of the cation exchange membrane is immersed in 20 ml of the triaminoguanidine hydrochloride solution at room temperature for one day;

[0071] S3, 37.4 mg of 2,5-dihydroxyterephthaldehyde powder is weighed and dissolved in 20 mL of 1,4-dioxane and ultrasonic dispersed to prepare a 2,5-dihydroxyterephthaldehyde solution with a concentration of 11.25 mmol / L;

[0072] S4, 20 ml of the 2,5-dihydroxyterephthaldehyde solution is injected into the triaminoguanidine hydrochloride solution, and the two solutions are gently stirred and mixed uniformly on the surface of the cation exchange membrane, and the cation exchange membrane is continuously immersed in the mixed solution at room temperature for three days, so that the COFs layer is prepared on one side of the cation exchange membrane by in-situ growth;

[0073] S5, the soaked cation exchange membrane is washed with deionized water to obtain a modified monovalent selective cation exchange membrane.

[0074] Another object of the application is to provide a monovalent selective cation exchange membrane prepared by a monovalent selective cation exchange membrane modification method.

[0075] Another object of the application is the application of the monovalent selective cation exchange membrane prepared by the monovalent selective cation exchange membrane modification method in an electrodialysis device.

[0076] The structure of the electrodialysis device is the same as that of Example 1.

[0077] The application of the electrodialysis ion sieve is the same as that of Example 1.

[0078] The experimental results are detected by atomic absorption, and the monovalent cation selectivity of the monovalent selective cation exchange membrane 3 is calculated according to formula (1) and formula (2) in Example 1. = 8.248.

[0079] Example 4:

[0080] A monovalent selective cation exchange membrane modification method comprises the following steps:

[0081] S1, 21.1 mg of triaminoguanidine hydrochloride powder is weighed and dissolved in 20 mL of deionized water and ultrasonic dispersed to prepare a triaminoguanidine hydrochloride solution with a concentration of 7.5 mmol / L;

[0082] S2, fixing the cation exchange membrane, immersing one side of the cation exchange membrane in 20 ml of the triaminoguanidine hydrochloride solution at room temperature for one day;

[0083] S3, weighing 49.8 mg of 2, 5-dihydroxyterephthaldehyde powder, dissolving the 2, 5-dihydroxyterephthaldehyde powder in 20 mL of 1, 4-dioxane and performing ultrasonic dispersion, to prepare a 2, 5-dihydroxyterephthaldehyde solution with a concentration of 15 mmol / L;

[0084] S4, injecting 20 ml of the 2, 5-dihydroxyterephthaldehyde solution into the triaminoguanidine hydrochloride solution, slightly stirring and mixing the two solutions on the surface of the cation exchange membrane, and continuously immersing the cation exchange membrane in the mixed solution at room temperature for three days, so that a COFs layer is prepared on one side of the cation exchange membrane through in-situ growth;

[0085] S5, washing the immersed cation exchange membrane with deionized water to obtain a modified monovalent selective cation exchange membrane.

[0086] Another object of the application is to provide a monovalent selective cation exchange membrane prepared by the monovalent selective cation exchange membrane modification method.

[0087] Another object of the application is the application of the monovalent selective cation exchange membrane prepared by the monovalent selective cation exchange membrane modification method in an electrodialysis device.

[0088] The electrodialysis device has the same structure as that in Embodiment 1.

[0089] The electrodialysis ion sieve application has the same application as that in Embodiment 1.

[0090] The atomic absorption detection experimental results are calculated according to the formula (1) and the formula (2) in Embodiment 1 to obtain the monovalent cation selectivity of the monovalent selective cation exchange membrane 3. = 9.437.

[0091] Embodiment 5:

[0092] A monovalent selective cation exchange membrane modification method comprises the following steps:

[0093] S1, weighing 21.1 mg of triaminoguanidine hydrochloride powder, dissolving the triaminoguanidine hydrochloride powder in 20 mL of deionized water and performing ultrasonic dispersion, to prepare a triaminoguanidine hydrochloride solution with a concentration of 7.5 mmol / L;

[0094] S2, fixing the cation exchange membrane, immersing one side of the cation exchange membrane in 20 ml of the triaminoguanidine hydrochloride solution at room temperature for one day;

[0095] S3, 37.4 mg of 2,5-dihydroxyterephthalaldehyde powder was dissolved in 20 mL of 1,4-dioxane and ultrasonically dispersed to prepare a 2,5-dihydroxyterephthalaldehyde solution with a concentration of 11.25 mmol / L;

[0096] S4, 20 ml of 2,5-dihydroxyterephthalaldehyde solution was injected into the triaminoguanidine hydrochloride solution, and the two solutions were mixed evenly on the surface of the cation exchange membrane under slight stirring, and the cation exchange membrane was immersed in the mixed solution at room temperature for three days, and the COFs layer was prepared on one side of the cation exchange membrane by in-situ growth;

[0097] S5, the soaked cation exchange membrane was washed with deionized water to obtain a modified monovalent selective cation exchange membrane.

[0098] Another object of the application is to provide a monovalent selective cation exchange membrane prepared by a monovalent selective cation exchange membrane modification method.

[0099] Another object of the application is the application of the monovalent selective cation exchange membrane prepared by the monovalent selective cation exchange membrane modification method in an electrodialysis device.

[0100] The structure of the electrodialysis device is the same as that of Example 1.

[0101] In this embodiment, the electrodialysis ion sieve separation application: the concentration of sodium chloride in the dilution chamber 7 is 0.05 mol / L, the concentration of magnesium chloride is 0.05 mol / L, the concentration of potassium chloride in the concentration chamber 8 is 0.05 mol / L, and the volume of the dilution chamber 7 and the concentration chamber 8 is 200 mL; the concentration of sodium sulfate in the cathode chamber 9 and the anode chamber 6 is 0.05 mol / L, and the total volume is 500 mL. Under the driving of the peristaltic pump, a constant current circulation mode is adopted. The liquid flow rate of the dilution chamber 7, the concentration chamber 8, the cathode chamber 9 and the anode chamber 6 is 100 mL / min, and the current density is 6 mA / cm 2 .

[0102] The experimental results were detected by atomic absorption, and the monovalent cation selectivity of the monovalent selective cation exchange membrane 3 was calculated according to formula (1) and formula (2) in Example 1. = 5.129.

[0103] Example 6:

[0104] A monovalent selective cation exchange membrane modification method, comprising the following steps:

[0105] S1, 21.1 mg of triaminoguanidine hydrochloride powder was dissolved in 20 mL of deionized water and ultrasonically dispersed to prepare a triaminoguanidine hydrochloride solution with a concentration of 7.5 mmol / L;

[0106] S2, the cation exchange membrane is fixed, and one side of the cation exchange membrane is soaked in 20 ml of a triaminoguanidine hydrochloride solution at room temperature for one day;

[0107] S3, 37.4 mg of 2,5-dihydroxyterephthaldehyde powder is dissolved in 20 mL of 1,4-dioxane and ultrasonically dispersed to prepare a 2,5-dihydroxyterephthaldehyde solution with a concentration of 11.25 mmol / L;

[0108] S4, 20 ml of the 2,5-dihydroxyterephthaldehyde solution is injected into the triaminoguanidine hydrochloride solution, and the two solutions are gently stirred and mixed uniformly on the surface of the cation exchange membrane, and the cation exchange membrane is continuously soaked in the mixed solution at room temperature for three days, so that the COFs layer is prepared on the side of the cation exchange membrane soaked by in-situ growth;

[0109] S5, the soaked cation exchange membrane is washed with deionized water to obtain a modified monovalent selective cation exchange membrane.

[0110] Another object of the application is to provide a monovalent selective cation exchange membrane prepared by a monovalent selective cation exchange membrane modification method.

[0111] Another object of the application is the application of the monovalent selective cation exchange membrane prepared by the monovalent selective cation exchange membrane modification method in an electrodialysis device.

[0112] The electrodialysis device has the same structure as that in Embodiment 1.

[0113] In this embodiment, the electrodialysis ion sieve application is as follows: the concentration of sodium chloride in the dilution chamber 7 is 0.05 mol / L, the concentration of magnesium chloride is 0.05 mol / L, the concentration of potassium chloride in the concentration chamber 8 is 0.05 mol / L, and the volume of the dilution chamber 7 and the concentration chamber 8 is 200 mL; the concentration of sodium sulfate in the cathode chamber 9 and the anode chamber 6 is 0.05 mol / L, and the total volume is 500 mL. Under the driving of the peristaltic pump, a constant current circulation mode is adopted. The liquid flow rate of the dilution chamber 7, the concentration chamber 8, the cathode chamber 9 and the anode chamber 6 is 100 mL / min, and the current density is 10 mA / cm 2 .

[0114] The experimental results are detected by atomic absorption, and the monovalent cation selectivity of the monovalent selective cation exchange membrane 3 is calculated according to formula (1) and formula (2) in Embodiment 1. = 3.164.

[0115] Comparative Example:

[0116] As Figure 2As shown, the electrodialysis device comprises an anode plate 1, a first anion exchange membrane 2, a cation exchange membrane 10, a second anion exchange membrane 4 and a cathode plate 5 arranged in sequence, an anode chamber 6 is formed between the anode plate 1 and the first anion exchange membrane 2, a dilution chamber 7 is formed between the first anion exchange membrane 2 and the cation exchange membrane 10, a concentration chamber 8 is formed between the cation exchange membrane 10 and the second anion exchange membrane 4, and a cathode chamber 9 is formed between the second anion exchange membrane 4 and the cathode plate 5.

[0117] In the comparative example, the electrodialysis ion sieve application is the same as that of Example 1.

[0118] It is tested that the monovalent cation selectivity of the cation exchange membrane 10 in the comparative example = 1.399.

[0119] Scanning electron microscope test:

[0120] As shown, the surface ( Figure 3 a) and cross-sectional morphology ( Figure 3 b) of the monovalent selective cation exchange membrane 3 of Example 3 are observed by scanning electron microscope. Figure 3 It can be seen from Figure 3 that the surface of the monovalent selective cation exchange membrane 3 of Example 3 has obvious modification, and the thickness of the modified layer is 0.45 μm.

[0121] The monovalent selective cation exchange membrane 3 prepared in other embodiments of the application is also observed by scanning electron microscope, and the obtained results are similar to those of Example 3.

[0122] Monovalent selective performance test:

[0123] The monovalent and divalent ion sieve electrodialysis experiments are carried out on the monovalent selective cation exchange membrane 3 of Example 3 and the unmodified cation exchange membrane 10 of the comparative example, and the desalination effect is shown in Figure 4 , and the maximum ion flux of sodium ions and magnesium ions and the monovalent selectivity of the cation exchange membrane are shown in Figure 5 .

[0124] As can be seen from Figure 4 and Figure 5 , compared with the comparative example, the sodium ion concentration in the concentration chamber 8 of Example 3 is further improved, and the ion flux is increased to a certain extent in the same desalination time; while the upward trend of magnesium ion concentration is obviously slowed down, the ion flux is significantly reduced, and the monovalent selectivity is obviously improved. It shows that the monovalent selective cation exchange membrane 3 obtained by the modification method of the application can effectively sieve sodium ions and magnesium ions, and does not affect the migration of sodium ions.

[0125] The monovalent selective electrodialysis ion sieve separation experiments were also carried out on the monovalent selective cation exchange membranes 3 and the cation exchange membranes 10 before modification prepared according to other embodiments of the present application and the corresponding comparative examples, and the obtained results were similar to the rules between the embodiments 3 and the comparative examples.

[0126] The above detailed the embodiments of the present application, but the content is only the preferred embodiments of the present application, and cannot be considered to limit the scope of the present application. Any equivalent changes and improvements made within the scope of the present application should still be attributed to the scope of the present application.

Claims

1. A method for modifying a monovalent selective cation exchange membrane, characterized in that: Includes the following steps: S1. Weigh out triaminoguanidine hydrochloride powder, dissolve it in deionized water, and disperse it by ultrasonication to prepare triaminoguanidine hydrochloride solution. S2. Fix the cation exchange membrane and immerse one side of the cation exchange membrane in triaminoguanidine hydrochloride solution at room temperature for one day; S3. Weigh 2,5-dihydroxyterephthalaldehyde powder, dissolve it in 1,4-dioxane and disperse it ultrasonically to prepare a 2,5-dihydroxyterephthalaldehyde solution. S4. Inject 2,5-dihydroxyterephthalaldehyde solution into triaminoguanidine hydrochloride solution, stir and mix the two solutions on the surface of cation exchange membrane, and continue to soak the cation exchange membrane in the mixed solution at room temperature for three days, so that the COFs layer can be prepared on the soaked side of the cation exchange membrane by in-situ growth. S5. Wash the soaked cation exchange membrane thoroughly with deionized water to obtain the modified monovalent selective cation exchange membrane.

2. The method for modifying a monovalent selective cation exchange membrane according to claim 1, characterized in that: The cation exchange membrane is a heterogeneous, homogeneous, or semi-homogeneous cation exchange membrane.

3. The method for modifying a monovalent selective cation exchange membrane according to claim 1, characterized in that: In step S1, the preparation method of the triaminoguanidine hydrochloride solution is as follows: weigh the triaminoguanidine hydrochloride powder, dissolve it in 20 mL of deionized water and disperse it by ultrasonication to make the concentration of triaminoguanidine hydrochloride 2.5~10 mmol / L.

4. The method for modifying a monovalent selective cation exchange membrane according to claim 1, characterized in that: In step S3, the 2,5-dihydroxyterephthalaldehyde solution is prepared as follows: 2,5-dihydroxyterephthalaldehyde powder is weighed, dissolved in 20 mL of 1,4-dioxane, and ultrasonically dispersed to make the concentration of 2,5-dihydroxyterephthalaldehyde 3.75~15 mmol / L.

5. A monovalent selective cation exchange membrane prepared by the method for modifying a monovalent selective cation exchange membrane as described in any one of claims 1 to 4.

6. The application of a monovalent selective cation exchange membrane prepared by the method for modifying a monovalent selective cation exchange membrane as described in any one of claims 1 to 4 in an electrodialysis device.

7. The application according to claim 6, characterized in that: The electrodialysis device includes an anode plate, a first anion exchange membrane, a monovalent selective cation exchange membrane, a second anion exchange membrane, and a cathode plate arranged sequentially. An anode chamber is formed between the anode plate and the first anion exchange membrane. A desalination chamber is formed between the first anion exchange membrane and the monovalent selective cation exchange membrane. A concentration chamber is formed between the monovalent selective cation exchange membrane and the second anion exchange membrane. A cathode chamber is formed between the second anion exchange membrane and the cathode plate.

8. The application according to claim 7, characterized in that: The COFs layer of the monovalent selective cation exchange membrane is located on the desalination chamber side.

9. The application according to claim 8, characterized in that: The method for ion sieving in the electrodialysis device is as follows: injecting a mixed solution of sodium chloride and magnesium chloride into the desalination chamber, injecting a potassium chloride solution into the concentration chamber, and injecting a sodium sulfate solution into the anode chamber and the cathode chamber; Under the action of a constant current, sodium ions in the desalination chamber are introduced into the concentration chamber, while magnesium ions in the desalination chamber are retained.

10. The application according to claim 9, characterized in that: The concentrations of sodium chloride and magnesium chloride in the desalination chamber are 0.05 mol / L and 0.05 mol / L respectively; the concentration of potassium chloride in the concentration chamber is 0.05 mol / L; the concentration of sodium sulfate in the cathode and anode chambers is 0.05 mol / L; the influent flow rate to the desalination, concentration, cathode, and anode chambers is 60-100 mL / min, and the current density is 5-10 mA / cm². 2 The volume of the desalination chamber and the concentration chamber is 200 mL each, and the total volume of the cathode chamber and the anode chamber is 500 mL.

Images