Modified cation exchange membrane, preparation method thereof and application of modified cation exchange membrane in ion rectification

Abstract

The invention discloses a modified cation exchange membrane and a preparation method and application thereof in ion rectification, and the preparation method of the modified cation exchange membrane comprises the following steps: (1) dissolving amphoteric polyethyleneimine in deionized water to prepare a solution A; dissolving trimesoyl chloride in n-hexane to prepare a solution B; and (2) pouring a certain amount of the solution B on the sulfonated polysulfone membrane, then pouring a certain amount of the solution A on the sulfonated polysulfone membrane, and continuously reacting for 10-30 minutes to obtain the modified cation exchange membrane. The invention provides an application of the modified cation exchange membrane in ion rectification. The modified cation exchange membrane prepared by the method has high selectivity on monovalent and multivalent cations, and also has lower membrane surface resistance and higher ion exchange capacity, so that the modified cation exchange membrane has lower energy consumption.

Description

Technical Field

[0001] The invention relates to a modified cation exchange membrane and a preparation method thereof and application thereof in ion rectification. Background Art

[0002] Special ion separation technologies play a vital role in many key areas, including chemical wastewater treatment, seawater desalination, lithium extraction from salt lakes, and biomedicine. Although these technologies perform well in separating target ions, they still have some limitations, such as high cost, environmental pollution, and insufficient stability.

[0003] In the treatment of chemical wastewater, traditional technologies such as ion exchange, solvent extraction and ion sieving adsorption rely on physical adsorption processes to screen target ions. These technologies are not only costly, but may also produce acidic wastewater containing heavy metal ions that are difficult to treat. Electrodialysis technology, as an electrically driven membrane separation technology, uses the differences in physical and chemical properties between ions to achieve efficient separation through special functional membranes. It has been widely used in fields such as green chemical production.

[0004] Electrodialysis technology is particularly suitable for treating high-salt wastewater. It can directly decompose salt water into acid and alkali, realize resource recycling, and turn waste into treasure. Compared with traditional thermal evaporation, the investment cost of electrodialysis technology is only 30% of that of thermal evaporation, and the operating cost is only 10% of that of thermal evaporation. It is an economically feasible, easy to operate and maintain, safe and reliable concentrated salt treatment technology, which is of great significance to truly achieve zero emissions.

[0005] In addition, electrodialysis technology also shows great potential in lithium extraction. The magnesium-lithium ratio in salt lake brine is very high, which makes lithium extraction difficult. Electrodialysis has the advantages of simple operation, high efficiency, and low energy consumption. It has a series of advantages in lithium extraction from salt lakes, such as mature technology, simple process, and good separation performance. In the process of electrodialysis lithium extraction, the type of exchange membrane is an important factor affecting the lithium extraction effect.

[0006] However, electrodialysis technology also faces some challenges in practical application, such as high maintenance and replacement costs of membranes, as well as electricity cost issues. In order to overcome these limitations, researchers are constantly exploring new electrodialysis processes, such as selective electrodialysis and bipolar membrane electrodialysis, to improve separation efficiency and reduce energy consumption.

[0007] As an electrically driven membrane separation technology, electrodialysis uses the differences in physical and chemical properties between target ions and other ions to achieve efficient separation through special functional membranes. However, the efficiency of the electrodialysis process is limited by the material residence time and the electric field strength, and multiple units need to be coupled and integrated to achieve the target screening, which limits its advantages of continuous operation. Traditional ion distillation technology improves the separation efficiency of ions by arranging single and multivalent ion exchange membranes multiple times, but its energy consumption is greatly increased and is accompanied by the risk of scaling.

[0008] In response to the above problems, this study proposed a surface modification method, which makes the non-selective cation exchange membrane selective while reducing its membrane surface resistance, thereby achieving low-energy ion distillation, improving separation efficiency, and helping to achieve the economy of chemical processes.

[0009] Technical content

[0010] The purpose of the present invention is to provide a method for preparing a modified cation exchange membrane, the prepared modified cation exchange membrane and the application of the modified cation exchange membrane in ion distillation. The modified cation exchange membrane prepared by the present invention has good monovalent and polyvalent cation selectivity, and has the characteristics of high ion exchange capacity, low membrane surface resistance and low energy consumption.

[0011] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0012] In a first aspect, the present invention provides a method for preparing a modified cation exchange membrane, comprising the following steps:

[0013] (1) dissolving amphoteric polyethyleneimine in deionized water to prepare solution A, wherein the feed ratio of amphoteric polyethyleneimine to deionized water is (0.1-0.5) g: (10-20) mL; then dissolving trimesoyl chloride in n-hexane to prepare solution B, wherein the feed ratio of trimesoyl chloride to n-hexane is (0.01-0.05) g: (100-500) mL;

[0014] (2) A certain amount of solution B is poured onto the sulfonated polysulfone membrane, which does not have the ability to select monovalent or polyvalent cations. Then a certain amount of solution A is poured onto the sulfonated polysulfone membrane, and the reaction is continued for 10 to 30 minutes to obtain a modified cation exchange membrane.

[0015] Preferably, in step (2), the amount of solution A and solution B is 10-20 mL / 64 cm 2 .

[0016] Preferably, the thickness of the modified cation exchange membrane is 100-130 μm.

[0017] The sulfonated polysulfone membrane of the present invention can be prepared by existing technology, and the specific steps are recommended: (a) weighing the sulfonated polysulfone into a three-necked flask, adding a solvent, and stirring for 1 to 6 hours to obtain a solution C;

[0018] (b) Solution C is measured and poured onto a glass plate, and then dried in a vacuum drying oven at 60 to 80° C. for 12 to 24 hours to obtain a sulfonated polysulfone membrane.

[0019] Preferably, in step (a), the solvent is at least one of dimethyl sulfoxide, DMAc, NMP and DMF.

[0020] Preferably, in step (a), the solvent is dimethyl sulfoxide, and the feed ratio of the sulfonated polysulfone to the solvent is 1-2 g: 10-30 mL. The amphoteric polyethyleneimine of the present invention can be prepared by the method reported in existing literature, and is specifically recommended to be prepared according to the following method: deionized water is added to a three-necked flask, and diethylenetriamine pentaacetic acid is added thereto, and heated and stirred at 30-60° C. for 3-6 hours. Then, 30% hydrogen peroxide solution is added to the solution, and the reaction is continued at 30-60°C for 3-6 hours; then oxygen is introduced into the reaction system, and polyethyleneimine with a molecular weight of 10,000-20,000 is dissolved in deionized water, and then slowly poured into a three-necked flask, and continuously heated at 40-70°C for 3-6 hours; the obtained product is subjected to rotary evaporation at 30-50°C to remove the solvent water to obtain a light yellow viscous liquid, which is dissolved in ethanol and purified by column chromatography, and the solution is collected and rotary evaporation is performed to remove the ethanol to obtain the product amphoteric polyethyleneimine; wherein the feed ratio of diethylenetriaminepentaacetic acid, 30% hydrogen peroxide solution, and polyethyleneimine with a molecular weight of 10,000-20,000 is 5-20g:1-10mL:5-20g.

[0021] Before use, the modified cation exchange membrane prepared by the present invention needs to be soaked in deionized water for 10 hours.

[0022] In a second aspect, the present invention provides a modified cation exchange membrane prepared according to the preparation method described in the first aspect.

[0023] In a third aspect, the present invention provides an application of the modified cation exchange membrane described in the second aspect in ion distillation, wherein the ion distillation is carried out in an electrodialysis device, wherein the electrodialysis device comprises at least one electrodialysis unit, each electrodialysis unit being composed of a common cation exchange membrane, a modified cation exchange membrane and a common cation exchange membrane arranged in sequence, and the common cation exchange membrane does not have monovalent or polyvalent cation selectivity.

[0024] In a specific embodiment of the present invention, the ion fractionation is Li + / Mg2+ Ion distillation.

[0025] In a specific embodiment of the present invention, each electrodialysis unit is composed of a common cation exchange membrane, a modified cation exchange membrane and a common cation exchange membrane arranged in sequence to form a concentrated chamber and a dilute chamber, and the mixed solution including monovalent multi-metal ions to be separated is introduced into the concentrated chamber and the dilute chamber.

[0026] The present invention first prepares a non-selective sulfonated polysulfone membrane, and then immerses it for modification so that its surface contains positive and negative charges, thereby obtaining high selectivity while having low membrane surface resistance and high ion exchange capacity. Compared with the prior art, the present invention has the following advantages:

[0027] 1) The cation exchange membrane prepared by the preparation method proposed in the present invention has excellent monovalent and multivalent selectivity.

[0028] 2) The cation exchange membrane prepared by the present invention has strong stability, is not easy to scale, and has high ion separation efficiency in the ion rectification system.

[0029] 3) The cation exchange membrane prepared by the preparation method proposed in the present invention is less prone to scaling than commercial membranes and has lower energy consumption.

[0030] 4) The cation exchange membrane prepared by the present invention has a simple preparation process, a low membrane cost, and is more conducive to industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 : Schematic diagram of electrodialysis triple positive membrane ion distillation used in the embodiment of the present invention;

[0032] Figure 2 :Data of ion concentration in the concentration chamber of different membranes during electrodialysis;

[0033] Figure 3 : Voltage data diagram on both sides of different membrane systems during electrodialysis. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is further described below through specific embodiments, but the protection scope of the present invention is not limited thereto.

[0035] If no specific conditions are specified in the examples of the present invention, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be obtained by conventional technical means or purchased commercially.

[0036] Example 1

[0037] (1) Weigh 1 g of sulfonated polysulfone into a three-necked flask, add 15 mL of dimethyl sulfoxide as solvent, and stir for 6 h to obtain solution A.

[0038] (2) 10 mL of solution A was poured onto a glass plate, and then dried in a vacuum drying oven at 80° C. for 24 h to obtain a sulfonated polysulfone membrane CEM-1.

[0039] Example 1 does not involve any modification process.

[0040] Example 2

[0041] (1) Weigh 1 g of sulfonated polysulfone into a three-necked flask, add 15 mL of dimethyl sulfoxide as solvent, and stir for 6 h to obtain solution A.

[0042] (2) 10 mL of solution A was poured onto a glass plate, and then dried in a vacuum drying oven at 80° C. for 24 h to obtain a sulfonated polysulfone membrane CEM-1.

[0043] (3) Add 10 mL of deionized water to a 100 mL three-necked flask, and add 5 g of diethylenetriaminepentaacetic acid thereto. Heat and stir at 60°C for 6 h. Then add 10 mL of 30% hydrogen peroxide solution to the solution, and continue to react at 60°C for 3 h. Then introduce oxygen into the reaction system, and take 5 g of polyethyleneimine with a molecular weight of 20,000 and dissolve it in 10 mL of deionized water, slowly pour it into the three-necked flask, and continue to heat at 70°C for 6 h. The obtained product is evaporated at 50°C to remove the solvent water to obtain a light yellow viscous liquid. It is dissolved in ethanol and purified by cationic silica gel column chromatography. The solution is collected and evaporated to remove ethanol to obtain the product amphoteric polyethyleneimine.

[0044] (4) Weigh 0.1 g of the above-mentioned amphoteric polyethyleneimine product and dissolve it in 10 mL of deionized water to prepare solution B. Then dissolve 0.01% trimesoyl chloride in 100 mL of n-hexane to prepare solution C. Prepare to perform interfacial polymerization on the surface of the CEM-1 membrane prepared in step (2).

[0045] (5) Pour 10 mL of solution C onto a sulfonated polysulfone membrane CEM-1 (8×8 cm 2 ), and then 10 mL of solution B was poured onto the membrane CEM-1, and the reaction was continued for 10 min to obtain a modified cation exchange membrane CEM-2.

[0046] Example 3

[0047] (1) Weigh 1 g of sulfonated polysulfone into a three-necked flask, add 15 mL of dimethyl sulfoxide as solvent, and stir for 6 h to obtain solution A.

[0048] (2) Pour 10 mL of solution A onto a glass plate and then dry it in a vacuum drying oven at 80 °C for 24 h.

[0049] Sulfonated polysulfone membrane CEM-1 was obtained

[0050] (3) Add 10 mL of deionized water to a 100 mL three-necked flask, and add 5 g of diethylenetriaminepentaacetic acid thereto. Heat and stir at 60°C for 6 h. Then add 10 mL of 30% hydrogen peroxide solution to the solution, and continue to react at 60°C for 3 h. Then introduce oxygen into the reaction system, and take 5 g of polyethyleneimine with a molecular weight of 20,000 and dissolve it in 10 mL of deionized water, slowly pour it into the three-necked flask, and continue to heat at 70°C for 6 h. The obtained product is evaporated at 50°C to remove the solvent water to obtain a light yellow viscous liquid. It is dissolved in ethanol and purified by cationic silica gel column chromatography. The solution is collected and evaporated to remove ethanol to obtain the product amphoteric polyethyleneimine.

[0051] (4) Weigh 0.1 g of the above-mentioned amphoteric polyethyleneimine product and dissolve it in 10 mL of deionized water to prepare solution B. Then dissolve 0.01 g of trimesoyl chloride in 100 mL of n-hexane to prepare solution C. Prepare to perform interfacial polymerization on the surface of the CEM-1 membrane prepared in step (2).

[0052] (5) Pour 10 mL of solution C onto a sulfonated polysulfone membrane CEM-1 (8×8 cm 2 ), and then 10 mL of solution B was poured onto the membrane CEM-1, and the reaction was continued for 15 min to obtain a modified cation exchange membrane CEM-3.

[0053] Example 4

[0054] (1) Weigh 1 g of sulfonated polysulfone into a three-necked flask, add 15 mL of dimethyl sulfoxide as solvent, and stir for 6 h to obtain solution A.

[0055] (2) Pour 10 mL of solution A onto a glass plate and then dry it in a vacuum drying oven at 80 °C for 24 h.

[0056] Sulfonated polysulfone membrane CEM-1 was obtained

[0057] (3) Add 10 mL of deionized water to a 100 mL three-necked flask, and add 5 g of diethylenetriaminepentaacetic acid thereto. Heat and stir at 60°C for 6 h. Then add 10 mL of 30% hydrogen peroxide solution to the solution, and continue to react at 60°C for 3 h. Then introduce oxygen into the reaction system, and take 5 g of polyethyleneimine with a molecular weight of 20,000 and dissolve it in 10 mL of deionized water, slowly pour it into the three-necked flask, and continue to heat at 70°C for 6 h. The obtained product is evaporated at 50°C to remove the solvent water to obtain a light yellow viscous liquid. It is dissolved in ethanol and purified by cationic silica gel column chromatography. The solution is collected and evaporated to remove ethanol to obtain the product amphoteric polyethyleneimine.

[0058] (4) Weigh 0.1 g of the above-mentioned amphoteric polyethyleneimine product and dissolve it in 10 mL of deionized water to prepare solution B. Then dissolve 0.01% trimesoyl chloride in 100 mL of n-hexane to prepare solution C. Prepare to perform interfacial polymerization on the surface of the CEM-1 membrane prepared in step (2).

[0059] (5) Pour 10 mL of solution C onto a sulfonated polysulfone membrane CEM-1 (8×8 cm 2 ), and then 10 mL of solution B was poured onto the membrane CEM-1, and the reaction was continued for 20 min to obtain a modified cation exchange membrane CEM-4.

[0060] The performance of the prepared cation exchange membrane is tested as follows:

[0061] Test 1: In order to evaluate the monovalent and multivalent separation performance of the prepared cation exchange membrane, the current density (I = 10 mA cm -2 ) was conducted under + / Mg 2+ Electrodialysis experiment of ion distillation. In the battery stack, Figure 1 The electrodialysis device made by ourselves consists of a battery of two ruthenium-coated titanium electrodes and a concentration chamber. In the electrodialysis device, the effective area of ​​the prepared cation exchange membrane is 7.065 cm 2 The initial concentrations of the concentrated and diluted chambers were a mixture of 0.025 M Li2SO4 and 0.05 M MgSO4, and the polar solution was a 0.1 M MgSO4 solution. During the concentration process, a 500 μL pipette was used to take samples at a current density of 10 mA cm -2 Under the condition of + / Mg 2+ The concentration of Figure 2 shown.

[0062] Test 2: Determine the voltage on both sides of the system at different time periods to characterize its energy consumption level and whether it has anti-scaling performance. -2 ) was conducted under + / Mg 2+ Electrodialysis experiment of ion distillation. In the battery stack, Figure 1 The homemade stack shown consists of a concentration chamber and two ruthenium-coated titanium electrodes. In the electrodialysis device, the effective area of ​​the prepared cation exchange membrane is 7.065 cm 2 The initial concentrations of the concentrated and diluted chambers were a mixture of 0.025M Li2SO4 and 0.05M MgSO4, and the cathode solution was a 0.1M MgSO4 solution. The voltage data on the voltmeter was recorded while sampling every 10 minutes. The results are as follows: Figure 3 shown.

[0063] Test 3: The membrane surface resistance and ion exchange capacity of the prepared membrane were measured to characterize the reasons for its lower energy consumption.

[0064] Before the membrane surface resistance test, the cation exchange membrane sample was immersed in 0.5mol / LNaCl solution for 12 hours. During the test, the polar liquid was 0.3mol / LNa2SO4 solution, and 0.5mol / LNaCl was pumped into both ends of the cation exchange membrane as the inlet liquid. Then, the potential at both ends of the anion exchange membrane was measured using a multimeter (DMM6000, Zhiyuan Electronics Co., Ltd.). The surface area resistance of the anion exchange membrane is calculated according to the formula:

[0065]

[0066] Where, U is the potential difference between the two sides of the ion exchange membrane, V;

[0067] U0——blank voltage, V;

[0068] I——Externally applied constant current, 0.1A;

[0069] S——effective area of ​​ion exchange membrane, 7.065cm 2 .

[0070] To determine the ion exchange capacity of the cation exchange membrane, the membrane was first dried at 60 °C to remove moisture. Then, the dried membrane was immersed in a 0.5 mol / L HCl solution for 24 h to exchange the Na + ions. Afterwards, the membrane was washed with deionized water to remove H + ions. In order to ensure that Na +The ions were completely replaced, and the membrane was immersed in 0.5 mol / L Na2SO4 solution for 24 hours. Finally, a certain volume of Na2SO4 solution was taken out and titrated with 0.1 mol / L NaOH solution to determine the H + The concentration of ions is used to calculate the ion exchange capacity of the membrane. The relevant formula is as follows:

[0071]

[0072] In the formula, V is the volume of the Na2SO4 solution taken, L;

[0073] m——dry weight of anion exchange membrane, g;

[0074] C H+ ——H + The concentration, M.

[0075] The test results are shown in Table 1:

[0076] Table 1: Types of ion exchange membranes used and their properties

[0077]

[0078]

Claims

1. A method for preparing a modified cation exchange membrane, characterized in that: The preparation method comprises the following steps: (1) dissolving amphoteric polyethyleneimine in deionized water to prepare solution A, wherein the feed ratio of amphoteric polyethyleneimine to deionized water is (0.1-0.5) g: (10-20) mL; then dissolving trimesoyl chloride in n-hexane to prepare solution B, wherein the feed ratio of trimesoyl chloride to n-hexane is (0.01-0.05) g: (100-500) mL; (2) Pour a certain amount of solution B onto the sulfonated polysulfone membrane, and then pour a certain amount of solution A onto the sulfonated polysulfone membrane. Continue the reaction for 10 to 30 minutes to obtain a modified cation exchange membrane.

2. The preparation method according to claim 1, characterized in that: In step (2), the amount of solution A and solution B is 10-20 mL / 64 cm 2 .

3. The preparation method according to claim 1, characterized in that: The thickness of the modified cation exchange membrane is between 100 and 130 μm.

4. A modified cation exchange membrane obtained according to the preparation method according to any one of claims 1 to 3.

5. Use of the modified cation exchange membrane as claimed in claim 4 in ion rectification.

6. The use according to claim 5, characterized in that: The ion rectification is carried out in an electrodialysis device, which includes at least one electrodialysis unit. Each electrodialysis unit is composed of a common cation exchange membrane, a modified cation exchange membrane and a common cation exchange membrane arranged in sequence. The common cation exchange membrane does not have the performance of selecting monovalent and polyvalent cations.

7. The use according to claim 5, characterized in that: The ion fractionation is Li + / Mg 2+ Ion distillation.

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