A modified cation exchange membrane, its preparation method and application in ionic rectification
By modifying the interfacial polymerization of cation exchange membranes, the problems of high energy consumption and high cost in electrodialysis technology are solved, achieving low energy consumption and high efficiency in ion distillation, which is suitable for chemical wastewater treatment and lithium extraction from salt lakes.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG UNIV OF TECH
- Filing Date
- 2024-09-29
- Publication Date
- 2026-06-16
AI Technical Summary
Existing electrodialysis technology suffers from high membrane maintenance and replacement costs, high energy consumption, and limited separation efficiency in the treatment of high-salinity wastewater and lithium extraction. In particular, energy consumption increases significantly and the risk of scaling is high during multiple ion distillation processes.
A selective modified cation exchange membrane was prepared by interfacial polymerization of amphoteric polyethyleneimine and sulfonated polysulfone membrane using a surface modification method. This reduced the membrane surface resistance and increased the ion exchange capacity, which can be used in ion distillation processes.
It achieves low energy consumption and high efficiency in selecting monovalent and multivalent cations, reduces the risk of scaling, lowers the cost of membrane use, and is suitable for industrial production.
Smart Images
Figure BDA0005067881650000061 
Figure BDA0005067881650000062 
Figure BDA0005067881650000063
Abstract
Description
Technical Field
[0001] This invention relates to a modified cation exchange membrane, its preparation method, and its application in ion distillation. Background Technology
[0002] Specialty ion separation technologies play a crucial role in several key fields, including chemical wastewater treatment, seawater desalination, lithium extraction from salt lakes, and biomedicine. While these technologies excel 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 for target ions. These technologies are not only costly but may also generate acidic wastewater containing heavy metal ions that is difficult to treat. Electrodialysis, as an electrically driven membrane separation technology, utilizes the differences in the physicochemical properties of ions to achieve efficient separation through specialized functional membranes, and has been widely used in fields such as green chemical production.
[0004] Electrodialysis technology is particularly suitable for treating high-salinity wastewater, enabling the direct decomposition of brine into acids and alkalis for resource recovery and recycling, turning waste into treasure. Compared with traditional thermal evaporation, the investment cost of electrodialysis technology is only 30% of that of thermal methods, and the operating cost is only 10% of that of thermal methods. It is an economical, feasible, easy-to-operate and maintain, safe and reliable concentrated salt treatment technology, which is of great significance for truly achieving zero emissions.
[0005] Furthermore, electrodialysis technology has shown great potential in lithium extraction. The high magnesium-to-lithium ratio in salt lake brines presents challenges for lithium extraction. Electrodialysis offers advantages such as simple operation, high efficiency, and low energy consumption, demonstrating a series of advantages in salt lake lithium extraction, including technological maturity, simple process, and good separation performance. During electrodialysis lithium extraction, the type of exchange membrane is a crucial factor affecting the extraction efficiency.
[0006] However, electrodialysis technology also faces some challenges in practical applications, such as the high cost of membrane maintenance and replacement, and the issue of electricity costs. 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] Electrodialysis, as an electrically driven membrane separation technology, utilizes the differences in physicochemical properties between target ions and other ions to achieve efficient separation through specialized functional membranes. However, the efficiency of the electrodialysis process is limited by the material residence time and electric field strength, and requires the coupling and integration of multiple units to achieve target sieving, which restricts its advantage of continuous operation. Traditional ion distillation technology improves ion separation efficiency by employing multiple arrangements of monovalent and multivalent ion exchange membranes, but this significantly increases energy consumption and carries the risk of scaling.
[0008] To address the aforementioned issues, this study proposes a surface modification method. By imparting selectivity to a non-selective cation exchange membrane and reducing its surface resistivity, this method enables low-energy ion distillation, improves separation efficiency, and contributes to the economicalization of chemical processes.
[0009] Technical content
[0010] The purpose of this invention is to provide a method for preparing a modified cation exchange membrane, the obtained modified cation exchange membrane, and the application of the modified cation exchange membrane in ion distillation. The modified cation exchange membrane prepared by this invention has good monovalent and polyvalent cation selectivity, as well as high ion exchange capacity, low membrane surface resistance, and low energy consumption.
[0011] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:
[0012] In a first aspect, the present invention provides a method for preparing a modified cation exchange membrane, comprising the following steps:
[0013] (1) Dissolve amphoteric polyethyleneimine in deionized water to prepare solution A, wherein the ratio of amphoteric polyethyleneimine to deionized water is (0.1-0.5) g: (10-20) mL; then dissolve trimesoyl chloride in n-hexane to prepare solution B, wherein the ratio of trimesoyl chloride to n-hexane is (0.01-0.05) g: (100-500) mL;
[0014] (2) Take a certain amount of solution B and pour it onto the sulfonated polysulfone membrane. The sulfonated polysulfone membrane does not have the ability to select monovalent or polyvalent cations. Then take a certain amount of solution A and pour it onto the sulfonated polysulfone membrane. Continue the reaction for 10 to 30 minutes to obtain the modified cation exchange membrane.
[0015] Preferably, in step (2), the amounts of solutions A and B used are 10–20 mL / 64 cm³, respectively. 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. Specifically, it is recommended to follow the steps as follows: (a) Weigh sulfonated polysulfone into a three-necked flask, add solvent, stir for 1 to 6 hours to obtain solution C;
[0018] (b) Measure solution C and pour it onto a glass plate, then dry it in a vacuum drying oven at 60-80°C for 12-24 hours to obtain a sulfonated polysulfone film.
[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 ratio of the sulfonated polysulfone to the solvent is 1-2 g: 10-30 mL. The amphoteric polyethyleneimine of this invention can be prepared by methods reported in existing literature. Specifically, it is recommended to prepare it as follows: add deionized water to a three-necked flask, add diethylenetriaminepentaacetic acid, and heat and stir at 30-60°C for 3-6 hours. Next, a 30% hydrogen peroxide solution was added to the solution, and the reaction was continued at 30–60°C for 3–6 hours. Then, oxygen was introduced into the reaction system, and polyethyleneimine with a molecular weight of 10,000–20,000 was dissolved in deionized water and slowly poured into a three-necked flask. The mixture was heated at 40–70°C for 3–6 hours. The product was then removed by rotary evaporation at 30–50°C to obtain a pale yellow viscous liquid, which was dissolved in ethanol and purified by column chromatography. The solution was collected and the ethanol was removed by rotary evaporation to obtain the product, amphoteric polyethyleneimine. The feed ratio of diethylenetriaminepentaacetic acid, 30% hydrogen peroxide solution, and polyethyleneimine with a molecular weight of 10,000–20,000 was 5–20 g: 1–10 mL: 5–20 g.
[0021] Before use, the modified cation exchange membrane prepared by this 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] Thirdly, the present invention provides the 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 apparatus, the electrodialysis apparatus comprising at least one electrodialysis unit, each electrodialysis unit being composed of a conventional cation exchange membrane, a modified cation exchange membrane, and a conventional cation exchange membrane arranged in sequence, wherein the conventional cation exchange membrane does not possess monovalent or multivalent cation selectivity.
[0024] In a specific embodiment of the present invention, the ion distillation is Li + / Mg2+ Ion distillation.
[0025] In a specific embodiment of the present invention, each electrodialysis unit consists of a concentration chamber and a dilute chamber formed by arranging a conventional cation exchange membrane, a modified cation exchange membrane, and a conventional cation exchange membrane in sequence. A mixed solution containing monovalent polymetallic ions to be separated is introduced into both the concentration chamber and the dilute chamber.
[0026] This invention first prepares a non-selective sulfonated polysulfone membrane, then modifies it by immersion, resulting in positive and negative charges on its surface. This achieves high selectivity while maintaining low membrane surface resistance and high ion exchange capacity. Compared with existing technologies, this invention has the following advantages:
[0027] 1) The cation exchange membrane prepared by the preparation method proposed in this invention has excellent monovalent and multivalent selectivity.
[0028] 2) The cation exchange membrane prepared by the present invention has strong stability, is not prone to scaling, and has high ion separation efficiency in ion distillation systems.
[0029] 3) The cation exchange membrane prepared by the preparation method proposed in this invention is less prone to fouling than commercial membranes, and at the same time, the membrane consumes less energy.
[0030] 4) The cation exchange membrane prepared by this invention has a simple preparation process, low membrane cost, and is more conducive to industrial production. Attached Figure Description
[0031] Figure 1 Schematic diagram of electrodialysis trication membrane ion distillation used in this embodiment of the invention;
[0032] Figure 2 Graph showing ion concentration data in the concentration chambers of different membranes during electrodialysis;
[0033] Figure 3 : Voltage data diagrams across different membrane systems during electrodialysis. Detailed Implementation
[0034] The technical solution of the present invention will be further described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.
[0035] Unless otherwise specified in the embodiments of this invention, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained through conventional technical means or commercially available.
[0036] Example 1
[0037] (1) Weigh 1 g of sulfonated polysulfone into a three-necked flask and add 15 mL of dimethyl sulfoxide as a solvent. Stir for 6 h to obtain solution A.
[0038] (2) Measure 10 mL of solution A and pour it onto a glass plate. Then, dry the plate in a vacuum drying oven at 80 °C for 24 h. This yields sulfonated polysulfone film CEM-1.
[0039] Example 1 did not involve any modification process.
[0040] Example 2
[0041] (1) Weigh 1 g of sulfonated polysulfone into a three-necked flask and add 15 mL of dimethyl sulfoxide as a solvent. Stir for 6 h to obtain solution A.
[0042] (2) Measure 10 mL of solution A and pour it onto a glass plate. Then, dry the plate in a vacuum drying oven at 80 °C for 24 h. This yields sulfonated polysulfone film CEM-1.
[0043] (3) Add 10 mL of deionized water to a 100 mL three-necked flask and add 5 g of diethylenetriaminepentaacetic acid. Heat and stir at 60 °C for 6 h. Then add 10 mL of 30% hydrogen peroxide solution to the solution and continue the reaction at 60 °C for 3 h. Then introduce oxygen into the reaction system, and dissolve 5 g of polyethyleneimine with a molecular weight of 20,000 in 10 mL of deionized water and slowly pour it into the three-necked flask, and continue heating at 70 °C for 6 h. Remove the solvent water by rotary evaporation at 50 °C to obtain a pale yellow viscous liquid. Dissolve it in ethanol and purify it by cationic silica gel column chromatography. Collect the solution and remove the ethanol by rotary evaporation 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 g of trimesoyl chloride in 100 mL of n-hexane to prepare solution C. Prepare for interfacial polymerization on the surface of the CEM-1 membrane obtained in step (2).
[0045] (5) Take 10 mL of solution C and pour it onto the sulfonated polysulfone membrane CEM-1 (8×8cm). 2 Then, take 10 mL of solution B and pour it onto membrane CEM-1. Continue the reaction for 10 min to obtain the modified cation exchange membrane CEM-2.
[0046] Example 3
[0047] (1) Weigh 1 g of sulfonated polysulfone into a three-necked flask and add 15 mL of dimethyl sulfoxide as a solvent. Stir for 6 h to obtain solution A.
[0048] (2) Measure 10 mL of solution A and pour it onto a glass plate. Then, dry it in a vacuum drying oven at 80°C for 24 hours.
[0049] Sulfonated polysulfone film 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. Heat and stir at 60 °C for 6 h. Then add 10 mL of 30% hydrogen peroxide solution to the solution and continue the reaction at 60 °C for 3 h. Then introduce oxygen into the reaction system, and dissolve 5 g of polyethyleneimine with a molecular weight of 20,000 in 10 mL of deionized water and slowly pour it into the three-necked flask, and continue heating at 70 °C for 6 h. Remove the solvent water by rotary evaporation at 50 °C to obtain a pale yellow viscous liquid. Dissolve it in ethanol and purify it by cationic silica gel column chromatography. Collect the solution and remove the ethanol by rotary evaporation 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 for interfacial polymerization on the surface of the CEM-1 membrane obtained in step (2).
[0052] (5) Take 10 mL of solution C and pour it onto the sulfonated polysulfone membrane CEM-1 (8×8cm). 2 Then, take 10 mL of solution B and pour it onto membrane CEM-1. Continue the reaction for 15 min to obtain the modified cation exchange membrane CEM-3.
[0053] Example 4
[0054] (1) Weigh 1 g of sulfonated polysulfone into a three-necked flask and add 15 mL of dimethyl sulfoxide as a solvent. Stir for 6 h to obtain solution A.
[0055] (2) Measure 10 mL of solution A and pour it onto a glass plate. Then, dry it in a vacuum drying oven at 80°C for 24 hours.
[0056] Sulfonated polysulfone film 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. Heat and stir at 60 °C for 6 h. Then add 10 mL of 30% hydrogen peroxide solution to the solution and continue the reaction at 60 °C for 3 h. Then introduce oxygen into the reaction system, and dissolve 5 g of polyethyleneimine with a molecular weight of 20,000 in 10 mL of deionized water and slowly pour it into the three-necked flask, and continue heating at 70 °C for 6 h. Remove the solvent water by rotary evaporation at 50 °C to obtain a pale yellow viscous liquid. Dissolve it in ethanol and purify it by cationic silica gel column chromatography. Collect the solution and remove the ethanol by rotary evaporation 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 g of trimesoyl chloride in 100 mL of n-hexane to prepare solution C. Prepare for interfacial polymerization on the surface of the CEM-1 membrane obtained in step (2).
[0059] (5) Take 10 mL of solution C and pour it onto the sulfonated polysulfone membrane CEM-1 (8×8cm). 2 Then, take 10 mL of solution B and pour it onto membrane CEM-1. Continue the reaction for 20 min to obtain the modified cation exchange membrane CEM-4.
[0060] The performance of the prepared cation exchange membrane was then tested:
[0061] Test 1: To evaluate the monovalent and multivalent separation performance of the prepared cation exchange membrane, a current density (I = 10 mA·cm⁻¹) was used. -2 Li was performed under ) + / Mg 2+ Electrodialysis experiment of ion distillation. In the fuel cell stack, [the following was used]. Figure 1 The self-made electrodialysis apparatus shown consists of a concentration chamber and two ruthenium-coated titanium electrodes. In this apparatus, the effective area of the prepared cation exchange membrane is 7.065 cm². 2 The initial concentrations in both the concentrate and dilute chambers were a mixed solution of 0.025 M Li₂SO₄ and 0.05 M MgSO₄, with the electrode solution being a 0.1 M MgSO₄ solution. During concentration, samples were taken using 500 μL pipettes at a current density of 10 mA cm⁻¹. -2 Under these conditions, samples were taken every 10 minutes to measure Li. + / Mg 2+ The concentration, the results are as follows Figure 2 As shown.
[0062] Test 2: The voltage across the system was measured at different time intervals to characterize its energy consumption level and whether it has anti-scaling properties. Referring to Test 1, at a current density (I = 10 mA·cm²), -2 Li was performed under ) + / Mg 2+ Electrodialysis experiment of ion distillation. In the fuel cell stack, [the following was used]. Figure 1 The self-made fuel cell stack shown consists of a concentration chamber and two ruthenium-coated titanium electrodes. In the electrodialysis apparatus, the effective area of the prepared cation exchange membrane is 7.065 cm². 2 The initial concentrations in both the concentrate and dilute chambers were a mixed solution of 0.025 M Li₂SO₄ and 0.05 M MgSO₄, with the electrode solution being a 0.1 M MgSO₄ solution. Samples were taken every 10 minutes, and the voltage readings on the voltmeter were recorded. The results are as follows: Figure 3 As shown.
[0063] Test 3: The membrane surface resistance and ion exchange capacity of the prepared membrane were measured to characterize the reason for its low energy consumption.
[0064] Before the surface resistivity test, the cation exchange membrane sample was immersed in a 0.5 mol / L NaCl solution for 12 hours. During the test, a 0.3 mol / L Na₂SO₄ solution was used as the electrode solution, and 0.5 mol / L NaCl was pumped into both ends of the cation exchange membrane as the feed solution. Then, the potential across the anion exchange membrane was measured using a multimeter (DMM6000, Zhiyuan Electronics Co., Ltd.). The surface resistivity of the anion exchange membrane was calculated using the formula:
[0065]
[0066] In the formula, U represents the potential difference across the ion exchange membrane, expressed as V.
[0067] U0 — Blank voltage, V;
[0068] I—Constant current applied externally, 0.1A;
[0069] S – Effective area of the ion exchange membrane, 7.065 cm² 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 hours to exchange Na+ from the membrane. + Ions. Afterwards, the membrane is washed with deionized water to remove surface-adsorbed H+. + Ions. To ensure Na+ in the membrane +After the ions were completely replaced, the membrane was immersed again in a 0.5 mol / L Na₂SO₄ solution for 24 hours. Finally, a certain volume of Na₂SO₄ solution was taken out and titrated with a 0.1 mol / L NaOH solution to determine the H₂ content in the solution. + The ion concentration 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, in L;
[0073] m—dry weight of the anion exchange membrane, in grams;
[0074] C H+ ——H + The concentration, M.
[0075] The test results are shown in Table 1:
[0076] Table 1: Types and properties of ion exchange membranes used
[0077]
[0078]
Claims
1. The application of a modified cation exchange membrane in ion distillation, characterized in that: The ion distillation is carried out in an electrodialysis apparatus, which includes at least one electrodialysis unit. Each electrodialysis unit consists of a conventional cation exchange membrane, a modified cation exchange membrane, and another conventional cation exchange membrane arranged sequentially. The conventional cation exchange membrane does not possess monovalent or multivalent cation selectivity. The ion distillation is carried out using Li... + / Mg 2+ Ion distillation; The method for preparing the modified cation exchange membrane includes the following steps: (1) Dissolve amphoteric polyethyleneimine in deionized water to prepare solution A, wherein the ratio of amphoteric polyethyleneimine to deionized water is (0.1~0.5) g: (10~20) mL; then dissolve trimesoyl chloride in n-hexane to prepare solution B, wherein the 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 as well. The amounts of solutions A and B are 10~20 mL / 64 cm², respectively. 2 The reaction is continued for 10-30 minutes to obtain a modified cation exchange membrane with a thickness of 100-130 μm.