A bipolar film and its preparation method

Abstract

This invention discloses a bipolar membrane and its preparation method. The bipolar membrane consists only of a cation exchange membrane and an anion exchange membrane. The cation exchange membrane is a TWEDC type, and the anion exchange membrane has an ion exchange capacity of 1.8 mmol / g and a thickness of 15-60 μm. In the preparation method, the membrane solution of the cathode membrane is sprayed onto the anode membrane and then dried to obtain the bipolar membrane. The bipolar membrane of this invention does not require an interfacial catalyst layer or an electrospun membrane to form a low water dissociation voltage, and has the advantage of simple processing.

Description

Technical Field

[0001] This invention relates to the field of bipolar films, specifically a bipolar film and its preparation method. Background Technology

[0002] Ion exchange membranes have a wide range of applications in electrochemistry and energy, and they include anion exchange membranes (AEM), cation exchange membranes (CEM), and bipolar membranes (BPM).

[0003] Bipolar membranes typically consist of a cation exchange layer (CEL), an anion exchange layer (AEL), and an interfacial bonding layer. When the cation exchange layer faces the cathode and the anion exchange layer faces the anode, salt ions cannot directly penetrate the interface due to Donnan repulsion. Under the influence of an applied electric field, water molecules at the interface dissociate, producing hydrogen ions (H+). + ) and hydroxide ions (OH) - This allows for the in-situ generation of acids and bases without the introduction of external salts.

[0004] Due to this characteristic, bipolar membranes are widely used in processes such as acid-base electrodialysis, fuel cells, carbon dioxide reduction, and seawater electrolysis, playing an important role in controlling the acid-base environment and improving energy conversion efficiency of the equipment.

[0005] In existing technologies, efforts to reduce the water dissociation voltage of bipolar membranes largely focus on optimizing the catalyst in the interfacial bonding layer. This includes selecting a suitable catalyst based on its isoelectric point, adjusting the catalyst loading distribution, or enhancing the local electric field at the interface. Additionally, some studies have improved interfacial bonding through electrospinning, surface pattern transfer, or selecting membrane materials with better chemical compatibility. While catalysts or electrospun membranes at the interface can reduce the water dissociation voltage of bipolar membranes, the fabrication process is complex due to the need for a catalyst layer or electrospun membrane. Summary of the Invention

[0006] This invention provides a bipolar membrane and its preparation method to solve the problem of existing bipolar membranes requiring the addition of a catalyst layer or electrospun membrane to reduce water dissociation voltage.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A bipolar membrane, consisting of a cation exchange membrane and an anion exchange membrane; The cation exchange membrane is a TWEDC type cation exchange membrane. The anion exchange membrane is made of quaternized polyarylbenzimidazole, has an ion exchange capacity of 1.8 mmol / g, and a thickness of 15 ~ 60 μm.

[0008] Furthermore, the anion exchange membrane has an ion exchange capacity of 1.8 mmol / g and a thickness of 15 μm.

[0009] Furthermore, the anion exchange membrane has an ion exchange capacity of 1.8 mmol / g and a thickness of 30 μm.

[0010] Furthermore, the anion exchange membrane has an ion exchange capacity of 1.8 mmol / g and a thickness of 45 μm.

[0011] Furthermore, the anion exchange membrane has an ion exchange capacity of 1.8 mmol / g and a thickness of 60 μm.

[0012] Furthermore, the quaternized polyarylbenzimidazole is prepared from 11-bromo-1-undecene and pyridine structural units. By controlling the molar ratio of 11-bromo-1-undecene and pyridine structural units to 1:0.9, a quaternized polyarylbenzimidazole with an ion exchange capacity of 1.8 mmol / g is obtained as an anion exchange membrane.

[0013] Furthermore, the pyridine structural unit is N-alkylpyridinium, or 4-vinylpyridine, or 4-(N,N-dimethylamine)methylpyridine.

[0014] A method for preparing the above-mentioned bipolar film, the process is as follows: Using the cation exchange membrane as the base membrane, anion exchange membrane solution is sprayed onto one surface of the cation exchange membrane, and then dried to obtain a bipolar membrane.

[0015] Furthermore, the spraying speed is 1 mL / min, and the coating is dried at 60°C for 1 min after spraying.

[0016] Compared with existing technologies, the bipolar membrane of this invention does not require an interfacial catalyst layer or electrospun membrane to form a low water dissociation voltage, and exhibits good ion conduction velocity and uniform interfacial deformation. This bipolar membrane can be directly processed by a spray coating process, offering the advantage of simple processing and suitability for the industrial production of bipolar membranes using various membrane framework materials. Attached Figure Description

[0017] Figure 1This is a schematic diagram of the bipolar film preparation method according to an embodiment of the present invention.

[0018] Figure 2 This is a graph showing the water dissociation voltage curves of bipolar films with different anion film thicknesses in embodiments of the present invention.

[0019] Figure 3 This is a diagram showing the swelling rate and water content of the bipolar membrane when the anion membrane thickness is 15 μm in an embodiment of the present invention.

[0020] Figure 4 This is a graph showing the conductivity of the bipolar membrane as a function of temperature when the anion membrane thickness is 15 μm in an embodiment of the present invention.

[0021] Figure 5 This is a graph showing the surface resistance of the bipolar membrane and its alkali production capacity during electrodialysis when the anion membrane thickness is 15 μm in an embodiment of the present invention. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] Example 1 This embodiment discloses a bipolar membrane consisting only of a cation exchange membrane and an anion exchange membrane, without containing a catalyst layer or an electrospun membrane.

[0024] In this embodiment, the cation exchange membrane (CEL) is a TWEDC cation exchange membrane manufactured by Shandong Tianwei Membrane Co., Ltd.

[0025] In this embodiment, the anion exchange membrane (AEL) is made of quaternized polyarylbenzimidazole with an ion exchange capacity (IEC) of 1.8 mmol / g. The thickness of the anion exchange membrane is 15 μm, or 30 μm, or 45 μm, or 60 μm.

[0026] Quaternized polyarylbenzimidazole, used as an anion exchange membrane, is prepared from 11-bromo-1-1-undecene and pyridine structural units.

[0027] During the preparation process, by adjusting the molar ratio of 11-bromo-1-undecene and pyridine structural units to 1:0.9, a quaternized polyarylbenzimidazole with an ion exchange capacity of 1.8 mmol / g was obtained as an anion exchange membrane.

[0028] The pyridine structural unit is N-alkylpyridinium, or 4-vinylpyridine, or 4-(N,N-dimethylamine)methylpyridine, preferably 4-acetylpyridine.

[0029] The following is a description of the test results for the bipolar membrane water dissociation voltage under different anion exchange membrane (i.e., anion membrane) thicknesses in this embodiment.

[0030] During the water dissociation voltage test, the four-electrode voltage-current testing method was used to test the working voltage and current of the bipolar membrane under different anion membrane thicknesses in this embodiment. The current density during the test was 0-200 mA / cm². 2 .

[0031] The measurement results of bipolar film working voltage and current under different anodizing film thicknesses in this embodiment are as follows: Figure 2 As shown, Figure 2 The curve at 15 μm represents the operating voltage and current of the bipolar membrane when the anion exchange membrane has an ion exchange capacity of 1.8 mmol / g and a thickness of 15 μm; the curve at 30 μm represents the operating voltage and current of the bipolar membrane when the anion exchange membrane has an ion exchange capacity of 1.8 mmol / g and a thickness of 30 μm; the curve at 45 μm represents the operating voltage and current of the bipolar membrane when the anion exchange membrane has an ion exchange capacity of 1.8 mmol / g and a thickness of 45 μm; and the curve at 60 μm represents the operating voltage and current of the bipolar membrane when the anion exchange membrane has an ion exchange capacity of 1.8 mmol / g and a thickness of 60 μm.

[0032] from Figure 2 As can be seen, in this embodiment, the water dissociation voltage of the bipolar membrane ranges from 0.94 to 1.94 V when the anion membrane thickness is 15 μm, 30 μm, 45 μm, and 60 μm, and the bipolar membrane can maintain high current density operation under different anion membrane thicknesses. Therefore, the water dissociation voltage of the bipolar membrane with different anion membrane thicknesses in this embodiment meets the requirements of practical applications in the industry.

[0033] Among them, when the anion membrane thickness is 15µm, the water dissociation voltage of the bipolar membrane is 0.94 V, which is the lowest. Therefore, the energy consumption of the bipolar membrane with anion membrane thickness of 15µm is lower than that of the bipolar membrane with other anion membrane thicknesses. Therefore, 15µm is the optimal anion membrane thickness for the bipolar membrane in this embodiment.

[0034] The following is a description of the tests conducted on the swelling rate, water content, conductivity, sheet resistance, and electrodialysis alkali production capacity of the bipolar membrane at the optimal anion membrane thickness (i.e., 15 μm) in this embodiment.

[0035] 1. Swelling rate and moisture content test The ambient temperature during testing was 25 ℃. The bipolar membrane with the optimal anion membrane thickness in this embodiment was immersed in deionized water for 12 h, and then the changes in length and width after water absorption were measured to calculate the swelling rate. The swelling rate of the bipolar membrane with the optimal anion membrane thickness in this embodiment is as follows: Figure 3 As shown, from Figure 3 It can be seen that the bipolar membrane has the highest swelling ratio of 3.67% when the anion membrane thickness is optimal in this embodiment.

[0036] The water content was characterized by the weight change of the bipolar membrane before and after immersion in deionized water at the optimal anion membrane thickness in this embodiment. The water content test results of the bipolar membrane at the optimal anion membrane thickness in this embodiment are as follows: Figure 3 As shown, from Figure 3 It can be seen that the water content of the bipolar membrane is the highest at the optimal anion membrane thickness in this embodiment, which is 9.31%.

[0037] 2. Conductivity test The conductivity test was conducted in a pure water environment. Before the test, the bipolar membrane with the optimal anion membrane thickness in this embodiment was soaked in acid and alkali solutions for 12 hours each, then washed three times with pure water and then soaked in pure water for 12 hours.

[0038] The tests were conducted using a four-electrode voltage-current method under pure water conditions, and the testing instrument was an electrochemical workstation. The OH groups in the anion membrane layer of the bipolar membrane at the optimal anion membrane thickness in this embodiment were measured using the four-electrode voltage-current method. - The electrical conductivity.

[0039] The conductivity test results of the bipolar membrane at the optimal anion film thickness in this embodiment are as follows: Figure 4 As shown, from Figure 4 It can be seen that, in this embodiment, the conductivity of the bipolar membrane increases with increasing temperature when the anion film thickness is optimal, reaching a maximum of 8.14 mS / cm.

[0040] 3. Surface resistance test The anion exchange membrane in the bipolar membrane at the optimal anion membrane thickness in this embodiment was subjected to unipolar membrane IV testing. The test solution for the anion exchange membrane was a 1 mol / L NaOH solution.

[0041] The current density range for unipolar membrane IV testing is 0~250 mA / cm². During testing, a silver / silver chloride reference electrode is used to measure the membrane surface voltage, and the anode and cathode are connected through a platinum sheet electrode.

[0042] The sheet resistance test results of the anion exchange membrane in the bipolar membrane at the optimal anion membrane thickness in this embodiment are as follows: Figure 5 As shown, the lowest surface resistivity of the anion exchange membrane is 8.11 Ω cm. 2 .

[0043] 4. Alkali production capacity of electrodialysis The test was conducted using an electrodialysis apparatus, which sequentially includes an anode plate, a cation exchange membrane (for the optimal anion exchange membrane thickness in this embodiment), an anion exchange membrane (for the optimal anion exchange membrane thickness in this embodiment), a cation exchange membrane (for the optimal anion exchange membrane thickness in this embodiment), and a cathode plate. The concentration chamber and desalination chamber are separated by an anion exchange membrane, and the electrode chambers are respectively connected to the cation exchange membrane and the anode and cathode plates.

[0044] The solution in the electrode chamber is a 0.3 mol / L Na₂SO₄ solution; the solutions in the concentration and desalination chambers are 1 mol / L NaOH solutions. Direct current is used during the test, with a preferred current density of 50 mA / cm²; the solution flow rate is 150 mL / min; and the test duration is 3 hours.

[0045] The test results of the bipolar membrane's electrodialysis alkali production capacity at the optimal anion membrane thickness in this embodiment are as follows: Figure 5 As shown, from Figure 5 It can be seen that, at the optimal anion membrane thickness in this embodiment, the electrodialysis alkali production capacity of the bipolar membrane is 25.25 mol / m³. 2 h.

[0046] In summary, at the optimal anion membrane thickness in this embodiment, the bipolar membrane exhibits a water dissociation voltage of 0.94 V, a swelling ratio of 3.67%, a water content of 9.31%, an electrical conductivity of 8.14 mS / cm, and a sheet resistivity of 8.11 Ω cm. 2 The alkali production capacity of electrodialysis is 25.25 mol / m³. 2 h. It can be seen that the bipolar membrane with the optimal anion membrane thickness in this embodiment, although composed only of a cation exchange membrane and anion exchange membrane and not containing a catalyst layer or electrospun membrane, still meets the requirements of practical applications in the industry.

[0047] Example 2 This embodiment discloses a method for preparing the bipolar film described in Embodiment 1, the process of which is as follows: like Figure 1 As shown, a cation exchange membrane (CEL) of model TWEDC was used as the substrate. An anion exchange membrane (AEL) solution with an ion exchange capacity (IEC) of 1.8 mmol / g was sprayed onto one side of the substrate membrane at a spraying speed of 1 L / min, forming an anion exchange membrane with a thickness of 15 μm, 30 μm, 45 μm, or 60 μm, thus obtaining a composite structure. After spraying, the composite structure was dried at 60℃ for 1 min to obtain a bipolar membrane.

[0048] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. These embodiments are merely descriptions of preferred embodiments and are not intended to limit the scope or concept of the invention. The specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. Such combinations, as long as they do not violate the spirit of the present invention, should also be considered as part of this disclosure. To avoid unnecessary repetition, the present invention will not further describe the various possible combinations.

[0049] This invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this invention and without departing from the design idea of ​​this invention, all modifications and improvements made by those skilled in the art to the technical solutions of this invention should fall within the protection scope of this invention. The technical content for which protection is sought in this invention has been fully described in the claims.

Claims

1. A bipolar membrane, characterized in that, It consists of cation exchange membranes and anion exchange membranes; The cation exchange membrane is a TWEDC type cation exchange membrane. The anion exchange membrane is made of quaternized polyarylbenzimidazole, has an ion exchange capacity of 1.8 mmol / g, and a thickness of 15 ~ 60 μm.

2. The bipolar film according to claim 1, characterized in that, The anion exchange membrane has an ion exchange capacity of 1.8 mmol / g and a thickness of 15 μm.

3. The bipolar film according to claim 1, characterized in that, The anion exchange membrane has an ion exchange capacity of 1.8 mmol / g and a thickness of 30 μm.

4. The bipolar film according to claim 1, characterized in that, The anion exchange membrane has an ion exchange capacity of 1.8 mmol / g and a thickness of 45 μm.

5. The bipolar film according to claim 1, characterized in that, The anion exchange membrane has an ion exchange capacity of 1.8 mmol / g and a thickness of 60 μm.

6. The bipolar film according to any one of claims 1-5, characterized in that, The quaternized polyarylbenzimidazole was prepared from 11-bromo-1-undecene and pyridine structural units. By controlling the molar ratio of 11-bromo-1-undecene and pyridine structural units to 1:0.9, a quaternized polyarylbenzimidazole with an ion exchange capacity of 1.8 mmol / g was obtained as an anion exchange membrane.

7. The bipolar film according to claim 6, characterized in that, The pyridine structural unit is N-alkylpyridinium, or 4-vinylpyridine, or 4-(N,N-dimethylamine)methylpyridine.

8. A method for preparing a bipolar film as described in any one of claims 1-7, characterized in that, The process is as follows: Using the cation exchange membrane as the base membrane, anion exchange membrane solution is sprayed onto one surface of the cation exchange membrane, and then dried to obtain a bipolar membrane.

9. The method for preparing a bipolar film according to claim 8, characterized in that, The spraying speed is 1 mL / min, and the coating is dried at 60℃ for 1 min after spraying.

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