Bipolar membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of ion exchange membranes, and discloses a bipolar membrane and a preparation method and application thereof.The bipolar membrane comprises a positive membrane layer, a catalyst layer and a negative membrane layer which are sequentially stacked, the positive membrane layer comprises a first positive membrane layer and a second positive membrane layer, the first positive membrane layer is located on the surface of one side of the catalyst layer, and the second positive membrane layer is located on the surface of the other side of the catalyst layer; the second positive membrane layer is positioned on the surface of one side, deviating from the catalyst layer, of the first positive membrane layer; the material of the first positive membrane layer is formed by polymerizing monomers comprising double bonds and sulfonic acid groups; and the material of the second positive membrane layer comprises a sulfonated polymer. The positive membrane layer comprises the first positive membrane layer and the second positive membrane layer, the first positive membrane layer mainly plays a role in ion transmission to ensure that hydrogen ions generated by water dissociation can be quickly and efficiently migrated to the acid chamber, and the second positive membrane layer mainly plays a role in blocking common ions to prevent a large number of common ions in the acid chamber from being migrated to the alkali chamber, so that the acid chamber is protected from being polluted. And the positive film layer can effectively block the same ions.

Description

Technical Field

[0001] This invention relates to the field of ion exchange membrane technology, specifically to a bipolar membrane, its preparation method, and its application. Background Technology

[0002] A bipolar membrane is a special type of ion exchange membrane, consisting of a cation exchange layer, an anion exchange layer, and an intermediate interface layer. Under reverse bias, water in the bipolar membrane interface layer dissociates to generate hydrogen ions and hydroxide ions. Therefore, an electrodialysis system composed of a bipolar membrane and cation / anion exchange membrane can convert salts into corresponding acids and bases, achieving zero discharge of waste salts and conversion of high-value-added chemicals.

[0003] Theoretically, the cation and anion exchange layers of bipolar membranes only allow counterions to pass through. However, because the selectivity of the cation and anion exchange layers is difficult to achieve 100%, during electrodialysis (taking the sodium sulfate system as an example), sulfate ions in the acid chamber can pass through the bipolar membrane into the alkali chamber, and sodium ions in the alkali chamber can also pass through the bipolar membrane into the acid chamber. This results in excessively high salt content in both the acid and alkali chambers, causing salt contamination, which is a major problem limiting the widespread adoption of bipolar membrane electrodialysis. Compared to acids, alkalis, with their higher added value, have higher purity requirements, which poses a greater challenge to the design of highly selective cation exchange membranes. Therefore, designing a highly selective cation exchange membrane that effectively blocks sulfate ions is crucial for the preparation of high-purity alkali.

[0004] In existing technologies, bipolar membranes can be broadly classified into two main types based on their preparation methods: monolithic and composite. One disclosed method involves impregnating a base membrane with styrene monomers to obtain the base membrane, followed by sulfonation on one side and chloromethylation and ammoniation on the other. Because the anion and cation layers of a monolithic bipolar membrane are a single unit, the layers are firmly bonded and less prone to delamination. However, this method results in an unclear membrane interface structure and a high water dissociation voltage. Another disclosed method involves preparing a low-salt-permeability bipolar membrane. This method uses a hot-melt process to tightly bond the second anion layer to the first anion layer, reducing salt permeation while maintaining a low water dissociation voltage. However, this method only reduces the salt content in the acid chamber and does not propose an improvement method for the cation layer to reduce the salt content in the alkali chamber. Furthermore, the hot-melt process is complex and energy-intensive, making industrial application difficult.

[0005] Therefore, developing a bipolar membrane for high-purity alkali production via electrodialysis with low energy consumption is one of the technical problems that urgently need to be solved in this field. Summary of the Invention

[0006] This invention provides a bipolar membrane to solve the problems of low purity and high energy consumption in existing electrodialysis alkali production.

[0007] In a first aspect, the present invention provides a bipolar membrane, the bipolar membrane comprising a cation membrane layer, a catalyst layer and an anion membrane layer stacked sequentially, the cation membrane layer comprising a first cation membrane layer and a second cation membrane layer, the first cation membrane layer being located on one side surface of the catalyst layer, and the second cation membrane layer being located on the side surface of the first cation membrane layer opposite to the catalyst layer. The material of the first cation membrane layer is polymerized from monomers including double bonds and sulfonic acid groups; The material of the second anodic membrane layer includes a sulfonated polymer; The relationship between the ion exchange capacity A1 of the first cation exchange membrane layer and the ion exchange capacity A2 of the second cation exchange membrane layer is 0 < (A1-A2) / A1 ≤ 0.96.

[0008] In one alternative embodiment, the degree of sulfonation of the sulfonated polymer is 5%-80%.

[0009] In one alternative embodiment, the ion exchange capacity of the first cation exchange membrane layer is 0.8 mmol / g to 2.4 mmol / g.

[0010] In one alternative embodiment, the ion exchange capacity of the second cation exchange membrane is 0.1 mmol / g to 1.2 mmol / g.

[0011] In one alternative embodiment, the monomer of the material of the first cation membrane layer includes 2-acrylamido-2-methylpropanesulfonic acid.

[0012] In one alternative embodiment, the sulfonated polymer is selected from at least one of sulfonated polyphenylene ether, sulfonated polysulfone, and sulfonated polyether ether ketone.

[0013] In one alternative embodiment, the catalyst layer is made of at least one of titanium dioxide, stannous chloride, zirconium oxide, aluminum oxide, and yttrium oxide.

[0014] In one optional embodiment, the anion membrane layer includes a quaternized polymer; the main chain structure of the quaternized polymer includes at least one of polyphenylene ether, polysulfone, and polyetheretherketone.

[0015] In one alternative embodiment, the thickness of the first anodic film layer is 20µm-500µm.

[0016] In one alternative embodiment, the thickness of the second anodic film layer is 5µm-50µm.

[0017] In one alternative embodiment, the thickness of the catalyst layer is 0.1µm-10µm.

[0018] In one alternative embodiment, the thickness of the anion film layer is 5µm-200µm.

[0019] In a second aspect, the present invention provides a method for preparing the bipolar film described in the first aspect, comprising the following steps: The first cation membrane solution, catalyst slurry, anion membrane slurry, and second cation membrane slurry were prepared separately. The substrate is immersed in the first cation film solution and cured to form the first cation film layer; The catalyst slurry is coated on one side surface of the first cation film layer to form a catalyst layer, thus obtaining the first preform. An anion film slurry is coated onto the catalyst layer of the first preform to form an anion film layer, thus obtaining a second preform; The second cation membrane slurry is coated on the side of the first cation membrane layer of the second preform that is away from the catalyst layer to form the second cation membrane layer, thereby obtaining the bipolar membrane.

[0020] In one alternative embodiment, the catalyst content in the catalyst slurry is 0.1wt%-10wt%.

[0021] In one optional embodiment, the solid content of the anion film slurry is 2wt%-40wt%.

[0022] In one optional embodiment, the solid content of the second cation exchange slurry is 2wt%-40wt%.

[0023] In one optional embodiment, the preparation step of the first cation exchange film solution includes: mixing sulfonic acid monomer, crosslinking agent, initiator and first solvent to obtain the solution.

[0024] In one alternative embodiment, the crosslinking agent comprises divinylbenzene.

[0025] In one alternative embodiment, the initiator includes at least one of benzoyl peroxide, azobisisobutyronitrile, dilauryl peroxide, and azobisisoheptanenitrile.

[0026] In one alternative embodiment, the first solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0027] In one optional embodiment, the preparation step of the anion film slurry includes: mixing a halomethylated polymer, an ammonifying agent, and a second solvent.

[0028] In one optional embodiment, the second solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0029] In one alternative embodiment, the main chain structure of the halomethylated polymer includes at least one of polyphenylene ether, polysulfone, and polyetheretherketone.

[0030] In one optional embodiment, the ammonifying agent includes at least one of chain tertiary amines, cyclic tertiary amines, and diamine-type tertiary amines; the chain tertiary amine includes at least one of trimethylamine, triethylamine, N,N-dimethylbutylamine, and N,N-dimethylhexylamine; the cyclic tertiary amine includes at least one of N-methylimidazole and N-methylpiperidine; and the diamine-type tertiary amine includes tetramethylhexamethylenediamine.

[0031] In one optional embodiment, the curing temperature is 30℃-150℃ and the time is 1h-48h.

[0032] In one optional embodiment, the basis weight of the substrate is 10 g / m³. 2 -500g / m 2 The porosity is 10%-90%.

[0033] In one alternative embodiment, prior to curing, the substrate impregnated with the first cation exchange solution is placed between two inert sheets.

[0034] Thirdly, the present invention provides the application of bipolar membranes prepared by the preparation method described in the first aspect or the second aspect in the field of electrodialysis.

[0035] The technical solution of this invention has the following advantages: 1. The bipolar membrane provided by the present invention comprises a cation membrane layer, a catalyst layer, and an anion membrane layer stacked sequentially. The cation membrane layer comprises a first cation membrane layer and a second cation membrane layer. The first cation membrane layer is located on one side surface of the catalyst layer, and the second cation membrane layer is located on the side surface of the first cation membrane layer opposite to the catalyst layer. The material of the first cation membrane layer is polymerized from a monomer comprising double bonds and sulfonic acid groups. The material of the second cation membrane layer comprises a sulfonated polymer. The relationship between the ion exchange capacity A1 of the first cation membrane layer and the ion exchange capacity A2 of the second cation membrane layer is 0 < (A1-A2) / A1 ≤ 0.96. The cation exchange membrane of this invention comprises a first cation exchange membrane layer and a second cation exchange membrane layer. The first cation exchange membrane layer mainly undertakes hydrogen ion transport, while the second cation exchange membrane layer mainly blocks sulfate and other salt ions. This invention controls the relationship between the ion exchange capacity A1 of the first cation exchange membrane layer and the ion exchange capacity A2 of the second cation exchange membrane layer to be 0 < (A1-A2) / A1 ≤ 0.96, so that H ions can quickly pass through the first cation exchange membrane layer, reducing energy consumption; at the same time, it prevents a large amount of like ions from migrating from the acid chamber to the alkali chamber, achieving effective blocking of like ions by the cation exchange membrane layer. The first and second cation exchange membrane layers of this invention have clearly defined functions and complement each other, resulting in a lower salt ion content and higher purity in the alkali chamber of the prepared bipolar membrane. If (A1-A2) / A1 > 0.96, the second cation exchange membrane layer basically does not play a role in hydrogen ion transport, leading to extremely high energy consumption.

[0036] 2. The bipolar membrane provided by the present invention comprises a monomer of 2-acrylamido-2-methylpropanesulfonic acid in the first cation membrane layer, which contains both double bonds and sulfonic acid groups; wherein the double bonds are used for the polymerization of the first cation membrane layer, and the sulfonic acid groups are used for the transport of hydrogen ions.

[0037] 3. The bipolar membrane provided by the present invention controls the thickness of the first anode layer to be 20µm-500µm and / or the thickness of the second anode layer to be 5µm-50µm, thereby reducing the resistance of the anode layer and reducing energy consumption.

[0038] 4. In the bipolar membrane preparation method provided by this invention, the substrate, as the carrier of the first cation exchange membrane solution, is required not only to have sufficient acid and alkali resistance, but also to meet appropriate basis weight and porosity. This invention controls the basis weight of the substrate to be 10 g / m³. 2 -500g / m 2 The porosity is 10%-90%. Too high a basis weight and too low a porosity will result in excessively high membrane resistance, while too low a basis weight and too high a porosity will cause severe membrane swelling. Attached Figure Description

[0039] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram of the structure of the bipolar film according to an embodiment of the present invention; Figure 2 This is a connection diagram of the bipolar film current-voltage curve testing device according to an embodiment of the present invention; Figure 3 The figures are current-voltage curves of Embodiments 1-2 and Comparative Example 1 of the present invention; wherein, (a) Embodiment 1; (b) Embodiment 2; (c) Comparative Example 1; Explanation of reference numerals in the attached figures: 1. First cation membrane layer; 2. Catalyst layer; 3. Anion membrane layer; 4. Second cation membrane layer. Detailed Implementation

[0041] To better understand this invention, the following embodiments are provided. However, these embodiments do not limit the content and scope of protection of this invention. Any product that is the same as or similar to this invention, derived by any person under the guidance of this invention or by combining features of this invention with other prior art, falls within the scope of protection of this invention.

[0042] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0043] like Figure 1 As shown, in a first aspect, the present invention provides a bipolar membrane, the bipolar membrane comprising a cation membrane layer, a catalyst layer and an anion membrane layer stacked sequentially, the cation membrane layer comprising a first cation membrane layer and a second cation membrane layer, the first cation membrane layer being located on one side surface of the catalyst layer, and the second cation membrane layer being located on the side surface of the first cation membrane layer opposite to the catalyst layer; The material of the first cation membrane layer is polymerized from monomers including double bonds and sulfonic acid groups; The material of the second anodic membrane layer includes a sulfonated polymer.

[0044] In one optional embodiment, the relationship between the ion exchange capacity A1 of the first cation exchange membrane layer and the ion exchange capacity A2 of the second cation exchange membrane layer is 0 ≤ (A1-A2) / A1 ≤ 0.96.

[0045] It should be noted that ion exchange capacity represents the number of moles of sulfonic acid groups contained in a unit mass of the first cation exchange membrane layer.

[0046] In one alternative embodiment, the sulfonated polymer material has a sulfonation degree of 5%-80%.

[0047] It should be noted that the degree of sulfonation refers to the ratio of the number of sulfonic acid groups introduced into the repeating units of a sulfonated polymer to the total number of repeating units.

[0048] In one alternative embodiment, the ion exchange capacity (IEC) of the first cation exchange membrane layer is 0.8 mmol / g to 2.4 mmol / g.

[0049] In one alternative embodiment, the ion exchange capacity of the second cation exchange membrane is 0.1 mmol / g to 1.2 mmol / g.

[0050] In one alternative embodiment, the monomer of the material of the first cation membrane layer includes 2-acrylamido-2-methylpropanesulfonic acid.

[0051] In one alternative embodiment, the sulfonated polymer is selected from at least one of sulfonated polyphenylene ether, sulfonated polysulfone, and sulfonated polyether ether ketone.

[0052] In one alternative embodiment, the catalyst layer is made of at least one of titanium dioxide, stannous chloride, zirconium oxide, aluminum oxide, and yttrium oxide.

[0053] In one optional embodiment, the anion membrane layer includes a quaternized polymer; the main chain structure of the quaternized polymer includes at least one of polyphenylene ether, polysulfone, and polyetheretherketone.

[0054] In one optional embodiment, the thickness of the first anodic film layer is 20µm-500µm, preferably 100µm-500µm.

[0055] In one optional embodiment, the thickness of the second anodic film layer is 5µm-50µm, preferably 5µm-30µm.

[0056] In one optional embodiment, the thickness of the catalyst layer is 0.1µm-10µm, preferably 0.1µm-3µm.

[0057] In one optional embodiment, the thickness of the anion film layer is 5µm-200µm, preferably 20µm-200µm.

[0058] In the cation exchange layer, the second cation exchange layer primarily functions to block like ions; therefore, its thickness is smaller than that of the first cation exchange layer to reduce the overall resistance of the cation exchange layer. Furthermore, the thickness of the cation and anode layers can be precisely controlled to achieve differentiated product design.

[0059] It should be noted that in existing technologies, the thickness of the first anolyte layer is determined by the substrate thickness, resulting in a fixed anolyte layer thickness. This invention introduces a second anolyte layer, which is formed by coating a polymer solution onto the first anolyte layer and then drying it. The thickness of the second anolyte layer can be controlled by altering the solid content of the polymer slurry, the doctor blade gap, etc., thereby achieving the purpose of regulating the overall anolyte layer thickness. The principle for controlling the anion layer thickness is the same.

[0060] In a second aspect, the present invention also provides a method for preparing the bipolar film described in the first aspect, comprising the following steps: The first cation membrane solution, catalyst slurry, anion membrane slurry, and second cation membrane slurry were prepared separately. The substrate is immersed in the first cation film solution and cured to form the first cation film layer; The catalyst slurry is coated on one side surface of the first cation film layer to form a catalyst layer, thus obtaining the first preform. An anion film slurry is coated onto the catalyst layer of the first preform to form an anion film layer, thus obtaining a second preform; The second cation membrane slurry is coated on the side of the first cation membrane layer of the second preform that is away from the catalyst layer to form the second cation membrane layer, thereby obtaining the bipolar membrane.

[0061] Further, a first cation exchange film solution is obtained by mixing sulfonic acid monomer, crosslinking agent, initiator, and first solvent; then, the substrate is immersed in the first cation exchange film solution for thorough wetting, and then placed between two inert sheets, and placed in an oven for polymerization and curing. The sheets on both sides are then peeled off to obtain the first cation exchange film layer. The crosslinking agent includes divinylbenzene; the initiator includes at least one of benzoyl peroxide, azobisisobutyronitrile, dilauryl peroxide, and azobisisoheptanenitrile; the first solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0062] It should be noted that the role of the first solvent is to improve the wettability between the first cation exchange solution and the substrate. The sulfonic acid monomer in the first cation exchange solution must contain both sulfonic acid functional groups and double bonds to facilitate subsequent high-temperature polymerization.

[0063] Furthermore, the mass ratio of the sulfonic acid monomer, crosslinking agent, and initiator is 60-110:25-27:0.7.

[0064] Furthermore, the substrate type includes at least one of microporous membrane and nonwoven fabric; the substrate material includes one of polyethylene, polypropylene, aramid, and polyetheretherketone; and the substrate basis weight is 10 g / m³. 2 -500g / m 2 The porosity is 10%-90%. As the carrier of the first cation exchange membrane solution, the substrate not only needs sufficient acid and alkali resistance but also a suitable porosity. Excessive porosity will lead to severe membrane swelling, while insufficient porosity will result in excessively high resistivity. The preferred substrate is a polyethylene nonwoven fabric with a basis weight of 30 g / m². 2 -100g / m 2 The porosity is 30%-50%.

[0065] Furthermore, the inert sheet material includes at least one of polyethylene terephthalate, polyimide, and glass. The sheet not only needs to be resistant to solvent corrosion and thermal stability, but also needs to resist high-temperature radiation during the thermal polymerization process. Glass is the preferred inert sheet material.

[0066] It should be noted that, in order to improve the adhesion between the first anodic film layer and the anion film layer and the second anodic film layer, the surface of the inert sheet can be corona-treated, polished or sandblasted to increase the surface roughness of the first anodic film layer.

[0067] In one optional embodiment, the curing temperature is 30℃-150℃, and the curing time is 1h-48h. The curing temperature should not be too high, and must not exceed the melting point of the substrate used; otherwise, the substrate will melt and deform due to heat, affecting the flatness of the film. The curing time affects the production capacity of the anodized film layer; excessively long curing times will lead to a significant reduction in the anodized film production capacity. Preferably, the curing temperature is 30℃-100℃, and the curing time is 1h-10h.

[0068] Further, the catalyst is dispersed in deionized water to obtain a catalyst slurry; then it is coated on one side surface of the first cation membrane layer to form a catalyst layer.

[0069] In one alternative embodiment, the catalyst content in the catalyst slurry is 0.1wt%-10wt%, preferably 0.5wt%-8wt%.

[0070] It should be noted that the catalyst can be coated by at least one of dip coating, spray coating, or brush coating. To ensure that the catalyst can be uniformly adhered to the surface of the first cation film layer, the preferred catalyst coating method is spray coating.

[0071] Further, after mixing the halomethylated polymer, ammonifying agent, and second solvent, an anion membrane slurry is obtained. After removing bubbles, it is uniformly coated onto the catalyst layer of the first preform with a scraper. The solvent is dried to form an anion membrane layer, thus obtaining a single-cation bipolar membrane.

[0072] In one optional embodiment, the solid content of the anion film slurry is 2wt%-40wt%, preferably 28wt%.

[0073] In one optional embodiment, the drying temperature is 25℃-150℃. The drying temperature of the anion film layer should not be too high to prevent cracking and wrinkling of the anion film layer. The preferred drying temperature is 60℃.

[0074] Further, the preparation steps of the quaternized polymer are as follows: First, polyphenylene ether is halogenated or polysulfone or polyether ether ketone is halogenated to obtain the corresponding halogenated polymer; for example, polyphenylene ether is brominated to obtain bromomethylated polyphenylene ether. The halogenated polymer is then reacted with an ammonifying agent to obtain the quaternized polymer. The ammonifying agent includes at least one of chain tertiary amines, cyclic tertiary amines, and diamine-type tertiary amines; the quaternized polymer must meet certain alkali resistance to prevent degradation under alkaline conditions, therefore the selection of the ammonifying agent is crucial. The chain tertiary amine includes at least one of trimethylamine, triethylamine, N,N-dimethylbutylamine, and N,N-dimethylhexylamine; the cyclic tertiary amine includes at least one of N-methylimidazole and N-methylpiperidine; the diamine-type tertiary amine includes tetramethylhexamethylenediamine; preferably N-methylpiperidine.

[0075] Furthermore, the mass ratio of the halomethylated polymer to the ammonifying agent is 4.5-5.5:1.

[0076] Further, the second solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0077] Further, the sulfonated polymer is dispersed in a third solvent to obtain a second cation membrane slurry. After removing air bubbles, the slurry is uniformly coated onto the side of the first cation membrane layer of the second preform away from the catalyst layer using a scraper. The solvent is then dried to form a second cation membrane layer, thus obtaining the bipolar membrane.

[0078] In one optional embodiment, the solid content of the second cation exchange slurry is 2wt%-40wt%, preferably 25wt%.

[0079] In one optional embodiment, the drying temperature is 25°C-150°C, preferably 80°C.

[0080] In one optional embodiment, the sulfonated polymer backbone structure includes at least one of polyphenylene ether, polysulfone, and polyether ether ketone, preferably polysulfone.

[0081] In one alternative implementation, the scraper gap is 50μm-200μm.

[0082] It should be noted that the preparation of brominated polyphenylene ether is based on the literature "Comb-shaped polymers to enhance hydroxide transport in anion exchange membranes" by Li et al., Energy & Environmental Science, 2012, 5(7):7888-7892, which includes the following steps: 12g of poly(2,6-dimethyl-1,4-phenylene ether) (PPO, 100mmol) is dissolved in chlorobenzene (100mL), and then 8.9g of N-bromosuccinimide (NBS, 50mmol) and 0.5g of 2,2'-azobisisobutyronitrile (3mmol) are added to the above solution, and the mixture is heated at 135℃ for 3h under reflux conditions. After cooling, the reaction mixture was poured into 10 times the excess of ethanol to precipitate the product. The mixture was filtered, washed with ethanol, and then redissolved in 120 mL of chloroform. The product was then precipitated in 10 times the excess of ethanol, and a pale yellow powder was collected and dried under vacuum overnight to prepare brominated polyphenylene ether with a yield of 92%.

[0083] The preparation of sulfonated polyphenylene ether, sulfonated polysulfone, and sulfonated polyether ether ketone is described in the literature "Synthesis and characterization of sulfonated poly(ether ether ketone) for proton exchange membranes" by Xing et al., Journal of Membrane Science 229 (2004) 95-106. The preparation method of sulfonated polyether ether ketone includes the following steps: Under an argon atmosphere, 40g of polyether ether ketone particles are added to a three-necked flask containing 1.4L of concentrated sulfuric acid (95wt%-98wt%) and equipped with a mechanical stirrer within 20 minutes. After reacting at room temperature for 24 hours, the acidic solution is precipitated into a large amount of ice water to collect the sulfonated polyether ether ketone. The precipitated sulfonated polyether ether ketone is repeatedly washed with deionized water until the pH of the rinsing water is 6-7. The filtered sulfonated polyether ether ketone is dried at room temperature for 2 days and then dried in a vacuum oven at 80℃ for 24 hours.

[0084] The preparation method of sulfonated polyphenylene ether includes the following steps: Under an argon atmosphere, 50 g of polyphenylene ether particles are added to a three-necked flask containing 1.4 L of concentrated sulfuric acid (95 wt%-98 wt%) and equipped with a mechanical stirrer within 20 min. After reacting at room temperature for 30 h, the above acidic solution is precipitated into a large amount of ice water to collect the sulfonated polyphenylene ether. The precipitated sulfonated polyphenylene ether is repeatedly washed with deionized water until the pH of the washing water is 6-7. The sulfonated polyphenylene ether obtained by filtration is dried at room temperature for 2 days and then dried in a vacuum oven at 80 °C for 24 h.

[0085] The preparation method of sulfonated polysulfone includes the following steps: Under an argon atmosphere, 40 g of polysulfone particles are added to a three-necked flask containing 1.4 L of concentrated sulfuric acid (95 wt%-98 wt%) and equipped with a mechanical stirrer over 20 min. After reacting at room temperature for 36 h, the above acidic solution is precipitated into a large amount of ice water to collect the sulfonated polysulfone. The precipitated sulfonated polysulfone is repeatedly washed with deionized water until the pH of the washing water is 6-7. The filtered sulfonated polysulfone is dried at room temperature for 2 days and then dried in a vacuum oven at 80 °C for 24 h.

[0086] In this invention, titanium dioxide, stannous chloride, zirconium oxide, aluminum oxide, yttrium oxide, trimethylamine, triethylamine, N,N-dimethylbutylamine, N,N-dimethylhexylamine, N-methylimidazolium, N-methylpiperidine, tetramethylhexanediamine, 2-acrylamido-2-methylpropanesulfonic acid, allyl polyoxyethylene sulfonate ammonium, and sodium methacrylate sulfonate were purchased from Beijing Innocare Technology Co., Ltd.

[0087] In this invention, the ion exchange capacity of the first cation exchange membrane layer and the second cation exchange membrane layer is tested according to the following method: A certain mass of cation exchange membrane was cut into fragments and soaked in pure water at 50°C for 12 hours. Then, it was placed in 1M hydrochloric acid and stirred for 12 hours. After washing with pure water, it was placed in 1M sodium chloride solution to completely exchange hydrogen ions for sodium ions. The membrane was then removed and exchanged again with 1M hydrochloric acid to the hydrogen form. The membrane was dried and its mass was measured as W. dry The mass of the solution is W, g; the hydrogen ion concentration of the solution is C, mmol / g; the calculation formula is as follows:

[0088] The first anolyte layer is tested by IEC after preparation; the second anolyte layer requires coating the sheet with the second anolyte slurry, drying it into a film, and then testing.

[0089] Example 1 This embodiment provides a method for preparing a bipolar film, including the following steps: (1) Preparation of the first cation exchange layer: 110g of 2-acrylamido-2-methylpropanesulfonic acid, 26g of divinylbenzene, 45g of N,N-dimethylacetamide and 0.7g of benzoyl peroxide were mixed evenly to obtain the first cation exchange solution; polyethylene nonwoven fabric (weight: 50g / m 2After being fully immersed in the first cation exchange solution with a porosity of 40% and a thickness of 90 μm for 20 min, the sample was clamped between two glass sheets. Then, it was placed between two glass plates and the gaps around the sample were sealed with tape. After that, it was placed in an 80°C forced-air drying oven for polymerization and curing for 5 h. Finally, the glass sheets on both sides were peeled off to obtain a first cation exchange layer with a thickness of 100 µm (IEC is 1.6 mmol / g). (2) Preparation of catalyst layer: 10g of titanium dioxide particles were added to 190g of water and mechanically stirred and dispersed for 30min to obtain catalyst slurry; the catalyst slurry was uniformly coated on the surface of the first cation film layer by ultrasonic spraying and placed in a 50℃ forced air drying oven for 20min to evaporate the water, thus preparing a catalyst layer with a thickness of 2µm. (3) Preparation of anion membrane layer: 40g of bromomethylated polyphenylene ether and 100g of N-methylpyrrolidone were placed in a 250mL three-necked flask and mechanically stirred to dissolve them completely. After complete dissolution, 8g of N-methylpiperidine was added dropwise to the above solution using a dropping funnel and reacted for 20h to fully ammonify it. After ammonification, the quaternized polymer anion membrane slurry was obtained by filtration and the solid content of the anion membrane slurry was 28wt%. The above anion membrane slurry was poured onto the first cation membrane layer coated with the catalyst layer. The doctor blade gap was set to 200μm. The anion membrane slurry was scraped onto the first cation membrane layer and placed in a 60℃ forced-air oven to dry for 2h to remove the solvent in the anion membrane slurry and prepare an anion membrane layer with a thickness of 20µm. (4) Preparation of the second cation membrane layer: 50g of sulfonated polysulfone (sulfonation degree of 20%) and 150g of N-methylpyrrolidone were placed in a 500mL three-necked flask and mechanically stirred to dissolve them completely. After filtration, a second cation membrane slurry without obvious impurities was obtained. The above cation membrane slurry was poured onto the other side of the first cation membrane layer. The doctor blade gap was set to 100μm. The cation membrane material was scraped onto the other side of the first cation membrane layer and placed in an 80℃ forced-air oven to dry for 1h to remove the solvent of the cation membrane material. A second cation membrane layer with a thickness of 20µm (IEC of 0.44mmol / g) was prepared.

[0090] Example 2 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Embodiment 1. The only difference is that in step (4), sulfonated polysulfone is replaced with the same mass of sulfonated polyphenylene ether, the degree of sulfonation is 20%, and the IEC of the second cation membrane layer is 0.50 mmol / g.

[0091] Example 3 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Example 1. The only difference is that in step (4), sulfonated polysulfone is replaced with the same mass of sulfonated polyether ether ketone, the degree of sulfonation is 20%, and the IEC of the second cation membrane layer is 0.40 mmol / g.

[0092] Example 4 This embodiment provides a method for preparing a bipolar film, which is basically the same as the steps in Embodiment 1, except that in step (4), the gap between the scrapers is 50 μm and the thickness of the second cation film layer is 10 µm.

[0093] Example 5 This embodiment provides a method for preparing a bipolar film, which is basically the same as the steps in Embodiment 1, except that in step (4), the gap between the scrapers is 200 μm and the thickness of the second cation film layer is 40 µm.

[0094] Example 6 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Example 1. The only difference is that in step (1), the thickness of the polyethylene nonwoven fabric is 180 μm, so that the thickness of the first cation membrane layer is 200 µm; in step (2), the catalyst solid content is adjusted to 8 wt%, so that the thickness of the catalyst layer is 3 µm; in step (3), the doctor blade gap is 800 µm, and the thickness of the anion membrane layer is 80 µm.

[0095] Example 7 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Example 1. The only difference is that in step (1), the thickness of the polyethylene nonwoven fabric is 450µm, so that the thickness of the first cation membrane layer is 500µm; in step (2), the catalyst solid content is adjusted to 0.5wt%, so that the thickness of the catalyst layer is 0.1µm; in step (3), the doctor blade gap is 2000µm, and the thickness of the anion membrane layer is 200µm.

[0096] Example 8 This embodiment provides a method for preparing a bipolar film, which is basically the same as the steps in Embodiment 1, except that in step (1), the basis weight of the polyethylene nonwoven fabric is 10 g / m³. 2 The porosity is 90%, and the IEC of the first cation exchange membrane is 2.0 mmol / g.

[0097] Example 9 This embodiment provides a method for preparing a bipolar film, which is basically the same as the steps in Embodiment 1, except that in step (1), the basis weight of the polyethylene nonwoven fabric is 100 g / m². 2 The porosity is 70%, and the IEC of the first cation exchange membrane is 1.8 mmol / g.

[0098] Example 10 This embodiment provides a method for preparing a bipolar film, which is basically the same as the steps in Embodiment 1, except that in step (1), the basis weight of the polyethylene nonwoven fabric is 300 g / m². 2The porosity is 50%, and the IEC of the first cation exchange membrane is 1.4 mmol / g.

[0099] Example 11 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Embodiment 1. The only difference is that in step (1), the glass plate is replaced with polyimide and the nonwoven fabric of polyethylene is replaced with a microporous membrane of polyether ether ketone of the same thickness.

[0100] Example 12 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Embodiment 1. The only difference is that in step (2), titanium dioxide is replaced with stannous chloride of the same mass, and the polyethylene nonwoven fabric is replaced with polypropylene nonwoven fabric of the same thickness.

[0101] Example 13 This embodiment provides a method for preparing a bipolar film, which is basically the same as the steps in Embodiment 1. The only difference is that in step (2), titanium dioxide is replaced with zirconium oxide of the same mass, and polyethylene nonwoven fabric is replaced with aramid nonwoven fabric of the same thickness.

[0102] Example 14 This embodiment provides a method for preparing a bipolar film, which is basically the same as the steps in Embodiment 1. The only difference is that in step (2), titanium dioxide is replaced with aluminum oxide of the same mass, and the polyethylene nonwoven fabric is replaced with polyether ether ketone nonwoven fabric of the same thickness.

[0103] Example 15 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Embodiment 1. The only difference is that in step (2), titanium dioxide is replaced with yttrium oxide of the same mass, and the polyethylene nonwoven fabric is replaced with a polyethylene microporous membrane of the same thickness.

[0104] Example 16 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Embodiment 1, except that the mass of the titanium dioxide particles is 15g and the polyethylene nonwoven fabric is replaced with a polypropylene microporous membrane.

[0105] Example 17 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Embodiment 1, except that the mass of the titanium dioxide particles is 20g, and the polyethylene nonwoven fabric is replaced with an aramid microporous membrane.

[0106] Example 18 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Embodiment 1, except that the mass of bromomethylated polyphenylene ether is 10g, the mass of N-methylpiperidine is 2g, and the solid content of the anion membrane slurry is 8wt%.

[0107] Example 19 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Example 1, except that the mass of bromomethylated polyphenylene ether is 60g, the mass of N-methylpiperidine is 12g, and the solid content of the anion membrane slurry is 34wt%.

[0108] Example 20 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Example 1, except that in step (1), the mass of 2-acrylamido-2-methylpropanesulfonic acid is 90g, so that the IEC of the first cation membrane layer is 1.4mmol / g; in step (4), the polysulfone with a sulfonation degree of 20% is replaced with polysulfone with a sulfonation degree of 30%, so that the IEC of the second cation membrane layer is 0.66mmol / g.

[0109] Example 21 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Example 1, except that in step (1), the mass of 2-acrylamido-2-methylpropanesulfonic acid is 90g, so that the IEC of the first cation membrane layer is 1.4mmol / g; in step (4), the polysulfone with a sulfonation degree of 20% is replaced with polysulfone with a sulfonation degree of 10%, so that the IEC of the second cation membrane layer is 0.22mmol / g.

[0110] Example 22 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Embodiment 1. The only difference is that in step (4), the polysulfone with a sulfonation degree of 20% is replaced with polysulfone with a sulfonation degree of 30%, so that the IEC of the second cation membrane layer is 0.66 mmol / g.

[0111] Example 23 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Embodiment 1. The only difference is that in step (4), the polysulfone with a sulfonation degree of 20% is replaced with polysulfone with a sulfonation degree of 10%, so that the IEC of the second cation membrane layer is 0.22 mmol / g.

[0112] Example 24 This embodiment provides a method for preparing a bipolar membrane, which is basically the same as the steps in Example 1, except that in step (1), the mass of 2-acrylamido-2-methylpropanesulfonic acid is 60g, so that the IEC of the first cation membrane layer is 0.9mmol / g; in step (4), the polysulfone with a sulfonation degree of 20% is replaced with polysulfone with a sulfonation degree of 36%, so that the IEC of the second cation membrane layer is 0.8mmol / g.

[0113] Comparative Example 1 This comparative example provides a method for preparing a bipolar film, which is basically the same as the steps in Example 1, except that step (4) is omitted.

[0114] Comparative Example 2 This comparative example provides a method for preparing a bipolar membrane, which is basically the same as the steps in Example 1, except that the first cation membrane solution is replaced with the second cation membrane slurry.

[0115] Comparative Example 3 This comparative example provides a method for preparing a bipolar membrane, which is basically the same as the steps in Example 1, except that in step (1), the mass of 2-acrylamido-2-methylpropanesulfonic acid is 20g, so that the IEC of the first cation membrane layer is 0.3mmol / g.

[0116] Comparative Example 4 This comparative example provides a method for preparing a bipolar membrane, which is basically the same as the steps in Example 1. The only difference is that in step (4), the polysulfone with a sulfonation degree of 20% is replaced with polysulfone with a sulfonation degree of 2%, so that the IEC of the second cation membrane layer is 0.05 mmol / g.

[0117] Experimental Example 1 Current-voltage curve testing: The IV curve of a bipolar membrane is obtained using... Figure 2 The four-compartment glass bath shown was measured. The bipolar membranes (7cm²) prepared in Examples 1-24 and Comparative Example 1 were used. 2 The bipolar membrane is placed in the middle of the compartments, with the cation exchange layer facing the cathode and the anion exchange layer facing the anode. The cation exchange layer forms an acid compartment with the perfluorosulfonic acid cation exchange layer on the left, and the anion exchange layer forms a base compartment with the perfluorosulfonic acid cation exchange layer on the right. Pt electrodes are placed at both ends of the apparatus, each Pt electrode forming an electrode compartment with the adjacent perfluorosulfonic acid cation exchange layer. A multimeter connected to a pair of reference electrodes (Ag / AgCl) is used to detect the transmembrane voltage of the bipolar membrane samples. 0.5 mol / L Na₂SO₄ solution and 0.5 mol / L NaCl solution are pumped into the electrode compartment and acid-base compartment, respectively. Before testing, all samples are soaked in 1.0 mol / L NaCl solution for at least 24 h. A low current density (0-20 mA / cm²) is obtained by applying current to the membrane cell through an electrochemical workstation. 2 IV curves within the range of ) such as Figure 3As shown. After converting this curve into an I-dV / dI curve, the current density corresponding to the maximum value of the I-dV / dI curve is the first limiting current density (I). lim1 The data is shown in Table 1.

[0118] Salt ion concentration test in the alkali chamber: Taking the sodium sulfate system as an example, the sulfate content in the alkali chamber of the bipolar membrane electrodialysis in Examples 1-24 and Comparative Example 1 of this invention was tested. The actual common ion leakage performance of the bipolar membrane was tested using Hangzhou Lanran's EX-3BT three-compartment bipolar membrane electrodialysis equipment. The effective area of ​​the bipolar membrane was 55 cm². 2 The membrane had 10 pairs and was tested using Hangzhou Lanran's AHT and CT-5 anion and cation exchange membranes. The test current density was set to 80 mA / cm². 2 The test lasted for 1 hour. After the test, the sulfate concentration of the alkaline chamber sample was measured using an inductively coupled plasma atomic emission spectrometer. The results are shown in Table 1.

[0119] Table 1. First limiting current density and sulfate content in the alkali chamber of the bipolar membrane.

[0120] I lim1 The lower the value, the worse the common ion leakage. As can be seen from Table 1, the values ​​of I in Examples 1-24 are... lim1 At 2.6 mA / cm 2 -4.3mA / cm 2 Within the range, while Comparative Example 1, due to the lack of a highly selective second cation exchange membrane layer, therefore its I lim1 Up to 10.2 mA / cm 2 This indicates that the addition of the second cation exchange layer can effectively block the permeation of common ions and improve the purity of the alkali. Meanwhile, the sulfate content in the alkali chambers produced in Examples 1 and 2 was only 180 ppm and 240 ppm, respectively, while the sulfate content in the alkali chamber of Comparative Example 1, which had a non-selective second cation exchange layer, was as high as 1500 ppm. This further verifies the effective blocking effect of the second selective cation exchange layer on common ions.

[0121] Experiment Example 2 The energy consumption of bipolar membranes in electrodialysis for acid and alkali production in Examples 1-24 and Comparative Examples 2-4 was calculated according to the following formula, and the results are shown in Table 2:

[0122] Where W represents the energy consumption per ton of alkali, in kWh / t; The average of two consecutive voltage values, in V; The current is the average of two consecutive currents, A; M is the molar mass of the base, g / mol; Vt is the final volume of the base, L; Ct is the final concentration of the base, mol / L; Δt is the time interval between two consecutive currents, s; the results are shown in Table 2.

[0123] Table 2 Energy consumption results per ton of alkali

[0124] As can be seen from Table 2, the energy consumption of Examples 1-24 is relatively low. However, Comparative Example 2 replaces the first cation membrane solution with the second cation membrane slurry, and Comparative Examples 3 and 4 do not satisfy the relationship between the ion exchange capacity A1 of the first cation membrane layer and the ion exchange capacity A2 of the second cation membrane layer, resulting in higher energy consumption.

[0125] In summary, this invention addresses the pain points of high common ion leakage and low alkali purity in bipolar membranes used in electrodialysis by designing the cation exchange membrane as a bilayer structure. The first cation exchange membrane layer, with its thicker thickness, primarily functions as an ion conductor, while the second cation exchange membrane layer, with its high selectivity, lower degree of sulfonation, and thinner thickness, primarily functions as a common ion barrier, thus enabling the preparation of high-purity alkali. Furthermore, the thickness of each membrane layer can be precisely controlled, allowing for differentiated product design and preparation.

[0126] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A bipolar membrane, characterized in that The bipolar membrane comprises a positive membrane layer, a catalyst layer and a negative membrane layer arranged in sequence, the positive membrane layer comprises a first positive membrane layer and a second positive membrane layer, the first positive membrane layer is located on one side surface of the catalyst layer, and the second positive membrane layer is located on one side surface of the first positive membrane layer away from the catalyst layer; The material of the first positive membrane layer is polymerized from a monomer comprising a double bond and a sulfonic acid group; The material of the second positive membrane layer comprises a sulfonated polymer; The ion exchange capacity A1 of the first positive membrane layer and the ion exchange capacity A2 of the second positive membrane layer satisfy the relationship 0<(A1-A2) / A1≤0.

96.

2. The bipolar membrane according to claim 1, characterized in that The sulfonation degree of the sulfonated polymer is 5%-80%; And / or, the ion exchange capacity of the first positive membrane layer is 0.8mmol / g-2.4mmol / g; And / or, the ion exchange capacity of the second positive membrane layer is 0.1mmol / g-1.2mmol / g.

3. The bipolar membrane according to claim 2, characterized in that The monomer of the material of the first positive membrane layer comprises 2-acrylamido-2-methylpropanesulfonic acid; And / or, the sulfonated polymer is selected from at least one of sulfonated polyphenylene ether, sulfonated polysulfone, and sulfonated polyether ether ketone.

4. The bipolar membrane according to claim 1, characterized in that The material of the catalyst layer comprises at least one of titanium dioxide, stannous chloride, zirconium oxide, aluminum oxide, and yttrium oxide; And / or, the negative membrane layer comprises a quaternary ammonium polymer; the main chain structure of the quaternary ammonium polymer comprises at least one of polyphenylene ether, polysulfone, and polyether ether ketone.

5. The bipolar membrane according to claim 1, characterized in that, The thickness of the first positive membrane layer is 20µm-500µm; And / or, the thickness of the second positive membrane layer is 5µm-50µm; And / or, the thickness of the catalyst layer is 0.1µm-10µm; And / or, the thickness of the negative membrane layer is 5µm-200µm.

6. A method for the production of a bipolar membrane according to any one of claims 1 to 5, characterized in that The method comprises the following steps: Respectively configuring a first positive membrane solution, a catalyst slurry, a negative membrane slurry, and a second positive membrane slurry; Immersion of a substrate in the first positive membrane solution, after solidification, a first positive membrane layer is formed; The catalyst slurry is coated on one side surface of the first positive membrane layer to form a catalyst layer, and a first blank body is obtained; The negative membrane slurry is coated on the catalyst layer of the first blank body to form a negative membrane layer, and a second blank body is obtained; The second positive membrane slurry is coated on one side surface of the first positive membrane layer of the second blank body away from the catalyst layer to form a second positive membrane layer, and the bipolar membrane is obtained.

7. The method for preparing a bipolar membrane according to claim 6, characterized in that, In the catalyst slurry, the content of the catalyst is 0.1wt%-10wt%; And / or, the solid content of the negative membrane slurry is 2wt%-40wt%; And / or, the solid content of the second positive membrane slurry is 2wt%-40wt%.

8. The method for preparing a bipolar membrane according to claim 6, characterized in that, The preparation method of the bipolar membrane satisfies at least one of the following A-B: A. The configuration step of the first positive membrane solution comprises: mixing a sulfonic acid monomer, a crosslinking agent, an initiator, and a first solvent to obtain; Optionally, the crosslinking agent comprises divinylbenzene; Optionally, the initiator comprises at least one of benzoyl peroxide, azobisisobutyronitrile, dilauroyl peroxide, and azobisisoheptyl nitrile; Optionally, the first solvent comprises at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide; B. The configuration step of the negative membrane paste comprises: mixing the halomethylated polymer, the ammoniating agent and the second solvent to obtain; Optionally, the second solvent comprises at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide; Optionally, the main chain structure in the halomethylated polymer comprises at least one of polyphenylene oxide, polysulfone, polyether ether ketone; Optionally, the ammoniating agent comprises at least one of chain tertiary amine, cyclic tertiary amine, diamine type tertiary amine; the chain tertiary amine comprises at least one of trimethylamine, triethylamine, N,N-dimethylbutylamine, N,N-dimethylhexylamine; the cyclic tertiary amine comprises at least one of N-methylimidazole, N-methylpiperidine; the diamine type tertiary amine comprises tetramethylhexanediamine.

9. The method for preparing a bipolar membrane according to claim 6, characterized in that, The temperature of the solidification is 30-150℃, and the time is 1-48h; and / or the grammage of the substrate is 10 g / m 2 - 500 g / m 2 , the porosity is 10-90%; And / or, before the solidification, further comprising placing the substrate impregnated with the first positive membrane solution between two inert sheets.

10. Use of the bipolar membrane according to any one of claims 1-5 or prepared by the preparation method according to any one of claims 6-9 in the field of electrodialysis.

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