A composite bipolar membrane and its preparation method and application

Abstract

The present invention belongs to the technical field of compound preparation, and particularly relates to a composite bipolar membrane, a preparation method thereof and an application. The composite bipolar membrane provided by the present invention comprises a cation exchange membrane, a MOF transition membrane and an anion exchange membrane which are stacked in sequence; the cation exchange membrane is formed by a first polymer, and the first polymer is a random copolymer having the structure shown in formula (1); the anion exchange membrane is formed by a second polymer, and the second polymer is a random copolymer having the structure shown in formula (2). Using the composite bipolar membrane provided by the present invention in the production of hexacyanocobaltate by bipolar membrane electrodialysis can continuously and efficiently obtain hexacyanocobaltate, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of compound preparation, and particularly relates to a composite bipolar membrane, a preparation method thereof, and an application thereof. Background Art

[0002] The chemical formula of cobalt hexacyanoate is usually H3Co(CN)6, which has a wide range of uses in the fields of chemical industry, materials science, and biomedicine. In the chemical industry, cobalt hexacyanoate has extensive applications in metal surface treatment, catalyst preparation, and synthesis of other organometallic compounds. For example, it can be used as an important raw material for the preparation of cyanide complex catalysts (DMC). In materials science, the special properties of cobalt hexacyanoate make it a key raw material for manufacturing high-performance materials. For example, it can be used to manufacture conductive materials, magnetic materials, and modifiers for polymer materials. In biomedicine, due to its strong complexing ability and biocompatibility, cobalt hexacyanoate is used as a carrier for certain drugs and biomolecules, which helps to improve the targeting and bioavailability of drugs.

[0003] The preparation methods of cobalt hexacyanoate mainly include chemical synthesis methods and bipolar membrane electrodialysis methods. Chemical synthesis methods include preparation via copper hexacyanoate and preparation via potassium hexacyanoate, etc. Among them, the preparation process via copper hexacyanoate includes reacting copper hexacyanoate with hydrogen sulfide to obtain cobalt hexacyanoate, or reacting copper hexacyanoate with calcium sulfide or barium sulfide to prepare calcium cobalt hexacyanoate or barium cobalt hexacyanoate, and then performing a double decomposition reaction of calcium cobalt hexacyanoate or barium cobalt hexacyanoate with dilute sulfuric acid to obtain cobalt hexacyanoate. The preparation process via potassium hexacyanoate includes introducing hydrogen chloride gas into a saturated solution of potassium hexacyanoate, and cobalt hexacyanoate and a small amount of potassium chloride will precipitate out simultaneously. Since cobalt hexacyanoate is soluble in ethanol, ethanol can be added to the precipitate to dissolve cobalt hexacyanoate, and then the ethanol in the dissolved solution can be removed under reduced pressure to obtain cobalt hexacyanoate; or cobalt hexacyanoate can be prepared by performing a double decomposition reaction of cobalt hexacyanoate with sulfuric acid, but this reaction needs to be carried out under acidic conditions, and in order to remove the generated potassium sulfate and potassium bisulfate as precipitants, a large amount of methanol needs to be used as a solvent. The bipolar membrane electrodialysis method usually includes feeding an aqueous solution of potassium hexacyanoate and deionized water into the acid chamber and the alkali chamber of a bipolar membrane electrodialysis device respectively for electrification treatment. After electrodialysis, a cobalt hexacyanoate solution can be obtained in the acid chamber, and a potassium hydroxide solution can be obtained in the alkali chamber. Although the bipolar membrane electrodialysis method has the advantages of low energy consumption, simple operation, and easy scale-up compared with the chemical synthesis method, it cannot efficiently generate cobalt hexacyanoate, and the service life of the bipolar membrane is short. With the extension of the use time of the bipolar membrane, the generation efficiency of cobalt hexacyanoate will decrease significantly, and the stability is poor. Summary of the Invention

[0004] The first object of the present invention is to provide a composite bipolar membrane that can improve the low production efficiency and poor stability of cobalt hexacyanoate.

[0005] The second object of the present invention is to provide a method for preparing the above-mentioned composite bipolar membrane.

[0006] The third object of the present invention is to provide the application of the above-mentioned composite bipolar membrane in the preparation of cobalt hexacyanoate.

[0007] Specifically, the composite bipolar membrane provided by the present invention comprises a cation exchange membrane, a MOF transition membrane and an anion exchange membrane stacked in sequence; the cation exchange membrane is formed by a first polymer, and the first polymer is a random copolymer having the structure shown in formula (1); the anion exchange membrane is formed by a second polymer, and the second polymer is a random copolymer having the structure shown in formula (2);

[0008]

[0009] m and n respectively represent the molar ratios of the two structural units in formula (1), and the ratio of m to n is 1:(0.5 - 2); p and q respectively represent the molar ratios of the two structural units in formula (2), and the ratio of p to q is 1:(0.5 - 2);.

[0010] The method for preparing the composite bipolar membrane provided by the present invention comprises the following steps:

[0011] S21. Sodium styrene sulfonate and butadiene are fed into an organic solvent according to a molar ratio of 1:(0.5 - 2) for a first copolymerization reaction, and then the obtained sodium styrene sulfonate / butadiene copolymer is subjected to a first thiol-ene click reaction with 2-fluoro-4-mercaptoaniline to obtain a solution containing the first polymer;

[0012] Styrene and butadiene are fed into an organic solvent according to a molar ratio of 1:(0.5 - 2) for a second copolymerization reaction, and then the obtained styrene / butadiene copolymer is subjected to a second thiol-ene click reaction with 3-amino-5-mercapto-1,2,4-triazole to obtain a solution containing the second polymer;

[0013] S22. The solution containing the first polymer is sprayed on the surface of the substrate and dried to obtain a cation exchange membrane layer; the solution containing the modified MOF material is sprayed on the surface of the cation exchange membrane and dried to obtain a MOF transition membrane; the solution containing the second polymer is sprayed on the surface of the MOF transition membrane and dried to obtain an anion exchange membrane.

[0014] The key to the present invention is that the cation exchange membrane is formed by a random copolymer represented by formula (1), and the anion exchange membrane is formed by a random copolymer represented by formula (2), and a MOF transition membrane is arranged between the cation exchange membrane and the anion exchange membrane. The composite bipolar membrane thus obtained can be used for the production of hexacyanocobalt acid by bipolar membrane electrodialysis to obtain hexacyanocobalt acid continuously and efficiently. The reason for this may be that: on the one hand, the MOF material can improve the efficiency of bipolar membrane electrolysis of water, and can provide [Co(CN)6] 3- More H + , which can promote the synthesis of hexacyanocobaltate; on the other hand, the existing bipolar membranes are usually based on aromatic carbon skeletons, but the carbon-oxygen bonds in the aromatic carbon skeletons are easily affected by the OH generated by the bipolar membrane. - The random copolymers shown in formula (1) and formula (2) both have a carbon-carbon double bond main chain and are not easily attacked by OH. - At the same time, the random copolymer having the structure shown in formula (1) has sodium benzenesulfonate groups and fluoroaniline groups evenly distributed on the side chain. As shown in formula (3), the sodium benzenesulfonate groups and fluoroaniline groups are spaced and suspended on the polymer chain. The presence of benzenesulfonic acid groups can promote the electrolysis of water. The presence of fluoroaniline groups can stabilize the chemical bonds of the anode membrane. The random copolymer having the structure shown in formula (2) has phenyl and nitrogen heterocyclic functional groups evenly distributed on the side chain. As shown in formula (4), the phenyl and nitrogen heterocyclic functional groups are spaced and suspended on the polymer chain. The presence of nitrogen heterocyclic functional groups can make the electron distribution of the second polymer more uniform, thereby giving the polymer stronger alkali resistance, making the bipolar membrane more resistant to high concentration OH. - Furthermore, the random copolymers shown in formula (1) and formula (2) have a relatively flexible main chain provided by CC and relatively rigid side chains provided by sodium benzenesulfonate group / fluoroaniline group and phenyl / nitrogen heterocyclic functional group. The flexible main chain can improve the impact resistance of the bipolar membrane, making it have good tolerance to the flow of liquid during use, while the rigid side chain can improve the supporting force, making the bipolar membrane less susceptible to the impact of liquid flow disturbance and affecting the service life.

[0015]

[0016] In formula (3), represent represent

[0017] In formula (4), represent represent

[0018] In a preferred embodiment, the MOF transition membrane is formed of a modified MOF material, and the modified MOF material is an Fe- and Cu-codoped MOF material. At this time, the production efficiency of hexacyanocobaltate can be further improved. Presumably, the reason may be that: ferric ions and cupric ions can synergistically improve the reactivity of water, weaken the molecular bond, and accelerate the hydrolysis dissociation in the middle layer of the bipolar membrane into H + and OH - , thereby promoting the synthesis of hexacyanocobaltate. Detailed implementation mode

[0019] The composite bipolar membrane provided by the present invention includes a cation exchange membrane, an MOF transition membrane, and an anion exchange membrane stacked in sequence; the cation exchange membrane is formed of a first polymer, and the first polymer is a random copolymer having the structure shown in formula (1); the anion exchange membrane is formed of a second polymer, and the second polymer is a random copolymer having the structure shown in formula (2);

[0020]

[0021] m and n respectively represent the molar ratios of the two structural units in formula (1), and the ratio of m to n is 1:(0.5 - 2), specifically it can be 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2 or any value therebetween. p and q respectively represent the molar ratios of the two structural units in formula (2), and the ratio of p to q is 1:(0.5 - 2), specifically it can be 1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2 or any value therebetween.

[0022] In a preferred embodiment, the thickness of the cation exchange membrane is 10 - 60 microns, specifically it can be 10 microns, 15 microns, 20 microns, 25 microns, 30 microns, 35 microns, 40 microns, 45 microns, 50 microns, 55 microns, 60 microns or any value therebetween; the thickness of the MOF transition membrane is 1 - 10 microns, specifically it can be 1 micron, 2 microns, 4 microns, 6 microns, 8 microns, 10 microns or any value therebetween; the thickness of the anion exchange membrane is 5 - 20 microns, specifically it can be 5 microns, 8 microns, 10 microns, 12 microns, 15 microns, 18 microns, 20 microns or any value therebetween.

[0023] The present invention places no particular limitation on the source of the first polymer, as long as it has the structure shown in formula (1). Formula (1) only represents the specific structure and ratio of each unit and cannot represent the connection relationship between the structural units. The polymer shown in formula (1) is a random polymer. In a preferred embodiment, the first polymer is prepared by the following method: Sodium styrene sulfonate and butadiene are fed into an organic solvent in a molar ratio of 1:(0.5 - 2) for the first copolymerization reaction, and then the obtained sodium styrene sulfonate / butadiene copolymer is subjected to the first thiol-ene click reaction with 2-fluoro-4-mercaptoaniline to obtain a solution containing the first polymer. Among them, the conditions of the first copolymerization reaction preferably include a polymerization temperature of 50 - 100 °C, such as 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, 100 °C or any value between them; a polymerization pressure of 0.1 - 0.5 MPa, such as 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa or any value between them; a polymerization time of 0.5 - 10 h, such as 0.5 h, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h or any value between them. The molar ratio of butadiene to 2-fluoro-4-mercaptoaniline is preferably (0.9 - 1.1):1, such as 0.9:1, 0.95:1, 1:1, 1.05:1, 1.1:1 or any value between them. The conditions of the first thiol-ene click reaction preferably include a temperature of 70 - 100 °C, such as 70 °C, 75 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C or any value between them; a polymerization pressure of 0.1 - 0.5 MPa, such as 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa or any value between them; a polymerization time of 0.5 - 5 h, such as 0.5 h, 1 h, 2 h, 4 h, 5 h or any value between them.

[0024] The present invention does not particularly limit the source of the second polymer, as long as it has the structure shown in formula (2). Formula (2) only represents the specific structure and ratio of each unit and cannot represent the connection relationship between the structural units. The polymer shown in formula (2) is a random polymer. In a preferred embodiment, the second polymer is prepared by the following method: Styrene and butadiene are fed into an organic solvent in a molar ratio of 1:(0.5 - 2) for a second copolymerization reaction, and then the obtained styrene / butadiene copolymer is subjected to a second thiol-ene click reaction with 3-amino-5-mercapto-1,2,4-triazole to obtain a solution containing the second polymer. Among them, the conditions of the second copolymerization reaction preferably include a polymerization temperature of 50 - 100°C, such as 50°C, 60°C, 70°C, 80°C, 90°C, 100°C or any value between them; a polymerization pressure of 0.1 - 0.5 MPa, such as 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa or any value between them; a polymerization time of 0.5 - 10 h, such as 0.5 h, 1 h, 2 h, 4 h, 6 h, 8 h, 10 h or any value between them. The molar ratio of butadiene to 3-amino-5-mercapto-1,2,4-triazole is preferably (0.9 - 1.1):1, such as 0.9:1, 0.95:1, 1:1, 1.05:1, 1.1:1 or any value between them. The conditions of the first thiol-ene click reaction preferably include a temperature of 70 - 100°C, such as 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C or any value between them; a polymerization pressure of 0.1 - 0.5 MPa, such as 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa or any value between them; a polymerization time of 0.5 - 5 h, such as 0.5 h, 1 h, 2 h, 4 h, 5 h or any value between them.

[0025] In the present invention, the terms "first" and "second" are only used to distinguish the same substances and / or conditions that appear at different times for the convenience of description and have no other special meanings. In addition, the pressures are all gauge pressures.

[0026] In the present invention, the MOF transition membrane can be formed from unmodified MOF materials or modified MOF materials, and is preferably formed from modified MOF materials. The modified MOF material can be an Fe-modified MOF material, and particularly preferably an Fe and Cu co-modified MOF material.

[0027] In a preferred embodiment, the Fe and Cu co-modified MOF material is prepared by the following method: S11. Dispersing 3,5-pyrazoledicarboxylic acid in an alkaline solution, adding aluminum chloride to the obtained dispersion and stirring until dissolved, then heating the obtained solution at 90-110 °C for 10-48 h and filtering, drying the obtained precipitate to obtain a MOF support; S12. Activating the MOF support at 140-160 °C for 10-24 h, then dispersing the obtained activated MOF support, iron nitrate and copper nitrate in an organic solvent, and then raising the temperature to 60-80 °C and reacting for 10-48 h, and cooling to room temperature after the reaction to obtain a solution containing the modified MOF material. Wherein, the mass ratio of the MOF support, iron nitrate and copper nitrate is preferably 1:(0.5-0.8):(0.1-0.3). Specifically, based on the amount of the MOF support being 1 part by weight, the amount of iron nitrate is 0.5-0.8 parts by weight, such as 0.5, 0.6, 0.7, 0.8 parts by weight or any value therebetween; the amount of copper nitrate is 0.1-0.3 parts by weight, such as 0.1, 0.15, 0.2, 0.25, 0.3 parts by weight or any value therebetween.

[0028] The preparation method of the composite bipolar membrane provided by the present invention comprises the following steps:

[0029] S21. Feeding sodium styrene sulfonate and butadiene in a molar ratio of 1:(0.5-2) into an organic solvent for a first copolymerization reaction, and then carrying out a first thiol-ene click reaction on the obtained sodium styrene sulfonate / butadiene copolymer and 2-fluoro-4-mercaptoaniline to obtain a solution containing a first polymer;

[0030] Feeding styrene and butadiene in a molar ratio of 1:(0.5-2) into an organic solvent for a second copolymerization reaction, and then carrying out a second thiol-ene click reaction on the obtained styrene / butadiene copolymer and 3-amino-5-mercapto-1,2,4-triazole to obtain a solution containing a second polymer;

[0031] S22. Spraying the solution containing the first polymer on the surface of the substrate, drying to obtain a cation exchange membrane layer; spraying the solution containing the modified MOF material on the surface of the cation exchange membrane, drying to obtain a MOF transition membrane; spraying the solution containing the second polymer on the surface of the MOF transition membrane, drying to obtain an anion exchange membrane.

[0032] In the preparation process of the above composite bipolar membrane, the concentrations of the solution containing the first polymer, the solution containing the second polymer, and the solution containing the modified MOF material are preferably each independently 0.1-10 wt%, such as 0.1 wt%, 1 wt%, 2 wt%, 4 wt%, 6 wt%, 8 wt%, 10 wt% or any value therebetween.

[0033] In the preparation process of the above-mentioned composite bipolar membrane, the raw materials and conditions of step S21 have been described above and will not be elaborated here.

[0034] In the preparation process of the above-mentioned composite bipolar membrane, in step S22, the conditions for drying the solution containing the first polymer, the solution containing the modified MOF material, and the solution containing the second polymer preferably each independently include a temperature of 50-100 °C, such as 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, 100 °C, or any value between them; and a time of 10 min-2 h, such as 10 min, 30 min, 60 min, 80 min, 100 min, 120 min, or any value between them.

[0035] The present invention also provides the application of the above-mentioned composite bipolar membrane in the preparation of hexacyanocobaltate.

[0036] The present invention will be described in detail below through examples.

[0037] Preparation Example 1-1

[0038] Sodium styrene sulfonate and butadiene were fed into trichloroethane at a molar ratio of 1:1.2, and reacted at a temperature of 50 °C and a pressure of 0.5 MPa for 10 h to obtain a sodium styrene sulfonate / butadiene copolymer. The sodium styrene sulfonate / butadiene copolymer was reacted with 2-fluoro-4-mercaptoaniline at a temperature of 70 °C and a pressure of 0.5 MPa for 5 h. The molar ratio of 2-fluoro-4-mercaptoaniline to butadiene was 1:1 to obtain a solution containing the first polymer with a concentration of 5 wt%.

[0039] Preparation Example 1-2

[0040] Sodium styrene sulfonate and butadiene were fed into trichloroethane at a molar ratio of 1:0.5, and reacted at a temperature of 100 °C and a pressure of 0.1 MPa for 0.5 h to obtain a sodium styrene sulfonate / butadiene copolymer. The sodium styrene sulfonate / butadiene copolymer was reacted with 2-fluoro-4-mercaptoaniline at a temperature of 100 °C and a pressure of 0.1 MPa for 0.5 h. The molar ratio of 2-fluoro-4-mercaptoaniline to butadiene was 1:1 to obtain a solution containing the first polymer with a concentration of 2 wt%.

[0041] Preparation Example 1-3

[0042] Sodium styrene sulfonate and butadiene were fed into trichloroethane at a molar ratio of 1:2, and reacted at a temperature of 80 °C and a pressure of 0.3 MPa for 5 h to obtain a sodium styrene sulfonate / butadiene copolymer. The sodium styrene sulfonate / butadiene copolymer was reacted with 2-fluoro-4-mercaptoaniline at a temperature of 80 °C and a pressure of 0.3 MPa for 2 h. The molar ratio of 2-fluoro-4-mercaptoaniline to butadiene was 1:1, and a solution containing the first polymer with a concentration of 8 wt% was obtained.

[0043] Comparative Preparation Example 1-1

[0044] Sodium styrene sulfonate and butadiene were fed into trichloroethane at a molar ratio of 1:1.2, and reacted at a temperature of 50 °C and a pressure of 0.5 MPa for 10 h to obtain a reference solution containing the first polymer with a concentration of 5 wt%.

[0045] Preparation Example 2-1

[0046] Styrene and butadiene were fed into trichloroethane at a molar ratio of 1:0.5, and reacted at a temperature of 50 °C and a pressure of 0.5 MPa for 10 h to obtain a styrene / butadiene copolymer; the styrene / butadiene copolymer was reacted with 3-amino-5-mercapto-1,2,4-triazole at a temperature of 70 °C and a pressure of 0.5 MPa for 5 h. The molar ratio of 3-amino-5-mercapto-1,2,4-triazole to butadiene was 1:1, and a solution containing the second polymer with a concentration of 5 wt% was obtained.

[0047] Preparation Example 2-2

[0048] Styrene and butadiene were fed into trichloroethane at a molar ratio of 1:1.2, and reacted at a temperature of 100 °C and a pressure of 0.1 MPa for 0.5 h to obtain a styrene / butadiene copolymer; the styrene / butadiene copolymer was reacted with 3-amino-5-mercapto-1,2,4-triazole at a temperature of 100 °C and a pressure of 0.1 MPa for 0.5 h. The molar ratio of 3-amino-5-mercapto-1,2,4-triazole to butadiene was 1:1, and a solution containing the second polymer with a concentration of 2 wt% was obtained.

[0049] Preparation Example 2-3

[0050] Styrene and butadiene were fed into trichloroethane at a molar ratio of 1:2, and reacted at a temperature of 80 °C and a pressure of 0.3 MPa for 5 h to obtain a styrene / butadiene copolymer; the styrene / butadiene copolymer was reacted with 3-amino-5-mercapto-1,2,4-triazole at a temperature of 80 °C and a pressure of 0.3 MPa for 2 h. The molar ratio of 3-amino-5-mercapto-1,2,4-triazole to butadiene was 1:1, and a solution containing the second polymer with a concentration of 8 wt% was obtained.

[0051] Comparative Preparation Example 2-1

[0052] Prepare a solution containing the second polymer according to the method of Preparation Example 2-1, except that styrene is replaced with the same molar amount of butadiene, and the other conditions are the same as those in Preparation Example 2-1, to obtain a reference solution containing the second polymer with a concentration of 5 wt%.

[0053] Preparation Example 3-1

[0054] S11. Disperse 5 g of 3,5-pyrazoledicarboxylic acid monohydrate in 1 L of an aqueous sodium hydroxide solution with a concentration of 0.3 wt%, add 10 g of aluminum chloride to the resulting dispersion and stir until dissolved, then heat the resulting solution at 90 °C for 48 h and filter, and vacuum-dry the resulting precipitate at 60 °C for 2 h to obtain a MOF support;

[0055] S12. Activate the MOF support at 140 °C for 24 h, then disperse the resulting activated MOF support, ferric nitrate, and copper nitrate in acetonitrile according to a mass ratio of 1:0.5:0.1, and then raise the temperature to 70 °C and react for 24 h. After the reaction is completed, cool to room temperature to obtain a solution containing the modified MOF material with a concentration of 5 wt%.

[0056] Preparation Example 3-2

[0057] S11. Disperse 5 g of 3,5-pyrazoledicarboxylic acid monohydrate in 1 L of an aqueous sodium hydroxide solution with a concentration of 0.3 wt%, add 10 g of aluminum chloride to the resulting dispersion and stir until dissolved, then heat the resulting solution at 110 °C for 10 h and filter, and vacuum-dry the resulting precipitate at 60 °C for 2 h to obtain a MOF support;

[0058] S12. Activate the MOF support at 160 °C for 10 h, then disperse the resulting activated MOF support, ferric nitrate, and copper nitrate in acetonitrile according to a mass ratio of 1:0.8:0.3, and then raise the temperature to 60 °C and react for 48 h. After the reaction is completed, cool to room temperature to obtain a solution containing the modified MOF material with a concentration of 5 wt%.

[0059] Preparation Example 3-3

[0060] S11. Disperse 5 g of 3,5-pyrazoledicarboxylic acid monohydrate in 1 L of an aqueous sodium hydroxide solution with a concentration of 0.3 wt%, add 10 g of aluminum chloride to the resulting dispersion and stir until dissolved, then heat the resulting solution at 100 °C for 24 h and filter, and vacuum-dry the resulting precipitate at 60 °C for 2 h to obtain a MOF support;

[0061] S12. Activate the MOF support at 150 °C for 15 h, then disperse the obtained activated MOF support, iron nitrate, and copper nitrate in acetonitrile at a mass ratio of 1:0.6:0.2, and then raise the temperature to 80 °C and react for 10 h. After the reaction, cool to room temperature to obtain a solution containing the modified MOF material with a concentration of 5 wt%.

[0062] Preparation Example 3-4

[0063] Prepare a solution containing the modified MOF material according to the method of Preparation Example 3-1. The difference is that copper nitrate is replaced with the same weight of iron nitrate, and the other conditions are the same as those in Preparation Example 3-1 to obtain a solution containing the modified MOF material.

[0064] Example 1

[0065] Spray the solution containing the first polymer (obtained from Preparation Example 1-1) on the surface of the substrate and vacuum dry at 60 °C for 2 h to obtain a cation exchange membrane; spray the solution containing the modified MOF material (obtained from Preparation Example 3-1) on the surface of the cation exchange membrane and vacuum dry at 60 °C for 2 h to obtain a MOF transition membrane; spray the solution containing the second polymer (obtained from Preparation Example 2-1) on the surface of the MOF transition membrane and vacuum dry at 60 °C for 2 h to obtain an anion exchange membrane. Then peel the cation exchange membrane from the substrate to obtain a composite bipolar membrane including a cation exchange membrane, a MOF transition membrane, and an anion exchange membrane stacked in sequence, denoted as SM-1. Among them, the thickness of the cation exchange membrane is 30 ± 0.5 microns, the thickness of the MOF transition membrane is 5 ± 0.5 microns, and the thickness of the anion exchange membrane is 10 ± 0.5 microns.

[0066] Example 2

[0067] Spray the solution containing the first polymer (obtained from Preparation Example 1-2) on the surface of the substrate and vacuum dry at 60 °C for 2 h to obtain a cation exchange membrane; spray the solution containing the modified MOF material (obtained from Preparation Example 3-2) on the surface of the cation exchange membrane and vacuum dry at 60 °C for 2 h to obtain a MOF transition membrane; spray the solution containing the second polymer (obtained from Preparation Example 2-2) on the surface of the MOF transition membrane and vacuum dry at 60 °C for 2 h to obtain an anion exchange membrane. Then peel the cation exchange membrane from the substrate to obtain a composite bipolar membrane including a cation exchange membrane, a MOF transition membrane, and an anion exchange membrane stacked in sequence, denoted as SM-2. Among them, the thickness of the cation exchange membrane is 30 ± 0.5 microns, the thickness of the MOF transition membrane is 5 ± 0.5 microns, and the thickness of the anion exchange membrane is 10 ± 0.5 microns.

[0068] Example 3

[0069] Spray the solution containing the first polymer (obtained from Preparation Examples 1-3) onto the surface of the substrate, and vacuum dry it at 60 °C for 2 h to obtain a cation exchange membrane; spray the solution containing the modified MOF material (obtained from Preparation Example 3-3) onto the surface of the cation exchange membrane, and vacuum dry it at 60 °C for 2 h to obtain a MOF transition membrane; spray the solution containing the second polymer (obtained from Preparation Example 2-3) onto the surface of the MOF transition membrane, and vacuum dry it at 60 °C for 2 h to obtain an anion exchange membrane. Then, peel the cation exchange membrane from the substrate to obtain a composite bipolar membrane including a cation exchange membrane, a MOF transition membrane, and an anion exchange membrane stacked in sequence, denoted as SM-3. Among them, the thickness of the cation exchange membrane is 30 ± 0.5 μm, the thickness of the MOF transition membrane is 5 ± 0.5 μm, and the thickness of the anion exchange membrane is 10 ± 0.5 μm.

[0070] Example 4

[0071] Prepare the composite bipolar membrane according to the method of Example 1, except that the solution containing the modified MOF material obtained from Preparation Example 3-1 is replaced with the solution containing the modified MOF material obtained from Preparation Example 3-4 in the same weight portion, and the other conditions are the same as those in Example 1 to obtain a composite bipolar membrane, denoted as SM-4. Among them, the thickness of the cation exchange membrane is 30 ± 0.5 μm, the thickness of the MOF transition membrane is 5 ± 0.5 μm, and the thickness of the anion exchange membrane is 10 ± 0.5 μm.

[0072] Comparative Example 1

[0073] Prepare the composite bipolar membrane according to the method of Example 1, except that the solution containing the first polymer obtained from Preparation Example 1-1 is replaced with the reference solution containing the first polymer obtained from Comparative Preparation Example 1-1 in the same weight portion, and the other conditions are the same as those in Example 1 to obtain a reference composite bipolar membrane, denoted as DSM-1. Among them, the thickness of the cation exchange membrane is 30 ± 0.5 μm, the thickness of the MOF transition membrane is 5 ± 0.5 μm, and the thickness of the anion exchange membrane is 10 ± 0.5 μm.

[0074] Comparative Example 2

[0075] Prepare the composite bipolar membrane according to the method of Example 1, except that the solution containing the second polymer obtained from Preparation Example 2-1 is replaced with the reference solution containing the second polymer obtained from Comparative Preparation Example 2-1 in the same weight portion, and the other conditions are the same as those in Example 1 to obtain a reference composite bipolar membrane, denoted as DSM-2. Among them, the thickness of the cation exchange membrane is 30 ± 0.5 μm, the thickness of the MOF transition membrane is 5 ± 0.5 μm, and the thickness of the anion exchange membrane is 10 ± 0.5 μm.

[0076] Test Example

[0077] This test example uses a two-compartment bipolar membrane electrodialysis device. The anode plate material is a reticulated metal DSA, and the cathode plate material is a reticulated titanium electrode plate. The bipolar membrane and the cation exchange membrane are BP-1 type bipolar membrane and CMX type cation exchange membrane ( CMX, manufactured by ASTOM Corporation, Japan), with a membrane area of 200 cm 2 . The membrane stack consists of 5 repeating units with a B1C2 configuration.

[0078] A potassium hexacyanocobaltate solution with a concentration of 6.5 wt% is introduced into the acid chamber inlet of the two-compartment bipolar membrane electrodialysis device, and deionized water is introduced into the alkali chamber. The DC power supply is turned on for constant voltage electrodialysis at 8 V. After 30 min, the concentration of hexacyanocobaltic acid in the acid chamber outlet is measured, and the results are shown in Table 1.

[0079] After using the bipolar membrane continuously for half a year in the electrodialysis preparation of hexacyanocobaltic acid, the concentration of hexacyanocobaltic acid in the acid chamber outlet after the completion of electrodialysis is measured according to the above method, and the results are shown in Table 1.

[0080] Table 1

[0081] Bipolar membrane When it is just put into operation After running for half a year SM-1 4.8wt% 4.6wt% SM-2 5.2wt% 5.1wt% SM-3 4.9wt% 4.9wt% SM-4 4.0wt% 3.9wt% DSM-1 3.8wt% 1.6wt% DSM-2 3.6wt% 1.5wt%

[0082] It can be seen from the results of Examples 1-4 and Comparative Examples 1-2 that using the composite bipolar membrane provided by the present invention in the bipolar membrane electrodialysis method for producing hexacyanocobaltic acid can continuously and efficiently obtain hexacyanocobaltic acid. From the comparison between Example 1 and Example 4, it can be seen that when the MOF material is co-modified with Fe and Cu, it is more conducive to promoting the synthesis of hexacyanocobaltic acid.

[0083] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention without departing from the principle and purpose of the present invention.

Claims

1. A composite bipolar membrane, characterized in that: The composite bipolar membrane comprises a cation exchange membrane, a MOF transition membrane and an anion exchange membrane stacked in sequence; the cation exchange membrane is formed by a first polymer, which is a random copolymer having a structure represented by formula (1); the anion exchange membrane is formed by a second polymer, which is a random copolymer having a structure represented by formula (2); Formula (1), Formula (2), m and n represent the molar proportions of the two structural units in formula (1), and the ratio of m to n is 1:(0.5~2); p and q represent the molar proportions of the two structural units in formula (2), and the ratio of p to q is 1:(0.5~2).

2. The composite bipolar membrane according to claim 1, characterized in that: The thickness of the cation exchange membrane is 10-60 microns, the thickness of the MOF transition membrane is 1-10 microns, and the thickness of the anion exchange membrane is 5-20 microns.

3. The composite bipolar membrane according to claim 1, characterized in that: The first polymer is prepared according to the following method: sodium styrene sulfonate and butadiene are added into an organic solvent at a molar ratio of 1:(0.5-2) to carry out a first copolymerization reaction, and then the obtained sodium styrene sulfonate / butadiene copolymer is subjected to a first thiol-ene click reaction with 2-fluoro-4-mercaptoaniline to obtain a solution containing the first polymer.

4. The composite bipolar membrane according to claim 3, characterized in that: The conditions of the first copolymerization reaction include a polymerization temperature of 50-100° C., a polymerization pressure of 0.1-0.5 MPa, and a polymerization time of 0.5-10 h.

5. The composite bipolar membrane according to claim 3, characterized in that: The molar ratio of butadiene to 2-fluoro-4-mercaptoaniline is (0.9-1.1):

1.

6. The composite bipolar membrane according to claim 3, characterized in that: The conditions of the first thiol-ene click reaction include a temperature of 70-100° C., a pressure of 0.1-0.5 MPa, and a time of 0.5-5 h.

7. The composite bipolar membrane according to claim 1, characterized in that: The second polymer is prepared according to the following method: styrene and butadiene are added into an organic solvent at a molar ratio of 1:(0.5-2) to carry out a second copolymerization reaction, and then the obtained styrene / butadiene copolymer is subjected to a second thiol-ene click reaction with 3-amino-5-mercapto-1,2,4-triazole to obtain a solution containing the second polymer.

8. The composite bipolar membrane according to claim 7, characterized in that: The conditions of the second copolymerization reaction include a polymerization temperature of 50-100° C., a polymerization pressure of 0.1-0.5 MPa, and a polymerization time of 0.5-10 h.

9. The composite bipolar membrane according to claim 7, characterized in that: The molar ratio of butadiene to 3-amino-5-mercapto-1,2,4-triazole is (0.9-1.1):

1.

10. The composite bipolar membrane according to claim 7, characterized in that: The conditions of the second thiol-ene click reaction include a temperature of 70-100° C., a pressure of 0.1-0.5 MPa, and a time of 0.5-5 h.

11. The composite bipolar membrane according to claim 1, characterized in that: The MOF transition film is formed by a modified MOF material, and the modified MOF material is a MOF material co-modified by Fe and Cu.

12. The composite bipolar membrane according to claim 11, characterized in that: The modified MOF material is prepared according to the following method: S11. 3,5-pyrazoledicarboxylic acid is dispersed in an alkaline solution, aluminum chloride is added to the obtained dispersion and stirred until dissolved, and then the obtained solution is heated at 90-110° C. for 10-48 hours and filtered, and the obtained precipitate is dried to obtain a MOF carrier; S12. Activate the MOF carrier at 140-160°C for 10-24h, then disperse the activated MOF carrier, ferric nitrate and copper nitrate in an organic solvent, then heat to 60-80°C for reaction for 10-48h, wait for the reaction result, and cool to room temperature to obtain a solution containing the modified MOF material.

13. The composite bipolar membrane according to claim 12, characterized in that: The mass ratio of the MOF carrier, ferric nitrate and copper nitrate is 1:(0.5-0.8):(0.1-0.3).

14. The method for preparing the composite bipolar membrane according to any one of claims 1 to 13, characterized in that: The method comprises the following steps: S21. sodium styrene sulfonate and butadiene are fed in an organic solvent at a molar ratio of 1: (0.5 to 2) to carry out a first copolymerization reaction, and then the obtained sodium styrene sulfonate / butadiene copolymer is subjected to a first thiol-ene click reaction with 2-fluoro-4-mercaptoaniline to obtain a solution containing a first polymer; Styrene and butadiene are added into an organic solvent at a molar ratio of 1:(0.5-2) to carry out a second copolymerization reaction, and then the obtained styrene / butadiene copolymer is subjected to a second thiol-ene click reaction with 3-amino-5-mercapto-1,2,4-triazole to obtain a solution containing a second polymer; S22. Spraying a solution containing the first polymer on the surface of the substrate and drying it to obtain a cation exchange membrane layer; spraying a solution containing the modified MOF material on the surface of the cation exchange membrane and drying it to obtain a MOF transition membrane; spraying a solution containing the second polymer on the surface of the MOF transition membrane and drying it to obtain an anion exchange membrane.

15. The method for preparing a composite bipolar membrane according to claim 14, characterized in that: The concentrations of the solution containing the first polymer, the solution containing the second polymer, and the solution containing the modified MOF material are each independently 0.1-10 wt %.

16. The method for preparing a composite bipolar membrane according to claim 14, characterized in that: The conditions for drying the solution containing the first polymer, the solution containing the modified MOF material, and the solution containing the second polymer independently include a temperature of 50-100° C. and a time of 10 min-2 h.

17. Use of the composite bipolar membrane according to any one of claims 1 to 13 in the preparation of hexacyanocobaltic acid.

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