A bipolar membrane and its preparation method

Abstract

The present invention belongs to the technical field of ion exchange membranes and relates to a bipolar membrane and a method for preparing the same. The bipolar membrane comprises a cation exchange membrane, an anion exchange membrane, and an intermediate layer; the cation exchange membrane is a sulfonated polysulfone; the anion exchange membrane is an aminated chloromethyl polysulfone; and the intermediate layer is prepared by reacting an organic amine compound containing a vinyl group with chloromethyl polysulfone. The three polymer layers of the bipolar membrane of the present invention all utilize a polysulfone matrix material, which has relatively consistent swelling properties. Since the three layers utilize the same material, their affinity is also relatively suitable. This allows for a relatively close affinity between the layers of the bipolar membrane. Furthermore, crosslinking is used to enhance the stability of the intermediate catalytic layer, preventing loss of the catalytic effect. The present invention solves the technical problem of the intermediate layer being susceptible to loss or blistering.

Description

Technical Field

[0001] The invention belongs to the technical field of ion exchange membranes and relates to a bipolar membrane and a preparation method thereof. Background Art

[0002] The treatment of saline wastewater is a serious problem for many industries. Mechanical steam recompression (MVR) is used to evaporate and crystallize saline wastewater, a process that consumes significant amounts of energy. Electrodialysis, which pre-concentrates wastewater before evaporation, can save significant energy but still requires significant energy consumption overall. Bipolar membrane electrodialysis utilizes a bipolar membrane to ionize water into hydrogen protons and hydroxide ions, converting salt into the corresponding acid and base. This avoids evaporation, enabling wastewater resource utilization and achieving true zero emissions. It also solves the problem of waste salt disposal. Therefore, the use of bipolar membrane electrodialysis for saline wastewater treatment has been recognized and accepted by the industry.

[0003] The bipolar membrane is the core and key material of the bipolar membrane electrodialysis process. A special type of ion exchange membrane, it is a composite of a cation exchange membrane and an anion exchange membrane. The interface between the two is often bonded by a compound with electrochemical catalytic properties. Because the membrane absorbs water and simultaneously transfers salt ions, the electric field, particularly the osmotic pressure of the salt ions, can cause blistering or even delamination, increasing membrane resistance and shortening its service life.

[0004] The invention patent application with publication number CN106040013A proposed to use sulfonated polyphenylene ether and ammonium polyphenylene ether to prepare bipolar membranes. However, the preparation process uses the solution viscoelastic state, which makes coating difficult. In addition, PVA is added, but PVA is easily lost, which reduces the activity. In addition, there is no chemical bond between the membrane layers, which is easy to cause stratification during application. The invention patent application with publication number CN105504325A discloses a nano Zn 2+ -TiO2 modified polyethyleneimine / sodium polyacrylate bipolar membrane preparation method, which uses polyethyleneimine as the cathode membrane layer and sodium polyacrylate as the anode membrane layer, and adds Zn 2+ -TiO2 powder changes the properties of the middle layer, making the prepared membrane tightly bonded and not easy to delaminate; however, since the sodium carboxylate group contained in the cation layer used is not highly dissociated, the ion exchange rate is slow; the active group contained in the anion layer used is weakly alkaline, which is not conducive to rapid ion exchange and transfer.

[0005] The invention patent application with publication number CN101983759A discloses a method for preparing a bipolar membrane with high ion conduction efficiency by doping an anionic fast ion conductor. The method comprises preparing a cationic membrane layer by copolymerizing sodium carboxymethyl cellulose and styrene-butadiene-styrene; copolymerizing 4,4-diaminodiphenylmethane and pyromellitic dianhydride at low temperature, and then doping with a fast ion conductor to finally prepare an anionic membrane liquid composite sol as the anionic membrane layer; however, since the styrene-butadiene-styrene contained in its cationic membrane layer does not contain cation exchange groups, its ion exchange capacity is insufficient; at the same time, the copolymerization step in the preparation of its anionic membrane liquid is difficult to control, and the operating conditions are relatively harsh, which is not conducive to actual production. The invention patent application with publication number CN108031302A proposes a bipolar membrane and a method for preparing the same. The spray solution is atomized on the surface of the anion exchange membrane using ultrasonic spraying equipment, and an adhesive and a cation layer material are sprayed layer by layer. First, a certain amount of adhesive is sprayed, and then three substances, a hydrophilic polyelectrolyte, a metal chelating agent, and a sulfonated reagent, are sprayed layer by layer in a certain proportion. However, due to the use of an adhesive, it is difficult to uniformly distribute and control the middle layer, the electrochemical reaction efficiency is relatively low, and the preparation of a cation exchange membrane layer of a certain thickness by spraying requires multiple spraying processes, making the production process complicated. Summary of the Invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides a bipolar membrane and a method for preparing the same. The specific technical solutions are as follows:

[0007] A first object of the present invention is to provide a bipolar membrane comprising a cation exchange membrane, an anion exchange membrane and an intermediate layer;

[0008] The cation exchange membrane is sulfonated polysulfone; the anion exchange membrane is aminated chloromethyl polysulfone; the intermediate layer is prepared by reacting an organic amine compound with a vinyl group with chloromethyl polysulfone;

[0009] The thickness of the cation exchange membrane is 10-200 microns, the optimized thickness is 80-150 microns, and the optimal thickness is 100-110 microns; the thickness of the anion exchange membrane is 10-150 microns, the optimized thickness is 50-100 microns, and the optimal thickness is 80-90 microns; the thickness of the intermediate layer is 1-100 microns, the optimized thickness is 1-30 microns, and the optimal thickness is 5-10 microns.

[0010] The bipolar membrane of the present invention uses a polymer substrate, polysulfone (PSU), which has excellent heat stability and antioxidant properties and is also very stable in alkaline environments, making it an ideal material for preparing bipolar membranes. Compared with other polymer substrates with strong oxidation resistance, such as polyetheretherketone (PEEK) and perfluorosulfonic acid (PFSA), it is low in cost and relatively simple to prepare anion and cation exchange membranes. The intermediate layer uses a basic polymer with a vinyl group to undergo an amination reaction with chloromethyl polysulfone. Subsequently, the vinyl groups on the basic polymer with a vinyl group are cross-linked through a free radical polymerization reaction, preventing the loss of basic groups that have a catalytic effect on water dissociation and enhancing the stability of the basic groups.

[0011] Furthermore, the organic amine compound having a vinyl group is one or more of vinyl pyridine, vinyl piperidine or vinyl imidazole.

[0012] Substances with water dissociation catalysis, such as imidazole compounds, are easily soluble in water and will also dissociate structurally, which can easily cause the loss of imidazole groups, thereby reducing water dissociation efficiency, increasing resistance, and increasing the energy consumption of the bipolar membrane; For example, using chloromethylated polymers to react with imidazole to obtain anionic polymers containing imidazole can reduce the loss of imidazole, but considering the microscopic environment of water dissociation in the middle layer of the bipolar membrane, OH - The concentration is very high and the alkalinity may be very strong. Imidazole may still dissociate in a strong alkaline environment. The middle layer uses vinyl imidazole and chloromethyl polymer to undergo an amination reaction. Subsequently, the vinyl groups on the vinyl imidazole can be cross-linked through free radical polymerization to prevent the loss of the imidazole group that has a catalytic effect on water dissociation, thereby enhancing the stability of the imidazole group.

[0013] Furthermore, the sulfonated polysulfone is prepared by a polysulfone sulfonation reaction, the sulfonating agent of the sulfonation reaction is sulfuric acid, fuming sulfuric acid or chlorosulfonic acid, preferably chlorosulfonic acid; the sulfonation exchange capacity IEC of the sulfonated polysulfone is 1.2-1.8, preferably the sulfonation exchange capacity IEC is 1.4-1.8, and most preferably the sulfonation exchange capacity IEC is 1.5-1.6.

[0014] Furthermore, the preparation method of the aminated chloromethyl polysulfone comprises the following steps:

[0015] 1) Chloromethyl polysulfone is obtained by chloromethylation of polysulfone;

[0016] 2) Chloromethyl polysulfone is subjected to amination reaction to obtain aminated chloromethyl polysulfone.

[0017] Furthermore, in step 1), the reagent for the chloromethylation reaction is chloromethyl ethyl ether or chloromethyl octyl ether, which is safer and more environmentally friendly; the chloromethylation degree of the chloromethyl polysulfone is 0.1-1.0, preferably 0.5-1.0, and most preferably 0.7-0.9.

[0018] Furthermore, in step 2), the amine reagent for the amination reaction is a linear strongly basic fatty amine or a cyclized amine; the linear strongly basic fatty amine is trimethylamine or triethylamine, and the cyclized amine is one or more of triethylenediamine, pyridine or piperidine.

[0019] Anion exchange membranes require strong basic groups to meet the requirements of low resistance. Chloromethyl reacts with amines to produce quaternary amines to achieve maximum alkalinity.

[0020] Furthermore, in step 2), the amine reagent for the amination reaction is a diamine or an olefin amine, such as diamine and vinylamine.

[0021] Amine reagents such as diamine or olefinamine are used to produce a certain degree of cross-linking in the anion exchange membrane, and cross-linking can enhance the strength of the anion exchange membrane.

[0022] Furthermore, in the step 2), polyvinylidene fluoride (PVDF) is added to the chloromethyl polysulfone for blending to reduce the swelling degree of the chloromethyl polysulfone.

[0023] If the chloromethylation degree is too high, the exchange capacity of the anion exchange membrane can be adjusted and its swelling degree can be reduced by adding polymer blends.

[0024] Furthermore, an initiator is added when the organic amine compound with a vinyl group reacts with chloromethyl polysulfone, and the amount of the initiator is 0.5-1% of the total molar ratio of the polymerization monomers; the initiator is azobisisobutyronitrile (AIBN) or dibenzoyl peroxide (BPO).

[0025] A second object of the present invention is to provide a preparation method based on the above-mentioned bipolar membrane, wherein the preparation method is preparation method 1 or preparation method 2, and the preparation method 1 comprises the following steps:

[0026] (1) Anion exchange membrane layer was prepared using aminated chloromethyl polysulfone solution;

[0027] (2) adding an initiator to the reaction solution of the organic amine compound with a vinyl group and chloromethyl polysulfone, spraying or scraping the solution onto the surface of the anion exchange membrane after degassing, and drying the solution to form an intermediate layer;

[0028] (3) coating the sulfonated polysulfone solution on the surface of the intermediate layer and drying it to obtain a bipolar membrane;

[0029] The second preparation method comprises the following steps:

[0030] (1) Using sulfonated polysulfone solution to prepare the cation exchange membrane layer;

[0031] (2) Adding an initiator to the reaction solution of the organic amine compound with a vinyl group and chloromethyl polysulfone, spraying or scraping the solution onto the surface of the cation exchange membrane after degassing, and drying the solution to form an intermediate layer;

[0032] (3) The aminated chloromethyl polysulfone solution is coated on the surface of the intermediate layer and dried to obtain a bipolar membrane.

[0033] The beneficial effects of the present invention are:

[0034] The matrix of the three polymer layers of the bipolar membrane of the present invention all adopts PSU material, and the swelling characteristics of the material are relatively consistent. Since the three layers adopt the same material, the affinity is also relatively appropriate. Such a bipolar membrane is relatively easy to be tightly attached. At the same time, the stability of the middle catalytic layer is enhanced by the cross-linking method to prevent the loss of the catalytic effect. The present invention solves the technical problem that the middle layer is easy to lose or foam. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is the nuclear magnetic spectrum of chloromethyl polysulfone of the present invention;

[0036] Figure 2 Figure 2 is a diagram of an electrochemical performance measurement device of the present invention;

[0037] Figure 3 The initial current-voltage curves of the bipolar membranes of Example 2 of the present invention and Comparative Example 1 are shown;

[0038] Figure 4 The current-voltage curves of the bipolar membranes of Example 2 of the present invention and Comparative Example 1 after half a year of operation are shown. DETAILED DESCRIPTION

[0039] The principles and features of the present invention are described below in conjunction with embodiments. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0040] Preparation of chloromethyl polysulfone:

[0041] In a 2500ml three-necked glass reaction bottle, 100g of PSU (Udel ® P-1700, Solvay Group) was dissolved in 1000 ml of dichloroethane solvent with stirring at room temperature, and 1.5 g of zinc dichloride (McLean's reagent) was added as a catalyst. Subsequently, 100 ml of chloromethyl ether (Nanjing Black Fine Chemical Co., Ltd.) was slowly added dropwise to the solution to react. The reaction temperature was controlled at 50°C and lowered to room temperature after 10 hours of reaction. The reactants were precipitated in 5 L of methanol and filtered to obtain a polymer. The obtained polymer was then stirred and heated in 10 L of water. The dichloroethane evaporated rapidly and was condensed and recovered by condensation. The solid polymer was collected by filtration and dried at 50°C to obtain 86 g of white powdered chloromethyl polysulfone with an NMR spectrum (1 H-NMR) Figure 1 shown.

[0042] From the NMR spectrum ( 1 H-NMR) analysis showed that the chloromethylation degree of chloromethyl polysulfone was 0.91, the corresponding Cl content was 6.64%, and the ion exchange capacity was 1.85 mmol / g.

[0043] Preparation of sulfonated polysulfone:

[0044] In a 2500ml three-necked glass reaction bottle, 100g of PSU (Udel ® P-1700, Solvay Group) was dissolved in 1000 ml of dichloroethane. 15 g of chilled chlorosulfonic acid (Shenyang Chemical Reagent) was added to 100 ml of dichloroethane and then added dropwise to the solution. A red, flocculent polymer precipitated quickly and slowly dissolved upon stirring. After a certain amount of chlorosulfonic acid was added, the polymer began to precipitate. After the chlorosulfonic acid addition was complete, the reaction was continued for 5 hours, and the solid polymer was separated from the solution. The polymer was further dissolved in 1000 ml of DMF and then precipitated into 1000 ml of methanol for washing. The solution was then washed with water several times until the water was neutral. The resulting polymer was dried at 50°C for 10 hours to yield 109.5 g of a light yellow sulfonated polysulfone.

[0045] The ion exchange capacity was determined to be 1.32 mmol / g and the degree of sulfonation was determined to be 0.65 mol-SO3H / mol sulfonated polysulfone by acid-base titration.

[0046] The chloromethyl polysulfone and sulfonated polysulfone prepared above were used in the following examples or comparative examples.

[0047] Example 1:

[0048] A bipolar membrane, the preparation method of which comprises the following steps:

[0049] (1) In a 250 ml three-necked flask, 15 g of chloromethyl polysulfone (27.75 mmol of chloromethyl) was dissolved in 85 g of NMP solvent to obtain a chloromethyl polysulfone NMP solution; 3.11 g of triolefin diamine (27.75 mmol, Macklin reagent) was dissolved in 10 g of NMP and then added to the chloromethyl polysulfone NMP solution. The mixture was stirred mechanically at a stirring speed of 100 rpm for 120 minutes to allow all the chloromethyl groups to be aminated, thereby obtaining a triolefin diamine aminated chloromethyl polysulfone NMP solution;

[0050] (2) Pour 50 g of triolefin diamine aminated chloromethyl polysulfone NMP solution onto a clean glass plate and coat it with a glass rod to form a film with a wet film thickness of 500 μm. Dry at 50 °C for half an hour and then at 90 °C for 1 hour to form the anion exchange membrane layer of the bipolar membrane with a dry film thickness of 75 μm and a water swelling degree of 67%;

[0051] (3) Dissolve 15 g of chloromethyl polysulfone (27.75 mmol of chloromethyl) in 85 g of DMF solvent to form a 15% solution; add 2.611 g of N-vinyl imidazole (27.75 mmol, Macklin reagent) into the solution, and then stir it evenly under mechanical stirring at a speed of 100 rpm. Stir it at room temperature for 20 hours to form an amination solution of chloromethyl polysulfone and vinyl imidazole. Then add 1% BPO and stir it evenly. After degassing, spray the solution on the surface of the anion exchange membrane layer, dry it at room temperature for half an hour, and then dry it at 80 ° C for 1 hour. Take it out of the oven and cool it to room temperature to form a 5 μm intermediate layer.

[0052] (4) 100 g of sulfonated polysulfone was dissolved in NMP solvent to form a 20% sulfonated polysulfone NMP solution, and then the sulfonated polysulfone NMP solution was coated on the surface of the intermediate layer to form a thickness of 490 μm, dried at 90°C for half an hour, and then dried at 120°C for 1 hour. The obtained bipolar membrane was soaked in 2% saline and peeled off from the glass surface. The formed cation exchange membrane layer had a thickness of 100 μm, and the peeled bipolar membrane was soaked for 2 hours.

[0053] Example 2:

[0054] A bipolar membrane, the preparation method of which comprises the following steps:

[0055] (1) 15 g of chloromethyl polysulfone (27.75 mmol of chloromethyl) was dissolved in 85 g of NMP solvent to obtain a chloromethyl polysulfone NMP solution; 2.299 g of triolefin diamine (24.975 mmol, Macklin reagent) was dissolved in 10 g of NMP and then added to the chloromethyl polysulfone NMP solution. The mixture was stirred mechanically at a stirring speed of 100 rpm and reacted under strong stirring for 60 minutes to obtain a 90% amination of the chloromethyl group. The remaining 10% of the unaminated chloromethyl group was cross-linked with the chloromethyl group through the diamine in the triolefin diamine, resulting in a triolefin diamine-aminated chloromethyl polysulfone NMP solution with a cross-linking degree of 5%;

[0056] (2) Pour 50 g of triolefin diamine aminated chloromethyl polysulfone NMP solution onto a clean glass plate and coat it with a glass rod to form a film with a wet film thickness of 500 μm. Dry at 50 °C for half an hour and then at 90 °C for 1 hour to form the anion exchange membrane layer of the bipolar membrane with a dry film thickness of 75 μm and a water swelling degree of 35%.

[0057] (3) Dissolve 15 g of chloromethyl polysulfone (27.75 mmol) in 85 g of DMF solvent to form a 15% solution; add 2.611 g of N-vinyl imidazole (27.75 mmol, MacLean reagent) into the solution, and then stir vigorously under mechanical stirring at a stirring speed of 100 rpm for 1 minute. Stir at room temperature for 20 hours to form an amination solution of chloromethyl polysulfone and vinyl imidazole. Then add 1% BPO and stir evenly. After degassing, spray the solution on the surface of the anion exchange membrane layer, dry at room temperature for half an hour, and then dry at 80 ° C for 1 hour. Take it out of the oven and cool it to room temperature to form a 5 μm intermediate layer.

[0058] (4) 100 g of sulfonated polysulfone was dissolved in NMP solvent to form a 20% sulfonated polysulfone NMP solution, and then the sulfonated polysulfone NMP solution was coated on the surface of the intermediate layer to form a thickness of 490 μm, dried at 90°C for half an hour, and then dried at 120°C for 1 hour. The obtained bipolar membrane was soaked in 2% saline and peeled off from the glass surface. The formed cation exchange membrane layer had a thickness of 100 μm, and the peeled bipolar membrane was soaked for 2 hours.

[0059] Example 3:

[0060] A bipolar membrane, the preparation method of which comprises the following steps:

[0061] (1) 15 g of chloromethyl polysulfone (27.75 mmol) was dissolved in 85 g of NMP solvent, and then 1.5 g of PVDF was added and stirred to dissolve, to obtain a chloromethyl polysulfone NMP solution containing PVDF; 2.799 g of triolefin diamine (24.975 mmol, Macklin reagent) was dissolved in 10 g of NMP, and then added to the chloromethyl polysulfone NMP solution containing PVDF, and the mixture was stirred mechanically at a stirring speed of 100 rpm and vigorously stirred for 120 minutes to obtain a 90% amination of chloromethyl groups, and the remaining 10% of the unaminated chloromethyl groups were cross-linked by the diamine in the triolefin diamine, and the triolefin diamine-aminated chloromethyl polysulfone NMP solution was actually 5% cross-linked;

[0062] (2) Pour 50 g of triolefin diamine aminated chloromethyl polysulfone NMP solution onto a clean glass plate and coat it with a glass rod to form a film with a wet film thickness of 500 μm. Dry at 50 °C for half an hour and then at 90 °C for 1 hour to form the anion exchange membrane layer of the bipolar membrane with a dry film thickness of 75 μm and a water swelling degree of 23%.

[0063] (3) Dissolve 15 g of chloromethyl polysulfone (27.75 mmol of chloromethyl) in 85 g of DMF solvent to form a 15% solution; add 2.611 g of N-vinyl imidazole (27.75 mmol, MacLean reagent) into the solution, and then stir vigorously under mechanical stirring at a speed of 100 rpm, stir at room temperature for 20 hours, and then add 1% BPO to the amination solution of chloromethyl polysulfone and vinyl imidazole, stir evenly, and spray the solution on the surface of the anion exchange membrane layer after degassing, dry at room temperature for half an hour, and then dry at 80 ° C for 1 hour, take it out of the oven and cool it to room temperature to form a 5 μm intermediate layer;

[0064] (4) 100 g of sulfonated polysulfone was dissolved in NMP solvent to form a 20% sulfonated polysulfone NMP solution, and then the sulfonated polysulfone NMP solution was coated on the surface of the intermediate layer to form a thickness of 490 μm, dried at 90°C for half an hour, and then dried at 120°C for 1 hour. The obtained bipolar membrane was soaked in 2% saline and peeled off from the glass surface. The formed cation exchange membrane layer had a thickness of 100 μm, and the peeled bipolar membrane was soaked for 2 hours.

[0065] Comparative Example 1:

[0066] A bipolar membrane, the preparation method of which comprises the following steps:

[0067] (1) Dissolve 15 g of chloromethyl polysulfone (27.75 mmol of chloromethyl) in 85 g of NMP solvent to obtain a chloromethyl polysulfone NMP solution; dissolve 3.11 g of triolefin diamine (27.75 mmol, Macklin reagent) in 10 g of NMP, and then add the mixture to the chloromethyl polysulfone NMP solution. Stir vigorously for 120 minutes under mechanical stirring at a stirring speed of 100 rpm to allow all the chloromethyl groups to be aminated, thereby obtaining a triolefin diamine aminated chloromethyl polysulfone NMP solution;

[0068] (2) Pour 50 g of triolefin diamine aminated chloromethyl polysulfone NMP solution onto a clean glass plate and coat it with a glass rod to form a film with a wet film thickness of 500 μm. Dry at 50 °C for half an hour and then at 90 °C for 1 hour to form the anion exchange membrane layer of the bipolar membrane with a dry film thickness of 75 μm and a water swelling degree of 67%;

[0069] (3) Dissolve 15 g of chloromethyl polysulfone (27.75 mmol of chloromethyl) in 85 g of DMF solvent to form a 15% chloromethyl polysulfone solution; add 0.85 g of N-methylimidazole to 50 g of the chloromethyl polysulfone solution and stir at room temperature for 20 hours to form an aminated polymer solution. After degassing, spray the solution on the surface of the anion exchange membrane layer, dry at room temperature for half an hour, and then dry at 80 ° C for 1 hour. Take it out of the oven and cool it to room temperature to form a 5 μm intermediate layer;

[0070] (4) 100 g of sulfonated polysulfone was dissolved in NMP solvent to form a 20% sulfonated polysulfone NMP solution, and then the sulfonated polysulfone NMP solution was coated on the surface of the intermediate layer to form a thickness of 490 μm, dried at 90°C for half an hour, and then dried at 120°C for 1 hour. The obtained bipolar membrane was soaked in 2% saline and peeled off from the glass surface. The formed cation exchange membrane layer had a thickness of 100 μm, and the peeled bipolar membrane was soaked for 2 hours.

[0071] Comparative Example 2:

[0072] A bipolar membrane, the preparation method of which comprises the following steps:

[0073] (1) 15 g of chloromethyl polysulfone (27.75 mmol of chloromethyl) was dissolved in 85 g of NMP to obtain a chloromethyl polysulfone NMP solution; 2.299 g of triolefin diamine (24.975 mmol, Macklin reagent) was dissolved in 10 g of NMP and then added to the chloromethyl polysulfone NMP solution. The mixture was stirred mechanically at a stirring speed of 100 rpm and stirred vigorously for 120 minutes to obtain a 90% amination of the chloromethyl groups. The remaining 10% of the unaminated chloromethyl groups were cross-linked by the diamine in the triolefin diamine, resulting in a triolefin diamine-aminated chloromethyl polysulfone NMP solution with a cross-linking degree of 5%.

[0074] (2) Pour 50 g of triolefin diamine aminated chloromethyl polysulfone NMP solution onto a clean glass plate and coat it with a glass rod to form a film with a wet film thickness of 500 μm. Dry at 50 °C for half an hour and then at 90 °C for 1 hour to form the anion exchange membrane layer of the bipolar membrane with a dry film thickness of 75 μm and a water swelling degree of 35%.

[0075] (3) 1 gram of small molecule N-methylimidazole and 0.2 gram of PVDF were mixed and dissolved in 4.8 grams of DMF solvent and stirred evenly to form a solution; after degassing, the solution was sprayed on the surface of the anion exchange membrane layer, dried at room temperature for half an hour, and then dried at 80°C for 1 hour, taken out of the oven and cooled to room temperature to form a 5-micron intermediate layer;

[0076] (4) 100 g of sulfonated polysulfone was dissolved in NMP solvent to form a 20% sulfonated polysulfone NMP solution, and then the sulfonated polysulfone NMP solution was coated on the surface of the intermediate layer to form a thickness of 490 μm, dried at 90°C for half an hour, and then dried at 120°C for 1 hour. The obtained bipolar membrane was soaked in 2% saline and peeled off from the glass surface. The formed cation exchange membrane layer had a thickness of 100 μm, and the peeled bipolar membrane was soaked for 2 hours.

[0077] Performance tests were performed on the bipolar membranes prepared in the examples and comparative examples.

[0078] 1. Vinyl imidazole cross-linking reaction

[0079] 15 g of chloromethyl polysulfone (27.75 mmol) was dissolved in 85 g of DMF solvent to form a 15% solution; 2.611 g of N-vinylimidazole (27.75 mmol, Macklin reagent) was added to the solution, and then stirred vigorously at 100 rpm under mechanical stirring, stirred at room temperature for 20 hours to form an amination solution of chloromethyl polysulfone and vinylimidazole, and then 0.075 g of BPO was added and stirred evenly. Vacuum degassing was carried out at room temperature, and then a film was coated on a glass plate, placed in an oven, and dried at 80 degrees for 30 minutes. The obtained film was cooled and placed in water; the film was peeled off from the glass plate, soaked in water for 1 hour, taken out, and dried in an oven at 60 degrees for 30 minutes; the film was placed in 100 ml of NMP solution, and the film formed a gel and no longer dissolved, indicating that the crosslinking was successful.

[0080] 2. Comparison of long-term performance of bipolar membranes

[0081] Before use, the bipolar membrane was tested for its water dissociation performance by testing its current-voltage curve, using a fixed current density of 600 A / m 2 The corresponding transmembrane voltage is used as a performance evaluation parameter. Low voltage means low energy consumption of the membrane. After running the membrane for a certain period of time in acid and alkali, the current-voltage curve of the membrane is tested again. 2 The voltage value under the condition of high voltage is used to judge the long-term performance change of the membrane.

[0082] The standard theoretical value of the typical water decomposition voltage is 0.83V. Due to the influence of overpotential, the water decomposition voltage is generally within a range of 0.6-1.0V. The corresponding current density presents three regions. In the low voltage region (0-0.6V), the current is almost very small. This region is the ion selection region. There is almost no current generated by water decomposition. The main source of current is the electrolyte ions passing through the membrane. As the voltage increases, the current density rises sharply. This region is the water dissociation region. The current increases from 10mA / cm 2 Can reach 60-100mA / cm 2 , indicating that H + With OH - Current is generated through the membrane. A higher current density indicates lower membrane resistance and lower energy consumption. At the same current density, the membrane voltage of a bipolar membrane may gradually increase over time. This is due to increased resistance within the membrane. Possible causes include catalyst loss or failure in the intermediate layer, or loosening of the bonds between the layers, leading to increased membrane swelling, blistering, and even delamination.

[0083] The electrochemical performance of the bipolar membrane was measured using Figure 2The apparatus shown in the figure consists of five pieces of acrylic glass divided into four compartments. The cathode chambers are located near the ends, while the bipolar membrane is placed in the center. A cathodic membrane and a cation membrane are placed in the two compartments on either side, respectively. Two capillary electrodes are inserted into each side of the bipolar membrane, and the membrane voltage is measured using a multimeter. A DC current can be introduced through the electrodes on both sides of the apparatus. During measurement, the membrane material is cut into the desired shape and size and placed in the test membrane stack in order. The anion exchange layer of the bipolar membrane faces the anode, and the cation exchange layer faces the cathode. A peristaltic pump is then turned on. Once the solution completely fills the compartments and no bubbles are present, a DC power supply is turned on. The current is adjusted while the corresponding multimeter voltage is recorded. The cathode solution is a 0.3 mol / L Na2SO4 solution, and the circulating fluid is a 0.5 mol / L NaCl solution. When a reverse voltage is applied to the bipolar membrane, a basic current-voltage curve is obtained, reflecting some of the basic electrochemical performance parameters of the bipolar membrane.

[0084] In the effective area of ​​0.021m 2 The three-chamber bipolar membrane electrodialysis stack was composed of 10 bipolar membranes prepared in Example 2 and paired with the concentrated cation-cation membranes fumasep® FAB and FKB from FUMATECH, Germany. Hydrochloric acid and sodium hydroxide were prepared using a 10% sodium chloride solution. Figure 3 、 Figure 4 As shown, the membrane current is maintained at 600 A / m 2 The bipolar membrane voltage was initially 1.56 V. After six months of continuous operation, the bipolar membrane voltage was approximately 1.82 V, a 24% increase. Table 1 shows a comparison of the initial membrane voltage and the membrane voltage after six months of operation for the present embodiment.

[0085] Table 1 Comparison of initial membrane voltage and membrane voltage after half a year of operation

[0086]

[0087] Comparative Example 1 has an effective area of ​​0.021m 2 The three-chamber bipolar membrane electrodialysis stack also uses 10 sheets of this bipolar membrane and is paired with the concentrated cation-cation membranes fumasep® FAB and FKB from the German FUMATECH company to produce hydrochloric acid and sodium hydroxide using a 10% sodium chloride solution. Figure 3 、 Figure 4 As shown, the current is maintained at 600A / m 2 The bipolar membrane voltage initially stood at 1.56V. After six months of continuous operation under the same conditions, the bipolar membrane voltage reached 2.6V, an increase of approximately 78%. Upon opening the membrane stack, blistering was observed within the membrane, indicating delamination of the intermediate layer.

[0088] Comparative Example 2 has an effective area of ​​0.021m 2A three-chamber bipolar membrane electrodialysis stack was constructed. Ten of these bipolar membranes were paired with the concentrated cation-cation membranes fumasep® FAB and FKB from FUMATECH, Germany. Hydrochloric acid and sodium hydroxide were prepared using a 10% sodium chloride solution. The current was maintained constant at 600 A / m. 2 The bipolar membrane voltage was initially 1.54 V. After being immersed in salt water for one month, the current-voltage curve was retested and it was found that the current density was 600 A / m 2 The lower voltage is above 3 V, indicating that imidazole is released from the membrane and the catalytic effect is lost.

[0089] 3. Determination of ion concentration:

[0090] An inductively coupled plasma optical emission spectrometer (ICP-OES; ARCOS; SPECTRO, Germany) was used to measure the ion content in the solution. The acid and base purities of the bipolar membranes of Example 1 and Comparative Example 1 are shown in Table 2.

[0091] Table 2 Acid and base purity of bipolar membranes of Example 1 and Comparative Example 1

[0092]

[0093] Since the ion selectivity of the anionic membrane is not 100%, a small amount of anions and cations will pass through the ion exchange membrane, resulting in a decrease in purity. As a result, a small amount of salt will be present in the acid and base prepared from the bipolar membrane, resulting in a decrease in purity. The ion selectivity of the bipolar membrane can be evaluated by the changing trend of the current density in the low voltage range. For the prepared acid and base, the purity can be evaluated by directly analyzing the salt content in the acid and base solution. There are many ways to improve ion selectivity, among which increasing the cross-linking degree of the membrane is an effective method. By comparing the acid and base purity of the bipolar membranes of Example 1 and Comparative Example 1, the test results clearly show that the acid and base purity of Example 1 of the present invention is significantly higher than that of the bipolar membrane of Comparative Example 1.

[0094] 4. Determination of current efficiency:

[0095] Current efficiency is the ratio of the effective power for water dissociation to the total input power during bipolar membrane electrodialysis. This is because the leakage effect of hydrogen protons and hydroxyl radicals limits the acid-base current efficiency of the entire dissociation process. Therefore, current efficiency (η) is an important parameter for measuring bipolar membrane electrodialysis. Its calculation expression is shown in the formula:

[0096]

[0097] in, Fis the Faraday constant (96485 C / mol), z is the charge carried by the migrating ion, C t and C 0 is the concentration of acid or base at time t and time 0, I is the applied current, N is the number of membrane stack units, t It is the running time.

[0098] Using a three-chamber bipolar membrane electrodialysis device, when an 18% sodium chloride solution was electrodialyzed to produce 2.11N alkali and 2.07N acid, the current efficiency of the bipolar membrane of Example 2, calculated based on alkali production, was 67%, while the current efficiency of the bipolar membrane of Comparative Example 1 was 55%. The present invention achieves membrane compactness through crosslinking, thereby improving current efficiency.

[0099] 5. Energy consumption

[0100] Energy consumption (E) is another important indicator of energy consumption in bipolar membrane electrodialysis and reflects the economic efficiency of the operation process. Here it is expressed in terms of per kilogram of acid or base produced. The expression is:

[0101]

[0102] Where U is the applied voltage, I is the applied current, and m is the mass of the acid or base.

[0103] At a current density of 600A / m 2 Under the operating conditions of , the energy consumption of Example 2 and Comparative Example 1, converted to the energy consumption of pure ash or pure acid, was calculated to be 1688 and 1639 kWh / t for alkali, and 1700 and 1677 kWh / t for acid, respectively, for preparing 2N acid and alkali. While cross-linking the film increases electrical resistance, a comparison of experimental data reveals that the cross-linking method of the present invention only slightly increases resistance, with energy consumption for alkali production increasing by approximately 2.99% and acid production by approximately 1.4%.

[0104] In summary, the matrix of the three-layer polymer of the bipolar membrane of the present invention all adopts PSU material, and the swelling characteristics of the material are relatively consistent. Since the three layers adopt the same material, the affinity is also relatively appropriate. Such a bipolar membrane is relatively easy to be tightly affinity-bound. At the same time, the cross-linking method is used to enhance the stability of the middle catalytic layer and the cross-linking polymerization of the middle layer to prevent the loss of the catalytic effect; it overcomes the defects of the bipolar membrane in the prior art, such as high water dissociation voltage, poor membrane structure stability, short life, poor conductivity, and easy deformation and expansion of the membrane layer or even falling off.

[0105] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A bipolar membrane, characterized in that It includes a cation exchange membrane, an anion exchange membrane and an intermediate layer; The cation exchange membrane is sulfonated polysulfone; the anion exchange membrane is aminated chloromethyl polysulfone; the intermediate layer is prepared by reacting an organic amine compound with a vinyl group with chloromethyl polysulfone; The thickness of the cation exchange membrane is 10-200 microns; the thickness of the anion exchange membrane is 10-150 microns; the thickness of the intermediate layer is 1-100 microns; The middle layer is made of vinyl imidazole and chloromethyl polymer through amination reaction, and then the vinyl groups on the vinyl imidazole can be cross-linked through free radical polymerization to prevent the loss of imidazole groups that have a catalytic effect of water dissociation; The organic amine compound with a vinyl group is vinyl imidazole; an initiator is added when the organic amine compound with a vinyl group reacts with chloromethyl polysulfone, and the amount of the initiator is 0.5-1% of the total molar ratio of the polymerization monomers; the initiator is azobisisobutyronitrile or dibenzoyl peroxide; The preparation method of the aminated chloromethyl polysulfone comprises the following steps: 1) Chloromethyl polysulfone is obtained by chloromethylation of polysulfone; 2) Chloromethyl polysulfone is subjected to amination reaction to obtain aminated chloromethyl polysulfone; In step 2), the amine reagent for the amination reaction is triolefin diamine.

2. The bipolar membrane according to claim 1, characterized in that The sulfonated polysulfone is prepared by a polysulfone sulfonation reaction, wherein the sulfonating agent of the sulfonation reaction is sulfuric acid, fuming sulfuric acid or chlorosulfonic acid; and the sulfonation exchange capacity of the sulfonated polysulfone is 1.5-1.

8.

3. The bipolar membrane according to claim 1, characterized in that In the step 1), the reagent for the chloromethylation reaction is chloromethyl ethyl ether or chloromethyl octyl ether; and the chloromethylation degree of the chloromethyl polysulfone is 0.1-1.

0.

4. The bipolar membrane according to claim 1, characterized in that In the step 2), polyvinylidene fluoride is added to the chloromethyl polysulfone for blending to reduce the swelling degree of the chloromethyl polysulfone.

5. A method for preparing a bipolar membrane according to any one of claims 1 to 4, characterized in that: The preparation method is preparation method 1 or preparation method 2, and the preparation method 1 comprises the following steps: (1) Anion exchange membrane was prepared using aminated chloromethyl polysulfone solution; (2) Adding an initiator to the reaction solution of the organic amine compound with a vinyl group and chloromethyl polysulfone, spraying or scraping the solution onto the surface of the anion exchange membrane after degassing, and drying to form an intermediate layer; (3) coating the sulfonated polysulfone solution on the surface of the intermediate layer and drying it to obtain a bipolar membrane; The second preparation method comprises the following steps: (1) Preparation of cation exchange membrane using sulfonated polysulfone solution; (2) Adding an initiator to the reaction solution of the organic amine compound with a vinyl group and chloromethyl polysulfone, spraying or scraping the solution onto the surface of the cation exchange membrane after degassing, and drying the solution to form an intermediate layer; (3) The aminated chloromethyl polysulfone solution is coated on the surface of the intermediate layer and dried to obtain a bipolar membrane.

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