A method for continuous production of a bipolar membrane

Abstract

The application discloses a kind of continuous production bipolar membrane method, comprising the following steps: 1) on PET base band, obtain the cation exchange layer covered with mesh cloth, and in the cation exchange layer, the wire diameter of the mesh cloth is at least 30-40% exposed;2) obtain the composite layer of cation exchange layer and intermediate layer, wherein the intermediate layer fills the hole between the mesh wire and wire, and the thickness of intermediate layer is 500nm-1000nm;3) obtain the anion exchange layer on the composite layer, and the anion exchange layer covers the mesh cloth completely;4) separate the film layer from PET base band, and the film layer is dried, rolled to obtain finished product bipolar membrane.The application solves the technical problems that the existing technology has not realized continuous and stable industrial production by using casting method to prepare bipolar membrane, and the film layer of bipolar membrane is easy to curl.

Description

Technical Field

[0001] This invention relates to a method for continuous production of bipolar membranes. Background Technology

[0002] In recent decades, ion exchange membranes have evolved from laboratory tools into industrial products with significant technological and commercial impact. Bipolar membranes are a special type of ion exchange membrane, composed of a cation exchange membrane, an intermediate layer, and an anion exchange membrane. Under the influence of a DC electric field, bipolar membranes can dissociate water molecules in the intermediate layer into H+. + and OH - This process generates acids and bases corresponding to salt ions. In recent years, bipolar membranes have been widely used in environmental pollution control, acid and base preparation, pharmaceutical industry, and seawater desalination, making a significant contribution to changing traditional industrial separation and preparation methods. An ideal bipolar membrane should possess advantages such as high permeability selectivity, low resistance, high current efficiency, and good chemical and mechanical stability. However, the high price, susceptibility to fouling, and instability of bipolar membranes currently severely restrict their development. Therefore, developing bipolar membranes that can achieve continuous industrial production, low cost, and low water dissociation voltage has become a major challenge in the development of EDBMs.

[0003] Chinese invention patent 202110079385.5 discloses a single-piece bipolar membrane roll with mesh support and its manufacturing method. The preparation steps are as follows: a cross-linked polystyrene-low molecular weight polyethylene composite membrane roll supported by ultra-high molecular weight polyethylene mesh is used as the substrate. One side is a cation exchange layer composed of sulfonated cross-linked polystyrene-low molecular weight polyethylene composite, and the other side is an anion exchange layer composed of quaternary ammonium cross-linked polystyrene-low molecular weight polyethylene composite. Between the two sides is a hydrolysis catalytic layer composed of tertiary ammonium cross-linked polystyrene-low molecular weight polyethylene composite. Although the single-piece bipolar membrane prepared by this method has a clear interface layer, the thickness accuracy and uniformity of the interface layer cannot be controlled. On the other hand, the functionalization of the entire membrane requires very high precision in reaction control.

[0004] Chinese invention patent 202110030016.7 discloses a method for preparing a semi-homogeneous bipolar membrane. The method is as follows: 1) Polyethylene and polyisobutylene are melt-blended and extruded into granules. After impregnation with styrene and divinylbenzene, the granules are polymerized with polyvinyl alcohol to obtain a plastic resin powder; 2) The plastic resin powder is sulfonated to obtain a semi-homogeneous cation resin, and then chloromethylated and quaternized to obtain a semi-homogeneous anion resin; 3) The plastic anion / cation resins are uniformly mixed with ion exchange resin powder, polyethylene powder, and titanium dioxide powder, respectively, and then melt-blended in a mixer and sheeted out in a two-roll mill to obtain single cation / anion resin sheets; 5) The cation / anion resin sheets are laminated together, covered with a reinforcing mesh, and pressed by a hot press to obtain a semi-homogeneous bipolar membrane. The semi-homogeneous bipolar membrane prepared by this method is actually a bipolar membrane obtained by simply hot-pressing and bonding a heterogeneous cation exchange membrane and anion exchange membrane, and has a high water dissociation voltage.

[0005] Chinese invention patents such as 201910403737.0, CN1250681A, CN116407955A, and CN110898861A all use the casting method to prepare bipolar films. However, none of these invention patents involve continuous industrial production, and most of the intermediate layers are prepared by spraying, resulting in poor thickness uniformity, high water dissociation voltage, and poor strength due to the lack of reinforcing mesh. Summary of the Invention

[0006] The purpose of this invention is to provide a method for continuous production of bipolar films, so as to solve the technical problems of the existing technology that the casting method for preparing bipolar films has not achieved continuous and stable industrial production and that the bipolar film layer is prone to curling.

[0007] The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions:

[0008] This invention provides a method for continuous production of bipolar films, comprising the following steps:

[0009] 1) The cation exchange layer casting solution is pumped into the first material tank, and after passing through the first transfer roller and being scraped to a certain thickness by a scraper, it is transferred to the PET base belt and then attached to the mesh cloth and put into the first drying oven for drying. The mesh cloth is made of PP, PE or PPS, with a mesh number of 80 to 120 mesh and a thickness of 0.18 to 0.22 mm. The cation exchange layer is obtained after exiting the first drying oven. In the cation exchange layer, at least 30 to 40% of the filament diameter of the mesh cloth is exposed (preferably 30 to 40% of the filament diameter of the mesh cloth is exposed).

[0010] 2) The intermediate layer liquid is pumped into the second material tank. The PET base belt loaded with the cation exchange layer passes through the second transfer roller. The intermediate layer liquid is carried through the second transfer roller and leveled by a scraper. The intermediate layer liquid is then transferred onto the cation exchange layer and enters the second drying oven. The composite layer of the cation exchange layer and the intermediate layer is obtained after exiting the second drying oven. The intermediate layer is filled in the pores between the mesh fibers and has a thickness of 500nm to 1000nm.

[0011] 3) The anion exchange layer casting solution is pumped into the third material tank. The PET base belt loaded with the composite layer passes through the third transfer roller. The anion exchange layer casting solution is carried through the third transfer roller and scraped to a certain thickness by a scraper. The anion exchange layer casting solution is then transferred to the intermediate layer and enters the third oven. In the third oven, the solvent residue of the overall coating is controlled at 10-15%. After exiting the third oven, the anion exchange layer is obtained, which completely covers the mesh fabric.

[0012] 4) Separate the film from the PET base tape after exiting the third drying oven. First, rewind the base tape, and then put the film into the fourth drying oven for drying. Control the residual solvent content of the film to be 3-5%. After exiting the fourth drying oven, rewind the film. The film is the finished bipolar film.

[0013] Preferably, excluding the exposed portion of the mesh in the cation exchange layer, the thickness of the cation exchange layer is 110-150 μm, and the thickness of the finished bipolar membrane is 210-250 μm.

[0014] Preferably, the viscosity of the cation exchange layer casting solution is 1000–3000 mPa·s, the viscosity of the anion exchange layer casting solution is 1000–2000 mPa·s, and the viscosity of the intermediate layer solution is 300–800 mPa·s.

[0015] Preferably, the casting solution for the cation exchange layer comprises a strongly acidic ion exchange resin and a DMF solvent; more preferably, the strongly acidic ion exchange resin is sulfonated polysulfone. Even more preferably, the thickness of the casting solution for the first transfer roller is 350–450 μm.

[0016] Preferably, the casting solution for the anion exchange layer comprises a strongly basic ion exchange resin and a DMF solvent. More preferably, the strongly basic ion exchange resin is chloro-amined polysulfone, which is obtained by polysulfone undergoing chloromethylation and amination reactions. The amination reagent for the amination reaction is preferably triethylamine. Even more preferably, the thickness of the casting solution on the third transfer roller is 280–380 μm.

[0017] Preferably, the intermediate layer casting solution is a mixed solution of cross-linked copolymer and cross-linked cation exchange resin powder, with a weight ratio of 100:10-20. The cross-linked copolymer is obtained by free radical copolymerization in solution of vinylpyridine, acrylic acid, and divinylbenzene in a mass ratio of 100:30-60:4-8. The composition of this intermediate layer casting solution results in the intermediate layer containing strong acid groups, weak acid groups, and weak base groups. Combined with a nanoscale coating, this effectively reduces the dissociation voltage of water.

[0018] As a further preferred embodiment, the initiator of the free radical copolymerization reaction is benzoyl peroxide, the solvent is DMF, the reaction temperature is 83-95°C, and the reaction time is 10-24 h.

[0019] As a further preferred embodiment, the cross-linked cation exchange resin powder has a particle size of 50–100 nm and an exchange capacity of 3.6–4.2 mmol / g.

[0020] As a further preferred embodiment, the preparation method of the intermediate layer casting solution is as follows: 1) Vinylpyridine, acrylic acid, divinylbenzene, solvent and initiator are added according to the mass ratio of 100:30~60:4~8:800~1200:2. After stirring and dissolving, the temperature is raised to 83~95℃ and reacted for 10~24h to obtain the crosslinked copolymer solution; 2) Crosslinked cation exchange resin powder is added in proportion and the crosslinked cation exchange resin powder is uniformly dispersed by high-speed stirring; 3) The viscosity of the intermediate layer casting solution is adjusted to a suitable range.

[0021] Preferably, the second transfer roller is a helical anilox roller with an anilox depth of 50–80 μm and a mesh size of 120; the first and third transfer rollers are mirror rollers. The second transfer roller used in the intermediate layer is a helical anilox roller, which can achieve quantitative coating, making the thickness of the intermediate interface layer uniform, and achieving a coating thickness of 500 nm to 1000 nm.

[0022] Preferably, the first, second, third, and fourth ovens are each composed of at least two oven sections connected together, and the temperature of each oven section increases sequentially from the inlet to the outlet.

[0023] Preferably, the lengths of the first and second ovens are 6–9 m; the length of the third oven is 6–12 m; and the length of the fourth oven is 12–24 m.

[0024] The strongly acidic ion exchange resin (such as sulfonated polysulfone) and cross-linked cation exchange resin described in this invention can be commercially available, while the strongly basic ion exchange resin (chloro-amine polysulfone) can be prepared by oneself according to the methods reported in the literature.

[0025] Preferably, when the strongly basic ion exchange resin is chloro-amine polysulfone, the present invention provides a method for preparing a continuous industrial production method of anion exchange layer casting solution, comprising the following steps:

[0026] 1) Ingredients: Add chloromethyl ether and anhydrous zinc chloride to the reaction vessel (701) in proportion and stir to dissolve;

[0027] 2) Dissolution: Dichloromethane and polysulfone are added to the reaction vessel (702) in proportion and stirred to dissolve, forming a transparent polymer solution;

[0028] 3) Chloromethylation reaction: The solution in the reaction vessel (701) is slowly added dropwise to the reaction vessel (702), and after the addition is complete, a reflux reaction is carried out;

[0029] 4) Alkaline cleaning: After the chlorine content (chlorine content refers to the mass ratio of chlorine atoms in the polysulfone molecular chain to the entire molecular chain) is qualified, the liquid in the reactor (702) is cooled to room temperature, and then the liquid is pumped into the reactor (703). Then, the alkaline solution in the reactor (707) is slowly added dropwise to the reactor (703). After stirring and cleaning, and settling to separate the layers to obtain the heavy phase liquid and cleaning wastewater, the heavy phase liquid is finally pumped into the reactor (704), and the cleaning wastewater is pumped into the wastewater tank. The alkaline solution is a weak alkaline aqueous solution.

[0030] 5) Pure water washing: Pure water is added to the reactor (704) for stirring and washing again. After standing and separating into layers, the heavy phase liquid and washing water are obtained. Finally, the heavy phase liquid is separated into the reactor (705). During the separation of the heavy phase liquid, it is ensured that no water is transferred with the heavy phase liquid. The washing water is separated into the reactor (707) and reused in the next batch of alkali solution.

[0031] 6) Amination reaction: The liquid in the reactor (705) is subjected to vacuum distillation to distill off part of the dichloromethane. After cooling, a part of fresh dichloromethane is added and N,N-dimethylformamide (DMF) is added and stirred evenly. The liquid is then pumped into the reactor (706), and triethylamine is added dropwise to carry out the amination reaction.

[0032] 7) After the amination reaction is completed, the remaining dichloromethane and unreacted triethylamine are distilled off under reduced pressure. After the viscosity of the solution is tested and found to be qualified, it is filtered and packaged to obtain the casting solution for anion exchange membranes.

[0033] The dichloromethane has a water content ≤0.1%; the triethylamine content is ≥99%, and the water content is ≤0.1%. Both the water content and the triethylamine content are mass fractions.

[0034] The key points of the above preparation method are: First, after the chloromethylation reaction, during the washing process of adding alkaline solution and pure water to the reaction solution, it is necessary to ensure that chloromethyl ether and anhydrous zinc chloride are thoroughly cleaned while preventing chloromethyl polysulfone from precipitating out; Second, after the chloromethylation reaction, the reaction solution is washed with pure water, and after standing and separating into layers, during the transfer of the heavy phase solution, it is necessary to ensure that no water is transferred with the heavy phase, otherwise gelation will occur during the amination process; Third, the water content of dichloromethane and triethylamine must be strictly controlled to ≤0.1%, that is, the water content of the materials during the reaction process must be strictly controlled, otherwise gelation is likely to occur during the reaction.

[0035] Preferably, the weight ratio of chloromethyl ether: anhydrous zinc chloride: dichloromethane: polysulfone is 50-70: 10-25: 700-900: 50.

[0036] Preferably, the alkaline solution is a sodium bicarbonate solution with a mass percentage concentration of 10-20%.

[0037] Preferably, the weight ratio of polysulfone:alkaline solution:pure water is 50:150-250:150-250.

[0038] Preferably, the weight ratio of polysulfone:N,N-dimethylformamide (DMF):triethylamine is 50:200-300:15-25.

[0039] Preferably, in step 3), the drop rate of the solution in the reactor (701) is 70-80 kg / h.

[0040] Preferably, in step 3), the chloromethylation reaction temperature is 38–42°C and the reaction time is 40–60 h.

[0041] Preferably, in step 4), the chlorine content is controlled at 5-8%.

[0042] Preferably, in step 4), the drip rate of the alkaline solution in the reactor (707) is 150-250 kg / h.

[0043] Preferably, in step 4), the stirring and washing time is 1-2 hours and the standing time is 1-3 hours.

[0044] Preferably, in step 5), the stirring and cleaning time is 1-2 hours and the standing time is 1-3 hours.

[0045] Preferably, in step 6), a portion of dichloromethane is distilled off, with the distilled volume being 40-70% of the total volume of the initial solvent; a portion of fresh dichloromethane is added, with the added volume being 7-15% of the total volume of the initial solvent.

[0046] Preferably, in step 6), the amination reaction temperature is 38–42°C and the reaction time is 12–24 h.

[0047] Preferably, in step 7), the viscosity of the casting solution is controlled between 800 and 3000 mPa·s, and the solid content is controlled between 14% and 20%. If the viscosity is greater than 3000 mPa·s, it is difficult to remove air bubbles during the film-forming process; if the viscosity is less than 800 mPa·s, it is easy to flow and cast during the film-forming process, resulting in uneven film thickness.

[0048] Preferably, the capacity of reactors 702 to 706 is 2000L to 10000L, and the capacity of reactors 701 and 702 is 500L to 2000L.

[0049] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0050] First, the bipolar membrane reinforced with mesh was prepared by casting method, which optimized the production process, realized the continuous industrial production of bipolar membrane, reduced labor intensity and improved product quality.

[0051] Secondly, by controlling the thickness of the mesh, after coating the mesh with cation exchange casting solution, the cation exchange layer is dried to a certain extent in the first oven. The cation exchange layer does not completely fill the pores between the mesh fibers. The intermediate layer is applied to the cation exchange layer, that is, the intermediate layer is fixed in the pores between the mesh fibers, and part of the fiber diameter is still exposed. Finally, the anion exchange layer is applied to completely coat and cover the mesh. This method can avoid the cation exchange layer, anion exchange layer and intermediate layer from having different water absorption rates, and ensure that the size expansion of each layer is basically the same, thereby solving the problem of bipolar membrane curling.

[0052] Third, by controlling the degree of drying after coating, the bipolar film and PET base tape can be separated on the production line. If the degree of drying after coating is too high, the film and base tape will stick together too much and need to be soaked in water before separation. If the degree of drying after coating is too low, the film will contain too much solvent after separation, and the film will stick to the roller when it enters the fourth drying oven.

[0053] Fourth, the composition of the intermediate layer casting solution results in the presence of strong acid groups, weak acid groups, and weak base groups in the intermediate layer. Combined with the nanoscale coating, this effectively reduces the dissociation voltage of water.

[0054] Fifth, the transfer roller used in the intermediate interface layer is a spiral knitted roller, which can achieve quantitative coating, making the thickness of the intermediate interface layer uniform and achieving a coating thickness of 500nm to 1000nm.

[0055] Sixth, the anion exchange layer casting solution prepared by this invention enables the entire reaction and operation to be completed inside the reactor. That is, after the chloromethylation reaction is completed, there is no need for external operation steps such as precipitation, filtration, and drying of chloromethylated polysulfone. This optimizes the production process, reduces labor intensity, and realizes continuous industrial production. Attached image description:

[0056] Figure 1 This is a flow chart of the continuous bipolar film production process of the present invention. In the figure: 1-PET unwinding device; 2, 10, 17-first, second, and third feed trough baffles; 3-first transfer roller; 4, 12, 19-first, second, and third scrapers; 5, 13, 20-first, second, and third liquid level sensors; 6, 14, 21-first, second, and third electronic valves; 7, 15, 22-first, second, and third feed tanks; 8-mesh unwinding device; 9-first drying oven; 11-second transfer roller; 16-second drying oven; 18-third transfer roller; 23-third drying oven; 24-winding device; 25-fourth drying oven; 26-film winding device; 27, 28, 29-deviation correction device; 30-mesh tension control system.

[0057] Figure 2 This is a plan view of the drying device (first, second, third and fourth drying ovens) of the present invention; in the figure: 9-1 fresh air inlet and air valve; 9-2 internal circulation air inlet and air valve; 9-3 circulating fan; 9-4 heating pack; 9-5 lower air inlet and air valve; 9-6 upper air inlet and air valve; 9-7 lower hull; 9-8 upper hull; 9-9 exhaust air inlet and air valve.

[0058] Figure 3 This is a schematic diagram of the cross-section of the bipolar membrane prepared by the present invention, wherein 31-anion exchange layer, 32-intermediate layer, 33-cation exchange layer, and 34-mesh filament.

[0059] Figure 4 This is a production process flow diagram of the anion exchange layer casting solution of the present invention, wherein 701, 702, 703, 704, 705, and 706 are all reaction vessels. Detailed implementation method:

[0060] The present invention will be further described below with reference to specific embodiments.

[0061] refer to Figure 1 An apparatus for continuously producing bipolar films includes a mounting bracket on which an unwinding device 1 and a winding device 24, on which a PET base tape is wound, are mounted. One end of the base tape is connected to the unwinding device 1 and the other end is connected to the winding device 24 to complete the conveying of the PET base tape. Above the base tape between the unwinding device 1 and the winding device 24, a first automatic feeding device, a second automatic feeding device, and a third automatic feeding device are arranged sequentially from left to right.

[0062] The first automatic feeding device, the second automatic feeding device, and the third automatic feeding device each include a first liquid tank 7, a second liquid tank 15, and a third liquid tank 22. A first coating transfer device, a second coating transfer device, and a third coating transfer device are respectively arranged below the first liquid tank 7, the second liquid tank 15, and the third liquid tank 22. A first drying oven 9, a second drying oven 16, and a third drying oven 23 are respectively arranged between the first coating transfer device and the second coating transfer device, between the second coating transfer device and the third coating transfer device, and at the rear end of the third coating transfer device.

[0063] The outlet end of the first liquid tank 7 is connected to one end of the first liquid delivery pipe, and the other end of the first liquid delivery pipe is used in conjunction with the first material tank; the outlet end of the second liquid tank 15 is connected to one end of the second liquid delivery pipe, and the other end of the second liquid delivery pipe is used in conjunction with the second material tank; the outlet end of the third liquid tank 22 is connected to one end of the third liquid delivery pipe, and the other end of the third liquid delivery pipe is used in conjunction with the third material tank.

[0064] The outlet end of the third oven 23 is provided with a film winding device 26 for winding the film layer. The film layer is connected to the base tape wound on the film winding device 26 by manual operation. A fourth oven 25 is provided on the base tape of the film winding device 26.

[0065] In one embodiment, the first coating transfer device includes a first scraper 4, a first transfer roller 3, and a first material trough baffle 2. The first material trough baffle 2 is inclinedly disposed below the first transfer roller 3, and the lower end of the first material trough baffle 2 contacts the first transfer roller 3. The first material trough is formed between the first material trough baffle 2 and the first transfer roller 3. The other end of the first liquid delivery pipe corresponds to the first material trough. The first scraper 4 is disposed above the first transfer roller 3, and the bottom of the first scraper 4 has a first gap with the upper end face of the first transfer roller 3. The size of the first gap is 350~450um.

[0066] The second coating transfer device includes a second doctor blade 12, a second transfer roller 11, and a second material trough baffle 10. The second material trough baffle 10 is inclinedly disposed below the second transfer roller 11, and the lower end of the second material trough baffle 10 contacts the second transfer roller 11, forming a second material trough between the second material trough baffle 10 and the second transfer roller 11. The other end of the second liquid delivery pipe corresponds to the second material trough. The second doctor blade 12 is disposed above the second transfer roller 11, and the bottom of the second doctor blade 12 has a second gap with the upper end face of the second transfer roller 11. The size of the second gap is 500nm to 1000nm.

[0067] The third coating transfer device includes a third doctor blade 19, a third transfer roller 18, and a third material trough baffle 17. The third material trough baffle 17 is inclinedly disposed below the third transfer roller 18, and the lower end of the third material trough baffle 17 contacts the third transfer roller 18. The third material trough is formed between the third material trough baffle 17 and the third transfer roller 18. The other end of the third liquid delivery pipe corresponds to the third material trough. The third doctor blade 19 is disposed above the third transfer roller 18, and the bottom of the third doctor blade 19 has a third gap with the upper end face of the third transfer roller 18. The size of the third gap is 280~380um.

[0068] In one embodiment, a mesh tension control system is arranged above the base belt on the inlet side of the first oven. The mesh tension control system includes a mesh unwinding device 8 and a mesh tension control device 30. The mesh is wound on the mesh unwinding device 8 and one end can be manually fixed to the base belt. The mesh tension control device 30 is disposed on the mesh to control the tension of the mesh. When the mesh tension is too low, the mesh tension control device can be moved downward. When the mesh tension is too high, the mesh tension control device can be moved upward.

[0069] In one embodiment, a first electronic valve 6 and a first liquid level sensor 5 are installed on the first liquid delivery pipe, and the opening and closing of the first electronic valve is controlled by the first liquid level sensor; a second electronic valve 14 and a second liquid level sensor 13 are installed on the second liquid delivery pipe, and the opening and closing of the second electronic valve is controlled by the second liquid level sensor; a third electronic valve 21 and a third liquid level sensor 20 are installed on the third liquid delivery pipe, and the opening and closing of the third electronic valve is controlled by the third liquid level sensor.

[0070] In one embodiment, pumps are respectively installed on the first, second, and third liquid delivery pipes.

[0071] In one embodiment, the first, second, third, and fourth ovens have the same structure.

[0072] In one embodiment, the lengths of the first and second ovens are 6–9 m; the length of the third oven is 6–12 m; and the length of the fourth oven is 12–24 m.

[0073] In one embodiment, the second transfer roller 11 is a spiral knitted roller with a knitting depth of 50-80 μm and a mesh count of 120 mesh; the first and third transfer rollers 3 and 18 are both mirror rollers.

[0074] In one embodiment, the device further includes a correction device 27, 28, 29, which is disposed on the base tape at the front end of the first liquid tank, the base tape at the front end of the winding device, and the base tape at the front end of the film winding device, and is used for correction of the base tape.

[0075] In one embodiment, the material of the mesh is one of PP, PE or PPS, with a mesh count of 80 to 120 mesh and a thickness of 0.18 to 0.22 mm.

[0076] The specific steps for preparing bipolar films using the above-mentioned equipment are as follows:

[0077] 1) The first electronic valve 6 is switched on and off by the first liquid level sensor 5. The cation exchange layer casting liquid in the first material tank 7 is pumped into the first material tank (between the first material tank baffle and the first transfer roller 3). After being carried by the first transfer roller 3 and scraped to a certain thickness by the first scraper 4, it is transferred to the PET base belt and then attached to the mesh fabric unwound by the mesh fabric unwinding device 8. It is then put into the first drying oven 9 with a length of 6m for drying. The cation exchange layer is obtained after exiting the first drying oven 9.

[0078] 2) The second electronic valve 14 is switched on and off by the second liquid level sensor 13. The intermediate layer liquid in the second liquid tank 15 is pumped into the second material tank (between the second material tank baffle 10 and the second transfer roller 11). The cation exchange layer and the base belt pass through the second transfer roller 11 with a texture depth of 60um. The intermediate layer liquid is carried by the second transfer roller 11 and scraped flat by the second scraper 12. The intermediate layer liquid is transferred to the cation exchange layer and then enters the second drying oven 16 with a length of 6m. The composite layer of cation exchange layer and intermediate layer is obtained after exiting the second drying oven 16.

[0079] 3) The third electronic valve 21 is switched on and off by the third liquid level sensor 20. The anion exchange layer casting solution in the third material tank 22 is pumped into the third material tank (between the third material tank baffle 17 and the third transfer roller 18). The composite layer and the base strip pass through the third transfer roller 18. The anion exchange layer casting solution is carried by the third transfer roller 18 and scraped to a certain thickness by the third scraper 19. The anion exchange layer casting solution is transferred to the intermediate layer and then enters the third drying oven 23 with a length of 12m. After exiting the third drying oven 23, the film layer and the base strip are separated (the base strip on the film winding device 26 is manually connected to the film layer). The base strip is first corrected by the correction device 28 and then wound into the PET winding device 24. The film layer then enters the fourth drying oven 25 with a length of 18m for drying. After exiting the fourth drying oven 25, the film layer is corrected by the correction system 29 and then wound into the film winding device 26. The film layer is the finished bipolar film.

[0080] The air paths for the drying units (i.e., the first, second, third, and fourth drying ovens) are as follows: (Refer to...) Figure 2Cold air enters through the fresh air inlet and air valve, mixes with the internal circulation air, and then enters the heating pack 9-4 through the internal circulation air inlet and air valve 9-2 and the circulating fan 9-3. After being heated, it enters the lower hull 9-7 through the lower air inlet and air valve 9-5, and enters the upper hull 9-8 through the upper air inlet and air valve 9-6. Hot air is blown out from the air nozzle and then discharged through the exhaust port and air valve 9-9.

[0081] Preparation of intermediate layer casting solution:

[0082] 1) Add vinylpyridine, acrylic acid, divinylbenzene, DMF, and initiator benzoyl peroxide in a mass ratio of 100:30-60:4-8:800-1200:2. After stirring and dissolving, raise the temperature to 83°C and react for 10 hours. Then raise the temperature to 90°C and react for 6 hours to obtain a crosslinked copolymer solution of vinylpyridine, acrylic acid, and divinylbenzene. 2) Add crosslinked cation exchange resin powder to the copolymer solution in step 1) in a mass ratio of copolymer to crosslinked cation exchange resin powder of 100:10-20. Stir at high speed to evenly disperse the crosslinked cation exchange resin powder. 3) Adjust the viscosity by adding appropriate solvent to adjust the viscosity to 300-800 mPa·s.

[0083] Preparation of anion exchange casting solution:

[0084] 1) Ingredient Preparation: Add 420 kg of chloromethyl ether and 140 kg of anhydrous zinc chloride to a 1000 L reactor 701 and stir to dissolve; 2) Dissolution: Add 6000 kg of dichloromethane (distilled before use to control the water content to ≤0.1%) and 350 kg of polysulfone (dried at 105℃ for 24 h before use) to a 10000 L reactor 702 in proportion and stir to dissolve, forming a transparent polymer solution; 3) Chloromethylation Reaction: Slowly add the solution from reactor 701 to reactor 702 dropwise, completing the addition in about 7 hours. Heat reactor 702 to 40℃ and maintain the temperature under reflux for 58 hours (sample for chlorine content testing after 54 hours of reaction); 4) Alkali Cleaning: With a chlorine content of 7.1% (qualified), cool the solution in reactor 702 to room temperature, then transfer the solution to a 10000 L reactor 703. Then, 1400 kg of 10% sodium bicarbonate solution from reactor 707 (2000L) is slowly added dropwise to reactor 703 over 7-8 hours. After the addition is complete, the mixture is stirred and cleaned for 2-3 hours, then allowed to stand for about 4 hours to separate into layers. Finally, the heavy phase solution is transferred to reactor 704 (10000L), and the cleaning wastewater is discharged to a wastewater tank. 5) Pure water cleaning: 1400 kg of pure water is added to reactor 704 and stirred and cleaned again for 2-3 hours, then allowed to stand for about 4 hours to separate into layers. Finally, the heavy phase solution is separated into reactor 705 (10000L), and the cleaning water is separated into reactor 707 (to be reused in the next batch of alkali solution). 6) Amination reaction: The solution in reactor 705 is subjected to vacuum distillation to distill off some dichloromethane (the amount distilled off is controlled at about 4000 kg). After cooling, 800 kg of fresh dichloromethane is added, along with 1800-2200 kg of pure water. After stirring N,N-dimethylformamide (DMF) evenly, the solution is poured into a 10000L reactor 706, and then 130kg of triethylamine (triethylamine content ≥99%, water content ≤0.1%) is added dropwise. After the addition is completed, the temperature is raised to 40℃ to carry out the amination reaction for 16h; 7) After the amination reaction is completed, the remaining dichloromethane and unreacted triethylamine are distilled off. The viscosity of the casting solution is controlled at 1000~2000mPa·s. After filtration with a 200-mesh filter, the casting solution for anion exchange membranes is obtained.

[0085] Preparation of cationic layer casting solution:

[0086] Sulfonated polysulfone (commercially available, with an exchange capacity of 1.1–1.2 mmol / g) is first dried at 80°C to a moisture content of ≤0.1%. Then, sulfonated polysulfone and DMF solvent are stirred and dissolved at a mass ratio of 20:60–80, with the dissolution temperature controlled at 40°C. After the sulfonated polysulfone is completely dissolved, the solution is filtered through a 200-mesh filter to obtain the casting solution for cation exchange membranes. The viscosity of the casting solution is controlled at 1000–3000 mPa·s.

[0087] Example 1: The preparation method of the continuous production of bipolar film in this example includes the following steps:

[0088] 1) The first electronic valve 6 is switched on and off by the first liquid level sensor 5. The cation exchange layer casting solution (viscosity of 2000 mPa·s) in the first material tank 7 is pumped into the first material tank (between the first material tank baffle 2 and the first transfer roller 3). After being carried by the first transfer roller 3 and scraped to a thickness of 400 μm by the first scraper 4, it is transferred (transfer speed of 0.25 m / min) to the PET base belt. Then, PPS mesh (mesh thickness of 0.2 mm, 100 mesh) unwound by the mesh unwinding device 8 is attached and put into the first drying oven 9 (two sections of drying oven connected, each section is 3 m, and the temperatures are 50℃ and 70℃ respectively) for drying. The cation exchange layer (the exposed part of the mesh is 0.065~0.07 mm) is obtained after exiting the first drying oven 9.

[0089] 2) The second electronic valve 14 is switched on and off by the second liquid level sensor 13. The intermediate layer liquid (viscosity of 500 mPa·s) in the second liquid tank 15 is pumped into the second material tank (between the second material tank baffle 10 and the second transfer roller 11). The cation exchange layer and the base belt pass through the second transfer roller 11 with a mesh depth of 60 μm and a mesh number of 120. The intermediate layer casting liquid is carried by the second transfer roller 11 and scraped flat by the second scraper 12. After the intermediate layer liquid is transferred to the cation exchange layer, it enters the second oven 16 with a length of 6 m (two oven sections are connected, each section is 3 m long, and the temperatures are 50℃ and 70℃ respectively). The composite layer of cation exchange layer and intermediate layer (the exposed part of the mesh is 0.065~0.07 mm) is obtained after exiting the second oven 16.

[0090] 3) The third electronic valve 21 is switched on and off by the third liquid level sensor 20. The anion exchange layer casting solution (viscosity 1500 mPa·s) in the third material tank 22 is pumped into the third material tank (between the third material tank baffle 17 and the third transfer roller 18). The composite layer and the base strip pass through the third transfer roller 18. The anion exchange layer casting solution is carried by the third transfer roller 18 and scraped to a thickness of 320 μm by the third scraper 19. After the anion exchange layer casting solution is transferred to the intermediate layer, it enters the third drying oven 23 (four sections of drying oven connected, each section is 3m long, with temperatures of 50℃, 60℃, 70℃ and 80℃ respectively). After exiting the third oven 23, the film layer (with a solvent residue of 13.8%) is separated from the base tape (the base tape on the film winding device 26 is manually connected to the film layer). The base tape is first corrected by the correction device 28 and then wound into the PET winding device 24. The film layer then enters the fourth oven 25 (six oven sections connected, each 3m long, with temperatures of 80℃, 90℃, 100℃, 110℃, 115℃ and 120℃) for drying. After exiting the fourth oven 25 (with a solvent residue of 3.9%), the film layer is corrected by the correction system 29 and then wound into the film winding device 26. The film layer is the finished bipolar film.

[0091] In the preparation of the intermediate layer casting solution, the mass ratio of vinylpyridine: acrylic acid: divinylbenzene: solvent: initiator benzoyl peroxide: cross-linked cation exchange resin powder (sulfonated cross-linked polystyrene resin, particle size of 60nm, exchange capacity of 4.0mmol / g) is 100:45:6:1000:2:20.

[0092] According to the testing method of industry standard HG / T 6093-2022 "Bipolar Membrane", the thickness of the bipolar membrane is 245um and the water dissociation voltage is 1.23V.

[0093] The test method for solvent residue is as follows: First, weigh the sample mass m1, then soak the sample in water for 4 hours, take it out, wipe the surface water dry, and then put the sample into an oven. Set the oven temperature to 105℃ and the drying time to 2 hours. Take out the sample, cool it, and weigh it. The mass is m2. The solvent residue is (m1-m2) / m1*100%.

[0094] Example 2: The preparation method of the continuous production of bipolar film in this example includes the following steps:

[0095] 1) The first electronic valve 6 is switched on and off by the first liquid level sensor 5. The cation exchange layer casting solution (viscosity of 2000 mPa·s) in the first material tank 7 is pumped into the first material tank (between the first material tank baffle 2 and the first transfer roller 3). After being carried by the first transfer roller 3 and scraped to a thickness of 350 μm by the first scraper 4 (transfer speed of 0.25 m / min), it is transferred to the PET base belt. Then, PPS mesh (mesh thickness of 0.18 mm, 120 mesh) unwound by the mesh unwinding device 8 is attached and put into the first drying oven 9 (two sections of drying oven connected, each section is 3 m, with temperatures of 50℃ and 70℃ respectively) for drying. The cation exchange layer (the exposed part of the mesh is 0.06~0.065 mm) is obtained after exiting the first drying oven 9.

[0096] 2) The second electronic valve 14 is switched on and off by the second liquid level sensor 13. The intermediate layer liquid (viscosity of 300 mPa·s) in the second liquid tank 15 is pumped into the second material tank (between the second material tank baffle 10 and the second transfer roller 11). The cation exchange layer and the base belt pass through the second transfer roller 11 with a mesh depth of 80 μm. The intermediate layer liquid is carried by the second transfer roller 11 and scraped flat by the scraper 12. After the intermediate layer liquid is transferred to the cation exchange layer, it enters the second drying oven 16 with a length of 6 m (two drying oven sections are connected, each section is 3 m long, and the temperatures are 50℃ and 70℃ respectively). The composite layer of cation exchange layer and intermediate layer (the exposed part of the mesh is 0.06~0.065 mm) is obtained after exiting the second drying oven 16.

[0097] 3) The third electronic valve 21 is switched on and off by the third liquid level sensor 20. The anion exchange layer casting solution (viscosity 1500 mPa·s) in the third material tank 22 is pumped into the third material tank (between the third material tank baffle 17 and the third transfer roller 18). The composite layer and the base strip pass through the third transfer roller 18. The anion exchange layer casting solution is carried by the third transfer roller 18 and scraped to a thickness of 300 μm by the third scraper 19. After the anion exchange layer casting solution is transferred to the intermediate layer, it enters the third drying oven 23 (four sections of drying oven connected, each section 3m long, with temperatures of 50℃, 60℃, 70℃ and 80℃ respectively). After exiting the third oven 23, the film layer (with a solvent residue of 13.2%) is separated from the base tape (the base tape on the film winding device 26 is manually connected to the film layer). The base tape is first corrected by the correction device 28 and then wound into the PET winding device 24. The film layer then enters the fourth oven 25 (six oven sections connected, each 3m long, with temperatures of 80℃, 90℃, 100℃, 110℃, 115℃ and 120℃) for drying. After exiting the fourth oven 25 (with a solvent residue of 3.5%), the film layer is corrected by the correction system 29 and then wound into the film winding device 26. The film layer is the finished bipolar film.

[0098] The mass ratio of the intermediate layer vinylpyridine: acrylic acid: divinylbenzene: solvent: initiator benzoyl peroxide: cross-linked cation exchange resin powder (sulfonated cross-linked polystyrene resin, particle size of 50nm, exchange capacity of 4.0mmol / g) is 100:45:6:1200:2:20.

[0099] According to the testing method of industry standard HG / T 6093-2022 "Bipolar Membrane", the thickness of the bipolar membrane is 220um and the water dissociation voltage is 1.18V.

[0100] Example 3: The preparation and method of continuous production of bipolar films in this example, the steps of which are as follows:

[0101] 1) The first electronic valve 6 is switched on and off by the first liquid level sensor 5. The cation exchange layer casting solution (viscosity of 2500 mPa·s) in the first material tank 7 is pumped into the first material tank (between the first material tank baffle 2 and the first transfer roller 3). After being carried by the first transfer roller 3 and scraped to a thickness of 400 μm by the first scraper 4 (transfer speed of 0.25 m / min), it is transferred to the PET base belt. Then, a PE mesh (mesh thickness of 0.2 mm, 100 mesh) unwound by the mesh unwinding device 8 is attached and put into the first drying oven 9 (two sections of drying oven connected, each section 4 m, with temperatures of 50℃ and 70℃ respectively) for drying. The cation exchange layer (the exposed part of the mesh is 0.06~0.065 mm) is obtained after exiting the first drying oven 9.

[0102] 2) The second electronic valve 14 is switched on and off by the second liquid level sensor 13. The intermediate layer liquid (viscosity of 500 mPa·s) in the second liquid tank 15 is pumped into the second material tank (between the second material tank baffle 10 and the second transfer roller 11). The cation exchange layer and the base belt pass through the second transfer roller 11 with a mesh depth of 50 μm. The intermediate layer liquid is carried by the second transfer roller 11 and scraped flat by the second scraper 12. After the intermediate layer liquid is transferred to the cation exchange layer, it enters the second drying oven 16 with a length of 8 m (two drying oven sections are connected, each section is 4 m long, and the temperatures are 50℃ and 70℃ respectively). The composite layer of cation exchange layer and intermediate layer (the exposed part of the mesh is 0.06~0.065 mm) is obtained after exiting the second drying oven 16.

[0103] 3) The third electronic valve 21 is switched on and off by the third liquid level sensor 20, and the anion exchange layer casting solution (viscosity 1800 mPa·s) in the third material tank 22 is pumped into the third material tank (between the third material tank baffle 17 and the third transfer roller 18). The composite layer and the base strip pass through the third transfer roller 18. The anion exchange layer casting solution is carried by the third transfer roller 18 and scraped to a thickness of 320 μm by the third scraper 19. After the anion exchange layer casting solution is transferred to the intermediate layer, it enters the third drying oven 23 (four sections of drying oven connected, each section 4m long, with temperatures of 50℃, 60℃, 70℃ and 160℃ respectively). After exiting the third oven 23 (80℃), the film layer (with a solvent residue of 11.9%) is separated from the base tape (the base tape on the film winding device 26 is manually connected to the film layer). The base tape is first corrected by the correction device 28 and then wound into the PET winding device 24. The film layer then enters the fourth oven 25 (six oven sections connected, each 4m long, with temperatures of 80℃, 90℃, 100℃, 110℃ and 120℃) for drying. After exiting the fourth oven 25 (with a solvent residue of 3.7%), the film layer is corrected by the correction system 29 and then wound into the film winding device 26. The film layer is the finished bipolar film.

[0104] The mass ratio of the intermediate layer vinylpyridine: acrylic acid: divinylbenzene: solvent: initiator benzoyl peroxide: cross-linked cation exchange resin powder (sulfonated cross-linked polystyrene resin, particle size of 70nm, exchange capacity of 4.2mmol / g) is 100:30:4:1000:2:25.

[0105] According to the testing method of industry standard HG / T 6093-2022 "Bipolar Membrane", the thickness of the bipolar membrane is 240um and the water dissociation voltage is 1.10V.

[0106] Example 4: The preparation and method of continuous production of bipolar films in this example, the steps of which are as follows:

[0107] 1) The first electronic valve 6 is switched on and off by the first liquid level sensor 5. The cation exchange layer casting solution (viscosity of 2000 mPa·s) in the first material tank 7 is pumped into the first material tank (between the first material tank baffle 2 and the first transfer roller 3). After being carried by the first transfer roller 3 and scraped to a thickness of 420 μm by the first scraper 4 (transfer speed of 0.25 m / min), it is transferred to the PET base belt. Then, a PP mesh (mesh thickness of 0.22 mm, 80 mesh) unwound by the mesh unwinding device 8 is attached and put into the first drying oven 9 (two sections of drying oven connected, each section is 3 m, with temperatures of 50℃ and 70℃ respectively) for drying. The cation exchange layer (the exposed part of the mesh is 0.07~0.075 mm) is obtained after exiting the first drying oven 9.

[0108] 2) The second electronic valve 14 is switched on and off by the second liquid level sensor 13. The intermediate layer liquid (viscosity of 650 mPa·s) in the second liquid tank 15 is pumped into the second material tank (between the second material tank baffle 10 and the second transfer roller 11). The cation exchange layer and the base belt pass through the second transfer roller 11 with a mesh depth of 50 μm. The intermediate layer liquid is carried by the second transfer roller 11 and scraped flat by the second scraper 12. After the intermediate layer liquid is transferred to the cation exchange layer, it enters the second drying oven 16 with a length of 6 m (two drying oven sections are connected, each section is 3 m long, and the temperatures are 50℃ and 70℃ respectively). The composite layer of cation exchange layer and intermediate layer (the exposed part of the mesh is 0.07~0.075 mm) is obtained after exiting the second drying oven 16.

[0109] 3) The third electronic valve 21 is switched on and off by the third liquid level sensor 20. The anion exchange layer casting solution (viscosity 1200 mPa·s) in the third material tank 22 is pumped into the third material tank (between the third material tank baffle 17 and the second transfer roller 18). The composite layer and the base belt pass through the third transfer roller 18. The anion exchange layer casting solution is carried by the third transfer roller 18 and scraped to a thickness of 360 μm by the third scraper 19. After the anion exchange layer casting solution is transferred to the intermediate layer, it enters the third drying oven 23 (four sections of drying oven connected together, each section 3m long, with temperatures of 50℃, 60℃, 70℃ and 80℃ respectively). After exiting the third oven 23, the film layer (with a solvent residue of 14.2%) is separated from the base tape (the base tape on the film winding device 26 is manually connected to the film layer). The base tape is first corrected by the correction device 28 and then wound into the PET winding device 24. The film layer then enters the fourth oven 25 (six oven sections connected, each 4m long, with temperatures of 80℃, 90℃, 100℃, 110℃, 115℃ and 120℃) for drying. After exiting the fourth oven 25 (with a solvent residue of 3.2%), the film layer is corrected by the correction system 29 and then wound into the film winding device 26. The film layer is the finished bipolar film.

[0110] The mass ratio of the intermediate layer vinylpyridine: acrylic acid: divinylbenzene: solvent: initiator benzoyl peroxide: cross-linked cation exchange resin powder (sulfonated cross-linked polystyrene resin, particle size of 80nm, exchange capacity of 3.6mmol / g) is 100:60:6:850:2:15.

[0111] According to the testing method of industry standard HG / T 6093-2022 "Bipolar Membrane", the thickness of the bipolar membrane is 245um and the water dissociation voltage is 1.13V.

Claims

1. A method for continuous production of bipolar films, characterized in that: The method includes the following steps: 1) The cation exchange layer casting solution is pumped into the first material tank, and after passing through the first transfer roller and being scraped to a certain thickness by a scraper, it is transferred to the PET base belt and then attached to the mesh cloth and put into the first drying oven for drying. The mesh cloth is made of PP, PE or PPS, with a mesh number of 80~120 mesh and a thickness of 0.18~0.22mm. The cation exchange layer is obtained after exiting the first drying oven. In the cation exchange layer, at least 30~40% of the filament diameter of the mesh cloth is exposed. 2) The intermediate layer liquid is pumped into the second material tank. The PET base belt loaded with the cation exchange layer passes through the second transfer roller. The intermediate layer liquid is carried through the second transfer roller and leveled by a scraper. The intermediate layer liquid is then transferred onto the cation exchange layer and enters the second drying oven. The composite layer of the cation exchange layer and the intermediate layer is obtained after exiting the second drying oven. The intermediate layer is filled in the pores between the mesh fibers and has a thickness of 500nm~1000nm. 3) The anion exchange layer casting solution is pumped into the third material tank. The PET base belt loaded with the composite layer passes through the third transfer roller. The anion exchange layer casting solution is carried through the third transfer roller and scraped to a certain thickness by a scraper. The anion exchange layer casting solution is then transferred to the intermediate layer and enters the third oven. In the third oven, the solvent residue of the overall coating is controlled at 10~15%. After exiting the third oven, the anion exchange layer is obtained, which completely covers the mesh fabric. 4) Separate the film from the PET base tape after exiting the third drying oven. First, rewind the base tape, and then put the film into the fourth drying oven for drying. Control the residual solvent content of the film to be 3-5%. After exiting the fourth drying oven, rewind the film. The film is the finished bipolar film.

2. The method as described in claim 1, characterized in that: Excluding the exposed portion of the mesh in the cation exchange layer, the thickness of the cation exchange layer is 110-150 μm, and the thickness of the finished bipolar membrane is 210-250 μm.

3. The method as described in claim 1 or 2, characterized in that: The viscosity of the cation exchange layer casting solution is 1000~3000 mPa·s, the viscosity of the anion exchange layer casting solution is 1000~2000 mPa·s, and the viscosity of the intermediate layer solution is 300~800 mPa·s.

4. The method as described in claim 3, characterized in that: The cation layer casting solution is composed of a strong acidic ion exchange resin and DMF solvent.

5. The method as described in claim 4, characterized in that: The strongly acidic ion exchange resin is sulfonated polysulfone.

6. The method as described in claim 3, characterized in that: The anion exchange layer casting solution is composed of a strong basic ion exchange resin and DMF solvent. The strong basic ion exchange resin is chloro-amined polysulfone, which is obtained by polysulfone through chloromethylation and amination reactions. The amination reagent in the amination reaction is triethylamine.

7. The method as described in claim 3, characterized in that: The intermediate layer solution is a mixed solution of cross-linked copolymer and cross-linked cation exchange resin powder, with a weight ratio of 100:10~20. The cross-linked copolymer is obtained by feeding vinylpyridine, acrylic acid and divinylbenzene in a mass ratio of 100:30~60:4~8 and then performing a free radical copolymerization reaction in the solution.

8. The method as described in claim 7, characterized in that: The initiator for the free radical copolymerization reaction is benzoyl peroxide, the solvent is DMF, the reaction temperature is 83~95℃, and the reaction time is 10~24 h.

9. The method as described in claim 7, characterized in that: The cross-linked cation exchange resin powder has a particle size of 50~100nm and an exchange capacity of 3.6~4.2mmol / g.

10. The method as described in claim 1 or 2, characterized in that: The second transfer roller is a spiral anilox roller with an anilox depth of 50~80um and a mesh count of 120; the first and third transfer rollers are mirror rollers.

11. The method as described in claim 1 or 2, characterized in that: The first, second, third, and fourth ovens are each composed of at least two oven sections connected together. In the first, second, third, and fourth ovens, the temperature of each oven section increases sequentially from the inlet to the outlet.

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