Bipolar membrane for producing high-purity acid-base and preparation method thereof

Abstract

The invention discloses a bipolar membrane for producing high-purity acid-base and a preparation method thereof, the preparation method of the bipolar membrane for producing high-purity acid-base comprises the following steps: preparing a hydrophobic base material layer: dissolving polyvinylidene fluoride in an organic solvent, adding nano-particles, performing coagulating bath, performing blade coating to form a hydrophobic base material, performing heat treatment, and drying to obtain the hydrophobic base material layer; a hydrophobic base material layer is obtained; preparing a cation exchange layer; constructing a catalyst layer; and preparing the anion exchange layer. The hydrophobicity of PVDF is utilized to reduce swelling of the membrane, and non-target ion permeation can be reduced at the same time; the nano-particles are added to improve the mechanical strength and the catalytic activity, meanwhile, the pore diameter and the charge density can be adjusted, screening is enhanced, the Donnan effect is improved, the blocking effect of ions in corresponding film layers on same ions is improved, and meanwhile the purity and the concentration of generated acid / alkali are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of bipolar membranes, and in particular to a bipolar membrane for producing high-purity acid and alkali and a preparation method thereof. Background Art

[0002] Bipolar membrane is the optimal solution for waste salt resource utilization and lithium salt refining optimization. Under the action of DC electric field, water decomposes at the interface layer of bipolar membrane to generate H + and OH - And migrate into the solution through the cation and anion membrane layers. The bipolar membrane realizes water dissociation to generate H + and OH - The process is simple and produces minimal waste. As the reverse reaction of neutralization, bipolar membranes are irreplaceable in the production of acids and bases from salts. Bipolar membranes are also widely used in the production of inorganic acids and bases such as sodium sulfate, sodium chloride, lithium sulfate, lithium chloride, and sodium nitrate.

[0003] Traditional bipolar membranes suffer from issues such as high salt permeability, insufficient acid and base purity, high water dissociation voltage, and easy stratification. These issues significantly limit the application, product quality, and impurity removal costs of bipolar membrane acid and base systems. For example, when converting lithium sulfate into sulfuric acid and lithium hydroxide using conventional bipolar membrane technology, the lithium salt yield and lithium hydroxide purity are both poor. Subsequent reduction of the lithium ions in the sulfuric acid requires the simultaneous use of a multi-stage alkali-resistant NF system to remove sulfate from the lithium hydroxide, significantly impacting product purity, purification costs, and process feasibility.

[0004] In particular, during the long-term operation of traditional bipolar membranes, due to the multiple effects of temperature, current, water and ions, the composite structure will be stratified, which greatly affects the long-term stability and deteriorates the acid and base purity. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the problems of insufficient acid and alkali purity, high water dissociation voltage and easy stratification during long-term operation of bipolar membranes in the prior art, thereby providing a bipolar membrane for producing high-purity acid and alkali and a preparation method thereof to solve the above problems.

[0006] A method for preparing a bipolar membrane for producing high-purity acid and base, characterized by comprising:

[0007] Preparation of a hydrophobic substrate layer: dissolving polyvinylidene fluoride (PVDF) in an organic solvent, adding nanoparticles, passing through a coagulation bath, and then applying the resulting coating to form a hydrophobic substrate. After heat treatment, a hydrophobic substrate layer is obtained.

[0008] Preparation of the cation exchange layer: The sulfonated monomer solution is infiltrated onto the surface of the hydrophobic substrate layer and chemically cross-linked with a cross-linking agent to form a cation exchange layer after polymerization;

[0009] Construction of the catalytic layer: spraying a dispersion containing a transition metal salt and a dopamine composite catalyst on the surface of the cation exchange layer, and forming a catalytic layer after drying;

[0010] Preparation of the anion exchange layer: A quaternary ammonium polymer solution is applied to the surface of the catalyst layer and chemically cross-linked with a cross-linking agent to form an anion exchange layer; the PVDF substrate layer containing nanoparticles, the cation exchange layer, the catalyst layer and the anion exchange layer constitute a composite membrane;

[0011] Post-treatment: The composite membrane is immersed in an acidic solution for activation, and then transformed into a bipolar membrane for producing high-purity acid and alkali through alkaline solution.

[0012] In an optional embodiment, the mass of the nanoparticles in the substrate layer is 1-10% of the mass of the polyvinylidene fluoride;

[0013] And / or, the particle size of the nanoparticles is 10-100 nm; for example, the particle size of the nanoparticles can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc.;

[0014] and / or, the nanoparticles are one or more of SiO2, TiO2, and Fe3O4;

[0015] And / or, the ratio of polyvinylidene fluoride to the organic solvent is (1.75-6):1; for example, the ratio of polyvinylidene fluoride to the organic solvent can be 1.75:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, etc.;

[0016] And / or, the organic solvent includes one or more of NMP (N-methylpyrrolidone), DMAC (N,N-dimethylacetamide), DMF (dimethylformamide), TEP (triethyl phosphate), and DMSO (dimethyl sulfoxide).

[0017] Preferably, the bath liquid in the coagulation bath includes water and an organic solvent. The organic solvent included in the bath liquid may only include an organic solvent that dissolves polyvinylidene fluoride (PVDF), or may include an organic solvent added separately from polyvinylidene fluoride; preferably, the organic solvent included in the bath liquid is the same as the organic solvent that dissolves polyvinylidene fluoride (PVDF), and is therefore also selected from one or more of NMP (N-methylpyrrolidone), DMAC (N,N-dimethylacetamide), DMF (dimethylformamide), TEP (triethyl phosphate), and DMSO (dimethyl sulfoxide); preferably, the bath liquid also includes ethanol and / or an inorganic salt solution, and more preferably, the inorganic salt solution includes one or more of sodium chloride solution and sodium sulfate solution. Specifically, the bath liquid in the coagulation bath may include an organic solvent and water that dissolves polyvinylidene fluoride (PVDF), or the bath liquid in the coagulation bath may include an organic solvent, water, and ethanol that dissolves polyvinylidene fluoride (PVDF), or the bath liquid in the coagulation bath may include an organic solvent, water, and an inorganic salt solution that dissolves polyvinylidene fluoride (PVDF), or the bath liquid in the coagulation bath may include an organic solvent, water, ethanol, and an inorganic salt solution that dissolves polyvinylidene fluoride (PVDF);

[0018] The water content of the bath liquid is ≥90%, the ethanol and / or inorganic salt solution content of the bath liquid is ≤5%, and the organic solvent content of the bath liquid is 1-5%. For example, the water content of the bath liquid can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, etc.; the organic solvent content of the bath liquid can be 1%, 2%, 3%, 4%, 5%, etc.; the ethanol and / or inorganic salt solution content of the bath liquid can be 1%, 2%, 3%, 4%, 5%, etc.

[0019] The temperature of the coagulation bath is 20-25°C, and the concentration of the inorganic salt solution is 200-250 g / L; for example, the temperature of the coagulation bath can be 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, etc., and the concentration of the inorganic salt solution can be 200 g / L, 210 g / L, 220 g / L, 230 g / L, 240 g / L, 250 g / L, etc.;

[0020] The thickness of the hydrophobic substrate layer is 90-200 μm; for example, the thickness of the hydrophobic substrate layer can be 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, 200 μm, etc.

[0021] Furthermore, the heat treatment temperature is 180-190°C, and the treatment time is 1-2h; for example, the heat treatment temperature can be 180°C, 182°C, 184°C, 186°C, 188°C, 190°C, etc., and the treatment time can be 1h, 1.5h, 2h, etc.

[0022] In an optional embodiment, the cross-linking agent includes one or more of 1-3 dibromopropane, polyvinylbenzene and glutaraldehyde, preferably one or more of divinylbenzene, trivinylbenzene, divinyltoluene and divinylethylbenzene among polyvinylbenzenes.

[0023] In an optional embodiment, in the step of preparing the cation exchange layer,

[0024] The molar ratio of the cross-linking agent to the sulfonated monomer is 1:(3-20); for example, the molar ratio of the cross-linking agent to the sulfonated monomer can be 1:3, 1:5, 1:7, 1:10, 1:12, 1:15, 1:18, 1:20, etc.;

[0025] and / or, the sulfonated monomer is a sulfonated polystyrene monomer;

[0026] And / or, the walking speed of the infiltration is 0.1-1 m / min, preferably 0.2-0.5 m / min; for example, the walking speed of the infiltration can be 0.1 m / min, 0.3 m / min, 0.5 m / min, 0.8 m / min, 1 m / min, etc.;

[0027] And / or, the temperature of the chemical crosslinking is 100-130° C., and the time is 10-20 h; preferably, the temperature of the chemical crosslinking is 110-120° C., and the time is 15-20 h; for example, the temperature of the chemical crosslinking may be 100° C., 105° C., 110° C., 115° C., 120° C., 125° C., 130° C., etc., and the time may be 10 h, 12 h, 15 h, 18 h, 20 h, etc.;

[0028] The ion exchange capacity IEC of the cation exchange layer is 1.2-2.5 mmol / g dry film. For example, the ion exchange capacity IEC of the cation exchange layer can be 1.2 mmol / g dry film, 1.5 mmol / g dry film, 1.7 mmol / g dry film, 2.0 mmol / g dry film, 2.3 mmol / g dry film, 2.5 mmol / g dry film, etc.

[0029] In an optional embodiment, in the step of constructing the catalytic layer,

[0030] The dispersion comprises a transition metal salt, dopamine and an acid solution, and the pH value of the dispersion is 1-3;

[0031] and / or, the transition metal element in the transition metal salt includes one of titanium, tin, chromium, cobalt, nickel, platinum, silver, or ruthenium;

[0032] and / or, the molar ratio of the transition metal salt to dopamine is 1:(1-50), preferably 1:(10-30);

[0033] And / or, the spraying method is ultrasonic spraying; for example, the molar ratio of the transition metal salt to dopamine can be 1:1, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, etc.;

[0034] And / or, the drying conditions are 90-120° C. and 0.5-2 h; for example, the drying temperature may be 90° C., 100° C., 105° C., 110° C., 115° C., 120° C., etc., and the drying time may be 0.5 h, 1 h, 1.5 h, 2 h, etc.;

[0035] And / or, the loading amount of the catalyst layer on the cation exchange layer is 0.5-5 g / m 2 , preferably 1-1.5g / m 2 For example, the loading amount of the catalyst layer on the cation exchange layer can be 0.5 g / m 2 , 1g / m 2 , 2g / m 2 , 3g / m 2 , 4g / m 2 , 5g / m 2 wait.

[0036] In an optional embodiment, in the step of preparing the anion exchange layer,

[0037] The molar ratio of the cross-linking agent to the quaternized polymer is 1:(3-20); for example, the molar ratio of the cross-linking agent to the quaternized polymer can be 1:3, 1:5, 1:10, 1:15, 1:20, etc.;

[0038] And / or, the quaternized polymer is a polystyrene-based quaternized polymer or a quaternized diphenylpyridine; both the polystyrene-based quaternized polymer and the quaternized diphenylpyridine are conventional quaternized polymers used in anion exchange layers in the art, and their effects are substantially equivalent.

[0039] And / or, the temperature of the chemical crosslinking is 40-70°C, and the time is 10-15 hours; preferably, the temperature of the chemical crosslinking is 50-60°C, and the time is 10-12 hours; for example, the temperature of the chemical crosslinking can be 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C, etc., and the time can be 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, etc.;

[0040] And / or, the thickness of the anion exchange layer is 20-100 μm; for example, the thickness of the anion exchange layer can be 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, etc.

[0041] In an optional embodiment, in the post-processing step,

[0042] The acidic solution is a 1-5wt% sulfuric acid solution; for example, the concentration of the sulfuric acid solution can be 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, etc.;

[0043] And / or, the activation time is 0.5-2h; for example, the activation time can be 0.5h, 1h, 1.5h, 2h, etc.;

[0044] And / or, the alkali solution is a 1-5wt% sodium hydroxide solution; for example, the concentration of the sodium hydroxide solution can be 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, etc.;

[0045] And / or, the transformation time is 0.5-2 hours; for example, the transformation time can be 0.5 hours, 1 hour, 1.5 hours, 2 hours, etc.

[0046] A bipolar membrane for producing high-purity acid and alkali is prepared by the above-mentioned preparation method.

[0047] The present invention also provides a method for using the bipolar membrane prepared by the above method, comprising:

[0048] The bipolar membrane is combined with mature commercial anion exchange membrane and cation exchange membrane to be installed in a three-compartment bipolar membrane electrodialysis membrane device or a two-compartment electrodialysis device for application in the fields of lithium extraction from salt lakes, waste salt resource utilization, material purification or recovery of organic acids and alkalis.

[0049] Three-compartment bipolar membrane electrodialysis device or two-compartment electrodialysis device is suitable for the preparation and recovery of high-purity acids and bases. The current density during use is 400-1000A / m 2 , preferably 600-1000A / m 2 , the water inlet conditions meet the water inlet requirements of conventional bipolar membrane electrodialysis;

[0050] And / or, the operating pressure is less than 0.1 MPa, and / or, the operating temperature is 25-45°C, and / or, the membrane surface flow rate during operation is 3-9 cm / s, preferably 5-9 cm / s, and the upper limit of the acid and alkali concentration (excluding oxidizing acids) can reach a maximum of 3.5N.

[0051] The technical solution of the present invention has the following advantages:

[0052] 1. The bipolar membrane for producing high-purity acids and bases prepared by the preparation method provided by the present invention utilizes the hydrophobicity of PVDF to reduce membrane swelling and reduce the penetration of non-target ions. The addition of nanoparticles improves mechanical strength and catalytic activity, while also adjusting the pore size and charge density, enhancing screening and increasing the Donnan effect to enhance the barrier effect of ions on common ions within the corresponding membrane layer, while also improving the purity and concentration of the generated acid / base.

[0053] 2. In the bipolar membrane provided by the present invention, a stable coordination structure is formed by combining a transition metal salt with dopamine, and the catalytic layer is optimized to reduce the water dissociation voltage. The stable coordination structure can effectively prevent the loss of the catalyst and ensure the long-term stability of the water dissociation voltage.

[0054] 3. In the bipolar membrane provided by the present invention, the preparation process conditions of the cation exchange layer and the anion exchange layer are further optimized to achieve the purpose of adopting a highly cross-linked structure in the cation / anion exchange layer, thereby reducing ion permeation; at the same time, due to the addition of nanoparticles and the optimization of the catalytic layer, the activation energy of water dissociation is reduced and the dissociation ability is improved, so the overall water dissociation voltage does not increase, so that the acid-base purity and energy consumption are balanced. At the same time, the cross-linked structure of the anion and cation membrane layers makes the binding force between the anion and cation membrane layers more stable, which can effectively prevent bubbling and stratification caused by excessive current density, thereby improving the service life and stability of the bipolar membrane.

[0055] 4. The bipolar membrane provided by the present invention can produce acid and alkali products with a purity and concentration that can meet the acid and alkali reuse and production needs in most scenarios, greatly reducing the cost and space required for purification and concentration, and improving the competitiveness of acid and alkali products. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0057] Figure 1 Schematic diagram of the structure of the bipolar membrane in Example 1 of the present invention;

[0058] Reference numerals:

[0059] 1- anion exchange layer, 2- catalytic layer, 3- hydrophobic substrate layer with cation exchange layer, 4- nanoparticles. DETAILED DESCRIPTION

[0060] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0061] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0062] Example 1

[0063] A method for preparing a bipolar membrane for producing high-purity acid and base, comprising:

[0064] S1. Preparation of hydrophobic substrate

[0065] 375g of N,N-dimethylformamide (DMF) was added to the reactor, and 750g of PVDF powder was added and stirred in a closed state at 40°C and mixed thoroughly for 4h. During this period, 24.5g of TiO2 particles with a diameter of 50nm were added to form a membrane-building solution. After 15min of ultrasonic dispersion, the membrane-building solution was replaced with a coagulation bath in a bath, wherein the bath included water, DMF and sodium chloride solution. The content of DMF in the bath was 4%, the content of sodium chloride solution in the bath was 1%, the content of water in the bath was 95%, and the concentration of sodium chloride solution was 200g / L; the temperature of the coagulation bath replacement was 20°C; and then the PVDF substrate was scraped onto a horizontal PET substrate, and the substrate was heated in an oven at 180°C for 2h. After being taken out and cooled to room temperature, a hydrophobic substrate containing nanoparticles was obtained, and the thickness of the hydrophobic substrate was 120μm.

[0066] S2. Preparation of cation exchange layer

[0067] 15 wt% sulfonated polystyrene (SPS) and 26.5 g divinylbenzene (DVB) (crosslinker) were added to a reaction kettle, and 14 g azobisisobutyronitrile (AIBN) (initiator) was added dropwise and mixed thoroughly to form a cationic membrane material. After the membrane material cooled to room temperature, the hydrophobic substrate containing nanoparticles described in S1 was infiltrated into the cationic membrane material at an infiltration rate of 0.2 m / min. The membrane material was then placed in a 110°C oven for polymerization for 20 h to obtain a cation exchange layer. The IEC of the cation exchange layer was 1.7 mmol / g dry film.

[0068] S3. Preparation of catalytic layer

[0069] Take 203.5g dopamine and 10g tin dichloride, adjust the pH to 1 with hydrochloric acid, and form a suspension by ultrasound. Use a fan-shaped ultrasonic atomizing nozzle for spraying. Spray the suspension onto one surface of the cation exchange membrane described in S2 in the above-mentioned manner. The spraying amount is 1.25g / m2 based on the weight of the final catalytic layer. 2 , and then placed in an oven at 120°C to dry for 0.5h, to obtain a catalytic layer containing transition metals on the basis of the cation exchange membrane.

[0070] Preparation of S4 anion exchange layer

[0071] 20 wt% of a polystyrene-based quaternized polymer (quaternized polystyrene resin microspheres produced by Xi'an Qiyue Biological) was prepared, 15 g of divinylbenzene DVB (cross-linking agent) was added and stirred evenly to obtain an anion membrane material; the anion membrane material was evenly scraped onto one side of a cation exchange membrane containing a transition metal catalyst layer, with a scraping thickness of 70 μm, treated at 50°C for 12 h, and naturally dried for 2 h to form an anion exchange layer, thereby obtaining a composite membrane consisting of a PVDF substrate layer containing nanoparticles, a cation exchange layer, a catalytic layer, and an anion exchange layer.

[0072] Post-activation treatment of S5 composite membrane

[0073] The cut composite membrane is placed in a 5wt% sulfuric acid solution and activated for 2 hours. After being rinsed with deionized water until the pH of the washing water is ≥5, it is placed in a 5wt% sodium hydroxide solution and activated for 2 hours. After being rinsed with deionized water until neutral, a bipolar membrane suitable for the production of high-purity acids and bases is obtained. The structure is as follows Figure 1 shown.

[0074] The activated bipolar membrane group of the present invention can be used to recover high-purity acid and alkali. During use, the operating pressure is 0.05 MPa, the operating temperature is 35°C, the operating membrane surface flow rate is 6 cm / s, and the operating current density is 800 A / m 2 .

[0075] Example 2

[0076] A method for preparing a bipolar membrane for producing high-purity acid and base, comprising:

[0077] S1. Preparation of hydrophobic substrate

[0078] 350g of N,N-dimethylformamide (DMF) was added to the reactor, and 700g of PVDF powder was added under heating and stirring at 40°C in a closed state and mixed thoroughly for 4h. During this period, 15g of Fe3O4 particles with a diameter of 25nm were added to form a membrane-building solution. After 15min of ultrasonic dispersion, the membrane-building solution was replaced with a coagulation bath in a bath containing 2% ethanol, the DMF content in the bath was 4%, the ethanol content in the bath was 3%, and the water content in the bath was 93%; the coagulation bath replacement temperature was 20°C; and then the PVDF substrate was scraped onto a horizontal PET substrate. The substrate was heated in an oven at 180°C for 2h, taken out and cooled to room temperature to obtain a hydrophobic substrate containing nanoparticles. The thickness of the hydrophobic substrate was 110μm.

[0079] S2. Preparation of cation exchange layer

[0080] 15 wt% sulfonated polystyrene (SPS) and 28.3 g trivinylbenzene (CAS: 3048-52-0) were added to a reaction kettle, and 14 g AIBN (initiator) was added dropwise and mixed thoroughly to form a cationic membrane material. After the membrane material cooled to room temperature, the hydrophobic substrate containing nanoparticles described in S1 was infiltrated into the cationic membrane material at an infiltration rate of 0.25 m / min. The membrane material was then placed in a 110°C oven for polymerization for 20 h to obtain a cation exchange layer. The IEC of the cation exchange layer was 1.65 mmol / g dry film.

[0081] S3. Preparation of catalytic layer

[0082] Take 200g dopamine and 14.9g platinum chloride, adjust the pH to 1 with hydrochloric acid, and form a suspension by ultrasound. Use a fan-shaped ultrasonic atomizing nozzle for spraying. Spray the suspension onto one surface of the cation exchange membrane described in S2 in the above-mentioned manner. The spraying amount is 1.0g / m2 based on the weight of the final catalytic layer. 2 , and then placed in an oven at 120°C to dry for 0.5h, to obtain a catalytic layer containing transition metals on the basis of the cation exchange membrane.

[0083] Preparation of S4 anion exchange layer

[0084] 20 wt% of a polystyrene-based quaternized polymer (quaternized polystyrene resin microspheres produced by Xi'an Qiyue Biological) was prepared, 24 g of trivinylbenzene (CAS: 3048-52-0) was added and stirred evenly to obtain an anion membrane material; the anion membrane material was evenly scraped onto one side of a cation exchange membrane containing a transition metal catalyst layer with a scraping thickness of 70 μm, treated at 60° C. for 10 h, and naturally dried for 2 h to form an anion exchange layer, thereby obtaining a composite membrane consisting of a PVDF substrate layer containing nanoparticles, a cation exchange layer, a catalytic layer, and an anion exchange layer.

[0085] Post-activation treatment of S5 composite membrane

[0086] The cut composite membrane was placed in a 5wt% sulfuric acid solution, activated for 1.5 hours, rinsed with deionized water until the pH of the washing water was ≥5, and then placed in a 5wt% sodium hydroxide solution, activated for 1.5 hours, and rinsed with deionized water until neutral, to obtain a bipolar membrane suitable for the production of high-purity acids and bases.

[0087] The activated bipolar membrane group of the present invention can be used to recover high-purity acid and alkali. During use, the operating pressure is 0.05 MPa, the operating temperature is 35°C, the operating membrane surface flow rate is 6 cm / s, and the operating current density is 750 A / m 2 .

[0088] Example 3

[0089] A method for preparing a bipolar membrane for producing high-purity acid and base, comprising:

[0090] S1. Preparation of hydrophobic substrate

[0091] 400 g of N,N-dimethylformamide (DMF) was added to the reactor, and 750 g of PVDF powder was added and stirred in a closed state at 40°C and mixed thoroughly for 3 hours. During this period, 26 g of TiO2 particles with a diameter of 10 nm were added to form a film-forming liquid. After 10 minutes of ultrasonic dispersion, the film-forming liquid was replaced with a coagulation bath in a bath containing 5% DMF and 95% water; the coagulation bath replacement temperature was 20°C; and then the PVDF substrate was scraped onto a horizontal PET substrate. The substrate was heated in an oven at 190°C for 1.5 hours, taken out and cooled to room temperature to obtain a hydrophobic substrate containing nanoparticles. The thickness of the hydrophobic substrate was 135 μm.

[0092] S2. Preparation of cation exchange layer

[0093] 18 wt% sulfonated polystyrene (SPS) and 29 g divinylbenzene (DVB) were added to a reaction kettle, and 16.5 g azobisisobutyronitrile (AIBN) (initiator) was added dropwise and mixed thoroughly to form a cationic membrane material. After the membrane material cooled to room temperature, the hydrophobic substrate containing nanoparticles described in S1 was infiltrated into the cationic membrane material at an infiltration rate of 0.4 m / min. The membrane material was then placed in a 120°C oven for polymerization for 15 h to obtain a cation exchange layer. The IEC of the cation exchange layer was 1.61 mmol / g dry film.

[0094] S3. Preparation of catalytic layer

[0095] Take 200g dopamine and 5g metatitanic acid, adjust the pH to 3 with hydrochloric acid, and form a suspension by ultrasound. Use a fan-shaped ultrasonic atomizing nozzle for spraying. Spray the suspension onto one surface of the cation exchange membrane described in S2 in the above-mentioned manner. The spraying amount is 1.5g / m2 based on the weight of the final catalytic layer. 2 , and then placed in an oven at 120°C for 1 hour to obtain a catalytic layer containing transition metals on the basis of the cation exchange membrane.

[0096] Preparation of S4 anion exchange layer

[0097] 80 wt% of a polystyrene-based quaternized polymer (quaternized polystyrene resin microspheres produced by Xi'an Qiyue Biological) was prepared, 2 g of 1,3-dibromopropane was added and stirred evenly to obtain an anion membrane material; the anion membrane material was evenly scraped onto one side of a cation exchange membrane containing a transition metal catalyst layer with a scraping thickness of 75 μm, treated at 50°C for 12 hours, and naturally dried for 2 hours to form an anion exchange layer, thereby obtaining a composite membrane consisting of a PVDF substrate layer containing nanoparticles, a cation exchange layer, a catalytic layer, and an anion exchange layer.

[0098] Post-activation treatment of S5 composite membrane

[0099] The cut composite membrane was placed in a 5wt% sulfuric acid solution, activated for 1.5 hours, rinsed with deionized water until the pH of the washing water was ≥5, and then placed in a 5wt% sodium hydroxide solution, activated for 1.5 hours, and rinsed with deionized water until neutral, to obtain a bipolar membrane suitable for the production of high-purity acids and bases.

[0100] The activated bipolar membrane group of the present invention can be used to recover high-purity acid and alkali. During use, the operating pressure is 0.05 MPa, the operating temperature is 40°C, the operating membrane surface flow rate is 7 cm / s, and the operating current density is 800 A / m 2 .

[0101] Example 4

[0102] The method is the same as that of Example 1, except that in step S1, the organic solvent in the hydrophobic PVDF substrate is replaced with 450 g of NMP, and other conditions remain unchanged to prepare a bipolar membrane.

[0103] Example 5

[0104] The method is the same as that of Example 1, except that in step S1, the composition of the bath liquid in the coagulation bath of the hydrophobic PVDF substrate is: DMF content is 4%, ethanol content is 5%, and the water content in the bath liquid is 91%. Other conditions remain unchanged to prepare a bipolar membrane.

[0105] Example 6

[0106] The method is the same as that of Example 1, except that in step S1, 27 g of TiO 2 with a diameter of 100 nm is added to the hydrophobic PVDF substrate, and other operations and conditions remain unchanged to prepare a bipolar membrane.

[0107] Example 7

[0108] The method is the same as that of Example 1, except that: in the preparation process of S2 and S4, DVB is used as the crosslinking agent, the amount added to the cation film layer is 15.5g, and the amount added to the anion film layer is 10.5g. Other operations and conditions remain unchanged.

[0109] Example 8

[0110] The method is the same as that of Example 1, except that: in step S1, the hydrophobic PVDF substrate is treated at a temperature of 185° C. for 1.5 h, and other operations and conditions remain unchanged.

[0111] Example 9

[0112] The method is the same as that of Example 1, except that the walking speed in step S2 is 0.5 m / min, and other operations and conditions remain unchanged.

[0113] Example 10

[0114] The method is the same as that of Example 1, except that in step S3, the amount of dopamine added is 68 g, and other operations and conditions remain unchanged.

[0115] Example 11

[0116] The method is the same as that of Example 1, except that in step S5, the soaking time of the activated acid and alkali is 1 hour respectively, and other operations and conditions remain unchanged.

[0117] Example 12

[0118] The method is the same as that of Example 1, except that in step S5, the concentrations of the activated acid and base are 1 wt % sulfuric acid and 1 wt % sodium hydroxide, respectively, and other operations and conditions remain unchanged.

[0119] Example 13

[0120] The method is the same as that of Example 1, except that the acid and alkali immersion activation work described in step S5 is not performed, and other operations and conditions remain unchanged to obtain a bipolar membrane.

[0121] Comparative Example 1

[0122] The method is the same as that of Example 1, except that: in the preparation process of S1 hydrophobic substrate, nanoparticles are not added, and other operations and conditions remain unchanged.

[0123] Comparative Example 2

[0124] The method is the same as that of Example 1, except that during the preparation of the hydrophobic substrate S1, the PVDF substrate is replaced with a PP diaphragm substrate with a porosity of 45%, and other operations and conditions remain unchanged to prepare a bipolar membrane.

[0125] Comparative Example 3

[0126] The method is the same as that of Example 13, except that: in the preparation process of S1 hydrophobic substrate, nanoparticles are not added, and other operations and conditions remain unchanged.

[0127] Experimental Example - Initial Performance Test of Bipolar Membrane Stack

[0128] The bipolar membranes prepared in the above examples and comparative examples were subjected to performance tests. The performance test parameters and corresponding test methods are as follows:

[0129] Current efficiency:

[0130] Where:

[0131] η—current efficiency, %;

[0132] F—Faraday constant 96485, C / mol;

[0133] —The average value of the voltage recorded twice adjacently,

[0134] n—number of pairs of membrane stacks;

[0135] V t —Acid-base endpoint volume, L;

[0136] C t —Acid and base endpoint concentration, mol / L;

[0137] Δt—time interval between two adjacent times, s;

[0138] Water dissociation voltage of bipolar membrane: 1000A / m 2 Direct current, the cation exchange layer of the bipolar membrane is 1 mol / L OH - , one side of the cation exchange layer is 1 mol / LH + The voltage across the bipolar membrane.

[0139] Purity of acid or base: C = (1-salt content in acid chamber or base chamber / total amount of acid or base).

[0140] The initial performance (10 h) of the operation under the sodium sulfate system is shown in Table 1 below.

[0141] Table 1

[0142]

[0143] By comparing the above Examples 1-13 with Comparative Examples 1-3, it can be seen that by adding nanoparticles to the hydrophobic PVDF substrate and increasing the cross-linking structure in the cation exchange layer and the anion exchange layer, the pore size and charge density can be adjusted, the screening and Donnan effect can be enhanced, and the cation exchange membrane and the anion exchange layer can be increased for H + and OH - It improves the selective permeability of the anion and cation membrane layers and the blocking effect of the impurity ions, thereby improving the purity and concentration limit of the prepared acid and alkali, effectively reducing the cost of impurity removal, and increasing the applicability of process development, with significant results.

[0144] Experimental Example 2-Life and Stability Performance Test

[0145] The results of long-term operation of the above embodiments and comparative examples are shown in Table 2.

[0146] Table 2

[0147]

[0148]

[0149] From the data in Tables 1-2 above, it can be seen that the present invention can not only improve the purity and concentration of acids and bases obtained in applications, but also ensure the stability of operating life and voltage stability by further optimizing the anion and cation exchange membrane layers, base membrane and catalytic layer, while enhancing the binding capacity of the anion and cation exchange membranes, thereby ensuring the stability of bipolar membrane applications.

[0150] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for producing a bipolar membrane for producing high-purity acid and base, characterized in that: include: Preparation of a hydrophobic substrate layer: dissolving polyvinylidene fluoride in an organic solvent, adding nanoparticles, passing through a coagulation bath, and then applying the solution by knife coating to form a hydrophobic substrate, followed by heat treatment to obtain a hydrophobic substrate layer; Preparation of the cation exchange layer: The sulfonated monomer solution is infiltrated onto the surface of the hydrophobic substrate layer and chemically cross-linked with a cross-linking agent to form a cation exchange layer after polymerization; Construction of the catalytic layer: spraying a dispersion containing a transition metal salt and a dopamine composite catalyst on the surface of the cation exchange layer, and forming a catalytic layer after drying; Preparation of anion exchange layer: quaternized polymer solution is coated on the surface of the catalyst layer and chemically cross-linked by a cross-linking agent to form an anion exchange layer; the PVDF substrate layer containing nanoparticles, the cation exchange layer, the catalyst layer and the anion exchange layer constitute a composite membrane.

2. The preparation method according to claim 1, characterized in that The method also includes a post-processing step, the specific process of which is: immersing the composite membrane in an acidic solution for activation, and then transforming it into a bipolar membrane for producing high-purity acid and alkali through alkaline solution.

3. The preparation method according to claim 1 or 2, characterized in that The mass of the nanoparticles in the substrate layer is 1-10% of the mass of the polyvinylidene fluoride; and / or, the particle size of the nanoparticles is 10-100 nm; and / or, the nanoparticles are one or more of SiO2, TiO2, and Fe3O4; And / or, the ratio of the polyvinylidene fluoride to the organic solvent is (1.75-6):1; And / or, the organic solvent comprises one or more of NMP, DMAC, DMF, TEP, and DMSO; And / or, the heat treatment temperature is 180-190° C., and the treatment time is 1-2 hours.

4. The preparation method according to any one of claims 1 to 3, characterized in that The bath liquid in the coagulation bath includes water and an organic solvent. Preferably, the bath liquid also includes ethanol and / or an inorganic salt solution. More preferably, the inorganic salt solution includes one or more of a sodium chloride solution and a sodium sulfate solution. The water content in the bath liquid is ≥90%, the ethanol and / or inorganic salt solution content in the bath liquid is ≤5%, and the organic solvent content in the bath liquid is 1-5%; The temperature of the coagulation bath is 20-25°C, and the concentration of the inorganic salt solution is 200-250g / L; The thickness of the hydrophobic substrate layer is 90-200 μm.

5. The preparation method according to any one of claims 1 to 4, characterized in that The cross-linking agent includes one or more of 1-3 dibromopropane, polyvinylbenzene and glutaraldehyde, and is preferably one or more of divinylbenzene, trivinylbenzene, divinyltoluene and divinylethylbenzene among polyvinylbenzenes.

6. The preparation method according to any one of claims 1 to 5, characterized in that In the preparation step of the cation exchange layer, The molar ratio of the cross-linking agent to the sulfonated monomer is 1:(3-20); and / or, the sulfonated monomer is a sulfonated polystyrene monomer; and / or, the walking speed of the infiltration is 0.1-1 m / min, preferably 0.2-0.5 m / min; And / or, the temperature of the chemical crosslinking is 100-130°C and the time is 10-20 hours; preferably, the temperature of the chemical crosslinking is 110-120°C and the time is 15-20 hours; The ion exchange capacity IEC of the cation exchange layer is 1.2-2.5 mmol / g dry film.

7. The preparation method according to any one of claims 1 to 6, characterized in that In the step of constructing the catalytic layer, The dispersion comprises a transition metal salt, dopamine and an acid solution, and the pH value of the dispersion is 1-3; and / or, the transition metal element in the transition metal salt includes one of titanium, tin, chromium, cobalt, nickel, platinum, silver, or ruthenium; and / or, the molar ratio of the transition metal salt to dopamine is 1:(1-50), preferably 1:(10-30); And / or, the spraying method is ultrasonic spraying; And / or, the drying conditions are 90-120° C., 0.5-2 h; And / or, the loading amount of the catalyst layer on the cation exchange layer is 0.5-5 g / m 2 , preferably 1-1.5g / m 2 .

8. The preparation method according to any one of claims 1 to 7, characterized in that In the step of preparing the anion exchange layer, The molar ratio of the cross-linking agent to the quaternized polymer is 1:(3-20); And / or, the quaternized polymer is a polystyrene-based quaternized polymer or a quaternized diphenylpyridine; And / or, the temperature of the chemical crosslinking is 40-70°C and the time is 10-15 hours; preferably, the temperature of the chemical crosslinking is 50-60°C and the time is 10-12 hours; And / or, the thickness of the anion exchange layer is 20-100 μm.

9. The preparation method according to claim 2, characterized in that In the post-processing step, The acidic solution is a 1-5wt% sulfuric acid solution; And / or, the activation time is 0.5-2h; and / or, the alkali solution is a 1-5wt% sodium hydroxide solution; And / or, the transformation time is 0.5-2h.

10. A bipolar membrane for producing high-purity acid and base, characterized in that The preparation method is described in any one of claims 1 to 9.

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