Monovalent selective cation exchange membrane and preparation method thereof

Abstract

The invention belongs to the technical field of membrane separation, and particularly relates to a monovalent selective cation exchange membrane and a preparation method thereof, the preparation method comprises the following steps: (1) mixing a first exchange monomer, a first cross-linking agent, a first solvent and a first initiator to obtain a first prepolymer solution; (2) mixing a second exchange monomer, a second cross-linking agent, a second solvent and a second initiator to obtain a second prepolymer solution; (3) coating the first prepolymer solution on a first substrate film to obtain a first composition; (4) coating a second substrate film with the second prepolymer solution to obtain a second composition; and (5) oppositely laminating the coating surfaces of the first composition and the second composition, and stripping the first substrate membrane and the second substrate membrane after initiation polymerization is completed, so as to obtain the monovalent selective cation exchange membrane.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of membrane separation, and particularly relates to a monovalent selective cation exchange membrane and a preparation method thereof. BACKGROUND

[0002] In the field of energy and environment, monovalent selective cation exchange membranes, as a kind of key functional materials, are playing an increasingly important role. Monovalent selective cation exchange membranes (M-CEMs) are a kind of functional membrane materials capable of selectively permeating monovalent cations (such as Li+, Na + ) and blocking multivalent cations (such as Mg 2+ , Ca 2+ ), and have important application value in the fields of salt lake lithium extraction, seawater desalination, heavy metal wastewater treatment, etc. At present, the core preparation technology thereof mainly depends on a surface modification method, and the monovalent selective cation exchange membrane is prepared by constructing a certain pore size of a positively charged functional layer on the surface of a base film, and the selective separation of monovalent / multivalent ions is realized by using electrostatic repulsion and pore size screening effect. However, the modified layer of the monovalent selective cation exchange membrane prepared by the related technology has the problems of unstable properties and easy falling off, resulting in a short service life. SUMMARY

[0003] The present application aims to at least solve one of the problems in the related art. To this end, the present application provides a monovalent selective cation exchange membrane and a preparation method thereof. The monovalent selective cation exchange membrane prepared by the preparation method has stable properties and does not have the problem of falling off of the modified layer of the existing selective cation exchange membrane.

[0004] The above technical purpose of the present application is achieved by the following technical solution:

[0005] A preparation method of a monovalent selective cation exchange membrane, comprising the following steps:

[0006] (1) mixing a first crosslinking monomer, a first crosslinking agent, a first solvent and a first initiator to obtain a first prepolymer solution;

[0007] (2) mixing a second crosslinking monomer, a second crosslinking agent, a second solvent and a second initiator to obtain a second prepolymer solution;

[0008] (3) coating the first prepolymer solution on a first substrate film to obtain a first composition;

[0009] (4) coating the second prepolymer solution on a second substrate film to obtain a second composition;

[0010] (5) The coated surfaces of the first composition and the second composition are brought into opposing contact, and after polymerization is initiated, the first substrate film and the second substrate film are peeled apart to obtain a monovalent selective cation exchange membrane.

[0011] In an embodiment, the first crosslinking monomer includes at least one of vinylbenzenesulfonic acid and its corresponding salt, vinylsulfonic acid and its corresponding salt, allylsulfonic acid and its corresponding salt, methacrylsulfonic acid and its corresponding salt, 2-acrylamido-2-methylpropanesulfonic acid and its corresponding salt, 2-methyl-2-acrylic acid-2-sulfoethyl ester and its corresponding salt, 3-sulfopropyl methacrylate and its corresponding salt, allyloxyhydroxypropyl sulfonic acid and its corresponding salt, acrylic acid and its corresponding salt, methacrylic acid and its corresponding salt, 4-vinylbenzoic acid and its corresponding salt, trichloroallyl acrylate and its corresponding salt, vinylphosphonic acid and its corresponding salt.

[0012] In an embodiment, the second crosslinking monomer includes at least one of dimethyldiallylammonium chloride, benzylvinyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, methacrylamidopropyltrimethylammonium chloride, (3-acrylamidopropyl)trimethylammonium chloride, 2-vinylpyridine, 4-vinylpyridine, and vinylimidazole.

[0013] In an embodiment, the first crosslinking agent and the second crosslinking agent include at least one of diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,3-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, tetraethylene glycol dimethacrylate, divinylbenzene, 4,4'-divinyl-1,1'-biphenyl, trimethylolpropane triacrylate, isophorone diisocyanate, trimethylolpropane trimethacrylate, ethoxylated bisphenol A di(meth)acrylate, ethoxylated trimethylolpropane triacrylate, and propoxylated trimethylolpropane triacrylate.

[0014] In an embodiment, the first solvent and the second solvent include at least one of 3- cyclobutene sulfone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, methanol, ethanol, isopropanol, glycerol, and diethylene glycol.

[0015] In an embodiment, the first initiator and the second initiator include at least one of azobisisobutyronitrile, azobisisoheptyl nitrile, dimethyl azobisisobutyrate, benzoyl peroxide, t-butyl benzoyl peroxide, methyl ethyl ketone peroxide, (2,4,6-trimethylbenzoyl) diphenylphosphine oxide, 2,4,6-trimethylbenzoyl ethyl phosphonate, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxy-cyclohexyl-phenyl ketone, 2-methyl-1-[4-methylthiophenyl]-2-morpholin-1-propanone, 2-hydroxy-2-methylpropiophenone, and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.

[0016] In an embodiment, the first substrate film and the second substrate film are a film including polyolefin, polyester, polyamide, polysulfone, or polyether ether ketone.

[0017] In an embodiment, the molar ratio of the first crosslinking monomer to the first crosslinking agent is (1-3):(0.5-3).

[0018] In an embodiment, the ratio of the sum of the mass of the first crosslinking monomer and the mass of the first crosslinking agent to the mass of the first initiator is 100:(0.1-1.5).

[0019] In an embodiment, the molar ratio of the second crosslinking monomer to the second crosslinking agent is (1-3):(0.5-3).

[0020] In an embodiment, the thickness of the first prepolymer solution coated on the first substrate film is 5-100 μm.

[0021] In an embodiment, the ratio of the thickness of the second prepolymer solution coated on the second substrate film to the thickness of the first prepolymer solution coated on the first substrate film is (0.01-1):1.

[0022] In an embodiment, in step (3), a polypropylene microporous film is first stacked on the first substrate film, and then the first prepolymer solution is coated, so that the first prepolymer solution completely impregnates the polypropylene microporous film and contacts the surface of the first substrate film, to obtain the first composition, and after the subsequent polymerization is completed, the polypropylene microporous film forms a support layer in the monovalent selective cation exchange membrane.

[0023] In an embodiment, the thickness of the polypropylene microporous film is 5-100 μm, the porosity of the polypropylene microporous film is 50%-54%, and the pore size in the polypropylene microporous film is less than 0.1 microns.

[0024] A monovalent selective cation exchange membrane is prepared by the preparation method described above.

[0025] The present application has the following advantages:

[0026] (1) The present invention adopts free radical polymerization to form a conventional cation exchange membrane, and the selective modification layer is also formed by free radical polymerization. Free radical polymerization has the characteristics of fast and high conversion rate. The first prepolymer solution coated on the first composition is polymerized to form a cation exchange membrane layer, and the second prepolymer solution coated on the second composition is polymerized to form a selective modification layer. The surfaces of the first composition and the second composition coated with the prepolymer solution are relatively attached. During the free radical polymerization process, the monomers and crosslinking agents between the first prepolymer solution and the second prepolymer solution will be slightly mixed with each other, and no clear interface layer will be formed. The first prepolymer solution is polymerized to form a cation exchange membrane and the modification layer formed by the second prepolymer solution can form an interface-free integrated membrane material, which will not show selective degradation in salt water of different concentrations. The problem of separation of the separation layer and the cation exchange membrane can solve the problem of peeling off of the modified layer in the existing selective cation exchange membrane prepared by physical adsorption or by increasing the contact area; at the same time, the modified layer is formed by a free radical polymerization scheme, and the main separation mechanism is high-density positive charge Donnan repulsion and pore size screening based on cross-linking agent. By selecting the second exchange monomer, different positively charged groups can be flexibly selected, and by adjusting the proportion of the second exchange monomer, modified layers with different charge densities can be obtained. At the same time, by adjusting the proportion of the cross-linker, the contribution of size screening to the selectivity of monovalent ions can be further enhanced. By regulating the type and proportion of different cross-linking agents, the pore size of the charged modified layer can be controlled, and the separation performance of the selective cation exchange membrane can be widely adjusted according to different application requirements.

[0027] (2) The monovalent selective cation exchange membrane prepared by the present invention, the cation exchange membrane body and the modified layer with separation selectivity are formed by initiating free radical polymerization, and are formed in one step. Compared with the existing multi-step modification technology (co-deposition, surface electrodeposition, post-crosslinking reaction, surface oxidation adsorption, grafting, etc.), the preparation process has the characteristics of simple process and high preparation efficiency. Since the ion exchange membrane is formed by free radical polymerization, the modification process is more compatible with the equipment for preparing the cation exchange membrane body. The existing cation exchange membrane production equipment can be used to complete the preparation of the monovalent selective cation exchange membrane, and the production cost can be greatly reduced.

[0028] (3) The monovalent selective cation exchange membrane prepared by the application, the modified layer and the cation exchange membrane body, at the same time, using the solution radical polymerization method, the interface monomer in solution state can be free copolymerization, forming a whole membrane layer without interface layer, the modified layer and the cation exchange membrane body are both formed by fusion copolymerization, and there is no monovalent selective ion exchange membrane obtained by using the roughened cation exchange membrane for deposition adsorption and other non-bonding methods in the prior art, which can not exist the problems of the modified layer falling off and unstable properties in the membrane working process, and has long-term stability under different concentration of brine conditions (the stability is equivalent to that of ordinary cation exchange membrane), the selective cation exchange membrane prepared by the existing process can only be subjected to conventional cleaning and scrubbing, and the monovalent selective cation exchange membrane of the application is formed by fusion radical polymerization, and can resist chemical cleaning.

[0029] (4) The monovalent selective cation exchange membrane prepared by the application, the modified layer of which is more flexible in the regulation process, and can be adjusted in a wide range in ion capacity and crosslinking degree during preparation according to the application requirements of the monovalent selective cation exchange membrane, so as to meet the requirements of the fields of selective separation of monovalent ions, separation of macromolecules such as dyes and organic matters and ions, whey desalting, flavor retention and seasoning desalting. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a structural schematic diagram of the first composition in Example 1 of the application;

[0031] Figure 2 It is a structural schematic diagram of the second composition in Example 1 of the application;

[0032] Figure 3 It is a structural schematic diagram of the first composition and the second composition after being attached in Example 1 of the application;

[0033] Figure 4 It is a structural schematic diagram of the monovalent selective cation exchange membrane prepared in Example 10 of the application;

[0034] Figure 5 It is a schematic diagram of the test device in the specific embodiment of the application.

[0035] REFERENCE NUMERALS:

[0036] 100. First composition; 101. First prepolymer solution layer; 102. First substrate film; 103. Support layer;

[0037] 200. Second composition; 201. Second prepolymer solution layer; 202. Second substrate film. DETAILED DESCRIPTION

[0038] The application will be further described below in combination with specific embodiments.

[0039] Example 1:

[0040] A method for preparing a monovalent selective cation exchange membrane, comprising the following steps:

[0041] (1) 9.21 g of vinyl benzene sulfonic acid (M: 184.2 g / mol, 0.05 mol) and 9.21 g of divinyl benzene (M: 130.19 g / mol, 0.07 mol) are heated and dissolved in 7.5 g of N-methyl pyrrolidone to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a first prepolymer solution;

[0042] (2) 5 g of dimethyl diallyl ammonium chloride aqueous solution (60% aqueous solution) (M: 161.672 g / mol, 0.0185 mol) and 10.20 g of ethylene glycol dimethacrylate (M: 198.216 g / mol; 0.051 mol) are heated and dissolved in 5 g of isopropyl alcohol to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a second prepolymer solution;

[0043] (3) The first prepolymer solution prepared in step (1) is coated on a transparent pet film with a thickness of 0.05 mm to obtain a first composition 100, and the coating thickness is 70 μm. The structure of the first composition 100 is shown in Figure 1 , which comprises a first prepolymer solution layer 101 and a first substrate film 102 (pet film);

[0044] (4) The second prepolymer solution prepared in step (2) is coated on a transparent pet film with a thickness of 0.05 mm to obtain a second composition 200, and the coating thickness is 15 μm. The structure of the second composition 200 is shown in Figure 2 , which comprises a second prepolymer solution layer 201 and a second substrate film 202 (pet film);

[0045] (5) The coated surfaces of the first composition 100 and the second composition 200 prepared in steps (3) and (4) are oppositely attached, and after attachment, as shown in Figure 3 , 365 nm ultraviolet light is irradiated for 5 min, and the irradiation intensity is 150 mW / cm 2 . After irradiation is completed, the two pet films are peeled off, and the cured monovalent selective cation exchange membrane is soaked in 4% NaCl for storage.

[0046] Example 2:

[0047] A method for preparing a monovalent selective cation exchange membrane, comprising the following steps:

[0048] (1) 8.0 g of 2-acrylamido-2-methylpropanesulfonic acid (M: 207.24 g / mol, 0.039 mol) and 6.4 g of divinylbenzene (M: 130.19 g / mol, 0.05 mol) are heated and dissolved in 7 g of N-methylpyrrolidone to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a first prepolymer solution;

[0049] (2) 5 g of a dimethyldiallylammonium chloride aqueous solution (60% aqueous solution) (M: 161.672 g / mol, 0.0185 mol) and 10.20 g of ethylene glycol dimethacrylate (M: 198.216 g / mol; 0.051 mol) are heated and dissolved in 5 g of isopropyl alcohol to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a second prepolymer solution;

[0050] (3) The first prepolymer solution prepared in step (1) is coated on a transparent pet film with a thickness of 0.05 mm to obtain a first composition, and the coating thickness is 70 μm;

[0051] (4) The second prepolymer solution prepared in step (2) is coated on a transparent pet film with a thickness of 0.05 mm to obtain a second composition, and the coating thickness is 15 μm;

[0052] (5) After the coated surfaces of the first composition and the second composition prepared in steps (3) and (4) are attached to each other, 365 nm ultraviolet light is irradiated for 5 min, and the irradiation intensity is 150 mW / cm 2 After the irradiation is completed, the two pet films are peeled off, and the cured monovalent selective cation exchange membrane is immersed in 4% NaCl for storage.

[0053] Example 3:

[0054] A method for preparing a monovalent selective cation exchange membrane, comprising the following steps:

[0055] (1) 5.0 g of sodium allylsulfonate (M: 144.1 g / mol, 0.035 mol) and 7.85 g of divinylbenzene (M: 130.19 g / mol, 0.06 mol) are heated and dissolved in 9.5 g of N-methylpyrrolidone to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a first prepolymer solution;

[0056] (2) 5 g of dimethyldiallylammonium chloride aqueous solution (60% aqueous solution) (M: 161.672 g / mol, 0.0185 mol) and 10.20 g of ethylene glycol dimethacrylate (M: 198.216 g / mol; 0.051 mol) were heated and dissolved in 5 g of isopropyl alcohol to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone was added to form a second prepolymer solution;

[0057] (3) The first prepolymer solution prepared in step (1) was coated on a transparent pet film with a thickness of 0.05 mm to obtain a first composition, and the coating thickness was 70 μm;

[0058] (4) The second prepolymer solution prepared in step (2) was coated on a transparent pet film with a thickness of 0.05 mm to obtain a second composition, and the coating thickness was 15 μm;

[0059] (5) After the coated surfaces of the first composition and the second composition prepared in steps (3) and (4) were attached to each other, 365 nm ultraviolet light was irradiated for 5 min, and the irradiation intensity was 150 mW / cm 2 After the irradiation was completed, the two pet films were peeled off, and the cured monovalent selective cation exchange membrane was immersed in 4% NaCl for storage.

[0060] Example 4:

[0061] A method for preparing a monovalent selective cation exchange membrane, comprising the following steps:

[0062] (1) 9.21 g of vinylbenzenesulfonic acid (M: 184.2 g / mol, 0.05 mol) and 9.21 g of divinylbenzene (M: 130.19 g / mol, 0.07 mol) were heated and dissolved in 7.5 g of N-methylpyrrolidone to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone was added to form a first prepolymer solution;

[0063] (2) 4 g of methacryloyloxyethyltrimethylammonium chloride aqueous solution (75% aqueous solution) (M: 207.7 g / mol, 0.0144 mol) and 7.2 g of ethylene glycol dimethacrylate (M: 198.216 g / mol; 0.036 mol) were heated and dissolved in 4 g of isopropyl alcohol to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone was added to form a second prepolymer solution;

[0064] (3) The first prepolymer solution prepared in step (1) was coated on a transparent pet film with a thickness of 0.05 mm to obtain a first composition, and the coating thickness was 70 μm;

[0065] (4) The second prepolymer solution prepared in step (2) is coated on a transparent pet film with a thickness of 0.05 mm to obtain a second composition, and the coating thickness is 15 μm;

[0066] (5) After the coated surfaces of the first composition and the second composition prepared in steps (3) and (4) are attached to each other, 365 nm ultraviolet light is irradiated for 5 min, the irradiation intensity is 150 mW / cm 2 After the irradiation is completed, the two pet films are peeled off, and the cured monovalent selective cation exchange membrane is immersed in 4% NaCl for storage.

[0067] Example 5:

[0068] A method for preparing a monovalent selective cation exchange membrane includes the following steps:

[0069] (1) 9.21 g of vinylbenzenesulfonic acid (M: 184.2 g / mol, 0.05 mol) and 9.21 g of divinylbenzene (M: 130.19 g / mol, 0.07 mol) are heated and dissolved in 7.5 g of N-methylpyrrolidone to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a first prepolymer solution;

[0070] (2) 4 g of an aqueous solution of (3-acrylamidopropyl)trimethylammonium chloride (74%-76% aqueous solution) (M: 206.71 g / mol, 0.0144 mol) and 7.2 g of ethylene glycol dimethacrylate (M: 198.216 g / mol; 0.036 mol) are heated and dissolved in 4 g of isopropyl alcohol to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a second prepolymer solution;

[0071] (3) The first prepolymer solution prepared in step (1) is coated on a transparent pet film with a thickness of 0.05 mm to obtain a first composition, and the coating thickness is 70 μm;

[0072] (4) The second prepolymer solution prepared in step (2) is coated on a transparent pet film with a thickness of 0.05 mm to obtain a second composition, and the coating thickness is 15 μm;

[0073] (5) After the coated surfaces of the first composition and the second composition prepared in steps (3) and (4) are attached to each other, 365 nm ultraviolet light is irradiated for 5 min, the irradiation intensity is 150 mW / cm 2 After the irradiation is completed, the two pet films are peeled off, and the cured monovalent selective cation exchange membrane is immersed in 4% NaCl for storage.

[0074] Example 6:

[0075] A method for preparing a monovalent selective cation exchange membrane, comprising the following steps:

[0076] (1) 9.21 g of vinyl benzene sulfonic acid (M: 184.2 g / mol, 0.05 mol) and 9.21 g of divinyl benzene (M: 130.19 g / mol, 0.07 mol) are heated and dissolved in 7.5 g of N-methyl pyrrolidone to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a first prepolymer solution;

[0077] (2) 3 g of benzyl vinyl trimethyl ammonium chloride (M: 211.731 g / mol, 0.0141 mol) and 10.20 g of ethylene glycol dimethyl acrylate (M: 198.216 g / mol; 0.051 mol) are heated and dissolved in 4.5 g of isopropyl alcohol to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a second prepolymer solution;

[0078] (3) The first prepolymer solution prepared in step (1) is coated on a transparent pet film with a thickness of 0.05 mm to obtain a first composition, and the coating thickness is 70 μm;

[0079] (4) The second prepolymer solution prepared in step (2) is coated on a transparent pet film with a thickness of 0.05 mm to obtain a second composition, and the coating thickness is 15 μm;

[0080] (5) After the coated surfaces of the first composition and the second composition prepared in steps (3) and (4) are oppositely attached, 365 nm ultraviolet light is irradiated for 5 min, and the irradiation intensity is 150 mW / cm 2 After irradiation, the two pet films are peeled off, and the cured monovalent selective cation exchange membrane is soaked in 4% NaCl for storage.

[0081] Example 7:

[0082] A method for preparing a monovalent selective cation exchange membrane, comprising the following steps:

[0083] (1) 9.21 g of vinyl benzene sulfonic acid (M: 184.2 g / mol, 0.05 mol) and 9.21 g of divinyl benzene (M: 130.19 g / mol, 0.07 mol) are heated and dissolved in 7.5 g of N-methyl pyrrolidone to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a first prepolymer solution;

[0084] (2) 4 g of benzyl vinyl trimethyl ammonium chloride (M: 211.731 g / mol, 0.0189 mol) and 7.2 g of ethylene glycol dimethacrylate (M: 198.216 g / mol; 0.036 mol) were heated and dissolved in 4.5 g of isopropyl alcohol to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone was added to form a second prepolymer solution;

[0085] (3) The first prepolymer solution prepared in step (1) was coated on a transparent pet film with a thickness of 0.05 mm to obtain a first composition, and the coating thickness was 70 μm;

[0086] (4) The second prepolymer solution prepared in step (2) was coated on a transparent pet film with a thickness of 0.05 mm to obtain a second composition, and the coating thickness was 15 μm;

[0087] (5) After the coated surfaces of the first composition and the second composition prepared in steps (3) and (4) were attached to each other, 365 nm ultraviolet light was irradiated for 5 min, and the irradiation intensity was 150 mW / cm 2 After the irradiation was completed, the two pet films were peeled off, and the cured monovalent selective cation exchange membrane was immersed in 4% NaCl for storage.

[0088] Example 8:

[0089] A method for preparing a monovalent selective cation exchange membrane, comprising the following steps:

[0090] (1) 9.21 g of vinyl benzene sulfonic acid (M: 184.2 g / mol, 0.05 mol) and 9.21 g of divinyl benzene (M: 130.19 g / mol, 0.07 mol) were heated and dissolved in 7.5 g of N-methyl pyrrolidone to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone was added to form a first prepolymer solution;

[0091] (2) 3 g of benzyl vinyl trimethyl ammonium chloride (M: 211.731 g / mol, 0.0141 mol) and 11.12 g of ethylene glycol dimethacrylate (M: 198.216 g / mol; 0.056 mol) were heated and dissolved in 4.5 g of isopropyl alcohol to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone was added to form a second prepolymer solution;

[0092] (3) The first prepolymer solution prepared in step (1) was coated on a transparent pet film with a thickness of 0.05 mm to obtain a first composition, and the coating thickness was 70 μm;

[0093] (4) The second prepolymer solution prepared in step (2) is coated on a transparent pet film with a thickness of 0.05 mm to obtain a second composition, and the coating thickness is 15 μm;

[0094] (5) After the coated surfaces of the first composition and the second composition prepared in steps (3) and (4) are attached to each other, 365 nm ultraviolet light is irradiated for 5 min, the irradiation intensity is 150 mW / cm 2 After the irradiation is completed, the two pet films are peeled off, and the cured monovalent selective cation exchange membrane is immersed in 4% NaCl for storage.

[0095] Example 9:

[0096] A method for preparing a monovalent selective cation exchange membrane includes the following steps:

[0097] (1) 9.21 g of vinylbenzenesulfonic acid (M: 184.2 g / mol, 0.05 mol) and 9.21 g of divinylbenzene (M: 130.19 g / mol, 0.07 mol) are heated and dissolved in 7.5 g of N-methylpyrrolidone to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a first prepolymer solution;

[0098] (2) 3 g of benzylvinyltrimethylammonium chloride (M: 211.731 g / mol, 0.0141 mol) and 14.12 g of ethylene glycol dimethacrylate (M: 198.216 g / mol; 0.0712 mol) are heated and dissolved in 4.5 g of isopropyl alcohol to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a second prepolymer solution;

[0099] (3) The first prepolymer solution prepared in step (1) is coated on a transparent pet film with a thickness of 0.05 mm to obtain a first composition, and the coating thickness is 70 μmμm;

[0100] (4) The second prepolymer solution prepared in step (2) is coated on a transparent pet film with a thickness of 0.05 mm to obtain a second composition, and the coating thickness is 15 μm;

[0101] (5) After the coated surfaces of the first composition and the second composition prepared in steps (3) and (4) are attached to each other, 365 nm ultraviolet light is irradiated for 5 min, the irradiation intensity is 150 mW / cm 2 After the irradiation is completed, the two pet films are peeled off, and the cured monovalent selective cation exchange membrane is immersed in 4% NaCl for storage.

[0102] Example 10:

[0103] A method for preparing a monovalent selective cation exchange membrane, comprising the following steps:

[0104] (1) 9.21 g of vinylbenzenesulfonic acid (M: 184.2 g / mol, 0.05 mol) and 9.21 g of divinylbenzene (M: 130.19 g / mol, 0.07 mol) are heated and dissolved in 7.5 g of N-methylpyrrolidone to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a first prepolymer solution;

[0105] (2) 5 g of dimethyldiallylammonium chloride aqueous solution (60% aqueous solution) (M: 161.672 g / mol, 0.0185 mol) and 10.20 g of ethylene glycol dimethacrylate (M: 198.216 g / mol; 0.051 mol) are heated and dissolved in 5 g of isopropyl alcohol to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a second prepolymer solution;

[0106] (3) A transparent pet film with a thickness of 0.05 mm is used as a substrate film, and a polypropylene microporous membrane with a thickness of 67 μm, a porosity of 52%, and a pore size of less than 0.1 microns is stacked on the substrate film, and then the first prepolymer solution prepared in step (1) is coated on the polypropylene microporous membrane, the first prepolymer solution completely impregnates the polypropylene microporous membrane and contacts the surface of the pet film, to obtain a first composition, and the coating thickness is 70 μm;

[0107] (4) The second prepolymer solution prepared in step (2) is coated on the transparent pet film with a thickness of 0.05 mm to obtain a second composition, and the coating thickness is 15 μm;

[0108] (5) After the coated surfaces of the first composition and the second composition prepared in steps (3) and (4) are oppositely attached, 365 nm ultraviolet light is irradiated for 5 min, and the irradiation intensity is 150 mW / cm 2 After irradiation, the two pet films are peeled off, and the cured monovalent selective cation exchange membrane is soaked in 4% NaCl for storage, and the structure of the obtained monovalent selective cation exchange membrane is shown in Figure 4 The polypropylene microporous membrane is fixed with the first prepolymer solution layer 101 as a support layer 103.

[0109] Comparative Example 1: (Surface modification of a commercial ion exchange membrane)

[0110] A method for preparing a monovalent selective cation exchange membrane, comprising the following steps:

[0111] (1) Adopting commercial ion exchange membrane as modified base film, the commercial cation exchange membrane is soaked in 4% hydrochloric acid and 4% NaCl for 4 hours respectively, then washed with deionized water, soaked in ethanol for 4 hours, then washed with deionized water, and naturally dried for 8 hours for standby;

[0112] (2) 5 g of dimethyl diallyl ammonium chloride aqueous solution (60% aqueous solution) (M: 161.672 g / mol, 0.0185 mol) and 10.20 g of ethylene glycol dimethacrylate (M: 198.216 g / mol; 0.051 mol) are heated and dissolved in 5 g of isopropyl alcohol to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a second prepolymer solution;

[0113] (3) The second prepolymer solution of step (2) is coated on the surface of the cation exchange membrane treated in step (1), and then irradiated with 365 nm ultraviolet light for 5 min, the irradiation intensity is 150 mW / cm 2 The cured ion exchange membrane is soaked in 4% NaCl for storage. The modified monovalent selective ion exchange membrane prepared above is soaked in pure water for 4 hours, and the modified layer and the cation membrane will be peeled off.

[0114] Comparative Example 2:

[0115] A method for preparing a monovalent selective cation exchange membrane, comprising the following steps:

[0116] (1) Adopting commercial ion exchange membrane as modified base film, the commercial cation exchange membrane is soaked in 4% hydrochloric acid and 4% NaCl for 4 hours respectively, then washed with deionized water, soaked in ethanol for 4 hours, then washed with deionized water, and naturally dried for 8 hours for standby;

[0117] (2) 4 g of methacryloyloxyethyl trimethyl ammonium chloride aqueous solution (75% aqueous solution) (M: 207.7 g / mol, 0.0144 mol) and 7.2 g of ethylene glycol dimethacrylate (M: 198.216 g / mol; 0.036 mol) are heated and dissolved in 4 g of isopropyl alcohol to form a homogeneous solution, and after cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a second prepolymer solution;

[0118] (3) The second prepolymer solution of step (2) is coated on the surface of the cation exchange membrane treated in step (1), and then irradiated with 365 nm ultraviolet light for 5 min, the irradiation intensity is 150 mW / cm 2The ion exchange membrane after curing can be preserved by immersing in 4% NaCl.

[0119] Comparative Example 3

[0120] A method for preparing a monovalent selective cation exchange membrane, comprising the following steps:

[0121] (1) Commercial ion exchange membrane is used as a modified base film. The commercial cation exchange membrane is immersed in 4% hydrochloric acid and 4% NaCl for 4 hours, respectively, and then washed with deionized water. After that, the membrane is immersed in ethanol for 4 hours, washed with deionized water, and then naturally dried for 8 hours for standby;

[0122] (2) 4 g of (3-acrylamidopropyl) trimethylammonium chloride aqueous solution (74%-76% aqueous solution) (M: 206.71 g / mol, 0.0144 mol) and 7.2 g of ethylene glycol dimethacrylate (M: 198.216 g / mol; 0.036 mol) are heated and dissolved in 4 g of isopropyl alcohol to form a homogeneous solution. After cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a second prepolymer solution;

[0123] (3) The second prepolymer solution of step (2) is coated on the surface of the cation exchange membrane treated in step (1), and then irradiated with 365 nm ultraviolet light for 5 min, with an irradiation intensity of 150 mW / cm 2 The ion exchange membrane after curing can be preserved by immersing in 4% NaCl.

[0124] Comparative Example 4

[0125] A method for preparing a monovalent selective cation exchange membrane, comprising the following steps:

[0126] (1) Commercial ion exchange membrane is used as a modified base film. The commercial cation exchange membrane is immersed in 4% hydrochloric acid and 4% NaCl for 4 hours, respectively, and then washed with deionized water. After that, the membrane is immersed in ethanol for 4 hours, washed with deionized water, and then naturally dried for 8 hours for standby;

[0127] (2) 4 g of (3-acrylamidopropyl) trimethylammonium chloride aqueous solution (74%-76% aqueous solution) (M: 206.71 g / mol, 0.0144 mol) and 7.2 g of ethylene glycol dimethacrylate (M: 198.216 g / mol; 0.036 mol) are heated and dissolved in 4 g of isopropyl alcohol to form a homogeneous solution. After cooling, 0.1 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone is added to form a second prepolymer solution;

[0128] (3) The second prepolymer solution of step (2) is coated on the surface of the cation exchange membrane treated in step (1), and then irradiated with 365 nm ultraviolet light for 5 min, with an irradiation intensity of 150 mW / cm 2 The cured ion exchange membrane is immersed in 4% NaCl for storage.

[0129] According to "Ion Exchange Membrane Part 1: Electrically Driven Membrane" HY / T 166.1-2013, the membrane surface resistance, water content, ion exchange capacity and selective permeability of the ion exchange membranes prepared in the examples and comparative examples are tested, and the test results are shown in Table 1, wherein the migration number refers to the proportion of cations passing through the cation exchange membrane.

[0130] Table 1. Performance test results

[0131]

[0132] The selective separation effect test method: the selective test device is formed in the order of anode-cation exchange membrane-measured membrane-anion exchange membrane-cathode as shown in Figure 5 .

[0133] The effective area of the measured membrane is 19.6 cm 2 , and the constant current is 100 A / m 2 . Run for 2h, dilute chamber: 3000ml of 0.1mol / L LiCl+0.5mol / L MgCl2 mixed solution, concentrated chamber: 300ml of 0.02mol / L LiCl solution, anode and cathode chamber: 1L of 0.5mol / L NaCl solution, take the concentrated chamber (10ml) sample after 2h to measure ICP, and detect the ion concentration change and pH change.

[0134] The selective separation performance of the membrane is represented by the monovalent ion selective separation coefficient (P), and the specific calculation process is:

[0135]

[0136] Wherein, A, V, t are the effective membrane area (m 2 ), the volume of the concentrated chamber (L) and the running time (h) respectively. C t and C0are the ion concentration (mol / L) of the concentrated chamber at the running time t and the initial time respectively. Li + and C Mg 2+ are the initial Li and Mg concentrations (mol / L) in the dilute chamber respectively, and J represents the ion flux.

[0137] The test results are shown in Table 2: wherein the current efficiency is the ratio of the number of migrated cations to the number of electrons passing through the electrode.

[0138] Table 2. Test results

[0139]

[0140] As can be seen from Table 2, the monovalent selective cation exchange membrane prepared by the integrated molding technology has a Li / Mg selective separation coefficient of 8 or more. Compared with Example 6, Example 7 improves the proportion of the second exchange monomer (benzyl ethylene group trimethyl ammonium chloride), so that the unit mass charge density of the exchange membrane of Example 7 is improved. The improvement of the charge density of the selective layer in Example 7 can significantly improve the repulsion of the monovalent selective cation exchange membrane to high-valence magnesium ions, so that the Li / Mg selective separation coefficient is improved, accompanied by the phenomenon of current efficiency decrease and pH disturbance of the test system, which shows that the control of the charge amount can effectively control the selectivity of the ion exchange membrane; the crosslinking degree of the selective layer in Example 8 and Example 9 is improved, so that the pore size of the exchange membrane is reduced, and the selective separation coefficient is also improved, which shows that the control of the pore size can also effectively control the selective separation effect of the monovalent selective cation exchange membrane of the application.

[0141] Comparative Examples 1-4 use commercial cation exchange membranes as base membranes, and a positive charge pre-polymer solution is coated on one surface of the cation exchange membrane to form a modified layer. As can be seen from Table 2, it has almost no good selectivity, which is almost the same as the unmodified cation exchange membrane. Comparative Examples 1 and 2 show that the modified membrane soaked in pure water has a problem of separation between the modified layer and the cation exchange membrane, which shows that the non-bonding method is not stable. Since the swelling rates of the base membrane and the modified layer in pure water are inconsistent, serious water separation occurs, so the selectivity is poor. The test results are consistent with the performance of the unmodified cation exchange membrane. Comparative Examples 3 and 4 do not have the problem of peeling of the modified layer after soaking in pure water, but the separation effect is poor and the current efficiency is low. The main reason is that the modified monomer forms an ion pair with the base membrane monomer, which reduces the current efficiency and consumes the positive charge of the modified layer, resulting in poor performance. The scheme of the application can realize the solidification of the modified layer and the base membrane in one step, and the above problems do not occur.

[0142] As can be seen from the above examples, the monovalent selective cation exchange membrane of the application completely abandons the preparation strategy of surface modification in conventional technology, and the base membrane and the modified layer are prepared by sequential molding. During the process of simultaneous molding of the modified layer and the base membrane, the monomers in the liquid interface diffuse and polymerize freely under the condition of photo initiation, forming a covalent bond without an interface layer, which has the same chemical stability as the base membrane. The preparation process is simple and does not require complex multi-step modification steps. The process can completely adapt to the preparation technology route of ordinary homogeneous cation exchange membranes, so the preparation cost of the monovalent selective cation exchange membrane can be greatly reduced.

Claims

1. A method for preparing a monovalent selective cation exchange membrane, characterized in that: The following steps are involved: (1) mixing a first exchange monomer, a first cross-linking agent, a first solvent, and a first initiator to obtain a first prepolymer solution; (2) mixing a second exchange monomer, a second cross-linking agent, a second solvent, and a second initiator to obtain a second prepolymer solution; (3) applying the first prepolymer solution on a first substrate film to obtain a first composition; (4) applying the second prepolymer solution on a second substrate film to obtain a second composition; (5) The coating surfaces of the first composition and the second composition are placed relative to each other. After the polymerization is initiated, the first substrate film and the second substrate film are peeled off to obtain a monovalent selective cation exchange membrane.

2. The method for preparing a monovalent selective cation exchange membrane according to claim 1, characterized in that: The first exchange monomer includes at least one of vinylbenzenesulfonic acid and its corresponding salts, vinylsulfonic acid and its corresponding salts, allylsulfonic acid and its corresponding salts, methacrylic acid and its corresponding salts, 2-acrylamide-2-methylpropanesulfonic acid and its corresponding salts, 2-sulfoethyl 2-methyl-2-acrylate and its corresponding salts, 3-sulfonyl methacrylate and its corresponding salts, allyloxyhydroxypropylsulfonic acid and its corresponding salts, acrylic acid and its corresponding salts, methacrylic acid and its corresponding salts, 4-vinylbenzoic acid and its corresponding salts, trichloroacrylic acid and its corresponding salts, and vinylphosphoric acid and its corresponding salts.

3. The method for preparing a monovalent selective cation exchange membrane according to claim 1, wherein: The second exchange monomer includes at least one of dimethyldiallylammonium chloride, benzylvinyltrimethylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, methacrylamidopropyltrimethylammonium chloride, (3-acrylamidopropyl)trimethylammonium chloride, 2-vinylpyridine, 4-vinylpyridine and vinylimidazole.

4. The method for preparing a monovalent selective cation exchange membrane according to claim 1, wherein: The first cross-linking agent and the second cross-linking agent include at least one of diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, 1,3-butanediol diacrylate, 1,4-butanediol dimethacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, tetraethylene glycol dimethacrylate, divinylbenzene, 4,4'-divinyl-1,1'-biphenyl, trimethylolpropane triacrylate, isophorone diisocyanate, trimethylolpropane trimethacrylate, ethoxylated bisphenol A di(meth)acrylate, ethoxylated trimethylolpropane triacrylate, and propoxylated trimethylolpropane triacrylate.

5. The method for preparing a monovalent selective cation exchange membrane according to claim 1, characterized in that: The first solvent and the second solvent include at least one of 3-cyclobutene sulfone, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, methanol, ethanol, isopropyl alcohol, glycerol and diethylene glycol.

6. The method for preparing a monovalent selective cation exchange membrane according to claim 1, characterized in that: The first initiator and the second initiator include at least one of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, benzoyl peroxide, tert-butyl benzoyl peroxide, methyl ethyl ketone peroxide, (2,4,6-trimethylbenzoyl)diphenylphosphine oxide, ethyl 2,4,6-trimethylbenzoylphosphonate, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxy-cyclohexyl-phenyl ketone, 2-methyl-1-[4-methylthiophenyl]-2-morpholinyl-1-propanone, 2-hydroxy-2-methylpropiophenone and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide.

7. The method for preparing a monovalent selective cation exchange membrane according to claim 1, characterized in that: The molar ratio of the first exchange monomer to the first cross-linking agent is (1-3): (0.5-3).

8. The method for preparing a monovalent selective cation exchange membrane according to claim 1, characterized in that: The mass ratio of the sum of the mass of the first exchange monomer and the first cross-linking agent to the mass of the first initiator is 100:(0.1-1.5).

9. The method for preparing a monovalent selective cation exchange membrane according to claim 1, characterized in that: The molar ratio of the second exchange monomer to the second cross-linking agent is (1-3): (0.5-3).

10. A monovalent selective cation exchange membrane, characterized in that: The invention is prepared by the preparation method according to any one of claims 1 to 9.

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