Preparation method of green light polymerization anion exchange membrane

Abstract

This invention provides a method for preparing a green photopolymerizable anion exchange membrane. The method first dissolves a brominated microporous polymer PIM-Br and a photoinitiator in chloromethylstyrene (VBC) to obtain a yellowish-brown solution. The solution is then cast onto a glass plate and photocured under a nitrogen atmosphere using ultraviolet light. After curing, the membrane is directly immersed in a bis-tertiary amine reagent. The green photopolymerizable anion exchange membrane is obtained through nucleophilic substitution reactions between the bromomethyl group in PIM-Br and the chloromethyl group in VBC and the bis-tertiary amine group. Compared with other methods, the anion exchange membrane preparation method provided by this invention utilizes a free radical polymerization reaction initiated by ultraviolet light irradiation, which has advantages such as short curing time, fast polymerization speed, and no reaction temperature limitation. Furthermore, the use of organic solvents is completely avoided during the preparation process. The prepared anion exchange membrane exhibits excellent electrodialysis desalination performance, resulting in significant economic and environmental benefits.

Description

Technical Field

[0001] This invention belongs to the field of membrane technology, specifically relating to a method for preparing a green photopolymerization anion exchange membrane. Background Technology

[0002] Ion exchange membranes are membrane-like ion exchange resins containing fixed ionic groups, enabling selective permeation of ions in solution. Therefore, ion exchange membranes have wide applications in water treatment, heavy metal recovery, and other fields. Anion exchange membranes are a type of ion exchange membrane carrying positively charged anion exchange groups, capable of conducting anions through ion exchange.

[0003] Currently, there are two common methods for preparing anion exchange membranes: (1) dissolving the monomer in an organic solvent, then polymerizing and modifying it, and finally removing the organic solvent to obtain the anion exchange membrane. (2) dissolving the polymer in an organic solvent, modifying it, and then removing the organic solvent to obtain the anion exchange membrane. Obviously, both methods require the use and discharge of large amounts of organic solvents, which increases the cost of membrane fabrication and causes serious environmental pollution.

[0004] Chinese Patent Application No. 200910157584.2 discloses a method for preparing anion exchange membrane. The method uses styrene as a monomer and divinylbenzene as a crosslinking agent. The mixture is then blended with a pore-forming agent and a dispersant mixed with an organic solvent (toluene), and subjected to high-temperature suspension polymerization for several hours to obtain a styrene copolymer. The styrene copolymer is then dissolved in an organic solvent (tetrahydrofuran) for chloromethylation and quaternization to obtain a modified polymer solution. Finally, the modified polymer solution is coated onto a substrate and immersed in deionized water to remove the organic solvent, thus obtaining an anion exchange membrane.

[0005] Chinese Patent Application No. 201010174360.5 discloses a method for preparing anion exchange membrane, which involves dissolving polyarylsulfone in an organic solvent (1,2-dichloroethane) for chloromethylation, precipitating it with methanol, then dissolving it in another organic solvent (N,N-dimethylformamide) for quaternization, and finally removing the organic solvent by heating to obtain the anion exchange membrane.

[0006] However, the existing technologies represented by the above methods have the following drawbacks in the preparation of anion exchange membranes: (1) the membrane preparation process is cumbersome; (2) the membrane preparation cost is high, and a large amount of organic solvent needs to be used repeatedly in the membrane formation process; (3) the environmental pollution is serious, and a large amount of organic solvent needs to be emitted in the membrane formation process. Therefore, it is very important to develop a green and simple method to prepare anion exchange membranes.

[0007] Chinese Patent Application No. 201110057825.3 discloses a solvent-free preparation method for anion exchange membranes. The method involves dissolving a polymeric reinforcing agent in a mixed solution of monomers and crosslinking agents, adding a thermal initiator to form a casting solution, coating it onto reinforcing fabric, and then performing a film-forming reaction via thermal polymerization for 6-48 hours. Finally, the membrane is obtained through quaternization. Although this method avoids the use of organic solvents during membrane preparation, the following problems still exist: (1) There is no crosslinking between the polymer and the monomer, resulting in a heterogeneous membrane with unstable performance; (2) The use of thermal polymerization in the preparation of the base membrane leads to long polymerization time and high energy consumption.

[0008] The above method does not require the use of organic solvents in the preparation of anion exchange membranes, avoiding the economic and environmental problems associated with their use, making it a green membrane fabrication process. However, the polymer and monomers are not cross-linked, resulting in unstable performance. Furthermore, the base membrane is prepared via thermal polymerization, which requires heating to initiate the polymerization reaction, leading to a slow initiation process and a long polymerization time.

[0009] In summary, the preparation of traditional anion exchange membranes is not only cumbersome, but also increases costs and causes serious environmental pollution due to the use of large amounts of organic solvents as reaction media. While existing technologies can avoid the use of organic solvents, they still suffer from problems such as lengthy membrane fabrication processes and poor membrane performance.

[0010] Photopolymerization, an environmentally friendly green technology developed in the 1960s, offers advantages over traditional thermally induced polymerization, including lower energy consumption, faster polymerization rates, no temperature limitations, environmental friendliness, and lower cost. It has been widely applied in traditional fields such as coatings and inks. Currently, photopolymerization is rapidly developing in the field of membrane preparation.

[0011] A method for preparing a high-performance anion exchange membrane was disclosed in the *Journal of the Electrochemical Society* (2015, 162(10): F1206-F1211). The method involves dissolving triallyl-1,3,5-triazine-2,4,6-trione (TATAO), 1,6-hexanedithiol, diallyl dimethyl ammonium chloride, and photoinitiator 651 in dimethyl sulfoxide (DMSO). The copolymer is obtained by irradiation with ultraviolet light for 10 minutes, and finally, the DMSO is removed to obtain the anion exchange membrane. Although this method employs photopolymerization technology, which avoids problems such as slow polymerization rate and long curing time, it still cannot avoid the use of organic solvents.

[0012] Therefore, to address the problems existing in traditional anion exchange membrane preparation methods, it is necessary to combine photopolymerization technology with solvent-free methods to explore a simple, green, environmentally friendly, pollution-free, and high-performance anion exchange membrane preparation route. Summary of the Invention

[0013] In view of this, the purpose of the present invention is to provide a method for preparing a green photopolymerization anion exchange membrane to solve the above problems.

[0014] To achieve the above objectives, the present invention adopts the following technical solution:

[0015] This invention claims a method for preparing a green photopolymerizable anion exchange membrane, comprising the following steps: first, dissolving a brominated self-porous polymer (PIM-Br) and a photoinitiator in chloromethylstyrene (VBC) to obtain a yellowish-brown solution. Then, casting the solution onto a glass plate to fix the thickness, curing it under a nitrogen atmosphere using ultraviolet light (365 nm, 500 W), followed by immersion in a bis-tertiary amine reagent. The bis-tertiary amine quaternizing reagent is then used to perform a nucleophilic substitution reaction between the bromomethyl group of PIM-Br and the chloromethyl group of VBC, resulting in a one-step crosslinking and quaternization process, yielding a homogeneous crosslinked photopolymerizable anion exchange membrane (AEMs).

[0016] The structural formula of the VBC is ( ); The structural formula of PIM-Br is: ( ); where x = 0.5 - 1.

[0017] The degree of bromination of the PIM-Br is 50%-100%, where the degree of bromination refers to the molar percentage of repeating units containing bromomethyl groups to all repeating units, i.e., x in the structural formula shown above.

[0018] The preparation method of PIM-Br includes the following steps: 3-methylcatechol is dissolved in a mixed solution of hydrobromic acid and glacial acetic acid. After complete dissolution, acetone is added, the temperature is raised to 120°C, and the mixture is stirred for 12 h to obtain a brown solution; the brown solution is then slowly poured into deionized water to precipitate, filtered, and washed to obtain white TTSBI-M; TTSBI-M, tetrafluoroterephthalonitrile, and K2CO3 are added to anhydrous NMP, stirred in an oil bath at 155°C, and then anhydrous toluene is added. The mixture is reacted under a nitrogen atmosphere for 6 h to obtain the microporous polymer PIM-M; PIM-M is dissolved in chlorobenzene, and then N-bromosuccinimide (NBS) and azobisisobutyronitrile (AIBN) are added sequentially. The mixture is reacted at 135°C for 6 h under a nitrogen atmosphere. h, by adjusting the molar ratio of PIM-M to NBS (PIM-M:NBS=1:(0.65~3)), PIM-Br with a bromination degree of 50%-100% can be obtained.

[0019] The photoinitiator is one of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxycyclohexylphenyl ketone, and 2-methyl-2-(4-morpholino)-1-[4-(methylthio)phenyl]-1-propanone.

[0020] The mass ratio of VBC, photoinitiator and PIM-Br is 1:0.05:(0.02~0.2).

[0021] The light curing time is 20-30 minutes.

[0022] The bis-tertiary amine reagent is a solution formed by dissolving one of the following in an organic solvent: 4,4'-bipyridine, 1,4-diazidobicyclo[2.2.2]octane, N,N,N',N'-tetramethylethylenediamine, or N,N,N',N'-tetramethyl-1,4-diaminobutane. The solvent is methanol or ethanol.

[0023] The base film is immersed in a bis-tertiary amine reagent at a temperature of 40-60°C for 0.5-3 hours.

[0024] The present invention also claims protection for the anion exchange membrane prepared by the above method, which is a polymer copolymer formed by polymerization of brominated microporous polymer, VBC and photoinitiator by ultraviolet light irradiation, and then grafting functional groups into the membrane through a one-step crosslinking quaternization reaction and crosslinking between the polymer and monomer to form a homogeneous polymer membrane.

[0025] The significant advantages of this invention are:

[0026] (1) Green and environmentally friendly: The present invention uses a one-step method of directly dissolving the polymer with monomers and then photopolymerizing to form a film, thereby avoiding the use of organic solvents in the film preparation process, achieving zero waste discharge, which is a green film preparation method with outstanding environmental benefits.

[0027] (2) Simple and efficient film formation: The present invention uses ultraviolet light to initiate monomer polymerization to form a film. Compared with thermally initiated polymerization, it has a shorter curing time and does not require harsh conditions such as high temperature and high pressure, which has higher economic benefits.

[0028] (3) Controllable performance: The present invention can effectively control the physicochemical properties of the prepared anion exchange membrane by adjusting the addition ratio of each component, the light irradiation time, and the soaking temperature and time of the bis-tertiary amine reagent, thereby selecting the anion exchange membrane with the best performance.

[0029] (4) Uniform structure: The present invention uses a bis-tertiary amine reagent to crosslink brominated self-microporous polymer with VBC, and the prepared anion exchange membrane has a uniform structure, which is a homogeneous anion exchange membrane.

[0030] (5) It has good potential for electrodialysis desalination: The anion exchange membrane prepared by the present invention has a high desalination capacity in the laboratory electrodialysis desalination performance test. Attached Figure Description

[0031] Figure 1 The images show the 1H NMR spectra of TTSBI-M, PIM-M, and PIM-Br synthesized in Example 1. Comparison of the characteristic 1H NMR peak positions, peak shapes, and peak areas of each substance indicates that PIM-Br with 100% bromination was successfully synthesized.

[0032] Figure 2 XPS images of the photopolymerized base membrane and the cross-linked photopolymerized anion exchange membrane after photocuring in Example 1 (without 4,4'-bipyridine crosslinking). Comparison of the characteristic peaks of the base membrane and the cross-linked modified membrane indicates that PIM-Br successfully reacted with VBC and 4,4'-bipyridine.

[0033] Figure 3 (a) is a SEM image of the photopolymerized base membrane without 4,4'-bipyridine crosslinking after photocuring in Example 1; (b) is a SEM image of the crosslinked modified photopolymerized anion exchange membrane. The morphology comparison shows that the crosslinked membrane with 4,4'-bipyridine changes from an uncrosslinked heterogeneous structure to a homogeneous structure. Detailed Implementation

[0034] The technical solution of the present invention will be clearly and completely described below using embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] All chemical reagents used in the embodiments of this invention are commercially available.

[0036] Example 1

[0037] 11.2 g (90 mmol) of 3-methylcatechol was dissolved in a mixed solution of hydrobromic acid (24 ml, 442 mmol) and glacial acetic acid (22 ml, 423 mmol). After complete dissolution, acetone (14 ml, 190 mmol) was added, the temperature was raised to 120 °C, and the reaction was stirred for 12 h to obtain a brown solution. The solution was then slowly poured into deionized water to precipitate the precipitate. After filtration and washing, white TTSBI-M was obtained. 5.527 g (15 mmol) of TTSBI-M, 3.014 g (15 ml) of tetrafluoroterephthalonitrile (TFTPN), and 5.183 g (37.5 mmol) of K2CO3 were placed in a round-bottom flask, 30 ml of anhydrous NMP was added, and the mixture was stirred in an oil bath at 155 °C. Subsequently, 10 ml of anhydrous toluene was added, and the reaction was carried out under a nitrogen atmosphere for 6 h to obtain a bright yellow viscous liquid. The solution was slowly poured into a large amount of methanol to obtain a bright yellow solid. After washing repeatedly with methanol and water, a microporous polymer (PIM-M) was obtained. 5 g (10 mmol) of PIM-M was placed in a round-bottom flask and dissolved in 100 ml of chlorobenzene. Then, 5.6 g (30 mmol) of N-bromosuccinimide (NBS) and 0.5916 g (3.6 mmol) of azobisisobutyronitrile (AIBN) were added sequentially to the solution. Under a nitrogen atmosphere, the mixture was refluxed in a constant temperature oil bath at 135 °C for 6 h to obtain an orange-yellow solution. This solution was then slowly poured into methanol to precipitate PIM-Br with 100% bromination.

[0038] 0.15 g of 100% bromide PIM-Br was dissolved in 1.0 g of VBC and 0.05 g of 2-hydroxy-2-methyl-1-phenyl-1-propanone, and then uniformly cast onto a glass plate. Free radical polymerization was initiated by irradiation with ultraviolet light at a wavelength of 365 nm for 20 minutes to obtain a base film. The base film was then immersed in a 4,4'-bipyridine ethanol solution at 60 °C for 2.5 h to obtain an anion exchange membrane.

[0039] The anion exchange membrane prepared in this embodiment has an ion exchange capacity of 2.23 mmol·g. -1 The limiting current density is 19.76 mA·cm⁻¹. -2 The surface resistivity of the film is 0.85 Ω·cm. 2 The ion transference number was 0.96. For comparison, the ion exchange capacity of the Japanese commercial membrane AMV was 2.20 mmol·L⁻¹. -1 The limiting current density is 16.98 mA·cm⁻¹. -2 The surface resistivity of the film is 2.4 Ω·cm. 2 The ion transport number is 0.95.

[0040] The membrane in this embodiment was used for laboratory electrodialysis desalination performance testing, and its desalination performance was compared with that of the Japanese commercial membrane AMV. The experimental conditions were as follows: effective membrane area 7.07 cm². 2 The operating current was 0.11 A, the duration was 270 min, and the desalination system was a 0.1 M NaCl solution. Electrodialysis desalination performance tests showed that the membrane in this embodiment achieved a desalination rate of 90.3%, a current efficiency of 97.73%, and a membrane stack energy consumption of 5.48 kWh·kg⁻¹. -1 The desalination rate of Japanese commercial AMV membrane is 79.3%, the current efficiency is 87.43%, and the membrane stack energy consumption is 6.83 kWh·kg⁻¹. -1 .

[0041] Compared to the commercially available Japanese membrane AMV, the anion exchange membrane prepared in Example 1 exhibits superior electrodialysis desalination performance. Specifically, the desalination rate increased by 13.9%, the current efficiency increased by 11.8%, and the membrane stack energy consumption decreased by 19.8%. This demonstrates that the use of the quaternizing agent 4,4'-bipyridine resulted in the formation of numerous charged groups within the membrane, thereby achieving excellent electrodialysis desalination performance. This also indicates that the membrane preparation method used in this example possesses certain environmental and economic benefits.

[0042] Example 2

[0043] PIM-Br with a bromide concentration of 0.025% was dissolved in 1.0 g of VBC and 0.05 g of photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone, and then uniformly cast onto a glass plate. Free radical polymerization was initiated under ultraviolet light with a wavelength of 365 nm for 20 minutes to obtain a base film. The base film was then immersed in a 4,4'-bipyridine ethanol solution at 60 °C for 2.5 h to obtain an anion exchange membrane.

[0044] The tests were conducted under the same conditions as in Example 1. The ion exchange capacity of the anion exchange membrane prepared in this example was 1.98 mmol·g. -1 The limiting current density is 17.03 mA·cm⁻¹. -2 The surface resistivity of the film is 1.2 Ω·cm. 2 The ion transport number is 0.92. Electrodialysis desalination performance tests show that the membrane in this embodiment has a desalination rate of 85.2%, a current efficiency of 89.51%, and a membrane stack energy consumption of 5.92 kWh·kg⁻¹. -1 .

[0045] Example 3

[0046] The molar ratio of PIM-M to NBS was adjusted to 1:0.65, and the remaining conditions were the same as in Example 1, to prepare PIM-Br with 50% bromide. 0.15 g of 50% bromide PIM-Br was dissolved in 1.0 g of VBC and 0.05 g of photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone, then uniformly cast onto a glass plate. Free radical polymerization was initiated under ultraviolet light at a wavelength of 365 nm for 20 minutes to obtain a base film, which was then immersed in a 4,4'-bipyridine ethanol solution at 60°C for 2.5 h to obtain an anion exchange membrane.

[0047] The tests were conducted under the same conditions as in Example 1. The ion exchange capacity of the anion exchange membrane prepared in this example was 2.03 mmol·g. -1 The limiting current density is 17.58 mA·cm⁻¹. -2 The surface resistivity of the film is 1.0 Ω·cm. 2 The ion transport number is 0.92. Electrodialysis desalination performance tests show that the membrane in this embodiment has a desalination rate of 85.80%, a current efficiency of 90.44%, and a membrane stack energy consumption of 5.95 kWh·kg⁻¹. -1 .

[0048] Example 4

[0049] By changing the illumination time used in Example 1 to 30 minutes, while keeping the other steps the same, an anion exchange membrane with similar performance and structure was obtained.

[0050] Example 5

[0051] The photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone used in Example 1 was replaced by 1-hydroxycyclohexylphenyl methyl ketone, and the remaining steps were the same, to obtain anion exchange membranes with similar performance and structure.

[0052] Example 6

[0053] The photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone used in Example 1 was replaced by an equal mass of 2-methyl-2-(4-morpholino)-1-[4-(methylthio)phenyl]-1-propanone, and the remaining steps were the same, to obtain an anion exchange membrane with similar performance and structure.

[0054] Example 7

[0055] The 4,4'-bipyridine ethanol solution used in Example 1 was replaced with a 1,4-diazidobicyclo[2.2.2]octane ethanol solution, and the remaining steps were the same, resulting in an anion exchange membrane with similar performance and structure.

[0056] Example 8

[0057] The 4,4'-bipyridine ethanol solution used in Example 1 was replaced with N,N,N',N'-tetramethylethylenediamine ethanol solution, and the remaining steps were the same, resulting in anion exchange membranes with similar performance and structure.

[0058] Example 9

[0059] The 4,4'-bipyridine ethanol solution used in Example 1 was replaced with N,N,N',N'-tetramethyl-1,4-diaminobutane ethanol solution, and the remaining steps were the same, resulting in anion exchange membranes with similar performance and structure.

[0060] Example 10

[0061] The 4,4'-bipyridine ethanol solution used in Example 1 was replaced with a 4,4'-bipyridine methanol solution, and the remaining steps were the same, resulting in anion exchange membranes with similar performance and structure.

[0062] Example 11

[0063] The 4,4'-bipyridine ethanol solution used in Example 1 was replaced with a 1,4-diazidobicyclo[2.2.2]octane methanol solution, and the remaining steps were the same, resulting in anion exchange membranes with similar performance and structure.

[0064] Example 12

[0065] The 4,4'-bipyridine ethanol solution used in Example 1 was replaced with N,N,N',N'-tetramethylethylenediamine methanol solution, and the remaining steps were the same, resulting in anion exchange membranes with similar performance and structure.

[0066] Example 13

[0067] The 4,4'-bipyridine ethanol solution used in Example 1 was replaced with an N,N,N',N'-tetramethyl-1,4-diaminobutane methanol solution, and the remaining steps were the same, resulting in an anion exchange membrane with similar performance and structure.

[0068] Example 14

[0069] By changing the soaking temperature used in Example 1 to 40°C, while keeping the other steps the same, an anion exchange membrane with similar performance and structure was obtained.

[0070] Example 15

[0071] By changing the soaking time used in Example 1 to 0.5 h, while keeping the other steps the same, an anion exchange membrane with similar performance and structure was obtained.

[0072] Example 16

[0073] The soaking time used in Example 1 was changed to 3.0 h, while the other steps remained the same, resulting in anion exchange membranes with similar performance and structure.

[0074] The results of the above embodiments show that by using the preparation method of the present invention, the properties of the prepared anion exchange membrane can be effectively controlled by controlling the composition of the casting solution during the membrane preparation process, including the content of polymer reinforcing agent and crosslinking agent, so as to meet the requirements of electrodialysis desalination application and select the anion exchange membrane with the best performance.

[0075] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a green light polymerized anion exchange membrane, characterized by, The method comprises the following steps: Dissolve brominated self-porous polymer PIM-Br and a photoinitiator in chloromethyl styrene VBC to obtain a uniform solution, then cast the solution on a glass plate, and directly immerse the base film in a di-tertiary amine base after curing by irradiation of an ultraviolet lamp with a wavelength of 365 nm under a nitrogen atmosphere to obtain the green photoanion exchange membrane through nucleophilic substitution reaction of bromomethyl in PIM-Br and chloromethyl in VBC with the di-tertiary amine base.

2. The method for preparing a green light polymerization anion exchange membrane according to claim 1, characterized by, The photoinitiator is one of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxycyclohexyl phenyl ketone, and 2-methyl-2-(4-morpholinyl)-1-[4-(methylthio)phenyl]-1-propanone.

3. The method for preparing the green photopolymerizable anion exchange membrane according to claim 1, characterized in that, The mass ratio of chloromethyl styrene, photoinitiator, and brominated self-porous polymer is 1:0.05:(0.02-0.08).

4. The method for preparing the green photopolymerizable anion exchange membrane according to claim 1, characterized in that, The light curing time is 20-30 minutes.

5. The method for preparing the green photopolymerizable anion exchange membrane according to claim 1, characterized in that, The di-tertiary amine base is a solution of one of 4,4'-dipyridyl, 1,4-diazidobicyclo[2.2.2]octane, N,N,N',N'-tetramethylethylenediamine, and N,N,N',N'-tetramethyl-1,4-diaminobutane dissolved in an organic solvent, and the solvent is methanol or ethanol.

6. The method for preparing the green photopolymerizable anion exchange membrane according to claim 1, characterized in that, The immersion temperature of the base film in the di-tertiary amine base is 40-60 DEG C, and the immersion time is 0.5-3 h.

7. The method for preparing the green photopolymerizable anion exchange membrane according to claim 1, characterized in that, The structural formula of PIM-Br is: wherein x = 0.5-1.

8. An anion exchange membrane prepared by the method of any one of claims 1-7.

Images