A method for preparing a microporous polymer anion exchange membrane

Abstract

The application discloses a preparation method of an anion exchange membrane for diffusion dialysis from a self-microporous material. The method reacts a self-microporous polymer containing methyl (PIM-M) with liquid bromine to prepare a bromomethylated self-microporous polymer (PIM-Br), dissolves the PIM-Br in an organic solvent to form a uniform casting solution, coats the casting solution on a glass plate, and prepares a PIM-Br-based membrane after solvent volatilization. Finally, the membrane is soaked in an N-substituted imidazole or tertiary amine solution for positive charge modification, thereby preparing a self-microporous polymer anion exchange membrane. The self-microporous membrane material is used as a film-forming material, the internal free space volume is used to greatly reduce the ion transmission resistance, thereby greatly improving the acid dialysis coefficient and acid treatment efficiency, and the application has important significance for the development of waste acid resource technology in China.

Description

Technical Field

[0001] This invention belongs to the field of ion exchange membrane technology, specifically relating to a method for preparing an anion exchange membrane with its own microporous material for diffusion dialysis. Background Technology

[0002] Diffusion dialysis, as the most economically promising waste acid treatment technology, is limited in its large-scale application due to its relatively low treatment efficiency. This is mainly caused by the low acid dialysis coefficient of the anion exchange membrane, the core component of diffusion dialysis. Taking the commercial DF-120 anion exchange membrane as an example, when applied to the diffusion dialysis HCl / FeCl2 system for HCl recovery, the acid dialysis coefficient is only 0.0085 m / h, and the separation coefficient is 18.5. This is because the dense membrane structure of the DF-120 anion exchange membrane hinders ion transport. According to the dissolution-diffusion model, the ion transport rate in the membrane is positively correlated with the free space volume within the membrane. Due to the low internal free space volume, the dense membrane has a slow ion transport rate, resulting in a low acid dialysis coefficient. To improve the acid recovery rate of diffusion dialysis, it is necessary to increase the free space volume within the anion exchange membrane.

[0003] The Dutch journal *Journal of Membrane of Science* (2023, 673) disclosed a method for preparing porous anion exchange membranes. The method involves dissolving chloromethylated polyethersulfone (CMPES) in NMP as a starting material and preparing a porous base membrane via a solvent-free phase inversion method. This base membrane is then immersed in a PMDETA (pentamethyldivinyltriamine) solution for simultaneous crosslinking and quaternization to obtain a porous crosslinked anion exchange membrane. Due to the ample free space within the porous membrane, this porous crosslinked anion exchange membrane exhibits superior acid recovery performance, with an acid dialysis coefficient 2.8 times that of the DF-120 anion exchange membrane. However, the mechanical strength of this porous ion exchange membrane is poor, with a tensile strength of only 4.7 MPa. Therefore, finding an anion exchange membrane that combines high free space volume with high mechanical properties remains an urgent problem to be solved in the field of diffusion dialysis acid recovery.

[0004] Polymers of Intrinsic Microporosity (PIMs) are rigid polymers with highly developed microporous structures. The ample free space provided by the micropores gives them broad application potential in fields such as gas separation and fuel cells. It is anticipated that using PIMs to prepare anion exchange membranes for diffusion dialysis acid recovery will significantly improve the treatment efficiency of waste acid. PIM-1 is one of the earliest studied and reported PIM materials and is currently one of the most widely used. Because PIM-1 does not contain active groups, current research generally uses N-bromosuccinimide (NBS) as a brominating agent and azobisisobutyronitrile (AIBN) as an initiator to brominate PIM-1 before further improvements.

[0005] The British journal *Journal of Materials Chemistry A* (2016, 4, 17655-17659) discloses a method for preparing an anion exchange membrane using a methyl-containing PIM-1 material (PIM-M) as a starting material, brominated with NBS, and then quaternized with trimethylamine. This membrane exhibits extremely high ionic conductivity due to its extremely high free space volume.

[0006] The Dutch journal *Journal of Membrane Science* (2021, 638, 119668) reported a method for functionalizing the structure of PIM-1. The method first uses N-bromosuccinimide (NBS) as a brominating agent and azobisisobutyronitrile (AIBN) as an initiator to modify PIM-1, preparing a bromomethylated microporous polymer (PIM-Br). Based on the high reactivity of bromomethyl groups, polybenzimidazole (PBI) is used to crosslink and modify PIM-1 to prepare a gas separation membrane. The report points out that bromination of PIM-1 with NBS and AIBN leads to a decrease in the molecular weight and mechanical strength of the final brominated polymer (PIM-Br), resulting in poor mechanical properties of the final membrane.

[0007] In summary, developing high free space volume anion exchange membranes is an effective means to address the low throughput challenges faced by diffusion dialysis acid recovery applications. PIM materials, due to their highly developed microporous structure, are expected to be among the most promising materials for anion exchange membranes used in diffusion dialysis acid recovery. However, existing improvement methods face problems such as decreased molecular weight of PIM materials and poor membrane mechanical strength. Therefore, seeking a method to avoid the decrease in molecular weight of PIM materials in the preparation of anion exchange membranes is of great significance to the development of diffusion dialysis acid recovery technology. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing anion exchange membrane for diffusion dialysis based on a self-porous material, in order to overcome the shortcomings of low acid treatment efficiency in the prior art.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for preparing a self-microporous polymer anion exchange membrane includes the following steps: dissolving a methylated self-microporous polymer (PIM-M) formed by polymerizing 5,5',6,6'-tetrahydroxy-3,3,4,3',3',4'-hexamethyl-1,1'-spirobisindane (TTSBI-M) monomer and 2,3,5,6-tetrafluoroterephthalonitrile (TFTPN) monomer in chlorobenzene to form a homogeneous solution; adding liquid bromine and carrying out a bromination reaction at 135°C for 3-24 h to obtain a bromomethylated self-microporous polymer (PIM-Br); dissolving it in an organic solvent to form a homogeneous casting solution; coating it on a glass plate; heating and drying it to obtain a base membrane; and then immersing it in a modifier solution for positive charge modification to obtain the final self-microporous polymer anion exchange membrane.

[0011] The molar ratio of liquid bromine to the repeating units contained in PIM-M is (1-10):1.

[0012] The bromomethylated self-porous polymer (PIM-Br) consists of repeating units containing bromomethyl groups and repeating units without bromomethyl groups. Its bromomethylation degree is 5%-100%, representing the molar percentage of bromomethylated repeating units in the bromomethylated self-porous polymer, i.e., X in the following structural formula:

[0013]

[0014] The organic solvent used to dissolve the bromomethylated microporous polymer is selected from any one of N-methylpyrrolidone, N-methylformamide, chloroform, and dimethyl sulfoxide.

[0015] The solute in the modifier solution is selected from compounds that can react with benzyl bromide groups to form positively charged compounds, preferably N-substituted imidazoles and tertiary amines, and more preferably one of trimethylamine, triethylamine, 1-methylimidazole and 1,2-2-methylimidazole.

[0016] The solvent of the modifier solution is selected from water, methanol, ethanol and acetone.

[0017] The temperature of the modifier solution is 25-80℃, and the concentration is 0.1-5mol / L.

[0018] The base film is immersed in the modifier solution for 1-12 hours.

[0019] The significant advantages of this invention are:

[0020] The method for fabricating membranes using self-porous polymers provided in this invention involves reacting a self-porous polymer with liquid bromine to obtain a bromomethylated self-porous polymer. This bromomethylated self-porous polymer is then dissolved in an organic solvent, and a base membrane is prepared using a solvent evaporation method. Finally, the base membrane is immersed in a modifier solution containing tertiary amine groups for modification, resulting in an anion exchange membrane. The anion exchange membrane prepared based on the bromomethylated self-porous polymer in this invention possesses a large free space volume, which significantly reduces ion transport resistance, thereby improving the acid dialysis coefficient of the membrane. Simultaneously, using liquid bromine as the bromination reagent does not reduce the molecular weight of the PIM material, thus endowing the prepared bromomethylated self-porous polymer with extremely high mechanical strength. The dense anion exchange membrane prepared by this invention has a maximum acid dialysis coefficient of 0.07 m / h, which is 8.2 times that of commercial membranes, and a separation factor of 74.4, which is 4 times that of commercial membranes. Detailed Implementation

[0021] The specific embodiments of the present invention will be clearly and completely described below in conjunction with the technical solutions, but the present invention is not limited thereto.

[0022] Example 1

[0023] According to the method for synthesizing PIM-M reported in the British journal *Materials Chemistry A* (2016, 4, 17655-17659), the required PIM-M material was prepared, and its molecular weight was measured to be approximately 60,000. The repeating units of a self-contained microporous polymer (PIM-M) with a repeating unit molar amount of 0.5 mmol were dissolved in chlorobenzene and stirred at 135 °C until completely dissolved. Then, 1 mmol of liquid bromine was added and reacted for 6 h to obtain a self-contained microporous polymer with a bromomethylation degree of 80%. This 80% bromomethylated self-contained microporous polymer was then dissolved in chloroform to form a 3 wt% casting solution. The casting solution was coated onto a glass plate, and after the solvent evaporated, a bromomethylated self-contained microporous polymer base film with a bromomethylation degree of 80% was obtained. This film was then immersed in a 1 mol / L, 40 °C aqueous solution of 1-methylimidazole for 8 h for positive charge modification. After modification, the prepared anion exchange membrane was stored in deionized water. The ion exchange capacity (IEC, i.e., the content of imidazolium groups in the membrane) was measured to be 1.6 mmol / g, and the specific surface area was 612 cm². 3 / g, tensile strength is 50MPa, molecular weight is 72000.

[0024] The anion exchange membrane prepared in Example 1 was subjected to a diffusion dialysis experiment at 25°C. A mixed solution of 1 mol / L HCl and 0.2 mol / L FeCl2 was used to simulate the recovery of HCl from waste acid solution. The acid dialysis coefficient of the membrane was tested to be 0.07 m / h and the separation coefficient was 87.5. Compared with the diffusion dialysis performance of the commercial membrane DF-120 (acid dialysis coefficient of 0.0085 m / h and separation coefficient of 18.5), it is significantly improved and can greatly improve the acid recovery efficiency of the membrane.

[0025] Example 2

[0026] Anion exchange membranes were prepared using a method similar to that in Example 1, except that the bromination reaction conditions were changed: the molar ratio of reactants was changed to 1:1, and the reaction time was changed to 3 hours. The resulting membrane material had a bromomethylation degree of 5%, and the membrane's ion exchange capacity was measured to be 0.3 mmol / g, with a specific surface area of ​​804 cm². 3 / g, tensile strength is 40MPa, molecular weight is 65000.

[0027] The anion exchange membrane (NPIM-10-8) prepared in Example 2 was subjected to a diffusion dialysis experiment at 25°C. A mixed solution of 1 mol / L HCl and 0.2 mol / L FeCl2 was used to simulate the recovery of HCl from waste acid solution. The acid dialysis coefficient of the membrane was tested to be 0.01 m / h and the separation coefficient was 27.9.

[0028] Example 3

[0029] Anion exchange membranes were prepared using a method similar to that in Example 1, except that the reaction conditions for the bromination reaction were changed: the molar ratio of reactants was changed to 1:10, and the reaction time was changed to 24 h. The resulting membrane material had a bromomethylation degree of 100%, and the membrane's ion exchange capacity was measured to be 2.2 mmol / g, with a specific surface area of ​​519 cm². 3 / g, with a tensile strength of 58MPa.

[0030] The anion exchange membrane prepared in Example 3 was subjected to a diffusion dialysis experiment at 25°C. A mixed solution of 1 mol / L HCl and 0.2 mol / L FeCl2 was used to simulate the recovery of HCl from waste acid solution. The acid dialysis coefficient of the membrane was tested to be 0.06 m / h and the separation coefficient was 64.1.

[0031] The above results indicate that both the reactant molar ratio and reaction time in the bromination reaction affect the degree of bromination of the self-porous polymer. As the degree of bromination increases, the specific surface area (free space volume) decreases, and the ion exchange capacity increases. When the degree of bromination is low, the ion exchange capacity has a greater impact on membrane performance than the specific surface area; at this point, due to the limited number of anion exchange groups, the performance is poor. When the degree of bromination is too high, the specific surface area has a greater impact than the ion exchange capacity; the smaller free space volume within the membrane creates greater resistance to ion transport, thus reducing performance. In summary, the anion exchange membrane prepared in this invention exhibits better diffusion dialysis performance only when the degree of bromination is moderate (80%).

[0032] Example 4

[0033] Anion exchange membranes were prepared using a method similar to that in Example 1, except that the solute in the modifier solution was changed to trimethylamine, the concentration was changed to 0.5 mol / L, the temperature was changed to 50°C, and the modification time of the base membrane was 10 h. The ion exchange capacity of the membrane was measured to be 1.8 mmol / g.

[0034] Example 5

[0035] The anion exchange membrane prepared in Example 4 was subjected to a diffusion dialysis experiment at 25°C. A mixed solution of 1 mol / L HCl and 0.2 mol / L FeCl2 was used to simulate the recovery of HCl from waste acid solution. The acid dialysis coefficient of the membrane was tested to be 0.04 m / h and the separation coefficient was 38.6.

[0036] Example 6

[0037] An anion exchange membrane was prepared using a method similar to that in Example 1, except that the solvent of the modifier solution was changed to ethanol, the concentration was changed to 2 mol / L, the temperature was changed to 20°C, and the modification time of the base membrane was 12 h, resulting in an anion exchange membrane with similar performance suitable for diffusion dialysis.

[0038] Example 7

[0039] Anion exchange membranes were prepared using a method similar to that in Example 1, except that the solute in the modifier solution was changed to 1,2-2-methylimidazole, the solution concentration was changed to 0.5 mol / L, the temperature was changed to 30 °C, and the modification time was 12 h. The ion exchange capacity (IEC) of the membrane was measured to be 1.4 mmol / g.

[0040] Example 8

[0041] The anion exchange membrane prepared in Example 7 was subjected to a diffusion dialysis experiment at 25°C. A mixed solution of 1 mol / L HCl and 0.2 mol / L FeCl2 was used to simulate the recovery of HCl from waste acid solution. The acid dialysis coefficient of the membrane was tested to be 0.05 m / h and the separation coefficient was 47.6.

[0042] Example 9

[0043] Anion exchange membranes were prepared using a method similar to that in Example 1, except that the solute in the modifier solution was changed to triethylamine, the solution concentration was changed to 1 mol / L, the temperature was changed to 25°C, and the modification time was 2 h. The ion exchange capacity (IEC) of the membrane was measured to be 0.7 mmol / g.

[0044] The anion exchange membrane prepared in Example 9 was subjected to a diffusion dialysis experiment at 25°C. A mixed solution of 1 mol / L HCl and 0.2 mol / L FeCl2 was used to simulate the recovery of HCl from waste acid solution. The acid dialysis coefficient of the membrane was tested to be 0.02 m / h and the separation coefficient was 37.5.

[0045] An anion exchange membrane was prepared using a method similar to that in Example 1, except that the solvent of the modifier solution was changed to methanol, resulting in an anion exchange membrane with similar performance suitable for diffusion dialysis.

[0046] An anion exchange membrane was prepared using a method similar to that in Example 1, except that the solvent of the modifier solution was changed to acetone, resulting in an anion exchange membrane with similar performance suitable for diffusion dialysis.

[0047] The results of the above embodiments demonstrate that the present invention utilizes a bromomethylated microporous polymer as the base membrane material and prepares a bromomethylated microporous polymer membrane via solvent evaporation. This membrane has a large amount of free space volume, which can reduce the resistance to ion transport. After being positively modified by a modifier solution containing tertiary amines, the base membrane is endowed with a certain amount of charge, thus preparing an anion exchange membrane with excellent diffusion performance and good mechanical properties and chemical stability. This meets the requirements of practical industrial applications and has a promising prospect for large-scale application in the field of diffusion dialysis acid recovery.

[0048] An anion exchange membrane was prepared using a method similar to that in Example 1, except that the organic solvent used to dissolve the microporous polymer was changed to dimethyl sulfoxide, resulting in an anion exchange membrane with similar performance suitable for diffusion dialysis.

[0049] An anion exchange membrane was prepared using a method similar to that in Example 1, except that the organic solvent used to dissolve the microporous polymer was changed to N-methylpyrrolidone, resulting in an anion exchange membrane with similar performance suitable for diffusion dialysis.

[0050] Anion exchange membranes were prepared using a method similar to that in Example 1, except that the organic solvent used to dissolve the microporous polymer was changed to N-methylformamide, resulting in anion exchange membranes with similar performance suitable for diffusion dialysis.

[0051] 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 self-porous polymer anion exchange membrane, characterized in that, A methyl-containing microporous polymer, formed by polymerizing 5,5′,6,6′-tetrahydroxy-3,3,4,3′,3′,4′-hexamethyl-1,1′-spirobisindane monomer and 2,3,5,6-tetrafluoroterephthalonitrile monomer, was dissolved in chlorobenzene to form a homogeneous solution. Liquid bromine was added, and a bromination reaction was carried out at 135 °C for 3-24 h to obtain a bromomethylated microporous polymer. This polymer was dissolved in an organic solvent to form a homogeneous casting solution, coated onto a glass plate, and dried to obtain a base film. The base film was then immersed in a modifier solution for positive charge modification to obtain the final microporous polymer anion exchange membrane. The molar ratio of liquid bromine to repeating units contained in the methyl-containing microporous polymer is 2:1; The degree of bromomethylation of the bromomethylated self-porous polymer is 80%, and the degree of methyl bromination is the molar percentage of repeating units containing bromomethyl groups to all repeating units. The solute in the modifier solution includes one of 1-methylimidazole and 1,2-dimethylimidazole.

2. The method for preparing a self-porous polymer anion exchange membrane according to claim 1, characterized in that: Organic solvents that dissolve bromomethylated microporous polymers include any one of N-methylpyrrolidone, N-methylformamide, chloroform, and dimethyl sulfoxide.

3. The method for preparing a self-porous polymer anion exchange membrane according to claim 1, characterized in that: The solvent of the modifier solution includes any one of water, methanol, ethanol, and acetone.

4. The method for preparing a self-porous polymer anion exchange membrane according to claim 1, characterized in that: The temperature of the modifier solution is 25-80℃, and the concentration is 0.1-5mol / L.

5. The method for preparing a self-porous polymer anion exchange membrane according to claim 1, characterized in that, The base film is immersed in the modifier solution for 1-12 hours.

6. A self-porous polymer anion exchange membrane, characterized in that, It is prepared using the method described in any one of claims 1-5.

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