Imidazolium functionalized polyimide anion exchange membrane for diffusion dialysis acid recovery and preparation method thereof

Abstract

The invention relates to an imidazolium functionalized polyimide anion exchange membrane for diffusion dialysis acid recovery and a preparation method of the imidazolium functionalized polyimide anion exchange membrane, and belongs to the technical field of polymer functional membrane materials. The method comprises the following steps: firstly, carrying out condensation polymerization on a dianhydride monomer BPA-2a and an aromatic diamine monomer to prepare intrinsic microporous polyimide PI-6B containing a hexabenzyl structural unit; performing bromomethylation modification on the polyimide PI-6B-Br by adopting liquid bromine to obtain brominated polyimide PI-6B-Br; and carrying out nucleophilic substitution reaction through an imidazole compound, and introducing an imidazolium cation functional group on a polymer main chain to obtain the imidazolium functionalized polyimide anion exchange membrane. The obtained anion exchange membrane has high ion exchange capacity, high acid dialysis coefficient and excellent acid / salt separation factors, and has good application prospects in the field of waste acid diffusion dialysis recovery.

Description

Technical Field

[0001] This invention belongs to the field of polymer functional membrane materials technology, specifically relating to an imidazolium-functionalized polyimide anion exchange membrane for diffusion dialysis acid recovery and its preparation method. Background Technology

[0002] Acids are essential raw materials in industrial production processes such as metallurgy, electroplating, chemical engineering, steel pickling, and electronics manufacturing. They are widely used in metal surface treatment, mineral leaching, pickling and rust removal, and chemical synthesis. In actual industrial operations, a large amount of acid solution becomes waste acid solution containing metal ions after use, such as Fe2+. 2+ Zn 2+ Cu 2 + Waste acids, such as hydrochloric acid or sulfuric acid systems containing metal ions, are prone to serious environmental pollution if discharged directly without treatment. This also leads to a waste of acid resources. Therefore, achieving efficient recovery and resource utilization of waste acids is of significant environmental and economic importance.

[0003] Currently, waste acid treatment methods mainly include neutralization precipitation, evaporation concentration, extraction, and membrane separation. Among these, neutralization precipitation is simple but generates large amounts of salt-containing sludge, posing secondary pollution problems; evaporation concentration is energy-intensive and has high operating costs; and extraction involves organic solvent loss and safety risks. In contrast, diffusion dialysis is a concentration-driven membrane separation technology that uses anion exchange membranes to selectively separate acids from metal salts. It requires no external electric field or high temperature, and boasts advantages such as low energy consumption, simple equipment structure, and stable operation, making it a promising candidate for waste acid resource recovery.

[0004] However, the core of diffusion dialysis technology lies in the performance of the anion exchange membrane. Currently, commonly used anion exchange membranes generally suffer from problems such as limited free volume, discontinuous ion transport channels, low acid permeation rates, and insufficient long-term stability in strong acid environments. Therefore, developing anion exchange membranes that combine high acid permeation rates, high separation selectivity, and good structural stability is of great significance. Summary of the Invention

[0005] The purpose of this invention is to provide an imidazolium-functionalized polyimide anion exchange membrane and its preparation method, so as to solve the problem that existing anion exchange membranes are difficult to balance mass transfer efficiency and structural stability during diffusion dialysis.

[0006] This invention uses a hexabenzyl polyimide with a large intrinsic free volume as the backbone material, introduces benzyl bromide active sites through liquid bromination, and then introduces imidazolium cationic functional groups through quaternization reaction of imidazole compounds, thereby constructing an anion exchange membrane structure with continuous ion transport channels.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing an imidazolium-functionalized polyimide anion exchange membrane for diffusion dialysis acid recovery includes the following steps:

[0009] S1. Preparation of dianhydride monomer BPA-2a:

[0010] (1) Using 3-methylcatechol as a raw material, a condensation reaction was carried out with acetone under acidic conditions to prepare the methylated tetrahydroxy monomer TTSBI-M.

[0011] (2) Under alkaline conditions, TTSBI-M was subjected to a nucleophilic substitution reaction with 4,5-dichlorophthalonitrile to obtain intermediate BPN-2a;

[0012] (3) The BPN-2a was hydrolyzed in an alkaline alcohol-water system to generate a tetracarboxylic acid intermediate, which was then subjected to an acetic anhydride dehydration cyclization reaction to obtain the dianhydride monomer BPA-2a;

[0013] S2. Preparation of polyimide PI-6B:

[0014] The dianhydride monomer BPA-2a and the aromatic diamine monomer were added to an organic solvent (m-cresol) and subjected to a polycondensation reaction in the presence of a catalyst (quinoline; anhydrous toluene) and under inert gas protection. After a high-temperature imidization reaction, the polymer was precipitated to obtain polyimide PI-6B containing hexabenzyl structural units.

[0015] S3, Bromomethylation Modification:

[0016] Under inert gas protection, PI-6B is dissolved in an aromatic organic solvent (chlorobenzene), heated to 120-150 °C, and a mixed solution of bromine and organic solvent is added dropwise to induce bromomethylation of the benzyl groups on the polyimide molecular chain, thereby obtaining brominated polyimide PI-6B-Br, and polyimide-based films are prepared by solvent casting method.

[0017] S4, imidazolyl functionalization:

[0018] The polyimide-based membrane is immersed in an organic solution containing imidazole compounds and subjected to a nucleophilic substitution reaction at 30–60 °C, so that the bromomethyl group reacts with the imidazole compound to generate an imidazole-onium cationic group, thereby obtaining an imidazole-onium functionalized polyimide anion exchange membrane.

[0019] The degree of methyl bromination of PI-6B-Br is 30-90%. PI-6B-Br is composed of repeating units containing bromomethyl and benzyl groups, and its structural formula is as follows:

[0020]

[0021] The aromatic diamine monomer in S2 is 2,3,5,6-tetramethyl-1,4-phenylenediamine.

[0022] The solvent for dissolving PI-6B-Br as described in S3 is any one of N,N-dimethylformamide, chloroform, N-methylpyrrolidone, etc.

[0023] The imidazole compound mentioned in S4 is any one of 1-methylimidazole, 2-methylimidazole, and 1,2-dimethylimidazole.

[0024] The concentration of imidazole solution in S4 is 0.2~2 mol L. -1 .

[0025] The nucleophilic substitution reaction time described in S4 is 1-5 hours, and the soaking temperature is 30-60 °C.

[0026] The prepared anion exchange membrane has a thickness of 30–60 μm. The anion exchange membrane is composed of a polyimide backbone containing hexamethylene structural units and imidazolium cationic functional groups.

[0027] Application: The use of polyimide anion exchange membranes in diffusion dialysis acid recovery.

[0028] The significant advantages of this invention are:

[0029] This invention innovatively utilizes a hexabenzyl-based microporous polyimide with a large intrinsic free space volume as the backbone material. Benzyl bromide active sites are introduced into the polymer molecular chain through liquid bromine modification, followed by quaternization with imidazole compounds to introduce imidazole-onium cationic functional groups, thus constructing an anion exchange membrane structure with continuous ion transport channels. This technical route effectively avoids the degradation problem of the polymer backbone caused by traditional free radical bromination systems, while simultaneously improving the efficiency of functional group introduction. The resulting polyimide anion exchange membrane exhibits good controllability of functional group density; as the degree of bromomethylation and the positive charge of imidazole-onium increase, the ion exchange capacity of the membrane material correspondingly increases, thereby enhancing the selective transport capability of anions in acids. The large free volume formed by the hexabenzyl-based microporous structure facilitates the construction of rapid proton-anion co-migration channels, improving the diffusion and dialysis rate of acids. The anion exchange membrane obtained by this invention has both a high acid dialysis coefficient and an excellent acid / salt separation factor, while maintaining good mechanical strength and chemical stability. It has good long-term operational stability in strong acid environments, can effectively improve waste acid recovery efficiency, reduce operating energy consumption, and has good potential for industrial application. Attached Figure Description

[0030] Figure 1 The following are the 1H NMR spectra prepared in Example 1: (a) TTSBI-M, (b) BPN-2a, (c) BPA-2a, (d) PI-6B, and (e) PI-6B-Br.

[0031] Figure 2 The image shows the infrared spectrum of the membrane prepared in Example 4.

[0032] Figure 3 The image shows the full-spectrum XPS spectrum of the membrane prepared in Example 3.

[0033] Figure 4 This is a SEM image of the membrane prepared in Example 3.

[0034] Figure 5 The image shown is the XRD pattern of the membrane prepared in Example 4.

[0035] Figure 6 The graph shows the diffusion dialysis acid recovery performance of the membrane prepared in Example 3. Detailed Implementation

[0036] The following detailed description of the embodiments of the present invention, in conjunction with specific technical solutions, provides a clear overview. The described embodiments are merely some preferred embodiments of the present invention, and not all embodiments, and do not constitute any limitation on the present invention.

[0037] Preparation of dianhydride monomer BPA-2a:

[0038] (1) Preparation of TTSBI-M: Weigh 11.2 g (90 mmol) of 3-methylcatechol and add it to a mixed solution of 43 mL of glacial acetic acid and 48 mL of hydrobromic acid (48 wt%). Stir until dissolved. Slowly add 14 mL (190 mmol) of acetone. After the addition is complete, heat to 120 °C and react at this temperature for 12 h. After the reaction is complete, pour the reaction solution into excess deionized water to precipitate the solid. Filter and wash repeatedly with glacial acetic acid until the color changes from dark brown to nearly white. Dry in a vacuum drying oven at 80 °C to constant weight to obtain the methylated tetrahydroxy monomer TTSBI-M.

[0039] (2) Preparation of BPN-2a: Under nitrogen protection, 4.676 g (12.7 mmol) of TTSBI-M, 5 g (25.4 mmol) of 4,5-dichlorophthalonitrile, 10 g (99.9 mmol) of anhydrous potassium carbonate, and 50 mL of DMF were added to a dry three-necked flask. The mixture was placed in an oil bath and heated to 80 °C with constant stirring for 3 h. After the reaction was completed, the mixture was cooled to room temperature, filtered to collect the precipitate, and washed repeatedly with distilled water to remove inorganic salts and residual DMF. The crude product was then dissolved in an appropriate amount of hot methanol and filtered while hot. After cooling and crystallization, the purified product BPN-2a was obtained by filtration and dried in a vacuum drying oven at 80 °C to constant weight.

[0040] (3) Preparation of BPA-2a: 6.167 g (0.01 mol) of BPN-2a was added to an ethanol / water mixed solvent (volume ratio 1:1, 200 mL), and 22.442 g (0.4 mol) of potassium hydroxide was added. The mixture was refluxed at 80 °C for 24 h. After the reaction was completed, the mixture was filtered while hot to remove insoluble impurities. The filtrate was allowed to cool naturally to room temperature, and concentrated hydrochloric acid was slowly added dropwise to adjust the pH to <3, resulting in a white precipitate. After standing and filtration, the precipitate was washed with excess cold water until neutral, and dried under vacuum at 80 °C to constant weight to obtain a tetracarboxylic acid intermediate. Subsequently, 6.927 g (0.01 mol) of tetracarboxylic acid was added to 70 mL of acetic anhydride, and the mixture was refluxed at 135 °C for 24 h under nitrogen protection to carry out a dehydration cyclization reaction. After cooling naturally to room temperature, the solid product was collected by filtration, washed 2-3 times with a small amount of toluene, and then dried in a vacuum drying oven at 80 °C to constant weight to obtain the target dianhydride monomer BPA-2a (pale yellow powder).

[0041] Example 1

[0042] This embodiment provides a hexabenzyl imidazolium-functionalized polyimide anion exchange membrane for diffusion dialysis acid recovery and its preparation method, which includes the following steps:

[0043] S1. BPA-2a (1.15 g, 1.83 mmol), 2,3,5,6-tetramethyl-1,4-phenylenediamine (0.30 g, 1.83 mmol), m-cresol (10 mL), quinoline (0.2 mL), and anhydrous toluene (2 mL) were added to a three-necked flask. The mixture was stirred at room temperature for 0.5 h under nitrogen protection, then heated to 200 °C and reacted for 5 h. Water was continuously removed using a toluene-water azeotropic system. After the reaction was complete, the mixture was cooled, diluted with chloroform, and precipitated in methanol. The precipitate was filtered, washed, and dried under vacuum at 80–100 °C to obtain pale yellow polyimide PI-6B.

[0044] S2. Under nitrogen protection, 1.0 g of PI-6B was dissolved in 20 mL of chlorobenzene, and the temperature was raised to 135 °C. 0.37 g of liquid bromine was dissolved in 10 mL of chlorobenzene and added dropwise to the reaction system. The reaction was carried out at 135 °C for 6 h to complete bromination. When the molar ratio of benzyl to liquid bromine in the repeating unit was controlled at 1:3, the degree of bromomethylation was 40%. The reaction solution was poured into methanol to precipitate, filtered, dried, and purified by dissolution in chloroform and washing with methanol to obtain PI-6B-Br. 0.3 g of PI-6B-Br was dissolved in 10 mL of chloroform to prepare a 3 wt% casting solution. After stirring overnight, the solution was cast into a film. After solvent evaporation, a polyimide-based film with a thickness of approximately 40 μm was obtained.

[0045] S3. Immerse the brominated polyimide-based film at 50 °C and 1 mol·L⁻¹. -1 The bromomethyl group was nucleophilically substituted with 1-methylimidazolium in a 100 mL ethanol solution for 2 hours, introducing imidazolium cationic groups into the polymer backbone to achieve positively charged functionalization of the membrane material. After the reaction, the membrane was removed and thoroughly washed with deionized water to remove unreacted substances and residual solvent, yielding an imidazolium-functionalized polyimide anion exchange membrane. A diffusion dialysis acid recovery test was conducted using 1 M HCl + 0.2 M FeCl2 to simulate waste acid. The results showed that the acid dialysis coefficient... It is 0.038 m·h -1 Selective It is 42.38.

[0046] Example 2

[0047] Using a method similar to that in Example 1, except that the molar ratio of benzyl to liquid bromine in the repeating unit was changed to 1:5, the degree of bromomethylation approached 80%. A 3 wt% casting solution was prepared by dissolving PI-6B-Br in chloroform, stirred overnight, and then cast into a film. After solvent evaporation, a polyimide-based film with a thickness of approximately 40 μm was obtained. Subsequently, the brominated polyimide-based film was immersed in a solution at 50°C and 1 mol·L⁻¹. -1The bromomethyl group was dissolved in an ethanol solution of 1-methylimidazolium for 2 hours, allowing a nucleophilic substitution reaction to occur between the bromomethyl group and 1-methylimidazolium. This introduced imidazolium cationic groups into the polymer backbone, achieving positively charged functionalization modification of the membrane material. After the reaction, the membrane was removed and thoroughly washed with deionized water to remove unreacted substances and residual solvent, yielding an imidazolium-functionalized polyimide anion exchange membrane. A diffusion dialysis acid recovery test was conducted using 1M HCl + 0.2M FeCl2 to simulate waste acid. The results showed that the acid dialysis coefficient of the polyimide anion exchange membrane was [missing information]. It is 0.066 m·h -1 Selective It is 44.26.

[0048] Example 3

[0049] Using a method similar to that in Example 2, the PI-6B-Br base film was immersed in an atmosphere at 50 °C with a concentration of 1 mol / L. -1 The bromomethyl group was immersed in a 1-methylimidazolium ethanol solution for 4 hours to undergo a nucleophilic substitution reaction with 1-methylimidazolium, introducing imidazolium cationic groups into the polymer backbone to achieve positively charged functionalization modification of the membrane material. After the reaction was completed, the membrane was removed and thoroughly washed with deionized water to remove unreacted substances and residual solvent, yielding an imidazolium-functionalized polyimide anion exchange membrane. A diffusion dialysis acid recovery test was conducted using 1M HCl + 0.2M FeCl2 to simulate waste acid. The results showed that the acid dialysis coefficient of the polyimide anion exchange membrane was [missing information]. It is 0.105 m·h -1 Selective It is 53.73.

[0050] Example 4

[0051] Using a method similar to that in Example 2, the PI-6B-Br base film was immersed in an atmosphere at 50 °C with a concentration of 1 mol / L. -1 The modification time was further extended by immersing the membrane in a 1-methylimidazolium ethanol solution for 5 hours. After the reaction was complete, the membrane was removed and thoroughly washed with deionized water to remove unreacted substances and residual solvent, yielding an imidazolium-functionalized polyimide anion exchange membrane. A diffusion dialysis acid recovery test was conducted using 1M HCl + 0.2M FeCl2 to simulate waste acid. The results showed that the acid dialysis coefficient of the polyimide anion exchange membrane was [not specified]. and selectivity Similar to Example 3.

[0052] Example 5

[0053] Using a method similar to that in Example 2, the PI-6B-Br base film was immersed in an atmosphere at 50 °C with a concentration of 1 mol / L. -1The bromomethyl group was immersed in a 2-methylimidazolium ethanol solution for 4 hours to undergo a nucleophilic substitution reaction with 2-methylimidazolium, introducing imidazolium cationic groups into the polymer backbone to achieve positively charged functionalization modification of the membrane material. After the reaction was completed, the membrane was removed and thoroughly washed with deionized water to remove unreacted substances and residual solvent, yielding an imidazolium-functionalized polyimide anion exchange membrane. A diffusion dialysis acid recovery test was conducted using 1M HCl + 0.2M FeCl2 to simulate waste acid. The results showed that the acid dialysis coefficient of the polyimide anion exchange membrane was [missing information]. It is 0.058 m·h -1 Selective It is 60.93.

[0054] Example 6

[0055] Using a method similar to that in Example 5, the PI-6B-Br base film was immersed in an atmosphere at 50 °C with a concentration of 1 mol / L. -1 The bromomethyl group was immersed in a 1,2-dimethylimidazolium ethanol solution for 4 hours to undergo a nucleophilic substitution reaction with 1,2-dimethylimidazolium, introducing imidazolium cationic groups into the polymer backbone to achieve positively charged functionalization modification of the membrane material. After the reaction was completed, the membrane was removed and thoroughly washed with deionized water to remove unreacted substances and residual solvent, yielding an imidazolium-functionalized polyimide anion exchange membrane. A diffusion dialysis acid recovery test was conducted using 1M HCl + 0.2M FeCl2 to simulate waste acid. The results showed that the acid dialysis coefficient of the polyimide anion exchange membrane was [missing information]. It is 0.073 m·h -1 Selective It is 55.64.

[0056] Example 7

[0057] Using a method similar to that in Example 3, the PI-6B-Br base film was immersed in an atmosphere at 50 °C with a concentration of 0.5 mol / L. -1 The bromomethyl group was immersed in a 1-methylimidazolium ethanol solution for 4 hours to undergo a nucleophilic substitution reaction with 1-methylimidazolium, introducing imidazolium cationic groups into the polymer backbone to achieve positively charged functionalization modification of the membrane material. After the reaction was completed, the membrane was removed and thoroughly washed with deionized water to remove unreacted substances and residual solvent, yielding an imidazolium-functionalized polyimide anion exchange membrane. A diffusion dialysis acid recovery test was conducted using 1M HCl + 0.2M FeCl2 to simulate waste acid. The results showed that the acid dialysis coefficient of the polyimide anion exchange membrane was [missing information]. It is 0.045 m·h -1 Selective It is 40.83.

[0058] Example 8

[0059] Using a method similar to that in Example 7, the PI-6B-Br base film was immersed in an atmosphere at 50 °C with a concentration of 2 mol / L. -1 The bromomethyl group was immersed in a 1-methylimidazolium ethanol solution for 4 hours to undergo a nucleophilic substitution reaction with 1-methylimidazolium, introducing imidazolium cationic groups into the polymer backbone to achieve positively charged functionalization modification of the membrane material. After the reaction was completed, the membrane was removed and thoroughly washed with deionized water to remove unreacted substances and residual solvent, yielding an imidazolium-functionalized polyimide anion exchange membrane. A diffusion dialysis acid recovery test was conducted using 1M HCl + 0.2M FeCl2 to simulate waste acid. The results showed that the acid dialysis coefficient of the polyimide anion exchange membrane was [missing information]. and selectivity Similar to Example 3.

[0060] Example 9

[0061] Using a method similar to that in Example 3, the PI-6B-Br base film was immersed in an atmosphere at 40 °C and a concentration of 1 mol / L. -1 The bromomethyl group was immersed in a 1-methylimidazolium ethanol solution for 4 hours to undergo a nucleophilic substitution reaction with 1-methylimidazolium, introducing imidazolium cationic groups into the polymer backbone to achieve positively charged functionalization modification of the membrane material. After the reaction was completed, the membrane was removed and thoroughly washed with deionized water to remove unreacted substances and residual solvent, yielding an imidazolium-functionalized polyimide anion exchange membrane. A diffusion dialysis acid recovery test was conducted using 1M HCl + 0.2M FeCl2 to simulate waste acid. The results showed that the acid dialysis coefficient of the polyimide anion exchange membrane was [missing information]. It is 0.092 m· -1 Selective It is 49.85.

[0062] Example 10

[0063] Using a method similar to that in Example 9, the PI-6B-Br base film was immersed in an atmosphere at 60 °C with a concentration of 1 mol / L. -1 The bromomethyl group was immersed in a 1-methylimidazolium ethanol solution for 4 hours to undergo a nucleophilic substitution reaction with 1-methylimidazolium, introducing imidazolium cationic groups into the polymer backbone to achieve positively charged functionalization modification of the membrane material. After the reaction was completed, the membrane was removed and thoroughly washed with deionized water to remove unreacted substances and residual solvent, yielding an imidazolium-functionalized polyimide anion exchange membrane. A diffusion dialysis acid recovery test was conducted using 1M HCl + 0.2M FeCl2 to simulate waste acid. The results showed that the acid dialysis coefficient of the polyimide anion exchange membrane was [missing information]. and selectivity Similar to Example 3.

[0064] Figure 1The following are the 1H NMR spectra prepared in Example 1: (a) TTSBI-M, (b) BPN-2a, (c) BPA-2a, (d) PI-6B, and (e) PI-6B-Br. Figure 1 As shown in (a): chemical shifts of 8.86 ppm and 7.67 ppm are characteristic peaks of hydroxyl hydrogen (Ha) and (Hb) on the benzene ring, respectively; chemical shift of 6.43 ppm is a characteristic peak of proton hydrogen (Hc) on the benzene ring; chemical shifts of 2.05–2.16 ppm are dual characteristic peaks of methylene hydrogen (Hd) on the five-membered ring; chemical shift of 1.51 ppm is a characteristic peak of methyl hydrogen (Hf) on the benzene ring; and chemical shifts of 1.22–1.25 ppm are characteristic peaks of methyl hydrogen (He) on the five-membered ring. This confirms the successful preparation of TTSBI-M. Figure 1 As shown in (b): chemical shifts of 7.21 ppm, 7.19 ppm, and 6.61 ppm are characteristic peaks of protonated hydrogens (Ha), (Hb), and (Hc) on the benzene ring; chemical shifts of 2.20–2.31 ppm are double characteristic peaks of methylene hydrogen (Hd) on the five-membered ring; chemical shift of 1.70 ppm is a characteristic peak of methyl hydrogen (Hf) on the benzene ring; and chemical shifts of 1.33–1.36 ppm are characteristic peaks of methyl hydrogen (He) on the five-membered ring. This confirms the successful preparation of BPN-2a. Figure 1 As shown in (c): chemical shifts of 7.21 ppm, 7.20 ppm, and 6.80 ppm are characteristic peaks of proton hydrogens (Ha), (Hb), and (Hc) on the benzene ring; chemical shifts of 2.13–2.27 ppm are double characteristic peaks of methylene hydrogen (Hd) on the five-membered ring; chemical shift of 1.66 ppm is a characteristic peak of methyl hydrogen (Hf) on the benzene ring; and chemical shifts of 1.28–1.33 ppm are characteristic peaks of methyl hydrogen (He) on the five-membered ring. This confirms the successful preparation of the dianhydride monomer BPA-2a. Figure 1 As shown in Figure 1(d), the characteristic peaks of proton hydrogens (Ha), (Hb), and (Hc) on the benzene ring are at chemical shifts of 7.20 ppm and 6.66 ppm; the double characteristic peak of methylene hydrogen (Hd) on the five-membered ring is at chemical shifts of 2.27–2.34 ppm; the characteristic peaks of methyl hydrogens (Hf) and (Hg) on ​​the benzene ring are at chemical shifts of 1.78 ppm and 2.09 ppm; and the characteristic peak of methyl hydrogen (He) on the five-membered ring is at chemical shifts of 1.37–1.40 ppm. This confirms the successful preparation of PI-6B. The 1H-NMR spectrum of PI-6B-Br is shown in Figure 1(e). Compared with PI-6B, PI-6B-Br has an additional characteristic peak of proton hydrogen (Hh) on the benzyl group at chemical shifts of 4.01–4.35 ppm, indicating that the bromination of PI-6B was successful.

[0065] Figure 2 The effect of modification time on the infrared absorption peak is investigated using Example 4 as a baseline: Compared with the PI-6B base film, the PI-6B-Br base film shows a higher peak at 610 cm⁻¹. -1 A distinct characteristic absorption peak appears at 1571 cm⁻¹, which can be attributed to the stretching vibration of the C-Br bond, indicating that the benzyl site in the PI-6B molecular chain has successfully undergone bromination. This result is consistent with the 1H NMR characterization results. After modification with 1-methylimidazole, new characteristic absorption peaks appear in the infrared spectrum of the PI-6B / Im-Yh anion exchange membrane, with a peak at 1571 cm⁻¹. -1 The corresponding stretching vibration of the C=N bond in the imidazolium group is 1158 cm⁻¹. -1 The stretching vibration at this point is attributed to the CN bond stretching vibration in the imidazolium group; simultaneously, at 610 cm⁻¹ -1 The characteristic absorption peak intensity of the C-Br bond decreased significantly, indicating that an effective substitution reaction occurred at the bromomethyl site. Furthermore, with prolonged modification time, the 1571 cm⁻¹ peak intensity of the PI-6B / Im-Yh series membrane increased. -1 and 1158 cm -1 The absorption peak gradually increases at 610 cm⁻¹, while at 610 cm⁻¹... -1 The absorption peaks at these locations continuously weaken, indicating a progressively increasing degree of imidazoleization. Furthermore, peaks are observed at 741 and 650 cm⁻¹. -1 The absorption peak of the out-of-plane bending vibration of the nearby aromatic ring CH also gradually weakened with the increase of the degree of modification, indicating that the benzyl substitution environment and the local structure of the aromatic ring changed, further confirming the successful introduction of the imidazolium group into the polymer backbone.

[0066] Figure 3The effect of modification time on XPS was investigated using Example 3 as a baseline. As shown in the figure, all samples exhibited distinct characteristic peaks at binding energies of 532.2 eV, 400.0 eV, and 284.8 eV, corresponding to photoelectron signals from the O 1s, N 1s, and C 1s orbitals, respectively. This is consistent with the expected elemental composition of the polymer matrix, confirming the integrity of the basic chemical structure of the membrane material. Notably, the PI-6B-Br membrane showed a characteristic peak at a binding energy of 70.5 eV, attributed to a photoelectron transition of the Br 3d orbital. This result is consistent with the bromination reaction design, further validating the successful introduction of bromine atoms into the PI-6B molecular chain. In stark contrast, no characteristic peak of the Br 3d orbital was detected in the full-spectrum XPS scans of the PI-6B / Im-1h and PI-6B / Im-4h anion exchange membranes. This phenomenon fully confirms that the nucleophilic substitution reaction of 1-methylimidazole with the bromine-containing group on the PI-6B-Br polymer chain has been fully carried out, and that the bromine element in the membrane matrix is ​​completely removed during the imidazole modification process, providing a structural basis for the formation of the imidazole onium group.

[0067] Figure 4 Based on Example 3, the effect of modification time on SEM was investigated. It was found that both the unmodified PI-6B-Br base membrane and the PI-6B / Im-Yh anion exchange membrane modified with 1-methylimidazole exhibited a uniform and dense microstructure on both the surface and cross-section. These results clearly demonstrate that the positively charged modification treatment based on 1-methylimidazole did not significantly affect the microstructure of this series of anion exchange membranes. The modified membrane material maintained a stable and dense structure, which is of great significance for maintaining the mechanical properties and selective permeability of the anion exchange membrane.

[0068] Figure 5 Based on Example 4, the effect of modification time on its XRD is investigated: Since polyimide is an amorphous polymer, its micropore characteristic peaks are presented in the form of arc-shaped curves; the segment spacing d is calculated by Bragg's formula (d=λ / 2sinθ). The characteristic peak at 3.75° in the XRD spectrum corresponds to the polymer segment stacking structure. After modification by introducing imidazolium groups, this characteristic peak shifts slightly to the right, and the peak position shifts from 3.75° to 3.57°.

[0069] Figure 6 Based on Example 3, the effect of modification time on the diffusion dialysis acid recovery performance was investigated: with the increase of soaking modification time, the acid dialysis coefficient of the PI-6B / Im-Yh series anion exchange membrane... and selectivity The trend is increasing; when the modification time is 4 hours, It reaches its maximum value of 0.105 ± 0.001 m·h -1 Selective It is 53.74±0.72.

[0070] The above embodiments are only some embodiments of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent application of the present invention shall be considered as within the scope of the present invention.

Claims

1. A method for preparing an imidazolium-functionalized polyimide anion exchange membrane for diffusion dialysis acid recovery, characterized in that, Includes the following steps: S1. Preparation of dianhydride monomer BPA-2a: (1) Using 3-methylcatechol as a raw material, a condensation reaction was carried out with acetone under acidic conditions to prepare the methylated tetrahydroxy monomer TTSBI-M. (2) Under alkaline conditions, TTSBI-M was subjected to a nucleophilic substitution reaction with 4,5-dichlorophthalonitrile to obtain intermediate BPN-2a; (3) The BPN-2a was hydrolyzed in an alkaline alcohol-water system to generate a tetracarboxylic acid intermediate, which was then subjected to an acetic anhydride dehydration cyclization reaction to obtain the dianhydride monomer BPA-2a; S2. Preparation of polyimide PI-6B: The dianhydride monomer BPA-2a and 2,3,5,6-tetramethyl-1,4-phenylenediamine were added to m-cresol and subjected to a polycondensation reaction in the presence of a catalyst and under inert gas protection. After a high-temperature imidization reaction, the polymer was precipitated to obtain polyimide PI-6B containing hexabenzyl structural units. S3, Bromomethylation Modification: Under inert gas protection, PI-6B is dissolved in an aromatic organic solvent and heated to 120-150 °C. A mixed solution of bromine and organic solvent is added dropwise to induce bromomethylation of the benzyl groups on the polyimide molecular chain, resulting in brominated polyimide PI-6B-Br. A polyimide-based film is then prepared by solvent casting. S4, imidazolyl functionalization: The polyimide-based membrane is immersed in an organic solution containing imidazole compounds and subjected to a nucleophilic substitution reaction at 30–60 °C, so that the bromomethyl group reacts with the imidazole compound to generate an imidazole-onium cationic group, thereby obtaining an imidazole-onium functionalized polyimide anion exchange membrane.

2. The preparation method according to claim 1, characterized in that: The catalyst in S2 is quinoline.

3. The preparation method according to claim 1, characterized in that: The degree of bromination of brominated polyimide PI-6B-Br is 30-90%.

4. The preparation method according to claim 1, characterized in that: The solvent for dissolving PI-6B-Br in S3 is any one of N,N-dimethylformamide, chloroform, and N-methylpyrrolidone.

5. The preparation method according to claim 1, characterized in that: The imidazole compound mentioned in S4 is any one of 1-methylimidazole, 2-methylimidazole, and 1,2-dimethylimidazole.

6. The preparation method according to claim 1, characterized in that: The concentration of the organic solution containing imidazole compounds described in S4 is 0.2~2 mol L. -1 .

7. The preparation method according to claim 1, characterized in that: The nucleophilic substitution reaction time described in S4 is 1~5h.

8. The preparation method according to claim 1, characterized in that: The thickness of the prepared anion exchange membrane is 30~60 μm.

9. The polyimide anion exchange membrane prepared by the method according to any one of claims 1-8, characterized in that: The anion exchange membrane is composed of a polyimide backbone containing hexamethylene structural units and imidazolium cationic functional groups.

10. The application of the polyimide anion exchange membrane as described in claim 9 in diffusion dialysis acid recovery.

Images