Acidic group modified polybenzimidazole polymer as well as preparation method and application thereof

Abstract

The invention discloses an acidic group modified polybenzimidazole polymer as well as a preparation method and application thereof, and belongs to the technical field of selective electrodialysis cation exchange membrane preparation. Aiming at the problem that a trade-off effect exists between hydrogen ion / divalent metal ion selectivity and hydrogen ion permeability of the existing cation exchange membrane, the polybenzimidazole-based polymer provided by the invention is provided. A benzimidazole structure of a polybenzimidazole main chain skeleton is used as a basic group, acid groups are chemically grafted on a benzimidazole molecular chain, and the acid groups (phosphate groups, cyanuric acid groups, carboxyl groups with different carbon chain lengths and carboxyl groups with different alkyl branched chains) with different strengths are introduced into the membrane, so that different acid-base pair structures are constructed; the dimensional stability and mechanical strength of the obtained material are improved, and the hydrogen separation selectivity and permeability are effectively improved. The invention further prepares the hydrogen ion selective membrane, and also provides application of the hydrogen ion selective membrane in the field of waste acid recovery.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of selective electrodialysis cation exchange membranes, and specifically relates to a series of polybenzimidazole polymers modified with different acidic groups, their preparation, and hydrogen ion selective membranes. Background Art

[0002] A selective ion exchange membrane is a functional membrane with specific ion permeation selectivity. While blocking other ions or molecules, it allows specific charged or specific types of ions to pass through. In the three-dimensional network structure of a selective cation exchange membrane, acidic fixed charge groups are uniformly distributed. These groups are fixed to the polymer backbone through chemical bonds to form an ion transport channel with a high density of negative charges. Compared with traditional cation exchange membranes, the single / multivalent selective cation exchange membrane significantly improves the retention ability of the membrane for divalent or multivalent cations by introducing positive charge groups, steric hindrance groups, or gradient charge density layers.

[0003] The harmless treatment and resource utilization of waste acid containing valuable metals or heavy metals generated in the metal smelting and surface processing industries are of great significance. Preparing a high-performance hydrogen ion selective membrane is the key to solving the problem of waste acid resource utilization.

[0004] Polybenzimidazole (PBI) is an aromatic heterocyclic polymer, and its repeating unit on the main chain is a benzimidazole group. Polybenzimidazole is an irreplaceable electrolyte membrane material in high-temperature proton exchange membrane fuel cells. Under harsh conditions of high temperature and anhydrous, it can exhibit extremely excellent proton conduction performance. Its aromatic rigid backbone structure endows it with good thermal stability, mechanical properties, and chemical stability. The weak basicity of polybenzimidazole makes it easy to be doped with acidic proton conductors. The imidazole ring and hydrophilic groups in its molecular structure make it both a hydrogen bond acceptor and a donor. These structural features endow it with the potential ability to form a certain proton concentration and construct a proton channel.

[0005] Traditional polybenzimidazole materials each have their own unique features, but they generally have problems such as low molecular weight, poor solubility, difficult processing, high swelling degree, low selectivity, and low acid loading, which limit their application in some scenarios that require high acid loading. Therefore, using polybenzimidazole to prepare a hydrogen ion selective membrane with good permeation selectivity, dimensional stability, thermal stability, acid resistance, and excellent mechanical properties is the key to developing a new type of hydrogen ion selective membrane. Summary of the Invention

[0006] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a polybenzimidazole-based polymer with good permeation selectivity, dimensional stability, thermal stability, acid resistance and excellent mechanical properties, and a hydrogen ion-selective membrane further prepared therefrom. The purpose of the present invention is also to provide an efficient and stable preparation method of a hydrogen ion-selective membrane that overcomes the "trade-off" effect problem between the hydrogen ion / divalent metal ion selectivity and the hydrogen ion permeability of a cation exchange membrane. This preparation method uses the benzimidazole structure in the polybenzimidazole main chain skeleton as a basic group, and by chemically grafting acidic groups onto the benzimidazole molecular chain, different strengths of acidic groups (phosphate groups, cyanuric acid groups, carboxyl groups with different carbon chain lengths and carboxyl groups with different alkyl branches) are introduced into the membrane to construct different acid-base pair structures, which not only improves the dimensional stability and mechanical strength of the obtained material, but also effectively enhances the hydrogen ion selectivity and permeability. The purpose of the present invention is also to provide the application of the above hydrogen ion-selective membrane in the field of waste acid recovery.

[0007] To solve the above technical problems, the present invention adopts the following technical solutions:

[0008] (1). The first aspect of the present invention provides a polybenzimidazole polymer modified with acidic groups, and its structural formula is shown as follows:

[0009]

[0010] Among them, Ar is an aromatic monomer structural unit containing a benzene ring, R is an acidic group, x is the grafting rate of the acidic group, and 0 < x ≤ 1;

[0011] The structural formula of the aromatic monomer structural unit containing a benzene ring is selected from at least one of the following structural formulas:

[0012]

[0013] The structural formula of the acidic group is selected from at least one of the following structural formulas:

[0014]

[0015] (2). The second aspect of the present invention provides a preparation method of a polybenzimidazole polymer modified with acidic groups, including the following steps: reacting a tetraamine monomer and a dicarboxylic acid monomer to obtain a polybenzimidazole polymer; then reacting the polybenzimidazole polymer with different acidic groups to obtain a modified polybenzimidazole polymer with different acidic groups grafted onto the main chain.

[0016] Further, the tetraamine monomer is selected from 3,3'-diaminobenzidine, and the dicarboxylic acid monomer is selected from any one of 1,4-naphthalenedicarboxylic acid and isophthalic acid; the acidic groups include phosphoric acid groups, cyanuric acid groups, carboxylic acid groups with different chain lengths, and carboxylic acid groups with different alkyl side chains.

[0017] (1) Synthesis of polybenzimidazole polymer:

[0018] In a three-necked flask equipped with mechanical stirring, add Eaton's reagent, 3,3'-diaminobenzidine, and the dicarboxylic acid monomer. The mixture is stirred at 140 °C for 8 hours under a nitrogen atmosphere to obtain a high-viscosity mixture; then add a first precipitating agent to the reacted system, and then purify the precipitated substance for the first time to obtain the polybenzimidazole polymer.

[0019] According to some preferred embodiments of the present invention, the molar ratio of the 3,3'-diaminobenzidine to the dicarboxylic acid monomer is 1:1.

[0020] According to some preferred embodiments of the present invention, the first precipitating agent is selected from deionized water.

[0021] According to some preferred embodiments of the present invention, the first purification includes: adding the polymer to deionized water for precipitation.

[0022] (2) Synthesis of polybenzimidazole polymer grafted with phosphoric acid groups:

[0023] Dissolve the polybenzimidazole polymer and phosphorus oxychloride respectively. Under the action of a catalyst, slowly drop the polybenzimidazole solution into the phosphorus oxychloride solution, and carry out the reaction under an ice-water bath condition. Drop deionized water into the reaction solution and continue stirring for 12 h. Then add a second precipitating agent to the reacted system, and then purify the precipitated substance for the second time to obtain the polybenzimidazole polymer grafted with phosphoric acid groups.

[0024] According to some preferred embodiments of the present invention, the molar ratio of the polybenzimidazole to the phosphorus oxychloride is 1:3.

[0025] According to some preferred embodiments of the present invention, the molar ratio of the polybenzimidazole to the catalyst is 1:3.

[0026] According to some preferred embodiments of the present invention, the catalyst reagent is selected from pyridine.

[0027] According to some preferred embodiments of the present invention, the reaction time under the ice-water bath condition is 12 h.

[0028] According to some preferred embodiments of the present invention, the solvents for dissolving the polybenzimidazole and the phosphorus oxychloride respectively are selected from N,N-dimethylacetamide.

[0029] According to some preferred embodiments of the present invention, the second precipitating agent is selected from a mixed solution of deionized water and ethanol.

[0030] According to some preferred embodiments of the present invention: the volume ratio of deionized water to ethanol is 1:1.

[0031] According to some preferred embodiments of the present invention, the second purification includes: boiling the precipitated substance in a sodium bicarbonate solution overnight, washing several times, and then drying at 100 °C.

[0032] According to some preferred embodiments of the present invention, the second purification further includes: soaking the obtained pale yellow precipitate in a potassium carbonate solution for 24 h, washing it with deionized water multiple times, and then drying.

[0033] (3) Synthesis of grafted cyanuric acid-based polybenzimidazole polymer:

[0034] Dissolve polybenzimidazole and cyanuric acid respectively. Under the action of an acid-binding agent, slowly drip the polybenzimidazole solution into the cyanuric chloride solution, and react under ice-water bath conditions. Then add a third precipitating agent to the reacted system, and then perform third purification on the precipitated substance to obtain the grafted cyanuric acid-based polybenzimidazole polymer.

[0035] According to some preferred embodiments of the present invention, the molar ratio of polybenzimidazole to cyanuric chloride is 1:3.

[0036] According to some preferred embodiments of the present invention, the molar ratio of polybenzimidazole to the acid-binding agent is 1:1.5.

[0037] According to some preferred embodiments of the present invention, the acid-binding agent is selected from potassium carbonate.

[0038] According to some preferred embodiments of the present invention, the reaction time under ice-water bath conditions is 5 h.

[0039] According to some preferred embodiments of the present invention, the solvents for dissolving polybenzimidazole and cyanuric acid respectively are selected from N,N-dimethylacetamide.

[0040] According to some preferred embodiments of the present invention, the third precipitating agent is selected from a mixed solution of deionized water and ethanol.

[0041] According to some preferred embodiments of the present invention: the volume ratio of deionized water to ethanol is 1:1.

[0042] According to some preferred embodiments of the present invention, the third purification includes: soaking the precipitated substance in HCl for 12 h.

[0043] According to some preferred embodiments of the present invention, the third purification further includes: soaking the precipitated product in NaOH at room temperature for 12 h and then washing it with deionized water until neutral.

[0044] (4) Synthesis of polybenzimidazole polymers grafted with carboxylic acid groups of different chain lengths:

[0045] Dissolve polybenzimidazole and carboxylic acids of different chain lengths separately. Under the action of a catalyst, slowly drop the carboxylic acid solution of different chain lengths into the polybenzimidazole solution and react at 80 °C for 8 h. Then add a fourth precipitating agent to the reacted system, and then purify the precipitated substance for the fourth time to obtain the polybenzimidazole polymer grafted with carboxylic acid groups of different chain lengths.

[0046] According to some preferred embodiments of the present invention, the molar ratio of the polybenzimidazole to the carboxylic acids of different chain lengths is 1:3.

[0047] According to some preferred embodiments of the present invention, the molar ratio of the polybenzimidazole to its catalyst is 1:6.

[0048] According to some preferred embodiments of the present invention, the solvents for dissolving the polybenzimidazole polymer and carboxylic acids of different chain lengths are selected from N,N-dimethylacetamide.

[0049] According to some preferred embodiments of the present invention, the carboxylic acids of different chain lengths are selected from chloroacetic acid, bromoacetic acid, 3-chloropropionic acid, 4-bromobutyric acid, 5-bromovaleric acid, 6-bromohexanoic acid, 7-bromoheptanoic acid, 8-bromooctanoic acid, 9-bromononanoic acid, 11-bromoundecanoic acid, 12-bromododecanoic acid, etc.

[0050] According to some preferred embodiments of the present invention, the catalyst reagent is selected from triethylamine.

[0051] According to some preferred embodiments of the present invention, the third precipitating agent is selected from a mixed solution of deionized water and ethanol.

[0052] According to some preferred embodiments of the present invention, the volume ratio of the deionized water to the ethanol is 1:1.

[0053] According to some preferred embodiments of the present invention, (4) the third purification includes: soaking the precipitated product in NaOH at room temperature for 12 h and then washing it with deionized water until neutral.

[0054] (5) Synthesis of carboxyl-functionalized polybenzimidazole polymers with different alkyl branches:

[0055] Dissolve polybenzimidazole and carboxylic acids with different alkyl side chains respectively. Under the action of a catalyst, slowly drip the solution of carboxylic acids with different alkyl side chains into the polybenzimidazole solution and react at 80 °C for 8 h; then add a fifth precipitating agent to the reaction system, and then purify the precipitated substance for the fifth time to obtain the carboxyl-functionalized polybenzimidazole polymer grafted with different alkyl side chains.

[0056] According to some preferred embodiments of the present invention, the molar ratio of the polybenzimidazole to the carboxylic acids with different alkyl side chains is 1:3.

[0057] According to some preferred embodiments of the present invention, the carboxylic acids with different alkyl side chains are 2-chloropropionic acid, 2-bromopropionic acid, 2-chlorobutyric acid, 2-bromobutyric acid, 2-bromovaleric acid, 2-bromohexanoic acid, 2-bromooctanoic acid, 2-bromododecanoic acid, 2-bromotetradecanoic acid, 2-bromohexadecanoic acid, etc.

[0058] The reaction time after adding the carboxylic acids with different alkyl side chains is preferably 5-10 h, more preferably 8 h.

[0059] According to some preferred embodiments of the present invention, the fifth precipitating agent is selected from a mixed solution of deionized water and ethanol.

[0060] According to some preferred embodiments of the present invention, the volume ratio of the deionized water to the ethanol is 1:1.

[0061] According to some preferred embodiments of the present invention, the third purification includes: soaking the precipitated product in NaOH at room temperature for 12 h and then washing it with deionized water until neutral.

[0062] (III). The third aspect of the present invention provides a hydrogen ion selective exchange membrane, which is formed according to the above-mentioned polybenzimidazole modified polymer.

[0063] The present invention further discloses a preparation method of a hydrogen ion selective membrane, which includes the following steps:

[0064] Dissolve the above-mentioned polybenzimidazole polymer in an organic solvent to obtain a transparent and homogeneous casting solution. Pour the casting solution onto a mold, dry it into a film, immerse it in deionized water after vacuum drying to make the film fall off from the mold, and obtain a hydrogen ion selective membrane.

[0065] It is also possible to cast and form a solution of the polybenzimidazole modified polymer, and then dry and cool it for use as a cation exchange membrane.

[0066] Soak the membrane material obtained by the above film formation in a dilute sulfuric acid solution.

[0067] Further, the solution modified with polybenzimidazole is formed into a film, which is then immersed in a dilute sulfuric acid solution for 24 h, and then washed until neutral to obtain the hydrogen ion selective membrane.

[0068] According to some preferred embodiments of the present invention, the concentration of the dilute sulfuric acid solution is 0.25 mol / L.

[0069] (IV). The fourth aspect of the present invention provides an application of a hydrogen ion selective membrane in waste acid recovery.

[0070] Compared with the prior art, the present invention has the following advantages:

[0071] The present invention uses polybenzimidazole polymer as a base, grafts different acidic groups including phosphoric acid, cyanuric acid, carboxylic acid groups with different chain lengths, and carboxylic acids with different alkyl side chains onto the main chain of polybenzimidazole to obtain an acid group modified polybenzimidazole polymer. The hydrogen ion selective membrane based on polybenzimidazole with regulated acid-base pair structure further obtained therefrom exhibits good hydrogen ion selectivity and permeability, low swelling, excellent dimensional stability and chemical stability, and has broad application prospects in waste acid recovery.

[0072] In the preparation of the hydrogen ion selective membrane based on polybenzimidazole with regulated acid-base pair structure of the present invention, by utilizing the reactivity of the N-H groups of polybenzimidazole, different acidic groups - phosphate groups are grafted to construct acid-base pairs, enhance the intermolecular force between polymer molecular chains in the membrane, inhibit membrane swelling, form a hydrogen ion transport channel, and improve the separation performance of the membrane. On the one hand, the dimensional stability and mechanical properties of the cation exchange membrane are synergistically enhanced. On the other hand, grafting carboxyl flexible chain segments with different side chain lengths to the main chain of polybenzimidazole can endow the membrane with an excellent microphase separation structure and form a high-speed hydrogen ion transport channel.

[0073] All the membrane materials prepared by the preparation method of the present invention have a uniform and flat surface.

[0074] The hydrogen ion selective membrane prepared by the present invention has low swelling and good dimensional stability.

[0075] In some specific embodiments, the preparation method of the present invention can achieve rapid conduction of hydrogen ions in the obtained exchange membrane by adjusting the side chain length.

[0076] The method for preparing the hydrogen ion selective membrane of the present invention is simple and efficient, the raw materials are easily available and pollution-free, and the prepared membrane has good comprehensive properties and can be applied to the field of waste acid recovery. Description of the Drawings

[0077] To more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0078] Figure 1 1H NMR spectra and solid-state 31P NMR spectra of the grafted phosphoric acid group-containing meta-polyphenylene benzimidazole polymer mPBI-P and the grafted phosphoric acid group-containing naphthalene-type polyphenylene benzimidazole polymer NPBI-P in Example 1 and Example 2.

[0079] Figure 2 1H NMR spectra and solid-state 13C NMR spectra of the grafted cyanuric acid group-containing meta-polyphenylene benzimidazole polymer mPBI-CA in Example 3.

[0080] Figure 3 1H NMR spectrum of the grafted 6-bromohexanoic acid group-containing meta-polyphenylene benzimidazole polymer mPBI-6CA in Example 4.

[0081] Figure 4 1H NMR spectrum of the grafted 9-bromononanoic acid group-containing meta-polyphenylene benzimidazole polymer mPBI-NA in Example 5.

[0082] Figure 5 1H NMR spectrum of the grafted 12-bromododecanoic acid group-containing meta-polyphenylene benzimidazole polymer mPBI-LA in Example 6.

[0083] Figure 6 Water absorption and swelling comparison diagrams of the polymers mPBI-P, mPBI-CA, mPBI-6CA in Example 1, 3, 4 and mPBI in Comparative Example 1.

[0084] Figure 7 Hydrogen ion selectivity and flux comparison diagrams of the polymers mPBI-P, mPBI-CA, mPBI-6CA in Example 1, 3, 4 and mPBI in Comparative Example 1. Detailed implementation manners

[0085] To deeply understand the present invention, we will describe it comprehensively and meticulously. However, the present invention has various implementation manners and is not limited to the specific embodiments listed herein. The presentation of these embodiments aims to deepen the comprehensive understanding of the disclosed content of the present invention.

[0086] According to the technical solution of the present invention, a specific preparation method of a polyphenylene benzimidazole-based hydrogen ion selective membrane based on the regulation of acid-base pair structure includes the following steps:

[0087] (1) Preparation of polybenzimidazole polymer:

[0088] React 3,3'-diaminobenzidine with a dicarboxylic acid monomer. After controlling the temperature and atmosphere for a period of reaction, precipitate it in a first precipitating agent, and further purify it with sodium bicarbonate to obtain a polybenzimidazole polymer;

[0089] (2) Synthesis of polybenzimidazole polymer grafted with phosphoric acid groups:

[0090] Dissolve polybenzimidazole, phosphorus oxychloride, and a first catalyst in a first solvent. Add the polybenzimidazole solution to the mixed solution of phosphorus oxychloride and the first catalyst, stir in an ice-water bath for 12 h, and react until the solution becomes viscous. Pour the product into a second precipitating agent to precipitate the product. Immerse the product in a sodium bicarbonate solution to remove the excess acid, filter and wash with water to obtain a light yellow polymer; The polymer obtained after drying by washing with deionized water multiple times is the polybenzimidazole polymer grafted with phosphoric acid groups;

[0091] (3) Synthesis of polybenzimidazole polymer grafted with cyanuric acid groups:

[0092] Dissolve polybenzimidazole and cyanuric chloride in a first solvent. Slowly add the polybenzimidazole solution to the cyanuric chloride solution, use anhydrous potassium carbonate as an acid-binding agent, stir in an ice-water bath for 5 h, and react until the solution becomes viscous. Pour the product into a second precipitating agent to precipitate the product. Immerse the product in a 1 M hydrochloric acid solution for 12 h, filter and wash with water, soak in NaOH at room temperature for 12 h, and then wash with deionized water until neutral to obtain a light yellow polymer, which is the polybenzimidazole polymer grafted with cyanuric acid groups;

[0093] (4) Synthesis of polybenzimidazole polymer grafted with carboxylic acid groups of different chain lengths:

[0094] Dissolve polybenzimidazole, carboxylic acids of different chain lengths, and a second catalyst in a first solvent. Slowly add the polybenzimidazole solution to the carboxylic acid solution, stir at 80 °C for 8 h, and react until the solution becomes viscous. Pour the product into a second precipitating agent to precipitate the product. Immerse the product in NaOH at room temperature for 12 h, and then wash with deionized water until neutral to obtain a light yellow polymer, which is the polybenzimidazole polymer grafted with carboxylic acid groups of different chain lengths;

[0095] (5) Synthesis of carboxyl-functionalized polybenzimidazole polymer grafted with different alkyl branches:

[0096] Dissolve polybenzimidazole and carboxylic acids with different alkyl side chains in the first solvent. Slowly add the polybenzimidazole solution to the carboxylic acid solution with different alkyl side chains and stir at 80 °C for 8 h until the solution becomes viscous. Pour the product into the second precipitant to precipitate the product. Soak the product in NaOH at room temperature for 12 h and then wash it with deionized water until neutral to obtain a pale yellow polymer, namely polybenzimidazole polymer grafted with carboxylic acids having different alkyl side chains;

[0097] (6) Preparation of polybenzimidazole solution grafted with different acidic groups:

[0098] Add an appropriate amount of N,N-dimethylacetamide to the modified polybenzimidazole polymers obtained in steps (2), (3), (4), and (5) to form a homogeneous mixed solution, thus obtaining the polybenzimidazole solution grafted with different acidic groups;

[0099] (7) Preparation of polybenzimidazole hydrogen ion selective membrane grafted with different acidic groups:

[0100] Pour the polymer solution obtained in step (6) onto a clean glass plate to cast a film, dry it for 24 h and then cool it to room temperature;

[0101] Preferably, soak the obtained film in 2 M sulfuric acid solution at room temperature for 24 h and rinse it with deionized water until the washing liquid is neutral to obtain a polybenzimidazole hydrogen ion selective membrane grafted with different acidic groups in the form of H + form.

[0102] Some of the preferred embodiments are as follows:

[0103] The first solvent is selected from N,N-dimethylacetamide.

[0104] The first precipitant is deionized water.

[0105] The first catalyst is selected from pyridine solution.

[0106] The second precipitant is a 1:1 mixed solution of ethanol and deionized water.

[0107] The second catalyst is triethylamine.

[0108] The molar ratio of polybenzimidazole to phosphorus oxychloride is 1:3.

[0109] The molar ratio of polybenzimidazole to its catalyst pyridine is 1:3.

[0110] The molar ratio of polybenzimidazole to cyanuric chloride reagent is 1:3.

[0111] The molar ratio of polybenzimidazole to the acid-binding agent potassium carbonate is 1:1.5.

[0112] The molar ratio of the polybenzimidazole to the carboxylic acid reagent with different chain lengths is 1:3.

[0113] The molar ratio of the polybenzimidazole to its catalyst triethylamine is 1:6.

[0114] The molar ratio of the polybenzimidazole to the carboxylic acid reagent with different alkyl side chains is 1:3.

[0115] The temperature of the reaction in step (1) is 140 °C, the atmosphere is N2 atmosphere, and / or the reaction time is 8 h.

[0116] The temperature of the reaction in step (2) is 0 °C, and / or the reaction time is 12 h.

[0117] The temperature of the reaction in step (3) is 0 °C, and / or the reaction time is 5 h.

[0118] The temperature of the reaction in step (4) is 80 °C, and / or the reaction time is 8 h.

[0119] The temperature of the reaction in step (5) is 80 °C, and / or the reaction time is 8 h.

[0120] The temperature of the film formation in step (7) is 80 °C, and / or the film formation time is 24 h.

[0121] The concentration of the dilute sulfuric acid solution in step (7) is 2 mol / L, and / or the soaking time is 12 - 24 h.

[0122] Some of the grafted polybenzimidazole polymers with different acidic groups obtained by the above preparation method were subjected to structural characterization, and it was confirmed that they have the following structural general formula (I):

[0123]

[0124] Among them, Ar is any one of the following groups:

[0125]

[0126] The R is any one of the following groups:

[0127]

[0128] To further understand the present invention, the preparation method provided by the present invention will be described in more detail below through specific examples. The protection scope of the present invention is not limited by the following examples, and the raw materials involved in the examples are all commercially available.

[0129] Example 1:

[0130] (1) Preparation of meta - polybenzimidazole polymer: 25.00 g of Eaton's reagent, 1.66 g of isophthalic acid, and 2.15 g of 3,3'-diaminobenzidine were added to a 250 mL flask. The mixture was stirred at 140 °C for 5 hours. The resulting high - viscosity mixture was poured into 1000 mL of deionized water to precipitate the meta - polybenzimidazole polymer. Then, the fibrous mPBI was boiled in sodium bicarbonate solution overnight to remove unreacted acid, washed several times, and dried at 100 °C.

[0131] (2) Synthesis of meta - polybenzimidazole polymer grafted with phosphoric acid groups: 0.5 g of mPBI was dissolved in 20 mL of N,N - dimethylacetamide, and 0.45 mL of phosphorus oxychloride and 0.39 mL of pyridine were dissolved in 20 mL of N,N - dimethylacetamide. Under ice - water bath conditions, the mPBI solution was slowly dropped into the mixed solution of phosphorus oxychloride and pyridine. After stirring for 12 h, 10 mL of deionized water was dropped into the reaction solution and stirring continued for 12 h. The reaction solution was poured into a mixed solution of deionized water and ethanol (volume ratio 1:1) for precipitation to obtain a pale - yellow precipitate. The precipitate was soaked in potassium carbonate solution for 24 h, washed repeatedly with deionized water, and then dried.

[0132] (3) Preparation of meta - polybenzimidazole hydrogen ion - selective membrane grafted with phosphoric acid groups: A certain amount of the polymer was dissolved in DMAc, controlling the mass fraction to be 5 wt%, to obtain a homogeneous and transparent solution. This solution was slowly poured onto a clean and horizontally placed glass plate. It was dried at 80 °C for 24 h to obtain a polymer film with uniform thickness.

[0133] After testing, the obtained product has the following structural formula:

[0134]

[0135] (4) Conduct electrodialysis testing: Use the FeSO4 and H2SO4 system to simulate waste acid. The dilute chamber was filled with 100 mL of a mixed solution, which was 0.5 M FeSO4 and 0.25 M H2SO4, and the concentrated chamber was 40 mL of a solution with a concentration of 0.3 M Na2SO4. The electrode chamber was filled with 100 mL of a solution with a concentration of 0.3 M Na2SO4. The effective membrane area between the two electrodes was 9 cm 2 , apply a certain current density, and conduct electrodialysis testing for 1 h. The calculation formula is:

[0136] Hydrogen ion flux:

[0137] Selectivity:

[0138] The hydrophilicity of the membrane was investigated by testing the swelling degree: Before the test, the membrane sample was cut into small slices with a size of 1 cm × 4 cm, and then the membrane slices were immersed in deionized water at 25 °C to ensure that the membrane slices were fully wetted for 24 h. After that, the water on the surface was wiped off with lint-free paper, and the swelling ratio (SR) of the membrane was measured using the length difference between the dry membrane (L dry ) and the wet membrane (L wet ). The calculation formula is as follows:

[0139] Swelling ratio:

[0140] The hydrogen ion flux was 1.2 mmol·m -2 ·s -1 , the selectivity was 339, and the swelling ratio was 4%.

[0141] Example 2:

[0142] (1) Preparation of naphthalene-based polybenzimidazole polymer: 25.00 g of Eaton's reagent, 2.16 g of 1,4-naphthalenediamine, and 2.15 g of 3,3'-diaminobenzidine were added to a 250 mL flask. The mixture was stirred at 140 °C for 5 hours. The resulting high-viscosity mixture was poured into 1000 mL of deionized water to precipitate the meta-polybenzimidazole polymer. Then, the fibrous NPBI was boiled in a sodium bicarbonate solution overnight to remove the unreacted acid, washed several times, and dried at 100 °C.

[0143] (2) Synthesis of naphthalene-based polybenzimidazole polymer grafted with phosphate groups: 0.3 g of NPBI was dissolved in 10 mL of N,N-dimethylacetamide, and 0.23 mL of phosphorus oxychloride and 0.2 mL of pyridine were dissolved in 10 mL of N,N-dimethylacetamide. Under the condition of an ice-water bath, the NPBI solution was slowly dropped into the mixed solution of phosphorus oxychloride and pyridine, and after stirring for 12 h, 5 mL of deionized water was dropped into the reaction solution and stirring was continued for 12 h. The reaction solution was poured into a mixed solution of deionized water and ethanol (volume ratio 1:1) for precipitation to obtain a light yellow precipitate, which was soaked in a potassium carbonate solution for 24 h, washed several times with deionized water, and then dried.

[0144] (3) Preparation of naphthalene-based polybenzimidazole hydrogen ion selective membrane grafted with phosphate groups: The same as in Example 1. After testing, the obtained product had the following structural formula:

[0145]

[0146] (4) Electrodialysis test was carried out in a mixed solution composed of 0.25 M H2SO4 and 0.5 M FeSO4, and the hydrogen ion flux was 4.6 mmol·m -2 ·s-1 , with a selectivity of 829; the swelling degree is 2.8%.

[0147] Example 3:

[0148] (1) Preparation of meta - polybenzimidazole polymer: The same as in Example 1.

[0149] (2) Synthesis of meta - polybenzimidazole polymer grafted with cyanuric acid groups: Dissolve 1 g of meta - polybenzimidazole in N,N - dimethylacetamide, and dissolve 1.79 g of cyanuric chloride in N,N - dimethylacetamide. Under ice - water bath conditions, slowly drip the N,N - dimethylacetamide solution of meta - polybenzimidazole into the N,N - dimethylacetamide solution of cyanuric chloride, using anhydrous potassium carbonate as an acid - binding agent, and react for 5 h; precipitate in a mixed solution of deionized water and ethanol (volume ratio 1:1), then soak in 1 M dilute hydrochloric acid for 12 h, and soak the product in sodium hydroxide at room temperature for 12 h, and then wash with deionized water until neutral.

[0150] (3) Preparation of meta - polybenzimidazole hydrogen - ion - selective membrane grafted with cyanuric acid: The same as in Example 1.

[0151] After testing, the obtained product has the following structural formula:

[0152]

[0153] (4) Perform electrodialysis test in a mixed solution composed of 0.25 M H2SO4 and 0.5 M FeSO4, and the hydrogen - ion flux is 3.0 mmol·m -2 ·s -1 , with a selectivity of 520; the swelling degree is 4%.

[0154] Example 4:

[0155] (1) Preparation of meta - polybenzimidazole polymer: The same as in Example 1.

[0156] (2) Synthesis of meta - polybenzimidazole polymer grafted with 6 - bromohexanoic acid groups: Dissolve 0.3 g of polybenzimidazole in 10 mL of N,N - dimethylacetamide at 80 °C, add 0.57 g of 6 - bromohexanoic acid and 0.81 mL of triethylamine, after reacting for 12 h, cool to room temperature, precipitate the reactant into a mixed solution of ethanol and water at a ratio of 1:1, soak in sodium hydroxide for 12 h, and then wash with deionized water until neutral.

[0157] (3) Preparation of meta - polybenzimidazole hydrogen - ion - selective membrane grafted with 6 - bromohexanoic acid: The same as in Example 1.

[0158] After testing, the obtained product has the following structural formula:

[0159]

[0160] (4) The electrodialysis test was carried out in a mixed solution composed of 0.25M H2SO4 and 0.5M FeSO4. The hydrogen ion flux was 1.3 mmol·m -2 ·s -1 , and the selectivity was 282; the degree of swelling was 5%.

[0161] Example 5:

[0162] (1) Preparation of meta-polyphenylene benzimidazole polymer: same as Example 1.

[0163] (2) Synthesis of meta-polyphenylene benzimidazole polymer grafted with 9-bromononanoic acid groups: Dissolve 0.3 g of polyphenylene benzimidazole in 10 mL of N,N-dimethylacetamide at 80 °C, add 0.69 g of 9-bromononanoic acid and 0.81 mL of triethylamine. After reacting for 12 h, cool to room temperature. Precipitate the reactant into a mixed solution of ethanol and water at a ratio of 1:1, soak it in sodium hydroxide for 12 h, and then wash it with deionized water until neutral.

[0164] (3) Preparation of meta-polyphenylene benzimidazole hydrogen ion selective membrane grafted with 9-bromononanoic acid: same as Example 1.

[0165] After testing, the obtained product has the following structural formula:

[0166]

[0167] (4) The electrodialysis test was carried out in a mixed solution composed of 0.25M H2SO4 and 0.5M FeSO4. The hydrogen ion flux was 1.65 mmol·m -2 ·s -1 , and the selectivity was 383; the degree of swelling was 4%.

[0168] Example 6:

[0169] (1) Preparation of meta-polyphenylene benzimidazole polymer: same as Example 1.

[0170] (2) Synthesis of meta-polyphenylene benzimidazole polymer grafted with 12-bromododecanoic acid groups: Dissolve 0.3 g of polyphenylene benzimidazole in 10 mL of N,N-dimethylacetamide at 80 °C, add 0.81 g of 12-bromododecanoic acid and 0.81 mL of triethylamine. After reacting for 12 h, cool to room temperature. Precipitate the reactant into a mixed solution of ethanol and water at a ratio of 1:1, soak it in sodium hydroxide for 12 h, and then wash it with deionized water until neutral.

[0171] (3) Preparation of meta-polyphenylene benzimidazole hydrogen ion selective membrane grafted with 12-bromododecanoic acid: same as Example 1.

[0172] After testing, the obtained product has the following structural formula:

[0173]

[0174] (4) Electrodialysis tests were carried out in a mixed solution composed of 0.25 M H2SO4 and 0.5 M FeSO4, and the hydrogen ion flux was 1.53 mmol·m -2 ·s -1 , and the selectivity was 343; the swelling degree was 4.5%.

[0175] Example 7:

[0176] (1) Preparation of meta-polyphenylene benzimidazole polymer: same as Example 1.

[0177] (2) Synthesis of meta-polyphenylene benzimidazole polymer grafted with 2-bromohexanoic acid groups: Dissolve 0.97 g of meta-polyphenylene benzimidazole polymer in 10 mL of polar solvent N,N-dimethylacetamide, and then add 0.14 g of 2-bromohexanoic acid to the mixed solution. Heat the system to 80 °C. During the reaction, the polymer solid gradually dissolves. After reacting for 8 h, pour the reaction solution into a mixed solution of 80 mL of poor solvent ethanol and water, and wash 3 times. After filtration, place the product in a vacuum drying oven and dry it at 60 °C for 24 h to obtain a carboxylic acid-functionalized polyphenylene benzimidazole polymer with an alkyl side chain.

[0178] (3) Preparation of a hydrogen ion selective membrane of meta-polyphenylene benzimidazole polymer grafted with 2-bromohexanoic acid groups: same as Example 1.

[0179] After testing, the obtained product has the following structural formula:

[0180]

[0181] (4) Electrodialysis tests were carried out in a mixed solution composed of 0.25 M H2SO4 and 0.5 M FeSO4, and the hydrogen ion flux was 1.3 mmol·m -2 ·s -1 , and the selectivity was 143; the swelling degree was 5%.

[0182] Comparative Example 1:

[0183] (1) Preparation of meta-polyphenylene benzimidazole polymer: same as Example 1.

[0184] (2) Preparation of a meta-polyphenylene benzimidazole hydrogen ion selective membrane: same as Example 1.

[0185] The obtained product has the following structural formula:

[0186]

[0187] (3) Electrodialysis tests were carried out in a mixed solution composed of 0.25 M H2SO4 and 0.5 M FeSO4. The hydrogen ion flux was 1.2 mmol·m -2 ·s -1 , and the selectivity was 80; the degree of swelling was 6%.

[0188] Comparative Example 2:

[0189] (1) Preparation of naphthalene-type polybenzimidazole polymer: The same as in Example 2.

[0190] (2) Preparation of naphthalene-type polybenzimidazole hydrogen ion selective membrane: The same as in Example 2.

[0191] The obtained product has the following structural formula:

[0192]

[0193] Compared with the prior art, in view of the "trade-off" effect problem existing between the hydrogen ion permeability and selectivity of the electrodialysis cation exchange membrane for waste acid separation and recovery, starting from the design of the membrane material structure and the regulation of the membrane microstructure, by chemically grafting different acidic groups onto the polybenzimidazole molecular chain, introducing phosphate groups, cyanuric acid groups and carboxylic acid groups with different chain segment lengths into the membrane respectively, different acid-base pair structures are constructed. Based on the above method, the synergistic regulation of the strength of acidic groups and the membrane microstructure is realized through the modification strategy, achieving high hydrogen ion permeability and selectivity of the membrane, low degree of swelling and excellent dimensional stability, and having broad application prospects in the field of waste acid recovery.

[0194] The content not described in detail in the specification of the present invention belongs to the prior art well known to those skilled in the art. Although the above-described illustrative specific embodiments of the present invention have been described for the convenience of those skilled in the art to understand the present invention, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

Claims

1. An acidic group-modified polybenzimidazole polymer, characterized in that, Its structural formula is as follows: Wherein, Ar is an aromatic monomer structural unit containing a benzene ring, R is an acidic group, x is the grafting rate of the acidic group, and 0 < x ≤ 1; The structural formula of the aromatic monomer structural unit containing a benzene ring is selected from at least one of the following structural formulas: The structural formula of the acidic group is selected from at least one of the following structural formulas:

2. A method for preparing an acidic group-modified polybenzimidazole polymer, characterized in that, It includes the following steps: reacting a tetraamine monomer and a dicarboxylic acid monomer to obtain a polybenzimidazole polymer; then reacting the polybenzimidazole polymer with different acidic groups to obtain a modified polybenzimidazole polymer with different acidic groups grafted on the main chain.

3. The preparation method of an acidic group-modified polybenzimidazole polymer according to claim 2, characterized in that, The specific method for reacting a tetraamine monomer and a dicarboxylic acid monomer to obtain a polybenzimidazole polymer is: mixing the tetraamine monomer and the dicarboxylic acid monomer with Eaton's reagent, stirring in a nitrogen atmosphere to obtain a high-viscosity mixture; then adding a first precipitant for precipitation, and subjecting the precipitated substance to a first purification to obtain a polybenzimidazole polymer.

4. The preparation method of an acidic group-modified polybenzimidazole polymer according to claim 3, characterized in that, The tetraamine monomer is selected from 3,3'-diaminobenzidine; the dicarboxylic acid monomer is selected from any one of 1,4-naphthalenedicarboxylic acid or isophthalic acid; the acidic group includes any one of a phosphate group, a cyanuric acid group, carboxylic acid groups with different chain lengths, and carboxylic acid groups with different alkyl side chains; the molar ratio of the tetraamine monomer to the dicarboxylic acid monomer is 1:1; the stirring temperature for stirring in a nitrogen atmosphere to obtain a high-viscosity mixture is 140 °C, and the stirring time is 8 - 10 hours; the first precipitant is selected from deionized water; the first purification is specifically adding the precipitated substance to deionized water for precipitation.

5. The preparation method of an acidic group-modified polybenzimidazole polymer according to claim 2, characterized in that, The reaction of the polybenzimidazole polymer with different acidic groups is specifically: when the acidic group is a phosphate group, the preparation method of the phosphate group-modified polybenzimidazole polymer: Dissolve the polybenzimidazole polymer and phosphorus oxychloride respectively, and under the action of a catalyst, slowly drop the polybenzimidazole solution into the phosphorus oxychloride solution, and react under ice-water bath conditions. Drop deionized water into the reaction solution and continue stirring for 12 h; then add a second precipitant to the reacted system, and then subject the precipitated substance to a second purification to obtain a polybenzimidazole polymer grafted with phosphate groups; The molar ratio of the polybenzimidazole to phosphorus oxychloride is 1:3; the molar ratio of the polybenzimidazole to the catalyst is 1:3; the catalyst reagent is selected from pyridine; the reaction time under ice-water bath conditions is 12 h; the solvents for dissolving the polybenzimidazole and phosphorus oxychloride respectively are selected from N,N-dimethylacetamide; the second precipitant is selected from a mixed solution of deionized water and ethanol; the volume ratio of deionized water to ethanol is 1:1; the second purification includes: boiling the precipitated substance in a sodium bicarbonate solution overnight, washing several times and drying at 100 °C, soaking the obtained pale yellow precipitate in a potassium carbonate solution for 24 h, and washing with deionized water multiple times and then drying.

6. The preparation method of an acidic group-modified polybenzimidazole polymer according to claim 2, characterized in that, The reaction of the polybenzimidazole polymer with different acidic groups is specifically: when the acidic group is a cyanuric acid group, the preparation method of the cyanuric acid group-modified polybenzimidazole polymer: Dissolve polybenzimidazole and cyanuric acid separately. Under the action of an acid-binding agent, slowly drip the polybenzimidazole solution into the cyanuric chloride solution, and react under the condition of an ice-water bath; then add a third precipitating agent to the reacted system, and then purify the precipitated substance for the third time to obtain the grafted cyanuric acid-based polybenzimidazole polymer; The molar ratio of the polybenzimidazole to the cyanuric chloride is 1:3; the molar ratio of the polybenzimidazole to the acid-binding agent is 1:1.5; the acid-binding agent is selected from potassium carbonate; the reaction time under the condition of the ice-water bath is 5 h; the solvents for dissolving the polybenzimidazole and the cyanuric acid separately are selected from N,N-dimethylacetamide. The third precipitating agent is selected from a mixed solution of deionized water and ethanol; the volume ratio of deionized water to ethanol is 1:1; the third purification includes: soaking the precipitated product in HCl for 12 h, soaking the precipitated product in NaOH at room temperature for 12 h, and then washing it with deionized water until neutral.

7. The preparation method of an acidic group-modified polybenzimidazole polymer according to claim 3, characterized in that, The reaction of the polybenzimidazole polymer with different acidic groups specifically is: when the acidic group is a carboxylic acid group with different chain segment lengths, the preparation method of the polybenzimidazole polymer modified with carboxyl groups at different carbon chain lengths at the end: Dissolve polybenzimidazole and carboxylic acids with different chain segment lengths separately. Under the action of a catalyst, slowly drip the carboxylic acid solution with different chain segment lengths into the polybenzimidazole solution, and react at 80 °C for 8 h; then add a fourth precipitating agent to the reacted system, and then purify the precipitated substance for the fourth time to obtain the grafted polybenzimidazole polymer with carboxylic acid groups with different chain segment lengths; The molar ratio of the polybenzimidazole to the carboxylic acids with different chain segment lengths is 1:3; the molar ratio of the polybenzimidazole to its catalyst is 1:6; the solvents for dissolving the polybenzimidazole polymer and the carboxylic acids with different chain segment lengths separately are selected from N,N-dimethylacetamide; the carboxylic acids with different chain segment lengths are selected from chloroacetic acid, bromoacetic acid, 3-chloropropionic acid, 4-bromobutyric acid, 5-bromovaleric acid, 6-bromohexanoic acid, 7-bromoheptanoic acid, 8-bromooctanoic acid, 9-bromononanoic acid, 11-bromoundecanoic acid, 12-bromododecanoic acid; the catalyst reagent is selected from triethylamine; the third precipitating agent is selected from a mixed solution of deionized water and ethanol; the volume ratio of deionized water to ethanol is 1:1; the third purification includes: soaking the precipitated product in NaOH at room temperature for 12 h, and then washing it with deionized water until neutral.

8. The preparation method of an acidic group-modified polybenzimidazole polymer according to claim 3, characterized in that, The reaction of the polybenzimidazole polymer with different acidic groups specifically is: when the acidic group is a carboxylic acid group with different alkyl side chains, the preparation method of the carboxyl-functionalized polybenzimidazole polymer containing different alkyl side chains: Dissolve polybenzimidazole and carboxylic acids with different alkyl side chains separately. Under the action of a catalyst, slowly drip the carboxylic acid solution with different alkyl side chains into the polybenzimidazole solution, and react at 80 °C for 8 h; then add a fifth precipitating agent to the reacted system, and then purify the precipitated substance for the fifth time to obtain the grafted carboxyl-functionalized polybenzimidazole polymer with different alkyl side chains; The molar ratio of the polybenzimidazole to the carboxylic acid with different alkyl side chains is 1:3; the carboxylic acid with different alkyl side chains is 2-chloropropionic acid, 2-bromopropionic acid, 2-chlorobutyric acid, 2-bromobutyric acid, 2-bromovaleric acid, 2-bromohexanoic acid, 2-bromooctanoic acid, 2-bromododecanoic acid, 2-bromotetradecanoic acid, 2-bromohexadecanoic acid; the reaction time after adding the carboxylic acid with different alkyl side chains is preferably 5 to 10 h; the fifth precipitating agent is selected from a mixed solution of deionized water and ethanol; the volume ratio of the deionized water to the ethanol is 1:1; the third purification includes: soaking the precipitated product in NaOH at room temperature for 12 h and then washing it with deionized water until neutral.

9. A method for preparing a hydrogen ion selective membrane from an acidic group modified polybenzimidazole polymer prepared by the preparation method according to any one of claims 2 to 8, characterized in that, It includes the following steps: dissolving the polybenzimidazole polymer in an organic solvent to obtain a transparent and homogeneous casting solution, pouring the casting solution onto a mold, drying to form a film, immersing it in deionized water after vacuum drying to make the film fall off the mold, and obtaining a hydrogen ion selective membrane.

10. Application of the hydrogen ion selective membrane according to claim 9 in waste acid recovery.

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