Modified anion exchange membrane as well as preparation method and application thereof

Abstract

According to the modified anion-exchange membrane and the preparation method thereof, the anion-exchange membrane is modified by the method, a tannic acid self-polymerization coating is formed on the surface of the anion-exchange membrane and in pore channels in the membrane, the hydrophilicity and the organic pollution resistance of the anion-exchange membrane are remarkably improved, the exchange capacity is not affected, and the service life of the anion-exchange membrane is prolonged. Meanwhile, the stability is good, the preparation process is simple, and the industrial prospect is achieved.

Description

Technical Field

[0001] This disclosure relates to the field of membrane separation technology, specifically to a modified anion exchange membrane, its preparation method, and its application. Background Technology

[0002] In the field of membrane separation technology, anion exchange membranes play a crucial role. They are widely used in numerous fields such as electrodialysis, diffusion dialysis, and fuel cells, and their performance directly affects the efficiency and stability of related processes.

[0003] Currently, while commercial anion exchange membranes can meet some application needs to a certain extent, several problems remain to be solved. On the one hand, traditional anion exchange membranes lack sufficient hydrophilicity, making them susceptible to contamination by organic matter in practical applications, especially when treating solutions containing organic compounds. This leads to decreased membrane performance and shortened lifespan. Adsorption of organic matter on the membrane surface can block ion channels, reducing ion exchange capacity and ion conductivity, thus affecting separation efficiency and energy efficiency. On the other hand, the stability of existing anion exchange membranes also needs improvement. During long-term use, the membrane structure may change, leading to gradual performance degradation. For example, in harsh working environments, membranes may be affected by chemical corrosion, mechanical stress, and other factors, thereby reducing their stability and reliability.

[0004] To address these issues, researchers have been exploring new modification methods to improve the performance of anion exchange membranes. However, existing modification methods often have limitations, such as complex processes, high costs, and adverse effects on exchange capacity. Therefore, developing a modified anion exchange membrane that does not affect exchange capacity, improves hydrophilicity and resistance to organic contamination, while also possessing good stability and a simple preparation process, has significant practical implications and broad application prospects. Summary of the Invention

[0005] The purpose of this disclosure is to provide a modified anion exchange membrane that does not affect the exchange capacity, improves hydrophilicity and resistance to organic fouling, and has good stability and a simple preparation process.

[0006] To achieve the above objectives, this disclosure provides a method for preparing a modified anion exchange membrane, the method comprising the following steps: S1. Dissolve tannic acid, copper-containing compounds and bromides in a mixed solvent of dichloromethane and water, add an acidic solution to the mixed solvent to make the pH value 2-3, and carry out an oxidation reaction under oxygen conditions to obtain the first reaction solution; S2. Place the anion exchange membrane to be modified in the middle of the electrodeposition device to form independent cathode and anode chambers; add water to the anode chamber and the first reaction solution and water to the cathode chamber to carry out the electrodeposition reaction; S3. Add an alkaline solution to the cathode chamber to make the pH value 7-9, and then add trimethylamine to carry out the quaternization reaction.

[0007] Optionally, the copper-containing compound includes copper nitrate trihydrate; the bromide includes potassium bromide; the acidic solution includes acetic acid; and the alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, and potassium carbonate.

[0008] Optionally, in step S1, the weight ratio of tannic acid, copper, bromine, dichloromethane and water is (1-10):(0.025-1.25):(0.33-1.68):(1-200):(1-200). The preferred ratio is (1-10):(0.025-0.25):(0.33-0.99):(20-100):(20-100).

[0009] Optionally, in step S1, the concentration of tannic acid is 20-500 g / L; the reaction conditions include: a reaction temperature of 60-120℃ and a reaction time of 5-30 h.

[0010] Optionally, in step S2, the mass concentration of tannic acid in the cathode chamber is adjusted to 0.1-15 g / L by adjusting the amount of water added to the cathode chamber; The conditions for electrodeposition include: reaction time of 0.2-2 h and current density of 1-100 mA / cm². 3 .

[0011] Optionally, the molar ratio of the bromide to the trimethylamine is 1:(1-4).

[0012] Optionally, the conditions for the quaternization reaction include: a reaction temperature of 40-80°C and a reaction time of 0.3-36 h.

[0013] On the other hand, this disclosure provides a modified anion exchange membrane prepared by the above method.

[0014] On the other hand, this disclosure provides the application of the modified anion exchange membrane prepared by the above method in the electrodialysis treatment of organic wastewater.

[0015] Through the above technical solution, this disclosure provides a modified anion exchange membrane and its preparation method. The method modifies the anion exchange membrane to form a tannic acid self-polymerization coating on the surface of the anion exchange membrane and in the membrane pores, which significantly improves the hydrophilicity and resistance to organic pollution of the anion exchange membrane without affecting the exchange capacity. It also has good stability and the preparation process is simple, showing promise for industrialization.

[0016] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Detailed Implementation

[0017] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0018] This disclosure provides a method for preparing a modified anion exchange membrane, the method comprising the following steps: S1. Dissolve tannic acid, copper-containing compounds and bromides in a mixed solvent of dichloromethane and water, add an acidic solution to the mixed solvent to make the pH value 2-3, and carry out an oxidation reaction under oxygen conditions to obtain the first reaction solution; S2. Place the anion exchange membrane to be modified in the middle of the electrodeposition device to form independent cathode and anode chambers; add water to the anode chamber and the first reaction solution and water to the cathode chamber to carry out the electrodeposition reaction; S3. Add an alkaline solution to the cathode chamber to make the pH value 7-9, and then add trimethylamine to carry out the quaternization reaction.

[0019] The preparation method disclosed herein forms a tannic acid self-polymerizing coating by electrodeposition on the surface and internal pores of anion exchange membrane. This coating imparts strong hydrophilicity to the anion exchange membrane, facilitating the migration of hydrated acetate ions, reducing the van der Waals forces between the anion exchange membrane and organic matter, and forming a hydration layer between the anion exchange membrane and water molecules through hydrogen bonding. This hinders the adsorption of pollutants to the membrane surface, thereby improving the antifouling ability of the anion exchange membrane. In addition, the introduction of amine groups into the modified coating increases the content of cation exchange groups in the modified anion exchange membrane, preventing the coating from covering the cation groups of the anion exchange membrane to be modified, thus ensuring the ion exchange capacity.

[0020] Optionally, the copper-containing compound includes copper nitrate trihydrate; the bromide includes potassium bromide; the acidic solution includes acetic acid; and the alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, and potassium carbonate.

[0021] In step S1, the weight ratio of tannic acid, copper, bromine, dichloromethane and water is (1-10):(0.025-1.25):(0.33-1.68):(1-200):(1-200). The preferred ratio is (1-10):(0.025-0.25):(0.33-0.99):(20-100):(20-100).

[0022] Tannic acid contains catechol and pyrogallol groups, exhibiting pH responsiveness. The chemical composition and physical structure of the coating can be controlled by adjusting the pH and tannic acid concentration. The method disclosed herein uses tannic acid as a raw material. By controlling the tannic acid concentration and pH value in the cathode chamber, the thickness and structure of the single coating are controlled, allowing tannic acid self-polymers to fill the macropores of the ion exchange membrane, thus making the membrane more dense and reducing the swelling effect of organic solvents such as acetone and ethanol on the anion exchange membrane.

[0023] Optionally, in step S1, the reaction conditions include: a reaction temperature of 60-120℃ and a reaction time of 5-30h; In step S2, the mass concentration of tannic acid in the cathode chamber is adjusted to 0.1-15 g / L by adding water to the cathode chamber; the electrodeposition reaction conditions include: a reaction time of 0.2-2 h and a current density of 1-100 mA / cm². 3 .

[0024] Optionally, the molar ratio of the bromide to the trimethylamine is 1:(1-4).

[0025] Optionally, the conditions for this quaternization reaction include: a reaction temperature of 40-80℃ and a reaction time of 0.3-36h.

[0026] On the other hand, this disclosure provides a modified anion exchange membrane prepared by the above method.

[0027] On the other hand, this disclosure provides the application of the modified anion exchange membrane prepared by the above method in the electrodialysis treatment of organic wastewater.

[0028] The present invention will be further described in detail below through examples.

[0029] Example 1 This embodiment is used to prepare a modified anion exchange membrane, and the process is as follows: S1. Take tannic acid, copper nitrate trihydrate, and potassium bromide, respectively, and dissolve them in a mixed solvent of dichloromethane and water. Adjust the pH to 2.6 with acetic acid. React under oxygen purging to obtain a tannic acid bromide solution. The weight ratio of tannic acid, copper, bromine, dichloromethane, and water is 1:0.16:0.9:100:80. The reaction temperature is 100℃ and the reaction time is 15h. S2. The anion exchange membrane to be modified (JAM-10 homogeneous anion exchange membrane, purchased from Beijing Huanyu Lida Environmental Protection Equipment Co., Ltd.) is placed in the middle of the DC electrodeposition device, forming two compartments: the cathode compartment and the anode compartment. Brominated tannic acid solution and pure water are added to the cathode compartment, and water is added to the anode compartment. The electrodeposition reaction is carried out by adjusting the tannic acid concentration to 12 g / L by adjusting the amount of pure water. The electrodeposition reaction time is 0.2 h, and the current density is 20 mA / cm². 2 ; S3. The pH of the cathode chamber solution was adjusted to 7 by using inorganic alkali sodium hydroxide, and then trimethylamine was added to carry out a quaternization reaction. The molar ratio of trimethylamine to potassium bromide added in step S1 was 2:1. The quaternization temperature was 40℃ and the reaction time was 36h to prepare a modified anion exchange membrane.

[0030] The modified anion exchange membrane prepared above was used for electrodialysis treatment of organic wastewater. The organic wastewater had the following characteristics: COD 4500 mg / L, sodium chloride concentration 3400 mg / L, ethanol concentration 1500 mg / L, and acetone concentration 350 mg / L.

[0031] The electrodialysis unit operated under the following conditions: 10 membrane pairs were used; the cation exchange membrane was purchased from JCM-10 (manufactured by Beijing Huanyu Lida Environmental Protection Equipment Co., Ltd.); the anion exchange membrane was the modified anion exchange membrane described above, with a size of 7cm × 12cm; the dilute solution was the organic wastewater described above, and the concentrate was pure water; the flow rate of the dilute and concentrate solutions was 20L / h; the electrode solution was a 5% sodium sulfate aqueous solution with a flow rate of 15L / h; constant voltage operation was used, with a voltage of 1.5V per membrane pair; the unit operated continuously and stably for 4 months; and the sheet resistance, exchange capacity, and burst strength were measured before and after use. The results are shown in Table 1.

[0032] Example 2 This embodiment is used to prepare a modified anion exchange membrane, and the process is as follows: S1. Take tannic acid, copper nitrate trihydrate, and potassium bromide, respectively, and dissolve them in a solvent of dichloromethane and water. Adjust the pH to 2.0 with acetic acid. React under oxygen purging to obtain a tannic acid bromide solution. The weight ratio of tannic acid, copper, bromine, dichloromethane, and water is 10:0.25:0.65:100:100. The reaction temperature is 80℃ and the reaction time is 30h. S2. Place the anion exchange membrane to be modified (the anion exchange membrane was purchased from Hangzhou Lanran Company as a standard homogeneous anion exchange membrane ATG-10) in the middle of the DC electrodeposition apparatus to form two compartments, namely the anode compartment and the cathode compartment. The cathode compartment contains a brominated tannic acid solution and pure water, while the anode compartment contains water. The electrodeposition reaction is carried out by adjusting the tannic acid concentration to 0.2 g / L by adjusting the pure water content. The electrodeposition reaction time is 2 hours, and the current density is 60 mA / cm². 2 ; S3. The pH of the cathode chamber solution was adjusted to 8 by using inorganic alkali sodium hydroxide, and then trimethylamine was added to carry out a quaternization reaction. The molar ratio of trimethylamine to potassium bromide was 4:1, the quaternization temperature was 60℃, and the reaction time was 24h, thus preparing a modified anion exchange membrane.

[0033] The modified anion exchange membrane prepared above was used for electrodialysis treatment of organic wastewater. The organic wastewater had the following characteristics: COD 4500 mg / L, sodium chloride concentration 3400 mg / L, ethanol concentration 1500 mg / L, and acetone concentration 350 mg / L.

[0034] The electrodialysis unit operated under the following conditions: 10 membrane pairs were used; the cation exchange membrane was purchased from Hangzhou Lanran Company's LANCYTOM series product - acid and alkali resistant CT-4 cation exchange membrane; the anion exchange membrane was the modified anion exchange membrane mentioned above, with a size of 7cm × 12cm; the dilute solution was the organic wastewater mentioned above, and the concentrate was pure water; the flow rate of the concentrated and dilute solutions was 20L / h; the electrode solution was a 5% sodium sulfate aqueous solution with a flow rate of 15L / h; constant voltage operation was used, with a voltage of 1.5V per membrane pair; the unit operated continuously and stably for 4 months; and the sheet resistance, exchange capacity, and burst strength were measured before and after use. The results are shown in Table 1.

[0035] Example 3 The preparation process of this embodiment is the same as that of Example 1, except that the weight ratio of tannic acid, copper, bromine, dichloromethane and water used in step S1 of this embodiment is 10:1.25:1:150:150, and the mass concentration of tannic acid in the cathode chamber is 15 g / L; an anion exchange membrane is prepared.

[0036] The surface resistivity, exchange capacity, and burst strength before and after use were determined using the same method as in Example 1, and the results are shown in Table 1.

[0037] Example 4 The preparation process in this embodiment is the same as that in Example 2, except that the weight ratio of tannic acid, copper, bromine, dichloromethane, and water used in step S1 of this embodiment is 1:0.05:0.5:20:20, the mass concentration of tannic acid in the cathode chamber is 1 g / L, the electrodeposition reaction time is 0.3 h, and the current density is 100 mA / cm².2 Anion exchange membranes were prepared.

[0038] The surface resistivity, exchange capacity, and burst strength before and after use were determined using the same method as in Example 2, and the results are shown in Table 1.

[0039] Example 5 The preparation method of this embodiment is the same as that of Example 2, except that in step S3, the molar ratio of trimethylamine to potassium bromide added in step S1 is 1:1, the quaternization reaction temperature is 80℃, and the reaction time is 10h; anion exchange membrane is prepared.

[0040] The surface resistivity, exchange capacity, and burst strength before and after use were determined using the same method as in Example 2, and the results are shown in Table 1.

[0041] Comparative Example 1 The anion exchange membrane provided in this comparative example is JAM-10 without modification. It was subjected to long-term continuous and stable operation for 4 months under the conditions of Test Example 1. The sheet resistance, exchange capacity and burst strength before and after use were measured, and the results are shown in Table 1.

[0042] Comparative Example 2 The comparative example anion exchange membrane ATG-10 was not modified and was subjected to long-term continuous and stable operation for 4 months under the conditions of test example 2. The sheet resistance, exchange capacity and burst strength before and after use were measured, and the results are shown in Table 1.

[0043] Table 1 Performance determination of anion exchange membranes

[0044] As can be seen from the table above, the use of anion exchange membranes in Comparative Examples 1 and 2 resulted in a significant decrease in sheet resistance, while the use of modified anion exchange membranes prepared in Examples 1-5 showed almost no change in sheet resistance. This is because the organic wastewater contains ethanol and acetone, which dissolve the anion membrane, causing membrane perforation and a decrease in sheet resistance. However, the modified anion exchange membranes prepared in the embodiments of this application have the ability to resist dissolution by organic solvents such as ethanol and acetone, so the sheet resistance is almost unaffected.

[0045] The burst strength of the anion exchange membranes in Comparative Examples 1-2 decreased significantly, with reductions of 23.68% and 31.72%, respectively. In contrast, the burst strength of the modified anion exchange membranes prepared in Examples 1-5 decreased by 1.31%, 2.25%, 1.97%, 3.37%, and 3.86%, respectively. This indicates that the modified anion exchange membranes prepared in Examples 1-5 can effectively improve the resistance to swelling and dissolution by organic solvents.

[0046] The exchange capacity of the anion exchange membranes in Comparative Examples 1-2 decreased significantly, with decreases of 8.90% and 14.46%, respectively. The decreases in Examples 1-5 were 0.65%, 1.22%, 1.29%, 1.22%, and 0.61%, respectively, indicating that even after modification, the exchange capacity of the anion exchange membranes in Examples 1-5 hardly decreased after four months of use in organic wastewater.

[0047] It is evident that the modified anion exchange membrane prepared in this application improves the membrane's hydrophilicity and resistance to organic fouling without affecting its exchange capacity, while also exhibiting good stability.

[0048] Furthermore, different anion exchange membranes were used for modification in Examples 1-5. Before and after the test, the sheet resistance, exchange capacity and bursting ability were almost unchanged. The method for modifying anion exchange membranes provided in this disclosure is applicable to a variety of anion exchange membranes and has good applicability.

[0049] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0050] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A method for preparing a modified anion exchange membrane, characterized in that, The method includes the following steps: S1. Dissolve tannic acid, copper-containing compounds and bromides in a mixed solvent of dichloromethane and water, add an acidic solution to the mixed solvent to make the pH value 2-3, and carry out an oxidation reaction under oxygen conditions to obtain the first reaction solution; S2. Place the anion exchange membrane to be modified in the middle of the electrodeposition device to form independent cathode and anode chambers; add water to the anode chamber and the first reaction solution and water to the cathode chamber to carry out the electrodeposition reaction; S3. Add an alkaline solution to the cathode chamber to make the pH value 7-9, and then add trimethylamine to carry out the quaternization reaction.

2. The method according to claim 1, wherein, The copper-containing compound includes copper nitrate trihydrate; the bromide includes potassium bromide; the acidic solution includes acetic acid; and the alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, and potassium carbonate.

3. The method according to claim 1, wherein, In step S1, the weight ratio of tannic acid, copper, bromine, dichloromethane and water is (1-10):(0.025-1.25):(0.33-1.68):(1-200):(1-200).

4. The method according to claim 3, wherein, In step S1, the weight ratio of tannic acid, copper, bromine, dichloromethane and water is (1-10):(0.025-0.25):(0.33-0.99):(20-100):(20-100).

5. The method according to claim 1, wherein, In step S1, the conditions for the oxidation reaction include: a reaction temperature of 60-120℃ and a reaction time of 5-30h.

6. The method according to claim 1, wherein, In step S2, the mass concentration of tannic acid in the cathode chamber is 0.1-15 g / L; The electrodeposition reaction conditions include: a reaction time of 0.2-2 hours and a current density of 1-100 mA / cm². 3 .

7. The method according to claim 1, wherein, The molar ratio of the bromide to the trimethylamine is 1:(1-4).

8. The method according to claim 1, wherein, The conditions for the quaternization reaction include: a reaction temperature of 40-80℃ and a reaction time of 0.3-36h.

9. The modified anion exchange membrane prepared by the method according to any one of claims 1-8.

10. The application of the modified anion exchange membrane according to claim 9 in the electrodialysis treatment of organic wastewater.

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