In-situ zwitterion modification method for polyamide membrane components

Abstract

The present invention relates to a kind of separation membrane preparation technology field, specifically a kind of in-situ zwitterion modification method of polyamide composite membrane assembly. The present invention is by using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride as activator, using tertiary amine small molecule material containing active group as functional material to be prepared into modified solution, using hydrogen peroxide as oxidant, to be prepared into oxidizing solution;Then the composite membrane assembly that needs to be processed is sequentially immersed in two solutions for a certain time to realize the in-situ zwitterion modification of polyamide composite membrane assembly. The advantage of the present invention is that zwitterions are introduced on the surface of polyamide composite membrane in a chemical grafting manner, on the one hand, the reaction conditions are simple, and it is easy to realize the large-scale modification of membrane assembly;On the other hand, without sacrificing the separation performance of composite membrane assembly, especially on the basis of initial flux, its anti-pollution performance is effectively and durably improved, and has good application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of separation membrane preparation, and specifically relates to an in-situ zwitterion modification method for a polyamide composite membrane component. Background Art

[0002] Membrane separation technology, due to its advantages such as high separation efficiency, low energy consumption, minimal environmental impact, wide applicability, ease of integration, and excellent operability, has been widely applied in seawater desalination, material concentration, zero industrial wastewater discharge, and drinking water production, playing a crucial role in addressing the water crisis. Polyamide composite membranes, prepared through interfacial polymerization using polyacyl chlorides and diamines as organic and aqueous monomers, offer high permeability and excellent separation performance, making them the current mainstream membrane product. However, on the one hand, because polyamide composite membranes contain hydrophobic structures such as benzene rings, their surface hydrophilicity is poor, and they are easily contaminated by organic pollutants (such as natural organic matter, humic acid, polysaccharides, biomacromolecules, etc.) in the feed solution during actual operation. On the other hand, the surface of polyamide composite membranes is rich in carboxyl groups, which not only causes calcium and magnesium ions in the feed solution to adsorb on the membrane surface to form crystals, leading to inorganic salt scaling pollution, but also further aggravates the deposition of organic pollutants through bridging, thereby affecting the water quality and water production efficiency, shortening the service life of the membrane, increasing investment and operating costs, and limiting the further application of membrane separation technology. Although the contamination of composite membrane components can be effectively alleviated by improving pretreatment, optimizing the system operation process, and performing maintenance chemical cleaning, such methods require the addition of additional operating units, increasing investment and operating costs. Therefore, it is of greater practical significance to develop membrane products with excellent anti-fouling properties targeting the membrane material itself.

[0003] Numerous studies have investigated the anti-fouling properties of polyamide composite membranes. A relatively simple approach involves depositing a hydrophilic polymer protective material, such as polyvinyl alcohol, on the surface of the membrane. However, these hydrophilic materials have weak binding forces with water molecules, resulting in limited improvement in anti-fouling properties. Furthermore, the coating material is easily lost during use, making long-term anti-fouling performance unattainable. In recent years, with the advancement of science and technology, a variety of functional polymer materials have been continuously developed. Among them, zwitterionic materials, which exhibit strong binding forces with water molecules and effectively form a thicker, more stable hydration layer, protect the membrane surface from direct contact with contaminants in the feed solution. These materials have been used to improve the anti-fouling properties of polyamide composite membranes. However, current research suggests that improving the anti-fouling properties of polyamide composite membranes with zwitterionic functional materials still has certain limitations. Firstly, zwitterionic polymers are difficult to synthesize and relatively expensive, hindering large-scale industrial application. Secondly, while introducing zwitterionic materials through specialized methods such as chemical grafting offers relatively stable anti-fouling properties, the reaction conditions are harsh, making them suitable only for laboratory membrane modification studies and difficult to commercialize. In particular, large-scale in-situ modification of membrane modules is not feasible.

[0004] Therefore, how to efficiently and conveniently achieve in-situ hydrophilic modification of membrane components and make them exert a lasting anti-pollution effect is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] In response to the problems existing in the prior art, the purpose of the present invention is to provide a method for in-situ zwitterion modification of a polyamide composite membrane assembly. First, the membrane assembly is activated in situ, and tertiary amine groups are introduced using the carboxyl groups on the membrane surface. Subsequently, zwitterions are constructed through oxide treatment, thereby achieving in-situ hydrophilic modification of the polyamide composite membrane assembly by chemical bonding without additionally increasing the permeation resistance, permanently improving the anti-pollution performance of the membrane assembly, and providing conditions for further expanding the application of membrane separation technology.

[0006] The in-situ zwitterion modification method of a polyamide composite membrane assembly is characterized by comprising the following steps:

[0007] A method for in-situ zwitterion modification of a polyamide composite membrane assembly, characterized by comprising the following steps:

[0008] S1. Using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride as an activator and a tertiary amine small molecule material containing an active group as a functional material, a modified solution is prepared. The mass concentration of the modified solution is 2-8%, and the pH value is adjusted to 6.0-9.0 using HCl solution or NaOH solution;

[0009] Using hydrogen peroxide as an oxidant, an oxidizing solution is prepared with a mass concentration of 10-40%;

[0010] S2. At room temperature, immerse the composite membrane assembly to be treated in two solutions in turn, and rinse with water after a certain period of time. The circulation time of the modification solution is 10-90 minutes, and the circulation time of the oxidation solution is 1-6 hours, so as to achieve in-situ zwitterion modification of the polyamide composite membrane assembly.

[0011] Preferably, the polyamide composite membrane described in the above-mentioned in-situ zwitterion modification method of a polyamide composite membrane assembly is a polyamide reverse osmosis membrane or a polyamide nanofiltration membrane; the composite membrane assembly can be in the form of a rolled membrane assembly, a hollow membrane assembly or a tubular membrane assembly.

[0012] Preferably, the tertiary amine small molecule material containing active groups described in the above-mentioned in-situ zwitterionic modification method of a polyamide composite membrane component is at least one of triethanolamine, N-ethyldiethanolamine, 2-hydroxyethylethylenediamine, N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine, trimethylhydroxyethylethylenediamine, or N,N-diethylethanolamine.

[0013] Preferably, in the above-mentioned in-situ zwitterion modification method of a polyamide composite membrane assembly, the mass concentration of the modified solution prepared by the tertiary amine small molecule material containing active groups in step S1 is 4-6%; and the pH of the aqueous solution is 6.5-7.5.

[0014] Preferably, in the above-mentioned in-situ zwitterionization modification method for a polyamide composite membrane assembly, the concentration of the hydrogen peroxide solution in step S1 is 15-25%.

[0015] Preferably, the circulation time of the modified solution in step S2 of the above-mentioned in-situ zwitterionization modification method of a polyamide composite membrane assembly is 30-60 minutes.

[0016] Preferably, the oxidation solution circulation time in step S2 of the above-mentioned in-situ zwitterionization modification method of a polyamide composite membrane assembly is 3-5 hours.

[0017] In this application, the operation process is as follows: a certain amount of tertiary amine small molecules containing active groups and 10 kg of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) are dissolved in 1000 l of pure water, and the pH is adjusted using HCl solution or NaOH solution to prepare a modified solution; then a certain amount of hydrogen peroxide is mixed with pure water to prepare 1000 l of a hydrogen peroxide solution of a specific concentration as an oxidizing solution; at room temperature, the prepared modified solution A is placed in a water storage barrel, the booster pump is turned on and the water inlet pressure is controlled below 0.1 MPa, and the modified solution A enters the membrane assembly and contacts the surface of the polyamide composite membrane. Then circulate back to the water storage tank; after running for a certain period of time, turn off the booster pump, empty the modified solution in the water storage tank, and use pure water for circulation 3 times, each circulation is 10 minutes to clean the membrane assembly; at room temperature, place the prepared oxidation solution in the water storage tank, turn on the booster pump and control the water inlet pressure below 0.1MPa, and the modified solution B enters the membrane assembly, contacts the surface of the polyamide composite membrane, and then circulates back to the water storage tank; after running for a certain period of time, turn off the booster pump, empty the modified solution B in the water storage tank, and use pure water for circulation 3 times, each circulation is 10 minutes to clean the membrane assembly, thus completing the zwitterion modification of the membrane assembly.

[0018] Beneficial effects:

[0019] This invention achieves in-situ zwitterionic modification of polyamide composite membrane assemblies through chemical grafting, introducing zwitterionic functional materials onto the surface of the polyamide composite membrane. The selected functional materials are all small molecules, effectively avoiding the problems of low initial flux caused by the dramatic increase in permeation resistance associated with conventional coating methods. Furthermore, zwitterionic modification of the composite membrane surface is achieved through chemical bonding via oxidation reactions, resulting in simple reaction conditions and ease of scalable membrane assembly modification. Furthermore, the method offers excellent and long-lasting anti-fouling properties, maintaining stability even at high operating pressures, and possesses promising application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the zwitterionic modification principle of the polyamide composite membrane component of the present invention

[0021] Figure 2 Schematic diagram of the experimental device for the zwitterionic modification of the polyamide composite membrane assembly of the present invention DETAILED DESCRIPTION

[0022] The following is a detailed description of the implementation of the present invention with reference to the accompanying drawings:

[0023] Comparative Example 1:

[0024] Commercial polyamide reverse osmosis membrane components are soaked in pure water, rinsed clean, and set aside.

[0025] The salt rejection rate and permeation flux of the reverse osmosis membrane module were tested under the conditions of NaCl concentration of 2000 mg / l, pressure of 1.55 MPa, temperature of 25°C, and pH value of 7.5±0.2. The results are shown in the table below:

[0026] Separation performance of reverse osmosis membrane modules

[0027]

[0028] From the data in the table above, it can be found that the water production of the modified reverse osmosis membrane assembly has almost no obvious attenuation. This is mainly because the zwitterionic functional material is introduced by chemical grafting, which does not increase the osmotic resistance of the polyamide reverse osmosis composite membrane. In addition, due to the increased hydrophilicity, the water production has also increased slightly. On the other hand, the chemical grafting does not destroy the integrity of the original polyamide separation layer, and its inorganic salt retention rate has not decreased.

[0029] The anti-fouling performance of the reverse osmosis membrane assembly was evaluated by cross-flow method, with dodecyltrimethylammonium bromide as the pollutant. The specific steps were as follows: (1) the reverse osmosis membrane assembly was cleaned, and pure water was used as the feed liquid. It was pre-pressed for 1 h under the conditions of pressure 1.0 MPa, 25±1℃, and 1000 ml / min water flow rate. The pure water flux was then tested as the initial flux (J0); (2) the operating pressure was maintained constant, 100 mg / l of dodecyltrimethylammonium bromide was added to the pure water, and the instantaneous permeation flux (J0) was tested at regular intervals. t ) until the operation is completed for 30 minutes; then the reverse osmosis membrane assembly is physically flushed with pure water for 30 minutes; (3) the feed liquid is replaced with pure water, and under the same pressure conditions, the pure water permeation flux J2 of the reverse osmosis membrane assembly is tested. The results are shown in the following table:

[0030] Anti-fouling performance of reverse osmosis membrane components

[0031]

[0032] Example 1:

[0033] S1. Dissolve 50 kg of triethanolamine and 10 kg of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) in 1000 l of pure water, and adjust the pH to 7.0 ± 0.2 using HCl solution or NaOH solution to prepare modified solution A.

[0034] S2. Take an appropriate amount of hydrogen peroxide and add pure water to 1000 l to prepare a 20% hydrogen peroxide solution as modified solution B;

[0035] S3. At room temperature, the prepared modified solution A is placed in a water storage bucket, the booster pump is turned on and the water inlet pressure is controlled below 0.1 MPa, the modified solution A enters the reverse osmosis membrane assembly, contacts the surface of the polyamide reverse osmosis membrane, and then circulates back to the water storage bucket; after running for 45 minutes, the booster pump is turned off, the modified solution A in the water storage bucket is emptied, and pure water is used for circulation 3 times, each cycle for 10 minutes to clean the reverse osmosis membrane assembly;

[0036] S4. At room temperature, place the prepared modified solution B in a water storage barrel, turn on the booster pump and control the water inlet pressure below 0.1MPa. The modified solution B enters the reverse osmosis membrane assembly, contacts the surface of the polyamide reverse osmosis membrane, and then circulates back to the water storage barrel. After running for 4 hours, turn off the booster pump, empty the modified solution B in the water storage barrel, and use pure water for 3 cycles, each cycle for 10 minutes to clean the reverse osmosis membrane assembly, thereby achieving zwitterionic modification of the reverse osmosis composite membrane assembly.

[0037] The anti-fouling performance evaluation of the reverse osmosis membrane module was carried out in a cross-flow manner. The specific steps were the same as those in Comparative Example 1. The results are listed in the following table:

[0038] Anti-fouling performance of reverse osmosis membrane components

[0039]

[0040]

[0041] Example 2:

[0042] S1. Dissolve 50 kg of N-ethyldiethanolamine and 10 kg of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) in 1000 l of pure water, and adjust the pH to 7.0 ± 0.2 using HCl solution or NaOH solution to prepare modified solution A.

[0043] S2. Take an appropriate amount of hydrogen peroxide and add pure water to 1000 l to prepare a 20% hydrogen peroxide solution as modified solution B;

[0044] S3. At room temperature, the prepared modified solution A is placed in a water storage bucket, the booster pump is turned on and the water inlet pressure is controlled below 0.1 MPa, the modified solution A enters the reverse osmosis membrane assembly, contacts the surface of the polyamide reverse osmosis membrane, and then circulates back to the water storage bucket; after running for 45 minutes, the booster pump is turned off, the modified solution A in the water storage bucket is emptied, and pure water is used for circulation 3 times, each cycle for 10 minutes to clean the reverse osmosis membrane assembly;

[0045] S4. At room temperature, place the prepared modified solution B in a water storage barrel, turn on the booster pump and control the water inlet pressure below 0.1MPa. The modified solution B enters the reverse osmosis membrane assembly, contacts the surface of the polyamide reverse osmosis membrane, and then circulates back to the water storage barrel. After running for 4 hours, turn off the booster pump, empty the modified solution B in the water storage barrel, and use pure water for 3 cycles, each cycle for 10 minutes to clean the reverse osmosis membrane assembly, thereby achieving zwitterionic modification of the reverse osmosis composite membrane assembly.

[0046] The anti-fouling performance evaluation of the reverse osmosis membrane module was carried out in a cross-flow manner. The specific steps are shown in Comparative Example 1. The results are listed in the following table:

[0047] Anti-fouling performance of reverse osmosis membrane components

[0048]

[0049] Example 3:

[0050] S1. Dissolve 50 kg of 2-hydroxyethylethylenediamine and 10 kg of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) in 1000 l of pure water, and adjust the pH to 7.0 ± 0.2 using HCl solution or NaOH solution to prepare modified solution A.

[0051] S2. Take an appropriate amount of hydrogen peroxide and add pure water to 1000 l to prepare a 20% hydrogen peroxide solution as modified solution B;

[0052] S3. At room temperature, the prepared modified solution A is placed in a water storage bucket, the booster pump is turned on and the water inlet pressure is controlled below 0.1 MPa, the modified solution A enters the reverse osmosis membrane assembly, contacts the surface of the polyamide reverse osmosis membrane, and then circulates back to the water storage bucket; after running for 45 minutes, the booster pump is turned off, the modified solution A in the water storage bucket is emptied, and pure water is used for circulation 3 times, each cycle for 10 minutes to clean the reverse osmosis membrane assembly;

[0053] S4. At room temperature, place the prepared modified solution B in a water storage barrel, turn on the booster pump and control the water inlet pressure below 0.1MPa. The modified solution B enters the reverse osmosis membrane assembly, contacts the surface of the polyamide reverse osmosis membrane, and then circulates back to the water storage barrel. After running for 4 hours, turn off the booster pump, empty the modified solution B in the water storage barrel, and use pure water for 3 cycles, each cycle for 10 minutes to clean the reverse osmosis membrane assembly, thereby achieving zwitterionic modification of the reverse osmosis composite membrane assembly.

[0054] The anti-fouling performance evaluation of the reverse osmosis membrane module was carried out in a cross-flow manner. The specific steps are shown in Comparative Example 1. The results are listed in the following table:

[0055] Anti-fouling performance of reverse osmosis membrane components

[0056]

[0057] Example 4:

[0058] S1. Dissolve 50 kg of trimethylolethylethylenediamine and 10 kg of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) in 1000 l of pure water, and adjust the pH to 7.0 ± 0.2 using HCl solution or NaOH solution to prepare modified solution A.

[0059] S2. Take an appropriate amount of hydrogen peroxide and add pure water to 1000 l to prepare a 20% hydrogen peroxide solution as modified solution B;

[0060] S3. At room temperature, the prepared modified solution A is placed in a water storage bucket, the booster pump is turned on and the water inlet pressure is controlled below 0.1 MPa, the modified solution A enters the reverse osmosis membrane assembly, contacts the surface of the polyamide reverse osmosis membrane, and then circulates back to the water storage bucket; after running for 45 minutes, the booster pump is turned off, the modified solution A in the water storage bucket is emptied, and pure water is used for circulation 3 times, each cycle for 10 minutes to clean the reverse osmosis membrane assembly;

[0061] S4. At room temperature, place the prepared modified solution B in a water storage barrel, turn on the booster pump and control the water inlet pressure below 0.1MPa. The modified solution B enters the reverse osmosis membrane assembly, contacts the surface of the polyamide reverse osmosis membrane, and then circulates back to the water storage barrel. After running for 4 hours, turn off the booster pump, empty the modified solution B in the water storage barrel, and use pure water for 3 cycles, each cycle for 10 minutes to clean the reverse osmosis membrane assembly, thereby achieving zwitterionic modification of the reverse osmosis composite membrane assembly.

[0062] The anti-fouling performance evaluation of the reverse osmosis membrane module was carried out in a cross-flow manner. The specific steps are shown in Comparative Example 1. The results are listed in the following table:

[0063] Anti-fouling performance of reverse osmosis membrane components

[0064]

[0065] Example 5:

[0066] S1. Dissolve 50 kg of N,N-diethylethanolamine and 10 kg of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) in 1000 l of pure water, and adjust the pH to 7.0 ± 0.2 using HCl solution or NaOH solution to prepare modified solution A.

[0067] S2. Take an appropriate amount of hydrogen peroxide and add pure water to 1000 l to prepare a 20% hydrogen peroxide solution as modified solution B;

[0068] S3. At room temperature, the prepared modified solution A is placed in a water storage bucket, the booster pump is turned on and the water inlet pressure is controlled below 0.1 MPa, the modified solution A enters the reverse osmosis membrane assembly, contacts the surface of the polyamide reverse osmosis membrane, and then circulates back to the water storage bucket; after running for 45 minutes, the booster pump is turned off, the modified solution A in the water storage bucket is emptied, and pure water is used for circulation 3 times, each cycle for 10 minutes to clean the reverse osmosis membrane assembly;

[0069] S4. At room temperature, place the prepared modified solution B in a water storage barrel, turn on the booster pump and control the water inlet pressure below 0.1MPa. The modified solution B enters the reverse osmosis membrane assembly, contacts the surface of the polyamide reverse osmosis membrane, and then circulates back to the water storage barrel. After running for 4 hours, turn off the booster pump, empty the modified solution B in the water storage barrel, and use pure water for 3 cycles, each cycle for 10 minutes to clean the reverse osmosis membrane assembly, thereby achieving zwitterionic modification of the reverse osmosis composite membrane assembly.

[0070] The anti-fouling performance evaluation of the reverse osmosis membrane module was carried out in a cross-flow manner. The specific steps are shown in Comparative Example 1. The results are listed in the following table:

[0071] Anti-fouling performance of reverse osmosis membrane components

[0072]

[0073] From the data obtained in Examples 1-5, it can be seen that the initial flux of the untreated comparative example 1 is 1725.5 l / h. After contact with dodecyl trimethyl ammonium bromide, the permeate flux drops sharply. After 30 minutes of operation, the flux drops to 462.0 l / h, a decrease of about 73.2%, and the cleaning recovery rate is about 28.8%. After treatment using the method of the present invention, although the permeate flux also decreases to varying degrees during operation, its amplitude is significantly reduced. After contact with dodecyl trimethyl ammonium bromide, the permeate flux can still be maintained at 750-1000 l / h, and the cleaning recovery rate also increases to about 40%, which is specifically related to the physicochemical properties of the introduced tertiary amine small molecules. This shows that the present invention can effectively improve the anti-fouling performance of the polyamide reverse osmosis membrane module while maintaining its initial flux and retention performance.

[0074] The embodiments of this specification are merely examples of implementations of the invention and are provided for illustrative purposes only. The scope of protection of the present invention should not be considered limited to the specific embodiments described in these embodiments. The scope of protection of the present invention also extends to equivalent technical means that can be conceived by a person of ordinary skill in the art based on the invention.

Claims

1. A method for in-situ zwitterionic modification of a polyamide composite membrane assembly, characterized in that The following steps are involved: S1. Using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride as an activator and a tertiary amine small molecule material containing an active group as a functional material, a modified solution is prepared. The mass concentration of the modified solution is 2-8%, and the pH value is adjusted to 6.0-9.0 using HCl solution or NaOH solution; Using hydrogen peroxide as an oxidant, an oxidizing solution is prepared with a mass concentration of 10-40%; S2. At room temperature, immerse the composite membrane assembly to be treated in two solutions in turn, and rinse with water after a certain period of time. The circulation time of the modification solution is 10-90 minutes, and the circulation time of the oxidation solution is 1-6 hours, so as to achieve in-situ zwitterion modification of the polyamide composite membrane assembly.

2. The in-situ zwitterion modification method of a polyamide composite membrane assembly according to claim 1, characterized in that: The polyamide composite membrane is a polyamide reverse osmosis membrane or a polyamide nanofiltration membrane; the composite membrane assembly can be in the form of a rolled membrane assembly, a hollow membrane assembly or a tubular membrane assembly.

3. The in-situ zwitterion modification method of a polyamide composite membrane assembly according to claim 1, characterized in that: The tertiary amine small molecule material containing active groups is at least one of triethanolamine, N-ethyldiethanolamine, 2-hydroxyethylethylenediamine, N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine, trimethylhydroxyethylethylenediamine, or N,N-diethylethanolamine.

4. The in-situ zwitterion modification method of a polyamide composite membrane assembly according to claim 1, characterized in that: In step S1, the mass concentration of the modified solution prepared by the tertiary amine small molecule material containing active groups is 4-6%; the pH of the aqueous solution is 6.5-7.

5.

5. The in-situ zwitterion modification method of a polyamide composite membrane assembly according to claim 1, characterized in that: The concentration of the hydrogen peroxide solution in step S1 is 15-25%.

6. The in-situ zwitterion modification method of a polyamide composite membrane assembly according to claim 1, characterized in that: The modified solution in step S2 has a circulation time of 30-60 min.

7. The in-situ zwitterion modification method of a polyamide composite membrane assembly according to claim 1, characterized in that: The oxidation solution circulation time in step S2 is 3-5 hours.

Images