Chlorine-resistant nanofiltration membrane and preparation method thereof
By generating a covalently cross-linked cation network on the surface of the nanofiltration membrane, the problem of nanofiltration membranes being susceptible to corrosion in chlorine-containing environments is solved, achieving high rejection rate and low flux stability, and extending the membrane's service life.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SUZHOU PUSHI ENVIRONMENTAL TECH CO LTD
- Filing Date
- 2026-02-06
- Publication Date
- 2026-04-24
AI Technical Summary
Existing nanofiltration membranes are susceptible to chemical corrosion in chlorine-containing environments, leading to damage to the membrane pore structure, reduced rejection rate, and shortened service life, especially limiting their application under strong acid or strong alkali conditions.
Polyacrylonitrile-based membranes were prepared using a solvent-inducible phase separation method, and an active layer was formed on their surface by interfacial polymerization. A Hoffmann alkylation reaction was then carried out using an aqueous solution containing polyamine monomers and an oil solution containing polyhalogenated alkyl aromatics to generate a chlorine-resistant layer, forming a covalently cross-linked cationic network.
It improves the chlorine resistance of nanofiltration membranes, enhances membrane stability and durability, maintains high rejection rate and low flux, and extends membrane lifespan.
Smart Images
Figure CN121911235A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of water treatment membrane technology, and in particular to a chlorine-resistant nanofiltration membrane and its preparation method. Background Technology
[0002] Nanofiltration membranes, as a pressure-driven separation membrane between reverse osmosis and ultrafiltration, have been widely used in seawater desalination pretreatment, industrial wastewater reuse, drinking water purification, and food and pharmaceutical separation due to their advantages such as low operating pressure, low energy consumption, and high rejection rate for divalent ions and small organic molecules. Currently, most commercial nanofiltration membranes adopt a polyamide composite membrane structure, and their separation layer is usually prepared by interfacial polymerization of aromatic polyamines (such as m-phenylenediamine, MPD) and acyl chloride monomers (such as trimesoyl chloride, TMC).
[0003] However, polyamide separation layers face severe chemical stability challenges in practical applications, especially in chlorine-containing environments. Chlorine-containing disinfectants such as sodium hypochlorite are commonly used for sterilization or membrane cleaning in water treatment processes, and the amide bonds (–CO–NH–) in the polyamide structure are highly susceptible to reactive chlorine (such as HOCl, OCl). - Attacks by nitrogen oxides (NOx) can cause irreversible degradation reactions such as N-chlorination, Orton rearrangement, or main chain breakage, leading to damage to the membrane pore structure, a significant decrease in rejection rate, and an abnormal increase in flux, ultimately shortening the membrane's lifespan. Furthermore, under strong acid or alkaline conditions, the polyamide layer may also hydrolyze, further limiting its application in extreme conditions.
[0004] Therefore, there is an urgent need to develop a new type of chlorine-resistant nanofiltration membrane. Summary of the Invention
[0005] The technical problem to be solved by the embodiments of the present invention is to provide a chlorine-resistant nanofiltration membrane and its preparation method, which can improve the chlorine resistance of the nanofiltration membrane.
[0006] To address the aforementioned technical problems, this invention provides a method for preparing a chlorine-resistant nanofiltration membrane. The method comprises the following steps: preparing a polyacrylonitrile-based membrane using a solvent-inducible phase separation method; preparing an active layer on the surface of the polyacrylonitrile-based membrane using interfacial polymerization to obtain a precursor membrane; coating the surface of the precursor membrane with a first aqueous solution containing a polyamine monomer, wherein the polyamine monomer contains at least two tertiary amine nitrogen atoms; after removing excess first aqueous solution, coating the surface of the precursor membrane with a first oil phase solution containing polyhalogenated alkyl aromatic hydrocarbons; and performing interfacial polymerization based on a Hoffmann alkylation reaction on the surface of the precursor membrane to generate a chlorine-resistant layer, thereby obtaining the target chlorine-resistant nanofiltration membrane.
[0007] In one feasible implementation, the preparation of a polyacrylonitrile-based membrane by a solvent-inducible phase separation method includes the following steps: a certain mass of polyacrylonitrile particles is weighed and dissolved in an organic solvent, stirred at 60℃-80℃ for 12h-24h until the polyacrylonitrile is completely dissolved, and after vacuum degassing, a casting solution is obtained. The casting solution is poured onto a nonwoven fabric and scraped to a thickness of 100μm-250μm. The polyacrylonitrile membrane is immersed in a coagulation bath in a water bath for solvent exchange. After the casting solution is completely solidified, a polyacrylonitrile-based membrane is obtained and stored in deionized water for later use. The organic solvent is selected from one or a mixture of N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). The mass percentage of the polyacrylonitrile particles in the solution ranges from 16% to 18%.
[0008] In one feasible implementation, the process of preparing the precursor membrane by interfacial polymerization is as follows: a polyacrylonitrile base membrane is fixed in an plexiglass frame, a second aqueous solution is poured onto the surface of the polyacrylonitrile base membrane for 0.5-5 minutes, and the excess second aqueous solution is removed by roller drying; then the membrane is immersed in the second oil phase solution to initiate interfacial polymerization, and after holding for 1-3 minutes, the excess second oil phase solution is removed, and the membrane is subjected to thermal curing treatment to obtain the precursor membrane, which is then stored in deionized water for later use.
[0009] In one feasible implementation, the second aqueous phase monomer of the second aqueous phase solution is selected from at least one of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, piperazine, and polyethyleneimine; In one feasible implementation, the second aqueous monomer has a mass fraction of 1%-4% in the aqueous solution.
[0010] In one feasible implementation, the second oil phase monomer of the second oil phase solution is pyromellitic trimethylol chloride; In one feasible implementation, the mass fraction of the second oil phase monomer in the oil phase solution is 0.1%-1%; In one feasible implementation, the solvent for the second oil phase solution is n-hexane.
[0011] In one feasible implementation, the polyamine monomer is 1,4,7,10-tetraazacyclododecane; In one feasible implementation, the mass fraction of the polyamine monomer in the first aqueous solution is 1%-5%.
[0012] In one feasible implementation, the polyhalogenated alkyl aromatic hydrocarbon is 1,2,4,5-tetrabromomethylbenzene; In one feasible implementation, the mass fraction of the polyhalogenated alkyl aromatic hydrocarbon in the first oil phase solution is 1.5%; In one feasible implementation, the first oil phase monomer in the first oil phase solution is selected from at least one of mesitylene, 1,3-benzene disulfonyl chloride, 1,3,5-benzene trisulfonyl chloride, and 1,3,6-naphthalene trisulfonyl chloride.
[0013] In one feasible implementation, the first aqueous solution also includes additives.
[0014] In one feasible implementation, the substance is sodium dodecyl sulfate.
[0015] In one feasible implementation, the mass fraction of the additive in the first aqueous solution is 0.05%-0.3%.
[0016] In one feasible implementation, the first aqueous phase solution is coated on the surface of the precursor film for 2-4 hours, and the second oil phase solution is coated on the surface of the precursor film for 10-12 hours. In one feasible implementation, after the chlorine-resistant layer is generated, it needs to be dried at 50-60℃ for 20 minutes to cure the chlorine-resistant layer.
[0017] Accordingly, the present invention also provides a chlorine-resistant nanofiltration membrane, which is prepared by any of the aforementioned methods for preparing chlorine-resistant nanofiltration membranes.
[0018] Implementing this invention has the following beneficial effects: The method for preparing the chlorine-resistant nanofiltration membrane provided in this application involves first preparing a polyacrylonitrile-based membrane using a non-solvent-induced phase separation method, then preparing an active layer on the base membrane layer using an interfacial polymerization method, and finally preparing a chlorine-resistant layer on the active layer using an interfacial polymerization based on a Hoffmann alkylation reaction using a first aqueous solution containing polyamine monomers and a first oil solution containing polyhalogenated alkyl aromatic hydrocarbons. This method replaces the previous amide structure, which is susceptible to chlorine corrosion, or the ester bond structure, which is susceptible to alkali hydrolysis. It improves the chlorine resistance of the membrane from the molecular structure, and the preparation method is simple and reliable, with high structural stability of the prepared chlorine-resistant layer.
[0019] The chlorine-resistant layer of the chlorine-resistant nanofiltration membrane provided in this application embodiment reacts with a first aqueous solution containing tertiary amines and a first oil phase containing haloalkanes, replacing the conventional amide structure that is susceptible to chlorine corrosion or the ester bond structure that is susceptible to alkali hydrolysis. This improves the chlorine resistance of the membrane from a molecular structure perspective, and generates a covalently cross-linked, cationic, chlorine-sensitive functional layer in situ, thereby replacing the conventional amide structure that is susceptible to chlorine corrosion or the ester bond structure that is susceptible to alkali hydrolysis, thus improving the chlorine resistance of the membrane from a molecular structure perspective. Attached Figure Description
[0020] Figure 1 This is a flowchart of the preparation method of the chlorine-resistant nanofiltration membrane according to the embodiments of this application; Figure 2This is a scanning electron microscope image of the chlorine-resistant nanofiltration membrane prepared in Example 1 of this application. Detailed Implementation
[0021] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.
[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.
[0023] This application provides a method for preparing a chlorine-resistant nanofiltration membrane. The method for preparing the chlorine-resistant nanofiltration membrane includes the following steps: S110. Preparation of polyacrylonitrile-based membranes by a solvent-inducible phase separation method; In one feasible implementation, the preparation of polyacrylonitrile-based membranes via solvent-inducible phase separation includes the following steps: A certain mass of polyacrylonitrile particles is weighed and dissolved in an organic solvent. The mixture is stirred at 60℃-80℃ for 12h-24h until the polyacrylonitrile is completely dissolved. After degassing under vacuum, a casting solution is obtained. The casting solution is poured onto a nonwoven fabric and scraped to a thickness of 100μm-250μm. The membrane is then immersed in a coagulation bath in a water bath for solvent exchange. Once the casting solution is completely solidified, a polyacrylonitrile-based membrane is obtained and stored in deionized water for later use.
[0024] The coagulation bath is a pure water coagulation bath.
[0025] The organic solvent is selected from one or a mixture of several of N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO).
[0026] The specific dissolution temperatures can be 60℃, 65℃, 70℃, 75℃, or 80℃, and the stirring times can be 12h, 15h, 18h, 20h, 22h, or 25h. The specific thicknesses of the polyacrylonitrile-based films can be 100μm, 110μm, 120μm, 130μm, 140μm, 150μm, 160μm, 170μm, 180μm, 190μm, 200μm, 210μm, 220μm, 230μm, 240μm, or 250μm.
[0027] In one feasible implementation, the mass percentage of the polyacrylonitrile particles in the solution ranges from 16% to 18%. Further, the mass percentage of the polyacrylonitrile particles in the solution can be, but is not limited to, any value between 16%, 17%, 18%, or 16%-18%.
[0028] S120. An active layer is prepared on the surface of the polyacrylonitrile-based membrane by interfacial polymerization to obtain a precursor membrane.
[0029] In this way, by constructing an active layer together with a chlorine-resistant layer, the retention performance of the chlorine-resistant nanofiltration membrane can be improved.
[0030] In a feasible implementation, the process of preparing the active layer and obtaining the precursor film by interfacial polymerization is as follows: A polyacrylonitrile-based membrane is fixed in an acrylic frame. The second aqueous solution is poured onto the surface of the polyacrylonitrile-based membrane for 0.5-5 minutes, and the excess second aqueous solution is removed by roller drying. Then, the membrane is immersed in the second oil phase solution to initiate interfacial polymerization. After holding for 1-3 minutes, the excess second oil phase solution is removed, and the membrane is subjected to thermosetting treatment to obtain the precursor membrane, which is stored in deionized water for later use.
[0031] The reaction time can be, but is not limited to, any specific time between 60s, 90s, 120s, 150s, 180s, or 60s-180s.
[0032] In one feasible implementation, the second aqueous phase monomer of the second aqueous phase solution is selected from at least one of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, piperazine, and polyethyleneimine. Optionally or preferably, the second aqueous phase monomer is m-phenylenediamine.
[0033] In one feasible implementation, the mass fraction of the second aqueous monomer in the aqueous solution is 1%-4%. Further, the mass fraction of the second aqueous monomer in the aqueous solution can be, but is not limited to, any specific value between 1%, 2%, 3%, 4%, or 1%-4%.
[0034] In one feasible implementation, the second oil phase monomer of the second oil phase solution is pyromellitic trimethylolpropionate (PMT).
[0035] In one feasible implementation, the mass fraction of the second oil phase monomer in the oil phase solution is 0.1%-1%. Further, the mass fraction of the second oil phase monomer in the oil phase solution can be, but is not limited to, any specific value between 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or 0.1%-1%.
[0036] In one feasible implementation, the solvent for the second oil phase solution is n-hexane.
[0037] S130. A first aqueous solution containing a polyamine monomer is coated onto the surface of the precursor film, wherein the polyamine monomer contains at least two tertiary amine nitrogen atoms.
[0038] In one feasible implementation, the polyamine monomer is 1,4,7,10-tetraazacyclododecane.
[0039] In one feasible implementation, the mass fraction of the polyamine monomer in the first aqueous solution is 1%-5%. Further, the mass fraction of the polyamine monomer in the first aqueous solution can be, but is not limited to, any specific value between 1%, 2%, 3%, 4%, 5%, or 1%-5%.
[0040] In one feasible implementation, the first aqueous solution further includes an additive. More specifically, the additive is sodium dodecyl sulfate.
[0041] In one feasible implementation, the mass fraction of the additive in the first aqueous solution is 0.05%-0.3%. Further, the mass fraction of the additive in the first aqueous solution can be, but is not limited to, any specific value between 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, or 0.05%-0.3%.
[0042] S140. After removing excess first aqueous solution, a first oil phase solution containing polyhalogenated alkyl aromatic hydrocarbons is coated onto the surface of the precursor membrane. Interfacial polymerization based on Hoffmann alkylation reaction occurs on the surface of the precursor membrane to generate a chlorine-resistant layer, thereby obtaining the target chlorine-resistant nanofiltration membrane.
[0043] In one feasible implementation, the polyhalogenated alkyl aromatic hydrocarbon is 1,2,4,5-tetrabromomethylbenzene.
[0044] In one feasible implementation, the mass fraction of the polyhalogenated alkyl aromatic hydrocarbon in the first oil phase solution is 1.5%.
[0045] In one feasible implementation, the first oil phase monomer in the first oil phase solution is selected from at least one of mesitylene, 1,3-benzene disulfonyl chloride, 1,3,5-benzene trisulfonyl chloride, and 1,3,6-naphthalene trisulfonyl chloride. Optionally or preferably, the first oil phase monomer in the first oil phase solution is mesitylene.
[0046] The preparation of the chlorine-resistant layer involves both Hoffmann alkylation and interfacial polymerization. However, because the interfacial polymerization requires a particularly long reaction time in this step, it is referred to as interfacial polymerization based on Hoffmann alkylation.
[0047] In one feasible implementation, the first aqueous phase solution is coated on the precursor film surface for 2-4 hours, and the second oil phase solution is coated on the precursor film surface for 10-12 hours. This time setting is beneficial for the complete reaction and improves the reliability of the prepared chlorine-resistant layer. Optionally or preferably, the first aqueous phase solution is coated on the precursor film surface for 2-4 hours, and the second oil phase solution is coated on the precursor film surface for 12 hours.
[0048] In one feasible implementation, after the chlorine-resistant layer is formed, it needs to be subjected to a thermosetting treatment. The thermosetting treatment conditions are: drying at 50-60°C for 5-20 minutes. Further, the drying and curing temperature can be, but is not limited to, 50°C, 55°C, 60°C, or any temperature between 50°C and 60°C. The thermosetting treatment time can be, but is not limited to, 5 minutes, 10 minutes, 15 minutes, 20 minutes, or any time between 5 minutes and 20 minutes. The specific thermosetting treatment time needs to be set in conjunction with the thermosetting treatment temperature.
[0049] The process involves coating the precursor membrane surface with a first aqueous solution, which constitutes the aqueous adsorption stage. SDS, as an anionic surfactant, may promote the enrichment of polyamine monomers on the membrane surface and improve wettability through electrostatic or hydrophobic interactions; polyamine monomer molecules diffuse and adsorb onto the surface of the formed polyamide interlayer. Afterwards, excess first aqueous solution is removed, and the membrane surface can be dried with nitrogen. This process of rolling and nitrogen purging removes free polyamine monomers, but some monomers are already anchored to the membrane surface through hydrogen bonds or van der Waals forces, providing reaction sites for subsequent reactions. Immediately following, a second oil phase solution is coated onto the precursor membrane surface. Here, polyhalogenated aromatic hydrocarbon molecules diffuse from the organic phase to the interface, and their -CH2Br groups undergo an SN2 reaction with the nitrogen atoms of the polyamine monomers adsorbed on the membrane surface. Each polyamine monomer (4 N atoms) can react with multiple polyhalogenated aromatic hydrocarbon molecules, and each polyhalogenated aromatic hydrocarbon (multiple -CH2Br atoms) can also connect to multiple polyamine monomer molecules, forming a three-dimensional cross-linked cationic network covalently bonded to the membrane surface. Finally, heat treatment is used to promote complete reaction, remove residual solvents such as mesitylene and moisture, and solidify the chlorine-resistant layer. This ultimately forms a cross-linked aromatic bridged multi-cationic polymer network on the surface of the active layer. Multiple -N + H(-R)-CH2-C6H2(CH2-)2-CH2-N + The H(-R)-type repeating unit is used. The benzene ring acts as a rigid linker, providing structural stability. A large number of fixed positive charges (from protonated or alkylated nitrogen) impart a Donnan repulsion effect to the membrane, which is beneficial for the retention of divalent ions. Furthermore, the absence of NH amide bonds and easily hydrolyzable ester bonds, along with the saturated CN bonds protected by alkyl / aryl groups, ensures high stability against hypochlorous acid oxidation. In addition, the chlorine-resistant layer based on the Hoffmann reaction also offers advantages in reliability and durability, resulting in a chlorine-resistant nanofiltration membrane with excellent durability.
[0050] Accordingly, this application also provides a chlorine-resistant nanofiltration membrane. This chlorine-resistant nanofiltration membrane is prepared using any of the aforementioned methods. Specifically, the chlorine-resistant nanofiltration membrane comprises, along its thickness direction, a base membrane layer, an active layer, and a chlorine-resistant layer. The base membrane layer is a polyacrylonitrile base membrane prepared by a solvent-inducible phase separation method; the active layer is a polyamide layer prepared on the base membrane layer by interfacial polymerization; and the chlorine-resistant layer is prepared by interfacial polymerization based on a Hoffmann alkylation reaction using a first aqueous solution containing a polyamine monomer and a first oil solution containing a polyhalogenated alkyl aromatic hydrocarbon, wherein the polyamine monomer contains at least two tertiary amine nitrogen atoms. The preparation of the chlorine-resistant layer involves both a Hoffmann alkylation reaction and an interfacial polymerization reaction; however, because the interfacial polymerization requires a particularly long reaction time in this step, this step is referred to as interfacial polymerization based on a Hoffmann alkylation reaction.
[0051] The chlorine-resistant layer of the chlorine-resistant nanofiltration membrane provided in this application embodiment reacts with a first aqueous solution containing tertiary amines and a first oil phase containing haloalkanes, replacing the conventional amide structure that is susceptible to chlorine corrosion or the ester bond structure that is susceptible to alkali hydrolysis. This improves the chlorine resistance of the membrane from a molecular structure perspective, and generates a covalently cross-linked, cationic, chlorine-sensitive functional layer in situ, thereby replacing the conventional amide structure that is susceptible to chlorine corrosion or the ester bond structure that is susceptible to alkali hydrolysis, thus improving the chlorine resistance of the membrane from a molecular structure perspective.
[0052] Referring to the above implementation details, in order to make the technical solution of this application more specific, clear, and easy to understand, examples of the technical solution of this application are given below. However, it should be noted that the content to be protected by this application is not limited to the following embodiments.
[0053] Example 1 Preparation of polyacrylonitrile-based membranes via a solvent-inducible phase separation method: 16g of polypropylene powder was dissolved in 84g of DMAC at 70℃ for 12h. After the polyacrylonitrile was completely dissolved, the mixture was degassed under vacuum to obtain a casting solution. The casting solution was poured onto a nonwoven fabric and scraped to a thickness of 140μm. The polyacrylonitrile membrane was then immersed in a coagulation bath in a water bath for solvent exchange. After the polyacrylonitrile membrane was completely cured, a polyacrylonitrile base membrane was obtained and stored in deionized water for later use. An active layer is prepared on the surface of the polyacrylonitrile-based film by interfacial polymerization: Pour a 2% MPD aqueous solution onto the membrane surface and let it stand for 2 minutes. Remove excess water by roller drying. Then immerse the membrane in 0.25% TMC n-hexane for 1 minute to carry out interfacial polymerization. After the reaction is complete, place the membrane in a 55°C oven for 10 minutes to obtain the precursor membrane. The precursor membrane was fixed on a glass plate. Then, a first aqueous solution containing 0.1 wt% sodium dodecyl sulfate and 1 wt% 1,4,7,10-tetraazacyclododecane (TAD) was poured onto the surface of the precursor membrane. After 3 hours, excess aqueous phase was rolled off, and the surface of the base membrane was dried with nitrogen. Next, a solution of mesitylene (first oil phase solution) containing 1.5 wt% 1,2,4,5-tetrabromomethylbenzene (TBB) was poured onto the membrane. After standing for 12 hours, interfacial polymerization based on Hoffmann alkylation occurred on the surface of the precursor membrane, generating a chlorine-resistant layer. This layer was then dried at 55°C for 20 minutes to obtain the target chlorine-resistant sodium membrane.
[0054] Figure 2 This is a scanning electron microscope (SEM) image of the chlorine-resistant nanofiltration membrane prepared in Example 1 of this application. Figure 2 It can be seen that the surface of the chlorine-resistant nanofiltration membrane prepared in Example 1 of this application is dense, with no visible cracks or pinholes, indicating that the membrane is relatively intact.
[0055] Example 2 This embodiment is basically the same as Embodiment 1, except that in this embodiment, the mass percentage of TAD in the first aqueous phase solution is 2.5%.
[0056] Example 3 This embodiment is basically the same as Embodiment 1, except that in this embodiment, the mass percentage of TAD in the first aqueous solution is 5%.
[0057] Comparative Example 1 Dissolve 16g of polypropylene powder in 84g of DMAC at 70℃ for 12h. After the polyacrylonitrile is completely dissolved, remove air bubbles under vacuum, pour the casting solution onto a nonwoven fabric, scrape it to a thickness of 140μm, immerse the polyacrylonitrile membrane in a coagulation bath of a water bath for solvent exchange, and store it in deionized water for later use.
[0058] Pour a 2% MPD aqueous solution onto the membrane surface and let it stand for 2 minutes. Remove excess water by roller drying, then immerse the membrane in 0.25% TMC hexane for 1 minute. Place the prepared membrane in a 55°C oven for 10 minutes. Afterward, store the membrane in deionized water for later use.
[0059] Comparative Example 2 Dissolve 16g of polypropylene powder in 84g of DMAC at 70℃ for 12h. After the polyacrylonitrile is completely dissolved, remove air bubbles under vacuum, pour the casting solution onto a nonwoven fabric, scrape it to a thickness of 140μm, immerse the polyacrylonitrile membrane in a coagulation bath of a water bath for solvent exchange, and store it in deionized water for later use.
[0060] A polyacrylonitrile membrane was fixed onto a glass plate. Then, an aqueous solution containing 0.1 wt% sodium dodecyl sulfate (SDS) and 1 wt% 1,4,7,10-tetraazacyclododecane (TAD) was poured onto the surface of the polyacrylonitrile membrane. After maintaining this state for 3 hours, excess aqueous phase was rolled off, and the surface of the membrane was dried with nitrogen. Next, a solution of mesitylene containing 1.5 wt% 1,2,4,5-tetrabromomethylbenzene (TBB) was poured onto the membrane. After standing for 12 hours, the membrane was dried at 55°C for 20 minutes.
[0061] Performance testing The nanofiltration membranes prepared in the examples and comparative examples were tested. The test solution was a 2000 ppm magnesium sulfate aqueous solution, the feed temperature was 25°C, and the test pressure was 5 bar. The chlorine resistance was tested by static immersion method. The membrane was immersed in a 500 ppm sodium hypochlorite aqueous solution for 3 days. After immersion, the sodium hypochlorite on the membrane surface was rinsed with deionized water. Finally, the water flux and rejection rate of the membrane were tested. The results are shown in Table 1.
[0062] Table 1. Results of water flux and retention rate before and after chlorine tolerance As shown in the table above, the nanofiltration membranes prepared in this application exhibit small differences in rejection rate and flux before and after the chlorine resistance test. The rejection rate after chlorine resistance is consistently above 98%. This demonstrates that the chlorine-resistant membranes prepared in this application possess excellent chlorine resistance. This is because the first aqueous phase solution containing tertiary amine reacts with the first oil phase containing haloalkanes to form a quaternary ammonium salt structure, replacing the previously chlorine-sensitive amide structure or the alkali-sensitive ester bond structure, thus improving the membrane's chlorine resistance from a molecular structure perspective.
[0063] Among them, the chlorine-resistant membrane prepared in Example 1 showed the least reduction in retention rate. The chlorine-resistant membrane prepared in Example 2 showed the highest retention rate both before and after chlorine resistance.
[0064] The basic concepts have been described above. Obviously, for those skilled in the art, the detailed disclosure above is merely illustrative and does not constitute a limitation of this specification. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements, and corrections to this specification. Such modifications, improvements, and corrections are suggested in this specification and therefore remain within the spirit and scope of the exemplary embodiments described herein.
[0065] Furthermore, this specification uses specific terms to describe embodiments thereof. For example, "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic associated with at least one embodiment of this specification. Therefore, it should be emphasized and noted that references to "an embodiment," "one embodiment," or "an alternative embodiment" in different locations throughout this specification do not necessarily refer to the same embodiment. Moreover, certain features, structures, or characteristics in one or more embodiments of this specification can be appropriately combined.
[0066] Furthermore, unless expressly stated in the claims, the order of processing elements and sequences, the use of numbers and letters, or other names described in this specification are not intended to limit the order of the processes and methods described herein. Although some inventive embodiments that are currently considered useful have been discussed by way of various examples in the foregoing disclosure, it should be understood that such details are for illustrative purposes only, and the appended claims are not limited to the disclosed embodiments. Rather, the claims are intended to cover all modifications and equivalent combinations that conform to the substance and scope of the embodiments described herein.
[0067] Similarly, it should be noted that, in order to simplify the description disclosed herein and thus aid in the understanding of one or more embodiments of the invention, the foregoing description of embodiments in this specification may sometimes combine multiple features into a single embodiment, drawing, or description thereof. However, this method of disclosure does not imply that the subject matter of this specification requires more features than those mentioned in the claims. In fact, the embodiments contain fewer features than all the features of a single embodiment disclosed above.
[0068] In some embodiments, numbers describing the quantity of components and attributes are used. It should be understood that such numbers used in the description of embodiments are modified in some examples with the terms "approximately," "approximately," or "generally." Unless otherwise stated, "approximately," "approximately," or "generally" indicates that the numbers are allowed to vary by ±20%. Accordingly, in some embodiments, the numerical parameters used in the specification and claims are approximate values, which may be changed depending on the characteristics required by individual embodiments. In some embodiments, numerical parameters should take into account specified significant digits and employ a general method of digit reservation. Although the numerical ranges and parameters used to confirm their breadth of range in some embodiments of this specification are approximate values, in specific embodiments, such values are set as precisely as feasible.
[0069] For each patent, patent application, patent application publication, and other material such as articles, books, specifications, publications, and documents referenced in this specification, the entire contents of which are incorporated herein by reference. This excludes historical application documents that are inconsistent with or conflict with the content of this specification, as well as documents that limit the broadest scope of the claims in this specification (currently or subsequently appended to this specification). It should be noted that in the event of any inconsistency or conflict between the descriptions, definitions, and / or terminology used in the supplementary materials to this specification and the content of this specification, the descriptions, definitions, and / or terminology used in this specification shall prevail.
[0070] Finally, it should be understood that the embodiments described in this specification are merely illustrative of the principles of the embodiments described herein. Other variations may also fall within the scope of this specification. Therefore, alternative configurations of the embodiments described herein are intended to be consistent with the teachings of this specification, rather than as examples or limitations. Accordingly, the embodiments described herein are not limited to those explicitly introduced and described herein.
Claims
1. A method for preparing a chloride-resistant nanofiltration membrane, characterized in that, The method for preparing the chlorine-resistant sodium filtration membrane includes the following steps: Polyacrylonitrile-based membranes were prepared by a solvent-inducible phase separation method. An active layer was prepared on the surface of the polyacrylonitrile-based membrane by interfacial polymerization to obtain a precursor membrane; A first aqueous solution containing a polyamine monomer is coated onto the surface of the precursor film, wherein the polyamine monomer contains at least two tertiary amine nitrogen atoms. After removing excess first aqueous solution, a first oil phase solution containing polyhalogenated alkyl aromatic hydrocarbons is coated onto the surface of the precursor membrane. Interfacial polymerization based on Hoffmann alkylation reaction occurs on the surface of the precursor membrane to generate a chlorine-resistant layer, thereby obtaining the target chlorine-resistant nanofiltration membrane.
2. The method for preparing the chloride-resistant nanofiltration membrane according to claim 1, characterized in that, The preparation of polyacrylonitrile-based membranes via a solvent-inducible phase separation method includes the following steps: A certain mass of polyacrylonitrile (PA) particles was weighed and dissolved in an organic solvent. The mixture was stirred at 60℃-80℃ for 12-24 hours until the PA was completely dissolved. After vacuum degassing, a casting solution was obtained. This solution was poured onto a non-woven fabric and scraped to a thickness of 100μm-250μm. The PA membrane was then immersed in a water bath for solvent exchange. Once the casting solution had completely solidified, a PA-based membrane was obtained and stored in deionized water for later use. The organic solvent is selected from one or a mixture of several of N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO); The mass percentage of the polyacrylonitrile particles in the solution ranges from 16% to 18%.
3. The method for preparing the chloride-resistant nanofiltration membrane according to claim 1, characterized in that, The procedure for preparing the precursor film by interfacial polymerization to obtain the active layer is as follows: A polyacrylonitrile-based membrane is fixed in an acrylic frame. The second aqueous solution is poured onto the surface of the polyacrylonitrile-based membrane for 0.5-5 minutes, and the excess second aqueous solution is removed by roller drying. Then, the membrane is immersed in the second oil phase solution to initiate interfacial polymerization. After holding for 1-3 minutes, the excess second oil phase solution is removed, and the membrane is subjected to thermosetting treatment to obtain the precursor membrane, which is stored in deionized water for later use.
4. The method for preparing the chloride-resistant nanofiltration membrane according to claim 3, characterized in that, The second aqueous phase monomer of the second aqueous phase solution is selected from at least one of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, piperazine, and polyethyleneimine; The second aqueous monomer has a mass fraction of 1%-4% in the aqueous solution.
5. The method for preparing the chloride-resistant sodium filtration membrane according to claim 3, characterized in that, The second oil phase monomer of the second oil phase solution is pyromellitic trimethylol chloride; The mass fraction of the second oil phase monomer in the oil phase solution is 0.1%-1%; The solvent for the second oil phase solution is n-hexane.
6. The method for preparing a chloride-resistant nanofiltration membrane according to claim 1, characterized in that, The polyamine monomer is 1,4,7,10-tetraazacyclododecane; The mass fraction of the polyamine monomer in the first aqueous solution is 1%-5%.
7. The method for preparing a chloride-resistant sodium filtration membrane according to claim 1, characterized in that, The polyhalogenated alkyl aromatic hydrocarbon is 1,2,4,5-tetrabromomethylbenzene; The mass fraction of the polyhalogenated alkyl aromatic hydrocarbon in the first oil phase solution is 1.5%; The first oil phase monomer in the first oil phase solution is selected from at least one of mesitylene, 1,3-benzene disulfonyl chloride, 1,3,5-benzene trisulfonyl chloride and 1,3,6-naphthalene trisulfonyl chloride.
8. The method for preparing a chloride-resistant nanofiltration membrane according to claim 1, characterized in that, The first aqueous solution also includes additives. The substance in question is sodium dodecyl sulfate; The mass fraction of the additive in the first aqueous solution is 0.05%-0.3%.
9. The method for preparing a chloride-resistant nanofiltration membrane according to claim 1, characterized in that, The first aqueous phase solution is coated on the surface of the precursor film for 2-4 hours, and the second oil phase solution is coated on the surface of the precursor film for 10-12 hours. After the chlorine-resistant layer is formed, it needs to be dried at 50-60℃ for 20 minutes to cure the chlorine-resistant layer.
10. A chlorine-resistant nanofiltration membrane, characterized in that, The chlorine-resistant nanofiltration membrane was prepared using the preparation method described in any one of claims 1-9.