A nanofiltration membrane, its preparation method and application

Abstract

This invention provides a nanofiltration membrane, its preparation method, and its applications, relating to the field of permeate membrane technology. Specifically, it includes a base membrane layer and a separation layer; wherein the base membrane layer comprises a porous polyethylene membrane; and the separation layer is an amide polymer comprising tripterene groups. By sequentially modifying one side of the base membrane layer, impregnating it with tripterene amine monomers, and performing two oiling polymerization reactions, a separation layer tightly bonded to the base membrane layer is obtained, exhibiting a unique morphology of a loose bottom layer, a dense surface layer, and internal cavities. The nanofiltration membrane of this invention possesses high retention capacity while exhibiting good permeate flux, excellent membrane integrity, and acid and alkali resistance. It is simple to prepare, low in cost, and has promising application prospects.

Description

Technical Field

[0001] This invention relates to the field of permeation membranes, and more specifically, to a nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] Polyethylene membranes are inexpensive and chemically stable, and have been fully domestically produced. However, research on polyethylene-based nanofiltration membranes is limited, and there are no commercially available nanofiltration membrane products based on porous polyethylene membranes. Therefore, the preparation of high-performance polyethylene-based nanofiltration membranes to replace traditional nonwoven fabric-based nanofiltration membranes, while simultaneously achieving stable mass production, is of great significance. Triptene compounds possess unique three-dimensional structures and large internal free cavities; using them as monomers in interfacial polymerization can effectively increase the free volume of the polymer, thereby reducing mass transfer resistance and increasing membrane flux. If a nanofiltration membrane existed that could simultaneously incorporate polyethylene membranes and triptene compounds, combining the performance advantages of both, it would have broad application prospects. However, current technologies rarely combine triptene compounds with polyethylene membranes.

[0003] In view of this, the present invention is hereby proposed. Summary of the Invention

[0004] The primary objective of this invention is to provide a nanofiltration membrane that, on the one hand, addresses the technological gap in the prior art of polyvinyl tripterene-type polyamide nanofiltration membranes, and on the other hand, solves the problems of poor washability and low permeation flux of nanofiltration membranes during chemical cleaning, improves the inherent defects of the separation layer, and effectively enhances membrane integrity.

[0005] The second objective of this invention is to provide a method for preparing the nanofiltration membrane described above, which is simple to prepare, requires no casting operation, has low preparation cost, and is easy to scale up for production.

[0006] A third objective of this invention is to provide an application of the nanofiltration membrane, specifically referring to a membrane element containing the nanofiltration membrane, which has the same advantages as the nanofiltration membrane described above.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0008] A nanofiltration membrane includes a base membrane layer and a separation layer; wherein the base membrane layer comprises a porous polyethylene membrane; and the separation layer is an amide polymer comprising triterpenoid groups.

[0009] Preferably, the pore size of the base film layer is 200nm to 300nm, and the thickness of the base film layer is 10μm to 30μm.

[0010] The method for preparing the nanofiltration membrane includes the following steps: (1) surface modification treatment of the base membrane to give it a hydrophilic surface layer; then immersion in an aqueous solution containing triterpenoid amine monomer for impregnation treatment; (2) coating the membrane treated in step (1) with an acyl chloride solution and performing an interfacial polymerization reaction, and removing the organic phase solution after the reaction; (3) coating the membrane treated in step (2) with an acyl chloride solution and performing an interfacial polymerization reaction, wherein the concentration of the acyl chloride solution used in step (3) is higher than that used in step (2); removing the organic phase solution after the reaction; (4) heat-treating the membrane treated in step (3) to obtain the nanofiltration membrane.

[0011] Preferably, in step (1), the aqueous solution comprises the triterpenoid amine monomer, a surfactant, an acid acceptor, and a buffer;

[0012] More preferably, the surfactant comprises at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, dodecyltrimethylammonium chloride, and SP-3036; more preferably, the acid acceptor comprises at least one of triethylamine, ethylenediamine, sodium hydroxide, and sodium carbonate; more preferably, the buffer comprises at least one of camphor sulfonic acid and sodium camphorate.

[0013] Preferably, in step (1), the tripterene amine monomer includes at least one of 2,6,14-triaminotriptene, 2,7,14-triaminotriptene, 2,7-dimethyl-3,6-diaminotriptene, and 1,3,6,8-tetramethyl-2,7-diaminotriptene.

[0014] Preferably, in step (1), the mass concentration of the triterpenoid amine monomer in the aqueous solution is 0.5% to 1.0%.

[0015] Preferably, in step (1), the immersion treatment time is 30s to 10min.

[0016] Preferably, the solute of the acyl chloride solution includes at least one of pyromellitic acid trimethylolpropionate chloride, terephthaloyl chloride, isophthaloyl chloride, and pyromellitic tetramethylolpropionate chloride; the solvent of the acyl chloride solution includes at least one of Isopar G, n-decane, and n-hexane.

[0017] Preferably, in step (2), the time for the interfacial polymerization reaction is 10s to 30s.

[0018] Preferably, the mass concentration of the acyl chloride solution used in step (2) is 0.05% to 0.1%.

[0019] Preferably, in step (3), the time for the interfacial polymerization reaction is 30s to 120s.

[0020] Preferably, the concentration of the acyl chloride solution used in step (3) is 0.2% to 0.4%.

[0021] Preferably, in step (4), the temperature of the heat treatment is 60°C to 90°C, and the time of the heat treatment is 1 min to 8 min.

[0022] A membrane element comprising the nanofiltration membrane described above, or a nanofiltration membrane prepared by the method described above.

[0023] Preferably, the width of the pure water flow channel cloth of the membrane element is >0.35mm and the height is >0.15mm.

[0024] Compared with existing technologies, the advantages of this invention are as follows: This invention uses triallene amine monomers and acyl chloride monomers to synthesize polyamide films. A two-step polymerization process achieves a unique morphology of a separation layer with a loose bottom layer, a dense surface layer, and internal cavities, resulting in a nanofiltration membrane with both high rejection and good permeate flux. Furthermore, in practical applications, nanofiltration membranes undergo chemical cleaning processes, making wash resistance a crucial indicator. This invention, through a two-step polymerization process, ensures sufficient interfacial polymerization, reduces defect sites and weak cross-linking points in the desalination layer, effectively improves membrane integrity, and thus significantly enhances the wash resistance of the nanofiltration membrane. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0026] A nanofiltration membrane includes a base membrane layer and a separation layer; wherein the base membrane layer comprises a porous polyethylene membrane; and the separation layer is an amide polymer comprising tripterene groups. Specifically, one side surface of the base membrane layer is sequentially modified, impregnated with a tripterene amine monomer, and coated twice with an acyl chloride monomer, thereby obtaining the separation layer tightly bonded to one side of the base membrane layer. After the modification treatment, the tripterene amine monomer is partially or completely embedded in the pores of the base membrane. Based on intermolecular forces and the surface properties of the modified base membrane, the two achieve a tight bond, while the acyl chloride monomer polymerizes with the amine, and through chemical bonding, the separation layer is ultimately constructed and fixed.

[0027] In a preferred embodiment, the pore size of the base film layer includes, but is not limited to, 200nm, 210nm, 220nm, 230nm, 240nm, 250nm, 260nm, 270nm, 280nm, 290nm, and 300nm, and the thickness of the base film layer includes, but is not limited to, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, 22μm, 24μm, 26μm, 28μm, and 30μm.

[0028] In a preferred embodiment, the thickness of the nanofiltration membrane includes, but is not limited to, 10μm, 12μm, 14μm, 16μm, 18μm, 20μm, 22μm, 24μm, 26μm, 28μm, and 30μm.

[0029] The method for preparing the nanofiltration membrane includes the following steps one through four performed sequentially.

[0030] Step 1: The base film is surface modified to give it a hydrophilic surface layer; then it is immersed in an aqueous solution containing triterpenoid amine monomer for impregnation treatment.

[0031] This step does not limit the specific method of surface modification treatment; in principle, it is sufficient to achieve a sufficiently strong hydrophilicity on one side of the base film. As a preferred embodiment, the surface modification treatment can be carried out by the following process: subjecting the base film to corona treatment, followed by isopropanol impregnation to obtain the modified base film.

[0032] In a preferred embodiment, the aqueous solution comprises the triptereneamine monomer, a surfactant, an acid acceptor, and a buffer; specifically, the mass concentrations of each component are as follows: triptereneamine monomer 0.5%–1.0%, surfactant 0.06%–0.1%, acid acceptor 0.3%–1.0%, buffer 0.5%–2.0%, and the remainder is water.

[0033] In a preferred embodiment, the impregnation time includes, but is not limited to, 30 seconds, 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, and 10 minutes; in a more preferred embodiment, the impregnation time is 1 minute. ～ 5 minutes.

[0034] In a preferred embodiment, the process after the impregnation treatment further includes: removing excess aqueous solution from the membrane surface; for example, a rubber roller can be used to remove the aqueous solution.

[0035] Step 2: Coat the membrane treated in Step 1 with an acyl chloride solution and carry out an interfacial polymerization reaction. After the reaction, remove the organic phase solution.

[0036] Step 3: Coat the membrane treated in Step 2 with an acyl chloride solution and carry out an interfacial polymerization reaction. After the reaction, remove the organic phase solution.

[0037] It is important to note that the concentration of the acyl chloride solution used in step three must be higher than that used in step two; that is, a low-concentration acyl chloride is used for polymerization first, followed by a high-concentration acyl chloride.

[0038] This invention uses triterpenoid amine monomers as aqueous monomers for synthesizing polyamide films. During the first interfacial polymerization process, free volume can be built, reducing mass transfer resistance. When a high-concentration organic phase is coated for the second time, it can promote the monomer to quickly pass through the primary desalination layer and undergo a secondary interfacial polymerization reaction, ultimately forming a separation layer structure with a loose bottom layer, a dense surface layer, and internal cavities. This resolves the contradiction between flux and retention, and improves the integrity and cleaning resistance of the membrane.

[0039] In a preferred embodiment, the mass concentration of the acyl chloride solution used in step two includes, but is not limited to, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, and 0.1%; while the concentration of the acyl chloride solution used in step three includes, but is not limited to, 0.2%, 0.24%, 0.28%, 0.3%, 0.32%, 0.36%, and 0.4%.

[0040] In a preferred embodiment, in step two, the time of the interfacial polymerization reaction includes, but is not limited to, 10s, 12s, 14s, 16s, 18s, 20s, 22s, 24s, 26s, 28s, and 30s; while in step three, the time of the interfacial polymerization reaction includes, but is not limited to, 30s, 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s, and 120s.

[0041] Step 4: Heat-treat the membrane after step 3 to obtain a nanofiltration membrane.

[0042] In a preferred embodiment, the heat treatment temperature includes, but is not limited to, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, and 90°C, and the heat treatment time includes, but is not limited to, 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, and 8 min.

[0043] Example 1

[0044] Base membrane specifications: Polyethylene (PE) porous membrane with a surface pore size of 200nm to 300nm and a thickness of 16μm; this specification of base membrane is used in all embodiments and comparative examples of the present invention.

[0045] 1) The polyethylene film was subjected to corona treatment with a power of 1.2KW, and then impregnated with isopropanol solution;

[0046] 2) Immerse the above-mentioned base film in an aqueous solution containing 0.5% 2,6,14-triaminetriptene, 0.06% sodium dodecyl sulfate, 0.3% triethylamine and 1.0% camphor sulfonic acid by mass concentration. The base film stays in the aqueous solution for 2 minutes, and then the excess aqueous solution on the surface is removed with a rubber roller.

[0047] 3) Pour a 0.05% (w / w) trimethylbenzene chloride organic solution onto the surface of the membrane treated in 2), allow the interfacial polymerization time to be 30 seconds, then discard the excess organic phase solution to obtain the nascent composite membrane.

[0048] 4) Pour a 0.3% (w / w) trimethylbenzene chloride organic solution onto the membrane surface treated in 3), allow the interfacial polymerization time to be 30 seconds, discard the excess organic phase solution, and heat treat at 80°C for 2 minutes to obtain the polyethylene nanofiltration membrane of this embodiment.

[0049] Example 2

[0050] Basically the same as Example 1 The only difference is:

[0051] In step 2), the aqueous solution consists of 0.8% 2,6,14-triaminetriptene, 0.06% sodium dodecyl sulfate, 0.3% triethylamine, and 1.0% camphor sulfonic acid.

[0052] Example 3

[0053] Basically the same as Example 2 The only difference is:

[0054] In step 3), the mass concentration of pyromellitic acid chloride is 0.1%.

[0055] Example 4

[0056] Basically the same as Example 2 The only difference is:

[0057] In step 3), the mass concentration of pyromellitic acid chloride is 0.2%.

[0058] Example 5

[0059] Basically the same as Example 1 The only difference is:

[0060] In step 2), the aqueous solution consists of 0.8% 2,6,14-triaminetriptene and 0.06% sodium dodecyl sulfate (without added acid acceptor and buffer).

[0061] Comparative Example 1

[0062] 1) The polyethylene film was subjected to corona treatment with a power of 1.2KW, and then impregnated with isopropanol solution;

[0063] 2) Immerse the above-mentioned base film in an aqueous solution containing 0.8% piperazine, 0.06% sodium dodecyl sulfate, 0.3% triethylamine and 1.0% camphor sulfonic acid by mass concentration. The base film stays in the aqueous solution for 2 minutes. Remove excess aqueous solution from the surface using a rubber roller.

[0064] 3) Pour a 0.3% (w / w) trimethylbenzene chloride organic solution onto the surface of the membrane treated in 2), allow the interfacial polymerization time to be 30 seconds, discard the excess organic phase solution, and heat treat at 80°C for 2 minutes to obtain a polyethylene nanofiltration membrane.

[0065] Comparative Example 2

[0066] 1) The polyethylene film was subjected to corona treatment with a power of 1.2KW, and then impregnated with isopropanol solution;

[0067] 2) Immerse the above-mentioned base film in an aqueous solution containing 0.8% 2,6,14-triaminetriptene, 0.06% sodium dodecyl sulfate, 0.3% triethylamine and 1.0% camphor sulfonic acid by mass concentration. The base film stays in the aqueous solution for 2 minutes. Remove excess aqueous solution from the surface using a rubber roller.

[0068] 3) Pour a 0.3% (w / w) trimethylbenzene chloride organic solution onto the surface of the membrane treated in 2), allow the interfacial polymerization time to be 30 seconds, discard the excess organic phase solution, and heat treat at 80°C for 2 minutes to obtain a polyethylene nanofiltration membrane.

[0069] Test case

[0070] The separation performance of the nanofiltration membranes prepared in Examples 1-5 and Comparative Examples 1-2 was tested. The specific test method included: (using 2000ppm magnesium sulfate solution as the test solution, operating pressure of 70psi, and operating temperature of 25℃, the membrane was pre-pressed under these conditions for 30min, and then 10min of permeate was collected. The mass and conductivity of the 10min permeate were tested, and the conductivity and temperature of the original solution were recorded). The rejection rate and solution flux of magnesium sulfate solution were obtained, as shown in Table 1 below.

[0071] The nanofiltration membranes prepared in Examples 1-5 and Comparative Examples 1-2 were subjected to alkali resistance tests. The specific test method included immersing the prepared membrane in a NaOH solution with pH=13 and treating it at a constant temperature of 25°C for 17 hours. After that, the membrane was taken out and the above separation performance test was repeated to obtain the rejection rate and solution flux of magnesium sulfate solution, as shown in Table 2 below.

[0072] Table 1. Separation performance test results

[0073] <![CDATA[Flux (L·m -2 ·h -1 )]]> Withholding (%) Comparative Example 1 46.07 99.18 Comparative Example 2 58.50 99.12 Example 1 60.03 99.00 Example 2 51.29 99.20 Example 3 46.78 99.25 Example 4 43.65 99.21 Example 5 49.53 99.14

[0074] Table 2 Results of Alkali Resistance Test

[0075]

[0076]

[0077] As shown in Tables 1 and 2, this invention uses a triterpenoid compound as the aqueous monomer for synthesizing the polyamide film and employs a secondary coating of a high-concentration organic phase. The resulting nanofiltration membrane desalination layer has free cavities, a loose bottom, and a dense surface, resulting in low mass transfer resistance. This solves the "trade-off" effect present in traditional membrane fabrication. The secondary coating process avoids surface defects and weak cross-linking points found in traditional membrane fabrication, improving the integrity of the separation layer and effectively enhancing the membrane's robustness and resistance to acid and alkali cleaning. The membrane fabrication process is simple and suitable for industrial production.

[0078] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A nanofiltration membrane, characterized in that, It includes a base membrane layer and a separation layer; wherein, the base membrane layer comprises a porous polyethylene membrane; and the separation layer is an amide polymer comprising triterene groups; The method for preparing the nanofiltration membrane includes the following steps: (1) The base film is surface modified to give it a hydrophilic surface layer; then it is immersed in an aqueous solution for impregnation. The aqueous solution comprises: a triterpenoid amine monomer, a surfactant, an acid acceptor, and a buffer; (2) Coat the membrane treated in step (1) with acyl chloride solution and carry out interfacial polymerization reaction. After the reaction, remove the organic phase solution. (3) Coat the membrane treated in step (2) with an acyl chloride solution and carry out an interfacial polymerization reaction, wherein the concentration of the acyl chloride solution used in step (3) is higher than that of the acyl chloride solution used in step (2); remove the organic phase solution after the reaction; (4) The membrane after step (3) is subjected to heat treatment to obtain a nanofiltration membrane; The concentration of the acyl chloride solution used in step (2) is 0.05% to 0.1%, and the concentration of the acyl chloride solution used in step (3) is 0.2% to 0.4%.

2. The nanofiltration membrane according to claim 1, characterized in that, The pore size of the base film layer is 200nm~300nm, and the thickness of the base film layer is 10μm~30μm.

3. The nanofiltration membrane according to claim 1, characterized in that, In step (1), the surfactant includes at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, dodecyltrimethylammonium chloride, and SP-3036.

4. The nanofiltration membrane according to claim 1, characterized in that, In step (1), the acid acceptor includes at least one of triethylamine, ethylenediamine, sodium hydroxide, and sodium carbonate.

5. The nanofiltration membrane according to claim 1, characterized in that, In step (1), the buffer includes at least one of camphor sulfonic acid and sodium camphor sulfonate.

6. The nanofiltration membrane according to claim 1, characterized in that, In step (1), the tripterene amine monomer includes at least one of 2,6,14-triaminotriptene, 2,7,14-triaminotriptene, 2,7-dimethyl-3,6-diaminotriptene and 1,3,6,8-tetramethyl-2,7-diaminotriptene; In the aqueous solution, the mass concentration of the triterpenoid amine monomer is 0.5% to 1.0%.

7. The nanofiltration membrane according to claim 1, characterized in that, The immersion treatment time is 30 seconds to 10 minutes.

8. The nanofiltration membrane according to claim 1, characterized in that, The solute in the acyl chloride solution includes at least one of pyromellitic trimethylolpropionate chloride, terephthaloyl chloride, isophthaloyl chloride, and pyromellitic tetramethylolpropionate chloride; The solvent of the acyl chloride solution includes at least one of Isopar G, n-decane, and n-hexane.

9. The nanofiltration membrane according to claim 1, characterized in that, In step (2), the time for the interfacial polymerization reaction is 10s to 30s.

10. The nanofiltration membrane according to claim 1, characterized in that, In step (3), the time for the interfacial polymerization reaction is 30s to 120s.

11. The nanofiltration membrane according to claim 1, characterized in that, In step (4), the temperature of the heat treatment is 60℃~90℃, and the time of the heat treatment is 1min~8min.

12. A membrane element, characterized in that, This includes the nanofiltration membrane according to any one of claims 1 to 11, or the nanofiltration membrane prepared by the method according to any one of claims 3 to 9.

13. The membrane element according to claim 12, characterized in that, The width of the pure water flow channel cloth of the membrane element is >0.35mm and the height is >0.15mm.

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