High-flux chlorine-resistant anti-pollution composite nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention provides a high-flux chlorine-resistant anti-pollution composite nanofiltration membrane and a preparation method and application thereof, and the preparation method comprises the following steps: immersing a porous base membrane into a water-phase monomer solution, taking out the porous base membrane, removing a surface solution, and immersing the porous base membrane into an organic-phase monomer solution to complete interfacial polymerization to obtain an initial polyamide active layer; immersing the prepared initial polyamide active layer in a mixed solution containing sodium lignin sulfonate, a surfactant and a catalyst to complete surface modification; and carrying out thermocuring on the prepared surface-modified polyamide active layer to obtain the high-flux chlorine-resistant anti-pollution composite nanofiltration membrane. The anti-pollution performance and water flux of the prepared composite nanofiltration membrane are obviously improved, the composite nanofiltration membrane is suitable for being used as drinking water terminal treatment, and softening and purification of drinking water are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of surface modification of nanofiltration membranes, and particularly relates to a high-flux chlorine-resistant and fouling-resistant composite nanofiltration membrane, a preparation method thereof, and an application thereof. Background Art

[0002] Nanofiltration membranes have the characteristics of low energy consumption, high efficiency, and simple operation, and are ideal terminal technologies for ensuring drinking water safety. Nanofiltration membranes usually have a composite structure composed of a support layer and an active layer, and the active layer is prepared by a two-phase interfacial polymerization reaction on a porous ultrafiltration membrane (support layer). Currently, most nanofiltration membranes are polyamide nanofiltration membranes, which generally have poor chlorine resistance. The main reason is that the amide bonds and benzene rings in their active layers contain attack sites for active chlorine. When attacked by active chlorine, the cross-linking groups are broken and damaged. In the actual engineering application of water treatment, a large amount of active chlorine is often added to the feed liquid. After pretreatment, the residual active chlorine will attack the surface layer of the nanofiltration membrane during long-term operation, resulting in a sharp decline or even exhaustion of the membrane performance. In addition, the nanofiltration membrane faces the problem of membrane fouling during long-term application, resulting in a decrease in the quality of the process effluent and an increase in the operating cost. To prevent and alleviate membrane fouling, chemical cleaning is often required. The free chlorine generated by the commonly used chlorine cleaning agent during chemical cleaning will erode the surface of the polyamide membrane, reducing the service life of the nanofiltration membrane. Therefore, simultaneously improving the chlorine resistance and fouling resistance of the nanofiltration membrane is an urgent problem to be solved in the existing technology.

[0003] CN117225201A uses surface esterification modification to graft erythritol molecules onto the membrane surface to obtain a chlorine-resistant and fouling-resistant composite nanofiltration membrane. CN116020281A uses grafting of amine-containing cyclic compounds and finally introduces quaternization modification to obtain a nanofiltration membrane with high chlorine resistance and fouling resistance. However, the above existing technologies have not achieved very good results. Summary of the Invention

[0004] In view of this, the present invention aims to overcome the defects in the existing technology and proposes a high-flux chlorine-resistant and fouling-resistant composite nanofiltration membrane, a preparation method thereof, and an application thereof.

[0005] To achieve the above object, the technical solution of the present invention is realized as follows: In the first aspect, the present invention provides a preparation method of a high-flux chlorine-resistant and fouling-resistant composite nanofiltration membrane, comprising the following steps: S1: Immerse a porous substrate membrane into an aqueous monomer solution, remove the surface solution after taking it out, and then immerse it into an organic monomer solution to complete interfacial polymerization to obtain an initial polyamide active layer; S2: Immerse the initial polyamide active layer obtained in step S1 into a mixed solution containing sodium lignosulfonate, a surfactant, and a catalyst to complete surface modification; S3: Thermally cure the surface-modified polyamide active layer obtained in step S2 to obtain a high-flux chlorine-resistant and fouling-resistant composite nanofiltration membrane.

[0006] In some embodiments of the present invention, the porous substrate membrane in step S1 is a ultrafiltration membrane made of polysulfone, polyethersulfone, polyacrylonitrile or polyvinylidene fluoride.

[0007] In some embodiments of the present invention, the cut-off molecular weight of the porous substrate membrane in step S1 is 50 - 150KDa.

[0008] In some embodiments of the present invention, the monomer in the aqueous monomer solution in step S1 is piperazine.

[0009] In some embodiments of the present invention, the mass fraction of the monomer in the aqueous monomer solution in step S1 is 0.5 - 20 wt%.

[0010] In some embodiments of the present invention, the monomer in the organic monomer solution in step S1 is any one or a mixture of two or more of 1,3,5-benzenetricarbonyl chloride, 1,2,4,5-benzenetetracarbonyl chloride, 1,3,5-benzenetrisulfonyl chloride.

[0011] In some embodiments of the present invention, the solvent in the organic monomer solution in step S1 is any one or a mixture of two or more of n-hexane, cyclohexane, toluene.

[0012] In some embodiments of the present invention, the mass fraction of the monomer in the organic monomer solution in step S1 is 0.1 - 1 wt%.

[0013] In some embodiments of the present invention, the mass fraction of sodium lignosulfonate in the mixed solution in step S2 is 1 - 20wt%.

[0014] In some embodiments of the present invention, the surfactant in step S2 is any one or a mixture of two or more of sodium dodecyl sulfonate, sodium dodecyl sulfate, cetyltrimethylammonium chloride.

[0015] In some embodiments of the present invention, the mass fraction of the surfactant in the mixed solution in step S2 is 0.1 - 1%; In some embodiments of the present invention, the catalyst in step S2 is any one or a mixture of two or more of sodium hydroxide, triethylamine, 4-dimethylaminopyridine.

[0016] In some embodiments of the present invention, the mass fraction of the catalyst in the mixed solution in step S2 is 1 - 10%.

[0017] In some embodiments of the present invention, the contact time between the porous base membrane and the aqueous monomer solution in step S1 is 1 - 10 min.

[0018] In some embodiments of the present invention, after the porous base membrane contacts with the aqueous monomer solution, an air knife is used to remove the excess solution on the surface of the porous base membrane.

[0019] In some embodiments of the present invention, the contact time between the porous base membrane and the organic phase monomer solution in step S1 is 0.5 - 3 min.

[0020] In some embodiments of the present invention, the surface modification time in step S2 is 3 - 10 min.

[0021] In some embodiments of the present invention, the temperature of thermal curing in step S3 is 50 - 90 °C, and the time is 2 - 15 min.

[0022] In a second aspect, the present invention provides a high - flux chlorine - resistant and anti - fouling composite nanofiltration membrane prepared by the above - mentioned preparation method.

[0023] In a third aspect, the present invention provides the application of the above - mentioned high - flux chlorine - resistant and anti - fouling composite nanofiltration membrane in the softening and purification treatment of drinking water.

[0024] Compared with the prior art, the present invention has the following advantages: (1) The preparation method of the present invention first prepares a polyamide nanofiltration membrane by the traditional interfacial polymerization method, and then immerses the prepared polyamide nanofiltration membrane into an aqueous solution of sodium lignosulfonate containing a surfactant and a catalyst. The surfactant and the catalyst assist the reaction between sodium lignosulfonate molecules and residual acyl chloride groups, so that more sodium lignosulfonate is anchored on the surface of the polyamide active layer. A large number of hydroxyl and sulfonic acid groups are introduced on the surface of the surface - esterified polyamide, which is beneficial to improving the intermolecular hydrogen - bond interaction; the sulfonic acid groups can increase the negative charge on the membrane surface and can effectively prevent active chlorine from contacting the membrane surface.

[0025] (2) After the composite nanofiltration membrane prepared by the present invention is exposed to 16000 ppm•h of active chlorine, the rejection rate of sodium sulfate is greater than 83%, and there is almost no change compared with that before exposure.

[0026] (3) The water flux and anti - fouling performance of the composite nanofiltration membrane prepared by the present invention are both significantly improved. It can greatly reduce the energy consumption in the actual drinking water treatment project and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the molecular structural formula of sodium lignosulfonate used in Example 1; Figure 2Schematic diagram of the surface modification process in Example 1 (in the figure, PIP is the abbreviation of piperazine, TMC is the abbreviation of 1,3,5-benzenetricarbonyl chloride in n-hexane, and SL is the abbreviation of sodium lignosulfonate); Figure 3 Diagram of the water droplet contact angle of the nanofiltration membranes in Example 1 and Comparative Examples 1 - 3; Figure 4 SEM surface morphology diagrams of the nanofiltration membranes in Example 1 and Comparative Examples 1 - 3; Figure 5 SEM cross-sectional diagrams of the nanofiltration membranes in Example 1 and Comparative Examples 1 - 3; Figure 6 Diagram of the anti-fouling performance of the nanofiltration membranes in Example 1 and Comparative Examples 1 - 3. Detailed implementation manners

[0028] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention and should not be construed as a limitation to the present invention.

[0029] In this article, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs.

[0030] In this article, when values are described as ranges, it should be understood that such disclosure includes the disclosure of all possible sub-ranges within the range, as well as the specific values falling within the range, regardless of whether the specific values or specific sub-ranges are explicitly indicated.

[0031] In this article, when referring to "a plurality of" etc., unless otherwise specified, it means greater than 2 or equal to 2 in quantity. For example, "one or more" means one or greater than or equal to two.

[0032] In this article, when referring to "preferred" and "more preferred", they are only used to describe the implementation manners or embodiments with better effects. It should be understood that they do not constitute a limitation to the protection scope of the present invention.

[0033] In this article, when referring to "further" etc. for descriptive purposes, it indicates a difference in content, but should not be construed as a limitation to the protection scope of the present invention.

[0034] In this article, the term "and / or" is a description of the association relationship of objects, indicating that there can be three relationships. For example, A and / or B means: A or B, or A and B these three relationships.

[0035] In this article, the term "about" means + / - 10% of the specified value, preferably + / - 5%, more preferably + / - 1%.

[0036] As used herein, terms such as "comprising", "including", "having", "containing", etc. are all open-ended terms, meaning including but not limited to.

[0037] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention.

[0038] The present invention will be described in detail below in conjunction with embodiments.

[0039] Example 1: A method for preparing a high-flux chlorine-resistant composite nanofiltration membrane, comprising the following steps: Pour an aqueous piperazine solution with a mass fraction of 0.5 wt% onto the surface of a polysulfone substrate membrane (with a molecular weight cut-off of 100 KDa) and hold for 3 min. Then pour off the excess aqueous solution on the surface of the substrate membrane, and blow off the obvious water droplets on the membrane surface with an air knife. Thereafter, pour an n-hexane solution of 1,3,5-benzenetricarbonyl chloride with a mass fraction of 0.3 wt% onto the membrane surface for interfacial polymerization, and the reaction time is 180 s. After pouring off the excess solution, pour an aqueous solution containing 5 wt% sodium lignosulfonate (whose molecular structural formula is as Figure 1 shown), 2 wt% 4-dimethylaminopyridine and 0.3 wt% sodium dodecylsulfonate onto the surface of the initial polyamide nanofiltration membrane and hold for 10 min. Place the prepared composite membrane in a blast drying oven at 50 °C for heat treatment for 10 min to obtain a high-flux chlorine-resistant composite nanofiltration membrane. The schematic diagram of the surface modification process of Example 1 is as Figure 2 shown.

[0040] Example 2: The difference from Example 1 is that an aqueous solution of 3 wt% sodium lignosulfonate, 2 wt% 4-dimethylaminopyridine and 0.3 wt% sodium dodecylsulfonate is used for surface modification. Other preparation conditions are the same as those in Example 1.

[0041] Example 3: The difference from Example 1 is that an aqueous solution of 5 wt% sodium lignosulfonate, 2 wt% sodium hydroxide and 0.3 wt% sodium dodecylsulfonate is used for surface modification. Other preparation conditions are the same as those in Example 1.

[0042] Example 4: The difference from Example 1 is that an aqueous solution of 20 wt% sodium lignosulfonate, 1 wt% sodium hydroxide and 1 wt% sodium dodecylsulfonate is used for surface modification. Other preparation conditions are the same as those in Example 1.

[0043] Example 5: The difference from Example 1 is that an aqueous solution of 1 wt% sodium lignosulfonate, 0.1 wt% sodium hydroxide and 1 wt% sodium dodecylsulfonate is used for surface modification. Other preparation conditions are the same as those in Example 1.

[0044] Example 6: The difference from Example 1 is that an interfacial polymerization reaction is carried out using a 5 wt% aqueous solution of piperazine and a 0.1 wt% cyclohexane solution of 1,2,4,5-benzenetetracarbonyl chloride, and then surface modification is carried out. Other preparation conditions are the same as those in Example 1.

[0045] Example 7: The difference from Example 1 is that an interfacial polymerization reaction is carried out using a 20 wt% aqueous solution of piperazine and a 1 wt% toluene solution of 1,3,5-benzenetrisulfonyl chloride, and then surface modification is carried out. Other preparation conditions are the same as those in Example 1.

[0046] Example 8: The difference from Example 1 is that an interfacial polymerization reaction is carried out using a 20 wt% aqueous solution of piperazine, and then surface modification is carried out. Other preparation conditions are the same as those in Example 1.

[0047] Comparative Example 1: The difference from Example 1 is that no surface modification is carried out after interfacial polymerization, and heat treatment is directly carried out. Other preparation conditions are the same as those in Example 1.

[0048] Comparative Example 2: The difference from Example 1 is that surface modification is carried out using an aqueous solution of 5 wt% sodium lignosulfonate and 2 wt% 4-dimethylaminopyridine. Other preparation conditions are the same as those in Example 1.

[0049] Comparative Example 3: The difference from Example 1 is that surface modification is carried out using an aqueous solution of 5 wt% sodium lignosulfonate. Other preparation conditions are the same as those in Example 1.

[0050] Test Example (1) Water contact angle test The nanofiltration membranes prepared in Example 1 and Comparative Examples 1 - 3 were subjected to the test using a contact angle measuring instrument with reference to the GBT30693 - 2014 standard. The test results are as Figure 3 shown. It can be seen that the nanofiltration membrane prepared by the present invention has good hydrophilic performance.

[0051] (2) The nanofiltration membranes prepared in Example 1 and Comparative Examples 1 - 3 were observed by scanning electron microscopy, and the results are as Figure 4 and Figure 5 shown. It can be seen that the thickness of the membrane prepared by the present invention is increased, confirming the success of the surface modification with sodium lignosulfonate.

[0052] (4)Nanofiltration performance test The nanofiltration membranes prepared in Examples 1 - 8 and Comparative Examples 1 - 3 were subjected to nanofiltration performance tests. At a temperature of 25 °C and an operating pressure of 0.5 MPa, the water flux (F) of the membrane and the rejection rate (R) of different divalent metal salts (including sodium sulfate, magnesium sulfate, magnesium chloride, and sodium chloride) at a concentration of 1000 ppm in the aqueous solution were tested.

[0053] Water flux: The volume (V) of water passing through a unit membrane area (S) per unit time (t) under a specific pressure. It can be expressed by the following formula.

[0054] ; where F is the water flux, V is the volume of the permeate, S is the membrane filtration area, and t is the filtration time.

[0055] Rejection rate: The percentage of solute removed from the feed water of the system after passing through the nanofiltration membrane. It can be expressed by the following formula: ; where R is the rejection rate, C f is the feed liquid concentration, and C p is the permeate concentration. The inorganic salt concentration was determined by a conductivity meter. The test results are shown in Table 1: Table 1 Performance test results of the surface - modified nanofiltration membranes of examples and comparative examples

[0056] As can be seen from the above table, the water fluxes of Examples 1 - 8 are significantly higher than those of Comparative Examples 1 - 3, indicating that the nanofiltration membranes prepared by the present invention have a relatively high flux.

[0057] (5)Chlorine resistance performance test The nanofiltration membranes prepared in Examples 1 - 8 and Comparative Examples 1 - 3 were subjected to chlorine resistance performance tests. They were statically immersed in a 2000 ppm NaClO solution at a temperature of 25 °C and pH = 7, and according to the above - mentioned nanofiltration performance test, the change in the rejection rate of the sodium sulfate solution under different chlorine exposure times was detected. The test results are shown in Table 2: Table 2 Chlorine resistance performance test results of the surface - modified nanofiltration membranes of examples and comparative examples

[0058] As can be seen from the above table, the rejection rates of sodium sulfate of Examples 1 - 8 are significantly higher than those of Comparative Examples 1 - 3, indicating that the nanofiltration membranes prepared by the present invention have good chlorine resistance performance.

[0059] (6)Anti - fouling performance test The anti-fouling performance of the nanofiltration membranes prepared in Example 1 and Comparative Examples 1-3 was tested. At a temperature of 25 °C, a stable membrane flux was obtained by filtering pure water for 2 hours; then, an aqueous solution of bovine serum albumin prepared was used as the feed solution for 5 hours of membrane fouling, and then a 2-hour rinsing test was carried out to test the membrane flux recovery ability. According to the above nanofiltration performance test, the change in the water flux of pure water was detected. The test results are as Figure 6 shown. It can be seen that the water flux recovery rate of Example 1 is significantly higher than that of Comparative Examples 1-3, indicating that the nanofiltration membrane prepared by the present invention has good anti-fouling performance.

[0060] In summary, the present invention uses sodium lignosulfonate, a surfactant, and a catalyst for the surface modification of a nanofiltration composite membrane. The surfactant and the catalyst assist the reaction of sodium lignosulfonate molecules with the residual acyl chloride groups, enabling more sodium lignosulfonate to be anchored on the surface of the polyamide active layer. By introducing a large number of hydroxyl and sulfonic acid groups, the intermolecular hydrogen bond interaction is enhanced; the negative charge of the membrane surface can be increased through the sulfonic acid groups, effectively preventing the contact of active chlorine with the membrane surface. By introducing more hydrophilic functional groups, the anti-fouling performance of the membrane is significantly improved. At the same time, sodium lignosulfonate has a large volume, which can increase the pore size of the membrane and improve the water flux. The prepared nanofiltration membrane is more suitable for use as the terminal treatment of drinking water to achieve the softening and purification of drinking water.

[0061] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a high-throughput chlorine-resistant and anti-pollution composite nanofiltration membrane, characterized in that: It includes the following steps: S1: Immerse the porous substrate membrane into the aqueous monomer solution. After taking it out and removing the surface solution, then immerse it into the organic monomer solution to complete interfacial polymerization, obtaining an initial polyamide active layer; S2: Immerse the initial polyamide active layer prepared in step S1 into a mixed solution containing sodium lignosulfonate, surfactant, and catalyst to complete surface modification; S3: Thermally cure the surface-modified polyamide active layer prepared in step S2 to obtain a high-flux chlorine-resistant and anti-pollution composite nanofiltration membrane.

2. The preparation method of the high-throughput chlorine-resistant and anti-pollution composite nanofiltration membrane according to claim 1, characterized in that: The porous substrate membrane in step S1 is a ultrafiltration membrane made of polysulfone, polyethersulfone, polyacrylonitrile, or polyvinylidene fluoride; and / or The cut-off molecular weight of the porous substrate membrane is 50 - 150 Kda.

3. The preparation method of the high-flux chlorine-resistant and anti-pollution composite nanofiltration membrane according to claim 1, characterized in that: The monomer in the aqueous monomer solution in step S1 is piperazine; and / or The mass fraction of the monomer in the aqueous monomer solution is 0.5 - 20 wt%.

4. The preparation method of the high-flux chlorine-resistant and anti-pollution composite nanofiltration membrane according to claim 1, characterized in that: The monomer in the organic monomer solution in step S2 is any one or a mixture of two or more of 1,3,5-benzenetricarbonyl chloride, 1,2,4,5-benzenetetracarbonyl chloride, and 1,3,5-benzenetrisulfonyl chloride; and / or The solvent in the organic monomer solution is any one or a mixture of two or more of n-hexane, cyclohexane, and toluene; and / or The mass fraction of the monomer in the organic monomer solution is 0.1 - 1 wt%.

5. The preparation method of the high-flux chlorine-resistant and anti-fouling composite nanofiltration membrane according to claim 1, wherein: The mass fraction of sodium lignosulfonate in the mixed solution in step S2 is 1 - 20wt%; and / or The surfactant is any one or a mixture of two or more of sodium dodecyl sulfonate, sodium dodecyl sulfate, and cetyltrimethylammonium chloride; and / or The mass fraction of the surfactant in the mixed solution is 0.1 - 1%.

6. The preparation method of the high-flux chlorine-resistant and anti-pollution composite nanofiltration membrane according to claim 1, characterized in that: The catalyst in step S2 is any one or a mixture of two or more of sodium hydroxide, triethylamine, and 4-dimethylaminopyridine; and / or The mass fraction of the catalyst in the mixed solution is 1 - 10%.

7. The preparation method of the high-flux chlorine-resistant and anti-fouling composite nanofiltration membrane according to claim 1, wherein: The contact time between the porous substrate membrane and the aqueous monomer solution in step S1 is 1 - 10 min; and / or After the porous substrate membrane contacts with the aqueous monomer solution, use an air knife to remove the excess solution on the surface of the porous substrate membrane; and / or The contact time between the porous substrate membrane and the organic monomer solution is 0.5 - 3 min.

8. The preparation method of the high-flux chlorine-resistant and anti-fouling composite nanofiltration membrane according to claim 1, characterized in that: The surface modification time in step S2 is 3 - 10min; and / or The temperature of thermal curing in step S3 is 50 - 90 °C, and the time is 2 - 15 min.

9. A high-flux chlorine-resistant and anti-pollution composite nanofiltration membrane prepared by the preparation method according to any one of claims 1 - 8.

10. Application of the high-flux chlorine-resistant and anti-pollution composite nanofiltration membrane according to claim 9 in drinking water softening and purification treatment.

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