Composite nanofiltration membrane and its preparation method and application

Abstract

The present invention provides a composite nanofiltration membrane, its preparation method, and application. The composite nanofiltration membrane comprises a supporting base membrane and an active separation layer supported on the supporting base membrane; the active separation layer comprises an interfacial polymerization product of a polyamine and a polyacyl chloride that has undergone post-treatment modification; the post-treatment modification comprises post-treatment with a mixed solution of an amine-containing solute and a swelling solvent. The composite nanofiltration membrane has a narrow pore size distribution, high hydrophilicity, and a smooth surface with a near-neutral charge. While significantly improving pure water permeation flux, it achieves high separation selectivity for small-molecule organic compounds and exhibits excellent anti-fouling properties and long-term operational stability. The composite nanofiltration membrane can be used for wastewater decolorization, wastewater desalination, resource recovery, or water softening.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanofiltration membranes, and in particular relates to a composite nanofiltration membrane and a preparation method and application thereof. Background Art

[0002] Due to rapid population growth, rapid industrialization, and severe water pollution worldwide, water shortage has become a pressing issue. Nanofiltration, a low-energy separation process that typically retains substances with a molecular weight cutoff of 100 to 2000 Da, offers excellent separation performance for water / salt or water / organic matter, and shows great potential for water purification and resource recovery. However, during operation, colloids, proteins, and small organic molecules in the feed solution can easily lead to membrane fouling, resulting in increased transmembrane resistance, reduced permeate flux, and changes in separation selectivity. Therefore, it is necessary to design high-performance, fouling-resistant nanofiltration membranes for precise solute separation.

[0003] Interfacial polymerization is widely used in the preparation of nanofiltration membranes. However, due to the uneven mass transfer of aqueous monomers, an active separation layer with a wide pore size distribution and rough surface is formed, resulting in poor membrane separation selectivity and anti-pollution properties. Therefore, CN115350598A discloses a method for preparing nanofiltration membranes using 1-methylimidazole as an aqueous phase additive. The hydrogen bond formed by 1-methylimidazole and piperazine inhibits piperazine from diffusing deeper into the reaction zone, making the generated membrane surface smoother and conducive to improving the anti-pollution properties of the membrane. However, the introduction of the additive can reduce the cross-linking degree of the polyamide separation layer, expand the membrane pore size, and the unreacted acyl chloride groups on the surface are hydrolyzed to form carboxyl groups, causing the membrane to be strongly negatively charged, so that the anti-pollution ability of the membrane to small molecules and positively charged substances decreases.

[0004] For nanofiltration separation systems with complex components, conventional single-charge nanofiltration membranes (positively or negatively charged) are difficult to achieve pollution resistance. Therefore, CN114768561A discloses a method for preparing an anti-pollution composite membrane, which utilizes the residual acyl chloride groups after the interfacial polymerization reaction to continue to react with the amino groups of the polyamine, so that the membrane surface is polyamine-positively charged, and then some of the amino groups on the surface undergo dehydration condensation reaction with the carboxyl groups of the polyacid, so that the outermost surface of the membrane is negatively charged, forming a double-layer charged structure protective layer to reduce the organic pollution of the nanofiltration membrane. CN114259884A discloses a positively charged composite nanofiltration membrane based on in-situ zwitterionization and its preparation method. After interfacial polymerization, polyethyleneimine and 1,4-butanesulfonate are used to perform in-situ zwitterionization on the membrane surface. The shift of the membrane isoelectric point to neutrality improves the anti-pollution performance of the membrane against positively or negatively charged pollutants. However, these surface modification methods only improve the surface properties of the separation layer. The introduction of an additional separation layer increases water mass transfer resistance and reduces membrane permeability. Furthermore, surface modification cannot improve the pore size distribution of the separation layer. A wider pore size distribution can lead to large local variations in permeation flux, resulting in poor separation selectivity and anti-fouling performance of nanofiltration membranes.

[0005] Therefore, it is necessary to develop a composite nanofiltration membrane with a narrow pore size distribution, high hydrophilicity, near neutral charge and a smooth surface to meet the needs of improving the permeation flux of pure water, high separation selectivity of small molecular organic matter, anti-pollution and long-term operation stability. Summary of the Invention

[0006] In response to the shortcomings of the prior art, the present invention provides a composite nanofiltration membrane, its preparation method, and its application. The composite nanofiltration membrane not only improves pure water permeation flux but also achieves high separation selectivity for sucrose / xylose. Its narrow pore size distribution, high hydrophilicity, and nearly neutrally charged smooth surface resist contamination by positively / negatively charged small molecules and proteins, preventing flux attenuation during separation. This effectively addresses the prior art issues of nanofiltration membranes being susceptible to contamination and poor separation selectivity when treating liquid feeds.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a composite nanofiltration membrane, comprising a supporting base membrane and an active separation layer supported on the supporting base membrane.

[0009] The active separation layer comprises an interfacial polymerization product of polyamine and polyacyl chloride that has been modified by post-treatment.

[0010] The post-treatment modification includes post-treatment with a mixed solution containing an amine solute and a swelling solvent.

[0011] In the present invention, the polyamide formed at the interface between the polyamine and the polyacyl chloride is soaked in a mixed solution consisting of an amine-containing solute and a swelling solvent. The swelling solvent can dissolve the small molecular weight polyamide fragments and the swollen polyamide chain segments, thereby enlarging the pores of the polyamide active layer. In addition, the swelling solvent can promote the amine-containing solute to enter the membrane pores, reach the interior of the polyamide, and react with the unhydrolyzed acyl chloride to form an amide reaction, thereby completing deep grafting. Figure 1 As shown, the structure and properties of the separation layer formed by the polyamine and the polyacyl chloride are reformed, so that the active separation layer has a narrower pore size distribution, higher hydrophilicity and a smooth surface with near neutral charge, which is beneficial to improving the separation selectivity and anti-pollution ability of small molecule organic matter.

[0012] Preferably, the polyamine includes any one of piperazine, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, polyethyleneimine (PEI), polyethyleneamine or s-phenylenediamine, or a combination of at least two thereof, wherein typical but non-limiting combinations include: a combination of piperazine and m-phenylenediamine, a combination of m-phenylenediamine, o-phenylenediamine and p-phenylenediamine, a combination of p-phenylenediamine, polyethyleneimine, polyethyleneamine and s-phenylenediamine, and the like.

[0013] Preferably, the polybasic acid chloride includes any one of trimesoyl chloride, phthaloyl chloride, terephthaloyl chloride, 1,5-naphthalene disulfonyl chloride, 1,3,6-naphthalene trisulfonyl chloride, 1,3,5-cyclohexane tricarbonyl chloride or pyromellitoyl chloride, or a combination of at least two thereof, wherein typical but non-limiting combinations include: a combination of trimesoyl chloride and phthaloyl chloride, a combination of terephthaloyl chloride, 1,5-naphthalene disulfonyl chloride and 1,3,6-naphthalene trisulfonyl chloride, a combination of 1,5-naphthalene disulfonyl chloride, 1,3,6-naphthalene trisulfonyl chloride, 1,3,5-cyclohexane tricarbonyl chloride and pyromellitoyl chloride, etc.

[0014] Preferably, the amine-containing solute includes any one of diethylenetriamine, tetraethylenepentamine, polyethylenepolyamine, polyethyleneimine, polyethyleneamine or polyglutamic acid, or a combination of at least two thereof.

[0015] Preferably, the molecular weight of the polyethyleneimine in the amine-containing solute is 600-1000 Da, such as 600 Da, 650 Da, 700 Da, 750 Da, 800 Da, 850 Da, 900 Da, 950 Da or 1000 Da.

[0016] Preferably, the polyethyleneimine includes any one of PEI 600, PEI 800 or PEI 1000, or a combination of at least two of them.

[0017] Typical but non-limiting combinations of the amine-containing solutes include: a combination of PEI600 and diethylenetriamine, a combination of PEI1000, diethylenetriamine, tetraethylenepentamine and PEI600, a combination of diethylenetriamine, tetraethylenepentamine, PEI600 and PEI800, and the like.

[0018] Preferably, the swelling solvent comprises a mixture of a green solvent and a swelling small molecule.

[0019] In the present invention, the weak interaction between the amine-containing solute and the green solvent allows the amine-containing solute to enter the interior of the polyamide and react with the unhydrolyzed acyl chloride to generate an amide reaction.

[0020] Preferably, the green solvent comprises an ionic liquid and / or a deep eutectic solvent.

[0021] Preferably, the ionic liquid includes any one or a combination of at least two of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-methyl-3-propylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1,3-dimethylimidazolium tetrafluoroborate, 1-(2-hydroxyethyl)-3-methyl-1H-imidazol-3-ium tetrafluoroborate or 1-ethyl-3-methylimidazolium hexafluorophosphate; typical but non-limiting combinations include: 1- A combination of butyl-3-methylimidazolium tetrafluoroborate and 1-methyl-3-propylimidazolium tetrafluoroborate, a combination of 1-methyl-3-propylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate and 1,3-dimethylimidazolium tetrafluoroborate, 1-(2-hydroxyethyl)-3-methyl-1H-imidazol-3-ium tetrafluoroborate, 1-ethyl-3-methylimidazolium hexafluorophosphate, choline chloride-citric acid, and choline chloride-malonic acid, etc.

[0022] Preferably, the deep eutectic solvent comprises any one or a combination of at least two of choline chloride-citric acid, choline chloride-malonic acid, choline chloride-lactic acid or choline chloride-sorbitol.

[0023] Preferably, the swelling small molecule comprises any one or a combination of at least two of methanol, anhydrous ethanol, acetone, dimethyl sulfoxide or acetonitrile; typical but non-limiting combinations include: a combination of methanol and anhydrous ethanol, a combination of anhydrous ethanol, acetone and dimethyl sulfoxide, a combination of anhydrous ethanol, acetone, dimethyl sulfoxide and acetonitrile, etc.

[0024] Preferably, the mass ratio of the green solvent to the swelling small molecule in the swelling solvent is (0.43-2.3):1, for example, it can be 0.5:1, 0.8:1, 1.0:1, 1.5:1, 0.5:1, 1.8:1, 2.0:1 or 2.3:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] In the present invention, if the amount of the green solvent is too small, the polyamide chain segments will not swell sufficiently, resulting in less deep grafting of amine-containing solutes and difficulty in controlling the charge of the active separation layer; if the amount of the green solvent is too large, the polyamide chain segments will swell excessively, and the grafting reaction will be difficult to offset the negative impact of the swelling, the pore size and charge of the active separation layer cannot be effectively regulated, and the separation selectivity and anti-pollution performance are reduced.

[0026] Preferably, based on 100 parts by mass of the swelling solvent, the mass fraction of the amine-containing solute is 0.1-5.0 parts, for example, 0.1 part, 0.2 part, 0.4 part, 0.6 part, 0.8 part, 1.0 part, 2.0 part, 3.0 part, 4.0 part or 5.0 parts, etc., but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable, and more preferably 0.1 to 1.5 parts.

[0027] In the present invention, if the amount of the amine-containing solute is too much, it will cause serious surface grafting and accumulation, which will increase the positive charge of the membrane and enhance the electrostatic attraction, making it difficult to resist pollution by negatively charged pollutants; if the amount of the amine-containing solute is too little, it will cause insufficient grafting, and the ability to reform the active separation layer structure is limited, making it difficult to achieve high separation selectivity for the solute.

[0028] Preferably, the post-treatment includes soaking and cross-linking reaction.

[0029] Preferably, the material of the supporting base membrane includes any one or a combination of at least two of polysulfone, polyethersulfone, polyimide, polyamide, polyethylene or polyacrylonitrile, among which typical but non-limiting combinations include: a combination of polysulfone and polyethersulfone, a combination of polyimide, polyamide and polyethylene, a combination of polyimide, polyamide, polyethylene and polyacrylonitrile, etc.

[0030] In a second aspect, the present invention provides a method for preparing the composite nanofiltration membrane according to the first aspect, the preparation method comprising the following steps:

[0031] (1) The supporting base film, polyamine and polyacyl chloride are mixed and reacted.

[0032] (2) The product of step (1) is mixed with a mixed solution containing an amine solute and a swelling solvent, and cross-linked to obtain the composite nanofiltration membrane.

[0033] In the present invention, the purpose of the cross-linking is to further increase the cross-linking degree of the active separation layer and to promote the continued reaction of unreacted amino groups and acyl chlorides.

[0034] Preferably, the mixing in step (1) is to immerse the supporting base film in a polyamine aqueous solution, take it out, dry it, and then coat it with a polyacyl chloride / n-hexane solution.

[0035] Preferably, the immersion time in the polyamine aqueous solution is 3 to 20 minutes, for example, 4 minutes, 6 minutes, 8 minutes, 10 minutes, 15 minutes, 20 minutes or 25 minutes.

[0036] Preferably, the mass percentage of the polyamine in the polyamine aqueous solution is 0.1-1%, for example, it can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8% or 0.9%.

[0037] Preferably, the mass percentage of the polyacyl chloride in the polyacyl chloride / n-hexane solution is 0.05-0.3%, for example, 0.10%, 0.12%, 0.15%, 0.18%, 0.20%, 0.22%, 0.25% or 0.28%.

[0038] Preferably, the reaction time of step (1) is 10 to 120 s, for example, it can be 12 s, 20 s, 30 s, 40 s, 50 s, 60 s, 70 s, 90 s, 100 s or 120 s.

[0039] Preferably, step (1) further includes drying after the reaction.

[0040] Preferably, the mixing in step (2) is performed by soaking the product of step (1) in a mixed solution containing an amine solute and a swelling solvent.

[0041] Preferably, the soaking time is 3 to 30 minutes, for example, 4 minutes, 6 minutes, 8 minutes, 10 minutes, 15 minutes, 20 minutes or 25 minutes.

[0042] Preferably, the soaking further includes rinsing with swelling small molecules, and the rinsing time is 10 to 30 seconds, for example, 10 seconds, 12 seconds, 14 seconds, 16 seconds, 18 seconds, 20 seconds, 22 seconds, 24 seconds, 26 seconds, 28 seconds or 30 seconds.

[0043] In the present invention, the purpose of flushing with swelling small molecules after soaking is to remove unreacted amine-containing solutes.

[0044] Preferably, the temperature of the cross-linking reaction in step (2) is 40-60°C, for example, it can be 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C or 60°C.

[0045] Preferably, the cross-linking reaction time in step (2) is 1 to 10 minutes, for example, 1 minute, 2 minutes, 3 minutes, 5 minutes, 8 minutes or 10 minutes.

[0046] In a third aspect, the present invention provides a composite nanofiltration membrane as described in the first aspect for use in wastewater decolorization, wastewater desalination, resource recovery or water softening.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The composite nanofiltration membrane provided by the present invention is prepared by soaking the interfacial polymerization product of polyamine and polyacyl chloride in a mixed solution consisting of an amine-containing solute and a swelling solvent, and completing a deep amide reaction while swelling and reforming the interfacial polymerization product to obtain an active separation layer, thereby achieving the regulation of the internal structure and surface properties of the active separation layer, and obtaining a composite nanofiltration membrane with a narrow pore size distribution, high hydrophilicity, near neutral charge and a smooth surface, which significantly improves the separation selectivity and anti-pollution performance of the composite nanofiltration membrane for small molecule organic matter. Compared with traditional polyamide nanofiltration membranes, the flux attenuation rate of the composite nanofiltration membrane is reduced, and the sucrose / xylose separation selectivity is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram of the swelling solvent promoting deep grafting of amine-containing solutes. DETAILED DESCRIPTION

[0050] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0051] In the present invention, the materials used in the embodiments and comparative examples are as follows:

[0052] Support membrane: polyethersulfone ultrafiltration membrane, 50kDa, Hunan Aowei Technology Co., Ltd.

[0053] Support membrane: polysulfone ultrafiltration membrane, 50kDa, Ande Membrane Technology Co., Ltd.

[0054] Support membrane: polyethylene ultrafiltration membrane, 50kDa, Ande Membrane Technology Co., Ltd.

[0055] Piperazine: Anhydrous piperazine, 99%, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0056] Trimesoyl chloride: 98%, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0057] n-Hexane: 97%, Shanghai MacLean Biochemical Technology Co., Ltd.

[0058] Ethanol: Anhydrous ethanol, 99.8%, Shanghai MacLean Biochemical Technology Co., Ltd.

[0059] Polyethyleneimine: PEI600, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0060] 1-Butyl-3-methylimidazolium tetrafluoroborate: 97%, Shanghai Myril Biochemical Technology Co., Ltd.

[0061] Chlorogenic acid: 95%, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0062] Methylene blue: 98%, Shanghai MacLean Biochemical Technology Co., Ltd.

[0063] Example 1

[0064] This embodiment provides a composite nanofiltration membrane and a preparation method thereof, wherein the composite nanofiltration membrane includes a supporting base membrane and an active separation layer loaded on the supporting base membrane; the active separation layer includes an interfacial polymerization product of a polyamine and a polyacyl chloride that has been modified by post-treatment; the post-treatment modification includes post-treatment with a mixed solution of an amine-containing solute and a swelling solvent; based on 100 parts by mass of the swelling solvent, the mass fraction of the amine-containing solute is 1.0 part; the mass ratio of the green solvent to the swelling small molecule in the swelling solvent is 1:1.

[0065] The preparation method comprises the following steps:

[0066] (1) The supporting base membrane (polyethersulfone ultrafiltration membrane) was immersed in a 0.5% by mass polyamine (piperazine) aqueous solution for 5 minutes. The immersed supporting base membrane was taken out and dried at room temperature until there were no water droplets visible on the surface. Then, a 0.15% by mass polyacyl chloride (trimethylbenzenecarboxylic acid chloride) / n-hexane solution was coated on the immersed supporting base membrane to perform interfacial polymerization reaction. After the reaction for 30 seconds, the membrane was taken out and dried.

[0067] (2) 50 g of green solvent (1-butyl-3-methylimidazolium tetrafluoroborate) and 50 g of swelling small molecule (anhydrous ethanol) were physically blended, and then 1 g of amine-containing solute (PEI600) was dissolved in the above blended solution to obtain a mixed solution of amine-containing solute and swelling solvent. The product obtained in step (1) was soaked in the mixed solution for 5 minutes. After soaking, the product was taken out and rinsed with swelling small molecule (anhydrous ethanol) for 20 seconds and cross-linked at 50°C for 3 minutes to obtain the composite nanofiltration membrane.

[0068] Example 2

[0069] This embodiment provides a composite nanofiltration membrane and a preparation method thereof, wherein the composite nanofiltration membrane includes a supporting base membrane and an active separation layer loaded on the supporting base membrane; the active separation layer includes an interfacial polymerization product of a polyamine and a polyacyl chloride that has been modified by post-treatment; the post-treatment modification includes post-treatment with a mixed solution of an amine-containing solute and a swelling solvent; based on 100 parts by mass of the swelling solvent, the mass fraction of the amine-containing solute is 1.5 parts; the mass ratio of the green solvent to the swelling small molecule in the swelling solvent is 0.43:1.

[0070] The preparation method comprises the following steps:

[0071] (1) The supporting base membrane (polyethersulfone ultrafiltration membrane) was immersed in a 0.5% by mass piperazine aqueous solution for 5 minutes. The immersed supporting base membrane was taken out and dried at room temperature until there were no water droplets visible on the surface. Then, a 0.15% by mass solution of trimesoyl chloride / n-hexane was coated on the immersed supporting base membrane to perform an interfacial polymerization reaction. After the reaction for 30 seconds, the membrane was taken out and dried.

[0072] (2) 30 g of 1-butyl-3-methylimidazolium tetrafluoroborate and 70 g of anhydrous ethanol were physically blended, and then 1.5 g of PEI600 was dissolved in the above blended solution to obtain a mixed solution containing an amine solute and a swelling solvent. The product obtained in step (1) was soaked in the mixed solution for 5 minutes. After soaking, the product was taken out and rinsed with anhydrous ethanol for 20 seconds and subjected to cross-linking reaction at 50°C for 3 minutes to obtain the composite nanofiltration membrane.

[0073] Example 3

[0074] This embodiment provides a composite nanofiltration membrane and a preparation method thereof, wherein the composite nanofiltration membrane includes a supporting base membrane and an active separation layer loaded on the supporting base membrane; the active separation layer includes an interfacial polymerization product of a polyamine and a polyacyl chloride that has been modified by post-treatment; the post-treatment modification includes post-treatment with a mixed solution of an amine-containing solute and a swelling solvent; based on 100 parts by mass of the swelling solvent, the mass fraction of the amine-containing solute is 0.1 parts; the mass ratio of the green solvent to the swelling small molecule in the swelling solvent is 2.3:1.

[0075] The preparation method comprises the following steps:

[0076] (1) The supporting base membrane (polyethersulfone ultrafiltration membrane) was immersed in a 0.5% by mass piperazine aqueous solution for 5 minutes. The immersed supporting base membrane was taken out and dried at room temperature until there were no water droplets visible on the surface. Then, a 0.15% by mass solution of trimesoyl chloride / n-hexane was coated on the immersed supporting base membrane to perform an interfacial polymerization reaction. After the reaction for 30 seconds, the membrane was taken out and dried.

[0077] (2) 30 g of 1-butyl-3-methylimidazolium tetrafluoroborate and 70 g of anhydrous ethanol were physically blended, and then 0.1 g of PEI600 was dissolved in the above blended solution to obtain a mixed solution containing an amine solute and a swelling solvent. The product obtained in step (1) was soaked in the mixed solution for 5 minutes. After soaking, the product was taken out and rinsed with anhydrous ethanol for 20 seconds and subjected to cross-linking reaction at 50°C for 3 minutes to obtain the composite nanofiltration membrane.

[0078] Example 4

[0079] This embodiment provides a composite nanofiltration membrane and a preparation method thereof. The only difference between this embodiment and Example 1 is that the amine-containing solute is a combination of PEI600 and diethylenetriamine (the mass ratio of PEI600 to diethylenetriamine is 1:1), and the other raw materials, amounts and preparation methods are the same as those in Example 1.

[0080] Example 5

[0081] This embodiment provides a composite nanofiltration membrane and a preparation method thereof. The only difference between the present embodiment and Example 1 is that the green solvent is a combination of 1-butyl-3-methylimidazolium tetrafluoroborate and choline chloride-citric acid (the mass ratio of 1-butyl-3-methylimidazolium tetrafluoroborate to choline chloride-citric acid is 1:1). The other raw materials, amounts and preparation methods are the same as those in Example 1.

[0082] Example 6

[0083] This embodiment provides a composite nanofiltration membrane and a preparation method thereof. The only difference between this embodiment and Example 1 is that the swelling small molecule is a combination of methanol and anhydrous ethanol (the mass ratio of methanol to anhydrous ethanol is 1:1), and the other raw materials, amounts and preparation methods are the same as those in Example 1.

[0084] Example 7

[0085] This embodiment provides a composite nanofiltration membrane and a preparation method thereof, which differs from Example 1 only in that, based on 100 parts by mass of the swelling solvent, the mass fraction of the amine-containing solute is 0.01 parts;

[0086] The mixed solution containing amine solute and swelling solvent was prepared by physically blending 50 g of green solvent (1-butyl-3-methylimidazolium tetrafluoroborate) and 50 g of swelling small molecule (anhydrous ethanol), and then dissolving 0.01 g of PEI600 in the above blended solution.

[0087] Other raw materials, amounts and preparation methods are the same as those in Example 1.

[0088] Example 8

[0089] This embodiment provides a composite nanofiltration membrane and a preparation method thereof, which differs from Example 1 only in that, based on 100 parts by mass of the swelling solvent, the mass fraction of the amine-containing solute is 10 parts;

[0090] The mixed solution containing amine solute and swelling solvent was prepared by physically blending 50 g of green solvent (1-butyl-3-methylimidazolium tetrafluoroborate) and 50 g of swelling small molecule (anhydrous ethanol), and then dissolving 10 g of PEI600 in the above blended solution.

[0091] Other raw materials, amounts and preparation methods are the same as those in Example 1.

[0092] Example 9

[0093] This embodiment provides a composite nanofiltration membrane and a preparation method thereof, which differs from Example 1 only in that the mass ratio of the green solvent to the swelling small molecule in the swelling solvent is 0.1:1;

[0094] The swelling solvent was prepared by physically blending 9.1 g of a green solvent (1-butyl-3-methylimidazolium tetrafluoroborate) and 90.9 g of a swelling small molecule (anhydrous ethanol).

[0095] Other raw materials, amounts and preparation methods are the same as those in Example 1.

[0096] Example 10

[0097] This embodiment provides a composite nanofiltration membrane and a preparation method thereof, which differs from Example 1 only in that the mass ratio of the green solvent to the swelling small molecule in the swelling solvent is 4:1;

[0098] The swelling solvent was prepared by physically blending 80 g of a green solvent (1-butyl-3-methylimidazolium tetrafluoroborate) and 20 g of a swelling small molecule (anhydrous ethanol).

[0099] Other raw materials, amounts and preparation methods are the same as those in Example 1.

[0100] Example 11

[0101] This embodiment provides a composite nanofiltration membrane and a preparation method thereof, wherein the composite nanofiltration membrane includes a supporting base membrane and an active separation layer loaded on the supporting base membrane; the active separation layer includes an interfacial polymerization product of a polyamine and a polyacyl chloride that has been modified by post-treatment; the post-treatment modification includes post-treatment with a mixed solution of an amine-containing solute and a swelling solvent; based on 100 parts by mass of the swelling solvent, the mass fraction of the amine-containing solute is 1.0 part; the mass ratio of the green solvent to the swelling small molecule in the swelling solvent is 1:1.

[0102] The preparation method comprises the following steps:

[0103] (1) The supporting base membrane (polysulfone ultrafiltration membrane) was immersed in a 0.1% by mass polyamine (m-phenylenediamine) aqueous solution for 20 minutes. The immersed supporting base membrane was taken out and dried at room temperature until there were no visible water droplets on the surface. Then, a 0.05% by mass polyacyl chloride (a combination of trimesoyl chloride and phthaloyl chloride in a mass ratio of 1:1) / n-hexane solution was coated on the immersed supporting base membrane to perform interfacial polymerization reaction. After the reaction for 120 seconds, the membrane was taken out and dried.

[0104] (2) 50 g of green solvent (1,3-dimethylimidazolium tetrafluoroborate) and 50 g of swelling small molecule (acetone) were physically blended, and then 5 g of amine-containing solute (diethylenetriamine) was dissolved in the above blended solution to obtain a mixed solution of amine-containing solute and swelling solvent. The product obtained in step (1) was soaked in the mixed solution for 30 minutes. After soaking, the product was taken out and rinsed with swelling small molecule (acetone) for 10 seconds and cross-linked at 40°C for 10 minutes to obtain the composite nanofiltration membrane.

[0105] Example 12

[0106] This embodiment provides a composite nanofiltration membrane and a preparation method thereof, wherein the composite nanofiltration membrane includes a supporting base membrane and an active separation layer loaded on the supporting base membrane; the active separation layer includes an interfacial polymerization product of a polyamine and a polyacyl chloride that has been modified by post-treatment; the post-treatment modification includes post-treatment with a mixed solution of an amine-containing solute and a swelling solvent; based on 100 parts by mass of the swelling solvent, the mass fraction of the amine-containing solute is 1.0 part; the mass ratio of the green solvent to the swelling small molecule in the swelling solvent is 1:1.

[0107] The preparation method comprises the following steps:

[0108] (1) The support base membrane (polyethylene ultrafiltration membrane) was immersed in a 1% by mass polyamine (a combination of o-phenylenediamine and p-phenylenediamine in a mass ratio of 1:0.5) aqueous solution for 3 minutes. The immersed support base membrane was taken out and dried at room temperature until there were no visible water droplets on the surface. Then, a 0.3% by mass polyacyl chloride (terephthaloyl chloride) / n-hexane solution was coated on the immersed support base membrane for interfacial polymerization reaction. After the reaction for 10 seconds, the membrane was taken out and dried.

[0109] (2) 50 g of green solvent (1-ethyl-3-methylimidazolium hexafluorophosphate) and 50 g of swelling small molecule (dimethyl sulfoxide) were physically blended, and then 1 g of amine-containing solute (PEI600) was dissolved in the above blended solution to obtain a mixed solution of amine-containing solute and swelling solvent. The product obtained in step (1) was soaked in the mixed solution for 3 minutes. After soaking, the product was taken out and rinsed with swelling small molecule (dimethyl sulfoxide) for 20 seconds and cross-linked at 60°C for 1 minute to obtain the composite nanofiltration membrane.

[0110] Comparative Example 1

[0111] This comparative example provides a composite nanofiltration membrane and a preparation method thereof, the preparation method comprising the following steps:

[0112] The supporting base membrane (polyethersulfone ultrafiltration membrane) is immersed in a 0.5% by mass polyamine (piperazine) aqueous solution for 5 minutes. The immersed supporting base membrane is taken out and dried at room temperature until there are no visible water droplets on the surface. Then, a 0.15% by mass polyacyl chloride (trimesoyl chloride) / n-hexane solution is coated on the immersed supporting base membrane for interfacial polymerization reaction. After the reaction for 30 seconds, the membrane is taken out and dried to obtain the composite nanofiltration membrane.

[0113] Comparative Example 2

[0114] This comparative example provides a composite nanofiltration membrane and a preparation method thereof, which differs from Example 1 only in that no amine-containing solute (PEI600) is added to the mixed solution used for post-treatment modification, and other raw materials, amounts and preparation methods are the same as those in Example 1.

[0115] Comparative Example 3

[0116] This comparative example provides a composite nanofiltration membrane and a preparation method thereof. The only difference between it and Example 1 is that no green solvent (1-butyl-3-methylimidazolium tetrafluoroborate) is added to the mixed solution used for post-treatment modification, and the other raw materials, amounts and preparation methods are the same as those in Example 1.

[0117] Comparative Example 4

[0118] This comparative example provides a composite nanofiltration membrane and a preparation method thereof, which differs from Example 1 only in that 50g of green solvent (1-butyl-3-methylimidazolium tetrafluoroborate) and 50g of swelling small molecules (anhydrous ethanol) in the mixed solution used for post-treatment modification are replaced with 100g of water, and the other raw materials, amounts and preparation methods are the same as those in Example 1.

[0119] Performance Testing

[0120] The composite nanofiltration membranes provided in Examples 1 to 12 and Comparative Examples 1 to 4 were tested for pure water permeation flux, sodium sulfate retention rate, magnesium chloride retention rate, sucrose retention rate, xylose retention rate, and flux attenuation rate at 25°C:

[0121] A homemade dead-end device was used to test the pure water permeation flux, sodium sulfate retention rate, magnesium chloride retention rate, sucrose retention rate, and xylose retention rate of the composite membrane. The effective volume of the membrane chamber is 13 mL, and the effective membrane area is 4.52 cm 2 , the concentration of each solute in the feed solution is 1 g L -1 , constant flux filtration mode, flux is 39.8Lm -2 h -1 , the test temperature is 25℃.

[0122] (1) The pure water permeation flux is calculated according to the following formula:

[0123]

[0124] The unit of pure water permeation flux is L m -2 h -1 bar -1 ; V p A is the volume of permeate collected in time t (L); m is the effective membrane area (m 2 ); t is the running time (h); TMP is the transmembrane pressure (bar).

[0125] (2) The retention rates of sodium sulfate, magnesium chloride, sucrose, and xylose were calculated according to the following formula:

[0126]

[0127] Among them C p , C f and C r Represent the concentrations of solutes in the permeate, feed solution and retentate respectively: the salt concentration was measured by conductivity meter, and the sucrose concentration was detected by high performance liquid chromatography (HPX-87N, 300 mm × 7.8 mm column).

[0128] (3) The sucrose / xylose separation factor is calculated according to the following formula:

[0129]

[0130] (4) A dead-end device was used to test the membrane flux attenuation rate.

[0131] The constant flux diafiltration mode (flux of 39.8 L m -2 h -1 ), first test the membrane pure water permeation flux (PWP0) at 25 °C, then -1 Chlorogenic acid and 0.8g L -1 Methylene blue was used as feed solution, and the membrane was contaminated at 25°C for 60 min. Finally, the contaminated membrane surface was rinsed with deionized water for 3 times. The pure water permeation flux (PWP) of the contaminated membrane was tested at 25°C. f ). The membrane flux attenuation rate is used to evaluate the membrane's anti-fouling ability, and the calculation formula is:

[0132]

[0133] The specific test results are shown in Table 1:

[0134] Table 1

[0135]

[0136]

[0137] As can be seen from the table above, the composite nanofiltration membrane provided by the present invention achieves the reformation of the internal structure and surface properties of the active separation layer by inducing swelling of the active separation layer and deep grafting of amine-containing solutes with solvent after interfacial polymerization. The obtained composite nanofiltration membrane has a narrow pore size distribution, high hydrophilicity, and a smooth surface with near neutral charge. While significantly improving the pure water permeation flux, it achieves high separation selectivity for sucrose / xylose, and also significantly improves the anti-fouling and long-term operation stability of the composite nanofiltration membrane. As can be seen from Examples 1 to 6, the pure water permeation flux of the composite nanofiltration membrane is 10.5 to 12.5 L m - 2 h -1 bar -1 The sodium sulfate retention rate is 93-95%, the magnesium chloride retention rate is 65-68%, and the sucrose / xylose separation factor is 7-8, with excellent sucrose / xylose separation selectivity; using chlorogenic acid and methylene blue as feed liquid, the flux attenuation rate after 60 minutes of contamination at 25°C is 6.5-7.5%, with excellent anti-pollution performance.

[0138] By comparing Example 1 with Examples 7 and 8, it can be seen that when the mass fraction of the amine-containing solute is not within the preferred range of 0.1-5.0 parts based on the mass of the swelling solvent as 100 parts, the charge of the composite nanofiltration membrane deviates from neutrality and the anti-pollution performance decreases; by comparing Example 1 with Examples 9 and 10, it can be seen that when the mass ratio of the green solvent and the swelling small molecules in the swelling solvent is not within the preferred range of (0.43~2.3):1, the swelling degree of the composite nanofiltration membrane does not match the depth of grafting, the pore size distribution becomes wider, and the separation selectivity and anti-pollution performance decrease.

[0139] By comparing Example 1 with Comparative Example 1, it can be seen that when the composite nanofiltration membrane is not post-treated and modified, the pure water permeation flux of the composite nanofiltration membrane is low, the separation selectivity is poor, and the anti-pollution performance is poor. After post-treatment modification (Example 1), the flux attenuation rate decreased by 63.2%, and the sucrose / xylose separation selectivity increased by 3.3 times.

[0140] From the comparison between Example 1 and Comparative Example 2, it can be seen that when the composite nanofiltration membrane is used in the mixed solution for post-treatment modification without adding amine-containing solute, the pore size distribution is wide and the anti-pollution performance is poor.

[0141] From the comparison between Example 1 and Comparative Example 3, it can be seen that when the composite nanofiltration membrane is used for post-treatment modification of the mixed solution without adding a green solvent, the anhydrous ethanol reforming capacity is limited and the anti-pollution performance is poor.

[0142] From the comparison of Example 1 and Comparative Example 4, it can be seen that when the composite nanofiltration membrane is used in the mixed solution for post-treatment modification and 50g of green solvent and 50g of swelling small molecules are replaced by 100g of water, the active separation layer has no swelling and reforming ability, and the separation selectivity is poor.

[0143] The applicant states that while the above-described embodiments illustrate the process of the present invention, the present invention is not limited to the above-described process steps, nor does it imply that the present invention must rely on the above-described process steps for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent substitutions for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A composite nanofiltration membrane, characterized in that: The composite nanofiltration membrane comprises a supporting base membrane and an active separation layer supported on the supporting base membrane; The active separation layer comprises an interfacial polymerization product of a polyamine and a polyacyl chloride that has been modified by post-treatment; The post-treatment modification includes post-treatment with a mixed solution containing an amine solute and a swelling solvent; The amine-containing solute includes any one or a combination of at least two of diethylenetriamine, tetraethylenepentamine, polyethylenepolyamine, polyethyleneimine, polyethyleneamine or polyglutamic acid; The swelling solvent includes a mixture of a green solvent and swelling small molecules; The green solvent includes an ionic liquid and / or a deep eutectic solvent; The swelling small molecule includes any one of methanol, anhydrous ethanol, acetone, dimethyl sulfoxide or acetonitrile, or a combination of at least two thereof; The mass ratio of the green solvent to the swelling small molecules in the swelling solvent is (0.43-2.3):1; Based on 100 parts by mass of the swelling solvent, the mass fraction of the amine-containing solute is 0.1 to 1.5 parts.

2. The composite nanofiltration membrane according to claim 1, characterized in that The polyamine includes any one of piperazine, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, polyethyleneimine, polyethyleneamine or mesitylenetriamine, or a combination of at least two thereof.

3. The composite nanofiltration membrane according to claim 1, characterized in that The polybasic acid chloride includes any one of trimesoyl chloride, phthaloyl chloride, terephthaloyl chloride, 1,5-naphthalenedisulfonyl chloride, 1,3,6-naphthalenetrisulfonyl chloride, 1,3,5-cyclohexanetricarboxylic acid chloride or pyromellitoyl chloride, or a combination of at least two thereof.

4. The composite nanofiltration membrane according to claim 1, characterized in that The molecular weight of the polyethyleneimine in the amine-containing solute is 600-1000 Da.

5. The composite nanofiltration membrane according to claim 1, characterized in that The ionic liquid includes any one of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-methyl-3-propylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazolium tetrafluoroborate, 1,3-dimethylimidazolium tetrafluoroborate, 1-(2-hydroxyethyl)-3-methyl-1H-imidazol-3-ium tetrafluoroborate or 1-ethyl-3-methylimidazolium hexafluorophosphate or a combination of at least two thereof.

6. The composite nanofiltration membrane according to claim 1, characterized in that The deep eutectic solvent includes any one of choline chloride-citric acid, choline chloride-malonic acid, choline chloride-lactic acid or choline chloride-sorbitol, or a combination of at least two thereof.

7. The composite nanofiltration membrane according to claim 1, characterized in that The post-treatment includes soaking and cross-linking reaction.

8. The composite nanofiltration membrane according to claim 1, characterized in that The material of the supporting base film includes any one of polysulfone, polyethersulfone, polyimide, polyamide, polyethylene or polyacrylonitrile, or a combination of at least two thereof.

9. The method for preparing a composite nanofiltration membrane according to any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: (1) mixing and reacting the supporting film, polyamine and polyacyl chloride; (2) The product of step (1) is mixed with a mixed solution containing an amine solute and a swelling solvent, and cross-linked to obtain the composite nanofiltration membrane.

10. The preparation method according to claim 9, characterized in that The mixing in step (1) is to immerse the supporting base film in a polyamine aqueous solution, take it out, dry it, and then coat it with a polyacyl chloride / n-hexane solution.

11. The preparation method according to claim 10, characterized in that: The immersion time in the polyamine aqueous solution is 3 to 20 minutes.

12. The preparation method according to claim 10, characterized in that The mass percentage of the polyamine in the polyamine aqueous solution is 0.1-1%.

13. The preparation method according to claim 10, characterized in that The mass percentage of the polyacyl chloride in the polyacyl chloride / n-hexane solution is 0.05-0.3%.

14. The preparation method according to claim 9, characterized in that The reaction time of step (1) is 10 to 120 seconds.

15. The preparation method according to claim 9, characterized in that The step (1) further comprises drying after the reaction.

16. The preparation method according to claim 9, characterized in that The mixing in step (2) is to soak the product of step (1) with a mixed solution containing an amine solute and a swelling solvent.

17. The preparation method according to claim 16, characterized in that The soaking time is 3 to 30 minutes.

18. The preparation method according to claim 16, characterized in that After the soaking, the method further comprises flushing with swelling small molecules, and the flushing time is 10 to 30 seconds.

19. The preparation method according to claim 9, characterized in that The temperature of the cross-linking reaction in step (2) is 40-60°C.

20. The preparation method according to claim 9, characterized in that The cross-linking reaction time in step (2) is 1 to 10 minutes.

21. The composite nanofiltration membrane according to any one of claims 1 to 8 is used for wastewater decolorization, wastewater desalination, resource recovery or water softening.

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