Modifiers, methods for modifying fouling-resistant nanofiltration membranes, fouling-resistant nanofiltration membranes and their applications

Abstract

The application relates to the field of nanofiltration membranes, and discloses a modifier, a modification method of a pollution-resistant nanofiltration membrane, the pollution-resistant nanofiltration membrane and application of the pollution-resistant nanofiltration membrane, wherein the modifier comprises glycerol, a polyhydric phenol, a polyhydric hydroxyl polymer and a pH regulator. The pollution-resistant nanofiltration membrane is obtained by modifying an initial nanofiltration membrane with the modifier, the pollution-resistant nanofiltration membrane has high interception rate and strong surface hydrophilicity, can reduce adsorption of hydrophobic organic pollutants on the membrane surface, ensures that the water flux reduction rate of the membrane is low during long-time operation, and the water flux of the polluted membrane has a high recovery rate after water cleaning.

Description

Technical Field

[0001] This invention relates to the field of nanofiltration membranes, specifically to a modifier, a method for modifying a fouling-resistant nanofiltration membrane, a fouling-resistant nanofiltration membrane, and its applications. Background Technology

[0002] Nanofiltration is a pressure-driven membrane separation process that falls between reverse osmosis and ultrafiltration. Nanofiltration membranes have pore sizes ranging from a few nanometers. They are less effective at removing monovalent ions and organic compounds with molecular weights less than 200, but have higher removal rates for divalent or polyvalent ions and organic compounds with molecular weights between 200 and 500. Nanofiltration membranes can be widely used in water softening, drinking water purification, water quality improvement, oil-water separation, wastewater treatment and reuse, seawater softening, and the classification, purification, and concentration of chemical products such as dyes, antibiotics, peptides, and polysaccharides.

[0003] Membrane fouling has always been a significant factor affecting membrane performance and reducing its service life. Membrane fouling refers to the irreversible phenomenon where particulates, colloidal particles, or large solute molecules in the feed solution that come into contact with the membrane are adsorbed and deposited on the membrane surface or within the pores due to physical and chemical interactions with the membrane, concentration polarization causing certain solutes to exceed their solubility, and mechanical effects. This leads to a reduction in membrane pore size or blockage, resulting in a significant decrease in membrane flux and separation characteristics. The flux decline and reduced membrane separation capacity caused by the adsorption of pollutants on the membrane surface and within the pores, especially protein adsorption, are the main causes of membrane flux decline.

[0004] Therefore, developing a modifier and modification method to improve the fouling resistance of commercial nanofiltration membrane elements can not only extend the service life of the membrane and reduce water treatment costs, but also reduce the use of raw materials. Summary of the Invention

[0005] The purpose of this invention is to overcome the problem of membrane fouling reducing the performance of nanofiltration membranes in the prior art, and to provide a modifier, a method for modifying fouling-resistant nanofiltration membranes, a fouling-resistant nanofiltration membrane, and its applications.

[0006] To achieve the above objectives, a first aspect of the present invention provides a modifier comprising glycerol, polyphenols, polyhydroxy polymers, and a pH adjuster.

[0007] The second method of the present invention provides a method for modifying a fouling-resistant nanofiltration membrane, wherein the modification method includes pre-cleaning an initial nanofiltration membrane and contacting the cleaned initial nanofiltration membrane with a modifier; wherein the initial nanofiltration membrane comprises a support layer and a separation layer stacked sequentially; and the modifier is the aforementioned modifier.

[0008] A third aspect of the present invention provides a fouling-resistant nanofiltration membrane prepared by the aforementioned modification method.

[0009] A fourth aspect of the present invention provides a fouling-resistant nanofiltration membrane, wherein the fouling-resistant nanofiltration membrane comprises a support layer, a separation layer and a modification layer stacked sequentially; the material constituting the separation layer comprises polyamide, and the material constituting the modification layer comprises polyphenols and polyhydroxy polymers.

[0010] The fifth aspect of the present invention provides an application of the aforementioned fouling-resistant nanofiltration membrane in the field of water treatment.

[0011] The beneficial effects achieved by the present invention through the above technical solution are as follows:

[0012] The surface of the initial nanofiltration membrane is modified by a modifier to form a modified layer. The polyphenols and polyhydroxy polymers in the modified layer undergo a self-assembly process on the separation layer surface of the initial nanofiltration membrane. The density of the modified fouling-resistant nanofiltration membrane surface increases, which increases the salt rejection rate of the fouling-resistant nanofiltration membrane and improves its fouling resistance.

[0013] Furthermore, the formation of numerous hydrogen bonds between the polyhydroxy polymer and the polyphenols enhances the hydrophilicity of the fouling-resistant nanofiltration membrane, resulting in higher water flux. The polyphenols in the modification layer of the fouling-resistant nanofiltration membrane are connected to the polyamide in the separation layer by chemical bonds "-CN-", making the modification layer and separation layer of the fouling-resistant nanofiltration membrane fit together better and improving the stability and service life of the fouling-resistant nanofiltration membrane.

[0014] Meanwhile, the modification method provided by this invention is simple and easy to operate, and has good prospects for industrialization. Attached Figure Description

[0015] Figure 1 This is a SEM image of the nanofiltration membrane surface of Example 1;

[0016] Figure 2 This is a SEM image of the nanofiltration membrane surface in Comparative Example 1;

[0017] Figure 3 These are the infrared spectra of Example 1 and Comparative Example 1;

[0018] Figure 4 The polyphenol in the middle is tannic acid, and the polyhydroxy polymer is polyvinyl alcohol. Figure 4 This is a schematic diagram illustrating one possible connection method between the two, where, Indication of hydrogen bond, The diagram illustrates the separation layer; * indicates the undrawn portion of polyvinyl alcohol; # indicates the undrawn portion of tannic acid. Detailed Implementation

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] The first aspect of the present invention provides a modifier comprising glycerol, polyphenols, polyhydroxy polymers and pH adjusters.

[0021] According to the present invention, in the modifier, the glycerol is 5-30 parts by weight, the polyphenol content is 0.0001-1 parts by weight, and the polyhydroxy polymer content is 0.0001-1 parts by weight.

[0022] In this invention, hydrogen bonds are formed between the polyphenols and the polyhydroxy polymers in the modifier, which increases the density of the fouling-resistant nanofiltration membrane and thus increases its salt rejection rate. At the same time, the formation of a large number of hydrogen bonds between the polyhydroxy polymers and the polyphenols improves the hydrophilicity of the fouling-resistant nanofiltration membrane.

[0023] The hydrogen bonding occurs when the H atoms from the polyphenols are bonded to the O atoms from the polyhydroxy polymers, or when the O atoms from the polyphenols are bonded to the H atoms from the polyhydroxy polymers.

[0024] A particularly preferred embodiment, such as Figure 4 As shown, Figure 4 The polyphenol in the middle is tannic acid, and the polyhydroxy polymer is polyvinyl alcohol. The -O group in the tannic acid... 1 H of O 1 Tannic acid is linked to the hydrogen atoms in polyvinyl alcohol via hydrogen bonds, and to the -O atoms in tannic acid via hydrogen bonds. 2 The H in H is linked to the O in polyvinyl alcohol through hydrogen bonds, while the -O in tannic acid is linked to the O in... 3 H, where O 3 It can also exist independently of H, and there are no hydrogen bonds.

[0025] In this invention, the density of the fouling-resistant nanofiltration membrane is characterized by the average pore size.

[0026] The high density of the fouling-resistant nanofiltration membrane results in a high rejection rate for pollutants, effectively trapping them.

[0027] Further, in the modifier, the content of glycerol is 10-20 parts by weight, the content of polyphenols is 0.0005-0.5 parts by weight, and the content of polyhydroxy polymers is 0.0005-0.5 parts by weight.

[0028] According to the present invention, the weight-average molecular weight of the polyphenol is 100-10000 g / mol, preferably 200-5000 g / mol.

[0029] According to the present invention, the weight-average molecular weight of the polyhydroxy polymer is 1,000-200,000 g / mol, preferably 5,000-100,000 g / mol.

[0030] In this invention, the multi-hydroxyl polymer with a specific weight-average molecular weight contains a large number of hydroxyl groups, which further improves the hydrophilicity of the fouling-resistant nanofiltration membrane.

[0031] According to the present invention, the polyphenols are selected from at least one of tannic acid, tea polyphenols, lignin, sodium lignin sulfonate, apple polyphenols, grape polyphenols, sennaol, naringin, epicatechin, luteolin, apigenin, calciferol, myricetin, and genistein; preferably tannic acid and / or lignin.

[0032] According to the present invention, the multi-hydroxyl polymer is selected from at least one of polyvinyl alcohol, hydroxyl-terminated polyethylene glycol, chitosan, hydroxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose, preferably selected from polyvinyl alcohol and / or hydroxymethyl cellulose. Commercially available examples include, for instance, PVA-124 from Bailingwei Technology Co., Ltd., and hydroxymethyl cellulose from Bailingwei Technology Co., Ltd.

[0033] According to the present invention, the modifier further comprises water.

[0034] In this invention, a water-containing modifier forms a modifier system, and the total amount of other components in the system, excluding the pH adjuster, plus the amount of water, makes the total weight parts of the system 100 parts by weight.

[0035] According to the present invention, a pH adjuster is added to make the pH of the modifier system 8-13, preferably 9-12.

[0036] Adding a pH adjuster here refers to adjusting the pH value of the water-containing modifier system.

[0037] In this invention, a specific pH value allows the polyphenols to fully react with the amino groups remaining on the polyamide.

[0038] According to the present invention, the pH adjuster is selected from at least one of disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium carbonate, potassium carbonate, sodium bicarbonate, and potassium bicarbonate, preferably disodium hydrogen phosphate.

[0039] The second method of the present invention provides a method for modifying a fouling-resistant nanofiltration membrane, wherein the modification method includes pre-cleaning an initial nanofiltration membrane and contacting the cleaned initial nanofiltration membrane with a modifier;

[0040] The initial nanofiltration membrane comprises a support layer and a separation layer stacked sequentially; the modifier is the aforementioned modifier.

[0041] According to the present invention, the material constituting the support layer is selected from at least one of polyacrylonitrile, polyarylethersulfone, polyethersulfone and polysulfone, preferably selected from polysulfone and / or polyethersulfone.

[0042] According to the present invention, the material constituting the separation layer is a polyamide prepared by reacting a polyamine with a polyacrylamide compound.

[0043] The reaction is an interfacial polymerization reaction. Specifically, unreacted amino groups on the polyamine in the polyamide can be linked to the polyphenols in the modifier via a chemical bond "-CN-", resulting in a tighter connection between the separation layer and the modified layer formed by contacting the modifier, thus improving the stability of the prepared fouling-resistant nanofiltration membrane.

[0044] In this invention, the chemical bond "-CN-" is detected by infrared spectroscopy.

[0045] According to the present invention, the polyamine is selected from at least one of polyethyleneimine, polyethyleneamine, polyethylene polyamine, polyetheramine and piperazine.

[0046] In this invention, the polyphenols in the modifier react with the residual amino groups in the polyamide to form chemical bonds; in addition, the polyhydroxy polymers in the modifier solution can be linked with the polyphenols through hydrogen bonds.

[0047] According to the present invention, the contact process is a conventional contact method, such as immersion, coating, spraying, etc., and preferably includes immersing the initial nanofiltration membrane in the modifier.

[0048] According to the present invention, the contact pressure is 0.1-2 MPa, the contact temperature is 10-50°C, and the contact time is 10-60 min.

[0049] The inventors of this invention discovered in their research that when the contact process meets the above-mentioned modification range, the final fouling-resistant nanofiltration membrane can have a high rejection rate and water flux.

[0050] Furthermore, the contact pressure is 0.5-1 MPa, the contact temperature is 20-30°C, and the contact time is 15-30 min.

[0051] A third aspect of the present invention provides a fouling-resistant nanofiltration membrane prepared by the aforementioned modification method.

[0052] A fourth aspect of the present invention provides a fouling-resistant nanofiltration membrane, wherein the fouling-resistant nanofiltration membrane comprises a support layer, a separation layer and a modification layer stacked sequentially; the material constituting the separation layer comprises polyamide, and the material constituting the modification layer comprises polyphenols and polyhydroxy polymers.

[0053] In this invention, a chemical bond "-CN-" is formed between the separation layer and the modification layer.

[0054] In this invention, hydrogen bonds are formed between the polyphenol and the polyhydroxy polymer.

[0055] According to the present invention, the thickness of the support layer is 20-60 μm, the thickness of the separation layer is 20-200 nm, and the thickness of the modification layer is 1-100 nm.

[0056] In this invention, the specific layer thickness between each layer of the fouling-resistant nanofiltration membrane ensures that the fouling-resistant nanofiltration membrane has excellent water permeability.

[0057] Furthermore, the thickness of the support layer is 30-50 μm, the thickness of the separation layer is 50-150 nm, and the thickness of the modification layer is 10-50 nm.

[0058] According to the present invention, the average pore size of the fouling-resistant nanofiltration membrane is 0.1-0.3 nm.

[0059] The initial nanofiltration membrane consists of a support layer and a separation layer stacked sequentially, with relatively large pore sizes. After modification, a modification layer is prepared on the upper surface of the separation layer, which reduces the average pore size of the fouling-resistant nanofiltration membrane. The reduction in membrane pore size improves the retention effect of the fouling-resistant nanofiltration membrane on salt ions.

[0060] Furthermore, the average pore size of the fouling-resistant nanofiltration membrane is 0.15-0.25 nm.

[0061] According to the present invention, the oxygen content in the modified layer is 15-30 at.%, preferably 20-25 at.%. The oxygen element comes from polyphenols and polyhydroxy polymers.

[0062] at.% stands for atomic%, and the oxygen content in the modified layer was tested using XPS.

[0063] According to the present invention, the Zeta potential of the modified layer is -20mV to 0mV.

[0064] In this invention, the polyphenols and polyhydroxy polymers in the modification layer contain a large amount of oxygen, and the polyamide material contained in the separation layer is negatively charged. The presence of the modification layer can be verified by detecting the oxygen content and zeta potential.

[0065] Furthermore, the Zeta potential of the modified layer is -15mV to -5mV.

[0066] According to the present invention, the contact angle of the modified layer is 10°-60°, preferably 20°-50°.

[0067] In this invention, the specific contact angle indicates that the fouling-resistant nanofiltration membrane has good hydrophilicity, which is conducive to the formation of a hydrophilic layer on the surface of the fouling-resistant nanofiltration membrane. Hydrophobic macromolecules such as proteins are less likely to accumulate on the surface and cause membrane blockage, resulting in irreversible changes in membrane flux. The fouling-resistant nanofiltration membrane can maintain a high water flux for a long time during operation and can be used for wastewater treatment.

[0068] According to the present invention, the material constituting the support layer is selected from at least one of polyacrylonitrile, polyarylethersulfone, polyethersulfone and polysulfone, preferably selected from polysulfone and / or polyethersulfone.

[0069] According to the present invention, the polyamide is prepared by reacting a polyamine with a polyacrylamide compound, the reaction being a conventional interfacial polymerization reaction; the polyamine has unreacted amino groups that can be chemically bonded to the polyphenols on the modification layer, and the chemical bonds "-CN-" can be detected by infrared spectroscopy, making the membrane layers more closely adhered and improving the stability of the fouling-resistant nanofiltration membrane.

[0070] According to the present invention, the polyamine is selected from at least one of polyethyleneimine, polyethyleneamine, polyethylene polyamine, polyetheramine and piperazine.

[0071] According to the present invention, the polyphenol is selected from at least one of tannic acid, tea polyphenol, lignin, sodium lignin sulfonate, apple polyphenol, grape polyphenol, sennaol, naringin, epicatechin, luteolin, apigenin, calciferol, myricetin and genistein, preferably selected from tannic acid and / or lignin.

[0072] According to the present invention, the multi-hydroxy polymer is selected from at least one of polyvinyl alcohol, hydroxy-terminated polyethylene glycol, chitosan, hydroxymethyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose, preferably selected from polyvinyl alcohol and / or hydroxymethyl cellulose.

[0073] According to the present invention, the weight ratio of the polyphenol to the polyhydroxy polymer is 0.01-100:1, preferably 0.1-10:1.

[0074] In this invention, polyphenols and polyhydroxy polymers are linked by hydrogen bonds, which increases the crosslinking density on the surface of the fouling-resistant nanofiltration membrane and helps to improve the salt rejection rate of the membrane. In addition, the large number of hydrogen bonds on the membrane surface increases the hydrophilicity of the fouling-resistant nanofiltration membrane and improves its fouling resistance.

[0075] According to the present invention, the weight-average molecular weight of the polyhydroxy polymer is 1,000-200,000 g / mol, preferably 5,000-100,000 g / mol.

[0076] The fifth aspect of the present invention provides an application of the aforementioned fouling-resistant nanofiltration membrane in the field of wastewater treatment.

[0077] The present invention will be described in detail below through embodiments.

[0078] Isopar E is an alkane solvent oil from Mobil (purchased from Xilong Chemical).

[0079] Polyvinyl alcohol (PVA-124, weight average molecular weight 95000 g / mol), hydroxyl-terminated polyethylene glycol (weight average molecular weight 25000 g / mol), tannic acid (weight average molecular weight 1701 g / mol), hydroxymethyl cellulose (weight average molecular weight 100000 g / mol), lignin (weight average molecular weight 505 g / mol), and tea polyphenols (weight average molecular weight 281 g / mol) were all purchased from Bailingwei Technology Co., Ltd.

[0080] The 8040 nanofiltration membrane element (model: NF-270, with a support layer made of polyethersulfone and a pore size of 0.38 nm, and a separation layer made of polyamide) was purchased from Dow Chemical Company.

[0081] All other chemical reagents were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0082] (1) The water flux of the fouling-resistant nanofiltration membrane was tested by the following method: the nanofiltration membrane element was installed in the membrane housing of the membrane element test system, the test solution was 2000 ppm magnesium sulfate, and the water flux Q1 (gpd) of the membrane element was measured at 0.6 MPa and 25 °C.

[0083] (2) The salt rejection rate of the fouling-resistant nanofiltration membrane was tested using the following method: The nanofiltration membrane element was installed in the membrane housing of the membrane element test system. The original aqueous solution was 2000 ppm magnesium sulfate. After pre-pressurization at 0.2 MPa for 30 min, the permeate was obtained at 0.6 MPa. The concentration of the permeate was measured by a conductivity meter, and the desalination rate was calculated using the following formula:

[0084] R(%)=(C f -C p ) / C f ×100%

[0085] Where R is the desalination rate, and C f Magnesium sulfate in the original solution, C p This represents the concentration of magnesium sulfate in the permeate.

[0086] (3) Fouling resistance test of nanofiltration membrane: The nanofiltration membrane was installed in the membrane housing of the membrane element test system. The test solution was 2000 ppm magnesium sulfate and 1000 ppm bovine serum albumin (BSA). After running for 6 hours at 0.6 MPa and 25℃, the water flux Q2 (gpd) of the nanofiltration membrane was measured. Then, the nanofiltration membrane was rinsed with clean water for 30 min, and its water flux Q3 (gpd) was tested under the same pressure conditions with 2000 ppm magnesium sulfate as the test solution.

[0087] The water flux reduction rate of a fouling-resistant nanofiltration membrane is obtained using the following formula:

[0088] D = (Q1 - Q2) / Q1 × 100%;

[0089] The water flux of a fouling-resistant nanofiltration membrane after washing is obtained using the following formula:

[0090] H = Q3 / Q1 × 100%.

[0091] (4) Average pore size of the fouling-resistant nanofiltration membrane: Measured using the PEG solute transfer method, the detailed steps of which are as follows:

[0092] I. Test the retention rate of the separation membrane for PEG of different molecular sizes;

[0093] II. Linearly fit the PEG size and retention rate in a log-probability coordinate system. The PEG size corresponding to a 50% retention rate is the average pore size of the separation membrane.

[0094] (5) Surface Zeta potential of the fouling-resistant nanofiltration membrane: measured by a Zeta potential analyzer, the test solution was a 0.001 mol / L KCl aqueous solution with a pH of 7.

[0095] (6) The oxygen content in the modified layer of the fouling-resistant nanofiltration membrane: measured by X-ray photoelectron spectroscopy (XPS): obtained by Al-Kα X-ray irradiation on an ESCALAB250 X-ray photoelectron spectrometer.

[0096] Example 1

[0097] An 8040 nanofiltration membrane element was installed in the membrane housing of the membrane element testing system and rinsed with deionized water for 30 minutes. Disodium hydrogen phosphate was added to adjust the pH of the modifier system to 10. The system was then contacted with the modifier at 0.6 MPa and 25°C for 30 minutes. The modifier was drained, and the testing system was repeatedly rinsed with deionized water to remove any remaining modifier, thus obtaining the fouling-resistant nanofiltration membrane N1. The modifier contained 20 wt% glycerol, 0.005 wt% tannic acid, 0.005 wt% polyvinyl alcohol, and 79.99 wt% water.

[0098] SEM testing was performed on N1, and the results were as follows: Figure 1 The image shows that the surface of the modified nanofiltration membrane becomes flat, confirming the presence of a modification layer containing polyphenols and polyhydroxy polymers on the surface of the nanofiltration membrane.

[0099] Figure 3 The infrared spectra of the polyamide films modified with tannic acid and polyvinyl alcohol were compared with those of the original polyamide film. The figures show that the modified film exhibits higher infrared spectra at 3300 cm⁻¹. -1 The signal peak at 1062 nm became stronger, indicating the presence of a large number of hydroxyl groups on the membrane surface, confirming the successful modification of the membrane surface with polyvinyl alcohol; furthermore, the modified membrane showed a stronger signal peak at 1062 nm. -1 The signal peak at the point also became stronger, indicating that the reaction between tannic acid and the amino groups remaining on the surface of polyamide formed more -CN-.

[0100] Figure 4 This is a representative structural diagram illustrating the possible hydrogen-bonded connection between a portion of tannic acid (# indicates the remaining portion) and a portion of polyvinyl alcohol (* indicates the remaining portion of polyvinyl alcohol), which can explain the connection mechanism between polyphenols and polyhydroxy polymers; the -O in tannic acid 1 H of O 1 Tannic acid is linked to the hydrogen atoms in polyvinyl alcohol via hydrogen bonds, and to the -O atoms in tannic acid via hydrogen bonds. 2 The H in H is linked to the O in polyvinyl alcohol through hydrogen bonds, while the -O in tannic acid is linked to the O in... 3 H, where O 3 It exists in isolation with H and has no hydrogen bonds; the tannic acid reacts with the unreacted -NH2 in the polyamide on the separation layer to form -CN-, which connects the separation layer and the modification layer.

[0101] Example 2

[0102] An 8040 nanofiltration membrane element was installed in the membrane housing of the membrane element testing system and rinsed with deionized water for 30 minutes. Disodium hydrogen phosphate was added to adjust the pH of the modifier system to 8. The system was then contacted with the modifier at 0.6 MPa and 25°C for 30 minutes. The modifier was drained, and the testing system was repeatedly rinsed with deionized water to remove any remaining modifier, thus obtaining a fouling-resistant nanofiltration membrane N2. The modifier contained 20 wt% glycerol, 0.001 wt% tannic acid, 0.001 wt% hydroxyl-terminated polyethylene glycol, and 79.998 wt% water.

[0103] Example 3

[0104] An 8040 nanofiltration membrane element was installed in the membrane housing of the membrane element testing system and rinsed with deionized water for 30 minutes. Disodium hydrogen phosphate was added to adjust the pH of the modifier system to 9. The system was then contacted with the modifier at 0.6 MPa and 25°C for 30 minutes. The modifier was drained, and the testing system was repeatedly rinsed with deionized water to remove any residual modifier, thus obtaining a fouling-resistant nanofiltration membrane N3. The modifier contained 20 wt% glycerol, 0.005 wt% tannic acid, 0.05 wt% hydroxymethyl cellulose, and 79.945 wt% water.

[0105] Example 4

[0106] An 8040 nanofiltration membrane element was installed in the membrane housing of the membrane element testing system and rinsed with deionized water for 30 minutes. Disodium hydrogen phosphate was added to adjust the pH of the modifier system to 8.5. The system was then contacted with the modifier at 0.6 MPa and 25°C for 30 minutes. The modifier was drained, and the testing system was repeatedly rinsed with deionized water to remove any residual modifier, thus obtaining the fouling-resistant nanofiltration membrane N4. The modifier contained 20 wt% glycerol, 0.005 wt% tea polyphenols, 0.05 wt% hydroxymethyl cellulose, and 79.945 wt% water.

[0107] Example 5

[0108] An 8040 nanofiltration membrane element was installed in the membrane housing of the membrane element testing system and rinsed with deionized water for 30 minutes. Disodium hydrogen phosphate was added to adjust the pH of the modifier system to 10. The system was then contacted with the modifier at 0.6 MPa and 25°C for 30 minutes. The modifier was drained, and the testing system was repeatedly rinsed with deionized water to remove any remaining modifier, resulting in a fouling-resistant nanofiltration membrane N5. The modifier contained 20 wt% glycerol, 0.005 wt% tea polyphenols, 0.005 wt% polyvinyl alcohol, and 79.99 wt% water.

[0109] Example 6

[0110] An 8040 nanofiltration membrane element was installed in the membrane housing of the membrane element testing system and rinsed with deionized water for 30 minutes. Disodium hydrogen phosphate was added to adjust the pH of the modifier system to 9.5. The system was then contacted with the modifier at 0.6 MPa and 25°C for 30 minutes. The modifier was drained, and the testing system was repeatedly rinsed with deionized water to remove any residual modifier, resulting in a fouling-resistant nanofiltration membrane N6. The modifier contained 20 wt% glycerol, 0.005 wt% lignin, 0.05 wt% hydroxymethyl cellulose, and 79.945 wt% water.

[0111] Example 7

[0112] An 8040 nanofiltration membrane element was installed in the membrane housing of the membrane element testing system and rinsed with deionized water for 30 minutes. Disodium hydrogen phosphate was added to adjust the pH of the modifier system to 10. The system was then contacted with the modifier at 0.6 MPa and 25°C for 30 minutes. The modifier was drained, and the testing system was repeatedly rinsed with deionized water to remove any residual modifier, resulting in a fouling-resistant nanofiltration membrane N7. The modifier contained 20 wt% glycerol, 0.005 wt% tannic acid, 0.005 wt% hydroxyethyl cellulose, and 79.99 wt% water.

[0113] Example 8

[0114] The modification was carried out in accordance with Example 1, except that the modifier contained 5 wt% glycerol, 0.0001 wt% tannic acid, 0.0001 wt% polyvinyl alcohol, and 94.9998 wt% water, resulting in a fouling-resistant nanofiltration membrane N8.

[0115] Example 9

[0116] The procedure was carried out in accordance with Example 1, except that a modifier with a pH of 8 was added to obtain a fouling-resistant nanofiltration membrane N9.

[0117] Example 10

[0118] The process was carried out in accordance with Example 1, except that the contact pressure was 0.1 MPa and the contact time was 15 min to obtain the fouling-resistant nanofiltration membrane N10.

[0119] Example 11

[0120] The procedure was carried out in accordance with Example 1, except that the contact pressure was 0 MPa, resulting in a fouling-resistant nanofiltration membrane N11.

[0121] Comparative Example 1

[0122] The nanofiltration membrane element was washed with deionized water for 30 minutes without adding any modifier to obtain nanofiltration membrane D1.

[0123] SEM testing was performed on D1, and the results were as follows: Figure 2 As shown in the photograph, the nanofiltration membrane surface exhibits a small protrusion structure, and there is no modification layer in D1.

[0124] Comparative Example 2

[0125] The process was carried out in accordance with Example 1, except that the modifier did not contain a polyhydroxy polymer, resulting in nanofiltration membrane D2.

[0126] Comparative Example 3

[0127] The process was carried out in accordance with Example 1, except that no pH adjuster was added to the modifier, resulting in nanofiltration membrane D3.

[0128] The structures of the fouling-resistant nanofiltration membranes prepared in the examples and the nanofiltration membranes prepared in the comparative examples were characterized, and the results are shown in Table 1.

[0129] Table 1

[0130]

[0131]

[0132] At 0.6 MPa and 25 °C, the fouling-resistant nanofiltration membranes prepared in the examples and the nanofiltration membranes prepared in the comparative examples were tested for water flux, desalination rate and fouling resistance. The results are shown in Table 2.

[0133] Table 2

[0134]

[0135] In this invention, the successful preparation of a modification layer on the surface of the separation layer was demonstrated by Zeta potential, oxygen atom content on the membrane surface, infrared spectroscopy, and electron microscopy images. The density of the fouling-resistant nanofiltration membrane was characterized by average pore size testing, showing that the high density of the fouling-resistant nanofiltration membrane enables effective retention of pollutants. The membrane thickness and electron microscopy images demonstrated that the support layer, separation layer, and modification layer are tightly bonded sequentially. The fouling resistance of the fouling-resistant nanofiltration membrane was characterized by salt rejection rate testing. The stability and service life of the fouling-resistant nanofiltration membrane were characterized by water flux decline rate and water flux recovery rate; a small water flux decline rate indicates good stability, while a large water flux recovery rate indicates that it can be used multiple times and has a long service life.

[0136] The modified layer is uncharged, and compared with Comparative Example 1, the Zeta potential of Example 1 is smaller and tends to be neutral; the oxygen content on the membrane surface is higher. Both of these factors prove the presence of the modified layer, which increases the density of the finally prepared fouling-resistant nanofiltration membrane and has a higher salt rejection rate.

[0137] Meanwhile, the formation of numerous hydrogen bonds between the polyphenols and polyhydroxy polymers in the modification layer enhances the hydrophilicity of the nanofiltration membrane, enabling it to achieve higher water flux, lower water flux decline rate, and higher water flux recovery rate in organic macromolecular pollutant solutions.

[0138] Compared to Example 1, the modifier in Comparative Example 2 does not contain a polyhydroxy polymer. The polyphenols in the modifier still function in the same way as in Example 1. As can be seen from the Zeta potential data in Table 1, the Zeta potential of Comparative Example 2 is smaller than that of Example 1, but larger than that of Comparative Example 1. This proves that the polyphenols are connected to the unreacted -NH2 on the polyamide in the separation layer through -CN-, which also plays a partial shielding role on the polyamide layer. However, as can be seen from Table 2, compared to Example 1, the salt rejection rate of Comparative Example 2 is lower, the water flux reduction rate is higher, and the water flux recovery rate is lower. This proves that the modifier of the present invention can enable the polyphenols and polyhydroxy polymers in the modified layer to undergo a self-assembly process on the upper surface of the separation layer of the initial nanofiltration membrane, thereby improving the fouling resistance of the fouling-resistant nanofiltration membrane. A single polyphenol in the modifier cannot achieve this performance.

[0139] Compared to Example 1, no pH adjuster was added to the modifier in Comparative Example 3. As can be seen from the Zeta potential and average pore size data in Table 1, a modified layer exists in Comparative Example 3. However, as can be seen from Table 2, compared to Example 1, the salt rejection rate of Comparative Example 3 decreased, the water flux reduction rate increased, and the water flux recovery rate decreased. This proves that the pH adjuster in the modifier of the present invention enables the self-assembly process of polyphenols and polyhydroxy polymers on the separation layer surface of the initial nanofiltration membrane to proceed more fully.

[0140] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A modifier for a fouling resistant nanofiltration membrane, characterized in that, The modifier comprises glycerol, polyphenol, polyhydroxy polymer and pH regulator.

2. The modifier of claim 1, wherein, In the modifier, the glycerol is 5-30 parts by weight, the content of the polyphenol is 0.0001-0.05 parts by weight, and the content of the polyhydroxy polymer is 0.0001-0.5 parts by weight.

3. The modifier of claim 2, wherein, In the modifier, the content of the glycerol is 10-20 parts by weight, the content of the polyphenol is 0.0005-0.05 parts by weight, and the content of the polyhydroxy polymer is 0.0005-0.5 parts by weight.

4. The modifier of claim 1, wherein, The weight average molecular weight of the polyphenol is 100-10000 g / mol.

5. The modifier of claim 4, wherein, The weight average molecular weight of the polyphenol is 200-5000 g / mol.

6. The modifier of claim 1, wherein, The weight average molecular weight of the polyhydroxy polymer is 1000-200000 g / mol.

7. The modifier of claim 6, wherein, The weight average molecular weight of the polyhydroxy polymer is 5000-100000 g / mol.

8. The modifier of claim 1, wherein, The polyphenol is at least one selected from tannic acid, tea polyphenol, lignin, sodium lignosulfonate, apple polyphenol, grape polyphenol, eriodictyol, naringenin, epicatechin, luteolin, apigenin, kaempferol, myricetin and genistein.

9. The modifier of claim 8, wherein, The polyphenol is tannic acid and / or lignin.

10. The modifier of claim 1, wherein, The polyhydroxy polymer is at least one selected from polyvinyl alcohol, hydroxyl-terminated polyethylene glycol, chitosan, hydroxymethyl cellulose, hydroxyethyl cellulose and hydroxypropyl cellulose.

11. The modifying agent of claim 10, wherein, The polyhydroxy polymer is polyvinyl alcohol and / or hydroxymethyl cellulose.

12. The modifier of claim 1, wherein, The modifier further comprises water.

13. The modifier of claim 1, wherein, The pH of the modifier is 8-13.

14. The modifying agent of claim 13, wherein, The pH of the modifier is 9-12.

15. The modifier of claim 1, wherein, The pH regulator is at least one selected from disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium carbonate, potassium carbonate, sodium bicarbonate and potassium bicarbonate.

16. The modifying agent of claim 15, wherein, The pH regulator is disodium hydrogen phosphate.

17. A method of modifying a fouling resistant nanofiltration membrane, characterized in that, The modification method comprises pre-cleaning an initial nanofiltration membrane, and contacting the cleaned initial nanofiltration membrane with a modifier; wherein the initial nanofiltration membrane comprises a support layer and a separation layer which are stacked in sequence; and the modifier is the modifier according to any one of claims 1-16.

18. The modification method of claim 17, wherein, The material constituting the support layer is at least one selected from polyacrylonitrile, polyarylether sulfone, polyether sulfone and polysulfone.

19. The modification method of claim 18, wherein, The material constituting the support layer is polysulfone and / or polyether sulfone.

20. The modification method of claim 17, wherein, The material constituting the separation layer is polyamide prepared by reacting a polyamine with a polyacyl chloride.

21. The modification method of claim 20, wherein, The polyamine is at least one selected from polyethyleneimine, polyvinylamine, polyethylene polyamine, polyether amine and piperazine.

22. The modification method of claim 17, wherein, The pressure of the contacting is 0.1-2 MPa; the temperature of the contacting is 10-50℃; and the time of the contacting is 10-60 min.

23. The modification method of claim 22, wherein, The pressure of the contacting is 0.5-1 MPa; the temperature of the contacting is 20-30℃; and the time of the contacting is 15-30 min.

24. A pollution-resistant nanofiltration membrane prepared by the modification method according to any one of claims 17-23.

25. The foul- resistant nanofiltration membrane according to claim 24, wherein, The pollution-resistant nanofiltration membrane comprises a support layer, a separation layer and a modification layer which are stacked in sequence; the material constituting the separation layer comprises polyamide, and the material constituting the modification layer comprises polyphenol and polyhydroxy polymer.

26. The foul- resistant nanofiltration membrane according to claim 25, wherein, A chemical bond is formed between the separation layer and the modification layer.

27. The foul- resistant nanofiltration membrane according to claim 25, wherein, The polybasic phenol and the polybasic hydroxyl polymer form hydrogen bonds.

28. The foul- resistant nanofiltration membrane according to claim 25, wherein, The thickness of the support layer is 20-60 μm, the thickness of the separation layer is 20-200 nm, and the thickness of the modification layer is 1-100 nm.

29. The foul- resistant nanofiltration membrane according to claim 28, wherein, The thickness of the support layer is 30-50 μm, the thickness of the separation layer is 50-150 nm, and the thickness of the modification layer is 10-50 nm.

30. The foul- resistant nanofiltration membrane of claim 25, wherein, The average pore size of the anti-fouling nanofiltration membrane is 0.1-0.3 nm.

31. The foul- resistant nanofiltration membrane according to claim 30, wherein, The average pore size of the anti-fouling nanofiltration membrane is 0.15-0.25 nm.

32. The foul- resistant nanofiltration membrane of claim 25, wherein, The content of oxygen element contained in the modification layer is 15-30 at.%.

33. The foul- resistant nanofiltration membrane according to claim 32, wherein, The content of oxygen element contained in the modification layer is 20-25 at.%.

34. The foul- resistant nanofiltration membrane of claim 25, wherein, The Zeta potential of the modification layer is -20 mV to 0 mV.

35. The foul- resistant nanofiltration membrane according to claim 34, wherein, The Zeta potential of the modification layer is -15 mV to -5 mV.

36. The foul- resistant nanofiltration membrane of claim 25, wherein, The contact angle of the modification layer is 10°-60°.

37. The foul- resistant nanofiltration membrane according to claim 36, wherein, The contact angle of the modification layer is 20°-50°.

38. The foul- resistant nanofiltration membrane of claim 25, wherein, The material constituting the support layer is selected from at least one of polyacrylonitrile, polyarylether sulfone, polyether sulfone, and polysulfone.

39. The foul- resistant nanofiltration membrane of claim 38, wherein, The material constituting the support layer is selected from polysulfone and / or polyether sulfone.

40. The foul- resistant nanofiltration membrane of claim 25, wherein, The polyamide is prepared by the reaction of a polybasic amine and a polybasic acid chloride compound.

41. The foul- resistant nanofiltration membrane of claim 40, wherein, The polybasic amine is selected from at least one of polyethyleneimine, polyvinylamine, polyethylene polyamine, polyether amine, and piperazine.

42. The foul- resistant nanofiltration membrane of claim 25, wherein, The polybasic phenol is selected from at least one of tannic acid, tea polyphenol, lignin, sodium lignosulfonate, apple polyphenol, grape polyphenol, rutin, naringenin, epicatechin, luteolin, apigenin, kaempferol, myricetin, and genistein.

43. The foul- resistant nanofiltration membrane of claim 42, wherein, The polybasic phenol is selected from tannic acid and / or lignin.

44. The foul-resistant nanofiltration membrane of claim 25, wherein, The polybasic hydroxyl polymer is selected from at least one of polyvinyl alcohol, hydroxyl-terminated polyethylene glycol, chitosan, hydroxymethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose.

45. The foul- resistant nanofiltration membrane of claim 44, wherein, The polybasic hydroxyl polymer is selected from polyvinyl alcohol and / or hydroxymethyl cellulose.

46. The foul- resistant nanofiltration membrane of claim 25, wherein, The weight ratio of the polybasic phenol to the polybasic hydroxyl polymer is 0.1-10:

1.

47. The foul- resistant nanofiltration membrane of claim 25, wherein, The weight average molecular weight of the polybasic hydroxyl polymer is 1000-200000 g / mol.

48. The foul- resistant nanofiltration membrane of claim 47, wherein, The weight average molecular weight of the polybasic hydroxyl polymer is 5000-100000 g / mol.

49. Use of the anti-fouling nanofiltration membrane according to any one of claims 24-48 in the field of water treatment.

Images