Modifier, pollution-resistant nanofiltration membrane modification method, pollution-resistant nanofiltration membrane and application of pollution-resistant nanofiltration membrane

Abstract

The invention 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, and the modifier comprises glycerin, polyphenol, a polyhydroxy polymer and a pH regulator. According to the present invention, the initial nanofiltration membrane is modified by the modifying agent with the specific components to obtain the pollution-resistant nanofiltration membrane, the pollution-resistant nanofiltration membrane has characteristics of high retention rate and strong surface hydrophilicity, can reduce the adsorption of the hydrophobic organic pollutants on the membrane surface, and can ensure the low water flux reduction rate during the long-time operation process, and after the polluted membrane is washed with water, the water flux reduction rate is low; and the water flux has a relatively high recovery rate.

Description

Technical Field

[0001] The present invention relates to the field of nanofiltration membranes, and in particular to a modifier, a method for modifying a pollution-resistant nanofiltration membrane, a pollution-resistant nanofiltration membrane and applications thereof. Background Art

[0002] Nanofiltration is a pressure-driven membrane separation process between reverse osmosis and ultrafiltration. The pore size of nanofiltration membranes is in the range of several nanometers. It has poor removal of monovalent ions and organic matter with a molecular weight less than 200, but has a higher removal rate for divalent or multivalent ions and organic matter with a molecular weight between 200-500. It can be widely used in water softening, drinking water purification, water quality improvement, oil-water separation, wastewater treatment and reuse, seawater softening, and classification, purification and concentration of chemical products such as dyes, antibiotics, peptides, polysaccharides, etc.

[0003] Membrane fouling has always been an important factor affecting membrane performance and reducing its service life. Membrane fouling refers to the irreversible change phenomenon that particles, colloidal particles or solute macromolecules in the feed liquid in contact with the membrane are adsorbed and deposited on the membrane surface or in the membrane pores due to physical and chemical reactions with the membrane or concentration polarization, which causes the concentration of certain solutes on the membrane surface to exceed their solubility and mechanical effects, resulting in a decrease in the membrane pore size or blockage, and a significant decrease in membrane flux and separation characteristics. The flux attenuation caused by the adsorption of pollutants on the membrane surface and in the membrane pores and the reduction in membrane separation capacity, especially protein adsorption, is the main cause of membrane flux attenuation.

[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 the cost of water treatment, but also reduce the use of raw materials. Summary of the invention

[0005] The purpose of the present invention is to overcome the problem in the prior art that membrane pollution reduces the performance of nanofiltration membranes, and to provide a modifier, a method for modifying a pollution-resistant nanofiltration membrane, a pollution-resistant nanofiltration membrane and applications thereof.

[0006] In order to achieve the above-mentioned object, the first aspect of the present invention provides a modifier, wherein the modifier comprises glycerol, polyphenol, polyhydroxy polymer and pH adjuster.

[0007] The second method of the present invention provides a method for modifying a pollution-resistant nanofiltration membrane, wherein 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 stacked in sequence; and the modifier is the aforementioned modifier.

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

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

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

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

[0012] The surface of the initial nanofiltration membrane is modified by a modifier to form a modified layer; the polyphenol and polyhydroxy polymer in the modified layer undergo a self-assembly process on the upper surface of the separation layer of the initial nanofiltration membrane, and the surface density of the modified anti-fouling nanofiltration membrane is increased, so that the salt rejection rate of the anti-fouling nanofiltration membrane is increased, and the anti-fouling performance of the anti-fouling nanofiltration membrane is improved;

[0013] Furthermore, a large number of hydrogen bonds are formed between the polyhydroxy polymer and the polyphenol, which improves the hydrophilicity of the pollution-resistant nanofiltration membrane, making it have a higher water flux. The polyphenol in the modification layer of the pollution-resistant nanofiltration membrane is connected with the polyamide in the separation layer through a chemical bond "-CN-", so that the modification layer and the separation layer of the pollution-resistant nanofiltration membrane are more closely attached, thereby improving the stability and service life of the pollution-resistant nanofiltration membrane.

[0014] At the same time, the modification method provided by the invention is simple and easy to operate, and has good industrialization prospects. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0018] Figure 4 The polyphenol in the mixture is tannic acid, and the polyhydroxy polymer is polyvinyl alcohol. Figure 4 This is a possible connection diagram between the two, where: Schematic diagram of hydrogen bonding. It indicates the separation layer, * indicates the remaining part of polyvinyl alcohol which is not shown, and # indicates the remaining part of tannic acid which is not shown. DETAILED DESCRIPTION

[0019] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0020] A first aspect of the present invention provides a modifier, wherein the modifier comprises glycerol, polyphenol, polyhydroxy polymer and a pH adjuster.

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

[0022] In the present invention, hydrogen bonds are formed between the polyphenols and the polyhydroxy polymers in the modifier, thereby improving the density of the pollution-resistant nanofiltration membrane and increasing the salt rejection rate of the pollution-resistant nanofiltration membrane; at the same time, a large number of hydrogen bonds are formed between the polyhydroxy polymers and the polyphenols, thereby improving the hydrophilicity of the pollution-resistant nanofiltration membrane.

[0023] The hydrogen bond connection mode is that H from the polyphenol is connected to O from the polyhydroxy polymer through hydrogen bonds; or O from the polyphenol is connected to H from the polyhydroxy polymer through hydrogen bonds.

[0024] A particularly preferred embodiment, as Figure 4 As shown, Figure 4 The polyphenol is tannic acid, and the polyhydroxy polymer is polyvinyl alcohol. 1 H of O 1 The H in polyvinyl alcohol is connected by hydrogen bonds, and the -O in tannic acid 2 The H of H is connected to the O of polyvinyl alcohol through hydrogen bonds, and the -O 3 H, where O 3 It can also exist independently with H without any hydrogen bond.

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

[0026] The pollution-resistant nanofiltration membrane has a high density and thus has a high retention rate for pollutants, and can effectively retain pollutants.

[0027] Furthermore, in the modifier, the content of the glycerol is 10-20 parts by weight, the content of the polyphenol is 0.0005-0.5 parts by weight, and the content of the polyhydroxy polymer 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 1000-200000 g / mol, preferably 5000-100000 g / mol.

[0030] In the present invention, the polyhydroxy polymer with a specific weight average molecular weight has a large number of hydroxyl groups, which further improves the hydrophilicity of the anti-fouling nanofiltration membrane.

[0031] According to the present invention, the polyphenol is selected from at least one of tannic acid, tea polyphenols, lignin, sodium lignin sulfonate, apple polyphenols, grape polyphenols, eriodictyol, naringenin, epicatechin, luteolin, apigenin, kaempferol, myricetin and genistein; preferably tannic acid and / or lignin.

[0032] According to the present invention, the polyhydroxy 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, for example, PVA-124 from J&K Technology Co., Ltd. and hydroxymethyl cellulose from J&K Technology Co., Ltd.

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

[0034] In the present invention, the modifier including water forms a modifier system, and the sum of the amounts of other components in the system excluding the pH adjuster and the amount of water makes the total weight parts of the system 100 weight parts.

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

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

[0037] In the present invention, the specific pH value can enable the polyphenol to fully react with the residual amino groups on the polyamide.

[0038] According to the present invention, the pH regulator 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 pollution-resistant nanofiltration membrane, wherein the modification method comprises pre-cleaning an initial nanofiltration membrane, contacting the cleaned initial nanofiltration membrane with a modifier;

[0040] Wherein, the initial nanofiltration membrane comprises a support layer and a separation layer stacked in sequence; and the modifier is the aforementioned modifier.

[0041] According to the present invention, the material constituting the support layer is at least one selected from 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 polyacyl chloride compound.

[0043] The reaction is an interfacial polymerization reaction. Specifically, the unreacted amino groups on the polyamine in the polyamide are connected to the polyphenol in the modifier through a chemical bond "-CN-", so that the separation layer and the modified layer formed by contacting the modifier are more closely connected, thereby improving the stability of the prepared pollution-resistant nanofiltration membrane.

[0044] In the present 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, polyethylenepolyamine, polyetheramine and piperazine.

[0046] In the present invention, the polyphenol of the modifier reacts with the residual amino group in the polyamide to form a chemical bond connection; in addition, the polyhydroxy polymer in the modifier solution can be connected with the polyphenol through a hydrogen bond.

[0047] According to the present invention, the contacting process is a conventional contacting method, such as immersing, coating, spraying, etc., preferably comprising 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 the present invention have found in their research that when the contact process meets the above-mentioned modification range, the pollution-resistant nanofiltration membrane finally obtained can have a higher retention 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] The third aspect of the present invention provides a pollution-resistant nanofiltration membrane obtained by the aforementioned modification method.

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

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

[0054] In the present 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 the present invention, the specific layer thickness between each layer of the pollution-resistant nanofiltration membrane can ensure that the pollution-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 pollution-resistant nanofiltration membrane is 0.1-0.3 nm.

[0059] The initial nanofiltration membrane includes a support layer and a separation layer stacked in sequence with a larger pore size; after the modification layer is prepared on the upper surface of the separation layer, the average pore size of the pollution-resistant nanofiltration membrane is reduced, and the retention effect of the pollution-resistant nanofiltration membrane on salt ions is improved by reducing the membrane pore size.

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

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

[0062] at.% stands for atomic%, atomic percentage. The oxygen content in the modified layer is tested by XPS.

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

[0064] In the present invention, the polyphenol and polyhydroxy polymer in the modification layer contain a large amount of oxygen elements, and the polyamide material contained in the separation layer is negatively charged. The existence of the modification layer can be proved 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 the present invention, the specific contact angle indicates that the pollution-resistant nanofiltration membrane has good hydrophilicity, which is conducive to the formation of a hydrophilic layer on the surface of the pollution-resistant nanofiltration membrane. Hydrophobic macromolecules such as proteins are not easy to aggregate on the surface to cause membrane blockage, resulting in irreversible changes in membrane flux. The pollution-resistant nanofiltration membrane can maintain a high water flux for a long time during operation and can be used for sewage treatment.

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

[0069] According to the present invention, the polyamide is prepared by the reaction of a polyamine and a polyacyl chloride compound, and the reaction is a conventional interfacial polymerization reaction; the polyamine has unreacted amino groups, which can be chemically bonded to the polyphenol on the modified layer, and the chemical bond "-CN-" can be detected by infrared spectroscopy, so that the membrane layers are more closely attached, thereby improving the stability of the pollution-resistant nanofiltration membrane.

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

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

[0072] According to the present invention, the polyhydroxy polymer is at least one selected from polyvinyl alcohol, hydroxyl-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 the present invention, polyphenols and polyhydroxy polymers are connected by hydrogen bonds, which increases the crosslinking density on the surface of the pollution-resistant nanofiltration membrane and helps to improve the salt rejection rate of the membrane; in addition, a large number of hydrogen bonds on the membrane surface increase the hydrophilicity of the pollution-resistant nanofiltration membrane and improve the pollution resistance of the pollution-resistant nanofiltration membrane.

[0075] According to the present invention, the weight average molecular weight of the polyhydroxy polymer is 1000-200000 g / mol, preferably 5000-100000 g / mol.

[0076] A fifth aspect of the present invention provides an application of the aforementioned pollution-resistant nanofiltration membrane in the field of sewage treatment.

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

[0078] Isopar E is Mobil's alkane solvent oil (purchased from Xilong Chemical);

[0079] Polyvinyl alcohol (model 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] 8040 nanofiltration membrane element (model: NF-270, the material of the support layer is polyethersulfone, the pore size is 0.38 nm, and the material of the separation layer is polyamide) was purchased from Dow Chemical Co., Ltd.;

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

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

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

[0084] R(%)=(C f -C p ) / C f ×100%

[0085] Among them, R is the desalination rate, C f is the magnesium sulfate in the stock solution, C p is the concentration of magnesium sulfate in the permeate.

[0086] (3) Pollution resistance test of the pollution-resistant nanofiltration membrane: The nanofiltration membrane was installed in the membrane shell of the membrane element test system. The test liquid was 2000 ppm magnesium sulfate and 1000 ppm bovine serum albumin (BSA). After running for 6 hours at 0.6 MPa and 25°C, the water flux Q of the nanofiltration membrane was measured. 2 (gpd); Then, the nanofiltration membrane was rinsed with clean water for 30 minutes, and the water flux Q was tested under the same pressure conditions when the test liquid was 2000ppm magnesium sulfate. 3 (gpd);

[0087] The water flux decline rate of the fouling-resistant nanofiltration membrane is obtained by the following formula:

[0088] D=(Q 1 -Q 2 ) / Q 1 ×100%;

[0089] The water flux of the pollution-resistant nanofiltration membrane after washing is obtained by the following formula:

[0090] H=Q 3 / Q 1 ×100%.

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

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

[0093] II. Linear fitting was performed between PEG size and retention rate in a logarithmic-probability coordinate system. The PEG size corresponding to 50% retention rate was the average pore size of the separation membrane.

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

[0095] (6) The content of oxygen atoms in the modified layer of the anti-fouling nanofiltration membrane was 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] The 8040 nanofiltration membrane element was installed in the membrane shell of the membrane element test system, rinsed with deionized water for 30 minutes, disodium hydrogen phosphate was added to adjust the pH value of the modifier system to 10, and the modifier was contacted with the modifier at 0.6 MPa and 25° C. for 30 minutes, the modifier was drained, and the test system was repeatedly rinsed with deionized water to clean the residual modifier in the system to obtain a pollution-resistant nanofiltration membrane N1; wherein the modifier contained glycerol with a glycerol content of 20wt%, tannic acid with a tannic acid content of 0.005wt%, polyvinyl alcohol with a content of 0.005wt%, and water with a content of 79.99wt%;

[0098] SEM test was performed on N1, and the following results were obtained: Figure 1 As shown in the photo, it can be seen from the figure that the surface of the nanofiltration membrane becomes flat after modification, 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 membrane modified with tannic acid and polyvinyl alcohol were compared with those of the original polyamide membrane. It can be seen from the figure that the modified membrane has a -1 The signal peak at 1062 m / s became stronger, indicating that a large number of hydroxyl groups existed on the membrane surface, confirming that polyvinyl alcohol was successfully modified on the membrane surface. -1 The signal peak at also becomes stronger, indicating that tannic acid reacts with the amino groups remaining on the surface of polyamide to form more -CN-;

[0100] Figure 4 This is a representative structural diagram of the possible hydrogen bond connection between part of tannic acid (# indicates the rest) and part of polyvinyl alcohol (* indicates the rest of polyvinyl alcohol), which can explain the connection mode between polyphenols and polyhydroxy polymers; -O 1 H of O 1 The H in polyvinyl alcohol is connected by hydrogen bonds, and the -O in tannic acid 2 The H of H is connected to the O of polyvinyl alcohol through hydrogen bonds, and the -O 3 H, O 3 It exists in isolation with H and has no hydrogen bond. Tannic acid and unreacted -NH 2 -CN- is formed to connect the separation layer with the modified layer.

[0101] Example 2

[0102] The 8040 nanofiltration membrane element was installed in the membrane shell of the membrane element test system, rinsed with deionized water for 30 minutes, disodium hydrogen phosphate was added to adjust the pH value of the modifier system to 8, and the membrane was in contact with the modifier at 0.6 MPa and 25°C for 30 minutes. The modifier was drained and the test system was repeatedly rinsed with deionized water to clean the residual modifier in the system to obtain a pollution-resistant nanofiltration membrane N2; wherein the content of glycerol in the modifier was 20wt%, the content of tannic acid was 0.001wt%, the content of hydroxyl-terminated polyethylene glycol was 0.001wt%, and the content of water was 79.998wt%.

[0103] Example 3

[0104] The 8040 nanofiltration membrane element was installed in the membrane shell of the membrane element test system, rinsed with deionized water for 30 minutes, disodium hydrogen phosphate was added to adjust the pH value of the modifier system to 9, and the membrane was in contact with the modifier at 0.6 MPa and 25°C for 30 minutes. The modifier was drained and the test system was repeatedly rinsed with deionized water to clean the residual modifier in the system to obtain a pollution-resistant nanofiltration membrane N3; wherein the glycerol content in the modifier is 20wt% of glycerol, the tannic acid content is 0.005wt%, the hydroxymethyl cellulose content is 0.05wt%, and the water content is 79.945wt%.

[0105] Example 4

[0106] The 8040 nanofiltration membrane element was installed in the membrane shell of the membrane element test system, rinsed with deionized water for 30 minutes, disodium hydrogen phosphate was added to adjust the pH value of the modifier system to 8.5, and the membrane was in contact with the modifier at 0.6 MPa and 25°C for 30 minutes. The modifier was drained and the test system was repeatedly rinsed with deionized water to clean the residual modifier in the system to obtain a pollution-resistant nanofiltration membrane N4; wherein the content of glycerol in the modifier was 20wt% of glycerol, the content of tea polyphenols was 0.005wt%, the content of hydroxymethyl cellulose was 0.05wt%, and the content of water was 79.945wt%.

[0107] Example 5

[0108] The 8040 nanofiltration membrane element was installed in the membrane shell of the membrane element test system, rinsed with deionized water for 30 minutes, disodium hydrogen phosphate was added to adjust the pH value of the modifier system to 10, and the membrane was in contact with the modifier at 0.6 MPa and 25°C for 30 minutes. The modifier was drained and the test system was repeatedly rinsed with deionized water to clean the residual modifier in the system to obtain a pollution-resistant nanofiltration membrane N5; wherein the content of glycerol in the modifier was 20wt% of glycerol, the content of tea polyphenols was 0.005wt%, the content of polyvinyl alcohol was 0.005wt%, and the content of water was 79.99wt%.

[0109] Example 6

[0110] The 8040 nanofiltration membrane element was installed in the membrane shell of the membrane element test system, rinsed with deionized water for 30 minutes, disodium hydrogen phosphate was added to adjust the pH value of the modifier system to 9.5, and contacted with the modifier for 30 minutes at 0.6 MPa and 25°C. The modifier was drained and the test system was repeatedly rinsed with deionized water to clean the residual modifier in the system to obtain a pollution-resistant nanofiltration membrane N6; wherein the glycerol content in the modifier is 20wt% glycerol, the lignin content is 0.005wt%, the hydroxymethyl cellulose content is 0.05wt%, and the water content is 79.945wt%.

[0111] Example 7

[0112] The 8040 nanofiltration membrane element was installed in the membrane shell of the membrane element test system, rinsed with deionized water for 30 minutes, disodium hydrogen phosphate was added to adjust the pH value of the modifier system to 10, and the membrane was in contact with the modifier at 0.6 MPa and 25°C for 30 minutes. The modifier was drained and the test system was repeatedly rinsed with deionized water to clean the residual modifier in the system to obtain a pollution-resistant nanofiltration membrane N7; wherein the content of glycerol in the modifier is 20wt% of glycerol, the content of tannic acid is 0.005wt%, the content of hydroxyethyl cellulose is 0.005wt%, and the content of water is 79.99wt%.

[0113] Example 8

[0114] The method of Example 1 was followed, except that the content of glycerol in the modifier was 5 wt% glycerol, the content of tannic acid was 0.0001 wt%, the content of polyvinyl alcohol was 0.0001 wt%, and the content of water was 94.9998 wt%, to obtain a pollution-resistant nanofiltration membrane N8.

[0115] Example 9

[0116] The method of Example 1 was followed, except that a modifier with a pH of 8 was added to obtain a pollution-resistant nanofiltration membrane N9.

[0117] Example 10

[0118] The method of Example 1 was followed, except that the contact pressure was 0.1 MPa and the contact time was 15 min to obtain the pollution-resistant nanofiltration membrane N10.

[0119] Embodiment 11

[0120] The method of Example 1 was followed, except that the contact pressure was 0 MPa, to obtain a contamination-resistant nanofiltration membrane N11.

[0121] Comparative Example 1

[0122] The nanofiltration membrane element was washed with deionized water for 30 min without adding a modifier to obtain nanofiltration membrane D1;

[0123] SEM test was performed on D1, and the following results were obtained: Figure 2 As shown in the photo, it can be seen that the surface of the nanofiltration membrane presents a small protrusion structure, and there is no modification layer in D1.

[0124] Comparative Example 2

[0125] The method of Example 1 was followed, except that there was no polyhydroxy polymer in the modifier, to obtain a nanofiltration membrane D2.

[0126] Comparative Example 3

[0127] The nanofiltration membrane D3 was obtained by carrying out the method of Example 1 except that no pH adjuster was added to the modifier.

[0128] The pollution-resistant nanofiltration membrane prepared in the example and the nanofiltration membrane prepared in the comparative example were structurally characterized, and the results are shown in Table 1.

[0129] Table 1

[0130]

[0131]

[0132] At 0.6 MPa and 25° C., the water flux, salt rejection rate and pollution resistance of the pollution-resistant nanofiltration membrane prepared in the example and the nanofiltration membrane prepared in the comparative example were tested. The results are shown in Table 2.

[0133] Table 2

[0134]

[0135] In the present invention, the Zeta potential, the oxygen atom content on the membrane surface, the infrared spectrum and the electron microscope image prove that the modified layer is successfully prepared on the surface of the separation layer; the density of the pollution-resistant nanofiltration membrane is characterized by the test of the average pore size, and the pollution-resistant nanofiltration membrane has a high density and can effectively intercept pollutants; the membrane thickness and the electron microscope image prove that the support layer, the separation layer and the modified layer are closely fitted in sequence; the salt interception rate test is used to characterize the pollution resistance of the pollution-resistant nanofiltration membrane; the water flux decrease rate and the water flux recovery rate are used to characterize the stability and service life of the pollution-resistant nanofiltration membrane; a small value of the water flux decrease rate proves that it has good stability, and a large value of the water flux recovery rate proves that it can be used multiple times and has a long service life.

[0136] The modified layer is not charged. 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 prove the existence of the modified layer, which increases the density of the finally prepared pollution-resistant nanofiltration membrane and has a higher salt rejection rate.

[0137] At the same time, because a large number of hydrogen bonds are formed between the polyphenols and the polyhydroxy polymers in the modified layer, the hydrophilicity of the nanofiltration membrane is improved, so that the nanofiltration membrane has a higher water flux, a lower water flux decrease rate and a higher water flux recovery rate in the organic macromolecular contaminated solution.

[0138] Compared with Example 1, the modifier of Comparative Example 2 does not contain a polyhydroxy polymer, and the action mode of the polyphenol in the modifier is still the same as that of Example 1. From the Zeta potential data in Table 1, it can be seen that the Zeta potential of Comparative Example 2 is smaller than that of the example, but larger than that of Comparative Example 1, which proves that the polyphenol reacts with the unreacted -NH 2 Through the -CN- connection, the polyamide layer is also partially shielded; however, it can be seen from Table 2 that, relative to Example 1, the salt rejection rate of Comparative Example 2 decreases, the water flux decrease rate increases, and the water flux recovery rate decreases; this proves that the modifier of the present invention can cause 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 pollution resistance of the pollution-resistant nanofiltration membrane, and a single polyphenol in the modifier cannot achieve this performance.

[0139] Compared with Example 1, the modifier in Comparative Example 3 does not contain a pH regulator. It can be seen from the Zeta potential and average pore size data in Table 1 that a modification layer exists in Comparative Example 3; however, it can be seen from Table 2 that, relative to Example 1, the salt rejection rate of Comparative Example 3 decreases, the water flux decrease rate increases, and the water flux recovery rate decreases; this proves that the pH regulator in the modifier of the present invention can make the self-assembly process of polyphenols and polyhydroxy polymers on the upper surface of the separation layer of the initial nanofiltration membrane more complete.

[0140] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A modifier, characterized in that: The modifier comprises glycerol, polyphenol, polyhydroxy polymer and pH adjuster.

2. The modifying agent according to claim 1, wherein In the modifier, the glycerol is 5-30 parts by weight, the polyphenol is 0.0001-1 part by weight, and the polyhydroxy polymer is 0.0001-1 part by weight; Preferably, in the modifier, the content of the glycerol is 10-20 parts by weight, the content of the polyphenol is 0.0005-0.5 parts by weight, and the content of the polyhydroxy polymer is 0.0005-0.5 parts by weight.

3. The modifying agent according to claim 1 or 2, wherein The weight average molecular weight of the polyphenol is 100-10000 g / mol, preferably 200-5000 g / mol; Preferably, the weight average molecular weight of the polyhydroxy polymer is 1000-200000 g / mol, preferably 5000-100000 g / mol.

4. The modifier according to any one of claims 1 to 3, wherein The polyphenol is selected from at least one of tannic acid, tea polyphenol, lignin, sodium lignin sulfonate, apple polyphenol, grape polyphenol, eriodictyol, naringenin, epicatechin, luteolin, apigenin, kaempferol, myricetin and genistein; preferably tannic acid and / or lignin; Preferably, the polyhydroxy 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.

5. The modifier according to any one of claims 1 to 4, wherein The modifier also contains water; Preferably, the pH of the modifier is 8-13, preferably 9-12; Preferably, 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.

6. A method for modifying a pollution-resistant nanofiltration membrane, characterized in that: The modification method comprises pre-cleaning the 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 in sequence; and the modifier is the modifier described in any one of claims 1-5.

7. The modification method according to claim 6, wherein: 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; Preferably, the material constituting the separation layer is a polyamide prepared by reacting a polyamine with a polyacyl chloride; Preferably, the polyamine is selected from at least one of polyethyleneimine, polyethyleneamine, polyethylenepolyamine, polyetheramine and piperazine.

8. The modification method according to claim 6 or 7, wherein: The contact pressure is 0.1-2 MPa, preferably 0.5-1 MPa; the contact temperature is 10-50°C, preferably 20-30°C; the contact time is 10-60 min, preferably 15-30 min.

9. A pollution-resistant nanofiltration membrane obtained by the modification method according to any one of claims 6 to 8.

10. A pollution-resistant nanofiltration membrane, characterized in that: The pollution-resistant nanofiltration membrane comprises a supporting 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.

11. The pollution-resistant nanofiltration membrane according to claim 10, wherein: A chemical bond is formed between the separation layer and the modification layer; Preferably, hydrogen bonds are formed between the polyphenol and the polyhydroxy polymer; Preferably, 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; preferably, 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; Preferably, the average pore size of the pollution-resistant nanofiltration membrane is 0.1-0.3 nm, preferably 0.15-0.25 nm; Preferably, the content of oxygen in the modified layer is 15-30 at.%, preferably 20-25 at.%; Preferably, the Zeta potential of the modified layer is -20 mV to 0 mV, preferably -15 mV to -5 mV; Preferably, the contact angle of the modified layer is 10°-60°, preferably 20°-50°.

12. The pollution-resistant nanofiltration membrane according to claim 10 or 11, wherein: 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; Preferably, the polyamide is prepared by the reaction of a polyamine and a polyacyl chloride compound; Preferably, the polyamine is selected from at least one of polyethyleneimine, polyethyleneamine, polyethylenepolyamine, polyetheramine and piperazine; Preferably, the polyphenol is selected from at least one of tannic acid, tea polyphenols, lignin, sodium lignin sulfonate, apple polyphenols, grape polyphenols, eriodictyol, naringenin, epicatechin, luteolin, apigenin, kaempferol, myricetin and genistein, preferably selected from tannic acid and / or lignin; Preferably, the polyhydroxy 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.

13. The pollution-resistant nanofiltration membrane according to any one of claims 10 to 12, wherein: Preferably, the weight ratio of the polyphenol to the polyhydroxy polymer is 0.01-100:1, preferably 0.1-10:1; Preferably, the weight average molecular weight of the polyhydroxy polymer is 1000-200000 g / mol, preferably 5000-100000 g / mol.

14. Use of the pollution-resistant nanofiltration membrane according to any one of claims 9 to 13 in the field of water treatment.

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