Method for preparing anti-fouling polyamide nanofiltration composite membrane based on hydrothermal method

Abstract

The application discloses a method for preparing an anti-pollution polyamide nanofiltration composite membrane based on a hydrothermal method, and comprises the following steps: (1) modifying a porous base membrane by using a polyphenol-polyethyleneimine intermediate layer modification liquid, and the modified membrane is recorded as a PSF membrane; (2) preparing a polyamide layer on the PSF membrane by using an organic amine and an organic acyl chloride to perform an interfacial polymerization reaction, and the prepared membrane is recorded as a TFC membrane; and (3) placing the TFC membrane in a fluorine-containing surfactant aqueous solution, and performing water bath heating at 50-80 DEG C to obtain a cross-linked stable anti-pollution nanofiltration composite membrane. The fluorine-containing surfactant is used to perform water bath thermal curing on the polyamide membrane, the hydrophilic end of the fluorine-containing surfactant penetrates into the membrane holes during the hydrothermal cross-linking, a hydration layer is constructed on the membrane surface to resist pollutants, the hydrophobic end is exposed on the membrane surface, the interaction between the membrane surface and the pollutants is weakened, the release of the pollutants on the membrane surface is promoted, the composite membrane has the ability of resisting the pollutants and releasing the pollutants, the preparation process is simple and easy to enlarge, and the method has an industrial application prospect.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of anti-pollution nanofiltration composite membranes, in particular to a method for preparing an anti-pollution polyamide nanofiltration composite membrane based on a hydrothermal method. BACKGROUND

[0002] In the field of sewage treatment, nanofiltration membrane (NF) separation technology has a broad application prospect due to low energy consumption and wide application range. However, in actual application, nanofiltration membranes have a serious membrane pollution problem. Pollutants adhere to the surface of the membrane, which leads to problems such as significant reduction of membrane flux, shortening of service life, increase of energy consumption and frequent cleaning. The main influencing factor of membrane pollution is membrane performance. The preparation of anti-pollution polyamide nanofiltration membranes through surface modification can slow down membrane pollution in the wastewater treatment process and fundamentally overcome the bottleneck of industrial application of nanofiltration membranes. At present, the preparation of anti-pollution polyamide nanofiltration membranes through surface modification usually adopts a method combining multiple grafting and thermal curing. The method has complicated steps, which increases the difficulty of membrane preparation. In addition, multiple grafting usually leads to an increase in membrane thickness, and the number of active sites on the membrane surface after thermal curing is limited, which has a certain influence on the permeability of water molecules. SUMMARY

[0003] To solve the above technical problems, the application provides a method for preparing an anti-pollution polyamide nanofiltration composite membrane based on a hydrothermal method. The method uses a fluorine-containing surfactant to perform water bath thermal curing on a polyamide membrane. The hydrophilic end of the fluorine-containing surfactant penetrates into the membrane pores during hydrothermal crosslinking, and a hydration layer is constructed on the membrane surface to resist pollutants. The hydrophobic end is exposed on the membrane surface, which simplifies the preparation process of the composite membrane and endows the composite membrane with anti-pollution performance through one-step preparation.

[0004] The technical scheme adopted by the application is as follows:

[0005] The method for preparing an anti-pollution polyamide nanofiltration composite membrane based on a hydrothermal method comprises the following steps:

[0006] (1) polyphenol is added to a NaOH solution, and after stirring and dissolving, polyethyleneimine is added. After continuous stirring until the polyethyleneimine is dissolved, a polyphenol-polyethyleneimine intermediate layer modification liquid is obtained. The polyphenol-polyethyleneimine intermediate layer modification liquid is coated on the surface of a porous support base film for immersion modification. After modification, the excess modification liquid is poured out, and then deionized water is used for sufficient washing to remove the residual modification liquid on the membrane surface and in the membrane pores, so that an intermediate layer modified porous base film is obtained, which is denoted as a PSF membrane;

[0007] (2) The PSF membrane prepared in step (1) is fixed on a plate frame, an organic amine aqueous solution is applied to the membrane surface and allowed to stand, and then excess aqueous solution is poured out and water droplets on the surface are blown away by an air knife; then an organic acyl chloride oil phase solution is uniformly poured onto the membrane surface to perform interfacial polymerization to form a polyamide layer, and after the reaction is completed, unreacted organic acyl chloride monomers are washed with an organic solvent to obtain a polyamide nanofiltration composite membrane, which is recorded as a TFC membrane;

[0008] (3) placing the TFC membrane prepared in step (2) in an aqueous solution of a fluorinated surfactant and heating it in a water bath at 50 to 80° C. to obtain a cross-linked, stable, and anti-fouling nanofiltration composite membrane.

[0009] Furthermore, the polyphenol in step (1) is at least one of hydroquinone, catechol, resorcinol, hydroquinone, pyrogallol and pyrogallol.

[0010] Furthermore, in the polyphenol-polyethyleneimine intermediate layer modification solution in step (1), the mass concentration of polyphenol is 0.5-3%, and the mass concentration of polyethyleneimine is 1-5%; and the modification time of the polyphenol-polyethyleneimine intermediate layer in step (1) is 1-10 minutes.

[0011] Furthermore, the porous supporting base membrane in step (1) is one of polysulfone ultrafiltration membrane, polyethersulfone ultrafiltration membrane, polyimide ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, polyethylene microfiltration membrane, and polypropylene microfiltration membrane.

[0012] Furthermore, the organic amine aqueous solution in step (2) is obtained by dissolving an organic amine in water, and the organic amine is at least one of piperazine, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 2-methylpiperazine, 2,5-dimethylpiperazine, 2,6-dimethylpiperazine, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, ethylenediamine, N,N-bis(2-aminoethyl)ethylenediamine, diethylenetriamine or polyethyleneimine;

[0013] The organic acid chloride oil phase solution in step (2) is obtained by dissolving the organic acid chloride in an organic solvent, wherein the organic acid chloride is at least one of trimesoyl chloride, terephthaloyl chloride, phthaloyl chloride, pyromellitoyl chloride, cyclohexanetricarboxylic acid chloride, cyclobutanetetracarboxylic acid chloride, cyclopentanetetracarboxylic acid chloride, malonyl chloride, glutaryl chloride and fumaroyl chloride; and the organic solvent is at least one of n-hexane, cyclohexane, n-heptane, toluene, benzene, isopar G, isopar E, isopar H, isopar L and isopar M.

[0014] Furthermore, in the process of washing the unreacted organic acid chloride monomer with an organic solvent in step (2), the organic solvent used is at least one of n-hexane, cyclohexane, n-heptane, toluene, benzene, isopar G, isopar E, isopar H, isopar L or isopar M.

[0015] Furthermore, in the step (2), the mass concentration of the organic amine aqueous solution is 0.1-5%; the mass concentration of the organic acid chloride oil solution is 0.01-2%.

[0016] Furthermore, the polymerization reaction time in step (2) is 10 to 90 seconds.

[0017] Furthermore, the mass concentration of the fluorine-containing surfactant aqueous solution in step (3) is 0.1 to 1.0%.

[0018] Furthermore, the fluorinated surfactant in step (3) is at least one of FS-63, sodium perfluorononenyloxybenzenesulfonate OBS, perfluorohexylethyl iodide, F-8903, FS-61, FC-4430, FS-3000, FS-3100, FS-8500, and FS-30.

[0019] Furthermore, the water bath heating time in step (3) is 0.5 to 5 minutes.

[0020] The beneficial effects of the present invention are:

[0021] The present invention provides a method for preparing a pollution-resistant polyamide nanofiltration composite membrane based on a hydrothermal method, and proposes a hydrothermal crosslinking method for preparing a pollution-resistant polyamide nanofiltration composite membrane. Compared with the multiple grafting method, the preparation process of this method is simple. During the hydrothermal crosslinking process, the hydrophilic end of the added fluorinated surfactant penetrates into the membrane pores, constructs a hydration layer on the membrane surface to resist pollutants, and the hydrophobic end is exposed on the membrane surface, constructs a low surface energy micro-region to release pollutants, weakens the interaction between the membrane surface and pollutants, and promotes the release of pollutants on the membrane surface, so that the composite membrane has excellent ability to resist and release pollutants; and the preparation process of the present invention is simple and easy to scale up, and has good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1This is a flow chart for preparing the anti-pollution nanofiltration composite membrane prepared by the present invention;

[0024] Figure 2 The fluorine element distribution diagram, surface morphology SEM diagram and cross-sectional morphology SEM diagram of the anti-pollution nanofiltration composite membrane of Examples 1 and 3 of the present invention;

[0025] Figure 3 The water-oil contact angle, i.e., the surface energy, of the composite films of Examples 1-4 and Comparative Example 1 of the present invention;

[0026] Figure 4 The normalized flux and anti-pollution performance index changes of the composite membranes of Example 1 of the present invention and Comparative Example 1 during the pump oil emulsion filtration process;

[0027] Figure 5 are the normalized flux and flux reduction rate in the gypsum scaling experiment of the composite membranes of Example 1 of the present invention and Comparative Example 1;

[0028] Figure 6 This is a comparison chart of the separation selectivity test of the composite membrane of Example 1 of the present invention, Comparative Example 1 and the commercial membrane NF270 for monovalent / divalent anions. DETAILED DESCRIPTION

[0029] The present invention provides a method for preparing a pollution-resistant polyamide nanofiltration composite membrane based on a hydrothermal process. To clarify and clarify the objectives, technical solutions, and effects of the present invention, the present invention is described in further detail below. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

[0030] The present invention will be described in detail below with reference to the accompanying drawings.

[0031] Example 1

[0032] like Figure 1 As shown, this embodiment provides a method for preparing an anti-pollution polyamide nanofiltration composite membrane based on a hydrothermal method, comprising the steps of:

[0033] (1) Add 1g of Noria to 100mL of 0.25mol·L -1 After stirring and dissolving in a NaOH solution, 3 g of polyethyleneimine (PEI) was added. PEI reacted with Noria to form a Schiff base reaction. After continuous stirring, the polyethyleneimine was dissolved to obtain a polyphenol-polyethyleneimine intermediate layer modification liquid. The polyphenol-polyethyleneimine intermediate layer modification liquid was applied to the surface of the rinsed polysulfone-based membrane for soaking modification. The modification time was 7 min. After the modification was completed, the excess modification liquid was poured out, and the membrane was thoroughly washed with deionized water to remove the modification liquid remaining on the membrane surface and in the membrane pores, thereby obtaining an intermediate layer modified porous base membrane, which was recorded as N-PSF membrane.

[0034] (2) The PSF membrane prepared in step (1) is fixed on a plate frame, 20 mL of 1 wt% piperazine (PIP) aqueous solution is applied on the surface of the membrane and left for 5 min, then the excess aqueous solution is poured out and the water droplets on the surface are blown away with an air knife; then 10 mL of 1.0 wt% trimesoyl chloride (TMC) n-hexane oil phase solution is uniformly poured on the surface of the membrane to form a polyamide layer by polymerization reaction, and after reaction for 30 s, the unreacted trimesoyl chloride is washed with n-hexane to obtain a polyamide nanofiltration composite membrane, which is recorded as N-TFC membrane;

[0035] (3) The TFC membrane prepared in step (2) is placed in a 0.2 wt% FS-63 aqueous solution and heated in a water bath at 60°C for 2 min to obtain a cross-linked stable anti-pollution nanofiltration composite membrane, which is recorded as N-TFC-FS63 membrane.

[0036] Example 2

[0037] The difference between this example 2 and example 1 is that in this example, the concentration of the FS-63 aqueous solution is 0.4 wt%.

[0038] Example 3

[0039] The difference between this example 3 and example 1 is that in this example, the concentration of the FS-63 aqueous solution is 0.6 wt%.

[0040] Example 4

[0041] The difference between this example 4 and example 1 is that in this example, the concentration of the FS-63 aqueous solution is 0.8 wt%.

[0042] Example 5

[0043] The difference between this example 5 and example 1 is that in this example, the concentration of the FS-63 aqueous solution is 1.0 wt%.

[0044] Example 6

[0045] The difference between this example 6 and example 1 is that in this example, the water bath heating time is 1 min.

[0046] Example 7

[0047] The difference between this example 7 and example 1 is that in this example, the water bath heating time is 4 min.

[0048] Example 8

[0049] The present example provides a method for preparing an anti-pollution polyamide nanofiltration composite membrane based on a hydrothermal method, comprising the steps of:

[0050] (1) 0.5 g of o-dihydroxybenzene and m-dihydroxybenzene are added to 100 mL of 0.5 mol·L-1 After stirring and dissolving in a NaOH solution, 1 g of polyethyleneimine (PEI) was added. PEI reacted with Noria to form a Schiff base reaction. After continuous stirring, the polyethyleneimine was dissolved to obtain a polyphenol-polyethyleneimine intermediate layer modification liquid. The polyphenol-polyethyleneimine intermediate layer modification liquid was applied to the surface of the rinsed polyethersulfone base membrane for soaking modification. The modification time was 1 min. After the modification was completed, the excess modification liquid was poured out, and the membrane was thoroughly washed with deionized water to remove the modification liquid remaining on the membrane surface and in the membrane pores, thereby obtaining an intermediate layer modified porous base membrane, which was recorded as a PSF membrane.

[0051] (2) The PSF membrane prepared in step (1) was fixed on a plate frame, and a 0.1 wt% aqueous solution of 2-methylpiperazine and 2,5-dimethylpiperazine was applied to the membrane surface and allowed to stand for 5 minutes. The excess aqueous solution was then poured out and water droplets on the surface were blown off with an air knife. Then, a 0.05 wt% cyclohexane oil phase solution of terephthaloyl chloride was uniformly poured on the membrane surface for polymerization reaction to form a polyamide layer. After the reaction lasted for 90 seconds, the unreacted trimesoyl chloride was washed with cyclohexane to obtain a polyamide nanofiltration composite membrane, which was recorded as a TFC membrane.

[0052] (3) The TFC membrane prepared in step (2) was placed in a 0.2 wt% FS-61 aqueous solution and heated in a water bath at 80° C. for 0.5 min to obtain a cross-linked, stable, and anti-fouling nanofiltration composite membrane, which was designated as TFC-FS61 membrane.

[0053] The test results show that the flux is 16.8 L·m -2 ·h -1 bar -1 , the retention rate was 93.5%.

[0054] Comparative Example 1

[0055] This comparative example provides a method for preparing a polyamide nanofiltration composite membrane, comprising the steps of:

[0056] (1) Add 1g of Noria to 100mL of 0.25mol·L -1 After stirring and dissolving in a NaOH solution, 3 g of polyethyleneimine (PEI) was added. PEI reacted with Noria to form a Schiff base reaction. After continuous stirring, the polyethyleneimine was dissolved to obtain a polyphenol-polyethyleneimine intermediate layer modification liquid. The polyphenol-polyethyleneimine intermediate layer modification liquid was applied to the surface of the rinsed polysulfone-based membrane for soaking modification. The modification time was 7 min. After the modification was completed, the excess modification liquid was poured out, and the membrane was thoroughly washed with deionized water to remove the modification liquid remaining on the membrane surface and in the membrane pores, thereby obtaining an intermediate layer modified porous base membrane, which was recorded as N-PSF membrane.

[0057] (2) The PSF membrane prepared in step (1) was fixed on a plate frame, 20 mL of a 1 wt% piperazine (PIP) aqueous solution was applied to the membrane surface and allowed to stand for 5 min, after which the excess aqueous solution was poured out and water droplets on the surface were blown off with an air knife; then 10 mL of a 1.0 wt% trimesoyl chloride (TMC) n-hexane oil phase solution was uniformly poured on the membrane surface for polymerization reaction to form a polyamide layer, and after reacting for 30 s, unreacted trimesoyl chloride was rinsed with n-hexane to obtain a polyamide nanofiltration composite membrane;

[0058] (3) The polyamide nanofiltration composite membrane prepared in step (2) was placed in an oven at 60° C. for heat treatment for 2 min to obtain a cross-linked and stable polyamide nanofiltration composite membrane, which was designated as N-TFC membrane.

[0059] Performance tests were conducted on the nanofiltration composite membranes prepared in Examples 1-7 and Comparative Examples 1 and 2, as shown in Table 1 below. Test conditions: The separation performance of the composite membranes was evaluated using a Na2SO4 solution. The composite membranes were first pre-pressed at 10 bar for 1 hour at 25°C to achieve a stable state. The separation performance test was then conducted. The permeate was collected and weighed to calculate the flux, and its conductivity was measured to calculate the retention rate.

[0060] Table 1

[0061]

[0062] Comparing the performance of the anti-pollution nanofiltration composite membranes of Examples 1-7 and Comparative Example 1, the flux and rejection rate of the anti-pollution nanofiltration composite membranes obtained in Examples 1-6 were significantly improved, and the rejection rate of Example 7 was the highest, but the flux decreased.

[0063] The anti-pollution nanofiltration composite membranes of Examples 1-4 and the nanofiltration composite membrane of Comparative Example 1 were subjected to the following tests to analyze the reasons for the performance differences between the two and to test their anti-pollution performance.

[0064] (1) Surface chemical properties of composite films

[0065] XPS spectroscopy was used to examine the surface chemical composition of the anti-fouling nanofiltration composite membranes of Examples 1-4 and the nanofiltration composite membrane of Comparative Example 1 to investigate changes in the surface chemical composition and structure of the composite membranes. Table 2 shows the surface chemical composition of the composite membranes of Examples 1-4 and Comparative Example 1. As can be seen from Table 2, the F element content of the prepared composite membranes gradually increases with increasing FS-63 concentration, indicating that FS-63 is effectively grafted onto the composite membrane surfaces.

[0066] Table 2

[0067]

[0068] (2) Surface morphology and cross-sectional morphology of composite membranes

[0069] The surface morphology and cross-sectional morphology of the anti-pollution nanofiltration composite membranes of Examples 1 and 3 were tested. Figure 2 As shown. Among them, Figure 2 (a1) and (a2) are EDX mapping images of the composite membranes of Example 1 (0.2 wt%) and Example 3 (0.6 wt%), respectively. The changes of element F in the separation layer of TFC-FS63 were analyzed using EDX mapping images. The yellow spots based on the black background represent the distribution of element F in the separation layer. Figure 2 As can be seen from (a1) and (a2), compared with the TFC-FS63 membrane with a FS-63 concentration of 0.2wt%, the content of F element in the membrane with a concentration of 0.6wt% is significantly increased, and the fluorine element is more densely distributed on the surface, which verifies that FS-63 is successfully exposed on the membrane surface, which is consistent with the results of XPS analysis. Figure 2 It can also be seen from (a1) and (a2) that the F element is evenly distributed on the surface of the composite membrane, indicating that FS-63 is evenly grafted onto the surface of the composite membrane. Figure 2 (b1) and (b2) are the surface SEM images of the composite membranes of Example 1 (0.2 wt%) and Example 3 (0.6 wt%). It can be seen from the SEM surface images that all membrane samples exhibit a typical amide membrane particle nodular structure formed by the condensation reaction of PIP and TMC, and as the FS-63 concentration increases, the particle nodular structure becomes smaller and denser, and the granular characteristics become more obvious. Figure 2 (c1) and (c2) are cross-sectional SEM images of the composite membranes of Example 1 (0.2 wt%) and Example 3 (0.6 wt%). It can be seen from the cross-sectional SEM images that the composite membrane with a higher FS-63 concentration is slightly thicker than that with a lower concentration, and the thickness change is relatively small. When the thickness change is not large, a rougher surface morphology is achieved, which helps to improve the water permeability performance.

[0070] (3) Surface wettability and surface energy of composite membranes

[0071] The surface wettability and surface energy of the composite films of Examples 1-4 and Comparative Example 1 were tested. Figure 3 As shown. Among them, Figure 3(a) The water-oil contact angle of the composite membranes of Examples 1-4 and Comparative Example 1, from which it can be seen that the composite membrane grafted with FS-63 has good hydrophilicity compared with Comparative Example 1, by analyzing the change of the oil contact angle, the oil contact angle before grafting FS-63 is 59°, the surface is oleophilic, which is easy to attract pollutants to adhere to the surface of the composite membrane, the oil contact angle after grafting FS-63 gradually increases with the increase of the concentration of FS-63, the surface becomes oleophobic, and the oil contact angle reaches 105° when the grafting concentration is 0.6wt%, that is, the TFC-FS63 composite membrane has a hydrophilic and oleophobic surface. This is because the electronegativity of fluorine (3.98) is the highest among all chemical elements, for example, the bond energy of the carbon-fluorine bond (486kJ / mol) in carbon tetrafluoride is higher than that of the carbon-hydrogen bond (414kJ / mol) in methane, so the electric dipole moment of the C-F bond is smaller than that of the C-H bond; compared with the hydrocarbon chain, the intermolecular force of the fluorocarbon chain is weaker, and one end containing the fluorocarbon group is more easily moved from the water phase to the surface of the aqueous solution, and the fluorocarbon chain has oleophobicity, thereby making the surface of the composite membrane oleophobic. That is, for the TFC-FS63 composite membrane, a hydrophilic and oleophobic surface is formed, which is beneficial to realize anti-pollution.

[0072] According to the above contact angle data, the surface energy (γ SV ) of the composite membrane was calculated, as shown in Figure 3 (b). From the figure, it can be seen that the surface energy (γ SV ) of the composite membrane after grafting FS63 decreases from 71.8mJ·m -2 to 51.9mJ·m -2 ; the introduction of FS63 also greatly reduces the dispersion component (γ d SV ) from 38.1mJ·m -2 to 6.4mJ·m -2 , which is due to the weak intermolecular force between fluorocarbon compounds and hydrocarbon groups, thereby reducing the interaction force between the surface of the composite membrane and the pollutants; in addition, the polar component (γ P SV ) increases from 33.6mJ·m -2 to 51.0mJ·m -2 , the increase of the polar component indicates that the interaction force between the composite membrane and water molecules increases, which is also the reason why the water flux of the composite membrane increases with the increase of the concentration of FS63. That is, the composite membrane prepared by grafting FS63 by hydrothermal crosslinking method has the ability to resist and release pollutants.

[0073] (IV) Anti-pollution performance

[0074] In addition, the anti-pollution performance of the anti-pollution nanofiltration composite membranes of the above Examples 1 and Comparative Example 1 was tested, including anti-organic pollutant test and anti-inorganic pollutant test.

[0075] For the anti-organic contaminant test, pump oil (100 ppm) was selected as the model contaminant for the anti-contamination performance test, and the test conditions were as follows: the experiment was initially passed by using deionized water to pre-press the membrane for 2 hours at a pressure of 4 bar to reach a steady state, and on this basis, the pure water flux (J w0 ) was measured every 0.5 hour, then the pump oil contaminant solution was added for testing, and the water flux (J p ) was measured every 1 hour during the test; after the contamination experiment was completed, deionized water was used to repeatedly clean the membrane surface at low pressure and high cross-flow speed for 3 times, each for about 15 minutes, to remove the reversible deposition and adsorption of the contaminants on the membrane surface, and finally the pure water flux (J w ) of the composite membrane after cleaning was measured.

[0076] The normalized flux during the test was monitored to study the anti-contamination effect of the membrane, and the results are shown in Figure 4 , wherein, Figure 4 (a) is the normalized flux of the composite membranes of Example 1 (N-TFC-FS63) and Comparative Example 1 (N-TFC) during the filtration of the pump oil emulsion, Figure 4 (b) is the anti-contamination performance index of the composite membranes of Example 1 and Comparative Example 1 during the filtration of the pump oil emulsion, wherein FRR is the flux recovery rate, Rt is the flux decline rate, DRr is the reversible flux decline rate, and DRir is the irreversible flux decline rate, and the calculation formulas are as follows:

[0077]

[0078] In the formula, J w0 is the initial pure water flux, L·m -2 ·h -1 ·bar -1 ; J w is the pure water flux after cleaning, L·m -2 ·h -1 ·bar -1 ; and J p is the stable permeation flux of the composite membrane during the contamination stage, L·m -2 ·h -1 ·bar -1 .

[0079] As can be seen from Figure 4 (a), the flux attenuation rate of Example 1 (N-TFC-FS63) is much smaller than that of Comparative Example 1 (N-TFC), indicating that it has superior anti-contamination performance, and the reason is that the hydrophilic end of the surfactant FS-63 can form a hydration layer on the surface of the composite membrane, and the hydration layer is beneficial to increase the Gibbs free energy during the deposition of the contaminants, thereby inhibiting the adhesion of the contaminants on the membrane surface. In addition, fromFigure 4 (b) It can be seen that the flux recovery rate of Example 1 (N-TFC-FS63) is significantly higher than that of Comparative Example 1 (N-TFC), and the reversible flux decline rate is reduced. This is because the grafting of FS-63 places the fluorine-containing end on the membrane surface, creating low surface energy microregions that are conducive to the release of pollutants. In addition, judging from the reversible flux decline rate and irreversible flux decline rate, the introduction of FS-63 can simultaneously reduce reversible and irreversible contamination of the composite membrane, greatly improving the anti-pollution effect.

[0080] For the test of resistance to inorganic pollutants, a gypsum scaling experiment was conducted using a cross-flow test device. The test conditions were: the experimental solution contained 2840 mg / L (30 mM) sodium sulfate and 2220 mg / L (30 mM) calcium chloride, the pH value was adjusted to 6, and the test was carried out in a full circulation mode at 25.0±1.0°C. The membrane was pre-pressed for 1 hour to reach a stable state, and then the water flux was measured every 0.5 hours for 14 hours. The test results are as follows: Figure 5 As shown, Figure 5 (a) is the normalized flux in the gypsum scaling test of the composite membranes of Example 1 (N-TFC-FS63) and Comparative Example 1 (N-TFC), Figure 5 (b) is the flux decrease rate. Figure 5 It can be seen that the normalized flux of the composite membranes of Example 1 (N-TFC-FS63) and Comparative Example 1 (N-TFC) begins to decrease slowly and then rapidly. After 13 hours of the experiment, until the end of the experiment, the flux attenuation rate of the membrane of Example 1 (N-TFC-FS63) is lower than that of the membrane of Comparative Example 1 (N-TFC).

[0081] Through the test of resistance to organic and inorganic pollutants, the anti-pollution performance of the composite membrane of Example 1 (N-TFC-FS63) is significantly better than that of Comparative Example 1 (N-TFC).

[0082] (V) Anti-pollution test on actual refining wastewater

[0083] The separation selectivity of the above embodiment 1, comparative example 1 and commercial membrane NF270 for monovalent / divalent anions was tested using actual refinery wastewater. The test results are shown in Table 3 and Figure 6 As shown, Table 3 is the wastewater composition table before and after composite membrane treatment, Figure 6 This is a comparison chart of the molecular selectivity of the composite membrane for monovalent / divalent anions.

[0084] Table 3

[0085] Waste water components NF270 N-TFC N-TFC-FS63 Concentration of the solution (g / L) -1 ​ 3963 3963 3963 <![CDATA[透过液电导率 / (μs·cm -1 )]]> 2073 2129 1863 COD of the stock solution (mg L -1 ) 68 68 68 <![CDATA[透过液COD / (mg·L -1 )]]> 59 53 42 <![CDATA[原液Cl - Concentration / (mg·L -1 )]]> 754.6 754.6 754.6 <![CDATA[透过液Cl-浓度 / (mg·L -1 )]]> 562.7 589.3 587.0 <![CDATA[原液SO4 2- Concentration / (mg·L -1 )]]> 618.2 618.2 618.2 <![CDATA[透过液SO4 2- Concentration / (mg·L -1 )]]> 9.1 9.0 5.9 Stock solution pH 7.9 7.9 7.9 Permeate pH 7.8 7.6 8.1

[0086] As can be seen from Table 3, the water quality of the treated wastewater has improved and meets the wastewater reuse standard (GB / T41016-2021), but the water quality of the N-TFC-FS63 membrane is better; in addition, Figure 6 It can be seen that the composite membrane of Example 1 (N-TFC-FS63) has a higher SO4 2- Retention rate, lower Cl - Retention rate, and Cl - / SO4 2- The ion selectivity is very high, indicating that the composite membrane of the embodiment exhibits good characteristics in terms of selectivity for chloride ions and sulfate ions. Such high ion selectivity is conducive to maintaining a high rejection rate for multivalent ions while allowing monovalent ions to pass through the membrane.

[0087] It should be noted that the parts not described in the present invention can be implemented by adopting or drawing on existing technologies.

[0088] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A method for preparing an anti-pollution polyamide nanofiltration composite membrane based on a hydrothermal method, characterized in that: Including steps: (1) Add polyphenol to NaOH solution, stir and dissolve, then add polyethyleneimine, continue stirring until polyethyleneimine is dissolved to obtain polyphenol-polyethyleneimine intermediate layer modification liquid, apply the polyphenol-polyethyleneimine intermediate layer modification liquid to the surface of the porous support base membrane for soaking modification, pour out the excess modification liquid after the modification is completed, and then wash thoroughly with deionized water to remove the modification liquid remaining on the membrane surface and in the membrane pores, thereby obtaining an intermediate layer modified porous base membrane, which is recorded as PSF membrane; (2) The PSF membrane prepared in step (1) is fixed on a plate frame, and an organic amine aqueous solution is applied to the membrane surface and allowed to stand, after which the excess aqueous solution is poured out and water droplets on the surface are blown away with an air knife; then, an organic acyl chloride oil phase solution is uniformly poured onto the membrane surface for interfacial polymerization to form a polyamide layer, and after the reaction is completed, unreacted organic acyl chloride monomers are washed with an organic solvent to obtain a polyamide nanofiltration composite membrane, which is referred to as a TFC membrane; (3) placing the TFC membrane prepared in step (2) in a fluorinated surfactant aqueous solution and heating it in a water bath at 50-80° C. to obtain a cross-linked, stable, and anti-fouling nanofiltration composite membrane; The polyphenol in step (1) is hydrophenol; The fluorinated surfactant in step (3) is FS-63.

2. The method for preparing an anti-pollution polyamide nanofiltration composite membrane based on a hydrothermal method according to claim 1, characterized in that: In the step (1), the mass concentration of polyphenol in the polyphenol-polyethyleneimine intermediate layer modification solution is 0.5-3%, and the mass concentration of polyethyleneimine is 1-5%; and the modification time of the polyphenol-polyethyleneimine intermediate layer in the step (1) is 1-10 minutes.

3. The method for preparing an anti-pollution polyamide nanofiltration composite membrane based on a hydrothermal method according to claim 1, characterized in that: The porous supporting base membrane in step (1) is one of polysulfone ultrafiltration membrane, polyethersulfone ultrafiltration membrane, polyimide ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, polyethylene microfiltration membrane and polypropylene microfiltration membrane.

4. The method for preparing an anti-pollution polyamide nanofiltration composite membrane based on a hydrothermal method according to claim 1, characterized in that: The organic amine aqueous solution in step (2) is obtained by dissolving an organic amine in water, wherein the organic amine is at least one of piperazine, m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 2-methylpiperazine, 2,5-dimethylpiperazine, 2,6-dimethylpiperazine, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, ethylenediamine, N,N-bis(2-aminoethyl)ethylenediamine, diethylenetriamine or polyethyleneimine; The organic acid chloride oil phase solution in step (2) is obtained by dissolving the organic acid chloride in an organic solvent, wherein the organic acid chloride is at least one of trimesoyl chloride, terephthaloyl chloride, phthaloyl chloride, pyromellitoyl chloride, cyclohexanetricarboxylic acid chloride, cyclobutanetetracarboxylic acid chloride, cyclopentanetetracarboxylic acid chloride, malonyl chloride, glutaryl chloride and fumaroyl chloride; and the organic solvent is at least one of n-hexane, cyclohexane, n-heptane, toluene, benzene, isopar G, isopar E, isopar H, isopar L and isopar M.

5. The method for preparing an anti-pollution polyamide nanofiltration composite membrane based on a hydrothermal method according to claim 1, characterized in that: The mass concentration of the organic amine aqueous solution in step (2) is 0.1-5%; the mass concentration of the organic acyl chloride oil phase solution is 0.01-2%.

6. The method for preparing an anti-pollution polyamide nanofiltration composite membrane based on a hydrothermal method according to claim 1, characterized in that: The polymerization reaction time in step (2) is 10 to 90 seconds.

7. The method for preparing an anti-pollution polyamide nanofiltration composite membrane based on a hydrothermal method according to claim 1, characterized in that: The mass concentration of the fluorinated surfactant aqueous solution in step (3) is 0.1-1.0%.

8. The method for preparing an anti-pollution polyamide nanofiltration composite membrane based on a hydrothermal method according to claim 1, characterized in that: The water bath heating time in step (3) is 0.5 to 5 minutes.

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