A polyamide desalination membrane with both high throughput, high salt rejection and anti-fouling performance, and its preparation method and application

Abstract

The present invention belongs to the technical field of functional materials, and particularly relates to a polyamide desalination membrane with both high-throughput high salt rejection and anti-fouling performance, and a preparation method and application thereof. The polyamide desalination membrane comprises a porous ultrafiltration substrate membrane and a polyamide dense functional layer, wherein the polyamide dense functional layer is prepared on the surface of the porous ultrafiltration substrate membrane by an interfacial polymerization method and has a double-layer zwitterionic property. This zwitterionic layer can provide good hydrophilicity and weaken the strong electronegativity of the polyamide layer itself. The polyamide thin-film composite desalination membrane has high permeation selectivity and excellent anti-fouling performance, and has the advantages of high regulation efficiency, easy control, wide application range, and easy scale-up, providing new ideas for the preparation of anti-fouling desalination membranes; and has wide applications in the fields of seawater desalination, sewage treatment, petrochemical industry, biology, medicine, food, etc.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and relates to an anti-pollution polyamide thin-film composite desalination separation membrane and a preparation method thereof, specifically to a polyamide desalination membrane with both high flux, high salt rejection and anti-pollution performance and a preparation method thereof. The polyamide desalination membrane can be applied to the separation, concentration and purification processes in the fields of seawater desalination, sewage treatment, biopharmaceuticals, petrochemical industry, etc. Background Art

[0002] As an advanced separation method in the world today, the desalination membrane technology can efficiently intercept salt ions and plays an increasingly important role in the fields of seawater and brackish water desalination, industrial wastewater treatment and zero discharge, food processing, pharmaceutical industry, pure water production, etc., and can maximize the recycling of water resources.

[0003] Among them, the thin-film composite polyamide membrane is the most widely used desalination membrane variety in large-scale applications due to its excellent separation selectivity and good chemical stability. However, the polyamide desalination membrane is prone to membrane fouling during application, resulting in attenuation of membrane performance and shortening of service life. Recent studies have shown that membrane fouling accounts for about 30% of the operating costs of water treatment plants using desalination processes. Among them, membrane replacement accounts for 40%-65% of the total cost of membrane fouling and is the main cost component. Therefore, developing anti-fouling desalination membranes to improve the flux stability of desalination membranes during use is the current research focus in the membrane field.

[0004] Previous studies have found that although surface hydrophilic modification can comprehensively improve its anti-fouling ability to various pollutants, the hydrophilic modification material can significantly reduce the surface contact angle from about 85° to less than 50°. In the short-term pollution test in the laboratory, the flux attenuation rate caused by macromolecular organic pollutants and negatively charged small organic pollutants is less than 30%, showing relatively excellent anti-fouling effects. However, the flux attenuation rate caused by positively charged organic small molecules on the membrane is still between 35% and 70%. This is because the hydrophilic groups on the surface can form hydrogen bond interactions with water molecules, thus forming a hydration layer on the surface to block the contact between pollutant molecules and the surface. However, the hydration layer can only play a physical shielding role and does not significantly improve the negative charge of the polyamide layer. Positively charged small water-soluble pollutants can still pass through the hydration layer under electrostatic interaction and then contact and adsorb on the membrane surface, causing serious membrane fouling. Therefore, it is difficult to fundamentally improve the anti-fouling ability of desalination membranes to positively charged organic small molecules by simply regulating surface hydrophilicity.

[0005] In recent years, researchers have also improved the negative charge on the membrane surface through charge regulation to enhance the fouling resistance of the membrane to positively charged pollutants. However, this method will lead to a decrease in the fouling resistance of the membrane to negatively charged pollutants. Therefore, there is still a need to further develop a preparation method for high-flux antifouling polyamide membranes that can simultaneously improve the antifouling ability against various charged pollutants and enhance the permeation selectivity of the membrane.

[0006] In particular, existing modification methods are difficult to exhibit good antifouling performance against small-molecule positively charged pollutants, and it is difficult to develop high-flux fouling-resistant polyamide desalination membranes that meet actual needs. Summary of the Invention

[0007] In view of this, the present invention aims at the poor effect of reducing membrane characteristics caused by typical small-molecule organic pollution or secondary pollution caused by it, and the problem that the fouling resistance to different types of pollutants cannot be improved simultaneously, and provides a solution technology that can simultaneously improve water permeability and fouling resistance to various pollutants. In addition, the technology of the present invention can also effectively solve the problem of reduced water permeability due to the additional setting of a coating layer on the surface of the separation membrane.

[0008] It should be noted that the present invention relates to a composite desalination membrane, which is a composite desalination membrane with an epidermal layer of polyamide resin having double-layer zwitterionic characteristics formed on the surface of a porous support. The inner and outer zwitterionic layers respectively regulate the electrostatic and hydrophobic interactions between pollutants and the membrane surface by significantly improving the electronegativity and hydrophilicity of the polyamide layer surface, and overall regulate the surface structure / property of the membrane to reduce the interfacial interaction between pollutants and the membrane surface, and can simultaneously enhance the permeation selectivity of the membrane, laying a foundation for broadening the preparation method and application field of antifouling desalination membranes.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] The first technical object of the present invention is to provide a polyamide desalination membrane with both high flux, high salt rejection and fouling resistance. The polyamide desalination membrane is of a flat plate type or a hollow fiber type, and the polyamide desalination membrane includes a porous ultrafiltration base membrane and a polyamide dense functional layer; wherein,

[0011] The polyamide dense functional layer is prepared on the surface of the porous ultrafiltration base membrane by interfacial polymerization and has double-layer zwitterionic characteristics; the polyamide dense functional layer has good hydrophilicity, and its water contact angle range is less than 40°, and the thickness of the hydration layer is greater than 2 nm; and the polyamide dense functional layer can also weaken the strong electronegativity carried by the polyamide layer itself, and its charge amount is greater than -30 eV.

[0012] Moreover, the schematic diagram of the polyamide dense functional layer with double-layer zwitterionic characteristics is as shown in Figure 1As shown, the surface structure / properties of the membrane are overall regulated by a double-layer zwitterionic layer to reduce the interfacial force between the pollutant and the membrane surface, and the permeation selectivity of the membrane can be simultaneously improved.

[0013] Optionally, the material of the porous ultrafiltration base membrane includes cellulose acetate, polyethersulfone, polyvinylidene fluoride, polysulfone or polyacrylonitrile.

[0014] The second technical object of the present invention is to provide a preparation method of the polyamide desalination membrane having both high flux, high salt rejection and anti-fouling properties, including the following steps:

[0015] 1) Contact an aqueous solution containing a polyfunctional amine component doped with positively charged molecules with an organic solution containing a polyfunctional acyl chloride component on a porous support to form a polyamide resin skin layer having an inner layer zwitterionic property on the surface of the porous support;

[0016] 2) Contact a solution containing zwitterionic property molecules with the skin layer to form an outer layer zwitterionic layer to modify the polyamide resin, and finally obtain the polyamide desalination membrane having both high flux, high salt rejection and anti-fouling properties.

[0017] This preparation method is a layer-by-layer interfacial polymerization method, which can integrate the preparation and modification processes, has simple operation, short reaction time, good stability, has the advantage of stable industrial preparation, and is conducive to industrial scale-up application.

[0018] The above polyfunctional amine component is a polyfunctional amine having two or more reactive amino groups, including aromatic, aliphatic and alicyclic polyfunctional amines. Among them,

[0019] Aromatic polyfunctional amines include m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,6-diaminotoluene, N,N'-dimethyl-m-phenylenediamine, 2,4-diaminoanisole, amiphenol, xylylenediamine, etc.

[0020] Aliphatic polyfunctional amines include ethylenediamine, propylenediamine, tris(2-aminoethyl)amine, N-phenylethylenediamine, etc.

[0021] The alicyclic polyfunctional amine is selected from 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 2,5-dimethylpiperazine, 4-aminomethylpiperazine, etc.

[0022] The above polyfunctional amine component can be used alone or in combination of two or more; and in order to obtain a skin layer with high salt rejection performance, aromatic polyfunctional amines are preferably used.

[0023] The above-mentioned polyfunctional acyl chloride component is a polyfunctional acyl chloride having two or more reactive carbonyl groups, and the polyfunctional acyl chloride includes aromatic, aliphatic and alicyclic polyfunctional acyl chlorides; among them,

[0024] The aromatic polyfunctional acyl chlorides include trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, biphenyl dicarboxylic acid dichloride, naphthalene dicarboxylic acid dichloride, benzene trisulfonyl chloride, benzene disulfonyl chloride, chlorosulfonyl phthaloyl chloride, etc.

[0025] The aliphatic polyfunctional acyl chlorides include propanedicarbonyl dichloride, butanedicarbonyl dichloride, pentanedicarbonyl dichloride, propanetricarbonyl trichloride, butanetricarbonyl trichloride, pentanetricarbonyl trichloride, glutaroyl dichloride, adipoyl dichloride, etc.

[0026] The alicyclic polyfunctional acyl chlorides include cyclopropanetricarbonyl trichloride, cyclobutanetetracarbonyl tetrachloride, cyclopentanetricarbonyl trichloride, cyclopentanetetracarbonyl tetrachloride, cyclohexanetricarbonyl trichloride, tetrahydrofuran tetracarbonyl tetrachloride, cyclopentanedicarbonyl dichloride, cyclobutanedicarbonyl dichloride, cyclohexanedicarbonyl dichloride, tetrahydrofuran dicarbonyl dichloride, etc.

[0027] These polyfunctional acyl chlorides can be used singly or in combination of two or more; and in order to obtain an epidermal layer with high salt rejection performance, it is preferably to use aromatic polyfunctional acyl chlorides. In addition, it is preferably to use polyfunctional acyl chlorides with three or more functional groups in at least a part of the polyfunctional acyl chloride component to form a crosslinked structure.

[0028] The above-mentioned positively charged molecules refer to substances that can improve the negative charge of the membrane surface and promote the water-oil interface reaction, including amine salt-type molecules and other compounds with nitrogen heterocycles; among them, the amine salt-type molecules are at least one of primary amine salts, secondary ammonium salts, tertiary amine salts, and quaternary amine salts.

[0029] These positively charged molecules can be used singly or in combination of two or more; and in order to obtain an epidermal layer with high crosslinking degree, it is preferably to use quaternary amine salt-type small molecule compounds.

[0030] In addition, in order to improve the performance of the polyamide resin epidermal layer, polymers such as polyvinyl alcohol, polyvinylpyrrolidone, and polyacrylic acid, and polyhydric alcohols such as sorbitol and glycerol can also be used for pore retention treatment.

[0031] The porous support can support the epidermal layer, and usually it is preferably to use an ultrafiltration membrane having micropores with an average pore diameter of about. As the forming material of the porous support, various materials such as polyaryl ether sulfones such as polysulfone and polyethersulfone, polyimide, and polyvinylidene fluoride can be used, but especially considering the aspects of chemical stability, mechanical stability, and thermal stability, it is preferably to use polysulfone and polyaryl ether sulfone.

[0032] The thickness of the porous support is usually about 25 - 125 μm, preferably about 40 - 75 μm, but is not necessarily limited to the above conditions. It should be noted that the porous support is usually a substrate based on fabrics, non-woven fabrics, etc., and its mechanical properties are strengthened.

[0033] All known methods can be used to form a polyamide resin skin layer on the surface of the porous support. For example, interfacial polymerization method, phase separation method, thin film coating method, etc. The so-called interfacial polymerization method generally has the following two operation methods: making an amine aqueous solution containing a diamine component contact with an organic solution containing a tricarboxylic acid chloride component for interfacial polymerization to form a skin layer, and then placing the skin layer on the porous support; or directly forming a polyamide skin layer on the porous support through the aforementioned interfacial polymerization on the porous support.

[0034] Furthermore, the present invention preferably adopts the following method: forming an aqueous solution coating layer formed by an amine aqueous solution containing a polyfunctional amine component and a positively charged molecule on the porous support, and then making an organic solution containing a polyfunctional acid chloride component contact with the aqueous solution coating layer for interfacial polymerization to form a polyamide skin layer.

[0035] In the aforementioned interfacial polymerization, the preferred concentration of the polyfunctional amine component in the diamine aqueous solution is 0.1 - 5 wt.%, and can be further preferably 0.5 - 2 wt.%. When the concentration of the polyfunctional amine component is lower than 0.1 wt.%, pinhole-like defects are likely to occur in the polyamide skin layer, resulting in a decrease in salt rejection performance. On the other hand, when the concentration of the polyfunctional amine component is higher than 5 wt.%, there is a tendency that the polyfunctional amine component easily penetrates into the porous support, making the generated polyamide membrane too thick, increasing the permeation resistance, and reducing the permeation flux.

[0036] The preferred concentration of the acyl chloride component in the aforementioned organic solution is 0.01 - 5 wt.%, and can be further preferably 0.05 - 3 wt.%. When the concentration of the polyfunctional acid chloride component is lower than 0.01 wt.%, there is a tendency that unreacted polyfunctional amine components are likely to remain, and pinhole-like defects are likely to occur in the skin layer, resulting in a decrease in salt rejection performance. On the other hand, when the concentration of the polyfunctional acid chloride component is higher than 5 wt.%, there is a tendency that unreacted polyfunctional acid chloride components are likely to remain, or the membrane thickness becomes too thick and the permeation resistance increases, reducing the permeation flux.

[0037] The preferred concentration of the aforementioned positively charged molecule is 0.01 - 5 wt.%, and can be further preferably 0.05 - 3 wt.%. When the concentration of the positively charged molecule is lower than 0.01 wt.%, there is a tendency that pinhole-like defects are likely to occur in the skin layer, resulting in a decrease in salt rejection performance.

[0038] As the organic solvent used in the aforementioned organic solution, it is sufficient that it has low solubility in water, does not deteriorate the porous support, and can dissolve the polyfunctional acyl chloride component, and there is no particular limitation. Saturated hydrocarbons such as cyclohexane, heptane, octane, and nonane, and halogenated hydrocarbons such as 1,1,2-trichlorotrifluoroethane can be selected. A saturated hydrocarbon or cycloalkane-based solvent having a boiling point of 300 °C or lower (more preferably 200 °C or lower) is preferred. The organic solvent can be used alone or in the form of a mixed solvent of two or more kinds.

[0039] In the present invention, after (or during) the formation of the skin layer on the surface of the porous support, a solution containing an amino group-containing zwitterionic small molecule is brought into contact with the aforementioned skin layer, thereby modifying the polyamide resin on the surface of the aforementioned skin layer into a modified polyamide resin. Specifically, the halogenated acyl group remaining in the polyamide resin forming the aforementioned skin layer is reacted with the aforementioned zwitterionic characteristic molecule, whereby the aforementioned halogenated acyl group is converted into an amide.

[0040] In view of the fact that the aforementioned zwitterionic characteristic molecule can further improve the water permeability and antifouling performance, a zwitterionic small molecule compound is preferred. The concentration is preferably 0.01 to 5 wt.%, and more preferably 0.5 to 3 wt.%.

[0041] Moreover, the molecular structure of the zwitterionic material is:

[0042]

[0043] Among them, R1, R2, R3, and R4 represent arbitrary groups, which can be single-atom groups or multi-atom groups; and among them, the R1 group provides one or more positive charges, and the R2 group provides one or more negative charges.

[0044] When the concentration of the zwitterionic characteristic molecule is lower than 0.5 wt.%, there is a tendency as follows: if the concentration is too low, the water flux of the membrane cannot be improved significantly. On the other hand, when the concentration of the zwitterionic characteristic molecule is higher than 5 wt.%, there is a tendency as follows: pinhole-like defects are likely to occur in the skin layer, and the salt rejection performance is reduced.

[0045] The method of bringing the aforementioned modified solution (aqueous solution or organic solution) into contact with the aforementioned skin layer is not particularly limited. For example, the method of pouring the aforementioned solution onto the aforementioned skin layer, the method of immersing the aforementioned skin layer in the aforementioned solution, etc.

[0046] The concentration of the modified solution in the aforementioned solution and the contact time (reaction time) between the aforementioned solution and the aforementioned skin layer are not particularly limited, and are appropriately adjusted so that the modification rate based on the aforementioned nitrogen-containing compound becomes the target value.

[0047] From the viewpoint of improving antifouling performance, the contact angle of the double-layer zwitterionic surface is preferably 30° or less, more preferably 20° or less, and the thickness of its hydration layer is greater than 2 nm. In addition, the surface charge of the membrane is preferably -30 eV or more, more preferably -10 eV or more. The thickness of the skin layer formed on the porous support is not particularly limited, and is usually about 0.01 to 2 μm, preferably 0.1 to 1 μm.

[0048] For the composite desalination membrane of the present invention, its shape is not restricted in any way. That is, it can be in all membrane shapes that can be considered, such as flat membrane shape, or spiral element shape, etc. In addition, in order to improve the salt rejection, water permeability, oxidation resistance, etc. of the composite desalination membrane, various treatments known in the past can be carried out.

[0049] From the above technical solutions, it can be seen that compared with the prior art, a kind of the present invention and its preparation method have the following excellent effects:

[0050] (1) In the present invention, the inner and outer zwitterionic layers respectively adjust the electrostatic force and hydrophobic force between the membrane surface and pollutant molecules, thereby comprehensively improving the comprehensive performance of the desalination membrane.

[0051] (2) The desalination membrane prepared in the present invention with double-layer zwitterionic characteristics has good stability, solves the problem that the antifouling material is easily eluted from the membrane surface, resulting in continuous attenuation of the membrane's antifouling performance, and has good industrial application prospects. Description of the Drawings

[0052] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative work.

[0053] Figure 1 It is a schematic structural diagram of a polyamide dense functional layer with double-layer zwitterionic characteristics.

[0054] Figure 2 It is a scanning electron micrograph of a polyamide desalination membrane with both high flux, high salt rejection and antifouling performance provided in Examples 1-4 of the present invention.

[0055] Figure 3 It is a schematic diagram of the selective permeation performance of a polyamide desalination membrane with both high flux, high salt rejection and antifouling performance provided in Examples 1-4 of the present invention.

[0056] Figure 4Schematic diagram of the Zeta potential and selective permeability of the membrane surface of a polyamide desalination membrane with both high flux, high salt rejection and anti-fouling performance provided in Embodiments 5-8 of the present invention.

[0057] Figure 5 Scanning electron micrograph of a polyamide desalination membrane with both high flux, high salt rejection and anti-fouling performance provided in Embodiments 9-11 of the present invention.

[0058] Figure 6 Schematic diagram of the water contact angle and selective permeability of a polyamide desalination membrane with both high flux, high salt rejection and anti-fouling performance provided in Embodiments 9-11 of the present invention.

[0059] Figure 7 Schematic diagram of the anti-fouling performance of a polyamide desalination membrane with both high flux, high salt rejection and anti-fouling performance provided in Embodiments 9-11 of the present invention. Detailed implementation manners

[0060] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention and the accompanying drawings of the specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0061] To better understand the present invention, the present invention will be further specifically described below through the following embodiments. However, it should not be construed as a limitation to the present invention. For some non-essential improvements and adjustments made by those skilled in the art according to the above-mentioned inventive content, they are also considered to fall within the protection scope of the present invention.

[0062] Next, the technical solutions of the present invention will be further described in conjunction with specific embodiments.

[0063] Embodiment 1

[0064] An amine aqueous solution containing 2.0 wt.% of m-phenylenediamine was coated on a porous polysulfone support membrane. After 2 minutes, the excess amine aqueous solution was removed to form an aqueous solution coating layer. Next, a n-hexane solution containing 0.1 wt.% of trimesoyl chloride (TMC) was coated on the surface of the aforementioned aqueous solution coating layer. After 1 minute, the excess n-hexane solution was removed, and then the n-hexane was allowed to volatilize in air for 2 minutes. Thereafter, it was kept in a blast dryer at 60 °C for 10 minutes to form an epidermal layer containing polyamide resin on the porous polysulfone support membrane, and a composite desalination membrane was fabricated.

[0065] Embodiments 2-4:

[0066] Compared with Example 1, in Examples 2-4, different types of positively charged molecules were added to the aqueous amine solution to adjust the process parameters, so as to modify the skin layer of the polyamide resin. Thus, a composite desalination membrane with a skin layer containing modified polyamide resin on a porous polysulfone support membrane was fabricated. The coating preparation conditions and parameters of Examples 2-4 are listed in Table 1, and the corresponding test methods are shown in the description at the back of this specification. The scanning electron micrographs of different types of positively charged molecules are as Figure 2 , and the selected permeation performance is as Figure 3 . As can be seen from Table 1, the positively charged molecules of the quaternary ammonium salt type have relatively excellent permeation selectivity and anti-fouling performance.

[0067] Table 1

[0068]

[0069]

[0070] Examples 5-8:

[0071] Through the comparison of Examples 2-4, the process parameters were continuously adjusted by adjusting the concentration of the positively charged molecules of the quaternary ammonium salt type to modify the skin layer of the polyamide resin. Thus, a composite desalination membrane with a skin layer containing modified polyamide resin on a porous polysulfone support membrane was fabricated. Compared with Example 2, the concentration of benzalkonium chloride was adjusted and set to 1 mmol / L, 10 mmol / L, 30 mmol / L, and 50 mmol / L respectively. The coating preparation conditions and parameters of Examples 5-7 are listed in Table 2, and the corresponding test methods are shown in the description at the back of this specification. The results show that when the BAC concentration is 30 mmol / L, the permeation selectivity and anti-fouling performance are the best, and the membrane surface Zeta potential and selected permeation performance are as Figure 4 shown.

[0072] Table 2

[0073]

[0074] Examples 9-11:

[0075] In Examples 9-11, a solution containing different types of zwitterionic characteristic molecules was brought into contact with the skin layer of Example 2 to form an outer zwitterionic layer to modify the polyamide resin, and finally the polyamide desalination membrane with both high flux, high salt rejection and anti-fouling performance was obtained. In the aqueous solution of each monomer modified with zwitterions recorded in Table 3, the aqueous solution was coated on the composite desalination membrane prepared based on 30 mmol / L benzalkonium chloride in Example 7 to modify the secondary polyamide resin forming the skin layer. Thus, a composite desalination membrane with a skin layer containing modified polyamide resin on a porous polysulfone support membrane was fabricated, and the membrane surface morphology diagram is as Figure 5As shown, the water contact angle and the selective permeability are as Figure 6 shown, the anti-pollution performance is shown in Figure 7, and the surface properties and membrane properties are shown in Table 3.

[0076] Table 3

[0077]

[0078] As shown in Table 3, compared with the composite desalination membrane of Comparative Example 1 having an epidermal layer formed of an unmodified polyamide resin, the polyamide desalination membrane having a bilayer zwitterionic characteristic membrane surface has an increased permeation flux, a lower flux decay rate, more excellent anti-fouling characteristics, and more excellent amino acid zwitterionic modification performance.

[0079] In addition, to further illustrate the performance advantages of the bilayer zwitterionic characteristic membrane surface of the present invention, we compared it with the existing reported monolayer zwitterionic coating technology, such as Comparative Example 1 and Comparative Example 2.

[0080] Comparative Example 1:

[0081] Different from the polyamide desalination membranes having a bilayer zwitterionic characteristic membrane surface in Examples 9-11, in Comparative Example 1, zwitterionic surface modification was carried out on the epidermal layer of the unmodified polyamide resin, that is, there is no inner zwitterionic layer. The specific preparation method is as follows: First, an aqueous solution (2.0 wt.% MPD, 1.1 wt.% TEA, and 2.4 wt.% CSA) was coated on a polysulfone ultrafiltration membrane, and the residual aqueous solution was removed after 1 minute. Next, an organic solution (0.1 wt.% TMC) was coated on the surface of the aforementioned aqueous solution coating layer, and after 1 minute, the excess organic solution was removed. Thereafter, a 2,6-DAP solution was coated on the surface of the aforementioned organic solution coating layer, and after 1 minute, the remaining 2,6-DAP solution was removed, and the membrane sheet was transferred to an oven at 80 °C for thermal crosslinking for 8 minutes to form a 2,6-DAP modified membrane. Finally, the 2,6-DAP modified membrane was subjected to a quaternary ammonium saltification reaction with 3-BPA to prepare a desalination membrane having a monolayer zwitterionic surface.

[0082] The selective permeability and anti-organic pollution performance of the membrane are shown in Table 4. As can be seen from Table 4, the permeation flux of the modified membrane in Comparative Example 1 is 2.37 Lm -2 h -1 bar -1 , and the permeation fluxes in Examples 9-11 are all higher than this value. In addition, the attenuation rates of the positively and negatively charged small molecule organic pollutants in Comparative Example 1 are 68.4% and 17.6% respectively, and the attenuation rates in Examples 9-11 are all lower than the corresponding values.

[0083] In summary, the polyamide desalination membrane with a bilayer zwitterionic characteristic membrane surface has significantly better permeation flux and antifouling properties than the desalination membrane with a monolayer zwitterionic surface.

[0084] Table 4

[0085]

[0086]

[0087] Comparative Example 2:

[0088] Similar to Comparative Example 1, in Comparative Example 2, zwitterionic surface modification was also carried out on the unmodified polyamide resin skin layer. First, the aqueous solution was coated on the polysulfone ultrafiltration membrane. After 2 minutes, the excess aqueous solution was removed. Next, the organic phase solution was coated on the surface of the aforementioned aqueous solution coating layer. After 2 minutes, the excess organic phase solution was removed. Then, the arginine modification solution was coated on the surface of the aforementioned organic phase coating layer. After 2 minutes, the excess modification solution on the membrane surface was removed. Finally, the membrane sheet was transferred to a blast dryer at 60 °C and kept for 10 minutes. The selective permeability and anti-pollution performance of the membrane are shown in Table 5.

[0089] As can be seen from Table 5, the permeation flux of the modified membrane in Comparative Example 2 was 3.79 Lm -2 h -1 bar -1 , which was lower than the permeation flux of 3.90 Lm -2 h -1 bar -1 in Example 10. In addition, the attenuation rates of the positively and negatively charged small molecule organic pollutants in Comparative Example 1 were 48.5% and 25.6% respectively, which were higher than the attenuation rates of 38.2% and 14.2% of the positively and negatively charged small molecule organic pollutants in Example 10.

[0090] In summary, the polyamide desalination membrane with a bilayer zwitterionic characteristic membrane surface has significantly better permeation flux and antifouling properties than the desalination membrane with a monolayer zwitterionic surface.

[0091] Table 5

[0092]

[0093] (Measurement of Permeation Flux and Salt Rejection Rate)

[0094] For the fabricated composite polyamide desalination membrane, a cross-flow test system (effective membrane surface area: 28.26 cm 2)The separation performance was evaluated by measuring the permeation flux (Flux) and the salt rejection rate (Rej). Initially, a pre-pressurization operation was carried out at a pressure of 20 bar for 2 hours to stabilize the permeation performance of the composite desalination membrane. Next, an aqueous solution containing 2000 mg / L of NaCl was used as the feed solution, and after operating at a pressure of 15 bar for 1 hour, the permeation flux of the composite desalination membrane was measured (the permeate was collected for 30 minutes). The permeation flux was calculated using Equation (1) below. In addition, a conductivity meter (Thermo, Eutech CON2700, USA) was used to measure the concentrations of the feed solution and the permeate. The salt rejection rate was calculated using Equation (2) below. At least 3 parallel samples were tested for each membrane sample, and the average value and the error range of the test results were calculated.

[0095]

[0096] In the formula, J w ——membrane permeation flux (Lm -2 h -1 bar -1 , LMH / bar);

[0097] M——mass of the permeate passing through the membrane sheet (kg);

[0098] ρ——density of the permeate (kgm -3 );

[0099] E——effective permeation area of the membrane sample (m 2 );

[0100] t——test time (h);

[0101] P——test pressure (bar).

[0102]

[0103] In the formula, R s —salt rejection rate of the membrane sample (%);

[0104] C o —salt concentration of the feed solution (mg / L);

[0105] C p —salt concentration of the permeate (mg / L).

[0106] (Anti-fouling evaluation)

[0107] As model contaminants, dodecyltrimethylammonium bromide (DTAB) and sodium dodecylbenzenesulfonate (SDBS) were used to evaluate the fouling resistance performance of the membrane. DTAB was adopted as an example of a surfactant with a positive charge, i.e., a small molecule contaminant. SDBS was adopted as an example of a surfactant with a negative charge. These are typical representative examples of common organic contaminants in aqueous systems.

[0108] The evaluation of fouling resistance was carried out by the normalized flux decline rate (%) of Flux. The measurement of the Flux decline rate was carried out in the following 4 stages.

[0109] In the first stage, the RO system was operated for 30 minutes under the conditions of 15 bar and a cross-flow velocity of 14 cm / s, using a feed aqueous solution containing 2000 mg / L of NaCl to determine the baseline permeate flux and salt rejection rate.

[0110] In the second stage, 200 ppm of the aforementioned model contaminant was added to the aforementioned feed aqueous solution, and the RO system was operated for 6 hours under the same conditions as in the first stage.

[0111] In the third stage, the composite desalination membrane was washed with deionized water for 30 minutes at a circulation flow rate of 3 L / min.

[0112] In the fourth stage, the permeate flux was measured again using a feed aqueous solution containing 2000 mg / L of NaCl.

[0113] Thus, the Flux decline rate can be calculated by the following formula, and the results are shown in Table 1.

[0114] Flux reduction rate (%) = {1 - (permeate flux in the second stage / permeate flux in the first stage)} × 100%

[0115] Flux recovery rate (%) = (permeate flux in the fourth stage / permeate flux in the first stage) × 100% Further, the industrial availability of the polyamide desalination membrane with both high flux and high salt rejection and fouling resistance performance is as follows:

[0116] The composite desalination membrane of the present invention is suitable for the manufacture of ultrapure water, desalination of brackish water or seawater, etc., and can remove pollutants such as those causing public nuisances from dyeing wastewater, electrodeposition coating wastewater, etc., and recover the pollution sources or effective substances contained therein, contributing to the closed treatment of wastewater. In addition, it can be used for the concentration of active ingredients in food applications, the removal of harmful ingredients in water purification applications, etc., and for wastewater treatment in oil fields, shale gas fields, etc.

[0117] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A polyamide desalination membrane with both high throughput, high salt rejection and anti-fouling performance, characterized in that, The polyamide desalination membrane is in the form of flat sheet or hollow fiber, and the polyamide desalination membrane comprises a porous ultrafiltration base membrane and a polyamide dense functional layer; wherein, the polyamide dense functional layer is prepared on the surface of the porous ultrafiltration base membrane by interfacial polymerization and has bilayer zwitterionic characteristics; the polyamide dense functional layer has good hydrophilicity, its water contact angle is less than 40°, and the hydration layer thickness is greater than 2 nm; and the polyamide dense functional layer can also weaken the strong negative charge carried by the polyamide layer itself, and its charge amount is greater than -30 eV; The bilayer zwitterions coordinately regulate the surface structure / property of the membrane to reduce the interfacial force between the pollutants and the membrane surface, and can simultaneously improve the permeation selectivity of the membrane; The preparation method of the polyamide desalination membrane with both high flux, high salt rejection and anti-fouling performance comprises the following steps: 1) Contact an aqueous solution containing a polyfunctional amine monomer doped with a positively charged molecule with an organic solution containing a polyfunctional acyl chloride monomer on a porous support to form a polyamide separation skin layer with inner layer zwitterionic characteristics on the surface of the porous support; 2) Contact a solution containing a zwitterionic material with the above polyamide separation skin layer and carry out a chemical reaction to form an outer layer zwitterionic layer to modify the polyamide separation skin layer, and finally obtain the polyamide desalination membrane with both high flux, high salt rejection and anti-fouling performance; The positively charged molecule is selected from amine salt type molecules or other compound molecules with nitrogen heterocycles; The zwitterionic material is a zwitterionic small molecule containing an amino group.

2. The polyamide desalination membrane with both high-throughput, high salt rejection and anti-fouling performance according to claim 1, wherein The material of the porous ultrafiltration base membrane includes but is not limited to cellulose acetate, polyethersulfone, polyvinylidene fluoride, polysulfone or polyacrylonitrile.

3. A polyamide desalination membrane with both high-throughput, high salt rejection and anti-fouling performance according to claim 1, characterized in that, The concentration of the positively charged molecule is 0.01~5 wt.%; The amine salt type molecule is at least one of primary amine salt, secondary ammonium salt, tertiary amine salt and quaternary amine salt.

4. A polyamide desalination membrane with both high-throughput, high salt rejection and anti-fouling performance according to claim 1, characterized in that The concentration of the polyfunctional amine monomer component is 0.1~5 wt.%, and the polyfunctional amine monomer is a polyfunctional amine having 2 or more reactive amino groups, including aromatic, aliphatic and alicyclic polyfunctional amines; wherein, the aromatic polyfunctional amine monomer includes but is not limited to m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,6-diaminotoluene, N,N'-dimethyl-m-phenylenediamine, 2,4-diaminoanisole, amiphenol, xylylenediamine; The aliphatic polyfunctional amine monomer includes but is not limited to ethylenediamine, propylenediamine, tris(2-aminoethyl)amine, N-phenylethylenediamine; The alicyclic polyfunctional amine monomer includes but is not limited to 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 2,5-dimethylpiperazine, 4-aminomethylpiperazine; 5. A polyamide desalination membrane with both high throughput, high salt rejection and anti-fouling performance according to claim 1, characterized in that, The concentration of the polyfunctional acyl chloride monomer is 0.01 to 5 wt.%, and the polyfunctional acyl chloride monomer is a polyfunctional compound molecule having two or more reactive acyl chlorides; the polyfunctional acyl chloride monomer includes aromatic, aliphatic and alicyclic polyfunctional acid chlorides; wherein, the aromatic polyfunctional acyl chloride monomer includes, but is not limited to, one of trimellitic acid chloride, terephthaloyl chloride, isophthaloyl chloride, biphenyl dicarboxylic acid chloride, naphthalene dicarboxylic acid chloride, benzene trisulfonyl chloride, benzene disulfonyl chloride, chlorosulfonyl phthalic acid chloride, the aliphatic polyfunctional acyl chloride monomer includes, but is not limited to, one of propanedicarbonyl chloride, butanedicarbonyl chloride, pentanedicarbonyl chloride, propanetricarbonyl chloride, butanetricarbonyl chloride, pentanetricarbonyl chloride, glutaroyl chloride, adipoyl chloride; The alicyclic polyfunctional acyl chloride monomer includes, but is not limited to, one of cyclopropanetricarbonyl chloride, cyclobutanetetracarbonyl chloride, cyclopentanetricarbonyl chloride, cyclopentanetetracarbonyl chloride, cyclohexanetricarbonyl chloride, tetrahydrofuran tetracarbonyl chloride, cyclopentanedicarbonyl chloride, cyclobutanedicarbonyl chloride, cyclohexanedicarbonyl chloride, tetrahydrofuran dicarbonyl chloride.

6. The polyamide desalination membrane with both high throughput, high salt rejection and fouling resistance as described in claim 1, wherein The concentration of the zwitterionic material is 0.01 to 5 wt.%, and the zwitterionic material is a neutral compound having both positive and negative charge groups; Moreover, the molecular structure of the zwitterionic material is: ； wherein, R1, R2, R3, and R4 represent any groups, which can be single-atom groups or multi-atom groups; and wherein the R1 group provides one or more positive charges, and the R2 group provides one or more negative charges.

7. An application of the polyamide desalination membrane with both high-throughput high salt rejection and anti-fouling performance as described in claim 1 in separation, concentration and purification.

8. The application according to claim 7, wherein The separation, concentration and purification process is used in the fields of seawater desalination, sewage treatment, biopharmaceuticals or petrochemical industry.

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