Acid and alkali resistant positively charged composite nanofiltration membrane, its preparation method and application

Abstract

This invention relates to the field of membranes, and discloses an acid and alkali resistant positively charged composite nanofiltration membrane, its preparation method, and its applications. The acid and alkali resistant positively charged composite nanofiltration membrane comprises a bottom layer, a porous support layer, and an acid and alkali resistant separation layer stacked sequentially; wherein the acid and alkali resistant separation layer contains a quaternary ammonium salt structure. The acid and alkali resistant separation layer contains inert chemical groups, enabling the nanofiltration membrane to be used in acidic / alkaline environments; the acid and alkali resistant separation layer also contains a quaternary ammonium salt structure, enabling the nanofiltration membrane to maintain a high water flux while exhibiting excellent retention performance for divalent and high-valent metal cations, achieving the concentration of divalent and high-valent metal cations and the recovery of waste acid.

Description

Technical Field

[0001] This invention relates to the field of membranes, specifically to an acid and alkali resistant positively charged composite nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] Titanium dioxide, the main component of titanium dioxide, is safe and non-toxic, and is widely used in industries such as coatings, papermaking, printing, chemical fibers, plastics, and rubber, with coatings accounting for over 60% of its production. my country is a major producer of titanium dioxide; since 2019, its overall production scale has ranked first in the world. The sulfuric acid process accounts for over 90% of China's total titanium dioxide production. In the sulfuric acid process, for every ton of titanium dioxide produced, 8-10 tons of waste sulfuric acid with a concentration of 15-20 wt% are generated. This waste sulfuric acid solution contains approximately 5 wt% Fe. 2+ It also contains small amounts of metal sulfates such as aluminum, manganese, calcium, and magnesium. How to solve the problem of low-cost treatment and pollution-free discharge of acidic wastewater from the sulfuric acid process for titanium dioxide is the primary challenge hindering the development of my country's titanium dioxide industry.

[0003] Currently, domestic titanium dioxide enterprises mainly employ three processes for the comprehensive treatment of waste acid: neutralization, waste acid concentration, and purification. Among these, alkali neutralization is the most widely used waste acid treatment process. However, this process not only fails to separate and recover sulfuric acid and numerous valuable metals from the waste acid, but also generates titanium gypsum, primarily composed of calcium sulfate, and other solid wastes, the treatment of which presents a new challenge. With the development of membrane separation technology, nanofiltration offers a new option for treating acidic wastewater from titanium dioxide production. Based on size sieving and the Donnan effect, nanofiltration membranes can selectively separate monovalent and divalent ions, showing promising application prospects in the aforementioned processes. Furthermore, membrane treatment processes are short, simple to operate, and have low production costs. Simultaneously treating waste acid also enables the recovery and utilization of sulfur resources, which is of great significance for the green and sustainable development of the titanium dioxide industry.

[0004] The problem is that currently commercially available polyamide nanofiltration membranes are not acid-resistant. Under acidic conditions, the C=O bonds in the polyamide structure are easily affected by H+. + Nucleophilic electron attack causes hydrolysis of the amide bonds, disrupting the membrane separation layer structure and significantly reducing retention performance. Furthermore, the hydrolysis of acyl chloride groups on the polyamide membrane surface forms numerous carboxyl groups, giving the membrane surface a negative charge. Due to the Donnan effect, the membrane's resistance to Fe... 2+ Ca 2+ Mg 2+ Divalent cations have low removal rates, while positively charged nanofiltration membranes better meet the needs of the above-mentioned application scenarios.

[0005] Therefore, there is an urgent need to develop a positively charged nanofiltration membrane that is simple to prepare and has excellent acid resistance. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of poor acid / alkali tolerance and low retention rate of divalent and high-valent metals in existing nanofiltration membranes. This invention provides an acid- and alkali-resistant positively charged composite nanofiltration membrane, its preparation method, and its applications. The acid- and alkali-resistant positively charged composite nanofiltration membrane has an acid- and alkali-resistant separation layer containing chemically inert groups, allowing the nanofiltration membrane to be used in acidic / alkaline environments. The acid- and alkali-resistant separation layer also contains a quaternary ammonium salt structure, enabling the nanofiltration membrane to maintain a high water flux while exhibiting excellent retention capacity for divalent and high-valent metal cations, thus achieving the concentration of divalent and high-valent metal cations and the recovery and reuse of acids.

[0007] To achieve the above objectives, the first aspect of the present invention provides an acid and alkali resistant positively charged composite nanofiltration membrane, wherein the acid and alkali resistant positively charged composite nanofiltration membrane comprises a bottom layer, a porous support layer and an acid and alkali resistant separation layer stacked sequentially.

[0008] The acid and alkali resistant separation layer contains a quaternary ammonium salt structure.

[0009] A second aspect of the present invention provides a method for preparing an acid- and alkali-resistant positively charged composite nanofiltration membrane, wherein the preparation method includes the following steps:

[0010] S1. Prepare a porous support layer on the bottom layer;

[0011] S2. The membrane layer obtained in step S1 is first contacted with an aqueous phase containing a polyamine containing tertiary amine groups, and then second contacted with an organic phase containing multiple polar monomers. After heat treatment, a composite nanofiltration membrane containing an acid and alkali resistant separation layer is obtained.

[0012] S3. The composite nanofiltration membrane is brought into a third contact with an organic solution containing haloalkanes and a catalyst, and then dried to obtain the acid and alkali resistant positively charged composite nanofiltration membrane.

[0013] A third aspect of the present invention provides an acid and alkali resistant positively charged composite nanofiltration membrane prepared by the aforementioned preparation method.

[0014] The fourth aspect of this invention provides an application of the aforementioned acid and alkali resistant positively charged composite nanofiltration membrane in the field of water treatment.

[0015] Through the above technical solutions, the acid and alkali resistant positively charged composite nanofiltration membrane, its preparation method, and its application provided by the present invention achieve the following beneficial effects:

[0016] The acid and alkali resistant positively charged composite nanofiltration membrane provided by this invention has chemically inert groups in its acid and alkali resistant separation layer, which improves the acid / alkali resistance of the membrane. The presence of quaternary ammonium salt groups in the separation layer increases the positive charge density on the surface of the composite nanofiltration membrane, resulting in good retention of divalent and high-valent metal cations. At the same time, it also allows the membrane to maintain a high water flux.

[0017] In the preparation method of the acid and alkali resistant positively charged composite nanofiltration membrane provided by the present invention, the haloalkanes react with the tertiary amine in the acid and alkali resistant separation layer under the action of an alkaline catalyst, converting the tertiary amine into a positively charged quaternary ammonium salt group. The repulsion effect between positive charges improves the nanofiltration membrane's ability to retain divalent and high-valent metal cations, while also enabling the acid and alkali resistant positively charged composite nanofiltration membrane to maintain a high water flux. Attached Figure Description

[0018] Figure 1 This is the XPS spectrum of nitrogen atoms on the surface of the acid and alkali resistant positively charged composite nanofiltration membrane of Example 1 of the present invention. Detailed Implementation

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

[0020] The first aspect of the present invention provides an acid and alkali resistant positively charged composite nanofiltration membrane, wherein the acid and alkali resistant positively charged composite nanofiltration membrane comprises a bottom layer, a porous support layer and an acid and alkali resistant separation layer stacked sequentially.

[0021] The acid and alkali resistant separation layer contains a quaternary ammonium salt structure.

[0022] In this invention, the acid and alkali resistant positively charged composite nanofiltration membrane contains a quaternary ammonium salt structure in its acid and alkali resistant separation layer, which significantly increases the positive charge density on the surface of the acid and alkali resistant positively charged composite nanofiltration membrane. The repulsion effect between the positive charges improves the retention effect of the acid and alkali resistant positively charged composite nanofiltration membrane on divalent iron ions. Thus, while maintaining the high water flux of the acid and alkali resistant positively charged composite nanofiltration membrane, it also improves the retention capacity of the acid and alkali resistant positively charged composite nanofiltration membrane for divalent and high-valent metal cations.

[0023] According to the present invention, the quaternary ammonium salt structure includes the structural formula shown in Formula I and / or the structural formula shown in Formula II.

[0024]

[0025] X is a halogen; n is an integer from 0 to 10; m is an integer from 2 to 10.

[0026] In this invention, * refers to the bonding position where the quaternary ammonium salt structure connects to the acid and alkali resistant separation layer.

[0027] Furthermore, X is Cl, Br, or I.

[0028] Furthermore, n is an integer from 0 to 7; m is an integer from 2 to 8.

[0029] According to the present invention, the acid and alkali resistant separation layer is selected from at least one of polyurea separation layer, polytriazine amine separation layer, polysulfonamide separation layer, poly(triazine amine-urea) separation layer, poly(sulfonamide-urea) separation layer, poly(triazine amine-sulfonamide) separation layer and poly(triazine amine-sulfonamide-urea) separation layer.

[0030] In this invention, a specific acid and alkali resistant separation layer introduces inert chemical groups into the composite nanofiltration membrane, improving the stability of the composite nanofiltration membrane and enabling the composite nanofiltration membrane of this invention to be used in acidic / alkaline environments, thus expanding its application range.

[0031] Furthermore, the acid and alkali resistant separation layer is selected from at least one of polyurea separation layer, polytriazine amine separation layer, and polysulfonamide separation layer.

[0032] According to the present invention, the nitrogen atom content in the quaternary ammonium salt group of the acid and alkali resistant positively charged composite nanofiltration membrane is 0.5-5 at.%.

[0033] In this invention, when the nitrogen atom content in the quaternary ammonium salt structure meets the above-mentioned range, it indicates that the acid and alkali resistant positively charged composite nanofiltration membrane contains a large number of quaternary ammonium salt groups, which enables the composite nanofiltration membrane to have a high surface positive potential.

[0034] Furthermore, the nitrogen atom content in the quaternary ammonium salt groups of the acid- and alkali-resistant positively charged composite nanofiltration membrane is 2-5 at.%.

[0035] In this invention, the surface Zeta potential of the nanofiltration membrane refers to the surface Zeta potential at pH=7.

[0036] According to the present invention, the surface Zeta potential of the acid and alkali resistant positively charged composite nanofiltration membrane is 0-30mV.

[0037] In this invention, when the surface Zeta potential of the acid and alkali resistant positively charged composite nanofiltration membrane meets the above-mentioned range, it indicates that the composite nanofiltration membrane has a high surface electrode potential. When used for the separation of divalent and high-valence metal cations, it can better repel metal cations, making it difficult for metal cations in the liquid to pass through the separation membrane, thereby obtaining a high retention capacity for divalent and high-valence metal cations.

[0038] Furthermore, the surface Zeta potential of the acid and alkali resistant positively charged composite nanofiltration membrane is 5-20mV.

[0039] According to the present invention, the average pore size of the acid and alkali resistant positively charged composite nanofiltration membrane is 0.1-0.5 nm.

[0040] In this invention, the average pore size of the acid and alkali resistant positively charged composite nanofiltration membrane was tested using the PEG solute transfer method.

[0041] In this invention, when the average pore size of the nanofiltration membrane meets the above-mentioned range, the acid and alkali resistant positively charged composite nanofiltration membrane has high density and can better repel divalent and high-valence metal cations, making it difficult for divalent and high-valence metal cations in the liquid to pass through the separation membrane, thereby obtaining a high retention capacity for divalent and high-valence metal cations.

[0042] Furthermore, the average pore size of the acid and alkali resistant positively charged composite nanofiltration membrane is 0.15-0.3 nm.

[0043] According to the present invention, the contact angle of the acid and alkali resistant positively charged composite nanofiltration membrane is 20°-80°.

[0044] In this invention, when the contact angle of the nanofiltration membrane meets the above-mentioned range, it indicates that the surface of the acid and alkali resistant positively charged composite nanofiltration membrane has good hydrophilicity, thereby obtaining a high water flux.

[0045] Furthermore, the contact angle of the acid and alkali resistant positively charged composite nanofiltration membrane is 30°-60°.

[0046] In this invention, the bottom layer and the porous support layer are not specifically limited and can be made of various existing materials with certain strength that can be used for nanofiltration and reverse osmosis membranes.

[0047] In this invention, the bottom layer is a non-woven fabric material, preferably polyester and / or polyethylene.

[0048] In this invention, the porous support layer material can be at least one of polyethersulfone, polysulfone, polyaryl ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride, and polyaryl etherketone.

[0049] According to the present invention, the thickness of the bottom layer, the porous support layer, and the acid and alkali resistant separation layer is not particularly limited and can be a conventional choice in the art. However, in order to enable these three layers to play a better synergistic role and enable the resulting composite nanofiltration membrane to better combine excellent retention capacity for divalent and high-valent metal cations and high water flux, in a preferred case, the thickness of the bottom layer is 30-150 μm, preferably 50-120 μm; the thickness of the porous support layer is 10-100 μm, preferably 30-60 μm; and the thickness of the acid and alkali resistant separation layer is 10-500 nm, preferably 50-300 nm.

[0050] In a particularly preferred embodiment, the thickness of the acid and alkali resistant separation layer is 120-180 nm.

[0051] A second aspect of the present invention provides a method for preparing an acid- and alkali-resistant positively charged composite nanofiltration membrane, wherein the preparation method includes the following steps:

[0052] S1. Prepare a porous support layer on the bottom layer;

[0053] S2. The membrane layer obtained in step S1 is first contacted with an aqueous phase containing a polyamine containing tertiary amine groups, and then second contacted with an organic phase containing multiple polar monomers. After heat treatment, a composite nanofiltration membrane containing an acid and alkali resistant separation layer is obtained.

[0054] S3. The composite nanofiltration membrane is brought into a third contact with an organic solution containing haloalkanes and a catalyst, and then dried to obtain the acid and alkali resistant positively charged composite nanofiltration membrane.

[0055] In this invention, the composite nanofiltration membrane is contacted with an organic solution containing haloalkanes and a catalyst. Under the action of the catalyst, the haloalkanes react with the tertiary amines in the acid and alkali resistant separation layer, and the tertiary amines are converted into positively charged quaternary ammonium salt groups. The repulsion effect between positive charges improves the retention capacity of the acid and alkali resistant positively charged composite nanofiltration membrane for divalent and high-valent metal cations, while also enabling the acid and alkali resistant positively charged composite nanofiltration membrane to maintain a high water flux.

[0056] In this invention, there is no particular limitation on the method for preparing the porous support layer on the bottom layer. Conventional methods in the art can be used for preparation, with phase inversion method preferred. Specifically, a polymer solution of porous support layer material is coated on one surface of the bottom layer, and the porous support layer is obtained through phase inversion.

[0057] In this invention, the phase inversion method is preferably as follows: dissolving the support layer polymer material in a solvent to obtain a polymer solution with a concentration of 10-20% by weight, degassing at 20-40°C for 10-180 min; then coating the polymer solution onto the bottom layer to obtain an initial film, and then immersing it in water at a temperature of 10-30°C for 10-60 min, thus forming the support layer polymer porous membrane through the phase inversion layer.

[0058] The solvent may be N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, etc.

[0059] According to the present invention, in step S2, the polyamine containing a tertiary amine group is selected from at least one of polyethyleneimine, polyethylene polyamine, 1-aminopiperazine, 1,4-diaminopiperazine, 1,4-piperazine diethylamine and 1,4-bisaminopropylpiperazine, preferably polyethyleneimine and / or polyethylene polyamine.

[0060] According to the present invention, in the aqueous phase of the polyamine containing tertiary amine groups, the concentration of the polyamine containing tertiary amine groups is 0.1wt%-10wt%, preferably 0.5wt%-2.5wt%.

[0061] According to the present invention, the multi-polar monomer is selected from at least one of polyisocyanates, triazine compounds containing at least two C-Cl bonds, and polysulfonyl chlorides.

[0062] According to the present invention, the polyisocyanate is selected from at least one of isophthalic diisocyanate, isophorone diisocyanate, 1,6-hexanediisocyanate, toluene-2,6-diisocyanate, 1,4-phenyl diisocyanate, toluene-2,4-diisocyanate, 4,4'-methylenebis(phenyl isocyanate), 1,3-phenyl diisocyanate, 3,3'-dichloro-4,4'-diisocyanate biphenyl, dicyclohexylmethane-4,4'-diisocyanate, trimethylhexamethylene diisocyanate, L-lysine-ethyl ester-diisocyanate, 1,4-cyclohexyl diisocyanate, and 4-chloro-6-methyl isophthalic diisocyanate; preferably selected from 1,4-phenyl diisocyanate and / or 1,3-phenyl diisocyanate.

[0063] According to the present invention, the triazine compound containing at least two C-Cl bonds is selected from at least one of cyanuric chloride, 2,4-dichloro-1,3,5-triazine, 2,5-dichloro-1,3,5-triazine and 2,4-dichloro-6-phenyl-1,3,5-triazine; preferably cyanuric chloride.

[0064] According to the present invention, the polysulfonyl chloride is selected from at least one of 1,3-benzene disulfonyl chloride, 1,2-benzene disulfonyl chloride, 1,4-benzene disulfonyl chloride, 2,4-disulfonyl chloride methyltrimethylbenzene, biphenyl-4,4'-disulfonyl chloride, 4,5-dichloro-1,3-benzene disulfonyl chloride, 2,6-naphthalene disulfonyl chloride, 1,3-naphthalene disulfonyl chloride, 2,7-naphthalene disulfonyl chloride, 1,3,5-benzene trisulfonyl chloride, and 1,3,6-naphthalene trisulfonyl chloride; preferably 1,3-benzene disulfonyl chloride.

[0065] According to the present invention, the concentration of the multi-polar monomer in the organic phase is 0.01wt%-2wt%, preferably 0.05-1wt%.

[0066] According to the present invention, the amounts of the aqueous phase containing the tertiary amine group and the organic phase containing the multi-polar monomer are such that the weight ratio of the polyamine containing the tertiary amine group to the multi-polar monomer is 2-200:1.

[0067] In this invention, when the weight ratio of the polyamine containing tertiary amine groups to the multi-polar monomers is controlled to meet the above-mentioned range, it can be ensured that the interfacial polymerization reaction between the polyamine containing tertiary amine groups and the multi-polar monomers is sufficient, thereby improving the crosslinking density of the obtained acid and alkali resistant separation layer.

[0068] Furthermore, the amounts of the aqueous phase containing the tertiary amine group and the organic phase containing the multi-polar monomer are such that the weight ratio of the polyamine containing the tertiary amine group to the multi-polar monomer is 5-80:1.

[0069] In this invention, there is no particular limitation on the type of solvent in the organic phase containing the multi-polar monomers, as long as it can dissolve the multi-polar monomers. Preferably, the solvent of the organic phase is one or more of hexane, dodecane, heptane, and alkane solvent oils (Isopar E, Isopar G, Isopar H, Isopar L and Isopar M).

[0070] According to the present invention, there are no particular limitations on the interfacial polymerization conditions of polyamines containing tertiary amine groups and polypolar monomers, and they can be carried out according to conventional conditions in the art. However, in order to enable the three layers to play a better synergistic role and enable the resulting composite nanofiltration membrane to better combine excellent retention capacity for divalent and high-valent metal cations and high water flux, preferably, the first contact time is 5-100s, preferably 10-60s; the second contact time is 10-200s, preferably 20-120s; the heat treatment conditions include: heat treatment temperature of 40-150℃, preferably 50-120℃; and heat treatment time of 0.5-10min, preferably 1-5min.

[0071] In this invention, in step S2, the ratio of the volume of the aqueous solution containing the tertiary amine group to the membrane area of ​​the membrane obtained in step S1 is 0.05-1 mL / cm². 2 Preferably, it is 0.1-0.5 mL / cm 2 .

[0072] In this invention, in step S2, the ratio of the volume of the organic phase solution containing multiple polar monomers to the membrane area of ​​the membrane obtained in step S1 is 0.25-0.5 mL / cm². 2 Preferably, it is 0.05-0.3 mL / cm 2 .

[0073] According to the present invention, in step S3, the haloalkane is selected from the haloalkane shown in Formula III and / or the haloalkane shown in Formula IV.

[0074]

[0075] X1, X2, and X3 are each an independent halogen; n is an integer from 0 to 10; m is an integer from 2 to 10.

[0076] By using haloalkanes with the specific structure described above, the positive charge density on the surface of the positively charged composite nanofiltration membrane can be further increased, and the average pore size of the nanofiltration membrane can be further reduced.

[0077] Furthermore, X1, X2, and X3 are each independently Cl, Br, or I.

[0078] Furthermore, n is an integer from 0 to 7; m is an integer from 2 to 8.

[0079] According to the present invention, the haloalkane is selected from iodomethane, iodoethane, iodopropane, iodobutane, iodopentane, iodohexane, iodoheptane, iodooctane, iodononane, iododecane, iodocyclopropane, iodocyclobutane, iodocyclopentane, iodocycloheptane, iodocyclooctane, 1,2-diiodoethane, 1,3-diiodopropane, 1,4-diiodobutane, 1,5-diiopentane, 1,6-diiodohexane, 1,7-diioheptane, 1,8-diiooctane, chloromethane, chloroethane, chloropropane, chlorobutane, chloropentane, chlorohexane, chloroheptane, chlorooctane, chlorononane, chlorodecane, chlorocyclopropane, chlorocyclobutane, chlorocyclopentane, chlorocycloheptane, chlorocyclooctane, 1,2-diiodoethane, 1,3-diiodopropane, 1,4-diiodobutane, 1,5-diiopentane, 1,6-diiodohexane, 1,7-diioheptane, 1,8-diiooctane, chloromethane, chloroethane, chloropropane, chlorobutane, chloropentane, chlorocycloheptane, chlorooctane, 1,2-diiodoethane, chloropropane, chlorobutane, chlorocyclo ... - At least one of dichloroethane, 1,3-dichloropropane, 1,4-dichlorobutane, 1,5-dichloropentane, 1,6-dichlorohexane, 1,7-dichloroheptane, 1,8-dichlorooctane, bromomethane, bromoethane, bromopropane, bromobutane, bromopentane, bromohexane, bromoheptane, bromooctane, bromononane, bromodecane, bromocyclopropane, bromocyclobutane, bromocyclopentane, bromocycloheptane, bromocyclooctane, 1,2-dibromoethane, 1,3-dibromopropane, 1,4-dibromobutane, 1,5-dibromopentane, 1,6-dibromohexane, 1,7-dibromoheptane, and 1,8-dibromooctane, preferably selected from at least one of bromoethane, chloropropane, and iodomethane.

[0080] In this invention, to ensure that the haloalkanes can react with the residual tertiary amine groups in the acid-base resistant separation layer, the catalyst is an alkaline catalyst. Further, the catalyst is selected from at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, potassium bicarbonate, potassium tert-butoxide, and sodium tert-butoxide, preferably selected from sodium hydroxide and / or sodium tert-butoxide.

[0081] According to the present invention, the organic solution is an alcohol solvent. There is no particular limitation on the specific type of alcohol solvent; for example, it can be one of methanol, ethanol, n-butanol, and isopropanol, preferably methanol or ethanol.

[0082] According to the present invention, in step S3, the concentration of the haloalkane in the organic solution is 1 wt%-20 wt%.

[0083] In this invention, when the concentration of haloalkanes in the organic solution in step S3 meets the above-mentioned range, it can ensure that the haloalkanes are in full contact with the acid and alkali resistant separation layer in the composite nanofiltration membrane, so that the tertiary amine groups remaining on the surface of the acid and alkali resistant separation layer can fully react with the haloalkanes and have high reaction efficiency. Ultimately, the surface of the obtained acid and alkali resistant positively charged composite nanofiltration membrane contains more quaternary ammonium salt groups.

[0084] Further, in step S3, the concentration of the haloalkane in the organic solution is 5wt%-10wt%.

[0085] According to the present invention, the concentration of the catalyst is 0.01 wt% to 5 wt%.

[0086] In this invention, when the concentration of the catalyst meets the above-mentioned range, the halogenated alkanes can react more fully with the tertiary amine groups on the surface of the composite nanofiltration membrane, introducing a specific amount of quaternary ammonium salt groups, without wasting the catalyst, thus improving economic efficiency.

[0087] Furthermore, the concentration of the catalyst is 0.1 wt% to 1 wt%.

[0088] According to the present invention, the weight ratio of the haloalkane to the catalyst is 2-50:1.

[0089] Furthermore, the weight ratio of the haloalkane to the catalyst is 5-30:1.

[0090] According to the present invention, the ratio of the volume of the organic solution to the membrane area of ​​the composite nanofiltration membrane is 0.1-1 mL / cm². 2 .

[0091] In this invention, by controlling the volume of the organic solution and the membrane area of ​​the composite nanofiltration membrane to meet the above-mentioned range, it is possible to ensure that the haloalkanes and the acid- and alkali-resistant separation layer in the composite nanofiltration membrane are in full contact, and to ensure that the haloalkanes can have a high reaction efficiency with the tertiary amine groups in the acid- and alkali-resistant separation layer. Ultimately, the surface of the obtained acid- and alkali-resistant positively charged composite nanofiltration membrane contains more quaternary ammonium salt groups.

[0092] Furthermore, the ratio of the volume of the organic solution to the membrane area of ​​the composite nanofiltration membrane is 0.3-0.5 mL / cm². 2 .

[0093] According to the present invention, the conditions for the third contact include: the third contact time is 1-120 min.

[0094] In this invention, when the contact time between the composite nanofiltration membrane and the organic solution containing haloalkanes and catalyst is controlled within the above-mentioned range, it can be ensured that the haloalkanes react fully with the tertiary amine groups remaining on the surface of the acid and alkali resistant separation layer, so that the surface of the obtained positively charged composite nanofiltration membrane contains more quaternary ammonium salt groups.

[0095] Furthermore, the conditions for the third contact include: the third contact time is 5-60 minutes.

[0096] In this invention, the temperature of the first contact, the second contact, and the third contact is not particularly limited, and can be, for example, room temperature (20-30°C).

[0097] According to the present invention, the drying conditions include: a drying temperature of 30-80°C and a drying time of 0.5-5 min.

[0098] Furthermore, the drying conditions include: a drying temperature of 40-60℃ and a drying time of 1-3 minutes.

[0099] A third aspect of the present invention provides an acid and alkali resistant positively charged composite nanofiltration membrane prepared by the aforementioned preparation method.

[0100] The fourth aspect of this invention provides an application of the aforementioned acid and alkali resistant positively charged composite nanofiltration membrane in the field of water treatment separation.

[0101] In this invention, the Fe of the acid and alkali resistant positively charged composite nanofiltration membrane 2+ Retention rate ≥90%, preferably ≥93%; H + The transmittance is 84-93%, preferably 88-91%, and the water flux is ≥20 LMH, preferably ≥22 LMH.

[0102] Other features and advantages of the present invention will be described in detail in the following detailed description section.

[0103] The present invention will be described in detail below through embodiments. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0104] In the following embodiments and comparative examples:

[0105] (1) The water flux of the acid and alkali resistant positively charged composite nanofiltration membrane was tested by the following method: The nanofiltration membrane was loaded into the membrane tank and pre-pressurized at 1.5 MPa for 1 hour. Then, the water permeation rate of the composite nanofiltration membrane was measured at a pressure of 2 MPa and a temperature of 25°C for a certain period of time, and the water flux was calculated by the following formula:

[0106] J = Q / (A·t), where J is the water flux, Q is the water permeation rate (L), and A is the effective membrane area of ​​the composite nanofiltration membrane (m²). 2 ), where t is time (h).

[0107] (2) Acid and alkali resistant positively charged composite nanofiltration membrane for divalent Fe 2+ Retention rate and H + The permeability was obtained by the following method: The composite nanofiltration membrane was loaded into the membrane tank. The original aqueous solution was a mixture of 0.2 wt% FeSO4 and 5% H2SO4. Pre-compression was performed at 1.5 MPa for 1 hour, followed by testing at 2 MPa and 25°C. The Fe content in the original aqueous solution and the permeate was measured after 1 hour. 2+ and H + The concentration of Fe. The membrane for divalent Fe. 2+ The retention rate is R = (C f -Cp ) / C f ×100%, where R is the retention rate, C f Fe in the original aqueous solution 2+ The concentration of C p To permeate Fe in the liquid 2+ The concentration of H. + The transmittance is T=C p ' / C f ×100%, of which C p 'For the permeation of H in the liquid + The concentration of C f 'For the original aqueous solution H + The concentration.

[0108] (3) The nitrogen atom content in the quaternary ammonium salt structure of the acid and alkali resistant positively charged composite nanofiltration membrane was determined by the following method:

[0109] Before measurement, the nanofiltration membrane was dried to constant weight in an oven, and the elemental composition of the nanofiltration membrane surface was determined using a SigmaProbe X-ray photoelectron spectroscopy system manufactured by Thermo VG, UK. The nitrogen atom content in the quaternary ammonium salt structure of the acid- and alkali-resistant separation layer was calculated using the following formula:

[0110]

[0111] Among them, A N + The peak area of ​​the nitrogen atom in the quaternary ammonium salt group in the XPS spectrum ( Figure 1 (peak area at the middle bond energy of 403 eV); A N The peak area of ​​nitrogen atoms in the separated layer in the XPS spectrum represents ( Figure 1 (The sum of the peak areas at 403 eV and 399 eV); S N This represents the atomic content (at.%) of nitrogen atoms in the quaternary ammonium salt groups of the acid- and alkali-resistant positively charged composite nanofiltration membrane.

[0112] (4) Average pore size test of acid and alkali resistant positively charged composite nanofiltration membrane: The average pore size was measured using the PEG solute transfer method, and the detailed steps are as follows:

[0113] (i) Test the retention rate of nanofiltration membranes for PEG of different molecular sizes;

[0114] (ii) Linearly fit the PEG size and the rejection rate in a log-probability coordinate system. The PEG size corresponding to a 50% rejection rate is the average pore size of the separation membrane.

[0115] (5) Surface Zeta potential test of acid and alkali resistant positively charged composite nanofiltration membrane: The test was performed using a Surpass electric analyzer (Anton Paar), the circulating solution was a dilute aqueous solution of KCl, and the pH of the test solution was 7.

[0116] (6) The contact angle of the acid and alkali resistant positively charged composite nanofiltration membrane was tested using a DSA100 surface contact angle meter manufactured by KRUSS GmbH, Germany, using the static drop method. Before the test, the sample was dried in a vacuum oven at 60℃ for 30 minutes to remove surface and internal moisture. Then, the dried membrane was attached to a flat glass slide with double-sided tape. During the test, the volume of each water droplet was 2μL. The water droplet was placed on the membrane surface for 3 seconds and the test was performed immediately. The final contact angle was determined by taking the average value after multiple measurements.

[0117] (7) The thickness of each layer in the acid and alkali resistant positively charged composite nanofiltration membrane is measured by a spiral micrometer.

[0118] Additionally, in the following embodiments and comparative examples:

[0119] Branched polyethyleneimine (weight average molecular weight 25000 g / mol), polyethylenepolyamine, 1,4-diaminopiperazine, 1,4-cyclohexanediamine, 1,4-phenylene diisocyanate, cyanuric chloride, 1,3-benzene disulfonyl chloride, bromoethane, chloropropane, iodomethane, bromohexane, iodohexane, 1,3-dibromopropane, and tetradecane were all purchased from Bailingwei Technology Co., Ltd. Other chemical reagents were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0120] The support layer is prepared using a phase transformation method, and the specific steps are as follows:

[0121] A certain amount of polysulfone (number average molecular weight of 80,000 g / mol) was dissolved in N,N-dimethylformamide to prepare a polysulfone solution with a concentration of 18 wt%. The solution was degassed at 25 °C for 120 min. Then, the polysulfone solution was coated onto a polyester nonwoven fabric (75 μm thick) using a doctor blade to obtain an initial film. The film was then immersed in water at 25 °C for 60 min, which allowed the polysulfone layer on the surface of the polyester nonwoven fabric to undergo phase transformation into a porous film. Finally, after three water washes, a bottom layer-porous support layer with a total thickness of 115 μm was obtained.

[0122] Example 1

[0123] (1) At 25℃, the above area of ​​400cm² 2The upper surface of the polysulfone support layer was first contacted with 50 mL of an aqueous solution containing 0.5 wt% polyethyleneimine, and the solution was drained after 60 s. Then, the upper surface of the support layer after the first contact was second contacted with 30 mL of an Isopar E solution containing 0.1 wt% 1,4-phenyl diisocyanate, and the solution was drained after 60 s. Finally, the membrane after the two contacts was placed in an oven and heated at 70 °C for 3 min to obtain the composite nanofiltration membrane A1.

[0124] (2) At 25°C, the obtained composite nanofiltration membrane A1 was immersed in 200 mL of a methanol solution containing 10 wt% bromoethane and 0.5 wt% potassium hydroxide (the weight ratio of bromoethane to potassium hydroxide was 20:1) for the third contact. After 5 min, it was taken out and dried at 70°C for 5 min to obtain acid and alkali resistant positively charged composite nanofiltration membrane N1.

[0125] from Figure 1 XPS spectra of nitrogen atoms on the surface of the acid and alkali resistant positively charged composite nanofiltration membrane show a new signal peak at 402.4 eV, corresponding to the signal of quaternary ammonium salt nitrogen atoms, proving that bromoethane reacts with the tertiary amine in the acid and alkali resistant separation layer to form a quaternary ammonium salt structure.

[0126] Example 2

[0127] (1) At 25℃, the above area of ​​400cm² 2 The upper surface of the polysulfone support layer was first contacted with 50 mL of an aqueous solution containing 0.5 wt% polyethylene polyamine, and the solution was drained after 60 s. Then, the upper surface of the support layer after the first contact was second contacted with 30 mL of an Isopar E solution containing 0.1 wt% 1,4-phenyl diisocyanate, and the solution was drained after 60 s. Finally, the membrane after the two contacts was placed in an oven and heated at 70 °C for 3 min to obtain the composite nanofiltration membrane A2.

[0128] (2) At 25°C, the obtained composite nanofiltration membrane A2 was immersed in 200 mL of a methanol solution containing 5 wt% chloropropane and 0.5 wt% potassium hydroxide (the weight ratio of chloropropane to potassium hydroxide was 10:1) for the third contact. After 5 min, it was taken out and dried at 70°C for 5 min to obtain acid and alkali resistant positively charged composite nanofiltration membrane N2.

[0129] Example 3

[0130] (1) At 25℃, the above area of ​​400cm² 2The upper surface of the polysulfone support layer was first contacted with 50 mL of an aqueous solution containing 0.5 wt% 1,4-diaminopiperazine, and drained after 60 s. Then, the upper surface of the support layer after the first contact was second contacted with 30 mL of an Isopar E solution containing 0.1 wt% 1,4-phenyl diisocyanate, and drained after 60 s. Finally, the membrane after the two contacts was placed in an oven and heated at 70 °C for 3 min to obtain the composite nanofiltration membrane A3.

[0131] (2) At 25°C, the obtained composite nanofiltration membrane A3 was immersed in 80 mL of a methanol solution containing 10 wt% iodomethane and 0.5 wt% potassium hydroxide (the weight ratio of iodomethane to potassium hydroxide was 20:1) for the third contact. After 5 min, it was taken out and dried at 70°C for 5 min to obtain acid and alkali resistant positively charged composite nanofiltration membrane N3.

[0132] Example 4

[0133] The preparation method is the same as in Example 1, except that in step (2), “200 mL of bromohexane containing 10 wt%” is used instead of “200 mL of bromoethane containing 10 wt%” (the weight ratio of bromohexane to potassium hydroxide is 20:1) to prepare acid and alkali resistant positively charged composite nanofiltration membrane N4.

[0134] Example 5

[0135] The preparation method is the same as in Example 1, except that in step (2), "200 mL of 10 wt% iodohexane" is used instead of "200 mL of 10 wt% bromoethane" (the weight ratio of iodohexane to potassium hydroxide is 20:1) to prepare acid and alkali resistant positively charged composite nanofiltration membrane N5.

[0136] Example 6

[0137] (1) At 25℃, the above area of ​​400cm² 2 The upper surface of the polysulfone support layer was first contacted with 50 mL of an aqueous solution containing 2 wt% polyethyleneimine, and the solution was drained after 60 s. Then, the upper surface of the support layer after the first contact was second contacted with 30 mL of an Isopar E solution containing 0.05 wt% cyanuric chloride, and the solution was drained after 60 s. Finally, the membrane after the two contacts was placed in an oven and heated at 70 °C for 3 min to obtain the composite nanofiltration membrane A6.

[0138] (2) At 25°C, the obtained composite nanofiltration membrane A6 was immersed in 200 mL of methanol solution containing 10 wt% bromoethane and 0.5 wt% potassium hydroxide (the weight ratio of bromoethane to potassium hydroxide was 20:1) for the third contact. After 5 min, it was taken out and dried at 70°C for 5 min to obtain acid and alkali resistant positively charged composite nanofiltration membrane N6.

[0139] Example 7

[0140] (1) At 25℃, the above area of ​​400cm² 2 The upper surface of the polysulfone support layer was first contacted with 50 mL of an aqueous solution containing 2 wt% polyethyleneimine, and the solution was drained after 60 s. Then, the upper surface of the support layer after the first contact was second contacted with 30 mL of an Isopar E solution containing 0.2 wt% 1,3-benzenedisulfonyl chloride, and the solution was drained after 60 s. Finally, the membrane after the two contacts was placed in an oven and heated at 70 °C for 3 min to obtain the composite nanofiltration membrane A7.

[0141] (2) At 25°C, the obtained composite nanofiltration membrane A7 was immersed in 200 mL of methanol solution containing 10 wt% bromoethane and 0.5 wt% potassium hydroxide (the weight ratio of bromoethane to potassium hydroxide was 20:1) for the third contact. After 5 min, it was taken out and dried at 70°C for 5 min to obtain acid and alkali resistant positively charged composite nanofiltration membrane N7.

[0142] Example 8

[0143] The preparation method is the same as in Example 1, except that in step (2), "200 mL of a mixed solution containing 5 wt% bromoethane and 5 wt% 1,3-dibromopropane" is used instead of "200 mL of bromoethane containing 10 wt%" (the ratio of the total weight of bromoethane and 1,3-dibromopropane to the weight of potassium hydroxide is 20:1), to obtain the acid and alkali resistant positively charged composite nanofiltration membrane N8.

[0144] Example 9

[0145] The preparation method is the same as in Example 1, except that in step (2), "200 mL of bromoethane containing 15 wt%" is used instead of "200 mL of bromoethane containing 10 wt%" to prepare acid and alkali resistant positively charged composite nanofiltration membrane N9.

[0146] Example 10

[0147] The preparation method is the same as in Example 1, except that in step (2), "200 mL of bromoethane containing 25 wt%" is used instead of "200 mL of bromoethane containing 10 wt%" to prepare acid and alkali resistant positively charged composite nanofiltration membrane N10.

[0148] Example 11

[0149] The preparation method is the same as in Example 1, except that in step (2), “take out after 5 minutes” is replaced by “take out after 0.5 minutes” to obtain acid and alkali resistant positively charged composite nanofiltration membrane N11.

[0150] Example 12

[0151] The preparation method is the same as that in Example 1, except that in step (2), “80 mL of potassium hydroxide containing 0.01 wt%” is used instead of “80 mL of potassium hydroxide containing 10 wt%” to prepare acid and alkali resistant positively charged composite nanofiltration membrane N12.

[0152] Example 13

[0153] The preparation method is the same as that in Example 1, except that in step (2), “80 mL of potassium hydroxide containing 0.005 wt%” is used instead of “80 mL of potassium hydroxide containing 10 wt%” to prepare acid and alkali resistant positively charged composite nanofiltration membrane N13.

[0154] Example 14

[0155] The preparation method is the same as that in Example 1, except that in step (1), “50 mL of 0.5 wt% 1,4-cyclohexanediamine” is used instead of “50 mL of 0.5 wt% polyethyleneimine” to prepare acid and alkali resistant positively charged composite nanofiltration membrane N14.

[0156] Example 15

[0157] The preparation method is the same as in Example 1, except that in step (2), “200 mL of bromotetradecane containing 10 wt%” is used instead of “200 mL of bromoethane containing 10 wt%” to prepare acid and alkali resistant positively charged composite nanofiltration membrane N15.

[0158] Comparative Example 1

[0159] At 25°C, the above area of ​​400 cm² 2 The upper surface of the polysulfone support layer was first contacted with 50 mL of an aqueous solution containing 0.5 wt% polyethyleneimine, and the solution was drained after 60 s. Then, the upper surface of the support layer after the first contact was second contacted with 30 mL of an Isopar E solution containing 0.1 wt% 1,4-phenyl diisocyanate, and the solution was drained after 60 s. Finally, the membrane after the two contacts was placed in an oven and heated at 70 °C for 3 min to obtain composite membrane D1.

[0160] Comparative Example 2

[0161] At 25°C, the above area of ​​400 cm² 2 The upper surface of the polysulfone support layer was first contacted with 50 mL of an aqueous solution containing 0.5 wt% polyethylene polyamine, and the solution was drained after 60 s. Then, the upper surface of the support layer after the first contact was second contacted with 30 mL of an Isopar E solution containing 0.1 wt% 1,4-phenyl diisocyanate, and the solution was drained after 60 s. Finally, the membrane after the two contacts was placed in an oven and heated at 70 °C for 3 min to obtain composite membrane D2.

[0162] Comparative Example 3

[0163] At 25°C, the above area of ​​400 cm² 2 The upper surface of the polysulfone support layer was first contacted with 50 mL of an aqueous solution containing 2 wt% polyethyleneimine, and the solution was drained after 60 s. Then, the upper surface of the support layer after the first contact was second contacted with 30 mL of an Isopar E solution containing 0.05 wt% cyanuric chloride, and the solution was drained after 60 s. Finally, the membrane after the two contacts was placed in an oven and heated at 70 °C for 3 min to obtain composite membrane D3.

[0164] Comparative Example 4

[0165] At 25°C, the above area of ​​400 cm² 2 The upper surface of the polysulfone support layer was first contacted with 50 mL of an aqueous solution containing 2 wt% polyethyleneimine at 25 °C for 60 s, and then drained. The upper surface of the support layer after the first contact was then contacted with 30 mL of an Isopar E solution containing 0.2 wt% 1,3-benzenedisulfonyl chloride for 60 s, and then drained. Finally, the membrane after the two contacts was placed in an oven and heated at 70 °C for 3 min to obtain the composite membrane D4.

[0166] The thickness, surface Zeta potential, average pore size, nitrogen atom content in the quaternary ammonium salt structure of the acid and alkali resistant positively charged composite nanofiltration membrane of the embodiment and the composite membrane of the comparative example, as well as the contact angle, are shown in Table 1.

[0167] Table 1

[0168]

[0169] The separation layer refers to an acid and alkali resistant separation layer;

[0170] a This refers to the nitrogen atom content in the quaternary ammonium salt structure of the acid and alkali resistant separation layer.

[0171] The acid- and alkali-resistant positively charged composite nanofiltration membrane of the embodiment and the composite membrane of the comparative example were loaded into a membrane tank and pre-pressurized at 1.5 MPa for 1 hour. Subsequently, under conditions of 2 MPa pressure and 25°C, the water flux and Fe content of the acid- and alkali-resistant positively charged composite nanofiltration membrane of the embodiment and the composite membrane of the comparative example were measured. 2+ The rejection rate was tested; and the acid and alkali resistant positively charged composite nanofiltration membrane of the example and the composite membrane of the comparative example were then immersed in a 5 wt% HCl aqueous solution for 7 days, pre-pressurized at 1.5 MPa for 1 hour, and then the water flux and Fe were tested at a pressure of 2 MPa and a temperature of 25°C. 2+ The retention rate was tested, and the results are shown in Table 2.

[0172] Table 2

[0173]

[0174] As shown in Table 2, under the action of an alkaline catalyst, surface post-treatment of the composite nanofiltration membrane with haloalkanes reacts with the tertiary amine groups in the acid- and alkali-resistant separation layer structure, converting them into positively charged quaternary ammonium salt groups. The increased positive charge on the membrane surface enhances the reaction with divalent Fe. 2+ The electrostatic repulsion between them significantly improved the membrane's resistance to divalent Fe. 2+ The retention rate.

[0175] Comparing Examples 6 and 7 reveals that different types of multi-polar monomers affect the initial rejection rate and initial water flux. Therefore, in this invention, it is beneficial to conduct longitudinal comparisons of acid- and alkali-resistant positively charged composite nanofiltration membranes prepared with the same multi-polar monomers. However, the acid- and alkali-resistant positively charged composite nanofiltration membranes prepared according to the examples that meet the requirements of multi-polar monomer types show better performance in comparative studies.

[0176] Comparing Examples 1 and 9 with Example 10, it can be seen that the amount of haloalkanes can affect the degree of reaction between haloalkanes and the tertiary amine groups remaining on the acid and alkali resistant separation layer, and ultimately affect the nitrogen content in the quaternary ammonium salt structure. When the amount of haloalkanes is excessive, the rejection rate is basically constant and the growth rate is small, but the water flux will decrease significantly.

[0177] Comparing Example 1 with Example 11, it can be seen that when the third contact time is too short, the reaction cannot proceed fully, and both the retention rate and water flux decrease.

[0178] Comparing Examples 1, 12 and 13, it can be seen that the amount of catalyst can promote a more complete reaction between haloalkanes and tertiary amine groups on the surface of the composite nanofiltration membrane, thereby improving the rejection rate and water flux of the acid and alkali resistant positively charged composite nanofiltration membrane.

[0179] Comparing Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that when no haloalkane is added, the composite nanofiltration membrane cannot achieve good rejection rate and water flux, nor does it have any use value in acid / alkali environments.

[0180] After treatment with 5 wt% HCl for 7 days, the acid- and alkali-resistant positively charged composite nanofiltration membrane showed improved performance against Fe. 2+ The changes in rejection rate and water flux of the membrane were not significant, indicating that the acid / alkali resistant positively charged composite nanofiltration membrane has good acid / alkali resistance. Therefore, this positively charged composite membrane can achieve the concentration of divalent and high-valent ions and high H+ ions under acidic conditions. + Transparency, high H + The permeability indicates that acid can pass through the acid- and alkali-resistant positively charged composite nanofiltration membrane, allowing for the recycling and reuse of acid solutions.

[0181] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An acid and alkali resistant, positively charged composite nanofiltration membrane, characterized in that, The acid and alkali resistant positively charged composite nanofiltration membrane comprises a bottom layer, a porous support layer, and an acid and alkali resistant separation layer stacked sequentially. The acid and alkali resistant separation layer contains a quaternary ammonium salt structure; The acid and alkali resistant separation layer is selected from at least one of the following: polytriazine amine separation layer, poly(triazine amine-urea) separation layer, poly(sulfonamide-urea) separation layer, poly(triazine amine-sulfonamide) separation layer, and poly(triazine amine-sulfonamide-urea) separation layer.

2. The acid and alkali resistant positively charged composite nanofiltration membrane according to claim 1, wherein, The quaternary ammonium salt structure includes the structure shown in Formula I and / or the structure shown in Formula II. Formula I; Formula II; X is a halogen; n is an integer from 0 to 10; m is an integer from 2 to 10.

3. The acid and alkali resistant positively charged composite nanofiltration membrane according to claim 1 or 2, wherein, X is Cl, Br, or I; And / or, n is an integer from 0 to 7; m is an integer from 2 to 8.

4. The acid and alkali resistant positively charged composite nanofiltration membrane according to claim 1 or 2, wherein, The nitrogen atom content in the quaternary ammonium salt groups of the acid and alkali resistant positively charged composite nanofiltration membrane is 0.5-5 at.%.

5. The acid and alkali resistant positively charged composite nanofiltration membrane according to claim 4, wherein, The nitrogen atom content in the quaternary ammonium salt groups of the acid and alkali resistant positively charged composite nanofiltration membrane is 2-5 at.%.

6. The acid- and alkali-resistant positively charged composite nanofiltration membrane according to claim 1 or 2, wherein, The surface zeta potential of the acid and alkali resistant positively charged composite nanofiltration membrane is 0-30mV.

7. The acid and alkali resistant positively charged composite nanofiltration membrane according to claim 6, wherein, The surface zeta potential of the acid and alkali resistant positively charged composite nanofiltration membrane is 5-20mV.

8. The acid- and alkali-resistant positively charged composite nanofiltration membrane according to claim 1 or 2, wherein, The average pore size of the acid and alkali resistant positively charged composite nanofiltration membrane is 0.1-0.5 nm.

9. The acid and alkali resistant positively charged composite nanofiltration membrane according to claim 8, wherein, The average pore size of the acid and alkali resistant positively charged composite nanofiltration membrane is 0.15-0.3 nm.

10. The acid- and alkali-resistant positively charged composite nanofiltration membrane according to claim 1 or 2, wherein, The contact angle of the acid and alkali resistant positively charged composite nanofiltration membrane is 20-80°.

11. The acid and alkali resistant positively charged composite nanofiltration membrane according to claim 10, wherein, The contact angle of the acid and alkali resistant positively charged composite nanofiltration membrane is 30°-60°.

12. The acid- and alkali-resistant positively charged composite nanofiltration membrane according to claim 1 or 2, wherein, The thickness of the bottom layer is 30-150 μm; And / or, the thickness of the porous support layer is 10-100 μm; And / or, the thickness of the acid and alkali resistant separation layer is 10-500 nm.

13. The acid and alkali resistant positively charged composite nanofiltration membrane according to claim 12, wherein, The thickness of the bottom layer is 50-120 μm; And / or, the thickness of the porous support layer is 30-60 μm; And / or, the thickness of the acid and alkali resistant separation layer is 50-300 nm.

14. A method for preparing an acid- and alkali-resistant positively charged composite nanofiltration membrane according to any one of claims 1-13, characterized in that, The preparation method includes the following steps: S1. Prepare a porous support layer on the bottom layer; S2. The membrane layer obtained in step S1 is first contacted with an aqueous phase containing a polyamine containing tertiary amine groups, and then second contacted with an organic phase containing multiple polar monomers. After heat treatment, a composite nanofiltration membrane containing an acid and alkali resistant separation layer is obtained. S3. The composite nanofiltration membrane is brought into a third contact with an organic solution containing haloalkanes and a catalyst, and then dried to obtain the acid and alkali resistant positively charged composite nanofiltration membrane.

15. The preparation method according to claim 14, wherein, In step S2, the polyamine containing a tertiary amine group is selected from at least one of polyethyleneimine, 1-aminopiperazine, 1,4-piperazine diethylamine, and 1,4-diaminopropylpiperazine; And / or, in the aqueous phase of the polyamine containing tertiary amine groups, the concentration of the polyamine containing tertiary amine groups is 0.1 wt%-10 wt%; And / or, the multi-polar monomer is selected from at least one of polyisocyanates, triazine compounds containing at least two C-Cl bonds, and polysulfonyl chlorides; And / or, the polyisocyanate is selected from at least one of isophthalic diisocyanate, isophorone diisocyanate, 1,6-hexanediisocyanate, toluene-2,6-diisocyanate, 1,4-phenyl diisocyanate, toluene-2,4-diisocyanate, 4,4'-methylenebis(phenyl isocyanate), 1,3-phenyl diisocyanate, 3,3'-dichloro-4,4'-diisocyanate biphenyl, dicyclohexylmethane-4,4'-diisocyanate, trimethylhexamethylene diisocyanate, L-lysine-ethyl ester-diisocyanate, 1,4-cyclohexyl diisocyanate, and 4-chloro-6-methyl isophthalic diisocyanate.

16. The preparation method according to claim 15, wherein, In step S2, the polyamine containing tertiary amine groups is polyethyleneimine and / or polyethylene polyamine; And / or, in the aqueous phase of the polyamine containing tertiary amine groups, the concentration of the polyamine containing tertiary amine groups is 0.5wt%-2.5wt%; And / or, the polyisocyanate is selected from 1,4-phenyl diisocyanate and / or 1,3-phenyl diisocyanate.

17. The preparation method according to claim 14 or 15, wherein, The triazine compound containing at least two C-Cl bonds is selected from at least one of cyanuric chloride, 2,4-dichloro-1,3,5-triazine, 2,5-dichloro-1,3,5-triazine, and 2,4-dichloro-6-phenyl-1,3,5-triazine; And / or, the polysulfonyl chloride is selected from 1,3-benzenedisulfonyl chloride, 1,2-benzenedisulfonyl chloride, 1,4-benzenedisulfonyl chloride, 2,4-disulfonyl chloride, 4,4'-disulfonyl chloride, 4,5-dichloro-1,3-benzenedisulfonyl chloride, 2,6-naphthalenedisulfonyl chloride, and 1,3-naphthalenedisulfonyl chloride. At least one of 2,7-naphthalene disulfonyl chloride, 1,3,5-benzenetrisulfonyl chloride and 1,3,6-naphthalene trisulfonyl chloride; And / or, in the organic phase, the concentration of the multi-polar monomer is 0.01wt%-2wt%; And / or, the amount of the aqueous phase containing the polyamine containing the tertiary amine group and the organic phase containing the multi-polar monomer are such that the weight ratio of the polyamine containing the tertiary amine group to the multi-polar monomer is 2-200:

1. And / or, the duration of the first contact is 5-100 seconds; And / or, the duration of the second contact is 10-200 s; And / or, the conditions for the heat treatment include: a heat treatment temperature of 40-150℃ and a heat treatment time of 0.5-10min.

18. The preparation method according to claim 17, wherein, The triazine compound containing at least two C-Cl bonds is cyanuric chloride; And / or, the polysulfonyl chloride is 1,3-benzenedisulfonyl chloride; And / or, in the organic phase, the concentration of the multi-polar monomer is 0.05-1 wt%; And / or, the amount of the aqueous phase containing the tertiary amine group and the organic phase containing the multi-polar monomer is such that the weight ratio of the polyamine containing the tertiary amine group to the multi-polar monomer is 5-80:

1. And / or, the duration of the first contact is 10-60 seconds; And / or, the duration of the second contact is 20-120 seconds; And / or, the conditions for the heat treatment include: a heat treatment temperature of 50-120°C and a heat treatment time of 1-5 min.

19. The preparation method according to claim 14 or 15, wherein, In step S3, the haloalkane is selected from the haloalkane shown in Formula III and / or the haloalkane shown in Formula IV; Formula III, Formula IV; X1, X2, and X3 are each an independent halogen; n is an integer from 0 to 10; m is an integer from 2 to 10.

20. The preparation method according to claim 19, wherein, X1, X2, and X3 are each independently Cl, Br, or I; And / or, n is an integer from 0 to 7; m is an integer from 2 to 8.

21. The preparation method according to claim 14 or 15, wherein, The halogenated alkanes are selected from iodomethane, iodoethane, iodopropane, iodobutane, iodopentane, iodohexane, iodoheptane, iodooctane, iodononane, iododecane, iodocyclopropane, iodocyclobutane, iodocyclopentane, iodocycloheptane, iodocyclooctane, 1,2-diiodoethane, 1,3-diiodopropane, 1,4-diiodobutane, 1,5-diiopentane, 1,6-diiodohexane, 1,7-diioheptane, 1,8-diiooctane, chloromethane, chloroethane, chloropropane, chlorobutane, chloropentane, chlorohexane, chloroheptane, chlorooctane, chlorononane, chlorodecane, chlorocyclopropane, chlorocyclobutane, chlorocyclopentane, chlorocycloheptane, chloro... At least one of the following: cyclooctane, 1,2-dichloroethane, 1,3-dichloropropane, 1,4-dichlorobutane, 1,5-dichloropentane, 1,6-dichlorohexane, 1,7-dichloroheptane, 1,8-dichlorooctane, bromomethane, bromoethane, bromopropane, bromobutane, bromopentane, bromohexane, bromoheptane, bromooctane, bromononane, bromodecane, bromocyclopropane, bromocyclobutane, bromocyclopentane, bromocycloheptane, bromocyclooctane, 1,2-dibromoethane, 1,3-dibromopropane, 1,4-dibromobutane, 1,5-dibromopentane, 1,6-dibromohexane, 1,7-dibromoheptane, and 1,8-dibromooctane; And / or, the catalyst is selected from at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, potassium bicarbonate, potassium tert-butoxide, and sodium tert-butoxide; And / or, the organic solution is an alcohol solvent.

22. The preparation method according to claim 21, wherein, The haloalkane is selected from at least one of bromoethane, chloropropane and iodomethane; And / or, the catalyst is selected from sodium hydroxide and / or sodium tert-butoxide.

23. The preparation method according to claim 14 or 15, wherein, In step S3, the concentration of the haloalkane in the organic solution is 1wt%-20wt%. And / or, in the organic solution, the concentration of the catalyst is 0.01wt%-5wt%; And / or, the weight ratio of the haloalkane to the catalyst is 2-50:1; And / or, the ratio of the volume of the organic solution to the membrane area of ​​the composite nanofiltration membrane is 0.1-1 mL / cm². 2 ; And / or, the conditions for the third contact include: the third contact time is 1-120 min; And / or, the drying conditions include: a drying temperature of 30-80℃ and a drying time of 0.5-5 min.

24. The preparation method according to claim 23, wherein, In step S3, the concentration of the haloalkane in the organic solution is 5-10 wt%. And / or, in the organic solution, the concentration of the catalyst is 0.1 wt%-1 wt%; And / or, the weight ratio of the haloalkane to the catalyst is 5-30:1; And / or, the ratio of the volume of the organic solution to the membrane area of ​​the composite nanofiltration membrane is 0.3-0.5 mL / cm². 2 ; And / or, the conditions for the third contact include: the third contact time is 5-60 min; And / or, the drying conditions include: a drying temperature of 40-60°C and a drying time of 1-3 minutes.

25. An acid- and alkali-resistant positively charged composite nanofiltration membrane prepared by the preparation method according to any one of claims 14-24.

26. The application of the acid and alkali resistant positively charged composite nanofiltration membrane according to any one of claims 1-13 and 25 in the field of water treatment.

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