Preparation methods of acid and alkali resistant positively charged nanofiltration membranes, their applications

Abstract

This invention relates to the field of membranes, and discloses a method for preparing an acid- and alkali-resistant positively charged nanofiltration membrane, the acid- and alkali-resistant positively charged nanofiltration membrane, and its applications. The method includes the following steps: S1, sequentially preparing a porous support layer and an acid- and alkali-resistant separation layer on a substrate to obtain a composite membrane; S2, contacting the composite membrane with an aqueous solution containing a catalyst, a quaternary ammonium halide, and / or a quaternary phosphate halide, and drying it to obtain an acid- and alkali-resistant positively charged nanofiltration membrane. This acid- and alkali-resistant positively charged nanofiltration membrane has good acid and alkali resistance, and can simultaneously achieve good retention of divalent and high-valent heavy metal ions and high water flux.

Description

Technical Field

[0001] This invention relates to the field of nanofiltration membranes, specifically to a method for preparing an acid and alkali resistant positively charged nanofiltration membrane, the acid and alkali resistant positively charged nanofiltration membrane, and its applications. Background Technology

[0002] Electroplating is a process that uses electrochemical technology to control the surface properties of metals and non-metals to obtain ideal surface corrosion resistance, conductivity, and decorative effects. Electroplating is widely used in my country, generating a large amount of wastewater annually, accounting for approximately 20% of total industrial wastewater discharge. Electroplating wastewater contains a large number of toxic and harmful substances, with wastewater containing heavy metal ions such as copper, nickel, chromium, and zinc accounting for about 40%. Furthermore, the acid pickling and activation processes commonly used in electroplating make this wastewater acidic. Comprehensive treatment of acidic electroplating wastewater is a requirement for environmental protection and an effective means of resource recycling of industrial wastewater to reduce costs and increase efficiency. Currently, the effective recovery of heavy metal ions from electroplating wastewater has become a key issue for the sustainable development of the electroplating industry.

[0003] Conventional chemical precipitation methods suffer from problems such as large amounts of toxic sludge and low recovery rates of heavy metal resources. In contrast, membrane separation technology has advantages such as high separation efficiency, no secondary pollution, low energy consumption, and convenient operation, and has been widely used to recover metal ions such as copper, nickel, chromium, and zinc from electroplating wastewater. Among these, nanofiltration separation shows promising application prospects. It is generally believed that nanofiltration separation performance is the result of the combined effects of size sieving and the Donnan effect. Besides the density of the membrane itself, the nanofiltration process exhibits significant charge selectivity. Polyamide membrane composite nanofiltration membranes are the most widely used commercial nanofiltration membranes. The acyl chloride groups on the membrane surface hydrolyze to form a large number of carboxyl groups, making the membrane surface negatively charged. Due to the Donnan effect, the membrane has a low removal rate of high-valence cations, resulting in low recovery rates of metal ions such as copper, nickel, chromium, and zinc.

[0004] Besides the charged properties of the membrane, the treatment of acidic electroplating wastewater also places higher demands on the membrane's acid resistance. Under acidic conditions, the C=O bonds in the structure of conventional polyamide nanofiltration membranes are easily affected by H+. + Nucleophilic electron attack causes hydrolysis of the amide bonds, damaging the membrane separation layer structure and reducing retention performance. To ensure the structural stability of the nanofiltration membrane, the feed water pH needs to be adjusted, which not only increases the amount of reagents used but also makes the treatment process more complex.

[0005] Therefore, there is an urgent need to develop a positively charged nanofiltration membrane that is simple to prepare and has excellent acid resistance, in order to enhance the Donnan effect in the nanofiltration separation process and achieve effective recovery of high-valence heavy metal cations. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of poor acid and alkali resistance and low retention rate of divalent and high-valence metal ions in nanofiltration membranes prepared by existing technologies. This invention provides a method for preparing acid and alkali resistant positively charged nanofiltration membranes, the acid and alkali resistant positively charged nanofiltration membranes, and their applications. By controlling specific raw materials, dosages, and reaction conditions, this invention enables the prepared nanofiltration membrane to contain chemically inert groups and be grafted with specific quaternary ammonium salt groups and / or quaternary phosphate salt groups. This nanofiltration membrane maintains high water flux while exhibiting excellent retention of divalent and high-valence metal ions, and can be applied to acid / alkali environments, including the treatment of acidic electroplating wastewater.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for preparing an acid- and alkali-resistant, positively charged nanofiltration membrane, wherein the method includes the following steps:

[0008] S1. A porous support layer and an acid- and alkali-resistant separation layer are sequentially prepared on the bottom layer to obtain a composite membrane;

[0009] S2. The composite membrane is contacted with an aqueous solution containing a catalyst, a quaternary ammonium halide, and / or a quaternary phosphorus halide, and then dried to obtain the acid- and alkali-resistant positively charged nanofiltration membrane.

[0010] A second aspect of the present invention provides an acid- and alkali-resistant positively charged nanofiltration membrane prepared by the aforementioned preparation method.

[0011] A third aspect of the present invention provides an application of the aforementioned acid and alkali resistant positively charged nanofiltration membrane in the field of water treatment.

[0012] Through the above technical solution, the technical solution provided by the present invention achieves the following beneficial effects:

[0013] The acid and alkali resistant positively charged nanofiltration membrane prepared by the method provided by this invention contains chemically inert groups and has a high hydrogen bond density, which makes the nanofiltration membrane have good acid and alkali resistance. Then, specific quaternary ammonium salt groups and / or quaternary phosphate salt groups are grafted, which significantly increases the positive charge density on the surface of the nanofiltration membrane. The repulsion effect between positive charges improves the retention effect of the nanofiltration membrane on divalent and high-valent heavy metal ions, while maintaining good water flux. Attached Figure Description

[0014] Figure 1 This is the XPS phosphorus elemental fine spectrum of the surface of the acid and alkali resistant composite nanofiltration membrane prepared in Example 1. Detailed Implementation

[0015] 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.

[0016] The first aspect of this invention provides a method for preparing an acid- and alkali-resistant, positively charged nanofiltration membrane, wherein the method includes the following steps:

[0017] S1. A porous support layer and an acid- and alkali-resistant separation layer are sequentially prepared on the bottom layer to obtain a composite membrane;

[0018] S2. The composite membrane is contacted with an aqueous solution containing a catalyst, a quaternary ammonium halide, and / or a quaternary phosphorus halide, and then dried to obtain the acid- and alkali-resistant positively charged nanofiltration membrane.

[0019] In this invention, the acid and alkali resistant positively charged nanofiltration membrane contains chemically inert groups that can be used in acidic / alkaline environments, and is grafted with specific quaternary ammonium salt groups and / or quaternary phosphate salt groups, so that the nanofiltration membrane can maintain a high water flux while having a high rejection rate for divalent and high-valence metal ions.

[0020] In this invention, the ratio of the amount of the aqueous solution containing the catalyst, the quaternary ammonium halide, and / or the quaternary phosphorus halide to the membrane area of ​​the composite membrane is 0.1-1 g / cm². 2 Preferably, it is 0.3-0.5 g / cm³. 2 .

[0021] 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.

[0022] In this invention, the bottom layer is a nonwoven fabric, preferably polyester and / or polyethylene.

[0023] In this invention, the porous support layer material is selected from at least one of polyethersulfone, polysulfone, polyaromatic ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride, and polyaryletherketone.

[0024] In this 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, preferably at least one of polyurea separation layer, polytriazine amine separation layer and polysulfonamide separation layer.

[0025] Furthermore, the acid and alkali resistant separation layer is generated by interfacial polymerization of polyamines and polypolar monomers.

[0026] In this invention, the interfacial polymerization process includes first contacting the surface of the porous support layer with an aqueous phase containing polyamines, then making a second contact with an organic phase containing multiple polar monomers, followed by heat treatment.

[0027] The reaction conditions for the first contact, the second contact, and the heat treatment described above are conventional conditions in the art. Preferably, the first contact time is 5-100s, more preferably 10-60s; the first contact temperature is 15-50℃, more preferably 20-40℃; the second contact time is 10-200s, more preferably 20-120s; the second contact temperature is 15-40℃, more preferably 20-30℃; and the heat treatment conditions include: a heat treatment time of 0.5-10min, more preferably 1-5min; and a heat treatment temperature of 40-150℃, more preferably 50-120℃.

[0028] 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.

[0029] The reaction of polyamines with at least one of polyisocyanates, triazine compounds containing at least two C-Cl bonds, and polysulfonyl chlorides introduces groups with strong conjugation effects and good chemical inertness into nanofiltration membranes. The resulting acid and alkali resistant separation layer contains polymers that have good structural stability in both acidic and alkaline environments, which greatly improves the acid and alkali resistance of nanofiltration membranes and makes them particularly suitable for acidic environments.

[0030] According to the present invention, the polyamine is at least one selected from polyethyleneimine, polyethyleneamine, triethylenetetramine, tetraethylenepentamine, diethylenetriamine, polyethylene polyamine, piperazine, m-phenylenediamine, and p-phenylenediamine; preferably polyethyleneimine and / or polyethylene polyamine.

[0031] 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 1,4-phenyl diisocyanate and / or 1,3-phenyl diisocyanate.

[0032] 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.

[0033] 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.

[0034] According to the present invention, the weight ratio of the polyamine in the aqueous phase to the multi-polar monomer in the organic phase is 2-200:1, preferably 5-80:1.

[0035] According to the present invention, the concentration of polyamine in the aqueous phase is 0.1wt%-10wt%, preferably 0.5wt%-2.5wt%.

[0036] According to the present invention, the concentration of the multi-polar monomer in the organic phase is 0.01wt%-2wt%, preferably 0.05wt%-1wt%.

[0037] In this invention, the ratio of the amount of aqueous phase containing polyamines to the membrane area of ​​the porous support layer is 0.05-0.5 g / cm³. 2 Preferably, it is 0.1-0.3 g / cm³. 2 .

[0038] In this invention, the ratio of the amount of the organic phase containing multiple polar monomers to the membrane area of ​​the porous support layer is 0.03-0.3 g / cm³. 2 The preferred concentration is 0.05-0.2 g / cm³. 2 .

[0039] According to the present invention, the haloquaternary ammonium salt has the structure shown in Formula I; the haloquaternary phosphate salt has the structure shown in Formula II;

[0040]

[0041] Wherein, R1' is a substituted or unsubstituted alkylene group of C1-C9; R2', R3', and R4' are each independently selected from alkyl or phenyl groups of C1-C3; R5' is an alkylene group of C1-C6, a phenyl group, or an aralkyl group of C7-C10; R6', R7', and R8' are each independently selected from phenyl groups or aralkyl groups of C7-C10.

[0042] X and X1 are halogens, each independently.

[0043] Furthermore, R1' is a substituted or unsubstituted alkylene group of C1-C6; R2', R3', and R4' are each independently CH3; R5' is an alkylene group of C1-C3, a phenyl group, or an aralkyl group of C8-C10; and R6', R7', and R8' are each independently phenyl.

[0044] Furthermore, R1' is a substituted alkylene group of C1-C3, wherein the substituent is a hydroxyl or carboxyl group, preferably a hydroxyl group.

[0045] Furthermore, X is Cl, Br, or I.

[0046] Furthermore, X1 can be F, Cl, Br, or I.

[0047] In one specific embodiment of the present invention, in formula I, R1' is ethylene, Propylene, butylene, pentylene, or hexylene; R2', R3', R4' are methyl, ethyl, or phenyl; X is Cl, Br, or I.

[0048] In one specific embodiment of the present invention, in formula II, R5' is propylidene, ethylidene, methylene, or... R6', R7', and R8' are phenyl groups; X is Cl, Br, or I.

[0049] According to the present invention, in step S2, the contact method is a common contact method in the art, preferably immersion.

[0050] According to the present invention, the contact time is 10s-10min; the contact temperature is 20-80℃.

[0051] In this invention, when the contact conditions are controlled within the above range, it is possible to ensure that the haloquaternary ammonium salt and / or haloquaternary phosphate salt react fully on the membrane surface, thereby increasing the positive charge density on the membrane surface. This allows the nanofiltration membrane to maintain a high water flux while having good retention capacity for divalent and high-valence metal ions. Furthermore, the process is compatible with existing industrial continuous production processes and is suitable for scale-up preparation.

[0052] Furthermore, the contact time is 20 seconds to 1 minute; the contact temperature is 30 to 50 degrees Celsius.

[0053] According to the present invention, the drying time is 0.5-10 min; the drying temperature is 40-80℃.

[0054] In this invention, when the drying conditions meet the above-mentioned range, the grafting reaction of haloquaternary ammonium salts and / or haloquaternary phosphate salts on the surface of the acid and alkali resistant separation layer can be further promoted, and the positive charge density on the membrane surface can be further increased. This further enhances the nanofiltration membrane's ability to retain divalent and high-valence metal ions and ensures a high water flux. At the same time, this process is compatible with existing industrial continuous production processes and can be scaled up for mass production.

[0055] Furthermore, the drying time is 3-5 minutes; the drying temperature is 50-70°C.

[0056] According to the present invention, in step S2, the catalyst is selected from at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, potassium bicarbonate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate; preferably potassium hydroxide.

[0057] According to the present invention, the haloquaternary ammonium salt is selected from at least one of 2-chloroethyltrimethylammonium chloride, 2-chloroethyltriethylammonium chloride, 2-chloroethyltriphenylammonium chloride, 3-chloro-2-hydroxypropyltrimethylammonium chloride, 3-chloropropyltrimethylammonium chloride, 4-chlorobutyltrimethylammonium chloride, 5-chloropentyltrimethylammonium chloride, 6-chlorohexyltrimethylammonium chloride, 2-bromoethyltrimethylammonium bromide, 3-bromopropyltrimethylammonium bromide, 4-bromobutyltrimethylammonium bromide, 5-bromopentyltrimethylammonium bromide, 6-bromohexyltrimethylammonium bromide, iodomethyltrimethylammonium iodide, 2-iodoethyltrimethylammonium iodide, 3-iodopropyltrimethylammonium iodide, 4-iodobutyltrimethylammonium iodide, 5-iodopentyltrimethylammonium iodide, and 6-iodohexyltrimethylammonium iodide; preferably 2-chloroethyltrimethylammonium chloride and / or 3-bromopropyltrimethylammonium bromide.

[0058] According to the present invention, the haloquaternary phosphorus salt is selected from 3-bromopropyltriphenylphosphine bromide, 2-bromoethyltriphenylphosphine bromide, 1-bromoethyltriphenylphosphine bromide, bromomethyltriphenylphosphine bromide, 3-chloropropyltriphenylphosphine chloride, 2-chloroethyltriphenylphosphine chloride, 1-chloroethyltriphenylphosphine chloride, chloromethyltriphenylphosphine chloride, 3-iodopropyltriphenylphosphine iodide, 2-iodoethyltriphenylphosphine iodide, 1-iodoethyltriphenylphosphine iodide, iodomethyltriphenylphosphine bromide, 4-bromomethylphosphine bromide, etc. At least one of benzyltriphenylphosphine bromide, 2-bromomethylbenzyltriphenylphosphine bromide, 3-bromomethylbenzyltriphenylphosphine bromide, 4-chloromethylbenzyltriphenylphosphine chloride, 2-chloromethylbenzyltriphenylphosphine chloride, 3-chloromethylbenzyltriphenylphosphine chloride, 4-iodomethylbenzyltriphenylphosphine iodide, 2-iodomethylbenzyltriphenylphosphine iodide, and 3-iodomethylbenzyltriphenylphosphine iodide; preferably 3-bromopropyltriphenylphosphine bromide and / or 4-bromomethylbenzyltriphenylphosphine bromide.

[0059] According to the present invention, the concentration of the catalyst in the aqueous solution is 0.01 wt% to 5 wt%.

[0060] In this invention, controlling the concentration of the catalyst in the aqueous solution to meet the above-mentioned range enables the reaction of the grafted haloquammonium salt and / or haloquammonium salt on the membrane surface to proceed more fully, while avoiding catalyst waste and improving the economic efficiency of the process.

[0061] Furthermore, the concentration of the catalyst in the aqueous solution is 0.1 wt% to 1 wt%.

[0062] According to the present invention, the concentration of haloquaternary ammonium salt and / or haloquaternary phosphorus salt in the aqueous solution is 1wt%-20wt%.

[0063] In this invention, when the concentration of haloquaternary ammonium salts and / or haloquaternary phosphate salts in the aqueous solution is controlled to meet the above-mentioned range, sufficient grafting of haloquaternary ammonium salts and / or haloquaternary phosphate salts on the membrane surface can be guaranteed, thereby increasing the surface charge density of the acid and alkali resistant positively charged nanofiltration membrane, thus improving the rejection rate of the nanofiltration membrane for divalent and high-valence metal ions, without causing waste, and improving the economic efficiency of the process.

[0064] Furthermore, the concentration of haloquaternary ammonium salt and / or haloquaternary phosphorus salt in the aqueous solution is 5wt%-10wt%.

[0065] A second aspect of the present invention provides an acid- and alkali-resistant positively charged nanofiltration membrane prepared by the aforementioned preparation method.

[0066] According to the present invention, the acid and alkali resistant positively charged nanofiltration membrane comprises, in sequence, a bottom layer, a porous support layer, and an acid and alkali resistant separation layer;

[0067] The acid and alkali resistant separation layer is grafted with N atoms to quaternary ammonium salt groups represented by Formula I and / or quaternary phosphate salt groups represented by Formula II;

[0068]

[0069] Wherein, R1 is a substituted or unsubstituted alkylene group of C1-C9; R2, R3, and R4 are each independently selected from alkyl or phenyl groups of C1-C3; R5 is an alkylene group of C1-C6, a phenyl group, or an aralkyl group of C7-C10; R6, R7, and R8 are each independently a phenyl group or an aralkyl group of C7-C10.

[0070] X is a halogen.

[0071] Furthermore, R1 is a substituted or unsubstituted alkylene group of C1-C6, and R2, R3, and R4 are each independently CH3; R5 is an alkylene group of C1-C3, a phenyl group, or an aralkyl group of C8-C10; R6, R7, and R8 are each independently phenyl.

[0072] Furthermore, R1 is a C1-C3 substituted alkylene group, wherein the substituent is a hydroxyl or carboxyl group.

[0073] Furthermore, X is Cl, Br, or I.

[0074] According to the present invention, the nitrogen atom content in the quaternary ammonium salt groups of the acid- and alkali-resistant positively charged nanofiltration membrane is 0.5-6 at.%.

[0075] In this invention, when the nitrogen atom content in the quaternary ammonium salt group of the acid-alkali resistant positively charged nanofiltration membrane meets the above-mentioned range, the acid-alkali resistant positively charged nanofiltration membrane has a high surface electrode potential and a small average pore size, which makes the acid-alkali resistant positively charged nanofiltration membrane have good retention performance for divalent and high-valent heavy metal cations; at the same time, the acid-alkali resistant separation layer does not affect the water flux of the membrane too much by grafting the quaternary ammonium salt group shown in Formula I with nitrogen atoms.

[0076] Furthermore, the nitrogen content in the acid- and alkali-resistant positively charged nanofiltration membrane is 2-5 at.%.

[0077] According to the present invention, the phosphorus content in the acid- and alkali-resistant positively charged nanofiltration membrane is 0.4-3 at.%.

[0078] In this invention, when the phosphorus atom content in the acid-alkali resistant positively charged nanofiltration membrane meets the above-mentioned range, the acid-alkali resistant positively charged nanofiltration membrane has a high surface electrode potential and a small average pore size, which makes the acid-alkali resistant positively charged nanofiltration membrane have good retention performance for divalent and high-valent heavy metal cations; at the same time, the acid-alkali resistant separation layer does not affect the water flux of the membrane too much by grafting quaternary phosphate groups of Formula II with nitrogen atoms, and the membrane can have good separation efficiency.

[0079] Furthermore, the phosphorus content in the acid- and alkali-resistant positively charged nanofiltration membrane is 0.5-2 at.%.

[0080] According to the present invention, the surface Zeta potential of the acid and alkali resistant positively charged nanofiltration membrane is 0-30mV.

[0081] In this invention, the surface Zeta potential of the acid and alkali resistant positively charged nanofiltration membrane refers to the surface Zeta potential at pH=7.

[0082] In this invention, when the surface Zeta potential of the acid- and alkali-resistant positively charged 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 high-valence heavy metal ions in acidic and alkaline environments, it can better repel high-valence heavy metal ions, making it difficult for high-valence heavy metal ions in liquids to pass through the nanofiltration membrane, thereby achieving effective recovery of high-valence heavy metal cations.

[0083] Furthermore, the surface Zeta potential of the acid- and alkali-resistant positively charged nanofiltration membrane is 5-20 mV.

[0084] According to the present invention, the average pore size of the acid and alkali resistant positively charged nanofiltration membrane is 0.1-0.5 nm.

[0085] In this invention, when the average pore size of the acid- and alkali-resistant positively charged nanofiltration membrane meets the above-mentioned range, it indicates that the acid- and alkali-resistant positively charged nanofiltration membrane has high density. When used for the separation of high-valence heavy metal ions in acidic and alkaline environments, it can better repel high-valence heavy metal ions, making it difficult for high-valence ions in the liquid to pass through the nanofiltration membrane, thereby obtaining a higher separation efficiency of high-valence heavy metal ions.

[0086] Furthermore, the average pore size of the acid and alkali resistant positively charged nanofiltration membrane is 0.15-0.3 nm.

[0087] According to the present invention, the contact angle of the acid and alkali resistant positively charged nanofiltration membrane is 30-80°.

[0088] In this invention, the acid- and alkali-resistant positively charged nanofiltration membrane has a contact angle within the range described in this invention, thereby indicating that the acid- and alkali-resistant positively charged nanofiltration membrane has excellent hydrophilicity, enabling it to have high water flux.

[0089] Furthermore, the contact angle of the acid- and alkali-resistant positively charged nanofiltration membrane is 30-60°.

[0090] 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.

[0091] In this invention, the bottom layer is a nonwoven fabric, preferably polyester and / or polyethylene.

[0092] In this invention, the porous support layer material is selected from at least one of polyethersulfone, polysulfone, polyaromatic ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride, and polyaryletherketone.

[0093] In this 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, preferably at least one of polyurea separation layer, polytriazine amine separation layer and polysulfonamide separation layer.

[0094] 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 is a conventional choice in the art. However, in order to enable these three layers to play a better synergistic role and enable the obtained acid and alkali resistant positively charged nanofiltration membrane to better combine excellent high-valence heavy metal ion separation coefficient and high water flux, preferably, 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.

[0095] A third aspect of the present invention provides an application of the aforementioned acid and alkali resistant positively charged nanofiltration membrane in the field of water treatment.

[0096] In this invention, the acid and alkali resistant positively charged nanofiltration membrane has a NiCl2 rejection rate of ≥85%, preferably ≥89%; a CuCl2 rejection rate of ≥88%, preferably ≥88.5%; and a water flux of ≥22 LMH, preferably ≥24 LMH.

[0097] Other features and advantages of the present invention will be described in detail in the following detailed description section.

[0098] The present invention will be described in detail below through embodiments.

[0099] (1) The water flux of the acid- and alkali-resistant positively charged nanofiltration membrane was tested by the following method: The nanofiltration membrane was loaded into the membrane tank and pre-pressed at 1.5 MPa for 1 hour. The water permeation rate of the acid- and alkali-resistant positively charged nanofiltration membrane was measured at a pressure of 2 MPa and a temperature of 25°C for a certain period of time. The water flux was calculated by the following formula:

[0100] J = Q / (A·t), where J is the water flux, Q is the water permeation rate (L), and A is the effective filtration membrane area (m²) of the acid- and alkali-resistant positively charged nanofiltration membrane. 2 ), where t is time (h).

[0101] (2) The rejection rate of the acid- and alkali-resistant positively charged nanofiltration membrane was obtained by the following method: The acid- and alkali-resistant positively charged nanofiltration membrane was loaded into the membrane tank and pre-pressed at 1.5 MPa for 1 hour. The salt concentration changes in the raw aqueous solution with an initial concentration of 2000 ppm and the permeate were measured within 1 hour under the conditions of pressure of 2 MPa and temperature of 25℃. The rejection rate was calculated by the following formula:

[0102] R = (C f -C p ) / C f ×100%, where R is the retention rate, C f C represents the concentration of NiCl2 or CuCl2 in the original aqueous solution (measured by a conductivity meter). pThis represents the concentration of NiCl2 or CuCl2 in the permeate.

[0103] (4) Test method for acid and alkali resistant positively charged nanofiltration membrane: Immerse the nanofiltration membrane in a 5wt% HCl solution for 7 days, take it out and clean it thoroughly, and then test the water flux and high-valence heavy metal ion rejection rate of the nanofiltration membrane.

[0104] (5) Determination of the surface contact angle of acid and alkali resistant positively charged nanofiltration membrane

[0105] The surface contact angle of nanofiltration membrane samples was tested using a DSA100 surface contact angle meter manufactured by KRUSS GmbH, Germany, via the static drop method. Before testing, the samples were dried in a vacuum oven at 60°C for 30 minutes to remove surface and internal moisture. The dried membrane was then attached to a flat glass slide with double-sided tape. During testing, the volume of each water droplet was 2 μL. The water droplet was placed on the membrane surface for 3 seconds before testing. The final contact angle was determined by taking the average value after multiple measurements.

[0106] (6) Determination of nitrogen atom content in quaternary ammonium salt groups on the surface of acid- and alkali-resistant positively charged nanofiltration membranes and phosphorus atom content in nanofiltration membranes:

[0107] Before measurement, the samples were dried to constant weight in an oven. The elemental composition of the nanofiltration membrane sample surface was determined using a Sigma Probe X-ray photoelectron spectrometer manufactured by Thermo VG, UK. For samples containing quaternary ammonium salt groups, the molar content of nitrogen atoms in the quaternary ammonium salt groups is equal to the corresponding molar content of halogens. The content of nitrogen atoms in the quaternary ammonium salt groups was determined by measuring the halogen content. The content of phosphorus atoms in quaternary phosphate salts could be directly measured by XPS spectroscopy.

[0108] (7) Acid and alkali resistant positively charged nanofiltration membrane pore size test: The pore size was measured using the PEG solute transfer method, and the detailed steps are as follows:

[0109] (i) Test the retention rate of acid and alkali resistant positively charged nanofiltration membranes for PEG of different molecular sizes;

[0110] (ii) Linearly fit the PEG size and rejection rate in a log-probability coordinate system. The PEG size corresponding to a 50% rejection rate is the average pore size of the nanofiltration membrane.

[0111] (8) Zeta potential test of acid and alkali resistant positively charged nanofiltration membrane surface: The test was performed using a Surpass electric analyzer (AntonPaar), the circulating solution was a dilute aqueous solution of KCl, and the pH of the test solution was 7.

[0112] Additionally, in the following embodiments and comparative examples:

[0113] Branched polyethyleneimine (weight average molecular weight of 25,000 g / mol), polyethylene polyamine, 1,4-phenyl diisocyanate, cyanuric chloride, 1,3-benzene disulfonyl chloride, 3-bromopropyltriphenylphosphine bromide, chloromethyltriphenylphosphine chloride, 2-chloroethyltrimethylammonium chloride, and 3-bromopropyltrimethylammonium bromide were all purchased from Bailingwei Technology Co., Ltd.

[0114] All other chemical reagents were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0115] The support layer is prepared using a phase transformation method, and the specific steps are as follows:

[0116] 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 caused 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 support layer with a total thickness of 115 μm was obtained. This support layer includes an underlayer and a porous support layer.

[0117] Example 1

[0118] 400cm 2 The upper surface of the polysulfone support layer was contacted with 50g of an aqueous solution containing 0.5wt% polyethyleneimine at 25°C for 60s, and then drained. Then, the upper surface of the support layer was contacted with 30g of an Isopar E solution containing 0.1wt% 1,4-phenyl diisocyanate at 25°C for 60s, and then drained. The membrane was then placed in an oven and heated at 70°C for 3min to obtain composite membrane A1.

[0119] At 30°C, the above composite membrane A1 was immersed in an aqueous solution containing 150g of 10wt% 3-bromopropyltriphenylphosphine bromide and 0.5wt% potassium hydroxide for 1 minute. After 1 minute, it was removed and dried at 70°C for 5 minutes to obtain the acid and alkali resistant positively charged nanofiltration membrane N1 modified with quaternary phosphorus salt.

[0120] The XPS phosphorus atom spectrum of acid and alkali resistant positively charged nanofiltration membrane N1 is as follows: Figure 1 As shown, by Figure 1 It can be seen that the phosphorus signal on the membrane surface is obvious (as a prominent single peak in the figure), indicating that the acid and alkali resistant separation layer has successfully grafted the quaternary phosphate salt group shown in Formula I through N atoms, thereby enhancing the positive charge on the surface of the acid and alkali resistant positively charged nanofiltration membrane and the retention effect of divalent and high-valence heavy metal ions.

[0121] Example 2

[0122] 400cm2 The upper surface of the polysulfone support layer was contacted with 50g of an aqueous solution containing 0.5wt% polyethylene polyamine at 25°C for 60s, and then drained. Then, the upper surface of the support layer was contacted with 30g of an Isopar E solution containing 0.1wt% 1,4-phenyl diisocyanate at 25°C for 60s, and then drained. The membrane was then placed in an oven and heated at 70°C for 3min to obtain composite membrane A2.

[0123] At 30°C, the above composite membrane A2 was immersed in an aqueous solution containing 150g of 5wt% 3-bromopropyltriphenylphosphine bromide and 0.5wt% potassium hydroxide for 1 minute. After 1 minute, it was removed and dried at 70°C for 5 minutes to obtain the acid and alkali resistant positively charged nanofiltration membrane N2 modified with quaternary phosphorus salt.

[0124] Example 3

[0125] The experiment was carried out in accordance with Example 1, except that “chloromethyltriphenylphosphine chloride” was used instead of “3-bromopropyltriphenylphosphine bromide” to obtain a quaternary phosphorus salt modified acid and alkali resistant positively charged nanofiltration membrane N3.

[0126] Example 4

[0127] The method of Example 1 was implemented, except that "2-chloroethyltrimethylammonium chloride" was used instead of "3-bromopropyltriphenylphosphine bromide" to obtain a quaternary ammonium salt modified acid and alkali resistant positively charged nanofiltration membrane N4.

[0128] Example 5

[0129] The method of Example 1 was implemented, except that "3-bromopropyltrimethylammonium bromide" was used instead of "3-bromopropyltriphenylphosphine bromide" to obtain a quaternary ammonium salt modified acid and alkali resistant positively charged nanofiltration membrane N5.

[0130] Example 6

[0131] The experiment was carried out in accordance with Example 1, except that "2 wt% polyethyleneimine aqueous solution" was used instead of "0.5 wt% polyethyleneimine aqueous solution", and "0.05 wt% cyanuric chloride Isopar E solution" was used instead of "0.1 wt% 1,4-phenyl diisocyanate Isopar E solution" to obtain a quaternary phosphate modified acid and alkali resistant positively charged nanofiltration membrane N6.

[0132] Example 7

[0133] The experiment was carried out in accordance with Example 1, except that "2 wt% polyethyleneimine aqueous solution" was used instead of "0.5 wt% polyethyleneimine aqueous solution", and "0.2 wt% Isopar E solution of 1,3-benzene disulfonyl chloride" was used instead of "0.1 wt% Isopar E solution of 1,4-benzene diisocyanate" to obtain a quaternary phosphate modified acid and alkali resistant positively charged nanofiltration membrane N7.

[0134] Example 8

[0135] The process was carried out in accordance with Example 1, except that "20 wt% of 3-bromopropyltriphenylphosphine bromide" was used instead of "10 wt% of 3-bromopropyltriphenylphosphine bromide" to obtain a quaternary phosphorus salt modified acid and alkali resistant positively charged nanofiltration membrane N8.

[0136] Example 9

[0137] The process was carried out in accordance with Example 1, except that "0.1 wt% of 3-bromopropyltriphenylphosphine bromide" was used instead of "10 wt% of 3-bromopropyltriphenylphosphine bromide" to obtain a quaternary phosphorus salt modified acid and alkali resistant positively charged nanofiltration membrane N9.

[0138] Example 10

[0139] The experiment was carried out in accordance with Example 1, except that "0.01 wt% potassium hydroxide" was used instead of "0.5 wt% potassium hydroxide" to obtain a quaternary phosphate modified acid and alkali resistant positively charged nanofiltration membrane N10.

[0140] Example 11

[0141] The experiment was carried out in accordance with Example 1, except that "0.005 wt% potassium hydroxide" was used instead of "0.5 wt% potassium hydroxide" to obtain a quaternary phosphate modified acid and alkali resistant positively charged nanofiltration membrane N11.

[0142] Example 12

[0143] The procedure was carried out in accordance with Example 1, except that the contact time was 10 s, resulting in a quaternary phosphate-modified acid and alkali resistant positively charged nanofiltration membrane N12.

[0144] Example 13

[0145] The procedure was carried out in accordance with Example 1, except that the contact temperature was 20°C, resulting in a quaternary phosphate-modified acid and alkali resistant positively charged nanofiltration membrane N13.

[0146] Comparative Example 1

[0147] The upper surface of the polysulfone support layer was contacted with 50g of an aqueous solution containing 0.5wt% polyethyleneimine at 25°C for 60s, and then drained. Then, the upper surface of the support layer was contacted with 30g of an Isopar E solution containing 0.1wt% 1,4-phenyl diisocyanate at 25°C for 60s, and then drained. The membrane was then placed in an oven and heated at 70°C for 3min to obtain composite membrane D1.

[0148] Comparative Example 2

[0149] The procedure was carried out in accordance with Example 1, except that no catalyst was added, resulting in composite membrane D2.

[0150] Thickness, surface zeta potential, contact angle, and average pore size were tested on the acid and alkali resistant positively charged nanofiltration membrane prepared in the examples and the composite membrane prepared in the comparative examples. The results are shown in Tables 1 and 2.

[0151] Table 1

[0152] Substrate thickness (μm) Porous support layer thickness (μm) Thickness of acid and alkali resistant separation layer (nm) N1 75 40 139 N2 75 40 134 N3 75 40 140 N4 75 40 138 N5 75 40 136 N6 75 40 157 N7 75 40 179 N8 75 40 154 N9 75 40 135 N10 75 40 138 N11 75 40 134 N12 75 40 135 N13 75 40 137 D1 75 40 132 D2 75 40 133

[0153] Note: The thickness of the acid and alkali resistant separation layer here refers to the acid and alkali resistant separation layer modified with quaternary ammonium salt and / or halogenated quaternary phosphorus salt.

[0154] Table 2

[0155]

[0156]

[0157] Note: a - The nitrogen atom content in the quaternary ammonium salt groups of acid and alkali resistant positively charged nanofiltration membranes;

[0158] b - The phosphorus content in acid and alkali resistant positively charged nanofiltration membranes;

[0159] "-" indicates that it cannot be measured.

[0160] The rejection rates of NiCl2 and CuCl2 and the water flux of the acid- and alkali-resistant positively charged nanofiltration membranes prepared in the examples and the composite membranes prepared in the comparative examples were tested respectively. After acid treatment, the rejection rates of NiCl2 and CuCl2 and the water flux of the acid- and alkali-resistant positively charged nanofiltration membranes prepared in the examples and the composite membranes prepared in the comparative examples were tested again. The results are shown in Table 3.

[0161] Table 3

[0162]

[0163]

[0164] As can be seen from Examples 1-7, the acid and alkali resistant positively charged nanofiltration membrane prepared by the preparation method of the present invention has good acid and alkali resistance, and takes into account both the retention effect of divalent and high-valence heavy metal ions and high water flux.

[0165] As can be seen from Examples 1, 8, and 9, the concentration of haloquaternary phosphate salts is fully grafted on the membrane surface, which increases the surface charge density of the acid and alkali resistant positively charged nanofiltration membrane, thereby increasing the rejection rate of divalent and high-valence metal ions of the nanofiltration membrane, while also having a high water flux. When the concentration of haloquaternary phosphate salts is too low, the rejection rate decreases; when the concentration of haloquaternary phosphate salts is too high, it will cause a decrease in water flux and waste of raw materials.

[0166] As can be seen from Examples 1, 10, and 11, the appropriate catalyst concentration of the present invention enables the reaction of the grafted haloquammonium salt and / or haloquammonium salt on the membrane surface to proceed more fully, thereby improving the rejection rate of divalent and high-valence metal ions of the nanofiltration membrane, while also having a high water flux.

[0167] Comparative Example 1, which was not modified with halogenated quaternary ammonium salts and / or halogenated quaternary phosphate salts, resulted in a decrease in the retention rate of divalent and high-valent metal ions in the nanofiltration membrane, making it unable to effectively retain divalent and high-valent metal ions.

[0168] In Comparative Example 2, no catalyst was added. As shown in Table 1, the surface Zeta potential and phosphorus atom content in the composite membrane are lower, which proves that the grafting of the acid and alkali resistant separation layer is insufficient. The data in Table 2 also show that the rejection rate of NiCl2 and CuCl2 in the composite membrane is reduced.

[0169] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing an acid- and alkali-resistant, positively charged nanofiltration membrane, characterized in that, The method includes the following steps: S1. A porous support layer and an acid- and alkali-resistant separation layer are sequentially prepared on the bottom layer to obtain a composite membrane; S2. The composite membrane is contacted with an aqueous solution containing a catalyst and a haloquaternary phosphate salt, and then dried to obtain the acid- and alkali-resistant positively charged nanofiltration membrane. The haloquaternary phosphate salt has the structure shown in Formula II; Formula II; Wherein, R5' is a C1-C6 alkylene, phenyl, or C7-C10 aralkyl; R6', R7', and R8' are each independently a phenyl or C7-C10 aralkyl. X and X1 are halogens, each independently.

2. The preparation method according to claim 1, wherein, R5' is a C1-C3 alkylene, phenyl, or C8-C10 aralkyl; R6', R7', and R8' are each independently phenyl. And / or, X is Cl, Br, or I; And / or, X1 is F, Cl, Br or I.

3. The preparation method according to claim 1 or 2, wherein, In step S2, the contact method is immersion.

4. The preparation method according to claim 1 or 2, wherein, The contact time is 10 seconds to 10 minutes; the contact temperature is 20 to 80 degrees Celsius. And / or, the drying time is 0.5-10 min; the drying temperature is 40-80℃.

5. The preparation method according to claim 4, wherein, The contact time is 20 seconds to 1 minute; the contact temperature is 30 to 50 degrees Celsius. And / or, the drying time is 3-5 minutes; the drying temperature is 50-70°C.

6. The preparation method according to claim 1 or 2, wherein, In step S2, the catalyst is selected from at least one of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, sodium bicarbonate, potassium bicarbonate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate. And / or, the haloquaternary phosphorus salt is selected from at least one of 3-bromopropyltriphenylphosphine bromide, 2-bromoethyltriphenylphosphine bromide, 1-bromoethyltriphenylphosphine bromide, bromomethyltriphenylphosphine bromide, 3-chloropropyltriphenylphosphine chloride, 2-chloroethyltriphenylphosphine chloride, 1-chloroethyltriphenylphosphine chloride, chloromethyltriphenylphosphine chloride, 3-iodopropyltriphenylphosphine iodide, 2-iodoethyltriphenylphosphine iodide, 1-iodoethyltriphenylphosphine iodide, iodomethyltriphenylphosphine bromide, 4-bromomethylbenzyltriphenylphosphine bromide, 2-bromomethylbenzyltriphenylphosphine bromide, 3-bromomethylbenzyltriphenylphosphine bromide, 4-chloromethylbenzyltriphenylphosphine chloride, 2-chloromethylbenzyltriphenylphosphine chloride, 3-chloromethylbenzyltriphenylphosphine chloride, 4-iodomethylbenzyltriphenylphosphine iodide, 2-iodomethylbenzyltriphenylphosphine iodide, and 3-iodomethylbenzyltriphenylphosphine iodide.

7. The preparation method according to claim 6, wherein, In step S2, the catalyst is potassium hydroxide; And / or, the haloquaternary phosphorus salt is 3-bromopropyltriphenylphosphine bromide and / or 4-bromomethylbenzyltriphenylphosphine bromide.

8. The preparation method according to claim 1 or 2, wherein, The concentration of the catalyst in the aqueous solution is 0.01wt%-5wt%; And / or, the concentration of the haloquatriphosphine in the aqueous solution is 1wt%-20wt%.

9. The preparation method according to claim 8, wherein, The concentration of the catalyst in the aqueous solution is 0.1 wt% - 1 wt%; And / or, the concentration of the haloquatriphosphine in the aqueous solution is 5wt%-10wt%.

10. An acid- and alkali-resistant positively charged nanofiltration membrane prepared by any one of claims 1-9.

11. The acid- and alkali-resistant positively charged nanofiltration membrane according to claim 10, wherein, The acid and alkali resistant positively charged nanofiltration membrane comprises, in sequence, a bottom layer, a porous support layer, and an acid and alkali resistant separation layer; The acid and alkali resistant separation layer is made by grafting N atoms with quaternary phosphate groups of Formula II. Formula II; Wherein, R5 is a C1-C6 alkylene, phenyl, or C7-C10 aralkyl; R6, R7, and R8 are each independently a phenyl or C7-C10 aralkyl. X is a halogen.

12. The acid- and alkali-resistant positively charged nanofiltration membrane according to claim 11, wherein, R5 is a C1-C3 alkylene group, a phenyl group, or a C8-C10 aralkyl group; R6, R7, and R8 are each independently a phenyl group; And / or, X is Cl, Br, or I.

13. The acid- and alkali-resistant positively charged nanofiltration membrane according to claim 10 or 11, wherein, The phosphorus content in the acid- and alkali-resistant positively charged nanofiltration membrane is 0.4-3 at.%.

14. The acid- and alkali-resistant positively charged nanofiltration membrane according to claim 13, wherein, The acid- and alkali-resistant positively charged nanofiltration membrane contains 0.5-2 at.% phosphorus atoms.

15. The acid- and alkali-resistant positively charged nanofiltration membrane according to claim 10 or 11, wherein, The surface zeta potential of the acid and alkali resistant positively charged nanofiltration membrane is 0-30mV.

16. The acid- and alkali-resistant positively charged nanofiltration membrane according to claim 15, wherein, The surface zeta potential of the acid and alkali resistant positively charged nanofiltration membrane is 5-20mV.

17. The acid- and alkali-resistant positively charged nanofiltration membrane according to claim 10 or 11, wherein, The acid and alkali resistant positively charged nanofiltration membrane has an average pore size of 0.1-0.5 nm.

18. The acid- and alkali-resistant positively charged nanofiltration membrane according to claim 17, wherein, The acid and alkali resistant positively charged nanofiltration membrane has an average pore size of 0.15-0.3 nm.

19. The acid- and alkali-resistant positively charged nanofiltration membrane according to claim 10 or 11, wherein, The contact angle of the acid and alkali resistant positively charged nanofiltration membrane is 30-80°.

20. The acid- and alkali-resistant positively charged nanofiltration membrane according to claim 19, wherein, The contact angle of the acid and alkali resistant positively charged nanofiltration membrane is 30-60°.

21. The acid- and alkali-resistant positively charged nanofiltration membrane according to claim 10 or 11, 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.

22. The acid- and alkali-resistant positively charged nanofiltration membrane according to claim 21, 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.

23. The application of the acid and alkali resistant positively charged nanofiltration membrane according to any one of claims 10-22 in the field of water treatment.

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