CN112403286A

CN112403286A - Positively charged nanofiltration membrane based on tertiary amine type amphiphilic copolymer and preparation method thereof

Info

Publication number: CN112403286A
Application number: CN202011363839.3A
Authority: CN
Inventors: 朱宝库; 崔月; 姚之侃; 杜世媛; 方立峰; 许云秋; 朱利平
Original assignee: Zhejiang University ZJU
Current assignee: Zhejiang University ZJU
Priority date: 2014-08-31
Filing date: 2014-12-04
Publication date: 2021-02-26
Also published as: CN105709608A; CN104190265A; CN105363359B; CN105363359A; CN105642129A; CN105363353A; CN105709619A; CN105363350B; CN105709619B; CN105709608B; CN105363350A; CN105363353B

Abstract

The invention discloses a positively charged nanofiltration membrane based on a tertiary amine type amphiphilic copolymer and a preparation method thereof. The nanofiltration membrane consists of a neutral macroporous supporting layer and a positively charged compact functional layer: the macroporous support layer comprises a membrane matrix material and a tertiary amine type amphiphilic copolymer, the compact functional layer comprises cross-linked macromolecular quaternary ammonium salt, and the macromolecular quaternary ammonium salt in the compact functional layer and the membrane matrix material in the macroporous support layer form an interpenetrating network structure. The preparation method of the nanofiltration membrane comprises the following steps: (1) dissolving a membrane matrix material and a tertiary amine type amphiphilic copolymer in a membrane preparation solvent to prepare an electric neutral membrane preparation solution, and curing the solution from a coagulating bath by a solution phase inversion method to prepare an active precursor membrane containing the tertiary amine type amphiphilic copolymer; (2) dip-coating the active precursor film in a cross-linking agent solution; (3) and taking out the membrane after dip coating, and carrying out heat treatment to obtain the positively charged nanofiltration membrane. The invention is suitable for various general membrane making materials, can be made into flat membranes or hollow fiber membranes, and has good industrial prospect.

Description

Positively charged nanofiltration membrane based on tertiary amine type amphiphilic copolymer and preparation method thereof

The application is a divisional application with the application date of 04 th 12 th 2014, the application number of 201410734310.6, the invention name of 'a positive charged nanofiltration membrane based on a tertiary amine type amphiphilic copolymer and a preparation method thereof', and the application person is Zhejiang university. Meanwhile, the present application claims priority of chinese patent application with the title "low pressure high flux chlorine-containing polymer nanofiltration membrane with stable separation layer and preparation method thereof" filed by chinese patent office of china, application No. 201410437650.2, on 31/8/2014, which is incorporated in the present application by reference in its entirety.

Technical Field

The invention belongs to the technical field of membrane separation, and particularly relates to a positively charged nanofiltration membrane based on a tertiary amine type amphiphilic copolymer and a preparation method thereof.

Background

The membrane separation technology is a high-efficiency pollution-free purification technology integrating concentration and separation, has the advantages of high separation efficiency, low energy consumption, small occupied area, simplicity and convenience in operation and the like, becomes one of the most important means in the current separation science, and is currently industrialized, such as Microfiltration (MF), Ultrafiltration (UF), Nanofiltration (NF), Reverse Osmosis (RO), Electrodialysis (ED) and Gas Separation (GS).

Nanofiltration is a novel membrane separation technology developed on the basis of reverse osmosis membranes, and a typical nanofiltration membrane has the following characteristics: (1) the nanofiltration membrane is generally a composite membrane and consists of a supporting layer and a functional layer, and the interception performance and flux of the nanofiltration membrane depend on the functional layer. (2) The relative molecular weight (200-2000) of the trapped substance is between that of reverse osmosis and ultrafiltration, and the pore diameter of the membrane is about 1 nm. (3) The retention performance of the membrane is influenced by the pore size sieving effect and the charge effect, and has different retention rates for ions with different valence states, generally for monovalent ions (NO)₃ ^-、Cl^-、Na⁺、K⁺) Has low retention rate to high valence ion (PO)₄ ^3-、SO₄ ^2-、Mg² ⁺、Ca²⁺) The retention rate of (A) is higher. (4) The operating pressure is lower than the pressure required by reverse osmosis, and the general operating pressure is between 0.8 and 2.0 MPa.

The solution phase inversion method is a common membrane preparation method for preparing ultrafiltration and microfiltration membranes, adopts a solvent which is mutually soluble with a membrane preparation solvent but can not dissolve a membrane matrix material as a coagulating bath (water is generally selected as the coagulating bath), realizes the solidification of the membrane through the exchange of the solvent and a non-solvent, and is the most common means for producing the ultrafiltration and microfiltration membranes in a large scale. When the solution phase inversion method is adopted to prepare the ultrafiltration membrane and the microfiltration membrane, water-soluble micromolecule additives (such as polyethylene glycol and the like) are usually added into a membrane preparation liquid, and in the phase inversion process, the water-soluble micromolecule additives rapidly migrate to a water coagulation bath and are finally dissolved in water to form micropores on the surface of the membrane, so that the ultrafiltration membrane and the microfiltration membrane with porous structures are prepared. Most of the membranes prepared by the solution phase inversion method are porous membranes, the porosity is high, and the pore diameter of the membranes is too large, so that the membranes cannot be directly used in the nanofiltration process even through the subsequent shrinkage effect. Chinese patent CN1395984A discloses a positively charged membrane and a preparation method thereof, wherein an acrylic amino ester polymer, a cross-linking agent and a membrane material are blended to form an interpenetrating network system, and a membrane is formed by a solution phase inversion method. The amino acrylate polymer selected by the method has good affinity with water, is easy to lose and form holes in the film forming process by a phase inversion method, and can only be made into an ultrafiltration membrane with a porous structure because the film forming liquid is an interpenetrating network crosslinking system and the film forming liquid is gelatinized due to too high concentration. The general nanofiltration membrane preparation method adopts an ultrafiltration membrane prepared by a solution phase inversion method as a bottom membrane, and then a compact functional layer is introduced on the surface of the ultrafiltration bottom membrane.

At present, in the preparation aspect of the nanofiltration membrane, methods such as interfacial polymerization, surface coating, in-situ polymerization and the like are mostly adopted to introduce a compact separation layer on the surface of the porous membrane. The interfacial polymerization is to coat a layer of polyamine aqueous solution on the surface of a support membrane, then coat a layer of organic solution of polybasic acyl chloride, and prepare a polyamide functional layer by utilizing the reaction of the polyamine and the polybasic acyl chloride, wherein the polybasic acyl chloride can be trimesoyl chloride, isophthaloyl chloride, terephthaloyl chloride and the like. The functional layer and the supporting layer of the nanofiltration membrane prepared by interfacial polymerization only depend on physical adsorption, strong acting force is not generated, and the combination is unstable; the nanofiltration functional layer constructed by the interfacial polymerization method is thicker, and the flux of the nanofiltration membrane can be reduced. Chinese patent CN1872400A discloses a preparation method of a hollow fiber nanofiltration composite membrane, which is to prepare the hollow fiber composite nanofiltration membrane by interfacial polymerization of a water phase solution of dimethylaminoethyl methacrylate and an oil phase solution of a cross-linking agent. Chinese patent CN102836644A discloses a method for synchronously preparing a hollow fiber composite nanofiltration membrane by immersion precipitation phase inversion/interfacial crosslinking, which comprises the steps of dissolving a polymer and a crosslinking agent in an organic solvent to obtain a membrane casting solution, dissolving a crosslinking prepolymer in water to obtain a core solution, and synchronously performing interfacial crosslinking in the phase inversion membrane forming process to prepare the nanofiltration membrane. The nanofiltration membrane prepared by the two methods through interfacial polymerization and interfacial crosslinking has no strong chemical action between the supporting layer and the compact functional layer, and the combination is unstable.

The preparation method of the nanofiltration membrane by ultraviolet radiation, plasma radiation and the like has high energy consumption and small application range, and is not beneficial to industrial production. Chinese patent CN102210979A discloses a positively charged polyvinyl chloride hollow fiber nanofiltration membrane and a preparation method thereof, wherein a polyvinyl chloride membrane material and a polyvinyl chloride cationic copolymer are blended and phase-converted into a membrane. Wherein, the compatibility of the polyvinyl chloride cationic copolymer and the polyvinyl chloride body material is poor, and the membrane-making solution is easy to phase separate, which is not beneficial to preparing the high-performance nanofiltration membrane. Chinese patent CN102000511A discloses a method for preparing a positively charged hollow fiber nanofiltration membrane by surface ultraviolet irradiation grafting, wherein a monomer containing a quaternary amine group is grafted on the surface of a polysulfone ultrafiltration membrane by ultraviolet irradiation. Chinese patent CN103071395A discloses a dynamic preparation method of an ultra-low pressure charged nanofiltration membrane, which is to prepare an ultrafiltration basement membrane by using a photosensitive polymer material and prepare the charged nanofiltration membrane by ultraviolet irradiation grafting of a functional monomer in a motion state. The two methods adopt an irradiation method to prepare the nanofiltration membrane, require that the basement membrane is made of photosensitive materials, have high energy consumption and are not beneficial to the popularization of the membrane.

The other common nanofiltration membrane preparation method is to construct a nanofiltration functional layer on the surface of an ultrafiltration membrane by using sulfonated aromatic polymers, and the method is suitable for few sulfonated polymers and has no universality; the prepared nanofiltration membrane is negatively charged, but has poor separation performance on positively charged substances, but in practical application, a lot of salts and proteins are positively charged, so that the preparation of the positively charged nanofiltration membrane has practical significance.

Although the prior preparation method of the nanofiltration membrane is various, the method still has some inevitable problems in the prior art: most of membranes prepared by the solution phase conversion method are porous membranes, and the pore diameter of the membranes is too large; the nanofiltration membrane prepared by the interfacial polymerization and interfacial crosslinking method has no strong chemical action between the supporting layer and the compact functional layer, and the combination is unstable; the functional layer of the nanofiltration membrane prepared by interfacial polymerization is too compact, so that the flux of the membrane is seriously reduced, and the production efficiency is not improved; in the anionic/cationic copolymer blending method, the compatibility of anions/cations and the membrane body material is poor, the membrane making solution is easy to phase separate, and the production is not easy to control; the methods of ultraviolet/plasma/electron beam irradiation and the like require that the bottom film is a photosensitive material, and the energy consumption in the irradiation process is extremely high, which is not beneficial to large-scale production. Therefore, the method for preparing the nanofiltration membrane suitable for large-scale industrial production is important to explore.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a positively charged nanofiltration membrane based on a tertiary amine type amphiphilic copolymer and a preparation method thereof. Different from the prior art, the positively charged nanofiltration membrane based on the tertiary amine type amphiphilic copolymer provided by the invention solves some problems existing in the prior art while ensuring the high performance of the nanofiltration membrane:

1) the invention discloses a positively charged nanofiltration membrane based on a tertiary amine type amphiphilic copolymer, which adopts the tertiary amine type amphiphilic copolymer, and can obtain an active layer with high tertiary amine content on the surface due to the surface enrichment action of the amphiphilic copolymer even if a small amount of the amphiphilic copolymer is added, thereby improving the retention rate of the polymer in the membrane and reducing the membrane preparation cost.

2) According to the positively charged nanofiltration membrane based on the tertiary amine type amphiphilic copolymer, the tertiary amine type amphiphilic copolymer macromolecule quaternary ammonium salt in the functional layer and the membrane matrix material macromolecule in the supporting layer form an interpenetrating network, so that the functional layer and the supporting layer are combined more stably, the functional layer cannot be separated from the surface of the supporting layer in the membrane preparation process and the use process, the composition, the structure and the performance of the membrane are stable, and the membrane is durable and pressure-resistant, and has a longer service life. The positively charged nanofiltration membrane based on the tertiary amine type amphiphilic copolymer is placed in deionized water at 60 ℃ and is vibrated for 20 days at constant temperature, and the flux and the interception performance are kept unchanged. And the nanofiltration membrane without chemical combination between the support layer and the functional layer has the rejection rate reduced to only 20% of the original rejection rate after being vibrated in deionized water at the temperature of 60 ℃ for 20 days, so that the performance stability is greatly different.

3) The polymer nanofiltration membrane prepared by the prior art, such as interfacial polymerization, surface coating and the like, has a thicker functional layer, greatly reduces the flux of the nanofiltration membrane, and is not beneficial to improving the separation efficiency; the invention is based onThe positively charged nanofiltration membrane of the tertiary amine type amphiphilic copolymer has good interception and permeability under low pressure, and the membrane flux is more than or equal to 30L/(m) under the pressure of more than or equal to 0.3MPa²H), the retention rate of the small molecular dye and the high-valence inorganic salt can reach more than 90 percent. Generally, the operating pressure of the nanofiltration membrane is linear with the membrane flux, i.e., the higher the operating pressure, the higher the membrane flux. The existing nanofiltration membrane, such as the nanofiltration membrane prepared by traditional interfacial polymerization, has an excessively compact functional layer, has good separation performance on inorganic salts and the like, but has low membrane flux, and in order to improve the separation efficiency, the requirement on the membrane flux can be met only by improving the operation pressure, which is generally over 0.8 MPa. However, the higher the operating pressure, the higher the requirements for equipment, and the higher the energy consumption, which greatly increases the operating cost. The positive charge nanofiltration membrane based on the tertiary amine type amphipathic copolymer can obtain 30L/(m) at 0.3MPa²H) membrane flux, not only meeting the requirements of nanofiltration operation on membrane flux, but also effectively improving separation efficiency and reducing operation cost.

4) According to the basic principle of nanofiltration membrane separation, the interception performance of the membrane is influenced by the aperture screening effect and the charge effect, if the prepared nanofiltration membrane is negatively charged, the nanofiltration membrane cannot well separate positively charged substances, a nanofiltration functional layer is constructed on the surface of the ultrafiltration membrane by adopting the sulfonated aromatic polymer, the prepared nanofiltration membrane is negatively charged, and the membrane can be used for positively charged substances (such as Na)⁺、K⁺、Mg²⁺、Ca²⁺) A good separation effect cannot be achieved. Therefore, the positively charged nanofiltration membrane is very important in order to prepare the nanofiltration membrane with practical application value. The positively charged multilayer nanofiltration membrane disclosed by the invention has the advantages that the surface is positively charged, the rejection effect on positively charged pollutants in water is more obvious, and the pollution resistance of the membrane is stronger.

5) The positively charged nanofiltration membrane disclosed by the invention has no special requirements on the material of the bottom membrane, is suitable for various general membrane-making materials, such as polyvinylidene fluoride, polyacrylonitrile, polyphenyl ether, polysulfone, polyether sulfone and the like, can be prepared into a flat membrane or a hollow fiber membrane, and has wide popularization value.

The invention adopts the following technical scheme:

the positively charged nanofiltration membrane based on the tertiary amine type amphiphilic copolymer comprises a charge-neutral macroporous supporting layer and a positively charged compact functional layer, wherein the macroporous supporting layer comprises a membrane matrix material and the tertiary amine type amphiphilic copolymer, the compact functional layer comprises cross-linked macromolecular quaternary ammonium salt, and the macromolecular quaternary ammonium salt in the compact functional layer and the membrane matrix material in the macroporous supporting layer form an interpenetrating network structure.

The nanofiltration membrane is realized by physically blending a membrane matrix material and a tertiary amine type amphiphilic copolymer, and the adopted tertiary amine type amphiphilic copolymer consists of a hydrophilic component and a hydrophobic component. The content of the tertiary amine groups on the surface of the nanofiltration membrane is far higher than that of the tertiary amine groups in the membrane body, and one end of the nanofiltration membrane rich in macromolecular quaternary ammonium salt is a compact functional layer; and the other end of the membrane is less in the content of the tertiary amine type amphiphilic copolymer, mainly consists of a membrane matrix material, mainly plays a supporting role and is a macroporous supporting layer. Due to the fact that the macromolecule quaternary ammonium salt in the compact functional layer and the macromolecule of the membrane matrix material in the macroporous support layer are mutually entangled, the compact functional layer and the macroporous support layer are combined stably, the functional layer cannot be separated from the surface of the support layer in the using process, long-time stability of membrane performance is guaranteed, and the membrane is endowed with longer service life. The effect can only be achieved by the amphiphilic copolymer, and if the hydrophilic tertiary amine polymer without the hydrophobic component is adopted, the hydrophilic tertiary amine polymer can become a pore-forming agent, and a plurality of macropores are formed on the surface of the membrane, so that a nanofiltration membrane with small pores cannot be prepared.

Preferably, the tertiary amine type amphiphilic copolymer is an amphiphilic copolymer obtained by polymerizing a vinyl monomer containing a tertiary amine group and a hydrophobic vinyl monomer; more preferably, the vinyl monomer containing the tertiary amine group is selected from any one or any more of dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl methacrylamide, dimethylaminopropyl acrylamide, 4-vinylpyridine, 2-vinylpyridine and vinylimidazole, and the hydrophobic vinyl monomer is selected from any one or any more of methyl methacrylate, methyl acrylate, styrene, vinyl chloride, trifluoroethyl methacrylate, perfluorooctyl methacrylate, trifluoroethyl acrylate and perfluorooctyl acrylate.

Preferably, the quaternary ammonium salt macromolecules of the invention are products of quaternization and crosslinking of tertiary amine type amphiphilic copolymers and crosslinking agents, and the crosslinking agents are any one of polyhalide micromolecules and unsaturated halide oligomers.

Preferably, the polyhalide small molecule of the present invention is selected from any one or more of diiodoethane, dibromoethane, diiodopropane, dibromopropane, diiodobutane, dibromobutane, diiodopentane, dibromopentane, diiodohexane, dibromohexane, dichlorobenzyl, and dibrombenzyl, and the unsaturated halide of the present invention is selected from any one of chloromethyl styrene, bromomethyl styrene, and iodomethyl styrene.

Preferably, the film substrate material of the present invention is selected from any one of polyvinylidene fluoride, polyamide, polyethylene, polypropylene, polysulfone, polyethersulfone, polyacrylonitrile, polyphenylene oxide, and polyetheretherketone.

The invention also provides a preparation method of the positively charged nanofiltration membrane based on the tertiary amine type amphiphilic copolymer, which comprises the following steps:

(1) dissolving a membrane matrix material and a tertiary amine type amphiphilic copolymer in a membrane preparation solvent, uniformly mixing to prepare an electrically neutral membrane preparation solution, and curing from a coagulating bath by a solution phase inversion method to prepare an active precursor membrane containing a tertiary amine type polymer;

(2) dip-coating the prepared active precursor film in a cross-linking agent solution;

(3) and taking out the membrane after dip coating, and carrying out heat treatment to obtain the positively charged nanofiltration membrane based on the tertiary amine type amphiphilic copolymer.

The solution phase inversion method is a method in which a solvent (for example, water) that is miscible with a film forming solvent but is incapable of dissolving a film base material is used as a coagulation bath, and the film is solidified by exchanging the solvent with a non-solvent. The amphiphilic copolymer consists of a hydrophilic component and a hydrophobic component, and in the solution phase inversion process, the amphiphilic copolymer migrates to the surface of the membrane (one end of a water coagulation bath) under the action of the hydrophilic component, but the membrane-forming liquid is rapidly solidified in the coagulation bath, so that the migration of the amphiphilic copolymer in the body of the membrane is prevented after the membrane is solidified, and a large amount of the amphiphilic copolymer stays on the surface of the membrane, thereby forming an enrichment phenomenon. This enrichment phenomenon also occurs on the pore walls within the membrane body during the specific process of solution phase inversion.

The tertiary amine type amphiphilic copolymer is obtained by copolymerizing a vinyl monomer containing a tertiary amine group and a hydrophobic vinyl monomer, wherein the vinyl monomer residue containing the tertiary amine group in the copolymer is a hydrophilic component, and the hydrophobic vinyl monomer residue is a hydrophobic component. After the tertiary amine type amphiphilic copolymer is blended with a membrane matrix material, in the process of solution phase conversion, due to the hydrophilic action of tertiary amine groups, the tertiary amine groups are enriched towards the membrane surface (close to one end of a water coagulation bath), so that the content of the tertiary amine groups on the membrane surface after curing and film forming is far higher than that in the membrane body, namely, an active layer rich in the tertiary amine groups is formed on the membrane surface. The hydrophobic component in the tertiary amine type amphiphilic copolymer has good affinity with the membrane matrix material with the same hydrophobicity, so that the migration rate in the membrane is reduced to a certain extent, and the copolymer is ensured not to be lost from the membrane into a water coagulation bath; and the tertiary amine type amphiphilic copolymer is of a long-chain macromolecular structure and is also of a long-chain macromolecular structure with a film matrix material, and macromolecules are intertwined with the macromolecules to form an interpenetrating network structure, so that the copolymer is not easy to run off from the film, and the retention rate of the tertiary amine type amphiphilic copolymer in the film is improved. The end of the formed active precursor film close to the water coagulation bath is rich in the tertiary amine type amphiphilic copolymer, and the layer becomes a surface active layer; and the end far away from the water coagulation bath has less content of the tertiary amine type amphiphilic copolymer, is mainly composed of a film matrix material, mainly plays a role of supporting and becomes a supporting layer. And because the tertiary amine type amphiphilic copolymer macromolecules in the surface active layer and the membrane matrix material macromolecules in the supporting layer are mutually entangled, the combination between the surface active layer and the supporting layer is stable, the functional layer cannot be separated from the surface of the supporting layer in the using process, the long-time stability of the membrane performance is ensured, and the membrane has longer service life.

The effect can be achieved only by using an amphiphilic copolymer, and if the amphiphilic copolymer is not used and a hydrophilic tertiary amine polymer only containing a hydrophilic tertiary amine component but not containing a hydrophobic component is used, the hydrophilic tertiary amine polymer can be enriched to the surface of the membrane in the phase inversion membrane forming process, but the diffusion rate of molecules in the membrane is higher due to the absence of the hydrophobic component, and the hydrophilic tertiary amine polymer is dissolved out of the surface of the membrane before the membrane is solidified and enters a water coagulation bath, so that the hydrophilic tertiary amine polymer can become a pore-forming agent, a plurality of macropores are formed on the surface of the membrane, and a nanofiltration membrane with small pores cannot be prepared.

Preferably, the membrane substrate material in step (1) is selected from any one of polyvinylidene fluoride, polyamide, polyethylene, polypropylene, polysulfone, polyethersulfone, polyacrylonitrile, polyphenylene oxide and polyetheretherketone.

Preferably, the film-forming solvent in step (1) is one or more selected from the group consisting of N, N-dimethylformamide, N-dimethylacetamide, and N-methylpyrrolidone.

Preferably, the coagulation bath water in the step (1) has a coagulation bath temperature of 10-40 ℃.

Preferably, the concentration of the membrane matrix material in the step (1) is 10-30% by mass, and the concentration of the tertiary amine type amphiphilic copolymer is 1-10% by mass.

Preferably, the tertiary amine type amphiphilic copolymer in the step (1) is an amphiphilic copolymer obtained by polymerizing a vinyl monomer containing a tertiary amine group and a hydrophobic vinyl monomer; more preferably, the vinyl monomer containing the tertiary amine group is selected from any one or more of dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl methacrylamide, dimethylaminopropyl acrylamide, 4-vinylpyridine, 2-vinylpyridine and vinylimidazole; the hydrophobic vinyl monomer is selected from any one or more of methyl methacrylate, methyl acrylate, styrene, vinyl chloride, trifluoroethyl methacrylate, perfluorooctyl methacrylate, trifluoroethyl acrylate and perfluorooctyl acrylate.

Preferably, the cross-linking agent in the step (2) is any one of polyhalide small molecules and unsaturated halide oligomers. Preferably, the polyhalide small molecule is selected from any one or more of diiodoethane, dibromoethane, diiodopropane, dibromopropane, diiodobutane, dibromobutane, diiodopentane, dibromopentane, diiodohexane, dibromohexane, dichlorobenzyl and dibrombenzyl, and the unsaturated halide is selected from any one of chloromethyl styrene, bromomethyl styrene and iodomethyl styrene.

Preferably, the solvent of the crosslinking agent solution in the step (2) is selected from any one or more of cyclohexane, n-hexane, n-heptane, petroleum ether, benzene and toluene, and the preferable concentration of the crosslinking agent is 0.5-5% by mass.

Preferably, the heat treatment temperature in the step (3) is 30-80 ℃, and the heat treatment time is 1-48 h; more preferably, the heat treatment temperature is 50-70 ℃, and the heat treatment time is 5-20 h.

The positively charged nanofiltration membrane based on the tertiary amine type amphiphilic copolymer can be made into membranes in various forms, including flat membranes and hollow fiber membranes, and can also be made into flat membranes and hollow fiber membrane components.

Specifically, the solution phase inversion in step (1) to prepare the active precursor membrane (flat membrane) can adopt the following method: and scraping the membrane-forming solution on a stainless steel carrier, a glass carrier or a non-woven fabric to form a liquid membrane, and soaking the liquid membrane into a coagulating bath at the temperature of 10-40 ℃ to solidify and form a membrane. The solution phase inversion method for preparing active precursor membrane (hollow fiber membrane) is as follows: extruding the membrane-forming liquid from a spinning nozzle under the pressure of 0.1-0.3 MPa, simultaneously enabling the core liquid at the temperature of 20-60 ℃ to flow out from a central tube of the spinning nozzle at the flow speed of 10-50 ml/min, and immersing the liquid membrane into a coagulating bath at the temperature of 10-40 ℃ for solidification and membrane formation after passing through an air gap of 5-20 cm.

The dip-coating in the step (2) is to enable the surface of the membrane to adsorb a layer of polybasic halide (oligomer comprising polyhalide micromolecules and unsaturated chloride) cross-linking agent solution, the heat treatment in the step (3) is carried out at 30-80 ℃ for 1-48 h, so that the tertiary amine groups rich in the surface active layer and the polybasic halide cross-linking agent adsorbed on the surface are subjected to quaternization cross-linking reaction, the quaternization cross-linking reaction has high reaction activity at 30-80 ℃ and cannot damage the membrane structure, and the heat treatment time of 1-48 h is used for improving the production efficiency to the maximum extent while ensuring the reaction degree. The crosslinking reaction generated during the thermal nursing can play a role of shrinking the pores, so that the pores on the surface are shrunk to about 1nm from 100nm, nano-level substances can be separated, and the nano-filtration requirement is met. The quaternization can convert the tertiary amine on the surface of the membrane into a quaternary ammonium salt structure, the quaternary ammonium salt is positively charged, and the positively charged membrane surface can effectively improve the rejection rate of the membrane to the positive electric substances. The quaternization reaction and the crosslinking reaction occur simultaneously, the membrane is positively charged while the pore diameter of the membrane is reduced, and the operation is simple, convenient and effective. The preparation method of the positively charged nanofiltration membrane disclosed by the invention adopts a blending method, and is simple to operate and low in energy consumption.

The invention has the beneficial effects that:

2) According to the positively charged nanofiltration membrane based on the tertiary amine type amphiphilic copolymer, the tertiary amine type amphiphilic copolymer macromolecule quaternary ammonium salt in the functional layer and the membrane matrix material macromolecule in the supporting layer form an interpenetrating network, so that the functional layer and the supporting layer are combined more stably, the functional layer cannot be separated from the surface of the supporting layer in the membrane preparation process and the use process, the composition, the structure and the performance of the membrane are stable, and the membrane is durable and pressure-resistant, and has a longer service life.

3) The positive charge nanofiltration membrane based on the tertiary amine type amphipathic copolymer can obtain 30L/(m) at 0.3MPa²H) membrane flux, not only meets the requirements of nanofiltration operation on membrane flux, but also effectively improves the separation efficiency,the operation cost is reduced.

4) The positively charged multilayer nanofiltration membrane disclosed by the invention has the advantages that the surface is positively charged, the rejection effect on positively charged pollutants in water is more obvious, and the pollution resistance of the membrane is stronger.

Drawings

FIG. 1 is a schematic representation of the principle of synthesis of the amphipathic copolymer of example 1;

FIG. 2 is a schematic diagram of the change in membrane structure at different stages of preparation of example 1;

FIG. 3 is an XPS analysis of the film of example 1 at different stages of preparation, wherein the pure Polyethylene (PE) film is a flat film obtained by mixing 20% by weight of polyethylene in N, N-dimethylacetamide to form a film forming solution, scraping the film forming solution into a liquid film, and immersing the liquid film in water at 40 ℃ to solidify and form the film, and the flat film is used as a reference;

FIG. 4 is a graph showing contact angle test curves of the membrane surface in different preparation stages of example 1, in which a Polyethylene (PE) pure membrane is a flat membrane obtained by mixing 20% by mass of polyethylene in N, N-dimethylacetamide to form a membrane-forming solution, scraping the membrane-forming solution into a liquid membrane, and immersing the membrane-forming solution in water at 40 ℃ to solidify and form the membrane, and the flat membrane is used as a reference;

FIG. 5 is Zeta potential test curve of membrane surface in different preparation stages of example 1, wherein Polyethylene (PE) pure membrane is prepared by dissolving 20% polyethylene in N, N-dimethylacetamide by weight, mixing to prepare membrane-forming solution, scraping the membrane-forming solution into liquid membrane, and immersing in water at 40 ℃ to solidify into membrane, and the obtained flat membrane is used as reference;

FIG. 6 is an electron micrograph of the upper surface, the lower surface and the cross-sectional surface of the activated precursor membrane prepared in example 1 and the flat nanofiltration membrane prepared by further treating with a cross-linking agent;

FIG. 7 is the electron microscope images of the cross section, inner functional layer, outer functional layer, inner surface and outer surface of the active precursor membrane prepared in example 2 and the hollow fiber nanofiltration membrane prepared by further treating with a cross-linking agent.

Detailed Description

The present invention will be described in detail with reference to examples.

The invention provides a positively charged nanofiltration membrane based on a tertiary amine type amphiphilic copolymer, which consists of a neutral-charged macroporous supporting layer and a positively charged compact functional layer, wherein the macroporous supporting layer comprises a membrane matrix material and the tertiary amine type amphiphilic copolymer, the compact functional layer comprises cross-linked macromolecular quaternary ammonium salt, and the macromolecular quaternary ammonium salt in the compact functional layer and the membrane matrix material in the macroporous supporting layer form an interpenetrating network structure.

Preferably, the tertiary amine type amphiphilic copolymer is an amphiphilic copolymer obtained by polymerizing a vinyl monomer containing a tertiary amine group and a hydrophobic vinyl monomer; more preferably, the vinyl monomer containing the tertiary amine group is selected from any one or more of dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl methacrylamide, dimethylaminopropyl acrylamide, 4-vinylpyridine, 2-vinylpyridine and vinylimidazole; the hydrophobic vinyl monomer is selected from any one or more of methyl methacrylate, methyl acrylate, styrene, vinyl chloride, trifluoroethyl methacrylate, perfluorooctyl methacrylate, trifluoroethyl acrylate and perfluorooctyl acrylate.

Preferably, the quaternary ammonium salt macromolecules are products of quaternization and crosslinking of tertiary amine type amphiphilic copolymers and crosslinking agents, and the crosslinking agents are any one of polyhalide micromolecules and unsaturated halide oligomers.

Preferably, the polyhalide small molecule is any one or more of diiodoethane, dibromoethane, diiodopropane, dibromopropane, diiodobutane, dibromobutane, diiodopentane, dibromopentane, diiodohexane, dibromohexane, dichlorobenzyl and dibrombenzyl, and the unsaturated halide is any one of chloromethyl styrene, bromomethyl styrene and iodomethyl styrene.

The preparation method of the positively charged nanofiltration membrane based on the tertiary amine type amphiphilic copolymer comprises the following steps:

(1) dissolving a membrane matrix material and a tertiary amine type amphiphilic copolymer in a membrane preparation solvent, uniformly mixing to prepare an electrically neutral membrane preparation solution, and curing from a coagulating bath by a solution phase inversion method to prepare the active precursor membrane containing the tertiary amine type polymer. The general preparation of active precursor membranes (flat sheet membranes) is as follows: and scraping the membrane-forming solution on a stainless steel carrier, a glass carrier or a non-woven fabric to form a liquid membrane, and soaking the liquid membrane into a coagulating bath at the temperature of 10-40 ℃ to solidify and form a membrane. The general preparation method of the active precursor membrane (hollow fiber membrane) is as follows: extruding the membrane-forming liquid from a spinning nozzle under the pressure of 0.1-0.3 MPa, simultaneously enabling the core liquid at the temperature of 20-60 ℃ to flow out from a central tube of the spinning nozzle at the flow speed of 10-50 ml/min, and immersing the liquid membrane into a coagulating bath at the temperature of 10-40 ℃ for solidification and membrane formation after passing through an air gap of 5-20 cm.

Preferably, the film-forming solvent in step (1) is one or more of N, N-dimethylformamide, N-dimethylacetamide, and N-methylpyrrolidone.

Preferably, the coagulation bath in the step (1) is water, and the temperature of the coagulation bath is 10-40 ℃.

Preferably, the tertiary amine type amphiphilic copolymer in the step (1) is an amphiphilic copolymer with molecular weight of more than 103 and obtained by polymerizing a tertiary amine group-containing vinyl monomer and a hydrophobic vinyl monomer, wherein the tertiary amine group-containing vinyl monomer is selected from any one or more of dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl methacrylamide, dimethylaminopropyl acrylamide, 4-vinylpyridine, 2-vinylpyridine and vinylimidazole; the hydrophobic vinyl monomer is selected from any one or more of methyl methacrylate, methyl acrylate, styrene, vinyl chloride, trifluoroethyl methacrylate, perfluorooctyl methacrylate, trifluoroethyl acrylate and perfluorooctyl acrylate.

Preferably, the crosslinking agent in step (2) is any one of polyhalide small molecules and unsaturated halide oligomers, the polyhalide small molecules are any one or more of diiodoethane, dibromoethane, diiodopropane, dibromopropane, diiodobutane, dibromobutane, diiodopentane, dibromopentane, diiodohexane, dibromohexane, dichlorobenzyl and dibrombenzyl, and the unsaturated halide is any one of chloromethyl styrene, bromomethyl styrene and iodomethyl styrene.

Preferably, the solvent of the crosslinking agent solution in the step (2) is any one or more of cyclohexane, n-hexane, n-heptane, petroleum ether, benzene and toluene, and the concentration of the crosslinking agent is 0.5-5% by mass.

According to the preparation method of the positively charged nanofiltration membrane based on the tertiary amine type amphiphilic copolymer, the following examples are given. The concrete steps of the embodiment are the same as the previous embodiment steps, but the invention is not limited by the embodiment:

example 1

Dissolving 20% by mass of Polyethylene (PE), 1% by mass of a copolymer of dimethylaminoethyl methacrylate and methyl methacrylate (the copolymerization mechanism is shown in figure 1) in N, N-dimethylacetamide, mixing to prepare a membrane-forming solution, scraping the membrane-forming solution into a liquid membrane, immersing the liquid membrane in water at 40 ℃ for curing to form a membrane, and immersing and cleaning the obtained flat membrane in water to obtain the active precursor membrane. And (2) taking an n-hexane solution of dichlorobenzyl with the mass percentage of 5% as a cross-linking agent solution, dip-coating the prepared active precursor film in the cross-linking agent solution, taking out the active precursor film, and carrying out heat treatment at 80 ℃ for 1 hour to obtain the positively-charged flat nanofiltration membrane. The membrane structure changes of the membrane preparation liquid, the active precursor membrane and the nanofiltration membrane at three different preparation stages are shown in figure 2, the tertiary amine type amphiphilic copolymer in the membrane preparation liquid is uniformly distributed, the tertiary amine type amphiphilic copolymer in the active precursor membrane is enriched to the surface, and the pores in the nanofiltration membrane are further shrunk due to quaternization crosslinking.

FIG. 3 shows XPS spectra of films at various stages of preparation in this example. As can be seen in FIG. 3, the new peak at around 399.5eV, which is the peak for N1s, demonstrates that the tertiary amine-based amphiphilic copolymer is effectively retained in the membrane by the solution phase inversion process. Through quantitative calculation, the retention rate of the tertiary amine type amphiphilic copolymer in the membrane is 95.58%, and the loss phenomenon is little.

FIG. 4 is a contact angle test curve of the film surface at different stages of the preparation in this example. The smaller the contact angle, the more hydrophilic the surface of the membrane. The contact angle of the PE pure film is 95 degrees, and the hydrophobicity is very strong; the active precursor film blended with the tertiary amine type amphiphilic copolymer has good hydrophilicity and a contact angle reduced to 60 degrees due to the fact that a layer of tertiary amine groups are enriched on the surface; after the treatment of the cross-linking agent, the cross-linking agent and the tertiary amine group are subjected to quaternization cross-linking reaction, the tertiary amine is converted into quaternary ammonium salt, the hydrophilicity of the quaternary ammonium salt is better than that of the tertiary amine, the contact angle of the prepared nanofiltration membrane is further reduced to 25 degrees, and the hydrophilicity is good. The good hydrophilicity of the membrane can effectively improve the flux of the membrane, which is the basis for preparing the low-pressure high-flux nanofiltration membrane.

FIG. 5 is a Zeta potential test curve of the membrane surface at different stages of the preparation in this example. The isoelectric point of the PE pure film is 4.5, and the PE pure film shows weak electronegativity; the active precursor membrane blended with the tertiary amine type amphiphilic copolymer is weak in electropositivity due to the fact that a layer of tertiary amine groups is enriched on the surface, and the isoelectric point of the prepared active precursor membrane is increased to 6; after being treated by the cross-linking agent, the cross-linking agent and tertiary amine groups are subjected to quaternization cross-linking reaction, the tertiary amine is converted into quaternary ammonium salt with strong positive charges, the isoelectric point of the prepared nanofiltration membrane is further increased to 10.5, and the nanofiltration membrane is always positive in a wider pH range. The nano-filtration membrane is always positively charged in the nano-filtration operation process, and has higher retention rate for positively charged substances.

FIG. 6 is an electron micrograph of the upper surface, the lower surface and the cross-section of the active precursor membrane and the nanofiltration membrane prepared in this example. The upper surface of the active precursor film has a plurality of micropores greater than 100 nm. The aperture of the upper surface of the nanofiltration membrane prepared by quaternization and crosslinking treatment of the crosslinking agent is reduced to 1nm, the surface structure is still compact and uniform, and the nanofiltration level is achieved. From the cross section structure of the membrane, the active precursor membrane has no obvious compact functional layer, and the nanofiltration membrane prepared by the treatment of the cross-linking agent has a very thin compact functional layer, so that the nanofiltration membrane has the functions of high flux and high interception.

The method comprises the steps of measuring the permeation flux of a nanofiltration membrane by taking 0.01mol/L inorganic salt aqueous solution as a feed liquid, calculating the flux of the membrane according to the volume of the membrane passing through unit area of unit time, deducing relevant concentration by measuring the conductivity of the feed liquid and an exudate, and calculating the rejection rate of the membrane to inorganic salt according to the concentration ratio of the feed liquid to the exudate. The pure water flux of the positively charged flat nanofiltration membrane prepared by the embodiment is 32L/(m) under the test conditions of 25 ℃ and 0.3MPa²H), the retention rate for 0.01mol/L calcium chloride is 99.4%, the retention rate for Congo red is 99.9%, the membrane is placed in deionized water at 60 ℃ and is shaken for 20 days at constant temperature, and the flux and the retention performance are kept unchanged.

Comparative example 1

Dissolving 20% by mass of polyethylene and 1% by mass of dimethylaminoethyl methacrylate homopolymer in N, N-dimethylacetamide, mixing to prepare a membrane preparation solution, scraping the membrane preparation solution into a liquid membrane, immersing the liquid membrane in water at 40 ℃ for curing to form a membrane, and immersing and cleaning the obtained flat membrane in water to obtain the active precursor membrane. And (2) taking an n-hexane solution of dichlorobenzyl with the mass percentage of 5% as a cross-linking agent solution, dip-coating the prepared active precursor film in the cross-linking agent solution, taking out the active precursor film, and carrying out heat treatment at 80 ℃ for 1 hour to obtain the positively-charged flat nanofiltration membrane.

Two nanofiltration membranes were prepared according to comparative example 1 and comparative example 1:

the pure water flux of the positively charged nanofiltration membrane prepared in the example 1 is 32L/(m) under the test conditions of 25 ℃ and 0.3MPa²H), a retention rate of 99.4% for 0.01mol/L calcium chloride, 49.7% for 0.01mol/L sodium chloride and 99.9% for Congo red. The pure water flux of the membrane prepared in comparative example 1 was 131.5L/(m) at 25 deg.C and 0.3MPa²H) a retention of 0 for 0.01mol/L calcium chloride and 21.9% for Congo red. It is shown that the membrane prepared by using the hydrophilic tertiary amine polymer in comparative example 1 has no interception effect and no practical application value although the flux is large because the hydrophilic tertiary amine polymer is completely lost from the membrane during membrane formation and a plurality of macropores are formed on the surface of the membrane. The above results demonstrate that in order to prepare high performance nanofiltration membranes, it is necessary to use tertiary amine-type amphiphilic copolymers.

Comparative example 2

Dissolving 20% of polyethylene in N, N-dimethylacetamide by mass, mixing to prepare a membrane preparation solution, scraping the membrane preparation solution into a liquid membrane, soaking the liquid membrane into water at 40 ℃ for curing and membrane formation, and soaking and cleaning the obtained flat membrane in water to obtain the polyethylene flat membrane. Taking a polyethylene flat membrane as a support membrane, adopting an interfacial polymerization method, firstly soaking the polyethylene flat membrane in a copolymer aqueous solution of dimethylaminoethyl methacrylate and methyl methacrylate with the mass percentage of 1%, taking out and draining; and soaking the membrane in a n-hexane solution of dichlorobenzyl with the mass percentage of 5%, taking out the membrane, and carrying out heat treatment at 80 ℃ for 1 hour to obtain the positively charged flat nanofiltration membrane.

The stability of the two nanofiltration membranes prepared in example 1 and comparative example 2 was compared:

the positively charged nanofiltration membrane prepared by re-crosslinking by the solution phase inversion method in example 1 is placed in deionized water at 60 ℃ and vibrated at constant temperature for 20 days, and the membrane flux and the rejection rate are kept unchanged.

After the positively charged nanofiltration membrane prepared by the interfacial polymerization method in comparative example 1 is placed in deionized water at 60 ℃ and is vibrated at constant temperature for 20 days, the rejection rate is reduced to 20 percent of the original rejection rate. The nano-filtration membrane prepared by adopting the same raw materials through interfacial polymerization has no connection with a strong chemical effect between the supporting layer and the functional layer, and the functional layer on the surface falls off from the supporting layer in the deionized water oscillation process at 60 ℃, so that the rejection rate is reduced sharply.

The nanofiltration membrane prepared by taking polyvinylidene fluoride, polyamide, polypropylene, polysulfone, polyethersulfone, polyphenylene oxide, polyacrylonitrile and polyetheretherketone as a supporting layer and adopting interfacial polymerization also has the phenomenon that the rejection rate is sharply reduced. The above results illustrate the advantages of using the solution phase inversion method of the present invention to prepare nanofiltration membranes relative to interfacial polymerization.

Example 2

Dissolving 18 mass percent of polyacrylonitrile, 5 mass percent of diethylaminoethyl acrylate and vinyl chloride copolymer in N, N-dimethylformamide, mixing to prepare a membrane preparation solution, extruding the membrane preparation solution from a spinning nozzle under the pressure of 0.3MPa, simultaneously allowing 30 ℃ core solution to flow out from a central tube of the spinning nozzle at the flow rate of 30ml/min, immersing the liquid membrane into 10 ℃ water after passing through an air gap of 20 cm, curing to form a membrane, and soaking and cleaning the obtained hollow fiber membrane in the water to obtain the active precursor membrane. And (2) taking an n-heptane solution of dibromopentane with the mass percentage content of 3% as a cross-linking agent solution, dip-coating the prepared active precursor membrane in the cross-linking agent solution, taking out the active precursor membrane, and carrying out heat treatment at 30 ℃ for 48 hours to obtain the positively-charged hollow fiber nanofiltration membrane.

FIG. 7 is an electron microscope image of the cross section, inner functional layer, outer functional layer, inner surface and outer surface of the active precursor membrane and nanofiltration membrane prepared in this example. The outer surface of the active precursor film has a plurality of micropores greater than 100 nm. The aperture of the outer surface of the nanofiltration membrane prepared by quaternization and crosslinking treatment of the crosslinking agent is reduced to 1nm, the surface structure is still compact and uniform, and the nanofiltration level is achieved. From the cross section structure of the membrane, the active precursor membrane has no obvious compact functional layer, and the nanofiltration membrane prepared by the treatment of the cross-linking agent has a very thin compact functional layer, so that the nanofiltration membrane has the functions of high flux and high interception.

The positively charged hollow fiber nanofiltration membrane prepared by the embodiment has the pure water flux of 51L/(m) under the test conditions of 25 ℃ and 0.3MPa²H), the retention rate for 0.01mol/L calcium chloride is 93.7%, the retention rate for Congo red is 99.2%, and the membrane is placed in deionized water at 60 ℃ and is vibrated at constant temperature for 20 days, so that the flux and the retention performance are kept unchanged.

Example 3

Dissolving 20% of polyvinylidene fluoride and 10% of copolymer of 4-vinylpyridine and styrene in N-methylpyrrolidone, mixing to prepare membrane preparation liquid, scraping the membrane preparation liquid into a liquid membrane, immersing the liquid membrane into water at 30 ℃ for curing to form a membrane, and immersing and cleaning the obtained flat membrane in water to obtain the active precursor membrane. Taking toluene solution of dibromohexane with the mass percentage content of 0.5%, dibromobutane with the mass percentage content of 0.5% and diiodopentane with the mass percentage content of 0.5% as cross-linking agent solution, dip-coating the prepared active precursor membrane in the cross-linking agent solution, taking out, and carrying out heat treatment at 60 ℃ for 3 hours to obtain the positively charged flat nanofiltration membrane.

The pure water flux of the positively charged flat nanofiltration membrane prepared by the embodiment is 47L/(m) under the test conditions of 25 ℃ and 0.3MPa²H), the retention rate for 0.01mol/L calcium chloride is 92.4%, the retention rate for Congo red is 99.8%, the membrane is placed in deionized water at 60 ℃ and is shaken at constant temperature for 20 days, and the flux and the retention performance are kept unchanged.

Example 4

Dissolving 30 mass percent of polyamide and 3.5 mass percent of copolymer of dimethylaminoethyl acrylate and methyl acrylate in a mixed solvent of N, N-dimethylformamide/N, N-dimethylacetamide (1:1) to prepare a membrane-forming solution, extruding the membrane-forming solution from a spinning nozzle under the pressure of 0.1MPa, simultaneously enabling a core solution at the temperature of 20 ℃ to flow out from a central tube of the spinning nozzle at the flow rate of 10ml/min, immersing the liquid membrane in water at the temperature of 25 ℃ after passing through an air gap of 10 cm to solidify into a membrane, and soaking and cleaning the obtained hollow fiber membrane in water to obtain the active precursor membrane. And (2) taking a cyclohexane solution of dibromide benzyl with the mass percentage of 3.5% and dibromoethane with the mass percentage of 0.5% as a cross-linking agent solution, dip-coating the prepared active precursor membrane in the cross-linking agent solution, taking out, and carrying out heat treatment at 50 ℃ for 20 hours to obtain the positively charged hollow fiber nanofiltration membrane.

The pure water flux of the positively charged hollow fiber nanofiltration membrane prepared by the embodiment is 55L/(m) under the test conditions of 25 ℃ and 0.3MPa²H), the retention rate for 0.01mol/L calcium chloride is 90.1%, the retention rate for Congo red is 99.5%, the membrane is placed in deionized water at 60 ℃ and is shaken for 20 days at constant temperature, and the flux and the retention performance are kept unchanged.

Example 5

Dissolving 10% by mass of polyphenyl ether and 10% by mass of a copolymer of diethylaminoethyl methacrylate and trifluoroethyl methacrylate in a mixed solvent of N, N-dimethylformamide/N, N-dimethylacetamide/N-methylpyrrolidone (1:1:1) to prepare a membrane-forming solution, scraping the membrane-forming solution into a liquid membrane, immersing the liquid membrane into water at 25 ℃ to solidify and form a membrane, and immersing and cleaning the obtained flat membrane in water to obtain the active precursor membrane. And (2) taking a benzene solution of diiodoethane with the mass percentage of 5% as a cross-linking agent solution, dip-coating the prepared active precursor membrane in the cross-linking agent solution, taking out, and carrying out heat treatment at 70 ℃ for 6 hours to obtain the positively-charged flat nanofiltration membrane.

The pure water flux of the positively charged flat nanofiltration membrane prepared by the embodiment is 57L/(m) under the test conditions of 25 ℃ and 0.3MPa²H), the retention rate for 0.01mol/L calcium chloride is 90.4%, the retention rate for Congo red is 99.0%, the membrane is placed in deionized water at 60 ℃ and is shaken for 20 days at constant temperature, and the flux and the retention performance are kept unchanged.

Example 6

15 percent of polypropylene, 3.5 percent of copolymer of dimethylamino propyl methacrylamide and perfluorooctyl methacrylate by mass percent are dissolved in N, N-dimethylacetamide to prepare membrane forming liquid, the membrane forming liquid is extruded from a spinning nozzle under the pressure of 0.2MPa, core liquid at 60 ℃ flows out from a central tube of the spinning nozzle at the flow rate of 50ml/min, the liquid membrane passes through an air gap of 15 cm and then is immersed into water at 30 ℃ to be solidified into a membrane, and the obtained hollow fiber membrane is immersed and cleaned by the water to obtain the active precursor membrane. And (2) taking a petroleum ether solution of polychloromethylstyrene with the mass percentage content of 0.5% as a cross-linking agent solution, dip-coating the prepared active precursor membrane in the cross-linking agent solution, taking out, and carrying out heat treatment at 65 ℃ for 17 hours to obtain the positively charged hollow fiber nanofiltration membrane.

The positively charged hollow fiber nanofiltration membrane prepared by the embodiment has the pure water flux of 31L/(m) under the test conditions of 25 ℃ and 0.3MPa²H), the retention rate for 0.01mol/L calcium chloride is 92.4%, the retention rate for Congo red is 99.2%, the membrane is placed in deionized water at 60 ℃ and is shaken at constant temperature for 20 days, and the flux and the retention performance are kept unchanged.

Example 7

Dissolving 10 mass percent of polysulfone, 10 mass percent of dimethylamino propyl acrylamide and 10 mass percent of perfluoro octyl acrylate copolymer in N, N-dimethylformamide to prepare membrane preparation liquid, scraping the membrane preparation liquid into a liquid membrane, immersing the liquid membrane into water at 25 ℃ to solidify and form a membrane, and immersing and cleaning the obtained flat membrane with water to obtain the active precursor membrane. Dissolving diiodohexane with the mass percentage of 1% in a benzene/petroleum ether (1:1) mixed solvent solution to serve as a cross-linking agent solution, dip-coating the prepared active precursor membrane in the cross-linking agent solution, taking out the active precursor membrane, and carrying out heat treatment at 60 ℃ for 10 hours to obtain the positively-charged flat nanofiltration membrane.

The pure water flux of the positively charged flat nanofiltration membrane prepared by the embodiment is 30.5L/(m) under the test conditions of 25 ℃ and 0.3MPa²H), the retention rate for 0.01mol/L calcium chloride is 92.1 percent, the retention rate for Congo red is 99.5 percent, the membrane is placed in deionized water at 60 ℃ and is vibrated for 20 days at constant temperature, and the flux and the retention performance are kept unchanged.

Example 8

Dissolving 18 mass percent of polyether sulfone, 2.5 mass percent of 2-vinylpyridine and trifluoroethyl acrylate copolymer in N, N-dimethylformamide to prepare a membrane-forming solution, extruding the membrane-forming solution from a spinning nozzle under the pressure of 0.3MPa, simultaneously enabling 45 ℃ core solution to flow out from a central tube of the spinning nozzle at the flow rate of 35ml/min, immersing the liquid membrane into 25 ℃ water after passing through an air gap of 5 cm to form a membrane by curing, and soaking and cleaning the obtained hollow fiber membrane in water to obtain the active precursor membrane. Dissolving diiodopropane with the mass percentage of 1.5% in a mixed solvent of n-hexane/n-heptane/petroleum ether (1:1:1) to serve as a cross-linking agent solution, dip-coating the prepared active precursor membrane in the cross-linking agent solution, taking out, and carrying out heat treatment at 55 ℃ for 16 hours to obtain the positively-charged asymmetric hollow fiber nanofiltration membrane.

The positively charged hollow fiber nanofiltration membrane prepared by the embodiment has the pure water flux of 32L/(m) under the test conditions of 25 ℃ and 0.3MPa²H), the retention rate for 0.01mol/L calcium chloride is 96.2%, the retention rate for Congo red is 99.2%, the membrane is placed in deionized water at 60 ℃ and is vibrated for 20 days at constant temperature, and the flux and the retention performance are kept unchanged.

Example 9

Dissolving 22% by mass of polyetheretherketone and 5% by mass of a copolymer of vinylimidazole and styrene in N, N-dimethylformamide to prepare a membrane preparation solution, scraping the membrane preparation solution into a liquid membrane, immersing the liquid membrane into water at 25 ℃ to solidify and form a membrane, and immersing and cleaning the obtained flat membrane in water to obtain the active precursor membrane. And (2) taking dibromopropane with the mass percentage of 0.5 percent and diiodobutane with the mass percentage of 1.5 percent as a cross-linking agent solution in petroleum ether solution, dip-coating the prepared active precursor membrane in the cross-linking agent solution, taking out, and carrying out heat treatment at 60 ℃ for 14 hours to obtain the positively charged flat nanofiltration membrane.

The pure water flux of the positively charged flat nanofiltration membrane prepared by the embodiment is 84L/(m) under the test conditions of 25 ℃ and 0.3MPa²H), the retention rate for 0.01mol/L calcium chloride is 92.9 percent, the retention rate for Congo red is 99.7 percent, the membrane is placed in deionized water at 60 ℃ and is vibrated for 20 days at constant temperature, and the flux and the retention performance are kept unchanged.

Example 10

Dissolving 20 mass percent of polyphenyl ether and 10 mass percent of copolymer of dimethylaminoethyl methacrylate and trifluoroethyl methacrylate in a mixed solvent of N, N-dimethylformamide/N, N-dimethylacetamide/N-methylpyrrolidone (1:1:1) to prepare a membrane-forming solution, scraping the membrane-forming solution into a liquid membrane, immersing the liquid membrane into water at 25 ℃ to solidify and form a membrane, and immersing and cleaning the obtained flat membrane in water to obtain the active precursor membrane. And (2) taking a benzene solution of polybromomethylstyrene with the mass percentage content of 2% as a cross-linking agent solution, dip-coating the prepared active precursor film in the cross-linking agent solution, taking out, and carrying out heat treatment at 65 ℃ for 8 hours to obtain the positively-charged flat nanofiltration membrane.

The pure water flux of the positively charged flat nanofiltration membrane prepared by the embodiment is 52L/(m) under the test conditions of 25 ℃ and 0.3MPa²H), the retention rate for 0.01mol/L calcium chloride is 91.2%, the retention rate for Congo red is 99.4%, the membrane is placed in deionized water at 60 ℃ and is shaken at constant temperature for 20 days, and the flux and the retention performance are kept unchanged.

Example 11

And (2) dissolving 23% by mass of polyacrylonitrile, 4.5% by mass of diethylaminoethyl acrylate and vinyl chloride copolymer in N, N-dimethylformamide, mixing to prepare a membrane preparation solution, extruding the membrane preparation solution from a spinning nozzle under the pressure of 0.3MPa, allowing a core solution at 30 ℃ to flow out from a central tube of the spinning nozzle at the flow rate of 25ml/min, immersing the liquid membrane into water at 15 ℃ after passing through an air gap of 10 cm, curing to form a membrane, and soaking and cleaning the obtained hollow fiber membrane in water to obtain the active precursor membrane. And (2) taking an n-heptane solution of 2.5% by mass of poly (iodomethylstyrene) as a cross-linking agent solution, dip-coating the prepared active precursor membrane in the cross-linking agent solution, taking out, and carrying out heat treatment at 40 ℃ for 40 hours to obtain the positively-charged hollow fiber nanofiltration membrane.

The pure water flux of the positively charged hollow fiber nanofiltration membrane prepared by the embodiment is 46L/(m) under the test conditions of 25 ℃ and 0.3MPa²H), the retention rate for 0.01mol/L calcium chloride is 95.3%, the retention rate for Congo red is 99.8%, the membrane is placed in deionized water at 60 ℃ and is shaken at constant temperature for 20 days, and the flux and the retention performance are kept unchanged.

Claims

1. A preparation method of a positively charged nanofiltration membrane based on a tertiary amine type amphiphilic copolymer is characterized by comprising the following steps:

(1) dissolving a membrane matrix material and a tertiary amine type amphiphilic copolymer in a membrane preparation solvent, uniformly mixing to prepare an electrically neutral membrane preparation solution, and curing from a coagulating bath by a solution phase inversion method to prepare an active precursor membrane containing the tertiary amine type amphiphilic copolymer;

(2) dip-coating the active precursor film prepared in the step (1) in a cross-linking agent solution;

(3) taking out the membrane subjected to dip coating in the step (2), and carrying out heat treatment to obtain a quaternized crosslinked positively charged nanofiltration membrane;

the tertiary amine type amphiphilic copolymer is a copolymer of dimethylaminoethyl methacrylate and methyl methacrylate, a copolymer of diethylaminoethyl acrylate and vinyl chloride, a copolymer of 4-vinylpyridine and styrene, a copolymer of dimethylaminoethyl acrylate and methyl acrylate, a copolymer of diethylaminoethyl methacrylate and trifluoroethyl methacrylate, a copolymer of dimethylaminopropyl methacrylamide and perfluorooctyl methacrylate, a copolymer of dimethylaminopropyl acrylamide and perfluorooctyl acrylate, a copolymer of 2-vinylpyridine and trifluoroethyl acrylate, a copolymer of vinylimidazole and styrene, a copolymer of dimethylaminoethyl methacrylate and trifluoroethyl methacrylate or a copolymer of diethylaminoethyl acrylate and vinyl chloride;

in the electrically neutral membrane-making liquid in the step (1), the concentration of a membrane matrix material is 10-30% by mass, and the concentration of a tertiary amine type amphiphilic copolymer is 1-10% by mass;

the cross-linking agent in the cross-linking agent solution in the step (2) is a polyhalide micromolecule or an unsaturated halide oligomer; the polyhalide small molecule comprises any one or more of diiodoethane, dibromoethane, diiodopropane, dibromopropane, diiodobutane, dibromobutane, diiodopentane, dibromopentane, diiodohexane, dibromohexane, dichlorobenzyl and dibrombenzyl; the unsaturated halide oligomer is polychloromethylstyrene, polybromomethylstyrene or polyiodomethylstyrene;

the temperature of the heat treatment in the step (3) is 30-80 ℃, and the time of the heat treatment is 1-48 h.

2. The method according to claim 1, wherein the film matrix material in step (1) is polyethylene, polyacrylonitrile, polyvinylidene fluoride, polyamide, polyphenylene oxide, polypropylene, polysulfone, polyethersulfone or polyetheretherketone.

3. The production method according to claim 1 or 2, characterized in that the film-forming solvent of step (1) includes any one or any plural of N, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone.

4. The method according to claim 1, wherein the temperature of the coagulation bath in the step (1) is 10 to 40 ℃, and the coagulation bath is a water coagulation bath.

5. The method according to claim 1, wherein the solvent of the crosslinking agent solution of step (2) comprises any one or more of cyclohexane, n-hexane, n-heptane, petroleum ether, benzene and toluene.

6. The preparation method according to claim 1 or 5, wherein the mass percentage of the cross-linking agent in the cross-linking agent solution in the step (2) is 0.5-5%.

7. The method according to claim 6, wherein the electrically neutral dope solution of step (2) is solidified from a coagulating bath by a solution phase inversion method, and the method for preparing the active precursor film containing the tertiary amine type amphiphilic copolymer comprises a first method and a second method;

the first method comprises the steps of:

scraping the electroneutral membrane-making solution on a stainless steel carrier, a glass carrier or a non-woven fabric to form a liquid membrane, and immersing the liquid membrane into a coagulating bath at the temperature of 10-40 ℃ for solidification to form a membrane;

the second method comprises the steps of:

and extruding the electrically neutral membrane-forming liquid from a spinning nozzle under the pressure of 0.1-0.3 MPa, simultaneously enabling the core liquid at the temperature of 20-60 ℃ to flow out from a central tube of the spinning nozzle at the flow speed of 10-50 mL/min, and immersing the liquid membrane into a coagulating bath at the temperature of 10-40 ℃ for solidification and membrane formation after passing through an air gap of 5-20 cm.

8. The positive charge nanofiltration membrane based on the tertiary amine type amphiphilic copolymer obtained by the preparation method of any one of claims 1 to 7, wherein the positive charge nanofiltration membrane consists of a charge-neutral macroporous support layer and a positively charged dense functional layer, the macroporous support layer comprises a membrane matrix material and the tertiary amine type amphiphilic copolymer, the dense functional layer comprises a cross-linked macromolecular quaternary ammonium salt, and the macromolecular quaternary ammonium salt in the dense functional layer and the membrane matrix material in the macroporous support layer form an interpenetrating network structure; the content of the tertiary amine groups on the surface of the nanofiltration membrane is far higher than that of the tertiary amine groups in the membrane body.