CN111659270A - Nanofiltration membrane, preparation method and application thereof - Google Patents

Nanofiltration membrane, preparation method and application thereof Download PDF

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Publication number
CN111659270A
CN111659270A CN201910165966.3A CN201910165966A CN111659270A CN 111659270 A CN111659270 A CN 111659270A CN 201910165966 A CN201910165966 A CN 201910165966A CN 111659270 A CN111659270 A CN 111659270A
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membrane
nanofiltration membrane
nanofiltration
superfine
microfiltration
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靳健
朱玉长
王祯宜
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Suzhou Institute of Nano Tech and Nano Bionics of CAS
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Suzhou Institute of Nano Tech and Nano Bionics of CAS
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/66—Polymers having sulfur in the main chain, with or without nitrogen, oxygen or carbon only
    • B01D71/68—Polysulfones; Polyethersulfones
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/027—Nanofiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0002—Organic membrane manufacture
    • B01D67/0006—Organic membrane manufacture by chemical reactions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/10—Supported membranes; Membrane supports
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/56—Polyamides, e.g. polyester-amides
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/442—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by nanofiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/24—Mechanical properties, e.g. strength
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/08—Seawater, e.g. for desalination
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A20/00—Water conservation; Efficient water supply; Efficient water use
    • Y02A20/124—Water desalination
    • Y02A20/131—Reverse-osmosis

Abstract

The invention discloses a nanofiltration membrane, a preparation method and application thereof. The nanofiltration membrane comprises a supporting base membrane and an active separation layer arranged on the supporting base membrane, wherein the active separation layer has an interpenetrating network structure, and the interpenetrating network structure is mainly formed by mutually penetrating polyamide and superfine nano-fibers which are formed by a polyethyleneimine monomer and an acyl chloride monomer through interfacial polycondensation reaction. The preparation method comprises the following steps: arranging a superfine nanofiber layer on the microfiltration membrane to prepare a superfine nanofiber/microfiltration membrane composite substrate; and carrying out interfacial polycondensation reaction on a polyethyleneimine monomer and an acyl chloride monomer on the surface of the superfine nanofiber/microfiltration membrane composite substrate, and then carrying out heat treatment to obtain the nanofiltration membrane. The preparation method of the nanofiltration membrane is simple, and the obtained nanofiltration membrane has high flux and high salt rejection performance, so that the desalination energy consumption cost is reduced, and the nanofiltration membrane has wide application prospects in the aspects of seawater desalination pretreatment, water softening and the like.

Description

Nanofiltration membrane, preparation method and application thereof
Technical Field
The invention relates to a nanofiltration membrane, in particular to an ultrahigh flux nanofiltration membrane with a novel structure, a preparation method thereof and application of the nanofiltration membrane in the field of water treatment, and belongs to the technical field of materials.
Background
The multivalent metal ions in the water body can cause harm to human health, and the deposited scale of calcium ions, magnesium ions and the like can cause serious problems of pipeline blockage, heat exchange degradation and the like on household and industrial equipment, so that the removal of multivalent cations in the water is necessary. Compared with the traditional lime softening and ion exchange resin method, the membrane separation method has great advantages in the aspect of water softening due to the characteristics of high separation efficiency, greenness and the like. However, the membrane separation method requires an external pressure to drive the filtration, which means additional energy consumption, so that it is necessary to prepare a high-flux membrane to reduce energy consumption. Nanofiltration is a membrane separation technology between ultrafiltration and reverse osmosis, mainly intercepts molecules with molecular weight more than 200 and divalent or high-valence salt ions, saves energy consumption due to adjustable selectivity, high flux and low operation pressure, and has great application prospect in the aspects of sewage treatment, seawater desalination pretreatment and the like. At present, commercial nanofiltration membranes are mainly of composite membrane structures and are composed of a polysulfone ultrafiltration membrane supporting layer and a selection layer obtained by interfacial polymerization on the polysulfone ultrafiltration membrane supporting layer by taking polyamine and polyacyl chloride as monomers, wherein the compactness and the charging performance of the polyamide selection layer play a key role in intercepting ions. However, most nanofiltration membranes are negatively charged and require a very dense selection layer for the rejection of positive ions, which means that flux is sacrificed. And the positive nanofiltration membrane can simultaneously utilize electrostatic repulsion to intercept multivalent positive ions, and a loose structure can provide higher flux under the condition of ensuring high interception, so that the energy consumption and the cost are saved. The electropositive nanofiltration membrane is mainly prepared by introducing molecules with positive charges by methods of interfacial polymerization, surface modification and the like, most commonly used methods are polyethyleneimine, and a large amount of amino groups in a macromolecular chain of the polyethyleneimine are easily protonated to ensure that the membrane is positively charged. But the flux of most positive electricity nanofiltration membranes is low at present. According to the related document Single-Walled Carbon Nanotube Supported nanofilation Membrane with a near 10nm thin Polyamide Selective Layer for High-Flux and High-rejection depletion, Small,12,36,5034-5041, the reduction of the thickness of the Polyamide Layer can effectively increase the Flux. However, due to the slow diffusion of the high molecular amine monomer, the thickness of the electropositive nanofiltration membrane obtained by interfacial polymerization on the traditional ultrafiltration membrane is difficult to reduce to below hundred nanometers, and the corresponding filtration flux is very low.
Disclosure of Invention
The invention mainly aims to provide an ultra-high flux nanofiltration membrane and a preparation method thereof, so as to overcome the defects in the prior art.
The invention also aims to provide application of the nanofiltration membrane in the field of water treatment.
In order to achieve the purpose, the technical scheme adopted by the invention comprises the following steps:
the embodiment of the invention provides a nanofiltration membrane, which comprises a supporting bottom membrane and an active separation layer arranged on the supporting bottom membrane, wherein the active separation layer has an interpenetrating network structure, and the interpenetrating network structure is mainly formed by mutually penetrating polyamide and superfine nanofibers, wherein the polyamide is formed by carrying out interfacial polycondensation reaction on a polyethyleneimine monomer and an acyl chloride monomer.
In some embodiments, the nanofiltration membrane comprises a supporting base membrane, an ultrafine nanofiber layer and an active separation layer, which are sequentially stacked.
In some embodiments, the ultra-fine nanofibers comprise any one or a combination of two or more of single-walled carbon nanotubes and/or single-walled carbon nanotube derivatives, metal oxide nanowires and/or metal oxide nanowire derivatives, metal hydroxide nanowires and/or metal hydroxide nanowire derivatives.
The embodiment of the invention also provides a preparation method of the nanofiltration membrane, which comprises the following steps:
arranging a superfine nanofiber layer on the microfiltration membrane to prepare a superfine nanofiber/microfiltration membrane composite substrate;
and carrying out interfacial polycondensation reaction on a polyethyleneimine monomer and an acyl chloride monomer on the surface of the superfine nanofiber/microfiltration membrane composite substrate, and then carrying out heat treatment to obtain the nanofiltration membrane.
In some embodiments, the preparation method specifically comprises: dispersing the superfine nano-fiber in a solvent to form a dispersion liquid, and depositing the dispersion liquid on a microfiltration membrane in a filtering mode to prepare the superfine nano-fiber/microfiltration membrane composite substrate.
In some embodiments, the preparation method specifically comprises: adding a polyethyleneimine monomer solution to the surface of the superfine nanofiber/microfiltration membrane composite substrate, and infiltrating the surface; and
and applying the acyl chloride monomer solution on the surface of the superfine nanofiber/microfiltration membrane composite substrate, and infiltrating the surface to perform interfacial polycondensation reaction on the polyethyleneimine monomer and the acyl chloride monomer.
The embodiment of the invention also provides a nanofiltration membrane prepared by the method.
The embodiment of the invention also provides application of the loose nanofiltration membrane in the fields of seawater desalination pretreatment, sewage treatment or water softening.
Compared with the prior art, the invention has the advantages that:
1) the nanofiltration membrane provided by the invention has a structure that the superfine nanofiber network and the polymer are mutually penetrated, and the superfine nanofiber penetrates through the polyamide layer to play a good mechanical supporting role, so that the ultrathin polyamide layer has pressure resistance and long-time filtration stability; the superfine nano-fiber also plays a role in doping and reducing water transmission resistance in the polyamide layer;
2) the separation layer of the nanofiltration membrane provided by the invention is ultrathin and can reach below 30 nm. In the forming process of polyamide, the superfine nano-fiber has a limiting effect on the diffusion of the polyethyleneimine, so that the polyamide grows in a superfine nano-fiber network, an ultrathin polyamide layer can be obtained, the quality of the polyamide layer is ensured, and the flux and interception of the nanofiltration membrane are maintained at a high level;
3) the nanofiltration membrane provided by the invention has ultrahigh separated water flux of 20-35L m-2h-1bar-1；
4) The nanofiltration membrane provided by the invention is used for the treatment of multivalent cation salt solution (such as MgCl)2) The retention rate is higher and can reach more than 96 percent;
5) the preparation method of the nanofiltration membrane provided by the invention is simple;
6) the nanofiltration membrane provided by the invention has high flux and high salt rejection performance, so that the desalting energy consumption cost is reduced, the nanofiltration membrane has good long-time stability, can be used for removing multivalent positive ions, dyes, organic molecules and the like in a water body, and has wide application prospects in the aspects of seawater desalting pretreatment, municipal sewage treatment, tap water quality softening and the like.
Drawings
Fig. 1 is a schematic structural diagram of a nanofiltration membrane according to an exemplary embodiment of the present invention.
Detailed Description
In view of the deficiencies in the prior art, the inventors of the present invention have long studied and found a great deal of practice that controlling the thickness of the polyamide layer by controlling the diffusion of the high molecular amine monomer would be an effective method. The high molecular amine monomer is limited in an ultrathin two-dimensional network structure, and a polyamide layer generated after crosslinking has a corresponding thickness. Therefore, the ultrathin defect-free electropositive nanofiltration membrane can be obtained, and the high salt rejection rate is ensured while the water flux is improved. Based on the discovery, the inventor provides an ultra-high flux nanofiltration membrane and a preparation method thereof.
The technical solution, its implementation and principles, etc. will be further explained as follows.
In one aspect of the technical scheme, the nanofiltration membrane comprises a supporting bottom membrane and an active separation layer arranged on the supporting bottom membrane, wherein the active separation layer has an interpenetrating network structure, and the interpenetrating network structure is mainly formed by mutually penetrating polyamide and superfine nanofibers, wherein the polyamide is formed by performing interfacial polycondensation on a polyethyleneimine monomer and an acyl chloride monomer.
In some embodiments, the nanofiltration membrane comprises a supporting base membrane, an ultrafine nanofiber layer and an active separation layer, which are sequentially stacked.
Further, the thickness of the active separation layer is 10-150 nm.
In some embodiments, the weight average molecular weight of the polyethyleneimine monomer is 600-150000 Da.
In some embodiments, the acid chloride monomer includes any one or a combination of two or more of 1,3, 5-trimesoyl chloride, isophthaloyl chloride, terephthaloyl chloride, and the like, but is not limited thereto.
In some embodiments, the ultra-fine nanofibers comprise any one or a combination of two or more of single-walled carbon nanotubes and/or single-walled carbon nanotube derivatives, metal oxide nanowires and/or metal oxide nanowire derivatives, metal hydroxide nanowires and/or metal hydroxide nanowire derivatives, and the like, but are not limited thereto.
Furthermore, the diameter of the superfine nano fiber is 2-50 nm.
Further, the thickness of the superfine nanofiber layer is 10-150 nm.
In some embodiments, the support basement membrane comprises a microfiltration membrane, primarily but not limited to a polyethersulfone microfiltration membrane, a polyvinylidene fluoride microfiltration membrane, a polyarylsulfone microfiltration membrane, a hydrophilic polytetrafluoroethylene microfiltration membrane, a polyacrylonitrile microfiltration membrane, or the like, with or without a nonwoven substrate.
Furthermore, the aperture of the microfiltration membrane is 0.1-1 μm.
Further, the form of the nanofiltration membrane includes a flat sheet membrane, a tubular membrane, or a hollow fiber membrane, but is not limited thereto.
Further, the nanofiltration membrane is sensitive to multivalent cation salts (e.g., MgCl)2) The retention rate of the water-soluble polymer is more than 96 percent, and the water flux is 20-35L m-2h-1bar-1The molecular weight cutoff is 200-1000 Da.
In conclusion, the nanofiltration membrane provided by the invention has high flux and high salt rejection performance.
As another aspect of the technical scheme of the invention, the invention also relates to a preparation method of the nanofiltration membrane, which comprises the following steps:
arranging a superfine nanofiber layer on the microfiltration membrane to prepare a superfine nanofiber/microfiltration membrane composite substrate;
and carrying out interfacial polycondensation reaction on a polyethyleneimine monomer and an acyl chloride monomer on the surface of the superfine nanofiber/microfiltration membrane composite substrate, and then carrying out heat treatment to obtain the nanofiltration membrane.
The preparation principle of the nanofiltration membrane of the invention may be as follows: the ultra-fine nanofibers play a key role in the formation process and separation performance of ultra-thin active separation layers. Firstly, the superfine nano-fiber penetrates through the polyamide layer to play a good supporting role, so that the ultrathin polyamide layer has pressure resistance and long-time filtration stability; secondly, the superfine nano-fiber plays a role in doping and reducing water transmission resistance in the polyamide layer; thirdly, in the forming process of the polyamide, the superfine nano-fiber has a diffusion limiting effect on the polyethyleneimine, so that the polyamide grows in a superfine nano-fiber network, an ultrathin high-quality polyamide layer can be obtained, and the nanofiltration membrane has the characteristics of high flux and high interception.
Furthermore, the active separation layer is ultrathin and can reach below 30 nm. In the forming process of polyamide, the superfine nano-fiber has a limiting effect on the diffusion of the polyethyleneimine, so that the polyamide grows in a superfine nano-fiber network, an ultrathin polyamide layer can be obtained, the quality of the polyamide layer is ensured, and the flux and interception of the nanofiltration membrane are maintained at a high level.
In some embodiments, the preparation method specifically comprises: dispersing the superfine nano-fiber in a solvent to form a dispersion liquid, and depositing the dispersion liquid on a microfiltration membrane in a filtering mode to prepare the superfine nano-fiber/microfiltration membrane composite substrate.
Further, the method can be used for preparing a novel materialThe deposition density of the superfine nano-fiber on the micro-filtration membrane is 0.5-10 mu g cm-2。
In some embodiments, the ultra-fine nanofibers comprise any one or a combination of two or more of single-walled carbon nanotubes and/or single-walled carbon nanotube derivatives, metal oxide nanowires and/or metal oxide nanowire derivatives, metal hydroxide nanowires and/or metal hydroxide nanowire derivatives, and the like, but are not limited thereto.
Furthermore, the diameter of the superfine nano fiber is 2-50 nm.
Further, the solvent includes water, ethanol, etc., but is not limited thereto.
In some embodiments, the preparation method specifically comprises: adding the polyethyleneimine monomer solution on the surface of the superfine nanofiber/microfiltration membrane composite substrate, and soaking the surface for 30 s-10 min; and
applying acyl chloride monomer solution on the surface of the superfine nano fiber/microfiltration membrane composite substrate, and infiltrating the surface for 30 s-10 min to perform interfacial polycondensation reaction of the polyethyleneimine monomer and the acyl chloride monomer, wherein the reaction temperature is 20-30 ℃.
Further, the weight average molecular weight of the polyethyleneimine monomer is 600-150000 Da.
In some embodiments, the polyethyleneimine monomer solution comprises polyethyleneimine monomer and water.
Further, the concentration of the polyethyleneimine monomer solution is 1-10 mg ml-1。
In some embodiments, the acid chloride monomer solution includes an acid chloride monomer and an organic solvent.
Further, the concentration of the acyl chloride monomer solution is 0.1-10 mg ml-1。
Further, the organic solvent includes n-hexane, Isopar G, etc., but is not limited thereto.
In some embodiments, the temperature of the heat treatment is 25-60 ℃ for 5-60 min.
In some embodiments, the support basement membrane comprises a microfiltration membrane, primarily but not limited to a polyethersulfone microfiltration membrane, a polyvinylidene fluoride microfiltration membrane, a polyarylsulfone microfiltration membrane, a hydrophilic polytetrafluoroethylene microfiltration membrane, a polyacrylonitrile microfiltration membrane, or the like, with or without a nonwoven substrate.
Furthermore, the aperture of the microfiltration membrane is 0.1-1 μm.
Wherein, as a more specific embodiment, the preparation method may comprise:
a) dispersing the superfine nano-fiber in water, ethanol or other solvents to form dispersion liquid;
b) depositing the superfine nano-fiber in the dispersion liquid on a macroporous support basement membrane in a vacuum filtration mode to form a superfine nano-fiber/microfiltration membrane composite basement;
c) soaking the superfine nanofiber/microfiltration membrane composite substrate in a polyethyleneimine solution for a period of time, and removing redundant solution on the surface of the membrane;
d) then soaking the membrane surface in 1,3, 5-trimesoyl chloride hexane solution, and washing off redundant 1,3, 5-trimesoyl chloride after the reaction is finished;
e) finally, the film is subjected to heat treatment at the temperature of 25-60 ℃ for 5-60 min, and then is stored in deionized water.
As another aspect of the technical scheme of the invention, the invention also relates to the nanofiltration membrane prepared by the method.
Furthermore, the rejection rate of the nanofiltration membrane on multivalent cation salts is more than 96%, and the water flux is 20-35 Lm-2h-1bar-1The molecular weight cut-off is adjustable between 200 Da and 1000 Da.
Further, the multivalent cation salt comprises MgCl2But is not limited thereto.
Further, the form of the nanofiltration membrane includes a flat sheet membrane, a tubular membrane, or a hollow fiber membrane, but is not limited thereto.
The embodiment of the invention also provides application of the nanofiltration membrane in the fields of seawater desalination pretreatment, sewage treatment or water softening and the like.
Furthermore, the nanofiltration membrane can be used for removing multivalent positive ions, dyes, organic molecules and the like in water, and can be used for municipal sewage treatment, tap water quality softening and the like.
By the technical scheme, the nanofiltration membrane has a structure that the superfine nanofiber network and the polymer are mutually penetrated, and the superfine nanofiber penetrates through the polyamide layer to play a good mechanical supporting role, so that the ultrathin polyamide layer has pressure resistance and long-time filtration stability; the superfine nano-fiber also plays a role in doping and reducing water transmission resistance in the polyamide layer; meanwhile, the preparation method is simple, and the obtained nanofiltration membrane has high flux and high salt rejection performance, so that the desalting energy consumption cost is reduced, and the method has wide application prospects in the aspects of seawater desalting pretreatment, water softening and the like.
The technical solution of the present invention is explained in more detail below with reference to several preferred embodiments. The specific examples set forth below are presented only to further illustrate and explain the present invention and are not intended to be limiting; simple modifications of the method according to the invention are intended to be covered by the scope of protection of the claims.
Example 1
The carbon nano-tube is filtered on a commercial polyethersulfone microfiltration membrane in a suction way, and the density is 2.3 mu g cm-2. Depositing polyethyleneimine with weight average molecular weight of 600 onto carbon nanotube substrate with concentration of 5mg ml-1Soaking the polyethyleneimine aqueous solution for 60s, sucking off the solution on the membrane surface, and soaking the membrane surface in a solution with the concentration of 0.3mg ml-1After reacting at 20 ℃ for 60s in the 1,3, 5-trimesoyl chloride hexane solution, the membrane is soaked in hexane to wash off the excess 1,3, 5-trimesoyl chloride. Finally, the membrane was heated at 60 ℃ for 25min and stored in deionized water.
1000ppm MgCl for the nanofiltration membrane prepared above2The aqueous solution test was carried out at 28 ℃ and an operating pressure of 5bar, at a flux of 30L m-2h-1bar-1The retention rate was 96%. The film is aligned to 1000ppm of CaCl2Has a retention rate of 94% and a flux of 31L m-2h-1bar-1(ii) a For 1000ppm MgSO4Has a retention rate of 86% and a flux of 35L m-2h-1bar-1(ii) a For 1000ppmNa2SO4Has a retention rate of 39% and a flux of 36L m-2h-1bar-1(ii) a The retention rate for 1000ppm NaCl was 57%, and the flux was 34L m-2h-1bar-1。
Example 2
The carbon nano-tube is filtered on a commercial polyethersulfone microfiltration membrane in a suction way, and the density is 2.3 mu g cm-2. Depositing polyethyleneimine with weight average molecular weight of 600 onto carbon nanotube substrate with concentration of 5mg ml-1Soaking the polyethyleneimine aqueous solution for 60s, sucking off the solution on the membrane surface, and soaking the membrane surface in a solution with the concentration of 0.6mg ml-1After reacting at 20 ℃ for 60s in the 1,3, 5-trimesoyl chloride hexane solution, the membrane is soaked in hexane to wash off the excess 1,3, 5-trimesoyl chloride. Finally, the membrane was heated at 60 ℃ for 25min and stored in deionized water.
1000ppm MgCl for the nanofiltration membrane prepared above2The aqueous solution test was carried out at 28 ℃ and an operating pressure of 5bar with a flux of 27L m-2h-1bar-1The retention rate was 97%. The film is aligned to 1000ppm of CaCl2Has a retention rate of 95% and a flux of 30L m-2h-1bar-1(ii) a For 1000ppm MgSO4Has a retention rate of 89% and a flux of 35L m-2h-1bar-1(ii) a For 1000ppmNa2SO4Has a retention rate of 46% and a flux of 40L m-2h-1bar-1(ii) a The retention rate for 1000ppm NaCl was 64%, and the flux was 35L m-2h-1bar-1。
Example 3
The carbon nano-tube is filtered on a commercial polyethersulfone microfiltration membrane in a suction way, and the density is 1.15 mu g cm-2. Depositing polyethyleneimine with weight average molecular weight of 600 onto carbon nanotube substrate with concentration of 5mg ml-1Soaking the polyethyleneimine aqueous solution for 60s, sucking off the solution on the membrane surface, and soaking the membrane surface in a solution with the concentration of 0.6mg ml-1In 1,3, 5-trimesoyl chloride hexane solution ofAfter reacting at 20 ℃ for 60s, the membrane was immersed in hexane to wash off excess 1,3, 5-trimesoyl chloride. Finally, the membrane was heated at 60 ℃ for 25min and stored in deionized water.
1000ppm MgCl for the nanofiltration membrane prepared above2The aqueous solution test was carried out at 28 ℃ and an operating pressure of 5bar with a flux of 27L m-2h-1bar-1The retention rate was 94%.
Example 4
The carbon nano-tube is filtered on a commercial polyethersulfone microfiltration membrane in a suction way, and the density is 2.3 mu g cm-2. Depositing polyethyleneimine with weight average molecular weight of 600 onto carbon nanotube substrate with concentration of 5mg ml-1Soaking the polyethyleneimine aqueous solution for 60s, sucking off the solution on the membrane surface, and soaking the membrane surface in a solution with the concentration of 3mg ml-1After reacting at 20 ℃ for 60s in the 1,3, 5-trimesoyl chloride hexane solution, the membrane is soaked in hexane to wash off the excess 1,3, 5-trimesoyl chloride. Finally, the membrane was heated at 60 ℃ for 25min and stored in deionized water.
1000ppm MgCl for the nanofiltration membrane prepared above2The aqueous solution test was carried out at 28 ℃ and an operating pressure of 5bar, a flux of 18L m-2h-1bar-1The retention rate was 98%. The film is aligned to 1000ppm of CaCl2Has a retention rate of 96% and a flux of 21L m-2h-1bar-1(ii) a For 1000ppm MgSO4Has a retention rate of 92% and a flux of 22L m-2h-1bar-1(ii) a For 1000ppmNa2SO4Has a retention rate of 68% and a flux of 24L m-2h-1bar-1(ii) a The retention rate for 1000ppm NaCl was 64%, and the flux was 23L m-2h-1bar-1。
Example 5
The carbon nano-tube is filtered on a commercial polyethersulfone microfiltration membrane in a suction way, and the density is 2.3 mu g cm-2. Depositing polyethyleneimine with weight average molecular weight of 600 onto carbon nanotube substrate with concentration of 5mg ml-1Soaking the polyethyleneimine aqueous solution for 60s, sucking off the solution on the membrane surface, and soaking the membrane surface in a solution with the concentration of 6mg ml-1After reacting at 20 ℃ for 60s in the 1,3, 5-trimesoyl chloride hexane solution, the membrane is soaked in hexane to wash off the excess 1,3, 5-trimesoyl chloride. Finally, the membrane was heated at 60 ℃ for 25min and stored in deionized water.
1000ppm MgCl for the nanofiltration membrane prepared above2The aqueous solution test was carried out at 28 ℃ and an operating pressure of 5bar, at a flux of 14L m-2h-1bar-1The retention rate was 98%. The film is aligned to 1000ppm of CaCl2Has a retention rate of 97% and a flux of 18L m-2h-1bar-1(ii) a For 1000ppm MgSO4Has a retention rate of 94% and a flux of 18L m-2h-1bar-1(ii) a For 1000ppmNa2SO4Has a retention rate of 88% and a flux of 19L m-2h-1bar-1(ii) a The retention rate for 1000ppm NaCl was 72%, and the flux was 19L m-2h-1bar-1。
Example 6
The carbon nano-tube is filtered on a commercial polyethersulfone microfiltration membrane in a suction way, and the density is 2.3 mu g cm-2. Depositing polyethyleneimine with weight average molecular weight of 1800 onto carbon nanotube substrate with concentration of 5mg ml-1Soaking the polyethyleneimine aqueous solution for 60s, sucking off the solution on the membrane surface, and soaking the membrane surface in a solution with the concentration of 0.6mg ml-1After reacting at 20 ℃ for 60s in the 1,3, 5-trimesoyl chloride hexane solution, the membrane is soaked in hexane to wash off the excess 1,3, 5-trimesoyl chloride. Finally, the membrane was heated at 60 ℃ for 25min and stored in deionized water.
1000ppm MgCl for the nanofiltration membrane prepared above2The aqueous solution test was carried out at 28 ℃ and an operating pressure of 5bar, at a flux of 24L m-2h-1bar-1The retention rate was 94%.
Example 7
The carbon nano-tube is filtered on a commercial polyethersulfone microfiltration membrane in a suction way, and the density is 2.3 mu g cm-2. Depositing polyethyleneimine with weight average molecular weight of 10000 on a carbon nanotube substrate with concentration of 5mg ml-1Soaking the membrane in the polyethyleneimine water solution for 60sThe solution was blotted dry and then the membrane surface was soaked at a concentration of 0.6mg ml-1After reacting at 20 ℃ for 60s in the 1,3, 5-trimesoyl chloride hexane solution, the membrane is soaked in hexane to wash off the excess 1,3, 5-trimesoyl chloride. Finally, the membrane was heated at 30 ℃ for 25min and stored in deionized water.
1000ppm MgCl for the nanofiltration membrane prepared above2The aqueous solution test was carried out at 28 ℃ and an operating pressure of 5bar with a flux of 17L m-2h-1bar-1The retention rate was 96%.
Example 8
The carbon nano-tube is filtered on a commercial polyethersulfone microfiltration membrane in a suction way, and the density is 2.3 mu g cm-2. Depositing polyethyleneimine with weight average molecular weight of 70000 on carbon nanotube substrate with concentration of 5mg ml-1Soaking the polyethyleneimine aqueous solution for 60s, sucking off the solution on the membrane surface, and soaking the membrane surface in a solution with the concentration of 0.6mg ml-1After reacting at 25 ℃ for 60s in the 1,3, 5-trimesoyl chloride hexane solution, the membrane is soaked in hexane to wash off the excess 1,3, 5-trimesoyl chloride. Finally, the film was heated at 40 ℃ for 25min and stored in deionized water.
1000ppm MgCl for the nanofiltration membrane prepared above2The aqueous solution test was carried out at 28 ℃ and an operating pressure of 5bar, at a flux of 16L m-2h-1bar-1The retention rate was 98%. The film is aligned to 1000ppm of CaCl2Has a retention rate of 96% and a flux of 19L m-2h-1bar-1(ii) a For 1000ppm MgSO4Has a retention rate of 89% and a flux of 18L m-2h-1bar-1(ii) a For 1000ppmNa2SO4Has a retention rate of 38% and a flux of 19L m-2h-1bar-1(ii) a The retention rate for 1000ppm NaCl was 69%, and the flux was 18L m-2h-1bar-1。
Example 9
The carbon nano-tube is filtered on a commercial polyethersulfone microfiltration membrane in a suction way, and the density is 0.5 mu g cm-2. Depositing polyethyleneimine with weight average molecular weight of 150000 onto a carbon nanotube substrate with a concentration of 5mg ml-1Soaking the polyethyleneimine aqueous solution for 10min, sucking off the solution on the membrane surface, and soaking the membrane surface in a solution with the concentration of 0.1mg ml-1After reacting at 20 ℃ for 120s in the 1,3, 5-trimesoyl chloride hexane solution, the membrane is soaked in hexane to wash off the excess 1,3, 5-trimesoyl chloride. Finally, the membrane was heated at 60 ℃ for 25min and stored in deionized water.
1000ppm MgCl for the nanofiltration membrane prepared above2The aqueous solution test was carried out at 28 ℃ and an operating pressure of 5bar, a flux of 18L m-2h-1bar-1The rejection was 90%.
Example 10
The carbon nanotubes were filtered onto a commercial polyethersulfone microfiltration membrane with a density of 10 μ g cm-2. Depositing polyethyleneimine with weight average molecular weight of 1800 onto carbon nanotube substrate with concentration of 5mg ml-1Soaking the polyethyleneimine aqueous solution for 1min, sucking off the solution on the membrane surface, and soaking the membrane surface in a solution with the concentration of 3mg ml-1After reacting at 20 ℃ for 60s, the membrane was soaked in hexane to wash off excess of the m-dibenzoyl chloride. Finally, the membrane was heated at 60 ℃ for 60min and stored in deionized water.
1000ppm MgCl for the nanofiltration membrane prepared above2Aqueous solution test, test temperature 25 deg.C, operating pressure 5bar, flux 11L m-2h-1bar-1The rejection was 99%. The membrane was paired with 1000ppm MgSO4Has a retention rate of 97% and a flux of 10L m-2h-1bar-1(ii) a For 1000ppm Na2SO4Has a retention rate of 82% and a flux of 9L m-2h-1bar-1(ii) a The retention rate to 1000ppm NaCl was 87%, and the flux was 10L m-2h-1bar-1。
Example 11
The carbon nano-tube is filtered on a commercial polyethersulfone microfiltration membrane in a suction way, and the density is 2.3 mu g cm-2. Depositing polyethyleneimine with weight average molecular weight of 600 onto carbon nanotube substrate with concentration of 1mg ml-1Soaking the polyethyleneimine in the aqueous solution for 30sSucking the solution on the membrane surface, and soaking the membrane surface in 0.1mg ml-1After the 1,3, 5-trimesoyl chloride hexane solution reacts for 10min at the temperature of 20 ℃, the membrane is soaked in hexane to wash away redundant 1,3, 5-trimesoyl chloride. Finally, the membrane is placed for 5min at 25 ℃ and stored in deionized water.
1000ppm MgCl for the nanofiltration membrane prepared above2The aqueous solution test was carried out at 28 ℃ and an operating pressure of 5bar, at a flux of 25L m-2h-1bar-1The retention rate was 91%.
Example 12
The carbon nano-tube is filtered on a commercial polyethersulfone microfiltration membrane in a suction way, and the density is 2.3 mu g cm-2. Depositing polyethyleneimine with weight average molecular weight of 600 onto carbon nanotube substrate with concentration of 10mg ml-1Soaking the polyethyleneimine aqueous solution for 30s, sucking off the solution on the membrane surface, and soaking the membrane surface in 10mg ml-1After the 1,3, 5-trimesoyl chloride hexane solution reacts for 30 seconds at the temperature of 30 ℃, the membrane is soaked in hexane to wash away redundant 1,3, 5-trimesoyl chloride. Finally, the membrane was heated at 60 ℃ for 25min and stored in deionized water.
1000ppm MgCl for the nanofiltration membrane prepared above2Aqueous solution test, test temperature 28 deg.C, operating pressure 5bar, flux 11L m-2h-1bar-1The retention rate was 98%.
It should be noted that: the nanofiltration membranes obtained in the above examples are all tested by applying a cross flow mode, and the raw water flux is controlled to be 6-8 LPH. The rejection of salt is calculated from the ratio of permeate concentration to feed concentration by the formula:
Figure BDA0001986261310000101
flux is based on the volume of liquid filtered per hour per square meter of membrane area and normalized to unit atmosphere:
Figure BDA0001986261310000102
wherein, Δ V: volume change of filtrate, a: membrane filtration area, t: filtration time, Δ P: the operating pressure.
Comparative example 1
The nanofiltration membranes which are commercialized at present are adopted: the polysulfone ultrafiltration membrane is composed of a polysulfone ultrafiltration membrane supporting layer and a selection layer obtained by interfacial polymerization on the polysulfone ultrafiltration membrane supporting layer by taking polyamine and polybasic acyl chloride as monomers. However, the traditional nanofiltration membrane is negatively charged and has low retention of positive ions. Such as typical NF 270(Dow) vs. 1000ppm Na2SO4The rejection rate reached 98%, however for 1000ppm MgCl2The retention rate of the catalyst is 50-60%.
In addition, the inventor also refers to the mode of example 1-example 12, tests are carried out by other raw materials, conditions and the like listed in the specification, and nanofiltration membranes with high flux and high salt rejection performance are also prepared.
It should be understood that the above is only a specific application example of the present invention, and the protection scope of the present invention is not limited in any way. All the technical solutions formed by equivalent transformation or equivalent replacement fall within the protection scope of the present invention.

Claims (25)

1. The nanofiltration membrane is characterized by comprising a supporting base membrane and an active separation layer arranged on the supporting base membrane, wherein the active separation layer has an interpenetrating network structure, and the interpenetrating network structure is formed by mutually penetrating polyamide and superfine nanofibers, wherein the polyamide is formed by a polyethyleneimine monomer and an acyl chloride monomer through interfacial polycondensation reaction.
2. Nanofiltration membrane according to claim 1, wherein: the nanofiltration membrane comprises a supporting base membrane, a superfine nanofiber layer and an active separation layer which are sequentially stacked.
3. Nanofiltration membrane according to claim 1, wherein: the thickness of the active separation layer is 10-150 nm.
4. Nanofiltration membrane according to claim 1, wherein: the weight average molecular weight of the polyethyleneimine monomer is 600-150000 Da.
5. Nanofiltration membrane according to claim 1, wherein: the acyl chloride monomer comprises any one or the combination of more than two of 1,3, 5-trimesoyl chloride, isophthaloyl dichloride and terephthaloyl dichloride.
6. Nanofiltration membrane according to claim 1, wherein: the superfine nanofiber comprises any one or combination of more than two of a single-walled carbon nanotube and/or a single-walled carbon nanotube derivative, a metal oxide nanowire and/or a metal oxide nanowire derivative, and a metal hydroxide nanowire and/or a metal hydroxide nanowire derivative.
7. Nanofiltration membrane according to claim 1 or 6, wherein: the diameter of the superfine nanofiber is 2-50 nm.
8. Nanofiltration membrane according to claim 2, wherein: the thickness of the superfine nanofiber layer is 10-150 nm.
9. Nanofiltration membrane according to claim 1, wherein: the supporting basement membrane comprises a microfiltration membrane; preferably, the microfiltration membrane comprises a polyethersulfone microfiltration membrane, a polyvinylidene fluoride microfiltration membrane, a polyarylsulfone microfiltration membrane, a hydrophilic polytetrafluoroethylene microfiltration membrane, a polyacrylonitrile microfiltration membrane, a substrate with or without a non-woven fabric substrate; preferably, the aperture of the microfiltration membrane is 0.1-1 μm.
10. Nanofiltration membrane according to claim 1, wherein: the nanofiltration membrane is in a form of a flat membrane, a tubular membrane or a hollow fiber membrane.
11. Nanofiltration membrane according to claim 1, wherein:the rejection rate of the nanofiltration membrane on multivalent cation salts is more than 96%, and the water flux is 20-35L m-2h-1bar-1The molecular weight cutoff is 200-1000 Da; preferably, the multivalent cation salt comprises MgCl2。
12. A preparation method of a nanofiltration membrane is characterized by comprising the following steps:
arranging a superfine nanofiber layer on the microfiltration membrane to prepare a superfine nanofiber/microfiltration membrane composite substrate;
and carrying out interfacial polycondensation reaction on a polyethyleneimine monomer and an acyl chloride monomer on the surface of the superfine nanofiber/microfiltration membrane composite substrate, and then carrying out heat treatment to obtain the nanofiltration membrane.
13. The method according to claim 12, comprising: dispersing the superfine nano-fiber in a solvent to form a dispersion solution, and depositing the dispersion solution on a microfiltration membrane in a filtering mode to prepare a superfine nano-fiber/microfiltration membrane composite substrate; preferably, the deposition density of the superfine nano-fibers on the micro-filtration membrane is 0.5-10 mu g cm-2。
14. The method of manufacturing according to claim 13, wherein: the superfine nanofiber comprises any one or combination of more than two of a single-walled carbon nanotube and/or a single-walled carbon nanotube derivative, a metal oxide nanowire and/or a metal oxide nanowire derivative, and a metal hydroxide nanowire and/or a metal hydroxide nanowire derivative.
15. The method of manufacturing according to claim 13, wherein: the diameter of the superfine nanofiber is 2-50 nm.
16. The method of manufacturing according to claim 13, wherein: the solvent comprises water and/or ethanol.
17. The method according to claim 12, comprising:
adding the polyethyleneimine monomer solution on the surface of the superfine nanofiber/microfiltration membrane composite substrate, and soaking the surface for 30 s-10 min; and
applying acyl chloride monomer solution on the surface of the superfine nano fiber/microfiltration membrane composite substrate, and infiltrating the surface for 30 s-10 min to perform interfacial polycondensation reaction of the polyethyleneimine monomer and the acyl chloride monomer at the temperature of 20-30 ℃.
18. The method of claim 17, wherein: the weight average molecular weight of the polyethyleneimine monomer is 600-150000 Da.
19. The method of claim 17, wherein: the polyethyleneimine monomer solution comprises a polyethyleneimine monomer and water; preferably, the concentration of the polyethyleneimine monomer solution is 1-10 mg ml-1。
20. The method of claim 17, wherein: the acyl chloride monomer comprises any one or the combination of more than two of 1,3, 5-trimesoyl chloride, isophthaloyl dichloride and terephthaloyl dichloride.
21. The method of claim 17, wherein: the acyl chloride monomer solution comprises acyl chloride monomers and an organic solvent; preferably, the concentration of the acyl chloride monomer solution is 0.1-10 mg ml-1(ii) a Preferably, the organic solvent comprises n-hexane and/or Isopar G.
22. The method of manufacturing according to claim 12, wherein: the temperature of the heat treatment is 25-60 ℃, and the time is 5-60 min.
23. The production method according to claim 12 or 13, characterized in that: the supporting basement membrane comprises a microfiltration membrane; preferably, the microfiltration membrane comprises a polyethersulfone microfiltration membrane, a polyvinylidene fluoride microfiltration membrane, a polyarylsulfone microfiltration membrane, a hydrophilic polytetrafluoroethylene microfiltration membrane, a polyacrylonitrile microfiltration membrane, a substrate with or without a non-woven fabric substrate; preferably, the aperture of the microfiltration membrane is 0.1-1 μm.
24. A nanofiltration membrane prepared by the process of any one of claims 12-23; preferably, the rejection rate of the nanofiltration membrane on multivalent cation salts is more than 96%, and the water flux is 20-35L m-2h-1bar-1The molecular weight cutoff is 200-1000 Da; preferably, the multivalent cation salt comprises MgCl2(ii) a Preferably, the form of the nanofiltration membrane comprises a flat membrane, a tubular membrane or a hollow fiber membrane.
25. Use of a nanofiltration membrane according to any one of claims 1 to 11 or 24 in the field of seawater desalination pretreatment, wastewater treatment or water softening.
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