CN115646222A - Polyamide desalting membrane with high flux, high salt rejection and stain resistance as well as preparation method and application thereof - Google Patents

Abstract

The invention belongs to the technical field of functional materials, and particularly relates to a polyamide desalting membrane with high flux, high salt rejection and stain resistance, and a preparation method and application thereof. The polyamide desalination membrane comprises a porous ultrafiltration base membrane and a polyamide compact functional layer, wherein the polyamide compact functional layer is prepared on the surface of the porous ultrafiltration base membrane through an interfacial polymerization method and has double-layer zwitterion characteristics, and the zwitterion layer can provide good hydrophilicity and weaken strong electronegativity of the polyamide layer. The polyamide thin-layer composite desalting membrane has the advantages of high permeation selectivity, excellent pollution resistance, high regulation efficiency, convenience in control, wide application range and easiness in large-scale production, and provides a new idea for preparation of the pollution-resistant desalting membrane; and has wide application in the fields of seawater desalination, sewage treatment, petrochemical industry, biology, medical treatment, food and the like.

Description

Polyamide desalting membrane with high flux, high salt rejection and stain resistance as well as preparation method and application thereof

Technical Field

The invention belongs to the technical field of functional materials, relates to an anti-pollution polyamide thin-layer composite desalting separation membrane and a preparation method thereof, and particularly relates to a polyamide desalting membrane with high flux, high salt rejection and pollution resistance and a preparation method thereof. The polyamide desalting membrane can be applied to separation, concentration and purification processes in the fields of seawater desalination, sewage treatment, biological pharmacy, petrochemical industry and the like.

Background

The desalination membrane technology is used as an advanced separation method in the world at present, can efficiently intercept salt ions, plays an increasingly important role in the fields of seawater and brackish water desalination, industrial wastewater treatment and zero discharge, food processing, pharmaceutical industry, pure water production and the like, and can maximally recycle water resources.

Among them, the thin-layer composite polyamide membrane is the most widely used desalting membrane variety in large scale at present due to its excellent separation selectivity and good chemical stability. However, polyamide desalination membranes are susceptible to membrane fouling in applications that result in reduced membrane performance and reduced lifetime. Recent studies have shown that membrane fouling accounts for around 30% of the operating cost of water plants using desalination processes. Among these, membrane replacement accounts for 40% -65% of the total cost of membrane fouling, being the most significant cost component. For this reason, the development of anti-fouling desalination membranes to improve the flux stability of desalination membranes in use is the focus of current membrane field research.

It has been found that although the surface hydrophilic modification can comprehensively improve the pollution resistance of the material to various pollutants, the hydrophilic modification material can greatly reduce the surface contact angle from about 85 degrees to below 50 degrees. In a short-time pollution test in a laboratory, the flux attenuation rate of the film on macromolecular organic pollutants and negatively charged micromolecular organic pollutants is less than 30%, the excellent anti-pollution effect is shown, but the flux attenuation rate of the film on positively charged organic micromolecules is still between 35% and 70%. This is because the hydrophilic groups on the surface can interact with water molecules through hydrogen bonds, thereby forming a hydrated layer on the surface and blocking the molecules of contaminants from contacting the surface. However, the hydration layer only can play a physical shielding role, the electronegativity of the polyamide layer is not obviously improved, and positively charged small molecular pollutants with strong water solubility can still pass through the hydration layer under the electrostatic interaction, so as to contact and be adsorbed on the surface of the membrane, thereby causing serious membrane pollution. Therefore, the surface hydrophilicity is singly regulated and controlled, and the pollution resistance of the desalting membrane to positively charged organic small molecules is difficult to be fundamentally and greatly improved.

In recent years, researchers improve the negative electrical property of the membrane surface through charge control to improve the anti-fouling capacity of the membrane to positively charged pollutants, but the method can cause the anti-fouling capacity of the membrane to negatively charged pollutants to be reduced. Therefore, a preparation method of a high-flux anti-pollution polyamide membrane needs to be further developed, which can synchronously improve the anti-pollution capability to various electrical pollutants and simultaneously improve the permselectivity of the membrane.

Particularly, the existing modification means are difficult to show good anti-pollution performance to micromolecular positive charge pollutants, and a high-flux anti-pollution polyamide desalting membrane meeting the actual requirement is difficult to develop.

Disclosure of Invention

In view of the above, the present invention provides a solution capable of simultaneously improving water permeability and contamination resistance against various contaminants, in order to solve the problems that the effect of reducing the membrane characteristics due to typical small-molecule organic contamination or secondary contamination caused by the small-molecule organic contamination is poor, and contamination resistance against different types of contaminants cannot be simultaneously improved. In addition, the technology of the invention can also effectively solve the problem of water permeability reduction caused by additionally arranging the coating layer on the surface of the separation membrane.

The composite desalting membrane is characterized in that a surface layer of polyamide resin with double-layer zwitterion characteristics is formed on the surface of a porous support, the inner zwitterion layer and the outer zwitterion layer respectively remarkably improve the electronegativity and the hydrophilicity of the surface of the polyamide resin layer to regulate and control the electrostatic acting force and the hydrophobic acting force of pollutants and the surface of the membrane, the surface structure/property of the membrane is comprehensively regulated and controlled to reduce the interface acting force between the pollutants and the surface of the membrane, the osmotic selectivity of the membrane can be synchronously improved, and a foundation is laid for widening the preparation method and the application field of the anti-pollution desalting membrane.

In order to achieve the above purpose, the invention provides the following technical scheme:

the first technical purpose of the invention is to provide a polyamide desalination membrane with high flux, high salt rejection and stain resistance, wherein the polyamide desalination membrane is in a flat plate type or a hollow fiber type and comprises a porous ultrafiltration base membrane and a polyamide compact functional layer; wherein the content of the first and second substances,

the polyamide compact functional layer is prepared on the surface of the porous ultrafiltration base membrane through an interfacial polymerization method and has the characteristic of double-layer zwitterions; the polyamide compact functional layer has good hydrophilicity, the water contact angle range of the polyamide compact functional layer is less than 40 degrees, and the thickness of a hydration layer is more than 2nm; and the polyamide compact functional layer can weaken strong electronegativity of the polyamide layer, and the charge quantity of the polyamide compact functional layer is more than-30 eV.

And the schematic diagram of the polyamide compact functional layer with the double-layer zwitterion characteristic is shown in fig. 1, the surface structure/property of the membrane is comprehensively regulated and controlled by the double-layer zwitterion layer to reduce the interface acting force between the pollutant and the membrane surface, and the permselectivity of the membrane can be synchronously improved.

Optionally, the material of the porous ultrafiltration membrane comprises cellulose acetate, polyethersulfone, polyvinylidene fluoride, polysulfone or polyacrylonitrile.

The second technical purpose of the invention is to provide a preparation method of the polyamide desalting membrane with high flux, high salt cut-off and stain resistance, which comprises the following steps:

1) Contacting an aqueous solution containing a molecule having a positive charge doped in a polyfunctional amine component with an organic solution containing a polyfunctional acid chloride component on a porous support to form a polyamide resin skin layer having an inner layer zwitterionic character on a surface of the porous support;

2) And (3) contacting a solution containing zwitterion characteristic molecules with the surface layer to form an outer zwitterion layer so as to modify the polyamide resin, and finally obtaining the polyamide desalting membrane with high flux, high salt cut-off and stain resistance.

The preparation method is a layer-by-layer interfacial polymerization method, can integrate preparation and modification processes, is simple to operate, short in reaction time and good in stability, has the advantage of industrial stable preparation, and is beneficial to industrial amplification application.

The polyfunctional amine component is a polyfunctional amine having 2 or more reactive amino groups, and includes aromatic, aliphatic, and alicyclic polyfunctional amines. Wherein, the first and the second end of the pipe are connected with each other,

the aromatic polyfunctional amines include m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3, 5-triaminobenzene, 1,2, 4-triaminobenzene, 3, 5-diaminobenzoic acid, 2, 4-diaminotoluene, 2, 6-diaminotoluene, N' -dimethyl-m-phenylenediamine, 2, 4-diaminoanisole, amonol, xylylenediamine, etc.

The aliphatic polyfunctional amine includes ethylenediamine, propylenediamine, tris (2-aminoethyl) amine, N-phenylethylenediamine, and the like.

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

The polyfunctional amine component may be used in 1 kind, or 2 or more kinds may be used in combination; and in order to obtain a skin layer with high salt rejection properties, it is preferred to use an aromatic polyfunctional amine.

The polyfunctional acid chloride component is a polyfunctional acid chloride having 2 or more reactive carbonyl groups, and the polyfunctional acid chloride component includes aromatic, aliphatic, and alicyclic polyfunctional acid chlorides; wherein, the first and the second end of the pipe are connected with each other,

aromatic polyfunctional acid chlorides include trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, biphenyldicarbonyl chloride, naphthaloyl chloride, benzenetrisulfonyl chloride, benzenedisulfonyl chloride, chlorosulfonyl dichloride, and the like.

Aliphatic polyfunctional acyl chlorides include malonyl chloride, succinyl chloride, glutaryl chloride, tricarboxyacyl chloride, butyrtrimoyl chloride, glutaryl chloride, adipoyl chloride, and the like.

The alicyclic polyfunctional acyl chloride includes cyclopropane trimethyl chloride, cyclobutane tetracarboxylic acid chloride, cyclopentane trimethyl acid chloride, cyclopentane tetracarboxylic acid chloride, cyclohexane trimethyl acid chloride, tetrahydrofuran tetracarboxylic acid chloride, cyclopentane dicarboxylic acid chloride, cyclobutane dicarboxylic acid chloride, cyclohexane dicarboxylic acid chloride, tetrahydrofuran dicarboxylic acid chloride and the like.

These polyfunctional acid chlorides may be used in 1 kind, or 2 or more kinds in combination; and in order to obtain a skin layer with high salt rejection properties, it is preferable to use an aromatic polyfunctional acid chloride. In addition, preferably in the polyfunctional acyl chloride component of at least a portion of the use of 3 or more polyfunctional acyl chloride to form a crosslinked structure.

The molecules with positive charges refer to substances which can improve the electronegativity of the membrane surface and promote the water-oil interface reaction, and comprise amine salt type molecules and other compound molecules with nitrogen heterocycles; wherein the amine salt type molecule is at least one of primary amine salt, secondary ammonium salt, tertiary amine salt and quaternary amine salt.

These positively charged molecules may be used in combination of 1 kind or 2 or more kinds; and in order to obtain a skin layer having a high degree of crosslinking, it is preferable to use a quaternary ammonium salt type small molecule compound.

In addition, in order to improve the performance of the skin layer containing a polyamide resin, a pore-retaining treatment may be performed using a polymer such as polyvinyl alcohol, polyvinyl pyrrolidone, or polyacrylic acid, or a polyol such as sorbitol or glycerin.

The porous support is capable of supporting the skin layer, and it is generally preferred to use a porous support having an average pore diameter of

And (3) ultrafiltration membranes with left and right micropores. As a material for forming the porous support, various materials such as polyaryl ether sulfone such as polysulfone and polyether sulfone, polyimide, polyvinylidene fluoride, and the like can be used, but polysulfone and polyaryl ether sulfone are preferably used particularly in view of chemical stability, mechanical stability, and thermal stability.

The thickness of the porous support is usually about 25 to 125. Mu.m, and preferably about 40 to 75 μm, but the thickness is not necessarily limited to the above condition. The porous support is usually a substrate based on a base material such as a woven fabric or a nonwoven fabric, and mechanical properties thereof are reinforced.

Any known method can be used to form a skin layer comprising a polyamide resin on the surface of the porous support. Such as interfacial polymerization, phase separation, thin film coating, and the like. The interfacial polymerization method generally includes two methods: bringing an amine aqueous solution containing a diamine component into contact with an organic solution containing a ternary acid chloride component and carrying out interfacial polymerization to form a skin layer, and placing the skin layer on a porous support; or by the interfacial polymerization on the porous support, a polyamide skin layer is directly formed on the porous support.

Further, the present invention preferably includes the following method: an aqueous solution coating layer formed of an amine aqueous solution containing a polyfunctional amine component and positively charged molecules is formed on a porous support, and then an organic solution containing a polyfunctional acid chloride component is brought into contact with the aqueous solution coating layer to carry out interfacial polymerization, thereby forming a polyamide skin layer.

In the interfacial polymerization, the concentration of the polyfunctional amine component in the aqueous diamine solution is preferably 0.1 to 5wt.%, and more preferably 0.5 to 2wt.%. At concentrations below 0.1wt.% of the polyfunctional amine ingredient, the polyamide skin layer is prone to pin-hole defects, resulting in reduced salt rejection. On the other hand, in the case where the concentration of the polyfunctional amine ingredient is higher than 5wt.%, there is a tendency that: the polyfunctional amine component easily permeates into the porous support, and the resulting polyamide membrane becomes too thick, and the permeation resistance increases, and the permeation flux decreases.

The concentration of the acid chloride component in the organic solution is preferably 0.01 to 5wt.%, and more preferably 0.05 to 3wt.%. In the case where the concentration of the polyfunctional acid chloride component is less than 0.01wt.%, there is a tendency that: unreacted polyfunctional amine components tend to remain, and pinhole-like defects tend to occur in the skin layer, resulting in a decrease in the salt-trapping performance. On the other hand, in the case where the concentration of the polyfunctional acyl chloride component is higher than 5wt.%, there is a tendency that: unreacted polyfunctional acid chloride components tend to remain, or the film thickness becomes too thick, which increases the permeation resistance and decreases the permeation flux.

The concentration of the positively charged molecule is preferably 0.01 to 5wt.%, and more preferably 0.05 to 3wt.%. In case the concentration of positively charged molecules is below 0.01wt.%, the following tendency exists: pinhole-like defects are easily generated in the skin layer, and the salt-trapping property is lowered.

The organic solvent used in the organic solution is not particularly limited as long as it has low solubility in water, does not deteriorate the porous support, and can dissolve the polyfunctional acyl chloride component, and saturated hydrocarbons such as cyclohexane, heptane, octane, and nonane, and halogenated hydrocarbons such as 1, 2-trichlorotrifluoroethane can be selected. The solvent is preferably a saturated hydrocarbon or naphthenic hydrocarbon solvent having a boiling point of 300 ℃ or lower (more preferably 200 ℃ or lower). The organic solvent may be used alone in 1 kind, or may be used in the form of a mixed solvent of 2 or more kinds.

In the present invention, after (or during) formation of a skin layer on the surface of a porous support, a solution of zwitterionic small molecules containing amino groups is brought into contact with the skin layer, thereby modifying the polyamide resin on the surface of the skin layer to a modified polyamide resin. Specifically, the acyl halide remaining in the polyamide resin forming the skin-like layer is reacted with the zwitterionic molecule to convert the acyl halide into an amide.

The zwitterionic small molecule compound is preferable from the viewpoint that the water permeability and the antifouling property can be further improved. The concentration is preferably 0.01 to 5wt.%, and more preferably 0.5 to 3wt.%.

And, the molecular structure of the zwitterionic material is:

wherein R is ₁ 、R ₂ 、R ₃ 、R ₄ Represents any group, can be a single atom group, and can also be a polyatomic group; and wherein R ₁ The radicals providing one or more positive charges, R ₂ The groups provide one or more negative charges.

In the case where the concentration of the zwitterionic characterizing molecule is below 0.5wt.%, there is a tendency to: the concentration is too low to improve the water flux of the membrane greatly. On the other hand, in the case where the concentration of the zwitterionic characteristic molecule is higher than 5wt.%, there is a tendency that: pinhole-like defects are easily generated in the skin layer, and the salt-trapping property is lowered.

The method of bringing the skin layer into contact with the solution (aqueous solution or organic solution) containing the modification is not particularly limited, and examples thereof include a method of pouring the solution into the skin layer, a method of immersing the skin layer in the solution, and the like.

The concentration of the modifying solution in the solution and the time (reaction time) for which the solution is in contact with the skin layer are not particularly limited, and are appropriately adjusted so that the modification ratio based on the nitrogen-containing compound becomes a target value.

From the viewpoint of improving the antifouling property, the contact angle of the double-layered zwitterionic surface is preferably 30 ° or less, more preferably 20 ° or less, the thickness of the hydrated layer thereof is more than 2nm, and the film surface charge is preferably-30 eV or more, more preferably-10 eV or more. The thickness of the skin layer formed on the porous support is not particularly limited, but is usually about 0.01 to 2 μm, preferably 0.1 to 1 μm.

The shape of the composite desalination membrane of the present invention is not limited. That is, the shape of the film may be any conceivable shape such as a flat film shape or a spiral element (spiral element) shape. In addition, various treatments known in the art may be performed to improve salt rejection, water permeability, and oxidation resistance of the composite desalination membrane.

According to the technical scheme, compared with the prior art, the preparation method and the preparation method thereof provided by the invention have the following excellent effects:

(1) According to the desalting membrane, the inner and outer amphoteric ion layers respectively adjust the electrostatic acting force and the hydrophobic acting force between the membrane surface and pollutant molecules, so that the comprehensive performance of the desalting membrane is comprehensively improved.

(2) The desalting membrane with the double-layer zwitterion characteristic prepared by the invention has good stability, solves the problem that the pollution-resistant material is easy to elute from the surface of the membrane so as to cause the continuous attenuation of the pollution-resistant performance of the membrane, and has good industrial application prospect.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the prior art descriptions will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is a schematic structural diagram of a dense functional polyamide layer with a double zwitterionic character.

FIG. 2 is a scanning electron microscope image of a polyamide desalting film with high flux, high salt cut-off and stain resistance provided in examples 1-4 of the present invention.

FIG. 3 is a schematic diagram showing the selective permeability of a polyamide desalination membrane having both high flux, high salt rejection and stain resistance according to examples 1-4 of the present invention.

FIG. 4 is a schematic diagram of Zeta potential and selective permeability of the membrane surface of a polyamide desalination membrane with high flux, high salt rejection and stain resistance provided in examples 5-8 of the present invention.

FIG. 5 is a scanning electron microscope image of a polyamide desalting film with high flux, high salt cut-off and stain resistance provided in examples 9-11 of the present invention.

Fig. 6 is a schematic diagram of the water contact angle and the selective permeability of a polyamide desalting membrane with high flux, high salt rejection and stain resistance provided in examples 9 to 11 of the present invention.

FIG. 7 is a graph showing the anti-contamination performance of polyamide desalination membranes of examples 9-11 of the present invention, which have both high flux and high salt rejection and anti-contamination performance.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely in the following description with reference to the embodiments of the present invention and the accompanying drawings, and it is to be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The present invention will be further specifically illustrated by the following examples for better understanding, but the present invention is not to be construed as being limited thereto, and certain insubstantial modifications and adaptations of the invention by those skilled in the art based on the foregoing disclosure are intended to be included within the scope of the invention.

The technical solution of the present invention will be further described with reference to the following specific examples.

Example 1

An aqueous amine solution containing 2.0wt.% of m-phenylenediamine was applied to a porous polysulfone support membrane, and after 2 minutes, the excess aqueous amine solution was removed, thereby forming an aqueous solution coating layer. Next, an n-hexane solution containing 0.1wt.% trimesoyl chloride (TMC) was applied to the surface of the aqueous solution coating layer, and after 1 minute, the excess n-hexane solution was removed, and then n-hexane was volatilized in the air for 2 minutes, and thereafter, the resultant was held in a forced air dryer at 60 ℃ for 10 minutes to form a skin layer containing a polyamide resin on the porous polysulfone support film, thereby producing a composite desalting film.

Examples 2 to 4:

in contrast to example 1, examples 2-4 modify the skin layer forming the polyamide resin by adding different types of positively charged molecules to the aqueous amine solution to adjust the process parameters. In this way, a composite desalination membrane having a skin layer containing a modified polyamide resin on a porous polysulfone support membrane was produced. The coating preparation conditions and parameters for examples 2 to 4 are listed in table 1, and the corresponding test methods are described later in this specification. The scanning electron micrographs of different types of positively charged molecules are shown in FIG. 2, and the selective permeability is shown in FIG. 3, and it can be seen from Table 1 that the quaternary ammonium salt type positively charged molecules are superior in permselectivity and anti-contamination properties.

TABLE 1

Examples 5 to 8:

by comparison of examples 2 to 4, the skin-forming layer of the polyamide resin is modified by continuing to adjust the process parameters by adjusting the concentration of the positively charged molecules of the quaternary ammonium salt type. In this way, a composite desalination membrane having a skin layer containing a modified polyamide resin on a porous polysulfone support membrane was produced. Compared with example 2, the concentration of benzalkonium chloride is adjusted and set to be 1mmol/L,10mmol/L,30mmol/L and 50 mmol/L respectively. The coating preparation conditions and parameters for examples 5-7 are listed in table 2, and the corresponding test methods are described later in this specification. As a result, it was found that the permeability selectivity and the anti-fouling property were the best at a BAC concentration of 30mmol/L, and the Zeta potential and the permselectivity of the membrane surface were as shown in FIG. 4.

TABLE 2

Examples 9 to 11:

examples 9 to 11 solutions containing different kinds of zwitterionic molecules were brought into contact with the skin layer of example 2 to form an outer zwitterionic layer to modify the polyamide resin, and finally the polyamide desalting membrane having both high flux, high salt cut and stain resistance was obtained. The aqueous solution of each zwitterionic modified monomer shown in table 3 was applied to a composite desalting film prepared based on 30mmol/L benzalkonium chloride in example 7 to modify the secondary polyamide resin forming the skin layer. Thus, a composite desalination membrane having a skin layer comprising a modified polyamide resin on a porous polysulfone support membrane was produced, the membrane surface topography was shown in fig. 5, the water contact angle and selective permeability were shown in fig. 6, the anti-fouling performance was shown in fig. 7, and the surface properties and membrane performance were shown in table 3.

TABLE 3

As shown in table 3, the polyamide desalination membrane having a bilayer zwitterionic characteristic membrane surface has an improved permeation flux, a lower flux attenuation ratio, more excellent anti-fouling characteristics, and more excellent amino acid-based zwitterionic modification performance, as compared to the composite desalination membrane of comparative example 1 having a skin layer formed of an unmodified polyamide resin.

In addition, to further illustrate the performance advantages of the two-layer zwitterionic feature film surface of the present invention, we compared it with the previously reported single-layer zwitterionic coating techniques, such as comparative example 1 and comparative example 2.

Comparative example 1:

unlike the polyamide desalination membranes of examples 9-11, which have a two-layer zwitterionic film surface, comparative example 1 was prepared by zwitterionic surface modification of an unmodified polyamide resin skin layer, i.e., without an inner zwitterionic layer. Specifically, the aqueous phase solution (2.0 wt.% MPD, 1.1wt.% TEA and 2.4wt.% CSA) was first coated onto a polysulfone ultrafiltration membrane and the residual aqueous phase solution was removed after 1 minute. Next, an organic phase solution (0.1 wt.% TMC) was applied to the surface of the aqueous coating layer, and after 1 minute, the excess organic phase solution was removed. Then, 2,6-DAP solution was applied to the surface of the coating layer of the organic solution, and after 1 minute, the remaining 2,6-DAP solution was removed, and the film sheet was transferred to an oven at 80 ℃ and thermally crosslinked for 8 minutes to form a 2,6-DAP modified film. Finally, the 2,6-DAP modified membrane was quaternized with 3-BPA to produce a desalting membrane having a single zwitterionic surface.

The permselectivity and resistance to organic fouling of the membrane are shown in table 4. As can be seen from Table 4, the permeation flux of the modified membrane in comparative example 1 was 2.37Lm ^-2 h ^-1 bar ^-1 The permeation flux in examples 9 to 11 was higher than this value. In addition, the attenuation rates for the positive and negative electronegative small molecule organic pollutants in comparative example 1 were 68.4% and 17.6%, respectively, and the attenuation rates in examples 9 to 11 were lower than the corresponding values.

In conclusion, the permeation flux and the anti-fouling property of the polyamide desalting membrane with the surface of the double-layer zwitter-ion membrane are obviously superior to those of the desalting membrane with the surface of the single-layer zwitter-ion membrane.

TABLE 4

Comparative example 2:

like comparative example 1, comparative example 2 was also prepared by zwitterionic surface modification of the unmodified polyamide resin skin layer. First, the aqueous phase solution was applied to a polysulfone ultrafiltration membrane, and after 2 minutes, the excess aqueous phase solution was removed. Next, the organic phase solution was applied to the surface of the aqueous coating layer, and after 2 minutes, the excess organic phase solution was removed. Thereafter, the arginine denaturing solution was applied to the surface of the organic phase coating layer, and after 2 minutes, the excessive denaturing solution on the film surface was removed. Finally, the film sheets were transferred to a 60 ℃ forced air dryer for 10 minutes. The permselectivity and anti-fouling properties of the membranes are shown in table 5.

As can be seen from Table 5, the permeation flux of the modified membrane in comparative example 2 was 3.79Lm ^-2 h ^-1 bar ^-1 Lower than 3.90Lm in example 10 ^-2 h ^-1 bar ^-1 . In addition, the attenuation rates of the positive and negative electric small molecule organic pollutants in the comparative example 1 are respectively 48.5 percent and 25.6 percent, which are higher than the attenuation rates of the positive and negative electric small molecule organic pollutants in the example 10, namely 38.2 percent and 14.2 percent.

In conclusion, the permeation flux and the anti-fouling property of the polyamide desalting membrane with the surface of the double-layer zwitter-ion membrane are obviously superior to those of the desalting membrane with the surface of the single-layer zwitter-ion membrane.

TABLE 5

(measurement of permeation flux and salt rejection)

For the fabricated composite polyamide desalination membrane, a cross-flow test system (effective membrane surface area: 28.26 cm) ² ) Separation performance evaluation was performed to determine permeation Flux (Flux) and salt rejection (Rej). The pre-pressing operation was initially carried out at a pressure of 20bar for 2 hours to stabilize the permeability of the composite desalination membrane. The permeation flux of the composite desalination membrane (30 minutes of permeate collected) was then measured after 1 hour of operation at 15bar pressure using an aqueous solution containing NaCl at a concentration of 2000mg/L as feed. The permeation flux was determined by the following formula (1). In addition, the concentrations of the feed solution and the permeate were measured using a conductivity meter (Thermo, eutechCON2700, USA). The salt rejection was determined by the following formula (2). At least 3 replicates of each film sample were tested and the mean and error range of the test results were calculated.

In the formula, J _w Membrane permeation flux (Lm) ^-2 h ^-1 bar ^-1 ,LMH/bar)；

M-permeate mass (kg) across the membrane;

rho-permeate Density (kgm) ^-3 )；

E-effective permeation area (m) of the membrane sample ² )；

t-test time (h);

p-test pressure (bar).

In the formula, R _s -salt rejection (%) of the membrane sample;

C _o -feed liquor salt concentration (mg/L);

C _p permeate salt concentration (mg/L).

(evaluation of fouling resistance)

As model contaminants, evaluation of the membrane fouling resistance was carried out using dodecyltrimethylammonium bromide (DTAB) and Sodium Dodecylbenzenesulfonate (SDBS). DTAB is used as an example of a small-molecule contaminant which is a surfactant having a positive charge. SDBS is used as an example of a surfactant having a negative charge. These are typical representatives of common organic pollutants in aqueous systems.

Evaluation of anti-contamination was evaluated as normalized Flux decay rate (%). The Flux attenuation rate was measured in 4 stages as follows.

In stage 1, the RO system was operated at 15bar and a cross-flow velocity of 14cm/s for 30 minutes, using a feed aqueous solution containing 2000mg/L NaCl, and baseline permeate flux and salt rejection were determined.

In the 2 nd stage, 200ppm of the model contaminant was added to the feed aqueous solution, and the RO system was operated under the same conditions as in the 1 st stage for 6 hours.

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

In stage 4, the permeate flux was again measured using an aqueous feed solution containing 2000mg/L NaCl.

The Flux attenuation ratio can be calculated from the following equation, and the results are shown in table 1.

Flux reduction rate (%) = {1- (permeation Flux at stage 2/permeation Flux at stage 1) }. Times.100%

A Flux recovery (%) = (permeation Flux in stage 4/permeation Flux in stage 1) × 100%, and further, the industrial applicability of the polyamide desalination membrane having both high Flux high salt cut and stain resistance is as follows:

the composite desalination membrane of the present invention is suitable for production of ultrapure water, desalination of salt water or seawater, and the like, and can remove contaminants causing public nuisance such as dyeing wastewater and electrodeposition coating wastewater, recover a contaminant source or an effective substance contained therein, and contribute to sealing treatment of wastewater. In addition, the method can be used for concentration of effective components in food applications, removal of harmful components in water purification applications, and the like, and for wastewater treatment in oil fields, shale gas fields, and the like.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (9)

1. The polyamide desalting membrane with high flux, high salt rejection and stain resistance is characterized by being flat or hollow fiber and comprising a porous ultrafiltration base membrane and a polyamide compact functional layer; wherein the content of the first and second substances,

the polyamide compact functional layer is prepared on the surface of the porous ultrafiltration base membrane through an interfacial polymerization method and has the characteristic of double-layer zwitterions; the polyamide compact functional layer has good hydrophilicity, the water contact angle of the polyamide compact functional layer is less than 40 degrees, and the thickness of a hydration layer is more than 2nm; and the polyamide compact functional layer can weaken strong electronegativity of the polyamide layer, and the charge quantity of the polyamide compact functional layer is larger than-30 eV.

2. The polyamide desalting membrane with high flux, high salt rejection and stain resistance as claimed in claim 1, wherein the material of the porous ultrafiltration membrane includes but is not limited to cellulose acetate, polyethersulfone, polyvinylidene fluoride, polysulfone or polyacrylonitrile.

3. A method for preparing the polyamide desalting membrane with high flux high salt rejection and stain resistance as claimed in claim 1, which comprises the following steps:

1) Contacting an aqueous solution containing a polyfunctional amine monomer doped with a positively charged molecule with an organic solution containing a polyfunctional acid chloride monomer on a porous support to form a polyamide separation skin layer having an inner zwitterionic character on the surface of the porous support;

2) And (3) enabling a solution containing a zwitterionic material to contact with the polyamide separation skin layer and carrying out chemical reaction to form an outer zwitterionic layer so as to modify the polyamide separation skin layer, and finally obtaining the polyamide desalting membrane with high flux, high salt cut and stain resistance.

4. The method for preparing the polyamide desalting membrane with high flux high salt rejection and stain resistance as claimed in claim 3, wherein the concentration of the positively charged molecules is 0.01-5 wt.%, and the positively charged molecules are selected from amine salt type molecules or other molecules of compounds with nitrogen heterocycle, including but not limited to one or more of small molecules, large molecules, hyperbranched molecules, and nano materials; wherein the amine salt type molecule is at least one of primary amine salt, secondary ammonium salt, tertiary amine salt and quaternary amine salt.

5. The method of claim 3, wherein the concentration of the polyfunctional amine monomer component is 0.1 to 5wt.%, and the polyfunctional amine monomer is a polyfunctional amine having 2 or more reactive amino groups, including aromatic, aliphatic, and alicyclic polyfunctional amines; wherein, the first and the second end of the pipe are connected with each other,

the aromatic polyfunctional amine monomer includes, but is not limited to, one of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3, 5-triaminobenzene, 1,2, 4-triaminobenzene, 3, 5-diaminobenzoic acid, 2, 4-diaminotoluene, 2, 6-diaminotoluene, N' -dimethyl-m-phenylenediamine, 2, 4-diaminoanisole, amikaol, xylylenediamine;

the aliphatic polyfunctional amine monomer includes, but is not limited to, one of ethylenediamine, propylenediamine, tris (2-aminoethyl) amine, N-phenylethylenediamine;

the alicyclic polyfunctional amine monomer includes, but is not limited to, one of 1, 3-diaminocyclohexane, 1, 2-diaminocyclohexane, 1, 4-diaminocyclohexane, piperazine, 2, 5-dimethylpiperazine, 4-aminomethylpiperazine.

6. The method for preparing a polyamide desalting membrane with high flux, high salt rejection and stain resistance according to claim 3, wherein the concentration of the multifunctional acyl chloride monomer is 0.01 to 5wt.%, and the multifunctional acyl chloride monomer is a multifunctional compound molecule with more than 2 reactive acyl chlorides; the multifunctional acyl chloride monomer comprises aromatic, aliphatic and alicyclic multifunctional acyl chloride; wherein, the first and the second end of the pipe are connected with each other,

the aromatic polyfunctional acyl chloride monomer comprises but is not limited to one of trimesoyl chloride, paraphthaloyl chloride, isophthaloyl chloride, biphenyldicarbonyl chloride, naphthaloyl chloride, benzene trisulfonyl chloride, benzene disulfonyl chloride and chlorosulfonyl phthaloyl chloride,

the aliphatic polyfunctional acyl chloride monomer comprises but is not limited to one of malonyl chloride, succinyl chloride, glutaryl chloride, trimetyl chloride, butyrtrimoyl chloride, glutaryl chloride and adipoyl chloride;

the alicyclic polyfunctional acyl chloride monomer includes, but is not limited to, one of cyclopropane trimethyl acyl chloride, cyclobutane tetramethyl acyl chloride, cyclopentane trimethyl acyl chloride, cyclopentane tetramethyl acyl chloride, cyclohexane trimethyl acyl chloride, tetrahydrofuran tetramethyl acyl chloride, cyclopentane dimethyl acyl chloride, cyclobutane dimethyl acyl chloride, cyclohexane dimethyl acyl chloride, tetrahydrofuran dimethyl acyl chloride.

7. The polyamide desalination film with both high flux high salt rejection and stain resistance of claim 3, wherein the concentration of the zwitterionic material is 0.01-5 wt.%, and the zwitterionic material is a neutral compound with both positively and negatively charged groups; wherein the content of the first and second substances,

the zwitterionic characteristic material monomer comprises but is not limited to an amphoteric micromolecule, an amphoteric macromolecule or an amphoteric macromolecule, and preferably, the zwitterionic material is an amphoteric micromolecule compound;

and, the molecular structure of the zwitterionic material is:

wherein R is ₁ 、R ₂ 、R ₃ 、R ₄ Represents any group, which can be a single atom group or a polyatomic group; and wherein R ₁ The radicals providing one or more positive charges, R ₂ The groups provide one or more negative charges.

8. Use of the polyamide desalting membrane with high flux high salt rejection and stain resistance as claimed in claim 1 or the polyamide desalting membrane with high flux high salt rejection and stain resistance prepared by the method as claimed in claim 3 in separation, concentration and purification.

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

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