CN114177786B - Preparation method of multilayer polyamide composite reverse osmosis membrane - Google Patents
Preparation method of multilayer polyamide composite reverse osmosis membrane Download PDFInfo
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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
- B01D71/56—Polyamides, e.g. polyester-amides
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- 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
- B01D61/025—Reverse osmosis; Hyperfiltration
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- 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
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- 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
- B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
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- 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
- B01D69/12—Composite membranes; Ultra-thin membranes
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- 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
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/48—Antimicrobial properties
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- 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
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- Y02A20/00—Water conservation; Efficient water supply; Efficient water use
- Y02A20/124—Water desalination
- Y02A20/131—Reverse-osmosis
Abstract
The invention relates to a preparation method of a multilayer polyamide composite reverse osmosis membrane, which is characterized in that polyvinyl alcohol or polyvinylpyrrolidone is added into a polysulfone membrane, dopamine solution is pressed on the polysulfone membrane in a pressing mode, the dopamine solution reacts to form a polydopamine layer on the surface and in membrane pores of the membrane, then a base membrane with the polydopamine layer is sequentially immersed into low-concentration water phase solution and oil phase solution, and because the water phase solution and the oil phase solution are low in concentration, part of amido groups carried by the polydopamine layer are remained on the surface of the membrane after the water phase is immersed, the amido groups can react with the following oil phase acyl chloride to generate amido bonds, so that an interpenetration structure is formed, and the relation between the polyamide layer and the polysulfone base membrane layer can be enlarged. And a polydopamine layer and a polyamide structure are formed in pores of the porous base membrane, so that the membrane flux is increased, and the rejection rate of the membrane is increased. The glutaraldehyde cross-linked chitosan complex silver is used as a polyamide protective layer, the chitosan surface has a plurality of hydroxyl groups and amino groups, so that the attack of chlorine can be prevented, the chlorine resistance of the membrane is improved, and the antibacterial property of the membrane is improved due to the antibacterial property of the silver.
Description
Technical Field
The invention relates to a multilayer polyamide film preparation process and a corresponding film product.
Background
The membrane technology is a common water treatment technology, and the conventional membrane technology is divided into reverse osmosis, forward osmosis, nanofiltration, ultrafiltration and the like. The reverse osmosis technology is a separation method for separating solute from solvent in solution by means of selective interception of reverse osmosis membrane under the action of certain pressure, and compared with other membrane types (nanofiltration, ultrafiltration, forward osmosis, microfiltration and the like), the reverse osmosis technology has smaller membrane pore size and can effectively remove impurities such as salts, organic matters, colloids, bacteria and the like in water. Polyamide is a common reverse osmosis membrane material, interfacial polymerization is a polyamide preparation method of manufacturers, but the conventional interfacial polymerization has the defects of weak contact force between a base membrane and an active layer, low water flux, reduced rejection rate while increasing the water flux and poor antibacterial performance.
In the prior art, the permeability and rejection rate of a polyamide reverse osmosis membrane are increased by adopting a surface treatment and mixed doping mode, but the conventional rejection rate and permeability cannot be simultaneously improved due to the TRADE-OFF effect, and a membrane with high antibacterial performance, which can increase the flux and rejection rate of the reverse osmosis membrane and increase the binding force between a polyamide layer and a supporting layer, is urgently needed.
Disclosure of Invention
The present invention aims to provide a stable reverse osmosis membrane having high rejection rate, high permeability and strong antibacterial property.
The application provides a preparation method of a composite reverse osmosis membrane, which comprises the following steps:
a) Preparation of a base film: weighing 17-19 wt% of polysulfone resin, dissolving the polysulfone resin in N, N-dimethylformamide, adding 4.0-5.0 wt% of additive, stirring for 3-6h at 50-100 ℃ to prepare uniformly dispersed solution; filtering, vacuum degassing, uniformly coating on non-woven fabric, wherein the thickness of a wet film is about 100-200 μm, immediately immersing in pure water at 20-30 ℃ for gel curing to form a film, and spraying 30-60% sulfuric acid solution at 25-50 ℃ on a polysulfone film to obtain a polysulfone base film;
b) Preparing a basement membrane surface modification layer, weighing 6.0-8.5g of trihydroxymethyl aminomethane into a beaker, adding a proper amount of ultrapure water for dissolving, transferring into a 1L volumetric flask, fixing the volume, and adjusting the pH to 6.0-8.0 by using hydrochloric acid to obtain the trihydroxymethyl aminomethane-hydrochloric acid buffer solution. Weighing 0.2-0.4g of dopamine, adding the dopamine into the buffer solution to form a dopamine modified solution, and pressurizing and filtering the dopamine modified solution on a polysulfone basal membrane to form a polydopamine layer on the surface of the membrane and in membrane pores.
C) Preparation of the bottom polyamide layer. Preparing aqueous phase liquid: dissolving aromatic polyfunctional amine and a surfactant in water in sequence, stirring uniformly, and adding sodium hydroxide into the obtained aqueous solution to adjust the pH value of the solution to 6-10 to obtain an aqueous phase solution, wherein the aromatic polyfunctional amine accounts for 0.06-0.10% of the mass concentration of the aqueous solution, and the surfactant accounts for 0.5% of the mass concentration of the aqueous solution; preparing an oil phase solution: dissolving aromatic polyfunctional acyl halide in naphtha, stirring uniformly to obtain oil phase liquid, wherein the mass concentration of the aromatic polyfunctional acyl halide in the oil solution is 0.01-0.03%, immersing the base film with the formed polydopamine layer in a water phase solution for 30-60 seconds, removing the excessive water phase liquid on the surface of the non-woven fabric base film by using a surface-polished stainless steel roller, immersing the base film in the oil phase liquid for 40-60 seconds, removing the residual oil phase liquid on the surface, then putting the base film in an oven at 60-90 ℃ for 4-8 minutes, and then cleaning to obtain a bottom polyamide layer.
D) A top polyamide layer.
And (3) ultrasonically dispersing 0.1-0.5g of graphene oxide in 100mL of water to prepare the graphene oxide/water dispersion. 0.1-0.5g of 3-aminopropylphosphonic acid was dissolved in 40mL of ethanol to prepare a 3-aminopropylphosphonic acid/ethanol solution. Adding the 3-aminopropyl phosphonic acid/ethanol solution into the graphene oxide/water dispersion, and stirring and refluxing for 10-15h at the temperature of 80-95 ℃. And (4) carrying out suction filtration, and washing filter residues in ethanol to obtain the phosphonic acid modified graphene oxide.
Preparing aqueous phase liquid: dissolving aromatic polyfunctional amine and a surfactant in water in sequence, stirring uniformly, adding sodium hydroxide into the obtained aqueous solution to adjust the pH value of the solution to 6-10 to obtain an aqueous phase solution, wherein the mass concentration of the aromatic polyfunctional amine in the aqueous solution is 0.3-0.5%, then adding the phosphonic acid modified graphene oxide, and stirring uniformly. Preparing an oil phase solution: dissolving aromatic polyfunctional acyl halide in naphtha, stirring uniformly to obtain oil phase liquid, wherein the mass concentration of the aromatic polyfunctional acyl halide in the oil solution is 0.1-0.3%, immersing the base membrane with the bottom polyamide layer into the water phase solution for 30-60 seconds, removing the redundant water phase liquid on the surface of the non-woven fabric base membrane by using a stainless steel roller with polished surface, immersing the base membrane into the oil phase liquid for 40-80 seconds, removing the residual oil phase liquid on the surface, then putting the base membrane into an oven with the temperature of 60-90 ℃ for 5 minutes, and then cleaning to obtain the membrane with the top polyamide layer.
E) And (4) preparing a protective layer.
Preparing a chitosan complex silver antibacterial agent, weighing soluble silver salt and chitosan according to the weight ratio of 1: 10-70, firstly adding water into a reaction kettle, starting a stirrer, controlling the reaction pH value to be 3.6-8.5, controlling the reaction temperature to be-16-70 ℃, slowly adding chitosan, stirring until the chitosan is completely dissolved to form a solution with the mass concentration of 0.3-0.9, then adding the soluble silver salt, stirring for reaction for 0.2-20 hours, adding glutaraldehyde, and preparing a protective layer modified solution with the mass concentration of 0.2-0.8% of glutaraldehyde.
And (3) immersing the membrane containing the top polyamide layer into a protective layer modification solution for 0.2-4h, and performing a crosslinking reaction to obtain the polyamide membrane of the surface-modified chitosan protective layer.
Preferably, the soluble silver salt comprises a nitrate, acetate or citrate salt.
Preferably, the surfactant is sodium benzene sulfonate, sodium dodecyl benzene sulfonate or sodium carboxymethyl sulfonate.
Preferably, the additive is polyvinyl alcohol or polyvinylpyrrolidone.
Preferably, the aromatic polyfunctional amine is p-phenylenediamine or m-phenylenediamine.
Preferably, the aromatic polyfunctional acid chloride is trimesoyl chloride.
Advantageous effects
According to the method, polyvinyl alcohol or polyvinylpyrrolidone is added into a polysulfone membrane, the porosity of the membrane is increased, the flux of the membrane is increased, a dopamine solution is filter-pressed on the polysulfone membrane in a pressing-in mode, a polydopamine layer is formed on the surface of the membrane and in membrane pores through reaction, then a base membrane with the polydopamine layer is sequentially immersed into a water phase solution and an oil phase solution, the water phase solution and the oil phase solution are low in concentration, after the water phase is immersed, part of amido groups carried by the polydopamine layer are arranged on the surface of the membrane, the amido groups can react with the following oil phase acyl chloride to generate amido bonds, an interpenetration structure is formed, and the relation between the membrane polyamide layer and the base membrane layer can be increased. And a polydopamine layer and a polyamide structure are formed in pores of the porous base membrane, so that the membrane flux is increased, and the rejection rate of the membrane is increased.
The concentration of the monomers applied in the preparation process of the top layer polyamide is higher than that of the monomers applied in the bottom layer, so that a compact polyamide layer is conveniently formed on the top layer, the retention rate of the membrane is ensured, meanwhile, in the preparation process of the top layer membrane, the phosphonic acid modified graphene oxide is added into the water phase monomers, the hydrophilicity of the membrane is increased, partial channels are provided, the treatment flux of the membrane is increased, and meanwhile, the phosphonic acid groups can be complexed with the acyl chloride groups, so that the acyl chloride groups are prevented from being hydrolyzed, the formation amount of the polyamide is increased, and the retention rate of the membrane is increased. In the membrane preparation process, the concentration applied in the bottom layer polyamide preparation process is low, amino exposed points of polydopamine exist on the membrane surface after the membrane surface is coated with the aqueous solution, a polyamide mechanism is formed by the amino exposed points and acyl chloride groups, a penetrating layer is formed, the connecting force of a polyamide layer and a base layer is increased, the polydopamine layer is generated by polymerization reaction of monomer dopamine on the polysulfone membrane, and the connecting force of the polydopamine layer and the polysulfone layer is enhanced.
Glutaraldehyde crosslinked chitosan complexed silver is used as a polyamide protective layer, and the chitosan surface has a plurality of hydroxyl groups and amino groups, so that chlorine attack can be prevented, the chlorine resistance of the membrane is improved, and the antibacterial property of the membrane is improved due to the antibacterial property of the silver.
Detailed Description
Example 1
The application provides a preparation method of a composite reverse osmosis membrane, which comprises the following steps:
a) Preparation of a base film: weighing polysulfone resin with the weight ratio of 18 percent, dissolving the polysulfone resin in N, N-dimethylformamide, adding polyvinyl alcohol with the weight ratio of 4.0 percent, stirring for 3 hours at the temperature of 60 ℃ to prepare uniformly dispersed solution; filtering, vacuum degassing, uniformly coating on non-woven fabric, wherein the thickness of a wet film is about 100 μm, immediately immersing in pure water at 20 ℃ for gel curing to form a film, and spraying 30% sulfuric acid solution at 25 ℃ on a polysulfone film to obtain a polysulfone base film;
b) Preparing a basement membrane surface modification layer, weighing 6.0g of tris (hydroxymethyl) aminomethane into a beaker, adding a proper amount of ultrapure water for dissolving, transferring into a 1L volumetric flask, fixing the volume, and adjusting the pH to 6.0 by using hydrochloric acid to obtain tris (hydroxymethyl) aminomethane-hydrochloric acid buffer solution. Weighing 0.2g of dopamine, adding the dopamine into the buffer solution to form a dopamine modified solution, and performing pressure filtration on the dopamine modified solution on a polysulfone basal membrane for 0.5h to obtain a polydopamine layer formed on the surface and in the pores of the membrane.
C) Preparation of the bottom polyamide layer. Preparing an aqueous phase liquid: sequentially dissolving p-phenylenediamine and sodium benzenesulfonate in water, stirring uniformly, and adding sodium hydroxide into the obtained aqueous solution to adjust the pH value of the solution to 7 to obtain an aqueous phase solution, wherein the mass concentration of the p-phenylenediamine in the aqueous solution is 0.06%, and the mass concentration of the surfactant in the aqueous solution is 0.5%; preparing an oil phase solution: dissolving trimesoyl chloride in naphtha, uniformly stirring to obtain an oil phase solution, wherein the mass concentration of the trimesoyl chloride in the oil solution is 0.01%, immersing the base membrane with the formed poly dopamine layer into the water phase solution for 30 seconds, removing the redundant water phase solution on the surface of the non-woven fabric base membrane by using a stainless steel roller with a polished surface, immersing the base membrane into the oil phase solution for 40 seconds, removing the residual oil phase solution on the surface, then, putting the base membrane into a 60 ℃ oven for 4 minutes, and then, cleaning to obtain a bottom polyamide layer.
D) A top polyamide layer.
0.1g of graphene oxide is dispersed in 100mL of water by ultrasonic to prepare graphene oxide/water dispersion. 0.1g of 3-aminopropyl phosphonic acid was dissolved in 40mL of ethanol to prepare a 3-aminopropyl phosphonic acid/ethanol solution. Adding the 3-aminopropyl phosphonic acid/ethanol solution into the graphene oxide/water dispersion, and stirring and refluxing for 10 hours at 80 ℃. And (4) carrying out suction filtration, and washing filter residues in ethanol to obtain the phosphonic acid modified graphene oxide.
Preparing aqueous phase liquid: sequentially dissolving p-phenylenediamine and sodium benzenesulfonate in water, stirring uniformly, adding sodium hydroxide into the obtained aqueous solution to adjust the pH value of the solution to 6 to obtain an aqueous phase solution, wherein the mass concentration of the p-phenylenediamine in the aqueous solution is 0.3%, the phosphonic acid modified graphene oxide accounting for 5% of the total mass of the aqueous phase solution is added, and stirring uniformly. Preparing an oil phase solution: dissolving trimesoyl chloride in naphtha, uniformly stirring to obtain an oil phase solution, wherein the mass concentration of the trimesoyl chloride in the oil solution is 0.1%, immersing the base membrane with the bottom polyamide layer into the water phase solution for 30 seconds, removing the redundant water phase solution on the surface of the non-woven fabric base membrane by using a stainless steel roller with a polished surface, immersing the base membrane into the oil phase solution for 40 seconds, removing the residual oil phase solution on the surface, then putting the base membrane into a 60 ℃ oven for 5 minutes, and then cleaning to obtain the membrane with the top polyamide layer.
E) And (4) preparing a protective layer.
Preparing a chitosan silver complex antibacterial agent, weighing silver nitrate and chitosan in a weight ratio of 1: 20, firstly adding water into a reaction kettle, starting a stirrer, controlling the reaction pH value to be 3.6, controlling the reaction temperature to be 20 ℃, slowly adding the chitosan, stirring until the chitosan is completely dissolved to prepare a chitosan solution with the mass concentration of 3%, then adding the silver nitrate, stirring for reaction for 0.3 hour, adding glutaraldehyde, and preparing a protective layer modified solution with the mass concentration of 0.3%.
And (3) immersing the membrane containing the top polyamide layer into a protective layer modification solution for 1h, and carrying out crosslinking reaction to obtain the polyamide membrane with the surface modified chitosan protective layer.
Example 2
A) Preparation of a base film: weighing 18 wt% of polysulfone resin, dissolving the polysulfone resin in N, N-dimethylformamide, adding 4.0 wt% of polyvinylpyrrolidone, and stirring at 60 ℃ for 3 hours to prepare a uniformly dispersed solution; filtering, vacuum degassing, uniformly coating on non-woven fabric, wherein the thickness of a wet film is about 100 μm, immediately immersing in pure water at 20 ℃ for gel curing to form a film, and spraying 30% sulfuric acid solution at 25 ℃ on a polysulfone film to obtain a polysulfone base film;
b) Preparing a basement membrane surface modification layer, weighing 6.0g of tris (hydroxymethyl) aminomethane into a beaker, adding a proper amount of ultrapure water for dissolving, transferring into a 1L volumetric flask, fixing the volume, and adjusting the pH to 6.0 by using hydrochloric acid to obtain tris (hydroxymethyl) aminomethane-hydrochloric acid buffer solution. Weighing 0.2g of dopamine, adding the dopamine into the buffer solution to form dopamine modified solution, and performing pressure filtration on the dopamine modified solution on a polysulfone basal membrane for 0.5h to obtain a membrane surface and a membrane hole to form a polydopamine layer.
C) Preparation of the bottom polyamide layer. Preparing an aqueous phase liquid: sequentially dissolving p-phenylenediamine and sodium dodecyl benzene sulfonate in water, uniformly stirring, and adding sodium hydroxide into the obtained aqueous solution to adjust the pH value of the solution to 7 to obtain an aqueous phase solution, wherein the m-phenylenediamine accounts for 0.06% of the mass concentration of the aqueous solution, and the surfactant accounts for 0.5% of the mass concentration of the aqueous solution; preparing an oil phase solution: dissolving trimesoyl chloride in naphtha, uniformly stirring to obtain an oil phase solution, wherein the mass concentration of the trimesoyl chloride in the oil solution is 0.01%, immersing the base membrane with the formed poly dopamine layer into the water phase solution for 30 seconds, removing the redundant water phase solution on the surface of the non-woven fabric base membrane by using a stainless steel roller with a polished surface, immersing the base membrane into the oil phase solution for 40 seconds, removing the residual oil phase solution on the surface, then, putting the base membrane into a 60 ℃ oven for 4 minutes, and then, cleaning to obtain a bottom polyamide layer.
D) A top polyamide layer.
0.1g of graphene oxide is dispersed in 100mL of water by ultrasonic to prepare graphene oxide/water dispersion. 0.1g of 3-aminopropyl phosphonic acid was dissolved in 40mL of ethanol to prepare a 3-aminopropyl phosphonic acid/ethanol solution. Adding the 3-aminopropyl phosphonic acid/ethanol solution into the graphene oxide/water dispersion, and stirring and refluxing for 10 hours at 80 ℃. And (4) carrying out suction filtration, and washing filter residues in ethanol to obtain the phosphonic acid modified graphene oxide.
Preparing aqueous phase liquid: sequentially dissolving p-phenylenediamine and sodium dodecyl benzene sulfonate in water, stirring uniformly, adding sodium hydroxide into the obtained aqueous solution to adjust the pH value of the solution to 6 to obtain an aqueous phase solution, wherein the mass concentration of the p-phenylenediamine in the aqueous solution is 0.3%, the phosphonic acid modified graphene oxide accounting for 5% of the total mass of the aqueous phase solution is added, and stirring uniformly. Preparing an oil phase solution: dissolving trimesoyl chloride in naphtha, uniformly stirring to obtain an oil phase solution, wherein the mass concentration of the trimesoyl chloride in the oil solution is 0.1%, immersing the base membrane with the bottom polyamide layer into the water phase solution for 30 seconds, removing the redundant water phase solution on the surface of the non-woven fabric base membrane by using a stainless steel roller with a polished surface, immersing the base membrane into the oil phase solution for 40 seconds, removing the residual oil phase solution on the surface, then putting the base membrane into a 60 ℃ oven for 5 minutes, and then cleaning to obtain the membrane with the top polyamide layer.
E) And (4) preparing a protective layer.
Preparing a chitosan complex silver antibacterial agent, weighing silver acetate and chitosan in a weight ratio of 1: 20, firstly adding water into a reaction kettle, starting a stirrer, controlling the reaction pH value to be 3.6, controlling the reaction temperature to be 20 ℃, slowly adding chitosan, stirring until the chitosan is completely dissolved to prepare a chitosan solution with the mass concentration of 3%, then adding the silver acetate, stirring for reaction for 0.3 hour, adding glutaraldehyde, and preparing a protective layer modified solution with the mass concentration of 0.3%.
And (3) immersing the membrane containing the top polyamide layer into a protective layer modification solution for 1h, and carrying out crosslinking reaction to obtain the polyamide membrane with the surface modified chitosan protective layer.
Comparative example 1
The other process was the same as in example 1 except that a 30% sulfuric acid solution at 25 ℃ was not sprayed on the polysulfone film during the preparation of the polysulfone-based film
Comparative example 2
The rest of the process is the same as that of example 1, except that in the preparation process of the bottom polyamide layer, the mass concentration of the p-phenylenediamine in the aqueous solution is 0.3%, and the mass concentration of the surfactant in the aqueous solution is 0.5%; the mass concentration of trimesoyl chloride in the oil solution is 0.1%.
Comparative example 3
Otherwise, the same as example 1 was repeated, except that a protective layer was not formed.
Comparative example 4
The procedure of example 1 was repeated except that the phosphonic acid-modified graphene oxide was not added to the aqueous solution in the top polyamide layer.
Comparative example 5
The rest was the same as example 1 except that the bottom polyamide layer was not formed.
Comparative example 6
The rest was the same as example 1 except that the polydopamine layer was not formed.
Comparative example 7
The procedure of example 1 was repeated, except that the polydopamine layer was not subjected to pressure filtration.
The membranes of the above examples and comparative examples were tested under 1400ppm sodium chloride solution at pH 7.5 at 20 ℃ under 150psi test pressure, and after running for a long time under 1500ppm active chlorine attack, the membrane properties were again measured as shown in Table 1
Table 1:
it can be seen that the base membrane is not subjected to acid treatment, the rejection rate and the water flux of the membrane are reduced, the main reason is that the porosity of the membrane is increased by the acid treatment, the membrane pores which are not subjected to the acid treatment are small, the amount of the dopamine solution entering the membrane pores is small in the suction filtration process, so that a polydopamine layer and a polyamide layer are not formed in part of the membrane pores, and the rejection rate of the membrane is reduced.
When the underlayer coating was treated with a high concentration polyamide, the salt rejection rate was high in comparative example 2, but the underlayer coating was formed by using a high concentration polyamide in successive layers. The rejection rate of the membrane is reduced.
As can be seen from comparison of comparative example 3 with example 1, the rejection rate of the membrane without the protective layer formed decreases more rapidly by the attack of active chlorine, further illustrating that the establishment of the protective layer has the property of making the membrane more resistant to chlorine attack.
As can be seen from comparison of comparative example 4 with example 1, the phosphonic acid-modified graphene oxide was not added, and both the rejection rate and flux of the membrane were reduced due to the fact that the phosphonic acid-modified graphene oxide can increase the hydrophilicity of the membrane and the phosphoric acid groups can form a complex with the amide to prevent hydrolysis of the amide during the reaction.
As can be seen from comparison between comparative example 5 and example 1, the rejection of the membrane is reduced without forming the bottom polyamide layer, the flux change is not large, and the bottom polyamide layer and the polydopamine layer form coupling penetration, so that the corresponding rejection is reduced without the bottom polyamide layer.
As can be seen from comparison between comparative example 6 and example 1, the non-formed polydopamine layer is not formed, the rejection rate of the membrane is reduced, the flux change is not large, and the main reason is that the bottom polyamide and the polydopamine layer can form coupling insertion, so that after the non-formed polydopamine layer does not exist, the corresponding coupling effect disappears, and the rejection rate is reduced.
As can be seen from comparison between comparative example 7 and example 1, the rejection of the membrane is reduced without filter pressing, the flux change is not large, and the corresponding rejection is reduced mainly when excessive poly-dopamine layers and polyamide layers are not formed in the corresponding membrane pores without filter pressing.
The membranes were also tested for long-term operation, and after 100 days at a temperature of 20 ℃ and a working pressure of 150psi at a pH of 7.5 in 1400ppm NaCl solution, the corresponding membrane properties are shown in Table 2:
TABLE 2
| Case(s) | Rate of decrease in rejection | Membrane crusherDamage ratio (ratio of film damage area to overall area) |
| Example 1 | 0.7% | 0.02% |
| Example 2 | 0.6% | 0.02% |
| Comparative example 1 | 2.0% | 1.0% |
| Comparative example 2 | 1.7% | 1.3% |
| Comparative example 3 | 2.1% | 0.5% |
| Comparative example 4 | 1.2% | 0.4% |
| Comparative example 5 | 1.6% | 1.4% |
| Comparative example 6 | 1.1% | 1.2% |
| Comparative example 7 | 1.0% | 0.5% |
As can be seen from the table 2, due to the chemical bonding between the bottom layer and the polyamide layer in the technical scheme of the application, the service life of the membrane is greatly prolonged, and the lower membrane breakage rate and rejection rate reduction rate can be ensured under the long-term operation of the membrane.
Film antibacterial property test experiment
Gram-negative escherichia coli and gram-positive staphylococcus aureus are used as bacterial models, the antibacterial performance of the membranes of the embodiment 1, the comparative example 4 and the comparative example 5 is tested by adopting a bacterial liquid oscillation method according to the national standard (GB/T20944.3-2008), a group of blank controls are set, and the calculation formula of the sterilization rate is as follows: ((A-B)/A) × 100%, A being the number of colonies of the bacteria in the blank control group, B being the number of colonies of the bacteria in the solution at each sampling. The performance of each film versus table 2:
table 2:
| case(s) | Sterilizing rate of Escherichia coli | Staphylococcus aureus bactericidal rate |
| Example 1 | 98.7% | 97.5% |
| Comparative example 3 | 94.7% | 92.7% |
| Commercially available polyamide membranes | 93.5% | 91.7% |
As can be seen from table 2, the formation of the protective layer during the film preparation process can increase the antibacterial performance of the film.
Claims (4)
1. A preparation method of a multilayer polyamide membrane composite reverse osmosis membrane comprises the following steps:
a) Preparation of a base film: weighing 17-19 wt% of polysulfone resin, dissolving the polysulfone resin in N, N-dimethylformamide, adding 4.0-5.0 wt% of additive, stirring for 3-6h at 50-100 ℃ to prepare uniformly dispersed solution; filtering, vacuum degassing, uniformly coating on non-woven fabric, wherein the thickness of a wet film is 100-200 μm, immediately immersing in pure water at 20-30 ℃ for gel curing to form a film, and spraying 30-60% sulfuric acid solution at 25-50 ℃ on a polysulfone film to obtain a polysulfone base film;
b) Preparing a base membrane surface modification layer, weighing 6.0-8.5g of tris (hydroxymethyl) aminomethane in a beaker, adding a proper amount of ultrapure water for dissolving, transferring to a 1L volumetric flask, fixing the volume, and adjusting the pH to 6.0-8.0 by using hydrochloric acid to obtain tris (hydroxymethyl) aminomethane-hydrochloric acid buffer solution; weighing 0.2-0.4g of dopamine, adding the dopamine into the buffer solution to form dopamine modified solution, and performing pressure filtration on the dopamine modified solution on a polysulfone basal membrane to form a polydopamine layer on the surface of the membrane and in membrane pores;
c) Preparing a bottom polyamide layer; preparing an aqueous phase liquid: dissolving aromatic polyfunctional amine and a surfactant in water in sequence, stirring uniformly, and adding sodium hydroxide into the obtained aqueous solution to adjust the pH value of the solution to 6-10 to obtain an aqueous phase solution, wherein the aromatic polyfunctional amine accounts for 0.06-0.10% of the aqueous solution by mass, and the surfactant accounts for 0.5% of the aqueous solution by mass; preparing an oil phase solution: dissolving aromatic polyfunctional acyl halide in naphtha, and uniformly stirring to obtain oil phase liquid, wherein the aromatic polyfunctional acyl halide accounts for 0.01-0.03% of the mass of the oil solution; immersing the basement membrane with the polydopamine layer into a water phase solution for 30-60 seconds, removing excessive water phase liquid on the surface of the non-woven fabric basement membrane by using a stainless steel roller with a polished surface, immersing the basement membrane into oil phase liquid for 40-60 seconds, removing residual oil phase liquid on the surface, then putting the basement membrane into a drying oven at 60-90 ℃ for 4-8 minutes, and then cleaning to obtain bottom polyamide;
d) A top polyamide layer; 0.1-0.5g of graphene oxide is placed in 100mL of water and subjected to ultrasonic dispersion to prepare graphene oxide/water dispersion; dissolving 0.1-0.5g of 3-aminopropyl phosphonic acid in 40mL of ethanol to prepare a 3-aminopropyl phosphonic acid/ethanol solution; adding the 3-aminopropyl phosphonic acid/ethanol solution into the graphene oxide/water dispersion, and stirring and refluxing for 10-15h at the temperature of 80-95 ℃; performing suction filtration, and washing filter residues in ethanol to obtain phosphonic acid modified graphene oxide; preparing aqueous phase liquid: sequentially dissolving aromatic polyfunctional amine and a surfactant in water, stirring uniformly, adding sodium hydroxide into the obtained aqueous solution to adjust the pH value of the solution to 6-10 to obtain an aqueous phase solution, wherein the aromatic polyfunctional amine accounts for 0.3-0.5% of the aqueous solution by mass, adding the phosphonic acid modified graphene oxide, and stirring uniformly; preparing an oil phase solution: dissolving aromatic polyfunctional acyl halide in naphtha, and uniformly stirring to obtain an oil phase liquid, wherein the aromatic polyfunctional acyl halide accounts for 0.1-0.3% of the oil phase liquid by mass; immersing the base film with the bottom polyamide layer into the aqueous phase solution for 30-60 seconds, removing excessive aqueous phase liquid on the surface of the non-woven fabric base film by using a stainless steel roller with a polished surface, immersing the base film into the oil phase liquid for 40-80 seconds, removing the residual oil phase liquid on the surface, then putting the base film into an oven at 60-90 ℃ for 5 minutes, and then cleaning to obtain the film with the top polyamide layer;
e) Preparing a protective layer; preparing a chitosan-silver complex antibacterial agent, weighing soluble silver salt and chitosan in a weight ratio of 1: 10-70, adding water into a reaction kettle, starting a stirrer, controlling the reaction pH value to be 3.6, controlling the reaction temperature to be-16-70 ℃, slowly adding chitosan, stirring until the chitosan is completely dissolved to form a solution with the mass ratio of 3%, adding the soluble silver salt, stirring for reaction for 0.2-20 hours, adding glutaraldehyde, and preparing a protective layer modified solution with the mass ratio of 0.2-0.8% of glutaraldehyde; and (3) immersing the membrane containing the top polyamide layer into a protective layer modification solution for 0.2-4h, and performing a crosslinking reaction to obtain the polyamide membrane of the surface-modified chitosan protective layer.
2. A method of preparing a composite reverse osmosis membrane according to claim 1 wherein said soluble silver salt comprises a nitrate, acetate or citrate salt.
3. A method of preparing a composite reverse osmosis membrane according to claim 1 wherein said surfactant is sodium benzene sulfonate or sodium dodecyl benzene sulfonate.
4. A method of preparing a composite reverse osmosis membrane according to claim 1 wherein the additive is polyvinyl alcohol or polyvinyl pyrrolidone.
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