CN106621841B - Preparation method of positively charged nanofiltration membrane - Google Patents
Preparation method of positively charged nanofiltration membrane Download PDFInfo
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
- B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- 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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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D2325/00—Details relating to properties of membranes
- B01D2325/16—Membrane materials having positively charged functional groups
Abstract
The invention relates to a preparation method of a positively charged nanofiltration membrane, which comprises the steps of preparing a pretreated base membrane, preparing coating liquid, coating, curing and the like. The positively charged nanofiltration membrane has good stability and resistance to loss. According to the invention, the charge property and the hydrophilicity and hydrophobicity of the positively charged nanofiltration membrane can be improved by adjusting the monomer composition and the proportion of the copolymer, and the water flux of the positively charged nanofiltration membrane can be effectively improved. The preparation method of the positively charged nanofiltration membrane is simple, the production cost is low, and the functional polymer material used in the invention is simple and easy to obtain, and has good industrial application prospect.
Description
[ technical field ] A method for producing a semiconductor device
The invention belongs to the technical field of membrane separation. More specifically, the invention relates to a preparation method of a positively charged nanofiltration membrane.
[ background of the invention ]
The membrane separation technology has the characteristics of small investment, small occupied area, no pollution, high efficiency, energy conservation and the like, and is gradually developed into a novel substance separation and purification method. Among them, nanofiltration has become a hot spot in the research of membrane separation technology as a novel pressure-driven membrane separation process. Nanofiltration is a membrane separation technology between reverse osmosis and ultrafiltration developed after the 80's of the 20 th century, and was early called "low pressure reverse osmosis" or "loose reverse osmosis" separation technology. The cut-off molecular weight of the nanofiltration membrane is 200-2000 Da, and the nanofiltration membrane is suitable for separating nanoscale dissolved components and cutting off organic matters with low relative molecular mass such as saccharides and the like, so the nanofiltration membrane is called as nanofiltration. Nanofiltration membranes separate substances primarily by means of both pore size sieving and electrostatic repulsion, whereby selective separation of substances is possible. The nanofiltration membrane has the unique separation effect and is widely applied to the substance separation and purification process in the fields of water softening, wastewater treatment, biopharmaceutical industry, petrochemical industry and the like.
Most commercial nanofiltration membranes are composite membranes and negatively charged membranes. The nanofiltration membrane mainly comprises a porous support layer and a surface functional layer. At present, polyamide PA membranes prepared mainly by an interfacial polymerization method and membranes prepared by a phase inversion method, such as cellulose acetate CA, sulfonated poly (ether) sulfone, sulfonated polyether ether ketone and the like, are mainly adopted. The former has high desalting rate, great flux and low operation pressure requirement, but is not resistant to free chlorine and has poor anti-scaling and pollution capabilities. The latter is easy to make, cheap, resistant to free chlorine, smooth in membrane surface and not easy to scale and pollute, but poor in heat resistance and easy to chemically and biologically degrade. In practical application, a positively charged membrane is often needed, and for example, the positively charged membrane is needed to be used in high-valence metal ion recovery, electroplating wastewater treatment, radioactive metal ion-containing treatment and the like. Few functional polymer materials and methods for preparing positively charged nanofiltration membranes have been developed.
The surface coating method is a simple film-making method, and the method only directly coats the functional polymer solution on the surface of the base film and then carries out immobilization treatment. The structure and performance of the composite membrane prepared by the method are easy to regulate and control, and the stability and the loss of the prepared positively charged composite nanofiltration membrane can be improved and regulated by adopting a post-crosslinking treatment mode and controlling the crosslinking degree of the crosslinking liquid. Meanwhile, the surface coating method is simple in film preparation process and easy to realize industrial production. CN 02103752 discloses a method for preparing a positively charged nanofiltration membrane by coating a polyacrylic amino ester polymer on the surface of a base membrane through a cross-linking method. However, the crosslinking time required by the method is 5 hours, the prepared composite nanofiltration membrane is difficult to realize industrial continuous production due to long-time crosslinking, and meanwhile, the problem of environmental pollution caused by the use of an organic solvent also exists.
Aiming at the defects of the prior art, the inventor develops a preparation method of the positively charged composite nanofiltration membrane through a large amount of experimental research and analysis on the basis of summarizing the prior art.
[ summary of the invention ]
[ problem to be solved ]
The invention aims to provide a preparation method of a positively charged nanofiltration membrane.
[ solution ]
The invention is realized by the following technical scheme.
The invention relates to a preparation method of a positively charged nanofiltration membrane.
The preparation method comprises the following steps:
A. preparation of pretreated base film
Preparing a polyvinyl alcohol aqueous solution with the concentration of 0.1-0.3% by weight and a tween aqueous solution with the concentration of 0.1-0.3% by weight; uniformly mixing a polyvinyl alcohol aqueous solution and a tween aqueous solution according to the volume ratio of 1: 0.8-1.2 to obtain an intermediate layer coating solution; then, uniformly coating the intermediate layer coating solution on a porous supporting layer, and drying to obtain the pretreated base membrane;
B. preparation of coating solution
Adding 2-5 parts by weight of polyvinyl alcohol and 3.6-4.4 parts by weight of cationic polyelectrolyte into 100 parts by weight of water, mixing, adjusting the pH value of the solution obtained by dissolving to 2 by using an inorganic acid or inorganic base aqueous solution, and then heating the solution to the temperature of 75-80 ℃ to obtain a mixed copolymer; then the
Adding 0.5-3.0 parts by weight of glutaraldehyde into the mixed copolymer, dissolving, uniformly mixing, pre-crosslinking for 7.2-8.2 min at room temperature, and then cooling to room temperature by using tap water to obtain the coating liquid;
C. coating and curing
And (3) uniformly coating the coating solution obtained in the step (B) on the pretreated base membrane obtained in the step (A), heating at the temperature of 70-75 ℃ to remove water, drying and curing to obtain the positively charged nanofiltration membrane.
According to a preferred embodiment of the present invention, in step a, the porous support layer is selected from polysulfone, polyacrylonitrile or polyvinylidene fluoride flat ultrafiltration membrane.
According to another preferred embodiment of the present invention, in the step a, the intermediate layer coating liquid is coated at a temperature of 20 to 30 ℃ and a relative air humidity of 55 to 65%, and the coating amount of the intermediate layer coating liquid is 28 to 43g/m2。
According to another preferred embodiment of the present invention, in the step a, the intermediate layer coating liquid is dried at a temperature of 60 to 80 ℃ for 10 to 25 min.
According to another preferred embodiment of the present invention, in step B, the inorganic acid is hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid; the concentration of the inorganic acid aqueous solution is 1-4M.
According to another preferred embodiment of the present invention, in step B, the inorganic base is sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate; the concentration of the inorganic alkaline water solution is 1-5M.
According to another preferred embodiment of the present invention, in step B, said cationic polyelectrolyte is selected from cationic cellulose, polyethyleneimine, polyallyl ammonium chloride, polyvinyl chloride imine or polydiallyl dimethyl ammonium chloride.
According to another preferred embodiment of the present invention, in the step C, the coating amount of the coating liquid on the pretreated base film is 40 to 55g/m2。
According to another preferred embodiment of the present invention, in the step C, the coating liquid is coated at a temperature of 20 to 30 ℃ and a relative humidity of air of 55 to 65%.
According to another preferred embodiment of the present invention, in the step C, the drying and curing are performed at a temperature of 60 to 80 ℃ for 10 to 25 min.
The present invention will be described in more detail below.
The invention relates to a preparation method of a positively charged nanofiltration membrane.
The preparation method comprises the following steps:
A. preparation of pretreated base film
Preparing a polyvinyl alcohol aqueous solution with the concentration of 0.1-0.3% by weight and a tween aqueous solution with the concentration of 0.1-0.3% by weight; uniformly mixing a polyvinyl alcohol aqueous solution and a tween aqueous solution according to the volume ratio of 1: 0.8-1.2 to obtain an intermediate layer coating solution; then, uniformly coating the intermediate layer coating solution on a porous supporting layer, and drying to obtain the pretreated base membrane;
in the invention, the polyvinyl alcohol mainly has the function of strengthening the binding force between the positive electricity coating and the porous supporting layer and solving the problem of coating loss. The main function of tween is that of a surfactant, so that the coating uniformity of polyvinyl alcohol is improved.
In the invention, if the concentration of the polyvinyl alcohol aqueous solution exceeds the range of 0.1-0.3%, the viscosity of the intermediate layer coating solution is high, and the defect of uneven coating is easily formed;
if the concentration of the Tween aqueous solution exceeds the range of 0.1-0.3%, the coating layer is easy to form thicker, so that the coating defects are caused;
if the volume ratio of the polyvinyl alcohol aqueous solution to the tween aqueous solution exceeds the range, the binding force of the intermediate coating solution is weak, and the problem of coating loss cannot be solved.
According to the invention, the porous support layer is selected from polysulfone, polyacrylonitrile or polyvinylidene fluoride flat ultrafiltration membranes. The flat ultrafiltration membrane used in the present invention is a product currently marketed, for example, a polysulfone flat ultrafiltration membrane sold under the trade name polysulfone PS ultrafiltration membrane by zhongkory sun membrane technology (beijing) ltd, a polyacrylonitrile flat ultrafiltration membrane sold under the trade name PAN50 by Sepro in usa, a polyvinylidene fluoride flat ultrafiltration membrane sold under the trade name ML _ DF series microporous membrane by shanghai brand name column chemical technology ltd.
In the invention, the intermediate layer coating liquid is coated under the conditions of the temperature of 20-30 ℃ and the relative air humidity of 55-65%, and the coating amount of the intermediate layer coating liquid is 28-43 g/m2。
In the present invention, the coating apparatus used in coating is a coating apparatus generally used in the art, such as a slit extrusion coater or a roll coater.
When the coating amount of the intermediate layer coating liquid exceeds the above range, the intermediate coating layer is too thick and the positively charged coating layer is liable to run off.
According to the invention, the intermediate layer coating solution is dried for 10-25 min at the temperature of 60-80 ℃ to obtain the pretreated base film.
B. Preparation of coating solution
Adding 2-5 parts by weight of polyvinyl alcohol and 3.6-4.4 parts by weight of cationic polyelectrolyte into 100 parts by weight of water, mixing, adjusting the pH value of the solution obtained by dissolving to 2 by using an inorganic acid or inorganic base aqueous solution, and then heating the solution to the temperature of 75-80 ℃ to obtain a mixed copolymer; then the
Adding 0.5-3.0 parts by weight of glutaraldehyde into the mixed copolymer, dissolving, uniformly mixing, pre-crosslinking for 7.2-8.2 min at room temperature, and then cooling to room temperature by using tap water to obtain the coating liquid;
in this step, the resulting mixed copolymer of polyvinyl alcohol and cationic polyelectrolyte is a pre-crosslinked positively charged coating solution.
The cationic polyelectrolyte is selected from cationic cellulose, polyethyleneimine, polyallyl ammonium chloride, polyvinyl chloride imine or polydiallyl dimethyl ammonium chloride. The cationic polyelectrolyte used in the present invention is a product currently commercially available, such as cationic cellulose sold under the trade name of cationic cellulose JR400 by Nanjia chemical technology Co., Ltd, Guangzhou, polyallyl ammonium chloride sold under the trade name of polyallyl ammonium chloride by Kaolingwei, polyvinyl chloride sold under the trade name of polyvinyl chloride by Kaolingwei, and polydiallyldimethylammonium chloride sold under the trade name of polydiallyldimethylammonium chloride by Kaolingwei.
In the invention, if the amount of the polyvinyl alcohol exceeds 2-5 parts by weight, more polyvinyl alcohol remains after the pre-crosslinking reaction, and the viscosity of the positively charged coating solution is higher, so that the coating film is uneven; if the amount of the cationic polyelectrolyte exceeds 3.6-4.4 parts by weight, the positively charged coating is more compact, and the membrane flux is influenced;
in this step, the inorganic acid is hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid; the concentration of the inorganic acid aqueous solution is 1-4M.
The inorganic alkali is sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate; the concentration of the inorganic alkaline water solution is 1-5M.
In the present invention, the main reaction of the mixed copolymer with glutaraldehyde is the condensation reaction of hydroxyl groups in the mixed copolymer with aldehyde groups in glutaraldehyde to form stable ether bonds.
In the present invention, if the amount of glutaraldehyde added exceeds the range, crosslinking is excessively caused to make coating impossible.
C. Coating and curing
And (3) uniformly coating the coating solution obtained in the step (B) on the pretreated base membrane obtained in the step (A), heating at the temperature of 70-75 ℃ to remove water, drying and curing to obtain the positively charged nanofiltration membrane.
According to the invention, the coating amount of the coating liquid on the pretreated base film is 40-55 g/m2. If the coating amount exceeds the range, the film flux is lowered due to the thicker film coating.
In the step, the coating liquid is coated under the conditions of the temperature of 20-30 ℃ and the relative humidity of air of 55-65%.
The drying and curing are carried out for 10-25 min at the temperature of 60-80 ℃.
The coating is performed by the coating apparatus used in this step as described above, and the drying and curing process is performed by the coating apparatus commonly used in the art, such as a slit extrusion coater or a roll coater.
The invention relates to a positively charged nanofiltration membrane for divalent salt CaCl2Has higher salt rejection rate, and the salt rejection rate of the monovalent salt NaCl is lower. Determined according to the national Standard analysis of reverse osmosis Membrane test methods, e.g., 250ppm CaCl at 25 deg.C and 0.41MPa2The desalination rate of the solution is generally 80-95%, the desalination rate of NaCl as a monovalent salt is generally 27-31%, and the water flux is 35-56L/(m)2H). In addition, the PEG600(500ppm) molecular weight cut-off of the positively charged nanofiltration membrane is up to 90 percent (25 ℃, 0.41 MPa). Therefore, the positively charged nanofiltration membrane can be used in different fields of water softening, wastewater treatment, metal recovery and the like, and has wide application prospect.
The invention can make the positively charged nanofiltration membrane have different performances by adjusting the types and the proportions of monomers in the coating liquid. The preparation method can effectively shorten the crosslinking time, improve the production speed, improve the flux of the positively charged nanofiltration membrane, improve the loss resistance and the stability of the positively charged nanofiltration membrane, is easy for continuous production and has no environmental pollution.
[ advantageous effects ]
The invention has the beneficial effects that:
(1) according to the invention, the charge property and the hydrophilicity and hydrophobicity of the positively charged nanofiltration membrane can be improved by adjusting the monomer composition and the proportion of the copolymer, and the Zeta potential and the contact angle representation data in the embodiment are specifically referred. In addition, the water flux of the positively charged nanofiltration membrane can be effectively improved by adjusting the thickness of the coating layer through the pre-crosslinking and post-crosslinking effects.
(2) The positively charged nanofiltration membrane has good stability and anti-loss property, and specific reference is made to final stable data of long-term running flux and salt rejection rate of calcium chloride of the membrane element in the example part. Therefore, the positively charged nanofiltration membrane can be conveniently used for water softening, wastewater treatment and other purposes, and has stable separation performance and wide application range.
(3) The preparation method of the positively charged nanofiltration membrane has the advantages of simple process, simple coating and membrane preparation process, clean and environment-friendly solvent water and low production cost, and the functional polymer material used by the preparation method is simple and easy to obtain, so the preparation method has good industrial application prospect.
[ detailed description ] embodiments
The invention will be better understood from the following examples.
Example 1: preparation of positively charged nanofiltration membrane
The implementation steps of this example are as follows:
A. preparation of pretreated base film
Preparing a polyvinyl alcohol aqueous solution with the concentration of 0.1 percent by weight and a tween aqueous solution with the concentration of 0.1 percent by weight; uniformly mixing a polyvinyl alcohol aqueous solution and a tween aqueous solution according to the volume ratio of 1:0.8 to obtain an intermediate layer coating solution; then, the coating amount of the intermediate layer coating liquid was 34g/m2Uniformly coating the middle layer coating solution on a porous support layer of a polysulfone flat ultrafiltration membrane at the temperature of 20 ℃ and the relative air humidity of 58%, and drying at the temperature of 80 ℃ for 10min to obtain the polysulfone flat ultrafiltration membraneTo said pre-treated base film;
B. preparation of coating solution
Adding 2 parts by weight of polyvinyl alcohol and 3.6 parts by weight of cationic cellulose cationic polyelectrolyte to 100 parts by weight of water, mixing and dissolving to obtain a solution, adjusting the pH value of the solution to 2 by using a hydrochloric acid inorganic acid solution with the concentration of 1M or a sodium hydroxide inorganic base aqueous solution with the concentration of 3M, and then heating the solution to the temperature of 75 ℃ to obtain a mixed copolymer; then the
Adding 2.0 parts by weight of glutaraldehyde into the mixed copolymer, dissolving, uniformly mixing, pre-crosslinking for 7.2min at room temperature, and then cooling to room temperature by using tap water to obtain the coating liquid;
C. coating and curing
According to a coating amount of 50g/m2And (3) uniformly coating the coating solution obtained in the step (B) on the pretreated base membrane obtained in the step (A) at the temperature of 20 ℃ and the relative air humidity of 55%, heating at the temperature of 74 ℃ to remove water, and drying and curing at the temperature of 60 ℃ for 25min to obtain the positively charged nanofiltration membrane.
According to the analysis and determination of the reverse osmosis membrane test method and the national standard analysis method, the positively charged nanofiltration membrane prepared in the embodiment is 250ppm of CaCl at the temperature of 25 ℃ and the pressure of 0.41MPa2The retention rate of the solution separation was 84.4%, and the water flux was 53.32L/(m)2·h)，250ppmCaCl2The retention rate of the solution in long-term operation is finally stabilized to 85.3 percent, and the water flux is finally stabilized to 52.25L/(m)2H), the flux and the salt rejection rate of the calcium chloride are not obviously reduced after long-term operation, which indicates that the positive electric coating is not basically lost; under the conditions of temperature of 25 ℃ and pressure of 0.48MPa, 2000ppm MgSO4The retention rate of the solution separation was 28.4%, and the water flux was 56.34L/(m)2H); under the conditions of 25 ℃ and 0.41MPa of pressure, the retention rate of the separation of 250ppm PEG600 solution is 82.2 percent, and the water flux is 56.24L/(m)2H). In addition, the ZTea potential value of the prepared membrane is 26 mv; the contact angle was 60 °.
Example 2: preparation of positively charged nanofiltration membrane
The implementation steps of this example are as follows:
A. preparation of pretreated base film
Preparing a polyvinyl alcohol aqueous solution with the concentration of 0.2 percent by weight and a tween aqueous solution with the concentration of 0.2 percent by weight; uniformly mixing a polyvinyl alcohol aqueous solution and a tween aqueous solution according to the volume ratio of 1:1.0 to obtain an intermediate layer coating solution; then, the coating amount of the intermediate layer coating liquid was 40g/m2Uniformly coating the middle layer coating solution on a porous support layer of a polyacrylonitrile flat ultrafiltration membrane at the temperature of 22 ℃ and the relative air humidity of 55%, and drying at the temperature of 80 ℃ for 20min to obtain the pretreated base membrane;
B. preparation of coating solution
Adding 4 parts by weight of polyvinyl alcohol and 3.8 parts by weight of polyethyleneimine cationic polyelectrolyte into 100 parts by weight of water, mixing and dissolving to obtain a solution, adjusting the pH value of the solution to 2 by using a 2M sulfuric acid inorganic acid or 2M potassium hydroxide inorganic base aqueous solution, and then heating the solution to the temperature of 77 ℃ to obtain a mixed copolymer; then the
Adding 0.5 weight part of glutaraldehyde into the mixed copolymer, dissolving, uniformly mixing, pre-crosslinking for 8.2min at room temperature, and then cooling to room temperature by using tap water to obtain the coating liquid;
C. coating and curing
According to a coating amount of 45g/m2And (3) uniformly coating the coating solution obtained in the step (B) on the pretreated base membrane obtained in the step (A) at the temperature of 28 ℃ and the relative humidity of air of 60%, heating at the temperature of 70 ℃ to remove water, and drying and curing at the temperature of 60 ℃ for 25min to obtain the positively-charged nanofiltration membrane.
According to the analysis and determination of the reverse osmosis membrane test method and the national standard analysis method, the positively charged nanofiltration membrane prepared in the embodiment is 250ppm of CaCl at the temperature of 25 ℃ and the pressure of 0.41MPa2The retention rate of the solution separation was 87.2% and the water flux was 45.45L/(m)2·h)，250ppmCaCl2The retention rate of the solution in long-term operation is finally stable to 87.8 percent, and the water flux is finally stable to 52.5L/(m)2H), no obvious attenuation of flux and salt rejection rate of calcium chloride in long-term operationThis indicates that the electropositive coating is not substantially lost; under the conditions of temperature of 25 ℃ and pressure of 0.48MPa, 2000ppm MgSO4The retention rate of the solution separation was 40.7%, and the water flux was 44.93L/(m)2H); under the conditions of 25 ℃ and 0.41MPa of pressure, the retention rate of the separation of 250ppm PEG600 solution is 84.5 percent, and the water flux is 53.2L/(m)2H). In addition, the ZTea potential value of the prepared membrane is 28 mv; the contact angle was 55 °.
Example 3: preparation of positively charged nanofiltration membrane
The implementation steps of this example are as follows:
A. preparation of pretreated base film
Preparing a polyvinyl alcohol aqueous solution with the concentration of 0.3 percent by weight and a tween aqueous solution with the concentration of 0.3 percent by weight; uniformly mixing a polyvinyl alcohol aqueous solution and a tween aqueous solution according to the volume ratio of 1:1.2 to obtain an intermediate layer coating solution; then, the coating amount of the intermediate layer coating liquid was 43g/m2Uniformly coating the intermediate layer coating solution on a polyvinylidene fluoride flat ultrafiltration membrane porous support layer at the temperature of 30 ℃ and the relative air humidity of 65%, and drying for 20min at the temperature of 70 ℃ to obtain the pretreated base membrane;
B. preparation of coating solution
Adding 3 parts by weight of polyvinyl alcohol and 4.4 parts by weight of polyallyl ammonium chloride cationic polyelectrolyte into 100 parts by weight of water, mixing and dissolving to obtain a solution, adjusting the pH value of the solution to 2 by using a nitric acid inorganic acid solution with the concentration of 3M or a sodium carbonate inorganic alkaline aqueous solution with the concentration of 1M, and then heating the solution to the temperature of 80 ℃ to obtain a mixed copolymer; then adding 3.0 parts by weight of glutaraldehyde into the mixed copolymer, dissolving, uniformly mixing, carrying out pre-crosslinking for 7.6min at room temperature, and then cooling to room temperature by using tap water to obtain the coating liquid;
C. coating and curing
According to a coating amount of 55g/m2Uniformly coating the coating solution obtained in the step B on the pretreated base film obtained in the step A under the conditions of the temperature of 30 ℃ and the relative humidity of air of 65%, heating at the temperature of 75 ℃ to remove water, drying and curing at the temperature of 80 ℃ 2And (5) 0min to obtain the positively charged nanofiltration membrane.
According to the analysis and determination of the reverse osmosis membrane test method and the national standard analysis method, the positively charged nanofiltration membrane prepared in the embodiment is 250ppm of CaCl at the temperature of 25 ℃ and the pressure of 0.41MPa2The retention rate of the solution separation was 90.3% and the water flux was 35.2L/(m)2H); under the conditions of temperature of 25 ℃ and pressure of 0.48MPa, 2000ppm MgSO4The retention rate of the solution separation was 53.1% and the water flux was 32.2L/(m)2·h)，250ppmCaCl2The retention rate of the solution in long-term operation is finally stabilized to 55.3 percent, and the water flux is finally stabilized to 35.7L/(m)2H), the flux and the salt rejection rate of the calcium chloride are not obviously reduced after long-term operation, which indicates that the positive electric coating is not basically lost; under the conditions of 25 ℃ and 0.41MPa of pressure, the retention rate of the separation of the 250ppm PEG600 solution is 90 percent, and the water flux is 35.5L/(m)2H). In addition, the ZTea potential value of the prepared membrane is 30 mv; the contact angle was 48 °.
Example 4: preparation of positively charged nanofiltration membrane
The implementation steps of this example are as follows:
A. preparation of pretreated base film
Preparing a polyvinyl alcohol aqueous solution with the concentration of 0.1 percent by weight and a tween aqueous solution with the concentration of 0.3 percent by weight; uniformly mixing a polyvinyl alcohol aqueous solution and a tween aqueous solution according to the volume ratio of 1:0.9 to obtain an intermediate layer coating solution; then, the coating amount of the intermediate layer coating liquid was 36g/m2Uniformly coating the middle layer coating solution on a porous support layer of a polysulfone flat ultrafiltration membrane at the temperature of 28 ℃ and the relative air humidity of 62%, and drying at the temperature of 80 ℃ for 20min to obtain the pretreated base membrane;
B. preparation of coating solution
Adding 5 parts by weight of polyvinyl alcohol and 4.0 parts by weight of polyvinyl imine chloride cationic polyelectrolyte to 100 parts by weight of water, mixing and dissolving to obtain a solution, adjusting the pH value of the solution to 2 by using a 4M phosphoric acid inorganic acid or 5M potassium carbonate inorganic base aqueous solution, and then heating the solution to the temperature of 78 ℃ to obtain a mixed copolymer; then the
Adding 1.0 part by weight of glutaraldehyde into the mixed copolymer, dissolving, uniformly mixing, pre-crosslinking for 7.4min at room temperature, and then cooling to room temperature by using tap water to obtain the coating solution;
C. coating and curing
According to a coating amount of 40g/m2And (3) uniformly coating the coating solution obtained in the step (B) on the pretreated base membrane obtained in the step (A) at the temperature of 24 ℃ and the relative humidity of air of 58%, heating at the temperature of 72 ℃ to remove water, and drying and curing at the temperature of 80 ℃ for 10min to obtain the positively-charged nanofiltration membrane.
According to the analysis and determination of the reverse osmosis membrane test method and the national standard analysis method, the positively charged nanofiltration membrane prepared in the embodiment is 250ppm of CaCl at the temperature of 25 ℃ and the pressure of 0.41MPa2The retention rate of the solution separation was 92.4%, and the water flux was 34.2L/(m)2H); under the conditions of temperature of 25 ℃ and pressure of 0.48MPa, 2000ppm MgSO4The retention rate of the solution separation was 55% and the water flux was 33.6L/(m)2·h)，250ppmCaCl2The retention rate of the solution in long-term operation is finally stabilized to 55.2 percent, and the water flux is finally stabilized to 35.6L/(m)2H), the flux and the salt rejection rate of the calcium chloride are not obviously reduced after long-term operation, which indicates that the positive electric coating is not basically lost; under the conditions of 25 ℃ and 0.41MPa of pressure, the retention rate of the separation of the 250ppm PEG600 solution is 87 percent, and the water flux is 38.4L/(m)2H). In addition, the ZTea potential value of the prepared membrane is 31 mv; the contact angle was 45 °.
Example 5: preparation of positively charged nanofiltration membrane
The implementation steps of this example are as follows:
A. preparation of pretreated base film
Preparing a polyvinyl alcohol aqueous solution with the concentration of 0.3 percent by weight and a tween aqueous solution with the concentration of 0.2 percent by weight; uniformly mixing a polyvinyl alcohol aqueous solution and a tween aqueous solution according to the volume ratio of 1:1.1 to obtain an intermediate layer coating solution; then, the coating amount of the intermediate layer coating liquid was 28g/m2The intermediate layer coating liquid is homogenized under the conditions of 26 ℃ and 60% of air relative humidityCoating the porous support layer on a polyvinylidene fluoride flat ultrafiltration membrane, and drying for 25min at the temperature of 60 ℃ to obtain the pretreated base membrane;
B. preparation of coating solution
Adding 4 parts by weight of polyvinyl alcohol and 4.2 parts by weight of poly (diallyldimethylammonium chloride) cationic polyelectrolyte into 100 parts by weight of water, mixing and dissolving to obtain a solution, adjusting the pH value of the solution to 2 by using a 2M hydrochloric acid inorganic acid or 4M sodium hydroxide inorganic base aqueous solution, and then heating the solution to the temperature of 78 ℃ to obtain a mixed copolymer; then the
Adding 2.5 parts by weight of glutaraldehyde into the mixed copolymer, dissolving, uniformly mixing, pre-crosslinking for 7.8min at room temperature, and then cooling to room temperature by using tap water to obtain the coating liquid;
C. coating and curing
According to a coating amount of 54g/m2And (3) uniformly coating the coating solution obtained in the step (B) on the pretreated base membrane obtained in the step (A) at the temperature of 25 ℃ and the relative humidity of air of 62%, heating at the temperature of 73 ℃ to remove water, and drying and curing at the temperature of 60 ℃ for 25min to obtain the positively-charged nanofiltration membrane.
According to the analysis and determination of the reverse osmosis membrane test method and the national standard analysis method, the positively charged nanofiltration membrane prepared in the embodiment is 250ppm of CaCl at the temperature of 25 ℃ and the pressure of 0.41MPa2The retention rate of the solution separation was 95% and the water flux was 32.4L/(m)2·h)，250ppmCaCl2The retention rate of the solution in long-term operation is finally stabilized to 95.3 percent, and the water flux is finally stabilized to 32.7L/(m)2H), the flux and the salt rejection rate of the calcium chloride are not obviously reduced after long-term operation, which indicates that the positive electric coating is not basically lost; under the conditions of temperature of 25 ℃ and pressure of 0.48MPa, 2000ppm MgSO4The retention rate of the solution separation was 58% and the water flux was 32.5L/(m)2H); under the conditions of 25 ℃ and 0.41MPa of pressure, the retention rate of the separation of 250ppm PEG600 solution is 90 percent, and the water flux is 35.2L/(m)2H). In addition, the ZTea potential value of the prepared membrane is 32 mv; the contact angle was 49 °.
Claims (7)
1. A preparation method of a positively charged nanofiltration membrane is characterized by comprising the following steps:
A. preparation of pretreated base film
Preparing a polyvinyl alcohol aqueous solution with the concentration of 0.1-0.3% by weight and a tween aqueous solution with the concentration of 0.1-0.3% by weight; uniformly mixing a polyvinyl alcohol aqueous solution and a tween aqueous solution according to the volume ratio of 1: 0.8-1.2 to obtain an intermediate layer coating solution; then, uniformly coating the middle layer coating solution on a porous support layer selected from polysulfone, polyacrylonitrile or polyvinylidene fluoride flat ultrafiltration membranes at the temperature of 20-30 ℃ and the relative air humidity of 55-65%, and drying to obtain the pretreated base membrane;
B. preparation of coating solution
Adding 2-5 parts by weight of polyvinyl alcohol and 3.6-4.4 parts by weight of cationic polyelectrolyte selected from cationic cellulose, polyethyleneimine, polyallyl ammonium chloride, polyvinyl chloride imine or polydiallyldimethyl ammonium chloride into 100 parts by weight of water, mixing, dissolving to obtain a solution, adjusting the pH value of the solution to 2 by using an inorganic acid or inorganic base aqueous solution, and heating the solution to the temperature of 75-80 ℃ to obtain a mixed copolymer; then adding 0.5-3.0 parts by weight of glutaraldehyde into the mixed copolymer, dissolving, uniformly mixing, pre-crosslinking for 7.2-8.2 min at room temperature, and then cooling to room temperature by using tap water to obtain the coating liquid;
C. coating and curing
Uniformly coating the coating liquid obtained in the step B on the pretreated base film obtained in the step A, wherein the coating amount of the coating liquid on the pretreated base film is 40-55 g/m2And heating at 70-75 ℃ to remove water, drying and curing to obtain the positively charged nanofiltration membrane.
2. The method according to claim 1, wherein in the step A, the coating amount of the intermediate layer coating liquid is 28 to 43g/m2。
3. The method according to claim 1, wherein in the step A, the intermediate layer coating solution is dried at a temperature of 60 to 80 ℃ for 10 to 25 min.
4. The method according to claim 1, wherein in the step B, the inorganic acid is hydrochloric acid, sulfuric acid, nitric acid or phosphoric acid; the concentration of the inorganic acid aqueous solution is 1-4M.
5. The process according to claim 1, wherein in the step B, the inorganic base is sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate; the concentration of the inorganic alkaline water solution is 1-5M.
6. The method according to claim 1, wherein in step C, the coating solution is applied at a temperature of 20 to 30 ℃ and a relative air humidity of 55 to 65%.
7. The preparation method according to claim 1, wherein in the step C, the drying and curing are performed at a temperature of 60 to 80 ℃ for 10 to 25 min.
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| CN110947307B (en) * | 2019-11-28 | 2020-08-28 | 烟台金正环保科技有限公司 | Preparation method of composite desalination layer nanofiltration membrane |
| CN110860214A (en) * | 2019-12-19 | 2020-03-06 | 上海洁晟环保科技有限公司 | Base film layer, preparation method thereof and composite nanofiltration membrane containing base film layer |
| CN112755810B (en) * | 2020-12-18 | 2023-05-12 | 中化(宁波)润沃膜科技有限公司 | Positively charged composite nanofiltration membrane and preparation method thereof |
| CN113289498B (en) * | 2021-05-10 | 2022-05-10 | 蓝星（杭州）膜工业有限公司 | Positively charged nanofiltration membrane and preparation method thereof |
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