CN112370976B - Interface enhanced composite nanofiltration membrane and preparation method thereof - Google Patents
Interface enhanced composite nanofiltration membrane and preparation method thereof Download PDFInfo
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- B01D69/12—Composite membranes; Ultra-thin membranes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
- B01D61/027—Nanofiltration
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D67/0006—Organic membrane manufacture by chemical reactions
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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
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- Y02A20/124—Water desalination
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Abstract
The invention discloses an interface enhanced composite nanofiltration membrane and a preparation method thereof, wherein the preparation method comprises the following steps: 1) Dissolving polyvinyl chloride resin in an organic solvent to form a casting solution, adding an aminating agent into the casting solution, stirring for 2-7h under a heating condition, and defoaming at constant temperature to obtain a modified casting solution; 2) Scraping the modified casting solution into a flat plate shape, and then immersing the flat plate into a coagulating bath to obtain a modified polyvinyl chloride base film; 3) Immersing the modified polyvinyl chloride-based film in the polyamine aqueous phase monomer solution for 1-10min, and taking out; 4) Immersing the membrane obtained in the step 3) into a polyacyl chloride organic phase monomer solution for 20-150s, and taking out; and (3) carrying out heat treatment at 40-70 ℃ for 2-15min to obtain the interface enhanced composite nanofiltration membrane. The supporting layer and the separating layer of the composite nanofiltration membrane are combined by chemical bonds, so that the composite nanofiltration membrane has long-term operation stability; the rejection rate for divalent salt is more than 82 percent, the rejection rate for monovalent salt is less than 20 percent, and the permeation and rejection performances are synchronously improved.
Description
Technical Field
The invention relates to the technical field of membrane separation, in particular to an interface enhanced composite nanofiltration membrane and a preparation method thereof.
Background
The rapid development of the social industry has led to the increasing problems of water pollution and water resource shortage, and the demand of people for purified water is increasing due to the economic development and population growth. Therefore, it is imperative to find an alternative clean water source to meet the needs of industrial and domestic water. With the national emphasis on environmental protection and resource recycling, wastewater treatment and recycling become new topics and trends of energy conservation and emission reduction, and are necessary choices for realizing sustainable development, wherein seawater and brackish water desalination is also an important method for solving the problem of shortage of fresh water resources. The membrane separation technology is a novel high-efficiency separation technology which is rapidly developed in recent years, compared with the traditional separation technology, the membrane technology not only can realize the recycling of waste water, but also can recover useful substances, has the advantages of low investment cost and operating cost, high separation efficiency, less energy consumption, simple and convenient operation and the like, and has better economic benefit and social benefit.
Nanofiltration (NF) is a pressure driven membrane separation process that is intermediate between reverse osmosis and ultrafiltration. The aperture of the nanofiltration membrane is 1-2 nm, the molecular weight cutoff is 200-1000 Da, small molecular organic pollutants can be effectively removed, decolorization is realized, the total solid concentration of solubility is reduced, divalent and multivalent ions can be efficiently cutoff, and monovalent ions are allowed to pass through. Due to the special separation performance of the nanofiltration membrane, the nanofiltration membrane has great application value in the fields of drinking water purification and softening, desalination, industrial wastewater treatment, printing and dyeing wastewater treatment, biomedicine, food and the like. The preparation method of the nanofiltration membrane mainly comprises a phase inversion method, a surface grafting method, an interface polymerization method, a blending method and a layer-by-layer assembly method. The interfacial polymerization method has the unique advantages that the method is simple and easy to operate, different materials can be used for the base membrane and the separation layer, the base membrane and the separation layer can be respectively prepared and optimized, and the like, so that the method becomes the most extensive preparation method of the nanofiltration membrane and is also the mainstream product in the current market. However, the interfacial polymerization method for preparing the composite nanofiltration membrane still has many technical problems and challenges, such as higher manufacturing cost, lower permeation flux, incapability of meeting the requirement of selection performance, difficulty in overcoming the ' upper limit balance effect ' (draw-off effect '), poor pollution resistance, poor interface bonding performance of a supporting layer and a separation layer, difficulty in adapting to a severe environment system or easiness in falling off of the separation layer after long-time operation, and the like, and the development of the nanofiltration technology and the expansion of the application field are seriously restricted.
Aiming at the problems of low permeation flux and poor pollution resistance of the composite nanofiltration membrane, most of researches are dedicated to modifying and optimizing the separation layer. CN111437732A discloses a method for preparing a high-selectivity high-flux nanofiltration membrane, which comprises adding one or more alkyl acids into an aqueous phase solution to regulate and control the pH value of the aqueous phase, so as to regulate and control the high-selectivity high-flux nanofiltration membrane. CN111514769A discloses a chlorine-resistant and pollution-resistant nanofiltration membrane for soft water and a preparation method thereof, wherein the method comprises the step of sequentially covering a polypiperazine amide layer and a surface modification layer on a polysulfone base membrane to prepare the nanofiltration membrane with excellent hardness removal capability, chlorine resistance and pollution resistance. The method can effectively improve the permeability of the nanofiltration membrane and the pollution resistance, but the operation process is relatively complex and the cost is higher. Aiming at the problem of poor interface bonding performance of the nanofiltration membrane, most researches are carried out by improving the physical interaction force between the support layer and the separation layer (methods of coating an adhesive on the surface of the base membrane, grafting a hydrophilic functional group to improve the hydrophilicity of the base membrane and the like). CN106621856A discloses a high-performance graphene oxide composite nanofiltration membrane with a stable structure and a preparation method thereof, and the method utilizes the characteristic that polydopamine has ultra-strong adhesion to deposit graphene oxide on a polysulfone-based membrane coated with polydopamine, so that the nanofiltration membrane has excellent structural stability. The nanofiltration membrane prepared by the method is difficult to maintain long-term operation stability in a severe environment, and the separation layer is still easy to fall off.
The structure and the physical and chemical properties of the base membrane of the supporting layer are important for the performance of the composite nanofiltration membrane, but the research on the influence of the structure and the physical and chemical properties of the base membrane on the performance of the composite nanofiltration membrane is less. Polyvinyl chloride (PVC) is a widely used thermoplastic synthetic resin, has good mechanical strength, excellent acid and alkali resistance and chemical corrosion resistance, particularly has low price which is only about 1/20 of that of polysulfone/polyether sulfone (the most common base membrane material of the composite nanofiltration membrane), and can obviously reduce the preparation cost of the nanofiltration membrane. At present, polyvinyl chloride has a large market in the field of microfiltration and ultrafiltration membrane preparation, but the research of using polyvinyl chloride as a support base membrane material of a composite nanofiltration membrane is few, and polyvinyl chloride also has potential active modification sites, so that the polyvinyl chloride can be subjected to functional design, and the possibility is provided for preparing an interface enhanced composite nanofiltration membrane. The method for preparing the interface enhanced composite nanofiltration membrane by using different aminated polyvinyl chloride membranes has not been reported so far.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a preparation method of an interface enhanced composite nanofiltration membrane, which takes different aminated modified polyvinyl chloride membranes as base membranes and adopts an interface polymerization method to prepare the interface enhanced composite nanofiltration membrane. The composite nanofiltration membrane can be used for removing divalent salt and dye, and has long-term operation stability in severe environment. The preparation method is simple and easy to operate, has low cost and is convenient for industrial production.
Therefore, the technical scheme of the invention is as follows:
a preparation method of an interface enhanced composite nanofiltration membrane comprises the following steps:
s1, preparing a casting solution: dissolving polyvinyl chloride resin in an organic solvent to form a uniform and transparent casting solution, then adding an aminating agent into the casting solution, fully stirring for 2-7h at 50-70 ℃, and defoaming for 1h at constant temperature to obtain a uniformly mixed aminated modified polyvinyl chloride casting solution;
s2, preparing the polyvinyl chloride base film through in-situ amination modification: uniformly scraping the obtained aminated modified polyvinyl chloride membrane casting solution into a flat plate shape by an automatic membrane scraping machine, and then immersing the flat plate into a coagulating bath to obtain an aminated modified polyvinyl chloride base membrane;
s3, preparing the composite nanofiltration membrane:
1) Treating an aminated modified polyvinyl chloride base film, immersing the treated aminated modified polyvinyl chloride base film in an aqueous solution of polyamine monomer with the concentration of 0.1-10w/v% for 1-10min, taking out the treated base film, and removing residual water on the surface;
2) Immersing the membrane obtained in the step 1) into an organic solution of 0.02-1w/v% of polyacyl chloride monomer for 20-150s, and taking out; and further, carrying out heat treatment for 2-15min at 40-70 ℃ to perfect the interfacial polymerization reaction, thus obtaining the interface enhanced composite nanofiltration membrane.
Preferably, in step S1, the organic solvent is N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran or dimethylsulfoxide.
Preferably, in step S1, the amination agent is at least one of ethylenediamine, propylenediamine, butylenediamine, pentylenediamine, hexylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, piperazine, o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine.
Preferably, in step S1, the formulation of the casting solution is:
polyvinyl chloride resin: 8 to 18 percent;
organic solvent: 82-92%;
aminating agent: 8-80% of the polyvinyl chloride resin.
Preferably, in step 1), the treatment method is freeze drying or drying the water on the membrane surface by using filter paper.
Preferably, in the step 1), the polyamine monomer is at least one of ethylenediamine, propylenediamine, butylenediamine, pentylenediamine, hexylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, piperazine, o-phenylenediamine, m-phenylenediamine and p-phenylenediamine.
Preferably, in the step 2), the organic solution of the polybasic acid chloride monomer is a solution of one or more polybasic acid chloride monomers dissolved in the organic alkane solvent; the polybasic acyl chloride monomer is at least one of trimesoyl chloride, pyromellitic chloride, phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, adipoyl chloride and azelaioyl chloride.
Preferably, the organic alkane solvent is at least one of Isopar G or Isopar L of n-hexane, cyclohexane, n-heptane and isoparaffin.
Preferably, in step S2, the thickness of the doctor blade used is 20-250 μm; the film scraping temperature is 10-70 ℃; the coagulating bath is water, and the temperature of the coagulating bath is 0-70 ℃.
Compared with the prior art, the invention has the beneficial effects that:
(1) According to the invention, the polyvinyl chloride with low price is selected as a base film raw material, and the chemical bond connection between the support layer and the separation layer is constructed by utilizing the active modification sites existing in the polyvinyl chloride, so that the composite nanofiltration membrane has strong interface bonding fastness, the problem that the separation layer is easy to fall off when the composite nanofiltration membrane is operated in a severe environment is solved, the preparation cost and the operation cost of the membrane are saved, and the industrial implementation is facilitated.
(2) According to the invention, the structure of the base membrane is regulated and controlled by adding aminating agents with different contents, so that interface polymerization is carried out, an ultrathin separation layer is formed on the surface of the aminated modified base membrane, and the problem that the permeability-selectivity of the composite nanofiltration membrane is difficult to synchronously improve is solved.
(3) The composite nanofiltration membrane prepared by the invention has the rejection rate of more than 82% for divalent salt and less than 20% for monovalent salt.
Drawings
FIG. 1 is a scanning electron microscope image of the surface of the aminated modified polyvinyl chloride-based membrane (a) and the interface enhanced composite nanofiltration membrane (b) prepared in example 2;
FIG. 2 is a surface scanning electron microscope image of the aminated modified polyvinyl chloride-based membrane (a) and the interface enhanced composite nanofiltration membrane (b) prepared in example 3;
FIG. 3 is a scanning electron microscope image of the surface of the aminated modified polyvinyl chloride base film (a) and the interface enhanced composite nanofiltration membrane (b) prepared in example 4;
fig. 4 is a surface scanning electron microscope image of the aminated modified polyvinyl chloride-based film (a) and the interface enhanced composite nanofiltration membrane (b) prepared in example 5.
Detailed Description
The technical solution of the present invention will be described in detail with reference to examples.
Example 1
(1) Preparing an in-situ amination modified polyvinyl chloride base film: dissolving 14 mass percent of polyvinyl chloride resin in 86 mass percent of N, N-dimethylacetamide, and fully stirring at 70 ℃ to form uniform and transparent casting solution; and adding triethylene tetramine with the mass of 10% of the mass of the polyvinyl chloride resin into the membrane casting solution system, then continuously stirring for 5 hours at the temperature of 70 ℃, and defoaming for 1 hour at constant temperature to obtain the aminated modified polyvinyl chloride membrane casting solution. Uniformly scraping the aminated modified polyvinyl chloride membrane casting solution into a flat plate shape by an automatic membrane scraping machine, and then immersing the flat plate into a deionized water coagulating bath at 25 ℃ to obtain the aminated modified polyvinyl chloride base membrane.
(2) Preparing an interface enhanced composite nanofiltration membrane: absorbing the water on the surface of the aminated modified polyvinyl chloride base film prepared in the step (1) with filter paper, immersing the aminated modified polyvinyl chloride base film into piperazine water solution with the concentration of 1.5w/v% for 5min, taking out the membrane, and removing the residual water on the surface of the membrane; then immersing the membrane into a n-hexane solution of trimesoyl chloride with the concentration of 0.3w/v% for 60s, and taking out; further, the nano-filtration membrane is subjected to heat treatment in a drying oven at the temperature of 60 ℃ for 8min, and the interfacial polymerization reaction is perfected, so that the interface enhanced composite nano-filtration membrane is obtained.
Through measurement, the surface nitrogen content of the aminated modified polyvinyl chloride base film prepared in the embodiment is 1.38%; under the test conditions of 0.6MPa and 25 ℃, the interface enhanced composite nanofiltration membrane is used for 1g/L sodium sulfate (Na) 2 SO 4 ) The retention rate of the aqueous solution was 87.2%, and the permeation flux was 4.72 L.m -2 ·h -1 The flux is improved by 37.61 percent compared with the flux of the polyamide/polyvinyl chloride composite nanofiltration membrane; for 1g/L magnesium sulfate (MgSO) 4 ) And the retention rates of the sodium chloride (NaCl) aqueous solution were 87.32% and 19.98%, respectively.
Example 2
(1) Preparing an aminated modified polyvinyl chloride base film: dissolving 14 mass percent of polyvinyl chloride resin in 86 mass percent of N, N-dimethylacetamide, and fully stirring at 70 ℃ to form uniform and transparent casting solution; and adding triethylene tetramine with the mass being 20% of the mass of the polyvinyl chloride resin into the membrane casting solution system, then continuously stirring for 5 hours at 70 ℃, and defoaming for 1 hour at constant temperature to obtain the aminated modified polyvinyl chloride membrane casting solution. Uniformly scraping the amination modified polyvinyl chloride membrane casting solution into a flat plate shape by an automatic membrane scraping machine, and then immersing the flat plate shape into a deionized water coagulating bath at 25 ℃ to obtain the amination modified polyvinyl chloride base membrane.
(2) Preparing an interface enhanced composite nanofiltration membrane: absorbing the water on the surface of the aminated modified polyvinyl chloride base film prepared in the step (1) with filter paper, immersing the aminated modified polyvinyl chloride base film into piperazine water solution with the concentration of 1.5w/v% for 5min, taking out the membrane, and removing the residual water on the surface of the membrane; then immersing the membrane into an oil phase solution of trimesoyl chloride n-hexane with the concentration of 0.3w/v% for 60s, and taking out; further, the nano-filtration membrane is subjected to heat treatment in an oven at 60 ℃ for 8min, and the interfacial polymerization reaction is perfected, so that the interface enhanced composite nano-filtration membrane is obtained.
Through measurement, the surface nitrogen content of the aminated modified polyvinyl chloride base film prepared in the embodiment is 2.18%; under the test conditions of 0.6MPa and 25 ℃, the interface enhanced composite nanofiltration membrane is used for 1g/L sodium sulfate (Na) 2 SO 4 ) The retention rate of the aqueous solution is 88.44%, and the permeation is smoothThe amount was 6.37 L.m -2 ·h -1 The flux is improved by 85.71 percent compared with the flux of the polyamide/polyvinyl chloride composite nanofiltration membrane; for 1g/L magnesium sulfate (MgSO) 4 ) And the retention rates of the sodium chloride (NaCl) aqueous solution were 88.61% and 19.59%, respectively.
Example 3
(1) Preparing an aminated modified polyvinyl chloride base film: dissolving 14 mass percent of polyvinyl chloride resin in 86 mass percent of N, N-dimethylacetamide, and fully stirring at 70 ℃ to form uniform and transparent casting solution; and adding triethylene tetramine with the mass of 40% of the mass of the polyvinyl chloride resin into the membrane casting solution system, then continuously stirring for 5 hours at the temperature of 70 ℃, and defoaming for 1 hour at constant temperature to obtain the aminated modified polyvinyl chloride membrane casting solution. Uniformly scraping the amination modified polyvinyl chloride membrane casting solution into a flat plate shape by an automatic membrane scraping machine, and then immersing the flat plate shape into a deionized water coagulating bath at 25 ℃ to obtain the amination modified polyvinyl chloride base membrane.
(2) Preparing an interface enhanced composite nanofiltration membrane: absorbing the water on the surface of the aminated modified polyvinyl chloride base film prepared in the step (1) with filter paper, immersing the aminated modified polyvinyl chloride base film into piperazine water solution with the concentration of 1.5w/v% for 5min, taking out the membrane, and removing the residual water on the surface of the membrane; then immersing the membrane into an oil phase solution of trimesoyl chloride n-hexane with the concentration of 0.3w/v% for 60s, and taking out; further, the membrane is subjected to heat treatment for 8mim in a drying oven at 60 ℃ to perfect the interfacial polymerization reaction, and the interface enhanced composite nanofiltration membrane is obtained.
Through determination, the surface nitrogen content of the aminated modified polyvinyl chloride base film prepared in the embodiment is 3.07%; under the test conditions of 0.6MPa and 25 ℃, the interface enhanced composite nanofiltration membrane is used for 1g/L sodium sulfate (Na) 2 SO 4 ) The retention rate of the aqueous solution is 88.46 percent, and the permeation flux is 9.45 L.m -2 ·h -1 The flux is improved by 175.51 percent compared with the flux of the polyamide/polyvinyl chloride composite nanofiltration membrane; for 1g/L magnesium sulfate (MgSO) 4 ) And the retention rates of the sodium chloride (NaCl) aqueous solution were 89.31% and 15.43%, respectively.
Example 4
(1) Preparing an aminated modified polyvinyl chloride base film: dissolving 14 mass percent of polyvinyl chloride resin in 86 mass percent of N, N-dimethylacetamide, and fully stirring at 70 ℃ to form uniform and transparent casting solution; and adding triethylene tetramine with the mass of 60% of the mass of the polyvinyl chloride resin into the membrane casting solution system, then continuously stirring for 5 hours at 70 ℃, and defoaming for 1 hour at constant temperature to obtain the aminated modified polyvinyl chloride membrane casting solution. And uniformly scraping the casting film liquid into a flat plate shape by an automatic film scraping machine, and then soaking the flat plate shape into a deionized water coagulating bath at 25 ℃ to obtain the aminated modified polyvinyl chloride base film.
(2) Preparing an interface enhanced composite nanofiltration membrane: after absorbing the moisture on the surface of the aminated modified polyvinyl chloride base film prepared in the step (1) with filter paper, soaking the aminated modified polyvinyl chloride base film into 1.5w/v% piperazine water solution for 5min, taking out the film, and removing the residual moisture on the surface of the film; then immersing the membrane into an oil phase solution of trimesoyl chloride n-hexane with the concentration of 0.3w/v% for 60s, and taking out; further, the nano-filtration membrane is subjected to heat treatment in a drying oven at the temperature of 60 ℃ for 8min, and the interfacial polymerization reaction is perfected, so that the interface enhanced composite nano-filtration membrane is obtained.
Through measurement, the surface nitrogen content of the aminated modified polyvinyl chloride base film prepared in the embodiment is 4.1%; under the test conditions of 0.6MPa and 25 ℃, the interface enhanced composite nanofiltration membrane is used for 1g/L sodium sulfate (Na) 2 SO 4 ) The retention rate of the aqueous solution was 89.40%, and the permeation flux was 18.68 L.m -2 ·h -1 The flux of the nano-filtration membrane is increased by 444.61 percent compared with that of the polyamide/polyvinyl chloride composite nano-filtration membrane; for 1g/L magnesium sulfate (MgSO) 4 ) And the retention rates of sodium chloride (NaCl) aqueous solution are 89.51 percent and 12.29 percent respectively; the rejection rate of the Congo red of 100mg/L is 99.6%, and the rejection rate is kept stable after continuous operation for 12 hours.
Example 5
(1) Preparing an aminated modified polyvinyl chloride base film: dissolving 14 mass percent of polyvinyl chloride resin in 86 mass percent of N, N-dimethylacetamide, and fully stirring at 70 ℃ to form uniform and transparent casting solution; and adding triethylene tetramine accounting for 70% of the mass of the polyvinyl chloride resin into the membrane casting solution system, continuously stirring for 5 hours at 70 ℃, and defoaming for 1 hour at constant temperature to obtain the aminated modified polyvinyl chloride membrane casting solution. And uniformly scraping the membrane casting solution into a flat plate shape by an automatic membrane scraping machine, and then soaking the flat plate shape into a deionized water coagulating bath at 25 ℃ to obtain the aminated modified polyvinyl chloride base membrane.
(2) Preparing an interface enhanced composite nanofiltration membrane: absorbing the water on the surface of the aminated modified polyvinyl chloride base film prepared in the step (1) with filter paper, immersing the aminated modified polyvinyl chloride base film into piperazine water solution with the concentration of 1.5w/v% for 5min, taking out the membrane, and removing the residual water on the surface of the membrane; then immersing the membrane into an oil phase solution of trimesoyl chloride n-hexane with the concentration of 0.3w/v% for 60s, and taking out; further, the nano-filtration membrane is subjected to heat treatment in a drying oven at the temperature of 60 ℃ for 8min, and the interfacial polymerization reaction is perfected, so that the interface enhanced composite nano-filtration membrane is obtained.
Through measurement, the surface nitrogen content of the aminated modified polyvinyl chloride base film prepared in the embodiment is 4.5%; under the test conditions of 0.6MPa and 25 ℃, the interface enhanced composite nanofiltration membrane is used for 1g/L sodium sulfate (Na) 2 SO 4 ) The retention rate of the aqueous solution was 74.19%, and the permeation flux was 4.46 L.m -2 ·h -1 The flux of the nano-filtration membrane is improved by 30.03 percent compared with that of the polyamide/polyvinyl chloride composite nano-filtration membrane; for 1g/L magnesium sulfate (MgSO) 4 ) And sodium chloride (NaCl) aqueous solution were 82.37%, 4.55%, respectively.
The surface scanning electron microscope images of the aminated modified polyvinyl chloride-based membrane prepared in examples 2-5 and the interface enhanced composite nanofiltration membrane are respectively shown in fig. 1-4, and it can be seen from the images that a uniform macroporous structure is formed on the surface of the aminated modified polyvinyl chloride-based membrane, and the size of pores on the surface of the aminated modified polyvinyl chloride-based membrane is gradually increased along with the increase of the content of the amination agent; a compact polyamide layer is formed on the surface of the interface enhanced composite nanofiltration membrane, and a uniform pit structure is formed on the surface of the interface enhanced composite nanofiltration membrane corresponding to the hole structure of the aminated modified polyvinyl chloride base membrane.
Claims (8)
1. A preparation method of an interface enhanced composite nanofiltration membrane comprises the following steps:
s1, preparing a casting solution: dissolving polyvinyl chloride resin in an organic solvent to form a uniform and transparent casting solution, then adding an aminating agent into the casting solution, fully stirring for 2-7h at 50-70 ℃, and defoaming for 1h at constant temperature to obtain a uniformly mixed aminated modified polyvinyl chloride casting solution;
s2, preparing the polyvinyl chloride base film through in-situ amination modification: uniformly scraping the obtained amination modified polyvinyl chloride membrane casting solution into a flat plate shape by an automatic membrane scraping machine, and then immersing the flat plate into a coagulating bath to obtain an amination modified polyvinyl chloride base membrane;
s3, preparing the composite nanofiltration membrane:
1) Immersing the aminated modified polyvinyl chloride base film after treatment in a polyamine monomer aqueous solution with the concentration of 0.1-10w/v% for 1-10min, taking out, and removing residual moisture on the surface;
2) Immersing the membrane obtained in the step 1) into an organic solution of 0.02-1w/v% of polyacyl chloride monomer for 20-150s, and taking out; further, carrying out heat treatment for 2-15min at 40-70 ℃, and perfecting an interface polymerization reaction to obtain the interface enhanced composite nanofiltration membrane;
wherein the formula of the casting solution in the step S1 is as follows:
polyvinyl chloride resin: 8 to 18 percent;
organic solvent: 82-92%;
aminating agent: 8-80% of the polyvinyl chloride resin.
2. The method for preparing the interface enhanced composite nanofiltration membrane according to claim 1, wherein the method comprises the following steps: in step S1, the organic solvent is N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, tetrahydrofuran, or dimethylsulfoxide.
3. The method for preparing the interface enhanced composite nanofiltration membrane according to claim 1, wherein the method comprises the following steps: in the step S1, the amination agent is at least one of ethylenediamine, propylenediamine, butylenediamine, pentylenediamine, hexylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, piperazine, o-phenylenediamine, m-phenylenediamine, and p-phenylenediamine.
4. The method for preparing the interface enhanced composite nanofiltration membrane according to claim 1, wherein the method comprises the following steps: in the step 1), the treatment method is freeze drying or drying the moisture on the surface of the membrane by using filter paper.
5. The preparation method of the interface enhanced composite nanofiltration membrane according to claim 1, wherein the preparation method comprises the following steps: in the step 1), the polyamine monomer is at least one of ethylenediamine, propylenediamine, butylenediamine, pentylenediamine, hexylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, piperazine, o-phenylenediamine, m-phenylenediamine and p-phenylenediamine.
6. The preparation method of the interface enhanced composite nanofiltration membrane according to claim 1, wherein the preparation method comprises the following steps: in the step 2), the organic solution of the polybasic acyl chloride monomer is a solution formed by dissolving one or more polybasic acyl chloride monomers in an organic alkane solvent; the polybasic acyl chloride monomer is at least one of trimesoyl chloride, pyromellitic chloride, phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, adipoyl chloride and azelaioyl chloride.
7. The method for preparing the interface enhanced composite nanofiltration membrane according to claim 6, wherein the method comprises the following steps: the organic alkane solvent is at least one of Isopar G or Isopar L of n-hexane, cyclohexane, n-heptane and isoparaffin.
8. The preparation method of the interface enhanced composite nanofiltration membrane according to claim 1, wherein the preparation method comprises the following steps: in the step S2, the thickness of the scraper is 20-250 μm; the film scraping temperature is 10-70 ℃; the coagulating bath is water, and the temperature of the coagulating bath is 0-70 ℃.
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