CN110548398B - Crosslinking type zwitterion group modified forward osmosis membrane and preparation method thereof - Google Patents
Crosslinking type zwitterion group modified forward osmosis membrane and preparation method thereof Download PDFInfo
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- CN110548398B CN110548398B CN201810565464.5A CN201810565464A CN110548398B CN 110548398 B CN110548398 B CN 110548398B CN 201810565464 A CN201810565464 A CN 201810565464A CN 110548398 B CN110548398 B CN 110548398B
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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
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- 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
- B01D69/12—Composite membranes; Ultra-thin membranes
- B01D69/125—In situ manufacturing by polymerisation, polycondensation, cross-linking or chemical reaction
Abstract
The invention discloses a crosslinking type zwitter-ion group modified forward osmosis membrane and a preparation method thereof. The preparation method comprises the following steps: providing a mixed reaction system containing a polymer, a zwitterion precursor containing a tertiary amine group, a hydrophilic monomer, an initiator and a solvent, and heating the mixed reaction system to enable the zwitterion precursor containing the tertiary amine group and the hydrophilic monomer to perform free radical copolymerization reaction to form a random copolymer containing the zwitterion polymer and the hydrophilic polymer so as to obtain a membrane preparation solution; and preparing the membrane preparation solution into a membrane, and immersing the membrane preparation solution into a coagulating bath and then into a crosslinking bath to obtain the crosslinking type zwitterionic group modified forward osmosis membrane. The forward osmosis membrane prepared by the method has the characteristics of strong hydrophilicity, large water flux, strong pollution resistance and the like, and meanwhile, the preparation process is simple, convenient and easy, is beneficial to large-scale development and production, and has wide industrial application prospect.
Description
Technical Field
The invention belongs to the technical field of membrane separation, and particularly relates to a crosslinking type zwitterionic group modified forward osmosis membrane and a preparation method thereof.
Background
With the rapid consumption of fresh water resources and the aggravation of water pollution, the problem of fresh water resource shortage is increasingly highlighted, and the membrane method water treatment technology is the most effective means for solving the problem. The organic separation membrane is also called a high-molecular separation membrane or a polymer separation membrane, is usually prepared from a polymer or a high-molecular composite material, and has the advantages of good flexibility, high air permeability, low density, low cost, simple preparation process, wide material source and the like. However, when the polymer membrane prepared from materials such as polysulfones, fluoropolymers and polyolefins with strong hydrophobicity is used for water treatment, substances such as proteins, bacteria and humic acid in water are adsorbed on the surface of the membrane through hydrophobic interaction, membrane pollution is caused, the water flux and the effluent quality of the membrane are reduced, the performance of the membrane is seriously affected, and the service life of the membrane is shortened. Therefore, it is often necessary to modify the hydrophilic property and the anti-pollution property.
The surface zwitterionization of the membrane material is an effective way for improving the hydrophilicity, the pollution resistance and the separation performance of the membrane material. The same molecular structure of the zwitterion simultaneously contains cation (such as quaternary ammonium group) and anion (such as sulfonic acid group, carboxylic acid group, phosphoric acid group and the like), and the zwitterion is introduced to the surface of the membrane material, can be combined with a large number of water molecules through electrostatic interaction and hydrogen bonds to form a hydration layer around the water molecules, shows strong hydration capability, can prevent the adhesion of organic substances such as protein, bacteria and the like, improves the anti-pollution capability of the membrane, simultaneously forms a water channel, promotes the rapid passing of the water molecules, and improves the separation efficiency.
The construction of the surface of the membrane material modified by the zwitterion group still faces a plurality of problems. The solubility of the zwitterionic polymer in an organic solvent is poor, and the zwitterionic polymer is difficult to prepare into a film by a classical blending method. Methods of surface grafting and surface coating often involve multi-step reactions, are inefficient, and have poor controllability. Therefore, a simple and fast membrane surface zwitterionization method is an urgent need for constructing an anti-pollution forward osmosis membrane.
Disclosure of Invention
The invention aims to provide a crosslinking type zwitterionic group modified forward osmosis membrane and a preparation method thereof, so as to overcome the defects in the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention comprises the following steps:
the embodiment of the invention provides a preparation method of a crosslinking type zwitterion group modified forward osmosis membrane, which comprises the following steps:
providing a mixed reaction system at least comprising a polymer, a tertiary amine group-containing zwitterionic precursor, a hydrophilic monomer, an initiator and a solvent;
heating the mixed reaction system to enable the zwitterion precursor containing the tertiary amine group and the hydrophilic monomer to perform free radical copolymerization reaction to form a random copolymer containing the zwitterion polymer and the hydrophilic polymer, so as to obtain a membrane preparation solution;
and preparing the membrane preparation solution into a membrane, and immersing the membrane preparation solution into a coagulating bath and then into a crosslinking bath to obtain the crosslinking type zwitterionic group modified forward osmosis membrane.
In some embodiments, the method of making comprises:
(1) at least uniformly mixing a polymer, a zwitterion precursor containing a tertiary amine group, a hydrophilic monomer, an initiator and a solvent to form a mixed reaction system, heating the mixed reaction system to 40-120 ℃, and reacting for 0.2-50 h to enable the zwitterion precursor and the hydrophilic monomer to perform free radical copolymerization reaction to form a random copolymer consisting of the zwitterion polymer and the hydrophilic polymer, thereby obtaining a membrane preparation solution;
(2) applying the film preparation solution to the surface of a base material, and then soaking the base material into a coagulating bath consisting of 5-60 wt% of a zwitterionic reagent and a non-solvent to react tertiary amine groups at 0-80 ℃ to generate zwitterionic groups, so as to obtain a zwitterionic group-modified forward osmosis membrane;
(3) and immersing the zwitterion-modified forward osmosis membrane into a crosslinking bath consisting of 1-30 wt% of crosslinking agent and water, and crosslinking a random copolymer consisting of the zwitterion polymer and the hydrophilic polymer on the surface of the forward osmosis membrane at 15-80 ℃ to obtain the crosslinking type zwitterion group-modified forward osmosis membrane.
The embodiment of the invention also provides a crosslinking type zwitterionic group modified forward osmosis membrane prepared by the method.
Preferably, the forward osmosis membrane comprises:
a forward osmosis membrane body;
a crosslinking modification layer which is at least distributed on the surface of the forward osmosis membrane body and is mainly formed by a random copolymer consisting of a zwitterionic polymer and a hydrophilic polymer; and
a crosslinked semi-interpenetrating network structure formed of a random copolymer of a zwitterionic polymer and a hydrophilic polymer distributed at least within the forward osmosis membrane body.
Compared with the prior art, the invention has the advantages that:
(1) according to the preparation method of the crosslinking type zwitterionic group modified forward osmosis membrane provided by the invention, the zwitterionic polymer and the hydrophilic polymer are crosslinked on the surface of the membrane, so that the zwitterionic on the surface of the forward osmosis membrane can be realized, excellent hydrophilicity and pollution resistance are endowed to the forward osmosis membrane, and the water flux is greatly improved;
(2) in the preparation method provided by the invention, the random copolymer composed of the zwitterionic polymer and the hydrophilic polymer forms a semi-interpenetrating network structure in the forward osmosis membrane, no macropores and finger-shaped pores exist, and the stability and durability of the membrane material can be improved;
(3) the preparation method provided by the invention has the advantages that the preparation and the surface modification of the forward osmosis membrane are synchronously completed, the efficiency is high, the speed is high, the steps of pre-synthesizing, separating, purifying and the like of the amphoteric ion polymer and the hydrophilic polymer are avoided, the production efficiency is high, the operation is easy, the large-scale development and production are facilitated, and the industrial application prospect is wide.
Detailed Description
In view of the defects in the prior art, the inventors of the present invention have made long-term research and extensive practice to propose a technical solution of the present invention, which is mainly to initiate polymerization of a zwitterionic precursor and a hydrophilic monomer in a polymer solution to generate a membrane-forming solution, apply the membrane-forming solution to the surface of a substrate, immerse the membrane-forming solution in a coagulation bath containing a zwitterionic reagent, and then immerse the membrane-forming solution in a crosslinking bath containing a crosslinking agent to obtain a crosslinking-type zwitterionic group-modified forward osmosis membrane. The technical solution, its implementation and principles, etc. will be further explained as follows.
In one aspect, the present invention relates to a method for preparing a crosslinked zwitterionic group-modified forward osmosis membrane, comprising:
providing a mixed reaction system at least comprising a polymer, a tertiary amine group-containing zwitterionic precursor, a hydrophilic monomer, an initiator and a solvent;
heating the mixed reaction system to enable the zwitterion precursor containing the tertiary amine group and the hydrophilic monomer to perform free radical copolymerization reaction to form a random copolymer consisting of the zwitterion polymer and the hydrophilic polymer, so as to obtain a membrane preparation solution;
and preparing the membrane preparation solution into a membrane, and immersing the membrane preparation solution into a coagulating bath and then into a crosslinking bath to obtain the crosslinking type zwitterionic group modified forward osmosis membrane.
In some embodiments, the method of making can comprise:
providing a mixed reaction system at least comprising a polymer, a tertiary amine group-containing zwitterionic precursor, a hydrophilic monomer, an initiator and a solvent;
heating the mixed reaction system to enable the zwitterion precursor containing the tertiary amine group and the hydrophilic monomer to perform free radical copolymerization reaction to form a random copolymer consisting of the zwitterion polymer and the hydrophilic polymer, so as to obtain a membrane preparation solution;
applying the film preparation solution to the surface of a base material, and then immersing the base material into a coagulating bath to react tertiary amine groups to generate zwitter-ion groups so as to obtain the zwitter-ion group modified forward osmosis membrane;
and immersing the zwitterion-modified forward osmosis membrane into a crosslinking bath to crosslink a random copolymer consisting of the zwitterion polymer and the hydrophilic polymer on the surface of the forward osmosis membrane, thereby obtaining the crosslinking type zwitterion group-modified forward osmosis membrane.
In some more specific embodiments, the preparation method may comprise:
(1) at least uniformly mixing a polymer, a zwitterion precursor containing a tertiary amine group, a hydrophilic monomer, an initiator and a solvent to form a mixed reaction system, heating the mixed reaction system to 40-120 ℃, and reacting for 0.2-50 h, preferably 0.2-50 h, so that the zwitterion precursor and the hydrophilic monomer are subjected to free radical copolymerization reaction to form a random copolymer consisting of the zwitterion polymer and the hydrophilic polymer, and a membrane preparation solution is obtained;
(2) applying the film preparation solution to the surface of a base material, and then soaking the base material into a coagulating bath consisting of 5-60 wt% of a zwitterionic reagent and a non-solvent to react tertiary amine groups at 0-80 ℃ to generate zwitterionic groups, so as to obtain a zwitterionic group-modified forward osmosis membrane;
(3) and immersing the zwitterion-modified forward osmosis membrane into a crosslinking bath consisting of 1-30 wt% of crosslinking agent and water, and crosslinking a random copolymer consisting of the zwitterion polymer and the hydrophilic polymer on the surface of the forward osmosis membrane at 15-80 ℃ to obtain the crosslinking type zwitterion group-modified forward osmosis membrane.
In some embodiments, the mixed reaction system comprises 4 to 35wt% of a polymer, 0.5 to 25wt% of a zwitterionic precursor containing a tertiary amine group, 2 to 15wt% of a hydrophilic monomer, 0.01 to 2wt% of an initiator, and the balance comprising a solvent.
Preferably, the polymer includes any one or a combination of two or more of polysulfone, sulfonated polysulfone, polyethersulfone, polyacrylonitrile, polyvinylidene fluoride, polyvinyl chloride, cellulose acetate, and the like, but is not limited thereto.
Preferably, the tertiary amine group-containing zwitterionic precursor includes, but is not limited to, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, and the like.
Preferably, the hydrophilic monomer includes any one or a combination of two or more of acrylic acid, hydroxyethyl methacrylate, N-isopropylacrylamide and the like, but is not limited thereto.
Preferably, the solvent includes any one or a combination of two or more of N-methylpyrrolidone, N '-dimethylformamide, N' -dimethylacetamide, acetone, and the like, but is not limited thereto.
Preferably, the initiator includes any one or a combination of two or more of azobisisobutyronitrile, azobisisoheptonitrile, dibenzoyl peroxide, and the like, but is not limited thereto.
In some embodiments, at least step (1) is performed in a protective atmosphere.
Preferably, the protective atmosphere is selected from inert atmospheres such as argon atmospheres.
In some embodiments, the substrate in step (2) comprises a non-woven fabric, but is not limited thereto.
Preferably, the zwitterionic reagent includes any one or a combination of two or more of 1, 3-propanesultone, 3-bromopropionic acid, 4-bromobutyric acid, 5-bromovaleric acid, 7-bromoheptanoic acid, and the like, but is not limited thereto.
Preferably, the non-solvent includes any one or a combination of two or more of water, ethanol, methanol, isopropanol, tetrahydrofuran, and the like, but is not limited thereto.
In some embodiments, the cross-linking agent in step (3) includes any one or a combination of two or more of glutaraldehyde, malic acid, sorbitol, glycerin, and the like, but is not limited thereto.
Wherein, as a more specific embodiment, the preparation method may comprise the steps of:
adding a polymer, a zwitterion precursor containing a tertiary amine group, a hydrophilic monomer, an initiator and a solvent into a reaction kettle, introducing argon, continuously stirring until the mixture is completely dissolved to form a uniform and transparent mixed solution, quickly heating to 40-120 ℃, and carrying out free radical copolymerization reaction on the zwitterion precursor containing the tertiary amine group and the hydrophilic monomer to generate a copolymer for 0.2-50 hours to obtain a membrane preparation solution; wherein the mass content of the polymer is 4-35%, the mass content of the tertiary amine group-containing zwitter-ion precursor is 0.5-25%, the mass content of the hydrophilic monomer is 2-15%, the mass content of the initiator is 0.01-2%, and the balance is solvent;
step (2) applying the membrane preparation solution prepared in the step (1) on a non-woven fabric, quickly immersing the non-woven fabric into a coagulating bath consisting of 5-60 wt% of a zwitterionic reagent and a non-solvent at 0-80 ℃, and reacting tertiary amine groups to generate zwitterionic groups to obtain a zwitterionic group-modified forward osmosis membrane;
and (3) immersing the zwitterion-modified forward osmosis membrane prepared in the step (2) into a crosslinking bath which is formed by 1-30 wt% of crosslinking agent and water at the temperature of 15-80 ℃, and crosslinking a random copolymer formed by the zwitterion polymer and the hydrophilic polymer on the surface of the forward osmosis membrane to obtain the crosslinking type zwitterion group-modified forward osmosis membrane.
As another aspect of the technical solution of the present invention, it also relates to a cross-linked zwitterionic group-modified forward osmosis membrane prepared by the foregoing method.
Specifically, the crosslinking type zwitterion group modified forward osmosis membrane comprises:
a forward osmosis membrane body;
a crosslinking modification layer which is at least distributed on the surface of the forward osmosis membrane body and is mainly formed by a random copolymer consisting of a zwitterionic polymer and a hydrophilic polymer; and
a crosslinked semi-interpenetrating network structure formed of a random copolymer of a zwitterionic polymer and a hydrophilic polymer distributed at least within the forward osmosis membrane body.
Preferably, the forward osmosis membrane further comprises a substrate, and the forward osmosis membrane body is formed on the surface of the substrate.
Particularly preferably, the substrate includes a non-woven fabric, etc., but is not limited thereto.
Preferably, the thickness of the forward osmosis membrane modified by the crosslinking type zwitterion group is 100nm to 500 μm.
Preferably, the contact angle between the surface of the crosslinking type zwitterionic group-modified forward osmosis membrane and water is 2-30 degrees.
Preferably, the pure water flux of the crosslinking type zwitterionic group modified forward osmosis membrane is 15-55L m-2h-1The rejection rate of sodium chloride is 80-98%.
By the preparation process, the random copolymer consisting of the zwitterionic polymer and the hydrophilic polymer is crosslinked on the surface of the membrane, so that the zwitterionic on the surface of the forward osmosis membrane is realized, the excellent hydrophilicity and pollution resistance are endowed, and the water flux is greatly improved. Meanwhile, a random copolymer consisting of the zwitterionic polymer and the hydrophilic polymer forms a cross-linked semi-interpenetrating network structure in the forward osmosis membrane, no macropores and finger-shaped pores exist, and the stability and durability of the membrane material are good. The preparation of the forward osmosis membrane and the modification of the membrane surface are synchronously completed, the method is efficient and quick, does not involve multiple steps of pre-synthesis, separation, purification and the like of the zwitterionic polymer, has high production efficiency, is easy to operate, is beneficial to large-scale development and production, and has wide industrial application prospect.
The technical solution of the present invention is explained in more detail below with reference to several preferred embodiments.
Example 1
(1) Adding 4 g of polysulfone, 25 g of dimethylaminoethyl methacrylate, 2 g of acrylic acid, 2 g of azobisisobutyronitrile and 77 g of N-methylpyrrolidone into a reaction kettle, introducing argon, continuously stirring until the materials are completely dissolved to form a uniform and transparent mixed solution, quickly heating to 120 ℃, carrying out free radical copolymerization reaction on dimethylaminoethyl methacrylate and acrylic acid, and carrying out polymerization for 0.2 hour to obtain a membrane preparation solution;
(2) applying the membrane preparation solution on non-woven fabrics, quickly immersing the non-woven fabrics into a coagulating bath consisting of 5 g of 1, 3-propane sultone and 95 g of water at 0 ℃, and reacting tertiary amine groups to generate zwitter-ion groups so as to obtain the zwitter-ion group modified forward osmosis membrane;
(3) immersing the forward osmosis membrane modified by the zwitter-ion groups into a crosslinking bath consisting of 1 g of glutaraldehyde and 99 g of water at 15 ℃ to crosslink the zwitter-ion polymers and the hydrophilic polymers on the surface of the membrane, thereby obtaining the crosslinking type zwitter-ion group modified forward osmosis membrane.
According to tests, the contact angle between the surface of the forward osmosis membrane prepared in the embodiment and water is 30 degrees, and when 2.5mol/L sodium chloride solution is used as an absorption liquid, the pure water flux is 15 L.m-2·h-1The retention rate for sodium chloride was 98%.
Example 2
(1) Adding 35 g of sulfonated polysulfone, 0.5 g of diethylaminoethyl methacrylate, 15 g of hydroxyethyl methacrylate, 0.01 g of azobisisoheptonitrile and 49.49 g of N, N' -dimethylformamide into a reaction kettle, introducing argon, continuously stirring until the materials are completely dissolved to form a uniform and transparent mixed solution, quickly heating to 60 ℃, and carrying out free radical copolymerization reaction on the diethylaminoethyl methacrylate and the hydroxyethyl methacrylate for 24 hours to obtain a membrane preparation solution;
(2) applying the membrane preparation solution on a non-woven fabric, quickly immersing the non-woven fabric into a coagulating bath consisting of 60 g of 3-bromopropionic acid and 40 g of ethanol at 80 ℃ to react tertiary amine groups to generate zwitter-ion groups, thereby obtaining the zwitter-ion group modified forward osmosis membrane;
(3) and immersing the forward osmosis membrane modified by the zwitter-ion groups into a crosslinking bath consisting of 30 g of malic acid and 70 g of water at the temperature of 80 ℃ to crosslink the zwitter-ion polymers and the hydrophilic polymers on the surface of the membrane, thereby obtaining the crosslinking type zwitter-ion group modified forward osmosis membrane.
According to tests, the contact angle between the surface of the forward osmosis membrane prepared in the embodiment and water is 28 degrees, and when 2.5mol/L sodium chloride solution is used as an absorption liquid, the pure water flux is 55 L.m-2·h-1The rejection rate for sodium chloride was 80%.
Example 3
(1) Adding 18 g of polyether sulfone, 5 g of dimethylaminoethyl methacrylate, 5 g of N-isopropyl acrylamide, 0.1 g of dibenzoyl peroxide and 71.9 g of N, N' -dimethyl acetamide into a reaction kettle, introducing argon, continuously stirring until the materials are completely dissolved to form a uniform and transparent mixed solution, quickly heating to 40 ℃, and carrying out free radical copolymerization reaction on the dimethylaminoethyl methacrylate and the N-isopropyl acrylamide for 50 hours to obtain a membrane preparation solution;
(2) applying the membrane preparation solution on a non-woven fabric, quickly immersing the non-woven fabric in a coagulating bath consisting of 10 g of 4-bromobutyric acid and 90 g of methanol at 10 ℃ to react tertiary amine groups to generate zwitterion groups, and obtaining the zwitterion group modified forward osmosis membrane;
(3) immersing the forward osmosis membrane modified by the zwitter-ion group into a crosslinking bath consisting of 15 g of sorbitol and 85 g of water at the temperature of 25 ℃ to crosslink the zwitter-ion polymer and the hydrophilic polymer on the surface of the membrane, thereby obtaining the crosslinking type zwitter-ion group modified forward osmosis membrane.
According to tests, the contact angle between the surface of the forward osmosis membrane prepared in the embodiment and water is 22 degrees, and when 2.5mol/L sodium chloride solution is used as an absorption liquid, the pure water flux is 37 L.m-2·h-1The rejection rate for sodium chloride was 83%.
Example 4
(1) Adding 20 g of polyacrylonitrile, 6 g of diethylaminoethyl methacrylate, 3 g of acrylic acid, 0.5 g of azobisisobutyronitrile and 70.5 g of N, N' -dimethylacetamide into a reaction kettle, introducing argon, continuously stirring until the materials are completely dissolved to form a uniform and transparent mixed solution, quickly heating to 70 ℃, and carrying out free radical copolymerization reaction on the diethylaminoethyl methacrylate and the acrylic acid for 15 hours to obtain a membrane preparation solution;
(2) applying the membrane preparation solution on a non-woven fabric, quickly immersing the non-woven fabric in a coagulating bath consisting of 20 g of 5-bromovaleric acid and 80 g of isopropanol at 25 ℃ to react tertiary amine groups to generate zwitter-ion groups, and obtaining the zwitter-ion group modified forward osmosis membrane;
(3) and immersing the forward osmosis membrane modified by the zwitter-ion groups into a crosslinking bath consisting of 22 g of glycerol and 78 g of water at the temperature of 20 ℃ to crosslink the zwitter-ion polymers and the hydrophilic polymers on the surface of the membrane, thereby obtaining the crosslinking type zwitter-ion group modified forward osmosis membrane.
According to tests, the contact angle between the surface of the forward osmosis membrane prepared in the embodiment and water is 23 degrees, and when 2.5mol/L sodium chloride solution is used as an absorption liquid, the pure water flux is 19 L.m-2·h-1The retention rate for sodium chloride was 84%.
Example 5
(1) Adding 15 g of polyvinylidene fluoride, 7 g of dimethylaminoethyl methacrylate, 5 g of hydroxyethyl methacrylate, 1 g of azobisisobutyronitrile and 72 g of N, N' -dimethylformamide into a reaction kettle, introducing argon, continuously stirring until the materials are completely dissolved to form a uniform and transparent mixed solution, quickly heating to 100 ℃, and carrying out free radical copolymerization reaction on the dimethylaminoethyl methacrylate and the hydroxyethyl methacrylate for 20 hours to obtain a membrane preparation solution;
(2) applying the membrane preparation solution on a non-woven fabric, quickly immersing the non-woven fabric into a coagulating bath consisting of 30 g of 7-bromoheptanoic acid and 70 g of tetrahydrofuran at 40 ℃ to react tertiary amine groups to generate zwitter-ion groups, and obtaining the zwitter-ion group modified forward osmosis membrane;
(3) and immersing the forward osmosis membrane modified by the zwitter-ion groups into a crosslinking bath consisting of 20 g of glycerin and 80 g of water at the temperature of 50 ℃ to crosslink the zwitter-ion polymers and the hydrophilic polymers on the surface of the membrane, thereby obtaining the crosslinking type zwitter-ion group modified forward osmosis membrane.
Through tests, the contact angle between the surface of the forward osmosis membrane prepared in the embodiment and water is 2 degrees, and when 2.5mol/L sodium chloride solution is used as an absorption liquid, the pure water flux is 45 L.m-2·h-1The rejection rate for sodium chloride was 88%.
Example 6
(1) Adding 24 g of polyvinyl chloride, 15 g of diethylaminoethyl methacrylate, 8 g of acrylic acid, 1 g of azobisisoheptonitrile and 62 g of N, N' -dimethylacetamide into a reaction kettle, introducing argon, continuously stirring until the materials are completely dissolved to form a uniform and transparent mixed solution, quickly heating to 90 ℃, and carrying out free radical copolymerization reaction on diethylaminoethyl methacrylate and acrylic acid for 36 hours to obtain a membrane preparation solution;
(2) applying the membrane preparation solution on a non-woven fabric, quickly immersing the non-woven fabric into a coagulating bath consisting of 18 g of 1, 3-propane sultone and 82 g of water at 60 ℃ to react tertiary amine groups to generate zwitter-ion groups, and obtaining the zwitter-ion group modified forward osmosis membrane;
(3) and immersing the forward osmosis membrane modified by the zwitter-ion groups into a crosslinking bath consisting of 25 g of malic acid and 75 g of water at 70 ℃ to crosslink the zwitter-ion polymers and the hydrophilic polymers on the surface of the membrane, thereby obtaining the crosslinking type zwitter-ion group modified forward osmosis membrane.
Through tests, the contact angle between the surface of the forward osmosis membrane prepared in the embodiment and water is 14 degrees, and when 2.5mol/L sodium chloride solution is used as an absorption liquid, the pure water flux is 42 L.m-2·h-1The retention rate for sodium chloride was 90%.
Example 7
(1) Adding 25 g of cellulose acetate, 3 g of dimethylaminoethyl methacrylate, 6 g of hydroxyethyl methacrylate, 1 g of azobisisobutyronitrile and 65 g of acetone into a reaction kettle, introducing argon, continuously stirring until the materials are completely dissolved to form a uniform and transparent mixed solution, quickly heating to 60 ℃, and carrying out free radical copolymerization reaction on the dimethylaminoethyl methacrylate and the hydroxyethyl methacrylate for 45 hours to obtain a film-making solution;
(2) applying the membrane preparation solution on a non-woven fabric, quickly immersing the non-woven fabric in a coagulating bath consisting of 40 g of 5-bromovaleric acid and 60 g of water at 65 ℃ to react tertiary amine groups to generate zwitter-ion groups, and obtaining the zwitter-ion group modified forward osmosis membrane;
(3) and immersing the forward osmosis membrane modified by the zwitter-ion groups into a crosslinking bath consisting of 26 g of glycerol and 74 g of water at the temperature of 35 ℃ to crosslink the zwitter-ion polymers and the hydrophilic polymers on the surface of the membrane, thereby obtaining the crosslinking type zwitter-ion group modified forward osmosis membrane.
According to tests, the contact angle between the surface of the forward osmosis membrane prepared in the embodiment and water is 19 degrees, and when 2.5mol/L sodium chloride solution is used as an absorption liquid, the pure water flux is 28 L.m-2·h-1The retention rate for sodium chloride was 84%.
Comparative example 1: this comparative example is substantially the same as example 5 except that: no zwitterionic precursor was added. The contact angle between the surface of the forward osmosis membrane obtained in this comparative example and water was 78 °, and the pure water flux was 8.6L m ° using 2.5mol/L sodium chloride solution as the draw solution-2h-1The rejection rate for sodium chloride was 68%.
Comparative example 2: this comparative example is substantially the same as example 5 except that: no hydrophilic monomer was added. The contact angle between the surface of the forward osmosis membrane obtained in this comparative example and water was 66 °, and the pure water flux was 11.3L m using 2.5mol/L sodium chloride solution as an extraction liquid-2h-1The rejection rate for sodium chloride was 57%.
Comparative example 3: this comparative example is substantially the same as example 5 except that: step (3) is not included. The contact angle between the surface of the forward osmosis membrane obtained in this comparative example and water was 73 °, and the pure water flux was 12.4L m using 2.5mol/L sodium chloride solution as an extraction liquid-2h-1The rejection rate for sodium chloride was 13.6%.
In addition, the present inventors have also conducted experiments using other raw materials and conditions listed in the present specification by referring to the modes of examples 1 to 7, and have similarly produced a forward osmosis membrane modified with a crosslinking type zwitterionic group which is excellent in hydrophilicity, excellent in anti-contamination ability, and large in forward permeation flux.
It should be understood that the above is only a specific application example of the present invention, and the protection scope of the present invention is not limited in any way. All the technical solutions formed by equivalent transformation or equivalent replacement fall within the protection scope of the present invention.
Claims (7)
1. A preparation method of a crosslinking type zwitterionic group modified forward osmosis membrane is characterized by comprising the following steps:
(1) at least uniformly mixing a polymer, a zwitterion precursor containing a tertiary amine group, a hydrophilic monomer, an initiator and a solvent to form a mixed reaction system, heating the mixed reaction system to 40-120 ℃, reacting for 0.2-50 h, and carrying out free radical copolymerization on the zwitterion precursor and the hydrophilic monomer to form a random copolymer consisting of the zwitterion polymer and the hydrophilic polymer to obtain a membrane preparation solution, wherein the mixed reaction system comprises 4-35 wt% of the polymer, 0.5-25 wt% of the zwitterion precursor containing the tertiary amine group, 2-15 wt% of the hydrophilic monomer and 0.01-2 wt% of the initiator, the balance is the solvent, the zwitterion precursor containing the tertiary amine group is selected from dimethylaminoethyl methacrylate and/or diethylaminoethyl methacrylate, and the hydrophilic monomer is selected from any one or more than two of acrylic acid, hydroxyethyl methacrylate and N-isopropyl acrylamide Combining;
(2) applying the film preparation solution to the surface of a base material, then immersing the base material into a coagulating bath consisting of 5-60 wt% of a zwitterionic reagent and a non-solvent, and reacting a tertiary amine group at 0-80 ℃ to generate a zwitterionic group to obtain a zwitterionic group-modified forward osmosis membrane, wherein the zwitterionic reagent is selected from any one or a combination of more than two of 1, 3-propane sultone, 3-bromopropionic acid, 4-bromobutyric acid, 5-bromovaleric acid and 7-bromoheptanoic acid;
(3) immersing the zwitterion-modified forward osmosis membrane into a crosslinking bath consisting of 1-30 wt% of a crosslinking agent and water, and crosslinking a random copolymer consisting of the zwitterion polymer and a hydrophilic polymer on the surface of the forward osmosis membrane at 15-80 ℃ to obtain a crosslinking type zwitterion group-modified forward osmosis membrane;
the crosslinking type zwitterion group modified forward osmosis membrane comprises:
a forward osmosis membrane body;
a crosslinking modification layer which is at least distributed on the surface of the forward osmosis membrane body and mainly formed by a random copolymer consisting of a zwitterionic polymer and a hydrophilic polymer; and
a crosslinked semi-interpenetrating network structure formed of a random copolymer comprised of a zwitterionic polymer and a hydrophilic polymer distributed at least within the forward osmosis membrane body;
the thickness of the forward osmosis membrane modified by the crosslinking type zwitter ion group is 100 nm-500 mu m, and the contact angle between the surface of the forward osmosis membrane modified by the crosslinking type zwitter ion group and water is2-30 degrees; the pure water flux of the crosslinking type zwitterionic group modified forward osmosis membrane is 15-55L m-2 h-1The rejection rate of sodium chloride is 80-98%.
2. The method of claim 1, wherein: the polymer is selected from one or the combination of more than two of polysulfone, sulfonated polysulfone, polyether sulfone, polyacrylonitrile, polyvinylidene fluoride, polyvinyl chloride and cellulose acetate.
3. The method of claim 1, wherein: the solvent is selected from one or the combination of more than two of N-methyl pyrrolidone, N '-dimethylformamide, N' -dimethylacetamide and acetone.
4. The method of claim 1, wherein: the initiator is selected from any one or the combination of more than two of azodiisobutyronitrile, azodiisoheptonitrile and dibenzoyl peroxide.
5. The method according to claim 1, wherein the base material in the step (2) is a nonwoven fabric.
6. The method according to claim 1, wherein the non-solvent in step (2) is selected from the group consisting of water, ethanol, methanol, isopropanol and tetrahydrofuran.
7. The method according to claim 1, wherein the crosslinking agent in the step (3) is selected from any one or a combination of two or more of glutaraldehyde, malic acid, sorbitol, and glycerol.
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