CN112755810B - Positively charged composite nanofiltration membrane and preparation method thereof - Google Patents
Positively charged composite nanofiltration membrane and preparation method thereof Download PDFInfo
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Abstract
The invention provides a positively charged composite nanofiltration membrane and a preparation method thereof. The positively charged composite nanofiltration membrane comprises a base membrane and an active layer formed on the surface of the base membrane, wherein the active layer comprises the reaction product of polyvinyl alcohol, bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea and optional polyethylene glycol and a cross-linking agent. The invention adopts polyvinyl alcohol as a skeleton matrix, and is mixed and dissolved with bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea and optional polyethylene glycol to form polymer surface active layer coating liquid, and the positively charged composite nanofiltration membrane with high selectivity and higher flux is prepared by a chemical crosslinking method, and the preparation method is simple, easy to operate and controllable in condition, and can realize continuous production.
Description
Technical Field
The invention belongs to the technical field of membranes, and particularly relates to a positively charged composite nanofiltration membrane prepared by blending polyvinyl alcohol (PVA) and bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea (PUB) and a preparation method thereof.
Background
Early membrane separation processes were based on the principle of physical sieving, i.e., a membrane that allows the permeation of components having a smaller particle size than its pore size while retaining components having a larger or similar pore size. In the application process, if the medium particle size of the components to be separated is small, the pore diameter of the used membrane is also required to be correspondingly reduced, which tends to cause the problems of flux reduction, operation cost increase and the like. In order to avoid the above-mentioned drawbacks, the development of charged membranes, in particular charged nanofiltration membranes, has been rapidly advanced in recent years, which have been emphasized due to their unique separation properties. The charged nanofiltration membrane is a membrane containing fixed charges, and the separation principle of the charged nanofiltration membrane has unique electrostatic adsorption and rejection effects besides physical screening of a neutral membrane based on pore size. The charged nanofiltration membrane is introduced with charged groups, the hydrophilicity of the membrane is enhanced, the water permeability is increased, the membrane is suitable for low-pressure operation, and the membrane has the advantages of pollution resistance and selective permeability, can be used for adsorbing and separating substances with smaller diameters by using a large-aperture membrane, and can be used for separating components with similar relative molecular mass and different charged properties. The charged nanofiltration membrane can be divided into a positively charged nanofiltration membrane and a negatively charged nanofiltration membrane according to the difference of fixed charge in the membrane.
Most commercial nanofiltration membranes are negatively charged nanofiltration membranes, and currently common nanofiltration membranes are: polyaromatic amides, polyglutazine amides, sulfonated polysulfones, polyvinyl alcohols, and the like. Aromatic polyamides and polyglutazine amides are prepared into a charged surface layer by adopting an interfacial polymerization method; the sulfonated polysulfones and polyvinyl alcohols are used for preparing the charged surface layer by a coating crosslinking method.
The positively charged membrane has the repulsive interaction on the same electric particles due to positive charge, and can be used for the separation of positively charged amino acid and protein, the clean production of the cathode electrophoretic paint coating process, the interception and recovery of heavy metal ions, the treatment of mining wastewater and the like.
Thus, there is a need in the art for a highly selective, higher flux positively charged nanofiltration membrane.
Polyvinyl alcohol (PVA) is an organic compound of the formula [ C ] 2 H 4 O] n The appearance is white flaky, flocculent or powdery solid, is odorless, is dissolved in water (more than 95 ℃), is slightly dissolved in dimethyl sulfoxide, and is insoluble in gasoline, kerosene, vegetable oil, benzene, toluene, dichloroethane, carbon tetrachloride, acetone, ethyl acetate, methanol, ethylene glycol and the like. The polyvinyl alcohol is easy to form a film, the mechanical property of the film is excellent, and the tensile strength of the film is enhanced along with the increase of the polymerization degree and the alcoholysis degree. Polyvinyl alcohol is also an important chemical raw material for manufacturing polyvinyl acetal, gasoline-resistant pipelines, vinylon synthetic fibers, textile treatment agents, emulsifiers, paper coatings, adhesives, glues and the like. The structural formula of PVA is as follows:
Bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea (PUB) is a water-soluble, linear polymer containing quaternary ammonium groups. There has not been a report of the use of PUB urea in the preparation of nanofiltration membranes. The formula of the PUB is as follows:
disclosure of Invention
The invention provides a positively charged blended composite nanofiltration membrane and a preparation method thereof. According to the invention, polyvinyl alcohol (PVA) is used as a skeleton matrix, and is mixed and dissolved with bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea (PUB) to form polymer surface active layer coating liquid, and a chemical crosslinking method is adopted to prepare the positively charged composite nanofiltration membrane with high selectivity and higher flux.
Specifically, the invention provides a positively charged composite nanofiltration membrane, which comprises a base membrane and an active layer formed on the surface of the base membrane, wherein the active layer comprises the reaction product of polyvinyl alcohol, bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea and optional polyethylene glycol and a cross-linking agent.
In one or more embodiments, the active layer has a mass ratio of polyvinyl alcohol to bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea of 1:1 to 10:1, preferably 4.5:1 to 8:1.
In one or more embodiments, the polyvinyl alcohol has a weight average molecular weight of 10,000 to 200,000Da.
In one or more embodiments, the active layer comprises the reaction product of polyvinyl alcohol, bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea, and optionally polyethylene glycol, and a cross-linking agent, wherein the mass ratio of polyvinyl alcohol to polyethylene glycol in the active layer is greater than or equal to 1:15, preferably 1:10 to 1:3.
in one or more embodiments, the crosslinking agent is a C2-C10 polyaldehyde, preferably one or both selected from glutaraldehyde and glyoxal.
In one or more embodiments, the base membrane is a polyethersulfone ultrafiltration membrane; preferably, the molecular weight cut-off of the polyethersulfone ultrafiltration membrane is 5,000-50,000da and/or the pure water permeation coefficient of the polyethersulfone ultrafiltration membrane is 100-300LMH/bar.
The invention also provides a method of making a positively charged composite nanofiltration membrane as described in any of the embodiments herein, the method comprising:
(1) Contacting the base film with a polymer surface active layer coating liquid, and optionally carrying out heat treatment to obtain a semi-finished film, wherein the polymer surface active layer coating liquid is an aqueous solution containing polyvinyl alcohol, bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea and optional polyethylene glycol;
(2) Contacting the semi-finished film with a crosslinking solution, wherein the crosslinking solution is a solution containing a crosslinking agent.
In one or more embodiments, the mass fraction of polyvinyl alcohol in the polymer surface active layer coating liquid is 0.1 to 10wt%, preferably 0.5 to 5wt%.
In one or more embodiments, the mass fraction of bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea in the polymeric surface active layer coating solution is 0.02 to 10wt%, preferably 0.25 to 2wt%.
In one or more embodiments, the mass ratio of polyvinyl alcohol to bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea in the polymer surface active layer coating liquid is 1:1 to 10:1, preferably 4.5:1 to 8:1.
in one or more embodiments, the polymeric surface active layer coating liquid contains polyethylene glycol having a weight average molecular weight of 100 to 2,000Da, preferably 150 to 500Da.
In one or more embodiments, the polymer surface active layer coating liquid contains polyethylene glycol, and the mass fraction of the polyethylene glycol in the polymer surface active layer coating liquid is less than or equal to 20wt%, preferably 5-15wt%.
In one or more embodiments, the polymer surface active layer coating liquid contains polyethylene glycol, and in the polymer surface active layer coating liquid, the mass ratio of polyvinyl alcohol to polyethylene glycol is equal to or greater than 1:15, preferably 1:10 to 1:3.
in one or more embodiments, the polymeric surface active layer coating liquid is disposed at 30-80 ℃, preferably at 50-80 ℃.
In one or more embodiments, the polymeric surface active layer coating liquid is disposed under magnetic stirring at 300-600 rpm.
In one or more embodiments, the heat treatment temperature of step (1) is from room temperature to 80 ℃, preferably 50-80 ℃.
In one or more embodiments, the heat treatment time of step (1) is from 1 to 60 minutes, preferably from 10 to 30 minutes.
In one or more embodiments, the crosslinking agent is a C2-C10 polyaldehyde, preferably one or both selected from glutaraldehyde and glyoxal.
In one or more embodiments, the crosslinking agent is present in the crosslinking solution in a mass fraction of 0.1 to 20wt%, preferably 0.5 to 10wt%.
In one or more embodiments, the crosslinking solution is a solution comprising an acid and a C2-C10 polyaldehyde; the acid is preferably selected from one or two of hydrochloric acid and sulfuric acid; the mass fraction of the acid in the crosslinking solution is preferably 0.001 to 0.05wt%, more preferably 0.001 to 0.01wt%; the C2-C10 polyaldehyde is preferably selected from one or two of glutaraldehyde and glyoxal; the mass fraction of the C2-C10 polyaldehyde in the crosslinking solution is preferably 0.1-15wt%, preferably 0.5-5wt%; the solvent of the crosslinking solution is preferably water, a C1-C3 alcohol or a mixture thereof.
In one or more embodiments, the contact temperature of step (2) is from 25 to 120 ℃, preferably from 25 to 60 ℃.
In one or more embodiments, the contact time of step (2) is from 1 to 150 minutes, preferably from 10 to 60 minutes.
The invention also provides the use of the positively charged composite nanofiltration membrane described in any of the embodiments herein or prepared by the method described in any of the embodiments herein in a water treatment process or water treatment assembly or device.
The invention also provides a polymer surface active layer coating liquid which is an aqueous solution containing polyvinyl alcohol and bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea.
In one or more embodiments, the polyvinyl alcohol has a weight average molecular weight of 10,000 to 200,000Da.
In one or more embodiments, the mass fraction of polyvinyl alcohol in the polymer surface active layer coating liquid is 0.1 to 10wt%, preferably 0.5 to 5wt%.
In one or more embodiments, the mass fraction of bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea in the polymeric surface active layer coating solution is 0.02 to 10wt%, preferably 0.25 to 2wt%.
In one or more embodiments, the mass ratio of polyvinyl alcohol to bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea in the polymer surface active layer coating liquid is 1:1 to 10:1, preferably 4.5:1 to 8:1.
in one or more embodiments, the polymeric surface active layer coating liquid further comprises polyethylene glycol; preferably, in the polymer surface active layer coating liquid, the mass fraction of polyethylene glycol is less than or equal to 20wt%, preferably 5-15wt%; in the polymer surface active layer coating liquid, the mass ratio of polyvinyl alcohol to polyethylene glycol is more than or equal to 1:15, preferably 1:10 to 1:3, a step of; preferably, the polyethylene glycol has a weight average molecular weight of from 100 to 2,000Da, preferably from 150 to 500Da.
The invention also provides a reagent combination, which comprises the polymer surface active layer coating liquid and a crosslinking solution, wherein the crosslinking solution is a solution containing a crosslinking agent.
In one or more embodiments, the crosslinking agent is a C2-C10 polyaldehyde, preferably one or both selected from glutaraldehyde and glyoxal.
In one or more embodiments, the crosslinking agent is present in the crosslinking solution in a mass fraction of 0.1 to 20wt%, preferably 0.5 to 10wt%.
In one or more embodiments, the crosslinking solution is a solution comprising an acid and a C2-C10 polyaldehyde; preferably, the acid is selected from one or both of hydrochloric acid and sulfuric acid; preferably, the mass fraction of acid in the crosslinking solution is 0.001-0.05wt%, preferably 0.001-0.01wt%; preferably, the C2-C10 polyaldehyde is selected from one or two of glutaraldehyde and glyoxal; preferably, the mass fraction of C2-C10 polyaldehydes in the crosslinking solution is 0.1-15wt%, preferably 0.5-5wt%; preferably, the solvent of the crosslinking solution is water, a C1-C3 alcohol or a mixture thereof.
The invention also provides the use of bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea, the polymer surface active layer coating solution described in any of the embodiments herein, or the reagent combination described in any of the embodiments herein, in the preparation of positively charged nanofiltration membranes.
Drawings
FIG. 1 is a graph showing the effect of PEG200 content on retention performance of PVA/PUB blend positively charged composite nanofiltration membranes of example 6 (2000 ppm MgCl) 2 Solution, room temperature, 1.0 MPa), the points from left to right in the figure correspond to the retention performance of the composite nanofiltration membrane when the concentration of PEG200 in the polymer surface active layer coating solution is 0wt%, 2wt%, 5wt%, 10wt%, 20wt%, 30wt%, 40wt%, respectively.
Detailed Description
So that those skilled in the art can appreciate the features and effects of the present invention, a general description and definition of the terms and expressions set forth in the specification and claims follows. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, and in the event of a conflict, the present specification shall control.
The theory or mechanism described and disclosed herein, whether right or wrong, is not meant to limit the scope of the invention in any way, i.e., the present disclosure may be practiced without limitation to any particular theory or mechanism.
Herein, "comprising," "including," "having," "containing," and similar terms are intended to cover the meaning of "consisting essentially of … …" and "consisting of … …," e.g., where "a comprises B and C" is disclosed herein, "a consisting of B and C" should be considered as having been disclosed herein.
In this document, all features such as values, amounts, and concentrations that are defined as ranges of values or percentages are for brevity and convenience only. Accordingly, the description of a numerical range or percentage range should be considered to cover and specifically disclose all possible sub-ranges and individual values (including integers and fractions) within the range.
Herein, when embodiments or examples are described, it should be understood that they are not intended to limit the invention to these embodiments or examples. On the contrary, all alternatives, modifications, and equivalents of the methods and materials described herein are intended to be included within the scope of the invention as defined by the appended claims.
In this context, not all possible combinations of the individual technical features in the individual embodiments or examples are described in order to simplify the description. Accordingly, as long as there is no contradiction between the combinations of these technical features, any combination of the technical features in the respective embodiments or examples is possible, and all possible combinations should be considered as being within the scope of the present specification.
According to the invention, polyvinyl alcohol (PVA) is used as a skeleton matrix, and is mixed with bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea (PUB) and optional polyethylene glycol (PEG) to be dissolved into polymer surface active layer coating liquid, an Ultrafiltration (UF) membrane is used as a supporting layer, polyaldehyde (such as glutaraldehyde and glyoxal) is used as a chemical crosslinking agent, and a positively charged composite nanofiltration membrane with high selectivity and high flux is prepared by a chemical crosslinking method, so that the preparation method is simple, easy to operate, controllable in condition and capable of realizing continuous production.
The composite nanofiltration membrane of the invention comprises a base membrane and an active layer formed on the base membrane, wherein the active layer comprises PVA, PUB and optional reaction products of PEG and a cross-linking agent. The total mass of the reaction product of PVA, PUB and optionally PEG with the cross-linking agent may be more than 60wt%, more than 70wt%, more than 80wt%, more than 90wt%, more than 95wt%, 98wt%, 99wt% more than or 100wt% of the total mass of the active layer.
The active layer of the composite nanofiltration membrane of the invention can be formed by contacting the base membrane with a coating solution of a polymer surface active layer containing PVA, PUB and optionally PEG, followed by a crosslinking reaction. Thus, the active layer of the composite nanofiltration membrane of the present invention may contain the reaction products of PVA and PUB with a cross-linking agent, or the reaction products of PVA, PUB and PEG with a cross-linking agent. In the present invention, the reaction product of PVA and PUB and the crosslinking agent means a water-insoluble polymer crosslinked network formed by the reaction of PVA and PUB with the crosslinking agent. The reaction products of PVA, PUB and PEG with cross-linking agents refer to the water insoluble polymeric cross-linked network formed by the reaction of PVA, PUB, PEG with cross-linking agents.
In the invention, the base membrane has the conventional meaning in the field and is a membrane layer which mainly plays a supporting role in the composite nanofiltration membrane. The thickness of the base film may be 50-200 μm, for example 100 μm, 120 μm, 130 μm, 140 μm, 150 μm or in the range of any two of these thickness values. The base membrane suitable for use in the present invention may be an ultrafiltration membrane. The ultrafiltration membrane may have a molecular weight cut-off (MWCO) of 5,000 to 50,000Da, for example 10,000 to 50,000Da, 10,000 to 30,000Da, 10,000 to 20,000Da. The ultrafiltration membrane may have a pure water permeability coefficient (pure water permeability, PWP) of 100-300LMH/bar, for example 100LMH/bar, 150LMH/bar, 161LMH/bar, 200LMH/bar, 250LMH/bar, 290LMH/bar, 300LMH/bar or within a range of any two of these values. The ultrafiltration membrane may be in the form of a hollow fiber membrane, a flat plate membrane, or the like. The ultrafiltration membrane can be made of polyethersulfone.
The active layer of the composite nanofiltration membrane plays a role in nanofiltration separation, and meanwhile, the active layer of the composite nanofiltration membrane is positively charged and has a repulsive effect on the same electric particles, so that the composite nanofiltration membrane can be used for positively charged amino acid and protein separation, clean production in a cathode electrophoretic paint coating process, mining wastewater treatment, heavy metal ion interception and recovery and other aspects.
The PVA suitable for use in the present invention has a weight average molecular weight (Mw) of 10,000-200,000Da, for example 12,000.+ -. 2,000Da, 30,000.+ -. 5,000Da, 50,000.+ -. 10,000Da, 100,000Da or in the range of any two of these molecular weights. Herein, the weight average molecular weight may be measured by a light scattering method, an ultracentrifuge sedimentation balance method, a Gel Permeation Chromatography (GPC), or the like.
In the active layer of the composite nanofiltration membrane, the mass ratio of PVA to PUB can be 1:1 to 10:1, preferably 4.5:1 to 8:1, for example 4.5: 1. 5: 1. 6: 1. 7: 1. 8:1 or in the range of any two of these ratios. The invention finds that the mass ratio of PVA to PUB in the active layer is 4.5:1 to 8:1 helps to achieve higher flux for the composite nanofiltration membrane while maintaining high selectivity. It is to be understood that herein, when describing PVA, PUB or PEG in the active layer or in the reaction product of PVA, PUB and optionally PEG with a cross-linking agent, and the mass and content thereof, the mass and content of PVA, PUB or PEG refers to the mass and content of structures of PVA, PUB or PEG that are incorporated into a water-insoluble polymeric cross-linked network via a cross-linking reaction.
In the active layer of the composite nanofiltration membrane of the invention, PVA, PUB and optionally PEG are crosslinked via a crosslinking agent. The crosslinking agent suitable for use in the present invention may be a polyaldehyde. Polyaldehydes refer to compounds containing two or more aldehyde groups. The polyaldehydes may be C2-C10 polyaldehydes, such as C2-C8 polyaldehydes, C2-C6 polyaldehydes, C4-C8 polyaldehydes, C4-C6 polyaldehydes, C5-C6 polyaldehydes. As used herein, the "C+ number" preceding a compound refers to the number of carbon atoms contained in the compound. The C2-C10 polyaldehydes are polyaldehydes having from 2 to 10 carbon atoms. The polyaldehyde may be a dialdehyde having two aldehyde groups. In some embodiments, the cross-linking agent used in the present invention is selected from one or both of glutaraldehyde and glyoxal. The polyaldehyde is used as a cross-linking agent, can be dissolved in water to be used as a cross-linking solution, can avoid the pollution problem caused by using an organic solvent, has low price, and is beneficial to reducing the production cost.
In some embodiments, the active layer of the composite nanofiltration membrane of the invention comprises the reaction products of PVA, PUB, and PEG with a cross-linking agent. The PEG suitable for use in the present invention may have a weight average molecular weight of 100-2,000Da, for example 100-500Da, 150-500Da, 200+ -100 Da, 200+ -50 Da. In the active layer of the composite nanofiltration membrane, the mass ratio of PVA to PEG can be 1: 15. 3: 40. 1: 10. 3: 20. 3:10. 1: 3. 3:4, preferably ≡1: 15. more preferably ≡3:40, preferably +.1: 3. more preferably 3:10, preferably 1:10 to 1: 3. for example 3:20 to 3:10. the invention discovers that the mass ratio of PVA and PEG in the polymer surface active layer coating liquid layer can be controlled within the preferable range, and the flux can be obviously improved while the high selectivity of the composite nanofiltration membrane is not affected basically.
The composite nanofiltration membrane can be prepared by adopting a method comprising the following steps:
(1) Contacting the base film with a polymer surface active layer coating liquid, optionally carrying out heat treatment, to obtain a semi-finished film;
(2) The semi-finished film is contacted with a crosslinking solution.
In the present invention, the polymer surface active layer coating liquid is a solution containing PVA and PUB and water as a solvent. The mass fraction of PVA in the polymer surface active layer coating liquid may be 0.1 to 10wt%, for example, 0.5 to 10wt%, 1 to 10wt%, preferably 0.5 to 5wt%, more preferably 1.5 to 5wt%, for example, may be 1.5wt%, 2wt%, 2.5wt%, 5wt%, or a range composed of any two of these contents. The present invention has found that the concentration of PVA in the polymer surface active layer coating liquid in the range of 1.5 to 5wt%, preferably 0.5 to 5wt%, helps to achieve higher flux of the composite nanofiltration membrane while maintaining high selectivity. The mass fraction of the PUB in the polymer surface active layer coating liquid is 0.02 to 10wt%, preferably 0.25 to 5wt%, more preferably 0.25 to 2wt%, and may be, for example, 0.25wt%, 0.3wt%, 0.35wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, or a range consisting of any two of these contents. The present invention has found that a concentration of PUB in the polymer surface active layer coating liquid in the range of 0.02-10wt%, preferably 0.25-2wt%, helps to achieve higher flux of the composite nanofiltration membrane while maintaining high selectivity. In the polymer surface active layer coating liquid, the mass ratio of PVA to PUB can be 1:1 to 10:1, preferably 4.5:1 to 8:1, for example 4.5: 1. 5: 1. 6: 1. 7: 1. 8:1 or in the range of any two of these ratios. The invention finds that the mass ratio of PVA to PUB in the active layer is 4.5:1 to 8:1 helps to achieve higher flux for the composite nanofiltration membrane while maintaining high selectivity.
The polymer surface active layer coating liquid of the present invention may optionally further contain polyethylene glycol (PEG). In some embodiments, the polymeric surface active layer coating liquids of the present invention consist essentially of PVA, PUB, water, and optionally PEG. The total mass of PVA, PUB, water and optionally PEG may account for 90wt% or more, 95wt% or more, 98wt%, 99wt% or more, or 100wt% of the total mass of the polymer surface active layer coating liquid of the present invention. The mass fraction of polyethylene glycol in the polymer surface active layer coating film liquid may be 2wt%, 3wt%, 5wt%, 7wt%, 9wt%, 10wt%, 12wt%, 15wt%, 17wt%, 20wt%, 30wt%, 40wt% or a range of any two of the above contents, preferably 20wt% or less, more preferably 17wt% or less, for example 15wt% or less, 10wt% or less, preferably 2wt% or more, more preferably 5wt% or more, for example 7wt% or more, 8wt% or more, 10wt% or more, preferably 5 to 15wt%, for example 5 to 10wt%, 10 to 15wt% or less. The invention discovers that the introduction of polyethylene glycol with the content within the above preferred range into the coating liquid layer of the polymer surface active layer can significantly improve the flux without substantially affecting the high selectivity of the composite nanofiltration membrane. In the polymer surface active layer coating liquid, the mass ratio of polyvinyl alcohol to polyethylene glycol can be 1: 15. 3: 40. 1: 10. 3: 20. 3:10. 1: 3. 3:4, preferably ≡1: 15. more preferably ≡3:40, preferably +.1: 3. more preferably 3:10, preferably 1:10 to 1: 3. for example 3:20 to 3:10. the invention discovers that the mass ratio of polyvinyl alcohol and polyethylene glycol in the polymer surface active layer coating liquid layer can be controlled within the preferable range, and the flux can be obviously improved while the high selectivity of the composite nanofiltration membrane is not affected basically.
The polymer surface active layer coating liquid of the present invention may optionally further contain a modifier known in the art as useful for coating liquids, such as an inorganic/organic additive, a porogen, a surfactant, and the like.
The polymer surface active layer coating liquid can be prepared by immersing PVA in water at 30-80℃and preferably at 50-80℃with magnetic stirring at 300-600rpm, adding other components (e.g., PUB and optional PEG) of the polymer surface active layer coating liquid after swelling and dissolution of PVA, and stirring for dissolution. In the present invention, the water is preferably deionized water. The invention finds that the uniform polymer surface active layer coating liquid can be prepared at 30-80 ℃, preferably at 50-80 ℃ and under magnetic stirring at 300-600rpm, and is beneficial to improving the interception performance of the composite nanofiltration membrane.
In the step (1), the base film may be immersed in or coated on the polymer surface active layer coating liquid. In some embodiments, the base film is contacted with the polymeric surface active layer coating liquid in a manner that the polymeric surface active layer coating liquid is applied to the surface of the base film. In some embodiments, the base film is contacted with the polymeric surface active layer coating liquid by immersing the base film in the polymeric surface active layer coating liquid for a period of time ranging from 1 to 120 minutes. The base film may be first soaked in water sufficiently (the soaking time may be overnight, for example, 24 hours), and optionally dried to remove excess water by air drying, or the like, and then contacted with the polymer surface active layer coating liquid.
In the step (1), the base film after the contact with the polymer surface active layer coating liquid may be subjected to heat treatment. Herein, heat treatment refers to an operation of holding a film at a certain temperature for a certain period of time. The temperature of the heat treatment may be from room temperature to 80 ℃, for example 30-80 ℃, preferably 50-80 ℃. The heat treatment time may be 1 to 60 minutes, preferably 10 to 30 minutes. The heat treatment can remove the excessive moisture on the surface of the film as soon as possible. Typically, when the solvent of the crosslinking solution used in step (2) is miscible with water, for example, the solvent of the crosslinking solution is water, a C1-C3 alcohol (e.g., ethanol), or a mixture thereof, heat treatment of the base film in contact with the polymer surface active layer coating liquid is required in step (1) to bring the film to near dryness, avoiding dissolution of the polymer surface active layer coating liquid adsorbed on the film surface into the crosslinking solvent.
In the present invention, the crosslinking solution is a solution containing a crosslinking agent. The solvent of the crosslinking solution may be water, an organic solvent, or a mixture of both. The organic solvent may be selected from C1-C3 alcohols (e.g., ethanol). The appropriate solvent may be selected according to the nature of the crosslinking agent. When the cross-linking agent is a polyaldehyde, the solvent may be water, a C1-C3 alcohol (e.g., ethanol), or a mixture thereof, such as water. The mass concentration of the crosslinking solution (the percentage by mass of the crosslinking agent based on the crosslinking solution) may be 0.1 to 20% by weight, preferably 0.5 to 10% by weight, and may be, for example, 0.5% by weight, 1% by weight, 1.5% by weight, 2% by weight, 2.5% by weight, 3% by weight, 4% by weight, 5% by weight, 6% by weight, 8% by weight, 10% by weight or in the range of any two of these concentration values.
In some embodiments, the crosslinking solution contains a C2-C10 polyaldehyde. The mass fraction of C2-C10 polyaldehydes in the crosslinking solution may be from 0.1 to 15% by weight, preferably from 0.5 to 5% by weight, for example from 0.5 to 2% by weight, 1.+ -. 0.5% by weight. The invention controls the content of C2-C10 polyaldehyde in the crosslinking solution within the range, which is favorable for obtaining a crosslinking product with proper crosslinking degree and is favorable for making the composite nanofiltration membrane have high selectivity and better flux. The solvent of the crosslinking solution containing the C2-C10 polyaldehyde may be water, a C1-C3 alcohol or a mixture thereof, for example water. The crosslinking solution containing the C2-C10 polyaldehydes may also contain an acid. The acid in the crosslinking solution is used to provide an acidic crosslinking environment. The acid in the crosslinking solution may be an inorganic acid, for example, one or both selected from hydrochloric acid and sulfuric acid. The mass fraction of the acid in the crosslinking solution may be 0.001 to 0.05wt%, preferably 0.001 to 0.01wt%, for example 0.001 to 0.005wt%, 0.002.+ -. 0.001wt%, 0.002.+ -. 0.0005wt%. The present invention controls the acid content in the crosslinking solution within the above-mentioned range, which is advantageous for the crosslinking reaction.
In step (2), the semi-finished film may be brought into contact with the crosslinking solution by pouring, immersing or coating. In some embodiments, the cross-linking solution is poured onto the surface of the semi-finished film, the semi-finished film is contacted with the cross-linking solution, and excess cross-linking solution on the surface of the film can be removed by draining or the like after pouring. In some embodiments, immersing the semi-finished film in the crosslinking solution brings the semi-finished film into contact with the crosslinking solution. The semi-finished film undergoes a crosslinking reaction when contacted with the crosslinking solution. The contact (reaction) temperature of step (2) may be 25 to 120 ℃, preferably 25 to 60 ℃, and the contact (reaction) time may be 1 to 150min, preferably 10 to 60min. After the crosslinking reaction, the membrane can be rinsed by water, so that the positively charged composite nanofiltration membrane with high selectivity and high flux is obtained.
In some preferred embodiments, the method of making the positively charged composite nanofiltration membranes of the invention comprises the steps of:
(1) The base film is contacted with the polymer surface active layer coating liquid, and a semi-finished film is obtained after heat treatment; wherein the base film is preferably a polyethersulfone ultrafiltration film having a molecular weight cut-off (MWCO) of 10,000 to 50,000Da, for example 20,000.+ -. 10,000Da, the polymer surface active layer coating liquid contains PVA and PUB, the weight average molecular weight of PVA is preferably 12000.+ -. 2000Da, the mass fraction of PVA is preferably 0.5 to 5wt%, for example 2.5 to 5wt%, the mass fraction of PUB is preferably 0.25 to 5wt%, for example 0.5 to 2wt%, the temperature of heat treatment may be room temperature to 80 ℃, for example 30 to 80 ℃, preferably 50 to 80 ℃, the time of heat treatment may be 1 to 60min, preferably 10 to 30min;
(2) Contacting the semi-finished film with a crosslinking solution; wherein the crosslinking solution contains an acid and a C2-C10 polyaldehyde, the mass fraction of the acid is preferably 0.001-0.01wt%, for example 0.002.+ -. 0.001wt%, the mass fraction of the C2-C10 polyaldehyde is preferably 0.5-5wt%, for example 1.+ -. 0.5wt%, the contact temperature may be 25-120 ℃, preferably 25-60 ℃, and the contact time may be 1-150min, preferably 10-60min.
In these preferred embodiments, the positively charged composite nanofiltration membranes of the present invention have a molecular weight cut-off of 200-2,000Da, for example 200-500Da; 2000ppm sodium sulfate (Na) 2 SO 4 ) The rejection rate (R) of the solution is 15-30%, preferably 20-30%, for 2000ppm sodium chloride (NaCl) solution 20-55%, preferably 30-55%, for 2000ppm sodium sulfate (MgSO) 4 ) The rejection rate (R) of the solution is 45-65%, preferably 55-65%, for 2000ppm magnesium chloride (MgCl) 2 ) The rejection rate (R) of the solution is 80% or more, preferably 90% or more, for example 90-98%.
In other preferred embodiments, the method of making the positively charged composite nanofiltration membranes of the invention comprises the steps of:
(1) The base film is contacted with the polymer surface active layer coating liquid, and a semi-finished film is obtained after heat treatment; wherein the base film is preferably a polyethersulfone ultrafiltration film having a pure water permeability coefficient (PWP) of 100 to 300LMH/bar, for example 200 to 300LMH/bar, the polymer surface active layer coating liquid contains PVA and PUB, the weight average molecular weight of PVA is preferably 30,000+ -5,000 Da, the mass fraction of PVA is preferably 0.5 to 5wt%, for example 1.5 to 5wt%, 2+ -0.5wt%, 2 to 5wt%, 2 to 2.5wt%, the mass fraction of PUB is preferably 0.25 to 5wt%, for example 0.25 to 1wt%, 0.25 to 0.5wt%, 0.3+ -0.05 wt%, the temperature of heat treatment may be room temperature to 80 ℃, for example 30 to 80 ℃, preferably 50 to 80 ℃, and the time of heat treatment may be 1 to 60min, preferably 10 to 30min;
(2) Contacting the semi-finished film with a crosslinking solution; wherein the crosslinking solution contains an acid and a C2-C10 polyaldehyde, the mass fraction of the acid is preferably 0.001-0.01wt%, for example 0.002.+ -. 0.001wt%, the mass fraction of the C2-C10 polyaldehyde is preferably 0.5-5wt%, for example 1.+ -. 0.5wt%, the contact temperature may be 25-120 ℃, preferably 25-60 ℃, and the contact time may be 1-150min, preferably 10-60min.
In these preferred embodiments, the rejection rate (R) of the positively charged composite nanofiltration membrane of the invention to 2000ppm sodium chloride (NaCl) solution can reach 20-55%, preferably 30-55%, to 2000ppm magnesium chloride (MgCl) at room temperature and 1.0MPa 2 ) The rejection rate (R) of the solution can be up to 80%, preferably 90%, for example 90-98%.
In other preferred embodiments, the method of making the positively charged composite nanofiltration membranes of the invention comprises the steps of:
(1) The base film is contacted with the polymer surface active layer coating liquid, and a semi-finished film is obtained after heat treatment; wherein the base film is preferably a polyethersulfone ultrafiltration film having a pure water permeability coefficient (PWP) of 100 to 300LMH/bar, for example 100 to 200LMH/bar, the polymer surface active layer coating liquid contains PVA, PUB and optionally PEG, the weight average molecular weight of PVA is preferably 50,000+ -10,000 Da, the mass fraction of PVA is preferably 0.5 to 5wt%, for example 1 to 5wt%, 1.5 to 5wt%, 1.5+ -0.5wt%, the mass fraction of PUB is preferably 0.25 to 5wt%, for example 0.25 to 1wt%, 0.25 to 0.5wt%, 0.3+ -0.05 wt%, the mass fraction of PEG is preferably not more than 20wt%, more preferably 5 to 15wt%, for example 5 to 10wt%, 10 to 15wt%, the mass ratio of PVA to PEG is preferably 1:10 to 1: 3. for example 3:20 to 3:10, the temperature of the heat treatment may be from room temperature to 80 ℃, for example, 30-80 ℃, preferably 50-80 ℃, and the time of the heat treatment may be from 1-60min, preferably from 10-30min;
(2) Contacting the semi-finished film with a crosslinking solution; wherein the crosslinking solution contains an acid and a C2-C10 polyaldehyde, the mass fraction of the acid is preferably 0.001-0.01wt%, for example 0.002.+ -. 0.001wt%, the mass fraction of the C2-C10 polyaldehyde is preferably 0.5-5wt%, for example 1.+ -. 0.5wt%, the contact temperature may be 25-120 ℃, preferably 25-60 ℃, and the contact time may be 1-150min, preferably 10-60min.
In these preferred embodiments, the positively charged composite nanofiltration membrane of the present invention is applied to 2000ppm magnesium chloride (MgCl) at room temperature and 1.0MPa 2 ) The rejection rate (R) of the solution can be greater than or equal to 80%, preferably greater than or equal to 85%, for example greater than or equal to 87%, and the flux (F) can be greater than or equal to 20 L.multidot.m -2 ·h -1 Preferably not less than 40 L.m -2 ·h -1 For example ≡60 L.multidot.m -2 ·h -1 。
In some embodiments, the method of making the positively charged composite nanofiltration membranes of the invention comprises the steps of:
(1) After fully soaking the ultrafiltration membrane in water (for example, soaking overnight), optionally airing or blowing in air until the ultrafiltration membrane is nearly dry, wherein the molecular weight cut-off (MWCO) of the ultrafiltration membrane can be 5,000-50,000Da, the ultrafiltration membrane can be in the form of hollow fibers, flat plates and the like, and the material of the ultrafiltration membrane is preferably Polyethersulfone (PES);
(2) Preparing a polymer surface active layer coating liquid at 30-80 ℃, preferably 50-80 ℃, wherein the polymer surface active layer coating liquid is an aqueous solution containing PVA and PUB, the concentration of PVA can be 0.1-10wt%, the concentration of PUB can be 0.02-10wt%, and the mass ratio of PVA to PUB is preferably 1:1 to 10:1, more preferably 4.5:1 to 8: the weight average molecular weight of the PVA is preferably 10,000-200,000Da, and the polymer surface active layer coating liquid optionally further contains PEG, wherein the content of the PEG is preferably less than or equal to 20wt%; preparing a crosslinking solution which is a solution containing acid and C2-C10 polyaldehyde, wherein the acid is preferably one or two selected from hydrochloric acid and sulfuric acid, the C2-C10 polyaldehyde is preferably one or two selected from glutaraldehyde and glyoxal, the solvent can be water, C1-C3 alcohol or a mixture thereof, the concentration of the acid is preferably 0.001-0.05wt%, and the concentration of the C2-C10 polyaldehyde is preferably 0.1-15wt%;
(3) Coating the polymer surface active layer coating liquid on the surface of the ultrafiltration membrane, or soaking the ultrafiltration membrane in the polymer surface active layer coating liquid for 1-120min, and then performing heat treatment to obtain a semi-finished membrane, wherein the heat treatment temperature is preferably room temperature to 80 ℃, more preferably 50-80 ℃, and the heat treatment time is preferably 1-60min, more preferably 10-30min;
(4) Immersing the semi-finished film in the crosslinking solution, or pouring the crosslinking solution on the surface of the semi-finished film, draining, and performing crosslinking reaction, wherein the reaction temperature is preferably 25-120 ℃, more preferably 25-60 ℃, and the reaction time is preferably 1-150min, more preferably 10-60min.
The positively charged composite nanofiltration membrane of the invention may have one or more or all of the following properties:
1. pure water permeability coefficient (PWP): 50-200 L.m -2 ·h -1 ·MPa -1 ；
2. Molecular weight cut-off: 200-2000 daltons (Da);
3. 2000ppm sodium sulfate (Na) 2 SO 4 ) Rejection rate of solution (R): 15-30%, preferably 20-30%;
4. rejection (R) of 2000ppm sodium chloride (NaCl) solution at room temperature, 1.0 MPa: 20-55%, preferably 30-55%;
5. 2000ppm sodium sulfate (MgSO) 4 ) Rejection rate of solution (R): 45-65%, preferably 55-65%;
6. At room temperature and 1.0MPa, 2000ppm of magnesium chloride (MgCl) 2 ) Rejection rate of solution (R): 80%, preferably 90%, for example 90-98%.
The invention also includes the application of the composite nanofiltration membrane. The composite nanofiltration membrane or the composite nanofiltration membrane prepared by the preparation method disclosed herein can be applied to a water treatment component or device and/or a water treatment method. The water treatment component or device can be any component or device which can be applied to the water treatment process and is provided with the composite nanofiltration membrane. The "application in a water treatment module or device" includes application to a module or device product in which the composite nanofiltration membrane of the invention is installed, as well as application to the preparation of such a module or device product. The modules may be, for example, spiral wound modules, disc tube modules, etc. The device can be, for example, a household/commercial nanofiltration water purifier, an industrial boiler water supply nanofiltration device, an industrial reclaimed water recycling nanofiltration device, a mining wastewater treatment device, an amino acid and protein separation device, a clean production device for a cathode electrophoretic paint coating process, a water quality purification device and the like. The water treatment method can be, for example, a method of innocuous treatment, recycling and the like of wastewater.
Compared with the prior art, the invention has the following advantages: according to the invention, PVA with good water solubility is used as a water-phase solute, and a chemical crosslinking method is adopted to introduce PUB into a positively charged composite nanofiltration membrane surface active layer, so that the hydrophilicity, water flux and selectivity of the positively charged composite nanofiltration membrane are improved; the positively charged composite nanofiltration membrane is prepared by adopting a blending-coating-crosslinking method, has controllable conditions, is simple to operate, has adjustable subsequent heat treatment conditions, can realize continuous production, and has industrialization prospect; the positively charged composite nanofiltration membrane prepared by the method has good interception performance on high-valence heavy metal ions, and can be used for water quality purification, positively charged amino acid and protein separation, clean production in a cathode electrophoretic paint coating process, mining wastewater treatment and other aspects; the source of the polyvinyl alcohol used as the raw material is wide and the cost is low; the prepared positively charged composite nanofiltration membrane has the advantages of environmental friendliness, no toxicity and low material cost.
The invention will be illustrated by way of specific examples. It should be understood that these examples are illustrative only and are not intended to limit the scope of the invention. The methods, reagents and materials used in the examples are those conventional in the art unless otherwise indicated. The starting compounds in the examples are all commercially available. The PUB used in the examples was purchased from Sigma-Aldrich, USA.
The definition of retention (R) and flux (F) is herein as follows:
retention (R): under certain operating conditions, the solute concentration (C) f ) And the concentration of solute (C) in the permeate p ) The specific calculation formula of the ratio of the difference to the concentration of the solute in the feed solution is as follows:
flux (F): under certain operating conditions, the volume (V) of water passing through the effective membrane area (S) per unit time (t) is expressed in L.m -2 ·h -1 The specific calculation formula is as follows:
in the examples, molecular weight cut-off (MWCO) was determined using the following method: and under the room temperature and 1.0MPa, taking 2000ppm of aqueous solution of polyethylene glycol (PEG) with different molecular weights (Mw is 200-2,000 Da) as a test solution, testing the retention rate of the nanofiltration membrane, and when the retention rate of the nanofiltration membrane to the PEG is 90%, determining the molecular weight of the PEG as MWCO of the nanofiltration membrane, wherein the content of the PEG is determined by a total organic carbon analyzer (TOC).
Example 1
Taking a Polyethersulfone (PES) Ultrafiltration (UF) membrane with molecular weight cut-off (MWCO) of 20,000Da as a base membrane, fully soaking the ultrafiltration membrane in deionized water, and airing in air; an aqueous solution containing 5wt% pva (mw=12000 Da) and 1wt% pub was prepared as a polymer surface active layer coating liquid at 50 ℃ under 500ppm magnetic stirring; preparing an aqueous solution containing 0.002wt% hydrochloric acid and 1wt% glutaraldehyde as a crosslinking solution; coating the polymer surface active layer coating liquid on the surface of an ultrafiltration membrane, and then placing the ultrafiltration membrane in a 50 ℃ oven for 30min to obtain a semi-finished membrane; taking out the semi-finished membrane, pouring a small amount of crosslinking solution on the surface of the membrane, draining the water on the surface of the membrane, reacting for 30min at 60 ℃, and thoroughly rinsing with deionized water after crosslinking to obtain the positively charged composite nanofiltration membrane with high selectivity and higher flux.
Test example 1
The positively charged composite nanofiltration membrane of example 1 was placed on a membrane evaluator for desalination experiments. At room temperature and 1.0MPa, 2000ppm MgSO 4 、Na 2 SO 4 、MgCl 2 The retention rates (R) of the aqueous NaCl solutions were 94.8%, 61.3%, 31.5% and 24.9%, respectively, and the fluxes (F) were 95.4 L.m, respectively -2 ·h -1 、92.6L·m -2 ·h -1 、98.3L·m -2 ·h -1 And 93.1 L.m -2 ·h -1 The method comprises the steps of carrying out a first treatment on the surface of the Its molecular weight cut-off (MWCO) is 295Da. The positively charged composite nanofiltration membrane of example 1 has good nanofiltration performance, and specific parameters are shown in table 1.
Table 1: interception performance of the positively charged composite nanofiltration membrane obtained in example 1 on various inorganic salt aqueous solutions
Examples 2 to 5
Polyether sulfone (PES) was dissolved in N, N-dimethylacetamide (DMAc) to prepare a 16wt% PES/DMAc solution; standing and defoaming at room temperature; the PES solution was scraped on a polyester nonwoven fabric by a doctor blade to obtain an initial membrane, which was immediately immersed in water and overflowed overnight to obtain a PES Ultrafiltration (UF) membrane having a total thickness of 120 μm and a pure water permeability coefficient (PWP) of 290 LMH/bar.
An aqueous solution containing 0.5 to 2wt% pva (mw=30,000 da) (0.5 wt% in example 2, 1wt% in example 3, 1.5wt% in example 4, 2wt% in example 5) and 0.3wt% pub was prepared as a polymer surface active layer coating liquid at 50 ℃ under 500ppm magnetic stirring; preparing an aqueous solution containing 0.002wt% hydrochloric acid and 1wt% glyoxal as a crosslinking solution; coating the polymer surface active layer coating liquid on the surface of an ultrafiltration membrane, and then placing the ultrafiltration membrane in a 50 ℃ oven for 30min to obtain a semi-finished membrane; taking out the semi-finished membrane, pouring a small amount of crosslinking solution on the surface of the membrane, draining the water on the surface of the membrane, reacting for 30min at 60 ℃, and thoroughly rinsing with deionized water after crosslinking to obtain the positively charged composite nanofiltration membrane with high selectivity and higher flux.
Test example 2
The positively charged composite nanofiltration membranes of examples 2-5 were placed on a membrane evaluator for desalination experiments. 2000ppm MgCl at room temperature and 1.0MPa 2 The flux (F) and retention (R) of the composite nanofiltration membrane were measured using an aqueous solution and a 2000ppm NaCl aqueous solution as a test solution, and the results are shown in Table 2.
Table 2: influence of PVA content on interception performance of PVA/PUB blend positively-charged composite nanofiltration membrane
The results in table 2 show that the flux and retention rate of the composite nanofiltration membrane can be adjusted by adjusting the PVA content in the polymer surface active layer coating liquid. In examples 2-5, the composite nanofiltration membrane had high selectivity to 2000MgCl when the PVA content was above 1.5wt% or above 2.0wt% 2 The retention rate of the aqueous solution can reach more than 80% or more than 90%, and the aqueous solution has good permeability.
Example 6
Polyether sulfone (PES) was dissolved in N, N-Dimethylformamide (DMF) to prepare a 17wt% PES/DMF solution; standing and defoaming at room temperature; the PES solution was scraped on a polyester nonwoven fabric by a doctor blade to obtain an initial membrane, which was immediately immersed in water and overflowed overnight to obtain a PES Ultrafiltration (UF) membrane having a total thickness of 130 μm and a pure water permeability coefficient (PWP) of 161 LMH/bar.
An aqueous solution containing 1.5wt% pva (mw=50,000 da), 0.3wt% pub, and 0-40wt% peg200 was prepared as a polymer surface active layer coating liquid at 50 ℃ under 500ppm magnetic stirring; preparing an aqueous solution containing 0.002wt% hydrochloric acid and 1wt% glyoxal as a crosslinking solution; coating the polymer surface active layer coating liquid on the surface of an ultrafiltration membrane, and then placing the ultrafiltration membrane in a 50 ℃ oven for 30min to obtain a semi-finished membrane; taking out the semi-finished membrane, pouring a small amount of crosslinking solution on the surface of the membrane, draining the water on the surface of the membrane, reacting for 30min at 60 ℃, and thoroughly rinsing with deionized water after crosslinking to obtain the positively charged composite nanofiltration membrane with high selectivity and higher flux.
Test example 3
The positively charged composite nanofiltration membrane of example 6 was placed on a membrane evaluator for desalination experiments. 2000ppm MgCl at room temperature and 1.0MPa 2 The flux (F) and retention (R) of the composite nanofiltration membrane were measured using the aqueous solution as a test solution, and the results are shown in fig. 1.
The results of fig. 1 show that introducing a proper amount of PEG into the active layer of the composite nanofiltration membrane of the present invention can improve the permeability of the nanofiltration membrane while maintaining the high selectivity of the nanofiltration membrane. In example 6, when the PEG content in the polymer surface active layer coating liquid was less than 20wt%, particularly less than 15wt%, the rejection rate of the composite nanofiltration membrane was not significantly reduced. When the PEG content is higher than 5wt%, the flux of the composite nanofiltration membrane basically reaches the same level as that of the nanofiltration membrane without PEG, and gradually increases along with the increase of the PEG content, and when the PEG content is higher than 10wt%, the flux increase is obvious. When the PEG content is between 5wt% and 20wt%, the composite nanofiltration membrane has higher removal rate and flux. When the PEG content is between 10wt% and 15wt%, the composite nanofiltration membrane has high removal rate, and the flux is obviously improved compared with the nanofiltration membrane without PEG.
Claims (17)
1. The positively charged composite nanofiltration membrane is characterized by comprising a base membrane and an active layer formed on the surface of the base membrane, wherein the active layer comprises the reaction product of polymer surface active layer coating liquid containing polyvinyl alcohol, bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea and polyethylene glycol and a cross-linking agent, and the mass ratio of polyvinyl alcohol to polyethylene glycol in the active layer is 1:10 to 3:20, polyvinyl alcohol and bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea in a mass ratio of 4.5:1 to 8:1, the weight average molecular weight of the polyvinyl alcohol is 10,000-200,000 Da, the mass fraction of the polyethylene glycol in the polymer surface active layer coating liquid is 10-15 wt%, the cross-linking agent is one or two selected from glutaraldehyde and glyoxal, and the base film is a polyethersulfone ultrafiltration film.
2. The positively charged composite nanofiltration membrane according to claim 1, wherein the polyethersulfone ultrafiltration membrane has a molecular weight cut-off of 5,000-50,000 Da and/or the polyethersulfone ultrafiltration membrane has a pure water permeation coefficient of 100-300 LMH/bar.
3. A method of making the positively charged composite nanofiltration membrane of claim 1 or 2, the method comprising:
(1) Contacting the base film with a polymer surface active layer coating liquid, and optionally carrying out heat treatment to obtain a semi-finished film, wherein the polymer surface active layer coating liquid is an aqueous solution containing polyvinyl alcohol, bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea and polyethylene glycol;
(2) Contacting the semi-finished film with a crosslinking solution, wherein the crosslinking solution is a solution containing a crosslinking agent.
4. A method of preparing a positively charged composite nanofiltration membrane according to claim 3, wherein the method is characterised by one or more of the following:
in the polymer surface active layer coating liquid, the mass fraction of polyvinyl alcohol is 1-2 wt%;
in the polymer surface active layer coating liquid, the mass fraction of the bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea is 0.25-0.5 wt%;
In the polymer surface active layer coating liquid, the weight average molecular weight of the polyethylene glycol is 100-2,000 Da;
the polymer surface active layer coating liquid is prepared at the temperature of 30-80 ℃;
the polymer surface active layer coating liquid is prepared under the magnetic stirring of 300-600 rpm;
the heat treatment temperature of the step (1) is between room temperature and 80 ℃;
the heat treatment time of the step (1) is 1-60 min;
in the crosslinking solution, the mass fraction of the crosslinking agent is 0.1-20 wt%;
the crosslinking solution is a solution containing a crosslinking agent and an acid;
the contact temperature of the step (2) is 25-120 ℃;
the contact time of the step (2) is 1-150 min.
5. A method of preparing a positively charged composite nanofiltration membrane according to claim 3, wherein the method is characterised by one or more of the following:
in the polymer surface active layer coating liquid, the mass fraction of the polyvinyl alcohol is 1.5-2 wt%;
in the polymer surface active layer coating liquid, the mass fraction of the bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea is 0.3-0.35 wt%;
in the polymer surface active layer coating liquid, the weight average molecular weight of polyethylene glycol is 150-500 Da;
the polymer surface active layer coating liquid is configured at 50-80 ℃;
The heat treatment temperature of the step (1) is 50-80 ℃;
the heat treatment time of the step (1) is 10-30 min;
in the crosslinking solution, the mass fraction of the crosslinking agent is 0.5-10 wt%;
the contact temperature of the step (2) is 25-60 ℃;
the contact time of the step (2) is 10-60 min.
6. The method of making a positively charged composite nanofiltration membrane according to claim 4, wherein the method is characterized by one or more of the following:
in the crosslinking solution, the mass fraction of the crosslinking agent is 0.1-15 wt%;
in the crosslinking solution, the acid is selected from one or two of hydrochloric acid and sulfuric acid;
in the crosslinking solution, the mass fraction of the acid is 0.001-0.05 wt%;
the solvent of the crosslinking solution is water, C1-C3 alcohol or a mixture thereof.
7. The method of preparing a positively charged composite nanofiltration membrane according to claim 4, wherein the cross-linking agent is present in the cross-linking solution in a mass fraction of 0.5 to 5 wt% and/or the acid is present in a mass fraction of 0.001 to 0.01 wt%.
8. Use of the positively charged composite nanofiltration membrane of claim 1 or 2 or prepared by the method of preparing a positively charged composite nanofiltration membrane of any one of claims 3-7 in a water treatment process or water treatment assembly or device.
9. The polymer surface active layer coating liquid for preparing the positively charged composite nanofiltration membrane is characterized by comprising aqueous solution of polyvinyl alcohol, bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea and polyethylene glycol, wherein the mass ratio of polyvinyl alcohol to polyethylene glycol in the polymer surface active layer coating liquid is 1:10 to 3:20, polyvinyl alcohol and bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea in a mass ratio of 4.5:1 to 8:1, the weight average molecular weight of the polyvinyl alcohol is 10,000-200,000 Da, the polymer surface active layer coating liquid reacts with a cross-linking agent to prepare an active layer of the positively charged composite nanofiltration membrane, and the cross-linking agent is one or two of glutaraldehyde and glyoxal; in the polymer surface active layer coating liquid, the mass fraction of polyethylene glycol is 10-15 wt%.
10. The polymer surface active layer coating liquid for preparing the positively charged composite nanofiltration membrane according to claim 9, wherein the polymer surface active layer coating liquid has one or more of the following characteristics:
in the polymer surface active layer coating liquid, the mass fraction of polyvinyl alcohol is 1-2 wt%;
In the polymer surface active layer coating liquid, the mass fraction of the bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea is 0.25-0.5 wt%;
the weight average molecular weight of the polyethylene glycol is 100-2,000 Da.
11. The polymer surface active layer coating liquid for preparing the positively charged composite nanofiltration membrane according to claim 10, wherein the polymer surface active layer coating liquid has one or more of the following characteristics:
in the polymer surface active layer coating liquid, the mass fraction of the polyvinyl alcohol is 1.5-2 wt%;
in the polymer surface active layer coating liquid, the mass fraction of the bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea is 0.3-0.35 wt%;
the weight average molecular weight of the polyethylene glycol is 150-500 Da.
12. A reagent combination for preparing a positively charged composite nanofiltration membrane active layer, which is characterized in that the reagent combination comprises the polymer surface active layer coating liquid for preparing a positively charged composite nanofiltration membrane according to any one of claims 9 to 11 and a crosslinking solution, wherein the crosslinking solution is a solution containing a crosslinking agent, and the crosslinking agent is one or two selected from glutaraldehyde and glyoxal.
13. The reagent combination for preparing the positively charged composite nanofiltration membrane active layer according to claim 12, wherein the cross-linking agent in the cross-linking solution has a mass fraction of 0.1-20 wt%; and/or the crosslinking solution is a solution containing an acid and a crosslinking agent.
14. The combination of reagents for preparing a positively charged composite nanofiltration membrane active layer according to claim 12, wherein the cross-linking agent comprises 0.5-10% wt% by mass of the cross-linking solution.
15. The combination of reagents for preparing a positively charged composite nanofiltration membrane active layer according to claim 13, wherein the cross-linking solution has one or more of the following characteristics:
in the crosslinking solution, the acid is selected from one or two of hydrochloric acid and sulfuric acid;
in the crosslinking solution, the mass fraction of the acid is 0.001-0.05 wt%;
in the crosslinking solution, the mass fraction of the crosslinking agent is 0.1-15 wt%;
the solvent of the crosslinking solution is water, C1-C3 alcohol or a mixture thereof.
16. The combination of reagents for preparing a positively charged composite nanofiltration membrane active layer according to claim 13, wherein the cross-linking solution comprises a cross-linking agent in an amount of 0.5 to 5% wt% by mass and/or an acid in an amount of 0.001 to 0.01% wt% by mass.
17. Use of the polymer surface active layer coating solution for preparing a positively charged composite nanofiltration membrane as defined in any one of claims 9 to 11 or the reagent combination for preparing a positively charged composite nanofiltration membrane active layer as defined in any one of claims 12 to 16 in the preparation of a positively charged nanofiltration membrane.
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