CN112755810A - Positively charged composite nanofiltration membrane and preparation method thereof - Google Patents

Positively charged composite nanofiltration membrane and preparation method thereof Download PDF

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CN112755810A
CN112755810A CN202011499885.6A CN202011499885A CN112755810A CN 112755810 A CN112755810 A CN 112755810A CN 202011499885 A CN202011499885 A CN 202011499885A CN 112755810 A CN112755810 A CN 112755810A
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CN112755810B (en
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苗晶
洪鑫军
曹春
朱建军
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Sinochem Ningbo Runwo Membrane Technology Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/12—Composite membranes; Ultra-thin membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0002—Organic membrane manufacture
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
    • C02F1/442—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by nanofiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01D2325/26—Electrical properties
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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 polyvinyl alcohol, bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea and a reaction product of optional polyethylene glycol and a crosslinking agent. The invention adopts polyvinyl alcohol as a skeleton matrix, mixes and dissolves the polyvinyl alcohol with bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea and optional polyethylene glycol to form a polymer surface active layer coating liquid, and prepares the positively charged composite nanofiltration membrane with high selectivity and high flux by a chemical crosslinking method.

Description

Positively charged composite nanofiltration membrane and preparation method thereof
Technical Field
The invention belongs to the technical field of membranes, and particularly relates to a positively charged composite nanofiltration membrane blended by 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., membranes that allow components with smaller particle sizes than their pore sizes to pass through and retain components with larger or similar pore sizes. In the application process, if the particle size of the component medium to be separated is small, the pore diameter of the used membrane needs to be correspondingly reduced, which inevitably causes the problems of flux reduction, operation cost increase and the like. In order to avoid the above drawbacks, charged membranes have developed rapidly in recent years, and in particular charged nanofiltration membranes have been regarded as important due to their unique separation characteristics. The charged nanofiltration membrane is a membrane containing fixed charges, and the separation principle of the charged nanofiltration membrane has unique electrostatic adsorption and repulsion effects besides the physical sieving based on the aperture size of a neutral membrane. The charged group is introduced into the charged nanofiltration membrane, so that the hydrophilicity of the membrane is enhanced, the water permeability is increased, the membrane is suitable for low-pressure operation, 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 charge performance. The charged nanofiltration membrane can be divided into a positively charged nanofiltration membrane and a negatively charged nanofiltration membrane according to the difference of the electric property of fixed charges in the membrane.
Most commercial nanofiltration membranes are negatively charged nanofiltration membranes, and the current commonly used nanofiltration membranes are: polyaromatic amides, polyaspartic amides, sulfonated polysulfones, polyvinyl alcohols, and the like. Aromatic polyamide and polyamide are prepared into charged surface layer through interfacial polymerization process; sulfonated polysulfones and polyvinyl alcohols are used for preparing the charged surface layer by a coating crosslinking method.
The positively charged membrane has repulsion effect on the same electric particle due to positive charge, and can be used for separation of positively charged amino acid and protein, clean production of cathode electrophoretic paint coating process, interception and recovery of heavy metal ions, treatment of mining wastewater and the like.
Therefore, there is a need in the art for a highly selective, higher flux positively charged nanofiltration membrane.
Polyvinyl alcohol (PVA) is an organic compound, chemicalIs of the formula [ C2H4O]nThe product is white flaky, flocculent or powdery solid, is odorless, is soluble in water (above 95 ℃), is slightly soluble in dimethyl sulfoxide, and is insoluble in gasoline, kerosene, vegetable oil, benzene, toluene, dichloroethane, carbon tetrachloride, acetone, ethyl acetate, methanol, ethylene glycol, etc. 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 polymerization degree and alcoholysis degree. Polyvinyl alcohol is also an important chemical raw material, and is used for manufacturing polyvinyl acetal, gasoline-resistant pipelines, vinylon synthetic fibers, fabric treating agents, emulsifiers, paper coatings, adhesives, glue and the like. The structural formula of PVA is as follows:
Figure BDA0002843285230000021
bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea (PUB) is a water-soluble, linear polymer containing quaternary ammonium groups. No report of applying PUB urea to the preparation of nanofiltration membranes is available. The structural formula of PUB is as follows:
Figure BDA0002843285230000022
disclosure of Invention
The invention provides a positively charged blended composite nanofiltration membrane and a preparation method thereof. The invention adopts polyvinyl alcohol (PVA) as a framework substrate, and the PVA and bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea (PUB) are blended and dissolved to form a 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 high 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 reaction products of polyvinyl alcohol, bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea and an optional polyethylene glycol and a crosslinking 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 10,000-200,000 Da.
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 crosslinking 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 selected from one or both of glutaraldehyde and adipaldehyde.
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 permeability coefficient of the polyethersulfone ultrafiltration membrane is 100-300 LMH/bar.
The present invention also provides a method of preparing a positively charged composite nanofiltration membrane according to any one of the embodiments herein, the method comprising:
(1) contacting a base film with a polymer surface active layer coating liquid, and optionally performing 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 optionally polyethylene glycol;
(2) and contacting the semi-finished membrane with a crosslinking solution, wherein the crosslinking solution is a solution containing a crosslinking agent.
In one or more embodiments, the mass fraction of the polyvinyl alcohol in the polymeric surface active layer coating solution is 0.1 to 10 wt%, preferably 0.5 to 5 wt%.
In one or more embodiments, the mass fraction of bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea in the polymeric surfactant layer coating solution is 0.02 to 10 wt%, preferably 0.25 to 2 wt%.
In one or more embodiments, the polymer surfactant layer coating solution 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 polymeric surface active layer coating solution comprises polyethylene glycol, wherein the polyethylene glycol has a weight average molecular weight of 100-.
In one or more embodiments, the polymer surface active layer coating solution contains polyethylene glycol, and the mass fraction of the polyethylene glycol in the polymer surface active layer coating solution is less than or equal to 20 wt%, and preferably 5-15 wt%.
In one or more embodiments, the polymer surface active layer coating solution contains polyethylene glycol, and the mass ratio of the polyethylene glycol to the polyethylene glycol in the polymer surface active layer coating solution is more than or equal to 1: 15, preferably 1: 10 to 1: 3.
in one or more embodiments, the polymeric surface active layer coating solution is formulated at 30-80 ℃, preferably 50-80 ℃.
In one or more embodiments, the polymeric surface active layer coating solution 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 from 50 to 80 ℃.
In one or more embodiments, the heat treatment time of step (1) is from 1 to 60min, preferably from 10 to 30 min.
In one or more embodiments, the crosslinking agent is a C2-C10 polyaldehyde, preferably selected from one or both of glutaraldehyde and adipaldehyde.
In one or more embodiments, the mass fraction of the crosslinking agent in the crosslinking solution is 0.1 to 20 wt%, preferably 0.5 to 10 wt%.
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; in the crosslinking solution, the mass fraction of the acid is preferably 0.001 to 0.05 wt%, more preferably 0.001 to 0.01 wt%; the C2-C10 polyaldehyde is preferably one or two selected from glutaraldehyde and adipic dialdehyde; in the crosslinking solution, the mass fraction of the C2-C10 polyaldehyde is preferably 0.1-15 wt%, preferably 0.5-5 wt%; the solvent of the crosslinking solution is preferably water, a C1-C3 alcohol, or a mixture thereof.
In one or more embodiments, the contacting 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 150min, preferably from 10 to 60 min.
The invention also provides the use of the positively charged composite nanofiltration membrane according to any one of the embodiments herein or the positively charged composite nanofiltration membrane prepared by the method according to any one of the embodiments herein in a water treatment method or a water treatment assembly or apparatus.
The invention also provides a polymer surface active layer coating solution 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 10,000-200,000 Da.
In one or more embodiments, the mass fraction of the polyvinyl alcohol in the polymeric surface active layer coating solution is 0.1 to 10 wt%, preferably 0.5 to 5 wt%.
In one or more embodiments, the mass fraction of bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea in the polymeric surfactant layer coating solution is 0.02 to 10 wt%, preferably 0.25 to 2 wt%.
In one or more embodiments, the polymer surfactant layer coating solution 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 polymeric surfactant layer coating solution further comprises polyethylene glycol; preferably, in the coating solution of the polymer surface active layer, the mass fraction of the polyethylene glycol is less than or equal to 20 wt%, preferably 5-15 wt%; in the coating liquid of the polymer surface active layer, the mass ratio of polyvinyl alcohol to polyethylene glycol is more than or equal to 1: 15, preferably 1: 10 to 1: 3; preferably, the polyethylene glycol has a weight average molecular weight of 100-2,000Da, preferably 150-500 Da.
The present invention also provides a reagent combination comprising the polymeric surface active layer coating solution according to any of the embodiments herein and a crosslinking solution, the crosslinking solution being a solution containing a crosslinking agent.
In one or more embodiments, the crosslinking agent is a C2-C10 polyaldehyde, preferably selected from one or both of glutaraldehyde and adipaldehyde.
In one or more embodiments, the mass fraction of the crosslinking agent in the crosslinking solution is 0.1 to 20 wt%, preferably 0.5 to 10 wt%.
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 to 0.05 wt%, preferably 0.001 to 0.01 wt%; preferably, the C2-C10 polyaldehyde is selected from one or two of glutaraldehyde and hexanedial; preferably, the mass fraction of the C2-C10 polyaldehyde in the crosslinking solution is 0.1-15 wt%, preferably 0.5-5 wt%; 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, a polymeric surface active layer coating solution according to any embodiment herein, or a combination of reagents according to any embodiment herein, in the preparation of a positively charged nanofiltration membrane.
Drawings
FIG. 1 shows the effect of PEG200 content on the rejection performance of the PVA/PUB blend positively charged composite nanofiltration membranes of example 6 (2000ppm MgCl)2Solution at room temperature and 1.0MPa), the points from left to right in the figure respectively correspond to the composite nanofiltration membrane when the concentration of PEG200 in the coating solution of the polymer surface active layer is 0 wt%, 2 wt%, 5 wt%, 10 wt%, 20 wt%, 30 wt% and 40 wt%The retention property of (c).
Detailed Description
To make the features and effects of the present invention comprehensible to those skilled in the art, general description and definitions are made below with reference to terms and expressions mentioned in the specification and claims. Unless defined otherwise, 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.
The theory or mechanism described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, i.e., the present disclosure may be practiced without limitation to any particular theory or mechanism.
The terms "comprising," "including," "containing," "having," and the like, herein, encompass the meanings of "consisting essentially of … …" and "consisting of … …," e.g., when "a comprises B and C" is disclosed herein, "a consists of B and C" should be considered to have been disclosed herein.
All features defined herein as numerical ranges or percentage ranges, such as numbers, amounts, levels and concentrations, are for brevity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to cover and specifically disclose all possible subranges and individual numerical values (including integers and fractions) within the range.
Herein, when embodiments or examples are described, it is to 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, for the sake of brevity, not all possible combinations of features in the various embodiments or examples are described. Therefore, the respective features in the respective embodiments or examples may be arbitrarily combined as long as there is no contradiction between the combinations of the features, and all the possible combinations should be considered as the scope of the present specification.
The invention adopts polyvinyl alcohol (PVA) as a skeleton matrix, blends and dissolves the PVA with bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea (PUB) and optional polyethylene glycol (PEG) to form a polymer surface active layer coating solution, adopts an Ultrafiltration (UF) membrane as a supporting layer, adopts polybasic aldehyde (such as glutaraldehyde and hexanedial) as a chemical cross-linking agent, prepares the positively charged composite nanofiltration membrane with high selectivity and higher flux by a chemical cross-linking method, has simple preparation method, easy operation and controllable conditions, and can realize continuous production.
The composite nanofiltration membrane comprises a base membrane and an active layer formed on the base membrane, wherein the active layer comprises reaction products of PVA, PUB and optional PEG and a cross-linking agent. The total mass of the reaction product of PVA, PUB, and optionally PEG and cross-linking agent may comprise more than 60 wt%, more than 70 wt%, more than 80 wt%, more than 90 wt%, more than 95 wt%, more than 98 wt%, more than 99 wt%, or 100 wt% of the total mass of the active layer.
The active layer of the composite nanofiltration membrane can be formed by contacting a base membrane with a polymer surface active layer coating solution containing PVA, PUB and optional PEG and then carrying out a crosslinking reaction. Therefore, the active layer of the composite nanofiltration membrane of the invention can 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 with the crosslinking agent means a water-insoluble polymer crosslinked network formed by the reaction of PVA and PUB with the crosslinking agent. The reaction product of PVA, PUB and PEG with the cross-linking agent refers to a water-insoluble macromolecular cross-linked network formed by the reaction of PVA, PUB and PEG with the cross-linking agent.
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 molecular weight cut-off (MWCO) of the ultrafiltration membrane may be 5,000-50,000Da, for example 10,000-50,000Da, 10,000-30,000Da, 10,000-20,000 Da. The pure water permeability coefficient (PWP) of the ultrafiltration membrane may be 100-300LMH/bar, such as 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 sheet membrane, or the like. The ultrafiltration membrane can be made of polyether sulfone.
The active layer of the composite nanofiltration membrane plays a role in nanofiltration separation, and the active layer of the composite nanofiltration membrane is positively charged and has a repulsion function on particles with the same electrical property, so the composite nanofiltration membrane can be used for separation of amino acid and protein which are positively charged, clean production in a cathode electrophoretic paint coating process, treatment of mining wastewater, interception and recovery of heavy metal ions and the like.
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 within a range of any two of these molecular weights. Herein, the weight average molecular weight can be measured by a light scattering method, an ultracentrifuge sedimentation equilibrium 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, e.g. 4.5: 1. 5: 1. 6: 1. 7: 1. 8: 1 or within the range of any two of these ratios. The invention discovers that the mass ratio of PVA to PUB in the active layer is 4.5: 1 to 8: the range of 1 is beneficial to ensuring that the composite nanofiltration membrane obtains higher flux 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 the structure in which PVA, PUB or PEG is introduced into the water-insoluble polymeric cross-linked network via a cross-linking reaction.
In the active layer of the composite nanofiltration membrane, PVA, PUB and optional PEG are crosslinked through a crosslinking agent. Suitable cross-linking agents for use in the present invention may be polyaldehydes. The polyaldehyde refers to a compound having two or more aldehyde groups. The polyaldehyde may be a C2-C10 polyaldehyde, such as a C2-C8 polyaldehyde, a C2-C6 polyaldehyde, a C4-C8 polyaldehyde, a C4-C6 polyaldehyde, a C5-C6 polyaldehyde. Herein, "C + number" before the compound indicates the number of carbon atoms contained in the compound. C2-C10 polyaldehydes are polyaldehydes having from 2 to 10 carbon atoms. The polyaldehyde can be a dialdehyde comprising two aldehyde groups. In some embodiments, the cross-linking agent used in the present invention is selected from one or both of glutaraldehyde and adipaldehyde. The polybasic aldehyde is used as a cross-linking agent, can be dissolved into water to form a cross-linking solution, can avoid the pollution problem caused by using an organic solvent, and is low in price (such as glutaraldehyde and hexanedial), thereby being beneficial to reducing the production cost.
In some embodiments, the active layer of the composite nanofiltration membrane of the present invention comprises the reaction product of PVA, PUB, and PEG with a cross-linking agent. The weight average molecular weight of the PEG suitable for the present invention can be 100-2,000Da, such as 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 to PEG in the coating liquid layer of the polymer surface active layer is controlled in the preferable range, so that the flux can be remarkably improved while the high selectivity of the composite nanofiltration membrane is not influenced basically.
The composite nanofiltration membrane can be prepared by adopting a method comprising the following steps of:
(1) contacting the base film with a polymer surface active layer coating liquid, and optionally performing heat treatment to obtain a semi-finished film;
(2) contacting the semi-finished membrane with a crosslinking solution.
In the present invention, the polymer surface active layer coating solution is a solution containing PVA and PUB and water as a solvent. The PVA may be present in the polymeric surface-active layer coating solution in a mass fraction of 0.1 to 10% by weight, for example 0.5 to 10% by weight, 1 to 10% by weight, preferably 0.5 to 5% by weight, more preferably 1.5 to 5% by weight, for example 1.5% by weight, 2% by weight, 2.5% by weight, 5% by weight or in the range of any two of these contents. The invention finds that the concentration of PVA in the coating solution of the polymer surface active layer is in the range of 1.5-5 wt%, preferably 0.5-5 wt%, which is helpful for enabling the composite nanofiltration membrane to obtain higher flux while maintaining high selectivity. In the polymer surface active layer coating solution, the mass fraction of PUB is 0.02 to 10 wt%, preferably 0.25 to 5 wt%, more preferably 0.25 to 2 wt%, and may be, for example, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, or in the range of any two of these contents. The invention finds that the concentration of PUB in the coating liquid of the polymer surface active layer in the range of 0.02-10 wt%, preferably 0.25-2 wt% is helpful for enabling the composite nanofiltration membrane to obtain higher flux while maintaining high selectivity. In the coating liquid of the polymer surface active layer, the mass ratio of PVA to PUB can be 1: 1 to 10: 1, preferably 4.5: 1 to 8: 1, e.g. 4.5: 1. 5: 1. 6: 1. 7: 1. 8: 1 or within the range of any two of these ratios. The invention discovers that the mass ratio of PVA to PUB in the active layer is 4.5: 1 to 8: the range of 1 is beneficial to ensuring that the composite nanofiltration membrane obtains higher flux while maintaining high selectivity.
The polymeric surface active layer coating solution of the present invention may optionally further comprise polyethylene glycol (PEG). In some embodiments, the polymeric surface active layer coating solution of the present invention consists essentially of PVA, PUB, water, and optionally PEG. The total mass of PVA, PUB, water, and optionally PEG may comprise more than 90 wt%, more than 95 wt%, more than 98 wt%, more than 99 wt%, or 100 wt% of the total mass of the polymeric surface active layer coating solution of the present invention. In the polymer surface active layer coating liquid, the mass fraction of the polyethylene glycol can be 2 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt%, 10 wt%, 12 wt%, 15 wt%, 17 wt%, 20 wt%, 30 wt%, 40 wt% or within the range of any two of the above contents, preferably 20 wt% or less, more preferably 17 wt% or less, such as 15 wt% or less, 10 wt% or less, preferably 2 wt% or more, more preferably 5 wt% or more, such as 7 wt% or more, 8 wt% or more, 10 wt% or more, preferably 5-15 wt% or more, such as 5-10 wt% or 10-15 wt%. The invention discovers that the introduction of the polyethylene glycol with the content in the preferable range in the coating liquid layer of the polymer surface active layer can obviously improve the flux without basically influencing the high selectivity of the composite nanofiltration membrane. In the coating liquid of the polymer surface active layer, the mass ratio of the polyvinyl alcohol to the 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 the polyvinyl alcohol to the polyethylene glycol in the coating liquid layer of the polymer surface active layer is controlled within the preferable range, so that the flux can be remarkably improved while the high selectivity of the composite nanofiltration membrane is not influenced basically.
The polymeric surface active layer coating solutions of the present invention optionally may also contain modifiers known in the art to be useful in coating solutions, such as inorganic/organic additives, porogens, surfactants, and the like.
The polymer surface active layer coating solution can be prepared by soaking PVA in water at 30-80 ℃, preferably at 50-80 ℃, with magnetic stirring at 600rpm of 300-. 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 the temperature of 30-80 ℃, preferably at the temperature of 50-80 ℃ and under the magnetic stirring of 300-600rpm, and is beneficial to improving the interception performance of the composite nanofiltration membrane.
In the step (1), the contact mode of the base film and the coating liquid of the polymer surface active layer can be soaking or coating. In some embodiments, the base film is contacted with the polymeric surface active layer coating solution by applying the polymeric surface active layer coating solution to the surface of the base film. In some embodiments, the base film is contacted with the polymeric surface active layer coating solution by immersing the base film in the polymeric surface active layer coating solution, and the immersing time can be 1-120 min. The base film may be first soaked in water for 24 hr, air dried to eliminate excessive water, and then contacted with the filming liquid for the surface active layer.
In the step (1), the base film after being contacted with the polymer surface active layer coating solution may be subjected to heat treatment. Herein, the heat treatment refers to an operation of holding the film at a certain temperature for a certain period of time. The temperature of the heat treatment may be room temperature to 80 deg.C, for example 30-80 deg.C, preferably 50-80 deg.C. The heat treatment time may be 1 to 60min, preferably 10 to 30 min. The heat treatment removes excess moisture from the film surface as quickly as possible. Generally, 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, the base film in contact with the polymer surfactant layer coating solution in step (1) needs to be subjected to a heat treatment to make the film nearly dry, so as to avoid the polymer surfactant layer coating solution adsorbed on the surface of the film from dissolving 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 solvent may be suitably selected depending on the nature of the crosslinking agent. When the crosslinking 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 (mass percentage of crosslinking agent to the crosslinking solution) may be 0.1 to 20 wt.%, preferably 0.5 to 10 wt.%, and may be, for example, 0.5 wt.%, 1 wt.%, 1.5 wt.%, 2 wt.%, 2.5 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, 8 wt.%, 10 wt.%, or within the range of any two of these concentration values.
In some embodiments, the crosslinking solution comprises a C2-C10 polyaldehyde. The mass fraction of C2-C10 polyaldehyde in the crosslinking solution may be 0.1-15 wt.%, preferably 0.5-5 wt.%, for example 0.5-2 wt.%, 1. + -. 0.5 wt.%. The method controls the content of C2-C10 polyaldehyde in the cross-linking solution within the range, is favorable for obtaining a cross-linking product with proper cross-linking degree, and is favorable for enabling the composite nanofiltration membrane to have high selectivity and better flux. The solvent for the crosslinking solution containing the C2-C10 polyaldehyde may be water, a C1-C3 alcohol, or a mixture thereof, such as water. The crosslinking solution containing C2-C10 polyaldehyde 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 two selected from hydrochloric acid and sulfuric acid. The mass fraction of acid in the crosslinking solution may be 0.001 to 0.05 wt.%, preferably 0.001 to 0.01 wt.%, for example 0.001 to 0.005 wt.%, 0.002. + -. 0.001 wt.%, 0.002. + -. 0.0005 wt.%. The present invention controls the acid content in the crosslinking solution within the above range to facilitate the crosslinking reaction.
In the step (2), the semi-finished film may be contacted with the crosslinking solution by pouring, soaking, coating or the like. In some embodiments, the crosslinking solution is poured onto the surface of the semi-finished film, the semi-finished film is contacted with the crosslinking solution, and excess crosslinking solution on the surface of the film can be removed by draining or the like after pouring. In some embodiments, the intermediate membrane is immersed in the crosslinking solution to contact the intermediate membrane with the crosslinking solution. The semi-finished film is subjected to a crosslinking reaction when being contacted with a crosslinking solution. The contact (reaction) temperature of the step (2) can be 25-120 ℃, preferably 25-60 ℃, and the contact (reaction) time can be 1-150min, preferably 10-60 min. After the cross-linking 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 for preparing the positively charged composite nanofiltration membrane of the invention comprises the following steps:
(1) contacting the base film with the polymer surface active layer coating liquid, and performing heat treatment to obtain a semi-finished film; wherein the basement membrane is preferably a polyether sulfone ultrafiltration membrane with the molecular weight cut-off (MWCO) of 10,000-50,000Da, such as 20,000 +/-10,000 Da, the polymer surface active layer coating liquid contains PVA and PUB, the weight average molecular weight of the PVA is preferably 12000 +/-2000 Da, the mass fraction of the PVA is preferably 0.5-5 wt%, such as 2.5-5 wt%, the mass fraction of the PUB is preferably 0.25-5 wt%, such as 0.5-2 wt%, the heat treatment temperature can be between room temperature and 80 ℃, such as 30-80 ℃, preferably 50-80 ℃, and the heat treatment time can be 1-60min, preferably 10-30 min;
(2) contacting the semi-finished membrane with a crosslinking solution; wherein the crosslinking solution contains acid and C2-C10 polyaldehyde, the mass fraction of the acid is preferably 0.001-0.01 wt%, such as 0.002 + -0.001 wt%, the mass fraction of the C2-C10 polyaldehyde is preferably 0.5-5 wt%, such as 1 + -0.5 wt%, the contact temperature can be 25-120 ℃, preferably 25-60 ℃, and the contact time can be 1-150min, preferably 10-60 min.
In these preferred embodiments, the positively charged composite nanofiltration membranes of the invention have a molecular weight cut-off of 200-; for 2000ppm sodium sulfate (Na) at room temperature and 1.0MPa2SO4) The retention 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 retention (R) of the solution is between 45 and 65%, preferably between 55 and 65%, for 2000ppm of magnesium chloride (MgCl)2) The retention (R) of the solution is 80% or more, preferably 90% or more, for example 90-98%.
In other preferred embodiments, the method for preparing the positively charged composite nanofiltration membrane according to the invention comprises the following steps:
(1) contacting the base film with the polymer surface active layer coating liquid, and performing heat treatment to obtain a semi-finished film; wherein the base membrane is preferably a polyethersulfone ultrafiltration membrane with a pure water permeability coefficient (PWP) of 100-300LMH/bar, such as 200-300LMH/bar, the polymeric surface active layer coating solution comprises PVA and PUB, the PVA has a weight average molecular weight of preferably 30,000 + -5,000 Da, the PVA has a mass fraction of preferably 0.5-5 wt%, such as 1.5-5 wt%, 2 + -0.5 wt%, 2-5 wt%, 2-2.5 wt%, the PUB has a mass fraction of preferably 0.25-5 wt%, such as 0.25-1 wt%, 0.25-0.5 wt%, 0.3 + -0.05 wt%, the heat treatment temperature can be room temperature to 80 ℃, such as 30-80 ℃, preferably 50-80 ℃, and the heat treatment time can be 1-60min, preferably 10-30 min;
(2) contacting the semi-finished membrane with a crosslinking solution; wherein the crosslinking solution contains acid and C2-C10 polyaldehyde, the mass fraction of the acid is preferably 0.001-0.01 wt%, such as 0.002 + -0.001 wt%, the mass fraction of the C2-C10 polyaldehyde is preferably 0.5-5 wt%, such as 1 + -0.5 wt%, the contact temperature can be 25-120 ℃, preferably 25-60 ℃, and the contact time can be 1-150min, preferably 10-60 min.
In the preferred embodiments, the retention 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 1.0MPa2) The retention (R) of the solution may be up to 80% or more, preferably 90% or more, for example 90-98%。
In other preferred embodiments, the method for preparing the positively charged composite nanofiltration membrane according to the invention comprises the following steps:
(1) contacting the base film with the polymer surface active layer coating liquid, and performing heat treatment to obtain a semi-finished film; wherein the base membrane is preferably a polyethersulfone ultrafiltration membrane with a pure water permeability coefficient (PWP) of 100-300LMH/bar, such as 100-200LMH/bar, the polymeric surface active layer coating solution comprises PVA, PUB and optionally PEG, the PVA preferably has a weight average molecular weight of 50,000 + -10,000 Da, the PVA preferably has a mass fraction of 0.5-5 wt%, such as 1-5 wt%, 1.5 + -0.5 wt%, the PUB preferably has a mass fraction of 0.25-5 wt%, such as 0.25-1 wt%, 0.25-0.5 wt%, 0.3 + -0.05 wt%, the PEG preferably has a mass fraction of ≦ 20 wt%, more preferably 5-15 wt%, such as 5-10 wt%, 10-15 wt%, and 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 can be between room temperature and 80 ℃, for example, between 30 and 80 ℃, preferably between 50 and 80 ℃, and the time of the heat treatment can be between 1 and 60min, preferably between 10 and 30 min;
(2) contacting the semi-finished membrane with a crosslinking solution; wherein the crosslinking solution contains acid and C2-C10 polyaldehyde, the mass fraction of the acid is preferably 0.001-0.01 wt%, such as 0.002 + -0.001 wt%, the mass fraction of the C2-C10 polyaldehyde is preferably 0.5-5 wt%, such as 1 + -0.5 wt%, the contact temperature can be 25-120 ℃, preferably 25-60 ℃, and the contact time can be 1-150min, preferably 10-60 min.
In these preferred embodiments, the positively charged composite nanofiltration membranes of the invention are resistant to 2000ppm magnesium chloride (MgCl) at room temperature, 1.0MPa2) The retention rate (R) of the solution can be more than or equal to 80%, preferably more than or equal to 85%, for example more than or equal to 87%, and the flux (F) can be more than or equal to 20 L.m-2·h-1Preferably not less than 40 L.m-2·h-1E.g.. gtoreq.60 L.m-2·h-1。
In some embodiments, the method of preparing a positively charged composite nanofiltration membrane of the invention comprises the steps of:
(1) after fully soaking the ultrafiltration membrane in water (for example, soaking overnight), optionally airing or blowing to be nearly dry in the air, 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 fiber, flat plate and the like, and the material of the ultrafiltration membrane is preferably polyether sulfone (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 the PVA can be 0.1-10 wt%, the concentration of the PUB can be 0.02-10 wt%, and the mass ratio of the PVA to the PUB is preferably 1: 1 to 10: 1, more preferably 4.5: 1 to 8: 1, the PVA preferably has a weight average molecular weight of 10,000-200,000Da, the polymer surface active layer coating liquid optionally further contains PEG, and the content of the PEG is preferably less than or equal to 20 wt%; preparing a crosslinking solution, wherein the crosslinking solution is a solution containing acid and C2-C10 polyaldehyde, the acid is preferably selected from one or two of hydrochloric acid and sulfuric acid, the C2-C10 polyaldehyde is preferably selected from one or two of glutaraldehyde and hexandialdehyde, the solvent can be water, C1-C3 alcohol or a mixture of the water and the C1-C3 alcohol, the concentration of the acid is preferably 0.001-0.05 wt%, and the concentration of the C2-C10 polyaldehyde is preferably 0.1-15 wt%;
(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 carrying out heat treatment on the membrane 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 10-30 min;
(4) immersing the semi-finished film into the crosslinking solution, or pouring the crosslinking solution on the surface of the semi-finished film, draining, and carrying out crosslinking reaction, wherein the reaction temperature is preferably 25-120 ℃, more preferably 25-60 ℃, and the reaction time is preferably 1-150min, more preferably 10-60 min.
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-;
3. for 2000ppm sodium sulfate (Na) at room temperature and 1.0MPa2SO4) Retention (R) of solution: 15-30%, preferably 20-30%;
4. retention (R) of 2000ppm sodium chloride (NaCl) solution at room temperature, 1.0 MPa: 20-55%, preferably 30-55%;
5. at room temperature, 1.0MPa, to 2000ppm sodium sulfate (MgSO)4) Retention (R) of solution: 45-65%, preferably 55-65%;
6. for 2000ppm magnesium chloride (MgCl) at room temperature and 1.0MPa2) Retention (R) of solution: 80% or more, preferably 90% or more, for example 90-98%.
The invention also comprises the application of the composite nanofiltration membrane. The composite nanofiltration membrane or the composite nanofiltration membrane prepared by the preparation method 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 term "applied to a water treatment component or device" includes application to a component or device product on which the composite nanofiltration membrane of the invention is installed, and also includes application to the preparation of such a component or device product. The modules may be, for example, spiral wound membrane modules, disk and tube membrane modules, and the like. The device can be used for household/commercial nanofiltration water purifier, industrial boiler feed water nanofiltration device, industrial reclaimed water reuse nanofiltration device, mining wastewater treatment device, amino acid and protein separation device, cathode electrophoretic paint coating process clean production device, water quality purification device and the like. The water treatment method may be, for example, a method of harmless treatment and reuse of wastewater.
Compared with the prior art, the invention has the following advantages: the invention takes PVA with good water solubility as a water phase solute, and introduces PUB into the surface active layer of the positively charged composite nanofiltration membrane by adopting a chemical crosslinking method so as to improve the hydrophilicity, water flux and selectivity of the positively charged composite nanofiltration membrane; the preparation method adopts a blending-coating-crosslinking method to prepare the positively charged composite nanofiltration membrane, has controllable conditions, simple operation and adjustable subsequent heat treatment conditions, can realize continuous production and has industrial 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 purification, separation of positively charged amino acid and protein, clean production in a cathode electrophoretic paint coating process, mining wastewater treatment and the like; the polyvinyl alcohol used as the raw material has wide source and low price; the prepared positively charged composite nanofiltration membrane has the advantages of environment-friendliness, no toxicity and low material cost.
The present invention will be illustrated below 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 present invention. The methods, reagents and materials used in the examples are, unless otherwise indicated, conventional in the art. The starting compounds in the examples are all commercially available. PUB used in the examples was purchased from Sigma-Aldrich, USA.
Herein, the retention (R) and flux (F) are defined as follows:
retention (R): feed solution solute concentration (C) under certain operating conditionsf) With the concentration of solute (C) in the permeatep) The specific calculation formula of the ratio of the difference to the solute concentration of the feed liquid is as follows:
Figure BDA0002843285230000161
flux (F): under certain operating conditions, the volume (V) of water passing through the active membrane area (S) per unit time (t) is expressed in L.m-2·h-1The specific calculation formula is as follows:
Figure BDA0002843285230000171
in the examples, the molecular weight cut-off (MWCO) was determined as follows: at room temperature and 1.0MPa, using 2000ppm polyethylene glycol (PEG) water solution with different molecular weights (Mw is 200-2,000Da) as test solution to test the rejection rate of the nanofiltration membrane, when the rejection rate of the nanofiltration membrane to the PEG is 90%, the molecular weight of the PEG is MWCO of the nanofiltration membrane, and the content of the PEG is measured by a total organic carbon analyzer (TOC).
Example 1
Taking a polyether sulfone (PES) Ultrafiltration (UF) membrane with the molecular weight cut-off (MWCO) of 20,000Da as a base membrane, fully soaking the ultrafiltration membrane in deionized water, and airing in the air; preparing an aqueous solution containing 5 wt% of PVA (Mw 12000Da) and 1 wt% of PUB as a polymer surface active layer coating solution at 50 ℃ under 500ppm magnetic stirring; preparing an aqueous solution containing 0.002 wt% of hydrochloric acid and 1 wt% of 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; and taking out the semi-finished membrane, pouring a small amount of cross-linking 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 cross-linking to obtain the positively charged composite nanofiltration membrane with high selectivity and high flux.
Test example 1
The positively charged composite nanofiltration membrane of example 1 was placed on a membrane evaluator for desalination testing. At room temperature and 1.0MPa, for 2000ppm MgSO4、Na2SO4、MgCl2The retention rates (R) of the NaCl aqueous solution were 94.8%, 61.3%, 31.5% and 24.9%, respectively, and the flux (F) was 95.4 L.m.-2·h-1、92.6L·m-2·h-1、98.3L·m-2·h-1And 93.1 L.m-2·h-1(ii) a Its molecular weight cut-off (MWCO) was 295 Da. The positive charge composite nanofiltration membrane of example 1 has better nanofiltration performance, and specific parameters are shown in table 1.
Table 1: interception performances of positively charged composite nanofiltration membrane obtained in example 1 on different inorganic salt aqueous solutions
Figure BDA0002843285230000172
Figure BDA0002843285230000181
Examples 2 to 5
Dissolving polyether sulfone (PES) in N, N-dimethylacetamide (DMAc) to prepare a 16 wt% PES/DMAc solution; standing and defoaming at room temperature; the PES solution was scraped off the polyester nonwoven fabric with a spatula 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 2 wt% of PVA (Mw 30,000Da) (0.5 wt% in example 2, 1 wt% in example 3, 1.5 wt% in example 4, 2 wt% in example 5) and 0.3 wt% of PUB was prepared as a polymer surface active layer coating solution at 50 ℃ under 500ppm magnetic stirring; preparing an aqueous solution containing 0.002 wt% of hydrochloric acid and 1 wt% of adipic dialdehyde 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; and taking out the semi-finished membrane, pouring a small amount of cross-linking 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 cross-linking to obtain the positively charged composite nanofiltration membrane with high selectivity and high flux.
Test example 2
The positively charged composite nanofiltration membranes of examples 2-5 were placed on a membrane evaluator for desalination testing. At room temperature, 1.0MPa, 2000ppm MgCl2The flux (F) and rejection (R) of the composite nanofiltration membrane were measured using an aqueous solution and 2000ppm NaCl aqueous solution as test solutions, and the results are shown in table 2.
Table 2: influence of PVA content on interception performance of PVA/PUB blended positively charged composite nanofiltration membrane
Figure BDA0002843285230000182
Figure BDA0002843285230000191
The results in table 2 show that the flux and rejection rate of the composite nanofiltration membrane can be adjusted by adjusting the content of PVA in the coating solution of the polymer surface active layer. In examples 2 to 5, the PVA containsWhen the amount is more than 1.5 wt% or more than 2.0 wt%, the composite nanofiltration membrane has high selectivity to 2000MgCl2The retention rate of the aqueous solution can reach more than 80 percent or more than 90 percent, and simultaneously, the aqueous solution has good permeability.
Example 6
Dissolving polyether sulfone (PES) in N, N-Dimethylformamide (DMF) to prepare a 17 wt% PES/DMF solution; standing and defoaming at room temperature; the PES solution was scraped off the polyester nonwoven fabric with a spatula 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.
Preparing an aqueous solution containing 1.5 wt% of PVA (Mw is 50,000Da), 0.3 wt% of PUB and 0-40 wt% of PEG200 as a polymer surface active layer coating solution at 50 ℃ under 500ppm magnetic stirring; preparing an aqueous solution containing 0.002 wt% of hydrochloric acid and 1 wt% of adipic dialdehyde 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; and taking out the semi-finished membrane, pouring a small amount of cross-linking 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 cross-linking to obtain the positively charged composite nanofiltration membrane with high selectivity and high flux.
Test example 3
The positively charged composite nanofiltration membrane of example 6 was placed on a membrane evaluator for desalination testing. At room temperature, 1.0MPa, 2000ppm MgCl2The flux (F) and the retention rate (R) of the composite nanofiltration membrane are measured by taking the aqueous solution as a test solution, and the result is shown in figure 1.
The results in fig. 1 show that the introduction of 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 content of PEG in the coating solution of the polymer surface active layer is lower than 20 wt%, particularly lower than 15 wt%, the rejection rate of the composite nanofiltration membrane is not obviously reduced. When the content of PEG is higher than 5 wt%, the flux of the composite nanofiltration membrane basically reaches the same level as that of the nanofiltration membrane without PEG, the flux is gradually increased along with the increase of the content of PEG, and when the content is higher than 10 wt%, the flux is obviously increased. When the content of PEG is between 5 wt% and 20 wt%, the composite nanofiltration membrane has higher removal rate and flux. When the content of PEG is between 10 wt% and 15 wt%, the composite nanofiltration membrane has high removal rate, and the flux is obviously improved compared with that of the nanofiltration membrane without PEG.

Claims (11)

1. 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 polyvinyl alcohol, bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea and an optional reaction product of polyethylene glycol and a crosslinking agent.
2. The positively-charged composite nanofiltration membrane according to claim 1, wherein the active layer comprises polyvinyl alcohol and bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea in a mass ratio of 1: 1 to 10: 1, preferably 4.5: 1 to 8: 1; and/or the weight average molecular weight of the polyvinyl alcohol is 10,000-200,000 Da.
3. The positively charged composite nanofiltration membrane according to claim 1, wherein the cross-linking agent is a C2-C10 polyaldehyde, preferably one or two selected from glutaraldehyde and adipaldehyde.
4. The positively-charged composite nanofiltration membrane according to claim 1, wherein the active layer comprises a reaction product of polyvinyl alcohol, bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea and optionally polyethylene glycol and a crosslinking agent, and the mass ratio of polyvinyl alcohol to polyethylene glycol in the active layer is not less than 1: 15, preferably 1: 10 to 1: 3.
5. the positively-charged composite nanofiltration membrane according to claim 1, wherein 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 permeability coefficient of the polyethersulfone ultrafiltration membrane is 100-300 LMH/bar.
6. A method of preparing a positively charged composite nanofiltration membrane according to any one of claims 1 to 5, wherein the method comprises:
(1) contacting a base film with a polymer surface active layer coating liquid, and optionally performing 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 optionally polyethylene glycol;
(2) and contacting the semi-finished membrane with a crosslinking solution, wherein the crosslinking solution is a solution containing a crosslinking agent.
7. The method of claim 6, wherein the method has one or more of the following features:
in the polymer surface active layer coating liquid, the mass fraction of polyvinyl alcohol is 0.1-10 wt%, preferably 0.5-5 wt%;
in the polymer surface active layer coating liquid, the mass fraction of bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea is 0.02-10 wt%, preferably 0.25-2 wt%;
in the coating liquid of the polymer surface active layer, the mass ratio of polyvinyl alcohol to bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea is 1: 1 to 10: 1, preferably 4.5: 1 to 8: 1;
the polymer surface active layer coating liquid contains polyethylene glycol, and the weight average molecular weight of the polyethylene glycol is 100-2,000Da, preferably 150-500 Da;
the polymer surface active layer coating liquid contains polyethylene glycol, and in the polymer surface active layer coating liquid, the mass fraction of the polyethylene glycol is less than or equal to 20 wt%, preferably 5-15 wt%;
the polymer surface active layer coating liquid contains polyethylene glycol, and in the polymer surface active layer coating liquid, the mass ratio of the polyethylene glycol to the polyethylene glycol is more than or equal to 1: 15, preferably 1: 10 to 1: 3;
the polymer surface active layer coating liquid is prepared at 30-80 ℃, preferably at 50-80 ℃;
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 ℃, and preferably between 50 and 80 ℃;
the heat treatment time of the step (1) is 1-60min, preferably 10-30 min;
the cross-linking agent is C2-C10 polybasic aldehyde, preferably one or two selected from glutaraldehyde and hexanedial;
in the crosslinking solution, the mass fraction of the crosslinking agent is 0.1-20 wt%, preferably 0.5-10 wt%;
the crosslinking solution is a solution containing C2-C10 polybasic aldehyde and acid; the C2-C10 polyaldehyde is preferably one or two selected from glutaraldehyde and adipic dialdehyde; in the crosslinking solution, the mass fraction of the C2-C10 polyaldehyde is preferably 0.1-15 wt%, preferably 0.5-5 wt%; the acid is preferably selected from one or two of hydrochloric acid and sulfuric acid; in the crosslinking solution, the mass fraction of the acid is preferably 0.001 to 0.05 wt%, more preferably 0.001 to 0.01 wt%; the solvent of the crosslinking solution is preferably water, C1-C3 alcohol or a mixture thereof;
the contact temperature of the step (2) is 25-120 ℃, and preferably 25-60 ℃;
the contact time of the step (2) is 1-150min, preferably 10-60 min.
8. Use of positively charged composite nanofiltration membranes according to any one of claims 1 to 5 or prepared by the method according to claim 6 or 7 in a water treatment process or a water treatment assembly or apparatus.
9. The polymer surface active layer coating liquid is characterized by comprising an aqueous solution of polyvinyl alcohol and bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea;
preferably, the weight average molecular weight of the polyvinyl alcohol is 10,000-200,000 Da;
preferably, in the coating solution of the polymer surface active layer, the mass fraction of the polyvinyl alcohol is 0.1-10 wt%, preferably 0.5-5 wt%;
preferably, in the coating liquid of the polymer surface active layer, the mass fraction of bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea is 0.02-10 wt%, preferably 0.25-2 wt%;
preferably, in the coating solution for the polymer surface active layer, the mass ratio of polyvinyl alcohol to bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea is 1: 1 to 10: 1, preferably 4.5: 1 to 8: 1;
preferably, the coating solution of the polymer surface active layer also contains polyethylene glycol; preferably, in the coating solution of the polymer surface active layer, the mass fraction of the polyethylene glycol is less than or equal to 20 wt%, preferably 5-15 wt%; in the coating liquid of the polymer surface active layer, the mass ratio of polyvinyl alcohol to polyethylene glycol is more than or equal to 1: 15, preferably 1: 10 to 1: 3; preferably, the polyethylene glycol has a weight average molecular weight of 100-2,000Da, preferably 150-500 Da.
10. A reagent set comprising the polymeric surfactant layer coating solution of claim 9 and a crosslinking solution, wherein the crosslinking solution is a solution containing a crosslinking agent;
preferably, the cross-linking agent is C2-C10 polybasic aldehyde, preferably one or two selected from glutaraldehyde and adipic dialdehyde;
preferably, the mass fraction of the cross-linking agent in the cross-linking solution is 0.1-20 wt%, preferably 0.5-10 wt%;
preferably, the crosslinking solution is a solution containing acid and 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 to 0.05 wt%, preferably 0.001 to 0.01 wt%; preferably, the C2-C10 polyaldehyde is selected from one or two of glutaraldehyde and hexanedial; preferably, the mass fraction of the C2-C10 polyaldehyde in the crosslinking solution is 0.1-15 wt%, preferably 0.5-5 wt%; preferably, the solvent of the crosslinking solution is water, a C1-C3 alcohol, or a mixture thereof.
11. Use of bis (2-chloroethyl) ether-alt-1, 3-bis [3- (dimethylamino) propyl ] urea, the polymeric surfactant layer coating solution of claim 9 or the reagent combination of claim 10 in the preparation of a positively charged nanofiltration membrane.
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