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CN114632429A - Composite nanofiltration membrane containing composite desalting layer and preparation method thereof - Google Patents

Composite nanofiltration membrane containing composite desalting layer and preparation method thereof Download PDF

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Publication number
CN114632429A
CN114632429A CN202011478640.5A CN202011478640A CN114632429A CN 114632429 A CN114632429 A CN 114632429A CN 202011478640 A CN202011478640 A CN 202011478640A CN 114632429 A CN114632429 A CN 114632429A
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phase solution
membrane
composite
nanofiltration membrane
oil phase
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CN114632429B (en
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吕朋朋
张旭良
曹春
朱建军
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Sinochem Ningbo Runwo Membrane Technology Co Ltd
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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
    • B01D69/125—In situ manufacturing by polymerisation, polycondensation, cross-linking or chemical reaction
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/027—Nanofiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/08—Apparatus therefor
    • 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
    • B01D67/0006—Organic membrane manufacture by chemical reactions
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A20/00—Water conservation; Efficient water supply; Efficient water use
    • Y02A20/124—Water desalination
    • Y02A20/131—Reverse-osmosis

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Water Supply & Treatment (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Nanotechnology (AREA)
  • Manufacturing & Machinery (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Hydrology & Water Resources (AREA)
  • Environmental & Geological Engineering (AREA)
  • Organic Chemistry (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

The invention provides a composite nanofiltration membrane and a preparation method thereof. The composite nanofiltration membrane comprises a base membrane and a composite desalting layer formed on the base membrane, wherein the composite desalting layer comprises polyamide and a reaction product of N-vinylpyrrolidone and a cross-linking agent. The method is characterized in that firstly, on the basis of an interfacial polymerization mechanism, polyamine and polyacyl chloride react to obtain a functional separation layer structure, and then a membrane formed by primary interfacial polymerization is placed in post-treatment liquid to obtain a composite nanofiltration membrane product with a stable structure and high flux in a mode of re-crosslinking N-vinylpyrrolidone. The composite nanofiltration membrane has high pure water flux, and the polyamide separation layer is tightly combined with the base membrane. The method has the advantages of cheap raw materials, low preparation cost, simple process and easy industrialization.

Description

Composite nanofiltration membrane containing composite desalting layer and preparation method thereof
Technical Field
The invention relates to the technical field of nanofiltration membranes, and particularly relates to a composite nanofiltration membrane containing a composite desalting layer and a preparation method thereof.
Background
The nanofiltration membrane is a membrane separation process between ultrafiltration and reverse osmosis, and can remove most of multivalent ions and small molecular organic matters in water. Compared with a reverse osmosis membrane, the nanofiltration membrane has the advantages of low operation pressure, large water production flux, low operation cost and the like, and is widely applied to the field of domestic purified water and industrial water treatment. In the application process of the nanofiltration membrane, people have higher and higher requirements on flux of the nanofiltration membrane, so how to improve pure water flux of the nanofiltration membrane becomes one of the important concerns of researchers under the condition of ensuring the service life and interception.
The method for improving the pure water flux of the nanofiltration membrane is more commonly used at present, for example, CN110694493A mentions that TiO is added into the water phase2Thereby increasing the membrane area and further increasing the pure water flux of the nanofiltration membrane. The nano particles are dispersed unevenly in the monomer and are easy to agglomerate, so that the consistency of the structure of the prepared nano-filtration membrane is poor, and the nano-filtration membrane is difficult to be widely applied to industrialization. CN105617875A mentions a preparation method of a high-flux hollow fiber composite nanofiltration membrane, which improves the flux of membrane filaments by a method of oxidizing a functional layer by an oxidant after a polyamide layer is generated by the reaction of polybasic amide and polybasic acyl chloride. The damage of the processing mode of the oxidant to the polyamide separation layer improves the permeability of the membrane to a certain degree, but also causes damage to the separation layer, and the service life is lost to a certain degree. The existing methods for improving the pure water flux of the nanofiltration membrane have advantages and disadvantages, and influence factors in actual reaction are complex and the stability is not high.
There remains a need in the art for a hollow fiber composite nanofiltration membrane having a stable structure and high flux.
Disclosure of Invention
Aiming at the problems, the invention provides a composite nanofiltration membrane with a stable structure. The method is characterized in that firstly, on the basis of an interfacial polymerization mechanism, polyamine and polyacyl chloride react to obtain a functional separation layer structure, and then a membrane formed by primary interfacial polymerization is placed in post-treatment liquid to obtain a composite nanofiltration membrane product with a stable structure and high flux in a mode of re-crosslinking N-vinylpyrrolidone.
Specifically, the invention provides a composite nanofiltration membrane, which comprises a base membrane and a composite desalting layer formed on the base membrane, wherein the composite desalting layer comprises polyamide and a reaction product of N-vinyl pyrrolidone and a crosslinking agent.
In one or more embodiments, the reaction product of the N-vinylpyrrolidone and crosslinker has a network-like structure.
In one or more embodiments, the reaction product of the N-vinylpyrrolidone and crosslinker is present both within and at the surface of the polyamide.
In one or more embodiments, the base membrane is a polysulfone hollow fiber base membrane.
In one or more embodiments, the polyamide is formed from the reaction of a polyamine and a polybasic acid chloride.
In one or more embodiments, the polyamine is selected from one or more of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3, 5-triaminobenzene, 1,2, 4-triaminobenzene, 2, 4-diaminotoluene, 2, 6-diaminotoluene, 1, 3-diaminocyclohexane, 1, 2-diaminocyclohexane, 1, 4-diaminocyclohexane, piperazine, 2, 5-dimethylpiperazine and 4-aminomethylpiperazine, preferably from one or both of piperazine and m-phenylenediamine.
In one or more embodiments, the polyacid chloride is selected from one or more of trimesoyl chloride, pyromellitic chloride, phthalic chloride, terephthaloyl chloride, isophthaloyl chloride, cyclohexanetetracarboxylic acid chloride, cyclohexanetricarboxylic acid chloride, cyclohexanedicarboxylic acid chloride, tetrahydrofurantecarboxylic acid chloride, preferably trimesoyl chloride.
In one or more embodiments, the crosslinking agent is selected from one or more of divinylbenzene, N-methylenebisacrylamide, and dimethylacrylacetylvinyl acetate.
The invention also provides a method for preparing the composite nanofiltration membrane, which comprises the following steps:
(1) contacting the base film with an aqueous solution containing a polyamine;
(2) contacting the basement membrane which is contacted with the water phase solution in the step (1) with an oil phase solution containing polyacyl chloride, N-vinyl pyrrolidone, an initiator and a cross-linking agent;
(3) carrying out heat treatment on the base film contacted with the oil phase solution in the step (2) to obtain a composite film;
(4) and (4) contacting the composite membrane in the step (3) with an aqueous solution of inorganic salt to obtain the composite nanofiltration membrane.
In one or more embodiments, the polyamine is present in the aqueous solution in an amount of 0.05 to 5 wt%, preferably 0.5 to 2.5 wt%, based on the total mass of the aqueous solution.
In one or more embodiments, the aqueous phase solution contains an acid absorbent.
In one or more embodiments, the acid absorber is selected from one or more of sodium carbonate, sodium phosphate, triethylamine, sodium hydroxide, and potassium hydroxide.
In one or more embodiments, the acid absorbent is present in the aqueous solution in an amount of 0.05 to 5 wt% based on the total mass of the aqueous solution.
In one or more embodiments, the polybasic acid chloride is contained in the oil phase solution in an amount of 0.02 to 1 wt%, preferably 0.05 to 0.4 wt%, based on the total mass of the oil phase solution.
In one or more embodiments, the content of N-vinylpyrrolidone in the oil phase solution is 0.05 to 3 wt%, preferably 0.1 to 1.5 wt%, of the total mass of the oil phase solution.
In one or more embodiments, the solvent of the oil phase solution is selected from one or more of n-hexane, cyclohexane, pentane, and isoparaffin.
In one or more embodiments, the initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptonitrile, and dibenzoyl peroxide.
In one or more embodiments, the initiator is present in the oil phase solution in an amount of 0.005 to 0.3 wt%, preferably 0.01 to 0.1 wt%, based on the total mass of the oil phase solution.
In one or more embodiments, the cross-linking agent is present in the oil phase solution in an amount of 0.02 to 0.3 wt%, preferably 0.06 to 0.175 wt%, based on the total mass of the oil phase solution.
In one or more embodiments, the inorganic salt is selected from one or more of a water soluble sulfate salt and a water soluble monohydrogen phosphate salt, for example, one or both of sodium sulfate and disodium hydrogen phosphate.
In one or more embodiments, the aqueous solution of inorganic salts contains from 2 to 30 weight percent, preferably from 5 to 20 weight percent, of the inorganic salt based on the total mass of the aqueous solution of inorganic salts.
In one or more embodiments, the contact time with the aqueous solution in step (1) is from 10 to 250s, preferably from 30 to 180 s.
In one or more embodiments, the contact time with the oil phase solution in step (2) is from 5 to 150 seconds, preferably from 10 to 120 seconds.
In one or more embodiments, in step (3), the heat treatment temperature is 40 to 120 ℃, preferably 50 to 100 ℃, and the heat treatment time is 5 to 300s, preferably 10 to 240 s.
In one or more embodiments, in step (4), the temperature of the aqueous solution of inorganic salts is from 40 to 90 ℃, preferably from 50 to 90 ℃, and the contact time with the aqueous solution of inorganic salts is from 1 to 10 hours, preferably from 2 to 8 hours.
The invention also provides the use of a composite nanofiltration membrane as described in any of the embodiments herein or prepared by a method as described in any of the embodiments herein in a water treatment process or a water treatment assembly or apparatus.
The invention also provides the use of the reaction product of N-vinylpyrrolidone and a cross-linking agent to improve the flux and/or salt rejection of a nanofiltration membrane.
In one or more embodiments, the crosslinking agent is selected from one or more of divinylbenzene, N-methylenebisacrylamide, and dimethylacrylacetylvinyl acetate.
In one or more embodiments, the reaction product of the N-vinylpyrrolidone and crosslinker has a network-like structure.
In one or more embodiments, the nanofiltration membrane has a polyamide-containing desalting layer, and the reaction product of the N-vinylpyrrolidone and crosslinker is present both inside and on the surface of the polyamide.
The invention also provides a method for improving the flux and/or the desalination rate of the nanofiltration membrane, which comprises the step of adding N-vinyl pyrrolidone and a cross-linking agent into the oil phase solution for preparing the desalination layer of the nanofiltration membrane.
In one or more embodiments, the crosslinking agent is selected from one or more of divinylbenzene, N-methylenebisacrylamide, and dimethylacrylacetylvinyl acetate.
In one or more embodiments, the method includes reacting N-vinylpyrrolidone with a crosslinking agent to form a network-like structure.
In one or more embodiments, the method includes causing the reaction product of N-vinylpyrrolidone and a crosslinking agent to be present in the interior and at the surface of the polyamide.
In one or more embodiments, the base membrane of the nanofiltration membrane is a polysulfone hollow fiber base membrane.
In one or more embodiments, the oil phase solution comprises a polybasic acid chloride, N-vinyl pyrrolidone, an initiator, and a crosslinking agent.
In one or more embodiments, the polyacyl chloride is present in the oil phase solution in an amount of 0.05 to 0.4 weight percent based on the total mass of the oil phase solution.
In one or more embodiments, the content of N-vinylpyrrolidone in the oil-phase solution is 0.1 to 1.5 wt% of the total mass of the oil-phase solution.
In one or more embodiments, the solvent of the oil phase solution is selected from one or more of n-hexane, cyclohexane, pentane, and isoparaffin.
In one or more embodiments, the initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptonitrile, and dibenzoyl peroxide.
In one or more embodiments, the initiator is present in the oil phase solution in an amount of 0.01 to 0.15 wt%, preferably 0.01 to 0.1 wt%, based on the total mass of the oil phase solution.
In one or more embodiments, the cross-linking agent is present in the oil phase solution in an amount of 0.06 to 0.175 wt% of the total mass of the oil phase solution.
In one or more embodiments, the method of increasing the flux and/or salt rejection rate of a nanofiltration membrane comprises preparing the nanofiltration membrane using the method of preparing a composite nanofiltration membrane as described in any embodiment herein.
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 as well as individual numerical values (including integers and fractions) within the ranges.
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.
Composite nanofiltration membranes are generally composed of a mainly supporting base membrane and a mainly separating polyamide layer. According to the invention, the network-shaped hydrophilic modification structure formed by the reaction of the N-vinylpyrrolidone and the cross-linking agent is introduced into the polyamide separation layer of the composite nanofiltration membrane, so that the separation layer and the hydrophilic modification structure are firmly combined into the composite desalination layer, the reaction product of the N-vinylpyrrolidone and the cross-linking agent not only improves the hydrophilic performance of the membrane surface, but also improves the compact structure of the polyamide layer, and the water production flow channel is increased, thereby improving the pure water flux of the nanofiltration membrane. In addition, the composite desalting layer has a complex network structure, so that the deposition effect of the polyamide separation layer on the surface of the base membrane is improved, and the combination is tighter.
The composite nanofiltration membrane comprises a base membrane and a composite desalting layer formed on the base membrane, wherein the composite desalting layer comprises polyamide and a reaction product of N-vinylpyrrolidone and a crosslinking agent. It will be appreciated that the reaction product of N-vinylpyrrolidone and crosslinker has a network-like structure.
The composite desalting layer comprises polyamide formed by interfacial polymerization reaction of polyamine and polybasic acyl chloride and a network-shaped hydrophilic modification structure formed by crosslinking reaction of N-vinyl pyrrolidone and a crosslinking agent in and on the surface of the polyamide, wherein the polyamide and the hydrophilic modification structure are firmly combined. Therefore, in the present invention, a network structure formed by the reaction of N-vinylpyrrolidone and a crosslinking agent exists inside and on the surface of polyamide, and constitutes a composite desalting layer together with the polyamide.
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 base membrane suitable for use in the present invention may be a hollow fiber base membrane, preferably a polysulfone hollow fiber base membrane. The polysulfone hollow fiber base membrane refers to a hollow fiber base membrane mainly made of polysulfone. In the polysulfone hollow fiber base membrane, the content of polysulfone is usually 90 wt% or more, 95 wt% or more, 98 wt% or more or 99 wt% or more of the total mass of the polysulfone hollow fiber base membrane. In the invention, the separation layer (also called desalination layer) has the conventional meaning in the field and is a membrane layer mainly playing a separation role in the composite nanofiltration membrane.
The polyamide in the desalting layer of the composite nanofiltration membrane is prepared by reacting polyamine and polybasic acyl chloride, and is specifically prepared by interfacial polymerization of a water phase solution containing polyamine and an oil phase solution containing polybasic acyl chloride.
The polyamine suitable for the present invention may be one or more selected from m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3, 5-triaminobenzene, 1,2, 4-triaminobenzene, 2, 4-diaminotoluene, 2, 6-diaminotoluene, 1, 3-diaminocyclohexane, 1, 2-diaminocyclohexane, 1, 4-diaminocyclohexane, piperazine, 2, 5-dimethylpiperazine and 4-aminomethylpiperazine, preferably one or both selected from piperazine and m-phenylenediamine. In some preferred embodiments, the polyamine used in the present invention is piperazine.
The polybasic acid chloride suitable for the present invention may be one or more selected from trimesoyl chloride (TMC), isophthaloyl chloride (IPC), terephthaloyl chloride (TPC), pyromellitic chloride, phthaloyl chloride, cyclohexanetetracarboxylic acid chloride, cyclohexanetricarboxylic acid chloride, cyclohexanedicarboxylic acid chloride, tetrahydrofuranetetracarboxylic acid chloride, tetrahydrofuranetricarboxylic acid chloride, tetrahydrofuranedicarboxyl chloride, and tetrahydrofuranedicarboxylic acid chloride, preferably one or more selected from trimesoyl chloride (TMC), isophthaloyl chloride (IPC), terephthaloyl chloride (TPC), and the like. In some embodiments, the polybasic acid chloride used in the present invention is TMC.
In the present invention, the crosslinking agent that reacts with N-vinylpyrrolidone may be one or more of divinylbenzene, N-methylenebisacrylamide, dimethylacrylacetylvinyl ester, and the like. The invention discovers that the divinyl benzene, the N, N-methylene bisacrylamide and the dimethyl propylene vinyl acetate can be dissolved in the oil phase solution and can generate a cross-linking reaction with the N-vinyl pyrrolidone to generate a hydrophilic network structure, so that the flux of the nanofiltration membrane is improved, and the polyamide separation layer is more tightly combined with the base membrane and is not easy to fall off due to the protection effect of the network hydrophilic layer.
The composite nanofiltration membrane can be prepared by adopting a method comprising the following steps of:
(1) contacting the base film with an aqueous solution containing a polyamine;
(2) contacting the basement membrane contacted with the water phase solution in the step (1) with an oil phase solution containing polyacyl chloride, N-vinyl pyrrolidone, an initiator and a cross-linking agent;
(3) carrying out heat treatment on the base film contacted with the oil phase solution in the step (2) to obtain a composite film;
(4) and (4) contacting the composite membrane in the step (3) with an aqueous solution of inorganic salt to obtain the composite nanofiltration membrane.
In the present invention, the aqueous solution has the meaning conventionally used in the art, and is a solution in which the polyamine-containing solvent used for preparing the polyamide separation layer is water. In the present invention, the water is preferably deionized water. In the present invention, the oil phase solution has the meaning conventionally used in the art, and is a solution in which a polybasic acid chloride-containing solvent used for preparing a polyamide separation layer is an organic solvent.
In step (1), the content of the polyamine in the aqueous phase solution may be 0.05 to 5% by weight, preferably 0.1 to 4.2% by weight, more preferably 0.5 to 2.5% by weight, for example, may be 0.1% by weight, 0.5% by weight, 1.2% by weight, 1.5% by weight, 2.2% by weight, 2.5% by weight, or within a range of any two of these contents, based on the total mass of the aqueous phase solution. To promote the interfacial polymerization reaction, the aqueous solution preferably contains an acid absorbent. The acid absorbent suitable for the present invention may be one or more of sodium carbonate, sodium phosphate, triethylamine, sodium hydroxide, potassium hydroxide, etc. The amount of the acid absorbent in the aqueous solution may be 0.05 to 5 wt%, preferably 0.1 to 2.5 wt%, for example, may be 0.1 wt%, 0.5 wt%, 0.7 wt%, 1.4 wt%, 2.5 wt% or in the range of any two of these contents, based on the total mass of the aqueous solution. In some embodiments, the aqueous phase solution contains or consists of polyamine, acid absorbent and water. A uniform aqueous solution can be obtained by mixing the components of the aqueous solution.
In step (1), the contact time of the polysulfone hollow fiber-based membrane with the aqueous solution may be 10 to 250s, preferably 30 to 180s, and may be, for example, 30s, 50s, 60s, 90s, 120s, 180s or a range of any two of these times. The polysulfone hollow fiber base membrane may be contacted with the aqueous solution by immersing the polysulfone hollow fiber base membrane in the aqueous solution. After contacting with the aqueous phase solution, the excess aqueous phase on the membrane surface can be removed and the subsequent operation can be carried out. Excess water phase on the surface of the membrane can be removed by draining and the like.
In the step (2), the content of the polybasic acid chloride in the oil phase solution may be 0.02 to 1 wt%, preferably 0.05 to 0.4 wt%, more preferably 0.05 to 0.25 wt%, for example, may be 0.05 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.23 wt%, 0.25 wt%, 0.4 wt%, or any two of these contents in the range of the total mass of the oil phase solution. The content of N-vinylpyrrolidone may be 0.05 to 3% by weight, preferably 0.1 to 1.5% by weight, of the total mass of the oil phase solution, and for example, may be 0.1% by weight, 0.2% by weight, 0.5% by weight, 0.8% by weight, 1% by weight, 1.2% by weight, 1.5% by weight, or within the range of any two of these contents. The invention discovers that N-vinyl pyrrolidone has limited dissolving capacity in an oil phase, the uniformity of an oil phase system can be influenced by overhigh content, the crosslinking degree of a product is low due to overlow content, and the product is easy to lose in the using process. The initiator may be one or more of azobisisobutyronitrile, azobisisoheptonitrile, dibenzoyl peroxide, and the like. The content of the initiator may be 0.005 to 0.3% by weight, preferably 0.01 to 0.15% by weight, more preferably 0.01 to 0.1% by weight, based on the total mass of the oil phase solution, and for example, may be 0.01%, 0.02%, 0.025%, 0.05%, 0.07%, 0.1% by weight, or within the range of any two of these contents. The invention finds that the initiator has limited solvent capacity in the oil phase solvent, and the uniformity of an oil phase system can be influenced by the high content of the initiator. The content of the crosslinking agent may be 0.02 to 0.3 wt%, preferably 0.06 to 0.175 wt%, more preferably 0.1 to 0.175 wt%, based on the total mass of the oil phase solution, and may be, for example, 0.06 wt%, 0.08 wt%, 0.1 wt%, 0.11 wt%, 0.12 wt%, 0.15 wt%, 0.175 wt%, or a range consisting of any two of these contents. The invention discovers that the content of the cross-linking agent is too high, which can cause the reaction product of the N-vinyl pyrrolidone and the cross-linking agent to have too high molecular weight and to easily agglomerate on the surface of the separation layer, and the content is too low, which can cause the conversion rate of the side reaction product of the polyvinylpyrrolidone (PVP) to increase. Therefore, the composite desalting layer of the invention comprises a product with a network structure formed by the reaction of N-vinyl pyrrolidone and a cross-linking agent, and is not linear PVP. The solvent of the oil phase solution can be one or more of n-hexane, cyclohexane, pentane, isoparaffin and the like. Examples of isoparaffins include the isoparaffin Isopar G and the isoparaffin Isopar E. In some embodiments, the oil phase solution contains or consists of a polybasic acid chloride, N-vinylpyrrolidone, initiator, crosslinker and solvent. A homogeneous oil phase solution can be obtained by mixing the components of the oil phase solution. The temperature of the oil phase solution is preferably controlled to 20 to 40 ℃ when it is contacted with the oil phase solution.
In the step (2), the contact time of the basement membrane obtained in the step (1) after contacting the aqueous phase solution and the oil phase solution may be 5 to 150s, preferably 10 to 120s, for example, 10s, 20s, 30s, 60s, 70s, 90s, or within the range of any two of these compositions. The base film may be contacted with the oil phase solution by immersing the base film in the oil phase solution.
In step (3), the heat treatment has a meaning known in the art and is an operation of holding the film at a certain temperature for a certain period of time. The heat treatment temperature may be 40 to 120 ℃, preferably 50 to 100 ℃, and for example, may be 50 ℃, 80 ℃, 90 ℃, 95 ℃, 100 ℃ or in the range of any two of these temperatures. The heat treatment time may be 5 to 300s, preferably 10 to 240s, and may be, for example, 10s, 30s, 45s, 60s, 120s, 240s or within a range of any two of these compositions. The invention discovers that the hollow fiber membrane has large specific surface area, overhigh temperature or overlong heat treatment time, and is easy to cause the collapse of the membrane silk structure. After heat treatment, a composite membrane, namely the primarily crosslinked hollow fiber nanofiltration membrane is obtained.
According to the invention, N-vinylpyrrolidone, an initiator and a cross-linking agent are added into an oil phase solution, and the N-vinylpyrrolidone and the cross-linking agent remained in the oil phase in a desalting layer in the heat treatment process are subjected to primary cross-linking under the action of the initiator. In the post-treatment process, N-vinylpyrrolidone, an initiator and a cross-linking agent in the desalting layer are slowly separated out, and under the action of inorganic salt anions in post-treatment liquid, the N-vinylpyrrolidone and the cross-linking agent further react with the surface of the desalting layer in the desalting layer to generate a water-insoluble N-vinylpyrrolidone cross-linked product, and finally a modified layer (namely a composite desalting layer) is formed. It is understood that, since the polybasic acid chloride, the N-vinylpyrrolidone, the initiator and the crosslinking agent are present together in the oil phase solution, when the polybasic acid chloride in the oil phase solution and the polyamine in the aqueous phase solution undergo interfacial polymerization to form the polyamide, the N-vinylpyrrolidone, the initiator and the crosslinking agent remain inside and on the surface of the polyamide network, and the N-vinylpyrrolidone and the crosslinking agent undergo crosslinking reaction inside and on the surface of the polyamide network under the action of the initiator during the heat treatment and the post-treatment, the reaction product of the N-vinylpyrrolidone and the crosslinking agent in the present invention exists inside and on the surface of the polyamide.
The step (4) is a post-treatment step. And (3) in the post-treatment process, contacting the composite membrane obtained in the step (3) with post-treatment liquid. In the present invention, the post-treatment liquid is an aqueous solution of an inorganic salt. The inorganic salt suitable for the present invention may be one or more selected from water-soluble sulfate and monohydrogen phosphate. Examples of the sulfate include sodium sulfate. Examples of the monohydrogen phosphate include disodium hydrogen phosphate. The invention discovers that sulfate ions or hydrogen phosphate ions can attract surrounding free ion groups, increase effective collision of the reactive free ion groups and promote the crosslinking reaction. The content of the inorganic salt in the aqueous solution of the inorganic salt may be 2 to 30% by weight, preferably 5 to 20% by weight, more preferably 5 to 10% by weight, of the total mass of the aqueous solution of the inorganic salt, and for example, may be 5% by weight, 6% by weight, 8% by weight, 10% by weight, 20% by weight, or within the range of any two of these contents. A uniform post-treatment liquid can be obtained by mixing inorganic salts and water.
In the step (4), the temperature of the post-treatment liquid may be 40 to 90 ℃, preferably 50 to 90 ℃, and for example, may be 50 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃, 90 ℃ or may be in the range of any two of these temperatures. The post-treatment time (i.e. the contact time of the composite membrane with the post-treatment liquid) may be 1 to 10 hours, preferably 2 to 8 hours, for example 2 hours, 4 hours, 5 hours, 6 hours, 8 hours or within the range of any two of these compositions. The post-treatment temperature and the post-treatment time are favorable for the precipitation of the N-vinyl pyrrolidone, the initiator and the cross-linking agent and the formation of a composite desalting layer with high flux and high removal rate. The composite membrane obtained in step (3) may be contacted with the post-treatment liquid in such a manner that the composite membrane is immersed in the post-treatment liquid.
In some embodiments, the composite nanofiltration membrane of the invention is prepared by a process comprising the steps of:
(1) contacting a base membrane (preferably polysulfone hollow fiber base membrane) with an aqueous solution containing 0.1-2.2 wt% of polyamine and 0.1-1.4 wt% of acid absorbent for 50-12s, and removing the excess aqueous phase on the surface of the membrane;
(2) contacting the base film obtained in the step (1) with an oil phase solution containing 0.05-0.4 wt% of polybasic acyl chloride, 0.2-1.2 wt% of N-vinyl pyrrolidone, 0.01-0.07 wt% of initiator and 0.06-0.15 wt% of cross-linking agent for 20-90s, wherein the cross-linking agent is selected from one or more of divinylbenzene, N-methylene bisacrylamide, dimethyl propylene vinyl acetate and the like;
(3) carrying out heat treatment on the base membrane contacted with the oil phase solution at 50-100 ℃ for 30-120s to obtain a primary cross-linked nanofiltration membrane;
(4) and (3) contacting the nanofiltration membrane obtained in the step (3) with an aqueous solution of inorganic salt with the concentration of 5-10 wt% at the temperature of 65-80 ℃ for 4-6h, wherein the inorganic salt is selected from one or more of water-soluble sulfate and monohydrogen phosphate, so as to obtain the composite nanofiltration membrane with a composite desalting layer.
The invention has the following advantages:
(1) the composite desalting layer of the composite nanofiltration membrane consists of polyamide and a network-shaped modified structure formed by the cross-linking reaction of N-vinylpyrrolidone and a cross-linking agent in the polyamide and on the surface of the polyamide, wherein the network-shaped modified structure not only improves the hydrophilic performance of the membrane surface, but also improves the compact structure of the polyamide layer, and increases a water production flow channel.
(2) Due to the existence of a complex network structure, the composite desalting layer improves the deposition effect of the polyamide separation layer on the surface of the base membrane, and is more tightly combined.
(3) The method has the advantages of cheap raw materials, low preparation cost, simple process and easy industrialization.
(4) Compared with the common nanofiltration membrane, the composite nanofiltration membrane with the modified structure formed by the N-vinylpyrrolidone and the cross-linking agent has improved pure water flux and removal rate.
(5) In the prior art by adding TiO to the aqueous phase2The method for improving the flux of the nanofiltration membrane has poor structural consistency of the prepared nanofiltration membrane and is difficult to be widely applied to industrialization because nanoparticles are dispersed unevenly in monomers and are easy to agglomerate. In the prior art, the method for improving the flux of the nanofiltration membrane by oxidizing the nanofiltration membrane by using the oxidant causes damage to the separation layer, so that the service life of the separation layer is lost to a certain extent. Compared with the method for improving the flux of the nanofiltration membrane in the prior art, the method provided by the invention has the advantages that the hydrophilic network structure formed by the reaction of the N-vinylpyrrolidone and the cross-linking agent is introduced into the polyamide desalting layer of the common nanofiltration membrane, so that the flux of the nanofiltration membrane is improved, the structural stability of the desalting layer and the bonding strength of the desalting layer and the base membrane are improved, and the service life of the nanofiltration membrane is not influenced.
The invention also includes the use of the reaction product of N-vinylpyrrolidone and a cross-linking agent to improve flux and/or salt rejection of a nanofiltration membrane. In the use of the present invention, the reaction product of N-vinylpyrrolidone and cross-linker, nanofiltration membrane, is preferably as described in any embodiment herein.
The flux of the composite nanofiltration membrane measured at 25 ℃, pure water and 0.4MPa can reach 27L/(m)2h) Above, 30L/(m)2h) Above, 32L/(m)2h) Above, 35L/(m)2h) Above, 38L/(m)2h) Above, 40L/(m)2h) Above, 42L/(m)2h) The above. The removal rate of the composite nanofiltration membrane measured at 25 ℃ under the pressure of 0.4MPa and with the magnesium sulfate aqueous solution of 2000ppm can reach more than 80%, more than 84%, more than 90%, more than 92% and more than 94%.
In some preferred embodiments, the composite desalting layer of the composite nanofiltration membrane comprises a polyamide and a reaction product of N-vinylpyrrolidone and divinylbenzene, wherein the polyamide is formed by reacting piperazine and trimesoyl chloride. In the embodiments, the flux of the composite nanofiltration membrane measured at 25 ℃, pure water and 0.4MPa can reach 30L/(m)2h) Above or 32L/(m)2h) The removal rate can reach over 84 percent when measured at 25 ℃, 2000ppm magnesium sulfate aqueous solution and 0.4 MPa. Compared with m-phenylenediamine, the desalting layer prepared by using piperazine as a polyamine monomer has higher flux.
In some preferred embodiments, the composite desalination layer of the composite nanofiltration membrane comprises polyamide and a reaction product of N-vinylpyrrolidone and divinylbenzene, the polyamide is formed by reacting piperazine and trimesoyl chloride, and the content of N-vinylpyrrolidone in the oil phase solution used for preparing the composite desalination layer is 0.5 to 1.5 wt%, for example 0.5 to 1.2 wt%, based on the total mass of the oil phase solution. In the embodiments, the flux of the composite nanofiltration membrane measured at 25 ℃, pure water and 0.4MPa can reach 30L/(m)2h) Above or 32L/(m)2h) The removal rate can reach more than 90 percent when measured at 25 ℃, 2000ppm magnesium sulfate aqueous solution and 0.4 MPa. The content of the N-vinyl pyrrolidone in the oil phase solution is controlled to be 0.5-1.5 wt% of the total mass of the oil phase solution, and the removal rate of the nanofiltration membrane is improved. If the content of the N-vinyl pyrrolidone in the oil phase solution is too low, the molecular weight of the reticular hydrophilic substance generated by the reaction is low, and a loss risk exists in the using process, so that the desalting layer has defects and the removal rate is low.
In some preferred embodiments, the composite desalting layer of the composite nanofiltration membrane comprises polyamide and a reaction product of N-vinylpyrrolidone and divinylbenzene, wherein the polyamide is formed by reacting piperazine and trimesoyl chloride, and the N-vinylpyridine in the oil phase solution for preparing the composite desalting layerThe pyrrolidone is present in an amount of 0.5 to 1.5 wt%, such as 0.5 to 1.2 wt%, 1.0 wt%, the polybasic acid chloride is present in an amount of 0.05 to 0.2 wt%, such as 0.1 to 0.15 wt%, and the crosslinking agent is present in an amount of 0.1 to 0.175 wt%, such as 0.1 to 0.15 wt%, 0.12 wt%, based on the total mass of the oil phase solution. In the embodiments, the flux of the composite nanofiltration membrane measured at 25 ℃, pure water and 0.4MPa can reach 40L/(m)2h) Above or 42L/(m)2h) The removal rate can reach more than 90 percent or more than 92 percent at 25 ℃ and under the conditions of 2000ppm magnesium sulfate aqueous solution and 0.4 MPa. The content of the polyacyl chloride is controlled to be 0.05-0.2 wt% of the total mass of the oil phase solution, so that the prepared nanofiltration membrane desalination layer is relatively thin in thickness, small in water production resistance and large in flux. The content of the cross-linking agent is controlled to be 0.1-0.175 wt% of the total mass of the oil phase solution, which is beneficial to improving the removal rate of the nanofiltration membrane. If the content of the cross-linking agent in the oil phase solution is too low, the molecular weight of the vinylpyrrolidone cross-linked product is relatively low, and a loss risk exists in the use process, so that a desalting layer has defects and the removal rate is low.
In a further preferred embodiment, the composite nanofiltration membrane of the invention has a volume of 40L/(m) measured at 25 ℃, pure water, 0.4MPa2h) Above or 42L/(m)2h) The flux is more than 90% or more than 92% measured at 25 ℃, 2000ppm magnesium sulfate aqueous solution and 0.4MPa, and the composite nanofiltration membrane is prepared by the method comprising the following steps:
(1) contacting the polysulfone hollow fiber-based membrane with an aqueous solution containing 0.5 + -0.05 wt% of piperazine and 0.5 + -0.05 wt% of an acid absorbent (such as sodium carbonate) for 60 + -10 s, and removing the excess aqueous phase on the surface of the membrane;
(2) contacting the base film treated in the step (1) with an oil phase solution containing 0.1 +/-0.01 wt% of trimesoyl chloride, 1.0 +/-0.1 wt% of N-vinyl pyrrolidone, 0.01-0.02 wt% of an initiator (such as azobisisobutyronitrile) and 0.12 +/-0.02 wt% of divinylbenzene for 30 +/-5 seconds;
(3) carrying out heat treatment on the basement membrane contacted with the oil phase solution at the temperature of 80 +/-10 ℃ for 120 +/-20 s;
(4) and (3) contacting the nanofiltration membrane treated in the step (3) with an aqueous solution of inorganic salt (such as sulfate and sodium sulfate) with the concentration of 5-10 wt% at 70 +/-10 ℃ for 6 +/-1 h.
In other preferred embodiments, the composite desalting layer of the composite nanofiltration membrane comprises polyamide and a reaction product of N-vinylpyrrolidone and N, N-methylenebisacrylamide, wherein the polyamide is prepared by reacting m-phenylenediamine and trimesoyl chloride. In the embodiments, the flux of the composite nanofiltration membrane measured at 25 ℃, pure water and 0.4MPa can reach 27L/(m)2h) The removal rate can reach more than 94 percent when measured at 25 ℃, 2000ppm magnesium sulfate aqueous solution and 0.4 MPa.
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, disc and tube flat membrane modules, and the like. The device can be used for example as a household/commercial nanofiltration water purifier, an industrial boiler feed water nanofiltration device, an industrial reclaimed water reuse nanofiltration device and the like. The water treatment method may be, for example, a method for producing drinking water, recycling waste water, concentrating a beverage, or the like.
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. The polysulfone hollow fiber base membrane used in the examples has a pore diameter of 20-50nm, an inner/outer diameter of 0.35/0.55mm, and a pure water flux of 350L/(m) at 25 ℃ and 0.1MPa2·h)。
The following test methods were used in the examples and comparative examples:
(1) pure water flux: measuring flux of the nanofiltration membrane at 25 ℃ and pure water under 0.4 MPa;
flux (F): under certain operating conditions, the volume (V) of water per unit time (t) that passes through the active membrane area (S) is expressed as L/(m)2H), the specific calculation formula is as follows:
Figure BDA0002836638970000151
(2) magnesium sulfate removal rate: measuring the removal rate of the nanofiltration membrane at 25 ℃ and 2000ppm of magnesium sulfate aqueous solution under 0.4 MPa;
removal rate (R): feed solution solute concentration (C) under certain operating conditionsf) With the concentration of solute (C) in the permeatep) The ratio of the difference to the feed solution solute concentration. The specific calculation formula is as follows:
Figure BDA0002836638970000152
example 1
(1) An aqueous solution containing 0.5 wt% piperazine and 0.5 wt% sodium carbonate was prepared. And (3) immersing the polysulfone hollow fiber base membrane into the aqueous phase solution for 60s, and draining water drops on the surface of the membrane.
(2) An oil phase solution containing 0.1 wt% of trimesoyl chloride, 1.0 wt% of N-vinylpyrrolidone, 0.01 wt% of azobisisobutyronitrile and 0.12 wt% of divinylbenzene was prepared, and the organic solvent was cyclohexane. And (2) soaking the basement membrane treated by the aqueous phase solution in the step (1) in the oil phase solution for 30 s.
(3) And (3) placing the composite membrane obtained in the step (2) in an oven with the temperature of 80 ℃ for heat treatment for 120 s.
(4) And (4) soaking the composite membrane obtained in the step (3) in a 5 wt% sodium sulfate aqueous solution at 70 ℃ for 6h, taking out to obtain the hollow fiber composite nanofiltration membrane with the composite desalting layer, and washing with pure water to be tested.
(5) After the hollow fiber composite nanofiltration membrane is tested, the pure water flux is 42.3L/(m) under 0.4MPa2h) For 2000ppm ofThe removal rate of the magnesium sulfate aqueous solution was 92.2%.
Example 2
(1) An aqueous solution containing 1.5 wt% piperazine and 0.7 wt% sodium phosphate was prepared. And (3) immersing the polysulfone hollow fiber base membrane into the aqueous phase solution for 90s, and draining water drops on the surface of the membrane.
(2) An oil phase solution containing 0.2 wt% of trimesoyl chloride, 0.5 wt% of N-vinylpyrrolidone, 0.05 wt% of azobisisobutyronitrile and 0.06 wt% of divinylbenzene was prepared, and the organic solvent was N-hexane. And (2) soaking the basement membrane treated by the aqueous phase solution in the step (1) in the oil phase solution for 60 s.
(3) And (3) placing the composite film obtained in the step (2) in an oven with the temperature of 100 ℃ for heat treatment for 60 s.
(4) And (4) soaking the composite membrane obtained in the step (3) in a 5 wt% disodium hydrogen phosphate aqueous solution at 65 ℃ for 4h, taking out to obtain the hollow fiber composite nanofiltration membrane with the composite desalting layer, and washing with pure water to be tested.
(5) After the hollow fiber composite nanofiltration membrane is tested, the pure water flux is 32.6L/(m) under 0.4MPa2h) The removal rate of the 2000ppm magnesium sulfate aqueous solution was 90.1%.
Example 3
(1) An aqueous solution containing 2.2 wt% of m-phenylenediamine and 0.5 wt% of triethylamine was prepared. And (3) immersing the polysulfone hollow fiber base membrane into the aqueous phase solution for 120s, and draining water drops on the surface of the membrane.
(2) Preparing an oil phase solution containing 0.05 wt% of trimesoyl chloride, 0.8 wt% of N-vinyl pyrrolidone, 0.025 wt% of azodiisobutyronitrile and 0.08 wt% of N, N-methylenebisacrylamide, wherein the organic solvent is N-hexane. And (2) soaking the basement membrane treated by the aqueous phase solution in the step (1) in the oil phase solution for 20 s.
(3) And (3) placing the composite film obtained in the step (2) in an oven with the temperature of 50 ℃ for heat treatment for 120 s.
(4) And (4) soaking the composite membrane obtained in the step (3) in a 10 wt% sodium sulfate aqueous solution at 75 ℃ for 5h, then taking out to obtain the hollow fiber composite nanofiltration membrane with the composite desalting layer, and washing with pure water to be tested.
(5) After the hollow fiber composite nanofiltration membrane is tested, the pure water flux is 0.4MPaIs 27.5L/(m)2h) The removal rate of the 2000ppm magnesium sulfate aqueous solution was 94.7%.
Example 4
(1) An aqueous solution containing 1.2 wt% piperazine and 1.4 wt% sodium hydroxide was prepared. And (3) immersing the polysulfone hollow fiber base membrane into the aqueous phase solution for 50s, and draining water drops on the surface of the membrane.
(2) An oil phase solution containing 0.23 wt% of trimesoyl chloride, 0.2 wt% of N-vinylpyrrolidone, 0.02 wt% of azobisisobutyronitrile and 0.11 wt% of divinylbenzene was prepared, and the organic solvent was cyclohexane. And (2) soaking the basement membrane treated by the aqueous phase solution in the step (1) in the oil phase solution for 70 s.
(3) And (3) placing the composite membrane obtained in the step (2) in an oven with the temperature of 90 ℃ for heat treatment for 30 s.
(4) And (4) soaking the composite nanofiltration membrane obtained in the step (3) in an 8 wt% sodium sulfate aqueous solution at 80 ℃ for 6h, then taking out the composite nanofiltration membrane to obtain the hollow fiber composite nanofiltration membrane with the composite desalination layer, and washing the hollow fiber composite nanofiltration membrane with pure water to be tested.
(5) After the hollow fiber composite nanofiltration membrane is tested, the pure water flux is 38.4L/(m) under 0.4MPa2h) The removal rate of the 2000ppm magnesium sulfate aqueous solution was 84.7%.
Example 5
(1) An aqueous solution containing 0.1 wt% piperazine and 0.1 wt% sodium hydroxide was prepared. And (3) immersing the polysulfone hollow fiber base membrane into the aqueous phase solution for 50s, and draining water drops on the surface of the membrane.
(2) An oil phase solution containing 0.4 wt% of trimesoyl chloride, 1.2 wt% of N-vinylpyrrolidone, 0.07 wt% of azobisisobutyronitrile and 0.15 wt% of divinylbenzene was prepared, and the organic solvent was cyclohexane. And (2) soaking the basement membrane treated by the water phase solution in the step (1) in the oil phase solution for 90 s.
(3) And (3) placing the composite membrane obtained in the step (2) in an oven with the temperature of 95 ℃ for heat treatment for 45 s.
(4) And (4) soaking the composite nanofiltration membrane obtained in the step (3) in a 6 wt% disodium hydrogen phosphate aqueous solution at 75 ℃ for 6h, taking out the composite nanofiltration membrane to obtain the hollow fiber composite nanofiltration membrane with the composite desalting layer, and washing with pure water to be tested.
(5) Hollow fiber composite nanofiltration membraneAfter the test, the pure water flux at 0.4MPa is 32.9L/(m)2h) The removal rate of the 2000ppm magnesium sulfate aqueous solution was 92.1%.
Comparative example 1
(1) An aqueous solution containing 0.5 wt% piperazine and 0.5 wt% sodium carbonate was prepared. And (3) immersing the polysulfone hollow fiber base membrane into the aqueous phase solution for 60s, and draining water drops on the surface of the membrane.
(2) Preparing oil phase solution containing 0.1 wt% of trimesoyl chloride, and the organic solvent is cyclohexane. And (2) soaking the basement membrane treated by the aqueous phase solution in the step (1) in the oil phase solution for 30 s.
(3) And (3) placing the composite membrane obtained in the step (2) in an oven with the temperature of 80 ℃ for heat treatment for 120s to obtain the hollow fiber nanofiltration membrane, and washing with pure water to be tested.
(4) After the hollow fiber nanofiltration membrane is tested, the pure water flux is 24.2L/(m) under 0.4MPa2h) The removal rate of the 2000ppm magnesium sulfate aqueous solution was 82.2%.
The preparation parameters and performance results of examples 1-5 and comparative example 1 are shown in table 1.
Table 1: preparation parameters and Performance results for examples 1-5 and comparative example 1
Figure BDA0002836638970000181
As can be seen from the examples and the comparative example 1, compared with the common nanofiltration membrane, the composite nanofiltration membrane provided by the invention has significantly improved flux and removal rate. The composite nanofiltration membrane of the embodiment has higher flux and removal rate, because the oil phase solution used in the preparation of the composite nanofiltration membrane of the embodiment contains N-vinylpyrrolidone, an initiator and a cross-linking agent, the desalination layer of the composite nanofiltration membrane of the embodiment contains a hydrophilic network structure formed by the reaction of the N-vinylpyrrolidone and the cross-linking agent, the hydrophilic network structure improves the hydrophilic performance of the membrane surface, increases the water production flow channel, improves the flux of the nanofiltration membrane, and improves the deposition effect of a polyamide separation layer on the surface of a base membrane by the hydrophilic network structure, thereby improving the removal rate; the oil phase solution used in the preparation of the composite nanofiltration membrane of comparative example 1 does not contain N-vinylpyrrolidone, an initiator and a crosslinking agent, and thus the desalting layer of the composite nanofiltration membrane of comparative example 1 does not contain the hydrophilic network structure, and the above effects cannot be obtained. Moreover, as can be seen from examples 1 to 5, the composite nanofiltration membrane of the present invention has excellent overall performance, and can have excellent removal rate while maintaining good flux, or can have excellent flux while maintaining good removal rate. Compared with the example 2, the oil phase solution in the example 1 has higher content of the cross-linking agent, the molecular weight of the vinyl pyrrolidone cross-linking product is relatively higher, the loss risk in the use process is lower, and the removal rate is higher. Compared with the embodiment 3, the embodiment 1 uses the piperazine as the polyamine monomer, and the generated desalting layer has lower compactness and obviously improved flux. Compared with the embodiment 4, the oil phase solution in the embodiment 1 has higher content of N-vinyl pyrrolidone, the molecular weight of the reticular hydrophilic substance generated by the reaction is higher, the loss risk in the use process is lower, and the desalting layer removal rate is higher. Compared with the embodiment 5, the oil phase solution in the embodiment 1 has lower polybasic acyl chloride concentration, and the prepared nanofiltration membrane has relatively thinner desalination layer thickness, small water production resistance and larger flux.

Claims (11)

1. The composite nanofiltration membrane comprises a base membrane and a composite desalting layer formed on the base membrane, wherein the composite desalting layer comprises polyamide and a reaction product of N-vinylpyrrolidone and a crosslinking agent.
2. The composite nanofiltration membrane of claim 1, wherein the composite nanofiltration membrane has one or more of the following characteristics:
the reaction product of the N-vinylpyrrolidone and the crosslinking agent has a network structure;
the reaction product of the N-vinylpyrrolidone and the crosslinking agent is present both inside and on the surface of the polyamide; and
the base membrane is a polysulfone hollow fiber base membrane.
3. The composite nanofiltration membrane according to claim 1, wherein the polyamide is formed by reacting a polyamine and a polyacyl chloride;
preferably, the polyamine is selected from one or more of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3, 5-triaminobenzene, 1,2, 4-triaminobenzene, 2, 4-diaminotoluene, 2, 6-diaminotoluene, 1, 3-diaminocyclohexane, 1, 2-diaminocyclohexane, 1, 4-diaminocyclohexane, piperazine, 2, 5-dimethylpiperazine and 4-aminomethylpiperazine, preferably from one or two of piperazine and m-phenylenediamine;
preferably, the polybasic acid chloride is selected from one or more of trimesoyl chloride, pyromellitic chloride, phthalic chloride, terephthaloyl chloride, isophthaloyl chloride, cyclohexanetetracarboxylic acid chloride, cyclohexanetricarboxylic acid chloride, cyclohexanecarboxoyl chloride, tetrahydrofuranetetracarboxylic acid chloride, tetrahydrofuranetricarboxylic acid chloride and tetrahydrofuranedicarboxylic acid chloride, and is preferably trimesoyl chloride.
4. The composite nanofiltration membrane of claim 1, wherein the cross-linking agent is selected from one or more of divinylbenzene, N-methylenebisacrylamide, and dimethylacrylacetylvinyl acetate.
5. Method for the preparation of a composite nanofiltration membrane according to any one of claims 1 to 4, comprising the steps of:
(1) contacting the base film with an aqueous solution containing a polyamine;
(2) contacting the basement membrane contacted with the water phase solution in the step (1) with an oil phase solution containing polyacyl chloride, N-vinyl pyrrolidone, an initiator and a cross-linking agent;
(3) carrying out heat treatment on the base film contacted with the oil phase solution in the step (2) to obtain a composite film;
(4) and (4) contacting the composite membrane in the step (3) with an aqueous solution of inorganic salt to obtain the composite nanofiltration membrane.
6. The method of claim 5,
in the aqueous phase solution, the content of the polyamine is 0.05-5 wt%, preferably 0.5-2.5 wt% of the total mass of the aqueous phase solution; and/or
The aqueous phase solution contains an acid absorbent; preferably, the acid absorbent is selected from one or more of sodium carbonate, sodium phosphate, triethylamine, sodium hydroxide and potassium hydroxide; preferably, the content of the acid absorbent in the aqueous phase solution is 0.05-5 wt% of the total mass of the aqueous phase solution.
7. The method of claim 5, wherein the method has one or more of the following features:
in the oil phase solution, the content of the polyacyl chloride is 0.02-1 wt%, preferably 0.05-0.4 wt% of the total mass of the oil phase solution;
in the oil phase solution, the content of N-vinyl pyrrolidone is 0.05-3 wt%, preferably 0.1-1.5 wt% of the total mass of the oil phase solution;
the solvent of the oil phase solution is selected from one or more of n-hexane, cyclohexane, pentane and isoparaffin;
the initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptonitrile and dibenzoyl peroxide;
in the oil phase solution, the content of the initiator is 0.005-0.3 wt%, preferably 0.01-0.1 wt% of the total mass of the oil phase solution; and
in the oil phase solution, the content of the cross-linking agent is 0.02-0.3 wt%, preferably 0.06-0.175 wt% of the total mass of the oil phase solution.
8. The method of claim 5,
the inorganic salt is selected from one or more of water-soluble sulfate and water-soluble monohydrogen phosphate, such as one or two of sodium sulfate and disodium hydrogen phosphate; and/or
The content of the inorganic salt in the aqueous solution of the inorganic salt is 2 to 30 wt%, preferably 5 to 20 wt% of the total mass of the aqueous solution of the inorganic salt.
9. The method of claim 5, wherein the method has one or more of the following features:
in the step (1), the contact time with the aqueous phase solution is 10-250 s;
in the step (2), the contact time of the solution and the oil phase solution is 5-150 s;
in the step (3), the heat treatment temperature is 40-120 ℃, and the heat treatment time is 5-300 s; and
in the step (4), the temperature of the aqueous solution of the inorganic salt is 40-90 ℃, and the contact time of the aqueous solution of the inorganic salt and the aqueous solution of the inorganic salt is 1-10 h.
10. Use of a composite nanofiltration membrane according to any one of claims 1 to 4 or prepared by the method according to any one of claims 5 to 9 in a water treatment process or a water treatment assembly or apparatus.
Use of the reaction product of N-vinylpyrrolidone and a cross-linking agent to improve the flux and/or salt rejection of a nanofiltration membrane;
preferably, the crosslinking agent is selected from one or more of divinylbenzene, N-methylenebisacrylamide and dimethylacrylacetylvinyl acetate;
preferably, the reaction product of the N-vinylpyrrolidone and the crosslinking agent has a network-like structure;
preferably, the nanofiltration membrane has a desalting layer containing polyamide, and the reaction product of the N-vinylpyrrolidone and the crosslinking agent is present in the interior and on the surface of the polyamide.
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