CN114642971B - Preparation method of nanofiltration membrane and nanofiltration membrane prepared by same - Google Patents

Preparation method of nanofiltration membrane and nanofiltration membrane prepared by same Download PDF

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CN114642971B
CN114642971B CN202011499516.7A CN202011499516A CN114642971B CN 114642971 B CN114642971 B CN 114642971B CN 202011499516 A CN202011499516 A CN 202011499516A CN 114642971 B CN114642971 B CN 114642971B
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nanofiltration membrane
membrane
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CN114642971A (en
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王兵辉
梁松苗
胡利杰
张佳佳
刘忠操
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Wharton 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
    • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
    • 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
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/56—Polyamides, e.g. polyester-amides
    • 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
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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    • C02F2101/30—Organic compounds
    • C02F2101/308—Dyes; Colorants; Fluorescent agents
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    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/30—Organic compounds
    • C02F2101/34—Organic compounds containing oxygen
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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    • C02F2101/00—Nature of the contaminant
    • C02F2101/30—Organic compounds
    • C02F2101/36—Organic compounds containing halogen
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
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Abstract

The invention relates to a preparation method of a nanofiltration membrane and the nanofiltration membrane prepared by the method. The nanofiltration membrane prepared by the preparation method disclosed by the invention has excellent tolerance in a strong-polarity organic solvent, can stably run for a long time, and can keep the high flux and excellent interception effect of the nanofiltration membrane.

Description

Preparation method of nanofiltration membrane and nanofiltration membrane prepared by same
Technical Field
The invention relates to the technical field of nanofiltration membranes, in particular to a preparation method of a nanofiltration membrane and the nanofiltration membrane prepared by the preparation method. The nanofiltration membrane prepared by the preparation method disclosed by the invention has excellent tolerance in a strong polar organic solvent, can stably run for a long time, and can keep high flux and excellent interception effect of the nanofiltration membrane.
Background
The solvent-resistant nanofiltration membrane has the advantages of high selectivity, greenness, high efficiency, simple and convenient operation and the like in an organic solvent, so that the solvent-resistant nanofiltration membrane has great potential application value in the fields of petrochemical industry, biomedicine, food and beverage and the like. According to statistics, the organic solvents used in China are thousands of in variety, however, the most important problem at present is that separation membranes which can keep thermochemical stability, high flux and high rejection rate in the face of various complex organic solvents are seriously insufficient, and as most of the organic solvent systems are involved in the actual industrial process and the traditional nanofiltration membranes are difficult to be expanded to be used in nonaqueous solution systems, the development of the nanofiltration technology to the organic solvent systems in a solvent-resistant nanofiltration manner is an important challenge at present.
The solvent-resistant nanofiltration technology has many advantages, can effectively separate required solutes or recover solvents, can reduce energy consumption, can alleviate related environmental problems, has great development potential in the fields of solvent recovery in chemical industry, municipal engineering sewage treatment, chemical pharmacy, food safety, petroleum refining and the like, and is extremely important for widening the application of nanofiltration process for further researching and developing solvent-resistant nanofiltration membranes.
The majority of the Harbin industry adopts trihydroxymethyl aminomethane to graft polyimide nanofiltration membrane, and adopts active amine to crosslink the obtained membrane, so as to obtain the modified polyimide solvent-resistant nanofiltration membrane. Along with the increase of the dosage of the tris (hydroxymethyl) aminomethane from 5% to 20%, the water contact angle of the modified membrane is reduced from 54 degrees to 46 degrees, the structural morphology of the membrane is improved, the hydrophilicity of the membrane is improved, and the retention rate of rose bengal is kept at 95%.
In patent document CN102019149A, polyisobutylene is added into an organic phase containing trimesoyl chloride, and a modified polyamide layer is prepared on a polyimide support membrane through an interfacial polymerization reaction, the nanofiltration membrane prepared by the method has good solvent resistance and high flux, the removal rate of sodium chloride is 50-60%, the removal rate of sodium sulfate is more than 97%, and the separation effect on an ethanol-water solution system is special.
In patent document CN104437141A, fluorosilicone oil, a cross-linking agent and a catalyst are dissolved in a solvent to prepare a casting solution, and after coating and curing, cross-linking is performed at a certain temperature, and the prepared fluorosilicone rubber solvent-resistant nanofiltration membrane is used for recovering hexane from soybean oil/hexane mixed oil, has excellent separation performance, breaks through the defect that common silicone rubber is not resistant to organic solvents, has excellent swelling resistance and long-term operation stability, and has a maximum retention rate of soybean oil of 98.6%.
From research results of scholars in related fields, the existing solvent-resistant membrane technology can only be selectively applied to a specific organic solvent system with weak polarity, but has poor tolerance to high-concentration protic solvents with strong polarity, such as N, N-Dimethylformamide (DMF), N-methylpyrrolidone (NMP) and the like, and a base layer and a surface functional layer of a membrane element are easy to swell and even dissolve in the solvent, so that the phenomena of poor solvent resistance, poor operation stability and the like are caused, and the application space is greatly limited.
The interception rate of the nanofiltration membrane can be obviously improved only by crosslinking the functional layer or the supporting layer, however, the flux loss is large, the interception rate and the flux cannot be effectively considered, the long-term operation stability cannot be guaranteed, and the feasibility method which meets the industrial production and requires that the supporting layer and the functional layer have high tolerance at the same time is not enough.
The current research mainly focuses on the modification of membrane materials and the synthesis of novel solvent-resistant membrane materials, and the scientific rules in the synthesis, preparation and application of the membrane materials are not sufficiently mastered, so that the flux and interception performance are difficult to achieve excellent balance effects and the like.
Disclosure of Invention
Problems to be solved by the invention
The invention aims to solve the problem that a supporting layer and a functional layer of a nanofiltration membrane are easy to swell and even dissolve in an organic solvent, break through the problem of poor interface interaction between the supporting layer and the functional layer, and develop a high-performance nanofiltration membrane which can stably run for a long time in different use environments such as strong-polarity organic solvents including polar aprotic solvents, polar protic solvents and the like.
Means for solving the problems
The inventors of the present invention have made extensive studies to achieve the above object and have found that:
(1) By adding the nano particles into the membrane casting solution, the structural morphology of a supporting layer (also called a base membrane) can be improved, the porosity and the hydrophilicity of the base membrane are improved, and the apparent strength and the flux of the nanofiltration membrane can be enhanced by establishing an ordered water channel by utilizing the properties and the structural characteristics of the nano particles;
(2) By introducing a novel functional layer (also called a desalting layer and a separating layer) imidization system containing anhydride substances and tertiary amine substances and a cross-linking type diamine micromolecule monomer, the formation of a cross-linking network structure of a supporting layer and the functional layer is promoted, the bonding force between the supporting layer and the functional layer is enhanced, and a polyamide nanofiltration membrane with excellent solvent resistance is obtained, wherein the polyamide nanofiltration membrane is fully cross-linked inside the supporting layer, between the supporting layer and the functional layer and inside the functional layer (also called a full cross-linking type), so that the polyamide nanofiltration membrane has long-term strong tolerance in strong-polarity organic solvents such as N-methylpyrrolidone (NMP), N-Dimethylformamide (DMF) and the like.
The invention provides a preparation method of a nanofiltration membrane, which comprises the following steps:
preparing a membrane casting solution, and coating the membrane casting solution on a non-woven fabric to form a base membrane, wherein the membrane casting solution comprises a polymer, a solvent and nanoparticles;
sequentially contacting the base film with an aqueous phase solution containing an amine monomer and an organic phase solution containing an acid chloride monomer to form a polyamide functional layer on the base film;
treating with a solution containing a diamine substance having 2 to 5 carbon atoms to crosslink the inside of the base film;
imidizing a polyamide functional layer by treating with a solution containing an acid anhydride-based substance and a tertiary amine-based substance;
treating with a solution containing a diamine substance having 6 to 10 carbon atoms to crosslink between the base film and the polyamide functional layer and to crosslink inside the polyamide functional layer;
and carrying out post-treatment and drying to obtain the nanofiltration membrane.
The preparation method of the nanofiltration membrane comprises the following steps of (1) preparing a polymer, wherein the polymer is at least one of polyimide, polyethyleneimine, sulfonated polyethyleneimine, polyamideimide and biphenyl polyaryletherketone modified bismaleimide; preferably, the mass percentage concentration of the polymer is 12-22% based on the total mass of the casting solution.
The preparation method of the nanofiltration membrane comprises the following steps of preparing nano-particles, wherein the nano-particles are at least one of nano-silica particles, graphene particles, carbon nano-tube particles, nano-molecular sieve particles, nano-titania particles, montmorillonite particles and metal organic framework material MOF particles; preferably, the nanoparticles are modified by a silane coupling agent, and the particle size of the nanoparticles is in the range of 50nm to 300 nm; preferably, the mass percentage concentration of the nanoparticles is 0.1-5% based on the total mass of the casting solution.
The preparation method of the nanofiltration membrane comprises the following steps of (1) enabling the amine monomer to be at least one of aromatic amine monomers with 6-12 carbon atoms; preferably, the mass percentage concentration of the amine monomer is 0.2-5.0%, preferably 0.5-3.0%, based on the total mass of the aqueous phase solution; preferably, the hydrogen atom on the aromatic ring of the amine monomer is substituted by a fluorinated alkyl group having 1 to 3 carbon atoms.
The preparation method of the nanofiltration membrane comprises the following steps of preparing an acyl chloride monomer, wherein the acyl chloride monomer is at least one of trimesoyl chloride, phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, 4' -diacyl chloride diphenyl ether, 2, 6-naphthaloyl chloride and 1, 8-naphthaloyl chloride; preferably, the concentration of the acid chloride monomer is 0.02 to 1.0% by mass, more preferably 0.05 to 0.75% by mass, based on the total mass of the organic phase solution.
The preparation method of the nanofiltration membrane comprises the following steps of preparing a nanofiltration membrane, wherein the diamine substance with the carbon number of 2-5 is at least one of ethylenediamine, 1, 2-propanediamine, 1, 3-propanediamine, 2' -dimethyl-1, 3-propanediamine, butanediamine, N-ethyl-1, 3-propanediamine and pentanediamine; the concentration of the diamine substance with 2 to 5 carbon atoms is 10 to 20 percent, preferably 12 to 18 percent, based on the total mass of the solution containing the diamine substance with 2 to 5 carbon atoms.
The preparation method of the nanofiltration membrane comprises the following steps of (1) preparing an acid anhydride substance, wherein the acid anhydride substance is at least one of pyromellitic dianhydride, 1,2,4, 5-cyclohexane tetracarboxylic anhydride, ethylenediamine tetraacetic dianhydride, 3', 4' -benzophenone tetracarboxylic dianhydride, 1,4,5, 8-naphthalene tetracarboxylic anhydride, 3', 4' -biphenyl tetracarboxylic dianhydride, aliphatic dibasic acid anhydride with 10-16 carbon atoms and aromatic dibasic acid anhydride with 10-16 carbon atoms; preferably, the tertiary amine is at least one of 2, 3-diaminopyridine, triethylamine, quinoline, isoquinoline, β -picoline, 2, 5-diaminopyridine and N, N' -dimethylaniline.
The preparation method of the nanofiltration membrane comprises the following steps that in the solution containing the acid anhydride substances and the tertiary amine substances, the volume ratio of a solvent to the acid anhydride substances to the tertiary amine substances is (1-10).
The preparation method of the nanofiltration membrane comprises the following steps of (1) preparing a C6-10 diamine substance from at least one of 3,3' -diaminodipropylamine, dimethylhexamethylenediamine, trimethylhexamethylenediamine and a C6-10 linear diamine substance; the mass percentage concentration of the diamine substance with 6 to 10 carbon atoms is 15 to 25 percent, preferably 22 to 25 percent based on the total mass of the solution containing the diamine substance with 6 to 10 carbon atoms.
The invention also provides a nanofiltration membrane prepared by the preparation method.
ADVANTAGEOUS EFFECTS OF INVENTION
The nanofiltration membrane prepared by the preparation method provided by the invention has excellent tolerance in a strong polar organic solvent, can stably run for a long time, and can keep high flux and excellent interception effect of the nanofiltration membrane. The nanofiltration membrane prepared by the method is a full-crosslinking nanofiltration membrane, has excellent separation performance, high flux, strong solvent resistance, excellent swelling resistance, high stability in long-time operation, and higher apparent strength and compressive tightness.
Detailed Description
The invention provides a preparation method of a nanofiltration membrane, which comprises the following steps:
preparing a membrane casting solution, and coating the membrane casting solution on a non-woven fabric to form a base membrane, wherein the membrane casting solution comprises a polymer, a solvent and nanoparticles;
sequentially contacting the base film with an aqueous phase solution containing an amine monomer and an organic phase solution containing an acid chloride monomer to form a polyamide functional layer on the base film;
treating with a solution containing a diamine substance having 2 to 5 carbon atoms to crosslink the inside of the base film;
imidizing the polyamide functional layer by treating with a solution containing an acid anhydride-based substance and a tertiary amine-based substance;
treating with a solution containing a diamine substance having 6 to 10 carbon atoms to crosslink between the base film and the polyamide functional layer and to crosslink inside the polyamide functional layer;
and carrying out post-treatment and drying to obtain the nanofiltration membrane.
The preparation method of the nanofiltration membrane comprises the step of preparing a polymer, wherein the polymer is at least one of polyimide, polyethyleneimine, sulfonated polyethyleneimine, polyamideimide and biphenyl polyaryletherketone modified bismaleimide. Preferably, the polyimide is a polyetherimide, a sulfonated polyetherimide.
The solvent in the casting solution is not particularly limited as long as it can sufficiently dissolve the polymer, and preferably, the solvent is at least one of N-methylpyrrolidone, N-dimethylformamide, N-dimethylacetamide, dimethylsulfoxide, tetrahydrofuran, and imidazolidinone.
Preferably, the mass percentage concentration of the polymer is 12-22%, more preferably 15-20%, based on the total mass of the casting solution. When the concentration of the polymer is lower than 12%, the viscosity of the casting solution is low, the thickness of the prepared base film/supporting layer is too thin, the strength is insufficient, the flux is too high, and the use performance is not achieved; when the concentration of the polymer is higher than 22%, the viscosity of the membrane casting solution is higher, the thickness of the prepared base membrane/supporting layer is too thick, and the flux is too low, so that the overall performance of the nanofiltration membrane is not facilitated.
The preparation method of the nanofiltration membrane comprises the following steps of preparing nano-particles, wherein the nano-particles are at least one of nano-silica particles, graphene particles, carbon nano-tube particles, nano-molecular sieve particles, nano-titania particles, montmorillonite particles and metal organic framework material MOF particles. Preferably, the nanoparticles are nanosilica particles. The particle size of the nano-particles is within the range of 50 nm-300 nm.
Preferably, the nanoparticles are modified with a silane coupling agent, the kind of the silane coupling agent is not particularly limited, and specific examples thereof include bis- [3- (triethoxysilyl) propyl ] -tetrasulfide, γ -glycidoxypropyltrimethoxysilane, γ -aminopropyltriethoxysilane, γ - (methacryloyloxy) propyltrimethoxysilane, vinyl- β -methoxyethoxysilane, and the like.
Preferably, the mass percentage concentration of the nanoparticles is 0.1% to 5%, more preferably 1% to 3%, based on the total mass of the casting solution. When the mass percentage concentration of the nano particles is lower than 0.1%, the control on the porosity and the hydrophilicity of the base membrane is not obvious, the flux increase amplitude is not large, and the action effect is limited; when the mass percentage concentration of the nanoparticles is higher than 5%, the structural defects of the nanofiltration membrane are caused by the aggregation of the nanoparticles, so that the desalting effect of the membrane is poor.
The solvent-resistant nanofiltration membrane provided by the invention is based on the improvement of the structure of the prepared composite membrane, and the nanoparticles are added into the membrane casting solution for forming the base membrane so as to adjust the structure and the appearance of the base membrane, improve the porosity and the hydrophilicity of the base membrane, and enhance the apparent strength and the flux of the nanofiltration membrane, thereby effectively solving the problems of poor compression resistance and insufficient flux of the nanofiltration membrane.
The following exemplary list gamma-aminopropyltriethoxysilane as one example of a silane coupling agent and hydrophilic nanosilica modified with a silane coupling agent. The silica particle surface modified by the silane coupling agent has a large number of hydroxyl groups, thereby remarkably improving hydrophilicity.
Figure BDA0002843150620000071
Gamma-aminopropyl triethoxy silane coupling agent modified hydrophilic nano silicon dioxide
In the method for preparing a nanofiltration membrane according to the present invention, the amine monomer is at least one of aromatic amine monomers having 6 to 12 carbon atoms, and specific examples of the amine monomer may include, but are not limited to, 1, 3-phenylenediamine, 1, 2-phenylenediamine, and 4,4' -diaminodiphenyl ether.
Based on the total mass of the aqueous phase solution, the mass percentage concentration of the amine monomer is 0.2-5.0%, preferably 0.5-3.0%; when the mass percentage concentration of the amine monomer is lower than 0.2%, the formed functional layer is insufficient in compactness and poor in desalting effect; when the mass percentage concentration of the amine monomer is higher than 5.0%, the formed functional layer has a high degree of compactness and a high desalination rate, but the flux of the nanofiltration membrane is too low.
Preferably, the hydrogen atom on the aromatic ring of the amine monomer is substituted with a fluorinated alkyl group having 1 to 3 carbon atoms, and specific examples thereof include, but are not limited to, 4-trifluoromethyl-1, 3-phenylenediamine, 5-trifluoromethyl-1, 3-phenylenediamine, 4-trifluoromethyl-1, 2-phenylenediamine, 3, 5-bis (trifluoromethyl) -1, 2-phenylenediamine, 4, 5-bis (trifluoromethyl) -1, 2-phenylenediamine, 3,4, 5-tris (trifluoromethyl) -1, 2-phenylenediamine and the like. By using the fluorine-containing amine monomer, hydrogen bond effect exists between fluorine atoms and water molecules, and a positive induction effect is achieved on the process that the water molecules penetrate through the membrane. By reasonably regulating and controlling the proportion of the fluorine content in the functional layer structure and comprehensively considering the density of the functional layer, the membrane element can achieve the purposes of keeping high flux and high interception.
The preparation method of the nanofiltration membrane comprises the step of preparing a nanofiltration membrane by using an acyl chloride monomer, wherein the acyl chloride monomer is at least one of trimesoyl chloride, phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, 4' -diacyl chloride diphenyl ether, 2, 6-naphthaloyl chloride and 1, 8-naphthaloyl chloride.
Preferably, the concentration of the acid chloride monomer is 0.02 to 1.0% by mass, more preferably 0.05 to 0.75% by mass, based on the total mass of the organic phase solution. When the mass percentage concentration of the acyl chloride monomer is lower than 0.02%, the functional layer/separation layer of the nanofiltration membrane has larger aperture, lower desalination rate and insufficient basic performance; when the mass percentage concentration of the acyl chloride monomer is higher than 1.0%, the flux of the nanofiltration membrane is greatly reduced due to the excessively high degree of crosslinking of the formed functional layer/separation layer, which is not beneficial to practical application.
In the method for preparing the nanofiltration membrane, the diamine substance with the carbon number of 2-5 is at least one of ethylenediamine, 1, 2-propanediamine, 1, 3-propanediamine, 2' -dimethyl-1, 3-propanediamine, butanediamine, N-ethyl-1, 3-propanediamine and pentanediamine, and the ethylenediamine is more preferable.
The concentration of the diamine substance with 2 to 5 carbon atoms is 10 to 20 percent, preferably 12 to 18 percent, based on the total mass of the solution containing the diamine substance with 2 to 5 carbon atoms. When the mass percentage concentration of the diamine substance with the carbon number of 2-5 is lower than 10%, the crosslinking of the supporting layer/the base film is insufficient, the crosslinking degree is low, and the requirement on action effect is not met; when the mass percentage concentration of the diamine substance with the carbon number of 2-5 is higher than 20%, a supporting layer/base film with higher crosslinking degree can be formed, the increase of water flux can be obviously inhibited, and the crosslinking between the supporting layer (base film) and the functional layer in the secondary amination process is not facilitated.
The preparation method of the nanofiltration membrane comprises the following steps of selecting at least one of pyromellitic dianhydride, 1,2,4, 5-cyclohexane tetracarboxylic anhydride, ethylenediamine tetraacetic dianhydride, 3', 4' -benzophenone tetracarboxylic dianhydride, 1,4,5, 8-naphthalene tetracarboxylic anhydride, 3', 4' -biphenyl tetracarboxylic dianhydride, aliphatic dibasic acid anhydride with the carbon number of 10-16 and aromatic dibasic acid anhydride with the carbon number of 10-16 as the acid anhydride; preference is given to 1,2,4, 5-cyclohexanetetracarboxylic anhydride, pyromellitic anhydride.
Preferably, the tertiary amine is at least one of 2, 3-diaminopyridine, triethylamine, quinoline, isoquinoline, β -picoline, 2, 5-diaminopyridine and N, N' -dimethylaniline, preferably triethylamine, 2, 3-diaminopyridine.
The method for preparing the nanofiltration membrane comprises the following steps of (1) in the solution containing the acid anhydride substances and the tertiary amine substances, wherein the volume ratio of the solvent to the acid anhydride substances to the tertiary amine substances is 10.
The preparation method of the nanofiltration membrane comprises the following steps of (1) preparing a C6-10 diamine substance, wherein the C6-10 diamine substance is at least one of 3,3' -diaminodipropylamine, dimethylhexamethylenediamine, trimethylhexamethylenediamine and a C6-10 linear diamine substance; the linear diamine having 6 to 10 carbon atoms includes, for example, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonanediamine, decanediamine, and the like.
Preferably, the concentration of the diamine-based substance having 6 to 10 carbon atoms is 15 to 25% by mass, preferably 22 to 25% by mass, based on the total mass of the solution containing the diamine-based substance having 6 to 10 carbon atoms. When the mass percentage concentration of the diamine substance with the carbon number of 6-10 is lower than 15%, the crosslinking effect between the functional layer (also called a separation layer) and the functional layer and between the functional layer and the support layer (base film) cannot be fully guaranteed, and the resistance of the diamine substance in a polar solvent is insufficient; when the mass percentage concentration of the diamine substance with the carbon number of 6-10 is higher than 25%, the whole structure of the nanofiltration membrane is limited by high crosslinking degree, so that the flux of the membrane is greatly lost, and the higher values of the desalination rate and the flux cannot be effectively considered.
In the preparation method of the nanofiltration membrane, diamine substances with 2-5 carbon atoms are introduced as cross-linked diamine micromolecule monomers and a novel functional layer imidization system containing anhydride substances and tertiary amine substances, so that the formation of a cross-linked network structure of a base membrane and a functional layer is promoted, the binding force of the base membrane and an active separation layer is enhanced, and the phenomena that the functional layer and the base membrane of the nanofiltration membrane are easy to peel and poor in solvent resistance in a strong polar solvent are fully inhibited. In addition, as described above, by using the fluorine-containing amine monomer, hydrogen bonding between the fluorine atom and the water molecule occurs, and a positive induction effect is exerted on the process of the water molecule penetrating the film. By reasonably regulating and controlling the proportion of the fluorine content in the functional layer structure and comprehensively considering the density of the functional layer, the membrane element can achieve the purposes of keeping high flux and high interception.
As a preparation method of the nanofiltration membrane of the present invention, non-limiting examples thereof are as follows:
(1) Preparing a casting solution which takes polyimide with the mass percentage concentration of 15-20% as a solute, coupling agent gamma-aminopropyltriethoxysilane modified nano silicon dioxide (the grain diameter is 50-300 nm) with the mass percentage concentration of 0.5-5% as an additive and N-methyl pyrrolidone (NMP) as a solvent, regulating the pH value to 8.5-9.0, uniformly stirring, filtering, defoaming and blade-coating the casting solution on non-woven fabrics to form a polyimide basement membrane;
(2) Placing the basement membrane into an aqueous solution of a mixture of 5-trifluoromethyl-1, 3-phenylenediamine and 3, 5-bis (trifluoromethyl) aniline with the mass percent concentration of 0.5-3.0%, and immersing for 0.5-3 min; rolling the polyimide base film soaked by the aqueous solution by using a rubber roller, and draining to remove the redundant solvent;
(3) Then immersing the polyimide base membrane treated in the step (2) in an organic phase solution with the mass percent concentration of trimesoyl chloride of 0.05-0.75% and the mass percent concentration of n-hexane of 85-95% for 0.5-3 min, taking out and draining to obtain a PI-PA nanofiltration membrane;
(4) And then, putting the PI-PA nanofiltration membrane into a methanol solution with the mass percentage concentration of ethylenediamine of 15% for amination treatment to complete the crosslinking of the polyimide base membrane (also called a support layer).
(5) Preparing 2000ml of a 1,2,4, 5-cyclohexane tetracarboxylic anhydride and 2, 3-diaminopyridine mixed solution with acetone as a solvent, wherein the volume ratio of the acetone to the 1,2,4, 5-cyclohexane tetracarboxylic anhydride to the 2, 3-diaminopyridine is 1-10.
(6) And (3) immersing the nanofiltration membrane obtained in the step (5) in a methanol solution with the mass percentage concentration of hexamethylene diamine of 20% at the temperature of 60-80 ℃, and fully crosslinking the support layer and the functional layer under the ultrasonic-assisted condition to obtain the full-crosslinking solvent-resistant polyamide nanofiltration membrane.
(7) Activating the fully-crosslinked solvent-resistant polyamide nanofiltration membrane obtained in the step (5) in an aqueous solution with the mass percentage concentration of DMF of 20%, soaking for 30-60 min, and removing non-crosslinked micromolecular monomers;
(8) And then, the nanofiltration membrane is immersed in water for 8 to 12 hours and then taken out, and then immersed in 50 percent lactic acid solution for 12 to 24 hours for hole preservation treatment, and the solution is put into a vacuum oven with the temperature of 60 to 120 ℃ for heat treatment for 48 hours to ensure complete crosslinking.
The invention also provides the nanofiltration membrane prepared by the preparation method, the application field of the nanofiltration membrane is expanded, the technical problem that the traditional nanofiltration membrane is difficult to expand into a non-aqueous solution system is solved, the nanofiltration membrane has excellent tolerance in a strong-polarity organic solvent, excellent flux and interception effects are kept, and guidance and reference are provided for the application of a separation membrane technology in the related industries of separation and purification of organic solvents. The nanofiltration membrane prepared by the invention is a full-crosslinking nanofiltration membrane, has excellent separation performance, high flux, strong solvent resistance, excellent swelling resistance, high stability for long-time operation, and higher apparent strength and compressive tightness.
The fully-crosslinked nanofiltration membrane prepared by the method has excellent solvent resistance, higher flux and selective permeability, high finger-shaped porosity of the base membrane, high density of the surface layer of the nanofiltration membrane, strong hydrophilicity, and expected higher apparent strength and compressive tightness. The retention rates of dyes methyl red (269.3 Da), bromothymol blue (624.4 Da) and rose bengal (1017.6 Da) in methanol solution reach 89%, 95% and 99.9% respectively; soaking in NMP for 90 days, soaking in DMF for 30 days, continuously running in rose bengal/DMF solution for three weeks, retaining rate of rose bengal is still over 99%, and long-term running stability is maintained. Salt solution with conductivity of 2000. Mu.s/cm at 225psi operating conditions, vs. MgSO 4 The interception rate of the sodium chloride is over 98 percent, and the interception rate of the sodium chloride to NaCl reaches over 65 percent. The invention not only has special separation effect on an organic solvent-aqueous solution system, but also shows excellent long-term tolerance on a pure organic solvent system, and can be widely applied to the field of water treatment and the separation industry of organic solvents.
Examples
The technical solution of the present invention is further described in detail with reference to the following examples, but the present invention is not limited thereto. It should be noted that the reagents and raw materials used in the examples of the present invention are commercially available conventional products unless otherwise specified.
Example 1
(1) Preparing a membrane casting solution, wherein the mass percent concentration of polyimide is 15%, the mass percent concentration of gamma-aminopropyltriethoxysilane-modified nano silicon dioxide is 1%, and the solvent is N-methylpyrrolidone, and blade-coating the membrane casting solution on non-woven fabrics to form a polyimide membrane as a base membrane;
(2) Immersing the basement membrane obtained in the step (1) in an aqueous phase solution with the mass percent concentration of 0.8% of amine monomer (wherein the mass percent concentration of 5-trifluoromethyl-1, 3-phenylenediamine is 0.75%, and the mass percent concentration of 3, 5-bis (trifluoromethyl) aniline is 0.05%) for 2min; then immersing the polyimide film in a normal hexane solution with the mass percentage concentration of trimesoyl chloride of 0.1% for 3min to form a polyamide film on the polyimide base film;
(3) Amination treatment is carried out on the base membrane with the polyamide membrane obtained in the step (2) in a methanol solution with the concentration of the ethylene diamine being 15% by mass;
(4) Preparing 2000ml of a mixed solution containing acetone, 1,2,4, 5-cyclohexane tetracarboxylic anhydride and 2, 3-diaminopyridine in a volume ratio of 10;
(5) Immersing the nanofiltration membrane obtained in the step (4) in a methanol solution with the mass percent concentration of hexamethylene diamine of 20% at 75 ℃, and completing secondary crosslinking under the ultrasonic-assisted condition to obtain a full-crosslinking polyamide nanofiltration membrane;
(6) And (3) activating the fully-crosslinked polyamide nanofiltration membrane obtained in the step (5) in an aqueous solution with the mass percent concentration of DMF being 20%, washing with pure water, immersing in an aqueous solution with the mass percent concentration of lactic acid being 50% for hole retention treatment, and then, putting into a vacuum oven with the temperature of 80 ℃ for heat treatment for 48 hours.
The rejection and flux tests were carried out on the fully crosslinked polyamide nanofiltration membranes obtained in example 1, under the following test conditions and results:
(1) retention test for dye in different organic solvents (dye concentration 50ppm, operating pressure 100 psi):
Figure BDA0002843150620000121
(2) at an operating pressure of 225psi, the conductivity was 2000. Mu.s/cm MgSO 4 Solution, run for 30min, retention 93.56%, flux 49.62L/m 2 h；
(3) Under the condition of the operation pressure of 225psi, the conductivity is 2000 mus/cm NaCl solution, the operation is carried out for 30min, the retention rate is 62.35 percent, and the flux is 55.76L/m 2 h。
Example 2
(1) Preparing a membrane casting solution, wherein the mass percent concentration of polyimide is 16%, the mass percent concentration of gamma-aminopropyltriethoxysilane-modified nano silicon dioxide is 1.5%, and a solvent is N-methylpyrrolidone, and blade-coating the membrane casting solution on non-woven fabrics to form a polyimide membrane as a base membrane;
(2) Immersing the base membrane obtained in the step (1) in an aqueous solution of which the mass percent concentration of the amine monomer is 1.2% (wherein the mass percent concentration of the 5-trifluoromethyl-1, 3-phenylenediamine is 1.1%, and the mass percent concentration of the 3, 5-bis (trifluoromethyl) aniline is 0.1%) for 2min; then immersing the polyimide film in a normal hexane solution with the mass percentage concentration of trimesoyl chloride of 0.15% for 3min to form a polyamide film on the polyimide base film;
(3) Amination treatment is carried out on the base membrane with the polyamide membrane obtained in the step (2) in a methanol solution with the concentration of the ethylene diamine being 15% by mass;
(4) Preparing 2000ml of a mixed solution containing acetone, 1,2,4, 5-cyclohexane tetracarboxylic anhydride and 2, 3-diaminopyridine in a volume ratio of 10;
(5) Immersing the nanofiltration membrane obtained in the step (4) in a methanol solution with the mass percent concentration of hexamethylene diamine of 20% at 75 ℃, and completing secondary crosslinking under the ultrasonic-assisted condition to obtain a full-crosslinking polyamide nanofiltration membrane;
(6) And (3) activating the full-crosslinked polyamide nanofiltration membrane obtained in the step (5) in an aqueous solution with the mass percent concentration of DMF being 20%, washing with pure water, immersing in an aqueous solution with the mass percent concentration of lactic acid being 50% for hole preservation, and then, putting into a vacuum oven with the temperature of 80 ℃ for heat treatment for 48 hours.
The rejection and flux tests were carried out on the fully crosslinked polyamide nanofiltration membranes obtained in example 2, under the following test conditions and results:
(1) retention test for dye in different organic solvents (dye concentration 50ppm, operating pressure 100 psi):
Figure BDA0002843150620000131
(2) at an operating pressure of 225psi, the conductivity was 2000. Mu.s/cm MgSO 4 Solution, operation for 30min, retention rate of 94.83%, flux of 44.58L/m 2 h；
(3) Under the condition of the operation pressure of 225psi, the conductivity is 2000 mus/cm NaCl solution, the operation is carried out for 30min, the retention rate is 63.51 percent, and the flux is 52.14L/m 2 h。
Example 3
(1) Preparing a film casting solution, wherein the mass percent concentration of polyimide is 17%, the mass percent concentration of gamma-aminopropyltriethoxysilane-modified nano silicon dioxide is 2.0%, and the solvent is N-methylpyrrolidone, and blade-coating the film casting solution on non-woven fabrics to form a polyimide film as a base film;
(2) Immersing the basement membrane obtained in the step (1) in an aqueous phase solution with the mass percent concentration of 1.6% of amine monomer (wherein the mass percent concentration of 5-trifluoromethyl-1, 3-phenylenediamine is 1.45%, and the mass percent concentration of 3, 5-bis (trifluoromethyl) aniline is 0.15%) for 2min; then immersing the polyimide film in a normal hexane solution with the mass percentage concentration of trimesoyl chloride of 0.2% for 3min to form a polyamide film on the polyimide base film;
(3) Amination treatment is carried out on the base film with the polyamide film obtained in the step (2) in a methanol solution with the mass percent concentration of ethylenediamine being 15%;
(4) Preparing 2000ml of a mixed solution containing acetone, 1,2,4, 5-cyclohexane tetracarboxylic anhydride and 2, 3-diaminopyridine in a volume ratio of 10;
(5) Immersing the nanofiltration membrane obtained in the step (4) in a methanol solution with the mass percent concentration of hexamethylene diamine of 20% at 75 ℃, and completing secondary crosslinking under the ultrasonic-assisted condition to obtain a full-crosslinking polyamide nanofiltration membrane;
(6) And (3) activating the full-crosslinked polyamide nanofiltration membrane obtained in the step (5) in an aqueous solution with the mass percent concentration of DMF being 20%, washing with pure water, immersing in an aqueous solution with the mass percent concentration of lactic acid being 50% for hole preservation, and then, putting into a vacuum oven with the temperature of 80 ℃ for heat treatment for 48 hours.
The rejection and flux tests were carried out on the fully crosslinked polyamide nanofiltration membranes obtained in example 3, under the following test conditions and results:
(1) retention test for dye in different organic solvents (dye concentration 50ppm, operating pressure 100 psi):
Figure BDA0002843150620000141
(2) at an operating pressure of 225psi, the conductivity was 2000. Mu.s/cm MgSO 4 Solution, run for 30min, retention 96.25%, flux 33.76L/m 2 h；
(3) Under the condition of the operation pressure of 225psi, the conductivity is 2000 mu s/cm NaCl solution, the operation time is 30min, the retention rate is 63.98 percent, and the flux is 45.23L/m 2 h。
Example 4
(1) Preparing a film casting solution, wherein the mass percent concentration of polyimide is 18%, the mass percent concentration of gamma-aminopropyltriethoxysilane-modified nano silicon dioxide is 2.5%, and a solvent is N-methylpyrrolidone, and blade-coating the film casting solution on a non-woven fabric to form a polyimide film as a base film;
(2) Immersing the basement membrane obtained in the step (1) in an aqueous phase solution with the mass percent concentration of 2.0 percent of amine monomer (wherein the mass percent concentration of 5-trifluoromethyl-1, 3-phenylenediamine is 1.8 percent, and the mass percent concentration of 3, 5-bis (trifluoromethyl) aniline is 0.2 percent) for 2min; then immersing the polyimide film in a normal hexane solution with the mass percentage concentration of trimesoyl chloride of 0.25% for 3min to form a polyamide film on the polyimide base film;
(3) Amination treatment is carried out on the base membrane with the polyamide membrane obtained in the step (2) in a methanol solution with the concentration of the ethylene diamine being 15% by mass;
(4) Preparing 2000ml of a mixed solution containing acetone, 1,2,4, 5-cyclohexane tetracarboxylic anhydride and 2, 3-diaminopyridine in a volume ratio of 10;
(5) Immersing the nanofiltration membrane obtained in the step (4) in a methanol solution with the mass percent concentration of hexamethylene diamine of 20% at 75 ℃, and completing secondary crosslinking under the ultrasonic-assisted condition to obtain a full-crosslinking polyamide nanofiltration membrane;
(6) And (3) activating the fully-crosslinked polyamide nanofiltration membrane obtained in the step (5) in an aqueous solution with the mass percent concentration of DMF being 20%, washing with pure water, immersing in an aqueous solution with the mass percent concentration of lactic acid being 50% for hole retention treatment, and then, putting into a vacuum oven with the temperature of 80 ℃ for heat treatment for 48 hours.
The rejection and flux tests were carried out on the fully crosslinked polyamide nanofiltration membranes obtained in example 4, under the following test conditions and results:
(1) retention test for dye in different organic solvents (dye concentration 50ppm, operating pressure 100 psi):
Figure BDA0002843150620000161
(2) at an operating pressure of 225psi, the conductivity was 2000. Mu.s/cm MgSO 4 Solution, operation 30min, retention rate 97.86%, flux 30.43L/m 2 h；
(3) 225psi strip at operating pressureUnder the condition of the condition that the conductivity is 2000 mu s/cm NaCl solution, the operation is carried out for 30min, the retention rate is 64.46 percent, and the flux is 40.10L/m 2 h。
Example 5
(1) Preparing a membrane casting solution, wherein the mass percent concentration of polyimide is 20%, the mass percent concentration of gamma-aminopropyltriethoxysilane-modified nano silicon dioxide is 3.0%, and a solvent is N-methylpyrrolidone, and the membrane casting solution is blade-coated on non-woven fabrics to form a polyimide membrane as a base membrane;
(2) Immersing the base membrane obtained in the step (1) in an aqueous solution of which the mass percent concentration of the amine monomer is 2.4% (wherein the mass percent concentration of the 5-trifluoromethyl-1, 3-phenylenediamine is 2.15%, and the mass percent concentration of the 3, 5-bis (trifluoromethyl) aniline is 0.25%) for 2min; then immersing the polyimide film in a normal hexane solution with the mass percent concentration of trimesoyl chloride of 0.3% for 3min to form a polyamide film on the polyimide base film;
(3) Amination treatment is carried out on the base membrane with the polyamide membrane obtained in the step (2) in a methanol solution with the concentration of the ethylene diamine being 15% by mass;
(4) Preparing 2000ml of a mixed solution containing acetone, 1,2,4, 5-cyclohexane tetracarboxylic anhydride and 2, 3-diaminopyridine in a volume ratio of 10;
(5) Immersing the nanofiltration membrane obtained in the step (4) in a methanol solution with the mass percent concentration of hexamethylene diamine of 20% at 75 ℃, and completing secondary crosslinking under the ultrasonic-assisted condition to obtain a full-crosslinking polyamide nanofiltration membrane;
(6) And (3) activating the fully-crosslinked polyamide nanofiltration membrane obtained in the step (5) in an aqueous solution with the mass percent concentration of DMF being 20%, washing with pure water, immersing in an aqueous solution with the mass percent concentration of lactic acid being 50% for hole retention treatment, and then, putting into a vacuum oven with the temperature of 80 ℃ for heat treatment for 48 hours.
The rejection and flux tests were carried out on the fully crosslinked polyamide nanofiltration membranes obtained in example 5, under the following test conditions and results:
(1) retention test for dye in different organic solvents (dye concentration 50ppm, operating pressure 100 psi):
Figure BDA0002843150620000171
(2) at an operating pressure of 225psi, the conductivity was 2000. Mu.s/cm MgSO 4 Solution, running for 30min, retention rate 98.15%, flux 27.55L/m 2 h；
(3) Under the condition of the operation pressure of 225psi, the conductivity is 2000 mus/cm NaCl solution, the operation is carried out for 30min, the retention rate is 66.37 percent, and the flux is 32.43L/m 2 h。
Industrial applicability
The invention provides a preparation method of a nanofiltration membrane, the nanofiltration membrane obtained by the method expands the application field of the nanofiltration membrane, solves the technical problem that the traditional nanofiltration membrane is difficult to widen into a non-aqueous solution system, has excellent tolerance in a strong polar organic solvent, keeps excellent flux and interception effect, and provides guidance and reference for the application of a separation membrane technology in the related industries of separation and purification of organic solvents. The nanofiltration membrane prepared by the invention is a full-crosslinking nanofiltration membrane, has excellent separation performance, high flux, strong solvent resistance, excellent swelling resistance, high stability for long-time operation, and higher apparent strength and compressive tightness.

Claims (7)

1. The preparation method of the nanofiltration membrane is characterized by comprising the following steps:
preparing a membrane casting solution, and coating the membrane casting solution on a non-woven fabric to form a base membrane, wherein the membrane casting solution comprises a polymer, a solvent and nanoparticles; the polymer is at least one of polyimide, polyethylene imine, sulfonated polyethylene imine, polyamide imide and biphenyl polyaryletherketone modified bismaleimide, and the mass percentage concentration of the polymer is 12-22% based on the total mass of the casting solution; the nano particles are at least one of nano silicon dioxide particles, graphene particles, carbon nano tube particles, nano molecular sieve particles, nano titanium dioxide particles, montmorillonite particles and Metal Organic Framework (MOF) particles, are modified by a silane coupling agent, have particle sizes ranging from 50nm to 300nm, and have a mass percent concentration of 0.1-5% based on the total mass of the casting solution;
sequentially contacting the base film with an aqueous phase solution containing an amine monomer and an organic phase solution containing an acyl chloride monomer to form a polyamide functional layer on the base film, wherein the amine monomer is at least one of aromatic amine monomers with 6 to 12 carbon atoms, the mass percentage concentration of the amine monomer is 0.5 to 3.0 percent based on the total mass of the aqueous phase solution, and hydrogen atoms on an aromatic ring of the amine monomer are substituted by fluorinated alkyl groups with 1 to 3 carbon atoms;
treating with a solution containing a diamine substance having 2 to 5 carbon atoms to crosslink the inside of the base film;
imidizing a polyamide functional layer by treating with a solution containing an acid anhydride-based substance and a tertiary amine-based substance;
treating with a solution containing a diamine substance having 6 to 10 carbon atoms to crosslink between the base film and the polyamide functional layer and to crosslink inside the polyamide functional layer;
and carrying out post-treatment and drying to obtain the nanofiltration membrane.
2. The nanofiltration membrane preparation method according to claim 1, wherein the acid chloride monomer is at least one of trimesoyl chloride, phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, 4' -diacyl diphenyl ether, 2, 6-naphthaloyl chloride and 1, 8-naphthaloyl chloride, and the concentration of the acid chloride monomer is 0.05-0.75% by mass based on the total mass of the organic phase solution.
3. The method for preparing nanofiltration membrane according to claim 1, wherein the diamine-based substance having 2 to 5 carbon atoms is at least one of ethylenediamine, 1, 2-propylenediamine, 1, 3-propylenediamine, 2' -dimethyl-1, 3-propylenediamine, butylenediamine, N-ethyl-1, 3-propylenediamine, and pentylenediamine; the mass percentage concentration of the diamine substance with the carbon number of 2-5 is 12-18 percent based on the total mass of the solution containing the diamine substance with the carbon number of 2-5.
4. The nanofiltration membrane manufacturing method according to claim 1, wherein the acid anhydride-based material is at least one of pyromellitic anhydride, 1,2,4, 5-cyclohexane tetracarboxylic anhydride, ethylenediaminetetraacetic dianhydride, 3', 4' -benzophenonetetracarboxylic dianhydride, 1,4,5, 8-naphthalene tetracarboxylic anhydride, 3', 4' -biphenyl tetracarboxylic dianhydride, aliphatic dibasic acid anhydride having a carbon number of 10 to 16, and aromatic dibasic acid anhydride having a carbon number of 10 to 16, and the tertiary amine-based material is at least one of 2, 3-diaminopyridine, triethylamine, quinoline, isoquinoline, β -picoline, 2, 5-diaminopyridine, and N, N ' -dimethylaniline.
5. The method for producing a nanofiltration membrane according to claim 1, wherein the volume ratio of the solvent to the acid anhydride-based substance to the tertiary amine-based substance in the solution containing the acid anhydride-based substance to the tertiary amine-based substance is 10.
6. The nanofiltration membrane preparation method according to claim 1, wherein the diamine-based substance having a carbon number of 6 to 10 is at least one of 3,3' -diaminodipropylamine, dimethylhexamethylenediamine, trimethylhexamethylenediamine, and a linear diamine-based substance having a carbon number of 6 to 10, and the concentration of the diamine-based substance having a carbon number of 6 to 10 is 22 to 25% by mass based on the total mass of the solution containing the diamine-based substance having a carbon number of 6 to 10.
7. A nanofiltration membrane prepared by the preparation method of any one of claims 1 to 6.
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