CN115888415A - Preparation method of nanofiltration membrane and nanofiltration membrane prepared therefrom - Google Patents

Abstract

The invention relates to a preparation method of a nanofiltration membrane and the nanofiltration membrane prepared by the method. The preparation method comprises the following steps: the method comprises the following steps of oxidizing a polypropylene microporous membrane to hydroxylate the surface of the polypropylene microporous membrane, sequentially contacting the polypropylene microporous membrane subjected to surface hydroxylation with a compound or polymer containing a plurality of hydroxyl groups and/or a plurality of amino groups and a cross-linking agent to perform hydrophilization modification, applying a nano material containing a plurality of hydroxyl groups and/or a plurality of amino groups on the polypropylene microporous membrane subjected to hydrophilization modification, sequentially contacting with an aqueous phase solution and an organic phase solution to perform interfacial polymerization reaction to form a polyamide separation layer, and performing post-treatment to obtain the nanofiltration membrane, wherein the post-treatment comprises treatment by using a carboxyl activating agent. The nanofiltration membrane provided by the invention has a thinner thickness, can bring a higher effective filtration area of a single membrane element, has higher flux and excellent separation performance (separation of salt ions and the like) in the water treatment process, and has stable performance in the long-term operation process.

Description

Preparation method of nanofiltration membrane and nanofiltration membrane prepared therefrom

technical field

The invention relates to the technical field of water treatment membranes, in particular to a preparation method of a nanofiltration membrane and a nanofiltration membrane prepared therefrom.

Background technique

Water resources are an indispensable natural resource for human life and production today. At present, with the rapid development of society, the contradiction between supply and demand of water resources has become more and more prominent. On the one hand, people’s overexploitation of surface water and groundwater has destroyed the sustainable cycle of water resources, resulting in the reduction of fresh water resources. On the other hand, due to industrial and agricultural The refractory pollutants discharged from production and other production have polluted a large amount of available water resources, further causing the shortage of available water resources, and having a serious impact on the sustainable development of society.

The existing solutions mainly include sewage treatment and reuse, seawater desalination, and inter-regional water diversion and other measures. In sewage treatment, it has been proven feasible in many countries and regions in the world to treat polluted water to form recycled water, which can alleviate the contradiction between supply and demand of water resources to a certain extent.

Membrane separation technology can be used in the sewage treatment process, which has high-efficiency separation performance and low energy consumption, and has been widely used in water treatment, medicine, food, biological purification, energy and chemical industries. Membrane separation technology is mainly pressure-driven membrane, including microfiltration, ultrafiltration, nanofiltration and reverse osmosis. Nanofiltration membranes have special separation performance, which can intercept inorganic salts and small molecular organic compounds in the solution. However, compared with reverse osmosis membranes, nanofiltration membranes have lower interception performance for monovalent salt ions, so they can be used for drinking water Treatment and other processes to ensure that some elements beneficial to the human body are retained, combined with its low energy consumption, nanofiltration membranes have been greatly developed in the field of water treatment.

How to reduce the cost of water treatment is a key to the practical application of nanofiltration membranes. In the current research, improving the water flux and pollution resistance of nanofiltration membranes is the main research direction. At present, reducing the thickness of the nanofiltration membrane and preparing a loose polyamide layer structure are considered to be a method that can improve the flux of the nanofiltration membrane. On the one hand, the penetration resistance of water molecules can be reduced by reducing the thickness. On the other hand, it has Due to the high relative porosity of the nanofiltration membrane with loose polyamide layer structure, the permeability of the membrane is increased.

In addition, the current nanofiltration membrane mainly adopts a three-layer structure, which is polyester non-woven fabric, polysulfone layer and polyamide separation layer. The overall thickness is mostly concentrated in 100-150 microns. For nanofiltration membranes of 100 microns or even less than 50 microns, thinner nanofiltration membranes can bring a higher packing area for a single membrane element and improve the permeability of a single membrane element, that is, under the same water production conditions Under this condition, the number of membrane elements can be reduced, which further reduces the cost of membrane water production, thereby reducing the cost of using nanofiltration membranes for water treatment.

Polypropylene microporous membrane for lithium batteries is a separator used in lithium-ion batteries. It has high porosity, high tear resistance, good acid and alkali resistance and good elasticity. Common thickness It is 20-60 microns, and the pore size is between 30-120 nanometers. Therefore, if the polyamide nanofiltration membrane with excellent comprehensive performance can be prepared with the polypropylene microporous membrane as the base membrane, and combined with its thinner characteristics, it can be obtained Nanofiltration membrane elements with a high filling area can greatly improve the permeability of a single membrane element, but due to the hydrophobic properties of the surface of the polypropylene microporous membrane, it cannot be directly used in the interfacial polymerization process to prepare polyamide nanofiltration membranes.

Contents of the invention

The problem to be solved by the invention

For the above-mentioned problems existing in the prior art, the object of the present invention is to provide a kind of preparation method and the nanofiltration membrane prepared by it with the polypropylene microporous membrane as the nanofiltration membrane of base membrane, this method is simple, easy to operate, There is no need to modify the existing equipment, and the operating cost is effective. The nanofiltration membrane prepared by it has a thinner thickness, which can bring a higher effective filtration area of a single membrane element, and has a higher throughput in the water treatment process. Quantity and excellent separation performance (separation of salt ions, etc.).

solutions to problems

In order to solve the above problems, the inventors of the present invention conducted in-depth research and creatively conceived of the following technical scheme: oxidize the polypropylene microporous membrane to make its surface hydroxylated, and then apply a multi-hydroxyl and/or multi- Compounds or polymers with two amino groups are hydrophilized and modified under the action of a cross-linking agent; then, nanoparticles containing multiple hydroxyl groups and/or multiple amino groups are applied on the hydrophilically modified polypropylene microporous membrane. The material thus provides a favorable reaction platform for the subsequent interfacial polymerization reaction; in the interfacial polymerization reaction, adding alcohol additives to the aqueous phase solution can promote the diffusion of the nanomaterial, and make the nanomaterial participate in the interfacial polymerization reaction, constructing A polyamide layer containing nano-water channels; in the post-treatment, the nanomaterials can be stably present in the polyamide layer by using a carboxyl activator to ensure stable performance of the nanofiltration membrane during long-term operation sex.

The invention provides a kind of preparation method of nanofiltration membrane, it is characterized in that, comprises the following steps:

Carrying out oxidation treatment to the polypropylene microporous membrane to make its surface hydroxylated, the oxidation treatment is carried out through an aqueous solution containing persulfate compounds;

The surface-hydroxylated polypropylene microporous membrane is sequentially contacted with a compound or polymer containing multiple hydroxyl groups and/or multiple amino groups, and a cross-linking agent to carry out hydrophilic modification;

Apply nanomaterials containing multiple hydroxyl groups and/or multiple amino groups on the hydrophilically modified polypropylene microporous membrane, and then contact the aqueous phase solution and the organic phase solution in sequence to perform interfacial polymerization to form a polyamide separation layer , wherein the aqueous phase solution contains alcohol additives and amine compounds as aqueous phase monomers, and the organic phase solution contains acid chloride compounds as organic phase monomers;

The nanofiltration membrane is obtained after post-treatment, wherein the post-treatment includes treatment with a carboxyl activator.

According to the preparation method of the present invention, the persulfate compound is at least one selected from potassium persulfate, sodium persulfate and ammonium persulfate.

According to the preparation method of the present invention, wherein the compound or polymer comprising multiple hydroxyl groups and/or multiple amino groups is selected from polyvinyl alcohol, polyethylene glycol, tannic acid, polyethyleneimine, carboxylated At least one of chitosan, sorbitol, polyacrylic acid polyol, polyaminopolyether and polyacrylamide.

According to the preparation method of the present invention, wherein the crosslinking agent is selected from aliphatic dialdehydes with 2 to 6 carbon atoms, N,N-methylenebisacrylamide, glycidyl methacrylate, cyclic At least one of oxychlorohydrin and polyethylene glycol glycidyl ether.

According to the preparation method of the present invention, wherein the nanomaterial comprising multiple hydroxyl groups and/or multiple amino groups is selected from carboxylated graphene oxide, aminated graphene oxide, aminated graphene, and aminated multi-walled carbon At least one of nanotubes, aminated single-walled carbon nanotubes, carboxylated single-walled carbon nanotubes, amino-functionalized metal-organic framework MOF, and aminated nanocrystalline cellulose.

According to the preparation method of the present invention, wherein the alcohol additive is at least one selected from aliphatic alcohols with 1 to 6 carbon atoms and aromatic alcohols with 7 to 12 carbon atoms.

According to the preparation method of the present invention, wherein the amine compound is selected from piperazine, homopiperazine, 2-methylpiperazine, m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, trimesene at least one of amine and polyethyleneimine.

According to the preparation method of the present invention, wherein the acyl chloride compound is selected from the group consisting of isophthaloyl chloride, terephthaloyl chloride, phthaloyl chloride, trimesoyl chloride, biphenyltetrayl chloride, cyanuric acid chloride, At least one of dansyl chloride and benzenesulfonyl chloride.

According to the preparation method of the present invention, wherein the carboxyl activator is N-hydroxysuccinimide and selected from 1,3-dicyclohexylcarbodiimide, 1-ethyl-3-(3-dimethyl Aminopropyl) carbodiimide hydrochloride, diethyl cyanomethyl phosphate, 4-dimethylaminopyridine, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride Combinations of at least one of salts.

The present invention also provides a nanofiltration membrane prepared according to the preparation method of the present invention.

The effect of the invention

The preparation method of the nanofiltration membrane provided by the present invention is simple, easy to operate, no need to modify the existing equipment, and the operating cost is effective. The nanofiltration membrane prepared by it has a thinner thickness, which can bring higher single membrane The effective filtration area of the element has high flux and excellent separation performance (separation of salt ions, etc.) in the water treatment process, and the performance is stable during long-term operation.

Description of drawings

FIG. 1 shows the results of stability tests for the nanofiltration membranes obtained in Examples 1 to 4 (abbreviated as Example 1, Example 2, Example 3, and Example 4).

Detailed ways

Various exemplary embodiments, features, and aspects of the invention are described in detail below. The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as superior or better than other embodiments.

In addition, in order to better illustrate the present invention, numerous specific details are given in the specific embodiments below. It will be understood by those skilled in the art that the present invention may be practiced without certain of the specific details. In other instances, methods, means, devices and steps well known to those skilled in the art are not described in detail in order to highlight the gist of the present invention.

Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values and numerical ranges appearing in the present invention should be understood as including inevitable systematic errors in industrial production.

In this specification, the meaning expressed by "may" includes the meaning of performing certain processing and not performing certain processing.

In this specification, references to "some specific/preferred embodiments", "other specific/preferred embodiments", "embodiments" and the like refer to specific elements described in relation to the embodiments (for example, A feature, structure, property and/or characteristic) is included in at least one embodiment described herein and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.

In this specification, the numerical range represented by "numerical value A - numerical value B" means the range which includes numerical value A and B of an end point.

In this specification, when "normal temperature" and "room temperature" are used, the temperature may be 10-40°C.

The invention provides a kind of preparation method of nanofiltration membrane, it comprises the following steps:

Carrying out oxidation treatment to the polypropylene microporous membrane to make its surface hydroxylated, the oxidation treatment is carried out through an aqueous solution containing persulfate compounds;

The surface-hydroxylated polypropylene microporous membrane is sequentially contacted with a compound or polymer containing multiple hydroxyl groups and/or multiple amino groups, and a cross-linking agent to carry out hydrophilic modification;

Apply nanomaterials containing multiple hydroxyl groups and/or multiple amino groups on the hydrophilically modified polypropylene microporous membrane, and then contact the aqueous phase solution and the organic phase solution in sequence to perform interfacial polymerization to form a polyamide separation layer , wherein the aqueous phase solution contains alcohol additives and amine compounds as aqueous phase monomers, and the organic phase solution contains acid chloride compounds as organic phase monomers;

The nanofiltration membrane is obtained after post-treatment, wherein the post-treatment includes treatment with a carboxyl activator.

The technical idea of the present invention is to oxidize the polypropylene microporous membrane to make its surface hydroxylated, and then apply a compound or polymer containing multiple hydroxyl groups and/or multiple amino groups to achieve hydrophilicity under the action of a crosslinking agent. modification; then apply nanomaterials containing multiple hydroxyl groups and/or multiple amino groups on the polypropylene microporous membrane modified by hydrophilicity to provide a favorable reaction platform for subsequent interfacial polymerization; in the interfacial polymerization In the water phase solution, adding alcohol additives can promote the diffusion of the nanomaterials, and make the nanomaterials participate in the interfacial polymerization reaction to construct a polyamide layer containing nano-water channels; in post-treatment, by using carboxyl activation The nanometer material can be stably present in the polyamide layer by treating it with an agent, so as to ensure the performance stability of the nanofiltration membrane during long-term operation.

Preferably, the polypropylene microporous membrane used in the present invention has a thickness of 20-40 microns and a pore diameter of 30-100 nanometers. If the thickness of the polypropylene microporous membrane is too thick, it is not conducive to the permeability of the membrane. If it is too thin, the mechanical properties of the prepared nanofiltration membrane will be insufficient. Density and uniformity.

The preparation method of the present invention, wherein the persulfate compound is at least one selected from potassium persulfate, sodium persulfate and ammonium persulfate.

Preferably, the oxidation treatment is carried out as follows: use an aqueous solution with a concentration of potassium persulfate of 5-15 wt%, and treat for 30-60 minutes at a temperature of 60-80°C. The reaction conditions can be adjusted to provide varying degrees of oxidation, as desired.

The preparation method of the present invention, wherein the compound or polymer containing multiple hydroxyl groups and/or multiple amino groups is selected from polyvinyl alcohol, polyethylene glycol, tannic acid, polyethyleneimine, carboxylated shell At least one of polysaccharides, sorbitol, polyacrylic acid polyols, polyamino polyethers, and polyacrylamides.

Preferably, the surface hydroxylated polypropylene microporous membrane is immersed in an aqueous solution containing compounds or polymers containing multiple hydroxyl groups and/or multiple amino groups to ensure that the polypropylene microporous membrane (including the membrane surface and membrane pores) It is wetted by an aqueous solution of a compound or polymer containing multiple hydroxyl groups and/or multiple amino groups; after wetting, it is immersed in an aqueous solution containing a crosslinking agent, through self-crosslinking between hydroxyl groups and through the above-mentioned oxidation treatment. The cross-linking of the hydroxyl groups introduced on the chain is used to realize the hydrophilic modification of the polypropylene microporous membrane, and to construct a hydrophilic membrane surface and pore channels.

Preferably, the concentration of the compound or polymer containing multiple hydroxyl groups and/or multiple amino groups in the aqueous solution is 5-10 wt%, the temperature of the aqueous solution is 30-50°C, and the soaking time is 20-40 minutes.

The preparation method of the present invention, wherein the crosslinking agent is selected from aliphatic dialdehydes with 2 to 6 carbon atoms, N,N-methylenebisacrylamide, glycidyl methacrylate, epoxy At least one of chloropropane and polyethylene glycol glycidyl ether.

Preferably, the crosslinking agent is at least one selected from glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, and N,N-methylenebisacrylamide.

Preferably, based on the total weight of the aqueous solution containing the crosslinking agent, the content of the crosslinking agent is 0.1 to 1 wt %; the immersion time in the aqueous solution containing the crosslinking agent is preferably 5 to 10 minutes, so The temperature of the aqueous solution containing the crosslinking agent is 20-40°C. The main purpose of this process is to ensure the stability of compounds or polymers containing multiple hydroxyl groups and/or multiple amino groups in the polypropylene microporous membrane through chemical bonds and intermolecular entanglement.

The preparation method of the present invention, wherein the nanomaterial comprising multiple hydroxyl groups and/or multiple amino groups is selected from carboxylated graphene oxide, aminated graphene oxide, aminated graphene, aminated multi-walled carbon nanomaterials At least one of tubes, aminated single-walled carbon nanotubes, carboxylated single-walled carbon nanotubes, amino-functionalized metal-organic framework MOF, and aminated nanocrystalline cellulose.

Preferably, the nanomaterials containing multiple hydroxyl groups and/or multiple amino groups are applied by spraying a dispersion containing the nanomaterials on the hydrophilized modified polypropylene microporous membrane, so as to construct Based on the platform of the subsequent interface polymerization reaction, the reaction process of the interface polymerization reaction is improved, and the nanomaterial participates in the construction of water molecule channels, which helps to improve the permeability of the membrane and ensure the separation performance of the membrane.

The nanomaterial has a certain number of hydroxyl groups and/or amino groups, and can be fixed on the polyamide layer during interfacial polymerization or subsequent treatment; preferably, the concentration of the nanomaterial in the dispersion is 0.01-1 wt%.

Preferably, the hydrophilically modified polypropylene microporous membrane applied with nanomaterials containing multiple hydroxyl groups and/or multiple amino groups is sequentially immersed in the aqueous phase solution containing amine compounds and the organic phase containing acid chloride compounds In the solution, the interfacial polymerization reaction is carried out to form the initial polyamide layer. In this process, the nanomaterials participate in the interfacial polymerization process with the diffusion of amine compounds, and then form nano water molecule channels to improve the permeation and separation performance of the polyamide layer; further, in the water containing amine compounds Alcohol additives are added to the phase solution, and the additives can promote the diffusion of the nanomaterials, and then promote the participation of the nanomaterials in the interfacial polymerization reaction.

The preparation method of the present invention, wherein the amine compound is selected from piperazine, homopiperazine, 2-methylpiperazine, m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, s-phenylenediamine and at least one of polyethyleneimine.

Preferably, the concentration of the amine compound in the aqueous phase solution is 0.5-1.5 wt%.

In the preparation method of the present invention, the alcohol additive is at least one selected from aliphatic alcohols with 1 to 6 carbon atoms and aromatic alcohols with 7 to 12 carbon atoms.

The alcohol additives include but not limited to methanol, ethanol, isopropanol, benzyl alcohol, glycerol, ethylene glycol, n-butanol. Preferably, the concentration of the alcohol additive in the aqueous phase solution is 3-5 wt%.

Preferably, the aqueous phase solution also contains a pH adjuster to adjust the pH value of the solution, promotes the solution to form an alkaline environment, and absorbs the hydrogen chloride produced by the interfacial polymerization process, thereby promoting the reaction; the pH adjuster is preferably It is at least one selected from sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium hydrogen phosphate, potassium hydrogen phosphate, sodium carbonate, ammonium bicarbonate, triethanolamine and triethylamine/camphorsulfonic acid composite solution. Preferably, a pH regulator is used to adjust the pH value of the aqueous phase solution to 10-11.

Preferably, the contact time with the aqueous phase solution is 30-60 seconds; there is no limitation on the contact temperature, which can be within the temperature range of 15-45°C.

The preparation method of the present invention, wherein the acyl chloride compound is selected from isophthaloyl chloride, terephthaloyl chloride, phthaloyl chloride, trimesoyl chloride, biphenyltetrayl chloride, cyanuric acid chloride, dan At least one of sulfonyl chloride and benzenesulfonyl chloride.

Preferably, based on the total weight of the organic phase solution, the content of the acid chloride compounds is 0.1-0.5 wt%.

Preferably, the organic phase solution also includes an organic solvent, and the organic solvent is at least one selected from n-hexane, n-heptane, cyclohexane, Isopar M, Isopar H, Isopar L, Isopar E and Isopar G.

Preferably, the contact time with the organic phase solution is 30-60 seconds. There is no limit to the contact temperature, and it may be in the temperature range of 15 to 45°C.

Preferably, after the interfacial polymerization reaction is completed, the nanofiltration membrane is initially heated to promote further crosslinking of the polyamide layer to obtain an initial nanofiltration membrane.

Preferably, the heating temperature ranges from 25 to 40° C., and the heating time is from 1 to 5 minutes; the purpose of heating is to promote the volatilization of the solvent and the further crosslinking and curing of the polyamide layer, thereby promoting the formation of the nanofiltration membrane.

Preferably, the initial nanofiltration membrane is immersed in an aqueous solution containing a carboxyl activator to cross-link the remaining substances between the polyamide layers of the initial nanofiltration membrane to ensure the stability of the water channel composed of nanomaterials.

In this step, through the soaking treatment of the carboxyl activator, the chemical reaction between the amino group on the nanomaterial and the carboxyl group hydrolyzed by the acid chloride group on the polyamide layer is promoted, thereby promoting the immobilization of the nanomaterial in the polyamide layer and ensuring nano water channels The stable structure prevents the change of membrane performance caused by the shedding of nanomaterials in the subsequent water treatment process.

The preparation method of the present invention, wherein the carboxyl activator is N-hydroxysuccinimide (NHS) and selected from 1,3-dicyclohexylcarbodiimide (DCC), 1-ethyl-3- (3-Dimethylaminopropyl) carbodiimide hydrochloride (EDAC), diethylcyanomethyl phosphate (DEPC), 4-dimethylaminopyridine (DMAP), 1-(3-dimethylamino A combination of at least one of propyl)-3-ethylcarbodiimide hydrochloride (EDC).

Preferably, based on the total weight of the aqueous solution containing the carboxyl activator, the content of the carboxyl activator is 0.5-2wt%; the immersion time is preferably 1-3 minutes, and the immersion temperature is preferably 40-60°C.

In the preparation method of the present invention, the post-treatment preferably further includes washing with pure water, pore preservation treatment and drying treatment.

The purpose of washing with pure water is to remove unreacted amine compounds, acid chloride compounds and unfixed compounds or polymers containing multiple hydroxyl groups and/or multiple amino groups, cross-linking agents and nanomaterials;

Preferably, soak in two sections of pure water for washing, the temperature is 60-80°C and 20-30°C respectively, the main purpose is to wash away the residues of the aforementioned process; preferably, the washing time is 10-20 minutes, in which hot water washes for 5 minute.

Further, immerse in the aqueous solution that comprises pore-preserving agent, because the nanofiltration membrane prepared by the present invention is relatively thin, in the follow-up drying process, the film that does not carry out pore-preserving shrinks seriously, affects the permeability of nanofiltration membrane, so need Preserve the pores to ensure the stability of the membrane pores in the subsequent drying process and ensure the performance of the membrane; preferably, the pore-preserving agent is one or more of glycerin and sorbitol; preferably, the concentration of the pore-preserving agent is 10-15 wt%, the temperature of the aqueous solution containing the pore-preserving agent is 20-30°C, and the treatment time is 5-10 minutes.

Further, heating and drying are carried out to obtain the final nanofiltration membrane, so as to prepare a moisture-free nanofiltration membrane, which is convenient for subsequent membrane module rolling.

Preferably, the heating and drying temperature range is 50-90° C., and the drying time is 1-3 minutes.

The present invention also provides the nanofiltration membrane prepared according to the preparation method of the present invention. The nanofiltration membrane has a thinner thickness, which can bring a higher effective filtration area of a single membrane element, and the membrane has nano-water channels, so it has higher flux and excellent separation performance in the water treatment process (separation of salt ions, etc.), and has stable performance during long-term operation. The nanofiltration membrane can be applied to separation and concentration technologies in the fields of water treatment, dyestuff, biochemical industry, food, environmental protection and the like.

Example

Embodiments of the present invention will be described in detail below in conjunction with examples, but those skilled in the art will understand that the following examples are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Those who do not indicate the specific conditions in the examples are carried out according to the conventional conditions or the conditions suggested by the manufacturer. The reagents or instruments used were not indicated by the manufacturer, and they were all commercially available conventional products.

Preparation Example 1

Prepare a polypropylene microporous membrane with a thickness of 30 ± 5 microns and an average pore diameter of 40 nanometers, immerse it in an aqueous solution of potassium persulfate with a concentration of 10 wt%, and heat it to 80°C for an oxidation reaction for 40 minutes to introduce Hydroxyl groups, washed with water to remove residual substances;

Immerse the polypropylene microporous membrane that has been oxidized and surface hydroxylated into an aqueous solution containing polyvinyl alcohol as a polymer containing multiple hydroxyl groups and having a concentration of 8 wt%, and soak for 30 minutes at 40°C to ensure that the membrane is covered by the aqueous solution. Wetting, and then immersing in an aqueous solution containing glutaraldehyde as a crosslinking agent (the concentration of the crosslinking agent is 0.5wt%, and the aqueous solution uses sulfuric acid to adjust the pH value to 2.5 to 3.5) to carry out the crosslinking reaction, and react at 30 ° C for 8 The polypropylene microporous membrane modified by hydrophilization was obtained as the polypropylene microporous base membrane 1 in 1 minute.

Preparation example 2

A polypropylene microporous base membrane 2 was obtained in the same manner as in Preparation Example 1 except that polyethylene glycol was used instead of polyvinyl alcohol.

Preparation example 3

A polypropylene microporous base membrane 3 was obtained in the same manner as in Preparation Example 1 except that tannic acid was used instead of polyvinyl alcohol.

Preparation Example 4

A polypropylene microporous base membrane 4 was obtained in the same manner as in Preparation Example 1 except that polyethyleneimine was used instead of polyvinyl alcohol.

Preparation Example 5

Prepare an aqueous dispersion of nanomaterials, wherein aminated graphene oxide is used as the nanomaterial at a concentration of 0.05wt%;

The dispersion liquid was spray-coated on the polypropylene microporous base membrane 1 obtained in Preparation Example 1 to obtain a polypropylene microporous base membrane 1-1.

Preparation example 6

A polypropylene microporous base film 2-1 was obtained in the same manner as in Preparation Example 5, except that the dispersion liquid was spray-coated on the polypropylene microporous base film 2 obtained in Preparation Example 2.

Preparation Example 7

A polypropylene microporous base membrane 3-1 was obtained in the same manner as in Preparation Example 5, except that the dispersion liquid was spray-coated on the polypropylene microporous base membrane 3 obtained in Preparation Example 3.

Preparation example 8

A polypropylene microporous base film 4-1 was obtained in the same manner as in Preparation Example 5, except that the dispersion liquid was spray-coated on the polypropylene microporous base film 4 obtained in Preparation Example 4.

Preparation Example 9

Except for using carboxylated graphene oxide instead of aminated graphene oxide as the nanomaterial, polypropylene microporous base membrane 1-2 was obtained in the same manner as in Preparation Example 5.

Preparation Example 10

The polypropylene microporous base membrane 1-3 was obtained in the same manner as in Preparation Example 5, except that amino-functionalized metal-organic framework MOF was used instead of aminated graphene oxide as the nanomaterial.

Preparation Example 11

Except for using aminated nanocrystalline cellulose instead of aminated graphene oxide as the nanomaterial, polypropylene microporous base membranes 1-4 were obtained in the same manner as in Preparation Example 5.

Preparation Example 12

Except for using aminated multi-walled carbon nanotubes instead of aminated graphene oxide as nanomaterials, polypropylene microporous base membranes 1-5 were obtained in the same manner as in Preparation Example 5.

For ease of comparison, in the following comparative examples and examples, the following aqueous phase solution, organic phase solution and aqueous solution containing carboxyl activator are used, and the contact time and temperature with the aqueous phase solution and organic phase solution are as follows :

Water phase solution: use piperazine as the water phase monomer, its concentration is 1wt%, add sodium hydrogen phosphate as pH regulator, adjust the pH value to 10-11, add isopropanol as alcohol additive, its concentration is 4wt %, the immersion temperature in the aqueous phase solution is 20°C, and the contact time with the aqueous phase solution is 40 seconds.

Organic phase solution: use trimesoyl chloride as the organic phase monomer, its concentration is 0.2wt%, use n-heptane as solvent, the reaction temperature in the organic phase solution is 25° C., and the reaction time is 40 seconds.

Aqueous solution containing carboxyl activator: 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinyl (NHS) in a weight ratio of 10:7 , the total concentration of the two is 1.2wt%, and hydrochloric acid is added dropwise to adjust the pH value of the solution to 5-6.

Comparative example 1

The polypropylene microporous base membrane 1 obtained in Preparation Example 1 is immersed in an aqueous phase solution and an organic phase solution in order to carry out interfacial polymerization reaction; after taking it out, it is heated in an oven at 30°C for 3 minutes; then immersed in an aqueous solution containing a carboxyl activator React in the medium for 2 minutes; however, immerse in hot water with a temperature of 65°C for 5 minutes and cold water with a temperature of 25°C for 10 minutes to wash off the remaining chemical substances on the film; Soak in an aqueous solution at 25°C for 8 minutes to ensure that the membrane is wetted by the aqueous glycerin solution, and the membrane does not shrink in the subsequent process; dry in an oven at a temperature of 85°C for 2 minutes to obtain the final nanofiltration membrane.

Comparative example 2

Comparative Example 2 was performed in the same manner as Comparative Example 1 except that the polypropylene microporous base membrane 2 obtained in Preparation Example 2 was used.

Comparative example 3

Comparative Example 3 was performed in the same manner as Comparative Example 1 except that the polypropylene microporous base membrane 3 obtained in Preparation Example 3 was used.

Comparative example 4

Comparative Example 4 was performed in the same manner as Comparative Example 1 except that the polypropylene microporous base membrane 4 obtained in Preparation Example 4 was used.

Example 1

Example 1 was performed in the same manner as Comparative Example 1 except that the polypropylene microporous base membrane 1-1 obtained in Preparation Example 5 was used.

Example 2

Example 2 was carried out in the same manner as Comparative Example 1 except that the polypropylene microporous base membrane 2-1 obtained in Preparation Example 6 was used.

Example 3

Example 3 was performed in the same manner as Comparative Example 1 except that the polypropylene microporous base membrane 3-1 obtained in Preparation Example 7 was used.

Example 4

Example 4 was performed in the same manner as Comparative Example 1 except that the polypropylene microporous base film 4-1 obtained in Preparation Example 8 was used.

Example 5

Example 5 was carried out in the same manner as in Example 1 except that the polypropylene microporous base membrane 1-2 obtained in Preparation Example 9 was used.

Example 6

Example 6 was carried out in the same manner as in Example 1 except that the polypropylene microporous base membrane 1-3 obtained in Preparation Example 10 was used.

Example 7

Example 7 was carried out in the same manner as in Example 1 except that the polypropylene microporous base membrane 1-4 obtained in Preparation Example 11 was used.

Example 8

Example 8 was carried out in the same manner as in Example 1 except that the polypropylene microporous base membrane 1-5 obtained in Preparation Example 12 was used.

Comparative example 5

Comparative Example 5 was performed in the same manner as in Example 1 except that the treatment using the aqueous solution containing a carboxyl group activator was not performed.

Performance Tests and Results

(1) Osmotic separation performance test

The nanofiltration membranes obtained in the above comparative examples and examples were subjected to the following tests.

A cross-flow diaphragm test bench is used for the diaphragm test. The test solution is 2000mg/L magnesium sulfate aqueous solution, the test pressure is 70psi, the temperature is 25°C, the pH value is 7, and the test stabilization time is 40 minutes. The test results are shown in Table 1 below:

Table 1

From the results of Comparative Examples 1 to 4, it can be seen that by surface hydroxylation and hydrophilic modification of polypropylene microporous membranes, subsequent interfacial polymerization reactions can be directly carried out, and the obtained nanofiltration membranes also have certain permeability, but As far as its desalination performance is concerned, it still cannot meet the high requirements for the desalination performance of the nanofiltration membrane, and the desalination rate of the obtained nanofiltration membrane is only 90.36% at most.

By comparing Comparative Example 1 with Comparative Example 5, it can be seen that the flux of the membrane obtained in Comparative Example 5 is higher than that of the membrane obtained in Comparative Example 1, and this is because the nanomaterial sprayed can play the role of an intermediate layer, On the one hand, the existence of the intermediate layer can make the prepared polyamide layer more uniform; on the other hand, it diffuses and participates in the water molecule transfer channel constructed by the interfacial polymerization reaction, so it brings better permeability to the prepared nanofiltration membrane , the flux is improved.

By comparing Comparative Example 5 with Examples 1 to 8, it can be seen that the desalination rate of the membrane obtained in Comparative Example 5 is lower than that of the membrane obtained in Examples 1 to 8, which is due to the absence of carboxyl activation in Comparative Example 5. Therefore, the membrane is unstable. During the operation, some nanoparticles are taken away due to the impact of water flow, resulting in the loss of the constructed water channel, defects in the membrane surface, and a decrease in the compactness of the membrane surface. Therefore, , the desalination performance is reduced, not as good as the membranes obtained in Examples 1 to 8; the flux of the membranes obtained in Examples 1 to 8 is slightly lower than that of the membranes obtained in Comparative Example 5, because, in Examples 1 to 8, there is also Carboxyl activator treatment was further carried out, therefore, the membrane surface was further cross-linked and became more stable and dense, and the improvement of compactness enhanced the pore size effect of the membrane, so the desalination performance increased, which was better than the membrane obtained in Comparative Example 5, However, the permeability of the membrane was slightly lower than that of the membrane of Comparative Example 5.

From the results of Examples 1 to 8, due to the surface hydroxylation and hydrophilic modification, nanomaterials containing multiple hydroxyl groups and/or multiple amino groups are further applied and the use of carboxyl activators Therefore, the obtained nanofiltration membrane has excellent overall performance, and has good permeability and desalination performance at the same time. The flux is equivalent to the nanofiltration membrane obtained in Comparative Examples 1 to 4, and the desalination rate is significantly higher than that of Comparative Examples 1 to 4 obtained nanofiltration membrane.

(2) Stability test

The nanofiltration membrane (abbreviated as example 1, example 2, example 3, example 4) obtained in embodiments 1 to 4 is carried out stability test, and test condition is: the magnesium sulfate aqueous solution that test solution is 2000mg/L, test pressure It is 70psi, the temperature is 25°C, and the pH value is 7.

The results are shown in Figure 1. It can be seen from Figure 1 that the prepared membranes have good stability during the 7-day operation process, and the flux and desalination rate are only slightly attenuated in the initial stage. remained stable without significant attenuation.

It should be noted that although the technical solutions of the present invention are described with specific examples, those skilled in the art can understand that the present invention should not be limited thereto.

Having described various embodiments of the present invention, the foregoing description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and alterations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principle of each embodiment, practical application or technical improvement in the market, or to enable other ordinary skilled in the art to understand each embodiment disclosed herein.

Industrial availability

The preparation method of the nanofiltration membrane provided by the present invention is simple, easy to operate, no need to modify the existing equipment, and the operating cost is effective. The nanofiltration membrane prepared by it has a thinner thickness, which can bring higher single membrane The effective filtration area of the element, the membrane has nano-water channels, so it has high flux and excellent separation performance (separation of salt ions, etc.) in the water treatment process, and has stable performance during long-term operation. The nanofiltration membrane can be applied to separation and concentration technologies in the fields of water treatment, dyestuff, biochemical industry, food, environmental protection and the like.

Claims (10)

1. a preparation method of nanofiltration membrane, is characterized in that, comprises the following steps: Carrying out oxidation treatment to the polypropylene microporous membrane to make its surface hydroxylated, the oxidation treatment is carried out through an aqueous solution containing persulfate compounds; The surface-hydroxylated polypropylene microporous membrane is sequentially contacted with a compound or polymer containing multiple hydroxyl groups and/or multiple amino groups, and a cross-linking agent to carry out hydrophilic modification; Apply nanomaterials containing multiple hydroxyl groups and/or multiple amino groups on the hydrophilically modified polypropylene microporous membrane, and then contact the aqueous phase solution and the organic phase solution in sequence to perform interfacial polymerization to form a polyamide separation layer , wherein the aqueous phase solution contains alcohol additives and amine compounds as aqueous phase monomers, and the organic phase solution contains acid chloride compounds as organic phase monomers; The nanofiltration membrane is obtained after post-treatment, wherein the post-treatment includes treatment with a carboxyl activator. 2. The preparation method according to claim 1, wherein the persulfate compound is at least one selected from potassium persulfate, sodium persulfate, and ammonium persulfate. 3. The preparation method according to claim 1 or 2, wherein the compound or polymer comprising multiple hydroxyl groups and/or multiple amino groups is selected from polyvinyl alcohol, polyethylene glycol, tannic acid, polyethylene At least one of imine, carboxylated chitosan, sorbitol, polyacrylic acid polyol, polyamino polyether, polyacrylamide. 4. The preparation method according to claim 1 or 2, wherein the crosslinking agent is selected from aliphatic dialdehydes with 2 to 6 carbon atoms, N,N-methylenebisacrylamide, methacrylic acid At least one of glycidyl ester, epichlorohydrin, polyethylene glycol glycidyl ether. 5. The preparation method according to claim 1 or 2, wherein the nanomaterial comprising a plurality of hydroxyl groups and/or a plurality of amino groups is selected from carboxylated graphene oxide, aminated graphene oxide, aminated graphene, At least one of aminated multi-walled carbon nanotubes, aminated single-walled carbon nanotubes, carboxylated single-walled carbon nanotubes, amino functionalized metal organic framework MOF, and aminated nanocrystalline cellulose. 6. The preparation method according to claim 1 or 2, wherein the alcohol additive is at least one selected from aliphatic alcohols with 1 to 6 carbon atoms and aromatic alcohols with 7 to 12 carbon atoms . 7. The preparation method according to claim 1 or 2, wherein the amine compound is selected from piperazine, homopiperazine, 2-methylpiperazine, m-phenylenediamine, p-phenylenediamine, ortho-phenylenediamine At least one of amine, s-phenylenetriamine and polyethyleneimine. 8. The preparation method according to claim 1 or 2, wherein the acyl chloride compound is selected from the group consisting of isophthaloyl chloride, terephthaloyl chloride, phthaloyl chloride, trimesoyl chloride, biphenyltetrayl chloride , at least one of cyanuric chloride, dansyl chloride and benzenesulfonyl chloride. 9. The preparation method according to claim 1 or 2, wherein the carboxyl activator is N-hydroxysuccinimide and selected from 1,3-dicyclohexylcarbodiimide, 1-ethyl-3- (3-Dimethylaminopropyl) carbodiimide hydrochloride, diethyl cyanomethyl phosphate, 4-dimethylaminopyridine, 1-(3-dimethylaminopropyl)-3-ethyl carbon Combinations of at least one of diimine hydrochlorides. 10. A nanofiltration membrane prepared by the preparation method according to any one of claims 1-9.

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