CN112221353B - A kind of polyelectrolyte composite nanofiltration membrane and its preparation method and application - Google Patents

Abstract

The invention belongs to the technical field of nanofiltration membranes, and in particular relates to a polyelectrolyte composite nanofiltration membrane and a preparation method and application thereof. The method comprises the steps of: 1) preparing a polymer solution; 2) adding a polyanion electrolyte to the polymer solution, dissolving and then standing for defoaming to obtain a coating liquid; 3) preparing a polycation electrolyte solution; 4) adding the coating film The solution is coated on the non-woven fabric, and then immersed in deionized water to solidify to obtain a nanofiltration membrane base membrane; 5) The polycation electrolyte solution is attached to the nanofiltration membrane base membrane, and reacts, and after the reaction is completed, pass through in turn A polyelectrolyte composite nanofiltration membrane is obtained by soaking treatment in an aqueous solution of glycerol and heat treatment at high temperature. The above technical solution introduces the polyanion electrolyte into the film-forming material of the nanofiltration membrane base membrane, and then combines the polycation electrolyte with the negatively charged groups on the surface of the base membrane to form an "ion pair" with a dense and ultra-thin selective separation layer Structured polyelectrolyte nanofiltration membranes.

Description

A kind of polyelectrolyte composite nanofiltration membrane and its preparation method and application

technical field

The invention belongs to the technical field of nanofiltration membranes, and in particular relates to a polyelectrolyte composite nanofiltration membrane and a preparation method and application thereof.

Background technique

In recent years, the problem of wastewater treatment has become increasingly prominent. Most of the wastewater contains a lot of harmful substances that are difficult to degrade, and if it is directly discharged into the natural environment without treatment, it will cause serious harm to human beings and the entire ecology. In response to this problem, membrane separation technology has been gradually applied in the field of wastewater treatment, while showing its broad development prospects.

The separation capacity of nanofiltration membrane is between ultrafiltration membrane and reverse osmosis membrane. It can effectively separate small organic molecules with molecular weight of 200-1000 and divalent ions. It has high separation accuracy and surface charge, low energy consumption, Environmentally friendly and so on. Among them, chargeability is one of the most important characteristics of nanofiltration membranes, which is also a widely studied nanofiltration membrane preparation method-the preparation principle of layer-by-layer self-assembly. Layer-by-layer self-assembly was first proposed by Dexher of the University of Mainz in Germany in 1991. The principle is to repeatedly contact and adsorb positively charged and negatively charged polyelectrolytes on the solid surface, so as to repeatedly form multilayer self-assembled films. It has been proved to be a nanofiltration membrane preparation method with good separation performance. Wanqin Jin, AliToutianoush et al [Jin Wanqin, Toutianoush A, Tieke B. Langmuir, 2005, 21: 10587-10592] prepared PVA/PVS nanofiltration membrane (membrane flux 0.7L/(m ² ·h), desalination rate 100 %) under similar operating conditions, its flux is much smaller than the PSS/PAH nanofiltration membrane of Brian W. Stanton [Stanton BW, Harris JJ, Miller MD, et al. The membrane flux is 50L/(m ² ·h), and the salt rejection rate is 96%). The main reason for such a large difference in flux is that the number of self-assembled layers of the former is as high as 60 bilayers, which is much higher than the 4.5 bilayers of the latter. The increase in the number of assembled layers can reduce the generation of defects in nanofiltration membranes, thereby achieving good separation performance, but at the same time, it also leads to cumbersome preparation processes and long time-consuming factors that are not conducive to popularization and application.

The polyelectrolyte composite nanofiltration membrane is designed to use polycation and polyanion electrolytes to form a multi-component system with a unique ionic cross-linked structure at the solution or solid interface, which can form dense and selective separation on the membrane surface through a single reaction Floor. Compared with the traditional layer-by-layer self-assembly, the polyelectrolyte composite nanofiltration membrane has the potential to solve the problems of many layers and complex processes.

SUMMARY OF THE INVENTION

In order to solve the deficiencies of the prior art and solve the shortcomings of complex preparation process and low flux caused by too many layers of traditional self-assembly assembly, the present invention provides a polyelectrolyte composite nanofiltration membrane and a preparation method thereof. application. The invention utilizes polycation and polyanion electrolyte to form a multi-component system with unique ionic cross-linking structure at the interface of solution or solid, and forms a dense selective separation layer on the membrane surface through one reaction. Compared with the traditional layer-by-layer self-assembly, the polyelectrolyte composite nanofiltration membrane provided by the present invention has the development potential to solve the problems of large number of assembled layers and complicated process.

The technical scheme provided by the present invention is as follows:

A preparation method of a polyelectrolyte composite nanofiltration membrane, comprising the following steps:

1) using an organic polymer as a film-forming material to prepare a polymer solution comprising the organic polymer and an organic solvent;

2) adding the polyanion electrolyte to the polymer solution obtained in step 1), dissolving it and letting it stand for defoaming to obtain a coating liquid;

3) preparing a solution of polycationic electrolyte;

4) coating the coating liquid obtained in step 2) on the non-woven fabric, and then immersing it in deionized water to solidify to obtain a nanofiltration membrane base membrane;

5) The polycation electrolyte solution obtained in step 3) is attached to the nanofiltration membrane base membrane obtained in step 4), and the reaction is carried out, and after the reaction is completed, the immersion treatment of the aqueous solution of glycerol and the high temperature heating treatment are performed in turn. , to obtain a polyelectrolyte composite nanofiltration membrane.

The above technical scheme introduces the polyanionic electrolyte into the film-forming material of the nanofiltration membrane base membrane, and then combines the polycationic electrolyte with the negatively charged groups on the surface of the base membrane to form a dense and ultra-thin selective separation layer. This method can be obtained by one self-assembly.

Specifically, in step 1), the mass percentage of the solute in the polymer solution is 14-20%.

Specifically, in step 1), the organic solvent is any one of N-N dimethylacetamide, N-N dimethylformamide, dimethyl sulfoxide or N-methylpyrrolidone.

Specifically, in step 1), the organic polymer is selected from any one of polyethersulfone, polysulfone or polyacrylonitrile.

Specifically, in step 2), the mass ratio of the polyanion electrolyte to the organic polymer is 1:(8-35).

Specifically, in step 2), the polyanion electrolyte is selected from any one of sulfonated polyether ether ketone, hydrolyzed polyacrylonitrile or sulfonated polysulfone.

Specifically, in step 3), the solvent of the polycationic electrolyte is any one of water, methanol, ethanol or isopropanol.

Specifically, in step 3), the mass percentage of the solute in the aqueous solution of the polycationic electrolyte is 0.5-1%.

Specifically, in step 3), the polycationic electrolyte is selected from any one of polyethyleneimine or dopamine.

Specifically, in step 3), the thickness of the coating liquid on the non-woven fabric is 200-300 μm.

Specifically, in step 5):

The reaction time is 10～60min;

The mass percentage of the aqueous solution of glycerol is 5-20%, and the soaking treatment time is 10-30 min;

The temperature of high temperature heating treatment is 80-120℃, and the time is 10-15min;

Specifically, the preparation method of the polyelectrolyte composite nanofiltration membrane comprises the following steps:

A) Dissolve the organic polymer in the organic solvent as a film-forming material, configure it into a polymer solution with a mass percentage of 14%-20wt%, and let it stand for use;

B) adding polyanion electrolyte to the solution prepared in step A), the mass ratio of the amount of polyanion electrolyte added to the organic polymer in step A) is 1: (8-35), stirring and dissolving, and then standing for defoaming, get the coating liquid;

C) configure the polycationic electrolyte into a solution with a mass percentage of 1%, and leave it to stand for use;

D) Pour the coating liquid in step B) on the non-woven fabric support, use a doctor blade to uniformly coat the organic solution on the non-woven fabric, and then quickly immerse it in deionized water to solidify to obtain a nanofiltration membrane base film, set aside for use;

E) Take the base membrane in step D), pour the aqueous solution in step C) on the surface of the base membrane, make the oppositely charged polyelectrolyte undergo a cross-linking reaction, and then post-process to obtain a polyelectrolyte composite nanofiltration membrane.

The present invention also provides the polyelectrolyte composite nanofiltration membrane prepared by the above preparation method.

The present invention also provides the application of the above-mentioned polyelectrolyte composite nanofiltration membrane, for dye removal in sewage treatment, or for organic matter removal in drinking water treatment.

Preferably, the molecular weight of the dye or organic matter in the water to be removed is 500-2000. High rejection for organics in this range.

Aiming at the shortcomings of the traditional layer-by-layer self-assembly method, the preparation process is cumbersome, and the polyelectrolyte is introduced into the composite nanofiltration membrane as the ultrafiltration base membrane of the support, so as to modify the ultrafiltration base membrane, so that the surface of the base membrane is charged and free of charge. It reacts with the oppositely charged polyelectrolyte to form a dense selective layer directly on the surface of the supporting membrane, which is only half of the double layer formed by the combination of the two polyelectrolytes in the layer-by-layer self-assembly, which greatly reduces the membrane thickness. Increased membrane flux. The ionic cross-linking between the polyelectrolytes and the strengthening of the cross-linking effect by post-treatment make the nanofiltration membrane have good stability. The separation performance of nanofiltration membranes can be controlled by adjusting the concentration of polymers and the concentration ratio between polymers, reaction time and various parameters of post-treatment to suit different separation requirements. The method of the invention is simple and economical, and has a wide application range.

Detailed ways

The principles and features of the present invention are described below, and the examples are only used to explain the present invention, but not to limit the scope of the present invention.

Example 1

1. Weigh 8g of PES and 1g of SPEEK respectively, add 41g of N-N dimethylacetamide organic solvent, and keep stirring at room temperature until PES and SPEEK are completely dissolved, and the solution is allowed to stand for defoaming to obtain a coating liquid;

2. Weigh 1g PEI into a 250mL volumetric flask, add deionized water to the mark, and keep stirring at room temperature until PEI is completely dissolved, and the solution is left to stand for use;

3. The non-solvent-induced phase separation method is used to uniformly coat the coating liquid on the non-woven fabric with a 250μm thick film blade, and then quickly immerse it in deionized water to make a base film, and let it stand for 12 hours before use ;

4. Take out the base film, clean the film surface, pour the PEI solution on the film, rinse with deionized water after 30 minutes of reaction to remove excess PEI on the film surface;

5. Immerse the film in an aqueous solution of glycerol with a mass percentage of 5% for 30 minutes;

6. Treat the membrane at 120°C for 10 minutes to prepare a polyelectrolyte composite nanofiltration membrane.

The separation performance of the nanofiltration membrane obtained in this example to the polyethylene glycol aqueous solution with an average molecular weight of 1000 was measured. When the concentration of polyethylene glycol in the feed liquid was 0.1 g/L, the temperature was 25 °C, and the operating pressure was 4 bar, the membrane The flux was 56.8 L/(m ² ·h) and the rejection was 99.2%.

Example 2

1. Weigh 7.11g of PES and 0.89g of SPEEK respectively, add 42g of DMAC organic solvent, and keep stirring at room temperature until PES and SPEEK are completely dissolved, and the solution is allowed to stand for defoaming to obtain a coating liquid;

2. Weigh 1g PEI into a 250mL volumetric flask, add deionized water to the mark, and keep stirring at room temperature until PEI is completely dissolved, and the solution is left to stand for use;

3. The non-solvent-induced phase separation method is used to uniformly coat the coating liquid on the non-woven fabric with a 250μm thick film blade, and then quickly immerse it in deionized water to make a base film, and let it stand for 12 hours before use ;

4. Take out the base film, clean the film surface, pour the PEI solution on the film, rinse with deionized water after 30 minutes of reaction to remove excess PEI on the film surface;

5. Immerse the film in an aqueous solution of glycerol with a mass percentage of 5% for 30 minutes;

6. Treat the membrane at 120°C for 10 minutes to prepare a polyelectrolyte composite nanofiltration membrane.

Determination of the separation performance of the nanofiltration membrane obtained in this example for four dyes: Rose Bengal, Congo red, methyl orange, and methyl blue. When the conductivity of the dye aqueous solution is 2mS/cm, the temperature is 25°C, and the operating pressure is 4bar , the membrane fluxes were 59.6L/(m ² ·h), 56.4L/(m ² ·h), 54.7L/(m ² ·h), and 13.7L/(m ² ·h), respectively, and the rejection rates were 99.6%, 99.3%, 96%, 86.4%.

Example 3

1. Weigh 7.11g of PES and 0.89g of SPEEK respectively, add 42g of DMAC organic solvent, and keep stirring at room temperature until PES and SPEEK are completely dissolved, and the solution is allowed to stand for defoaming to obtain a coating liquid;

2. Weigh 1g PEI into a 250mL volumetric flask, add deionized water to the mark, and keep stirring at room temperature until PEI is completely dissolved, and the solution is left to stand for use;

3. Using the non-solvent phase separation method, the coating liquid is uniformly coated on the non-woven fabric with a 250μm thick film blade, and then quickly immersed in deionized water to make a base film, and let stand for 12 hours before use ;

4. Take out the base film, clean the film surface, pour the PEI solution on the film, rinse with deionized water after 30 minutes of reaction to remove excess PEI on the film surface;

5. Immerse the film in an aqueous solution of glycerol with a mass percentage of 5% for 30 minutes;

6. Treat the membrane at 120°C for 10 minutes to prepare a polyelectrolyte composite nanofiltration membrane.

The separation performance of the nanofiltration membrane obtained in this example for ibuprofen solution and naproxen solution was measured. When the drug concentration was 5 mg/L, the temperature was 25 °C, the operating pressure was 4 bar, and the membrane flux was 40.6 L/( m ² ·h) and 66.7 L/(m ² ·h), the rejections were 80.9% and 75.9%, respectively.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (10)

1. The preparation method of the polyelectrolyte composite nanofiltration membrane is characterized by comprising the following steps:

1) preparing a polymer solution comprising an organic polymer and an organic solvent, with the organic polymer as a film-forming material;

2) adding polyanion electrolyte into the polymer solution obtained in the step 1), dissolving, standing and defoaming to obtain a coating solution;

3) coating the film coating liquid obtained in the step 2) on a non-woven fabric, and then immersing the non-woven fabric in deionized water for curing to obtain a nanofiltration membrane base film;

4) attaching a polycation electrolyte solution to the nanofiltration membrane base membrane obtained in the step 3), reacting, and sequentially performing soaking treatment and high-temperature heating treatment on a glycerol aqueous solution after the reaction is finished to obtain a polyelectrolyte composite nanofiltration membrane;

wherein:

the mass percentage of the water solution of the glycerol is 5-20%, and the soaking time is 10-30 min;

the temperature of the high-temperature heating treatment is 80-120 ℃, and the time is 10-15 min.

2. The method for preparing a polyelectrolyte complex nanofiltration membrane according to claim 1, wherein the method comprises the following steps: in the step 1), the mass percentage of solute in the polymer solution is 14-20%; the organic solvent is any one of N-N dimethyl acetamide, N-N dimethyl formamide, dimethyl sulfoxide or N-methyl pyrrolidone.

3. The method for preparing a polyelectrolyte complex nanofiltration membrane according to claim 2, wherein the method comprises the following steps: the organic polymer is selected from any one of polyether sulfone, polysulfone or polyacrylonitrile.

4. The method for preparing a polyelectrolyte complex nanofiltration membrane according to claim 1, wherein the method comprises the following steps: in the step 2), the mass ratio of the polyanionic electrolyte to the organic polymer is 1 (8-35).

5. The method for preparing a polyelectrolyte complex nanofiltration membrane according to claim 1, wherein the method comprises the following steps: in the step 2), the polyanionic electrolyte is selected from any one of sulfonated polyether ether ketone, hydrolyzed polyacrylonitrile or sulfonated polysulfone.

6. The method for preparing a polyelectrolyte complex nanofiltration membrane according to claim 1, wherein the method comprises the following steps: in the step 4), the solvent of the polycation electrolyte solution is any one of water, methanol, ethanol or isopropanol, and the mass percentage of the solute is 0.1-1%.

7. The method for preparing a polyelectrolyte complex nanofiltration membrane according to claim 1, wherein the method comprises the following steps: in the step 4), the polycationic electrolyte is selected from any one of polyethyleneimine or dopamine.

8. The method for preparing a polyelectrolyte complex nanofiltration membrane according to any one of claims 1 to 7, wherein in the step 4): the reaction time is 10-60 min.

9. A polyelectrolyte complex nanofiltration membrane prepared according to the preparation method of any one of claims 1 to 8.

10. Use of a polyelectrolyte complex nanofiltration membrane according to claim 9, wherein: used for dye removal in sewage treatment or organic matter removal in drinking water treatment.