Preparation method of hollow fiber nanofiltration membrane

Abstract

The invention relates to a preparation method of a hollow fiber nanofiltration membrane, which comprises the following steps: S1, dropwise adding a first solution in which 1, 3-propane sultone is dissolved into a second solution in which tris (2-aminoethyl) amine is dissolved for reaction, and then sequentially precipitating, dialyzing and freeze-drying the reaction solution to obtain quaternized tris (2-aminoethyl) amine; s2, adding tannic acid into the Tris solution, stirring and dissolving to oxidize phenolic hydroxyl into quinonyl, and carrying out self-crosslinking polymerization; then adding quaternized tris (2-aminoethyl) amine, stirring, and carrying out a cross-linking reaction to obtain a membrane soaking solution; s3, sealing the two ends of the hollow fiber ultrafiltration membrane, soaking the hollow fiber ultrafiltration membrane in the membrane soaking liquid for 1-6 hours, and then airing the hollow fiber ultrafiltration membrane; and S4, soaking the hollow fiber ultrafiltration membrane soaked in the membrane soaking solution in a cysteamine solution, and further carrying out a cross-linking reaction to obtain the hollow fiber nanofiltration membrane. According to the invention, the nanofiltration membrane with good anti-pollution performance and separation performance can be prepared.

Description

Technical Field

[0001] This invention relates to the field of separation membrane technology, and in particular to a method for preparing a hollow fiber nanofiltration membrane. Background Technology

[0002] In today's rapidly developing technological landscape, membrane separation technology, as a highly efficient and energy-saving separation method, is widely used in numerous fields. From seawater desalination to wastewater treatment, from food and beverage production to biopharmaceutical research and development, membrane separation technology is ubiquitous. Within the field of separation membranes, hollow fiber nanofiltration membranes are gradually emerging as a prominent and highly regarded membrane separation technology in the industry.

[0003] Compared to spiral wound nanofiltration membranes, hollow fiber nanofiltration membranes offer a larger filtration area and higher packing density per unit volume. Furthermore, they are easier to clean and have lower operating costs. Hollow fiber nanofiltration membranes typically have a molecular weight cutoff between 200 and 2000 Da, effectively removing polyvalent salt ions, small organic pollutants, and dyes from water. Common methods for preparing hollow fiber nanofiltration membranes include interfacial polymerization, layer-by-layer self-assembly, and coating crosslinking. Among these methods, coating crosslinking offers simpler operation steps and a more stable preparation process.

[0004] Separation membranes face a common problem during operation – membrane fouling. During the filtration process, some large molecules in the liquid, such as proteins and humic acids, have hydrophobic sites in their molecular structure that interact with the hydrophobic sites on the membrane surface. As the filtration process continues, these large molecules gradually accumulate on the membrane surface, causing membrane fouling, which leads to a rapid decrease in membrane flux and a shortened lifespan. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a hollow fiber nanofiltration membrane, which produces a nanofiltration membrane with good antifouling properties.

[0006] To achieve the above objectives, this invention discloses a method for preparing a hollow fiber nanofiltration membrane, which includes the following steps: S1: A first solution containing 1,3-propanesulfonate lactone was added dropwise to a second solution containing tris(2-aminoethyl)amine to carry out the reaction. Then, the reaction solution was subjected to precipitation, dialyzing and freeze-drying in sequence to obtain quaternized tris(2-aminoethyl)amine. S2: Tannic acid is added to Tris solution and stirred to dissolve it, causing its phenolic hydroxyl groups to be oxidized to quinone groups and undergo self-crosslinking polymerization; then quaternized tri(2-aminoethyl)amine is added and stirred to carry out the crosslinking reaction, resulting in an impregnation solution; S3: After sealing both ends of the hollow fiber ultrafiltration membrane, immerse it in the impregnation solution for 1-6 hours, and then air dry it; S4: The hollow fiber ultrafiltration membrane that has been soaked in the impregnation solution is soaked in a cysteine ​​solution to further undergo a cross-linking reaction, thereby obtaining the hollow fiber nanofiltration membrane.

[0007] Preferably, in step S1, the mass ratio of 1,3-propanesulfonate lactone to tris(2-aminoethyl)amine is 1-4:1.

[0008] Preferably, in step S1, both the first solution and the second solution are dimethyl sulfoxide solutions; the first solution containing 1,3-propanesulfonate lactone and the second solution containing tris(2-aminoethyl)amine are reacted at 40-60°C for 6-12 hours; the reaction solution is poured into acetone for precipitation and dialyzed with water.

[0009] Preferably, in step S2, the amount of tannic acid added is 1.0-2.5 wt%, and the amount of quaternized tri(2-aminoethyl)amine added is 1.0-2.5 wt%.

[0010] Preferably, in step S2, the crosslinking reaction time of tannic acid and quaternized tri(2-aminoethyl)amine is 3-6 h.

[0011] Preferably, in step S3, the hollow fiber ultrafiltration membrane is cleaned before being immersed in the membrane soaking solution.

[0012] Preferably, in step S4, the concentration of the cysteamine solution is 0.5-2.0 wt%.

[0013] Preferably, in step S4, after the hollow fiber ultrafiltration membrane is immersed in cysteine ​​solution for 1-6 hours, it is taken out and placed in pure water for later use.

[0014] Preferably, the hollow fiber ultrafiltration membrane is made of one or more materials selected from polyvinylidene fluoride, polysulfone, and polyethersulfone.

[0015] Preferably, the hollow fiber ultrafiltration membrane has a molecular weight cutoff of 10,000-50,000 Da.

[0016] The present invention has the following beneficial effects: This invention uses tannic acid, quaternized tri(2-aminoethyl)amine, and cysteine ​​to construct a hollow fiber nanofiltration membrane with a zwitterionic separation layer. First, oxidized tannic acid and quaternized tri(2-aminoethyl)amine undergo Michael addition and Schiff base reactions to construct a hydrophilic separation layer on the surface of the hollow fiber ultrafiltration membrane. The quaternized tri(2-aminoethyl)amine, which has multiple functional groups, acts as both a crosslinking agent and introduces zwitterionic groups with excellent hydrophilicity. Then, cysteine ​​is further crosslinked with oxidized tannic acid to prepare a hollow fiber nanofiltration membrane with good separation performance and antifouling properties. Attached Figure Description

[0017] Figure 1 This is a surface electron microscope image of the hollow fiber ultrafiltration membrane used in Example 3.

[0018] Figure 2 This is a surface electron microscope image of the hollow fiber nanofiltration membrane prepared in Example 3. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0020] This invention discloses a method for preparing a hollow fiber nanofiltration membrane, which includes the following steps: S1: The mass ratio of 1,3-propanesulfonate lactone to tris(2-aminoethyl)amine is controlled at 3:1. A first solution containing dissolved 1,3-propanesulfonate lactone is added dropwise to a second solution containing dissolved tris(2-aminoethyl)amine to carry out the reaction. After reacting at 40°C for 12 hours, the reaction solution is poured into acetone for precipitation, then dialyzed with water, and finally freeze-dried to obtain quaternized tris(2-aminoethyl)amine. Both the first and second solutions are dimethyl sulfoxide solutions. Step S1 involves quaternizing tris(2-aminoethyl)amine with trifunctional groups, introducing zwitterionic groups into its molecular structure.

[0021] S2: A Tris buffer solution was prepared by weighing a certain proportion of tris(hydroxymethyl)aminomethane, hydrochloric acid, and pure water. Tannic acid was added to the Tris solution and stirred to dissolve it, causing its phenolic hydroxyl groups to oxidize to quinone groups and undergo self-crosslinking polymerization. Then, quaternized tri(2-aminoethyl)amine was added and stirred for 3 hours to carry out the crosslinking reaction, obtaining the membrane impregnation solution. The amount of tannic acid added was 1.0-2.5 wt%, and the amount of quaternized tri(2-aminoethyl)amine added was 1.0-2.5 wt%. Step S2 utilizes the Michael addition and Schiff base reaction between oxidized tannic acid and quaternized tri(2-aminoethyl)amine to construct a separation layer with zwitterionic groups on the surface of the hollow fiber ultrafiltration membrane.

[0022] S3: After cleaning, seal both ends of the hollow fiber ultrafiltration membrane and immerse it in the impregnation solution for 1-6 hours. Then remove and air dry to introduce zwitterionic groups onto the surface of the hollow fiber ultrafiltration membrane. The hollow fiber ultrafiltration membrane is a polysulfone hollow fiber nanofiltration membrane with a molecular weight cutoff of 10,000-50,000 Da.

[0023] S4: The hollow fiber ultrafiltration membrane that has been soaked in the impregnation solution is immersed in a cysteine ​​solution to further undergo a cross-linking reaction. After reacting for 1-6 hours, it is taken out and placed in pure water for later use, thus obtaining the hollow fiber nanofiltration membrane.

[0024] The hollow fiber nanofiltration membrane with zwitterionic groups prepared in this invention was used to determine its separation and permeation performance using a cross-flow filtration device. Specifically, the hollow fiber nanofiltration membrane was tested in a Rhodamine B solution test system at different time points to measure the rejection rate of Rhodamine B and the permeate flux of the hollow fiber nanofiltration membrane.

[0025] Retention rate (R) reflects the separation performance of the membrane, R = (1 - C) / ( ... p / C f )×100%. Where C f With C p These represent the concentrations of the solute components in the feed solution and the permeate, respectively.

[0026] Water flux (J) reflects the membrane's permeability performance, J = V / (A·t). Where V is the volume of permeate on the permeate side (L); A is the effective filtration area of ​​the membrane (m²). 2 ); t is the infiltration time (h).

[0027] Examples 1-4 The method for preparing the hollow fiber nanofiltration membrane with zwitterionic groups according to the present invention includes the following steps: 1. The reaction ratio of 1,3-propanesulfonate lactone and tris(2-aminoethyl)amine was controlled at 3:1. A dimethyl sulfoxide solution containing 1,3-propanesulfonate lactone was slowly added dropwise to a dimethyl sulfoxide solution containing tris(2-aminoethyl)amine. After reacting at 40°C for 12 hours, the reaction solution was poured into acetone for precipitation. Finally, the solution was dialyzed with water and then freeze-dried to obtain quaternized tris(2-aminoethyl)amine.

[0028] 2. Prepare a Tris buffer solution by weighing a certain proportion of tris(hydroxymethyl)aminomethane, hydrochloric acid, and pure water. Add 1.0wt%–2.5wt% of tannic acid to the Tris solution and stir to dissolve it, causing the phenolic hydroxyl groups to oxidize to quinone groups and undergo self-crosslinking polymerization. Add 1.0wt%–2.5wt% of quaternized tris(2-aminoethyl)amine to the tannic acid solution and continue stirring for 3 hours to allow the crosslinking reaction to occur.

[0029] 3. After the cleaned polysulfone hollow fiber ultrafiltration membrane is sealed at both ends, it is immersed in the solution obtained in step 2). After 5 hours, it is taken out and dried to introduce zwitterionic groups on the surface of the polysulfone membrane.

[0030] 4. Finally, the hollow fiber membrane is immersed in a 0.5 wt% cysteine ​​solution to further undergo a cross-linking reaction. After 3 hours, it is removed and placed in pure water for later use.

[0031] The separation and permeation performance of the prepared hollow fiber nanofiltration membrane with zwitterionic groups was determined using a cross-flow filtration device. The rejection rate and permeate flux of the nanofiltration membrane for 0.1 g / L Rhodamine B solution were tested after 1 h and 24 h of operation at 0.3 MPa and 25 °C. The specific contents and test results of tannic acid and quaternized tri(2-aminoethyl)amine in Examples 1-4 are shown in Table 1.

[0032] Table 1

[0033] As shown in Table 1, the rejection rate of Rhodamine B in the prepared hollow fiber nanofiltration membrane increased with the increase of tannic acid and quaternized tri(2-aminoethyl)amine concentrations. Furthermore, the permeate flux decay rate of the membrane decreased after 24 hours of operation, indicating that the nanofiltration separation layer with zwitterionic groups has good antifouling properties.

[0034] The morphology of the ultrafiltration membrane from Example 3 and the prepared nanofiltration membrane were compared using electron microscopy. Figure 1-2 As shown, where, Figure 1 The polysulfone ultrafiltration membrane surface has obvious ultrafiltration membrane pores, while Figure 2 The nanofiltration membrane prepared by the method of this invention forms a dense separation layer, proving that a nanofiltration separation layer has been successfully prepared on the surface of the polysulfone ultrafiltration membrane.

[0035] Examples 5-7 The method for preparing the hollow fiber nanofiltration membrane with zwitterionic groups according to the present invention includes the following steps: 1. The reaction ratio of 1,3-propanesulfonate lactone and tris(2-aminoethyl)amine was controlled at 3:1. A dimethyl sulfoxide solution containing 1,3-propanesulfonate lactone was slowly added dropwise to a dimethyl sulfoxide solution containing tris(2-aminoethyl)amine. After reacting at 40°C for 12 hours, the reaction solution was poured into acetone for precipitation. Finally, the solution was dialyzed with water and then freeze-dried to obtain quaternized tris(2-aminoethyl)amine.

[0036] 2. Prepare a Tris buffer solution by weighing a certain proportion of tris(hydroxymethyl)aminomethane, hydrochloric acid, and pure water. Add 2.0 wt% tannic acid to the Tris solution and stir to dissolve it, causing the phenolic hydroxyl groups to oxidize to quinone groups and undergo self-crosslinking polymerization. Add 2.0 wt% quaternized tris(2-aminoethyl)amine to the tannic acid solution and continue stirring for 3 hours to allow the crosslinking reaction to occur.

[0037] 3. After the cleaned polysulfone hollow fiber ultrafiltration membrane is sealed at both ends, it is immersed in the solution obtained in step 2). After 5 hours, it is taken out and dried to introduce zwitterionic groups on the surface of the polysulfone membrane.

[0038] 4. Finally, the hollow fiber membrane is immersed in a 0.5wt% to 2.0wt% cysteine ​​solution to further undergo cross-linking reaction. After 3 hours, it is taken out and placed in pure water for later use.

[0039] The prepared hollow fiber nanofiltration membrane with zwitterionic groups was used to determine its separation and permeation performance using a cross-flow filtration device. The rejection rate and permeate flux of the nanofiltration membrane for 0.1 g / L Rhodamine B solution were tested after 1 h and 24 h of operation at 0.3 MPa and 25 °C. The specific cysteine ​​content and corresponding test results in Examples 5-7 are shown in Table 2.

[0040] Table 2

[0041] As shown in Tables 1 and 2, the separation performance of nanofiltration membrane can be easily controlled by adjusting the concentration of cysteine ​​solution. As the concentration of cysteine ​​solution increases, the degree of cross-linking of nanofiltration separation layer also increases. Under the condition of maintaining a certain water flux, the rejection rate of Rhodamine B by nanofiltration membrane is improved to a certain extent.

[0042] Examples 8-9 The method for preparing the hollow fiber nanofiltration membrane of the present invention includes the following steps: 1. The reaction ratio of 1,3-propanesulfonate lactone and tris(2-aminoethyl)amine was controlled at 3:1. A dimethyl sulfoxide solution containing 1,3-propanesulfonate lactone was slowly added dropwise to a dimethyl sulfoxide solution containing tris(2-aminoethyl)amine. After reacting at 40°C for 12 hours, the reaction solution was poured into acetone for precipitation. Finally, the solution was dialyzed with water and then freeze-dried to obtain quaternized tris(2-aminoethyl)amine.

[0043] 2. Prepare a Tris buffer solution by weighing a certain proportion of tris(hydroxymethyl)aminomethane, hydrochloric acid, and pure water. Add 2.0 wt% tannic acid to the Tris solution and stir to dissolve it, causing the phenolic hydroxyl groups to oxidize to quinone groups and undergo self-crosslinking polymerization. Add 2.0 wt% quaternized tris(2-aminoethyl)amine to the tannic acid solution and continue stirring for 3 hours to allow the crosslinking reaction to occur.

[0044] 3. After the cleaned hollow fiber ultrafiltration membrane is sealed at both ends, it is immersed in the solution obtained in step 2). After 5 hours, it is taken out and dried. Amphoteric groups are introduced on the membrane surface. The selected ultrafiltration membrane is a hollow fiber ultrafiltration membrane made of polyvinylidene fluoride, polysulfone, and polyethersulfone.

[0045] 4. Finally, the hollow fiber membrane is immersed in a 1.5 wt% cysteine ​​solution to further undergo a cross-linking reaction. After 3 hours, it is removed and placed in pure water for later use.

[0046] The separation and permeation performance of the prepared hollow fiber nanofiltration membrane was determined using a cross-flow filtration device. The rejection rate and permeate flux of the nanofiltration membrane for 0.1 g / L Rhodamine B solution were tested after 1 h and 24 h of operation at 0.3 MPa and 25 °C.

[0047] Table 3

[0048] As shown in Tables 2 and 3, due to the stronger hydrophobicity of polyvinylidene fluoride (PVDF) ultrafiltration membranes, the dispersion uniformity and density of the nanofiltration separation layer material on the membrane surface are not as good as those of polysulfone-based ultrafiltration membranes. Therefore, the retention rate of Rhodamine B in the prepared nanofiltration membranes is somewhat reduced. Hollow fiber nanofiltration membranes prepared from polysulfone and polyethersulfone materials not only have better separation performance but also have certain advantages in raw material cost.

[0049] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a hollow fiber nanofiltration membrane, characterized in that, Includes the following steps: S1: A first solution containing 1,3-propanesulfonate lactone was added dropwise to a second solution containing tris(2-aminoethyl)amine to carry out the reaction. Then, the reaction solution was subjected to precipitation, dialyzing and freeze-drying in sequence to obtain quaternized tris(2-aminoethyl)amine. S2: Tannic acid is added to Tris solution and stirred to dissolve it, causing its phenolic hydroxyl groups to be oxidized to quinone groups and undergo self-crosslinking polymerization; then quaternized tri(2-aminoethyl)amine is added and stirred to carry out the crosslinking reaction, resulting in an impregnation solution; S3: After sealing both ends of the hollow fiber ultrafiltration membrane, immerse it in the impregnation solution for 1-6 hours, and then air dry it; S4: The hollow fiber ultrafiltration membrane that has been soaked in the impregnation solution is soaked in a cysteine ​​solution to further undergo a cross-linking reaction, thereby obtaining the hollow fiber nanofiltration membrane.

2. The method for preparing the hollow fiber nanofiltration membrane according to claim 1, characterized in that: In step S1, the mass ratio of 1,3-propanesulfonate lactone to tris(2-aminoethyl)amine is 1-4:

1.

3. The method for preparing the hollow fiber nanofiltration membrane according to claim 1, characterized in that: In step S1, both the first and second solutions are dimethyl sulfoxide solutions; the first solution containing 1,3-propanesulfonate lactone and the second solution containing tris(2-aminoethyl)amine are reacted at 40-60°C for 6-12 hours; the reaction solution is poured into acetone for precipitation and dialyzed with water.

4. The method for preparing the hollow fiber nanofiltration membrane according to claim 1, characterized in that: In step S2, the amount of tannic acid added is 1.0-2.5 wt%, and the amount of quaternized tri(2-aminoethyl)amine added is 1.0-2.5 wt%.

5. The method for preparing a hollow fiber nanofiltration membrane according to claim 1, characterized in that: In step S2, the crosslinking reaction time of tannic acid and quaternized tri(2-aminoethyl)amine is 3-6 h.

6. The method for preparing a hollow fiber nanofiltration membrane according to claim 1, characterized in that: In step S3, the hollow fiber ultrafiltration membrane is cleaned before being immersed in the membrane soaking solution.

7. The method for preparing a hollow fiber nanofiltration membrane according to claim 1, characterized in that: In step S4, the concentration of the cysteamine solution is 0.5-2.0 wt%.

8. The method for preparing a hollow fiber nanofiltration membrane according to claim 1, characterized in that: In step S4, the hollow fiber ultrafiltration membrane is immersed in cysteine ​​solution for 1-6 hours and then removed and placed in pure water for later use.

9. The method for preparing a hollow fiber nanofiltration membrane according to claim 1, characterized in that: The hollow fiber ultrafiltration membrane is made of one or more materials selected from polyvinylidene fluoride, polysulfone, and polyethersulfone.

10. The method for preparing a hollow fiber nanofiltration membrane according to claim 1, characterized in that: The hollow fiber ultrafiltration membrane has a molecular weight cutoff of 10,000-50,000 Da.

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