Hollow fiber nanofiltration membrane and preparation method thereof

Abstract

The present application relates to a hollow fiber nanofiltration membrane and its preparation method. The method comprises first preparing a hollow fiber spinning feed solution containing 20% high-molecular-weight polyethersulfone, 40% polyethylene glycol (molecular weight 400g / mol), and 40% N-methyl-2-pyrrolidone, stirring at 70°C, degassing, and cooling; then preparing a core solution containing 5% N-methyl-2-pyrrolidone and 95% reverse osmosis pure water. The core solution is then extruded through a spinning spinneret to form a phase transition base membrane. After drying, crosslinking solution 1 and crosslinking solution 2 are prepared. The base membrane is immersed in these solutions for 10 minutes and 30 minutes, respectively, and then cleaned and dried to obtain a nanofiltration membrane with excellent antioxidant and acid-base resistance.

Description

Technical Field

[0001] The present application relates to the field of nanofiltration membrane technology, and in particular to an enhanced anti-oxidation, acid and alkali resistant hollow fiber nanofiltration membrane and a preparation method thereof. Background Art

[0002] Nanofiltration membrane technology has attracted much attention in the field of water treatment. The current mainstream in the market is polyamide rolled nanofiltration membrane, but it has technical disadvantages such as high operating pressure and strict pretreatment requirements, which limits its application. In contrast, the hollow fiber nanofiltration membrane structure has a higher membrane surface area and better operational flexibility. It performs well in practical applications and is especially suitable for high-demand wastewater treatment. However, the poor antioxidant capacity and insufficient acid and alkali resistance of polyamide materials limit the application of polyamide nanofiltration membranes in the field of wastewater treatment. Even if hollow fiber nanofiltration membranes are made, their inherent chemical properties still bring certain limitations. The water quality of industrial wastewater varies, and it is extremely challenging to treat it to meet standards, especially for wastewater containing oxides or high acidity and alkalinity. The market urgently needs enhanced antioxidant and acid- and alkali-resistant hollow fiber nanofiltration membranes to cope with complex conditions. Summary of the Invention

[0003] The purpose of this application is to address the above-mentioned problems existing in the prior art and to provide an enhanced antioxidant, acid and alkali resistant hollow fiber nanofiltration membrane and a preparation method thereof.

[0004] In order to achieve the above application objectives, the present application adopts the following technical solution: A method for preparing a hollow fiber nanofiltration membrane comprises the following steps:

[0005] S00, preparing a hollow fiber spinning solution and heating and stirring it, wherein the hollow fiber spinning solution comprises 20% high molecular weight polyethersulfone, 40% polyethylene glycol, and 40% N-methyl-2-pyrrolidone;

[0006] S10, after stirring evenly, perform vacuum degassing and cool to room temperature;

[0007] S20, preparing a hollow fiber spinning core solution comprising 5% N-methyl-2-pyrrolidone and 95% reverse osmosis pure water, stirring the solution evenly and setting aside;

[0008] S30, extruding the hollow fiber spinning material solution and the hollow fiber spinning core solution through a spinning spinneret, exposing them to air, and then placing them in a pure water tank for phase change to form a stable hollow fiber base membrane;

[0009] S40, collecting the hollow fiber base membrane to obtain the hollow fiber base membrane required for preparing the hollow fiber nanofiltration membrane and drying or naturally drying it;

[0010] S50, preparing a cross-linking solution 1, wherein the components thereof include polyethyleneimine, polyvinyl alcohol, sodium hydroxide, and pure water, and uniformly stirring after heating to obtain a cross-linking solution 1; preparing a cross-linking solution 2, wherein the components thereof include succinaldehyde, polyethylene glycol diglycidyl ether, and pure water, and stirring to obtain a cross-linking solution 2;

[0011] S60, soaking the dried hollow fiber base membrane in the cross-linking solution 1 for a first set time, then taking it out and cleaning and drying it to obtain dried membrane fibers;

[0012] S70, soaking the dried membrane fibers in the cross-linking solution 2 for a second set time, taking them out, cleaning them, and drying them to obtain an enhanced antioxidant and acid- and alkali-resistant hollow fiber nanofiltration membrane.

[0013] Furthermore, in step S00, a hollow fiber spinning solution is prepared and placed in a 70° C. environment with stirring to ensure that the polyethersulfone is completely dissolved.

[0014] Furthermore, in step S00, the molecular weight of polyethylene glycol is 400 g / mol.

[0015] Furthermore, in step S50, the molecular weight of polyethyleneimine is 25000 g / mol.

[0016] Furthermore, in step S50, the molecular weight of the polyvinyl alcohol is 90,000 g / mol.

[0017] Furthermore, in step S50, the components of the cross-linking solution 1 include 2% polyethyleneimine, 2% polyvinyl alcohol, 0.1% sodium hydroxide and 95.9% pure water.

[0018] Furthermore, in step S50, the cross-linking solution 2 comprises 3% succinaldehyde, 1% polyethylene glycol diglycidyl ether, and 96% pure water.

[0019] Furthermore, in step S60, the first set time is ten minutes.

[0020] Furthermore, in step S70, the second set time is half an hour.

[0021] A hollow fiber nanofiltration membrane is prepared by the above-mentioned hollow fiber nanofiltration membrane preparation method.

[0022] Compared with the prior art, the present invention has the following effects:

[0023] 1. Significantly enhanced antioxidant and acid / base resistance (pH 0, pH 14): Through a specific preparation method and material combination, this membrane overcomes the poor antioxidant capacity and acid / base resistance of traditional polyamide nanofiltration membranes. This allows it to better handle industrial wastewater containing oxidants or high acidity and alkalinity, expanding the application range of nanofiltration membranes in wastewater treatment. Compared to typical polyamide nanofiltration membranes, it offers greater chemical stability, effectively addressing the susceptibility of polyamide bonds to oxidation and hydrolysis in environments containing oxidants and high acidity and alkalinity. Its chlorine resistance can reach 250,000 ppm / hr.

[0024] 2. Good operational flexibility: The hollow fiber structure has a higher membrane surface area and better operational flexibility than the rolled nanofiltration membrane, and performs better in actual application scenarios.

[0025] 3. Clear composition and process parameters: The instructions provide detailed information on the specific composition and proportion of the materials used in each step, as well as process parameters such as operating temperature and time, providing a reliable basis for the stable preparation of high-quality nanofiltration membranes.

[0026] 4. Step-by-step cross-linking treatment: By successively immersing the hollow fiber base membrane in cross-linking solution 1 and cross-linking solution 2 with specific components, the performance of the nanofiltration membrane is further improved. The preparation method is scientific and reasonable, and has strong operability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a flow chart of a preparation method according to an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the structure of the enhanced antioxidant and acid-alkali resistant hollow fiber nanofiltration membrane obtained according to the embodiment of the present invention. Figure 1 ;

[0029] Figure 3 This is a schematic diagram of the structure of the enhanced antioxidant and acid-alkali resistant hollow fiber nanofiltration membrane obtained according to the embodiment of the present invention. Figure 2 ;

[0030] Figure 4 is a data curve diagram of the membrane module according to the membrane manufacturing scheme 1 in implementation case 1 according to an embodiment of the present invention;

[0031] Figure 5 is a data curve diagram of the membrane module according to the membrane manufacturing scheme 1 in the implementation case 2 according to an embodiment of the present invention;

[0032] Figure 6 It is a data curve diagram of the membrane module of the membrane manufacturing scheme 1 according to an embodiment of the present invention in implementation case 3. DETAILED DESCRIPTION

[0033] The following will be combined with the accompanying drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of this application.

[0034] Those skilled in the art should understand that, in the disclosure of this application, the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the above terms cannot be understood as limiting this application.

[0035] Example 1

[0036] like Figure 1 As shown, the hollow fiber nanofiltration membrane preparation method includes the following:

[0037] Step 1 – Prepare a hollow fiber spinning solution consisting of 20% high-molecular-weight polyethersulfone, 40% polyethylene glycol (molecular weight 400 g / mol), and 40% N-methyl-2-pyrrolidone. Place the solution in a stirring tank and stir it evenly for 24 hours at 70°C.

[0038] Step 2: After ensuring that the polyethersulfone is completely dissolved in the solvent, the spinning solution is vacuum-degassed for more than 7 hours, and the temperature is allowed to drop to room temperature for later use;

[0039] Step 3 – Prepare the hollow fiber spinning core solution, which contains 5% N-methyl-2-pyrrolidone and 95% reverse osmosis pure water, stir well and set aside;

[0040] Step 4 – The spinning material solution and core solution are transported to the spinning spinneret through a gear pump and extruded from the spinneret, exposed to about 10 cm of air, and then contacted with water in a pure water tank to undergo phase change, forming a stable hollow fiber base membrane;

[0041] Step 5: The formed hollow fiber base membrane is collected by a collection wheel to obtain the hollow fiber base membrane required for preparing the hollow fiber nanofiltration membrane;

[0042] Step 6: drying or natural drying the hollow fiber base membrane obtained by spinning;

[0043] Step 7 – Prepare crosslinking solution 1, which contains 2% polyethyleneimine (molecular weight 25,000 g / mol), 2% polyvinyl alcohol (molecular weight 90,000 g / mol), 0.1% sodium hydroxide, and 95.9% pure water. Heat to 80°C and stir evenly for 4 hours to obtain a stable and uniform crosslinking solution 1;

[0044] Step 8: Prepare crosslinking solution 2, which contains 3% succinaldehyde, 1% polyethylene glycol diglycidyl ether, and 96% pure water, and stir for 1 hour to obtain a stable and uniform crosslinking solution 2;

[0045] Step 9: Soak the dried hollow fiber membrane in crosslinking solution 1 for 10 minutes;

[0046] Step 10 – Remove the membrane from the cross-linking solution 1, remove excess solution from the membrane surface, and air dry.

[0047] Step 11 – Soak the dried membrane in cross-linking solution 2 for 30 minutes;

[0048] Step 12 – Remove the membrane filaments from the cross-linking solution 2, remove excess solution, and then allow them to dry naturally in the air to obtain an enhanced antioxidant and acid- and alkali-resistant hollow fiber nanofiltration membrane formed after the cross-linking reaction.

[0049] See also Figure 2 , it can be seen that the cross section of the spun hollow fiber base membrane presents a porous structure, see Figure 3 It can be seen that the cross-linked layer on the hollow fiber base membrane is a dense and firm desalination layer.

[0050] Example 2:

[0051] According to the preparation method of Example 1, the characteristics and performance of the hollow fiber nanofiltration membrane obtained are shown in Table 1 below:

[0052] Table 1

[0053]

[0054] [1] The pure water flux test uses reverse osmosis water as the test raw water, and the test conditions are 3 bar and 25°C;

[0055] [2] The test for magnesium sulfate retention uses 200 mg / L magnesium sulfate solution as the test raw water, and the test conditions are 3 bar and 25°C.

[0056] Control group 1 in Table 1 is a polyamide hollow fiber nanofiltration membrane, and its preparation method is the same as that of Example 1, but its cross-linking solution formula is as follows:

[0057] Cross-linking solution 1: 2% piperazine, 0.1% sodium hydroxide, and 97.9% pure water;

[0058] Cross-linking solution 2: 0.1% 1,3,5-benzenetricarboxylic acid chloride and 99.9% n-hexane.

[0059] Control group 2 in Table 1 is another polyamide hollow fiber nanofiltration membrane. Compared with the polyamide hollow fiber nanofiltration membrane of control group 1, its flux is higher. Its preparation method is the same as that of Example 1, but its cross-linking solution formula is as follows:

[0060] Cross-linking solution 1: 2% 1-methylpiperazine, 0.2% sodium hydroxide, 1% sodium camphorsulfonate, and 96.8% pure water;

[0061] Crosslinking solution 2: 0.1% isophthaloyl dichloride, 1% acetone, and 98.9% n-hexane.

[0062] Example 3 (Implementation Case 1): Oxidation Test

[0063] The hollow fiber nanofiltration membrane filaments prepared in Example 2 were assembled into membrane modules for testing, including membrane preparation case 1, control groups 1 and 2. Sodium hypochlorite is often used as a disinfectant and bleaching agent in water treatment and has strong oxidizing ability. Therefore, in this test, a 100 mg / L sodium hypochlorite solution was prepared as a representative of raw water containing oxides. The membrane module was immersed in the sodium hypochlorite solution. At specific time intervals, the membrane module was removed from the solution and tested with a 200 mg / L magnesium sulfate solution. The test conditions were 3 bar and 25°C, and its water flux and magnesium sulfate retention rate were recorded. The test results are shown in Table 2 below:

[0064] Table 2

[0065]

[0066] See also Figure 4 As shown in Table 2, under the same test conditions, membrane Case 1, using the present invention's solution, maintained an extremely high average magnesium sulfate rejection compared to Controls 1 and 2, while maintaining essentially unchanged flux. The cumulative test duration was significantly longer than both control groups, and chlorine resistance was also significantly higher. Both the water flux and magnesium sulfate rejection of membrane Case 1 exhibited stable curves, with a cumulative chlorine resistance of 264,000 ppm / hr.

[0067] Example 4 (Implementation Case 2): Strong Acid Test

[0068] The hollow fiber nanofiltration membrane prepared in Example 2 was assembled into membrane modules for testing, including membrane preparation case 1 and control groups 1 and 2. This test was performed using hydrochloric acid solution as a representative acidic raw water, with a pH controlled between 0 and 1. The membrane modules were immersed in the hydrochloric acid solution. At specific time intervals, the modules were removed from the solution and tested with a 200 mg / L magnesium sulfate solution at 3 bar and 25°C. The water flux and magnesium sulfate retention rate were recorded. The test results are shown in Table 3 below:

[0069] Table 3

[0070]

[0071] See also Figure 5 As shown in Table 3, under the same test conditions, the membrane case 1 using the present invention maintained an extremely high average magnesium sulfate rejection rate compared to the control groups 1 and 2 while maintaining essentially unchanged flux, and the cumulative test duration was much longer than the two control groups. Both the water flux and magnesium sulfate rejection of membrane case 1 showed stable curves, with a cumulative test duration of up to 76 days in a strong acid environment.

[0072] Example 5 (Implementation Case 3): Strong Alkali Test

[0073] The hollow fiber nanofiltration membrane prepared in Example 2 was assembled into membrane modules for testing, including membrane preparation case 1 and control groups 1 and 2. This test was performed using sodium hydroxide solution as a representative alkaline raw water solution, with a pH controlled between 13 and 14. The membrane modules were immersed in the sodium hydroxide solution. At specific time intervals, the modules were removed from the solution and tested with a 200 mg / L magnesium sulfate solution at 3 bar and 25°C. The water flux and magnesium sulfate retention rate were recorded. The test results are shown in Table 4 below:

[0074] Table 4

[0075]

[0076] See also Figure 6 As shown in Table 4, under the same test conditions, the membrane case 1 using the present invention maintained an extremely high average magnesium sulfate rejection rate compared to the control groups 1 and 2 while maintaining essentially unchanged flux, and the cumulative test duration was much longer than the two control groups. Furthermore, both the water flux and magnesium sulfate rejection of membrane case 1 showed stable curves, with a cumulative test duration of up to 80 days in a strong alkaline environment.

[0077] The parts not described in detail in this application are prior art, so this application does not describe them in detail.

[0078] It is to be understood that the term "one" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element may be one, while in another embodiment, the number of the elements may be multiple, and the term "one" should not be understood as a limitation on the quantity.

[0079] Although this document uses a lot of professional terms, it does not exclude the possibility of using other terms. These terms are used only to more conveniently describe and explain the essence of this application; interpreting them as any additional restrictions is contrary to the spirit of this application.

[0080] This application is not limited to the above-mentioned optimal implementation method. Anyone can derive various other forms of products based on the inspiration of this application. However, no matter what changes are made in their shape or structure, any technical solution that is the same or similar to that of this application falls within the scope of protection of this application.

Claims

1. A method for preparing a hollow fiber nanofiltration membrane, characterized in that: The following steps are involved: S00, preparing a hollow fiber spinning solution and heating and stirring it, wherein the solution comprises 20% high molecular weight polyethersulfone, 40% polyethylene glycol, and 40% N-methyl-2-pyrrolidone; the molecular weight of the polyethylene glycol is 400 g / mol; S10, after stirring evenly, perform vacuum degassing and cool to room temperature; S20, preparing a hollow fiber spinning core solution comprising 5% N-methyl-2-pyrrolidone and 95% reverse osmosis pure water, stirring the solution evenly and setting aside; S30, extruding the hollow fiber spinning material solution and the hollow fiber spinning core solution through a spinning spinneret, exposing them to air, and then placing them in a pure water tank for phase change to form a stable hollow fiber base membrane; S40, collecting the hollow fiber base membrane to obtain the hollow fiber base membrane required for preparing the hollow fiber nanofiltration membrane and drying or naturally drying the hollow fiber base membrane; S50, preparing a cross-linking solution 1, wherein the components thereof include 2% polyethyleneimine, 2% polyvinyl alcohol, 0.1% sodium hydroxide, and 95.9% pure water, and uniformly stirring after heating to obtain a cross-linking solution 1; preparing a cross-linking solution 2, wherein the components thereof include 3% succinaldehyde, 1% polyethylene glycol diglycidyl ether, and 96% pure water, and stirring to obtain a cross-linking solution 2; Wherein, the molecular weight of the polyethyleneimine is 25000 g / mol; the molecular weight of the polyvinyl alcohol is 90000 g / mol; S60, soaking the dried hollow fiber-based membrane in the cross-linking solution 1 for a first set time, then taking it out and cleaning and drying it to obtain dried membrane fibers; S70, soaking the dried membrane fibers in the cross-linking solution 2 for a second set time, taking them out, cleaning them, and drying them to obtain an enhanced antioxidant and acid- and alkali-resistant hollow fiber nanofiltration membrane.

2. The method for preparing a hollow fiber nanofiltration membrane according to claim 1, wherein: In step S00, a hollow fiber spinning solution is prepared and placed in a 70° C. environment and stirred to ensure that the polyethersulfone is completely dissolved.

3. The method for preparing a hollow fiber nanofiltration membrane according to claim 1 or 2, wherein: In step S60, the first set time is ten minutes.

4. The method for preparing a hollow fiber nanofiltration membrane according to claim 1 or 2, wherein: In step S70, the second set time is thirty minutes.

5. Hollow fiber nanofiltration membrane, characterized in that The hollow fiber nanofiltration membrane is prepared by the hollow fiber nanofiltration membrane preparation method according to any one of claims 1 to 4.

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