Preparation method of nanofiltration membrane

Abstract

This invention belongs to the field of semi-permeable membrane preparation technology, specifically relating to a method for preparing a nanofiltration membrane. The preparation method includes the following steps: (1) cleaning the support layer for later use; mixing diamine, aminoβ-cyclodextrin derivative, inorganic hybrid agent, zwitterionic compound and water to obtain an aqueous phase for later use; mixing aromatic acyl chloride, co-solvent and organic solvent to obtain an oil phase for later use; (2) sequentially impregnating the support layer in the aqueous phase once, scraping the membrane, impregnating it in the oil phase a second time, and heating and curing it, and finally performing post-treatment to obtain the nanofiltration membrane. This invention introduces aminoβ-cyclodextrin derivative, inorganic hybrid agent and other components into polyamide to prepare a nanofiltration membrane, further improving the water flux and the ability to effectively separate ions of different valence states of the polyamide nanofiltration membrane.

Description

Technical Field

[0001] This invention belongs to the field of semi-permeable membrane preparation technology, specifically relating to a method for preparing a nanofiltration membrane. Background Technology

[0002] Nanofiltration membranes, or NF for short, utilize pore size sieving and charge repulsion to specifically retain small organic molecules and high-valence ions, producing purified water containing low-valence ions. They offer advantages such as high production capacity, low energy consumption, and high separation efficiency. Currently, nanofiltration membrane products are generally multi-layered composite structures, including a non-woven fabric base layer, a support layer, and a separation layer. The separation layer is made of polyamide. However, due to the difficulty in precisely controlling the surface charge density and distribution of polyamide, the Doonnan effect based on charge repulsion has limited ability to separate ions of different valence states. This often manifests as unsatisfactory separation of ions of different valence states by the nanofiltration membrane, or sacrificing water flux to achieve a high rejection rate for high-valence ions. Therefore, there is an urgent need to develop a nanofiltration membrane with high water flux and the ability to effectively separate ions of different valence states.

[0003] Chinese patent CN102872726A discloses a method for preparing a Ti-Zr composite nanofiltration membrane. The method consists of the synthesis of Ti-Zr composite sol, coating, and drying / sintering. The synthesis of the Ti-Zr composite sol involves mixing a zirconium precursor, a titanium precursor, and a solvent in a certain proportion, adding a chelating agent, mixing, diluting with water in an ice bath, and finally reacting in a constant-temperature water bath. The zirconium precursor is one of zirconium oxychloride, zirconium propoxide, or zirconium butoxide; the titanium precursor is one of titanium ethoxide, titanium isopropoxide, or titanium tert-butoxide. The drying / sintering involves drying the carrier coated with the membrane solution, heating it to 300-600℃ at a rate of 0.2-2℃ / min, holding it at that temperature for 1-10 hours, and then allowing it to cool naturally.

[0004] This patent uses zirconium and titanium organometallic precursors as raw materials to prepare Ti-Zr composite sol and use it as a membrane substrate. At the same time, the Ti-Zr composite sol needs to be further coated on γ-Al2O3 membrane, ZrO2 membrane or TiO2 membrane carrier and slowly heated and sintered. These raw material selections and operations directly lead to low production efficiency and high cost of nanofiltration membranes, which is not conducive to the application of large-scale production scenarios. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a nanofiltration membrane, which further improves the water flux and the ability of polyamide nanofiltration membranes to effectively separate ions of different valence states.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The method for preparing the nanofiltration membrane according to the present invention includes the following steps:

[0008] (1) Clean the support layer for later use; mix the diamine, aminoβ-cyclodextrin derivative, inorganic hybrid agent, zwitterionic compound and water to obtain an aqueous phase for later use; mix the aromatic acyl chloride, cosolvent and organic solvent to obtain an oil phase for later use;

[0009] (2) The support layer is sequentially immersed in the aqueous phase once, scraped, immersed in the oil phase a second time, and heated and cured. Finally, after post-treatment, a nanofiltration membrane is obtained.

[0010] in:

[0011] The support layer is one of polysulfone, polyetherketone, or polyethersulfone, and the thickness of the support layer is 45~70μm; during cleaning, the support layer is placed in the cleaning solution and acidic water in sequence for ultrasonic cleaning.

[0012] The cleaning solution is prepared according to a mass ratio of isomeric fatty alcohol polyoxyethylene ether to water of 1:(40~70), a mass ratio of support layer to cleaning solution of 1:(10~13), and a mass ratio of support layer to acidic water of 1:(13~15). The pH of the acidic water is 4.2~5.0. During ultrasonic cleaning in the cleaning solution, the ultrasonic power is 180~220W and the ultrasonic time is 6~10min. During ultrasonic cleaning in the acidic water, the ultrasonic power is 180~220W and the ultrasonic time is 2~4min. The isomeric fatty alcohol polyoxyethylene ether is one of TO-8, TO-10, or XL-90.

[0013] In step (1), the diamine is piperazine, the aminoβ-cyclodextrin derivative is mono-(6-ethylenediamino-6-deoxy)-β-cyclodextrin or mono-(6-amino-6-deoxy)-β-cyclodextrin, the inorganic hybrid agent is mesoporous nano silica with a pore size of 7.8 nm and an average particle size of 200 nm, and the zwitterionic compound is 1-butylsulfonic acid-3-methylimidazolium chloride.

[0014] In step (1), the aromatic acyl chloride is trimesoyl chloride, the co-solvent is tributyl phosphate, and the organic solvent is one of n-hexane, tetrahydrofuran, or cyclohexane.

[0015] In step (1), the mass ratio of diamine, aminoβ-cyclodextrin derivative, inorganic hybrid agent, zwitterionic compound and water is (3~4):(1.4~1.8):(1.65~2):(2~4):(42~46); the mass ratio of aromatic acyl chloride, cosolvent and organic solvent is 5:(1.9~3):(36~48).

[0016] The first immersion temperature is 26~35℃ and the first immersion time is 120~180s; the second immersion temperature is 25~32℃ and the second immersion time is 50~90s. After the second immersion, the mixture is left to stand for 8~20 minutes until there are no drips within 60s of vertical drainage, which completes the second immersion.

[0017] During the first and second impregnation processes, the mass ratio of the support layer, diamine, and aromatic acyl chloride is 500:5:(3~4):5.

[0018] The linear pressure during the scraping process is 0.38~0.60 bar, the scraping speed is 15~25 cm / s, and the scraping temperature is 15~30℃. The scraping process is completed when there are no drips within 60 seconds of vertical drainage.

[0019] The heating and curing temperature is 65~75℃, and the heating and curing time is 4~8 minutes.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention uses the mesoporous structure of mesoporous nano-silica and the truncated conical macrocyclic structure of amino-β-cyclodextrin derivatives as anchors to uniformly anchor zwitterionic compounds. This composite structure can form a stable hydration region on the membrane surface with the help of zwitterions. Since the zwitterionic compounds carry negatively charged sulfonate ions and positively charged imidazole rings, a double layer can spontaneously form in the hydration region without the need to capture salt ions to form a double layer. This makes the Donnan repulsion effect more stable. At the same time, this double layer setting in the mesoporous structure can avoid the rapid decrease in water flux caused by the formation of a double layer on the membrane surface, balancing the trade-off effect of nanofiltration membranes. It can provide a longer action path for the Donnan repulsion effect, further separating monovalent ions (sodium chloride, Na+). + Cl - ) and divalent ions (magnesium sulfate, Mg) 2+ SO4 2- This prevents monovalent ions from passing through the nanofiltration membrane along with divalent ions.

[0022] Amino-β-cyclodextrin derivatives possess a truncated conical macrocyclic structure with a hydrophilic outer ring and a hydrophobic inner ring. The amino groups on the outer ring can be embedded into the polyamide structure, making the polyamide structure more porous and providing more nanoscale water channels for the nanofiltration membrane. Mesoporous nano-silica interacts with the macrocyclic structure of the amino-β-cyclodextrin derivative through hydrogen bonding, effectively increasing water flux through a funnel effect. Furthermore, the mesoporous nano-silica itself has a regular and continuous mesoporous structure, exhibiting rigidity and low resistance, ensuring that the stability of water flux is not easily affected by changes in external conditions.

[0023] The zwitterionic compound of this invention, through the hydration capacity of its zwitterionic groups, can combine with the silanol groups on the surface of mesoporous nano-silica, the outer ring hydrophilic groups of amino β-cyclodextrin derivatives, and the cosolvent through hydrogen bonding to form a composite hydrophilic interface. This composite hydrophilic interface improves the retention rate of divalent ions. In addition, it promotes the uniform dispersion of amino β-cyclodextrin derivatives in the polyamide matrix, further reducing the resistance of water molecules entering the mesopores. Together with the sieving effect of mesoporous nano-silica, it increases the water flux of the membrane.

[0024] The co-solvent (tributyl phosphate) interacts with mesoporous nano-silica, amino-β-cyclodextrin derivatives, and zwitterionic compounds through phosphate groups. Utilizing symmetrically distributed ester chains, it allows macromolecules such as amino-β-cyclodextrin derivatives and the complex hydrophilic interface structure to embed into the polyamide network, optimizing the pore size uniformity of the polyamide membrane. Macroscopically, this results in a certain degree of balance between water flux and rejection rate, achieving higher water flux and better rejection rate. Simultaneously, the co-solvent and zwitterionic compounds jointly promote the uniform dispersion of β-cyclodextrin derivatives, which, in synergy with the double electric layer of this invention, further improves the selectivity of the nanofiltration membrane. Attached Figure Description

[0025] Figure 1 This is a SEM image of the nanofiltration membrane in Example 1. Detailed Implementation

[0026] The present invention will now be described and illustrated in detail with reference to the embodiments.

[0027] Example 1

[0028] Prepare a cleaning solution by mixing TO-10 and pure water at a mass ratio of 1:70. Place 500g of a 45μm thick polysulfone membrane in 6500g of the cleaning solution, sonicate at 200W for 6.5min, then remove and place in 7000g of acidic water (pH 4.2), sonicate at 200W for 2min, and dry for later use. Mix 400g of piperazine, 180g of mono-(6-ethylenediamino-6-deoxy)-β-cyclodextrin, 180g of mesoporous nano-silica (7.8nm pore size, 200nm average particle size), 260g of 1-butylsulfonic acid-3-methylimidazolium chloride, and 4600g of water until a suspension is obtained, and prepare the aqueous phase for later use. Mix 500g of trimesoyl chloride, 190g of tributyl phosphate, and 3600g of n-hexane to obtain the oil phase for later use.

[0029] At 28℃, a cleaned polysulfone membrane was immersed on one side in an aqueous phase for 180s. After removal, it was scraped parallel across the polysulfone membrane using a rubber roller under online pressure of 0.38 bar, a scraping speed of 25 cm / s, and a scraping temperature of 30℃, resulting in a uniformly thick aqueous liquid membrane. The scraping was completed when no dripping occurred within 60s of vertical leaching. At 32℃, a cleaned polysulfone membrane was again immersed on one side in an oil phase for 90s. After removal and standing for 15 minutes, the second immersion was completed when no dripping occurred within 60s of vertical leaching. Subsequently, it was heated at 65℃ for 8 minutes; removed, cooled to room temperature, and then immersed in hexane and pure water for 20 minutes respectively, followed by vacuum drying to constant weight to obtain a nanofiltration membrane. Its SEM image is shown below. Figure 1 As shown.

[0030] Example 2

[0031] Prepare a cleaning solution by mixing XL-90 with pure water at a mass ratio of 1:40. Place 500g of a 60μm thick polysulfone membrane in 6000g of the cleaning solution, sonicate at 190W for 8 minutes, then remove and place in 7500g of acidic water (pH 4.8), sonicate at 190W for 4 minutes, and dry for later use. Mix 320g of piperazine, 170g of mono-(6-ethylenediamino-6-deoxy)-β-cyclodextrin, 190g of mesoporous nano-silica (7.8nm pore size, 200nm average particle size), 200g of 1-butylsulfonic acid-3-methylimidazolium chloride, and 4500g of water until a suspension is obtained, and prepare the aqueous phase for later use. Mix 500g of trimesoyl chloride, 300g of tributyl phosphate, and 4800g of cyclohexane to obtain the oil phase for later use.

[0032] At 26°C, a cleaned polysulfone membrane was immersed on one side in an aqueous phase for 160 seconds. After removal, it was scraped parallel across the polysulfone membrane using a rubber roller under online pressure of 0.42 bar, a scraping speed of 20 cm / s, and a scraping temperature of 25°C, resulting in a uniformly thick aqueous liquid membrane. The scraping was completed when no dripping occurred within 60 seconds after vertical leaching. At 25°C, a cleaned polysulfone membrane was then immersed on one side in an oil phase for 60 seconds. After removal and standing for 20 minutes, the second immersion was completed when no dripping occurred within 60 seconds after vertical leaching. Subsequently, it was heated at 70°C for 7 minutes; removed, cooled to room temperature, and then immersed in cyclohexane and pure water for 25 minutes respectively, followed by vacuum drying to constant weight to obtain a nanofiltration membrane.

[0033] Example 3

[0034] Prepare a cleaning solution by mixing XL-90 and pure water at a mass ratio of 1:45. Place 500g of a 70μm thick polyethersulfone membrane in 5500g of the cleaning solution, sonicate at 220W for 6min, then remove and place in 6800g of pH 5.0 acidic water, sonicate at 220W for 3.5min, and dry for later use. Stir 360g of piperazine, 150g of mono-(6-amino-6-deoxy)-β-cyclodextrin, 200g of mesoporous nano-silica (7.8nm pore size, 200nm average particle size), 350g of 1-butylsulfonic acid-3-methylimidazolium chloride with 4200g of water until a suspension is obtained, and prepare the aqueous phase for later use. Blend 500g of trimesoyl chloride, 280g of tributyl phosphate, and 3800g of n-hexane to obtain the oil phase for later use.

[0035] At 30°C, a cleaned and prepared polyethersulfone membrane was immersed in an aqueous phase on one side for 130 seconds. After removal, it was scraped parallel across the polyethersulfone membrane using a rubber roller under online pressure of 0.46 bar, a scraping speed of 18 cm / s, and a scraping temperature of 20°C, resulting in a uniformly thick aqueous phase liquid membrane. The scraping was completed when no dripping occurred within 60 seconds after vertical leaching. At 30°C, a cleaned and prepared polyethersulfone membrane was then immersed in an oil phase on one side for 70 seconds. After removal and standing for 8 minutes, the second immersion was completed when no dripping occurred within 60 seconds after vertical leaching. Subsequently, it was heated at 75°C for 5 minutes; removed, cooled to room temperature, and then immersed in n-hexane and pure water for 30 minutes respectively, followed by vacuum drying to constant weight to obtain a nanofiltration membrane.

[0036] Example 4

[0037] Prepare a cleaning solution by mixing TO-8 and pure water at a mass ratio of 1:60. Place 500g of a 55μm thick polyetherketone membrane in 5000g of the cleaning solution, sonicate at 180W for 10min, then remove and place in 6500g of acidic water (pH=4.3), sonicate at 180W for 3min, and dry for later use. Mix 300g of piperazine, 140g of mono-(6-amino-6-deoxy)-β-cyclodextrin, 165g of mesoporous nano-silica (7.8nm pore size, 200nm average particle size), 400g of 1-butylsulfonic acid-3-methylimidazolium chloride, and 4400g of water until a suspension is obtained, and prepare the aqueous phase for later use. Mix 500g of trimesoyl chloride, 200g of tributyl phosphate, and 4100g of tetrahydrofuran to obtain the oil phase for later use.

[0038] At 35°C, a cleaned and prepared polyetherketone (PEK) membrane was immersed in an aqueous phase on one side for 120 seconds. After removal, it was scraped parallel across the PAK membrane using a rubber roller under online pressure of 0.60 bar, a scraping speed of 15 cm / s, and a scraping temperature of 15°C, resulting in a uniformly thick aqueous phase membrane. The scraping was completed when no dripping occurred within 60 seconds after vertical leaching. At 28°C, a cleaned and prepared PAK membrane was immersed in an oil phase on one side for 50 seconds. After removal and standing for 16 minutes, the second immersion was completed when no dripping occurred within 60 seconds after vertical leaching. Subsequently, it was heated at 72°C for 4 minutes; removed, cooled to room temperature, and then immersed in tetrahydrofuran and pure water for 22 minutes respectively, followed by vacuum drying to constant weight to obtain a nanofiltration membrane.

[0039] Comparative Example 1

[0040] Without adding aminoβ-cyclodextrin derivatives, the remaining operating steps and raw materials are the same as in Example 1.

[0041] Comparative Example 2

[0042] Without adding mesoporous nano-silica, the remaining operation steps and raw materials used are the same as in Example 1.

[0043] Comparative Example 3

[0044] Without adding zwitterionic compounds, the remaining operating steps and raw materials are the same as in Example 1.

[0045] Comparative Example 4

[0046] No co-solvent was added, and the remaining operating steps and raw materials used were the same as in Example 1.

[0047] Implementation effect evaluation

[0048] The nanofiltration membranes prepared in Examples 1-4 and Comparative Examples 1-4, as well as commercially available nanofiltration membranes, were cut to have an effective area of ​​0.6 m². 2 ±0.1cm 2 Pre-pressurize the sample by introducing pure water at 0.3 MPa and 25 ± 0.2℃ for 20 minutes until the water flux stabilizes, then immerse it in pure water for later use. Prepare a test solution containing 5000 mg / L sodium chloride and 5000 mg / L magnesium sulfate for later use.

[0049] Standard influent conditions were set: pressure 0.3 ± 0.05 MPa, temperature 25 ± 0.2 °C. The test solution was introduced into the nanofiltration membrane. After 20 minutes, the permeate volume V0 was recorded, and the initial water flux J0 was calculated. After 220 hours of continuous operation, the concentrations and volumes V of sodium chloride and magnesium sulfate on the permeate side were recorded. t Calculate the retention rate and the water flux J after 220 hours. t .

[0050] Water flux calculation (J, unit L·m)-2 ·h -1 ):

[0051] Where V represents the product water volume (in L); A represents the effective area of ​​the nanofiltration membrane (m²). 2 ); t represents the operation time (h).

[0052] Calculation of water flux attenuation rate (ΔJ):

[0053] Where J0 represents the initial water flux; J t This indicates the water flow rate after 220 hours.

[0054] The specific test results are shown in Table 1.

[0055] Table 1. Test results of nanofiltration membrane performance

[0056]

[0057] As shown in Table 1, compared with Comparative Examples 1-4 and commercially available nanofiltration membranes, the nanofiltration membrane prepared by this invention has higher initial water flux and higher water flux after 220 hours of influent, and a lower water flux decay rate, indicating that the nanofiltration membrane prepared by this invention has more stable water production performance in high-salt environments. Furthermore, the magnesium sulfate removal rate of the embodiments of this invention is greater than 99%, and the sodium chloride removal rate is less than 23%, demonstrating superior salt separation performance. Finally, the raw materials used in the preparation of this invention are readily available, the cost is controllable, the production operation is safe and simple, and it is easy to scale up production, showing good application prospects in the field of salt separation nanofiltration membranes.

Claims

1. A method for producing a nanofiltration membrane, characterized by, The method comprises the following steps: (1) washing the support layer for standby; blending binary amine, amino β-cyclodextrin derivative, inorganic hybrid agent, and amphoteric ionic compound with water to obtain an aqueous phase for standby; blending aromatic acyl chloride, cosolvent, and organic solvent to obtain an oil phase for standby; The amino β-cyclodextrin derivative is mono-(6-ethylenediamine-6-deoxy)-β-cyclodextrin or mono-(6-amino-6-deoxy)-β-cyclodextrin, the inorganic hybrid agent is mesoporous nanometer silicon dioxide, and the amphoteric ionic compound is 1-butyl sulfonic acid-3-methyl imidazole chloride salt. The cosolvent is tributyl phosphate, and the mass ratio of the aromatic acyl chloride, the cosolvent, and the organic solvent is 5:(1.9-3):(36-48). (2) sequentially immersing the support layer in the aqueous phase, scraping the membrane, immersing the support layer in the oil phase for the second time, and heating and curing, and finally performing post-processing to obtain a nanofiltration membrane.

2. The method for producing a nanofiltration membrane according to claim 1, characterized by, In step (1), the support layer is one of polysulfone, polyether ketone, or polyether sulfone, and the thickness of the support layer is 45-70 μm; when washing, the support layer is sequentially placed in a cleaning solution and acidic water for ultrasonic cleaning.

3. The method for producing a nanofiltration membrane according to claim 2, characterized by, In step (1), the cleaning solution is prepared according to a mass ratio of isomeric fatty alcohol polyoxyethylene ether to water of 1:(40-70), the mass ratio of the support layer to the cleaning solution is 1:(10-13), the mass ratio of the support layer to the acidic water is 1:(13-15), and the pH of the acidic water is 4.2-5.0; when ultrasonic cleaning in the cleaning solution, the ultrasonic power is 180-220 W, and the ultrasonic time is 6-10 min; when ultrasonic cleaning in the acidic water, the ultrasonic power is 180-220 W, and the ultrasonic time is 2-4 min.

4. The method for producing a nanofiltration membrane according to claim 1, characterized by, In step (1), the binary amine is piperazine.

5. The method for producing a nanofiltration membrane according to claim 1, wherein In step (1), the aromatic acyl chloride is trimesoyl chloride, and the organic solvent is one of n-hexane, tetrahydrofuran, or cyclohexane.

6. The method for producing a nanofiltration membrane according to claim 1, characterized by, In step (1), the mass ratio of the binary amine, the amino β-cyclodextrin derivative, the inorganic hybrid agent, the amphoteric ionic compound, and water is (3-4):(1.4-1.8):(1.65-2):(2-4):(42-46).

7. The method for producing a nanofiltration membrane according to claim 1, wherein In step (2), the first immersion temperature is 26-35 °C, and the first immersion time is 120-180 s; the second immersion temperature is 25-32 °C, the second immersion time is 50-90 s, and the support layer is placed for 8-20 min after the second immersion is completed.

8. The method for producing a nanofiltration membrane according to claim 1, characterized by, In step (2), the mass ratio of the support layer, the binary amine, and the aromatic acyl chloride is 5:(3-4):5 during the first and second immersions.

9. The method for producing a nanofiltration membrane according to claim 1, characterized by, In step (2), the linear pressure is 0.38-0.60 bar, the scraping rate is 15-25 cm / s, and the scraping temperature is 15-30 °C during the membrane scraping.

10. The method for producing a nanofiltration membrane according to claim 1, characterized by, In step (2), the heating and curing temperature is 65-75 °C, and the heating and curing time is 4-8 min.

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