A method for preparing a polyamide nanofiltration membrane containing titanium dioxide

Abstract

This invention relates to a membrane material, specifically a polyamide nanofiltration membrane material. The invention employs a high-roughness ultrafiltration membrane, resulting in more adsorption sites on the membrane surface. Combined with alcohol-water treatment, the adsorption capacity of the membrane tip for titanium dioxide precursor alcohol solution is enhanced. The vertical placement of the support and a suitable settling time prevent the formation of continuous sheets of titanium dioxide precursor alcohol solution on the support surface, thus preventing hydrolysis to form dispersed titanium dioxide. This maintains the hydrophilicity of the support within a suitable range, thereby ensuring the separation performance of the polyamide membrane layer.

Description

Technical Field

[0001] This invention relates to a membrane material, specifically a polyamide nanofiltration membrane material. Background Technology

[0002] Nanofiltration is a novel membrane separation technology that falls between ultrafiltration and reverse osmosis. It features low operating pressure, high removal rate of divalent and higher salts, and low removal rate of monovalent salts. It is widely used in water reuse, water softening, pharmaceutical, food and biological industries.

[0003] Polyamide nanofiltration membranes are common nanofiltration membrane materials, typically prepared via interfacial polymerization. To meet industrial demands, high water flux is a fundamental requirement for polyamide nanofiltration membranes. To enhance water flux, various hydroxyl-containing inorganic materials are added to polyamide membranes, such as titanium dioxide, molecular sieves, carbon nanotubes, graphene, and silicon dioxide. Common addition methods include blending and surface coating, and common addition sites include within the support structure and within the polyamide membrane layer.

[0004] Existing technologies have shown that researchers have chosen to coat titanium dioxide inorganic materials or precursors onto a support to form an intermediate layer, using this as an interfacial polymerization site, thus improving water flux. In particular, compared to directly coating titanium dioxide particles, in-situ synthesis of titanium dioxide can significantly reduce the degree of titanium dioxide agglomeration. However, the applicant found in experiments that when titanium dioxide is used as a continuous layer on the support layer, its excessively high hydroxyl content leads to excessively high hydrophilicity, making it difficult for aqueous monomers to spread on the titanium dioxide intermediate layer, thus hindering the formation of a dense polyamide film.

[0005] Therefore, it is urgent to solve the problem of how to improve the fixation method of titanium dioxide to enhance the separation performance of polyamide nanofiltration membranes. Summary of the Invention

[0006] This invention provides a method for preparing a polyamide nanofiltration membrane containing titanium dioxide. By using a high-roughness ultrafiltration membrane as a support and combining it with a special pretreatment method, the titanium dioxide precursor impregnated on the membrane surface is dispersed and then hydrolyzed in sequence to form non-sheet titanium dioxide. This maintains the hydrophilicity of the support within a suitable range, thereby ensuring the compactness of the polyamide membrane layer.

[0007] This invention provides a method for preparing a polyamide nanofiltration membrane containing titanium dioxide, the method comprising the following steps:

[0008] Immerse the high-roughness support in pure water for 1-600 min, then dry it, and continue to immerse the side of the support to be filmed in an alcohol-water solution for 30-300 s.

[0009] After impregnation, lay the support flat and pour the alcohol solution containing the titanium dioxide precursor onto the surface of the support. Let it stand for 10-60 seconds, then stand the support upright for 20-100 seconds to remove the solution from the surface of the support, and continue to stand flat at room temperature for 1-5 minutes.

[0010] After uniformly dripping ultrapure water onto the surface of the support, let it stand for 10-20 minutes, then rinse the membrane surface with pure water and dry it.

[0011] A dried support is sequentially impregnated with a polyamine aqueous solution and a polyacrylamide organic solution to form a polyamide film on the support surface.

[0012] Preferably, the average roughness (Ra) of the support is ≥0.9μm.

[0013] Preferably, the support material is one of polysulfone, polyethersulfone, polyvinylidene fluoride, epoxy resin, polyacrylonitrile, and polyethylene.

[0014] Preferably, the alcohol in the aqueous alcohol solution is selected from one of ethanol, propanol, isopropanol, butanol, isobutanol, 1-pentanol, 2-pentanol, and tert-pentanol, with a concentration of 20-60 wt%.

[0015] Preferably, the titanium dioxide precursor is one of tetrabutyl titanate and tetraisopropyl titanate, and its concentration in the alcohol solution is 5-20 wt%.

[0016] Preferably, the alcohol in the alcohol solution of the titanium dioxide precursor is one of methanol, ethanol, and propanol, and preferably the polyamine is selected from m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 1,3,5-phenyltriamine, 3-chloro-1,4-phenylenediamine, and 5-chloro-1,3-phenylenediamine, with a concentration of 0.5-5 wt%.

[0017] Preferably, the polyacryl chloride is selected from one of trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride, and the concentration is 0.05-2wt%.

[0018] The present invention also provides a polyamide nanofiltration membrane containing titanium dioxide prepared according to the above method, wherein the titanium dioxide is located between the support and the polyamide membrane layer, and the titanium dioxide is discontinuous.

[0019] The application of the titanium dioxide-containing polyamide nanofiltration membrane prepared by this invention in water treatment can include household water purification, industrial wastewater filtration, and municipal sewage treatment.

[0020] Compared with existing technologies, this invention uses a high-roughness ultrafiltration membrane, which gives the membrane surface more adsorption sites. Combined with alcohol-water treatment, it can enhance the adsorption capacity of the membrane end for the titanium dioxide precursor alcohol solution. The vertical placement of the support and the appropriate settling time can prevent the formation of continuous sheets of titanium dioxide precursor alcohol solution on the support surface, and thus hydrolyze to form dispersed titanium dioxide. This keeps the hydrophilicity of the support within a suitable range, thereby ensuring the separation performance of the polyamide membrane layer. Detailed Implementation Example 1

[0021] The nanofiltration membrane of Example 1 was prepared by the following steps:

[0022] A polyvinylidene fluoride support with an average roughness of 1.1 μm was immersed in pure water for 60 min, then dried in an oven at 60 °C, and the side of the support to be film-forming was immersed in an ethanol / water solution (ethanol concentration of 40 wt%) for 60 s.

[0023] After the impregnation is completed, lay the support flat and slowly pour the ethanol solution of tetrabutyl titanate (the concentration of tetrabutyl titanate is 5wt%) onto the surface of the support. Let it stand for 30 seconds, then slowly place the support vertically and continue for 60 seconds to remove the solution from the surface of the support. Then lay it flat and let it stand at room temperature for 2 minutes.

[0024] After uniformly and densely dripping ultrapure water onto the surface of the support, let it stand for 10 minutes, rinse the membrane surface with pure water, and then dry it.

[0025] The dried support was sequentially immersed in an aqueous monomer solution of m-phenylenediamine (concentration of 1 wt%) for 5 min, then the surface solution was removed, and the support was further immersed in a hexane solution of trimesoyl chloride (concentration of 0.5 wt%) for 1 min to form a polyamide film on the surface of the support.

[0026] Comparative Example 1

[0027] A polyvinylidene fluoride support with an average roughness of 1.1 μm was immersed in pure water for 60 min and then dried in an oven at 60 °C.

[0028] Lay the support flat and slowly pour the ethanol solution of tetrabutyl titanate (concentration of tetrabutyl titanate is 5wt%) onto the surface of the support, and let it stand for 30 seconds.

[0029] After uniformly and densely dripping ultrapure water onto the surface of the support, let it stand for 10 minutes, rinse the membrane surface with pure water, and then dry it.

[0030] The dried support was sequentially immersed in an aqueous monomer solution of m-phenylenediamine (concentration of 1 wt%) for 5 min, then the surface solution was removed, and the support was further immersed in a hexane solution of trimesoyl chloride (concentration of 0.5 wt%) for 1 min to form a polyamide film on the surface of the support.

[0031] Comparative Example 2

[0032] A polyvinylidene fluoride support with an average roughness of 1.1 μm was immersed in pure water for 60 min, then dried in an oven at 60 °C, and the side of the support to be film-forming was immersed in an ethanol / water solution (ethanol concentration of 40 wt%) for 60 s.

[0033] After impregnation, lay the support flat and slowly pour the ethanol solution of tetrabutyl titanate (concentration of tetrabutyl titanate is 5wt%) onto the surface of the support. Let it stand for 30 seconds and then stand at room temperature for 2 minutes.

[0034] After uniformly and densely dripping ultrapure water onto the surface of the support, let it stand for 10 minutes, rinse the membrane surface with pure water, and then dry it.

[0035] The dried support was sequentially immersed in an aqueous monomer solution of m-phenylenediamine (concentration of 1 wt%) for 5 min, then the surface solution was removed, and the support was further immersed in a hexane solution of trimesoyl chloride (concentration of 0.5 wt%) for 1 min to form a polyamide film on the surface of the support.

[0036] Comparative Example 3

[0037] A polyvinylidene fluoride support with an average roughness of 1.1 μm was immersed in pure water for 60 min and then dried in an oven at 60 °C.

[0038] Lay the support flat and slowly pour the ethanol solution of tetrabutyl titanate (concentration of tetrabutyl titanate is 5wt%) onto the surface of the support. Let it stand for 30 seconds, then slowly place the support vertically and continue for 60 seconds to remove the solution from the surface of the support. Then lay it flat and let it stand at room temperature for 2 minutes.

[0039] After uniformly and densely dripping ultrapure water onto the surface of the support, let it stand for 10 minutes, rinse the membrane surface with pure water, and then dry it.

[0040] The dried support was sequentially immersed in an aqueous monomer solution of m-phenylenediamine (concentration of 1 wt%) for 5 min, then the surface solution was removed, and the support was further immersed in a hexane solution of trimesoyl chloride (concentration of 0.5 wt%) for 1 min to form a polyamide film on the surface of the support.

[0041] Comparative Example 4

[0042] A polyvinylidene fluoride support with an average roughness of 0.5 μm was immersed in pure water for 60 min, then dried in an oven at 60 °C, and the side of the support to be film-forming was immersed in an ethanol / water solution (ethanol concentration of 40 wt%) for 60 s.

[0043] After the impregnation is completed, lay the support flat and slowly pour the ethanol solution of tetrabutyl titanate (the concentration of tetrabutyl titanate is 5wt%) onto the surface of the support. Let it stand for 30 seconds, then slowly place the support vertically and continue for 60 seconds to remove the solution from the surface of the support. Then lay it flat and let it stand at room temperature for 2 minutes.

[0044] After uniformly and densely dripping ultrapure water onto the surface of the support, let it stand for 10 minutes, rinse the membrane surface with pure water, and then dry it.

[0045] The dried support was sequentially immersed in an aqueous monomer solution of m-phenylenediamine (concentration of 1 wt%) for 5 min, then the surface solution was removed, and the support was further immersed in a hexane solution of trimesoyl chloride (concentration of 0.5 wt%) for 1 min to form a polyamide film on the surface of the support.

[0046] Comparative Example 5

[0047] A polyvinylidene fluoride support with an average roughness of 0.5 μm was immersed in pure water for 60 min and then dried in an oven at 60 °C.

[0048] Lay the support flat and slowly pour the ethanol solution of tetrabutyl titanate (concentration of tetrabutyl titanate is 5wt%) onto the surface of the support, and let it stand for 30 seconds.

[0049] After uniformly and densely dripping ultrapure water onto the surface of the support, let it stand for 10 minutes, rinse the membrane surface with pure water, and then dry it.

[0050] The dried support was sequentially immersed in an aqueous monomer solution of m-phenylenediamine (concentration of 1 wt%) for 5 min, then the surface solution was removed, and the support was further immersed in a hexane solution of trimesoyl chloride (concentration of 0.5 wt%) for 1 min to form a polyamide film on the surface of the support.

[0051] The nanofiltration membranes of the above examples and comparative examples were tested for desalination performance of 2 g / L NaCl aqueous solution under the conditions of operating pressure of 1.2 MPa and solution temperature of 20 °C. The results are shown in Table 1.

[0052]

[0053] Therefore, the method of the present invention can significantly improve the membrane rejection rate without significantly reducing the flux, thereby enabling the nanofiltration membrane to be used for desalination of monovalent salt solutions.

Claims

1. A method for producing a polyamide nanofiltration membrane containing titanium dioxide, characterized by The method includes the following steps: (1) Immerse the high-roughness support in pure water for 1-600 min, then dry it, and continue to immerse the side of the support to be film-forming in an alcohol-water solution for 30s-300s. The support material is one of polysulfone, polyethersulfone, polyvinylidene fluoride, epoxy resin, polyacrylonitrile, and polyethylene. The average roughness (Ra) of the support is ≥0.9μm. (2) After impregnation, lay the support flat and pour the alcohol solution containing the titanium dioxide precursor onto the surface of the support. Let it stand for 10-60 seconds, then stand the support upright for 20-100 seconds to remove the solution from the surface of the support. Continue to lay it flat and let it stand at room temperature for 1-5 minutes to prevent the formation of continuous sheets of titanium dioxide precursor alcohol solution on the surface of the support. The concentration of the titanium dioxide precursor in the alcohol solution is 5-20 wt%. (3) After uniformly adding ultrapure water to the surface of the support, let it stand for 10-20 minutes, clean the membrane surface with pure water, and then dry it. (4) The dried support is sequentially impregnated with a polyamine aqueous solution and a polyacrylamide organic solution to form a polyamide film on the surface of the support.

2. The method of claim 1, wherein The alcohol in the aqueous solution is selected from one of ethanol, propanol, isopropanol, butanol, isobutanol, 1-pentanol, 2-pentanol, and tert-pentanol, with a concentration of 20-60 wt%.

3. The method of claim 1, wherein The titanium dioxide precursor is one of tetrabutyl titanate and tetraisopropyl titanate.

4. The method of claim 1, wherein The alcohol in the alcohol solution of the titanium dioxide precursor is one of methanol, ethanol, and propanol.

5. The method of claim 1, wherein The polyamine is selected from one of m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 1,3,5-phenyltriamine, 3-chloro-1,4-phenylenediamine, and 5-chloro-1,3-phenylenediamine, with a concentration of 0.5-5 wt%.

6. The method of claim 1, wherein The polyacryl chloride is selected from one of trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride, and the concentration is 0.05-2wt%.

7. A polyamide nanofiltration membrane comprising titania prepared according to the method of claim 1, characterized by The titanium dioxide is located between the support and the polyamide film, and the titanium dioxide is discontinuous.

8. The application of the titanium dioxide-containing polyamide nanofiltration membrane according to claim 7 in water treatment.

Images