Preparation method of polyamide nanofiltration membrane containing titanium dioxide

Abstract

The invention relates to a membrane material, in particular to a polyamide nanofiltration membrane material. According to the invention, the ultrafiltration membrane with high roughness is adopted, so that the surface of the membrane has more adsorption sites, and the adsorption capacity of the membrane end to a titanium dioxide precursor alcohol solution can be improved by combining with alcohol-water solution treatment; and the vertical placement of the support body and the standing treatment for a proper time can ensure that continuous sheets of titanium dioxide precursor alcoholic solution are not formed on the surface of the support body, and dispersed titanium dioxide is formed by hydrolysis, so that the hydrophilicity of the support body is maintained in a proper range, and the separation performance of the polyamide membrane layer is ensured.

Description

Technical Field

[0001] The invention relates to a membrane material, in particular to a polyamide nanofiltration membrane material. Background Art

[0002] Nanofiltration is a new membrane separation technology between ultrafiltration and reverse osmosis. It has the characteristics of 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, medicine, food and biology industries.

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

[0004] Prior art researchers have already chosen to coat titanium dioxide inorganic materials or precursors on a support to form an intermediate layer and use this as an interfacial polymerization site, which has improved water flux. In particular, compared to directly coating titanium dioxide particles, the in-situ synthesis of titanium dioxide can significantly reduce the degree of titanium dioxide agglomeration. However, the applicant discovered in experiments that when titanium dioxide is positioned as a continuous layer on a support layer, its excessively high hydroxyl content leads to excessive hydrophilicity, making it difficult for aqueous monomers to spread across the titanium dioxide intermediate layer, thereby hindering the formation of a dense polyamide film layer.

[0005] Therefore, how to improve the fixation method of titanium dioxide to enhance the separation performance of polyamide nanofiltration membranes needs to be solved urgently. Summary of the Invention

[0006] The present invention provides a method for preparing a polyamide nanofiltration membrane containing titanium dioxide. By adopting 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 sequentially hydrolyzed to form non-flaky titanium dioxide, thereby maintaining the hydrophilicity of the support within an appropriate range, thereby ensuring the density of the polyamide membrane layer.

[0007] The present invention provides a method for preparing a polyamide nanofiltration membrane containing titanium dioxide, the method comprising the following steps: Immerse the high-roughness support in pure water for 1-600 minutes, then dry it, and then immerse the side of the support to be film-formed in an alcohol-water solution for 30 seconds to 300 seconds; Lay the impregnated support flat, pour the alcohol solution containing the titanium dioxide precursor on 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 on the surface of the support, and continue to lay it flat at room temperature for 1-5 minutes; Evenly add ultrapure water to the surface of the support and let it stand for 10-20 minutes. Rinse the membrane surface with pure water and dry it. The dried support is sequentially immersed in a polyamine aqueous solution and a polyacyl chloride organic solution to form a polyamide film layer on the surface of the support.

[0008] Preferably, the average roughness (Ra) of the support body is ≥0.9 μm.

[0009] Preferably, the support material is one of polysulfone, polyethersulfone, polyvinylidene fluoride, epoxy resin, polyacrylonitrile and polyethylene.

[0010] Preferably, the alcohol in the alcohol aqueous solution is selected from ethanol, propanol, isopropanol, butanol, isobutanol, 1-pentanol, 2-pentanol, and tert-pentanol, and the concentration is 20-60 wt%.

[0011] Preferably, the titanium dioxide precursor is one of tetra-n-butyl titanate and tetra-isopropyl titanate, and its concentration in the alcohol solution is 5-20 wt%.

[0012] Preferably, the alcohol in the alcohol solution of the titanium dioxide precursor is one of methanol, ethanol, and propanol, and the polyamine is preferably selected from m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 1,3,5-phenyltriamine (1,3,5-phenyltriamine), 3-chloro-1,4-phenylenediamine, 5-chloro-1,3-phenylenediamine (5-chloro-1,3-phenylenediamine), and the concentration is 0.5-5wt%.

[0013] Preferably, the polyacyl chloride is selected from one of trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride, and the concentration is 0.05-2 wt%.

[0014] 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.

[0015] The titanium dioxide-containing polyamide nanofiltration membrane prepared by the present invention is used in water treatment, and the water treatment can include household water purification, industrial wastewater filtration, municipal sewage treatment, etc.

[0016] First, with respect to the existing technology, the present invention adopts a high-roughness ultrafiltration membrane so that the membrane surface has more adsorption sites, and combined with alcohol-water solution treatment, the adsorption capacity of the membrane end to the titanium dioxide precursor alcohol solution can be improved. The vertical placement of the support body and the static treatment for an appropriate time can prevent the formation of continuous sheets of titanium dioxide precursor alcohol solution on the surface of the support body, and hydrolyze to form dispersed titanium dioxide, so that the hydrophilicity of the support body is maintained within an appropriate range, thereby ensuring the separation performance of the polyamide membrane layer. DETAILED DESCRIPTION Example 1

[0017] The nanofiltration membrane of Example 1 was prepared by the following steps: 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. The side of the support to be film-formed was then immersed in an ethanol / water solution (ethanol concentration of 40 wt%) for 60 s. Lay the impregnated support flat, slowly pour a tetrabutyl titanate ethanol solution (tetrabutyl titanate concentration is 5 wt%) onto the surface of the support, let it stand for 30 seconds, then slowly turn the support upright for 60 seconds to remove the solution on the surface of the support, and then lay it flat and continue to stand at room temperature for 2 minutes; Add ultrapure water evenly and densely onto the surface of the support and let it stand for 10 minutes. Rinse the membrane surface with pure water and then dry it. The dried support was immersed in an aqueous monomer solution of m-phenylenediamine (concentration of 1 wt%) for 5 min, and then the surface solution was removed. The support was then immersed in an n-hexane solution of trimesoyl chloride (concentration of 0.5 wt%) for 1 min to form a polyamide film layer on the surface of the support.

[0018] Comparative Example 1 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; Place the support flat, slowly pour the ethanol solution of tetra-n-butyl titanate (the concentration of tetra-n-butyl titanate is 5 wt%) on the surface of the support, and let it stand for 30 seconds; Add ultrapure water evenly and densely onto the surface of the support and let it stand for 10 minutes. Rinse the membrane surface with pure water and then dry it. The dried support was immersed in an aqueous monomer solution of m-phenylenediamine (concentration of 1 wt%) for 5 min, and then the surface solution was removed. The support was then immersed in an n-hexane solution of trimesoyl chloride (concentration of 0.5 wt%) for 1 min to form a polyamide film layer on the surface of the support.

[0019] Comparative Example 2 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. The side of the support to be film-formed was then immersed in an ethanol / water solution (ethanol concentration of 40 wt%) for 60 s. Lay the impregnated support flat, slowly pour the ethanol solution of tetra-n-butyl titanate (the concentration of tetra-n-butyl titanate is 5 wt%) on the surface of the support, let it stand for 30 seconds, and then let it stand at room temperature for 2 minutes; Add ultrapure water evenly and densely onto the surface of the support and let it stand for 10 minutes. Rinse the membrane surface with pure water and then dry it. The dried support was immersed in an aqueous monomer solution of m-phenylenediamine (concentration of 1 wt%) for 5 min, and then the surface solution was removed. The support was then immersed in an n-hexane solution of trimesoyl chloride (concentration of 0.5 wt%) for 1 min to form a polyamide film layer on the surface of the support.

[0020] Comparative Example 3 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; Lay the support flat, slowly pour a tetrabutyl titanate ethanol solution (tetrabutyl titanate concentration is 5 wt%) onto the surface of the support, let it stand for 30 seconds, then slowly turn the support upright for 60 seconds to remove the solution on the surface of the support, and then lay it flat and continue to stand at room temperature for 2 minutes; Add ultrapure water evenly and densely onto the surface of the support and let it stand for 10 minutes. Rinse the membrane surface with pure water and then dry it. The dried support was immersed in an aqueous monomer solution of m-phenylenediamine (concentration of 1 wt%) for 5 min, and then the surface solution was removed. The support was then immersed in an n-hexane solution of trimesoyl chloride (concentration of 0.5 wt%) for 1 min to form a polyamide film layer on the surface of the support.

[0021] Comparative Example 4 A polyvinylidene fluoride support with an average roughness of 0.5 μm was immersed in pure water for 60 minutes, then dried in an oven at 60°C. The side of the support to be film-formed was then immersed in an ethanol / water solution (ethanol concentration of 40 wt%) for 60 seconds. Lay the impregnated support flat, slowly pour a tetrabutyl titanate ethanol solution (tetrabutyl titanate concentration is 5 wt%) onto the surface of the support, let it stand for 30 seconds, then slowly turn the support upright for 60 seconds to remove the solution on the surface of the support, and then lay it flat and continue to stand at room temperature for 2 minutes; Add ultrapure water evenly and densely onto the surface of the support and let it stand for 10 minutes. Rinse the membrane surface with pure water and then dry it. The dried support was immersed in an aqueous monomer solution of m-phenylenediamine (concentration of 1 wt%) for 5 min, and then the surface solution was removed. The support was then immersed in an n-hexane solution of trimesoyl chloride (concentration of 0.5 wt%) for 1 min to form a polyamide film layer on the surface of the support.

[0022] Comparative Example 5 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; Place the support flat, slowly pour the ethanol solution of tetra-n-butyl titanate (the concentration of tetra-n-butyl titanate is 5 wt%) on the surface of the support, and let it stand for 30 seconds; Add ultrapure water evenly and densely onto the surface of the support and let it stand for 10 minutes. Rinse the membrane surface with pure water and then dry it. The dried support was immersed in an aqueous monomer solution of m-phenylenediamine (concentration of 1 wt%) for 5 min, and then the surface solution was removed. The support was then immersed in an n-hexane solution of trimesoyl chloride (concentration of 0.5 wt%) for 1 min to form a polyamide film layer on the surface of the support.

[0023] The nanofiltration membranes of the above examples and comparative examples were tested for their desalination performance for a 2 g / L NaCl aqueous solution at an operating pressure of 1.2 MPa and a solution temperature of 20° C. The results are shown in Table 1.

[0024]

[0025] It can be seen that the method of the present invention can significantly improve the retention rate of the membrane without significantly reducing the flux, thereby enabling the nanofiltration membrane to be used for the desalination of monovalent salt solutions.

Claims

1. A method for preparing a polyamide nanofiltration membrane containing titanium dioxide, characterized in that The method comprises the following steps: Immerse the high-roughness support in pure water for 1-600 minutes, then dry it, and then immerse the side of the support to be film-formed in an alcohol-water solution for 30 seconds to 300 seconds; Lay the impregnated support flat, pour the alcohol solution containing the titanium dioxide precursor on 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 on the surface of the support, and continue to lay it flat at room temperature for 1-5 minutes; Evenly add ultrapure water to the surface of the support and let it stand for 10-20 minutes. Rinse the membrane surface with pure water and dry it. The dried support is sequentially immersed in a polyamine aqueous solution and a polyacyl chloride organic solution to form a polyamide film layer on the surface of the support.

2. The method according to claim 1, characterized in that The average roughness (Ra) of the support body is ≥0.9 μm.

3. The method according to claim 1, characterized in that The support material is one of polysulfone, polyethersulfone, polyvinylidene fluoride, epoxy resin, polyacrylonitrile and polyethylene.

4. The method according to claim 1, characterized in that The alcohol in the alcohol aqueous solution is selected from one of ethanol, propanol, isopropanol, butanol, isobutanol, 1-pentanol, 2-pentanol, and tert-pentanol, and the concentration is 20-60wt%.

5. The method according to claim 1, characterized in that The titanium dioxide precursor is one of tetra-n-butyl titanate and tetra-isopropyl titanate, and its concentration in the alcohol solution is 5-20 wt%.

6. The method according to claim 1, characterized in that The alcohol in the alcohol solution of the titanium dioxide precursor is one of methanol, ethanol and propanol.

7. The method according to claim 1, characterized in that The polyamine is selected from one of m-phenylenediamine, o-phenylenediamine, p-phenylenediamine, 1,3,5-phenyltriamine (1,3,5-phenyltriamine), 3-chloro-1,4-phenylenediamine, and 5-chloro-1,3-phenylenediamine (5-chloro-1,3-phenylenediamine), and the concentration is 0.5-5wt%.

8. The method according to claim 1, characterized in that The polybasic acid chloride is selected from one of trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride, and the concentration is 0.05-2 wt %.

9. A titanium dioxide-containing polyamide nanofiltration membrane prepared according to the method of claim 1, characterized in that The titanium dioxide is located between the support and the polyamide film layer, and the titanium dioxide is discontinuous.

10. Use of the titanium dioxide-containing polyamide nanofiltration membrane according to claim 1 in water treatment.

Images