A method for preparing a double-skinned forward osmosis membrane by one-step interfacial polymerization

Abstract

This invention relates to the field of membrane separation technology, specifically a method for preparing double-skin forward osmosis membranes with different densities on both surfaces of a support in a one-step process. This invention optimizes existing methods for preparing double-skin polyamide forward osmosis membranes, enabling the preparation of double-skin polyamide forward osmosis membranes with different densities through a single-step interfacial polymerization process. This method alleviates concentration polarization while increasing the flux of the double-skin forward osmosis membrane.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, specifically a method for preparing a double-skin forward osmosis membrane with different densities on both surfaces of a support in a one-step process. Background Technology

[0002] Forward osmosis membrane technology, as a novel water treatment technology, has shown great application potential in seawater desalination, wastewater treatment, and industrial liquid separation due to its advantages such as low energy consumption, low pollution, and high separation efficiency. However, in the practical application of forward osmosis membranes, concentration polarization is inevitably encountered, which significantly affects the membrane's permeation performance. Concentration polarization is mainly divided into external concentration polarization (ECP) and internal concentration polarization (ICP), with the ICP effect being particularly significant. It leads to a decrease in the effective osmotic pressure across the membrane, resulting in a permeation flux far lower than the theoretical value, severely restricting the promotion and application of forward osmosis membrane technology.

[0003] In the development of forward osmosis membrane technology, researchers have developed double-skin polyamide forward osmosis membranes to improve membrane permeability selectivity and alleviate concentration polarization. This membrane structure has polyamide skins fabricated on both sides of the support, forming a membrane structure with dual protective layers. However, while traditional double-skin polyamide membranes improve membrane performance to some extent, their two skin layers increase water mass transfer resistance and reduce flux.

[0004] To further optimize the performance of double-skin polyamide forward osmosis membranes, existing technologies have proposed double-skin polyamide forward osmosis membranes with both loose and dense layers. One side of this membrane has a dense polyamide skin to provide excellent retention performance, preventing solute molecules from passing through; while the other side has a relatively loose polyamide skin to promote water permeation and alleviate internal concentration polarization. This design combines the advantages of both dense and loose skins, mitigating concentration polarization while improving membrane permeation performance. However, existing methods for preparing such double-skin polyamide forward osmosis membranes with both loose and dense layers are often complex and costly, requiring two independent steps to prepare two polyamide skins with different densities. Furthermore, the type of monomer required in each preparation step may differ, significantly increasing the membrane preparation process and cost, thus limiting its widespread adoption in practical applications. Therefore, there is an urgent need to optimize existing methods to reduce the preparation process and production cost of polyamide forward osmosis membranes to suit industrial applications. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a one-step interfacial polymerization method for preparing a double-layer forward osmosis membrane, utilizing the influence of silica under different interfacial polymerization environments to achieve the preparation of polyamide skins with varying densities.

[0006] This invention discloses a method for preparing a double-layer polyamide forward osmosis membrane via one-step interfacial polymerization, comprising the following steps:

[0007] Step 1: Pre-treatment of the support body. Select the support body and perform soaking, cleaning, and drying treatments.

[0008] Step 2: Prepare a silica suspension with a silica particle concentration of 0.5-2wt%, then coat the first surface of the support with the silica suspension once, dry it, and then coat the second surface of the support with the silica suspension 3-5 times.

[0009] Step 3: Vertically immerse the support coated with silica layer into the m-phenylenediamine monomer solution, remove the support and remove excess solution from the surface.

[0010] Step 4: Place the support impregnated with m-phenylenediamine monomer horizontally with the first surface of the support facing upwards, and immerse the entire support in a solution of m-phenyltrimethylammonium chloride to carry out an interfacial polymerization reaction, forming a highly dense polyamide skin on the first surface and a low-density polyamide skin on the second surface.

[0011] Step 5: Clean and dry the membrane after the reaction to obtain a double-layer polyamide forward osmosis membrane.

[0012] As a preferred embodiment, the soaking step involves immersing the support in deionized water for 4-24 hours; the cleaning step involves repeatedly rinsing the support with deionized water; and the drying step involves drying the support at 50-60°C for 4-12 hours.

[0013] As a preferred embodiment, the silica particles in the second step are either amorphous or crystalline, with a particle size range of 10-100 nanometers.

[0014] As a preferred embodiment, the silica coating in the second step is completed by one of the following methods: wiping, spraying, or dipping.

[0015] As a preferred embodiment, the support in the first step is a nanofiber membrane or a phase inversion flat plate membrane, and the material is polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), or polyethersulfone (PES).

[0016] As a preferred embodiment, in the first step, the pore size of the support is in the range of 50-500 nanometers, and the porosity is greater than 50%.

[0017] As a preferred embodiment, the concentration of the intermediate phenylenediamine monomer solution in the third step is 1.0-5.0 wt%, and the immersion time is 1-5 minutes.

[0018] As a preferred embodiment, the concentration of the intermediate benzoyl chloride solution in the fourth step is 0.1-0.5 wt%, the interfacial polymerization reaction time is 2-10 minutes, and the reaction temperature is room temperature to 60°C.

[0019] Compared with the prior art, the solution of the present invention has the following beneficial effects:

[0020] This invention optimizes existing methods for preparing double-skin polyamide forward osmosis membranes. A single-step interfacial polymerization process can produce double-skin polyamide forward osmosis membranes with varying densities, mitigating concentration polarization while increasing flux. This method, involving only one interfacial polymerization step, reduces synthesis steps and costs, demonstrating significant application potential. Specifically, this invention coats the upper surface of the support with a low-concentration silica coating, which reduces gaps between polymer chains, thereby increasing membrane density. A higher-concentration silica coating is applied to the lower surface; due to gravity, the silica particles undergo displacement, influencing the interfacial polymerization process and preventing the formation of a low-density skin. Furthermore, the silica particles enhance the overall hydrophilicity of the membrane, further mitigating concentration polarization. Detailed Implementation

[0021] Example 1

[0022] Step 1: Support Pretreatment

[0023] Support selection: Polyacrylonitrile (PAN) nanofiber membranes were selected as the support, with an average pore size range of 200 nm and a porosity of 65%.

[0024] Immersion treatment: Immerse the PAN nanofiber membrane in deionized water for 12 hours to ensure the support is fully wetted.

[0025] Cleaning process: Rinse the surface of the support repeatedly with deionized water to remove impurities.

[0026] Drying process: Place the cleaned support in a 55℃ oven for 8 hours to ensure that the support is dry.

[0027] Step 2: Preparation and application of silica suspension

[0028] Preparation of silica suspension: An amorphous silica suspension with a concentration of 1.0 wt% and a particle size of 51 nm was prepared.

[0029] First surface coating: A layer of silica suspension is uniformly coated on the first surface (upper surface) of the support by dip coating and then naturally dried at room temperature.

[0030] Step 3: Impregnation with m-phenylenediamine monomer solution

[0031] Preparation of m-phenylenediamine monomer solution: Prepare an aqueous solution of m-phenylenediamine (MPD) with a concentration of 3.0 wt%.

[0032] Vertical immersion: The support coated with a silica layer is vertically immersed in the MPD solution for 3 minutes.

[0033] Remove excess solution: Gently remove the soaked support and remove excess solution from the surface with filter paper.

[0034] Step 4: Interfacial polymerization reaction

[0035] Horizontal placement: Place the support impregnated with MPD monomer horizontally with the first surface facing upward.

[0036] Iso-phenyltricarboxylic acid chloride solution impregnation: Prepare a 0.3 wt% hexane solution of iso-phenyltricarboxylic acid chloride (TMC), and impregnate the entire support in the TMC solution to carry out interfacial polymerization reaction for 5 minutes at room temperature.

[0037] Step 5: Washing and drying

[0038] Cleaning process: Remove the membrane after reaction and wash it sequentially with hexane and deionized water to remove unreacted monomers and solvents.

[0039] Drying treatment: The cleaned membrane is placed in a 60℃ oven and dried for 6 hours to obtain a single-layer polyamide forward osmosis membrane.

[0040] Example 2

[0041] Step 1: Support Pretreatment

[0042] Support selection: Polyacrylonitrile (PAN) nanofiber membranes were selected as the support, with an average pore size range of 200 nm and a porosity of 65%.

[0043] Immersion treatment: Immerse the PAN nanofiber membrane in deionized water for 12 hours to ensure the support is fully wetted.

[0044] Cleaning process: Rinse the surface of the support repeatedly with deionized water to remove impurities.

[0045] Drying process: Place the cleaned support in a 55℃ oven for 8 hours to ensure that the support is dry.

[0046] Step 2: Preparation and application of silica suspension

[0047] Preparation of silica suspension: An amorphous silica suspension with a concentration of 1.0 wt% and a particle size of 51 nm was prepared.

[0048] Second surface coating: The silica suspension is repeatedly coated four times on the second surface (lower surface) of the support by dip coating, and is naturally dried after each coating.

[0049] Step 3: Impregnation with m-phenylenediamine monomer solution

[0050] Preparation of m-phenylenediamine monomer solution: Prepare an aqueous solution of m-phenylenediamine (MPD) with a concentration of 3.0 wt%.

[0051] Vertical immersion: The support coated with a silica layer is vertically immersed in the MPD solution for 3 minutes.

[0052] Remove excess solution: Gently remove the soaked support and remove excess solution from the surface with filter paper.

[0053] Step 4: Interfacial polymerization reaction

[0054] Horizontal placement: Place the support impregnated with MPD monomer horizontally with the second surface facing down.

[0055] Iso-phenyltricarboxylic acid chloride solution impregnation: Prepare a 0.3 wt% hexane solution of iso-phenyltricarboxylic acid chloride (TMC), and impregnate the entire support in the TMC solution to carry out interfacial polymerization reaction for 5 minutes at room temperature.

[0056] Step 5: Washing and drying

[0057] Cleaning process: Remove the membrane after reaction and wash it sequentially with hexane and deionized water to remove unreacted monomers and solvents.

[0058] Drying treatment: The cleaned membrane is placed in a 60℃ oven and dried for 6 hours to obtain a single-layer polyamide forward osmosis membrane.

[0059] Example 3

[0060] Step 1: Support Pretreatment

[0061] Support selection: Polyacrylonitrile (PAN) nanofiber membranes were selected as the support, with an average pore size range of 200 nm and a porosity of 65%.

[0062] Immersion treatment: Immerse the PAN nanofiber membrane in deionized water for 12 hours to ensure the support is fully wetted.

[0063] Cleaning process: Rinse the surface of the support repeatedly with deionized water to remove impurities.

[0064] Drying process: Place the cleaned support in a 55℃ oven for 8 hours to ensure that the support is dry.

[0065] Step 2: Preparation and application of silica suspension

[0066] Preparation of silica suspension: An amorphous silica suspension with a concentration of 1.0 wt% and a particle size of 51 nm was prepared.

[0067] First surface coating: A layer of silica suspension is uniformly coated on the first surface (upper surface) of the support by dip coating and then naturally dried at room temperature.

[0068] Second surface coating: After the first surface is dried, the same dip coating method is used to repeatedly coat the second surface (lower surface) of the support with silica suspension four times, and each coating is naturally dried after each coating.

[0069] Step 3: Impregnation with m-phenylenediamine monomer solution

[0070] Preparation of m-phenylenediamine monomer solution: Prepare an aqueous solution of m-phenylenediamine (MPD) with a concentration of 3.0 wt%.

[0071] Vertical immersion: The support coated with a silica layer is vertically immersed in the MPD solution for 3 minutes.

[0072] Remove excess solution: Gently remove the soaked support and remove excess solution from the surface with filter paper.

[0073] Step 4: Interfacial polymerization reaction

[0074] Horizontal placement: Place the support impregnated with MPD monomer horizontally with the first surface facing upward.

[0075] Iso-phenyltricarboxylic acid chloride solution impregnation: Prepare a 0.3 wt% hexane solution of iso-phenyltricarboxylic acid chloride (TMC), and impregnate the entire support in the TMC solution to carry out interfacial polymerization reaction for 5 minutes at room temperature.

[0076] Step 5: Washing and drying

[0077] Cleaning process: Remove the membrane after reaction and wash it sequentially with hexane and deionized water to remove unreacted monomers and solvents.

[0078] Drying treatment: The cleaned membrane is placed in a 60℃ oven and dried for 6 hours to obtain a double-layer polyamide forward osmosis membrane.

[0079] Comparative Example 1

[0080] Step 1: Support Pretreatment

[0081] Support selection: Polyacrylonitrile (PAN) nanofiber membranes were selected as the support, with an average pore size range of 200 nm and a porosity of 65%.

[0082] Immersion treatment: Immerse the PAN nanofiber membrane in deionized water for 12 hours to ensure the support is fully wetted.

[0083] Cleaning process: Rinse the surface of the support repeatedly with deionized water to remove impurities.

[0084] Drying process: Place the cleaned support in a 55℃ oven for 8 hours to ensure that the support is dry.

[0085] Step 2: Impregnation with m-phenylenediamine monomer solution

[0086] Preparation of m-phenylenediamine monomer solution: Prepare an aqueous solution of m-phenylenediamine (MPD) with a concentration of 3.0 wt%.

[0087] Vertical immersion: Immerse the support vertically in the MPD solution for 3 minutes.

[0088] Remove excess solution: Gently remove the soaked support and remove excess solution from the surface with filter paper.

[0089] Step 3: Interface polymerization reaction

[0090] Horizontal placement: Place the support impregnated with MPD monomers horizontally.

[0091] Iso-phenyltricarboxylic acid chloride solution impregnation: Prepare a 0.3 wt% hexane solution of iso-phenyltricarboxylic acid chloride (TMC), and impregnate the entire support in the TMC solution to carry out interfacial polymerization reaction for 5 minutes at room temperature.

[0092] Step 4: Washing and drying

[0093] Cleaning process: Remove the membrane after reaction and wash it sequentially with hexane and deionized water to remove unreacted monomers and solvents.

[0094] Drying treatment: The cleaned membrane is placed in a 60℃ oven and dried for 6 hours to obtain a double-layer polyamide forward osmosis membrane.

[0095] Comparative Example 2

[0096] Step 1: Support Pretreatment

[0097] Support selection: Polyacrylonitrile (PAN) nanofiber membranes were selected as the support, with an average pore size range of 200 nm and a porosity of 65%.

[0098] Immersion treatment: Immerse the PAN nanofiber membrane in deionized water for 12 hours to ensure the support is fully wetted.

[0099] Cleaning process: Rinse the surface of the support repeatedly with deionized water to remove impurities.

[0100] Drying process: Place the cleaned support in a 55℃ oven for 8 hours to ensure that the support is dry.

[0101] Step 2: Preparation and application of silica suspension

[0102] Preparation of silica suspension: An amorphous silica suspension with a concentration of 1.0 wt% and a particle size of 51 nm was prepared.

[0103] First surface coating: A layer of silica suspension is uniformly coated on the first surface (upper surface) of the support by dip coating and then naturally dried at room temperature.

[0104] Second surface coating: After the first surface is dried, a silica suspension is applied to the second surface (lower surface) of the support using the same dip coating method, and then naturally dried.

[0105] Step 3: Impregnation with m-phenylenediamine monomer solution

[0106] Preparation of m-phenylenediamine monomer solution: Prepare an aqueous solution of m-phenylenediamine (MPD) with a concentration of 3.0 wt%.

[0107] Vertical immersion: The support coated with a silica layer is vertically immersed in the MPD solution for 3 minutes.

[0108] Remove excess solution: Gently remove the soaked support and remove excess solution from the surface with filter paper.

[0109] Step 4: Interfacial polymerization reaction

[0110] Horizontal placement: Place the support impregnated with MPD monomer horizontally with the first surface facing upward.

[0111] Iso-phenyltricarboxylic acid chloride solution impregnation: Prepare a 0.3 wt% hexane solution of iso-phenyltricarboxylic acid chloride (TMC), and impregnate the entire support in the TMC solution to carry out interfacial polymerization reaction for 5 minutes at room temperature.

[0112] Step 5: Washing and drying

[0113] Cleaning process: Remove the membrane after reaction and wash it sequentially with hexane and deionized water to remove unreacted monomers and solvents.

[0114] Drying treatment: The cleaned membrane is placed in a 60℃ oven and dried for 6 hours to obtain a double-layer polyamide forward osmosis membrane.

[0115] Comparative Example 3

[0116] Step 1: Support Pretreatment

[0117] Support selection: Polyacrylonitrile (PAN) nanofiber membranes were selected as the support, with an average pore size range of 200 nm and a porosity of 65%.

[0118] Immersion treatment: Immerse the PAN nanofiber membrane in deionized water for 12 hours to ensure the support is fully wetted.

[0119] Cleaning process: Rinse the surface of the support repeatedly with deionized water to remove impurities.

[0120] Drying process: Place the cleaned support in a 55℃ oven for 8 hours to ensure that the support is dry.

[0121] Step 2: Preparation and application of silica suspension

[0122] Preparation of silica suspension: An amorphous silica suspension with a concentration of 1.0 wt% and a particle size of 51 nm was prepared.

[0123] First surface coating: The silica suspension is uniformly coated four times on the first surface (upper surface) of the support by dip coating, and is naturally dried after each coating.

[0124] Second surface coating: After the first surface is dried, the same dip coating method is used to repeatedly coat the second surface (lower surface) of the support with silica suspension four times, and each coating is naturally dried after each coating.

[0125] Step 3: Impregnation with m-phenylenediamine monomer solution

[0126] Preparation of m-phenylenediamine monomer solution: Prepare an aqueous solution of m-phenylenediamine (MPD) with a concentration of 3.0 wt%.

[0127] Vertical immersion: The support coated with a silica layer is vertically immersed in the MPD solution for 3 minutes.

[0128] Remove excess solution: Gently remove the soaked support and remove excess solution from the surface with filter paper.

[0129] Step 4: Interfacial polymerization reaction

[0130] Horizontal placement: Place the support impregnated with MPD monomer horizontally with the first surface facing upward.

[0131] Iso-phenyltricarboxylic acid chloride solution impregnation: Prepare a 0.3 wt% hexane solution of iso-phenyltricarboxylic acid chloride (TMC), and impregnate the entire support in the TMC solution to carry out interfacial polymerization reaction for 5 minutes at room temperature.

[0132] Step 5: Washing and drying

[0133] Cleaning process: Remove the membrane after reaction and wash it sequentially with hexane and deionized water to remove unreacted monomers and solvents.

[0134] Drying treatment: The cleaned membrane is placed in a 60℃ oven and dried for 6 hours to obtain a double-layer polyamide forward osmosis membrane.

[0135] The filtration performance of the single-layer forward osmosis membranes prepared in Examples 1-2 and the double-layer forward osmosis membranes prepared in Examples 1 and 1-2 was tested using a 2 mol / L sodium chloride solution as the draw solution. The results are shown in Table 1.

[0136] Table 1

[0137]

[0138] Based on the filtration performance tests of Examples 1 and 2, it is evident that the polyamide skin layer formed on the upper surface exhibits higher density (i.e., higher rejection rate and lower flux) compared to the polyamide skin layer formed on the lower surface. Furthermore, compared to the results of Comparative Examples 1-3, the double-skin forward osmosis membrane prepared in Example 3 demonstrates a high sodium chloride rejection rate and a high pure water flux, indicating significant application potential.

[0139] It should be understood that the above are merely specific application examples of the present invention and do not constitute any limitation on the scope of protection of the present invention. All technical solutions formed by equivalent transformations or equivalent substitutions fall within the scope of protection of the present invention.

Claims

1. A method for preparing a double-layer forward osmosis membrane by one-step interfacial polymerization, comprising the following steps: Step 1: Pretreatment of the support. Select the support and perform soaking, cleaning, and drying. The pore size of the support should be 50-500 nanometers and the porosity should be greater than 50%. Step 2: Prepare a silica suspension with a silica particle concentration of 0.5-2wt%, then coat the first surface of the support with the silica suspension once, dry it, and then coat the second surface of the support with the silica suspension 3-5 times. The silica particles are amorphous or crystalline, with a particle size range of 10-100 nanometers. Step 3: Vertically immerse the support coated with silica layer into the m-phenylenediamine monomer solution, remove the support, and remove excess solution from the surface. The concentration of the m-phenylenediamine monomer solution is 1.0-5.0 wt%, and the immersion time is 1-5 minutes. Step 4: Place the support impregnated with m-phenylenediamine monomer horizontally with the first surface facing upwards, and immerse the entire support in an isophthaloyl chloride solution for interfacial polymerization. A highly dense polyamide skin is formed on the first surface, and a less dense polyamide skin is formed on the second surface. The concentration of the isophthaloyl chloride solution is 0.1-0.5 wt%, the interfacial polymerization reaction time is 2-10 minutes, and the reaction temperature is room temperature to 60°C. Step 5: Clean and dry the membrane after the reaction to obtain a double-layer polyamide forward osmosis membrane.

2. The method of claim 1, wherein, The first step involves soaking the support in deionized water for 4-24 hours; cleaning involves repeatedly rinsing the support with deionized water; and drying involves drying the support at 50-60°C for 4-12 hours.

3. The method of claim 1, wherein, In the second step, the silica coating is completed by one of the following methods: wiping, spraying, or dipping.

4. The method of claim 1, wherein, In the first step, the support is a nanofiber membrane or a phase inversion flat plate membrane, and the material is polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), or polyethersulfone (PES).

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