Method for preparing double-skin forward osmosis membrane through one-step interfacial polymerization

Abstract

The invention relates to the technical field of membrane separation, in particular to a method for preparing double-skin-layer forward osmosis membranes with different densities on double surfaces of a supporting body through a one-step method. According to the present invention, the existing double-skin layer polyamide forward osmosis membrane preparation method is optimized, the double-skin layer polyamide forward osmosis membrane with different densities can be prepared through the one-step interfacial polymerization preparation, and the flux of the double-skin layer polyamide forward osmosis membrane can be improved while the concentration polarization phenomenon is relieved.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane separation, and specifically to a method for preparing a double-cortex forward osmosis membrane with different compactness on both surfaces of a support by a one-step method. Background Art

[0002] As a new type of water treatment technology, forward osmosis membrane technology has shown great application potential in the fields of seawater desalination, sewage and wastewater treatment, and industrial liquid separation due to its advantages such as low energy consumption, low pollution, and high separation efficiency. However, during the actual application process of forward osmosis membranes, the phenomenon of concentration polarization will inevitably occur, which significantly affects the permeation performance of the membranes. The concentration polarization phenomenon is mainly divided into external concentration polarization (ECP) and internal concentration polarization (ICP), among which the ICP effect is particularly significant, which will lead to a decrease in the effective osmotic pressure on both sides of the membrane, and further cause the permeation flux of the membrane to be much lower than the theoretical value, severely restricting the popularization and application of forward osmosis membrane technology.

[0003] During the development of forward osmosis membrane technology, in order to improve the permeation selectivity of the membranes and alleviate the concentration polarization phenomenon, researchers have developed double-cortex polyamide forward osmosis membranes. This membrane structure prepares polyamide cortices on both sides of the support, forming a membrane structure with double protective layers. However, although the traditional double-cortex polyamide membranes have improved the membrane performance to a certain extent, the two cortices increase the mass transfer resistance of water and reduce the flux.

[0004] In order to further optimize the performance of double-cortex polyamide forward osmosis membranes, the prior art has further proposed double-cortex polyamide forward osmosis membranes with loose and dense layers. A dense polyamide cortex is prepared on one side of this membrane to provide excellent rejection performance and prevent solute molecules from passing through; while a relatively loose polyamide cortex is prepared on the other side to promote water permeation and alleviate the internal concentration polarization phenomenon. This design combines the advantages of dense and loose cortices, which not only alleviates the concentration polarization phenomenon but also improves the permeation performance of the membranes. However, the methods for preparing such double-cortex polyamide forward osmosis membranes with loose and dense layers in the prior art are often complex and costly. It is necessary to prepare two polyamide cortices with different compactness in two independent steps, and the types of monomers required in each preparation process may also be different, which significantly increases the membrane preparation process and cost, thus limiting its wide popularization in practical applications. Therefore, it is urgent to optimize the existing methods to reduce the preparation process and production cost of polyamide forward osmosis membranes to adapt to industrial applications. Summary of the Invention

[0005] In view of the above problems, the present invention proposes a method for preparing a double-cortex forward osmosis membrane by one-step interfacial polymerization, and uses the influence of silica in different interfacial polymerization environments to prepare polyamide cortices with different compactness.

[0006] A method for preparing a double - skin polyamide forward osmosis membrane by one - step interfacial polymerization according to the present invention comprises the following steps: First step: Pretreatment of the support. Select a support and perform soaking, cleaning, and drying treatments. Second step: Prepare a silica suspension with a silica particle concentration of 0.5 - 2 wt%. Then, coat the silica suspension on the first surface of the support once. After drying, coat the silica suspension on the second surface of the support 3 - 5 times. Third step: Vertically immerse the support coated with the silica layer in a m - phenylenediamine monomer solution. Take out the support and remove the excess solution on the surface. Fourth step: Horizontally place the support impregnated with the m - phenylenediamine monomer, with the first surface of the support facing upward, and immerse it entirely in a trimesoyl chloride solution for interfacial polymerization reaction to form a highly dense polyamide skin layer on the first surface and a less dense polyamide skin layer on the second surface. Fifth step: Clean and dry the reacted membrane to obtain a double - skin polyamide forward osmosis membrane.

[0007] As a preferred solution, in the first step, the soaking is to immerse the support in deionized water for 4 - 24 h; the cleaning is to repeatedly rinse the support with deionized water; the drying is to dry the support at 50 - 60 °C for 4 - 12 h.

[0008] As a preferred solution, in the second step, the type of silica particles is amorphous or crystalline, and the particle size range is 10 - 100 nm.

[0009] As a preferred solution, in the second step, the coating of silica is completed by one of wiping coating, spraying, or dip coating.

[0010] As a preferred solution, in the first step, the support is a nanofiber membrane or a phase - inversion flat membrane, and the material is polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), or polyethersulfone (PES).

[0011] As a preferred solution, in the first step, the pore size range of the support is 50 - 500 nm, and the porosity is greater than 50%.

[0012] As a preferred solution, in the third step, the concentration of the m - phenylenediamine monomer solution is 1.0 - 5.0 wt%, and the impregnation time is 1 - 5 minutes.

[0013] As a preferred solution, in the fourth step, the concentration of the trimesoyl chloride solution is 0.1 - 0.5 wt%, the interfacial polymerization reaction time is 2 - 10 minutes, and the reaction temperature is from room temperature to 60 °C.

[0014] Compared with the prior art, the solution of the present invention has the following beneficial effects: The present invention optimizes the existing preparation method of the double-skin polyamide forward osmosis membrane. The double-skin polyamide forward osmosis membrane with different compactness can be prepared by one-step interfacial polymerization, which can alleviate the concentration polarization phenomenon while improving the flux of the double-skin forward osmosis membrane. This method only has one-step interfacial polymerization process, reducing the synthesis steps and costs, and has high application potential. Specifically, in the present invention, a silica coating with a lower concentration is coated on the upper surface of the support, which can reduce the voids between polymer chains, thereby increasing the compactness of the membrane; while a silica coating with a higher concentration is coated on the lower surface. Due to the influence of gravity, the silica particles have a displacement process, which affects the interfacial polymerization process to form a less compact skin layer. In addition, the silica particles improve the hydrophilicity of the whole membrane, alleviating the concentration polarization phenomenon from another aspect. Detailed implementation mode

[0015] Example 1

[0016] The first step: Pretreatment of the support Selection of the support: A polyacrylonitrile (PAN) nanofiber membrane is selected as the support, with an average pore size range of 200 nanometers and a porosity of 65%.

[0017] Soaking treatment: The PAN nanofiber membrane is immersed in deionized water for 12 hours to ensure that the support is fully wetted.

[0018] Cleaning treatment: The surface of the support is repeatedly rinsed with deionized water to remove impurities.

[0019] Drying treatment: The cleaned support is placed in an oven at 55 °C and dried for 8 hours to ensure that the support is dry.

[0020] The second step: Preparation and coating of the silica suspension Preparation of the silica suspension: An amorphous silica suspension with a concentration of 1.0 wt% and a particle size of 51 nanometers is prepared.

[0021] Coating on the first surface: By means of dip coating, a layer of silica suspension is evenly coated on the first surface (upper surface) of the support and dried naturally at room temperature.

[0022] The third step: Immersion of the m-phenylenediamine monomer solution Preparation of the m-phenylenediamine monomer solution: An aqueous solution of m-phenylenediamine (MPD) with a concentration of 3.0 wt% is prepared.

[0023] Vertical immersion: The support coated with the silica layer is vertically immersed in the MPD solution for 3 minutes.

[0024] Removing the excess solution: The immersed support is gently fished out and the excess solution on the surface is removed with filter paper.

[0025] Step 4: Interfacial polymerization Horizontal placement: Horizontally place the support impregnated with MPD monomer with the first surface facing upward.

[0026] Trimesoyl chloride solution impregnation: Prepare a 0.3 wt% trimesoyl chloride (TMC) n - hexane solution, and immerse the entire support in the TMC solution for interfacial polymerization reaction. The reaction time is 5 minutes and the reaction temperature is room temperature.

[0027] Step 5: Cleaning and drying Cleaning treatment: Take out the reacted membrane and wash it successively with n - hexane and deionized water to remove unreacted monomers and solvents.

[0028] Drying treatment: Place the washed membrane in an oven at 60 °C and dry it for 6 hours to obtain a single - skin polyamide forward osmosis membrane.

[0029] Example 2

[0030] Step 1: Support pretreatment Support selection: Select a polyacrylonitrile (PAN) nanofiber membrane as the support, with an average pore size range of 200 nm and a porosity of 65%.

[0031] Soaking treatment: Immerse the PAN nanofiber membrane in deionized water for 12 hours to ensure that the support is fully wetted.

[0032] Cleaning treatment: Rinse the surface of the support repeatedly with deionized water to remove impurities.

[0033] Drying treatment: Place the cleaned support in an oven at 55 °C and dry it for 8 hours to ensure that the support is dry.

[0034] Step 2: Preparation and coating of silica suspension Silica suspension preparation: Prepare an amorphous silica suspension with a concentration of 1.0 wt% and a particle size of 51 nm.

[0035] Second - surface coating: Adopt the dip - coating method to repeatedly coat the second surface (lower surface) of the support with the silica suspension four times, and allow it to dry naturally after each coating.

[0036] Step 3: Impregnation with m - phenylenediamine monomer solution m - Phenylenediamine monomer solution preparation: Prepare an aqueous solution of m - phenylenediamine (MPD) with a concentration of 3.0 wt%.

[0037] Vertical impregnation: Vertically immerse the support coated with the silica layer in the MPD solution for 3 minutes.

[0038] Removing excess solution: Gently lift out the impregnated support and use filter paper to remove the excess solution on the surface.

[0039] Fourth step: Interfacial polymerization reaction Horizontal placement: Place the support impregnated with MPD monomer horizontally with the second surface facing down.

[0040] Impregnation with trimesoyl chloride solution: Prepare a 0.3 wt% solution of trimesoyl chloride (TMC) in n - hexane, and immerse the entire support in the TMC solution for interfacial polymerization reaction. The reaction time is 5 minutes and the reaction temperature is room temperature.

[0041] Fifth step: Cleaning and drying Cleaning treatment: Take out the reacted membrane and wash it successively with n - hexane and deionized water to remove unreacted monomers and solvents.

[0042] Drying treatment: Place the washed membrane in an oven at 60 °C for 6 hours to obtain a single - skin polyamide forward osmosis membrane.

[0043] Example 3

[0044] First step: Support pretreatment Support selection: Select a polyacrylonitrile (PAN) nanofiber membrane as the support, with an average pore size range of 200 nm and a porosity of 65%.

[0045] Soaking treatment: Immerse the PAN nanofiber membrane in deionized water for 12 hours to ensure that the support is fully wetted.

[0046] Cleaning treatment: Rinse the surface of the support repeatedly with deionized water to remove impurities.

[0047] Drying treatment: Place the cleaned support in an oven at 55 °C for 8 hours to ensure that the support is dry.

[0048] Second step: Preparation and coating of silica suspension Preparation of silica suspension: Prepare an amorphous silica suspension with a concentration of 1.0 wt% and a particle size of 51 nm.

[0049] Coating on the first surface: Adopt the impregnation coating method to uniformly coat a layer of silica suspension on the first surface (upper surface) of the support and dry it naturally at room temperature.

[0050] Coating on the second surface: After drying the first surface, also adopt the impregnation coating method to repeatedly coat the second surface (lower surface) of the support with silica suspension four times, and dry it naturally each time.

[0051] Third step: Impregnation with m - phenylenediamine monomer solution Preparation of m-phenylenediamine monomer solution: Prepare an aqueous solution of m-phenylenediamine (MPD) with a concentration of 3.0 wt%.

[0052] Vertical impregnation: Vertically immerse the support coated with a silica layer in the MPD solution for 3 minutes.

[0053] Removal of excess solution: Gently lift out the impregnated support and remove the excess solution on the surface with filter paper.

[0054] Step 4: Interfacial polymerization reaction Horizontal placement: Place the support impregnated with MPD monomer horizontally with the first surface facing up.

[0055] Impregnation with trimesoyl chloride solution: Prepare a 0.3 wt% solution of trimesoyl chloride (TMC) in n-hexane and immerse the entire support in the TMC solution for interfacial polymerization reaction for 5 minutes at room temperature.

[0056] Step 5: Cleaning and drying Cleaning treatment: Take out the reacted membrane and wash it successively with n-hexane and deionized water to remove unreacted monomers and solvents.

[0057] Drying treatment: Place the washed membrane in an oven at 60 °C for 6 hours to obtain a double-skinned polyamide forward osmosis membrane.

[0058] Comparative example 1 Step 1: Support pretreatment Support selection: Select a polyacrylonitrile (PAN) nanofiber membrane as the support with an average pore size range of 200 nm and a porosity of 65%.

[0059] Soaking treatment: Immerse the PAN nanofiber membrane in deionized water for 12 hours to ensure that the support is fully wetted.

[0060] Cleaning treatment: Rinse the surface of the support repeatedly with deionized water to remove impurities.

[0061] Drying treatment: Place the cleaned support in an oven at 55 °C for 8 hours to ensure that the support is dry.

[0062] Step 2: Impregnation with m-phenylenediamine monomer solution Preparation of m-phenylenediamine monomer solution: Prepare an aqueous solution of m-phenylenediamine (MPD) with a concentration of 3.0 wt%.

[0063] Vertical impregnation: Vertically immerse the support in the MPD solution for 3 minutes.

[0064] Removal of excess solution: Gently lift out the impregnated support and remove the excess solution on the surface with filter paper.

[0065] Step 3: Interfacial Polymerization Horizontal placement: The support body impregnated with MPD monomer is placed horizontally.

[0066] Immersion in isophthaloyl chloride solution: prepare a 0.3 wt % isophthaloyl chloride (TMC) n-hexane solution, immerse the whole support in the TMC solution for interfacial polymerization reaction, the reaction time is 5 minutes, and the reaction temperature is room temperature.

[0067] Step 4: Wash and dry Cleaning treatment: The membrane after the reaction is taken out and cleaned with n-hexane and deionized water in sequence to remove unreacted monomers and solvents.

[0068] Drying treatment: The cleaned membrane was placed in a 60°C oven and dried for 6 hours to obtain a double-layer polyamide forward osmosis membrane.

[0069] Comparative Example 2 Step 1: Support pretreatment Support selection: Polyacrylonitrile (PAN) nanofiber membrane was selected as the support, with an average pore size range of 200 nanometers and a porosity of 65%.

[0070] Soaking treatment: The PAN nanofiber membrane was immersed in deionized water for 12 hours to ensure that the support was fully wetted.

[0071] Cleaning treatment: Rinse the support surface repeatedly with deionized water to remove impurities.

[0072] Drying treatment: Place the cleaned support in a 55°C oven for 8 hours to ensure that the support is dry.

[0073] Step 2: Preparation and coating of silica suspension Preparation of silica suspension: Amorphous silica suspension with a concentration of 1.0 wt % and a particle size of 51 nm was prepared.

[0074] First surface coating: a layer of silicon dioxide suspension is uniformly coated on the first surface (upper surface) of the support body by dip coating, and then dried naturally at room temperature.

[0075] Second surface coating: After the first surface is dried, the second surface (lower surface) of the support is coated with a silica suspension by dipping and then dried naturally.

[0076] Step 3: Impregnation of m-phenylenediamine monomer solution Preparation of meta-phenylenediamine monomer solution: prepare a 3.0 wt% meta-phenylenediamine (MPD) aqueous solution.

[0077] Vertical impregnation: The support coated with a silica layer was vertically impregnated in the MPD solution for 3 minutes.

[0078] Removing excess solution: The impregnated support was gently fished out and the excess solution on the surface was removed with filter paper.

[0079] Step 4: Interfacial polymerization reaction Horizontal placement: The support impregnated with MPD monomer was placed horizontally with the first surface facing up.

[0080] Trimesoyl chloride solution impregnation: A 0.3 wt% solution of trimesoyl chloride (TMC) in n - hexane was prepared, and the entire support was impregnated in the TMC solution for interfacial polymerization reaction. The reaction time was 5 minutes and the reaction temperature was room temperature.

[0081] Step 5: Cleaning and drying Cleaning treatment: The reacted membrane was taken out and washed successively with n - hexane and deionized water to remove unreacted monomers and solvents.

[0082] Drying treatment: The washed membrane was placed in an oven at 60 °C and dried for 6 hours to obtain a double - skinned polyamide forward osmosis membrane.

[0083] Comparative example 3 Step 1: Support pretreatment Support selection: A polyacrylonitrile (PAN) nanofiber membrane was selected as the support, with an average pore size range of 200 nm and a porosity of 65%.

[0084] Soaking treatment: The PAN nanofiber membrane was impregnated in deionized water for 12 hours to ensure that the support was fully wetted.

[0085] Cleaning treatment: The surface of the support was repeatedly rinsed with deionized water to remove impurities.

[0086] Drying treatment: The cleaned support was placed in an oven at 55 °C and dried for 8 hours to ensure that the support was dry.

[0087] Step 2: Preparation and coating of silica suspension Silica suspension preparation: An amorphous silica suspension with a concentration of 1.0 wt% and a particle size of 51 nm was prepared.

[0088] First - surface coating: By means of dip - coating, the silica suspension was uniformly coated on the first surface (upper surface) of the support four times, and each time after coating, it was naturally dried.

[0089] Second - surface coating: After the first surface was dried, in the same way of dip - coating, the silica suspension was repeatedly coated on the second surface (lower surface) of the support four times, and each time after coating, it was naturally dried.

[0090] Step 3: Impregnation with m-Phenylenediamine Monomer Solution Preparation of m-Phenylenediamine Monomer Solution: Prepare an aqueous solution of m-phenylenediamine (MPD) with a concentration of 3.0 wt%.

[0091] Vertical Impregnation: Vertically immerse the support coated with a silica layer in the MPD solution for 3 minutes.

[0092] Removal of Excess Solution: Gently take out the impregnated support and remove the excess solution on the surface with filter paper.

[0093] Step 4: Interfacial Polymerization Reaction Horizontal Placement: Place the support impregnated with MPD monomer horizontally with the first surface facing up.

[0094] Impregnation with Trimesoyl Chloride Solution: Prepare a 0.3 wt% solution of trimesoyl chloride (TMC) in n-hexane, and immerse the entire support in the TMC solution for interfacial polymerization reaction. The reaction time is 5 minutes and the reaction temperature is room temperature.

[0095] Step 5: Cleaning and Drying Cleaning Treatment: Take out the reacted membrane and wash it successively with n-hexane and deionized water to remove unreacted monomers and solvents.

[0096] Drying Treatment: Place the washed membrane in an oven at 60 °C and dry it for 6 hours to obtain a double-skin polyamide forward osmosis membrane.

[0097] The single-skin forward osmosis membranes prepared in Examples 1-2 above and the double-skin forward osmosis membranes prepared in Example 1 and Comparative Examples 1-2 were tested for filtration performance using a 2 mol / L sodium chloride solution as the draw solution. The results are shown in Table 1.

[0098] Table 1

[0099] Based on the above filtration performance tests of Example 1 and Example 2, the polyamide skin layer formed on the upper surface has higher denseness (i.e., higher rejection rate and lower flux) compared to the polyamide skin layer formed on the lower surface. And compared with the results of Comparative Examples 1-3, the double-skin forward osmosis membrane prepared in Example 3 has a high sodium chloride rejection rate and a relatively high pure water flux, showing high application potential.

[0100] It should be understood that the above are only specific application examples of the present invention and do not constitute any limitation to the protection scope of the present invention. Any technical solutions formed by equivalent transformation or equivalent substitution fall within the scope of the present invention's rights protection.

Claims

1. A method for preparing a dual-cortex forward osmosis membrane by one-step interfacial polymerization, comprising the following steps: The first step: Pretreatment of the support, selecting a support and performing soaking, cleaning, and drying treatments; The second step: Preparing a silica suspension with a silica particle concentration of 0.5-2 wt%, then coating the silica suspension on the first surface of the support once, and after drying, coating the silica suspension on the second surface of the support 3-5 times; The third step: Vertically immersing the support coated with the silica layer in a m-phenylenediamine monomer solution, fishing out the support, and removing the excess solution on the surface; The fourth step: Horizontally placing the support impregnated with the m-phenylenediamine monomer, with the first surface of the support facing upward, and immersing the whole in a trimesoyl chloride solution for interfacial polymerization reaction to form a highly dense polyamide cortex on the first surface and a less dense polyamide cortex on the second surface; The fifth step: Cleaning and drying the reacted membrane to obtain a dual-cortex polyamide forward osmosis membrane.

2. The method according to claim 1, wherein In the first step, the soaking is to immerse the support in deionized water for 4-24 h; the cleaning is to repeatedly rinse the support with deionized water; the drying is to dry the support at 50-60 °C for 4-12 h.

3. The method according to claim 1, characterized in that In the second step, the type of the silica particles is amorphous or crystalline, and the particle size range is 10-100 nm.

4. The method according to claim 1, wherein In the second step, the coating of the silica is completed by one of wiping coating, spraying, and dip coating.

5. The method according to claim 1, characterized in that In the first step, the support is a nanofiber membrane or a phase inversion flat membrane, and the material is polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), or polyethersulfone (PES).

6. The method according to claim 1, characterized in that In the first step, the pore size range of the support is 50-500 nm, and the porosity is greater than 50%.

7. The method according to claim 1, characterized in that In the third step, the concentration of the m-phenylenediamine monomer solution is 1.0-5.0 wt%, and the immersion time is 1-5 minutes.

8. The method according to claim 1, wherein In the fourth step, the concentration of the trimesoyl chloride solution is 0.1-0.5 wt%, the interfacial polymerization reaction time is 2-10 minutes, and the reaction temperature is from room temperature to 60 °C.

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