Preparation method of high desalination seawater desalination composite reverse osmosis membrane

Abstract

The present invention discloses a preparation method of a high-desalination seawater desalination composite reverse osmosis membrane, which includes the preparation of a casting solution, an ultrafiltration membrane substrate membrane, a PDA mixed solution, an aqueous solution, an organic phase solution, and an intermediate layer. Then, the entire intermediate layer is immersed in the aqueous solution, and then taken out and the excess water on the surface is blown dry until there are no obvious water droplets on the membrane surface. After that, the entire membrane sheet is immersed in the organic phase solution for soaking. After taking it out and naturally drying it, it is washed with a citric acid solution and then immersed in a glycerol solution for moisture preservation treatment. Then, the membrane sheet is completely dried in an oven to obtain a high-desalination seawater desalination composite reverse osmosis membrane. In the present invention, nanomaterials are dispersed in a dopamine (PDA) solution, and the nanomaterials are deposited on the surface of the substrate material through the self-polymerization reaction of PDA, and then a high-desalination seawater desalination composite reverse osmosis membrane is prepared through an interfacial polymerization reaction.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane production and processing, and particularly relates to a method for preparing a high-desalination seawater desalination composite reverse osmosis membrane. Background Art

[0002] With the continuous growth of the population and the rapid development of industry, the global demand for fresh water is increasing day by day. Meeting the challenge of global water shortage requires more sustainable water resource management. Membrane separation technology is a very promising technology for solving the global water shortage problem, including nanofiltration (NF) and reverse osmosis (RO) processes, which have attracted much attention due to their advantages over other processes in terms of simplicity, scalability, small footprint and energy efficiency. The wide application of membrane processes (including NF and RO processes) provides a good solution to the problem of fresh water shortage. At present, the most widely used and advanced membrane technology in seawater desalination applications is the polyamide reverse osmosis membrane prepared by interfacial polymerization (IP). Although polyamide reverse osmosis membranes have been widely used in seawater desalination, their practical applications are still hindered by some technical obstacles. The problems of TFC membranes largely stem from the inherent limitations of polyamide chemistry and the interfacial polymerization reaction mechanism.

[0003] The functional layer of common polyamide membranes is usually formed on a porous substrate through an interfacial polymerization (IP) process, in which two monomers polymerize at the interface of two immiscible phases. The formed dense and cross-linked polyamide layer is highly selective, allowing water molecules to pass through effectively and intercepting the target solutes. Although polyamide membranes are widely used in NF and RO, there is a trade-off relationship between the membrane flux and the rejection rate of polyamide membranes, which hinders the simultaneous improvement of membrane water permeability and solute rejection rate. Therefore, it is necessary to modify the membrane performance by other methods. It is not only necessary to precisely control the structure of the polyamide layer to improve permeability, but also to increase the solute rejection performance in the composite structure of the polyamide membrane. However, due to the relatively fast IP reaction rate and the relatively high diffusion rate of amine monomers, the average thickness of the polyamide layer is between dozens and hundreds of nanometers. Therefore, precise control of the interfacial polymerization process is particularly important.

[0004] Therefore, introducing an intermediate layer on the porous substrate before the interfacial polymerization reaction is an effective way to regulate the interfacial polymerization process and the structure of the amide layer. Compared with the traditional interfacial polymerization process, this intermediate layer can increase the amine storage amount in the reaction interface and control amine diffusion. Therefore, it is beneficial to form an ultrathin, defect-free and dense polyamide active layer, making the membrane have high water permeability and good solute rejection rate. By designing intermediate layers with different types, structures and chemical functions, the interfacial polymerization reaction can be precisely controlled.

[0005] Due to the rich and adjustable functional groups of organic materials, the organic interlayer is used to prepare high-performance TFC membranes by regulating the interactions between the interlayer and reactive monomers and between the porous matrix and the interlayer. Generally speaking, by using organic materials, a uniform and continuous interlayer can be easily constructed on the porous substrate to regulate the structure and properties of thin-film composite polyamide membranes. In addition, due to the closely contacting spatial configuration of nanomaterials, by distributing well-dispersed one-dimensional (1D, such as nanowires, nanotubes, etc.) or two-dimensional (2D, such as nanosheets) nanomaterials onto the porous substrate, a continuous and uniform interlayer can be more easily formed during the interfacial polymerization process. However, due to the poor compatibility between nanomaterials and matrix materials, it is difficult for nanomaterials to be uniformly and stably coated on the surface of matrix materials, which affects the interfacial polymerization. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a method for preparing a high-desalination seawater desalination composite reverse osmosis membrane. In the present invention, nanomaterials are dispersed in a dopamine (PDA) solution, and the nanomaterials are deposited on the surface of the matrix material through the self-polymerization reaction of PDA, and then a high-desalination seawater desalination composite reverse osmosis membrane is prepared through an interfacial polymerization reaction.

[0007] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0008] A method for preparing a high-desalination seawater desalination composite reverse osmosis membrane, comprising the following steps:

[0009] (1) Preparation of the casting solution: Weigh polyethersulfone and a solvent by weight parts and mix them evenly, stir and heat, and perform vacuum filtration to obtain the casting solution;

[0010] (2) Preparation of the ultrafiltration membrane substrate: Use the liquid-solid phase conversion method to make the casting solution act on the support material to form the ultrafiltration membrane substrate;

[0011] (3) Preparation of the PDA mixed solution: Take PDA and hydrochloric acid and add them to pure water, stir evenly to prepare a PDA hydrochloric acid solution, and take nanomaterials and add them to the PDA hydrochloric acid solution and stir to make them evenly dispersed to obtain the PDA mixed solution;

[0012] (4) Preparation of the aqueous solution: Weigh m-phenylenediamine, NaOH, and pure water by weight parts, mix them evenly to make the aqueous solution;

[0013] (5) Preparation of the organic solution: Weigh trimesoyl chloride and ethylcyclohexane by weight parts, mix them evenly to make the organic solution;

[0014] (6) Preparation of the intermediate layer: Fix the ultrafiltration membrane substrate prepared in step (2) onto a flat plate, then immerse the flat plate with the fixed ultrafiltration membrane substrate into the PDA mixed solution in step (3), adjust the pH value and soak it, then take out the flat plate with the fixed ultrafiltration membrane substrate, and then clean the excess substances by vacuum filtration to obtain the intermediate layer;

[0015] (7) Immerse the whole intermediate layer in step (6) in the aqueous solution in step (4) for soaking, then take it out and blow dry the excess water on the surface until there are no obvious water droplets on the membrane surface. Then immerse the whole membrane into the organic phase solution in step (5) for soaking, take it out and let it dry naturally, wash it with citric acid solution and then immerse it in glycerol solution for moisture retention treatment, and then completely dry the membrane in an oven to obtain a high desalination seawater desalination composite reverse osmosis membrane.

[0016] Further, in step (1), the mass ratio of the polyethersulfone to the solvent is 16 - 21:79 - 84; the solvent is N,N-dimethylformamide; the temperature of the stirring and heating is 75 - 95°C, and the time is 8 - 11 h; the time of the vacuum filtration is 2 - 4 h, and the vacuum degree is 0.2 - 0.5 MPa.

[0017] Further, in step (2), the time of the liquid-solid phase transformation is 0.5 - 1 min, the temperature of the phase inversion water bath is 11 - 13°C, and the temperature of the thermal curing water bath is 65 - 75°C; the support material is non-woven fabric with a thickness of 3.2 - 3.5 mil; the thickness of the ultrafiltration membrane substrate is 5.5 - 6 mil.

[0018] Further, in step (3), the mass ratio of the PDA, hydrochloric acid, nanomaterial and pure water is 0.1 - 0.15:0.1 - 0.2:0.08 - 0.12:99.53 - 99.72; the stirring time is 28 - 32 min.

[0019] Further, in step (3), the nanomaterial is one of graphene oxide, molybdenum disulfide, phosphorene, and molybdenum selenide.

[0020] Further, in step (4), the m-phenylenediamine, NaOH and pure water are in the following weight ratio: m-phenylenediamine 50 - 150 parts, NaOH 10 - 20 parts, pure water 4830 - 4940 parts, and the monomer concentration of the aqueous solution is 1 - 3 wt%.

[0021] Further, in step (5), the trimesoyl chloride and ethylcyclohexane are in the following weight ratio: trimesoyl chloride 2 - 6 parts, ethylcyclohexane 3994 - 3998 parts, and the monomer concentration of the organic phase solution is 0.05 - 0.15 wt%.

[0022] Further, in steps (4) and (5), the mass ratio of the aqueous solution to the organic solution = 5:4.

[0023] Further, in step (6), the pH value is adjusted to pH > 8.5 by adding NaOH; the soaking time is 40 - 60 min.

[0024] Further, in step (7), the soaking time in the aqueous solution is 12 - 18 s, and the soaking time in the organic solution is 5 - 7 s; the concentration of the citric acid solution is 20 - 30 wt%, the cleaning temperature is 60 - 80 °C, and the time is 4 - 5 min; the concentration of the glycerol solution is 15 - 25 wt%.

[0025] Since the present invention adopts the above technical solutions, it has the following beneficial effects:

[0026] (1) The present invention combines the characteristics that PDA has good compatibility with nanomaterials and the ultrafiltration membrane base membrane material, and the two-dimensional nanomaterials are easy to form a continuous and uniform sandwich structure, constructs a uniform, continuous and stable composite intermediate layer structure, realizes the regulation of the structure of the interfacial polymerization desalination layer, and finally prepares a thin and very dense desalination layer structure to obtain the high-desalination seawater desalination composite reverse osmosis membrane.

[0027] (2) The flux and desalination rate of the high-desalination seawater desalination composite reverse osmosis membrane prepared in this application were tested. According to the test results, the flux of the prepared high-desalination seawater desalination composite reverse osmosis membrane > 48.0 L / m 2 ·h, and the desalination rate ≥ 99.91%. Specific Embodiments

[0028] The following further elaborates on the specific embodiments of the present invention in detail, but the present invention is not limited to these embodiments. Any improvement or substitution based on the basic spirit of this embodiment still falls within the scope protected by the claims of the present invention.

[0029] Example 1

[0030] A method for preparing a high-desalination seawater desalination composite reverse osmosis membrane, comprising the following steps:

[0031] (1) Preparation of the casting solution: Weigh polyethersulfone and a solvent by weight parts, mix them evenly, stir and heat, and perform vacuum filtration to obtain the casting solution; the mass ratio of the polyethersulfone to the solvent is 16:84; the solvent is N,N-dimethylformamide; the temperature of the stirring and heating is 80 °C, and the time is 8 h; the time of the vacuum filtration is 4 h, and the vacuum degree is 0.5 MPa;

[0032] (2) Preparation of the ultrafiltration membrane substrate: The casting solution reacts with the support material by the liquid-solid phase conversion method to form the ultrafiltration membrane substrate; the time of the liquid-solid phase conversion is 1 min, the phase inversion water bath temperature is 12 °C, and the thermal curing water bath temperature is 75 °C; the support material is non-woven fabric with a thickness of 3.2 - 3.5 mil; the thickness of the ultrafiltration membrane substrate is 5.5 - 6 mil;

[0033] (3) Preparation of the PDA mixed solution: Take PDA and hydrochloric acid and add them to pure water, stir evenly to prepare the PDA hydrochloric acid solution, and then take the nanomaterial and add it to the PDA hydrochloric acid solution and stir for 30 min to make it evenly dispersed to obtain the PDA mixed solution; the mass ratio of PDA, hydrochloric acid, nanomaterial and pure water is 0.1:0.1:0.08:99.72; the nanomaterial is graphene oxide, that is, 0.5 parts of PDA, 0.5 parts of hydrochloric acid, 0.4 parts of graphene oxide, and 498.6 parts of pure water;

[0034] (4) Preparation of the aqueous solution: Weigh m-phenylenediamine, NaOH and pure water according to parts by weight, mix them evenly to make the aqueous solution; the m-phenylenediamine, NaOH and pure water are in the following weight ratio: 50 parts of m-phenylenediamine, 10 parts of NaOH, and 4940 parts of pure water, and the monomer concentration of the aqueous solution is 1 wt%, and 5 kg of the aqueous solution is prepared;

[0035] (5) Preparation of the organic solution: Weigh trimesoyl chloride and ethylcyclohexane according to parts by weight, mix them evenly to make the organic solution; the trimesoyl chloride and ethylcyclohexane are in the following weight ratio: 2 parts of trimesoyl chloride and 3998 parts of ethylcyclohexane, and the monomer concentration of the organic solution is 0.05 wt%, and 4 kg of the organic solution is prepared;

[0036] (6) Preparation of the intermediate layer: Fix the ultrafiltration membrane substrate obtained in step (2) to the flat plate, then immerse the flat plate with the fixed ultrafiltration membrane substrate into the PDA mixed solution in step (3), adjust the pH value and then soak it, then take out the flat plate with the fixed ultrafiltration membrane substrate, and then wash the excess substances clean by vacuum filtration to obtain the intermediate layer; the pH value is adjusted to pH > 8.5 by adding NaOH; the soaking time is 40 min;

[0037] (7) Immerse the entire intermediate layer from step (6) in the aqueous solution from step (4) for soaking, then take it out and blow dry the excess moisture on the surface. After there are no obvious water droplets on the surface of the membrane sheet, immerse the entire membrane sheet in the organic phase solution from step (5) for soaking. After taking it out and air drying naturally, wash it with citric acid solution and then immerse it in glycerol solution for moisturizing treatment. Then dry the membrane sheet completely in an oven to obtain a high-desalination seawater desalination composite reverse osmosis membrane; the soaking time in the aqueous solution is 12 s, and the soaking time in the organic phase solution is 5 s; the concentration of the citric acid solution is 20 wt%, the washing temperature is 60 °C, and the time is 4 min; the concentration of the glycerol solution is 15 wt%.

[0038] Example 2

[0039] A preparation method of a high-desalination seawater desalination composite reverse osmosis membrane includes the following steps:

[0040] (1) Preparation of the casting solution: Weigh polyethersulfone and a solvent by weight parts, mix them evenly, stir and heat, and perform vacuum filtration to obtain the casting solution; the mass ratio of polyethersulfone to the solvent is 20:80; the solvent is N,N-dimethylformamide; the temperature of the stirring and heating is 90 °C, and the time is 11 h; the time of the vacuum filtration is 2 h, and the vacuum degree is 0.35 MPa;

[0041] (2) Preparation of the ultrafiltration membrane substrate: Use the liquid-solid phase conversion method to make the casting solution act on the support material to form the ultrafiltration membrane substrate; the time of the liquid-solid phase conversion is 45 s, the phase conversion water bath temperature is 11 °C, and the thermal curing water bath temperature is 75 °C; the support material is non-woven fabric, and the thickness is 3.2 - 3.5 mil; the thickness of the ultrafiltration membrane substrate is 5.5 - 6 mil;

[0042] (3) Preparation of the PDA mixed solution: Take PDA and hydrochloric acid and add them to pure water together, stir evenly to prepare a PDA hydrochloric acid solution, and take nanomaterials and add them to the PDA hydrochloric acid solution and stir for 30 min to make them evenly dispersed to obtain the PDA mixed solution; the mass ratio of PDA, hydrochloric acid, nanomaterials, and pure water is 0.15:0.2:0.12:99.53; the nanomaterials are graphene oxide, that is, 0.75 parts of PDA, 1.0 part of hydrochloric acid, 0.6 part of graphene oxide, and 497.65 parts of pure water;

[0043] (4) Preparation of the aqueous solution: Weigh m-phenylenediamine, NaOH, and pure water by weight parts, mix them evenly to make the aqueous solution; the m-phenylenediamine, NaOH, and pure water are in the following weight part ratio: 150 parts of m-phenylenediamine, 20 parts of NaOH, and 4830 parts of pure water. The monomer concentration of the aqueous solution is 3 wt%, and 5 kg of the aqueous solution is prepared;

[0044] (5) Preparation of organic phase solution: Weigh trimellitic acid trichloride and ethylcyclohexane by weight parts, mix them evenly to prepare an organic phase solution; the weight part ratio of trimellitic acid trichloride to ethylcyclohexane is as follows: 6 parts of trimellitic acid trichloride and 3994 parts of ethylcyclohexane, and the monomer concentration of the organic phase solution is 0.15 wt%, and 4 kg of organic phase solution is prepared.

[0045] (6) Preparation of the intermediate layer: Fix the ultrafiltration membrane substrate prepared in step (2) to a flat plate, then immerse the flat plate with the fixed ultrafiltration membrane substrate in the PDA mixed solution of step (3), adjust the pH value and soak it, then take out the flat plate with the fixed ultrafiltration membrane substrate, and then wash the excess substances clean by vacuum filtration to obtain the intermediate layer; the adjustment of the pH value is to adjust the pH value to pH > 8.5 by adding NaOH; the soaking time is 60 min.

[0046] (7) Immerse the whole intermediate layer of step (6) in the aqueous solution of step (4) for soaking, then take it out and blow dry the excess water on the surface until there are no obvious water droplets on the membrane surface, then immerse the whole membrane in the organic phase solution of step (5) for soaking, take it out and let it dry naturally, wash it with citric acid solution and then immerse it in glycerol solution for moisturizing treatment, and then completely dry the membrane in an oven to obtain a high desalination seawater desalination composite reverse osmosis membrane; the soaking time in the aqueous solution is 18 s, and the soaking time in the organic phase solution is 7 s; the concentration of the citric acid solution is 30 wt%, the washing temperature is 80 °C, and the time is 5 min; the concentration of the glycerol solution is 25 wt%.

[0047] Example 3

[0048] A preparation method of a high desalination seawater desalination composite reverse osmosis membrane includes the following steps:

[0049] (1) Preparation of casting solution: Weigh polyethersulfone and solvent by weight parts and mix them evenly, stir and heat, and perform vacuum filtration to obtain a casting solution; the mass ratio of polyethersulfone to solvent is 16:79; the solvent is N,N-dimethylformamide; the temperature of stirring and heating is 75 °C, and the time is 11 h; the time of vacuum filtration is 2 h, and the vacuum degree is 0.4 MPa.

[0050] (2) Preparation of ultrafiltration membrane substrate: Use the liquid-solid phase conversion method to make the casting solution act with the support material to form an ultrafiltration membrane substrate; the time of liquid-solid phase conversion is 0.5 min, the phase conversion water bath temperature is 11 °C, and the thermal curing water bath temperature is 65 °C; the support material is non-woven fabric, and the thickness is 3.2 - 3.5 mil; the thickness of the ultrafiltration membrane substrate is 5.5 - 6 mil.

[0051] (3) Preparation of PDA mixed solution: Add PDA and hydrochloric acid into pure water, stir evenly to prepare PDA hydrochloric acid solution, and add nanomaterials into the PDA hydrochloric acid solution and stir for 28 min to make it evenly dispersed, obtaining PDA mixed solution; the mass ratio of PDA, hydrochloric acid, nanomaterials and pure water is 0.1:0.1:0.08:99.53; the nanomaterials are molybdenum disulfide, that is, 0.5 parts of PDA, 0.5 parts of hydrochloric acid, 0.4 parts of molybdenum disulfide, and 497.65 parts of pure water;

[0052] (4) Preparation of aqueous solution: Weigh m-phenylenediamine, NaOH and pure water according to parts by weight, mix evenly to make an aqueous solution; the m-phenylenediamine, NaOH and pure water are in the following weight ratio: 50 parts of m-phenylenediamine, 10 parts of NaOH, and 4830 parts of pure water, and the monomer concentration of the aqueous solution is 1 wt%, preparing 5 kg of aqueous solution;

[0053] (5) Preparation of organic solution: Weigh trimesoyl chloride and ethylcyclohexane according to parts by weight, mix evenly to make an organic solution; the trimesoyl chloride and ethylcyclohexane are in the following weight ratio: 2 parts of trimesoyl chloride, 3994 parts of ethylcyclohexane, and the monomer concentration of the organic solution is 0.05 wt%, preparing 4 kg of organic solution;

[0054] (6) Preparation of intermediate layer: Fix the ultrafiltration membrane substrate prepared in step (2) on a flat plate, then immerse the flat plate with the fixed ultrafiltration membrane substrate into the PDA mixed solution in step (3), adjust the pH value and soak, then take out the flat plate with the fixed ultrafiltration membrane substrate, and then wash the excess substances clean by vacuum filtration to obtain the intermediate layer; the adjustment of the pH value is to adjust the pH value to pH > 8.5 by adding NaOH; the soaking time is 40 min;

[0055] (7) Immerse the whole intermediate layer in the aqueous solution in step (4) for soaking, then take it out, blow dry the excess water on the surface until there are no obvious water drops on the membrane surface, then immerse the whole membrane into the organic solution in step (5) for soaking, take it out and dry it naturally, wash it with citric acid solution and then immerse it in glycerol solution for moisturizing treatment, and then dry the membrane completely in an oven to obtain a high-desalination seawater desalination composite reverse osmosis membrane; the soaking time in the aqueous solution is 12 s, and the soaking time in the organic solution is 5 s; the concentration of the citric acid solution is 20 wt%, the washing temperature is 60 °C, and the time is 4 min; the concentration of the glycerol solution is 15 wt%.

[0056] Example 4

[0057] A preparation method of a high-desalination seawater desalination composite reverse osmosis membrane, comprising the following steps:

[0058] (1) Preparation of casting solution: Weigh polyethersulfone and solvent according to parts by weight, mix them evenly, stir and heat, and perform vacuum filtration to obtain the casting solution; the mass ratio of polyethersulfone to solvent is 21:84; the solvent is N,N-dimethylformamide; the temperature of stirring and heating is 95°C, and the time is 8 h; the time of vacuum filtration is 4 h, and the vacuum degree is 0.2 MPa;

[0059] (2) Preparation of ultrafiltration membrane substrate: Use the liquid-solid phase conversion method to make the casting solution act on the support material to form the ultrafiltration membrane substrate; the time of liquid-solid phase conversion is 1 min, the phase inversion water bath temperature is 13°C, and the thermal curing water bath temperature is 75°C; the support material is non-woven fabric with a thickness of 3.2 - 3.5 mil; the thickness of the ultrafiltration membrane substrate is 5.5 - 6 mil;

[0060] (3) Preparation of PDA mixed solution: Add PDA and hydrochloric acid together to pure water, stir evenly to prepare a PDA hydrochloric acid solution, and add nanomaterials to the PDA hydrochloric acid solution and stir for 32 min to make it evenly dispersed to obtain the PDA mixed solution; the mass ratio of PDA, hydrochloric acid, nanomaterials and pure water is 0.15:0.2:0.12:99.72; the nanomaterial is phosphorene, that is, 0.75 parts of PDA, 1 part of hydrochloric acid, 0.6 parts of phosphorene, and 498.6 parts of pure water;

[0061] (4) Preparation of aqueous solution: Weigh m-phenylenediamine, NaOH and pure water according to parts by weight, mix them evenly to make an aqueous solution; m-phenylenediamine, NaOH and pure water are in the following parts by weight ratio: 150 parts of m-phenylenediamine, 20 parts of NaOH, and 4940 parts of pure water, and the monomer concentration of the aqueous solution is 3 wt%, and 5 kg of aqueous solution is prepared;

[0062] (5) Preparation of organic solution: Weigh trimesoyl chloride and ethylcyclohexane according to parts by weight, mix them evenly to make an organic solution; trimesoyl chloride and ethylcyclohexane are in the following parts by weight ratio: 6 parts of trimesoyl chloride and 3998 parts of ethylcyclohexane, and the monomer concentration of the organic solution is 0.15 wt%, and 4 kg of organic solution is prepared;

[0063] (6) Preparation of intermediate layer: Fix the ultrafiltration membrane substrate obtained in step (2) to a flat plate, then immerse the flat plate with the fixed ultrafiltration membrane substrate in the PDA mixed solution in step (3), adjust the pH value and perform immersion treatment, then take out the flat plate with the fixed ultrafiltration membrane substrate, and then wash the excess substances clean by vacuum filtration to obtain the intermediate layer; the adjustment of the pH value is to adjust the pH value to pH > 8.5 by adding NaOH; the time of immersion treatment is 60 min;

[0064] (7) Immerse the entire intermediate layer from step (6) in the aqueous solution from step (4) for soaking, then take it out and blow dry the excess water on the surface until there are no obvious water droplets on the membrane surface. After that, immerse the entire membrane in the organic phase solution from step (5) for soaking. After taking it out and air-drying naturally, wash it with citric acid solution and then immerse it in glycerol solution for moisturizing treatment. Then, completely dry the membrane in an oven to obtain a high-desalination seawater desalination composite reverse osmosis membrane. The soaking time in the aqueous solution is 18 s, and the soaking time in the organic phase solution is 7 s. The concentration of the citric acid solution is 30 wt%, the washing temperature is 80 °C, and the time is 5 min. The concentration of the glycerol solution is 25 wt%.

[0065] Example 5

[0066] A preparation method of a high-desalination seawater desalination composite reverse osmosis membrane includes the following steps:

[0067] (1) Preparation of the casting solution: Weigh polyethersulfone and a solvent by weight parts, mix them evenly, stir and heat, and perform vacuum filtration to obtain the casting solution. The mass ratio of polyethersulfone to the solvent is 19:82. The solvent is N,N-dimethylformamide. The temperature of stirring and heating is 85 °C, and the time is 10.5 h. The time of vacuum filtration is 3 h, and the vacuum degree is 0.3 MPa.

[0068] (2) Preparation of the ultrafiltration membrane substrate: Use the liquid-solid phase conversion method to make the casting solution act on the support material to form the ultrafiltration membrane substrate. The time of liquid-solid phase conversion is 0.8 min, the phase conversion water bath temperature is 12 °C, and the thermal curing water bath temperature is 70 °C. The support material is non-woven fabric with a thickness of 3.2 - 3.5 mil. The thickness of the ultrafiltration membrane substrate is 5.5 - 6 mil.

[0069] (3) Preparation of the PDA mixed solution: Take PDA and hydrochloric acid and add them to pure water, stir evenly to prepare a PDA hydrochloric acid solution, and take nanomaterials and add them to the PDA hydrochloric acid solution and stir for 30 min to make them evenly dispersed to obtain the PDA mixed solution. The mass ratio of PDA, hydrochloric acid, nanomaterials, and pure water is 0.13:0.15:0.10:99.65. The nanomaterials are molybdenum diselenide, that is, 0.65 parts of PDA, 0.75 parts of hydrochloric acid, 0.5 parts of molybdenum disulfide, and 498.25 parts of pure water.

[0070] (4) Preparation of the aqueous solution: Weigh m-phenylenediamine, NaOH, and pure water by weight parts, mix them evenly to make an aqueous solution. The m-phenylenediamine, NaOH, and pure water are in the following weight part ratio: 100 parts of m-phenylenediamine, 15 parts of NaOH, and 4890 parts of pure water. The monomer concentration of the aqueous solution is 2 wt%, and 5 kg of aqueous solution is prepared.

[0071] (5) Preparation of organic phase solution: Weigh trimellitic acid trichloride and ethylcyclohexane according to parts by weight, mix them evenly to prepare an organic phase solution; the trimellitic acid trichloride and ethylcyclohexane are in the following weight ratio: 4 parts of trimellitic acid trichloride and 3996 parts of ethylcyclohexane. The monomer concentration of the organic phase solution is 0.10 wt%, and 4 kg of organic phase solution is prepared.

[0072] (6) Preparation of the intermediate layer: Fix the ultrafiltration membrane substrate prepared in step (2) onto a flat plate, then immerse the flat plate with the fixed ultrafiltration membrane substrate into the PDA mixed solution in step (3), adjust the pH value and soak it, then take out the flat plate with the fixed ultrafiltration membrane substrate, and then wash away the excess substances by vacuum filtration to obtain the intermediate layer; the pH value is adjusted to pH > 8.5 by adding NaOH; the soaking time is 50 min.

[0073] (7) Immerse the whole intermediate layer in the aqueous solution in step (4) for soaking, then take it out and blow dry the excess water on the surface until there are no obvious water droplets on the membrane surface. Then immerse the whole membrane into the organic phase solution in step (5) for soaking, take it out and air dry it naturally, wash it with citric acid solution and then immerse it in glycerol solution for moisture retention treatment, and then completely dry the membrane in an oven to obtain a high desalination seawater reverse osmosis composite membrane; the soaking time in the aqueous solution is 15 s, and the soaking time in the organic phase solution is 6 s; the concentration of the citric acid solution is 25 wt%, the washing temperature is 70 °C, and the time is 4.5 min; the concentration of the glycerol solution is 20 wt%.

[0074] Comparative Example 1

[0075] A preparation method of a seawater reverse osmosis composite membrane includes the following steps:

[0076] (1) Take polyethersulfone and mix it evenly with a solvent, and the mixing mass ratio is 16:84; place it at 80 °C and heat and stir for 8 h, and vacuum filter for 4 h to obtain a casting solution.

[0077] (2) Use non-woven fabric as a support material, and through the liquid-solid phase conversion method, make the casting solution act on the support material to form an ultrafiltration membrane. The phase conversion time is 1 min, the phase conversion water bath temperature is 12 °C, and the thermal curing water bath temperature is 75 °C to obtain an ultrafiltration membrane substrate.

[0078] (3) Weigh 50 parts of m-phenylenediamine and 10 parts of NaOH with an analytical balance, add them to 4940 parts of pure water to prepare 5 kg of aqueous solution, and the monomer concentration of the aqueous solution is 1 wt%.

[0079] (4) Weigh 2 portions of trimesoyl chloride using an analytical balance and add them to 3998 portions of ethylcyclohexane to prepare a 4 kg organic phase solution, where the monomer concentration of the organic phase solution is 0.05 wt%.

[0080] (5) Fix the ultrafiltration membrane substrate prepared in (2) to a flat plate, then immerse the flat plate with the fixed ultrafiltration membrane substrate in the PDA solution, and then adjust the pH value to pH > 8.5 by adding NaOH. After soaking for 40 min, take out the ultrafiltration membrane, and then wash away the excess substances by vacuum filtration to obtain the intermediate layer.

[0081] (6) Immerse the whole ultrafiltration membrane sheet in the aqueous solution for 12 s, then take it out and blow dry the excess water on the surface until there are no obvious water droplets on the membrane sheet surface. Then immerse the whole membrane sheet in the organic phase solution for 5 s, then take it out and let it dry naturally. Then wash it in a citric acid solution with a concentration of 20 wt% and a temperature of 60 °C for 4 min, and finally immerse it in a 15 wt% glycerol solution for moisture retention treatment. Then completely dry the membrane sheet in an oven to obtain a high desalination seawater reverse osmosis composite membrane.

[0082] Comparative Example 2

[0083] A method for preparing a seawater reverse osmosis composite membrane, comprising the following steps:

[0084] (1) Take polyethersulfone and mix it evenly with a solvent, and the mixing mass ratio is 16:84; place it in a heating and stirring at 80 °C for 8 h, and perform vacuum filtration for 4 h to obtain a casting solution.

[0085] (2) Use non-woven fabric as a support material, and let the casting solution act on the support material through the liquid-solid phase conversion method to form an ultrafiltration membrane. The phase conversion time is 1 min, the phase conversion water bath temperature is 12 °C, and the thermal curing water bath temperature is 75 °C to obtain an ultrafiltration membrane substrate.

[0086] (3) Take 0.5 portion of hydrochloric acid and 0.4 portion of graphene oxide and add them to 499.1 portions of pure water, and stir for 30 min until the solute is evenly dispersed in the solution.

[0087] (4) Weigh 50 portions of m-phenylenediamine and 10 portions of NaOH using an analytical balance, and add them to 4940 portions of pure water to prepare a 5 kg aqueous solution, where the monomer concentration of the aqueous solution is 1 wt%.

[0088] (5) Weigh 2 portions of trimesoyl chloride using an analytical balance and add them to 3998 portions of ethylcyclohexane to prepare a 4 kg organic phase solution, where the monomer concentration of the organic phase solution is 0.05 wt%.

[0089] (6) Fix the ultrafiltration membrane substrate prepared in (2) to a flat plate, then immerse the flat plate with the fixed ultrafiltration membrane substrate in the PDA solution, and then adjust the pH value to pH > 8.5 by adding NaOH. After soaking for 40 min, take out the ultrafiltration membrane, and then wash away the excess substances by vacuum filtration to obtain the intermediate layer;

[0090] (7) Immerse the whole ultrafiltration membrane sheet in the aqueous solution for 12 s, then take it out and blow dry the excess water on the surface until there are no obvious water droplets on the membrane sheet surface. Then immerse the whole membrane sheet in the organic phase solution for 5 s, then take it out and let it dry naturally. Then wash it in a citric acid solution with a concentration of 20 wt% and a temperature of 60 °C for 4 min. Finally, immerse it in a 15 wt% glycerol solution for moisture retention treatment, and then completely dry the membrane sheet in an oven to obtain a high desalination seawater reverse osmosis composite membrane.

[0091] Comparative Example 3

[0092] A preparation method of a seawater reverse osmosis composite membrane, comprising the following steps:

[0093] (1) Mix polyethersulfone and a solvent evenly, with a mixing mass ratio of 16:84; place it in an 80 °C heating and stirring for 8 h, and vacuum filter for 4 h to obtain a casting solution;

[0094] (2) Use non-woven fabric as a support material, and make the casting solution act on the support material through the liquid-solid phase conversion method to form an ultrafiltration membrane. The phase conversion time is 1 min, the phase conversion water bath temperature is 12 °C, and the thermal curing water bath temperature is 75 °C to obtain an ultrafiltration membrane substrate;

[0095] (3) Take 0.5 parts of PDA and 0.5 parts of hydrochloric acid, add them to 499 parts of pure water, and stir for 30 min until the solute is evenly dispersed in the solution;

[0096] (4) Weigh 50 parts of m-phenylenediamine and 10 parts of NaOH with an analytical balance, add them to 4940 parts of pure water, and prepare a 5 kg aqueous solution, where the monomer concentration of the aqueous solution is 1 wt%;

[0097] (5) Weigh 2 parts of trimesoyl chloride with an analytical balance, add them to 3998 parts of ethyl cyclohexane, and prepare a 4 kg organic phase solution, where the monomer concentration of the organic phase solution is 0.05 wt%;

[0098] (6) Fix the ultrafiltration membrane substrate prepared in (2) to a flat plate, then immerse the flat plate with the fixed ultrafiltration membrane substrate in the PDA solution, and then adjust the pH value to pH > 8.5 by adding NaOH. After soaking for 40 min, take out the ultrafiltration membrane, and then wash away the excess substances by vacuum filtration to obtain the intermediate layer;

[0099] (7) Immerse the whole ultrafiltration membrane sheet in the aqueous solution for 12 s, then take it out and blow dry the excess water on the surface until there are no obvious water droplets on the membrane sheet surface. Then immerse the whole membrane sheet in the organic phase solution for 5 s, then take it out and let it dry naturally. Then wash it in a citric acid solution with a concentration of 20 wt% and a temperature of 60 °C for 4 min. Finally, immerse it in a 15 wt% glycerol solution for moisture retention treatment. Then completely dry the membrane sheet in an oven to obtain a high-desalination seawater desalination composite reverse osmosis membrane.

[0100] Table 1 Performance Comparison of Embodiment Cases

[0101] <![CDATA[Flux (L / m 2 ·h)]]> Desalination rate (%) Example 1 52.3 99.91 Example 2 51.9 99.96 Comparative Example 1 48.5 99.32 Comparative Example 2 49.1 99.34 Comparative Example 3 50.6 99.46

[0102] It can be seen from the experimental data results in Table 1 that after constructing a composite intermediate layer in the reverse osmosis membrane to adjust the desalination layer of the reverse osmosis membrane, both the flux and desalination rate of the membrane sheet have been improved. From the test results of Comparative Example 2, it is difficult to deposit the nanomaterial on the porous substrate membrane to form an intermediate layer structure by simply adding the nanomaterial. And from Comparative Example 3, it can be seen that simply adding PDA as the intermediate layer has a small improvement in the performance of the membrane sheet. In summary, the high-desalination seawater desalination composite reverse osmosis membrane prepared by the present invention has a high flux and desalination rate, overcomes the trade-off relationship between the flux and desalination rate of the traditional seawater desalination reverse osmosis membrane, and is of great significance for promoting the research of seawater desalination.

[0103] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to include all changes falling within the equivalent meaning and scope of the claims within the protection scope of the present invention.

Claims

1. A preparation method of a high-desalination seawater desalination composite reverse osmosis membrane, characterized in that, it comprises the following steps: (1) Preparation of the casting solution: Weigh polyethersulfone and a solvent by weight parts, mix them evenly, stir and heat, and perform vacuum filtration to obtain the casting solution; (2) Preparation of the ultrafiltration membrane substrate: Use the liquid-solid phase conversion method to make the casting solution act on the support material to form the ultrafiltration membrane substrate; (3) Preparation of the PDA mixed solution: Add PDA and hydrochloric acid to pure water together, stir evenly to prepare a PDA hydrochloric acid solution, and add nanomaterials to the PDA hydrochloric acid solution and stir to make them evenly dispersed to obtain the PDA mixed solution; (4) Preparation of the aqueous solution: Weigh m-phenylenediamine, NaOH and pure water by weight parts, mix them evenly to make the aqueous solution; (5) Preparation of the organic solution: Weigh trimesoyl chloride and ethylcyclohexane by weight parts, mix them evenly to make the organic solution; (6) Preparation of the intermediate layer: Fix the ultrafiltration membrane substrate prepared in step (2) on a flat plate, then immerse the flat plate with the fixed ultrafiltration membrane substrate in the PDA mixed solution in step (3), adjust the pH value and soak, then take out the flat plate with the fixed ultrafiltration membrane substrate, and then wash the excess substances clean by vacuum filtration to obtain the intermediate layer; (7) Immerse the whole intermediate layer in the aqueous solution in step (4) for soaking, then take it out, blow dry the excess water on the surface until there are no obvious water droplets on the membrane surface, then immerse the whole membrane in the organic solution in step (5) for soaking, take it out and let it dry naturally, wash it with a citric acid solution and then immerse it in a glycerol solution for moisturizing treatment, and then completely dry the membrane in an oven to obtain the high-desalination seawater desalination composite reverse osmosis membrane.

2. The preparation method of a high-desalination seawater desalination composite reverse osmosis membrane according to claim 1, characterized in that: In step (1), the mass ratio of the polyethersulfone to the solvent is 16-21:79-84; the solvent is N,N-dimethylformamide; the temperature of the stirring and heating is 75-95°C, and the time is 8-11h; the time of the vacuum filtration is 2-4h, and the vacuum degree is 0.2-0.5MPa.

3. The preparation method of a high-desalination seawater desalination composite reverse osmosis membrane according to claim 1, characterized in that: In step (2), the time of the liquid-solid phase conversion is 0.5-1min, the phase inversion water bath temperature is 11-13°C, and the thermal curing water bath temperature is 65-75°C; the support material is non-woven fabric, and the thickness is 3.2-3.5mil; the thickness of the ultrafiltration membrane substrate is 5.5-6mil.

4. The preparation method of a high-desalination seawater desalination composite reverse osmosis membrane according to claim 1, characterized in that: In step (3), the mass ratio of the PDA, hydrochloric acid, nanomaterials and pure water is 0.1-0.15:0.1-0.2:0.08-0.12:99.53-99.

72.

5. The preparation method of a high-desalination seawater desalination composite reverse osmosis membrane according to claim 1, characterized in that: In step (3), the nanomaterial is one of graphene oxide, molybdenum disulfide, phosphorene, and molybdenum selenide.

6. The preparation method of a high-desalination seawater desalination composite reverse osmosis membrane according to claim 1, characterized in that: In step (4), the m-phenylenediamine, NaOH, and pure water are in the following weight ratio: m-phenylenediamine 50 - 150 parts, NaOH 10 - 20 parts, pure water 4830 - 4940 parts, and the monomer concentration of the aqueous solution is 1 - 3 wt%.

7. The preparation method of a high-desalination seawater desalination composite reverse osmosis membrane according to claim 1, characterized in that: In step (5), the trimesoyl chloride and ethylcyclohexane are in the following weight ratio: trimesoyl chloride 2 - 6 parts, ethylcyclohexane 3994 - 3998 parts, and the monomer concentration of the organic solution is 0.05 - 0.15 wt%.

8. The preparation method of a high-desalination seawater desalination composite reverse osmosis membrane according to claim 1, characterized in that: In steps (4) and (5), the mass ratio of the aqueous solution to the organic solution = 5:

4.

9. The preparation method of a high-desalination seawater desalination composite reverse osmosis membrane according to claim 1, characterized in that: In step (6), the pH value is adjusted to pH > 8.5 by adding NaOH; the soaking time is 40 - 60 min.

10. The preparation method of a high-desalination seawater desalination composite reverse osmosis membrane according to claim 1, characterized in that: In step (7), the soaking time in the aqueous solution is 12 - 18 s, and the soaking time in the organic solution is 5 - 7 s; the concentration of the citric acid solution is 20 - 30 wt%, the cleaning temperature is 60 - 80 °C, and the time is 4 - 5 min; the concentration of the glycerol solution is 15 - 25 wt%.