Method for preparing reverse osmosis membrane based on plasma polymerization, reverse osmosis membrane and application

Abstract

The application discloses a reverse osmosis membrane preparation method based on plasma polymerization, a reverse osmosis membrane and application; the application designs a reverse osmosis membrane preparation method, a base film is subjected to surface treatment through an aqueous phase, a first polymerization chamber atmosphere, a first polymerization chamber gas is introduced to carry out a first step plasma polymerization; in the polymerization process, the back of the base film is pasted on a back plate with a heating function through polymerization deposition, plasma polymerization is continuously carried out, polymerization is stopped and the film piece is placed in an oven for drying; the film piece is placed in a second polymerization chamber, a second polymerization chamber atmosphere, a second polymerization chamber gas is introduced to carry out a second step plasma polymerization; a second polymerization chamber supplementary gas is added, and the process is continued; the film piece is subjected to oxidation protection modification treatment, is immersed in a mixed solution of sodium bisulfite glycerol, is taken out for drying, and a reverse osmosis membrane is obtained. The application also provides a reverse osmosis membrane prepared by the above preparation method and application of the reverse osmosis membrane in the field of water treatment.

Description

Technical Field

[0001] This application relates to the field of reverse osmosis membrane preparation technology, and in particular to a method for preparing reverse osmosis membranes based on plasma polymerization, reverse osmosis membranes, and their applications. Background Technology

[0002] Reverse osmosis membrane separation technology, due to its excellent separation performance of inorganic salt ions, has become one of the most effective water treatment methods in the world. It plays an increasingly important role in domestic water purification, industrial water treatment, municipal wastewater treatment, seawater desalination, zero discharge, and separation and concentration. A conventional reverse osmosis membrane consists of three layers: a bottom non-woven fabric layer, a middle polysulfone layer, and an upper polymer desalination layer. The desalination layer, as the core functional material, plays a crucial role in separating salt and water.

[0003] Currently, almost all reverse osmosis membranes on the market are asymmetric reverse osmosis membranes, requiring specific wet-laid nonwoven fabric and casting processes. Interfacial polymerization demands high-quality base membrane materials, especially the flatness and uniformity of the nonwoven fabric; only wet-laid processes can meet the requirements for reverse osmosis membranes. However, membranes using plasma polymerization significantly reduce the requirements for the substrate, even eliminating the need for casting and allowing direct polymerization on PP or PE membranes to prepare reverse osmosis membranes, offering a wider range of substrate options.

[0004] Conventional reverse osmosis membranes are prepared using interfacial polymerization, where a base membrane is first coated with an aqueous phase, followed by an oil phase, to form a polymeric desalination layer through interfacial polycondensation. This technology requires the use of an organic phase as a solvent to dissolve the acyl chloride monomers; commonly used substances include Isopar E / G / H / L, n-hexane, and n-decane, all of which are flammable and explosive. Furthermore, drying the organic phase on the membrane surface in an oven generates a large amount of high-VOC gas, which must be treated by an RTO (Reverse Osmosis Toxin Oxide) to meet emission standards before being released. The use of flammable and explosive organic phases not only places higher demands on production safety control but also necessitates the installation of waste gas after-treatment equipment, increasing production line investment costs; otherwise, it can pollute the environment. Plasma polymerization completely avoids these problems.

[0005] On the other hand, in reverse osmosis membrane materials prepared using interfacial polymerization, the benzene rings are linked by amide bonds. Aromatic polyamides are highly sensitive to active chlorine. Prolonged exposure to active chlorine causes hypochlorite ions to first substitute chlorine atoms on the hydrogen atoms of the amide bonds, breaking the hydrogen bonds between the polymer chains. Subsequently, an Orton rearrangement reaction occurs, leading to the breakage of the amide bonds in the desalination layer of the reverse osmosis membrane. This causes the polyamide layer of the reverse osmosis membrane to transform from a regular crystalline state to an amorphous state, increasing the free volume of the polymer membrane, making the membrane more porous, and reducing its rejection rate. This is one of the main problems currently facing commercially available reverse osmosis membranes.

[0006] Therefore, given that existing membrane materials have high requirements for the substrate and must be prepared using interfacial polymerization processes, and that the prepared membranes have poor chlorine resistance, as well as high requirements for production and environmental protection, this patent proposes a novel plasma polymerization method for preparing reverse osmosis membranes, which has a better market advantage compared to membranes prepared using interfacial polymerization processes.

[0007] Currently, the application of plasma polymerization technology for preparing reverse osmosis membranes is mostly focused on using gaseous monomer components as polymerizing materials or performing discharge polymerization in an inert gas, resulting in membranes prepared by this process having less than ideal overall performance. Summary of the Invention

[0008] To address at least one of the aforementioned technical problems, this application provides a method for preparing a reverse osmosis membrane based on plasma polymerization, the reverse osmosis membrane itself, and its applications.

[0009] On the one hand, the reverse osmosis membrane preparation method based on plasma polymerization provided in this application includes the following steps:

[0010] S1. The reverse osmosis membrane base membrane is surface treated with an aqueous solution to remove excess aqueous solution from the surface of the reverse osmosis membrane base membrane. Under the atmosphere of the first polymerization chamber, the first polymerization chamber gas is introduced into the first polymerization chamber to carry out the first step of plasma polymerization.

[0011] S2. During the polymerization process, after polymerization deposition for 2 to 9 minutes, the back of the base film is attached to a back plate with heating function. The heating temperature is 40 to 70°C. Plasma polymerization continues for 2 to 8 minutes. After that, polymerization is stopped and the film is placed in an oven to dry the moisture inside the film.

[0012] S3. Place the membrane treated in S2 in the second polymerization chamber. In the atmosphere of the second polymerization chamber, introduce gas into the second polymerization chamber to carry out the second plasma polymerization step. After reacting for a period of time, introduce gas into the second polymerization chamber to replenish the gas and continue the second plasma polymerization step.

[0013] S4. The membrane treated in S3 is subjected to oxidative protection modification treatment, then immersed in a mixed solution containing sodium bisulfite and glycerol. After wetting, it is taken out and dried to obtain a reverse osmosis membrane.

[0014] Optionally, the surface treatment time of the reverse osmosis membrane base membrane in the aqueous phase is 5 to 40 seconds;

[0015] And / or, the aqueous phase is obtained by mixing component a, component b, sodium dodecyl sulfate and water in a weight ratio of 0.25-4.5:0.5-5:0.05-0.75:95-99;

[0016] And / or, component a is at least one of sodium bicarbonate, sodium bisulfite, ammonium chloride, sodium carbonate, calcium bicarbonate, and potassium carbonate;

[0017] And / or, component b is at least one of sodium camphor sulfonate, sodium sulfite, sodium lactate, sodium citrate, sodium dihydrogen phosphate, sodium phosphate, and triethylamine hydrochloride.

[0018] Optionally, the first step of plasma polymerization is dielectric barrier discharge with a bias voltage of 150V, a monomer flow rate of 1-8mg / s, a set gas pressure of 50-500pa in the polymerization chamber, a plasma polymerization power of 20-120W, a plasma polymerization electrode spacing of 13-30mm, and a polymerization chamber temperature of 25℃-45℃.

[0019] Optionally, the atmosphere of the first polymerization chamber is a gaseous atmosphere containing at least one of argon, helium, oxygen, nitrogen, carbon dioxide, water vapor, sulfur hexafluoride, and ammonia.

[0020] And / or, the gas in the first polymerization chamber is at least two of the following: triethylamine, ethylenediamine, propylenediamine, butanediamine, 1,3-dimethylbutylamine, di-n-butylamine, n-propylamine, isopropylamine, diisopropylamine, 2-allylamine, 3-aminopropylene, 3-buten-1-amine, 3-buten-2-amine, and 2-buten-1-amine.

[0021] Optionally, the atmosphere of the second polymerization chamber is a gas atmosphere containing at least one of argon, helium, oxygen, nitrogen, carbon dioxide, nitric oxide, and nitrogen dioxide.

[0022] And / or, the gas in the second polymerization chamber is at least two of the following: aniline, benzylamine, phenethylamine, styrene, benzyl alcohol, toluidine, ethylaniline, N,N-dimethylaniline, m-phenylenediamine, p-phenylenediamine, and 4-vinylpyridine;

[0023] And / or, the supplemental gas for the second polymerization chamber is at least one of the following: acrylic acid, hydroxyethyl acrylate, methyl butyrate, propionic acid, butyric acid, methyl acrylate, allyl alcohol, and butenol.

[0024] Optionally, the second step of plasma polymerization is performed using dielectric barrier discharge with a bias voltage of 150V, a monomer flow rate of 2–9 mg / s, and atmospheric pressure in the polymerization chamber. The plasma polymerization power is 30–150W, the plasma polymerization electrode spacing is 10–40 mm, the polymerization time is 4–18 min, the polymerization time for introducing supplementary gas into the second polymerization chamber is 4–12 min, and the polymerization chamber temperature is 25–45℃.

[0025] Optionally, the oxidation protection modification treatment involves immersing the membrane in an oxidation protection modification solution, wherein the oxidation protection modification solution is composed of component c, component d, and component e in a weight ratio of 0.35–1.85:1.5–4.5:0.25–1.25:92–98.

[0026] And / or, component c is at least one of selenium dioxide, sodium periodate, Des Martin periodane, iodobenzene, sodium chlorite, diacetoxyiodobenzene, and bis(trifluoroacetoxyiodobenzene).

[0027] And / or, the component d is at least one selected from 2-methyl-2-butene, 3-methyl-1-butene, 2-methyl-1-butene, 1-pentene, 2-pentene, cyclopentene, and 1,3-butadiene;

[0028] And / or, component e is at least one of sodium dihydrogen phosphate, sodium phosphate, potassium dihydrogen phosphate, potassium phosphate, disodium hydrogen phosphate, and dipotassium hydrogen phosphate;

[0029] And / or, the pH of the oxidative protective modification solution is 3-7, the temperature is 30±2℃, and the membrane is immersed in the oxidative modification solution for 0.5-5 min.

[0030] Optionally, in the mixed solution, the mass fraction of sodium bisulfite is 0.3%, the mass fraction of glycerol is 8%, the temperature is 25±2℃, and the membrane is immersed in the sodium bisulfite solution for 0.5 to 3 minutes.

[0031] Secondly, this application provides a reverse osmosis membrane prepared by the above-described preparation method.

[0032] Thirdly, this application provides the application of the aforementioned reverse osmosis membrane in the field of water treatment.

[0033] In summary, this application includes at least one of the following beneficial technical effects:

[0034] 1. The reverse osmosis composite membrane directly prepared by plasma polymerization process addresses the problem of poor desalination performance of reverse osmosis membranes prepared by conventional plasma polymerization. This invention uses multiple monomers for polymerization and controls the type and degree of reaction of the monomers at different stages. The phased plasma polymerization and secondary plasma polymerization processes make the reverse osmosis membrane more commercially viable. Furthermore, the process described in this patent is operable on various reverse osmosis substrates.

[0035] 2. This invention employs a desalination layer morphology shaping process during plasma polymerization. Conventionally, membrane products produced by plasma polymerization have a relatively smooth or rough desalination layer morphology. When the salt rejection rate of the desalination layer is sufficiently high, it is not conducive to improving the overall flux. According to the method provided by this invention, the morphology of the desalination layer can be shaped by decomposing the salt components in the base membrane during the first stage of plasma polymerization deposition, so that the surface of the desalination layer has vesicle or ridge structures, increasing the specific surface area of ​​water passing through the reverse osmosis membrane desalination layer, maintaining the membrane desalination rate while having a higher flux.

[0036] 3. To address the issues of unstable membrane performance and batch-to-batch performance fluctuations in plasma polymerization, this invention modifies the membrane in the post-treatment oxidation modification tank, removing the free radicals remaining on the desalination layer or substrate that cause unstable membrane performance, thus allowing the membrane performance of the plasma polymerization process to reach a stable state in advance.

[0037] 4. The plasma polymerization process provided by this invention changes the current state of reverse osmosis membrane materials, which are mainly polyamide, making the selectivity and functionality of reverse osmosis membrane materials more diversified. The developed reverse osmosis membrane, because its chemical bonds are formed by free radical polymerization under ionization, has stronger chemical bonds than those formed through interfacial polymerization, resulting in an overall change in membrane material properties and better chlorine resistance than traditional polyamide reverse osmosis membranes. It also provides a new approach for developing better chlorine-resistant reverse osmosis membranes. Detailed Implementation

[0038] The present application will be further described in detail below with reference to the embodiments.

[0039] This application designs a method for preparing a reverse osmosis membrane, which differs from the commonly used interfacial polymerization process in the prior art. This application prepares the reverse osmosis membrane through plasma polymerization.

[0040] Specifically, the following steps are included:

[0041] S1. The reverse osmosis membrane base membrane is surface treated with an aqueous phase to remove excess aqueous droplets from the surface of the reverse osmosis membrane base membrane. Under the atmosphere of the first polymerization chamber, the first polymerization chamber gas is introduced into the first polymerization chamber to carry out the first step of plasma polymerization.

[0042] S2. During the polymerization process, after polymerization deposition for 2 to 9 minutes, the back of the base film is attached to a back plate with heating function. The heating temperature is 40 to 70°C. Plasma polymerization continues for 2 to 8 minutes. After that, polymerization is stopped and the film is placed in an oven to dry the moisture inside the film.

[0043] S3. Place the membrane treated in S2 in the second polymerization chamber. In the atmosphere of the second polymerization chamber, introduce gas into the second polymerization chamber to carry out the second plasma polymerization step. After reacting for a period of time, add supplementary gas to the second polymerization chamber and continue the second plasma polymerization step.

[0044] S4. The membrane treated in S3 is subjected to oxidative protection modification treatment, then immersed in a mixed solution containing sodium bisulfite and glycerol. After wetting, it is taken out and dried to obtain a reverse osmosis membrane.

[0045] This application also provides a reverse osmosis membrane prepared by the above preparation method, and the application of the reverse osmosis membrane in the field of water treatment.

[0046] When designing the technical solution for preparing reverse osmosis membranes using plasma polymerization in this application, the inventors adopted the idea of ​​gradually building a desalination layer. First, a preliminary plasma polymerization was used to shape the "skeleton" of the desalination layer on the surface of the substrate. At the same time, the morphology of the desalination layer was shaped by heating the substrate with a backplate and releasing gases during the reaction.

[0047] The second step, plasma polymerization, modifies and improves the desalination layer formed in the first step, ensuring the integrity of the membrane desalination layer.

[0048] The hydrophilicity of the membrane surface is altered by adding supplementary gas in a second polymerization chamber midway through polymerization.

[0049] Finally, an oxidation modification protection process is used to convert residual free radicals and other unreacted groups in advance, thereby stabilizing the membrane performance.

[0050] The reverse osmosis membrane preparation process described in this application is operable for base membranes made of materials such as PP, PE, PSF (PSU), PTFE, PVC, and PPS. Single-layer hydrophobic substrates such as PP and PE require corona treatment to ensure effectiveness, but all can be used to prepare reverse osmosis membranes that meet the requirements.

[0051] Compared to conventional interfacial polymerization methods for preparing reverse osmosis membranes, this invention directly employs only plasma polymerization, using different stages of plasma polymerization to gradually shape the desalination layer. This provides a novel reverse osmosis membrane preparation process, expanding the range of suitable substrates beyond traditional polysulfone ultrafiltration membranes, and significantly simplifying the reverse osmosis membrane coating process. It also solves the safety and environmental concerns associated with high-temperature drying of flammable and explosive organic solvents during reverse osmosis membrane production.

[0052] Reverse osmosis membranes prepared using plasma polymerization have a greater advantage in overall performance stability compared to those prepared using interfacial polymerization. This is because interfacial polymerization requires substances such as m-phenylenediamine, and if the amino functional groups are not thoroughly cleaned, they can easily lead to color differences on the membrane surface during storage and also affect the membrane's performance. Plasma-polymerized membranes, on the other hand, completely avoid these problems because they do not contain m-phenylenediamine.

[0053] This invention prepares reverse osmosis membranes via plasma polymerization, which significantly reduces production line energy consumption. Overall performance can be controlled simply by adjusting the conditions in the polymerization chamber. The requirements for manufacturing and auxiliary equipment are also lower compared to interface polymerization equipment.

[0054] In the following embodiments of this application, the reverse osmosis membrane base membrane is exemplary selected as polysulfone (PSF).

[0055] Unless otherwise specified, the main components involved in the following embodiments of this application are all purchased from commercially available products.

[0056] Preparation of the reverse osmosis membrane base in the examples:

[0057] After heating N,N-dimethylformamide to 70°C, polysulfone was added and stirred for more than 12 hours to obtain a casting solution; the casting solution contained 15.5% polysulfone and 84.5% solvent. Specific Implementation

[0059] Example 1

[0060] Preparation of aqueous solution:

[0061] Sodium bicarbonate, triethylamine hydrochloride, sodium dodecyl sulfate, and pure water were mixed in a mass ratio of 0.95:2:0.15:96.9 to prepare an aqueous solution.

[0062] Preparation of the oxidation-modification protective solution:

[0063] Sodium chlorite, 2-methyl-2-butene, sodium dihydrogen phosphate, and pure water were mixed in a mass ratio of 0.85:2:0.35:96.8 to prepare an oxidation modification protective solution. The temperature was 30±2 degrees Celsius and the pH was 4.5.

[0064] Preparation of sodium bisulfite solution:

[0065] A mixed solution containing 0.3% sodium bisulfite and 8% glycerol was prepared using pure water at 25°C.

[0066] Preparation of reverse osmosis membrane:

[0067] The reverse osmosis membrane base membrane is immersed in an aqueous solution for 25 seconds. After removing excess aqueous solution from the surface and back of the membrane with an air knife, it is placed on the heating plate in the first polymerization chamber.

[0068] Argon gas was introduced into the first polymerization chamber, and the gas pressure was set to 150 Pa, the discharge power to 80 W, the bias voltage to 150 V, the electrode spacing to 20 mm, and the polymerization chamber temperature to 30 °C.

[0069] 1,3-Dimethylbutylamine was vaporized in a vaporization chamber at 140°C, with a monomer flow rate set to 4 mg / s. 3-Buten-1-amine was vaporized in a vaporization chamber at 90°C, with a monomer flow rate set to 3 mg / s. After mixing the 1,3-dimethylbutylamine and 3-buten-1-amine gases for 20 s, plasma polymerization was carried out.

[0070] After 6 minutes of polymerization deposition, the film was back-attached to a backplate heated to 45°C, and the discharge power was reduced to 70W. Plasma polymerization continued for another 8 minutes before the reaction was stopped.

[0071] Dry the membrane in an oven at 70°C for 2 minutes to remove excess moisture from the base membrane.

[0072] Helium gas at atmospheric pressure was introduced into the second polymerization chamber, with a discharge power of 90W, a bias voltage of 150V, an electrode spacing of 35mm, and a polymerization chamber temperature of 35℃.

[0073] m-Phenylenediamine was vaporized in a vaporization chamber at 270°C, with a monomer flow rate set to 5 mg / s. Styrene was vaporized in a vaporization chamber at 180°C, with a monomer flow rate set to 3 mg / s. Hydroxyethyl acrylate was vaporized in a vaporization chamber at 240°C, with a monomer flow rate set to 4 mg / s.

[0074] The membrane was placed in the second polymerization chamber, and vaporized m-phenylenediamine and styrene were introduced and mixed for 20 seconds to carry out the second plasma polymerization step. After 12 minutes of polymerization deposition, vaporized hydroxyethyl acrylate was introduced to continue the polymerization for 10 minutes.

[0075] Immerse the membrane in the oxidative modification protective solution for 3 minutes, then remove it and use an air knife to remove excess water droplets from the surface.

[0076] Immerse the membrane in a sodium bisulfite and glycerol mixed solution for 1 minute, remove it and use an air knife to remove water droplets from the surface, and dry it in an oven at 70°C for 2 minutes to obtain the finished reverse osmosis membrane.

[0077] Example 2

[0078] The difference between this embodiment and Embodiment 1 is that the aqueous solution is prepared in this embodiment as follows:

[0079] Sodium bicarbonate, triethylamine hydrochloride, sodium dodecyl sulfate, and pure water were mixed in a mass ratio of 0.25:2:0.15:97.6 to prepare an aqueous solution.

[0080] Example 3

[0081] The difference between this embodiment and Embodiment 1 is that the aqueous solution is prepared in this embodiment as follows:

[0082] Sodium bicarbonate, triethylamine hydrochloride, sodium dodecyl sulfate, and pure water were mixed in a mass ratio of 0.95:0.5:0.15:98.4 to prepare an aqueous solution.

[0083] Example 4

[0084] The difference between this embodiment and Embodiment 1 is that the atmosphere of the first polymerization chamber in this embodiment is a carbon dioxide gas atmosphere.

[0085] Example 5

[0086] The difference between this embodiment and Embodiment 1 is that the gas in the first polymerization chamber of this embodiment is vaporized triethylamine and diisopropylamine.

[0087] Example 6

[0088] The difference between this embodiment and Embodiment 1 is that in this embodiment, after 4 minutes of polymerization deposition, the film is back-attached to a backing plate heated to 45°C.

[0089] Example 7

[0090] The difference between this embodiment and Embodiment 1 is that:

[0091] The film is back-attached to a backplate heated to 45°C, while the discharge power is increased to 100W.

[0092] Example 8

[0093] The difference between this embodiment and Embodiment 1 is that in this embodiment, the atmosphere of the second polymerization chamber is a nitrogen dioxide gas atmosphere.

[0094] Example 9

[0095] The difference between this embodiment and Embodiment 1 is that in this embodiment, the gas in the second polymerization chamber is vaporized aniline and p-phenylenediamine.

[0096] Example 10

[0097] The difference between this embodiment and Embodiment 1 is that in this embodiment, the supplementary gas in the second polymerization chamber is vaporized butyric acid.

[0098] Example 11

[0099] The difference between this embodiment and Embodiment 1 is that in this embodiment,

[0100] After gasified m-phenylenediamine and styrene were mixed and subjected to a second plasma polymerization step for 20 seconds, gasified hydroxyethyl acrylate was introduced to continue the polymerization after 18 minutes of polymerization deposition.

[0101] Example 12

[0102] The difference between this embodiment and Embodiment 1 is that in this embodiment, the gasified hydroxyethyl acrylate continues to polymerize for 5 minutes.

[0103] Example 13

[0104] The difference between this embodiment and Embodiment 1 is that in this embodiment, the oxidative modification protective liquid is prepared by mixing iodobenzoylbenzene, 2-methyl-2-butene, sodium dihydrogen phosphate, and pure water in a mass ratio of 0.85:2:0.35:96.8.

[0105] Example 14

[0106] The difference between this embodiment and Embodiment 1 is that in this embodiment, the membrane is immersed in the oxidative modification protective solution for 0.5 min.

[0107] Comparative Example 1

[0108] The difference between this comparative example and Example 1 is that this comparative example uses the existing interfacial polymerization method to prepare the reverse osmosis membrane; specifically as follows:

[0109] Preparation of aqueous solution:

[0110] An aqueous solution was prepared by mixing m-phenylenediamine, triethylamine hydrochloride, and pure water in a mass ratio of 2:2:96.

[0111] Preparation of oil phase solution:

[0112] A solution of pyromellitic methyl chloride, tributyl phosphate, and n-hexane was prepared in a mass ratio of 0.15:0.35:99.5.

[0113] Preparation of sodium carbonate solution:

[0114] Prepare a sodium carbonate solution with a mass fraction of 0.3%.

[0115] Preparation of sodium bisulfite solution:

[0116] Prepare a sodium bisulfite solution with a mass fraction of 0.3%.

[0117] Using an interfacial polymerization process, the reverse osmosis base membrane is first passed through the aqueous phase solution prepared above for 30 seconds. After removing excess water droplets from the surface using a pressure roller and an air knife, the oil phase solution prepared above is coated onto the base membrane. After reacting for 30 seconds, the excess oil phase on the membrane surface is poured off or removed. The oil phase on the membrane surface and the internal moisture are dried in an oven at 100°C.

[0118] The membrane was immersed in a 0.3% sodium carbonate solution for 30 seconds, then rinsed with pure water, and then soaked in 70℃ pure water for 3 minutes. The membrane was then removed and soaked in a 0.3% sodium bisulfite solution for 30 seconds, and then dried in a 70℃ oven to obtain the finished reverse osmosis membrane.

[0119] Comparative Example 2

[0120] The difference between this comparative example and Example 1 is that the aqueous solution in this comparative example does not contain sodium bicarbonate.

[0121] Comparative Example 3

[0122] The difference between this comparative example and Example 1 is that the aqueous solution in this comparative example does not contain triethylamine hydrochloride.

[0123] Comparative Example 4

[0124] The difference between this comparative example and Example 1 is that in this comparative example, the gas in the first polymerization chamber is 3-butene-1-amine gas.

[0125] Comparative Example 5

[0126] The difference between this comparative example and Example 1 is that a backplate heating film is not used in this comparative example.

[0127] Comparative Example 6

[0128] The difference between this comparative example and Example 1 is that in this comparative example, plasma polymerization is carried out using only m-phenylenediamine instead of styrene.

[0129] Comparative Example 7

[0130] The difference between this comparative example and Example 1 is that in this comparative example, plasma polymerization is carried out using only m-phenylenediamine, instead of introducing hydroxyethyl acrylate.

[0131] Comparative Example 8

[0132] The difference between this comparative example and Example 1 is that the oxidative modification protective solution in this comparative example does not contain 2-methyl-2-butene.

[0133] The reverse osmosis membrane products prepared in Examples 1-14 and Comparative Examples 1-8 were subjected to membrane performance testing: the performance data obtained under the conditions of 500 ppm NaCl as test solution, 25°C, pH=7-8, and external pressure of 72.5 psi are shown in Table 1.

[0134] Table 1

[0135] Reverse osmosis membrane Difference from Example 1 Membrane flux / LMH Membrane desalination / % Example 1 / 43.35 99.20 Example 2 Sodium bicarbonate concentration decreased 40.24 99.14 Example 3 Triethylamine hydrochloride concentration decreased 26.99 98.80 Example 4 The atmosphere in the first aggregation room changed. 42.22 99.24 Example 5 The gas composition in the first polymerization chamber changes 47.85 98.87 Example 6 The first aggregation time decreased 45.48 98.82 Example 7 The first polymerization power is increased. 40.34 99.24 Example 8 The atmosphere in the second aggregation room changed. 41.24 99.27 Example 9 The gas composition in the second polymerization chamber changes. 43.35 99.03 Example 10 The composition of the supplementary gas in the second polymerization chamber is changed. 39.67 99.20 Example 11 The second aggregation time is extended. 41.19 99.31 Example 12 The polymerization time of polyacrylic acid is reduced by introducing it. 40.29 99.23 Example 13 Changes in the composition of the oxidation protection modified liquid 42.29 99.24 Example 14 Reduced protection time during oxidation modification 40.24 99.25 Comparative Example 1 Interface polymerization process 45.00 99.19 Comparative Example 2 The aqueous phase does not contain sodium bicarbonate. 35.78 99.29 Comparative Example 3 The aqueous phase does not contain triethylamine hydrochloride. 29.47 99.17 Comparative Example 4 The first polymerization process was changed to a single-component polymerization. 39.49 99.17 Comparative Example 5 The first polymer film is not heated. 38.46 99.11 Comparative Example 6 The second polymerization was changed to single-component polymerization. 44.01 99.02 Comparative Example 7 No supplemental gas for the second polymerization chamber 39.02 99.23 Comparative Example 8 Oxidative modification reduces protective components 40.08 99.28

[0136] Based on the data from Examples 1-14, Comparative Examples 1-8, and Table 1, it can be seen that:

[0137] The flux of Example 2 was lower than that of Example 1. This was due to the reduced sodium bicarbonate content, fewer bubbles generated during heating, decreased ability to shape the morphology of the desalination layer, and reduced specific surface area of ​​water passing through the membrane surface.

[0138] The significant decrease in throughput in Example 3 was due to the reduced concentration of triethylamine hydrochloride, which decreased the pore-retention capacity of the salt during base film drying, leading to an overall decline in throughput.

[0139] As can be seen from Examples 4 and 8, the performance fluctuation is small when the polymerization atmosphere is changed without affecting the overall polymerization efficiency.

[0140] Since the reaction in the second polymerization chamber is to enhance the integrity of the membrane and improve the hydrophilicity of the membrane surface, the desalination performance of the membrane fluctuates after changing the composition of the gas in the second polymerization chamber. The decrease in desalination performance in Example 9 is due to the replacement of styrene, which reduces the content of unsaturated bonds during polymerization and affects part of the polymerization efficiency.

[0141] The change in the composition of the supplementary gas introduced into the second polymerization chamber in Example 10 is due to the fact that butyric acid produces fewer oxygen-containing free radicals, especially hydrophilic groups, compared to hydroxyethyl acrylate, and the membrane surface also has fewer hydrophilic groups, resulting in a decrease in flux; this is similar to the phenomenon in Example 12.

[0142] Example 13 illustrates that changes in the composition of the oxidizing protective solution have minimal impact on the membrane performance while maintaining the same function. However, changes in time have some effect. This is because, to ensure sufficient oxidation, a certain amount of free radicals or charges remain on the membrane surface, resulting in a higher overall desalination rate, but this is not the final stable state.

[0143] Compared to interfacial polymerization, the performance of the two processes is similar according to the process of this invention, but plasma polymerization offers greater safety, environmental friendliness, and ease of use. Comparative Examples 2 and 3 demonstrate that the salt content of the aqueous phase component and the heating of the membrane backside in Comparative Example 5 significantly affect the membrane flux. Comparative Examples 4 and 6 show that changes in the polymerization gas composition can significantly affect the desalination rate, as the type or quantity of the polymerization gas directly influences the type of free radicals generated and the polymerization efficiency. While reducing the protective component through oxidative modification results in a higher desalination rate, it also leads to a deviation in stability, which corresponds to the data in Example 14.

[0144] The performance data of the reverse osmosis membranes of some examples and comparative examples were measured after being dried in a sealed and light-proof environment for one month, using 500 ppm NaCl as the test solution, at 25°C, pH=7-8, and an applied pressure of 72.5 psi. The results are shown in Table 2.

[0145] Table 2

[0146]

[0147] The data in the table shows that, compared to the preservation performance of the reverse osmosis membrane prepared by the normal interfacial polymerization process in Comparative Example 1, the desalination reduction of the reverse osmosis membranes prepared by the plasma polymerization process is relatively small in most examples. However, some examples show a larger reduction. This indicates that the influence of component gases on the membrane is very significant during the preparation of reverse osmosis membranes by the plasma polymerization process, which is a key point in the preparation of plasma reverse osmosis membranes.

[0148] Data from Examples 13-14 illustrate that changes in the composition of the oxidatively modified protective solution have a significant impact on the overall stability of the membrane, particularly in terms of flux variation. This is because the oxidatively modified protective solution can reduce or transform unreacted free radicals in advance, while the buffer component prevents excessive oxidation that could alter other chemical bonds. Therefore, pre-converting the reactive groups in the desalination layer is fundamental to stabilizing membrane performance.

[0149] The performance data of the membranes of some examples and comparative examples were obtained by soaking them in a NaClO solution of 250 ppm at 25°C and pH=8 for 24 h, and then measuring them in a test solution of 500 ppm NaCl at 25°C, pH=7-8 and an applied pressure of 72.5 psi. The results are shown in Table 3.

[0150] Table 3

[0151]

[0152] Regarding overall chlorine resistance, the data in Table 3 shows that, under similar initial performance conditions, the reverse osmosis membrane prepared by plasma polymerization exhibits higher desalination rates than the membrane prepared by interfacial polymerization under almost all conditions after prolonged chlorine resistance. Extending the plasma polymerization time makes the desalination layer more robust and chlorine-resistant, as evidenced by the data in Example 11. Therefore, plasma polymerization offers a more significant advantage over conventional interfacial polymerization in terms of chlorine resistance.

[0153] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for preparing a reverse osmosis membrane based on plasma polymerization, characterized in that, The method comprises the following steps: S1, surface treatment of the reverse osmosis membrane base film by water phase solution, removing the excess water phase solution on the surface of the reverse osmosis membrane base film, and carrying out first step plasma polymerization in the first polymerization chamber under the atmosphere of the first polymerization chamber by introducing the first polymerization chamber gas into the first polymerization chamber; S2, during the polymerization process, after 2-9 min of polymerization deposition, the back of the reverse osmosis membrane base film is pasted on the back plate with heating function, the heating temperature is 40-70℃, the plasma polymerization is continuously carried out, and after 2-8 min, the polymerization is stopped and the membrane piece is placed in the oven to dry the moisture in the membrane piece; S3, the membrane piece treated by S2 is placed in the second polymerization chamber, the second step plasma polymerization is carried out under the atmosphere of the second polymerization chamber by introducing the second polymerization chamber gas into the second polymerization chamber, after a period of time, the second polymerization chamber is supplemented with gas, and the second step plasma polymerization is continuously carried out; S4, the membrane piece treated by S3 is treated by oxidation protection modification, then is immersed in a mixed solution containing sodium bisulfite and glycerol, is taken out after soaking, and is dried to obtain a reverse osmosis membrane; The time for surface treatment of the reverse osmosis membrane base film by water phase solution is 5-40s; The water phase solution is obtained by mixing component a, component b, sodium dodecyl sulfate and water in a weight ratio of 0.25-4.5:0.5-5:0.05-0.75:95-99; The component a is at least one of sodium bicarbonate, sodium bisulfite, ammonium chloride, sodium carbonate, calcium bicarbonate and potassium carbonate; The component b is at least one of sodium camphorsulfonate, sodium sulfite, sodium lactate, sodium citrate, sodium dihydrogen phosphate and sodium phosphate; The oxidation protection modification treatment is that the membrane piece is immersed in an oxidation protection modification solution, and the oxidation protection modification solution is composed of component c, component d, component e and pure water in a weight ratio of 0.35-1.85:1.5-4.5:0.25-1.25:92-98; The component c is at least one of selenium dioxide, sodium periodate, Dess-Martin periodinane, iodosylbenzene, sodium chlorite, diacetoxyiodobenzene and bistrifluoroacetoxyiodobenzene; The component d is at least one of 2-methyl-2-butene, 3-methyl-1-butene, 2-methyl-1-butene, 1-pentene, 2-pentene, cyclopentene and 1,3-butadiene; The component e is at least one of sodium dihydrogen phosphate, sodium phosphate, potassium dihydrogen phosphate and potassium phosphate; The pH of the oxidation protection modification solution is 3-7, the temperature is 30±2℃, and the time for the membrane piece to be immersed in the oxidation protection modification solution is 0.5-5min.

2. The production method according to claim 1, characterized by, The first step plasma polymerization is dielectric barrier discharge, the bias voltage is 150V, the flow rate of each monomer is 1-8mg / s, the gas pressure value of the polymerization chamber is set to 50-500Pa, the plasma polymerization power is 20-120W, the electrode spacing of the plasma polymerization is 13-30mm, and the polymerization chamber temperature is 25-45℃.

3. The preparation method according to claim 1, characterized in that, The first polymerization chamber atmosphere is a gas atmosphere with at least one of argon, helium, oxygen, nitrogen, carbon dioxide, water vapor, sulfur hexafluoride, ammonia; And / or, the first polymerization chamber gas is at least two of triethylamine, ethylenediamine, propylenediamine, butylenediamine, 1,3-dimethylbutylamine, di-n-butylamine, n-propylamine, isopropylamine, diisopropylamine, 2-allylamine, 3-aminopropylene, 3-butene-1-amine, 3-butene-2-amine, 2-butene-1-amine.

4. The preparation method of claim 1, wherein, The second polymerization chamber atmosphere is a gas atmosphere with at least one of argon, helium, oxygen, nitrogen, carbon dioxide, nitric oxide, nitrogen dioxide; And / or, the second polymerization chamber gas is at least two of aniline, benzylamine, phenethylamine, styrene, benzyl alcohol, toluidine, ethyl aniline, N,N-dimethylaniline, m-xylylenediamine, p-xylylenediamine, 4-vinylpyridine; And / or, the second polymerization chamber supplemental gas is at least one of acrylic acid, hydroxyethyl acrylate, methyl butenylate, propionic acid, butyric acid, methyl acrylate, propylene alcohol, butylene alcohol.

5. The preparation method of claim 1, wherein, The second step plasma polymerization is dielectric barrier discharge, bias voltage 150V, each monomer flow rate 2~9mg / s, the polymerization chamber is at normal pressure, the plasma polymerization power is 30~150W, the plasma polymerization electrode spacing is 10~40mm, the polymerization time is 4-18min, the polymerization time of the second polymerization chamber supplemental gas is 4-12min, and the polymerization chamber temperature is 25~45℃.

6. The method of claim 1, wherein, In the mixed solution, the mass fraction of sodium bisulfite is 0.3%, the mass fraction of glycerol is 8%, the temperature is 25±2℃, and the membrane is immersed in the mixed solution for 0.5~3min.

7. A reverse osmosis membrane, characterized by, Prepared by the preparation method of any one of claims 1~6.

8. Use of the reverse osmosis membrane of claim 7 in the field of water treatment.

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