Reverse osmosis membrane as well as preparation method and application thereof

Abstract

The invention relates to a reverse osmosis membrane and a preparation method and application thereof.The preparation method of the reverse osmosis membrane comprises the following steps that oil, a surfactant and water are mixed to prepare an oil-in-water type nano-emulsion, the surfactant comprises a nonionic surfactant, the average particle size of the oil-in-water type nano-emulsion is 80-200 nm, and the polydispersity index is smaller than or equal to 0.3; an aqueous solution of inorganic metal salt and an oil-in-water type nano-emulsion are sequentially placed on the same surface of a supporting film, dendrites are formed through heat treatment, and the mass ratio of the inorganic metal salt to the oil-in-water type nano-emulsion is 1: 50-1: 30; and preparing a polyamide separation layer on the surface of the support membrane on which the dendrites are distributed through reverse interfacial polymerization to obtain the reverse osmosis membrane. When the reverse osmosis membrane prepared by the preparation method is applied to water treatment, high desalination rate can be maintained, and meanwhile, high water flux is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment membranes, and particularly to a reverse osmosis membrane, a preparation method thereof, and an application thereof. Background Art

[0002] Reverse osmosis is an energy-efficient water treatment method and has been widely used in seawater desalination, drinking water treatment, water reuse, etc. There are many preparation methods for reverse osmosis membranes. Among them, the interfacial polymerization method is one of the commonly used methods for preparing reverse osmosis membranes. However, for the reverse osmosis membranes prepared by traditional interfacial polymerization methods, it is still difficult to have a high water flux while maintaining a high salt rejection rate. Summary of the Invention

[0003] Based on this, in view of the above problems, it is necessary to provide a reverse osmosis membrane, a preparation method thereof, and an application thereof. When the reverse osmosis membrane prepared by this preparation method is applied to water treatment, it can have a high water flux while maintaining a high salt rejection rate.

[0004] A preparation method of a reverse osmosis membrane includes the following steps:

[0005] Mix oil, a surfactant, and water to prepare an oil-in-water nanoemulsion. Among them, the surfactant includes a nonionic surfactant, and the average particle size of the oil-in-water nanoemulsion is 80 nm - 200 nm, and the polydispersity index ≤ 0.3;

[0006] Place an aqueous solution of an inorganic metal salt and the oil-in-water nanoemulsion on the same surface of a support membrane in sequence, and form dendritic crystals through heat treatment. The mass ratio of the inorganic metal salt to the oil-in-water nanoemulsion is 1:50 - 1:30;

[0007] Prepare a polyamide separation layer on the surface of the support membrane distributed with the dendritic crystals through reverse interfacial polymerization to obtain a reverse osmosis membrane.

[0008] In one embodiment, in the step of preparing the oil-in-water nanoemulsion, the volume ratio of the oil to the water is 1:200 - 1:100.

[0009] In one embodiment, the mass fraction of the oil in the oil-in-water nanoemulsion is 0.1% - 0.8%;

[0010] And / or, the mass fraction of the surfactant in the oil-in-water nanoemulsion is 20% - 40%.

[0011] In one embodiment, the surfactant further includes an ionic surfactant, and the mass ratio of the nonionic surfactant to the ionic surfactant is 5:1 - 10:1.

[0012] In one embodiment, the mass fraction of the inorganic metal salt in the aqueous solution of the inorganic metal salt is 1% - 5%.

[0013] In one embodiment, the oil is selected from at least one of alkanes, stearic acid esters, and tributyl citrate;

[0014] and / or, the non-ionic surfactant is selected from at least one of Tween 80, alkylphenol polyoxyethylene ether, and alkyl alcohol polyoxyethylene ether;

[0015] and / or, the inorganic metal salt is selected from at least one of sodium chloride, potassium chloride, magnesium chloride, and calcium chloride.

[0016] In one embodiment, in the step of forming dendritic crystals by heat treatment, the temperature of the heat treatment is 50°C - 80°C, and the time of the heat treatment is 3 min - 5 min.

[0017] In one embodiment, in the step of preparing a polyamide separation layer on the surface of the support membrane distributed with the dendritic crystals by interfacial polymerization, the oil phase solution and the aqueous phase solution are sequentially placed on the surface of the support membrane distributed with the dendritic crystals, and the polyamide separation layer is prepared by heat treatment, wherein the oil phase solution contains polyacyl chloride and the aqueous phase solution contains polyamine.

[0018] A reverse osmosis membrane prepared by the preparation method of the reverse osmosis membrane described above.

[0019] An application of the reverse osmosis membrane described above in a water treatment device.

[0020] In the preparation method of the reverse osmosis membrane of the present invention, by controlling the average particle size and polydispersity index of the oil-in-water nanoemulsion, the nano oil droplets in the nanoemulsion are uniformly dispersed in water, ensuring the long-term stability of the nanoemulsion; at the same time, by controlling the mass ratio of the inorganic metal salt to the oil-in-water nanoemulsion, there is an obvious concentration gradient difference and surface tension difference between the aqueous solution of the inorganic metal salt and the oil-in-water nanoemulsion. Subsequently, when the aqueous solution of the inorganic metal salt contacts the oil-in-water nanoemulsion, significant capillary phenomena will occur, promoting the rapid penetration and diffusion of the inorganic metal salt into the water in the nanoemulsion. Moreover, since the nano oil droplets are uniformly dispersed in the water of the nanoemulsion, many tiny pore structures are formed between the nano oil droplets, inducing the inorganic metal salt to form dendritic penetration paths along the pore structures between the nano oil droplets and penetrate and diffuse into the water. When heat-treated, the inorganic metal salt will precipitate and form dendritic crystals distributed on the surface of the support membrane; the existence of these dendritic crystals will greatly increase the specific surface area of the water-oil interface during the subsequent interfacial polymerization to prepare the polyamide separation layer, making the polyamide separation layer have a large specific surface area, thereby significantly improving the water flux of the reverse osmosis membrane without affecting the salt rejection rate of the reverse osmosis membrane. Moreover, by using the method of interfacial polymerization in reverse to prepare the polyamide separation layer, the morphology of the dendritic crystals can be effectively guaranteed, enabling the interfacial polymerization to occur on the crystal surface and form a separation layer with a high specific surface area, avoiding the problem of the crystal structure being damaged due to the crystal being dissolved in water.

[0021] Therefore, when the reverse osmosis membrane of the present invention is applied to water treatment, it can maintain a high salt rejection rate while having a high water flux. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the electron microscope image of the reverse osmosis membrane prepared in Example 1 of the present invention;

[0023] Figure 2 It is the electron microscope image of the reverse osmosis membrane prepared in Comparative Example 6 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] To facilitate the understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure content of the present invention more thorough and comprehensive.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the description of the present invention herein are for the purpose of describing specific embodiments or examples only and are not intended to limit the present invention. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of the related listed items. The any and all combinations include any two related listed items, any more related listed items, or the combination of all related listed items.

[0026] The preparation method of the reverse osmosis membrane provided by the present invention includes the following steps:

[0027] S1. Mix oil, surfactant and water to prepare an oil-in-water nanoemulsion. Among them, the surfactant includes a non-ionic surfactant. The average particle size of the oil-in-water nanoemulsion is 80 nm - 200 nm, and the polydispersity index ≤ 0.3. It can be understood that in step S1, in the oil-in-water nanoemulsion, the oil is dispersed in water in the form of nano-droplets, that is, nano-oil droplets are dispersed in water to form an emulsion. By controlling the average particle size and polydispersity index of the oil-in-water nanoemulsion, the nano-oil droplets in the oil-in-water nanoemulsion have a small particle size and a uniform size distribution, can be uniformly dispersed in water, and ensure the long-term stability of the oil-in-water nanoemulsion. Moreover, since the nano-oil droplets are uniformly dispersed in water, many tiny pore structures are formed between the nano-oil droplets. These pore structures are similar to capillaries and can drive the aqueous solution of inorganic metal salts in the subsequent step S2 to penetrate and diffuse into the nanoemulsion through surface tension, and the penetration and diffusion path is dendritic.

[0028] Optionally, in the step of preparing the oil-in-water nanoemulsion, the volume ratio of the oil to the water is 1:200 - 1:100; with such a setting, the oil-in-water nanoemulsion can be better formed by adjusting the volume ratio of the oil to the water.

[0029] Optionally, the mass fraction of the oil in the oil-in-water nanoemulsion is 0.1% - 0.8%; the mass fraction of the surfactant in the oil-in-water nanoemulsion is 20% - 40%; with such a setting, by adjusting the mass fractions of the oil and the surfactant in the oil-in-water nanoemulsion, it is beneficial to better form an oil-in-water nanoemulsion with a smaller particle size, a uniform particle size distribution and high stability, and further beneficial to the better penetration and diffusion of inorganic metal salts into the water of the nanoemulsion in the subsequent step S2.

[0030] Furthermore, the oil is selected from at least one of alkanes, stearic acid esters, and tributyl citrate, preferably alkanes. The alkanes are selected from the mixture of normal alkanes and isoparaffins or straight-chain alkanes, and further preferably liquid paraffin.

[0031] Optionally, the surfactant further includes an ionic surfactant, and the mass ratio of the non-ionic surfactant to the ionic surfactant is 5:1 - 10:1. With such a setting, by the combined use of the non-ionic surfactant and the ionic surfactant, the non-ionic surfactant is used to reduce the interfacial tension, and the ionic surfactant provides an electrostatic stabilization effect, which can effectively control the particle size distribution of the nanoemulsion, and better obtain an oil-in-water nanoemulsion with a smaller particle size and a uniform distribution, thereby better ensuring the long-term stability of the oil-in-water nanoemulsion.

[0032] Further, the non-ionic surfactant is selected from long-chain fatty alcohol polyoxyethylene ethers, alkylphenol polyoxyethylene ethers, fatty acid polyoxyethylene esters, alkyl alcohol polyoxyethylene ethers, polyoxyethylene alkylamines, polyoxyethylene alkylamides, and polyethers, preferably two or more of Tween 80, alkylphenol polyoxyethylene ethers, and alkyl alcohol polyoxyethylene ethers.

[0033] Optionally, the ionic surfactant is preferably an anionic surfactant, and the anionic surfactant is preferably at least one of sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, sodium stearate, and sodium lauryl sulfate.

[0034] In one embodiment, the preparation method of the oil-in-water nanoemulsion is as follows: Mix the oil, the surfactant, and water, then place them in a hot water bath for ultrasonic treatment, and then place them in an ice-water bath to cool down to room temperature to obtain the oil-in-water nanoemulsion, wherein the temperature of the hot water bath is 90°C - 110°C, preferably 100°C, and the ultrasonic treatment time is 0.5 h - 2 h.

[0035] S2, Place the aqueous solution of the inorganic metal salt and the oil-in-water nanoemulsion on the same surface of the support membrane in sequence, and form dendritic crystals through heat treatment. The mass ratio of the inorganic metal salt to the oil-in-water nanoemulsion is 1:50 - 1:30.

[0036] In step S2, the present invention controls the mass ratio of the inorganic metal salt to the oil-in-water nanoemulsion, so that there is an obvious concentration gradient difference between the aqueous solution of the inorganic metal salt and the oil-in-water nanoemulsion, and then there is an obvious surface tension difference between the aqueous solution of the inorganic metal salt and the oil-in-water nanoemulsion. Therefore, when the aqueous solution of the inorganic metal salt and the oil-in-water nanoemulsion come into contact on the surface of the support membrane, significant capillary phenomena will occur, prompting the inorganic metal salt to rapidly penetrate and diffuse into the water of the nanoemulsion. Moreover, in this process, since nano oil droplets are uniformly dispersed in the water of the oil-in-water nanoemulsion, many tiny pore structures are formed between the nano oil droplets, inducing the inorganic metal salt to penetrate and diffuse into the water along the pore structures between the nano oil droplets to form dendritic penetration paths. During heat treatment, the inorganic metal salt will precipitate and form dendritic crystals, and then dendritic crystals distributed on the surface of the support membrane are formed. The existence of the dendritic crystals correspondingly increases the specific surface area of the support membrane.

[0037] Optionally, the mass fraction of the inorganic metal salt in the aqueous solution of the inorganic metal salt is 1%-5%. With such a setting, the concentration difference and surface tension difference between the aqueous solution of the inorganic metal salt and the nanoemulsion can be regulated by adjusting the mass fraction of the inorganic metal salt in the aqueous solution of the inorganic metal salt, which is beneficial to enhancing the capillary phenomenon of the inorganic metal salt in the nanoemulsion and forming dendritic penetration paths.

[0038] Further, the inorganic metal salt is selected from at least one of sodium chloride, potassium chloride, magnesium chloride, and calcium chloride.

[0039] Optionally, the temperature of the heat treatment is 50°C - 80°C, and the time of the heat treatment is 3 min - 5 min. With such a setting, it can better ensure that the inorganic metal salt precipitates to form dendritic crystals.

[0040] In one embodiment, the support membrane is selected from at least one of polysulfone membranes, polypropylene membranes, or polyacrylonitrile membranes. Among them, polysulfone is inexpensive and easy to obtain, the membrane preparation is simple, it has good mechanical strength, good compression resistance performance, stable chemical properties, is non-toxic, and can resist biodegradation. Therefore, the support membrane is preferably a polysulfone membrane.

[0041] S3, a polyamide separation layer is prepared on the surface of the support membrane with the dendritic crystals distributed thereon through reverse interfacial polymerization to obtain a reverse osmosis membrane.

[0042] It should be noted that in step S3, compared with traditional interfacial polymerization, reverse interfacial polymerization means that the oil phase solution is first placed on the surface of the support membrane, and then the water phase solution is placed on the surface of the support membrane. Specifically, the oil phase solution and the water phase solution are sequentially placed on the surface of the support membrane with the dendritic crystals distributed thereon, and a polyamide separation layer is prepared through heat treatment, wherein the oil phase solution contains polyfunctional acyl chloride, and the water phase solution contains polyamine.

[0043] It can be understood that when the oil-phase solution and the water-phase solution are sequentially placed on the surface of the support membrane distributed with the dendritic crystals, the water-phase solution and the oil-phase solution will contact on the surface of the support membrane to form a water-oil interface. Since the dendritic crystals are distributed on the surface of the support membrane, the water-oil interface is formed on the dendritic crystals, so that the water-oil interface has a large specific surface area. Correspondingly, the polyamide separation layer formed by the interfacial polymerization of polyamine and polyacyl chloride at the water-oil interface also has a large specific surface area, thereby significantly improving the water flux of the reverse osmosis membrane without affecting the salt rejection rate of the reverse osmosis membrane.

[0044] At the same time, in order to prevent the water-phase solution from damaging the morphology of the dendritic crystals on the surface of the support membrane and affecting the specific surface area of the support membrane, in the present invention, the oil-phase solution is first placed on the surface of the support membrane to form a protective layer, and then the water-phase solution is placed on the surface of the support membrane. On the one hand, the formation of the protective layer can effectively prevent the direct contact between the water-phase solution and the dendritic crystals, avoiding the problem that the crystals on the surface of the support membrane are dissolved by water and the crystal structure is damaged, ensuring that the polyamide separation layer has a large specific surface area, thereby improving the water flux of the reverse osmosis membrane. On the other hand, it can make the oil phase and the crystals have good compatibility, facilitating the interfacial polymerization reaction between polyacyl chloride and polyamine on the surface of the support membrane to form a polyamide separation layer, ensuring the high salt rejection rate of the reverse osmosis membrane.

[0045] It can be seen that the present invention adopts the method of exchanging the order of the water phase and the oil phase and placing them on the surface of the support membrane distributed with dendritic crystals, that is, using reverse interfacial polymerization, which can effectively ensure the morphology of the dendritic crystals on the surface of the support membrane, enabling the interfacial polymerization to occur on the crystal surface and form a separation layer with a high specific surface area, avoiding the problem that the crystals on the surface of the support membrane are dissolved by water and the crystal structure is damaged.

[0046] Therefore, when the reverse osmosis membrane of the present invention is applied to water treatment, it can maintain a high salt rejection rate while having a high water flux.

[0047] It should be noted that since the freshly prepared reverse osmosis membrane is usually immersed in water, and the inorganic metal salt crystals will dissolve in water and escape from the reverse osmosis membrane, thereby correspondingly increasing the water production channel and further improving the water flux of the reverse osmosis membrane.

[0048] In one embodiment, the mass fraction of polyamine in the water-phase solution is 1%-3%, and the mass fraction of polyacyl chloride in the oil-phase solution is 0.1%-0.5%. Such a setting is conducive to enabling a sufficient reaction between polyamine and polyacyl chloride to form a relatively dense polyamide separation layer, which is conducive to the reverse osmosis membrane maintaining a high salt rejection rate.

[0049] Further, the polyamine is selected from at least one of m-phenylenediamine, piperazine, p-phenylenediamine, and tetraethylenepentamine, preferably m-phenylenediamine; the polyacyl chloride is selected from at least one of trimesoyl chloride, isophthaloyl chloride, and terephthaloyl chloride, preferably trimesoyl chloride.

[0050] In order to better remove the hydrochloric acid generated by the interfacial polymerization reaction to ensure the forward progress of the polymerization reaction between the polyamine and the polyacyl chloride, in the present invention, the aqueous solution further includes an acid absorbent, and the mass fraction of the acid absorbent in the aqueous solution is 0.5% - 3%.

[0051] Further, the acid absorbent is selected from at least one of triethylamine, sodium hydroxide, potassium hydroxide, sodium carbonate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, and dipotassium hydrogen phosphate, preferably triethylamine.

[0052] In one embodiment, in the step of forming the polyamide separation layer by heat treatment, the temperature of the heat treatment is 70°C - 90°C, and the time of the heat treatment is 2 min - 4 min. With such settings, the integrity and uniformity of the cross-linking of the polyamide separation layer can be further ensured, and the desalination rate and water flux of the reverse osmosis membrane can be further improved.

[0053] In one embodiment, the solvent of the oil phase solution is selected from isoparaffin solvents, and the isoparaffin solvents are selected from at least one of Isopar-E, Isopar-G, and Isopar-L; the solvent of the aqueous solution is water.

[0054] Meanwhile, the present invention also provides a reverse osmosis membrane prepared by using the preparation method of the reverse osmosis membrane described above. When this reverse osmosis membrane is applied to water treatment, it can maintain a high desalination rate while also having a high water flux.

[0055] In addition, the present invention also provides an application of the reverse osmosis composite membrane in a water treatment device.

[0056] In one embodiment, the water treatment device can be a purifier. When the reverse osmosis membrane is applied to a water purifier, during the water purification process, the raw water to be purified enters from the separation layer of the reverse osmosis membrane, and the raw water forms pure water by passing through the reverse osmosis membrane under the action of pressure.

[0057] In one embodiment, the water treatment device can also be a seawater desalination device.

[0058] Hereinafter, the reverse osmosis membrane, its preparation method and application will be further described through the following specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. For those conditions not specified in the examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial purchase.

[0059] Example 1

[0060] Liquid paraffin, Tween 80, sodium dodecyl sulfate and water were mixed and placed in a hot water bath at 100 °C for ultrasonic treatment for 1 h, and then cooled to room temperature in an ice-water bath to obtain an oil-in-water nanoemulsion. Among them, the volume ratio of liquid paraffin to water was 1:200, the average particle size of the oil-in-water nanoemulsion was 100 nm, the polydispersity index ≤ 0.25, and in the oil-in-water nanoemulsion, the mass fraction of liquid paraffin was 0.1%, the mass fraction of Tween 80 was 20%, and the mass fraction of sodium dodecyl sulfate was 2%; m-phenylenediamine, triethylamine and water were mixed evenly to prepare an aqueous solution. Among them, in the aqueous solution, the mass fraction of m-phenylenediamine was 1%, and the mass fraction of triethylamine was 0.5%; trimellitic acid chloride and isoparaffin solvent (Isopar-L) were mixed evenly to prepare an oil-phase solution. Among them, the mass fraction of trimellitic acid chloride in the oil-phase solution was 0.15%.

[0061] An aqueous solution of sodium chloride was coated on the surface of the polysulfone support membrane. After standing for 60 s, the excess aqueous solution of sodium chloride was poured out, and the membrane surface was air-dried. Among them, the mass fraction of sodium chloride in the aqueous solution of sodium chloride was 10%; the above-mentioned oil-in-water nanoemulsion was poured on the air-dried polysulfone support membrane surface. After standing for 60 s, the excess nanoemulsion was poured out, and it was placed in a blast drying oven at 50 °C for heat treatment for 5 min to form dendritic crystals distributed on the surface of the polysulfone support membrane. Among them, the mass ratio of sodium chloride to the oil-in-water nanoemulsion was 1:50.

[0062] The above-mentioned oil-phase solution was coated on the surface of the polysulfone support membrane distributed with dendritic crystals. After standing for 30 s, the excess oil-phase solution was poured out, and the membrane surface was air-dried; then the above-mentioned aqueous solution was coated on the surface of the polysulfone support membrane absorbing the oil-phase solution. After standing for 60 s, the excess aqueous solution was poured out, and finally it was placed in a blast drying oven at 80 °C for heat treatment for 2 min, and after taking out, the reverse osmosis membrane as shown in Figure 1 was obtained.

[0063] Example 2

[0064] Liquid paraffin, Tween 80, sodium dodecyl sulfate, and water were mixed and placed in a hot water bath at 85 °C for ultrasonic treatment for 1.5 h, and then placed in an ice-water bath to cool down to room temperature to obtain an oil-in-water nanoemulsion. Among them, the volume ratio of liquid paraffin to water was 1:150, the average particle size of the oil-in-water nanoemulsion was 95 nm, the polydispersity index ≤ 0.24, and in the oil-in-water nanoemulsion, the mass fraction of liquid paraffin was 0.5%, the mass fraction of Tween 80 was 30%, and the mass fraction of sodium dodecyl sulfate was 6%; m-phenylenediamine, triethylamine, and water were mixed evenly to prepare an aqueous solution. Among them, in the aqueous solution, the mass fraction of m-phenylenediamine was 2%, and the mass fraction of triethylamine was 2%; trimellitic trichloride and isoparaffin solvent (Isopar-L) were mixed evenly to prepare an oil-phase solution. Among them, the mass fraction of trimellitic trichloride in the oil-phase solution was 0.3%.

[0065] An aqueous solution of sodium chloride was coated on the surface of the polysulfone support membrane. After standing for 60 s, the excess aqueous solution of sodium chloride was poured out, and the membrane surface was air-dried. Among them, the mass fraction of sodium chloride in the aqueous solution of sodium chloride was 10%; the above-mentioned oil-in-water nanoemulsion was poured on the air-dried polysulfone support membrane surface. After standing for 60 s, the excess nanoemulsion was poured out, and it was placed in a blast drying oven at 60 °C for heat treatment for 4 min to form dendritic crystals distributed on the surface of the polysulfone support membrane. Among them, the mass ratio of sodium chloride to the oil-in-water nanoemulsion was 1:40.

[0066] The above-mentioned oil-phase solution was coated on the surface of the polysulfone support membrane with dendritic crystals distributed. After standing for 30 s, the excess oil-phase solution was poured out, and the membrane surface was air-dried; then the above-mentioned aqueous solution was coated on the surface of the polysulfone support membrane absorbing the oil-phase solution. After standing for 60 s, the excess aqueous solution was poured out, and finally it was placed in a blast drying oven at 75 °C for heat treatment for 4 min. After taking it out, a reverse osmosis membrane was obtained.

[0067] Example 3

[0068] Liquid paraffin, Tween 80, sodium dodecyl sulfate, and water were mixed and placed in a hot water bath at 85 °C for ultrasonic treatment for 1.5 h, and then placed in an ice-water bath to cool down to room temperature to obtain an oil-in-water nanoemulsion. Among them, the volume ratio of liquid paraffin to water was 1:100, the average particle size of the oil-in-water nanoemulsion was 100 nm, the polydispersity index ≤ 0.25, and in the oil-in-water nanoemulsion, the mass fraction of liquid paraffin was 0.8%, the mass fraction of Tween 80 was 35%, and the mass fraction of sodium dodecyl sulfate was 5%; m-phenylenediamine, triethylamine, and water were mixed evenly to prepare an aqueous solution. Among them, in the aqueous solution, the mass fraction of m-phenylenediamine was 3%, and the mass fraction of triethylamine was 3%; trimellitic trichloride and isoparaffin solvent (Isopar-L) were mixed evenly to prepare an oil-phase solution. Among them, the mass fraction of trimellitic trichloride in the oil-phase solution was 0.4%.

[0069] Apply an aqueous solution of sodium chloride to the surface of the polysulfone support membrane. After standing for 60 s, pour out the excess aqueous solution of sodium chloride, and air-dry the membrane surface. Among them, the mass fraction of sodium chloride in the aqueous solution of sodium chloride is 10%; pour the above oil-in-water nanoemulsion onto the air-dried polysulfone support membrane surface. After standing for 60 s, pour out the excess nanoemulsion, and place it in a blast drying oven at 80 °C for heat treatment for 5 min to form dendritic crystals distributed on the surface of the polysulfone support membrane. Among them, the mass ratio of sodium chloride to the oil-in-water nanoemulsion is 1:30.

[0070] Apply the above oil phase solution to the surface of the polysulfone support membrane distributed with dendritic crystals. After standing for 30 s, pour out the excess oil phase solution, and air-dry the membrane surface; then apply the above aqueous phase solution to the surface of the polysulfone support membrane absorbing the oil phase solution. After standing for 60 s, pour out the excess aqueous phase solution, and finally place it in a blast drying oven at 90 °C for heat treatment for 2 min. After taking it out, a reverse osmosis membrane is obtained.

[0071] Example 4

[0072] Compared with Example 1, Example 4 is only different in that the volume ratio of liquid paraffin to water is 1:300, and the mass fraction of liquid paraffin in the oil-in-water nanoemulsion is 0.1%. The other conditions are the same, and an oil-in-water nanoemulsion and a reverse osmosis membrane are obtained. Among them, the average particle size of the oil-in-water nanoemulsion is 110 nm, and the polydispersity index ≤ 0.27.

[0073] Example 5

[0074] Compared with Example 1, Example 5 is only different in that the volume ratio of liquid paraffin to water is 1:50, and the mass fraction of liquid paraffin in the oil-in-water nanoemulsion is 0.8%. The other conditions are the same, and an oil-in-water nanoemulsion and a reverse osmosis membrane are obtained. Among them, the average particle size of the oil-in-water nanoemulsion is 115 nm, and the polydispersity index ≤ 0.28.

[0075] Example 6

[0076] Compared with Example 1, Example 6 is only different in that the mass fraction of Tween 80 in the oil-in-water nanoemulsion is 30%, and the mass fraction of sodium dodecyl sulfate is 2%. The other conditions are the same, and an oil-in-water nanoemulsion and a reverse osmosis membrane are obtained. Among them, the average particle size of the oil-in-water nanoemulsion is 100 nm, and the polydispersity index ≤ 0.27.

[0077] Example 7

[0078] Example 7 is different from Example 1 only in that in the oil-in-water nanoemulsion, the mass fraction of Tween 80 is 30% and the mass fraction of sodium dodecyl sulfate is 8%, and the other conditions are the same. An oil-in-water nanoemulsion and a reverse osmosis membrane are obtained. Among them, the average particle size of the oil-in-water nanoemulsion is 98 nm, and the polydispersity index ≤ 0.27.

[0079] Example 8

[0080] Example 8 is different from Example 1 only in that the oil-in-water nanoemulsion does not contain sodium dodecyl sulfate, and the other conditions are the same. An oil-in-water nanoemulsion and a reverse osmosis membrane are obtained. Among them, the average particle size of the oil-in-water nanoemulsion is 105 nm, and the polydispersity index ≤ 0.28.

[0081] Example 9

[0082] Example 9 is different from Example 1 only in that in the oil-in-water nanoemulsion, the mass fraction of liquid paraffin is 0.05%, and the other conditions are the same. An oil-in-water nanoemulsion and a reverse osmosis membrane are obtained. Among them, the average particle size of the oil-in-water nanoemulsion is 100 nm, and the polydispersity index ≤ 0.25.

[0083] Example 10

[0084] Example 10 is different from Example 1 only in that in the oil-in-water nanoemulsion, the mass fraction of liquid paraffin is 1.0%, and the other conditions are the same. An oil-in-water nanoemulsion and a reverse osmosis membrane are obtained. Among them, the average particle size of the oil-in-water nanoemulsion is 120 nm, and the polydispersity index ≤ 0.28.

[0085] Example 11

[0086] Example 11 is different from Example 1 only in that in the oil-in-water nanoemulsion, the mass fraction of Tween 80 is 18% and the mass fraction of sodium dodecyl sulfate is 1%, and the other conditions are the same. An oil-in-water nanoemulsion and a reverse osmosis membrane are obtained. Among them, the average particle size of the oil-in-water nanoemulsion is 100 nm, and the polydispersity index ≤ 0.27.

[0087] Example 12

[0088] Example 12 is different from Example 1 only in that in the oil-in-water nanoemulsion, the mass fraction of Tween 80 is 40% and the mass fraction of sodium dodecyl sulfate is 6%, and the other conditions are the same. An oil-in-water nanoemulsion and a reverse osmosis membrane are obtained. Among them, the average particle size of the oil-in-water nanoemulsion is 94 nm, and the polydispersity index ≤ 0.27.

[0089] Example 13

[0090] Example 13 is different from Example 1 only in that the mass fraction of sodium chloride in the aqueous solution of sodium chloride is 0.5%, and the rest of the conditions are the same, obtaining a reverse osmosis membrane.

[0091] Example 14

[0092] Example 14 is different from Example 1 only in that the mass fraction of sodium chloride in the aqueous solution of sodium chloride is 8%, and the rest of the conditions are the same, obtaining a reverse osmosis membrane.

[0093] Example 15

[0094] Example 15 is different from Example 1 only in that tributyl citrate is used to replace liquid paraffin, alkylphenol polyoxyethylene ether is used to replace Tween 80; an aqueous solution of potassium chloride is used to replace the aqueous solution of sodium chloride, and the rest of the conditions are the same, obtaining a reverse osmosis membrane.

[0095] Comparative Example 1

[0096] Comparative Example 1 is different from Example 1 only in that the volume ratio of liquid paraffin to water is 1:50, the average particle size of the oil-in-water nanoemulsion is 250 nm, the polydispersity index ≤ 0.41, and in the oil-in-water nanoemulsion, the mass fraction of liquid paraffin is 0.5%, the mass fraction of Tween 80 is 20%, and the mass fraction of sodium dodecyl sulfate is 4%, and the rest of the conditions are the same, obtaining a reverse osmosis membrane.

[0097] Comparative Example 2

[0098] Comparative Example 2 is different from Example 1 only in that the volume ratio of liquid paraffin to water is 1:20, the average particle size of the oil-in-water nanoemulsion is 200 nm, the polydispersity index is about 0.52, and in the oil-in-water nanoemulsion, the mass fraction of liquid paraffin is 0.6%, the mass fraction of Tween 80 is 30%, and the mass fraction of sodium dodecyl sulfate is 3%, and the rest of the conditions are the same, obtaining a reverse osmosis membrane.

[0099] Comparative Example 3

[0100] Comparative Example 3 is different from Example 1 only in that the mass ratio of sodium chloride to the oil-in-water nanoemulsion is 1:100, and the rest of the conditions are the same, obtaining a reverse osmosis membrane.

[0101] Comparative Example 4

[0102] Comparative Example 4 is different from Example 1 only in that the mass ratio of sodium chloride to the oil-in-water nanoemulsion is 1:10, and the rest of the conditions are the same, obtaining a reverse osmosis membrane.

[0103] Comparative Example 5

[0104] Comparative Example 5 is different from Example 1 only in that it does not contain the step of coating the oil-in-water nanoemulsion on the surface of the polysulfone support membrane. That is, an aqueous solution of sodium chloride is coated on the surface of the polysulfone support membrane, and after standing for 60 s, the excess aqueous solution of sodium chloride is poured off, and then it is placed in a blast drying oven at 60 °C for heat treatment for 4 min to form sodium chloride crystals distributed on the surface of the polysulfone support membrane.

[0105] The above oil-phase solution is coated on the surface of the polysulfone support membrane on which sodium chloride crystals are distributed. After standing for 30 s, the excess oil-phase solution is poured off, and the membrane surface is air-dried; the other conditions are the same, and a reverse osmosis membrane is obtained.

[0106] Comparative Example 6

[0107] Comparative Example 6 is different from Example 1 only in that it does not contain the step of coating the aqueous solution of sodium chloride on the surface of the polysulfone support membrane. That is, the oil-in-water nanoemulsion in Example 1 is directly coated on the surface of the polysulfone support membrane. After standing for 60 s, the excess nanoemulsion is poured off, and after air-drying; the above oil-phase solution is coated on the surface of the polysulfone support membrane containing the nanoemulsion. After standing for 30 s, the excess oil-phase solution is poured off, and the membrane surface is air-dried; the other conditions are the same, and a reverse osmosis membrane as Figure 2 shown is obtained.

[0108] Comparative Example 7

[0109] Comparative Example 7 is different from Example 1 only in that the above aqueous-phase solution is coated on the surface of the polysulfone support membrane on which dendritic crystals are distributed. After standing for 60 s, the excess aqueous-phase solution is poured off, and the membrane surface is air-dried; then the above oil-phase solution is coated on the surface of the polysulfone support membrane that has absorbed the aqueous-phase solution. After standing for 30 s, the excess oil-phase solution is poured off, and finally it is placed in a blast drying oven at 80 °C for heat treatment for 2 min, and the other conditions are the same, and a reverse osmosis membrane is obtained.

[0110] The reverse osmosis membranes prepared in Examples 1 to 15 and Comparative Examples 1 to 7 were subjected to performance tests. The test conditions were: the test pressure was 1.55 MPa, the concentrated water flow rate was 1.0 GPM, the ambient temperature was 25 °C, the pH value of the concentrated water was 6.5 - 7.5, the concentrated water was a 2000 ppm aqueous solution of sodium chloride, and the test results are shown in Table 1.

[0111] Table 1

[0112]

[0113] It should be noted that in Table 1, the membrane water flux (F) is calculated from the volume of water passing through the reverse osmosis membrane in a certain time. The formula is: F = V / (A×T), where V is the volume of water passing through the reverse osmosis membrane per unit time, A is the effective membrane area, and T is the time.

[0114] The rejection rate (R) is calculated based on the concentrations of the feed liquid and the permeate liquid, and the calculation formula is: R = (1 - C1 / C0) × 100%, where C1 is the concentration of the permeate liquid and C0 is the concentration of the feed liquid.

[0115] It can be seen from Figure 1 that there are a large number of interconnected blade-like structures on the surface of the reverse osmosis membrane prepared in Example 1, which can effectively increase the specific surface area of the reverse osmosis membrane and effectively improve the water flux of the reverse osmosis membrane.

[0116] It can be seen from Figure 2 that in Comparative Example 6, since dendritic crystals cannot be formed, the number of granular protrusions on the surface of the formed separation layer increases. Compared with the blade-like structure, the reverse osmosis membrane has a very small specific surface area, thus affecting the water flux of the reverse osmosis membrane.

[0117] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0118] The above-described embodiments merely represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for preparing a reverse osmosis membrane, characterized in that, It includes the following steps: Mix oil, surfactant, and water to prepare an oil-in-water nanoemulsion. Among them, the surfactant includes a non-ionic surfactant, and the average particle size of the oil-in-water nanoemulsion is 80 nm - 200 nm, and the polydispersity index ≤ 0.3; Place the aqueous solution of inorganic metal salt and the oil-in-water nanoemulsion on the same surface of the support membrane in sequence, and form dendritic crystals through heat treatment. The mass ratio of the inorganic metal salt to the oil-in-water nanoemulsion is 1:50 - 1:30; Prepare a polyamide separation layer on the surface of the support membrane with the dendritic crystals distributed thereon through interfacial polymerization in reverse to obtain a reverse osmosis membrane.

2. The method for preparing a reverse osmosis membrane according to claim 1, characterized in that, In the step of preparing the oil-in-water nanoemulsion, the volume ratio of the oil to the water is 1:200 - 1:

100.

3. The preparation method of the reverse osmosis membrane according to claim 1, characterized in that, The mass fraction of the oil in the oil-in-water nanoemulsion is 0.1% - 0.8%; And / or, the mass fraction of the surfactant in the oil-in-water nanoemulsion is 20% - 40%.

4. The preparation method of the reverse osmosis membrane according to claim 3, wherein, The surfactant also includes an ionic surfactant, and the mass ratio of the non-ionic surfactant to the ionic surfactant is 5:1 - 10:

1.

5. The method for preparing a reverse osmosis membrane according to claim 1, characterized in that, The mass fraction of the inorganic metal salt in the aqueous solution of inorganic metal salt is 1% - 5%.

6. The method for preparing a reverse osmosis membrane according to claim 1, wherein The oil is selected from at least one of alkanes, stearic acid esters, and tributyl citrate; And / or, the non-ionic surfactant is selected from at least one of Tween 80, alkylphenol polyoxyethylene ether, and alkyl alcohol polyoxyethylene ether; And / or, the inorganic metal salt is selected from at least one of sodium chloride, potassium chloride, magnesium chloride, and calcium chloride.

7. The preparation method of the reverse osmosis membrane according to claim 1, characterized in that, In the step of forming dendritic crystals through heat treatment, the temperature of the heat treatment is 50°C - 80°C, and the time of the heat treatment is 3 min - 5 min.

8. The method for preparing a reverse osmosis membrane according to any one of claims 1 to 7, characterized in that, In the step of preparing a polyamide separation layer on the surface of the support membrane with the dendritic crystals distributed thereon through interfacial polymerization in reverse, place the oil phase solution and the water phase solution on the surface of the support membrane with the dendritic crystals distributed thereon in sequence, and prepare the polyamide separation layer through heat treatment. Among them, the oil phase solution contains polyacyl chloride, and the water phase solution contains polyamine.

9. A reverse osmosis membrane prepared by the preparation method of the reverse osmosis membrane according to any one of claims 1 to 8.

10. An application of the reverse osmosis membrane according to claim 9 in a water treatment device.

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