Preparation Method of Reverse Osmosis Membrane for a Portable and Lightweight PEM Water Electrolysis Oxygen Generation Device

Abstract

The present invention relates to a preparation method of a reverse osmosis membrane used in a portable and lightweight PEM water electrolysis oxygen generation device, belonging to the technical field of reverse osmosis membranes. The ultra-thin reverse osmosis membrane obtained by doping with modified multi-walled carbon nanotubes has a high water flux and can meet the water flow requirements of an oxygen generator; the pure water conductivity of the prepared reverse osmosis membrane is lower than 5 μS / cm, which can meet the requirements of the PEM oxygen generator for pure water; and the trace metal ions in the pure water prepared by this reverse osmosis membrane are at the ppb level, with little damage to the membrane electrode of the PEM oxygen generator, and can effectively improve the service life of the oxygen generator.

Description

Technical Field

[0001] The present invention belongs to the technical field of reverse osmosis membranes, and relates to a preparation method of a reverse osmosis membrane used in a portable and lightweight PEM water electrolysis oxygen generation device. Background Art

[0002] PEM water electrolysis for hydrogen production has high requirements for water and also has a water consumption problem during use. Therefore, by adding a pure water filtration membrane to the oxygen generation device, users can take water nearby for oxygen generation; truly achieving portability and lightweight, and at the same time eliminating the anxiety of being unable to generate oxygen when the pure water is consumed. The core of the pure water filtration device is the pure water filtration membrane, and reverse osmosis membrane technology has developed rapidly in recent decades and has been widely used in fields such as seawater and brackish water desalination, pure water and ultrapure water preparation, and wastewater treatment.

[0003] Therefore, it is necessary to prepare a reverse osmosis membrane that can be used in a PEM water electrolysis oxygen generation device. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of a reverse osmosis membrane used in a portable and lightweight PEM water electrolysis oxygen generation device. The reverse osmosis membrane prepared by the present invention has high water flux, low pure water conductivity, and high NaCl rejection rate.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A preparation method of a reverse osmosis membrane used in a portable and lightweight PEM water electrolysis oxygen generation device, comprising the following steps:

[0007] S1. Add multi-walled carbon nanotubes to a mixed acid solution of sulfuric acid and nitric acid, heat to 70 - 80 °C and reflux for 5 - 6 h, wash until the solution pH = 6.5 - 7.5, and obtain acidified multi-walled carbon nanotubes after drying;

[0008] S2. Under nitrogen protection, stir polylysine and deionized water evenly to form a polylysine solution, then add polyvinyl alcohol and acidified multi-walled carbon nanotubes and mix evenly, stir at room temperature for 6 - 9 h, after the stirring ends, naturally cool to room temperature, collect the product and perform vacuum distillation, and dry at 90 °C for 8 h to obtain modified multi-walled carbon nanotubes, wherein the mass ratio of the polylysine solution, polyvinyl alcohol, and acidified multi-walled carbon nanotubes is 60:10:(10 - 15);

[0009] S3. At room temperature, dissolve m-phenylenediamine monomer in ultrapure water to prepare an aqueous solution with a concentration of 6-12 wt%, and disperse the modified multi-walled carbon nanotubes evenly in the aqueous solution to obtain an MPD dispersion. First, soak the polysulfone ultrafiltration substrate membrane in pure water for 20 h. After drying the surface pure water with nitrogen, lay the polysulfone ultrafiltration substrate membrane flat on a glass plate, then immerse it in the MPD dispersion. After soaking for 10-15 min, take it out and use nitrogen to remove the excess aqueous phase on the surface until there are no obvious liquid droplets to obtain a polysulfone support membrane;

[0010] S4. At room temperature, dissolve trimesoyl chloride monomer in n-hexane to prepare an organic phase solution. Then soak the polysulfone support membrane obtained in step S3 in the organic phase solution, and form a composite layer on the surface of the polysulfone support membrane through an interfacial polymerization reaction. Take it out after 1-3 min and dry it in the air to obtain a nascent composite membrane;

[0011] S5. After heat-treating the nascent composite membrane, wash the membrane surface with deionized water 3-5 times to remove unreacted monomers and solvents, and obtain the reverse osmosis membrane used in the portable lightweight PEM water electrolysis oxygen generation device.

[0012] As a preferred technical solution of the present invention, in step S1, the volume ratio of concentrated sulfuric acid to concentrated nitric acid in the mixed acid solution is 3:1.

[0013] As a preferred technical solution of the present invention, in step S1, the dosage ratio of the multi-walled carbon nanotubes to the mixed acid solution is 0.3-0.5 mg / mL.

[0014] As a preferred technical solution of the present invention, in step S1, the temperature during drying is 90-95 °C and the time is 8-12 h.

[0015] As a preferred technical solution of the present invention, in step S2, the mass fraction of the polylysine solution is 10-15%.

[0016] As a preferred technical solution of the present invention, in step S3, the solid-liquid ratio of the modified multi-walled carbon nanotubes to the aqueous solution in the MPD dispersion is (1-5):100 g / mL.

[0017] As a preferred technical solution of the present invention, in step S4, the concentration of the organic phase solution is 0.1-0.5 wt%.

[0018] As a preferred technical solution of the present invention, in step S5, the temperature of the heat treatment is 65-75 °C and the time is 20-30 min.

[0019] In the present invention, multi-walled carbon nanotubes are acidified to obtain acidified multi-walled carbon nanotubes. m-Phenylenediamine and trimesoyl chloride polymerize to form a polyamide active layer, which can be used as a functional nano-filler and composite with polyamide to form a reverse osmosis membrane with excellent separation performance. The acidification treatment makes the surface of the carbon nanotubes carry carboxyl functional groups, enhancing the interfacial interaction between them and the polymer matrix, which is beneficial to improving the separation performance of the membrane.

[0020] After the acidification treatment, polylysine and polyvinyl alcohol are used for modification. The acidification treatment before the modification can remove the impurities on the surface of the carbon nanotubes and increase the oxygen-containing functional groups on the surface (such as carboxyl, hydroxyl, etc.), thereby improving its hydrophilicity and chemical reactivity. This treatment makes it easier for polylysine to interact with the carbon nanotubes and form a more stable modified product. In addition, the acidification treatment can also improve the dispersibility of the carbon nanotubes and further broaden its application scope in various fields.

[0021] At the same time, polyvinyl alcohol has good water solubility and film-forming properties. It can form a uniform coating layer on the surface of the acidified multi-walled carbon nanotubes, effectively preventing the aggregation and precipitation of the acidified multi-walled carbon nanotubes. The addition of polylysine further enhances the interaction between the carbon nanotubes and polyvinyl alcohol, making the modified carbon nanotubes disperse more uniformly in the reverse osmosis membrane. And in order to avoid the large hygroscopicity and poor water resistance of polyvinyl alcohol from weakening the bonding force between polyamide membranes and causing a decrease in material strength. Therefore, the addition of acidified multi-walled carbon nanotubes can increase the material strength. The carbon nanotubes themselves have the characteristics of high strength and high toughness. Adding them to the reverse osmosis membrane can significantly improve the mechanical strength of the membrane, which helps the reverse osmosis membrane maintain stable separation performance and structural integrity during long-term use. This enables the membrane to better intercept impurities and ions in water while ensuring sufficient water flux.

[0022] Adding the modified multi-walled carbon nanotubes during the polymerization process of m-phenylenediamine and trimesoyl chloride to form a polyamide active layer can improve its compatibility with the polymer matrix, reduce the risk of chemical corrosion and degradation, which helps to extend the service life of the membrane and maintain stable separation performance.

[0023] And because the modified multi-walled carbon nanotubes can endow the membrane surface with more hydrophilic groups, thereby improving the hydrophilicity of the membrane, which helps to reduce the pollution and fouling on the membrane surface and improve the separation efficiency and stability of the membrane. Since the modified multi-walled carbon nanotubes can improve the hydrophilicity and chemical stability of the membrane surface, the anti-fouling performance of the membrane can be enhanced.

[0024] Advantages of the present invention:

[0025] The ultra-thin reverse osmosis membrane obtained by doping with modified multi-walled carbon nanotubes in the present invention has a high water flux and can meet the water flow requirements of an oxygen generator. The pure water conductivity of the prepared reverse osmosis membrane is lower than 5 μS / cm, which can meet the requirements of a PEM oxygen generator for pure water. Moreover, the trace metal ions in the pure water prepared by this reverse osmosis membrane are at the ppb level, causing little damage to the membrane electrode of the PEM oxygen generator and effectively improving the service life of the oxygen generator. Detailed implementation manners

[0026] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following, in combination with embodiments, details the specific implementation manners, structures, features and their effects of the present invention as follows.

[0027] In the following examples and comparative examples:

[0028] Multi-walled carbon nanotubes: purchased from Zhejiang Asia-America Nano-Tech Co., Ltd.; polylysine: purchased from Shanghai Yuanye Bio-Technology Co., Ltd.; polyvinyl alcohol: purchased from Sichuan Lite Polytrust Pharmaceutical Excipients Co., Ltd.; m-phenylenediamine: purchased from Shandong Yukang Chemical Co., Ltd.; trimesoyl chloride: purchased from Hubei Jiahui Xingcheng Biotechnology Co., Ltd.

[0029] Example 1

[0030] S1. Add multi-walled carbon nanotubes into a mixed acid solution of sulfuric acid and nitric acid, heat to 70 °C and reflux for 5 h, wash until the solution pH = 6.5, and dry at 90 °C for 8 h to obtain acidified multi-walled carbon nanotubes. The volume ratio of concentrated sulfuric acid to concentrated nitric acid in the mixed acid solution is 3:1, and the dosage ratio of the multi-walled carbon nanotubes to the mixed acid solution is 0.3 mg / mL;

[0031] S2. Under nitrogen protection, stir polylysine and deionized water evenly to form a 10% (by mass) polylysine solution, then add polyvinyl alcohol and acidified multi-walled carbon nanotubes and mix evenly, stir at room temperature for 6 h. After stirring, naturally cool to room temperature, collect the product and perform vacuum distillation, and dry at 90 °C for 8 h to obtain modified multi-walled carbon nanotubes, where the mass ratio of the polylysine solution, polyvinyl alcohol and acidified multi-walled carbon nanotubes is 60:10:10;

[0032] S3. At room temperature, dissolve m-phenylenediamine monomer in ultrapure water to prepare an aqueous solution with a concentration of 6 wt%, and disperse the modified multi-walled carbon nanotubes and the aqueous solution evenly to obtain an MPD dispersion. First, soak the polysulfone ultrafiltration bottom membrane in pure water for 20 h, blow dry the surface pure water with nitrogen, then lay the polysulfone ultrafiltration bottom membrane flat on a glass plate, and then immerse it in the MPD dispersion. After soaking for 10 min, take it out and use nitrogen to remove the excess aqueous phase on the surface until there are no obvious liquid drops to obtain a polysulfone support membrane, where the solid-liquid ratio of the modified multi-walled carbon nanotubes to the aqueous solution in the MPD dispersion is 1:100 g / mL;

[0033] S4. At room temperature, dissolve the trimesoyl chloride monomer in n - hexane to prepare an organic phase solution with a concentration of 0.1 wt%. Then immerse the polysulfone support membrane obtained through step S3 in the organic phase solution. Through interfacial polymerization reaction, a composite layer is formed on the surface of the polysulfone support membrane. Take it out after 1 minute and air - dry it to obtain the as - formed composite membrane;

[0034] S5. Heat - treat the as - formed composite membrane at 65 °C for 20 minutes, wash the membrane surface 3 times with deionized water to remove unreacted monomers and solvents, and obtain the reverse osmosis membrane used in the portable lightweight PEM water electrolysis oxygen generation device.

[0035] Example 2

[0036] S1. Add multi - walled carbon nanotubes into the mixed acid solution of sulfuric acid and nitric acid, heat to 75 °C and reflux for 5.5 h, wash until the solution pH = 7, and dry at 93 °C for 10 h to obtain acid - treated multi - walled carbon nanotubes. The volume ratio of concentrated sulfuric acid to concentrated nitric acid in the mixed acid solution is 3:1, and the dosage ratio of multi - walled carbon nanotubes to the mixed acid solution is 0.4 mg / mL;

[0037] S2. Under nitrogen protection, stir polylysine and deionized water evenly to form a polylysine solution with a mass fraction of 13%. Then add polyvinyl alcohol and acid - treated multi - walled carbon nanotubes and mix evenly. Stir at room temperature for 7 h. After stirring, naturally cool to room temperature, collect the product and carry out vacuum distillation, and dry at 90 °C for 8 h to obtain modified multi - walled carbon nanotubes. The mass ratio of the polylysine solution, polyvinyl alcohol and acid - treated multi - walled carbon nanotubes is 60:10:13;

[0038] S3. At room temperature, dissolve the m - phenylenediamine monomer in ultrapure water to prepare an aqueous phase solution with a concentration of 8 wt%, and disperse the modified multi - walled carbon nanotubes evenly with the aqueous phase solution to obtain an MPD dispersion. First, immerse the polysulfone ultrafiltration bottom membrane in pure water for 20 h. After drying the surface pure water with nitrogen, lay the polysulfone ultrafiltration bottom membrane flat on a glass plate, then immerse it in the MPD dispersion. Take it out after soaking for 13 minutes, and use nitrogen to remove the excess aqueous phase on the surface until there are no obvious liquid drops to obtain the polysulfone support membrane. The solid - liquid ratio of the modified multi - walled carbon nanotubes to the aqueous phase solution in the MPD dispersion is 3:100 g / mL;

[0039] S4. At room temperature, dissolve the trimesoyl chloride monomer in n - hexane to prepare an organic phase solution with a concentration of 0.3 wt%. Then immerse the polysulfone support membrane obtained through step S3 in the organic phase solution. Through interfacial polymerization reaction, a composite layer is formed on the surface of the polysulfone support membrane. Take it out after 2 minutes and air - dry it to obtain the as - formed composite membrane;

[0040] S5. Heat-treat the nascent composite membrane at 70 °C for 25 min, and wash the membrane surface 4 times with deionized water to remove unreacted monomers and solvents, obtaining the reverse osmosis membrane used in the portable lightweight PEM water electrolysis oxygen generation device.

[0041] Example 3

[0042] S1. Add multi-walled carbon nanotubes to a mixed acid solution of sulfuric acid and nitric acid, heat to 80 °C and reflux for 6 h, wash until the solution pH = 7.5, and dry at 95 °C for 12 h to obtain acidified multi-walled carbon nanotubes. The volume ratio of concentrated sulfuric acid to concentrated nitric acid in the mixed acid solution is 3:1, and the dosage ratio of the multi-walled carbon nanotubes to the mixed acid solution is 0.5 mg / mL.

[0043] S2. Under nitrogen protection, stir polylysine and deionized water evenly to form a 15% (by mass) polylysine solution, then add polyvinyl alcohol and acidified multi-walled carbon nanotubes and mix evenly, stir at room temperature for 9 h, after stirring, naturally cool to room temperature, collect the product and perform vacuum distillation, and dry at 90 °C for 8 h to obtain modified multi-walled carbon nanotubes, where the mass ratio of the polylysine solution, polyvinyl alcohol and acidified multi-walled carbon nanotubes is 60:10:15.

[0044] S3. Dissolve m-phenylenediamine monomer in ultrapure water at room temperature to prepare an aqueous solution with a concentration of 12 wt%, and disperse the modified multi-walled carbon nanotubes evenly in the aqueous solution to obtain an MPD dispersion. First, soak the polysulfone ultrafiltration substrate membrane in pure water for 20 h, blow dry the pure water on the surface with nitrogen, then lay the polysulfone ultrafiltration substrate membrane flat on a glass plate, and then immerse it in the MPD dispersion. After soaking for 10 - 15 min, take it out and use nitrogen to remove the excess aqueous phase on the surface until there are no obvious liquid droplets, obtaining a polysulfone support membrane, where the solid-liquid ratio of the modified multi-walled carbon nanotubes to the aqueous solution in the MPD dispersion is 1:100 g / mL.

[0045] S4. Dissolve trimesoyl chloride monomer in n-hexane at room temperature to prepare an organic phase solution with a concentration of 0.5 wt%, then soak the polysulfone support membrane obtained in step S3 in the organic phase solution, and form a composite layer on the surface of the polysulfone support membrane through an interfacial polymerization reaction. Take it out after 3 min and air dry it to obtain a nascent composite membrane.

[0046] S5. Heat-treat the nascent composite membrane at 75 °C for 30 min, and wash the membrane surface 5 times with deionized water to remove unreacted monomers and solvents, obtaining the reverse osmosis membrane used in the portable lightweight PEM water electrolysis oxygen generation device.

[0047] Comparative Example 1

[0048] The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, the multi-walled carbon nanotubes were not acidified, and the rest of the operations were the same.

[0049] Comparative Example 2

[0050] The difference between Comparative Example 2 and Example 1 is that in Comparative Example 2, step S2 was not carried out, and the rest of the operations were the same.

[0051] Comparative Example 3

[0052] The difference between Comparative Example 3 and Example 1 is that in Comparative Example 3, the multi-walled carbon nanotubes were not treated by steps S1 and S2, and the rest of the operations were the same.

[0053] Performance test:

[0054] 1. Water permeation flux and rejection rate: A sodium chloride solution with a concentration of 2 g / L was prepared. Under the conditions of a pressure of 1.55 MPa and a flow rate of 3 L / min, after pre-pressing for 1 h, it was tested for 1 h, and the conductivity and volume of the filtrate were recorded, and the water permeation flux and rejection rate were calculated according to formula (1) and formula (2) respectively.

[0055] Formula (1): J / Vp = At, where J represents the water permeation flux, with the unit of L·m -2 ·h -1 ; Vp represents the passed volume, with the unit of L; A represents the effective area of the membrane, with the unit of m 2 ;

[0056] Formula (2): R = (1 - Cp / Cf) × 100%, where R is the apparent rejection rate of salt ions, %; Cp represents the salt ion concentration in the permeate, mg / L; Cf represents the salt ion concentration in the feed liquid, mg / L;

[0057] 2. The contact angle of the reverse osmosis membrane was tested by a water contact angle tester;

[0058] 3. The conductivity of pure water was tested by a conductivity tester;

[0059] The obtained test results are as follows in the table:

[0060]

[0061] According to the above data, it can be seen that the reverse osmosis membrane prepared by the present invention has a high water flux, a relatively low conductivity of pure water, and a high NaCl rejection rate.

[0062] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments by using the disclosed technical content within the scope of the technical solution of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a reverse osmosis membrane used in a portable lightweight PEM water electrolysis oxygen production device, characterized in that: The following steps are involved: S1, adding multi-walled carbon nanotubes to a mixed acid solution of sulfuric acid and nitric acid, heating to 70-80°C and reflux for 5-6 hours, washing until the solution pH is 6.5-7.5, and drying to obtain acidified multi-walled carbon nanotubes, wherein the volume ratio of concentrated sulfuric acid to concentrated nitric acid in the mixed acid solution is 3:1; S2. Under nitrogen protection, polylysine and deionized water are stirred evenly to form a polylysine solution, and polyvinyl alcohol and acidified multi-walled carbon nanotubes are added and mixed evenly, and stirred at room temperature for 6 to 9 hours. After the stirring is completed, the mixture is naturally cooled to room temperature, and the product is collected for vacuum distillation. After drying at 90°C for 8 hours, modified multi-walled carbon nanotubes are obtained, wherein the mass ratio of the polylysine solution, polyvinyl alcohol and acidified multi-walled carbon nanotubes is 60:10:(10-15); S3, dissolving m-phenylenediamine monomer in ultrapure water at room temperature to prepare an aqueous solution with a concentration of 6-12wt%, and uniformly dispersing the modified multi-walled carbon nanotubes with the aqueous solution to obtain an MPD dispersion, first soaking the polysulfone ultrafiltration bottom membrane in pure water for 20 hours, blowing the surface pure water with nitrogen, and then laying the polysulfone ultrafiltration bottom membrane on a glass plate, and then immersing it in the MPD dispersion, soaking for 10-15 minutes and then taking it out, removing the excess water phase on the surface with nitrogen until there are no obvious droplets, and obtaining a polysulfone support membrane; S4, dissolving trimesoyl chloride monomer in n-hexane at room temperature to prepare an organic phase solution, and then immersing the polysulfone support membrane obtained in step S3 in the organic phase solution, forming a composite layer on the surface of the polysulfone support membrane through interfacial polymerization reaction, taking out after 1 to 3 minutes, and drying in air to obtain a primary ecological composite membrane; S5. After heat-treating the nascent composite membrane, wash the membrane surface with deionized water for 3 to 5 times to remove unreacted monomers and solvents, thereby obtaining a reverse osmosis membrane used in the portable lightweight PEM water electrolysis oxygen production equipment.

2. The method for preparing a reverse osmosis membrane used in a portable lightweight PEM water electrolysis oxygen production device according to claim 1, characterized in that: In step S1, the dosage ratio of the multi-walled carbon nanotubes to the mixed acid solution is 0.3-0.5 mg / mL.

3. The method for preparing a reverse osmosis membrane used in a portable lightweight PEM water electrolysis oxygen production device according to claim 1, characterized in that: In step S1, the drying temperature is 90-95° C. and the drying time is 8-12 hours.

4. The method for preparing a reverse osmosis membrane used in a portable lightweight PEM water electrolysis oxygen production device according to claim 1, characterized in that: In step S2, the mass fraction of the polylysine solution is 10-15%.

5. The method for preparing a reverse osmosis membrane used in a portable lightweight PEM water electrolysis oxygen production device according to claim 1, characterized in that: In step S3, the solid-liquid ratio of the acidified multi-walled carbon nanotubes to the aqueous phase solution in the MPD dispersion is (1-5): 100 g / mL.

6. The method for preparing a reverse osmosis membrane used in a portable lightweight PEM water electrolysis oxygen production device according to claim 1, characterized in that: In step S4, the concentration of the organic phase solution is 0.1-0.5 wt %.

7. The method for preparing a reverse osmosis membrane used in a portable lightweight PEM water electrolysis oxygen production device according to claim 1, characterized in that: In step S5, the heat treatment temperature is 65-75° C. and the time is 20-30 min.

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