A reverse osmosis membrane and its preparation method

Abstract

The present invention relates to the field of water treatment technology, and more particularly to a kind of reverse osmosis membrane and preparation method thereof.The preparation method of the reverse osmosis membrane includes:Basement membrane is soaked in aqueous phase solution, after taking out surface drying, oil phase solution is coated on basement membrane and carries out interfacial polymerization reaction, after solidification, coating modifier solution, after drying, obtain reverse osmosis membrane;The modifier includes 2,4,6-tris (4-aminophenyl) ‑1,3,5-triazine ‑1,3,5-tris (4-methylphenyl) benzene.The COFs successfully grafted by the present invention can improve the water permeability of membrane to a certain extent, and can also improve the anti-pollution property, acid resistance and oxidation resistance of membrane, and then improve the service life of membrane.The present invention further compares the different effects that the same type of imino COFs are introduced into reverse osmosis membrane, so as to highlight the excellence of the imino COFs selected by the present invention.

Description

Technical Field

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

[0002] Water scarcity has always been one of the most worrying issues in the world and one of the challenges we all face.

[0003] Reverse osmosis membrane element pollution mainly includes the following categories: (1) Particle pollution: mainly comes from suspended matter, colloids, etc. in the raw water. Particles will block the pores of the membrane element and affect its water permeability. (2) Organic pollution: mainly comes from organic matter in the raw water, such as humic acid. These organic matter will adhere to the membrane surface, forming a gel layer, reducing its water production and desalination rate. (3) Microbial pollution: mainly comes from bacteria, algae, fungi and other microorganisms in the raw water. These microorganisms will form biofilms on the membrane surface, blocking the membrane pores and aggravating the growth of bacteria. (4) Inorganic pollution: mainly comes from inorganic salts such as calcium, magnesium, silicon, iron, and manganese in the raw water. These inorganic salts will form calcium carbonate, calcium sulfate, silicate, etc. on the surface of the membrane, thereby affecting its water permeability. (5) Colloid pollution: Some colloidal particles in the raw water will form a dense layer on the membrane surface, thereby affecting the water permeability. (6) Oxidant contamination: The use of oxidants such as chlorine and ozone in the water treatment process destroys the chemical structure of the membrane, resulting in a decrease in membrane performance. (7) Membrane material aging: Long-term use of the membrane material itself will reduce the permeability and selectivity of the membrane.

[0004] Therefore, the disadvantages of existing reverse osmosis membranes include: (1) poor acid resistance, short membrane life under acidic conditions, and increased cost of replacing membrane materials; (2) while certain technologies improve the membrane's acid resistance, the flux is greatly affected, the operating pressure is high, and the energy consumption and operating costs are high. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a reverse osmosis membrane and a preparation method thereof. The reverse osmosis membrane prepared by the present invention has excellent water permeability, anti-pollution, acid resistance and antioxidant properties.

[0006] The present invention provides a method for preparing a reverse osmosis membrane, comprising the following steps:

[0007] The base membrane is immersed in an aqueous solution, taken out and dried, and then an oil phase solution is coated on the base membrane to perform interfacial polymerization reaction. After solidification, a modifier solution is coated and dried to obtain a reverse osmosis membrane.

[0008] The modifier includes 2,4,6-tris(4-aminophenyl)-1,3,5-triazine-1,3,5-tris(4-methylphenyl)benzene.

[0009] Preferably, the mass concentration of the modifier solution is 0.05% to 0.2%; the solvent of the modifier solution includes at least one of water, N,N-dimethylformamide, N,N-dimethylacetamide, isopropanol, methanol and ethanol.

[0010] Preferably, the aqueous solution comprises a polyfunctional amine, a surfactant, an aqueous solvent and water;

[0011] In the aqueous phase solution, the mass content of the multifunctional amine is 0.5% to 5%, the mass content of the surfactant is 0.05% to 2%, and the mass content of the aqueous phase solvent is 3% to 10%.

[0012] Preferably, the polyfunctional amine includes at least one of m-phenylenediamine, ethylenediamine, propylenediamine, butylenediamine, p-phenylenediamine, o-phenylenediamine, mesitylenetriamine and piperazine;

[0013] The surfactant includes at least one of sodium dodecylbenzenesulfonate, sodium lauryl sulfate and sodium lauryl sulfate;

[0014] The aqueous phase solvent includes at least one of water, N,N-dimethylformamide, N,N-dimethylacetamide, isopropyl alcohol, methanol, ethanol, hexamethylphosphoric triamide, triethanolamine, dimethyl sulfoxide and trichloroethylene.

[0015] Preferably, the oil phase solution comprises an acyl halide and an oil phase solvent;

[0016] In the oil phase solution, the mass content of the acyl halide is 0.05% to 0.3%.

[0017] Preferably, the acyl halide comprises at least one of trimesoyl chloride, phthaloyl chloride, o-phthaloyl chloride, isophthaloyl chloride, biphenyl dichloride and benzene disulfonyl chloride;

[0018] The oil phase solvent includes at least one of n-hexane, Isopar G and Isopar L.

[0019] Preferably, the base film is immersed in the aqueous solution for 10 to 30 seconds.

[0020] Preferably, the coating amount of the oil phase solution is 50-100 mg / m 2 .

[0021] Preferably, the interfacial polymerization reaction is carried out at room temperature for 20 to 50 seconds.

[0022] The present invention also provides a reverse osmosis membrane prepared by the above preparation method.

[0023] In this invention, COFs offer advantages such as large specific surface area, adjustable pore size, stable structure, a two-dimensional layered structure, and the presence of π-π stacking interactions within the layered structure. Successfully grafted COFs can improve the membrane's water permeability, as well as its anti-fouling, acid resistance, and antioxidant properties, thereby increasing its service life. The present invention further compares the different effects of similar imine-based COFs introduced into reverse osmosis membranes, highlighting the superiority of the imine-based COFs selected in this invention. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0025] The present invention provides a method for preparing a reverse osmosis membrane, comprising the following steps:

[0026] The base membrane is immersed in an aqueous solution, taken out and dried, and then an oil phase solution is coated on the base membrane to perform interfacial polymerization reaction. After solidification, a modifier solution is coated and dried to obtain a reverse osmosis membrane.

[0027] The modifier is 2,4,6-tris(4-aminophenyl)-1,3,5-triazine-1,3,5-tris(4-methylphenyl)benzene.

[0028] In some embodiments of the present invention, the method for preparing the basement membrane comprises the following steps:

[0029] The casting solution is coated on a non-woven fabric and solidified into a film through phase inversion to obtain a base film;

[0030] The casting solution is a solution of sulfonated polysulfone. The solvent of the casting solution is N,N-dimethylformamide (DMF). The mass concentration of the casting solution is 16% to 20%. The casting solution is obtained by dissolving sulfonated polysulfone in N,N-dimethylformamide (DMF) and then standing to degas. The dissolution temperature is 70°C to 80°C, for example, 70°C. The degassing time is 12 to 36 hours, for example, 24 hours.

[0031] The coating amount of the casting solution is 60~110 mg / m 2 , for example 75 mg / m 2 .

[0032] The phase inversion method may be soaking in deionized water.

[0033] After the film is solidified, the process further includes: cleaning and drying.

[0034] In some embodiments of the present invention, the aqueous solution comprises a polyfunctional amine, a surfactant, an aqueous solvent, and water. In the aqueous solution, the mass content of the polyfunctional amine is 0.5% to 5%, the mass content of the surfactant is 0.05% to 2%, and the mass content of the aqueous solvent is 3% to 10%.

[0035] The polyfunctional amine is selected from at least one of m-phenylenediamine, ethylenediamine, propylenediamine, butylenediamine, p-phenylenediamine, o-phenylenediamine, mesitylenetriamine and piperazine.

[0036] The surfactant is selected from at least one of sodium dodecylbenzenesulfonate, sodium lauryl sulfate and sodium lauryl sulfate.

[0037] The aqueous phase solvent is selected from at least one of water, N,N-dimethylformamide, N,N-dimethylacetamide, isopropanol, methanol, ethanol, hexamethylphosphoric triamide, triethanolamine, dimethyl sulfoxide and trichloroethylene; specifically, it can be dimethyl sulfoxide and hexamethylphosphoric triamide, with a mass ratio of 2 to 3:1, such as 2.5:1.

[0038] The present invention has no particular limitation on the method for preparing the aqueous solution. In certain embodiments of the present invention, the method for preparing the aqueous solution comprises the following steps:

[0039] The multifunctional amine, surfactant, aqueous phase solvent and water are mixed to obtain an aqueous phase solution.

[0040] The mixing is carried out at room temperature.

[0041] In some embodiments of the present invention, the oil phase solution comprises an acyl halide and an oil phase solvent. The mass content of the acyl halide in the oil phase solution is 0.05% to 0.3%, such as 0.15%.

[0042] The acyl halide is at least one selected from trimesoyl chloride, phthaloyl chloride, phthaloyl chloride, isophthaloyl chloride, biphenyl dichloride and benzene disulfonyl chloride.

[0043] The oil phase solvent is selected from at least one of n-hexane, Isopar G and Isopar L.

[0044] The present invention has no particular limitation on the method for preparing the oil phase solution. In certain embodiments of the present invention, the method for preparing the oil phase solution comprises the following steps:

[0045] The acyl halide and the oil phase solvent are mixed to obtain an oil phase solution.

[0046] The mixing is carried out at room temperature.

[0047] The invention soaks the base membrane in an aqueous solution, takes it out and allows it to dry, then coats the base membrane with an oil solution for interfacial polymerization, solidifies it, coats it with a modifier solution, and dries it to obtain a reverse osmosis membrane.

[0048] In some embodiments of the present invention, the base film is immersed in the aqueous solution for 10 to 30 seconds, such as 20 seconds.

[0049] The present invention has no particular limitation on the surface drying method, and any surface drying method well known to those skilled in the art may be used.

[0050] In some embodiments of the present invention, the oil phase solution is coated on the base film, and the coating amount is 50-100 mg / m 2 , for example 70 mg / m 2 .

[0051] In some embodiments of the present invention, the interfacial polymerization reaction is carried out at room temperature for 20 to 50 seconds, such as 30 seconds.

[0052] In some embodiments of the present invention, the curing method is drying. The drying temperature is 50-60°C, for example, 55°C, and the drying time is 1-5 minutes, for example, 2 minutes. The drying is performed in an oven. The curing process involves evaporation of the oil phase solution and the cross-linking curing reaction.

[0053] In the present invention, the modifier includes 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT)-1,3,5-tris(4-methylphenyl)benzene (TFPB). The modifier is an imine-based covalent organic framework (COFs).

[0054] In some embodiments of the present invention, the solvent of the modifier solution (modifier solvent) is selected from at least one of water, N,N-dimethylformamide, N,N-dimethylacetamide, isopropanol, methanol, and ethanol. The mass concentration of the modifier solution is 0.05% to 0.2%, preferably 0.18% to 0.22%, such as 0.05%, 0.1%, 0.15%, and 0.2%.

[0055] The present invention has no particular limitation on the method for preparing the modifier solution. In certain embodiments of the present invention, the method for preparing the modifier solution comprises the following steps:

[0056] The modifier and the modifier solution are mixed evenly to obtain a modifier solution.

[0057] The mixing is carried out at room temperature.

[0058] The present invention also provides a reverse osmosis membrane prepared by the above preparation method.

[0059] The present invention has no particular limitation on the sources of the raw materials used above, and they can be generally commercially available.

[0060] Beneficial effects:

[0061] 1. In the present invention, COFs materials have advantages such as large specific surface area, adjustable pore size, stable structure, two-dimensional layered structure, and the presence of π-π stacking between the layers. The successfully grafted COFs can improve the water permeability of the membrane to a certain extent, and can also improve the membrane's anti-fouling and acid resistance. This can further increase the membrane's service life.

[0062] 2. The present invention further compares the different effects of the same type of imine-based COFs introduced into the reverse osmosis membrane, thereby highlighting the superiority of the imine-based COFs selected in the present invention.

[0063] In order to further illustrate the present invention, a reverse osmosis membrane and a preparation method thereof provided by the present invention are described in detail below with reference to examples, but they should not be construed as limiting the scope of protection of the present invention.

[0064] In the examples and comparative examples, the basement membrane is prepared as follows:

[0065] 1) Preparation of casting solution: 86 parts by mass of N,N-dimethylformamide and 14 parts by mass of sulfonated polysulfone (BASF, Germany, S2010G6) were mixed and stirred at 70°C until dissolved. The mixture was allowed to stand for 24 hours to degas. A uniform and transparent casting solution was obtained.

[0066] 2) Apply the casting solution on the non-woven fabric at a coating amount of 75 mg / m 2 After soaking in deionized water, phase conversion and solidification are performed to form a film, and after cleaning and drying, a base film is obtained.

[0067] Example 1

[0068] Preparation of aqueous solution:

[0069] A polyfunctional amine (m-phenylenediamine), a surfactant (sodium lauryl sulfate), an aqueous solvent (dimethyl sulfoxide and hexamethylphosphoric triamide, in a mass ratio of 2.5:1) and water are mixed at room temperature to obtain an aqueous solution; in the aqueous solution, the mass content of the polyfunctional amine is 2%, the mass content of the surfactant is 0.8%, and the mass content of the aqueous solvent is 5%.

[0070] Preparation of oil phase solution:

[0071] An acyl halide (trimesoyl chloride) and an oil phase solvent (Isopar G) were mixed at room temperature to obtain an oil phase solution. The oil phase solution contained 0.15% by weight of the acyl halide.

[0072] Preparation of modifier solution:

[0073] The modifier 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT)-1,3,5-tris(4-methylphenyl)benzene (TFPB) and the modifying liquid solvent (N,N-dimethylformamide) are mixed at room temperature to obtain a modifier solution; the mass concentration of the modifier solution is 0.05%.

[0074] Preparation of reverse osmosis membrane:

[0075] The base film was immersed in the aqueous solution for 20 s, and then coated with the oil solution after it was dried. The coating amount was 70 mg / m 2 After the interfacial polymerization reaction was carried out at room temperature for 30 seconds, the membrane was placed in a 55°C oven for thermal curing for 2 minutes, and then coated with a modifier solution. After drying, a reverse osmosis membrane was obtained.

[0076] Example 2

[0077] The difference from Example 1 is:

[0078] The mass concentration of the modifier solution is 0.1%.

[0079] The remaining steps were the same as in Example 1 to obtain a composite reverse osmosis membrane.

[0080] Example 3

[0081] The difference from Example 1 is:

[0082] The mass concentration of the modifier solution is 0.15%.

[0083] The remaining steps were the same as in Example 1 to obtain a composite reverse osmosis membrane.

[0084] Example 4

[0085] The difference from Example 1 is:

[0086] The mass concentration of the modifier solution is 0.2%.

[0087] The remaining steps were the same as in Example 1 to obtain a composite reverse osmosis membrane.

[0088] Comparative Example 1

[0089] The difference from Example 1 is:

[0090] The modifier is an imine covalent organic framework: 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT)-trialdehyde phloroglucinol (TP).

[0091] The remaining steps were the same as in Example 1 to obtain a composite reverse osmosis membrane.

[0092] Comparative Example 2

[0093] The difference from Example 1 is:

[0094] The modifier is an imine covalent organic framework: 2,4,6-triformylphloroglucinol-p-phenylenediamine-COF (COF-TpPa).

[0095] The remaining steps were the same as in Example 1 to obtain a composite reverse osmosis membrane.

[0096] Comparative Example 3

[0097] The difference from Example 1 is:

[0098] The modifier is an imine covalent organic framework: p-phenylenediamine-pyromellitic acid-COF (COF-LZU1).

[0099] The remaining steps were the same as in Example 1 to obtain a composite reverse osmosis membrane.

[0100] Comparative Example 4

[0101] The difference from Example 1 is:

[0102] The modifier is an imine covalent organic framework, which is prepared according to the following method:

[0103] The amino monomer dihydroxy-benzylaniline (BD-(OH)2)-COF and the aldehyde monomer 1,3,5-triformylphloroglucinol (Tp) were prepared in a mass ratio of 1:1. The reaction solvent was mesitylene and 1,4-dioxane (volume ratio of 1:1). The reaction was carried out at 120°C in a vacuum and nitrogen-filled environment for 48 hours. After the reaction was completed, the mixture was dried and set aside.

[0104] The remaining steps were the same as in Example 1 to obtain a composite reverse osmosis membrane.

[0105] Comparative Example 5

[0106] The difference from Example 1 is:

[0107] The modifier is an imine covalent organic framework: specifically, an ethylenediimine-based covalent organic framework prepared according to the method of Example 1 of application document CN116535593A.

[0108] The remaining steps were the same as in Example 1 to obtain a composite reverse osmosis membrane.

[0109] (1) Diaphragm performance evaluation:

[0110] The reverse osmosis membranes obtained in the above examples and comparative examples were tested for performance on a standard membrane test bench:

[0111] The calculation formula of flux F is shown in formula (1):

[0112] Formula (1);

[0113] In formula (1), V is the permeate volume, gallons (gal); S is the effective membrane area, square feet (ft); and t is time, days (d).

[0114] The calculation formula of the desalination rate R is shown in formula (2):

[0115] Formula (2);

[0116] In formula (2), C f is the NaCl concentration in the stock solution, ppm; C p is the NaCl concentration in the permeate, ppm.

[0117] Specifically:

[0118] The test was conducted using a 2000 mg / L NaCl aqueous solution at 15.5 bar pressure, pH = 7.5, and 25°C. The results are shown in Table 1.

[0119] Table 1 Initial performance test results of the reverse osmosis membranes obtained in Examples and Comparative Examples

[0120]

[0121] From the perspective of the initial performance of the membrane, the changes in the membrane flux of Examples 1, 2, and 3 are related to the amount of COFs added. A large number of aldehyde groups and hydroxyl groups are distributed in the COFs structure, which has good dispersibility and hydrophilicity, and can effectively improve the membrane flux. Example 4 can illustrate that the amount of COFs introduced has a threshold, so Examples 1 to 4 confirm the optimal amount of COFs introduced. Comparative Examples 1 to 5 are all different imine COFs. In contrast to the examples, it can be proved through initial performance testing that Example 3 is the best combination condition, and the modifier solution in Example 3 has the best effect on membrane performance improvement.

[0122] (2) Evaluation of antifouling ability: The test was conducted using a 2000 mg / L NaCl aqueous solution and a 400 mg / L pollutant aqueous solution (bovine serum albumin, humic acid, etc.) at a pressure of 15.5 bar and a temperature of 25 ± 0.4°C.

[0123] The permeate reduction rate (PDR) (in %) of the sewage solution after continuous filtration is calculated according to formula (3), and the corresponding permeate recovery rate (PRR) (in %) after physical washing is calculated according to formula (4);

[0124] Formula (3);

[0125] Formula (4).

[0126] In formula (3) and formula (4), J0 is the flux measured under the condition of 2000 mg / L NaCl aqueous solution as the test solution for 1 h, GFD; J t When 400 mg / L of pollutants are added to a 2000 mg / L NaCl aqueous solution, the flux is measured for 8 h under this test solution condition, GFD; J wc The recovery flux (GFD) is measured after washing with RO water for 15 minutes three times.

[0127] The results are shown in Table 2.

[0128] Table 2 Antifouling ability test results of reverse osmosis membranes obtained in Examples and Comparative Examples

[0129]

[0130] As shown in Table 2, as pollutants gradually accumulate, the transport resistance of the leachate gradually increases. Based on these results, Example 3 performs optimally. The anti-pollution ability is related to the steric hindrance of COFs. COFs can effectively reduce the accumulation of pollutants on the polyamide layer, and the flux of the COF-modified reverse osmosis membranes has been improved to a certain extent.

[0131] (3) Acid resistance test:

[0132] To verify the acid resistance of the membrane prepared by the present invention, a hydrochloric acid solution with a pH of 2 was prepared, heated and maintained at 40±0.5°C. After the membrane was immersed for 24 hours, it was tested under the conditions of 15.5 bar pressure, pH=7.5, and 25±0.4°C.

[0133] Table 3 Acid resistance test results of the reverse osmosis membranes obtained in the examples and comparative examples

[0134]

[0135] As can be seen from Table 3, after acid treatment, the flux of all membranes increased, while the desalination decreased to a certain extent, with the smallest decrease in Example 3. This indicates that the COFs introduced in Example 3 can better bind to the polyamide layer due to their greater steric hindrance and are less susceptible to attack by hydrated protons.

[0136] (IV) Antioxidant test:

[0137] The membrane was immersed in 1000 mg / L HClO solution for 24 h and tested at 15.5 bar pressure, pH = 7.5, and 25 ± 0.4 °C.

[0138] Table 4 Antioxidant performance test results of the reverse osmosis membranes obtained in the examples and comparative examples

[0139]

[0140] As shown in Table 4, the changes in flux and desalination of Example 3 after HClO immersion are the lowest. This is because the imine-based COFs have abundant NH groups, which can serve as sacrificial units for free chloride ion attack, significantly improving the oxidation resistance of the modified reverse osmosis membrane.

[0141] The above embodiments are intended only to facilitate understanding of the methods and core concepts of the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein, but is intended to be construed in the widest manner consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a reverse osmosis membrane, characterized in that: The following steps are involved: The base membrane is immersed in an aqueous solution, taken out and dried, and then an oil phase solution is coated on the base membrane to perform interfacial polymerization reaction. After solidification, a modifier solution is coated and dried to obtain a reverse osmosis membrane. The modifier includes 2,4,6-tris(4-aminophenyl)-1,3,5-triazine-1,3,5-tris(4-methylphenyl)benzene.

2. The preparation method according to claim 1, characterized in that The mass concentration of the modifier solution is 0.05% to 0.2%; the solvent of the modifier solution includes at least one of water, N,N-dimethylformamide, N,N-dimethylacetamide, isopropanol, methanol and ethanol.

3. The preparation method according to claim 1, characterized in that The aqueous phase solution includes a polyfunctional amine, a surfactant, an aqueous phase solvent and water; In the aqueous phase solution, the mass content of the multifunctional amine is 0.5% to 5%, the mass content of the surfactant is 0.05% to 2%, and the mass content of the aqueous phase solvent is 3% to 10%.

4. The preparation method according to claim 3, characterized in that The polyfunctional amine includes at least one of m-phenylenediamine, ethylenediamine, propylenediamine, butylenediamine, p-phenylenediamine, o-phenylenediamine, mesitylenetriamine and piperazine; The surfactant includes at least one of sodium dodecylbenzenesulfonate, sodium lauryl sulfate and sodium lauryl sulfate; The aqueous phase solvent includes at least one of water, N,N-dimethylformamide, N,N-dimethylacetamide, isopropyl alcohol, methanol, ethanol, hexamethylphosphoric triamide, triethanolamine, dimethyl sulfoxide and trichloroethylene.

5. The preparation method according to claim 1, characterized in that The oil phase solution comprises an acyl halide and an oil phase solvent; In the oil phase solution, the mass content of the acyl halide is 0.05% to 0.3%.

6. The preparation method according to claim 5, characterized in that The acyl halide comprises at least one of trimesoyl chloride, phthaloyl chloride, o-phthaloyl chloride, isophthaloyl chloride, biphenyl dichloride and benzene disulfonyl chloride; The oil phase solvent includes at least one of n-hexane, Isopar G and Isopar L.

7. The preparation method according to claim 1, characterized in that The base film is immersed in the aqueous solution for 10 to 30 seconds.

8. The preparation method according to claim 1, characterized in that The coating amount of the oil phase solution is 50~100 mg / m 2 .

9. The preparation method according to claim 1, characterized in that The interfacial polymerization reaction is carried out at room temperature for 20 to 50 seconds.

10. The reverse osmosis membrane obtained by the preparation method according to any one of claims 1 to 9.

Images