Method for preparing acid-resistant reverse osmosis membrane and acid-resistant reverse osmosis membrane

Abstract

The application discloses a preparation method of an acid-resistant reverse osmosis membrane and the acid-resistant reverse osmosis membrane. The preparation method comprises the following steps: (1) adding polyether sulfone into an organic solvent under heating and stirring, stirring for a period of time after the feeding is completed, and obtaining a mixed solution; (2) continuing to add a pore former after the mixed solution is cooled, stirring for a period of time after the feeding is completed, and obtaining a precursor solution; (3) performing vacuum defoaming treatment on the precursor solution, and obtaining a casting solution; (4) loading the casting solution on a carrier, and then performing gel bath treatment, and obtaining a base film; (5) sequentially immersing the base film in an aqueous solution and a mixed organic phase solution for polyamide treatment, and obtaining the reverse osmosis membrane; wherein the aqueous solution comprises m-phenylenediamine; and the mixed organic phase solution is a mixed solution of trimesoyl chloride and 1,3,6 naphthalene trisulfonyl chloride. The application has the advantages of simple process, good separation effect and mechanical property of the obtained acid-resistant reverse osmosis membrane, and significantly improved acid-erosion resistance.

Description

Technical Field

[0001] This invention relates to the technical field of reverse osmosis membranes, and more specifically, to a method for preparing an acid-resistant reverse osmosis membrane and the acid-resistant reverse osmosis membrane itself. Background Technology

[0002] Reverse osmosis membranes are a key membrane separation technology that uses high pressure to separate water or other solutions from a solution, thereby purifying or concentrating substances. They are widely used in water treatment, wastewater treatment, and seawater desalination. In reverse osmosis membranes, the base membrane is the crucial component supporting the entire membrane structure, determining its mechanical properties, chemical stability, and separation efficiency. Currently, polysulfone is the primary substrate for reverse osmosis membranes. Polysulfone possesses excellent chemical stability, high-temperature resistance, and mechanical strength, making it widely used in reverse osmosis membrane fabrication. However, traditional polysulfone-based membranes have some shortcomings, such as uneven pore structure, limited separation efficiency, and insufficient elastic modulus, all of which can lead to membrane compaction and failure under high pressure.

[0003] The applicant of this application has filed Chinese invention patent CN119258820A, which discloses a method for preparing a reverse osmosis membrane and the reverse osmosis membrane itself. By introducing polyethersulfone and polymerizing it at the interface, the membrane's heat resistance, chemical stability, mechanical strength, hydrophilicity, biocompatibility, and solute rejection rate are significantly improved compared to traditional polysulfone-based membranes. However, in application scenarios with extremely acidic conditions, the membrane's acid corrosion resistance is poor, and the membrane separation performance still suffers from a decrease due to amide bond hydrolysis during use. Summary of the Invention

[0004] To further improve acid resistance while ensuring separation efficiency, this invention provides a method for preparing an acid-resistant reverse osmosis membrane and the acid-resistant reverse osmosis membrane itself. The technical solution is as follows:

[0005] The preparation method of acid-resistant reverse osmosis membrane includes the following steps:

[0006] (1) Polyethersulfone is added to an organic solvent under heating and stirring conditions. After the addition is completed, the mixture is stirred for a period of time to obtain a mixture.

[0007] (2) After cooling the mixture, continue to add the pore-forming agent. After the addition is complete, stir for a period of time to obtain the precursor solution;

[0008] (3) Vacuum degassing treatment is performed on the precursor solution to obtain the casting solution;

[0009] (4) Load the casting solution onto the carrier and then perform a gel bath treatment to obtain the base film;

[0010] (5) The base membrane is sequentially immersed in an aqueous solution and a mixed organic solution for polyamide treatment to obtain a reverse osmosis membrane; wherein the aqueous solution includes m-phenylenediamine; and the mixed organic solution is a mixed solution of pyromellitic acid chloride and 1,3,6-naphthalenetrisulfonyl chloride.

[0011] The advantages of the preparation method of the present invention are: (1) A mixed organic phase solution prepared by compounding pyromellitic chloride and 1,3,6-naphthalenetrisulfonyl chloride with different structures and reactivity will undergo two reactions: the amino group (-NH2) of m-phenylenediamine reacts with the acyl chloride group (-COCl) of pyromellitic chloride to form an amide bond (-CO-NH-), and the amino group (-NH2) of m-phenylenediamine reacts with the sulfonyl chloride group (-SO2Cl) of 1,3,6-naphthalenetrisulfonyl chloride to form a sulfonamide bond (-SO2-NH-); among which, -SO2- in the sulfonamide bond is a very strong electron-withdrawing group, which can reduce the electron cloud density of the carbonyl oxygen atom on the adjacent amide bond through the conjugated system or inductive effect, making it more difficult for H in the acid to react. + Protonation (the first step and rate-determining step of acid-catalyzed hydrolysis) significantly reduces the rate of the entire hydrolysis reaction. (2) Both reactions occur simultaneously at the interface, forming a three-dimensional hybrid copolymer network chemically bonded by amide and sulfonamide bonds. The naphthalene ring structure in the 1,3,6-naphthalenetrisulfonyl chloride molecule is integrated into the three-dimensional hybrid copolymer network, which generates a steric hindrance effect, physically hindering the acidic medium from approaching and attacking the amide bond, thereby slowing down the degradation rate of the amide bond. (3) The introduction of 1,3,6-naphthalenetrisulfonyl chloride can change the kinetics of interfacial polymerization, reduce interfacial defects caused by side reactions, effectively shrink pores, form a denser, more uniform network structure with fewer defects, reduce the channels for acidic medium to penetrate into the polymer matrix, and improve the mechanical strength of the three-dimensional hybrid copolymer network structure.

[0012] As a further improvement to the above-mentioned method for preparing acid-resistant reverse osmosis membrane: in step (1), the organic solvent is N,N-dimethylformamide; polyethersulfone is added when the temperature reaches 50-60°C, and the mixture is stirred for 24-36 hours after the addition is completed.

[0013] As a further improvement to the above-mentioned method for preparing acid-resistant reverse osmosis membranes: step (2) further includes the addition of carbon materials, wherein the carbon materials are at least one of graphene oxide, sulfonated graphene, and carboxylated carbon nanotubes. The addition of these carbon materials can improve the hydrophilicity of the base membrane and enhance its antifouling ability; in particular, carbon materials treated with sulfonation or carboxylation have better acid resistance and compatibility with polymers.

[0014] As a further improvement to the above-mentioned method for preparing acid-resistant reverse osmosis membrane: in step (2), when the mixture is cooled to 20-40°C, the pore-forming agent and carbon material are added, and the mixture is stirred for 24-48 hours after the addition is completed; the pore-forming agent is polyvinylpyrrolidone-K30; the mass ratio of organic solvent, polyethersulfone, pore-forming agent and carbon material is (75-85):(15-25):(1-6):(0.2-0.6).

[0015] As a further improvement to the above-mentioned method for preparing acid-resistant reverse osmosis membranes:

[0016] In step (3), the precursor solution is degassed under vacuum at 50°C for 6 to 12 hours;

[0017] In step (4), nonwoven fabric is used as a carrier, and casting solution at a temperature of 20-40°C is loaded onto the nonwoven fabric and subjected to a gel bath treatment in pure water at 10-40°C for 1-10 minutes.

[0018] As a further improvement to the above-mentioned method for preparing acid-resistant reverse osmosis membranes: step (5) includes the following steps performed sequentially:

[0019] First, the base membrane is immersed in an aqueous solution;

[0020] Then use a compressed air knife to blow away the surface of the base film;

[0021] The base membrane is then immersed in a mixed organic phase solution;

[0022] Then rinse the base film surface with deionized water;

[0023] The base membrane is then heat-treated to obtain the reverse osmosis membrane.

[0024] As a further improvement to the above-mentioned method for preparing acid-resistant reverse osmosis membrane: In step (5), the aqueous solution is a mixed solution of m-phenylenediamine and cyclohexanediamine, with the mass fraction of m-phenylenediamine being 0.5–3 wt% and the mass fraction of cyclohexanediamine being 0.1–1 wt%; the base membrane is immersed in the aqueous solution for 1–5 minutes. Thus, by adding a small amount of cyclohexanediamine to the aqueous solution, the degree of crosslinking can be controlled, the rigidity of the three-dimensional hybrid copolymer network structure can be improved, and the mechanical strength of the membrane material can be optimized while maintaining acid resistance.

[0025] As a further improvement to the above-mentioned method for preparing acid-resistant reverse osmosis membrane: the mass fraction of pyromellitic chloroformyl chloride in the mixed organic phase solution is 0.05-0.15 wt%, the mass fraction of 1,3,6-naphthalenetrisulfonyl chloride is 0.05-0.15 wt%, and the base membrane is immersed in the mixed organic phase solution for 5-60 seconds.

[0026] As a further improvement to the above-mentioned method for preparing acid-resistant reverse osmosis membrane, the heat treatment involves immersing the base membrane in pure water at 70–90°C for 10–20 minutes. This heat treatment promotes the rearrangement and relaxation of polymer chains, eliminates internal stress, and makes the polyamide layer structure denser and more stable, thereby improving its performance under acidic conditions.

[0027] The acid-resistant reverse osmosis membrane is prepared by the above-described method for preparing acid-resistant reverse osmosis membranes.

[0028] In summary, the preparation method of the acid-resistant reverse osmosis membrane of the present invention is simple in process and low in material cost. The resulting acid-resistant reverse osmosis membrane not only has a good separation effect, but also significantly improved acid corrosion resistance. It can operate stably at a high flux under extreme acid conditions, has a wider range of applications, and is highly practical.

[0029] The present invention will be further described below through specific embodiments. Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0030] The present invention will now be clearly and completely described. Those skilled in the art will be able to implement the present invention based on this description. Before describing the present invention, it should be particularly noted that:

[0031] The technical solutions and features provided in the various parts of this invention, including the following description, can be combined with each other without conflict.

[0032] Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0033] Regarding the terminology and units used in this invention: The terms "comprising," "having," and any variations thereof in the specification, claims, and related parts of this invention are intended to cover non-exclusive inclusion.

[0034] Example 1

[0035] The method for preparing the acid-resistant reverse osmosis membrane in this embodiment includes the following steps:

[0036] (1) Add N,N-dimethylformamide to a three-necked flask, place the three-necked flask in an electric heating mantle and heat it while stirring. When the temperature reaches 60°C, add polyethersulfone to the N,N-dimethylformamide. After the addition is complete, stir for 24 hours to obtain a mixture.

[0037] (2) When the temperature of the mixture is lowered to 30°C, polyvinylpyrrolidone-K30 is added and the mixture is stirred for 12 hours to obtain the precursor solution; wherein, the mass ratio of N,N-dimethylformamide, polyethersulfone and polyvinylpyrrolidone-K30 is 75:25:6.

[0038] (3) The precursor solution was degassed under vacuum at 50°C for 12 hours to obtain the casting solution.

[0039] (4) Using a doctor blade with a blade spacing of 150 μm and a moving speed of 10 m / min, the casting solution at a temperature of 40 °C is loaded onto the nonwoven fabric. Then, a gel bath treatment is performed in pure water for 10 minutes to allow N,N-dimethylformamide and pure water to exchange and solidify into a film, thus obtaining the base film.

[0040] (5) The base film is sequentially immersed in an aqueous solution and a mixed organic solution for polyamidation treatment, specifically as follows:

[0041] First, the base film is immersed in an aqueous solution for 2 minutes, wherein the aqueous solution is a m-phenylenediamine solution with a mass fraction of 3.5 wt%.

[0042] Then use a compressed air knife to blow away the surface of the base film;

[0043] The base film was then immersed in a mixed organic phase solution for 15 seconds. The mixed organic phase solution was a mixture of pyromellitic trisulfonyl chloride and 1,3,6-naphthalenetrisulfonyl chloride (the solvent was n-hexane, the same below), with a mass fraction of 0.1 wt% for both pyromellitic trisulfonyl chloride and 0.1 wt% for 1,3,6-naphthalenetrisulfonyl chloride.

[0044] The base membrane surface is then rinsed with deionized water to obtain an acid-resistant reverse osmosis membrane.

[0045] After soaking in a 20 wt% H₂SO₄ solution for 16 days, the acid-resistant reverse osmosis membrane flux was measured to be 31 L / (m²). 2 (·h), the sodium chloride desalination rate is 99.09%.

[0046] Example 2

[0047] Compared with Example 1, the difference in the preparation method of the acid-resistant reverse osmosis membrane in this example is that the aqueous solution is a mixed solution of m-phenylenediamine and cyclohexanediamine, with the mass fraction of m-phenylenediamine being 3 wt% and the mass fraction of cyclohexanediamine being 1 wt%.

[0048] After soaking in a 20wt% H2SO4 solution for 16 days, the acid-resistant reverse osmosis membrane flux was measured to be 33 L / (m²). 2 (·h), the sodium chloride desalination rate is 99.23%.

[0049] Example 3

[0050] Compared with Example 2, the preparation method of the acid-resistant reverse osmosis membrane in this example is different in that: in step (2), graphene oxide is added, and the mass ratio of N,N-dimethylformamide, polyethersulfone, polyvinylpyrrolidone-K30 and graphene oxide is 75:25:6:0.6.

[0051] After soaking in a 20wt% H2SO4 solution for 16 days, the acid-resistant reverse osmosis membrane flux was measured to be 33 L / (m²). 2 (·h), the sodium chloride desalination rate is 99.31%.

[0052] Example 4

[0053] Compared with Example 3, the difference in the preparation method of the acid-resistant reverse osmosis membrane in this example is that: in step (5), the base membrane is further immersed in pure water at 80°C for 15 minutes.

[0054] After soaking in a 20wt% H2SO4 solution for 16 days, the acid-resistant reverse osmosis membrane flux was measured to be 36 L / (m²). 2 (·h), the sodium chloride desalination rate is 99.25%.

[0055] Example 5

[0056] Compared with Example 4, the difference in the preparation method of the acid-resistant reverse osmosis membrane in this example is that the aqueous solution is a mixed solution of m-phenylenediamine and cyclohexanediamine, with a mass fraction of 0.5 wt% for m-phenylenediamine and a mass fraction of 0.1 wt% for cyclohexanediamine.

[0057] After soaking in a 20wt% H2SO4 solution for 16 days, the acid-resistant reverse osmosis membrane flux was measured to be 34 L / (m²). 2 (·h), the sodium chloride desalination rate is 99.17%.

[0058] Example 6

[0059] Compared with Example 4, the difference in the preparation method of the acid-resistant reverse osmosis membrane in this example is that the mass ratio of N,N-dimethylformamide, polyethersulfone, polyvinylpyrrolidone-K30, and graphene oxide is 85:15:1:0.2.

[0060] After soaking in a 20 wt% H₂SO₄ solution for 16 days, the acid-resistant reverse osmosis membrane flux was measured to be 32 L / (m²).2 (·h), the sodium chloride desalination rate is 99.25%.

[0061] Example 7

[0062] Compared with Example 4, the difference in the preparation method of the acid-resistant reverse osmosis membrane in this example is that the mass fraction of pyromellitic methyl chloride in the mixed organic phase solution is 0.05 wt%, and the mass fraction of 1,3,6-naphthalenetrisulfonyl chloride is 0.05 wt%.

[0063] After soaking in a 20 wt% H₂SO₄ solution for 16 days, the acid-resistant reverse osmosis membrane flux was measured to be 31 L / (m²). 2 (·h), the sodium chloride desalination rate is 99.20%.

[0064] Example 8

[0065] Compared with Example 4, the difference in the preparation method of the acid-resistant reverse osmosis membrane in this example is that the mass fraction of pyromellitic methyl chloride and the mass fraction of 1,3,6-naphthalenetrisulfonyl chloride in the mixed organic phase solution is 0.15 wt%.

[0066] After soaking in a 20 wt% H₂SO₄ solution for 16 days, the acid-resistant reverse osmosis membrane flux was measured to be 32 L / (m²). 2 (·h), the sodium chloride desalination rate is 99.19%.

[0067] Comparison Example

[0068] Compared with Example 1, the difference in the preparation method of the reverse osmosis membrane in this comparative example is that the organic phase solution is a 0.1 wt% trimesoyl chloride solution.

[0069] After soaking in a 20 wt% H₂SO₄ solution for 16 days, the membrane was removed, and the reverse osmosis membrane flux was measured to be 26 L / (m²). 2 (·h), the sodium chloride desalination rate is 95.29%.

[0070] The flux (pure water) and sodium chloride desalination rate of the reverse osmosis membranes in the above examples and control examples were tested according to the "Test Methods for Reverse Osmosis Membranes" (GB / T 32373-2015), as follows:

[0071] 1. Take several (no fewer than 4) samples. The samples should be free of obvious defects such as wrinkles and damage. The size of the samples should meet the requirements of completely covering the sealing ring of the evaluation cell. The effective membrane area of ​​the samples in the evaluation cell should not be less than 2.5 × 10⁻⁶. -3 m 2 ;

[0072] Prepare a sodium chloride solution with a concentration of 32000 ppm and adjust the pH to 7 ± 0.5.

[0073] 2. Soak the sample in a 20wt% H2SO4 solution for 16 days, then remove and use it for later use;

[0074] 3. Flux test: Put the sample into the evaluation cell, turn on the water supply pump, slowly adjust the operating pressure to 55 bar for cross-flow filtration, maintain the temperature at 25℃±0.5℃, and after running stably for 30 minutes, collect the permeate produced after passing through the sample with a measuring cup (no less than 30 ml for a single sample), and use a stopwatch to calculate the required time.

[0075] Sodium chloride desalination rate test: Take another sample and put it into the evaluation cell. Turn on the booster pump and adjust the operating pressure to 55 bar. Maintain the temperature at 25℃±0.5℃. After running stably under constant pressure for 24 hours, determine the total dissolved solids (TDS) of the original solution (sodium chloride solution) and the permeate in accordance with GB / T 5750.4.

[0076] 4. After the test is completed, slowly reduce the operating pressure to below 0.05MPa and turn off the booster pump or water supply pump.

[0077] Flux is calculated using the following formula:

[0078]

[0079] In the formula, J represents flux, with units of L / (m²). 2 ﹒ h); V is the volume of the graduated cylinder sample, in L; T is the sampling time, in h; A is the effective area of ​​the sample, in m². 2 .

[0080] The sodium chloride desalination rate is calculated using the following formula:

[0081]

[0082] In the formula, R is the sodium chloride desalination rate, in units of %; C P The total dissolved solids (TDS) of the permeate is expressed in mg / L; C f The TDS of the stock solution is expressed in mg / L.

[0083] The foregoing has described the relevant content of the present invention. Those skilled in the art will be able to implement the present invention based on these descriptions. All other embodiments obtained by those skilled in the art based on the above description of the present invention without inventive effort should fall within the scope of protection of the present invention.

Claims

1. A method for preparing an acid-resistant reverse osmosis membrane, characterized in that: Includes the following steps: (1) Polyethersulfone is added to an organic solvent under heating and stirring conditions. After the addition is completed, the mixture is stirred for a period of time to obtain a mixture. (2) After cooling the mixture, continue to add the pore-forming agent and carbon material. After the addition is completed, stir for a period of time to obtain the precursor solution; the carbon material is at least one of graphene oxide, sulfonated graphene, and carboxylated carbon nanotubes. (3) Vacuum degassing treatment is performed on the precursor solution to obtain the casting solution; (4) Load the casting solution onto the carrier and then perform a gel bath treatment to obtain the base film; (5) The base membrane is sequentially immersed in an aqueous solution and a mixed organic solution for polyamide treatment to obtain a reverse osmosis membrane; wherein the aqueous solution includes m-phenylenediamine; and the mixed organic solution is a mixed solution of pyromellitic acid chloride and 1,3,6-naphthalenetrisulfonyl chloride. Step (5) includes the following steps performed sequentially: First, the base membrane is immersed in an aqueous solution; the aqueous solution is a mixed solution of m-phenylenediamine and cyclohexanediamine, with the mass fraction of m-phenylenediamine being 0.5-3 wt% and the mass fraction of cyclohexanediamine being 0.1-1 wt%; the base membrane is immersed in the aqueous solution for 1-5 minutes; Then use a compressed air knife to blow away the surface of the base film; The base membrane is then immersed in a mixed organic phase solution; the mixed organic phase solution contains 0.05-0.15 wt% pyromellitic chloromethyl chloride and 0.05-0.15 wt% 1,3,6-naphthalenetrisulfonyl chloride, and the base membrane is immersed in the mixed organic phase solution for 5-60 seconds. Then rinse the base film surface with deionized water; The base membrane is then heat-treated to obtain the reverse osmosis membrane.

2. The method for preparing the acid-resistant reverse osmosis membrane as described in claim 1, characterized in that: In step (1), the organic solvent is N,N-dimethylformamide; polyethersulfone is added when the temperature reaches 50-60°C, and the mixture is stirred for 24-36 hours after the addition is completed.

3. The method for preparing the acid-resistant reverse osmosis membrane as described in claim 1, characterized in that: In step (2), the mixture is cooled to 20-40°C before the pore-forming agent and carbon material are added. After the addition is completed, the mixture is stirred for 24-48 hours. The pore-forming agent is polyvinylpyrrolidone-K30. The mass ratio of organic solvent, polyethersulfone, pore-forming agent and carbon material is (75-85):(15-25):(1-6):(0.2-0.6).

4. The method for preparing the acid-resistant reverse osmosis membrane as described in claim 1, characterized in that: In step (3), the precursor solution is degassed under vacuum at 50°C for 6 to 12 hours; In step (4), nonwoven fabric is used as a carrier, and casting solution at a temperature of 20-40°C is loaded onto the nonwoven fabric and subjected to a gel bath treatment in pure water at 10-40°C for 1-10 minutes.

5. The method for preparing the acid-resistant reverse osmosis membrane as described in claim 1, characterized in that: The heat treatment involves immersing the base film in pure water at 70–90°C for 10–20 minutes.

6. An acid-resistant reverse osmosis membrane, characterized in that: It is prepared by the method for preparing acid-resistant reverse osmosis membrane according to any one of claims 1-5.

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