High-selectivity acid-resistant nanofiltration membrane, preparation method and application thereof

Abstract

The application relates to a high-selectivity acid-resistant nanofiltration membrane and a preparation method and application thereof, and belongs to the field of membrane separation technology. The preparation method of the high-selectivity acid-resistant nanofiltration membrane comprises the following steps: (1) soaking a polysulfone membrane in an aqueous solution containing a strong oxidant and a metal chloride; (2) immersing the membrane treated in the step (1) into a n-hexane solution containing a pyrrole molecule and standing; (3) spraying a mixed ethanol solution of phenol and formaldehyde onto the membrane treated in the step (2); and (4) post-treating the membrane treated in the step (3) in a hot sodium hydroxide solution containing a surfactant to obtain the high-selectivity acid-resistant nanofiltration membrane. The application has the advantages of simple process, easily-obtained raw materials and suitability for industrial production. Meanwhile, the high-selectivity acid-resistant nanofiltration membrane has high selectivity of divalent ions and monovalent ions on the premise of strong acid resistance, and is suitable for salt separation treatment of acid industrial wastewater.

Description

Technical Field

[0001] This invention relates to a highly selective acid-resistant nanofiltration membrane, its preparation method, and its application, belonging to the field of membrane separation technology. Background Technology

[0002] Industries such as electroplating, metallurgy, and mining generate large amounts of acidic wastewater annually, making its efficient treatment crucial for environmental protection. Compared to technologies like chemical precipitation, ion exchange, extraction, and adsorption, nanofiltration membrane separation offers advantages such as low energy consumption, high efficiency, and low cost, making it a promising candidate for acidic wastewater treatment. However, traditional polyamide nanofiltration membranes are prone to hydrolysis under acidic conditions, and their separation performance deteriorates rapidly over long-term use. Therefore, acid-resistant nanofiltration membranes are gaining popularity. Polysulfonamides, polyamines, polyelectrolytes, and polyurea materials possess strong acid resistance and are currently being used in the development of acid-resistant nanofiltration membranes. For example, Park et al. (Journal of Membrane Science, 2022, 645:120175) prepared a polyamide-polysulfonamide nanofiltration membrane, which maintained a magnesium sulfate rejection rate of over 98% after treatment in 15 wt% sulfuric acid for 83 days; Wang et al. (Journal of Membrane Science, 2024, 692:122286) prepared a polyurea nanofiltration membrane, which maintained a magnesium chloride rejection rate of over 90% after treatment in sulfuric acid at pH=1 for 440 hours; and Yin et al. (Journal of Membrane Science, 2025, 716:123502) prepared a polyamine nanofiltration membrane, which maintained a magnesium chloride rejection rate of over 80% after treatment in sulfuric acid at pH=1 for 30 days. Currently, the acid resistance of acid-resistant nanofiltration membranes has been improved, but they generally face the problem of low selectivity, especially the difficulty in achieving efficient and selective separation of divalent and monovalent ions, which cannot meet the salt separation requirements of industrial acidic wastewater. Summary of the Invention

[0003] This invention provides a highly selective acid-resistant nanofiltration membrane, its preparation method, and its application to solve the technical problems existing in the prior art as described above.

[0004] The technical solution provided by this invention is as follows: One objective of this invention is to provide a method for preparing a highly selective acid-resistant nanofiltration membrane, comprising the following steps: (1) The polysulfone membrane was immersed in an aqueous solution containing a strong oxidant and a metal chloride. (2) Immerse the membrane treated in step (1) in a hexane solution containing pyrrole molecules and let it stand; (3) Spray a mixed ethanol solution of phenol and formaldehyde onto the membrane treated in step (2); (4) The membrane after step (3) is placed in a hot sodium hydroxide solution containing surfactant for post-treatment to obtain the highly selective acid-resistant nanofiltration membrane.

[0005] Based on the above technical solution, the present invention can be further improved as follows: Furthermore, the strong oxidant is one or more of hydrogen peroxide, ammonium persulfate, potassium persulfate, and ferric chloride, with a concentration of 0.1~6wt%.

[0006] Further, the metal chloride is one or more of sodium chloride, potassium chloride, lithium chloride, and magnesium chloride, with a concentration of 0.05~2wt%. Further, the pyrrole molecule is one or more of pyrrole, 3-hexylpyrrole, 3-methoxypyrrole, and N-methylpyrrole, with a concentration of 0.01~3wt%.

[0007] Further, the phenol is one or more of phenol, resorcinol, p-tert-butylphenol, and cashew phenol; in the ethanol mixture of phenol and formaldehyde, the concentration of phenol is 15-35 wt% and the concentration of formaldehyde is 25-45 wt%.

[0008] Further, the surfactant is one or more of sodium dodecyl diphenyl ether disulfonate, decyl glucoside, isooctyl phosphate, and dodecyl dimethylamine oxide, with a concentration of 0.02~2wt%.

[0009] Furthermore, the temperature of the hot sodium hydroxide solution is 50~75℃, and the concentration is 0.5~10wt%.

[0010] Furthermore, in step (1), the soaking time is 30 min to 2 h; in step (2), the standing time is 2 min to 1 h; and in step (4), the post-treatment time is 2 to 5 h.

[0011] The second objective of this invention is to provide a highly selective acid-resistant nanofiltration membrane, which is prepared by the method described above for preparing a highly selective acid-resistant nanofiltration membrane.

[0012] A third objective of this invention is to provide the application of the highly selective acid-resistant nanofiltration membrane described above in the desalination treatment of acidic industrial wastewater.

[0013] This invention utilizes the synergistic effect of a mixed ethanol solution of metal chloride, phenol, and formaldehyde for spraying, followed by post-treatment with a hot sodium hydroxide solution containing surfactants (at a specific temperature). Compared to existing technologies, this invention offers the following advantages: 1. Excellent selectivity, suitable for acidic wastewater desalination requirements: The synergistic effect of the three can regulate the pore size of the separation layer and the charge distribution inside the membrane, significantly improving the membrane's selectivity for divalent / monovalent ions, while taking into account the water permeate flux. It can efficiently achieve desalination treatment of acidic industrial wastewater and solve the problem of poor separation effect of existing membranes.

[0014] 2. Strong acid resistance, broadening application scenarios: The dense modified layer formed by synergistic effect can isolate acidic media erosion, improve the chemical stability of the membrane, and enable the membrane to operate stably in acidic systems for a long time. It breaks through the acid resistance shortcomings of traditional nanofiltration membranes and is suitable for the acidic wastewater treatment needs in chemical, environmental protection and other fields.

[0015] 3. Simple process and easy to industrialize: The preparation steps are clear, no complex equipment or harsh conditions are required, the raw materials are readily available, the key parameters can be precisely controlled, the repeatability is good, it can achieve large-scale production, reduce production costs, and has good prospects for industrial application. Attached Figure Description

[0016] Figure 1 The rejection rate of the nanofiltration membrane prepared in Example 1 of the present invention for different solutions is shown in the figure. Figure 2 The attenuation rate diagram is shown for the nanofiltration membrane prepared in Example 1 of the present invention after soaking for different times. Detailed Implementation

[0017] The principles and features of the present invention are described below with reference to examples. The examples are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0018] Example 1 A method for preparing a highly selective acid-resistant nanofiltration membrane includes the following steps: (1) The polysulfone membrane was immersed in an aqueous solution containing 0.1 wt% hydrogen peroxide and 2 wt% sodium chloride for 30 minutes; (2) Immerse the membrane treated in step (1) in a hexane solution containing 3 wt% pyrrole and let it stand for 1 hour; (3) Spray a mixed ethanol solution containing 35 wt% resorcinol and 25 wt% formaldehyde onto the membrane treated in step (2); (4) The membrane after step (3) is placed in a hot sodium hydroxide solution (10 wt%, 70 °C) containing 0.02 wt% decyl glucoside for 3 hours to obtain the highly selective acid-resistant nanofiltration membrane.

[0019] Example 2 A method for preparing a highly selective acid-resistant nanofiltration membrane includes the following steps: (1) The polysulfone membrane was immersed in an aqueous solution containing 6 wt% ferric chloride and 0.05 wt% lithium chloride for 2 hours; (2) Immerse the membrane treated in step (1) in a hexane solution containing 1 wt% 3-methoxypyrrole and let it stand for 1 hour; (3) Spray a mixed ethanol solution containing 18 wt% phenol and 45 wt% formaldehyde onto the membrane treated in step (2); (4) The membrane after step (3) is placed in a hot sodium hydroxide solution (5 wt%, 75°C) containing 2 wt% sodium dodecyl diphenyl ether disulfonate for 5 hours to obtain the highly selective acid-resistant nanofiltration membrane.

[0020] Example 3 A method for preparing a highly selective acid-resistant nanofiltration membrane includes the following steps: (1) The polysulfone membrane was immersed in an aqueous solution containing 4 wt% ammonium persulfate, 1 wt% ferric chloride and 1 wt% potassium chloride for 30 minutes; (2) Immerse the membrane treated in step (1) in a hexane solution containing 0.01 wt% N-methylpyrrole and let it stand for 2 minutes; (3) Spray a mixed ethanol solution containing 25 wt% cashew phenol and 25 wt% formaldehyde onto the membrane treated in step (2); (4) The membrane after step (3) is placed in a hot sodium hydroxide solution (0.5 wt%, 50°C) containing 0.1 wt% dodecyl dimethylamine oxide and 1.2 wt% isooctyl phosphate and post-treated for 2 hours to obtain the highly selective acid-resistant nanofiltration membrane.

[0021] Example 4 A method for preparing a highly selective acid-resistant nanofiltration membrane includes the following steps: (1) The polysulfone membrane was immersed in an aqueous solution containing 3 wt% ammonium persulfate, 0.5 wt% magnesium chloride, and 1 wt% potassium chloride for 50 minutes; (2) Immerse the membrane treated in step (1) in a hexane solution containing 0.5 wt% 3-hexylpyrrole and 0.01 wt% N-methylpyrrole, and let it stand for 40 minutes; (3) Spray a mixed ethanol solution containing 15 wt% phenol and 30 wt% formaldehyde onto the membrane treated in step (2); (4) The membrane after step (3) is placed in a hot sodium hydroxide solution (1.5 wt%, 70°C) containing 0.8 wt% sodium dodecyl diphenyl ether disulfonate for 2 hours to obtain the highly selective acid-resistant nanofiltration membrane.

[0022] Example 5 A method for preparing a highly selective acid-resistant nanofiltration membrane includes the following steps: (1) The polysulfone membrane was immersed in an aqueous solution containing 5 wt% ammonium persulfate and 1.5 wt% sodium chloride for 1 hour; (2) Immerse the membrane treated in step (1) in a hexane solution containing 2.5 wt% 3-methoxypyrrole and 0.05 wt% pyrrole, and let it stand for 30 minutes; (3) Spray a mixed ethanol solution containing 15 wt% phenol, 15 wt% p-tert-butylphenol and 40 wt% formaldehyde onto the membrane treated in step (2); (4) The membrane after step (3) is placed in a hot sodium hydroxide solution (3 wt%, 75°C) containing 0.8 wt% sodium dodecyl diphenyl ether disulfonate and post-treated for 5 hours to obtain the highly selective acid-resistant nanofiltration membrane.

[0023] Example 6 A method for preparing a highly selective acid-resistant nanofiltration membrane includes the following steps: (1) The polysulfone membrane was immersed in an aqueous solution containing 3 wt% potassium persulfate and 0.1 wt% lithium chloride for 1.5 hours; (2) Immerse the membrane treated in step (1) in a hexane solution containing 2 wt% 3-methoxypyrrole and let it stand for 50 minutes; (3) Spray a mixed ethanol solution containing 25 wt% phenol and 40 wt% formaldehyde onto the membrane treated in step (2); (4) The membrane after step (3) is placed in a hot sodium hydroxide solution (2 wt%, 75°C) containing 1 wt% sodium dodecyl diphenyl ether disulfonate and 0.2 wt% isooctyl phosphate and post-treated for 2 hours to obtain the highly selective acid-resistant nanofiltration membrane.

[0024] Comparative Example 1 A method for preparing a nanofiltration membrane includes the following steps: (1) The polysulfone membrane was immersed in an aqueous solution containing 3 wt% potassium persulfate for 1.5 hours; (2) Immerse the membrane treated in step (1) in a hexane solution containing 2 wt% 3-methoxypyrrole and let it stand for 50 minutes; (3) Spray a mixed ethanol solution containing 25 wt% phenol and 40 wt% formaldehyde onto the membrane treated in step (2); (4) The membrane after step (3) is placed in a hot sodium hydroxide solution (2 wt%, 75°C) containing 1 wt% sodium dodecyl diphenyl ether disulfonate and 0.2 wt% isooctyl phosphate and post-treated for 2 hours to obtain the nanofiltration membrane.

[0025] Comparative Example 2 A method for preparing a nanofiltration membrane includes the following steps: (1) The polysulfone membrane was immersed in an aqueous solution containing 3 wt% potassium persulfate and 0.1 wt% lithium chloride for 1.5 hours; (2) Immerse the membrane treated in step (1) in a hexane solution containing 2 wt% 3-methoxypyrrole and let it stand for 50 minutes; (3) The membrane after step (2) is placed in a hot sodium hydroxide solution (2 wt%, 75°C) containing 1 wt% sodium dodecyl diphenyl ether disulfonate and 0.2 wt% isooctyl phosphate and post-treated for 2 hours to obtain the nanofiltration membrane.

[0026] Comparative Example 3 A method for preparing a nanofiltration membrane includes the following steps: (1) The polysulfone membrane was immersed in an aqueous solution containing 3 wt% potassium persulfate and 0.1 wt% lithium chloride for 1.5 hours; (2) Immerse the membrane treated in step (1) in a hexane solution containing 2 wt% 3-methoxypyrrole and let it stand for 50 minutes; (3) Spray a mixed ethanol solution containing 25 wt% phenol and 40 wt% formaldehyde onto the membrane treated in step (2); (4) The membrane after step (3) is placed in a sodium hydroxide solution (2 wt%, 25°C) containing 1 wt% sodium dodecyl diphenyl ether disulfonate and 0.2 wt% isooctyl phosphate and post-treated for 2 hours to obtain the nanofiltration membrane.

[0027] The nanofiltration membranes prepared in each embodiment and comparative example were tested using the following methods: 1. Retention rate test: The retention rate was tested using a cross-flow flat sheet membrane evaluation device; the test conditions were 1.0 MPa, 25℃, and the feed solutions were Na2SO4 and NaCl solutions, both with a concentration of 2000 ppm.

[0028] In addition, the nanofiltration membrane prepared in Example 1 was further tested for the rejection rates of MgCl2, LiCl, and KCl solutions as feed solutions, with a concentration of 2000 ppm for each solution. The test results are as follows. Figure 1 As shown.

[0029] 2. Selectivity coefficient α: Calculated using the formula α = (1 - NaCl rejection rate) / (1 - Na2SO4 rejection rate); 3. Retention rate decay rate test: The membrane was immersed in a 15 wt% sulfuric acid solution for 30 days. Its acid resistance was evaluated by the decay rate of Na2SO4 retention rate. The decay rate = (initial Na2SO4 retention rate - Na2SO4 retention rate after immersion) / initial Na2SO4 retention rate.

[0030] In addition, the soaking time of the nanofiltration membrane prepared in Example 1 was extended to 60 days, and the decay rate of Na2SO4 rejection was tested. The results are as follows: Figure 2 As shown.

[0031] The test results for each embodiment and comparative example are shown in Table 1.

[0032] Table 1 Test Results

[0033] As can be seen from the data in Table 1, the high-selectivity acid-resistant nanofiltration membrane prepared by this invention has a rejection rate of over 93.7% for divalent salt Na2SO4, while the rejection rate for monovalent salt NaCl is around 5%, indicating that the high-selectivity acid-resistant nanofiltration membrane prepared by this invention has high selectivity. After being soaked in 15 wt% sulfuric acid solution for 30 days, the rejection rate of Na2SO4 decreased by 2-7.3%, indicating that the high-selectivity acid-resistant nanofiltration membrane prepared by this invention has excellent acid resistance.

[0034] from Figure 1 It can be seen that the nanofiltration membrane prepared in Example 1 has a rejection rate of more than 80% for divalent salts, while the rejection rate for monovalent salts is about 5%, indicating that the nanofiltration membrane of the present invention has high selectivity.

[0035] from Figure 2 It can be seen that the nanofiltration membrane prepared in Example 1, after being soaked in a 15 wt% sulfuric acid solution for 60 days, showed a decrease in the Na2SO4 rejection rate of less than 10%, indicating that the nanofiltration membrane of the present invention has excellent acid resistance.

[0036] As can be seen from the comparison of the examples and comparative examples in Table 1, the addition of metal chlorides can improve the selectivity of nanofiltration membranes for divalent and monovalent salts; the overall rejection rate and acid resistance of the membrane can be improved by spraying a mixed ethanol solution of phenol and formaldehyde and by increasing the temperature of the sodium hydroxide solution.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a highly selective acid-resistant nanofiltration membrane, characterized in that, Includes the following steps: (1) The polysulfone membrane is immersed in an aqueous solution containing a strong oxidant and a metal chloride; the strong oxidant is one or more of hydrogen peroxide, ammonium persulfate, potassium persulfate, and ferric chloride; the metal chloride is one or more of sodium chloride, potassium chloride, lithium chloride, and magnesium chloride. (2) Immerse the membrane treated in step (1) in a hexane solution containing pyrrole molecules and let it stand; (3) Spray a mixed ethanol solution of phenol and formaldehyde onto the membrane treated in step (2); (4) The membrane after step (3) is placed in a hot sodium hydroxide solution containing surfactant for post-treatment to obtain the highly selective acid-resistant nanofiltration membrane.

2. The method for preparing a highly selective acid-resistant nanofiltration membrane according to claim 1, characterized in that, The concentration of the strong oxidant is 0.1~6wt%.

3. The method for preparing a highly selective acid-resistant nanofiltration membrane according to claim 1, characterized in that, The concentration of the metal chloride is 0.05~2wt%.

4. The method for preparing a highly selective acid-resistant nanofiltration membrane according to claim 1, characterized in that, The pyrrole molecule is one or more of pyrrole, 3-hexylpyrrole, 3-methoxypyrrole, and N-methylpyrrole, with a concentration of 0.01~3wt%.

5. The method for preparing a highly selective acid-resistant nanofiltration membrane according to claim 1, characterized in that, The phenol is one or more of phenol, resorcinol, p-tert-butylphenol, and cashew phenol; in the ethanol mixture of phenol and formaldehyde, the concentration of phenol is 15-35 wt% and the concentration of formaldehyde is 25-45 wt%.

6. The method for preparing a highly selective acid-resistant nanofiltration membrane according to claim 1, characterized in that, The surfactant is one or more of sodium dodecyl diphenyl ether disulfonate, decyl glucoside, isooctyl phosphate, and dodecyl dimethylamine oxide, with a concentration of 0.02~2wt%.

7. The method for preparing a highly selective acid-resistant nanofiltration membrane according to claim 1, characterized in that, The hot sodium hydroxide solution has a temperature of 50~75℃ and a concentration of 0.5~10wt%.

8. The method for preparing a highly selective acid-resistant nanofiltration membrane according to claim 1, characterized in that, In step (1), the soaking time is 30 min to 2 h; in step (2), the standing time is 2 min to 1 h; in step (4), the post-treatment time is 2 to 5 h.

9. A highly selective acid-resistant nanofiltration membrane, characterized in that, Prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the highly selective acid-resistant nanofiltration membrane as described in claim 9 in the desalination treatment of acidic industrial wastewater.

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