Acid-resistant and anti-pollution composite nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention provides an acid-resistant and anti-pollution composite nanofiltration membrane as well as a preparation method and application thereof, and relates to the technical field of membrane materials. The preparation method comprises the following steps: soaking the surface of a support membrane with a mixed solution I; the mixed solution I is prepared from doxycycline, 4-aminopyridine and deionized water; pouring an oil phase solution into the surface of the soaked support membrane to carry out interfacial polymerization reaction; the oil phase solution is composed of 1, 3-benzene disulfonyl chloride and cyclohexane; and carrying out heat treatment on the support membrane after the interfacial polymerization reaction to obtain the acid-resistant anti-pollution composite nanofiltration membrane. According to the prepared composite nanofiltration membrane, doxycycline is selected as a water-phase monomer for the first time, meanwhile, 1, 3-benzene disulfonyl chloride is selected as an oil-phase monomer, 4-aminopyridine is selected as an additive, and the prepared composite nanofiltration membrane not only has acid resistance and pollution resistance, but also has high permeation flux and high separation performance.

Description

Technical Field

[0001] This application relates to the field of membrane materials technology, specifically to an acid-resistant and anti-fouling composite nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] Membrane separation technology is a simple, fast, efficient, selective, economical, and energy-saving new technology that is currently widely used in many fields such as water treatment, hydrometallurgy, biochemical industry, pharmaceutical industry, food industry, and environmental protection.

[0003] Nanofiltration membranes are a membrane separation technology between ultrafiltration and reverse osmosis membranes, widely used in water treatment, environmental protection, and biomedicine. With the increasing discharge of acidic industrial wastewater and the growing severity of water scarcity, nanofiltration technology, with its high efficiency and energy saving, has significant advantages in treating high-concentration brine. However, its application in treating acidic wastewater remains limited, primarily due to the limited acid resistance and fouling resistance of nanofiltration membranes. Furthermore, current acid-resistant nanofiltration membranes on the market suffer from low flux and inability to be used in strongly polar solvents. Moreover, there are currently no commercially available acid-resistant and fouling-resistant nanofiltration membranes in China; most are still in the laboratory stage. Today's acid-resistant and fouling-resistant nanofiltration membranes face challenges such as poor material solvent resistance, high price, low flux, and susceptibility to fouling.

[0004] Therefore, there is an urgent need to develop a nanofiltration membrane with high flux, excellent acid resistance and antifouling performance to meet the needs of acidic wastewater resource treatment. Summary of the Invention

[0005] To address one of the aforementioned technical deficiencies, this application provides an acid-resistant and anti-fouling composite nanofiltration membrane, its preparation method, and its application.

[0006] According to the first aspect of this application, a method for preparing an acid-resistant and antifouling composite nanofiltration membrane is provided, comprising the following steps: Preparation of support membrane; The surface of the supporting membrane is immersed in a mixed solution I, which consists of doxycycline, 4-aminopyridine, and deionized water. An oil phase solution was poured onto the surface of the soaked support membrane to carry out an interfacial polymerization reaction; the oil phase solution consisted of 1,3-benzenedisulfonyl chloride and cyclohexane. The support membrane after the interfacial polymerization reaction was subjected to heat treatment to obtain an acid-resistant and fouling-resistant composite nanofiltration membrane.

[0007] Preferably, the mass ratio of doxycycline to 4-aminopyridine in the mixed solution I is 10:1 to 20:1; the mass concentration of doxycycline in the mixed solution I is 0.1% to 5%; and the mass concentration of 4-aminopyridine in the mixed solution I is 1% to 10%.

[0008] Preferably, the oil phase solution has a mass-to-volume ratio of 0.1% to 5%.

[0009] Preferably, the soaking time is 2-30 min, the reaction time of the interfacial polymerization reaction is 1-30 min, and the heat treatment time is 1 min.

[0010] Preferably, the preparation of the support membrane specifically includes the following steps: mixing polyetherimide, polytetrafluoroethylene, and an organic solvent to obtain a mixed solution II; stirring mixed solution II at 60°C for 4-10 hours, allowing it to stand and cool, and then degassing for 3-24 hours to obtain a casting solution; uniformly coating the casting solution onto a nonwoven fabric, and then immediately immersing the nonwoven fabric coated with the casting solution in water at 25°C for 0.5-1 hour, then removing the soaked nonwoven fabric coated with the casting solution and refrigerating it; washing the refrigerated nonwoven fabric coated with the casting solution with deionized water 2-4 times to obtain the support membrane.

[0011] Preferably, the mass concentration of polyetherimide in the mixed solution II is 1% to 25%, and the mass concentration of polytetrafluoroethylene is 0.1% to 10%.

[0012] Preferably, the organic solvent is a mixture of N,N-dimethylacetamide and kerosene, and the volume ratio of N,N-dimethylacetamide to kerosene is 10:1.

[0013] Preferably, the thickness of the casting solution coated on the nonwoven fabric is 100~250µm, and the nonwoven fabric coated with the casting solution is immersed in water for 0.5~1h.

[0014] According to a second aspect of this application, an acid-resistant and anti-fouling composite nanofiltration membrane is provided, which is prepared by the preparation method of the acid-resistant and anti-fouling composite nanofiltration membrane as described in any of the preceding claims.

[0015] According to a third aspect of this application, the application of the acid-resistant and anti-fouling composite nanofiltration membrane as described above in the treatment of acidic wastewater is provided.

[0016] The beneficial effects of this application are as follows: This application provides a method for preparing an acid-resistant and antifouling composite nanofiltration membrane. For the first time, doxycycline is selected as the aqueous phase monomer, 1,3-benzenedisulfonyl chloride as the oil phase monomer, and 4-aminopyridine as an additive. The method involves interfacial polymerization of the amino and phenolic hydroxyl groups of doxycycline with 1,3-benzenedisulfonyl chloride to prepare an acid-resistant and antifouling interfacial polymer layer. This results in a composite nanofiltration membrane with high acid and antifouling resistance, as well as high permeate flux and high separation performance. Doxycycline, as an antibiotic, effectively prevents bacterial growth, and its amino and phenolic hydroxyl groups can serve as potential antifouling membrane materials that can undergo interfacial polymerization with substances such as acyl chlorides. Furthermore, 1,3-benzenedisulfonyl chloride, as a material for preparing the composite membrane, exhibits better acid resistance compared to currently available trimesoyl chloride. The sulfonyl chloride group (-SO2Cl) of 1,3-benzenedisulfonyl chloride undergoes an interfacial reaction to form a sulfonamide bond (-SO2-N-), which exhibits excellent chemical inertness in acidic environments and is difficult to be hydrolyzed by proton attack. Compared to the amide bond (-CO-NH-) of existing polyamide films on the market, the sulfonamide bond significantly enhances resistance to strong acids, maintaining the structural integrity of the material. The benzene ring on 1,3-benzenedisulfonyl chloride acts as a rigid framework, protecting the sulfonamide bond through steric hindrance, inhibiting acid molecules from contacting active sites, and the sulfonyl chloride group in its molecular structure is located in the meta position (1,3-position), reducing molecular polarity and further reducing the risk of acid corrosion. 1,3-benzenedisulfonyl chloride forms a three-dimensional cross-linked network of polyamide-polyarylate with doxycycline, and its hydrophobic barrier effectively blocks the penetration of hydrated hydrogen ions. 4-Aminopyridine, as an additive in the reaction of doxycycline and 1,3-benzenedisulfonyl chloride, neutralizes H+ in the product. + This process promotes the forward reaction of interfacial polymerization while preventing the protonation of doxycycline groups. By controlling the dissociation state of doxycycline, the interfacial polymerization rate can be influenced, thereby preparing a high-throughput, high-rejection-rate composite membrane. Furthermore, during the heat treatment stage, vacuuming can promptly remove small molecule products such as HCl generated in the interfacial polymerization reaction, disrupting the reversible condensation equilibrium and further improving reaction efficiency.

[0017] Other features and advantages of this application will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of what is pointed out in the written description, claims, and drawings. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1Infrared spectra of the supporting membrane, the acid-resistant and anti-fouling composite nanofiltration membrane, and the composite nanofiltration membrane without doxycycline provided in the embodiments of this application, wherein a is the supporting membrane, b is the composite nanofiltration membrane without doxycycline, and c is the acid-resistant and anti-fouling composite nanofiltration membrane; Figure 2 The image shows an SEM image of the acid-resistant and anti-fouling composite nanofiltration membrane provided in Embodiment 4 of this application. In the image, A is a surface view of the composite nanofiltration membrane, B is a cross-sectional view of the composite nanofiltration membrane at 1000x magnification, and C is a cross-sectional view of the interfacial polymer layer at 20000x magnification. Figure 3 for Figure 2 Another angle view of C. Detailed Implementation

[0019] In the process of developing this application, the applicant discovered that nanofiltration membrane technology has great advantages in treating high-concentration brine due to its high efficiency and energy saving characteristics, but its application in treating acidic wastewater is still limited. The main challenge lies in the limited acid resistance and antifouling properties of nanofiltration membranes.

[0020] To address the aforementioned problems, this application provides an acid-resistant and anti-fouling composite nanofiltration membrane, its preparation method, and its applications. To make the objectives, technical solutions, and advantages of this application clearer, the following examples, in conjunction with the accompanying drawings, illustrate these points. Figure 1-3 The embodiments of this application will be further described in detail below. It should be understood that the specific embodiments described herein are only for explaining this application and are not intended to limit this application.

[0021] Unless otherwise specified, the reagents and materials used in the examples are commercially available; the test methods used in the following examples are conventional methods in the art.

[0022] The amount of raw materials added and the reaction conditions in Examples 1 to 5 are shown in Table 1 below.

[0023] The preparation method of the acid-resistant and antifouling composite nanofiltration membrane in Examples 1 to 5 of this application includes the following steps: S10. Prepare the support membrane, specifically including the following steps: S101. First, polyetherimide is added to a mixture of N,N-dimethylacetamide and kerosene in a volume ratio of 10:1 to obtain a polyetherimide solution. Then, polytetrafluoroethylene is added to the polyetherimide solution to obtain mixed solution II. The mass concentration of polyetherimide in mixed solution II is 1%~25%, and the mass concentration of polytetrafluoroethylene is 0.1%~10%. S102. Place mixed solution II in a water bath and stir at a constant temperature of 60°C for 4-10 hours. After standing and cooling, place it in a desiccator to remove bubbles for 3-24 hours to obtain the casting solution. S103. Apply the casting solution evenly to the polypropylene nonwoven fabric fixed on the glass plate using a stainless steel doctor blade, controlling the distance between the blade of the stainless steel doctor blade and the polypropylene nonwoven fabric to be 100~250µm. Then, immediately immerse the polypropylene nonwoven fabric coated with the casting solution in water at 25℃ for 0.5~1h. After that, remove the nonwoven fabric coated with the casting solution and refrigerate it. Specifically, the thickness of the casting solution coated on the nonwoven fabric is 100~250µm, and the nonwoven fabric coated with the casting solution is immersed in water for 1~10h. The nonwoven fabric coated with casting solution after refrigeration is washed with deionized water 2-4 times to obtain the support membrane.

[0024] S20. Fix the support membrane to the plate frame, then pour the mixed solution I onto the surface of the support membrane, soak for 2-30 minutes, pour out the excess mixed solution I, and wipe the surface moisture of the support membrane with filter paper; the mixed solution I is composed of doxycycline, 4-aminopyridine and deionized water, the mass concentration of doxycycline in the mixed solution I is 0.1%-5%, the mass concentration of 4-aminopyridine in the mixed solution I is 1%-10%; the mass ratio of doxycycline to 4-aminopyridine in the mixed solution I is 10:1-20:1; S30. Pour the oil phase solution onto the surface of the dried support membrane for interfacial polymerization reaction. The reaction time is 1~30 min. After the reaction is completed, pour off the excess oil phase solution from the surface of the support membrane. The oil phase solution is composed of 1,3-benzenedisulfonyl chloride and cyclohexane, and the mass-to-volume ratio of the oil phase solution is 0.1%~5% (i.e., the ratio between the mass of 1,3-benzenedisulfonyl chloride and the volume of cyclohexane is 0.1%~5%). The plate frame is made of polytetrafluoroethylene. S40. Place the support membrane after the interfacial polymerization reaction into a microwave vacuum dryer and adjust the vacuum pump until the vacuum gauge reading reaches -0.1 MPa. Heat-treat for 1 minute, remove it, and wash the surface of the heat-treated composite membrane with deionized water to obtain an acid-resistant and anti-fouling composite nanofiltration membrane. Then, refrigerate the obtained acid-resistant and anti-fouling composite nanofiltration membrane.

[0025] This application provides a method for preparing an acid-resistant and antifouling composite nanofiltration membrane. For the first time, doxycycline is selected as the aqueous phase monomer, 1,3-benzenedisulfonyl chloride as the oil phase monomer, and 4-aminopyridine as an additive. The method involves interfacial polymerization of the amino and phenolic hydroxyl groups of doxycycline with 1,3-benzenedisulfonyl chloride to prepare an acid-resistant and antifouling interfacial polymer layer. This results in a composite nanofiltration membrane with high acid and antifouling resistance, as well as high permeate flux and high separation performance. Doxycycline, as an antibiotic, effectively prevents bacterial growth, and its amino and phenolic hydroxyl groups can serve as potential antifouling membrane materials that can undergo interfacial polymerization with substances such as acyl chlorides. Furthermore, 1,3-benzenedisulfonyl chloride, as a material for preparing the composite membrane, exhibits better acid resistance compared to currently available trimesoyl chloride. The sulfonyl chloride group (-SO2Cl) of 1,3-benzenedisulfonyl chloride undergoes an interfacial reaction to form a sulfonamide bond (-SO2-N-), which exhibits excellent chemical inertness in acidic environments and is difficult to be hydrolyzed by proton attack. Compared to the amide bond (-CO-NH-) of existing polyamide films on the market, the sulfonamide bond significantly enhances resistance to strong acids, maintaining the structural integrity of the material. The benzene ring on 1,3-benzenedisulfonyl chloride acts as a rigid framework, protecting the sulfonamide bond through steric hindrance, inhibiting acid molecules from contacting active sites, and the sulfonyl chloride group in its molecular structure is located in the meta position (1,3-position), reducing molecular polarity and further reducing the risk of acid corrosion. 1,3-benzenedisulfonyl chloride forms a three-dimensional cross-linked network of polyamide-polyarylate with doxycycline, and its hydrophobic barrier effectively blocks the penetration of hydrated hydrogen ions. 4-Aminopyridine, as an additive in the reaction of doxycycline and 1,3-benzenedisulfonyl chloride, neutralizes H+ in the product. + This process promotes the forward reaction of interfacial polymerization while preventing the protonation of doxycycline groups. By controlling the dissociation state of doxycycline, the interfacial polymerization rate can be influenced, thereby preparing a high-throughput, high-rejection-rate composite membrane. Furthermore, during the heat treatment stage, vacuuming can promptly remove small molecule products such as HCl generated in the interfacial polymerization reaction, disrupting the reversible condensation equilibrium and further improving reaction efficiency.

[0026] Specifically, the microwave vacuum dryer is a power box-type intelligent hot air flat microwave vacuum dryer with a power of 2500W and a temperature of 100℃.

[0027] More specifically, in step S103, the casting solution is uniformly coated onto the polypropylene nonwoven fabric fixed on the glass plate using a stainless steel scraper in a constant temperature chamber at 25°C.

[0028]

[0029] To demonstrate the beneficial effects of the acid-resistant and anti-fouling composite nanofiltration membrane prepared using the preparation method of this application, relevant tests were conducted on the acid-resistant and anti-fouling composite nanofiltration membranes prepared in Examples 1 to 5.

[0030] This application used infrared spectroscopy to characterize the supported membrane, the acid-resistant and antifouling composite nanofiltration membrane, and the composite nanofiltration membrane without doxycycline prepared in Example 4 (the remaining conditions for preparing the composite nanofiltration membrane were the same as in Example 4). Figure 1 As shown. By Figure 1 It can be seen that the composite nanofiltration membrane with added doxycycline at 3400 cm⁻¹... -1 The increased peak value and intensity of hydroxyl groups at 1540 cm⁻¹ indicate that the composite nanofiltration membrane introduces more hydroxyl groups. Furthermore, at 1540 cm⁻¹... -1 and 1230cm -1 The new peak originates from the amide bond, at 1052 cm⁻¹. -1 The new peaks that appeared came from the ester bonds, further proving that the reaction of 1,3-benzenesulfonyl chloride with the amine and phenolic hydroxyl groups in doxycycline produced the structure of polyamide-polyarylate.

[0031] This application characterized the composite nanofiltration membrane prepared in Example 4 using scanning electron microscopy (SEM), such as... Figure 2 and Figure 3 As shown. By Figure 2 and Figure 3 It can be seen that the surface of the composite nanofiltration membrane belongs to the typical structure of composite membrane materials. This is due to the Bénard convection that occurs during the interfacial polymerization process. That is, during interfacial polymerization, 4-aminopyridine and doxycycline in the aqueous phase migrate to the cyclohexane system of 1,3-benzenedisulfonyl chloride in the oil phase, and polymerization occurs at the interface, thus forming a relatively smooth skin. At the same time, the cross-sectional diagram shows that the prepared composite nanofiltration membrane has an asymmetric membrane structure and a large number of finger-like pores.

[0032] This application also tested the water flux, acid resistance, and antifouling properties of the acid-resistant and antifouling composite nanofiltration membranes prepared in Examples 1 to 5. Specifically, the acid-resistant and antifouling composite nanofiltration membranes prepared in Examples 1 to 5 were placed in a sodium sulfate solution with a pH of 2 (the pH of the sodium sulfate solution was adjusted with citric acid), and the retention performance of each composite nanofiltration membrane was then tested. The acid-resistant and antifouling composite nanofiltration membranes prepared in Examples 1 to 5 were then fouled using a bovine serum albumin solution with a mass concentration of 1 g / L (i.e., each acid-resistant and antifouling composite nanofiltration membrane was immersed in the bovine serum albumin solution for 48 hours), and the water flux of each fouled acid-resistant and antifouling composite nanofiltration membrane was tested. The results are shown in Table 2.

[0033]

[0034] As shown in Table 2, the acid-resistant and antifouling composite nanofiltration membrane prepared in this application exhibits good retention rate after immersion in a sodium sulfate solution (pH=2) treated with citric acid, indicating that the acid-resistant composite nanofiltration membrane prepared in this application has good acid resistance. The acid-resistant and antifouling composite nanofiltration membrane prepared in this application also exhibits good water flux before and after the use of bovine serum albumin, proving that the acid-resistant and antifouling composite nanofiltration membrane prepared in this application has good antifouling properties. Furthermore, since the doxycycline mass concentration in Example 1 is relatively low at 0.1%, the sodium sulfate retention rate is relatively low. In contrast, the doxycycline mass concentrations in the other examples are all higher than those in Example 1, resulting in higher sodium sulfate retention rates in the other examples. Therefore, doxycycline can effectively improve the acid resistance of the membrane.

[0035] In summary, the acid-resistant and antifouling composite nanofiltration membrane prepared in this application has the following effects: 1. For the first time, doxycycline was selected as the aqueous phase monomer. The prepared acid-resistant and antifouling composite nanofiltration membrane has good acid resistance, high permeation flux and high separation performance, and is suitable for the treatment of acidic wastewater. 2. Adding polytetrafluoroethylene during the preparation of the above-mentioned composite nanofiltration membrane can increase the antifouling properties of the supporting membrane and form a porous structure within the supporting membrane, thereby significantly improving the membrane flux. 3. 1,3-Benzenedisulfonyl chloride was used for the first time to prepare an acid-resistant polyester polyamide composite nanofiltration membrane. After the sulfonyl chloride group (-SO2Cl) of 1,3-Benzenedisulfonyl chloride undergoes an interfacial reaction, a sulfonamide bond (-SO2-N-) is formed. This bond exhibits excellent chemical inertness in acidic environments and is difficult to be hydrolyzed by proton attack, thereby improving the acid resistance of the acid-resistant and antifouling composite nanofiltration membrane.

[0036] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0037] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing an acid-resistant and anti-fouling composite nanofiltration membrane, characterized in that, The method comprises the following steps: preparing a support membrane; immersing the surface of the support membrane in a mixed solution I; the mixed solution I is composed of doxycycline, 4-aminopyridine and deionized water; pouring an oil phase solution onto the surface of the immersed support membrane to perform an interfacial polymerization reaction; the oil phase solution is composed of 1,3-benzenedisulfonyl chloride and cyclohexane; performing heat treatment on the support membrane after the interfacial polymerization reaction to obtain an acid-resistant and anti-pollution composite nanofiltration membrane.

2. The method for preparing the acid-resistant and anti-fouling composite nanofiltration membrane according to claim 1, characterized in that, The mass ratio of doxycycline to 4-aminopyridine in the mixed solution I is 10:1-20:1; The mass concentration of doxycycline in the mixed solution I is 0.1%-5%; The mass concentration of 4-aminopyridine in the mixed solution I is 1%-10%.

3. The method for preparing the acid-resistant and anti-fouling composite nanofiltration membrane according to claim 1, characterized in that, The mass-volume ratio of the oil phase solution is 0.1%-5%.

4. The method for preparing the acid-resistant and anti-fouling composite nanofiltration membrane according to claim 1, characterized in that, The immersion time is 2-30 min, the reaction time of the interfacial polymerization reaction is 1-30 min, and the heat treatment time is 1 min.

5. The method for preparing the acid-resistant and anti-fouling composite nanofiltration membrane according to claim 1, characterized in that, The preparation of the support membrane specifically comprises the following steps: mixing polyetherimide, polytetrafluoroethylene and an organic solvent to obtain a mixed solution II; stirring the mixed solution II at 60°C for 4-10 h, and after standing and cooling, performing defoaming treatment for 3-24 h to obtain a casting solution; uniformly coating the casting solution onto a non-woven fabric, then immediately placing the non-woven fabric coated with the casting solution into water at 25°C, immersing for 0.5-1 h, then taking out the immersed non-woven fabric coated with the casting solution and performing cold storage; washing the cold-stored non-woven fabric coated with the casting solution with deionized water for 2-4 times to obtain the support membrane.

6. The method for preparing the acid-resistant and anti-fouling composite nanofiltration membrane according to claim 5, characterized in that, The mass concentration of polyetherimide in the mixed solution II is 1%-25%, and the mass concentration of polytetrafluoroethylene is 0.1%-10%.

7. The method for preparing the acid-resistant and anti-fouling composite nanofiltration membrane according to claim 5, characterized in that, The organic solvent is a mixture of N,N-dimethylacetamide and kerosene, and the volume ratio of N,N-dimethylacetamide to kerosene is 10:

1.

8. The method for preparing the acid-resistant and anti-fouling composite nanofiltration membrane according to claim 5, characterized in that, The thickness of the casting solution coated onto the non-woven fabric is 100-250 µm, and the time for placing the non-woven fabric coated with the casting solution into water is 0.5-1 h.

9. An acid-resistant and anti-fouling composite nanofiltration membrane, characterized in that, The acid-resistant and anti-pollution composite nanofiltration membrane is prepared by the method for preparing the acid-resistant and anti-pollution composite nanofiltration membrane according to any one of claims 1-8.

10. The acid-resistant and anti-pollution composite nanofiltration membrane according to claim 9 is applied to the treatment of acid wastewater.

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