Method for preparing nanofiltration membrane by using sodium p-styrenesulfonate as aqueous phase additive

Abstract

The invention relates to a method for preparing a nanofiltration membrane by using sodium p-styrenesulfonate as a water phase additive. Infiltrating the support membrane in a water phase solution containing sodium p-styrenesulfonate and piperazine so that the support membrane is fully infiltrated by the water phase solution; coating the surface of the membrane with the oil-phase solution, and carrying out interfacial polymerization reaction to form an aromatic polyamide separation layer; and placing the membrane in an oven at 70-90 DEG C for heat treatment to prepare the aromatic polyamide composite nanofiltration membrane. Sodium p-styrenesulfonate can reduce the interfacial tension of a water / oil phase in the interfacial polymerization process, promote diffusion and uniform distribution of piperazine, strengthen the interfacial polymerization reaction and improve the cross-linking degree of a separation layer. The aromatic polyamide composite nanofiltration membrane prepared by the method has the characteristics of high flux and high selectivity at the same time. The method has the advantages of being simple in preparation process, low in cost and easy to implement. In addition, reference can be provided for preparation of other high-performance interfacial polymerization nanofiltration membranes.

Description

A method for preparing nanofiltration membranes using sodium styrene sulfonate as an aqueous phase additive. Technical Field

[0001] This invention relates to a method for preparing nanofiltration membranes using sodium styrene sulfonate as an aqueous phase additive, belonging to the field of composite nanofiltration membrane preparation. Background Technology

[0002] Nanofiltration is a membrane separation process that falls between ultrafiltration and reverse osmosis. It offers advantages such as low operating pressure, high separation efficiency, and simple operation, and is widely used in seawater desalination, drinking water purification, and wastewater treatment in the dyeing and printing industry. Currently, nanofiltration membranes are often limited by the "trade-off" effect, meaning that increasing the water flux tends to decrease the rejection rate, and vice versa. High permeate flux helps reduce process energy consumption and equipment investment, while high rejection rate helps improve process efficiency and product water quality. Therefore, designing a nanofiltration membrane that combines high permeate flux and high selectivity is crucial.

[0003] The current mainstream nanofiltration membrane is a polyamide composite nanofiltration membrane prepared by interfacial polymerization, which contains a three-layer structure: a nonwoven fabric layer, a porous support layer, and a polyamide separation layer. It is generally believed that the polyamide separation layer is the key component determining the separation performance of the nanofiltration membrane and contributes the majority of the mass transfer resistance. Therefore, optimizing the structure of the polyamide separation layer is a current research hotspot. Introducing surfactants into the water / oil phase is a commonly used method for optimizing the separation layer structure. This method is simple to operate and effective. Surfactants are commonly used additives that can not only regulate the interfacial tension between the aqueous and organic phases during interfacial polymerization but also regulate the formation of nanopores within the polyamide layer. However, some polyamide composite nanofiltration membranes prepared with traditional surfactants face the problem that improving salt rejection often reduces water flux due to increased separation layer thickness, decreased average pore size, or increased polyamide layer crosslinking. Sarkar et al. prepared polyamide nanofilm composite nanofiltration membranes by adding sodium dodecyl sulfate as a surfactant to an aqueous solution. The Na2SO4 rejection rate increased from 98.94 ± 0.37% to 99.96 ± 0.03%, while the pure water permeability increased from 21.1 ± 0.6 L∙m 2 ∙h -1 ∙bar -1 Decreased to 12.4 ± 0.8 L∙m -2 ∙h -1 ∙bar -1(P. Sarkar, S. Modak, S. Karan, Ultraselective and Highly Permeable Polyamide Nanofilms for Ionic and Molecular Nanofiltration, Adv. Funct. Mater. 31(3) (2021) 2007054.). Some researchers have attempted to simultaneously improve water flux and rejection rate by changing the type of surfactant. Jia et al. used sodium dodecyl sulfate and dodecyl phosphate as surfactants in the aqueous / oil phases, respectively, to regulate the flux for Li + / Mg 2+ The separated nanofiltration membrane, SIAIP-DDP membrane prepared by interfacial polymerization, showed a MgCl2 rejection rate of 98.36% and a LiCl rejection rate of 42.07%, with a pure water permeability of 15.62 L∙m. -2 ∙h -1 ∙bar -1 Decreased to 6.53 L∙m -2 ∙h -1 ∙bar -1 (R. Jia, + / Mg 2+ (Separation efficiency, J.Membr. Sci. 712 (2024) 123235.). Therefore, it remains challenging to prepare nanofiltration membranes that combine high permeation flux and high selectivity. Summary of the Invention

[0004] To prepare nanofiltration membranes with both high permeation flux and high selectivity, we conducted research and experiments, discovering a novel additive: sodium p-styrene sulfonate. Sodium p-styrene sulfonate is a surfactant containing hydrophilic groups and short hydrophobic chains. Its structural formula is shown below:

[0005]

[0006] The present invention aims to provide a method for preparing polyamide composite nanofiltration membranes with both high permeation flux and high selectivity using sodium styrene sulfonate as an aqueous phase additive. This method is simple, low-cost, easy to operate, and highly compatible with industrial membrane fabrication processes. The present invention is achieved through the following technical solution:

[0007] This invention relates to a method for preparing nanofiltration membranes based on interfacial polymerization using sodium p-styrene sulfonate as an aqueous phase additive, comprising the following steps:

[0008] 1) Immerse the support membrane in an aqueous solution containing sodium p-styrene sulfonate and piperazine to ensure that the support membrane is fully wetted by the aqueous solution;

[0009] 2) The oil phase solution is coated on the membrane surface to carry out an interfacial polymerization reaction to form an aromatic polyamide separation layer;

[0010] 3) The membrane was heat-treated in an oven at 70-90 ℃ to obtain an aromatic polyamide composite nanofiltration membrane.

[0011] The support membrane in step 1) is immersed in an aqueous solution containing sodium p-styrene sulfonate and piperazine for 20 to 40 seconds.

[0012] In step 1), the aqueous solution containing sodium p-styrene sulfonate and piperazine has a concentration of 0.005 ~ 0.02 g / mL for sodium p-styrene sulfonate and a concentration of 0.0025 ~ 0.0075 g / mL for piperazine.

[0013] The oil phase solution in step 2) is n-heptane containing trimesoyl chloride, wherein the concentration of trimesoyl chloride is 0.0005 ~ 0.0015 g / mL.

[0014] An oil-phase solution is coated onto the membrane surface for interfacial polymerization to form an aromatic polyamide separation layer structure as follows:

[0015]

[0016] The polymerization reaction time of the oil phase solution containing trimesoyl chloride in step 2) with the membrane surface is 20 to 40 seconds.

[0017] The aromatic polyamide composite nanofiltration membrane prepared in step 3) is washed with deionized water.

[0018] Compared with existing technologies, this invention uses sodium p-styrene sulfonate as a novel surfactant, which can effectively reduce the interfacial tension between the water / oil phase during interfacial polymerization, increase the wettability of the aqueous solution on the supporting membrane, promote the diffusion and uniform distribution of piperazine, form a uniform polyamide layer, and improve the membrane selectivity. Compared with traditional surfactants such as sodium dodecyl sulfate, sodium p-styrene sulfonate has a shorter hydrophobic chain and a higher critical micelle concentration, making it easier to incorporate into the polyamide layer without compromising membrane selectivity. Furthermore, the π-π conjugation between the benzene ring structure in the molecule and the polyamide also facilitates the incorporation of sodium p-styrene sulfonate, directly affecting the membrane structure and performance. Due to the presence of sulfonic acid groups in sodium p-styrene sulfonate, the negative charge and hydrophilicity of the membrane surface can be improved. Increased hydrophilicity helps improve the water flux of the membrane, while increased negative charge enhances the electrostatic repulsion against anions. Furthermore, the incorporation of sodium styrene sulfonate effectively increases the average pore size of the separation layer, enhances membrane permeability and selectivity, and breaks the "trade-off" effect, thus enabling the selective separation of monovalent and divalent anions (i.e., Cl-). - SO4 2- This provides promising strategies for extracting and recovering substances from high-salinity wastewater, as well as for removing sulfates from chlor-alkali salt solutions.

[0019] This invention offers advantages such as a simple preparation process, short operation time, ease of implementation, and low cost. Furthermore, the prepared polyamide composite nanofiltration membrane exhibits both high permeation flux and high selectivity. This invention is not only applicable to the preparation of polyamide composite nanofiltration membranes but also to the preparation of other high-performance interfacial polymerization separation membranes. Attached Figure Description

[0020] Figure 1 is a schematic diagram of nanofiltration membrane preparation by interfacial polymerization with sodium p-styrene sulfonate.

[0021] Figure 2 is a cross-sectional scanning electron microscope image of the polyamide composite nanofiltration membrane with added sodium p-styrene sulfonate prepared in Example 1.

[0022] Figure 3 is a cross-sectional scanning electron microscope image of the polyamide composite nanofiltration membrane with added sodium p-styrene sulfonate prepared in Example 2.

[0023] Figure 4 is a cross-sectional scanning electron microscope image of the polyamide composite nanofiltration membrane with added sodium p-styrene sulfonate prepared in Example 3. Detailed Implementation

[0024] Example 1

[0025] 1) Weigh 0.075 g piperazine and 0.15 g sodium p-styrene sulfonate and add them to 30 mL of deionized water. Pour the prepared aqueous solution onto the surface of the support membrane, ensuring that the aqueous solution only contacts the front side of the support membrane. After fully wetting for 20 seconds, pour off the excess aqueous solution.

[0026] 2) Weigh 0.015 g of pyromellitic acid chloride and add it to 30 mL of n-heptane. Pour the prepared oil phase solution onto the membrane surface and react for 20 s. Then remove the excess oil phase solution.

[0027] 3) The membrane was placed in a 70 ℃ oven for 4 min to obtain a polyamide composite nanofiltration membrane (10 cm × 14 cm) with added sodium p-styrene sulfonate, named SSS-0.5%. The specific membrane preparation steps are shown in Figure 1. Sodium p-styrene sulfonate and piperazine were introduced into the aqueous solution, and an interfacial polymerization reaction occurred on the surface of the supported membrane with n-heptane containing trimesoyl chloride. The introduction of sodium p-styrene sulfonate promoted the formation of a polyamide layer with uniform pore size and a larger average pore size, enriching the membrane surface with sulfonic acid groups, enhancing the hydrophilicity and negative charge of the membrane surface, and resulting in higher permeation flux and Cl-. - SO4 2- Selectivity.

[0028] Under conditions of 0.60 MPa and 25 ℃, the flux and rejection rate of SSS-0.5% in 2000 mg / L NaCl solution were 61.7 ± 0.1 L / (m 2 The flux and rejection rate in 2000 mg / L Na₂SO₄ solution were 56.8 ± 1.1 L / (m·h) and 25.99 ± 1.25%, respectively. 2 The average pore size of the separation layer was 0.50 nm, the geometric standard deviation was 1.28, and the cross-sectional SEM image is shown in Figure 2. The thickness of the separation layer was 133.92 ± 10.16 nm.

[0029] Example 2

[0030] 1) Weigh 0.150 g piperazine and 0.30 g sodium p-styrene sulfonate and add them to 30 mL of deionized water. Pour the prepared aqueous solution onto the surface of the support membrane, ensuring that the aqueous solution only contacts the front side of the support membrane. After fully wetting for 30 seconds, pour off the excess aqueous solution.

[0031] 2) Weigh 0.030 g of pyromellitic acid chloride and add it to 30 mL of n-heptane. Pour the prepared oil phase solution onto the membrane surface and react for 30 s. Then remove the excess oil phase solution.

[0032] 3) The membrane was placed in an 80 ℃ oven for 5 min to obtain a polyamide composite nanofiltration membrane (10 cm × 14 cm) with added sodium p-styrene sulfonate, named SSS-1.0%.

[0033] Under conditions of 0.60 MPa and 25 ℃, the flux and rejection rate of SSS-1.0% in 2000 mg / L NaCl solution were 62.9 ± 0.9 L / (m 2 The flux and rejection rate in 2000 mg / L Na₂SO₄ solution were 62.9 ± 2.3 L / (m·h) and 27.59 ± 0.39%, respectively. 2 The average pore size of the separation layer was 0.50 nm, the geometric standard deviation was 1.30, and the cross-sectional SEM image is shown in Figure 3. The thickness of the separation layer was 404.28 ± 55.50 nm.

[0034] Example 3

[0035] 1) Weigh 0.225 g piperazine and 0.60 g sodium p-styrene sulfonate and add them to 30 mL of deionized water. Pour the prepared aqueous solution onto the surface of the support membrane, ensuring that the aqueous solution only contacts the front side of the support membrane. After fully wetting for 40 seconds, pour off the excess aqueous solution.

[0036] 2) Weigh 0.045 g of pyromellitic acid chloride and add it to 30 mL of n-heptane. Pour the prepared oil phase solution onto the membrane surface and react for 40 s. Then remove the excess oil phase solution.

[0037] 3) The membrane was placed in a 90 ℃ oven for 6 min to obtain a polyamide composite nanofiltration membrane (10 cm × 14 cm) with added sodium p-styrene sulfonate, named SSS-2.0%.

[0038] Under conditions of 0.60 MPa and 25 ℃, the flux and rejection rate of SSS-2.0% in 2000 mg / L NaCl solution were 62.6 ± 0.8 L / (m 2 The flux and rejection rate in 2000 mg / L Na₂SO₄ solution were 58.7 ± 1.1 L / (m·h) and 29.26 ± 0.39%, respectively. 2 The average pore size of the separation layer was 0.49 nm, with a geometric standard deviation of 1.27. The cross-sectional SEM image is shown in Figure 4, and the thickness of the separation layer was 196.14 ± 12.24 nm.

[0039] Comparative Example

[0040] The performance of nanofiltration membranes prepared using sodium dodecyl sulfate as an aqueous phase additive was compared with that prepared using sodium p-styrene sulfonate as an aqueous phase additive. Under conditions of 0.60 MPa and 25 °C, the water flux of the composite nanofiltration membrane prepared with added sodium dodecyl sulfate was 36.1 L / (m²). 2 ·h), the sodium sulfate rejection rate was 96.04%, and the sodium chloride rejection rate was 27.80% (Y. Liu, X. Dong, M. Wang, S. Guo, H. Zhang, Z. Wang, Modulating interfacial polymerization via 1-methylimidazole as reactive additive for nanofiltration membrane with high-performance, Desalination 568 (2023)117021.). Compared with Example 2, it can be seen that the water flux of the nanofiltration membrane prepared using sodium styrene sulfonate as an aqueous phase additive is significantly improved, and the sodium sulfate rejection rate is slightly increased while the sodium chloride rejection rate is slightly decreased, i.e., Cl - SO4 2- Selectivity has improved. In summary, sodium p-styrene sulfonate is more advantageous as an aqueous phase additive than the traditional surfactant sodium dodecyl sulfate in the preparation of nanofiltration membranes with both high permeation flux and high selectivity.

[0041] Aromatic polyamide composite nanofiltration membranes were prepared by interfacial polymerization using sodium p-styrene sulfonate as a surfactant. A supporting membrane was immersed in an aqueous solution containing sodium p-styrene sulfonate and piperazine to ensure thorough wetting; then, it was immersed in an oil solution for interfacial polymerization. Sodium p-styrene sulfonate reduces the interfacial tension between the water and oil phases during polymerization, promotes the diffusion and uniform distribution of piperazine, enhances the interfacial polymerization reaction, and increases the crosslinking degree of the separation layer. Furthermore, this additive can be effectively introduced into the separation layer to increase its average pore size, and the sulfonic acid groups in the additive improve the membrane's hydrophilicity and charge-negativity. The aromatic polyamide composite nanofiltration membrane prepared by this method exhibits both high flux and high selectivity. The advantages of this invention are its simple preparation process, low cost, and ease of implementation. Moreover, this invention can also provide a reference for the preparation of other high-performance interfacial polymerization nanofiltration membranes.

[0042] This invention discloses a method for preparing composite nanofiltration membranes using sodium styrene sulfonate as an aqueous phase additive. Those skilled in the art can implement this method by appropriately modifying conditions and procedures, drawing upon the content of this document. Although the method and preparation technique of this invention have been described through preferred embodiments, those skilled in the art can clearly modify or recombine the methods and techniques described herein without departing from the content, spirit, and scope of this invention to achieve the final preparation technique. It is particularly important to note that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the spirit, scope, and content of this invention.

Claims

1. A method for preparing nanofiltration membranes using sodium p-styrene sulfonate as an aqueous phase additive, characterized in that, The process includes the following steps: 1) Immersing the supporting membrane in an aqueous solution containing sodium p-styrene sulfonate and piperazine to ensure that the supporting membrane is fully wetted by the aqueous solution; 2) Coating the membrane surface with an oil solution to carry out an interfacial polymerization reaction to form an aromatic polyamide separation layer; 3) Placing the membrane in an oven at 70~90℃ for heat treatment to obtain an aromatic polyamide composite nanofiltration membrane.

2. The method for preparing nanofiltration membranes using sodium p-styrene sulfonate as an aqueous phase additive as described in claim 1, characterized in that, The support membrane of step 1) is immersed in an aqueous solution containing sodium p-styrene sulfonate and piperazine for 20 to 40 seconds.

3. The method for preparing nanofiltration membranes using sodium p-styrene sulfonate as an aqueous phase additive as described in claim 1, characterized in that, In step 1), the aqueous solution containing sodium p-styrene sulfonate and piperazine has a concentration of 0.005~0.02 g / mL for sodium p-styrene sulfonate and a concentration of 0.0025~0.0075 g / mL for piperazine.

4. The method for preparing nanofiltration membranes using sodium p-styrene sulfonate as an aqueous phase additive as described in claim 1, characterized in that, The oil phase solution in step 2) is n-heptane containing trimesoyl chloride, wherein the concentration of trimesoyl chloride is 0.0005 ~ 0.0015 g / mL.

5. The method for preparing nanofiltration membranes using sodium p-styrene sulfonate as an aqueous phase additive as described in claim 1, characterized in that, The polymerization reaction time of the oil phase solution containing trimesoyl chloride in step 2) with the membrane surface is 20 to 40 seconds.

6. The method for preparing nanofiltration membranes using sodium p-styrene sulfonate as an aqueous phase additive as described in claim 1, characterized in that, The aromatic polyamide composite nanofiltration membrane prepared in step 3) is washed with deionized water.

Images