Method for preparing SPEEK / MS porous composite membrane by non-solvent induced phase separation and application thereof

Abstract

This invention discloses a method for preparing SPEEK / MS porous composite membranes using solvent-inducing phase separation and its application, belonging to the field of cation separation membranes. This invention incorporates mesoporous silica into post-sulfonated polyether ether ketone (SPEEK), significantly improving the separation performance of the prepared cation porous composite membrane. The method is simple and easy to operate, and less susceptible to interference from external factors; simultaneously, this method can obtain SPEEK / MS composite membranes with high separation performance even with a small amount of inorganic particles added: the hydroxide ion dialysis coefficient (U0.05) of the composite membrane is [missing information]. OH The flow rate was 0.0089–0.0139 m / h, and the separation coefficient (S) was 21.4–35.6.

Description

Technical Field

[0001] This invention relates to a method for preparing porous composite membranes with asymmetric membrane structures, specifically to a method for preparing SPEEK / MS porous composite membranes using non-solvent-induced phase separation and its application. Background Technology

[0002] With the increasing demands of modern industry for environmental protection and wastewater discharge, the treatment of large and continuous volumes of industrial wastewater has become a major concern. Traditional treatment methods, including neutralization, concentration, and incineration, are not only energy-intensive but also environmentally unfriendly. Membrane separation offers an environmentally friendly, low-energy-consumption, and easy-to-operate treatment method for industrial wastewater. Currently, researchers focus primarily on dense membranes, but there are fewer reports on the application of porous ion exchange membranes in diffusion dialysis. In comparison, the porous structure of porous ion exchange membranes provides ions with more free space, thereby reducing ion movement resistance and facilitating ion transport.

[0003] Because pure polymer membranes suffer from poor separation performance due to low sulfonation levels, their performance needs to be improved. Existing research indicates that mesoporous silica, with its unique structural characteristics, low production cost, ease of synthesis and surface functionalization, easily controllable pore size and morphology, and good stability, is a hot research topic in materials and chemical engineering. Furthermore, mesoporous silica, with its regular channel structure, high specific surface area, and porosity, is often introduced into polymer membranes as a carrier for ion transport channels to improve membrane performance.

[0004] Nonsolvent Induced Phase Separation (NIPS) membrane fabrication is a highly efficient membrane fabrication method invented in the 1960s. NIPS stands for Nonsolvent Induced Phase Separation, also known as the wet process. Its process involves dissolving a polymer in a solvent to form a homogeneous solution. Then, a reagent with stronger miscibility with the solvent (called an extractant) is slowly added to extract the solvent, forming a two-phase structure with the polymer as the continuous phase and the solvent as the dispersed phase. The solvent is then removed, yielding a polymer with a specific porous structure. The basic principle of NIPS membrane fabrication is to use specific physical methods to induce double diffusion between the solvent and non-solvent in a homogeneous polymer solution of a certain composition. This alters the thermodynamic instability of the polymer solution, resulting in solid-liquid or liquid-liquid phase separation, ultimately transforming it into a three-dimensional macromolecular network gel structure (i.e., polymer-rich phase solidification). The polymer-poor phase is eluted to form a porous structure, and this three-dimensional network gel structure constitutes the main body of the membrane. The asymmetric membrane formed by the NIPS method includes a dense skin layer on the membrane surface and a porous support layer beneath it. By selecting appropriate casting solution formulations and process conditions, various polymer membranes can be prepared. The pore structures of the membranes can be roughly divided into four types: spheroidal, spongy, macroporous, and open network. Zhang Wenjuan et al. [1] used γ-butyrolactone (γ-BL) and TEP as mixed solvents to prepare PVDF membranes using the NIPS method and studied the effects of different solvent ratios on the structure and performance of PVDF membranes. The results showed that when the γ-BL content in the mixed solvent was high (greater than 80%), the skin of the obtained membrane was thicker and the spherulites in the cross section were densely packed; as the TEP content in the solvent increased, the skin of the prepared membrane gradually thinned to disappear, and the spherulite structure in the cross section of the membrane became increasingly loose. Xu Zhenliang et al. [2] prepared NIPS method PVDF hollow fiber ultrafiltration membranes using DMAc and N-methylpyrrolidone (NMP) as solvents, respectively, and studied the effects of different solvent compositions on the performance of hollow fiber membranes. The results showed that the pure water flux of the membrane prepared with NMP as solvent was greater than that of the membrane prepared with DMAc as solvent, while the rejection rate was less than that of the membrane prepared with DMAC as solvent.

[0005] Compared with traditional porous membrane preparation processes, the NIPS method has many advantages. The asymmetric membrane structure prepared by this method endows the membrane with excellent selective permeation performance, and the membrane pore structure is easy to control. Therefore, we are committed to preparing structurally controllable porous cation composite membranes using the NIPS method.

[0006] [1] Zhang Wenjuan, Wang Lei, Meng Xiaorong, et al. Effects of γ-BL / TEP mixed solvent on the structure and properties of PVDF membranes [J]. Water Treatment Technology, 2013, 39(10): 40-49.

[0007] [2] Xu Zhenliang, Zhai Xiaodong, Chen Guie. Study on high porosity polyvinylidene fluoride hollow fiber ultrafiltration membrane [J]. Membrane Science and Technology, 2000, 20(4): 10-13. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing membrane technologies by providing a method for preparing SPEEK / MS porous composite membranes using solvent-inducible phase separation, thereby obtaining porous cation-coated composite membranes with excellent selective separation properties for alkaline diffusion dialysis. This method is simple and easy to operate, and is less susceptible to interference from external factors. Furthermore, this method can obtain SPEEK / MS composite membranes with high separation performance even with a small amount of inorganic particles added: the hydroxide ion dialysis coefficient (U0.05) of the composite membrane is... OH The flow rate was 0.0089-0.0139 m / h, and the separation coefficient (S) was 21.4-35.6.

[0009] This invention employs a solvent-inducing phase separation method to prepare SPEEK / MS porous composite membranes. By doping self-made mesoporous silica into sulfonated polyether ether ketone (SPEEK), the separation performance of the prepared cation-containing porous composite membrane is significantly improved. The specific steps include:

[0010] Step 1: The dried polyetheretherketone (PEEK) granules were slowly added to a three-necked flask containing concentrated sulfuric acid (98%). Under a nitrogen atmosphere and at room temperature, the mixture was mechanically stirred for 12 hours to obtain a dark red homogeneous solution. The temperature was then raised to continue the reaction. After the solution cooled to room temperature, it was slowly poured into an ice-water mixture and stirred with a glass rod to obtain a white fibrous precipitate. The precipitate was washed repeatedly with a large amount of deionized water until the pH of the washing solution was around 7. The resulting precipitate was then vacuum dried to obtain a yellow fibrous solid, SPEEK. Its degree of sulfonation was tested by titration.

[0011] Step 2: Dissolve P123 in a diluted HCl solution (2 mol / L), add the silicon source TEOS dropwise to the mixed solution, stir the mixture for a certain time, and then heat and stir; filter to recover the solid product and dry it; remove the template agent by high-temperature calcination to obtain white mesoporous silica microspheres MS. Store in a desiccator for later use.

[0012] Step 3: Crush the mesoporous silica microspheres (MS) obtained in Step 2 and add them to 16 mL of LDM. Disperse the mixture ultrasonically for 1 hour, then add 4 g of SPEEK. Stir magnetically at 70°C for 12 hours until completely dissolved to form a pale yellow, viscous, transparent homogeneous solution. Stop stirring and let stand for 2 hours to remove air bubbles from the solution. Then pour the solution onto a clean glass plate and use a film casting machine to cast the liquid into a thin film. Immediately immerse the cast film in an ethanol solution. After 24 hours, remove it and allow it to dry naturally to obtain the SPEEK / MS composite porous cation exchange membrane.

[0013] In step 1, the ratio of polyetheretherketone particles to concentrated H2SO4 is 1 g / 25 mL; after obtaining a dark red homogeneous solution, the temperature is raised to 60 °C for sulfonation, and the sulfonation reaction time is about 3 h.

[0014] In step 1, the degree of sulfonation of the prepared SPEEK is 48%-65%. As the degree of sulfonation increases, the content of sulfonic acid groups in the molecular chain increases. An increase in the number of sulfonic acid groups can improve the separation performance of the membrane, but a higher degree of sulfonation makes it prone to swelling, ultimately affecting the mechanical stability of the membrane. SPEEK with a sulfonation degree higher than 80% will experience excessive swelling, while SPEEK membranes with a sulfonation degree in the range of 48%-65% exhibit good separation performance and water resistance.

[0015] In step 2, the addition ratio of P123 is 1g / 30mL HCl solution.

[0016] In step 2, TEOS should be added drop by drop. For example, when adding 8-10mTEOS, the dripping time should be controlled at 8-10 minutes.

[0017] In step 2, the calcination temperature is 550℃, the calcination time is 4h, and the heating rate is 10℃ / min.

[0018] In step 3, the added MS mass is 2-8% of the SPEEK mass.

[0019] HCl not only promotes the hydrolysis of silicates and the formation of ordered mesoporous structures during MS synthesis, but its dosage also regulates the microstructure of the synthesized product. With increasing HCl dosage, the microstructure of the MS mesoporous material changes from short rod-shaped to near-spherical. The mesoporous silica prepared in this invention is amorphous mesoporous silica, but its pores are regular and ordered, with a pore size of 5-6 nm.

[0020] This method can obtain SPEEK / MS composite membranes with good separation performance at relatively low inorganic particle addition levels: the hydroxide ion dialysis coefficient of the composite membrane (U... OH The concentration of particulate matter (S) is 0.0089-0.0139 m / h, and the separation coefficient (S) is 21.4-35.6.

[0021] The SPEEK / MS porous composite membrane prepared in this invention is used as a cation exchange membrane in alkaline diffusion dialysis.

[0022] The composite membrane prepared by this invention has both a dense structure and a porous structure, wherein the porous structure provides OH groups. -The higher free space volume and faster migration rate of ions, coupled with the dense structure, contribute to the separation effect. Furthermore, the added inorganic salt mesoporous silica can not only be added to the casting solution as a pore-forming agent to increase the porosity of the SPEEK membrane, but also the inherent porous structure of mesoporous silica improves the cation separation efficiency to a certain extent.

[0023] The thickness of the dense layer of the composite membrane of the present invention is 0.01-0.1 μm. If the dense layer is too thin, the compressive strength is poor. If the pressure is too high during use, it will cause irreversible damage to the cation membrane. If the dense layer is too thick, the ion flux is too low, which will affect the ion migration rate. Attached Figure Description

[0024] Figure 1 The images shown are SEM images of the SPEEK porous cation composite membrane prepared in Example 1 of this invention (surface and cross-section, respectively).

[0025] Figure 2 This is a TEM image of a cross-section of the SPEEK porous cation composite membrane prepared in Example 1 of the present invention.

[0026] Figure 3 The separation performance test data are for the porous cation composite membranes prepared in Examples 1-4 of this invention. Detailed Implementation

[0027] The technical solution of the present invention will be further analyzed and explained through specific embodiments below.

[0028] Example 1:

[0029] 1. Sulfonation of PEEK: 10g of dried polyetheretherketone (PEEK) granules were slowly added to a three-necked flask containing 250mL of concentrated sulfuric acid (98%). Under a nitrogen atmosphere and at room temperature, the mixture was mechanically stirred for 12 hours to obtain a dark red homogeneous solution. The temperature was then raised to 60℃, and the reaction continued for 3 hours. After the solution cooled to room temperature, it was slowly poured into an ice-water mixture and stirred with a glass rod to obtain a white fibrous precipitate. The precipitate was washed repeatedly with a large amount of deionized water until the pH of the washing solution was around 7. The product was vacuum dried at 80℃ for 24 hours to obtain a yellow fibrous solid, SPEEK. The degree of sulfonation was determined to be 64.4% by titration.

[0030] 2. Preparation of mesoporous silica microspheres: 4 g of P123 was dissolved in 120 mL of 2 M HCl solution at 40 °C. Then, 10 mL of LTEOS was added dropwise, and the mixture was stirred for 20 h. The mixture was then stirred at 100 °C for 24 h. The solid product was recovered by filtration and dried at 50 °C for 16 h. The template agent was removed by high-temperature calcination at 550 °C for 4 h. The synthesized white MS was stored in a desiccator until use.

[0031] 3. Preparation of porous cation exchange membrane: Spherical mesoporous silica (2% by mass of SPEEK, i.e., 0.08 g) was crushed and added to 16 mL of LDMF and ultrasonically dispersed for 1 h. The solution was then poured into a three-necked flask, and 4 g of SPEEK was added. The mixture was magnetically stirred at 70 °C for 12 h until completely dissolved. Stirring was stopped, and the mixture was allowed to stand for 2 h to remove air bubbles. The solution was then poured onto a clean glass plate and cast into a thin film using a film casting machine. The cast film was immediately immersed in an ethanol solution and removed after 24 h. After natural drying, the SPEEK / MS composite porous cation exchange membrane was obtained.

[0032] 4. Performance Testing:

[0033] Diffusion dialysis process: Before testing, the membrane was immersed in a 1M NaOH / Na2WO4 mixed alkali solution for 1 hour. After removal, the membrane was rinsed clean before testing. The effective area of ​​the membrane was 6.0 cm². 2 Add 100 mL of deionized water and 100 mL of mixed alkaline solution to each of the two membrane chambers, respectively. Avoid concentration polarization by mechanical stirring. After 1 hour of operation, pour out the solutions from both sides and determine the OH- concentration on the alkaline and water sides using a 0.1 M HCl solution titration method. - Ion concentration yields the dialysis coefficient (U) of hydroxide ions. OH WO4 was determined by ultraviolet spectrophotometry. 2- The concentration yields the dialysis coefficient (U) of tungstate. W ), thus obtaining the membrane separation coefficient (S).

[0034] The performance parameters of the composite membrane obtained in this embodiment, as tested, are: hydroxide ion permeation coefficient (U... OH The flow rate was 0.0089 m / h, and the separation coefficient was 21.4.

[0035] Example 2:

[0036] The preparation method and performance test of the porous cation composite membrane in this embodiment are the same as in Example 1. The difference is that the mass fraction of spherical mesoporous silica added in this example is 4% of SPEEK, i.e., 0.16g.

[0037] The performance parameters of the composite membrane obtained in this embodiment, as tested, are: hydroxide ion permeation coefficient (U... OH The flow rate was 0.0113 m / h, and the separation coefficient was 27.8.

[0038] Example 3:

[0039] The preparation method and performance test of the porous cation composite membrane in this embodiment are the same as in Example 1. The difference is that the mass fraction of spherical mesoporous silica added in this example is 6% of SPEEK, i.e., 0.24g.

[0040] The performance parameters of the porous cation composite membrane obtained in this embodiment, as tested, are as follows: hydroxide ion permeation coefficient (U... OH The flow rate was 0.0139 m / h, and the separation coefficient was 35.6.

[0041] Example 4:

[0042] The preparation method and performance test of the porous cation composite membrane in this embodiment are the same as in Example 1. The difference is that the mass fraction of spherical mesoporous silica added in this example is 8% of SPEEK, i.e., 0.32g.

[0043] The performance parameters of the porous cation composite membrane obtained in this embodiment, as tested, are as follows: hydroxide ion permeation coefficient (U... OH The flow rate was 0.0097 m / h, and the separation coefficient was 24.0.

[0044] Figure 1 The images shown are SEM images (surface and cross-section) of the SPEEK porous cation composite membranes prepared in Examples 1-4 of this invention. It can be seen that the membrane structure prepared by the NIPS method is asymmetrical, including a dense skin layer on the membrane surface and a porous support layer under the skin layer. In the NIPS method, the exchange rate of solvent DMF and non-solvent ethanol is fast, and the polymer chain segments are fixed in a short time, making it difficult to adjust their chain segment structure. This easily leads to the formation of macropores. The macroporous structure improves the separation efficiency of the membrane, which provides a good idea for solving the problem of low membrane separation efficiency in alkaline diffusion dialysis.

[0045] Figure 2 The images show TEM images of cross-sections of the SPEEK porous cation composite membranes prepared in Examples 1-4. It can be clearly seen from the images that MS is uniformly dispersed and maintains a good mesoporous structure in the membrane matrix. MS shows good stability during the membrane preparation process and works synergistically with the macropores of SPEEK to jointly promote ion transfer.

[0046] Figure 3 The separation performance of the composite membranes prepared in Examples 1-4 was tested. It can be seen that with the increase of mesoporous silica content, the separation performance of the composite membranes first increases and then decreases. The -OH groups inherent in MS have a certain effect on the OH groups. - The adsorption selectivity of ions significantly increases the selectivity of the membrane. However, with further increases in MS content, the likelihood of inorganic particles agglomeration increases, and excessive particle content also increases the probability of structural defects, leading to a decrease in membrane separation performance. Introducing an appropriate amount (not exceeding 6%) of inorganic particles can significantly improve the ion-selective permeability of the membrane.

[0047] The embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing SPEEK / MS porous composite membranes using solvent-inducible phase separation, characterized in that... Includes the following steps: Step 1: Add the dried polyetheretherketone granules to concentrated sulfuric acid, and mechanically stir for 12 hours under a nitrogen atmosphere and at room temperature to obtain a dark red homogeneous solution; The temperature was then raised and the reaction continued. After the solution cooled to room temperature, it was slowly poured into an ice-water mixture and stirred with a glass rod to obtain a white fibrous precipitate. The precipitate was washed with deionized water until the pH of the washing solution was around 7. The precipitate was then vacuum dried to obtain a yellow fibrous solid, namely SPEEK. Step 2: Dissolve P123 in diluted HCl solution, add silicon source TEOS dropwise to the mixed solution, stir the mixture for a certain time, then heat and stir; filter to recover the solid product and dry it, remove the template agent by high temperature calcination, and obtain white mesoporous silica microspheres MS; Step 3: After crushing the mesoporous silica microspheres (MS) obtained in Step 2, add them to 16 mL of LDM and ultrasonically disperse for 1 hour. Then add 4 g of SPEEK and magnetically stir at 70°C for 12 hours until completely dissolved to form a pale yellow, viscous, transparent homogeneous solution. Stop stirring and let stand for 2 hours to remove air bubbles from the solution. Then pour the solution onto a clean glass plate and use a film casting machine to cast the liquid into a thin film. Immediately immerse the cast film in an ethanol solution. After 24 hours, remove it and let it dry naturally to obtain the SPEEK / MS composite porous cation exchange membrane. In step 1, the degree of sulfonation of the prepared SPEEK is 48%-65%; In step 2, the addition ratio of P123 is 1g / 30mL HCl solution; In step 3, the added MS mass is 2-8% of the SPEEK mass; The SPEEK / MS porous composite membrane includes a dense skin layer on the membrane surface and a porous support layer below the skin layer, wherein the thickness of the dense skin layer is 0.01-0.1 μm.

2. The method according to claim 1, characterized in that: In step 1, the ratio of polyetheretherketone particles to concentrated H2SO4 is 1 g / 25 mL; after obtaining a dark red homogeneous solution, the temperature is raised to 60 °C for sulfonation, and the sulfonation reaction time is 3 h.

3. The method according to claim 1, characterized in that: In step 2, the calcination temperature is 550℃, the calcination time is 4h, and the heating rate is 10℃ / min.

4. The application of the SPEEK / MS porous composite membrane prepared by any one of the preparation methods according to claims 1-3, characterized in that: The SPEEK / MS porous composite membrane is used as a cation exchange membrane in alkaline diffusion dialysis.

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