Microporous polydimethylsiloxane-doped composite membrane as well as preparation method and application thereof

Abstract

The preparation method comprises the following steps: dissolving docusate sodium in n-heptane to obtain a docusate sodium solution, adding water, uniformly mixing to obtain a micro-emulsion, adding polydimethylsiloxane into the micro-emulsion, uniformly mixing, adding tetraethyl orthosilicate, uniformly mixing, adding dibutyltin dilaurate, uniformly mixing, standing and cross-linking to obtain the microporous polydimethylsiloxane-doped composite membrane. And uniformly coating the surface of a PVDF substrate membrane with the coating liquid, crosslinking at normal temperature, and drying to obtain the PVDF film. According to the invention, docusate sodium with low boiling point is used as a surfactant, n-heptane is used as a continuous phase and water is used as a dispersion phase to construct a W / O type emulsion, the W / O type emulsion is used as a diluent, PDMS is added into the W / O type emulsion to obtain a film coating liquid, the preparation process is mild in condition and simple in step, the uniformity of a polymerization process is ensured, and the prepared pervaporation film is high in separation factor and good in stability. The membrane flux is up to 600-1200 g / m < 2 >. H, and the separation performance of the pervaporation membrane is enhanced.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to a microporous doped polydimethylsiloxane composite membrane, its preparation method, and its application. Background Technology

[0002] Pervaporation is a molecular-scale membrane separation technology that has been developed in recent years. This method utilizes the difference in affinity between the separating material and different components in the mixture, using the vapor pressure difference between the components on both sides of the membrane as the driving force to achieve selective separation of specific components. It has advantages such as mild separation conditions, low energy consumption, simple operation, and easy coupling with chemical and biological processes. It has broad development prospects in areas such as rational utilization of resources and energy, transformation of traditional processes, environmental protection, and green manufacturing in the food and pharmaceutical industries.

[0003] Pervaporation membranes are the core components of the pervaporation separation process and have received widespread attention in recent years for the efficient extraction of plant-derived aromatic components. These membrane materials, especially organoaffinity membranes represented by polydimethylsiloxane (PDMS), have been successfully applied in the recovery of volatile aromatic substances during food processing such as lemon oil, rose syrup, concentrated fruit juice, and tea, demonstrating excellent separation performance. However, due to their dense polymer structure, traditional PDMS membranes exhibit significant mass transfer resistance and limited separation efficiency when processing natural aromatic components with high molecular weight and high boiling points, severely hindering the large-scale industrial application of this technology in the extraction of aromatic components.

[0004] To improve membrane performance, researchers have focused on developing mixed matrix membranes (MMMs). These MMMs introduce hydrophobic nanofillers—such as zeolites, silica, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs)—into a PDMS matrix to modulate the separation layer structure and construct nanoscale transport channels, thereby enhancing the selective permeation of aromatic molecules. These MMMs exhibit significantly improved separation efficiency during pervaporation. However, a major challenge remains in their fabrication: nanofillers are prone to aggregation and uneven distribution in heterogeneous casting solutions, leading to structural defects after membrane formation and affecting the overall performance and stability of the membrane. Furthermore, the nanoparticle filling method also faces challenges in large-scale production. Currently, this problem remains unresolved, severely limiting the industrial-scale application of pervaporation technology in the separation of natural aromatic compounds. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a microporous doped polydimethylsiloxane composite membrane, which addresses the shortcomings of the prior art.

[0006] The technical problem to be solved by the present invention is to provide a microporous doped polydimethylsiloxane composite membrane prepared by the above preparation method.

[0007] The final technical problem to be solved by this invention is to provide the application of the above-mentioned microporous doped polydimethylsiloxane composite membrane in the separation of ethanol.

[0008] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0009] A method for preparing a microporous doped polydimethylsiloxane composite film includes the following steps:

[0010] Step 1: Dissolve sodium docusate in n-heptane to obtain a sodium docusate solution. Add water and mix well to obtain a white, semi-transparent microemulsion.

[0011] Step 2: Add polydimethylsiloxane to the microemulsion obtained in Step 1, mix well, add tetraethyl orthosilicate, mix well, add dibutyltin dilaurate, mix well, and allow to stand for crosslinking to obtain the coating liquid.

[0012] Step 3: Coat the PVDF base film surface with the coating solution obtained in step (2), crosslink it at room temperature and then dry it.

[0013] In step 1, the concentration of sodium docusate in the sodium docusate solution is 0.05 ~ 0.08 g / mL, preferably 0.08 g / mL.

[0014] In step 1, the molar ratio of water to sodium docusate is 24 to 60:1, preferably 36 to 60:1, more preferably 48 to 60:1, and most preferably 60:1.

[0015] In step 1, under stirring conditions, the water is added to the sodium docusate solution; the water is added dropwise to the sodium docusate solution 4 to 6 times at a flow rate of 4 to 8 mL / min.

[0016] Preferably, in step 1, the water is added to the sodium docusate solution under stirring conditions; the water is added dropwise to the sodium docusate solution 5 times at a flow rate of 6 mL / min.

[0017] In step 2, the mass ratio of the polydimethylsiloxane to the microemulsion is 10 to 20:1, preferably 15 to 20:1, and most preferably 18:1.

[0018] In step 2, the mass ratio of tetraethyl orthosilicate to polydimethylsiloxane is 1:10 to 15, preferably 1:10; the mass ratio of dibutyltin dilaurate to polydimethylsiloxane is 1:10 to 20, preferably 1:10.

[0019] Preferably, in step 2, after the tetraethyl orthosilicate is added, the resulting mixture is stirred and mixed for 3 to 5 minutes, and then dibutyltin dilaurate is added.

[0020] Preferably, in step 2, after the dibutyltin dilaurate is added, the resulting mixture is stirred and mixed for 25-30 minutes, and then allowed to stand for crosslinking.

[0021] In step 2, the static crosslinking is performed until the viscosity of the coating liquid reaches 10,000 to 15,000 cP.

[0022] In step 3, the coating thickness of the coating liquid on the PVDF substrate film surface is 5 ~ 30 μm, preferably 5 ~ 20 μm, more preferably 5 ~ 10 μm, and most preferably 10 μm; the crosslinking time at room temperature is 8 ~ 12 h; and the drying temperature is 85 ~ 90℃, and the time is 48 ~ 60 h.

[0023] The present invention also claims protection for the microporous doped polydimethylsiloxane composite membrane prepared by the above preparation method.

[0024] This invention also claims protection for the application of the above-mentioned microporous doped polydimethylsiloxane composite membrane in volatile organic compounds and water.

[0025] Preferably, the volatile organic compound is a volatile aromatic compound and / or ethanol.

[0026] More preferably, the volatile organic compound is ethanol.

[0027] Preferably, when the microporous doped polydimethylsiloxane composite membrane is used to separate volatile organic compounds and water, the operating temperature is 30 ~ 50℃, the vacuum degree is 160 ~ 400 Pa, and the feed rate is 0.1 ~ 0.4 L / min.

[0028] Preferably, when the microporous doped polydimethylsiloxane composite membrane is used to separate volatile organic compounds and water, the operating temperature is 50°C, the vacuum degree is 200~400 Pa, and the feed rate is 0.4 L / min.

[0029] This invention proposes a method for preparing microporous doped polydimethylsiloxane composite membranes using an emulsion template method. The method uses low-boiling-point sodium docusate (AOT, boiling point 82.7℃) as a surfactant, n-heptane as the continuous phase, and water as the dispersed phase to construct a stable W / O emulsion. This emulsion is then used to replace n-heptane as a diluent to prepare a PDMS pervaporation membrane. When the continuous phase of the emulsion is n-heptane, the addition of low-boiling-point sodium docusate (AOT, boiling point 82.7℃) as a surfactant (exceeding the critical micelle concentration) during the gradual addition of water exposes the non-polar tails of AOT to the organic solvent n-heptane, while the polar heads of AOT spontaneously form "polar water pools" that repel each other. This spontaneously forms water-in-oil emulsion spheres within the n-heptane organic phase, allowing the microspheres to be uniformly dispersed in the coating solution, acting as a "template" to increase the distance between PDMS polymer chains and thus regulate their crosslinking polymerization. Furthermore, since the emulsion components all have low boiling points, they can vaporize and separate upon heating, forming a micron-sized cavity structure within the separation layer. This not only increases the adsorption area but also facilitates the permeation and diffusion of organic molecules. The microporous polydimethylsiloxane composite membrane prepared by the method of this invention solves the problems of limited free volume, insufficient selectivity for low concentrations of volatile aromatics in complex systems, and the tendency for a "flux-selectivity trade-off" leading to low pervaporation efficiency inherent in pure PDMS membranes. Simultaneously, this invention optimizes the ratio of AOT to water and n-heptane to prepare a high-performance microporous polydimethylsiloxane composite membrane and verifies its separation performance in an ethanol / water system.

[0030] Beneficial effects:

[0031] This invention utilizes low-boiling-point sodium docusate as a surfactant, with n-heptane as the continuous phase and water as the dispersed phase to construct a W / O emulsion. PDMS is then added as a diluent to obtain a casting solution. The preparation process is mild and simple, ensuring the uniformity of the polymerization process. The resulting pervaporation membrane exhibits a high separation factor (i.e., separation coefficient) and a membrane flux of 600-1200 g / m³. 2 •h, which enhances the separation performance of the pervaporation membrane. Attached Figure Description

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0033] Figure 1 The images shown are actual photographs of the microemulsions prepared in Examples 1 to 4; wherein, Figures A to D are actual photographs of the microemulsions prepared in Examples 1 to 4, respectively.

[0034] Figure 2This is a scanning electron microscope image of the surface of the microporous doped polydimethylsiloxane composite film prepared in Example 4.

[0035] Figure 3 This is a cross-sectional scanning electron microscope image of the microporous doped polydimethylsiloxane composite membrane prepared in Example 4.

[0036] Figure 4 This is a low-magnification cryo-transmission electron microscope (CRTEM) image of the cross-section of the microporous doped polydimethylsiloxane composite membrane prepared in Example 4.

[0037] Figure 5 This is a high-magnification cryo-transmission electron microscope (CTEM) image of the cross-section of the microporous doped polydimethylsiloxane composite membrane prepared in Example 4.

[0038] Figure 6 This is a statistical graph showing the separation performance of microporous doped polydimethylsiloxane composite membranes prepared under different microemulsion water content conditions in Example 9 for a mixed system of ethanol and water.

[0039] Figure 7 This is a statistical graph showing the separation performance of microporous doped polydimethylsiloxane composite membranes of different thicknesses for a mixture of ethanol and water in Example 10.

[0040] Figure 8 This is a statistical graph showing the separation performance of the microporous doped polydimethylsiloxane composite membrane for the mixture of ethanol and water at different feed temperatures in Example 11. Detailed Implementation

[0041] The present invention will be further described below with reference to the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0042] The polyvinylidene fluoride (PVDF) membrane used in the following examples was purchased from Zhongke Ruiyang Membrane Technology (Beijing) Co., Ltd., item number MF010, with a pore size of 0.1 μm.

[0043] Example 1

[0044] The specific steps for preparing microporous doped polydimethylsiloxane composite films are as follows:

[0045] (1) Preparation of emulsion

[0046] Add 0.8 g of sodium docusate to 10 mL of n-heptane and stir at 600 rpm with a magnetic stirrer to obtain a sodium docusate-n-heptane mixed solution with a concentration of 0.08 g / mL. Add water dropwise to the sodium docusate-n-heptane mixed solution at a water to sodium docusate molar ratio of 24:1 and continue stirring at 600 rpm to obtain a stable white semi-transparent microemulsion. Figure 1A is a photograph of the microemulsion prepared in this embodiment.

[0047] (2) Preparation of coating solution

[0048] Mix 6.00 g PDMS and 0.33 g microemulsion (mass ratio 18:1) for 30 min to obtain mixture I. Add 0.6 g tetraethyl orthosilicate (10% of the mass of PDMS) to the mixture and stir for 5 min to obtain mixture II. Add 0.6 g dibutyltin dilaurate (10% of the mass of PDMS) to the mixture and stir for 30 min. Let stand at room temperature for 3 to 5 h until the viscosity of the resulting coating solution is approximately 15000 cP.

[0049] (3) Preparation of microporous doped polydimethylsiloxane composite membrane

[0050] The coating solution was slowly poured onto the PVDF membrane. An adjustable coating applicator was used to evenly coat the PVDF membrane surface with the coating solution (coating thickness of 10 μm). The membrane was left to stand at room temperature for 12 h. After full cross-linking, it was placed in an oven and dried continuously at 85°C for 48 h to obtain a microporous doped polydimethylsiloxane composite membrane.

[0051] Example 2

[0052] The specific steps for preparing microporous doped polydimethylsiloxane composite films are as follows:

[0053] (1) Preparation of emulsion

[0054] Add 0.8 g of sodium docusate to 10 mL of n-heptane and stir at 600 rpm with a magnetic stirrer to obtain a sodium docusate-n-heptane mixed solution with a concentration of 0.08 g / mL. Slowly add water dropwise to the sodium docusate-n-heptane mixed solution at a water to sodium docusate molar ratio of 36:1 and continue stirring at 600 rpm to obtain a stable white semi-transparent microemulsion. Figure 1 B is a photograph of the microemulsion prepared in this embodiment.

[0055] (2) Preparation of coating solution

[0056] Mix 6.00 g PDMS and 0.33 g microemulsion (mass ratio 18:1) for 30 min to obtain mixture I. Add 0.6 g tetraethyl orthosilicate (10% of the mass of PDMS) to the mixture and stir for 5 min to obtain mixture II. Add 0.6 g dibutyltin dilaurate (10% of the mass of PDMS) to the mixture and stir for 30 min. Let stand at room temperature for 3 to 5 h until the viscosity of the resulting coating solution is approximately 15000 cP.

[0057] (3) Preparation of microporous doped polydimethylsiloxane composite membrane

[0058] The coating solution was slowly poured onto the PVDF membrane. An adjustable coating applicator was used to evenly coat the PVDF membrane surface with the coating solution (coating thickness of 10 μm). The membrane was left to stand at room temperature for 12 h. After full cross-linking, it was placed in an oven and dried continuously at 85°C for 48 h to obtain a microporous doped polydimethylsiloxane composite membrane.

[0059] Example 3

[0060] The specific steps for preparing microporous doped polydimethylsiloxane composite films are as follows:

[0061] (1) Preparation of emulsion

[0062] Add 0.8 g of sodium docusate to 10 mL of n-heptane and stir at 600 rpm with a magnetic stirrer to obtain a sodium docusate-n-heptane mixed solution with a concentration of 0.08 g / mL. Slowly add water dropwise to the sodium docusate-n-heptane mixed solution at a water to sodium docusate molar ratio of 48:1 and continue stirring at 600 rpm to obtain a stable white semi-transparent microemulsion. Figure 1 C is a photograph of the microemulsion prepared in this embodiment.

[0063] (2) Preparation of coating solution

[0064] Mix 6.00 g PDMS and 0.33 g microemulsion (mass ratio 18:1) for 30 min to obtain mixture I. Add 0.6 g tetraethyl orthosilicate (10% of the mass of PDMS) to the mixture and stir for 5 min to obtain mixture II. Add 0.6 g dibutyltin dilaurate (10% of the mass of PDMS) to the mixture and stir for 30 min. Let stand at room temperature for 3 to 5 h until the viscosity of the resulting coating solution is approximately 15000 cP.

[0065] (3) Preparation of microporous doped polydimethylsiloxane composite membrane

[0066] The coating solution was slowly poured onto the PVDF membrane. An adjustable coating applicator was used to evenly coat the PVDF membrane surface with the coating solution (coating thickness of 10 μm). The membrane was left to stand at room temperature for 12 h. After full cross-linking, it was placed in an oven and dried continuously at 85°C for 48 h to obtain a microporous doped polydimethylsiloxane composite membrane.

[0067] Example 4

[0068] The specific steps for preparing microporous doped polydimethylsiloxane composite films are as follows:

[0069] (1) Preparation of emulsion

[0070] Add 0.8 g of sodium docusate to 10 mL of n-heptane and stir at 600 rpm with a magnetic stirrer to obtain a sodium docusate-n-heptane mixed solution with a concentration of 0.08 g / mL. Slowly add water dropwise to the sodium docusate-n-heptane mixed solution at a water to sodium docusate molar ratio of 60:1 and continue stirring at 600 rpm to obtain a stable white semi-transparent microemulsion. Figure 1 D is a photograph of the microemulsion prepared in this embodiment.

[0071] (2) Preparation of coating solution

[0072] Mix 6.00 g PDMS and 0.33 g microemulsion (mass ratio 18:1) for 30 min to obtain mixture I. Add 0.6 g tetraethyl orthosilicate (10% of the mass of PDMS) to the mixture and stir for 5 min to obtain mixture II. Add 0.6 g dibutyltin dilaurate (10% of the mass of PDMS) to the mixture and stir for 30 min. Let stand at room temperature for 3 to 5 h until the viscosity of the resulting coating solution is approximately 15000 cP.

[0073] (3) Preparation of microporous doped polydimethylsiloxane composite membrane

[0074] The coating solution was slowly poured onto the PVDF membrane. An adjustable coating applicator was used to evenly coat the PVDF membrane surface with the coating solution (coating thickness of 10 μm). The membrane was left to stand at room temperature for 12 h. After full cross-linking, it was placed in an oven and dried continuously at 85°C for 48 h to obtain a microporous doped polydimethylsiloxane composite membrane.

[0075] Figure 2 and Figure 3 The images show scanning electron microscope (SEM) images of the surface and cross-section of the microporous doped polydimethylsiloxane composite membrane prepared in this embodiment. As can be seen from the images, the surface of the microporous doped polydimethylsiloxane composite membrane is smooth and without defects. The upper layer of the composite membrane is a microporous doped polydimethylsiloxane mixed layer (selective layer) prepared by the emulsion template method, the middle layer is a PVDF substrate membrane, and the lower layer is a non-woven fabric support layer. The three layers are tightly composited. Figure 4 and Figure 5 The images show low-power and high-power cryo-transmission electron microscopy (CRTEM) images of the cross-section of the microporous polydimethylsiloxane composite membrane prepared in this embodiment. As can be seen from the figures, the micropores in the membrane cross-section are uniformly distributed, forming a "cheese-like" structure with the polydimethylsiloxane, which increases the contact area while reducing mass transfer resistance. Figure 4 Meanwhile, the micropore surface is smooth and defect-free, and the micropore particle size within the composite membrane is in the micrometer range. Figure 5 ).

[0076] Example 5

[0077] The specific steps for preparing microporous doped polydimethylsiloxane composite films are as follows:

[0078] (1) Preparation of emulsion

[0079] Add 0.8 g of sodium docusate to 10 mL of n-heptane and stir at 600 rpm with a magnetic stirrer to obtain a sodium docusate-n-heptane mixed solution with a concentration of 0.08 g / mL. Slowly add water dropwise to the sodium docusate-n-heptane mixed solution at a water to sodium docusate molar ratio of 60:1 and continue stirring at 600 rpm to obtain a stable white semi-transparent microemulsion.

[0080] (2) Preparation of coating solution

[0081] Mix 6.00 g PDMS and 0.33 g microemulsion (mass ratio 18:1) for 30 min to obtain mixture I. Add 0.6 g tetraethyl orthosilicate (10% of the mass of PDMS) to the mixture and stir for 5 min to obtain mixture II. Add 0.6 g dibutyltin dilaurate (10% of the mass of PDMS) to the mixture and stir for 30 min. Let stand at room temperature for 3 to 5 h until the viscosity of the resulting coating solution is approximately 15000 cP.

[0082] (3) Preparation of microporous doped polydimethylsiloxane composite membrane

[0083] The coating solution was slowly poured onto the PVDF membrane. An adjustable coating applicator was used to evenly coat the PVDF membrane surface with the coating solution (coating thickness of 20 μm). The membrane was left to stand at room temperature for 12 h. After full cross-linking, it was placed in an oven and dried continuously at 85°C for 48 h to obtain a microporous doped polydimethylsiloxane composite membrane.

[0084] Example 6

[0085] The specific steps for preparing microporous doped polydimethylsiloxane composite films are as follows:

[0086] (1) Preparation of emulsion

[0087] Add 0.8 g of sodium docusate to 10 mL of n-heptane and stir at 600 rpm with a magnetic stirrer to obtain a sodium docusate-n-heptane mixed solution with a concentration of 0.08 g / mL. Slowly add water dropwise to the sodium docusate-n-heptane mixed solution at a water to sodium docusate molar ratio of 60:1 and continue stirring at 600 rpm to obtain a stable white semi-transparent microemulsion.

[0088] (2) Preparation of coating solution

[0089] Mix 6.00 g PDMS and 0.33 g microemulsion (mass ratio 18:1) for 30 min to obtain mixture I. Add 0.6 g tetraethyl orthosilicate (10% of the mass of PDMS) to the mixture and stir for 5 min to obtain mixture II. Add 0.6 g dibutyltin dilaurate (10% of the mass of PDMS) to the mixture and stir for 30 min. Let stand at room temperature for 3 to 5 h until the viscosity of the resulting coating solution is approximately 15000 cP.

[0090] (3) Preparation of microporous doped polydimethylsiloxane composite membrane

[0091] The coating solution was slowly poured onto the PVDF membrane. An adjustable coating applicator was used to evenly coat the PVDF membrane surface with the coating solution (coating thickness of 30 μm). The membrane was left to stand at room temperature for 12 h. After full cross-linking, it was placed in an oven and dried continuously at 85°C for 48 h to obtain a microporous doped polydimethylsiloxane composite membrane.

[0092] Example 7

[0093] The specific steps for preparing microporous doped polydimethylsiloxane composite films are as follows:

[0094] (1) Preparation of emulsion

[0095] Add 0.8 g of sodium docusate to 10 mL of n-heptane and stir at 600 rpm with a magnetic stirrer to obtain a sodium docusate-n-heptane mixed solution with a concentration of 0.08 g / mL. Slowly add water dropwise to the sodium docusate-n-heptane mixed solution at a water to sodium docusate molar ratio of 60:1 and continue stirring at 600 rpm to obtain a stable white semi-transparent microemulsion.

[0096] (2) Preparation of coating solution

[0097] Mix 6.00 g PDMS and 0.33 g microemulsion (mass ratio 18:1) for 30 min to obtain mixture I. Add 0.6 g tetraethyl orthosilicate (10% of the mass of PDMS) to the mixture and stir for 5 min to obtain mixture II. Add 0.3 g dibutyltin dilaurate (5% of the mass of PDMS) to the mixture and stir for 30 min. Let stand at room temperature for 3 to 5 h until the viscosity of the resulting coating solution is approximately 15000 cP.

[0098] (3) Preparation of microporous doped polydimethylsiloxane composite membrane

[0099] The coating solution was slowly poured onto the PVDF membrane. An adjustable coating applicator was used to evenly coat the PVDF membrane surface with the coating solution (coating thickness of 10 μm). The membrane was left to stand at room temperature for 12 h. After full cross-linking, it was placed in an oven and dried continuously at 85°C for 48 h to obtain a microporous doped polydimethylsiloxane composite membrane.

[0100] Example 8

[0101] The specific steps for preparing microporous doped polydimethylsiloxane composite films are as follows:

[0102] (1) Preparation of emulsion

[0103] Add 0.5 g of sodium docusate to 10 mL of n-heptane and stir at 600 rpm with a magnetic stirrer to obtain a sodium docusate-n-heptane mixed solution with a concentration of 0.05 g / mL. Slowly add water dropwise to the sodium docusate-n-heptane mixed solution at a water to sodium docusate molar ratio of 60:1 and continue stirring at 600 rpm to obtain a stable white semi-transparent microemulsion.

[0104] (2) Preparation of coating solution

[0105] Mix 6.00 g PDMS and 0.33 g microemulsion (mass ratio 18:1) for 30 min to obtain mixture I. Add 0.6 g tetraethyl orthosilicate (10% of the mass of PDMS) to the mixture and stir for 5 min to obtain mixture II. Add 0.6 g dibutyltin dilaurate (10% of the mass of PDMS) to the mixture and stir for 30 min. Let stand at room temperature for 3 to 5 h until the viscosity of the resulting coating solution is approximately 15000 cP.

[0106] (3) Preparation of microporous doped polydimethylsiloxane composite membrane

[0107] The coating solution was slowly poured onto the PVDF membrane. An adjustable coating applicator was used to evenly coat the PVDF membrane surface with the coating solution (coating thickness of 10 μm). The membrane was left to stand at room temperature for 12 h. After full cross-linking, it was placed in an oven and dried continuously at 85°C for 48 h to obtain a microporous doped polydimethylsiloxane composite membrane.

[0108] Example 9

[0109] Ethanol-water separation experiments were conducted using microporous doped polydimethylsiloxane composite membranes with a thickness of 10 μm prepared in Examples 1-4 to investigate the effect of microemulsion water content on the performance of the composite membrane in separating ethanol-water mixtures. Pervaporation was carried out in an ethanol-water (5% v / v) system with a feed-side temperature of 50 °C and a membrane area of ​​20 cm². 2The membrane flow rate was 0.40 L / min, and the permeate-side pressure was maintained at 200–400 Pa using a vacuum pump. Each pervaporation experiment was conducted 0.5 h after the system had been running stably. The permeate was collected in a cold trap (placed in a liquid nitrogen thermos), and the concentration of ethanol in the permeate was determined by gas chromatography. The pervaporation performance of the membrane was characterized by membrane flux and separation coefficient. The experimental results are shown in Table 1 and... Figure 6 As shown. The calculation methods for membrane flux (J) and separation factor (α) are as follows:

[0110]

[0111] In the formula:

[0112] J—membrane flux, g·m -2 ·h -1 ;

[0113] W—mass of the liquid on the osmotic side, in grams;

[0114] A – Effective area of ​​the membrane, m 2 ;

[0115] Δt — the time of pervaporation, in hours;

[0116]

[0117] In the formula:

[0118] Y A Y B —The concentrations of substances A (ethanol) and B (water) in the osmotic liquid, in g / L;

[0119] X A X B —The concentrations of substance A (ethanol) and substance B (water) in the raw material solution, in g / L.

[0120] Table 1. Effect of microemulsion water content on the performance of composite membrane separation of ethanol-water mixtures

[0121]

[0122] As can be seen from Table 1, when the mass ratio of PDMS to microemulsion is 18:1, the higher the water content of the microemulsion, the more considerable the permeation flux and separation factor of ethanol and water are when the microporous doped polydimethylsiloxane composite membrane is used to separate the mixed system of ethanol and water, and the better the separation effect.

[0123] Example 10

[0124] Ethanol-water separation experiments were conducted using microporous doped polydimethylsiloxane composite membranes with thicknesses of 10 μm, 20 μm, and 30 μm, prepared in Examples 4-6, to investigate the effect of membrane thickness on the performance of the composite membrane in separating ethanol-water mixtures. Pervaporation was carried out in an ethanol-water (5% v / v) system with a feed-side temperature of 50°C and a membrane area of ​​20 cm². 2 The membrane flow rate was 0.40 L / min, and the permeate-side pressure was maintained at 200–400 Pa using a vacuum pump. Each pervaporation experiment was conducted 0.5 h after the system had been running stably. The permeate was collected in a cold trap (placed in a liquid nitrogen thermos), and the ethanol concentration was determined by gas chromatography. The pervaporation performance of the membrane was characterized by membrane flux and separation coefficient. The experimental results are shown in Table 2 and... Figure 7 As shown.

[0125] Table 2. Effect of membrane thickness on the performance of composite membrane separation of ethanol-water mixtures

[0126]

[0127] As can be seen from Table 2, as the thickness of the separation layer decreases, the permeation flux and separation factor of the microporous doped polydimethylsiloxane composite membrane both show an increasing trend.

[0128] Example 11

[0129] Ethanol-water separation experiments were conducted using a 10 μm thick microporous doped polydimethylsiloxane composite membrane prepared in Example 4 to investigate the effect of feed temperature on the membrane's performance in separating ethanol-water mixtures. Pervaporation was performed in an ethanol-water (5% v / v) system, with feed-side temperatures set at 30°C, 40°C, and 50°C, and a membrane area of ​​20 cm². 2 The membrane flow rate was 0.40 L / min. The permeate pressure was maintained at 200–400 Pa using a vacuum pump. Each pervaporation experiment was conducted 0.5 h after the system had been running stably. The permeate was collected in a cold trap (placed in a liquid nitrogen thermos), and the ethanol concentration was determined by gas chromatography. The pervaporation performance of the membrane was characterized by membrane flux and separation coefficient. The experimental results are shown in Table 3 and... Figure 8 As shown.

[0130] Table 3. Effect of feed temperature on the performance of composite membrane separation of ethanol-water mixtures

[0131]

[0132] As can be seen from Table 3, the permeation flux and separation factor of the microporous doped polydimethylsiloxane composite membrane increase with the increase of feed liquid temperature.

[0133] This invention provides a microporous doped polydimethylsiloxane composite film, its preparation method, and its application. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for producing a microporous, doped polydimethylsiloxane composite membrane, characterized by, The preparation method comprises the following steps: Step 1, dissolving docusate sodium in n-heptane to obtain a docusate sodium solution, adding water, and mixing to obtain a microemulsion; Step 2, adding polydimethylsiloxane to the microemulsion obtained in step 1, mixing, adding tetraethyl orthosilicate, mixing, adding dibutyltin dilaurate, mixing, and standing for crosslinking to obtain a coating solution; Step 3, uniformly coating the coating solution obtained in step (2) on the surface of a PVDF base film, crosslinking at room temperature, and drying to obtain the product.

2. The production method according to claim 1, characterized by, In step 1, the concentration of docusate sodium in the docusate sodium solution is 0.05-0.08 g / mL.

3. The production method according to claim 1, characterized by, In step 1, the molar ratio of water to docusate sodium is 24-60:

1.

4. The method of claim 1, wherein, In step 1, the water is added to the docusate sodium solution under stirring; the water is added dropwise to the docusate sodium solution in 4-6 portions, and the flow rate of dropwise addition is 4-8 mL / min.

5. The preparation method according to claim 1, characterized in that, In step 2, the mass ratio of polydimethylsiloxane to the microemulsion is 10-20:

1.

6. The method of claim 1, wherein, In step 2, the mass ratio of tetraethyl orthosilicate to polydimethylsiloxane is 1:10-15; the mass ratio of dibutyltin dilaurate to polydimethylsiloxane is 1:10-20.

7. The preparation method according to claim 1, characterized in that, In step 2, the standing for crosslinking is standing for crosslinking until the viscosity value of the coating solution is 10,000-15,000 cP.

8. The method of claim 1, wherein, In step 3, the coating thickness of the coating solution on the surface of the PVDF base film is 5-30 μm; the crosslinking time at room temperature is 8-12 h; and the drying temperature is 85-90°C.

9. The microporous doped polydimethylsiloxane composite membrane prepared by the preparation method in any one of claims 1-8.

10. The use of the microporous doped polydimethylsiloxane composite membrane in claim 9 in separating volatile organic compounds and water.

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