A PDMS composite membrane prepared on a polyolefin base membrane and its preparation method and application

Abstract

The present invention belongs to the field of gas separation membrane technology and relates to a PDMS composite membrane prepared on a polyolefin-based membrane, its preparation method, and its application. This invention provides an innovative method for preparing a PDMS composite membrane on a polyolefin-based membrane, effectively resolving the numerous challenges faced by traditional methods for preparing PDMS composite membranes on polyolefin-based membranes. By impregnating the polyolefin-based membrane with a weakly polar solvent of a specific viscosity that is miscible with water, and combining this with a subsequent impregnation step in water, the membrane's pores are effectively pretreated.

Description

Technical Field

[0001] The invention belongs to the technical field of gas separation membranes and relates to a PDMS composite membrane prepared on a polyolefin base membrane and a preparation method and application thereof. Background Art

[0002] Coal flue gas contains a large amount of and As well as a small amount of water vapor, sulfur oxides and nitrogen oxides, it has large gas volume, many types of impurities and The low partial pressure leads to high separation energy consumption and cost. Separation is the core link of air separation, and its technological innovation is directly related to the production efficiency and carbon emission intensity in key fields such as metallurgy, chemical industry, and medical care.

[0003] Compared with traditional gas separation methods, membrane separation technology has the characteristics of low energy consumption, high efficiency, small footprint, and no secondary pollution. It is expected to achieve carbon capture and energy gas purification at a lower cost. Polydimethylsiloxane (PDMS), as a common rubber-like polymer, contains a large free volume due to its flexible silicon-oxygen bond, and is one of the most permeable gas separation membrane materials. In the fields of carbon capture, permeation gasification, and oxygen-nitrogen separation, PDMS homogeneous membranes have been widely studied. Traditional PDMS composite membranes generally use polysulfone (PSf), polyethersulfone (PES) or polyvinylidene fluoride (PVDF) as the base membrane. The smaller surface pore size and lower porosity ensure that the composite membrane has good mechanical strength and pressure resistance, and has been used in fields such as natural gas decarbonization and organic vapor recovery. However, for low-pressure separation scenarios with extremely large gas volumes, such as flue gas from coal-fired power plants, it is necessary to develop high-pressure separation membranes. The composite membrane has high permeability, low cost and is easy to scale up, thereby reducing the cost and footprint of the membrane device.

[0004] Polyolefin-based membranes not only have high porosity and high pore size, but also have a cost much lower than the existing mainstream base membranes, making them a good solution to the above problems. In the field of gas separation such as flue gas carbon capture and air separation, the development of PDMS composite membranes with high gas permeability based on polyolefin-based membranes is of great value. However, the defect-free preparation of thin and dense PDMS functional layers on polyolefin-based membranes faces huge challenges, especially the super-hydrophobic PE pores are difficult to wet by traditional non-solvent plugging methods, which will cause the low viscosity hydrophobic PDMS coating liquid to have serious pore penetration in the PE base membrane, hindering the permeation of gas molecules and causing membrane surface wrinkle defects.

[0005] To address this issue, the prior art CN117339405A discloses that the base membrane is first wetted with a wetting agent for a long time, and then immersed in water to achieve glycerol filling of the base membrane voids and removal of glycerol at the base membrane pore ports, thereby achieving depth-controlled pore penetration. However, the wetting agent used is a high-viscosity, weakly polar solvent, which has low wetting efficiency and is difficult to quickly penetrate into the hydrophobic polyolefin base membrane pores. In addition, it has poor miscibility with water, and the solvent replacement is not complete. Residual glycerol may interfere with subsequent PDMS coating, and the processing time is long (requiring more than several hours), resulting in poor anti-pore penetration effect and greater challenges in large-scale preparation. To this end, the applicant tried to use a low-viscosity, weakly polar solvent such as isopropyl alcohol to soak the base membrane, but found that low-viscosity, weakly polar solvents such as isopropyl alcohol are miscible with the organic solvent in the PDMS coating solution. The coating solution can still easily penetrate into the PE base membrane pores, thereby generating wrinkles, resulting in increased gas mass transfer resistance and non-selective defects.

[0006] Therefore, it is urgent to optimize the methods for controlling pore permeability and enhancing gas separation performance during the coating of the PDMS functional layer on the polyolefin-based membrane. Summary of the Invention

[0007] To address the above problems, the present invention sequentially infiltrates a polyolefin base membrane with a low-viscosity weakly polar solvent and water, so that the pores of the base membrane are infiltrated with sufficient water, and then a PDMS coating solution of appropriate concentration is prepared to prepare a PDMS thin layer on the polyolefin base membrane.

[0008] First, the present invention provides a method for preparing a PDMS composite film on a polyolefin base film, which comprises the following steps:

[0009] (1) Immersing the polyolefin base film in a weak polar solvent for 0.5-10 min, wherein the weak polar solvent has a solvent viscosity of less than 5 mPa·s at 25° C. and is miscible with water;

[0010] (2) removing the polyolefin-based base film from the weakly polar solvent and immediately transferring it to water, continuing to soak for 0.1-60 min (preferably, the soaking time is 0.5-60 min, more preferably, the polyolefin-based base film is soaked in water until the film curls up), and then removing it for use;

[0011] (3) Preparation of PDMS coating solution;

[0012] (4) The PDMS coating liquid is evenly applied on the surface of the polyolefin base film treated in step (2), and dried to form a PDMS composite film.

[0013] Preferably, in step (1), the weak polar solvent is selected from one or more of isopropanol, ethanol, N,N-dimethylformamide, acetone, and ethyl acetate.

[0014] Preferably, in step (1), the polyolefin base membrane is a base membrane prepared by a thermally induced phase separation method or a base membrane with a polyester non-woven fabric support, and the base membrane material is selected from one or more of polyethylene, polypropylene, polyvinylidene fluoride, ethylene-vinyl alcohol copolymer, ethylene-acrylic acid copolymer, and poly(4-methyl-1-pentene); the polyolefin base membrane has a thickness of 1-500 μm (preferably, a thickness of 10-100 μm), a pore size of 1-500 nm (preferably, a pore size of 30-100 nm), a porosity of 1-90% (preferably, a porosity of 10-50%), and a contact angle of 10-170° (preferably, a contact angle of 80-150°).

[0015] Preferably, in step (3), the PDMS coating solution is formed by adding a PDMS prepolymer to an organic solvent, then adding a cross-linking agent and a catalyst, and stirring the polymerization reaction at a certain temperature for a period of time; the polymerization reaction temperature is 20-150°C (preferably, the polymerization reaction temperature is 30-80°C), and the cross-linking time is 1-120 minutes (preferably, the cross-linking time is 10-120 minutes).

[0016] The mass concentration of the PDMS prepolymer in the coating solution is 0.1%-20% (preferably, the mass concentration is 0.1%-10%), the PDMS prepolymer is one of a terminal olefin or a terminal hydroxyl group, and the viscosity of the PDMS prepolymer is 500-200,000 mPa·s (preferably, the viscosity is 5,000-200,000 mPa·s); when the PDMS prepolymer is a terminal hydroxyl prepolymer, the weight ratio of the prepolymer, the crosslinker, and the catalyst is 1: 0.1-2: 0.1-1, and the crosslinker and catalyst are tetraethoxysilane (TEOS) and dibutyltin dilaurate (DBTD), respectively; when the PDMS prepolymer is a terminal olefin prepolymer, the weight ratio of the prepolymer to the curing agent is 5-50:1, and the curing agent is dimethylmethylhydrogensiloxane. Preferably, the terminal olefin prepolymer used is Dow Corning Sylgard 184 Silicone Elastomer Base (Sylgard 184A), and the curing agent used is Dow Corning Sylgard 184 Silicone Elastomer Curing Agent (Sylgard 184B).

[0017] Preferably, in step (4), the coating thickness of the PDMS coating liquid is 10-500 microns (preferably, the coating thickness of the PDMS coating liquid is 30-300 microns), the thickness of the PDMS layer after drying is 10-500 nm (preferably, the thickness of the PDMS layer after drying is 50-500 nm), the drying temperature is 30-100°C, and the drying time is 0.5-12 hours.

[0018] Secondly, the present invention also provides a PDMS composite membrane prepared according to the method for preparing a PDMS composite membrane on a polyolefin-based base membrane, wherein the composite membrane Permeability ≥ 1000 GPU (preferably, the composite membrane Penetration rate ≥ 5000GPU), Selectivity ≥ 2 (preferably, Selectivity ≥5), Selectivity ≥ 1 (preferably, Selectivity ≥1.4).

[0019] In addition, the present invention also provides the use of the above-mentioned PDMS composite membrane in gas separation, wherein the gas separation field includes flue gas carbon capture, air separation or gas separation in a membrane oxygen enricher.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] First, the present invention provides an innovative method for preparing a PDMS composite membrane on a polyolefin-based membrane, effectively resolving the many difficulties faced by traditional methods when preparing PDMS composite membranes on polyolefin-based membranes. By using a weakly polar solvent with a specific viscosity and miscible with water to infiltrate the polyolefin-based membrane for a reasonable period of time, combined with a subsequent infiltration step in water for a reasonable period of time, effective pretreatment of the basement membrane pores is achieved. Compared with the existing technology, the weakly polar solvent used in this method has high infiltration efficiency, can quickly penetrate into the pores of the hydrophobic polyolefin-based membrane, has good miscibility with water, and thoroughly replaces the solvent, avoiding interference of solvent residues on subsequent PDMS coating, greatly shortening the processing time, making it possible to prepare on a large scale, and significantly improving production efficiency.

[0022] Secondly, the present invention optimizes the preparation and coating process of the PDMS coating liquid. By precisely controlling the ratio of each component in the PDMS coating liquid, the polymerization reaction temperature and time and other parameters, a PDMS coating liquid with excellent performance is prepared. During the coating process, the coating thickness as well as the drying temperature and time are strictly controlled so that the thickness of the PDMS layer formed after drying is uniform and the performance is stable. This fine process control avoids the difficulty of defect-free preparation of a thin and dense PDMS functional layer on a polyolefin base membrane, effectively prevents serious pore penetration of the PDMS coating liquid in the base membrane pores, reduces the gas mass transfer resistance, and significantly improves the gas separation performance of the composite membrane. The prepared PDMS composite membrane has high Penetration rate and excellent and Selective.

[0023] In addition, the PDMS composite membrane prepared based on the method of the present invention is suitable for various gas separation scenarios such as flue gas carbon capture, air separation or gas separation in membrane oxygen enrichment machine, and can meet the needs of gas separation in different fields. Especially in the low-pressure separation scenario of ultra-large volume such as coal-fired power plant flue gas, its high The high permeability and low cost of this composite membrane effectively reduce the cost and footprint of membrane devices, providing a viable solution for large-scale, low-cost gas separation. Furthermore, the composite membrane's preparation method is based on a polyolefin-based membrane, which is significantly less expensive than existing mainstream base membranes, further reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0025] Figure 1 Shows a comparison between the PE base film used in the embodiment of the present invention and the PSf base film used in Comparative Example 1;

[0026] Figure 2 The surface electron micrographs of the PE base film and the prepared PDMS composite film used in the embodiments of the present invention are shown;

[0027] Figure 3 The cross-sectional electron micrographs of the PDMS composite membranes prepared under different conditions in the embodiments of the present invention are shown;

[0028] Figure 4 The cross-sectional morphology and Si element line scan of the PDMS composite membrane prepared in Example 1 are shown;

[0029] Figure 5 The infrared spectra of the PE base film used in the embodiment of the present invention, the PSf base film used in Comparative Example 1, the PDMS composite films prepared in Examples 3 and 4, and the PDMS composite film prepared in Comparative Example 1 are shown;

[0030] Figure 6 The image shows a laboratory-made composite membrane permeation pure gas performance evaluation device. DETAILED DESCRIPTION

[0031] The following is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it is not intended that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art of the present invention, without departing from the inventive concept, several simple deductions or replacements can also be made, all of which should be considered to belong to the scope of protection of the present invention. The specific conditions not indicated in the examples are carried out according to conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used, unless otherwise specified, are conventional products obtained through commercial channels.

[0032] The following examples use PE base film parameters: thickness 2-20 μm, average pore size 80 nm, porosity 40-50%, water contact angle 110-120°; the following comparative example 1 uses PSF base film parameters: thickness 120-140 μm, average pore size 15 nm, porosity 10-20%, water contact angle 60-80°. SEM characterization of the surface of PE base film and PSF base film is shown below. Figure 1 shown.

[0033] Example 1

[0034] 1) Select a PE porous base membrane with a dense skin thickness of 40 microns and soak it in isopropyl alcohol and water for 1 minute in sequence;

[0035] 2) Dissolve the hydroxyl-terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100,000 mPa·s in n-heptane at a mass concentration of 0.5%, then add TEOS and DBTD at the same concentrations at 50 o C and then react for 60 minutes and then stand for use;

[0036] 3) Set the film thickness of the scraper to 150 microns, and scrape PDMS on the PE base film at 50 o C for 4 hours to obtain a PDMS / PE composite membrane.

[0037] Example 2

[0038] 1) Select a PE porous base membrane with a dense skin thickness of 40 microns and soak it in isopropyl alcohol and water for 5 minutes in sequence;

[0039] 2) Dissolve the hydroxyl-terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100,000 mPa·s in n-heptane at a mass concentration of 0.5%, then add TEOS and DBTD at the same concentrations at 50 o C and then react for 60 minutes and then stand for use;

[0040] 3) Set the film thickness of the scraper to 150 microns, and scrape PDMS on the PE base film at 50 o C for 4 hours to obtain a PDMS / PE composite membrane.

[0041] Example 3

[0042] 1) Select a PE porous base membrane with a dense skin thickness of 40 microns and soak it in isopropyl alcohol and water for 5 minutes in sequence;

[0043] 2) Dissolve the hydroxyl-terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100,000 mPa·s in n-heptane at a mass concentration of 0.3%, then add TEOS and DBTD at the same concentrations at 50 oC and then react for 60 minutes and then stand for use;

[0044] 3) Set the film thickness of the scraper to 150 microns, and scrape PDMS on the PE base film at 50 o C for 4 hours to obtain a PDMS / PE composite membrane.

[0045] Example 4

[0046] 1) Select a PE porous base membrane with a dense skin thickness of 40 microns and soak it in isopropyl alcohol and water for 5 minutes in sequence;

[0047] 2) Dissolve the hydroxyl-terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100,000 mPa·s in n-heptane at a mass concentration of 0.67%, then add TEOS and DBTD at the same concentrations at 50 o C and then react for 60 minutes and then stand for use;

[0048] 3) Set the film scraping machine thickness to 150 microns, and scrape PDMS on the PE base film at 50 o C for 4 hours to obtain a PDMS / PE composite membrane.

[0049] Example 5

[0050] 1) Select a PE porous base membrane with a dense skin thickness of 40 microns and soak it in isopropyl alcohol and water for 5 minutes in sequence;

[0051] 2) 0.67% terminal olefin PDMS (Dow Corning Sylgard 184) was dissolved in n-heptane. The prepolymer was Dow Corning Sylgard 184 silicone elastomer base (Sylgard 184A). The curing agent was Dow Corning Sylgard 184 silicone elastomer curing agent (Sylgard 184B). The ratio of prepolymer to curing agent was 10:1. The mixture was heated at 80 o C and cross-link and cure for 30 minutes, then let it stand for use;

[0052] 3) Set the film scraping machine thickness to 150 microns, and scrape PDMS on the PE base film at 50 o C for 4 hours to obtain a PDMS / PE composite membrane.

[0053] Comparative Example 1

[0054] 1) Select a PSf porous base membrane with a dense skin thickness of 40 μm and soak it in isopropyl alcohol and water for 5 minutes respectively;

[0055] 2) Dissolve the hydroxyl-terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100,000 mPa·s in n-heptane at a mass concentration of 0.67%, then add TEOS and DBTD at the same concentrations at 50 o C and then react for 60 minutes and then stand for use;

[0056] 3) Set the film scraping machine thickness to 150 microns, and scrape PDMS on the PE base film at 50 o C for 4 h to obtain a PDMS / PSf composite membrane.

[0057] Comparative Example 2

[0058] 1) Select a PE porous base membrane with a dense cortex thickness of 40 microns, do not soak it in any solvent, and rinse it directly with deionized water for later use;

[0059] 2) Dissolve the hydroxyl-terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100,000 mPa·s in n-heptane at a mass concentration of 0.67%, then add TEOS and DBTD at the same concentrations at 50 o C and then react for 60 minutes and then stand for use;

[0060] 3) Set the film scraping machine thickness to 150 microns, and scrape PDMS on the PE base film at 50 o C for 4 hours to obtain a PDMS / PE composite membrane.

[0061] Comparative Example 3

[0062] 1) Select a PE porous base membrane with a dense cortex thickness of 40 microns and soak it in glycerol and water for 5 minutes in sequence;

[0063] 2) Dissolve the hydroxyl-terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100,000 mPa·s in n-heptane at a mass concentration of 0.67%, then add TEOS and DBTD at the same concentrations at 50 o C and then react for 60 minutes and then stand for use;

[0064] 3) Set the film scraping machine thickness to 150 microns, and scrape PDMS on the PE base film at 50 o C for 4 hours to obtain a PDMS / PE composite membrane.

[0065] Comparative Example 4

[0066] 1) A PE porous base membrane with a dense cortex thickness of 40 μm was used and treated with glycerol for only 5 minutes;

[0067] 2) Dissolve the hydroxyl-terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100,000 mPa·s in n-heptane at a mass concentration of 0.67%, then add TEOS and DBTD at the same concentrations at 50 o C and then react for 60 minutes and then stand for use;

[0068] 3) Set the film scraping machine thickness to 150 microns, and scrape PDMS on the PE base film at 50 o C for 4 hours to obtain a PDMS / PE composite membrane.

[0069] Performance Testing

[0070] The performance of the composite membrane samples prepared in Examples 1-5 and Comparative Examples 1-4 was tested. The composite membrane permeation pure gas performance evaluation devices used were all developed by our laboratory. Figure 6 As shown, the membrane is sealed in the membrane pool, and the effective membrane area is The raw gas used in the test is and Pure gas, the pressure on the raw material side is 0.2 MPa, the pressure on the permeate side is normal pressure, and the test temperature is 25 o C, no purge. The flow rate of the feed gas after it passes through the membrane cell is measured by a soap film flowmeter, and the gas on the retentate side is directly vented. The gas permeation rate can be calculated from the measured flow rate.

[0071] Gas separation membranes are often evaluated by permeation performance and selectivity. The permeation performance of separation membranes is usually evaluated by permeation rate ( R ) or permeability coefficient ( P ) for evaluation, the permeation rate can better reflect the speed of gas passing through the separation membrane. The definition of permeation rate is shown in formula (1-1):

[0072] (1-1).

[0073] In the above formula, For components i The permeation rate through the separation membrane, in units of

[0074] ; Q i For components i The volume flow rate through the gas separation membrane at standard temperature and standard pressure, in units of (STP) / s; P i It is a component i The partial pressure difference on both sides of the gas separation membrane, in cmHg; A is the effective membrane area, in units of .

[0075] At the same time, the selectivity of the separation membrane is usually expressed by the separation factor ( ) to reflect that the size of the separation factor reflects the speed at which different components pass through the separation membrane. i and j The permeability ratio of ) or the permeability ratio ( ) is defined as the ideal separation factor, as shown in formula (1-2):

[0076] (1-2).

[0077] Test results

[0078] The composite membranes prepared by different base films, solvent replacement time, PDMS end group type, and PDMS concentration in the above examples are shown in FIG. 、 Separation performance is shown in Table 1:

[0079] Table 1 Gas separation performance of composite membranes prepared with different base films, solvent replacement time, PDMS end group type, and PDMS concentration

[0080]

[0081]

[0082] Note: The permeability is the system fast gas permeability, the unit is GPU, ;

[0083] Selectivity is Permeability and The permeability ratio.

[0084] As shown in Table 1, the PDMS composite membrane can be effectively improved by treating the polyolefin-based membrane with weakly polar solvents and water. and Separation performance. Figure 2 As shown, the porous PE base membrane used in the present invention has a well-developed pore structure, with an average pore size of approximately 50 nm. After PDMS coating, the base membrane pores are gradually covered, and the composite membrane made with 0.67% PDMS has a smooth surface without any exposed pores. However, in Comparative Example 2, where direct coating was performed without solvent displacement, the membrane surface exhibited significant ridges. This is primarily due to the numerous wrinkles generated during the drying process of the PE base membrane by the PDMS coating solution, which formed uneven ridges during the drying process of the cortex. These ridges resulted in uneven thickness during the drying process of the composite membrane, which was prone to non-selective defect areas.

[0085] In combination with Examples 1 and 2 and Comparative Example 2, when the treatment time of IPA and water is from 0 to 1 min and 5 min, the non-solvent pore plugging effect of the PE-based membrane gradually increases, and the degree of pore permeation gradually decreases. When the solvent replacement time is insufficient, the low-concentration PDMS coating solution will experience pore permeation, and the PDMS polymer chain segments will enter the pores of the PE-based membrane, thereby generating additional gas mass transfer resistance, resulting in a decrease in the gas permeability and selectivity of the composite membrane. In combination with Comparative Example 3, when glycerol with a high viscosity (about 25mPa·s) is used as the pre-wetting solvent, even if the replacement time reaches 5 min, pore permeation still occurs, resulting in low membrane performance. This is mainly because the high viscosity leads to low wetting efficiency and difficulty in quickly penetrating into the pores of the PE-based membrane. At the same time, compared with low-viscosity solvents such as isopropyl alcohol, glycerol has poor miscibility with water, the solvent replacement is not complete, and residual glycerol causes defects in the PDMS layer. Combined with Comparative Example 4, when water replacement is not used, the gas permeability and selectivity of the membrane are significantly reduced compared with Example 4. The main reason is that the PDMS coating liquid solvent n-heptane and isopropanol are miscible, and the coating liquid can easily penetrate into the pores of the PE-based membrane, thereby generating wrinkles, resulting in an increase in gas mass transfer resistance and non-selective defects.

[0086] Attachment Figure 4 This is a line scan of the Si element from the dense cortex to the base membrane of the composite membrane prepared in Example 1. As can be seen, the Si content in the dense PDMS layer is high and essentially stable. Within the detection range from 0.12 to 0.22 μm, the Si intensity gradually decreases until it stabilizes. It can be inferred that the depth of PDMS porosity in Example 1 is approximately 100 nm. Furthermore, the lower the PDMS concentration and the lower the viscosity of the coating solution, the more severe the porosity.

[0087] In combination with Examples 2, 3, and 4, under the same PE base film treatment conditions, as the concentration of the PDMS coating solution increases, the thickness of the separation layer gradually increases. Figure 3 As shown, the gas permeability of the membrane also gradually decreased, while the gas selectivity gradually increased, indicating that the defects in the membrane gradually decreased. The results of Example 5 show that defect-free PDMS composite membranes can also be prepared using PDMS with terminal olefins. The membrane permeability is low when the coating solution concentration is selected to be 3%.

[0088] In combination with Example 4 and Comparative Example 1, compared with the PDMS composite membrane made on the PSf base membrane, the PE base membrane has a larger surface pore size and a higher porosity, which leads to more water in the wetted membrane pores, thereby forming a denser water layer on the base membrane surface, which hinders the excessive deposition of the hydrophobic PDMS layer. Ultimately, the PDMS thickness on the PE base membrane is thinner and dense enough in the dry state.

[0089] Attachment Figure 5The infrared spectra of the base film used in the present invention and the PDMS composite films of Examples 3, 4, and Comparative Example 1 are shown. Since the detection depth of ATR-FTIR characterization is several microns, and the thickness of the dense skin layer of PDMS in the present invention is less than 300 nm, the characteristic absorption peaks of the PE and PSf base films appear in the ATR-FTIR spectra of the composite films. 、 and Characteristic absorption peaks appeared at , which belonged to the Si-CH3 bending vibration peak, Si-O-Si antisymmetric stretching vibration peak and Si-O-Si symmetric stretching vibration peak of PDMS respectively.

[0090] The membrane materials, preparation methods, and applications disclosed and proposed by this invention can be implemented by researchers in the field by appropriately changing the process parameters based on the content of this invention. Although the methods and apparatus of the present invention have been described through preferred embodiments, it is obvious that those skilled in the art can modify or re-combine the methods and apparatus described herein to achieve the ultimate preparation technology without departing from the content, spirit, and scope of this invention. It is particularly important to point out that all similar substitutions and modifications that are obvious to researchers in the field are considered to be included in the spirit, scope, and content of this invention.

Claims

1. A method for preparing a PDMS composite film on a polyolefin base film, characterized in that: The steps include: (1) Immersing the polyolefin base film in a weak polar solvent for 0.5-10 min, wherein the weak polar solvent has a solvent viscosity of less than 5 mPa·s at 25° C. and is miscible with water; (2) Remove the polyolefin base film from the weak polar solvent and immediately transfer it to water, continue soaking for 0.1-60 minutes, and then remove it for use; (3) preparing a PDMS coating solution, wherein the mass concentration of the PDMS prepolymer in the coating solution is 0.1%-10%, the PDMS prepolymer is one of a terminal olefin or a terminal hydroxyl group, and the viscosity of the PDMS prepolymer is 500-200000 mPa·s; when the PDMS prepolymer is a terminal hydroxyl group prepolymer, the weight ratio of the prepolymer, the crosslinker, and the catalyst is 1: 0.1-2: 0.1-1, and the crosslinker and the catalyst are tetraethoxysilane and dibutyltin dilaurate, respectively; when the PDMS prepolymer is a terminal olefin prepolymer, the weight ratio of the prepolymer to the curing agent is 5-50:1; (4) The PDMS coating liquid is evenly applied on the surface of the polyolefin base film treated in step (2), and dried to form a PDMS composite film.

2. The method according to claim 1, characterized in that In step (1), the weak polar solvent is selected from one or more of isopropanol, ethanol, N,N-dimethylformamide, acetone, and ethyl acetate.

3. The method according to claim 1, characterized in that In step (1), the polyolefin base membrane is a base membrane prepared by a thermally induced phase separation method or a base membrane with a non-woven fabric support, and the base membrane material is selected from one or more of polyethylene, polypropylene, polyvinylidene fluoride, ethylene-vinyl alcohol copolymer, ethylene-acrylic acid copolymer, and poly(4-methyl-1-pentene); the polyolefin base membrane has a thickness of 1-500 microns, a pore size of 1-500 nm, a porosity of 1-90%, and a contact angle of 10-170°.

4. The method according to claim 1, wherein In step (3), the PDMS coating solution is formed by adding a PDMS prepolymer to an organic solvent, then adding a crosslinking agent and a catalyst, and stirring the polymerization reaction at a certain temperature for a period of time; the polymerization reaction temperature is 20-150°C, and the crosslinking time is 1-120 minutes.

5. The method according to claim 1, wherein In step (4), the coating thickness of the PDMS coating liquid is 10-500 microns, the thickness of the PDMS layer after drying is 10-500 nm, the drying temperature is 30-100°C, and the drying time is 0.5-12 hours.

6. A PDMS composite membrane prepared by the method for preparing a PDMS composite membrane on a polyolefin-based base membrane according to claim 1, characterized in that: The CO2 permeability of the composite membrane is ≥1000 GPU, Selectivity ≥ 2, Selectivity ≥1.

7. Use of the PDMS composite membrane according to claim 6 in gas separation, wherein the field of gas separation comprises one of carbon capture, air separation or gas separation in a membrane oxygen enricher.

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