PDMS (Polydimethylsiloxane) composite membrane prepared on polyolefin base membrane as well as preparation method and application of PDMS composite membrane

Abstract

The invention belongs to the technical field of gas separation membranes, and relates to a PDMS (polydimethylsiloxane) composite membrane prepared on a polyolefin base membrane as well as a preparation method and application of the PDMS composite membrane. The invention provides an innovative method for preparing a PDMS composite film on a polyolefin base film, and effectively solves a plurality of problems confronted when the PDMS composite film is prepared on the polyolefin base film by a traditional method. According to the method, a polyolefin base membrane is subjected to infiltration treatment by adopting a weak-polarity solvent which has specific viscosity and can be mutually soluble with water, and the subsequent infiltration step in water is matched, so that effective pretreatment on channels of the base membrane is realized.

Description

Technical Field

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

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

[0003] Compared with traditional gas separation methods, membrane separation technology has the characteristics of low energy consumption, high efficiency, small floor area, no secondary pollution, etc., and is expected to achieve carbon capture and energy gas purification at a lower cost. Polydimethylsiloxane (PDMS), as a common rubbery polymer, has 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, pervaporation, 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), etc. as the base membrane. The small surface pore size and low porosity ensure that the prepared composite membrane has good mechanical strength and pressure resistance, and has been applied in fields such as natural gas decarbonization and organic vapor recovery. However, for low-pressure separation scenarios with ultra-large gas volumes such as coal-fired power plant flue gas, it is necessary to develop a composite membrane with high permeability and low cost and easy to scale up, thereby reducing the cost and floor area of the membrane device.

[0004] Polyolefin-based membranes not only have a high porosity and a large pore size, but also the cost of polyolefin-based membranes is much lower than that of existing mainstream base membranes, which is a good solution to solve the above problems. In the field of gas separation such as flue gas carbon capture and air separation, it is of great value to develop a PDMS composite membrane with high gas permeability based on polyolefin-based membranes. However, the defect-free preparation of a thin and dense PDMS functional layer on a polyolefin-based membrane faces great challenges. In particular, it is difficult to wet the super-hydrophobic PE pores by traditional non-solvent pore-blocking methods, which will cause serious pore penetration of the hydrophobic PDMS coating solution with a lower viscosity in the PE base membrane, hinder the permeation of gas molecules and produce membrane surface wrinkling defects.

[0005] To address this issue, the prior art CN117339405A discloses that the base film is first wetted with a wetting agent for a long time and then immersed in water to achieve the filling of the voids in the base film with glycerol and the removal of glycerol at the pore ports of the base film, thereby achieving depth-controllable pore permeability. However, the wetting agent used is a high-viscosity weakly polar solvent, which has low infiltration efficiency, is difficult to quickly penetrate into the pores of the hydrophobic polyolefin base film, has poor miscibility with water, incomplete solvent replacement, and residual glycerol may interfere with subsequent PDMS coating. Moreover, the treatment time is long (more than several hours), resulting in poor anti-pore-permeability effect and great challenges in large-scale preparation. Therefore, the applicant tried to use low-viscosity weakly polar solvents such as isopropanol to infiltrate the base film, but found that low-viscosity weakly polar solvents such as isopropanol are miscible with the organic solvents in the PDMS coating solution, and the coating solution can still easily penetrate into the pores of the PE base film, resulting in wrinkles, increasing the gas mass transfer resistance and generating non-selective defects at the same time.

[0006] Therefore, there is an urgent need to optimize the methods for pore permeability control and gas separation performance enhancement during the process of coating the PDMS functional layer on the polyolefin base film. Summary of the Invention

[0007] To solve the above problems, the present invention infiltrates the polyolefin base film with a low-viscosity weakly polar solvent and water in sequence, so that sufficient water infiltrates into the pores of the base film, and then a PDMS coating solution with an appropriate concentration is prepared, thereby preparing a PDMS thin layer on the polyolefin base film.

[0008] First, the present invention provides a method for preparing a PDMS composite membrane on a polyolefin-based film, which comprises the following steps: (1) Immerse the polyolefin-based film in a weakly polar solvent for 0.5 - 10 min, wherein the weakly polar solvent has a solvent viscosity less than 5 mPa·s at 25°C and is miscible with water; (2) Take out the polyolefin-based film from the weakly polar solvent and immediately transfer it to water, and continue to immerse for 0.1 - 60 min (preferably, the immersion time is 0.5 - 60 min, and more preferably, the polyolefin-based film is immersed in water until the film sheet curls), and then take it out for standby; (3) Prepare a PDMS coating solution; (4) Uniformly coat the PDMS coating solution on the surface of the polyolefin-based film treated in step (2), and dry to form a PDMS composite membrane.

[0009] Preferably, in step (1), the weakly polar solvent is selected from one or more of isopropanol, ethanol, N,N-dimethylformamide, acetone, and ethyl acetate.

[0010] Preferably, in step (1), the polyolefin-based film is a film prepared by the thermally induced phase separation method or a film with a polyester non-woven fabric support, and the material of the film 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 thickness of the polyolefin-based film is 1-500 μm (preferably, the thickness is 10-100 μm), the pore size is 1-500 nm (preferably, the pore size is 30-100 nm), the porosity is 1-90% (preferably, the porosity is 10-50%), and the contact angle is 10-170° (preferably, the contact angle is 80-150°).

[0011] Preferably, 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 and polymerizing 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 crosslinking time is 1-120 minutes (preferably, the crosslinking time is 10-120 minutes).

[0012] 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 terminal olefins or terminal hydroxyl groups, and the viscosity of the PDMS prepolymer is 500-200000 mPa·s (preferably, the viscosity is 5000-200000 mPa·s); when the PDMS prepolymer is a terminal hydroxyl prepolymer, the weight ratio of the prepolymer, the crosslinking agent, and the catalyst is 1: 0.1-2: 0.1-1, and the crosslinking agent and the catalyst are tetraethoxysilane (TEOS) and dibutyltin dilaurate (DBTD), respectively; when the PDMS prepolymer is a terminal olefin prepolymer, the weight ratio of the prepolymer and the curing agent is 5-50:1, and the curing agent is dimethylmethylhydrogensiloxane. Preferably, the used terminal olefin prepolymer is Dow Corning Sylgard 184 silicone elastomer base (Sylgard 184A), and the used curing agent is Dow Corning Sylgard 184 silicone elastomer curing agent (Sylgard 184B).

[0013] Preferably, in step (4), the coating thickness of the PDMS coating solution is 10-500 μm (preferably, the coating thickness of the PDMS coating solution is 30-300 μm), 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.

[0014] Secondly, the present invention also provides a PDMS composite membrane prepared by the method for preparing a PDMS composite membrane on the above-mentioned polyolefin-based membrane. The permeability of the composite membrane is ≥1000 GPU (preferably, the permeability of the composite membrane is ≥5000 GPU), the selectivity is ≥2 (preferably, the selectivity is ≥5), the selectivity is ≥1 (preferably, the selectivity is ≥1.4).

[0015] In addition, the present invention also provides the application of the above PDMS composite membrane in gas separation. The gas separation field includes one of flue gas carbon capture, air separation or gas separation in a membrane oxygen enrichment machine.

[0016] Compared with the prior art, the present invention has the following advantages: First of all, the present invention provides an innovative method for preparing a PDMS composite membrane on a polyolefin-based membrane, effectively solving many problems faced in the preparation of a PDMS composite membrane on a polyolefin-based membrane by traditional methods. By using a weakly polar solvent with a specific viscosity and water miscibility to infiltrate the polyolefin-based membrane for a reasonable time, and cooperating with subsequent infiltration steps in water for a reasonable time, effective pretreatment of the pore channels of the base membrane is achieved. Compared with the prior art, the weakly polar solvent used in this method has high infiltration efficiency, can quickly penetrate into the pore channels of the hydrophobic polyolefin-based membrane, has good water miscibility, and the solvent replacement is complete, avoiding the interference of solvent residues on the subsequent PDMS coating, greatly shortening the processing time, providing the possibility for large-scale preparation, and significantly improving the production efficiency.

[0017] Secondly, the present invention optimizes the preparation and coating process of the PDMS coating solution. By precisely controlling parameters such as the proportion of each component, the polymerization reaction temperature and time in the PDMS coating solution, a PDMS coating solution 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 precise process control avoids the difficulty of defect-free preparation of a thin and dense PDMS functional layer on a polyolefin-based membrane, effectively prevents serious pore penetration of the PDMS coating solution in the pore channels of the base membrane, reduces the gas mass transfer resistance, and significantly improves the gas separation performance of the composite membrane. The prepared PDMS composite membrane has high permeability and excellent and selectivity.

[0018] In addition, the PDMS composite membrane prepared based on the method of the present invention is applicable to various gas separation scenarios such as flue gas carbon capture, air separation, or gas separation in membrane-based oxygen enrichment machines, and can meet the gas separation requirements in different fields. Especially in low-pressure separation scenarios with ultra-large gas volumes such as flue gas from coal-fired power plants, its high permeability and low cost can effectively reduce the cost and floor area of membrane devices, providing a feasible solution for large-scale and low-cost gas separation. At the same time, the preparation method of this composite membrane is based on a polyolefin-based membrane with a cost much lower than that of existing mainstream base membranes, further reducing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and easy to understand from the description of the embodiments in conjunction with the following drawings, where: Figure 1 shows a comparison between the PE-based membrane used in the embodiment of the present invention and the PSf-based membrane used in Comparative Example 1; Figure 2 shows the surface electron micrographs of the PE-based membrane used in the embodiment of the present invention and the PDMS composite membrane prepared; Figure 3 shows the cross-sectional electron micrographs of the PDMS composite membrane under different preparation conditions in the embodiment of the present invention; Figure 4 shows the cross-sectional morphology of the PDMS composite membrane prepared in Example 1 and the line scan of Si element; Figure 5 shows the infrared spectra of the PE-based membrane used in the embodiment of the present invention, the PSf-based membrane used in Comparative Example 1, the PDMS composite membranes prepared in Examples 3 and 4, and the PDMS composite membrane prepared in Comparative Example 1; Figure 6 shows the evaluation device for the pure gas permeation performance of the composite membrane self-made in the laboratory. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The following content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should all be regarded as belonging to the protection scope of the present invention. The specific conditions not specified in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used, unless otherwise specified, are all conventional products obtained through commercial channels.

[0021] The parameters of the PE-based membrane used in the following examples are: thickness 2 - 20 μm, average pore diameter 80 nm, porosity 40 - 50%, water contact angle 110 - 120°; the parameters of the PSF-based membrane used in the following Comparative Example 1 are: thickness 120 - 140 μm, average pore diameter 15 nm, porosity 10 - 20%, water contact angle 60 - 80°. The SEM characterization of the surfaces of the PE-based membrane and the PSF-based membrane is as Figure 1 shown.

[0022] Example 1 1) Select a PE porous base membrane with a dense skin layer thickness of 40 μm, and soak and treat it with isopropanol and water in sequence for 1 minute; 2) Use n-heptane to dissolve a hydroxyl-terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100000 mPa·s, with a mass concentration of 0.5%, then add TEOS and DBTD with the same concentration, and react at 50 o °C for 60 minutes and then let it stand for later use; 3) Set the thickness of the film coater to 150 μm, scrape and coat PDMS on the PE-based membrane, and dry it at 50 o °C for 4 hours to obtain a PDMS / PE composite membrane.

[0023] Example 2 1) Select a PE porous base membrane with a dense skin layer thickness of 40 μm, and soak and treat it with isopropanol and water in sequence for 5 minutes; 2) Use n-heptane to dissolve a hydroxyl-terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100000 mPa·s, with a mass concentration of 0.5%, then add TEOS and DBTD with the same concentration, and react at 50 o °C for 60 minutes and then let it stand for later use; 3) Set the thickness of the film coater to 150 μm, scrape and coat PDMS on the PE-based membrane, and dry it at 50 o °C for 4 hours to obtain a PDMS / PE composite membrane.

[0024] Example 3 1) Select a PE porous base membrane with a dense skin layer thickness of 40 μm, and soak and treat it with isopropanol and water in sequence for 5 minutes; 2) Use n-heptane to dissolve a hydroxyl-terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100000 mPa·s, with a mass concentration of 0.3%, then add TEOS and DBTD with the same concentration, and react at 50 o °C for 60 minutes and then let it stand for later use; 3) Set the thickness of the film coater to 150 μm, scrape and coat PDMS on the PE-based membrane, and dry it at 50 o °C for 4 hours to obtain a PDMS / PE composite membrane.

[0025] Example 4 1) Select a PE porous base film with a dense skin layer thickness of 40 microns, and soak it in isopropanol and water for 5 minutes in sequence; 2) Dissolve the hydroxyl-terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100000 mPa·s in n-heptane, with a mass concentration of 0.67%, then add TEOS and DBTD with the same concentration, and react at 50 o °C for 60 minutes and then let it stand for later use; 3) Set the thickness of the film coater to 150 microns, scrape PDMS on the PE base film, and dry it at 50 o °C for 4 hours to obtain a PDMS / PE composite film.

[0026] Example 5 1) Select a PE porous base film with a dense skin layer thickness of 40 microns, and soak it in isopropanol and water for 5 minutes in sequence; 2) Dissolve the terminal olefin PDMS with a mass concentration of 0.67% (Dow Corning Sylgard 184) in n-heptane. The prepolymer 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). The ratio of the prepolymer to the curing agent is 10:1. Crosslink and cure at 80 o °C for 30 minutes and then let it stand for later use; 3) Set the thickness of the film coater to 150 microns, scrape PDMS on the PE base film, and dry it at 50 o °C for 4 hours to obtain a PDMS / PE composite film.

[0027] Comparative Example 1 1) Select a PSf porous base film with a dense skin layer thickness of 40 microns, and soak it in isopropanol and water for 5 minutes in sequence; 2) Dissolve the hydroxyl-terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100000 mPa·s in n-heptane, with a mass concentration of 0.67%, then add TEOS and DBTD with the same concentration, and react at 50 o °C for 60 minutes and then let it stand for later use; 3) Set the thickness of the film coater to 150 microns, scrape PDMS on the PE base film, and dry it at 50 o °C for 4 hours to obtain a PDMS / PSf composite film.

[0028] Comparative Example 2 1) Select a PE porous base film with a dense skin layer thickness of 40 microns, do not soak it in any solvent, and directly rinse it with deionized water for later use; 2) Use n - heptane to dissolve the hydroxyl - terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100000 mPa·s at a mass concentration of 0.67%. Then add TEOS and DBTD at the same concentration and react at 50 o °C for 60 minutes, and then let it stand for later use; 3) Set the thickness of the film - scraping machine to 150 microns. After scraping PDMS on the PE base film, dry it at 50 o °C for 4 hours to obtain the PDMS / PE composite film.

[0029] Comparative Example 3 1) Select a PE porous base film with a dense skin layer thickness of 40 microns, and infiltrate it with glycerol and water in turn for 5 minutes; 2) Use n - heptane to dissolve the hydroxyl - terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100000 mPa·s at a mass concentration of 0.67%. Then add TEOS and DBTD at the same concentration and react at 50 o °C for 60 minutes, and then let it stand for later use; 3) Set the thickness of the film - scraping machine to 150 microns. After scraping PDMS on the PE base film, dry it at 50 o °C for 4 hours to obtain the PDMS / PE composite film.

[0030] Comparative Example 4 1) Select a PE porous base film with a dense skin layer thickness of 40 microns, and only infiltrate it with glycerol for 5 minutes; 2) Use n - heptane to dissolve the hydroxyl - terminated PDMS prepolymer (107 silicone rubber) with a viscosity of 100000 mPa·s at a mass concentration of 0.67%. Then add TEOS and DBTD at the same concentration and react at 50 o °C for 60 minutes, and then let it stand for later use; 3) Set the thickness of the film - scraping machine to 150 microns. After scraping PDMS on the PE base film, dry it at 50 o °C for 4 hours to obtain the PDMS / PE composite film.

[0031] Performance Test Perform performance tests on the composite film samples prepared in Examples 1 - 5 and Comparative Examples 1 - 4. The composite film pure - gas permeation performance evaluation device used is developed by our laboratory. As Figure 6 shown, the film is sealed in the film cell, and the effective film area is . The raw material gases used in the test are and pure gases. The pressure on the raw material side is 0.2 MPa, the pressure on the permeation side is atmospheric pressure, and the test temperature is 25 oC, without purging. The gas flow rate after the raw gas passes through the membrane cell is measured by a soap film flowmeter, and the gas on the rejection side is directly exhausted. The gas permeation rate can be calculated from the measured flow rate.

[0032] The performance of gas separation membranes is usually evaluated by their permeation performance and selectivity performance. The permeation performance of separation membranes is usually evaluated by the permeation rate ( R ), or the permeability coefficient ( P ). The permeation rate can better reflect the speed of gas passing through the separation membrane. The definition formula of the permeation rate is shown in Equation (1-1): (1-1).

[0033] In the above formula, is the permeation rate of component i passing through the separation membrane, with the unit of ; Q i is the volumetric flow rate of component i passing through the gas separation membrane under standard temperature and standard pressure, with the unit of (STP) / s; P i is the partial pressure difference of component i on both sides of the gas separation membrane, with the unit of cmHg; A is the effective membrane area, with the unit of .

[0034] At the same time, the selectivity performance of the separation membrane is usually reflected by the separation factor ( ). The magnitude of the separation factor reflects the speed of different components passing through the separation membrane. The ratio of the permeability coefficients ( i and j ) or the ratio of the permeation rates ( ) of components is defined as the ideal separation factor, as shown in Equation (1-2): ((Note:

[0035] Test results The , separation performance of the composite membranes prepared with different base membranes, solvent replacement times, PDMS end group types, and PDMS concentrations in the above examples is shown in Table 1: Table 1 Gas separation performance of composite membranes prepared with different base membranes, solvent replacement times, PDMS end group types, and PDMS concentrations Note: The permeability is the fast gas permeability of the system, with the unit of GPU. ; The selectivity is the ratio of the permeability to the permeability.

[0036] As can be seen from Table 1, by treating the polyolefin-based membrane with a weakly polar solvent and water, the and separation performance of the PDMS composite membrane can be effectively improved. As shown in the appendix Figure 2 , the porous PE-based membrane used in the present invention has a well-developed pore structure, and the average pore diameter is about 50 nm. After coating with PDMS, the pores of the base membrane are gradually covered, and the surface of the composite membrane prepared with 0.67% concentration of PDMS is smooth without any exposed pores. However, in Comparative Example 2, when directly coating without solvent replacement, there are obvious protrusions on the membrane surface. This is mainly because a large number of wrinkles are generated during the process of the PDMS coating solution infiltrating and drying the PE-based membrane, and uneven protrusions are formed during the drying process of the skin layer. These protrusions make the thickness of the composite membrane uneven during the drying process and are prone to generate non-selective defect areas.

[0037] Combining Examples 1, 2 and Comparative Example 2, when the treatment time of IPA and water ranges from 0 to 1 min and 5 min, the non-solvent pore-blocking effect of the PE-based membrane gradually increases, and the degree of pore penetration gradually weakens. When the solvent replacement time is insufficient, the low-concentration PDMS coating solution will experience pore penetration, and the PDMS polymer segments will enter the pores of the PE-based membrane, thereby generating additional gas mass transfer resistance, resulting in a decrease in both the gas permeability and selectivity of the composite membrane. Combining Comparative Example 3, when using glycerol with a high viscosity (about 25 mPa·s) as the pre-wetting solvent, even when the replacement time reaches 5 min, pore penetration still occurs and the membrane performance is not high. This is mainly because the high viscosity leads to low infiltration efficiency and it is difficult to quickly penetrate into the pores of the PE-based membrane. At the same time, compared with low-viscosity solvents such as isopropanol, the miscibility of glycerol and water is poor, and the solvent replacement is not complete. The residual glycerol causes defects to easily occur in the PDMS layer. Combining Comparative Example 4, when water replacement is not used, the gas permeability and selectivity of the membrane both decrease significantly compared with Example 4. The main reason is that the solvent of the PDMS coating solution, n-heptane, is miscible with isopropanol, and the coating solution can easily penetrate into the pores of the PE-based membrane, thereby generating wrinkles, resulting in an increase in gas mass transfer resistance and the generation of non-selective defects.

[0038] Appendix Figure 4For the line scan process of Si element from the dense skin layer to the base membrane of the composite membrane prepared in Example 1, as can be seen from the figure, the Si element content in the PDMS dense layer is relatively high and basically stable. In the interval where the detection position ranges from 0.12 to 0.22 μm, the intensity of the Si element gradually decreases until it is basically stable. It can be speculated that the pore penetration depth of PDMS in Example 1 is approximately 100 nm. At the same time, the lower the PDMS concentration, the smaller the viscosity of the coating solution, which will lead to more serious pore penetration phenomenon.

[0039] Combined with Examples 2, 3, and 4, under the same treatment conditions of the PE base membrane, as the concentration of the PDMS coating solution increases, the thickness of the separation layer gradually increases. As shown in the appendix Figure 3 , the gas permeability of the membrane also gradually decreases, and the gas selectivity gradually increases, indicating that the defects in the membrane gradually decrease. The results of Example 5 show that PDMS using terminal olefins can also prepare defect-free PDMS composite membranes, and the permeability of the membrane is relatively low when the coating solution concentration is selected as 3%.

[0040] Combined with Example 4 and Comparative Example 1, compared with the PDMS composite membrane prepared on the PSf base membrane, due to the larger surface pore size and higher porosity of the PE base membrane, there is more water in the wetted membrane pores, which further forms a denser water layer on the surface of the base membrane, hindering the excessive deposition of the hydrophobic PDMS layer. Finally, the PDMS thickness on the PE base membrane is thinner and dense enough in the dry state.

[0041] Appendix Figure 5 is the infrared spectrogram of the base membrane used in the present invention and the PDMS composite membranes of Examples 3, 4, and Comparative Example 1. Since the detection depth of ATR-FTIR characterization is several micrometers, and the thickness of the PDMS dense skin layer in the present invention is less than 300 nm. Therefore, the characteristic absorption peaks of the PE and PSf base membranes will appear in the ATR-FTIR spectrogram of the composite membrane. The PDMS / PSf composite membrane spectrogram shows characteristic absorption peaks at , and , which respectively belong to the Si-CH3 bending vibration peak, the asymmetric stretching vibration peak of Si-O-Si, and the symmetric stretching vibration peak of Si-O-Si of PDMS.

[0042] The membrane materials, preparation methods, and applications disclosed and proposed in the present invention can be realized by those skilled in the art by referring to the content of this article and appropriately changing the process parameters. Although the methods and devices of the present invention have been described through preferred embodiments, those skilled in the art can obviously make changes or re-combinations to the methods and devices described in this article without departing from the content, spirit, and scope of the present invention to achieve the final preparation technology. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all regarded as included in the spirit, scope, and content of the present invention.

Claims

1. A method for preparing a PDMS composite membrane on a polyolefin-based membrane, characterized in that, It includes the following steps: (1) Immerse the polyolefin-based film in a weakly polar solvent for 0.5 - 10 min. The weakly polar solvent has a solvent viscosity less than 5 mPa·s at 25°C and is miscible with water; (2) Take out the polyolefin-based film from the weakly polar solvent and immediately transfer it to water, and continue to immerse it for 0.1 - 60 min, then take it out for standby; (3) Prepare the PDMS coating solution; Uniformly coat the PDMS coating solution on the surface of the polyolefin-based film treated in step (2), and form a PDMS composite film after drying.

2. The method according to claim 1, characterized in that, In step (1), the weakly 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, wherein In step (1), the polyolefin-based film is a film prepared by the thermally induced phase separation method or a film with a non-woven fabric support. The film 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 thickness of the polyolefin-based film is 1 - 500 microns, the pore size is 1 - 500 nm, the porosity is 1 - 90%, and the contact angle is 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 and polymerizing 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 The mass concentration of the PDMS prepolymer in the coating solution is 0.1% - 20%. The PDMS prepolymer is one of terminal olefins or terminal hydroxyl groups. The viscosity of the PDMS prepolymer is 500 - 200000 mPa·s; when the PDMS prepolymer is a terminal hydroxyl prepolymer, the weight ratio of the prepolymer, crosslinking agent, and catalyst is 1: 0.1 - 2:0.1 - 1, and the crosslinking agent and catalyst are respectively tetraethoxysilane and dibutyltin dilaurate; when the PDMS prepolymer is a terminal olefin prepolymer, the weight ratio of the prepolymer and curing agent is 5 - 50:

1.

6. The method according to claim 1, characterized in that, In step (4), the coating thickness of the PDMS coating solution 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.

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

8. The application of the PDMS composite film according to claim 7 in gas separation, and the gas separation field includes one of carbon capture, air separation, or gas separation in a membrane oxygen enricher.

Images