CN115738758A - Sandwich structure multilayer composite membrane for fluid separation and preparation method thereof - Google Patents

Abstract

The invention relates to a sandwich structure composite membrane for fluid separation and a preparation method thereof. The composite membrane structure is composed of a top microporous membrane protective layer, a middle ultra-thin dense active separation layer and a bottom porous support layer. The top layer can isolate the active layer and avoid its direct contact with the outside world, specifically to protect the active layer from the scouring shear force of the separation system, avoid direct damage from external mechanical impact, not be decomposed by the complex components of the separated material liquid, and limit the swelling of the active layer; The middle layer plays the role of bonding the top layer and the bottom layer and separating the fluid; the bottom support layer has strong mechanical properties, which can ensure the ability of the entire composite film to resist external force damage. The preparation steps are: configure the active layer solution and apply it on the support layer porous membrane occupied by the solvent, and cover the occupied top layer porous membrane when the active layer solution is in a gel state and has strong adhesion , respectively cross-linked at room temperature and medium temperature after compaction, and then washed and dried to obtain a composite film. The preparation process is simple and easy, and industrialized production can be easily realized.

Description

Sandwich structure multilayer composite membrane for fluid separation and preparation method thereof

technical field

The invention relates to a sandwich-structured multilayer composite membrane with strong separation function, fluid scouring shear force resistance, swelling resistance and mechanical performance and a preparation method thereof.

Background technique

Membrane technology is an emerging high-tech. Compared with traditional separation technologies such as distillation, adsorption and extraction, it has the advantages of low energy consumption, simple equipment, normal temperature operation, strong adaptability and high reliability. In fluid separation, such as Gas separation, reverse osmosis and pervaporation have been widely used [1]. Polymer polymer materials commonly used in fluid separation membranes include polydimethylsiloxane (PDMS), polyamide (PA), polyvinyl alcohol (PVA), polyether block amide (PEBA) and polytrimethylsilane Pyl propyne (PTMSP) and so on. When these materials are made into fluid separation membranes alone, there are problems such as insufficient strength if the thickness is too thin, and poor separation performance if the thickness is too thick. Therefore, polyamide (PA), polypropylene (PP), polysulfone (PSF), Materials such as polyacrylonitrile (PAN), polyetherimide (PEI), polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) or other polymer materials are used as support layers to form a double layer with high strength Or a three-layer composite membrane. In order to ensure that the separation membrane has high separation performance, the thickness of the active layer is generally controlled at the nanometer to micrometer level.

In the general two-layer or three-layer composite membrane structure, the ultra-thin active separation layer is on the top layer and will directly contact the separation material liquid. However, due to its extreme fragility, when it is used for fluid separation, especially when the separation contains complex components Such as the solid particle feed liquid, it is usually threatened by two aspects: the first is the shear force on the membrane surface caused by fluid scouring or the external mechanical force during installation and use. During the separation process, in order to reduce the membrane surface The enhanced mass transfer of the boundary layer will use a higher flow rate of the feed liquid. When the high flow rate feed liquid flows through the membrane surface, it will have a strong shearing effect on it, causing the membrane surface to wear. In practical application, when the membrane is transported or installed, when the surface of the flexible and fragile membrane encounters the mechanical force of the extremely rigid membrane components, screws, etc., it is extremely easy to be scratched and scratched or directly punctured, so the entire membrane is scrapped The second problem is that when the content of organic components or acidic substances in the separation feed liquid is high, the separation layer formed by the high molecular polymer material will swell and the structure will be destroyed, resulting in the decline of membrane separation performance. . In addition, when membrane separation technology is used to treat fermentation broth, the microbial cells in it may decompose the material of the separation layer, resulting in partial or overall thinning of the separation layer, and the shear force of the fluid on the membrane surface and the decomposition of microorganisms may cause Promote each other to further reduce the membrane life.

Regarding the shearing effect of the fluid on the surface of the membrane and the mechanical force during use, the current research field is blank. To solve the problem of membrane swelling, the current research focuses on post-treatment after film formation, adding inorganic ions, or increasing the crosslinking degree of the separation membrane. However, these methods still have long heat treatment time, high treatment temperature, poor particle dispersion, and complicated membrane production process. And the shortcomings such as the decline of separation performance [2-6].

Contents of the invention

In order to improve the durability of the membrane and increase the service life of the membrane, the invention proposes a multilayer composite membrane with a sandwich structure. In this structure, the active layer is separated as the middle layer, the top microporous membrane separates the fluid from the active layer, and the bottom non-woven fabric supports the entire composite membrane while protecting the other surface of the active layer. The composite membrane under this structure has High mechanical properties and separation performance.

In this structure, the microporous membrane structure on the top layer plays the role of isolating the active layer from direct contact with the outside world, specifically to protect the ultra-thin active layer from the scouring and shearing force of the separated substance system, avoiding direct damage from external mechanical impact, and not The complex components of the separated feed liquid decompose and fix and limit the swelling of the active layer; the middle ultra-thin active separation layer acts as a bond between the top layer and the bottom layer and separates the fluid; the bottom porous support structure is used to support the top layer structure and the active layer to strengthen the composite membrane Mechanical behavior.

The sandwich structure multi-layer composite membrane can be made into various types of membrane modules, including but not limited to frame type, roll type, folded type, disc type, etc.

The microporous membrane of the top protective layer can be polypropylene (PP), polysulfone (PSF), polyetherimide (PEI), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF) or other hydrophobic polymer materials , the pore size of the microporous membrane is between 0.05 and 10 microns, and the thickness is between 20 and 1000 microns; the polymer used in the polymer membrane solution of the dense active layer is polydimethylsiloxane (PDMS) , polyamide (PA), polyvinyl alcohol (PVA), polyether block amide (PEBA), polytrimethylsilylpropyne (PTMSP) or other polymer materials, with a thickness ranging from a few nanometers to a few microns ; The material of the bottom porous support layer is polypropylene (PP), polyterephthalic acid (PET), polyacrylonitrile (PAN), polysulfone (PSF), polyamide (PA) or other high mechanical properties that can be bonded The connected microporous polymer material has a pore size between 0.01 and 1000 microns.

The composite membrane can be applied to gas separation, pervaporation or reverse osmosis, and the separation system can be a gas mixture, a liquid homogeneous mixture, a liquid heterogeneous mixture or a gas-liquid two-phase mixture.

The preparation of the sandwich composite membrane includes the following steps: firstly, the first solvent is coated on the substrate; Occupy; Dissolve another polymer and corresponding cross-linking agent, additives, and compounding agents in the second solvent to make a membrane-forming solution for the active layer; use the third solvent to pore the porous support layer at the bottom Occupation: pouring the film-making solution of the active layer on the bottom support layer occupied by the third solvent; when the active layer solution is in a gel state, the microporous membrane of the top protective layer occupied by the first solvent Turn it over and cover it on the bottom support layer, and apply a compressive force; then heat treatment to cross-link and solidify the polymer film-making solution to form an active layer; after the active layer is cured to form a film and stabilize, the formed film is placed under high temperature and vacuum dry under the sun; the dried composite membrane is placed in pure water and soaked for a certain period of time to remove the occupying solvent (the first solvent) in the pores of the protective layer microporous membrane, and then continue to dry to finally obtain a dry sandwich structure. layer composite film.

During the preparation process of the sandwich composite membrane, when the top layer of the microporous membrane is occupied, not the entire channel is covered with solvent, and a certain space needs to be left. The active layer film-making solution is a dilute solution of the polymer used, and the concentration is between 2% and 20% based on the mass ratio of the polymer to the solvent. The hole occupation method of the bottom support layer can be that the support layer floats on the surface of the third solvent or covers the substrate coated with the third solvent, and the occupation time depends on the micropores of the support layer being partially occupied rather than fully occupied. .

The solvent (the first solvent) of the polymer microporous membrane as the top protective layer can be glycerol or other solvents whose volatile vacuum is higher than 90kPa, as a solution for dissolving another polymer and corresponding crosslinking agents, additives and The solvent (the second solvent) of the compounding agent can be water, benzene, n-heptane or other solvents that can evaporate cleanly between 60-100 ° C, and the solvent used for the hole occupation of the bottom porous support layer (the third solvent) solvent) can be benzene, water or other solvents that can evaporate cleanly between 60-100 °C, the first solvent and the second solvent are not miscible, the third solvent is not miscible with the second solvent, The relative volatility of the three solvents should be the first solvent > the third solvent > the second solvent.

Compared with the existing technical solutions, this research has the following advantages.

(1) Long service time: In this sandwich structure composite membrane, the separation active layer is located in the middle. The microporous membrane on the top separates the active layer from the separation fluid, which effectively avoids the shear force of the fluid flow on the active layer and reduces the swelling and decomposition of the active layer by the complex components in the separation fluid; at the same time, the top protection The layer prevents the active layer from being directly subjected to external mechanical force during packaging, transportation, installation, disassembly and reassembly, and improves the service life of the membrane.

(2) The production method is simple, and it is easy to realize industrialized production: the film-making process has no strict requirements on temperature and humidity, and there is no complicated reaction process. The membrane making process mainly includes occupying space, coating of membrane liquid and adhesion of support layer. The occupancy can be completed by floating on the surface of a flat plate or solvent. Membrane liquid coating technologies such as scraping film and spin coating are mature and have been applied in industry. The adhesion of the support layer is mainly achieved by pressure. Gravity pressure and roller pressure can be used. Extruding with equal force, the technology is mature and reliable.

Description of drawings

Fig. 1 is a schematic diagram of the manufacturing process of the PP/PDMS/PA composite membrane in Example 1 of the present invention.

Fig. 2 is the SEM cross-sectional characterization of the PP/PDMS/PA composite membrane prepared in Example 1 of the present invention.

Detailed ways

Below in conjunction with specific embodiment, the present invention is described in detail, but the present invention is not limited to following embodiment, without departing from the content and scope of the present invention, variation implementation all should be included in the technical scope of the present invention.

Example 1: Pervaporation separation of 5% ethanol aqueous solution with PP/PDMS/PA flat composite membrane with a concentration of 2% membrane-forming solution.

In this example, a polyamide (PA) porous membrane with a thickness of 100 μm and a thickness of 0.22 μm was selected as the bottom support layer, polydimethylsiloxane (PDMS) was used as the active layer material, and a porous membrane with a pore diameter of 50 nm and a thickness of 29 μm was used. A porous polypropylene (PP) film is the top protective layer. The space-occupying solvent used for the top protective layer porous membrane is glycerin, the space-occupying solvent used for the bottom support layer porous membrane is water, the solvent for dissolving PDMS is n-heptane, and the concentration of the PDMS active layer solution is 2%, which is used for testing the composite membrane The separation performance, choose ethanol aqueous solution as the separation system, and separate ethanol by pervaporation method, the specific implementation steps are as follows:

Coat the solvent glycerin on the glass plate of the film scraping machine, cut a PP film with a length of 24 cm and a width of 20 cm and spread it on the glycerin; dissolve PDMS, crosslinking agent orthosilicate and catalyst dibutyltin dilaurate, etc. Make the membrane-making solution of the active layer in n-heptane; float the PA membrane on the water surface to occupy the holes; pour the PDMS membrane-making solution on the PA membrane; take out the membrane-making solution and place it on a flat plate after it is in a gel state ;Turn over the top layer of PP porous membrane with the hole occupied on the PDMS in a gel state; use a glass rod to remove air bubbles, and apply a compressive force to the PP/PDMS/PA membrane; place it at room temperature for 4 hours, and then put it in The PP/PDMS/PA composite membrane was obtained by washing and drying in a 60°C drying oven overnight. It was used to separate 5% ethanol aqueous solution. At 40°C, the flux was 956gm ^-2 h ^-1 and the separation factor was 8.4.

Example 2: Pervaporation separation of 5% ethanol aqueous solution with PP/PDMS/PP flat composite membrane with membrane-forming liquid concentration of 10%.

In this embodiment, polypropylene (PP) non-woven fabric is selected as the bottom support layer, polydimethylsiloxane (PDMS) is used as the active layer material, and the microporous polypropylene (PP) film with a pore diameter of 50 nm and a thickness of 29 μm is Top protection layer. The space-occupying solvent used for the top porous membrane is glycerin, and the concentration of PDMS in the active layer solution is 10%. In order to test the separation performance of the composite membrane, an aqueous ethanol solution is selected as the separation system, and the pervaporation method is used to separate ethanol. The specific implementation steps are as follows:

Coat the solvent glycerin on the glass plate of the wiper machine, cut out a polypropylene porous membrane with a length of 24 cm and a width of 20 cm, and spread it on the glycerin for 5-10 minutes. Dissolve PDMS, tetraethyl orthosilicate and dibutyltin dilauric acid in the solvent n-heptane to prepare a membrane-forming solution for the PDMS active skin layer, and the concentration of PDMS is 10% (W/W). The polyPDMS membrane-making solution was coated on the porous polypropylene membrane with partially occupied micropores using a doctor blade. After 5-10 minutes, when the PDMS membrane liquid on the surface of the polypropylene membrane is in a semi-gel state, the cut polypropylene non-woven fabric with a length of 24 cm and a width of 20 cm is covered on it. Select a flat plate with a certain weight as a pressure source and place it on the top of the non-woven fabric. After drying at room temperature for 2 hours, send it to a 60°C vacuum oven for heat treatment for 12 hours. Soak the dried film in pure water for 2 hours to remove glycerin and other uncrosslinked substances, and continue drying at 60°C for 2 hours to obtain a sandwich-structured PP-PDMS-PP composite film. The performance of the composite membrane was evaluated by pervaporation with 5% ethanol aqueous solution. At 38℃, the permeation flux of the membrane was 900gm ^-2 h ^-1 and the separation factor was 9.4.

Example 3: Pervaporation separation of 5% ethanol aqueous solution with PP/PDMS/PA flat composite membrane with membrane-forming liquid concentration of 20%.

In this example, a polyamide (PA) porous membrane with a thickness of 100 μm and a thickness of 0.22 μm was selected as the bottom support layer, polydimethylsiloxane (PDMS) was used as the active layer material, and a porous membrane with a pore diameter of 50 nm and a thickness of 29 μm was used. A porous polypropylene (PP) film is the top protective layer. The space-occupying solvent used for the top protective layer porous membrane is glycerin, the space-occupying solvent used for the bottom supporting layer porous membrane is water, the solvent for dissolving PDMS is n-heptane, and the concentration of the PDMS active layer solution is 20%, which is used for testing the composite membrane The separation performance, choose ethanol aqueous solution as the separation system, and separate ethanol by pervaporation method, the specific implementation steps are as follows:

Coat the solvent glycerin on the glass plate of the scraping film machine, cut a PP film with a length of 24 cm and a width of 20 cm and spread it on the glycerin; dissolve PDMS, tetraethyl orthosilicate and dibutyltin dilaurate in n-heptane Make the membrane-making solution of the active layer; float the PA membrane on the water surface to occupy the holes; pour the PDMS membrane-making solution on the PA membrane; take out the membrane-making solution and place it on a flat plate after the membrane-making solution is in a gel state; place the hole occupancy The finished top-layer PP porous membrane is turned over and buckled on the PDMS in a gel state; the air bubbles are removed with a glass rod, and a compressive force is applied to the PP/PDMS/PA membrane; it is placed at room temperature for 4 hours, and then placed in a 60°C drying oven overnight , washed and dried with clean water to obtain PP/PDMS/PA composite membrane; use it to separate 5% ethanol aqueous solution, the flux at 40°C is 215gm ^-2 h ^-1 , and the separation factor is 6.9.

references

[1]Cheng XX, Pan FS, Wang MR, Li WD, Song YM, Liu GH, et al.Hybridmembranes for permeability separations.J Membrane Sci.2017;541:329-46.

[2] Nakagawa K, Kunimatsu M, Yasui K, Yoshioka T, Shintani T, Kamio E, et al. Laminar HNb3O8-based membranes supported on anodic aluminum oxide with enhanced anti-swelling property for organic solvent nanofiltration. J Membrane Sci. 2021; 640: 119799.

[3] Cesaria M, Arima V, Manera MG, Rella R. Protocol of thermal aging against the swelling of poly(dimethylsiloxane) and physical insight inswelling regimes. Polymer. 2018; 139:145-54.

[4] Zhou Z, Wang Y, Lin J, Zhang Y, Qu L, Wu W, et al. In-situ molecular-level hybridization enabling high-sulfonation-degree sulfonated poly(ether ketone) membrane with excellent anti-swelling ability and protonconduction. Int J Hydrogen Energ. 2021; 46(61): 31312-23.

[5] Rosli A, Ahmad AL, Low SC. Functionalization of silica nanoparticles to reduce membrane swelling in CO2 absorption process. Journal of Chemical Technology & Biotechnology. 2020; 95(4). [6] Ji CH, Xue SM, Xu ZL. Novel Swelling- Resistant Sodium Alginate Membrane Branching Modified by Glycogen for Highly Aqueous Ethanol Solution Pervaporation.Acs Applied Materials&Interfaces.2016;8(40):27243-53.

Claims (10)

1. A sandwich structure multilayer composite membrane for fluid separation and its preparation, characterized in that the structure consists of a top microporous membrane protective layer, an ultra-thin and dense active separation layer in the middle and a bottom porous support layer structure. 2. The sandwich structure multilayer composite membrane according to claim 1 and its preparation, characterized in that the top microporous membrane structure plays the role of isolating the active layer in direct contact with the outside world, specifically protecting the ultra-thin active layer from separation The effect of the scouring and shearing force of the substance system, avoiding direct damage from external mechanical impact, not being decomposed by the complex components of the separated material liquid, and fixing and limiting the swelling of the active layer; the middle ultra-thin active separation layer acts as a bond between the top layer and the bottom layer and the fluid Separation; the underlying porous support layer structure is used to enhance the mechanical properties of the composite membrane. 3. The sandwich structure multilayer composite membrane and its preparation according to claim 1, characterized in that the prepared composite membrane can be made into various types of membrane modules, including but not limited to plate and frame, roll, folded type, disc type, etc. 4. sandwich structure multilayer composite membrane according to claim 1 and its preparation, it is characterized in that the microporous membrane of top protective layer can be polypropylene (PP), polysulfone (PSF), polyetherimide ( PEI), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF) or other hydrophobic polymer materials, the pore size of the microporous membrane is between 0.05 and 10 microns, and the thickness is between 20 and 1000 microns; dense active The polymer used in the film-making solution of the layer is polydimethylsiloxane (PDMS), polyamide (PA), polyvinyl alcohol (PVA), polyether block amide (PEBA), polytrimethyl Silylpropyne (PTMSP) or other polymer materials, the thickness is between several nanometers and several micrometers; the material of the bottom porous support layer is polypropylene (PP), polyterephthalic acid (PET), polyacrylonitrile ( PAN), polysulfone (PSF), polyamide (PA) or other microporous polymer materials with high mechanical properties that can be bonded, with a pore size between 0.01 and 1000 microns. 5. The sandwich structure multilayer composite membrane according to claim 1 and its preparation, is characterized in that the composite membrane can be applied to gas separation, pervaporation or reverse osmosis, and the separation system can be a gas mixture, a liquid homogeneous mixture, Liquid heterogeneous mixture or gas-liquid two-phase mixture. 6. according to claim 1, a kind of sandwich composite membrane for fluid separation and preparation method thereof, it is characterized in that the preparation of composite membrane comprises the following steps: first on substrate, coat a kind of solvent (4); The protective layer microporous membrane (1) is tiled on a solvent (4), so that the pores of the microporous membrane (1) are partially occupied by the solvent (4); another polymer and the corresponding crosslinking agent, Additives and compounding agents are dissolved in another solvent (5) to make a film-making solution (6) for the active layer (2); use the third solvent (7) to fill the pores of the bottom porous support layer (3) position; the film-making solution (6) of the active layer (2) is poured on the bottom support layer (3) occupied by the solvent (7); when the active layer solution is in a gel state, it will be occupied by the solvent (4) The microporous membrane (1) of the top protective layer in the position is turned over and covered on the bottom support layer (3), and a compressive force is applied; then heat treatment is performed to cross-link and solidify the polymer film-making solution to form an active layer (2); After the layer (2) is solidified into a film and stabilized, the formed film is dried under high temperature and vacuum; the dried composite film is soaked in pure water for a certain period of time to remove the protective layer in the pores of the microporous film (1). The space-occupying solvent (4), and then continue to dry, and finally make a dry multi-layer composite film with a sandwich structure. 7. the preparation process of composite membrane according to claim 6 is characterized in that, the amount of solvent (4) coated on the substrate and the hole occupancy time of protective layer microporous membrane (1) occupy top layer with part The microporous volume of the microporous membrane is not occupied by all pores. 8. The preparation process of the composite membrane according to claim 6, characterized in that the active layer membrane-making solution (6) is a dilute solution of the polymer used, and in terms of its mass ratio to the solvent, the concentration is 2 to 20%. between. 9. the preparation process of composite membrane according to claim 6, is characterized in that, the hole occupancy mode of bottom supporting layer (3) can be that supporting layer floats on solvent (7) liquid level or covers on the surface that is coated with solvent (7) ) on the substrate, the occupation time is based on the fact that the holes in the support layer are partially occupied rather than fully occupied. 10. the preparation process of composite membrane according to claim 6 is characterized in that, the solvent (4) of the polymer microporous membrane (1) that is used to occupy the top protective layer can be glycerin or other volatile vacuum degree higher than 90kPa solvent, as a solvent (5) for dissolving another polymer and corresponding cross-linking agent, additive and compounding agent, it can be water, benzene, n-heptane or other solvents that can evaporate cleanly between 60-100°C solvent, the solvent (7) used to occupy the pores of the bottom porous support layer (3) can be benzene, water or other solvents that can evaporate cleanly between 60-100 ° C, the solvent (4) and the solvent (5 ) are immiscible, solvent (7) and solvent (5) are immiscible, and the relative volatility of the three solvents should be solvent (4)>solvent (7)>solvent (5).

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