A method for preparing a direct coater flat sheet membrane module using gel hole blocking

Abstract

The application provides a method for preparing a direct-coating flat plate membrane module using a gel to block holes, which avoids the influence of hole penetration on a porous support plate during coating. The method uses a water-soluble polymer gel to fill the pores of the porous plate, and before the porous support plate is coated with a casting solution, it is first soaked in a water-soluble polymer solution to infiltrate the pores, then taken out and cooled to form a gel, and after film formation, the gel is re-dissolved by soaking in an aqueous solution. The membrane module prepared by the method of the application can effectively avoid the problem of penetration of the casting solution into the pores of the porous support plate when coating a polymer film on the surface of the porous support plate, ensuring uniform film thickness, enhancing the pressure resistance and permeability of the membrane module, and being more suitable for deep-sea high-pressure environments, combined with various sensors or analysis instruments, to realize in-situ and rapid analysis of deep-sea dissolved gases.

Description

Technical Field

[0001] This invention relates to the field of analytical instruments and sensor technology, and more particularly to a method for preparing a direct-coating flat sheet membrane module using gel plugging. Background Technology

[0002] Determining the content of gases such as carbon dioxide and methane in seawater is of great significance in many fields, including marine ecological cycles, global climate, mariculture, and marine energy exploration. Currently, the traditional method for sampling dissolved gases in water involves collecting water samples using samplers and other devices, then bringing them back to ships or onshore laboratories for analysis. This method yields too few samples, making it difficult to obtain the spatiotemporal distribution of the target gas content across the entire ocean area. Furthermore, the high pressure and low temperature of the deep-sea environment place extremely stringent requirements on this method.

[0003] Therefore, various sensors and analytical instruments capable of in-situ determination of dissolved gases underwater or in the deep sea have gradually become mainstream. Among various in-situ detection instruments, apart from Raman spectroscopy which directly detects the aqueous phase, the other instruments, including sensors based on semiconductor, non-dispersive infrared, or other optical principles, as well as analytical instruments such as underwater mass spectrometry and chromatography, are all based on membrane degassing technology. That is, they use a permeable membrane to remove dissolved gases from the water and allow them to permeate into a gas phase detection chamber on the other side for detection.

[0004] Therefore, the material and structure of the degassing membrane module are key factors affecting detection performance. At depths of 4000–6000 m, the pressure difference between the inside and outside of the membrane can reach 40–60 MPa. This necessitates that membrane materials used in deep-sea applications possess excellent gas permeability and pressure resistance. Currently, degassing membrane materials used for underwater gas separation include polydimethylsiloxane (PDMS), Teflon AF, PNC, and polyethylene, among which PDMS membranes are the most widely used.

[0005] Studies have found that single membranes have relatively weak mechanical strength, which can lead to membrane rupture or reduced permeability under high pressure. Therefore, porous support structures are usually added after the membrane to enhance its mechanical strength. Common porous support structure materials include sintered metal plates, metal mesh, and porous ceramic materials. Membrane module types include flat-sheet membrane structures and tubular membrane structures. Tubular membrane structures can increase the air intake, but the interfaces of their porous support materials usually require bonding and sealing with epoxy adhesives, making them prone to damage under high pressure. Flat-sheet membrane structures are relatively simple, easy to prepare and operate, have better overall pressure resistance, and are more widely used.

[0006] Currently, flat-plate membrane modules in use can be divided into two types. The first type consists of separate components for the degassing membrane and the support material, such as invention patent CN107884365 A, which provides a structure in which a sintered metal support plate is installed at the rear end of the membrane during use. Although this type of split-plate membrane module is simple to manufacture, the poor mechanical strength (tensile resistance) of the degassing membrane makes it prone to damage at the pores or seals of the porous support plate under high pressure, leading to water ingress and malfunction or damage to the instrument. To further enhance the pressure resistance of the membrane module, the casting solution can be directly coated onto the porous support plate and dried to form an integrated membrane module. However, during the coating process, due to capillary action, the casting solution easily seeps into the pores of the support plate, and the degree of penetration varies, resulting in a significant increase in membrane thickness and uneven thickness, ultimately leading to problems such as insufficient membrane permeability and pressure resistance. To reduce the impact of pore leakage, invention patent CN113509847A discloses a method for preparing solid porous nanoparticle / polydimethylsiloxane films through liquid-liquid interface crosslinking, and invention patent CN107297148A discloses a method for preparing an organosilane ultrathin skin by polycondensation of silane monomers on a hydroxylated PDMS membrane surface and using self-assembly technology. Both of these methods require modification of the casting solution and preparation under specific solution conditions, and the preparation conditions directly affect the membrane performance. These methods are cumbersome and lack universality.

[0007] In summary, it is necessary to provide a method for preparing a flat-sheet membrane module to solve the above problems. Summary of the Invention

[0008] To address the aforementioned technical problems encountered in the preparation of flat-sheet membrane modules, such as uneven coating, insufficient pressure resistance, and inadequate permeability, this invention provides a method for preparing direct-coating flat-sheet membrane modules using gel plugging. This invention primarily employs a water-soluble polymeric gel as a filler to fill porous support materials with relatively large pore sizes. The properties of the water-soluble polymeric gel ensure uniform filling, eliminating the incomplete pore filling and permeation problems caused by evaporation and flow, as seen in wetting methods. Furthermore, by immersing one side of the porous support material in the filling liquid while the other side is used to coat the permeate membrane, the step of removing the filler before membrane coating is eliminated, thus ensuring uniform membrane thickness. The resulting membrane module exhibits superior pressure resistance and permeability, making it more suitable for high-pressure environments in the deep sea. Combined with various sensors or analytical instruments, it enables in-situ, rapid analysis of dissolved gases in the deep sea.

[0009] The technical means employed in this invention are as follows:

[0010] A method for preparing a direct-coating flat-sheet membrane module using gel plugging includes the steps of filling the pores of a porous support plate, coating a casting solution onto the upper surface of the porous support plate and curing it into a film, and removing the filler from the pores of the porous support plate; characterized in that...

[0011] The specific process for filling the pores of the porous support plate is as follows: while stirring, water-soluble polymer is added to water, the solution is heated and stirred thoroughly to completely dissolve the water-soluble polymer, thus obtaining a filling liquid; the upper surface of the porous support plate is sealed, and then the porous support plate with the upper surface sealed is immersed in the above filling liquid for a period of time to ensure that the lower surface and internal pores of the porous support plate are fully wetted, and then it is taken out and cooled to room temperature to allow the polymer in the lower surface and internal pores to form a gel; the seal on the upper surface is removed, and the upper surface is cleaned to remove oil or dust that may affect the surface coating.

[0012] The water-soluble polymer is any one of polyvinyl alcohol, gelatin, cellulose, and sodium polyacrylate, and the mass fraction of the water-soluble polymer in the polymer solution is 1% to 10%.

[0013] The porous support plate is any one of porous sintered metal, porous ceramic, or porous metal screen.

[0014] Furthermore, the pore diameter of the porous support plate is at least 1 μm, and for deep-sea applications, the pore diameter of the support plate is preferably 1 to 10 μm.

[0015] Furthermore, the upper surface of the porous support plate is sealed by fastening the porous support plate to a non-porous metal sheet, heat-resistant plastic sheet, or heat-resistant film with screws or by compression.

[0016] Furthermore, the porous support plate with the upper surface sealed is immersed in the filling liquid for 5 to 30 minutes.

[0017] Furthermore, the film material coated on the upper surface of the porous support plate is one of polydimethylsiloxane (PDMS), Teflon AF2400, and Teflon AF1600.

[0018] Furthermore, the composition of the casting solution coated on the surface of the porous support plate depends on the membrane material: in the PDMS casting solution, the mass ratio of PDMS to the crosslinking agent tetraethyl orthosilicate and the catalyst dibutyltin dilaurate is 10:(0.9-1.1):(0.1-0.3); the mass percentage concentration of the solvent in the casting solution is 0%-10%; the solvent is any one of ethanol, toluene, and n-hexane; in the Telfon AF casting solution, the mass ratio of Teflon AF2400 or AF1600 to the solvent is 1:(80-200), and the solvent is any one of perfluorocyclohexane, perfluoromethylcyclohexane, perfluorotoluene, FC50, FC770, or Galden HT80.

[0019] Further, the step of coating the casting solution and curing it into a film involves thoroughly mixing and degassing the casting solution. Before the casting solution crosslinks or gels, the casting solution is uniformly coated onto the upper surface of the filled porous support plate. The support plate coated with the casting solution is then further degassed by ultrasonication or vacuum for 5–30 minutes. After the solvent evaporates, it is initially cured at room temperature for 1–2 hours, and then transferred to a vacuum oven for curing at 80–150°C for 4–10 hours to form a film.

[0020] Furthermore, the coating method is any one of spin coating, blade coating, or dip coating.

[0021] Furthermore, the specific steps for removing the gel filling the pores of the porous support plate are as follows: place the porous support plate in deionized water at 50-80°C and sonicate for 5-15 minutes to completely dissolve the polymer in the pores, then remove and dry it.

[0022] This invention provides a method for preparing a direct-coating flat-panel membrane module using gel plugging, avoiding the influence of pore leakage on the porous support plate during the coating process. The method uses a water-soluble polymer gel to fill the pores of the porous plate. Before coating the porous support plate with the casting solution, it is first immersed in a water-soluble polymer solution to wet the pores, then removed and cooled. After film formation, the gel is redissolved by immersion in an aqueous solution. The membrane module prepared by this method effectively avoids the problem of casting solution seeping into the pores of the support plate when coating a polymer film on the surface of the porous support plate, ensuring uniform membrane thickness, improving the pressure resistance, permeability, and mechanical strength of the enhanced membrane module, making it more suitable for high-pressure environments in the deep sea. Combined with various sensors or analytical instruments, it enables in-situ, rapid analysis of dissolved gases in the deep sea.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. It avoids the phenomenon of pore blockage caused by the seepage of the casting solution during coating on the porous support plate, resulting in a uniform coating thickness of the permeate membrane. Furthermore, the integrated design of the permeate membrane and the porous support plate enhances the mechanical strength and pressure resistance of the membrane module.

[0025] 2. This invention allows for the application of common coating methods to the casting solution without requiring special treatment of the casting solution, making it simple to operate and universally applicable.

[0026] Based on the above reasons, the present invention can be used to separate dissolved gases in water under high pressure conditions in the deep sea. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the method for preparing a direct-coating flat sheet membrane module using gel plugging according to the present invention.

[0029] Figure 2 This is a schematic diagram of the apparatus for testing the pressure resistance performance of the membrane module according to the present invention.

[0030] Figure 3 The graph shows the test results of the pressure resistance performance of the membrane module of the present invention, where numbers 1-5 correspond to the pressure resistance performance of the membrane modules of Examples 1-4 and Comparative Example 1, respectively.

[0031] In the diagram: 1. High-pressure water chamber; 2. Permeable membrane; 3. Porous support plate. Detailed Implementation

[0032] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0035] like Figure 1 As shown, a method for preparing a direct-coating flat-sheet membrane module using gel plugging includes the following steps:

[0036] (1) Pore filling of porous support plate:

[0037] While stirring, water-soluble polymers are added to water, and the solution is heated and stirred thoroughly until completely dissolved to prepare a filling solution. The water-soluble polymer can be one of polyvinyl alcohol, gelatin, cellulose, or sodium polyacrylate. A porous support plate is then tightly bonded to a non-porous metal sheet, heat-resistant plastic sheet, or heat-resistant film using screws and compression. The pore size of the porous support plate is at least 1 μm; for deep-sea applications, a pore size of 1–10 μm is preferred. The sealed porous support plate is immersed in the above solution for 5–30 minutes. After the lower surface and internal pores of the porous support plate are fully wetted by the polymer solution, it is removed and cooled to room temperature. The polymer in the lower surface and internal pores forms a gel upon condensation, which effectively and uniformly fills the pores. The seal on the upper surface is then removed, and the upper surface is cleaned with alcohol swabs to remove any oil or dust that may affect the coating.

[0038] (2) Preparation and coating of gas permeation membrane:

[0039] The preparation method of PDMS casting solution is as follows: Polydimethylsiloxane, crosslinking agent tetraethyl orthosilicate, and catalyst dibutyltin dilaurate are added to a solvent. The mass ratio of polydimethylsiloxane, crosslinking agent, and catalyst is 10:(0.9-1.1):(0.1-0.3). The mass fraction of polydimethylsiloxane in the casting solution is 0.1-10%. The solvent used can be one of ethanol, toluene, or n-hexane, which serves to disperse the film. Alternatively, no solvent may be used for dispersion. In Teflon AF2400 or Teflon AF1600 casting solutions, the mass ratio of AF2400 or AF1600 to the solvent is 1:(80-200). The solvent used can be one of fluorinated solvents such as perfluorocyclohexane, perfluoromethylcyclohexane, perfluorotoluene, FC50, FC770, or Galden HT80.

[0040] After the casting solution is prepared, it is degassed by ultrasound or vacuum to remove as many air bubbles as possible. The degassed time depends on the viscosity of the casting solution. Before the casting solution crosslinks or gels, the casting solution is uniformly coated on the upper surface of the porous support plate in step (1). The support plate coated with the casting solution is further degassed for 5 to 30 minutes. After the solvent evaporates, it is placed in an oven at room temperature for preliminary curing for 1 to 2 hours, and then transferred to a vacuum oven at 80 to 150°C for curing for 4 to 10 hours.

[0041] (3) Removal of filler from porous support plate:

[0042] The gel on the lower surface of the porous support plate is scraped off, and the plate is immersed in deionized water at a temperature of 50-80℃ and sonicated for 5-15 minutes to completely dissolve the polymer in the pores. After drying, the direct-coating flat sheet membrane module is obtained.

[0043] Example 1

[0044] A direct-coating flat sheet membrane module includes the following steps:

[0045] (1) Filling the surface of the porous support plate: Weigh 5g of polyvinyl alcohol and slowly add it to 100mL of deionized water while stirring. First, stir the solution at room temperature for 15 minutes, then heat the solution to 70℃ while stirring, and continue to stir thoroughly for 2 hours until the polyvinyl alcohol is completely dissolved. After tightly attaching the upper surface of the porous stainless steel sieve plate with a diameter of 3.8cm to the metal cover plate of the same size with screws, immerse it in the above solution for 15 minutes, remove it, cool it to room temperature, remove the metal plate, and wipe and clean the upper surface of the sieve plate with alcohol cotton.

[0046] (2) Spin-coating PDMS: 10g of polydimethylsiloxane, 0.9g of crosslinking agent tetraethyl orthosilicate, and 0.1g of catalyst dibutyltin dilaurate were weighed and dissolved in 100mL of toluene. The mixture was stirred for 10 minutes until completely mixed to obtain the casting solution. The casting solution was placed in a vacuum oven for 20 minutes to remove air bubbles. A stainless steel sieve plate was placed on the substrate of the spin coater. 5g of the degassed casting solution was drawn up with a dropper and dropped onto the upper surface of the sieve plate. Spin coating was then performed, first at 500rpm for 10 seconds, then at 3000rpm for 30 seconds. After coating, the mixture was cured at room temperature for 1 hour, then transferred to a vacuum oven and cured at 60℃ for 3 hours. The bottom layer air bubbles were removed by vacuuming again, and finally cured at 120℃ for 4 hours. The thickness of the coated PDMS film was 50μm.

[0047] (3) Removal of porous support plate filler: Peel off the polyvinyl alcohol layer on the lower surface of the flat sheet membrane module and immerse it in deionized water at 50°C. After ultrasonic elution for 5 minutes, repeat the process to completely remove the polyvinyl alcohol remaining in the pores. Dry it to obtain a flat sheet membrane module directly coated with PDMS, which does not contain PDMS in its pores.

[0048] Example 2

[0049] (1) Filling the surface of the porous support plate: Weigh 5g of gelatin and slowly add it to 100mL of deionized water while stirring. First, stir the solution at room temperature for 10 minutes, then heat the solution to 80℃ while stirring, and continue to stir thoroughly until the gelatin is completely dissolved. After sealing the polyimide film and the 8cm diameter circular stainless steel sieve with O-rings, immerse them in the above solution for 15 minutes, then remove them, cool them to room temperature, remove the metal plate, and wipe and clean the surface of the sieve plate with alcohol cotton.

[0050] (2) PDMS coating by blade coating: The casting solution is prepared as described in step (2) of Example 1, except that 10g of polydimethylsiloxane, 0.9g of crosslinking agent and 0.1g of catalyst are weighed and dissolved together in ethanol reagent. The mass fraction of PDMS is 5%. After ultrasonic degassing for 10 minutes, the porous support substrate is placed on the blade coating machine platform. The coating is applied twice at room temperature at a constant speed and then dried for 1 hour. The substrate is then transferred to a vacuum oven and cured at 50°C for 2 hours. The bottom layer bubbles are removed by vacuuming again and finally cured at 80°C for 2 hours. The thickness of the coated PDMS film is 30μm.

[0051] (3) Removal of filler from porous support plate: scrape off the gelatin on the lower surface of the flat sheet membrane module, immerse the membrane module in deionized water at 80°C, and ultrasonically wash for 5 minutes. Repeat this process to wash away the residual polyvinyl alcohol in the pores. Dry the membrane module to obtain the flat sheet membrane module directly coated with PDMS.

[0052] Example 3

[0053] (1) Filling the surface of the porous support plate: The method is as described in step (1) of Example 1, except that the porous support material used is a porous ceramic with a diameter of 5 cm.

[0054] (2) PDMS coating by blade coating: As described in step (2) of Example 1, the difference is that the ratio is 10g polydimethylsiloxane, 1.1g crosslinking agent, 0.3g catalyst, the solvent is n-hexane, the mass fraction of PDMS is 5%, after ultrasonic degassing for 5 minutes, the porous support substrate is placed on the blade coating machine platform, coated twice at room temperature at a constant speed and dried for 1 hour, then transferred to a vacuum oven, cured at 50°C for 4 hours, vacuumed again to remove bottom layer bubbles, and finally cured at 80°C for 8 hours. The thickness of the coated PDMS film is 30μm.

[0055] (3) Removal of filler from porous support plate: Same as step (3) in Example 1.

[0056] Example 4

[0057] (1) Surface filling of porous support plate: as described in Example 1.

[0058] (2) Spin coating of Teflon AF2400: Weigh 1g of Teflon AF2400 resin and dissolve it in 100g of perfluoromethylcyclohexane solvent, and degas it by sonication for 30 minutes. Prepare a 1%wt Teflon AF2400 casting solution. Place a stainless steel sieve plate on the substrate of the spin coater, use a dropper to draw and drop 5g of casting solution onto the upper surface of the sieve plate, coat it at a certain speed for 1 minute, dry it at room temperature for 1 hour, then transfer it to a vacuum oven and cure it at 60℃ for 3 hours. Vacuum the bottom layer of air bubbles again, and finally cure it at 80℃ for 4 hours. The thickness of the coated Teflon AF2400 film is 50μm.

[0059] (3) Removal of filler from porous support plate: same as the preparation method described in Example 1.

[0060] Example 5

[0061] (1) Surface filling of porous support plate: the preparation method is as described in Example 1, except that a circular heat-resistant polypropylene sheet with a thickness of 8 mm and a diameter of 4 cm is used as the sealing material.

[0062] (2) Spin coating of Teflon AF2400: The preparation method is the same as described in Example 3, except that the ratio is: 1g of Teflon AF2400, 80g of perfluorotoluene, and the thickness of the coated Teflon AF1600 film is 50μm.

[0063] (3) Removal of filler from porous support plate: same as the preparation method described in Example 1.

[0064] Example 6

[0065] The preparation method described in Example 4 differs in that the water-soluble polymer material used in step (1) is water-soluble cellulose. The solution preparation method is as follows: weigh 1g of cellulose, add it slowly to 100mL of water while stirring rapidly, stir the solution at room temperature for 10 minutes, heat the solution to 70°C while stirring, and continue stirring thoroughly for 1 hour until the sodium polyacrylate is completely dissolved. The casting solution used in step (2) has the following ratio: 1g of Teflon AF2400 and 100g of Galden HT80. The coating method used is the immersion method, specifically: immerse the porous stainless steel sieve plate in the casting solution for 10 seconds, then quickly remove the casting solution horizontally and solidify it according to the method described in Example 4.

[0066] Example 7

[0067] The preparation method described in Example 4 differs in that the water-soluble polymer material used in step (1) is sodium polyacrylate, and the solution is prepared as follows: 10g of sodium polyacrylate is weighed and slowly added to 100mL of water while stirring rapidly. The solution is stirred at room temperature for 15 minutes, and then heated to 70°C while stirring. The solution is then stirred thoroughly for 1 hour until the sodium polyacrylate is completely dissolved. The porous support plate is immersed in the sodium polyacrylate solution for 5 minutes. The casting solution used in step (2) has the following ratio: 1g of Teflon AF2400 and 100g of perfluorocyclohexane. The conditions for dissolving the sodium polyacrylate gel in the pores in step (3) are: ultrasonic elution in deionized water at 70°C for 5 minutes, followed by repeating this process twice more.

[0068] Example 8

[0069] The preparation method described in Example 4 differs in that the water-soluble polymer material used in step (1) of this example is gelatin. The porous support plate is immersed in the gelatin solution for 5 minutes. The casting solution used in step (2) has the following ratio: 1g Teflon AF2400 and 100g FC50. The conditions for dissolving the sodium polyacrylate gel in the pores in step (3) are: ultrasonic elution in deionized water at 70°C for 5 minutes, followed by repeating this process twice more.

[0070] Example 9

[0071] The preparation method described in Example 4 differs in that the casting solution ratio is: Teflon AF1600 1g, FC770 200g.

[0072] Comparative Example 1

[0073] A split-type membrane module was prepared by bonding a commercially available PDMS membrane (BD Film-KYN, 100 μm) to a porous stainless steel sieve plate with a diameter of 3.8 cm using an O-ring extrusion sealing method. The pressure resistance performance of the integrated membrane module prepared in Examples 1-4 above was compared with that of the split-type membrane module. The membrane module pressure resistance testing device is as follows: Figure 2 As shown, during the test, the membrane module was installed in a self-made pressure testing device. The permeate membrane 2 and the porous support plate 3 were placed in a sealed space, forming a high-pressure water chamber 1 on top. The membrane-coated side of the membrane module was in contact with the high-pressure water, while a filter paper was placed on the other side, with atmospheric pressure on the filter paper side. A high-performance liquid chromatography pump was used as the pressure source, and the pressure was slowly increased to 10, 20, 30, and 40 MPa, each pressure maintained for 48 hours. Afterward, the pressure was restored to normal. The pressure resistance of the membrane module was judged by checking for any damage to the membrane surface and whether the filter paper was wetted. The pressure resistance test results of the membrane modules in Examples 1-4 and Comparative Example 1 are as follows. Figure 3 As shown, from Figure 3As can be seen from the present invention, the pressure resistance of various integrated membrane modules prepared using the technical solution of the present invention is significantly enhanced compared with that of split membrane modules.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a direct-coating flat sheet membrane module using gel plugging, comprising the steps of filling the pores of a porous support plate, coating a casting solution onto the upper surface of the porous support plate and curing it into a film, and removing the filler from the pores of the porous support plate; characterized in that, The steps for filling the pores of the porous support plate are as follows: water-soluble polymer is added to water while stirring, the solution is heated and stirred thoroughly to completely dissolve the water-soluble polymer to obtain a filling liquid; the upper surface of the porous support plate is sealed, and then the porous support plate with the upper surface sealed is immersed in the above filling liquid for a period of time to fully wet the lower surface and internal pores of the porous support plate. After that, it is taken out and cooled to room temperature to allow the polymer in the lower surface and internal pores to form a gel; the seal on the upper surface is removed and the upper surface is cleaned to remove oil or dust that may affect the surface coating. The water-soluble polymer is any one of polyvinyl alcohol, gelatin, cellulose, and sodium polyacrylate, and the mass fraction of the water-soluble polymer in the filling liquid is 1% to 10%. The porous support plate is any one of porous sintered metal, porous ceramic, or porous metal screen.

2. The method for preparing a direct-coating flat-sheet membrane module using gel plugging according to claim 1, characterized in that, The pore diameter of the porous support plate is at least 1 μm.

3. The method for preparing a direct-coating flat sheet membrane module using gel plugging according to claim 1, characterized in that, The sealing method for the upper surface of the porous support plate is to tightly bond the porous support plate to a non-porous metal sheet, heat-resistant plastic sheet, or heat-resistant film by means of screw fastening or compression.

4. The method for preparing a direct-coating flat sheet membrane module using gel plugging according to claim 1, characterized in that, The porous support plate with the upper surface sealed is immersed in the filling liquid for 5 to 30 minutes.

5. The method for preparing a direct-coating flat sheet membrane module using gel plugging according to claim 1, characterized in that, The membrane material coated on the upper surface of the porous support plate is one of polydimethylsiloxane (PDMS), Teflon AF2400, or Teflon AF1600.

6. The method for preparing a direct-coating flat sheet membrane module using gel plugging according to claim 5, characterized in that, The composition of the casting solution coated on the surface of the porous support plate depends on the membrane material: In the PDMS casting solution, the mass ratio of PDMS to crosslinking agent tetraethyl orthosilicate and catalyst dibutyltin dilaurate is 10:(0.9~1.1):(0.1~0.3); the mass percentage concentration of the solvent in the casting solution is 0%~10%; the solvent is any one of ethanol, toluene, and n-hexane; In the Telfon AF casting solution, the mass ratio of Teflon AF2400 or AF1600 to the solvent is 1:(80~200), and the solvent is any one of perfluorocyclohexane, perfluoromethylcyclohexane, perfluorotoluene, FC770, or Galden HT80.

7. The method for preparing a direct-coating flat sheet membrane module using gel plugging according to claim 6, characterized in that, The steps of coating the casting solution and curing it into a film are as follows: the casting solution is thoroughly mixed and degassed. Before the casting solution crosslinks or gels, it is uniformly coated onto the upper surface of the filled porous support plate. The support plate coated with the casting solution is further degassed by ultrasonication or vacuum for 5-30 minutes. After the solvent evaporates, it is initially cured at room temperature for 1-2 hours. Then it is transferred to a vacuum oven and cured at 80-150°C for 4-10 hours to form a film.

8. The method for preparing a direct-coating flat sheet membrane module using gel plugging according to claim 7, characterized in that, The coating method can be any one of spin coating, blade coating, or dip coating.

9. The method for preparing a direct-coating flat sheet membrane module using gel plugging according to claim 1, characterized in that, The step of removing the filler in the pores of the porous support plate is to place the porous support plate in deionized water at 50~80℃ and sonicate it for 5~15 minutes to completely dissolve the polymer in the pores, then remove it and dry it.

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