Asymmetric multi-channel metal film and preparation method thereof

Abstract

The invention discloses an asymmetric multi-channel metal film and a preparation method thereof, the asymmetric multi-channel metal film comprises a metal carrier with a channel, and the inner wall of the channel is provided with a separation layer; the raw material of the metal carrier at least comprises metal powder A, and the metal powder A is at least one of stainless steel powder and nickel metal powder; the raw material of the separation layer at least comprises metal powder B, and the metal powder B is at least one of stainless steel powder, nickel metal powder, titanium alloy powder and nickel alloy powder. The asymmetric multi-channel metal film has multiple channels, the effective filtering area is increased to a great extent, the separation layer and the metal carrier are tightly combined, the use stability is good, the preparation process is simple, the condition controllability is high, the separation layer is uniform and complete, and the thickness is controllable.

Description

Technical Field

[0001] This invention belongs to the field of membrane material technology, specifically relating to an asymmetric multichannel metal membrane and its preparation method. Background Technology

[0002] Metal membranes possess advantages such as high mechanical strength, good thermal conductivity, weldability, and excellent sealing performance, along with good thermal and chemical stability, making them widely used in high-temperature and high-pressure industrial applications. Traditional tubular metal membranes have only one axial channel. In industrial filtration applications, as filtration time increases, impurities deposited on the outer surface of the metal membrane gradually form a filter cake, clogging the membrane pores. Therefore, frequent cleaning and replacement of the metal membrane are necessary, leading to decreased membrane efficiency and increased operating costs.

[0003] To improve the efficiency and filtration capacity of metal membranes, researchers have developed multi-channel metal membranes. Multi-channel metal membranes possess high specific surface area and high flux, effectively increasing filtration capacity. However, existing multi-channel metal membranes are prone to damage during use, and their stability needs further improvement. Summary of the Invention

[0004] The purpose of this invention is to provide an asymmetric multichannel metal membrane and its preparation method. The process is simple to operate, the parameters are easy to control, and the cost is low. The prepared asymmetric multichannel metal membrane has high throughput characteristics, uniform and dense membrane layer, and adjustable thickness, and has good prospects for industrial application.

[0005] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:

[0006] An asymmetric multichannel metal membrane, the asymmetric multichannel metal membrane comprising a metal carrier having channels, wherein a separation layer is provided on the inner wall of the channels;

[0007] The raw material of the metal carrier includes at least metal powder A, wherein metal powder A is at least one of stainless steel powder and nickel metal powder;

[0008] The raw material of the separation layer includes at least metal powder B, which is at least one of stainless steel powder, nickel metal powder, titanium alloy powder, and nickel alloy powder.

[0009] In one or more embodiments of the present invention, the pore size of the metal carrier is 3 μm-11 μm, the pore size of the separation layer is 0.8 μm-4.5 μm, and the pore size of the separation layer is smaller than the pore size of the metal carrier; and / or,

[0010] The thickness of the separation layer is 60μm-90μm.

[0011] Another specific embodiment of the present invention provides the following technical solution:

[0012] A method for preparing an asymmetric multichannel metal film includes the following steps:

[0013] Take the inner mold, coat the surface of the inner mold with ceramic slurry, and after drying, form an isolation layer to obtain the pretreated inner mold;

[0014] Take the outer mold, place the fixed mold with multiple channels at one end of the outer mold, insert the pre-treated inner mold into the outer mold and place it in the channel of the fixed mold, so that a cavity is formed between the outer mold and the pre-treated inner mold;

[0015] Metal powder A is filled into the cavity, and a fixing mold is installed at the other end of the outer mold to seal it, thus obtaining a metal billet.

[0016] The metal billet is heat-treated, then cleaned and dried to obtain a metal carrier with channels.

[0017] Metal powder B and binder are mixed to form a suspension. The suspension is introduced into the channel of a metal carrier. Vacuum suction is performed from the outer wall of the metal carrier to form a coating film on the inner wall of the channel. Then, heat treatment is performed to form a separation layer on the inner wall of the channel, resulting in an asymmetric multi-channel metal film.

[0018] In one or more embodiments of the present invention, the ceramic slurry comprises ceramic powder and a binder solution, wherein the ceramic powder has a mass fraction of 30%-50%, a particle size of 4μm-5μm, and is at least one of alumina, zirconium oxide, and titanium oxide; the binder solution is at least one of a polyvinyl butyral solution, a polyvinyl alcohol solution, and a methylcellulose solution with a mass fraction of 1%-5%; and / or,

[0019] The adhesive is at least one of a 1%-5% (w / w) solution of polyvinyl butyral, polyvinyl alcohol, or methylcellulose; and / or,

[0020] The mass fraction of metal powder B in the suspension is 15%-50%; and / or,

[0021] The particle size of the metal powder A is 5μm-500μm; and / or,

[0022] The particle size of the metal powder B is 1μm-20μm.

[0023] In one or more embodiments of the present invention, in the preparation step of the pretreated inner mold, the drying temperature is 65℃-75℃, and the time is 1.5h-2.5h; and / or,

[0024] The heat treatment operation of the metal billet is as follows: under vacuum, argon, or hydrogen atmosphere, first heat to 400℃-600℃ at a rate of 2℃ / min-5℃ / min, hold for 0.5h-1.5h; then heat to 1000℃-1200℃ at a rate of 5℃ / min-10℃ / min, hold for 1h-3h; and / or,

[0025] The vacuum aspiration operation is as follows: aspirate the suspension at a vacuum level of 0.08 MPa-0.1 MPa for a time of 60 s-600 s; and / or,

[0026] After the vacuum suction operation is completed, the heat treatment operation is as follows: under vacuum, reducing or inert atmosphere conditions, the temperature is increased to 950℃-1100℃ at a heating rate of 2℃ / min-5℃ / min, and held for 1h-3h.

[0027] In one or more embodiments of the present invention, the diameter of the inner mold is 2mm-50mm; and / or,

[0028] The inner diameter of the outer mold is 10mm-200mm; and / or,

[0029] The fixed mold has 3 to 37 holes.

[0030] Another specific embodiment of the present invention provides the following technical solution:

[0031] A method for preparing an asymmetric multichannel metal film includes the following steps:

[0032] Take the inner mold, coat the surface of the inner mold with ceramic slurry, and after drying, form an isolation layer to obtain the pretreated inner mold;

[0033] Metal powder B and binder are mixed to form a suspension. The suspension is then coated onto the isolation layer of the pretreated inner mold to obtain the treated inner mold.

[0034] Take the outer mold, place the fixed mold with multiple channels at one end of the outer mold, insert the processed inner mold into the outer mold and place it in the channel of the fixed mold, so that a cavity is formed between the outer mold and the processed inner mold;

[0035] Metal powder A is filled into the cavity, and a fixing mold is installed at the other end of the outer mold to seal it, thus obtaining a metal billet.

[0036] The metal blank is heat-treated, then cleaned and dried to obtain an asymmetric multichannel metal film.

[0037] In one or more embodiments of the present invention, the ceramic slurry comprises ceramic powder and a binder solution, wherein the ceramic powder has a mass fraction of 30%-50%, a particle size of 4μm-5μm, and is at least one of alumina, zirconium oxide, and titanium oxide; the binder solution is at least one of a polyvinyl butyral solution, a polyvinyl alcohol solution, and a methylcellulose solution with a mass fraction of 1%-5%; and / or,

[0038] The adhesive is at least one of a 1%-5% (w / w) solution of polyvinyl butyral, polyvinyl alcohol, or methylcellulose; and / or,

[0039] The mass fraction of metal powder B in the suspension is 15%-50%; and / or,

[0040] The particle size of the metal powder A is 5μm-500μm; and / or,

[0041] The particle size of the metal powder B is 1μm-20μm; and / or,

[0042] The particle size difference between metal powder A and metal powder B is less than or equal to 50 μm.

[0043] In one or more embodiments of the present invention, in the preparation step of the pretreated inner mold, the drying temperature is 65℃-75℃, and the time is 1.5h-2.5h; and / or,

[0044] The heat treatment operation of the metal billet is as follows: under vacuum, reducing or inert atmosphere conditions, the temperature is raised to 950℃-1100℃ at a heating rate of 2℃ / min-5℃ / min, and held for 1h-3h.

[0045] In one or more embodiments of the present invention, the diameter of the inner mold is 2mm-50mm; and / or,

[0046] The inner diameter of the outer mold is 10mm-200mm; and / or,

[0047] The fixed mold has 3 to 37 holes.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 1. This invention effectively prevents metal powder from adhering to the rigid inner mold by coating an isolation layer on the surface of the rigid inner mold, ensuring smooth demolding of the multi-channel carrier and the integrity of the structure. It also effectively improves the surface roughness of the channels, allowing the mold to be recycled after demolding and reducing production costs. The metal film prepared by co-sintering also significantly reduces the complexity of the process. Furthermore, depending on the application scenario, different specifications of film layers can be prepared by changing the size and number of rigid inner molds, achieving flexible production.

[0050] 2. This invention uses loose-pack sintering instead of isostatic pressing, which avoids uneven stress caused by the complex channel structure during pressing. The performance of the carrier can be controlled by adjusting the powder particle size and sintering temperature, and the sintering shrinkage is uniform, making the carrier easy to form.

[0051] 3. This invention forms a separation layer on the inner surface of the carrier channel by using a suction coating method. Compared with traditional coating methods, this avoids local accumulation or voids in the membrane layer caused by gravity. The membrane layer and the carrier are more tightly bonded, the bonding strength is higher, and the membrane layer is uniform and complete without voids or peeling. Combined with the structure of the multi-channel carrier, the effective filtration area is greatly increased. Attached Figure Description

[0052] 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 only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0053] Figure 1 This is a schematic diagram of the assembly of the inner mold, outer mold, and fixed mold in one embodiment of the present invention;

[0054] Figure 2 This is a schematic diagram of a separation layer formed by vacuum suction on the inner wall of a metal carrier channel in one embodiment of the present invention;

[0055] Figure 3 This is a physical image of the asymmetric multichannel metal film in Embodiment 1 of the present invention;

[0056] Figure 4 This is a SEM image of the inner surface of the asymmetric multichannel metal film channel in Embodiment 1 of the present invention;

[0057] Figure 5 This is a cross-sectional SEM image of the asymmetric multichannel metal film in Embodiment 1 of the present invention;

[0058] Figure 6 This is a cross-sectional SEM image of the asymmetric multichannel metal film in Comparative Example 1 of the present invention;

[0059] Figure 7 This is a cross-sectional SEM image of the asymmetric multichannel metal film in Comparative Example 2 of the present invention;

[0060] Figure 8 This is a long-term stability flux test diagram of the asymmetric multichannel metal film in Embodiment 1 of the present invention.

[0061] Explanation of key figure labels:

[0062] 11. Pre-treated inner mold; 12. Treated inner mold; 2. Fixed mold; 3. Outer mold; 4. Beaker; 5. Metal carrier; 6. Circulating pump; 7. Filter flask; 8. Water circulating vacuum pump. Detailed Implementation

[0063] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0064] For existing multi-channel metal membranes, such as patent application 2010105677072, a mold for forming multi-channel filter elements and a method for forming intermetallic compound multi-channel filter elements are provided. The mold is constructed by designing a mandrel as a support tube with several through holes in its wall, multiple elastic structures fitted onto the support tube, and other assemblies. An intermetallic compound is filled into the mold cavity, and after cold pressing, the mandrel is removed to obtain a multi-channel intermetallic compound filter element. While the mold used in this method is suitable for forming various materials, the manufacturing process is complex. Furthermore, uneven pressure during pressing leads to poor density uniformity in the filter element, making it prone to damage during demolding and resulting in a low yield.

[0065] Patent application 2010106176377 improves upon existing patent technology by providing a cold isostatic pressing mold for multi-channel filter elements and a method for producing intermetallic compound multi-channel filter elements. By adding an outer and inner rubber sleeve to the mold, pressure is uniformly applied to the inner and outer surfaces of the filter element during the cold isostatic pressing process, resulting in uniform filter element density and thus improved filter element quality. This method solves the uniformity problem during cold isostatic pressing; however, the resulting filter elements have lower filtration accuracy and are difficult to demold.

[0066] Patent application 2013200527966 discloses a multi-channel stainless steel powder sintered filter element. The filter element has multiple axially penetrating channels and uses a cross-flow filtration method for fluid separation, eliminating the need for frequent filter element replacement and cleaning, and extending the filter element's service life. However, this filter element has relatively low filtration accuracy, limiting its application. Typically, improving the filtration accuracy of metal membranes involves using a porous metal support as a carrier, loading one or two transition membrane layers onto the carrier, gradually reducing the pore size.

[0067] Researchers using patent application 201310606646X combined the advantages of ceramic and metal membranes to provide a multi-channel ceramic / metal composite membrane and its preparation method. This membrane uses a multi-channel porous metal material as a support, with a microporous ceramic layer loaded on the inner surface of the channels to prepare a high-precision multi-channel ceramic / metal composite membrane. This method is simple, achieving one-step molding through co-sintering. However, due to the difference in thermal expansion coefficients between the ceramic and metal materials, the membrane layer is prone to cracking and detachment; simultaneously, the porous metal support material has a large pore size, allowing the coating liquid to easily penetrate into the pores of the porous metal support, affecting membrane performance.

[0068] The journal *Journal of Membrane Science* (J Membrane Sci 515 (2016) 144-153) reported the successful fabrication of a three-channel stainless steel hollow fiber membrane with an asymmetric structure using a solvent-free phase separation method combined with sintering, which exhibits high specific surface area and high flux. However, the channel structure of the carrier prepared by this method is prone to deformation during phase transformation, affecting the product's performance.

[0069] The journal Separation and Purification Technology (SEP PURIF TECHNOL 222 (2019) 75-84) reported the preparation of stainless steel carriers using a non-solvent phase separation method combined with sintering, and the preparation of TiO2 films by the traditional impregnation method to improve the performance of metal films. However, the interfacial bonding between the film and the carrier is weak and easy to fall off, and the film thickness is thin and easily damaged during use.

[0070] A specific embodiment of the present invention provides an asymmetric multichannel metal membrane, which includes a metal carrier having channels and a separation layer provided on the inner wall of the channels; the raw material of the metal carrier includes at least metal powder A, wherein the metal powder A is at least one of 316 stainless steel powder and nickel metal powder; the raw material of the separation layer includes at least metal powder B, wherein the metal powder B is at least one of 316 stainless steel powder, nickel metal powder, titanium alloy powder and nickel alloy powder.

[0071] Furthermore, the pore size of the metal carrier is 3μm-11μm, the pore size of the separation layer is 0.8μm-4.5μm, and the thickness of the separation layer is 60μm-90μm.

[0072] Specifically, the pore size of the separation layer is smaller than that of the metal carrier, forming an asymmetric structure. The small pore size of the separation layer can improve the retention capacity of the metal membrane, while the large pore size of the metal carrier enables the metal membrane to have a high throughput. Furthermore, the channels in the metal carrier can improve the processing efficiency of the metal membrane.

[0073] Another specific embodiment of the present invention provides a method for preparing an asymmetric multichannel metal film, which specifically includes the following steps:

[0074] Step 1: Take the inner mold, coat the surface of the inner mold with ceramic slurry, and after drying, form an isolation layer to obtain the pretreated inner mold.

[0075] Specifically, the inner mold is an alloy rod with a diameter of 2mm-50mm. The ceramic slurry includes ceramic powder and a binder solution. The ceramic powder has a mass fraction of 30%-50%, a particle size of 4μm-5μm, and is at least one of alumina, zirconium oxide, and titanium oxide. The binder solution is at least one of the following: a polyvinyl butyral solution (solvent is ethanol), a polyvinyl alcohol solution (solvent is water), and a methylcellulose solution (solvent is water) with a mass fraction of 1%-5%.

[0076] The coating method is the dip-coating method, which involves placing the inner mold in the ceramic slurry and then pulling it up at a uniform speed. The pulling method can be done manually or by using mechanical equipment to coat the surface of the inner mold with a ceramic slurry with a thickness of 20μm-100μm. Then, it is dried at 65℃-75℃ for 1.5h-2.5h.

[0077] By setting an isolation layer to modify the surface of the inner mold, the isolation layer can block the direct contact between the mold and the metal powder, prevent the two from sticking together during the heat treatment process, which would make it difficult to remove the inner mold, and ensure the integrity of the asymmetric multi-channel metal film structure.

[0078] Step 2, as follows Figure 1 As shown, take the outer mold 3, place the fixed mold 2 with multiple channels at one end of the outer mold 3, insert the pre-processed inner mold 11 into the outer mold 3 and place it in the channel of the fixed mold 2, so that a cavity is formed between the outer mold 3 and the pre-processed inner mold 11.

[0079] Specifically, the inner diameter of the outer mold is 10mm-200mm, and the number of holes in the fixed mold is 3-37.

[0080] Step 3: Fill the cavity with metal powder A, and install a fixing mold at the other end of the outer mold to seal it, thus obtaining a metal blank.

[0081] Specifically, the particle size of metal powder A is 5μm-500μm. When filling with metal powder A, it can be manually compacted or compacted using a vibrating screen to give the metal billet a certain mechanical strength.

[0082] Step 4: Heat treat the metal billet, then clean and dry it to obtain a metal carrier with channels.

[0083] Specifically, the heat treatment operation is as follows: under vacuum, argon or hydrogen atmosphere, first heat up to 400℃-600℃ at a rate of 2℃ / min-5℃ / min and hold for 0.5h-1.5h for degreasing treatment; then heat up to 1000℃-1200℃ at a rate of 5℃ / min-10℃ / min and hold for 1h-3h for sintering.

[0084] The cleaning process is as follows: the technical carrier obtained after heat treatment is placed in a 5%-20% PVP (polyvinylpyrrolidone) solution, ethanol solution or NMP (N-methylpyrrolidone) solution for ultrasonic cleaning to remove surface residues, and then dried at 40℃-70℃ for later use.

[0085] Step 5: Mix metal powder B and binder to form a suspension. Pass the suspension into the channel of the metal carrier and vacuum-pump it from the outer wall of the metal carrier to form a coating film on the inner wall of the channel. Then, perform heat treatment to form a separation layer on the inner wall of the channel, and obtain an asymmetric multi-channel metal film.

[0086] Specifically, the particle size of metal powder B is 1μm-20μm, the binder is at least one of polyvinyl butyral solution, polyvinyl alcohol solution, and methylcellulose solution with a mass fraction of 1%-5%, and the mass fraction of metal powder B in the suspension is 15%-50%.

[0087] like Figure 2 As shown, a metal carrier 5 is placed in a plastic tube with an inner diameter slightly larger than that of the metal carrier 5. Both ends of the plastic tube are fixed with gaskets. A circulation pump 6 is connected to one end of the plastic tube, and a filtration flask 7 is connected to the plastic tube via a rubber tube. The suspension in beaker 4 is fed into the channel of the metal carrier 5 using the circulation pump 6. Then, under a vacuum of 0.08 MPa-0.1 MPa, the filtration flask 7 and a water-circulating vacuum pump 8 are used to suction from the outer wall of the metal carrier 5, forming a tightly bonded filter cake with a thickness of 10 μm-300 μm on the inner wall of the metal carrier channel. The filtration time is 60-600 s. This method improves the interfacial bonding strength of the coated film during the heat treatment, i.e., sintering process. Furthermore, by adjusting the filtration time or the solid content of the suspension, the thickness of the filter cake can be controlled, thereby controlling the thickness of the final separation layer.

[0088] The heat treatment process involves heating to 950℃-1100℃ at a rate of 2℃ / min-5℃ / min under vacuum, reducing, or inert atmosphere conditions, and holding at that temperature for 1-3 hours. A reducing atmosphere, such as low-temperature nitrogen followed by high-temperature vacuum calcination, can prevent oxidation reactions; an inert atmosphere, such as argon, is used.

[0089] Another specific embodiment of the present invention provides a method for preparing an asymmetric multichannel metal film, which specifically includes the following steps:

[0090] Step 1: Take the inner mold, coat the surface of the inner mold with ceramic slurry, and after drying, form an isolation layer to obtain the pretreated inner mold.

[0091] Specifically, the inner mold is an alloy rod with a diameter of 2mm-50mm. The ceramic slurry includes ceramic powder and a binder solution. The ceramic powder has a mass fraction of 30%-50%, a particle size of 4μm-5μm, and is at least one of alumina, zirconium oxide, and titanium oxide. The binder solution is at least one of the following: a polyvinyl butyral solution (solvent is ethanol), a polyvinyl alcohol solution (solvent is water), and a methylcellulose solution (solvent is water) with a mass fraction of 1%-5%.

[0092] The coating method is the dip-coating method, which involves placing the inner mold in the ceramic slurry and then pulling it up at a uniform speed. The pulling method can be done manually or by using mechanical equipment to coat the surface of the inner mold with a ceramic slurry with a thickness of 20μm-100μm. Then, it is dried at 65℃-75℃ for 1.5h-2.5h.

[0093] Step 2: Mix metal powder B and binder to form a suspension, and coat the suspension onto the isolation layer of the pretreated inner mold to obtain the treated inner mold.

[0094] Specifically, the particle size of metal powder B is 1μm-20μm, the binder is at least one of polyvinyl butyral solution, polyvinyl alcohol solution, and methylcellulose solution with a mass fraction of 1%-5%, and the mass fraction of metal powder B in the suspension is 15%-50%.

[0095] The suspension coating is performed using the dip-lift method, which involves placing the pre-treated inner mold in the suspension and then lifting it at a uniform speed. The lifting method can be done manually or by using mechanical equipment.

[0096] Step 3, as follows Figure 1 As shown, take the outer mold 3, place the fixed mold 2 with multiple channels at one end of the outer mold 3, insert the processed inner mold 12 into the outer mold 3 and place it in the channel of the fixed mold 2, so that a cavity is formed between the outer mold 3 and the processed inner mold 12.

[0097] Specifically, the particle size of metal powder A is 5μm-500μm. When filling with metal powder A, it can be manually compacted or compacted using a vibrating screen to give the metal billet a certain mechanical strength.

[0098] Preferably, the particle size difference between metal powder A and metal powder B is less than or equal to 50 μm, so as to obtain a high-performance asymmetric multichannel metal film in the subsequent co-sintering step 4, which is still easy to demold after co-sintering.

[0099] Step 4: Heat-treat the metal billet, then clean and dry it to obtain an asymmetric multichannel metal film.

[0100] Specifically, the heat treatment operation is as follows: under vacuum, reducing or inert atmosphere conditions, the temperature is increased to 950℃-1100℃ at a heating rate of 2℃ / min-5℃ / min, and held for 1h-3h.

[0101] The cleaning process involves placing the heat-treated metal carrier in a 5%-20% PVP (polyvinylpyrrolidone) solution, ethanol solution, or NMP (N-methylpyrrolidone) solution for ultrasonic cleaning to remove surface residues, followed by drying at 40℃-70℃.

[0102] The present invention will be further described in detail below with reference to specific embodiments.

[0103] Example 1

[0104] The method for preparing the asymmetric multichannel metal film in this embodiment is as follows:

[0105] Step 1: Mix 3% polyvinyl alcohol aqueous solution and 5μm alumina to prepare 30% alumina ceramic slurry. Apply the alumina ceramic slurry as an isolation layer evenly to the surface of a 4 mm 304 stainless steel rod metal inner mold with a coating thickness of 50μm. After drying at 70℃ for 2 hours, a pretreated rigid inner mold is obtained.

[0106] Step 2: The mold is composed of an outer mold of a quartz tube with an inner diameter of 20 mm, a 7-hole fixed mold, and 7 rigid inner molds coated with an isolation layer. Stainless steel powder with a particle size of 48μm-75μm is filled into the annular cavity between the inner wall of the quartz tube and the pretreated metal mold.

[0107] Step 3: After fixing both ends, heat the mold to 500°C in a vacuum atmosphere at a heating rate of 3°C / min and hold for 1 hour for degreasing treatment. Then heat to 1100°C at a heating rate of 3°C / min and hold for 2 hours to obtain a metal sintered body with the inner mold attached.

[0108] Step 4: After removing the 7-hole fixing molds at both ends of the sintered metal body, take out the 304 stainless steel metal rod to obtain the metal carrier, place it in an ethanol solution for ultrasonication, cleaning, and drying before use.

[0109] Step 5: Stainless steel powder with a particle size of 1μm-10μm and an ethanol solution of 2% polyvinyl butyral by mass are mixed to form a suspension, with the stainless steel powder concentration being 30%. Then, the suspension is uniformly coated on the inner surface of the channels of the metal carrier by suction. The suction filtration time is 120s. After drying at 70℃ for 2h, it is first degreased by holding at 350℃ for 1h under vacuum atmosphere, and then heated to 1000℃ for 2h at a heating rate of 5℃ / min. After cooling, an asymmetric multichannel metal membrane is obtained.

[0110] A physical image of the asymmetric multichannel metal film in this embodiment is shown below. Figure 3 As shown, the SEM image of the inner surface of the channel is as follows. Figure 4 As shown, the cross-sectional SEM image of the asymmetric multichannel metal film is as follows. Figure 5 As shown, the thickness of the separation layer on the inner wall of the metal carrier channel is 88 μm.

[0111] Example 2

[0112] The method for preparing the asymmetric multichannel metal film in this embodiment is as follows:

[0113] Step 1: Mix 3% polyvinyl alcohol aqueous solution and 5μm alumina to prepare 30% alumina ceramic slurry. Apply the alumina ceramic slurry as an isolation layer evenly to the surface of a 3mm 304 stainless steel rod metal inner mold with a coating thickness of 50μm. After drying at 70℃ for 2h, a pretreated rigid inner mold is obtained.

[0114] Step 2: The mold is composed of an outer mold of a quartz tube with an inner diameter of 16mm, a 7-hole fixing mold, and 7 rigid inner molds coated with an isolation layer. Nickel metal powder with a particle size of 38μm-48μm is filled into the annular cavity between the inner wall of the quartz tube and the pretreated metal mold.

[0115] Step 3: After fixing both ends, heat the mold to 400°C in a vacuum atmosphere at a heating rate of 5°C / min and hold for 1 hour for degreasing treatment. Then heat to 1000°C at a heating rate of 3°C / min and hold for 2 hours to obtain a metal sintered body with the inner mold attached.

[0116] Step 4: After removing the 7-hole fixing molds at both ends of the sintered metal body, take out the 304 stainless steel metal rod to obtain the metal carrier, place it in an ethanol solution for ultrasonication, cleaning, and drying before use.

[0117] Step 5: Stainless steel powder with a particle size of 1μm-10μm is mixed with a 2% (w / w) polyvinyl alcohol aqueous solution to form a suspension, with a stainless steel powder concentration of 25%. The suspension is then uniformly coated onto the inner surface of the channels of the metal carrier by suction filtration for 120 seconds. After drying at 70℃ for 2 hours, the membrane is first degreased by holding at 350℃ for 1 hour under vacuum, and then heated to 950℃ for 2 hours at a heating rate of 5℃ / min. After cooling, an asymmetric multichannel metal membrane is obtained.

[0118] Example 3

[0119] The method for preparing the asymmetric multichannel metal film in this embodiment is as follows:

[0120] Step 1: Mix 3% polyvinyl alcohol aqueous solution and 5μm titanium dioxide to prepare 50% titanium dioxide ceramic slurry. Apply the titanium dioxide ceramic slurry isolation layer evenly to the surface of a 2mm 304 stainless steel rod metal inner mold with a coating thickness of 50μm. After drying at 70℃ for 2h, a pretreated rigid inner mold is obtained.

[0121] Step 2: The mold is composed of an outer mold of a quartz tube with an inner diameter of 12mm, a 7-hole fixing mold, and 7 rigid inner molds coated with an isolation layer. Stainless steel powder with a particle size of 25μm-38μm is filled into the annular cavity between the inner wall of the quartz tube and the pretreated metal mold.

[0122] Step 3: After fixing both ends, heat the mold to 500°C in a vacuum atmosphere at a heating rate of 5°C / min and hold for 0.5h for degreasing treatment. Then heat to 1100°C at a heating rate of 3°C / min and hold for 3h to obtain a metal sintered body with the inner mold attached.

[0123] Step 4: After removing the 7-hole fixing molds at both ends of the sintered metal body, take out the 304 stainless steel metal rod to obtain the metal carrier, place it in an ethanol solution for ultrasonication, cleaning, and drying before use.

[0124] Step 5: Stainless steel powder with a particle size of 1μm-10μm and 2% methylcellulose aqueous solution are mixed to form a suspension. The concentration of stainless steel powder is 15%. The suspension is uniformly coated on the inner surface of the channel of the metal carrier by suction. The suction filtration time is 180s. After drying at 70℃ for 2h, it is first degreased at 350℃ for 2h under vacuum atmosphere, and then heated to 1100℃ for 2h at a heating rate of 3℃ / min. After cooling, an asymmetric multichannel metal membrane is obtained.

[0125] Example 4

[0126] The method for preparing the asymmetric multichannel metal film in this embodiment is as follows:

[0127] Step 1: Mix 3% polyvinyl alcohol aqueous solution and 5μm alumina to prepare 30% alumina ceramic slurry. Apply the alumina ceramic slurry isolation layer evenly to the surface of a 4mm 304 stainless steel rod metal inner mold with a coating thickness of 50μm. After drying at 70℃ for 2h, a pretreated rigid inner mold is obtained.

[0128] Step 2: The mold is composed of an outer mold of a quartz tube with an inner diameter of 20mm, a 7-hole fixing mold, and 7 rigid inner molds coated with an isolation layer. Nickel metal powder with a particle size of 25μm-38μm is filled into the annular cavity between the inner wall of the quartz tube and the pretreated metal mold.

[0129] Step 3: After fixing both ends, heat the mold to 500°C in a vacuum atmosphere at a heating rate of 5°C / min and hold for 1.5 hours for degreasing treatment. Then heat it to 1150°C at a heating rate of 3°C / min and hold for 2 hours to obtain a metal sintered body with the inner mold attached.

[0130] Step 4: After removing the 7-hole fixing molds at both ends of the sintered metal body, take out the 304 stainless steel metal rod to obtain the metal carrier, place it in an ethanol solution for ultrasonication, cleaning, and drying before use.

[0131] Step 5: Stainless steel powder with a particle size of 1μm-10μm and an ethanol solution of 2% polyvinyl butyral by mass are mixed to form a suspension. The concentration of stainless steel powder is 25%. The suspension is uniformly coated on the inner surface of the channel of the metal carrier by suction. The suction filtration time is 120s. After drying at 70℃ for 2h, it is first degreased by holding at 350℃ for 1h under vacuum atmosphere, and then heated to 1050℃ for 2h. The heating rate is 5℃ / min. After cooling, an asymmetric multichannel metal membrane is obtained.

[0132] Example 5

[0133] The method for preparing the asymmetric multichannel metal film in this embodiment is as follows:

[0134] Step 1: Mix 3% polyvinyl alcohol aqueous solution and 5μm alumina to prepare 30% alumina ceramic slurry. Apply the 30% alumina ceramic slurry as an isolation layer evenly to the surface of a 4 mm 304 stainless steel rod metal inner mold with a coating thickness of 50μm. After drying at 70℃ for 2 hours, a pretreated rigid inner mold is obtained.

[0135] Step 2: Mix stainless steel powder with a particle size of 10μm-20μm and methylcellulose aqueous solution with a mass fraction of 2% to form a suspension with a powder-to-liquid ratio of 2:1. Use the dip-coating method to coat the suspension onto the pretreated rigid inner mold, that is, place the pretreated rigid inner mold in the suspension and then slowly pull it up to obtain a rigid inner mold coated with an isolation layer and a film layer.

[0136] Step 3: The mold is composed of an outer mold of a quartz tube with an inner diameter of 20mm, a 7-hole fixing mold, and 7 rigid inner molds coated with an isolation layer and a film layer. Stainless steel powder with a particle size of 38μm-53μm is filled into the annular cavity between the metal inner molds on the inner wall of the quartz tube.

[0137] Step 4: After fixing both ends, heat the mold to 350°C in a vacuum atmosphere at a heating rate of 5°C / min and hold for 2 hours for degreasing treatment. Then heat to 1000°C at a heating rate of 3°C / min and hold for 2 hours to obtain a metal sintered body with the inner mold attached.

[0138] Step 5: After removing the 7-hole fixing molds at both ends of the sintered metal body, take out the 304 stainless steel metal rod, and perform ultrasonication, cleaning and drying in an ethanol solution to obtain a co-sintered asymmetric multichannel metal film.

[0139] Comparative Example 1

[0140] The preparation method of the asymmetric multichannel metal film in this comparative example is basically the same as that in Example 1, except that the isolation layer in step 1 was not coated.

[0141] The cross-sectional SEM image of the asymmetric multichannel metal film in this comparative example is shown below. Figure 6 As shown, the thickness of the separation layer on the inner wall of the metal carrier channel is 71 μm. In this comparative example, because the rigid inner mold was not modified with an isolation layer first, defects appeared on the inner surface of the prepared metal carrier channel, which affected the subsequent coating process of the separation layer.

[0142] Comparative Example 2

[0143] The preparation method of the asymmetric multichannel metal membrane in this comparative example is basically the same as that in Example 1, except that the coating method of the separation layer in step 5 is different: a heat shrink tube is sleeved on the surface of the metal carrier obtained in step 4, the metal carrier with the heat shrink tube is placed in the suspension, and then it is pulled up at a uniform speed so that the suspension attaches a film on the inner surface of the channel of the metal carrier. After drying, it is first degreased by keeping it at 350°C for 1 h under vacuum atmosphere, and then heated to 1000°C for 2 h with a heating rate of 5°C / min. After cooling, the asymmetric multichannel metal membrane is obtained.

[0144] The cross-sectional SEM image of the asymmetric multichannel metal film in this comparative example is shown below. Figure 7As shown, in this comparative example, the lack of suction during coating resulted in insufficient adhesion between the metal carrier and the film, leading to separation between the film and the carrier, which in turn affected the performance of the asymmetric multichannel metal film.

[0145] Performance testing

[0146] 1. The pore size of the samples in each embodiment and comparative example was measured using a pore size analyzer based on the bubble point method, the porosity was measured using the Archimedes principle method, and the N2 flux was measured using a pore size analyzer. The results are shown in Table 1.

[0147] Table 1. Maximum pore size, average pore size, and N2 flux of each embodiment and comparative sample.

[0148]

[0149] 2. Simulated industrial wastewater was prepared using 2g of powdered activated carbon (D50=5.02), 1g of polyvinyl alcohol, 1g of sodium sulfate, and 996g of water. The long-term stability of the asymmetric multichannel metal membrane in Example 1 was tested using a cross-flow filtration method. The results are as follows: Figure 8 As shown.

[0150] Referring to Table 1, comparing Examples 1-4 with Comparative Example 1, we can see that Comparative Example 1 did not use an isolation layer to modify the surface of the 304 stainless steel metal rod. During the removal of the inner mold after sintering, large defects easily formed on the surface of the sintered metal carrier channel, affecting the subsequent coating of the suspension and resulting in a larger average pore size in the separation layer. If an isolation layer was used to modify the surface of the 304 stainless steel metal rod, the impact on the sintered metal carrier surface after removing the rigid inner mold was smaller, the prepared metal carrier structure was more complete, the subsequent separation layer coating was more complete, and the average pore size was smaller.

[0151] Comparing Examples 1-4 with Comparative Example 2, we can see that Comparative Example 2 uses a dip-coating method to coat the separation layer, immersing the sintered metal carrier in a suspension and then drying it. However, due to gravity, uneven coating occurs on the surface of the separation layer, resulting in a larger pore size. In contrast, this invention uses a suction method. Under the action of a vacuum system, the suspension can be uniformly coated within the channels of the metal carrier, ensuring the integrity of the asymmetric multichannel metal film.

[0152] Comparing Example 5 and Comparative Example 1, we can see that Example 5 uses powder with a larger particle size (10-20 μm) to prepare the separation layer, while Comparative Example 1 does not use an isolation layer modification and uses powder with a smaller particle size (1-10 μm) to prepare the separation layer. However, the pore size of the separation layer is not much different from that of Example 5, indicating that the bonding strength between the separation layer and the carrier is weak, and the separation layer separates from the carrier, which greatly affects the performance of the membrane.

[0153] Combination Figure 8 As can be seen from the figure, the asymmetric multichannel metal membrane in this invention maintains a stable flux even after 30 hours of long-term operation, demonstrating excellent stability.

[0154] The test results from the above embodiments and comparative examples show that:

[0155] The present invention first modifies the surface of the rigid inner mold by coating an isolation layer to isolate the rigid inner mold from the filling metal powder, thereby preventing the metal powder from being co-fired with the rigid inner mold. After sintering and demolding, a complete multi-channel structure metal carrier is formed.

[0156] This invention combines a filtration process with a suction method to coat a separation layer onto a multi-channel metal carrier, which can better integrate the functional layer with the carrier, resulting in a more complete and more uniformly distributed separation layer.

[0157] This invention first obtains a shaped multi-channel metal carrier by modifying and sintering an isolation layer, and then coats a uniform separation layer by suction. This process is simple and controllable, the separation layer is uniform and complete, and the scale-up and scale-down experiments can be carried out by changing the size of the mold, making it suitable for industrial production.

[0158] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from the spirit or essential characteristics of this disclosure. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this disclosure.

[0159] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An asymmetric multichannel metal film, characterized in that, The asymmetric multichannel metal membrane includes a metal carrier with channels, and a separation layer is provided on the inner wall of the channels; The raw material of the metal carrier includes at least metal powder A, wherein metal powder A is at least one of stainless steel powder and nickel metal powder; The raw material of the separation layer includes at least metal powder B, which is at least one of stainless steel powder, nickel metal powder, titanium alloy powder, and nickel alloy powder.

2. The asymmetric multichannel metal film according to claim 1, characterized in that, The metal carrier has a pore size of 3μm-11μm, and the separation layer has a pore size of 0.8μm-4.5μm, wherein the pore size of the separation layer is smaller than that of the metal carrier; and / or, The thickness of the separation layer is 60μm-90μm.

3. A method for preparing the asymmetric multichannel metal film according to claim 1, characterized in that, Includes the following steps: Take the inner mold, coat the surface of the inner mold with ceramic slurry, and after drying, form an isolation layer to obtain the pretreated inner mold; Take the outer mold, place the fixed mold with multiple channels at one end of the outer mold, insert the pre-treated inner mold into the outer mold and place it in the channel of the fixed mold, so that a cavity is formed between the outer mold and the pre-treated inner mold; Metal powder A is filled into the cavity, and a fixing mold is installed at the other end of the outer mold to seal it, thus obtaining a metal billet. The metal billet is heat-treated, then cleaned and dried to obtain a metal carrier with channels. Metal powder B and binder are mixed to form a suspension. The suspension is introduced into the channel of a metal carrier. Vacuum suction is performed from the outer wall of the metal carrier to form a coating film on the inner wall of the channel. Then, heat treatment is performed to form a separation layer on the inner wall of the channel, resulting in an asymmetric multi-channel metal film.

4. The method for preparing an asymmetric multichannel metal film according to claim 3, characterized in that, The ceramic slurry comprises ceramic powder and a binder solution. The ceramic powder has a mass fraction of 30%-50%, a particle size of 4μm-5μm, and is at least one of alumina, zirconium oxide, and titanium oxide. The binder solution is at least one of polyvinyl butyral solution, polyvinyl alcohol solution, and methylcellulose solution, with a mass fraction of 1%-5%. And / or, The coating thickness of the ceramic slurry is 20μm-100μm; And / or, The adhesive is at least one of a 1%-5% (w / w) solution of polyvinyl butyral, polyvinyl alcohol, or methylcellulose; and / or, The mass fraction of metal powder B in the suspension is 15%-50%; and / or, The particle size of the metal powder A is 5μm-500μm; and / or, The particle size of the metal powder B is 1μm-20μm.

5. The method for preparing an asymmetric multichannel metal film according to claim 3, characterized in that, In the preparation step of the pretreated inner mold, the drying temperature is 65℃-75℃, and the time is 1.5h-2.5h; and / or, The heat treatment operation of the metal billet is as follows: under vacuum, argon, or hydrogen atmosphere, first heat to 400℃-600℃ at a rate of 2℃ / min-5℃ / min, hold for 0.5h-1.5h; then heat to 1000℃-1200℃ at a rate of 5℃ / min-10℃ / min, hold for 1h-3h; and / or, The vacuum aspiration operation is as follows: aspirate the suspension at a vacuum level of 0.08 MPa-0.1 MPa for a time of 60 s-600 s; and / or, After the vacuum suction operation is completed, the heat treatment operation is as follows: under vacuum, reducing or inert atmosphere conditions, the temperature is increased to 950℃-1100℃ at a heating rate of 2℃ / min-5℃ / min, and held for 1h-3h.

6. The method for preparing an asymmetric multichannel metal film according to claim 3, characterized in that, The diameter of the inner mold is 2mm-50mm; and / or, The inner diameter of the outer mold is 10mm-200mm; and / or, The fixed mold has 3 to 37 holes.

7. A method for preparing the asymmetric multichannel metal film according to claim 1, characterized in that, Includes the following steps: Take the inner mold, coat the surface of the inner mold with ceramic slurry, and after drying, form an isolation layer to obtain the pretreated inner mold; Metal powder B and binder are mixed to form a suspension. The suspension is then coated onto the isolation layer of the pretreated inner mold to obtain the treated inner mold. Take the outer mold, place the fixed mold with multiple channels at one end of the outer mold, insert the processed inner mold into the outer mold and place it in the channel of the fixed mold, so that a cavity is formed between the outer mold and the processed inner mold; Metal powder A is filled into the cavity, and a fixing mold is installed at the other end of the outer mold to seal it, thus obtaining a metal billet. The metal blank is heat-treated, then cleaned and dried to obtain an asymmetric multichannel metal film.

8. The method for preparing an asymmetric multichannel metal film according to claim 7, characterized in that, The ceramic slurry comprises ceramic powder and a binder solution. The ceramic powder has a mass fraction of 30%-50%, a particle size of 4μm-5μm, and is at least one of alumina, zirconium oxide, and titanium oxide. The binder solution is at least one of polyvinyl butyral solution, polyvinyl alcohol solution, and methylcellulose solution, with a mass fraction of 1%-5%. And / or, The coating thickness of the ceramic slurry is 20μm-100μm; And / or, The adhesive is at least one of a 1%-5% (w / w) solution of polyvinyl butyral, polyvinyl alcohol, or methylcellulose; and / or, The mass fraction of metal powder B in the suspension is 15%-50%; and / or, The particle size of the metal powder A is 5μm-500μm; and / or, The particle size of the metal powder B is 1μm-20μm; and / or, The particle size difference between metal powder A and metal powder B is less than or equal to 50 μm.

9. The method for preparing an asymmetric multichannel metal film according to claim 7, characterized in that, In the preparation step of the pretreated inner mold, the drying temperature is 65℃-75℃, and the time is 1.5h-2.5h; and / or, The heat treatment operation of the metal billet is as follows: under vacuum, reducing or inert atmosphere conditions, the temperature is raised to 950℃-1100℃ at a heating rate of 2℃ / min-5℃ / min, and held for 1h-3h.

10. The method for preparing an asymmetric multichannel metal film according to claim 7, characterized in that, The diameter of the inner mold is 2mm-50mm; and / or, The inner diameter of the outer mold is 10mm-200mm; and / or, The fixed mold has 3 to 37 holes.

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