Asymmetric nanoscale porous hollow metal fibers and their preparation methods

Abstract

This invention discloses an asymmetric nanoporous hollow metal fiber and its preparation method. The asymmetric nanoporous metal fiber has an outer separation layer with nanoscale pores and an inner support layer with micron-sized finger-like pores. The thickness of the separation layer is 1-30 µm, and the pore size distribution of the channels ranges from 20 to 850 nm. The thickness of the support layer is 30-300 µm, and the pore size distribution of the finger-like pores in the support layer ranges from 1-50 µm. The asymmetric nanoporous hollow metal fiber membrane of this invention, with its outer separation layer with nanoscale pores and inner support layer with micron-sized finger-like pores, can reduce the thickness of the separation layer while achieving a nanoscale pore separation layer, thereby reducing transmission resistance.

Description

Technical Field

[0001] This invention relates to a support material for metal membranes used in hydrogen separation, specifically to asymmetric nanoscale porous hollow metal fibers and their preparation method. Background Technology

[0002] Hydrogen, as a clean, sustainable, and renewable alternative to fossil fuels, is crucial for future energy sustainability and global security. The demand for high-purity hydrogen is increasing significantly in fields such as solid oxide fuel cells, semiconductors, and fine chemicals. Compared to traditional gas separation technologies such as pressure swing adsorption and cryogenic separation, membrane separation technology offers advantages such as low cost, low energy consumption, and small footprint.

[0003] Palladium and palladium alloy membranes have attracted widespread attention due to their high hydrogen flux and theoretically unlimited hydrogen selectivity. However, due to the high price of palladium, palladium and palladium alloy membranes are generally loaded onto an additional porous support to form an ultrathin separation membrane layer, in order to reduce the amount of palladium used while increasing the hydrogen permeability of the membrane.

[0004] However, among various support materials, porous ceramic supports have poor mechanical strength. Furthermore, due to the difference in thermal expansion coefficients between metals and ceramics, the membrane layer easily separates and detaches from the support during repeated heating and cooling processes. In addition, ceramic materials make it difficult to assemble and integrate composite membranes into industrial equipment. Research by Ryi et al. (SK Ryi, et al. J.Membr.Sci., 2006, 883, 888) indicates that the main reason for the pressure index deviation of the composite membrane from Sivets' law is the support resistance rather than surface reaction; the resistance of the support layer is another important factor affecting the hydrogen permeability of asymmetric membranes. According to Park et al. (JS Park, et al. J. Membr. Sci., 2008, 318, 346-354), the surface roughness of porous stainless steel supports significantly affects the coating quality. Lower surface smoothness easily leads to pores and the formation of uneven films. Furthermore, the minimum thickness required for a defect-free coating is directly related to the pore size of the porous support. Only composite metal films with a coating thickness of more than three times the average pore size of the carrier can guarantee sufficient hydrogen selectivity.

[0005] In terms of the geometry of the supporting material, the specific surface area of ​​hollow fibers is as high as 10. -4 m -1 Its ultrathin fiber tube wall provides lower gas permeation resistance than sheet or tubular structures, but metal porous hollow fibers prepared by traditional methods have too large a pore size (>1μm), requiring a very thick coating to ensure the membrane is defect-free.

[0006] Therefore, there is an urgent need in the market for small-pore porous hollow metal fibers as a support material for metal membranes used in hydrogen separation. Summary of the Invention

[0007] In view of the shortcomings of the prior art, after research, it was found that by using the asymmetric nanoscale porous metal hollow fiber of the present invention as a support material, the problem of the excessively large pore size of the existing metal hollow fiber, which leads to the requirement of a thick coating, can be solved, thus completing the present invention.

[0008] One object of the present invention is to provide asymmetric nanoporous hollow metal fibers that have nanoscale pores so as to serve as a support material for a metal membrane for hydrogen separation, and which can produce a membrane with no defects or fewer defects even when the thickness of the supported metal membrane is reduced.

[0009] Another object of the present invention is to provide a method for preparing asymmetric nanoscale metal hollow fibers with nanoscale porosity, wherein the asymmetric nanoscale metal hollow fibers prepared by the method can produce a membrane with no defects or fewer defects when used as a support material for a metal membrane for hydrogen separation, even if the thickness of the supported metal membrane is reduced.

[0010] The aforementioned objective of this invention is achieved through the following technical solution:

[0011] [1]. An asymmetric nanoporous hollow metal fiber, comprising: a separation layer with nanoscale pores on the outer side and a support layer with micron-scale finger pores on the inner side,

[0012] The thickness of the separation layer is 1~30µm, and the pore size distribution of the channels is in the range of 20~850nm;

[0013] The thickness of the support layer is 30~300µm, and the diameter distribution of the finger-shaped holes in the support layer is in the range of 1~50µm.

[0014] [2]. The asymmetric nanoscale porous metal hollow fiber according to [1], wherein the metal is at least one selected from nickel, iron, copper, silver, zinc, vanadium, niobium and alloys thereof.

[0015] [3]. The asymmetric nanoscale porous metal hollow fiber according to [1] or [2], wherein the porosity of the asymmetric nanoscale porous metal hollow fiber is in the range of 20% to 60%.

[0016] [4]. The method for preparing asymmetric nanoscale porous metal hollow fibers according to any one of [1] to [3] is characterized in that it comprises the following steps:

[0017] Casting solution preparation process: Dissolve the organic polymer in an organic solvent, then add the metal powder, stir thoroughly, and then add the spinning aid to form the casting solution;

[0018] Precursor preparation process: The casting solution is degassed under vacuum, and then the casting solution and the inner coagulation solution are simultaneously extruded into the outer coagulation solution through the outer and inner holes of the dual-hole spinning head to solidify, thereby obtaining the precursor;

[0019] Oxidation sintering process: After the precursor is first roasted in an oxidizing atmosphere to remove organic matter, it is roasted a second time in the same oxidizing atmosphere to completely oxidize the metal in the precursor and obtain an intermediate product. The roasting temperature of the first roasting is 300~800℃ and the roasting temperature of the second roasting is 500~1200℃.

[0020] Reduction sintering process: The intermediate product is calcined in a reducing atmosphere to completely reduce the metal oxidized by the oxidation sintering process, thereby obtaining asymmetric nanoscale porous metal hollow fibers.

[0021] [5]. According to the preparation method of asymmetric nanoscale porous metal hollow fiber described in [4], wherein, in the casting solution preparation step, the organic polymer is at least one selected from polysulfone, polyethersulfone, polyacrylonitrile and polyetherimide;

[0022] The organic solvent is at least one selected from N-methylpyrrolidone, N,N-dimethylamide, N,N-dimethylacetamide and dimethyl sulfoxide;

[0023] The metal powder is selected from at least one of nickel powder, iron powder, copper powder, silver powder, zinc powder, vanadium powder, niobium powder, and their alloy powders, and the particle size of the metal powder is 0.2~5μm.

[0024] [6]. The method for preparing asymmetric nanoscale porous metal hollow fibers according to [4] is characterized in that, in the precursor preparation process, the inner coagulation liquid is a solvent or a mixture of solvent and non-solvent, the solvent is N-methylpyrrolidone, the non-solvent is water, ethanol or a mixture of the two, and the mass percentage of the non-solvent in the inner coagulation liquid is less than 50%.

[0025] [7]. The method for preparing asymmetric nanoscale porous metal hollow fibers according to [4] is characterized in that, in the oxidation sintering process, the oxidizing atmosphere is air or an air / N2 mixture;

[0026] In the first calcination, the temperature is increased to 300-800℃ at a heating rate of 1-20℃ / min, and the calcination time is 2-10h;

[0027] In the second roasting, the temperature is increased to 500-1200℃ at a heating rate of 1-20℃ / min, and the roasting time is 2-10h.

[0028] [8]. The method for preparing asymmetric nanoscale porous metal hollow fibers according to [4] is characterized in that, in the reduction sintering process, the reducing atmosphere is a mixture of H2-Ar or H2-N2, wherein the volume fraction of hydrogen is 5-80%;

[0029] In the reduction sintering process, the temperature is increased to 500-900℃ at a heating rate of 1-20℃ / min, and the calcination time is 2-10h.

[0030] The asymmetric nanoporous hollow metal fiber membrane of the present invention comprises a separation layer with nanoscale pores on the outer side and a support layer with micron-scale finger-like pores on the inner side. Because the outer side is a separation layer with nanoscale pores, when used as a support material for a metal membrane for hydrogen separation, a defect-free or minimally defective metal membrane can be obtained even with a reduced thickness of the supported metal membrane. Simultaneously, the inner support layer with micron-scale finger-like pores reduces hydrogen permeability. Thus, the effect of both reducing hydrogen permeability resistance and reducing the thickness of the supported metal membrane can be achieved.

[0031] The method for manufacturing the asymmetric nanoporous hollow metal fiber membrane of the present invention involves removing organic matter from the hollow fiber precursor through a first oxidation calcination, followed by a second oxidation calcination to completely oxidize the metal in the hollow fiber precursor. During the oxidation of the metal to metal oxides, the grains expand and bond together to form a dense membrane layer. Finally, the oxidized metal is reduced by calcination in a reducing atmosphere. During this reduction process, oxygen is continuously carried away, causing the grains to shrink and form abundant nanoscale pores. This results in an asymmetric nanoporous hollow metal fiber membrane of the present invention, which achieves both reduced hydrogen permeation resistance and reduced thickness of the supported metal membrane. The membrane consists of an outer separation layer with nanoscale pores and an inner support layer with micron-sized finger-like pores. Attached Figure Description

[0032] Figure 1 The asymmetric nanoporous nickel hollow fiber membrane prepared in Example 1, wherein, Figure 1 Image a is an electron microscope image of the wall of an asymmetric nanoporous nickel hollow fiber membrane. Figure 1 Image b is an electron microscope image of the pore structure of the outer side (separation layer) of the asymmetric nanoporous nickel hollow fiber membrane; Figure 1 c represents the pore size distribution of the aforementioned pore structure; Figure 1 d represents the gas permeability.

[0033] Figure 2The asymmetric nanoporous nickel hollow fiber membrane prepared in Example 2, wherein... Figure 2 Image a is an electron microscope image of the wall of an asymmetric nanoporous nickel hollow fiber membrane. Figure 2 Image b is an electron microscope image of the pore structure of the outer side (separation layer) of the asymmetric nanoporous nickel hollow fiber membrane; Figure 2 c represents the pore size distribution of the aforementioned pore structure; Figure 2 d represents the gas permeability.

[0034] Figure 3 The asymmetric nanoporous nickel hollow fiber membrane prepared in Example 3, wherein... Figure 3 Image a is an electron microscope image of the wall of an asymmetric nanoporous iron hollow fiber membrane. Figure 3 Image b is an electron microscope image of the pore structure of the outer side (separation layer) of the asymmetric nanoporous iron hollow fiber membrane; Figure 3 c represents the pore size distribution of the aforementioned pore structure; Figure 3 d represents the gas permeability.

[0035] Figure 4 The asymmetric nanoporous iron hollow fiber membrane prepared in Example 4, wherein... Figure 4 Image a is an electron microscope image of the wall of an asymmetric nanoporous iron hollow fiber membrane. Figure 4 Image b is an electron microscope image of the pore structure of the outer side (separation layer) of the asymmetric nanoporous iron hollow fiber membrane; Figure 4 c represents the pore size distribution of the aforementioned pore structure; Figure 4 d represents the gas permeability.

[0036] Figure 5 A photograph of the porous nickel hollow fiber membrane prepared in Comparative Example 1, in which... Figure 5 Image a is an electron microscope image of the wall of a porous nickel hollow fiber membrane; Figure 5 Image b is an electron microscope image of the pore structure of the outer side (separation layer) of the porous nickel hollow fiber membrane. Detailed Implementation

[0037] To better understand the present invention, the following detailed description is provided in conjunction with embodiments. However, the scope of protection of the present invention is not limited to the scope shown in the embodiments. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of this disclosure.

[0038] Unless otherwise specified, percentages in this manual refer to mass percentages, and temperatures are in degrees Celsius (°C).

[0039] To better understand the present invention, the present invention will be further described in detail below with reference to the embodiments. However, the scope of protection of the present invention is not limited to the scope shown in the embodiments.

[0040] Asymmetric nanoscale porous metal hollow fibers

[0041] In the asymmetric nanoscale porous hollow metal fiber of the present invention, "nanoscale" refers to the size of the pores being at the nanoscale, that is, having pores with a size at the nanoscale. The aforementioned pore size is preferably below 900 nm. Therefore, when the asymmetric nanoscale porous hollow metal fiber is used as a support material for a metal membrane used for hydrogen separation, even if the thickness of the supported metal membrane is reduced, a metal membrane with no defects or few defects can be obtained.

[0042] From the perspective of mass transfer resistance, excessively small dimensions will increase the mass transfer resistance of the support. Therefore, the aforementioned pore size is preferably 20 nm or more. The aforementioned pore size is preferably in the range of 50 to 800 nm, and more preferably in the range of 50 to 500 nm.

[0043] The asymmetric nanoporous hollow metal fiber of the present invention has: a separation layer with nanoscale pores on the outer side and a support layer with micron-scale finger pores on the inner side.

[0044] In one embodiment of the asymmetric nanoscale porous hollow metal fiber, the thickness of the aforementioned separation layer can be, for example, in the range of 1 to 30 µm. Furthermore, the pore size distribution of the channels in the aforementioned separation layer can be, for example, in the range of 20 to 850 nm. The aforementioned pore size distribution is obtained by pore size analysis using a capillary flow pore size analyzer.

[0045] In one embodiment of the asymmetric nanoscale porous hollow metal fiber, the thickness of the aforementioned support layer can be, for example, in the range of 30 to 300 µm, and the pore size distribution of the finger-like pores in the support layer can be in the range of 1 to 50 µm. The aforementioned pore size distribution is obtained by pore size analysis using a capillary flow pore size analyzer.

[0046] The metal used in asymmetric nanoporous hollow metal fibers is not particularly limited as long as it can serve as a support material for metal membranes used for hydrogen separation; it can be a metal or an alloy. In one embodiment, the metal in the aforementioned hollow metal fibers can be, for example, at least one selected from nickel, iron, copper, silver, zinc, vanadium, niobium, and alloys thereof.

[0047] In one embodiment, the porosity of the asymmetric nanoscale porous hollow metal fiber is, for example, in the range of 20% to 60%.

[0048] Preparation method of asymmetric nanoscale porous hollow metal fibers

[0049] The preparation method of asymmetric nanoscale porous hollow metal fibers includes the following steps:

[0050] Casting solution preparation process: Dissolve the organic polymer in an organic solvent, then add the metal powder, stir thoroughly, and then add the spinning aid to form the casting solution;

[0051] Precursor preparation process: The casting solution is degassed under vacuum, and then the casting solution and the inner coagulation solution are simultaneously extruded into the outer coagulation solution through the outer and inner holes of the double-hole spinning head to solidify, thereby obtaining the precursor;

[0052] Oxidation sintering process: After the precursor is first roasted in an oxidizing atmosphere to remove organic matter, it is roasted a second time in the same oxidizing atmosphere to completely oxidize the metal in the precursor and obtain an intermediate product. The roasting temperature of the first roasting is 300~800℃ and the roasting temperature of the second roasting is 500~1200℃.

[0053] Reduction sintering process: The intermediate product is calcined in a reducing atmosphere to completely reduce the metal oxidized in the oxidation sintering process, thereby obtaining asymmetric nanoscale porous metal hollow fibers.

[0054] Preferably, the organic polymer used in the aforementioned casting solution preparation process is, for example, one selected from polysulfone, polyethersulfone, polyacrylonitrile, or polyetherimide.

[0055] Preferably, the organic solvent used in the aforementioned casting solution preparation process can be at least one selected from N-methylpyrrolidone, N,N-dimethylamide, N,N-dimethylacetamide, and dimethyl sulfoxide.

[0056] Preferably, the metal powder used in the aforementioned casting solution preparation process is at least one selected from nickel powder, iron powder, copper powder, silver powder, zinc powder, vanadium powder, niobium powder, and their alloy powders. The particle size of the metal powder used can be, for example, in the range of 0.2 to 5 μm. From the perspective of uniform mixing, the metal powder is preferably added in batches. After adding the metal powder, it is thoroughly stirred using a stirrer or the like to prepare a stable and uniform casting solution.

[0057] In the aforementioned casting solution preparation process, the purpose of adding the spinning aid is to adjust the viscosity and flowability of the casting solution to a range suitable for spinning. Therefore, the amount of spinning aid used is such that the viscosity and flowability of the casting solution are adjusted to a range suitable for spinning. Preferably, the aforementioned spinning aid is at least one selected from polyvinylpyrrolidone, polyammonium methacrylate, polymethyl methacrylate, and phosphate esters.

[0058] In one embodiment of the method for preparing asymmetric nanoscale porous metal hollow fibers, the composition of the casting solution prepared in the aforementioned casting solution preparation step can be the following combination, for example: 5-20 parts by mass of organic polymer, 10-50 parts by mass of organic solvent, 40-80 parts by mass of metal powder, and 5-15 parts by mass of spinning aid.

[0059] In one embodiment of the preparation method of asymmetric nanoscale porous metal hollow fiber, the aforementioned precursor preparation step can be performed as follows: the aforementioned prepared casting solution is placed in a vacuum chamber for degassing, and then transferred to a stainless steel syringe. A high-pressure injection pump is used to force the casting solution through the outer hole of the double-hole spinning head, while the inner coagulation solution is simultaneously extruded through the inner hole of the double-hole spinning head into the outer coagulation solution for solidification. After drying, the precursor is obtained.

[0060] Preferably, the atmospheric pressure of the degassing environment is in the range of 0.01~0.1 MPa. The extrusion speed of the aforementioned metal casting solution can be 1~15 mL / min, and the extrusion speed of the internal coagulation solution can be 1~15 mL / min.

[0061] The aforementioned internal coagulation liquid is a solvent or a mixture of a solvent and a non-solvent, preferably a mixture of a solvent and a non-solvent. The aforementioned solvent may be, for example, N-methylpyrrolidone, and the aforementioned non-solvent may be, for example, water, ethanol, or a mixture of both.

[0062] When the aforementioned internal coagulation liquid is a mixture of solvent and non-solvent, the mass percentage of non-solvent in the internal coagulation liquid is preferably in the range of 50% or less. By setting the mass percentage of non-solvent in the internal coagulation liquid to this range, the thickness of the finger pore layer in the prepared asymmetric nanoscale porous metal hollow fiber can be effectively reduced, and the porosity and gas flux can be further improved.

[0063] Preferably, the aforementioned external coagulation solution is deionized water. The temperature of the external coagulation solution can be, for example, in the range of 20~80°C.

[0064] Preferably, the outer diameter of the dual-hole spinning head used in the aforementioned precursor preparation process is, for example, in the range of 1 to 3 mm, and the inner diameter can be, for example, in the range of 0.6 to 1 mm.

[0065] The aforementioned oxidation sintering process can be carried out as follows: for example, the precursor obtained in the aforementioned precursor preparation process is placed in an electric furnace and heated to 300~800°C at a certain heating rate in an oxidizing atmosphere. The precursor is then subjected to a first calcination to remove organic matter. Then, under the same oxidizing atmosphere, the temperature is raised to 500~1200°C at a certain heating rate of 1~5°C / min for a second oxidation calcination, so that the metal in the precursor is completely oxidized to obtain an intermediate product.

[0066] The aforementioned oxidizing atmosphere is preferably air or an air-N2 mixture.

[0067] Preferably, in the aforementioned first calcination, the heating rate is, for example, in the range of 1~20℃ / min. Preferably, the temperature of the aforementioned first calcination is in the range of 300~800℃. Preferably, the calcination time of the aforementioned first calcination is 2~10h. Through the aforementioned first calcination, organic matter in the precursor is removed.

[0068] Preferably, the heating rate of the aforementioned second oxidation roasting is in the range of 1~20℃ / min. Preferably, the roasting temperature of the aforementioned second oxidation roasting is in the range of 500~1200℃. Preferably, the roasting time of the aforementioned second oxidation roasting is 2~10h. Through the aforementioned second roasting, the metal in the precursor is completely oxidized.

[0069] In the aforementioned reduction sintering process, the reducing atmosphere can be, for example, a mixture of H2-Ar or H2-N2. In the aforementioned H2-Ar or H2-N2 mixture, the volume percentage of hydrogen can be, for example, 2-80%. Preferably, in the aforementioned reduction sintering process, the heating rate of the reducing atmosphere is 1-20°C / min. Preferably, the calcination temperature in the preceding reduction sintering process is 500-900°C. Through the reduction sintering process, the metal oxidized in the aforementioned oxidation sintering process is completely reduced, thereby obtaining asymmetric nanoscale porous hollow metal fibers.

[0070] Example

[0071] Performance testing

[0072] Pore ​​size analysis: The pore size distribution of the support was obtained by analyzing the pore size using a capillary flow pore size analyzer based on the bubble point method.

[0073] Nitrogen permeability: When a certain pressure of N is applied to the outside of the membrane... 2 The inner side of the membrane was kept at constant atmospheric pressure, and the N2 flow rate out of the membrane was recorded. 2 The flow rate; by continuously adjusting the N on the outside of the membrane 2 The pressure, thus obtaining different N 2 Flux; while nitrogen permeability = N 2 Flux / Effective membrane area / Pressure difference between the inside and outside of the membrane.

[0074] Porosity: Measured using Archimedes' drainage method.

[0075] Example 1

[0076] 10g of polysulfone was dissolved in 40g of N-methylpyrrolidone, and then 80g of nickel powder with a particle size of 0.6μm was slowly added. The mixture was stirred for 24h to obtain a uniform and stable casting solution. 90g of N-methylpyrrolidone and 10g of ethanol were weighed and stirred for 5min to ensure complete mixing to obtain an internal solidification solution.

[0077] The prepared casting solution and internal coagulation solution were transferred to metal syringes and placed in a 0.02 MPa vacuum chamber for 1 hour for degassing. The casting solution and internal coagulation solution were then injected into a double-hole spinneret with spinneret orifices of 2 mm and 1 mm respectively, from the outside to the inside. The spinnerets were then extruded into deionized water at 25°C (the external coagulation solution) using a high-pressure injection pump at rates of 7 mL / min and 10 mL / min respectively, to solidify and obtain an asymmetric nanoporous nickel hollow fiber precursor.

[0078] The aforementioned precursor was straightened and naturally dried, then placed in an atmosphere furnace for sintering. First, it was slowly heated to 500°C in air at a rate of 3°C per minute, and continued for 2 hours to remove organic matter. Then, the temperature was increased to 700°C at a rate of 2°C per minute, and oxidative calcination was continued for 2 hours to ensure all metals were oxidized to oxides, yielding an intermediate product. Next, a mixed gas containing 50% H2 and 50% N2 was introduced, and the temperature was increased to 500°C at a rate of 2°C per minute. After reduction calcination for 2 hours, it was naturally cooled to room temperature, thereby obtaining an asymmetric nanoporous nickel hollow fiber membrane 1. Figure 1 Image a is an electron microscope image of the wall of the asymmetric nanoporous nickel hollow fiber membrane 1. Figure 1 Image b is an electron micrograph of the pore structure on the outer side (separation layer) of the asymmetric nanoporous nickel hollow fiber membrane 1. Figure 1 Figures a and b show the structure of the wall of the asymmetric nanoporous nickel hollow fiber 1 prepared in Example 1, as well as the distribution of the pore structure on the outer side (separation layer).

[0079] The obtained asymmetric nanoporous nickel hollow fiber membrane 1 was subjected to pore size analysis, nitrogen permeability and porosity testing. The results are as follows: Figure 1 As shown in c and d. Figure 1 As shown in c and d, the asymmetric nanoporous nickel hollow fiber membrane 1 prepared in Example 1 has a pore size distribution of 70~430nm, an average pore size of 225nm, a bubble point pore size of 430nm, and a gas flux of 2.8×10⁻⁶. 3 GPU, porosity 34%.

[0080] Example 2

[0081] The precursor was prepared using the same method as in Example 1, and then sintered in an atmosphere furnace. First, it was slowly heated to 500°C in air at a rate of 3°C per minute and continued for 2 hours to remove organic matter. Then, the temperature was increased to 800°C at a rate of 2°C per minute, and oxidative calcination was continued for 2 hours to ensure that all metals were oxidized to metal oxides, yielding an intermediate product. Next, a mixed gas containing 50% H2 and 50% N2 was introduced, and the temperature was increased to 600°C at a rate of 2°C per minute, followed by reduction calcination for 2 hours to obtain an asymmetric nanoporous nickel hollow fiber membrane 2. Figure 2 Image a is an electron microscope image of the wall of the asymmetric nanoporous nickel hollow fiber membrane 2. Figure 2 Image b is an electron micrograph of the pore structure of the outer layer (separation layer) of the asymmetric nanoporous nickel hollow fiber membrane 2. Figure 2 Figures a and b show the structure of the wall of the asymmetric nanoporous nickel hollow fiber 2 prepared in Example 2 and the distribution of the pore structure on the outer side (separation layer).

[0082] Furthermore, the obtained asymmetric nanoporous nickel hollow fiber membrane 2 was subjected to pore size analysis, nitrogen permeability and porosity testing, and the results are as follows: Figure 2 As shown in c and d. From Figure 2 From points c and d, we can see that the pore size distribution of the asymmetric nanoporous nickel hollow fiber membrane 2 is 70~520nm, the average pore size is 260nm, the bubble point pore size is 520nm, and the gas flux is 5×10⁻⁶. 4 GPU, porosity 44%.

[0083] Example 3

[0084] The precursor was prepared using the same method as in Example 1, and then sintered in an atmosphere furnace. First, it was slowly heated to 500°C in air at a rate of 3°C per minute and continued for 2 hours to remove organic matter. Then, the temperature was increased to 900°C at a rate of 2°C per minute, and oxidative calcination was continued for 2 hours to ensure that all metals were oxidized to metal oxides, yielding an intermediate product. Next, a mixed gas containing 10% H2 and 90% N2 was introduced, and the temperature was increased to 700°C at a rate of 2°C per minute, followed by reduction calcination for 2 hours to obtain an asymmetric nanoporous nickel hollow fiber membrane 3. Figure 3 Image a is an electron microscope image of the wall of the asymmetric nanoporous nickel hollow fiber membrane 3. Figure 3 Image b is an electron micrograph of the pore structure on the outer side (separation layer) of the asymmetric nanoporous nickel hollow fiber membrane 3. Figure 3 Figures a and b show the structure of the asymmetric nanoporous nickel hollow fiber membrane 3 prepared in Example 3 and the distribution of the pore structure on the outer side (separation layer).

[0085] Furthermore, the obtained asymmetric nanoporous nickel hollow fiber membrane 3 was subjected to pore size analysis, nitrogen permeability and porosity testing, and the results are as follows: Figure 3 As shown in c and d. From Figure 3 From c and d, we can see that the pore size distribution of the asymmetric nanoporous nickel hollow fiber membrane 3 is 70~520nm, the average pore size is 400nm, the bubble point pore size is 653nm, and the gas flux is ~1×10 5 GPU, porosity 55%.

[0086] Example 4

[0087] Dissolve 5g of polyacrylonitrile in 40g of N-methylpyrrolidone, then slowly add 100g of metallic iron powder with a particle size of 2μm, and stir for 24h to obtain a uniform and stable casting solution. Weigh 90g of N-methylpyrrolidone and 10g of ethanol, and stir for 5min to mix them completely to obtain an internal coagulation solution.

[0088] After transferring the prepared casting solution and internal coagulation solution to metal syringes, they were placed in a 0.02 MPa vacuum chamber for 1 hour for degassing. Then, the casting solution and internal coagulation solution were injected into a double-hole spinning head with spinneret orifices of 2 mm and 1 mm from the outside to the inside, respectively. The spinneret was then extruded into deionized water at 25°C, which served as the external coagulation solution, using a high-pressure injection pump at speeds of 6 mL / min and 10 mL / min, respectively, to solidify and obtain the precursor.

[0089] The aforementioned precursor was straightened, naturally dried, and then sintered in an atmosphere furnace. First, it was slowly heated to 500°C in air at a rate of 3°C per minute, and this process was continued for 2 hours to remove organic matter. Then, the temperature was increased to 900°C at a rate of 2°C per minute, and oxidative calcination was continued for 2 hours to ensure that all metals were oxidized to oxides, yielding an intermediate product. Next, a mixed gas containing 50% H2 and 50% N2 was introduced, and the temperature was increased to 800°C at a rate of 2°C per minute. After reduction calcination for 2 hours, the mixture was naturally cooled to room temperature to obtain an asymmetric nanoporous iron hollow fiber membrane 4. Figure 4 Image a is an electron microscope image of the wall of the asymmetric nanoporous iron hollow fiber membrane 4. Figure 4 Image b is an electron micrograph of the pore structure of the outer layer (separation layer) of the asymmetric nanoporous iron hollow fiber membrane 4. Figure 4 Figures a and b show the structure of the asymmetric nanoporous iron hollow fiber membrane 4 prepared in Example 4 and the distribution of the pore structure on the outer side (separation layer).

[0090] Furthermore, the obtained asymmetric nanoporous hollow iron fibers 4 were subjected to pore size analysis, nitrogen permeability testing, and porosity testing. The results are as follows: Figure 4 As shown in c and d. From Figure 4From points c and d, we can see that the pore size distribution of the asymmetric nanoporous hollow iron fiber 4 is 70~830nm, the average pore size is 700nm, the bubble point pore size is 830nm, and the gas flux is ~1.4×10⁻⁶. 5 GPU, porosity 51%.

[0091] Comparative Example 1

[0092] 10g of polysulfone was dissolved in 40g of N-methylpyrrolidone, and then 70g of nickel powder with a particle size of 1 μm was slowly added. The mixture was stirred for 24 hours to obtain a uniform and stable casting solution. The prepared casting solution was transferred to a metal syringe and placed in a vacuum chamber at 0.02 MPa for 1 hour for degassing. Then, it was injected into the spinneret using a high-pressure syringe, with deionized water as the internal and external coagulation solution. After spinning, a hollow fiber precursor was obtained.

[0093] The aforementioned precursor was straightened and naturally dried, then placed in an atmosphere furnace for sintering. First, it was slowly heated to 500°C in air at a rate of 3°C per minute, and this process was continued for 2 hours to remove organic matter. Then, a mixed gas containing 50% H2 and 50% N2 was introduced, and the temperature was increased to 1000°C at a rate of 2°C per minute. After reduction calcination for 2 hours, it was naturally cooled to room temperature to obtain a porous nickel hollow fiber membrane. Figure 5 The image shown is an electron microscope image of the wall of a porous nickel hollow fiber membrane. Figure 5 Image b is an electron microscope image of the pore structure on the outer side of this porous nickel hollow fiber membrane. Figure 5 As can be seen in a and b, the porous nickel hollow fiber wall prepared in the comparative example exhibits a uniform symmetrical structure instead of the asymmetrical structure as in Examples 1-4, and has a wide pore size distribution of 0.5-10 µm with a porosity of 30%.

[0094] Obviously, the above embodiments of this disclosure are merely examples for clearly illustrating this disclosure, and are not intended to limit the implementation of this disclosure. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all implementation methods here. Any obvious variations or modifications derived from the technical solutions of this disclosure are still within the protection scope of this disclosure.

Claims

1. A method for preparing asymmetric nanoscale porous hollow metal fibers, characterized in that, The asymmetric nanoscale porous hollow metal fiber has a separation layer with nanoscale pores on the outer side and a support layer with micron-scale finger pores on the inner side. The thickness of the separation layer is 1–30 μm, and the pore size distribution of the channels is in the range of 20–850 nm. The thickness of the support layer is 30–300 μm, and the pore size distribution of the finger-shaped pores in the support layer is in the range of 1–50 μm. The method for preparing the asymmetric nanoscale porous metal hollow fiber includes the following steps: Casting solution preparation process: Dissolve the organic polymer in an organic solvent, then add metal powder, stir thoroughly, and then add spinning aid to form a casting solution. The metal is at least one selected from nickel, iron, copper, silver, zinc, vanadium, niobium, and their alloys. Precursor preparation process: The casting solution is degassed under vacuum, and then the casting solution and the inner coagulation solution are simultaneously extruded into the outer coagulation solution through the outer and inner holes of the dual-hole spinning head to solidify, thereby obtaining the precursor; Oxidation sintering process: After the precursor is first roasted in an oxidizing atmosphere to remove organic matter, it is roasted a second time in the same oxidizing atmosphere to completely oxidize the metal in the precursor and obtain an intermediate product. The roasting temperature of the first roasting is 500-800℃ and the roasting temperature of the second roasting is 700-1200℃. Reduction sintering process: The intermediate product is calcined in a reducing atmosphere to completely reduce the metal oxidized by the oxidation sintering process, thereby obtaining asymmetric nanoscale porous metal hollow fibers.

2. The method for preparing asymmetric nanoscale porous metal hollow fibers according to claim 1, wherein, The porosity of the asymmetric nanoscale porous metal hollow fiber is in the range of 20% to 60%.

3. The method for preparing asymmetric nanoscale porous metal hollow fibers according to claim 1, wherein, In the casting solution preparation process, the organic polymer is at least one selected from polysulfone, polyethersulfone, polyacrylonitrile, and polyetherimide; The organic solvent is at least one selected from N-methylpyrrolidone, N,N-dimethylamide, N,N-dimethylacetamide and dimethyl sulfoxide; The metal powder is selected from at least one of nickel powder, iron powder, copper powder, silver powder, zinc powder, vanadium powder, niobium powder, and their alloy powders, and the particle size of the metal powder is 0.2 to 5 μm.

4. The method for preparing asymmetric nanoscale porous hollow metal fibers according to claim 1, characterized in that, In the precursor preparation process, the internal coagulation liquid is a solvent or a mixture of solvent and non-solvent, the solvent is N-methylpyrrolidone, the non-solvent is water, ethanol or a mixture of both, and the mass percentage of the non-solvent in the internal coagulation liquid is less than 50%.

5. The method for preparing asymmetric nanoscale porous metal hollow fibers according to claim 1, characterized in that, In the oxidation sintering process, the oxidizing atmosphere is air or an air / N2 mixture; In the first calcination, the temperature is increased to 500-800℃ at a heating rate of 1-20℃ / min, and the calcination time is 2-10h; In the second roasting, the temperature is increased to 700-1200℃ at a heating rate of 1-20℃ / min, and the roasting time is 2-10h.

6. The method for preparing asymmetric nanoscale porous metal hollow fibers according to claim 1, characterized in that, In the reduction sintering process, the reducing atmosphere is a mixture of H2-Ar or H2-N2, wherein the volume fraction of hydrogen is 5-80%. In the reduction sintering process, the temperature is increased to 500-900℃ at a heating rate of 1-20℃ / min, and the calcination time is 2-10h.

Images