Double-layer hollow fiber membrane, method for manufacturing a double-layer hollow fiber membrane, method for separating gas from a feed gas stream, use of a double-layer hollow fiber membrane, and method for measuring the separation performance of a double-layer hollow fiber membrane.

Abstract

A double-layer hollow fiber membrane for separating gas from a supply gas stream includes an inner layer of a polymer. The polymer is polysulfone. The double-layer hollow fiber membrane includes an outer layer made from a combination of polymers. The combination of polymers is selected from at least one imide-based polymer and at least one imidazole-based polymer. The imide-based polymer is polyamide-imide, PAI, and the imide-based polymer contains 5-50% by weight of PAI relative to the outer layer.

Description

[Technical Field]

[0001] The present invention includes a double-layer hollow fiber membrane, a method for producing a double-layer hollow fiber membrane, and a method for obtaining a purer gas mixture from a feed gas stream. [Background technology]

[0002] Numerous patent applications teaching double-layer hollow fiber membranes are known. For example, U.S. Patent Application No. 2016 / 0375410A1 teaches a double-layer hollow fiber membrane for separating and recovering gases containing hydrogen and carbon dioxide from a feed mixture. This double-layer hollow fiber membrane comprises an inner layer and an outer layer made from the same polymer, which is polybenzimidazole (PBI). U.S. Patent Application No. 2016 / 0375410A1 further discloses a method for producing a double-layer hollow fiber membrane. The method for producing a double-layer hollow fiber membrane comprises the step of preparing a polymer dope containing PBI. The method further comprises the step of extruding the polymer dope and bore fluid through an orifice of a hollow fiber die. The bore fluid includes acetonitrile, acetone, methanol, ethanol, or a mixture of isopropanol and N,N-dimethylacetamide.

[0003] Canadian Patent Application CA3122213A1 discloses a double-layer hollow fiber membrane for gas separation processes. This double-layer hollow fiber membrane comprises an inner layer and an outer layer made from the same polymer. The polymer is selected from polyimide, copolyimide, block copolyimide, polyetherimide, and polyamideimide. The Canadian Patent Application further discloses a method for producing a double-layer hollow fiber membrane. This method includes the step of preparing a polymer-doped composition comprising the aforementioned polymer and solvent. This method further includes the step of co-extruding the composition comprising an amine component and a non-solvent through a second orifice of a hollow fiber die.

[0004] U.S. Patent Application No. 2015 / 0011815A1 discloses a double-layer hollow fiber membrane. This double-layer hollow fiber membrane comprises an inner layer made of polyamide-imide and an outer layer made of polyimide. The patent application further discloses a method for obtaining a purer gas mixture from a feed gas mixture. The purer gas mixture substantially contains carbon dioxide.

[0005] U.S. Patent Application No. 2015 / 0020685A1 discloses a double-layer hollow fiber membrane comprising an inner layer made from polyethersulfone and an outer layer made from polydimethylsiloxane. U.S. Patent Application No. 2015 / 0020685A1 further discloses a method for producing a double-layer hollow fiber membrane, comprising the step of co-extruding a first composition made from polyethersulfone, a second composition made from polydimethylsiloxane, and a third composition made from bore fluid.

[0006] International Patent Application No. 2021 / 018852A1 teaches a method for obtaining a purer gas mixture containing hydrogen from a feed gas mixture. The method comprises the step of supplying the feed gas mixture into the internal volume of an electrochemical cell equipped with an anion exchange membrane. The anion exchange membrane comprises a polymer containing inorganic and / or organic fillers. The polymer may be polybenzimidazole. The inorganic filler comprises hygroscopic particles such as clay nanoparticles, and the organic filler comprises ionomer nanoparticles or fibers.

[0007] U.S. Patent Application No. 2011 / 192281A1 discloses a hollow fiber comprising a lumen and a polymer membrane defining the lumen. This polymer membrane comprises a first polymer and a second polymer. The first polymer is polybenzimidazole, and the second polymer is polyimide or polyamide-imide. The hollow fiber further comprises a porous tubular substrate, the outer surface of which is in contact with the inner surface of the polymer membrane. The substrate is formed from a third polymer, such as polysulfone or polyethersulfone. The first polymer constitutes more than 20% by weight of the polymer blend.

[0008] The double-layer hollow fibers of U.S. Patent No. 281 can be produced, for example, by co-extrusion of polymer materials using a dry-jet wet spinning process (where a void exists between the spinneret tip and the coagulation bath). To crosslink the polyimide component of the blend, a solution containing 10 wt.% p-xylenediamine in methanol is prepared. To crosslink the FBI phase, a solution containing 2 wt.% p-xylenedichloride in methanol is used.

[0009] Examples 14–17 of U.S. Patent No. 281 disclose hollow fibers comprising a Matrimid / PBI blend and a polysulfone substrate. The Matrimid:PBI ratio is 1:1. Matrimid is a commercially available polyimide (PI). [Overview of the project] [Problems that the invention aims to solve]

[0010] Hosseini et al., "Gas separation membranes developed through integration of polymer blending and dual-layer hollow fiber spinning process for hydrogen and natural gas enrichments," Journal of Membrane Science, Elsevier BV, NL, Vol. 349, Nos. 1-2, March 1, 2010 (2010-03-01), pp. 156-166, XP026874423, ISSN:0376-7388, discloses a polymer blend composed of prepared Matrimid and poly(benzimidazole) (PSI), which is used as the outer layer material for the fabrication of a dual-layer hollow fiber membrane. Polysulfone (PSf) was selected as the inner support material.

[0011] Wang et al. "Miscibility study of TorlonA(R) polyamide-imide with MatrimidA(R) 5218 polyimide and polybenzimidazole" "Polybenzimidazole," Polymer, Elsevier, Amsterdam, NL, Vol. 48, No. 10, April 24, 2007 (2007-04-24), pp. 2901-2909, XP022044129, SSN:0032-3861, doi:10.1016 / J.POLYMER.2007.03.040 discloses two miscible polymer blend systems, namely Torlon® 4000T and Matrimid® 5218 and Torlon® 4000T and polybenzimidazole (PBI). Torlon® 4000T is a polyamide (PAI) powder for adhesive applications. Matrimid 5218 is a commercially available polyimide (PI). Wang et al. further disclose morphological analysis, differential scanning calorimetry (DSC) analysis, Fourier transform infrared spectroscopy (FTIR), and dynamic mechanical analysis (DMA) of PAI / PI and PI / PBI blends. Wang et al. teach the study of two types of miscible polymer blend systems.

[0012] Shao et al., "Comparison of diamino cross-linking in different polyimide solutions and membranes by precipitation observation and gas transport," Journal of Membrane Science, Elsevier BV, NL, Vol. 312, Nos. 1-2, January 5, 2008 (2008-01-05), pp. 174-185, XP022500579, ISSN:0376-7388, DOI:10.1016 / J.MEMSCI.2007.12.060, discloses membrane preparations of Matrimid® 5218 powder (PI) and 6FDA-Durene.

[0013] Naderi et al., "High performance dual-layer hollow fiber membrane of sulfonated polyphenylsulfone / Polybenzimidazole for hydrogen purification," Journal of Membrane Science, Elsevier BV, NL, Vol. 591, July 29, 2019 (2019-07-29), XP085764692, ISSN:0376-7388, DOI:10.1016 / J.MEMSCI.2019.117292, discloses a dual-layer hollow fiber membrane comprising a miscible polybenzimidazole (PBI) / polyphenylsulfone (sPPSU) blend as a selective layer, or in other words, an inner layer, and polysulfone as a supporting layer, or in other words, an outer layer.

[0014] Wickramanayake, Shan et al., "Mechanically robust hollow fiber supported ionic liquid membranes for CO2 separation applications," Journal of Membrane Science 470 (2014): 52-59, demonstrates that Torlon 4000T, or PAI, has higher mechanical strength than Matrix 5218, or PI. This mechanical property may be due to the higher degree of polymer chain linkage in PAI compared to PI. [Means for solving the problem]

[0015] This disclosure teaches a double-layer hollow fiber membrane that enables the separation of gases from a feed gas stream. The double-layer hollow fiber membrane includes an inner layer of a polymer used as a mechanical support layer. The polymer is made from polysulfone. In one embodiment, the inner layer is made from polysulfone mixed with a first solvent to yield a first dope. The first solvent may be N-methyl-2-pyrrolidone (NMP). The polysulfone allows the inner layer to withstand high-temperature and high-pressure operating conditions for gas separation. The concentration of the polymer solution is below its critical concentration. The structure of the inner layer is a porous structure obtained at the end of a method for producing a double-layer hollow fiber membrane while maintaining mechanical strength, assuming a non-solvent-induced phase separation method (NIPS). The porous inner layer has substantially low transport resistance for gas separation. Polysulfone provides excellent mechanical, physical, and economic properties for the double-layer hollow fiber membrane.

[0016] The bilayer hollow fiber membrane further comprises an outer layer made from a polymer combination. The polymer combination is selected from imide polymers and imidazole polymers. In one embodiment, the imide polymer may be polyamide-imide (PAI), and the imidazole polymer may be polybenzimidazole (PBI). In one embodiment, a second dope is obtained by mixing the polymer combination with a second solvent. The second solvent may be dimethylacetamide (DMAc).

[0017] PAI is known to be a more flexible polymer with higher toughness compared to PBI, which is a very brittle polymer. However, PAI has lower chemical and heat resistance and a lower plasticizing pressure to carbon dioxide compared to PBI. PBI has high chemical and heat resistance and does not plasticize to carbon dioxide even under increasing pressure. Since PAI and PBI are compatible polymers, an outer layer combining the properties of PAI and PBI can be obtained by fabricating the outer layer of a film with a combination of PAI and PBI. This results in an outer layer with high toughness, chemical and heat resistance, and that does not plasticize to carbon dioxide even under increasing pressure.

[0018] As described above, PBI is brittle, making film fabrication difficult. Therefore, combining PBI with PAI makes film fabrication substantially easier, and after crosslinking with α,α'-dibromo-p-xylene (DBX) and 1,4-butanediamine (BuDA), the outer layer can have substantially good chemical stability and good separation properties.

[0019] Polysulfone is one of the following types: poly(arylene sulfone) (PAS), poly(bisphenol-A sulfone) (PSF), polyethersulfone (PES), polyphenylene sulfone (PPSU), and polysulfone (PSU).

[0020] In one aspect, the imide-based polymer of the double-layer hollow fiber membrane contains 5 to 20% by weight of PAI with respect to the outer layer, and the imidazole-based polymer of the double-layer hollow fiber membrane contains 80 to 95% by weight of PBI with respect to the outer layer.

[0021] In one aspect, the double-layer hollow fiber membrane has an inner diameter of at least 100 μm and a maximum of 1000 μm, but the present invention is not limited thereto.

[0022] The double-layer hollow fiber membrane has a permeability of at least 0.05 gas permeation units (GPU) at a temperature between 25 °C and 150 °C for carbon dioxide. In one aspect, the gas permeability of carbon dioxide into the double-layer hollow fiber membrane is between 3 gas permeation units (GPU) and 10 GPU at 25 °C.

[0023] The outer layer of the double-layer hollow fiber membrane has a thickness of at least 0.5 μm and / or a maximum of 100 μm.

[0024] The double-layer hollow fiber membrane is used to separate hydrogen and carbon dioxide from the feed gas stream.

[0025] A method for manufacturing the double-layer hollow fiber membrane is also described. This method includes the step of co-extruding a bore fluid, a polymer mixed with a first solvent, and a combination of polymers mixed with a second solvent, where the polymer is polysulfone. The combination of polymers is selected from at least one imide-based polymer and at least one imidazole-based polymer. By co-extruding the bore fluid, the polymer mixed with the first solvent, and the combination of the polymer and the second solvent, it is possible to obtain a double-layer hollow fiber membrane. The double-layer hollow fiber membrane is immersed in a first solution in a first container. Next, the membrane is immersed in a second solution in a second container, enabling chemical modification of the double-layer hollow fiber membrane.

[0026] In one aspect, the first solution contains α,α'-dibromo-p-xylene (DBX) in methanol.

[0027] In a further embodiment, the second solution contains 1,4-butanediamine (BuDA) in methanol.

[0028] A method for separating gas from a supply gas stream to obtain a purer gas stream is also taught. This method includes supplying the supply gas stream to a membrane module containing at least one double-layer hollow fiber membrane. This method further includes increasing the pressure along the membrane module to output a purer gas stream.

[0029] In one embodiment, a double-layer hollow fiber membrane is used to remove hydrogen from a supply gas stream (i.e., an inlet gas stream) and / or to capture carbon dioxide from the supply gas stream. A purer gas stream is one that contains substantially dihydrogen. It has been found that the purity of hydrogen can reach 99 mol%. [Brief explanation of the drawing]

[0030] [Figure 1] This figure shows a double-layer hollow fiber membrane including an inner layer and an outer layer. [Figure 1A] This is a field emission scanning electron microscope (FESEM) image of a double-layer hollow fiber membrane, showing a cross-sectional view of the outer layer of the double-layer hollow fiber membrane. [Figure 1B] This is a field emission scanning electron microscope (FESEM) image of a double-layer hollow fiber membrane, showing a cross-sectional view of the outer layer of the double-layer hollow fiber membrane. [Figure 1C] This is a field emission scanning electron microscope (FESEM) image of a double-layer hollow fiber membrane, showing a cross-sectional view of the outer layer of the double-layer hollow fiber membrane. [Figure 1D] This is a field emission scanning electron microscope (FESEM) image of a double-layer hollow fiber membrane, showing the outer layer of the membrane. [Figure 1E] This is a field emission scanning electron microscope (FESEM) image of a double-layer hollow fiber membrane, showing the inner layer of the membrane. [Figure 2] This is a flowchart illustrating a method for manufacturing a double-layer hollow fiber membrane. [Figure 3] This figure shows an apparatus for manufacturing a double-layer hollow fiber membrane. [Figure 4] This is a schematic top view of the triple orifice of the spinneret. [Figure 5] This is a schematic side view of a triple orifice. [Figure 6A] This flowchart explains the method for obtaining the behavior of a double-layer hollow fiber membrane regarding its pure gas separation performance. [Figure 6B] This is a flowchart illustrating a method for measuring the mixed gas separation performance of a double-layer hollow fiber membrane. [Figure 7] This figure shows an example of a triple orifice spinning head. [Figure 8] This diagram shows an overview of a pure gas permeable cell. Fig. 8A shows a schematic diagram of the membrane module of the pure gas permeable cell, and Fig. 8B shows a double-layer hollow fiber membrane when a supply gas stream is supplied. [Figure 9] This figure shows a mixed gas permeation cell. An exploded view is shown in Fig. 9A. [Figure 10] This figure shows an image of a double-layer hollow fiber membrane in a mixed gas permeable cell. [Figure 11] This figure shows an image of a double-layer hollow fiber membrane in a mixed gas permeable cell. [Figure 12] This graph shows a Robeson plot as a benchmark for comparing the performance of double-layer hollow fiber membranes. [Modes for carrying out the invention]

[0031] The present invention will now be described with reference to the drawings. It will be understood that the embodiments and aspects of the present invention described herein are merely examples and do not in any way limit the scope of protection of the claims. The present invention is defined by the claims and their equivalents. It will be understood that features of one aspect or embodiment of the present invention can be combined with features of one or more different aspects and / or embodiments of the present invention.

[0032] Figure 1 shows an exemplary diagram of a double-layer hollow fiber membrane 10 including an inner layer 15 and an outer layer 20. The inner layer 15 is made from a polymer, which is a polysulfone, and the outer layer 20 is made from a combination of polymers. The combination of polymers is selected from either imide-based polymers or imidazole-based polymers. The inner layer 15 encloses an internal volume 16 through which gas can flow, as will be described later.

[0033] The polysulfone may be one of the following: poly(arylene sulfone) (PAS), poly(bisphenol-A sulfone) (PSF), polyethersulfone (PES), polyphenylene sulfone (PPSU), or polysulfone (PSU). The imide polymer may be polyamide-imide (PAI), and the imidazole polymer may be polybenzimidazole (PBI).

[0034] Figure 2 shows a flowchart illustrating a method for producing the double-layer hollow fiber membrane 10 shown in Figure 1. In step 100, a first dope 25 is prepared by mixing a polymer with a first solvent. The first solvent may be N-methyl-2-pyrrolidone (NMP). Separately, in step 102, a second dope 35 is prepared by mixing a polymer combination with a second solvent. The second solvent may be N,N-dimethylacetamide (DMAc).

[0035] The polymer is mixed with the first solvent at a concentration between 24 wt.% and 29 wt.%. By mixing the polymer at a concentration of 27 wt.% with the first solvent, the gas transport resistance in the inner layer 15 of the double-layer hollow fiber membrane 10 can be kept low.

[0036] The polymer combination is mixed with the second solvent at a concentration of at least 22 wt.%. In one embodiment, the polymer combination is mixed with the second solvent at a concentration between 22 wt.% and 26 wt.%. The concentration of the polymer combination in the second dope 35 is higher than the critical concentration of the polymer combination. The outer layer 20 is substantially free of defects on its surface. The supply gas stream 90 can be supplied from the outer layer 20 of the double-layer hollow fiber membrane 10 and can pass through the double-layer hollow fiber membrane 10 by solution diffusion and molecular sieving mechanisms. Since the outer layer 20 is free of defects, the supply gas stream 90 does not pass through the double-layer hollow fiber membrane 10 by the Knudsen diffusion mechanism.

[0037] Figure 3 shows a diagram of an apparatus 85 for manufacturing a double-layer hollow fiber membrane. The apparatus 85 includes a triple-orifice spinneret 45, a coagulation bath 70, and a winding roller 80. A guide roller 60 is positioned within the coagulation bath 70. The apparatus 85 further includes the winding roller 80.

[0038] As can be seen from Figures 4 and 5, the triple orifice spinneret 45 includes an outer opening 35, an intermediate opening 25, and an inner opening 55. The outer opening 35 has an inner diameter between 1 mm and 1.8 mm and an outer diameter between 1.2 mm and 2.2 mm. The intermediate opening 25 has an inner diameter between, for example, 0.5 mm and 1.2 mm and an outer diameter between 0.8 mm and 1.7 mm. The inner opening 55 has a diameter between 0.4 mm and 0.9 mm.

[0039] As can be seen in Figure 2, in step 105, the second dope 35 is extruded through the outer opening of the triple orifice spinneret 45.

[0040] In step 105, the first dope 25 is extruded through the intermediate opening of the triple orifice spinneret 45, while the second dope 35 is extruded through the outer opening of the triple orifice spinneret 45.

[0041] As can be seen from Figure 2, in step S105, the bore fluid 55 is extruded through the inner opening of the triple orifice 45 at the same time as the extrusion of the first dope 25 and the second dope 35. The bore fluid 55 may contain a mixture of a non-solvent and a solvent, or it may contain only a non-solvent. The non-solvent may be, for example, water, and the solvent may be selected from either NMP or DMAc. In one example, the bore fluid 55 contains 90 wt.% NMP and 10 wt.% water. By extruding the bore fluid 55 through the inner opening of the triple orifice 45, an internal volume 16 can be formed within the double-layer hollow fiber membrane 10.

[0042] The simultaneous extrusion of the first dope 25, the second dope 35, and the bore fluid 55 is carried out at a temperature between 20°C and 100°C, for example, 25°C. As can be seen from Figure 2, in step S130, the extrusion of the second dope 35, the simultaneous extrusion of the first dope 25, and the simultaneous extrusion of the bore fluid 55 yield a double-layered hollow fiber membrane 10 in the form of liquid fibers.

[0043] As can be seen in Figure 2, in step 140, the fibers of the double-layer hollow fiber membrane 10 are introduced into the solidification bath 70 after passing through adjustable voids. The solidification bath 70 is filled with a non-solvent 72 such as water. By introducing the fibers of the double-layer hollow fiber membrane 10 into adjustable voids, the desired dimensions and shape of the hollow fiber membrane can be obtained. The length of the voids varies depending on the polymer concentration in the first dope 25 and the second dope 35, the winding speed, the flow rate of the bore fluid, and the relative humidity. The length of the voids is optimized so that the polymer chains in the first dope 25 and the second dope 35 are oriented at the output portion of the spinneret 45, and so that the first and second solvents are extruded from the first dope 25 and the second dope 35. The voids are further optimized so that die swells are prevented and the formation of macrovoids in the inner layer 15 is prevented. As shown in Figures 1A to 1E, the double-layer fiber film 10 contains almost no macrovoids.

[0044] The length of the void is, for example, between 1 cm and 5 cm, but the present invention is not limited thereto. Using a shorter void distance means that the elimination of macrovoids becomes easier. On the other hand, if the void distance is too short (i.e., length < critical length), the macrovoids induced by die swell cannot be eliminated by extension, and thus macrovoids are formed. A short but appropriate void distance is still necessary to produce hollow fibers without macrovoids. The most likely cause of this contradiction is that it takes time to eliminate the effects of die swell, and a certain distance is required in the void for the tensile stress induced by winding and its effect on the film morphology to fully manifest.

[0045] The coagulation bath 70 is at a temperature between 5 and 70°C. The first and second solvents are soluble in the non-solvent 72, but the polysulfone, imide polymer, and imidazole polymer are insoluble in the non-solvent 72. By introducing the fibers of the double-layer hollow fiber membrane 10 into the non-solvent 72, the fibers precipitate, resulting in a substantially porous and asymmetric solid double-layer hollow fiber membrane 10. The guide roller 60 guides the double-layer hollow fiber membrane 10 to the outside of the coagulation bath 70. The double-layer hollow fiber membrane 10 passes through the winding roller 80 before step S150. The winding roller 80 allows for the winding of the double-layer hollow fiber membrane 10.

[0046] As can be seen from Figure 2, in step S150, the double-layer hollow fiber membrane 10 is subjected to solvent exchange. Solvent exchange involves immersing the double-layer hollow fiber membrane 10 in methanol solvent three times for 30 minutes each time. Next, the double-layer hollow fiber membrane 10 is immersed in hexane solvent three times for 30 minutes each time, followed by air drying at room temperature for 24 hours. The solvent exchange in step S150 allows for fine-tuning of the morphological structure of the double-layer hollow fiber membrane 10 so that it has substantially high permeability and high selectivity. Methanol and hexane have lower surface tension and vapor pressure than water. By immersing the fibers in solvents with lower surface tension and vapor pressure than water (i.e., methanol and hexane), more homogeneous pores are formed in the double-layer hollow fiber membrane 10. Homogeneous pores are formed when methanol and hexane solvents replace water in the double-layer hollow fiber membrane 10.

[0047] As can be seen from Figure 2, in step S160, the double-layer hollow fiber membrane 10 is immersed in the first solution 75 in the first container 76 at 60°C for 18 hours. The first solution 75 is, for example, a 3 wt.% solution of α,α'-dibromo-p-xylene (DBX) in methanol. Next, in step 165, the double-layer hollow fiber membrane 10 is washed with methanol. By immersing the double-layer hollow fiber membrane 10 in the first solution 75, the imidazole polymer of the outer layer 20 can be crosslinked with the first solution 75.

[0048] As can be seen from Figure 2, in step 170, the double-layer hollow fiber membrane 10 is immersed in the second solution 77 in the second container 78 at 24°C for 1 hour. The second solution 77 is, for example, a 5 wt.% solution of 1,4-butanediamine (BuDA) in methanol. By immersing the double-layer hollow fiber membrane 10 in the second solution 77, the imide polymer of the outer layer 20 can be crosslinked with the second solution 77. Next, in step 175, the double-layer hollow fiber membrane 10 is washed with methanol.

[0049] As can be seen from Figure 2, in step 180, the double-layer hollow fiber membrane 10 is dried at a temperature between 80°C and 150°C for, for example, 3 hours.

[0050] Figure 6A shows a flowchart illustrating a method for measuring the pure gas separation performance of the double-layer hollow fiber membrane 10 from a supply gas stream 90. This method can also be used to measure the pure gas separation performance of the double-layer hollow fiber membrane 10.

[0051] The membrane module 130 is a module comprising at least two double-layer hollow fiber membranes 10, for example, ten double-layer hollow fiber membranes. As shown in Figure 6A, in step 200, a supply gas stream 90 is supplied to the double-layer hollow fiber membranes 10 of the membrane module 130. The supply gas stream 90 contains one of the following gases: hydrogen (H2), carbon dioxide (CO2), nitrogen (N2), and methane (CH4). The supply gas stream 90 is supplied to the outside of the double-layer hollow fiber membranes 10 (this is called the "shell-side" mode).

[0052] In step 210, the temperature rises along the membrane module 130. The temperature along the membrane module 130 is between 25°C and 150°C.

[0053] In step 220, the pressure increases along the membrane module 130. The pressure difference between the supply side (outside) and the permeate side, i.e., the lumen side, i.e., the inside, of the hollow fiber membrane 10 is between 2 and 14 bar. As shown in Figure 8B, in step S225, the permeate gas stream 100 is output from the inner layer 16 of the double-layer hollow fiber membrane 10 of module 130.

[0054] The double-layer hollow fiber membrane 10 can be used to separate hydrogen gas (ditudin) from the supply gas stream 90.

[0055] The gas separation performance of the double-layer hollow fiber membrane 10 can be measured.

[0056] Figure 6B shows a flowchart illustrating a method for measuring the mixed gas separation performance of a double-layer hollow fiber membrane 10. The membrane module 131 is a module containing at least two double-layer hollow fiber membranes 10, for example, 100 double-layer hollow fiber membranes. The method includes supplying a feed gas stream 91 to the membrane module 131 in step S201. The feed gas stream 91 contains two or all of the following gases: hydrogen (H2), carbon dioxide (CO2), nitrogen (N2), and methane (CH4). The feed gas stream 91 is supplied to the outside of the double-layer hollow fiber membrane 10 (this is called the "shell-side" mode). In step 211, the temperature is increased along the membrane module 131. The method further includes increasing the pressure along the membrane module 131 in step S221 and outputting a purer gas mixture 101 in step S226. The purer gas mixture 101 is the permeate gas stream output from the lumen side 16 of the double-layer hollow fiber membrane 10 of module 131 in step S226, as shown in Figure 9A. This method includes step S231, which measures the separation performance of the double-layer hollow fiber membrane 10. The separation performance is measured by evaluating the difference between the pressure of the supply gas stream 91 at a first pressure sensor 161 and the pressure of the purer gas stream 101 (i.e., atmospheric pressure) at a second pressure sensor 162. The pressure difference is measured at elevated temperatures between 25°C and 150°C. The flow rates and gas compositions of the supply gas stream 91 and the purer gas stream 101 are also measured.

[0057] The measurement of the separation performance of the double-layer hollow fiber membrane 10 includes determining the gas permeability and gas selectivity of the double-layer hollow fiber membrane 10, as will be explained later. [Examples]

[0058] Examples of compositions and process conditions for double-layer hollow fiber membranes The compositions listed in these examples are merely examples of preferred formulations, and the present invention is not limited thereto (all by weight percentage).

[0059] The imide polymer of outer layer 20 is commercially available polyamide-imide (e.g., Torlon® PAI), purchased from Solvay Advanced Polymers in Singapore. The imidazole polymer of outer layer 20 is commercially available polybenzimidazole (e.g., 27000 g.mol). -1 The material is Celazole S26 with a molecular weight (Mw) of 15 (purchased from PBI Performance Products Inc., USA). The Celazole S26 formulation consists of 72.5 wt.% DMAc, 26 wt.% PBI, and 1.5 wt.% lithium chloride (LiCl). The polysulfone for the inner layer 15 was purchased from Solvay Advanced Polymers, Singapore. The PAI and PSF polymers were dried at 110°C for 24 hours before producing the bilayer fiber membrane 10. The first solution 75 contains 97% DBX, purchased from Sigma Aldrich. The second solution 76 contains BuDA, purchased from Sigma Aldrich. DMAc and NMP were purchased from Merck. Hexane and methanol were procured from Merck and used during solvent exchange, crosslinking, and coating.

[0060] Examples of compositions for the second dope 35 are listed below. For each of compositions 1 to 5, the concentration of the polymer combination in the second dope 35 is 26 wt.%. The concentration of DMAc in the second dope 35 is 74 wt.%.

[0061] Composition 1 [Table 1]

[0062] Composition 2 [Table 2]

[0063] Composition 3 [Table 3]

[0064] Composition 4 [Table 4]

[0065] Composition 5 [Table 5]

[0066] As can be seen in Figure 2, each of compositions 1 to 5 was prepared in step S102 by mixing PBI and PAI in the proportions disclosed in the table, based on the corresponding second dope 35. The first dope 25 containing PSF was simultaneously prepared by mixing PSF and NMP (step S100). The shear viscosity of each of compositions 1 to 5 and the first dope 25 containing PSF was measured at 25°C with a shear rate of 10 seconds using a cone-plate rheometer (ARES rheometer). -1 The viscosity was measured. From the measured viscosity, the critical polymer concentrations of the PAI-PBI blend in the second dope 35 and the PSF in the first dope 25 could be calculated. The measured critical polymer concentration for the PAI-PBI blend in the second dope 35 was 22 wt.%. The concentration of the polymer PAI and PBI combination (i.e., PAI-PBI blend) in the second dope 35 was greater than 22 wt.%, so 26 wt.% was selected. The PSF concentration in the first dope 25 was selected as 27 wt.%. The second dope 35 was stirred at 60°C for 24 hours to completely dissolve the PBI, PAI, and PBI / PAI in DMAc. The first dope 25 containing PSF and NMP was stirred at 25°C for 24 hours. Next, the first dope 25 and the second dope 35 were injected into an ISCO syringe pump and degassed for 24 hours. The bore fluid contains 90 wt.% NMP and 10 wt.% water.

[0067] As can be seen in Figure 2, the double-layer hollow fiber membrane 10 was fabricated using a dry-jet wet spinning process by simultaneously extruding the first dope 25, the second dope 35, and the bore fluid 55 through a triple-orifice spinneret 45 (S105). The triple-orifice spinneret 45 can be seen in Figure 5. The coagulation bath 70 was tap water. The bore fluid 55 was a mixture of NMP / water (90 / 10 wt.%). The flow rate of the first dope 25 was in the range of 2 mL / min to 20 mL / min. The flow rate of the second dope 35 was in the range of 0.3 mL / min to 3 mL / min. The flow rate of the bore fluid 55 was in the range of 0.5 mL / min to 5 mL / min. The void length was in the range of 1 cm to 5 cm. The winding speed was free fall. The method for manufacturing the double-layer hollow fiber membrane 10 was carried out at ambient temperature.

[0068] As can be seen in Figure 3, the double-layer hollow fiber membrane 10 was immersed in tap water for two days to remove residual solvent. Furthermore, the double-layer hollow fiber membrane 10 was subjected to solvent exchange, which included a first step of immersing the double-layer hollow fiber membrane 10 in methanol three times for 30 minutes each time, followed by a second step of immersing the double-layer hollow fiber membrane 10 in hexane three times for 30 minutes each time.

[0069] The next step is to air dry the double-layer hollow fiber membrane 10 at room temperature for 24 hours, S150. The next step is to chemically modify the double-layer hollow fiber membrane 10. The double-layer hollow fiber membrane 10 is immersed in a methanol solution of DBX (3 wt.%) at 60°C for 18 hours, S160. The double-layer hollow fiber membrane 10 is washed with methanol, S165. The double-layer hollow fiber membrane 10 is immersed in a methanol solution of BuDA (5 wt.%) at 24°C for 1 hour, S170, then washed with methanol, S175, and the double-layer hollow fiber membrane 10 is dried at 120°C for 3 hours, S180.

[0070] The gas separation performance of the double-layer hollow fiber membrane 10 was measured using the following two devices: a) The apparatus is a pure gas permeable cell 110, as shown in Figures 8 and 8A, and b) An apparatus which is a mixed gas permeation cell 120, as shown in Figures 9 and 9A.

[0071] In the pure gas permeation cell 110, in step S200, a supply gas stream 90 in the form of pure gas is supplied (or purged) to the membrane module 130 at a desired pressure (e.g., 7 bar) and a range of temperatures (e.g., 50°C, 100°C, and 150°C). The membrane module 130 contains a double-layer hollow fiber membrane 10, as previously described. The supply gas stream 90 is a gas selected from H2, N2, CH4, CO2, propane (C3H8), and propene (C3H6). In Figure, Table 1, Table 2, and Table 3, the double-layer hollow fiber membrane 10 is denoted as Divi-HP-b, where b refers to the temperature applied to the double-layer hollow fiber membrane 10.

[0072] In the mixed gas permeation cell 120, the separation performance of the double-layer hollow fiber membrane 10 is measured by determining the permeability of the gas streams to the double-layer hollow fiber membrane 10, namely the supply gas stream 91 and the purer gas stream 101, as shown in Figures 9 and 9A. The supply gas stream 91 is a gas mixture containing H2, N2, CH4, and CO2. Determining the permeability means evaluating the pressure, flow rate, and gas composition of the purer gas stream 101 and the supply gas stream 91 in step S231.

[0073] The supply gas stream 91 originates from the mass flow controller, passes through the first valve 163, and is then supplied to the membrane module 131. The purer gas stream 101 output from the membrane module 131 passes through the second valve 175 and the third valve 176 to measure the flow rate and composition of the purer gas, respectively. The pressure of the purer gas stream 101 is atmospheric pressure. Next, the purer gas stream 101 passes through the third valve 176 to reach gas chromatography (GC) for measuring the gas composition.

[0074] Both the permeated gas stream (i.e., the purer gas stream 101) and the impermeated gas stream 141 are shown in Figure 9A. The impermeated gas stream 141 is the gas mixture that does not pass through the double-layer hollow fiber membrane 10.

[0075] The pure gas permeable cell 110 includes seven membrane modules 130, denoted as T1 to T7. Each membrane module 130 contains ten double-layer hollow fiber membranes 10. An example of a membrane module 130 containing three double-layer hollow fiber membranes 10 can be seen in Figure 8A. An example of a double-layer hollow fiber membrane 10 is shown in Figure 8B. The membrane modules 130 of the pure gas permeable cell 110 are approximately 15 cm long, but the present invention is not limited thereto. The membrane modules 130 are used to determine the pure gas permeability and ideal gas pair selectivity of the double-layer hollow fiber membrane 10. The supply gas stream 90 permeates from the outer layer 20 (supply side) to the inner layer 16 (lumen side) of the double-layer hollow fiber membrane 10. The pure gas permeability and ideal gas pair selectivity of the double-layer hollow fiber membrane 10 were calculated according to equations (1) and (2), respectively.

[0076]

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[0077]

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[0078] JPEG2026509800000009.jpg48161

[0079] The measurement procedure is as follows: The double-layer hollow fiber membrane 10 is attached to the module holder, and the other end of the double-layer hollow fiber membrane 10 is sealed (i.e., forms a terminal). Sealing the other end ensures that the only path for the supply gas stream 90 through the double-layer hollow fiber membrane 10 is from the supply side to the lumen side. The double-layer hollow fiber membrane 10 is attached to and secured to the membrane module 130 of the pure gas permeable cell 110. The inlet valve 180 is opened to allow the supply gas stream 90 to flow into the gas permeable cell 110 formed from the double-layer hollow fiber membrane 10. The flow rate (i.e., permeation flow rate) is measured at the outlet of the double-layer hollow fiber membrane 10. In step S210, the membrane module 130 is heated so that the supply gas stream 90 is heated. In step S220, the pressure is increased along the membrane module 130. In step S225, the permeable gas stream 100 is output from the membrane module 130.

[0080] The results for the pure gas permeability of the double-layer hollow fiber membrane 10 and the ideal selectivity of the supply gas stream 90 are shown in the table below. These results were obtained at 50°C (Table 1), 100°C (Table 2), and 150°C (Table 3).

[0081] Table 1: [Table 6]

[0082] Table 2: [Table 7]

[0083] Table 3: [Table 8]

[0084] The mixed gas separation performance of the double-layer hollow fiber membrane 10 is further measured for a feed gas stream 91 containing a two-component mixture of H2 / CO2 (50:50). The mixed gas separation performance is measured using the mixed gas permeation cell 120 shown in Figures 9 and 9A.

[0085] The mixed gas permeable cell 120 includes a membrane module 131. As can be seen from Figures 10 and 11, the membrane module 131 contains 100 double-layer hollow fiber membranes 10, each approximately 25 cm long. Three identical membrane modules, named Module 1, Module 2, and Module 3, were manufactured for the mixed gas separation test, with the test being repeated three times. Furthermore, the average gas permeability of all three membrane modules (Module 1, Module 2, and Module 3) was measured. The average deviation of the test was ensured to be less than 5%.

[0086] The supply gas stream 91 was supplied to the membrane module 131 at a pressure of 14 bar. Tests were conducted at 50°C, 100°C, and 150°C. Using a gas chromatography apparatus, the gas composition of the purer gas mixture 101, i.e., the permeate gas mixture, and the composition of the unpermeated material, i.e., the outlet gas stream 141, were analyzed.

[0087] The permeability of the mixed gas through the double-layer hollow fiber membrane 10 was determined by equations (3) and (4) as follows:

[0088]

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[0089]

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[0091]

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[0092] Table 4 shows the gas transport properties of the double-layer hollow fiber membrane 10 after step S160 of immersing the double-layer hollow fiber membrane 10 in the first solution 75 containing DBX and step 170 (crosslinking step) of immersing the double-layer hollow fiber membrane 10 in the second solution 77 containing BuDA. Table 4 shows the effect of the PAI / PBI ratio on the gas permeability and separation performance of the double-layer hollow fiber membrane 10. Table 4 includes the notation Divi-HP-50-c, where 50 is the temperature at which the results were obtained and c is the concentration expressed as the weight % of PAI with respect to the outer layer 20 of the double-layer hollow fiber membrane 10.

[0093] Table 4:

Table 9

[0094] Table 4 shows that by increasing the amount of PAI incorporated into the polymer blend containing PBI, the gas permeabilities of H2 and CO2 increase, but the H2 / CO2 selectivity decreases due to the increase in the intermolecular chain distance in the double-layer hollow fiber membrane 10. In other words, the increase in the intermolecular chain distance reduces the molecular sieving ability of the double-layer hollow fiber membrane 10, and as a result, the selectivity of the double-layer hollow fiber membrane 10 decreases.

[0095] Figure 12 shows a Robeson plot as a benchmark for comparing the performance of Divi-HP-50-c films. The Divi-HP-50-c films presented in Figure 12 are derived from Table 4. The Robeson plot in Figure 12 includes an affine line called the "Robeson upper bound in 2008." The affine line, the "Robeson upper bound in 2008," is quoted from Lloyd M. Robeson, "The Upper Bound Revisited," Journal of Membrane Science, Vol. 320, 1st-2nd editions, 2008, pp. 390-400, ISSN 0376-7388, https: / / doi.org / 10.1016 / j.memsci.2008.04.030.

[0096] As explained in “Revised Upper Limits,” the 2008 Robeson upper limit illustrates a trade-off between membrane permeability and selectivity. As membrane permeability increases, membrane selectivity tends to decrease, and vice versa. The benchmark concept disclosed in “Revised Upper Limits” applies to polymer membranes for various gas pairs. This benchmark concept has been used in membrane science as a guideline for evaluating the performance of different membrane materials. The 2008 Robeson upper limit is presented graphically as a line in a permeability-to-selectivity plot. Most membranes are predicted to be below this line. Membranes above this line are considered high-performance membranes. To achieve separation performance exceeding the 2008 Robeson upper limit for any particular gas pair, the polymer membrane needs to be designed accordingly.

[0097] The Robeson upper limit for 2008 shown in Figure 12 is based on the "revised upper limit" and assumes an outer layer thickness of 1 μm. Figure 12 shows a comparison of the H2 / CO2 separation performance of the double-layer hollow fiber membrane 10 with the straight line representing the "Robeson upper limit for 2008".

[0098] As explained earlier, a double-layer hollow fiber membrane 10 that exceeds "Robeson's upper limit for 2008" is considered a high-performance membrane. Therefore, based on Figure 12, a double-layer hollow fiber membrane 10 having points corresponding to Divi-HP-50-0 (1), Divi-HP-50-5 (2), Divi-HP-50-10 (3), Divi-HP-50-15 (4), Divi-HP-50-20 (5), Divi-HP-50-25 (6), and Divi-HP-50-50 (7) has substantially high-performance properties. In other words, a double-layer hollow fiber membrane 10 containing an imide polymer of PAI at a concentration between 5 and 50% by weight relative to the outer layer (20) has substantially high-performance properties.

[0099] From Figure 12, it can be seen that there is a shoulder, or step, in the curve at point (3). Point (3) corresponding to Divi-HP-50-10 of the double-layer hollow fiber membrane 10 in Figure 12 shows a more balanced H2 permeability / H2 / CO2 selectivity, with a GPU of 8.7 and a selectivity of 22.8. Therefore, the double-layer hollow fiber membrane 10 (i.e., Divi-HP-50-10) containing an imide polymer of PAI at a concentration of 10 wt.% is considered to be the best for separating gas from a supply gas stream. [Explanation of Symbols]

[0100] 10. Double-layer hollow fiber membrane 15 Inner Layer 16 Internal volume 20 outer layer 25. The first dope 35. The second dope 45 Triple orifice spinning nozzle 55 Bore Fluid 60 Guide Rollers 70 Coagulation bath 72 Non-solvents 75 First solution 76 First container 77 Second solution 78 Second container 80 winding rollers 85 Equipment 90, 91 Supply gas streams 100, 101 Permeation gas stream 110 Pure Gas Permeable Cell 120 Mixed Gas Permeation Cell 130, 131 Membrane Modules 140, 141 Unpermeable gas mixture 161 First pressure sensor 162 Second pressure sensor 163 First electromagnetic valve 166 Second valve 167 Third valve 172 The fourth valve 180 Inlet Valve

Claims

1. A double-layer hollow fiber membrane (10) for separating gas from supply gas streams (90, 91), The inner layer (15) of the polymer polysulfone, and An outer layer (20) made from a combination of polymers selected from at least one imide polymer and at least one imidazole polymer. Includes, The imide polymer is polyamide-imide, PAI, and the imide polymer contains 5 to 50% by weight of PAI relative to the outer layer (20). Double-layered hollow fiber membrane (10).

2. The double-layer hollow fiber membrane (10) according to claim 1, wherein the polysulfone is one of poly(arylene sulfone) (PAS), poly(bisphenol-A sulfone) (PSF), polyethersulfone (PES), polyphenylene sulfone (PPSU), and polysulfone (PSU).

3. The double-layer hollow fiber membrane (10) according to any one of the claims, wherein the imide polymer contains 5 to 20% by weight of PAI relative to the outer layer (20), preferably 10% by weight (wt.%) of PAI relative to the outer layer (20).

4. The double-layer hollow fiber membrane (10) according to any one of the claims, wherein the imidazole polymer is polybenzimidazole, PBI.

5. The double-layer hollow fiber membrane (10) according to any one of the claims, wherein the imidazole polymer contains 80 to 95% by weight of PBI relative to the outer layer (20).

6. A double-layer hollow fiber membrane (10) according to any of the claims, having an inner diameter of at least 100 μm and a maximum of 1000 μm.

7. The double-layer hollow fiber membrane (10) according to any one of the claims, wherein the outer layer (20) has a thickness of at least 0.5 μm and / or up to 100 μm.

8. The double-layer hollow fiber membrane (10) according to any one of the claims, wherein the outer layer (20) further comprises at least one of 1,4-butanediamine (BuDA), α,α'-dibromo-p-xylene (DBX), or a combination thereof.

9. A double-layer hollow fiber membrane (10) according to any one of the claims for separating hydrogen and carbon dioxide from a supply gas stream (91).

10. A method for producing a double-layer hollow fiber membrane (10), The step (S105) is to simultaneously extrude a bore fluid (55), a polymer mixed with a first solvent, and a polymer mixed with a second solvent, wherein the polymer is a polysulfone, and the polymer combination is selected from at least one imide polymer and at least one imidazole polymer. The steps include obtaining a double-layered hollow fiber membrane (10) (S130), Step (S160) involves immersing the double-layer hollow fiber membrane (10) in the first solution (75) in the first container (76), The step (S170) is to immerse the double-layer hollow fiber membrane (10) in a second solution (77) in a second container (78), wherein the imide polymer of the double-layer hollow fiber membrane (10) is polyamide-imide, PAI, and the imide polymer contains 5 to 50% by weight of PAI relative to the outer layer (20) of the double-layer hollow fiber membrane (10), and Methods that include...

11. The method according to claim 10, wherein the bore fluid (55) is a mixture of N-methyl-2-pyrrolidone (NMP) and water.

12. The method according to claim 10 or 11, wherein the simultaneous extrusion step (S105) is a dry jet wet spinning process.

13. The method according to any one of claims 10 to 12, wherein the polysulfone is one of poly(arylene sulfone) (PAS), poly(bisphenol-A sulfone) (PSF), polyethersulfone (PES), polyphenylene sulfone (PPSU), and polysulfone (PSU).

14. The method according to any one of claims 10 to 13, wherein the imidazole polymer is polybenzimidazole (PBI).

15. The method according to any one of claims 10 to 14, wherein the first solution (75) contains in methanol one of α,α'-dibromo-p-xylene (DBX), 1,3,5-tris(bromomethyl)benzene, α,α'-dibromo-m-xylene, terephthaloyl chloride, 1,3,5-benzenetricarbonyl trichloride, isophthaloyl chloride, or a combination thereof.

16. The method according to any one of claims 10 to 15, wherein the second solution (77) comprises 1,4-butanediamine (BuDA) in methanol.

17. A method for separating gas from a supply gas stream (90), Step (S200) is to supply a supply gas stream (90) to a membrane module (130, 131) comprising at least one double-layer hollow fiber membrane (10), wherein the double-layer hollow fiber membrane (10) comprises an inner layer (15) of a polymer that is polysulfone, and an outer layer (20) made from a combination of polymers selected from at least one imide polymer and at least one imidazole polymer, wherein the imide polymer is polyamide-imide, PAI, and the imide polymer contains 5 to 50% by weight of PAI relative to the outer layer (20), Steps (S220, S221) of increasing the pressure along the membrane modules (130, 131), Steps (S225, S226) to output a purer gas mixture (100, 101) and Methods that include...

18. A purer gas mixture (100, 101) contains hydrogen (H) and carbon dioxide (CO). ２ ), methane (CH ４ ), nitrogen (N ２ ), propane (C ３ H ８ ), propene (C ３ H ６ The method according to claim 17, comprising at least one of the following: ), or a combination thereof.

19. Use of the double-layer hollow fiber membrane (10) according to any one of claims 1 to 9 for separating hydrogen or carbon dioxide from a supply gas stream (90, 91).

20. A method for measuring the separation performance of a double-layer hollow fiber membrane (10), Step (S200, S201) is to supply a supply gas stream (90, 91) to a membrane module (130, 131) comprising at least one double-layer hollow fiber membrane (10), wherein the double-layer hollow fiber membrane (10) comprises an inner layer (15) of a polymer that is polysulfone, and an outer layer (20) made from a combination of polymers selected from at least one imide polymer and at least one imidazole polymer, wherein the imide polymer is polyamide-imide, PAI, and the imide polymer contains 5 to 50% by weight of PAI relative to the outer layer (20), Steps (S220, S221) of increasing the pressure along the membrane modules (130, 131), Steps (S225, S226) include outputting a purer gas mixture (100, 101), Steps (S230, S231) to measure the separation performance of the double-layer hollow fiber membrane (10) by evaluating the pressure difference between the supply gas stream (90, 91) and the permeate gas stream (100, 101), and by measuring the flow rate and gas composition of the supply gas stream (90, 91) and the permeate gas stream (100, 101), and Methods that include...

21. The method according to claim 20, wherein the step of measuring the separation performance of the double-layer hollow fiber membrane (10) (S230, S231) includes determining the gas permeability and gas selectivity of the double-layer hollow fiber membrane (10).

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