Carbon hollow fiber membrane

Abstract

The present invention relates to a method for producing asymmetric cellulose hollow fibers and the use of such fibers in the production of asymmetric carbon hollow fiber membranes (CHFMs). In particular, the present invention provides a facile and scalable method for producing asymmetric CHFM by direct pyrolysis of the polymer precursor, without the need for complex pyrolysis pretreatment steps to prevent pore collapse. The present invention also relates to the use of the asymmetric CHFM produced according to the method for separating hydrogen gas from a mixed gas source, particularly for separating hydrogen from CO in a steam methane reforming reaction.

Description

[Technical Field]

[0001] The present invention relates to a method for producing asymmetric cellulose hollow fibers and the use of such fibers for the production of asymmetric carbon hollow fiber membranes (CHFMs). In particular, the present invention provides a facile and scalable method for producing asymmetric CHFMs by direct pyrolysis of a polymer precursor, without the need for complex pyrolysis pretreatment steps to prevent pore collapse. The present invention also relates to the use of asymmetric CHFMs produced according to the method for separating hydrogen gas from mixed gas sources, particularly for separating hydrogen from CO in steam methane reforming reactions. [Background technology]

[0002] Hydrogen, as a clean and efficient energy carrier, is also a versatile raw material used to produce a wide range of products, such as petrochemicals, semiconductors, ammonia, methanol, and vitamins. Hydrogen production from natural gas is considered one of the most promising large-scale technologies for realizing a hydrogen economy for a low-carbon energy future and reducing greenhouse gas emissions.

[0003] Compared with traditional hydrogen purification technologies such as pressure swing adsorption (PSA) and fractional distillation / cryogenic distillation, membrane-based separation technologies are currently considered promising alternatives due to their low investment costs, inherent high energy efficiency, and environmental compatibility. Various membrane materials, including polymeric membranes, graphene oxide (GO), inorganic-based membranes such as MoS2, zeolitic imidazolate frameworks (ZIFs), and metal-organic frameworks (MOFs), have been developed for H2 / CO2 separation. However, achieving commercially viable membranes for H2 purification remains challenging due to their low separation performance, complex fabrication processes (high cost), and limited stability under adverse conditions (e.g., high temperature and pressure in the steam methane reforming process).

[0004] Carbon molecular sieve (CMS) membranes have a rigid pore structure and are fabricated by the controlled carbonization of porous polymer precursors at high temperatures. Therefore, CMS is a promising candidate for a heat- and pressure-resistant material when used in hollow fibers suitable for membrane modules. The bimodal pore structure of CMS membranes, consisting of small ultramicropores and larger micropores, results in favorable gas selectivity for H2-related separations, such as H2 / CH4 and H2 / C2H4. However, relatively low H2 / CO2 selectivity has been reported due to strong adsorption between the carbon surface and CO2 molecules.

[0005] Recently, Ma et al. (Non-Patent Document 1) reported an H2-assisted method for creating "medium-sized" ultramicropores (5-7 Å) in CMS membranes by introducing H2 into the carbonization environment. The introduction of H2 into the carbonization process suppressed aromatization during pyrolysis of the polymer network, resulting in structures with wider ultramicropores compared to CMS membranes fabricated using an argon atmosphere. As reported by Qiu et al. (Non-Patent Document 2), the introduction of an additional heat treatment step at temperatures ranging from 90 to 250 °C to newly fabricated CMS membranes, known as the "hyperaging treatment," to accelerate aging, was shown to create smaller ultramicropores. However, CMS membranes reported to date still exhibit relatively large ultramicropores, which do not allow for precise gas sieving between H2 and CO2.

[0006] Another challenge often faced in CMS membrane fabrication is pore collapse. Many polymer precursors commonly used in CMS membrane fabrication exhibit pore collapse during carbonization, leading to densification of the resulting membrane. This densification is often detrimental to the membrane's performance in gas separation applications, particularly with regard to membrane permeability. Furthermore, pore collapse can destroy the asymmetry present in the polymer precursor fibers, leading to symmetrical CMS membranes that are unsuitable for gas separation applications.

[0007] Several authors have attempted to address the issue of pore collapse. Bhuwania et al. (Non-Patent Document 3, Patent Document 1) present a method to reduce pore collapse during pyrolysis and thus protect the asymmetric structure of polymer precursors. This method (called "V treatment") involves contacting the polymer precursor with a silicon-containing compound, such as vinyltrimethylsilane (VTMS), prior to pyrolysis, thereby forming a "crosslinked" network within the precursor structure that prevents pore collapse.

[0008] While such methods are effective in preventing pore collapse, the use of additional processing steps is costly and increases the overall process complexity. Furthermore, the use of potentially toxic silicon-containing compounds is undesirable and can result in significant amounts of residual silicon in the CHFM, which can lead to reduced membrane performance. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Patent No. 9,211,504 [Non-patent literature]

[0010] [Non-Patent Document 1] Angewandte Chemie International, 58th edition, pp. 13259-13265 (2019) [Non-patent document 2] Angewandte Chemie International, 58th edition, pp. 11700-11703 (2019) [Non-patent document 3] Carbon 76, pp. 417-434 (2014) Summary of the Invention [Problem to be solved by the invention]

[0011] Therefore, new methods for producing asymmetric CHFM that address these challenges are needed. In particular, methods are needed for producing asymmetric CHFM that do not require complex pyrolysis pretreatment steps to avoid pore collapse and that lead to CHFM suitable for use in separating hydrogen gas from mixed gas streams. Furthermore, such CHFM should have good high-temperature and high-pressure stability, as required for applications such as separating hydrogen gas from CO in steam methane reforming reactions. It is also desirable that such CHFM production methods allow for easy tuning of pore morphology, i.e., the relative proportions of micropores and ultrafine pores.

[0012] The present inventors have demonstrated that asymmetric CHFMs can be produced using asymmetric cellulose hollow fibers as polymer precursors without the need for complex pyrolysis pretreatment steps to avoid pore collapse. The present inventors have also demonstrated that suitable asymmetric cellulose hollow fibers can be produced by a dry-wet spinning process that involves careful control of the coagulation bath temperature. Therefore, a method for producing suitable asymmetric cellulose hollow fibers constitutes a further aspect of the present invention.

[0013] The resulting asymmetric CHFM has been shown to have good permeability and selectivity for hydrogen relative to larger gas molecules such as CO2, as well as high stability under high-temperature and high-pressure conditions. Therefore, CHFM produced according to the production methods disclosed herein is particularly suitable for use in separating hydrogen gas in steam methane reforming reactions. The CHFM production method provided by the inventors also provides for easy tuning of the membrane pore morphology (and therefore relative permeability / selectivity) by changing the pyrolysis temperature. [Means for solving the problem]

[0014] In one aspect, the present invention provides a method for producing a pharmaceutical composition comprising: a) providing a dope solution comprising cellulose, at least one ionic liquid, and optionally one or more co-solvents; b) co-extruding the dope solution and a core liquid comprising water, at least one ionic liquid, and optionally one or more co-solvents into a gas atmosphere; c )water The coextruded dope solution and the core liquid are coagulated in at least one coagulation bath containing Quench and form water-based fibers wherein the temperature of the coagulation bath is greater than 40°C; d) contacting the water-wet fiber with at least one organic solvent having a surface tension lower than that of water; and optionally e) drying the fibers; The present invention relates to a method for producing an asymmetric cellulose hollow fiber, comprising:

[0015] In another aspect, the present invention relates to an asymmetric cellulose hollow fiber produced according to such a production method, in particular, said asymmetric cellulose hollow fiber having a dense outer layer and a porous inner layer.

[0016] In another aspect, the present invention provides a method for producing an asymmetric carbon hollow fiber membrane (CHFM), comprising: a) providing an asymmetric cellulose hollow fiber; b) pyrolyzing the asymmetric cellulose hollow fibers; and optionally c) constructing a module comprising a plurality of said asymmetric cellulose hollow fibers; The present invention relates to a method for producing an asymmetric carbon hollow fiber membrane (CHFM), comprising:

[0017] In a preferred embodiment, the step a) of providing an asymmetric cellulose hollow fiber comprises carrying out a method for producing an asymmetric cellulose hollow fiber according to the first aspect of the present invention.

[0018] In another aspect, the invention relates to an asymmetric carbon hollow fiber membrane made by any of the manufacturing methods described herein.

[0019] In another embodiment, the asymmetric carbon hollow fiber membrane has a dense outer layer and a porous inner layer.

[0020] In yet another aspect, the present invention relates to the use of an asymmetric carbon hollow fiber membrane for separating hydrogen gas from a mixed gas stream, for example, for separating H2 from CO2 in a steam methane reforming reaction. [Brief explanation of the drawings]

[0021] [Figure 1] A) Schematic of the dry-wet spinning method for producing asymmetric cellulose hollow fibers. B) Schematic of the dried cellulose hollow fiber precursor. C) Carbonization procedure for the production of CHFM. D) Schematic of the asymmetric CHFM. The key step is the production of asymmetric cellulose hollow fibers by controlling the coagulation temperature to >40 °C (60 °C was used in this example). Step 2 is a non-solvent exchange using a low-surface tension solvent, e.g., isopropanol or n-hexane, to remove the remaining water inside the hollow fibers before drying, preventing the collapse of the pore morphology. Step 3 is a step for adjusting the ultrafine and micropore structure of the carbon membrane by varying the final carbonization temperature from 550 to 850 °C. [Figure 2] A and B) Cross-sectional SEM images of dried cellulose hollow fiber precursors after anti-collapse treatment. Scale bars: A - 200 μm, B - 50 μm. [Figure 3] A and B) Cross-sectional SEM images of air-dried cellulose hollow fiber carbon membrane precursors directly from water-wet membranes. Scale bars: A - 200 μm, B - 30 μm. [Figure 4] Comparative cross-sectional SEM images of flat sheet membranes injected at different coagulation bath temperatures. Scale bar: 100 μm. [Figure 5] Conversion mechanism of cellulose precursor to amorphous carbon films with two modes of pore structure. [Figure 6] Carbonization procedure of cellulose hollow fiber precursor. [Figure 7] A-B) Cross-sectional SEM images of CHFM-700. The inset shows the fiber in a bent state. Scale bars: a-100 μm, b-20 μm. C) XRD patterns of CHFM carbonized at different temperatures. And D) Pore size distribution of CHFM. [Figure 8]A) Performance of CHFM for single gases. B) Single gas permeability of CHFM-850 as a function of gas kinetic diameter. Inset: Selectivity of membrane for H2 over CO2, N2, and CH4. [Figure 9] FIG. 1 is an explanatory diagram of a high-pressure mixed gas permeation device. [Figure 10] A typical module used for mixed gas permeability measurement. [Figure 11] Measurement of 50mol%H2 / 50mol%CO2 mixed gas using CHFM-700 at different operating pressures (5-18bar) and 70℃. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention relates to a method for producing asymmetric cellulose hollow fibers and the use of such fibers for the production of asymmetric carbon hollow fiber membranes (CHFMs).

[0023] As used herein, the term "asymmetric" refers to the cross-sectional structure of cellulose hollow fibers and CHFMs characterized by the presence of at least two concentric layers in the fiber, each having a different level of porosity. For example, in one embodiment, an asymmetric cellulose hollow fiber or CHFM has at least a relatively less porous or "dense" outer layer and a relatively porous "porous" inner layer. This is in contrast to "symmetric" hollow fibers, which do not exhibit a distinctive layer structure characterized by differences in porosity.

[0024] Generally, particularly in gas separation applications, the dense outer layer acts as a selective layer, allowing certain chemical species to pass through the membrane while blocking the passage of other larger chemical species, while the porous layer acts primarily as a carrier for the dense outer layer, providing a mechanism by which chemical species can be transported into the dense layer.

[0025] Fabrication of asymmetric cellulose hollow fibers The asymmetric cellulose hollow fibers disclosed herein are produced by a dry-wet spinning process. A schematic diagram of an example of this production method is shown in Figure 1A. The individual steps leading to the production of asymmetric cellulose hollow fibers are described in detail below.

[0026] Step a) - Preparation of the dope solution In the first step of the method for producing asymmetric cellulose hollow fibers according to the present invention, a dope solution is prepared. The dope solution contains cellulose, at least one ionic liquid, and optionally one or more cosolvents. The cellulose used may be derived from plant sources such as wood pulp and cotton pulp. The cellulose used is generally in the form of a powder. In a preferred embodiment, the cellulose used is "unmodified," i.e., it is not a cellulose derivative such as a cellulose ester or cellulose ether.

[0027] Thus, in one embodiment, the dope solution contains less than 5% by weight of a cellulose derivative, such as cellulose acetate, cellulose triacetate, cellulose propionate, methylcellulose, or carboxymethylcellulose. In a preferred embodiment, the dope solution does not contain a cellulose derivative. In a particularly preferred embodiment, the cellulose added to the dope solution is microcrystalline cellulose (MCC).

[0028] Typically, the amount of cellulose dissolved in the dope solution is between 1.0 and 25.0% by weight. In one embodiment, the amount of cellulose in the dope solution is 5.0% by weight or more, e.g., 5.0 to 25.0% by weight, more preferably 5.0 to 20.0% by weight, e.g., 5.0 to 15.0% by weight. In a particularly preferred embodiment, 10.0 to 15.0% by weight of cellulose is dissolved in the dope solution.

[0029] In addition to cellulose, the dope solution contains an ionic liquid. Ionic liquids are salts that are liquid at 25°C and atmospheric pressure. Room-temperature ionic liquids often contain large, unsymmetrical organic cations based on heterocyclic compounds such as 1-alkyl-3-methylimidazolium, 1-alkylpyridinium, fluorosulfonyl-trifluoromethanesulfonylimide (FTFSI), N-methyl-N-alkylpyrrolidinium, and ammonium ions. Phosphonium cations are also possible. A wide range of anions are available, ranging from simple halides to inorganic anions such as tetrafluoroborate and hexafluorophosphate, and large and small organic anions such as bistriflimide, acetate, cyanamide, triflate, and tosylate.

[0030] Suitable ionic liquids include [Emim][OAc], [Emim][Cl], [Emim][dicyanamide], [Emim][DEP], [Emim][DMP], and 1-butyl-3,5-dimethylpyridinium bromide. In certain embodiments, the ionic liquid comprises a 1-ethyl-3-methylimidazolium cation ([Emim]) or a 1-butyl-3-methylimidazolium cation. 1-Ethyl-3-methylimidazolium acetate ([Emim][OAc]) is particularly preferred. Generally, ionic liquids have melting points in the range of 25 to 100°C.

[0031] Generally, the amount of ionic liquid in the dope solution should be sufficient to dissolve the cellulose component. In one embodiment, the ionic liquid comprises at least 25 wt. %, preferably at least 50 wt. %, more preferably at least 60 wt. %, e.g., at least 75 wt. % of the dope solution. In one embodiment, the ionic liquid comprises less than 95 wt. %, e.g., less than 90 wt. % of the dope solution.

[0032] Optionally, the dope solution contains one or more co-solvents in addition to the ionic liquid. The use of a co-solvent can increase the ionic strength of the ionic liquid, thereby increasing the solubility of the cellulose component in the dope solution. In one embodiment, the co-solvent is a polar solvent, preferably an aprotic polar solvent such as dimethylformamide (DMF), 1,3-dimethyl-2-imidazolidinone (DMI), dimethyl sulfoxide (DMSO), and mixtures thereof. DMSO is particularly preferred. A particularly preferred combination of ionic liquid and co-solvent is a mixture of [Emim][OAc] and DMSO.

[0033] When a cosolvent is present, the amount of cosolvent in the dope solution is generally in the range of 10.0% to 90.0% by weight. In a preferred embodiment, the cosolvent is present in an amount of 10.0 to 70.0% by weight, more preferably 10.0 to 50.0% by weight, e.g., 15.0 to 30% by weight. In one embodiment, the weight ratio of the ionic liquid to the cosolvent is in the range of 1:10 to 10:1, preferably 1:3 to 5:1, more preferably 2:1 to 5:1. In a particularly preferred embodiment, the dope solution comprises [Emim][OAc] and DMSO in a weight ratio of about 3:1.

[0034] Step b) - Co-extrusion with the core liquid In the second step of the process for producing asymmetric cellulose hollow fibers according to the present invention, the dope solution prepared in step a) is co-extruded with a core liquid into a gas atmosphere. The co-extrusion step, also known as the "spinning" step, involves surrounding the core liquid with the dope solution and co-extruding it through a spinneret into a gas atmosphere, usually air. This is commonly referred to as the "dry" stage of the wet-dry spinning process.

[0035] The gap between the spinneret die and the water bath is often called the air gap, and the size of this air gap can vary. Typically, the air gap is 0.5 to 25 cm, e.g., 5 to 15 cm. A larger air gap generally results in more stretchable fibers, which in turn results in more aligned cellulose chain orientation.

[0036] The core liquid comprises water, at least one ionic liquid, and optionally one or more co-solvents. The types of ionic liquids and co-solvents described herein that are suitable for use in the dope solution are also suitable for use in the core liquid. The ionic liquid and optional co-solvent components in the core liquid can be the same as or different from the ionic liquid and optional co-solvents present in the dope solution.

[0037] In a preferred embodiment, the ionic liquid and co-solvent (if present) in the core liquid are the same as those used in the dope solution. In a preferred embodiment, the core liquid comprises an ionic liquid containing a 1-ethyl-3-methylimidazolium cation, e.g., [Emim][OAc]. The co-solvent (if present) is preferably a polar solvent, more preferably an aprotic polar solvent, e.g., DMSO.

[0038] The amount of water in the core liquid is generally in the range of 5 to 50% by weight, preferably 5 to 30% by weight, more preferably 10 to 30% by weight, for example, 10 to 25% by weight. To obtain cellulose hollow fibers with an asymmetric structure, the composition of the core liquid must be different from that of the dope solution. Therefore, it is preferable that the amount of water in the core liquid is different (preferably greater) than the amount of water present in the dope solution (if present). In one embodiment, non-solvent water constitutes at least 10% by weight, preferably at least 15% by weight, of the core liquid.

[0039] In one embodiment, the ionic liquid constitutes at least 10% by weight of the core liquid, e.g., at least 50% by weight, preferably at least 60% by weight. In one embodiment, the ionic liquid constitutes less than 95% by weight, e.g., less than 90% by weight, of the core liquid. The amount of cosolvent in the core liquid is generally in the range of 1.0 to 90.0% by weight, e.g., 10 to 25% by weight. In one embodiment, the weight ratio of the amount of ionic liquid to the cosolvent is in the range of 1:3 to 10:1, preferably 2:1 to 5:1. In a particularly preferred embodiment, the core liquid comprises [Emim][OAc] and DMSO in a weight ratio of about 3:1.

[0040] The temperatures of the dope solution and the core liquid in the co-extrusion step may be the same or different and are preferably in the range of 5 to 80° C., preferably 15 to 70° C., for example 20 to 60° C. Dope solutions and core liquids at 20 to 40° C. are particularly preferred.

[0041] Step c) - Quench The dope solution and the core liquid are coextruded, contacted with a gas atmosphere, and then coagulated in at least one coagulation bath. Quench The coagulation bath causes phase separation within the coextruded dope solution and core liquid, leading to the formation of water-wet cellulose hollow fibers.

[0042] The coagulation bath comprises water alone or in a mixture with one or more other solvents, hi a preferred embodiment, the coagulation bath comprises only water.

[0043] The present inventors have demonstrated that the temperature of the coagulation bath is important in the production of cellulose hollow fibers having an asymmetric structure. Specifically, the present inventors have demonstrated that the temperature of the coagulation bath is 40°C or less when the coextruded dope solution and core liquid are coagulated. Quench When this is done, the resulting cellulose hollow fibers have been shown to exhibit a compact symmetrical structure (see Example 2 and Figure 4).

[0044] Therefore, to obtain cellulose hollow fibers with an asymmetric structure, a coagulation bath temperature of above 40° C., preferably above 41° C., for example above 45° C., is required. The coagulation bath temperature may also be as high as 80° C., for example between 41 and 80° C., preferably between 41 and 70° C. In a particularly preferred embodiment, the coagulation bath temperature is above 45° C., for example in the range of from 45 to 80° C., preferably from 45 to 70° C., in particular from 45 to 65° C.

[0045] In one embodiment, the coextruded dope solution and core liquid are passed through two or more coagulation baths. In this case, the requirement that the coagulation bath temperature be above 40°C applies only to the first coagulation bath in the series. The second and subsequent coagulation baths may have temperatures ranging from 10 to 80°C, preferably from 20 to 70°C, e.g., from 25 to 60°C. If second and subsequent coagulation baths are present, they preferably have the same composition as the first coagulation bath. In a particularly preferred embodiment, two water-containing coagulation baths are used in succession, with the first coagulation bath having a higher temperature than the second coagulation bath.

[0046] Steps d) and e) - Solvent exchange and drying Quench Afterwards, the water-wet fiber is subjected to a solvent exchange step to remove water from the fiber. If such a step is omitted and the water-wet fiber is directly dried, strong capillary forces may cause the pore structure of the hollow fiber to collapse (see Figure 3). Therefore, to prevent pore collapse, the water-wet fiber produced in step c) is contacted with at least one organic solvent having a surface tension lower than that of the water in the fiber. To reduce the capillary forces resulting from the fluid present in the pores of the fiber, the organic solvent must have a surface tension lower than that of water. Replacing the water in the fiber with a solvent having a lower surface tension reduces the capillary forces and reduces pore collapse during drying.

[0047] In one embodiment, the fibers are washed with water to remove residual ionic liquid and core liquid. Whether or not this washing step is performed, the water-wet fibers are then contacted with at least one organic solvent having a surface tension lower than that of water. In one embodiment, the organic solvent is selected from the group consisting of C1-C6 alcohols, C5-C8 linear or branched aliphatic hydrocarbons, and mixtures thereof. In a preferred embodiment, the organic solvent is selected from isopropanol, n-hexane, and mixtures thereof.

[0048] In a particularly preferred embodiment, the water-wet fiber is sequentially contacted with at least two different organic solvents. For example, in one embodiment, the fiber is first contacted with a C1-C6 alcohol solvent, such as isopropanol, followed by a second contact step with a solvent selected from the group of C5-C8 linear or branched aliphatic hydrocarbons, e.g., n-hexane. When two or more contact steps are used, it is particularly preferred that the second and subsequent solvents have a lower surface tension than the solvent used in the preceding step. In this way, the surface tension of the fluid present in the pores of the fiber is gradually reduced until the fiber can be dried without pore collapse.

[0049] Once the solvent exchange process has taken place, the fibers are dried. Typically, the fibers are dried in air at room temperature, although any conventional drying method may be used.

[0050] The resulting dried cellulose hollow fibers have an asymmetric structure, with at least a thin dense outer layer and a more porous carrier inner layer. An SEM image of a cellulose hollow fiber produced according to the production method of the present invention is shown in Figure 2. The fiber diameter is generally in the range of 300 to 800 μm, preferably 400 to 600 μm. The fiber wall thickness (i.e., measured from the inner wall to the outer wall of the fiber) is generally in the range of 25 to 200 μm, preferably 50 to 100 μm. The dense outer layer thickness is generally less than 50 μm, e.g., less than 25 μm, preferably less than 10 μm.

[0051] Viewed from another aspect, the present invention provides an asymmetric cellulosic hollow fiber having a dense outer layer and a concentric porous inner layer, the dense outer layer being substantially free of macrovoids larger than 500 nm, and the inner porous layer comprising a plurality of pores having a maximum pore size of 500 nm or greater.

[0052] Viewed from another aspect, the present invention provides an asymmetric cellulose hollow fiber having a dense outer layer less than 10 μm thick and a concentric porous inner layer 25 to 100 μm thick, wherein the dense outer layer is substantially free of macrovoids larger than 500 nm, and the inner porous layer comprises a plurality of pores having a maximum diameter of 500 nm or greater.

[0053] Viewed from another aspect, the present invention provides an asymmetric cellulosic hollow fiber having a dense outer layer less than 10 μm thick and a concentric porous inner layer 25 to 100 μm thick.

[0054] Typically, the asymmetric cellulose hollow fibers produced by the methods described herein consist primarily of cellulose II, while the cellulose component in the dope solution is typically cellulose I. In one embodiment, the asymmetric cellulose hollow fibers consist essentially of (i.e., at least 95% by weight, e.g., at least 99% by weight) cellulose II. The asymmetric cellulose hollow fibers are typically substantially free of cellulose acetate monomer (e.g., less than 5% by weight, e.g., less than 1% by weight).

[0055] Fabrication of asymmetric carbon hollow fiber membranes (CHFM) In one aspect, the present invention provides a method for producing a pharmaceutical composition comprising: a) providing an asymmetric cellulose hollow fiber; b) pyrolyzing the asymmetric cellulose hollow fibers; The present invention relates to a method for producing an asymmetric carbon hollow fiber membrane (CHFM), comprising:

[0056] The pyrolysis step, commonly referred to as "carbonization," is generally carried out under vacuum or in an inert gas environment such as CO2, N2, Ar, and He.

[0057] In a particularly preferred embodiment, the step a) of providing an asymmetric cellulose hollow fiber comprises carrying out a method for producing an asymmetric cellulose hollow fiber as described herein. a) providing a dope solution comprising cellulose, at least one ionic liquid, and optionally one or more co-solvents; b) co-extruding the dope solution and a core liquid comprising water, at least one ionic liquid, and optionally one or more co-solvents into a gas atmosphere; c )water The coextruded dope solution and the core liquid are coagulated in at least one coagulation bath containing Quench and form water-based fibers wherein the temperature of the coagulation bath is greater than 40°C; d) contacting the water-wet fiber with at least one organic solvent having a surface tension lower than that of water; e) drying the fibers to form asymmetric cellulose hollow fibers; and f) pyrolyzing the asymmetric cellulose hollow fibers; The present invention provides a method for producing an asymmetric CHFM, comprising:

[0058] Figure 5 outlines the basic steps of the carbonization mechanism of CHFM. Generally, the carbonization process begins with the physical removal of free water below 150 °C, followed by dehydration (150–200 °C) to remove bound water. Above 200–250 °C, 1,6-glycosidic bond cleavage occurs, where cellulose depolymerization forms levoglucosan (b). The carbon plate (c) formed by cellulose chain cleavage via 1,6-glycosidic bond cleavage and subsequent polymerization via intermolecular rearrangement at 250–300 °C leads to the formation of a weakly ordered microstructure, the “carbon lattice” (d), with micropores and ultramicropores. The heating rate in the temperature range of 250–300 °C is typically up to 4 °C / min. These micropores can be further narrowed by internal condensation at higher carbonization temperatures (e.g., >600 °C) (e). Finally, a carbon film (f) with a bimodal pore structure containing both micropores and ultramicropores is obtained.

[0059] In the pyrolysis step, the cellulose hollow fibers are preferably heated to at least 500°C, for example, 500 to 900°C, preferably at least 600°C, and more preferably at least 800°C.

[0060] In general, increasing pyrolysis temperatures correlate with improved selectivity to small gases such as hydrogen, but have been observed to slightly decrease permeability. Without wishing to be bound by theory, it is believed that the observed performance difference between CHFM produced at high and low carbonization temperatures is the result of the relative proportions of ultramicropores and (larger) micropores. Ultramicropores are the interstices and smaller spaces between highly aromatic carbon chains. While ultramicropores dominate gas pair selectivity, micropores formed by the voids between aromatic carbon plates contribute to high gas permeability. CHFM exhibits a more ordered graphitic carbon structure (sp) with increasing carbonization temperature. 2 The aromatic carbon plates tend to form three-dimensional sp 3 Due to the lower content of hybrid carbon, it is more compressible. Therefore, controlling the pyrolysis temperature during the manufacturing process allows for control over the gas separation performance of the resulting CHFM.

[0061] 7A-B show the structure of a CHFM produced according to the manufacturing method of the present invention. The fiber exhibits a distinct asymmetric structure, with a dense outer layer with substantially no pore collapse and a porous, carrier inner layer. In one embodiment, the thickness of the dense layer is less than 20 μm, e.g., less than 10 μm, and most preferably less than 5 μm.

[0062] The pores in the inner layer can be considered macropores because they generally allow the gas to be separated to pass through without any separation process. Therefore, the porous inner layer does not separate the gases in the gas mixture supplied to the CHFM. The dense layer generally does not contain macropores larger than 50 nm, but may contain micropores and ultra-micropores that allow separation of the target gas. Suitable pore sizes are 2.0 to 8.0 angstroms.

[0063] Viewed from another aspect, the present invention provides an asymmetric carbon hollow fiber membrane having a dense outer layer and a concentric porous inner layer, the dense outer layer being substantially free of pores larger than 8.0 Å.

[0064] Viewed from another aspect, the present invention provides an asymmetric carbon hollow fiber membrane having a dense outer layer less than 10 μm thick and a concentric porous inner layer 25 to 100 μm thick, wherein the dense outer layer is substantially free of pores larger than 8.0 Å and the inner porous layer comprises a plurality of macropores.

[0065] Viewed from another aspect, the present invention provides an asymmetric cellulose hollow fiber membrane having a dense outer layer less than 10 μm thick and a concentric porous inner layer 25 to 100 μm thick.

[0066] Surprisingly, the inventors have demonstrated that asymmetric CHFM can be produced using asymmetric cellulose hollow fibers as a polymer precursor without the need for an additional pyrolysis pretreatment step to prevent pore collapse. Because such treatments are often complex and expensive, by eliminating the need for such a step, the present invention provides a simpler and less expensive method for producing CHFM.

[0067] One example of a pretreatment that has been used to prevent pore collapse during carbonization is the "V treatment" proposed by Bhuaniah et al. (Carbon 76, pp. 417-434 (2014); U.S. Pat. No. 9,211,504), which involves contacting the polymeric precursor fiber with a silicon-containing compound. However, this results in a significant amount of residual silicon in the CHFM, which can lead to reduced membrane performance.

[0068] Thus, in one embodiment, the CHFM of the present invention contains less than 1.0 atomic %, for example, less than 0.5 atomic %, preferably less than 0.1 atomic %, and most preferably less than 0.05 atomic % silicon, as measured by X-ray photoelectron spectroscopy (XPS). In another embodiment, the CHFM contains more than 95 atomic % carbon, oxygen, and nitrogen elements. In one aspect, the CHFM consists essentially (i.e., more than 99 atomic %) of these elements.

[0069] The CHFM of the present invention may contain at least 85 atomic % C, 5 to 15 atomic % O, and up to 1.0 atomic % N.

[0070] The CHFM manufactured according to the manufacturing method of the present invention exhibits good flexibility. In one embodiment, the CHFM may have a bending radius of less than 1.5 cm, for example, less than 1 cm. In some embodiments, the CHFM may have a bending radius as small as 0.5 cm.

[0071] Purpose The CHFM produced according to the present invention is particularly suitable for use in gas separation applications. Accordingly, in one aspect, the present invention provides the use of an asymmetric carbon hollow fiber membrane (CHFM) produced by the production method described herein for separating hydrogen gas from a mixed gas stream, for example, for separating H from CO in a steam methane reforming reaction. In one embodiment, the CHFM of the present invention has an H permeability of at least 140 GPU and an H / CO selectivity of at least 10.0, preferably at least 45.0, e.g., at least 80.0.

[0072] Multiple carbon hollow fibers may be combined to form a module. A single carbon hollow fiber is considered herein to be a membrane. However, the present invention also relates to the combination of multiple CHFMs to produce a module. The present invention includes, for example, the following aspects. [Section 1] a) providing a dope solution comprising cellulose, at least one ionic liquid, and optionally one or more co-solvents; b) co-extruding the dope solution and a core liquid comprising water, at least one ionic liquid, and optionally one or more co-solvents into a gas atmosphere; c) quenching the co-extruded dope solution and core liquid in at least one coagulation bath containing water to form a water-wet fiber, wherein the temperature of the coagulation bath is greater than 40°C; d) contacting the water-wet fiber with at least one organic solvent having a surface tension lower than that of water; and optionally e) drying the fibers; A method for producing an asymmetric cellulose hollow fiber, comprising: [Section 2] Item 2. The method for producing an asymmetric cellulose hollow fiber according to Item 1, wherein the cellulose in the dope solution is microcrystalline cellulose (MCC). [Section 3] Item 3. The method for producing an asymmetric cellulose hollow fiber according to Item 1 or 2, wherein the amount of the cellulose in the dope solution is 1.0 to 25.0% by mass, preferably 5.0 to 25.0% by mass, more preferably 5.0 to 20.0% by mass, for example, 10.0 to 15.0% by mass. [Section 4] Item 4. The method for producing an asymmetric cellulose hollow fiber according to any one of Items 1 to 3, wherein the ionic liquid contains a 1-ethyl-3-methylimidazolium cation, and is, for example, selected from the group consisting of [Emim][OAc], [Emim][Cl], [Emim][dicyanamide], [Emim][DEP], [Emim][DMP], and 1-butyl-3,5-dimethylpyridinium bromide, and is most preferably [Emim][OAc]. [Section 5] Item 5. The method for producing an asymmetric cellulose hollow fiber according to any one of items 1 to 4, wherein the co-solvent is a polar solvent, preferably an aprotic polar solvent, such as dimethyl sulfoxide (DMSO) or DMF. [Section 6] Item 6. The method for producing an asymmetric cellulose hollow fiber according to any one of Items 1 to 5, wherein the temperature of the coagulation bath is in the range of 41 to 80°C, preferably 41 to 70°C, more preferably 45 to 70°C, for example, 45 to 60°C. [Section 7] Item 7. The method for producing an asymmetric cellulose hollow fiber according to any one of Items 1 to 6, wherein the organic solvent having a surface tension lower than that of water is selected from the group consisting of C1 to C6 alcohols, C5 to C8 linear or branched aliphatic hydrocarbons, and mixtures thereof, and preferably the organic solvent is selected from isopropanol, n-hexane, and mixtures thereof. [Section 8] Item 8. The method for producing an asymmetric cellulose hollow fiber according to any one of Items 1 to 7, wherein step d) comprises successively contacting the water-wet fiber with at least two organic solvents having a surface tension lower than that of water, for example, a first contacting step of contacting the water-wet fiber with a solvent selected from the group consisting of C1 to C6 alcohols, such as isopropanol, followed by a second contacting step of contacting the water-wet fiber with a solvent selected from the group consisting of C5 to C8 linear or branched aliphatic hydrocarbons, such as n-hexane. [Section 9] Item 9. An asymmetric cellulose hollow fiber manufactured by the manufacturing method according to any one of items 1 to 8, wherein the asymmetric cellulose hollow fiber consists essentially of cellulose II. [Section 10] a) providing an asymmetric cellulose hollow fiber; b) pyrolyzing the asymmetric cellulose hollow fibers; A method for producing an asymmetric carbon hollow fiber membrane (CHFM), comprising: A method for producing an asymmetric carbon hollow fiber membrane (CHFM), wherein the step a) of preparing the asymmetric cellulose hollow fiber comprises carrying out the production method described in any one of items 1 to 8. [Section 11] Item 11. The method for producing an asymmetric carbon hollow fiber membrane (CHFM) according to item 10, wherein the asymmetric cellulose hollow fiber is directly pyrolyzed, i.e., pyrolyzed without being subjected to any additional treatment step (such as contact with a silicon-containing compound) before pyrolysis. [Section 12] Item 10 or 11, wherein the pyrolysis step b) comprises heating the asymmetric cellulose hollow fiber to a temperature of at least 500 ° C., for example, 500 to 900 ° C., preferably at least 600 ° C., more preferably at least 800 ° C. The method for producing an asymmetric carbon hollow fiber membrane (CHFM) according to Item 10 or 11. [Section 13] Item 13. An asymmetric carbon hollow fiber membrane (CHFM) produced by the production method according to any one of items 10 to 12. [Section 14] An asymmetric carbon hollow fiber membrane having a dense outer layer and a concentric porous inner layer. [Section 15] Item 13 or 14, wherein the silicon content determined by X-ray photoelectron spectroscopy (XPS) is less than 1.0 atomic %, for example, less than 0.5 atomic %, preferably less than 0.1 atomic %, and most preferably less than 0.05 atomic %. [Section 16] At 130°C and 2 bar pressure, at least 140 GPU of H 2 and a H of at least 10.0, preferably at least 45.0, for example at least 80.0. 2 / CO 2 16. The asymmetric CHFM according to any one of items 13 to 15, having selectivity. [Section 17] 17. The asymmetric CHFM according to any one of items 13 to 16, comprising at least 85 atomic % C, 5 to 15 atomic % O, and up to 1.0 atomic % N. [Section 18] 18. A module comprising a CHFM according to any one of items 13 to 17. [Section 19] For separating hydrogen gas from a mixed gas stream, for example, CO in a steam methane reforming reaction 2 From H 2 Item 18. Use of the asymmetric carbon hollow fiber membrane (CHFM) according to any one of items 13 to 17, or the module according to item 18, for separating

[0073] The invention will now be further described with reference to the following examples and figures. [Example]

[0074] material Microcrystalline cellulose (MCC) powder (Avicel PH-101), isopropanol (≥99.7%, FCC grade), n-hexane (ReagentPlus®, ≥99%), and dimethyl sulfoxide (DMSO, FCC grade) were purchased from Sigma-Aldrich. 1-Ethyl-3-methylimidazolium acetate (EmimOAc, >95%) was purchased from IOLITEC GmbH. All chemicals were used as received. Single gases (e.g., H2, CO2) and a 50 mol% 50 mol% H2 / CO2 mixture were purchased from AGA Norway. All supplies used for membrane module construction were purchased from Swagelok.

[0075] Characterization SEM images were acquired using a Hitachi SU-6600 field emission scanning electron microscope (FESEM). XRD analysis of CHFM was performed in the 2θ range of 5° to 70°, 0.05 s -1 Measurements were performed on a Bruker D8 Focus instrument operated at 45 kV and 200 mA at a scan rate of 100 kV (Cu-Kα radiation, λ = 0.154 nm). CO physisorption was measured at 0 °C using a Quantachrome® A SiQwin™ automatic gas sorption analyzer. XPS spectra were acquired on an ESCALAB250 operated at 150 W and 200 eV using monochromated Al-Kα radiation. Raman analysis was performed using a Renishaw inVia Raman microscope with a 532 nm laser. [Example]

[0076] Fabrication of asymmetric cellulose hollow fibers Asymmetric cellulose hollow fibers, which are precursors for the final carbonized CHFM, were fabricated by a dry-wet spinning method as shown in Figure 1A. A 12 wt% MCC / (EmimOAc + DMSO) dope solution was used for the spinning process. MCC (60 g) (cellulose I) was gradually added to 440 g of EmimOAc / DMSO (3:1 mass ratio) cosolvent with mechanical stirring in a N2-atmosphere glove box and maintained at 50 °C overnight to completely dissolve the cellulose. Next, asymmetric cellulose (cellulose II) hollow fibers were fabricated by a dry-wet spinning method under the conditions shown in Table 1.

[0077] [Table 1]

[0078] The resulting hollow-spun fibers were cut into approximately 1.2 m long pieces and placed in a deionized water bath for 48 h to completely exchange the solvent (EmimOAc + DMSO) with water. The water-wet cellulose hollow fibers were immersed in pure isopropanol for 2 h, followed by n-hexane for 2 h, after which all the fibers were dried under ambient conditions.

[0079] Cross-sectional SEM images of the resulting dried cellulose hollow fibers are shown in Figures 2A and 2B. The hollow fibers exhibit a distinct asymmetric structure, with a relatively dense outer layer, a macrovoid-rich middle layer, and a more porous, supportive inner layer. This is in stark contrast to the structure of comparative cellulose hollow fibers shown in Figures 3A and 3B, which were fabricated in a similar manner, except that they were directly fabricated from water-wet fibers, i.e., air-dried without solvent exchange. The cellulose hollow fibers in Figures 3A and 3B have a dense, symmetric structure, most likely the result of pore collapse. Therefore, the solvent exchange process is crucial for obtaining asymmetric cellulose hollow fibers. [Example]

[0080] Investigating the effect of coagulation bath temperature on cellulose hollow fiber structure To determine the optimal conditions for cellulose hollow fiber production, the coagulation bath temperature (T c To achieve this, the effect of doping temperature (T d ) was maintained at 25°C, various flat sheet membranes were heated to various T c The membranes were prepared under atmospheric conditions. No core solution was used for the preparation of flat sheet membranes. The water-wet cellulose membranes were then immersed in pure isopropanol for 2 hours, followed by n-hexane for 2 hours. All membranes were then dried under atmospheric conditions.

[0081] Cross-sectional SEM images of the resulting flat sheet membranes are shown in Figure 4 (A) 25°C, B) 35°C, C) 40°C, D) 45°C, E) 50°C, and F) 60°C). c = 40 °C or less) produces cellulose membranes with a dense and symmetric structure (Figure 4A-C). c At temperatures above 45°C, a clear asymmetric structure is formed, with a dense upper layer and a more porous carrier layer (Figures 4D-F). In further tests, simply increasing the dope temperature while maintaining the coagulation bath temperature below 40°C did not produce the desired asymmetric structure.

[0082] Therefore, the temperature of the coagulation bath is important for obtaining cellulose hollow fibers with an asymmetric structure. Furthermore, we show that adjusting the temperature of the coagulation bath makes it possible to control the relative thicknesses of the dense and porous layers. [Example]

[0083] Carbon hollow fiber membrane manufacturing The dried cellulose hollow fibers prepared in Example 1 were carbonized in a tube furnace (Carbolite Gero Limited Horizontal Split Tube Furnace) under a continuous flow of 80 mL / min of high-purity argon (Ar, 99.999%) purge gas by applying the specific carbonization procedure shown in Figure 6. Considering the significant mass loss due to cellulose depolymerization at 300 °C, a reaction time of 2 h was adopted. Except for the final temperatures of 550 °C, 700 °C, and 850 °C, all other carbonization parameters (e.g., heating rate, reaction time, etc.) were kept the same to obtain three types of carbon membranes (referred to as CHFM-550, CHFM-700, and CHFM-850, respectively). The tube furnace was evacuated overnight at approximately 3 mbar before purging with Ar. After the carbonization process was completed, the system was allowed to cool naturally, and the resulting carbon hollow fiber membranes (CHFM) were removed when the temperature reached below 50 °C.

[0084] Cross-sectional SEM images of CHFM-700 are shown in Figures 7A and 7B. The asymmetric structure of the hollow fiber, with an outer selective layer of approximately 3 μm and an integrated porous carrier inner layer, was well maintained. The fabricated CHFM also exhibited good mechanical flexibility, with a bending radius of <1.5 cm, as shown in the inset of Figure 7A.

[0085] The XRD patterns for these CHFMs are shown in Figure 7C. The XRD patterns show a characteristic peak at approximately 2θ 24°, which corresponds to the graphite phase (sp 2 The interplanar spacing d was calculated using the Bragg equation. The large peak shift in 2θ when the carbonization temperature was increased from 550 to 850°C corresponds to the average interplanar spacing (d 002) decreases from 3.78 Å to 3.50 Å, indicating that carbon films prepared at higher carbonization temperatures tend to form graphitic carbon (approximately 3.4 Å) with a more ordered graphitic structure and smaller pores.

[0086] The pore size distribution shown in Figure 7D, calculated by the NLDFT model from CO physisorption in the range of 3–10 Å at 0 °C, indicates a narrowing of the pore width of CHFM-850 compared to CHFM-550. This CHFM exhibits a strong peak for ultrafine pores in the range of 3–4 Å, which is in the size range required to enable molecular sieving between H (2.9 Å) and other larger gas molecules (e.g., CO, N, and CH). With increasing carbonization temperature, the ultrafine pore peak (<5 Å) increases, while the fine pore peak (>5 Å) becomes weaker, indicating a decrease in the average pore size in CHFM carbonized at higher temperatures.

[0087] The CHFMs were investigated by XPS and their elemental compositions are shown in Table 2. With increasing carbonization temperature, the carbon content increases.

[0088] [Table 2] [Example]

[0089] Gas Permeation Test To demonstrate its suitability for gas separation, single-gas and mixed-gas permeation experiments were conducted on the CHFM prepared in Example 3. Single-gas permeation measurements were performed by utilizing the constant permeate volume method with a feed pressure of 2 bar. Gas permeability and selectivity were calculated using the following equation (1):

[0090]

number

[0091] In the formula, P / l(GPU, 1GPU=1×10 -6 cm3 (STP)·cm -2 ·s -1 cm Hg -1 =3.35×10 -10 mol·s -1 m -2 Pa -1 ) is the single gas permeability. V (cm 3 ) is the downstream (permeation) volume (previously determined using He calibration) and T (K) is the experimental temperature. A (cm 2 ) is the external effective surface area of ​​the hollow fiber membrane (shell side feed). P F and p (bar) are the pressures of the feed and permeate sides, respectively. Δt (s) is the test time at steady state. The ideal H / CO selectivity is calculated by the ratio of the H permeance to the CO permeance.

[0092] Figure 8A shows the single-gas performance of the CHFM prepared in Example 3 at 2 bar feed pressure and temperatures of 25°C, 60°C, 100°C, and 130°C. Open symbols represent predicted performance at 200°C. Membranes prepared at higher carbonization temperatures yield higher H / CO selectivities but at the expense of some H permeability. For example, CHFM-850 has a H / CO selectivity of 46.2 at 25°C, which is approximately four times higher than that of CHFM-550, but at the same time, its H permeability decreases from 102.1 GPU to 16.2 GPU. The solid and dashed lines in a) are based on Robeson's 2008 upper limit by converting permeability to permeability, assuming membrane selective layer thicknesses of 1 and 3 μm, respectively.

[0093] Figure 8B shows the single gas permeability of CHFM-850 as a function of gas kinetic diameter at 130 °C and 2 bar. There is a clear cutoff between the gas permeability of small molecules (148.2 GPU for H and 139.6 GPU for He) and large molecules, indicating that the gas permeability is primarily governed by the kinetic diameter of the gas molecules, i.e., using a molecular sieve transport mechanism. The inset shows the selectivity of H over CO, N, and CH.

[0094] Gas permeability and selectivity change significantly with temperature. By increasing the temperature from 25 to 130 °C, a significant increase in gas permeability and selectivity is observed, especially for membranes prepared at higher carbonization temperatures (Figure 8A). At 130 °C, the H2 / CO2 selectivity and H2 permeability of CHFM-850 increase to 83.9 and 148.2 GPU, respectively, which are approximately two and nine times higher than those obtained at 25 °C. Higher temperatures promote gas diffusion, which increases gas permeability. Conversely, lower CO2 adsorption at higher temperatures improves H2 / CO2 selectivity. Therefore, considering practical industrial applications, such as H2 purification from natural gas-derived syngas (usually operated at temperatures above 150 °C), higher operating temperatures are preferred to improve H2 / CO2 separation performance.

[0095] To test the potential of CHFM for H purification in steam methane reforming (typically performed at pressures up to 15–20 bar), a laboratory-scale hollow fiber module containing CHFM-700 was tested using a high-pressure gas permeation apparatus at 70 °C and various feed pressures (5–18 bar) with a 50 / 50 mol% H / CO mixture (Figures 9 and 10). All lines and membrane modules were preheated to the set temperature for the gas permeation test. During the test, the feed flow was controlled at 150 NmL / min. Argon was used as the sweep gas. Permeate gas flow rate and composition were measured by a bubble flow meter and a gas chromatograph (SRI Instruments GC 8610C), respectively. Three CHFM-700 membrane modules (eight carbon hollow fibers per module) were tested to determine experimental error. Using argon as the sweep gas, operated in countercurrent mode, gas was fed to the shell side and permeate gas exited from the hole side. The selectivity was calculated by the following formula:

[0096]

number

[0097] In the formula, y i and xi are the concentrations of the permeate gas component and the feed gas component, respectively.

[0098] The results of the mixed gas test are shown in Figure 11. As the total feed pressure increases from 5 to 18 bar, the H permeability gradually decreases (about 15.8%), but the H / CO selectivity increases from 31.8 to 37.7 (an increase of 18.6%). Therefore, the CHFM of the present invention is particularly suitable for high-pressure gas separation conditions, such as those in steam methane reforming reactions.

Claims

1. a) providing a dope solution comprising cellulose, at least one ionic liquid comprising a 1-ethyl-3-methylimidazolium cation, and optionally one or more co-solvents; b) co-extruding the dope solution with a core liquid comprising water, at least one ionic liquid comprising 1-ethyl-3-methylimidazolium cations, and optionally one or more co-solvents into a gas atmosphere; c) quenching the co-extruded dope solution and core liquid in at least one coagulation bath containing water to form a water-wet fiber, wherein the temperature of the coagulation bath is greater than 40°C; d) contacting the water-wet fibers with at least one organic solvent having a surface tension lower than that of water; and optionally e) drying the fibers; A method for producing an asymmetric cellulose hollow fiber, comprising:

2. 2. The method for producing an asymmetric cellulose hollow fiber according to claim 1, wherein the cellulose in the dope solution is microcrystalline cellulose (MCC).

3. 3. The method for producing an asymmetric cellulose hollow fiber according to claim 1, wherein the amount of the cellulose in the dope solution is 1.0 to 25.0% by mass.

4. 4. The method for producing an asymmetric cellulose hollow fiber according to claim 1, wherein the amount of the cellulose in the dope solution is 5.0 to 25.0% by mass.

5. 5. The method for producing an asymmetric cellulose hollow fiber according to claim 1, wherein the amount of the cellulose in the dope solution is 5.0 to 20.0% by mass.

6. 6. The method for producing an asymmetric cellulose hollow fiber according to claim 1, wherein the amount of the cellulose in the dope solution is 10.0 to 15.0% by mass.

7. 7. The method for producing an asymmetric cellulose hollow fiber according to claim 1, wherein the ionic liquid is selected from the group consisting of [Emim][OAc], [Emim][Cl], [Emim][dicyanamide], [Emim][DEP], and [Emim][DMP].

8. The method for producing an asymmetric cellulose hollow fiber according to any one of claims 1 to 7, wherein the ionic liquid is [Emim][OAc].

9. The method for producing an asymmetric cellulose hollow fiber according to claim 1 , wherein the co-solvent is a polar solvent.

10. The method for producing an asymmetric cellulose hollow fiber according to any one of claims 1 to 9, wherein the co-solvent is an aprotic polar solvent.

11. 11. The method for producing an asymmetric cellulose hollow fiber according to claim 1, wherein the co-solvent is dimethyl sulfoxide (DMSO) or DMF.

12. 12. The method for producing an asymmetric cellulose hollow fiber according to claim 1, wherein the temperature of the coagulation bath is in the range of 41 to 80°C.

13. 13. The method for producing an asymmetric cellulose hollow fiber according to claim 1, wherein the temperature of the coagulation bath is in the range of 41 to 70°C.

14. 14. The method for producing an asymmetric cellulose hollow fiber according to claim 1, wherein the temperature of the coagulation bath is in the range of 45 to 70°C.

15. 15. The method for producing an asymmetric cellulose hollow fiber according to claim 1, wherein the temperature of the coagulation bath is in the range of 45 to 60°C.

16. 16. The method for producing an asymmetric cellulose hollow fiber according to any one of claims 1 to 15, wherein the organic solvent having a surface tension lower than that of water is selected from the group consisting of C1 to C6 alcohols, C5 to C8 linear or branched aliphatic hydrocarbons, and mixtures thereof.

17. 17. The method for producing an asymmetric cellulose hollow fiber according to claim 1, wherein step d) comprises contacting the water-wet fiber successively with at least two organic solvents having a surface tension lower than the surface tension of water.

18. a) providing an asymmetric cellulose hollow fiber; b) pyrolyzing the asymmetric cellulose hollow fibers; A method for producing an asymmetric carbon hollow fiber membrane (CHFM), comprising:

18. A method for producing an asymmetric carbon hollow fiber membrane (CHFM), wherein step a) of providing the asymmetric cellulose hollow fiber comprises carrying out the method of any one of claims 1 to 17.

19. 20. The method for producing an asymmetric carbon hollow fiber membrane (CHFM) according to claim 18, wherein the asymmetric cellulose hollow fibers are directly pyrolyzed without being subjected to any additional processing steps before pyrolysis.

20. 20. The method for producing an asymmetric carbon hollow fiber membrane (CHFM) according to claim 18 or 19, wherein the pyrolysis step b) comprises heating the asymmetric cellulose hollow fibers to a temperature of at least 500°C.

21. 1. An asymmetric carbon hollow fiber membrane (CHFM) having a dense outer layer and a concentric porous inner layer, An asymmetric carbon hollow fiber membrane (CHFM) comprising at least 85 atomic % C, 5 to 15 atomic % O, and up to 1.0 atomic % N.

22. 22. The asymmetric CHFM of claim 21, having a silicon content of less than 1.0 atomic percent as determined by X-ray photoelectron spectroscopy (XPS).

23. At 130°C and 2 bar pressure, at least 140 GPU of H ２ and has a H of at least 10.0 ２ / CO ２ 23. The asymmetric CHFM of claim 21 or 22, which has selectivity.

24. 24. A module comprising a CHFM according to any one of claims 21 to 23.

25. 25. Use of an asymmetric carbon hollow fiber membrane (CHFM) according to any one of claims 21 to 23, or a module according to claim 24, for separating hydrogen gas from a mixed gas stream.

26. CO in the steam methane reforming reaction ２ From H ２ 26. Use of the asymmetric carbon hollow fiber membrane or module according to claim 25 for separating:

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