Carbon molecular sieve and preparation method thereof

Abstract

A method for preparing a carbon molecular sieve described herein can include applying a binder to an exterior surface of a polymeric hollow fiber at a first end of a plurality of polymeric hollow fibers, where the polymeric hollow fiber comprises a polyimide, polyvinylidene chloride, or a combination thereof, and where the binder is a polymer based on a total weight of the binder. The binder comprises at least 75% by weight of a polyimide, polyvinylidene chloride, or a combination thereof; curing the binder on the exterior surface of the polymeric hollow fiber to form a carbon molecular sieve precursor; and pyrolyzing the carbon molecular sieve precursor to form a carbon molecular sieve, wherein the carbon molecular sieve comprises a plurality of carbon hollow fibers and a carbonaceous binder residue on a first end of the plurality of carbon fibers.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 386,934, filed Dec. 12, 2022, the entire disclosure of which is hereby incorporated by reference herein. Technical Field

[0003] The embodiments described herein generally relate to carbon molecular sieves and methods for preparing carbon molecular sieves. Background Art

[0004] Carbon molecular sieves can be used to separate gas mixtures. Some carbon molecular sieves include bundles of hollow carbon fibers, and the ends of the bundles of hollow carbon fibers can be sealed together. To separate a gas mixture, the ends of the carbon molecular sieve can be sealed to a housing. When the gas mixture passes through the housing, the gas mixture can be separated, with some gases being retained within the housing and other gases passing through the hollow carbon fibers and exiting the housing. The selectivity of this separation can depend at least in part on the integrity of the seal between the outer surface of the hollow carbon fibers and the housing. Thus, there is a need for an improved carbon molecular sieve for gas separation. Summary of the Invention

[0005] Embodiments of the present disclosure relate to a carbon molecular sieve useful for gas separation and a method for producing such a carbon molecular sieve. A carbon molecular sieve including a bundle of hollow carbon fibers can be formed by pyrolyzing a precursor bundle of hollow fibers. According to one or more embodiments described herein, at least one end of the precursor bundle of hollow fibers can be sealed with an adhesive to form a carbon molecular sieve precursor. The carbon molecular sieve precursor can then be pyrolyzed to form a carbon molecular sieve that includes a seal around the outer surface of the carbon hollow fibers at at least one end of the bundle of carbon hollow fibers. Applying the adhesive to the precursor hollow fibers prior to pyrolysis can improve the contact between the adhesive and the precursor hollow fibers, which in turn can result in an improved seal around the outer surface of the carbon hollow fibers after pyrolysis. This can improve the selectivity of the carbon molecular sieve of one or more embodiments described herein.

[0006] According to one or more embodiments described herein, a method for preparing a carbon molecular sieve can include applying an adhesive to an outer surface of a plurality of polymer hollow fibers at a first end of the plurality of polymer hollow fibers, wherein the polymer hollow fibers comprise polyimide, polyvinylidene chloride, or a combination thereof, and wherein based on the total weight of the adhesive, the adhesive comprises at least 75 wt% of polyimide, polyvinylidene chloride, or a combination thereof; curing the adhesive on the outer surface of the polymer hollow fibers to form a carbon molecular sieve precursor; and pyrolyzing the carbon molecular sieve precursor to form a carbon molecular sieve, wherein the carbon molecular sieve comprises a plurality of carbon hollow fibers and a carbonaceous adhesive residue on a first end of the plurality of carbon fibers.

[0007] According to one or more embodiments described herein, a carbon molecular sieve can include a plurality of carbon hollow fibers having a first end and a second end, wherein each carbon hollow fiber has a tubular shape that includes an outer surface and an inner surface and defines a cavity, wherein each carbon hollow fiber comprises a first opening and a second opening; and a carbonaceous adhesive residue on a first end of the plurality of carbon fibers, wherein the carbonaceous adhesive residue directly contacts the outer surface of each carbon hollow fiber of the plurality of carbon hollow fibers.

[0008] Additional features and advantages of the inventive techniques disclosed herein will be set forth in the following detailed description, and in part will be apparent to those skilled in the art from the description, or may be recognized by practicing the inventive techniques as described herein, which include the following detailed description, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The following detailed description of specific embodiments of the present disclosure may be best understood when read in conjunction with the following drawings, in which like reference numerals indicate like structures and in which:

[0010] Figure 1A Schematically depicts a cross-section of a polymer hollow fiber according to one or more embodiments described herein;

[0011] Figure 1B Schematically depicts a cross-section of a polymer hollow fiber according to one or more embodiments described herein;

[0012] Figure 2 Schematically depicts an end of a carbon molecular sieve precursor according to one or more embodiments described herein;

[0013] Figure 3A Schematically depicts an end of a carbon molecular sieve according to one or more embodiments described herein;

[0014] Figure 3BSchematically depicts a carbon molecular sieve according to one or more embodiments described herein;

[0015] Figure 4 Depicts a photograph of a carbon molecular sieve precursor according to an embodiment 2 embodiment; and

[0016] Figure 5 Depicts a carbon molecular sieve according to an embodiment 2 embodiment.

[0017] Reference will now be made in more detail to various embodiments, some of which are shown in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. Detailed Description

[0018] As described herein, a method of preparing a carbon molecular sieve includes applying an adhesive to an outer surface of a polymeric hollow fiber at at least a first end of the polymeric hollow fiber. In some embodiments, the adhesive may be applied to both ends of the polymeric hollow fiber. The polymeric hollow fiber may comprise polyimide, polyvinylidene chloride, or a combination thereof, and based on the total weight of the adhesive, the adhesive comprises at least 75 wt% of polyimide, polyvinylidene chloride, or a combination thereof. The method may include curing the adhesive on the outer surface of the polymeric hollow fiber to form a carbon molecular sieve precursor and pyrolyzing the carbon molecular sieve precursor to form a carbon molecular sieve. The carbon molecular sieve may comprise a plurality of carbon hollow fibers and a carbonaceous adhesive residue at a first end of the plurality of carbon fibers.

[0019] Conventional methods for sealing the ends of a plurality of carbon fibers typically include applying an adhesive to the hollow carbon fibers, i.e., fibers that have undergone pyrolysis. Without wishing to be bound by theory, applying an adhesive to carbon fibers can be challenging due to the relatively low wettability of many conventional adhesives to carbon fibers. When exposed to temperature and pressure variations, such as those that may occur during the process of separating gas mixtures, this may lead to seal failure between the carbon fibers and the adhesive. However, without wishing to be bound by theory, applying an adhesive to a polymeric hollow fiber and subsequently pyrolyzing both the adhesive and the polymeric hollow fiber simultaneously can produce a carbon molecular sieve having a strong seal between the outer surface of the carbon hollow fibers and the carbonaceous adhesive residue (the material produced by pyrolysis of the adhesive). This seal is capable of withstanding harsh separation conditions, such as high temperature and pressure, exposure to high pH and low pH, and exposure to various hydrocarbons that may be present when separating gas mixtures.

[0020] The method for preparing a carbon molecular sieve described herein may include applying an adhesive to the outer surface of a polymeric hollow fiber. In one or more embodiments, the polymeric hollow fiber may comprise polyimide, polyvinylidene chloride, or a combination thereof. For example, but not limited to, the polymeric hollow fiber may comprise polyimide; the polymeric hollow fiber may comprise polyvinylidene chloride; the polymeric hollow fiber may comprise both polyimide and polyvinylidene chloride. As used herein, "polyimide" is a polymer that contains imide groups in the polymer backbone. Any suitable polyimide may be used in the polymeric hollow fiber. Exemplary polyimides for use in polymeric hollow fibers are described in International Publication No. WO 2020 / 154146 A1, the entire content of which is incorporated herein by reference. Suitable polyimides may include at least two different moieties resulting from diamine and dianhydride monomers selected from 2,4,6-trimethyl-1,3-phenylenediamine (DAM), dimethyl-3,7-diaminobiphenyl-thiophene-5,5'-dioxide (DDBT), 3,5-diaminobenzoic acid (DABA), 5(6)-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane (DAPI), 2,3,5,6-tetramethyl-1,4-phenylenediamine (durene), tetramethyl-m-xylenediamine (TMMDA), 4,4'-diamino-2,2'-biphenyldisulfonic acid (BDSA); 5,5'-[2,2,2-trifluoro-1-(trifluoromethyl)ethylidene]-1,3-isobenzofurandione (6FDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), and benzophenone tetracarboxylic dianhydride (BTDA). In one or more embodiments, the polyimide comprises at least one of the following diamines: 2,4,6-trimethyl-1,3-phenylenediamine (DAM), 3,5-diaminobenzoic acid (DABA), 2,3,5,6-tetramethyl-1,4-phenylenediamine (durene), or tetramethyl-m-xylenediamine (TMMDA). In one or more embodiments, the polyimide may comprise MATRIMID TM 5218 (Huntsman Advanced Materials Americas, The Woodlands, Texas), a commercially available polyimide that is a copolymer of 3,3',4,4'-benzophenonetetracarboxylic dianhydride and 5(6)-amino-1-(4'-aminophenyl)-1,3,3-trimethylindane (BTDA-DAPI). In one or more embodiments, the polymeric hollow fiber does not undergo pyrolysis to form a carbon hollow fiber prior to applying the adhesive to the outer surface of the polymeric hollow fiber.

[0021] In an embodiment, the plurality of polymeric hollow fibers can include from 10 to 50,000 polymeric hollow fibers. For example, but not limited to, the plurality of polymeric hollow fibers can include from 10 to 50,000, from 50 to 50,000, from 100 to 50,000, from 250 to 50,000, from 500 to 50,000, from 1000 to 50,000, from 5000 to 50,000, from 10,000 to 50,000, from 20,000 to 50,000, from 30,000 to 50,000, from 40,000 to 50,000, from 10 to 40,000, from 10 to 30,000, from 10 to 20,000, from 10 to 10,000, from 10 to 5000, from 10 to 1000, from 10 to 500, from 10 to 250, from 10 to 100, from 10 to 50, or any combination or subset of these ranges. In an embodiment, each fiber of the plurality of polymeric hollow fibers can include polyimide, polyvinylidene chloride, or a combination thereof.

[0022] Now referring Figure 1A and Figure 1B , each polymeric hollow fiber 100 can have a tubular shape and can include an inner surface 102 and an outer surface 104. The inner surface 102 can define a lumen 106. In an embodiment, each polymeric hollow fiber 100 can have a circular, elliptical, oval, or any other suitable cross-sectional shape. For example, but not limited to, Figure 1B the polymeric hollow fiber 100 depicted in has a circular cross-sectional shape. It should be noted that in some embodiments, due to minor defects in the fiber, the cross-sectional shape may not be a perfect circle, ellipse, or oval. Thus, in some embodiments, the polymeric hollow fiber 100 can have a substantially circular, elliptical, or oval cross-sectional shape. Each polymeric hollow fiber 100 can have a first end 110 and a second end 120. In an embodiment, the first end 110 of each polymeric hollow fiber 100 includes an opening that leads to the lumen 106, and the second end 120 of each polymeric hollow fiber 100 includes an opening that leads to the lumen 106.

[0023] The method for producing a carbon molecular sieve described herein includes applying an adhesive to the outer surface 104 of the polymeric hollow fiber 100. The adhesive can be applied to the outer surface 104 of the polymeric hollow fiber 100 by any suitable means, including but not limited to spraying, brushing, dipping, casting, and the like. In one or more embodiments, the adhesive can be applied to the outer surface 104 of the polymeric hollow fiber 100 at the first end 110 of the plurality of polymeric hollow fibers 100, at the second end 120 of the plurality of polymeric hollow fibers 100, or at both the first end 110 and the second end 120 of the plurality of polymeric hollow fibers 100. It should be noted that the adhesive does not contact the entire outer surface 104 of the polymeric hollow fiber 100. In an embodiment, at least a portion of the outer surface 104 of the polymeric hollow fiber 100 is not coated with the adhesive. For example, in an embodiment where both the first end 110 and the second end 120 of the outer surface 104 of the polymeric hollow fiber 100 are coated with the adhesive, there is a portion of the hollow fiber that is not coated between the first end 110 and the second end 120. In an embodiment, applying the adhesive to the outer surface 104 of the polymeric hollow fiber 100 does not block or otherwise cover the opening of the cavity 106 of the polymeric hollow fiber. For example, but not limited to, the adhesive may not block at least 50%, at least 60%, at least 70%, at least 80%, or even at least 99% of the surface area of the polymeric hollow fiber opening.

[0024] In an embodiment, based on the total weight of the adhesive, the adhesive can comprise at least 75 wt% of polyimide, polyvinylidene chloride, or a combination thereof. For example, but not limited to, based on the total weight of the adhesive, the adhesive can comprise at least 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, or even 99 wt% of polyimide, polyvinylidene chloride, or a combination thereof. In an embodiment, the adhesive can consist essentially of polyimide, polyvinylidene chloride, or a combination thereof or even consist of polyimide, polyvinylidene chloride, or a combination thereof. In one or more embodiments, the adhesive may further comprise polyvinyl acetate. Without intending to be bound by theory, polyvinyl acetate can be added to the adhesive to adjust the viscosity of the adhesive.

[0025] In one or more embodiments, both the polymeric hollow fibers 100 and the binder comprise polyimide, polyvinylidene chloride, or a combination thereof. For example, based on the total weight of the binder, the binder can comprise at least 75 wt% of the polyimide, polyvinylidene chloride, or a combination thereof that makes up the plurality of polymeric hollow fibers. By way of example and not limitation, based on the total weight of the binder, the binder can comprise at least 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%, or even 99 wt% of the polyimide, polyvinylidene chloride, or a combination thereof that makes up the plurality of polymeric hollow fibers. Without being bound by theory, when the binder comprises at least 75 wt% of the polyimide, polyvinylidene chloride, or a combination thereof that makes up the polymeric hollow fibers 100, the wettability between the polymeric hollow fibers 100 and the binder can be improved. This can result in the formation of an improved seal between the binder and the outer surface of the polymeric hollow fibers.

[0026] The method for forming a carbon molecular sieve described herein includes curing a binder on the outer surface 104 of the polymeric hollow fibers 100 to form a carbon molecular sieve precursor. Now referring to Figure 2 , the carbon molecular sieve precursor 200 comprises a plurality of polymeric hollow fibers 100. For simplicity of the drawings, Figure 2 only two polymeric hollow fibers 100 are depicted. The carbon molecular sieve precursor 200 further comprises a cured binder 210. The cured binder 210 can be in direct contact with the outer surface 104 of the polymeric hollow fibers 100. In an embodiment, the cured binder 210 does not block the openings of the cavities 106 of the polymeric hollow fibers 100. The binder on the outer surface of the polymeric hollow fibers 100 can be cured by any suitable means. Without being bound by theory, the curing process can be operated to crosslink the binder. Upon crosslinking, the binder can have improved structural stability to prevent softening and melting during subsequent pyrolysis steps. In an embodiment, curing the binder can include exposing the binder to gamma radiation, electron beam radiation, or ultraviolet radiation, or heat.

[0027] In one or more embodiments, the binder can be cured at a temperature of from 120 °C to 160 °C. By way of example, without being bound by theory, curing the binder can occur at the following temperatures: 120 °C to 160 °C, 120 °C to 150 °C, 120 °C to 140 °C, 120 °C to 130 °C, 130 °C to 160 °C, 140 °C to 160 °C, 150 °C to 160 °C, or any combination or subset of these ranges.

[0028] In one or more embodiments, curing of the adhesive can occur for a time period of from 1 hour to 48 hours. By way of example, and not limitation, curing of the adhesive can occur for the following time periods: 1 hour to 48 hours, 1 hour to 42 hours, 1 hour to 36 hours, 1 hour to 30 hours, 1 hour to 24 hours, 1 hour to 18 hours, 1 hour to 12 hours, 1 hour to 6 hours, 1 hour to 3 hours, 3 hours to 48 hours, 6 hours to 48 hours, 12 hours to 48 hours, 18 hours to 48 hours, 24 hours to 48 hours, 30 hours to 48 hours, 36 hours to 48 hours, 42 hours to 48 hours, or any combination or subset of these ranges.

[0029] The method for forming a carbon molecular sieve described herein includes pyrolyzing a carbon molecular sieve precursor 200 to form a carbon molecular sieve. As described herein, "pyrolysis" refers to the thermal decomposition of a material at an elevated temperature in an inert atmosphere. Generally, the pyrolysis product can be carbon-rich compared to the reactant undergoing pyrolysis. In an embodiment, pyrolyzing the carbon molecular sieve precursor can form a carbon molecular sieve. Based on the weight of the carbon molecular sieve, the carbon molecular sieve can have a greater carbon content than the carbon content of the carbon molecular sieve precursor 200 based on the weight of the carbon molecular sieve precursor. The carbon molecular sieve precursor 200 can be pyrolyzed in any suitable furnace, oven, or other apparatus operable to heat the carbon molecular sieve temperature to a temperature sufficient for pyrolysis in an inert atmosphere.

[0030] In one or more embodiments, the pyrolytic carbon molecular sieve precursor 200 occurs at a temperature of 500°C to 1500°C. Within this temperature range, the pyrolysis of polyimide and PVDC can form a selective permeation carbon molecular sieve membrane. For example, but not limited to, the pyrolytic carbon molecular sieve precursor 200 can occur at the following temperatures: 500°C to 1500°C, 600°C to 1500°C, 700°C to 1500°C, 800°C to 1500°C, 900°C to 1500°C, 1000°C to 1500°C, 1100°C to 1500°C, 1200°C to 1500°C, 1300°C to 1500°C, 1400°C to 1500°C, 500°C to 1400°C, 500°C to 1300°C, 500°C to 1200°C, 500°C to 1100°C, 500°C to 1000°C, 500°C to 900°C, 500°C to 800°C, 500°C to 700°C, 500°C to 600°C, or any combination or subset of these ranges. In some embodiments, the pyrolytic carbon molecular sieve precursor 200 occurs at a temperature of 500°C to 1000°C. In an embodiment, the pyrolytic carbon molecular sieve precursor occurs at a temperature of 500°C to 900°C. Without being bound by theory, when the carbon molecular sieve precursor is pyrolyzed at a temperature of 500°C to 1500°C, the carbon molecular sieve precursor can form a carbon molecular sieve membrane that is operable to separate species of a gas mixture, such as but not limited to separating olefins and paraffins (e.g., propane and propylene). Additionally, pyrolyzing the carbon molecular sieve precursor at such temperatures can produce a selective permeation carbon molecular sieve membrane.

[0031] In one or more embodiments, the pyrolytic carbon molecular sieve precursor 200 occurs for a time of 1 hour to 1 week. For example, but not limited to, the pyrolytic carbon molecular sieve precursor 200 can occur for the following times: 1 hour to 1 week, 3 hours to 1 week, 6 hours to 1 week, 12 hours to 1 week, 18 hours to 1 week, 1 day to 1 week, 2 days to 1 week, 3 days to 1 week, 4 days to 1 week, 5 days to 1 week, 6 days to 1 week, 1 hour to 6 days, 1 hour to 5 days, 1 hour to 4 days, 1 hour to 3 days, 1 hour to 2 days, 1 hour to 1 day, 1 hour to 18 hours, 1 hour to 12 hours, 1 hour to 6 hours, 1 hour to 3 hours, or any combination or subset of these ranges. It should be noted that in some embodiments, the pyrolysis can occur for a period of time required for the reaction to form a carbon molecular sieve having a pore size distribution suitable for separating gases from a gas mixture, such as but not limited to separating olefins and paraffins (e.g., propane and propylene). Additionally, pyrolyzing the carbon molecular sieve precursor at such temperatures can produce a selective permeation carbon molecular sieve membrane.

[0032] In one or more embodiments, the pyrolytic carbon molecular sieve precursor 200 is carried out under an inert atmosphere. The inert atmosphere can be any suitable inert atmosphere for pyrolysis. In an embodiment, the inert atmosphere can be substantially free of oxidizing substances such as oxygen (O2). As used herein, a composition is "substantially free" of a component when the component is not intentionally added to the composition; however, it should be noted that the component may be present in small amounts as a contaminant. In an embodiment, the inert atmosphere can include nitrogen, argon, carbon dioxide, or a combination thereof. In some embodiments, the inert atmosphere can consist essentially of nitrogen, argon, or carbon dioxide, or even consist of nitrogen, argon, or carbon dioxide. Without wishing to be bound by theory, the pyrolytic carbon molecular sieve precursor 200 can occur under an inert atmosphere to prevent the occurrence of undesired side reactions such as, but not limited to, combustion and hydrolysis.

[0033] The pyrolytic carbon molecular sieve precursor 200 can form a carbon molecular sieve. In an embodiment, the carbon molecular sieve can include a carbonaceous binder residue and a plurality of carbon hollow fibers. In one or more embodiments, the carbonaceous binder residue directly contacts at least a portion of the outer surface of each carbon hollow fiber in the carbon molecular sieve. It should be noted that at least a portion of the outer surface of each carbon hollow fiber does not contact the carbonaceous binder residue. Now referring to Figure 3A , the carbon molecular sieve 300 includes a carbonaceous binder residue 310 and a plurality of carbon hollow fibers 320. For simplicity, Figure 3A only two carbon hollow fibers 320 are depicted. Each carbon hollow fiber 320 includes an inner surface 322 and an outer surface 324. The inner surface 322 of the carbon hollow fiber 320 defines a cavity 326.

[0034] In an embodiment, the direct contact between the carbonaceous binder residue 310 and the outer surface 324 of the carbon hollow fiber 320 results in a seal between the carbonaceous binder residue 310 and the outer surface 324 of the carbon hollow fiber 320. This seal can prevent a gas mixture from passing between the carbonaceous binder residue 310 and the outer surface 324 of the carbon hollow fiber 320. Without wishing to be bound by theory, reducing the amount of gas mixture that can pass between the carbonaceous binder residue 310 and the outer surface 324 of the carbon hollow fiber 320 can result in greater selectivity of the carbon molecular sieve 300. In one or more embodiments, the seal between the carbonaceous binder residue 310 and the outer surface 324 of the carbon hollow fiber 320 can be durable enough to withstand high temperatures and pressures, exposure to materials with high and low pH values, and exposure to various hydrocarbons that may occur during the separation of various gas mixtures.

[0035] In embodiments where an adhesive is applied to the second end portion 120 of the outer surface of the polymeric hollow fiber 100, the carbon molecular sieve may further include a second carbonaceous adhesive residue on the second end portion of the plurality of carbon hollow fibers 320. The second carbonaceous adhesive residue may directly contact the outer surface 324 of each carbon hollow fiber 320 in the carbon molecular sieve 300. In embodiments, the second carbonaceous adhesive residue does not block the opening of the cavity of the carbon hollow fiber 320. In Figure 3B the depicted embodiment, the carbon molecular sieve 300 includes a carbonaceous adhesive residue 310 at the first end portion 328 of the carbon hollow fiber 320 and a second carbonaceous adhesive residue 312 at the second end portion 329 of the carbon hollow fiber 320. It should be noted that at least a portion of the outer surface 324 of each carbon hollow fiber 320 does not contact the carbonaceous adhesive residue 310 and the second carbonaceous adhesive residue 312.

[0036] In one or more embodiments, the carbonaceous adhesive residue 310 does not cover or otherwise block the opening of the cavity of the carbon hollow fiber 320. For example, but not limited to, the carbonaceous adhesive residue may not block the openings of at least 50%, at least 60%, at least 70%, at least 80%, or even at least 99% of the plurality of carbon hollow fibers. Without being bound by theory, blocking the opening of the carbon hollow fiber 320 with the carbonaceous adhesive residue 310 may reduce the effectiveness of the carbon molecular sieve 300 in separating gas mixtures. When the opening of the carbon hollow fiber 320 is blocked by the carbonaceous adhesive residue 310, the gas mixture may not be able to pass through the carbon hollow fiber 320, thereby reducing the number of carbon hollow fibers 320 available in the carbon molecular sieve 300 for separating the gas mixture.

[0037] In embodiments, the carbonaceous adhesive residue 310 may be formed from the adhesive of the carbon molecular sieve precursor 200. In embodiments, based on the total weight of the adhesive, after pyrolysis at 550 °C, the weight of the carbonaceous adhesive residue 310 is greater than 10 wt% of the adhesive. For example, but not limited to, based on the total weight of the adhesive, after pyrolysis at 550 °C, the weight of the carbonaceous adhesive residue 310 is greater than 10 wt%, 20 wt%, 30 wt%, 40 wt%, or even 50 wt% of the adhesive. It should be noted that the time at which pyrolysis occurs is the time required for the pyrolysis reaction to reach equilibrium at a temperature of 550 °C. Without being bound by theory, when the weight of the carbonaceous adhesive residue 310 after pyrolysis at 550 °C is greater than 10 wt% of the adhesive, the carbonaceous adhesive residue 310 may provide a seal with mechanical strength for gas separation applications.

[0038] In one or more embodiments, pyrolysis of the carbon molecular sieve precursor 200 can produce a carbon molecular sieve 300, where the carbon hollow fibers 320 and the carbonaceous binder residue 310 have substantially the same composition. Without being bound by theory, this can result in a strong bond between the carbonaceous binder residue 310 and the carbon hollow fibers 320.

[0039] In one or more embodiments, one or more gases from a gas mixture, such as a mixture of H2, CO2, and CH4 and a mixture of C3H6 and C3H8, can be separated by the carbon molecular sieve 300 described in the embodiments herein. Without being bound by theory, when the carbon molecular sieve 300 includes a carbonaceous binder residue 310 on at least one end of a plurality of carbon hollow fibers 320, the carbon molecular sieve 300 can be operable for at least some gas separations. For example, but not limited to, the carbon molecular sieve 300 can be sealed in a housing operable to separate one or more gases from a gas mixture. The carbon molecular sieve 300 can be positioned within the housing such that the outer surface 324 of the carbon hollow fibers 320 is exposed to the interior of the housing, and the openings of the carbon hollow fibers 320 are exposed to the exterior of the housing. The carbonaceous binder residue 310 can form a seal between the carbon hollow fibers 320 and the housing to prevent or at least significantly reduce gas passage between the housing and the outer surface 324 of the carbon hollow fibers 320. The gas mixture can be introduced into the interior of the housing, and one or more gases can pass through the carbon hollow fibers 320 and exit from at least one opening of the carbon hollow fibers 320. At the high temperatures and pressures that can occur in some gas separations, the durability of the seal between the carbonaceous binder residue 310, the carbon hollow fibers 320, and the housing can result in improved selectivity of the carbon molecular sieve described herein.

[0040] Example

[0041] The following examples illustrate features of the present disclosure but are not intended to limit the scope of the present disclosure. The following examples discuss the production of carbon molecular sieves according to one or more embodiments described herein.

[0042] Example 1 - Production of Polymer Hollow Fibers

[0043] A polyvinylidene chloride hollow fiber was melt-extruded continuously using a continuous extruder equipped with a multifilament die. The outer diameter of the fiber was 164 μm, and the inner diameter of the fiber was 76 μm.

[0044] Polyimide-PVDC blend hollow fibers were produced by the method disclosed in Example 6 of International Publication No. WO 2020 / 154146 A1, the entire content of which is incorporated herein by reference.

[0045] Example 2 - Preparation of Carbon Molecular Sieves

[0046] A bundle of 40 - 50 polyvinylidene chloride hollow fibers of Example 1 was adhered to aluminum foil with tape at both ends of the bundle. An adhesive was formed by mixing SL 158 (aqueous polyvinylidene chloride latex) from Owensboro Specialty Polymers, Inc., Owensboro, KY with Elmer's PVA glue in a mass ratio of 4:1. The SL 158 latex was mixed with the glue to thicken the adhesive to a honey-like consistency. The adhesive was brushed onto both ends of the fiber bundle. The adhesive was applied to approximately three inches of the fiber bundle at each end of the fiber bundle. The middle part (about 2 inches long) of the fiber bundle was not coated with the adhesive. The fiber bundle with the adhesive coating was cured for about three days to form a carbon molecular sieve precursor. The carbon molecular sieve precursor is depicted in Figure 4 in.

[0047] The carbon molecular sieve precursor was placed between two honeycomb-structured ceramic plates. A piece of Whatman filter paper (Whatman 1003 - 125) was placed between the carbon molecular sieve precursor and each ceramic plate to buffer the molecular sieve precursor. The carbon molecular sieve precursor was placed in an air-purged oven for pretreatment. The flow rate of air was 2 L / min. The temperature of the oven was raised to 130 °C at a rate of 1 °C / min. The oven was maintained at a temperature of 130 °C for 24 hours to form a pretreated carbon molecular sieve precursor. The pretreated carbon molecular sieve precursor located between the ceramic plates was taken out of the oven and cooled to a temperature below 60 °C.

[0048] The pretreated carbon molecular sieve precursor located between the ceramic plates was placed in a quartz tube furnace. The quartz tube furnace had a 6-inch diameter and a 24-inch length. The quartz tube furnace was purged with nitrogen. The flow rate of nitrogen was 5 L / min. The quartz tube furnace was heated to 250 °C at a rate of 0.1 °C / min. Then the quartz tube furnace was heated to 550 °C at a rate of 3 °C / min. The quartz tube furnace was maintained at 550 °C for 120 minutes to form a carbon molecular sieve. The quartz tube furnace was cooled, and then the carbon molecular sieve was taken out of the quartz tube furnace and cooled to a temperature below 60 °C. Figure 5 The carbon molecular sieve is depicted in, and Figure 5 the cross-section of the end of the carbon molecular sieve is also depicted in, where the hollow carbon fiber passes through the carbonized adhesive residue.

[0049] Example 3 - Preparation of Carbon Molecular Sieves

[0050] By the method of Example 2, a carbon molecular sieve was prepared using an adhesive formed by mixing Methocel 4FM, Elmer's PVA glue, and SL 158 latex in a weight ratio of 0.2:1:99 respectively.

[0051] Example 4 - Preparation of Carbon Molecular Sieves

[0052] Eight polyimide-PVDC blend hollow fibers of Example 1 were taped to aluminum foil at both ends of the bundle. An adhesive was formed by mixing SL 158 (aqueous polyvinylidene chloride latex) from Owensboro Specialty Polymers, Inc., Owensboro, KY with Elmer's PVA glue in a mass ratio of 4:1. The SL 158 latex was mixed with the glue to thicken the adhesive to a honey-like consistency. The adhesive was brushed onto both ends of the fiber bundle. The adhesive was applied to about three inches of the fiber bundle at each end of the fiber bundle. The middle part of the fiber bundle (about 2 inches long) was not coated with the adhesive. The fiber bundle with the adhesive coating was cured for about three days to form a carbon molecular sieve precursor. As described in Example 2, a carbon molecular sieve was prepared from the carbon molecular sieve precursor of Example 4.

[0053] Example 5 - Preparation of Comparative Carbon Molecular Sieves

[0054] Using J-B Weld high-temperature RTV silicone as the adhesive, a comparative carbon molecular sieve was prepared by the method of Example 2. The comparative carbon molecular sieve of Example 4 was very brittle, and the ends of the carbon molecular sieve were broken after pyrolysis.

[0055] Example 6 - Preparation of Comparative Carbon Molecular Sieves

[0056] Using Parabond 905 polyurethane as the adhesive, a comparative carbon molecular sieve was prepared by the method of Example 2. The comparative carbon molecular sieve of Example 5 was very brittle, and the ends of the carbon molecular sieve were broken after pyrolysis.

[0057] Example 7 - Preparation of Comparative Carbon Molecular Sieves

[0058] Using 3M acrylic DP8407 as the adhesive, a comparative carbon molecular sieve was prepared by the method of Example 2. After pyrolysis at 550 °C, the solid yield of 3M acrylic DP8407 was low, with a solid residue of 4.5 wt%. Therefore, no comparative carbon molecular sieve was formed.

[0059] Example 8 - Preparation of Comparative Carbon Molecular Sieves

[0060] Using 3M acrylic DP8010 as the adhesive, a comparative carbon molecular sieve was prepared by the method of Example 2. After pyrolysis at 550 °C, there was no solid yield of 3M acrylic DP8010. The solid yield was 0 wt% solid residue. Therefore, no comparative carbon molecular sieve was formed.

[0061] Table 1 includes information on the adhesives used for the carbon molecular sieves of Examples 2-8, the adhesive viscosities, and the adhesive residues after pyrolysis at 550 °C.

[0062] Table 1

[0063]

[0064] Example 8 - Permeation Test

[0065] The permeation of the carbon molecular sieves of Example 2 and Example 3 was tested using a loop permeation cell. The loop permeation cell has an outer diameter of 5 inches and an inner diameter of 3 inches. The loop permeation cell has four 0.5-inch openings and SAE / MS 9 / 16-inch O-ring fittings in the wall, and a 0.25-inch thick cover with O-ring seals on both sides. The two ends of the carbon molecular sieve were glued to aluminum sheets using Scotch Weld DP100 epoxy resin. The aluminum sheets are sized 0.4 inches × 2.0 inches × 0.02 inches. The aluminum sheets provide mechanical integrity to the carbon molecular sieve.

[0066] A sheet of polyolefin heat shrink tape (McMaster-Carr #636k212) with a thickness of 0.03 inches was placed on both sides of the carbon molecular sieve. A heat gun was used to shrink the tape to tightly wrap the carbon molecular sieve onto the aluminum sheet. Two parts of epoxy resin Scotch Weld DP100 were mixed and applied to the interface between the carbon molecular sieve and the heat shrink tape to form a seal. The two sides of the heat shrink tape were inserted into the holes on one side of the loop cell. Teflon tape was used to create a cofferdam around the heat shrink tape inside the hole. The hole was filled with Scotch Weld DP100 epoxy resin to form a seal.

[0067] The permeability of the carbon molecular sieve was measured in the loop permeation cell. A mixed gas was supplied to the reservoir inside the loop permeation cell. Helium at 10 sccm and 2 psig was continuously purged to transport the permeate through the hollow fibers of the carbon molecular sieve membrane to gas chromatography analysis. The permeation rate was calculated using the purge flow rate and the concentration of the permeating gas measured by gas chromatography, normalized by the transmembrane pressure difference and the total hollow fiber surface area. The total hollow fiber surface area is the product of the unsealed length of the fiber, the number of fibers in the carbon molecular sieve, and the outer diameter of the fiber.

[0068] Two permeate retention tests were conducted at low pressure. In the low-pressure test, the retentate was kept at 0 psig. In the first test, an equimolar mixture of H2, CO2, and CH4 was fed to the loop permeation cell at a temperature of 35 °C. In the second test, an equimolar mixture of C3H6 and C3H8 was fed to the loop permeation cell at a temperature of 35 °C.

[0069] Two low-pressure permeate retention tests were conducted on the carbon molecular sieve membranes produced as described in Example 2 and Example 3, and one low-pressure permeate retention test was conducted on the carbon molecular sieve membrane produced as described in Example 4. The results of the low-pressure permeate retention tests are shown in Table 2. Specifically, Table 2 includes in GPU [1×10-6 cm 3 (STP) / (s·cm 2 .cm Hg)] for each gas and the selectivity between gases. All carbon molecular sieves showed good permeability, with an H2 permeability greater than 150 GPU and a CO2 permeability greater than 90 GPU. Additionally, the carbon molecular sieves had good selectivity, with a CO2 / CH4 selectivity greater than 40 and a C3H6 / C3H8 selectivity greater than 9. The relatively high selectivity means that the seal between the fibers in the carbon molecular sieve is defect-free.

[0070] Table 2

[0071]

[0072] According to a first aspect of the present disclosure, a method for preparing a carbon molecular sieve may include applying an adhesive to an outer surface of a plurality of polymeric hollow fibers at a first end thereof, wherein the polymeric hollow fibers comprise polyimide, polyvinylidene chloride, or a combination thereof, and wherein, based on the total weight of the adhesive, the adhesive comprises at least 75 wt% of polyimide, polyvinylidene chloride, or a combination thereof; curing the adhesive on the outer surface of the polymeric hollow fibers to form a carbon molecular sieve precursor; and pyrolyzing the carbon molecular sieve precursor to form a carbon molecular sieve, wherein the carbon molecular sieve comprises a plurality of carbon hollow fibers and a carbonaceous adhesive residue on the first ends of the plurality of carbon fibers.

[0073] A second aspect of the present disclosure may include the first aspect, wherein the polymeric hollow fibers comprise polyimide.

[0074] A third aspect of the present disclosure may include the first aspect, wherein the polymeric hollow fibers comprise polyvinylidene chloride.

[0075] A fourth aspect of the present disclosure may include any one of the first to third aspects, wherein the plurality of polymeric hollow fibers includes 10 to 50,000 polymeric hollow fibers.

[0076] A fifth aspect of the present disclosure may include any one of the first to fourth aspects, wherein each polymeric hollow fiber includes an inner surface and an outer surface, wherein the inner surface defines a cavity.

[0077] A sixth aspect of the present disclosure may include the fifth aspect, wherein applying the adhesive to the outer surface of the polymeric hollow fibers does not block the opening of the cavity of the polymeric hollow fibers.

[0078] A seventh aspect of the present disclosure may include any one of the first to sixth aspects, wherein the adhesive comprises polyimide.

[0079] The eighth aspect of the present disclosure may include any one of the first to sixth aspects, wherein the binder comprises polyvinylidene chloride.

[0080] The ninth aspect of the present disclosure may include any one of the first to eighth aspects, wherein the binder further comprises ethyl polyacetate.

[0081] The tenth aspect of the present disclosure may include any one of the first to ninth aspects, wherein both the polymeric hollow fiber and the binder comprise polyimide, polyvinylidene chloride, or a combination thereof.

[0082] The eleventh aspect of the present disclosure may include any one of the first to tenth aspects, wherein, based on the total weight of the binder, the binder comprises at least 75% by weight of the polyimide, the polyvinylidene chloride, or the combination thereof that constitutes the plurality of polymeric hollow fibers.

[0083] The twelfth aspect of the present disclosure may include any one of the first to eleventh aspects, wherein curing of the binder occurs at a temperature of 120 °C to 160 °C.

[0084] The thirteenth aspect of the present disclosure may include any one of the first to twelfth aspects, wherein curing of the binder occurs for a time of 1 hour to 48 hours.

[0085] The fourteenth aspect of the present disclosure may include any one of the first to thirteenth aspects, wherein curing of the binder comprises exposing the binder to gamma radiation, electron beam radiation, or ultraviolet radiation.

[0086] The fifteenth aspect of the present disclosure may include any one of the first to fourteenth aspects, wherein pyrolysis of the carbon molecular sieve precursor occurs at a temperature of 200 °C to 1500 °C.

[0087] The sixteenth aspect of the present disclosure may include any one of the first to fifteenth aspects, wherein pyrolysis of the carbon molecular sieve precursor occurs at a temperature of 400 °C to 1000 °C.

[0088] The seventeenth aspect of the present disclosure may include any one of the first to sixteenth aspects, wherein pyrolysis of the carbon molecular sieve precursor occurs at a temperature of 500 °C to 900 °C.

[0089] The eighteenth aspect of the present disclosure may include any one of the first to seventeenth aspects, wherein pyrolysis of the carbon molecular sieve precursor occurs for a time of 1 hour to 1 week.

[0090] The nineteenth aspect of the present disclosure may include any one of the first to eighteenth aspects, wherein pyrolysis of the carbon molecular sieve precursor occurs in an inert atmosphere.

[0091] The twentieth aspect of the present disclosure may include any one of the first to nineteenth aspects, wherein, based on the total weight of the binder, the weight of the carbonaceous binder residue after pyrolysis at 550 °C is greater than 10% by weight of the binder.

[0092] The twenty-first aspect of the present disclosure may include any one of the first to twentieth aspects, wherein the carbonaceous binder residue directly contacts the outer surface of each carbon hollow fiber in the carbon molecular sieve.

[0093] The twenty-second aspect of the present disclosure may include any one of the first to twenty-first aspects, wherein the carbonaceous binder residue does not block the opening of the cavity of the carbon hollow fiber.

[0094] The twenty-third aspect of the present disclosure may include any one of the first to twenty-second aspects, wherein the method further includes applying the binder to the outer surface of the polymer hollow fiber at a second end of the plurality of polymer hollow fibers.

[0095] The twenty-fourth aspect of the present disclosure may include the twenty-third aspect, wherein the carbon molecular sieve further includes a second carbonaceous binder residue on a second end of the plurality of carbon hollow fibers.

[0096] The twenty-fifth aspect of the present disclosure may include any one of the twenty-third to twenty-fourth aspects, wherein the second carbonaceous binder residue directly contacts the outer surface of each carbon hollow fiber in the carbon molecular sieve.

[0097] The twenty-sixth aspect of the present disclosure may include any one of the twenty-third to twenty-fifth aspects, wherein the second carbonaceous binder residue does not block the opening of the cavity of the carbon hollow fiber.

[0098] According to the twenty-seventh aspect of the present disclosure, a carbon molecular sieve may include a plurality of carbon hollow fibers having a first end and a second end, wherein each carbon hollow fiber has a tubular shape, the tubular shape including an outer surface and an inner surface and defining a cavity, wherein each carbon hollow fiber includes a first opening and a second opening; and a carbonaceous binder residue on the first end of the plurality of carbon fibers, wherein the carbonaceous binder residue directly contacts the outer surface of each carbon hollow fiber in the plurality of carbon hollow fibers.

[0099] The twenty-eighth aspect of the present disclosure may include the twenty-seventh aspect, wherein the carbonaceous binder residue does not block the first opening of at least 50% of the carbon hollow fibers.

[0100] The twenty-ninth aspect of the present disclosure may include any one of the twenty-seventh to twenty-eighth aspects, wherein the carbonaceous binder residue does not block the first opening of each of the plurality of carbon hollow fibers.

[0101] The thirtieth aspect of the present disclosure may include any one of the twenty-seventh to twenty-ninth aspects, wherein the composition of the plurality of carbon hollow fibers is substantially the same as the composition of the carbonaceous binder residue.

[0102] The thirty-first aspect of the present disclosure may include any one of the twenty-seventh to thirtieth aspects, wherein the carbon molecular sieve further includes a second carbonaceous binder residue on the second end of the plurality of carbon hollow fibers.

[0103] The thirty-second aspect of the present disclosure may include the thirty-first aspect, wherein the second carbonaceous binder residue directly contacts the outer surface of each of the plurality of carbon hollow fibers.

[0104] The thirty-third aspect of the present disclosure may include any one of the thirty-first to thirty-second aspects, wherein the second carbonaceous binder residue does not block the second openings of at least 50% of the carbon hollow fibers.

[0105] The thirty-fourth aspect of the present disclosure may include any one of the thirty-first to thirty-third aspects, wherein the second carbonaceous binder residue does not block the second openings of each of the plurality of carbon hollow fibers.

[0106] The thirty-fifth aspect of the present disclosure may include any one of the thirty-first to thirty-fourth aspects, wherein the carbonaceous binder residue is spaced apart from the second carbonaceous binder residue.

[0107] It should be noted that one or more of the appended claims utilize the term "wherein" as a transitional phrase. For the purpose of defining the present technology, it should be noted that this term is introduced in the claims as an open transitional phrase that is used to introduce a recitation of a series of characteristics of a structure and should be interpreted in a manner similar to the more commonly used open preamble term "comprising".

[0108] It should be understood that in cases where a first component is described as "comprising" a second component, it is contemplated that in some embodiments, the first component "consists of" or "consists essentially of" the second component. Additionally, the term "consisting essentially of" is used in the present disclosure to refer to quantitative values that do not substantially affect the basic and novel characteristics of the present disclosure. For example, a chemical composition that "consists essentially of" a particular chemical component or group of chemical components should be understood to mean that the composition contains at least about 99.5% of that particular chemical component or group of chemical components.

[0109] The subject matter of the present disclosure has been described in detail and with reference to specific embodiments. It should be understood that any detailed description of a component or feature of an embodiment does not necessarily imply that the component or feature is essential for a particular embodiment or any other embodiment. Further, it will be apparent to those skilled in the art that various modifications and changes can be made to the described embodiments without departing from the spirit and scope of the claimed subject matter.

Claims

1. A method for preparing a carbon molecular sieve, the method comprising: Applying an adhesive to an outer surface of a plurality of polymer hollow fibers at a first end thereof, wherein the polymer hollow fibers comprise polyimide, polyvinylidene chloride, or a combination thereof, and wherein based on the total weight of the adhesive, the adhesive comprises at least 75 wt% of polyimide, polyvinylidene chloride, or a combination thereof; Curing the adhesive on the outer surface of the polymer hollow fibers to form a carbon molecular sieve precursor; And Pyrolyzing the carbon molecular sieve precursor to form a carbon molecular sieve, wherein the carbon molecular sieve comprises a plurality of carbon hollow fibers and a carbonaceous adhesive residue on a first end of the plurality of carbon fibers.

2. The method according to claim 1, wherein the polymer hollow fibers comprise polyimide.

3. The method according to claim 1, wherein the polymer hollow fibers comprise polyvinylidene chloride.

4. The method according to any one of the preceding claims, wherein the adhesive comprises polyimide.

5. The method according to any one of claims 1 to 3, wherein the adhesive comprises polyvinylidene chloride.

6. The method according to any one of the preceding claims, wherein based on the total weight of the adhesive, the adhesive comprises at least 75 wt% of the polyimide, the polyvinylidene chloride, or the combination thereof that constitutes the plurality of polymer hollow fibers.

7. The method according to any one of the preceding claims, wherein pyrolyzing the carbon molecular sieve precursor occurs at a temperature of 200 °C to 1500 °C for a time of 1 hour to 1 week in an inert atmosphere.

8. The method according to any one of the preceding claims, wherein based on the total weight of the adhesive, the weight of the carbonaceous adhesive residue after pyrolysis at 550 °C is greater than 10 wt% of the adhesive.

9. The method according to any one of the preceding claims, wherein the carbonaceous adhesive residue directly contacts an outer surface of each carbon hollow fiber in the carbon molecular sieve.

10. The method according to any one of the preceding claims, wherein the polymer hollow fibers do not undergo pyrolysis before the adhesive is applied to the outer surface of the polymer hollow fibers.

11. The method according to any one of the preceding claims, wherein the method further comprises applying the adhesive to the outer surface of the polymer hollow fibers at a second end of the plurality of polymer hollow fibers.

12. The method according to claim 11, wherein the carbon molecular sieve further comprises a second carbonaceous adhesive residue on a second end of the plurality of carbon hollow fibers.

13. A carbon molecular sieve, the carbon molecular sieve comprising: A plurality of carbon hollow fibers having a first end and a second end, wherein each carbon hollow fiber has a tubular shape, the tubular shape comprising an outer surface and an inner surface and defining a cavity, wherein each carbon hollow fiber comprises a first opening and a second opening; and Carbonaceous binder residues on the first ends of the plurality of carbon fibers, wherein the carbonaceous binder residues directly contact the outer surfaces of each of the plurality of carbon hollow fibers.

14. The carbon molecular sieve according to claim 13, wherein the composition of the plurality of carbon hollow fibers is substantially the same as the composition of the carbonaceous binder residues.

15. The carbon molecular sieve according to claim 13 or claim 14, wherein the carbon molecular sieve further comprises second carbonaceous binder residues on the second ends of the plurality of carbon hollow fibers.

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