WO2019006438A1

WO2019006438A1 - Cost-effective carbon molecular sieve hollow fiber membranes

Info

Publication number: WO2019006438A1
Application number: PCT/US2018/040521
Authority: WO
Inventors: William J. Koros; Kuang Zhang; Yuhe CAO
Original assignee: Georgia Tech Research Institute; Georgia Tech Research Corp
Current assignee: Georgia Tech Research Institute; Georgia Tech Research Corp
Priority date: 2017-06-30
Filing date: 2018-06-30
Publication date: 2019-01-03
Anticipated expiration: 2019-12-30

Abstract

Disclosed herein are asymmetric multilayer CMS hollow fiber membranes having good selectivities and permeabilities, where the CMS hollow fiber membranes include a support layer and a skin layer, the support layer includes a core layer and an optional sheath layer, and the core layer optionally includes nanoparticles or a silane, and where the CMS hollow fiber membranes provide efficient and cost-effective separation of certain gases, such as carbon dioxide (CO2), from a feedstock stream. Also disclosed herein are precursor polymeric hollow fibers that can be used to forming the CMS hollow fiber membranes, processes for making the CMS hollow fiber membranes, and processes for separating gas streams using the CMS hollow fiber membranes.

Description

COST-EFFECTIVE CARBON MOLECULAR SIEVE

HOLLOW FIBER MEMBRANES

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 62/527,583, filed June 30, 2017, the contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to multilayer carbon molecular sieve ("CMS") membranes and methods for their preparation and use.

BACKGROUND OF THE INVENTION

Processes using CMS membranes upgrade the value of gas streams by efficiently separating components from various feed sources. Examples of such processes include removing carbon dioxide (CO2), nitrogen (N2), and/or hydrogen sulfide (H2S) from methane (CH₄) in natural gas streams; separation of propylene (C3H5) from propane (C3¾) and ethylene (C2H4) from ethane (C2H5) in hydrocarbon mixtures; and separation of oxygen (O2) and or N2 from air. In these examples one or more valuable products can be separated from a less valuable feed stream in an energy efficient manner. Asymmetric multilayer CMS hollow fiber membranes are preferred for large scale high pressure applications due to their ability to be formed into compact modules with high surface-to-volume ratio.

Dense flat polymer films have been used as precursors for forming CMS membranes, but the productivity of these membranes tends to be low. To increase the surface to volume ratio, the CMS membranes can be formed from precursor asymmetric polymer fibers, which can be formed in a so-called dry -jet/wet-quench spinning process. Important functional properties of CMS hollow fiber membranes include permeance and selectivity. Permeance measures the pressure-normalized flux of a given penetrant and provides a measure of membrane productivity. Selectivity measures the comparative ability of different gases to permeate through a membrane and provides a measure of separation efficiency. These properties, and the methods by which asymmetric multilayer CMS hollow fiber membranes may be tested to determine these properties, are described in more detail in, for example, U.S.

Patent Nos. 6,565,631 and 8,486, 179. Pyrolysis of an appropriate precursor fiber at temperatures above the glass transition temperature (T_g) of the polymer creates a CMS fiber.

Unfortunately, since the pyrolysis occurs above the polymer T_g, partial or even total collapse of the porous core layer typically occurs. This collapse creates a layer that is much thicker and that has a much lower permeance, and is therefore much less productive, than would be expected if the collapse could be avoided. Substructure morphology collapse occurs when high temperatures during pyrolysis relax the polymer chains in the porous core layer. The movement of the polymer segments allows collapse of the substructure, thereby undermining the productivity advantage provided by the asymmetric fiber.

U.S. Patent Application No. US201301522793A1, and International Patent Application No. WO2013095775A1 describe a method for post-treating precursor fibers in order to limit substructure collapse during pyrolysis. By soaking precursor fibers in a chemical modifying agent, such as vinyl trimethoxy silane (VTMS), before pyrolysis, asymmetric multilayer CMS hollow fibers having an increased permeance are formed. The chemical modifying agent stabilizes the precursor fiber prior to pyrolysis to prevent collapse of the substructure morphology between the polymer T_g and point of actual carbon formation. Silane or silica derived from the silane treatment may be found at least in the core layer.

VTMS has, in some cases, been replaced by spinning a multilayer CMS precursor hollow fiber including an inner core support layer and an outer sheath layer, and incorporating properly selected nanoparticle fillers into the core support layer. However, the core dope and the sheath dope must be formulated independently according to the polymer used.

Both the VTMS treated membranes and nanoparticle supported membranes require certain high-performance polymers to achieve desired selectivities, and those high- performance polymers are available only at high cost, which makes the final CMS hollow fiber membranes quite expensive. There remains a need for a multilayer CMS hollow fiber membrane that is capable of providing desired selectivity and permeance, while minimizing manufacturing cost and difficulty. In particular, there remains a need for new materials and methods for efficient and cost-effective separation of acid gases, such as carbon dioxide (CO2) and hydrogen sulfide (H2S), from a feedstock stream.

SUMMARY OF THE INVENTION

It has now been found that spinning a CMS precursor hollow fiber from a relatively cost effective polymer dope to form a support layer, optionally including a core layer and a sheath layer, and then coating the support layer with a thin skin layer of a high-performance polymer prior to pyrolysis provides an economical method of producing a multilayer CMS hollow fiber membrane having both high selectivity and permeance. In one aspect, polymeric precursor hollow fibers having a support layer and a skin layer are disclosed herein. The support later has a core layer comprising a first polymer and a sheath layer comprising a second polymer. The skin layer comprises a third polymer. The core layer, the sheath layer, and the skin layer have substantially annular cross-sections with the sheath layer adjacent to and radially outward from the core layer and the skin layer adjacent to and radially outward from the sheath layer. The core layer further comprises at least one of a silane or a plurality of nanoparticles.

In some examples, the skin layer comprises a high-performance polymer. In some examples, the skin layer comprises one or more of 6FDA/BPDA-DAM, 6FDA-6FpDA, 6FD A-DETD A : D ABE, 6FDA-DETDA:DABA, 6FDA-BPDA/DAM:DABA, BTDA-DAPI, or 6FDA/BTDA-DAM. In some examples, the second polymer and the third polymer comprise one or more of 6FDA/BPD A-D AM, 6FDA-6FpDA, 6FD A-DETD A: D ABE, 6FDA- DETDA:DABA, 6FDA-BPDA/DAM:DABA, BTDA-DAPI, or 6FDA/BTDA-DAM.

In some examples, the first polymer comprises one or more of a polyvinylidene chloride, a polyacrylonitrile, a polyvinyl chloride, a polyvinylidene difluoride, a polyimide, a polyetherimide, a polysulfone, or a polyethersulfone. In some examples, wherein the second polymer comprises one or more of polyvinylidene chloride, polyacrylonitrile, a polyvinyl chloride, a polyvinylidene difluoride, a polyimide, a polyetherimide, a polysulfone, or a polyethersulfone. the core layer and the sheath layer do not comprise a high performance polymer. In some examples, the core layer and the sheath layer do not comprise a high performance polymer.

In some examples, the core layer comprises a plurality of nanoparticles. In some examples, the plurality of nanoparticles are hydrophobic. In some examples, the plurality of nanoparticles are polyhedral oligomeric silsesquioxane ("POSS") silica nanoparticles. In some examples, the core layer comprises 2 to 30 wt% nanoparticles, based on the weight of the core layer. In some examples, the core layer comprises 90 to 98 wt% of the total weight of the polymeric hollow fiber. In some examples, the support layer has a radial thickness of 100 to 500 micrometers. In some examples, the skin layer may have a radial thickness of 0.05 to 2.0 micrometers.

In a second aspect, a carbon molecular sieve (CMS) hollow fiber membranes having a support layer and a skin layer are disclosed herein. The support layer comprises core layer comprising a pyrolyzed first polymer and a sheath layer comprising a pyrolyzed second polymer. The skin layer comprises a pyrolyzed third polymer. The core layer, the sheath layer, and the skin layer have substantially annular cross-sections with the sheath layer adjacent to and radially outward from the core layer and the skin layer adjacent to and radially outward from the sheath layer. In some examples, the CMS hollow fiber membrane has a C02:CH4 selectivity of greater than 20.

In some examples, the core layer further comprises silane. In other examples, the core layer further comprises a plurality of nanoparticles. In some examples, when the core layer comprises a plurality of nanoparticles, the plurality of nanoparticles are hydrophobic. In some examples, when the core layer comprises a plurality of nanoparticles, the plurality of nanoparticles are polyhedral oligomeric silsesquioxane ("POSS") silica nanoparticles. In some examples, when the core layer comprises a plurality of nanoparticles, the core layer comprises 25 to 40 wt% nanoparticles based on weight of the core layer.

In some examples, the CMS hollow fiber membrane has a C02:CH4 selectivity of greater than 40. In other examples still, the CMS hollow fiber membrane has a C02:CH4 selectivity of greater than 75. In some examples, the CMS hollow fiber membrane has a CO2 permeance of greater than 200 GPU.

In some examples, the third polymer comprises a high-performance polymer. In some examples, the third polymer comprises one or more of 6FDA/BPDA-DAM, 6FDA- 6FpDA, 6FDA-DETDA:DABE, 6FD A-DETD A : DAB A, 6FDA-BPDA/DAM:DABA, BTDA-DAPI, or 6FDA/BTDA-DAM.

In some examples, the first polymer and the second polymer independently comprise a polyvinylidene chloride, a polyacrylonitrile, a polyvinyl chloride, a polyvinylidene difluoride, a polyimide, a polyetherimide, a polysulfone, or a polyethersulfone.

In some examples, the core layer and the sheath layer do not comprise a high performance polymer. In some examples, the skin layer has a radial thickness of from 0.05 to 2.0 micrometers.

In a third aspect, processes for preparing CMS hollow fiber membranes comprising at least three steps are disclosed herein. The processes comprise pyrolyzing a coated precursor fiber to form a CMS hollow fiber membrane, wherein the coated precursor fiber comprises a polymeric fiber comprising a core layer comprising a first polymer and optionally a sheath layer comprising a second polymer; and a skin layer comprising a third polymer.

In some examples, the method further comprises coating the polymeric fiber with the third polymer to produce the coated precursor fiber. In some examples, the method further comprises extruding a core dope, and when the optional sheath layer is present co-extruding a sheath dope with the core dope, through a spinneret to produce the polymeric fiber, where the core dope comprises a first polymer and a first solvent, and when present the sheath dope comprises a second polymer and a second solvent.

In some examples, the core layer further comprises a plurality of nanoparticles. In some examples, the plurality of nanoparticles are hydrophobic. In some examples, the plurality of nanoparticles are polyhedral oligomeric silsesquioxane ("POSS") silica nanoparticles.

In some examples, the process further comprises contacting the coated precursor fiber with a modifying agent before the pyrolyzing step. In some examples, the modifying agent comprises a silane. In some examples, the modifiying agent comprises vinyltrimethoxysilane or vinyltriethoxysilane.

In some examples, the first polymer comprises one or more of a polyvinylidene chloride, a polyacrylonitrile, a polyvinyl chloride, a polyvinylidene difluoride, a polyimide, a polyetherimide, a polysulfone, or a polyethersulfone. In some examples, the first polymer comprises BTDA-TDI/MDI, which is a copolyimide of 3,3'4,4'-benzophenone tetracarboxylic dianhydride and 80% methylphenylene-diamine + 20% methylene diamine and is commercially available as P84®. In some examples, the second polymer comprises BTDA-TDI/MDI.

In some examples, the third polymer comprises a high-performance polymer. In some examples, the third polymer comprises one or more of 6FDA/BPDA-DAM, 6FDA-6FpDA, 6FD A-DETD A : D ABE, 6FDA-DETDA:DABA, 6FDA-BPDA/DAM:DABA, BTDA-DAPI, or 6FDA/BTDA-DAM.

In some examples, the first polymer and the second polymer independently comprise one or more of a polyvinylidene chloride, a polyacrylonitrile, a polyvinyl chloride, a polyvinylidene difluoride, a polyimide, a polyetherimide, a polysulfone, or a polyethersulfone. In some examples, the second polymer comprises P84®. In other examples, the second polymer comprises one or more of 6FDA/BPDA-DAM, 6FDA-6FpDA, 6FDA- DETDA:DABE, 6FDA-DETDA:DABA, 6FDA-BPDA/DAM:DABA, BTDA-DAPI, or 6FDA/BTDA-DAM. In some examples, the first polymer comprises BTDA-TDI/MDI, the second polymer comprises BTDA-TDI/MDI, and the coating polymer comprises BTDA- DAPI. In some examples, the core layer and the sheath layer do not comprise a high- performance polymer

In some examples, the coating step is conducted at a relative humidity of between

5% and 85%. In some examples, the coating step is conducted at a relative humidity of between 5% and 40%. In some examples, the coating step is conducted at a relative humidity of between 50% and 85%. In some examples, the pyrolyzing step is conducted at a temperature of at least 550 °C. In some examples, the pyrolyzing step is conducted at a temperature of at least 675 °C. In other examples still, the pyrolyzing step is conducted at a temperature of at least 800 °C.

In a fourth aspect, processes for separating mixtures of at least two gases are disclosed herein. The processes comprise contacting a mixture of at least two gases with a CMS hollow fiber membrane described herein to separate the mixture into a permeate stream that is enriched in a first gas and a retentate stream that is enriched in a second gas. In some examples, the mixture of at least two gases comprises CO2 and CH₄; H2S and CH₄; CO2, H2S, and CH₄; CO2 and N2; O2 and N2; N2 and CH₄; He and CH₄; He and N2; He and SF₆; H₂ and CH₄; H2 and C2¾; ethylene and ethane; propylene and propane; or ethane/propane and ethylene/propylene. In some examples, the mixture of at least two gases comprises a natural gas comprising at least one acid gas and at least one hydrocarbon gas, wherein the permeate stream is enriched in the at least one acid gas, and wherein the retentate stream is enriched in the at least one hydrocarbon gas. In some examples, the acid gas comprises CO2. In some examples, hydrocarbon gas comprises CH₄. In some examples, the process has a C02:CH₄ selectivity of greater than 40.

BRIEF DESCRIPTION OF THE DRAWINGS

A clear conception of the advantages and features of one or more embodiments will become more readily apparent by reference to the exemplary, and therefore non-limiting, embodiments illustrated in the drawings:

Fig. 1 is an upper bound correlation for C02/CH₄ separation, reproduced from L.M. Robeson, The upper bound revisited. J. Membrane Sci. 320 (2008) 380-400 (Figure 2).

Fig. 2 is an illustration of an exemplary nanoparticle free precursor fiber coating process according to various embodiments of the present invention.

Fig. 3 is an illustration of an exemplary nanoparticle containing precursor fiber coating process according to various embodiments of the present invention.

Fig. 4 is an illustration of an exemplary of a continuous dip-coating process according to various embodiments of the present invention.

Fig. 5 is an SEM image of a cross-section of a nanoparticle free precursor hollow fiber membrane. Fig. 6 is an SEM image of a cross-section of a 4% 6 FDA/BPDA-DAM coated nanoparticle free precursor hollow fiber membrane prepared according to the present disclosure, where the coating is carried out at 65% relative humidity (RH).

Fig. 7 is an SEM image of a cross-section of nanoparticle free CMS hollow fiber membrane prepared by coating with 4% 6FDA/BPDA-DAM, where the coating is carried out at 65% relative humidity (RH), and pyrolyzed at 550 °C.

Fig. 8 is an SEM image of a cross-section of nanoparticle free CMS hollow fiber membrane prepared by coating with 4% 6FDA/BPDA-DAM, where the coating is carried out at 65% relative humidity (RH), and pyrolyzed at 675 °C.

Fig. 9 is an SEM image of a cross-section of nanoparticle free CMS hollow fiber membrane prepared by coating with 4% 6FDA/BPDA-DAM, where the coating is carried out at 65%) relative humidity (RH), and pyrolyzed at 800 °C.

Fig. 10 is a graph showing the CO2/CH4 separation performance of nanoparticle free hollow fiber membrane prepared by coating with different 6FDA/BPDA-DAM concentrations, where the coating is carried out at 60% relative humidity (RH).

Fig. 11 is a graph showing the CO2/CH4 separation performance of nanoparticle free CMS hollow fiber membrane prepared by coating with 4% 6FDA/BPDA-DAM and pyrolyzed at different temperature.

Fig. 12 is an SEM image of a cross-section of a 2% 6 FDA/BPDA-DAM coated nanoparticle free precursor hollow fiber membrane, where the coating is carried out at 10% relative humidity (RH), and prepared according to the present disclosure.

Fig. 13 is an SEM image of a cross-section of nanoparticle containing CMS hollow fiber membrane prepared by coating with 2% 6FDA/BPDA-DAM, where the coating is carried out at 10% relative humidity (RH), and pyrolyzed at 675 °C.

Fig. 14 is a set of four SEM images at various magnifications of a cross-section of a 4% 6 FDA/BPDA-DAM coated nanoparticle containing precursor hollow fiber membrane (with 65%) RH) prepared according to the present disclosure.

Fig. 15 is an SEM image of a cross-section of nanoparticle containing CMS hollow fiber membrane prepared by coating with 4% 6FDA/BPDA-DAM (with 65% RH) and pyrolyzed at 800 °C.

DETAILED DESCRIPTION OF THE INVENTION

Carbon molecular sieve (CMS) membranes have separation advantages compared with polymeric membranes. Narrow pore size distribution, better molecular sieving capabilities, and higher chemical stability make them promising candidates for gas separations (e.g. separation of olefin/paraffin, CO2/CH4, H2S/CH4, N2/CH4, CO2/N2, etc.). Hollow fiber membrane modules can provide high volumetric productivity while maintaining compact system sizes even for applications requiring huge membrane areas. Hollow-fiber- derived CMS membranes also have attracted attention owing to their high selectivities and permeances in gas separation. Unfortunately, polymers preferred for CMS membrane fabrication (for example, 6FDA/BPDA-DAM, 6FDA-6FpDA, 6FD A-DETD A : D ABE, 6FDA-DETDA:DABA, 6FDA-BPDA/DAM:DABA, BTDA-DAPI, or 6FDA/BTDA-DAM) are expensive and hard to synthesize. Described herein are precursor hollow fibers, asymmetric multilayer CMS hollow fiber membranes made from the precursor hollow fibers, processes for making the CMS hollow fiber membranes, and processes for separating gas streams using the CMS hollow fiber membranes. The CMS hollow fiber membranes described herein provide for efficient and cost-effective separation of an acid gas, such as carbon dioxide (CO2) or hydrogen sulfide (H2S), from a feedstock stream.

Precursor Hollow Fibers

The CMS hollow fiber membranes described herein are formed by pyrolysis of precursor polymeric hollow fibers. Generally, the precursor polymeric hollow fibers include a support layer and a thin skin layer coating the outer surface of the support layer. The support layer is formed from relatively inexpensive materials and has good permeance when the precursor polymeric hollow fiber is pyrolyzed to form the CMS hollow fiber membrane. The thin skin layer is formed by coating the support layer with a relatively small amount of a high-performance polymer that had good selectivity when the precursor polymeric hollow fiber is pyrolyzed to form the CMS hollow fiber membrane.

In one aspect, the precursor hollow fibers disclosed herein have a support layer and a skin layer. In some examples, the support layer includes two layers, a first, innermost layer that is a core layer comprising a first polymer and a second layer that is a sheath layer comprising a second polymer. The skin layer is the outermost, third layer and comprises a third polymer. The core layer, the sheath layer, and the skin layer have substantially annular cross-sections with the sheath layer adjacent to and radially outward from the core layer and the skin layer adjacent to and radially outward from the sheath layer. The core layer further comprises at least one of a silica or a plurality of nanoparticles.

The core layer and the sheath layer together form the support layer, and the support layer is coated with a thin skin layer of a high-performance polymer. Fig. 1 is an annotated version of Fig. 2 of Robeson, L. M., Journal of Membrane Science 320 (2008) 390-400 ("Robeson") and demonstrates the typical trade-off between selectivity (on the Y-axis) and permeability (on the X-axis). For purposes of this application, a "high-performance polymer" is defined as any polymer that can be formed as a membrane that has a CO2 pure gas permeance of at least 1 Barrer and a C0₂:CH4 selectivity that corresponds to a point above line A on the permeance-selectivity chart in Fig. 1 when tested at about 35 °C with a 15-100 psia feed gas. Line A was added to Robeson's chart for purposes of this application and goes through the points permeance = 1 Barrer, selectivity = 400 and permeance = 4000 Barrer, selectivity = 10. Thus, line A can be represented by the equation y = 400x^("° ⁴⁴⁴⁾. Accordingly, a high performance polymer, as defined herein, would have a CO2 pure gas permeance of at least 1 Barrer and a C0₂:CH4 selectivity greater than or equal to 400x^{("0 444)} where x is the CO2 permeance. A C0₂:CH4 selectivity estimated based on CO2 and CH4 pure gas permeabilities is considered sufficiently close to the actual C0₂:CH4 to be used to determine whether a polymer is a "high-performance polymer," as defined above.

The high-performance polymer is used as the skin layer and also can be used as all or part of the support layer; however, material cost to prepare the CMS hollow fiber membranes described herein can be reduced as compared to known membranes by minimizing the amount of high-cost, high-performance material in the fibers. Moreover, in some cases, the high-performance polymers can be difficult to formulate into a dope for spinning. Therefore, using the high performance polymers only as the skin layer (i.e., as a coating) can reduce manufacturing costs, compared to spinning all layers. Accordingly, in some examples, the high-performance polymer is only included as the skin layer, and the core and sheath layers do not include a high-performance polymer. Ideally, after coating and pyrolysis, the dense skin layer of high-performance polymer provides a CMS hollow fiber membrane with high selectivity, while the support layer ensures high permeance.

Optionally the first polymer (i.e., the core polymer) and the second polymer (i.e., the sheath polymer) are the same polymer, but alternatively, they may be different polymers. When the first and second polymers are different polymers, optionally the second polymer may have a T_g that is equal to or greater than the T_g of the first polymer, but alternatively the second polymer may have a T_g that is equal to or less than the T_g of the first polymer.

The sheath and core polymers, in principle, can include any polymeric materials that, when processed and treated as described hererin and after undergoing pyrolysis, produce a

CMS membrane with a desired permeance. In some examples, the first and/or the second polymer comprises one or more of a polyvinylidene chloride, polyacrylonitrile, polyvinyl chloride, polyvinylidene difluoride, polyimide, polyetherimide, polysulfone, polyethersulfone, or a combination thereof. Some other non-limiting examples of suitable first or second polymers include polysulfones; polystyrenes, including styrene-containing copolymers such as acrylonitrile-styrene copolymers, styrene-butadiene copolymers and styrene-vinylbenzylhalide copolymers: polycarbonates; polyfurfuryl alcohol; cellulosic polymers, such as cellulose acetate-butyrate, cellulose propionate, ethyl cellulose, methyl cellulose, nitrocellulose, etc.; poly-amides and polyimides, including aryl polyamides and aryl polyimides; polyethers; polyetherimides; polyetherketones; poly(arylene oxides) such as poly(phenylene oxide) and poly(xylene oxide); poly(esteramide-diisocyanate); polyurethanes; polyesters (including polyarylates), such as poly(ethylene terephthalate), poly(alkyl methacrylates), poly(acrylates), poly(phenylene terephthalate), etc.; polypyrrolones; polysulfides; polymers from monomers having alpha-olefinic unsaturation other than mentioned above such as poly(ethylene), poly(propylene), poly(butene-l), poly(4-methyl pentene-1); polyvinyls such as poly(vinyl chloride), poly(vinyl fluoride), poly(vinylidene chloride), poly(vinylidene fluoride), poly(vinyl alcohol), poly(vinyl esters) such as poly(vinyl acetate) and poly(vinyl propionate), poly(vinyl pyridines), poly(vinyl pyrrolidones), poly(vinyl ethers), poly(vinyl ketones), poly(vinyl aldehydes) such as poly(vinyl formal) and poly(vinyl butyral), poly(vinyl amides), poly(vinyl amines), poly(vinyl urethanes), poly(vinyl ureas), poly(vinyl phosphates), and poly(vinyl sulfates)); polyallyls; poly(benzobenzimidazole); polyhydrazides; polyoxadiazoles; polytriazoles; poly(benzimidazole); polycarbodiimides; polyphosphazines; etc., and interpolymers, including block interpolymers containing repeating units from the above such as terpolymers of acrylonitrile-vinyl bromide-sodium salt of para-sulfophenylmethallyl ethers; and grafts and blends containing any of the foregoing. Typical substituents providing substituted polymers include halogens such as fluorine, chlorine and bromine; hydroxyl groups; lower alkyl groups; lower alkoxy groups; monocyclic aryl; lower acyl groups and the like.

Preferably, the first and second polymers are rigid, glassy polymers at room temperature as opposed to a rubbery polymer or a flexible glassy polymer. Glassy polymers are differentiated from rubbery polymers by the rate of segmental movement of polymer chains. Polymers in the glassy state do not have the rapid molecular motions that give rubbery polymers their liquid-like nature and their ability to adjust segmental configurations rapidly over large distances (>5 nm). Glassy polymers exist in a non-equilibrium state with entangled molecular chains with immobile molecular backbones in frozen conformations.

The glass transition temperature (Tg) is the dividing point between the rubbery or glassy state. Above the Tg, the polymer exists in the rubbery state, and below the Tg, the polymer exists in the glassy state. Generally, glassy polymers provide a more size-selective environment for gas diffusion and are favored for gas separation applications. Rigid, glassy polymers describe polymers with rigid polymer chain backbones that have limited intramolecular rotational mobility and are often characterized by having high glass transition temperatures. Preferred polymer precursors have a glass transition temperature of at least 200 °C. Such polymers are well known in the art and include polyimides, polysulfones and cellulosic polymers.

In general, the skin layer includes a high-performance polymer that imparts high selectivity to the CMS hollow fiber membrane after the precursor fiber is pyrolyzed. While these same high-performance polymers can be used to form the core and/or the sheath layers, the high-performance polymers tend to be costly and/or difficult to prepare. Accordingly, in some examples the high-performance polymers are used only in the skin layer. In other embodiments, the high-performance polymer may further be used in the sheath layer.

In some examples, the skin (or coating) polymer includes a polyimide. The polyimide family are useful materials for CMS precursor polymers because they provide CMS membranes of good selectivity. Polyimides typically are formed from dianhydrides and diamines. Examples of dianhydrides and diamines useful for forming high performance polyimide polymers and copolymers include the following.

3, 3', 4, 4'-biphenyl tetracarboxylic acid dianhydride ("BPDA");

2-trifluoro- 1 -(trifluoromethyl)ethylidene]bis- 1 ,2-isobenzofuranidone

("6FDA");

benzophenone tetracarboxylic dianhydride ("BTDA");

4,4'-(hexafluoroisopropylidene) dianiline ("6FpDA");

2,4,6-triemethyl-l,3-phenylene diamine ("DAM");

diethyltoluenediamine ("DETDA");

isophorondiamine ("IPDA")

3,5-diaminobenzoic acid ("DABA");

5,6-amino-l-(4'-aminophenyl)-l,3,3-trimethylindane ("DAPI").

Polyimides suitable for forming the skin layer on the support layer include polymers and copolymers. Different combinations and ratios of dianhydrides, such as 6FDA, BPDA, and BTDA, can be used, and optionally diamines or mixtures of diamines, including but not limited to DAM, DABA, DAPI, 6FpDA, DETDA IPDA, and DABE can be used with the dianhydrides to tailor the properties of the polyimides, forming a broad family of useful polymers. For example, the skin polymer can be a relatively expensive polymer such as 6FDA/BPDA-DAM, 6FDA-6FpDA, 6FD A-DETD A : DABE, 6FDA-DETDA:DABA, 6FDA- BPDA/DAM:DABA, BTDA-DAPI, or 6FDA/BTDA-DAM.

In some examples the skin polymer is a thermoplastic polyimide obtained by polycondensation of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) and a mixture of two cycloaliphatic monomers such as 5,6-amino-l-(4'-aminophenyl)-l,3,3- trimethylindane (DAPI), producing BTDA-diaminophenylindane (BTDA-DAPI) which is commercially available as Matrimid® 5218 from Huntsman International, LLC. Its structure is:

Another polymer useful in the materials and methods described herein is 6FDA/BPDA-DAM, which is a co-polymer formed from the monomers 2,4,6-Trimethyl-l,3- phenylene diamine (DAM); 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA); and 5,5'- [2,2,2-trifluoro-l-(trifluoromethyl)ethylidene]bis-l,3-isobenzofurandione (6FDA). The structure of 6FD A/BPD A-D AM is

To obtain the above-mentioned polymers one can use available sources or synthesize them. For example, synthesis of such polymers is described in US Patent No. 5,234,471.

Polymers of intrinsic microporosity (PIMs) refer to organic polymers that lack sufficient conformational flexibility to pack efficiently, thereby producing a highly rigid and contorted macromolecuiar structure that is unable to pack efficiently. PIMS are, therefore, microporous materials with interconnected porosity. Despite their rigid structures, PIMs are soluble in some organic solvents, such as THF, thereby allowing them to be coated onto a fiber as a skin layer in embodiments of the present invention. The ΡΓΜ skin layer on a support layer can be used for separation or can be pyrolyzed to form a CMS composite membrane according the current disclosure. While PIMs are relatively difficult to make and/or more costly than other polymers suitable for the sheath and/or core layers, optionally a

PIM could be used as either the sheath or core layer of a membrane disclosed herein. Mixed matrix materials (MMMs) have the potential to surpass the intrinsic separation performance of pure polymeric materials. The incorporation of molecular sieving zeolite, metal organic framework (MOF) or carbon (CMS) filler particles into a polymer phase can improve the separation performance of the MMM to overcome the so-called upper bound of pure polymers. Mixed matrix membrane with MOF fillers in the sheath layer of a sheath-core composite fiber have been reported for propylene-propane separation. Accordingly, the present disclosure is directed to use of MMMs as the sheath layer in asymmetric multilayer CMS precursor hollow fibers. The MMM sheath layer on a nanoparticle-stabilized polymer core layer can be used for separation or can be pyrolyzed to form a CMS composite membrane according the current invention.

In some examples, the support layer, and in particular the core layer, comprises a plurality of nanoparticles to limit collapse of pores during pyrolysis of the fibers to CMS membranes. Limiting pore collapse increases the gas permeance of the support layer, and thus of the CMS hollow fiber membrane. The terms nanoparticle and nanoparticle stabilizing fillers as used herein refer to particles with at least one dimension below 500 nm. In some examples, the nanoparticles are in the core layer, and the sheath layer is substantially free of nanoparticles. Substantially free of nanoparticles means that the sheath is either free of nanoparticles or includes only those nanoparticles that inadvertently cross into the sheath layer from the core layer during the spinning or quenching process of forming the polymeric hollow fibers.

The nanoparticle stabilizing fillers are non-uniformly attached to the polymer matrix of the porous core layer. Such non-uniform attachment leads to incomplete interfacial bonding between the nanoparticle and surrounding matrix, which avoids the collapse of pores during pyrolysis while maintaining adequate flexibility for handling. Particle size and hydrophobicity are controllable features of the nanoparticles that can be used to tune the dispersibility and degree of non-uniform attachment within the core layer to obtain the desired core layer non-collapse, with adequate flexibility in the final CMS fiber.

In some examples, the nanoparticle stabilizing fillers may be porous. Where the nanoparticle stabilizing filler is porous, the flow of gas through the CMS hollow fiber membrane core may be promoted, and the weight of the fiber can be reduced.

In some examples, the core polymer may contain functional reactive groups that react with the nanoparticle stabilizing fillers. Reaction of the nanoparticle stabilizing fillers and the polymer precursor fiber is not necessary for the utility of the nanoparticle stabilizing fillers in the CMS hollow fiber membrane. However, it is contemplated that some precursor polymer materials may react with the nanoparticle stabilizing fillers. For example, precursor fibers prepared using polymer materials that contain hydroxyl (-OH) or acid (for example, -COOH) functional groups may react with the nanoparticle stabilizing fillers; however, control of the reaction is required to avoid gelation of the core spinning dope, so reaction after formation of the asymmetric precursor membrane is preferred, if it occurs.

The nanoparticle stabilizing fillers may contain non-carbon elements, such as silicon or other elements, thereby decreasing the weight percent of carbon in the nanoparticle stabilized core CMS hollow fiber membrane. A nanoparticle stabilized CMS hollow fiber membrane is, therefore, not defined by the amount or percentage of carbon in its elemental makeup and does not require a particular minimum amount or percentage of carbon to be present.

In some examples, the plurality of nanoparticles are hydrophobic. In some examples, the plurality of nanoparticles are polyhedral oligomeric silsesquioxane ("POSS") silica nanoparticles. Optionally the nanoparticles used in the asymmetric multilayer CMS hollow fiber membranes and the process described herein are coated silicon dioxide nanoparticles. One example of suitable nanoparticles are silane-coated silicon dioxide nanoparticles having a bulk density of 0.056 g/cm³ with 15 nm average particle size (commercially available from U.S. Research Nanomaterials, Inc. as product # US3448). Those silane-coated silicon dioxide nanoparticles are coated with 2 wt% silane, are strongly hydrophobic, and are easily dispersed in organic solvent.

When nanoparticles are present in the core layer and include coated silicon dioxide, the low bulk density coated silicon dioxide occupies a large portion of the volume in composite fibers and maintains the porous structure during pyrolysis, without comprising a large mass fraction of the fiber. Use of silicon dioxide with higher bulk density (around 0.326 g/cm³) at the same 25 wt% S1O2 loading as used with the preferred case is not able to maintain the porous structure during pyrolysis.

It will be understood by a person of ordinary skill in the art that other nanoparticles can be used as stabilizers. Other high-temperature-resistant materials suitable as nanoparticles include other coated or chemically modified silicon dioxide, POSS silica nanoparticles, aminopropylisooctyl POSS, octa trimethylsiloxy POSS, metal oxides, metal carbides, and metal nitrides.

If nanoparticles of the above materials can be well dispersed in organic solvents, have low bulk density, and do not degrade during pyrolysis to the point where they damage the structure, they may also be good fillers to restrict substructure collapse during pyrolysis of composite fibers. Lack of these important properties, however, leads to unsuccessful results. For example, commercial silicon dioxide nanoparticles lacking a silane coating or other modification are not preferred in the materials and methods described herein.

As an alternative to nanoparticles being included in the support layer to maintain porosity during pyrolysis, a silane or other modifying agent may be included in the support layer to restrict movement of the polymer chain above the Tg and preventing collapse of any pores that are present to provide good permeance when pyrolyzed to form a CMS hollow fiber membrane. The silane or other modifying agent may be added to the support layer after the precursor polymeric hollow fiber is formed by contacting the precursor fiber with one or more solvent exchange materials including a modifying agent (e.g., a silane, a vinyltrimethoxysilane, a vinyltriethoxysilane). The modifying agent is present in an amount effective to improve the gas permeance of the asymmetric multilayer CMS hollow fiber membrane. In some examples, the precursor fibers were soaked in vinyltrimethoxysilane (VTMS) solutions of selected concentrations in hexane for 24 h. Following the soaking period, excess VTMS solution was removed by light blotting with Kimwipes®. The fibers were then transferred to a glove-bag which was maintained at 100% RH by flowing compressed air through DI water. The glove-bag was inflated and deflated four times before being sealed to ensure 100% RH, and the fibers were stored in it for another 24 h. Upon exposure to moisture, VTMS cross-links on the support "struts" comprising the porous substructure of the precursor fibers via a standard sol-gel crosslinking reaction. Following this moisture-induced crosslinking step, the fibers were dried in vacuum overnight at 150 °C to remove residual VTMS and moisture

In some examples, the silane or other modifying agent may be included in the precursor fiber that also includes nanoparticles. Thus, the core layer may comprise both nanoparticles and a silane. In other examples, the silane or other modifying agent is included in a precursor fiber that does not include nanoparticles. Thus, the core layer may comprise a silane but not nanoparticles.

Radial thickness is the average difference between the radius of the outer surface of an annular layer and the radius of the inner surface of the annular layer, as measured from the center of the fiber cross-section. For example, a skin layer having an outer radius of 10.2 micrometers and an inner radius of 10.0 micrometers from the center of the fiber cross- section would have an radial thickness of 0.2 micrometers. In some examples, the skin layer of a precursor polymeric hollow fiber has a radial thickness of 0.05 to 3.0 micrometers. In some examples, the skin layer may have a radial thickness of about 0.5 micrometers. In some examples, the skin layer has a radial thickness of 0.05 to 2.0 micrometers, 0.075 to 1.8 micrometers, 0.10 to 1.6 micrometers, 0.20 to 1.4 micrometers, 0.25 to 1.25 micrometers, 0.25 to 1.0 micrometers, or 0.25 to 0.75 micrometers.

In some examples, the sheath layer may have a radial thickness of 0.05 to 3.0 micrometers. In some examples, the sheath layer may have a radial thickness of about 0.5 micrometers. In some examples, the sheath layer has a radial thickness of 0.07 to 2.8 micrometers, 0.10 to 2.5 micrometers, 0.20 to 2.0 micrometers, 0.25 to 1.5 micrometers, 0.25 to 1.0 micrometers, or 0.25 to 0.75 micrometers.

In some examples, the support layer has a radial thickness of 100 to 500 micrometers. In some examples, the support layer has a radial thickness of 150 to 450 micrometers, 200 to 400 micrometers, or 250 to 350 micrometers. In some cases, the outer radius of the support layer comprises 90-99 % of the total radius of the polymeric hollow fiber. For example, a fiber having a support layer outer radius of 300 micrometers and a total radius of 315 micrometers would have an outer radius of the support layer that comprises 95% of the total radius of the polymeric hollow fiber

In some examples, the support layer comprises 90 to 98 wt% of the total weight of the polymeric hollow fiber. In some examples, the support layer comprises 91 to 97 wt%, 92 to 96 wt% , 90 to 95 wt% , or 95 to 98 wt% of the total weight of the polymeric hollow fiber.

In some examples, the core layer comprises 2 to 30 wt% nanoparticles, based on the weight of the core layer. In some examples, the core layer comprises 4 to 25 wt%, 6 to 20 wt%, 8 to 16 wt%, 2 to 15 wt% , or 15 to 30 wt% nanoparticles, based on the weight of the core layer.

Fig. 2 is a cross-sectional view of a schematic of a coated precursor fiber 100 as described herein showing a substantially annular core 102 surrounded by a substantially annular sheath 104. The coated precursor fiber 100 has a skin layer 106. Fig. 3 is a cross- sectional view of a schematic of a nanoparticle-containing precursor fiber 200 as described showing a substantially annular core 206 surrounded by a substantially annular sheath 208. The coated precursor fiber 200 has a skin layer 210.

CMS Hollow Fiber Membranes

Any of the precursor fibers described above may be transformed to CMS hollow fiber membranes by heating, as detailed below. Accordingly, disclosed herein are carbon molecular sieve (CMS) hollow fiber membranes having at least three layers. The innermost layer is a core layer comprising a pyrolyzed first polymer; the second layer is a sheath layer comprising a pyrolyzed second polymer; and the third layer is a skin layer comprising a pyrolyzed third polymer. The core layer, the sheath layer, and the skin layer have substantially annular cross-sections with the sheath layer adjacent to and radially outward from the core layer and the skin layer adjacent to and radially outward from the sheath layer. In some examples, the core layer further comprises a silane. In some examples, the core layer further comprises a plurality of nanoparticles.

When nanoparticles are include in the core layer of the precursor fiber, the core layer of the pyrolyzed CMS hollow fiber membrane includes substantially all of the plurality of nanoparticles from the core layer of the coated polymeric precursor fiber. Optionally, the sheath layer of the pyrolyzed asymmetric multilayer CMS hollow fiber membrane is substantially free of nanoparticles. The core layer of the coated polymeric precursor fiber optionally may include 25-40 wt% nanoparticles based on polymer weight in the core layer. Alternatively, the core layer of the extruded multilayer CMS membrane precursor fiber optionally may include 10-25 wt% nanoparticles based on polymer weight in the core layer.

When the core layer comprises a plurality of nanoparticles, in some examples the plurality of nanoparticles are hydrophobic. In some examples, the plurality of nanoparticles are polyhedral oligomeric silsesquioxane ("POSS") silica nanoparticles. In some examples, the core layer comprises 25 to 40 wt% nanoparticles based on weight of the core layer.

In some examples, the first polymer comprises a polyvinylidene chloride, a polyacrylonitrile, a polyvinyl chloride, a polyvinylidene difluoride, a polyimide, a polyetherimide, a polysulfone, or a polyethersulfone. In some examples, the second polymer comprises one or more of a polyvinylidene chloride, a polyacrylonitrile, a polyvinyl chloride, a polyvinylidene difluoride, a polyimide, a polyetherimide, a polysulfone, or a polyethersulfone. In other examples, the second polymer comprises 6FDA/BPDA-DAM, 6FDA-6FpDA, 6FDA-DETDA, DABE, 6FDA-BPD A/DAM, 6FDA-DETDA:DABA, 6FDA- DETDA:DABE, BTDA-DAPI, or 6FDA/BTDA-DAM. In some examples, the third polymer comprises one or more of 6FDA/BPDA-DAM, 6FDA-6FpDA, 6FDA-DETDA, DABE, 6FDA-BPD A/DAM, 6FDA-DETDA:DABA, 6FD A-DETD A : DABE, BTDA-DAPI, or 6FDA/BTDA-DAM.

To obtain both high selectivity and permeance of CMS composite hollow fiber membrane, the coated precursor hollow fiber membrane comprises a thin but dense skin layer of polymer on the porous support layer, as shown in Fig. 2 and Fig. 3. Density refers to concentration of the polymer on the outer surface of the support layer. Thin refers to a low radial thickness, such as up to 3.0 micron. The dense skin layer of pure polymer after coating can provide the resultant CMS fiber with high selectivity, while the porous support layer can secure the high permeance. When nanoparticles, such as silicon dioxide nanoparticles, are present in the support layer, the low bulk density silicon dioxide occupies a large portion of the volume and maintains the porous structure during pyrolysis, without comprising a large mass fraction of the fiber. Other high-temperature-resistant materials include metal oxides, metal, carbide, and nitride that can also be used as stabilizer fillers in this invention. If nanoparticles of the above materials can be well dispersed in organic solvents and have low bulk density and do not degrade during pyrolysis to the point where they damage the structure, they may also be good fillers to make support layer fibers to restrict substructure collapse during pyrolysis

Preferred thermally re-arranged polymer membranes comprise aromatic polymers that are interconnected with heterocyclic rings. Examples include polybenzoxazoles, polybenzothiazoles, and polybenzimidazoles. Preferred thermally re-arranged polymer precursors comprise polyimides with ortho-positioned functional groups, such as for example HAB-6FDA a polyimide having the following structure.

The phenylene-heterocyclic ring units in such materials have rigid chain elements and a high- torsional energy barrier to rotation between the two rings, which prevents indiscriminant rotation. Thermal re-arrangement of these polymers can thus be controlled to create pores having a narrow size distribution, rendering them useful for gas separation applications.

The temperature at which the thermal rearrangement occurs is generally lower than the temperatures used for pyrolysis, as pyrolysis would convert the polymer fiber into a carbon fiber. Polyimides, for example, are typically heated to a temperature between about 250° C and about 500° C, more preferably between about 300° C and about 450°. The heating of the polymers generally takes place in an inert atmosphere for a period of several hours. Although the polymer is not subjected to the same stresses of pyrolysis, heating of the polymer at a temperature sufficient to cause thermal re-arrangement also results in undesirable pore collapse. Crosslinkable polyimides utilizes a diaminobenzoic acid (DABA) moiety in the polyimide backbone as a site for interchain crosslinking. The use of 1,3-prodanediol, leads to "PDMC" (propanediol monoester cross-linkable) polyimide. After a membrane is made from the material, cross-linking may be carried out by heating the membrane in the solid state at temperatures above -150 °C under vacuum or an inert sweep gas to activate a transesterification reaction. This material may be formed into an asymmetric membrane as described by Omole et al., in Macromolecules, 2008, 41, 6367-6375. After cross-linking occurs, the material becomes insoluble and more resistant to swelling by feed components that undermine intrinsic selectivity. Crosslinkable polymers can be used as the sheath layer of a sheath-core composite, and the current disclosure encompasses use of such crosslinkable polymers as the sheath layer in asymmetric multilayer CMS precursor hollow fibers. The cross-linkable polymer sheath layer on a nanoparticle-stabilized polymer core layer be pyrolyzed to form a CMS composite membrane according the current disclosure.

Processes for preparing CMS Hollow Fiber Membranes

Processes for preparing asymmetric multilayer CMS hollow fiber membranes are described herein. In some examples, a process a preparing a CMS membrane described herein includes pyrolyzing a coated precursor polymeric hollow fiber as described herein. In other examples, a process for preparing a CMS membrane described herein further includes coating a polymeric hollow fiber as described herein to form the coated precursor polymeric hollow fiber prior to pyrolyzing the precursor polymeric hollow fiber. In still other examples, a process for preparing a CMS membrane described herein further includes extruding one or more polymer dopes to form the polymeric hollow fiber. Optionally the process further comprises contacting the polymeric hollow fiber or the coated polymer fiber with one or more solvent exchange materials including a modifying agent (e.g., a silane, a vinyltrimethoxysilane, a vinyltriethoxysilane). The polymeric hollow fiber is then coated and pyrolyzed as described herein.

The processes described herein include pyrolyzing a coated polymeric precursor fiber to form a CMS hollow fiber membrane. Pyrolysis generally is carried out under an inert atmosphere, for example, an atmosphere of ultra-high purity argon (99.9 % pure). The pyrolysis temperature may be between about 500 °C and about 1000 °C (e.g., 500 °C and 800

°C, 500 °C and 700 °C, 500 °C and 650 °C, 500 °C and 600 °C, 500 °C and 550 °C, 550 °C and 1000 °C, 550 °C and 800 °C, 550 °C and 700 °C, 500 °C and 650 °C, 600 °C and 1000

°C, 600 °C and 800 °C, 600 °C and 700 °C, 600 °C and 650 °C). The pyrolysis temperature is typically reached by a process in which the temperature is slowly ramped up. For example, when using a pyrolysis temperature of 650° C, the pyrolysis temperature may be achieved by increasing the temperature from 50° C to 250° C at a ramp rate of 13 .3 ° C/min, increasing the temperature from 250° C to 635° C at a ramp rate of 3.85° C/min, and increasing the temperature from 635° C to 650° C at a ramp rate of 0.25° C/min. Once the pyrolysis temperature is reached, the fibers are heated at the pyrolysis temperature for a soak time, which may be a number of hours.

In some examples, defects in the skin layer of the coated polymer, such as any discontinuity of the skin layer, were progressively reduced as the pyrolysis temperature was increased (e.g, from 550 °C to 675 °C to 800 °C). In some examples, the pyrolyzing step is conducted at a temperature of at least 550 °C. In some examples, the pyrolyzing step is conducted at a temperature of at least 675 °C. In some examples, the pyrolyzing step is conducted at a temperature of at least 800 °C.

In some examples, the process of forming a CMS hollow fiber membrane further comprises coating a polymeric fiber with a coating polymer solution to form a coated precursor polymeric fiber prior to pyrolysis. The coating layer, also referred to herein as the skin layer, is formed by coating the fiber, which serves as a support layer for the coating, and which can include a core layer and a sheath layer. Any polymer described herein for use as a skin/coating polymer may be used in the step of coating the polymeric hollow fiber. The coating polymer is dissolved in a solvent, which may include chloroform, toluene, 1,4- dioxane, dimethylbenzene, acetone, ethyl acetate, dimethylbenzene, tetrahydrofuran, acetonitrile. While the solvent should not dissolve the polymer from the core and sheath layer. For example, THF could be used to prepare the coating solution, while P84® could be used to form core and sheath layer. Then the coating step may be accomplished by any known coating process, for example dip-coating or spraying. In some examples, the coating/skin layer is applied by dip coating.

Fig. 4 is an illustration of an exemplary coating process according to various examples of the present invention. Fibers are continuously coated on the outer surface from hollow fiber spool 1001 to coated hollow fiber spool 1005. The fibers are drawn through a coating bath 1003 and afterwards passed up a 1.5 -meter-long chamber 1004, in which the humidity is controlled by a humidifier and dry air purge line. There is a thread tension regulator 1002 to adjust the fiber tension during the coating step. The coated fibers are collected by the take-up drum. In some examples, the coating step is carried out by dipping the precursor in the polymer solution with contacting time varying from 5 seconds to 120 seconds. In some examples, after the coating step, the coated precursor fibers are kept in a vacuum oven at about 75 °C for about 2 hours.

In some examples, the coating step is carried out with humidity control. Humidity was found to have a considerable effect on morphology of the coated precursor fiber and consequently on the final CMS fiber as well. The presence of moisture in the air can potentially lead to a "phase-separation process" during the coating process and induce undesirable pore formation in the skin layer. Accordingly, the relative humidity during the coating step can be selected in order to obtain a CMS membrane having a desired combination of gas permeance and selectivity properties. In some examples, the coating step is conducted at a relative humidity of between about 1 and about 90 percent. In some examples, coating step is conducted at a relative humidity of between 10% and 85%, between 10% and 75%, between 5% and 65%, between 25% and 75%, between 30% and 70%, or between 25% and 65%.

In some examples, the coating step uses a very low concentration of polymer in a solution (LCPS) (e.g., no more than 5 wt%) under very low relative humidity (LRH) (e.g., 5- 15%). Optionally, the coating step uses a very high concentration of polymer in a solution (HCPS) (e.g., up to 30 wt%) under very high relative humidity (HRH) (e.g., 50-100%).

Optionally, the coating step uses very low concentration of polymer in a solution (LCPS) under very high relative humidity (HRH) Optionally, the coating step uses very high concentration of polymer in a solution (HCPS) under very high relative humidity (LRH).

In some examples, the concentration of coating polymer in the coating solution can be between 0.5 wt% and 5.0 wt% polymer, based on the weight of the solution. In some examples, the concentration of coating polymer can be no more than 5 wt%, no more than 4 wt%, no more than 3 wt%, no more than 1 wt%, no more than 1 wt%, or no more than 0.5 wt%. In some examples, the concentration of coating polymer in the coating solution can be between 20 wt% and 50 wt%. In some examples, the concentration of coating polymer can be at least 25 wt%, at least 30 wt%, at least 35 wt%, at least 40 wt%, at least 45 wt%, or at least 50 wt%,

In some examples, the coating process can be carried out at a relatively low humidity

(LRH) of up to 50%). In some examples, the coating process can be carried out at a relative humidity of up to 5%, up to 10%, up to 15% up to 35%, or up to 40%. In some examples, coating process can be carried out at a relative humidity of greater than or equal to 50%, greater than or equal to 55%, greater than or equal to 60%, greater than or equal to 65%, greater than or equal to 70%, greater than or equal to 75%, or greater than or equal to 80%. In some examples, processes for preparing CMS hollow fiber membranes further include preparing the polymeric hollow fiber prior to coating the fiber. The polymeric fiber may be formed by extruding a core dope and optionally a sheath dope through a spinneret to produce the polymeric hollow fiber. The core dope comprises a first polymer and a first solvent. The first polymer may be any polymer described herein for forming a core layer. The first solvent may be n-methyl pyrrolidone ( MP), dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), dimethylformamide (DMF) The sheath dope when present comprises a second polymer and a second solvent. The second polymer may be any polymer described herein for forming a sheath layer. The second solvent may be NMP, dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), dimethylformamide (DMF). The first and second polymer can be the same or different. The first and second solvents can be the same or different.

In some cases, the core dope further comprises a plurality of nanoparticles. Any of the nanoparticles described above may be used in the process at any weight percent described above. In some examples, the plurality of nanoparticles are hydrophobic. In some examples, the plurality of nanoparticles are polyhedral oligomeric silsesquioxane ("POSS") silica nanoparticles. Optionally, the sheath dope may include additional components such as a non- solvent and/or a pore former.

In some examples, preparing the polymeric hollow fiber further comprises contacting the polymeric hollow fiber or the coated polymeric precursor fiber with a modifying agent before the coating step. Alternatively, the coated precursor fiber may be contacted with the modifying agent after the coating step. The fiber that is contacted with the modifying agent may comprise nanoparticles, or may be free of nanoparticles. The modifying agent may be any modifying agent described above. In some examples, the modifying agent comprises a silane. In some examples, the modifiying agent comprises vinyltrimethoxysilane or vinyltriethoxysilane. In some examples, the precursor fibers were soaked in vinyltrimethoxysilane (VTMS) solutions of selected concentrations in hexane for 24 h. Following the soaking period, excess VTMS solution was removed by light blotting with Kimwipes®. The fibers were then transferred to a glove-bag which was maintained at 100% RH by flowing compressed air through DI water. The glove-bag was inflated and deflated four times before being sealed to ensure 100% RH, and the fibers were stored in it for another 24 h. Upon exposure to moisture, VTMS cross-links on the support "struts" comprising the porous substructure of the precursor fibers via a standard sol-gel crosslinking reaction. Following this moisture-induced crosslinking step, the fibers were dried in vacuum overnight at 150 °C to remove residual VTMS and moisture.

Properties of Polymeric Hollow Fibers and CMS Hollow Fibers

In some examples, the coated polymeric precursor hollow fibers described herein have a C02:CH4 selectivity of about 5 to about 25. In some examples, the coated polymeric precursor hollow fibers have a CO2 permeance of about 10 GPU to about 50 GPU.

In some examples, a CMS hollow fiber membrane produced by the processes described herein has a carbon dioxide/methane selectivity of greater than 50, greater than 60, or greater than 70. In some examples, the CMS hollow fiber membrane has a carbon dioxide/methane selectivity of from 50 to 90. In some examples, a CMS hollow fiber membrane produced by the processes described herein has a carbon dioxide permeance of at least about 250 GPU, at least about 400 GPU, or at least about 1000 GPU. In some examples, the carbon dioxide/methane selectivity can be at least about 45 and the carbon dioxide permeance can be at least about 150 GPU. Alternatively, the carbon dioxide/methane selectivity can be at least about 70 and the carbon dioxide permeance can be at least about 100 GPU.

Also disclosed herein are enrichment devices comprising a gas stream inlet, an enriched (permeate) gas stream outlet, a depleted (retinate) gas stream outlet, and a plurality of substantially aligned hollow carbon fibers, wherein the hollow carbon fiber can comprise a CMS hollow fiber membranes having a carbon dioxide/methane selectivity and a carbon dioxide permeance as defined above. The polymeric hollow fiber carbon molecular sieve can include a bore or lumen passing through the length of the fiber, and a membrane surrounding the bore or lumen as part of the outside of the fiber. In some embodiments, the gas stream inlet can be on the bore-side of the polymeric hollow fiber. In an alternative embodiment, the gas stream inlet can be on the membrane-side of the polymeric hollow fiber.

Processes for separating gases using CMS Hollow Fiber Membranes

Processes for separating a mixture of at least two gases are disclosed herein. The processes comprise contacting a mixture of at least two gases with the CMS hollow fiber membranes disclosed herein or made by the processes disclosed herein to separate the mixture into a permeate stream that is enriched in a first gas and a retentate stream that is enriched in a second gas. In some examples, the mixture of at least two gases comprises CO2 and CH₄; H2S and CH₄; CO2, H2S, and CH₄; CO2 and N2; O2 and N2; N2 and CH₄; He and CH₄; He and N2; He and SF₆; H2 and CH₄; H2 and C2H4; ethylene and ethane; propylene and propane; or ethane/propane and ethylene/propylene. In some examples, the mixture of at least two gases comprises a natural gas comprising an acid gas and at least one hydrocarbon gas, wherein the permeate stream is enriched in the acid gas, and wherein the retentate stream is enriched in the hydrocarbon gas. In some examples, the acid gas comprises CO2. In some examples, the acid gas comprises H2S.

In some examples, when the acid gas comprises CO2 and the hydrocarbon gas comprises CH4, the process has a C02:CH4 selectivity of greater than 20, greater than 40, or greater than 75. In some examples, the process can have a carbon dioxide/methane selectivity of greater than 50, and a carbon dioxide permeance of at least about 250 GPU. In some cases, the process can have a carbon dioxide/methane selectivity of greater than 60. In other cases, the carbon dioxide/methane selectivity can be greater than 70. In alternative examples, the carbon dioxide permeance can be greater than about 150 GPU. In yet other examples, the carbon dioxide permeance can be greater than about 200 GPU. In some examples, the separation membrane can have a carbon dioxide/methane selectivity of greater than 58 and a carbon dioxide permeance of at least 150 GPU. In some examples, the carbon dioxide/methane selectivity can be at least about 45 and the carbon dioxide permeance can be at least about 150 GPU. Alternatively, the carbon dioxide/methane selectivity can be at least about 70 and the carbon dioxide permeance can be at least about 100 GPU.

The CMS hollow fiber membranes were tested for selectivity and permeance in a single fiber module. Hollow fibers are epoxied into laboratory-scale membrane modules for permeation tests. The detailed protocol for module making and testing procedures were documented by Koros et al. in U.S. Patent No. 6,565,631. The number of fibers required for a membrane module was determined by the membrane transport properties and testing protocol The measurements were taken at 35 °C using a feed on the shell side of the fiber at 100 psia with permeate at atmospheric pressure. The permeate flow rate was measured from the bore side with a bubble flowmeter at atmospheric pressure. The permeance (P/L) can be calculated using the following Equation 1 :

P _ 6 Qp-273.15

L Α·Τ·Δρ·5.17 (1)

Where Q_P is the permeate flow rate in mL/sec, A is the active membrane area in cm², T is the room temperature in Kelvin, Δρ is the transmembrane pressure difference in psia. The calculated permeance is in "Gas Permeation Units" (GPU) defined as:

cm³ (stp)

1 GPU = 1 X 10-⁶

cm² -s-cmHg (2) To characterize the separation performance of a polymeric hollow fiber membrane, two key factors, permeance and selectivity, can be considered. The permeance, Pi/L, represents the separation productivity of a polymeric hollow fiber membrane and is defined as the flux of penetrant i normalized by the partial pressure or fugacity difference across the membrane, as shown in Equation 3,

= (3)

L ΔΡ;

In Equation 3, Pi represents the permeability of penetrant i; L describes the effective membrane thickness; ni represents the flux of penetrant i through the membrane; Δρ refers the partial pressure or fugacity difference of each penetrant across the membrane. The selectivity, ay, measures the membrane separation efficacy for a gas pair under conditions where the upstream pressure is much greater than the downstream. It is defined by the ratio of the fast gas (i) permeance to the slow gas (j) permeance, as shown in Equation 4,

a ^{U l}-J = Pj/±L (4)

EXAMPLES

In examples described herein that contain nanoparticles, the nanoparticles were first dried in a vacuum oven at 180 °C overnight, to remove any moisture in the pores. The dried nanoparticles were dispersed in an appropriate solvent or solvent mixture described herein. A sonication bath was used to assist the dispersion of nanoparticles, and sonication was stopped when no visible agglomerates could be found. A solution containing about 10 wt% of the total core polymer was first added slowly to the nanoparticle dispersion in an attempt to avoid clumping of the nanoparticles. The remaining solvent and dried polymer solids were then added to make dopes with the desired composition. The dopes were rolled on a standard lab roll mixer to be homogenous before being put into pumps for spinning. Low-bulk-density of the preferred fillers helps provide a fiber that maintains its porous core structure during pyrolysis.

Materials and Preparation of Hollow Fiber Polymer Precursor Membranes are described in Examples 1-9 below.

Example 1

Asymmetric dual-layer hollow fiber membranes were formed by a modified dry- jet/wet-quench spinning process such as that reported in U.S. Pat. No. 9,718,031. This dual- layer fiber comprises one sheath layer of neat P84® and one porous core layer with P84® and Polyvinylpyrrolidone (PVP) with a hollow bore. A bore fluid (of 95% NMP in water) and two spinning dopes (core spinning dope and sheath spinning dope) were used to spin P84®/(PVP+ P84®) dual-layer fiber membranes. The core spinning dope contained P84® and PVP, with N-Methyl-2-pyrolidone (NMP) used as solvent. P84® was obtained from HP POLYMER GMBH. The sheath spinning dope contained P84 and solvent (NMP). Table 1 shows the composition of the core and sheath dopes. Table 2 shows the spinning parameters.

TABLE 1

Dope composition of core spinning dope and sheath spinning

dope to spin P84®/(PVP + P84® ^|) dual-layer fiber membranes.

Dope composition

Core (PVP+ P84®) sheath(P84®)

Component Mass (g) Mass (g)

P84® 54 88.8

NMP 219 31.2

PVP 27 0

TABLE 2

Spinning conditions for P84®/(PVP + P84®) dual-layer fiber membranes.

Spinning parameter Value

Sheath dope flow rate 20 mL/hr

Core dope flow rate 900 mL/hr

Bore fluid flow rate 300 mL/hr

Bore fluid composition 90 wt%/10 wt%

Take-up rate 5 m/min

Quench bath temperature 50°C

Spinneret temperature 65°C

Air gap height 10 cm

After spinning, the fibers were soaked in water baths for 3 days to remove the last traces of solvent. The fibers were then solvent exchanged in glass containers with three separate 20 min methanol baths followed by three separate 20 min hexane baths and dried under vacuum at 75° C for 3 hrs. Fig. 5 shows the SEM image of uncoated precursor fiber without nanoparticles.

A coating solution was prepared with a composition of 2 wt% 6FDA/BPDA-DAM and 98 wt% Tetrahydrofuran (THF, Sigma-Aldrich Inc., 99.5%) in a Qorpak® glass jar sealed with a Teflon® cap. The mixture was dissolved by placing the jar on a roller at room temperature to produce a homogeneous solution (usually one day). The fibers were drawn through a coating bath containing 6FDA/BPDA-DAM solution with the humidity controlled at 65% by a humidifier. The coating velocity was 0.2 m/s. The coated precursor fiber was dried at under vacuum at 75°C. for 2 hrs. The fibers were tested with a mixed gas of 50/50 vol.% CO2/CH4 at 100 psi and 35 °C, with shell side feed. The CO2 permeance was about 48 GPU with a CO2/CH4 selectivity of 2.1. Data is shown in Fig. 10

Example 2

The precursor fiber of Example 1 was coated with 6FDA/BPDA-DAM at the same conditions as in Example 1, but the 6FDA/B PDA-DAM polymer solution concentration is 3 wt%. The fibers were tested with a mixed gas of 50/50 vol.% CO2/CH4 at 100 psi and 35 °C, with shell side feed. The CO2 permeance was about 30 GPU with a CO2/CH4 selectivity of 6.1. Data is shown in Fig. 10.

Example 3

The precursor fiber of Example 1 was coated with 6FDA/BPDA-DAM at the same conditions as in Example 1, but the 6FDA/B PDA-DAM polymer solution concentration is 4 wt%. The fibers were tested with a mixed gas of 50/50 vol.% CO2/CH4 at 100 psi and 35 °C, with shell side feed. The CO2 permeance was about 14 GPU with a CO2/CH4 selectivity of 21.7. Data is shown in Fig. 10. Fig. 6 shows the SEM image of coated precursor fiber without nanoparticles.

Example 4

The coated precursor fiber of Example 3 were further treated with 10% vinyl trimethoxy silane (VTMS) treatment prior to pyrolysis. The precursor fibers were soaked in vinyltrimethoxysilane (VTMS) solutions of selected concentrations in hexane for 24 h.

Following the soaking period, excess VTMS solution was removed by light blotting with

Kimwipes®. The fibers were then transferred to a glove-bag which was maintained at 100%

RH by flowing compressed air through DI water. The glove-bag was inflated and deflated four times before being sealed to ensure 100% RH, and the fibers were stored in it for another

24 h. Upon exposure to moisture, VTMS cross-links on the support "struts" comprising the porous substructure of the precursor fibers via a standard sol-gel crosslinking reaction.

Following this moisture-induced crosslinking step, the fibers were dried in vacuum overnight at 150 °C to remove residual VTMS and moisture VTMS treated fibers were placed on a stainless-steel wire mesh and held in place by wrapping a length of wire around the mesh and fibers. The fibers were placed on a stainless steel wire mesh (McMaster Carr, Robbinsville, NT) and loaded into a quartz Tube (55 mm ID and 4 ft. long) (National Scientific Co. Quakertown, PA). The ends of the tube were sealed with metal flanges and Silicon O-rings (Model # EQ-FI-60, MTI Corporation, Richmond, CA). For all experiments described in this paper, the pyrolysis was carried out under an inert atmosphere by maintaining a constant flow of 200 cc (STP)/min UHP Argon (Airgas). Flow rate of the purge gas was monitored by a mass flow controller (model # MC-500-SCCM-D, Alicat Scientific, Marana, AZ). Pyrolysis was performed under an atmosphere of ultra-high purity argon (99.9% pure) as follows:

1. 50° C. to 250° C. at a ramp rate of 13.3° C./min

2. 250° C. to 535° C. at a ramp rate of 3.85° C./min

3. 535° C. to 550° C. at a ramp rate of 0.25° C./min

4. Soak for 2 hours at 550° C.

The resulting CMS fibers were tested in a single fiber module and/or in a constant- volume variable pressure permeation system such as the one described by Koros et al. in U.S. Pat. No. 6,565,631, the contents of which are hereby incorporated by reference. The CMS fiber module was tested using a constant pressure permeation system for both pure and mixed gas feeds similar to the one described in the literature, such as Clausi, D. T., & Koros, W. J. (2000). Formation of defect-free polyimide hollow fiber membranes for gas separations. Journal of Membrane Science, 167(1), 79-89. The CMS fibers were tested using a mixed gas feed containing 50 mol % CO2 and 50 mol % CH₄ at a pressure of 200 psi (pounds per square inch). The temperature was maintained at 35° C. A SEM image of the CMS fiber at 550 °C is shown in Fig. 7. The permeance of CO2 through the CMS fibers was measured to be about 1356 GPU. The CO2/CH4 selectivity was determined to be about 10. Data is shown in Fig. 11

Example 5

The coated precursor fibers of Example 3 were further treated with 10% vinyl trimethoxy silane (VTMS) treatment prior to pyrolysis as in Example 4. VTMS treated fibers were placed on a stainless-steel wire mesh and held in place by wrapping a length of wire around the mesh and fibers. The mesh support containing the fibers was then loaded to a pyrolysis setup as in Example 4. Pyrolysis was performed under an atmosphere of ultra-high purity argon (99.9% pure) as follows:

1. 50° C. to 250° C. at a ramp rate of 13.3° C./min 2. 250° C. to 660° C. at a ramp rate of 3.85° C./min

3. 660° C. to 675° C. at a ramp rate of 0.25° C./min

4. Soak for 2 hours at 675° C.

The resulting CMS fibers were tested in a single fiber module, such as the one described by Koros et al. in U.S. Pat. No. 6,565,631. The CMS fiber module was tested using a constant pressure permeation system for both pure and mixed gas feeds similar to the one described in the literature, such as Clausi, D. T., & Koros, W. J. (2000). Formation of defect- free polyimide hollow fiber membranes for gas separations. Journal of Membrane Science, 167(1), 79-89. The CMS fibers were tested using a mixed gas feed containing 50 mol % CO2 and 50 mol % CH₄ at a pressure of 200 psi (pounds per square inch). The temperature was maintained at 35° C. A SEM image of the CMS fiber at 675 °C is shown in Fig. 8. The permeance of CO2 through the CMS fibers was measured to be about 415 GPU. The CO2/CH4 selectivity was determined to be about 58. Data is shown in Fig. 11.

Example 6

1. 50° C. to 250° C. at a ramp rate of 13.3° C./min

2. 250° C. to 785° C. at a ramp rate of 3.85° C./min

3. 785° C. to 800° C. at a ramp rate of 0.25° C./min

4. Soak for 2 hours at 800° C.

The resulting CMS fibers were tested by the methods described in Example 4. The CMS fibers were tested using a mixed gas feed containing 50 mol % CO2 and 50 mol % CH₄ at a pressure of 200 psi (pounds per square inch). The temperature was maintained at 35° C. A SEM image of the CMS fiber at 800 °C is shown in Fig. 9. The permeance of CO2 through the CMS fibers was measured to be about 236 GPU. The CO2/CH4 selectivity was determined to be about 87. Data is shown in Fig. 11.

Example 7 The precursor fiber of Example 1 was coated with 6FDA/BPDA-DAM at the same conditions as in Example 1, but the relative humidity was controlled at 10%. Fig. 12 shows the SEM image of the 2% 6FDA/BPDA-DAM coated precursor fiber.

Example 8

The coated precursor fibers of Example 7 were further treated with 10% vinyl trimethoxy silane (VTMS) treatment prior to pyrolysis. VTMS treated fibers were placed on a stainless-steel wire mesh and held in place by wrapping a length of wire around the mesh and fibers. The mesh support containing the fibers was then loaded to a pyrolysis setup. Pyrolysis was performed under an atmosphere of ultra-high purity argon (99.9% pure) as follows:

1. 50° C. to 250° C. at a ramp rate of 13.3° C./min

2. 250° C. to 660° C. at a ramp rate of 3.85° C./min

3. 660° C. to 675° C. at a ramp rate of 0.25° C./min

4. Soak for 2 hours at 675° C.

The resulting CMS fibers were tested by the methods described in Example 4. The CMS fibers were tested using a mixed gas feed containing 50 mol % CO2 and 50 mol % CH₄ at a pressure of 200 psi (pounds per square inch). The temperature was maintained at 35° C. A SEM image of the CMS fiber at 675 °C is shown in Fig. 13. The permeance of CO2 through the CMS fibers was measured to be about 78 GPU. The CO2/CH4 selectivity was determined to be about 72, as shown in Table 6.

Example 9

1. 50° C. to 250° C. at a ramp rate of 13.3° C./min

2. 250° C. to 535° C. at a ramp rate of 3.85° C./min

3. 535° C. to 550° C. at a ramp rate of 0.25° C./min

4. Soak for 2 hours at 550° C.

The resulting CMS fibers were tested by the methods described in Example 4. The CMS fibers were tested using a mixed gas feed containing 50 mol % CO2 and 50 mol % CH₄ at a pressure of 200 psi (pounds per square inch). The temperature was maintained at 35° C. The permeance of CO2 through the CMS fibers was measured to be about 441 GPU. The CO2/CH4 selectivity was determined to be about 14, as shown in Table 6.

Materials and Preparation of Hollow Fiber Polymer Precursor Membranes with nanoparticles are described in Examples 10-17 below.

Example 10

Asymmetric dual-layer hollow fiber membranes were formed by a modified dry- jet/wet-quench spinning process such as that reported in U.S. Pat. No. 9,718,031B2. This dual-layer hollow bore fiber comprises one sheath layer of neat P84® and one porous core layer with P84® and commercial silane-coated (S1O2) silicon dioxide nanoparticles (Product # US3448, US Research Nanomatertials, Inc.). A bore fluid /and two spinning dopes (core spinning dope and sheath spinning dope) were used to spin P84®/(Si02+ P84®) dual-layer fiber membranes. The core spinning dope contained P84®, NMP solvent, and S1O2 nanoparticles. The sheath spinning dope contained P84®, solvents (NMP and THF), and S1O2 nanoparticles. Table 3 shows the composition of the core and sheath dopes. Table 4 shows the spinning parameters.

TABLE 3

Dope composition of core spinning dope and sheath spinning

dope to spin P84®/(Si0₂ + P84® ⁾) dual-layer fiber membranes.

Dope composition

Core (S1O2 + sheath(P84®)

P84®)

Component Mass (g) Mass (g)

P84® 137.3 97.71

NMP 357 153

THF 0 52.29

TABLE 4

Spinning conditions for P84®/(Si02 + P84®) dual-layer fiber membranes.

Spinning parameter Value

Sheath dope flow rate 30 mL/hr

Core dope flow rate 600 mL/hr

Bore fluid flow rate 200 mL/hr

Bore fluid composition 90 wt%/10 wt%

Take-up rate 5 m/min

Quench bath temperature 50°C Spinneret temperature 65°C

Air gap height 18 cm

After spinning, the fibers were soaked in water baths for 3 days to remove the last traces of solvent. The fibers were then solvent exchanged in glass containers with three separate 20 min methanol baths followed by three separate 20 min hexane baths and dried under vacuum at 75° C. for 3 hrs.

A coating solution was prepared with a composition of 4 wt. % 6FDA/BPDA-DAM and 96 wt. % Tetrahydrofuran (THF, Sigma-Aldrich Inc., 99.5%) in a Qorpak® glass jar sealed with a Teflon® cap. The mixture was dissolved by placing the jar on a roller at room temperature to produce a homogeneous solution (usually one day).

The fibers were drawn through a coating bath containing 6FDA/BPDA-DAM solution with the humidity controlled at 65% by a humidifier. The coating velocity was 0.2 m/s. The coated precursor fiber was dried at under vacuum at 75°C. for 2 hrs. Fig. 14 shows the SEM image of coated precursor fiber with nanoparticles.

Example 1 1

The 4 wt. % 6FDA/BPDA-DAM coated precursor fibers of Example 10 were placed on a stainless-steel wire mesh and held in place by wrapping a length of wire around the mesh and fibers. The mesh support containing the fibers was then loaded to a pyrolysis setup. Pyrolysis was performed under an atmosphere of ultra-high purity argon (99.9% pure) as follows:

1. 50° C. to 250° C. at a ramp rate of 13.3° C./min

2. 250° C. to 660° C. at a ramp rate of 3.85° C./min

3. 660° C. to 675° C. at a ramp rate of 0.25° C./min

4. Soak for 2 hours at 675° C.

The resulting CMS fibers were tested by the methods described in Example 4. The CMS fibers were tested using a mixed gas feed containing 50 mol % CO2 and 50 mol % CH₄ at a pressure of 200 psi (pounds per square inch). The temperature was maintained at 35° C. The permeance of CO2 through the CMS fibers was measured to be about 507 GPU. The CO2/CH4 selectivity was determined to be about 20.

Example 12

1. 50° C. to 250° C. at a ramp rate of 13.3° C./min

2. 250° C. to 785° C. at a ramp rate of 3.85° C./min

3. 785° C. to 800° C. at a ramp rate of 0.25° C./min

4. Soak for 2 hours at 800° C.

The resulting CMS fibers were tested by the methods described in Example 4. The CMS fibers were tested using a mixed gas feed containing 50 mol % CO2 and 50 mol % CH₄ at a pressure of 200 psi (pounds per square inch). The temperature was maintained at 35° C. A SEM image of the CMS fiber at 800 °C is shown in Fig. 15. The permeance of CO2 through the CMS fibers was measured to be about 358 GPU. The CO2/CH4 selectivity was determined to be about 30.

Example 13

The precursor fiber of Example 10 was used to coat with 6FDA/BPDA-DAM at the same conditions as in Example 1, but the relative humidity was controlled at 10%. 2 wt. % 6FDA/BPDA-DAM coated precursor fibers of Example 10 were placed on a stainless-steel wire mesh and held in place by wrapping a length of wire around the mesh and fibers. The mesh support containing the fibers was then loaded to a pyrolysis setup. Pyrolysis was performed under an atmosphere of ultra-high purity argon (99.9% pure) as follows:

1. 50° C. to 250° C. at a ramp rate of 13.3° C./min

2. 250° C. to 660° C. at a ramp rate of 3.85° C./min

3. 660° C. to 675° C. at a ramp rate of 0.25° C./min

4. Soak for 2 hours at 675° C.

The resulting CMS fibers tested by the methods described in Example 4. The CMS fibers were tested using a mixed gas feed containing 50 mol % CO2 and 50 mol % CH₄ at a pressure of 200 psi (pounds per square inch). The temperature was maintained at 35° C. The permeance of CO2 through the CMS fibers was measured to be about 607 GPU. The CO2/CH4 selectivity was determined to be about 18.

Example 14

The precursor fiber of Example 10 was used to coat with 6FDA/BPDA-DAM at the same conditions as in Example 1, but the relative humidity was controlled at 10%. 3 wt. % 6FDA/BPDA-DAM coated precursor fibers of Example 10 were placed on a stainless-steel wire mesh and held in place by wrapping a length of wire around the mesh and fibers. The mesh support containing the fibers was then loaded to a pyrolysis setup. Pyrolysis was performed under an atmosphere of ultra-high purity argon (99.9% pure) as follows:

1. 50° C. to 250° C. at a ramp rate of 13.3° C./min

2. 250° C. to 660° C. at a ramp rate of 3.85° C./min

3. 660° C. to 675° C. at a ramp rate of 0.25° C./min

4. Soak for 2 hours at 675° C.

The resulting CMS fibers were tested by the methods described in Example 4. The CMS fibers were tested using a mixed gas feed containing 50 mol % CO2 and 50 mol % CH₄ at a pressure of 200 psi (pounds per square inch). The temperature was maintained at 35° C. The permeance of CO2 through the CMS fibers was measured to be about 267 GPU. The CO2/CH4 selectivity was determined to be about 31.

Example 15

The precursor fiber of Example 10 was used to coat with 6FDA/BPDA-DAM at the same conditions as in Example 1, but the relative humidity was controlled at 10%. 4 wt. % 6FDA/BPDA-DAM coated precursor fibers of Example 10 were placed on a stainless-steel wire mesh and held in place by wrapping a length of wire around the mesh and fibers. The mesh support containing the fibers was then loaded to a pyrolysis setup. Pyrolysis was performed under an atmosphere of ultra-high purity argon (99.9% pure) as follows:

1. 50° C. to 250° C. at a ramp rate of 13.3° C./min

2. 250° C. to 660° C. at a ramp rate of 3.85° C./min

3. 660° C. to 675° C. at a ramp rate of 0.25° C./min

4. Soak for 2 hours at 675° C.

The resulting CMS fibers were tested by the methods described in Example 4. The CMS fibers were tested using a mixed gas feed containing 50 mol % CO2 and 50 mol % CH₄ at a pressure of 200 psi (pounds per square inch). The temperature was maintained at 35° C. The permeance of CO2 through the CMS fibers was measured to be about 200 GPU. The CO2/CH4 selectivity was determined to be about 58.

Example 16

1. 50° C. to 250° C. at a ramp rate of 13.3° C./min

2. 250° C. to 530° C. at a ramp rate of 3.85° C./min

3. 530° C. to 550° C. at a ramp rate of 0.25° C./min

4. Soak for 2 hours at 550° C.

The resulting CMS fibers were tested by the methods described in Example 4. The CMS fibers were tested using a mixed gas feed containing 50 mol % CO2 and 50 mol % CH₄ at a pressure of 200 psi (pounds per square inch). The temperature was maintained at 35° C. The permeance of CO2 through the CMS fibers was measured to be about 455 GPU. The CO2/CH4 selectivity was determined to be about 34.

Example 17

1. 50° C. to 250° C. at a ramp rate of 13.3° C./min

2. 250° C. to 785° C. at a ramp rate of 3.85° C./min

3. 785° C. to 800° C. at a ramp rate of 0.25° C./min

4. Soak for 2 hours at 800° C.

The resulting CMS fibers were tested by the methods described in Example 4. The CMS fibers were tested using a mixed gas feed containing 50 mol % CO2 and 50 mol % CH₄ at a pressure of 200 psi (pounds per square inch). The temperature was maintained at 35° C. The permeance of CO2 through the CMS fibers was measured to be about 189 GPU. The CO2/CH4 selectivity was determined to be about 81.

The coating conditions and testing results of the above Examples are summarized in Table 5, Table 6, and Table 7.

TABLE 5

Example Content and Preparation of the Example

1 CMS of 4 wt. % 6FDA/BPDA-DAM coated P84®/ (PVP + P84®) with 65% Relative

Humidity, Example 4 (Pyrolysis Temperature 550° C)

2 CMS of 4 wt. % 6FDA/BPDA-DAM coated P84®/ (PVP + P84®) with 65% Relative Humidity, Example 5 (Pyrolysis Temperature 675° C)

CMS of 4 wt. % 6FDA/BPDA-DAM coated P84®/ (PVP + P84® ) with 65% Relative

Humidity, Example 6 (Pyrolysis Temperature 800° C)

CMS of 2 wt. % 6FDA/BPDA-DAM coated P84®/ (PVP + P84® ) with 10% Relative

Humidity, Example 8 (Pyrolysis Temperature 675° C)

CMS of 2 wt. % 6FDA/BPDA-DAM coated P84®/ (PVP + P84® ) with 10% Relative

Humidity, Example 9 (Pyrolysis Temperature 550° C)

CMS of 4 wt. % 6FDA/BPDA-DAM coated P84®/ (SiC-2 + P84® ) with 65% Relative

Humidity, Example 11 (Pyrolysis Temperature 675° C)

CMS of 4 wt. % 6FDA/BPDA-DAM coated P84®/ (SiC-2 + P84® ) with 65% Relative

Humidity, Example 12 (Pyrolysis Temperature 800° C)

CMS of 2 wt. % 6FDA/BPDA-DAM coated P84®/ (SiC-2 + P84® ) with 10% Relative

Humidity, Example 13 (Pyrolysis Temperature 675° C)

CMS of 3 wt. % 6FDA/BPDA-DAM coated P84®/ (SiC-2 + P84® ) with 10% Relative

Humidity, Example 14 (Pyrolysis Temperature 675° C)

CMS of 4 wt. % 6FDA/BPDA-DAM coated P84®/ (SiC-2 + P84® ) with 10% Relative

Humidity, Example 15 (Pyrolysis Temperature 675° C)

CMS of 4 wt. % 6FDA/BPDA-DAM coated P84®/ (SiC-2 + P84® ) with 10% Relative

Humidity, Example 16 (Pyrolysis Temperature 550° C)

CMS of 4 wt. % 6FDA/BPDA-DAM coated P84®/ (SiC-2 + P84® ) with 10% Relative Humidity, Example 17 (Pyrolysis Temperature 800° C)

TABLE 6

TABLE 7

As demonstrated by the above Examples, polymer coated precursor fiber can be used to create highly attractive CMS membranes with proper selection of the concentration of the polymer solution, relative humidity of the coating atmosphere and the pyrolysis temperature. In various embodiments, the nanoparticle free precursor fiber coated under high relative humidity can create CMS membrane (Example 3) that is at least 200% CO2 permeance increase over CMS membrane (Example 4) obtained from a precursor coated with low relative humidity. In various embodiments, the nanoparticle-free precursor fiber coated with high relative humidity could create CMS membrane (Example 3) that is at least 200% selectivity increase over a CMS membrane (Example 7) that obtained from nanoparticle- containing precursor fiber. In various embodiments, the higher pyrolysis temperature could increase the selectivity dramatically compared with low pyrolysis temperature. For example, by coating the nanoparticle free precursor fibers at high relative humidity, the selectivity of the resultant CMS membrane increased from 10 to 58 and 87 (Example 1 to Example 2 and 3) when the pyrolysis temperature increased from 550° C to 800° C. In various embodiments, the higher pyrolysis temperature could decrease the permeance compared with low pyrolysis temperature. There is a similar trend for the nanoparticle-containing precursor fiber, the selectivity of the resultant CMS membrane increased from 34 to 81 (Example 11 to Example 12) when the pyrolysis temperature increased from 550° C to 800° C. In various embodiments, the concentration of the coating polymer solution is crucial to get high selectivity CMS membrane with good permeance for the nanoparticle-containing precursor fibers. There is a critical concentration to get CMS membrane with high selectivity and permeance. For example, the selectivity increased from 18 to 31 and 58 (Example 8 to Example 9 and 10) when the coating polymer solution concentration increased from 2% to 3% and 4%.

Although the above examples show the manner in which coating precursor fiber with different polymer concentration and relative humidity prior to pyrolysis with different temperature to obtain a CMS hollow fiber membrane having properties that are desirable for the separation of CO2 and CH4, it will be understood by a person of ordinary skill in the art that by testing CMS hollow fiber membranes prepared using coating and pyrolysis temperatures for the separation of any gas stream, one may readily determine the coating condition and the pyrolysis temperature that produces a CMS hollow fiber membrane that is particularly desirable for separation of any gas stream.

The described embodiments provide unique and novel treatment processes, polymeric hollow precursor fibers, asymmetric multilayer CMS hollow fiber membranes, methods of making the asymmetric multilayer CMS hollow fiber membranes, and methods of using the membranes that have a number of advantages over those in the art. While there is shown and described herein certain specific structures embodying the invention, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims.

Also, in describing the exemplary embodiments, specific terminology will be resorted to for the sake of clarity. It must also be noted that, as used in the specification and the appended claims, the singular forms "a," "an" and "the" include plural references unless the context clearly dictates otherwise. For example, reference to a component is intended also to include composition of a plurality of components. References to a composition containing "a" constituent is intended to include other constituents in addition to the one named.

Also, in describing the exemplary embodiments, terminology will be resorted to for the sake of clarity. It is intended that each term contemplates its broadest meaning as understood by those skilled in the art and includes all technical equivalents that operate in a similar manner to accomplish a similar purpose.

As used herein, "substantially free" of something, or "substantially pure", and like characterizations, can include both being "at least substantially free" of something, or "at least substantially pure", and being "completely free" of something, or "completely pure." By comprising" or "containing" or "including" is meant that at least the named compound, element, particle, or method step is present in the composition or article or method, but does not exclude the presence of other compounds, materials, particles, method steps, even if the other such compounds, material, particles, method steps have the same function as what is named.

It is also to be understood that the mention of one or more method steps does not preclude the presence of additional method steps or intervening method steps between those steps expressly identified. Similarly, it is also to be understood that the mention of one or more components in a composition does not preclude the presence of additional components than those expressly identified.

The materials described as making up the various elements of the present invention are intended to be illustrative and not restrictive. Many suitable materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of the present invention. Such other materials not described herein can include, but are not limited to, for example, materials that are developed after the time of the development of the present invention.

Numerous characteristics and advantages have been set forth in the foregoing description, together with details of structure and function. While the invention has been disclosed in several forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions, especially in matters of shape, size, and arrangement of parts, can be made therein without departing from the spirit and scope of the invention and its equivalents as set forth in the following claims. Therefore, other modifications or embodiments as may be suggested by the teachings herein are particularly reserved as they fall within the breadth and scope of the claims here appended.

Claims

CLAIMS What is claimed is:

1. A polymeric hollow fiber comprising:

a. a support layer comprising

a core layer comprising a first polymer and

a sheath layer comprising a second polymer; and

b. a skin layer comprising a third polymer;

wherein the core layer, the sheath layer, and the skin layer have substantially annular cross-sections with the sheath layer adjacent to and radially outward from the core layer and the skin layer adjacent to and radially outward from the sheath layer, and

wherein the core layer further comprises at least one of a silane or a plurality of nanoparticles.

2. The polymeric hollow fiber of claim 1, wherein the skin layer comprises a high- performance polymer.

3. The polymeric hollow fiber of claim 2, wherein the skin layer comprises one or more of 6FDA/BPDA-DAM, 6FDA-6FpDA, 6FD A-DETD A : D ABE, 6FDA-DETDA:DABA, 6FDA-BPDA/DAM:DABA, BTDA-DAPI, or 6FDA/BTDA-DAM.

4. The polymeric hollow fiber of any one of claims 1-3, wherein the first polymer comprises one or more of a polyvinylidene chloride, a polyacrylonitrile, a polyvinyl chloride, a polyvinylidene difluoride, a polyimide, a polyetherimide, a polysulfone, or a polyethersulfone.

5. The polymeric hollow fiber of any one of claims 1 -4, wherein the second polymer comprises one or more of polyvinylidene chloride, polyacrylonitrile, a polyvinyl chloride, a polyvinylidene difluoride, a polyimide, a polyetherimide, a polysulfone, or a polyethersulfone.

6. The polymeric hollow fiber of any one of claims 1-5, wherein the core layer and the sheath layer do not comprise a high performance polymer.

7. The polymeric hollow fiber of any one of claims 1-6, wherein the core layer comprises a plurality of nanoparticles, and wherein the plurality of nanoparticles are hydrophobic.

8. The polymeric hollow fiber of any one of claims 1-7, wherein the core layer comprises a plurality of nanoparticles, and wherein the plurality of nanoparticles are polyhedral oligomeric silsesquioxane ("POSS") silica nanoparticles.

9. The polymeric hollow fiber of any one of claims 1-8, wherein the core layer comprises a plurality of nanoparticles, and wherein the core layer comprises 2 to 30 wt% nanoparticles, based on the weight of the core layer.

10. The polymeric hollow fiber of any one of claims 1-9, wherein the support layer comprises 90 to 98 wt% of the total weight of the polymeric hollow fiber.

11. The polymeric hollow fiber of any one of claims 1-10, wherein the support layer has a radial thickness of 100 to 500 micrometers.

12. The polymeric hollow fiber of any one of claims 1-11, wherein the skin layer has a radial thickness of 0.05 to 2.0 micrometers.

13. A carbon molecular sieve (CMS) hollow fiber membrane comprising:

a. a support layer comprising

a core layer comprising a pyrolyzed first polymer and a sheath layer comprising a pyrolyzed second polymer; and

b. a skin layer comprising a pyrolyzed third polymer,

wherein the CMS hollow fiber membrane has a C0₂:CH4 selectivity of greater than

20.

14. The CMS hollow fiber membrane of claim 13, wherein the core layer further comprises a silane.

15. The CMS hollow fiber membrane of claim 13 or claim 14, wherein the core layer further comprises a plurality of nanoparticles.

16. The CMS hollow fiber membrane of claim 15, wherein the plurality of nanoparticles are hydrophobic.

17. The CMS hollow fiber membrane of claim 15 or claim 16, wherein the core layer comprises 25 to 40 wt% nanoparticles based on weight of the core layer.

18. The CMS hollow fiber membrane of any one of claims 13-17, wherein the CMS hollow fiber membrane has a C0₂:CH4 selectivity of greater than 40.

19. The CMS hollow fiber membrane of any one of claims 13-18, wherein the CMS hollow fiber membrane has a C0₂:CH₄ selectivity of greater than 75.

20. The CMS hollow fiber membrane of any one of claims 13-19, wherein the CMS hollow fiber membrane has a C0₂ permeance of greater than 200 GPU.

21. The CMS hollow fiber membrane of any one of claims 13-20, wherein the third polymer comprises a high-performance polymer.

22. The CMS hollow fiber membrane of any one of claims 13-21, wherein the third polymer comprises one or more of 6FDA/BPDA-DAM, 6FDA-6FpDA, 6FDA- DETDA:DABE, 6FDA-DETDA:DABA, 6FDA-BPDA/DAM:DABA, BTDA-DAPI, or 6FDA/BTDA-DAM.

23. The CMS hollow fiber membrane of any one of claims 13-22, wherein the first and the second polymer independently comprise one or more of a polyvinylidene chloride, a polyacrylonitrile, a polyvinyl chloride, a polyvinylidene difluoride, a polyimide, a polyetherimide, a polysulfone, or a polyethersulfone.

24. The CMS hollow fiber membrane of any one of claims 13-23, wherein the core layer and the sheath layer do not comprise a high performance polymer.

25. The CMS hollow fiber membrane of any one of claims 13-24, wherein the skin layer has a radial thickness of from 0.05 to 2.0 micrometers.

26. A process for preparing a CMS hollow fiber membrane, comprising:

pyrolyzing a coated precursor fiber to form a CMS hollow fiber membrane, wherein the coated precursor fiber comprises

a polymeric fiber comprising a core layer comprising a first polymer and

optionally a sheath layer comprising a second polymer; and

a skin layer comprising a third polymer.

27. The process of claim 26, further comprising coating the polymeric fiber with the third polymer to produce the coated precursor fiber.

28. The process of claim 26 or claim 27, further comprising extruding a core dope, and when the optional sheath layer is present co-extruding a sheath dope with the core dope, through a spinneret to produce the polymeric fiber,

wherein the core dope comprises a first polymer and a first solvent, and when present the sheath dope comprises a second polymer and a second solvent.

29. The process of any one of claims 26-28, wherein the core layer further comprises a plurality of nanoparticles.

30. The process of claim 29, wherein the plurality of nanoparticles are hydrophobic.

31. The process of claim 29 or claim 30, wherein the plurality of nanoparticles are polyhedral oligomeric silsesquioxane ("POSS") silica nanoparticles.

32. The process of any one of claims 26-31, wherein the process further comprises contacting the coated precursor fiber with a modifying agent before the pyrolyzing step.

33. The process of claim 32, wherein the modifying agent comprises a silane.

34. The process of claim 33, wherein the modifiying agent comprises vinyltrimethoxysilane or vinyltriethoxysilane.

35. The process of any one of claims 26-34, wherein the third polymer comprises a high- performance polymer.

36. The process of any one of claims 26-35, wherein the third polymer comprises one or more of 6FDA/BPDA-DAM, 6FDA-6FpDA, 6FDA-DETDA:DABE, 6FDA- DETDA:DABA, 6FDA-BPDA/DAM:DABA, BTDA-DAPI, or 6FDA/BTDA-DAM.

37. The process of any one of claims 26-36, wherein the first polymer and the second polymer independently comprise one or more of a polyvinylidene chloride, a polyacrylonitrile, a polyvinyl chloride, a polyvinylidene difluoride, a polyimide, a polyetherimide, a polysulfone, or a polyethersulfone.

38. The process of any one of claims 26-37, wherein the core layer and the sheath layer do not comprise a high-performance polymer.

39. The process of claim 27, wherein the coating step is conducted at a relative humidity of between 5% and 85%.

40. The process of claim 27, wherein the coating step is conducted at a relative humidity of between 5% and 40%.

41. The process of claim 27, wherein the coating step is conducted at a relative humidity of between 50 and 85%.

42. The process of any one of claims 26-41, wherein the pyrolyzing step is conducted at a temperature of at least 550 °C.

43. The process of any one of claims 26-42, wherein the pyrolyzing step is conducted at a temperature of at least 675 °C.

44. The process of any one of claims 26-43, wherein the pyrolyzing step is conducted at a temperature of at least 800 °C.

45. A process for separating a mixture of at least two gases comprising contacting a mixture of at least two gases with a CMS hollow fiber membrane of any one of claims 13-25 or a CMS hollow fiber membrane produced by the process of any of claims 26-44 to separate the mixture into a permeate stream that is enriched in a first gas and a retentate stream that is enriched in a second gas.

46. The process of claim 45, wherein the mixture of at least two gases comprises CO2 and CH₄; H2S and CH₄; CO2, H2S, and CH₄; CO2 and N2; O2 and N2; N2 and CH₄; He and CH₄; He and N2; He and SF₆; H2 and C¾; H2 and C2H4; ethylene and ethane; propylene and propane; or ethane/propane and ethyl ene/propylene.

47. The process of claim 45 or claim 46, wherein the mixture of at least two gases comprises a natural gas comprising at least one acid gas and at least one hydrocarbon gas, wherein the permeate stream is enriched in the at least one acid gas, and wherein the retentate stream is enriched in the at least one hydrocarbon gas.

48. The process of claim 47, wherein the at least one acid gas comprises CO2.

49. The process of claim 47 or claim 48, wherein the at least one hydrocarbon gas comprises CH4, and wherein the process has a C0₂:CH₄ selectivity of greater than 40.