CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application is a PCT application claiming priority to U.S. Provisional

Patent Application No. 63/224,047, filed July 21, 2021, the entire disclosure of which is hereby incorporated herein by reference.

TECHNICAL FIELD

[0002] Embodiments of the present disclosure generally relate to hollow fiber carbon molecular sieve (CMS) membranes for use in gas separation, and in particular, a polyimide derived hollow fiber CMS membranes with reverse selectivity.

BACKGROUND

[0003] Membranes are widely used for the separation of gases and liquids, including for example, separating acid gases, such as CO2 and H2S from natural gas, and the removal of O2 from air. Gas transport through such membranes is commonly modeled by the sorption-diffusion mechanism. Currently, polymeric membranes are well studied and widely available for gaseous separations due to easy processability and low cost. CMS membranes, however, have been shown to have attractive separation performance properties exceeding that of polymeric membranes.

[0004] CMS membranes are typically produced through thermal pyrolysis of polymer precursors. For example, it is known that defect-free hollow fiber CMS membranes can be produced by pyrolyzing cellulose hollow fibers. In addition, many other polymers have been used to produce CMS membranes in fiber and dense film form, among which polyimides have been favored. Polyimides have a high glass transition temperature, are easy to process, and perform better than most other polymeric membranes, even prior to pyrolysis.

[0005] CMS membrane separation properties are primarily affected by the following factors: (1) pyrolysis precursor, (2) pyrolysis temperature, (3) thermal soak time, and (4) pyrolysis atmosphere. For example, increases in both temperature and thermal soak time have been shown to increase the selectivity but decrease permeance for CO2/CH4 separation. In addition, a precursor polymer with a rigid, tightly packed structure tends to lead to a CMS membrane having higher selectivity compared with less rigid precursor polymers. The impact of pyrolysis atmosphere gas has not been studied in great detail, nor have the long term use of the CMS membranes and the stability of the membranes with respect to maintaining the permeance and selectivity for particular gas molecules of interest.

SUMMARY

[0006] One type of separation application in which CMS membranes may find utility is olefin-paraffin separation. In olefin-paraffin separations, it is necessary to separate olefins from paraffins and lighter gases, such as Eh, CO2, and CH4. New CMS membranes and methods of making these CMS membranes are needed.

[0007] According to aspects, an article includes an asymmetric hollow fiber carbon molecular sieve (CMS) membrane. The hollow fiber CMS membrane is made by a method comprising: heating a polymeric precursor to a pyrolysis temperature that is greater than or equal to 500 °C and less than or equal to 1200 °C; pyrolyzing the polymeric precursor at the pyrolysis temperature, thereby forming a pyrolyzed polymeric membrane; exposing the pyrolyzed polymeric membrane to an atmosphere comprising greater than or equal to 50 ppm oxidant; and cooling the pyrolyzed polymeric membrane to a cooling temperature that is less than or equal to 50 °C. The exposing and the cooling are performed sequentially or simultaneously, thereby forming the hollow fiber CMS membrane. The hollow fiber CMS membrane has a permeate/retentate selectivity greater than or equal to 5 and a permeate permeability greater than or equal to 50 GPU when measured while separating an analyte stream comprising the permeate and the retentate at a temperature that is greater than or equal to 20 °C and less than or equal to 30 °C.

[0008] According to aspects, an article includes an asymmetric hollow fiber carbon molecular sieve (CMS) membrane. The hollow fiber CMS membrane comprises a pyrolyzed and oxidized polyimide membrane. The hollow fiber CMS membrane has a permeate/retentate selectivity greater than or equal to 10 and a permeate permeability greater than or equal to 100 GPU when measured while separating an analyte stream comprising the permeate and the retentate at a temperature that is greater than or equal to 20 °C and less than or equal to 30 °C. The permeate is C2H4 and the retentate is ¾.

[0009] According to aspects, a method for separating hydrogen from a gas feed, the gas feed comprising at least one retentate and at least one other gas molecule includes flowing the gas feed through the article of any other aspect. The retentate is selected from the group consisting of hydrogen, nitrogen, and a mixture of hydrogen and nitrogen. The retentate is retained by the article and a product stream comprising the other gas molecule is produced.

[0010] It is to be understood that both the foregoing brief summary and the following detailed description present embodiments of the technology, and are intended to provide an overview or framework for understanding the nature and character of the technology as it is claimed. The accompanying drawings are included to provide a further understanding of the technology, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments and, together with the description, serve to explain the principles and operations of the technology. Additionally, the drawings and descriptions are meant to be merely illustrative, and are not intended to limit the scope of the claims in any manner.

[0011] Additional features and advantages of the described embodiments will be set forth in the detailed description that follows. The additional features and advantages of the described embodiments will be, in part, readily apparent to those skilled in the art from that description or recognized by practicing the described embodiments, including the detailed description that follows as well as the drawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:

[0013] FIGURE (FIG.) 1 provides a schematic of a system for pyrolysis and oxidation of a hollow fiber CMS membrane in accordance with embodiments described herein; and [0014] FIG. 2 is a chart of temperature on the x-axis and simulated O2 concentration on the y-axis for use with embodiments described herein.

DETAILED DESCRIPTION

[0015] According to one or more embodiments described herein, an article comprises an asymmetric hollow fiber CMS membrane.

[0016] In embodiments, the hollow fiber CMS membrane may be made by a method comprising: heating a polymeric precursor to a pyrolysis temperature that is greater than or equal to 500 °C and less than or equal to 1200 °C; pyrolyzing the polymeric precursor at the pyrolysis temperature, thereby forming a pyrolyzed polymeric membrane; exposing the pyrolyzed polymeric membrane to an atmosphere comprising greater than or equal to 50 ppm oxidant; and cooling the pyrolyzed polymeric membrane to a cooling temperature that is less than or equal to 50 °C. The exposing and the cooling are performed sequentially or simultaneously, thereby forming the hollow fiber CMS membrane.

[0017] The polymeric precursor may be any useful polymer for making hollow fiber CMS membranes, such as polyimides for example. When a polyimide is used, the polyimide may be a conventional or fluorinated polyimide. In embodiments, the polymeric precursor may comprise a polymer comprising monomers Ac, Bg, and Cz, where X, Y, and Z are the mole fraction of each of A, B, and C, respectively, present in the polymer. In embodiments, X + Y + Z = l. In other embodiments, X + Y + Z < 1 , and other monomers are present in the polymer.

[0018] Each of A, B, and C is a monomer selected from the group consisting of 2, 4,6- trimethyl- 1,3 -phenylene diamine (DAM); oxydianaline (ODA); dimethyl-3, 7-diaminodiphenyl- thiophene-5,5'-dioxide (DDBT); 3,5-diaminobenzoic acid (DABA); 2.3,5,6-tetramethyl-l,4- phenylene diamine (durene); meta-phenylenediamine (m-PDA); 2,4-diaminotolune (2,4-DAT); tetramethylmethylenedianaline (TMMDA); 4,4'-diamino-2,2'-biphenyl disulfonic acid (BDSA); 5,5'-[2,2,2-trifluoro-l-(trifluoromethyl)ethylidene]-l,3-iso benzofurandion (6FDA); 3,3 ',4,4'- biphenyl tetracarboxylic dianhydride (BPDA); pyromellitic dianhydride (PMDA); 1,4,5,8- naphthalene tetracarboxylic dianhydride (NTDA); 4,4'-oxydiphthalic anhydride (ODPA); 5(6)- amino-l-(4’-aminophenyl)-l,3,3-trimethylindane (DAPI); and 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA). In embodiments, polyimides may contain at least two different moieties selected from DAM; ODA; DDBT; DAB A; durene; m-PDA; 2,4-DAT; TMMDA; BDSA; 6FDA; BPDA; PMDA; NTDA; and BTDA.

[0019] In embodiments, A is a monomer selected from the group consisting of 6FDA,

ODPA, and BTDA; B is DAM; and C is a monomer selected from the group consisting of BPDA and PMDA. In embodiments, A is 6FDA; B is DAM; and Z is 0. In embodiments, the polyimide may be MATRIMID™ 5218 (Huntsman Advanced Materials), a commercially available polyimide in which A is BTDA; B is DAPI; and Z is 0.

[0020] In embodiments, the polyimide may comprise, consist essentially of, or consist of

6FDA/BPDA-DAM, as shown in formula (1), which may be synthesized via thermal or chemical processes from a combination of three commercially available monomers: DAM; 6FDA, and BPDA. In embodiments of formula (1), X + Y may be from 0.1 to 0.9, and Z may be from 0.1 to 0.9. In embodiments of formula (1), X + Y may be from 0.1 to 1, and Z may be from 0 to 0.9. In embodiments of formula (1), X may be 0 and Y + Z may be 1. In embodiments, X and Z may be from 0.25, 0.3, or 0.4 to 0.9, 0.8, or 0.75. In embodiments, X + Y is 0.5 and Z is 0.5. Formula (2) below shows a representative structure for 6FDA/BPDA-DAM, with a potential for adjusting the ratio between X and Z to tune polymer properties. In embodiments, a 1 : 1 ratio of X to Z may also abbreviated as 6FDA/BPDA(1:1)-DAM. [0021] In embodiments, the polyimide may be formed by the reaction of a diamine with a dianhydride. In such embodiments, at least one of A, B, and C, is a diamine, and at least one other of A, B, and C, is a dianhydride. In embodiments, the total diamine and the total dianhydride may be in a molar ratio of diamine to dianhydride of greater than or equal to 49:51 to 51:49. In embodiments, the diamine and dianhydride may be in a molar ratio of diamine to dianhydride of about 50:50.

[0022] In embodiments, more than one dianhydride may be used with one diamine. In such embodiments using two dianhydrides, dianhydride 1 and dianhydride 2, the molar ratio of dianhydride 1 to dianhydride 2 may be greater than or equal to 20:80 and less than or equal to 80:20. For example, this molar ratio may be greater than or equal to 25:75 and less than or equal to 75:25, greater than or equal to 30:70 and less than or equal to 70:30, greater than or equal to 35:65 and less than or equal to 65:35, greater than or equal to 40:60 and less than or equal to 60:40, or even greater than or equal to 45:55 and less than or equal to 55:45. In embodiments, the molar ratio of dianhydride 1 to dianhydride 2 may be about 50:50. In embodiments, one dianhydride may be used with more than one diamines. In such embodiments using two diamines, diamine 1 and diamine 2, the molar ratio of diamine 1 to diamine 2 may be greater than or equal to 20:80 and less than or equal to 80:20. For example, this molar ratio may be greater than or equal to 25:75 and less than or equal to 75:25, greater than or equal to 30:70 and less than or equal to 70:30, greater than or equal to 35:65 and less than or equal to 65:35, greater than or equal to 40:60 and less than or equal to 60:40, or even greater than or equal to 45:55 and less than or equal to 55:45. In embodiments, the molar ratio of diamine 1 to diamine 2 may be about 50:50.

[0023] In embodiments, the polymeric precursor membranes as produced, but not pyrolyzed, are substantially defect-free. “Defect-free” means that selectivity of a gas pair through a hollow fiber membrane is at least 90 percent of the selectivity for the same gas pair through a dense film prepared from the same composition as that used to make the polymeric precur membrane. By way of illustration, a 6FDA/BPDA(1:1)-DAM polymer has an O2/N2 selectivity (also known as “dense film selectivity”) of 4.1.

[0024] In embodiments, the precursor polymers may be formed into hollow fibers or films.

Conventional procedures to make these may be used. For example, coextrusion procedures including a dry -jet wet spinning process (in which an air gap exists between the tip of the spinneret and the coagulation or quench bath) or a wet spinning process (with zero air-gap distance) may be used to make hollow fibers.

[0025] In embodiments, the hollow fiber CMS membrane may be asymmetric. As used herein, the term “asymmetric” referes to a property of the hollow fiber CMS membrane in which the hollow fiber CMS membrane has at least one relatively more dense layer and at least one relatively less dense layer. For instance, in embodiments, one layer of the hollow fiber CMS membrane may be greater than or equal to 1 pm and less than or equal to 10 pm and be more dense than a second layer. The second layer may be thicker than the first layer, such as greater than or equal to 20 pm and less than or equal to 200 pm. In embodiments, the asymmetric membrane may be an entity composed of an extremely thin, dense skin over a thick porous substructure, which may be of the same or different material as that of the dense skin layer. In embodiments, the asymmetric membrane may be fabricated in a single step by phase inversion, or the thin layer may be coated on the pre-prepared porous support using a dip coating method. These layers in the asymmetric membranes may be created physically by coating or created by chemical modification. The asymmetric membrane may be in the form of a hollow fiber configuration or a film configuration. In embodiments, the asymmetric membrane may contain a third layer of the same or different material as needed to enhance the membrane performance.

[0026] Pyrolysis conditions influence hollow fiber CMS membrane physical properties.

Any suitable supporting means for holding the hollow fiber CMS membranes may be used during the pyrolysis including sandwiching between two metallic wire meshes or using a stainless steel mesh plate in combination with stainless steel wires and as described by US Pat. No. 8,709,133 at col. 6, line 58 to col. 7, line 4, which is incorporated by reference. [0027] Precursor polymers may be pyrolyzed to form the hollow fiber CMS membranes

(i.e., carbonize the precursor polymer) under various inert gas purge or vacuum conditions (e.g. a a pressure less than or equal to 0.1 millibar). U.S. Pat. No. 6,565,631 describes a heating method for pyrolysis of polymeric fibers to form hollow fiber CMS membranes, and is incorporated herein by reference. For either polymeric films or fibers, the pyrolysis temperature may be greater than or equal to 500 °C and less than or equal to 1200 °C. The pyrolysis temperature may be adjusted in combination with the pyrolysis atmosphere to tune the performance properties of the resulting hollow fiber CMS membrane. For example, the pyrolysis temperature may be 1000 °C or more. Optionally, the pyrolysis temperature may be greater than or equal to 900 °C and less than or equal to 1000 °C. In embodiments, the pyrolysis temperature may be greater than or equal to 550 °C and less than or equal to 1200 °C, greater than or equal to 600 °C and less than or equal to 1200 °C, greater than or equal to 650 °C and less than or equal to 1200 °C, greater than or equal to 700 °C and less than or equal to 1200 °C, greater than or equal to 750 °C and less than or equal to 1200 °C, greater than or equal to 800 °C and less than or equal to 1200 °C, greater than or equal to 850 °C and less than or equal to 1200 °C, greater than or equal to 900 °C and less than or equal to 1200 °C, greater than or equal to 950 °C and less than or equal to 1200 °C, greater than or equal to 1000 °C and less than or equal to 1200 °C, greater than or equal to 1150 °C and less than or equal to 1200 °C, greater than or equal to 500 °C and less than or equal to 1150 °C, greater than or equal to 500 °C and less than or equal to 1100 °C, greater than or equal to 500 °C and less than or equal to 1050 °C, greater than or equal to 500 °C and less than or equal to 1000 °C, greater than or equal to 500 °C and less than or equal to 950 °C, greater than or equal to 500 °C and less than or equal to 900 °C, greater than or equal to 500 °C and less than or equal to 850 °C, greater than or equal to 500 °C and less than or equal to 800 °C, greater than or equal to 500 °C and less than or equal to 750 °C, greater than or equal to 500 °C and less than or equal to 700 °C, greater than or equal to 500 °C and less than or equal to 650 °C, greater than or equal to 500 °C and less than or equal to 600 °C, or even greater than or equal to 500 °C and less than or equal to 550 °C. It is envisioned that the range of acceptable pyrolysis temperatures may be greater than or equal to any of the temperatures described herein and less than or equal to any of the temperatures described herein.

[0028] The pyrolysis soak time (i.e., the duration of time at the pyrolysis temperature) may vary (and may include no soak time) but may be, for example, greater than or equal to 1 hour and less than or equal to 10 hours, greater than or equal to 2 hours and less than or equal to 8 hours, greater than or equal to 4 hours and less than or equal to 6 hours. An exemplary heating protocol may include: (1) starting at a first set point of about 50 °C; (2) heating to a second set point of about 250 °C at a rate of about 13.3 °C per minute; (3) heating to a third set point of about 535 °C at a rate of about 3.85 °C per minute; (4) heating to a fourth set point of about 550 °C to 700 °C at a rate of about 0.25 °C per minute. The fourth set point may then be maintained for the determined soak time.

[0029] As noted above, the precursor polymers may be pyrolyzed under various inert gas purge or vacuum conditions. In embodiments, the precursor polymers may be pyrolyzed under vacuum at low pressures (e.g. less than or equal to 0.1 millibar). In embodiments, the pyrolysis utilizes a controlled inert purge gas atmosphere. By way of example, an inert gas such as argon is used as the purge gas atmosphere. Other suitable inert gases include, but are not limited to, nitrogen, helium, or any combination thereof.

[0030] In embodiments, after the completion of the pyrolysis, during a cooling stage, using any suitable method such as a valve the inert gas containing a specific concentration of oxidant may be introduced into the pyrolysis chamber. The oxidant may be introduced in the presence or absence of the inert gas. For example, the amount of oxidant in the purge atmosphere may be greater than 0 ppm and less than or equal to 250 ppm. For example, the amount of oxidant may be greater than 0 ppm and less than or equal to 240 ppm, greater than 0 ppm and less than or equal to 230 ppm, greater than 0 ppm and less than or equal to 220 ppm, greater than 0 ppm and less than or equal to 210 ppm, greater than 0 ppm and less than or equal to 200 ppm, greater than 0 ppm and less than or equal to 190 ppm, greater than 0 ppm and less than or equal to 180 ppm, greater than 0 ppm and less than or equal to 170 ppm, greater than 0 ppm and less than or equal to 160 ppm, greater than 0 ppm and less than or equal to 150 ppm, greater than 0 ppm and less than or equal to 140 ppm, greater than 0 ppm and less than or equal to 130 ppm, greater than 0 ppm and less than or equal to 120 ppm, greater than 0 ppm and less than or equal to 110 ppm, greater than 0 ppm and less than or equal to 100 ppm, greater than 0 ppm and less than or equal to 90 ppm, greater than 0 ppm and less than or equal to 80 ppm, greater than 0 ppm and less than or equal to 70 ppm, greater than 0 ppm and less than or equal to 60 ppm, greater than 0 ppm and less than or equal to 50 ppm, greater than 0 ppm and less than or equal to 40 ppm, greater than 0 ppm and less than or equal to 30 ppm, greater than 0 ppm and less than or equal to 20 ppm, greater than 0 ppm and less than or equal to 10 ppm, greater than or equal to 10 ppm and less than or equal to 250 ppm, greater than or equal to 20 ppm and less than or equal to 250 ppm, greater than or equal to 30 ppm and less than or equal to 250 ppm, greater than or equal to 40 ppm and less than or equal to 250 ppm, greater than or equal to 50 ppm and less than or equal to 250 ppm, greater than or equal to 60 ppm and less than or equal to 250 ppm, greater than or equal to 70 ppm and less than or equal to 250 ppm, greater than or equal to 80 ppm and less than or equal to 250 ppm, greater than or equal to 90 ppm and less than or equal to 250 ppm, greater than or equal to 100 ppm and less than or equal to 250 ppm, greater than or equal to 110 ppm and less than or equal to 250 ppm, greater than or equal to 120 ppm and less than or equal to 250 ppm, greater than or equal to 130 ppm and less than or equal to 250 ppm, greater than or equal to 140 ppm and less than or equal to 250 ppm, greater than or equal to 150 ppm and less than or equal to 250 ppm, greater than or equal to 160 ppm and less than or equal to 250 ppm, greater than or equal to 170 ppm and less than or equal to 250 ppm, greater than or equal to 180 ppm and less than or equal to 250 ppm, greater than or equal to 190 ppm and less than or equal to 250 ppm, greater than or equal to 200 ppm and less than or equal to 250 ppm, greater than or equal to 210 ppm and less than or equal to 250 ppm, greater than or equal to 220 ppm and less than or equal to 250 ppm, greater than or equal to 230 ppm and less than or equal to 250 ppm, or even greater than or equal to 240 ppm and less than or equal to 250 ppm. It is envisioned that the range of acceptable concentration of oxidant in the pyrolysis purge gas atmosphere may be greater than or equal to any of the concentrations described herein, including 0 ppm, and less than or equal to any of the temperatures described herein.

[0031] In embodiments, the oxidant added to the purge gas atmosphere used in the pyrolysis may be selected from the group consisting of gaseous oxygen, CO2, CO, nitrogen oxide, ozone, hydrogen peroxide, steam, and air.

[0032] After pyrolysis and before fully cooling the pyrolyzed hollow fiber CMS membrane, the hollow fiber CMS membrane may be oxidized by exposing it to an atmosphere containing greater than or equal to 50 ppm and less than or equal to 40,000 ppm oxidant in the purge gas or another carrier gas. For instance, the concentration of oxidant in the purge gas or another carrier gas is greater than or equal to 1000 ppm and less than or equal to 40,000 ppm, greater than or equal to 2000 ppm and less than or equal to 40,000 ppm, greater than or equal to 3000 ppm and less than or equal to 40,000 ppm, greater than or equal to 4000 ppm and less than or equal to 40,000 ppm, greater than or equal to 5000 ppm and less than or equal to 40,000 ppm, greater than or equal to 6000 ppm and less than or equal to 40,000 ppm, greater than or equal to 7000 ppm and less than or equal to 40,000 ppm, greater than or equal to 8000 ppm and less than or equal to 40,000 ppm, greater than or equal to 9000 ppm and less than or equal to 40,000 ppm, greater than or equal to 10,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 11,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 12,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 13,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 14,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 15,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 16,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 17,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 18,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 19,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 20,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 21,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 22,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 23,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 24,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 25,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 26,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 27,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 28,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 29,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 30,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 31,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 32,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 33,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 34,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 35,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 36,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 37,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 38,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 39,000 ppm and less than or equal to 40,000 ppm, greater than or equal to 50 ppm and less than or equal to 39,000 ppm, greater than or equal to 50 ppm and less than or equal to 38,000 ppm, greater than or equal to 50 ppm and less than or equal to 37,000 ppm, greater than or equal to 50 ppm and less than or equal to 36,000 ppm, greater than or equal to 50 ppm and less than or equal to 35,000 ppm, greater than or equal to 50 ppm and less than or equal to 34,000 ppm, greater than or equal to 50 ppm and less than or equal to 33,000 ppm, greater than or equal to 50 ppm and less than or equal to 32,000 ppm, greater than or equal to 50 ppm and less than or equal to 31,000 ppm, greater than or equal to 50 ppm and less than or equal to 30,000 ppm, greater than or equal to 50 ppm and less than or equal to 29,000 ppm, greater than or equal to 50 ppm and less than or equal to 28,000 ppm, greater than or equal to 50 ppm and less than or equal to 27,000 ppm, greater than or equal to 50 ppm and less than or equal to 26,000 ppm, greater than or equal to 50 ppm and less than or equal to 25,000 ppm, greater than or equal to 50 ppm and less than or equal to 24,000 ppm, greater than or equal to 50 ppm and less than or equal to 23,000 ppm, greater than or equal to 50 ppm and less than or equal to 22,000 ppm, greater than or equal to 50 ppm and less than or equal to 21,000 ppm, greater than or equal to 50 ppm and less than or equal to 20,000 ppm, greater than or equal to 50 ppm and less than or equal to 19,000 ppm, greater than or equal to 50 ppm and less than or equal to 18,000 ppm, greater than or equal to 50 ppm and less than or equal to 17,000 ppm, greater than or equal to 50 ppm and less than or equal to 16,000 ppm, greater than or equal to 50 ppm and less than or equal to 15,000 ppm, greater than or equal to 50 ppm and less than or equal to 14,000 ppm, greater than or equal to 50 ppm and less than or equal to 13,000 ppm, greater than or equal to 50 ppm and less than or equal to 12,000 ppm, greater than or equal to 50 ppm and less than or equal to 11,000 ppm, greater than or equal to 50 ppm and less than or equal to 10,000 ppm, greater than or equal to 50 ppm and less than or equal to 9,000 ppm, greater than or equal to 50 ppm and less than or equal to 8,000 ppm, greater than or equal to 50 ppm and less than or equal to 7,000 ppm, greater than or equal to 50 ppm and less than or equal to 6,000 ppm, greater than or equal to 50 ppm and less than or equal to 5,000 ppm, greater than or equal to 50 ppm and less than or equal to 4,000 ppm, greater than or equal to 50 ppm and less than or equal to 3,000 ppm, greater than or equal to 50 ppm and less than or equal to 2,000 ppm, or even greater than or equal to 50 ppm and less than or equal to 1 ,000 ppm. In embodiments, the hollow fiber CMS membrane may be exposed to an atmosphere containing greater than or equal to 500 ppm oxidant in the carrier gas. In embodiments, the carrier gas is the same as the purge gas of the pyrolysis. In other embodiments, the carrier gas is not the same as the purge gas but may also be selected from inert gases such as argon, nitrogen, helium, or any combination thereof.

[0033] In embodiments, the flow of purge gas over the hollow fiber CMS membrane may be decreased while the flow of the mixture of oxidant and carrier gas is increased. The temperature at which the flow of the purge gas stops completely and the flow of the mixture of oxidant and carrier gas is at its maximum is referred to throughout as the “oxidant exposure temperature” or the “air exposure temperature” when the oxidant is air. The oxidant exposure temperature may be greater than or equal to 300 °C and less than or equal to 700 °C. For instance, the oxidant exposure temperature may be greater than or equal to 300 °C and less than or equal to 650°C, greater than or equal to 300 °C and less than or equal to 600 °C, greater than or equal to 300 °C and less than or equal to 550 °C, greater than or equal to 300 °C and less than or equal to 500 °C, greater than or equal to 300 °C and less than or equal to 450 °C, greater than or equal to 300 °C and less than or equal to 400 °C, greater than or equal to 350 °C and less than or equal to 700 °C, greater than or equal to 400 °C and less than or equal to 700 °C, greater than or equal to 450 °C and less than or equal to 700 °C, greater than or equal to 500 °C and less than or equal to 700 °C, greater than or equal to 550 °C and less than or equal to 700 °C, or even greater than or equal to 600 °C and less than or equal to 700 °C. It is envisioned that the range of acceptable oxidant exposure temperatures may be greater than or equal to any of the temperatures described herein and less than or equal to any of the temperatures described herein.

[0034] The hollow fiber CMS membrane may undergo oxidation for greater than or equal to 0.5 hours and less than or equal to 24 hours, greater than or equal to 1 hours and less than or equal to 24 hours, greater than or equal to 1.5 hours and less than or equal to 24 hours, greater than or equal to 2.5 hours and less than or equal to 24 hours, greater than or equal to 3.5 hours and less than or equal to 24 hours, greater than or equal to 4.5 hours and less than or equal to 24 hours, greater than or equal to 5.5 hours and less than or equal to 24 hours, greater than or equal to

6.5 hours and less than or equal to 24 hours, greater than or equal to 7.5 hours and less than or equal to 24 hours, greater than or equal to 8.5 hours and less than or equal to 24 hours, greater than or equal to 9.5 hours and less than or equal to 24 hours, greater than or equal to 10.5 hours and less than or equal to 24 hours, greater than or equal to 11.5 hours and less than or equal to 24 hours, greater than or equal to 12.5 hours and less than or equal to 24 hours, greater than or equal to 13.5 hours and less than or equal to 24 hours, greater than or equal to 14.5 hours and less than or equal to 24 hours, greater than or equal to 15.5 hours and less than or equal to 24 hours, greater than or equal to 16.5 hours and less than or equal to 24 hours, greater than or equal to

17.5 hours and less than or equal to 24 hours, greater than or equal to 18.5 hours and less than or equal to 24 hours, greater than or equal to 19.5 hours and less than or equal to 24 hours, greater than or equal to 20.5 hours and less than or equal to 24 hours, greater than or equal to 21.5 hours and less than or equal to 24 hours, greater than or equal to 22.5 hours and less than or equal to 24 hours, greater than or equal to 23.5 hours and less than or equal to 24 hours, greater than or equal to 0.5 hours and less than or equal to 23 hours, greater than or equal to 0.5 hours and less than or equal to 22 hours, greater than or equal to 0.5 hours and less than or equal to 21 hours, greater than or equal to 0.5 hours and less than or equal to 20 hours, greater than or equal to 0.5 hours and less than or equal to 19 hours, greater than or equal to 0.5 hours and less than or equal to 18 hours, greater than or equal to 0.5 hours and less than or equal to 17 hours, greater than or equal to 0.5 hours and less than or equal to 16 hours, greater than or equal to 0.5 hours and less than or equal to 15 hours, greater than or equal to 0.5 hours and less than or equal to 14 hours, greater than or equal to 0.5 hours and less than or equal to 13 hours, greater than or equal to 0.5 hours and less than or equal to 12 hours, greater than or equal to 0.5 hours and less than or equal to 11 hours, greater than or equal to 0.5 hours and less than or equal to 10 hours, greater than or equal to 0.5 hours and less than or equal to 9 hours, greater than or equal to 0.5 hours and less than or equal to 8 hours, greater than or equal to 0.5 hours and less than or equal to 7 hours, greater than or equal to 0.5 hours and less than or equal to 6 hours, greater than or equal to 0.5 hours and less than or equal to 5 hours, greater than or equal to 0.5 hours and less than or equal to 4 hours, greater than or equal to 0.5 hours and less than or equal to 3 hours, greater than or equal to 0.5 hours and less than or equal to 2 hours, or even greater than or equal to 0.5 hours and less than or equal to 1 hours.

[0035] Without intending to be bound by any particular theory, it is believed that oxidation of the hollow fiber CMS membrane enhances its ability to separate components of a mixture stream. This may be because the oxidation helps to create a porous suface and increases polarity of that surface. As a result, transport of larger gas molecules may be enhanced due to increased solubility and a pore blocking transport mechanism.

[0036] After oxidizing or while oxidizing, the hollow fiber CMS membrane that has formed is cooled to temperature near room temperature, such as less than or equal to 50 °C. The cooling may be at any useful rate, such as passively cooling (e.g., turning off the power to the furnace and allowing to cool naturally). Alternatively, it may be desirable to more rapidly cool such as by using known techniques to realize faster cooling. Known techniques include, but are not limited to, cooling fans or employment of water cooled jackets, purging with a gas having a lower temperature than the hollow fiber CMS membrane, or opening the furnace to the surrounding environment.

[0037] The gas permeation properties of a hollow fiber CMS membrane may be determined by gas permeation experiments. Two intrinsic properties have utility in evaluating separation performance of a membrane material: its “permeability,” a measure of the hollow fiber CMS membrane’s intrinsic productivity; and its “selectivity,” a measure of the hollow fiber CMS membrane’s separation efficiency. One typically determines “permeability” in Barrer (1 Barrer=10 ¹⁰ [cm ³ (STP) cm]/[cm ² s cmHg], calculated as the flux (h _έ ) divided by the partial pressure difference between the hollow fiber CMS membrane upstream and downstream (Dr,), and multiplied by the thickness of the hollow fiber CMS membrane (Z).

[0038] Another term, “permeance,” is defined herein as productivity of asymmetric hollow fiber membranes and is typically measured in Gas Permeation Units (GPU) (1 GPU = 1CT ⁶ [cm ³ (STP)]/[cm ² s cmHg]), determined by dividing permeability by effective membrane separation layer thickness.

[0039] Finally, “selectivity” is defined herein as the ability of one gas’s permeability through the hollow fiber CMS membrane or permeance relative to the same property of another gas. It is measured as a unitless ratio.

[0040] In embodiments, the hollow fiber CMS membrane, which has been pyrolyzed and oxidized, has a permeate/retentate selectivity of greater than or equal to 5, such greater than or equal to 5 and less than or equal to 100, greater than or equal to 10 and less than or equal to 100, greater than or equal to 15 and less than or equal to 100, greater than or equal to 20 and less than or equal to 100, greater than or equal to 25 and less than or equal to 100, greater than or equal to 30 and less than or equal to 100, greater than or equal to 35 and less than or equal to 100, greater than or equal to 40 and less than or equal to 100, greater than or equal to 45 and less than or equal to 100, greater than or equal to 50 and less than or equal to 100, greater than or equal to 55 and less than or equal to 100, greater than or equal to 60 and less than or equal to 100, greater than or equal to 65 and less than or equal to 100, greater than or equal to 70 and less than or equal to 100, greater than or equal to 75 and less than or equal to 100, greater than or equal to 80 and less than or equal to 100, greater than or equal to 85 and less than or equal to 100, greater than or equal to 90 and less than or equal to 100, greater than or equal to 5 and less than or equal to 95, greater than or equal to 5 and less than or equal to 90, such greater than or equal to 5 and less than or equal to 85, greater than or equal to 5 and less than or equal to 80, greater than or equal to 5 and less than or equal to 75, greater than or equal to 5 and less than or equal to 70, greater than or equal to 5 and less than or equal to 65, greater than or equal to 5 and less than or equal to 60, greater than or equal to 5 and less than or equal to 55, greater than or equal to 5 and less than or equal to 50, greater than or equal to 5 and less than or equal to 45, greater than or equal to 5 and less than or equal to 40, greater than or equal to 5 and less than or equal to 35, greater than or equal to 5 and less than or equal to 30, greater than or equal to 5 and less than or equal to 25, greater than or equal to 5 and less than or equal to 20, greater than or equal to 5 and less than or equal to 15, or even greater than or equal to 5 and less than or equal to 10. It is envisioned that the range of permeate/retentate selectivity may be greater than or equal to any of the selectivities described herein and less than or equal to any of the selectivities described herein.

[0041] In embodiments, the hollow fiber CMS membrane, which has been pyrolyzed and oxidized, has a permeate permeability of greater than or equal to 50 GPU when measured while separating an analyte stream comprising the permeate and the retentate at a temperature that is greater than or equal to 20 °C and less than or equal to 30 °C. For example, the permeate permeability may be greater than or equal to 50 GPU and less than or equal to 1500 GPU, greater than or equal to 100 GPU and less than or equal to 1500 GPU, greater than or equal to 150 GPU and less than or equal to 1500 GPU, greater than or equal to 200 GPU and less than or equal to 1500 GPU, greater than or equal to 250 GPU and less than or equal to 1500 GPU, greater than or equal to 300 GPU and less than or equal to 1500 GPU, greater than or equal to 350 GPU and less than or equal to 1500 GPU, greater than or equal to 400 GPU and less than or equal to 1500 GPU, greater than or equal to 450 GPU and less than or equal to 1500 GPU, greater than or equal to 500 GPU and less than or equal to 1500 GPU, greater than or equal to 550 GPU and less than or equal to 1500 GPU, greater than or equal to 600 GPU and less than or equal to 1500 GPU, greater than or equal to 650 GPU and less than or equal to 1500 GPU, greater than or equal to 700 GPU and less than or equal to 1500 GPU, greater than or equal to 750 GPU and less than or equal to 1500 GPU, greater than or equal to 800 GPU and less than or equal to 1500 GPU, greater than or equal to 850 GPU and less than or equal to 1500 GPU, greater than or equal to 900 GPU and less than or equal to 1500 GPU, greater than or equal to 950 GPU and less than or equal to 1500 GPU, greater than or equal to 1000 GPU and less than or equal to 1500 GPU, greater than or equal to 1050 GPU and less than or equal to 1500 GPU, greater than or equal to 1100 GPU and less than or equal to 1500 GPU, greater than or equal to 1150 GPU and less than or equal to 1500 GPU, greater than or equal to 1200 GPU and less than or equal to 1500 GPU, greater than or equal to 1250 GPU and less than or equal to 1500 GPU, greater than or equal to 1300 GPU and less than or equal to 1500 GPU, greater than or equal to 1350 GPU and less than or equal to 1500 GPU, greater than or equal to 1400 GPU and less than or equal to 1500 GPU, greater than or equal to 50 GPU and less than or equal to 1500 GPU, greater than or equal to 50 GPU and less than or equal to 1450 GPU, greater than or equal to 50 GPU and less than or equal to 1400 GPU, greater than or equal to 50 GPU and less than or equal to 1350 GPU, greater than or equal to 50 GPU and less than or equal to 1300 GPU, greater than or equal to 50 GPU and less than or equal to 1250 GPU, greater than or equal to 50 GPU and less than or equal to 1200 GPU, greater than or equal to 50 GPU and less than or equal to 1150 GPU, greater than or equal to 50 GPU and less than or equal to 1100 GPU, greater than or equal to 50 GPU and less than or equal to 1050 GPU, greater than or equal to 50 GPU and less than or equal to 1000 GPU, greater than or equal to 50 GPU and less than or equal to 950 GPU, greater than or equal to 50 GPU and less than or equal to 900 GPU, greater than or equal to 50 GPU and less than or equal to 850 GPU, greater than or equal to 50 GPU and less than or equal to 800 GPU, greater than or equal to 50 GPU and less than or equal to 750 GPU, greater than or equal to 50 GPU and less than or equal to 700 GPU, greater than or equal to 50 GPU and less than or equal to 650 GPU, greater than or equal to 50 GPU and less than or equal to 600 GPU, greater than or equal to 50 GPU and less than or equal to 550 GPU, greater than or equal to 50 GPU and less than or equal to 500 GPU, greater than or equal to 50 GPU and less than or equal to 450 GPU, greater than or equal to 50 GPU and less than or equal to 400 GPU, greater than or equal to 50 GPU and less than or equal to 350 GPU, greater than or equal to 50 GPU and less than or equal to 300 GPU, greater than or equal to 50 GPU and less than or equal to 250 GPU, greater than or equal to 50 GPU and less than or equal to 200 GPU, or even greater than or equal to 50 GPU and less than or equal to 150 GPU. It is envisioned that the range of permeate permeance may be greater than or equal to any of the permeances described herein and less than or equal to any of the permeances described herein. [0042] Having described a hollow fiber CMS membrane, a system 100 for oxidizing and cooling the hollow fiber CMS membrane is provided in FIG. 1. Flow control device 10 is first set to an “on” configuration, meaning that fluid is permitted to flow through conduit 12 from purge gas reservoir 14 to furnace 16, which contains the hollow fiber CMS membrane (not shown). During the pyrolysis step, most or even all of the fluid entering furnace 16 originates from purge gas reservoir 14. When the temperature within furnace 16 decreases to the desired oxidation initiation temperature, such as greater than or equal to 100 °C to less than or equal to 600 °C, flow control device 10 reduces flow of the fluid from the purge gas reservoir 14 and flow control device 18 increases flow of the fluid from the oxidant reservoir 20 into furnace 16 via conduit 22. In the embodiment shown in FIG. 1 , conduit 12 and conduit 22 both feed into inlet 24. The oxidant reservoir 20 may contain a premixed volume of oxidant and carrier gas, such as air (oxygen gas as oxidant and nitrogen gas as carrier) or a mixture of oxygen gas (oxidant) and argon (carrier).

[0043] During both pyrolysis and oxidation, gases from the furnace 16 may pass through outlet 26 and eventually be vented via conduit 28. Conveniently, these gases may be analyzed using oxygen sensor 30 for process control.

[0044] As used herein, the term “conduit” includes, but is not limited to, casings, liners, pipes, tubes, coiled tubing, and mechanical structures with interior voids.

[0045] As used herein, the term “reservoir” includes any container of any size capable of containing a fluid, whether in liquid or gaseous form. Exemplary reservoirs include, but are not limited to, gas cylinders, holding tanks, bladders, inflatable membranes (such as a balloon), drums, and bottles.

[0046] As used herein, the term “flow control device” includes, but is not limited to, a ball valve, a butterfly valve, a choke valve, a diaphragm valve, a gate valve, a globe valve, a knife valve, a needle valve, a pinch valve, a piston valve, a plug valve, a solenoid valve, and a spool valve.

[0047] The articles described above may be used in processes for separating a gas feed.

The processes involve flowing a gas feed containing at least one retentate and at least one other gas molecule through the hollow fiber CMS membrane. The flowing may result in a retentate retained in the hollow fiber CMS membrane and a product stream comprising the other gas molecule, sometimes referred to as the permeate. In embodiments, the hollow fiber CMS membrane may be fabricated into a module comprising a sealable enclosure comprising a plurality of CMS membranes, in which at least one hollow fiber CMS membrane produced by the method described above is contained within the sealable enclosure. The sealable enclosure may have an inlet for introducing the gas feed and one or more outlets for collecting the permeate. In some embodiments, the retentate is dissociated from the hollow fiber CMS membrane and is collected from one such outlet.

[0048] In embodiments, the retentate may be hydrogen or nitrogen and the permeate may be selected from ethylene, ethane, propylene, propane, butylene, butane, methane, carbon dioxide, oxygen, nitrogen, hydrogen sulfide, and combinations of two or more thereof. As would be evident to one of skill in the art, when hydrogen is the retentate, it cannot also be the permeate. Likewise, when nitrogen is the retentate, nitrogen cannot also be the permeate. Illustratively, in one embodiment, the feed gas may be composed of at least 5% the permeate gas molecule with the remainder being one of the aforementioned gases or mixture of two or more of said gases. It is understood that when referring to retentate gas molecule, this refers the gas molecule that has a lower permeability or, in other words, slowly permeates through the membrane or is retained. Likewise, permeate refers to the gas molecule that has a higher permeability through the membrane or, in other words, permeates faster through the membrane.

[0049] In embodiments, the permeate is C2H4 and the retentate is Lb; the hollow fiber

CMS membrane may have a C2H4/H2 selectivity greater than or equal to 10 and a C2H4 permeability greater than or equal to 100 GPU when measured while separating an analyte stream comprising C2H4 and Lb at a temperature that is greater than or equal to 20 °C and less than or equal to 30 °C. In embodiments, the permeate is CO2 and the retentate is N2; the hollow fiber CMS membrane may have a CO2/N2 selectivity greater than or equal to 5 and a CO2 permeability greater than or equal to 300 GPU, or even greater than or equal to 700 GPU, when measured while separating an analyte stream comprising CO2 and N2 at a temperature that is greater than or equal to 20 °C and less than or equal to 30 °C.

[0050] In embodiments, the CMS membranes have a stability such that said permeability and selectivity vary less than 20% after being used to continuously separate a feed gas comprising hydrogen gas molecule for 10 days. In embodiments, the permeability and selectivity vary less than 15%, 10%, or even 5% after being use to continuously separate a feed gas comprising a retentate and permeate gas molecule pair for 10, 30, or 60 days.

[0051] According to an aspect, either alone or in combination with any other aspect, an article includes an asymmetric hollow fiber carbon molecular sieve (CMS) membrane. The hollow fiber CMS membrane is made by a method comprising: heating a polymeric precursor to a pyrolysis temperature that is greater than or equal to 500 °C and less than or equal to 1200 °C; pyrolyzing the polymeric precursor at the pyrolysis temperature, thereby forming a pyrolyzed polymeric membrane; exposing the pyrolyzed polymeric membrane to an atmosphere comprising greater than or equal to 50 ppm oxidant; and cooling the pyrolyzed polymeric membrane to a cooling temperature that is less than or equal to 50 °C. The exposing and the cooling are performed sequentially or simultaneously, thereby forming the hollow fiber CMS membrane. The hollow fiber CMS membrane has a permeate/retentate selectivity greater than or equal to 5 and a permeate permeability greater than or equal to 50 GPU when measured while separating an analyte stream comprising the permeate and the retentate at a temperature that is greater than or equal to 20 °C and less than or equal to 30 °C.

[0052] According to a second aspect, either alone or in combination with any other aspect, the permeate is C2H4 and the retentate is Th, the hollow fiber CMS membrane having a C2H4/H2 selectivity greater than or equal to 10 and a C2H4 permeability greater than or equal to 100 GPU when measured while separating an analyte stream comprising C2H4 and Tb at a temperature that is greater than or equal to 20 °C and less than or equal to 30 °C.

[0053] According to a third aspect, either alone or in combination with any other aspect, the permeate is CO2 and the retentate is N2, the hollow fiber CMS membrane having a CO2/N2 selectivity greater than or equal to 5 and a CO2 permeability greater than or equal to 300 GPU when measured while separating an analyte stream comprising CO2 and N2 at a temperature that is greater than or equal to 20 °C and less than or equal to 30 °C.

[0054] According to a fourth aspect, either alone or in combination with any other aspect, the hollow fiber CMS membrane has a CO2 permeability greater than or equal to 700 GPU when measured while separating an analyte stream comprising CO2 and N2 at a temperature that is greater than or equal to 20 °C and less than or equal to 30 °C.

[0055] According to a fifth aspect, either alone or in combination with any other aspect, the exposure temperature is greater than or equal to 500 °C.

[0056] According to a sixth aspect, either alone or in combination with any other aspect, the atmosphere comprises greater than or equal to 500 ppm oxidant.

[0057] According to a seventh aspect, either alone or in combination with any other aspect, the heating is conducted in an atmosphere comprising greater than 0 ppm and less than or equal to 150 ppm oxidant.

[0058] According to an eighth aspect, either alone or in combination with any other aspect, the polymeric precursor comprises a polyimide.

[0059] According to a ninth aspect, either alone or in combination with any other aspect, the polymeric precursor comprises a polymer formed from one or more monomers selected from the group consisting of 2, 4, 6-trimethyl- 1, 3 -phenylene diamine (DAM); oxydianaline (ODA); dimethyl-3, 7-diaminodiphenyl-thiophene-5,5'-dioxide (DDBT); 3,5-diaminobenzoic acid (DABA); 2.3,5,6-tetramethyl-l,4-phenylene diamine (durene); meta-phenylenediamine (m- PDA); 2,4-diaminotolune (2,4-DAT); tetramethylmethylenedianaline (TMMDA); 4,4'-diamino- 2,2'-biphenyl disulfonic acid (BDSA); 5,5'-[2,2,2-trifluoro-l-(trifluoromethyl)ethylidene]-l,3- isobenzofurandion (6FDA); 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA); pyromellitic dianhydride (PMDA); 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA); 4,4'- Oxydiphthalic anhydride (ODPA); and benzophenone tetracarboxylic dianhydride (BTDA).

[0060] According to a tenth aspect, either alone or in combination with any other aspect, the polymeric precursor comprises a polymer comprising monomers Ac, Bg, and Cz, where X, Y, and Z are a mole fraction of each of A, B, and C, respectively, present in the polymer. The sum of X, Y, and Z is less tha or equal to 1. Each of A, B, and C is a monomer selected from the group consisting of 2, 4, 6-trimethyl- 1,3 -phenylene diamine (DAM); oxydianaline (ODA); dimethyl-3, 7- diaminodiphenyl-thiophene-5,5'-dioxide (DDBT); 3,5-diaminobenzoic acid (DABA); 2.3, 5, 6- tetramethyl- 1 ,4-phenylene diamine (durene); meta-phenylenediamine (m-PDA); 2,4- diaminotolune (2,4-DAT); tetramethylmethylenedianaline (TMMDA); 4,4'-di ^_, amino-2,2'- biphenyl disulfonic acid (BDSA); S^-P^^-trifluoro-l^trifluoromethy^ethyl-ideneJ-l^- isobenzofurandion (6FDA); 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA); pyromellitic dianhydride (PMDA); 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA); 4,4'- oxydiphthalic anhydride (ODPA); 5(6)-amino-l-(4 ^, -aminophenyl)-l,3,3-tri ^_, methylindane (DAPI); and 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA).

[0061] According to an eleventh aspect, either alone or in combination with any other aspect, A is a monomer selected from the group consisting of 6FDA, ODPA, and BTDA; B is DAM; and C is a monomer selected from the group consisting of BPDA and PMDA.

[0062] According to a twelfth aspect, either alone or in combination with any other aspect,

A is 6FDA; B is DAM; and Z is 0.

[0063] According to a thirteenth aspect, either alone or in combination with any other aspect, the oxidant is selected from the group consisting of gaseous oxygen, CO2, CO, nitrogen oxide, ozone, hydrogen peroxide, steam, and air.

[0064] According to a fourteenth aspect, either alone or in combination with any other aspect, an article includes an asymmetric hollow fiber carbon molecular sieve (CMS) membrane. The hollow fiber CMS membrane comprises a pyrolyzed and oxidized polyimide membrane. The hollow fiber CMS membrane has a permeate/retentate selectivity greater than or equal to 10 and a permeate permeability greater than or equal to 100 GPU when measured while separating an analyte stream comprising the permeate and the retentate at a temperature that is greater than or equal to 20 °C and less than or equal to 30 °C. The permeate is C2H4 and the retentate is Ff.

[0065] According to a fifteenth aspect, either alone or in combination with any other aspect, a method for separating hydrogen from a gas feed, the gas feed comprising at least one retentate and at least one other gas molecule includes flowing the gas feed through the article of any other aspect. The retentate is selected from the group consisting of hydrogen, nitrogen, and a mixture of hydrogen and nitrogen. The retentate is retained by the article and a product stream comprising the other gas molecule is produced. [0066] One or more features of the present disclosure are illustrated in view of the examples as follows:

EXAMPLES

[0067] The following examples are illustrative in nature and should not serve to limit the scope of the present application.

[0068] Example 1 - Oxidant concentration calibration

[0069] The relationship between the increases in the average O2 concentration in the furnace with the decrease in temperature is determined using the ideal gas law, PV = nRT, where P is pressure, V is volume, n is the number of moles of the O2, R is the ideal gas constant, and T is temperature. In the calculations, the volume is constant and the pyrolysis temperature is 925 °C. Intially, 100 % argon gas is used as the purge gas. After reaching the pyrolysis temperature, the furnace is allowed to cool naturally. When the temperature reaches 575 °C, gas purging is stopped, and the O2 concentration induced by the air back-diffusion inside the furnace is determined.

[0070] FIG. 2 provides a chart of temperature on the x-axis and simulated O2 concentration on the y-axis. As is evident from the chart, the concentration of O2 increases linearly as the temperature decreases. Further, this relationship may be used to determine an expected concentration of O2 when performing a pyrolysis and oxidation.

[0071] Example 2 - Pyrolysis and Oxidation of a Hollow Fiber CMS Membrane

[0072] CMS membranes were prepared using 6FDA:BPDA-DAM polymer acquired from

Akron Polymer Systems, Akron, OH. The polymer was dried under vacuum at 110 °C for 24 hours and then a dope was formed by mixing the 6FDA:BPDA-DAM polymer (25 wt%) with N-methyl- 2-pyrrolidone (NMP; 43 wt%), tetrahydrofuran (THF; 10 wt%), and ethanol (EtOH; 22 wt%). This mixture was roll mixed in a glass bottle sealed with a polytetrafluoroethylene (TEFLON™) cap at a rolling speed of five revolutions per minute (rpm) for a period of about 3 weeks, thereby forming a homogeneous dope. [0073] The homogeneous dope was loaded into a 500 milliliter (mL) syringe pump and allowed to degas overnight by heating the pump to a set point temperature from 50 °C to 60 °C using a heating tape.

[0074] Bore fluid (85 wt% NMP and 15 wt% water, based on total bore fluid weight) was loaded into a separate 100 mL syringe pump and then the dope and bore fluid were co-extruded through a spinneret operating at a flow rate of 180 milliliters per hour (mL/hr) for the dope and 60 mh/hr bore fluid, filtering both the bore fluid and the dope in line between delivery pumps and the spinneret using 40 pm and 2 pm metal filters. The temperature was controlled using thermocouples and heating tape placed on the spinneret, dope filters, and dope pump at a set point temperature of 70 °C.

[0075] After passing through a fifteen centimeter (cm) air gap, the nascent fibers that were formed by the spinneret were quenched in a water bath (50 °C), and the fibers were allowed to phase separate. The fibers were collected using a 0.32 meter (m) diameter polyethylene drum passing over TEFLON guides and operating at a take-up rate of 30 meters per minute (m/min).

[0076] The fibers were cut from the drum and rinsed at least four times in separate water baths over a span of 48 hours. The rinsed fibers underwent solvent exchange three times with methanol for 20 minutes and then hexane for 20 minutes before recovering the fibers and drying them under vacuum at a set point temperature of 110 °C for one hour or drying under vacuum at 75 °C for 3 hours.

[0077] The precursor fibers were pyrolized in a pyrolysis chamber having an oxygen content at room temperature less than 10 ppm. Argon was used as the inert purge gas. After the pyrolysis, the pyrolysis chamber was allowed to cool, and the gas line to suppy purging argon gas was discontinued at various temperatures (i.e., 375 °C, 485 °C, and 575 °C) to enable the air flow into the furnace from the exhaust line at the outlet of the furnace. After the membranes were pyrolyzed and cooled, a single fiber module was fabricated and tested for CO2/N2 and C2H4/C2H6 gas pair permeance. [0078] Example 3 - Gas Separation

[0079] In order to evaluate the method of producing asymmetric hollow fiber CMS membranes disclosed herein, seven samples were prepared. The pyrolyzed and/or oxidized CMS hollow fibers are encased in a stainless-steel casing, thereby forming a membrane module for further testing. The membrane module is housed in an oven (Quincy Lab, Inc., Chicago, IL) with temperature control. The test gas flow rates are controlled by mass flow controllers (Brooks Instrument, Hatfield, PA), and pressures are monitored and controlled by pressure transducers. In these experiments, the single-fiber CMS fiber modules are maintained under constant upstream pressure at 35 °C. Argon was used as the sweep gas to carry the permeate to the downstream flowmeter and gas chromatograph (GC). A Maxum II process GC (Siemens, Munich, Germany) is used to measure the composition of the permeate & sweep mixture, and a Mesalabs Bios Drycal flowmeter (Mesa Labs, Inc., Butler, NJ) is used for the permeate flow rate measurement. The volumetric flow rate from the Bios DryCal flowmeter and the composition from the GC were used to analyze the permeance and selectivity of the fibers in the test gas system.

[0080] Table 1 provides gas separation properties of control and air exposed oxidized samples made in accordance with the subject matter described herein. Samples 1 and 7 were not oxidized and are thus comparative examples. Samples 2-6 were exposed to air at the initial air exposure temperature provided.

Table 1. Gas Separation Properties of Control and Oxidized Samples

Pyrolysis Air exposure C0 ₂ C2H4

CO2/N2 C2H4/H2 Sample Temperature Temperature Permeance Permeance

_ (I _ TO Selectivity Selectivity

(GPU) (GPU)

1 ^* 925 N/A ¹ 126 49A 5.9 (L96

2 925 575 1010 7.7 442 13.0

3 925 485 854 15.7 263 13.3

4 925 375 39 50.4 0.54 0.1

5 975 575 1105 7.2 611 16.6

6 675 575 257 16.9 N/D ² N/D ²

7 ^* 675 N/A ¹ 56.7 40 N/D ² N/D ²

Comparative example ¹ N/A = not applicable ² N/D = not determined for this sample

[0081] Permeance for both CO2 and ethylene with samples 2 and 3 is higher than the the permeance of comparative samples 1 and 7. Additionally, ethylene selectivity over ¾ increases upon oxidation, highlighting the formation of a reverse selective membrane. A selectivity greater than 1 suggests ethylene is permeating more than Fb through the membrane. Stated differently, Fh is the retentate and ethylene is the permeate.

[0082] Sample 4 was exposed to air at a temperature lower than the air exposure temperature of samples 2 and 3. A drop in perrmeance of both CO2 and C2H4 was observed. Further, the selectivity of ethylene to Fb fell below 1, indicating the transport to be size selective, as opposed to reverse selective. In this case Fb is the permeate and ethylene is the retentate.

[0083] Samples 5 and 6 highlight the impact of pyrolysis temperature. Permeability of

CO2 drops significantly as the pyrolysis temperature is decreased from 975 °C to 675 °C.

[0084] The results highlight the impact of oxidation and temperature on the hollow fiber

CMS membrane performance. Without intending to be bound by any particular theory, it is believe that the temperature variability affects the kinetics and available concentration of oxidant during the oxidation process, thereby affecting the performance of the membranes.

[0085] It should be apparent to those skilled in the art that various modifications can be made to the described embodiments without departing from the spirit and scope of the claimed subject matter. Thus, it is intended that the specification cover modifications and variations of the described embodiments provided such modification and variations come within the scope of the appended claims and their equivalences.