WO2025105974A1

WO2025105974A1 - Mixed-matrix membranes containing a norbornene-based polymer and methods associated therewith

Info

Publication number: WO2025105974A1
Application number: PCT/RU2023/000344
Authority: WO
Inventors: Vera Aleksandrovna SOLOVYEVA; Elena Evgenevna PANKRATOVA; Hassan Sakar Alqahtani; Khalid Mohammed Alruwaili
Original assignee: Saudi Arabian Oil Co
Current assignee: Saudi Arabian Oil Co
Priority date: 2023-11-14
Filing date: 2023-11-14
Publication date: 2025-05-22
Anticipated expiration: 2026-05-14

Abstract

Mixed-matrix membranes containing carbon nanotubes may be utilized for separation of carbon dioxide from a gas stream comprising one or more additional gases. The mixed-matrix membranes are polymer membranes comprising: a matrix material comprising a norbornene-based polymer, and a plurality of carbon nanotubes dispersed in the matrix material. The norbornene-based polymer may be obtained through ring-opening polymerization or addition polymerization of a suitable norbornene-based monomer. Arene annulation of norbornadiene may also be used to form the norbornene-based polymer. Carbon dioxide separation methods may comprise contacting the polymer membrane with a gas stream comprising carbon dioxide, and separating at least a first portion of the carbon dioxide from the gas stream using the polymer membrane.

Description

MIXED-MATRIX MEMBRANES CONTAINING A NORBORNENE-BASED POLYMER AND METHODS ASSOCIATED THEREWITH

FIELD OF THE DISCLOSURE

[0001] The present disclosure relates to membrane-based gas separations and, more particularly, to gas separations conducted using mixed-matrix membranes.

BACKGROUND OF THE DISCLOSURE

[0002] Carbon capture strategies are of ever-increasing interest due to the issue of global warming. Removal of carbon dioxide from natural gas and other gas streams is often laborious and utilizes energy-intensive separation processes. For example, a common technique for removing carbon dioxide from natural gas and other gas streams utilizes amine-based sorbents, which may be present in a liquid phase for countercurrent contacting with the gas stream in a separation tower. Alternately, membranes may be used to promote separation of carbon dioxide from natural gas and other gas streams. Unfortunately, separation of carbon dioxide from natural gas and other gas streams using conventional membranes is often difficult due to a tradeoff in membrane selectivity versus membrane permeability. That is, if the selectivity is high, the membrane throughput may be poor due to low permeability, and if the membrane throughput is high due to high permeability, inadequate separation of carbon dioxide from other gases may occur. The efficiency, selectivity, diffusivity, and permeability of membranes are among the factors that may be impacted by the composition, porosity, and thickness of the membrane, among other parameters.

[0003] Most membranes suitable for separating carbon dioxide from other gases incorporate amine groups, which may bond the carbon dioxide through chemisorption by forming a bound carbamate species. The high binding energy of carbon dioxide to these types of membranes often leads to energy-intensive removal of the carbon dioxide in order to isolate the carbon dioxide and regenerate the membrane, thereby making their use costly and impractical, especially for large-scale separations. As discussed above, selectivity when separating carbon dioxide from a mixture of gases may also be problematic. To maintain adequate selectivity, the recovery and/or throughput of carbon dioxide or another gas of interest may be low.

[0004] Polymers suitable for separating carbon dioxide from natural gas and other gas mixtures vary widely in composition. Primary cellulose acetate membranes have broadly been used in industry. Polyimides (Pls) (such as MATRIMID® and poly[2,2’-bis-(3,4- dicarboxyphenyl)hexafluoroproane dianhydride-3 ,3 ’ -dihydroxy-4,4 ’ -diamino-biphenyl] (poly(6FDA-HAB)) polyimide), polybenzoxazoles, poly(trimethylsilylpropyne) (PTMSP), polytriazole, polyvinyl acetate, poly etherimide (e.g., ULTEM®), polyvinyl acetate, polysulfones (e.g., UDEL®), polydimethylsiloxanes, and polyethersulfones are also commonly used polymers. Unfortunately, commercial membranes are reaching practical limits of throughput and selectivity.

[0005] Mixed-matrix membranes (MMMs) are promising candidates for separating gas mixtures with high levels of both selectivity and permeability. MMMs utilize an inorganic material mixed within a polymeric matrix to improve gas separation properties. Commonly used inorganic materials include porous structures such as, for example, zeolites, metal-organic frameworks (MOFs), metal oxides, and carbon-based mesoporous materials.

SUMMARY OF THE DISCLOSURE

[0006] Various details of the present disclosure are hereinafter summarized to provide a basic understanding. This summary is not an exhaustive overview of the disclosure and is neither intended to identify certain elements of the disclosure, nor to delineate the scope thereof. Rather, the primary purpose of this summary is to present some concepts of the disclosure in a simplified form prior to the more detailed description that is presented hereinafter.

[0007] According to embodiments consistent with the present disclosure, polymer membranes may comprise: a matrix material comprising a norbomene-based polymer; and a plurality of carbon nanotubes dispersed in the matrix material.

[0008] In another embodiment, separation of a gas stream may comprise: providing a polymer membrane comprising a matrix material comprising a norbomene-based polymer, and a plurality of carbon nanotubes dispersed in the matrix material; contacting the polymer membrane with a gas stream comprising carbon dioxide and one or more additional gases; and separating at least a first portion of the carbon dioxide from the gas stream using the polymer membrane.

[0009] Any combinations of the various embodiments and implementations disclosed herein can be used in a further embodiment, consistent with the disclosure. These and other aspects and features can be appreciated from the following description of certain embodiments presented herein in accordance with the disclosure and the accompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Not applicable. DETAILED DESCRIPTION

[0011] Embodiments of the present disclosure generally relate to membrane-based gas separations and, more particularly, to gas separations conducted using mixed-matrix membranes.

[0012] In the following detailed description of embodiments of the present disclosure, numerous specific details are set forth in order to provide a more thorough understanding of the claimed subject matter. However, it will be apparent to one of ordinary skill in the art that the embodiments disclosed herein may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0013] The present disclosure addresses current shortcomings associated with membrane-based separation of carbon dioxide from gas streams, such as carbon dioxide from natural gas. In particular, the present disclosure provides polymer membranes comprising a matrix material comprising a norbomene-based polymer, and a plurality of carbon nanotubes dispersed within the matrix material, thereby affording mixed-matrix membranes (MMMs) that may have good selectivity for separating carbon dioxide from natural gas and other gas streams with good efficiency and throughput. Norbomene-based monomers (including norbomene, norbomene derivatives, and norbomadiene) may undergo polymerization by several different mechanisms to produce norbomene-based polymers having significantly different structures. Further details regarding various species of norbomene-based polymers are provided hereinbelow. The term “norbomene-based polymer” refers herein to any homopolymer or copolymer produced from a norbomene-based monomer. Depending on the particular norbomene-based monomer and the chosen mechanism by which the norbomene-based monomer undergoes polymerization, particular norbomene-based polymers may be a “polynorbomene,” a “polytricyclononene,” or a “catalytic arene-norbomene annulation polymer (CANAL)”, the latter of which is a ladder polymer. Unless otherwise evident from context, the generic term “norbomene-based polymer” may refer equivalently to any of these polymer species in the following description.

[0014] Norbomene-based polymers may be advantageous for performing gas separations because these types of polymers may frequently exhibit high gas permeability coefficients. In the disclosure herein, the permeability and gas separation properties of norbomene-based polymers may be further enhanced by incorporating one or more carbon nanomaterials therein to form a mixed-matrix membrane. Suitable carbon nanomaterials may include those such as, for example, graphite, graphene, carbon nanotubes (CNTs), fullerenes, and the like. In addition to providing a high surface area for contacting a gas stream containing carbon dioxide, the carbon nanomaterials may be further modified covalently or non-covalently to additionally tailor various gas-interaction properties associated therewith and wetting properties of the carbon nanomaterials with the norbomene-based polymer. More specific details are provided hereinbelow regarding how the carbon nanomaterials may be further modified to accomplish the foregoing. Together, the norbomene-based polymer and the carbon nanomaterial may provide advantaged separation performance compared to conventional membranes comprising only a polymer material, namely by providing both good separation performance and high gas permeability values. In particular embodiments, the carbon nanomaterial may comprise a plurality of optionally modified carbon nanotubes to promote separation of carbon dioxide from a gas stream, such as natural gas stream. Carbon nanotubes may be further advantageous in terms of strengthening the polymer matrix, thereby increasing durability of the polymer membrane.

[0015] Polymer membranes of the present disclosure may therefore comprise a matrix material comprising a norbomene-based polymer, and a plurality of carbon nanotubes dispersed in the matrix material. The polymer membranes may be configured to promote separation of carbon dioxide from a gas stream comprising carbon dioxide and one or more additional gases. Among desirable attributes of the polymer membranes disclosed herein include their good permeability to gases while simultaneously affording selectivity toward separation of carbon dioxide from other gases in a gas stream. Additionally, the polymer membranes of the present disclosure may be exhibit good thermal and mechanical stability under the temperature and pressure conditions commonly associated with commercial natural gas streams, including those obtained from a subterranean formation during oilfield production. Carbon dioxide-containing gas streams obtained from other industrial processes may also be suitably processed with the polymer membranes disclosed herein as well.

[0016] Suitable norbomene-based polymers may be synthesized by polymerization techniques including ring-opening metathesis polymerization, addition polymerization, catalytic arene-norbomene annulation, or any combination thereof. Other polymerization techniques that may be applicable in some circumstances may include radical polymerization or cationic polymerization. Depending on the chosen polymerization technique, the structure of the polymer backbone in the resulting norbomene-based polymer may differ. Suitable norbomene-based polymers resulting from norbomene-based monomers under different polymerization techniques are discussed subsequently. It is to be appreciated that although a given norbomene-based monomer may undergo polymerization by a preferred polymerization technique according to the description herein, it is to be understood that the norbomene-based monomer may also suitably undergo polymerization by a different polymerization technique to afford a different polymer backbone in some cases. Selected examples of different polymer backbones that may result by varying the chosen polymerization technique are described hereinbelow. It is further to be appreciated that any of the norbomene-based polymers described herein may be homopolymers or copolymers.

[0017] The polymer membranes disclosed herein may have a thickness ranging from about 0.1 microns to about 800 microns, or about 0.5 microns to about 500 microns, or about 0.3 microns to about 350 microns, or about 1 micron to about 10 microns, or about 10 microns to about 50 microns, or about 50 microns to about 150 microns, or about 150 microns to about 500 microns.

[0018] In some examples, the polymer membranes of the present disclosure may be multi-layered.

Ring-Opening Metathesis Polymerization

[0019] In some examples, the norbomene-based polymer may comprise a ring-opening metathesis polymerization reaction product of norbomene or a norbomene derivative. The ring-opening metathesis polymerization reaction product may comprise a homopolymer or a copolymer.

[0020] Ring-opening metathesis polymerization of norbomene or a norbomene derivative may afford a polymer backbone containing a plurality of double bonds and a divalent cyclopentyl ring within the polymer backbone. Therefore, ring-opening metathesis polymerization removes the bridged ring structure of the norbomene-based monomer. Optionally, at least a portion of the double bonds within the polymer backbone may be removed through hydrogenation. A generic ring-opening metathesis polymerization of a norbomene derivative (Formula 1) to form a norbomene-based polymer (Formula 2) having unsaturation in the polymer backbone is shown below.

Formula 1 Formula 2

In the depicted reaction, Q is optional substitution, n is an integer ranging from 0 to 4, preferably 0, 1 or 2, or two Q may be joined to form a substituted or unsubstituted, saturated or unsaturated, cyclic or polycyclic ring structure, or a combination thereof. Preferably, one or two bulky substituents are present to afford improved gas separation and thermal stability of the backbone double bonds. Optional substitution Q may be on the two carbon atoms immediately adjacent to the depicted location of Q (z.e., the alkyl, non-bridgehead carbon atoms). In non-limiting examples, Q may be a bulky substituent such as, for example, a tertiary alkyl group (e.g., t-butyl, neopentyl, or the like), a trialkylsilyl group (containing any Ci+ straight-chain or branched alkyl group), a trialkoxy silyl group (containing any Ci+ straightchain or branched alkoxy group), a trialky Igermyl group (containing any Ci+ straight-chain or branched alkyl group), or any combination thereof. Other suitable examples of Q may include, but are not limited to, non-tertiary alkyl groups, cycloalkyl groups, alkoxy groups, aryl groups, aryloxy groups, heterocyclic groups, heteroaromatic groups, halogens, carboxylic acids, carboxamides, carboxylic esters, amine groups, sulfonamide groups, and the like. Other substituents may also be envisioned. Alternately, two Q may be joined to form a carbocyclic or heterocyclic ring structure, which may be optionally substituted as well. Variable x is an integer having a value of 2 or greater and that results in a desired molecular weight in the norbomene-based polymer. In non-limiting examples, variable x may range from about 10 to about 10,000, or about 20 to about 5,000, or about 50 to about 1,000, or any subrange thereof. Exemplary norbomene-based monomers may include a nadimide and its corresponding polymer (Formulas 3 and 4) and a tricyclononene and its corresponding polymer (Formulas 5 and 6), each of the polymers being formed by ring-opening metathesis polymerization.

Formula 3 Formula 4

In Formulas 3 and 4, R is an optionally substituted hydrocarbyl group, such as an optionally substituted Ci+ alkyl group, an optionally substituted C6+ aryl group, an optionally substituted C3+ cycloalkyl group, an optionally substituted Ci+ alkylsilyl group, an optionally substituted Ci+ alkoxysilyl group, an optionally substituted heterocyclic group, or an optionally substituted heteroaryl group. In Formulas 5 and 6, R’ is an optionally substituted hydrocarbyl group, such as an optionally substituted Ci+ alkyl group, an optionally substituted C2+ alkenyl group, an optionally substituted C&+ aryl group, an optionally substituted C3+ cycloalkyl group, an optionally substituted Ci+ alkylsilyl group, an optionally substituted Ci+ alkoxysilyl group, an optionally substituted heterocyclic group, an optionally substituted heteroaryl group, an optionally substituted Ci+ alkoxy group, an optionally substituted Ce+ aryloxy group, and the like. In particular examples, R’ may be a trialkoxysilyl group, such as a trimethylsiloxy group. Other suitable examples of R’ may include, but are not limited to, halogens, carboxylic acids, carboxamides, carboxylic esters, amine groups, sulfonamide groups, and the like. Other substituents may also be envisioned.

[0021] The nadimide represented by Formula 3 may be synthesized in two steps starting from dicyclopentadiene. In particular, dicyclopentadiene may be heated in the presence of maleic anhydride under conditions wherein the dicyclopentadiene reverts (cracks) to form cyclopentadiene, which then reacts with maleic anhydride via a thermal 4+2 cycloaddition to form an intermediate fused cyclic anhydride. Reaction of the intermediate fused cyclic anhydride with a primary amine bearing substituent R may then afford a nadimide polymer having a structure represented by Formula 4.

[0022] The tricyclononene having a structure represented by Formula 5 may be synthesized by reaction of quadricyclane with a substituted vinyl compound in a 2o + 2 a + 2TT cycloaddition, wherein the substituted vinyl compound contains the R’ group or a precursor to the R’ group. For example, in some embodiments, R’ may be a trialkoxysilyl group, wherein the corresponding tricyclononene having a structure represented by Formula 5 may be obtained by reacting trichlorovinylsilane with quadricyclane in a 2CT + 2 a + 2 cycloaddition, followed by hydrolysis of the trichlorosilyl group with an alcohol following the cycloaddition reaction to afford substituted tricyclononene. The trialkoxysilyl group may be maintained in the tricyclononene polymer having a structure represented by Formula 6.

[0023] For any of the foregoing ring-opening metathesis polymerization reactions, the polymerization may be conducted in the presence of a suitable catalyst effective to promote ring-opening and subsequent polymerization. Suitable examples of catalysts effective for promoting ring-opening metathesis polymerization include, but are not limited to, transition metal carbenes. Transition metal carbenes are characterized in having a carbon-to-transition metal double bond. Examples include Grubb’s catalyst (e.g., a ruthenium carbene, with benzylidene-bis(tricyclohexylphosphino)-dichlororuthenium being a specific example) and similar ruthenium carbenes. Many other variants of Grubb’s catalyst will be familiar to persons having ordinary skill in the art. Other suitable transition metal carbenes that may be effective for promoting ring-opening metathesis polymerization in the disclosure herein include Schrock molybdenum carbenes, variants of which will also be familiar to persons having ordinary skill in the art.

[0024] Ring-opening metathesis polymerization of the foregoing norbomene-based monomers may be conducted by contacting a solution of the norbomene-based monomer with a suitable amount of the catalyst. The solvent may be selected to allow the transition metal carbene to maintain reactivity toward promoting the ring-opening metathesis polymerization. Suitable solvents and other details regarding conditions for promoting ring-opening metathesis polymerization will be familiar to persons having ordinary skill in the art.

Addition Polymerization

[0025] In some examples, the norbomene-based polymer may comprise an addition polymerization reaction product of norbomene or a norbomene derivative. The addition polymerization reaction product may comprise a homopolymer or a copolymer.

[0026] Addition polymerization of norbomene or a norbomene derivative may afford a polymer backbone containing only carbon-carbon single bonds, with the bridged norbomene carbon skeleton being maintained and incorporated as a polymerized monomer unit within the polymer backbone. A generic addition polymerization of a norbomene derivative (Formula 7) to form a norbomene-based polymer (Formula 8) having an intact norbomene carbon skeleton and no unsaturation in the polymer backbone is shown below.

Formula 7 Formula 8

In the depicted reaction, Q is optional substitution, n is an integer ranging from 0 to 4, preferably 0, 1, or 2, or two Q may be joined to form a substituted or unsubstituted, saturated or unsaturated, cyclic or polycyclic ring structure, or a combination thereof. Optional substitution Q may be on the two carbon atoms immediately adjacent to the depicted location of Q (z.e., the alkyl, non-bridgehead carbon atoms). In non-limiting examples, Q may be an optionally substituted hydrocarbyl group or a reaction product thereof (e.g., an epoxide or a ring-opened epoxide, a dihydroxylation reaction product of a vinyl group, an oxidative cleavage product of a vinyl group, or the like), a bulky substituent such as, for example, a tertiary alkyl group (e.g., t-butyl, neopentyl, and the like), a trialkylsilyl group (containing any Ci+ straight-chain or branched alkyl group), a trialkoxysilyl group (containing any Ci+ straightchain or branched alkoxy group), a trialky Igermyl group (any Ci+ straight-chain or branched alkyl group), or any combination thereof. Other suitable examples of Q may include, but are not limited to, non-tertiary alkyl groups, cycloalkyl groups, alkoxy groups, aryl groups, aryloxy groups, heterocyclic groups, heteroaromatic groups, halogens, carboxylic acids, carboxamides, carboxylic esters, amine groups, sulfonamide groups, and the like. Other substituents may also be envisioned. Alternately, two Q may be joined to form a carbocyclic or heterocyclic ring structure, which may be optionally substituted as well. Variable x is an integer having a value of 2 or greater that results in a desired molecular weight in the norbomene-based polymer. In non-limiting examples, variable x may range from about 10 to about 10,000, or about 20 to about 5,000, or about 50 to about 1 ,000, or any subrange thereof. Exemplary norbomene-based monomers may include a vinyl-substituted norbomene derivative (Formula 9), its further polymerization reaction product (Formula 10), and a further reaction product thereof to promote epoxide formation and opening (Formula 11).

Above, the vinyl-substituted norbomene represented by Formula 9 is polymerized by addition polymerization to form a vinyl-substituted norbomene addition polymer having a structure represented by Formula 10. The vinyl group may then be transformed by epoxidation (e.g., with a peracid, dimethyldioxirane, or similar epoxidation reagents) to form an intermediate epoxide functional group (not shown), which may then be opened with an amine to afford an amine-functionalized norbomene addition polymer having a structure represented by Formula 11. Although a primary amine (R”-NH2) is depicted in the reaction to form the norbomene- based polymer having a structure represented by Formula 11, it is to be appreciated that secondary amines may similarly promote nucleophilic opening of the intermediate epoxide. Other nucleophiles may likewise promote nucleophilic opening of the epoxide ring to form alternative products. Substituent R” may comprise a Ci+ hydrocarbyl group, such as an optionally substituted Ci+ alkyl group, an optionally substituted Ce+ aryl group, an optionally substituted C3+ cycloalkyl group, an optionally substituted heterocyclic group, or an optionally substituted heteroaryl group, or the like.

[0027] Alternately, the vinyl-substituted norbomene addition polymer having a structure represented by Formula 10 may have its vinyl group functionally transformed in a different manner than through epoxidation. In one example, the vinyl group may be dihydroxylated (e.g., with OSO4), and the resulting hydroxyl groups may be optionally further functionalized. In another example, the vinyl group may be oxidatively cleaved to remove one carbon atom (e.g., with ozone or NalCM), and further functionalization may optionally take place (e.g., by esterification or reductive amination, for instance).

[0028] Addition polymerization of the foregoing norbomene-based monomers may be conducted by contacting a solution of the norbomene-based monomer with a suitable amount of a catalyst effective to promote addition polymerization of the norbomene-based monomer. In non-limiting examples, a suitable catalyst to promote addition polymerization may include a three-component catalyst system comprising a N-heterocyclic carbene Pd-complex activated with Na⁺[B(3,5-(CF3)2C6H3)4]^(Na-BARF) in the presence of tricyclohexylphosphine (PCya). Other suitable catalysts for promoting addition polymerization of norbomene-based monomers will be familiar to persons having ordinary skill in the art. The solvent may be selected to allow the catalyst to maintain activity toward promoting addition polymerization. Suitable solvents and other details regarding suitable conditions for promoting addition polymerization will be familiar to persons having ordinary skill in the art.

Catalytic Arene Annulation Polymerization

[0029] In some examples, the norbomene-based polymer may comprise an arene annulation polymerization reaction product of norbomadiene. The arene annulation polymerization reaction product may comprise a homopolymer or a copolymer.

[0030] Arene annulation may be conducted onto norbomadiene under catalytic conditions to afford a ladder polymer which may also be suitable for applications in which gas permeability is desirable. A generic arene annulation polymerization of norbomadiene (Formula 12) with a dibromobenzene (Formula 13), having the two bromo substituents nonadj acent to each other, (z. e. , m- or p-) to form a norbomene-based polymer (Formula 14) having a ladder polymer structure is shown below.

Formula 12 Formula 13 Formula 14

In Formulas 13 and 14, R’” is H, an optionally substituted hydrocarbyl group, an amine, an ether, an ester, a heterocyclic group, a heteroaryl group, or the like. Polymerization reaction conditions and Pd catalysts effective to promote arene annulation in the foregoing manner will be familiar to persons having ordinary skill in art. In non-limiting examples, the catalyst may be palladium (II) acetate combined with a phosphine ligand. Typical polymerization reaction conditions for such arene annulation reactions may utilize an ether solvent (e.g. , dioxane or tetrahydrofuran) at a temperature of about 100°C or above.

Carbon Nanotubes and Modification Thereof [0031] The amount of carbon nanotubes in the polymer membranes disclosed herein may vary over a wide range to promote a desired selectivity for carbon dioxide separation. The polymer membranes of the present disclosure may contain carbon nanotubes dispersed in the matrix material and comprise up to about 50 wt% of the polymer membrane based on total mass. In non-limiting examples, the amount of carbon nanotubes may range from about 0.01 wt% to about 40 wt%, or about 0.05 wt% to about 5 wt%, or about 0.1 wt% to about 10 wt%, or about 0.5 wt% to about 2 wt%, or about 0.5 wt% to about 5 wt%, or about 0.5 wt% to about 20 wt%, or about 1 wt% to about 30 wt%, or about 5 wt% to about 40 wt% of the polymer membranes, each based on total mass of the polymer membrane.

[0032] Suitable carbon nanotubes may include single walled-carbon nanotubes, multiwalled carbon nanotubes, or any combination thereof. The molecular structure of as-produced carbon nanotubes generally consists of rolled up sheets of sp²-hybridized carbon atoms (graphene sheets) having rounded ends. The carbon nanotubes may be unfunctionalized, functionalized, or any combination thereof. Functionalization of carbon nanotubes may include surface modifications that are covalent or non-covalent in nature. Further details are provided hereinbelow.

[0033] Suitable carbon nanotubes may have a diameter of about 1 nm to about 200 nm, or about 20 nm to about 100 nm, or about 10 nm to about 80 nm, or about 4 nm to about 20 nm, or about 2 nm to about 12 nm. The carbon nanotubes may have a length of about 20 pm to about 500 pm, or about 20 pm to about 200 pm, or about 20 pm to about 150 pm, or about 20 pm to about 100 pm, or about 50 pm to about 500 pm, or about 50 pm to about 200 pm, or about 50 pm to about 150 pm, or about 50 pm to about 100 pm, or about 100 pm to about 500 pm, or about 100 pm to about 200 pm, or about 100 pm to about 150 pm, or about 150 pm to about 500 pm, or about 150 pm to about 200 pm, or about 200 pm to about 500 pm. The carbon nanotubes may have an aspect ratio (ratio of length to width) of about 100 to about 100,000, or about 100 to about 50,000, or about 500 to about 30,000, or about 1,000 to about 20,000, or about 1,000 to about 100,000, or about 1,000 to about 50,000, or about 1,000 to about 40,000, or about 1,000 to about 30,000, or about 1,000 to about 25,000, or about 1,000 to about 20,000, or about 1,000 to about 15,000, or about 1,000 to about 12,000, or about 1,000 to about 10,000, or about 1,000 to about 8,000.

[0034] Covalent modifications may alter the surface properties of the carbon nanotubes. Numerous types of covalent modifications are now known for carbon nanotubes, any of which may be utilized in the carbon nanotubes present in the polymer membranes disclosed herein. In some examples, the carbon nanotubes may be covalently bonded to the matrix material within the polymer membranes. For example, carbon nanotubes that have been covalently modified to incorporate an amine may become covalently bonded to the matrix material by performing nucleophilic epoxide ring-opening to form a norbornene-based polymer in which R” is the carbon nanotube (Formula 11). In another example, carbon nanotubes having a carboxylic acid group may be reacted with an amine within the polymer matrix.

[0035] In some examples, carbon nanotubes may be covalently modified through treatment with mineral acids such as nitric acid, sulfuric acid, or a mixture of the acids to result in hydroxyl or carboxylic acid groups distributed upon the surface of the carbon nanotubes. Such functional groups may help facilitate dispersion of the carbon nanotubes throughout a polymer matrix comprising a norbomene-based polymer. Additionally, surface oxidation of carbon nanotubes may be conducted with KMnC>4 and/or piranha acid (H2SO4/H2O2), succinic or glutaric acid acyl peroxides, or ozone. Additional covalent surface modifications may be achieved via cycloaddition with alkynes, nitrile imines, nitrile oxides, diaryl diazomethane, diazo derivatives, or by nucleophilic carbenes. Amidation of carbon nanotubes may be achieved through use of ammonia and thionyl chloride. Additionally, amination or polyamination of carbon nanotubes may be conducted with an organolithium reagent, such as lithium ethylenediamine, lithium octadecylamine, or lithium polyamines. Polymer grafting onto the surface of carbon nanotubes may also be performed, such as with poly(n-butyl methacrylate), poly(methylene bisacrylamide), polyetherimides, poly (hydroxyethyl acrylate), polyacrylamide, poly(acryloyl morpholine), polysaccharides, polypyrroles, polyethyleneimines, polyanilines, or any combination thereof. Plasma treatment, in the presence of gases, may also be used to introduce covalent modifications onto the surface of carbon nanotubes.

[0036] Oxidized carbon nanotubes may be opened on their ends and contain a plurality of hydroxyl groups and carboxylic acid groups at this location. Suitable oxidizing agents for opening the ends of carbon nanotubes may include oxidizing acids such as, for example, nitric acid, sulfuric acid/hydrogen peroxide, and the like. Illustrative techniques for oxidizing carbon nanotubes using an oxidizing acid are described further in U.S. Patent 7,008,604, which is incorporated herein by reference.

[0037] Carbon nanotubes suitable for use in the polymer membranes disclosed herein may alternately or additionally include a non-covalent modification. Non-covalent modifications may include a modification that alters or introduces Van der Waals forces, 7r-7r stacking interactions, electrostatic interactions, or any combination thereof that may hamper aggregation of carbon nanotubes or alter interaction of the carbon nanotubes with the matrix material.

[0038] Reagents to promote C-JC stacking of carbon nanotubes may include but are not limited to aromatic and condensed polyaromatic compounds, such as napthalen-l-ylmethyl phosphonic acid (NYPA), 3,6-diamino-l,2,4,5-tetrazine, pyrenes, porphyrins, tertiary phosphines, carbazoles, and triptycenes. Phenyl-substituted carbon nanotubes may also undergo JC-TT stacking to some degree.

[0039] Another class of reagents suitable to promote non-covalent interactions surface modifiers are surfactants. Suitable surfactants may include, but are not limited to, cationic, anionic, zwitterionic, or neutral surfactants, including but not limited to cyclodextrins, polyvinylpyrrolidone (PVP), sodium dodecyl sulfate (SDS), polyethylene glycol (PEG), dodecylbenzene sulfonic acid (DBSA), cetyltrimethylammonium bromide (CTAB), l-butyl-3- methylimidazolium tetrafluoroborate, 3-aminoethylimidazolium bromide, and 3- aminopropyltriethoxysilane. Polar organic solvents, such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), or dimethylsulfoxide (DMSO), for example, may also provide a non-covalent modification upon the surface of the carbon nanotubes. Ionic liquids, such as but not limited to, l-butyl-3-methyl-imidazolium tetrafluoroborate (BMITFB) or 1- butyl-3-methlimidazolium bis(trifluoromethylsulfonyl)imide (BMI) may similarly provide a suitable non-covalent modification of carbon nanotubes.

[0040] The carbon nanotubes may be randomly aligned (non-aligned) in the matrix material or be at least partially aligned, including folly aligned. Alignment refers to a parallel or partially parallel arrangement of carbon nanotubes along their longitudinal axes. Partial or full alignment of the carbon nanotubes in the matrix material may enhance their ability to promote gas separation according to the disclosure herein. Alignment of the carbon nanotubes may be achieved using electric fields, magnetic fields, extrusion, or other alignment techniques known in the art.

[0041] Suitable techniques for blending carbon nanotubes, optionally with alignment, in a matrix material are well known. A person having ordinary skill in the art, with the benefit of the present disclosure, will be able to choose a suitable technique for dispersing carbon nanotubes in a norbomene-based polymer, optionally with at least partial alignment, in the course of forming the polymer membranes disclosed herein.

Carbon Dioxide Separations

[0042] As indicated above, the polymer membranes disclosed herein may be utilized in conjunction with separating carbon dioxide from a gas stream comprising a gas mixture containing at least carbon dioxide and one or more additional gases, such as a natural gas stream. Suitable conditions and locations for separating carbon dioxide from the gas stream are discussed subsequently.

[0043] Methods of the present disclosure may comprise providing a suitable polymer membrane of the present disclosure, contacting the polymer membrane with a gas mixture comprising carbon dioxide and one or more additional gases, and separating at least a first portion of the carbon dioxide from the gas stream using the polymer membrane.

[0044] Separation of the gas mixture may occur under pressure and result in production of two separate flows as a retentate stream and a permeate stream. The difference of the partial pressures in the gas mixture on the retentate side of the membrane (higher pressure) and permeate side of the membrane (lower pressure) is the driving force for the separation process. Separation may occur as a result of differences in the transport rates of chemical species through the interphase of the membrane. The different transport rates result in selectivity for separation of some substances relative to others. In the case of separation of a gas mixture, each gas component has a specific permeation rate that is determined by its ability to dissolve and diffuse through the membrane material, while experiencing interactions such as physisorption therein. Highly soluble, small molecules (e.g., CO2 and H2S) may permeate faster than do larger molecules (e.g., N2, Ci+ hydrocarbons, and the like). In gas separations conducted with membranes comprising a fiber bundle, the gas mixture may flow along the fiber bundle, and more soluble acid gas components (e.g. , CO2 and H2S) may preferentially permeate to the bore side of each fiber. Hydrocarbons within the gas mixture may fail to permeate and continue through a plant for further processing. The same may occur with non-fibrous membranes, such as membranes comprising a cast matrix material. The mobility and concentration of solute (gas from the gas mixture) within the polymer membrane determines how large a flux is produced by a given driving force. Mobility may be determined by, among other factors, the solute’s molecular size and the physical structure of the polymer membrane (e.g., hardness, crystallinity, polymer chain flexibility, and the like). The concentration of the solute in the polymer membrane may be determined by, among other factors, chemical compatibility and chemical interactions between the solute and the matrix material.

[0045] Contacting the polymer membrane with the gas stream may occur a wide range of suitable conditions. In non-limiting examples, suitable conditions may include a temperature of about 5°C to about 60°C, or about 20°C to about 45°C, or about 30°C to about 60°C, or about 10°C to about 100°C, and a total pressure of about 0.01 bar to about 50 bar, or about 1 bar to about 40 bar, or about 1 about to about 20 bar. The carbon dioxide partial pressure in the gas stream may reside within the same ranges and be lower than the overall pressure of the gas stream.

[0046] In non-limiting examples, the polymer membrane may be contacted with a natural gas stream in a wellbore or as the natural gas stream exits a wellbore. For example, the polymer membrane may be present in the wellhead to promote carbon dioxide separation as the natural gas stream exits the wellbore. Alternately, the polymer membrane may be contacted with a natural gas stream exiting a wellbore, wherein the contacting takes place on the earth’s surface outside the wellbore and wellhead. Optionally, the wellhead pressure may be decreased (at least partially released) to facilitate contacting between the natural gas stream and the polymer membrane in the wellhead.

[0047] The polymer membranes of the present disclosure may promote separation of carbon dioxide by retaining (adsorbing or absorbing) at least a portion of the carbon dioxide within the polymer membrane, or the polymer membranes may preferentially retain other gases in preference to carbon dioxide, thereby allowing the carbon dioxide to pass through the polymer membrane more readily than do the other gases. Accordingly, the carbon dioxide may be enriched upon either the permeate side or the retentate side of the polymer membrane. When at least a portion of the carbon dioxide is retained by the polymer membrane, the carbon dioxide may be physisorbed or chemisorbed by the polymer membrane. Preferably, the portion of the carbon dioxide retained by the polymer membrane may be physisorbed to facilitate easier release of the carbon dioxide therefrom during regeneration of the polymer membrane.

[0048] Accordingly, in some examples, the polymer membranes may promote separations in which a first portion of the carbon dioxide passes from a first side (retentate side) to a second side (permeate side) of the polymer membrane, and a second portion of the carbon dioxide is retained within the polymer membrane, such as through physisorption. A third portion of the carbon dioxide may remain upon the first side of the polymer membrane. The third portion of carbon dioxide may remain within the gas stream undergoing separation according to the disclosure herein.

[0049] It is to be further appreciated that separation of carbon dioxide in accordance with the disclosure herein need not necessarily take place using a single polymer membrane. For example, a plurality of polymer membranes of the present disclosure may be arranged in series, such that carbon dioxide or a gas mixture containing an enriched loading of carbon dioxide passes through a first polymer membrane in the series. The carbon dioxide or the gas mixture can subsequently be enriched by passage through one or more subsequent polymer membranes in the series. When used in series, the polymer membranes need not necessarily all have the same composition, thickness, lateral dimensions, porosity, or the like. Each polymer membrane in the series, for example, may have its norbomene-based polymer, carbon nanotubes, and amounts thereof adjusted in response to various application- specific needs.

Example Embodiments

[0050] Embodiments disclosed herein include:

[0051] Embodiment A: Polymer membranes. The polymer membranes comprise: a matrix material comprising a norbomene-based polymer; and a plurality of carbon nanotubes dispersed in the matrix material.

[0052] Embodiment B: Gas separation methods. The methods comprise: providing the polymer membrane of A; comprising carbon dioxide and one or more additional gases; and separating at least a first portion of the carbon dioxide from the gas stream using the polymer membrane.

[0053] Each of Embodiments A and B may have one or more of the following additional elements in any combination:

[0054] Element 1 : wherein the carbon nanotubes comprise about 0.01 wt% to about 40 wt% of the polymer membrane based on total mass.

[0055] Element 2: wherein the polymer membrane has a thickness ranging from about 0.1 microns to about 800 microns.

[0056] Element 3 : wherein the plurality of carbon nanotubes comprises single- walled carbon nanotubes, multi-walled carbon nanotubes, or any combination thereof.

[0057] Element 4: wherein at least a portion of the plurality of carbon nanotubes is modified with a covalent surface modification.

[0058] Element 5: wherein at least a portion of the plurality of carbon nanotubes is modified with a non-covalent surface modification.

[0059] Element 6: wherein the carbon nanotubes are at least partially aligned in the matrix material.

[0060] Element 7: wherein the norbomene-based polymer comprises at least one homopolymer of a norbomene-based monomer.

[0061] Element 8: wherein the norbomene-based polymer comprises a ring-opening metathesis polymerization reaction product, an addition polymerization reaction product, an arene-norbomene annulation polymerization reaction product, or any combination thereof.

[0062] Element 9: wherein the norbomene-based polymer comprises a ring-opening metathesis polymerization reaction product of an optionally substituted norbomene. [0063] Element 10: wherein the norbomene-based polymer comprises an addition polymerization reaction product of an optionally substituted norbomene.

[0064] Element 11 : wherein the norbomene-based polymer comprises a homopolymer or a copolymer comprising a polymerized reaction product of a nadimide monomer.

[0065] Element 12: wherein the nadimide monomer is polymerized by ring-opening metathesis polymerization.

[0066] Element 13: wherein the nadimide monomer is polymerized by addition polymerization.

[0067] Element 14: wherein the norbomene-based polymer comprises a homopolymer or a copolymer comprising a polymerized reaction product of a vinyl norbomene monomer.

[0068] Element 15: wherein a vinyl group of the vinyl norbomene monomer is further functionalized after polymerization.

[0069] Element 16: wherein the vinyl group is epoxidized and then ring-opened with a nucleophile.

[0070] Element 17: wherein the vinyl norbomene monomer is polymerized by addition polymerization.

[0071] Element 18: wherein the norbomene-based polymer comprises a homopolymer or a copolymer comprising a polymerized reaction product of a tricyclononene monomer.

[0072] Element 19: wherein the tricyclononene monomer is polymerized by ringopening metathesis polymerization.

[0073] Element 20: wherein the norbomene-based polymer comprises an arene- norbomene annulation polymerization reaction product.

[0074] Element 21 : wherein the gas stream comprises a natural gas stream.

[0075] Element 22: wherein the natural gas stream has a pressure of about 0.01 bar to about 50 bar, and/or wherein the natural gas stream has a temperature of about 10°C to about 100°C.

[0076] Element 23: wherein the natural gas stream contacts the polymer membrane as the natural gas stream exits a wellbore.

[0077] By way of non-limiting example, exemplary combinations applicable to Embodiments A and B include, but are not limited to: 1 and/or 2, and 3, 4, 5, and/or 6; 1 and/or 2, and 7; 1 and/or 2, and 8; 1 and/or 2, and 9; 1 and/or 2, and 10; 1 and/or 2, and 11; 1 and/or 2, and 11 and 12; 1 and/or 2, and 11 and 13; 1 and/or 2, and 14; 1 and/or 2, and 14 and 15; 1 and/or 2, and 14 and 16; 1 and/or 2, and 14 and 17; 1 and/or 2, and 18; 1 and/or 2, and 18 and 19; 1 and/or 2, and 20; 3, 4, 5, and/or 6, and 7; 3, 4, 5, and/or 6, and 8; 3, 4, 5, and/or 6, and 9; 3, 4, 5, and/or 6, and 10; 3, 4, 5, and/or 6, and 11; 3, 4, 5, and/or 6, and 11 and 12; 3, 4, 5, and/or 6, and 11 and 13; 3, 4, 5, and/or 6, and 14; 3, 4, 5, and/or 6, and 14 and 15; 3, 4, 5, and/or 6, and 14 and 16; 3, 4, 5, and/or 6, and 14 and 17; 3, 4, 5, and/or 6, and 18; 3, 4, 5, and/or 6, and 18 and 19; and 3, 4, 5, and/or 6, and 20. Any one or more of 21, 22, and/or 23 may be present in combination with any of the foregoing. Additional combinations applicable to B include, but are not limited to 21 and 22; 21 and 23; 22 and 23; and 21-23.

[0078] Additional embodiments disclosed herein include:

[0079] Clause 1. A polymer membrane comprising: a matrix material comprising a norbomene-based polymer; and a plurality of carbon nanotubes dispersed in the matrix material.

[0080] Clause 2. The polymer membrane of clause 1, wherein the carbon nanotubes comprise about 0.01 wt% to about 40 wt% of the polymer membrane based on total mass.

[0081] Clause 3. The polymer membrane of clause 1 or clause 2, wherein the polymer membrane has a thickness ranging from about 0.1 microns to about 800 microns.

[0082] Clause 4. The polymer membrane of any one of clauses 1-3, wherein the plurality of carbon nanotubes comprises single-walled carbon nanotubes, multi- walled carbon nanotubes, or any combination thereof.

[0083] Clause 5. The polymer membrane of any one of clauses 1-4, wherein at least a portion of the plurality of carbon nanotubes is modified with a covalent surface modification.

[0084] Clause 6. The polymer membrane of any one of clauses 1-5, wherein at least a portion of the plurality of carbon nanotubes is modified with a non-covalent surface modification.

[0085] Clause 7. The polymer membrane of any one of clauses 1-6, wherein the carbon nanotubes are at least partially aligned in the matrix material.

[0086] Clause 8. The polymer membrane of any one of clauses 1-7, wherein the norbomene-based polymer comprises at least one homopolymer of a norbomene-based monomer.

[0087] Clause 9. The polymer membrane of any one of clauses 1-8, wherein the norbomene-based polymer comprises a ring-opening metathesis polymerization reaction product, an addition polymerization reaction product, an arene-norbomene annulation polymerization reaction product, or any combination thereof. [0088] Clause 10. The polymer membrane of clause 9, wherein the norbomene- based polymer comprises a ring-opening metathesis polymerization reaction product of an optionally substituted norbomene.

[0089] Clause 11. The polymer membrane of clause 9, wherein the norbomene- based polymer comprises an addition polymerization reaction product of an optionally substituted norbomene.

[0090] Clause 12. The polymer membrane of clause 9, wherein the norbomene- based polymer comprises a homopolymer or a copolymer comprising a polymerized reaction product of a nadimide monomer.

[0091] Clause 13. The polymer membrane of clause 12, wherein the nadimide monomer is polymerized by ring-opening metathesis polymerization.

[0092] Clause 14. The polymer membrane of clause 12, wherein the nadimide monomer is polymerized by addition polymerization.

[0093] Clause 15. The polymer membrane of clause 9, wherein the norbomene- based polymer comprises a homopolymer or a copolymer comprising a polymerized reaction product of a vinyl norbomene monomer.

[0094] Clause 16. The polymer membrane of clause 15, wherein a vinyl group of the vinyl norbomene monomer is further functionalized after polymerization.

[0095] Clause 17. The polymer membrane of clause 16, wherein the vinyl group is epoxidized and then ring-opened with a nucleophile.

[0096] Clause 18. The polymer membrane of clause 15, wherein the vinyl norbomene monomer is polymerized by addition polymerization.

[0097] Clause 19. The polymer membrane of clause 9, wherein the norbomene- based polymer comprises a homopolymer or a copolymer comprising a polymerized reaction product of a tricyclononene monomer.

[0098] Clause 20. The polymer membrane of clause 19, wherein the tricyclononene monomer is polymerized by ring-opening metathesis polymerization.

[0099] Clause 21. The polymer membrane of clause 9, wherein the norbomene- based polymer comprises an arene-norbomene annulation polymerization reaction product.

[0100] Clause 22. A method comprising: providing the polymer membrane of any one of clauses 1-21; contacting the polymer membrane with a gas stream comprising carbon dioxide and one or more additional gases; and separating at least a first portion of the carbon dioxide from the gas stream using the polymer membrane

[0101] Clause 23. The method of clause 22, wherein the gas stream comprises a natural gas stream.

[0102] Clause 24. The method of clause 23, wherein the natural gas stream has a pressure of about 0.01 bar to about 50 bar.

[0103] Clause 25. The method of clause 23 or clause 24, wherein the natural gas stream has a temperature of about 10°C to about 100°C.

[0104] Clause 26. The method of any one of clauses 23-25, wherein the natural gas stream contacts the polymer membrane as the natural gas stream exits a wellbore.

[0105] To facilitate a better understanding of the embodiments described herein, the following examples of various representative embodiments are given. In no way should the following examples be read to limit, or to define, the scope of the present disclosure.

EXAMPLES

[0106] Prophetic Example. A mixed-matrix membrane will be fabricated by dispersing a plurality of optionally modified carbon nanotubes in a solvent. For example, the carbon nanotubes may be surface modified by an oxidation conducted in H2SO4/HNO3. The optionally modified carbon nanotubes will be sonicated in the solvent for a period of time to promote dispersion, such as from about 1 hour to about 3 hours. Separately, a solution of norbomene-based polymer will be prepared and filtered through a 0.2 micron pore filter. The solution of the norbomene-based polymer will then be slowly combined with the dispersion of carbon nanotubes under stirring and/or sonication. The combined mixture will then be cast into a membrane support structure, and the solvent will be removed to yield a solid membrane film. The solid membrane film will then be washed with a low boiling point solvent e.g., methanol) in which the membrane materials are insoluble. Finally, the membrane film will be placed under vacuum and optionally heated for a few hours.

[0107] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “contains”, “containing”, “includes”, “including,” “comprises”, and/or “comprising,” and variations thereof, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[0108] Terms of orientation used herein are merely for purposes of convention and referencing and are not to be construed as limiting. However, it is recognized these terms could be used with reference to an operator or user. Accordingly, no limitations are implied or to be inferred. In addition, the use of ordinal numbers (e.g., first, second, third, etc.) is for distinction and not counting. For example, the use of “third” does not imply there must be a corresponding “first” or “second.” Also, if used herein, the terms “coupled” or “coupled to” or “connected” or “connected to” or “attached” or “attached to” may indicate establishing either a direct or indirect connection, and is not limited to either unless expressly referenced as such.

[0109] While the disclosure has described several exemplary embodiments, it will be understood by those skilled in the art that various changes can be made, and equivalents can be substituted for elements thereof, without departing from the spirit and scope of the invention. In addition, many modifications will be appreciated by those skilled in the art to adapt a particular instrument, situation, or material to embodiments of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, or to the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative.

[0110] While the present disclosure has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments may be devised which do not depart from the scope of the disclosure as described herein. Accordingly, the scope of the disclosure should be limited only by the attached claims.

[0U1] All documents described herein are incorporated by reference herein for purposes of all jurisdictions where such practice is allowed, including any priority documents and/or testing procedures to the extent they are not inconsistent with this text. As is apparent from the foregoing general description and the specific embodiments, while forms of the disclosure have been illustrated and described, various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the disclosure be limited thereby. For example, the compositions described herein may be free of any component, or composition not expressly recited or disclosed herein. Any method may lack any step not recited or disclosed herein. Likewise, the term “comprising” is considered synonymous with the term “including.” Whenever a method, composition, element or group of elements is preceded with the transitional phrase “comprising,” it is understood that we also contemplate the same composition or group of elements with transitional phrases “consisting essentially of,” “consisting of,” “selected from the group of consisting of,” or “is” preceding the recitation of the composition, element, or elements and vice versa. [0112] Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth used in the present specification and associated claims are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by one or more embodiments described herein. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claim, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Claims

CLAIMS The invention claimed is:

1. A polymer membrane comprising: a matrix material comprising a norbomene-based polymer; and a plurality of carbon nanotubes dispersed in the matrix material.

2. The polymer membrane of claim 1 , wherein the carbon nanotubes comprise about 0.01 wt% to about 40 wt% of the polymer membrane based on total mass.

3. The polymer membrane of claim 1 , wherein the polymer membrane has a thickness ranging from about 0.1 microns to about 800 microns.

4. The polymer membrane of claim 1 , wherein at least a portion of the plurality of carbon nanotubes is modified with a covalent surface modification or a non-covalent surface modification.

5. The polymer membrane of claim 1, wherein the norbomene-based polymer comprises at least one homopolymer of a norbomene-based monomer.

6. The polymer membrane of claim 1, wherein the norbomene-based polymer comprises a ring-opening metathesis polymerization reaction product, an addition polymerization reaction product, an arene-norbomene annulation polymerization reaction product, or any combination thereof.

7. The polymer membrane of claim 6, wherein the norbomene-based polymer comprises a ring-opening metathesis polymerization reaction product of an optionally substituted norbomene or an addition polymerization reaction product of an optionally substituted norbomene.

8. The polymer membrane of claim 6, wherein the norbomene-based polymer comprises a homopolymer or a copolymer comprising a polymerized reaction product of a nadimide monomer.

9. The polymer membrane of claim 8, wherein the nadimide monomer is polymerized by ring-opening metathesis polymerization or is polymerized by addition polymerization.

10. The polymer membrane of claim 6, wherein the norbomene-based polymer comprises a homopolymer or a copolymer comprising a polymerized reaction product of a vinyl norbomene monomer.

11. The polymer membrane of claim 10, wherein a vinyl group of the vinyl norbomene monomer is further functionalized after polymerization.

12. The polymer membrane of claim 11, wherein the vinyl group is epoxidized and then ring-opened with a nucleophile.

13. The polymer membrane of claim 10, wherein the vinyl norbomene monomer is polymerized by addition polymerization.

14. The polymer membrane of claim 6, wherein the norbomene-based polymer comprises a homopolymer or a copolymer comprising a polymerized reaction product of a tricyclononene monomer.

15. The polymer membrane of claim 1 , wherein the tricyclononene monomer is polymerized by ring-opening metathesis polymerization.

16. The polymer membrane of claim 6, wherein the norbomene-based polymer comprises an arene-norbomene annulation polymerization reaction product.

17. A method comprising : providing the polymer membrane of claim 1 ; contacting the polymer membrane with a gas stream comprising carbon dioxide and one or more additional gases; and separating at least a first portion of the carbon dioxide from the gas stream using the polymer membrane.

18. The method of claim 17, wherein the gas stream comprises a natural gas stream.

19. The method of claim 18, wherein the natural gas stream has a pressure of about 0.01 bar to about 50 bar and/or has a temperature of about 10°C to about 100°C.

20. The method of claim 18, wherein the natural gas stream contacts the polymer membrane as the natural gas stream exits a wellbore.