WO2013070912A1

WO2013070912A1 - Synthesis of silicone ionomer membranes and the use thereof

Info

Publication number: WO2013070912A1
Application number: PCT/US2012/064146
Authority: WO
Inventors: Gang Lu
Original assignee: Dow Corning Corporation
Priority date: 2011-11-10
Filing date: 2012-11-08
Publication date: 2013-05-16

Abstract

The present invention relates to membranes and methods of making and using the same. In some examples, the membrane can be supported or unsupported. The membrane includes a cured product of a modified silicone composition. The modified silicone composition includes (A) a curable silicone composition. The modified silicone composition also includes (B) a salt of a carboxylic acid.

Description

SYNTHESIS OF SILICONE lONOMER MEM BRANES AND THE USE THEREOF

CLAIM OF PRIORITY

This application claims the benefit of priority of U.S. Patent Application Serial No. 61/558,052, entitled "SYNTHESIS OF SILICONE lONOMER

MEMBRANES AND THE USE THEREOF," filed on November 10, 201 1 , which application is incorporated by reference herein in its entirety.

Artificial membranes can be used to perform separations on both a small and large scale, which makes them very useful in many settings. For example, membranes can be used to purify water, to cleanse blood during dialysis, and to separate gases. Some common driving forces used in membrane separations are pressure gradients and concentration gradients. Membranes can be made from polymeric structures, for example, and can have a variety of surface chemistries, structures, and production methods. Membranes can be made by hardening or curing a composition.

Membrane-based gas separation has become an important chemical process which can compete commercially with cryogenic distillation, absorption and pressure swing adsorption. The use of membranes to separate gases is an important technique that can be used in many industrial procedures. Examples can include recovery of hydrogen gas in ammonia synthesis, recovery of hydrogen in petroleum refining, separation of methane from other components in biogas synthesis, enrichment of air with oxygen for medical or other purposes, removal of water vapor from natural gas, removal of carbon dioxide (CO2) and dihydrogen sulfide (H2S) from natural gas, and carbon capture applications such as the removal of CO2 from flue gas streams generated by combustion processes.

SU MMARY OF THE INVENTION

In various embodiments, the present invention provides an unsupported membrane. The unsupported membrane includes a cured product of a modified silicone composition. The membrane is free-standing. The membrane has a CO2/CH4 selectivity of at least 3.0. The modified silicone composition includes

(A) a curable silicon composition. The modified silicone composition also includes

(B) a salt of a carboxylic acid. In various embodiments, the present invention provides a supported membrane. The supported membrane includes a porous substrate. The supported membrane also includes a membrane. The membrane includes a cured product of a modified silicone composition. The cured product of the modified silicone composition is on the porous substrate. The membrane has a CO2/CH4 selectivity of at least 3.0. The modified silicone composition includes

(A) a curable silicone composition. The modified silicone composition also includes (B) a salt of a carboxylic acid.

In various embodiments, the present invention provides a method of separating gas components in a feed gas mixture. The method includes contacting a first side of a membrane with a feed gas mixture to produce a permeate gas mixture on a second side of the membrane and a retentate gas mixture on the first side of the membrane. The membrane includes a cured product of a modified silicone composition. The permeate gas mixture is enriched in the first gas component. The retentate gas mixture is depleted in the first gas component. The modified silicone composition includes (A) a curable silicone composition. The modified silicone composition also includes (B) a salt of a carboxylic acid.

Various embodiments of the present invention provide advantages over other membranes and methods of making and using the same, some of which are surprising and unexpected. For example, some embodiments of the membrane exhibit both high permeability and high selectivity for particular components in a gas mixture, compared to a membrane prepared using a similar silicone composition without a salt of a carboxylic acid. For example, in some embodiments the membrane exhibits high CO2/CH4 selectivity compared with a membrane prepared using a similar silicone composition without a salt of a carboxylic acid. In some embodiments, the present invention provides a simpler method of forming membranes than other methods. In some examples, the curing time to form the membranes can be conveniently shorter than other methods, such as for example 5 to 30 minutes. In various examples, the curing conditions used to form the membrane can be more mild than that used in other methods. In some embodiments, the starting materials for membrane formation can be readily available. In various embodiments, the membranes of the present invention can have excellent and advantageous mechanical properties. Often carboxylic acid salts do not have good dissolution properties in organic systems. Additionally, silicone compositions are known to generally be less polar than organic systems. Further, the formation of membranes from heterogeneous mixtures is generally not a standard technique for membrane formation. Therefore, one of skill in the art would generally assume that carboxylic acid salts would dissolve in silicone compositions even less well than they dissolve in organic solutions, and thus would generate an even more heterogeneous mixture than occurs with and organic solution and a carboxylic salt; therefore, it would be unexpected to one of skill in the art that the combination of a carboxylic acid salt and a silicone composition could be used to successfully generate membranes, and even more surprising that the membranes can have advantageous properties over certain membranes generated without a carboxylic acid salt.

Membranes including a cured product of a silicone composition including a carboxylic acid salt are not known, and methods of making or using such membranes are not known.

BRIEF DESCRIPTION OF THE FIGURES

In the drawings, which are not necessarily drawn to scale, like numerals describe substantially similar components throughout the several views. Like numerals having different letter suffixes represent different instances of substantially similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

FIG. 1 illustrates selectivity versus nominal ionic strength, in accordance with various embodiments.

FIG. 2 illustrates permeance versus nominal ionic strength, in accordance with various embodiments.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to certain embodiments of the disclosed subject matter, examples of which are illustrated in part in the accompanying drawings. While the disclosed subject matter will be described in conjunction with the enumerated claims, it will be understood that the exemplified subject matter is not intended to limit the claims to the disclosed subject matter. Values expressed in a range format should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a range of "about 0.1 % to about 5%" or "about 0.1 % to 5%" should be interpreted to include not just about 0.1 % to about 5%, but also the individual values (e.g., 1 %, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.1 % to 0.5%, 1 .1 % to 2.2%, 3.3% to 4.4%) within the indicated range. The statement "about X to Y" has the same meaning as "about X to about Y." Likewise, the statement "about X, Y, or about Z" has the same meaning as "about X, about Y, or about Z."

In this document, the terms "a," "an," or "the" are used to include one or more than one unless the context clearly dictates otherwise. The term "or" is used to refer to a nonexclusive "or" unless otherwise indicated. In addition, it is to be understood that the phraseology or terminology employed herein, and not otherwise defined, is for the purpose of description only and not of limitation. Any use of section headings is intended to aid reading of the document and is not to be interpreted as limiting; information that is relevant to a section heading may occur within or outside of that particular section. Furthermore, all publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference should be considered supplementary to that of this document; for irreconcilable

inconsistencies, the usage in this document controls.

In the methods of manufacturing described herein, the steps can be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited.

Furthermore, specified steps can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed step of doing X and a claimed step of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.

The term "about" can allow for a degree of variability in a value or range, for example, within 10%, within 5%, or within 1 % of a stated value or of a stated limit of a range. The term "substantially" as used herein refers to a majority of, or mostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more.

The term "organic group" as used herein refers to but is not limited to any carbon-containing functional group. Examples include acyl, cycloalkyl, aryl, aralkyi, heterocyclyl, heteroaryl, or heteroarylalkyi, linear and/or branched groups such as alkyl groups, fully or partially halogen-substituted haloalkyl groups, alkenyl groups, alkynyl groups, acrylate and methacrylate functional groups; and other organic functional groups such as ether groups, cyanate ester groups, ester groups, carboxylate salt groups, and masked isocyano groups.

The term "substituted" as used herein refers to an organic group as defined herein or molecule in which one or more bonds to a hydrogen atom contained therein are replaced by one or more bonds to a non-hydrogen atom. The term "functional group" or "substituent" as used herein refers to a group that can be or is substituted onto a molecule, or onto an organic group. Examples of substituents or functional groups include, but are not limited to, any organic group, a halogen (e.g., F, CI, Br, and I); a sulfur atom in groups such as thiol groups, alkyl and aryl sulfide groups, sulfoxide groups, sulfone groups, sulfonyl groups, and sulfonamide groups; a nitrogen atom in groups such as amines,

hydroxylamines, nitriles, nitro groups, N-oxides, hydrazides, azides, and enamines; and other heteroatoms in various other groups.

The term "alkyl" as used herein refers to straight chain and branched alkyl groups and cycloalkyl groups having from 1 to about 20 carbon atoms, and typically from 1 to 12 carbons or, in some embodiments, from 1 to 8 carbon atoms. Examples of straight chain alkyl groups include those with from 1 to 8 carbon atoms such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, and n-octyl groups. Examples of branched alkyl groups include, but are not limited to, isopropyl, isobutyl, sec-butyl, t-butyl, neopentyl, isopentyl, and 2,2- dimethylpropyl groups. As used herein, the term "alkyl" encompasses all branched chain forms of alkyl. Representative substituted alkyl groups can be substituted one or more times with any functional group, for example, amino, hydroxy, cyano, carboxy, nitro, thio, alkoxy, and halogen groups.

The term "alkenyl" as used herein refers to straight and branched chain and cyclic alkyl groups as defined herein, except that at least one double bond exists between two carbon atoms. Thus, alkenyl groups have from 2 to about 20 carbon atoms, and typically from 2 to 12 carbons or, in some embodiments, from 2 to 8 carbon atoms. Examples include, but are not limited to

vinyl, -CH=CH(CH₃), -CH=C(CH₃)₂, -C(CH₃)=CH₂, -C(CH₃)=CH(CH₃), -C(CH₂C

H₃)=CH2, cyclohexenyl, cyclopentenyl, cyclohexadienyl, butadienyl, pentadienyl, and hexadienyl, among others.

The term "aryl" as used herein refers to cyclic aromatic hydrocarbons that do not contain heteroatoms in the ring. Thus aryl groups include, but are not limited to, phenyl, azulenyl, heptalenyl, biphenyl, indacenyl, fluorenyl, phenanthrenyl, triphenylenyl, pyrenyl, naphthacenyl, chrysenyl, biphenylenyl, anthracenyl, and naphthyl groups. In some embodiments, aryl groups contain about 6 to about 14 carbons in the ring portions of the groups. Aryl groups can be unsubstituted or substituted, as defined herein. Representative substituted aryl groups can be mono-substituted or substituted more than once, such as, but not limited to, 2-, 3-, 4-, 5-, or 6-substituted phenyl or 2-8 substituted naphthyl groups, which can be substituted with carbon or non-carbon groups.

The term "resin" as used herein refers to polysiloxane material of any viscosity that includes at least one siloxane monomer that is bonded via a Si-O-Si bond to three or four other siloxane monomers. In one example, the polysiloxane material includes T or Q groups, as defined herein.

The term "radiation" as used herein refers to energetic particles travelling through a medium or space. Examples of radiation are visible light, infrared light, microwaves, radio waves, very low frequency waves, extremely low frequency waves, thermal radiation (heat), and black-body radiation.

The term "cure" as used herein refers to exposing to radiation in any form, heating, or allowing to undergo a physical or chemical reaction that results in hardening or an increase in viscosity.

The term "pore" as used herein refers to a depression, slit, or hole of any size or shape in a solid object. A pore can run all the way through an object or partially through the object. A pore can intersect other pores.

The term "free-standing" or "unsupported" as used herein refers to a membrane with the majority of the surface area on each of the two major sides of the membrane not contacting a substrate, whether the substrate is porous or not. In some embodiments, a membrane that is "free-standing" or "unsupported" can be 100% not supported on both major sides. A membrane that is "free-standing" or "unsupported" can be supported at the edges or at the minority (e.g. less than about 50%) of the surface area on either or both major sides of the membrane. The term "supported" as used herein refers to a membrane with the majority of the surface area on at least one of the two major sides contacting a substrate, whether the substrate is porous or not. In some embodiments, a membrane that is "supported" can be 100% supported on at least one side. A membrane that is "supported" can be supported at any suitable location at the majority (e.g. more than about 50%) of the surface area on either or both major sides of the membrane.

The term "enrich" as used herein refers to increasing in quantity or concentration, such as of a liquid, gas, or solute. For example, a mixture of gases A and B can be enriched in gas A if the concentration or quantity of gas A is increased, for example by selective permeation of gas A through a membrane to add gas A to the mixture, or for example by selective permeation of gas B through a membrane to take gas B away from the mixture.

The term "deplete" as used herein refers to decreasing in quantity or concentration, such as of a liquid, gas, or solute. For example, a mixture of gases A and B can be depleted in gas B if the concentration or quantity of gas B is decreased, for example by selective permeation of gas B through a membrane to take gas B away from the mixture, or for example by selective permeation of gas A through a membrane to add gas A to the mixture.

The term "solvent" as used herein refers to a liquid that can dissolve a solid, liquid, or gas. Nonlimiting examples of solvents are silicones, organic compounds, water, alcohols, ionic liquids, and supercritical fluids.

The term "selectivity" or "ideal selectivity" as used herein refers to the ratio of permeability of the faster permeating gas over the slower permeating gas, measured at room temperature. Unless otherwise designated, "selectivity" as used herein designates ideal selectivity.

The term "permeability" as used herein refers to the permeability coefficient (P_x) of substance X through a membrane, where q_mx = P_x ^* A ^* Δρ_χ ^*

(1 /δ), where q_mx is the volumetric flow rate of substance X through the membrane, A is the surface area of one major side of the membrane through which substance X flows, Δρ_χ is the difference of the partial pressure of substance

X across the membrane, and δ is the thickness of the membrane. P_x can also be expressed as V-5/(A-t-Ap), wherein P_x is the permeability for a gas X in the membrane, V is the volume of gas X which permeates through the membrane, δ is the thickness of the membrane, A is the area of the membrane, t is time, Δρ is the pressure difference of the gas X at the retente and permeate side.

Permeability is measured at room temperature, unless otherwise indicated.

The term "permeance" as used herein refers to the normalized

permeability (M_x) of substance X through a membrane, wherein M_x = Ρ_χ/ δ = V/(A-t-Ap_x), wherein P_x is the permeability for a gas X in the membrane, V is the volume of gas X which permeates through the membrane, δ is the thickness of the membrane, A is the area of the membrane, t is time, Δρ_χ is the difference of the partial pressure of substance X across the membrane. Permeance is measured at room temperature, unless otherwise indicated.

The term "Barrer" or "Barrers" as used herein refers to a unit of permeability, wherein 1 Barrer = 10^"^ (cm³ gas) cm cm^-2 s^~1 mmHg^"'' , or 10^~"Ό

(cm³ gas) cm cm^-2 s^"1 cm Hg^~1 , where "cm³ gas" represents the quantity of the gas that would take up one cubic centimeter at standard temperature and pressure.

The term "air" as used herein refers to a mixture of gases with a composition approximately identical to the native composition of gases taken from the atmosphere, generally at ground level.

The term "room temperature" as used herein refers to ambient temperature, which can be, for example, between about 15 °C and about 28 °C.

The term "coating" refers to a continuous or discontinuous layer of material on the coated surface, wherein the layer of material can penetrate the surface and can fill areas such as pores, wherein the layer of material can have any three- dimensional shape, including a flat or curved plane. In one example, a coating can be formed on one or more surfaces, any of which may be porous or nonporous, by immersion in a bath of coating material.

The term "surface" refers to a boundary or side of an object, wherein the boundary or side can have any perimeter shape and can have any three- dimensional shape, including flat, curved, or angular, wherein the boundary or side can be continuous or discontinuous.

The term "mil" as used herein refers to a thousandth of an inch, such that 1 mil = 0.001 inch = 25.4 microns.

In various embodiments, the present invention relates to an unsupported membrane comprising a cured product of a modified silicone composition, the composition comprising a curable silicone composition and a salt of a carboxylic acid. The invention also relates to a supported membrane comprising a porous substrate and a membrane on the porous substrate. The invention further relates to a method of separating gas components in a feed gas mixture.

Membrane

In one embodiment, the present invention includes a membrane that includes a cured product of a modified silicone composition. The modified silicone composition includes a curable silicone composition. The curable silicone composition of the present invention can include any suitable polysiloxane, in combination with any other suitable ingredient. The modified silicone composition also includes a salt of a carboxylic acid.

In another embodiment, the present invention provides a method of forming a membrane. The present invention can include the step of forming a membrane. The membrane can be formed on at least one surface of a substrate. For any membrane to be considered "on" a substrate, the membrane can be attached (e.g. adhered) to the substrate, or be otherwise in contact with the substrate without being adhered. The substrate can have any surface texture, and can be porous or non-porous. The substrate can include surfaces that are not coated with the membrane by the step of forming the membrane. All surfaces of the substrate can be coated by the step of forming the membrane, one surface can be coated, or any number of surfaces can be coated.

In an example, forming a membrane can include two steps. In the first step, the modified silicone composition can be applied to at least one surface of the substrate. In the second step, the applied composition can be cured to form the membrane. In some embodiments, the curing process of the composition can begin before, during, or after application of the composition to the surface. The curing process transforms the modified silicone composition into the membrane. The composition that forms the membrane can be in a liquid state. The membrane can be in a solid state.

The modified silicone composition be applied using conventional coating techniques, for example, immersion coating, die coating, blade coating, extrusion, curtain coating, drawing down, solvent casting, spin coating, dipping, spraying, brushing, roll coating, extrusion, screen-printing, pad printing, or inkjet printing.

Curing the modified silicone composition can include the addition of a curing agent or initiator such as, for example, a hydrosilylation catalyst. In some embodiments, the curing process can begin immediately upon addition of the curing agent or initiator. The addition of the curing agent or initiator may not begin the curing process immediately, and can require additional curing steps. In other embodiments, the addition of the curing agent or initiator can begin the curing process immediately, and can also require additional curing steps. The addition of the curing agent or initiator can begin the curing process, but not bring it to a point where there composition is cured to the point of being fully cured, or of being unworkable. Thus, the curing agent or initiator can be added before or during the coating process, and further processing steps can complete the cure to form the membrane.

The membrane can have any suitable thickness. In some examples, the membrane can have a thickness of from about 1 μιτι to about 20 μιτι. In some examples, the membrane can have a thickness of from about 0.1 μιτι to about 200 μιτι. In other examples, the membrane can have a thickness of from about 0.01 μιτι to about 2000 μιτι.

The membrane can be selectively permeable to one substance over another. In one example, the membrane is selectively permeable to one gas over other gases or liquids. In another example, the membrane is selectively permeable to more than one gas over other gases or liquids. In some examples, the membrane has a CO2/CH4 ideal selectivity of at least about 2.8, at least about

3.0, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 50, 75, 100, 150, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000,3000, 4000, or at least about 5000 at room temperature. In some embodiments, the membrane has an CO2 permeability coefficient of at least about 300 Barrer, 500 Barrer, 700 Barrer, 900 Barrer, 1000 Barrer, 1200 Barrer, 1400 Barrer, 1600 Barrer, 1800 Barrer, 2000 Barrer, 2500 Barrer, or at least about 3000 Barrer at room temperature.

The membrane of the present invention can have any suitable shape. In some examples, the membrane can be a plate-and-frame membrane, spiral wound membrane, tubular membrane, capillary fiber membrane, or hollow fiber membrane. In some embodiments, the membrane can be used in conjunction with a liquid that enhances gas transport, such as in a membrane contactor (e.g. a device that permits mass transfer between a gaseous phase and a liquid phase across a membrane without dispersing the phases in one another).

Supported Membrane

In some embodiments of the present invention, the membrane is supported on a porous or highly permeable non-porous substrate. A supported membrane has the majority of the surface area of at least one of the two major sides of the membrane contacting a porous or highly permeable non-porous substrate. A supported membrane on a porous substrate can be referred to as a composite membrane, where the membrane is a composite of the membrane and the porous substrate. The porous substrate on which the supported membrane is located can allow gases to pass through the pores and to reach the membrane. The supported membrane can be attached (e.g. adhered) to the porous substrate. The supported membrane can be in contact with the substrate without being adhered. The porous substrate can be partially integrated, fully integrated, or not integrated into the membrane.

In some examples, a supported membrane can be made by providing a substrate, wherein at least one surface of the substrate includes a plurality of pores or is highly permeable to the materials of interest. The substrate can be any suitable shape, including planar, curved, or any combination thereof.

Examples of porous substrates or highly permeable non-porous substrates includes a sheet, tube or hollow fiber. The porous substrate or highly permeable non-porous substrate can be smooth, be corrugated or patterned, or have any amount of surface roughness. A coating can be formed on the at least one porous surface of the substrate or on the at least one surface of the highly permeable non-porous substrate. Alternately, a porous or highly permeable non- porous substrate can be placed in contact with the formed coating before, during, or after curing of the coating. For example, the porous or highly permeable non- porous substrate can be laid upon an uncured, partially cured or fully cured coating, or drawn through an uncured or fully cured coating. Forming the coating can include applying the coating, and curing the coating. The steps of applying and curing can occur in any order and can occur simultaneously.

In another example, a supported membrane can be made by providing a substrate, wherein at least one surface of the substrate includes a plurality of pores or is highly permeable to the materials of interest. A first coating can be formed on the at least one porous or highly permeable surface of the substrate. Forming the first coating can include applying the coating, and curing the coating. The first coating can be formed sufficiently to at least partially fill the pores. The first coating can be removed, such that a substantially exposed substrate surface is formed, and such that the cured coating remains at least partially in the pores of the substrate. The first coating can be any suitable material, and can include materials that swell and absorb solvent or water. A second coating can be formed on the exposed substrate surface. Forming the second coating can include applying the coating, and curing the coating. The second coating can include a membrane, where the membrane includes a cured product of a curable silicone composition. The method can further include at least partially restoring the porosity of the porous substrate. For example, in embodiments with a first coating that swells and absorbs solvent or water, the porosity of substrate can be at least partially recovered by drying the first coating to remove the majority of the absorbed solvent or water.

In another example, the supported membrane is made in a manner identical to that disclosed herein pertaining to a free-standing membrane, but with the additional step of placing or adhering the free-standing membrane on a porous substrate to make a supported membrane.

The porous substrate can be, for example, a filter, or any substrate of any suitable shape that includes a fibrous structure or any structure. The porous substrate can be woven or non-woven. The porous substrate can be a frit, a porous sheet, or a porous hollow fiber. The porous substrate can be any suitable porous material known to one of skill in the art, in any shape. For example, the at least one surface can be flat, curved, or any combination thereof. The surface can have any perimeter shape. The porous substrate can have any number of surfaces, and can be any three-dimensional shape. Examples of three- dimensional shapes include cubes, spheres, cones, and planar sections thereof with any thickness, including variable thicknesses. The porous substrate can have any number of pores, and the pores can be of any size, depth, shape, and distribution. In one example, the porous substrate has a pore size of from about 0.2 nm to about 500 μιτι. The at least one surface can have any number of pores. In some examples, the pores size distribution may be asymmetric across the thickness of the porous sheet, film or fiber.

Suitable examples of porous substrates include porous polymeric films, fibers or hollow fibers, or porous polymers or any suitable shape or form.

Examples of polymers that can form porous polymers suitable for use as a porous substrate in embodiments of the present invention include those disclosed in U.S. Patent No. 7,858,197. For example, suitable polymers include polyethylene, polypropylene, polysulfones, polyamides, polyether ether ketone (PEEK), polyarylates, polyaramides, polyethers, polyarylethers, polyimides,

polyetherimides, polyphthalamides, polyesters, polyacrylates, polymethacrylates, cellulose acetate, polycarbonates, polyacrylonitrile, polytetrafluoroethylene and other fluorinated polymers, polyvinylalcohol, polyvinylacetate, syndiotactic or amorphous polystyrene, Kevlar™ and other liquid crystalline polymers, epoxy resins, phenolic resins, polydimethylsiloxane elastomers, silicone resins, fluorosilicone elastomers, fluorosilicone resins, polyurethanes, and copolymers, blends or derivatives thereof. Polymers that can form porous polymers suitable for use as a porous substrate in embodiments of the present invention can also include other copolymers or polymeric alloys, which can be two or more miscible or partially miscible polymers, and polymeric blends, which can have discrete non- miscible phases. Examples of polymers that can form porous polymers suitable for use as a porous or highly permeable substrate in embodiments of the present invention include thermoplastic or thermoset polymers, including but not limited to those commonly known in the art. The polymers that can form porous polymers suitable for use as a porous substrate in embodiments of the present invention may be modified with supplemental additives including, but not limited to, antioxidants, coloring agents such as pigments and dyes, flame retardants, process aids, antistatic agents, impact modifiers, nucleating agents, flow aids, ignition resistant additives, coupling agents, lubricants, antiblocking agents, mold release additives, plasticizers, ultraviolet ray inhibitors, or thermal stabilizers.

Suitable porous substrates can include, for example, porous glass, various forms and crystal forms of porous metals, ceramics and alloys, including porous alumina, zirconia, titania, steel, stainless steel, titanium, aluminum, copper, nickel, zinc, iron, manganese, magnesium, iron, chromium, vanadium, silver, gold, platinum, palladium, rhodium, lead, tin, antimony, silicon, germanium, silicon carbide, tungsten carbide.

Unsupported Membrane

In some embodiments of the present invention, the membrane is unsupported, also referred to as free-standing. The majority of the surface area on each of the two major sides of a free-standing membrane are not contacting a substrate, whether the substrate is porous or not. In some embodiments, a freestanding membrane can be 100% unsupported. A free-standing membrane can be supported at the edges or at the minority (e.g. less than 50%) of the surface area on either or both major sides of the membrane. The support for a freestanding membrane can be a porous or highly permeable substrate, or a nonporous or non-highly permeable substrate. Examples of suitable supports for a free-standing membrane can include but is not limited to any examples of supports given herein for supported membranes. A free-standing membrane can have any suitable shape, regardless of the percent of the free-standing membrane that is supported. Examples of suitable shapes for free-standing membranes include, for example, squares, rectangles, circles, tubes, cubes, spheres, cones, and planar sections thereof, wherein the free-standing membrane can have any suitable thickness, including variable thicknesses.

A support for a free-standing membrane can be attached to the membrane in any suitable manner, for example, by clamping, with use of adhesive, by melting the membrane to the edges of the substrate, or by chemically bonding the membrane to the substrate by any suitable means. The support for the freestanding membrane can be unattached to the membrane but nonetheless in contact with the membrane and held in place by friction or gravity or other suitable means. The support can include, for example, a frame around the edges of the membrane, which can optionally include one or more cross-beam supports within the frame. The frame can be any suitable shape, including a square or circle, and the cross-beam supports, if any, can form any suitable shape within the frame. The frame can be any suitable thickness. The support can be, for example, a cross-hatch pattern of supports for the membrane, where the cross-hatch pattern has any suitable dimensions.

A free-standing membrane can be made, for example, by the steps of coating or applying a silicone composition onto a release substrate, curing the composition, and removing the membrane from the release substrate. After application of the composition to the release substrate, the assembly can be referred to as a laminated film or fiber. During or after the curing process the membrane can be at least partially removed from at least one release substrate. In some examples, after the unsupported membrane is removed from a release substrate, the membrane is then attached to a support, as described herein. In some examples, an unsupported membrane is made by the steps of coating a composition onto one or more release substrates, curing the composition, and removing the membrane from at least one of the one or more release substrates, while leaving at least one of the one of more substrates in contact with the membrane. In some embodiments, the membrane is entirely removed from the release substrate. In one example, the membrane can be peeled away from the release substrate. The release substrate can be any suitable release substrate that allows a membrane formed thereon to be removed, such as for example Teflon or another slippery material.

After application of the silicone composition, and before, during, or after the curing process, the thickness or shape of the applied composition can be altered via any suitable means, for example leveled or otherwise adjusted, such that the membrane that results after the curing process has the desired thickness and shape. In one example, a doctor blade or drawdown bar is used to adjust the thickness of the applied composition. In another example, a conical die is used to adjust the thickness of the applied composition on a fiber that is later removed.

In examples that include a substrate, the substrate can be porous or nonporous. The substrate can be any suitable material, and can be any suitable shape or size, including planar, curved, solid, hollow, or any combination thereof. Suitable materials for porous or nonporous substrates include any polymers described above as suitable for use as porous substrates in supported membranes. The substrate can be a water soluble polymer that is dissolved by purging with water. The substrate can be a fiber or hollow fiber, as described in US 6,797,212 B2. In some examples, the substrate is coated with a material prior to formation of the membrane that facilitates the removal of the membrane once formed. The material that forms the substrate can be selected to minimize sticking between the membrane and the substrate. In some examples, the membrane can be heated, cooled, washed, etched or otherwise treated to facilitate removal from the substrate. In other examples, air pressure can be used to facilitate removal of the membrane from the substrate.

Method of Gas Separation

The present invention also provides a method of separating gas components in a feed gas mixture by use of the membrane described herein. The method includes contacting a first side of a membrane with a feed gas mixture to produce a permeate gas mixture on a second side of the membrane and a retentate gas mixture on the first side of the membrane. The permeate gas mixture is enriched in the first gas component. The retentate gas mixture is depleted in the first gas component.

The membrane can be free-standing or supported by a porous or permeable substrate. In some embodiments, the pressure on either side of the membrane can be about the same. In other embodiments, there can be a pressure differential between one side of the membrane and the other side of the membrane. For example, the pressure on the retentate side of the membrane can be higher than the pressure on the permeate side of the membrane. In other examples, the pressure on the permeate side of the membrane can be higher than the pressure on the retentate side of the membrane.

The feed gas mixture can include any mixture of gases. For example, the feed gas mixture can include air, hydrogen, carbon dioxide, nitrogen, ammonia, methane, water vapor, hydrogen sulfide, or any combination thereof. The feed gas can include any gas known to one of skill in the art. The membrane can be selectively permeable to any one gas in the feed gas, or to any of several gases in the feed gas. The membrane can be selectively permeable to all but any one gas in the feed gas.

Any number of membranes can be used to accomplish the separation. For example, one membrane can be used. In other examples, two, three, four, five, six, seven, eight, nine, ten, or any suitable number of membranes can be used. The membranes need not all include the same reaction product. In some embodiments, all the membranes include the same reaction product. The membranes can have different properties, and can have different permeability for a particular gas. In other embodiments, the membranes have the same properties. Any combination of free-standing and supported membranes can be used.

The membranes can be manufactured as flat sheets or as fibers and can be packaged into any suitable variety of modules including hollow fibers, sheets or arrays of hollow fibers or sheets. Modules can include hollow fiber modules, spiral wound modules, plate-and-frame modules, tubular modules and capillary fiber modules. The sheets, fibers or leaflets may be of any size or aspect ratio and can assume any packing density in the module. Methods of making hollow fibers modules and spiral wound modules are known in the art, such as described in Baker, R. W. Membrane Technology and Applications, 2nd Edition; 2nd ed. ; John Wiley & Sons Inc. : West Sussex, England, 2004, and in U.S. Patents 3,339,341 and 4,871 ,379 (Maxwell et al., Edwards et al.) and U.S. Patent 5,034, 126 (Reddy et al.). Various methods and configurations for delivering the feed gas mixture and recovering the permeate and retentate mixtures are also known in the art.

One versed in the art of membrane separations can identify operating conditions for a given combination of membrane performance properties such as selectivity and flux to achieve a desired level of separation optimized on the basis of capital and operating costs, plant footprint, environmental conditions, and maintenance and reliability. The membrane system can be operated in conjunction with compressors, vacuum systems, pre-filters, heaters, chillers, condensers, or any other type of suitable operation either upstream or downstream of the membrane system. The permeate side of the membrane can be operated under a positive pressure, ambient pressure, or negative pressure (e.g. vacuum) with or without a sweep gas or a sweep liquid such as found in a membrane contactor (e.g. a device that permits mass transfer between a gaseous phase and a liquid phase across a membrane without dispersing the phases in one another). The sweep gas can be any gas, and can originate from outside the process or be recycled from within the process, or include a mixture thereof. For example, hollow fiber modules can be fed from the bore side or from the shell side, at any position of entry. The feed gas inlets and permeate gas outlets can be positioned to permit a counter-current, cross-current or co-current flow configuration.

The modules can be operated as single membrane modules or organized further into arrays or banks of modules. The individual membrane modules or arrays or banks of modules can further be configured into additional staged superstructures, such as in series, parallel or cascade configurations, to allow enhanced flux or separation. Partial recycling of the permeate or retentate can be used to achieve a more efficient separation. For example, if the residue stream requires further purification, it may be passed to a second bank of membrane modules for further separation. Likewise, if the permeate stream requires further concentration, it may be passed to a second bank of membrane modules for a second-stage separation. Such multi-stage or multi-step processes, and variants thereof, will be familiar to those of skill in the art, who will appreciate that the membrane separation step may be configured in many possible ways, including single-stage, multistage, multistep, or more complicated arrays of two or more units in serial or cascade arrangements.

Curable Silicone Composition

The membrane of the present invention includes the cured product of a modified silicone composition. The modified silicone composition of the present invention includes a curable silicone composition. The curable silicone composition includes at least one suitable polysiloxane compound. The silicone composition includes suitable ingredients to allow the composition to be curable in any suitable fashion. In addition to the at least one suitable polysiloxane, the silicone composition can include any suitable additional ingredients, including any suitable organic or inorganic component, including components that do not include silicon, including components that do not include a polysiloxane structure. In some examples, the cured product of the modified silicone composition includes a polysiloxane.

The curable silicon composition can include molecular components that have properties that allow the composition to be cured. In some embodiments, the properties that allow the silicone composition to be cured are specific functional groups. In some embodiments, an individual compound contains functional groups or has properties that allow the silicone composition to be cured by one or more curing methods. In some embodiments, one compound can contain functional groups or have properties that allow the silicone composition to be cured in one fashion, while another compound can contain functional groups or have properties that allow the silicone composition to be cured in the same or a different fashion. The functional groups that allow for curing can be located at pendant or, if applicable, terminal positions in the compound.

The silicone composition can include an organic compound. The organic compound can be any suitable organic compound. The organic compound can be, for example, an organosilicon compound. The organosilicon compound can be any organosilicon compound. The organosilicon compound can be, for example, a silane, polysilane, siloxane, or a polysiloxane, such as any suitable one of such compound as known in the art. The silicone composition can contain any number of suitable organosilicon compounds, and any number of suitable organic compounds. An organosilicon compound can include any functional group that allows for curing.

In some embodiments, the organosilicon compound can include a silicon- bonded hydrogen atom, such as organohydrogensilane or an

organohydrogensiloxane. In some embodiments, the organosilicon compound can include an alkenyl group, such as an organoalkenylsilane or an organoalkenyl siloxane. In other embodiments, the organosilicon compound can include any functional group that allows for curing. The organosilane can be a monosilane, disilane, trisilane, or polysilane. Similarly, the organosiloxane can be a disiloxane, trisiloxane, or polysiloxane. The structure of the organosilicon compound can be linear, branched, cyclic, or resinous. Cyclosilanes and cyclosiloxanes can have from 3 to 12 silicon atoms, alternatively from 3 to 10 silicon atoms, alternatively from 3 to 4 silicon atoms.

In one example, an organohydrogensilane can have the formula HR¹2Si-

R²-SiR¹2H, wherein R¹ is C-| _-| Q hydrocarbyl or C-| _-| Q halogen-substituted hydrocarbyl, both free of aliphatic unsaturation, linear or branched, and R² is a hydrocarbylene group free of aliphatic unsaturation having a formula selected from monoaryl such as 1 ,4-disubstituted phenyl, 1 ,3-disubstituted phenyl; or bisaryl such as 4,4'-disubstituted-1 ,1 '-biphenyl, 3,3'-disubstituted-1 ,1 '-biphenyl, or similar bisaryl with a hydrocarbon chain including 1 to 6 methylene groups bridging one aryl group to another.

The organosilicon compound can be an organopolysiloxane compound. In some examples, the organopolysiloxane compound has an average of at least one, two, or more than two functional groups that allow for curing. The organopolysiloxane compound can have a linear, branched, cyclic, or resinous structure. The organopolysiloxane compound can be a homopolymer or a copolymer. The organopolysiloxane compound can be a disiloxane, trisiloxane, or polysiloxane.

In one example, an organopolysiloxane can include a compound of the formula

(a) R¹ ₃SiO(R¹ ₂SiO)_a(R¹ R²SiO)_pSiR¹ ₃, or

(b) R⁴R³ ₂SiO(R³ ₂SiO)_%(R³R⁴SiO)5SiR³ ₂R⁴.

In formula (a), a has an average value of about 0 to about 2000, and β has an average value of about 2 to about 2000. Each R¹ is independently a monovalent functional group. Suitable monovalent functional groups include, but are not limited to, acrylic groups; alkyl; halogenated hydrocarbon groups; alkenyl; alkynyl ; aryl ; and cyanoalkyl. Each R² is independently a functional group that allows for curing of the silicone composition, or R^ .

In formula (b), χ has an average value of 0 to 2000, and δ has an average value of 0 to 2000. Each R³ is independently a monovalent functional group. Suitable monovalent functional groups include, but are not limited to, acrylic groups; alkyl; halogenated hydrocarbon groups; alkenyl ; alkynyl; aryl ; and cyanoalkyl. Each R⁴ is independently a functional group that allows for curing of the silicone composition, or R³.

An organopolysiloxane compound can contain an average of about 0.1 mole% to about 100 mole% of functional groups that allow for curing of the silicone composition, and any range of mole% therebetween. The mole percent of functional groups that allow for curing of the silicon composition in the resin is the ratio of the number of moles of siloxane units in the resin having a functional group that allows for curing of the silicone composition to the total number of moles of siloxane units in the organopolysiloxane, multiplied by 100.

The organopolysiloxane compound can be a single organopolysiloxane or a combination including two or more organopolysiloxanes that differ in at least one of the following properties: structure, viscosity, average molecular weight, siloxane units, and sequence.

Examples of organopolysiloxanes can include compounds having the average unit formula

(Rl R4R5si0₁/2)w(R¹ R⁴Si02/2)x(R⁴Si0₃/2)_y(Si04/2)z (I), wherein R¹ is a functional group independently selected from any optionally further substituted C-| ,-\ 5 functional group, including C-| ,-\ 5 monovalent aliphatic hydrocarbon groups, 04.-15 monovalent aromatic hydrocarbon groups, and monovalent epoxy-substituted functional groups, R⁴ is a functional group that allows for curing of the silicone composition or R^ or R^ , R^ is R^ or R⁴,

0<w<0.95, 0<x<1 , 0<y<1 , 0<z<0.95, and w+x+y+z∞1. In some embodiments, R^ is C-| _-| 0 hydrocarbyl or C-| _-| Q halogen-substituted hydrocarbyl, both free of aliphatic unsaturation, or C4 to C14 aryl. In some embodiments, w is from 0.01 to

0.6, x is from 0 to 0.5, y is from 0 to 0.95, z is from 0 to 0.4, and w+x+y+z∞1.

In descriptions of average unit formula, such as formula I, the subscripts w, x, y, and z are mole fractions. It is appreciated that those of skill in the art understand that for the average unit formula (I), the variables R¹ , R⁴, and R⁵ can independently vary between individual siloxane formula units. Alternatively, the variables R^ , R⁴, and R^ can independently be the same between individual siloxane formula units. For example, average unit formula (I) above can include the following average unit formula:

(R1 R⁴R5Si0_{1 /2})w(R^{1 a}R⁴Si0₂/₂)xl (R^{1 b}R⁴Si02/2)x2(R⁴Si0₃/2)_y(

Si0₄/₂)z

wherein subscripts x1 +x2 = x, and where R^ ^a is not equal to R^""³. Alternatively, R^{1 a} can be equal to R^{1 b}.

Salt of a Carboxylic Acid

The membrane of the present invention includes the cured product of a modified silicone composition. The modified silicone composition of the present invention includes a salt of a carboxylic acid. The inclusion of a carboxylic acid salt in the modified silicone composition can allow the resulting membrane to have advantageous properties over other membranes made without a carboxylic acid salt. In some examples, the carboxylic acid salt can allow the resulting membrane to have a higher selectivity or permeability for one or more gases than a membrane prepared without the carboxylic acid salt.

In some examples, the carboxylic acid salt chemically cross-links with one or more components of the curable silicone composition during curing, for example via free-radical polymerization of free-radical polymerizable groups, as described herein, such as carbonyl, carboxylate, vinyl, or other groups. In another example, cross-linking can occur via a hydrosilylation reaction of Si-H groups on one or more components of the curable silicone composition with unsaturated bonds that can be present in the salt. In other examples, some or all of an unsaturated carboxylic acid salt does not undergo chemical cross-linking, but is nonetheless integrated into the resulting cured product. In examples with a carboxylic acid salt with multiple unsaturated bonds, all, some, or none of the unsaturated bonds can cross-link during curing. Likewise, in examples with a carboxylic salt with multiple groups that can undergo cross-linking such as via free-radical polymerization, all, some, or none of the cross-linkable groups can cross-link during curing.

The anionic portion of the carboxylic acid salt can be any suitable deprotonated carboxylic acid. For example, the carboxylic acid from which the anion is derived can be any C-| .30, C-| .20. C-| ,-\ 2, or C-| .Q linear or branched alkanoic acid, alkenoic acid, alkynoic acid, or aryloic acid, substituted or unsubstituted. The acid can have zero, one, two, or any suitable number of unsaturated carbon-carbon bonds, including aromatic or aliphatic bonds. If substituted, the acid can be substituted at any suitable position, with any suitable substituent, such as for example halo, alkyl, heteroalkyl, aryl, heteroaryl, acyl, amino, cyano, hydroxy, and the like.

In various embodiments, the carboxylic acid can be a carboxylic acid that has no unsaturated aliphatic carbon-carbon bonds. In some examples, the carboxylic acid can have one or more unsaturated aromatic carbon-carbon bonds, or can have zero unsaturated carbon-carbon bonds. Examples of carboxylic acids with one or more unsaturated aromatic carbon-carbon bonds can include benzoic acid, salicylic acid; salts include for example silver benzoate. Examples of carboxylic acids with zero unsaturated carbon-carbon bonds can include propionic acid, butyric acid, lauric acid, or pentanoic acid; salts include, for example, zinc laurate. Acetoacetic acid is also an example, with example salts including titanium acetoacetate and zirconium acetate; however, one of skill in the art will readily recognize the enolic form of acetoacetic acid and salts thereof, relatively stable due to conjugation with a carbonyl group, can be considered to contain a unsaturated aliphatic carbon-carbon double bond.

In various embodiments, the carboxylic acid can be a carboxylic acid that has at least one unsaturated aliphatic carbon-carbon bond. For example, the unsaturated aliphatic carbon-carbon bond can be a double or a triple bond. In some examples, the anionic portion of the carboxylic acid salt can be any suitable carboxylic acid having at least one unsaturated aliphatic carbon-carbon bond. The acid can have one, two, or any suitable number of double or triple bonds. The unsaturation can occur at terminal or pendant positions. Specific examples of suitable carboxylic acids containing at least one unsaturated aliphatic carbon- carbon bond, wherein the acid can be deprotonated to provide the anion, include undecenoic acid, including 10-undecenoic acid, also called 10-undecylenic acid. Other examples include myristonleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic acid, arachidonic acid, eicosapentaenoic acid, erocic acid, docosahexaenoic acid, omega-3 fatty acids, omega-6 fatty acids, omega-9 fatty acids, conjugated fatty acids, pinolenic acid, and podocarpic acid. Specific examples of carboxylic acid salts having at least one unsaturated aliphatic carbon-carbon bond include methacrylate salts such as zinc or copper methacrylate, undecenoate salts such as zinc or copper undecenoate, ricinolate salts such as aluminum, magnesium, calcium, or sodium ricinolate.

The acid can be a monoacid, diacid, or have any suitable number of acidic protons which can form salts. Each deprotonated carboxylic acid can provide a -1 charge. In the salt, any suitable number of the carboxylic acidic protons can be deprotonated, including all or less than all of the carboxylic acid protons.

Examples of suitable polyacids include HOOC(CH2)xCOOH wherein X is 0-30, phthalic acid (o-, m-, or p-), maleic acid, fumaric acid, glutaconic acid, muconic acid, citric acid, and 1 ,3,5-tribenzoic acid.

The cationic portion of the carboxylic acid can be any one or more suitable cations. For example, the cation can be any suitable element having a positive charge such as an alkali metal cation, an alkaline earth metal cation, a transition metal cation, or a lanthanide metal cation. In another example, the cation can be any suitable polyatomic cation, such as for example NH4+ or H30+. Overall, the cation can have any suitable positive charge, e.g., +1 , +2, +3, such that for each deprotonated acid in the anion, a +1 charge is provided by the anion. For a cation with a +1 charge, the cation forms an ionic bond with one deprotonated carboxylic acid (-1 charge). For a cation with an overall positive charge greater than +1 , the charge can be supplied by a single cation or by multiple cations. In examples in which a single cation provides more than +1 charge, multiple deprotonated carboxylic acids can form ionic bonds to the single cation. Specific examples of suitable cations include Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, Fe²⁺, and Fe³⁺.

The carboxylic acid salt can have any suitable form prior to addition to the mixture. In some embodiments, the salt can be ground or otherwise processed to make it more suitable for integration into a cured silicone composition. In one example, the carboxylic acid salt is a powder prior to addition to the modified silicone composition. In one example, upon addition to the mixture, the salt completely or partially dissolves in the mixture. In some examples, the salt does not dissolve in the mixture. In some examples, the salt is stirred into the mixture to achieve an even dispersion of the salt within the mixture, whether the salt is completely or partially dissolved, or undissolved. In some examples, the particle size of the salt can influence the difficulty of achieving an approximately even dispersion; for example, larger particle sizes can cause agglomeration of particles causing an even dispersion of the salt to be more difficult to achieve.

In some examples, the carboxylic acid salt can be present in from about 0 wt% to about 90 wt%, about 0 wt % to about 80 wt%, or about 0 wt% to about 70 wt% of the modified silicone composition. In some embodiments, the carboxylic acid salt can be present in from about 10 wt% to about 70 wt%, about 20 wt% to about 60 wt%, or about 30 wt% to about 50 wt% of the modified silicone composition. In some embodiments, the carboxylic acid salt can be present in from about 30 wt% to about 35 wt%, about 35 wt% to about 40 wt%, about 40 wt% to about 45 wt%, or about 45 wt% to about 50 wt%. Wt% in this paragraph refers to the percent by weight based on the total weight of the modified silicone composition.

Curing

Embodiments of the membrane include a cured product of a modified silicone composition. Various methods of curing can be used, including any suitable method of curing, including for example hydrosilylation curing, condensation curing, free-radical curing, amine-epoxy curing, radiation curing, cooling, or any combination thereof. A composition that is cured via one curing method can be cured by other curing methods in addition to the one curing method. The modified silicone composition can include molecules with properties that allow one curing method, as well as molecules that allow different curing methods. In some embodiments, the modified silicone composition can include multiple features on the same molecule that allow the composition to be cured via one curing method and cured via other curing methods, and in some

embodiments, the modified silicone composition can include features that allow it to be cured via one curing method on one molecule and features that allow it to be curing via other curing methods on a different molecule.

A modified silicone composition that is curable via a particular method can include other compounds curable via the particular method in addition to silicone compounds. In some embodiments, the other compounds curable via the particular curing method can participate with the silicone compounds curable via the particular curing method during the application of the particular curing method. In other embodiments, the other compounds curable via the particular curing method do not participate with the silicone compounds curable via the particular curing method during application of the particular curing method.

In hydrosilylation curing, for example, an organosilicon compound that includes a silicon atom with a silicon-bonded hydrogen atom reacts with an unsaturated group such as an alkenyl group, adding across the unsaturated group and causing the unsaturated group to lose at least one degree of unsaturation (e.g. a double bond is converted to a single bond), such that the silicon atom is bound to one carbon atom of the originally unsaturated group, and the hydrogen atom is bound to the other carbon atom of the originally unsaturated group.

Having an average of at least two unsaturated groups on one or more molecules and an average of greater than two silicon-bonded hydrogen atoms on one or more molecules can help cross-linking to occur. In another example, having an average of greater than two unsaturated groups on one or more molecules and an average of at least two silicon-bonded hydrogen atoms on one or more molecules can help cross-linking to occur. In one example, a curable silicone composition that is hydrosilylation curable can include a compound having an average of at least two unsaturated groups per molecule; an organosilicon compound having an average of at least two silicon-bonded hydrogen atoms per molecule; and an optional hydrosilylation catalyst. In some embodiments, the hydrosilylation catalyst is present. In other embodiments, the hydrosilylation catalyst is not present. In some embodiments, the unsaturated groups are alkenyl groups.

In some embodiments, the hydrosilylation catalyst can be any

hydrosilylation catalyst including a platinum group metal or a compound containing a platinum group metal. Platinum group metals can include platinum, rhodium, ruthenium, palladium, osmium and iridium.

Examples of hydrosilylation catalysts include the complexes of chloroplatinic acid and certain vinyl-containing organosiloxanes disclosed by Willing in U.S. Pat. No. 3,419,593, such as the reaction product of chloroplatinic acid and 1 ,3-divinyl-1 ,1 ,3,3-tetramethyldisiloxane; microencapsulated

hydrosilylation catalysts including a platinum group metal encapsulated in a thermoplastic resin, as exemplified in U.S. Pat. No. 4,766,176 and U.S. Pat. No. 5,017,654; and photoactivated hydrosilylation catalysts, such as platinum(ll) bis(2,4-pentanedioate), as exemplified in U.S. Patent No. 7,799,842. An example of a suitable hydrosilylation catalyst can include a platinum(IV) complex of 1 ,3- diethenyl-1 ,1 ,3,3-tetramethyldisiloxane.

In another embodiment, the hydrosilylation catalyst can be at least one photoactivated hydrosilylation catalyst. The photoactivated hydrosilylation catalyst can be any of the well-known hydrosilylation catalysts including a platinum group metal or a compound containing a platinum group metal. The suitability of particular photoactivated hydrosilylation catalyst for use in a silicone composition of the present invention can be readily determined by routine experimentation.

The concentration of the hydrosilylation catalyst can be sufficient to catalyze hydrosilylation of the curable silicone composition, for example sufficient to catalyze the addition reaction (hydrosilylation) of an organosilicon compound having an average of at least two silicon-bonded hydrogen atoms per molecule with an organopolysiloxane having an average of at least two silicon-bonded alkenyl groups per molecule. Typically, the concentration of the hydrosilylation catalyst is sufficient to provide from about 0.1 to about 1000 ppm of a platinum group metal, from about 0.5 to about 500 ppm of a platinum group metal, and more preferably from about 1 to about 100 ppm of a platinum group metal, based on the total weight of the uncured composition. The rate of cure can be very slow below about 0.1 ppm of platinum group metal. The use of more than 1000 ppm of platinum group metal is possible, but is generally undesirable because of catalyst cost.

In condensation curing, for example, an organosilicon compound that includes a silicon-bonded hydrolysable group reacts with water to form a hydroxy- substituted silicon atom. The reactive hydroxy group can then attack other silicon atoms, including other silicon atoms with hydrolysable groups or with hydroxy groups, forming a polysiloxane. In some embodiments, the silicon atom that is attacked by the reactive hydroxy group can have a protonated hydroxy group or a hydrolysable group, wherein the protonated hydroxy group or the hydrolysable group is a good leaving group. In some embodiments, water is not required to hydrolyze a hydrolysable group, but rather a reactive hydroxy-substituted organosilicon is already present in the curable silicone composition, which can attack other silicon atoms, including silicon atoms with hydroxy groups or silicon atoms with hydrolysable groups. An acid or base catalyst is an optional component in condensation curable silicone compositions, such as any suitable organic or mineral acid, or any suitable base. In some embodiments, an acid or base catalyst is present. In other embodiments, an acid or base catalyst is not present.

A condensation curable silicone composition can include an organosilicon with at least one silicon-substituted hydrolysable group, or with at least one silicon-substituted hydroxy group. The organosilicon can be a silane, a polysilane, a siloxane, or a polysiloxane. The organosilicon can include an average of one silicon-substituted hydrolysable group per molecule, an average of two silicon- substituted hydrolysable groups per molecule, or more.

A hydrolysable group can be a group that reacts with water in the absence of a catalyst at any temperature from room temperature to 100 °C within several minutes, for example thirty minutes, to form a silanol (Si-OH) group, or another hydroxy-substituted group. Examples of hydrolysable groups can include, but are not limited to, -CI, -Br, -OR⁷, -OCH₂CH₂OR⁷, CH₃C(=0)0-, Et(Me)C=N-

0-, CH₃C(=0)N(CH₃)-, and -ONH₂, wherein R⁷ is C-| to C₈ hydrocarbyl or C-| to Cs halogen-substituted hydrocarbyl. In one example, a condensation curable silicone composition includes one or more of the following : Me2ViSiCI, Me₃SiCI, MeSi(OEt)₃, PhSiCI₃, MeSiCI₃, Me₂SiCI₂, PhMeSiCI₂, SiCI₄, Ph₂SiCI₂,

PhSi(OMe)₃, MeSi(OMe)₃, PhMeSi(OMe)₂, and Si(OEt)₄, wherein Me is methyl,

Et is ethyl, and Ph is phenyl.

Optionally, a condensation curable composition can include a

condensation catalyst. In some embodiments, a condensation catalyst is present. In other embodiments, a condensation catalyst is not present. Examples of condensation catalysts include, for example, amines, and complexes of lead, tin, zinc, titanium, zirconium, aluminum and iron with carboxylic acids. In one example, the condensation catalyst can be selected from tin(ll) and tin(IV) compounds such as tin dilaurate, tin dioctoate, and tetrabutyl tin; and titanium compounds such as titanium tetrabutoxide.

In free-radical curing, for example, a free-radical is generated. The free- radical then can attack a free-radical polymerizable functional group. The attacking group forms a bond to the free-radical polymerizable group, and transfers a radical thereto. The free-radical polymerizable functional group can then go on to attack other free-radical polymerizable functional groups.

A free-radical curable silicone composition can include an organosilicon with at least one free-radical polymerizable group. The organosilicon can be a silane, a polysilane, a siloxane, or a polysiloxane. The organosilicon can include an average of one free-radical polymerizable group per molecule, an average of two free-radical polymerizable groups per molecule, or more. In some embodiments, a free-radical curable silicone composition can include an organic compound that does not include silicon that has at least one free-radical polymerizable group. The organic compound that does not include silicon can include an average of one free-radical polymerizable groups per molecule, an average of two free-radical polymerizable groups per molecule, or more.

Examples of free-radical polymerizable groups include, for example, alkenyl groups and alkynyl groups, as well as groups such as ethers, ketones, aldehydes, carboxylates, ketals, acetals, cyano groups, nitro groups, or halogens.

Free-radicals can be generated by any suitable method. Free radicals can be initiated by, for example, thermal decomposition, photolysis, redox reactions, persulfates, ionizing radiation, electrolysis, plasma, sonication, or a combination thereof. In one example, a free-radical is generated using a free- radical initiator. A free-radical initiator is an optional ingredient. In some embodiments, a free-radical initiator is present. In other embodiments, a free- radical initiator is not present. In one example, the free-radical initiator can be a free-radical photoinitiator, an organic peroxide, or a free-radical initiator activated by heat. Further, a free-radical photoinitiator can be any free radical photoinitiator capable of initiating cure (cross-linking) of the free-radical polymerizable functional groups upon exposure to radiation, for example, having a wavelength of from 200 to 800 nm. In another example, the free-radical initiator is a organoborane free- radical intiator. In one example, the free-radical initiator can be an organic peroxide. For example, elevated temperatures can allow a peroxide to decompose and form a highly reactive radical, which can initiate free-radical polymerization. In some examples, decomposed peroxides and their derivatives can be byproducts.

The free-radical photoinitiator can be a single free-radical photoinitiator or a mixture comprising two or more different free-radical photoinitiators. The concentration of the free-radical photoinitiator can be from 0.1 to 6% (w/w), alternatively from 1 to 3% (w/w), based on the weight of the silicon compounds in the free-radical curable silicone composition.

In amine-epoxy curing, for example, a primary- or secondary-amine reacts with an epoxy compound to produce, for example, aminoalcohols. The epoxy-containing compound can be an organosilicon compound, or an organic compound that does not include silicon. The primary- or secondary-amine- containing compound can be an organosilicon, or an organic compound that does not include silicon. An amine-functional compound can be an amine- functionalized organopolysiloxane.

In an example, an amine-epoxy curable composition includes an epoxy- functional organosilicon compound and an amino-functional curing agent. In one example, the epoxy-functional organosilicon compound is a polysiloxane compound. The epoxy-functional organosilicon compound can have an average or at least two silicon-bonded epoxy-substituted functional groups per molecule and the curing agent can have an average of at least two nitrogen-bonded hydrogen atoms per molecule.

Radiation that can be used for radiation curing includes, for example, visible light, infrared light, microwaves, radio waves, very low frequency waves, extremely low frequency waves, thermal radiation (heat), and black-body radiation. Any of the curing methods disclosed herein can include radiation curing; for example, any of the curing methods disclosed herein can include the application of heat or light. For example, any of a hydrosilylation curable composition, a condensation curable composition, an epoxy-amine curable composition, or a composition curable by cooling, a free-radical curable composition, can include one or more steps that include the application of radiation, and the application of radiation to the curable composition can initiate, assist, or cause the chemical or physical processes that are part of the curing process. In some embodiments, any of hydrosilylation curing, condensation curing, epoxy-amine curing, free-radical curing, or curing via cooling can also be described as radiation curing, due to the application of radiation during the curing process. In other embodiments, any of hydrosilylation curing, condensation curing, epoxy-amine curing, free-radical curing, or curing via cooling are not described as radiation curing, due to the lack of applied radiation during the curing process.

In one example of cooling giving a cured product of a silicone composition, an organosilicone composition that essentially has a liquid flowable state is cooled at least as low as room temperature to give a silicone composition that essentially has a solid nonflowable state. Silicone compositions that include compounds that can behave as thermoplastics are an example of silicon composition that can be cooled to give a cured product of the silicon composition. The compound that behaves as a thermoplastic can be a polymer.

One example of a composition that includes a platinum catalyst is Karstedt's catalyst. One example of a free-radical initiator, which can operate thermally or with light activation, is VAROX DCBP-50 which includes bis(2,4- dichlorobenzoyl) peroxide, 50% in silicone oil.

Optional Ingredients

The membrane or the modified silicone composition that forms the membrane can, in some embodiments, include additional optional components. Any optional ingredient described herein can be present in the membrane or in the composition that forms the membrane; alternatively, any optional ingredient described herein can be absent from the membrane or the composition that forms the membrane. Without limitation, examples of such optional additional components include surfactants, emulsifiers, dispersants, polymeric stabilizers, crosslinking agents, combinations of polymers, crosslinking agents, catalysts useful for providing a secondary polymerization or crosslinking of particles, rheology modifiers, density modifiers, aziridine stabilizers, cure modifiers such as hydroquinone and hindered amines, free radical initiators, polymers, diluents, acid acceptors, antioxidants, heat stabilizers, flame retardants, scavenging agents, silylating agents, foam stabilizers, solvents, diluents, plasticizers, fillers and inorganic particles, pigments, dyes and dessicants. Liquids can optionally be used. An example of a liquid includes water, an organic solvent, any liquid organic compound, a silicone liquid, organic oils, ionic fluids, and supercritical fluids. Other optional ingredients include polyethers having at least one alkenyl group per molecule, thickening agents, fillers and inorganic particles, stabilizing agents, waxes or wax-like materials, silicones, organofunctional siloxanes, alkylmethylsiloxanes, siloxane resins, silicone gums, silicone carbinol fluids can be optional components, water soluble or water dispersible silicone polyether compositions, silicone rubber, hydrosilylation catalyst inhibitors, adhesion promoters, heat stabilizers, UV stabilizers, and flow control additives.

The present invention can be better understood by reference to the following examples which are offered by way of illustration. The present invention is not limited to the examples given herein.

General

Vinyl-substituted organopolysiloxane fluid was mixed with salts of a carboxylic acid in the presence of peroxides and thermally cured into membrane form. The elastomer membranes were evaluated for CO2/CH4 separation.

A variety of methods can be used to measure the permeability of a membrane to particular gases. In the following examples, gas permeability coefficients and ideal selectivities in a binary gas mixture were measured using a permeation cell including upstream (feed/retentate) and downstream (permeate) chambers that were separated by the membrane. The upstream chamber had one gas inlet and one gas outlet. The downstream chamber had one gas outlet. The upstream chamber was maintained at 35 psig pressure and was continuously supplied with a suitable mixture of CO2 gas and CH4 gas at a flow rate of between 0-200 standard cubic centimeters per minute (seem). The membrane was supported on a glass fiber filter disk with a diameter of 83 mm and a maximum pore diameter range of 10-20 μιτι (Ace Glass). The membrane area was defined by a placing a butyl rubber gasket with a diameter of 50 mm (Exotic Automatic & Supply) on top of the membrane. The downstream chamber was maintained at 5 psig pressure and was continuously supplied with a pure He stream at a flow rate of 20 seem. To analyze the permeability and selectivity of the membrane, the outlet of the downstream chamber was connected to a 6-port injector equipped with a 1 -ml_ injection loop. On command, the 6-port injector injected a 1 -mL sample into a gas chromatograph (GC) equipped with a thermal conductivity detector (TCD). The amount of gas permeated through the membrane was calculated by calibrating the response of the TCD detector to the gases of interest. The reported values of gas permeability and selectivity were obtained from measurements taken after the system had reached a steady state in which the permeate side gas composition became invariant with time.

Permeability of gas component i can be calculated by the following equation: Pj=V-5/(A-t-Ap), whereas Pj is the permeability for a gas i in a given membrane, V is the volume of gas which permeates through the membrane, δ is the thickness of the membrane, A is the area of the membrane, t is time, Δρ is the pressure difference of the gas i at the retente and permeation side. Ideal selectivity (a) of gas pair i and j is determined by a=Pj/Pj. Permeance (M) is normalized permeability of gas components: Mj=Pj/ δ.

"Filler loading" as given below indicates the wt% of the carboxylic acid salt used, based on the total weight of the composition that forms the membrane. "Parts" in these Examples indicates parts by weight unless otherwise indicated.

Examples 1 -3 were performed on a scale such that the total weight of the composition that forms the membrane was about 3-10 grams. Embodiments of the present invention encompass a total weight of the composition that forms the membrane of any suitable scale, as will be readily appreciated by one of skill in the art. About 3 measurements of data were taken at each filler loading %.

Example 1 . Fabrication and evaluation of silicone elastomer membrane containing zinc methacrylate.

Vinyl-terminated polydimethylsiloxane (average MW=77220,

viscosity=30, 000-40, 550 cSt (room temperature), vinyl content=0.07% wt., 68.0 parts), zinc methacrylate powder (29.9 parts), VAROX DCBP-50 (Bis(2,4- dichlorobenzoyl) peroxide, 50% in silicone oil, 2.1 parts) were mixed using a

SpeedyMixer® for about 5 minutes at about 3540 rotations per minute (rpm). The formulation was sandwiched in-between two fluorosilicone-coated release liners and extruded from a roll mill with a defined gap (about 10-mil). The thin film was heated at about 95 °C for about 30 minutes to afford a white membrane. The permeability and selectivity of the membrane were determined using the general procedure described above. Several other filler loadings and membrane thickness were also tried. Gas separation results are summarized in the table below:

39.8 199 3.71 520.40 1930.17

50 210 3.82 423.71 1618.10

Example 2. Fabrication and evaluation of silicone elastomer membrane containing zinc undecenoate.

Vinyl-terminated polydimethylsiloxane (average MW=77220, viscosity=30, 000-40, 550 cSt (room temperature), vinyl content=0.07% wt., 67.8 parts), zinc undecenoate powder (30.2 parts), VAROX DCBP-50 (Bis(2,4- dichlorobenzoyl) peroxide, 50% in silicone oil, 2 parts) were mixed using

SpeedyMixer® for about 5 minutes at about 3540 rpm. The formulation was sandwiched in-between two fluorosilicone-coated release liners and extruded from a roll mill with a defined gap (about 10-mil). The thin film was heated at about 95 °C for about 30 minutes to afford a white membrane. The permeability and selectivity of the membrane were determined using the general procedure described above. Several other filler loadings and membrane thickness were also tried. Gas separation results are summarized in the table below:

containing zinc undecenoate.

Vinyl-terminated polydimethylsiloxane (average MW=77220, viscosity=30, 000-40, 550 cSt (room temperature), vinyl content=0.07% wt., 5.2 parts), polymethylhydrogensiloxane-polydimethylsiloxane copolymer (average MW=721 , viscosity=5 (room temperature), Si-H wt% = 0.78% (average 3 Si-H per chain), 5.2 parts), zinc undecenoate powder (16.4 parts), and 1 -ethynyl-1 - cyclohexanol were mixed using SpeedyMixer® to form a clear mixture. Karstedt catalyst in polydimethylsiloxane (Pt% wt=2.4%, 2 parts) was then added and the resulting mixture was mixed again in the SpeedyMixer® for 2 minutes at about 3540 rpm, and then the mixture was degassed in a vacuum oven (room temperature, 1 torr, 5 minutes). The formulation was sandwiched in-between two fluorosilicone-coated release liners and extruded from a roll mill with a defined gap (about 1 0-mil). The thin film was heated at about 95 °C overnight to afford a translucent membrane. The permeability and selectivity of the membrane were determined using the general procedure described above. Several other filler loadings and membrane thickness were also tried. Gas separation results are summarized in the table below:

Examples 1 -3 demonstrate that inclusion of the salts enhanced CO2/CH4 separation efficiency while maintaining high gas permeability.

For the peroxide-cured system of Examples 1 and 2, the degree of the enhancement was found to positively correlate with the nominal ionic strength of the membranes. Without being bound to any theory of operation, the nominal ionic strength can be calculated by the following equation:

wherein q is the molar concentration of ion i (mole/Kg), Zj is the charge number of that ion, and the sum is taken over all ions (cations and anions) in the membrane. Since the membranes include a solid polymer matrix, the ionic strength is nominal and does not have the physical meaning as in solution chemistry; rather, it is a way to quantify how much salts are present in the membranes. As the nominal ionic strength of the membranes increases, both CO2 and CH4 permeability go down, while the CO2/CH4 selectivity increases. For both selectivity (Example 1 ,

FIG. 1 ) and permeability (Example 2, FIG. 2), linear correlations exist.

Particle size of the salts in silicone matrix was found to negatively impact the membrane performance, generally. Without being bound to any theory of operation, it was observed that with larger particle sizes, it was more difficult to achieve an even dispersion of the salt within the silicone material, due to for example the formation of agglomerates of the particles.

For zinc undecenoate, and other salts, high salt loading (>60%) can be detrimental to CO2/CH4 separation efficiency. Without being bound by any theory of operation, it was observed that when salt loading reaches a certain level, generally, the amount of silicone material available to bind the salt into the membrane, either via cross-linking or via any other method of incorporation, can decrease to the point wherein insufficient material is available to maintain the structure of the membrane. Thus, if too great an amount of salt is used, the membrane can suffer from structural problems, such as leaking, ripping, holes, gaps, and the like.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention that in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed. Thus, it should be understood that although the present invention has been specifically disclosed by preferred embodiments and optional features, modification and variation of the concepts herein disclosed may be resorted to by those skilled in the art, and that such modifications and variations are considered to be within the scope of this invention as defined by the appended claims.

Claims

CLAIMS What is claimed is:

1 . An unsupported membrane comprising:

a cured product of a modified silicone composition, wherein the membrane is free-standing, and the modified silicone composition comprises (A) a curable silicone composition and (B) a salt of a carboxylic acid.

2. The unsupported membrane of claim 1 , wherein the membrane has a CO2/CH4 selectivity of at least 3.0.

3. The unsupported membrane of any one of claims 1 -2, wherein the salt of the carboxylic acid is a salt of a carboxylic acid having at least one unsaturated aliphatic carbon-carbon bond.

4. The unsupported membrane of any one of claims 1 -3, wherein the curable silicone composition is a free radical-curable silicone composition selected from a peroxide-curable silicone composition, a radiation-curable silicone composition comprising a free radical initiator, and a high energy radiation-curable silicone composition.

5. The unsupported membrane of any one of claims 1 -4, wherein the curable silicone composition is selected from a hydrosilylation-curable silicone composition and a condensation-curable silicone composition.

6. The unsupported membrane of any one of claims 1 -5, wherein the salt of the carboxylic acid comprises a metal cation.

7. The unsupported membrane of claim 6, wherein the metal cation is selected from a transition metal cation and a lanthanide metal cation.

8. The unsupported membrane of any one of claims 1 -7, wherein the salt of the carboxylic acid is a zinc salt.

9. The unsupported membrane of any one of claims 1 -8, wherein the salt of the carboxylic acid comprises a nonmetal cation.

10. The unsupported membrane of claim 9, wherein the nonmetal cation is a quaternary ammonium cation.

1 1 . The unsupported membrane of any one of claims 1 -10, wherein the membrane is selected from a plate membrane, a spiral membrane, tubular membrane, and hollow fiber membrane.

12. A supported membrane, comprising:

a porous substrate; and

a membrane comprising a cured product of a modified silicone composition on the porous substrate; wherein the modified silicone composition comprises (A) a curable silicone composition and (B) a salt of a carboxylic acid.

13. The supported membrane of claim 12, wherein the porous substrate is a frit comprising a material selected from glass, ceramic, alumina, and a porous polymer.

14. A method of separating gas components in a feed gas mixture, the method comprising contacting a first side of a membrane comprising a cured product of a modified silicone composition with a feed gas mixture comprising at least a first gas component and a second gas component to produce a permeate gas mixture on a second side of the membrane and a retentate gas mixture on the first side of the membrane, wherein the permeate gas mixture is enriched in the first gas component, the retentate gas mixture is depleted in the first gas component, and the modified silicone composition comprises (A) a curable silicone composition and (B) a salt of a carboxylic acid.

15. The method of claim 14, wherein the permeate gas mixture comprises carbon dioxide and the feed gas mixture comprises at least one of nitrogen and methane.