WO2011028342A2

WO2011028342A2 - Enhanced transport selectivity using nanoparticle filled polymers

Info

Publication number: WO2011028342A2
Application number: PCT/US2010/043947
Authority: WO
Inventors: Benny D. Freeman; Scott Matteucci; Michael Becker; Desiderio Kovar; John Keto
Original assignee: Board Of Regents, The University Of Texas System
Priority date: 2009-08-24
Filing date: 2010-07-30
Publication date: 2011-03-10
Also published as: WO2011028342A3

Abstract

The present invention provides a nanoparticle-filled polymer comprising one or more nanoparticles dispersed within the one or more polymeric materials, wherein the one or more nanoparticles have a diameter of between 0.1 nm and 100 nm, wherein the nanoparticle-filled rubbery polymer behaves as a nanocomposite exhibiting higher permeability than the native polymer membrane.

Description

ENHANCED TRANSPORT SELECTIVITY USING NANOPARTICLE FILLED POLYMERS Technical Field of the Invention

The present invention relates generally to gas mixture separation, and in particular, to the addition of metal, alloy and composite nanoparticles to a polymer that adjusts the overall membrane permeability to gases and vapors.

Background Art

Without limiting the scope of the invention, its background is described in connection with polymeric membrane separation of gas mixture components, as an example. Polymeric membranes and polymers have been used to separate, remove, purify or partially recover a variety of components from mixtures, e.g., gases including hydrogen, helium, oxygen, nitrogen, argon, carbon monoxide, carbon dioxide, ammonia, water vapor, methane and other light hydrocarbons. Generally, this separation is dependent on the permeability and the selectivity of the molecules through the polymer. For example, one of the components may selectively permeate the polymer and/or diffuse through the polymer more readily than another component of the mixture; whereas a relative non-permeating component passes less readily through the polymer than other components of the mixture.

The separation of diffusants using a polymer is dependent on both the polymer and the diffusants. Therefore, there are many factors that influence diffusion including: (1) the molecular size of the diffusant; (2) the physical state of the diffusant; (3) the composition of the polymer; (4) the morphology of the polymer; (5) the compatibility of the polymer and the diffusant; (6) solubility limit of the diffusant within the polymer matrix; and (7) surface or interfacial energies of the polymer.

Diffusivity plays a role in the separation of the gases of a mixture and can be thought of on a simple level as relating to the size of the molecules diffusing through the polymer. Smaller molecules can more easily penetrate and diffuse through a polymer matrix. The separation of diffusants is also based on the relative permeability of the diffusant through the polymer. Permeability is a measure of the steady-state rate at which a particular gas moves through a membrane of standard thickness under a standard pressure difference. Permeability depends both on the solubility of the permeating gas in the polymer and its diffusion coefficient. The diffusants contact one side of a polymer, which is selectively permeable, allowing the one diffusant to pass through the polymer more readily than another diffusant. The differences in permeabilities of two diffusants allows them to be separated when an appropriate membrane is selected.

In spite of the considerable research effort in separation membranes and polymers there has been limited advances in gas separations. Furthermore, improvements in selectivity for one gas over another are generally obtained at the expense of permeability. Currently in the art, it is not possible to predict the gas selectivity or the intrinsic permeability of a polymer for given gases under a given set of conditions from knowledge of the selectivity of another pair of gases, even under the same conditions (e.g. temperature, pressure) as it is dependent on the structure of the polymer, the morphology of the membrane, the gas composition and properties. The gas selectivity and permeability must be determined experimentally.

Disclosure of the Invention

The present invention provides a polymeric material that allows for selective separation of various gases, while retaining acceptable permeability and diffusivity at a variety of temperatures. In addition, nanoparticles may be combined with polymers to form nanocomposite materials that impart properties that allow superior separation of gases. The present inventors recognized nanoparticles (e.g., up to 500 nm primary particle diameter) of an inorganic material may be added to the polymer matrix and processed to form a polymer/inorganic nanocomposite membrane to achieve the desired performance properties.

The present invention also provides a method for making highly permeable membranes with selectivities similar to or better than the native polymer, by suspending inorganic nanoparticles in a polymer liquid, and polymerizing the polymeric suspension to form a particle-filled nanocomposite membrane. The present invention also includes a method for making membranes that have extremely high permeabilities and high chemical stability in organic solvents by dissolving the polymeric material, adding one or more nanoparticles to the polymeric material and polymerizing the polymeric material to form a nanocomposite.

The present invention provides a method for making highly permeable and selective membranes by forming one or more nanoparticles having a diameter of between 1 nm and 20 nm by laser ablation; collecting the one or more nanoparticles in a polymeric solution comprising one or more monomers that prevents the one or more nanoparticles forming an agglomeration; and polymerizing the a polymeric solution to form a highly permeable and selective nanoparticle membrane.

The present invention also provides a method for making highly permeable and selective membranes by forming one or more nanoparticles having a diameter of between 1 nm and 20 nm by laser ablation; collecting the one or more nanoparticles in a polymeric solution comprising one or more monomers that allows the formation of an agglomeration; and polymerizing the a polymeric solution to form a highly permeable and selective nanoparticle membrane.

The present invention includes a method for making a gas separation device by providing a highly permeable and selective nanoparticle membrane made by forming one or more metal nanoparticles having a diameter of between 1 nm and 20 nm by laser ablation, collecting the one or more metal nanoparticles in a polymeric solution comprising one or more monomers that prevents the one or more metal nanoparticles from forming an agglomeration and polymerizing the a polymeric solution; and positioning one or more containers about the highly permeable and selective nanoparticle membrane to separated at least a first and a second gas.

Description of the Drawings

For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures and in which:

FIGURE 1 is a plot of the pure gas ethylene/ethane selectivity verses the ethylene permeability.

FIGURE 2 is a plot of the effect of 2.5 nm MgO nanoparticles on CO₂ permeability and CO₂/N₂ pure gas selectivity at 35°C in (1,2-PB) based nano-composites.

FIGURE 3 is a schematic of the laser ablation of microparticle aerosols (LAMA) apparatus.

FIGURE 4 is an image of NPs produced by LAMA that are charged by photoionization and thermionic emission immediately after they form which prevents agglomeration until they can be collected.

FIGURE 5 is an image of the double ablation process to produce core-shell and other structured NPs.

FIGURE 6 is a plot of selective and permeability for polybenzimidazole PBI.

FIGURE 7 is a SERS plot showing the successful stabilization of the particles resulted from a change in the orientation of the surfactant molecules on the NP surface.

FIGURE 8A is a plot of gold NPs supported on Ti0₂.

FIGURE 8B is a comparison of the electronic structure and reactivity of particles with ordered surfaces used to determine catalytically activity of nanostructured materials.

FIGURE 9A is an image of scanning electrochemical measurements of (¾ reduction at Co_xPdi__x. FIGURE 9B is a graph that shows that 11% Co alloyed with Pd (1/9 of the top layer) lowers the barrier for O₂ dissociation.

FIGURES 10A and 10B are images of the apparatus to collect silver NP produced by LAMA.

Description of The Invention

While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The terminology used and specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

As used herein, the term "separation factor" refers to the separation for a membrane for a given pair of gases "a" and "b" is defined as the ratio of the permeability constant of the membrane for gas "a" to the permeability constant of the membrane for gas "b." As used herein, the term "nanoparticle" refers to particles that are on the order of 10^"9 meter, or one billionth of a meter. The size distribution of the nanoparticles may be monodisperse or polydisperse and the variation in diameters of the particles of a given dispersion may vary, e.g., particle diameters of between about 0.1 to 100's of nm. The nanoparticles may consist of any inorganic material including single elements (e.g. Au, Pt, Ag, Cu, Si, Ge etc.), compounds (SiC, Ti0₂, TiC, CuAu, Cu₃Au, CoPt₃, etc.), or alloys (Cuo9.₅Auo.05, TiC₀.₅SiC₀.5, Ago.2₅Auo.75, etc.). Further, nanoparticles can also consist of combinations of these constituents and be alloy nanoparticles, composite nanoparticles, etc. For example, core/shell nanoparticles may consist of an inner core of an element, alloy or compound and a shell of another element alloy or compound. The shell thickness may vary from less than a monolayer, in which case an incomplete shell is formed consisting of islands of the shell material, to a thickness of several hundred nanometers. The nanoparticles may be at equilibrium or may be metastable.

As used herein, the term "single element catalyst" refers to a catalyst particle containing a single chemical element rather than an alloy or compound.

As used herein, the term "olefin" or "olefin" or "alkene" refers to an unsaturated chemical compound containing at least one carbon-to-carbon double bond. The simplest acyclic alkenes, with only one double bond and no other functional groups, form a homologous series of hydrocarbons with the general formula C_nH2_n. The simplest alkene is ethylene (C₂H₄), which has the International Union of Pure and Applied Chemistry (IUPAC) name ethene. Alkenes are also called olefins (an archaic synonym, widely used in the petrochemical industry).

As used herein, the term "paraffin" refers to alkane hydrocarbons with the general formula C_nH_2n+2- The simplest paraffin molecule is that of methane, CH₄, a gas at room temperature. Heavier members of the series, such as that of octane CsHig, appear as liquids at room temperature. Paraffin refers to the technical name for an alkane in general, and includes linear and branched alkanes.

As used herein Glass Transition Temperature (Tg) can loosely be defined as a temperature point where a polymer experiences a significant change in properties. Typically, a large change in Young's Modulus is experienced. The Tg is where a polymer structure turns "rubbery" upon heating and "glassy" upon cooling. Amorphous polymers are structural below Tg. Amorphous materials go through one stage of the change from a glassy to a rubbery consistency with a simultaneous loss in stiffness (modulus of elasticity or Young's Modulus). This stage of going from stiff to flowing is over a wide temperature range. Crystalline, materials, on the other hand, go through a stage of becoming leathery before becoming rubbery. There is a loss of stiffness (modulus of elasticity or Young's Modulus) in both of these stages. However, crystalline materials have a sharp, defined melting point.

The term polymer as used herein refers generally to a rigid, glassy polymer, rubbery polymers or flexible glassy polymers. Glassy polymers are differentiated from rubbery polymers by the rate of segmental movement of polymer chains. Polymers in the glassy state do not have the rapid molecular motion that permits rubbery polymers their liquid-like nature and their ability to adjust segmental configurations rapidly over large distances (>0.5 nm). Glassy polymers exist in a non-equilibrium state with entangled molecular chains with immobile molecular backbones in frozen conformations. The glass transition temperature (Tg) is the dividing point between the rubbery or glassy state. Above the Tg, the polymer exists in the rubbery state; below the Tg, the polymer exists in the glassy state. Rigid, glassy polymers describe polymers with rigid polymer chain backbones that have limited intramolecular rotational mobility and are often characterized by having high glass transition temperatures.

The polymers may include, e.g., stiff chain, glassy polymers including: poly(l-phenyl-2-[p- trimethylsilylphenyl] acetylene (hereafter referred to as "PTMSDPA") and poly(l-trimethylsilyl-l- propyne) (hereafter referred to as "PTMSP") and elastomeric and rubbery polymers including poly(ethylene octene). Typical polymers suitable for the present invention can be substituted or unsubstituted polymers and may include polysulfone, copolymers of styrene and acrylonitrile poly(arylene oxide), polycarbonate, and cellulose acetate, polysulfones; poly(styrenes), including styrene-containing copolymers such as acrylonitrilestyrene copolymers, styrene-butadiene copolymers and styrene -vinylbenzylhalide copolymers; polycarbonates; cellulosic polymers, such as cellulose acetate-butyrate, cellulose propionate, ethyl cellulose, methyl cellulose, nitrocellulose, etc.; polyamides and polyimides, including aryl polyamides and aryl polyimides; polyethers; poly(arylene oxides) such as poly(phenylene oxide) and poly(xylene oxide); poly(esteramide-diisocyanate); polyurethanes; polyesters (including polyarylates), such as poly(ethylene terephthalate), poly(alkyl methacrylates), poly(acrylates), poly(phenylene terephthalate), etc.; polysulfides; polymers from monomers having alpha-olefmic unsaturation other than mentioned above such as poly (ethylene), poly(propylene), poly(butene- l), poly(4-methyl pentene-1), polyvinyls, e.g., poly(vinyl chloride), poly(vinyl fluoride), poly(vinylidene chloride), poly(vinylidene fluoride), polyvinyl alcohol), polyvinyl esters) such as poly(vinyl acetate) and poly(vinyl propionate), polyvinyl pyridines), poly(vinyl pyrrolidones), poly(vinyl ethers), poly(vinyl ketones), poly(vinyl aldehydes) such as poly(vinyl formal) and poly(vinyl butyral), poly(vinyl amides), poly(vinyl amines), polyvinyl urethanes), polyvinyl ureas), polyvinyl phosphates), and poly(vinyl sulfates); polyallyls; poly(benzobenzimidazole); polyhydrazides; polyoxadiazoles; polytriazoles; poly (benzimidazole); polycarbodiimides; polyphosphazines; etc., and interpolymers, including block interpolymers having repeating units from the above such as terpolymers of acrylonitrile-vinyl bromide- sodium salt of para-sulfophenylmethallyl ethers; and grafts and blends having any of the foregoing. Typical substituents providing substituted polymers include halogens such as fluorine, chlorine and bromine; hydroxyl groups; lower alkyl groups; lower alkoxy groups; monocyclic aryl; lower acyl groups and the like.

The polymer may be made into a membrane for gas separation, however, films or hollow filaments or fibers, having a porous separation membrane, or substrate, and a coating in occluding contact with the porous separation membrane are also contemplated. The NP polymer composites of the present invention may be used to make a mixed matrix membrane that includes a polymer or small, discrete molecular sieving entities or particles encapsulated in the polymer wherein the mixed matrix membrane contains metal oxide. The mixed matrix membrane may have more strength than the polymer alone may also be used. A mixed matrix membrane may also be used in the form of a dense film, tube or hollow fiber. The present invention addresses a variety of separation problems in the art. The present invention allows high permeability membrane materials that require less membrane surface area or pressure differential across the membrane to achieve the desired gas flux. In some instances the higher permeability produced by the nanocomposite polymers of the present invention, allows the polymer membrane to be much thicker.

The present invention incorporates nanoparticles into stabilizing polymers and the use of the resulting materials for olefin/paraffin separation using polymer membrane technologies. The nanoparticles can be produced by laser ablation of microparticle aerosols (LAMA) or using other methods. Particles produced by LAMA can be collected in a manner that prevents particle agglomeration while at the same time eliminating the need for surfactants or capping agents on the nanoparticles that can subsequently interfere with functionality with the polymer or diffusants if the nanoparticles are collected prior to recombintation with electrons. Conversely, agglomerates of nanoparticles can be produced by LAMA by collecting the nanoparticles subsequent to recombination. The nanoparticle processing and stabilization can be performed in a single or multiple instruments. Films can be prepared that exhibit ethylene/ethane selectivities of 3.3 and ethylene permeability of 20 barrer. Experiments were conducted at a pressure differential of 3.4 atm and 30°C. Greater selectivities may be achieved with optimization by varying the composition parameter such as NP density, size, or alloy composition.

FIGURE 1 is a plot of pure gas ethylene permeability and pure gas (a) ethylene/ethane selectivity. Permeability is reported at 30°C and a transmembrane pressure difference of 4.4 atm. The line represents an empirical trade-off between permeability and selectivity in polymeric membranes. 1 barrer = 10^"10 cm³ (STP)cm (cm² s (cm Hg)). Olefin/paraffin separations are the most energy intensive separations in the petrochemical industry. Ethane and ethylene are produced in large quantities in the chemical industry. The two gases need to be separated. However, the current method, cryodistillation, requires extremely large amounts of energy. It would be preferable to use a low energy separation technology such as membranes to perform this separation. However, ethylene and ethane are of similar size and condensabilities. This fact renders ethylene/ethane selectivity in polymers films to be around 1, as shown in FIGURE 1.

The present invention provides metal, alloy, oxide, carbide, or nitride nanoparticles dispersed into various polymer matrixes to facilitate transport of the olefin (ethylene) across the membranes. The nanoparticles can also have a structured morphology such as core/shell, small island particles supported on other metals or metal oxides. These films have demonstrated a remarkable capacity to improve olefin/paraffin selectivity. The nanoparticles are produced by LAMA. The nanoparticles are collected in a monomer liquid which prevents the nanoparticles from agglomerating. The nanoparticle processing and stabilization are performed in a single instrument. The nanoparticle filled monomer suspension is then polymerized using common free radical polymerization techniques (i.e., thermal or UV initiated free radical reactions). The resulting nanocomposite films can exhibit ethylene/ethane selectivities that are considered of industrial interest (i.e., 3.3 for existing formulations) with ethylene permeability of 20 barrier. Studies were conducted at a pressure differential of 3.4 atm and 30°C. Nanoparticle processing and particle dispersion are accomplished in such a way as to eliminate the need for nanoparticle purification and mixing steps.

The present invention provides olefin/paraffin enrichment by incorporating nanoparticles into stabilizing polymers and the use of the resulting materials for olefin/paraffin separation using polymer membrane technologies. The present invention teaches the addition of metal nanoparticles (in some embodiments between about 0.1-100 nm particle diameter) to rubbery polymers as a method for substantially increasing overall membrane selectivity of olefins relative to parafins. In some embodiments, enhancements in permeability allow for a reduction in membrane area and/or driving force required to achieve a desired gas flux.

In various embodiments, a nanoparticle composition of the present inventions and/or formed by a method of the present inventions has a mean diameter in the range between about 0.1 nm to about 100 nm (including all incremental variations thereof). In various embodiments, the nanoparticle has a mean diameter in one or more of the ranges between: about 1 nm to about 10 nm; about 10 nm to about 30 nm; about 15 nm to about 50 nm; and about 50 nm to about 100 nm. It is to be understood that the term "mean diameter" is not meant to imply any sort of specific morphology (e.g., spherical, ellipsoidal, etc.) of a nanoparticle. Rather, the nanoparticle or composite nanoparticle could be highly irregular and asymmetric.

The present invention provides a wide variety of constituents can be used to form the nanoparticle including, but not limited to, inorganic elements, charged ions or a combination thereof. In various preferred embodiments, the nanoparticle comprises an elemental metal, alloy comprising a metal, or a metal species-containing compound, the metal is preferably Cd, Zn, Pb, Mn, Ni, Mg, Fe, Ag, Cu, Au, Pd, Co, Pt or a combination or alloy of one or more thereof. As used herein, by the term "metal species- containing compound" is meant a compound containing a metal or metalloid in any valence state. In various preferred embodiments, the nanoparticle comprises semiconductor crystals, including, but not limited, to SiC, TiC, Si₃N₄, TiN, CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, PbS, PbSe, PbTe, Cul, HgS, HgSe, and HgTe. These semiconductors can be ternary or quaternary semiconductors, including, but not limited to, CdTe/S, CdSe/S, CdTe/Se, Cd/ZnTe, Cd/ZnSe/Te, and the like. In various preferred embodiments, the nanoparticle comprises oxides, such as ZnO, Sn0₂, CuO, Cu0₂, CoO, NiO, CdO, In0₂, and the like. They might also include compositions in the previous list with other group 6 elements such as sulfur of selenium. In various preferred embodiments, the nanoparticle comprises more complex systems, including alloys such as Ag/Au, Ag/Cu, Au/Cu, phosphates such as LiFeP0₄, chromates such as PbCr0₄ , and carbides, sulfides and nitrides and the like. In various preferred embodiments, the nanoparticle comprises more complex systems, including mixtures of the above elements, alloys, or compounds including core/shell nanoparticles.

The present invention includes the addition of nanoparticles into polymers. The nanoparticles of the present invention may contain a variety of components and the polymers may include stiff-chain, rigid, glassy polymers, rubbery polymers and elastomeric polymers. The present invention includes nanocomposite membranes consisting of inorganic nanoparticles in polymer membranes. The major benefit of this approach is greatly enhanced functionality for separations. The nanoparticles may enhance separation performance by increasing solubility for one or more diffusant, selectively increasing diffusivity of one or more diffusant, or by catalyzing the reaction of one diffusant. This can be achieved through the multi-scale nature of the nanocomposite membranes and the scale up of the required nanoparticle manufacturing processes, and through active nanostructures using nanostructured catalysts and novel separation systems with molecular resolution. The present invention uses the functional properties of alloy metal NPs and the other related NPs to achieve unexpected changes in gas separation performance of polymer membranes upon incorporation of NPs.

The present invention may use NPs made by any method provided they are the desired size. For example, NPs may be produced by Laser Ablation of Microparticle Aerosols (LAMA) and incorporated into polymer membranes to enhance their ability to separate gas mixtures and catalyze reactions in the transported gas to enhance purification. NPs produced by LAMA offer significant advantages over those produced by other methods; they have bare surfaces (i.e. free of adsorbed species or organic ligands) and are in an inert carrier gas. They can be collected directly into the monomer of the membrane polymer or in polymer solutions. Thus, the NPs can be collected into one polymer or polymer solution, washed, and then subsequently mixed into a different polymer or polymer solution. By doing so chemical "hooks" can added to the NP surfaces that control the attachment of NPs to the polymer chains and by otherwise controlling dispersion and polymer structure in the vicinity of the nanoparticles, better control of selective membrane transport can be obtained and agglomeration of the NPs can be controlled. Polymer "hooks" may be used by depositing in one liquid, washing all but a monolayer or two of liquid polymer molecules off, then depositing into a second liquid.

Alloy or shelled NPs of the instant invention can enhance their catalytic properties. For example, the catalytic activity of Cu may be tuned through the addition of Au, or vice versa. In general, catalysts alter the barrier for chemical reaction, but also must release the reaction products in order for the catalyst to be reused. Catalysts should also not react strongly with impurities present in the process; such impurties can eventually poison the catalyst. As an example, the catalytic activity of Cu NPs is rapidly suppressed by oxidation, and Cu in general is too reactive to act as a catalyst for many processes. When making Cu NPs by LAMA, partial oxidation occurred rapidly when the particles were exposed to air; however, alloying with a small amount of gold completely inhibited oxidation. The alloy composition can be tuned to enhance the desired reaction while avoiding the binding of products. Theoretical simulations of catalytic reactions of gases at the NP surfaces can provide guidance in choosing other alloys that both inhibit oxidation while simultaneously optimizing catalytic behavior.

The present invention provides broad applications for membranes and catalysts, including olefin/paraffin separations and ¾ production from hydrocarbons. The current generation of polymer membranes do not have sufficient selectivity for high-volume, energy intensive separations such as ethylene/ethane or propylene/propane fractionation, and current hydrogen production methods (steam reforming of hydrocarbons followed by a water-gas shift reaction) leave product streams laced with low levels of contaminants such as CO that can poison the catalysts used in fuel cells. CO is difficult to remove using membranes because of its low concentration, catalytically active membranes can be used to assist in removing CO from mixtures with H2 for applications such as fuel cells. Due to their enhanced separation properties, nanocomposite membranes of the present invention have an impact far broader than that of conventional polymer membranes to purify gas mixtures. These cases above constitute enormous production volume and energy consumption; increasing their efficiency with nanocomposite membranes would have significant economic impact. The present invention provides that even low level of LAMA- produced Ag NPs, when collected in cross-linked poly (ethylene oxide) (hereafter referred to as "XLPEO") which is subsequently UV photo-polymerized to form a stable membrane exhibit extraordinarily high selectivity and stable olefin-paraffin separation properties.

FIGURE 1 is a graph of ethylene-ethane separation properties in conventional polymers and in XLPEO doped with approximately 0.05 vol. % LAMA Ag NPs at 35°C. The Ag NPs were nominally 8 nm diameter. Permeability coefficients were determined at an upstream pressure of 4.4 arm.

These separation properties are very far beyond those of conventional polymers. Interestingly, even prolonged exposure to UV and visible light in ambient air (7 months) does not deteriorate the unusual and outstanding properties presented in this figure; this result is in marked contrast to the behavior of silver salts dispersed in polymer films to enhance olefin/paraffin separation. LAMA NPs can be used to enhance the separation performance of polymers to levels that are unprecedented.

Whereas previous studies using silver salts to enhance olefin/paraffin separation properties have been largely confined to silver salts that were commercially available (and these salts were too reactive, which led to high rates of oxidation and side reactions with contaminants (e.g., sulfur compounds and acetylenes) present in these streams), the LAMA particles are almost infinitely tailorable. For example, the LAMA process can be used to make metal alloys, tune the interaction properties of Ag NPs, or Cu NPs, since Cu also interacts reversibly with olefins and incorporate these NPs into nanocomposite membranes for olefin/paraffin separation. Cu has not been used in such applications because it oxidizes to Cu₂0, which is not active for interaction with olefins. However, the LAMA process can be used to prepare Cu NPs alloyed with low levels of Au, and they are remarkably (and surprisingly) stable against oxidation. Since sulfur compounds are trace contaminants in olefin/paraffin streams and sulfur deactivates pure silver and copper salts, alloy NPs have greater tolerance to sulfur compounds. Gas Transport Properties: For gas A, the permeability P A , through a membrane of thickness i is:

N_A1

P_A=

where N_A is the steady-state gas flux through the membrane, 1 is the membrane thickness, and P2 and pi are the feed (i.e., high) pressure and permeate (i.e., low) pressure, respectively. In a gas mixture, P2 and i are the partial pressures of A. When the downstream pressure, pi, is much lower than the upstream pressure, p₂, the permeability is often expressed as follows:

where DA is the effective concentration-averaged diffusivity. The solubility coefficient, SA, is defined as C/p, where C is the gas concentration in the polymer at the upstream face of the membrane. The ability of a membrane to separate two components is often characterized by the ideal selectivity, a_{A /} B , which is the ratio of permeabilities of the two components:

PA SAD_A

<XA= ----- = (3)

DA/DB is the diffusivity selectivity, which is the ratio of diffusion coefficients of components A and B, and SA/SB is the solubility selectivity. As equation 3 shows, the balance of gas diffusivity and solubility selectivities determines overall selectivity. Equations 2 and 3 do not account for chemical reaction of gases inside the membrane. If a membrane could react with CO and convert it to another species (e.g., C02), the overall separation of, e.g. H₂ from CO, should be higher than that anticipated from equation 3. Such catalytic membranes would show enhanced separation performance.

U. S. Patent number 5,585,020 entitled "Process for the production of nanoparticles," for producing NPs by Laser Ablation of Microparticle Aersols (LAMA is hereby incorporated by reference.

The process makes NPs of a wide variety of inorganic materials (metals, semiconductors, and dielectrics. The LAMA apparatus, shown schematically in FIGURE 3, consists of a high-energy laser that illuminates a flowing aerosol of microparticles (1-20 μιη dia.). The aerosol flow and the laser pulse rate are timed so that the laser pulse strikes each particle once. The process can benefit by ablating the aerosol twice. This removes agglomerates of microparticles, reduces the mean size of the nanoparticles and the dispersion of the size distribution. The laser pulse results in breakdown and shock-wave formation at each microparticle. NPs are nucleated in the rarefaction behind the shock. Since the nucleation of NPs follows the shock as a traveling wave, the absorbed energy can be as low as 10-25% of the microparticle's heat of vaporization. The produced NPs are spherical and have a narrow size distribution (Ad/d = 25%). An electrostatic technique for further narrowing the size dispersion to 8% has been demonstrated. The mean size of metallic NPs from about 3 nm up to about 40 nm can be varied by the background gas type and gas pressure in the ablation cell.

FIGURE 4 is an image of NPs produced by LAMA that were charged by photoionization and thermionic emission immediately after they formed which prevented agglomeration until they were collected. The isolated nature of LAMA-produced NP suspensions is similar to that observed in NP suspensions grown by chemical methods; however, because LAMA-produced NPs are collected cold rather than grown in a solvent, there are no restrictions on the liquids into which they can be collected. The LAMA aerosol process is capable of high production rates. For example, it is possible to produce up to a 100 g/hr of NPs using a laboratory-scale laser, and the process is scalable for larger lasers.

Production and Collection by LAMA: The inventors have produced NPs of metals, compounds, alloys, ceramics, glasses, and semiconductors with the LAMA process using several approaches. For the first approach, compound or alloy feedstock microparticles (MPs) were used to demonstrate that, when a shock fully develops, the composition of the resulting NP was nearly identical to that of the feedstock MPs. NiFe, CdSe, FeiTbJDy_Lx, and other alloys and compounds were successfully produced using this method. For the second approach, the inventors produced Au-Cu alloy NPs by mixing individual MPs of Au and Cu powders in the powder feeder. If the aerosol density of MPs in the ablation region is sufficiently high, the NPs ejected from an ablated MP are cast into the vaporized material from adjacent MPs. The nuclei of each NP then grow by condensation of the vapor of the other material to produce alloy NPs. A third method, double ablation, can be used to produce core-shell NPs such as that shown in FIGURE 5.

For this approach, MP feedstock of a material is ablated to form NPs that are then fed into a second ablation cell where they are mixed with MPs with a different composition. Although the MPs in the second ablation cell are ablated, the NPs in the second cell are smaller than the laser absorption depth and remain largely intact, though we observe size reduction and narrowing of the size distribution. The NPs then act as nuclei for the growth of the shell. Using this method, highly non- equilibrium, core-shell structures can be produced. Core-shell NPs with 4-6 nm diameters have been produced using this method. Since an image of the shell is not distinct as in FIGURE 5, spatially dependent x-ray fluorescence was used to prove the core/shell structure. The inventors improved the measurement of shell thickness using high-resolution electron energy loss spectroscopy (EELS) as a diagnostic.

The inventors have demonstrated two methods for collecting NPs into liquids. For the first method, the NP aerosol is expanded through a supersonic jet and impacted into a flowing liquid. The advantage of this method is that the efficiency of collection is near 100%. However, the impaction method requires that the liquid have a sufficiently low vapor pressure for collection in vacuum. A second method utilizes the charged nature of the NPs to collect electrostatically into a liquid of our choosing. Since vacuum is not necessary, the liquid can have a high vapor pressure.

Nanocomposite Polymer Membranes. The polymers selected will provide a broad platform of potential matrix materials to maximize the potential for good dispersion of the NPs while, at the same time, using readily available materials when possible. The polymer matrices of the present invention are divided into two categories, rubbery and glassy polymers. Rubbery polymers have glass transition temperatures (Tg) below room temperature and are soft, flexible materials. On the other hand, glassy polymers are rigid, hard materials with Tg values above room temperature, in many cases significantly above room temperature. Most commercial gas separation membrane materials are made from glassy polymers. Some applications of the present invention include H₂ purification from the water-gas _shift reaction gas streams at high temperature (up to 270°C), and thus require highly thermal-stable polymers, which are usually glassy, as matrix materials.

In contrast to prior art where the NPs were mixed with polymers during membrane synthesis leading to agglomerated NPs, the present invention improves dispersion by two processes: 1) synthesizing polymers with quasi-periodic reactive "hooks" that can react with the NPs, thus systemizing the NP spacing along the polymer chains, or 2) first attaching monomers to NPs, followed by insertion of the monomers quasi- periodically into the polymer during polymerization.

Rubbery Polymers: The present invention provides dispersion of metal NPs in polymer networks based on poly(ethylene glycol) methyl ether acrylate (PEGMEA) crosslinked with poly(ethylene glycol) diacrylate (PEGDA) to form so-called XLPEO networks:

Nanocomposites based on these materials are prepared by mixing monomer, crosslinker and NPs with a small amount of a photocrosslinker and then photopolymerizing the mixture with UV radiation. For example, PEGMEA is an acrylate monomer I) used to prepare nanocomposites with metal oxides e.g.,

These monomers are commercially available with l<n<23, however the present invention also provides materials with a wide range of side group lengths. Examples, include materials with n<10 or 15 and are of interest since these do not crystallize - materials prepared from much longer side chain variants crystallize and, consequently, have dramatically reduced gas permeation properties. An example of a diacrylate (II) crosslinker is PEGDA, where

PEGDA is readily available with l<n<100; one embodiment includes materials with n<15 that avoid significant crystallinity. One can vary crosslinker length, n, in membrane nanocomposites to better understand the impact of NPs on polymer crystallinity.

Table I. Carhoxyhc Acid Monomers for P Fmcfeoiiayzaitoa

NPs can be prepared by the LAMA process bound to molecules bearing carboxylic acid groups, such as nonanoic acid to improve particle dispersion in the composites. In aery late networks, it is possible to introduce carboxylic acid functionality by incorporating monomers bearing this group into the initial mixture of monomers and crosslinkers and then polymerizing such groups into the polymer backbone. The resulting networks can be swollen with a solvent solution containing NPs to form the composites. In another embodiment, one can bind NPs to monomers bearing such groups and then polymerize the functionalized NPs into the polymer. Using either approach, one or more monomers from Table 1 can be employed. If more flexible connections between the polymer backbone (formed by polymerization of the C]¾=CH moieties) and the NPs are desired, longer tethers may be used; commercial monomers are available with l<n<4.

Glassy Polymers: Polymers, in general, have low thermal stability compared to other materials (e.g., ceramics, metals, etc.), undergoing softening and/or decomposition at relatively low temperatures. However, highly aromatic polymers with decomposition and softening temperatures exceeding the 200- 270°C requirement of the low-temperature water-gas shift (WGS) reaction do exist. For example, polybenzimidazole [PBI] has exceptional thermal stability and mechanical properties and is commonly used as an asbestos replacement in fire blocking and thermal protective clothing. Moreover, PBI is not only amorphous (i.e., non-crystalline) but also sufficiently soluble in NA-dimethylacetamide (DMAc) that it can be processed in solution, which greatly simplifies the preparation of films

FIGURE 6 is a plot of selectivity and permeability. PBI is highly size-selective for Ι¾ over many gases (e.g., CO₂ or CH₄) found in reforming gas mixtures. It has a H₂/CO₂ selectivity greater than 20 and a H₂/CH₄ selectivity between 100-200 at temperatures of 250-300 °C. The H₂/CO selectivity of PBI is expected to be about 60-160 in this temperature range, assuming that N₂ permeability is a fair representation of CO permeability in this material. Such H₂ selectivities are well within the range of attractive values for commercially practiced H₂ production. As shown in FIGURE 6, H₂ permeability of PBI is around 100 Barrers at 300 °C, which is already in a range of potential interest. For comparison, polysulfone is used successfully as a membrane material for 0₂/N₂ separation (i.e., air separation). Its 0₂ permeability at the use temperature (~40 °C) is only approximately 1 Barrer. PBI is commercially available, has thermal stability properties of interest, and is soluble in solvents which facilitate nanocomposite preparation.

Polybenzoxazoles [PBOs] are another group of aromatic polymers for high-temperature applications because of their excellent thermo-oxidative stability. This family has been studied extensively because they have very good fire-safe properties. However, their permeation properties at elevated temperatures are not known and are generally difficult to process because they are soluble only in strong acids. In addition, flexible linkages can be incorporated into the PBO chain backbone, thus making PBO variants that are soluble in more common solvents while still maintaining their superior thermal stability. Moreover, PBO can be synthesized by reacting bis(aminophenol) with aromatic diacid chlorides in a solution polycondensation reaction. In the first step, which proceeds to high yield rapidly at - 5 to 20 °C using monomers, a highly soluble precursor of PBO, polyhydroxyamide [PHA], is formed as shown below:

II PHA

im i^'isitl iig polymer sin closure follows at 220-500 ^*C to yield PBO: [64]

A series of random copolymers of varying compositions can be prepared by replacing portions of the diamine (I) and diacid chloride (II) with groups containing either flexible linkages or bulky, order- disrupting substituents on the aromatic rings of the diamines. Many of these copolymers exhibit excellent thermo-oxidative properties when converted to the equivalent PBO structures. The copolymers are soluble in DMAc, dimethylsulfoxide [DMSO], and l-methyl-2-pyrrolidinone [NMP]. The addition of even low levels of the aliphatic diacid chloride yields PHA materials that are not crystalline, e.g., more open materials (i.e., higher free volume, more permeable). The addition of these co-monomers also yields materials that have detectable calorimetric Tg's of 150-220 °C at the PHA stage. Other compositions, including that of the PHA above (prepared from I and II) do not exhibit a calorimetric Tg before onset of the ring closure reaction. Inclusion of such co-monomers results in PBO precursors that are more flexible than the one prepared from I and II, which may enhance nanoparticle dispersion in the resulting nanocomposites.

To further assist NP dispersion in such polymers, varying amounts of the diamine in the polymer can be replaced with diaminobenzoic acid (DABA). DABA provides carboxylic acid moieties to act as hooks for the NPs, and DABA can be easily incorporated into the synthesis outlined above. Consistent with the approach discussed earlier, one can impact NPs into DABA prior to polymerization to essentially functionalize the particles with diamines that could participate in the condensation polymerization outlined above. The present invention provides for the preparation of the polymer and expose it in solution to NPs to prepare nanocomposite films. Alternatively, the particles can be functionalize and polymerize them into the backbone of the polymer chains.

As an alternative method to preparing PBO-based nanocomposites by adding NPs directly to PBO or to PBO variants with DABA hooks incorporated into the polymer chains, NPs can also be added to solutions of PBO precursors (i.e., PHA and its variants). The films from these NP-loaded precursor solutions can then be cast, and then the rings can be closed by thermal annealing. Because the precursors are more soluble than PBO, this procedure enhances dispersion of the particles in the final nanocomposite by delaying the onset of particle -polymer phase separation, thereby allowing access to nanocomposite compositions that would otherwise be inaccessible if the particles are mixed with PBO itself. If one casts a film from a suspension of NPs and a more soluble precursor, as solvent evaporates from the film, the solids concentration where the polymer would begin to demix from the NPs, (i.e., the onset of particle aggregation), may be delayed to higher solids concentrations, where the polymer solution may be sufficiently vitrified to kinetically prohibit particle aggregation. The present invention also provides solution blending a polymer with a soluble, flexible, rigid-rod precursor, casting films and drying them, then thermally processing the films to rigidify the rigid-rod precursor produces composites with much better compatibility (i.e., less phase segregation) and, in turn, better properties than direct mixing of a rigid-rod component and a polymer in solution.

Functionalization of the NP surface: Large quantities of NPs can be produced by LAMA and collected in solution. In addition, the present invention provides surface functionalization of Ag NPs to stabilize individual NPs in suspensions. To maintain catalytic properties, the majority of the surface of the NPs must remain reactive after it is incorporated into the polymer film. At the same time, ligands that bind the NPs to the polymer molecules must be attached to the NP surface. Several rubbery and glassy polymers with various ligands for attaching NPs include (1,2-PB), PEGDA and PEGMEA. The present invention includes a mix of up to 40 vol.% of NPs (including capping) into the weakly polar polymer 1,2-PB to form freestanding composite samples for permeation testing.

Attaching ligands appropriate to PEGDA and PEGMEA are listed in Table 1. These ligands were chosen because they contain either carboxyl groups or double bond oxide sites that are known to bind strongly to metal NPs. To avoid covering the NPs completely with ligands, they can be solvated in weakly binding solvents. At a sufficiently small concentration relative to the NP concentration, only a few monomers are be bound to the NP surface. The solvent molecules are removed during and/or after polymer formation.

The orientation of the ligands on the NP surface are important for incorporating NPs periodically in the polymer chains. To monitor the concentration of ligand molecules on the NP surface and the removal of solvent during or after polymerization, surface enhanced Raman spectroscopy (SERS) can be used. This technique has been used to study the reaction of nonanoic acid with Ag NPs. A review of those results demonstrates how SERS can be used to monitor the functionalization of NPs and shows the feasibility of SERS on small samples of NPs. In the case of Ag NPs deposited into nonanoic acid, the surface passivation was not complete, resulting in loose flocculation of the particles. This behavior is valuable because it allows NP suspensions to be concentrated after collection to produce suspensions approaching 15% mass density.

As collected, the suspensions were opaque and a dark grey to black in color, and if allowed to settle, a dense precipitate formed. However, the suspensions could be stabilized by annealing at temperatures as low as 75°C for several hours. After dispersing the particles ultrasonically, a sequence of color changes occurred with increasing temperature, progressing from a muddy brown color, to dark orange, and translucent yellow. Finally, the samples became transparent, though the density of NPs was -0.01 g/ml. The measured light attenuation decreased by several orders of magnitude during the color change. The reaction was found to be first order with an activation energy of 41.8 kJ/mole (0.44 eV/mole).

FIGURE 7 is a SERS plot showing the successful stabilization of the particles resulting from a change in the orientation of the surfactant molecules on the NP surface. Both asymmetric and symmetric stretch modes of the COOH/COO- group of the molecule bound was bound to the surface were seen. On silver NPs there is an additional enhancement and broadening of the peak due to a resonance between the electronic virtual state of the molecule excited by the scattered photon and the plasmon mode of the nanoparticle. The asymmetric mode is not observed for planar silver surfaces but has been observed on both copper and aluminum surfaces. On flat silver surfaces the absence of this mode has been used to argue that the COO- group of nonanoic acid is bound by the oxygen atoms equally to two different surface sites, forming a symmetric isosceles structure. The asymmetric mode observed in this spectrum indicates that the COO- bond has a larger angle relative to the surface normal compared to flat surfaces. This is consistent with the picture of the backbone lying on the surface of the nanoparticle. As the sample is annealed, this mode becomes weaker compared to the symmetric mode indicating that the angle relative to the surface normal becomes smaller. Distinct peaks in the region 1200-1300 cm^"1 are assigned to CH₂ wagging modes of the backbone of the molecule, and the peak at 950 cm^"1 to the CCOO- stretch. These hydrocarbon modes decrease in intensity with increasing annealing times and are completely absent in the fully annealed samples. The activation energy of 0.44 eV/mole then results both from breaking the backbone's attraction to the surface as well as the barrier to displacing the H atom. Annealing causes the molecule to stand upright on the surface and additional molecules can then attach to the newly-uncovered surface sites. The reaction is irreversible because of the change in bonding and the additional surface coverage.

FIGURE 8A is a plot of gold NPs supported on T1O₂ that are highly active for CO oxidation at room temperature. FIGURE 8B is a comparison of the electronic structure and reactivity of particles with ordered surfaces (e.g. Au on Mo(l 10)/TiC>₂) (B) used to determine nanostructured materials catalytically activity. The reactivity of particles can be very sensitive to size and composition, and qualitatively different from the bulk material. An example is gold, which is inert as a bulk metal, but has been shown to catalyze the oxidation of CO at room temperature, when supported on T1O₂ as NPs. Particles of 2 nm are active (see FIGURE 8A), whereas particles larger than 10 nm are inactive, showing that the catalytic activity is an intrinsically nanoscale phenomena.

Reactions in membranes: For NPs to catalyze reactions, such as the removal of CO from H₂, as the molecules diffuse through membranes, there must be a large number of collisions with the NP. A (typical) thermally activated process with an energy barrier of 0.23 eV requires ten thousand collisions to induce a reaction at 30°C. A sufficiently high concentration of NPs will ensure enough collisions as molecules diffuse through the membrane. Assuming a purely diffusive model, molecules will have fL²/(R-r)² collisions, where L is the membrane thickness, R is NP separation, r is the NP radius, and /is their volume fraction. A 0.5 μηι thick membrane, loaded with 25% volume fraction of 4 nm NPs, will generate over ten thousand collisions, sufficient for reaction. Molecules that become caged near the NP- polymer interface will collide with the NP many times before diffusing on through the polymer. Enhanced diffusion on the scale of the NP separation, due to the anisotropic polymer structure, will also increase the number of NP interactions. These additional interactions will increase catalytic activity near NPs and allow for the use of thinner membranes, and lower NP loading. The present invention provides effective removal of trace CO amounts from a H₂ stream and thus prevents catalyst poisoning in fuel cells, e.g., removal of CO by oxidation to C0₂ and/or by reduction to CH₄. Several metals can be used as catalysts for these reactions. Ni is currently used for the steam reforming of CH₄. This endothermic reaction, however, is run at higher temperatures than most separation membranes can withstand, to avoid carbon coking. The present invention provides a reverse (exothermic and low temperature) reduction of C0+3H₂- >CH₄+H₂0, for which Ni will also act as a catalysts (by microscopic reversibility). Addition of Au can be used to block the strongest binding sites (Au atoms decorate defect sites on Ni), to prevent carbon formation. Au NPs can be used to catalyze the C0+H₂0->C0₂+H₂ oxidation reaction. Reactivity can be tuned by alloying with Cu, to provide a catalyst that operates near room temperature to allow incorporation into a wide range of polymer membranes. Core-shell NPs using Au in the shell, (for example as made with double ablation) can be used to capture the reactivity seen for CO oxidation for thin Au layers on flat surfaces. NPs made by the LAMA process are free of surfactants and include a variety of sizes, compositions, and bimetallic alloys, compounds, and core-shell, e.g., 0₂ dissociation at Cu-Au NPs; Ni-Au metal alloys and tuning the composition and choice of metal in order to optimize catalytic reactivity.

FIGURE 9A is an image of scanning electrochemical measurements of (¾ reduction at Co_xPdi__x show high activity at 20% Co. FIGURE 9B is a graph that shows that 1 1% Co alloyed with Pd (1/9 of the top layer) lowers the barrier for O₂ dissociation. Alloy NPs include alloyed Cu NPs with a small fraction of less reactive Au to suppress oxidation and the addition of Au to Ni NPs has been shown to block the highly reactive edge and kink sites that results in coking during steam reforming while still retaining catalytic activity.

The present invention also provides a core and shell arrangement where a core made of a first metal is covered with a second metal, the metals can be the same or different and pure, alloys or mixtures. The present invention provides core-shell NPs consisting of a gold shell over an oxide particle (e.g., T1O₂) for further enhanced nano structures. The LAMA process can be used to produce NPs with a wide range of compositions, including non-equilibrium structures. In addition, the NPs are produced unagglomerated and without capping agents and can be collected either onto solid surfaces or into almost any liquid so that the NPs can be incorporated directly into polymer membranes. Thus, both the intrinsic behavior of the NPs and the in-situ behavior within the membranes can be exploited. The present invention includes alloy and core-shell NPs that suppress oxidation while at the same time improving catalytic activity.

The present invention provides for the production of olefins and for the production of pure H₂ streams: 1) S1O₂ as non-reactive NPs for enhanced membrane permeability 2) Au-Cu for oxidation sulfurization- resistant, in-situ catalysts that can be used at low temperature and that may enhance permeability, 3) Au- Ni and Au-Co for coking resistant, NP catalysts enhanced activity such that they may be used at low temperatures, and 4) Novel Au-oxide, core-shell NPs with enhanced low-temperature catalytic activity. The present invention provides Si0₂ and alloys such as Au-Cu NPs produced by LAMA using commercially available, 2 - 20 μηι diameter MP powder feedstock. The Au-alloy NPs use pre-alloyed micron-sized powder that can be purchased as the feedstock for the LAMA process. In addition, the present invention provides the use of the double ablation method to produce Au-Si0₂ or Au-Ti0₂ structured nanoparticles. These particles have small Au particles of 1 -5 nm diameter bound to the surface of the oxide core particle. Other metals or metal alloys, which may wet the oxide particle, will form a core-shell particle similar to those observed in FIGURE 5.

The present invention provides nanocomposite films for gas separations, such as N₂, O₂, CO, H₂, He, CH₄, C0₂, and the C2 and C3 olefins and paraffins. Pure-gas permeabilities can be determined using a constant-volume/variable-pressure technique at pressures up to 30 bar and at temperatures from 35 to 270°C, as appropriate. Pure-gas selectivities can be computed using equation 3. Pure gas solubility measurements can be made using a dual transducer barometric sorption system modified for operation at elevated temperature. From permeability and sorption data, one can calculate diffusion coefficients according to equation 2. Then, independent correlations of solubility with gas condensability (e.g., critical temperature) and diffusivity with gas molecule size (e.g., kinetic dia.) can be determined for various materials. The present invention provides gas separation of olefin/paraffin mixtures, e.g., ethylene/ethane and propylene/propane mixtures at varied compositions, temperatures and pressures relevant to industrial separation conditions for these systems. The present invention provides larger quantities (100 grams/hr) of NPs via the LAMA process using efficient collection of the produced NPs in the desired solution and in feeding the microparticle feedstock to the laser ablation region in a uniform density, non-agglomerated aerosol.

Collection by impaction can approach 100% collection efficiency, given the surfactant or collection liquid is compatible with a vacuum environment, e.g., PEG based monomers. The apparatus to collect silver NP into nonanoic acid and into PEG is shown in FIGURES 10A and 10B. A controlled flow of surfactant is directed out through the center of a conical surface that faces the supersonic flat-plate nozzle at a spacing of a few mm. During ablation, the vacuum is typically 15-30 Pa (100-200 mT). The surfactant can be continuously recirculated back through the impactor in order to achieve a higher loading of NPs.

The totally non- agglomerated (isolated) nature of the NPs produced by LAMA is quite striking and results from charging of the NPs immediately after they form by photoionization and thermionic emission. The charged nature of the NPs allows them to be collected electrostatically and is similar to an aerosol mobility analyzer where the NP aerosol is surrounded by buffer gas (~1 atm.) and flows slowly (<1 m/s) between two electrodes with a high- voltage potential. The smallest particles are deflected more rapidly because of their smaller aerodynamic drag while larger particles travel further before collection on the negative electrode. Measured collection efficiencies suggest that a large fraction of the NPs are charged. The charged nature of the NPs allow for electrostatic collection with in situ size filtering of the NPs to further narrow their size distribution. Two charge collection grids can be placed in the aerosol flow that were designed to capture the mobile charged species: free electrons and positively charged gas atoms or molecules. The NPs were sufficiently massive to pass through the 92% open space between grid wires. The present invention provides the use of a charge collector that allows separate measure the various currents versus downstream position by collecting charged molecules and free electrons on two appropriately biased grids, and the charged Ag NPs on a dense mesh. This mesh consisted of 4 grids, each 36% open space, that acted as a diffusion battery to collect NPs by Brownian diffusion. In the aerosol as generated by the LAMA process, the 1/e NP charge recombination distance was found to be 4 cm and the recombination time slightly less than 0.1 s (v = 45 cm/s).

The present invention provides an aerosol of micron-sized particles to obtain a constant aerosol concentration over long times for the chosen number density, gas flow rate, and specie to aerosolize. For example, the aerosol generators use a fluidized bed with either continuous or pulsed flow of gas and mechanical vibration. Other techniques for aerosolizing MP feedstock powders include a high aerodynamic shear cell to break loose agglomerates and the addition of ultrasonic energy to improve the performance of fluidized bed sources.

The present invention provides a wide variety of contitutents can be used to form the nanoparticle including, but not limited to, inorganic elements or inorganic charged ions or a combination thereof. In various preferred embodiments, the nanoparticle comprises an elemental metal, alloy comprising a metal, or a metal species-containing compound, the metal is Cd, Zn, Cu, Pb, Ag, Mn, Ni, Au, Mg, Fe, Co, Cr, Au, Zr,Ti, V, Nb, Mo, Pt or a combination or alloy of one or more thereof. As used herein, by the term " metal species-containing compound" is meant a compound containing a metal or metalloid in any valence state. In various preferred embodiments, the nanoparticle comprises semiconductor crystals, including, but not limited, to CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, PbS, PbSe, PbTe, and Cul. These semiconductors can be ternary or quaternary semiconductors, including, but not limited to, CdTe/S, CdSe/S, CdTe/Se, Cd/ZnTe, Cd/ZnSe/Te, and the like. In various preferred embodiments, the nanoparticle comprises oxides, such as Si0₂, Ti0₂, ZnO, Sn0₂, CoO, NiO, CdO, In0₂, and the like. It also include carbides, such as TiC, SiC, CrC, and the like and nitrides, such as Si₃N₄, TiN, and the like. The NPs may also consist of an alloy of any of these elements, or compounds such as Cuo.0₅Auo.95, Cdo.4Zn₀.6S,Tio.3Sio.7C. In various preferred embodiments, the nanoparticle comprises more complex systems, including phosphates such as LiFeP0₄ , chromates such as PbCr0₄ , and the like. In addition, the pure metal and alloy nanostructured materials of the present invention may be made from Au, Ag, Co, Cu, Fe, Cr, Al, Ga, In, Hf, Sn, Zr, Mo, Ti, V, Ni, Cu, Y, Ta, W, Pb, B, Nb, Ge, Pr, U, Ce, Er Nd, Mg, Ca, Ba, Sr, Au, Ag, Si or combinations thereof.

The present invention involves a method of making nanostructured metal nanoparticle polymer compositions. The present invention involves a method of making metal nanoparticle polymers, wherein metal nanoparticles fill the polymer. The present inventors discovered that adding metal nanoparticles (e.g., < 100 nm particle diameter) to high free volume, stiff chain, glassy polymers (e.g., poly(l- trimethylsilyl- l-propyne [PTMSP]) increases membrane permeability while maintaining selectivity near the values of the neat polymer.

The present invention also teaches the addition of nonporous metal nanoparticles to stiff chain, glassy polymers for membrane applications. Counterintuitively, the nanoparticles increase the permeability of the membrane for olefin/paraffin separation.

The polymerization occurs by a thermal reaction, a UV initiated reaction, a light initiated, or a free radical reaction. The one or more metal nanoparticles include one or more atom of Fe, Cr, Al, Ga, In, Hf, Sn, Zr, Mo, Ti, V, Co, Ni, Cu, Y, Ta, W, Pb, B, Nb, Ge, Pr, U, Ce, Er, Nd, Si, Mg, Ca, Ba, Sr, Au, C, O, or combination thereof. The highly permeable and selective nanoparticle membrane may be a shape chosen from a microring, a microdisk, a microsphere, a microplate, a microline and a combination thereof.

The polymeric solution may be chosen from polymethylmethacrylates, polystyrenes, polycarbonates, polyimides, epoxy resins, cyclic olefin copolymers, cyclic olefin polymers, acrylate polymers, polyethylene teraphthalate, polyphenylene vinylene, polyether ether ketone, poly (N-vinylcarbazole), acrylonitrile-styrene copolymer, polyetherimide poly(phenylenevinylene) and may include one or more functional groups chosen from ROOH, ROSH, RSSH, OH, S0₃H, S0₃R, S0₄R, COOH, NH₂, NHR, NR₂, CONH₂, and NH— Nt¾, wherein R denotes: linear or branched hydrocarbon-based chains, capable of forming at least one carbon-based ring, being saturated or unsaturated; alkylenes, siloxanes, silanes, ethers, polyethers, thioethers, silylenes, and silazanes. The polymeric solution may also include one or more polysulfone, copolymer of styrene and acrylonitrile poly(arylene oxide), polycarbonate, cellulose acetate, polysulfones; poly(styrenes), styrene-containing copolymers, acrylonitrilestyrene copolymers, styrene-butadiene copolymers, styrene-vinylbenzylhalide copolymers; polycarbonates; cellulosic polymers, cellulose acetate-butyrate, cellulose propionate, ethyl cellulose, methyl cellulose, nitrocellulose, polyamides, polyimides, aryl polyamides, aryl polyimides, polyethers, poly(arylene oxides), poly(phenylene oxide), poly(xylene oxide); poly(esteramide-diisocyanate), polyurethanes, polyesters (including polyarylates), poly(ethylene terephthalate), poly(alkyl methacrylates), poly(acrylates), poly(phenylene terephthalate), polysulfides one or more monomers from the group poly (ethylene), poly(propylene), poly(butene-l), poly(4-methyl pentene-1), polyvinyls, poly(vinyl chloride), poly(vinyl fluoride), poly(vinylidene chloride), poly(vinylidene fluoride), polyvinyl alcohol), polyvinyl esters), poly(vinyl acetate), poly(vinyl propionate), poly(vinyl pyridines), poly(vinyl pyrrolidones), poly(vinyl ethers), poly(vinyl ketones), poly(vinyl aldehydes), poly(vinyl formal), poly(vinyl butyral), poly(vinyl amides), polyvinyl amines), poly(vinyl urethanes), polyvinyl ureas), polyvinyl phosphates), poly(vinyl sulfates), polyallyls; poly(benzobenzimidazole), polyhydrazides, polyoxadiazoles, polytriazoles, poly (benzimidazole), polycarbodiimides, polyphosphazines and combinations thereof. The first and the second gas may be olefins and paraffins and the one or more metal nanoparticles are selected from Cu-Au nanoparticles, Ni-Au nanoparticles, Au-Ni nanoparticles, Au-Co nanoparticles, Ni nanoparticles, Ni-Cu nanoparticles, Pd nanoparticles, Au-oxide core-shell nanoparticles, Au-Si0₂ core- shell nanoparticles, or Au-Ti0₂ core-shell nanoparticles. Advantages/Special Characteristics: High permeability membrane materials solve numerous design problems for membrane applications. Metal nanoparticle filled stiff chain, glassy polymer membranes require as little as one tenth the membrane surface area or pressure differential across the membrane to achieve a desired gas flux. Also, with higher permeability, the nanocomposite membrane can be much thicker than an unfilled stiff chain, glassy polymeric membrane. This eases process design and reduces the likelihood of creating defects such as pinholes and tears in the membrane.

The present invention also provides the addition of nanoparticles to rubbery polymers as a method for substantially increasing the overall membrane permeability to gases and vapors. The present invention also provides metal oxide nanoparticles that are added to selected rubbery polymers, with no significant reduction in selectivity. Such enhancements to permeability allow for a reduction in membrane area and/or driving force (i.e. costs) required to achieve a desired gas flux. Photo- and thermally-initiated crosslinking and/or further polymerization remains possible after the addition of nanoparticles to monomer or polymer solution. For instance, by dispersing nanoscale impermeable metal oxide particles into XLPEO, the overall composite demonstrates substantially improved gas transport properties over those of the neat-polymer.

Traditionally, the addition of impermeable particles to a rubbery polymer results in a reduction in permeability. Therefore, the addition of particles has been avoided for membrane applications. This invention teaches the addition of NPs to rubbery polymers, to increase the overall membrane permeability. Moreover, when NPs are added to selected rubbery polymers, there is no reduction in selectivity. Such enhancements in permeability allow for a reduction in membrane size and/or driving force required to achieve a desired gas flux.

One example of the nanocomposite preparation protocol for rubbery polymers: Samples of a rubbery polymer (e.g., poly(ethylene octane), 1,2-polybutadiene; (however, a person of skill in the art will recognize that other polymers may be used) were added to toluene at 1.5 g / 100 mL solution and allowed to stir until the polymer was dissolved. Depending on polymer solubility in the selected solvent, the temperature of the solution must be raised while mixing to allow the polymer to fully dissolve in the solvent. Nanoparticles were added to the polymer solution and mixed sufficiently to allow for good particle dispersion in the solution. In some embodiments, the nanoparticles are of a single type; however, other embodiments may contain mixtures of nanoparticles (e.g., differing sizes and/or compositions). The nanoparticle filled solution is allowed to stir (e.g., overnight with a magnetic stirring bar). The sample solution was then poured onto a clean, dry level casting plate and allowed to cast until the toluene has completely evaporated, which usually requires two days. Persons of skill in the art will recognize that these procedures are intended to illustrate one embodiment and synthesis; other synthesis maybe used to form different embodiments of the present invention. One example of the nanocomposite polyacetylene preparation protocol. PTMSP Nanocomposite Film Preparation: Samples of PTMSP were added to toluene at 1.5 g / 100 mL solution and allowed to stir until the polymer is dissolved. Nanoparticles were added to the polymer solution and mixed using a Warring Handheld High Speed Blender at 15000 rpm. The nanoparticle filled solution is allowed to stir overnight with a magnetic stirring bar. The sample solution was then poured onto a clean, dry level casting plate and allowed to cast until the toluene has completely evaporated, which usually requires two days. All sample preparation involving particles was conducted in a closed glove box under an N₂ blanket with a feed pressure between 1.5 and 5 cm H₂0, and a relative humidity of 0%. Persons of skill in the art will recognize that these procedures are intended to illustrate one embodiment and synthesis; other synthesis maybe used to form different embodiments of the present invention.

One example of the crosslinked poly( ethylene oxide) preparation protocol: The prepolymer solution was prepared by adding 0.1 wt.% initiator (i.e., HCPK or Irgacure 2959) to PEGDA. After stirring, the solution was mixed with a known amount of ultrapure water to form the target composition before being sonicated for about 10 minutes to eliminate bubbles (Ultra sonic cleaner, Model FS60, Fisher Scientific, Pittsburg, PA). After about 1 hr. of stirring, nanoparticles were added while the prepolymer solution was stirring. When large amounts of nanoparticles are being added to the prepolymer, organic solvents are added to the prepolymer solution to prevent the nanoparticle filled solution from becoming too viscous for mixing. In some experiments, N₂ was bubbled through the solution for 30 minutes prior to polymerization to remove dissolved oxygen. The solution was sandwiched between two quartz plates, separated by spacers to control film thickness. The solution was polymerized by exposure to 312 nm UV light in a UV Crosslinker (Model FB-UVXL-1000, Fisher Scientific) for 90 seconds at 3 mw/cm². The solid films obtained by this process were crosslinked three dimensional networks (i.e., gels) and contained a negligible low molecular weight polymer (i.e., sol) that was not bound to the network. The as-synthesized film was then immersed in a large amount of ultrapure water for at least 5 days to allow the sol to diffuse out of the gels. The water was changed daily. Many commercial NPs (e.g. oxides) are environmentally and biologically inert and cost less than the matrix polymer material, thus reducing overall membrane costs, e.g., poly(l-phenyl-2-[p-trimethylsilylphenyl]acetylene, poly(l-trimethylsilyl-l- propyne) and XLPEO.

It will be understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

All of the compositions and/or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations can be applied to the compositions and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

Claims

CLAIMS:

1. A nanoparticle-filled polymer comprising one or more nanoparticles dispersed within the one or more polymeric materials, wherein the one or more nanoparticles have a diameter of between 0.1 nm and 100 nm, wherein the nanoparticle-filled rubbery polymer behaves as a nanocomposite exhibiting higher permeability than the native polymer membrane.

2. The composition of claim 1, wherein the polymeric material comprising a rubbery polymer, wherein the polymer has a glass transition temperature (Tg) at or below the use temperature.

3. The composition of claim 1, wherein the polymeric material comprising a glassy polymer.

4. The composition of claim 1, wherein the polymer is a rigid, glassy polymer having a glass transition temperature (Tg) greater than 150 degrees C.

5. The composition of claim 1, wherein the polymer is a rigid, glassy polymer having a glass transition temperature (Tg) less than 150 degrees C.

6. The composition of claim 1, wherein the one or more nanoparticles comprising one or more atom of Fe, Cr, Al, Ga, In, Hf, Sn, Zr, Mo, Ti, V, Co, Ni, Cu, Y, Ta, W, Pb, B, Nb, Ge, Pr, U, Ce, Er, Nd, Si, Mg, Ca, Ba, Sr, Au or combination thereof.

7. The composition of claim 1, wherein the one or more nanoparticles are elements, alloys, compounds, or core/shell nanoparticles consisting of a mixture thereof.

8. The composition of claim 1, wherein the diameter of the one or more nanoparticles are between about 0.1 and 50 nm.

9. The composition of claim 1, wherein one or more nanoparticles act simultaneously to improve selectivity for one more of the diffusants and as a catalyst for the reaction of one more of the diffusants.

10. The composition of claim 1, wherein the one or more nanoparticles that is catalytically active are elements, alloys, compounds, or core/shell nanoparticles consisting of a mixture thereof.

11. The composition of claim 1, wherein the one or more inorganic nanoparticles are bonded to the polymer through the use of ligands that attach simultaneously to the polymer and inorganic nanoparticle mical hooks").

12. The composition of claim 1, wherein the polymeric material comprises poly(l-phenyl-2-[p- trimethylsilylphenyl] acetylene, poly(l-trimethylsilyl-l-propyne) or a combination thereof.

13. The composition of claim 1, wherein the polymeric material comprises poly(ethylene octene), polybutadiene, poly(ethylene oxide) or a combination thereof.

14. The composition of claim 1, wherein the polymeric material is a substituted polymer comprising one or more halogens, hydroxyl groups, lower alkyl groups, lower alkoxy groups, monocyclic aryl, lower acyl groups and combinations thereof.

15. A method for making highly permeable and selective membranes comprising the steps of:

a. forming one or more nanoparticles having a diameter of between 1 nm and 20 nm by laser ablation; b. collecting the one or more nanoparticles in a polymeric solution comprising one or more monomers that prevents the one or more nanoparticles forming an agglomeration; and

c. polymerizing the polymeric solution to form a highly permeable and selective nanoparticle membrane.

16. A method for making highly permeable and selective membranes comprising the steps of:

a. forming one or more nanoparticles having a diameter of between 1 nm and 20 nm by laser ablation; b. collecting the one or more nanoparticles in a polymeric solution comprising one or more monomers that allows the formation of an agglomeration; and

c. polymerizing the a polymeric solution to form a highly permeable and selective nanoparticle membrane.

17. The composition of claim 15 or 16, wherein the polymerizing occurs by a thermal reaction, a UV initiated reaction, a light initiated, or a free radical reaction.

18. The composition of claim 15 or 16, wherein the one or more metal nanoparticles comprising one or more atom of Fe, Cr, Al, Ga, In, Hf, Sn, Zr, Mo, Ti, V, Co, Ni, Cu, Y, Ta, W, Pb, B, Nb, Ge, Pr, U, Ce, Er, Nd, Si, Mg, Ca, Ba, Sr, Au or combination thereof.

19. The composition of claim 15 or 16, wherein the one or more nanoparticles are metal alloys, pure metals, metal compounds, core-shell nanoparticles or a mixture thereof.

20. The composition of claim 15 or 16, wherein the diameter of the one or more metal nanoparticles are between about 5 and 50 nm.

21. The composition of claim 15 or 16, wherein the polymeric solution comprises poly(l-phenyl-2-[p- trimethylsilylphenyl] acetylene, poly(l-trimethylsilyl-l-propyne) or a combination thereof.

22. The composition of claim 15 or 16, wherein the polymeric solution comprises poly(ethylene octene), polybutadiene, poly(ethylene oxide) or a combination thereof.

23. The nanocomposite material of claim 15 or 16, wherein the one or more metal nanoparticles are substantially uniformly distributed within the polymeric solution.

24. A method for making a gas separation device comprising the steps of: a. providing a highly permeable and selective nanoparticle membrane made by forming one or more metal nanoparticles having a diameter of between 1 nm and 20 nm by laser ablation, collecting the one or more metal nanoparticles in a polymeric solution comprising one or more monomers that prevents the one or more metal nanoparticles from forming an agglomeration and polymerizing the a polymeric solution; and

b. positioning one or more containers about the highly permeable and selective nanoparticle membrane to separated at least a first and a second gas.

25. The gas separation device of claim 24, wherein the polymerization occurs by a thermal reaction, a UV initiated reaction, a light initiated, or a free radical reaction.

26. The gas separation device of claim 24, wherein the one or more metal nanoparticles comprising one or more atom of Fe, Cr, Al, Ga, In, Hf, Sn, Zr, Mo, Ti, V, Co, Ni, Cu, Y, Ta, W, Pb, B, Nb, Ge, Pr, U, Ce, Er, Nd, Si, Mg, Ca, Ba, Sr, Au, C, O, or combination thereof.

27. The gas separation device of claim 24, wherein the highly permeable and selective nanoparticle membrane comprises a shape chosen from a microring, a microdisk, a microsphere, a microplate, a microline and a combination thereof.

28. The gas separation device of claim 24, wherein the polymeric solution is chosen from

polymethylmethacrylates, polystyrenes, polycarbonates, polyimides, epoxy resins, cyclic olefin copolymers, cyclic olefin polymers, acrylate polymers, polyethylene teraphthalate, polyphenylene vinylene, polyether ether ketone, poly (N-vinylcarbazole), acrylonitrile-styrene copolymer,

polyetherimide poly(phenylenevinylene).

29. The gas separation device of claim 24, wherein the polymeric solution comprises one or more functional groups chosen from ROOH, ROSH, RSSH, OH, S0₃H, S0₃R, S0₄R, COOH, NH₂, NHR, NR₂, CONH₂, and H— NH₂, wherein R denotes: linear or branched hydrocarbon-based chains, capable of forming at least one carbon-based ring, being saturated or unsaturated; alkylenes, siloxanes, silanes, ethers, polyethers, thioethers, silylenes, and silazanes.

30. The gas separation device of claim 24, wherein the polymeric solution comprises one or more polysulfone, copolymer of styrene and acrylonitrile poly(arylene oxide), polycarbonate, cellulose acetate, polysulfones; poly(styrenes), styrene-containing copolymers, acrylonitrilestyrene copolymers, styrene- butadiene copolymers, styrene-vinylbenzylhalide copolymers; polycarbonates; cellulosic polymers, cellulose acetate-butyrate, cellulose propionate, ethyl cellulose, methyl cellulose, nitrocellulose, polyamides, polyimides, aryl polyamides, aryl polyimides, polyethers, poly(arylene oxides), poly(phenylene oxide), poly(xylene oxide); poly(esteramide-diisocyanate), polyurethanes, polyesters (including polyarylates), poly(ethylene terephthalate), poly(alkyl methacrylates), poly(acrylates), poly(phenylene terephthalate), polysulfides and combinations thereof.

31. The gas separation device of claim 24, wherein the polymeric solution comprises one or more monomers from the group poly (ethylene), poly(propylene), poly(butene-l), poly(4-methyl pentene- 1), polyvinyls, poly(vinyl chloride), poly(vinyl fluoride), poly(vinylidene chloride), poly(vinylidene fluoride), poly(vinyl alcohol), poly(vinyl esters), poly(vinyl acetate), poly(vinyl propionate), poly(vinyl pyridines), polyvinyl pyrrolidones), poly(vinyl ethers), polyvinyl ketones), poly(vinyl aldehydes), poly(vinyl formal), poly(vinyl butyral), poly(vinyl amides), poly(vinyl amines), poly(vinyl urethanes), poly(vinyl ureas), poly(vinyl phosphates), poly(vinyl sulfates), polyallyls; poly(benzobenzimidazole), polyhydrazides, polyoxadiazoles, polytriazoles, poly (benzimidazole), polycarbodiimides,

polyphosphazines and combinations thereof.

32. The gas separation device of claim 24, wherein the first and the second gas comprise olefins and paraffins.

33. The gas separation device of claim 24, wherein the one or more metal nanoparticles are selected from Cu-Au nanoparticles, Ni-Au nanoparticles, Au-Ni nanoparticles, Au-Co nanoparticles, Ni nanoparticles, Ni-Cu nanoparticles, Pd nanoparticles, Au-oxide core-shell nanoparticles, Au-SiCh core-shell nanoparticles, or Au-TiC core-shell nanoparticles.