Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/12—Composite membranes; Ultra-thin membranes
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
  • B01D71/06—Organic material
  • B01D71/30—Polyalkenyl halides
  • B01D71/32—Polyalkenyl halides containing fluorine atoms
  • B01D71/36—Polytetrafluoroethene
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/10—Supported membranes; Membrane supports
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/10—Supported membranes; Membrane supports
  • B01D69/106—Membranes in the pores of a support, e.g. polymerized in the pores or voids
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/10—Supported membranes; Membrane supports
  • B01D69/107—Organic support material
  • B01D69/1071—Woven, non-woven or net mesh
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
  • B01D69/10—Supported membranes; Membrane supports
  • B01D69/108—Inorganic support material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
  • B01D71/02—Inorganic material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
  • B01D71/06—Organic material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
  • B01D71/06—Organic material
  • B01D71/30—Polyalkenyl halides
  • B01D71/32—Polyalkenyl halides containing fluorine atoms
  • B01D71/34—Polyvinylidene fluoride
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
  • B82B1/00—Nanostructures formed by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82B—NANOSTRUCTURES FORMED BY MANIPULATION OF INDIVIDUAL ATOMS, MOLECULES, OR LIMITED COLLECTIONS OF ATOMS OR MOLECULES AS DISCRETE UNITS; MANUFACTURE OR TREATMENT THEREOF
  • B82B3/00—Manufacture or treatment of nanostructures by manipulation of individual atoms or molecules, or limited collections of atoms or molecules as discrete units
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D2256/00—Main component in the product gas stream after treatment
  • B01D2256/22—Carbon dioxide
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/22—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion
  • B01D53/228—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by diffusion characterised by specific membranes

Definitions

• the present invention relates to gas separation and ion transport membranes generally, and more particularly to a composite membrane structure having a backbone of an array of nanotubes.
• a long list of polymers have been studied in the past for their utility in the formation of membranes for a variety of purposes. Of importance to the present invention is the use of such polymer membranes for separations and selective transport to modify a feed material and/or to recover one or more target species from the feed material.
• a host of polymers have been determined to be useful for such applications, with each material exhibiting its own benefits and drawbacks for particular membrane separation and transport applications.
• An application of particular interest to the Applicant is the degassing of liquids through contact with a gas-permeable, liquid-impermeable membrane.
• Such liquid-gas contactors typically rely upon Henry's Law of partial pressures and Ficke 's law of diffusion to drive gas transport through the membrane, while small pore size, or the absence of through-pores in a "nonporous" media, restricts or prevents liquid transport through the membrane.
• fluoropolymers has greatly aided the membrane liquid degassing field by providing membrane polymers that are generally inert, and can be formed into a gas-permeable, liquid-impermeable membrane structure.
• a particular fluoropolymer of note is a class of amorphous perfluoropolymers, such as those available from Du Pont under the trade name "Teflon®", as well as other amorphous fluoropolymers available from Asahi Glass Corporation and Solvay Solexis.
• Such materials are oftentimes employed in gas separation membranes for their inertness and high permeability characteristics.
• Membranes are typically selected for a combination of their compatibility with the contacting materials, their permeability to the targeted transport species, and their selectivity of one molecule over another. It has been shown that, while membrane selectivity may be constant as a function of the membrane thickness, the throughput (permeance) changes inversely to the thickness of the membrane.
• Reinforcement materials for thin film membranes have typically been in the form of lattice structures, support films, and particulate dopants.
• the electron cloud associated with the sp 2 bonding structure functions as an interaction between proximate carbon nanotubes, such that nanotubes may be formed into coherent sheets, tapes, ribbons, ropes, and other macrofabrics, with a tensile strength that is sufficient to facilitate handling.
• Strength reinforcement materials including glass fibers, carbon fibers, metal fibers, carbon nanotubes, and the like, when conventionally added as a reinforcement material, are dependent upon surface energy compatibility between the reinforcement material and the matrix for the degree of strength enhancement. Matching of the respective surface energies permits van der Walls interactions to assist in the load transfer between the reinforcement material and the matrix. In some cases, surface energy matching is not possible without chemical modification of the reinforcing material, which chemical modification can be expensive or even impossible.
• a thin membrane for separations may be prepared with significantly less polymer material while maintaining, or even enhancing strength properties of the membrane.
• separation membrane cost may correspondingly be significantly reduced.
• the reinforcement structure of this composite membrane is a non-woven carbon nanotube fabric that is single or multiple layers, while the carbon nanotubes are intermingled.
• a method for preparing a composite gas separation membrane for separating a gas-liquid mixture includes providing a fabric having a non-woven array of intermingled carbon nanotubes, wherein the non-woven array defines interstices between the intermingled carbon nanotubes.
• the method further includes providing a dopant and at least partially immersing the fabric in the dopant.
• the dopant is sonicated with an ultrasonic transducer such that the dopant penetrates the fabric interstices to an extent sufficient to establish a non-porous but permeable composite structure with the fabric.
• Figure 1 is a schematic illustration of a testing apparatus for testing permeability, permeance, and gas selectivity of composite films of the present invention
• Figure 2 is a cross-sectional scanning electron microscopy (SEM) image of a composite film of the present invention
• Figure 3 is a cross-sectional SEM image of a composite film of the present invention.
• FIG. 4 is a schematic illustration of a membrane separation system of the present invention.
• FIG. 5 is a schematic illustration of a membrane ion exchange system of the present invention.
• Figure 6 is a photograph of a cross-section of a sample composite membrane taken under scanning electron microscopy
• Figure 7 is a spectral analysis chart illustrating the presence of carbon, fluorine, and oxygen at respective spectral analysis locations identified in the photograph of Figure 6;
• Figure 8 is a spectral analysis chart illustrating the presence of carbon, fluorine, and oxygen at respective spectral analysis locations identified in the photograph of Figure 6;
• Figure 9 is a tensile strength chart illustrating Young's Modulus values for various sample composite membranes, in comparison to a nonwoven carbon nanotube fabric labeled "Pure".
• nanotubes is intended to mean single wall or multiple wall tubular structures having a diameter in the range of about 1-100 nanometers (nm), and a length in the range of about 0.001-10 millimeters (mm).
• the nanotubes described in the experimental section hereof are multiple wall carbon nanotubes typically having a diameter of between about 1- 25 nanometers (nm), and a length of between about 0.1-5 millimeters (mm). Both single wall and multiple wall carbon nanotubes, however, are well understood in the art and are contemplated as being useful in the present invention.
• membrane is intended to mean a barrier structure that is capable of permitting selective transport thereacross.
• a “composite membrane” is a membrane structure having two or more bodies coordinating with one another in a single membrane structure.
• the bodies may be comprised of the same or different materials, and are exemplified in this description as a polymer matrix body incorporated with a carbon nanotube fabric.
• non-porous is intended to mean that the subject composite film is substantially free from open pathways extending continuously from one side of the composite film to the other.
• a "pore” is defined as an opening by which matter passes through a wall or membrane.
• non-porous is intended to mean the absence or substantial absence of pores.
• a "pore” could be defined as a lumen of a carbon nanotube that extends through the thickness of the composite membrane to provide a pathway through the composite membrane.
• the non-porous composite membranes of the present invention are free from such lumenal pathways through the composite membrane.
• the term "permeable" is intended to mean transport through the composite membrane that relies primarily upon a solution-diffusion mechanism, and not as a result of porosity in the structure permitting material transport through the composite membrane without a solution-diffusion mechanism.
• carbon nanoparticles structurally similar to nanotubes have been employed in numerous applications, primarily as a mechanical strengthening agent.
• the addition of carbon nanoparticles in the form of graphene has resulted in a significant reduction in polymer film permeability.
• nanoparticles have been demonstrated and intentionally used to limit permeability in a substrate, such as in U.S. Patent No. 7,745,528 and U.S. Patent Application Publication No. 2007/0137477. Consequently, the Applicant's finding that a carbon nanotube support structure to a polymer film does not significantly inhibit permeability performance is a surprising result of the present invention.
• a "buckypaper” found by the Applicant to be useful in the composite membranes of the present invention are available from Nanocomp Technologies, Inc. of Merrimack, New Hampshire.
• the Nanocomp buckypapers are described in, for example, U.S. Patent Application Publication Nos. 2011/0316183 and 2009/0215344, as well as U.S. Patent No. 7,993,620 as a non-woven fabric of intermingled nanotubes generated through chemical vapor deposition (CVD) or other gas phase pyrolysis procedure, the contents of which patents and patent applications being incorporated herein by reference.
• CVD chemical vapor deposition
• the intermingled nanotubes are randomly dispersed in a random orientation in the non-woven fabric, with the fabric being comprised of multiple layers of randomly -oriented non- woven nanotubes that, taken together, form the carbon nanotube fabric.
• the nanotubes making up the tested non-woven fabric included multiple wall nanotubes having an outside diameter of approximately 10-15 nm, and a length of between about 0.1-5 mm randomly arranged within layers of a multiple layer non-woven fabric weighing between 1-20 g/m 2 .
• the example nanotube fabrics have between 5-95% open structure, and more preferably between 30-70% open structure, with a thickness of between 1-50 micrometers.
• nonwoven fabric is intended to mean a sheet, web or bat of directionally or randomly oriented fibers, bonded through various means, including friction and/or cohesion and/or adhesion. It is believed that the carbon nanotube fabrics described above are bonded through ⁇ - ⁇ electron cloud interaction among the carbon nanotubes. It is contemplated that the fabric may include partially or completely directionally oriented fibers, or may instead be randomly oriented nanotubes.
• dopants may be incorporated with the nanotube fabric to form the composite membranes of the present invention.
• the term "dopant” is intended to mean a material that is capable of penetrating into interstices of the non-woven fabric, and which is capable of forming a network that is sufficient to establish a non-porous but permeable barrier.
• Example dopants include monomers/polymers in neat form or in solution. The polymers described in the following examples were selected for their inertness and relatively high gas permeabilities. It is to be understood, however, that other materials, including other polymers, polymer blends, and non-polymers may be utilized in the formation of the composite membranes of the present invention.
• the selected dopant material is preferably capable of depositing within the open interstitial space of the nanotube fabric to an extent to form a nonporous but permeable composite structure having a target gas permeance of at least 0.1 gas permeation units (GPU).
• GPU gas permeation units
• the term "incorporated with” is intended to describe the relationship between the dopant and the nonwoven fabric, wherein the dopant is not merely deposited upon or adjacent to the nonwoven fabric surface, but additionally or instead penetrated into interstices of the nonwoven fabric to the extent that, upon any necessary polymerization or cure of the dopant, the dopant and the nanotubes interact as a composite membrane exhibiting significantly greater absolute strength (Young's modulus) than the respective absolute strengths (Young's Modulus) of either of the polymerized/cured dopant or the nonwoven fabric alone.
• Such synergistic strengthening of the composite membranes of the present invention is a surprising and important aspect, and defines the extent of penetration of the dopant into interstices of the nonwoven fabric necessary in order to be "incorporated with” the nanotube fabric for the purposes of the present invention.
• Penetration may be defined as the distance that the dopant penetrates into the nonwoven fabric, and can be inferred in the following examples by measuring the fluorine concentration through the thickness of the dried composite membrane in the case of a fluoropolymer dopant. It has been determined that, in order to form the composite membranes of the present invention, the dopant must penetrate into the surface of the nanotube fabric. Penetration of the dopant into the nonwoven fabric depends upon the viscosity of the dopant, including as solvated in solution, and the surface energy difference between the dopant/dopant solution and the nonwoven fabric. Penetration is also dependent upon the molecular size of the dopant.
• Dopant penetration as measured by energy dispersive x-ray analysis through the thickness of the membrane monitoring fluorine concentration showed a strength to depth of penetration relationship consistent with the relative depth of dopant penetration.
• Dopant impregnations resulting in a substantially uniform dopant dispersion throughout the fabric exhibit the highest absolute strengths.
• sufficiently strong, permeable, but nonporous composite membranes may be formed when only one side of the nonwoven fabric is exposed to the dopant/dopant solution. In the case of a dip tank, one side of the fabric may be protected from exposure to the dopant solution by use of a solid, impermeable barrier to which the dopant solution will not permanently adhere.
• the frame-attached nonwoven fabric is then exposed to the dopant solution for a period of time necessary to provide sufficient penetration into the nonwoven fabric.
• One benefit of such one-side impregnated fabrics, wherein the non-impregnated side of the fabric remains free of dopant, is that gasses permeating from the impregnated side of the membrane to the non-impregnated side may be vented to atmosphere, removed, by vacuum, or purged from the non- impregnated side of the membrane using gas pressure.
• Typical composite membranes of the present invention permit at least 90% of mass transport only through a solution-diffusion mechanism, and more preferably at least 95%, and still more preferably at least 99% of the mass transport through the composite membrane only by a solution-diffusion mechanism.
• Such a composite membrane preferably transports sufficient mass through the membrane per unit area as is required for a given application.
• a testing apparatus 10 includes a cell 12 having a chamber 14 that is divided into an upper compartment 16 and a lower compartment 18 by the membrane 20 being tested.
• the tested membranes were each 0.95 cm 2 held in place by a clamp 22.
• Upper compartment 16 had a volume of greater than 1000cm 3
• lower compartment 18 had a volume of 25cm 3 .
• both compartments 16, 18 are first purged with an identical gas for about 30 min., followed by an additional 100 kPa of the gas added to upper compartment 16.
• the pressure of both compartments 16, 18 is measured with two Omegadyne model PX 209-015G5V pressure transducers as a function of time.
• the pressure of upper compartment 16 does not change during the test.
• the rate of pressure increase on the lower compartment 18 reaches its pseudo-steady-state, the permeability was calculated as follows:
• V volume of lower compartment 18 (cm 3 )
• A area of membrane 20 (cm 2 )
• Example 1 illustrate composite membranes of the present invention, but are not intended to be limiting as to the materials and methods of formation for such membranes.
• Example 1 illustrate composite membranes of the present invention, but are not intended to be limiting as to the materials and methods of formation for such membranes.
• the composite membrane of Case 1 from Table 4 was prepared by dip coating the carbon nanotube fabric in the polymer solution for 72 hours while stretched over an aluminum frame. Following submersion for 72 hours, the composite material was withdrawn from solution and held in an atmosphere saturated with FC-770 solvent to prevent drying of the composite, and the excess solution was allowed to drain from the surface of the wet composite. The composite was then allowed to dry under ambient conditions under sufficient tension to remove wrinkles.
• the dried composite membrane was then laser cut into one inch by two inch samples for tensile strength measurements, permeability and permeance testing, and scanning electron microscopy.
• Table 5 sets forth testing results of the composite membrane, in comparison to neat polymer films formed from Teflon® AF-2400 through extrusion, solution casting, melt pressing, and laboratory bench casting.
• Each of the laser-cut composite membranes was weighed to the nearest 0.1 mg, and the thickness determined to the nearest micrometer.
• the weight of the carbon nanotube fabric was subtracted from the total composite weight to determine the amount of polymer remaining within the composite structure.
• the weight of polymer was converted to an equivalent film thickness by density correcting the weight to volume using a factor of 1.67 grams of polymer per cm 3 .
• An equivalent film thickness was then determined by dividing the volume by the length and width of the composite membrane.
• the composite exhibits a tensile strength greater than that of the neat polymer, and dramatically greater than expected under the "Rule of Mixtures". Applicant believes that an unexplained interaction between the polymer and the carbon nanotubes is responsible for the unexpected strengthening property demonstrated in the results table.
• FIG. 2 A cross-sectional image of the composite is illustrated in Figure 2, which shows an asymmetrically formed membrane at section “A” with air inclusions to a depth of approximately four micrometers.
• Section “B” is approximately 15 micrometers thick, and is the bulk of the composite, while section “C” is an out of focus inner edge of the cross-section.
• the composite of this Example 1 exhibits a surprisingly higher tensile strength than either the base carbon nanotube fabric or the polymer in a neat film format. Moreover, the permeability of the composite membrane is also surprisingly unobstructed by the carbon nanotube fabric, contrary to what would be expected under Nielsen's Model.
• the composite membrane described in Case 2 of Table 4 was prepared by soaking the carbon nanotube fabric in solution for 72 hours. Following soak, the composite was pressed while in the presence of polymer solution, and subsequently placed on a glass surface. Excess polymer solution was removed from the composite using a squeegee while compressing the composite surface to ensure the polymer solution beneath the composite against the glass was minimized and to remove air bubbles regained between the glass surface and the composite membrane. The composite membrane was then dried at ambient, followed by oven drying at 60°C for four hours.
• the permeability of the composite membrane closely matches the solution cast film permeability described in Table 5 with reference to a Teflon® AF 2400 film, as that employed in the present Example. In this instance, the weight of polymer remaining in the composite membrane is equivalent of a 9 micrometer neat polymer film thickness.
• the elemental analysis shows a distribution of the polymer throughout the thickness of the composite membrane, though the polymer concentration in this Example 2 appears to be higher throughout the thickness of the composite membrane in comparison to the composite membrane of Example 1.
• the elevated polymer concentration may be attributed to the mechanical force applied to the composite membrane in the fabrication technique described in this Example 2.
• a composite membrane in accordance with Case 3 of Table 4 was prepared using the procedure of Example 2. The tensile strength of the composite membrane was compared to a membrane cast from Solution 5 of Table 3 :
• a composite membrane in accordance with Case 4 of Table 4 was prepared using the procedure set forth in Example 2, and compared to a polymer cast film of the solution of Table 3, Type 5. Permeation testing of the composite membrane exhibited low selectivity, due to the extremely low permeability of the utilized polymer.
• a composite membrane in accordance with Case 5 of Table 4 was prepared using the procedure set forth in Example 2. The composite membrane was tested for strength in both dry and water-saturated conditions, and compared to films of the neat polymer. Table 11
• the polymer utilized in this example includes a sulfonated tetrafluoroethylene that is commonly used in ion exchange membranes to permit ionic species to migrate thereacross.
• the example composite membrane may therefore permit transport of cations thereacross, substantially to the exclusion of anions and electrons.
• films formed from such polymer are also typically highly selective to carbon dioxide (CO2), thereby rendering it a good candidate material for carbon sequestration applications.
• the dry composite membrane is not expected to demonstrate desired gas permeability or selectivity, because the sulfonic acid regions of the sulfonated tetrafluoroethylene polymer must be hydrated so that carbon dioxide can be transported as the dissolved carbonate base, CO3 "2 .
• the sulfonic acid portion of the polymer in the composite membrane may then carry the ionic species across the barrier.
• the modified carbon nanotube fabric was oven dried at 60°C for four hours. The modified carbon nanotube fabric was then impregnated with polymer solution 7 in accordance with the procedure of Example 2.
• the composite membrane was tested for strength in both a wet and dry state:
• the composite membrane was also tested for permeability with wet paper towels placed in the space above and below the wet composite membrane to maintain humid conditions during permeability testing.
• a composite membrane was prepared from a 5 g/m 2 nonwoven carbon nanotube fabric (Case 4, Table 1) and Teflon AFTM 2400 dopant.
• the carbon nanotube sheet was laser cut into 6in x 6in squares for mounting over a steel frame.
• the dopant solution was prepared as 3% by weight Teflon AFTM2400 polymer in NovecTM7500 solvent from 3M Company of St. Paul, Minnesota. 3 kg of dopant solution was placed in an immersion tank, which was then placed in a water sonication apparatus.
• the immersion tank was placed in a water sonication tank so that ultrasonic energy emitted by an ultrasonic transducer 314 may be transmitted from the water medium in the water sonication tank through the immersion tank into the dopant solution.
• the ultrasonic transducer was a Fischer Sonic Cleaner emitting at 400 W and 30 kHz frequency.
• the water sonication tank may be heated to warm the dopant solution to a desired impregnation temperature, typically in the range of 60-90°C.
• a desired impregnation temperature typically in the range of 60-90°C.
• dopant solution was warmed to 85 °C to achieve desired viscosity levels of the dopant solution.
• the dopant solution was warmed to the temperature set point, sonication from the ultrasonic transducer was initiated.
• the framed carbon nanotube fabric was then immersed in the dopant solution in the immersion tank for sixty minutes, with a typical immersion time ranging from 30-120 minutes. Sonication was then ceased and the framed membrane was removed from the remaining dopant solution in the immersion tank, and allowed to dry at ambient.
• a cross-section of an example composite membrane generated through sonicated impregnation of the dopant solution into a non-woven carbon nanotube fabric is illustrated in Figure 6, identifying multiple locations at which spectral analysis was performed to determine relative elemental composition among carbon, oxygen, and fluorine.
• the presence of fluorine and oxygen in the spectral analysis locations within the composite membrane cross-section indicate the presence of the fluoropolymer dopant.
• the spectral analysis results are illustrated in Figures 7 and 8, illustrating a strong presence of fluorine and oxygen throughout the cross-section of the composite membrane. This evidences the fact that substantially complete dopant penetration through the fabric cross-section was accomplished with the sonication technique.
• the chart shown at Figure 7 indicates analysis by Internally normalized Dispersive Energy X-Ray to show dispersion of the carbon, fluorine, and oxygen through the thickness of the composite membrane. Normalizing the concentration to a value of numeral 1 for each concentration of oxygen, fluorine, and carbon individually removes the bias of their individual responsive relative to that of carbon.
• the chart of Figure 8 indicates relative weight percent contribution of each of carbon, fluorine, and oxygen at each spectral analysis location.
• Young's Modulus of the composite membranes were compared to the nonwoven carbon nanotube fabric alone.
• the data is illustrated in Figure 9, evidencing Young's Modulus values for the composite membranes of at least about 4 GPa, which is substantially greater than Young's Modulus value of the bare Nanocomp 5 g/m 2 density nonwoven carbon nanotube fabric, identified as "pure” at 0.5 GPa, or the neat Teflon AFTM 2400 membrane having a thickness substantially equivalent to the reduced film thickness of the composite membrane samples, at 1.7 GPa. Accordingly, the composite membranes of the present invention far exceed the expected Young's Modulus values of the respective components under the "Rule of Mixtures".
• a system 110 for separating a target gas from a liquid includes a housing 112 defining a chamber 114, and a composite membrane 116 separating chamber 114 into a permeate side 118 and a retentate side 120.
• Housing 112 includes an inlet 122 and an outlet 124 opening to retentate side 120 of chamber 114.
• Housing 112 may further include a gas port 126 opening to permeate side 118 of chamber 114.
• System 110 may include a pump 128 for evacuating permeate side 118 of chamber 114 through gas port 126, with pump 128 being fluidly connected to gas port 126 through, for example, pipe 130.
• a liquidous fluid containing the target gas may be delivered to retentate side 120 of chamber 114 through inlet 122 via pipe 132.
• pipe as used herein, is not intended to be limiting, and may include any conveyance member of suitable size, configuration, and material to permit the conveyance of fluid to an intended destination.
• Composite membrane 116 may be suitably configured to be capable of separating the target gas from the liquid at retentate side 120, and may preferably form a non-porous, permeable barrier exhibiting a permeance of at least 0.1 gas permeance units (GPU) to the target gas.
• GPU gas permeance units
• permeate side 118 of chamber 114 may be conditioned to exert a first partial pressure of the target gas that is less than a second partial pressure of the target gas in the liquidous fluid in retentate side 120 of chamber 114.
• the target gas may be driven across the barrier defined by the nonporous composite film 116.
• Pump 128 may be operated to condition permeate side 118 of chamber 114, such as by evacuating permeate side 118 to an extent at which the first partial pressure of the target gas is less than the corresponding partial pressure of the target gas in a liquidous fluid at retentate side 120. In this manner, separated target gas permeated into permeate side 118 may be removed from chamber 114 through gas port 126.
• Permeate side 118 of chamber 114 may also or instead be suitably conditioned by passing a sweep fluid through permeate side 118, wherein the target gas partial pressure within the sweep fluid is less than the corresponding target gas partial in the liquidous fluid at retentate side 120, so as to generate a driving force for permeation of the target gas through composite membrane 116 to permeate side 118.
• a sweep fluid may be introduced to permeate side 118 through a port in housing 112.
• a composite membrane 216 includes an ionomer that is capable of transporting ionic species from a first fluid to a second fluid on opposed sides of the barrier defined by the composite membrane 216.
• a system 210 for transporting ionic species across a barrier between a first fluid and a second fluid includes a housing 212 defining a chamber 214, and a composite membrane 216 defining the barrier and separating chamber 214 into a first side 218 and a second side 220.
• Composite membrane 216 preferably includes a fabric comprising a non-woven array of intermingled carbon nanotubes and a dopant incorporated with the fabric to form a nonporous permeable composite.
• the dopant is an ionomer that permits transport of cations across the barrier, substantially to the exclusion of anions and electrons.
• Such an ion exchange apparatus may be operated by applying a driving force to chamber 214, wherein the driving force is effective to motivate ionic species across the barrier defined by composite membrane 216.
• driving force may be in the form of electrical current generated in chamber 214 between first and second electrodes 230, 232 of opposite polarity.
• first and second electrodes 230, 232 are positioned at opposed sides of composite membrane 216, with a first electrode 230 disposed in first side 218 of chamber 214, and second electrode 232 being positioned in second side 220 of chamber 214.
• First and second electrodes 230, 232 are coupled to an electrical energy source 240 for generating a voltage potential and current passing between first and second electrodes 230, 232.
• An applied current across composite membrane 216 to motivate ionic species transport is well understood in the art for membrane-based ion exchange systems.
• driving forces are contemplated as being useful in motivating ionic species transport across composite membrane 216 between a first fluid delivered to first side 220 of chamber 214 through inlet 222, and a second fluid delivered to second side 218 of chamber 214 of inlet 224.
• a driving force may be generated based upon the properties of the first and second fluids on opposed sides of composite film 216.
• membrane-based ion exchange systems employ an applied electrical current as the force driving ion species transport across the membrane.

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• 2015
  • 2015-12-09 WO PCT/US2015/064697 patent/WO2016094511A1/en active Application Filing
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