Composite media for ion processing

Composite media, systems, and devices for substantially removing, or otherwise processing, one or more constituents of a fluid stream. The composite media comprise a plurality of beads, each having a matrix substantially comprising polyacrylonitrile (PAN) and supporting one or more active components which are effective in removing, by various mechanisms, one or more constituents from a fluid stream. Due to the porosity and large surface area of the beads, a high level of contact is achieved between composite media of the present invention and the fluid stream being processed. Further, the homogeneity of the beads facilitates use of the beads in high volume applications where it is desired to effectively process a large volume of flow per unit of time.

FIELD OF THE INVENTION

The present invention relates generally to the preparation and use of composite media for use in ion processing. More particularly, embodiments of the present invention relate to the preparation and use of composite media that include active components supported by large surface area matrix materials and are suitable for facilitating removal of various ions from fluid streams.

BACKGROUND OF THE INVENTION

Effective and efficient ion processing is an important consideration in numerous chemical and industrial processes. In general, ion processing refers to those processes, and/or devices which implement such processes that are used to facilitate neutralization, removal, concentration, or other processing, of one or more ions present in a fluid stream, examples of which include industrial waste and process streams. One example of such a process concerns the removal of materials such as cesium, strontium, and/or uranium from an industrial waste stream prior to the discharge of the fluid stream into the environment.

While ion processing components and processes are often employed to remove undesirable constituents of a fluid volume or stream, such components and processes may also be used to collect and concentrate one or more desirable constituents of a fluid volume or stream so that those constituents can then be reserved for future use.

One area where ion processing techniques, materials, and devices are particularly useful is in the industrial environment. Typical industrial waste and process streams present at least two significant challenges to ion processing efforts. The first challenge relates to the flow rates of such industrial waste and process streams. Because industrial waste and process streams are often characterized by relatively high flow rates, the associated ion processing materials, systems, and components must be capable of admitting and processing the high flow rate waste and process streams without introducing an undue pressure drop or other resistance to flow that would tend to compromise the flow rate of those streams, and thereby slow down the overall rate at which ion processing occurs.

Another challenge that must be considered when implementing the treatment of industrial waste and process streams relates to the level of cleanliness that must be attained in the processed stream. In particular, the streams produced in industrial environments are often required to meet stringent standards with regard to the permissible concentration of various contaminants or other materials that are ultimately discharged into the environment. Thus, the treatment systems and devices must not only be able to handle relatively high fluid flow rates, but they must do so at a high level of efficiency.

Generally, the effectiveness and efficiency of a particular ion processing material is at least partially a function of the total surface area of the active component that contacts the material or fluid to be processed. The surface area, in turn, is a function of the porosity, or pore volume, of the ion processing material, so that relatively more porous ion processing materials typically possess a relatively greater surface area than relatively less porous ion processing materials. Thus, when considering two ion processing materials equivalent in all other regards, an ion processing material with a relatively larger surface area is capable of removing a relatively greater amount of contaminants or impurities from a fluid stream than an ion processing material with a relatively smaller surface area. In light of this relationship, a number of ion processing materials, systems, and devices have been devised with a view towards providing a relative increase in the surface area of the ion processing material so as to improve its effectiveness.

Various methods may be used to prepare ion processing materials so as to provide a relative increase in the surface area of the active component, of the ion processing material, that comes into contact with the fluid stream to be processed. In one case, the ion processing material takes the form of a composite medium that generally includes a supporting matrix and one or more active components dispersed within the matrix. Typically, the matrix comprises a plurality of small, slightly porous particles, sometimes referred to as beads. As suggested above, the overall surface area of the ion processing material that contacts the fluid stream simply comprises the sum of the surface areas of each of the individual beads which, in turn, is a function of pore volume.

In order to form the ion processing material, the matrix material is mixed with a particular active component selected for its ability to remove one or more pre-determined constituents from the fluid stream. The ion processing material thus produced is typically disposed in a column through which the fluid stream to be processed is passed. Because the beads of the matrix material often assume a somewhat spherical shape, a plurality of spaces is cooperatively defined by adjacent beads. Accordingly, the fluid stream is able to flow through the ion processing material by working its way through the spaces between the individual beads.

While the slight porosity of some beads allows for a relatively greater ion processing area than would be possible if the beads were simply solid, such matrix materials have, as a result of their relatively small pore volume, proven rather ineffective in providing the performance required for effective and efficient processing of high volume fluid streams. Of course, the surface area of such ion processing materials can be increased somewhat by increasing the number of beads present in a particular column. However, there are practical limits to the attainment of very small bead sizes. Furthermore, while an increase in the number of beads produces a desirable overall increase in pore volume, and thus ion processing area, the increase represents a tradeoff with respect to the flow rate that a particular ion processing material can effectively accommodate.

In particular, as bead size is reduced, the size of the air spaces between adjacent beads is correspondingly reduced. Reduction in the size of the air spaces has at least one unfavorable consequence with respect to the flow of the fluid stream. Specifically, assuming a constant flow velocity, the volume of fluid that can flow through an opening is primarily a function of the size or area of that opening. This idea is generally expressed in the relationship Q=Va, where “Q” is the volume of fluid flow per unit of time, “V” is the velocity of the fluid, and “a” is the area through which the fluid passes.

In general then, where two volumes of ion processing materials in the form of respective composite media, equal in all other respects, have different numbers of beads, the volume of the ion processing material with relatively more beads defines a relatively smaller space through which the process stream can flow. In view of the aforementioned flow relationship, this means that the volume of ion processing material with a relatively greater number of beads is relatively more resistant to the flow of the process stream. Accordingly, in the case of an ion processing material comprised of very small particles, a powdered ion processing material for example, the resistance of the ion processing material to fluid flow is significant.

Thus, in the case of ion processing materials comprised of a composite medium employing a bead-type matrix, the surface area of the ion processing material can be readily increased by increasing the number of beads. However, due to the inverse relationship, discussed above, between the air volume defined by the ion processing material and the ability of a given volume of the ion processing material to pass a predetermined flow, there are practical limits to the extent to which the surface area may usefully be increased.

As suggested earlier, another common ion processing material configuration is designed along the same general principles as those ion processing materials formed as composite media, but takes on a somewhat different form. In this particular configuration, no matrix is employed. Rather, a finely granulated or powdered active component is simply compressed under high pressure to form an ion processing material comprising a plurality of granules, or pellets, which are then disposed in a column for processing of a fluid stream.

While ion processing materials using compressed active component configurations typically have relatively large surface areas, they suffer from a variety of significant shortcomings. First, because the active component is initially in a powdered form, the flow of the fluid through a bed of granules of the active component of the ion processing material tends to wash away some of the active component, thus reducing the effectiveness and efficiency of the ion processing material over time. Another problem is that granules or pellets of the compressed active component tend to be rather brittle and can be easily broken and thereby rendered ineffective. Further, ion processing materials formed in this manner tend to crumble and fall apart over a period of time. Such ion processing material configurations are not well suited to withstand the rough handling and other conditions that may occur in many industrial environments.

Yet another shortcoming of compressed active component ion processing materials concerns the compression process that is used to form the granules or pellets of the compressed active component. In particular, large compressive forces are typically employed in order to ensure that the active component granules assume and retain the desired shape and size. However, the forces used to form the active component granules compress the active component so tightly that it is often the case that the fluid flow being processed never penetrates to the active component at the inner portion of the granules. Thus, the ion processing capacity of the active component in these types of ion processing materials is not fully utilized and much of the active component is essentially wasted. Such waste unnecessarily increases the amount, and thus the cost, of the ion processing material.

While the aforementioned shortcomings are of some concern in low volume ion processing applications such as might be encountered in a laboratory, these characteristics of ion processing materials that comprise compressed active component granules render such ion processing materials particularly unsuited for high volume applications such as are typically encountered in industrial environments.

In view of the foregoing problems and shortcomings with existing ion processing materials, it would be an advancement in the art to provide a composite medium comprising one or more active components uniformly dispersed in a matrix material having a relatively high surface area, and to provide a composite medium that offers relatively little resistance to fluid flow while affording the ability to employ a wide range of active component weight percent loading conditions.

BRIEF SUMMARY OF THE INVENTION

The present invention has been developed in response to the current state of the art, and in particular, in response to these and other problems and needs that have not been fully or adequately addressed by currently available ion processing materials.

Briefly summarized, embodiments of the invention are directed to composite media suitable for use in ion processing, and comprising a large surface area matrix material within which one or more active components are disposed. Embodiments of the invention are particularly well suited for use in high volume applications requiring effective and efficient removal, or other processing, of actinides such as uranium (U), plutonium (Pu), and americium (Am), lanthanides such as europium (Eu) and cerium (Ce), alkali metals such as cesium (Cs), alkaline earth metals such as strontium (Sr), organic contaminants, and chlorine, such as from water that is to be used for human consumption. In general, however, embodiments of the invention are effective in any application where efficient and effective ion processing of high volume flows is required.

Note that, as used herein, “actinides” include any and all elements of the Actinide Series as depicted by the periodic chart of the elements, as well as any and all compounds substantially comprising an element of the Actinide Series. Similarly, “lanthanides” refer to any and all elements of the Lanthanide Series as depicted by the periodic chart of the elements, as well as any and all compounds substantially comprising an element of the Lanthanide Series.

In one embodiment of the invention, the matrix material of the composite medium comprises an organic polymer, such as polyacrylonitrile (PAN), formed as a plurality of substantially spherical and porous beads. An active component, such as crystalline silicotitanate (CST), carbon, or octyl (phenyl) N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) for example, is dispersed throughout the matrix material.

In one embodiment of the invention, the composite medium is prepared by first dissolving a desired amount of PAN in a solvent, nitric acid (HNO3) for example, so as to produce a matrix solution of a desired concentration. One or more active components are then mixed with the matrix solution to produce a composite medium solution (CMS), which may comprise a suspension, emulsion, solution, or other form. Preferably, both the dissolution of the PAN and the mixing of the active component(s) with the matrix solution are performed at room temperature and pressure. The CMS thus formed is then dispensed through one end of a fluid conduit.

Substantially simultaneously with the dispensation of the CMS from the fluid conduit, a flow of gas is directed through the end of the fluid conduit so that the flow of gas cooperates with that end to draw at least a portion of the CMS out of the fluid conduit as a plurality of drops. The plurality of drops thus formed may be deposited in a bath, such as a water bath, so as to dilute the solvent in the CMS and thereby cause solidification of the drops. After dilution of the solvent is complete, the drops are then dried to form a plurality of substantially spherical and porous beads.

In operation, the beads of composite medium are disposed in a chamber, or column, that is connected in-line with a flow of fluid to be processed, such as a waste stream. Due to the relatively large pore volume defined by the matrix material, the beads collectively define a relatively large surface area and thus the active component distributed through the matrix possesses a relatively high ion processing capacity with respect to the fluid flow passing through the composite medium. Additionally, the uniform size and shape of the beads contribute to the enhancement of the kinetic properties of the composite medium. Finally, because the beads are relatively durable, they are well suited to withstand the rough handling and environmental conditions typically encountered in industrial applications.

These and other features and advantages of the present invention will become more fully apparent from the following description and appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made to figures wherein like structures will be provided with like reference designations. It is to be understood that the drawings are diagrammatic and schematic representations of exemplary embodiments of the invention, and are not to be construed as limiting the scope of the invention in any way.

Briefly summarized, the present invention relates to composite media having one or more active components that use various mechanisms to process various constituents of a fluid stream.FIGS. 1 through 7indicate various exemplary embodiments of composite media, and related devices and systems.

Reference is first made toFIG. 1, wherein an ion processing system is indicated generally at100, and the direction of the flow of fluid through ion processing system100is indicated by arrows. In general, ion processing system100includes column assembly200, column inlet piping102and column outlet piping104. Disposed upstream and downstream of column assembly200are isolation valves106.

Further, a differential pressure gauge108is connected across column assembly200. Differential pressure gauge108includes a high pressure connection110in fluid communication with column inlet piping102, and a low pressure connection112in fluid communication with column outlet piping104. Of course, various other types of diagnostic and/or monitoring instrumentation may also be provided in ion processing system100, including, but not limited to, devices for measuring temperatures, flow rates, and ion concentration, at one or more points throughout ion processing system100.

Ion processing system100also includes a reservoir114in fluid communication with column outlet piping104. Of course, ion processing system100may include a variety of other components as well, wherein such other components may include, but are not limited to, prime movers such as pumps.

In one embodiment, ion processing system100is used in conjunction with the processing of a fluid stream containing one or more actinides such as uranium (U), plutonium (Pu), and/or americium (Am), or their compounds, lanthanides such as europium (Eu) and cerium (Ce), and/or with fluid streams containing alkali metals such as cesium (Cs), or alkaline earth metals such as strontium (Sr), or their compounds. Other embodiments of ion processing system100are well suited to effectuate the removal of organic contaminants, and chlorine (Cl) from fluid streams. Yet other exemplary applications include industrial water treatment, drinking water treatment, alkaline waste treatment, radioactive waste treatment, and treatment of various types of waste produced, for example, as a result of industrial operations and processes.

In general however, ion processing system100may be used in any of a variety of applications where it is desired to remove, neutralize, concentrate, or otherwise desirably process, one or more constituents of a fluid stream. Further, ion processing system100may be used either alone, or in conjunction with mechanical filtration systems and devices, so as to allow both filtration and ion processing of a fluid stream.

In operation, the fluid stream to be processed is directed into column inlet piping102and passes through column assembly200, preferably oriented vertically, and is then directed to reservoir114, by way of column outlet piping104, preparatory to further processing, or disposal. Depending upon such variables as the contents, temperature, and volume of the fluid stream, the fluid stream may alternatively be directed to a waterway or other portion of the environment after treatment, as suggested by the phantom lines inFIG. 1.

Note that, as contemplated herein, “fluid stream” includes streams having both gaseous and liquid components, as well as streams which are substantially liquid in form and streams which substantially comprise one or more gaseous components. Further, while ion processing system100and its components are preferably employed in the context of high volume fluid streams such as might be encountered in the utilities industries, other industrial environments, or in environmental applications, embodiments of ion processing system100and its components may also be profitably employed in the processing of low volume fluid streams that may be produced or generated as a result of, for example, laboratory processes and operations.

As the fluid stream passes through ion processing system100, one or more constituents of the fluid stream are substantially removed, or otherwise processed, by column assembly200. As column assembly200removes constituents from the fluid stream, those constituents may clog column assembly200over a period of time. Such clogging causes the pressure drop across column assembly200to gradually increase over time, thereby compromising the rate at which ion processing system100is able to process the fluid stream. Similarly, as ion processing sites in composite medium300(seeFIG. 2) are utilized, the effectiveness of composite medium300will diminish over time. This situation can be remedied by either regenerating the composite medium300in column assembly200, or by replacing composite medium300altogether.

With continued reference toFIG. 1, differential pressure gauge108indicates the pressure drop across column assembly200and thus serves to provide a relative measure of the cleanliness of column assembly200. In particular, by comparing the pressure drop across column assembly200, as indicated by differential pressure gauge108, with the pressure drop across column assembly200when it is clean, an evaluation can be made as to the degree of clogging that is present in column assembly200. Thus, differential pressure gauge108serves as a diagnostic tool to indicate when column assembly200should be cleaned or replaced. In the event column assembly200requires cleaning or replacement, isolation valves106can be shut so as to prevent flow through column inlet piping102and column outlet piping104, and thereby facilitate the removal and/or replacement of column assembly200.

Turning now toFIG. 2, various details and features of column assembly200are illustrated. In particular, column assembly200includes a column housing202, defining a chamber204. Column housing202further includes a column housing inlet206and a column housing outlet208that are configured for connection to, and communication with, column inlet piping102and column outlet piping104, respectively. Note that such connection may be accomplished in any of a variety of ways including, but not limited to, welding, brazing, soldering, nuts and bolts, threaded connections, or the like.

Column housing202further includes perforated plates210or the like, wherein one perforated plate210is disposed between chamber204and column housing inlet206, and the other perforated plate210is disposed between chamber204and column housing outlet208. Further, an amount of composite medium300is disposed in chamber204. In the exemplary embodiment illustrated inFIG. 2, composite medium300is embodied as a plurality of beads302each having matrix material303combined with one or more active components304. However, various alternative forms and configurations of composite medium300may be employed as necessary to suit the requirements of a particular application.

With continued reference toFIG. 2, the fluid stream that is to be processed enters column housing inlet206by way of column inlet piping102connected thereto. Openings in perforated plate210permit the fluid flow to enter chamber204and contact beads302of composite medium300, while at the same time, perforated plate210substantially confines beads302within column housing202. As the fluid stream passes into contact with active component304dispersed within matrix material303, active component304acts to process one or more constituents of the fluid stream. In one exemplary embodiment, the ion(s) are removed from the fluid stream by active component304and transferred to beads302. After passing through chamber204, the fluid flow then exits column assembly200by way of column housing outlet208.

With reference now toFIGS. 3-5, additional details are provided regarding one embodiment of a bead302geometry in accordance with the teachings of the present invention. In the illustrated embodiment, beads302are generally homogeneous and substantially spherical in shape. The embodiment illustrated inFIGS. 3-5is exemplary only however, and any of a variety of geometries and configurations other than beads may be employed as required to suit a particular application. In general, any configuration that is effective in facilitating implementation of the functionality disclosed herein may be used.FIG. 3shows a negative image depiction of an active component-impregnated PAN bead302.FIG. 4is an SEM picture of a PAN bead302impregnated with CMPO, whileFIG. 5is a cross-sectional view of the bead302ofFIG. 4.

Generally, each bead302of composite medium300includes a matrix material303that defines a plurality of openings, or pores302A. Due to the large number of pores302A, matrix material303of bead302accordingly defines a relatively large pore volume through which one or more active components304(not shown) can be distributed. As noted elsewhere herein, it is generally the case that the effectiveness of a composite medium is at least partially a function of the size of the ion processing area with which the fluid desired to be processed comes into contact. Thus, the relatively large surface area collectively defined by pores302A of beads302facilitates a relative improvement in processing capacity over known composite media, pelletized active components, for example, and ion processing systems and devices where it is often the case that only a fraction of the active component may come into contact with the fluid stream, or where the volume of active component that can be usefully employed is otherwise restricted. That is, due to the homogeneity of beads302and the large surface area defined by matrix material303of beads302, a relatively greater amount of active component304can be exposed to the fluid stream than is typically the case with known ion processing materials.

Because relatively more active component304is exposed to the fluid stream than would otherwise be the case, a given amount of active component304supported by matrix material303of beads302removes, or otherwise processes, relatively more material from the fluid stream than would a comparable volume of that active component disposed in a conventional composite medium, system, or device. Thus, composite medium300is relatively more efficient in removing, or otherwise processing, materials from a fluid stream than are known composite media, and accordingly has a higher processing capacity than those materials.

In some instances at least, the processing capacity of active component304can be quantified as being the maximum value of the ratio of the mass of the ion removed from the fluid stream to the mass of active component304present in column assembly200. In view of the improved processing capacity of composite medium300, the cost of an ion processing system employing composite medium300may be materially lower than the cost of devices employing less efficient ion processing materials.

Not only does the geometry of beads302serve to facilitate an increase in the processing capacity of active component304to a level higher than would otherwise be possible, but that geometry has other useful implications as well. One such implication relates to the amount of active component304that beads302can effectively hold. In particular, the large pore volume defined by beads302permits the weight of active component304as a percentage of the total weight of composite medium300to be varied over a wide range, from about 5% to about 95% by weight. In contrast, the weight percentage of active component in some known composite media is typically limited to a much narrower range.

Thus, beads302of composite medium300are well suited to facilitate wide variations in the concentrations, or loading, of active component304, and the relative weight percent loading of active component304in beads302may desirably be varied as required to suit particular applications and/or to achieve one or more desired results. Further, multiple active components304may be used in conjunction with beads302so as to produce a composite medium300that can be employed to effect simultaneous and substantial removal, or other processing, of more than one constituent of a fluid stream. As noted elsewhere herein, such active components may employ any of a variety of mechanisms to effectuate such removal and/or processing.

The geometry of beads302also lends desirable kinetic characteristics to composite medium300. In particular, the homogeneity of the size and shape of beads302facilitates improved flow through composite medium300. Thus, composite medium300is particularly well-suited for use in high flow rate applications such as are often encountered in industrial environments.

As the foregoing discussion suggests, beads302of composite medium300possess a variety of properties that make them desirable for use in any number of applications, and that suit them particularly well for use in those situations wherein it is desired to effectively and efficiently treat high volume and/or high flow rate fluid streams. By way of example, the relatively large pore volume defined by matrix material303of beads302facilitates high loading capacities and effective and efficient use of active component304. As another example, the porosity of beads302permits ions to be readily transported into each bead302of composite medium300and thus facilitates the effective and efficient processing of high flow rate fluid streams.

Attention is directed now to a discussion of various exemplary active components304. Generally, “active component” refers to those materials, however embodied, that use a variety of mechanisms to process the fluid stream, wherein such mechanisms include, but are not limited to, ion exchange, adsorption, absorption, extraction, complexation, or various combinations thereof. By employing one or more of such mechanisms, various embodiments of active components304are able to, among other things, remove, extract, separate, concentrate, or otherwise desirably process, one or more constituents of a fluid stream. Sorbents and similar materials comprise but one example of an active component.

In one embodiment, active component304comprises an inorganic compound such as crystalline silicotitanate (CST), or the like. However, any of a wide variety of other active components, both organic and inorganic, may be used, either individually or in various combinations, as required to suit a particular application and/or to achieve one or more desired effects. Exemplary active components include various types of carbon, ammonium molybdophosphate (AMP), octyl (phenyl) N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and other carbamoyl phosphine oxides, 4,4′(5′)di-(t-butylcyclohexano)-18-crown-6, bis (2,4,4-trimethylpentyl) dithiophosphinic acid, various amines, alkylphosphoric acids such as bis(2-ethylhexyl)phosphoric acid (HDEHP), neutral organophosphorus compounds such as tributyl phosphate (TBP), organic compounds such as crown ethers and polyethylene glycol (PEG) and their mixtures, and all organic extractants that are stable in the solution of the binding polymer, PAN for example, and are able to form an organic phase inside the matrix.

Organic active components, including various types of carbon such as activated carbon, are particularly well-suited for the treatment of water, and are effective in removing, among other things, chlorine, organic pesticides, and heavy metals such as mercury. Other exemplary applications of active components304include odor control, air cleaning and/or purification, as well as removal of undesirable color(s) from a fluid stream, as is required in some pharmaceutical applications. Note that “carbon” refers to activated carbon as well as to various other types and forms of carbon or materials substantially comprising carbon.

Another embodiment of a composite medium300employs CMPO as active component304. CMPO is particularly useful in metal ion sorption applications including, but not limited to, treatment of radioactive waste solutions or analysis of samples, wherein those radioactive waste solutions and samples contain actinides such as americium, plutonium and uranium, or their compounds, and/or lanthanides and their compounds.

Directing attention now toFIG. 6, one embodiment of a process400for producing composite medium300is indicated. In step402, a matrix material, preferably PAN in a solid form, is dissolved in a solvent to form a matrix solution whose concentration of PAN with respect to the solvent may be varied as required to facilitate achievement of a particular desired result.

As used herein, “PAN” includes, among other things, an acrylonitrile polymer or copolymer containing at least forty percent (40%) acrylonitrile units. Typically, the acrylonitrile homopolymer includes crystalline, quasicrystalline, and amorphous phases. Note however, that various other polymeric matrix materials, both organic and inorganic, may profitably be substituted for PAN in order to suit the requirements of a particular application.

In one embodiment, the solvent comprises nitric acid. Other suitable solvents include, but are not limited to, aprotic polar organic solvents such as dimethylformamide, dimethylacetamide, dimethylsulfoxide (DMSO), sulfolane, ethylene carbonate, and N-methylpyrrolidone, acids such as concentrated sulfuric acid, and concentrated aqueous solutions of certain organic salts such as lithium bromide, sodium thiocyanate, and zinc chloride. In general however, any solvent providing the functionality disclosed herein is contemplated as being within the scope of the present invention.

In one embodiment, step402is performed at room temperature (defined herein to be a range from about 50 degrees Fahrenheit to about 80 degrees Fahrenheit) and standard pressure (1.0 atmospheres, or 14.65 pounds per square inch), though other temperatures and/or pressures may be desirable for certain applications or to achieve particular results.

Upon dissolution of the PAN in the solvent, process400then proceeds to step404wherein a pre-determined amount of one or more active components304is combined with the matrix solution to form the CMS. Alternatively, the CMS may be formed in situ by precipitation or other processes. In the case where only organic active component(s)304are employed, the CMS comprises an emulsion while, on the other hand, where only inorganic active component(s)304are employed, the CMS comprises a suspension. As used herein however, “CMS” refers to any combination of solvent, matrix material, and active components, whether such combination takes the form of a suspension, emulsion, solution, or other form. In at least some embodiments of the invention, active component304comprises CST. As noted elsewhere herein however, a variety of active components304, both organic and inorganic, may be employed singly, or in various combinations so as to result in the formation of a CMS, and ultimately a composite medium300, having particular desired properties.

It will further be appreciated that the amount of active component(s)304mixed with the matrix solution may be varied as required to achieve formation of beads302having particular desired properties and capabilities. After the CMS has been formed, process400proceeds to step406, wherein the CMS is formed into a plurality of discrete portions. Preferably, each discrete portion comprises a drop. However, such discrete portions may alternatively comprise any other geometry and/or volume necessary to suit the requirements of a particular application. In step408, the solvent in the drops thus formed is diluted, removed, or otherwise neutralized, so that each drop substantially comprises PAN and one or more active components304. The solvent is preferably diluted by depositing the drops into a water bath, or the like. It will be appreciated that variables such as the temperature of the water bath may be varied as required to achieve a particular result or effect. Likewise, other aqueous solutions may be substituted for water so as to facilitate achievement of a desired result.

Upon dilution, removal, or neutralization, of the solvent, the PAN then solidifies to form a bead comprising a matrix material303which has entrapped active component(s)304in a porous support. Note that, as contemplated herein, “bead” generally refers to a discrete portion of composite medium300that has been substantially cleansed of solvent and comprises a matrix material303wherein the matrix material303supports, i.e., contain, entraps, is bonded to, or otherwise includes or is attached to in any way, one or more active components304.

In one alternative embodiment, the solvent is reconstituted from the water bath by heating the water bath until the water evaporates and only solvent remains. In this way, the solvent can be reused for multiple processes. A variety of other techniques may alternatively be employed to facilitate reconstitution of the solvent.

In step410, the drops are then dried, preferably in air, to form beads302of composite medium300. The air drying process lends mechanical strength and durability to beads302. Such strength and durability makes beads302well-suited to withstand rough handling and other adverse environmental conditions. Once formed, beads302can be sieved, or otherwise sorted, to provide a desired size fraction necessary for a particular application. As an alternative to drying, beads302may be allowed to remain wet after the solvent has been diluted or removed, and used in that state.

Turning now toFIG. 7, one embodiment of a bead generation apparatus adapted to perform step406of process400is indicated generally as500. Bead generation apparatus500includes a reservoir502having a cap502A and terminating in a dispensing tip502B. In those instances where it is desired to stir or otherwise agitate CMS contained in fluid reservoir502, cap502A need not be employed. As indicated inFIG. 7, reservoir502is substantially disposed within an air chamber504and rests on an annular lip504A defined by air chamber504. A coupling506ensures that reservoir502remains in place. It will be appreciated that a variety of other structures and/or devices may be employed to provide the functionality of coupling506, as disclosed herein, wherein such structures and devices include, but are not limited to, threaded connections and the like. Such other structures and devices are accordingly contemplated as being within the scope of the present invention. With continued reference toFIG. 7, air chamber504further includes an air inlet connection504B and an air outlet504C. Air chamber504and reservoir502are preferably constructed substantially of materials such as glass, plastic, fiberglass, or the like.

In operation, a pre-determined amount of CMS is disposed in fluid reservoir502. Gravitational force and/or other pressurization of fluid reservoir502causes CMS to pass downward through dispensing tip502B. It will be appreciated that dispensing tip502B may comprise any of a variety of fluid conduits configured to facilitate dispensation of CMS. Note that, in one embodiment, bead generation apparatus500further includes a valve or the like to control the flow of CMS through dispensing tip502B. Substantially simultaneous with the flow of CMS through dispensing tip502B, a flow of air, or other suitable gas, is directed into air chamber504by way of air inlet connection504B.

As drops of CMS form at dispensing tip502B, the flow of air through air outlet504C facilitates detachment of those drops from dispensing tip502B. The air flow through air outlet504C thus cooperates with dispensing tip502B of fluid reservoir502to produce a plurality of CMS drops which, as discussed above, are ultimately transformed into beads302of composite medium300. It will be appreciated that variables including, but not limited to, the pressure of CMS in reservoir502, rate of air flow through chamber504, the diameter of dispensing tip502B, the diameter of air outlet504C, and the position of dispensing tip502B relative to air outlet504C, may individually and/or collectively be varied as required to achieve a particular size of CMS drop and/or CMS drop production rate.

The following example serves to explain an embodiment of the beads302of the composite medium300in more detail. For comparative purposes, a substrate impregnated with PAN and CMPO, as described in U.S. Pat. No. 6,514,566 to Mann et al., is also described. The example is not to be construed as being exhaustive or exclusive as to the scope of the invention.

EXAMPLES

Formation of PAN/CMPO Beads

Beads302of the composite medium300were formed by dissolving fibrous PAN in nitric acid at room temperature. The PAN/nitric acid mixture included from approximately 3% by weight (“wt %”) to approximately 5 wt % fibrous PAN and from approximately 55 wt % to approximately 60 wt % nitric acid. The PAN/nitric acid mixture was stirred for approximately 1 hour. A neat organic extractant, such as CMPO, was added to the PAN/nitric acid mixture and mixed to form a solution that appeared homogenous. From approximately 20 wt % to approximately 33 wt % of CMPO was added to the PAN/nitric acid mixture. The solution was then placed in an apparatus for dispersing the material into droplets, which is referred to as the bead generation apparatus500and is shown inFIG. 7.

The solution was gravity fed from the reservoir502to the dispensing tip502B, where droplets are formed. The formation and release of droplets from the dispensing tip502B is accelerated by the flow of air downward around the dispensing tip502B. The droplets of the solution were dropped into a constantly mixed bath of deionized water, which diluted the nitric acid sufficiently to allow the PAN, with the CMPO, to solidify into a highly porous sphere or bead302, as shown inFIGS. 3-5. The droplets were left in the deionized water bath for from approximately 10 minutes to approximately 15 minutes to completely wash the nitric acid from the beads302. The beads302were then removed and air dried.

After drying, the beads302were sieved to the desired size fraction. Typically, beads302in a size that ranges from approximately 0.1 mm to approximately 0.75 mm are most effective for use in a column. However, smaller or larger sizes may also be utilized.

Comparative Example 2

A substrate impregnated with PAN and CMPO was formed as described in U.S. Pat. No. 6,514,566 to Mann et al. The impregnated substrate was formed by dissolving fibrous PAN in nitric acid at room temperature. From approximately 3 wt % to approximately 5 wt % of the PAN was dissolved in from approximately 55 wt % to 60 wt % nitric acid. The PAN/nitric acid mixture was stirred for approximately 0.5 hours. A neat organic extractant (approximately 20 wt % to approximately 33 wt % of the extractant), such as CMPO, was added to the PAN/nitric acid mixture and mixed until the solution appeared homogenous. The solution of nitric acid, PAN, and CMPO was then evenly dispensed onto a glass filter (Gelman Type A/E glass filter, 1.0 μm particle size retention) supported by a filter assembly. The glass filter800before impregnation with the solution of nitric acid, PAN, and CMPO is shown inFIG. 8. A vacuum was then applied to the volume below the glass filter800to draw the solution into the interstices (fibers) of the glass filter800. The glass filter800was thoroughly impregnated (coated) with the nitric acid, PAN, and CMPO solution using this method. The impregnated filter was then removed from the filter apparatus and placed into a deionized water bath. The deionized water diluted the nitric acid sufficiently to allow the PAN and the CMPO to solidify within interstices of the glass filter800. The glass filter800, which was impregnated with composite medium300, was then left in the deionized water bath for from approximately 10 minutes to approximately 15 minutes to completely wash the nitric acid from the solidified PAN. The impregnated filter was then removed from the deionized water bath and air dried. The impregnated filter is as shown inFIG. 9.

As evidenced by a comparison betweenFIGS. 3-5andFIGS. 8 and 9, beads302of the composite medium300are formed by the method described in Example 1. In contrast, the composite medium300is impregnated in a substrate by the method described in Comparative Example 2.