Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
1998-09-02
2004-03-30
Elve, M. Alexandra (Department: 1725)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S348000, C210S500100, C210S502100, C210S503000, C210S510100, C095S090000, C502S400000, C502S401000, C502S404000, C502S405000, C502S407000, C502S410000, C502S415000, C502S060000, C502S080000
Reexamination Certificate
active
06712974
ABSTRACT:
TECHNICAL FIELD
This invention relates to composites comprising one or more adsorbent components and one or more filtration components, and methods for preparing and using same. More particularly, this invention pertains to filterable composite adsorbents and filterable composite adsorbent products which are suitable for use in filtration applications, and which comprise one or more microparticulate or colloidal adsorbent components selected from the group consisting of silica gel, fumed silica, neutral clay, alkaline clay, zeolite, solid catalyst, alumina, adsorbent polymer, alkaline earth silicate hydrate, and combinations thereof, which bear the property of adsorption, which are intimately bound to one or more functional filtration components selected from the group consisting of biogenic silica (e.g., diatomite, rice hull ash, sponge spicules), natural glass (e.g., expanded perlite, pumice, expanded pumice, pumicite, expanded obsidian, expanded volcanic ash), buoyant glass, buoyant polymer, cellulose, and combinations thereof, which bear a distinguishing porous and intricate structure and buoyancy suitable for filtration.
DESCRIPTION OF THE RELATED ART
Throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation; full citations for these documents may be found at the end of the specification immediately preceding the claims. The disclosures of the publications, patents, and published patent specifications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
Adsorption is the term commonly used to describe the tendency of molecules from an ambient fluid phase to adhere to the surface of a solid, and has been recently reviewed in detail (Ruthven, 1991). Adsorption is a fundamental property of matter, having its origin in the attractive forces between molecules. The solid's force field creates a region of low potential energy near the solid's surface such that the molecular density close to the solid's surface is generally greater than in the bulk fluid. This results in the phenomenon of adsorption, in which the solid surface adsorbs various constituents from a multiconstituent fluid, to a degree which varies according to the solid surface's affinity for a particular constituent.
To achieve a significant adsorptive capacity, and thus to be highly practical for commercial use, an adsorbent preferably has a high specific area, which implies a highly porous structure with very small micropores. A method that is often preferred for determining specific area is performed by specialized instruments which use a BET (Brunauer et al., 1938) modification of Langmuir adsorption (Langmuir, 1916a, 1916b, 1918) of nitrogen, krypton, or other suitable gas at the surface of a sample of the solid under highly controlled conditions. Pore size and distribution are often determined by mercury intrusion porosimetry instruments operated under highly controlled conditions, which are capable of providing detailed information about pore sizes from about 6 nanometers to about 300 micrometers in diameter. Generally speaking, specific surface areas of practical adsorbents range from about 300 to 1200 m
2
/g, with macropores greater than about 0.050 &mgr;m (i.e., 50 nanometers) in diameter contributing little to adsorptive behavior.
The specific adsorptive properties of a practical adsorbent depend on its pore size and pore size distribution as well as on the nature of the solid surface. For example, a crystalline zeolite has a comparatively narrow pore size distribution and a polar surface; an amorphous silica gel has a comparatively broad pore size distribution and a polar surface; and a carbon molecular sieve is comparatively narrow in pore size distribution with a nonpolar surface. These principal characteristics for many adsorbents have been successfully engineered to permit the selective adsorption of components from fluids.
One common method of using an adsorbent is to simply place it in contact with a fluid containing one or more constituents that need to be adsorbed from it, either to purify the fluid by selectively removing the constituents, or to isolate the constituents so as to purify them from the fluid in which they are contained. Usually, the adsorbent containing the adsorbed constituents is then separated from the fluid, typically by filtration.
One typical method for separating adsorbents from fluids is through the use of filtration, in which the fluid can be in either a liquid or gaseous state. In the field of filtration, many methods of particle separation from fluids employ, for example, expanded perlite or natural glasses, or diatomite products, as porous filtration media. Although not usually as effective for the selective adsorption as commercial adsorbents, these products do have intricate and porous structures of greater size that are uniquely suited to the effective physical entrapment of particles, for example in filtration processes. These intricate and porous structures create networks of void spaces that result in buoyant filtration media particles that have apparent densities similar to those of the fluids in which they are suspended. It is common practice to employ porous filtration media when improving the clarity of fluids that contain suspended particles or particulate matter such as adsorbents, or have turbidity.
Since the requirement for high specific surface area is inextricably coupled with extremely fine pore size in order to create an effective, practical adsorbent, many adsorbents are not readily separated (e.g., filtered) from the fluids in which they have been suspended, because the individual particles of adsorbents cannot be made larger than the colloidal or fine microparticulate size range in their pure form and still retain both buoyancy and the desired adsorbent properties. The efficiency of many adsorbents in fluid system applications would be improved if the adsorbents were made more permeable or if more buoyant adsorbents were possible.
The filtration of microparticulate or colloidal adsorbents is usually difficult, since the adsorbent particles are not readily and/or effectively filterable. For example, merely blending microparticulate or colloidal adsorbents into porous filtration media products reduces the efficiency and permeability of the porous filtration media, as the adsorbents are typically of such a size as to behave as particles that detrimentally occupy the valuable void spaces that result from the intricate structure of the porous filtration media. Often, blended mixtures do not have the flow rate of the more permeable filterable composite adsorbent products of the present invention.
References which pertain to the filtration problems associated with adsorbents and methods of overcoming these problems in conjunction with the use of filter aids include Guiambo et al. (1991), Patel et al. (1992), Kucera et al. (1987), Machel et al. (1973), Schuler et al. (1990), and Fukua (1988).
McCollum (1961) describes a method of introducing an acidic montmorillonite clay as a mixture into a perlite ore prior to subjecting the mixture to a conventional perlite expansion process. This method appears to be highly limited with regard to the quantity of acidic montmorillonite clay that can be effectively bound to the perlite after expansion, as perlite particles greatly increase in volume, up to twenty times, during expansion. In fact, it appears that McCollum achieved at most about 15% attached acidic montmorillonite clay. McCollum did not teach that more buoyant glasses, such as expanded perlite, can be used as starting materials, or that materials other than acidic montmorillonite clay could be used as an adsorbent component. McCollum also did not teach that material other than perlite or its derivatives could be used as a functional filtration component. While McCollum does not disclose any means to discriminate whether the acidic clay has
Palm Scott K.
Roulston John S.
Shiuh Jerome C.
Smith Timothy R.
Advanced Minerals Corporation
Ildebrando Christina
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