Liquid purification or separation – Processes – Separating
Reexamination Certificate
1998-07-06
2003-02-25
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Processes
Separating
C210S502100, C210S500250, C210S500260, C210S490000, C210S500100, C210S510100, C210S503000, C502S001000, C502S150000
Reexamination Certificate
active
06524489
ABSTRACT:
TECHNICAL FIELD
This invention relates to advanced composite filtration media comprising a functional filtration component and a matrix component, and methods for preparing and using same. More particularly, this invention pertains to advanced composite filtration media and advanced composite filtration media products comprised of a functional filtration component, such as a biogenic silica product (e.g., diatomite), a natural glass product (e.g., expanded perlite), or a natural or synthetic crystalline mineral (e.g., titanium dioxide), which is thermally sintered to a matrix component, such as an engineering polymer (e.g., glasses, natural or synthetic crystalline minerals, thermoplastics, and metals) or a suitable natural material (e.g., rice hull ash, sponge spicules) that has a softening temperature below that of the functional filtration component. This invention also relates to advanced composite media and advanced composite media products, generally, which are also useful in non-filtration applications.
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.
The present invention relates to advanced composite filtration media comprising heterogeneous media particles, each of said media particles comprising (i) a functional filtration component and (ii) a matrix component, wherein said matrix component has a softening point temperature less than the softening point temperature of said functional filtration component, and wherein said functional filtration component is intimately and directly bound to said matrix component. Unlike simple mixtures, which tend to segregate upon suspension (e.g., in fluids) or conveyance or transport, the functional filtration components and matrix components of the advanced composite filtration media of the present invention are intimately and directly bound, as achieved, for example, by thermal sintering.
The advanced composite filtration media of the present invention are useful in many of the same applications as currently available filtration media, but offer one or more unique properties such as, for example, increased permeability, low centrifuged wet density, low cristobalite content, and/or uniquely shaped particles (e.g., fibers), as well as improved efficiency and/or economy, which are particularly valuable for filtration applications.
In the field of filtration, many methods of particle separation from fluids employ diatomite products or natural glass products as filter aids. The intricate and porous structures unique to these siliceous materials is particularly effective for the 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 filtration products when improving the clarity of fluids that contain suspended particles or particulate matter, or have turbidity.
Diatomite or natural glass products are often applied to a septum to improve clarity and increase flow rate in filtration processes, in a step sometimes referred to as “precoating.” Diatomite or natural glass products are also often added directly to a fluid as it is being filtered to reduce the loading of undesirable particulate at the septum while maintaining a designed liquid flow rate, in a step often referred to as “body feeding.” Depending on the particular separation involved, diatomite or natural glass products may be used in precoating, body feeding, or both. The working principles involved with porous media filtration have been developed over many years (Carman, 1937; Heertjes, 1949, 1966; Ruth, 1949; Sperry, 1916; Tiller, 1953, 1962, 1964), and have been recently reviewed in detail from both practical perspectives (Cain, 1984; Kiefer, 1991) as well as from their underlying theoretical principles (Bear, 1988; Nordén, 1994).
In certain circumstances, diatomite or natural glass products may also exhibit unique adsorptive properties during filtration that can greatly enhance clarification or purification of a fluid. These adsorptive properties are highly specific, and depend upon weak forces for attraction of the adsorbed species to weak electrical charges at the surface of diatomite, or upon the reactivity of silanol (i.e., ≡Si—OH) functional groups that often occur at the diatomite surface. For example, an ionized silanol group (i.e., ≡Si—O
−
) may react with a hydronium ion (i.e., H
3
O
+
) contributed by an acidic substance in solution, for example, citric acid (i.e., C
6
H
8
O
7
), adsorbing the donated H
+
at the surface in the process. In certain circumstances, perlite products, especially those which are surface treated, may also exhibit unique properties during filtration that can greatly enhance clarification or purification of a fluid (Ostreicher, 1986).
In some filtration applications, different diatomite products may be blended together, or different natural glass products may be blended together, to further modify or optimize the filtration process. Alternatively, diatomite products and natural glass products may sometimes be blended with each other, or with other substances. In some cases, these combinations may involve simple mixtures, for example, with cellulose, activated charcoal, clay, asbestos, or other materials. In other cases, these combinations are more elaborate mixtures in which diatomite products or natural glass products are intimately blended with other ingredients to make sheets, pads, cartridges, or monolithic or aggregate media used as supports, substrates, or in the preparation of catalysts.
Still more elaborate modifications of any of these diatomite or natural glass products are used for filtration or separation, involving, for example surface treatment or the absorption of chemicals to diatomite or natural glass products, mixtures, or their combinations.
The intricate and porous structure of silica unique to diatomite and natural glass products also permits their commercial use to provide antiblock properties to polymers. Diatomite products are often used to alter the appearance or properties of paints, enamels, lacquers, and related coatings and finishes. Diatomite products are also used as chromatographic supports, and are especially suited to gas-liquid chromatographic methods. Diatomite products are also useful as carriers in which other substances, particularly liquids, are blended in. Diatomite products are also frequently used as absorbents. Recent reviews (Breese, 1994; Engh, 1994) provide particularly useful introductions to the properties and uses of diatomite. Many natural glass products, including, for example, expanded perlite, pumice, and expanded pumice, also possess unique filler properties. For example, expanded perlite products are often used as insulating fillers, resin fillers, and in the manufacture of textured coatings. Expanded perlite products are also useful as absorbents, such as in horticultural applications.
The method of preparing monolithic or aggregate media is distinguished from that of preparing advanced composite filtration media by the fact that components added for monolithic or aggregate media are added prior to thermal treatment as processing aids (e.g., clay) usually prior to thermal treatment to provide green strength to the unfired mixture (e.g., to enable the extruding, forming, molding, casting, or shaping of green mixtures), rather than added as desired functional components of an advanced composite filtration media. The addition
Palm Scott K.
Roulston John S.
Shiuh Jerome C.
Smith Timothy R.
Advanced Minerals Corporation
Fortuna Ana
Morrison & Foerster / LLP
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