Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Organic component
Reexamination Certificate
1999-12-14
2001-11-20
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Organic component
C422S173000, C422S177000, C423S213700, C423S247000, C502S071000, C502S074000, C502S077000, C502S078000, C502S079000, C502S407000, C502S414000
Reexamination Certificate
active
06319484
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composition for abatement of pollution dispersed in the air and to an apparatus and a method using the composition. More specifically, the abatement composition of the invention comprises an intimate combination of first and second zeolites and an oxidation catalytic component. The abatement composition adsorbs and oxidizes volatile organic compounds, such as hydrocarbons, aldehydes, ketones, etc., in alternating adsorption and oxidation temperature ranges which lie within a low to moderate operating temperature range.
2. Related Art
A great deal of effort and a resulting large body of patent and technical literature is directed toward pollution abatement at its source, for example, by treating the exhaust of combustion devices such as internal combustion engine exhaust, plant stack gases, etc. Rather less effort has been devoted towards taking steps to clean the atmosphere, i.e., to treat ambient air to abate pollutants already contained therein. Illustrative of this latter approach is U.S. Pat. No. 3,738,088, “Mobile Air Cleaning Apparatus for Pollution Removal”, issued on Jun. 12, 1973 to L. E. Colosimo. This patent discloses an air filtering assembly for abating ambient air pollution by providing duct work on a vehicle to direct an air stream of controlled velocity to various filter means to filter particulate pollutants from the air. Post-filter catalysts are also disclosed for catalytic abatement of ambient carbon monoxide, unburned hydrocarbons, nitrous oxide, sulfur oxides and the like. German Patent DE 43 18 738 C1, for “Verfahren zur physikalischen und chemischen Reinigung der Aussenluft” (“Method for the Physical and Chemical Cleaning of Atmospheric Air”), published on Jul. 14, 1994, similarly discloses a process for the physical and chemical cleaning of air utilizing a motor vehicle whose travel flows the air through the treatment devices.
U.S. Pat. No. 5,147,429, “Mobile Airborne Air Cleaning Station”, issued on Sep. 15, 1992 to J. Bartholomew et al, discloses a dirigible carrying a plurality of different air-cleaning devices, including wet scrubbers, filtration machines and cyclonic spray scrubbers, to treat air which is flowed through the devices by movement of the dirigible through the air.
The use of a combination of adsorbents for hydrocarbons and a catalytic composition to promote the oxidation of the hydrocarbons is known in the art. For example, Japanese patent publication (Kokai) 8-10566 was published on Jan. 16, 1996 based on Japanese patent application of NGK Insulators, filed on Jul. 5, 1994 and entitled “A Catalyst Adsorbent For Purification of Exhaust Gases and An Exhaust Gas Purification Method.” This document discloses the use of a silver-containing ZSM-5 zeolite and a platinum oxidation catalytic component for the treatment of the exhaust of internal combustion engines. At low exhaust temperature, such as that encountered upon initial startup of the engine, the silver-containing ZSM-5 zeolite adsorbs hydrocarbons in the exhaust and retains them until the temperature increases sufficiently to reach the light-off temperature of the platinum catalytic component, i.e., the temperature at which the catalytic component becomes effective for promoting oxidation of the hydrocarbons. Conventionally, the light-off temperature is considered to be that temperature at which the catalytic component is able to promote the oxidation of at least fifty percent of the hydrocarbons contacting the catalytic component. The objective of such compositions is to retain the hydrocarbons adsorbed in the adsorbent, typically zeolite, until a temperature of at least 250° C. has been attained, so that upon desorption of the hydrocarbon at the elevated temperature, the catalytic component is effective for promoting oxidation of the hydrocarbon.
SUMMARY OF THE INVENTION
Generally, the present invention provides a composition for abatement of gas-borne pollution, e.g., atmospheric pollution, caused by volatile organic compounds, and an apparatus and method using the same. The composition comprises a protective adsorbent zeolite and a second adsorbent zeolite and protective and second oxidation catalysts associated respectively therewith, with the second oxidation catalyst essentially being intimately intermingled with the second adsorbent and the protective oxidation catalyst preferably being intimately intermingled with the protective adsorbent. The protective adsorbent adsorbs, and thereby protects the second adsorbent from, certain relatively large molecule volatile organic compounds which, if they were to be adsorbed by the second adsorbent, would not readily, if at all, desorb from the second adsorbent or migrate to catalytic sites thereon for oxidation thereof. Although it is preferable that the protective oxidation catalyst be intimately intermingled with the protective adsorbent, it may alternatively be separate therefrom and interposed between the protective adsorbent and the second adsorbent in the flow path of the gas (e.g., air) stream being treated. In either case, the protective oxidation catalyst serves to promote oxidation of the relatively large molecule volatile organic compounds before they can contact the second adsorbent and be adsorbed thereon. The second adsorbent adsorbs relatively small volatile organic compounds which pass through the protective adsorbent. The second oxidation catalyst, which is always intimately contacted with, e.g., intimately intermingled with, the second adsorbent in the practices of the present invention, promotes the oxidation of the adsorbed small molecule volatile organic compounds while they are retained on the second adsorbent. The first and second oxidation catalysts may be identical to, or different from, each other and may be present in the same or different concentrations relative to their respective adsorbents.
Without wishing to be bound thereby, it is believed that volatile organic compounds adsorbed on an adsorbent zeolite which has a catalytic component intimately intermingled therewith, will migrate within or on the adsorbent from adsorption sites to catalytic sites thereof, a phenomenon sometimes herein referred to as “spillover”. At the catalytic sites oxidation of the volatile organic compounds is promoted, even at temperatures well below those normally required to promote heterogeneous phase oxidation of hydrocarbons desorbed from the adsorbent. The spillover effect occurs with both the protective adsorbent and the second adsorbent, and so it is advantageous to intimately intermingle the protective oxidation catalyst with the protective adsorbent just as the second oxidation catalyst is intermingled with the second adsorbent. In this way the advantage of the spillover effect is gained for the protective adsorbent as well as for the second adsorbent. As noted above, the protective oxidation catalyst may, however, be interposed between the protective adsorbent and the second adsorbent, e.g., in a separate catalyst bed, to promote the oxidation of large molecule volatile organic compounds desorbed from the protective adsorbent before they contact the second adsorbent.
Unlike the prior art concerning the use of catalyzed zeolite adsorbents to oxidize, for example, hydrocarbons contained in the exhaust of internal combustion engines, the abatement compositions of the present invention do not require the attainment of temperatures sufficient to desorb the adsorbed volatile organic compounds from the zeolite adsorbents and into a gas stream to release them for catalyzed oxidation in the gas phase at the catalytic sites. Rather, the present invention is predicated on the finding that the compositions of the present invention will retain the adsorbed volatile organic compounds on their respective zeolite adsorbents, but permit the adsorbed compounds to migrate on the compositions, in the above-noted “spillover” effect, from the zeolitic adsorbent sites to catalytic sites on the adsorbent, wherein oxidation of the retained compounds is
Deeba Michel
Farrauto Robert J.
Heck Ronald M.
Lampert Jordan K.
Shore Lawrence
Engelhard Corporation
Griffin Steven P.
Medina Maribel
Negin Richard A.
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