Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Molecular oxygen or ozone component
Reexamination Certificate
1994-07-07
2001-03-20
Tran, Hien (Department: 1764)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Molecular oxygen or ozone component
C422S177000, C422S180000, C502S439000
Reexamination Certificate
active
06203771
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to improvements in monolithic catalytic converters, particularly, but not limited to, those used to remove ozone from the conditioned air supplied to aircraft cabins.
Environmental control systems for aircraft supply pressurized and conditioned air to the aircraft cabin. The temperature, pressure, and relative humidity must be controlled to provide for the comfort of flight crew and passengers within the aircraft.
Modern jet aircraft are typically designed for fuel-efficient operation at relatively high altitudes of 25,000 feet or more above sea level. At such altitudes, the ozone content in ambient air is relatively high and thus the air supplied to the aircraft environmental control system can contain a substantial amount of ozone. It can cause lung and eye irritation, headaches, fatigue and/or breathing discomfort.
Catalytic converters have been used to reduce or eliminate undesirable ozone in the air supplied to aircraft cabins. Ceramic monolithic supports have been used which carry catalysts on a washcoat applied to their surfaces, for example, in U.S. Pat. No. 4,405,507. Aluminum honeycomb was treated with NaOH and then solutions of catalytic metals in the ozone converter described in U.S. Pat. No. 4,348,360. In published European patent application 0 388 094 (U.S. Pat. No. 5,080,882) an ozone catalyst is disclosed in which an aluminum surface is oxidized at high temperature to produce an alumina to support a coprecipitated catalyst. Another ozone catalyst was described in published European patent application 0 461 452 (U.S. Pat. No. 5,145,822). In this instance, particulate catalysts were attached by an elastic organic adhesive to a metal foil support.
In co-pending U.S. patent application Ser. No. 07/926,798 an improved catalytic ozone converter of compact size and lightweight construction is disclosed.
The present invention relates to the catalyst employed in such converters, the catalyst being integral with the converter structure and comprising aluminum oxide formed by anodizing the converter structure.
Formation of alumina catalyst by anodization of an aluminum surface was reported by D. Honicke in Applied Catalysis, 5 (1983) 179-198, Elsevier Scientific Publishing Company. Similarly Yamada et al., 8th International Congress on Catalysis, 1984, Vol. IV, p. 835-846, reported an investigation of anodizing aluminum and its use as a catalyst.
The use of an anodized aluminum as a support for automobile catalytic converters was disclosed in Japanese Patent 52 048594. Another method of preparing an anodized surface for use in catalysts is described in European Patent Application 0 281 364. The aluminum is electrolytically etched before anodizing in order to increase the surface area of the alumina film. In this instance, the catalytic metals are also electrolytically deposited as suggested in U.S. Pat. No. 4,472,533.
The monolithic converters of the invention need not be limited to ozone destruction, but also may be employed in many applications where ceramic monoliths have been used. Such ceramic monoliths are commonly coated with a high surface area support which is not required by the present invention.
SUMMARY OF THE INVENTION
In general, the invention is a catalytic converter and the method of making it in which an aluminum or aluminum alloy monolith is anodized and thereafter optionally calcined under certain conditions which provide a suitable surface and then impregnated with catalytic metals.
The catalytic converter structure preferably comprises one or more plate-fin elements which incorporate the catalyst and are retained within a housing in a generally cylindrical configuration. The plate-fin element or elements define a large plurality of fins arranged in an axial succession of offset or staggered fin rows to obtain relatively high mass transfer between a gas flow stream and the catalyst, but with minimal pressure drop.
The converter structure is made of aluminum or an aluminum alloy which provides lightweight and low cost. The catalyst is integral with the aluminum structure rather than being deposited on the structure by washcoating. This result is achieved by anodizing the structure to provide an aluminum oxide surface layer at least about 2 &mgr;m thick, preferably at least about 10 &mgr;m and having a relatively high surface area of about 30 to 150 m
2
/g of the oxide layer. The surface layer has deposited on and within it Group VIII noble metals such as Pt, Pd, Rh and the like, optionally with base metals from Group VIII such as Ni, Fe, and Co or from Groups Ib, IIb, IIIa to VIIa, depending on the intended use. The amount of the Group VIII metals may be about 10 to 150 g/ft
3
of the monolith (0.35 to 5.30 g/L), preferably 25 to 75 g/ft
3
of the monolith (0.88 to 2.65 g/L). The base metals will comprise up to about 500 g/ft
3
(17.6 g/L) of the monolith, preferably about 200 to 400 g/ft
3
(7.06 to 14.1 g/L).
In one embodiment, the converter structure is anodized in an aqueous bath of 5-20 wt.% sulfuric acid at a constant temperature of 30°-37° C., preferably about 32° C., employing a direct current of about 9 amps/ft
2
(99.7 amps/m
2
) at about 8-15 volts. After being anodized, the structure is washed with water, dried, and calcined at temperatures in the range of 150° to 540° C., preferably about 440° to 540° C. Optionally, the calcination may be omitted since the structure is heated to similar temperatures after impregnation with compounds of the catalytic metals.
In another embodiment the invention comprises a method for destroying ozone in air using the catalyst described above. The catalyst may be applied also in a method of oxidizing atmospheric pollutants such as hydrocarbons and carbon monoxide.
REFERENCES:
patent: 3083662 (1963-04-01), Zeidler
patent: 3542124 (1970-11-01), Manfredo
patent: 4348360 (1982-09-01), Chang et al.
patent: 4405507 (1983-09-01), Carr et al.
patent: 4472533 (1984-09-01), Moskovits
patent: 4665051 (1987-05-01), Nonnenmann
patent: 4672809 (1987-06-01), Cornelion et al.
patent: 5145822 (1992-09-01), Falke et al.
patent: 0 152 560 (1984-11-01), None
patent: 0 281 364 (1988-09-01), None
patent: 0 388 094 (1990-09-01), None
patent: 0 461 452 (1991-12-01), None
patent: 52-048594 (1977-12-01), None
D. Honicke, Applied Catalysis, 5 (1983) p. 179-198 Elsevier Scientific Publishing Co.
Yamada et al., 8th International Congress on Catalysis, 1984, vol. IV, p. 835-846.
L. Hegedus Pet. Div. ACS Preprints, Aug., 1973, p. 487-502.
Homeyer Stephen Thomas
Lester George Ronald
Allied-Signal Inc.
Tran Hien
Zak, Jr. Esq. William J.
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