Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
2000-02-18
2002-03-19
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S275000, C060S287000, C060S288000, C060S308000, C422S186040, C204S177000
Reexamination Certificate
active
06357223
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a method and apparatus for improving and maintaining the performance of catalytic reactors and catalytic convertors, particularly catalytic reactors used in fuel cells for producing electricity and vehicle catalytic convertors used to reduce the emission of pollutants. More particularly, the invention is directed to a method and apparatus where the improved performance of the catalysts is achieved by producing highly oxidizing free radicals, such as hydroxyl radicals, OH, hydroperoxyl radicals, HO
2
, atomic hydrogen, H, and atomic oxygen, O, and other active species, including related oxidizing gaseous species, such as hydrogen peroxide, H
2
O
2
, nitrogen dioxide, NO
2
, and ozone, O
3
, by any means known in the art, but preferably with a corona discharge, and introducing these active species into the gas stream flowing into and through a catalyst, such as the catalytic reactor fuel reformer used to produce hydrogen gas from a hydrocarbon fuel for use in a fuel cell, a catalytic combuster, or a catalytic convertor associated with an internal combustion engine.
BACKGROUND OF THE INVENTION
Heterogeneous catalysts have been shown to be useful in enhancing the rate and/or efficiency of gas phase reactions in a number of applications. These applications include emerging technologies, such as catalytic reactors or fuel reformers that are used to produce hydrogen gas, H
2
, from hydrocarbon fuels, such as gasoline, natural gas, and alcohols, as well as relatively mature technologies, such as the catalytic convertors used to reduce the emission of pollutants from automobile and truck engines. The performance of heterogeneous catalysts may be severely degraded by exposure to catalyst poisons, such as the sulfur and phosphorous compounds that are found in varying amounts in automotive fuels, such as gasoline. As gasoline is expected to be used, at least initially, in automotive applications of fuel cells, the possible poisoning of both fuel cell catalytic reactors, automotive catalytic convertors, and other catalytic combusters by fuel contaminants is a major concern regarding the effectiveness of these devices.
Fuel cells are electrochemical devices that convert the chemical energy of a fuel directly into electrical and thermal energy, and have been used for a number of years in aerospace applications, such as the space shuttle, where hydrogen and oxygen gas are combined to produce electric power. In a typical fuel cell, a gaseous fuel, e.g., hydrogen, H
2
, is fed continuously to an anode or negative electrode compartment, and an oxidant, e.g., oxygen or an oxygen containing gas, which is typically air, is fed continuously to a cathode or positive electrode compartment. The hydrogen and oxygen are combined at the electrodes, producing water and an electric current. In addition to water, fuel cells that utilize catalytic reactors to produce hydrogen gas from hydrocarbon fuels also release carbon dioxide, and may also release very small amounts of carbon monoxide.
Theoretically, a fuel cell is capable of producing electrical energy for as long as the fuel and oxidant are supplied to the electrodes. However, pure hydrogen is difficult to store, particularly in a vehicle, and its use may not be practical in many applications. In those cases, a catalytic fuel reformer may be used to produce hydrogen gas from a hydrocarbon fuel, and, thus, the life and performance of the fuel cell is limited by the performance and efficiency of the catalytic reactor. As discussed above, if one or more catalyst poisons are present in the fuel used to produce hydrogen in the catalytic fuel reformer, the performance of the reformer will be degraded, thereby reducing the performance of the fuel cell.
In addition, fuel cells are sensitive to carbon monoxide, and, thus, the amount of carbon monoxide is typically minimized in the fuel gas by removal by the catalytic reactor to achieve optimum efficiency of the fuel cell. However, where the catalyst is contaminated or poisoned, carbon monoxide will remain in the fuel gas after passing through the catalytic reactor. Therefore, for the fuel cell to function efficiently, the catalyst should be substantially free of poisons that prevent the removal of carbon monoxide from the fuel gas.
Similarly, in virtually all modern gasoline engines used in vehicles, such as automobiles and light trucks, the exhaust gases produced during combustion of fuel are conveyed by an exhaust pipe to a catalytic converter where pollutants, such as carbon monoxide (CO), hydrocarbons (HC), and oxides of nitrogen (NO
x
), are substantially converted to non-polluting species, and, thus, are removed from the exhaust gas. In addition, it is expected that catalytic convertors will soon be developed for use with diesel engines. Most modern engines employ three way catalytic converters (“TWC”), which simultaneously oxidize CO and HC to CO
2
and H
2
O, and reduce NO and NO
2
to N
2
. The amount of CO, HC, NO
x
, and other pollutants produced will vary with the design and operating conditions of the engine and the fuel and air used. In particular, as with fuel cell catalytic reactors, the presence of catalyst poisons in the fuel will result in a degradation of the performance of the catalytic convertor, and, thus, an increase in the amount of pollutant released into the air.
In general terms, a catalytic convertor used with an internal or external combustion engine may be considered to be a sophisticated catalytic combuster, which is typically used to enhance the oxidation of a fuel to produce heat. The heterogeneous catalyst in a catalytic combuster provides a surface on which a fuel and an oxidizer react. In a typical catalytic combuster, a vaporized fuel and air are passed over the surface of the catalyst. By providing a catalytic site for the reaction of the fuel and oxidizer, the catalyst lowers the activation energy of the reaction, allowing the reaction to occur at a lower temperature with greater efficiency. However, the presence of catalyst poisons that may be adsorbed onto the catalyst surface in any of the fuel, oxidizer, or reaction products will degrade the performance and the efficiency of the catalytic combuster by occupying active sites on the catalyst surface. This reduces the number of sites available to the fuel and oxidizer, decreasing the reaction rate.
In general terms, the heterogeneous catalysts, used in fuel cell catalytic fuel reformers or reactors, vehicle catalytic convertors, and catalytic combusters, provide a catalytic surface that enhances the reaction rate and efficiency of various gas phase reactions. Although a number of different heterogeneous catalysts are known, the heterogeneous catalysts used in catalytic reactors and catalytic convertors usually utilize a noble metal catalyst. The structure of the catalyst support may vary, depending on the application, e.g., ceramic beads that are coated with the catalytic material may be used. However, where a large throughput of gas is required, the noble metal catalyst is preferably held in a honeycomb monolithic structure, which has excellent strength and crack-resistance under physical and thermal shock.
The honeycomb construction and the geometries chosen provide a relatively low pressure drop and a large total surface area that enhances the mass transfer controlled reactions that produce fuel for the fuel cell or remove pollutants from the exhaust of an engine. The honeycomb is often set in a steel container, and protected from vibration by a resilient matting where needed. Although a single catalyst may be use, a typical modern three way catalytic convertor comprises an outer steel shell that contains at least two honeycomb catalyst “bricks”, i.e., honeycomb monolithic structures holding the noble metal catalyst, as described above, where one of the bricks is mounted at the upstream, inlet end of the catalytic convertor, and the second is mounted at the downstream, outlet end of the catalytic convertor.
An adherent washcoat, frequently made of stabilized
Caren Robert P.
Christeller David
Ekchian Jack A.
Denion Thomas
Litex, Inc.
Pennie & Edmonds LLP
Tran Binh
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