Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Reexamination Certificate
2001-02-22
2003-11-04
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
C422S198000, C422S198000, C422S211000
Reexamination Certificate
active
06641789
ABSTRACT:
This application claims priority from G.B. Patent Application No. 9812459.7, filed Jun. 11, 1998 and G.B. Patent Application No. 9812460.5, filed Jun. 11, 1998, the disclosures of which are incorporated by reference herein in their entirety.
The present invention relates to a device for decomposing the oxides of nitrogen and more particularly to a device for removing the oxides of nitrogen contained in gaseous effluents, such as the exhaust gases generated by automotive combustion engines. The present invention also relates to a process for decomposing these oxides, e.g. using such a device.
The use of catalytic devices in vehicle exhaust systems to remove the oxides of nitrogen (NO
x
) contained in the exhaust gases is well known. These devices, which are more commonly referred to as catalytic converters, typically comprise a surrounding metal shell or casing which houses a ceramic or metal monolith. The ceramic or metal monolith comprises a plurality of parallel flow channels which contain a catalytic material for catalysing the reduction of the nitrogen oxides to molecular nitrogen. In use, the exhaust gas generated by the engine is conveyed through the flow channels in the monolith so that it contacts the catalytic material.
We have now developed a device which is able to decompose the oxides of nitrogen (NO
x
) contained in effluent compositions, such as the exhaust gases generated by automotive combustion engines. In one embodiment, the device is able to reduce nitrogen oxides of nitrogen oxidation states greater than 2 and especially nitrogen dioxide (NO
2
), to molecular nitrogen. We have also developed a process for reducing nitrogen oxides of nitrogen oxidation states greater than 2 to molecular nitrogen which uses such a device.
According to a first aspect of the present invention there is provided a device for decomposing a nitrogen oxide(s) of nitrogen oxidation state greater. than 2, especially nitrogen dioxide, comprising a reaction chamber, an oxidisable material contained in the reaction chamber which in use will undergo an oxidation/reduction reaction with the nitrogen oxide(s) to generate nitrogen and an oxide(s) of the oxidisable material.
According to a second aspect of the present invention there is provided a process for decomposing a nitrogen oxide(s) of nitrogen oxidation state greater than 2, especially nitrogen dioxide, which comprises passing the nitrogen oxide(s) through a reaction chamber where it is contacted with an oxidisable material at a temperature in the range of from 100 to 1000° C. so as to at least partially reduce the nitrogen oxide(s) to nitrogen and oxidise at least a proportion of the oxidisable material to form an oxide(s) thereof.
The present invention in its first and second aspects is particularly concerned with the treatment of gaseous effluents containing one or more nitrogen oxides of nitrogen oxidation states greater than 2, and more particularly with the treatment of gaseous effluents containing nitrogen dioxide, such as plasma effluent gas and especially the exhaust gases which are produced by automotive combustion engines such as lean burn engines. The devices used to treat such exhaust gases are more commonly known as catalytic converters.
In the device of the first aspect of the present invention the reaction chamber is preferably enclosed by a metal shell or casing. The oxidisable material contained in the reaction chamber will preferably form a layer on a suitable substrate. Conveniently, the oxidisable material will form an outer layer on a plurality of wires, particularly metal containing,wires, which are loaded into the reaction chamber. Preferably, the wires will be knitted or otherwise joined together to form an integral wire mass, although we do not exclude the possibility that the wires may be discrete or perhaps loosely consolidated to form a wool.
The reaction chamber is provided with an inlet and outlet for the effluent composition to which conduits for conveying the composition to and from the reaction chamber may be attached.
The oxidisable material which is contained in the reaction chamber is able to reduce nitrogen oxides of nitrogen oxidation states greater than 2 and especially NO
2
to molecular nitrogen and is itself oxidised to form an oxide(s). As a result, the oxidisable material is gradually consumed.
Combinations of two or more oxidisable materials may be used if desired.
In a preferred embodiment, the oxidisable material contained in the reaction chamber is preferably one which will undergo an oxidation/reduction reaction with a nitrogen oxide(s) of nitrogen oxidation state greater than 2 to generate nitrogen and an oxide(s) of the oxidisable material which can be reduced in order to regenerate the oxidisable material.
In this embodiment, the device of the present invention preferably comprises means for reducing the oxide(s) so as to regenerate the oxidisable material. More particularly, the device is equipped with means for reducing the oxide(s) which is operable concurrently with the oxidation/reduction process between the oxidisable material and the nitrogen oxide(s) of nitrogen oxidation state greater than 2. In this way, the oxidisable material can be regenerated at the same time as it is consumed.
Similarly, in the process of the present invention, the oxidisable material is preferably regenerated by reducing the oxide(s) which is formed. This regeneration of the oxidisable material preferably takes place concurrently with the oxidation/reduction process.
In a particularly preferred embodiment, the oxide(s) which is formed from the oxidisable material is one which can be reduced to regenerate the oxidisable material by being subjected to an electromotive force.
Accordingly, in a third aspect of the present invention there is provided a device for decomposing a nitrogen oxide(s) of nitrogen oxidation state greater than 2, especially nitrogen dioxide, comprising a reaction chamber, an oxidisable material contained in the reaction chamber which in use will undergo an oxidation/reduction reaction with the nitrogen oxide(s) to generate nitrogen and an oxide(s) of the oxidisable material which decomposes on being subjected to an electromotive force to regenerate the oxidisable material and means for applying an electromotive force which is in electrical communication with the oxidisable material for regenerating the oxidisable material by reducing the oxide(s) which is formed.
In a fourth aspect of the present invention there is provided a process for decomposing a nitrogen oxide(s) of nitrogen oxidation state greater than 2, especially nitrogen dioxide, which comprises (1) passing the nitrogen oxide(s) through a reaction chamber where it is contacted with an oxidisable material at a temperature in the range of from 100 to 1000° C. so as to at least partially reduce the nitrogen oxide(s) to nitrogen and oxidise at least a proportion of the oxidisable material to form an oxide(s) and (2) regenerating the oxidisable material by subjecting the oxide(s) which is formed to an electromotive force.
Although the above described devices and processes may be used to reduce any oxide of nitrogen in which the nitrogen has an oxidation state greater than 2, they are particularly concerned with the reduction of effluents containing nitrogen dioxide (NO
2
), and hereinafter these inventions will be explained with reference to nitrogen dioxide. However, any references to nitrogen dioxide or NO
2
should be taken to include other oxides of nitrogen in which the nitrogen has an oxidation state greater than 2 unless the context requires otherwise.
The electromotive force which is preferably applied to regenerate the oxidisable material should be a direct current. The electromotive force may be continuous or pulsed and is preferably applied concurrently with the oxidation/reduction process between the oxidisable material and the NO
2
so that the oxidisable material is regenerated at the same time as it is consumed.
The potential of the applied electromotive force should, of course, be sufficient to regenerate t
Scott Steven Paul
Thomson James
Medina Maribel
Myers Bigel & Sibley Sajovec, PA
Silverman Stanley S.
University of Dundee
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