Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Nitrogen or nitrogenous component
Reexamination Certificate
1994-08-24
2001-09-04
Gray, Linda (Department: 1734)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Nitrogen or nitrogenous component
C423S24000R, C423S245300, C423S247000, C502S347000, C502S305000, C502S317000, C502S312000, C502S353000
Reexamination Certificate
active
06284211
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas cleaner for effectively removing nitrogen oxides from an exhaust gas containing nitrogen oxides and an excess proportion of oxygen, and a method for removing nitrogen oxides with such an exhaust gas cleaner.
Various exhaust gases discharged from internal combustion engines such as automobile engines, etc., combustion apparatuses installed in factories, home fun heaters, etc. contain nitrogen oxides such as nitrogen monoxide and nitrogen dioxide together with an excess proportion of oxygen. The term “containing an excess proportion of oxygen” means that the oxygen content is larger than its stoichiometric proportion relative to unburned components such as carbon monoxide, hydrogen, hydrocarbons in the exhaust gas. The term “nitrogen oxides” means nitrogen monoxide and/or nitrogen dioxide.
The nitrogen oxides are one cause of acid rain, posing a serious problem of environmental pollution. For these reasons, various methods have been proposed to remove nitrogen oxides from exhaust gases emitted from various combustion equipment.
In the case of large, stationary combustion apparatuses such as large combustion apparatuses of factories, ammonia is employed to catalytically and selectively reduce nitrogen oxides in an exhaust gas containing an excess proportion of oxygen, thereby removing nitrogen oxides from the exhaust gas.
However, such a method is disadvantageous, because ammonia is expensive, because ammonia is so toxic that the proportion of ammonia should be controlled by measuring the concentration of nitrogen oxides in the exhaust gas, and because this reduction system generally needs large apparatuses.
There has been proposed a method in which gases serving as a reducing agent, such as hydrogen, carbon monoxide, hydrocarbons etc. are brought into contact with nitrogen oxides, whereby the nitrogen oxides are non-selectively and catalytically reduced. In this method, the reducing agent must be added to the exhaust gas in a greater proportion than a stoichiometric proportion relative to oxygen in the exhaust gas to effectively remove nitrogen oxides from the exhaust gas, leading to an increased consumption of the reducing agent. For this reason, the method is applicable merely to the exhaust gas containing a small proportion of residual oxygen such as those generated almost under a theoretical air fuel ratio, resulting in limited application of the method to a narrow range of exhaust gases.
There have also been proposed methods of reducing nitrogen oxides by adding to an exhaust gas hydrocarbons in a smaller proportion than a stoichiometric proportion relative to oxygen in the exhaust gas, in the presence of a catalyst such as zeolite with or without carrying a transition metal (Japanese Patent Laid-Open Nos. 63-100919, 63-283727 and 1-130735; Thesis 2A526, 1990, the 59th Spring Conference of the Japan Chemical Society; Theses 3L420, 3L422 and 3L423, 1990, the 66th Catalysis Symposium, the Catalysis Society of Japan, 1990; and “Catalyst”, Vol. 33, No. 2, p.59 (1991)).
However, these methods are effective only for removal of NOx having a narrow temperature range. Also, their efficiency of removing nitrogen oxides is extremely low in the case of an actual exhaust gas because it contains moisture.
OBJECT AND SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an exhaust gas cleaner and a method capable of efficiently removing nitrogen oxides from an exhaust gas containing nitrogen oxides and oxygen in a proportion larger than the stoichiometric proportion relative to unburned components such as carbon monoxide, hydrogen, hydrocarbons, etc., which is discharged from stationary combustion apparatuses, gasoline engines operated under the condition of excess oxygen, and diesel engines.
As a result of intense research in view of the above objects, the inventors have found that when the exhaust gas is treated with a catalyst containing a silver component supported on a porous inorganic oxide, ammonia is produced as a by-product resulting from a reaction of oxygen-containing organic compounds such as ethanol, oxygen and nitrogen oxides. From this fact, the inventors have further found that nitrogen oxides are effectively removed even from exhaust gas containing about 10% of moisture by adding oxygen-containing organic compounds to the exhaust gas and by bringing the exhaust gas into contact with an exhaust gas cleaner comprising, in combination, (1) a first catalyst containing the silver component supported on the porous inorganic oxide and (2) a second catalyst containing tungsten oxide and/or vanadium oxide which are capable of reducing nitrogen oxides in the presence of ammonia. The present invention has been completed based on these findings.
Thus, the exhaust gas cleaner for removing nitrogen oxides from an exhaust gas containing nitrogen oxides and oxygen in a proportion larger than its stoichiometric proportion relative to unburned components in the exhaust gas according to the present invention comprises (1) a first catalyst composed of 0.2-20 parts by weight (on a metal basis) of silver or silver oxide as a catalytically active component supported on a porous inorganic oxide, and (2) a second catalyst composed of 1-50 parts by weight of tungsten oxide and/or vanadium oxide as a catalytically active component supported on a porous inorganic oxide.
The method for removing nitrogen oxides from an exhaust gas containing nitrogen oxides and oxygen in a proportion larger than its stoichiometric proportion relative to unburned components in the exhaust gas according to the present invention comprises (i) disposing an exhaust gas cleaner in a flow path of the exhaust gas, the exhaust gas cleaner comprising a first catalyst composed of 0.2-20 parts by weight (on a metal basis) of silver or silver oxide as a catalytically active component supported on a porous inorganic oxide, and a second catalyst composed of 1-50 parts by weight of tungsten oxide and/or vanadium oxide as a catalytically active component supported on a porous inorganic oxide; (ii) introducing oxygen-containing organic compounds having 2 or more carbon atoms or a fuel containing the oxygen-containing organic compounds into the exhaust gas on an upstream side of the exhaust gas cleaner; and (iii) bringing the exhaust gas into contact with the exhaust gas cleaner at a temperature of 150-650° C., thereby causing a reaction of nitrogen oxides with the oxygen-containing organic compounds to remove the nitrogen oxides.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
An exhaust gas cleaner of the present invention comprises (1) a first catalyst composed of 0.2-20 parts by weight (on a metal basis) of silver or silver oxide as a catalytically active component supported on a porous inorganic oxide, and (2) a second catalyst composed of 1-50 parts by weight of tungsten oxide and/or vanadium oxide as a catalytically active component supported on a porous inorganic oxide. The exhaust gas cleaner is disposed in a flow path of the exhaust gas and brought into contact with the exhaust gas containing oxygen-containing organic compounds which is introduced to the flow path on an upstream side of the exhaust gas cleaner, whereby nitrogen oxides in the exhaust gas is efficiently reduced.
As mentioned above, in the exhaust gas cleaner of the present invention, a combination of the first and second catalysts is employed. Preferably, the first catalyst is disposed on an inlet side of the exhaust gas cleaner and the second catalyst is disposed on an outlet side of the exhaust gas cleaner. By such a configuration of the exhaust gas cleaner, a removal of nitrogen oxides from the exhaust gas can be performed in a wide temperature range.
(A) First Catalyst
The first catalyst is composed of a silver component as a catalytically active component and a porous inorganic oxide supporting the silver component on a surface thereof.
The silver component used as a catalytically active component of th
Miyadera Tatsuo
Yoshida Kiyohide
Browdy and Neimark
Gray Linda
Jiro Hiraishi of Director-General of Agency of Industrial Scienc
LandOfFree
Exhaust gas cleaner and method for removing nitrogen oxides does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Exhaust gas cleaner and method for removing nitrogen oxides, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Exhaust gas cleaner and method for removing nitrogen oxides will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2530947