Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Carbon monoxide component
Reexamination Certificate
1999-02-11
2002-12-17
Tran, Hien (Department: 1764)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Carbon monoxide component
C423S437200, C422S172000, C422S177000, C422S198000, C422S211000
Reexamination Certificate
active
06495113
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of Japanese Patent Application No. HEI 10-76727 filed on Mar. 9, 1998 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a technology for reducing the carbon monoxide concentration in a hydrogen-rich gas containing hydrogen and carbon monoxide that is less in concentration than hydrogen.
2. Description of Related Art
In a typical fuel cell system that uses a hydrogen-rich gas as a fuel, a hydrogen-rich gas is produced by a reformer, and then supplied to a fuel cell. The hydrogen-rich gas is produced in the reformer by introducing thereinto methanol as a fuel material and also introducing water, and causing a water vapor reforming reaction of methanol by using a copper-zinc (Cu-Zn) catalyst, that is, a methanol reformation catalyst. Since the water vapor reforming reaction of methanol is an endothermic reaction, it is necessary to supply heat from outside and maintain an optimal temperature of 200-300° C. for the reaction.
The water vapor reforming reaction of methanol can normally be expressed by formula (1):
CH
3
OH+H
2
O→3H
2
+CO
2
(1)
For a more specific description, the reaction expressed by formula (1) can be divided into two reactions expressed by formulas (2) and (3):
CH
3
OH→CO+2H
2
(2)
CO+H
2
O→CO
2
+H
2
(3)
As is apparent from the above formulas, the water vapor reforming reaction of methanol produces carbon monoxide (CO) as a byproduct.
In some cases, in order to eliminate the need for a heat supply from outside, an oxygen-containing oxidative gas (for example, air) is introduced into the reformer so that along with the water vapor reforming reaction of methanol, a partial oxidation reaction as expressed by formula (4), which is an exothermic reaction, is caused.
CH
3
OH+1/2O
2
→2H
2
+CO
2
(4)
In such a case, too, the water vapor reforming reaction of methanol occurs along with the reaction expressed by formula (4), so that carbon monoxide is still produced as a byproduct. Therefore, in any case, the hydrogen-rich gas produced by this type of reformer contains carbon monoxide.
If the hydrogen-rich gas produced by this type of reformer is directly supplied to a fuel cell, carbon monoxide contained in the hydrogen-rich gas is adsorbed to a platinum (Pt) catalyst provided in an electrode in the fuel cell. If the carbon monoxide concentration in the hydrogen-rich gas exceeds a predetermined allowable level, the correspondingly increased amount of carbon monoxide adsorbed to the Pt catalyst reduces the catalytic function thereof to an undesired level, so that a hydrogen decomposing reaction, that is, an anodic reaction in the fuel cell, is impeded and, therefore, the performance of the fuel cell decreases.
The allowable carbon monoxide concentration in the hydrogen-rich gas supplied to a fuel cell, for example, a polymer electrolyte fuel cell, is about several parts per million.
Therefore, in a typical fuel cell system that uses a hydrogen-rich gas as a fuel, a carbon monoxide concentration reducing device is disposed between the reformer and the fuel cell in order to reduce the carbon monoxide concentration in the hydrogen-rich gas.
The carbon monoxide concentration reducing device has a CO-selective oxidation portion whose interior is filled with a selective oxidation catalyst that selectively accelerates the oxidation of carbon monoxide. An oxygen-containing oxidative gas (for example, air) and the hydrogen-rich gas produced by the reformer are mixed, and the mixture thereof is introduced into the CO-selective oxidation portion, in which carbon monoxide in the hydrogen-rich gas is selectively oxidized by oxygen contained in the oxidative gas via the function of the selective oxidation catalyst so as to reduce the carbon monoxide concentration in the hydrogen-rich gas to a level of several ppm.
This type of carbon monoxide concentration reducing device is described in, for example, Japanese Patent Application Laid-open No. HEI 9-30802, which exemplifies several selective oxidation catalysts including a platinum-ruthenium (Pt-Ru) alloy catalyst, a ruthenium (Ru) catalyst, and the like.
However, this carbon monoxide concentration reducing device has the following problems. That is, immediately after the carbon monoxide concentration reducing device starts to be driven at the time of start of the fuel cell system, the internal temperature of the CO-selective oxidation portion is substantially equal to a room temperature (that is, an ambient temperature of the carbon monoxide concentration reducing device). Since the internal temperature of the reformer is relatively quickly raised to 200-300° C. as stated above, introduction of a warmed-up hydrogen-rich gas from the reformer into the CO-selective oxidation portion causes gradual increases in the internal temperature of the CO-selective oxidation portion. The temperature range in which an ordinary selective oxidation catalyst becomes able to perform its catalytic function (hereinafter, described as “becomes activated”) is considerably higher than the ambient temperature of the carbon monoxide concentration reducing device, that is, a normal room temperature (for example, the aforementioned temperature range is 100° C. or higher). Therefore, it takes a considerably long time for the internal temperature of the CO-selective oxidation portion to reach the temperature range in which the selective oxidation catalyst becomes activated, after the carbon monoxide concentration reducing device starts to be driven. That is, a certain length of time is needed in some cases before the carbon monoxide concentration reducing device comes to effectively function. As a result, there is a danger that a longer time may be required before the fuel cell, disposed downstream of the carbon monoxide concentration reducing device, begins to effectively function.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a carbon monoxide concentration reducing apparatus which solves the aforementioned problems, that is, raises the internal temperature of a CO-selective oxidation unit carrying a selective oxidation catalyst as quickly as possible when the apparatus is started, and to provide a driving method for the apparatus.
To achieve some of the objects of the invention, a first aspect of the invention provides a carbon monoxide concentration reducing apparatus for reducing a concentration of carbon monoxide contained in a hydrogen-rich gas by using oxygen contained in an oxidative gas, the carbon monoxide concentration reducing apparatus including: a selective oxidizer into which the hydrogen-rich gas and the oxidative gas are introduced; a selective oxidation catalyst provided in the selective oxidizer, the selective oxidation catalyst selectively facilitating oxidation of carbon monoxide; and an oxidation catalyst provided in the selective oxidizer, the oxidation catalyst facilitating oxidation of at least one component of the hydrogen-rich gas. The oxidation catalyst facilitates the oxidation at least at a temperature substantially equal to an ambient temperature of the apparatus.
In this aspect of the invention, the selective oxidizer contains the selective oxidation catalyst and the oxidation catalyst that facilitates the oxidation of at least one component of the hydrogen-rich gas at a temperature at least substantially equal to an ambient temperature of the carbon monoxide concentration reducing apparatus, that is, substantially equal to a normal room temperature. Therefore, even when the internal temperature of the selective oxidizer is substantially equal to a normal room temperature, the selective oxidizer is able to produce heat through the oxidation of at least one component of the hydrogen-rich gas by oxygen in the oxidative gas, thereby raising the internal temperature of the selective oxidizer.
That is, according to
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
Tran Hien
LandOfFree
Carbon monoxide concentration reducing apparatus and method... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Carbon monoxide concentration reducing apparatus and method..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Carbon monoxide concentration reducing apparatus and method... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2975997