Chemistry of inorganic compounds – Hydrogen or compound thereof – Elemental hydrogen
Reexamination Certificate
1998-06-15
2002-08-13
Johnson, Jerry D. (Department: 1764)
Chemistry of inorganic compounds
Hydrogen or compound thereof
Elemental hydrogen
C429S010000, C048S179000
Reexamination Certificate
active
06432378
ABSTRACT:
BACKGROUND AND SUNDRY OF THE INVENTION
This application claims the priority of German Patent Document No. 197 25 007.6, filed on Jun. 13, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a process for operating a methanol reforming system using a methanol reforming catalyst in which the reforming reaction operation is interrupted periodically for catalyst reactivation phases.
Processes for the catalytic reforming of methanol are known and are used, for example, for generating hydrogen for the fuel cells of a fuel-cell-operated motor vehicle by means of water vapor reforming of methanol carried along in the liquid state. A catalytically active Cu/ZnO material on an aluminum oxide carrier, for example, is suitable to be used as the catalyst material. Additional usable catalyst compositions are described, for example, in German Published Patent Application DE 35 31 757 A1 and European Published Patent Application EP 0 201 070 A1. The catalyst material is usually charged as bulk pellets into the reforming reaction space of the concerned methanol reforming reactor.
It is a known characteristic of current methanol reforming catalysts that they exhibit a decrease of their specific activity during the reforming reaction operation. This is particularly true during an operation under a high load which is desired in mobile applications. For this field of application, a particularly compact construction of the reactor is desired for space and weight reasons. The reactor is then operated at a correspondingly high load for achieving the required conversion output.
Taking into account the mobility and service expectations of motor vehicle users, a more frequent exchange of the catalyst material is difficult to accept.
Various processes have been suggested for maintaining a high catalytic activity or for achieving a high service life of the methanol reforming catalyst. Thus, a special recipe of various metal oxides is indicated in Japanese Published Patent Application JP 4-141234 (A) for obtaining a catalyst with a long service life as well as a high activity and selectivity.
In Japanese Published Patent Application JP 63-310703 (A), the catalyst material is subjected to a reduction reaction in the reforming reaction space of a methanol reforming reactor before the start of the reforming reaction operation. The reduction reaction results in a decrease in the volume of the catalyst. A pressure-spring-loaded movable cover plate holds the catalyst material, charged into the reaction space as bulk pellets, compressed as a dense packing. The reduction reaction is a process required for the operation of a Cu catalyst. The decrease in volume occurring in this case is clearly lower than the decrease in volume that occurs during the normal reforming operation.
Published Japanese Patent Application JP 63-315501 (A) suggests the placing of an air chamber between a burner and a reforming reaction space. By way of the air chamber, air can be supplied in a controlled manner in order to hold the catalyst temperature at a defined value.
In a process disclosed in German Published Patent Application DE 33 14 131 A1, for extending the service life of the methanol reforming catalyst, the methanol is freed of compounds of chlorine which may be contained therein before the methanol is brought in contact with the catalyst.
A process of the initially mentioned type is indicated in German Patent Document DE 1 246 688. According to this process, the reforming reaction operation is periodically interrupted for catalyst reactivation phases for the purpose of an activity-regenerating treatment of the catalyst. The activity-regenerating treatment comprises subjecting the catalyst to an oxygen-containing gas flow, such as air, at a raised temperature of preferably 150° C. to 450° C. After this regenerating of the catalyst, the catalyst may be subjected, as required, to a hydrogen-containing gas at a raised temperature in order to reactivate it before the reforming reaction is started again. An activity-regenerating treatment of a methanol reforming catalyst by subjecting it to an oxygen-containing gas flow is also disclosed in Japanese Published Patent Application JP 4-200640 (A).
From German Published Patent Application DE 33 14 131 A1, it is known to raise the reaction temperature successively over the service life of a methanol reforming catalyst in order to compensate the decreasing catalyst activity.
In Japanese Published Patent Application JP 3-247501 (A), a process is described for the operation of a methanol reforming reactor which, when the reforming reactor is switched off, comprises a rinsing of the reformation catalyst bed with reformed gas under a high pressure. This rinsing prevents a weakening of the effect of the catalyst by methanol condensing on the catalyst bed. A rinsing with nitrogen gas is mentioned as a conventional alternative to this approach.
The present invention is based on the technical problem of providing a process of the initially mentioned type by means of which a methanol reforming system can be operated at comparatively low expenditures for longer operating periods with a reforming conversion output that does not noticeably decrease.
The present invention solves this problem by providing the following process for operating a methanol reforming system having catalyst reactivation phases. In this process, the reforming reaction operation is periodically interrupted for catalyst reactivation phases during which the methanol reforming catalyst, whose catalytic activity decreases during the reforming to reaction operation, is treated in an activity-regenerating manner. By means of the interposition of such reactivation phases, the original activity of the catalyst can be restored at least partially which, on the whole, permits longer operating periods of the system without a noticeably decreasing reformation conversion output and without the necessity of exchanging the catalyst. When the system is used in motor vehicles, the reactivation phases can be integrated in the normal driving operation.
According to a first embodiment, the catalyst reactivation phases comprise a reformation reaction operation wherein, in comparison with the remaining reformation reaction operation, the load is reduced and/or the temperature is higher. In another embodiment, a gas purification step follows the reactor and is also carried out during these catalyst reactivation phases. The gas purification step has an increased output with respect to the CO-conversion or CO-separation, which is higher than in the phases of the normal reformation reaction operation. As a result, a CO-fraction in the reformate gas flow, which may be higher during the reactivation phases, can be compensated so that no higher CO-fraction occurs during the reactivation phases at the outlet side of the gas purification step than in the normal reformation reaction operation.
In the case of a second embodiment, the reactor containing the methanol reforming catalyst is rinsed with inert gas for the activity-regenerating catalyst treatment and in the process is therefore operated without load. This was found to be a suitable method for the simple, at least partial restoring of the initial catalyst activity.
According to another embodiment of the present invention, a process for methanol reforming systems in motor vehicles is provided. In this process, the catalyst reactivation phases are triggered by a driver's demand or automatically by means of occurring vehicle stoppage phases. Thus, it is possible to integrate the catalyst reactivation phases in the normal driving operation without the requirement of interrupting the driving operation of the vehicle specifically for this purpose.
Also representing numerous other possible implementations of the present invention, a methanol reforming system arranged in a fuel-cell-operated motor vehicle is an embodiment by means of which the hydrogen required for the fuel cells is generated by means of the water vapor reforming of methanol carried along
Autenrieth Rainer
Christen Andreas
Megede Detlef zur
Schuessler Martin
Crowell & Moring LLP
Johnson Jerry D.
Varcoe Frederick
Xcellsis GmbH
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