Compositions – Gaseous compositions – Carbon-oxide and hydrogen containing
Reexamination Certificate
2000-12-22
2004-03-09
Silverman, Stanley S. (Department: 1754)
Compositions
Gaseous compositions
Carbon-oxide and hydrogen containing
C423S650000, C423S651000, C502S325000, C502S326000, C502S327000
Reexamination Certificate
active
06702960
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the catalytic partial oxidation of a hydrocarbonaceous feedstock.
BACKGROUND OF THE INVENTION
The partial oxidation of hydrocarbons, for example methane or natural gas, in the presence of a catalyst is an attractive route for the preparation of mixtures of carbon monoxide and hydrogen, known in the art as synthesis gas. The partial oxidation of a hydrocarbon is an exothermic reaction and, in the case in which methane is the hydrocarbon, proceeds by the following reaction:
2CH
4
+O
2
→2CO+4H
2
A mixture of carbon monoxide and hydrogen prepared by this process is particularly suitable for use in the synthesis of hydrocarbons, for example by means of the Fisher-Tropsch synthesis, or the synthesis of oxygenates, for example methanol. Processes for the conversion of the mixture of carbon monoxide and hydrogen into such products are well known in the art.
Hydrogen, or a mixture of hydrogen with other gases prepared by this process may be particularly suitable for use as a combustible fuel either directly or indirectly.
The catalytic partial oxidation process could very suitably be used to provide the hydrogen feed for a fuel cell. In fuel cells, hydrogen and oxygen are passed over the fuel cell in order to produce electricity and water. Fuel cell technology is well known in the art.
In order to obtain high yields of carbon monoxide and hydrogen, it is for thermodynamic reasons preferred to operate the partial oxidation process at relatively high temperatures.
The literature contains a number of documents disclosing details of experiments relating to the catalytic oxidation of hydrocarbons, in particular methane, employing a wide range of catalysts. Reference is made for instance to U.S. Pat. No. 5,149,464 and WO 92/11199.
To be commercially attractive, a catalytic partial oxidation process should be able to operate at relatively severe conditions, i.e. the combination of high temperature and high gas hourly space velocity. An important factor when considering a catalyst for application in a commercial process, is the stability of that catalyst under the prevailing process conditions.
EP-A-0 629 578 discloses that, at a temperature of at least 950° C. and at a very high gas hourly space velocity, a marked difference in the stability of the Group VIII metal catalysts exists. It has been found that catalysts comprising rhodium, iridium or ruthenium display a significantly higher stability in terms of both selectivity and activity than the remaining Group VIII metal catalysts.
U.S. Pat. No. 5,648,582 concerns a catalytic partial oxidation process at very high gas hourly space velocity and at a catalyst temperature in the range of from 850 to 1150° C. using a catalyst comprising rhodium, nickel or platinum.
In WO 95/18063, it is disclosed that partial oxidation catalysts comprising rhodium, iridium or platinum as the catalytically-active metal, generate significantly lower amounts of ammonia and hydrogen cyanide than catalysts comprising other catalytically-active metals.
In GB-A-2 274 284, a catalytic partial oxidation process is described using a catalyst arranged as a cascade of a plurality of catalytic beds, wherein the first and most upstream bed comprises rhodium in combination with platinum or palladium and the second bed comprises rhodium and iridium.
SUMMARY OF THE INVENTION
There still exists a problem in the art in that catalysts comprising either rhodium or iridium in their upstream layer slowly deactivate under the severe process conditions required for commercial operation to produce mixtures of carbon monoxide and hydrogen.
DETAILED DESCRIPTION OF THE INVENTION
Surprisingly, it has now been found that the stability of a catalytic partial oxidation catalyst can be improved by using rhodium and iridium in intimate association with each other as the catalytically active material in the upstream layer of the catalyst.
Accordingly, the present invention relates to a process for the catalytic partial oxidation of a hydrocarbonaceous feedstock, which process comprises contacting a feed comprising the hydrocarbonaceous feedstock and an oxygen-containing gas with a catalyst, wherein the total feed is contacted with the upstream layer of the catalyst and the upstream layer of the catalyst comprises rhodium and iridium in intimate association with each other.
Reference herein to intimate association of the rhodium with the iridium, is to its incorporation in suitable manner on or with the iridium thereby modifying the catalytic performance properties of each other. Rhodium and iridium are essentially present as an intimate admixture or as layers which resemble an admixture, thereby affecting the stability and/or catalytic performance of each other. Essentially present as an admixture means that at least 50%, preferably at least 90%, of the iridium and rhodium is present within a distance of 10 &mgr;m of the other metal, preferably within a, distance of 5 &mgr;m. Preferably, the admixture is a rhodium-iridium alloy. The presence of an alloy can be determined by methods known in the art, for example by XRD.
The catalyst may comprise rhodium and iridium in the form of wires or gauzes of a rhodium-iridium alloy. Preferably, the catalyst comprises rhodium and iridium supported on a catalyst carrier material. Suitable catalyst carrier materials are well known in the art and include refractory oxides, such as silica, alumina, titania, zirconia and mixtures thereof, and metals. High-alloy, alumina-containing steel, such as fecralloy-type materials are particularly suitable metals. Preferred refractory oxides are zirconia-based, more preferably comprising at least 70% by weight zirconia, for example selected from known forms of (partially) stabilised zirconia or substantially pure zirconia. Most preferred zirconia-based materials comprise zirconia stabilised or partially-stabilised by one or more oxides of Mg, Ca, Al, Y, La or Ce. Most suitable carrier materials are Ce-ZTA (zirconia-toughened alumina) and Y-PSZ (partially-stabilised zirconia), both commercially available.
In the case that rhodium and iridium are supported on a catalyst carrier material as hereinbefore defined, a suitable method for associating rhodium and iridium is impregnation. Preferably, the carrier is impregnated with a solution of a rhodium compound and a solution of an iridium compound, followed by drying and, optionally, calcining the resulting material. The solutions are preferably combined in a suitable amount and co-impregnated. Alternatively, impregnation may be sequential, with a first stage impregnation with an iridium solution and a second stage impregnation with a rhodium solution or in a reverse order.
The catalyst comprises rhodium and iridium in any suitable amount to achieve the required level of activity. Typically, the catalyst comprises rhodium and iridium in a total concentration in the range of from 0.02 to 10% by weight, more preferably from 0.1 to 7.5% by weight based on the weight of the carrier material. Preferably, the rhodium-to-iridium weight ratio is in the range of from 0.1 to 10, more preferably in the range of from 0.2 to 5, even more preferably in the range of from 0.5 to 2.
The rhodium and iridium may be associated with at least one inorganic metal cation in such a way that the inorganic metal cation is present in intimate association, supported on or with the rhodium and iridium as described in International patent application PCT/EP99/00324.
The cation is selected from Groups IIA, IIIA, IIIB, IVA and IVB of the Periodic Table and the lanthanides, for example Al, Mg, Zr, Ti, La, Hf, Si and Ba, of which Zr is preferred. The cation is preferably in the form of its oxide.
Reference herein to intimate association of the cation is to its incorporation in suitable manner on or with the rhodium and iridium, thereby modifying the catalytic performance properties thereof.
Suitably therefore, the intimate association of cation and rhodium/iridium is present at the surface of the catalyst. Preferably, the catalyst
Schaddenhorst David
Schoonebeek Ronald Jan
Shell Oil Company
Silverman Stanley S.
Strickland Jonas N.
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