Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Metal – metal oxide or metal hydroxide
Reexamination Certificate
2001-02-21
2003-04-22
Bos, Steven (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Metal, metal oxide or metal hydroxide
Reexamination Certificate
active
06551959
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the partial oxidation of hydrocarbons, and more particularly, to the partial oxidation of hydrocarbons to produce hydrogen and carbon monoxide in the presence of a metal catalyst.
BACKGROUND OF THE INVENTION
The conversion of hydrocarbons to hydrogen and carbon monoxide containing gases is well known in the an. Examples of such processes include catalytic steam reforming, autothermal catalytic reforming, catalytic partial oxidation and non-catalytic partial oxidation. Each of these processes has advantages and disadvantages and produce various ratios of hydrogen and carbon monoxide, also known as synthesis gas.
Partial oxidation is an exothermic reaction wherein a hydrocarbon gas, such as methane, and an oxygen-containing gas, such as air, are contacted with a catalyst at elevated temperatures to produce a reaction product containing high concentrations of hydrogen and carbon monoxide. The catalysts used in these processes are typically noble metals, such as platinum or rhodium, and other transition metals, such as nickel on a suitable support.
Partial oxidation processes convert hydrocarbon containing gases, such as natural gas or naphtha to hydrogen (H
2
), carbon monoxide (CO) and other trace components such as carbon dioxide (CO
2
), water (H
2
O) and other hydrocarbons. The process is typically carried out by injecting preheated hydrocarbons and an oxygen-containing gas into a combustion chamber where oxidation of the hydrocarbons occurs with less than stoichiometric amounts of oxygen for complete combustion. This reaction is conducted at very high temperatures, such as in excess of 700° C. and often in excess of 1,000° C., and pressures up to 150 atmospheres. In some reactions, steam or carbon dioxide can also be injected into the combustion chamber to modify the synthesis gas product and to adjust the ratio of hydrogen to carbon monoxide.
More recently, partial oxidation processes have been disclosed in which the hydrocarbon gas is contacted with the oxygen-containing gas at high space velocities in the presence of a catalyst such as a metal deposited on a ceramic foam monolith support. The monolith supports are impregnated with a noble metal such as platinum, palladium or rhodium, or other transition metals such as nickel, cobalt chromium and the like. Typically, these monolith supports are prepared from solid refractory or ceramic materials such as alumina, zirconia, magnesia and the like. During operation of these reactions, the hydrocarbon feed gases and oxygen-containing gases are initially contacted with the metal catalyst at temperatures in excess of 350° C., typically in excess of 600° C., and at a standard gas hourly space velocity (GHSV) of over 10,000 hr
−1
, and often over 100,000 hr
−1
.
A drawback of these prior art partial oxidation processes is the relatively high temperature required for initiating the reaction. As stated above, the partial oxidation reaction is exothermic and once the reaction is started, the heat of the reaction will maintain the elevated temperature without the addition of external heat energy. However, since the process requires temperatures in excess of 350° C. to start or initiate the reaction, an external heat source is often required. Of course, this requires additional capital costs and adds engineering complexities to the process thereby reducing its commercial attractiveness. Therefore, there is an ongoing need for other alternative methods of initiating the reaction at lower temperatures.
Furthermore, during the formation of synthesis gas by partial oxidation of hydrocarbons, small amounts of H
2
O and CO
2
are also formed as a result of a combustion reaction. The combustion reaction is not desirable because it competes with the partial oxidation reaction for the available oxygen source, and results in lower than expected conversion of the hydrocarbons. Thus, it is desirable to minimize the formation of combustion products such as H
2
O and CO
2
and increase the selectivity for the desired products, H
2
and CO.
SUMMARY OF THE INVENTION
The present invention relates to partial oxidation of hydrocarbons using a metal catalyst. One aspect of the invention provides an improved process for the catalytic partial oxidation of hydrocarbons to produce hydrogen and carbon monoxide. The process permits the reaction to be initiated at lower temperatures than previously possible, thereby reducing operating and capital costs. The inventive process employing a metal catalyst on a ceria monolith support also exhibits higher conversions of hydrocarbons to synthesis gas and higher selectivity to hydrogen and carbon monoxide.
In one aspect, the invention provides a process for the partial oxidation of hydrocarbons to produce hydrogen and carbon monoxide with less than 3%, preferably less than about 2% carbon dioxide. The process comprises contacting a mixture of a hydrocarbon-containing feed gas and an oxygen-containing feed gas with a catalytically effective amount of a reduced metal catalyst consisting essentially of a transition or noble metal selected from the group of nickel, cobalt, iron, platinum, palladium, iridium, rhenium, ruthenium, rhodium, osmium and combinations thereof supported on or in a ceria monolith support at a pressure of between about 1 and 20 atmospheres, with the feed gas mixture flowing at a standard gas hourly space velocity of about 50,000 to about 500,000 hr
−1
, and a linear velocity of about 0.5 to 5.0 feet per second (f/s).
In another aspect, the invention provides a process for the partial oxidation of hydrocarbons to produce hydrogen and carbon monoxide by contacting a metal catalyst consisting essentially of a transition or noble metal selected from the group of nickel, cobalt, iron, platinum, palladium, iridium, rhenium, ruthenium, rhodium and osmium and combinations thereof supported on or in a ceria monolith support with a reducing environment to substantially reduce the metal catalyst (including the ceria monolith support) and subsequently contacting the substantially reduced metal catalyst with a mixture of a hydrocarbon-containing feed gas and an oxygen-containing feed gas, where the partial oxidation of hydrocarbons having between one and five carbon atoms can be initiated at temperatures less than about 200° C.
In another aspect, the invention provides a monolith substrate for supporting a catalyst for use in catalytic reactions. The monolith substrate comprises titania and ceria, with a titania concentration of preferably between about 0.1% and about 3% by weight and between about 75% and about 99.9% ceria.
In yet another aspect, the invention provides a metal catalyst comprising a transition or noble metal supported by a monolith substrate comprising between about 0.1% and about 3% titania and between about 75% and about 99.9% ceria.
In a further aspect of the invention, a process is provided for partial oxidation reaction of a hydrocarbon by contacting a feed gas mixture with a metal catalyst comprising a transition or noble metal supported by a monolith substrate comprising about 1% by weight of titania and about 99% of ceria.
DETAILED DESCRIPTION
The present invention relates to partial oxidation of hydrocarbons by contacting a mixture of hydrocarbon-containing gas and an oxygen-containing gas with a catalytically effective amount of a reduced metal catalyst. One aspect of the invention relates to a process that provides high yields of synthesis gas and less than about 3% (by volume) each of carbon dioxide (CO
2
) and water (H
2
O). In some preferred embodiments, carbon dioxide of less than about 2% and most preferably less than about 1% are also achieved. Furthermore, improved CO:CO
2
ratios of at least about 4, preferably at least about 10, are also obtained. Another aspect of the invention provides an improved partial oxidation process in which the initiation temperature can be below about 200° C., preferably below about 100° C. The present process either reduces or eliminates the need for an external heat source to
Chen YuDong
Ramprasad Narayanan
Tamhankar Satish S.
Tomczak Mark S.
Bos Steven
Neida Philip H. Von
Pace Salvatore P.
The BOC Group Inc.
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