Chemistry of inorganic compounds – Carbon or compound thereof – Oxygen containing
Reexamination Certificate
2000-03-02
2002-10-01
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Oxygen containing
C423S651000
Reexamination Certificate
active
06458334
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 at high gas space velocities and low reaction initiation temperatures. The catalyst is comprised of certain transition metals or combinations thereof on a ceria monolith support.
BACKGROUND OF THE INVENTION
The conversion of hydrocarbons to hydrogen and carbon monoxide containing gases is well known in the art. 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. The present invention is directed to a catalytic partial oxidation process.
Partial oxidation processes are also well known and the art is replete with various catalytic partial oxidation processes. Partial oxidation is an exothermic reaction wherein a hydrocarbon gas, such as methane, and an oxygen-containing gas, such as air, is 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, carbon monoxide and other trace components such as carbon dioxide, water 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° 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 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 400° C., typically in excess of 600° C., and at a standard gas hourly space velocity (GHSV) of over 100,000 hr
−1
.
A significant drawback of all of these prior art partial oxidation processes is that they require an external source of heat to initiate the partial oxidation 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 400° C. to start or initiate the reaction, an external heat source is still required. Of course, this requires additional capital costs and adds engineering complexities to the process thereby reducing its commercial attractiveness. To attempt to address this issue, some prior processes have employed special initiator compounds to decrease the initiation temperature. For example, U.S. Pat. No. 4,879,253 discloses the use of methanol as an initiating compound to reduce the initiating temperature in the range of 100° to 500° C. However, the inventive process can be initiated at low temperatures in the absence of a low temperature initiating compound.
The present invention provides an improved partial oxidation process in which the initiation temperature can be below 400° C., preferably less than 200° C. and most preferably below 120° C. The present process either reduces or eliminates the need for an external heat source to initiate the reaction thereby increasing the commercial attractiveness of the process. The present process also has been found to exhibit a higher conversion of hydrocarbon to synthesis gas than conventional partial oxidation processes with only trace amounts of carbon dioxide and water.
SUMMARY OF THE INVENTION
The present invention provides an improved process for the catalytic partial oxidation of hydrocarbons to produce hydrogen and carbon monoxide and less than 3% carbon dioxide. Accordingly, 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 high conversions of hydrocarbons to synthesis gas.
In one aspect, the invention provides a process for the partial oxidation of hydrocarbons to produce hydrogen and carbon monoxide comprising 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 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 1 and 20 atmospheres, a feed gas 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, this invention provides a process for the partial oxidation of hydrocarbons to produce hydrogen and carbon monoxide which can be initiated at temperatures of less than 400° C. by contacting a metal catalyst consisting essentially of a transition 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 then subsequently contacting the substantially reduced metal catalyst with a mixture of a hydrocarbon-containing feed gas and an oxygen-containing feed gas at a standard gas hourly space velocity of between about 50,000 and about 200,000 hr−1.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides an improved process for the 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. The present process provides high yields of synthesis gas and less than 3% (by volume) carbon dioxide.
The hydrocarbon-containing feed gas, which can be used with the present invention, will typically contain C
1
-C
8
alkanes or alkenes with the C
1
-C
4
alkanes preferred and methane most preferred. Of course, natural gas and certain refinery off gases containing methane or higher hydrocarbons can be employed. Alternatively, fuel oil, crude oil and other sources of fuel may be adapted for use in the present process. The oxygen-containing gas is typically air, but can include air enriched with oxygen, oxygen mixed with other gases, or even pure oxygen.
The hydrocarbon-containing feed gas and the oxygen-containing feed gas can be in various ratios in the feed gas mixture. The precise mixture of feed gases introduced into the reaction zone will depend on the particular hydrocarbons chosen and the amount of oxygen necessary to conduct the partial oxidation reaction. Operable ratios can be easily d
Chen YuDong
Ramprasad Narayanan
Tamhankar Satish S.
Tomczak Mark S.
Bos Steven
Cheung Wan Yee
Pace Salvatore P.
The BOC Group Inc.
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