Chemistry of hydrocarbon compounds – Plural serial diverse syntheses – To produce unsaturate
Reexamination Certificate
2000-09-11
2002-08-13
Griffin, Walter D. (Department: 1764)
Chemistry of hydrocarbon compounds
Plural serial diverse syntheses
To produce unsaturate
C585S651000, C585S652000, C585S653000
Reexamination Certificate
active
06433234
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for the production of olefins. Olefins such as ethylene and propylene may be produced by the catalytic dehydrogenation or cracking of a hydrocarbon feed. In this application the term “cracking” will be used to embrace both these chemical reactions. In an auto-thermal cracking process, a hydrocarbon feed is mixed with an oxygen-containing gas and contacted with a catalyst capable of supporting combustion beyond the fuel rich limit of flammability. The hydrocarbon feed is partially combusted and the heat produced is used to drive the cracking reaction.
An example of an auto-thermal cracking process is described in EP 0 332 289. The document describes the use of a paraffinic feed of, for example, ethane, propane and/or butane which is mixed with oxygen, and cracked to produce an olefinic mixture. The cracking reaction is endothermic and is carried out at elevated temperatures above 800° C.
The energy required for the cracking reaction is provided by combustion of a part of the feed. The feed may also be preheated but the temperature is limited due to the risk of auto ignition. It is desirable to maximise the amount of feed available for cracking by reducing the amount of feed required for combustion.
It is among the objects of the present invention to find an additional or alternative source of heat to drive the cracking step of the auto-thermal cracking process.
SUMMARY OF THE INVENTION
This is achieved by providing an auto-thermal process comprising a preliminary heat-generating step. In this step, a gaseous fuel such as a hydrocarbon reacts with oxygen in an exothermic reaction in the presence of a catalyst. The reaction conditions are controlled to ensure that not all of the oxygen is consumed during this process. The thermal energy produced by the reaction heats the unreacted oxygen, thereby providing an additional source of heat to drive the cracking of the hydrocarbon feedstock.
According to the present invention, there is provided a process for the production of olefins from a hydrocarbon, said process comprising the steps of:
a) providing a first feed stream comprising a gaseous fuel and an oxygen-containing gas,
b) contacting said first feed stream with a first catalyst under conditions so as to produce a product stream and unreacted oxygen,
c) providing a second feed stream comprising a hydrocarbon feedstock, and
d) contacting said second feed stream, said product stream of step b) and said unreacted oxygen of step b) with a second catalyst which is capable of supporting oxidation, thereby consuming at least a part of the unreacted oxygen to produce an olefin product.
According to a preferred embodiment of the present invention, there is provided a process for the production of olefins from a hydrocarbon, said process comprising the steps of:
a) providing a first feed stream comprising a gaseous hydrocarbon and an oxygen-containing gas,
b) contacting said first feed stream with a first catalyst under conditions so as to produce a product stream and unreacted oxygen,
c) providing a second feed stream comprising a hydrocarbon feedstock, and
d) contacting said second feed stream, said product stream of step b) and said unreacted oxygen of step b) with a second catalyst which is capable of supporting oxidation, thereby consuming at least a part of the unreacted oxygen to produce an olefin product.
DETAILED DESCRIPTION OF THE INVENTION
The process of the present invention provides a means of minimising the amount of hydrocarbon feedstock consumed to generate the heat required to drive the cracking of the hydrocarbon feedstock. By reducing the amount of hydrocarbon consumed in this manner, a larger proportion of the hydrocarbon feedstock is available for conversion into olefinic products. This may result in higher olefin yields and enhanced selectivities towards the olefin product. The throughput through the reactor is also enhanced.
The process of the present invention also provides a means of maintaining the second catalyst at an elevated temperature. In doing so, non-volatile hydrocarbons are prevented from condensing on the catalyst and reducing the catalyst's activity. This allows a higher through put through the reactor. On heavy residue-containing feeds the process of the present invention provides the additional advantage of increasing the time on oil processing between catalyst decokes.
The gaseous fuel of the first feed stream is any gaseous fuel which is capable of reacting with oxygen in an exothermic reaction. Suitable examples include hydrocarbons, such as methane, ethane, propane and butane; with methane being preferred. Other suitable fuels include hydrogen, carbon monoxide, alcohols (eg methanol, ethanol), oxygenates and/or ammonia. Waste fuel streams may also be employed.
The oxygen-containing gas may comprise air, oxygen and/or an air/oxygen mixture. The oxygen-containing gas may be mixed with an inert gas such as nitrogen, helium or argon. Additional feed components such as hydrogen, carbon monoxide, carbon dioxide and steam may also be included.
The first feed stream is preferably fuel-rich with a fuel to oxygen ratio above the stoichiometric ratio required for complete combustion. For example, the fuel to oxygen ratio in the feed may be 1.5 to 4 times, preferably 3 times, the stoichiometric ratio required for complete combustion to carbon dioxide to water.
The gaseous fuel and oxygen-containing gas are contacted with a first catalyst under reaction conditions which are controlled to ensure that some of the oxygen in the first feed stream remains unreacted during step b). The thermal energy produced in step b) heats the unreacted oxygen, thereby providing part of the heat necessary for cracking the hydrocarbon feedstock in step d).
The reaction between the gaseous fuel and oxygen-containing gas may be a combustion reaction. Accordingly, gaseous fuel (eg hydrocarbon) in the first feed stream may react with oxygen to produce a product stream comprising oxides (eg carbon oxides) and water. In such an embodiment, a combustion catalyst is employed as the first catalyst. Suitable combustion catalysts include Group VIII metals such as platinum and/or palladium. The catalyst may comprise 0.1 to 5 wt % and, preferably, 0.25 to 3 wt %, of metal. It will be understood that the metal loadings of the catalyst may be selected to ensure that not all the oxygen in the first feed stream is consumed in step b).
In an alternative embodiment, the gaseous fuel of the first feed stream reacts with the oxygen-containing gas to produce synthesis gas. In this embodiment, a first feed stream comprising a hydrocarbon (e.g., methane) is employed, which reacts with oxygen to produce carbon monoxide and hydrogen. These gaseous products may react exothermically, for example with oxygen, thereby providing a further source of heat to drive the cracking reaction in step d). In this embodiment, the catalyst employed is one which is capable of supporting a synthesis gas production reaction. Suitable catalysts comprise rhodium, platinum, palladium, nickel or mixtures thereof. Preferably, a rhodium catalyst is used. The catalyst may comprise 0.1 to 5 wt % and, preferably, 0.25 to 3 wt %, of metal. As with combustion catalysts, the metal loadings of the catalyst may be varied to ensure that not all the oxygen in the first feed stream is consumed in step b).
In a further embodiment, a gaseous fuel is reacted with an oxygen-containing gas in a combustion reaction, and another gaseous fuel (which may or may not be the same as the first gaseous fuel) is reacted with an oxygen-containing gas to produce synthesis gas. Both these reactions are exothermic, and may provide part of the heat for driving the subsequent cracking reaction in step d). In at least one of these reactions, however, not all of the oxygen-containing gas employed is consumed. At least part of this unreacted oxygen is consumed in step d) to produce the olefin product of the present invention. The first catalysts of present invention may be supported. Suit
Griffiths David Charles
Oehlers Cord
Reid Ian Allan Beattie
BP Chemicals Limited
Finnegan, Henderson Farabow, Garrett and Dunner L.L.P.
Griffin Walter D.
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