Chemistry of hydrocarbon compounds – Saturated compound synthesis – By alkyl transfer – e.g. – disproportionation – etc.
Reexamination Certificate
2002-01-09
2004-04-27
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Saturated compound synthesis
By alkyl transfer, e.g., disproportionation, etc.
Reexamination Certificate
active
06727397
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for the manufacture of alkanes by a catalytic reaction employing methane with at least one other alkane.
Alkanes, such as methane, are generally products which are difficult to employ because of their chemical inertia. Nevertheless, the conversion of alkanes into other alkanes is known. Hydrogenolysis reactions, which consist of cleavage or opening reactions of a carbon-carbon bond by hydrogen, are known, for example. Isomerization reactions, which convert an alkane into one of its isomers, for example n-butane into isobutane, are also known. All these reactions are generally carried out at relatively high temperatures and in the presence of catalysts based on metals, in particular on transition metals, in the bulk form or in the form of films or alternatively in the form of metal particles deposited on inorganic supports essentially based on metal oxide or refractory oxide. Thus, for example, the catalyst can be of the following types: nickel black, Ni/SiO
2
, platinum black Pt/SiO
2
, Pd/Al
2
O
3
, or tungsten or rhodium film, optionally mixed with copper, tin or silver. With some metal catalysts, it was possible simultaneously to observe alkane homologation reactions, which consist of reactions which convert alkanes into higher homologous alkanes. However, alkane homologation reactions are generally very minor reactions in comparison with the hydrogenolysis or isomerization reactions and their results are very poor.
Nevertheless, it remains the case that a process for the conversion of an alkane into one of its homologues would constitute a means for enhancing these alkanes in value, in particular methane. It is known that, as a general rule, alkanes of low molecular weight cannot be exploited to any great extent in chemistry or petrochemistry, other than as fuels, whereas heavier alkanes are often of greater commercial interest, such as, for example, to increase the octane number of engine fuels or alternatively to involve these heavier alkanes in thermal or thermal catalytic cracking or steam cracking reactions in order to manufacture, for example, olefins or dienes.
In this sense, Patent Application PCT/FR 97/01266 discloses a process for the metathesis of alkanes. A metathesis is a double decomposition reaction of two identical or different compounds which forms two new compounds by a double recombination. In this case, at least one alkane is reacted with itself or several alkanes with one another in the presence of a solid catalyst comprising a metal hydride grafted to and dispersed over a solid oxide. Thus, the metathesis reaction is carried out in the presence of this metal hydride by cleavage and recombination of the carbon-carbon bonds, converting an alkane simultaneously into its higher and lower homologues. The reaction can be written according to the following equation (1):
2C
n
H
2n+2
→C
n−i
H
2(n−i)+2
C
n+i
H
2(n+i)+2
(1)
where i=1, 2, 3, . . . n−1 and n can range from 2 to 30 and even beyond.
The catalyst used is a catalyst based on metal hydride and comprises a transition metal chosen in particular from those from groups 5 and 6 of the Table of the Periodic Classification of the Elements (as defined by IUPAC in 1991 and illustrated in “Hawley's Condensed Chemical Dictionary”, 12
th
edition, by Richard J. Lewis, Sr., published by Van Nostrand Reinhold Company, New York, 1993), such as, in particular, tantalum, chromium or tungsten. The preparation of the catalyst comprises a stage of hydrogenation of an organometallic precursor comprising a transition metal dispersed over and grafted to a solid oxide beforehand, so that the transition metal is reduced to an oxidation state lower than its maximum value, thus resulting in the metal hydride. However, as in any metathesis of alkanes, in particular carried out in the presence of this metal hydride, higher and lower homologous alkanes are simultaneously manufactured, by cleavage and recombination reactions of carbon-carbon bonds, employing at least C
2
alkanes (ethane).
SUMMARY OF THE INVENTION
A novel process for the manufacture of alkanes has now been found which makes use of a reaction resulting from bringing methane into contact with at least one other starting alkane in the presence of a catalyst capable of catalysing a metathesis of alkanes. The process has the advantage of enhancing the value of methane, which is available in large amounts on the market and is known for being used essentially as a fuel. Finally, the process makes possible the direct manufacture of the desired product without forming a large number of by-products and thus makes it possible to avoid or to cut back on lengthy and expensive operations for the separation and isolation of the desired product.
A subject-matter of the invention is therefore a process for the manufacture of alkanes, characterized in that it comprises, as main stage, a reaction resulting from bringing methane into contact with at least one other starting alkane (A) in the presence of a catalyst based on a metal M capable of catalysing a metathesis of alkanes, which reaction results in the formation of at least one or two final alkanes (B) having a number of carbon atoms less than or equal to that of the starting alkane (A) and at least equal to 2.
DETAILED DESCRIPTION OF THE INVENTION
More particularly, a catalytic reaction is carried out which results from bringing methane into contact with at least one other starting C
n
alkane (A) (that is to say, comprising n carbon atoms), with n being equal to at least 2, preferably to at least 3, so that the reaction results in the formation of at least one or two final C
2
to C
n
alkanes (B) (that is to say, having a number of carbon atoms ranging from 2 to n).
The reaction can be written according to one or more of the following equations (2):
in which equation (2) n is an integer at least equal to 2, preferably at least equal to 3, and a is an integer ranging from 1 to n−1.
Thus, the process of the invention comprises, as main stage, one or more reactions resulting from bringing methane into contact with at least one other starting alkane (A), the mechanisms of which reactions have not yet been clearly determined. This is because it is particularly surprising to find that methane, which does not comprise a carbon-carbon bond, can react directly or indirectly with another starting alkane (A) in the presence of a catalyst capable of catalysing a reaction for the metathesis of alkanes by cleavage and recombination of the carbon-carbon bonds. The reaction employed in the process of the present invention is carried out by simply bringing methane into contact with at least one other starting alkane (A) in the presence of a catalyst for the metathesis of alkanes and under relatively mild conditions, as described a little later.
The starting alkane (A) can be a substituted or unsubstituted acyclic alkane, that is to say composed of a linear or branched but unclosed carbon-comprising chain. It can correspond to the general formula:
C
n
H
2n+2
(3)
in which n is an integer ranging from 2 to 60 or from 3 to 60, preferably from 3 to 50, in particular from 3 to 20.
The starting alkane (A) can also be a cyclic alkane or cycloalkane substituted in particular by a linear or branched carbon-comprising chain, for example by an alkyl radical. It can correspond to the general formula:
C
n
H
2n
(4)
in which n is an integer ranging from 5 to 60, preferably from 5 to 20, in particular from 5 to 10.
Use may be made of one or more starting alkanes (A) such as those described above.
More particularly, the starting alkane (A) can be chosen from C
3
to C
10
or C
3
to C
17
alkanes, for example propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, n-heptane, n-octane, n-nonane and n-decane.
Thus, for example, in the process of the present invention, methane can be brought into contact with propane to form ethane or alternatively methane can be brought into cont
Basset Jean-Marie
Coperet Christophe
Lefort Laurent
Maunders Barry Martin
Maury Olivier
BP Chemicals Limited
Dang Thuan D.
Finnegan, Henderson Farabow, Garrett and Dunner L.L.P.
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