Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By alkyl transfer – e.g. – disproportionation – etc.
Reexamination Certificate
2000-01-28
2002-08-20
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By alkyl transfer, e.g., disproportionation, etc.
C585S643000, C585S646000, C585S647000
Reexamination Certificate
active
06437209
ABSTRACT:
This invention relates to a catalytic process for metathesis of olefins in the presence of a stabilizing agent that makes it possible to reduce the deactivation of the catalyst. The invention applies very advantageously when the reaction is carried out in a distillation column that comprises at least one catalytic reactive zone, called reactive distillation column below.
The metathesis of the olefins is a balanced reaction that consists of a statistical redistribution of the alkylidene groups of olefins that are brought together. They have a great deal of practical interest, for example for the rebalancing between one another of the light olefins that are obtained from steam cracking or catalytic cracking (FCC) or optionally a Fischer-Tropsch reaction, such as ethylene, propylene, butenes or pentenes. In a general way, it is catalyzed by the compounds of tungsten, molybdenum or rhenium. Due to its statistical nature, the reaction provides as a product a generally complex mixture that must be fractionated to be able to recycle unconverted reagents in the reactor so as to increase their conversion rate.
The metathesis reaction is usually carried out either in batch mode or continuously by using a reactor in which the catalyst is in the form of a fixed bed, a stirred bed, a fluid bed or a fluidized bed. At the end of the reaction (by batch) or at the outlet of the reactor (continuously), the effluent is directed toward the distillation columns to separate the products and the untransformed reagents. The diagrams of the metathesis processes are therefore generally complex due to the balanced nature of the reaction.
The use of a reactive distillation column in which the metathesis reaction and the separation of the reagents and products is done simultaneously can then in principle have numerous advantages, as is described in U.S. Pat. No. 4,709,115 for the dismutation of butene-1. In this case, the separation in situ, on the one hand of the reagents and products, and on the other hand of products between one another, makes it possible to increase significantly the conversion of the reagents and also the selectivity of the reaction by reducing the possibilities of secondary reactions of the products between one another. The possibility of use of a reactive metathesis distillation is also mentioned in Patent EP 832 867.
It was noted, however, that the metathesis catalysts, whether they are based on tungsten, molybdenum or rhenium, deactivate quickly over time and therefore require frequent regenerations. The regeneration method differs slightly depending on the metal and nearly always comprises at least one calcination phase of the catalyst at high temperature, for example between 400 and 1000° C. This does not pose any particular problem for implementation when the catalyst is placed in a fixed bed in a reactor that is designed accordingly or else transferred from the reactor into a regenerator thanks to a fluid bed or a fluidized bed. In contrast, the frequency of the regenerations considerably reduces the productivity of the installation.
On the contrary, the necessary implementation of frequent regenerations is a virtually insoluble problem if the catalyst is placed inside a distillation column that comprises plates or packing that are intended to promote the liquid-vapor contact. The technology of the reactive distillation thus cannot be applied at the industrial level with the conventional metathesis catalysts.
It has now been found, unexpectedly, that injection continuously, separately or with the metathesis feedstock of an aluminum compound X
q
AIR′
r
makes it possible to reduce considerably the deactivation of the catalyst. Thus, it is possible to consider the implementation of the metathesis either in a conventional reactor with much more spaced regenerations or in a reactive distillation column.
The invention therefore relates specifically to a process for olefin metathesis in the presence of a catalyst or a stabilizing agent that is injected into the reaction medium. This means that the stabilizing agent is injected during the entire course of the metathesis process, whereby the injection takes place continuously or discontinuously.
An object of the invention is more specifically a process for metathesis of olefins, in which an aluminum compound X
q
AIR′
r
—in which X is a radical that is selected from the group that is formed by alkoxides and aryloxides RO—, sulfides RS— and amides R
2
N—; R is a hydrocarbyl radical that contains 1 to 40 carbon atoms; R′ is an alkyl radical that contains 1 to 20 carbon atoms; q and r are equal to 1 or 2 so that the sum of q+r is equal to 3—is injected into the reaction medium.
The stabilizing aluminum compound corresponds to general formula X
q
AIR′
r
. In this formula, X is a radical that is selected from the group that is formed by alkoxides and aryloxides RO—, sulfides RS— and amides R
2
N—, R is a hydrocarbyl radical that contains 1 to 40 carbon atoms, for example, alkyl, cycloalkyl, alkenyl, aryl, substituted aryl or cycloalkyl, preferably a hydrocarbyl radical of 2 to 30 carbon atoms, whereby this radical can be substituted by at least one alkoxy group or at least one halogen. As an example, and without the list being limiting, R can be an ethyl, n-propyl, isopropyl, n-butyl, t-butyl, cyclohexyl, benzyl, diphenylmethyl, phenyl, methyl-2-phenyl, methyl-4-phenyl, methoxy-2-phenyl, methoxy-4-phenyl, dimethyl-2,6-phenyl, diisopropyl-2,6-phenyl, t-butyl-2-phenyl, t-butyl-2-methyl-4-phenyl, di-t-butyl-2,6-phenyl, di-t-butyl-2,6-methyl-4-phenyl, tri-t-butyl-2,4,6-phenyl, phenyl-2-phenyl, diphenyl-2,6-phenyl, fluoro-2-phenyl, fluoro-4-phenyl, pentafluorophenyl radical. In amides R
2
N—, R
2
can constitute with nitrogen a nitrogenous heterocycle, such as pyrrolidine or piperidine. R′ is an alkyl radical that contains 1 to 20 carbon atoms, preferably 1 to 6 carbon atoms, for example, methyl, ethyl, isobutyl, and q and r are equal to 1 or 2 so that the sum of q+r is equal to 3.
As preferred aluminum compounds, those will be cited that correspond to general formula (RO)
q
AIR′
r
, in which R is a hydrocarbyl radical that is selected from the group that is formed by the alkyl, cycloalkyl, alkenyl, aryl, substituted aryl or cycloalkyl radicals, a hydrocarbyl radical of 2 to 30 carbon atoms, whereby this radical can be substituted by at least one alkoxy group or at least one halogen, whereby the aryl and substituted aryl radicals are preferred. R′ is selected from the group that is formed by the methyl, ethyl, isobutyl radicals, whereby the radicals contain 1 to 20 carbon atoms and whereby the radicals contain 1 to 6 carbon atoms.
The more particularly preferred aluminum compounds are selected from the group that is formed by bis-(di-t-butyl-2,6-methyl-4-phenoxy)-isobutyl-aluminum, bis-(di-t-butyl-2,6-methyl-4-phenoxy)-ethyl-aluminum, bis-(di-t-butyl-2,6-methyl-4-phenoxy)-methyl-aluminum.
The preparation of the X
q
AIR′
r
is known in the literature. Any process for preparation of these compounds is suitable. In the case of compounds (RO)
q
AIR′
r
(case where X=RO—), it is possible, for example, to react an alcohol or an ROH phenol with an AIR′
3
trialkylaluminum in an organic solvent, for example a hydrocarbon or an ether.
The injected stabilizing agent therefore plays the role of anti-deactivating agent, i.e., it reduces the deactivation of the catalyst and therefore makes it possible to increase the cycle length between two regenerations of the catalyst, thus considerably reducing the frequency of these regenerations.
The invention pertains to any metathesis catalyst, for example, the catalysts that are used conventionally and that comprise at least one element that is selected from among rhenium, molybdenum and tungsten, whereby rhenium is preferred. Among the conventional catalysts that contain rhenium, it is possible to cite the catalysts that are described in U.S. Pat. Nos. 4,795,734 and 5,449,852.
Metathesis catalysts with a rhenium base that are much more a
Commereuc Dominique
Mikitenko Paul
Dang Thuan D.
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
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