U.S. patent application number 09/493255 was filed with the patent office on 2002-08-29 for process for metathesis of olefins in the presence of a stabilizing agent of the catalyst.
Invention is credited to Commereuc, Dominique, Mikitenko, Paul.
Application Number | 20020120173 09/493255 |
Document ID | / |
Family ID | 9541582 |
Filed Date | 2002-08-29 |
United States Patent
Application |
20020120173 |
Kind Code |
A1 |
Commereuc, Dominique ; et
al. |
August 29, 2002 |
PROCESS FOR METATHESIS OF OLEFINS IN THE PRESENCE OF A STABILIZING
AGENT OF THE CATALYST
Abstract
Catalytic process for metathesis of olefins in the presence of a
catalyst and a stabilizing agent that is injected into the reaction
medium. Application in particular to rebalancing between one
another the light olefins that are obtained from steam cracking or
catalytic cracking (FCC), such as ethylene, propylene, butenes or
pentenes.
Inventors: |
Commereuc, Dominique;
(Meudon, FR) ; Mikitenko, Paul; (Noisy Le Roi,
FR) |
Correspondence
Address: |
Millen White Zelano & Branigan P C
Arlington Courthouse Plaza l
2200 Clarendon Boulevard Suite 1400
Arlington
VA
22201
US
|
Family ID: |
9541582 |
Appl. No.: |
09/493255 |
Filed: |
January 28, 2000 |
Current U.S.
Class: |
585/643 ;
585/645; 585/646; 585/647 |
Current CPC
Class: |
C07C 2523/36 20130101;
C07C 2531/32 20130101; C07C 6/04 20130101; C07C 2531/14 20130101;
Y02P 20/582 20151101; C07C 2523/00 20130101; C07C 2523/28 20130101;
Y02P 20/10 20151101; C07C 2523/30 20130101; Y02P 20/127
20151101 |
Class at
Publication: |
585/643 ;
585/645; 585/646; 585/647 |
International
Class: |
C07C 006/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 29, 1999 |
FR |
99/01.277 |
Claims
1. Process for metathesis of olefins in the presence of a catalyst
and a stabilizing agent that is injected into the reaction medium
to reduce the deactivation of the catalyst:
2. Process for metathesis of olefins according to claim 1,
characterized in that an aluminum compound X.sub.qAIR'.sub.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.sub.2N--; 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.
3. Process for metathesis of olefins according to one of the
preceding claims, wherein the stabilizing agent of the catalyst
corresponds to general formula (RO).sub.qAIR'.sub.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 1 to 40 carbon atoms,
whereby this radical can be substituted by at least one alkoxy
group or at least one halogen, and 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.
4. Process for metathesis of the olefins according to one of the
preceding claims, wherein the stabilizing agent corresponds to
general formula (RO).sub.qAIR'.sub.r, in which R is a hydrocarbyl
radical that is selected from the group that is formed by the aryl
or substituted aryl radicals.
5. Process for metathesis of the olefins according to one of the
preceding claims, wherein the stabilizing agent is selected from
the group that is formed by
bis-(di-t-butyl-2,6-methyl-4-phenoxy)-isobutylaluminum,
bis-(di-t-butyl-2,6-methyl-4-phenoxy)-ethyl-aluminum,
bis-(di-t-butyl-2,6-methyl-4-phenoxy)-methyl-aluminum.
6. Process according to one of the preceding claims, wherein the
process is carried out with a fixed-bed catalyst.
7. Process according to one of claims 1 to 5, wherein the process
is carried out with a fluid-bed or stirred-bed catalyst.
8. Process according to one of claims 1 to 5, wherein the process
is carried out with a fluidized-bed catalyst.
9. Process according to one of claims 1 to 5, wherein the process
is carried out in a reactive distillation column.
10. Process according to one of claims 1 to 5, wherein the process
is carried out in a reactive distillation column, in which the
catalyst is placed so as to be traversed only by a rising flow of
liquid phase.
11. Process for metathesis of olefins according to one of the
preceding claims, wherein the stabilizing agent of the catalyst is
mixed with the olefinic feedstock.
12. Process for metathesis of the olefins according to one of
claims 9 to 11, wherein the stabilizing agent of the catalyst is
injected separately into the reactive distillation column.
13. Process for metathesis of the olefins according to one of the
preceding claims, wherein the catalyst contains at least one
element that is selected from the group that is formed by
molybdenum, tungsten, rhenium.
14. Process for metathesis of olefins according to one of the
preceding claims, wherein the catalyst contains rhenium.
15. Process for metathesis of olefins according to one of the
preceding claims, wherein the catalyst comprises a porous mineral
substrate, 0.01 to 20% by weight of rhenium in oxide form, and 0.01
to 10% by weight of aluminum that is introduced in the form of a
promoter aluminum compound of general formula (RO).sub.qAIR'.sub.r,
in which 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 such that the sum of q+r is equal to
3.
16. Process for metathesis of olefins according to one of the
preceding claims, wherein a feedstock that consists of ethylene and
a butene-2-rich C.sub.4 fraction is brought into contact with the
catalyst to produce propylene.
17. Process for metathesis of olefins according to one of the
preceding claims, wherein a feedstock that consists of ethylene and
a C.sub.5 fraction that is enriched with pentene-2 and
methyl-2-butene-2 is brought into contact with the catalyst to
produce propylene, isobutene and n-butenes.
18. Process for metathesis of olefins according to one of the
preceding claims, wherein a feedstock that consists of propylene
and a C.sub.5 fraction that is enriched with pentene-2 and
methyl-2-butene-2 is brought into contact with the catalyst to
produce isobutene and n-butenes.
19. Process for metathesis of olefins according to one of the
preceding claims, wherein it operates at a temperature of between
-20 and 200.degree. C. and under a pressure of 0.01 to 10 MPa.
20. Process for metathesis of olefins according to one of the
preceding claims, wherein 0.01 to 20% by weight of stabilizing
agent (counted relative to the flow that enters the reactor) is
added during the reaction.
Description
[0001] 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.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] 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.degree. 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.
[0006] 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.
[0007] It has now been found, unexpectedly, that injection
continuously, separately or with the metathesis feedstock of an
aluminum compound X.sub.qAIR'.sub.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.
[0008] 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.
[0009] An object of the invention is more specifically a process
for metathesis of olefins, in which an aluminum compound
X.sub.qAIR'.sub.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.sub.2N--; 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.
[0010] The stabilizing aluminum compound corresponds to general
formula X.sub.qAIR'.sub.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.sub.2N--, 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.sub.2N--,
R.sub.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.
[0011] As preferred aluminum compounds, those will be cited that
correspond to general formula (RO).sub.qAIR'.sub.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.
[0012] The more particularly preferred aluminum compounds are
selected from the group that is formed by
bis-(di-t-butyl-2,6-methyl-4-phenoxy)-is- obutyl-aluminum,
bis-(di-t-butyl-2,6-methyl-4-phenoxy)-ethyl-aluminum,
bis-(di-t-butyl-2,6-methyl-4-phenoxy)-methyl-aluminum.
[0013] The preparation of the X.sub.qAIR'.sub.r is known in the
literature. Any process for preparation of these compounds is
suitable. In the case of compounds (RO).sub.qAIR'.sub.r (case where
X=RO--), it is possible, for example, to react an alcohol or an ROH
phenol with an AIR'.sub.3 trialkylaluminum in an organic solvent,
for example a hydrocarbon or an ether.
[0014] 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.
[0015] 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.
[0016] Metathesis catalysts with a rhenium base that are much more
active than the conventional catalysts have been described in
Patent EP 769 323. They comprise at least three components: a
porous mineral substrate, 0.01 to 20% by weight of rhenium in oxide
form, and 0.01 to 10% by weight of aluminum that is introduced in
the form of a promoter aluminum compound of general formula
(RO).sub.qAIR'.sub.r, in which 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 such that the sum
of q+r is equal to 3, whereby a heat treatment follows the
impregnation.
[0017] In the case of these unconventional metathesis catalysts
with a rhenium base, the aluminum compound of general formula
(RO).sub.qAIR'.sub.r is therefore used both as a catalyst promoter
during its preparation and then injected, preferably continuously,
as a stabilizing agent of this catalyst.
[0018] The description of the preferred catalyst is restated below
as in Patent EP 769 323.
[0019] The porous mineral substrate is advantageously a substrate
with an acidic or neutral nature, more particularly an alumina, a
silica or a silica-alumina that has a specific surface area of 10
to 400 m.sup.2/g. The porous substrate preferably consists of
alumina or a compound that contains at least 75% by weight of
alumina, which is advantageously to have an appreciable surface
area, for example at least 10 m.sup.2/g, and preferably at least 50
m.sup.2/g, an adequate pore volume, for example at least 0.1 ml/g
and preferably 0.3-1 ml/g. It is possible to use, for example, an
alumina of the same type as those of the catalytic reforming
catalysts.
[0020] The precursor of the rhenium compound that is used is
preferably selected from the group that is formed by rhenium
heptoxide, ammonium perrhenate and perrhenic acid. The rhenium
compound can be introduced onto the substrate by, for example,
sublimation in vapor phase or by impregnation in solution. It is
generally preferred to use the method of dry impregnation, where
the rhenium compound is put into solution in the water or in an
organic solvent, for example a hydrocarbon, an alcohol or an ether.
The amount of rhenium on the substrate is regulated by the
selection of the concentration of the impregnation solution,
whereby its amount is such that the volume of this solution is
equal to or slightly less than the pore volume of the solid that is
to be impregnated. When the amount of rhenium that it is desired to
impregnate is greater than that that makes it possible to introduce
a solution at its saturation limit, the operation should be carried
out several times with intermediate drying to eliminate the
impregnation solvent at a temperature of, for example, 90 to
250.degree. C., preferably 100 to 180.degree. C. This makes it
possible to introduce 0.01 to 20%, preferably 0.1 to 15% and even
more advantageously 0.5 to 8% by weight of rhenium (expressed in
metal rhenium).
[0021] After the rhenium precursor is introduced onto the
substrate, drying is carried out at a temperature of, for example,
90 to 250.degree. C., preferably 100 to 180.degree. C., then a
calcination at a temperature of, for example, 250 to 1000.degree.
C., and preferably 300 to 600.degree. C., for a duration of 10
minutes to 10 hours, and preferably 30 minutes to 5 hours. After
calcination, the solid is cooled under a dry and inert atmosphere,
for example, under nitrogen or under argon.
[0022] Promoter aluminum compound (RO).sub.qAIR'.sub.r can be
introduced onto the substrate by any methods that are known to one
skilled in the art, but it is imperative to operate protected from
air and moisture. It is possible to impregnate the substrate by
excess solution that contains the aluminum compound. After a
contact time which can range from several minutes to several days,
the solid is drained and washed with solvent to eliminate the
portion of the compound which is not attached. It is also possible,
in an operating procedure that is preferred, to use the dry
impregnation method. The concentration of aluminum of the solution
is then adjusted based on the amount of aluminum that it is desired
to deposit on the solid, so that the volume of this solution is
equal to or slightly less than the pore volume of the solid that is
to be impregnated. The solvent that is used in this impregnation is
preferably an organic solvent, for example a hydrocarbon or an
ether. This makes it possible to introduce 0.01 to 10%, preferably
0.05 to 5% and even more advantageously 0.1 to 5% by weight of
aluminum (expressed in terms of metal aluminum).
[0023] After the compound of the promoter aluminum is introduced,
the preparation of the catalyst can end with drying, under vacuum
or under a gas stream that is preferably inert, at a temperature of
0 to 1000.degree. C., preferably at a temperature that is close to
ambient temperature, 0 to 50.degree. C. No activation operation,
chemical or thermal, is necessary to trigger the activity of these
catalysts, and calcination is not recommended. It is sufficient to
bring them into contact with an olefin so that the metathesis
reaction starts.
[0024] Instead of preparing the compound (RO).sub.qAIR'.sub.r and
bringing it into contact with the catalyst that is supported with
rhenium, as described above, it is possible to put said catalyst
that is supported with rhenium directly into contact wtih the
precursors of compound (RO).sub.qAIR'.sub.r which are, for example,
ROH and AIR'.sub.3. In the same way as above, the preparation can
end with drying.
[0025] In the metathesis process, the olefins that are able to
react are monoolefins that have 2 to 30 carbon atoms, for example,
ethylene, propylene, butenes, pentenes, hexenes, octenes,
cycloolefins that have 3 to 20 carbon atoms, for example
cyclopentene, cyclooctene, norbornene, polyolefins that have 4 to
30 carbon atoms, for example hexadiene-1,4, octadiene-1,7,
cyclopolyolefins that have 5 to 30 carbon atoms, for example,
cyclooctadiene-1,5, norbornadiene, dicyclopentadiene.
[0026] Other olefins that can react by metathesis are monolefins or
polyolefins that are linear or cyclic and that carry functional
groups, such as, for example, halogens, ethers, nitriles, amines,
amides, silanes or ester groups, such as methyl oleate. The process
can also use in co-metathesis a mixture of the olefins above.
[0027] The metathesis process according to the invention pertains
more particularly to rebalancing between one another of the light
olefins that are obtained from steam cracking or catalytic cracking
(FCC), such as ethylene, propylene, butenes, or pentenes. It makes
it possible, for example, to produce propylene from ethylene and a
butene-2-rich olefinic C.sub.4 fraction, such as a steam-cracking
raffinate-2 that was previously subjected to isomerization after
removal or transformation of butadiene and isobutene. It is also
possible to produce propylene in two stages from a feedstock that
contains butene-1 and butene-2 that provides in a first stage
propylene and pentene-2, whereby the latter is brought into contact
in a second stage with ethylene to provide again propylene as well
as butene-1. It also makes it possible to produce a mixture of
propylene, isobutene, and butene-1-rich n-butenes from ethylene and
a C.sub.5 fraction that is enriched with pentene-2 and methyl-2
butene-2. It also makes it possible to produce a mixture of
isobutene and butene-1-rich n-butenes from propylene and a C.sub.5
fraction that is enriched with pentene-2 and methyl-2 butene-2.
[0028] The process according to the invention can be used with a
catalyst that is placed in a fixed bed, a fluid bed or a stirred
bed, a fluidized bed. The catalyst is advantageously prepared
ex-situ and therefore introduced in prepared form into the reactor.
The process can be carried out in batch mode, continuously or
discontinuously, for example when the flow of the catalyst in a
fluid bed is interrupted for a stage of the process.
[0029] The process can also be implemented by reactive
distillation, whereby the catalytic reaction and the distillation
of the reagents and products take place simultaneously in the
column.
[0030] The reactive distillation column that is used in the process
according to the invention can be of any type. In a preferred
arrangement, at least one zone that contains the catalyst is
arranged. The mechanical arrangement of the catalyst in the
catalytic zone or zones is to be such that it impedes the flow of
vapor and liquid as little as possible between the two separation
zones that enclose it. At the same time, the catalyst is to be used
so that an adequate surface area is exposed to catalyze the
metathesis reaction suitably. The catalyst can be, for example,
used in bulk or in a thin layer on the perforated plates or on
grids or in bags that are suspended or placed on substrates that
ensure their mechanical behavior or any other way that is known to
one skilled in the art. On the other hand, the catalyst can be used
in the column to be traversed only by a rising flow of liquid
phase. It can also be used in the form of catalytic packing,
according to the various known implementations (such as structured
packing). The separation zones that enclose the catalytic zones can
comprise plates or packing. All of the technologies that are
derived from the latter are included here.
[0031] As an example of columns, those that are described in
documents EP-A-0 332 525, FR-A-2 628 737, FR-A-2 684 893, U.S. Pat.
No. 5,221,441 and EP-466 954 will be cited.
[0032] The reactive distillation column is operated under such
conditions as occur both in the metathesis reaction and a
fractionation between the various olefins. For example, the
pressure in the column will be adjusted based on the boiling points
of the reagents and products, and the optimal temperature of use of
the catalyst. The operative temperature can vary from -20 to
200.degree. C., preferably 10 to 100.degree. C., and the pressure
can vary from 0.01 to 10 MPa, preferably 0.1 to 5 MPa.
[0033] These conditions can also be used on other types of reactors
to carry out the metathesis.
[0034] According to the invention, the stabilizing agent is
injected directly (separately) into the reactor, or into the
feedstock that is entering the reactor, or more generally into a
reagent or a recycling flow that enters the reactor or else with
the catalyst in circulation. The injection is carried out
continuously or discontinuously according to needs. It takes place
for the entire time of the metathesis reaction. In general, 0.01 to
20%, and preferably 0.01 to 5% by weight of stabilizing agent and
in particular of aluminum compound (RO).sub.qAIR'.sub.r, counted
relative to the flow that enters the reactor, will be introduced
into the reaction medium.
[0035] As an illustrative example, the process is now described
from FIG. 1, for the production of propylene from ethylene and a
butene-2-rich olefinic fraction C.sub.4 in an implementation with
reactive distillation.
[0036] Reactive column (DR) is arranged, for example, with
alternate reaction and separation zones. It is supplied by the
reagents so that the latter naturally intersect inside due to their
respective boiling points. The fresh ethylene (reagent) is thus
injected via pipe (1) into the bottom of reactive column (DR) while
the feedstock that contains the butene-2-rich olefinic C.sub.4
fraction is introduced into the recycling flow (pipe (9) that comes
into the high zone of the column) via pipe (2). The stabilizing
agent is introduced via a pipe (7) into pipe (9) and is thus
injected with the feedstock.
[0037] At the top of reactive column (DR), an ethylene-propylene
mixture exits via pipe (6). This mixture is separated in
distillation column (C1) from where a flow of ethylene that is sent
to the bottom of column (DR) after mixing with the fresh ethylene
of pipe (1) exits at the top via pipe (5). A small purge for
ensuring the elimination of the traces of ethane that are still
present in the ethylene is carried out by pipe (4). The propylene
that is produced is evacuated via pipe (3) to the bottom of column
(C1).
[0038] At the bottom of reactive column (DR), a section
C.sub.4.sup.+ that comprises all of the saturated and olefinic
C.sub.4 that have not reacted, the C.sub.5 and C.sub.6 by-product
olefins and the stabilizing agent exits via pipe (10).
[0039] A small auxiliary column (C2) that is supplied by pipe (10)
separates at the top a purge C.sub.4 that prevents the accumulation
of isobutane and isobutene via pipe (8) and at the bottom a
recycling flow C.sub.4 via pipe (9). This flow that contains
butenes is recycled to column (DR). A purge of the stabilizing
agent, of which in general at least one portion is degraded and
should be replaced, n-butane and C.sub.5 and C.sub.6 by-product
olefins is ensured via pipe (11).
[0040] In a variant of this diagram, illustrated by FIG. 2, it is
possible to not recycle the stabilizing agent. The C.sub.4
recycling flow that is ensured by pipe (9) is then taken on pipe
(8) at the top of column (C2), whose operation is to be adapted to
this situation. This recycling flow can also be ensured by a
lateral draw-off in column (C2). Pipe (11) at the bottom of column
(C2) ensures no more than a purge function of the stabilizing
agent, n-butane and C.sub.5 and C.sub.6 by-product olefins. The
function of pipe (8) is unchanged, just like the remainder of the
diagram.
[0041] The following examples illustrate the invention without
limiting its scope.
EXAMPLE 1
Comparative
[0042] Preparation of the Catalyst:
[0043] In a first stage, a cubic gamma alumina that has a specific
surface area of 184 m.sup.2/g and a pore volume of 0.67 ml/g is
calcined at 300.degree. C. under air. After cooling to ambient
temperature, 10 g of calcined alumina is sampled. A solution for
the impregnation of rhenium is prepared by diluting 0.24 ml of a
concentrated aqueous solution of perrhenic acid that contains 54%
by weight of rhenium (specific mass: 2.4 g/ml) in 5 ml of water.
This solution is impregnated on the 10 g of alumina that is
sampled. After 30 minutes of contact at ambient temperature, the
solid that is obtained is dried in a drying oven at 120.degree. C.
for one night. It is calcined then dried under a stream of air
(about 20 l/h) by passage through a molecular sieve bed at a
temperature of 550.degree. C. for 2 hours. During the subsequent
cooling period, a stream of dry nitrogen is substituted for the
stream of air. The solid that is obtained is maintained and
manipulated in dry nitrogen atmosphere. Its metal rhenium content
is 3% by weight.
[0044] In a 250 ml flask that is placed under argon atmosphere and
equipped with a bar magnet, a solution of 0.493 g of
triisobutylaluminum in 20 ml of pentane is introduced, and then a
solution of 1.095 g of d-t-butyl-2,6-methyl-4-phenol in 30 ml of
pentane is injected drop by drop while being stirred and at room
temperature. After about 30 hours of reaction, the pentane is
evaporated under a vacuum, and the analysis of the remaining white
solid indicates that it consists essentially of
bis-(di-t-butyl-2,6-methyl-4-phenoxy)-isobutylaluminum. This
compound is put back into solution in 5 ml of heptane.
[0045] The solution in the heptane of
bis-(di-t-butyl-2,6-methyl-4-phenoxy- )-isobutylaluminum is then
impregnated on the solid that contains the rhenium that is obtained
in the first stage. After about 30 minutes of contact, the heptane
that is absorbed into the solid is eliminated by evaporation under
a vacuum at ambient temperature. A metathesis catalyst that
contains 3% by weight of rhenium and 0.67% by weight of aluminum
(in addition to the aluminum that is included in the alumina),
which is kept in a dry and inert atmosphere before use, is thus
obtained.
[0046] Use of the Propylene in Metathesis:
[0047] Examples 1 and 2 relate to the metathesis of propylene for
providing ethylene and butene-2. This reaction that is easy to use
since it requires only a single reagent is the opposite of the
reaction that is described in Example 3 that produces propylene
from ethylene and butene-2. The deactivation of the catalyst is the
same in these two reactions.
[0048] In a reactor that consists of a stainless steel tube that is
equipped with a double jacket with water circulation that makes
possible the regulation of the temperature, the catalyst that is
prepared above is loaded into the fixed bed that is protected from
air and moisture. Liquid propylene is injected using a pump through
the bottom of the reactor, with a flow rate of 49.6 g/h. The
temperature is adjusted to 35.degree. C., and the pressure is kept
at 3.5 MPa using a regulator that is placed downstream from the
reactor. Under these conditions, the conversion of the propylene at
the outlet of the reactor is initially 30% into an equimolar
mixture of ethylene and butene-2. It evolves over time as indicated
in Table 1. The catalyst lost half of its activity at the end of 30
hours.
EXAMPLE 2
[0049] Preparation of the Catalyst:
[0050] A second feedstock of 10 g of catalyst is prepared according
to the operating procedure that is described in Example 1.
[0051] Use of the Propylene in Metathesis:
[0052] The same reactor and the same procedures as in Example 1 are
used. Unlike Example 1, however, the metathesis feedstock consists
of liquid propylene that is mixed with 0.24% by weight of
bis-(di-t-butyl-2,6-methy- l-4-phenoxy)-isobutylaluminum. The
bis-(di-t-butyl-2,6-methyl-4-phenoxy)-i- sobutylaluminum was
prepared as described in Example 1. The metathesis feedstock is
injected using a pump through the bottom of the reactor, with a
flow rate of 49.6 g/h. The temperature is adjusted to 35.degree.
C., and the pressure is kept at 3.5 MPa. Under these conditions,
the conversion of the propylene at the outlet of the reactor is
initially 30% of an equimolar mixture of ethylene and butene-2. It
evolves over time as indicated in Table 1. The catalyst lost only
16% of its activity at the end of 30 hours.
1 TABLE 1 Conversion of propylene (%) Time (h) Example 1 Example 2
0 30 30 10 25.8 28.9 20 20.3 27.4 30 14.6 25.6
[0053] This example illustrates the beneficial effect that is
provided by continuous injection with the feedstock of
bis-(di-t-butyl-2,6-methyl-4-p- henoxy) -isobutylaluminum.
EXAMPLE 3
[0054] The methathesis reaction is carried out in a reactive
distillation column. The column consists of a stainless steel drum
that has an inside diameter of 5 cm and a height of 250 cm, filled
with three packing beds or, in order starting from the bottom: a
distillation packing bed over a height of 100 cm, a catalytic
packing bed over 50 cm and a distillation packing bed over 100 cm.
Each bed is supported by a V-shaped grid, made integral with the
drum.
[0055] The distillation packing is an unstructured packing that
consists of metal elements that have the appearance of
approximately helicoidal springs with contiguous coils, a length of
3 mm and a diameter of 1 mm, known under the name of Dixon, and
known to be efficient in distillation.
[0056] The catalytic packing consists of the distillation packing
that is defined above and catalyst that is prepared according to
the operating procedure that is described in Example 1. The
catalytic packing is obtained by mixing these two components, at a
ratio of one volume of catalyst in the form of balls of a mean
diameter that is equal to 2 mm, and 25 distillation packing
volumes. This mixture is stirred by hand in a glass container to
make the distribution of the catalyst homogeneous in the
distillation packing.
[0057] The column is connected at the bottom to a boiler that is
heated electrically and at the top to a condenser and a reflux
flask. It is made adiabatic by compensation of heat losses, using
ten heating elements that are arranged over its entire height. Each
heating element is controlled separately so that the temperature in
the immediate vicinity of the outside wall of the column is equal
to the one that is established inside the column, on the same side.
Further, the column is equipped with sensors and instruments that
are necessary for the regulation of the operating parameters.
[0058] The column that is thus equipped is operated continuously
under a pressure of 2 MPa. It is supplied at the catalytic packing
at a rate of 265 g/h by an olefinic fraction that consists
primarily of butene-2 (77.3% by weight) and butane, in which
bis-(di-t-butyl-2,6-methyl-4-pheno- xy)-isobutylaluminum is
dissolved at a rate of 0.24% by weight.
Bis-(di-t-butyl-2,6-methyl-4-phenoxy)-isobutylaluminum was prepared
as described in Example 1. At low catalytic packing, the column
receives ethylene with a flow rate of 670 g/h. The heating of the
column is regulated so as to separate ethylene and propylene at the
top. The reflux rate is set at 1.8.
[0059] Under these conditions, after steady operation of the column
is achieved, on the one hand 870 g/h of distillate that consists
primarily of propylene that has formed (34.4% by weight) and
ethylene that has not reacted, and on the other hand 61 g/h of
residue that consists of the butane that has remained inert in the
reaction and the stabilizing agent are collected.
[0060] The distillate that is collected and redistilled according
to a known procedure would ultimately provide 300 g/h of propylene
and 570 g/h of ethylene which would be for recycling in the
reactive distillation column.
* * * * *