Catalyst and process for olefin oligomerization

An improved catalyst composition is obtained by contacting at least one bivalent nickel compound with at least one hydrocarbyl aluminum halide, at least one Bronsted organic acid and at least one anhydride of a carboxylic acid. The composition can be used as a catalyst for olefin oligomerization.

BACKGROUND OF THE INVENTION 
The present invention relates to an improved catalytic composition and its 
use as an oligomerization catalyst, particularly as a dimerization or 
trimerization catalyst, for monoolefins. The invention more specifically 
concerns certain compositions obtained by contacting, in any order, at 
least one bivalent nickel compound with at least one hydrocarbyl aluminum 
halide, at least one Bronsted organic acid and at least one anhydride of a 
carboxylic acid. 
It is already known to prepare catalysts for dimerizing or co-dimerizing 
monoolefins such as ethylene, propylene or n-butenes, particularly by 
reacting bivalent nickel carboxylates with hydrocarbyl aluminum halides. 
The use of these catalysts is however sometimes objectionable since, in 
continuous operations, the activity is often lower than in batch 
operations and this activity also tends to decrease in the course of time. 
A first improvement has been obtained by associating a bivalent nickel 
compound with a hydrocarbyl aluminum halide and a compound having Bronsted 
acid properties, as disclosed in the published French patent application 
No. 2 443 877, corresponding to U.S. Pat. No. 4,283,305. 
SUMMARY OF THE INVENTION 
It has now surprisingly been found, and this is an object of the present 
invention, that the addition of an anhydride of carboxylic acid to the 
above association of a bivalent nickel compound with a hydrocarbyl 
aluminum halide and a compound having Bronsted acid properties leads to a 
catalytic composition which is more active than the association of the 
above three compounds: the total amount of catalytic composition necessary 
to obtain a given conversion rate of the olefins is lower and the 
proportion of hydrocarbyl aluminum halide can be decreased with respect to 
the amount of nickel compound. 
DETAILED DISCUSSION 
The nickel compound may consist of one or more bivalent nickel compounds of 
any type, preferably those having a solubility of at least 1 g per liter 
in a hydrocarbon medium (for example in n-heptane at 20.degree. C.), and 
more particularly in the reactants or the reaction medium, preferably 
carboxylates of the general formula (RCOO).sub.2 Ni wherein R is 
hydrocarbyl, for example alkyl, cycloalkyl, alkenyl, aryl, aralkyl or 
alkaryl having up to 20 carbon atoms, preferably a hydrocarbyl group 
having from 5 to 20 carbon atoms. The two radicals R may also constitute 
an alkylene group, having preferably from 6 to 18 carbon atoms. The 
following bivalent nickel salts are examples of nickel compounds: octoate, 
2-ethyl hexanoate, decanoate, stearate, oleate, salicylate, 
acetylacetonate, hydroxydecanoate. Many other examples can be found in the 
literature and the patents and the invention is not limited to the sole 
examples given above. The radical R may be substituted with 1 to 4 or more 
halogen atoms, hydroxy, ketone, nitro, cyano groups or other groups which 
do not impede the reaction. 
The hydrocarbyl aluminum halides are of the general formula AlR.sub.x 
X.sub.y wherein R is a hydrocarbon group having, for example, up to 12 
carbon atoms, such as alkyl, aryl, aralkyl or cycloalkyl; X represents 
halogen, F, Cl, Br, I and x has a value from 1 to 1.5, y a value from 1.5 
to 2, with x+y=3; preferably x=1 and y=2. Examples of these compounds are 
ethyl aluminum sesquichloride, dichloroethylaluminum and 
dichloroisobutylaluminum. 
The Bronsted acid is a compound of the formula HX, wherein X is an organic 
anion, for example a carboxylic, sulfonic or phenolic anion. The acids 
having a pKa at 20.degree. C. of at most 3 are preferred, particularly 
those soluble in the nickel compound or in its solution in a hydrocarbon 
or other appropriate solvent, at the desired concentration, and which do 
not contain phosphorus. A preferred group of acids includes the 
halogenocarboxylic acids of the formula R.sub.1 COOH, wherein R.sub.1 is a 
haloalkyl radical, particularly those having at least one halogen atom in 
.alpha. to the COOH group, with a total of 2 to 10 carbon atoms. A 
preferred group of acids comprises the halogenocarboxylic acids of the 
formula R.sub.1 COOH wherein R.sub.1 is a halogenoalkyl group having from 
1 to 3 carbon atoms, of the formula C.sub.m H.sub.p X.sub.q, wherein X is 
halogen, F, Cl, Br, I, m=1, 2 or 3, p is zero or an integer and q is an 
integer, provided that p+q= 2m+1. There is preferably used a 
halogenoacetic acid of the formula R.sub.2 COOH wherein R.sub.2 is a 
halogenomethyl radical of the formula CX.sub.n H.sub.3-n, where X is 
halogen, F, Cl, Br, I with n being an integer from 1 to 3. In the above 
formulas, the preferred halogen is F. Useful acids are trifluoroacetic 
acid, monofluoroacetic acid, trichloroacetic acid, tribromoacetic acid, 
monobromoacetic acid, triiodoacetic acid, monoiodoacetic acid, 
pentafluoropropionic acid, 2-fluoropropionic acid, heptafluorobutyric acid 
or 2-chlorobutyric acid. Other useful acids are, for example, arylsulfonic 
acids, alkylsulfonic acids, picric acid, nitroacetic acid, nitrobenzoic 
acid or cyanacetic acid. These examples constitute no limitation. 
The anhydride of a carboxylic acid is a compound of the formula (R.sub.3 
CO).sub.2 O wherein R.sub.3 is a hydrocarbon group having up to 20 carbon 
atoms, preferably 5 to 20 carbon atoms, such as alkyl, aralkyl or 
cycloalkyl which is--or not--substituted in .alpha. of the anhydride group 
with one or more halogen atoms, F, Cl, Br, I. A preferred group of 
anhydrides comprises compounds of the formula (R.sub.2 CO).sub.2 O wherein 
R.sub.2 is defined as above. Non limitative examples are: octoic, 2-ethyl 
hexanoic, decanoic, stearic, oleic, trifluoroacetic, monofluoroacetic, 
trichloroacetic, monochloroacetic, pentafluoropropionic and 
heptafluorobutyric anhydrides. The R.sub.2 and R.sub.3 groups forming part 
of the anhydride formula may be identical (symmetrical anhydrides) or not 
(dissymmetrical anhydrides). 
The invention has also for object a process for oligomerizing monoolefins 
in the presence of the above catalytic system, at a temperature of 
-20.degree. C. to +60.degree. C., under such pressure conditions that the 
reactants are maintained, at least in major part, in liquid or condensed 
phase. 
Monoolefins which can dimerize or oligomerize are, for example, ethylene, 
propylene, n-butenes, n-pentenes, either pure or as mixtures, such as 
those obtained by synthesis processes, for example, steam-cracking or 
catalytic cracking. They can co-dimerize or co-oligomerize as mixtures or 
with isobutene, for example ethylene with propylene and n-butenes, 
propylene with n-butenes, n-butenes with isobutene. 
The concentration, expressed as nickel, of the catalytic composition in the 
liquid oligomerization phase is normally between 5 and 200 parts per 
million by weight. The molar ratio of the hydrocarbyl aluminum halide to 
the nickel compound is normally from 1:1 to 30:1 and more advantageously 
from 2:1 to 15:1. The molar ratio of the Bronsted acid to the aluminum 
compound is from 0.001:1 to 1:1, preferably from 0.01:1 to 0.5:1. The 
preferred value of the molar ratio of the Bronsted acid to the nickel 
compound is from 0.25:1 to 5:1. The molar ratio of the anhydride of 
carboxylic acid to the nickel compound is advantageously from 0.001:1 to 
1:1, preferably from 0.01:1 to 0.5:1. 
The process can be operated in a reactor with one or more serially arranged 
reaction stages; the olefinic charge and/or the constituents of the 
catalytic system are introduced continuously, either into the first stage 
or into the first and anyone of the stages; or only one, two or three 
constituents of the catalytic mixture are introduced into the second 
and/or the n.sup.th stage. 
When discharged from the reactor, the catalyst can be deactivated, for 
example with ammonia and/or an aqueous sodium hydroxide solution or an 
aqueous sulfuric acid solution. The unconverted olefins and the alkanes 
are then separated from the oligomers by distillation.

The following examples are given by way of illustration and do not limit 
the invention in any respect. 
EXAMPLE 1 
An oligomerization reactor comprises two serially arranged reaction stages, 
each consisting of a 0.25 liter cylindrical steel reactor having a double 
jacket and a heat regulation by water circulation. 
The first stage reactor is continuously fed with a C.sub.4 cut whose 
composition is: 
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propane: 1.1 (% b.w.) 
isobutane: 6.7 
n-butane: 23.0 
1-butene: 5.2 
trans 2-butene: 46.4 
cis 2-butene: 17.6 
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and with 0.19 g/h of dichloroethylaluminum as a solution in isohexane, 
0.054 g/h of a nickel 2-ethylhexanoate solution (11% b.w. nickel content), 
0.011 g/h of trifluoroacetic acid and 0.001 g/h of trifluoroacetic 
anhydride, the latter three components being introduced as a common 
solution in isohexane. The reactor pressure is maintained at 5 bars by 
continuous discharge of the reaction product and the temperature at 
42.degree. C. by means of a thermostatic bath. 
After 4 hours, steady running is observed, corresponding to a 64% 
conversion of butenes at the outlet of the first stage and 76% at the 
outlet of the second stage. The products consist essentially of butenes 
dimers, trimers and tetramers. The yield of dimers, trimers and tetramers 
is 97%, including the recovered butene. 
EXAMPLE 2 
This example is not part of the invention and is given by way of 
comparison. 
The apparatus and the operating conditions were the same as in Example No. 
1; the C.sub.4 cut and the constituents of the catalyst were introduced at 
the same feed rates, except that trifluoroacetic anhydride was not 
present. 
After 4 hours of run, steady conditions were obtained, the butenes 
conversion being 57% at the outlet of the first stage and 72% at the 
outlet of the second stage. The dimers, trimers and tetramers yield, as 
defined in example No. 1, was 95%. 
EXAMPLE 3 
The apparatus and the operating conditions were the same as in example No. 
1; the C.sub.4 cut and the constituents of the catalyst were introduced at 
the same feed rates, except that trifluoroacetic acid and trifluoroacetic 
anhydride were introduced at the respective feed rates of 0.001 and 0.008 
g/h. 
After 4 hours of run, steady conditions were obtained, the butenes 
conversion being 65% at the outlet of the first stage and 77% at the 
outlet of the second stage. The yield of dimers, trimers and tetramers, as 
defined in example No. 1, was 96%. 
EXAMPLE 4 
The apparatus and the operating conditions were the same as in example No. 
1; The C.sub.4 cut and the nickel compound were introduced at the same 
feed rate. 0.23 g/h of dichloroisobutylaluminum as a solution in 
isohexane, 0.0157 g/h of trichloroacetic acid and 0.00145 g/h of 
trichloroacetic anhydride were also introduced, the latter two compounds 
as a solution in isobutane. 
After 4 hours of run, steady conditions were obtained, corresponding to a 
butene conversion of 63% at the outlet of the first stage and 75% at the 
outlet of the second stage. The dimers, trimers and tetramers yield, as 
defined in example No. 1, was 96%. 
EXAMPLE 5 
The apparatus was the same as in example No. 1; the first stage reactor was 
continuously fed with 80 g/h of a C.sub.3 cut of the following 
composition: 
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propane: 
25% b.w. 
propylene: 
75% b.w. 
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and with 0.053 g/h of ethylaluminum sesquichloride as a solution in 
isooctane, 0.019 g/h of a solution of nickel 2-ethylhexanoate in isooctane 
(11% b.w. of nickel), 0.004 g/h of trifluoroacetic acid and 0.00095 g/h of 
the anhydride of 2-ethylhexanoic acid, the latter two components being 
introduced simultaneously as a solution in isooctane. The reactor pressure 
was 15 bars and the temperature 42.degree. C. 
After 4 hours of run, steady conditions were obtained, the propylene 
conversion being 85% at the outlet of the first stage and 94% at the 
outlet of the second stage. The products consisted essentially of 
propylene dimers, trimers and tetramers. The yield was 97%, including the 
recovered propylene.