Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By addition of entire unsaturated molecules – e.g.,...
Reexamination Certificate
2001-08-30
2004-05-18
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By addition of entire unsaturated molecules, e.g.,...
C585S532000, C585S533000
Reexamination Certificate
active
06737555
ABSTRACT:
The present invention relates to a process for oligomerizing C
6
-olefins, in particular for preparing C
12
-olefins by dimerization.
Processes for the oligomerization of olefins are known. DE-A-43 39 713 describes a process for oligomerizing olefins to give highly linear oligomers. In this process, C
2-6
-olefins are reacted at superatmospheric pressure and elevated temperature over a fixed-bed catalyst comprising from 10 to 70% by weight of nickel oxide, from 5 to 30% by weight of titanium dioxide and/or zirconium dioxide, from 0 to 20% by weight of aluminum oxide as significant active constituents and silicon dioxide as the remainder.
U.S. Pat. No. 4,959,491 describes a process for dimerizing C
6
-olefins to form C
12
-olefins which can be used for preparing surfactants. Catalyst used are nickel-containing catalysts such as hexafluoro-acetoacetylnickel(cyclooctadiene).
DE-A-39 14 817 describes a process for oligomerizing C
2-8
-olefins, in which the reaction is carried out over nickel-exchanged montmorillonite, a nickel-aluminum-silicon oxide catalyst or nickel-impregnated molecular sieves or zeolites. The olefin mixture used is passed over a molecular sieve prior to the catalytic reaction.
A disadvantage of the known processes is that the catalyst life is frequently too short. The catalyst is, in particular, clogged by higher oligomers and therefore loses its activity.
It is an object of the present invention to provide a process for oligomerizing C
6
-olefins which avoids the disadvantages of the known processes.
We have found that this object is achieved by a process for oligomerizing C
6
-olefins by reaction of a C
6
-olefin-containing reaction mixture over a nickel-containing fixed-bed catalyst, wherein the reaction over the fixed-bed catalyst is run at a conversion to oligomerized C
6
-olefins of not more than 30% by weight, based on the reaction mixture.
The reaction over the fixed-bed catalyst is preferably carried out at a conversion of from 10 to 30% by weight, particularly preferably from 10 to 25% by weight, based on the reaction mixture. The oligomerization is preferably essentially a dimerization.
According to the present invention, it has been found that deactivation of the catalyst can be avoided and the dimer selectivity can be increased if the conversion over the catalyst is in the range indicated. The process can be carried out batchwise or continuously. It is preferably carried out continuously in the liquid phase. The conversion is then based on a throughput of the reaction mixture through the catalyst.
The reaction is preferably carried out at from 30 to 300° C. and a pressure in the range from 10 to 300 bar.
In order to achieve a high total conversion in the process, part of the unreacted reaction mixture obtained can, after separating off the oligomers, be returned to the reaction. Adjustment of the recycled amount of reaction mixture enables very high total conversions to be achieved. The term “oligomers” includes dimers and higher-boiling compounds.
The process of the present invention makes it possible to realize a total conversion of over 90% together with a C
12
selectivity of over 80%. Adherence to the conversion specified according to the present invention over the catalyst (based on a single pass) greatly increases the operating life of the catalyst, since the formation of high-boiling compounds which can deposit on the catalyst and thus cause a drop in activity is suppressed.
C
6
-olefins which are suitable for use in the process of the present invention can be synthesized on an industrial scale by methods such as propylene dimerization. The most important industrial propylene dimerization processes are described, for example, in A. Chauvel and G. Lefebvre, Petrochemical Process, Edition Technip (1989), pp. 183 to 187 and F. Asinger, Die petrochemische Industrie, Akademier-Verlag (1971), pp. 278 to 299. The oligomerization is carried out industrially in the presence of either homogeneous or heterogeneous catalysts. The heterogeneous catalysts which can be used are listed in, for example, C.T. O'Connor et al., Catalysis Today Vol. 6 (1990), pp. 329 to 349.
The most important, based on the amount produced, homogeneously catalyzed process is the Dimnerol-G process of IFP. It is described in detail in Erdöl, Erdgas and Kohle, number 7/8, July/August 1990, pp. 309 to 315. The product obtained by means of this process (known as “Dimate”) has the following average olefin
C
3
:
4%
by weight
C
6
:
73%
by weight
C
9
:
17%
by weight
C
12
:
4%
by weight
C
15+
:
2%
by weight
The C
6
fraction is composed of:
4-methyl-1-pentene:
0.9%
by weight
2,3-dimethyl-1-butene:
2.3%
by weight
cis-4-methyl-2-pentene:
3.1%
by weight
trans-4-methyl-2-pentene:
21.7%
by weight
2-methyl-1-pentene:
5.0%
by weight
1-hexene:
0.3%
by weight
trans-3-hexene:
4.4%
by weight
cis-3-hexene:
0.7%
by weight
trans-2-hexene:
13.6%
by weight
2-methyl-2-pentene:
39.2%
by weight
cis-2-hexene:
3.7%
by weight
2,3-dimethyl-2-butene:
4.8%
by weight
Another source of C
6
-olefins is provided by metathesis processes.
Possible catalysts are generally nickel-containing catalysts known per se which give little branching, as are described, for example, in Catalysis Today vol. 6 (1990), pp. 336 to 338, DE-A43 39 713, U.S. Pat. No. 5,169,824, DD2 73 055, DE-A-20 51 402, EP-A-0 202 670, Appl. Catal. 31 (1987), pages 259 -266, EP-A-0 261 730, NL 8 500 459, DE-A-23 47 235, U.S. Pat. No. 5,134,242, EP-A-0 329 305, U.S. Pat. Nos. 5,146,030, 5,073,658, 5,113,034 and 5,169,824.
In a preferred embodiment of the process of the present invention, the oligomerization is carried out in the liquid phase using the catalysts described in DE-A 43 39 713.
The catalysts described there consist essentially of nickel oxide, silicon oxide, titanium oxide and/or zirconium oxide and, if desired, aluminum oxide and have a nickel oxide content of from 10 to 70% by weight, a content of titanium dioxide and/or zirconium dioxide of from 5 to 30% by weight and an aluminum oxide content of from 0 to 20% by weight, with the remainder being silicon dioxide. They are obtainable by precipitation of the catalyst composition at a pH of from 5 to 9 by addition of an aqueous solution of nickel nitrate to an alkali metal water glass solution containing titanium oxide and/or zirconium dioxide, filtration, drying and heating at from 350 to 650° C.
The catalysts preferably contain essentially from 10 to 20% by weight of titanium dioxide, from 0 to 10% by weight of aluminum oxide and from 40 to 60% by weight of nickel oxide as main constituent and active component and silicon dioxide as the remainder.
Especially preferred catalysts have the composition 50% by weight of NiO, 34% by weight of SiO
2
, 3% by weight of Al
2
O
3
and 13% by weight of TiO
2
. They are largely free of alkali metals (Na
2
O content <0.3% by weight).
The catalysts are preferably arranged in a fixed bed and are therefore preferably in the form of discrete bodies, e.g. in the form of pellets (5 mm ×5 mm, 5 mm ×3 mm, 3 mm ×3 mm), rings (7 mm ×7 mm ×3 mm, 5 mm ×5 mm ×2 mm, 5 mm ×2 mm ×2 mm) or extrudates (1.5 mm diameter, 3 mm diameter, 5 mm diameter).
In the process of the present invention, preference is given to reacting a hydrocarbon stream comprising n-hexene and/or methylpentene, preferably in the liquid phase, over the abovementioned Ni-containing catalysts.
Suitable C
6
-hydrocarbons are, for example, mixtures having the following composition:
paraffin:
from 10 to 90% by weight
olefin:
from 10 to 90% by weight,
where the olefin fraction can have the following composition:
n-hexenes:
preferably from 0.1 to 99.8% by weight
methylpentenes:
preferably from 0.1 to 99.8% by weight
dimethylbutenes:
preferably from 0.1 to 99.8% by weight
The hydrocarbon streams used are advantageously freed of oxygen-containing compounds such as alcohols, aldehydes, ketones or ethers by adsorption using a protective bed such as molecular sieves, aluminum oxides, aluminum oxide-containing solids, aluminum phosphates, silico
Brox Wolfgang
Maas Heiko
Schulz Ralf
Schwab Peter
Walter Marc
BASF - Aktiengesellschaft
Dang Thuan D.
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