Catalyst for oligomerization of alpha-olefins

A catalyst composition for use in oligomerization of olefins contained in refinery distillate streams including paraffins, naphthenes, and aromatics therein, the catalyst consisting of a first constituent which is at least one aluminum halide; and a second constituent which is at least one alkoxide of a transition metal of Group IVB of the Periodic Table and which has a general formula: EQU M(OR).sub.4, where M is selected from the group consisting of metals of Group IVB of the Periodic Table and R is one of (a) an alkyl group having from 1-12 carbon atoms or (b) an alkylaryl group having an alkyl chain having from 1-12 carbon atoms.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to a novel catalyst composition comprised 
of an aluminum halide and a metal alkoxide belonging to group IVB, for 
selectively oligomerizing olefins, present in a mixture of olefins, 
aromatics, paraffins and cycloparaffins, to polyolefins in good yields. A 
particular application of the invention is oligomerization of olefins 
contained in cracked refinery distillate streams to give polyolefins 
which, after the steps of distillation and stabilization by hydrogenation, 
give oligomers suitable for use as lubricating oil base stocks. 
2. Description of the Related Art 
Synthetic oil base stocks having viscosities of about 4 to 30 cSt or above 
at 100.degree. C. have been prepared in the prior art by oligomerization 
of olefins by conventional or modified Friedel-Craft catalysts. Thus, by 
contacting the alpha-olefins with boron trifluoride containing various 
promoters, synthetic oils suitable for lubricant use have been prepared, 
such as described in U.S. Pat. Nos. 4,400,565; 5,068,487 and 5,191,140. 
However, boron trifluoride is a pulmonary irritant and is fast being 
replaced by less hazardous catalysts like aluminum halides. 
A number of aluminum halide catalyst systems have been disclosed for 
oligomerization of alpha-olefins to poly-alpha-olefins which could be used 
as lubricating oil base stocks possessing low pour points, higher 
viscosity index and good oxidation stability. U.S. Pat. No. 3,637,503 
discloses the oligomerization of alpha-olefins having from 4 to 16 carbon 
atoms in the presence of aluminum chloride and a non-polymerizing 
hydrocarbon diluent. Similarly, aluminum chloride alone or along with 
organic promoters have been used to oligomerize alpha-olefins either pure 
alpha-olefins or alpha-olefins in the presence of a non-oligomerizing 
hydrocarbon diluent, see, for example, U.S. Pat. Nos. 5,196,635; 
5,136,118; 4,107,080; 4,219,691 and 4,031,159. It is also known in the 
related field to oligomerize olefins in which the double bond is 
statistically distributed along the entire carbon chain. Thus, U.S. Pat. 
No. 4,167,534 discloses the oligomerization of olefins obtained from a 
OL-OLEX process, by contacting with aluminum chloride to obtain 
oligomers which, after distillation and catalytic hydrogenation, gave 
lubricating oil. Even though the feed stock for oligomerization was 
predominantly olefinic (up to 95%), the yield and the viscosity of the 
resulting oligomer were very poor. 
However, all these processes pertain to oligomerization of either pure 
alpha-olefins or mixtures of pure alpha-olefins and, surprisingly, there 
are no reports on the utilization of linear olefins contained in refinery 
streams for the production of synthetic lubricant base stocks. Various 
refinery produced cracked distillate streams, particularly from Coker and 
FCC units, are quite rich in desired alpha-olefins which can be 
selectively concentrated by the process of urea adduction. 
A major deficiency of the conventional Friedel-Craft catalysts is their 
inability to selectively oligomerize olefins in the presence of other 
unsaturated compounds like aromatics. However, aluminum chloride alone or 
with promoters is known to promote the alkylation of aromatics with 
olefins when applied to cracked refinery distillate streams which 
contained appreciable amounts of aromatics along with olefins. The 
oligomeric product thus obtained contain alkylated aromatics which made 
these products unsuitable for use as lubricating oils because of very poor 
oxidation stability. No prior art method either discloses or teaches any 
catalyst system which can selectively oligomerize olefins to polyolefins 
in the presence of aromatics. Consequently, it is in fact impossible to 
prepare an olefin oligomer having high viscosity index and high oxidation 
stability which could be qualified for such uses as gas turbine oil, 
hydraulic fluid for aircraft, crankcase oils, etc. by selective 
oligomerization of olefins present in the cracked refinery stream 
distillates which also contain aromatics, besides paraffins and 
cycloparaffins, by use of Friedel-Craft catalyst systems disclosed in the 
prior art. The present invention provides for a catalyst composition for 
preparation of olefin oligomers suitable for use as lubricating oils by 
selective oligomerization of olefins, contained in cracked refinery stream 
distillates, which have been processed through a step of urea adduction. 
An object of the present invention is to propose a catalyst composition for 
selectively oligomerizing olefins present in cracked refinery stream 
distillates which are comprised of olefins, aromatics, paraffins and 
cycloparaffins having 8 to 20 carbon atoms. 
A further object of this invention is to propose a catalyst composition 
which provides higher conversion of olefins present in the cracked 
refinery stream distillates, processed through a step of urea adduction 
and containing up to 5% aromatics. 
Yet another object of the present invention is to propose a catalyst system 
for selective oligomerization of olefins contained in refinery distillate 
streams to produce oligomers having high viscosity index, low pour point 
and higher oxidation stability for use as base stocks in synthetic 
lubricants. 
SUMMARY OF THE INVENTION 
According to this invention, there is provided a catalyst composition for 
use in oligomerization of olefins contained in refinery distillate streams 
comprising an aluminum halide component and a catalyst component selected 
from an alkoxide of a metal belonging to group IVB. 
Further according to this invention, there is provided a process for 
preparing poly-alpha-olefin synthetic lubricants comprising 
oligomerization of olefins of cracked refinery streams having 8 to 20 
carbon atoms in the presence of corresponding paraffins, naphthenes and 
aromatics, and in the presence of a catalyst consisting of an aluminum 
halide and group IVB transition metal alkoxide, to provide an olefin 
oligomer having a viscosity of 7-30 cSt at 100.degree. C. 
The catalyst composition used in the oligomerization process of the present 
invention is a two component system comprising (A) an aluminum halide 
component and (B) a second catalyst component which is an alkoxide of a 
metal belonging to group IV B. The aluminum halides which are suitable for 
use in the catalyst system of the present invention include aluminum 
fluoride, aluminum chloride, aluminum bromide and aluminum iodide and 
mixtures thereof. The preferred aluminum halide is aluminum chloride. The 
second component of the proposed oligomerization catalyst system comprises 
a metal alkoxide having the general formula M(OR).sub.4, wherein M is 
selected from the group of metals belonging to group IVB of the periodic 
table and R is an alkyl group of 1 to 12 carbon atoms or an alkylaryl 
having an alkyl chain of 1-12 carbon atoms. Preferably R is a lower alkyl 
of 2 to 6 carbon atoms. 
A preferred catalyst composition is obtained when the metal alkoxide is a 
titanium alkoxide. A particularily preferred catalyst composition contains 
aluminum chloride and a titanium alkoxide such as titanium 
tetra-isopropoxide or titanium tetra-n-butoxide. 
The molar ratio of aluminum halide to the transition metal alkoxide is 
important for optimum catalyst activity and for product quality in terms 
of viscosity and pour points. Generally the molar ratio of aluminum to 
transition metal is from 100:1 to 4:1, preferably about 60:1 to 10:1. The 
amount of aluminum-halide catalyst can vary and amounts of from about 0.5 
to 10 weight percent based on the amount of olefin is preferred. The 
specially preferred amount of aluminum halide is from 1 to 4 weight 
percent based on the amount of olefins. 
The raw material suitable for the present catalyst composition can consist 
of alpha-olefins having a number of carbon atoms between 8 and 24, 
n-olefins having the double bond statistically distributed along the 
entire carbon chain and having a number of carbon atoms between 8 and 24, 
and the mixtures of n-olefins and alpha-olefins in any ratio. The proposed 
catalyst composition is also suitable for raw materials obtained from the 
OL process or from wax cracking and containing a mixture of olefins and 
paraffins and having a number of carbon atoms between 8 and 24. Yet 
another raw material suitable for the present catalyst composition is the 
cracked refinery distillate cuts, i.e., distillate cuts from FCC or coker 
units. These cuts were mixtures of olefins, aromatics, paraffins and 
cycloparaffins having a number of carbon atoms between 8 and 24. 
A preferred feed for oligomerization with the catalyst composition of the 
present invention is that obtained through the process of urea adduction 
of cracked refinery distillate streams. Methods are generally known in the 
prior art to obtain linear olefins and linear paraffins mixtures by urea 
adduction of cracked refinery distillate streams, viz., naphtha, kerosene, 
diesel and gas oil. See, for example, A.Hoope, in "Advances in Petroleum 
Chemistry and Refining", Vol. 8, Ed., Kobe-McKetta, Inter-Science 
Publication, New York, 1964, which is incorporated by reference. However 
the urea adducted olefin rich feed is generally contaminated with 0.1-5.0% 
aromatics, depending upon the process conditions. Surprisingly, it was 
found that the catalyst composition of the present invention results in 
selective oligomerization of olefins contained in the cracked refinery 
distillate streams processed through the step of urea adduction. 
The olefins are oligomerized in contact with the present catalyst 
composition under conventional oligomerization conditions. Oligomerization 
is conducted at temperatures ranging from 30-200.degree. C., 
preferentially from about 70 to 120.degree. C. The reactions can either be 
conducted under reflux conditions or in an autoclave under autogeneous 
pressure. For effecting the oligomerization of olefins by the catalyst 
composition of the present invention, the appropriate amount of aluminum 
halide and transition metal alkoxide are premixed in the presence of an 
inert non-polymerizing solvent (i.e., n-heptane, n-octane etc.) and the 
resulting mixture added slowly to the olefinic feed stock. However, no 
difference was observed even by dissolving the transition metal alkoxide 
in the olefinic feed stock and subsequent stepwise addition of aluminum 
halide to this mixture or vice versa. Lower reaction temperatures were 
generally associated with enhancement in the viscosity of the oligomer and 
a decrease in the overall yield. The reaction is normally carried out over 
a period of about 1 to 12 hours, preferably for about 1 to 4 hours. 
The regulation of the molecular weight of the oligomers produced and hence 
other physical characteristics like viscosity, viscosity index and pour 
point, can be controlled during the oligomerization by changing the ratio 
of aluminum halide to metal alkoxide, by variation in reaction temperature 
and by variation in reaction duration. After completing the 
oligomerization reaction, the product is passed through a column of 
silica/alumina to remove the residual catalyst, and then subjected to 
distillation under reduced pressure to remove unoligomerised products and 
olefin dimers. To further improve the oxidation stability and/or thermal 
stability of the product, it can be subjected to hydrogenation treatment 
by use of typical hydrogenation catalysts, such as Raney nickel, nickel on 
Kieselguhr or Pd on charcoal. At present, the reaction mechanism of the 
complex of aluminum halide with transition metal alkoxide which is 
responsible for the selective oligomerization of olefins in the presence 
of other unsaturated compounds like aromatics is yet to be clarified. 
However, it is likely that oligomer chain growth occurs as a result of 
olefin coordination on a transition metal which has unoccupied 
co-ordination sites. Subsequently, olefin insertion can take place into a 
transition metal carbon bond to give oligomeric chain growth. However, the 
bulky aromatics are not able to make transition metal-carbon bonds and 
hence are excluded in the chain growth step. Finally the chain transfer 
can occur as a result of P-hydrogen elimination from the oligomeric chain 
attached to the transition metal and the catalytic center, namely, the 
transition metal-carbon bond is restored again. 
As will be understood from the foregoing elucidation, according to the 
oligomerization catalyst composition of the present invention it is 
possible to selectively oligomerize olefins in the presence of aromatics, 
to get the oligomer oil. These oligomers can be tailor made to a viscosity 
range of 7 to 30 cSt at 100.degree. C. by variation effected in the 
catalyst composition and by process parameters. After stabilization by 
hydrogenation, these oligomers show high viscosity index, low pour points, 
excellent thermal/oxidation stability and can be used as synthetic 
lubricant base stock. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will be further illustrated by, but by no means is 
limited to, the following examples. In the following examples, the 
kinematic viscosity was determined in the manner described in ASTM-D-45, 
the viscosity index was determined in the manner described in ASTM-D-2270, 
and the pour point was determined in the manner described in ASTM-D-97. 
The detection of aromatics in the feed stock and oligomeric oil was 
carried out by NMR spectroscopy.

EXAMPLE 1 
The reaction was carried out in a 1 liter four necked round bottom flask, 
fitted with a mechanical stirrer, a solid addition funnel, a thermometer 
and a gas purging tube. The system was kept under a positive pressure of 
dry nitrogen and 2% of anhydrous aluminum chloride and 0.2% titanium 
isopropoxide were added. Keeping the Al/Ti ratio equal to 21, 500 g of 
1-decene was dropwise added to the mixture over a period of 1 hour. The 
temperature of this stirred mixture was raised to 100.degree. C. and 
oligomerization was carried out for a period of 2 hours. After completion 
of reaction, the product mixture was filtered through a bed of silica to 
remove the deactivated catalyst. The filtrate was subjected to flushing at 
160.degree. C./0.5 mm Hg to remove unreacted decene and its dimers, to 
obtain the oligomerized oil. The performance evaluation of products 
obtained is described in Tables 1 and 2. 
EXAMPLE 2 
In an experimental set up similar to the one as described for Example 1, 2% 
aluminum chloride and 0.05% Ti(Obu)4 were mixed together and reacted with 
1-decene. The oligomerization reaction was carried out at 80/100.degree. 
C. and oligomeric product was isolated as described in Example 1. The 
results are reported in Tables 1 and 2. 
EXAMPLE 3 
The reaction was carried out as described for Example I and using the 
identical catalyst composition except that the oligomerization feed stock 
was a Pacol product cut comprised of C.sub.10 to C.sub.14 olefin-paraffin 
mixture having 15% olefins. Some typical results are described in Tables 1 
and 2. 
EXAMPLE 4 
The reaction was carried out as described for Example 1 and using the 
identical catalyst composition except that the oligomerization feed stock 
was a cracked refinery stream cut having a boiling range of 
180-220.degree. C., and being comprised of linear C.sub.10 to C.sub.14 
hydrocarbons, having 32% olefins, 44% paraffins, 20% naphthenes and 4% 
aromatics. Some typical results are described in Tables 1 and 2. 
EXAMPLE 5 
The reaction was earned out as described for Example 1, and using the 
identical catalyst composition, except that the oligomenzation feed stock 
was a cracked refinery stream cut, processed through the step of urea 
adduction, having boiling range of 180-220.degree. C., comprised of linear 
C.sub.10 to C.sub.14 hydrocarbons, having 29% olefins, 68% paraffins and 
3% aromatics. Some typical results are described in Tables 1 and 2. 
TABLE 1 
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PERFORMANCE EVALUATION OF SYNTHESIZED OLIGOMERS 
EXAMPLE CONVERSION KV,cSt POUR 
NO. (%)** (100.degree. C.) 
VI POINT (.degree. C.) 
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1 97 22.1 140 -27 
2 98 12.3 132 -30 
3 94 26.5 134 -27 
4 93 20.4 142 -30 
5 95 20.9 138 -30 
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**CONVERSION BASED ON OLEFIN CONTENT 
TABLE 2 
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IP-48 OXIDATION TEST RESULTS ON SYNTHESIZED 
OLIGOMERS AFTER HYDROGENATION 
Kinematic 
Viscosity CCR TAN 
at 100.degree. C. 
(%) (mg KOH/g) 
Example 
Before After Before After Before 
After 
No. Test Test Test Test Test Test 
______________________________________ 
1 22.1 30.9 0.01 0.13 0.15 6.4 
2 12.3 17.6 0.01 0.12 0.17 6.8 
3 26.5 36.8 0.01 0.17 0.13 8.3 
4 20.4 29.8 0.01 0.14 0.15 8.7 
5 20.9 30.5 0.01 0.15 0.16 7.9 
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