Process for oligomerization of C.sub.2 to C.sub.10 normal olefins

A process for the oligomerization of normal C.sub.2 -C.sub.10 olefins, for example n-butenes by passing a feed containing said olefins in liquid phase through a fixed bed of acid, cation exchange resin at a temperature in the range of 40.degree. to 185.degree. C. at LHSV of 0.10 to 10 and recovering the oligomer product. In the case of n-butenes the principal component of the oligomer product is C.sub.8 dimer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a novel process for the production of 
oligomers of normal olefins of C.sub.2 to C.sub.10 carbon atoms and in 
particular C.sub.8 olefins by the dimerization of n-butenes. 
2. Prior Art 
The reaction of olefins to form longer chains of two or more monomer units 
is well known. It is well known that ethylene and other olefins can be 
polymerized to form relatively low molecular weight products through the 
use of certain organo-metallic catalyst. Broadly, these catalysts are 
compounds of metals of groups IV to VI of the Periodic Table of elements 
in combination with other compounds of metals of groups I to III. The 
Ziegler catalysts are representatives of such catalysts and are preferably 
specific combinations of titanium halide and a trialkyl aluminum 
component, with or without other metal promoters. Other catalysts such as 
alkyl aluminum halides (preferably the chloride) in combination with alkyl 
titanium esters have also been used to carry out this reaction. 
These catalysts are homogeneous in that they are soluble in the reaction 
medium. The catalysts are very effective, that is the reaction can easily 
be carried out to produce high molecular weight compounds, with the 
appropriate amounts of catalyst. In some instances, by using extremely low 
concentrations of catalyst in the reaction system, low molecular weight 
products may be produced, in particular dimers, trimers and tetramers. 
Free radicals, carbonium ions and carbanions have also been used to promote 
the reaction of olefins, particularly alpha-olefins to produce polymers of 
high molecular weight. 
The use of acid catalysts such as sulfuric acid to selectively react 
isoolefins in the presence of other olefins to produce lower molecular 
weight products, e.g., U.S. Pat. Nos. 3,564,317 and 3,832,418 is also well 
known. U.S. Pat. No. 4,065,512 discloses the use of perfluorosulfonic acid 
resin, particularly in the form of films for the polymerization of 
isobutene to produce dimers, trimers and higher oligomers. 
More recently, U.S. Pat. No. 4,215,011 disclosed the use of acid cation 
exchange resin in a heterogenous combination reaction-distillation system 
for the selective dimerization of isobutene in the presence of normal 
butenes. The reaction is highly preferential for the reaction of isobutene 
with itself, although some codimer between n-butenes and isobutene are 
formed, and provides a means to separate isobutene from a C.sub.4 stream. 
It would appear from the art that normal butenes are not reactive, other 
than with isobutene in the presence of acid catalyst or acid cation 
exchange resin. 
SUMMARY OF THE INVENTION 
The present process, briefly, is a process for the production of oligomers, 
i.e., principally dimers, trimers and tetramers of normal C.sub.2 to 
C.sub.10 olefins, preferably C.sub.3 to C.sub.5 normal olefins in liquid 
phase in the presence of acid cation exchange resins at temperatures in 
the range of 40.degree. to 185.degree. C., preferably above 70.degree. C. 
and more preferably above 80.degree. C. 
In particular, it has now been found that normal butenes, both butene-1 and 
butene-2are reactive to form oligomers, in particular dimers, in liquid 
phase in the presence of acid cation exchange resins at temperatures in 
the recited range of 40.degree. to 185.degree. C. (preferably from 
70.degree. C.). Preferably the temperature is in the range of 80.degree. 
to 130.degree. C. The temperature of the reaction is determined by 
standard means using type K thermocouple probe. Generally a longer 
residence time of the reactants in the catalyst bed is used at the lower 
reaction temperatures. Thus, over the range of temperatures disclosed, 
residence times expressed as, liquid hourly space velocity (LHSV) of 0.10 
to 10 preferably 2 to 5 LHSV, would be employed and adjusted to obtain the 
maximum yield of oligomers. Lower reaction temperatures in the recited 
range would be used with longer residence times of the reactants in the 
catalyst bed.

DETAILED DESCRIPTION OF THE INVENTION 
In the case of normal butenes, a very interesting result of the present 
process is that the reaction product is a similar mixture notwithstanding 
whether the monomer feed is butene-1 or butene-2 or a mixture of the two. 
It should be appreciated that any isobutene present in the reaction system 
is preferably reacted, either to form dimer or codimer with the normal 
butenes. Thus, the amount of isobutene present should be minimized so as 
not to alter or change the purity of the desired normal butene 
dimerization product. The feed to the reactor should contain no more than 
10 mole percent isoolefin and preferably less than 5 mole percent thereof. 
Most preferably the feed will contain less than 1 mole percent of the 
isoolefin. Larger amounts of isobutene result in a product of sufficiently 
different characteristics from the n-butene dimer product that the product 
may not be useful for the purposes for which the n-butene dimer is 
employed. 
The product of the normal butenes oligomerization reaction contains in 
addition to n-butene dimer, codimer of isobutene or diisobutene, if 
isobutene is present in the reaction system, and higher oligomers of the 
normal butenes and/or isobutene, usually trimers and tetramers. In the 
reactor the normal C.sub.4 olefins contact the catalyst and react to form 
a polymer predominately of number average molecular weight of a C.sub.16 
hydrocarbon or less. Some higher polymers of non-specific configuration 
may be formed as very minor by-products. The various components of the 
product stream, e.g., n-butene dimer, trimer, etc., are separated by 
distillation. 
The dimer portion of the reaction product of normal butenes according to 
the present invention is surprisingly linear compared to similar materials 
made by prior procedures. The n-butene dimer product of the present 
invention is principally dimethyl hexenes, with some methyl heptenes and 
with very little of the trimethyl pentenes, i.e., less than 5 mole % 
(typically less than 1-3 mole % with the dimer product being 
3,4-dimethylhexenes. This product composition differs significantly to 
that obtained for example from phosphoric acid oligomerizations of normal 
butenes which typically produce considerably more of the trimethyl 
pentenes (10 to 80 times more). 
The feed in the present process may contain olefins of various carbon chain 
lengths, and the products will be a mixture of the reaction of the various 
olefins, particularly n-olefins present, e.g., a n-butene, propylene feed 
will produce C.sub.8, C.sub.7 and C.sub.6 dimer products as well as the 
higher oligomers of the various monomers present. The feed to the reactor 
should be free of any entrained, second phase water. 
In the case of normal-butene the location of the double bond, i.e., in the 
1 or 2 position, has not proved to be of critical significance in carrying 
out the reaction. However, in normal olefins of longer chains, e.g., 5 to 
10 carbon atoms, the location of the double bond in the alpha position 
would facilitate the reaction. 
Although the present process can be carried out batchwise, it is 
contemplated that in actual practice the process will be operated 
continuously with a separation of unreacted normal olefins and recycle of 
a portion thereof to the reactor. 
The product of the reaction is a low molecular weight polymer, i.e., 
oligomer which is a predominately dimers, but containing some trimers and 
tetramers of the olefins in the feed. The term "predominate amount" or 
"predominately" as used herein means over 60 mole %. The unreacted 
materials in the product stream are not considered to be product. Hence, 
if the conversion of normal olefins is 33% of those present, the product 
stream will contain 67% unreacted material and 33% of the reacted material 
which will preferably comprise at least 80 mole % of the dimer, trimer and 
tetramer. 
The nature of the catalyst is such that in carrying out the polymerization 
of the normal olefins as described, there is no tendency to produce any 
substantial amounts of higher polymers, that is, the principal or 
predominate reaction products are tetramers or lower polymers, i.e., 
trimers and dimers, with a strong tendency to favor the dimers. 
Generally the reaction as described is carried out with streams containing 
at least 10 mole % of the normal olefin to be oligomerized, preferably 50 
mole % up to substantially pure feeds of the normal olefins, and more 
preferably the feed to the reactor and catalyst bed contains at least 70 
mole % of the normal olefins. At very low concentrations of normal butenes 
the isoolefin should likewise be low. Preferably the normal olefins will 
comprise at least 60 mole % and more preferably 90 mole % or more of the 
olefins present, particularly in view of the greater reactivity of the 
corresponding isoolefins. 
It is, of course, apparent that the ethylene and propylene have only the 
one form, corresponding to normal olefins of C.sub.4 to C.sub.10, however, 
for simplicity all of the olefins within the scope of the present 
invention are designated as "normal". 
In addition to the normal olefins, normal paraffins may be present and have 
not been of any significance in carrying out the present process. In 
addition to the linear paraffins, branched paraffins may be present. 
Catalysts suitable for the new process are cation exchangers, which contain 
sulfonic acid groups, and which have been obtained by polymerization or 
copolymerization of aromatic vinyl compounds followed by sulfonation. 
Examples of aromatic vinyl compounds suitable for preparing polymers or 
copolymers are: styrene, vinyl toluene, vinyl naphthalene, vinyl 
ethylbenzene, methyl styrene, vinyl chlorobenzene and vinyl xylene. A 
variety of methods may be used for preparing these polymers; for example, 
polymerization alone or in admixture with other monovinyl compounds, or by 
crosslinking with polyvinyl compounds; for example, with divinyl benzenes, 
divinyl toluenes, divinylphenylethers and others. The polymers may be 
prepared in the presence or absence of solvents or dispersing agents, and 
various polymerization initiators may be used, e.g., inorganic or organic 
peroxides, persulfates, etc. 
The sulfonic acid group may be introduced into these vinyl aromatic 
polymers by various known methods; for example, by sulfating the polymers 
with concentrated sulfuric acid or chlorosulfonic acid, or by 
copolymerizing aromatic compounds which contain sulfonic acid groups (see 
e.g., U.S. Pat. No. 2,366,007). Further sulfonic acid groups may be 
introduced into these polymers which already contain sulfonic acid groups; 
for example, by treatment with fuming sulfuric acid, i.e., sulfuric acid 
which contains sulfur trioxide. The treatment with fuming sulfuric acid is 
preferably carried out at 0.degree. to 150.degree. C., and the sulfuric 
acid should contain unreacted sulfur trioxide after the reaction. The 
resulting products preferably contain an average of 1.3 to 1.8 sulfonic 
acid groups per aromatic nucleus. Particularly, suitable polymers which 
contain sulfonic acid groups are copolymers of aromatic monovinyl 
compounds with aromatic polyvinyl compounds, particularly, divinyl 
compounds, in which the polyvinyl benzene content is preferably 1 to 20% 
by weight of the copolymer (see, for example, German Patent Specification 
No. 908,247). 
The ion exchange resin is preferably used in a granular size of about 0.25 
to 2 mm, although particles from 0.15 mm up to about 2 mm may be employed. 
The finer catalysts provide high surface area, but also result in high 
pressure drops through the reactor. Both gel types and the macroreticular 
form of these catalysts may be employed. In a preferred embodiment, the 
catalyst is the macroreticular form which has surface areas of from about 
20 to 600 square meters per gram preferably about 20-50 square meters per 
gram. The catalyst is employed in a fixed bed. 
The reaction is carried on in liquid phase and sufficient pressure is 
employed in the system to maintain the liquid phase under the conditions 
of reaction. For the full range of C.sub.2 to C.sub.10 normal olefins, the 
pressure would range from about 50 psig to 3500 psig; however for C.sub.3 
to C.sub.5 normal olefins, pressures would be in the range of 75 to 800 
psig. 
In carrying out the present process, it was determined that temperature of 
the catalyst (which reflects the exotherm in the catalyst bed) was of 
particular importance. The temperature range of 40.degree. to 185.degree. 
C. reflects the operable range which may be used to carry out the reaction 
over a useful time trend of the catalyst, which tends to decline in 
activity at higher temperatures. The nature of the catalyst too, requires 
the control of the upper temperature, since it can be deactivated by 
excessive temperatures in the bed. The maximum temperature which the 
catalyst can withstand varies with its particular characteristics, and 
even for the high temperature types (stated to be in the range of 
175.degree.-200.degree. C. for aqueous systems), in the present process a 
rapid decline in activity is noted above 190.degree. C. Further, 
temperatures above 150.degree. C. tend to promote trimer formation. 
The feed to the catalyst should be free or substantially free of catalyst 
poisons such as organic or inorganic bases or metal cations. The feed may 
contain controlled amounts of water or alcohol, not sufficient to form a 
second phase in the feed, to serve as catalyst modifiers to maintain the 
catalyst performance. 
The term liquid hourly space velocity (LHSV) means the liquid volumes of 
hydrocarbon per volume of reactor containing catalyst, per hour. 
Referring to FIG. 1, a schematic representation of a preferred embodiment 
of the present process is shown. A normal olefin containing feed stream 
enters reactor 16 via line 10 where it is contacted with the resin 
catalyst (not shown). The reaction temperature is maintained constant by 
means of a fluid medium entering the reactor through line 11 where it is 
in indirect contact with the catalyst to either remove heat or supply 
heat, such as on start-up. The fluid medium exits the reactor via line 12 
and is treated elsewhere as required to maintain the desired temperature 
in the reactor. 
The fluid medium can be any fluid capable of providing indirect heat 
exchange with the fixed bed catalyst. Water, air, steam or organic liquids 
could be employed for this purpose. 
In the reactor, the olefin stream contacts the catalyst and the olefin is 
reacted with itself or other olefins to form a mixture of dimers, trimers 
and tetramers polymer. This product passes via line 13 into fractionator 
17 where by simple distillation the product is split to recover the 
oligomer as a bottoms fraction which is removed through line 14 and the 
unreacted portions removed as an overhead, through line 15, hence to 
further treatment for separation if desired. 
The heat exchange fluid is in indirect contact with the fixed catalyst bed. 
FIG. 2 shows a conventional and preferred means of obtaining this contact. 
Reactor 20 is a multitube reactor comprising a shell 30 having mounted 
therein tubes 22, usually of 1/8 to 2 inches outside diameter. The reactor 
is shown horizontally, however it could be vertical or inclined. The tubes 
22 are mounted through plates 25 and 26 and attached at each end to header 
plates 23 and 24 which are to prevent fluid communication between the 
coolant area A, which is adjacent to the tubes, and the feed entry area B 
and product exit area C. The tubes 22 are in liquid communication with 
areas B and C. A feed entry pipe 21 is located in the B area and a product 
exit pipe 27 is located in the C area. Heat exchange medium is provided 
into the A area via pipe 28 and an exit is provided via pipe 29. 
The tubes 22 are packed with the cation exchange resin in granular form 31 
and means such as screens (not shown) are fitted to each tube to retain 
the catalyst therein. FIG. 3 shows an arrangement of tubes 22 in header 
plate 23. 
The reaction is exothermic and the heat exchange medium, e.g., water 
provides the means for controlling the reaction. 
The following examples are presented to illustrate the invention and are 
not intended to limit its scope. The olefin product analyses were obtained 
by gas chromatography of the hydrogenated olefins. 
EXAMPLE 1 
300 ml of Amberlyst 15 (a sulfonated copolymer of styrene and divinyl 
benzene having a porosity of 32% and surface area of 45 square meters per 
gram (a product of Rohm and Haas Co.) was placed in a 1-inch O.D. 
stainless steel reactor tube. 
The reactor tube was housed inside a 21/2 inch O.D. coaxial tube through 
which heated water or oil was continually recirculated to maintain the 
desired reaction temperature. Temperature measurements were made with a 
calibrated thermocouple inserted into a 1/8 inch O.D. stainless steel tube 
coaxial to the reactor tube. A feed of n-butenes was passed downflow over 
the catalyst at reaction conditions of 2-4 LHSV, 100.degree. C. and a 
pressure of 200 psig. The catalyst was dried prior to use by washing with 
acetone and drying in a Pyrex dish in an oven at 90.degree. C. for 4-5 
hours. 
The feed to the reactor contained 20 mole % butane, and typically 47 mole % 
trans-butene-2, 27 mole % cis butene-2 and 6 mole % butene-1. The 
oligomerized products from several runs were combined and distilled. The 
product dimer distilled at 111.degree.-119.degree. C. About 80 mole % of 
the oligomer product was dimer and gas chromatographic analysis showed 92 
mole % of the dimer was dimethylhexenes as follows: 
______________________________________ 
3,4 Dimethylhexenes 71 mole % 
2,2 Dimethylhexenes 1 mole % 
2,4 Dimethylhexenes 8 mole % 
3,3 Dimethylhexenes 3 mole % 
2,3 Dimethylhexenes 9 mole % 
______________________________________ 
The analysis also showed the presence of 4 mole % methylheptenes and 1% 
trimethyl pentenes. 
EXAMPLE 2 
In the following example, the reactor consisted of a preheat section of 
coiled 1/8" OD stainless steel tubing connected to 1/4" OD stainless steel 
tubing packed with 25 cc of dry resin as described. Both sections were 
immersed in a water bath of controlled temperature which is the 
temperature reported. A back-pressure regulator located downstream of the 
catalyst bed was used to maintain the desired pressure in the reactor 
system. Product effluent was collected in a stainless steel, high pressure 
vessel, downstream of the pressure regulator. After a sufficient volume of 
effluent had been collected for analysis, the contents of the SS vessel 
were transferred to a tared and evacuated Pyrex bottle fitted with a 
rubber septum mounted in a perforated metal cap. A 20-gauge needle 
attached to the SS vessel was inserted through the rubber septum of the 
bottle and the reaction products were collected for weighing. The contents 
of the Pyrex bottle were then evaporated at room temperature and later at 
90.degree. F. via a transfer line into a second evacuated bottle immersed 
in a mixture of acetone and solid CO.sub.2. Separation of the lower 
boiling, unreacted C.sub.4 hydrocarbons from the higher boiling 
oligomerized products was thus effected, and the weight percent of 
oligomers calculated. The composition of each of the two hydrocarbon 
fractions was determined chromatographically. 
The feed to the reactor was 4.34 mole % normal butane, 0.67 mole % 
butene-1, 57.63 mole % trans butene-2 and 37.34 mole % cis butene-2. The 
catalyst was Amberyst 15 (a Rohm and Haas product) which had been washed 
with acetone and dried prior to use. The reaction temperature (determined 
by the temperature of the water bath) was between 90.degree. and 
100.degree. C. at 400 psig, and LHSV=2.3-4.6. At 77 hours on stream 73.4 
wt.% oligomers were produced. The product was analysed by hydrogenation 
gas chromatography and showed: 3,4-dimethyl hexene=68 mole %, 3-methyl 
heptene=6 mole %, 2,3,4-trimethyl pentene=1 mole %, 2,3-dimethyl hexene=9 
mole %, 3,3-dimethyl hexene=3 mole %, 2,4-dimethyl hexene=11 mole %, 
2,5-plus 2,2-dimethyl hexene=1 mole %. 
EXAMPLE 3 
The reactor was the same as Example 2. The catalyst was twenty-five grams 
of Amberlyst XN-1010 (a sulfonated copolymer of styrene and divinyl 
benzene having a porosity of 47% and surface area of 570 square meters per 
gram) product of Rohm & Haas Co. The reactor feed was a C.sub.4 stream 
having the following analysis: 
______________________________________ 
Neopentene 0.01 mole % 
Normal butane 21.86 mole % 
Butene-1 0.28 mole % 
Trans butene-2 
47.84 mole % 
Cis butene-2 29.98 mole % 
______________________________________ 
The conditions of reaction were: temperature 100.degree. C., pressure 300 
psig; LHSV=2.5. At 18 hours on stream the product was 49.1 wt.% oligomer. 
Near the end of the run, at 25% conversion of butenes, the dimer had the 
following gas-chromatographic analysis: 3,4-dimethyl hexene=88 mole %, 
3-methyl heptene=6 mole %, 2,3 dimethyl hexene plus 2,3,4-trimethyl 
pentene=1 mole %, 3,3-dimethyl hexene=1 mole %, 2,4-dimethyl hexene=4 mole 
%. 
EXAMPLE 4 
The reactor was a jacketed 1/2" O.D. 316 SS reactor tube (with coaxial 1/8" 
O.D. 306 SS thermowell) containing 50 cc of catalyst. The reactor was 
heated with recirculated oil from a constant temperature bath and entered 
at the bottom of the jacket and exited at the top. Liquid hydrocarbons 
were fed to the top of the reactor and exited at the bottom. The reactor 
contained 50 cc of Amberlite 252H catalyst (a sulfonated styrene divinyl 
benzene copolymer) product of Rohm & Haas Co. The conditions were: 
temperature 100.degree. C., pressure 225 psig; LHSV 2.5. The feed 
composition was: 21.9 mole % n-butane, 0.3 mole % butene-1, 47.8 mole % 
trans butene-2, 30.0 mole % cis butene-2. After 420 hours on stream, the 
reactor effluent contained 33.6 weight % oligomer of which 85% was dimer. 
At 700 hours on stream, the dimer had the following analysis: 3,4-dimethyl 
hexene=73 mole %, 3-methyl heptene=11 mole %, 2,3-dimethyl hexene plus 
2,3,4-trimethyl pentene=6 mole %, 3,3-dimethyl hexene=3 mole %, 
2,4-dimethyl hexene=7 mole %. 
EXAMPLE 5 
The feedstock used was butene-1 (99.9%) in the reactor of Example 2 with 
conditions similar to those in Example 2 except that the temperature was 
80.degree. C. The product dimer contained 2,4-dimethyl hexene=10 mole %, 
2,3-dimethyl hexene, plus 2,3,4-trimethyl pentene=6 mole %, 3,4-dimethyl 
hexene=72 mole %, 3-methyl heptene=6 mole %, 3,3-dimethyl hexene=4 mole %, 
and 2,2-plus 2,5-dimethyl hexene=1 mole % at 17.3 mole % conversion of the 
n-butene 1. 
EXAMPLE 6 
Using the reactor of Example 4 with a 80 mole % butene-2, 20 mole % 
n-butane feed at an inlet temperature of 99.degree. C. and a measured 
exotherm to 145.degree. C. (.DELTA.46.degree. C.), a conversion of 77.7 
mole % produced an oligomer of the following analysis: 3,4-dimethyl 
hexene=mole %, 3-methyl heptene=6 mole %, 2,3-dimethyl hexene=6 mole %, 
2,3,4-tri-methyl pentene=1 mole %, 3,3-dimethyl hexene=2 mole %, 
2,4-dimethyl hexene=12 mole %, 2,2-dimethyl hexene=1 mole %, C.sub.12 plus 
C.sub.16 =33 mole %. 
EXAMPLE 7 
This example demonstrates the operation of the process at low temperature 
and low LHSV. The reactor and catalyst of Example 4 was employed. The feed 
to the reactor was 15.1 mole % n-butane, 1.2 mole % butene-1. 48.9 mole % 
trans butene-2 and 33.1 mole % cis butene-2. The pressure was 250 psig and 
LHSV was 0.5. Two temperatures were used. At 40.degree. C., 3.0 wt.% 
oligiomer was produced at 115 hours on stream and at 44.degree. C., 7.4 
wt.% oligomer was produced at 91 hours on stream. 
The dimer product of n-butenes according to the present process are novel 
and different from those of prior art processes. Surprisingly, the product 
is relatively uniform as to isomer distribution over the range of process 
conditions. The very high dimethylhexene fraction of the dimer is 
especially unique. 
It has been found that the dimer product of n-butene as well as the entire 
oligomer product have very high research octane and motor octane numbers 
(typically 95 andand 82, respectively). 
A particularly valuable use for the C.sub.8 dimer or oligomer fraction is a 
feed for hydrocarbonylation (oxonation reaction) to produce long chain 
alcohols. The prior art dimer product has been employed for this purpose 
and the resultant alcohols are used as plasticizers, surface active agents 
and pesticides. Because of the presence of only a few octenes in large 
concentrations (&gt;10%), of desirable structure, the hydrocarbonylated 
C.sub.8 dimer of the present invention exhibits unexpected improved 
qualities as an oxonation feedstock to produce plasticizers for polymers. 
The higher C.sub.4 oligomers and other olefin oligomers of about C.sub.12 
are useful as gasoline blending stocks; and higher carbon chain lengths 
produce viscous liquids useful as oil viscosifiers or synthetic lubricants 
and plasticizers.