Alpha olefins from lower alkene oligomers

Internally unsaturated near linear oligomers of lower olefins are converted into alpha olefins, or 1-alkenes, of essentially the same degree of linearity. The internally unsaturated olefins are the product of lower alkene oligomerization using a surface deactivated zeloite, such as ZSM-5 or ZSM-23, and contain about 1 to 2 methyl branches per twelve (12) carbon atoms. The feedstock is converted to alpha olefin oligomers which also contain approximately 1 to 2 methyl branches per thirteen (13) carbon atoms. The conversion is achieved by hydroformylation of the near linear internal olefins to provide a novel 1-alkanol oligomer structure without further branching of the carbon oligomeric chain. Acetylation of the 1-alkanol followed by deesterification by pyrolysis provides the sought for near linear 1-alkene. The near-linear oligomers of lower olefins so produced comprise vinyl hydrocarbon monomers that can be further oligomerized by cationic and coordination catalysts.

This invention relates to a process for the production of near linear 
higher alpha olefins from olefinic oligomers prepared from lower alkenes 
More particularly, the invention relates to a process for the conversion 
of near linear lower alkene oligomers containing internal olefinic 
unsaturation to alpha olefins by hydroformylation to 1-alkanols of 
equivalent linearity, followed by esterification and pyrolysis to 
1-alkenes. The near linear alpha olefins so produced are useful, inter 
alia, for the production of high quality synthetic lubricants. 
BACKGROUND OF THE INVENTION 
Recent work in the field of olefin upgrading has resulted in a catalytic 
process for converting lower olefins to heavier hydrocarbons. Heavy 
distillate and lubricant range hydrocarbons can be synthesized over ZSM-5 
type catalysts at elevated temperature and pressure to provide a product 
having substantially linear molecular conformations due to the ellipsoidal 
shape selectivity of certain medium pore catalysts. 
Conversion of olefins to gasoline and/or distillate products is disclosed 
in U.S. Pat. Nos. 3,960,978 and 4,021,502 (Givens, Plank and Rosinski) 
wherein gaseous olefins in the range of ethylene to pentene, either alone 
or in admixture with paraffins are converted into an olefinic gasoline 
blending stock by contacting the olefins with a catalyst bed made up of a 
ZSM-5 type zeolite. Particular interest is shown in a technique developed 
by Garwood, et al., as disclosed in European patent application No. 
83301391.5, published Sept. 29, 1983. In U.S. Pat. Nos. 4,150,062; 
4,211,640 and 4,227,992 Garwood, et al., disclose the operating conditions 
for the Mobil Olefin to Gasoline/Distillate (MOGD) process for selective 
conversion of C.sub.3 + olefins to mainly aliphatic hydrocarbons. 
In the process for catalytic conversion of olefins to heavier hydrocarbons 
by catalytic oligomerization using a medium pore, shape selective, acid, 
crystalline zeolite, such as ZSM-5 type catalyst, process conditions can 
be varied to favor the formation of hydrocarbons of varying molecular 
weight. At moderate temperature and relatively high pressure, the 
conversion conditions favor C.sub.10 + aliphatic product. Lower olefinic 
feedstocks containing C.sub.2 -C.sub.8 alkenes may be converted; however, 
the distillate mode conditions do not convert a major fraction of ethylene 
A typical reactive feedstock consists essentially of C.sub.3 -C.sub.6 
mono-olefins, with varying amounts of nonreactive paraffins and the like 
being acceptable components. 
U.S. Pat. Nos. 4,520,221, 4,568,786 and 4,658,079 to C. S. H. Chen, et al., 
incorporated herein by reference in their entirety, disclose further 
advances in zeolite catalyzed olefin oligomerization. These patents 
disclose processes for the preparation of lubricant range hydrocarbons by 
oligomerization of light olefins using zeolite catalyst such as ZSM-5. The 
oligomers so produced are essentially linear in structure and contain 90% 
internal olefin unsaturation. These unique olefinic oligomers are produced 
by surface deactivation of the ZSM-5 type catalyst by pretreatment with a 
surface-neutralizing base. Process conditions can be controlled to favor 
the recovery of near linear olefin oligomers containing six to twenty 
carbon atoms. Optionally, lubricant quality oligomers of higher carbon 
number can also be produced. 
It is known that synthetic lubricating fluids of superior quality can be 
produced by oligomerization of 1-alkenes, particularly 1-decene. Building 
on that prior art resource, oligomers of 1-alkenes from C.sub.6 to 
C.sub.20 have been prepared, with commercially useful synthetic lubricants 
from 1-decene oligomerization yielding a distinctly superior lubricant 
product via either cationic, Ziegler or chromium catalyst known to be 
effective in the polymerization of 1-alkenes. 
Theoretically, the oligomerization of 1-decene, for example, to lubricant 
oligomers in the C.sub.30 and C.sub.40 range can result in a very large 
number of structural isomers. Characterizing those oligomers that produce 
a preferred and superior synthetic lubricant meeting the specification 
requirements of wide-temperature fluidity while maintaining low pour point 
represents a prodigious challenge to the workers in the field. Brennan, 
Ind. Eng. Chem. Prod. Res. Dev. 1980, 19, 2-6, cites 1-decene trimer as an 
example of a structure compatible with structures associated with superior 
low temperature fluidity wherein the concentration of atoms is very close 
to the center of a chain of carbon atoms. 
One characteristic of the molecular structure of 1-alkene oligomers that 
has been found to correlate very well with improved lubricant properties 
in commercial synthetic lubricants is the ratio of methyl to methylene 
groups in the oligomer. The ratio is called the branch ratio and is 
calculated from infra red data as discussed in "Standard Hydrocarbons of 
High Molecular Weight", Analytical Chemistry, Vol. 25, no. 10, p. 1466 
(1953). Viscosity index has been found to increase with lower branch 
ratio. Oligomers prepared from 1-decene by cationic polymerization have 
branch ratios of greater than 0.20. Those prepared by chromium or Ziegler 
catalyzed oligomerization have lower branch ratios. Whether by 
rearrangement, isomerization or a yet to be elucidated mechanism, it is 
clear that in the art of 1-alkene oligomerization to produce synthetic 
lubricants as practiced to-date branching occurs and constrains the limits 
of achievable lubricant properties, particularly with respect to viscosity 
index Obviously, increased branching increases the number of isomers in 
the oligomer mixture, orienting the composition away from the structure 
which would be preferred from a consideration of the theoretical concepts 
accepted in the art. 
In view of the foregoing, the practice in the synthetic lubricants field 
has been to oligomerize linear 1-alkene, more particularly single 
compounds such as 1-decene, in order to help control branching and the 
number of oligomeric species in the lubricant fluid. However, 1-decene and 
similar 1-alkenes are expensive and produce expensive lubricant fluids. 
Unfortunately, potentially less expensive olefins from the process of 
Chen, et al., are largely internal olefins and are also sightly branched, 
where unbranched alpha olefins are preferred. Their internal olefin 
structure also does not lend itself to oligomerization with either 
Ziegler-Natta or chromium catalysts used to produce very high quality 
synthetic lubricants. Cationic catalysts, e.g., BF.sub.3 or AlCl.sub.3 
complexes, polymerize internal olefins but result in more branched or 
lower VI lubes. 
Accordingly, it is an object of the present invention to provide a process 
for the conversion of slightly branched internal olefin oligomers, 
prepared from lower alkenes using surface deactivated zeolite catalyst, to 
alpha olefins or 1-alkenes. 
Another object of the present invention is to provide a process for 
converting the aforementioned internal olefins to alpha olefins while 
retaining the low degree of branching in the internal olefin. 
Yet another object of the instant invention is to prepare novel slightly 
branched 1-alkanol compositions from said internal olefins. 
A further object of the present invention is to provide a process for 
production of less expensive 1-alkenes useful in the preparation of high 
quality polyalphaolefin (PAO) synthetic lubricant fluids. 
SUMMARY OF THE INVENTION 
An integrated series of process steps has been discovered that effectively 
converts internally unsaturated near linear oligomers of lower olefins 
into alpha olefins, or 1-alkenes, of essentially the same degree of 
linearity. The internally unsaturated olefins are the product of lower 
alkene oligomerization using a surface deactivated zeolite, such as ZSM-5 
or ZSM-23, and contain about 1 to 2 methyl branches per fifteen carbon 
atoms. This feedstock is converted in the present invention to alpha 
olefin oligomers which also contain approximately 1 to 2 methyl branches 
per fifteen carbon atoms. The conversion is achieved by hydroformylation 
of the near linear internal olefins to provide a novel 1-alkanol oligomer 
structure without further branching of the carbon oligomeric chain. 
Acetylation of the 1-alkanol followed by deesterification by pyrolysis 
provides the sought for 1-alkene, without increasing the non-linearity of 
the 1-alkanol. The acetylation can be achieved in situ during the 
pyrolysis by cofeeding acetic anhydride and the 1-alkanol. In this manner, 
near-linear oligomers of lower olefins are converted to vinyl hydrocarbon 
monomers that can be further oligomerized by cationic and coordination 
catalysts. 
More particularly, a process is disclosed for the production of near linear 
1-alkene comprising vinyl hydrocarbon monomer, or a mixture of vinyl 
monomers, from near linear lower alkene oligomer having between six and 
twenty carbon atoms and containing internal olefinic unsaturation. The 
process comprises reacting the oligomer, or a mixture of oligomers, with 
H.sub.2 and CO mixture in contact with a hydroformylation catalyst under 
hydroformylation conditions sufficient to convert the oligomer to 
aliphatic 1-alkanol. The 1-alkanol contains a methyl to methylene branch 
ratio equal to or less than the oligomer. The 1-alkanol is recovered by 
conventional means and converted to an ester under esterification 
conditions in contact with an aliphatic acylating agent. The ester is 
recovered and deesterified by pyrolyzing the ester under conditions 
sufficient to produce 1-alkene comprising near linear vinyl hydrocarbon 
monomer, or a mixture of monomers. 
Preferably, the oligomer comprises the oligomerization product of C.sub.3 
-C.sub.5 alkene in contact with surface deactivated, acidic, shape 
selective, medium pore metallosilicate and has a methyl to methylene 
branch ratio less than 0.21. The hydroformylation is carried out using a 
sterically hindered catalyst such as Co.sub.2 (CO).sub.6 [(n--C.sub.4 
H.sub.9).sub.3 P].sub.2. 
The invention also provides a novel mixture of near linear aliphatic 
1-alkanols containing between six and twenty carbon atoms and having a 
methyl to methylene branch ratio less than 0.21. Preferably, the alkanols 
comprise C.sub.9 -C.sub.12 1-alkanols having a methyl to methylene branch 
ratio less than 0.18. 
DETAIL DESCRIPTION OF THE INVENTION 
Near linear alpha olefins are produced in the present invention according 
to the following general sequence of reactions where R is the olefin 
oligomer hydrocarbyl moiety: 
##STR1## 
NEAR-LINEAR OLEFIN 
The olefin oligomers used as starting material in the present invention are 
prepared from C.sub.3 -C.sub.5 olefins according to the methods presented 
by Chen, et al., in the aforementioned patents cited and N. Page and L. 
Young in allowed application Ser. No. 105,438, filed Oct. 7, 1987 and 
incorporated herein as references. Shape-selective oligomerization, as it 
applies to conversion of C.sub.3 -C.sub.5 olefins over ZSM-5, is known to 
produce higher olefins up to C.sub.30 and higher. Reaction conditions 
favoring higher molecular weight products are low temperature 
(200.degree.-260.degree. C.), elevated pressure (about 2000 kPa or 
greater) and long contact times (less than 1 WHSV). The reaction under 
these conditions proceeds through the acid catalyzed steps of 
oligomerization, isomerization-cracking to a mixture of intermediate 
carbon number olefins, and interpolymerization to give a continuous 
boiling product containing all carbon numbers. The channel system of ZSM-5 
type catalysts impose shape selective constraints on the configuration of 
large molecules, accounting for the differences with other catalysts 
The shape-selective oligomerization/polymerization catalysts preferred for 
use herein to prepare the olefin oligomers used as starting material in 
the invention include the crystalline aluminosilicate zeolites having a 
silica to alumina molar ratio of at least 12, a constraint index of about 
1 to 12 and acid cracking activity of about 50-300. Representative of the 
ZSM-5 type zeolites are ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35 and ZSM-38. 
ZSM-5 is disclosed and claimed in U.S. Pat No. 3,702,886 and U.S. Pat. No. 
Re. 29,948; ZSM-11 is disclosed and claimed in U.S. Pat. No. 3,709,979. 
Also, see U.S. Pat. Nos. 3,832,449 for ZSM-12; 4,076,842 for ZSM-23; 
4,016,245 for ZSM-35 and 4,046,839 for ZSM-38. The disclosures of these 
patents are incorporated herein by reference. A suitable shape selective 
medium pore catalyst for fixed bed is a small crystal H-ZSM-5 zeolite 
(silica:alumina ratio=70:1) with alumina binder in the form of cylindrical 
extrudates of about 1-5 mm. Unless otherwise stated in this description, 
the catalyst shall consist essentially of ZSM-5, which has a crystallite 
size of about 0.02 to 0.05 micron, or ZSM-23. Other pentasil catalysts 
which may be used in one or more reactor stages include a variety of 
medium pore siliceous material disclosed in U.S. Pat. Nos. 4,414,423 and 
4,417,088, incorporated herein by reference. 
The acid catalysts are deactivated by pretreatment with a 
surface-neutralizing base, as disclosed by Chen, et al., and Page, et al., 
in the patent and allowed application incorporated by reference. Surface 
deactivation is carried out using bulky or sterically hindered bases, 
typically those comprising trialkyl substituted pyridines. These hindered 
bases have very limited access to the internal pore structure of the 
catalyst, leaving the pores active sites for near linear oligomerization. 
However, active surface sites which are not constrained, as pores are, to 
low branching oligomerization are neutralized. 
Considering propylene oligomerization for purposes of illustration, the 
olefinic oligomerization-polymerization products include C.sub.10 + 
substantially linear aliphatic hydrocarbons. The ZSM-5 catalytic path for 
propylene feed provides a long chain with approximately one lower alkyl 
(e.g., methyl) substituent per 8 or more carbon atoms in the straight 
chain. 
When propylene or butene are oligomerized according to processes described 
herein, a unique mixture of liquid hydrocarbon products are formed. More 
particularly, this mixture of hydrocarbons may comprise at least 95% by 
weight of mono-olefin oligomers of the empirical formula: 
EQU C.sub.n H.sub.2n 
where n is 3 to 30, the mono-olefin oligomers comprising at least 20 
percent by weight of olefins having at least 12 carbon atoms, the olefins 
having at least 12 carbon atoms having an average of from 0.80 to 2.00 
methyl side groups per carbon chain, the olefins not having any side 
groups other than methyl. 
It will be understood that methYl side groups are methyl groups which 
occupy positions other than the terminal positions of the first and last 
(i.e., alpha and omega) carbon atoms of the longest carbon chain. This 
longest carbon chain is also referred to herein as the carbon backbone 
chain of the olefin. The average number of methyl side groups for the 
C.sub.12 olefins may comprise any range with the range of 0.80 to 2.00. 
These oligomers may be separated into fractions by conventional 
distillation separation When propylene is oligomerized, olefin fractions 
containing the following number of carbon atoms can be obtained 6, 9, 12, 
15, 18 and 21. When butene is oligomerized, olefin fractions containing 
the following numbers of carbon atoms may be obtained 8, 12, 16, 20, 24 
and 28. It is also possible to oligomerize a mixture of propylene and 
butene and to obtain a mixture of oligomers having at least 6 carbon 
atoms. 
Page and Young (allowed application Ser. No. 105,438, filed Oct. 7, 1987) 
described these new olefins as multi-component mixtures of propylene 
oligomers having relatively few branching methyl groups on the carbon 
backbone. As an example of branching, the dodecene fraction prepared from 
propylene and HZSM-23 surface modified by collidine [ZSM-23-dodecenes] 
typically has 1.3 methyl branches. This can be reduced to 1.0 or less by 
varying reaction conditions. 
HYDROFORMYLATION 
Hydroformylation, a rhodium or cobalt catalyzed addition of carbon monoxide 
and hydrogen gas to an olefin, produces aldehydes. See J. Falbe, New 
Syntheses with Carbon Monoxide, New York (1980); E. J. Wickson, Monohydric 
Alcohols, ACS Symposium Series 159, Washington, D.C. (1981); Ford, P. C., 
Catalytic Activation cf Carbon Monoxide, ACS Symposium Series 152, 
Washington, D. C. (1981), all references hereby incorporated by reference. 
However, Slaugh and Mullineaux discovered that hydroformylations using 
complexes of tri-n-butylphosphine and cobalt carbonyl catalyze the 
conversion of olefins directly to alcohols (i.e., the initially formed 
aldehydes concurrently hydrogenate). Also, the new alcohol function 
(--CH.sub.2 OH) bonds predominately on the carbon chain-end. See Slaugh, 
L., Mullineaux, R. D., Hydroformylation Catalysts, J. Organomet. Chem., 
13, 469-477 (1968); U.S. Pat. Nos. 3,239,569; 3,239,570; 3,329,566; 
3,488,158; and 3,488,157, all references hereby incorporated by reference. 
This permits using a variety of internal olefins as feeds, because they 
isomerize to a terminal position before hydroformylating. In contrast, 
rhodium-based catalysts do not promote olefin isomerization, and 
hydroformylation occurs predominately on the original double bond. See 
Asinger, F., Fell, B., Rupilius, W., Hydroformylation of 1-Olefins in 
Tertiary Orqanophosphine-Colbalt Hydrocarbonyl Catalyst Systems, Chem. 
Process Des. Dev., 8(2), 214 (1969); Stefani, A., Consiglio, G., Botteghi, 
C., Pino, P., Stereochemistry of the Hydroformylation of Olefinic 
Hydrocarbons with Cobalt and Rhodium Catalysts, J. Amer. Chem. Soc., 
99(4), 1058-1063. 
ESTERIFICATION 
The formation of esters from primary alcohols analogous to the 
hydroformylation product of the near-linear olefins described above is a 
reaction well known in the art. The 1-alkanols used in the present 
invention can be converted to esters using acylating agents that include 
aliphatic carboxyl acids, acyl halides, carboxyl acid anhydrides or 
corboxyl acid esters. Other, less common, routes to esterification may 
also be used such as those using ketenes and alcoholysis of nitriles. The 
art is well described in "Synthetic Organic Chemistry" by Wagner and Zuck, 
published by John Wiley and Sons, pages 480-498, incorporated herein by 
reference. 
Acylating agents used in the present invention comprise aliphatic carboxyl 
acids and derivatives thereof having C.sub.1 -C.sub.20 carbon atoms, 
particularly carboxyl acid anhydrides. The preferred acylating agent is 
acetic anhydride which converts the primary alcohol of the invention to 
the acetate ester. The reaction is typically carried out in the presence 
of a catalyst such as small amounts of sulfuric acid, sodium acetate, 
pyridine or Al.sub.2 O.sub.3. Generally, the esters are formed using 
carboxyl acid derivatives containing 2 to 6 carbon atoms and, in addition 
to acetic acid, include proprionic and buturic acid. 
PYROLYSIS 
The final synthetic step in the synthesis of the alpha-olefins according to 
the present invention involves the conversion of the aforementioned esters 
to the alpha-olefin by pyrolysis or deesterification. It is known in the 
art that olefins, including alpha-olefins can be produced by dehydration 
of primary alcohols typical of those produced in this invention. However, 
an important consideration in the present invention is to conduct all the 
processes including this final synthetic step without increasing the 
branching of the oligomeric molecule. Maintaining linearity in order to 
produce near-linear alpha-olefins is an important part of the overall 
inventive concept. Directly dehydrating the alkanol can, in some cases, 
lead to isomerization which may increase branching. This possibility is 
obviated by preparing the alpha-olefin by deesterification which does not 
result in isomerization or increased branching of the alpha-olefin. 
The pyrolysis of esters to olefins is known in the art and described in 
"Synthetic Organic Chemistry" by Wagner and Zuck, John Wiley and Son, 
Publisher, pages 41-42, incorporated herein by reference. Pyrolysis can be 
carried out at temperatures between 300.degree.-750.degree. C. to yield 
the olefin, in this case alpha-olefin, in high yield. 
As previously described herein the near-linear olefins used as starting 
material in this invention are typically prepared comprising a mixture of 
olefins containing a wide range of carbon numbers. The starting material 
may be used in this condition to produce a mixture of 1-alkanols and 
alpha-olefins containing a wide range of carbon numbers. Optionally the 
near-linear olefins can be separated by distillation or other means common 
and known in the art to narrow the range of carbon numbers in the starting 
material. For purposes of utilizing the present invention to prepare 
alpha-olefins suitable for oligomerization to synthetic lubricants carbon 
numbers in the range of C.sub.9 -C.sub.12 are preferred. A more 
particularly preferred carbon number for an alpha-olefin is 1-decene.

The following prophetic Examples are presented to illustrate the overall 
process of the present invention and are not intended to limit the scope 
of the invention. 
EXAMPLE 1 
(a) Near-linear olefins are prepared from propylene or isobutene or 
refinery mixtures of propylene, butenes, propane and butanes using 
2,6-di-tert-butylpyridine surface deactivated HZSM-5B as the shape 
selective catalyst according to the procedure described in U.S. Pat. No. 
4,520,221. 
(b) The above olefins are hydroformylated at 180.degree. C. using a mixture 
of carbon monoxide and hydrogen and Co.sub.2 (CO).sub.6 [(n--C.sub.4 
H.sub.9).sub.3 P].sub.2 as catalyst. The hydroformylation is carried out 
under these conditions for a period of time sufficient to convert the 
near-linear olefins starting material to a mixture of 1-alkanols. 
(c) The 1-alkanols from (b) are separated by distillation and esterified 
using acetic acid and A.sub.2 O.sub.3 as catalyst to produce the acetate 
ester of the 1-alkanols. 
(d) The acetate esters prepared in (c) are separated and pyrolyzed at 
500.degree. C. over pyrexhelices to produce a mixture of alpha-olefins 
having a methyl to methylene branch ratio of 0.15 to 0.25. 
EXAMPLE 2 
(a) Near-linear olefins with 1 to 2 methyl branches per 12 carbon atoms are 
prepared by propylene or refinery mixtures of propylene, butenes, propane 
and butane using 2,4,6-collidine modified HZSM-23 as the shape selective 
catalyst according to procedures described by Page and Young in the 
reference previously cited herein. Hydroformylation, esterification and 
pyrolysis steps are carried out as described in steps (b), (c) and (d) in 
Example 1. The alpha olefins produced have a methyl to methylene branch 
ratio of 0.1 to 0.2. 
EXAMPLE 3 
1-alkanols are prepared as described in step (b) of Example 1. In a 
continuous process the 1-alknaols are reacted with an excess of acetic 
anhydride and passed over silica at 600.degree. C., in a nitrogen 
atmosphere, to pyrolyze the acetate ester formed in situ to alpha-olefins 
having a methyl to methylene branch ratio of 0.15 to 0.25. 
EXAMPLE 4 
1-alkanols are prepared as described in step (b) of Example 2. In a 
continuous process the 1-alkanols are reacted with an excess of acetic 
anhydride and passed over silica at 600.degree. C., in a nitrogen 
atmosphere, to pyrolyze the acetate formed in situ to alpha olefins having 
a methyl to methylene branch ration of 0.1 to 0.2. 
The branch ratios defined as the ratios of CH.sub.3 groups to CH.sub.2 
groups are calculated from the weight fractions of methyl groups obtained 
by infrared methods, published in Analytical Chemistry. Vol. 25, No. 10, 
p. 1466 (1953). 
##EQU1## 
While the instant invention has been described by specific examples and 
embodiments, there is no intent to limit the inventive concept except as 
set forth in the following claims.