Note: Descriptions are shown in the official language in which they were submitted.
3~3,
K 2412 CAN
ETXYLENE OLIGOMERIZATION PROCESS
This invention relates to an improvement in a process for the
production of the linear alpha-olefin oligomers of ethylene. More
particularly, this invention is directed to an improvement in a
process for the conversion of ethylene to oligomers by contact with
a catalytic nickel complex dissolved in a polar organic solvent.
Linear mono-olefins are compounds having established utility in
a variety of applications. Linear mono-olefins having carbon numbers
in the detergent range (e.g., about C8 to C20) are known to be
particularly useful as intermediates in the production of various
surfactants, including, for example, olefin sulphonates, and alcohol
ethoxylates.
It is known in the prior art to prepare linear mono-olefins by
oligomerizing ethylene at elevated temperature and pressure in a
reaction solvent containing a catalytic nickel complex. Particularly
useful as catalysts for this service are the complexes prepared as
the reaction product of an olefinic nickel compound and a bidentate
ligand. The olefinic nickel compound is suitably a reduced nickel
compound or ~-allyl nickel compound. The reaction solvent in such a
process is preferably a diol-based solvent, particularly an alipha-
tic diol of 2 to 7 carbon atoms. Illustrative ethylene oligomeriza-
tion processes employing a nickel complex catalyst and a diol-based
solvent are described in: U.S. Patent No. 3,676,523, U.S. Patent No.
3,686,351 and U.S. Patent No. 3,737,475, all to R.F. Mason; U.S.
Patent No. 3,644564 to Van Zwet et al.; U.S. Patent No. 3,647,914 to
Glockner et al.; U.S. Patent No. 3,647,915 to
Bauer et al.; and U.S. Patent No. 3,825,615 to E.F. Lutz.
The present invention centers on the use for one such oligomeri-
zation process of a diol-based solvent which comprises a limited
quantity of water as a reaction promotor. Heretofore, processes of
this type have been practiced under essentially
~6
3()3
anhydrous conditions. Although small amounts of water are commonly
introduced into the reaction system together with the catalyst or
the solvent make-up, efforts have consistently been made to hold the
water content of the diol-based solvent to a level of no more than
about 0,2 %w, calculated on diol.
Summary of the Invention
The present invention provides an improvement in the conventi-
onal process for the oligomerization of ethylene in the presence of
a nickel chelate catalyst and in a diol solvent. According to the
invention, the ethylene is contacted with the catalyst in a diol-
solvent which comprises a specified minor amount of water. It has
been found that the presence of water in a specified proportion
relative to the solvent substantially enhances the rate of the
ethylene oligomerization reaction. For example, reaction rates are
increased by as much as 30 to 50 per cent, under preferred opera-
tion.
Only small amounts of water, i.e., between about 0.5 and 4.0
per cent by weight (%w) relative to diol, are sufficient and
necessary to achieve the desired rate enhancement. Neither lesser
nor greater proportions of water are suitable for this purpose. In
the amount specified, water is readily soluble in the diol-based
solvent and is compatible with other components of the oligomeriza-
tion system.
Thus, in the broad sense, the invention is an improvement in a
process for the preparation of oligomers of ethylene which comprises
reacting ethylene at elevated temperature and pressure in a diol-
based solvent and in the presence of a catalyst which is a chelate
of nickel with a bidentate ligand. The particular improvement is
directed to the presence in the diol-based solvent of water in a
quantity between about 0.5 and 4.0 per cent by weight (calculated on
weight of diol).
In a more narrow aspect, the invention further relates to the
discovery that such an improved process can be practiced to achieve
the desired rate enhancement without a concomitant drawback in the
distribution in the product of the various ethylene oligomers. In
~2~LC~ 3
~ 3 ~ 32a3-2575
general practice the presence of the specified small amount of water
is found to have a potential drawback from the s~andpoint of the
desirability of the production of oli~omers having a certain carbon
number distribution. It has, however, been found that in certain
preferred embodiments the invention can be practiced, under quanea-
titive limitations on catalyst nickel and ligand ccmponents, wiehout
significant sacrifice in product oligomer distribution.
Description of the Preferred Embodiments
The improved process of this invention is broadly applicable to
any ethylene oligomerization process employing a diol reaction
solvent and a nickel complex catalyst.
Oligomers are addition products which contain two or more of
the monomer units (in this case, two or more ethylene unies?~ bue
not as many units as the relatively high molecular weight addition
products which are referred to as polymers. The present invention is
particularly adapted for the production of linear mono-olefinic
oligomers of ethylene containing from 2 to about 20 monomer units
(i.e., from 4 to about 40 carbon atoms).
Catalyses suitable for use in the invention are complexes of
nickel comprising an atom of nickel chelated with a bidentate
chelating ligand. Such catalysts are typically prepared by reacting
a suitable bidentate ligand either with an olefinic nickel compound
such as bis (cyclooctadiene)nickel(0) or a ~-allyl nickel compound,
or, more preferably, with a simple divalent nickel salt and reducing
agent, e.g. boron hydride, in the presence of ethylene and in a
suitable polar organic solvent. Preparation and use of catalysts of
the former type are described in U.S. Patent No. 3,644,564 to Van
Zwet et al., U.S. Patent No. 3,647,914 to Glockner et al., and U.S.
Patent No. 3,647,415 to Bauer et al. Preparation and use of catal-
ysts of the latter type are described in U.S. PatentsNo. 3,676,523, No. 3,686,351 and No. 3,737,475, all to R.F. Mason,
as well as U.S. Patent No. 3,825,615 to E.F. Lutz.
-- 4 --
Preferred bidentate chelating ligands for such catalyst are
known to include those having a tertiary organophosphorous moiety
with a suitable functional group substituted on a carbon atom
attached directly to, or separated by no more than two carbon atoms
from, the phosphorous atom of the organophosphorous moiety.
Representative ligands of this type are the compounds
~L PCH2CH2COOM,
R
CO~M
CHz
R- p _ (OR~ , and
R ~1
R _ p _ (CH2~y - C- - N- A2
wherein R (independantly in each occurrence) represents a monovalent
organo (preferably aromatic) group suitably of up to 10 carbon
atoms,
R' (independantly in each occurrence) represents a monovalent
hydrocarbyl group, X is carboxymethyl or carboxyethyl, A is hydrogen
or an aromatic group of up to ten carbon atoms, M is hydrogen or an
alkali metal (preferably sodium or potassium), and x and y
(independently) are each either zero, one or two and the sum of x
and y is two, with the proviso ehat when x is two, the R groups may,
together with the phosphorous atom form a mono- or bycyclic
heterocyclic phosphine having from 5 to 7 carbon atoms in each ring
thereof. Particularly preferred complexes are those described in
~.S. Patent No. 3,676,523 in which the ligand is an
o-dihydrocarbylphosphinobenzoic acid or an alkali metal salt thereof
and most preferably o-diphenylphosphinobenzoic acid; in another
preferred complex described in U.S. Patent No. 3,825J615, the ligand
is dicyclohexylphosphinopropionic acid or an alkali metal salt
thereof.
Although it is not desired to be bound by any particular
theory, it has been suggested that the catalyst molecule undergoes
chemical transfor~nation during the course of the oligomerization
reaction, possibly involving coordination and/or bonding of ethylene
to the nickel moiety. However, the bidentate chelating ligand
apparently remains complexed and/or chemirally bonded to the nickel
moiety during the course of the oligomerization reaction and this
complex of the nickel and the chelating ligand is then the effective
catalytic species of the oligomerization process. In any event, the
bidentate ligand, such as the phosphorous-containing chelating
ligand, is considered as essential component of the catalyst and,
provided the nickel catalyst contains the required bidentate ligand,
the nickel catalyst may be complexed with a variety of additional
organic complexing ligands.
As is the case in prior art practice with such nickel chelate
catalysts, the molar ratio of nickel to bidentate ligand used in
catalyst preparation is preferably at least 1 19 i.e., the nickel is
present in equimolar amount or in molar excess. In the p.eparation
of catalyst complexes from a nickel salt, a ligand and a reducing
agent, the molar ratio of nickel salt to ligand is suitably in the
range from 1:1 to 5:1 with molar ratios of about 1.5:1 to 3:1
preferred and ratios of about 2:1 especially suitably. In these
preparations, the reducing agent such as boron hydride is suitably
present in equimolar amount or molar excess relative to the nickel
salt. For economic reasons, it is preferred that the reducing
agent/nickel ratio not exceed about 15:1. More preferably, this
ratio is between about 1:1 and about 10:1, while a ratio of about
1.5:1 is considered particularly preferred. Ratios somewhat below
1:1 are also suitable.
The nickel complex catalysts are suitably preformed by contac-
ting the catalyst precursors in the presence of ethylene in a
suitable polar organic diluent or solvent, which is relatively
unreactive toward the (boron hydride) reducing agent. In a preferred
modification of producing the preferred catalyst complexes as
detailed in the patents to Mason and Lutz, supra, the solvent,
nickel salt and ligand are contacted in the presence of ethylene
before the addition of reducing agent. It is essential that such
catalyst compositions be prepared in the presence of ethylene. The
catalysts are suitably prepared at temperatures of about 0 to
50 C, with substantially ambient temperatures e.g., 10 - 30 C
preferred. The ethylene pressure and contacting conditions should be
sufficient to substantially saturate the catalyst solution. For
example, ethylene pressures may be in the range from 1.7 to
104.4 bar or higher. Substantially elevated ethylene pressures,
e.g., in the range from 28.6 to 104.4 bar are preferred.
The ethylene oligomerization process of the invention is
necessarily carried out in a solvent which, for purposes of the
particular improvement of the invention, is necessarily a glycol-
based solvent. Preferably, this solvent is based on glycol(s)
selected from the group consisting of C2 to C7 aliphatic diols and
mixtures thereof. These diols include, for example, both the vicinal
alkanediols such as ethylene glycol, propylene glycol, 2-methyl-
1,2-propanediol, 1,2-butanediol and 2,3-butanediol, and the alpha-
omega alkanediols such as 1,4-butanediol, 1,5~pentanediol, 1,6-hexa-
nediol, aDd 1,7-heptanediol. Alpha-omega alkanediols of 4 to
3~
6 carbon atoms per molecule are preferred solvents with 1,4-butane-
diol being particularly preferred. In some cases, it may be desira-
ble to employ mixtures of the above-mentioned alkanediols for the
glycol-based solvent in the process of the invention.
While the solvent is glycol-based, it may also suitably contain
lesser amounts of other substances which react in some respects as
solvents for the ethylene reactant and the catalyst. Such other
solvent substances include, for eY~ample, impurities commonly present
in (essentially anhydrous) commercial diol solvents or in the nickel
chelate catalyst preparation and reaction modifiers other than
water. As the oligomerization proceeds, the solvent will, of course,
contain substantial amounts of ethylene and of oligomerization
products and by-products.
In its broader aspects, the present invention centers upon an
improvement in process performance which is provided by the presence
of water in the oligomerization solvent, and the amount of water in
the diol-based solvent is a critical aspect of the invention. For
good results from the standpoint of reaction rate enhancement, water
content of the solvent is suitably in the range from about 0.5 to
4.0 per cent by weight, calculated on the weight of the diol. No
meaningful rate enhancement is observed for either lesser or greater
water content. Water is readily soluble in the diol solvent phase in
quantities within the specified range.
It has been the practice in the prior art relative to oligomeri-
zation processes of the sort now claimed to utilize an essentially
anhydrous diol solvent containing no more than about
0.2 %w water and typically no more than about 0.1 %w water. Water is
present up to a level of about 0.1 %w in the commercially available
anhydrous grade of diols heretofore used in oligomer production.
Preferably, the diol-based solvent in the process of the
invention contains between about 0.7 and 3.5 %w water, while a water
content between about 1.0 and 3.0 %w is more preferred. Considered
most preferred is a quantity of water in the range from about 1.0 to
2.5 %w.
Without intending to be bound to one theory or mechanism of
operation for the invention, it can be said that the presence of
water in the solvent appears to essentially eliminate an induction
period which has been characteristic of such oligomerization proces-
ses in the prior art. In the absence of water, or in the presence of
only small amounts (e.g., 0.1 %w to 0.2 ~w) of water, the maximum
rate of oligomerization is not attained until near the end of a
batch reaction. Under practice of the invention, on the other hand,
the maximum rate occurs early in the course of a batch reaction.
An important aspect of ethylene oligomerization processes in
general is the distribution of the various ethylene oligomers in the
process product. The aforementioned patents rel~ting to ethylene
oligomerization catalyzed by nickel chelate complexes describe a
geometric distribution pattern for any given product which can be
defined by a single constant, referred to as the "product distribut-
ion constant" or "K factor", according to the mathematical expres-
sion: .
mols of Cn+2 olefin
K = ; (for n = 4,6,8...).
mols of C olefin
It is known that this product distribution constant is affected
by a number of parameters, including the type of bidentate ligand
employed in the catalyst complex, the type of reaction solvent or
diluent, the reaction conditions of temperature and pressure, the
catalyst concentration in the solvent and the degree of ethylene
saturation of the reaction solution. Furthermore, it has been
recognized that the use of a large proportion of water in the
reaction solvent, in particular, the use of a water-based solvent
rather than a glycol-based solvent, leads to a product in which
ethylene polymers rather than oligomers predominate. It has now also
been found out that the K factor is potentially affected to a
significant degree by the presence of small quantities of water in
the reaction solvent under practice in accordance with the invent-
ion. As a rule, it is considered preferable that the presence of
water in the diol-based solvent not induce significant change in the
process K factor, when compared to the results of a process carried
out under substantially anhydrous conditions. For instance, a
relatively high K factor9 e,g., on the order of about 0.75 to 0.80,
is often desirable to maximize the production of olefins in the
intermediate carbon number range of about C8 to C20 and to minimize
the production of higher carbon number polymeric molecules. The
presence of water in the solvent phase of the process of the inven~-
ion is, however, in many cases responsible for a significant decline
in K factor, e.g., a decrease of approximately 5 per cent.
A further important aspect of the invention is the discovery
that the reaction rate enhancement associated with the presence of
water in the diol-based solvent can be achieved without significant
change in the product distribution constant. Specifically it has
been found that rate enhancement benefits can be realized without
- significant modification of the process K factor if the process is
practiced under particular restrictions upon the concentration of
nickel and ligand in the diol-based solvent. In this regard, is has
been found to be very desirable to limit the ligand concentration to
a value up to about 700 ppm and in particular 600 ppm (parts per
million by weight, calculated on the weight of solvent) and to limit
the molar ratio of nickel to ligand in the reaction solvent to a
value greater than about 1.8. More preferably, the ligand
concentration is less than about 500 ppm and the molar ratio of
nickel to ligand in the solvent is at least about 2.0, while carry-
ing out the process of the invention with concentration of ligand
less than about 400 ppm and with molar ratio of nickel to ligand of
at least about 2.3 is considered most preferred.
Under conventional practice, K factor is initially relatively
high in a batch reaction, but declines as the reaction progresses.
In the practice of the invention, K factor is initially lower than
with dry solvent (e.g., one with no more than about 0.2 %w water)
~L ~2 L?~ 3 t} ~
-- 10 --
but remains essentially constant throughout a batch process.
With the exception of the presence of water in the diol-based
solvent 9 the process of this invention may be practiced according to
methods and under conditions well known in the prior art. Very
suitably, a mixture of catalyst precursors and diol-based solvent is
prepared and charged to an autoclave or similar pressure reactor.
The water may suitably be introduced into the diol-based solvent
either before, during of after catalyst preparation and/or addition
to the solvent. Ethylene and then sodium borohydride are introduced
to complete catalyst formation and the reaction mixtu{e is maintai-
ned with agitation at the desired reaction temperature and pressure
for oligomerization. Reaction temperature may vary over a wide
range, e.g., ~5 C to 150 C, but is preferably at least about
70 C, particularly between about 80 C and 110 C. The pressure
must be at least sufficient to maintain the reaction mixture
substantially in the liquid phase, although excess ethylene will
also be present in a vapor phase. As a rule, the total pressure is
less significant to the performance of the process than is the
partial pressure of ethylene. Under preferred practice, ethylene
partial pressure is in the range from about 49.3 to 173 bar, particul-
arly in the range from aboue 70 to 139 bar. For achieving the
greatest benefit from reaction rate enhancement in accordance with
the invention, the ethylene partial pressure is most preferably in
the range from about 77 to 104 bar. Contact between ethylene and the
catalyst in the solvent is continued until the desired degree of
oligomerization has occurred. The liquid product mixture is then
suitably treated according to conventional procedures, typically
including a separation of an oligomer-rich liquid phase from the
diol-based solvent phase, scrubbing of the oligomer-rich phase to
remove residual catalyst, dP-ethanization of the scrubbed liquid,
and further work-up of the de-ethanized product to separate it into
various product fractions. The above-referenced patents describe
suitable procedures for carrying out the several steps of the
overall oligomerization process for purposes of the invention in
either a batch or a continuous manner.
l~Z~3~)3
The invention is further illustrated by reference to the
following examples.
EXAMPLES 1-3
A series of examples (according to the invention) and compar-
ative experiments (not according to the invention) were conducted ina baech mode.
In each case, a solution of nickel complex catalyst in diol-
based solvent (95 %w 1,4-butanediol, 5 %w benzene) was first
prepared at ambient temperature by introducing into a stirred
stainless steel autoclave reactor: solvent (1,000 g), NiCl26H2O
(500 ml of a 0.3 molar solution in the solvent), KOH (499 g of a 0.1
molar solution in the solvent), and ligand (502 g of a 0.1 molar
solution of o-diphenylphosphinobenzoic acid in the solvent). Ethy-
lene was then introduced to a pressure of 35.5 bar, followed by
NaBH4 reducing agent (200 g of 0.8 molar solution in diglyme contain-
ing 0.8 g of NaOH), and finally by a further addition of ethylene to
bring the pressure to 49.3 bar.
For initiation of thè oligomerization reaction~ the catalyst
solution was heated to the desired temperature (65 ~C) and pressure
in the reactor was adjusted to and maintained at 76.9 bar by further
addition of ethylene. After 250 g of ethylene had been taken up by
the reaction, a sample of the mixture was withdrawn to monitor K-
factor of the intermediate oligomer product. After 500 g of ethylene
had been taken up, the liquid mixture in the reactor was drained and
allowed to separate into a solvent phase and a final oligomer
product phase. K factors of the intermediate and final products were
determined by gas-liquid chromatographic analyses.
Two comparative experiments, designated A and B, were carried
out to establish the rate of the oligomerization reaction in the
diol-based solvent, which contained only about 0.1 %w water. (This
0.1 %w water was attributed to water impurity in the butanediol, to
water in the nickel chloride hydrate and to water resulting from
neutralization of KOH). Examples 1, 2, and 3, all in accordance with
the invention, were carried out to illustrate the rate enhancement
associated with the presence of greater quantities of water (0.6 %w,
3~
1.1 %w, and 2.1 %wl respectively, calculated on cliol-based solvent).
The results (summarized in Table 1) indicate rate enhancement
of approximately 30 to 50 per cent for the oligomerization reaction
examples in which 0.6 to 2.1 %w was present in the diol-based
solvent, relative to those comparative examples in which minimal
water was present in the solvent.
TABLE 1
Ethylene Uptake
Solvent, 8 per g of
Comparative Example water content ligand g per l solvent
Experiment No. %w per h per h K Factor
A 0.1 162 130 0.74 (1.7 h)
0.72 (2.8 h~
B 0.1 151 122 0.77 (1.7 h)
0.76 (2.8 h)
1 0.6 214 170 0.76 (1.5 h)
0.74 (2.2 h)
2a 1.1 233 188 0.71 (1 h)
3 2.1 217 169 0.71 (1.2 h)
0.70 (2.2 h)
)In example 2, water was introduced during catalyst preparation
through use of an aqueous NaBH4 solution (3.18 g NaBH4 and 0.40 g
NaOH/100 g solution).
EXAMPLFS 4-10
A further series of examples and comparative experiments were
carried out in the following manner to illustrate preferred
practices of the invention in which reaction rate enhancement is
attained without significant change in product K factor.
For each of examples 4-7 and comparative experiments C-F, a
3~)~
- 13 -
solution of catalyst in 1,4-butanediol sc,lvent was prepared by
mixing solvent, NiCl26H20, o-diphenylphosphinobenzoic acid, KOH, and
sodium borohydride in the proportions inclicated in Table II, with
the reducing agent added in the presence of ethylene. In each case,
addition was made to a 500 ml stirred round bottom flask under
nitrogen atmosphere of: about 301 g of anhydrous 1,4-butanediol
(1,4-BD), about 1.32 g of a solution of NiCl26H20 in 1,4-BD (0.017 g
of Ni per gram of solution); about 8.11 g of a solution of o-diphenyl-
phosphinobenzoic acid in 1,4-BD (0.0128 g of ligand per gram of
solution, and about 2.24 g of a solution of KOH in 1,4-BD
(0.00905 g of KOH per g of solution). The resulting clear yellow
mixture was pressured into a one-litre autoclave, together with 35 g
of ethylene, and stirred for 30 minutes. To the autoclave was then
added a solution containing about 0.0227 g of sodium borohydride in
0.400 g of 1,4-BD and 0.400 g of water, followed by a further 2.47 g
of butanediol and 87.5 g of ethylene. In examples 8-10 and
comparative experiments I and J, the same procedures were followed
- except that the catalyst was formed by adding the NiCl2 and KOH to
the solvent, followed by ethylene, NaBH4 and ligand.
Different amounts of water were added to the solvent/catalyst
mixture for the several examples. In the comparative experiments,
the mixture contained about 0.2 %w water which was introduced with
the various components during catalyst preparation.
The autoclave was rapidly heated to 95 C to initiate the
oligomerization reaction, and maintained at this temperature for the
full reaction period. Ethylene was introduced to maintain a pressure
of about 92.7 bar. Samples of the reaction mixture were taken after
60 grams of ethylene uptake and after 136 g of ethylene uptake for
determination of K factors.
The results of examples 4-10 and comparative experiments C-J
are presented in Table 2, as a function of water content of the
solvene. The reaction rate is expressed in terms of the maximum rate
of ethylene uptake in g per litre of catalyst/diol solution per h.
303
- 14 -
TABLE 2
Solvent,
K Factor
Comperative Example water con.ent maximum
Experiment No. %w reaction rate intermediate final
C 0.2 354 0.79 0.76
D 0.2 413 0.80 0.77
E 0.2 413 ---- 0.76
F 0.2 435 ---- 0.76
4 1.0 5h5 0.73 0.78
2.0 566 0.77 0.77
6 2.0 558 0.77 0.77
7 4.0 441 0.78 0.775
G 8.0 348 0.765 0.76
H 8.0 396 0.765 0.76
I 0.2 368 0.71 -----
J 0.2 364 0.75 0.70
8 2.1 581 0.73 0.70
9 2.1 576 0.71 0.69
2.0 559 0.70 0.67
