U.S. patent application number 13/293889 was filed with the patent office on 2012-06-07 for heat management in ethylene oligomerization.
Invention is credited to Russell Kirk Archer, Michel Berghmans, Keith Wayne Besenski, Stephen John Brown, Charles Ashton Garret Carter, P. Scott Chisholm, Eric Clavelle, Oleksiy Golovchenko, Mackenzie Alexander Harris, Isam Jaber, Ian Ronald Jobe, Andrzej Krzywicki, Yves Lacombe, Anita Sylvia Magis, Kamal l Elias Serhal, Dale Alexander Sieben, Vernon Lindsay Strom.
Application Number | 20120142989 13/293889 |
Document ID | / |
Family ID | 46162845 |
Filed Date | 2012-06-07 |
United States Patent
Application |
20120142989 |
Kind Code |
A1 |
Jaber; Isam ; et
al. |
June 7, 2012 |
HEAT MANAGEMENT IN ETHYLENE OLIGOMERIZATION
Abstract
The oligomerization of ethylene using a chromium catalyst having
a heteroatomic ligand may be used to provide oligomerization
products that are selective towards hexene and/or octene. However,
such processes also typically produce some polymer as an
undesirable by product. The present invention is directed towards
improvements in the selective oligomerization of ethylene.
Inventors: |
Jaber; Isam; (CALGARY,
CA) ; Jobe; Ian Ronald; (CALGARY, CA) ;
Chisholm; P. Scott; (CALGARY, CA) ; Krzywicki;
Andrzej; (CALGARY, CA) ; Carter; Charles Ashton
Garret; (CALGARY, CA) ; Strom; Vernon Lindsay;
(CALGARY, CA) ; Serhal; Kamal l Elias; (CALGARY,
CA) ; Clavelle; Eric; (CALGARY, CA) ; Brown;
Stephen John; (CALGARY, CA) ; Lacombe; Yves;
(CALGARY, CA) ; Magis; Anita Sylvia; (CALAGRY,
CA) ; Harris; Mackenzie Alexander; (CALGARY, CA)
; Archer; Russell Kirk; (CALGARY, CA) ; Besenski;
Keith Wayne; (CALGARY, CA) ; Berghmans; Michel;
(CALGARY, CA) ; Golovchenko; Oleksiy; (CALGARY,
CA) ; Sieben; Dale Alexander; (CALGARY, CA) |
Family ID: |
46162845 |
Appl. No.: |
13/293889 |
Filed: |
November 10, 2011 |
Current U.S.
Class: |
585/532 ;
585/520 |
Current CPC
Class: |
C07C 2/36 20130101; C07C
2531/24 20130101; C07C 2/36 20130101; C07C 2523/26 20130101; C07C
2/36 20130101; Y02P 20/52 20151101; C07C 11/02 20130101; C07C
11/107 20130101; C07C 2531/14 20130101 |
Class at
Publication: |
585/532 ;
585/520 |
International
Class: |
C07C 2/02 20060101
C07C002/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 1, 2010 |
CA |
2723515 |
Claims
1. A solution process for the oligomerization of ethylene, said
process comprising contacting ethylene with: a) oligomerization
catalyst; b) an activator; and c) a solvent for said catalyst, said
process being conducted under oligomerization conditions in an
oligomerization reactor system, characterized in that said process
is conducted with process equipment that includes: 1) a first heat
exchanger that is used to provide heat to said process; and 2) a
second heat exchanger that is used to remove heat from said
oligomerization reactor system.
2. The process of claim 1 wherein: a) said catalyst consists
essentially of a source of chromium that is soluble in said solvent
and a bridged diphosphine ligand; and b) said activator consists
essentially of an aluminoxane.
3. The process of claim 1 wherein said oligomerization reactor
system comprises at least one liquid full continuously stirred tank
reactor.
4. The process of claim 1 wherein said oligomerization reactor
system comprises a continuously stirred tank reactor and a tubular
reactor, with the further provisos that: a) said continuously
stirred tank reactor is upstream of said tubular reactor; b) said
tubular reactor is fed a combination of i) first product from said
continuously stirred tank reactor; and ii) fresh feed comprising
ethylene and solvent, with the additional proviso that said fresh
feed is colder than said first product.
5. The process of claim 4, further characterized in that first
product is initially cooled in a heat exchanger prior to being fed
to said tubular reactor.
6. The process of claim 1 wherein said oligomerization reactor
system comprises two continuously stirred tank reactors in series,
with the further proviso that: a) an upstream continuously stirred
tank reactor having a first reactor volume produces a first
oligomerization product; and b) said first oligomerization product
and fresh feed comprising ethylene and solvent are fed to a
downstream continuously stirred tank reactor having a second
reactor volume that is greater than said first reactor volume.
7. The process of claim 3 wherein each of said at least one
continuously stirred tank reactor is characterized by having an
agitator shaft seal that contains a fluid channel contained therein
that permits fluid flushing of said agitation shaft.
8. The process according to claim 1, further characterized in that
a portion of said ethylene is dissolved in solvent in a solution
absorber that is external to said reactor system, with the further
proviso that said solution absorber is equipped with a third heat
exchanger for removal of heat of absorbtion.
9. The process according to claim 1, wherein 1) said
oligomerization catalyst comprises: 1.1) a source of chromium that
is soluble in said solvent; and 1.2) a ligand defined by the
formula
(R.sup.1)(R.sup.2)--P.sup.1-bridge-P.sup.2(R.sup.3)(R.sup.4)
wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are independently
selected from the group consisting of hydrocarbyl and
heterohydrocarbyl and the bridge is a divalent moiety that is
bonded to both phosphorus atoms. 2) said activator comprises an
aluminoxane; 3) said oligomerization conditions comprises a
temperature of from 10 to 100.degree. C. and a pressure of from 5
to 100 atmospheres.
10. The process according to claim 9 wherein said bridge is
--N(R.sup.5)-- wherein R.sup.5 is selected from the group
consisting of hydrogen, alkyl, substituted alkyl, aryl, substituted
aryl, aryloxy, substituted aryloxy, halogen, alkoxycarbonyl,
carbonyloxy, alkoxy, aminocarbonyl, carbonylamino, dialkylamino,
silyl groups or derivatives thereof and an aryl group substituted
with any of these substituents.
Description
FIELD OF THE INVENTION
[0001] This invention relates to selective ethylene oligomerization
reactions.
BACKGROUND OF THE INVENTION
[0002] Alpha olefins are commercially produced by the
oligomerization of ethylene in the presence of a simple alkyl
aluminum catalyst (in the so called "chain growth" process) or
alternatively, in the presence of an organometallic nickel catalyst
(in the so called Shell Higher Olefins, or "SHOP" process). Both of
these processes typically produce a crude oligomer product having a
broad distribution of alpha olefins with an even number of carbon
atoms (i.e. butene-1, hexene-1, octene-1 etc.). The various alpha
olefins in the crude oligomer product are then typically separated
in a series of distillation columns. Butene-1 is generally the
least valuable of these olefins as it is also produced in large
quantities as a by-product in various cracking and refining
processes. Hexene-1 and octene-1 often command comparatively high
prices because these olefins are in high demand as comonomers for
linear low density polyethylene (LLDPE).
[0003] Technology for the selective trimerization of ethylene to
hexene-1 has been recently put into commercial use in response to
the demand for hexene-1. The patent literature discloses catalysts
which comprise a chromium source and a pyrrolide ligand as being
useful for this process--see, for example, U.S. Pat. No. ("USP")
5,198,563 (Reagen et al., assigned to Phillips Petroleum).
[0004] Another family of highly active trimerization catalysts is
disclosed by Wass et al. in WO 02/04119 (now U.S. Pat. Nos.
7,143,633 and 6,800,702). The catalysts disclosed by Wass et al.
are formed from a chromium source and a chelating diphosphine
ligand and are described in further detail by Carter et al. (Chem.
Comm. 2002, p 858-9). As described in the Chem. Comm. paper, these
catalysts preferably comprise a diphosphine ligand in which both
phosphine atoms are bonded to two phenyl groups that are each
substituted with an ortho-methoxy group. Hexene-1 is produced with
high activity and high selectivity by these catalysts.
[0005] Similar diphosphine/tetraphenyl ligands are disclosed by
Blann et al. in WO04/056478 and WO 04/056479 (now US 2006/0229480
and US 2006/0173226). However, in comparison to the ligands of Wass
et al., the disphosphine/tetraphenyl ligands disclosed by Blann et
al. generally do not contain polar substituents in ortho positions.
The "tetraphenyl" diphosphine ligands claimed in the '480
application must not have ortho substituents (of any kind) on all
four of the phenyl groups and the "tetraphenyl" diphosphine ligands
claimed in '226 are characterized by having a polar substituent in
a meta or para position. Both of these approaches are shown to
reduce the amount of hexenes produced and increase the amount of
octene (in comparison to the ligands of Wass et al.). Other bridged
diphosphine ligands that are useful for the selective
oligomerization of ethylene are disclosed in the literature. The
formation of polymer as a by-product is a general problem with many
of these ligands.
SUMMARY OF THE INVENTION
[0006] In one embodiment, the present invention provides a solution
process for the oligomerization of ethylene, said process
comprising contacting ethylene with:
a) oligomerization catalyst; b) an activator; and c) a solvent for
said catalyst, said process being conducted under oligomerization
conditions in an oligomerization reactor system characterized in
that said process is conducted with process equipment that
includes: 1) a first heat exchanger that is used to provide heat to
said process; and 2) a second heat exchanger that is used to remove
heat from said oligomerization reactor system.
[0007] It will be appreciated by those skilled in the art that the
present invention is somewhat unusual in that heat is both provided
to and removed from the oligomerization process. It is recognized
that this process is not optimal from the perspective of energy
efficiency. However, the present process provides the capability to
improve temperature control, particularly during non-steady state
operations such as encountered when fluctuations in process flows
or poison levels (especially during start up) cause the reactor to
become unstable.
[0008] We have observed severe reactor fouling when the temperature
in the oligomerization reactor suddenly drops and the process of
this invention mitigates this problem. This invention is generally
useful for any selective oligomerization process. It is especially
useful when the catalyst comprises a bridged diphosphine ligand and
when the reactor system includes a liquid full CSTR.
[0009] For further clarity: the two heat exchangers described above
are independent of each other--that is, they both may be operated
at the same time. (This is to distinguish the present invention
from a common design in which a single heat exchanger may be used
either to heat or cool a process stream).
[0010] In another embodiment, the ethylene feed stream is equipped
with a third heat exchanger to cool the feed stream (as discussed
later, with reference to the so called "solution absorber"). In a
preferred embodiment, the "first heat exchanger" (i.e. the heat
exchanger that may be used to provide heat to the process) is
located "downstream" of the third heat exchanger--i.e. the third
heat exchanger may be used to heat the feed stream before the feed
stream is sent to the reactor. In plain language, the first heat
exchanger may be used to heat the cooled feed from the "third" heat
exchanger. It will be recognized by those skilled in the art that
such a cooling/heating cycle is not energy efficient and that it
should be avoided during steady state operations. However, this
ability to both cool and heat the feed stream has been found to be
useful to mitigate unwanted polymer formation during unsteady
operations (such as encountered at start up or during a reactor
upset).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Part A Catalyst System
[0011] The preferred catalyst system used in the process of the
present invention must contain three essential components,
namely:
[0012] (i) a source of chromium that is soluble in the process
solvent;
[0013] (ii) a diphosphine ligand; and
[0014] (iii) an activator.
Preferred forms of each of these components are discussed below.
Chromium Source ("Component (i)")
[0015] Any source of chromium that is soluble in the process
solvent and which allows the oligomerization process of the present
invention to proceed may be used. Preferred chromium sources
include chromium trichloride; chromium (III) 2-ethylhexanoate;
chromium (III) acetylacetonate and chromium carbonyl complexes such
as chromium hexacarbonyl. It is preferred to use very high purity
chromium compounds as these should generally be expected to
minimize undesirable side reactions. For example, chromium
acetylacetonate having a purity of higher than 99% is commercially
available (or may be readily produced from 97% purity
material--using recrystallization techniques that are well known to
those skilled in the art).
Ligand Used in the Oligomerization Process ("Component (ii)")
[0016] In general, the ligand used in the oligomerization process
of this invention is defined by the formula
(R.sup.1)(R.sup.2)--P.sup.1-bridge-P.sup.2(R.sup.3)(R.sup.4)
wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are independently
selected from the group consisting of hydrocarbyl and
heterohydrocarbyl and the bridge is a divalent moiety that is
bonded to both phosphorus atoms.
[0017] The term hydrocarbyl as used herein is intended to convey
its conventional meaning--i.e. a moiety that contains only carbon
and hydrogen atoms. The hydrocarbyl moiety may be a straight chain;
it may be branched (and it will be recognized by those skilled in
the art that branched groups are sometimes referred to as
"substituted"); it may be saturated or contain unsaturation and it
may be cyclic. Preferred hydrocarbyl groups contain from 1 to 20
carbon atoms. Aromatic groups--especially phenyl groups--are
especially preferred. The phenyl may be unsubstituted (i.e. a
simple C.sub.6H.sub.5 moiety) or contain substituents, particularly
at an ortho (or "o") position.
[0018] Similarly, the term heterohydrocarbyl as used herein is
intended to convey its conventional meaning--more particularly, a
moiety that contains carbon, hydrogen and heteroatoms (such as O,
N, R and S). The heterohydrocarbyl groups may be straight chain,
branched or cyclic structures. They may be saturated or contain
unsaturation. Preferred heterohydrocarbyl groups contain a total of
from 2 to 20 carbon+heteroatoms (for clarity, a hypothetical group
that contains 2 carbon atoms and one nitrogen atom has a total of 3
carbon+heteroatoms).
[0019] It is preferred that each of R.sup.1, R.sup.2, R.sup.3 and
R.sup.4 is a phenyl group (with an optional substituent in an ortho
position on one or more of the phenyl groups).
[0020] Highly preferred ligands are those in which R.sup.1 to
R.sup.4 are independently selected from the group consisting of
phenyl, o-methylphenyl (i.e. ortho-methylphenyl), o-ethylphenyl,
o-isopropylphenyl and o-fluorophenyl. It is especially preferred
that none of R.sup.1 to R.sup.4 contains a polar substituent in an
ortho position. The resulting ligands are useful for the selective
tetramerization of ethylene to octene-1 with some co product hexene
also being produced. The term "bridge" as used herein with respect
to the ligand refers to a divalent moiety that is bonded to both of
the phosphorus atoms in the ligand--in other words, the "bridge"
forms a link between P.sup.1 and P.sup.2. Suitable groups for the
bridge include hydrocarbyl and an inorganic moiety selected from
the group consisting of N(CH.sub.3)--N(CH.sub.3)--, --B(R.sup.6)--,
--Si(R.sup.6).sub.2--, --P(R.sup.6)-- or --N(R.sup.6)-- where
R.sup.6 is selected from the group consisting of hydrogen,
hydrocarbyl and halogen.
[0021] It is especially preferred that the bridge is --N(R.sup.5)--
wherein R.sup.5 is selected from the group consisting of hydrogen,
alkyl, substituted alkyl, aryl, substituted aryl, aryloxy,
substituted aryloxy, halogen, alkoxycarbonyl, carbonyloxy, alkoxy,
aminocarbonyl, carbonylamino, dialkylamino, silyl groups or
derivatives thereof and an aryl group substituted with any of these
substituents. A highly preferred bridge is amino isopropyl (i.e.
when R.sup.5 is isopropyl).
[0022] In one embodiment, two different types of ligands are used
to alter the relative amounts of hexene and octene being produced.
For clarity: the use of a ligand that produces predominantly hexene
may be used in combination with a ligand that produces
predominantly octene.
Activator ("Component (iii)")
[0023] The activator (component (iii)) may be any compound that
generates an active catalyst for ethylene oligomerization with
components (i) and (ii). Mixtures of activators may also be used.
Suitable compounds include organoaluminum compounds, organoboron
compounds and inorganic acids and salts, such as tetrafluoroboric
acid etherate, silver tetrafluoroborate, sodium
hexafluoroantimonate and the like. Suitable organoaluminum
compounds include compounds of the formula AlR.sub.3, where each R
is independently C.sub.1-C.sub.12 alkyl, oxygen or halide, and
compounds such as LiAlH.sub.4 and the like. Examples include
trimethylaluminium (TMA), triethylaluminium (TEA),
tri-isobutylaluminium (TIBA), tri-n-octylaluminium, methylaluminium
dichloride, ethylaluminium dichloride, dimethylaluminium chloride,
diethylaluminium chloride, ethylaluminiumsesquichloride,
methylaluminiumsesquichloride, and alumoxanes. Alumoxanes are well
known in the art as typically oligomeric compounds which can be
prepared by the controlled addition of water to an alkylaluminium
compound, for example trimethylaluminium. Such compounds can be
linear, cyclic, cages or mixtures thereof. Commercially available
alumoxanes are generally believed to be mixtures of linear and
cyclic compounds. The cyclic alumoxanes can be represented by the
formula [R.sup.6AlO].sub.s and the linear alumoxanes by the formula
R.sup.7(R.sup.6AlO).sub.s wherein s is a number from about 2 to 50,
and wherein R.sup.6, R.sup.7, and R.sup.8 represent hydrocarbyl
groups, preferably C.sub.1 to C.sub.6 alkyl groups, for example
methyl, ethyl or butyl groups. Alkylalumoxanes especially
methylalumoxane (MAO) are preferred.
[0024] It will be recognized by those skilled in the art that
commercially available alkylalumoxanes may contain a proportion of
trialkylaluminium. For instance, commercial MAO usually contains
approximately 10 wt % trimethylaluminium (TMA), and commercial
"modified MAO" (or "MMAO") contains both TMA and TIBA. Quantities
of alkylalumoxane are generally quoted herein on a molar basis of
aluminium (and include such "free" trialkylaluminium).
[0025] Examples of suitable organoboron compounds are boroxines,
NaBH.sub.4, trimethylboron, triethylboron,
dimethylphenylammoniumtetra(phenyl)borate,
trityltetra(phenyl)borate, triphenylboron, dimethylphenylammonium
tetra(pentafluorophenyl)borate, sodium
tetrakis[(bis-3,5-trifluoromethyl)phenyl]borate,
trityltetra(pentafluorophenyl)borate and tris(pentafluorophenyl)
boron.
[0026] Activator compound (iii) may also be or contain a compound
that acts as a reducing or oxidizing agent, such as sodium or zinc
metal and the like, or oxygen and the like.
[0027] In the preparation of the catalyst systems used in the
present invention, the quantity of activating compound to be
employed is easily determined by simple testing, for example, by
the preparation of small test samples which can be used to
oligimerize small quantities of ethylene and thus to determine the
activity of the produced catalyst. It is generally found that the
quantity employed is sufficient to provide 0.5 to 1000 moles of
aluminium (or boron) per mole of chromium. MAO is the presently
preferred activator. Molar Al/Cr ratios of from 1/1 to 500/1 are
preferred.
Part B Process Conditions
[0028] The chromium (component (i)) and ligand (component (ii)) may
be present in any molar ratio which produces oligomer, preferably
between 100:1 and 1:100, and most preferably from 10:1 to 1:10,
particularly 3:1 to 1:3. Generally the amounts of (i) and (ii) are
approximately equal, i.e. a ratio of between 1.5:1 and 1:1.5.
[0029] Components (i)-(iii) of the catalyst system utilized in the
present invention may be added together simultaneously or
sequentially, in any order, and in the presence or absence of
ethylene in any suitable solvent, so as to give an active catalyst.
For example, components (i), (ii) and (iii) and ethylene may be
contacted together simultaneously, or components (i), (ii) and
(iii) may be added together simultaneously or sequentially in any
order and then contacted with ethylene, or components (i) and (ii)
may be added together to form an isolable metal-ligand complex and
then added to component (iii) and contacted with ethylene, or
components (i), (ii) and (iii) may be added together to form an
isolable metal-ligand complex and then contacted with ethylene.
Suitable solvents for contacting the components of the catalyst or
catalyst system include, but are not limited to, hydrocarbon
solvents such as heptane, toluene, 1-hexene and the like, and polar
solvents such as diethyl ether, tetrahydrofuran, acetonitrile,
dichloromethane, chloroform, chlorobenzene, acetone and the like. A
preferred solvent is the oligomer product that is produced by the
present process or some fraction thereof--such as hexene, octene or
a mixture of the two.
[0030] For further clarity: the catalyst components may be mixed
together in the oligomerization reactor, or--alternatively--some or
all of the catalyst components may be mixed together outside of the
oligomerization reactor. In general, it is preferred to mix the
catalyst components outside of the reactor (due to comparative ease
of control) then add the catalyst to the reactor shortly thereafter
(because "aged" catalyst may suffer from some loss of activity).
This method of catalyst synthesis is illustrated in the examples.
The solvent that is used to prepare the catalyst is preferably the
olefinic product that is produced by the reactor (or some portion
thereof). We have found that the use of octene generally works
well. However, some catalyst components have comparatively low
solubility in octene. For example, MAO that is made solely with
trimethylaluminum (as opposed to "modified MAO" which also contains
some higher alkyl aluminum, such as triisobutyl aluminum) is less
soluble in octene than in some cyclic hydrocarbons such as xylene
or tetralin. Accordingly, when one or more catalyst components are
mixed together outside of the oligomerization reactor, the use of
ortho-xylene or tetralin as the solvent may be preferred. The
xylene may be a mixture of ortho, meta and para isomers--i.e. it is
not necessary to use a pure isomer.
[0031] A variety of methods are known to purify solvents used in
the oligomerization process including use of molecular sieves (3A),
adsorbent alumina and supported de-oxo copper catalyst. Several
configurations for the purifier system are known and depend on the
nature of the impurities to be removed, the purification efficiency
required and the compatibility of the purifier material and the
process solvent. In some configurations, the process solvent is
first contacted with molecular sieves, followed by adsorbent
alumina, then followed by supported de-oxo copper catalyst and
finally followed by molecular sieves. In other configurations, the
process solvent is first contacted with molecular sieves, followed
by adsorbent alumina and finally followed by molecular sieves. In
yet another configuration, the process solvent is contacted with
adsorbent alumina. When alpha olefinic solvents are used in the
process, the preferred purifier system consists of molecular
sieves, followed by adsorbent alumina and finally followed by
another set of molecular sieves.
[0032] The catalyst components (i), (ii) and (iii) utilized in the
present invention can be unsupported or supported on a support
material, for example, silica, alumina, MgCl.sub.2 or zirconia, or
on a polymer, for example polyethylene, polypropylene, polystyrene,
or poly(aminostyrene). If desired the catalysts can be formed in
situ in the presence of the support material, or the support
material can be pre-impregnated or premixed, simultaneously or
sequentially, with one or more of the catalyst components. The
quantity of support material employed can vary widely, for example
from 100,000 to 1 gram per gram of metal present in the transition
metal compound. In some cases, the support material can also act as
or as a component of the activator compound (iii). Examples include
supports containing alumoxane moieties.
[0033] Oligomerization reactions can generally be conducted under
solution phase, slurry phase, gas phase or bulk phase conditions.
Suitable temperatures range from 10.degree. C. to +300.degree. C.
preferably from 10.degree. C. to 100.degree. C., especially from 20
to 80.degree. C. Suitable pressures are from atmospheric to 800
atmospheres (gauge) preferably from 5 atmospheres to 100
atmospheres, especially from 10 to 50 atmospheres.
[0034] Irrespective of the process conditions employed, the
oligomerization is typically carried out under conditions that
substantially exclude oxygen, water, and other materials that act
as catalyst poisons. In addition, the reactor is preferably purged
with a nonreactive gas (such as nitrogen or argon) prior to the
introduction of catalyst. A purge with a solution of MAO and/or
aluminum alkyl may also be employed to lower the initial level of
catalyst poisons. Also, oligomerizations can be carried out in the
presence of additives to control selectivity, enhance activity and
reduce the amount of polymer formed in oligomerization processes.
Potentially suitable additives include, but are not limited to,
hydrogen or a halide source (especially the halide sources
disclosed in U.S. Pat. No. 7,786,336, Zhang et al.). Other
(optional) additives include antistatic agents (such as the
polysulfone polymer sold under the trademark Stadis.RTM.) and/or
fluorocarbons to mitigate reaction fouling; or amines to alter the
hexene/octene ratio of the product oligomer (as disclosed in U.S.
application 20090118117, Elowe et al.). The use of hydrogen is
especially preferred because it has been observed to reduce the
amount of polymer that is formed. It is within the scope of this
invention that an oligomerization product might also serve as a
solvent or diluent. The preferred catalysts of this invention
predominantly produce hexene and octene (as shown in the examples)
but smaller quantities of butene and C.sub.10+ olefins are also
produced. The crude product stream may be separated into various
fractions using, for example, a conventional distillation system.
It is within the scope of this invention to recycle the "whole"
oligomer product or some fraction(s) thereof to the reaction for
use as the oligomerization solvent/diluents. For example, by
recycling a butene rich stream it might be possible to lower the
refrigeration load in distillation. Alternatively, the C.sub.10+
fraction might be preferentially recycled to improve the solubility
of one or more components of the catalyst system. Mixtures of inert
diluents or solvents also could be employed. The preferred diluents
or solvents are aliphatic and aromatic hydrocarbons and halogenated
hydrocarbons such as, for example, isobutane, pentane, toluene,
xylene, ethylbenzene, cumene, mesitylene, heptane, cyclohexane,
methylcyclohexane, 1-hexene, 1-octene, chlorobenzene,
dichlorobenzene, and the like, and mixtures such as Isopar.TM..
[0035] Techniques for varying the distribution of products from the
oligomerization reactions include controlling process conditions
(e.g. concentration of components (i)-(iii), reaction temperature,
pressure, residence time) and properly selecting the design of the
process and are well known to those skilled in the art.
[0036] In another embodiment, a catalyst that produces ethylene
homopolymer is deliberately added to the reactor in an amount
sufficient to convert from 1 to 5 weight % of the ethylene feed to
an ethylene homopolymer. This catalyst is preferably supported. The
purpose is to facilitate the removal of by-product
polyethylene.
[0037] The ethylene feedstock for the oligomerization may be
substantially pure or may contain other olefinic impurities and/or
ethane. One embodiment of the process of the invention comprises
the oligomerization of ethylene-containing waste streams from other
chemical processes or a crude ethylene/ethane mixture from a
cracker as more fully described in co-pending Canadian patent
application 2,708,011 (Krzywicki et al.).
[0038] The feedstock is preferably treated to remove catalyst
poisons (such as oxygen, water and polar species) using techniques
that are well known to those skilled in the art. The technology
used to treat feedstocks for polymerizations is suitable for use in
the present invention and includes the molecular sieves, alumina
and de-oxo catalysts described above for analogous treatment of the
process solvent.
Reactor Systems
[0039] A general review of suitable reactors for selective
oligomerization is provided first, followed by a detailed
description of preferred reactor designs. There exist a number of
options for the oligomerization reactor including batch,
semi-batch, and continuous operation. Oligomerization reactions can
generally be performed under a range of process conditions that are
readily apparent to those skilled in the art: as a homogeneous
liquid phase reaction in the presence or absence of an inert
hydrocarbon diluent such as toluene or heptanes; as a two-phase
liquid/liquid reaction; as a slurry process where the catalyst is
in a form that displays little or no solubility; as a bulk process
in which essentially neat reactant and/or product olefins serve as
the dominant medium; as a gas-phase process in which at least a
portion of the reactant or product olefin(s) are transported to or
from a supported form of the catalyst via the gaseous state.
Evaporative cooling from one or more monomers or inert volatile
liquids is but one (prior art) method that can be employed to
effect the removal of heat from the reaction. The reactions may be
performed in the known types of gas-phase reactors, such as
circulating bed, vertically or horizontally stirred-bed, fixed-bed,
or fluidized-bed reactors, liquid-phase reactors, such as a
plug-flow reactor, or a continuously stirred tank reactor (CSTR),
or a loop reactor, or combinations thereof. A wide range of methods
for effecting product, reactant, and catalyst separation and/or
purification are known to those skilled in the art and may be
employed: distillation, filtration, liquid-liquid separation,
slurry settling, extraction, etc. One or more of these methods may
be performed separately from the oligomerization reaction or it may
be advantageous to integrate at least some with the reaction; a
non-limiting example of this would be a process employing catalytic
(or reactive) distillation. Also advantageous may be a process
which includes more than one reactor, a catalyst kill system
between reactors or after the final reactor, or an integrated
reactor/separator/purifier. While all catalyst components,
reactants, inerts, and products could be employed in the present
invention on a once-through basis, it is often economically
advantageous to recycle one or more of these materials; in the case
of the catalyst system, this might require reconstituting one or
more of the catalysts components to achieve the active catalyst
system.
[0040] More specific reactor designs have been described in the
patent literature: [0041] a liquid phase reactor with "bubbling"
ethylene feed is taught as a means to mitigate PE formation (WO
2009/060342, Kleingeld et al.); [0042] a liquid phase reactor with
an inert, condensable liquid is claimed as a means to improve
temperature control (WO 2009/060343, Crildenhuys). The condensable
liquid boils from the reaction liquid and is condensed overhead;
and [0043] the use of a liquid/gas phase reactor in which cooling
coils are present in the gas phase head space is described in WO
2007/016996, Fritz et al.).
[0044] The present invention provides additional reactor designs
for selective oligomerizations. The present invention is
characterized (in part) by the requirement that a non adiabatic
reactor system is used. The term "non adiabatic" means that heat is
added to and/or removed from the oligomerization reactor. The term
"reactor system" means that one or more reactors are employed (and
the term "non adiabatic reactor system" means that at least one of
the reactors is equipped with a heat exchanger that allows heat to
be added to or removed from it). One embodiment relates to a CSTR
with an external heat exchanger. A second embodiment relates to a
tubular plug flow equipped with multiple feed ports for ethylene
along the length of the reactor. A third embodiment relates to a
combination of a CSTR followed by a tubular reactor. A fourth
embodiment provides a loop reactor. A fifth embodiment provides a
reactor having an internal cooling system (such as a draft tube
reactor).
[0045] One preferred CSTR for use in the present invention is
equipped at least one external heat exchanger--meaning that the
heat exchanger surface(s) are not included within the walls of the
CSTR. The term "heat exchanger" is meant to include its broad,
conventional meaning. Most importantly, the heat exchanger will
preferably be designed so as to allow heating of the reactor
contents (which may be desirable during start up) and to provide
heat removal during the oligomerization. A preferred external heat
exchanger for a CSTR comprises a conventional shell and tube
exchanger with a "process" side tube system and a shell for the
exchange side. In one embodiment the "process side" (i.e. the side
of the exchanger that contains the fluid from the oligomerization
process) is a tube that exits the reactor and flows through the
shell for heat exchange, then reenters the reactor with cooled (or
heated) process fluid. For clarity: during an oligomerization
reaction a portion of the hot reactor contents or "process fluid"
will flow from the reactor to the external heat exchanger, through
a tube. The exterior of the tube comes into contact with cold fluid
on the shell side of the exchanger, thus cooling the process fluid.
The cooled process fluid is then returned to the reactor.
[0046] The use of two of more CSTR reactors in series is also
contemplated. In particular, the use of a first CSTR having a small
volume followed by a larger CSTR might be used to facilitate
startup.
[0047] In another embodiment, a heat exchanger is located between
two CSTRs. In this embodiment, the product from the first
oligomerization reactor leaves that reactor through an exit tube.
The oligomerization products in this exit tube are then directed
through a heat exchanger. After being cooled by the heat exchanger,
the oligomerization products are then directed into a second CSTR.
Additional ethylene (and, optionally, catalyst) is added to the
second CSTR and further oligomerization takes place.
[0048] The amount of heat generated by the oligomerization reaction
is generally proportional to the amount of ethylene being
oligomerized. Thus, at high rates of oligomerization, a high rate
of coolant flow is required in the shell side of the exchanger.
[0049] The rate of oligomerization is generally proportional to the
amount of ethylene and catalyst that are fed to the CSTR. In one
preferred embodiment the ethylene is first contacted with solvent
in a mixing vessel that is external to the CSTR. For convenience,
this mixing vessel is referred to herein as a "solution absorber".
The solution absorber is preferably equipped with a heat exchanger
to remove the heat of absorbtion--i.e. heat is generated when the
ethylene dissolves in the solvent and this heat exchanger removes
the heat of solution. The solution absorber may be a CSTR, or
alternatively, a simple plug flow tube. Thus, the heat exchanger on
the solution absorber is used to provide cooled feed. In one
embodiment the heat exchanger may be used to chill the feed to
below ambient conditions--this is desirable to maximize reactor
throughput.
[0050] In a preferred embodiment, another heat exchanger is
provided that allows the feed stream to be heated. This heat
exchanger may be located in direct contact with the solution
absorber or--alternatively, this heat exchanger may be located
between the solution absorber and the oligomerization reactor. In
general, this heat exchanger will be used during non-steady state
conditions (such as are encountered at start up or during a reactor
upset) to quickly provide heat to the reactor.
[0051] In a highly preferred embodiment, the ethylene/solvent is
fed to the CSTR through a plurality of feed ports. In one such
embodiment, the feed is provided by way of a tubular ring that
contains a plurality of holes and follows a circle around an
interior diameter of the CSTR. The ethylene/solvent is preferably
directed into liquid contained in the reactor (as opposed to gas)
and even more preferably, the CSTR is operated in a liquid full
mode. As used herein, the term "liquid full" means that the reactor
is at least 90% full of liquid (by volume). More preferably, the
ethylene is co-fed with hydrogen (i.e. hydrogen is added to the
solvent/ethylene mixture). Even more preferably, the CSTR is
equipped with at least two impellers that are separated from each
other along the length of the agitator shaft and the
ethylene/solvent/hydrogen feed is directed to the tip of one
impeller and the catalyst feed is directed to the tip of the second
impeller that is located at a different point along the length of
the agitator shaft.
[0052] Conventional baffles that run vertically along the interior
wall of the CSTR may be included to enhance mixing.
[0053] The average feed velocity for the ethylene/solvent is
preferably from 0.1 to 100 mm/s. Feed velocity is calculated by
dividing the volumetric flow rate (mm.sup.3/s) by the total area of
openings in the feed ports (mm.sup.2). High feed velocity (and a
plurity of feed ports) helps to rapidly disperse the ethylene.
Optimum feed velocity will, in general, be influenced by a number
of variables--including reactor geometry, reactor agitation and
production rates. The optimization of feed rates may require that
the size and number of feed ports is changed--but such optimization
and changes are well within the scope of those of ordinary skill in
the art.
[0054] The CSTR is preferably operated in continuous flow
mode--i.e. feed is continuously provided to the CSTR and product is
continuously withdrawn.
[0055] The CSTR described above may be used to provide the high
degree of temperature control that we have observed to be
associated with a low degree of polymer formation.
[0056] In another embodiment, the CSTR is equipped with one or more
of the mixing elements described in U.S. Pat. No. 6,319,996 (Burke
et al.). In particular, Burke et al. disclose the use of a tube
which has a diameter that is approximately equal to the diameter of
the agitator of the CSTR. This tube extends along the length of the
agitator shaft, thereby forming a mixing element that is often
referred to as a "draft tube" by those skilled in the art. The
reactor used in this invention may also employ the mixing helix
disclosed by Burke et al. (which helix is located within the draft
tube and forms a type of auger or Archimedes screw within the draft
tube). The use of stationary, internal elements (to divide the CSTR
into one or more zones) may also be employed. In one such example,
two impellers are vertically displaced along the length of the
agitation shaft i.e. one in the top part of the reactor and another
in the bottom. An internal "ring" or "doughnut" is used to divide
the CSTR into a top reaction zone and a bottom reaction zone. The
ring is attached to the diameter of the CSTR and extends inwardly
towards the agitation shaft to provide a barrier between the top
and bottom reaction zones. A hole in the center of the ring allows
the agitation shaft to rotate freely and provides a pathway for
fluid flow between the two reactions zones. The use of such rings
or doughnuts to divide a CSTR into different zones is well known to
those skilled in the art of reactor design.
[0057] In another embodiment, two or more separate agitators with
separate shafts and separate drives may be employed. For example, a
small impeller might be operated at high velocity/high shear rate
to disperse the catalyst and/or ethylene as it enters the reactor
and a separate (larger) impeller with a draft tube could be used to
provide circulation within the reactor.
[0058] An alternative reactor design is a tubular/plug flow reactor
with an external heat exchanger. Tubular/plug flow reactors are
well known to those skilled in the art. In general, such reactors
comprise one or more tubes with a length/diameter ratio of from
10/1 to 1000/1. Such reactors are not equipped with active/powered
agitators but may include a static mixer. Examples of static mixers
include those manufactured and sold by Koch-Glitsch Inc. and
Sulzer-Chemtech.
[0059] Tubular reactors for use in the present invention are
preferably characterized by two features: [0060] 1) external
cooling; and [0061] 2) the use of at least one incremental ethylene
feed port along the length of the tubular reactor (i.e. in addition
to the initial ethylene feed at the start of the tubular
reactor).
[0062] In one embodiment, the tubular reactor is a so called
"heat-exchange reactor" which is generally configured as a tube and
shell heat exchanger. The oligomerization reaction occurs inside
the tube(s) of this reactor. The shell side provides a heat
exchange fluid (for the purposes described above, namely to heat
the reaction during start up and/or to cool the reaction during
steady state operations).
[0063] In one embodiment, the tubes are bent so as to form a type
of static mixer for the fluid passing through the shell side. This
type of heat exchanger is known to those skilled in the art and is
available (for example) from Sulzer-Chemtech under the trade name
SMR.
[0064] It is especially preferred that the Reynolds number of the
reaction fluid that flows through the tube (or tubes) of the
tubular reactor is from 2000 to 10,000,000. Reynolds number is a
dimensionless number that is readily calculated using the following
formula:
Re = pVL .mu. ##EQU00001##
where: V is the mean fluid velocity (SI units: m/s); L is a
characteristic linear dimension (e.g. internal diameter of tube);
.mu. is the dynamic viscosity of the fluid (Pas or Ns/m.sup.2 or
kg/(ms)); and p is the density of the fluid (kg/m.sup.3).
[0065] In one such embodiment a plurality of heat exchange reactors
are connected in series. Thus, the process flow that exits the
first reactor enters the second reactor. Additional ethylene is
added to the process flow from the first reactor but additional
catalyst is preferably not added.
[0066] In another embodiment, a CSTR is connected in series to a
tubular reactor. One sub embodiment of this dual reactor system
comprises a CSTR operated in adiabatic mode, followed by a tubular
reactor having an external heat exchanger--in this embodiment the
amount of ethylene that is consumed (i.e. converted to oligomer) in
the CSTR is less than 50 weight % of the total ethylene that is
consumed in the reactors. In another sub embodiment of this dual
reactor system, a CSTR that is equipped with an external heat
exchanger is connected to a downstream tubular reactor that is
operated in adiabatic mode. In this embodiment, the amount of
ethylene that is converted/consumed in the CSTR is in excess of 80
weight % of the ethylene that is consumed in the reactor. The
tubular reactor may also have several different ports which allow
the addition of catalyst killer/deactivator along the length of the
reactor. In this manner, some flexibility is provided to allow the
reaction to be terminated before the product exits from the
reactor.
[0067] Another reactor design for use in the present invention is a
loop reactor. Loop reactors are well known and are widely described
in the literature. One such design is disclosed in U.S. Pat. No.
4,121,029 (Irvin et al.). The loop reactor disclosed by Irvin et
al. contains a "wash column" that is connected to the upper leg of
the loop reactor and is used for the collection of polymer. A
similar "wash column" is contemplated for use in the present
invention to collect by-product polymer (and/or supported
catalyst). A hydrocyclone at the top end of the wash column may be
used to facilitate polymer separation.
[0068] A fifth reactor design for use in the present invention is
another type of heat exchange reactor in which the process side
(i.e. where the oligomerization occurs) is the "shell side" of the
exchanger. One embodiment of this reactor design is a so called
"draft tube" reactor of the type reported to be suitable for the
polymerization of butyl rubber. This type of reactor is
characterized by having an impeller located near the bottom of the
reactor, with little or no agitator shaft extending into the
reactor. The impeller is encircled with a type of "draft tube" that
extends upwards through the center of the reactor. The draft tube
is open at the bottom (to allow the reactor contents to be drained
into the tube, for upward flow) and at the top--where the reactor
contents are discharged from the tube. A heat exchanger tube bundle
is contained within the reactor and is arranged such that the tubes
run parallel to the draft tube and are generally arranged in a
concentric pattern around the draft tube. Coolant flows through the
tubes to remove the heat of the reaction.
[0069] Monomer and solvent are preferably added by one or more feed
ports that are located on the perimeter of the reactor (especially
near the bottom of the reactor) and oligomerization product is
withdrawn through at least one product exit port (preferably
located near the top of the reactor). Catalyst is preferably added
through a separate feed line that is not located close to any of
the monomer feed ports(s) or product exit port(s). Draft tube
reactors are well known and are described in more detail in U.S.
Pat. No. 4,007,016 (Weber) and U.S. Pat. No. 2,474,592 (Palmer) and
the references therein. FIG. 2 of U.S. Pat. No. 2,474,592
illustrates the use of a fluid flushing system to flush the
agitator shaft in the vicinity of the agitator shaft seal. More
specifically, a fluid chamber through the agitator shaft seal is
connected to a source of flushing fluid (located outside of the
reactor) and the channel terminates in the area where the agitator
shaft enters the reactor. "Flushing fluid" is pumped through the
channel to flush the base of the agitator and thereby reduce the
amount of polymer build up at this location.
[0070] Another form of this type of reactor (i.e. in which the
process is undertaken on the "shell" side of an internally heat
exchanged reactor) is sold by ABB Lummus under the trademark
Helixchanger.RTM.
[0071] Another known technique to reduce the level of fouling in a
chemical reactor is to coat the reactor walls and/or internals
and/or agitators with a low fouling material such as glass or
polytetrafluoroethylene (PTFE). The use of coatings can be
especially beneficial on high fouling areas such as agitator shafts
and impellers.
Reactor Control
[0072] The control systems required for the operation of CSTR's and
tubular reactors are well known to those skilled in the art and do
not represent a novel feature of the present invention. In general,
temperature, pressure and flow rate readings will provide the basis
for most conventional control operations. The increase in process
temperature (together with reactor flow rates and the known
enthalpy of reaction) may be used to monitor ethylene conversion
rates. The amount of catalyst may be increased to increase the
ethylene conversion (or decreased to decrease ethylene conversion)
within desired ranges. Thus, basic process control may be derived
from simple measurements of temperature, pressure and flow rates
using conventional thermocouples, pressure meters and flow meters.
Advanced process control (for example, for the purpose of
monitoring product selectivity or for the purpose of monitoring
process fouling factors) may be undertaken by monitoring additional
process parameters with more advanced instrumentation.
Known/existing instrumentation that may be employed include
in-line/on-line instruments such as NIR infrared, Fourier Transform
Infrared (FTIR), Raman, mid-infrared, ultra violet (UV)
spectrometry, gas chromatography (GC) analyzer, refractive index,
on-line densitometer or viscometer. The use of NIR or GC to measure
the composition of the oligomerization reactor and final product
composition is especially preferred.
[0073] The measurement may be used to monitor and control the
reaction to achieve the targeted stream properties including but
not limited to concentration, viscosity, temperature, pressure,
flows, flow ratios, density, chemical composition, phase and phase
transition, degree of reaction, polymer content, selectivity.
[0074] The control method may include the use of the measurement to
calculate a new control set point. The control of the process will
include the use of any process control algorithms, which include,
but are not limited to the use of PID, neural networks, feedback
loop control, forward loop control and adaptive control.
Catalyst Deactivation, Catalyst Removal and Polymer Removal
[0075] In general, the oligomerization catalyst is preferably
deactivated immediately downstream of the reactor as the product
exits the reaction vessel. This is to prevent polymer formation and
potential build up downstream of the reactor and to prevent
isomerisation of the 1-olefin product to the undesired internal
olefins. It is generally preferred to flash and recover unreacted
ethylene before deactivation. However, the option of deactivating
the reactor contents prior to flashing and recovering ethylene is
also acceptable. The flashing of ethylene is endothermic and may be
used as a cooling source. In one embodiment, the cooling provided
by ethylene flashing is used to chill a feedstream to the
reactor.
[0076] In general, many polar compounds (such as water, alcohols
and carboxylic acids) will deactivate the catalyst. The use of
alcohols and/or carboxylic acids is preferred--and combinations of
both are contemplated. It is generally found that the quantity
employed to deactivate the catalyst is sufficient to provide
deactivator to metal (from activator) mole ratio between about 0.1
to about 4. The deactivator may be added to the oligomerization
product stream before or after the volatile unreacted
reagents/diluents and product components are separated. In the
event of a runaway reaction (e.g. rapid temperature rise) the
deactivator can be immediately fed to the oligomerization reactor
to terminate the reaction. The deactivation system may also include
a basic compound (such as sodium hydroxide) to minimize
isomerization of the products (as activator conditions may
facilitate the isomerization of desirable alpha olefins to
undesired internal olefins).
[0077] Polymer removal (and, optionally, catalyst removal)
preferably follows catalyst deactivation. Two "types" of polymer
may exist, namely polymer that is dissolved in the process solvent
and non-dissolved polymer that is present as a solid or
"slurry".
[0078] Solid/non-dissolved polymer may be separated using one or
more of the following types of equipment: centrifuge; cyclone (or
hydrocyclone), a decanter equipped with a skimmer or a filter.
Preferred equipment include so called "self cleaning filters" sold
under the name V-auto strainers, self cleaning screens such as
those sold by Johnson Screens Inc. of New Brighton, Minn. and
centrifuges such as those sold by Alfa Laval Inc. of Richmond, Va.
(including those sold under the trade name Sharpies).
[0079] Soluble polymer may be separated from the final product by
two distinct operations. Firstly, low molecular weight polymer that
remains soluble in the heaviest product fraction (C.sub.20+) may be
left in that fraction. This fraction will be recovered as "bottoms"
from the distillation operations (described below). This solution
may be used as a fuel for a power generation system.
[0080] An alternative polymer separation comprises polymer
precipitation caused by the removal of the solvent from the
solution, followed by recovery of the precipitated polymer using a
conventional extruder. The technology required for such
separation/recovery is well known to those skilled in the art of
solution polymerization and is widely disclosed in the
literature.
[0081] In another embodiment, the residual catalyst is treated with
an additive that causes some or all of the catalyst to precipitate.
The precipitated catalyst is preferably removed from the product at
the same time as by-product polymer is removed (and using the same
equipment). Many of the catalyst deactivators listed above will
also cause catalyst precipitation. In a preferred embodiment, a
solid sorbent (such as clay, silica or alumina) is added to the
deactivation operation to facilitate removal of the deactivated
catalyst by filtration or centrifugation.
[0082] Reactor fouling (caused by deposition of polymer and/or
catalyst residue) can, if severe enough, cause the process to be
shut down for cleaning. The deposits may be removed by known means,
especially the use of high pressure water jets or the use of a hot
solvent flush. The use of an aromatic solvent (such as toluene or
xylene) for solvent flushing is generally preferred because they
are good solvents for polyethylene. The use of the heat exchanger
that provides heat to the present process may also be used during
cleaning operations to heat the cleaning solvent.
Distillation
[0083] In one embodiment of the present invention, the
oligomerization product produced from this invention is added to a
product stream from another alpha olefins manufacturing process for
separation into different alpha olefins. As previously discussed,
"conventional alpha olefin plants" (wherein the term includes i)
those processes which produce alpha olefins by a chain growth
process using an aluminum alkyl catalyst, ii) the aforementioned
"SHOP" process and iii) the production of olefins from synthesis
gas using the so called Lurgi process) have a series of
distillation columns to separate the "crude alpha product" (i.e. a
mixture of alpha olefins) into alpha olefins (such as butene-1,
hexene-1 and octene-1). The mixed hexene-octene product which is
preferably produced in accordance with the present invention is
highly suitable for addition/mixing with a crude alpha olefin
product from an existing alpha olefin plant (or a "cut" or fraction
of the product from such a plant) because the mixed hexene-octene
product produced in accordance with the present invention can have
very low levels of internal olefins. Thus, the hexene-octene
product of the present invention can be readily separated in the
existing distillation columns of alpha olefin plants (without
causing the large burden on the operation of these distillation
columns which would otherwise exist if the present hexene-octene
product stream contained large quantities of internal olefins). As
used herein, the term "liquid product" is meant to refer to the
oligomers produced by the process of the present invention which
have from 4 to (about) 20 carbon atoms.
[0084] In another embodiment, the distillation operation for the
oligomerization product is integrated with the distillation system
of a solution polymerization plant (as disclosed in Canadian patent
application no. 2,708,011, Krzywicki et al.).
[0085] If toluene is present in the process fluid (for example, as
a solvent for a MAO activator), it is preferable to add water to
the "liquid product" prior to distillation to form a water/toluene
azeotrope with a boiling point between that of hexene and
octene.
[0086] The liquid product from the oligomerization process of the
present invention preferably consists of from 20 to 80 weight %
octenes (especially from 35 to 75 weight %) octenes and from 15 to
50 weight % (especially from 20 to 40 weight %) hexenes (where all
of the weight % are calculated on the basis of the liquid product
by 100%.
[0087] The preferred oligomerization process of this invention is
also characterized by producing very low levels of internal olefins
(i.e. low levels of hexene-2, hexene-3, octene-2, octene-3 etc.),
with preferred levels of less than 10 weight % (especially less
than 5 weight %) of the hexenes and octenes being internal
olefins.
In-Situ Polymerization
[0088] One embodiment of the present invention encompasses the use
of components (i) (ii) and (iii) in conjunction with one or more
types of olefin polymerization catalyst system (iv) to trimerise
ethylene and subsequently incorporate a portion of the
trimerisation product(s) into a higher polymer.
[0089] Component (iv) may be one or more suitable polymerization
catalyst system(s), examples of which include, but are not limited
to, conventional Ziegler-Natta catalysts, metallocene catalysts,
monocyclopentadienyl or "constrained geometry" catalysts,
phosphinimine catalysts, heat activated supported chromium oxide
catalysts (e.g. "Phillips"-type catalysts), late transition metal
polymerization catalysts (e.g. diimine, diphosphine and
salicylaldimine nickel/palladium catalysts, iron and cobalt
pyridyldiimine catalysts and the like) and other so-called "single
site catalysts" (SSC's).
[0090] Ziegler-Natta catalysts, in general, consist of two main
components. One component is an alkyl or hydride of a Group I to
III metal, most commonly Al(Et).sub.3 or Al(iBu).sub.3 or
Al(Et).sub.2Cl but also encompassing Grignard reagents,
n-butyllithium, or dialkylzinc compounds. The second component is a
salt of a Group IV to VIII transition metal, most commonly halides
of titanium or vanadium such as TiCl.sub.4, TiCl.sub.3, VCl.sub.4,
or VOCl.sub.3. The catalyst components when mixed, usually in a
hydrocarbon solvent, may form a homogeneous or heterogeneous
product. Such catalysts may be impregnated on a support, if
desired, by means known to those skilled in the art and so used in
any of the major processes known for co-ordination catalysis of
polyolefins such as solution, slurry, and gas-phase. In addition to
the two major components described above, amounts of other
compounds (typically electron donors) may be added to further
modify the polymerization behaviour or activity of the
catalyst.
[0091] Metallocene catalysts, in general, consist of transition
metal complexes, most commonly based on Group IV metals, ligated
with cyclopentadienyl(Cp)-type groups. A wide range of structures
of this type of catalysts is known, including those with
substituted, linked and/or heteroatom-containing Cp groups, Cp
groups fused to other ring systems and the like. Additional
activators, such as boranes or alumoxane, are often used and the
catalysts may be supported, if desired.
[0092] Monocyclopentadienyl or "constrained geometry" catalysts, in
general, consist of transition metal complexes, most commonly based
on Group IV metals, ligated with one cyclopentadienyl(Cp)-type
group, often linked to additional donor group. A wide range of
structures of this type of catalyst is known, including those with
substituted, linked and/or heteroatom-containing Cp groups, Cp
groups fused to other ring systems and a range of linked and
non-linked additional donor groups such as amides, amines and
alkoxides. Additional activators, such as boranes or alumoxane, are
often used and the catalysts may be supported, if desired.
[0093] A typical heat activated chromium oxide (Phillips) type
catalyst employs a combination of a support material to which has
first been added a chromium-containing material wherein at least
part of the chromium is in the hexavalent state by heating in the
presence of molecular oxygen. The support is generally composed of
about 80 to 100 wt. % silica, the remainder, if any, being selected
from the group consisting of refractory metal oxides, such as
aluminium, boria, magnesia, thoria, zirconia, titania and mixtures
of two or more of these refractory metal oxides. Supports can also
comprise alumina, aluminium phosphate, boron phosphate and mixtures
thereof with each other or with silica. The chromium compound is
typically added to the support as a chromium (III) compound such as
the acetate or acetylacetonate in order to avoid the toxicity of
chromium (VI). The raw catalyst is then calcined in air at a
temperature between 250 and 1000.degree. C. for a period of from a
few seconds to several hours. This converts at least part of the
chromium to the hexavalent state. Reduction of the Cr (VI) to its
active form normally occurs in the polymerization reaction, but can
be done at the end of the calcination cycle with CO at about
350.degree. C. Additional compounds, such as fluorine, aluminium
and/or titanium may be added to the raw Phillips catalyst to modify
it.
[0094] Late transition metal and single site catalysts cover a wide
range of catalyst structures based on metals across the transition
series.
[0095] Component (iv) may also comprise one or more polymerization
catalysts or catalyst systems together with one or more additional
oligomerization catalysts or catalyst systems. Suitable
oligomerization catalysts include, but are not limited to, those
that dimerise (for example, nickel phosphine dimerisation
catalysts) or trimerise olefins or otherwise oligomerize olefins
to, for example, a broader distribution of 1-olefins (for example,
iron and cobalt pyridyldiimine oligomerization catalysts).
[0096] Component (iv) may independently be supported or
unsupported. Where components (i) and (ii) and optionally (iii) are
supported, (iv) may be co-supported sequentially in any order or
simultaneously on the same support or may be on a separate support.
For some combinations, the components (i) (iii) may be part or all
of component (iv). For example, if component (iv) is a heat
activated chromium oxide catalyst then this may be (i), a chromium
source and if component (iv) contains an alumoxane activator then
this may also be the optional activator (iii).
[0097] The components (i), (ii), (iii) and (iv) may be in
essentially any molar ratio that produces a polymer product. The
precise ratio required depends on the relative reactivity of the
components and also on the desired properties of the product or
catalyst systems.
[0098] An "in series" process could be conducted by first
conducting the oligomerization reaction, then passing the
oligomerization product to a polymerization reaction. In the case
of an "in series" process various purification, analysis and
control steps for the oligomeric product could potentially be
incorporated between the trimerization and subsequent reaction
stages. Recycling between reactors configured in series is also
possible. An example of such a process would be the oligomerization
of ethylene in a single reactor with a catalyst comprising
components (i)-(iii) followed by co-polymerization of the
oligomerization product with ethylene in a separate, linked reactor
to give branched polyethylene. Another example would be the
oligomerization of an ethylene-containing waste stream from a
polyethylene process, followed by introduction of the
oligomerization product back into the polyethylene process as a
co-monomer for the production of branched polyethylene.
[0099] An example of an "in situ" process is the production of
branched polyethylene catalyzed by components (i)-(iv), added in
any order such that the active catalytic species derived from
components (i)-(iii) are at some point present in a reactor with
component (iv).
[0100] Both the "in series" and "in situ" approaches can be
adaptions of current polymerization technology for the process
stages including component (iv). All major olefin existing
polymerization processes, including multiple reactor processes, are
considered adaptable to this approach. One adaption is the
incorporation of an oligomerization catalyst bed into a recycle
loop of a gas phase polymerization process, this could be as a side
or recycle stream within the main fluidization recycle loop and or
within the degassing recovery and recycle system.
[0101] Polymerization conditions when component (iv) is present can
be, for example, solution phase, slurry phase, gas phase or bulk
phase, with temperatures ranging from -100.degree. C. to
+300.degree. C., and at pressures of atmospheric and above,
particularly from 1.5 to 50 atmospheres. Reaction conditions, will
typically have a significant impact upon the properties (e.g.
density, melt index, yield) of the polymer being made and it is
likely that the polymer requirements will dictate many of the
reaction variables. Reaction temperature, particularly in processes
where it is important to operate below the sintering temperature of
the polymer, will typically, and preferably, be primarily selected
to optimize the polymerization reaction conditions. Also,
polymerization or copolymerization can be carried out in the
presence of additives to control polymer or copolymer molecular
weights. The use of hydrogen gas as a means of controlling the
average molecular weight of the polymer or copolymer applies
generally to the polymerization process of the present
invention.
[0102] Slurry phase polymerization conditions or gas phase
polymerization conditions are particularly useful for the
production of high or low density grades of polyethylene, and
polypropylene. In these processes the polymerization conditions can
be batch, continuous or semi-continuous. Furthermore, one or more
reactors may be used, e.g. from two to five reactors in series.
Different reaction conditions, such as different temperatures or
hydrogen concentrations may be employed in the different
reactors.
[0103] Once the polymer product is discharged from the reactor, any
associated and absorbed hydrocarbons are substantially removed, or
degassed, from the polymer by, for example, pressure let-down or
gas purging using fresh or recycled steam, nitrogen or light
hydrocarbons (such as ethylene). Recovered gaseous or liquid
hydrocarbons may be recycled to a purification system or the
polymerization zone.
[0104] In the slurry phase polymerization process the
polymerization diluent is compatible with the polymer(s) and
catalysts, and may be an alkane such as hexane, heptane, isobutane,
or a mixture of hydrocarbons or paraffins. The polymerization zone
can be, for example, an autoclave or similar reaction vessel, or a
continuous liquid full loop reactor, e.g. of the type well-known in
the manufacture of polyethylene by the Phillips Process. When the
polymerization process of the present invention is carried out
under slurry conditions the polymerization is preferably carried
out at a temperature above 0.degree. C., most preferably above
15.degree. C. Under slurry conditions the polymerization
temperature is preferably maintained below the temperature at which
the polymer commences to soften or sinter in the presence of the
polymerization diluent. If the temperature is allowed to go above
the latter temperature, fouling of the reactor can occur.
Adjustment of the polymerization within these defined temperature
ranges can provide a useful means of controlling the average
molecular weight of the produced polymer. A further useful means of
controlling the molecular weight is to conduct the polymerization
in the presence of hydrogen gas which acts as chain transfer agent.
Generally, the higher the concentration of hydrogen employed, the
lower the average molecular weight of the produced polymer.
[0105] In bulk polymerization processes, liquid monomer such as
propylene is used as the polymerization medium.
[0106] Methods for operating gas phase polymerization processes are
well known in the art. Such methods generally involve agitating
(e.g. by stirring, vibrating or fluidizing) a bed of catalyst, or a
bed of the target polymer (i.e. polymer having the same or similar
physical properties to that which it is desired to make in the
polymerization process) containing a catalyst, and feeding thereto
a stream of monomer (under conditions such that at least part of
the monomer polymerizes in contact with the catalyst in the bed.
The bed is generally cooled by the addition of cool gas (e.g.
recycled gaseous monomer) and/or volatile liquid (e.g. a volatile
inert hydrocarbon, or gaseous monomer which has been condensed to
form a liquid). The polymer produced in, and isolated from, gas
phase processes forms directly a solid in the polymerization zone
and is free from, or substantially free from liquid. As is well
known to those skilled in the art, if any liquid is allowed to
enter the polymerization zone of a gas phase polymerization process
the quantity of liquid in the polymerization zone is small in
relation to the quantity of polymer present. This is in contrast to
"solution phase" processes wherein the polymer is formed dissolved
in a solvent, and "slurry phase" processes wherein the polymer
forms as a suspension in a liquid diluent.
[0107] The gas phase process can be operated under batch,
semi-batch, or so-called "continuous" conditions. It is preferred
to operate under conditions such that monomer is continuously
recycled to an agitated polymerization zone containing
polymerization catalyst, make-up monomer being provided to replace
polymerized monomer, and continuously or intermittently withdrawing
produced polymer from the polymerization zone at a rate comparable
to the rate of formation of the polymer, fresh catalyst being added
to the polymerization zone to replace the catalyst withdrawn from
the polymerization zone with the produced polymer.
[0108] Methods for operating gas phase fluidized bed processes for
making polyethylene, ethylene copolymers and polypropylene are well
known in the art. The process can be operated, for example, in a
vertical cylindrical reactor equipped with a perforated
distribution plate to support the bed and to distribute the
incoming fluidizing gas stream through the bed. The fluidizing gas
circulating through the bed serves to remove the heat of
polymerization from the bed and to supply monomer for
polymerization in the bed. Thus the fluidizing gas generally
comprises the monomer(s) normally together with some inert gas
(e.g. nitrogen or inert hydrocarbons such as methane, ethane,
propane, butane, pentane or hexane) and optionally with hydrogen as
molecular weight modifier. The hot fluidizing gas emerging from the
top of the bed is led optionally through a velocity reduction zone
(this can be a cylindrical portion of the reactor having a wider
diameter) and, if desired, a cyclone and or filters to disentrain
fine solid particles from the gas stream. The hot gas is then led
to a heat exchanger to remove at least part of the heat of
polymerization. Catalysts are preferably fed continuously or at
regular internals to the bed. At start up of the process, the bed
comprises fluidizable polymer which is preferably similar to the
target polymer. Polymer is produced continuously within the bed by
the polymerization of the monomer(s). Preferably means are provided
to discharge polymer from the bed continuously or at regular
internals to maintain the fluidized bed at the desired height. The
process is generally operated at relatively low pressure, for
example, at 10 to 50 atmospheres, and at temperatures for example,
between 50 and 135.degree. C. The temperature of the bed is
maintained below the sintering temperature of the fluidized polymer
to avoid problems of agglomeration.
[0109] In the gas phase fluidized bed process for polymerization of
olefins the heat evolved by the exothermic polymerization reaction
is normally removed from the polymerization zone (i.e. the
fluidized bed) by means of the fluidizing gas stream as described
above. The hot reactor gas emerging from the top of the bed is led
through one or more heat exchangers wherein the gas is cooled. The
cooled reactor gas, together with any make-up gas, is then recycled
to the base of the bed. In the gas phase fluidized bed
polymerization process of the present invention it is desirable to
provide additional cooling of the bed (and thereby improve the
space time yield of the process) by feeding a volatile liquid to
the bed under conditions such that the liquid evaporates in the bed
thereby absorbing additional heat of polymerization from the bed by
the "latent heat of evaporation" effect. When the hot recycle gas
from the bed enters the beat exchanger, the volatile liquid can
condense out. In one embodiment of the present invention the
volatile liquid is separated from the recycle gas and reintroduced
separately into the bed. Thus, for example, the volatile liquid can
be separated and sprayed into the bed. In another embodiment of the
present invention the volatile liquid is recycled to the bed with
the recycle gas. Thus the volatile liquid can be condensed from the
fluidizing gas stream emerging from the reactor and can be recycled
to the bed with recycle gas, or can be separated from the recycle
gas and then returned to the bed.
[0110] A number of process options can be envisaged when using the
catalysts of the present invention in an integrated process to
prepare higher polymers i.e. when component (iv) is present. These
options include "in series" processes in which the oligomerization
and subsequent polymerization are carried in separate but linked
reactors and "in situ" processes in which a both reaction steps are
carried out in the same reactor.
[0111] In the case of a gas phase "in situ" polymerization process,
component (iv) can, for example, be introduced into the
polymerization reaction zone in liquid form, for example, as a
solution in a substantially inert liquid diluent. Components
(i)-(iv) may be independently added to any part of the
polymerization reactor simultaneously or sequentially together or
separately. Under these circumstances it is preferred the liquid
containing the component(s) is sprayed as fine droplets into the
polymerization zone. The droplet diameter is preferably within the
range 1 to 1000 microns.
[0112] Although not usually required, upon completion of
polymerization or copolymerization, or when it is desired to
terminate polymerization or copolymerization or at least
temporarily deactivate the catalyst or catalyst component of this
invention, the catalyst can be contacted with water, alcohols,
acetone, or other suitable catalyst deactivators a manner known to
persons of skill in the art.
[0113] A range of polyethylene polymers are considered accessible
including high density polyethylene, medium density polyethylene,
low density polyethylene, ultra low density polyethylene and
elastomeric materials. Particularly important are the polymers
having a density in the range of 0.91 to 0.93, grams per cubic
centimeter (g/cc) generally referred to in the art as linear low
density polyethylene. Such polymers and copolymers are used
extensively in the manufacture of flexible blown or cast film.
[0114] Depending upon the use of the polymer product, minor amounts
of additives are typically incorporated into the polymer
formulation such as acid scavengers, antioxidants, stabilizers, and
the like. Generally, these additives are incorporated at levels of
about 25 to 2000 parts per million by weight (ppm), typically from
about 50 to about 1000 ppm, and more typically 400 to 1000 ppm,
based on the polymer. In use, polymers or copolymers made according
to the invention in the form of a powder are conventionally
compounded into pellets. Examples of uses for polymer compositions
made according to the invention include use to form fibres,
extruded films, tapes, spunbonded webs, molded or thermoformed
products, and the like. The polymers may be blown or cast into
films, or may be used for making a variety of molded or extruded
articles such as pipes, and containers such as bottles or drums.
Specific additive packages for each application may be selected as
known in the art. Examples of supplemental additives include slip
agents, anti-blocks, anti-stats, mould release agents, primary and
secondary anti-oxidants, clarifiers, nucleants, uv stabilizers, and
the like. Classes of additives are well known in the art and
include phosphite antioxidants, hydroxylamine (such as N,N-dialkyl
hydroxylamine) and amine oxide (such as dialkyl methyl amine oxide)
antioxidants, hindered amine light (uv) stabilizers, phenolic
stabilizers, benzofuranone stabilizers, and the like.
[0115] Fillers such as silica, glass fibers, talc, and the like,
nucleating agents, and colourants also may be added to the polymer
compositions as known by the art.
[0116] The present invention is illustrated in more detail by the
following non-limiting examples.
EXAMPLES
[0117] The following abbreviations are used in the examples: [0118]
.ANG.=Angstrom units [0119] NMR=nuclear magnetic resonance [0120]
Et=ethyl [0121] Bu=butyl [0122] iPr=isopropyl [0123] c*=comparative
[0124] rpm=revolutions per minute [0125] GC=gas chromatography
[0126] Rx=reaction [0127] Wt=weight [0128] C.sub.4's=butenes [0129]
C.sub.6's=hexenes [0130] C.sub.8's=octenes [0131]
PE=polyethylene
Part I: Preferred Ligand Synthesis
General
[0132] This section illustrates the synthesis of a preferred but
non-limiting ligand for use in the present invention.
[0133] All reactions involving air and or moisture sensitive
compounds were conducted under nitrogen using standard Schlenk or
cannula techniques, or in a glovebox. Reaction solvents were
purified prior to use (e.g. by distillation) and stored over
activated 4 .ANG. sieves. Diethylamine, triethylamine and
isopropylamine were purchased from Aldrich and dried over 4 .ANG.
molecular sieves prior to use. 1-Bromo-2-fluoro-benzene, phosphorus
trichloride (PCl.sub.3), hydrogen chloride gas and n-butyllithium
were purchased from Aldrich and used as is. The methylalumoxane
(MAO), 10 wt % Al in toluene, was purchased from Akzo and used as
is. Deuterated solvents were purchased (toluene-d.sub.8,
THF-d.sub.8) and were stored over 4 .ANG. sieves. NMR spectra were
recorded on a Bruker 300 MHz spectrometer (300.1 MHz for .sup.1H,
121.5 MHz for .sup.31P, 282.4 for .sup.19F).
Preparation of Et.sub.2NPCl.sub.2
[0134] Et.sub.2NH (50.00 mmol, 5.17 mL) was added dropwise to a
solution of PCl.sub.3 (25.00 mmol, 2.18 mL) in diethyl ether (will
use "ether" from here) (200 mL) at -78.degree. C. After the
addition, the cold bath was removed and the slurry was allowed to
warm to room temperature over 2 hours. The slurry was filtered and
the filtrate was pumped to dryness. The residue was distilled (500
microns, 55.degree. C.) to give the product in quantitative
yield.
[0135] .sup.1H NMR (6, toluene-d.sub.8): 2.66 (doublet of a
quartets, 4H, J.sub.PH=13 Hz, J.sub.HH=7 Hz), 0.75 (triplet, 6H,
J=7 Hz).
Preparation (ortho-F--C.sub.6H.sub.4).sub.2P-NEt.sub.2
[0136] To solution of n-BuLi (17.00 mL of 1.6 M n-BuLi hexane
solution, 27.18 mmol) in ether (100 mL) maintained at -85.degree.
C., was added dropwise a solution of 1-bromo-2-fluorobenzene (4.76
g, 27.18 mmol) in ether (40 mL) over 2 hours. After addition, the
reaction flask was stirred for 1 hour at -78.degree. C., resulting
in a white slurry. Et.sub.2NPCl.sub.2 (2.36 g, 13.58 mmol) in ether
(20 mL) was then added very slowly while the reaction temperature
was maintained at -85.degree. C. The reaction was allowed to warm
to -10.degree. C. overnight. Toluene (10 mL) was then added to the
reaction flask and the volatiles were removed in vacuo. The residue
was extracted with toluene and the solution was pumped to dryness.
The crude product was distilled (300 microns, 100.degree. C.)
yielding 3.78 g (95%) of product. .sup.1H NMR (.delta.,
THF-d.sub.8): 7.40-7.01 (4 equal intense multiplets, 8H), 3.11
(doublets of quartet, 4H, J.sub.PH=13 Hz, J.sub.HH=7 Hz), 0.97
(triplet, 6H, J=7 Hz). .sup.19F NMR (6, THF-d.sub.8): -163.21
(doublet of multiplets, J=48 Hz). GC-MS. M.sup.+=293.
Preparation of (ortho-F--C.sub.6H.sub.4).sub.2PCI
[0137] Anhydrous HCl.sub.(g) was introduced to the head space of an
ethereal solution (100 mL) of (ortho-F--C.sub.6H.sub.4)P--NEt.sub.2
(3.73 g, 12.70 mmol) to a pressure of 3 psi. A white precipitate
formed immediately. The reaction was stirred for an additional 0.5
hours at which point the slurry was pumped to dryness to remove
volatiles. The residue was re-slurried in ether (100 mL) and
filtered. The filtrate was pumped to dryness yielding
(ortho-F--C.sub.6H.sub.4).sub.2PCI as a colorless oil in
quantitative yield. .sup.1H NMR (.delta., THF-d.sub.8): 7.60 (m,
4H), 7.20 (m, 2H), 7.08 (m, 2H). .sup.19F NMR (.delta.,
THF-d.sub.8): -106.94 (doublet of multiplets, J=67 Hz).
Preparation of (ortho-F--C.sub.6H.sub.4).sub.2PNH(i-Pr)
[0138] To a solution of (ortho-F--C.sub.6H.sub.4)PCI (1.00 g, 3.90
mmol) in ether (50 mL) and NEt.sub.3 (3 mL) was added an ethereal
solution of i-PrNH.sub.2 (0.42 mL, 4.90 mmol) at -5.degree. C.
Immediate precipitate was observed. The slurry was stirred for 3
hours and filtered. The filtrate was pumped to dryness to give a
colorless oil of (ortho-F--C.sub.6H.sub.4)PNH(i-Pr) in quantitative
yield.
[0139] .sup.1H NMR (6, THF-d.sub.8): 7.42 (m, 2H), 7.30 (m, 2H),
7.11 (m, 2H), 6.96 (m, 2H), 3.30 (septet, 1H, J=7 Hz), 2.86 (br s,
1H), 1.15 (d, 6H, J=7 Hz). .sup.19F NMR (6, THF-d.sub.8): -109.85
(doublet of multiplets, J=40 Hz). GC-MS, M.sup.+=279.
Preparation of
(ortho-F--C.sub.6H.sub.4).sub.2PN(i-Pr)P(ortho-F--C.sub.6H.sub.4),
("Ligand 1")
[0140] To a solution of (ortho-F--C.sub.5H.sub.4).sub.2PNH(i-Pr)
(3.90 mmol) [made from i-PrNH.sub.2 and
(ortho-F--C.sub.6H.sub.4).sub.2PCI (1.00 g, 3.90 mmol)] in ether
(100 mL) maintained at -70.degree. C. was added dropwise a solution
of n-BuLi (2.43 mL of 1.6 M n-BuLi hexane solution, 3.90 mmol)).
The mixture was stirred at -70.degree. C. for 1 hour and allowed to
warm to -10.degree. C. in a cold bath (2 hours). The solution was
re-cooled to -70.degree. C. and (ortho-F--C.sub.6H.sub.4).sub.2PCI
(1.00 g, 3.90 mmol) was slowly added. The solution was stirred for
1 hour at -70.degree. C. and allowed to slowly warm to room
temperature forming a white precipitate. The slurry was pumped to
dryness and the residue was extracted with toluene and filtered.
The filtrate was pumped to dryness and recrystallized from heptane
at -70.degree. C. (2.times.) yielding 1.13 g (58%) of product. At
room temperature this material was an oil which contained both the
desired ligand
(ortho-F--C.sub.6H.sub.4).sub.2PN(i-Pr)P(ortho-F--C.sub.6H.sub.4).sub.2
and its isomer
(ortho-F--C.sub.6H.sub.4).sub.2P[.dbd.N(i-Pr]P(ortho-F--C.sub.6H.sub.4).s-
ub.2. A toluene solution of this mixture and 50 mg of
(ortho-F--C.sub.5H.sub.4).sub.2PCI was heated at 65.degree. C. for
three hours to convert the isomer to the desired ligand. .sup.1H
NMR (THF-d8, .delta.): 7.35 (m, 8H), 7.10 (m, 4H), 6.96 (m, 4H),
3.94 (m, 1H), 1.24 (d, 6H, J=7 Hz). .sup.19F NMR (THF-d.sub.8,
.delta.): -104.2 (br. s).
[0141] In a more preferred procedure the initial steps of the
synthesis are conducted in pentane at -5.degree. C. (instead of
ether) with 10% more of the (ortho-F--C.sub.6H.sub.4).sub.2PCI
(otherwise as described above). This preferred procedure allows
(ortho-F--C.sub.6H.sub.4).sub.2PN(i-Pr)P(ortho-F--C.sub.6H.sub.4).sub.2
to be formed in high (essentially quantitative) yield without the
final step of heating in toluene.
Catalyst Preparation
[0142] The term catalyst refers to the chromium molecule with the
heteroatom ligand bonded in place. The preferred P--N--P ligand
does not easily react with some Cr (III) molecules--especially when
using the most preferred P--N--P ligands (which ligands contain
phenyl groups bonded to the P atoms, further characterized in that
at least one of the phenyl groups contains an ortho fluoro
substituent).
[0143] While not wishing to be bound by theory, it is believed that
the reaction between the ligand and the Cr species is facilitated
by aluminum alkyl or MAO. It is also believed that the reaction is
facilitated by an excess of Al over Cr. Accordingly, it is most
preferred to add the Cr/ligand mixture to the MAO (and/or Al alkyl)
instead of the reverse addition sequence. In this manner, the
initiation of the reaction is believed to be facilitated by the
very high Al/Cr ratio that exists when the first part of the
Cr/ligand is added to the MAO.
[0144] In a similar vein, it is believed that the ligand/Cr ratio
provides another kinetic driving force for the reaction--i.e. the
reaction is believed to be facilitated by high ligand/Cr ratios.
Thus, one way to drive the reaction is to use an excess of ligand.
In another, (preferred) reaction, a mixture with a high ligand/Cr
ratio is initially employed, followed by lower ligand/Cr ratio
mixtures, followed by Cr (in the absence of ligand).
Part II: Ethylene Oligomerization
Batch Operation (Comparative)
[0145] A stirred reactor having a volume of about 600 cc was used
in more than 20 (comparative) batch experiments. Chromium ("Cr", as
chromium (III) acetylacetonate) plus
(ortho-F--C.sub.6H.sub.4).sub.2PN(i-Pr)P(ortho-F--C.sub.6H.sub.4).sub.2
("ligand 1", as described above) and methylaluminoxane ("MAO",
purchased from Albemarle) were added to the reactor under a wide
variety of conditions. In general, a Cr/ligand ratio of about 1/1
and Al/Cr ratio of from 100/1 to 500/1 were tested. Cyclohexane was
used as solvent.
[0146] Ethylene was added on demand to maintain pressure but the
reactor was operated in "batch" mode in the sense that product was
not withdrawn and catalyst was not added during the reaction. Batch
oligomerization experiments were typically operated for about 12-18
minutes.
[0147] The reactor was equipped with an external jacket. Hot water
was run through the jacket to warm the reactor prior to start up.
This was replaced with cool water to remove heat during the
reaction.
[0148] The reaction produced hexene and octene in high yield and
high selectivity over a range of conditions. Combined octene/hexene
yields were typically from 400-500,000 grams of oligomer per gram
of chromium per hour and represented more than 85% of the converted
ethylene (i.e. less than 15 weight % of the ethylene was converted
into butene plus C.sub.10.sup.+ products). Octene/hexene ratios
were generally in excess of 2/1 but less than 3/1 and the purity of
both streams was typically in excess of 95% alpha olefins (i.e.
only small amounts of internal olefins were produced). These
oligomerizations were not conducted in a liquid full reactor.
Continuous Operation
[0149] A continuous stirred tank reactor having a volume of 1000 cc
was used for these experiments. A range of operating conditions
were tested.
[0150] Reactor temperatures between about 40.degree. C. and
80.degree. C. and pressures of about 4 to 8 MPa were tested.
[0151] The reactor was fitted with external cooling jacket. Cool
water from a municipal supply was run through the jacket. The
reactor was operated over the course of many months. The
temperature of the water supply was generally in the range of from
about 10 to 20.degree. C. depending upon the season. A "solution
absorber" unit was installed to allow ethylene to be dissolved in
solvent prior to being added to the reactor. The solution was also
equipped with a cooling jacket (to remove heat of absorbtion) and
thus cool the feed to the reactor. The reactor was operated "liquid
full"--i.e. the feed port and product exit port were arranged such
that the reactor was essentially full of liquid during the
process.
[0152] MAO was purchased as a solution of methylaluminoxine (10
weight % Al in toluene) from Albemarle.
[0153] The reactor was operated in a continuous manner--i.e.
product was removed from the reactor during the reaction and
make-up feed was added. Typical flow rates and reactor
concentrations were as follows:
[0154] Chromium (as Cr(acac).sub.3): 0.025 mmol/litre
[0155] Ligand/Cr mole ratio=1/1
[0156] Al/Cr mole ratio=300/1 (Albemarle MAO)
[0157] Ethylene feed rate=3 g/minute
[0158] MAO solution+cyclohexane.about.33 ml/minute
[0159] The liquid fraction produced in these experiments was
similar to that produced in the batch experiments--i.e. both of the
octene and hexene streams were typically greater than 95% alpha
olefins and octene/hexene ratio was typically at least 2/1.
[0160] Severe polymer formation was often encountered during
initial attempts at continuous operation.
[0161] A hydrogen feed line was installed for a subsequent group of
experiments. The addition of hydrogen did mitigate polymer
formation and it became possible to operate the reactor over
extended periods of time. It is important to note that the hydrogen
was not observed to hydrogenate the feed or the products in any
meaningful manner (i.e. no ethane, hexane or octane were
detected).
[0162] The feed preparation unit and reactor were then reconfigured
so that the hydrogen feed line to the reactor was removed and a
hydrogen feed line to the feed preparation unit was installed. In
this manner, hydrogen was contacted with the ethylene and solvent
prior to being introduced to the reactor and the ethylene, hydrogen
and solvent were added via a common feed line.
[0163] The reconfigured unit was successfully tested for several
three hour tests and only very low levels of polymer formation were
observed. However, some polymer formation was observed--especially
when episodes of fluctuating reactor conditions (such as changes in
pressure and/or temperature) were encountered.
Continuous Operation (Inventive)
[0164] In addition to the above described cooling jacket, the
reactor was equipped with an external heating coil (i.e. the coil
was external to the reactor). A reservoir of heated water was
fitted to the heating coil.
[0165] Improved reactor continuity was achieved by having both of
the cooling jacket and heating coil operational during the
oligomerization reaction.
[0166] This inventive configuration of process equipment allows the
"heating" coil to be used to add heat to the reactor when a drop in
reactor temperature is observed. The cooling system is used during
normal/steady state operation to remove heat of reaction.
[0167] The above described process allowed for improved reactor
continuity. Some polymer build up was still observed on the
impeller blade and on the agitator shaft--especially where the
agitator shaft entered the reactor. Accordingly, in one preferred
embodiment, the agitator shaft is flushed with process
solvent--especially at the point where the agitator shaft enters
the reactor.
* * * * *