Note: Descriptions are shown in the official language in which they were submitted.
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
-1-
PROCESSES FOR PREVENTING GENERATION OF HYDROGEN
HALIDES IN AN OLIGOMERIZATION PRODUCT RECOVERY SYSTEM
BACKGROUND OF THE INVENTION
This invention relates generally to the catalytic production of olefins.
This invention relates more specifically to a process of quenching the
catalyst in the
effluent from an oligomerization reactor, such as a trimerization reactor, to
avoid
the generation of hydrogen halides.
Olefins, particularly alpha-olefins, also referred to as 1-olefins, have
many uses as specific chemicals and as monomers or co-monomers in poly-
merization processes. Higher alpha-olefins and other olefins can be produced
by
contacting lower olefins, for example ethylene, with a catalyst, producing
trimers of
mono-olefins, dimers of diolefms, or other reaction products in an addition
reaction.
This reaction can be referred to as "trimerization" or "oligomerization".
Often, the
catalyst system is dispersed in a process solvent, and the reactants, a lower
1-olefin
and optionally hydrogen, are fed in as gases. The reaction product or higher
olefins
dissolve in the process solvent as they are formed.
Product olefins and spent catalyst system are recovered by removing
the process solvent containing them, i.e. the reactor effluent, from the
reactor.
Preferably, a catalyst kill agent is added to the reaction system prior to
separating
any of the reaction components. The effluent can be treated to quench or
"kill" the
catalyst. The effluent can be separated for catalyst system waste disposal,
recycle
any remaining lower 1-olefin and process solvent content, and recover product
olefins.
A quenching agent can be used to quench the aluminum alkyl portion
of the catalyst system. Quenching of the catalyst system is important to
prevent
isomerization of the 1-olefin product to undesirable internal, i.e. 2- and
higher,
olefins, which lowers the product purity. Quenching of the catalyst system
also can
remove hazards associated with the air- and water- sensitive aluminum alkyls.
Previous patents teach that an alcohol can be added to the catalyst
discharge in the effluent of an olefin oligomerization reactor to quench or
"kill" the
catalyst. U.S. Patent No. 5,689,028 discloses adding 2-ethylhexanol to the
reactor
effluent of a trimerization reactor as a quenching agent to quench the
catalyst
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
-2-
system. U.S. Patent No. 5,859,303, Example 1, discloses that addition of an
alcohol
can quench or kill the catalyst system. U.S. Patent No. 5,750,817 discloses
the use
of ethanol to quench an ethylene trimerization reaction.
U.S. Patent No. 5,750,816 teaches the addition of alcohols, phenols,
carboxylic acids, primary or secondary amines, or ammonia to the effluent of
an
ethylene trimerization reactor as a "metal solubilizing agent". The patent
states, "the
percentage of the metal solubilizing agent used may be selected from a wide
range
from a trace amount to a solvent equivalent, but it is preferably in a range
from
0.001 to 50% by weight, more preferably 0.01 to 10% by weight in terms of
concentration in the solvent". For example 0.022% by weight 1-hexanol
(Examples
5 and 13), hexylamine (Examples 6 and 14), or ammonia (Examples 7 and 15) is
used. The patent teaches generally that this step "maintain[s] the dispersed
state of
principally the catalyst components in the reaction dispersion" "in the
process line
from the outlet of the oligomerization reactor to the inlet of the
distillation tower."
U.S. Patent No. 5,750,816, col. 12, lines 20-23 and 49-67.
SUMMARY OF THE INVENTION
The present inventors have discovered that alcohols, used as
quenching agents to quench a halogenated trimerization catalyst system,
following
an oligomerization reaction, can produce hydrogen halides. For example,
quenching
a chlorinated catalyst with an alcohol, particularly in the presence of water
or the
kettle bottoms found in a plant (which may contain ferrous chloride), may lead
to
the production of hydrogen chloride gas. Hydrogen halides can be highly
corrosive
to process equipment.
Accordingly it is desirable to provide catalyst quenching materials
and methods that do not produce hydrogen halides.
Again it is desirable to reduce or eliminate the generation of
hydrogen halides when alcohols are used as quenching agents.
One or more of the preceding desires, or one or more other desires
which will become plain upon consideration of the present specification, are
satisfied in whole or in part by the invention described here.
One aspect of the invention is an oligomerization process. In the
process a catalyst system, a lower olefin reactant, and a process medium are
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
-3-
provided. The lower olefin is reacted in the presence of the catalyst system
to
produce a product stream. The product stream includes a higher olefin product
and
catalyst system residue, both dispersed in the process solvent or medium.
The resulting product stream is treated with a quenching material
comprising an aliphatic primary amine, an aliphatic secondary amine, or a
combination of those materials. Optionally, an alcohol or other quenching
materials
also can be combined with the selected amine to form composite quenching
materials. The quenching material is provided in an amount at least
substantially
effective to quench the catalyst.
Amine quenching materials have been found to generate few or no
hydrogen halides when used to quench oligomerization catalysts.
Another aspect of the invention is an oligomerization process in
which the product stream is treated with an alcohol in an amount at least
partially
effective to quench the catalyst. The product stream is also treated with a
stabilizing material that forms a stable hydrogen halide salt. The stabilizing
material is provided in an amount effective to at least reduce the generation
of free
hydrogen halides.
Although alcohol quenching materials have been found to generate
hydrogen halides, the stabilizing material alleviates the problem, apparently
by
interacting with any hydrogen halides to produce a stable material (though the
present invention is not limited to any particular mode of action).
DETAILED DESCRIPTION OF THE INVENTION
While the invention will be described in connection with one or more
embodiments, it will be understood that the invention is not limited to those
embodiments. On the contrary, the invention includes all alternatives,
modifications, and equivalents as may be included within the spirit and scope
of the
appended claims. The mention of or statement of a preference for certain
embodiments does not indicate an intent to exclude other embodiments that are
not
mentioned or stated to be preferred.
The reaction contemplated here broadly. relates to the oligomerization
of ethylene and other lower olefins to produce higher olefins. In this
context,
"lower" and "higher" are relative; a lower olefin, as used in this disclosure
is any 1-
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
-4-
olefin that can be converted to a higher 1-olefin, wherein the higher 1-olefin
has a
greater number of carbon atoms than the lower olefin. The reaction is carried
out in
the presence of one or more catalysts under conditions encouraging the
reaction to
proceed.
The present invention will be exemplified in the context of a
trimerization reaction, although it is contemplated that the invention will
find use in
other oligomerization reactions. "Trimerization", as used in this disclosure,
is
defined as any combination of any two, three, or more olefins reducing the
number
of olefin, i.e., carbon-carbon, double bonds by two. For example, the three
olefin
bonds in the combination of three ethylene units can be reduced by two, to one
olefin bond, in 1-hexene. In another example, the four olefin bonds in the
combination of two 1,3-butadiene units can be reduced by two, to two olefin
bonds,
in 1,5-cyclooctadiene.
As used here, the term "trimerization" is intended to include
dimerization of diolefins, as well as "co-trimerization", each as further
discussed
below. The reactants, catalysts, equipment, and reaction conditions useful in
the
present process and the reaction products and by-products formed as a result
of the
trimerization reaction are further described below.
Reactants
The reactants applicable for use in the trimerization process of this
invention include olefmic compounds which can self react, i.e., trimerize, to
give
useful products. For example, the self reaction of ethylene can give 1-hexene,
and
the self reaction of 1,3-butadiene can give 1,5-cyclooctadiene. The reactants
applicable for use in the trimerization process of this invention also include
olefinic
compounds which can react with other olefinic compounds, i.e., co-trimerize,
to
give useful products. For example, co-trimerization of ethylene plus hexene
can
give 1-decene or 1-tetradecene. Co-trimerization of ethylene and 1-butene can
give
1-octene. Co-trimerization of 1-decene and ethylene can give 1-tetradecene or
1-
docosene.
Suitable trimerizable olefin compounds are those compounds having
from about 2 to about 30 carbon atoms per molecule and having at least one
olefinic double bond. Exemplary olefins include, but are not limited to the
CA 02392233 2002-05-17
WO 01/47839 PCT/LTS00/35366
-5-
following.
Acyclic olefins are contemplated such as, for example, ethylene,
propylene, 1-butene, 2-butene, isobutylene, 1-pentene, 2-pentene, 1-hexene,
2-hexene, 3-hexene, 1-heptene, 2-heptene, 3-heptene, the four normal octenes,
the
four normal nonenes, and mixtures of any two or more of those.
Exemplary diolefm compounds contemplated here include, but are not
limited to, 1,3-butadiene, 1,4-pentadiene, and 1,5-hexadiene.
If branched or cyclic olefins are used as reactants, while not wishing
to be bound by theory, it is believed that steric hindrance could hinder the
trimerization process. Therefore, the branched or cyclic portion of the olefin
generally will be distant from the carbon-carbon double bond. The present
invention is not limited to use with the olefins suggested by this theory to
be useful.
Any olefin that will participate in the reaction is contemplated for use
according to
the present invention.
1 S Catalyst Systems
One trimerization catalyst system contemplated in accordance with
this invention is a three-part system comprising the combination of a chromium
source, a pyrrole-containing compound and a metal alkyl. Optionally, the
catalyst
system can be supported on an inorganic oxide support. These catalyst systems
are
especially useful for the dimerization and trimerization of olefins, such as,
for
example, ethylene to 1-hexene. For present purposes, any catalyst or catalyst
system comprising a metal alkyl is more broadly contemplated. The catalyst
system
commonly includes a halide source, for example, a chloride, bromide, iodide,
or
fluoride compound.
The chromium source can be one or more organic or inorganic
compounds, in which the chromium oxidation state is from 0 to 6. Generally,
the
chromium source will have a formula of CrX", in which each X can be the same
or
different, and can be any organic or inorganic radical, and n is an integer
from 1 to
6. Exemplary organic radicals can have from about 1 to about 20 carbon atoms
per
radical, and can be alkyl, alkoxy, ester, ketone, carboxylate or amido
radicals, for
example. The organic radicals can be straight-chained or branched, cyclic or
acyclic,
aromatic or aliphatic, can be made of mixed aliphatic, aromatic, or
cycloaliphatic
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
-6-
groups. Exemplary inorganic radicals include, but are not limited to, any
anion or
oxidizing radical, for example, halides, sulfates, or oxides.
Preferably, the chromium source is a chromium (II)- or
chromium (III)-containing compound that can yield a catalyst system with
improved
oligomerization or trimerization activity.
Most preferably, the chromium source is a chromium (III) compound
because of its ease of use, availability, and enhanced catalyst system
activity.
Exemplary chromium (III) compounds include, but are not limited to, chromium
carboxylates, chromium naphthenates, chromium halides, chromium pyrrolides,
and
chromium dionates. Specific exemplary chromium (III) compounds (followed in
some instances below by their respective abbreviations) include, but are not
limited
to chromium (III) 2,2,6,6,-tetramethylheptanedionate - Cr(TMHD)3; chromium
(III)
2-ethylhexanoate - Cr(EH)3; chromium (III) tris-(2-ethylhexanoate); chromium
(III)
naphthenate - Cr(Np)3; chromium (III) chloride; chromic bromide; chromic
fluoride;
chromium (III) acetylacetonate; chromium (III) acetate; chromium (III)
butyrate;
chromium (III) neopentanoate; chromium (III) laurate; chromium (III) stearate;
chromium (III) pyrrolide; chromium (III) oxalate; or combinations of two or
more.
Specific exemplary chromium (II) compounds include, but are not
limited to chromous bromide; chromous fluoride; chromous chloride; chromium
(II)
bis-(2-ethylhexanoate); chromium (II) acetate; chromium (II) butyrate;
chromium
(II) neopentanoate; chromium (II) laurate; chromium (II) stearate; chromium
(II)
oxalate; chromium (II) pyrrolides; or combinations of two or more. Chromium
(II)
and chromium (III) compounds can also be combined.
The pyrrole-containing compound of the catalyst system can be any
one, two or more of those that will react with a chromium source to form a
chromium pyrrolide complex. As used in this disclosure, the term "pyrrole-
containing compound" refers to hydrogen pyrrolide (i.e. pyrrole -- C4HSN),
derivatives of hydrogen pyrrolide, and substituted pyrrolides, as well as
metal
pyrrolide complexes and mixtures thereof. A "pyrrolide" is defined as a
compound
comprising a 5-membered, nitrogen-containing heterocycle.
Broadly, the pyrrole-containing compound can be pyrrole or any
heteroleptic or homoleptic metal complex or salt containing a pyrrolide
radical or
CA 02392233 2002-05-17
WO 01/47839 PCT/C1S00/35366
-
ligand. The pyrrole-containing compound can be either affirmatively added to
the
reaction or generated in-situ.
Generally, the pyrrole-containing compound will have from about 4
to about 20 carbon atoms per molecule. Exemplary pyrrolides, mentioned because
of
their high reactivity and activity with the other reactants, include pyrrole;
lithium
pyrrolide; sodium pyrrolide; potassium pyrrolide; cesium pyrrolide; the salts
of
substituted pyrrolides; or combinations thereof. The useful substituted
pyrrolides
include, but are not limited to pyrrole-2-carboxylic acid; 2-acetylpyrrole;
pyrrole-2-carboxaldehyde; tetrahydroindole; 2,5-dimethylpyrrole; 2,4-dimethyl-
3-
ethylpyrrole; 3-acetyl-2,4-dimethylpyrrole; ethyl-2,4-dimethyl-5-
(ethoxycarbonyl)-3-
pyrrole-propionate; ethyl-3,5-dimethyl-2-pyrrolecarboxylate; or combinations
thereof. When the pyrrole-containing compound contains chromium, the resultant
chromium compound can be called a chromium pyrrolide.
The most preferred pyrrole-containing compounds useful in a
trimerization catalyst system can be selected from the group consisting of
hydrogen
pyrrolide, 2,5-dimethylpyrrole or chromium pyrrolides because of enhanced
trimerization activity. Optionally, for ease of use, a chromium pyrrolide can
provide both the chromium source and the pyrrole-containing compound. As used
in
this disclosure, when a chromium pyrrolide is used to form a catalyst system,
a
chromium pyrrolide is considered to provide both the chromium source and the
pyrrole-containing compound. While all pyrrole-containing compounds can
produce
catalyst systems with high activity and productivity, use of pyrrole or 2,5-
dimethylpyrrole can produce a catalyst system with enhanced activity and
selectivity
to a desired product.
The metal alkyl of the catalyst system can be any heteroleptic or
homoleptic metal alkyl compound. One or more metal alkyls can be used. The
alkyl ligands on the metal can be aliphatic, aromatic, or both (if more than
one
ligand is present). Preferably, the alkyl ligands are any saturated or
unsaturated
aliphatic radical.
The metal alkyl can have any number of carbon atoms. However, due
to commercial availability and ease of use, the metal alkyl will usually
comprise
less than about 70 carbon atoms per metal alkyl molecule and preferably less
than
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
_g_
about 20 carbon atoms per molecule.
Exemplary metal alkyls include, but are not limited to,
alkylaluminum compounds, alkylboron compounds, alkylmagnesium compounds,
alkylzinc compounds or alkyl lithium compounds. Exemplary metal alkyls
include,
but are not limited to n-butyl lithium; s-butyllithium; t-butyllithium;
diethylmagnesium; diethylzinc; triethylaluminum; trimethylaluminum;
triisobutylaluminum; or combinations thereof.
Preferably, the metal alkyl is selected from the group consisting of
non-hydrolyzed, i.e., not pre-contacted with water, alkylaluminum compounds,
derivatives of alkylaluminum compounds, halogenated alkylaluminum compounds,
and mixtures thereof. Mixed metal alkyls can provide improved product
selectivity,
as well as improved catalyst system reactivity, activity, or productivity. The
use of
hydrolyzed metal alkyls can result in decreased olefin (i.e. liquid)
production and
increased polymer (i.e. solid) production.
Most preferably, the metal alkyl is a non-hydrolyzed alkylaluminum
compound expressed by the general formulas A1R3, A1RZX, AIRXz, A1RZOR,
A1RXOR, or Al2R3X3, in which A1 is an aluminum atom, each R is an alkyl group,
O is an oxygen atom, and X is a halogen atom. Exemplary compounds include, but
are not limited to triethylaluminum; tripropylaluminum; tributylaluminum;
diethylaluminum chloride; diethylaluminum bromide; diethylaluminum ethoxide;
diethylaluminum phenoxide; ethylaluminum dichloride; ethylaluminum
sesquichloride; and mixtures thereof for best catalyst system activity and
product
selectivity. The most preferred single alkylaluminum compound is triethyl-
aluminum, for the best catalyst system activity and product selectivity.
Catalyst
systems most pertinent to the present invention comprise aluminum alkyls
containing a halide, such as a chloride or a bromide.
While not wishing to be bound by theory, it is believed that a
chloride containing-compound can improve product purity and selectivity. Any
chloride-containing compound can be used, such as, for example, DEAC and
organo
chlorides. Exemplary organochlorides include, but are not limited to, carbon
tetrachloride, methylene chloride, chloroform, benzylchloride, 1-
hexachloroethane
and mixtures thereof.
CA 02392233 2005-05-26
-9-
One F~articular composite catalyst contemplated here is the
combination of chromium (II1) ethylhexanoate, 2,5-dimethylpyrrole, triethyl-
aluminum, and diethylaluminum chloride. This composite catalyst system can be
used to trimerize ethylene, forming 1-hexene. U.S. Patent No. 5,198,563
teaches the
use of a suitable trirnerization catalyst for the present W vent~on.
Media
Usually, the chromium source, the p5~-role-containing compound, and
the metal alkyl are combined in an olefinically or aromatically unsaturated
hydrocarbon reaction medium. The hydrocarbon can be any aromatic or aliphatic
hydrocarbon, in a gaseous, liquid or solid state. Preferably, to thoroughly
contact the
chromium source, p:yrrole-containing compound, and metal alkyl, the
hydrocarbon is
in a liquid state.
The hydrocarbon can have any number of carbon atoms per molecule.
I S Usually, the hydroc~u-bon will comprise less than about 70 carbon atoms
per
molecule. and preferably, less than about 20 carbon atoms per molecule, due to
the
commercial availability and ease of use of low-molecular-weight compounds. The
most preferred hydrocarbon compound is a reaction product formed by use of the
catalyst system. For example, if 1-hexene is a reaction product, some of the 1-
hexene product can be recycled for use as a reaction medium.
Exemplary unsaturated aliphatic hydrocarbon compounds
contemplated for use as catalyst reaction media include, but are not limited
to,
ethylene, 1-hexene, 1,3-butadiene, and mixtures thereof. Exemplary unsaturated
aromatic hydrocarbons useful as reaction media include, but are not limited
to,
benzene, toluene, ethylbenzene, xylene, mesitylene, hexamethylbenzene, and
mixtures thereof. Unsaturated aromatic hydrocarbons are preferred to improve
the
stability of the catalyst system and to produce a highly active and selective
catalyst
system. The most preferred unsaturated aromatic hydrocarbon is eihylbenzene
for
best catalyst system activity and product selectiviiy.
The U~imerization process generally is carried out in a slurry of the
catalyst components in an inert medium or diluent. Broadly, the common
trimerization reaction diluents can be liquid paraffins, cycloparaffins,
olefins or
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
-10-
aromatic hydrocarbons. Exemplary reactor diluents include, but are not limited
to,
isobutane, cyclohexane, and methylcyclohexane. Isobutane can be used for
enhanced compatibility with known olefin polymerization processes. However, a
homogenous trimerization catalyst system is more easily dispersed in
cyclohexane.
Therefore, a preferred diluent for a homogeneous catalyzed trimerization
process is
cyclohexane.
In accordance with another embodiment of this invention, a slurry
process can be carried out in a diluent (medium), which is a product of the
olefin
oligomerization process. Therefor, the choice of reactor diluent, or medium,
is
based on the selection of the initial olefin reactant. For example, if the
oligomerization catalyst is used to trimerize ethylene to 1-hexene, the
solvent for the
oligomerization reaction would be 1-hexene. If ethylene and hexene were
trimerized to produce 1-decene, the oligomerization reaction solvent would be
1-
decene. If 1,3-butadiene was trimerized to 1,5-cyclooctadiene, the
trimerization
reactor solvent would be 1,5-cyclooctadiene.
The catalyst system comprising a chromium source, pyrrole-
containing compound, metal alkyl, and reaction media can contain additional
components that do not adversely affect and can enhance the resultant catalyst
system, such as, for example, halides.
Equipment
The trimerization reaction can be conveniently carried out in a
suitable reactor, preferably a continuous-feed autoclave reactor with a fluid
jacket or
internal heat transfer coil and any suitable stirring mechanism, such as, for
example,
mechanical stirring or an inert gas, typically nitrogen, purge, piping and
valves. Any
other suitable reaction equipment may also be used. For example, a loop
reactor
with mechanical stirring, such as, for example, a stirring pump, can be used
Reaction Conditions
Trimerization reaction products, as defined in this specification, can
be prepared from catalyst systems of this invention by dispersion reaction,
slurry
reaction, or gas phase reaction techniques using conventional equipment and
contacting processes. Contacting of the monomer or monomers with a catalyst
system can be effected by any manner known in the art. One convenient process
is
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
- 11 -
to suspend the catalyst system in the reaction medium and to agitate the
mixture to
maintain the catalyst system in dispersion throughout the trimerization
process.
Other known contacting processes also can be employed.
Commonly, the catalyst system and reaction media are introduced to
the reactor either continuously or in one or more charges, and the olefin
reactant is
continuously or intermittently introduced throughout the reaction as a gas
under
pressure. The pressure in the reactor usually is maintained by adding a
gaseous
olefin reactant at a suitable rate to replace the olefin consumed by the
reaction.
Hydrogen gas can be charged to the reactor during the reaction to
improve the rate of reaction and enhance the catalyst system activity and
trimer
product selectivity. The presence of hydrogen can be advantageous for reducing
the
by-product polymers into a powdery, non-tacky form that is easily removed from
the reactor and easily separated from the effluent, as by filtering and/or
evaporation.
The partial pressure of hydrogen present is usually from about 0.1 to about
100
kg/cm2 (about 1 to 1000 N/cmz), preferably from about 0.1 to about 80 kg/cm2
(about 1 to 800 N/cm2)
The reaction temperature employed can be any temperature that can
trimerize the olefin reactants. Generally, reaction temperatures are within a
range of
from about 0°C to about 250°C Preferably, reaction temperatures
within a range of
from about 60°C to about 200°C, and most preferably within a
range of from about
80°C to about 150°C are employed. When the reactant is
predominately ethylene, a
temperature in the range of from about 0°C to about 300°C
generally can be used.
Preferably, when the reactant is predominately ethylene, a temperature in the
range
of from about 60°C to about 110°C is employed. If the reaction
temperature is too
low, the polymer tends to stick to the reactor surfaces. If the reaction
temperature is
too high, the catalyst system and reaction products may decompose.
The overall reaction pressure employed can be any pressure that can
trimerize the olefin reactants. Generally, reaction pressures are within a
range of
from about atmospheric pressure (0 psig or 0 N/cm2 gauge pressure) to about
2500
psig (about 1700 N/cmz gauge pressure). Preferably, reaction pressures within
a
range of from about atmospheric pressure to about 1000 psig (690 N/cmz gauge
pressure), and most preferably within a range of 300 to 900 psig (about 200 to
CA 02392233 2002-05-17
WO 01/47839 PCT/CTS00/35366
-12-
about 620 N/cmz gauge pressure), are employed. If the reaction pressure is too
low,
the catalyst system activity can be too low. The maximum pressure generally is
dictated by safety concerns and the desire for vessels having walls no thicker
than
necessary.
The contents of the reactor can be agitated or stirred by an inert gas
(e.g. nitrogen) purge, by introducing the reactant, hydrogen, fluid medium, or
catalyst or exhausting the effluent in a manner causing agitation, by
mechanical or
magnetic stirring, or in any other suitable manner.
The reaction usually is run continuously by steadily charging lower
1-olefin reactant(s), catalyst system, and process medium and removing the
liquid
contents of the reactor. For example, a continuous stirred tank reactor system
can
be employed that includes feed systems for catalyst system, reactant and
medium
and a discharge system for the effluent. A batch process can also be employed,
however.
The reactor effluent is treated to kill the remainder of the catalyst
system, separate products, recycle the residual reactants, medium, and other
components suitable for recycling, and dispose of any components that are not
recycled.
The trimerization reaction is exothermic, so the reaction temperature
usually can be regulated by circulating cooling water through a jacket or heat
transfer coil, thus transferring heat out of the reactor. It is important to
be able to
transfer heat efficiently out of the reactor, so the reactor can be
effectively
maintained at the desired reaction temperature and the heat can be removed
using a
minimum quantity of the cooling medium. Another advantage of more effective
heat transfer is that the trimerization reaction can be run at a higher
throughput for
a given temperature, which can improve production efficiency.
After the catalyst system has been used to prepare one or more olefin
products, the reactor effluent stream comprising olefin trimer product(s),
catalyst
system, and some polymer or higher oligomer by-products, is contacted with a
catalyst kill agent to "kill", deactivate or quench the catalyst. Exemplary
catalyst kill
agents contemplated here are alcohols, primary or secondary amines, or
alkanolamines.
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
-13-
Any alcohol that can be easily dispersed in the reactor effluent stream
can be used as a catalyst kill agent. For example, lower alcohols such as
methanol,
ethanol, propanol, isopropanol, etc. can kill the catalyst system. Preferably,
however, an alcohol is selected that has a boiling point, or molecular weight,
such
that the alcohol will not form an azeotrope with the olefin monomer product.
Generally, materials with similar boiling points and similar molecular weights
are
more likely to form azeotropes.
In an exemplary process, in which the catalyst system is used to
trimerize ethylene to 1-hexene, a monofunctional alcohol with six or more
carbon
atoms per molecule is preferred as the catalyst kill agent. Most preferably, a
monofunctional alcohol having six to twelve carbon atoms per molecule is used
for
best catalyst system quenching. Such alcohols are easily removable from the 1-
hexene olefin product. Exemplary monofunctional alcohols include, but, are not
limited to 1-hexanol; 2-hexanol; 3-hexanol; 2-ethyl-1-hexanol; 3-octanol; 1-
heptanol;
2-heptanol; 3-heptanol; 4-heptanol; 2-methyl-3-heptanol; 1-octanol; 2-octanol;
3-octanol; 4-octanol; 7-methyl-2-decanol; 1-decanol; 2-decanol; 3-decanol; 4-
decanol; 5-decanol; 2-ethyl-1-decanol; and mixtures thereof.
Alternatively, a low-molecular-weight diol or polyol, for example
ethylene glycol, can be used as a catalyst kill agent. Diols and polyols
commonly
have much higher boiling points than monoalcohols of comparable molecular
weight, and thus can be separated more easily from 1-hexene.
The alcohol is used in an amount at least partially effective to quench
the catalyst. For example, alcohol may be added in a molar ratio of from about
0.01 to about 100, preferably from about 0.01 to about 10, most preferably
from
about 0.05 to about 2, in relation to the metal content of the catalyst to be
deactivated.
If an alcohol is used as the catalyst kill agent for a halogenated
catalyst system, hydrogen halides can be generated, as described previously.
Practitioners that manufacture higher olefins commonly will elect to avoid or
reduce
the production of hydrogen halides. The hydrogen halide problem can be
addressed
by treating the product stream with a stabilizing material that forms a stable
halide
or hydrogen halide salt.
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
-14-
The stabilizing material contemplated here can be an aliphatic amine,
an aromatic amine, a metal salt of an amide, a metal salt of a butoxide, a
metal salt
of a carboxylic acid, or a combination of these materials. More specifically,
the
stabilizing material in the present invention can be selected from cyclic and
acyclic,
aromatic and aliphatic amines, nitriles, amides, etc.
The primary amines contemplated as stabilizing materials include
ethylamine; isopropylamine; cyclohexylamine; benzylamine; naphthylamine; and
others. The secondary amines include diethylamine; diisopropylamine; dibutyl-
amine; dicyclohexylamine; dibenzylamine, and bis(trimethylsilyl)amine. The
stabilizing material can be a tertiary amine such as tributylamine.
The cyclic and aromatic amines and related compounds contemplated
here as stabilizing materials include aniline; pyridine; dimethylpyridine;
morpholine;
imidazole; indoline; indole; pyrrole; 2,5-dimethylpyrrole; 3,4-
dimethylpyrrole;
3,4-dichloropyrrole; 2,3,4,5-tetrachloropyrrole; 2-acetylpyrrole; pyrazole;
pyrrolidine; pyrrolidone, and dipyrrylmethane.
The stabilizing materials contemplated here can be alkanolamines.
One particular advantage of alkanolamines is that the same molecule possesses
both
alcohol functionality and amine functionality, which may contribute both to
deactivating, or killing, the catalyst system and to stabilize against the
generation of
corrosive hydrogen halides. Exemplary alkanolamines include isopropanolamine,
monoethanolamine, diethanolamine, and triethanolamine.
The stabilizing materials contemplated here also include polyamines.
Exemplary polyamines are ethylenediamine, diethylenetriamine, and
tetramethylethylenediamine.
The metal salts of amides usable in the present invention as
stabilizers include salts of, for example, dimethylformamide; N-
methylformamide;
acetamide; N-methylhexaneamide; succinamide; maleamide; N-methylbenzamide;
imidazole-2-carboxamide; di-2-thenolamine; beta-lactam; delta-lactam, or
epsilon-
lactam with metals of IA, IIA or IIIB Group of the periodic table. Examples of
such metal amides are lithium amide; sodium ethylamide; calcium diethylamide;
lithium diisopropylamide; potassium benzylamide; sodium bis
(trimethylsilyl)amide;
lithium indolide; sodium pyrrolide; lithium pyrrolide; potassium pyrrolide;
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
- 15 -
potassium pyrrolidide; diethylaluminum pyrrolide; ethylaluminum dipyrrolide;
aluminum tripyrrolide; sodium 2,5-dimethylpyrrolide; lithium 2,5-
dimethylpyrrolide;
potassium 2,5-dimethylpyrrolide; potassium 2,5-dimethylpyrrolidide; diethyl-
aluminum; 2,5-dimethylpyrrolide; ethylaluminum; di(2,5-dimethylpyrrolide);
aluminum tri(2,5-dimethylpyrrolide), and combinations of those.
The imides usable in the present invention as stabilizers include
1,2-cyclohexanedicarboxyimide, succinimide, phthalimide, maleimide, 2,4,
6-piperidinetrione, and perhydroazesine-2,10-dione.
The metal salts of butoxides usable herein are the butoxide salts of
alkali metals (describe further). An exemplary butoxide salt is potassium tert-
butoxide.
The metal salts of carboxylic acids useful herein as stabilizers include
the metal salts, more particularly the lithium, sodium, potassium and/or
rubidium
salts of, carboxylic acids. Examples of the carboxylic acids include acetic
acid,
propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid,
octanoic
acid, nonanoic acid, decanoic acid, benzoic acid, phenylacetic acid, phthalic
acid,
malonic acid, succinic acid, glutaric acid, adipic acid, acrylic acid, malefic
acid,
fumaric acid, and salicylic acid. An exemplary carboxylic acid salt
contemplated
here is silver acetate, lithium acetate, sodium acetate, potassium acetate,
and
mixtures thereof.
Exemplary phosphines useful herein as stabilizers include tributyl-
phosphine oxide and triethylphosphine.
The stabilizing material should be provided in an amount effective to
at least reduce the generation of hydrogen halide gas. For example, from about
0.01 to about 100 moles, preferably from about 0.01 to about 10 moles, more
preferably from 0.05 to 2 moles of the stabilizing material can be added per
mole of
halogen in the catalysts.
The use of an alcohol is not essential to quench or kill the catalyst.
Other materials, for example primary or secondary amines, can be used to kill
a
catalyst, either alone or in combination with one or more alcohols. Generally,
an
aliphatic primary amine, an aliphatic secondary amine, or a combination of
those
materials is contemplated for use as a catalyst kill agent. More specifically,
the
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
-16-
amines may be acyclic aliphatic amines or cyclic aliphatic amines, within the
scope
of the invention.
As with the alcohol, the amine quenching material can be provided in
an amount effective to at least substantially quench the catalyst, either
alone or
when combined with an alcohol or other quenching agent.
Enough of the catalyst kill agent is added to the reactor effluent
stream to at least substantially quench, deactivate, or "kill", the olefin
production
catalyst system and to reduce or eliminate the production of undesirable
solids,
particularly polymer or catalyst solids. If an insufficient amount of catalyst
kill
agent is used, any metals in the catalyst system, such as chromium or
aluminum,
can precipitate and interfere with future effluent processing. Generally, up
to about
five molar equivalents of catalyst kill agent can be added, per mole of metals
in the
effluent stream. Preferably, the amount of catalyst kill agent added is from
about
one to about four molar equivalents, and most preferably the amount of
catalyst kill
agent added is from about two to about three molar equivalents of catalyst
kill agent
per mole of metals in the reactor effluent stream. Too much catalyst kill
agent can
cause corrosion of the reactor.
After the catalyst system has been quenched and treated to stabilize
any halides, the olefin products, such as, for example, 1-hexene, can be
removed.
Any removal process can be used, although distillation is preferred for ease
of use.
In a simple distillation, ethylene is removed from the reaction product, then
1-
hexene and the medium are distilled away from the reaction dispersion while
the
catalyst components are concentrated and recovered together with the by-
product
polyethylene. Typical distillation temperatures in the distillation kettles
are about
190°C to about 210°C. These distillation temperatures are
believed to be sufficient
to promote the decomposition of aluminum halides present in the spent catalyst
to
produce hydrogen halides, unless steps are taken as described in this
disclosure to
prevent hydrogen halide generation.
The concentrated dispersion containing by-product polymer and
catalyst components may be discarded, or can be further treated as described
below.
The product stream produced by the ethylene trimerization process
commonly contains one of more of the following compounds butene; 1-hexene;
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
-17-
internal hexenes (i.e. 2-hexene or 3-hexene); octenes; decenes; reaction
medium; and
"heavies".
The waste product steam formed by removing the desired olefin
monomer products can be further processed by contacting it with an aqueous
base to
remove metals. Organic bases are not preferred at this point because organic
bases
can be too weak to precipitate heavy metals, such as chromium. The preferred
aqueous inorganic bases are sodium hydroxide and potassium hydroxide, due to
their ease of use, availability, low cost, and beneficial effects on future
processing.
The amount of aqueous inorganic base added can be any amount
sufficient to precipitate most or substantially all of the chromium. The most
important goal of this step is to remove chromium or other heavy metals, as
any
remaining dispersed aluminum does not raise the same environmental issues.
Addition of too much or too little of the aqueous inorganic base can
prevent precipitation of the chromium. Generally, about up to about 4 molar
equivalents of aqueous inorganic base should be used per mole of chromium and
aluminum. Preferably, from about 0.2 to about 3 molar equivalents, and most
preferably from about 1 to 2 molar equivalents of the aqueous inorganic base
should
be used per mole of chromium and aluminum. The chromium-containing solid
precipitate then can be removed and disposed of properly.
Following removal of the chromium containing solid precipitate, the
aqueous and organic layers, or portions, are separated. The organic layer can
be
disposed of.
Removing~Residues
The trimerization process commonly produces two residues that can
build up on the internal surfaces of the reactor.
One residue, long recognized to build up on the walls of the reactor,
is an oligomer or a polymer having a chain length higher than the intended
product,
formed as a by-product. This higher oligomer or polymer residue is referred to
here, for the sake of simplicity, as just "polymer residue". For example, in
the case
of an ethylene reaction, polyethylene or paraffin wax residue can be formed
and
build up on the internal surfaces of the reactor. This polymer residue
detracts from
the heat transfer efficiency of the internal surfaces of the reactor.
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
-18-
Polymer residue may be removed from the reactor by washing the
reactor with a solvent for the residue. The trimerization reactor commonly is
supplied with a solvent for by-product polymers - such as cyclohexane or
methylcyclohexane - as the process medium. When a polymer solvent is used as
S the process medium, the same process medium can be used to periodically
flush out
the reactor. The washing conditions can be more stringent than the usual
process
conditions, to remove the polymer residue that is not removed under the usual
process conditions. For example, the washing step can be a "hot wash", carried
out
by circulating the usual process medium at a higher temperature than the
process
temperature to melt, more quickly dissolve, or otherwise dislodge the polymer
residue.
In a continuous ethylene trimerization process, the hot wash can be
carried out as follows. The reaction can be halted by stopping the feed of
catalyst
and reactants while continuing to inject and drain the reactor medium, which
can be,
1 S but is not limited to, cyclohexane and/or methylcyclohexane and increasing
the
medium temperature by about 60°C to 70°C. The hot wash is
continued for several
hours, or as long as necessary to remove all or substantially all of the
polymer
residue. This hot wash has been found to remove the buildup of the polymer
residue.
A second residue, which also detracts substantially from the heat
transfer efficiency of the reactor, is referred to here as catalyst residue.
The exact
chemical constitution of this catalyst residue is not known. It may be a
precipitate
or deposit of the entire catalyst or one or more of the catalyst ingredients,
the
product of a reaction between the catalyst ingredients, the catalyst and the
reactor
wall, spent catalyst constituents, a combination of these residues, or
something else.
The residue is believed to be associated with the catalyst, though the present
invention is not limited by the accuracy of that theory.
A further understanding of how to make and use the present
invention and its advantages will be provided by reference to the following
examples.
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
-19-
EXAMPLES
Example 1
To an inert gas purged one liter, three-necked flask equipped with
nitrogen purge, magnetic stirrer, glass column, Dean-Stark tube and condenser
was
added 250 mL dry dodecane and 260 mL of 2-ethyl-1-hexanol. The system was
purged again for 20 minutes and 50 mL of selective 1-hexene catalyst (5 mg
Cr/mL) was added. Water (2 mL) was added and the system was heated to reflux.
Nine samples were taken over 5 hours. Acidity was assessed by water extraction
of
the samples taken from the Dean Stark tube and testing the water with pH
paper.
The first sample was mildly acidic and all of the other samples were very
acidic.
Water was observed to be present in the last sample.
Example 2
Example 1 was repeated but in addition to the 2 mL of water, 4 mL
of tri-n-butylamine also was added. None of the subsequent nine samples from
the
Dean-Stark tube were acidic demonstrating the effectiveness of adding an amine
to
the process. Water was observed in the ninth sample, as was observed in
Example
1. The presence of the amine removed all indications of acidity.
Experimental Apparatus for Examples 3 and 4
The apparatus used for Examples 3 and 4 was a one liter, three-
necked round bottom flask equipped with a glass well for a thermocouple to
monitor the kettle temperature, an addition funnel and a Dean-Stark tube. A
condenser was placed at the top of the Dean-Stark tube as was a thermocouple
to
measure overhead temperature and a wire that held a piece of pH paper at the
top of
the Dean-Stark tube. The flask also was equipped with a magnetic stirring bar
and
a stirrer and a heating mantle. A nitrogen stream constantly swept material
through
the apparatus and a bubbler containing water.
General Procedure for Examples 3 and 4
In a typical experiment, 200 g dodecane was added to the flask and
the system purged with nitrogen. Diethylaluminum chloride (DEAC) (1.9M) in
dodecane then was charged to the flask from a metal cylinder. The desired
amount
of 2-ethyl-1-hexanol was then added slowly and allowed to react. The
temperature
would rise to approximately 50-70°C and gas evolution was observed. The
contents
CA 02392233 2002-05-17
WO 01/47839 PCT/US00/35366
-20-
were stirred for 30 minutes to allow complete reaction and the kettle sampled.
The
contents then were heated to reflux. Overhead was removed as necessary to
obtain
the desired kettle temperature. The overhead was sampled (about 2 mL)
periodically from the Dean-Stark tube.
Example 3
The following materials were added to the apparatus described above:
200 g of dry dodecane, 80.8 mL of a 1.9M solution of DEAC in dodecane and 96
mL of 2-ethyl-1-hexanol was slowly added. This mixture was heated to a kettle
temperature of 170°C to 209°C over 2.75 hours. The following
observations were
made. Immediately after the addition of the alcohol, there was no change in
color
of the pH paper in the top of the Dean- Stark tube and the pH of the water
bubbler
was neutral. Upon heating, the pH paper in the Dean-Stark tube turned reddish-
purple (strongly acidic). Samples from the bottom of the Dean-Stark tube
turned
moist pH paper to indicate acidity and the test for chloride with silver
acetate was
positive. It was clear that the acidic hydrochloric acid was present.
Example 4
The following materials were added to the apparatus described above:
200 g of dry dodecane, 81 mL of a 1.9M solution of DEAC in dodecane and 96 mL
of 2-ethyl-1-hexanol was slowly added. Tri-n-butylamine (40.25 g) was added.
This mixture was heated to a kettle temperature of 208°C over 4
hours. The
following observations were made. There was no change in color of the pH paper
in
the top of the Dean Stark tube throughout the experiment. The pH of the water
bubbler was neutral at the end of the experiment. Samples from the bottom of
the
Dean Stark tube were neutral or slightly basic as indicated by moist pH paper.
It
was clear that any acid formed was removed from the system by the addition of
the
amore.
While this invention has been described in detail for the purpose of
illustration, it is not to be construed as limited thereby but is intended to
cover all
changes and modifications within the spirit and scope thereof.
