Note: Descriptions are shown in the official language in which they were submitted.
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ANTI-STATICS
FIELD OF THE INVENTION
The present invention relates to a process to control static electricity
in the gas phase polymerization of alpha olefins such as co (including
terpolymers) and homopolymers of ethylene and co (including
terpolymers) and homopolymers of propylene.
BACKGROUND OF THE INVENTION
The build up of static electricity (static) in a gas phase fluidized or
stirred bed reactor during the polymerization of alpha olefins leads to a
number of different problems such as formation of sheets (sheeting),
polymer build up in parts of the reactor and product quality issues. These
problems tend to require that the reactor be shut down and cleaned on a
periodic basis.
United States patent 4,792,592 issued Dec. 20, 1988 to Fulks, et al.
assigned to Union Carbide Corporation teaches applying and maintaining
a static electric charge to a fluid bed gas phase polymerization reactor at
locations where sheet build up is expected to occur at a level below that at
which sheeting will occur.
United States patent 4,855,370 issued Aug. 8, 1989 to Chirillo, et al.
assigned to Union Carbide teaches reducing sheeting during a fluid bed
gas phase polymerization using a titanium or vanadium catalyst by adding
small amounts of water to the reactor (sometimes called water add back)
to maintain the static levels sufficiently low to prevent or reduce sheeting.
United States patent 4,532,311 issued July 30, 1985 to Fulks, et al.
teaches treating the internal surface of a reactor with a solution of a
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chromocene compound prior to fluid bed polymerization of alpha olefins in
the presence of a titanium containing catalyst. The patent teaches the
treatment to reduce static and consequently sheeting.
U.S. patent 5,034,481 issued July 23, 1991 to Funk et al. assigned
to BASF teaches adding chromium salts of salicylic acid to a fluid bed gas
phase reactor as an antistat agent in the presence of a titanium containing
catalyst.
United States Patent 5,731,392 issued March 24, 1998 to Ali, et al.
assigned to Mobil Oil Company teaches adding TEOS
(tetraethylorthosilicate) as an antistatic agent (or antistat) to a fluid bed
gas
phase reactor in an amount from 16 to 40 ppm based on the ethylene feed
stream. The tetraethylorthosilicate may be used in conjunction with water
add back to control negative and positive static respectively. The patent
does not teach adding clay as an antistatic agent.
U.S. patent 6,201,076 issued March 13, 2001 to Etherton, et al.
assigned to Equistar teaches adding from about 10 to 75 weight % based
on the weight of the support of a fatty amine to reduce fouling and
sheeting in the polymerization of olefins in the presence of a single site
catalyst.
There are a number of patents, which teach the use of a
combination of polysulfones, polyamides and sulphonic acid as antistat in
gas phase and slurry polymerization of alpha olefins. These include
United States Patents 4,182,810 and 5,026,795 issued Jan. 8, 1980 to
Wilcox and June 25, 1991 to Hogan both assigned to Phillips Petroleum
Company.
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U.S. patent 6,689,846 issued Feb.10, 2004, to Leskinen et al.
assigned to Borealis teaches adding an antistat and catalyst deactivator to
the second reactor of a tandem reactor polymerization process. The
antistat agent is a STADIS type antistat (a mixture of lower alkanol (C1_6);
aromatic (C6_12) sulphonic acid(s); polymeric polyamines; and polysulflone
copolymers).
WO 0142320 published June 14, 2001 in the name of The Dow
Chemical Company teaches the use of clay supports for single site
catalysts. However, the patent does not teach or suggest that the use of
one or more clays as a support or being added to the reactor reduces
static in the reactor.
United States Patent 5,225,458 issued July 6, 1993 in the names of
Bailly et al. assigned to BP Chemicals Limited teaches the addition of
0.005 to 0.2 weight % of a pulverulent inorganic material to a gas phase
polymerization. The pulverulent material may be mineral oxides such as
silica, alumina or magnesium oxide. However, the patent does not
expressly teach that clays can be use as antistatic agents. The
polymerization catalyst seems to be limited to Ziegler Natta catalyst and
specifically prepolymerized catalyst.
None of the above art suggests clays per se could be useful as an
antistatic agent in gas phase, typically fluidized bed but also stirred bed
polymerization typically of alpha olefin homo or copolymers.
The present invention seeks to provide a simple, inexpensive
method to help control static in a gas phase polymerization process for
alpha olefins.
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SUMMARY OF THE INVENTION
The present invention seeks to provide a process to control static in
a gas phase olefin polymerization reactor comprising feeding to the reactor
clay or modified clay or mixtures of the two where the rate of addition of
the clay component, to the reactor is in an amount from 0.001 to 1.0
weight (:)/0 of the polymer production rate. (e.g. typically pounds or tonnes
per hour). Modified clays are clays in which the clay has undergone some
type of chemical or physical transformation. This can include but is not
limited to mixing with additives, adjuvants, inorganic compounds and the
like or partaken in some form of a chemical reaction such as being
modified with an exchangeable cation, reacted with a surface modifying
reagent and the like.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a plot of the electrostatic charge in a technical scale
stirred tank reactor of granular resin produced with a chromium catalyst
before and after the addition of clay.
Figure 2 is a plot of the electrostatic charge in a technical scale
stirred tank reactor of granular resin produced with single site catalyst
before and after the addition of clay.
DETAILED DESCRIPTION
There are a number of types of catalyst which may be used in gas
phase polymerization, either in stirred or fluidized reactor, of alpha olefins
such as ethylene or propylene or copolymerization of ethylene or
propylene with one or more monomers selected from the group consisting
of C3_8 alpha olefins such as 1-butene, 1-pentene, isopentene, 4-methyl-1-
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pentene, 1-hexene and 1-octene, preferably 1-butene and 1-hexene.
Typically, polyethylene has a density from 0.910 to 0.960 g/cc. Typically
the polyolefin may comprise from 100 to 80, preferably from 100 to 85
most preferably from 100 to 90 weight % of ethylene and from 0 to 20,
preferably less than 15, most preferably less than 10 weight % of one or
more comonomers selected from the group consisting of C3_8 alpha olefins.
Generally, the polymers having a higher amount of comonomer, typically
from about 85 to 95 weight % of ethylene and from about 15 to 5 weight %
of one or more C3..8 alpha olefins will have a density of less than 0.930 g/cc
and polymers comprising from 100 to 95 weight % of ethylene and from 0
to 5 weight % of one or more C3-8, preferably C4_6, alpha olefins prepared
with a chrome catalyst (which is not a single site type catalyst ) will have a
density of greater than 0.930 g/cc typically greater than 0.940, preferably
greater than 0.945 g/cc. Similar compositions prepared in the presence of
a single site catalyst will have a lower density (e.g. for 6 weight % of
hexene in the copolymer may have a density in the range of about 0.920
g/cc).
The gas phase polymerization process may be a stirred bed or
fluidized bed process. Such processes are well known in the ail.
Fluidized bed polymerization processes are discussed in a number of
patents including the above noted U.S. patents to Union Carbide.
Generally, in the gas phase polymerization process the temperature of the
reactor for single site and/or chromium catalyst will be from 75 to 120 C,
typically from 80 to 115 C, preferably from 85 to 110 C. The reactor
pressure (e.g. total pressure in the reactor) will be from 100 to 500 psi
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(689 to 3,445 kPa), typically from 150 to 300 psi (1,033 to 2,067 kPa),
preferably from 200 to 300 psi (1,378 to 2,067 kPa). The reaction may be
in dry mode, condensed mode (e.g. U.S. patents to Jenkins III et al., such
as U.S. patent 4,543,399) or super condensed mode (U.S. patent to Griffin
or DeChellis such as U.S. patent 5,352,749). The reaction may take place
in the presence of hydrogen and a non-polymerizable gas, which may be
inert or may be an alkane, or a mixture thereof.
The catalyst for the polymerization may comprise a Phillips type
chromium oxide catalyst, a hydrocarbylsilyl chromium catalyst (e.g. silyl
chromate type catalysts), a Ziegler Natta supported catalyst such as
disclosed in United States Patent 7,211,535 issued May 1, 2007 to Kelly et
al., assigned to NOVA Chemicals Corporation and Ineos Europe Limited,
or a single site, a metallocene, a constrained geometry, or a bulky ligand
single site catalyst and conventional activators/co-catalysts and mixtures
thereof. Reviews by Mulhaupt, R. Macromol. Chem. Phys. 2004, 289 ¨
327, 2003 and Boussie, T.R. et al. in J. Am Chem. Soc., 125, 4306 - 4317,
2003 and references within give a good understanding by what is meant
by single site catalysts.
The chromium-based catalysts may comprise chromium oxide on a
support as described below. The oxide catalysts are typically prepared by
contacting the support as described below with a solution comprising an
inorganic (e.g. Cr(NO3)3 or an organometallic (e.g. chromium acetate, silyl
chromate ¨ e.g. a bis hydrocarbyl silyl chromate) chromium compound.
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The bis hydrocarbyl silyl chromate compound may be of the formula
R 0 R
I ii I
R-Si-O-Cr-O-Si-R
It II
0 I
R
wherein each R is selected from the group consisting of C1-14 alkyl or
aromatic radicals preferably C1-6 alkyl or aromatic compounds. Some
suitable ayl chromates include bis(trimethylsilyl)chromate;
bis(triethylsilyl)chromate; bis(tributylsilyl)chromate;
bis(tripentylsilyl)chromate, bis(triphenylsilyl)chromate,
bis(tritolylsilyl)chromate, bis(triethylhexylsilyl)chromate, and
bis(tridecylsilyl)chromate, bis(tritetradecylsilyl)chromate,
bis(tribenzylsilyl)chromate, preferably bis(triphenylsilyl)chromate
The inorganic chromium catalysts and chromium acetate type
catalysts are activated by being oxidized in air at elevated temperatures
(e.g. 400 to 800 C). The silyl chromate compounds may also be activated
through a reduction with an aluminum compound preferably to provide a
molar ratio of Al:Cr from 0.5:1 to 30:1, preferably from 1:1 to 10:1, most
preferably from 1:1 to 6:1. The aluminum compound may be of the
formula R1bAl(0R1)a wherein a is from 0 to 2, typically 0 or 1, b is an
integer from 1 to 3, a+b is equal to 3, R1 is independently selected from a
Ci_io alkyl radical. Some activators include tri alkyl aluminums such as
triethylaluminium or triisobutylaluminum and dialkyl aluminum alkoxides
such as diethyl aluminum ethoxide. The aluminum activator may be
added to the support prior to the chromium compound.
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Single site, metallocene, constrained geometry and bulky ligand
single site catalyst may have the formula:
(L)¨M--(Y)p
wherein M is selected from the group consisting of Ti, Zr, and Hf; Lisa
monoanionic ligand independently selected from the group consisting of
cyclopentadienyl-type ligands and bulky heteroatom ligands containing not
less than five atoms in total (typically of which at least 20%, preferably at
least 25% numerically are carbon atoms) and further containing at least
one heteroatom selected from the group consisting of boron, nitrogen,
oxygen, phosphorus, sulfur and silicon, said bulky heteroatom ligand being
sigma or pi-bonded to M, Y is independently selected for the group
consisting of activatable ligands; n may be from 1 to 3; and p may be from
1 to 3, provided that the sum of n+p equals the valence state of M, and
further provided that two L ligands may be bridged.
Non-limiting examples of bridging groups include bridging groups
containing at least one Group 13 to 16 atom, often referred to as a divalent
moiety such as but not limited to at least one of a carbon, oxygen,
nitrogen, silicon, boron, germanium and tin atom or a combination thereof.
Preferably the bridging group contains a carbon, silicon or germanium
atom, most preferably at least one silicon atom or at least one carbon
atom. The bridging group may also contain substituent radicals as defined
above including halogens.
Some bridging groups include but are not limited to a di C1_6 alkyl
radical (e.g. an alkylene radical such as an ethylene bridge), a di C6-10 aryl
radical (e.g. a benzyl radical having two bonding positions available),
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silicon or germanium radicals substituted by one or more radicals selected
from the group consisting of C1_6 alkyl, C6.10 aryl, phosphine or amine
radical which are unsubstituted or up to fully substituted by one or more
C1_6 alkyl or C6-10 aryl radicals, or a hydrocarbyl radical such as a C1_6
alkyl
radical or a C6_10 arylene (e.g. divalent aryl radicals); divalent C1_6
alkoxide
radicals and the like.
Exemplary of the silyl species of bridging groups are dimethylsilyl,
methylphenylsilyl, diethylsilyl, ethylphenylsilyl or diphenylsilyl radicals.
Most preferred of the bridged species are dimethylsilyl, diethylsilyl and
methylphenylsilyl bridging radicals.
Exemplary hydrocarbyl radicals for bridging groups include
methylene, ethylene, propylene, butylene, phenylene and the like, with
methylene being preferred.
Exemplary bridging amides include dimethylamide, diethylamide,
methylethylamide, di-t-butylamide, diisoproylamide and the like.
The term "cyclopentadienyl" refers to a 5-member carbon ring
having delocalized bonding within the ring and typically being bound to the
active catalyst site, generally a group 4 metal (M) throughil5 - bonds. The
cyclopentadienyl ligand may be unsubstituted or up to fully substituted with
one or more substituents selected from the group consisting of C1-10
hydrocarbyl radicals in which hydrocarbyl substituents are unsubstituted or
further substituted by one or more substituents selected from the group
consisting of a halogen atom; a C1_4 alkyl radical; a C1_6 alkoxy radical; a
C6_10 aryl or aryloxy radical; an amido radical which is unsubstituted or
substituted by up to two C1.8 alkyl radicals; a phosphido radical which is
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unsubstituted or substituted by up to two C1_8 alkyl radicals; silyl radicals
of
the formula ¨Si¨(R)3 wherein each R is independently selected from the
group consisting of hydrogen, a C1_8 alkyl or alkoxy radical, and C6_10 aryl
or aryloxy radicals; and germanyl radicals of the formula Ge¨(R)3 wherein
R is as defined above.
Typically the cyclopentadienyl-type ligand is selected from the
group consisting of a cyclopentadienyl radical, an indenyl radical and a
fluorenyl radical where the radicals are unsubstituted or up to fully
substituted by one or more substituents selected from the group consisting
of a fluorine atom, a chlorine atom; C1_4 alkyl radicals; and a phenyl or
benzyl radical which is unsubstituted or substituted by one or more fluorine
atoms.
In the above formula for the single site catalysts if none of the L
ligands is a bulky heteroatom ligand then the catalyst could be a bis Cp
catalyst (a traditional metallocene) or a bridged constrained geometry type
catalyst or tris Cp catalyst.
If the catalyst contains one or more bulky heteroatom ligands the
catalyst would have the formula:
(D)m
(On ¨ M
wherein M is a transition metal selected from the group consisting of Ti, Hf
and Zr; D is independently a bulky heteroatom ligand (as described
below); L is a monoanionic ligand selected from the group consisting of
cyclopentadienyl-type ligands (as described above); D and L may
optionally be joined by a bridging group as described above; Y is
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independently selected from the group consisting of activatable ligands; m
is 1 or 2; n is 0, 1 or 2 and p is an integer and the sum of m+n+p equals
the valence state of M, provided that when m is 2, D may be the same or
different bulky heteroatom ligands and may optionally be bridged .
For example, the catalyst may be a bis (phosphinimine), or a mixed
phosphinimine ketimide dichloride complex of titanium, zirconium or
hafnium. Alternately, the catalyst could contain one phosphinimine ligand
or one ketimide ligand, one "L" ligand (which is most preferably a
cyclopentadienyl-type ligand) and two "Y" ligands (which are preferably
both chloride).
The preferred metals (M) are from Group 4 (especially titanium,
hafnium or zirconium) with titanium being most preferred. In one
embodiment the catalysts are group 4 metal complexes in the highest
oxidation state.
The bulky heteroatom ligands (D) include but are not limited to
phosphinimine ligands (PI) and ketimide (ketimine) ligands. The
phosphinimine ligand (PI) is defined by the formula:
R21
\
R21 _ p = N _
/
R21
wherein each R21 is independently selected from the group consisting of a
hydrogen atom; a halogen atom; C1_20, preferably C1_10 straight chain or
branched hydrocarbyl radicals which are unsubstituted by or further
substituted by a halogen atom; a C1_8 alkoxy radical; a C6_10 aryl or aryloxy
radical; an amido radical; a silyl radical of the formula:
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¨Si¨(R22)3
wherein each R22 is independently selected from the group consisting of
hydrogen, a C1_8 alkyl or alkoxy radical, and C6-10 aryl or aryloxy radicals;
and a germanyl radical of the formula:
¨Ge¨(R22)3
wherein R22 is as defined above.
The preferred phosphinimines are those in which each R21 is a
hydrocarbyl radical, preferably a C1-6 straight chained or branched (e.g.
secondary or tertiary) hydrocarbyl radical.
Suitable phosphinimine catalysts are Group 4 organometallic
complexes, which contain one phosphinimine ligand (as described above)
and one ligand L that is either a cyclopentadienyl-type ligand or a
heteroatom ligand.
As used herein, the term "ketimide ligand" refers to a ligand which:
(a) is bonded to the transition metal via a metal¨nitrogen atom
bond;
(b) has a single substituent on the nitrogen atom (where this
single substituent is a carbon atom which is doubly bonded to the N atom);
and
(c) has two substituents Sub 1 and Sub 2 (described below)
which are bonded to the carbon atom.
Conditions a, b and c are illustrated below:
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Sub 1 Sub 2
\ /
C
ii
N
1
metal
The substituents "Sub 1" and "Sub 2" may be the same or different
and may be further bonded together through a bridging group to form a
ring. Exemplary substituents include hydrocarbyls having from 1 to 20,
preferably from 3 to 6, carbon atoms, silyl groups (as described below),
amido groups (as described below) and phosphido groups (as described
below). For reasons of cost and convenience it is preferred that these
substituents both be hydrocarbyls, especially simple alkyls and most
preferably tertiary butyl.
Suitable ketimide catalysts of the present invention are Group 4
organometallic complexes that contain one ketimide ligand (as described
above) and one ligand L that is either a cyclopentadienyl-type ligand or a
heteroatom ligand.
The term bulky heteroatom ligand (D) is not limited to
phosphinimine or ketimide ligands and includes ligands that contains at
least one heteroatom selected from the group consisting of boron,
nitrogen, oxygen, phosphorus, sulfur and silicon. The heteroatom ligand
may be sigma or pi-bonded to the metal. Exemplary heteroatom ligands
include silicon-containing heteroatom ligands, amido ligands, alkoxy
ligands, boron heterocyclic ligands and phosphole ligands, as all described
below.
Silicon containing heteroatom ligands are defined by the formula:
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¨ (Y)SiRxRyRz
wherein the ¨ denotes a bond to the transition metal and Y is sulfur or
oxygen.
The substituents on the Si atom, namely Rx, Ry and Rz are required
in order to satisfy the bonding orbital of the Si atom. The use of any
particular substituent Rx, Ry or Rz is not especially important to the
success of this invention. It is preferred that each of Rx, Ry and Rz is a C1-
2
hydrocarbyl group (i.e. methyl or ethyl) simply because such materials are
readily synthesized from commercially available materials.
The term "amido" is meant to convey its broad, conventional
meaning. Thus, these ligands are characterized by (a) a metal-nitrogen
bond; and (b) the presence of two substituents (which are typically simple
alkyl or silyl groups) on the nitrogen atom.
The terms "alkoxy" and "aryloxy" is also intended to convey its
conventional meaning. Thus, these ligands are characterized by (a) a
metal oxygen bond; and (b) the presence of a hydrocarbyl group bonded
to the oxygen atom. The hydrocarbyl group may be a C1_10 straight
chained, branched or cyclic alkyl radical or a C6_13 aromatic radical which
radicals are unsubstituted or further substituted by one or more C1_4 alkyl
radicals (e.g. 2,6 di-tertiary butyl phenoxy).
Boron heterocyclic ligands are characterized by the presence of a
boron atom in a closed ring ligand. This definition includes heterocyclic
ligands that also contain a nitrogen atom in the ring. These ligands are
well known to those skilled in the art of olefin polymerization and are fully
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described in the literature (see, for example, U.S. Patent's 5,637,659;
5,554,775; and the references cited therein).
The term "phosphole" is also meant to convey its conventional
meaning. "Phospholes" are cyclic dienyl structures having four carbon
atoms and one phosphorus atom in the closed ring. The simplest
phosphole is C41-14P (which is analogous to cyclopentadiene with one
carbon in the ring being replaced by phosphorus). The phosphole ligands
may be substituted with, for example, C1_20 hydrocarbyl radicals (which
may, optionally, contain halogen substituents); phosphido radicals; amido
radicals; or silyl or alkoxy radicals. Phosphole ligands are also well known
to those skilled in the art of olefin polymerization and are described as
such in U.S. Patent 5,434,116 (Sone, to Tosoh).
The single site type catalysts may be activated with an activator
selected from the group consisting of:
(i) a complex aluminum compound of the formula
R122A10(R12A10)mAIR122 wherein each R12 is independently selected from
the group consisting of C1-20 hydrocarbyl radicals and m is from 3 to 50,
and optionally a hindered phenol to provide a molar ratio of Al:hindered
phenol from 2:1 to 5:1 if the hindered phenol is present;
(ii) ionic activators selected from the group consisting of:
(A) compounds of the formula [R13]+ [B(R14)4]- wherein B
is a boron atom, R13 is a cyclic C5..7 aromatic cation or a triphenyl
methyl cation and each R14 is independently selected from the
group consisting of phenyl radicals which are unsubstituted or
substituted with 3 to 5 substituents selected from the group
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consisting of a fluorine atom, a C1_4 alkyl or alkoxy radical which is
unsubstituted or substituted by a fluorine atom; and a silyl radical of
the formula -Si-(R15)3; wherein each R15 is independently selected
from the group consisting of a hydrogen atom and a C1_4 alkyl
radical; and
(B) compounds of the formula [(R15)t ZHr[B(R14)4T
wherein B is a boron atom, H is a hydrogen atom, Z is a nitrogen
atom or phosphorus atom, t is 2 or 3 and R18 is independently
selected from the group consisting of C1-18 alkyl radicals, a phenyl
radical which is unsubstituted or substituted by up to three C1_4 alkyl
radicals, or one R18 taken together with the nitrogen atom may form
an anilinium radical and R14 is as defined above; and
(C) compounds of the formula B(R14)3 wherein R14 is as
defined above; and
(iii) mixtures of (i) and (ii).
Preferably the activator is a complex aluminum compound of the
formula R122A10(R12A10)mAIR122 wherein each R12 is independently
selected from the group consisting of C1_4 hydrocarbyl radicals and m is
from 3 to 50, and optionally a hindered phenol to provide a molar ratio of
Al:hindered phenol from 2:1 to 5:1 if the hindered phenol is present. In the
aluminum compound, preferably R12 is methyl radical and m is from 10 to
40. The preferred molar ratio of Al:hindered phenol, if it is present, is from
3.25:1 to 4.50:1. Preferably the phenol is substituted in the 2, 4 and 6
position by a C2..6 alkyl radical. Desirably the hindered phenol is 2,6-di-
tert-
butyl-4-ethyl-phenol.
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The aluminum compounds (alumoxanes and optionally hindered
phenol) are typically used as activators in substantial molar excess
compared to the amount of the transition metal in the catalyst.
Aluminum:transition metal molar ratios of from 10:1 to 10,000:1 are
preferred, most preferably 10:1 to 500:1 especially from 10:1 to 120:1.
Ionic activators are well known to those skilled in the art. The "ionic
activator" may abstract one activatable ligand so as to ionize the catalyst
center into a cation, but not to covalently bond with the catalyst and to
provide sufficient distance between the catalyst and the ionizing activator
to permit a polymerizable olefin to enter the resulting active site.
Examples of ionic activators include:
triethylammonium tetra(phenyl)boron,
tripropylammonium tetra(phenyl)boron,
tri(n-butyl)ammonium tetra(phenyl)boron,
trimethylammonium tetra(p-tolyl)boron,
trimethylammonium tetra(o-toly0boron,
tributylammonium tetra(pentafluorophenyl)boron,
tripropylammonium tetra(o,p-dimethylphenyl)boron,
tributylammonium tetra(m,m-dimethylphenyl)boron,
tributylammonium tetra(p-trifluoromethylphenyl)boron,
tributylammonium tetra(pentafluorophenyl)boron,
tri(n-butyl)ammonium tetra(o-tolyl)boron,
N,N-dimethylanilinium tetra(phenyl)boron,
N,N-diethylanilinium tetra(phenyl)boron,
N,N-diethylanilinium tetra(phenyl)n-butylboron,
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di-(isopropyl)ammonium tetra(pentafluorophenyl)boron,
dicyclohexylammonium tetra(phenyl)boron,
triphenylphosphonium tetra(phenyl)boron,
tri(methylphenyl)phosphonium tetra(phenyl)boron,
tri(dimethylphenyl)phosphonium tetra(phenyl)boron,
tropillium tetrakispentafluorophenyl borate,
triphenylmethylium tetrakispentafluorophenyl borate,
tropillium phenyltrispentafluorophenyl borate,
triphenylmethylium phenyltrispentafluorophenyl borate,
benzene (diazonium) phenyltrispentafluorophenyl borate,
tropillium tetrakis (2,3,5,6-tetrafluorophenyl) borate,
triphenylmethylium tetrakis (2,3,5,6-tetrafluorophenyl) borate,
tropillium tetrakis (3,4,5-trifluorophenyl) borate,
benzene (diazonium) tetrakis (3,4,5-trifluorophenyl) borate,
tropillium tetrakis (1,2,2-trifluoroethenyl) borate,
triphenylmethylium tetrakis (1,2,2-trifluoroethenyl) borate,
tropillium tetrakis (2,3,4,5-tetrafluorophenyl) borate, and
triphenylmethylium tetrakis (2,3,4,5-tetrafluorophenyl) borate.
Readily commercially available ionic activators include:
N,N-dimethylaniliniumtetrakispentafluorophenyl borate;
triphenylmethyli urn tetrakispentafluorophenyl borate (tritylborate); and
trispentafluorophenyl borane.
Ionic activators may also have an anion containing at least one
group comprising an active hydrogen or at least one of any substituent
able to react with the support. As a result of these reactive substituents,
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the ionic portion of these ionic activators may become bonded to the
support under suitable conditions. One non-limiting example includes
ionic activators with tris (pentafluorophenyl) (4-hydroxyphenyl) borate as
the anion. These tethered ionic activators are more fully described in U.S.
Patents 5,834,393; 5,783,512; and 6,087,293.
The ionic activators may be used in amounts to provide a molar
ratio of transition metal to boron from 1:1 to 1:6, preferably from 1:1 to
1:2.
The catalysts of the present invention are typically used on an
inorganic oxide support. Typically the support comprises an inorganic
substrate usually of alumina or silica having a pendant reactive moiety.
The reactive moiety may be a siloxyl radical or more typically is a hydroxyl
radical. The preferred support is silica. The support should have an
average particle size from about 10 to 150 microns, preferably from about
to 100 microns. The support should have a large surface area typically
15 greater than about 100 m2/g, preferably greater than about 200 m2/g,
most
preferably from 250 m2/g to 1,000 m2/g. The support will be porous and
will have a pore volume from about 0.3 to 5.0 ml/g, typically from 0.5 to 3.0
ml/g.
It is also believed titanium silicates such as those disclosed in U.S.
20 Patent 4,853,202 issued Aug. 1, 1989 to Kuznicki assigned to Engelhard
Corporation would be useful as supports in accordance with the present
invention.
It is important that the support be dried prior to contact with the
catalyst or catalyst components. Generally, the support may be heated at
a temperature of at least 200 C for up to 24 hours, typically at a
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temperature from 500 C to 800 C for about 2 to 20, preferably 4 to 10
hours. The resulting support will be free of adsorbed water and should
have a surface hydroxyl content from about 0.1 to 5 mmol/g of support,
preferably from 0.5 to 3 mmol/g.
Silicas suitable for use in the present invention have high surface
area and are amorphous. For example, commercially available silicas are
marketed under the trademark of Sylopol 958 and 955 by the Davison
Catalysts a Division of W. R. Grace and Company and ES-70W by Ineos
Silica.
The amount of the hydroxyl groups in silica may be determined
according to the method disclosed by J. B. Pen i and A. L. Hensley, Jr., in J.
Phys. Chem., 72 (8), 2926, 1968.
While heating is the most preferred means of removing OH groups
inherently present in many carriers, such as silica, the OH groups may
also be removed by other removal means, such as chemical means. For
example, a desired proportion of OH groups may be reacted with a
suitable chemical agent, such as a hydroxyl reactive aluminum compound
(e.g. triethylaluminum) or a silane compound. This method of treatment
has been disclosed in the literature and two relevant examples are: U.S.
Patent 4,719,193 to Levine in 1988 and by Noshay A. and Karol F.J. in
Transition Metal Catalyzed Polymerizations, Ed. R. Quirk, 396, 1989. For
example the support may be treated with an aluminum compound of the
formula RibAl(OR1)aX3_(a+b) wherein a is 0 to 2, preferably 0 or 1, b is an
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integer from 1 to 3, a+b is from 1 to 3, R1 is a independently selected from
C1_10 alkyl radicals and X is a chlorine atom.
Clay has an amorphous or crystalline layered mineral structure,
having the strongest chemical bonds in two dimensions (e.g. forming
planes or sheets of material which are stacked on top of each other to
form a three dimensional structure). Sheets or layers may typically be of
two types of structure. The plane or sheet may have a tetrahedral
structure in which a central silicon atom coordinates oxygen atoms or an
octahedral structure in which a central aluminum, magnesium or iron atom
coordinates oxygen or hydroxide. Adjacent planes are held together by
weaker chemical bonds such as Van der Waals forces, electrostatic
interactions, and hydrogen bonding. There may also be inter-lamina
bridging molecules between layers. Ions are generally located between
the layers or planes. In this respect, the clay mineral is substantially
different from metal oxides having a three-dimensional structure such as
silica, alumina, and zeolite.
Clay is typically composed of crystalline hydrated silicates of
aluminum, magnesium and iron. Most clays have a surface electrical
charge typically, negative. In the present invention the clay should have a
negative surface charge. Negatively surfaced charged clays typically have
cations (+) between the planes. Such cations can be ion-exchanged by
other organic or inorganic cations. Typically the clays useful in the present
invention have the ability to exchange cations typically. Fr, Nat, Kt, Ca2+,
Al3+, Fe2"r3+ Ti3+ r 4 or NR4+ and phosphonium (R4P+) compounds
wherein R is selected from the group consisting of hydrogen, C1-12 alkyl
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and C6_12 aryl. The ability to exchange cations between the layers is the
cation exchange capacity (CEC) in milliequivalents per 100 g of clay.
Different clays have different CEC's. Some representative CEC's are
kaolinite: 3 to 15 meq/100 g, halloysite: 5 to 40 meq/100 g,
montmorillonite: 80 to 150 meq/100 g, illite: 10 to 40 meq/100 g,
vermiculite: 100 to 150 meq/100 g, chlorite: 10 to 40 meq/100 g, zeolite,
attapulgite: 20 to 30 meq/100 g.
Clay useful in accordance with the present invention may be
classified by the amount of negative surface charge: (1) biophilite,
kaolinite, dickalite, and talc have no negative surface charge (e.g. charge
of 0 (zero)), (2) smectite clays have a negative surface charge of from -
0.25 to -0.6, (3) vermiculite clays have a negative surface charge of from -
0.6 to -0.9, (4) mica clays have a negative surface charge of from about -1,
and (5) brittle mica clays have a negative surface charge of about -2.
Each of the above groups includes various sub groups of clays. For
example, the smectite group includes montmorillonite, bentonite, beidellite,
saponite, nontronite, hectorite, teniolite, suconite and related analogues;
the mica group includes white mica, palagonite and illite. While these clays
are naturally occurring they may also be artificially synthesized with a high
purity.
Any of the natural or synthetic clays having a negative surface
charge may be used in accordance with the present invention. Preferred
clays are of the smectite family, including the most preferred
montmorillonite (e.g., sodium montmorillonite). The clays may be used as
they are without subjecting them to any further treatment. Alternatively,
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they may be ball milled, screened, acid treated or the like prior to use.
They may have water added and adsorbed or may be dehydrated typically
by heating to a moisture content of less than 1 weight %, preferably less
than 0.05 weight %. The clays may be used alone or in combination.
Typically the clays have pores having a diameter from about
4 X 10-3 microns to 1 X 10-1microns. (e.g., 40-1000 angstroms) as
measured using a mercury porosimeter and a pore volume of at least 0.1
cc/g, more preferably from 0.1 to 1 cc/g. The clay may have an average
particle size from about 0.01 to about 50, preferably from about 0.1 to
about 25, and most preferably from about 0.5 to about 15 microns,
desirably from 0.5 to 10 microns (micrometers).
The clays should be dried prior to use under conditions that may be
comparable to or different from drying the support.
The clay may be used alone or in combination with other
conventional additives or adjuvants such as heat and light stabilizers, UV
stabilizers, other anti static agents, inorganic agents including catalysts
and activators as described above, typically oxides such as alumina, silica
(as described above) and magnesium oxide, and organic materials such
as polymeric supports including polyethylene, polystyrene, acrylamides
and functionalized (e.g. typically acid or ester copolymers) derivatives
thereof. The clay is fed to the reactor as a component (stream) separate
from the catalyst and support.
The clay may be used in the polymerization reaction in an amount
from 0.001 to 1 weight %, preferably from 0.002 to 0.5 weight % most
preferably from 0.005 to 0.3 weight % of the polymer production rate.
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The clay is independently fed to the reactor using a feeder such as
a catalyst feeder, for example the solid catalyst feeder disclosed in U.S.
patent 3,779,712 issued Dec. 18, 1973 to Calvert et at. assigned to Union
Carbide Corporation. This approach requires two catalyst feeders per
reactor; however, it gives the flexibility of being able to change the ratio
of
clay to catalyst in the reactor giving one more control parameter than the
situation when the clay is premixed with the catalyst.
The clay and supported catalyst could be dry blended
(homogeneously mixed) and fed using one catalyst feeder. In this
approach care needs to be taken that the clay and catalyst support do not
segregate. While the particles should be attracted to each other by
electrostatic charges, the particle size and flow properties of the different
particles may lead to separation or segregation during the storage and
feeding process.
The resulting granular polymer (powder) is recovered in the normal
manner and is useful for conventional applications for polyolefins of
comparable density and molecular weight. Properties such as tear
properties, dart impact, Environmental Stress Crack Resistance (ESCR),
tensile strength, elongation, gloss, clarity etc. are not compromised.
The present invention will now be illustrated by the following non-
limiting examples.
EXAMPLES
Example 1
Two kg of polyethylene resin in granular form (i.e. not pelletized),
having an Melt Flow Rate (ASTM D1238 121190 C /21.6 kg) of 5, and a
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density of 0.955 g/cc, prepared with a chrome-based catalyst were dried in
a vacuum oven at 60 C for at least 3 hours to remove any residual
moisture. It was then loaded to a gas phase technical scale reactor (TSR)
as described in European Patent 0 659 773 equipped with an electrostatic
monitoring probe (Correstat 3410, Progression, Inc., Haverhill, MA). The
reactor was pressurized with dry nitrogen (to 2000 kPa) and the
temperature was raised to 80 C. The granular material was stirred for 60
minutes prior to the injection of lg of montmorillonite clay (sold under the
trademark CLOISITE Na+ from Southern Clay Products Inc.). Both clay
and resin had been dried and kept in an oven for several days. Ninety per
cent by volume of the particles of the clay have particle size less than 13
micrometers.
The electrostatic response was monitored throughout the
experiment as shown in Figure 1. Figure 1 shows that upon injection of
the clay at point A, the polarity of the signal reversed and did not change
back to its initial condition. Subsequent addition of more clay (1g) at point
B after 45 minutes had little effect on the electrostatic signal.
The experiment shows the addition of a very small amount of clay
having a negative surface charge into a stirred bed gas phase reactor can
alter electrification patterns in the reactor to control static charge in the
polymer bed.
Example 2
Two kg of PE resin (MI=1, density = 0.918 g/cc), prepared with a
single-site phosphinimide catalyst (as described in NOVA Chemicals
United States Patent 5,965,677) in granular form was dried in a vacuum
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oven for at least 3 hours. It was then loaded to the TSR equipped with an
electrostatic monitoring probe as described above. The reactor was
pressurized with dry nitrogen (to 2000 kPa) and the temperature was
raised to 80 C. The granular material was stirred for 60 minutes prior to
the injection of 0.62g of montmorillonite clay at point A in Figure 2. The
clay and resin were predried as in Example 1.
The electrostatic response was monitored throughout the
experiment. Figure 2 shows that upon injection of the clay, the polarity of
the signal reversed. Furthermore, the electrostatic signal became less
agitated as time progressed. Even though addition of more clay (0.98g)
after 45 minutes at point B resulted in a more agitated electrostatic
response, the signal started to pacify as time progressed.
Again the results show that the addition of very small amounts of
clay having a negative surface charge into a stirred bed reactor can
reduce static significantly.
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