U.S. patent application number 11/136136 was filed with the patent office on 2005-10-20 for polyolefin production with a high performance support for a metallocene catalyst system.
This patent application is currently assigned to FINA Technology, Inc.. Invention is credited to Gauthier, William, Henry, Shady, Rauscher, David, Tian, Jun.
Application Number | 20050233892 11/136136 |
Document ID | / |
Family ID | 29734734 |
Filed Date | 2005-10-20 |
United States Patent
Application |
20050233892 |
Kind Code |
A1 |
Tian, Jun ; et al. |
October 20, 2005 |
Polyolefin production with a high performance support for a
metallocene catalyst system
Abstract
The invention is directed to a metallocene catalyst system and a
process for preparing the system. The metallocene catalyst system
comprises a support and metallocene bound substantially throughout
the support. The selection of certain supports facilitates the
production of metallocene catalyst systems having increased
catalytic activity than previously recognized.
Inventors: |
Tian, Jun; (LaPorte, TX)
; Gauthier, William; (Houston, TX) ; Rauscher,
David; (Angleton, TX) ; Henry, Shady;
(Seabrook, TX) |
Correspondence
Address: |
FINA TECHNOLOGY INC
PO BOX 674412
HOUSTON
TX
77267-4412
US
|
Assignee: |
FINA Technology, Inc.
Houston
TX
|
Family ID: |
29734734 |
Appl. No.: |
11/136136 |
Filed: |
May 24, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11136136 |
May 24, 2005 |
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10178620 |
Jun 24, 2002 |
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Current U.S.
Class: |
502/117 ;
502/150 |
Current CPC
Class: |
C08F 10/00 20130101;
C08F 4/65912 20130101; C08F 4/76 20130101; Y10T 428/2982 20150115;
C08F 4/65927 20130101; C08F 10/00 20130101; C08F 4/65916 20130101;
C08F 110/06 20130101; C08F 2500/12 20130101; C08F 2500/18 20130101;
C08F 2500/24 20130101; C08F 2500/15 20130101 |
Class at
Publication: |
502/117 ;
502/150 |
International
Class: |
B01J 031/00 |
Claims
What is clamed is:
1. A metallocene catalyst system (MCS) comprising: a support; and a
metallocene bound substantially throughout said support, wherein on
exposure to a reaction environment comprising about 300 g to about
400 g propylene per Liter of reactor volume, about 23 ppm by weight
of said MCS, about 37 ppm by weight H.sub.2, and about 46 ppm
triethylaluminum in a 4 liter reactor at about 67.degree. C. and
about one hour reaction time, said MCS has a catalytic activity of
at least about 10,400 g of polypropylene/g of MCS/hr.
2. The MCS as recited in claim 1 wherein said metallocene comprises
rac dimethylsilanediyl bis(2-methyl-4-phenyl indenyl)zirconium
dichloride and said propylene comprises polymer grade propylene
further purified to having COS levels of less than about 20 ppb,
O.sub.2 levels of less than about 5 ppm and H.sub.2O levels of less
than about 5 ppm.
3. The MCS as recited in claim 1 wherein said catalytic activity is
obtained for a metallocene loading up to about 1 wt %.
4. The MCS as recited in claim 3 wherein said catalytic activity is
at least about 11,800 g of said polypropylene/g of said MCS/hr.
5. The MCS as recited in claim 1 wherein said catalytic activity is
at least about 14,040 g of said polypropylene/g of said MCS/hr.
6. The MCS as recited in claim 5 wherein said catalytic activity is
obtained for a metallocene loading of up to about 2 wt %.
7. The MCS as recited in claim 1 wherein said catalytic activity
obtained for a metallocene loading of about 2 wt % is at least
about 20 percent higher than said catalytic activity obtained for a
metallocene loading of about 1 wt %.
8. A metallocene catalyst system (MCS) comprising: a catalyst
support system including a support having an average pore diameter
of greater than about 140 Angstroms; and a metallocene bound
substantially throughout said support, said MCS having a catalytic
activity for a metallocene loading of about 2 wt % that is at least
about 20 percent higher than said catalytic activity for said
metallocene loading of about 1 wt
9. The MCS as recited in claim 8 wherein said average pore diameter
is between about 150 Angstroms and about 450 Angstroms.
10. The MCS as recited in claim 8 wherein said metallocene is one
or more of an isospecific stereo rigid metallocene characterized by
the formula: R.sup.2 bis(C.sub.5(R.sup.1).sub.n)MeQp wherein each
(C.sub.5(R.sup.1).sub.n) is a substituted cyclopentadienyl ring; n
may range from 1 to 20 so long as the number of sites available for
substitution are not exceeded; each R.sup.1 is the same or
different and is a hydrogen or hydrocarbyl radical having 1-20
carbon atoms; R.sup.2 is a structural bridge between said two
(C.sub.5(R.sup.1).sub.n) rings imparting stereorigidity to said
metallocene, Me, and imparting a chiral environment to a metal, Me,
and R.sup.2 is selected from the group consisting of an alkylene
radical having 1-4 carbon atoms, a silicon hydrocarbyl radical, a
germanium hydrocarbyl radical, a phosphorus hydrocarbyl radical, a
nitrogen hydrocarbyl radical, a boron hydrocarbyl radical, and an
aluminum hydrocarbyl radical; said Me is a group 4, 5, or 6 metal
as designated in the Periodic Table of Elements; each Q may be
independently selected from a hydrocarbyl radical having 1-20
carbon atoms or is a halogen; and 0.ltoreq.p.ltoreq.3.
11. The MCS as recited in claim 8 wherein said metallocene is
selected from the group consisting of: rac dimethylsilanediyl
bis(2-methyl-4-phenyl indenyl)zirconium dichloride; rac
dimethylsilanediyl bis(2-methyl indenyl)zirconium dichloride, rac
dimethylsilanediyl bis(2-methyl-4,5-benzoindenyl)zirconium
dichloride; and rac dimethylsilanediyl bis(2-methyl-4-(1-naphthyl)
indenyl) zirconium dichloride.
12. The MCS as recited in claim 8 wherein said MCS catalyzes the
polymerization of a propylene comprising polymer grade propylene
further purified to having COS levels of less than about 20 ppb,
O.sub.2 levels of less than about 5 ppm and H.sub.2O levels of less
than about 5 ppm.
13. A process for the preparation of a metallocene catalyst system
(MCS) comprising: providing a support having a surface defining
pores; and attaching a metallocene substantially throughout said
support to form a MCS having a catalytic activity for a metallocene
loading of about 2 wt % that is at least about 20 percent higher
than said catalytic activity for said metallocene loading of about
1 wt %.
14. The process as recited in claim 13 further including said
support comprising silica, attaching an activator to said silica
support substantially throughout said pore volume and attaching
said metallocene to said activator to form said MCS.
15. The process as recited in claim 13 wherein said support is
substantially spheroidal and said pores have a peak pore volume of
greater than about 0.115 mL/g at a pore diameter between about 250
Angstroms and about 350 Angstroms.
16. The process as recited in claim 13 wherein said support is
substantially spheroidal and said pores provide a peak surface area
of at least about 14.3 m.sup.2/g at a pore diameter between about
250 Angstroms and about 330 Angstroms.
17. A process for the polymerization of polyolefin comprising:
preparing a metallocene catalyst system (MCS) having a catalytic
activity for a metallocene loading of about 2 wt % that is at least
about 20 percent higher than said catalytic activity for said
metallocene loading of about 1 wt %; introducing said MCS into a
polymerization reaction chamber; and contacting at least one olefin
monomer with said MCS in said reaction chamber.
18. The process as recited in claim 17 wherein said olefin monomer
comprises an alpha olefin comprising ethylenically unsaturated
hydrocarbons having between 2 and 20 Carbon atoms.
19. The process as recited in claim 17 wherein said olefin monomer
is selected from the group consisting of: a mixture of propylene
and ethylene; a mixture of propylene, butene and ethylene; and a
mixture of propylene and butene.
20. The process as recited in claim 17 wherein said olefin monomer
comprises polymer grade propylene further purified to having COS
levels of less than about 20 ppb, O.sub.2 levels of less than about
5 ppm and H.sub.2O levels of less than about 5 ppm.
21. A polyolefin produced by the process comprising: introducing a
metallocene catalyst system (MCS) into a polymerization reaction
chamber said MCS having a catalytic activity for a metallocene
loading of about 2 wt % that is at least about 20 percent higher
than said catalytic activity for said metallocene loading of about
1 wt %; and contacting at least one olefin monomer with said MCS in
said reaction chamber.
22. The polyolefin as recited in claim 21 wherein said polyolefin
has an average particle diameter between about 400 and about 2000
microns.
23. The polyolefin as recited in claim 21 wherein said polyolefin
has an average particle diameter between about 600 and about 1500
microns.
24. The polyolefin as recited in claim 21 wherein said polyolefin
has a bulk density of at least about 0.37 g/cc.
25. The polyolefin as recited in claim 21 wherein said polyolefin
is converted into a resin used for the manufacture of films, fibers
or injection molded articles.
26. The process as recited in claim 21 wherein said olefin monomer
comprises polymer grade propylene further purified to having COS
levels of less than about 20 ppb, O.sub.2 levels of less than about
5 ppm and H.sub.2O levels of less than about 5 ppm.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention is directed, in general, to a
metallocene catalyst system for the production of polyolefins and
more specifically, to a metallocene catalyst system that includes
the selection of silica supports within the catalyst system that
provide increased catalytic activity.
BACKGROUND OF THE INVENTION
[0002] Metallocenes are of increasing importance as a commercial
olefin polymerization catalyst. Typically, a metallocene catalytic
system (MCS) is used in the polymerization of olefins. The MCS may
comprise a metallocene and an activator on a support, for example,
an inorganic support. Such activators are well known and typically
include an aluminum alkyl or aluminoxanes, such as
methylaluminoxane (MAO). To form a conventional MCS, the
metallocene and the optional alumoxane activator may be reacted in
the presence of the support to provide a supported
metallocene-alumoxane reaction product. For example, a silica gel
support may be coated with an alumoxane, such as methylalumoxane
(MAO). A metallocene may be complexed with the alumoxane bound to
the support to form a MCS that can then be used in an olefin
polymerization process. A trialkylaluminum or organoaluminum
activator or scavenger maybe employed during the polymerization
process to increase catalytic activity.
[0003] However, for such MCSs to provide an economically viable
alternative to conventional catalysts, a number of limitations must
be overcome. For example, the MCS must be capable of producing
polymers of the desired stereospecificity and morphology. For
example, stereoregular polymers produced from such MCSs should have
a certain desired tacticity. Isotactic polypropylene (iPP) or
syndiotactic polypropylene (sPP), for example, can be described as
having the methyl groups attached to the tertiary carbon atoms of
successive monomeric units oriented on the same side, or
alternating sides for sPP, of a hypothetical plane through the main
chain of the polymer.
[0004] Desirable morphologic properties may include polymers
comprising uniform compact generally spherical particles, having a
particular particle size distribution, or a certain bulk density,
and low content of fine particles. The generation of undesirable
fine particles (i.e., particle diameter less than about 106
microns) can cause plant process difficulties, such as plugging
filters, and affect the accuracy of level gauge readings.
Alternatively, large particles (i.e., having a low bulk density)
are also undesirable because they require more power to circulate
though loop reactors, leading to high power consumption and lower
production rates.
[0005] Additionally, MCSs should ideally have high catalytic
activity. One limiting factor in the production of MCSs with high
activity is thought to be the low amount of activator or
metallocene loaded onto to the support. Another factor limiting
catalytic activity is thought to be the low amount of activated
metallocene loaded onto the support. Moreover, as the costs for
metallocene or activator can be substantial, their efficient use is
important to controlling the total cost of producing a MCS.
[0006] Accordingly, what is needed in the art is a MCS that
provides improved activity, and yet still having acceptable
morphological properties, while overcoming the above-mentioned
problems.
SUMMARY OF THE INVENTION
[0007] To address the above-discussed deficiencies, the present
invention provides, in one embodiment, a metallocene catalyst
system (MCS) that includes a support and a metallocene bound
substantially throughout the support. On exposure to a reaction
environment comprising about 300 g to about 400 g propylene per
liter of reactor volume, about 23 ppm by weight of said MCS, about
37 ppm by weight H.sub.2, and about 46 ppm by weight
triethylaluminum in a 4 liter reactor at about 67.degree. C. and
about one hour reaction time, the MCS has a catalytic activity of
at least about 10,400 g of polypropylene/g of MCS/hr.
[0008] Another embodiment is a MCS comprising a catalyst support
system including a support having an average pore diameter of
greater than about 140 Angstroms and a metallocene bound
substantially throughout the support. The MCS has a catalytic
activity for a metallocene loading of about 2 wt % that is at least
about 20 percent higher than said catalytic activity for said
metallocene loading of about 1 wt %.
[0009] Another embodiment includes a process for the preparation of
a MCS. The process includes providing a support having a surface
defining pores and attaching a metallocene substantially throughout
the support to form a MCS. The MCS has a catalytic activity for a
metallocene loading of about 2 wt % that is at least about 20
percent higher than the catalytic activity for the metallocene
loading of about 1 wt %.
[0010] In yet another embodiment, the present invention provides a
process for producing a polyolefin. The process comprises preparing
a metallocene catalyst system (MCS) having a catalytic activity for
a metallocene loading of about 2 wt % that is at least about 20
percent higher than the catalytic activity for the metallocene
loading of about 1 wt %. The process further includes introducing
the MCS into a polymerization reaction chamber and contacting at
least one olefin monomer with the MCS in the reaction chamber.
[0011] Still another embodiment comprises a polyolefin produced by
introducing a metallocene catalyst system (MCS) into a
polymerization reaction chamber and contacting at least one olefin
monomer with the MCS in the reaction chamber. The MCS has a
catalytic activity for a metallocene loading of about 2 wt % that
is at least about 20 percent higher than the catalytic activity for
the metallocene loading of about 1 wt %.
[0012] The foregoing has outlined preferred and alternative
features of the present invention so that those skilled in the art
may better understand the detailed description of the invention
that follows. Additional features of the invention will be
described hereinafter that form the subject of the claims of the
invention. Those skilled in the art should appreciate that they can
readily use the disclosed conception and specific embodiment as a
basis for designing or modifying other structures for carrying out
the same purposes of the present invention. Those skilled in the
art should also realize that such equivalent constructions do not
depart from the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] For a more complete understanding of the invention,
reference is now made to the following descriptions taken in
conjunction with the accompanying drawing, in which:
[0014] FIG. 1 illustrates a cross section through a portion of a
MCS of the present invention;
[0015] FIG. 2 illustrates BJH-DFT analysis results of pore volume
distribution with respect to pore diameter for different
silicas;
[0016] FIG. 3 illustrates BJH-DFT analysis results of surface area
distribution with respect to pore diameter for different
silicas;
[0017] FIG. 4 illustrates a particle size distribution analysis of
the MAO-modified silica supports; and
[0018] FIG. 5 illustrates a particle size distribution of polymer
produced using different silica supported MCS.
DETAILED DESCRIPTION
[0019] As further described below, the present invention discloses
a metallocene catalyst system (MCS), a process for preparing the
MCS, a process for preparing a polyolefin using the MCS, and the
polyolefin produced by that process, improving on that disclosed in
U.S. Pat. Nos. 6,143,683, 6,211,109, 6,225,251 and 6,239,058 to
Shamshoum et al., and U.S. patent application Ser. Nos. 09/782,752
and 09/782,753 to Gauthier et al., all of which are incorporated
herein by reference.
[0020] While not limiting its scope, the present invention is
founded on the theory that the final catalytic activity and
performance of a MCS depends on the support material used in the
MCS. In particular, it has been discovered that the catalyst
polymerization activity of the MCS is strongly dependent on the
pore volume and surface area of the support. In particular, the
selection of supports having optimal pore volume and surface area
distributions with respect to pore diameter can substantially
improve the activity of the MCS.
[0021] In certain preferred embodiments, the pore volume and
surface area distributions, as a function of pore diameter, are
coincident with each other. The terms pore volume and surface area
distribution as used herein refer, respectively, to the pore volume
and surface area measured for the entire range of pore diameters
present in a support. These parameters may be expressed as a total
pore volume or total surface area, respectively, for example, as
measured by conventional gas absorption/desorption techniques and
using the Brunauer, Emmett and Teller model (BET).
[0022] More usefully, however, the distributions of pore volumes
and surface areas over the range of pore diameters present in the
support material, may be measured using conventional methods, such
as the Barrett-Joyner-Halenda (BJH) method, and the Oliver-Conklin
Density Function Theory (DFT). It is believed that supports, such
as silicas, having different pore volume and surface area
distribution, may also have different metallocene and activator
supporting mechanisms and polymerization behavior. Knowledge about
the pore volume and surface area distribution for different silicas
thus allows for the selection of an optimal support for producing a
MCS.
[0023] While not limiting the scope of the present invention by
theory, it is believed that MCS activity is facilitated through the
selection of supports of sufficiently large pore diameter to allow
the metallocene to penetrate and interact with substantially all of
the inner surface of the support. At the same time, the pore volume
must not be too large so as to decrease the surface area available
for activator-metallocene-support interactions, or to create too
fragile a MCS, such that it does not remain intact during the
process for formation of the MCS or during the MCS's transport to a
reactor.
[0024] In one embodiment, the present invention is directed to a
MCS comprising a support and a metallocene bound substantially
throughout the support wherein on exposure to a particular reaction
environment the MCS has a catalytic activity of at least about
10,400 g of polypropylene/g of MCS/hr. The reaction environment may
comprise about 300 g to about 400 g propylene per Liter of reactor
volume, about 23 ppm by weight of the MCS, about 37 ppm by weight
H.sub.2, and about 46 ppm triethylaluminum in a 4 liter reactor at
about 67.degree. C. and about one hour reaction time. In one
preferred embodiment, the metallocene, for example, comprises rac
dimethylsilanediyl bis(2-methyl-4-phenyl indenyl)zirconium
dichloride.
[0025] For all catalytic reactions described herein, the use of
polymer grade olefin monomers are preferred. Methods of preparing
such monomers, and the purity of such monomers are well known to
those of ordinary skill in the art. In certain embodiments, the
monomer is further purified. For example, when the monomer is
propylene, polymer grade propylene having a minimum purity of 99.5
wt % was used after further purification. Specifically, the polymer
grade propylene was further purified to remove known catalytic
poisons, by sequential passage through columns containing: (1) a
Nickel catalyst supported on Alumina for carbonyl sulfide (COS)
removal; (2) copper on alumina for O.sub.2 removal, (using e.g.,
BASF R3-11, BASF Corp., Mount Olive, N.J.); (3) molecular sieves
for H.sub.2O removal (using e.g., 3A, 4A, 5A or 13X or similar
molecular sieves). Columns were activated using means well known to
those skilled in the art. Such treatments are expected to reduce
COS levels to less than about 20 ppb, and more preferably less than
about 5 ppb; reduce O.sub.2 levels to less than about 5 ppm, and
more preferably less than about 2 ppm; and reduce H.sub.2O levels
to less than 5 ppm, and more preferably less than about 2 ppm.
[0026] In other preferred embodiments, the MCS has an activity of
at least about 11,900, and even more preferably at least about
12,100 of polypropylene/g of MCS/hr (g/g/hr), when the metallocene
loading onto the support is about 1 wt % (weight of metallocene per
unit weight of support). In other preferred embodiments, the MCS
has an activity of at least about 11,800, and more preferably at
least about 14,040, and still more preferably at least about
19,000, and even more preferably at least about 23,000
polypropylene/g of MCS/hr, when the metallocene loading is about
2%.
[0027] The term metallocene loading as used herein refers to the
weight percent of metallocene presented to the support during the
preparation of the MCS, and resulting in metallocene bound
substantially throughout the support. As further disclosed below,
in certain preferred embodiments, the support comprises silica and
an activator comprising an alumoxane, for example, MAO, bound
substantially throughout the silica support and the metallocene
bound to the silica support via the activator.
[0028] One skilled in the art would understand that in testing
catalytic activity, the amounts of the components in the reaction
environment may be varied, so as to provide about 30 to 50%
conversion of monomer to polymer. Moreover, one skilled in the art
would understand that the desired reaction environment for testing
the optimal catalytic activity of different metallocenes may differ
from that described above. The polymerization reaction mixture may
comprise, for example, different proportions of propylene, MCS,
hydrogen and TEAl. For example, the amount of MCS may range from
about 10 ppm to about 150 ppm, by weight of the support, and more
preferably from 10 ppm to and 100 pmm, with decreased amounts used
for higher activity MCSs. The amount of H.sub.2 may be varied to
provide a polymer having a melt flow between about 2 and about 60
g/10 min, and preferably about 10 g/10 min. H.sub.2 may preferably
be at least about 5 ppm, and more preferably range between about 28
ppm to about 37 ppm. The amount of TEAl used, typically ranging
from about 46 ppm to about 56 ppm, should be sufficient to scavenge
inactivators of MCS and provided a polymer having the desired melt
flow. Moreover, cocatalysts other than TEAl, such as
triisobutylaluminum (TiBAL), may be used.
[0029] A second aspect of the present invention is directed to a
MCS comprising a catalyst support system including a support
material having an average pore diameter of a certain size. The MCS
may comprise a catalyst support system including a support having
an average pore diameter of greater than about 140 Angstroms and a
metallocene bound substantially throughout the support. The MCS has
a catalytic activity for a metallocene loading of about 2 wt % that
is at least about 20 percent higher than the catalytic activity for
the metallocene loading of about 1 wt %. More preferably, with 2 wt
% of metallocene loading, the catalytic activity is at least about
55% higher, and more preferably about 85% higher, as compared to 1
wt % loading. In certain preferred embodiments, for example, the
MCS has a catalytic activity of at least about 11,800 g/g/hr in a
one hour reaction time under the reaction environment previously
described herein.
[0030] Illustrated in FIG. 1 is a cross section through a portion
of a MCS 100 of the present invention having an idealized,
spherical pore 110. In certain embodiments, the MCS 100 comprises a
catalyst support system 100, including a silica support 105 having
pores 110 with a diameter D.sub.pore. In certain embodiments,
D.sub.pore may be greater than about 140 Angstroms, depending on
the size of the metallocene and activator bound to the support, as
further discussed below. In certain preferred embodiments
D.sub.pore may range from about 150 Angstroms to about 450
Angstroms, and more preferably about 300 to about 310
Angstroms.
[0031] In yet other embodiments, the MCS may further include an
optional activator 115, such as an aluminoxane, having a diameter
D.sub.act, and bound to the support 105. In such embodiments, the
D.sub.act may range from about 1.0 nm to about 5.0 nm, and more
preferably the D.sub.act has a value of about 1.5 nm. A metallocene
120 having a diameter D.sub.Me, may be bound to the activator 115
within the pore 110. D.sub.Me may range from about 0.5 nm to about
3.0 nm, and in certain preferred embodiments D.sub.Me may equal
about 1.3 nm. Ideally, after the metallocene complexes with the
support, either directly or through an optional activator 115,
there remains an open space within the pore 110 defined by a
critical pore diameter (CPD).
[0032] The D.sub.pore is preferably sufficiently large to allow the
optional activator 115 to diffuse into and interact with
substantially the entire surface area (i.e., both the exterior and
interior) of the support 105 and attach thereto. Additionally, the
CPD is sufficiently large to allow the metallocene 120 to diffuse
throughout and interact with the support 105 and attach thereto, or
with the activator 115 bound to the support 105.
[0033] Any metallocene may be used in the practice of the
invention. As used herein unless otherwise indicated, "metallocene"
includes a single metallocene composition or two or more
metallocene compositions. Metallocenes are typically bulky ligand
transition metal compounds generally represented by the
formula:
[L].sub.mM[A].sub.n (1)
[0034] where L is a bulky ligand, A is a leaving group, M is a
transition metal and m and n are such that the total ligand valency
corresponds to the transition metal valency.
[0035] The ligands L and A may be bridged to each other, and if two
ligands L or A are present, they may be bridged. The metallocene
compound may be full-sandwich compounds having two or more ligands
L which, for example, may be cyclopentadienyl ligands (Cp) or
cyclopentadiene derived ligands or half-sandwich compounds having
one ligand L, which is a cyclopentadienyl ligand or
cyclopentadienyl derived ligand. Other examples of ligands include
fluorenyl (Flu), indenyl (Ind), azulenyl or benzylindenyl groups
and their substituted derivatives.
[0036] The transition metal atom may be a Group 4, 5, or 6
transition metal and/or a metal from the lanthanide and actinide
series. Zirconium, titanium, and hafnium are desirable. Other
ligands may be bonded to the transition metal, such as a leaving
group, such as, but not limited to, halogens, hydrocarbyl, hydrogen
or any other univalent anionic ligand. A bridged metallocene may,
for example, be described by the general formula:
RCp(R')Cp'(R")MeQn (2)
[0037] Me denotes a transition metal element and Cp and Cp' each
denote a cyclopentadienyl group, each being the same or different
and which can be either substituted with R' and R" groups having
from 1 to 20 carbons, respectively, or unsubstituted, the Q groups
may be independently selected from an alkyl or other hydrocarbyl or
a halogen group, n is a number and may be within the range of 1-3
and R is a structural bridge extending between the cyclopentadienyl
rings and comprising a hydrocarbyl radical.
[0038] Preferred metallocene-containing catalyst systems that
produce isotactic polyolefins are disclosed in U.S. Pat. Nos.
4,794,096 and 4,975,403 which are incorporated by reference herein.
These patents disclose chiral, stereorigid metallocenes that
polymerize olefins to form isotactic polymers and are especially
useful in the polymerization of highly isotactic polypropylene.
[0039] Other suitable metallocenes are disclosed in, for example,
U.S. Pat. Nos. 4,530,914; 4,542,199; 4,769,910; 4,808,561;
4,871,705; 4,933,403; 4,937,299; 5,017,714; 5,026,798; 5,057,475;
5,120,867; 5,132,381; 5,155,180; 5,198,401; 5,278,119; 5,304,614;
5,324,800; 5,350,723; 5,391,790; 5,436,305; 5,510,502; 5,145,819;
5,243,001; 5,239,022; 5,329,033; 5,296,434; 5,276,208; 5,672,668;
5,304,614, 5,374,752; 5,510,502; 4,931,417; 5,532,396; 5,543,373;
6,100,214; 6,228,795; 6,124,230; 6,114,479; 6,117,955; 6,087,291;
6,140,432; 6,245,706; 6,194,341; 6,399,723; 6,380,334; 6,380,331;
6,380,330; 6,380,124; 6,380,123; 6,380,122; 6,380,121; 6,380,120;
6,376,627; 6,376,413; 6,376,412; 6,376,411; 6,376,410; 6,376,409;
6,376,408; 6,376,407; 6,087,29; 5,635,437; 5,554,704; 6,218,558;
6,252,097; 6,255,515 and EP 549 900; EP 576 970; EP 611 773, and WO
97/32906; WO 98/014585; WO 98/22486; and WO 00/12565, each of which
is fully incorporated by reference herein in its entirety.
[0040] In certain preferred embodiments, the metallocene is one or
more of an isospecific stereo rigid metallocene characterized by
the formula:
R.sup.2 bis(C.sub.5(R.sup.1).sub.n)MeQ.sub.p (3)
[0041] wherein each (C.sub.5(R.sup.1).sub.n) is a substituted
cyclopentadienyl ring and n may range from 1 to 20 so long as the
number of sites available for substitution are not exceeded. Each
R.sup.1 is the same or different and is a hydrogen or hydrocarbyl
radical having 1-20 carbon atoms. R.sup.2 is a structural bridge
between the two (C.sub.5(R.sup.1).sub.n) rings imparting
stereorigidity to the metallocene, and imparting a chiral
environment to a metal, Me. R.sup.2 is selected from the group
consisting of an alkylene radical having 1-4 carbon atoms, a
silicon hydrocarbyl radical, a germanium hydrocarbyl radical, a
phosphorus hydrocarbyl radical, a nitrogen hydrocarbyl radical, a
boron hydrocarbyl radical, and an aluminum hydrocarbyl radical. The
Me is a group 4, 5, or 6 metal as designated in the Periodic Table
of Elements. Each Q may be independently selected from a
hydrocarbyl radical having 1-20 carbon atoms or is a halogen; and
0.ltoreq.p.ltoreq.3.
[0042] In certain advantageous embodiments, the structural bridge
R.sup.2, among other things, holds the two (C.sub.5(R.sup.1).sub.n)
rings in a desired chiral orientation to facilitate the production
of an isotactic polymer. For example, when the two
(C.sub.5(R.sup.1).sub.n) rings are identical, a racemic orientation
is preferred over a meso orientation. In cases where the two
(C.sub.5(R.sup.1).sub.n) rings are nonidentical, then the
structural bridge R.sup.2 holds the ring's orientation to generate
the appropriate chirality, for example, to produce isotactic
polymer.
[0043] In other advantageous embodiments, the
(C.sub.5(R.sup.1).sub.n) groups are indenyl groups which are
substituted or unsubstituted. In still other preferred embodiments,
the metallocene may be rac dimethylsilanediyl bis(2-methyl-4-phenyl
indenyl)zirconium dichloride. In yet other advantageous embodiments
metallocene may be selected from the group consisting of rac
dimethylsilanediyl bis(2-methyl indenyl)zirconium dichloride, rac
dimethylsilanediyl bis(2-methyl-4,5-benzoindenyl)zirconiu- m
dichloride and rac dimethylsilanediyl bis(2-methyl-4-(1-naphthyl)
indenyl)zirconium dichloride.
[0044] The term activator, as used herein, refers to any compound
or component, or combination of compounds or components, capable of
enhancing the ability of one or more metallocenes to polymerize
olefins to polyolefins. In particular embodiments, the activator is
any compound capable of generating a catalytically activated
cationic center. One particularly useful class of activators are
based on organoaluminum compounds, which may take the form of an
alumoxane, such as MAO or a modified alkylaluminoxane compound.
Alumoxane (also referred to as aluminoxane) is an oligomeric or
polymeric aluminum oxy compound containing chains of alternating
aluminum and oxygen atoms, whereby the aluminum carries a
substituent, preferably an alkyl group. The exact structure of
aluminoxane is not known, but is generally believed to be
represented by a caged or clustered compound, comprised of
components having the following general formula:
--(Al(R)--O--)--.sub.m, for cyclic alumoxane components, and
R.sub.2Al--O--(Al(R)--O).sub.m--AlR.sub.2 for linear alumoxane
components, wherein R independently in each occurrence is a
C.sub.1-C.sub.8 hydrocarbyl, preferably alkyl, more preferably
C.sub.1, or halide, and m is preferably an integer ranging from
about 1 to about 40, and more preferably about 4 to about 30, and
even more preferably about 10 to about 20.
[0045] Alumoxanes are typically the reaction products of water and
an aluminum alkyl, which in addition to an alkyl group may contain
halide or alkoxide groups. Reacting several different aluminum
alkyl compounds, for example, trimethylaluminum (TMA) and
tri-isobutyl aluminum, with a correct stoichiometry of water yields
so-called modified or mixed alumoxane activators. Other
non-hydrolytic routes for the production of activators are well
known to those of ordinary skill in the art. Preferred alumoxanes
are MAO and MAO modified with minor amounts of other higher alkyl
groups such as isobutyl. Alumoxanes generally contain minor to
substantial amounts of starting aluminum alkyl compound(s). Other
activators include trialkylaluminum, such as TEAl or
triisobutylaluminum (TIBAL) or mixtures thereof. Alumoxane
solutions, particularly MAO solutions, may be obtained from
commercial vendors as solutions having various concentrations
(e.g., Albermarle Corp., Baton Rouge, La.; Akzo Nobel Catalysts
Ltd., Houston, Tex.; Crompton Corp., Greenwich, Conn.).
[0046] There are a variety of methods for preparing alumoxane,
non-limiting examples of which are described in U.S. Pat. Nos.
4,665,208, 4,952,540, 5,091,352, 5,206,199, 5,204,419, 4,874,734,
4,924,018, 4,908,463, 4,968,827, 5,308,815, 5,329,032, 5,248,801,
5,235,081, 5,103,031 and EP-A-0 561 476, EP 0 279 586, EP-A-0 594
218 and WO 94/10180, each fully incorporated herein by reference.
As used herein, unless otherwise stated, "solution" refers to any
mixture including suspensions.
[0047] Ionizing activators may also be used to activate
metallocenes. These activators are neutral or ionic, or organoboron
compounds, such as tri(n-butyl)ammonium tetrakis
(pentaflurophenyl)borate, which ionize the neutral metallocene
compound. Such ionizing compounds may contain an active proton, or
some other cation associated with, but not coordinated or only
loosely coordinated to, the remaining ion of the ionizing compound.
Combinations of activators may also be used, for example, alumoxane
and ionizing activators in combinations, see e.g., WO 94/07928,
incorporated herein by reference.
[0048] Descriptions of ionic catalysts for coordination
polymerization comprised of metallocene cations activated by
non-coordinating anions appear in EP-A-0 277 003, EP-A-0 277 004
and U.S. Pat. No. 5,198,401 and WO-A-92/00333 (incorporated herein
by reference). These teach a method of preparation wherein
metallocenes, such as biscp and monocp, are protonated by an anion
precursor such that an alkyl/hydride group is abstracted from a
transition metal to make it both cationic and charge-balanced by
the non-coordinating anion. Suitable ionic salts include
tetrakis-substituted borate or aluminum salts having fluorinated
aryl-constituents such as phenyl, biphenyl and naphthyl.
[0049] The term noncoordinating anion (NCA) as used herein refers
to an anion that either does not coordinate to the cation or that
is only weakly coordinated to the cation, thereby remaining
sufficiently labile to be displaced by a neutral Lewis base, and
allows for monomer coordination and insertion. "Compatible"
noncoordinating anions are those which are not degraded to
neutrality when the initially formed complex decomposes. Further,
the anion will not transfer an anionic substituent or fragment to
the cation so as to cause it to form a neutral four coordinate
metallocene compound and a neutral by-product from the anion.
[0050] The use of ionizing ionic compounds not containing an active
proton but capable of producing both the active metallocene cation
and a noncoordinating anion are also known. See e.g., EP-A-0 426
637 and EP-A-0 573 403, both incorporated herein by reference. An
additional method of making the ionic catalysts uses ionizing anion
precursors which are initially neutral Lewis acids but form the
cation and anion upon ionizing reaction with the metallocene
compounds, for example, the use of tris(pentafluorophenyl) borane,
see e.g., EP-A-0 520 732, incorporated herein by reference. Ionic
catalysts for addition polymerization can also be prepared by
oxidation of the metal centers of transition metal compounds by
anion precursors containing metallic oxidizing groups along with
the anion groups, see e.g., EP-A-0 495 375, incorporated herein by
reference.
[0051] Where the metal ligands include halogen moieties, for
example, bis-cyclopentadienyl zirconium dichloride, that are not
capable of ionizing abstraction under standard conditions, they can
be converted via known alkylation reactions with organometallic
compounds, such as lithium or aluminum hydrides or alkyls,
alkylalumoxanes, Grignard reagents, and other reaction well know to
those skilled in the art. See EP-A-O 500 944 and EP-Al-0 570 982,
both incorporated herein by reference, for in situ processes
describing the reaction of alkyl aluminum compounds with
dihalo-substituted metallocene compounds prior to or with the
addition of activating anionic compounds.
[0052] Methods for supporting ionic catalysts comprising
metallocene cations and NCA are described in U.S. Pat. Nos.
5,643,847, 6,143,686 and 6,228,795, all incorporated herein by
reference. When using the support composition, these NCA support
methods generally comprise using neutral anion precursors that are
sufficiently strong Lewis acids to react with the hydroxyl reactive
functionalities present on the silica surface such that the Lewis
acid becomes covalently bound.
[0053] Additionally, when the activator for the metallocene
supported catalyst composition is a NCA, the NCA is preferably
first added to the support composition followed by the addition of
the metallocene. When the activator is MAO, the MAO is preferably
contacted with the support, and then the metallocene is contacted
to the supported MAO. Alternatively, the MAO and metallocene may be
dissolved together in solution and then the support is contacted
with the MAO/metallocene solution. Other methods and order of
addition will be apparent to those of ordinary skill in the art,
and as further described below.
[0054] Various types of metallocenes are known in the art which may
be supported. The supports may include talc, inorganic oxides, clay
minerals, ion-exchanged layered compounds, diatomaceous earth,
silicates, zeolites or a resinous support material such as a
polyolefin or mixtures therefrom. Specific inorganic oxides include
clay, silica and alumina, used alone or in combination with other
inorganic oxides such as magnesia, titania, zirconia and the like.
Non-metallocene transition metal compounds, such as titanium
tetrachloride, may also be incorporated into the supported catalyst
component.
[0055] In certain embodiments when the support comprises an
inorganic oxide, the support may be substantially granular. In
certain preferred embodiments, the inorganic oxide support is
substantially spheroidal. In such embodiments, the support may have
an average particle size diameter ranging from about 1 to about 100
microns, and more preferably about 10 to about 60 microns.
[0056] In certain preferred embodiments, the support has an average
particle size ranging from about 10 to about 33 microns, and more
preferably from about 10 to about 20 microns. Such preferred
embodiments may be conducive to the production of smaller sized
polymer fluffs having average diameters of less than about 600
microns yet still having a desirably high bulk density, for
example, at least about 0.40 g/cc, and more preferably at least
about 0.44 g/cc.
[0057] In certain alternative preferred embodiments, the support
has an average particle size ranging from about 20 to about 80
microns, and more preferably from about 25 to about 60 microns. For
a MCS of a given activity, such preferred embodiments may be
conducive to the production of larger sized polymer fluffs having
average diameters of greater than about 600 microns, and yet still
having the above-mentioned desirably high bulk density.
[0058] A third aspect of the present invention is directed to a
process for the preparation of a MCS. The process comprises
providing a support having a surface defining pores. The process
further comprises attaching a metallocene substantially throughout
the support to form a MCS having a catalytic activity for a
metallocene loading of about 2 wt % that is at least about 20
percent higher than the catalytic activity for the metallocene
loading of about 1 wt %. In certain preferred embodiments, for
example, the process results in a MCS having a catalytic activity
of at least about 11,800 g/g/hr in a one hour reaction time under
the reaction environment previously described herein. In other
preferred embodiments, the support comprises granular or
substantially spheroidal materials, such as silica. In yet other
preferred embodiments, an activator, such as MAO, may be
conventionally attached to the pores substantially throughout the
support material to form a catalyst support to which the
metallocene attaches.
[0059] In other embodiments, the pores in the support provides a
peak pore volume of greater than about 0.115 mL/g at a pore
diameter of greater than about 240 Angstroms. Preferably, however,
at the peak pore volume, the pore diameter ranges between about 250
Angstroms and about 350 Angstroms. More preferably, the spheroidal
supports have a peak pore volume of greater than about 0.125 mL/g
at a pore diameter between about 290 Angstroms and about 320
Angstroms. Even more preferably, the peak pore volume is greater
than about 0.13 mL/g at a pore diameter of about 300 to about 310
Angstroms. In other advantageous embodiments, the pore volume is
distributed over a narrow range. For example, the support's pore
diameter may be between about 230 Angstroms and about 410
Angstroms, at one-half of the peak pore volume.
[0060] In still other embodiments, the pores in the support provide
a peak surface area of at least about 14.3 m.sup.2/g at a pore
diameter between about 250 Angstroms and about 330 Angstroms, and
preferably, between about 260 Angstroms and about 320 Angstroms.
Even more preferably, the support may have a peak surface area of
at least about 17 m.sup.2/g in the above-cited range of pore
diameters.
[0061] Although pore volume and surface area distributions are the
preferred measures for the purpose of selecting and providing
optimal supports, alternative selection criteria may be used. For
example, in certain embodiments, the support further may have a
total pore volume of greater than about 1.68 mL/g and an average
pore diameter between about 242 Angstroms and about 253 Angstroms.
In an alternative embodiment, however, the total pore volume may be
less than about 1.79 mL/g for a support having the above-cited
range of average pore diameters. In still other embodiments, the
total surface area is greater than about 272 m.sup.2/g for a
support having the above-cited range of average pore diameters.
[0062] A fourth aspect of the present invention is directed to a
process for the polymerization of polyolefin. The process includes
preparing a metallocene catalyst system (MCS) having a catalytic
activity for a metallocene loading of about 2 wt % that is at least
about 20 percent higher than the catalytic activity for the
metallocene loading of about 1 wt %. Preparing the MCS includes the
selection of supports based on considerations of the critical pore
diameter, and the pore volume and surface area distribution of
candidate supports as described elsewhere herein. The process also
includes introducing the MCS into a conventional polymerization
reaction chamber. The process further includes contacting at least
one olefinic monomer with the MCS in the reaction chamber under
conventional conditions.
[0063] In certain preferred embodiments, for example, the process
results in a MCS having a catalytic activity of at least about
11,800 g/g/hr in a one hour reaction time under the reaction
environment previously described herein. In other preferred
embodiments, any alpha olefins, comprising ethylenically
unsaturated hydrocarbons having between 2 and 20 Carbon atoms, may
be used as the monomer. In yet other preferred embodiments, the
process for polymerization may include, for example, an olefinic
monomer comprising propylene contacted with the MCS to produce a
homopolymer. Preferred reaction conditions may include a reaction
temperature between about 50 to about 75.degree. C., and preferably
67.degree. C., a reaction period between about 15 minutes and 120
minutes, and include hydrogen gas and TEAl in the reaction chamber,
in amount described elsewhere herein. Other embodiments may further
comprise, for example rac dimethylsilanediyl bis(2-methyl-4-phenyl
indenyl)zirconium dichloride, having up to about 2 wt % of the
metallocene loaded onto the support, and an alumoxane activator
comprising methylaluminoxane.
[0064] In yet other embodiments, the above-described process may be
used to produce a polyolefin comprising a copolymer under reaction
conditions previously described herein. Any combination of alpha
olefins, comprising ethylenically unsaturated hydrocarbons having
between 2 and 20 Carbon atoms, may be used as the monomer. For
example, one preferred monomer mixture comprises propylene and
ethylene. Other preferred monomer mixtures may include propylene,
butene and ethylene, or propylene and butene.
[0065] A fifth aspect of the present invention is directed to a
polyolefin produced by any of the above-described processes. The
process comprises introducing a MCS into a polymerization reaction
chamber. The MCS has a catalytic activity for a metallocene loading
of about 2 wt % that is at least about 20 percent higher than the
catalytic activity for the metallocene loading of about 1 wt %. The
process further comprises contacting at least one olefin monomer
with the MCS in the reaction chamber.
[0066] In certain preferred embodiments, the polyolefin is produced
by a MCS having a catalytic activity of at least about 11,800
g/g/hr in a one hour reaction time under the reaction environment
previously described herein. In other preferred embodiments, the
polyolefins may be converted to resins used in the manufacture a
variety of end products such as films, fibers, injection molded
articles and other materials well known to one of ordinary skill in
the art. In other advantageous embodiments, the metallocene may
comprise rac dimethylsilanediyl bis(2-methyl-4-phenyl
indenyl)zirconium dichloride and an alumoxane activator comprises
methylaluminoxane.
[0067] In yet other preferred embodiments, the polyolefin produced,
for example isotactic polypropylene, has an average particle size
diameter of greater than about 200 microns. Certain preferred
embodiments may include polymer fluffs having a certain particle
size. For example, the average polymer fluff diameter may be
between about 400 microns and about 2000 microns, and preferably
between about 600 and about 1500 microns. Such particle sizes may
be more advantageously produced in certain plant-scale reactor
facilities, such as loop type reactors, and post-reactor processing
facilities that are designed to handle such sized polymer
fluffs.
[0068] In yet other preferred embodiments, the production of
different sized polymer fluffs may be advantageous. For example,
the average polymer fluff diameter may be between about 500 microns
and about 1500 microns, and more preferably between about 600 and
about 1200 microns. Such particle sizes may be more advantageous in
certain plant-scale production facilities having reactors, such as
Spheripol.TM. type reactors, and post-reactor processing, such as
the devolitization and transport, designed to handle such sized
polymer fluffs.
[0069] In still other embodiments, the polyolefin produced, for
example isotactic polypropylene, may have a bulk density of at
least about 0.37 and more preferably at least about 0.40 g/cc, and
even more preferably at least about 0.44 g/cc.
[0070] Having described the present invention, it is believed that
the same will become even more apparent by reference to the
following experiments. It will be appreciated that the experiments
are presented solely for the purpose of illustration and should not
be construed as limiting the invention. For example, although the
experiments described below may be carried out in laboratory or
pilot plant settings, one skilled in the art could adjust specific
numbers, dimensions and quantities up to appropriate values for a
full scale plant.
Experiments
[0071] Four experiments were conducted to compare: (1) the pore
characteristics of several silica supports; (2) the loading of
activator onto the supports; (3) the catalytic activity of MCSs
prepared using the supports; and (4) the properties of polymers
produced from polymerization reactions catalyzed by the
above-prepared MCSs.
[0072] Experiment 1
[0073] Six silica supports were selected for comparison: (1)
product number Cariact P-10, from Fuji Silysia Chemical Company,
Ltd. (Japan); (2) product number Sylopol 948 ("G-948"), (3) product
number Sylopol 952-1836 ("G-952"), and (4) product number XPO-2412,
all from Grace Davison Chemicals (Columbia, Md.); (5) product
number ES747JR, from INEOS Silicas Ltd. (England); and (6) product
number Sunsphere H202, from Asahi Glass Co. Ltd. (Japan). The
average particle size of the silicas was determined using a
conventional Malvern sizer and methodology in hexane or acetone.
The analysis of the pore characteristics (i.e., pore volume,
surface area, pore diameter and distributions) was conducted on an
ASAP 2400 (Micromeritics Instrument Corp., Norcross, Ga.), using
nitrogen as the adsorbate for the conventional measurements of
adsorption and desorption isotherms. The data was used for the
calculation, using the BET model, of total surface area, total pore
volume and average pore diameter. In addition, the data were
analyzed to determine, using the BJH method and DFT, the pore
volume and surface area distributions.
[0074] TABLE 1 summarizes the total surface area, total pore volume
and average pore diameter for the six silicas. Typical standard
deviations are +5% for determination of surface area, pore volume
and pore diameter, and +10% for the determination of particle size,
using hexane. All six silicas had total surface areas of at least
about 260 m.sup.2/g and high pore volume of at least about 1.4
mL/g. The average support particle size ranged from about 20 to
about 33 microns, except for G-948 at about 55 microns.
1TABLE 1 Surface Pore Area Volume Average Pore Avg. Particle
Support (m.sup.2/g) (mL/g) Diameter (.ANG.) Size (.mu.m) P10
.about.270 .about.1.5 .about.222 .about.20 G-952 .about.278
.about.1.68 .about.242 .about.33 G-948 .about.272 .about.1.71
.about.253 .about.55 ES747JR .about.263 .about.1.60 .about.244
.about.20 XPO-2412 .about.474 .about.1.53 .about.129 .about.21 H202
.about.678 .about.1.53 .about.90 .about.23
[0075] The pore volume and surface area distributions for the
silicas were also measured. The BJH method was used for calculating
these distributions, based on a model of the adsorbent (i.e., the
silica carrier) as a collection of cylindrical pores. The
calculation accounts for capillary condensation in the pores using
the classical Kelvin equation (free energy of surface tension),
which in turn assumes a hemispherical liquid-vapor meniscus and a
well-defined surface tension. The calculation also incorporates
thinning of the adsorbed layer through the use of a reference
isotherm, so that the Kelvin equation is only applied to the "core"
fluid.
[0076] In addition, the DFT was used to make distribution
calculations using conventional mathematical, statistical, and
numerical techniques for interpreting data from the ASAP 2400
instruments. The DFT offers a unified approach to analyzing the
entire adsorption isotherm from about 4 to about 1000 .ANG. in
diameter. All pores, from the smallest to the largest, are reported
using a single data reduction technique, termed as the BJH-DFT
reduction, thereby providing a broad picture of adsorption
activity.
[0077] FIG. 2 illustrates BJH-DFT analysis results of pore volume
distribution with respect to pore diameter for the different
silicas. FIG. 2 reveals that, even though XPO-2412 and H202 have
high total pore volumes (TABLE 1), most of the pores had diameters
of less than about 150 .ANG.. As such, these silicas are unlikely
to provide substantial numbers of pores having a CPD in a range
suitable for most metallocenes. In addition, it is thought that
silicas having a substantial number of pores with a pore diameter
larger than about 400 .ANG., may not be suitable because some of
the pore space may be incompletely filled, thus inefficiently used
as a support. Silicas, such as G-948, G-952, ES747JR and P10, have
the bulk of their pore volumes distributed between 150 and 400
.ANG.. Among these four silicas, G-948 had the highest amount of
pore volume distributed between 150 and 400 .ANG., and P10 the
lowest.
[0078] FIG. 3 illustrates BJH-DFT analysis results of surface area
distribution with respect to pore diameter for the different
silicas. Again, although H202 and XPO-2412 have high total surface
areas (TABLE 1), most of the surface area, is allotted to small
pores with diameters of less about 150 .ANG.. For example, most of
the surface area for H.sub.2O.sub.2 is accounted by small pores,
having diameters of less than about 40 .ANG.. Taking the results
from FIGS. 3 and 4 together, for XPO-2412 and H202, most of the
pores with the small pore diameters account for the main surface
area but little of the pore volume. For the G-948, G-952, ES747JR
and P10 silicas, the main pore volume is distributed between 140
and 400 .ANG.. Moreover, comparison of FIGS. 3 and 4 reveal that
both the pore volume and surface area have the same distribution
trends versus pore diameter for these four silica carriers. Again,
among these four, G-948 had the highest amount of surface area
distributed between 150 and 400 .ANG., and P10 the lowest.
[0079] Experiment 2
[0080] The loading of activator into the six silica supports was
also examined. The reaction between silicas and MAO (Albermarle
Corp., Baton Rouge, La.) was conducted substantially as described
in U.S. patent application Ser. Nos. 09/782,752 and 09/782,753 to
Gauthier et al, incorporated by reference. Briefly, unless
otherwise indicated, all the silica supports were dried at
150.degree. C. for 12 hours under nitrogen flow of 6 mL/min. Two
processes were used, as described in the above-cited applications:
room temperature grafting (Process 1) and grafting at 115.degree.
C. (Process 2). For Process 1, room temperature grafting in toluene
was carried out with the starting concentration ratio of MAO:silica
equal to about 0.70:1.00, except for XPO-2412 and H202, where the
ratio was about 1:1. Process 2, involved grafting at 115.degree. C.
in toluene for 4 hours, with the starting concentration ratio of
MAO:silica equaled about 1.0:1.0 MAO:silica for all silicas, except
H.sub.2O.sub.2 whose ratio was 1.35:1. Following grafting, both
Process 1 and 2 work-ups included filtration and several toluene
washes to remove excess Al species.
[0081] The extent of MAO grafting achieved for the six silicas was
assessed by measuring Maximium Grafting Yield (MGY), defined by the
formula:
MGY=((W.sub.2-W.sub.1)/W.sub.1).times.100% (3)
[0082] where W.sub.2 is defined as the weight of the MAO-modified
silica support, and W.sub.1 is the weight of the support before
grafting. The standard deviation in MGY values is estimated to be
about +0.2 wt %. The result of these measurements are shown in
TABLE 2.
[0083] For all six silicas, Process 2 resulted in a higher loading
of MAO onto the silica support than Process 1. Using Process 1, P10
had the lowest MGY at room temperature, with G-948 and G-952 having
about 20% greater yields. The MGY for ES747JR, G-948, and G-952,
were all less than about 6.4% higher for Process 1 compared to
Process 2.
2 TABLE 2 MGY (wt %) Support Process 1 Process 2 P10 .about.44.0
.about.62.5 ES747JR .about.52.8 .about.57.2 G-948 .about.57.1
.about.61.1 G-952 .about.59.2 .about.65.6 XPO-2412 .about.72.5
.about.83.6 H202 .about.100.0 .about.135.0
[0084] A particle size distribution analysis of the MAO-modified
silica supports was performed using the above-mentioned Malvern
Sizer. The analysis, illustrated in FIG. 4, reveals that all the
MAO-modified supports contain a small shoulder peak having an
average particle size of less than about 20 .mu.m, which has been
tentatively assigned to MAO gels. FIG. 4 reveals that ES747JR had a
relatively larger MAO gel content than the other five silicas.
[0085] Experiment 3
[0086] In another series of experiments, the catalytic activity of
MCSs prepared using the above-described silica supports was
measured. An additional support, product number MS-1733 from PQ
Corp. (valley Forge, Pa.), was also tested. The total surface area
(-311 m.sup.2/g), pore volume (-1.79 mL/g) and average particle
size (-74 .mu.m) of the MS-1733 support was determined using the
same methodology as described above.
[0087] The metallocene, rac dimethylsilanediyl
bis(2-methyl-4-phenyl indenyl)zirconium dichloride, was loaded in
the MAO-modified silicas that were prepared similar to that
described above for Experiment 2. To prepare the MCS, about 2.5 g
of MAO-modified silica was mixed with 25 mLs of toluene at room
temperature under nitrogen. The metallocene (about 25 mg;
designated as 2% metallocene loading) in about 10 mL of toluene was
added to MAO-modified silica under stirring. The mixture was
allowed to react for about 2 hours at room temperature (about
22.degree. C.). The MCS was then filtered and washed three times
with toluene (3.times.10 mL) and three times with hexane
(3.times.10 mL) under nitrogen at room temperature. After an
optional drying step at room temperature under vacuum to a constant
weight, the resulting MCS was diluted into about 25 g of mineral
oil and then isolated as a solid slurry. The process for preparing
the MCS with a lower amount of metallocene loading (designated as
1% metallocene loading) was carried out similar to that described
above except that a correspondingly lower ratio of metallocene to
MAO-modified silica was used.
[0088] The catalytic activity (CA) of the MCS was measured using
the methodology substantially similar to that described in U.S.
patent application Ser. Nos. 09/782,752 and 09/782,753 to Gauthier
et al. Specifically, polymerization was carried out in a
conventional 2 or 4 Liter reaction chamber, in the presence of
about 28 ppm H.sub.2 (2 L reactor) or 37 ppm (4L reactor), about 28
ppm (2 L reactor) or about 23 ppm (4 L reactor) of MCS, about 56
ppm (2 L reactor) or about 46 ppm (4 L reactor) of TEAL, at about
67.degree. C. for about one hour using about 300 to about 400 g
propylene per liter of reactor volume. Catalytic activity is thus
expressed as g of polypropylene produced per g of MCS per 1 hr
(g/g/hr). For all experiments, polymer grade propylene (minimum
purity 99.5 wt %) was used after further purification steps,
described elsewhere herein, to reduce levels of COS, O.sub.2, and
H.sub.2O.
[0089] The catalytic activity for MCSs prepared from the seven
different MAO-modified silica carriers prepared at room temperature
(Process 1) and 1 wt % metallocene loading, and high temperature
(Process 2) and 1 or 2 wt % metallocene loading are illustrated in
TABLE 3.
3 TABLE 3 Process 1 Process 2 Process 2 (1 wt % loading) (1 wt %
loading) (2 wt % loading) Silica MAO:Si MAO:Si MAO:Si Support
(wt:wt) CA (g/g/hr) (wt:wt) CA (g/g/hr) (wt:wt) CA (g/g/hr) P10
0.44:1 .about.3400 0.62:1 .about.10300 0.62:1 .about.11700 G-948
0.57:1 .about.5400 0.61:1 .about.12100 0.61:1 .about.18800 G-952
0.59:1 .about.6500 0.69:1 .about.11900 0.69:1 .about.22200 ES747JR
0.53:1 .about.4100 0.57:1 .about.8500 XPO-2412 0.72:1 .about.5500
0.84:1 .about.9700 H202 1.0:1 .about.6600 MS-1733 0.76:1
.about.23,500
[0090] For supports prepared with similar starting ratios of MAO to
silica (MAO:Si), the MCSs produced from either Process 1 or 2,
having G-948 and G-952 supports, had the highest catalytic
activity. As indicated in TABLE 3, similar MAO:Si ratios were used,
except for XPO-2412 and H.sub.2O.sub.2, where higher ratios were
used. Also, the MCSs produced from Process 2 had higher activity
than the MCSs produced from Process 1. It is thought that heating
and refluxing facilitates the fixation of MAO on the silica, thus
increasing the space available to contribute to the CPD, as
compared to MAO fixation done at room temperature. It is thought
that the pore volume and pore area distribution of preferred
supports, such as G-948, G-952, and MS-1733 allow greater amounts
of metallocene to be bound and activated in the interior pores in
these supports, as compared to other non-preferred supports, such
as P10, thereby resulting in greater catalytic activity.
[0091] The beneficial effect of higher amounts of metallocene
loading on catalytic activity for certain MCSs having high surface
area and pore volume supports is illustrated in TABLE 3. For
example, for P10 supported MCSs, the enhancement in catalytic
activity per unit weight of MCS was less than about 14% when the
metallocene loading was increased to about 2 wt %, compared to the
catalytic activity obtained with about 1 wt % metallocene loading.
In contrast, the catalytic activity for G-948 supported MCS using a
metallocene at 2.0 wt % loading was at least about 20% higher, and
in some cases greater than about 55% or greater than about 85%
higher, as compared to the catalytic activity at 1.0 wt % loading.
In another experiment even higher activity, 22,600 g/g/hr, was
obtained when a G-952 supported MCS was loaded with 2.5 wt %
metallocene.
[0092] Experiment 4
[0093] A fourth series of experiments were conducted to
characterize the polymers produced from polymerization reactions
carried out under conditions similar to that described in
Experiment 3. For all of the MCSs, an isotactic polypropylene was
produced, having for example, a meso pentad content of at least
about 95% and a regioregularity of greater than about 99.0%.
Polymer melt flow (MF) was recorded on a Tinius-Olsen Extrusion
Plastometer at 230.degree. C. with a 2.16 Kg mass. Polymer powder
was stabilized with approximately 1 mg of 2,6-ditert-butyl-4-methy-
lphenol (BHT) to prevent degradation in the MF indexer. Bulk
density (BD) measurements were conducted by weighing the unpacked
contents of a 100 mL graduated cylinder containing the polymer
powder. The polymer fluff particle size distribution was measured
using a conventional sieve shaker.
[0094] TABLE 4 illustrates the melt flow and bulk density
properties of polypropylene produced under the conditions used to
produce the MCS described in TABLE 3. The melt flow of the
polymers, including polymer produced using G-948 and G-952
supported MCS, was acceptable, having a value of greater than about
0.1 g/10 min. The bulk densities of polymer produced using Process
1 or 2 with G-948 and G-952 supported MCS were also had acceptable
values, greater than about 0.35 g/cc, similar to that obtained for
polymers produced using MCSs supported by the other silicas.
4 TABLE 4 Process 1 Process 2 Silica MF BD MF BD Support (g/10 min)
(g/cc) (g/10 min) (g/cc) P10 .about.5 .about.0.42 .about.2
.about.0.42 G-948 .about.9 .about.0.37 .about.1 .about.0.37 G-952
.about.3 .about.0.38 .about.0.8 .about.0.41 ES747JR .about.11
.about.0.36 .about.0.4 .about.0.40 XPO-2412 .about.8 .about.0.38
.about.2 .about.0.40 H202 .about.3 .about.0.44
[0095] The particle size distribution of polymer produced using
Process 2 and six of the silica supported MCS is shown in FIG. 5.
Of these, polymer produced using G-948 supported MCS had the
largest particle size. The polypropylene produced using G-948 and
G-952 supported MCS both had a median particle size (an
accumulative wt % equal to about 50%) of greater than about 600
microns.
[0096] Although the present invention has been described in detail,
those skilled in the art should understand that they can make
various changes, substitutions and alterations herein without
departing from the scope of the invention.
* * * * *