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| United States Patent |
5,242,876
|
|
Shamshoum
, et al.
|
September 7, 1993
|
Homogeneous-heterogeneous catalyst system for polyolefins
Abstract
This invention concerns a catalyst system comprising at least one
homogeneous catalyst and at least one heterogeneous catalyst,
specifically, a metallocene catalyst and a conventional Ziegler-Natta
catalyst, respectively. This invention is useful in the polymerization of
any polymer in which separate polymerizations with a homogeneous catalyst
and with a heterogeneous catalyst are possible, but preferably,
polymerization of olefins, more preferably, .alpha.-olefins, and, most
preferably, propylene. This invention provides a catalyst system which
facilitates use of a homogeneous catalyst but eliminates the disadvantages
of such a system. This invention produces a polymer with molecular weight
distribution (MWD) as broad or broader than the MWD of the heterogeneous
catalyst alone. Hydrogen can be used to control molecular weight
distribution of a polymer produced with this invention.
| Inventors:
|
Shamshoum; Edwar S. (Houston, TX);
Elder; Michael J. (Friendswood, TX);
Reddy; Baireddy R. (Baytown, TX);
Rauscher; David J. (Webster, TX)
|
| Assignee:
|
Fina Technology, Inc. (Dallas, TX)
|
| Appl. No.:
|
768783 |
| Filed:
|
September 30, 1991 |
| Intern'l Class: |
C08F 004/02 |
| Field of Search: |
526/114,119
502/104,113,114,115,116,158
|
References Cited
U.S. Patent Documents
| 4701432 | Oct., 1987 | Welborn, Jr. | 526/114.
|
| Foreign Patent Documents |
| 0299712 | Mar., 1989 | EP.
| |
Primary Examiner: Schofer; Joseph L.
Assistant Examiner: Wu; David
Attorney, Agent or Firm: Wheelington; Jim D., Cheairs; M. Norwood, Abokhair; John K.
Claims
What is claimed as new and desired to be secured by Letter of Patent of the
United States is:
1. A catalyst system for the polymerization of olefins comprising a
combination of at least one homogeneous catalyst and at least one
heterogeneous catalyst wherein the homogeneous catalyst is a metallocene
catalyst comprising
a) a neutral metallocene of the general formula
R".sub.b (C.sub.p Rphd 4pl )(C.sub.p R'.sub.4)MR.sup.*.sub.v-2
where R" is a bridge imparting stereorignidityto the structure to the
metallocene by connecting the two cyclopentadienyl rings, b is 0 or 1, Cp
is a cyclopentadienyl ring, R and R' are substituents on the
cyclopentadienyl rings and can be a hydride or a hydrocarbyl from 1-9
carbon atoms, each R and R' being the same or different, each (CpR.sub.4)
and (CpR'.sub.4) being the same or different, M is a Group IIIB, IVB, VB
or VIB metal, R.sup.* is a hydride, a halogen or a hydrocarbyl from 1-20
carbon atoms, v is the valence of M and
b) an ionizing agent which will ionize a neutral metallocene compound to
form a cationic metallocene catalyst
wherein the heterogeneous is a conventional Ziegler-Natta transition metal
compound catalyst comprising:
a) a transition metal of the general formula MR.sup.+.sub.x where M is a
Group IIIB, IVB, VB or VIB metal, R.sup.+ is a halogen or a hydrocarboxyl
and x is the valence of the metal and
b) an aluminum alkyl of the general formula AlR.sup.#.sub.3 where R.sup.#
is an alkyl of from 1-8 carbon atoms and R.sup.# may be the same or
different.
2. A catalyst system as recited in claim 1 wherein b is 1, R" is a
hydrocarbyl radical chosen from the group consisting of an alkenyl radical
having one to four carbon atoms, a dialkyl germanium, a dialkyl silicon,
an alkyl phosphine and an amine radical, M is a group IVB metal, R.sup.*
is a halogen or alkyl.
3. A catalyst system as recited in claim 2 wherein R" is a dimethyl silyl
radical, an ethylenyl radical or a isopropenyl radical.
4. A catalyst system as recited in claim 3 wherein R" is an ethylenyl
radical.
5. A catalyst system as recited in claim 1 wherein (CpR.sub.4) is an
substituted cyclopentadienyl ring such that it is
3-t-butyl-cyclopentadienyl, indenyl or cyclopentadienyl and (CpR'.sub.4)
is a substituted cyclopentadienyl ring such that it is fluorenyl, indenyl
or flurenyl, respectively.
6. A catalyst system as recited in claim 5 wherein (CpR.sub.4) is indenyl
and (CpR'.sub.4) is indenyl.
7. A catalyst system as recited in claim 1 wherein the ionizing agent is
chosen from the group consisting of an alumoxane, an aluminum alkyl, other
Lewis acids and combinations thereof.
8. A catalyst system as recited in claim 1 wherein the ionizing agent is
methyl alumoxane.
9. A catalyst system as recited in claim 1 wherein M is a group IVB,
R.sup.+ is chlorine, bormine, an alkoxy or a phenoxy.
10. A catalyst system as recited in claim 9 wherein M is titanium and R is
chlorine or ethoxy.
11. A catalyst system as recited in claim 10 wherein the heterogeneous
catalyst is chosen from the group consisting of TiCl.sub.4, TiBr.sub.4,
Ti(OC.sub.2 H.sub.5).sub.3 Cl, Ti(OC.sub.2 H.sub.5)Cl.sub.3, Ti(OC.sub.4
H.sub.9).sub.3 Cl, Ti(OC.sub.3 H.sub.7).sub.2 Cl.sub.2 , Ti(OC.sub.6
H.sub.13).sub.2 Cl.sub.2, Ti(OC.sub.2 H.sub.5).sub.2 Br.sub.2 and
Ti(OC.sub.12 H.sub.25)Cl.sub.3.
12. A catalyst system as recited in claim 1 wherein the aluminum alkyl is
chosen from the group consisting of trimethyl aluminum, triethyl aluminum
and triisobutyl aluminum.
13. A catalyst system as recited in claim 1 further comprising an electron
donor organosilicon compound.
14. A catalyst system as recited in claim 13 wherein the electron donor is
chosen from the group consisting of methylcyclohexyl dimethyoxysilane,
diphenyldimethoxysilane and isobutyltrimethoxy silane.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a catalyst system which is a combination of at
least one homogeneous catalyst and at least one heterogeneous catalyst.
Changing the homogeneous catalyst used with the heterogeneous catalyst
effects the molecular weight distribution of the resulting polymer.
2. Description of the Prior Art
It is known that two or more homogeneous catalysts, such as those based on
metallocene compounds, may be combined to effect properties, such as
molecular weight distribution. U.S. Pat. No. 4,530,914 discloses use of a
catalyst system comprising two or more metallocenes in the polymerization
of .alpha.-olefins, primarily ethylene, to obtain a broad molecular weight
distribution. The metallocenes each have different propagation and
termination rate constants. The metallocenes are mixed with an alumoxane
to form the catalyst system.
It is also known that metallocenes may be affixed to a support to simulate
a heterogeneous catalyst. In U.S. Pat. No. 4,808,561 discloses reacting a
metallocene with an alumoxane and forming a reaction product in the
presence of a support. The support is a porous material like talc,
inorganic oxides such as Group IIA, IIIA IVA OR IVB metal oxides like
silica, alumina, silica-alumina, magnesia, titania, zirconia and mixtures
thereof, and resinous material such as polyolefins like finely divided
polyethylene. The metallocenes and alumoxanes are deposited on the
dehydrated support material.
In U.S. Pat. No. 4,701,432 a support is treated with at least one
metallocene and at least one non-metallocene transition metal compound. To
form a catalyst system a cocatalyst comprising an alumoxane and an
organometallic compound of Group IA, IIA, IIB and IIIA is added to the
supported metallocene/non-metallocene. The support is a porous solid such
as talc or inorganic oxides or resinous materials, preferably an inorganic
oxide, such as silica, alumina, silica-alumina, magnesia, titania or
zirconia, in finely divided form. By depositing the soluble metallocene on
the support material it is converted to a heterogeneous supported
catalyst. The transition metal compound, such as TiCl.sub.4, is contacted
with the support material prior to, after, simultaneously with or
separately from contacting the metallocene with the support.
An advantage of a homogeneous (metallocene) catalyst system is the very
high activity of the catalyst and the narrow molecular weight distribution
of the polymer produced with a metallocene catalyst system. The
metallocene catalysts suffer from a disadvantage in that the ratio of
alumoxane cocatalyst to metallocene is high, requiring extensive treatment
of the polymer product to remove the aluminum. Another disadvantage of the
homogenous catalyst system is that the polymer product has small particle
size and low bulk density. Another disadvantage of the homogeneous
catalyst system is that the reactor fouls during polymerization.
It would be advantageous to provide a catalyst system which facilitates use
of a homogeneous catalyst but eliminates the disadvantages of such a
system. A combination of a homogeneous catalyst with a heterogeneous
catalyst in a single reactor will eliminate the disadvantages of the
homogeneous catalyst alone and will facilitate use of a homogeneous
catalyst. A combination of a homogeneous catalyst with a heterogeneous
catalyst in a single reactor will also provide a means to control
molecular weight distribution and polydispersity.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a chart of gel permeation chromatography (GPC) of a polymer
produced with a conventional Ziegler-Natta heterogeneous catalyst.
FIG. 2 is a chart of GPC of a polymer produced with a metallocene
homogeneous catalyst.
FIG. 3 is an overlay of FIGS. 1 and 2.
FIG. 4 is chart of GPC of a polymer produced with a
homogeneous-heterogeneous catalyst system.
FIG. 5 is a chart of GPC of a polymer produced with a
homogeneous-heterogeneous catalyst system and a low level of hydrogen (3.9
mmol).
FIG. 6 is a chart of GPC of a polymer produced with a
homogeneous-heterogeneous catalyst system and a high level of hydrogen
(15.7 mmol).
SUMMARY OF THE INVENTION
Accordingly, an object of this invention is to provide a catalyst system
which eliminates extensive treatment of the polymer product to remove
impurities.
And, an object of this invention is to provide a catalyst system which
produces polymer with little or no small particle size and high bulk
density.
Also, an object of this invention is to provide a catalyst system which
eliminates reactor fouling during polymerization.
Further, an object of this invention is to provide a catalyst system which
controls the molecular weight distribution by varying the catalyst.
Additionally, an object of this invention is to provide a catalyst system
which produces polymer with a bimodal molecular weight distribution.
As well, an object of this invention is to provide a catalyst system which
produces a reactor blend of polymer with a broad molecular weight
distribution in a single reactor.
In addition, an object of this invention is to provide a process for using
hydrogen to control molecular weight distribution.
These and other objects are accomplished by a catalyst system comprising at
least one homogeneous catalyst and at least one heterogeneous catalyst,
i.e, metallocene catalyst and conventional Ziegler-Natta catalyst,
respectively.
DETAILED DESCRIPTION OF THE INVENTION
The multi-catalyst system of the present invention is useful in the
polymerization of any polymer in which separate polymerizations with a
homogeneous catalyst and with a heterogeneous catalyst are possible.
Preferably, the multi-catalyst system is useful in the polymerization of
olefins, more preferably, .alpha.-olefins, and, most preferably,
propylene.
The multi-catalyst system of the present invention is obtained by mixing
the components of at least one homogeneous catalyst system and at least
one heterogeneous system. The components may be combined in any order.
Generally, the components of a homogeneous catalyst system are a
metallocene compound and an ionizing agent. Generally, the components of a
heterogeneous catalyst system are an aluminum alkyl and a transition metal
compound with, optionally, an electron donor.
Any of the conventional heterogeneous Ziegler-Natta transition metal
compound catalyst components can be used as the heterogeneous catalyst of
the catalyst system of the present invention. The compound is preferably
of the general formula MR.sup.+.sub.x where M is the metal, R.sup.+ is a
halogen or a hydrocarbyloxy and x is the valence of the metal. Preferably,
M is a Group IVB, VB or VIB metal, more preferably a Group IVB, and most
preferably titanium. Preferably, R.sup.+ is chlorine, bromine, an alkoxy
or a phenoxy, more preferably chlorine or ethoxy and most preferably,
chlorine. Illustrative examples of the transition metal compound catalyst
components are TiCl.sub.4, TiBr.sub.4, Ti(OC.sub.2 H.sub.5).sub.3 Cl,
Ti(OC.sub.2 H.sub.5)Cl.sub.3, Ti(OC.sub.4 H.sub.9).sub.3 Cl, Ti(OC.sub.3
H.sub.7).sub.2 Cl.sub.2, Ti(OC.sub.6 H.sub.13).sub.2 Cl.sub.2, Ti(OC.sub.2
H.sub.5).sub.2 Br.sub.2 and Ti(OC.sub.12 H.sub.25)Cl.sub.3. Mixtures of
the transition metal compounds may be used. No restriction on the number
of transition metal compounds is made as long as at least one transition
metal compound is present.
The transition metal compound may be either supported or unsupported. If
supported, the support should be an inert solid which is chemically
unreactive with any of the components of the heterogeneous or homogeneous
catalyst.
The aluminum alkyl is of the general formula AlR'.sub.3 where R' is alkyl
of from 1-8 carbon atoms and R' may be the same or different. Examples of
aluminum alkyls are trimethyl aluminum (TMA), triethyl aluminum (TEAl) and
triisobutyl aluminum (TiBAl). The preferred aluminum alkyl is TEAl.
The electron donor is any one of the electron donors which are effective
with Ziegler-Natta catalysts. Typically, an electron donor is an
organosilicon compound. Examples of electron donors are cyclohexylmethyl
dimethoxysilane (CMDS), diphenyldimethoxy silane (DPMS) and
isobutyltrimethoxysilane (IBMS). Other examples of electron donors are
disclosed in U.S. Pat. Nos. 4,218,339; 4,395,360; 4,328,122; 4,473,660;
4,562,173 and 4,547,552, which are hereby incorporated by reference.
The homogeneous catalyst component may be a metallocene or
cyclopentadienide, i.e., a metal derivative of a cyclopentadiene. The
metallocene should contain two cyclopentadiene rings and be of the general
formula:
R".sub.b (CpR.sub.4)(CpR'.sub.4)M'R.sup.*.sub.v-2
where R" is a bridge imparting stereoridigity to the structure to the
metallocene by connecting the two cyclopentadienyl rings, b is 0 or 1, Cp
is a cyclopentadienyl ring, R and R' are substituents on the
cyclopentadienyl rings and can be a hydride or a hydrocarbyl from 1-9
carbon atoms, each R and R' being the same or different, each (CpR.sub.4)
and (CpR'.sub.4) being the same or different, M' is a Group IIIB, IVB, VB
or VIB metal, R.sup.* is a hydride, a halogen or a hydrocarbyl from 1-20
carbon atoms, v is the valence of M'. Preferably, b is 1 and R" is a
hydrocarbyl radical, more preferably an alkenyl radical having one to four
carbon atoms, a dialkyl germanium, a dialkyl silicon, an alkyl phosphine
or amine radical, such as a dimethyl silyl radical, an ethylenyl radical
or a isopropenyl radical and, most preferably, is an ethylenyl radical.
Preferably, (CpR.sub.4) is an substituted cyclopentadienyl ring such that
it is 3-t-butyl-cyclopentadienyl, indenyl or cyclopentadienyl and
(CpR'.sub.4) is a substituted cyclopentadienyl ring such that it is
fluorenyl, indenyl or fluorenyl, respectively; most preferably,
(CpR.sub.4) is indenyl and (CpR'.sub.4) is indenyl. Preferably, M' is a
Group IVB metal, most preferably zirconium, which has a valence of 4.
Preferably, R.sup.* is a halogen or alkyl, most preferably chlorine or
methyl.
The ionizing agent is an alumoxane, an aluminum alkyl, other Lewis acid or
a combination thereof which will ionize a neutral metallocene compound to
form a cataionic metallocen catalyst. Examples of such ionzing agents are
methyl alumoxane (MAO), triethyl aluminum (TEAl) and
tris(pentafluorophenyl)boron. Other ionizing agents are disclosed in U.S.
Pat. application Ser. Nos. 07/419,057 and 07/419,222 and European Patent
Publication Nos. 0-277-003 and 0-277-004 which are hereby incorporated by
reference.
By using a multi-catalyst system having at least one homogeneous catalyst
and at least one heterogeneous catalyst a polymer can be produced with
molecular weight distribution (MWd) as broad or broader than the MWD of
the heterogeneous catalyst alone. MWD can be represented by a chart of gen
permeation chromatography (GPC). The homogeneous catalyst produces a
polymer with a MWD which is narrow relative to a polymer produced by a
heterogeneous. For example, using aheterogeneous catalyst alone produces a
polymer with a MWD of approximately 5-7 (FIG. 1) and using a homogeneous
catalyst alone produces a MWD of approximately 2-3.5 (FIG. 2). By
superimposing FIG. 1 and FIG. 2 (FIG. 3), it can be predicted that using
the two catalysts together will result in a polymer having a MWD of 5-7.
When the two catalysts are used together in an actual polymerization, a
polymer having a MWD of 5-7 results, as shown is FIG. 4. A comparison of
FIGS. 3 and 4 show a near identity in the shape and location of the plot.
By using different ratios of the homogeneous heterogeneous catalysts, the
polydispersity, i.e., the distribution of molecular weights, can be
effected. Since the molecular weight of the polymer produced with the
homogeneous catalyst is different from that of the heterogeneous catalyst,
changing the relative amount of one catalyst to another in a
multi-catalyst system of this invention will change the polydispersity of
the polymer produced.
The effect of hydrogen on a catalyst system having one or more homogeneous
catalysts alone is known to be negligible. The effect of hydrogen on a
catalyst system having one or more heterogeneous catalysts alone is known
to have an inverse proportional effect on the peak molecular weight of the
polymer, but there is no effect on molecular weight distribution. However,
when a catalyst system comprises one or more homogeneous catalysts and one
or more heterogeneous, the effect of hydrogen in decreasing the peak
molecular weight of the polymer produced by the heterogeneous catalyst
while the polymer produced by the homogeneous catalyst remains unaffected
results in on overall change in the molecular weight distribution. The
effect of using a relative low amount of hydrogen compared to using a
relative high amount of hydrogen is shown in FIGS. 5 and 6, respectively.
Therefore, hydrogen can be used to control molecular weight distribution
of a polymer produced by a multi-catalyst of the present invention.
The invention having been generally described, the following examples are
given as particular embodiments of the invention and to demonstrate the
practice and advantages thereof. It is understood that the examples are
given by way of illustration and are not intended to limit the
specification or the claims to follow in any manner.
EXAMPLE 1
5.0 mg of conventional Ziegler-Natta catalyst was placed in a stainless
steel bomb with 0.2 mmol CMDS. 5.0 mg of Et(Ind).sub.2 ZrCl.sub.2 were
placed in a mixing bottle with 2.0 mmol TEAl. The metallocene-TEAl mixture
was placed in the bomb. 2.5 ml of MAO were placed in a second stainless
steel bomb. 1.0 liter of propylene was placed in a 2 liter Zipperclave
reactor at 30.degree. C. Contents of the first bomb were charged to the
reactor with 0.3 liter of propylene and 15.7 mmol of hydrogen. Contents of
the second bomb were charged to the reactor with 0.3 liter of propylene.
The reactor temperature was increased from 30.degree. C. to 60.degree. C.
Polymerization continued for one hour during which time the react
maintained at the polymerization temperature. At the end of this time
polymerization was terminated by rapidly venting the reactor of unreacted
monomer. The polymer yield and analysis is shown in Table I.
EXAMPLE 2
The procedure of Example 1 was followed except 2.5 mg of conventional
Ziegler-Natta catalyst and 5.0 mg of Et(Ind).sub.2 ZrCl.sub.2 and 3.9 mmol
of hydrogen was used. The polymer yield and analysis is shown in Table I.
Example 3
5.0 mmol of conventional Ziegler-Natta catalyst were placed in a bomb with
2.0 mmol of TEAl and 0.2 mg of CMDS. 2.5 mg of Et(Ind).sub.2 ZrCl.sub.2
were placed in a second bomb with 2.5 ml of MAO. 1.0 liter of propylene
was placed in a 2 liter Zipperclave reactor at 32.degree. C. Contents of
the first bomb were charged to the reactor with 0.3 liter of propylene and
4 mmol of hydrogen. The contents of the second bomb were charged to the
reactor with 0.3 liter of propylene. The reactor temperature was increased
form 32.degree. C. to 60.degree. C. Polymerization continued for one hour
during which time the reactor was maintained at the polymerization
temperature. At the end of this time polymerization was terminated by
rapidly venting the reactor of unreacted monomer. The polymer yield and
analysis is shown in Table I.
EXAMPLE 4
5.0 mg of conventional Ziegler-Natta catalyst were placed in a stainless
steel bomb with 2.0 mmol TEAl and 0.2 mmol of CMDS. 2.5 mg of
Et(Ind).sub.2 ZrCl.sub.2 were placed in a mixing bottle with 2.5 ml of
MAO. The metallocene-MAO mixture was placed in the bomb. 1.0 liter of
propylene was placed in a 2 liter Zipperclave reactor at 31.degree. C.
Contents of the bomb were charged to the reactor with 0.3 liter of
propylene and 4 mmol of hydrogen. The reactor temperature was increased
from 31.degree. C. to 60.degree. C. Polymerization continued for one hour
during which time the reactor was maintained at the polymerization
temperature. At the end of this time polymerization was terminated by
rapidly venting the reactor of unreacted monomer. The polymer yield and
analysis is shown in Table I.
EXAMPLE 5
The procedure of Example 1 was followed except 2.5 mg of conventional
Ziegler-Natta catalyst, 5.0 mg of Me.sub.2 Si(t-b-Cp) (Flu)ZrCl.sub.2 and
4 mmol of hydrogen were used and the initial reactor temperature was
33.degree. C. The polymer yield and analysis is shown in Table I.
TABLE I
__________________________________________________________________________
HETERO- BULK
GENEOUS
METALLOCENE/ DEN-
TEA1
CMDS
CATALYST
AMOUNT MAO H.sub.2
YIELD
SITY
T.sub.m
MW** MWD
RUN (mmol)
(mmol)
(mg) */(mg) (ml)
(mmol)
(g) (g/cc)
(.degree.C.)
(.times. 1000)
(M.sub.w
/M.sub.n)
__________________________________________________________________________
1 2.0 0.2 5.0 Et(Ind).sub.2 ZrCl.sub.2 /2.5
2.5 15.7
105 0.42
161
220 21.3
2 2.0 0.2 2.5 Et(Ind).sub.2 ZrCl.sub.2 /5.0
2.5 3.9 164 0.50
161
294 13.7
3 2.0 0.2 5.0 Et(Ind).sub.2 ZrCl.sub.2 /2.5
2.5 3.9 235 0.48
160
153 15.5
4 2.0 0.2 5.0 Et(Ind).sub.2 ZrCl.sub.2 /2.5
2.5 3.9 67 0.48
163
298 13.6
5 2.0 0.2 2.5 Me.sub.2 Si(t-b-Cp)(Flu)ZrCl.sub.2 /5.0
2.5 3.9 54 0.31
161
224 16.4
__________________________________________________________________________
*Et(Ind).sub.2 ZrCl.sub.2 ethylenebis(indenyl)zirconium dichloride
Me.sub.2 Si(tb-Cp)(Flu)ZrCl.sub.2
dimethylsilyl(3t-butyl-cyclopentadienyl)(fluorenyl)zirconium dichloride
**obtained from GPC
Obviously, numerous modifications and variations of the present invention
are possible in light of the above teachings. It is therefore to be
understood that within the scope of the appended claims, the invention may
be practiced otherwise than as specifically described herein.
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