Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Plural component system comprising a - group i to iv metal...
Reexamination Certificate
1995-03-10
2002-05-21
Wood, Elizabeth D. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Plural component system comprising a - group i to iv metal...
C502S102000, C502S103000
Reexamination Certificate
active
06391817
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a catalyst system for the polymerization of olefins, more specifically, to the prepolymerization of supported catalyst systems and the use thereof
BACKGROUND OF THE INVENTION
Supported metallocene catalyst systems are used primarily in slurry, bulk liquid, and gas-phase polymerization processes. In general the catalyst systems and various methods to make them from transition metal components and activators are well known and exploited. These supported catalyst systems may be subjected to a prepolymerization step to enhance performance. Prepolymerization often confers the advantages of reduced fines formation, and superior product properties such as better granular morphology, higher bulk density, and improved granule flow properties. See EPA 447,071.
EPA 279,863 discloses a method for preparing a supported, prepolymerized metallocene catalyst system. The specific metallocene used is Cp
2
ZrCl
2
which is supported on silica and prepolymerized with ethylene. EPA 279,863 suggests using a molecular weight controlling agent such as hydrogen to produce a prepolymer having certain intrinsic viscosities. Applicants have found that certain low activity catalyst systems containing certain metallocenes such as Cp
2
ZrCl
2
may be supported and prepolymerized without fouling the prepolymerization reactor and without producing agglomerated catalyst particles.
However, other catlyst systems, such as high activity catalyst systems tend to foul the prepolymerization reactor and/or produce agglomerated catalyst system particles. It would be highly desirable to have an efficient method for using such catalyst systems without fouling and agglomeration in the prepolymerization reactor.
SUMMARY OF THE INVENTION
This invention relates to a method for yielding a non-fouling, non-agglomerating supported prepolymerized catalyst system. The invention involves use of hydrogen to control the fouling and agglomeration observed during prepolymerization of high activity supported catalyst systems which tend to foul during prepolymerization.
The invention relates to a method for controlling fouling in a prepolymerization reactor, said method comprising the step of combining:
(a) a supported metallocene catalyst system having an activity greater than about 100,000 g/g/hr.;
(b) at least one alpha olefin monomer feed; and,
(c) added hydrogen
under suitable prepolymerization reaction conditions. Ethylene and/or propylene are used as the preferred monomer feed for the prepolymerization of these supported catalysts.
Preferably, the metallocene catalyst system of this invention has a known tendency to foul a prepolymerization reactor and/or produce agglomerated catalyst system particles upon prepolymerization. Even more preferably, the metallocene catalyst system has an activity of from about 100,000 g polymer/g metallocene/hr to about 1,000,000 g polymer/g metallocene/hr. preferably greater than 150,000 g polymer/g metallocene/hr., even more preferably greater than 200,000 g polymer/g metallocene/hr. or from about 150,000 g polymer/g metallocene/hr to about 900,000 g polymer /g metallocene/hr., preferably from about 200,000 g polymer /g metallocene/hr to about 500,000 g polymer/g metallocene/hr.
Hydrogen is generally added in an amount of from about 0.1 to about 10 mole percent relative to the monomer feed rate. The monomer feed is generally added at a rate of about 0.1 to about 10 g olefin/g catalyst solid/hour. Suitable prepolymerization reaction conditions are typically run at low temperatures, for example in the range of from about −20° C. to about 40° C., preferably from about −10° C. to about 20° C., most preferably from about 0° C. to about 10° C.
Still further, the invention relates to use of the prepolymerized catalyst system formed by the method described herein and further relates to a method for controlling agglomermation of catalyst particles during the prepolymerization procedure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Prepolymerization reactor fouling and catalyst agglomeration which are observed during the prepolymerization of some metallocene catalyst systems, particularly high activity metallocene catalyst systems, can be minimized or eliminated by the use of hydrogen during prepolymerization. In a preferred embodiment, a supported metallocene catalyst system having high activity, monomer feed containing at least one alpha olefin, and added hydrogen are combined in a prepolymerization reactor, under suitable prepolymerization reaction conditions to control fouling and agglomeration of the supported catalyst system during prepolymerization. A further embodiment of the invention relates to the use of the prepolymerized supported catalyst system prepared by the method described herein for the polymerization of olefins to polyolefins.
For purposes of this application and claims, the phrase “added hydrogen” is defined to mean hydrogen which is purposely added during the prepolymerization reaction. Hydrogen which may be generated in-situ is excluded from this definition. Fouling is defined occurs when material sticks to the walls of the reactor. Agglomeration occurs when the catalyst system particles stick to each other. Fouling and agglomeration may or may not occur together.
As used herein, “metallocene” and “metallocene catalyst component” mean those bulky ligand transition metal compounds represented by the formula:
Cp
m
MR
n
X
q
wherein Cp is a cyclopentadienyl ring or derivative thereof, M is a Group 4, 5,or 6 transition metal and/or a metal from the lanthanide or actinide series, R is a hydrocarbyl group or hydrocarboxy group having from 1 to 20 carbon atoms, X is a halogen, and m=1-3, n=0-3, q=0-3, and the sum of m+n+q is equal to the oxidation state of the transition metal. The metallocene may be bridged or unbridged, and include heteroatoms in the structure. In addition, one or more bulky ligands may be &tgr;-bonded to the transition metal atom. Other ligands may be bonded to the transition metal, for example, a leaving group, such as but not limited to hydrocarbyl, hydrogen or any other univalent anionic ligand. Non-limiting examples of metallocenes and metallocene catalyst systems are discussed in for example, U.S. Pat. Nos. 4,530,914, 4,952,716, 5,124,418, 4,808,561, 4,897,455, 5,278,264, 5,278,119, 5,304,614 all of which are herein fully incorporated by reference. Also, the disclosures of EP-A-0 129 368, EP-A-0 591 756, EP-A-0 520 732, EP-A-0 420 436, WO 91/04257 WO 92/00333, WO 93/08221, and WO 93/08199 are all fully incorporated herein by reference. The preferred transition metal component of the catalyst system of the invention are those of Group 4, particularly, zirconium, titanium and hafnium. The transition metal may be in any oxidation state, preferably +3 or +4 or a mixture thereof.
Preferred metallocenes comprise a Group 4, 5, or 6 transition metal, biscyclopentadienyl derivatives, preferably bridged bis-indenyl metallocene components having the following general structure:
wherein M
1
is a metal of Group 4, 5, or 6 of the Periodic Table, for example titanium, zirconium, hafnium, vanadium niobium, tantalum, chromium, molybdenum and tungsten, preferably, zirconium, hafnium and titanium, most preferably zirconium;
R
1
and R
2
are identical or different, are one of a hydrogen atom, a C
1
-C
10
alkyl group, preferably a C
1
-C
3
alkyl group, a C
1
-C
10
alkoxy group, preferably a C
1
-C
3
alkoxy group, a C
6
-C
10
aryl group, preferably a C
6
-C
8
aryl group, a C
6
-C
10
aryloxy group, preferably a C
6
-C
8
aryloxy group, a C
2
-C
10
alkenyl group, preferably a C
2
-C
4
alkenyl group, a C
7
-C
40
arylalkyl group, preferably a C
7
-C
10
arylalkyl group, a C
7
-C
40
alkylaryl group, preferably a C
7
-C
12
alkylaryl group, a C
8
-C
40
arylalkenyl group, preferably a C
8
-C
12
arylalkenyl group, or a halogen atom, preferably chlorine;
R
3
and R
4
are hydrogen atoms;
R
5
and R
6
are identical or different, preferably identical, are one of a h
ExxonMobil Chemical Patents Inc.
Faulkner Kevin M.
Miller Douglas W.
Schmidt Paige
Wood Elizabeth D.
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