Controlling long-chain branch content with dual activator-supports
Methods for controlling the long chain branch content of ethylene homopolymers and copolymers produced in a polymerization process include the steps of contacting a metallocene compound, an organoaluminum compound, a high LCB activator-support, and a low LCB activator-support to form a catalyst composition, contacting the catalyst composition with ethylene and an optional olefin comonomer in a polymerization reactor system under polymerization conditions to produce an ethylene polymer having a LCB content, and controlling the relative amount of the high LCB activator-support and the low LCB activator-support in the catalyst composition to adjust the LCB content of the ethylene polymer.
1. A polymerization process comprising:
(a) contacting a metallocene compound, an organoaluminum compound, a first activator-support, and a second activator-support to form a catalyst composition; wherein:
the first activator-support comprises a fluorided silica-coated alumina; and
the second activator-support comprises a sulfated bentonite;
(b) contacting the catalyst composition with ethylene and an optional olefin comonomer in a polymerization reactor system under polymerization conditions to produce an ethylene polymer having a long chain branch (LCB) content; and
(c) controlling a relative amount of the first activator-support and the second activator-support in the catalyst composition in step (a) to adjust the LCB content of the ethylene polymer.
2. The process of claim 1 , wherein:
step (a) comprises pre-contacting the organoaluminum compound, the first activator-support, and the second activator-support, and then contacting the metallocene compound, to form the catalyst composition; or
step (a) comprises contacting the organoaluminum compound, the first activator-support, the second activator-support, and the metallocene compound substantially contemporaneously to form the catalyst composition.
3. The process of claim 1 , wherein the polymerization reactor system comprises a slurry reactor, a gas-phase reactor, a solution reactor, or a combination thereof.
4. The process of claim 1 , wherein the metallocene compound comprises:
a bridged zirconium or hafnium based metallocene compound with a cyclopentadienyl group and a fluorenyl group;
a bridged zirconium based metallocene compound containing two cyclopentadienyl groups, two indenyl groups, or a cyclopentadienyl and an indenyl group;
an unbridged zirconium or hafnium based metallocene compound containing two cyclopentadienyl groups, two indenyl groups, or a cyclopentadienyl and an indenyl group; or
any combination thereof.
5. The process of claim 1 , wherein the metallocene compound comprises:
(1) rac-ethylene-bis(1-indenyl) zirconium dichloride;
(2) methyl(buten-3-yl)methylidene(η5-cyclopentadien-1-ylidene)(η5-2,7-di-tert-butylfluoren-9-ylidene) zirconium dichloride;
(3) diphenylmethylidene[η5-[3-(pent-4-enyl)cyclopentadien-1-ylidene]][η5-(2,7-di-tert-butylfluoren-9-ylidene)] hafnium dichloride;
(4) (n-butylcyclopentadienyl)(1-allylindenyl)zirconium dichloride;
(5) rac-dimethylsilylbis(1-indenyl)zirconium dichloride;
(6) 1-ethylpropylidene[(η5-cyclopentadien-1-ylidene)(η5-(3-propyl)inden-1-ylidene)] zirconium dichloride; or
any combination thereof.
6. The process of claim 1 , wherein:
a weight ratio of the first activator-support to the second activator-support is in a range from 10:1 to 1:10; and
the ethylene polymer has from 1 to 150 LCBs per million total carbon atoms.
7. The process of claim 1 , wherein the organoaluminum compound comprises trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-n-butylaluminum, triisobutylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum, diisobutylaluminum hydride, diethylaluminum ethoxide, diethylaluminum chloride, or any combination thereof.
8. The process of claim 1 , wherein the ethylene polymer comprises an ethylene homopolymer, an ethylene/1-butene copolymer, an ethylene/1-hexene copolymer, an ethylene/1-octene copolymer, or any combination thereof.
9. The process of claim 8 , further comprising the steps of:
measuring the LCB content of the ethylene polymer; and
adjusting the relative amount of the first activator-support and the second activator-support in the catalyst composition based on a difference between the measured LCB content and a target LCB content.
10. The process of claim 8 , wherein:
a weight ratio of the metallocene compound to the first activator-support and the second activator-support is in a range from 1:1 to 1:100,000; and
a molar ratio of the organoaluminum compound to the metallocene compound is in a range from 1:1 to 1000:1.
11. The process of claim 8 , wherein a weight ratio of the first activator-support to the second activator-support is in a range from 10:1 to 1:10.
12. The process of claim 8 , wherein two or more metallocene compounds are contacted in step (a) to form the catalyst composition.
13. The process of claim 8 , wherein:
the fluorided silica-coated alumina comprises from 2 to 15 wt. % fluoride.
14. The process of claim 13 , wherein the fluorided silica-coated alumina comprises from 15 to 60 wt. % silica, based on a weight of silica-coated alumina.