Processes for preparing metallocene-based catalyst systems

1. A process to produce a dual metallocene catalyst composition, the process comprising:

(A) contacting an activator-support and an organoaluminum compound for a first period of time to form a precontacted mixture;

(B) contacting the precontacted mixture with a first metallocene compound for a second period of time to form a first mixture; and

(C) contacting the first mixture with a second metallocene compound for a third period of time to form the dual metallocene catalyst composition;

wherein an activity of the dual metallocene catalyst composition is greater than that of a dual catalyst system obtained by combining the activator-support, a mixture of the first metallocene compound and the second metallocene compound, and the organoaluminum compound, under the same polymerization conditions.

2. The process of claim 1 , wherein:

the activator-support comprises a fluorided solid oxide, a sulfated solid oxide, a phosphated solid oxide, or a combination thereof;

the organoaluminum compound comprises trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-n-butylaluminum, triisobutylaluminum, or any combination thereof;

the first metallocene compound comprises a bridged zirconium or hafnium based metallocene compound with a cyclopentadienyl group and a fluorenyl group; and

the second metallocene compound comprises an unbridged zirconium or hafnium based metallocene compound containing two cyclopentadienyl groups, two indenyl groups, or a cyclopentadienyl and an indenyl group.

3. The process of claim 2 , wherein:

the activator-support comprises sulfated alumina;

the first metallocene compound is less reactive with the activator-support than the second metallocene compound; and

a weight ratio of the first metallocene compound to the second metallocene compound is in a range from about 1:10 to about 10:1.

4. The process of claim 1 , wherein an activity of the dual metallocene catalyst composition is greater than that of a catalyst system obtained by first combining the activator-support and a mixture of the first metallocene compound and the second metallocene compound, and then combining the organoaluminum compound, under the same polymerization conditions.

5. The process of claim 1 , wherein:

the activator-support comprises a sulfated solid oxide and/or a fluorided solid oxide;

the first metallocene compound comprises a bridged metallocene compound and is less reactive with the activator-support than the second metallocene compound;

the second metallocene compound comprises an unbridged metallocene compound; and

a weight ratio of the first metallocene compound to the second metallocene compound is in a range from about 1:10 to about 10:1.

6. The process of claim 5 , wherein the organoaluminum compound comprises trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-n-butylaluminum, triisobutylaluminum, or any combination thereof.

7. The process of claim 1 , wherein the first period of time is from about 30 seconds to about 6 hours.

8. An olefin polymerization process, the olefin polymerization process comprising:

(A) contacting an activator-support and an organoaluminum compound for a first period of time to form a precontacted mixture;

(B) contacting the precontacted mixture with a first metallocene compound for a second period of time to form a first mixture;

(C) contacting the first mixture with a second metallocene compound for a third period of time to form the dual metallocene catalyst composition; and

(D) contacting the dual metallocene catalyst composition with an olefin monomer and an optional olefin comonomer in a polymerization reactor system under polymerization conditions to produce an olefin polymer;

wherein a Mw of the olefin polymer produced by the polymerization process is greater than a Mw of an olefin polymer produced under the same polymerization conditions using a dual catalyst system obtained by combining the activator-support, a mixture of the first metallocene compound and the second metallocene compound, and the organoaluminum compound.

9. The olefin polymerization process of claim 8 , wherein:

the polymerization reactor system comprises a slurry reactor, a gas-phase reactor, a solution reactor, or a combination thereof;

the dual metallocene catalyst composition is contacted with ethylene and an olefin comonomer comprising a C 3 -C 10 alpha-olefin; and

the first metallocene compound produces a higher molecular weight component of the olefin polymer than the second metallocene compound.

10. The olefin polymerization process of claim 8 , wherein:

the activator-support comprises a fluorided solid oxide, a sulfated solid oxide, a phosphated solid oxide, or a combination thereof; and

the olefin polymer comprises an ethylene homopolymer, an ethylene/1-butene copolymer, an ethylene/1-hexene copolymer, an ethylene/1-octene copolymer, or a combination thereof.

11. The olefin polymerization process of claim 10 , wherein:

the activator-support comprises fluorided silica-alumina, fluorided silica-coated alumina, sulfated alumina, phosphated alumina, or a combination thereof;

the organoaluminum compound comprises trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-n-butylaluminum, triisobutylaluminum, or any combination thereof;

the first metallocene compound comprises a bridged zirconium or hafnium based metallocene compound with a cyclopentadienyl group and a fluorenyl group; and

the second metallocene compound comprises an unbridged zirconium or hafnium based metallocene compound containing two cyclopentadienyl groups, two indenyl groups, or a cyclopentadienyl and an indenyl group.

12. The process of claim 1 , wherein the activity of the dual metallocene catalyst composition is from about 15% to about 1000% greater than that of the catalyst system obtained by combining the activator-support, a mixture of the first metallocene compound and the second metallocene compound, and the organoaluminum compound, under the same polymerization conditions.

13. The process of claim 4 , wherein the activity of the dual metallocene catalyst composition is from about 15% to about 1000% greater than that of the catalyst system obtained by first combining the activator-support and a mixture of the first metallocene compound and the second metallocene compound, and then combining the organoaluminum compound, under the same polymerization conditions.

14. The olefin polymerization process of claim 10 , wherein an activity of the dual metallocene catalyst composition is greater than that of a dual catalyst system obtained by combining the activator-support, a mixture of the first metallocene compound and the second metallocene compound, and the organoaluminum compound, under the same polymerization conditions.

15. The olefin polymerization process of claim 10 , wherein an activity of the dual metallocene catalyst composition is greater than that of a catalyst system obtained by first combining the activator-support and a mixture of the first metallocene compound and the second metallocene compound, and then combining the organoaluminum compound, under the same polymerization conditions.

16. An olefin polymerization process, the olefin polymerization process comprising:

(A) contacting an activator-support and an organoaluminum compound for a first period of time to form a precontacted mixture;

(B) contacting the precontacted mixture with a first metallocene compound for a second period of time to form a first mixture;

(C) contacting the first mixture with a second metallocene compound for a third period of time to form the dual metallocene catalyst composition; and

(D) contacting the dual metallocene catalyst composition with an olefin monomer and an optional olefin comonomer in a polymerization reactor system under polymerization conditions to produce an olefin polymer, wherein:

the olefin polymer comprises a higher molecular weight component and a lower molecular weight component; and

a ratio of the higher molecular weight component to the lower molecular weight component of the olefin polymer produced by the polymerization process is greater than a ratio of the higher molecular weight component to the lower molecular weight component of an olefin polymer produced under the same polymerization conditions using a dual catalyst system obtained by combining the activator-support, a mixture of the first metallocene compound and the second metallocene compound, and the organoaluminum compound.

17. The olefin polymerization process of claim 16 , wherein:

the olefin polymer comprises an ethylene homopolymer, an ethylene/1-butene copolymer, an ethylene/1-hexene copolymer, an ethylene/1-octene copolymer, or a combination thereof; and

the activator-support comprises a fluorided solid oxide, a sulfated solid oxide, a phosphated solid oxide, or a combination thereof.

18. The olefin polymerization process of claim 16 , wherein the first metallocene compound produces the higher molecular weight component.

19. The olefin polymerization process of claim 18 , wherein:

the activator-support comprises a fluorided solid oxide, a sulfated solid oxide, a phosphated solid oxide, or a combination thereof;

the organoaluminum compound comprises trimethylaluminum, triethylaluminum, tri-n-propylaluminum, tri-n-butylaluminum, triisobutylaluminum, or any combination thereof;

the first metallocene compound comprises a bridged zirconium or hafnium based metallocene compound with a cyclopentadienyl group and a fluorenyl group; and

the second metallocene compound comprises an unbridged zirconium or hafnium based metallocene compound containing two cyclopentadienyl groups, two indenyl groups, or a cyclopentadienyl and an indenyl group.

20. The olefin polymerization process of claim 16 , wherein the polymerization reactor system comprises a slurry reactor, a gas-phase reactor, a solution reactor, or a combination thereof.