Modified supported chromium catalysts and ethylene-based polymers produced therefrom
Supported chromium catalysts with an average valence less than +6 and having a hydrocarbon-containing or halogenated hydrocarbon-containing ligand attached to at least one bonding site on the chromium are disclosed, as well as ethylene-based polymers with terminal alkane, aromatic, or halogenated hydrocarbon chain ends. Another ethylene polymer characterized by at least 2 wt. % of the polymer having a molecular weight greater than 1,000,000 g/mol and at least 1.5 wt. % of the polymer having a molecular weight less than 1000 g/mol is provided, as well as an ethylene homopolymer with at least 3.5 methyl short chain branches and less than 0.6 butyl short chain branches per 1000 total carbon atoms.
1. A polymerization process comprising:
(I) irradiating a hydrocarbon reductant and a supported chromium catalyst comprising chromium in a hexavalent oxidation state with a light beam at a wavelength in the UV-visible spectrum to convert at least a portion of the supported chromium catalyst to form a reduced chromium catalyst; and
(II) contacting the reduced chromium catalyst and an optional co-catalyst with ethylene in a polymerization reactor system under polymerization reaction conditions comprising an ethylene pressure of less than or equal to 30 psig to produce an ethylene homopolymer;
wherein the ethylene homopolymer has a number of methyl short chain branches (SCB's) in a range from about 3.5 to about 15 per 1000 total carbon atoms.
2. The process of claim 1 , wherein the number of methyl SCB's is in a range from about 5 to about 10 per 1000 total carbon atoms.
3. The process of claim 1 , wherein the ethylene homopolymer has a number of butyl SCB's of less than or equal to about 0.6 per 1000 total carbon atoms.
4. The process of claim 3 , wherein the number of butyl SCB's is less than or equal to about 0.2 per 1000 total carbon atoms.
5. The process of claim 3 , wherein the ethylene homopolymer has a ratio of vinyl chain ends to saturated chain ends per 1000 total carbon atoms of less than or equal to about 0.3.
6. The process of claim 5 , wherein the ratio of vinyl chain ends to saturated chain ends per 1000 total carbon atoms is less than or equal to about 0.1.
7. The process of claim 5 , wherein the supported chromium catalyst comprises a solid oxide and from about 0.01 to about 20 wt. % chromium.
8. The process of claim 7 , wherein the solid oxide comprises silica.
9. The process of claim 8 , wherein the supported chromium catalyst further comprises from about 1 to about 10 wt. % titanium.
10. The process of claim 1 , wherein the polymerization reaction conditions further comprise a polymerization temperature in a range from 0 to 80° C.
11. The process of claim 1 , wherein the ethylene homopolymer has:
a ratio of Mw/Mn in a range from about 4 to about 10; or
a ratio of Mz/Mw in a range from about 2.5 to about 7; or
a Mw in a range from about 30,000 to about 200,000 g/mol; or
a density in a range from about 0.93 to about 0.96 g/cm 3 ; or
a number of ethyl SCB's in a range from about 0.8 to about 5 per 1000 total carbon atoms; or
any combination thereof.
12. A polymerization process comprising:
contacting a supported chromium catalyst and an optional co-catalyst with ethylene in a polymerization reactor system under polymerization reaction conditions comprising an ethylene pressure of less than or equal to 30 psig to produce an ethylene homopolymer;
wherein the supported chromium catalyst has an average valence of less than or equal to about 4; and
wherein the ethylene homopolymer has number of methyl short chain branches (SCB's) in a range from about 3.5 to about 15 per 1000 total carbon atoms.
13. The process of claim 12 , wherein the ethylene homopolymer has a number of butyl SCB's of less than or equal to about 0.6 per 1000 total carbon atoms.
14. The process of claim 13 , wherein the ethylene homopolymer has a ratio of vinyl chain ends to saturated chain ends per 1000 total carbon atoms of less than or equal to about 0.3.
15. The process of claim 14 , wherein:
the number of methyl SCB's is in a range from about 5 to about 10 per 1000 total carbon atoms; or
the number of butyl SCB's is less than or equal to about 0.2 per 1000 total carbon atoms; or
the ratio of vinyl chain ends to saturated chain ends per 1000 total carbon atoms is less than or equal to about 0.1; or
any combination thereof.
16. The process of claim 14 , wherein the supported chromium catalyst comprises a solid oxide and from about 0.01 to about 20 wt. % chromium.
17. The process of claim 16 , wherein the solid oxide comprises silica.
18. The process of claim 17 , wherein the supported chromium catalyst further comprises from about 1 to about 10 wt. % titanium.
19. The process of claim 12 , wherein:
the supported chromium catalyst is a supported chromium (II) catalyst; and
the polymerization reaction conditions further comprise a polymerization temperature in a range from 0 to 80° C.
20. The process of claim 12 , wherein the ethylene homopolymer has:
a ratio of Mw/Mn in a range from about 4 to about 10; or
a ratio of Mz/Mw in a range from about 2.5 to about 7; or
a Mw in a range from about 30,000 to about 200,000 g/mol; or
a density in a range from about 0.93 to about 0.96 g/cm 3 ; or
a number of ethyl SCB's in a range from about 0.8 to about 5 per 1000 total carbon atoms; or
any combination thereof.
21. The process of claim 12 , wherein the process further comprises a step of contacting a supported catalyst comprising chromium in a hexavalent oxidation state with carbon monoxide (CO) to produce the supported chromium catalyst.