Methods for making supported chromium catalysts with increased polymerization activity
Methods for making a supported chromium catalyst are disclosed, and can comprise contacting a silica-coated alumina containing at least 30 wt. % silica with a chromium-containing compound in a liquid, drying, and calcining in an oxidizing atmosphere at a peak temperature of at least 650° C. to form the supported chromium catalyst. The supported chromium catalyst can contain from 0.01 to 20 wt. % chromium, and typically can have a pore volume from 0.5 to 2 mL/g and a BET surface area from 275 to 550 m 2 /g. The supported chromium catalyst subsequently can be used to polymerize olefins to produce, for example, ethylene-based homopolymers and copolymers having high molecular weights and broad molecular weight distributions.
1. An olefin polymerization process comprising contacting a catalyst with an olefin monomer and an optional olefin comonomer in a polymerization reactor system under polymerization conditions to produce an olefin polymer; wherein the catalyst comprises:
from about 0.01 to about 20 wt. % chromium, based on the weight of the catalyst; and
a silica-coated alumina containing at least about 30 wt. % silica and less than 0.05 wt. % fluorine, based on the weight of the silica-coated alumina; wherein the catalyst has:
a pore volume from about 0.5 to about 2 mL/g; and
a BET surface area from about 275 to about 550 m 2 /g.
2. The olefin polymerization process of claim 1 , wherein:
the silica-coated alumina contains from about 35 to about 95 wt. % silica; and
the catalyst contains from about 0.2 to about 10 wt. % chromium.
3. The olefin polymerization process of claim 1 , wherein:
the silica-coated alumina contains from about 35 to about 45 wt. % silica; or
the silica-coated alumina contains from about 70 to about 95 wt. % silica.
4. The olefin polymerization process of claim 1 , wherein:
the pore volume is from about 1 to about 1.5 mL/g; and
the BET surface area is from about 300 to about 525 m 2 /g.
5. The olefin polymerization process of claim 1 , wherein the catalyst contains from about 0.5 to about 5 wt. % chromium.
6. The olefin polymerization process of claim 1 , wherein the catalyst has an average (d50) particle size in a range from about 25 to about 250 microns.
7. The olefin polymerization process of claim 6 , wherein the catalyst average (d50) particle size is in a range from about 30 to about 100 microns.
8. The olefin polymerization process of claim 1 , wherein the olefin monomer comprises ethylene.
9. The olefin polymerization process of claim 1 , wherein the catalyst is contacted with ethylene and an olefin comonomer comprising a C 3 -C 10 alpha-olefin.
10. The olefin polymerization process of claim 1 , wherein the polymerization reactor system comprises a slurry reactor, a gas-phase reactor, a solution reactor, or a combination thereof.
11. The olefin polymerization process of claim 1 , wherein the polymerization reactor system comprises a loop slurry reactor.