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 . A phosphated or titanated chromium/silica-coated alumina catalyst comprising:
from about 0.01 to about 20 wt. % chromium and less than 0.05 wt. % fluorine, based on the weight of the catalyst;
from about 3 to about 30 wt. % phosphate or from about 0.5 to about 20 wt. % titanium, based on the weight of the catalyst; and
a silica-coated alumina containing at least about 30 wt. % silica, 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 catalyst 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 catalyst 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 catalyst 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 catalyst of claim 1 , wherein the catalyst contains from about 0.5 to about 5 wt. % chromium.
6 . The catalyst of claim 1 , wherein a catalyst activity of the catalyst is greater than about 4000 grams of polyethylene per gram of the catalyst per hour, under slurry polymerization conditions, with no co-catalyst, using isobutane as a diluent, and with a polymerization temperature of 105° C. and a reactor pressure of 550 psig.
7 . An olefin polymerization process comprising contacting the catalyst of claim 1 with an olefin monomer and an optional olefin comonomer in a polymerization reactor system under polymerization conditions to produce an olefin polymer.
8 . The catalyst of claim 1 , wherein:
the silica-coated alumina contains from about 35 to about 95 wt. % silica; and
the catalyst contains from about 0.5 to about 5 wt. % chromium.
9 . The catalyst of claim 8 , wherein the catalyst has an average (d50) particle size in a range from about 25 to about 250 microns.
10 . The catalyst of claim 8 , wherein at least about 65 wt. % of the chromium is present in an oxidation state of +6 (VI).
11 . The catalyst of claim 8 , wherein:
the catalyst is a chromium/phosphated silica-coated alumina catalyst; and
the catalyst contains from about 3 to about 30 wt. % phosphate.
12 . The catalyst of claim 11 , wherein the silica-coated alumina contains from about 35 to about 45 wt. % silica.
13 . The catalyst of claim 11 , wherein the silica-coated alumina contains from about 70 to about 95 wt. % silica.
14 . The catalyst of claim 11 , 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.
15 . The catalyst of claim 14 , wherein the catalyst contains from about 3 to about 25 wt. % phosphate.
16 . The catalyst of claim 8 , wherein:
the catalyst is a chromium/titanated silica-coated alumina catalyst; and
the catalyst contains from about 0.5 to about 20 wt. % titanium.
17 . The catalyst of claim 16 , wherein the silica-coated alumina contains from about 35 to about 45 wt. % silica.
18 . The catalyst of claim 16 , wherein the silica-coated alumina contains from about 70 to about 95 wt. % silica.
19 . The catalyst of claim 16 , 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.
20 . The catalyst of claim 19 , wherein the catalyst contains from about 1 to about 15 wt. % titanium.