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 process for preparing a supported chromium catalyst, the process comprising:
(i) contacting a support comprising a silica-coated alumina containing at least 30 wt. % silica with a chromium-containing compound in a liquid, and drying; and
(ii) calcining at a peak temperature of at least 650° C., optionally in an oxidizing atmosphere, to form the supported chromium catalyst;
wherein:
the supported chromium catalyst does not contain fluorine;
at least 65 wt. % of the chromium of the supported chromium catalyst is in an oxidation state of +6;
a catalyst activity of the supported chromium catalyst is greater than that of an otherwise identical catalyst obtained using a peak calcining temperature of 625° C. or less, under the same polymerization conditions; and/or
a catalyst activity of the supported chromium catalyst is greater than that of an otherwise identical catalyst obtained using a silica-coated alumina containing 28 wt. % silica or less, under the same polymerization conditions.
2. The process of claim 1 , wherein:
the silica-coated alumina contains from about 35 to about 95 wt. % silica;
the peak temperature is in a range from 650° C. to about 900° C.; and
calcining is performed in the oxidizing atmosphere.
3. The process of claim 1 , wherein:
drying comprises spray drying; and
the supported chromium catalyst contains from about 0.2 to about 10 wt. % chromium.
4. The process of claim 1 , wherein:
the supported chromium catalyst is a chromium/silica-coated alumina containing from about 35 to about 45 wt. % silica; and
the peak temperature is in a range from about 700° C. to about 900° C.
5. The process of claim 1 , wherein:
the supported chromium catalyst contains from about 0.5 to about 2.5 wt. % chromium;
the silica-coated alumina contains from about 70 to about 95 wt. % silica; and
the peak temperature is in a range from 650° C. to about 900° C.
6. The process of claim 1 , wherein the supported chromium catalyst comprises chromium/sulfated silica-coated alumina, chromium/phosphated silica-coated alumina, or chromium/titanated silica-coated alumina.
7. The process of claim 1 , wherein:
the silica-coated alumina contains from about 35 to about 95 wt. % silica;
the peak temperature is in a range from 650° C. to about 900° C.;
calcining is performed in the oxidizing atmosphere; and
the supported chromium 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.
8. The process of claim 7 , wherein:
the supported chromium catalyst is a chromium/silica-coated alumina containing from about 35 to about 45 wt. % silica; and
the supported chromium catalyst contains from about 0.5 to about 5 wt. % chromium.
9. The process of claim 7 , wherein:
the supported chromium catalyst is a chromium/silica-coated alumina containing from about 70 to about 95 wt. % silica; and
the supported chromium catalyst contains from about 0.5 to about 5 wt. % chromium.
10. A process for preparing a supported chromium catalyst, the process comprising contacting a support comprising a silica-coated alumina with a chromium-containing compound while calcining at a peak temperature of at least 650° C., optionally in an oxidizing atmosphere, to form the supported chromium catalyst,
wherein the silica-coated alumina contains at least 30 wt. % silica; and
wherein the supported chromium catalyst does not contain fluorine and does not contain vanadium, and at least 65 wt. % of the chromium of the supported chromium catalyst is in an oxidation state of +6.
11. The process of claim 10 , wherein:
the silica-coated alumina contains from about 35 to about 95 wt. % silica;
the peak temperature is in a range from 650° C. to about 900° C.; and
calcining is performed in the oxidizing atmosphere.
12. The process of claim 11 , wherein:
drying comprises spray drying; and
the supported chromium catalyst contains from about 0.2 to about 10 wt. % chromium.
13. The process of claim 10 , wherein:
the supported chromium catalyst is a chromium/silica-coated alumina containing from about 35 to about 45 wt. % silica; and
the peak temperature is in a range from about 700° C. to about 900° C.
14. The process of claim 10 , wherein:
the supported chromium catalyst contains from about 0.5 to about 2.5 wt. % chromium;
the silica-coated alumina contains from about 70 to about 95 wt. % silica; and
the peak temperature is in a range from 650° C. to about 900° C.
15. The process of claim 10 , wherein the supported chromium catalyst comprises chromium/sulfated silica-coated alumina, chromium/phosphated silica-coated alumina, or chromium/titanated silica-coated alumina.
16. The process of claim 10 , wherein:
a catalyst activity of the supported chromium catalyst is greater than that of an otherwise identical catalyst obtained using a peak calcining temperature of 625° C. or less, under the same polymerization conditions; and/or
a catalyst activity of the supported chromium catalyst is greater than that of an otherwise identical catalyst obtained using a silica-coated alumina containing 28 wt. % silica or less, under the same polymerization conditions.
17. The process of claim 10 , wherein:
the silica-coated alumina contains from about 35 to about 95 wt. % silica;
the peak temperature is in a range from 650° C. to about 900° C.;
calcining is performed in the oxidizing atmosphere; and
the supported chromium 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.
18. The process of claim 17 , wherein:
the supported chromium catalyst is a chromium/silica-coated alumina containing from about 35 to about 45 wt. % silica; and
the supported chromium catalyst contains from about 0.5 to about 5 wt. % chromium.
19. The process of claim 17 , wherein:
the supported chromium catalyst is a chromium/silica-coated alumina containing from about 70 to about 95 wt. % silica; and
the supported chromium catalyst contains from about 0.5 to about 5 wt. % chromium.