Polymerization catalysts and polymers
A method comprising contacting a support material with a transition metal compound to produce a mixture; thermally treating the mixture in the presence of oxygen at a temperature in a range of from about 100° C. to about 500° C. for a period of from about 1 hour to about 10 hours, wherein at least a portion of the transition metal sublimes onto the support material to produce a support material comprising a dispersed transition metal; and thermally treating the support material comprising the dispersed transition metal in an oxidizing atmosphere at a temperature in a range of from about 550° C. to about 900° C. for a period of from about 1 hour to about 10 hours to produce a polymerization catalyst.
1. A method comprising:
subjecting a support material to a first thermal treatment at a temperature in a range of from about 550° C. to about 900° C. for a period of from about 1 hour to about 10 hours to produce a thermally-treated support material;
cooling the thermally-treated support material to a temperature in the range of from about 100° C. to about 150° C.;
contacting the thermally-treated support material with chromium (III) acetylacetonate, which is in powder or crystal form, to produce a mixture; and
subjecting the mixture in the presence of oxygen to a second thermal treatment at a temperature in a range of from about 100° C. to about 500° C. for a period of from about 1 hour to about 10 hours, wherein at least a portion of the chromium(III) acetylacetonate sublimes onto the support material to produce a polymerization catalyst and wherein the second thermal treatment occurs at a temperature that is less than the first thermal treatment.
2. The method of claim 1 wherein the support material comprises silica, alumina, silica-titania, aluminophosphate, zirconia, titania, or combinations thereof.
3. The method of claim 1 wherein support material comprises silica-titania.
4. The method of claim 1 wherein chromium is present in the polymerization catalyst in an amount of from about 0.5 wt. % to about 2 wt. % based on the weight of the support material.
5. The method of claim 1 wherein a percentage conversion of chromium in the (+3) oxidation state to chromium in the (+6) oxidation state for the polymerization catalyst is from about 20% to about 100% at a temperature range of from about 200° C. to about 600° C.
6. The method of claim 1 further comprising producing a polymer by contacting the polymerization catalyst with an olefin monomer and recovering the polymer.
7. The method of claim 6 wherein the polymer has a melt index that is from about 0.5 g/10 min to about 5 g/10 min.
8. The method of claim 6 wherein the polymer has a high load melt index that is from about 50 g/10 min to about 200 g/10 min.
9. The method of claim 6 wherein the polymer comprises polyethylene.
10. The method of claim 1 wherein the support material has an average particle size of from about 25 μm to about 500 μm.