Additives to chromium catalyst mix tank
Systems and methods for the maintenance of active chromium-based catalysts and their use in polymerization processes are described. In one embodiment, a system for the introduction of multiple polymerization components to activate a chromium based catalyst within a mix tank is described. Other described features may include materials and methods to purify the liquid medium of a catalyst slurry so that the catalyst slurry maintains a high level of activity. The active chromium-based catalyst may provide polyolefins with a number of desirable properties in a reliable, consistent, and predictable manner.
1. A method of preparing a catalyst slurry as a supply for a polymerization reactor comprising the acts of:
combining, at least one chromium-based olefin polymerization catalyst and at least one additive capable of increasing an activity of the chromium-based olefin polymerization catalyst within a liquid medium to form a catalyst slurry;
wherein the combining results in contacting the at least one chromium-based olefin polymerization catalyst and the at least one additive under non-polymerization conditions in a mix tank upstream of a run tank; and
directing the catalyst slurry to the run tank for storage or eventual supply to a polymerization reactor.
2. The method of claim 1 , wherein the at least one chromium-based olefin polymerization catalyst is chromium oxide on a solid support;
wherein the solid support comprises silica, alumina, silica-titania, aluminophosphates, clays, or mixtures thereof.
3. The method of claim 1 , wherein the at least one additive comprises one or more metal alkyl cocatalysts selected from alkyl-containing derivatives of at least one of aluminum, boron, magnesium, zinc, and lithium, or any combination thereof.
4. The method of claim 1 , wherein the at least one additive comprises a Lewis acid and the liquid medium comprises a reducing agent.
5. The method of claim 4 , wherein the Lewis acid comprises a SSA comprising at least one of:
halided or sulfated alumina, silica, titania, zirconia, boria, aluminophosphate, or any combination thereof.
6. The method of claim 1 , wherein the liquid medium comprises a reducing agent; and
wherein the at least one additive comprises 4 Å molecular sieves, zeolites, silica-alumina, silica-titania, silica-zirconia, charcoal, clay, or any combination thereof.
7. The method of claim 1 , wherein the catalyst to additive ratio is between 0.1 to 10 and 0.5 to 3.
8. A method of preparing a catalyst slurry comprising the acts of:
contacting, under non-polymerization conditions in a mix tank, at least one chromium-based olefin polymerization catalyst, and a liquid medium comprising a reducing agent to produce a primary catalyst slurry comprising catalyst poisons; and
passing a liquid of the primary catalyst slurry through one or more vessels comprising a porous medium capable of removing the catalyst poisons from the liquid.
9. The method of claim 8 , wherein the liquid of the catalyst slurry is returned to the mix tank after treatment.
10. The method of claim 8 , wherein the liquid of the catalyst slurry is used for flush points to a polymerization reactor and replaced in the mix tank with fresh liquid to maintain a desired slurry concentration.
11. The method of claim 8 , wherein the at least one chromium-based olefin polymerization catalyst is chromium oxide on a solid support;
wherein the solid support comprises silica, alumina, silica-titania, aluminophosphates, clays, or mixtures thereof.
12. The method according to claim 8 , wherein the porous medium comprises halided or sulfated alumina, silica, titania, zirconia, boria, aluminophosphate, zeolites, silica-alumina, silica-titania, silica-zirconia, charcoal, clay or any combination thereof.
13. The method according to claim 8 , wherein the reducing agent comprises isobutane, substituted and unsubstituted alkanes, toluene, olefins, and alkynes, or any combination thereof.
14. The method according to claim 8 , wherein the reducing agent comprises 1-hexene.
15. The method according to claim 8 , wherein the one or more vessels comprise a fixed bed having the porous medium.
16. The method according to claim 8 , wherein the one or more vessels comprise a column having the porous medium.
17. The method according to claim 8 , wherein the porous medium comprises a SSA or Lewis acid.