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 polymerizing olefins, comprising:
combining, within a liquid medium under non-polymerization conditions in a mix tank, at least one chromium-based olefin polymerization catalyst and at least one additive capable of increasing the activity of the at least one chromium-based olefin polymerization catalyst such that the chromium-based olefin polymerization catalyst and the at least one additive contact to produce a contact product, wherein the liquid medium comprises a reducing agent and the at least one additive comprises zeolites, silica-alumina, silica-titania, silica-zirconia, clay, or any combination thereof; and
introducing the contact product, as needed, into a polymerization reactor containing at least one olefin monomer under polymerization conditions.
2. The method of claim 1 , wherein the at least one additive further comprises a metal alkyl co-catalyst comprising alkyl-containing derivatives of at least one of aluminum, boron, magnesium, zinc, and lithium, or any combination thereof.
3. The method of claim 1 , wherein the at least one olefin monomer comprises ethylene.
4. The method of claim 1 , wherein the at least one chromium-based olefin polymerization catalyst is chromium oxide on a solid support, and wherein the solid support comprises silica, alumina, silica-titania, aluminophosphates, clays, or mixtures thereof.
5. The method of claim 1 , wherein the at least one additive further comprises a solid super acid (SSA), and wherein the ratio of SSA to chromium-based olefin polymerization catalyst is from 0.1 to 0.5 and the concentration of the reducing agent is from 1 to 10 mol %.
6. The method of claim 1 , wherein the at least one additive further comprises a solid oxide treated with an electron withdrawing substituent.
7. The method of claim 6 , wherein the electron withdrawing substituent is fluoride, chloride, bromide, phosphate, triflate, bisulfate, sulfate, fluorophosphate, or any combination thereof.
8. The method of claim 1 , wherein the at least one additive further comprises sulfated alumina, fluorided silica-alumina, fluorided alumina, fluorided silica-zirconia, or any combination thereof.
9. The method of claim 1 , comprising maintaining the at least one chromium-based olefin polymerization catalyst and the at least one additive within the liquid medium under non-polymerization conditions in the mix tank for between 12 hours and 5 days.
10. A liquid medium purification system, comprising:
a vessel;
an additive disposed within the vessel;
a mix tank fluidly connected to the vessel via a flow path arranged to facilitate flow of contents from the mix tank to the vessel, wherein the mix tank contains a catalyst slurry comprising a chromium-based olefin polymerization catalyst, a liquid medium, and a catalyst poison; and
wherein the additive disposed within the vessel comprises a solid oxide treated with an electron withdrawing substituent, and the additive is capable of absorbing the catalyst poison.
11. The liquid medium purification system of claim 10 , comprising a filter disposed within a line forming the flow path fluidly connecting the mix tank and the vessel, wherein the filter is capable of separating the catalyst from the liquid medium and the catalyst poison of the catalyst slurry.
12. The liquid medium purification system of claim 10 , comprising a bed disposed within the vessel, wherein the bed comprises the additive disposed within the vessel.
13. The liquid medium purification system of claim 10 , wherein the vessel is a column, and wherein the additive disposed within the vessel comprises a solid super acid (SSA) packed within the vessel.
14. The liquid medium purification system of claim 10 , wherein the solid oxide treated with an electron withdrawing substituent comprises any one or a combination of halided or sulfated alumina, silica, titania, zirconia, boria, aluminophosphates, or any combination thereof.
15. A polymerization system, comprising:
a mix tank holding a catalyst slurry under non-polymerization conditions, wherein the catalyst slurry comprises:
at least one chromium-based olefin polymerization catalyst;
a liquid medium; and
a catalyst poison;
a vessel disposed downstream of the mix tank;
and additive disposed within the vessel, wherein the additive comprises a solid oxide treated with an electron withdrawing substituent and is capable of absorbing the catalyst poison;
a polymerization reactor disposed downstream of the mix tank, wherein during operation of the system, the polymerization reactor receives the catalyst slurry and a feed of at least one olefin monomer, and subjects the catalyst slurry and the at least one olefin monomer to polymerization conditions.
16. The polymerization system of claim 15 , wherein the solid oxide treated with the electron withdrawing substituent comprises a solid super acid (SSA) and the liquid medium comprises a reducing agent, and wherein the concentration of the reducing agent is from 1 to 10 mol %.
17. The polymerization system of claim 16 , wherein the SSA comprises: halided or sulfated alumina, silica, titania, zirconia, boria, aluminophosphate, or any combination thereof.
18. The polymerization system of claim 15 , wherein the at least one olefin monomer comprises ethylene, 1-hexene, or a combination thereof.
19. A method of polymerizing olefins, comprising:
combining, within a liquid medium under non-polymerization conditions in a mix tank, at least one chromium-based olefin polymerization catalyst and at least one additive capable of increasing the activity of the at least one chromium-based olefin polymerization catalyst such that the chromium-based olefin polymerization catalyst and the at least one additive contact to produce a contact product, wherein the at least one additive comprises a solid oxide treated with an electron withdrawing substituent; and
introducing the contact product, as needed, into a polymerization reactor containing at least one olefin monomer under polymerization conditions.
20. The method of claim 19 , wherein the electron withdrawing substituent is fluoride, chloride, bromide, phosphate, triflate, bisulfate, sulfate, fluorophosphate, or any combination thereof.
21. The method of claim 19 , wherein the solid oxide treated with the electron withdrawing substituent comprises sulfated alumina, fluorided silica-alumina, fluorided alumina, fluorided silica-zirconia, or any combination thereof.