Preparation of large pore silicas and uses thereof in chromium catalysts for olefin polymerization
Silica composites and supported chromium catalysts having a bulk density of 0.08 to 0.4 g/mL, a total pore volume of 0.4 to 2.5 mL/g, a BET surface area of 175 to 375 m 2 /g, and a peak pore diameter of 10 to 80 nm are disclosed herein. These silica composites and supported chromium catalysts can be formed by combining two silica components. The first silica component can be irregularly shaped, such as fumed silica, and the second silica component can be a colloidal silica or a silicon-containing compound, and the second silica component can act as a glue to bind the silica composite together.
1. A process for preparing a silica composite, the process comprising:
(1) combining silica component I and silica component II in a diluent comprising at least about 70 wt. % water to form a mixture; and
(2) forming the silica composite in the mixture; wherein:
silica component I comprises irregular and non-spherical silica particles characterized by an average aspect ratio of at least about 2:1 and a BET surface area in a range from about 150 to about 1000 m 2 /g;
silica component II comprises a colloidal silica; and
the silica composite is characterized by:
a bulk density from about 0.08 to about 0.4 g/mL;
a total pore volume from about 0.4 to about 2.5 mL/g;
a BET surface area from about 175 to about 375 m 2 /g; and
a peak pore diameter from about 10 to about 80 nm.
2. The process of claim 1 , wherein silica component I comprises a fumed silica.
3. The process of claim 1 , further comprising:
combining a chromium-containing compound and an optional titanium-containing compound with the silica composite to form a supported chromium catalyst; and
calcining the supported chromium catalyst.
4. The process of claim 1 , wherein:
step (1) comprises combining a chromium-containing compound and an optional titanium-containing compound with silica component I and silica component II in the diluent to form the mixture; and
step (2) comprises forming a supported chromium catalyst in the mixture.
5. A process for preparing a silica composite, the process comprising:
(1) combining silica component I and silica component II in a solvent to form a mixture; and
(2) forming the silica composite in the mixture; wherein:
silica component I comprises a fumed silica;
silica component II comprises a silicon compound; and
the silica composite is characterized by:
a bulk density in a range from about 0.08 to about 0.4 g/mL;
a total pore volume from about 0.4 to about 2.5 mL/g;
a BET surface area from about 175 to about 375 m 2 /g; and
a peak pore diameter from about 10 to about 80 nm.
6. The process of claim 5 , wherein the silicon compound comprises a silicon alkoxide, a silicon halide, a silicon hydride, a silane, a hydrocarbyl silane, a siloxane, or any combination thereof.
7. The process of claim 5 , wherein the silicon compound comprises sodium silicate, an ethyl silicate, a silicate oligomer, or any combination thereof.
8. The process of claim 5 , further comprising:
combining a chromium-containing compound and an optional titanium-containing compound with the silica composite to form a supported chromium catalyst; and
calcining the supported chromium catalyst.
9. The process of claim 5 , wherein:
step (1) comprises combining a chromium-containing compound and an optional titanium-containing compound with silica component I and silica component II in the solvent to form the mixture; and
step (2) comprises forming a supported chromium catalyst in the mixture.
10. The process of claim 1 , wherein the colloidal silica has a d50 particle size from about 3 to about 25 nm.
11. The process of claim 1 , wherein an amount of silica component II, based on total amount of silica component I and silica component II, is from about 2 to about 25 wt. %.
12. The process of claim 1 , wherein silica component I is non-porous.
13. The process of claim 1 , wherein the average aspect ratio is from about 3:1 to about 50:1.
14. The process of claim 1 , wherein step (1) comprises combining a titanium-containing compound with silica component I and silica component II in the diluent.
15. The process of claim 3 , wherein the supported chromium catalyst comprises from about 0.5 to about 5 wt. % chromium, based on the total weight of the catalyst.
16. The process of claim 4 , wherein the supported chromium catalyst comprises from about 0.5 to about 5 wt. % chromium, based on the total weight of the catalyst.
17. The process of claim 5 , wherein an amount of silica component II, based on total amount of silica component I and silica component II, is from about 10 to about 90 wt. %.
18. The process of claim 5 , wherein silica component I is non-porous.
19. The process of claim 5 , wherein step (1) comprises combining a titanium-containing compound with silica component I and silica component II in the solvent.
20. The process of claim 8 , wherein the supported chromium catalyst comprises from about 0.5 to about 5 wt. % chromium, based on the total weight of the catalyst.
21. The process of claim 9 , wherein the supported chromium catalyst comprises from about 0.5 to about 5 wt. % chromium, based on the total weight of the catalyst.