Claims
- 1. A process for preparing granules of alumina comprising:
- (a) pretreating alumina powder by admixing said powder with cold water in a mixer at a temperature below about 20.degree. C. to form a stabilized alumina having a pore volume partially saturated with water; and
- (b) agglomerating said pretreated alumina in a fluidized bed to form granules having a high macropore volume.
- 2. A process as set forth in claim 1 wherein said alumina powder consists essentially of rehydratable alumina.
- 3. A process as set forth in claim 2 wherein the pretreatment temperatures are controlled by using a water bath around said mixer.
- 4. A process as set forth in claim 3 wherein said pretreating temperature is in the range of about 5.degree.-10.degree. C.
- 5. A process as set forth in claim 4 wherein said alumina powder is cooled in a cold hopper to a temperature in the range of about 5.degree.-10.degree. C. prior to said pretreating step.
- 6. A process as set forth in claim 5 wherein said agglomerating step includes maintaining a constant superficial velocity of air in said fluidized bed.
- 7. A process as set forth in claim 6 wherein said superficial velocity of air is about 0.8-1.4 m/sec.
- 8. A process as set forth in claim 7 wherein said air has a relative humidity of 80% or higher to reduce the loss of water from the bed while agglomerating.
- 9. A process as set forth in claim 8 wherein said agglomerating step comprises introducing about 20-70% of the total air to the fluidized bed as a jet stream.
- 10. A process as set forth in claim 9 wherein residence time in the fluidized bed is between about 10-60 minutes.
- 11. A process as set forth in claim 10 further comprising withdrawing granules from the fluidized bed and screening the granules to separate oversize particles sized above about 3 mm diameter.
- 12. A process as set forth in claim 11 further comprising steam aging and water aging said particles to increase strength.
- 13. A process as set forth in claim 12 further comprising activating said granules by heating to develop increased porosity and surface area.
- 14. A process as set forth in claim 13 further comprising crushing said oversized particles and recirculating to said screening step.
- 15. A process as set forth in claim 15 wherein a portion of said granules sized smaller than about 1 mm diameter are fed to said fluidized bed as seed feed.
- 16. A process as set forth in claim 15 comprising capturing carried-over fine particles from said fluidized bed in a cyclone and returning to said fluidized bed and wet scrubbing the carried-over fine from said cyclone.
- 17. A process for preparinq qranules of alumina comprising:
- (a) pretreating rehydratable alumina powder by admixing with water having a temperature in the range of about 5.degree.-10.degree. C. in a mixer controlled to maintain a temperature in the range of about 5.degree.-10.degree. C. to form a pretreated alumina having a pore volume partially saturated with water;
- (b) agglomerating said pretreated alumina in a fluidized bed to form granules;
- (c) withdrawing agglomerate from said fluidized bed and screening to separate granules of 1-3 mm diameter from oversize granules;
- (d) crushing said oversize granules and recirculating crushed material to said fluidized bed; and
- (e) steam aging, water aging, and activating said granules.
- 18. A process a set forth in claim 17 wherein said alumina powder is cooled in a cold hopper to a temperature in the range of 5.degree.-10.degree. C. prior to said pretreating step.
- 19. A process as set forth in claim 18 further comprising maintaining a constant superficial velocity of air in said fluidized bed.
- 20. A process for preparing granules of rehydratable alumina comprising:
- (a) cooling rehydratable alumina powder in a cold hopper to a temperature of about 5.degree. C. to form a cooled alumina powder;
- (b) feeding said cooled alumina powder to a mixer maintained at a temperature of about 5.degree. C.;
- (c) feeding water at a temperature of about 5.degree. C. to said mixer;
- (d) mixing said powder and said water in said mixer to form a pretreated alumina having a pore volume partially saturated with water and having a surface layer of gel structure; and
- (e) agglomerating said pretreated alumina in a fluidized bed to form granules.
CROSS-REFERENCE TO RELATED PATENT APPLICATION
This application is a continuation-in-part application of U.S. Ser. No. 16,631 filed Feb. 19, 1987, now U.S. Pat. No. 4,704,378 issued Nov. 3, 1987.
US Referenced Citations (22)
Non-Patent Literature Citations (1)
Entry |
"Fluidized-Bed Spray Granulation" by Sten Mortensen and Svend Hovmand, CEP, Apr. 3, 1983, pp. 37-42. |
Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
16631 |
Feb 1987 |
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