Claims
- 1. A process for preparing a finely divided alumina from an ammonium-alum based composition comprising the following steps:
- (a) mixing an ammonium alum with a sweling agent, and heating said mixture above its fusion temperature, thereby obtaining a dehydrated alum composition having a bulk density less than 0.2kg/dm.sup.3 ;
- (b) calcining the dehydrated material at a first temperature stage of from about 750.degree. to 850.degree. C. and a second temperature stage of from about 900.degree. to 1050.degree. C.; and then
- (c) recovering said alumina having a homogeneous unimodal pore structure with maximum pore radii between 4 and 5 mm and a specific area greater than 145 m.sup.2 /g.
- 2. The process of claim 1 wherein said dehydrated alum composition is calcined in a fixed bed in granular, pelleted, or compacted form.
- 3. The process of claim 1 wherein the calcination is carried out in a down-flow bed with a gas flow rate above the minimum fluidization velocity of the material.
- 4. The process of claim 1 wherein gas is passed through a bed of the dried material during calcination.
- 5. The process of claim 4 wherein the gas contains water vapor, sulfur oxides, or a mixture thereof.
- 6. The process of claim 1 wherein said first temperature stage heating is carried out for from about one to about five hours.
- 7. The process of claim 1 wherein said second temperature heating step is carried out for from about one to about three hours.
- 8. The process of claim 1 wherein said swelling agent added is selected from the group consisting of sugars, starches and urea.
- 9. A process for preparing a finely divided non-stoichiometric alumina-magnesium spinel powder from an ammonium-alum based composition comprising the following steps:
- (a) mixing an ammonium alum, a magnesium salt and a swelling agent, and heating said mixture above its fusion temperature, thereby obtaining a dehydrated alum composition having a bulk density less than 0.2 kg/dm.sup.3 ;
- (b) calcining the dehydrated at a first temperature stage of from about 750.degree. to 850.degree. C. and a second temperature stage of from about 900.degree. to 1050.degree. C.; and then
- (c) recovering said spinel powder having a homogeneous unimodal pore structure with maximum pore radii between 4 and 5 mm and a specific area greater than 145 m.sup.2 /g.
- 10. The process of claim 9 for the preparation of spinel powder in which the ratio of Al.sub.2 O.sub.3 /MgO is three or more.
- 11. The process of claim 10 wherein the ratio is from three to six.
- 12. The process of claim 9 wherein said swelling agent added is selected from the group consisting of sugars, starches and urea.
- 13. The process of claim 9 wherein said dehydrated material is calcined in a fixed bed in granular, pelleted, or compacted form.
- 14. The process of claim 9 wherein the calcination is carried out in a down-flow bed with a gas flow rate above the minimum fluidization velocity of the material.
- 15. The process of claim 9 wherein gas is passed through a bed of the dried material during calcination.
- 16. The process according to claim 15 wherein the gas contains water vapor, sulfur oxides, or a mixture thereof.
- 17. The process of claim 9 wherein said first temperature stage heating is carried out for from about one to about five hours.
- 18. The process of claim 9 wherein said second temperature heating step is carried out for from about one to about three hours.
Priority Claims (1)
Number |
Date |
Country |
Kind |
81 10872 |
Jun 1981 |
FRX |
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Parent Case Info
This application is a continuation, of application Ser. No. 373,430, filed Apr. 30, 1982 and now abandoned.
US Referenced Citations (8)
Foreign Referenced Citations (2)
Number |
Date |
Country |
426968 |
Dec 1974 |
SUX |
560827 |
Sep 1977 |
SUX |
Continuations (1)
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Number |
Date |
Country |
Parent |
373430 |
Apr 1982 |
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