Process for producing enhanced alumina
The present invention provides an essentially dry method for preparation of enhanced alumina powders. The first step involves rapid calcination of an aluminum compound to produce alumina powder. The alumina powder is mixed with solid ammonium carbonate and a small amount of water. This mixture heats itself although some external heat is helpful to produce ammonium aluminum hydroxycarbonate (dawsonite-type) NH 4 AlCO 3 (OH) 2 upon curing which is then decomposed to produce enhanced alumina having a specific desired morphology and nano-sized dimensions.
1. A process for producing alumina comprising:
a) providing a quantity of alumina powder;
b) mixing said alumina powder with a solid ammonium carbonate and from 5 to 30 weight percent water to form a mixture;
c) allowing said mixture to cure at a temperature from about 45° to 85° C. to produce ammonium aluminum hydroxycarbonate; and
d) then decomposing said ammonium aluminum hydroxycarbonate at a temperature from about 130° to 320° C. to produce an enhanced alumina.
2. The process of claim 1 wherein after said mixture has cured an additional amount of said solid ammonium carbonate is added to said ammonium aluminum hydroxycarbonate and allowed to cure at 45° to 85° C.
3. The process of claim 1 wherein said alumina powder is selected from the group consisting of calcined Al(OH) 3 , alumina produced by hydrolysis of aluminum alkoxide, precipitated alumina and hydrothermally treated alumina.
4. The process of claim 1 wherein said alumina powder has a BET surface area greater than 50 m 2 /g.
5. The process of claim 1 wherein said mixture is allowed to cure without application of heat to said mixture.
6. The process of claim 1 wherein heat is applied to said mixture in addition to heat produced by an exothermic reaction from said mixture.
7. The process of claim 1 wherein said ammonium carbonates are ammonium bicarbonate, ammonium carbonate, ammonium carbamate or ammonium sesqui carbonate.
8. The process of claim 1 wherein said ammonium carbonate comprises about 2 to 10 mass-% ammonium aluminum hydroxycarbonate.
9. The process of claim 1 wherein carbon dioxide and ammonia produced from said decomposition of said ammonium dawsonite are combined to produce a bicarbonate that comprises at least a portion of said solid ammonium carbonate.
10. The process of claim 1 wherein said enhanced alumina has a BET surface area greater than about 400 BET m 2 /g.
11. The process of claim 1 wherein said enhanced alumina has a BET surface area greater than about 450 BET m 2 /g.
12. The process of claim 1 wherein said enhanced alumina has a pore volume greater than about 0.6 cc/g.
13. The process of claim 1 wherein said enhanced alumina is additionally treated with acid solutions to remove the residual sodium contained in source alumina.