# US 4,377,566 A · Novel process for the preparation of high purity alumina from ammonium alum > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 4,377,566 A - Document ID: US4377566A - Status: Granted - Kind: A - Application number: 06/278,977 - Filed: 1981-06-29 - Granted: 1983-03-22 - Earliest claimed: 1980-07-01 - Assignees: Produits Chimiques Ugine Kuhlmann - Inventors: Roland Bachelard; Robert Barral - Web page: https://patentgrep.com/patent/US4377566A ## CPC - C01F 7/32: Thermal decomposition of sulfates including complex sulfates, e.g. alums - C01P 2006/11: Powder tap density - C01P 2006/12: Surface area - C01P 2006/13: thermal stability thereof at high temperatures - C01F: COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS (metal hydrides {monoborane, diborane or addition complexes thereof} C01B6/00; salts of oxyacids of halogens C01B11/00; peroxides, salts of peroxyacids C01B15/00; sulfides or polysulfides of magnesium, calcium, strontium, or barium C01B17/42; thiosulfates, dithionites, polythionates C01B17/64; compounds containing selenium or tellurium C01B19/00; binary compounds of nitrogen with metals C01B21/06; azides C01B21/08; {compounds other than ammonia or cyanogen containing nitrogen and non-metals and optionally metals C01B21/082; amides or imides of silicon C01B21/087}; metal {imides or} amides C01B21/092, {C01B21/0923}; nitrites C01B21/50; {compounds of noble gases C01B23/0005}; phosphides C01B25/08; salts of oxyacids of phosphorus C01B25/16; carbides C01B32/90; compounds containing silicon C01B33/00; compounds containing boron C01B35/00; compounds having molecular sieve properties but not having base-exchange properties C01B37/00; compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites, C01B39/00; cyanides C01C3/08; salts of cyanic acid C01C3/14; salts of cyanamide C01C3/16; thiocyanates C01C3/20; {double sulfates of magnesium with sodium or potassium C01D5/12; with other alkali metals C01D15/00, C01D17/00}) - C01P: INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS ## Abstract Process for preparing high purity aluminas from ammonium alum, the process comprising separately dehydrating the alum and thereafter thermally decomposing the dehydrate, wherein the thermal decomposition is carried out by forcing a gas through a layer of the dehydrated alum so as to continuously remove the gaseous reaction products formed without removal of solids by the carrier gas, and providing improved productivity of high purity transition aluminas having specific surfaces above 125 m.sup.2 /g and/or bulk densities above 0.2 g/cm.sup.3, the transition aluminas so obtained being characterized by their greater reactivity for the preparation of corundum so that corundum having a bulk density greater than 0.4 g/cm.sup.3 can be economically prepared. ## Claims ### Claim 1 A process for the preparation of alumina from ammonium alum comprising first dehydrating ammonium alum at a temperature above the fusion point of the alum and below the temperature which calcines the alum to alumina and then thermally decomposing the dehydrated alum with hot gas to produce alumina, the thermal decomposition being carried out with a flow of the hot gas forced through a layer of the dehydrated alum to heat and decompose the dehydrated alum and to continuously remove the decomposition products as they are formed, the movement of the dehydrated solid alum along with the gas flow being prevented. ### Claim 2 (depends on 1) A process according to claim 1 wherein the dehydration is carried out under vacuum with the alum in contact with a surface heated to a temperature above the melting point of the ammonium alum. ### Claim 3 (depends on 1) A process according to claim 1 wherein the dehydration is carried out by fluidizing the alum with the gas heated to a temperature above the melting point of the alum. ### Claim 4 (depends on 1) A process according to claim 1 wherein the thermal decomposition is carried out in a fixed bed having the alum distributed in a substantially uniform layer and wherein the hot gas moves downwardly through the bed at a speed greater than the fluidization velocity of the charge. ### Claim 5 (depends on 1) A process according to claim 1 wherein the thermal decomposition is carried out by conducting the dehydrated alum downwardly through a conduit having gas permeable walls and sweeping the hot gas through the walls transversely to the downward movement of the dehydrated alum. ### Claim 6 (depends on 5) A process according to claim 5 wherein the dehydration of the alum is continuously effected by conducting the ammonium alum starting material downwardly through the conduit having porous walls and sweeping hot gas transversely to the downward movement of the alum, the gas being at a temperature to dehydrate the alum but lower than the temperature required to calcine the alum to alumina. ### Claim 7 (depends on 1) A process according to claim 1 wherein the dehydration is effected by heating the ammonium alum with microwave radiation to a temperature above the fusion point of the alum. ### Claim 8 (depends on 1) A process according to claim 1 wherein the thermal decomposition produces transition alumina and the transition alumina is thereafter heated to a temperature above the thermal decomposition temperature of the transition alumina to produce .alpha.-alumina. ### Claim 9 (depends on 1) A process according to claim 1 wherein the thermal decomposition is carried out at a temperature of at least 600.degree. C. ### Claim 10 (depends on 1) A process according to claim 1 wherein the thermal decomposition is carried out at a temperature of from 600.degree. to 1250.degree. C. ### Claim 11 (depends on 10) A process according to claim 10 wherein the temperature is at least about 1100.degree. C.