GB757104A - Process and apparatus for the production of aluminum oxide - Google Patents

Abstract

<PICT:0757104/III/1> <PICT:0757104/III/2> Aluminium oxide is produced from hydrated aluminium sulphate i.e. containing 6 or more molecules of water of crystallization, by introducing the sulphate at a controlled rate into the upper end of an elongated vertical reactor externally heated to an internal temperature above 770 DEG C., thereby decomposing the aluminium sulphate to aluminium oxide and gaseous sulphur oxides and liberating water therefrom as it flows by gravity through the reactor, removing the gaseous oxides and water vapour from the upper end of the reactor, separating entrained solids from the gas stream and recycling the solids to the reaction zone, collecting the solid aluminium oxide formed in the lower end of the reaction zone out of contact with the gaseous oxides and water vapour and heating it therein in a substantially moisture free atmosphere to decompose the remaining sulphate and obtain pure aluminium oxide. The sulphate may be supplied in solid particulate or molten form and is preferably supplied at a point substantially distant from the point of gaseous oxides withdrawal. As shown in Fig. 1, sulphate is fed through line 12 to an externally heated reactor 10 from which solid aluminium oxide is withdrawn at 14 and gaseous oxides with water vapour at 16 to pass to a cyclone separator 18 from which separated solids are recycled to line 12 via line 20. The gases containing sulphur oxides leave cyclone 18 by line 22 and pass to a scrubber 24 where the sulphur values may be recovered as sulphuric acid. The reactor is shown in Fig. 2 wherein a central refractory reaction tube 44 is surrounded by a furnace 40 provided with burners 46 and combustion gas effluent 48. The reactor tube is provided with a feed line 12 which may be heated if molten sulphate is fed or cooled if solid sulphate is used, preferably jacketed at 60, the line 12 being provided with an extension tube 58 into the body of the reaction tube. Gases are withdrawn at 16 and the solid aluminium oxide falls to the bottom of the reaction tube which is provided with a plug 52 preferably having vanes 56, which plug may be rotated to agitate the solid product collecting, and moved vertically to permit solids withdrawal through valved line 62. The retention time of the oxide in the reactor is suitably 30 to 120 minutes.