GB878827A - Catalytic treatment of alumina - Google Patents

Abstract

a -alumina alumina is produced by calcining an alumina hydrate in a fluidised bed (24) to form g -alumina and heating the latter in a separate fluidised bed (31) in the presence of a fluoride catalyst whereby a -alumina is formed. The gas arising from the catalytic bed is discharged in such manner that it does not pass through the calcining bed or mix with the gas arising therefrom. Specified fluoride catalysts are calcium fluoride, sodium fluoride and (preferably) aluminium fluoride, the latter <PICT:0878827/III/1> of which may be formed in situ with hydrogen fluoride. In the preferred embodiment, illustrated in the Figure (to which the above numerals relate) the hydrated alumina is fed conventionally through a reactor R containing two preheating beds 22 and 23 and a calcining bed 24 to which fuel is supplied at 35 maintained at 1600-2000 DEG F. Gases arising from the uppermost bed are withdrawn and fines entrained therein separated and returned through lines 54 or 56 either to the calcining bed or the catalytic bed 31. The calcined material is passed through fluidised trap 37 to the fluidised catalytic conversion bed 31 maintained at 1600-2000 DEG F. if necessary with the addition of fuel or with cooling coils or sprays or by using otherwise heated fluidising gas. Catalyst is admitted to bed 31 as a fine powder (which vaporizes under reaction conditions) through line 39. The so-formed a -alumina is then passed to a cooling bed 42 and thence discharged at 48. Air for fluidisation is admitted to the cooling bed 42 from wind box 44, is preheated and used in part to fluidise the catalytic bed 31 and in part the calcining bed and superimposed beds. Gas arising from the catalytic bed first has entrained a -alumina removed at 58 (said alumina after passage through fluidised trap 61 being combined with the cooled product) and is then cooled in a boiler or other heat exchange apparatus 64. The conduits between the catalytic bed and the boiler are insulated. Vaporized catalyst condenses and is discharged through line 73 and returned to the catalytic bed. The resultant gas may still contain very fine catalyst particles and may be passed through a further separator to recover the catalyst, before discharging to the atmosphere. By adjustment of valve 71, the amount of gas passing through the catalytic bed and hence also, through the reactor R may be regulated. The amount of gas may be further regulated by means of valve 77, in the outflow line from the reactor R.