GB656374A - Improvements in the production of aluminium fluoride - Google Patents

Abstract

Aluminium fluoride is prepared by reacting alumina, aluminium hydroxide or a mixture thereof with hydrogen fluoride gas at 350-650 DEG C., using a fluidized solids technique. The hydrogen fluoride may be diluted with inert gases such as air or recirculated spent gas. The operation may be effected in two or more stages, batchwise or continuously. The aluminium hydroxide may be partially dehydrated in a first stage at 200-500 DEG C. by the rising hot gases, aided by the heat from a pulverized coal, oil or gas burner. Heat may alternatively be supplied through tubes carrying hot gases, or by removing and returning the bed continuously, and heating it externally. In the second stage, dehydration is completed and the reaction partially so; the temperature is suitably controlled by regulation of the moisture content of the incoming material, this regulation being effected by adjustment of the fuel burnt in the previous zone. Reaction is completed and cooling effected in the lower zones. Temperature may also be controlled by recycling aluminium fluoride fines, collected in the usual cyclone and filter or precipitator, equivalent, say, to 10 per cent of the product, or by the use of cooling water tubes in the bed. Two forms of apparatus are shown, one consisting of a single reactor having three superposed beds with a fuel burner under the top and bottom beds, and the other of three separate reactors. In each case, the cross-sectional area of the top or first reaction zone increases upwardly so as to reduce the gas velocity.