GB907211A - Vapour phase oxidation of halides - Google Patents

Abstract

<PICT:0907211/III/1> <PICT:0907211/III/2> <PICT:0907211/III/3> In the production of metal or metalloid oxides by vapour phase oxidation of halides, the halide and the oxygenating gas are introduced to an empty reaction chamber either in adjacent streams or as a mixture, at least one of the reactants being admitted with such kinetic energy and with a Reynolds number of above 50,000, so that or near the point of injection there will be re-entrained in the incoming reactants sufficient of the reaction products, returning in the opposite direction to the reactant inflow, that the heat derived therefrom will preheat the incoming reactants to reaction temperature without the supply of auxiliary heat; the reaction chamber must be sufficiently wide not to impede the recirculatory flow and it is preferable that the recirculatory flow is enhanced by withdrawing reaction products from the same end of the reaction chamber as that to which the reactants are fed. The reaction vessel, normally cylindrical, generally has a diameter at least 20 times the diameter of the inlet orifice delivering the gas at high velocity. As shown in Fig. 1, a thermally insulated reaction vessel 1 is provided with a burner 10 to which reactants, for example titanium tetrachloride and oxygen are fed through inlets 11 and 12 respectively; reaction products are withdrawn through line 14. A burner 18 is provided at the opposite end of the furnace to preheat the furnace initially to reaction temperature. According to an example, titanium tetrachloride at 150 DEG C. was fed with oxygen at 170 DEG C. to a reaction vessel which reached a steady state operating temperature of 1050 DEG -1100 DEG C. Titanium dioxide of 2-5 micron mean particle size was recovered. Burners may be either as shown in Fig. 2 where the two reactants are fed through lines 34 and 35 to mix prior to ejection through an orifice 36, or as shown in Fig. 3 where a concentric nozzle is shown, air being admitted through a line 45, whilst titanium tetrachloride is fed by the central tube 37. The particle size of the titanium tetrachloride may be controlled by additions of water vapour to the reaction mixture, or, where the reactants are fed separately, to the oxygen containing gases. Silicon tetrachloride may also be premixed with the titanium tetrachloride vapours to modify the particle size of the titanium dioxide. Further examples relate to the oxidation of silicon tetrachloride, introduced at 120 DEG C., with oxygen fed at 100 DEG C., whereby at a reaction temperature of 1020 DEG C., silicon dioxide of 50 millimicron particle size was obtained, and to the oxidation of ferric chloride, containing 3% by volume of free chlorine, which was introduced at 350 DEG C. together with oxygen at 100 DEG C. into a reaction chamber preheated to 900 DEG C.; the reaction heat was maintained autogenously at 700 DEG -750 DEG C. and ferric oxide of 2-3 microns particle size was recovered. Reference is also made to the production of oxides by oxidation of the chlorides, bromides or iodides of Ti, Si, Al, Nb, Fe, Cr, Zr, V, Sn, and U or mixtures thereof.