GB805572A - Improvements in or relating to the production of titanium dioxide - Google Patents

Abstract

In the production of titanium dioxide by the vapour phase oxidation of titanium tetrahalide vapour containing minor proportions of an aluminium halide, the aluminium halide is formed in situ in the titanium tetrahalide vapour by fluidizing a bed formed of discrete aluminium metal particles and a major proportion of finely divided inert solid particles, with a gaseous mixture of titanium tetrahalide and chlorine, bromine or iodine. The fluidized bed is maintained below the softening temperature of aluminium and above the condensation temperature of the resulting aluminium halides, for example at 180 DEG to 400 DEG C. A secondary chlorine inlet stream may be provided above the level of the fluidized bed to chlorinate any metallic aluminium particles entrained in the product gases. The aluminium halide formed preferably constitutes from 0.1 to 10 per cent by weight of the titanium tetrahalide. The inert solid employed may be quartz or a metal silicate and should preferably constitute about three times by weight the aluminium metal present. The aluminium metal is preferably of a larger size than the inert solid and the aluminium addition may take place continuously, the rate of addition controlling the rate of aluminium halide production. The invention is applicable to the production of aluminium chloride, bromide and iodide, normally in the presence of the corresponding titanium halide, but a mixture of chlorine and bromine vapour may be used to obtain a mixed aluminium halide product or the fluidizing gas may consist for example of chlorine with titanium bromide. The titanium halide fluidizing gas normally constitutes twenty times the weight of the halogen vapour employed. According to an example, 18 mols. of titanium tetrachloride vapour was mixed with 3 mols. of chlorine and employed to fluidize a bed consisting of mullite and granulated aluminium in a weight ratio of three to one. Granulated aluminium was added at about 1 minute intervals at approximately 1 mol. per hour rate. The bed temperature was held at 365 DEG C. and the resulting titanium tetrachloride - aluminium trichloride-chlorine mixture was preheated to 850 DEG C. and reacted with hot oxygen bearing gas containing 10 per cent excess oxygen and a small amount of water vapour. The titania pigment contained about 1.05 per cent alumina by weight. Specifications 707,560 is referred to.