GB876672A - Improvements in or relating to the production of pigmentary titanium dioxide - Google Patents

Abstract

Pigmentary titanium dioxide is prepared by decomposing titanium tetrachloride with an oxygen containing gas in the vapour phase at an elevated temperature in the presence of from 0.01 to 10,000 parts by weight per million of alkali metal, especially potassium, based on the titanium dioxide being produced. Reaction temperatures may be from 800-1400 DEG C., and the preheated oxidizing gas may contain from 10-100% oxygen by volume. The reaction may be effected in the presence of small amounts of water vapour or aluminium. The alkali metal may be supplied in the elemental state or preferably as a water soluble inorganic or organic compound such as the nitrate, chloride or sulphate, halide, phosphate, alcoholate, acetate, benzoate, hydroxide or oxide, supplied as an aqueous solution charged to the reaction zone via a separate inlet. The reaction may be effected in the reactor described in Specification 757,703 where one reactant is discharged as a thin sheeted stream directly into the other reactant in the direction angular to the axis of flow thereof. The oxygen containing gas may be air, oxygen or mixtures thereof; inert gases such as nitrogen or carbon dioxide may be present. Thus for example, preheated vaporized anhydrous titanium tetrachloride containing 1% of aluminium chloride may be charged to a reaction zone maintained at 900-1400 DEG C., together with preheated air containing 50 to 100,000 parts per million of water vapour and 0.1 to 400 parts per million of potassium and in the form of an aqueous soluton of potassium chloride, nitrate or sulphate. The resulting gaseous suspension at 1150 DEG C. is quenched below 600 DEG C. for example by the method disclosed in Specification 776,419, and the resulting pigment subjected to mild calcination in air at 600 to 900 DEG C. to remove residual chlorine. The pigment may then be dry milled or disintegrated. Specification 707,560 also is referred to.