GB707560A - Improvements in and relating to the manufacture of pigmentary titanium dioxide - Google Patents

Abstract

Pigmentary titanium dioxide is produced by reacting in the vapour phase, at 800-1350 DEG C., titanium tetrachloride and a small amount, say 0.1-10 per cent. by weight, aluminium chloride. with an oxygen-containing gas, in the presence of 0.1-5 per cent. by volume of water vapour, and in a chamber in which the reactants remain for 0.01-1 seconds, withdrawing the reaction products and cooling them to below 600 DEG C. within, say, 1-5 secs., and at the most, 10 secs., and recovering the titanium dioxide. The quenching is effected by adding cooled product gases, or by a blast of cold, finely divided solid such as silica, which is later separated by passing the gaseous suspension through a cyclone &c. separator operating at a suitable rate. Other volatilizable halides, e.g. 0.1-10 per cent. by weight silicon, zirconium, antimony, zinc or tin chloride may be present in the reaction. The product may be calcined at 500-800 DEG C., and thereafter milled. The aluminium and titanium chlorides may be mixed in liquid or vapour state. The reaction chamber, which may be made of silica, or the reactants may be preheated. Water may be supplied to the reaction zone separately, or with the reaction gases. Alternatively, it may be formed in the reaction zone by the addition of hydrogen, a hydrocarbon, or hydrogen chloride. Air and/or oxygen may be used as the oxidizing gas. The process may be effected at atmospheric, or higher or lower, pressure. By suitably choosing the conditions of operation, anatase or rutile may be obtained. Specification 464,836 is referred to.