GB686568A - Production of finely divided titanium dioxide - Google Patents

Abstract

Pigmentary titanium dioxide is produced by discharging a uniform pre-mixture of titanium tetrachloride vapours, gases containing free oxygen, and a volatile silicon compound in amount sufficient to yield a product containing 0.01-10 per cent silica, into a combustion zone, suitably at a linear flow rate of 1-50 metres per second, the mixture being at a temperature of 135-500 DEG C, and continuously contacting the premixture with an auxiliary flame sustained by a separate inflow of combustible gas to ignite the premixture and maintain it at a flaming state. Suitable silicon compounds are silicon tetrachloride, -hexachloride, -tetra-bromide, -chloroform, or -tetraethyl ester, chloromethyl silicane, dimethyl silicane, tetraethyl silicane, silicon hydride &c. The silicon compound may be added to the silicon tetrachloride to be vaporized, e.g. by passing oxygen-containing gas therethrough. Alternatively, the vapours may be mixed, the silicon tetrachloride, say, being produced by passing chlorine, with or without a diluent, over heated silicon. The premixture should contain at least 50 per cent, up to a surplus, of oxygen, for the decomposition of the titanium tetrachloride. Inert gas such as carbon dioxide or nitrogen may also be present. Methane, acetylene, hydrogen &c., or preferably, carbon monoxide, are employed as combustible gases. Temperatures of 750-1200 DEG C immediately ambient to the auxiliary flame are specified. Examples disclose burners consisting of three concentric tubes, the titanium tetrachloride &c., premixture being passed through the central tube, and the combustible gas and oxygen for its combustion being passed through the outer tubes. The product, which is largely anatase with a content of rutile varying with the reaction conditions, may be subjected to evacuation to remove chlorine and hydrogen chloride, and neutralized with a small amount of lime.