GB916250A - Manufacture of titanium dioxide pigment - Google Patents

Abstract

<PICT:0916250/III/1> <PICT:0916250/III/2> Titanium dioxide is formed by supplying a preformed homogeneous mixture of titanium tetrachloride and oxygen at a temperature below 700 DEG C. to a combustion space through which it flows substantially uniformly so that the average speed of the combustion mixture is between two thirds and four thirds of its axial speed. The walls of the reaction chamber are preferably formed of porous refractory and an inert gas or chlorinating is passed transversely therethrough to prevent adhesion of titanium dioxide particles. According to a modification, the preformed homogeneous mixture of titanium tetrachloride and oxygen is fed into a reaction chamber directly against an opposing column of gas, which may be inert or combustible or the same, and the combined stream of gas is withdrawn at their junction. As shown in Fig. 1, a reaction vessel is provided with porous walls 5 through which a purge gas can be passed from line 10. Above is a smaller nucleating section provided with porous walls 3 through which a purge gas is fed through line 9. A reacting gas mixture is fed through a line 12 into a turbulence suppressor 13 formed of nesting aluminium tubes. The nucleating zone and the reaction zone are joined by a porous disc 4 which is flushed on its inside by purging gas. Suitable purge gases are ammonia, nitrogen oxide, water vapour or gases forming water vapour on combustion, such as ethyl acetate, butane, butanol, diethyl ether or diethyl ketone or preferably carbon monoxide. Purge gas, admitted through the pipe 10 to the lower reaction zone, may be titanium tetrachloride, (liquid or gaseous), chlorine, carbon monoxide, carbon dioxide or the noble gases. A sight port 21 is provided, alternatively an apparatus as shown in Fig. 3 may be employed where two opposing tubes 123 and 124 are supplied, by tangentially arranged pipes 105 and 106, with fuel or reactant gases which move with a slow rotary motion. Screens 111 to 122 ensure a uniform gas velocity. The gases meet in a cooled reaction space bounded by a jacket 129. The gases fed to the opposing tubes 123 and 124 may be the same, i.e. a mixture of titanium tetrachloride and oxygen, or the opposing stream may be a mixture of chlorine and carbon dioxide, carbon monoxide and oxygen, or an inert gas such as nitrogen. Fuel gases referred to include hydrogen, volatile hydrocarbons, esters, ketones and alcohols, but carbon monoxide is preferred. The necessary oxygen for combustion is also supplied and it is suggested that ozone be included. Rutile production, favoured by a high flame temperature, may be promoted by the addition of aluminium chloride, and other metal chlorides such as silicon, vanadium, nickel, zinc, antimony or zirconium chlorides; lower titanium chlorides may be added. Reference has been directed by the Comptroller to Specification 764,084.