Patent GB-758409-A (GB)
Title: Improvements in production of titanium dioxide pigments
Inventor: SCHAUMANN HOLGER HEINRICH
IPC: C01G23/07
Filed: 1954-07-07
Abstract: Titanium dioxide is prepared by reacting vaporized titanium tetrachloride preheated to 400 DEG C. or less, and molten aluminium in a dispersed state in an amount from 0.1 to 2 per cent by weight of the tetrachloride, with an oxygen-containing gas having a regulated or added moisture content from 0.05 to 10 per cent by volume of H2O, at 800 to 1400 DEG C.  The resulting titanium pigment may be calcined at 500 to 800 DEG C. and milled.  The aluminium may be added as a spray of molten metal or fed as a wire or bar to melt and disperse in the reaction zone under radiant heat.  The gaseous pigment suspension leaving the reactor at about 1100 to 1300 DEG C. should be cooled to below 600 DEG C. within less than 10 seconds after leaving the reactor, suitably by contacting the hot suspension with recirculated cooled product gases or by adding a blast of cold inert solids such as silica.  The required water vapour content can be supplied by the reactant air or oxygen or may be added independently or formed in situ by the supply of free hydrogen.  The reactant retention time is preferably 0.05 to 1 second and the reaction may take place at sub or superatmospheric pressures if desired.  According to Examples (1) a nickel reactor cooled by a circulating molten salt mixture was provided with three inlet conduits arranged so that their axes converged to a common point.  A ceramic lined nozzle for the introduction of aluminium was surrounded by a concentric air supplying conduit, the aluminium entering at 775 DEG C. and the air at 1050 DEG C.  Titanium tetrachloride vapour at 300 DEG C. and humidified air were admitted through the other conduits and the reaction occurred in 0.15 seconds at 1260 DEG C.  The resulting titanium pigment contained 95.7 per cent TiO2 and 4.3 per cent Al2O3. (2) A slot jet type of mixing and reaction vessel as described and claimed in Specification 757,703 was employed.  Air at 1080 DEG C. containing 0.5 per cent H2O was fed through a cooled vertical cylindrical vessel provided with a continuous transverse peripheral slot through which titanium tetrachloride vapour was admitted at 150 DEG C.  Simultaneously aluminium metal was sprayed continuously into the air stream just above the peripheral slot admitting the tetrachloride vapour.  The reaction occurred at 1250 DEG C. with a reactant retention time of 0.12 seconds, to produce a pigment containing 5.7 per cent Al2O3.  Such pigment after calcining at 700 DEG C. for 4 hours and dry grinding in a fluid energy mill had a pH of 7.  The titanium tetrachloride employed is preferably pure, as may be obtained by fractional distillation of titanium tetrachloride obtained by chlorinating ilmenite or the titanium tetrachloride may be freed from copper vanadium iron and other impurities by the process of Specification 384,875 or by treating the anhydrous titanium tetrachloride with 2.5 to 5 per cent of soya bean oil which binds the vanadium as a non-volatile readily separable polymerization compound which can be removed from the tetrachloride liquid by distillation, filtration or centrifuging. Specification 707,560 also is referred to.