Improvements in or relating to the production of metal oxides

摘要

In the vapour phase decompositions of a chloride, bromide or iodide of a metal to form the corresponding oxide with an oxidizing gas the reaction zone is provided with a porous refractory wall through which a shielding gas is passed from an external source to prevent scale decomposition. In the drawing an oxygen containing gas enters a vertical tube 3 through an inlet 4 and titanium tetrachloride for example enters through an inlet 11 to pass to a chamber 12 surrouding the tube 3 and from which chamber the titanium tetrachloride is introduced into the oxygen stream as a sheet through a sloted inlet 13 as in Specification 757,703. The reactant inlet arrangement is enclosed in a furnace 1 which may be heated or insulated. The reactant mixture passes to the reactor 6 formed with a porous wall 7 which is in turn encased in a jacket 15 through which the shielding gas is passed. Reaction products are removed at 5. Typical metal oxides which may be formed by the process are those of iron, titanium, silicon, zirconium antimony, tin, zinc and aluminium employing oxygen, air or other oxygen containing gas preferably humidified, or steam. The shielding gas may be nitrogen, carbon dioxide, chlorine, helium or argon which are inert to the reaction product, or the gaseous reaction products may be recycled in admixture with the shielding gases. Alternatively the shielding gas may be composed of gases which react with the oxide scale as described in Specification 715,255; for example, a mixture of carbon monoxide and chlorine may be employed which decomposes oxide scale to tetrachloride which is then re-oxidized to the oxide. The porous wall may be formed or porcelain, silica, nickel, steel porous carbon or graphite the average pore size of which is less than 130 microns. The pore size may be reduced to the desired value by applying a porous coating thereto such as by burning a metal halide within the wall. According to a typical example titanium tetrachloride and humidified air preheated to 1020 DEG C. were passed into a reaction vessel having a porous wall through which dry nitrogen at 20 DEG C. was passed. The reaction retention time is normally from 0.1 to 5 seconds. If desired the porous wall may be extended up to the lower side of the slotted inlets 13 thereby minimizing scale decomposition about that inlet.