Improvements in the production of metal oxides

摘要

In the production of metal oxides by vapour phase oxidation of the corresponding metal chlorides, bromides or iodides at temperatures of 800 DEG -1450 DEG C., the reactor wall is made of porous carbon or graphite and is maintained at 500 DEG -800 DEG C. whilst chlorine, bromine or iodine gas is passed inwardly through the porous wall to form a continuous protective gas film to prevent oxide scale deposition. The ratio by weight of halogen so employed to that liberated in the main reaction per unit time is from 0,1 to 1. The reactor, Fig. 1, may be the same as that described in the parent Specification. The reaction zone 6 is fed with an oxidizing gas such as oxygen or oxygen enriched air, which may contain 0,05 to 10% water vapour, through line 4 and the halide is fed through line 11 to a circumferential slot 13 into the oxidizing gas preferably at right angles to the main axis of flow, as described and claimed in Specification 757,703. The reactant inlet arrangement is surrounded by a furnace 1. The porous walls 7 of the reaction zone are formed of carbon or graphite and are surrounded by a jacket 15 to which the halogen shielding gas is fed from line 16. The pores of the carbon or graphite wall may be from 0,05 to 200 microns and the wall and surrounding jacket may extend up to or beyond the circumferential slot to prevent scale deposit thereon. The halogen shielding gas may be heated to 300 DEG -600 DEG C. before passage through the wall and it may be mixed with an inert gas such as nitrogen helium, argon or neon or with a non-oxidizing gas such as carbon monoxide or carbon tetrachloride. The stated effect of the halogen in titanium tetrachloride oxidation is to form a subchloride such as titanium oxychloride with the already formed titanium dioxide near the wall, the subchloride reacting with chlorine to form tetrachloride which is then reoxidized. According to a typical example, titanium tetrachloride and oxygen containing 2,4% water were fed to the reactor inlets enclosed in a furnace maintained at 1020 DEG C., whilst dry chlorine at 20 DEG C. was fed through porous graphite walls of the reactor. Reactor retention times may be 0,01 to 5 seconds. Production of titanium, zirconium, aluminium, antimony, iron, tin and zinc oxides is referred to.