GB1049282A - Improvements in and relating to the manufacture of oxides - Google Patents

Abstract

An oxide of titanium, zirconium, iron, aluminium or silicon is made by vapour-phase reaction of a chloride of the element with an oxidizing gas, the two gases being preheated and introduced into an empty reaction chamber through separate inlets forming a turbulent stream wherein finely divided oxide is formed; an inert particulate refractory material is introduced so as to impinge on the reactor surfaces adjacent to the gas inlets, thereby preventing the deposition of the product oxide on the surfaces. The particulate material and product oxide are carried out of the chamber in the turbulent gas stream, and are then separated. The reactant gases are preheated to temperatures such that were the gases to be mixed without reaction taking place, the temperature of the resultant mixture would be at least 700 DEG C. The gases may be preheated indirectly, or the oxidizing gas may be preheated directly by burning a fuel gas, e.g. CO, therein. The turbulence corresponds to a Reynold's flow number of at least 10,000. The particulate material is a hard solid not attacked by chlorine under reaction conditions, e.g. zircon, alumina, titania or silica, and is introduced at 75-400 ft./sec., at a lower temperature than the preheated gas but above the dew point of the chloride; particle size is - 8 to +85 mesh (B.S.S.) The material is introduced in one or both reactants, or in an inert carrier gas, e.g. N, or Cl2, 0.2 lb. material per cu. ft. gas, and a jet or jets of the particles may be formed inside or outside the reactant inlets, and may be upstream of the termination of the inlets in the reactor. The particle inlet nozzle may be fixed or movable; a movable nozzle may operate intermittently to supplement a fixed nozzle. Inlets for a reactant may be separated from inlets for the other reactant or from the reaction chamber, by an inert barrier gas stream, e.g. Cl2 or N2, preferably at 600-1000 DEG C. The reactor surfaces may be indirectly cooled, in whole or in part, by a coolant fluid, e.g. water, steam, oil, molten salt or a mixture of molten salts, and cooled parts may be made of metal, e.g. Ni or Ni alloy; uncooled parts are made of a non-metallic refractory, e.g. SiO2 or Al2O3. Detention times in the reactor are 0.01-10 secs., such detention being terminated by quenching, e.g. by mixing cooled product gas, e.g. Cl2, with the product stream, or passing the product stream through cooled tubes, or by dispersing in the stream cold particles of inert refractory material, e.g. that used in the reactor, after which the material is separated, cooled and recycled, part to the quencher and part to the reactor. The gaseous reaction products are quenched to a temperature below 900 DEG C. The product oxide is separated from the particulate material in a settling chamber and/or dry or wet cyclones. The oxidizing gas may contain oxygen, pure or in admixture, e.g. as air, or ozone, and is introduced in stoichiometric proportions \sB10%. 0.05-10% by volume of the total volume of gas introduced into the reacton zone may be water vapour, e.g. in the air. When TiO2 is being made, Al2O3 may be formed therewith by introduction of AlCl3 vapour or Al powder into the reaction chamber; similarly, SiCl4, Al2O3, SiO2, titanium oxychloride, titanium esters or hydrocarbons, which provide material for nucleation, may be introduced. The product oxide may be subsequently heated at e.g. 650 DEG C. to remove absorbed gases and decompose oxychlorides. In the examples, TiO2 is produced in the rutile form.