GB1069071A - Improvements in and relating to the manufacture of oxides - Google Patents

Abstract

In the production of an oxide of Ti, Zr, Fe, Al or Si by vapour phase reaction of a preheated chloride of the element with a preheated oxidizing gas, the generally tubular reaction chamber (see Fig. 1) comprises a refractory part 2, constructed of, e.g. silica and/or alumina and situated within preheat furnace 20, and metal part 1 constructed of, e.g. Al, Mg, Ni or an alloy and cooled by fluid, say air, water, steam, oil, a molten metal or metal salt or a molten mixture of metal salts, e.g. a mixture of 40% NaNO2, 7% NaNO3 and 53% KNO3 having a melting point of 141.2 DEG C., contained in jacket 4 to such an extent that the surface in contact with the reactants is at a temperature substantially equal to the dew point of the chloride. Movement of metal ring 13, which is cooled by fluid in copper pipe 19 and separated from part 2 by a layer of thermally insulating material, towards part 1 and relative to part 2 is limited by tapering of the ring and outward flaring of wall 6. Ring 13 is connected to and resiliently urged towards, part 2 by bolts 16, which are secured by nuts 17 and spring-loaded by springs 18, so that gasket 12, of thermally insulating material, is compressed and a gas-tight joint is formed. In the production of TiO2, TiCl4 may be introduced through pipe 8 and annular slot 9, the second inlet means, and oxidizing gas, e.g. substantially pure O2, O2 in admixture with an inert gas, or air, is introduced through pipe 10, the first inlet means, or vice versa, to produce a stream of gases flowing in the direction of the length of the chamber. The oxidizing gas is introduced at a rate within, say, 90 to 110% of that required for stoichiometric reaction with the chloride and the velocity at which the reactant is fed to the second inlet means may be <PICT:1069071/C1/1> <PICT:1069071/C1/2> 100 to 300 feet per second. Particulate refractory material, e.g. zircon, alumina, titanium dioxide or silica sand, may be introduced through nozzle 11, as described in Specification 1,049,282, in suspension in a carrier gas, e.g. O2, air, N2 or Cl2, and at a velocity of at least 100 feet per second and a temperature of not more than 100 DEG C. Water vapour in quantity 0.05 to 10% of the total volume of gas and vapour introduced may be introduced into the oxidation zone with the carrier gas or with the oxidizing gas. At a time within 0.01 to 10 seconds of the introduction of TiCl4, the products leaving the oxidation zone may be quenched to below 900 DEG C. by, e.g. mixing with cooled product gas, by dispersing cold silica sand in the product stream or by passing the products at high velocity through cooled tubes. Modifications of the chamber include division of part 1 into two portions separated by a gasket, the internal surface of the upstream portion being tapered towards part 2 and both portions having cooling jackets. In addition, the upstream portion may be made up of two portions rigidly interconnected but with their inner walls separated by a slot constituting a third inlet means. Part 2 may be provided with an inlet for a barrier gas, e.g. U2 or N2, comprising a supply pipe and an intermediate portion, between walls 6 and 7, which may have a short length of reduced diameter at its downstream end, from which a frusto-conical part leads to the main part. Fig. 5 includes chamber 50. Flash boiler 51 can be supplied with liquid TiCl4 through pipe 52 and purged with N2 from pipe 53. TiCl4 vapour leaves by pipe 54 and enters silica preheater tube 55, which is made up of straight portions 56 with axes horizontal and parallel to one another and separated by portions 56 extending at right angles to the axes, the arrangement being such that the axes of portions 56 lie alternately in two vertical planes. The tube is supported by means that does not prevent its upward or horizontal movement, say by supporting members constructed of refractory material and mounted on a fluid-cooled metal structure shielded by refractory bricks. The tube may be heated by radiant heat from brickwork, electric heaters or oil heaters. Tube 55 leads to supply pipe 8 and a similar tube 58 is used to preheat oxidizing gas and leads to pipe 10. The reactants are generally preheated to such a degree that, if no reaction were to take place, the temperature of the gaseous mixture within the reaction chamber would be in the range 850 DEG to 1100 DEG C. The oxidizing gas may be preheated directly by incorporating with it a hot gaseous combustion product obtained by burning a fuel gas, e.g. CO. Pebble heaters or fluidized bed heaters may also be used for preheating the reactants. Aluminium oxide may be incorporated with the product TiO2 in quantity 0.5 to 10% by introducing aluminium chloride vapour, from generator 61, in admixture with the TiCl4 vapour. Closed vessel 62 and open vessel 63 are connected by passages 64 and 65 and constructed of, e.g. steel lined with brickwork or graphite or coated with refractory material. Retractable chlorine inlet tube 66 may be of graphite, alumina or cooled metal. Vessel 62 may be purged with N2 from tube 67. Aluminium chloride vapour passes through tubes 68 and 69 into tube 55. Nozzle 11 is supplied with air under pressure by tube 70, into which the particulate refractory material is introduced through tube 71. The upstream portion of chamber 50 is fired and the downstream end is connected to cooling and separating equipment. An additional supply pipe is required when a barrier gas is used. Aluminium oxide may also be incorporated by introducing aluminium chloride vapour through the third inlet means or by incorporating powdered aluminium with the particulate material introduced through nozzle 11 or with the TiCl4 vapour. SiCl4 may be introduced similarly or in admixture with chlorine used as a barrier gas. At least one substance selected from titanium oxychloride, finely divided oxide, organic compounds and titanium esters may be introduced to act as, or provide material for, material for nucleation of the product oxide. In examples TiO2 more than 99% in rutile form and of particle size 0.21 to 0.23 micron was produced.