Patent GB-1045453-A (GB)
Title: Improvements in and relating to the production of metal oxides
IPC: C01G23/07
Filed: 1963-11-01
Abstract: <PICT:1045453/C1/1> In the production of metal or silicon oxides by vapour phase oxidation of the corresponding halides, the reaction temperature of above 800 DEG  C. is achieved in the reaction zone without excessive preheating of the halide by either (a) contacting an oxygen stream with a heat source at at least 1250 DEG  C., feeding the halide into the heated oxygen stream and delivering the mixture into the reaction zone along a path which is the direct line of sight between the heat source and the interior of the reaction zone or (b) feeding separately to a combustion zone a plurality of streams of carbon monoxide and at least one stream of oxygen to form a combustion product which is at a temperature of at least 1250 DEG C., the linear velocities of the carbon monoxide streams being greater than that of each oxygen stream and the amount of oxygen fed being at least stoichiometric with the amount of oxygen fed, and passing the combustion product stream via a passageway to the reaction zone where it is mixed with the halide. In case (b) the carbon monoxide should contain less than 2.5% by volume, measured at 20 DEG  C., of water or water forming content, to avoid the need for supplementary purification of the product from contaminants due to greater water content.  Oxygen in excess over that required to react with the carbon monoxide may be at least 75% of the molar amount of halide fed and preferably meets the whole requirement for oxidation of the halide.  Alternatively, supplementary oxidizing agent, e.g. a free oxygen containing gas or a gas releasing oxygen on decomposition, e.g. nitric oxide, nitrous oxide or hydrogen peroxide, may be mixed with the halide stream which must be kept below 500 DEG C.  The combustion zone has a cross-sectional area greater than that of the passageway, preferably at least half as great again, and the effective length of the combustion zone may be 0.01 to 20 times the length of the passageway.  The length of the passageway is such that the combustion product stream on entering the reaction zone contains less than 20% by volume of carbon monoxide and is preferably substantially free therefrom.  The process is particularly described with reference to titanium dioxide, but also mentions the oxides of Al, Zn, Zr, Si, Fe, and Cr.  In addition to the main reactants there may be added to the reaction zone an inert gas, e.g. chlorine, nitrogen, carbon dioxide, argon and recycled reaction gases, fed via an inlet adjacent to or surrounding the path of the combustion product stream to prevent reaction and deposition of oxide at the inlet, and metal or metalloid halides other than the halide to be oxidized, metal oxides, aromatic organic compounds, halogen gas or an alkali metal and/or alkaline earth metal compound fed with the halide stream or inert gas stream.  The halide additive may be aluminium chloride, bromide or iodide or zirconium tetrachloride in amount 0.5-10 mole per cent of titanium tetrachloride, or silicon tetrachloride, tetrabromide or tetraiodide in amount 0.001 to 2.7 mole per cent titanium tetrachloride, or mixtures of these compounds. The alkali metal compound is preferably a potassium compound, e.g. potassium chloride, sulphate, nitrate or acetate or mixtures thereof, organo-potassium compounds including alkyl, aryl, alkaryl, and aralkyl compounds, and these may also be introduced in a separate stream or fed to the combustion product stream.  The organopotassium compounds are preferably added with the titanium tetrahalide stream at below 600 DEG  C.  As well as, or instead of, the potassium compounds may be added metals or compounds of metals of groups IA and IB of atomic weight below 133, and of groups IIA and IIB of atomic weight below 138; e.g. Mg, Ca, Cu and Zn.  These may be employed as the metal vapour or as salts, e.g. magnesium chloride or phosphate, calcium chloride or acetate, cupric chloride or sulphate or zinc oxalate, or as organo-metallic compounds.  These metals and potassium may be added in amounts of 0.01 to 10,000 parts by weight metal per million parts TiO2 obtained.  As shown, reactor A has a steel shell 30 lined with heat resistant firebrick 31 surrounding chamber 37. Burner B fits into an opening in the upper section of A, and has a combustion chamber 4 leading via passageway 8 to reaction chamber 37. Combustion chamber 4 and passageway 8 are surrounded by high alumina refractory firebrick 3 capable of withstanding the temperature of the combustion product stream for at least a day.  Carbon monoxide at ambient temperature, e.g. 25 DEG  C., enters manifold 9 via pipe 10 and passes to the combustion zone 4 via burner jets 11, and oxygen also at ambient temperature is introduced via opening 33.  The downstream end of passageway 8 is formed by lip 12 of the refractory lining 3 which is contained by metal can 1. Cans 20 and 21 concentric therewith and having lips 23 and 24 at their lower end enclose annular ducts for inert gas and titanium tetrachloride respectively. Fig. 7 (not shown) illustrates a refractory combustion burner having a plurality of holes.  Carbon monoxide is fed to the hollow interior of the burner, and oxygen is fed to the exterior of the burner.  Fig. 7 also illustrates an additional metal can to allow for the introduction of a mixture of, for example, chlorine and aluminium chloride to the combustion product stream before contact with the titanium tetrachloride.  By this means, finely divided alumina, or other metal oxide particles, e.g. below 0.15 microns, may be introduced as a desirable additive to the reaction zone.  The outer surfaces of the cans are maintained at 700 DEG  C. or lower, preferably below 600 DEG  C., e.g. by adjusting the rate of flow of reactant gases. The temperature within the reaction zone is above 800 DEG  C., typically 900 DEG  to 1100 DEG  C. Preferably a temperature gradient of 25 DEG  to 200 DEG  C. per second of residence time is maintained in the reaction chamber.  This may be achieved by introducing coolant inert gases tangentially into the chamber via ports 34, 35, 36.  Alternatively the depth of the refractory lining may be reduced, or a metal chamber may be employed whose external walls are cooled by means of air, water or perchloroethylene.  The temperature of the product stream leaving the reaction zone is above 750 DEG  C.