GB763369A - Process for the catalytic conversion of gases and/or vapours - Google Patents

Abstract

<PICT:0763369/III/1> A catalyst obtained by condensing an aerosol consisting of solid particles formed from the vapour phase is fluidized by means of gases and/or vapours to effect reactions therein. Processes specifically referred to are; single stage oxidation of hydrogen sulphide or sulphur dioxide to sulphuric acid or sulphur trioxide; oxidation of sulphur with air to sulphur trioxide; preferably with a catalyst prepared from vanadium oxide and potassium sulphate; reduction of sulphur dioxide to sulphur with carbon monoxide or hydrocarbons using alumina; and organic catalyses, followed by continuous regeneration of a portion of the catalyst e.g. by reburning, evaporating and recondensing with the addition of fresh metal powder. In the fluidized bed the catalyst is stated to form small agglomerated flakes. The catalyst may be prepared by vaporizing the constituents, (or forming them in the vapour phase), cooling by admitting a cold gas, to produce an aerosol and then precipitating the aerosol on a cooled surface, or electrically or by means of sonic or supersonic iradiation. A metal or metal mixtures in powder form may be injected into a combustion chamber at above the ignition speed with a reactive gas e.g. air and ignited therein; other ingredients may be added as such or as a material yielding them, e.g. salts. If desired a metal forming a catalytically inert oxide may be employed and an active oxide added to the combustion mixture. Oxidic catalysts so formed may be subsequently reduced partly or entirely to metal, preferably with gaseous reducing agents. A filter is preferably used to remove entrained catalyst from the emerging gases, and the fluidized bed may be expanded sufficiently to come into contact therewith. Perforated plates, nets or porous filters may be used, but apertures need not be smaller than 0.1-2 mm. The catalyst may be in several beds vertically or horizontally disposed; in the former case they may be kept separate by the use of a filter, which also acts as a grate for the upper bed or by a constriction in the containing chamber resulting in a zone of increased velocity between the beds. If desired stages in which the bed of catalyst is stationary may be used e.g. to perform the last stages of a reaction. Thus a stationary bed of catalyst in the form of balls may be employed through which gases from the fluidized bed pass. The entrained solids may be separated by the stationary catalyst but in the last mentioned case this is preferably not so and a filter may be provided after the stationary catalyst. The temperature of the fluidized layer may be regulated by direct or indirect heating or cooling of the walls or by incorporation of heating or cooling elements in the reaction vessel. In the apparatus shown in Fig. 1, when used for production of sulphur trioxide from sulphur dioxide, cold roasting gases enter a heat exchanger 9 at 10 and pass to a fluidized bed of a catalyst comprising 5 per cent V2O5, 7 per cent K2O and 88 per cent SiO2 in the upwardly flared chamber 1 having a temperature of 420 DEG C. The rising gases pass through a perforated filter plate 2 (although this is not necessary with a flared reactor) to a stationary contact mass 3 and thence to the heat exchanger where the inlet gases are heated up. If desired, a plurality of fluidized zones may be used, operation temperature then varying from 500 DEG C. in the first to 420 DEG C. in the last. A similar apparatus, in which the stationary bed is omitted, and containing cooling tubes is described with respect to the oxidation of hydrogen sulphide to sulphuric acid at 440 DEG C.