GB836212A - Improvements in or relating to the separation of gaseous or vaporous mixtures by condensation - Google Patents

Abstract

A gaseous or vaporous mixture of volatile materials is separated by fractional condensation by passing into a packed condensation zone the packing material of which has a particle size below 100 microns and a free volume and area sufficient to hold all condensed liquid on to the packing material and has been precooled to below the condensation temperature of the most volatile material, so that at least a portion of the mixture is condensed on the packing, continuing the passage of the mixture so that condensation of the lesser volatile material causes revaporization of the most volatile material which recondenses further along the zone thereby forming a series of advancing fronts, the most volatile material passing first from the zone; terminating the flow of material before the second front begins to emerge from the zone and the materials are recovered from the packing, e.g. by driving them out by passing in a stream of the least volatile material or a less volatile material or by reducing the pressure or by elution with a suitable gas not condensed at the working temperature and collecting the fractions as they emerge. The process is theoretically adiabatic and all material on the packing is removed, e.g. by reducing the pressure thereby restoring the packing to its original cold temperature. Temperature adjustment may be made by passing an inert gas at the desired temperature and this may be combined with the stripping of material remaining on the packing; if the fractions on the column are eluted by a gas a temperature adjustment will have to be made as the packing will be heated by the eluting gas. Packing materials referred to are siliceous earths, powdered glass, glass fibre, cotton, wool, paper, sawdust, solvent extracted sawdust, non-activated charcoal and coke preferably of a particle size less than 0.1 mm., kieselguhr however is preferred. Selective adsorbants may be used but are not generally desirable. The column is preferably used vertically to avoid channelling and in long columns the packing may be supported at intervals on grids. Gas flow rates of 0.1-10 ft. per sec. may be used. In a preferred embodiment the vapours or gases flow through a warm section first where no condensation occurs, then through the cold section then through a further warm section. The cold product issuing from the cold section cools the final warm section, the result being that the cold section moves towards the end. When it reaches the end the components are stripped off and the cold section cooled if necessary, then the process worked in the opposite direction to move the cold section back to the other end. By this means the product is recovered as a vapour at its original temperature. Wide columns are preferred, but, to compensate for heat losses at the outer surface, material collected from an annular section by the wall is discarded by using a simple annular guard ring at the exit. Between each band of pure material issuing from the condenser will be a mixture of the two adjacent components which is discarded. The process is suitable for the separation of vaporizable olefines, paraffins, aldehydes, ketones, esters, organic halogen compounds and aromatic compounds of 2-35 carbon atoms, air, rare gases, heavy from ordinary water and volatile compounds of isotopes.