GB338497A - Process for the separation of constituents from gas or vapour mixtures - Google Patents

Abstract

338,497. Caro, N., and Frank, A. R. Aug. 13, 1929. Nitric acid; nitrogen tetroxide; calcium cyanamide; hydrocyanic acid; ammonium carbonate and other ammonium salts.-Mixtures of gases or vapours, obtained as the products of chemical reaction, are treated by a process of condensation in which the temperature of the cooling agent is kept as far as possible below the temperature of the gases issuing from the condenser, when the large fall of partial pressure towards the cooling wall results in precipitation of one of the constituents, in solid or liquid form, without the dew point being reached in the bulk of the gas. A substance may be added to reactant gases and this substance, or its reaction products, removed by the process after passing the reaction zone but before further treating the mixture. Hot aqueous nitrous gases produced by combustion of ammonia, with the addition of steam, hydrogen, oxygen or sulphurous acid in some cases, can be treated to separate the water, free from, or poor in nitric acid, while avoiding a low temperature of the final gas mixture, the ammonia combustion apparatus, the heat utilizing boiler, and the condenser being connected one behind the other. A more concentrated acid, together with saving in cooling surface, is obtained using mixtures rich in oxygen and in nitrogen oxides, prepared e.g. according to Specification 273,718, employing the present process of condensation. Mixtures containing nitrogen oxides and water vapour from other sources such as from oxidation of hydrocyanic acid with air or oxygen, with or without addition of water vapour, may be similarly worked up. The reaction of ammonia and calcium carbonate to give calcium cyanamide may be carried out, using the present process for removing the water formed, the unconverted ammonia, which is still at a comparatively high temperature, being again introduced into the process. The gas mixture resulting from the reaction between carbon monoxide and ammonia to produce hydrocyanic acid and water may be similarly treated. If excess of carbon monoxide is used formation of carbon dioxide occurs which retards the reaction, as is also the case in the cyanide formation referred to above when carbon monoxide is added. To avoid this, ammonium carbonate solution may be separated instead of water, without the gas mixture being saturated with the separated solution. Ammonium salts can be separated from other ammonia-containing gas mixtures, or ammonia separated in liquid form from mixtures such as from the ammonia synthesis.