Patent GB-190304513-A (GB)
Title: Improvements in the Manufacture of Cyanides, and the Recovery of Bye-products.
Filed: 1903-02-26
Granted: 1904-02-25
Abstract: 4513. Grossmann's Cyanide Patents Syndicate, and Crossmann, J. Feb. 26. Cyanides.-Consists in manufacturing potassium, sodium, and calcium cyanides by heating potassium or sodium ferrocyanide, or mixtures thereof, or calcium-potassium ferrocyanide and similar compounds, with sulphuric acid or suitable acid sulphates, such as sodium or potassium bisulphate, nitre cake, or the like, or with hydrochloric, phosphoric, or other acid, and absorbing the hydrogen cyanide with caustic soda or potash, or a mixture of both, or with milk of lime, or with a mixture of slaked lime and potassium or sodium sulphate or both. Consists also in re-converting the insoluble residue, Everitt's salt K2Fe2Cy6, produced in the above operation, into ferrocyanide, by first forming Prussian blue, and then heating the latter with caustic alkali, alkali-carbonate, or alkaline earths, or a mixture of these. The distillation with, say, sulphuric acid is carried out in a lead still, or one of enamelled iron, pipes for supplying air, live steam, acid, and ferrocyanide leading to the bottom of the still, which may also contain a steam coil for heating by confined steam. The amount of acid is about 2-5 per cent. in excess of the quantity necessary for the theoretical reaction :- and the hydrogen cyanide passes through a water or air-cooled iron fractionating-apparatus, to the iron absorbing-vessels, which are fitted with suitable agitating apparatus. The whole system is connected at its outlet with a Korting exhauster or similar device, for producing a partial vacuum or drawing air through under a partial vacuum or otherwise, the distillation taking place under a pressure of about four inches of mercury. Two or three absorbing-vessels are arranged in series, preferably at increasing heights, so that the liquid from the higher can be drawn into the lower vessel, and the gas entering the lower vessel is taken to the bottom and leaves through a pipe at the top, passing to the next vessel, and so on. In all cases, the alkali must be kept in excess and the temperature below 40‹ C. In the case where calcium cyanide is formed, but only as an intermediate product in the making of potassium or sodium cyanide, the cyanide is treated with the sulphate produced in the first distillation, and the insoluble calcium sulphate filtered off. The hydrogen cyanide may be absorbed by mixing the potassium sulphate with the slaked lime, when the insoluble calcium sulphate is formed directly, along with potassium cyanide. In both cases, the alkali sulphate is previously neutralized by calcium carbonate, alkali carbonate, or the like, and then concentrated or crystallized. After decanting off the alkali sulphate, the Everitt's salt is boiled with an oxidizing-agent, which becomes reduced thereby to a lower state of oxidation: Instead of a higher oxide, a lower oxide, or an acid such as sulphuric acid, together with air may be used. In the example given, a ferric-salt solution is used, and is boiled with the Everitt's salt, either in the still or in a separate vessel. Prussian blue is formed, and is separated from the alkali sulphate and ferrous salt. It is then washed well with water. Or the Everitt's salt may be first washed, and then treated with the ferric salt. The alkaline-sulphate and ferrous-salt solutions are treated to precipitate the iron, and the alkali sulphate purified by concentrating, crystallizing, or fishing. The Prussian blue is boiled with caustic alkali, alkaline oarbonate, or a mixture of caustic and carbonate or a mixture of carbonate and oxide or hydrate of an alkaline earth to form ferrocyanide, which is neutralized and sent back for re-use. In all cases, whatever the first yield of hydrogen cyanide, the resulting Everitt's salt contains exactly the amount of cyanogen corresponding to the difference between the total oyanogen in the ferrocyanide and that evolved as hydrogen cyanide. The ferrocyanide should be reasonably free from carbonate, sulphides, and other ingredients interfering with reaction or influencing the quality of the cyanide produced.