Patent GB-190300036-A (GB)
Title: Improvements in the Manufacture of Cyanides, and the Recovery of Bye-products.
Filed: 1903-01-01
Granted: 1903-09-24
Abstract: 36. Grosstmann. J., and Grossman's Cyanide Patents Syndicate. Jan. 1. Cyanides.-Consists in manufacturing cyanides by heating potassium or sodium feirocyanide, or mixtures of these, 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 acids, 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. Also in re-converting the insoluble residue, the potassium salt K2Fe2Cy6, Everitt's salt, produced in the above operation, into ferrocyanide, by heating it with caustic alkali and subjecting it to the action of air. 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 enters 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 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 washed and made neutral by caustic alkali or alkali carbonate, and then mixed with an equivalent quantity, plus about 5 per cent. of caustic soda or potash, or a mixture of both. It is boiled and violently agitated in a large vessel, and air is passed through by means of a compressor or steam injector, or else the whole is violently agitated in the presence of air, the colour of the iron oxide precipitated being brownish black at the finish of the operation. The reaction takes place according to the equation :- where x approaches unity, or may exceed it. The ferrocyanide is neutralized, and used again for the first distillation. 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 cyanogen in the ferrocyanide and that evolved as hydrogen cyanide. The ferrocyanide should be reasonably free from carbonates, sulphides, and other ingredients interfering with the reaction or influencing the quality of the cyanide produced.