Patent GB-190126396-A (GB)
Title: Improvements in, and relating to, the Recovery of Hydrocyanic Acid from Gases
Inventor: FELD WALTHER
Filed: 1901-12-24
Granted: 1902-12-24
Abstract: 26,396. Feld, W. Dec. 24. Hydrocyanic acid.-Relates to the recovery of hydrocyanic acid from illuminating-gas, blast-furnace and coke-furnace gases, and the like, and consists in the following processes for obtaining the whole of the cyanogen as pure hydrocyanic acid :- (1) Treating the gas with a basic compound which will, when cold, absorb cyanogen and decompose ammonium cyanide (forming a cyanide), such as the neutral or basic carbonates, the hydrates and oxides of magnesium, aluminium, zinc, lead, and manganese, or mixtures thereof, or mixtures of their salts with oxides, hydroxides, or carbonates of the alkalies or alkaline earths, and then heating the cyanides in solution or suspension, whereby hydrocyanic acid is liberated. The reactions may be represented, for example, by the following equations- The process may also be carried out by absorbing the cyanogen by an oxide, hydrate, or carbonate of an alkali or alkaline earth, and then liberating the hydrocyanic acid by beating the product with a solution of a magnesium, aluminium, zinc, manganese, or lead compound or mixtures thereof. (2) When the gases contain carbonic acid, as well as hydrocyanic acid or ammonium cyanide, the carbonic acid is first absorbed by means of a hot solution or suspension of a basic magnesium compound, such as magnesium hydroxide. Or the hydrocyanic acid and carbonic acid are both absorbed by an alkali, an alkaline earth, or magnesium hydroxide, in the cold, and then the solution is distilled with a salt of magnesium, aluminium, zinc, manganese, or lead, whereby the hydrocyanic acid is liberated. The process is carried out without absorption of the carbonic acid, by employing a cold solution or suspension of magnesium carbonate, or of a basic compound of aluminium, zinc, manganese, or lead, and then heating the mixture. Absorption of the hydrocyanic acid without absorption of the carbonic acid is also effected by employing a basic or neutral ferric or ferrous compound, or a basic, neutral, or acid solution or suspension of mercury or copper, and the hydrocyanic acid is then liberated bv boiling with or without an acid, such as hydrochloric acid. (3) When the gas contains sulphuretted hydrogen as well as cyanogen compounds, a cold solution or suspension of a hydrate or basic or neutral carbonate of magnesium, or of aluminium, whereby the sulphuretted hydrogen is unaffected, is used, and the mixture is subsequently boiled. Alternatively, a cold solution of or suspension of a basic compound of zinc, manganese, or lead is used to absorb both the sulphuretted hydrogen and the hydrocyanic acid, and the latter is subsequently liberated by boiling. Another method consists in absorbing the sulphuretted hydrogen alone by a hot basic solution or suspension of a compound of zinc, manganese, or lead, or by a hot solution or suspension of a neutral or basic compound of iron mixed with a salt of magnesium or aluminium, or by a hot acid solution of a compound of mercury, copper, lead, or iron, and afterwards absorbing the hydrocyanic acid by one of the processes mentioned under (1) above. When iron compounds are used in hot acid solution, the sulphuretted hydrogen is oxidized to water and sulphur. When both the sulphuretted hydrogen and hydrocyanic acid are absorbed by a basic compound of zinc, manganese, or lead, as above described, the hydrocyanic acid may be subsequently liberated by acting on the mixture with sulphuretted hydrogen, and then the hydrocyanic acid is absorbed as described under (1) above. (4) When the gas contains sulphuretted hydrogen and carbonic acid in addition to cyanogen compounds, the sulphuretted hydrogen is absorbed by any of the methods described under (3) above, except the first, and then the carbonic acid by any of the methods described under (2) above ; or the hydrocyanic acid may be freed from both the other gases by the first method described under (3) above. The hydrocyanic acid liberated in all the above processes is absorbed by an alkali or alkaline earth. Some of the sulphides produced in absorbing sulphuretted hydrogen are reconverted into hydroxides by a current of air.