560
MODERN GASWORKS PRACTICE
Bueb’s Process
The process of Dr. J. Bueb is one which has beeil used fairly widely, particularly on the Continent. The apparatus made use of is a washer-scrubber, in which a solution of ferro ns sulphate dissolved in ammoaiacal liquor is employed for washing the gas. The sulphate is converted into iron sulphide by the sulphurettedhydrogen in the crude gas—
FeS04 + H2S + 2 NH3 = FeS + (NH4)2SO4.
The sulphide, ammonia, and hydrocyanic acid then combine to form__
(a) Ammonium ferrocyanide—
FeS + 6 NH3 + 6 HCN = (NH4)4Fe(CN)6 + (NH4)aS.
(b) Cyanide of iron—
FeS+2 NH3+2 HCN==Fe(CN)2+ (NH4)2S. '
(c) Ammonium ferrous-ferrocyanide—■
2 FeS + 6 NH3 + 6 HCN = (NH4)2Fe2(CN)6 + 2 (NH4)2S.
By treating with lime the insoluble ferrous-ferrocyanide is converted into a soluble calcium ferrocyanide—
(NH4)2Fe2(CN)6 + 2 Ca(0H)2= 2 NH40H + Ca2Fe(CN)G + Fe(OH)2.
The free ammonia may then be distilled off by means of steam and recovered whilst the residual liquor is mixed with the required quantity of sodium carbonate or hydrate, when. sodium ferrocyanide results—
C^Fe(CN)6 + 2 Na2CO3= Na4Fe(CN)6 + 2 CaCO3.
Ciselet and Deguide, in their process, first bring the gas into contact with ferric hydrate, which. absorbs the sulphuretted hydrogen and hydrocyanic acid in. the gas. The sulphur and cyanogen are precipitated in the form of iron sulphide and iron cyanide. The iron sulphide is then regenerated to the hydrate by means of an air-blast, the sulphur being precipitated in the free form. Äfter regeneration, the ferric-hydrate solution is treated with sulphuric acid, which. renders the iron soluble whilst the sulphur and cyanogen remain insoluble. The two last-named can then be separated with. an alkaline solution, which dissolves the cyanogen compounds and forms alkaline ferrocyanides. Meanwliile, the free sulphur remains insoluble and can be filtered out.
South Metropolitan Gas Company’s Process
The South. Metropolitan Gas Company liave introduced a process by means of which. the cyanogen in the gas is recovered as hydrocyanic acid. The crude gas is washed with a solution of ferrous sulphate, the resulting liquor being treated with. an ammonium salt and boiled with lime, so that a double cyanide—-i.e. calcium-ammonium ferrocyanide, Ca(NH4)2Fe(CN)6—is formed. The acid radicle, namely, the hydrocyanide acid portion of the salt, is unaffected by the action of sulphuric acid, whilst the remainder is converted into ferrous ammonium ferrocyanide and