Improvements in Process and Apparatus for Procuring Cyanogen and its Compounds from Gases.
Year: 1891

page_text: Date of Application. 14th May, 1891
Complete Specification Left, 6th Aug., 1891-Accepted, 5th Sept., 1891
PROVISIONAL SPECIFICATION.
[Communicated from abroad by JULES ELSNER, of No. 30, Boulevard de Magenta,
Paris, in the Republic of France, Engineer, and ROBERT GASCH, of Mainz,
in the German Empire, Chemical Engineer.]
Improvements in Process and Apparatus for Procuring Cyanogen
and its Compounds from Gases.
I, HENRY HARINGTON LEIGH, Assoc. M. Inst. C.E., Fel. Inst. P.A.,
practising as Phillips & Leigh, of No. 22, Southampton Buildings, Chancery Lane,
in the County of Middlesex, Engineer and Patent Agent, do hereby declare the
nature of this invention to be as follows:-
This invention relates to improvements in process and apparatus for procuring
cyanogen and its compounds from gases, and is applicable to the gases developed
during the dry distillation, or the combustion, of coal, coke, anthracites, bituminous
schists, peat, bones, leather, and other substances of an analogous chemical
composition, the object of the invention being to save the cyanogen and its
compounds and to utilise them for industrial purposes.
It has been demonstrated by numerous experiments conducted by my com-
municators that the cyanogens above mentioned may be easily saved if the gases
containing them are led over or through liquors which hold, either in solution or in
suspension, metallic sulphurets, cyanide precipitates prepared by the action of
metallic sulphurets upon cyanide lyes, or liquors containing cyanides; alkaline,
magnesian, or alumina sulphates with milk of lime; any metallic salt soluble in
water; a carbonate sulphate or an oxalate having an alkaline, magnesian, ammonia
or alumina base, or hydrated proto or other oxide or salt of iron.
The transformation of the cyanogen compounds may be effected not only in
respect of the ferro-cyanides usually met with, but also in respect of the salts in
which the iron in the radicle is replaced by other metals, as for instance in the case
of the mangano-cyanides. This can be accomplished easily and expeditiously by
precipitation with suitable metallic sulphurets provided that free ammonia be
present.
at one of
The transformation is facilitated by an increased temperature;
from 50° to 60° C. it is instantaneous. The presence too, of a small quantity
in the liquor of the compound to be produced has been found to expedite the
reactions.
In those industries in which the presence of free ammonia is rendered impossible
by reason of it being burnt, an alkaline sulphate of ammonia of magnesia or of
alumina with milk of lime is used. This means of providing the necessary alkalinity
is preferable, outside the question of cost, to other methods, even to the use of
carbonates, by reason of the formation of sulphate of lime.
The practical working of this invention is capable of different modifications
according as to whether the cyanogen has to be extracted from the products of a
dry distillation process or of combustion, or whether it becomes a question of
extracting a product of small or of considerable value from large volumes.
Local circumstances, such as the particular nature of the industry which yields
the cyanogen gases to be treated, have naturally a modifying influence upon the
working of the invention. But the apparatus employed is fundamentally an
aggregation or combination of scrubbers condensers and similar vessels of any
suitable construction in respect of detail, provided that the gases can be brought
into intimate contact with the bodies in the liquors.
In a combustion process, e.g., in a blast furnace, there will not be any tar and
little enough ammonia. In such a case, it becomes possible to absorb all the

page_text: cyanogen, not exactly because, there being no tar to deal with, the absorption
apparatus can be fixed closer to the furnace where a high and therefore favorable
temperature can be enjoyed, but principally because hot gas is richer in ammonium
cyanide than cold gas. But when the process is one of dry distillation, it is not
possible to recover all the cyanogen under the conditions just mentioned. Never-
theless, it should be pointed out that the total quantity of cyanogen from a dry
distillation process, per ton of stuff operated on, is much higher than from a
combustion process., The absence of tar has the advantage of permitting the
production of a more valuable result.
When high priced metallic sulphurets are used, sulphuret of copper for instance,
solutions are obtained which resemble prussiate of potash, and from which
characteristic colours can be extracted. These colours may be obtained directly
by employing only a proper metallic sulphuret or a cyanogen precipitate prepared
with high-priced cyanogen lye and a metallic salt.
In dry distillation plant, it is even possible to recover nearly all the cyanogen.
This is accomplished by establishing the absorption apparatus in a position
favourable for the gases to traverse it at a temperature as high as 36° C., or
otherwise sulpho-cyanite will form. In this case, it is well to work in the direction
of obtaining ferro-cyanide of ammonium, consequently to employ only sulphuret of
iron without excluding the admission of the two other substances in certain
determinate circumstances. The extra yield of cyanogen compensates for the
increased consumption of the sulphuret of iron.
Local circumstances alone will determine whether condensers or scrubbers shall
be used, or if one large or several smaller absorption apparatus shall be erected.
There is this advantage with scrubbers that the cyanogen lye can be brought to
one pitch of concentration without repumping being necessary.
The metallic sulphurets may be prepared from, or in the liquors, or supplied
thereto in bulk.
It is evident that this new process yields larger quantities of cyanogen than have
hitherto been extracted by prior processes. A further advantage is the high
degree of concentration and purity of the cyanogen lye, as well as the convenient
form for ulterior treatment in which the cyanogen is present. The only impurities
which can be produced during work with metallic sulphurets are a small quantity
of sulphuret of ammonium, or sulphuret of potassium, which can be eliminated as
follows: Let us take, for example, that class of cyanogen compounds from the
treatment of which will result sulphuret of iron as well as prussiate, the latter
consequently containing some alkaline sulphuret. The latter is decomposed by the
light blue cyanide precipitate which had been previously prepared from a portion
of the cyanide lye and a solution of ferric sulphate. The precipitate gives with the
alkaline sulphurct a fresh quantity of ferro-cyanide lye and of sulphuret of iron,
which serves for a fresh absorption, as first or fresh matter. This treatment of the
lye has the further advantage of making the process a continuous one.
The addition of the charge of light blue cyanide precipitate may take place near
the end of the operation, that is to say a short time before the lye has concentrated
enough. But the charge may also be introduced at an earlier stage, that is to say
as soon as as much of the ferro-cyanide lye has been obtained by means of sulphuret
of iron as is necessary to make a portion of light blue precipitate. From that point,
the work can be carried on only with the light blue precipitate instead of with the
sulphuret of iron, the object being to prevent the formation of alkaline sulphuret at
first.
This method substitutes the preparation of light blue precipitate for the
preparation of sulphuret of iron, and does not introduce fresh quantities of sulphur ;
and this is why that it is, in the majority of cases, so preferable to the metallic
sulphuret method.
If it is desired to produce metallic cyanides, soluble metallic salts in solution
are presented to the action of the gaseous currents without any precipitate in
suspension.

page_text: Generally speaking, the metallic chlorides are the most suitable, but for certain.
metals other soluble metallic salts may be used.
Dated this 14th day of Nov 1801
HENRY H. LEIGH.
COMPLETE SPECIFICATION.
Improvements in Process and Apparatus for Procuring Cyanogen
and its Compounds from Gases.
I, HENRY HARINGTON LEIGH, Assoc. M. Inst. C.E., Fel. Inst. P.A.,
practising as Phillips & Leigh, of No. 22, Southampton Buildings, Chancery
Lane, in the County of Middlesex, Engineer and Patent Agent, do hereby
declare the nature of this invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:-
The object of the present invention is to enable the various cyanogen compounds
contained in the gases produced in various industries, such as the manufacture of
pig iron in blast furnaces, the production of gas for illuminating purposes from
coal, and other processes involving dry distillation, such as the manufacture of coke
in coke ovens, to be recovered satisfactorily and economically so as to enable them
to be employed technically.
Among others, De Vigne of London has attempted to solve this problem by
making use of iron filings, or of a mixture of a ferrous salt with carbonate of soda,
while Dr. Knublauch of Cologne has made use of the oxides, hydrates, or carbonates.
of iron, manganese and zinc, either suspended mechanically or dissolved in water
already containing a certain amount of alkalies in solution.
Neither of these processes has proved to be of any practical value, and even
where they are made use of, the cyanogen compounds which they have been
designed to recover, pass off, and are as completely lost as if they were not
employed.
As a general rule the gases such as I have described above in which cyanogen
compounds occur, contain larger or smaller quantities of ammonia, and it is conse-
quently advisable that any substances or mixtures of substances by means of which
it is desired to "fix" the cyanogen compounds should contain bodies with which the
ammonia can readily combine.
By an extended series of experiments I have ascertained that the cyanogen-
compounds contained in the gases produced by blast-furnaces, gas-works, or coke-
ovens, may be most conveniently and economically recovered by conducting a
current of the said gases through a liquid containing metallic sulphides, such as the
sulphides of iron, copper, nickel, &c., &c., also lime in a fine state of division
mechanically suspended in it. This liquid should also contain a certain amount
of soluble sulphates or oxalates of alkali, ammonia, magnesia or alumina.
The gases containing the cyanogen are preferably brought into contact with the
liquid above described by means of some arrangement similar to a scrubber, or
sulphuric acid tower, in which, while the gases ascend vertically, the liquid falls
from the top of the apparatus to the bottom. The result of the reactions which
ensue is to give rise on the one hand to the formation of certain cyanogen compounds
analogous to the prussiates of potash in constitution, and on the other, to form
sulphate and oxalate of lime and ammonia and finally of calcium sulphide. The
superficial attraction existing between the particles of the last named compounds
exercises a scrubbing or purifying action upon the solution containing the
cyanogen salts tending to free it from the so called "brown bodies" and other
impurities.
I do not of course regard the above method of bringing the gases and the liquid
into contact with one another as novel, and any other suitable method of effecting
the same object may be employed without altering the nature of my invention.

page_text: After the process of bringing the gases into contact with the liquid has been
continued for a certain length of time a weak solution of sodium ferro-cyanide is
obtained which may be run off from the precipitate described above and subjected
to further treatment.
It is, however, especially in the case of the solution first obtained, desirable that
it should be subjected to concentration.
I effect this concentration in a special manner. I first of all draw off a certain
amount of the solution. This I render slightly acid, and then add a suitable
quantity of a soluble metallic salt-in the present instance a salt of iron. This
gives rise to the formation of a precipitate which is, to all intents and purposes,
basic Paris blue when a ferrous salt has been employed, and neutral Paris blue
when a ferric salt has been used.
The remaining portion of the solution first obtained is then treated with this
insoluble precipitate. This causes a double decomposition of the precipitate
producing on the one hand sodium ferro-cyanide and so increasing the amount of
that body in the solution; on the other hand the action of the sodium sulphide
contained in the solution on the iron of the precipitate, effects the formation of
sulphide of iron which forms a fresh precipitate and may be collected and employed
for the further recovery of cyanogen from the gases.
The advantages attending this method of procedure are that in addition to con-
centrating the original solution of ferro-cyanide, it, at the same time, eliminates in
a practical and simple manner the soluble sulphides present without introducing
fresh sulphur in the form of sulphide of iron.
This operation is repeated until the solution has attained the desired degree of
concentration when it will be found that it has at the same time become both purer
and more transparent. From the solution obtained by this process a product may
be prepared possessing a much higher market value than any of those which have
been recovered by other methods.
The process may be carried out practically with great case and simplicity as
follows:-
The gas from which the cyanogen-compounds are to be recovered is, as indicated
above, conducted by means of a tube or pipe into a chamber constructed on the
principle of a scrubber, washer, or combination of both, in accordance with the
standard system, or with the system of Ledig, and which may or may not be
provided with a spray jet.
The solution or liquid which has been prepared as described above drops or
trickles inside the scrubber from the top to the bottom where it meets the current
of gas containing the cyanogen-compounds, depriving it of these bodies, and finally
collecting in a receptacle provided at the bottom of the apparatus. From this
receptacle it may be pumped up again to the top of the scrubber to be again
subjected to the same operation, or may be drawn off to be concentrated to the
desired degree and at the same time desulphurized by means of the process which I
have described in detail above.
Having now particularly described and ascertained the nature my said inven
tion and in what manner the same is to be performed I declare that what I
claim is,
1. A process for the recovery of cyanogen and its compounds from gases
produced by combustion or dry distillation, and consisting essentially of a method
by means of which the said gases are brought into intimate contact with a liquid
containing in solution an amount of oxalates or sulphates of alkali, ammonia,
magnesium hydrate, or a similar salt, corresponding to or depending on the quantity
of ammonia contained in the gases treated, this said liquid or solution containing
also suspended in it lime and a metallic sulphide, both in a minute state of division,
for the purpose of obtaining a solution of cyanogen-compounds analogous in consti-
tution to the prussiates of potash, essentially as described.
2. The concentration and purification of the liquor or solution obtained by the

page_text: process described in Claim 1, by means of treating a portion of the said liquor with
such metallic salts as will form insoluble cyanides, and adding the precipitate
formed to the remaining portion of the said liquor whereby the alkaline sulphides
contained in the precipitate are reduced into insoluble metallic sulphides and
soluble combinations of metallic cyanides.
1901
HENRY H. LEIGH,
22, Southampton Buildings, Chancery Lane, W.C.