Improvements in the Manufacture of Sodium Cyanide.
Year: 1899

page_text: Date of Application, 5th Jan.. 1899
Complete Specification Left, 3rd Oct., 1899-Accepted, 25th Nov., 1899
Improvements in the Manufacture of Sodium Cyanide.
I, GEORGE WILLIAM JOHNSON, of 47, Lincoln's Inn Fields, in the County of
London, Patent Agent, do hereby declare the nature of this invention (which has
been communicated to me from abroad by the Deutsche Gold & Silver Scheide-
Anstalt vorinals Roessler, of Frankfurt-on-Maine, in the German Empire) to be as
follows:
The majority of methods for obtaining evanides synthetically, yield, in variable
proportions, a mixture of charcoal, alkali cyanide, and alkali carbonate, from which a
marketable product is only derived by lixiviation, evaporation, and fusion.
Numerous difficulties attend these operations. Lixiviating the mixture yields a
lye which contains so much carbonate mixed with the cyanide, that direct evapora-
tion gives a product of low value. Moreover it is known that cyanide solutions, when
evaporated without a vacuum, undergo decomposition. Complete evaporation to dry-
ness in a vacuum is, however, rendered almost impossible, because the salt which
separates forms a sticky mass on the flour of the vessel, prohibiting agitation by
means of stirrers. Furthermore, this deposit is a bad conductor of heat, and so
retards evaporation.
Siepermann's method (D. K. P. No. 51562) takes advantage of the difference in
solubility of potassium cyanide and potassium carbonate, the former being salted out
from a warm, concentrated solution by adding potassium carbonate. The method is
not applicable to the sodium salts; as the solubility relationship is quite different.
In synthesising cyanides, however, the sodium salts offer a series of other advan-
tages over the potassium compounds, which makes it desirable to employ them.
The objects of the present method are to obtain from a mixture of sodium cyanide
and carbonate of soda in any proportions a sodium cyanide lye which is nearly free
from sodium carbonate, and to avoid complete evaporation and the loss of oyanide
which this involves, and prepare from this lye a pure, anhydrous sodium cyanide
which can be converted direct into the marketable form by fusion.
The first part of the process depends on the fact, not hitherto observed, that, con-
trary to the behaviour of the potassium salts, the sodium cyanide precipitates sodium
carbonate from the lyes.
Whilst a solution containing 320 grams of sodium cyanide (NaCy) per liter is
capable of dissolving 65 grams of sodium carbonate (Na,CO), a sodium cyanide
solution concentrated at 24° C. (containing 424 grams of NaCy per liter) only dis-
solves 47 grams of Na,CO, a solution concentrated at 83° C. (with 517 grams of
NaCy per liter) dissolving only 26 grams of Na₂CO₂. The maximum solubility of
sodium cyanide (517 grams in 1 liter of solution) is attained at 33° C. No further
quantity of sodium cyanide dissolves on raising the temperature.
If therefore a mixture of sodium cyanide and carbonate of soda be treated with
moderately warın water in quantity insufficient to completely dissolve the sodium
cyanide, the maximum concentration should yield, according to the above data, a lye

page_text: containing 517 grams of NaCy and 26 grains of Na₂CO₂ per liter. A second treat-
ment with water would then yield a lye which contained the remainder of the NaCy,
and much more sodium carbonate than existed in the first lye. If this second solu-
tion be used for lixiviating a fresh quantity of the mixture of NaCy and Na₂CO₂, a
further amount of NaCy passes into solution, no Na,CO, being dissolved, but rather
a portion of the Na,CO, originally present in the lye is precipitated, in proportion to
the NaCy dissolved. On washing the residue there is obtained a lye which, being
again poorer in cyanide and richer in carhouate, can be used for extracting the
subsequent portions.
By systematic extraction at a moderate temperature it is in this manner possible
to obtain from a chance mixture of sodium cyanide and sodium carbonate, a lye con-
taining NaCy and Na,CO, in the proportion of 100: 5.
If the whole mass be lixiviated with sufficient water to bring all the salts into
solution, the carbonate of soda, in which the lye is comparatively rich, can be salted
out by addition of sodium cyanide. Or the lye is evaporated in a vacuum until it
reaches the concentration corresponding to 517 grams of NaCy and 26 grams
of Na Co, per liter, this process precipitating sodium carbonate but not sodium
cyanide.
"
The lye which has been concentrated in this manner yields on cooling a copious
deposit of crystals consisting of NaCy + aq.
These crystals can be freed from water of crystallisation by exposure to a vacuum
at ordinary temperatures over sulphuric acid or calcium chloride.
The following is a more rational method depending on the fact, hitherto unobserved,
that if the crystals of NaCy+2aq are dissolved in their water of crystallisation at 33°,
they do not yield a clear liquid. Forty per cent. of the NaCy which they contain
separates as anhydrous salt, which is not redissolved on raising the temperature.
The anhydrous salt separates in a granular form and is quite easily freed from
supernatant liquid by suction.
The latter solution again contains 517 grams of NaCy per liter, and deposits crystals
of NaCy+aq on cooling. The mother liquors obtained in the crystallisation are used
for dissolving fresh quantities of cyanide or concentrated in a vacuum until con-
taining 517 grams of NaCy per liter.
Avoiding crystallisation, the anhydrous NaCy can be obtained direct from the lye
produced in the manner herein before described. If the lye concentrated at 33° C. be
freed from the sodium carbonate which has separated and further evaporated in a
vacuum, the crystals of NaCy + 2aq are fused in their water of crystallisation further
evaporation yielding copious deposits of anhydrous NaCy.
On the manufacturing scale it is advantageous to employ a vacuum apparatus with
continuous projection, working so that the thin lye, rich in sodium carbonate, is first
evaporated to the concentration represented by 517 grams of NaCy per liter, thus
depositing the greater part of the sodium carbonate, but no sodium cyanide. After
removing the carbonate, further concentration in the same apparatus yields a
deposit of anhydrous sodium cyanide with only a small proportion of sodium carbonate,
the product being filtered by suction, and fused.
This property of Na Cy + 2Aq to melt in its water of crystallisation at 33° C.
yielding the anhydrons salt, and the insolubility of the anhydrous salt at higher
temperatures, can be advantageously applied to the production of sodium cyanide
from hydrogen cyanide, or gases containing hydrogen cyanide, and caustic soda.
If hydrogen cyanide be passed into cold, concentrated caustic soda, NaCy+ Aq
crystallises out at a certain concentration. If however, caustic soda at 33° C. be used in
the absorption, anhydrous NaCy separates immediately on the concentration reaching
517 grams NaCy per liter.
1000

page_text: Improvements in the Manufacture of Sodium Cyanide.
I, GEORGE WILLIAM JOHNSON, of 47, Lincoln's Inn Fields, in the County of
London, Patent Agent, do hereby declare the nature of this invention (which has
been communicated to me from abroad by the Deutsche Gold & Silber Scheide
Anstalt vormals Roessler, of Frankfurt-on-Maine, in the German Empire) and in what
manner the same is to be performed, to be particularly described and ascertained in
and by the following statement:—
The majority of methods for obtaining cyanides synthetically, yield, in variable
proportions, a mixture of charcoal, alkali cyanide, and alkali carbonate, from which
a marketable product is only derived by lixiviation, evaporation, and fusion.
Numerous difficulties attend these operations. Lixiviating the mixture yields a
lye which contains so much carbonate mixed with the cyanide, that direct evapora-
tion gives a product of low value. Moreover it is known that cyanide solutions,
when evaporated without a vacuum, uudergo decomposition. Complete evaporation
to dryness in a vacuum is, however, rendered almost impossible, because the salt
which separates forms a sticky mass on the floor of the vessel, prohibiting agitation
by means of stirrers. Furthermore, this deposit is a bad conductor of heat, and so
retards evaporation.
Siepermann's method (D.R.P. No. 51562) takes advantage of the difference in
solubility of potassium cyanide and potassium carbonate, the former being salted out
from a warm, concentrated solution by adding potassium carbonate. The method
is not applicable to the sodium salts, as the solubility relation-ship is quite different.
In synthesising cyanides, however, the sodium salts offer a series of other advan-
tages over the potassium compounds, which makes it desirable to employ them.
The objects of the present method are to obtain from a mixture of sodium cyanide
and carbonate of soda in any proportions, a sodium cyanide lye which is nearly free
from sodium carbonate and to avoid complete evaporation and the loss of cyanide
which this involves, and prepare from this lye a pure, anhydrous sodium cyanide
which can be converted direct into the marketable form by fusion,
The first part of the process depends on the fact, not hitherto observed, that,
contrary to the behaviour of the potassium salts, the sodium cyanide precipitates
sodium carbonate from the lyes.
Whilst a solution containing 320 grams of sodium cyanide (Na Cy) per liter is
capable of dissolving 65 grams of sodium carbonate (Na, CO₂), a sodium cyanide
solution concentrated at 24° C. (containing 424 grams of Na. Cy. per liter) only
dissolves 47 grams of Na. CO,, a solution concentrated at 33° C. (with 517 grams of
Na. Cy. per liter) dissolving only 26 grams of Na, Co. The maximum solubility of
sodium cyanide (517 grams in 1 liter of solution) is attained at 33° C. No further
quantity of sodium cyanide dissolves on raising the temperature.
If therefore a mixture of sodium cyanide and carbonate of soda be treated with
moderately warm water in quantity insufficient to completely dissolve the sodium
cyanide, the maximum concentration should yield, according to the above data, a lye
containing 517 grams of Na. Cy. and 26 grams of Na, CO, per liter. A second treat-
ment with water would then yield a lye which contained the remainder of the Na.Cy.,
and much more sodium carbonate than existed in the first lye. If this second solution
be used for lixiviating a fresh quantity of the mixture of Na. Cy. and Na₂ CO₂, a
further amount of Na. Cy. passes into solution, no Na, CO, being dissolved, but rather
a portion of Na, CO, originally present in the lye is precipitated, in proportion to the
Na. Cy. dissolved. On washing the residue, there is obtained a lye which, being again
poorer in cyanide and richer in carbonate, can be used for extracting the subsequent
portions.

page_text: By systematic extraction at a moderate temperature, it is in this manner possible
to obtain, from a chance mixture of sodium cyanide and sodium carbonate, a lye
containing Na. Cy. and Na, CO, in the proportion of 100: 5.
If the whole mass be lixiviated with sufficient water to bring all the salts into
solution, the carbonate of soda, in which the lye is comparatively rich, can be salted
out by addition of sodium cyanide. Or the lye is evaporated in a vacuum until it
reaches the concentration corresponding to 517 grams of Na. Cy. and 26 grams of
Na, CO, per liter, this process precipitating sodium carbonate, but not sodium
cyanide.
The lye which bas been concentrated in this manner yields ou cooling a copious
deposit of crystals, consisting of Na. Cy. + aq.
These crystals can he freed from water of crystallisation by exposure to a vacuum
at ordinary teinperatures over sulphuric acid or calcium chloride.
The following is a more rational method, depending on the fact, hitherto unobserved,
that if the crystals of Na Cy + 2 aq. are dissolved in their water of crystallisation at
33°, they do not yield a clear liquid. Forty per cent. of the Na. Cy. which they
contain separates as anhydrons salt, which is not redissolved on raising the tempera-
ture. The anhydrous salt separates in a granular form, and is quite easily freed from
supernatant liquid by suction.
The latter solution again contains 17 grains of Na. Cy. per liter, and deposits
crystals of Na. Cy. +2 aq. on cooling. The mother-liquors obtained in the crystal-
lisation are used for dissolving fresh quantities of cyanide, or concentrated in a
vacuum until containing 517 grams of Na. Cy. per liter.
Avoiding crystallisation, the anhydrous Na. Cy. can be obtained direct from the
lye produced in the manner herein before described. If the lye concentrated at 33°C.
he freed from the sodium carbonate which has separated, and further evaporated in a
vacnuin, the crystals of Na. Cy. + 2 aq. are fused in their water of crystallisation,
further evaporation yielding copious deposits of anhydrous Na. Cy.
On the manufacturing scale it is advantageous to employ a vacuum apparatus with
continuous removal of the precipitate working so that the thin lye, rich in sodium
carbonate, is first evaporated to the concentration represented by 517 grams of Na. Cy.
per liter, thus depositing the greater part of the sodium carbonate, but no sodium
cyanide. After removing the carbonate, further concentration in the same apparatus
yields a deposit of anhydrous sodium cyanide with only a small proportion of sodium
carbonate, the product being filtered by suction, and fused.
This property of Na. Cy. + 2 aq. to melt in its water of crystallisation at 33° C.,
yielding the anhydrous salt, and the insolubility of the anhydrous salt at higher
temperatures, can be advantageously applied to the production of sodium cyanide
from hydrogen cyanide, or gases containing hydrogen cyanide, and caustic soda.
If hydrogen cyanide be passed into cold, concentrated caustic soda, Na. Cy. + aq.
crystallizes out at a certain concentration. If, however, caustic soda at 33° C. he
used in the absorption, anhydrous Na. Cy. separates immediately on the concentration
reaching 517 grams Na. Cy. per liter.
Having now particularly described and ascertained the nature of this invention,
and in what manner the same is to be performed, I declare that what I claim
is :-
1. The manufacture, from a mixture of sodium carbonate and sodium cyanide, of a
sodium cyanide lye very nearly free from sodium carbonate, by systematic extraction
at a moderate temperature (about 33° C.), using the second lye from the previous
operation, being poor in cyanide and rich in carbonate, for the purpose of extracting
a fresh charge, whereby the sodium carbonate is displaced from solution by the
sodium cyanide,
2. In a process according to the preceding claim, extracting the whole mass with
just sufficient water to dissolve the salts, and precipitating from this lye, com-
paratively rich in carbonate, the carbonate by adding sodium cyanide at about 38° C
3. In a process according to the precedings claims, evaporating in a vacuum the

page_text: lye rich in carbonate until it reaches a concentration at which only carbonate, and no
sodium cyanide, separates.
4. Ju a process according to the preceding claims, cooling the lye obtained in such
process, and allowing the hydrated sodium cyanide crystals which separate to effloresce
in a vacuum at ordinary temperatures over sulphuric acid or calcium chloride, thus
obtaining the cyanide in the pure, anhydrous, marketable form.
5. In a process according to the preceding Claims 1, 2 and 3, cooling the lye obtained
in such process and fusing the hydrated salt in its water of crystallisation, so as to
obtain sodium cyanide in the anhydrous condition.
6. In a process according to the preceding Claims 1, 2 and 3, further evaporating
in a vacuum the lye obtained to obtain a deposit of anhydrous sodium cyanide.
7. The preparation of anhydrous sodium cyanide as herein before described, by
passing hydrogen cyanide, or gases containing hydrogen cyanide, into concentrated
caustic soda heated to above 33° C., when the salt is deposited in the anhydrous state
as in the processes hereinbefore described.
1 1
1000
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.