IMPROVEMENTS IN THE MANUFACTURE OF CARBONATE OF SODA BY THE AMMONIA PROCESS
Year: 1878

page_text: LETTERS PATENT to Sydney Pitt, of Sutton, in the County of Surrey, for the
Invention of "IMPROVEMENTS IN THE MANUFACTURE OF CARBONATE OF SODA
BY THE AMMONIA PROCESS." A communication from abroad by Theophile
Schloesing, of 67, Quai d'Orsay, in the City of Paris, France.
Sealed the 5th November 1878, and dated the 28th May 1878.
PROVISIONAL SPECIFICATION left by the said Sydney Pitt at the Office of
the Commissioners of Patents on the 28th May 1878.
SYDNEY PITT, of Sutton, in the County of Surrey. "IMPROVEMENTS IN THE
MANUFACTURE OF CARBONATE OF SODA BY THE AMMONIA PROCESS.". [A com-
munication from abroad by Theophile Schloesing, of 67, Quai d'Orsay, in the City
of Paris, France.]
This Invention has for its object improvements in the manufacture of carbonate
of soda by the ammonia process.
:
When it is desired to produce carbonate of soda on a large scale by the ammonia
process, an ammoniacal solution is exposed to carbonic acid gas so as to cause the
formation of bicarbonate of ammonia, an intermediate product which is essential
to the production of bicarbonate of soda. With this object, a solution is usually
formed containing both common salt and ammonia, and this is brought into contact
with the carbonic acid gas. The production of bicarbonate of ammonia and its
transformation into bicarbonate of soda is thus effected at one operation and in
the same vessel.
It has, however, now been found more advantageous to bring the carbonic acid
gas into contact with an ammoniacal solution which does not contain salt, and to
produce, in this way, first, bicarbonate of ammonia in crystals, which is separated
from the solution, and which is afterwards transformed, at a second operation, by
means of salt water into bicarbonate of soda.
This mode of manufacture is based upon the following fundamental and novel
fact:When an ammoniacal solution, containing from 10 to 20 parts by weight of

page_text: real ammonia, is brought into contact with carbonic acid gas, the precipitation of
crystals of bicarbonate of ammonia commences almost at once after that the whole
of the alkali has passed into the state of protocarbonate, whilst the mother liquor
still possesses, so long as it is not too much reduced by the separation of bicarbonate,
a power of absorbing carbonic acid gas, which is comparable to that of a solution of
protocarbonate. It is therefore so arranged that the crystals of bicarbonate are
continually removed as rapidly as they are produced, and that the solution of bi-
carbonate is constantly recharged with a quantity of caustic ammonia equal to that
which has been removed by the separation of the crystals. In this way, the
continuous manufacture of bicarbonate of ammonia is realised, and the manufacture
is favoured, as to its activity, by the powerful absorption of carbonic acid gas by
the protocarbonate, whilst, on the other hand, when the carbonic acid gas is brought
into contact with the ammonia and the common salt at the same time, it is neces-
sary to bicarbonate the whole of the ammonia, which much retards the absorption
of the gas, and, consequently, the manufacture, for the last portions of ammonia
only exert a very feeble power of absorption.
The bicarbonate of ammonia, produced as above-described, is mixed with a
solution of salt in a vessel provided with agitators, and is so transformed into
bicarbonate of soda, which is roasted to reduce it to the simple carbonate.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Sidney Pitt in the Great Seal Patent Office on the 27th November
1878.
SYDNEY PITT, of Sutton, in the County of Surrey. "IMPROVEMENTS IN THE
MANUFACTURE OF CARBONATE OF SODA BY THE AMMONIA PROCESS." A communi-
cation from abroad by Theopliile Schloesing, of 67, Quai d'Orsay, in the City of
Paris, France:
The manufacture of carbonate of soda by ammonia is founded in principle upon
the double decomposition which takes place in water between common salt and
bicarbonate of ammonia, from which a precipitation of bicarbonate of soda results.
This reaction may be obtained by two distinct processes.
The first consists in dissolving the salt and the ammonia in water in suitable
proportions, which are now well known, and in causing carbonic acid gas, either
pure or mixed with enert gases, to act upon the mixture until no longer absorbed;
the bicarbonate of ammonia, which is first formed, re-acts immediately upon the
common salt in the midst of the liquor and produces bicarbonate of soda.
In the second process, bicarbonate of ammonia is first produced separately by the
combination of liquid ammonia with carbonic acid gas, either pure or diluted, then
at a second operation this bicarbonate of ammonia is brought into contact with
dissolved common salt.
In the first process, the absorption of carbonic acid gas is very satisfactory so long
as caustic ammonia remains in the liquid, but it falls off gradually, because the

page_text: alkali loses its affinity for the carbonic acid more and more as it absorbs it, and
because, besides, the quantity of real alkali is diminished by its partial transforma-
tion into hydrochlorate of ammonia. In applying the first process, it has always
been necessary to multiply the contacts between the carbonic gas and the liquids,
either by agitation or by repeated passages of the gas through the liquors.
The second process appears less simple than the first because it requires two
distinct operations in place of but one. It is, however, preferably with regard to
obtaining the absorption of the carbonic acid gas by the ammonia, as will be seen
from the following explanation:-In place of carrying the carbonization of the
ammonia from one end to the other, commencing with the caustic alkali and
finishing with the bicarbonate, my correspondent invented the proces of operating
with an ammoniacal solution which is already carbonated and brought just to the
state at which the further action of the carbonic acid will cause a deposition of
crystals, and of rendering this state constant by removing the crystals as they are
produced, and by replacing with fresh ammonia that which has been eliminated in
the state of crystals. There is obtained in this way, besides the advantage of
working under fixed conditions as to the richness of the ammoniacal solution and
its degree of carbonatation, the realization of a continuous process, another advan-
tage of great value.
A new fact observed by my correspondent is altogether favourable to these
conceptions; it is as follows:-When an ammoniacal solution is carbonated to the
point of commencing to deposit crystals of bicarbonate it contains ammonia and
carbonic acid nearly in the proportion of their equivalents 17 and 22; in other
words, the two bodies exist there in the form of protocarbonate, always provided
that the strength of the solution is comprised between 100 and 200 grammes of
real ammonia to the litre of liquid; if the strength be inferior to 100 grammes to
the litre the equivalence is no longer maintained, and the precipitation of bicarbonate
of ammonia does not commence until after the absorption of more carbonic acid
than corresponds to the protocarbonate. It results, evidently, from these facts that
in operating with a solution containing from 100 to 200 grammes of ammonia to
the litro, and brought to the point where a further quantity of carbonic acid
brought in produces a deposition of crystals, one is really working with a solution
of protocarbonate. Now such a solution, although it does not absorb carbonic acid
with the energy of ammonia, possesses a power of absorption amply sufficient for
the production of bicarbonate of ammonia on a manufacturing scale. It is not
even necessary to present to it pure carbonic acid gas, but a gaseous mixture,
such as is produced by a limekiln, answers the purpose; and this is a further
great advantage, as it relieves the manufacture from the troublesome condition of
producing pure carbonic acid gas. It is true that it is necessary to employ some-
what strong ammoniacal solutions, in which, consequently, the ammonia has a
somewhat strong gaseous tension, which occasions a very sensible loss of alkali,
passing off with the gas containing the carbonic acid. But these losses are not at
all disquieting; it is sufficient to apply to this manufacture the processes for the
absorption of volatile bodies, described in the Specification of my Patent, No. 643,
in the present year, to recover the ammonia which thus passes off.
In short, this Invention substitutes for a variable power of absorption, at first
energetic but gradually dying away to nothing, a power of absorption which,
although moderate, is sufficient, and constancy and continuity in work is thus
obtained.
I will now describe the means of working which appear to my correspondent the
most suitable, although other means may be resorted to without departing from the
Invention. I. distinguish six operations in the manufacture of carbonate of soda by
ammonia :-
1. The production of the bicarbonate of ammonia..
2. The reaction of this salt upon a solution of common salt and the precipitation
of bicarbonate of soda.

page_text: 4. The torrification of the bicarbonate of soda to convert it into the neutral
carbonate.
5. The revivification of ammonia by lime, and its extraction from the mother
liquors.
6. The production of caustic lime and carbonic acid by means of a limekiln.
In my description, it will be unnecessary for me to dwell upon the four last-
mentioned operations, which are conducted in ordinary and well-known manners.
Production of the Bicarbonate of Ammonia-It is requisite to multiply the con-
tacts between the gas containing the carbonic acid and the solution of protocarbonate
of ammonia. In such cases, it is usual with chemists to compress the gas to oblige
it to bubble through the absorbing liquid. Well-known precautions are taken to
divide the gas into small bubbles and thus to multiply the contacts between the
two masses. The mechanical work expended in this operation is proportional to the
volumn of gas to be injected and to the depth of the layer of liquid which the gas
has to traverse.
On its
Although means of this sort may be employed, I will indicate a process which is
more economical, and which is more certain to bring about a multiplicity of contacts
In place of projecting the gas into the midst of the liquid, the liquid is projected in
the form of rain into the midst of the gaseous current. This remains at the
ordinary pressure and is acted upon only to the extent necessary to determine its
free passage through a chamber, where it encounters the liquid in the form of rain.
As one of the meams which may be employed to project the liquid in the form of
rain, I will describe the following:--The liquid occupies the lower part of a
closed chamber through the upper part of which the gases pass; centrifugal pumps
draw it from this chamber and project it into horizontal pipes placed a little above
the surface of the liquid. These pipes are furnished with nozzles which divide the
liquid into as many separate jets. On escaping from the nozzles, each jet encounters
a small plane, suitably inclined, against which it flattens itself; the jet is then
replaced by a thin sheet which rises upwards into the air and divides into small
drops. The chamber is of lead and about two metres wide by three or four metres
high, and of an indefinite length, which depends, as does also the number of the
pumps, upon the quantity of bicarbonate which it is desired to produce The
gaseous current and the liquid traverse the chamber in opposite directions.
entrance at one end of the chamber the solution of protocarbonate is limpid, but as
it passes along the chamber it becomes charged with small crystals of bicarbonate
which the incessent motion produced by the pumps maintains in suspension; hence
the liquid leaving the chamber is a mixture of the solution and a multitude of
small crystals. This mixture, as it runs out of the chamber, is passed into vertical
· cylinders of metal, of which the bottoms are formed of gratings supporting cloths or
felts.
The crystals are here retained whilst the liquid flows away. When the
cylinder is full of crystals, carbonic acid, either pure or diluted, is made to pass
through it, either by suction or by pressure, in order to completely bicarbonate the
protocarbonate in the solution, which moistens the crystals. The mass is then
removed and put into contact with a solution of the common salt to be transformed
into bicarbonate of soda. A current of cold water should be passed over the leaden
chamber to prevent the temperature within rising to a degree to interfere with the
absorption of the carbonic acid. The solution of protocarbonate is not returned to
the chamber until it has been recharged with a quantity of caustic ammonia equal
to that which it has lost in the chamber in the form of bicarbonate. For this
purpose ammoniacal gas is condensed in it. This gas is continually reproduced in
the course of the manufacture, and the condensation is also effected in a leaden
chamber of small size, where the ammoniacal gas encounters the liquid projected
into it in small drops. The heat produced by the condensation is carried off by the
constant circulation of the liquid in cast-iron pipes immersed in a tank of cold
water.
Re-action of the Bicarbonate of Ammonia upon the Dissolved Common Salt.-The
bicarbonate of ammonia obtained is thrown into a large vat which also receives the

page_text: water and the chloride of sodium. An agitator combines the materials, from which
there results the precipitation of the bicarbonate of soda.
I would remark that the manufacturer can easily measure the different re-acting
bodies, and thus he is able to employ them all in the quantities best suited to give
a good yield. The re-action produces a very marked reduction of temperature,
which determines the precipitation of a further quantity of bicarbonate of soda.
Finally, I will call attention to another very marked advantage in this method
of working: When carbonic acid gas in a more or less diluted state is made to
re-act upon an aminoniacal solution of common salt a precipitate of extreme tenuity
is always obtained, because the salt is formed in the midst of a liquid which is
violently agitated, and of which the crystallization is necessarily troubled. This
state of the precipitate renders the filtration, the washing, and the drying very
difficult. But when bicarbonate, already formed, is made to re-act apon common
salt with the intervention of water, one can add either common salt or bicarbonate
by successive portions, so that the quantity of bicarbonate of soda which can forin at
any moment shall be small, and that the precipitation consequently shall be slow;
besides, the liquid may be almost at rest during the precipitation which conse-
quently can take place under the conditions most favourable to the formation of
crystals of much larger size. The filtration, the washing, and the drying of such
crystals are very simple operations.
It is evident that in this process the common salt may be replaced by the nitrate
or the sulphate of soda, as, indeed, has been proposed by other inventors proposing
the manufacture of carbonate of soda by ammonia.
I claim as the improvements in the manufacture of carbonate of soda by the
ammonia process, which form the subject of the above in part recited Letters
Patent,―
First. The part of the said improved process of manufacture which consists in
precipitating bicarbonate of ammonia by means of carbonic acid gas from an
ammoniacal solution, the strength of which is constantly maintained by recharging
it with caustic ammonia.
Second. The part of the said improved process of manufacture which consists in
the continuous precipitation of bicarbonate of ammonia by the re-action of carbonic
acid gas upon an ammoniacal solution, which, flowing through the apparatus,
carries away the precipitate as it is formed, and, being filtered and recharged with
caustic ammonia, returns and is again acted upon by the gas.
Third. The part of the said combined process of manufacture which consists in
effecting the absorption of carbonic acid gas and the precipitation of bicarbonate of
ammonia, by projecting in a rain-like form a solution containing protocarbonate of
ammonia in solution into the midst of a gaseous current containing carbonic acid.
Fourth. The manufacture of carbonate of soda by the improved ammonia process,
substantially as described.
•
In witness whereof, I, the said Sydney Pitt, have hereunto set my hand
and seal, this Twenty-seventh day of November, in the year of our Lord
One thousand eight hundred and seventy-eight.