IMPROVEMENTS IN THE MANUFACTURE OF CARBONATE OF SODA BY THE AID OF AMMONIA
Year: 1882

page_text: LETTERS PATENT to Sydney Pitt of Sutton in the County of Surrey, for an
invention of "IMPROVEMENTS IN THE MANUFACTURE OF CARBONATE OF SODA
BY THE AID OF AMMONIA "
A communication from abroad by Theophile
Schloesing of Paris in the Republic of France
PROVISIONAL SPECIFICATION left by the said Sydney Pitt at the Office
of the Commissioners of Patents on the 4th May 1882.
SYDNEY PITT of Sutton in the County of Surrey.
"IMPROVEMENTS IN THE
MANUFACTURE OF CARBONATE OF SODA BY THE AID OF AMMONIA
"
A communi-
cation from abroad by Theophile Schloesing of Paris in the Republic of France.
This Invention has for its object improvements in the manufacture of carbonate
of soda by the aid of ammonia.
I have described in the Specification of a Patent No 2130 in the year 1878 an
improvement in the manufacture of carbonate of soda by the aid of ammonia,
consisting principally in the preparation of bicarbonate of ammonia by a new
process and making it react immediately upon salt water to produce bicarbonate of
soda. The preparation of bicarbonate of ammonia, depends as I have said upon
the following conditions.
When a solution of ammonia containing at least 100 grammes of real alkali to
the litre, is kept in an ordinary temperature, and is traversed by a current of
carbonic acid until crystals of bicarbonate are deposited, the mother liquor after
the separation of the crystals, is found to contain a combination of carbonic acid
and ammonia constituting nearly a protocarbonate, Then again if carbonic acid be
offered to this solution of protocarbonate, even although the gas be diluted with
other gases, it is capable of absorbing the gas with sufficient energy, bicarbonate of
ammonia precipitating. If then an aminoniacal solution is exposed to a current of
gas containing carbonic acid, (such for example as issues from a lime kiln, contact
between the gas and the liquid being obtained by mechanical or other means
dividing the liquid in the midst of the gascous atmosphere or the gas in the midst
Price 4d1

page_text: of the liquid) a part of the ammonia of the solution is precipitated in the state of
bicarbonate. The crystals are separated by suitable filters. As to the mother
liquor which is a solution of protocarbonate of ammonia it is recharged with
alkali by causing it to absorb aminonia which in this process of manufacture is
constantly revivified by the distillation, with lime, of the liquids from which the
bicarbonate of soda has been precipitated. Thus the same solution, circulating
through apparatus where it comes in contact with carbonic acid, then through
filters and through the condensers of the stills becomes charged in the first
apparatus with bicarbonate of ammonia is robbed of this by the filters, is recharged
with ammonia in the condensers, and then returns and passes again over the
same course.
Now in the application of this process a difficulty is experienced. The absorption
of the carbonic acid gas by the ammoniacal solution causes a rise of temperature
which must be controlled by a flow of cold water over the exterior of the absorbing
apparatus. In fact if the liquor is not sufficiently cooled the production of
bicarbonate is lessened from two causes. 1. The carbonic acid gas is absorbed
with so much the less energy as the temperature is higher. 2 The precipitation of
bicarbonate is less abundant because a part remains in solution in the tepid liquor.
But the cooling by the flow of fresh water over the exterior surfaces of the
apparatus is hindered by the formation on the interior of crusts of bicarbonate
which are very imperfect conductors of heat, a circumstance which much diminishes
the yield of the apparatus.
In place of endeavouring to control the heat generated by these reactions, the
idea has occured to my correspondent to enlist it to his aid. He has ascertained
first that a solution of protocarbonate of ammonia containing at least 100 grammes
of real alkali to the litre brought to a temperature from 45 to 50 degrees Centigrade
can dissolve up to 15 per cent of its weight of bicarbonate of ammonia which it
deposits on cooling. He has ascertained further that the said solution brought to
temperatures included between 30 and 40 can still absorb to a certain extent the
diluted carbonic acid gas found in lime kiln gases; but that, if it he wished to
saturate it at the temperature of 45 to 50 it is necessary to offer to it much
gas
richer in carbonic acid. Again he has ascertained that the same solution gives off
a mixture of carbonic acid, ammonia and vapour of water, in which carbonic acid
is very abundant, when it is submitted to methodical distillation as practiced with
alcoholic liquids in columns containing trays. The solution in descending the
column whilst the gas and vapours pass in the contrary direction, loses much more
carbonic acid than ammonia, so that after the distillation it contains a certain part
of its ammonia in a caustic state, provided, always that the temperature of the gas
does not exceed 70 degrees as it passes out of the still.
The observation of these facts has led to the following arrangements. Let us
consider the mother liquor which issues from the bicarbonate filters and which
contains principally protocarbonate of ammonia. This mother liquor is submitted
to a methodical distillation which gives gaseous products very rich in carbonic
acid; consequently a part of the ammonia becomes caustic in the liquid running
out of the apparatus. The mother liquor is now cooled by a known process, for
example by passing it through coils plunged in cold water; then it is recharged
with ammonia by causing it to absorb the products of the revivification by lime.
It is again cooled and placed in contact with dilute carbonic acid coming from a
lime kiln, or other source, in suitable apparatus, such as coke towers, scrubbers and
others. No effort is made to cool the solution; its temperature consequently rises
and the liquid retains in solution the bicarbonate formed in the course of this first
carbonization. But it is not yet sufficiently charged with bicarbonate; hence it is
made to absorb the gaseous products, carbonic acid, ammonia, and vapour of water,
which are disengaged from the apparatus where the mother liquors are distilled.
This new absorption takes place in apparatus suitable to multiply the contacts
between the liquid and the gas, such as coke towers scrubbers, and others. The
solution attains now a temperature of about 50 degrees. The precipitation of the

page_text: bicarbonate which it holds in solution has now to be determined by cooling. For
this purpose the liquor is caused to pass through series of cylinders of cast iron lead
or other material furnished with agitators and cooled exteriorly by a flow of cold
water under these conditions, crusts of bicarbonate of ammonia no longer form
upon the inner sides and the cooling by water can have full effect. The crystals
are then separated from the mother liquor by the filters.
Thus the circulation of the mother liquor is as follows. On leaving the filters, it
is submitted to a distillation which furnishes gas very rich in carbonic acid.
Thence a part of its ammonia has become caustic. The liquor is sent in this state
to absorb the products from the revivification by lime. After cooling it passes
into the absorption apparatus where it is placed in contact with the dilute carbonic
acid; then it passes into the apparatus where it meets with gas much richer in
carbonic acid resulting from the distillation of the mother liquor. Finally it is
cooled; it lets fall the bicarbonate of ammonia passes through the filters and
recommences the circulation indicated.
The products from the revivification may be employed directly in place of steam,
to heat and distil the mother liquor, this economises the expense of steam and
obviates cooling the mother liquor in two separate operations. It is then in the
still that the revivified ammonia is restored to it. It is sufficient to cool in one
operation on coming out of this apparatus.
The distillation of the mother liquor has for its object to afford an economical
source of carbonic acid, but it may be omitted if a gaseous mixture rich in carbonic
acid be available from any other source, for example from the distillation of
bicarbonate of soda in a closed vessel,

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Sydney Pitt in the Great Seal Patent Office on the 3rd November
1882.
"
SYDNEY PITT of Sutton in the County of Surrey "IMPROVEMENTS IN THE
MANUFACTURE OF CARBONATE OF SODA BY THE AID OF AMMONIA (A Commu-
nication from abroad by Theophile Schloesing of Paris in the Republic of France)
This Invention has for its object improvements in the manufacture of carbonate
of soda by the aid of Ammonia.
I have described in the specification of a Patent No 2130 in the year One
thousand eight hundred and seventy-eight an improvement in the manufacture of
carbonate of soda by the aid of ammonia, consisting principally in the preparation
of bicarbonate of ammonia by a new process and making it react immediately
upon salt water to produce bicarbonate of soda. The preparation of bicarbonate
of ammonia depends, as I have said, upon the following conditions:-
When a solution of ammonia containing at least 100 grammes of real alkali to
the litre is kept at an ordinary temperature, and is traversed by a current of
carbonic acid until crystals of bicarbonate are deposited. The mother liquor after
the separation of the crystals is found to contain a combination of carbonic acid
and ammonia constituting nearly a protocarbonate. Then again if carbonic acid
be offered to this solution of protocarbonate, even although the gas be diluted with
other gases, it is capable of absorbing the gas with sufficient energy bicarbonate of
ammonia precipitating. If then an ammoniacal solution is exposed to a current of
gas containing carbonic acid (such for example as issues from a lime kiln, contact
between the gas and the liquid being obtained by mechanical or other means
dividing the liquid in the midst of the gaseous atmosphere or the gas in the midst
of the liquid) a part of the ammonia of the solution is precipitated in the state of
bicarbonate, The crystals are separated by suitable filters, as to the mother liquor
which is a solution of protocarbonate of ammonia it is recharged with alkali by
causing it to absorb ammonia which in this proces of manufacture is constantly
revivified by the distillation, with lime, of the liquids from which the bicarbonate
of soda has been precipitated. Thus the same solution, circulating through
apparatus where it comes in contact with carbonic acid, then through filters and
then through the condensers of the stills; becomes charged in the first apparatus
with bicarbonate of ammonia is robbed of this by the filters, is recharged with
ammonia in the condensers, and then returns and passes again over the same
course.
Now in the application of this process a difficulty is experienced. The absorption
of the carbonic acid gas by the ammoniacal solution causes a rise of temperature
which must be controlled by a flow of cold water over the exterior of the absorbing
apparatus, in fact, if the liquor is not sufficiently cooled the production of
bicarbonate is lessened from two causes. 1. The carbonic acid gas is absorbed
with so much the less energy as the temperature is higher. 2. The precipitation
of bicarbonate is less abundant because a part remains in solution in the tepid
liquor. But the cooling by the flow of fresh water over the exterior surfaces of
the apparatus is hindered by the formation on the interior, of crusts of bicarbonate
which are very imperfect conductors of heat, a circumstance which much diminishes
the yield of the apparatus
In place of endeavouring to control the heat generated by these reactions, the
idea has occurred to my correspondent to enlist it to his aid. He has ascertained

page_text: first that a solution of protocarbonate of ammonia containing at least one hundred
grammes of real alkali to the litre brought to a temperature from 45 to 50 degrees
Centigrade can dissolve up to 15 per cent of its weight of bicarbonate of ammonia
which it deposits on cooling. He has ascertained further that the said solution
brought to temperatures included between 30 and 40 can still absorb to a certain
extent the diluted carbonic acid gas found in lime kiln gases; but, that, if it be
wished to saturate it at the temperature of 45 to 50 it is necessary to offer to it
gas much richer in carbonic acid. Again he has ascertained that the same solution
gives off a mixture of carbonic acid ammonia and vapour of water, in which
carbonic acid is very abundant when it is submitted to methodical distillation as
practiced with Alcoholic Liquids in columns containing trays. The solution in
descending the column whilst the gas and vapours pass in the contrary direction
loses much more carbonic acid than Ammonia, so that after the distillation it
contains a certain part of its ammonia in a caustic state provided always that the
temperature of the Gas does not exceed seventy degrees as it passes out of
the still.
The observation of these facts has led to the following arrangements. Let us
consider the mother liquor which issues from the Bicarbonate Filters and which
contains principally proto-carbonate of ammonia-This mother liquor is submitted
to a methodical distillation which gives gaseous products very rich in carbonic
acid; consequently a part of the ammonia becomes caustic in the liquid running
out of the apparatus-The mother liquor is now cooled by a known process, for
example by passing it through coils plunged in cold water; then it is recharged
with Ammonia by causing it to absorb the products of revivification by Lime. It
is again cooled and placed in contact with dilute Carbonic acid coming from a
Lime kiln, or other source, in suitable apparatus, such as coke towers, scrubbers
and others. No effort is made to cool the solution; its temperature consequently
rises and the liquid retains in solution the bicarbonate formed in the course of this
first carbonization-But it is not yet sufficiently charged with bicarbonate; hence
it is made to absorb the gaseous products Carbonic acid, ammonia, and vapour of
water, which are disengaged from the apparatus where the mother liquors are
distilled. This new absorption takes place in apparatus suitable to multiply the
contacts between the liquid and the gas such as coke towers, scrubbers, and others
the solution attains now a temperature of about fifty degrees. The precipitation
of the bicarbonate which it holds in solution has now to be determined by cooling.
For this purpose the liquor is caused to pass through series of Cylinders of cast
iron lead or other material furnished with agitators and cooled exteriorly by a flow
of cold water. Under these conditions, crusts of bicarbonate of aminonia no longer
form upon the inner sides and the cooling by water can have full effect. The
crystals are then separated from the mother liquor by the Filters.
Thus the circulation of the mother liquor is as follows:-
On leaving the filters, it is submitted to a distillation which furnishes gas very
rich in Carbonic acid. Thence a part of its Ammonia has become caustic. The
liquor is sent in this state to absorb the products from the revivification by lime.
After cooling it passes into the absorption apparatus where it is placed in contact
with the dilute Carbonic acid; then it passes into the apparatus where it meets
with Gas, much richer in Carbonic acid resulting from the distillation of the mother
liquor. Finally it is cooled; it lets fall the bicarbonate of Aminonia; passes
through the filters and recommences the circulation indicated.
The products from the revivification may be employed directly in place of steam
to heat and distil the mother liquor this economises the expense of steam and
obviates cooling the mother liquor in two separate operations It is then in the
still that the revivified ammonia is restored to it. It is sufficient to cool in one
operation on coming out of this apparatus.
The distillation of the mother liquor has for its object to afford an economical
source of Carbonic acid, but it may be omitted if a gaseous mixture rich in

page_text: Carbonic Acid be available from any other source, for example from the distillation
of bicarbonate of soda in closed vessel.
Having thus described the nature of the said Invention and the manner of
performing the same, what I claim is
The improvements in the manufacture of Carbonate of Soda by the aid of
Ammonia substantially as herein before described.
In witness whereof I the said Sydney Pitt have hereunto set my hand and
seal this second day of November in the year of our Lord One thousand
eight hundred and eighty two.