Improvements in the Manufacture of Caustic Soda or Caustic Potash, and of Carbonic Acid from Mono or other Carbonate of Soda or Potash.
Year: 1887

page_text: Improvements in the Manufacture of Caustic Soda or
Caustic
Potash, and of Carbonic Acid from Mono or other Carbonate
of Soda or Potash.
We LUDWIG MOND of Winnington Hall and DAVID BASIL HEWITT of Winnington
House both near Northwich in the County of Chester, Alkali Manufacturers do
hereby declare the nature of this invention to be as follows:-
This invention relates to improvements founded upon the process set forth in the
specification of Patent No. 4364 of 1882 granted to William Lloyd Wise, a
communication from Professor Doctor Carl Löwig of Breslau.
In the said specification a process is described for making caustic alkalies by heating
their respective carbonates with oxide of iron used in stated proportions in closed
retorts or muffes or as an alternative in reverberatory furnaces.
Now we have found that great improvement may be made in the employment of
oxide of iron as proposed by Wise which will obviate to a very considerable extent the
waste of fuel which occurs whether iron or clay retorts, or inuffle furnaces or even
reverberatory furnaces be employed and that the ordinary low test carbonate of soda
of commerce (soda ash) especially that made by the Le Blanc process is not well
suited for this process, probably because of its impurities and density, and that any
impurity has a tendency to prevent the intimate mixture of the molecules of carbonate
of soda and oxide of iron and that the impurities usually present in low test alkali
bring about fluxing of the mass which would prevent the carbonic acid from escaping
rom the mixture when heated to the proper temperature. The process requires a
nost intimate mixture of the corbonate of soda with the oxide of iron. We therefore
refer to employ a very pure and fine carbonate of soda, obtained by heating the
bicarbonate of soda obtained in the ammonia soda process to a moderate temperature
hot exceeding 300 degrees centigrade. The carbonate of soda so obtained is an
nfinitesimally fine powder which by proper mixing apparatus can be brought into the
host intimate contact with the oxide of iron. Good results can also be obtained by
sing the mixture of mono-carbonate and bicarbonate of soda which results from
eating the bicarbonate of soda of the ammonia soda process to a temperature of
etween 80 and 100 degrees centigrade until all the ammonia contained in the said

page_text: bicarbonate has been driven off; or the bicarbonate of soda from the ammonia soda
process may directly be mixed with the necessary quantity of oxide of iron and this
mixture be heated to obtain caustic soda. In this latter case we prefer to heat the
mixture of bicarbonate of soda and oxide of iron in the first instance in closed
apparatus such as is now used in ammonia soda works for converting the bicarbonate
into mono carbonate of soda and which allows of the collection and utilization of the
ammonia and carbonic acid given off in the operation. The hot mixture of mono
carbonate of soda and oxide of iron obtained from the closed forms of apparatus we
then transfer while still hot into another apparatus or furnace where we submit it to
the necessary temperature for driving out the rest of the carbonic acid in order to
obtain caustic soda.
It has been found in practice when working the process as described in the
specification of Wise that as soon as the reaction has once commenced, the mixture of
alkaline carbonate with oxide of iron becomes surrounded by an atmosphere of
of nearly pure carbonic acid produced by the reaction itself. In such an atmosphere the
reaction proceeds only very slowly. Even in the ordinary reverberatory furnace the
carbonic acid being much heavier than the fire gases passing through the furnace
remains near the floor of the furnace surrounds the material employed and prevents
the reaction proceeding with sufficient rapidity and completeness. We have discovered
however that if the process be carried out in such a way as to constantly remove the
materials employed out of the atmosphere of nearly pure carbonic acid produced by
the reaction and to bring them again and again into an atmosphere relatively poor in
carbonic acid, the reaction proceeds quickly and can be completed in a reasonable
time and also that the presence of steam materially facilitates the reaction.
We find that our object may be advantageously effected by using a cylindrical or barrel
shaped furnace revolving in a horizontal or nearly horizontal axis and lined with fire clay
blocks in such a way as to form a number of projecting radial ribs or breakers of fire brick
parallel to the axis of the cylinder. In some cases in place of projecting ribs the
lining can be arranged in the form of steps or serrations the one face of which is radial,
the other tangential, curved or oblique to the radius. The furnace employed in this
case is revolved with the radial faces advancing. Hot gases relatively poor in CO2
are passed through the interior of the revolving furnace. We can for this purpose
employ the hot products of combustion of an ordinary fire place to which steam
preferably superheated may advantageously be added but only in such quantity as not
to reduce the temperature of the furnace below that required for expeditious working.
But as it is preferable to use hot gases containing as little CO, and as much steam as
possible we propose to employ the products of combustion of ordinary producer gas
with air, both previously heated in regenerators or otherwise to which steam preferably
superheated may be added in such quantity as the temperature required will permit,
or we employ instead of ordinary producer gas the gas produced by the imcomplete
combustion of coal by a mixture of air and steam, or still better the gas produced by
passing steam alone through incandescent fuel (commonly called water gas) which
both produce steam on being burnt with air and yield a gas of high temperature
containing much less CO₂ than that obtained from ordinary producer gas under the
same circumstances.
The material introduced into the furnace is lifted up by the projecting ribs or steps
or serrations to a certain height and then falls through the gases passing through the
furnace whereby the nearly pure carbonic acid formed in the interstices of the mass
becomes replaced by the gases and does no longer hinder the progress and completion
of the reaction between the substances employed, which can now be completed within
a few hours and at a reasonable expense of fuel, thus effecting great economy and
improvement in the manufacture of caustic soda or caustic potash. The apparatus
employed may be modified in various ways.

page_text: COMPLETE SPECIFICATION.
Improvements in the Manufacture of Caustic Soda or Caustic
Potash, and of Carbonic Acid from Mono or other Carbonate
of Soda or Potash.
We, LUDWIG MOND, of Winnington Hall, and DAVID BASIL HEWITT of
Winnington House, both near Northwich, in the county of Chester, Alkali
Manufacturers, 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 :—
This invention relates to improvements founded upon the process set forth in the
specification of patent No. 4364 of 1882 granted to William Lloyd Wise, a
communication from Professor Doctor Carl Löwig of Breslau.
In the said specification a process is described for making caustic alkalies by
heating their respective carbonates with sesqui-oxide of iron used in stated proportions
in closed retorts or muffles, or as an alternative in reverberatory furnaces.
Now we have found that great improvement may be made in the employment
of sesqui-oxide of iron as proposed by Wise, which will obviate to a very considerable
extent the waste of fuel which occurs whether iron or clay retorts, or muffle furnaces,
or even reverberatory furnaces be employed, and that the ordinary low test carbonate
of soda of commerce, (soda ash), especially that made by the Le Blanc process, is not
well suited for this process, probably because of its impurities and density, and that
any impurity has a tendency to prevent the intimate mixture of the molecules of
carbonate of soda, and sesqui-oxide of iron, and that the impurities usually present in
low test alkali bring about fluxing of the mass, which would prevent the carbonic acid
from escaping from the mixture when heated to the proper temperature. The process
requires a most intimate mixture of the carbonate of soda with the sesqui-oxide of iron.
We therefore prefer to employ a very pure and fine carbonate of soda, obtained by
heating the bicarbonate of soda obtained in the ammonia soda process to a moderate
temperature, not exceeding 300 degrees Centigrade. The carbonate of soda so obtained
is an infinitesimally fine powder, which by proper mixing apparatus can be brought
into the most intimate contact with the sesqui-oxide of iron. Good results can also
be obtained by using the mixture of monocarbonate and bicarbonate of soda, which
results from heating the bicarbonate of soda of the ammonia soda process to a
temperature of between 80 and 100 degrees Centigrade until all the ammonia
contained in the said bicarbonate has been driven off; or the bicarbonate of soda from
the ammonia soda process may be directly mixed with the necessary quantity of
sesqui-oxide of iron, anhydrous or hydrated, but as free as practicable from silica or
alumina, and this mixture be heated to obtain caustic soda. In this latter case we
prefer to heat the mixture of bicarbonate of soda, and sesqui-oxide of iron, in the first

page_text: instance in closed apparatus, such as is now used in the ammonia soda works for
converting the bicarbonate into monocarbonate of soda, and which allows of the
collection and utilization of the ammonia and carbonic acid given off by the operation.
The hot mixture of monocarbonate of soda, and oxide of iron obtained from the closed
forms of apparatus, we then transfer while still hot into another apparatus or furnace,
where we submit it to the necessary temperature for driving out the rest of the carbonic
acid, in order to obtain caustic soda.
It has been found in practice when working the process as described in the
specification of Wise that as soon as the reaction has once commenced, the mixture of
alkaline carbonate with sesqui-oxide of iron becomes surrounded by an atmosphere of
nearly pure carbonic acid produced by the reaction itself, and that the reaction proceeds
only very slowly. Even in the ordinary reverberatory furnace the carbonic acid
being much heavier than the fire gases passing through the furnace remains near the
Hoor of the furnace, surrounds the materials employed, and prevents the reaction
proceeding with sufficient rapidity and completeness. We have discovered, however,
that if the process he carried out in such a way as to constantly remove the materials
employed out of the atmosphere of nearly pure carbonic acid produced by the reaction;
and to bring them again and again into an atmosphere relatively poor in carbonic acid,
the reaction proceeds quickly, and can be completed in a reasonable time, and also
that the presence of steam materially facilitates the reaction.
We find that our object may be advantageously effected by using a cylindrical or
barrel shaped furnace revolving on a horizontal or nearly horizontal axis, and lined
with fire clay blocks, which may be set so as to form a smooth surface, or in such a
way as to form a number of projecting radial ribs or breakers of fire brick parallel to the
axis of the cylinder, or they may be arranged so as to form steps or serrations, the one
face of which is radial, the other tangential, curved or oblique to the radius. In the
case where the furnace with steps or serrations is employed, it is revolved with the
radial face advancing. Hot gases relatively poor in carbonic acid are passed through
the interior of the revolving furnace. We can, for this purpose, employ the hot
products of combustion of an ordinary fire place, to which steam, preferably superheated,
may advantageously be added, but only in such quantity as not to reduce the
temperature of the furnace below that required for expeditions working. But as it is
preferable to use hot gases containing alittle carbonic acid and as much steam as possible,
we propose to employ the products of combustion of ordinary producer gas with air,
both previously heated in regenerators or otherwise, to which steam, preferably
superheated, may be added in such quantity as the temperature required (about 800 to
900 degrees centigrade) will permit, or we employ instead of ordinary producer gas,
the gas produced by the incomplete combustion of coal by a mixture of air and steam,
or still better, gas produced by passing steam alone through incandescent fuel
(commonly called water gas), which both produces steam on being burnt with air, and
yields a gas of high temperature containing much less carbonic acid than that
obtained from ordinary producer gas under the same circumstances.
The material introduced into the furnace is lifted up by friction against the revolving
face of the furnace, or by the projecting ribs or steps or serrations, if these be used,
to a certain height, and then falls through the gases passing through the furnace,
whereby the nearly pure carbonic acid formed in the interstices of the mass becomes
replaced by the gases, and does no longer hinder the progress and completion of the
action between the substances employed, which can now be completed in a few hours
at a reasonable expense of fuel, thus effecting great economy and improvement in the
manufacture of caustic soda or caustic potash. The apparatus employed may be
modified in various ways, for instance, the furnace can be made to revolve on an
oblique axis, with a flat bed at right angles to that axis. This bed as it revolves would
raise the materials out of the carbonic acid, and a stationary plough could turn them
over at the highest point, or a rocking, or combination rocking and revolving furnace
can be used, in fact, almost any furnace arranged to stir the material, and continually
expose fresh surfaces of it (above the atmosphere of carbonic acid) to the furnace
gases.

page_text: Having now particularly described and ascertained the nature of the said
invention, and in what manner the same is to be performed, we declare that what we
claim is
1. In the manufacture of caustic soda or caustic potash by furnacing the respective
carbonate with sesqui-oxide of iron, constantly or intermittently removing the materials
out of the atmosphere of nearly pure carbonic acid produced by the reaction, and
exposing them to hot gases comparatively poor in carbonic acid.
2. The use in the manufacture of caustic alkali from the carbonate by aid of sesqui-
oxide of iron of a cylindrical or barrel shaped revolving furnace, substantially as
described, through which the products of combustion are passed.
3. The use in the manufacture of caustic alkali from the carbonate by means of
sesqui-oxide of iron, of a furnace lined with refractory materials in such form, whether
with ribs, breakers, serratures, or otherwise, so as in revolving, to retain and carry up
the materials resting on the same, out of the atmosphere of nearly pure carbonic
acid, for some distance before letting them return back to the lowest part of the furnace.
4. In the manufacture of caustic alkali from carbonate by refurnacing the latter
with sesqui-oxide of iron, the addition of steam to the fire gases, substantially as
described.
5. In the manufacture of caustic alkalies from their carbonates by furnacing the
latter with sesqui-oxide of iron, heating the furnace by means of gases especially rich
in hydrogen, such as water gas, or the gas produced by gas producers worked with an
excess of steam, so as to obtain a hot flame containing comparatively little carbonic
acid, and a comparatively large amount of steam.
6. The use, for the purposes described, of bicarbonate of soda or of a carbonate of
soda obtained by heating bicarbonate of soda to a temperature between 80 degrees
and 300 degrees centigrade.
7. Heating the mixture of sesqui-oxide of iron with bicarbonate of soda (or the
intermediate carbonates obtained by heating bicarbonate of soda to a temperature of
between 80 to 100 degrees centigrade) in closed apparatus in order to recover part of
the carbonic acid in a comparatively pure state, and subsequently continuing and
finishing the operation in another furnace or apparatus heated by direct flame.
111 0711. ... of Ostaba 1887
WM. P. THOMPSON & Co.,
Of 6, Lord Street, Liverpool,
Patent Agents for the Applicants.