Improvements in or relating to the Separation of Caustic Alkalies from the Liquors Obtained by the Electrolysis of Alkaline Salts.
Year: 1894

page_text: Date of Application, 4th Aug. 1804
Complete Specification Left, 3rd May, 1895-Accepted 8th June, 1895
PROVISIONAL SPECIFICATION.
Improvements in or relating to the Separation of Caustic Alkalies
from the Liquors Obtained by the Electrolysis of Alkaline
Salts.
A communication from SOLVAY & Co., 25, Rue du Prince Albert, Brussels,
Belgiumn.
I, WILLIAM LLOYD WISE, of No. 46 Lincoln's Inn Fields, in the County
of London, Consulting Engineer, and Chartered Patent Agent, do hereby
declare the nature of this invention to be as follows:-
In the electrolysis of alkaline chlorides, usually not more than about 10% of
caustic alkali is obtained, whilst the remainder of the chloride remains
unconverted.
In order to effect the separation of the caustic alkali from the chloride, the
mother liquor may be subjected to evaporation, whereby when the solution has
reached a certain degree of concentration, the salt becomes insoluble in the caustic
alkali and precipitates. It is however difficult to evaporate a liquid of such a degree
of concentration, and in which a fine precipitate is continuously being formed in
proportion to the progress of the concentrating operation, and in any case this
evaporating process precludes the use of economically acting apparatus, such as
triple-effect apparatus.
Now it has been discovered that the same object can be effected more easily by
the following means :—
Instead of evaporating the caustic mother liquor resulting from electrolysis,
there is poured into the same a solution of caustic soda, preferably of about
40° Beaume, produced by a prior operation. This addition has the effect of causing
the whole of the salt present in the liquor to be precipitated and produces a solution
which is practically free from chloride of sodium and which can therefore be readily
evaporated by means of triple-effect apparatus.
The quantity of liquid that can be thus obtained free from salt is comparatively
very small.
The greater portion of it remains, notwithstanding all efforts, in the
condition of soft or thin mud.
If attempts be made to take out the separated salt, it is found to be impregnated
with soda solution to such a degree that the result of the operation is practically
nil. The most prolonged draining, suction, or compression produces only a small
quantity of caustic liquor, and washing is impracticable without unduly diluting the
caustic liquor.
To overcome this new difficulty, the following washing process is adopted. The
mixture of salt and caustic liquor is placed in a vessel that may be of cylindrical
form, provided with a double casing for enabling it to be heated by means of
steam, and with a false bottom for keeping back the solid portion and allowing
only the liquid portion to pass through. The whole is heated to a temperature of
approximately 100° C. after which there is poured on the top of the mixture by
means of a suitable apparatus that will not cause the mixing of the contents of the
vessel, a layer of saturated salt, water or brine equal in volume to the volume of
the caustic solution with which the precipitated salt is impregnated. On opening
a discharge cock at the bottom of the said vessel, a displacement of a molecular

page_text: nature so to speak is produced. The caustic solution is expelled practically in
successive horizontal layers and is replaced by the salt water without any mixing
taking place.
By this means practically the whole of the caustic solution can be recovered without
diluting the saine and a mother liquor is also obtained for a succeeding operation,
the slight causticity of such mother liquor causing no inconvenience in its subsequent
treatment.
Thus the said washing process enables all loss to be avoided. As already stated,
the washing process should be carried out with the aid of heat; it takes place very
much less regularly in the cold.
Dated this 4th day of August 1894.
W. LLOYD WISE,
46, Lincoln's Inn Fields, London, W.C., Chartered Patent Agent.
Improvements in or relating to the Separation of Caustic Alkalies
from the Liquors Obtained by the Electrolysis of Alkaline
Salts.
A communication from SOLVAY & Co., 25, Rue du Prince Albert, Brussels,
Belgium.
J, WILLIAM LLOYD WISE, of No. 46 Lincoln's Inn Fields, in the County
of London, Consulting Engineer, and Chartered 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:-
In the electrolysis of alkaline chlorides, usually not more than about 10% of
caustic alkali is obtained, whilst the remainder of the chloride remains unconverted.
This invention has for object to obviate this disadvantage.
For this purpose in order to effect the separation of the caustic alkali from the
chloride, the mother liquor may be subjected to evaporation, whereby when the
solution has reached a certain degree of concentration, the salt becomes insoluble in
the caustic alkali and precipitates. It is however difficult to evaporate a liquid of
such a degree of concentration, and in which a fine precipitate is continuously being
formed in proportion to the progress of the concentrating operation, and in any case
this evaporating process precludes the use of economically acting apparatus, such as
triple-effect apparatus.
Now it has been discovered that the same object can be effected more easily by
the following means:-
Instead of evaporating the caustic mother liquor resulting from electrolysis, there
is poured into the same, a strong solution of caustic soda, preferably of about
10° Beaume, produced by a prior operation. This addition has the effect of causing
the whole of the salt present in the liquor to be precipitated, and produces a solution
which is practically free from chloride of sodium and which can therefore be readily
evaporated by means of triple-effect apparatus.
In each case, the quantity of liquid that can be thus obtained free from salt is
comparatively very small. The greater portion of it remains, notwithstanding all
efforts, in the condition of soft or thin mud.
If attempts be made to take out the separated salt, it is found to be impregnated
with soda solution to such a degree that the result of the operation is practically
mil. The most prolonged draining, suction, or compression produces only a small
quantity of caustic liquor, and washing is impracticable without unduly diluting
the caustic liquor.

page_text: To overcome this new difficulty, the following washing process is adopted. The
mixture of salt and caustic liquor is placed in a vessel that may be of cylindrical
form, provided with a double casing for enabling it to be heated by means of steam,
and with a perforated, reticulated or permeable false bottom for keeping back the
solid portion and allowing only the liquid portion to pass through. The whole is
heated to a temperature of approximately 100° C., after which there is poured on
the top of the mixture by means of a suitable apparatus that will not cause the
mixing of the contents of the vessel, a layer of saturated salt water or brine equal
in volume to the volume of the caustic solution with which the precipitated salt is
impregnated. On opening a discharge cock at the bottom of the said vessel, a
displacement of a molecular nature so to speak of the caustic solution is produced.
The caustic solution is expelled practically in successive horizontal layers and is
replaced by the salt water without any mixing taking place. The discharge cock
should be closed when the causticity of the liquor being drawn off' practically ceases,
that is when the volume of the drawn off caustic solution is about equal to that of
the salt water poured into the top of the vessel.
By this means practically the whole of the caustic solution can be recovered without
diluting the same, and a mother liquor is also obtained for a succeeding operation,
the slight causticity of such mother liquor causing no inconvenience in its subsequent
treatment.
Thus the said washing process enables all loss to be avoided. As already stated,
the washing process should be carried out with the aid of heat; it takes place very
much less regularly in the cold.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed declare that what
I claim is :-
1. The herein described process of separating the caustic alkali from the liquor
obtained by the electrolysis of an alkaline chloride consisting in precipitating the
alkaline chloride remaining in solution after electrolysis, either by evaporation of
the solution, or preferably, by the addition thereto of a strong solution of caustic
alkali obtained from a previous operation, and in effecting the washing of the resulting
soft or thin mud by vertical displacement in a suitable apparatus with the aid of
heat as set forth.
2. For carrying out the washing operation referred to in the preceding claim,
an apparatus comprising a vessel constructed so as to be capable of being heated,
and provided with a false bottom adapted to retain the salt and allow only of the
passage of the caustic alkaline liquor mixed therewith, with a device for admitting
the washing liquid at its upper part, and with a discharging device at its lower part,
the whole being arranged in such a manner that the pure salt washing water will
descend by gravity and effect the removal of the caustic alkaline liquid from the
salt by displacement, substantially as herein described.
Dated this 3rd day of May 1895.
W. LLOYD WISE,
46, Lincoln's Inn Fields, London, W.C., Chartered Patent Agent.