Improvements in the Electrolytic Manufacture of Alkali-chlorates.
Year: 1895

page_text: Date of Application, 10th Apr., 1895
Complete Specification Left, 24th Dec., 1895-Accepted, 1st Feb., 1896
PROVISIONAL SPECIFICATION.
Improvements in the Electrolytic Manufacture of Alkali-chlorates.
I, JASPER WETTER, Patent Agent, of 433 Strand, in the County of London,
do hereby declare the nature of this invention, as communicated to me by The
Elektrizitäts-Aktiengesellschaft, vormals Schuckert & Co., Electrical Engineers, of
Nürnberg, in the Kingdom of Bavaria, to be as follows:-
In the manufacture of chlorine and alkali by the electrolytic decomposition of
chlorides and the transformation of the products into alkali-chlorates by chemical
means, difficulties and losses occur at various stages of the process. The quantities
of caustic alkali and chlorine are not nearly equal to those which theoretically
correspond to the electric current used. The recovery of the chlorine presents
many inconveniences and requires extensive plant. Attempts have been made,
while retaining the diaphragm, to conduct the alkaline kathode-liquid (containing
caustic alkali and alkali-chloride) to the anode, and there to liberate its chlorine,
which then would immediately form alkali-chlorate. The quantity of chlorine
obtained at the anode in this way is, however, very small, and none but platinum
electrodes are found to be sufficiently durable in the strongly alkaline solution.
The production of chlorates from the chloride has been attempted, but no
industrially applicable method has been evolved in this way.
According to the present invention, the baths are used without diaphragms, and
the process carried out at a temperature from 40 to 100° C., with a current density
of 500 to 1500 ampères per square meter (although any other current density may
be employed); The electrolyte is a moderately concentrated solution of alkali-
chloride, which is maintained sufficiently alkaline by the addition of alkali-bicar-
bonates (from 1 to 5 per cent.), to ensure that the alkalinity at the anode is mainly
caused by alkali carbonates. The last mentioned fact not only serves to avoid the
occurrence of free caustic alkalies injurious to the anode carbons, but also to
increase the yield of chlorine, for owing to their great conductivity, free caustic
alkalies participate much more in the conduction of the current, than chlorides and
alkali-carbonates or bi-carbonates.
The alkalinity due to the presence of carbonates as mentioned above, may be
maintained by the constant or periodical introduction of carbonates (or of carbonic
acid), and an excess of alkalinity may be neutralised by hydrochloric acid. Instead
of carbonates, organic compounds adapted to yield carbonic acid by oxidation at
the anode, may be added to the bath. Such compounds are, for instance, fatty
acids or oxy-fatty-acids, especially acetic acid and oxalic acid, or carbohydrates,
such as saccharose, dextrose or dextrin, which although no good conductors
themselves, are quickly split into products yielding carbonic acid on their further
oxidation. As a rule, any soluble organic bodies are suitable for the process,
provided that they are added to the electrolyte in very minute quantities only.
In carrying out this process, I employ preferably a solution of potassium chloride
(saturated at ordinary temperature) to which has been added from 2 to 3 per cent.
of potassium bicarbonate, said solution being contained in a receptacle of earthen-
ware or iron, with electrodes of platinum or carbon, and subjected to electrolysis
while periodically admitting carbonic acid, care being taken that the temperature and
the current density are as stated above. The yield of chlorate is a maximum at
the beginning of the process, and drops as the contents of chlorate increases. The
process should therefore be interrupted, as soon as the consumption of current for

page_text: the further production of chlorate exceeds a limit determined by the cost of the
motive power. The solution is then drawn off, and the greatest part of the
potassium chlorate produced crystallises out. The mother liquor is utilised by
introducing it again into the process.
If carbon electrodes are used for the production of chlorates, a brown colouring
matter passes from these carbons into the solution, especially from the anode,
which is only slightly decomposed. During crystallisation the said colouring
matter remains partly in the mother liquor and partly adheres to the crystals.
The colouring matter may be removed by conducting the electrolyte, before it
has attained the desired high percentage of chlorate, into another bath, where it is
further exposed to the action of the current under the same conditions, with
platinum electrodes, or with kathodes of any other material and anodes of
platinum.
The formation of chlorate is then continued, while the colouring matter is
destroyed and a clear liquid obtained. The greatest part of said colouring matter
is oxidised at the anode, while a small portion is reduced at the kathode and forms
on it a black precipitate. This electrolytic purification may be effected with any
temperature and current density suitable for the formation of chlorate. High
current densities (from 2000 to 4000 ampères) may be employed with advantage,
and accelerate the process of discoloration. Instead of the electrolyte itself, a
solution of the chlorate may be relieved of colouring matter in the same manner,
in which case the presence of alkali-carbonates may be dispensed with.
In the manufacture of sodium-chlorate the salt-solution containing the sodium
chlorate is concentrated by evaporation, and the sodium chloride which separates
at a high temperature is scooped out. It always contains sodium chlorate and is
subsequently used for preparing a fresh sodium chloride solution for the baths.
The sodium chlorate is recovered from the mother-liquor, which may be relieved of
colouring matter in the same way as described above.
Dated this 10th day of April 1895.
FAIRFAX & WETTER,
Agents for the Applicant.
COMPLETE SPECIFICATION.
Improvements in the Electrolytic Manufacture of Alkali-chlorates.
I, JASPER WETTER, Patent Agent, of 433 Strand, in the County of London,
do hereby declare the nature of this invention, and in what manner the same is
to be performed, as communicated to me by The Elektrizitäts-Aktiengesellschaft,
vormals Schuckert & Co., Electrical Engineers, of Nürnberg, in the Kingdom of
Bavaria, to be particularly described and ascertained in and by the following
statement :-
In the manufacture of chlorine and alkali by the electrolytic decomposition of
chlorides and the transformation of the products into alkali-chlorates by chemica!
means, difficulties and losses occur at various stages of the process. The quantities
of caustic alkali and chlorine are not nearly equal to those which theoretically
correspond to the electric current used. The recovery of the chlorine presents
many inconveniences and requires extensive plant. Attempts have been made,
while retaining the diaphragm, to conduct the alkaline kathode liquid (containing
caustic alkali and alkali-chloride) to the anode, and there to liberate its chlorine,
which then would immediately form alkali-chlorate. The quantity of chlorine
obtained at the anode in this way is, however, very small, and none but platinum
electrodes are found to be sufficiently durable in the strongly alkaline solution.
Attempts have been made to produce chlorate from the chloride in baths without
diaphragms and at a high temperature, without however, leading to a commercially
useful process.

page_text: According to the present invention the baths are used without diaphragms, and
the process is carried out at a high temperature, preferably from 40° to 100° C.,
with a current density of 500 to 1000 ampères per square meter; the electrolyte is
a moderately concentrated solution of alkali-chloride, which is maintained
sufficiently alkaline by the addition of alkali-bicarbonates (from 1 to 5 per cent.),
to ensure that the alkalinity at the anode is mainly caused by alkali-carbonates.
The last-mentioned fact not only serves to avoid the occurrence of free caustic
alkalies injurious to the anode carbons, but also to increase the yield of chlorine,
for owing to their great conductivity, free caustic alkalies participate much more
in the conduction of the current than chlorides and alkali-carbonates or bi-
carbonates.
It is true, that the alkali-carbonates are also decomposed by the current, caustic
alkali being formed at the kathode, and oxygen together with carbonic acid, at the
anode. This carbonic acid combines with the caustic alkali coming from the
kathode to form carbonate, and in smaller quantity also with the carbonate present
to form bicarbonate. In order to decompose as much chloride as possible with a
given current density, the quantity of alkali-carbonates contained in the solution
should be as low as may be allowed in view of the secondary chemical reaction of
the formation of chlorate from the alkali-carbonate and the primarily separated
chlorine.
As is well-known, the action of chlorine on a comparatively large quantity of
alkali produces chiefly or generally chloric acid, and hypochloric acid is produced
if the quantity of alkali is small. The hypochloric acid may be subsequently
converted into chloric acid by the mere heat of the bath, but a portion will reach
the kathode, where it forms chloride. A few tenths per cent. of hypochloric acid
in the bath are sufficient to exercise a decidedly injurious effect on the yield of
chloric acid. In the present process the conditions are arranged in such a manner,
that the small quantity of. carbonate employed will be sufficient to cause the
immediate formation of chloric acid at the given current densities and temperatures,
and to reduce the hypo-chloric acid present in the solution to mere traces; while
on the other hand, the small quantities of carbonate can only take an unimportant
part in the electrolysis.
The alkalinity due to the presence of carbonates, as mentioned above, may be
maintained by the constant or periodical intro.luction of carbonates (or of carbonic
acid), and an excess of alkalinity may be neutralised by hydrochloric acid. Instead
of carbonates, organic compounds adapted to yield carbonic acid by oxidation at
the anode, may be added to the bath. Such compounds are, for instance, fatty
acids, or oxy-fatty acids, especially acetic acid and oxalic acid, or carbo-hydrates,
such as saccharose, dextrose, or dextrin, which although not good conductors
themselves, are quickly split into products yielding carbonic acid on their further
oxidation. As a rule, any soluble organic bodies are suitable for the process,
provided that they are added to the electrolyte in very minute quantities only.
In carrying out this process, I employ preferably a solution of potassium chloride
(saturated at ordinary temperature) to which has been added from 2 to 3 per cent.
of potassium bicarbonate, said solution being contained in a receptacle of earthen-
ware or iron, with electrodes of platinum or carbon, and subjected to electrolysis
while periodically admitting carbonic acid, care being taken that the temperature
and the current density are as stated above. The yield of chlorate is a maximum
at the beginning of the process, and drops as the contents of chlorate increases.
The process should therefore be interrupted as soon as the consumption of current
for the further production of chlorate exceeds a limit determined by the cost of
the motive power. The solution is then drawn off, and the greatest part of the
potassium chlorate produced crystallises out. The mother liquor is utilised by
introducing it again into the process.
In the manufacture of sodium chlorate the salt-solution containing the sodium
chlorate is concentrated by evaporation, and the sodium chloride which separates
at a high temperature is scooped out. It always contains some sodium chlorate

page_text: and is subsequently used for preparing a fresh sodium chloride solution for the baths.
The sodium chlorate is recovered from the mother liquor.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:
1. The improvement in the manufacture of alkali-chlorates by electrolysing
alkali-chlorides at a high temperature, and without the use of diaphragms, which
consists in imparting to the electrolyte an alkaline reaction mainly due to the
presence of alkali-carbonates.
2. The improvement in the manufacture of alkali-chlorates by electrolysing
alkali-chlorides at a high temperature and without the use of diaphragms, which
consists in imparting to the electrolyte an alkaline reaction by means of carbonates
produced by the continuous or intermittent supply of carbonic acid, or of organic.
compounds adapted to yield carbonic acid as a final product by oxidation at the
anode, substantially as described.
Dated this 23rd day of December 1895.
FAIRFAX & WETTER,
433, Strand, London, Agents.