of Chromie Acid by Electrolytic Oxidation of Solutions of Chromium Oxide Salts.
Year: 1898

page_text: Date of Application, 18th July, 1898
Complete Specification Left, 12th Apr., 1899-Accepted, 13th May, 1899
PROVISIONAL SPECIFICATION
Production of Chromie Acid by Electrolytic Oxidation of Solutions
of Chromium Oxide Salts.
I, OLIVER IMRAY, of Birkbeck Bank Chambers, Southampton Buildings,
Chancery Lane, in the County of London, Chartered Patent Agent, do hereby
declare the nature of this invention (as communicated to me from abroad by The
Farbwerke vormals Meister Lucius and Brüning, of Hoechst a/Main, in the
Empire of Germany, Chemical Manufacturers) to be as follows:-
As
The method employed on a large scale for regenerating chromic acid from
lyes containing chromium oxide salts is complicated and scarcely rational.
is known, the lyes containing for the most part chromium sulphate are mixed
with lime and the paste thus obtained, which consists of chromium oxide, an
excess of caustic potash, besides large quantities of calcium sulphate, is heated
to blood-red with access of air. Chromate of lime is thus formed, which in an
aqueous solution of sodium sulphate changes into soluble sodium chromate and
calcium sulphate.
On removing the latter, the solution of sodium chromate may be employed for
oxidation.
Not only is the quantity of chromic acid obtained by this process small
compared with the quantity of chromium oxide employed, but also considerable
quantities of sulphuric acid are lost, and many other inconveniences attend
the process. For the sodium chromate can only have a sufficient oxidising action
in an acid solution, in this case a sulphuric acid solution, and the whole of the
acid added forms by this method of regeneration a worthless product, namely,
refuse calcium sulphate.
Lately it has been proposed to regenerate the chromic acid from the lyes
containing chromium oxide salts by means of the electric current (Zeitschr. f.
angew. Chem. 1893, 360; Hilfsbuch fi. d. Electrotechnik v. Grawinkel &
Strecker, A Aufl: p. 506. 1895). The chromium oxide is dissolved in an excess
of caustic soda lye and this solution is poured into the anode compartment of a
vessel provided with a diaphragm, while as cathode a fluid, for instance caustic
soda lye, is employed.
At the anode sodium chromate is formed by the current, whilst caustic soda
lye is produced at the cathode. The sodium chromate thus formed can be changed
into bichromate by further electrolysis.
Apart from the great consumption of energy, according to the description (at
least 5 volts at a current density of somewhat more than 200 ampère to the square
metre), this method of oxidation is inapplicable in practice, as sodium chromate
is employed for oxidation in a sulphuric acid solution, and the loss of sulphuric
acid is in this process accompanied by a further loss of the expensive caustic
soda lye.

page_text: All the drawbacks mentioned,-loss of chromic acid, sulphuric acid and other
products are avoided by a new rational method of great economical importance
as is already proved experimentally. There is used the solution of a chromium
salt in some acid, for instance chromium sulphate dissolved in sulphuric acid
and preferably a solution of the highest possible electric conductivity-about
100 grams Cr2O3 and 350 grams H₂SO can be made up with water to 1 litre.
With this solution are filled the anode and cathode compartments of a vessel
coated with lead, provided with a diaphragm, and having lead plates as electrodes.
By the action of the current, chromic acid is formed at the anode whilst hydrogen
is evolved at the cathode. A migration of sulphuric acid also takes place, the
concentration increasing on the anode side and decreasing on the cathode side.
The lye oxidised at the anode can at once be employed in manufacture and the
chromic acid therein being thus retransformed into chromium oxide can then
be moved to the cathode, whilst the lye at first in the cathode compartment is
now transferred to the anode compartment.,
The cathode lye is at the beginning of the second operation richer in sulphuric
acid than the anode lye; yet on the passing of the current, the excess of sulphur
acid is transferred to the anode. By this arrangement of circulation, moving
alternatively the lye from the cathode to the anode, it results that an accumulation
of sulphuric acid nowhere takes place and that in fact the same lye can be
employed indefinitely, in its unchanged composition and without any loss in
substance, as an excellent carrier of oxygen.
1
At a current density of more than 300 ampères per square metre the tension
amounts to hardly 3.5 volts.
Dated this 18th day of Inle 1900
ABEL & IMRAY,
Agents for the Applicant.
Production of Chromic Acid by Electrolytic Oxidation of Solutions
of Chromium Oxide Salts.
I, OLIVER IMRAY, of Birkbeck Bank Chambers, Southampton Buildings,
Chancery Lane, in the County of London, Chartered Patent Agent, do hereby
declare the nature of this invention (as communicated to me from abroad by The
Farbwerke vormals Meister Lucius and Brüning, of Hoechst a/Main, in the
Empire of Germany, Chemical Manufacturers), and in what manner the same is
to be performed to be particularly described and ascertained in and by the
following statement:―
The method employed on a large scale for regenerating chromic acid from
lyes containing chromium oxide salts is complicated and scarcely rational. As
is known, the lyes containing for the most part chromium sulphate are mixed
with lime and the paste thus obtained, which consists of chromium exide, an
excess of caustic lime, besides large quantities of calcium sulphate, is heated
to blood-red with access of air. Chromate of lime is thus formed, which in an
aqueous solution of sodium sulphate changes into soluble sodium chromate and
calcium sulphate.
On removing the latter, the solution of sodium chromate may be employed for
oxidation.
Not only is the quantity of chromic acid obtained by this
Proc
الوصف

page_text: compared with the quantity of chromium oxide employed, but also considerable
quantities of sulphuric acid are lost, and many other inconveniences attend
the process. For the sodium chromate can only have a sufficient oxidising action
in an acid solution, in this case a sulphuric acid solution, and the whole of the
acid added forms by this method of regeneration a worthless product, namely,
refuse calcium sulphate.
&
Lately it has been proposed to regenerate the chromic acid from the lyes
containing chromium oxide salts by means of the electric current (Zeitschr. f.
angew. Chem. 1893, 360; Hilfsbuch fd. Electrotechnik v. Grawinkel
Strecker, 4 Aufl: p. 506. 1895). The chromium oxide is dissolved in an excess
of caustic soda lye and this solution is poured into the anode compartment of a
vessel provided with a diaphragm, while as cathode fluid for instance, caustic
soda lye, is employed.
At the anode, sodium chromate is formed by the current, whilst caustic soda
lye is produced at the cathode. The sodium chromate thus formed can be changed
into bichromate by further electrolysis.
Apart from the great consumption of energy necessary according to the above
description (at least 5 volts at a current density of somewhat more than 200
ampère to the square metre), this method of oxidation is inapplicable in practice,
as sodium chromate is employed for oxidation in a sulphuric acid solution and
the loss of sulphuric acid is in this process accompanied by a further loss of the
expensive causic soda lye.
All the drawbacks mentioned,-loss of chromic acid, sulphuric acid and other
products are avoided by a new rational method of great economical importance
as is already proved experimentally. There is used the solution of a chromium
salt in some acid, for instance chromium sulphate dissolved in sulphuric acid,
and preferably a solution of the highest possible electric conductivity-about
100 grams Cr,0, and 350 grams H₂SO, can be made up with water to 1 litre.
With this solution are filled the anode and cathode compartments of a vessel
lined with lead, provided with a diaphragm, and having lead plates as electrodes.
By the action of the current, chromic acid is formed at the anode whilst hydrogen
is evolved at the cathode. A migration of sulphuric acid also takes place, the
concentration increasing on the anode side and decreasing on the cathode side.
The lye oxidised at the anode can at once be employed in manufacture and the
chromic acid therein being thus retransformed into chromium oxide can then
be moved to the cathode, whilst the lye at first in the cathode compartment is
now transferred to the anode compartment.
The cathode lye is at the beginning of the second operation richer in sulphuric
acid than the anode lye; yet on the passing of the current the excess of sulphuric
acid is transferred to the anode. By this arrangement of circulation, moving
the lye from the cathode to the anode, it results that an accumulation of sulphuric
acid nowhere takes place and that in fact the same lye can be employed
indefinitely in its unchanged composition and without any loss in substance, as
an excellent carrier of oxygen.
At a current density of more than 300 ampères per square metre the tension
amounts to hardly 3.5 volts.
Having now particularly described and ascertained the nature of this invention
and in what manner the same is to be performed I declare that what I claim is :-
The herein described process for production of chromic acid by first electrolysing
a solution of a chromium oxide salt in an aqueous solution of the corresponding
acid, as for instance solution of chromium sulphate in aqueous sulphuric acid,
then employing the mixture of chromic and other acid resulting from the
electrolysis, for reactions by which it is reconverted into the solution of the
oxide salt in acid, charging this at the cathode when the fluid formerly at the

page_text: cathode has been transferred to the anode for formation again of chromic acid,
and so on continuously.
ABEL & IMRAY,
Agents for the Applicant.