Improvements in and relating to 'the' Manufacture of 'Chlorine.
Year: 1891

page_text: Date of Application, 19th Nov.; 1891
Complete Specification Left, 8th Aug., 1892-Accepted; 15th Oct., 1892
PROVISIONAL SPECIFICATION.
.:Improvements in and relating to 'the' Manufacture of 'Chlorine.
I, Dr. CARL HOEPFNER of 36 Frankfurterstrasse, Giessen, in the Empire of
Germany, do hereby declare the nature of this invention to be as follows:-
"This invention. relates to the manufacture of chlorine.
"For the electrolytic production of chlorine I preferably: employ a solution of
hydrochloric acid. I produce chlorine in a very cheap manner from liquids con-
taining chlorides and especially from: liquids containing calcium, barium or strontium
of any origin. By means of sulphuric acid these metals may be precipitated and
hydrochloric acid solution formed which. is electrolyzed and chlorine produced
therefrom. Sulphuric acid may be formed by the action of air upon a solution
containing sulphurous acid. This process is of very great value. for instance in the
manufacture of chlorate, of potassium, whereby, a great, quantity of chloride, of
calcium is produced.
*
Or I make use of hydrochloric acid gas, which is absorbed by. water or any salt
solution and then subjected to the action of an electric.current and decomposed.
"The remaining liquid may again be saturated with hydrochloric acid gas, and
electrolytically decomposed.
The decomposition of the hydrochloric acid may be facilitated by using chloride
of copper at the cathodes. Cuprous chloride is formed and may..be regenerated by
any suitable means such as by the action of air.or.of oxygen.
"
Or I electrolyse a saturated, solution.of. common salt or any other suitable
chloride whereby at the cathodes this liquid,may be. acidulated, by sulphuric acid
thereby setting free hydrochloric acid. Glauber. salt is formed,, the presence, of
which is not.noxious for the solutions,saturated with chlorides.
"For these purposes, but especially for the decomposition of common salt or other
chlorides I sometimes make use of a double diaphragm,between..the..anodes and
cathodes in order to prevent diffusion.
"The diaphragm.enclosing the anodes consists. wholly or partly of nitrated organic
matters such as nitrocellulose, whilst that enclosing the cathodes may consist of
common linen cotton or the like. Into the liquid between the two diaphragms, if
desired carbonic acid may be introduced.
Dated this 9th day of November 1891.
HASELTINE, LAKE & Co.,
*.45; Southampton Buildings, London, W.C., Agents for the Applicant.
COMPLETE SPECIFICATION.
"Improvements in and relating to the Manufacture of Chlorine.
I, Dr. CARL HOEPFNER..of 36 Frankfurterstrasse, Giessen, in the Empire of
Germany, 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 the manufacture of chlorine.
It is well-known that many endeavours have been made to find means for cou-
verting a greater proportion of the chlorine contained in hydrochloric acid into free
chlorine than has heretofore been possible. In the Weldon process two-thirds of
the hydrochloric acid used are lost in the form of calcium chloride.
It is also well known that many attempts have been made to produce hydrochloric

page_text: acid and enforine from liquors of calcium chloride such as are obtained in the
manufacture of ammonia soda.
Both requirements are fulfilled by the following electrolytic process.
Instead of decomposing common salt or potassium chloride by electrolytic means
and producing chlorine as has frequently been attempted, the electrolytic production
of chlorine is based according to the present invention upon the decomposition of
hydrochloric acid. When present in a more or less concentrated solution the
hydrochloric acid possesses the faculty of becoming a very good conductor for the
electric current, so that nearly the theoretical output is obtained, the expenditure
of one horse-power producing from 10 to 12 kilogrammes of chlorine per day. The
use of hydrochloric acid also permits of the construction of very durable and
effective apparatus, which is not possible in the process of decomposing common
salt. By the latter decomposition only about 5 kilogrammes of chlorine can be
produced per day by the expenditure of one horse-power, and the caustic soda and
sodium carbonate obtained in the same is impure and of very little value.
Now in order to obtain for the electrolysis, the necessary hydrochloric acid
cheaply, without loss, and of the requisite concentration or with the requisite con-
ductivity use is made according to the present invention of special means. If the
hydrochloric acid of commerce were directly subjected to electrolysis the con-
ductivity would decrease to a minimum the more completely the chlorine contained
therein is evolved in the gaseous form, and removed, and consequently the
consumption of current would considerably increase.
In practice only a portion of the hydrochloric acid could be utilized electroly-
tically dilute acid would remain behind valueless, and would perhaps have to be
rendered innocuous at considerable expense.
For obviating excessive losses of current or expensive losses of hydrochloric
acid, the following process is used, which ensures a good conductivity to the liquid
which remains acid avoids all losses of hydrochloric acid and in special cases
enables the raw hydrochloric acid to be extracted at any extremely cheap rate.
Hydrochloric acid of more or less high concentration or more or less concentrated
hydrochloric solutions of salts or solutions of chloride with sulphuric acid or
sulphurous acid are submitted to electrolysis in apparatus with membranes and
anodes capable of withstanding chlorine, in such a manner that the hydrochloric
acid or the solution of salt flows in and out.
The liquor is so conducted that on flowing out it still contains sufficient free
hydrochloric acid for keeping the tension at the pole of the last cell at no more
than 2.5 volts. The circulation need only take place at the cathodes, if gaseous
chlorine and not aqueous chlorine is to be obtained. The liquor is then saturated
in a suitable manner with gaseous hydrochloric acid say by blowing in such acid.
A less suitable and simple process is to introduce gaseous hydrochloric acid during
the electrolysis into the decomposing cells, because the chlorine evolved will by
this means be caused to contain hydrochloric acid. The lye may also be acidified
by common hydrochloric acid with 70 per cent. of water but the water has to be
removed again by evaporation after the completion of the electrolysis.
How the raw hydrochloric acid is produced for these purposes is immaterial. It
may, as heretofore, be produced from culinary salt and sulphuric acid or by mixing
valueless liquors of calcium chloride or barium chloride with sulphuric acid, which
can often be done cheaply and conveniently.
Instead of introducing hydrochloric acid into the liquid to be electrolysed, I may
so proceed and so maintain the requisite good conductivity of the same, that more
or less concentrated otherwise valueless liquors of calcium chloride or barium
chloride are mixed with sulphuric acid so that a portion, or, when culinary salt is
present in the liquors, all the calcium or barium is precipitated as gypsum or
barium sulphate.
The liquors may then be electrolysed, all the hydrochloric acid set free can be
obtained electrolytically as chlorine, and the liquid retains its good conductivity by
reason of the salts it contains.

page_text: If desired it can again be evaporated, mixed again with sulphuric acid, and
electrolysed until nearly all the chlorine has disappeared from the same.
Such liquors of calcium chloride occur in the manufacture of ammonia soda
manufacture, in the manufacture of potassium chlorate and can also be produced
cheaply in the well-known manner from other desired solutions of chlorides of the
heavy metals and of magnesium.
Such treatment of the liquors of calcium chloride produced in the manufacture
of potassium chlorate is especially advantageous for in that case only sulphuric
acid, lime and potassium chloride is required for this manufacture, the output is
great and all the chlorine of the potassium chloride is utilized.
To render the manufacture of chlorine profitable where the price of sulphuric
acid is high, but where sulphur or metallic sulphides and consequently sulphurous.
acid can be procured cheaply, and where perhaps cheap water power is at disposal,
the sulphuric acid is produced very conveniently and with simple and cheap
apparatus say by introducing sulphurous acid gas into a solution of copper chloride
or manganous salts by known means, which sulphurous acid may be oxidized by
introducing oxygen gas or air by known means into the same solution.
In the electrolysis of hydrochloric acid I obtain, as a by-product hydrogen which
may be used in any desired manner.
The most rational use of the same will be that which enables reductions to be
carried out with it in the nascent state and the electrical tension at the poles to be
lowered at the same time.
This takes place by suspending substances in the circulating cathode liquid or
keeping them dissolved and in motion, which substances may undergo reduction.
By this means very valuable decompositions may be brought about by which part
of the cost of the process can be covered or a considerable decrease of the tension
at the poles can be obtained.
In both cases the production of chlorine from the hydrochloric acid used is
rendered very cheap. As such a reducing agent I may use copper chloride which
is reduced to protochloride and can be oxidized again by oxygen or air.
A very important item for the electric production of chlorine and especially for
the present process is the procuring of the above mentioned durable membranes
that is to say such as with sufficient current conductivity and mechanical durability,
are chemically so resistant that neither the chlorine of the anode nor the hydrogen
and other reducing agents alkalies or alkaline earths which may occur at the cathode
will injure them.
Nitro-parchment is a very suitable membrane against chlorine, but it does not
resist the reducing action of the reducing or alkaline substances occurring regularly
or only at times at the cathode.
For this purpose I preferably use a double membrane, between the anode and
cathode so that there are then two membranes between the anode and cathode one
being nitrated and consisting of paper or cloth like nitrocellulose and the other not
nitrated and made of ordinary parchment paper, both strengthened if desired by
strong cloths, sieves or the like.
Between the two membranes a space of suitable size can be left which is filled
with a conducting liquid which will not injure either membrane.
Carbonic acid gas may be introduced into the liquid within the space between
the two membranes, which carbonic acid combines with alkaline bodies or neutralizes
the same if produced or liberated by the electrolytic process so as to change
uch alkaline bodies into carbonates or bicarbonates which do not injure the
nembranes.
Having now particularly described and ascertained the nature of this inven-
ion and in what manner the same is to be performed, I declare that what 1
laim is:-
1. The utilization of highly concentrated solutions of hydrochloric acid with or
without the presence of other acids or salts for the electrolysis or electrolytic

page_text: production of chlorine in such a manner that the solution is caused to flow con-
stantly or at short intervals to and from the baths, or only the cathodes of the
same, the electric resistance of the liquid or the tension at the poles being kept
constant within narrow limits, by the liquor to be electrolysed being kept acid and
being constantly or intermittently enriched with aqueous or gaseous hydrochloric
acid or with sulphuric acid sulphurous acid or with solid salts, especially chlorides,
and sulphuric acid or sulphurous acid, preventing a deleterious dilution by constant
or intermittent evaporation, and thus enriching the same quantity of water
repeatedly with hydrochloric acid, and electrolysing it.
2. The production of hydrochloric acid for use in a process such as is herein-
before described by mixing liquors of calcium chloride or barium chloride with a
certain quantity of sulphuric acid, the gypsum or barium sulphate produced being
removed and the hydrochloric acid being either evolved in the gaseous state and
treated according to the process set forth in the first claim or else is immediately
subjected to electrolysis until the solution of salt containing hydrochloric acid has
lost nearly the whole of the said acid.
3. For use in the process herein before described the production of cheap
sulphuric acid by oxidizing sulphurous acid in an aqueous solution of copper
chloride or of manganous salts by means of oxygen or air.
4. In the process conducted according to the first, second and third claims the
reduction of the tension at the poles, or the profitable utilization of the hydrogen
occurring at the cathode by dissolving or suspending and keeping in motion in
the cathode liquor, substances which are reducible by the hydrogen in a nascent
state.
5. For the electrolytic production of halogens especially for the process com-
prised in the preceding claims the employment of membranes which are composed
largely of nitrated organic substances and which are protected on the cathode side
by non-nitrated membranes, cloths or their substitutes, carbonic acid being if
desired introduced into the space which may exist between the nitrated and non-
nitrated membranes.
Dated this 8th day of August 1892.
HASELTINE, LAKE & Co.,
. 45, Southampton Buildings, London, W.C., Agents for the Applicant.