Extraction of Chlorine from Solutions of Chloride of Magnesium.
Year: 1887

page_text: Date of Application, 31st Aug., 1887
Complete Left, 26th Apr, 1888
Complete Accepted, 29th June, 1888
PROVISIONAL SPECIFICATION.
Extraction of Chlorine from Solutions of Chloride of Magnesium.
I, Professor THEOPHILE SCHLOESING, Chemist, of Paris, Quai d'Orsay, 67, do
hereby declare the nature of this invention to be as follows:-
:-
It is well known that chloride of magnesium raised to a red heat in contact with air
is decomposed by the oxygen into magnesia and free chlorine. This re-action, upon
which a process for the manufacture of chlorine may he founded, is not altogether
satisfactory unless the chloride of magnesium is anhydrous. If it contains water this
re-acts upon its elements both by its oxygen and its hydrogen to form magnesia and
hydrochloric gas.
It is required then in order to extract the chlorine from chloride of magnesium to
obtain the salt in the first place in an anhydrous condition. Now its principal sources
present it in a state of solution and experience has shown that the ordinary methods
employed for the extraction of salts from their solutions are not applicable to chloride
of magnesium in consequence of its disposition to decompose before becoming
dehydrated. It is necessary then to find a new industrial method for the extraction
of anhydrous chloride of magnesium from its solutions. I will presently describe how
this problem may be solved.
To entirely expel the water of solution and obtain an anhydrous chloride I have
recourse to heat, and 1 divide the application of it into three phases.
First phase. I simply heat the solution in a boiler analogous for example to those
in salt works. I thus concentrate the solution until it attains the temperature of
165 to 170 degrees centigrade. The foreign salts are deposited during this con-
centration and are eliminated. It is unnecessary to say more about this elementary
operation which is well known to all chemists.
Second phase. When the temperature exceeds 170 degrees the solution becomes
pasty and foams a great deal. I could only continue to heat it with extreme slowness

page_text: from underneath through the bottom of the boiler. I prefer to continue the evaporation
by heating the matter from above, for example by spreading it upon the sole of a
reverberatory furnace analogous to the furnaces used in drying soda sali. Then the
foaming no longer takes place. By stirring the matter frequently it is finally obtained
in the form of porous grains solid and dry in appearance but containing still about
30 per cent. of water. 1 then stop the second phase. To simplify the description
I will call the product now obtained chloride in grains.
I attach very great importance to obtaining this chloride in grains. The grains aro
porous and solid, and the heat to which they are afterwards to be exposed does not
melt them or even soften them. In this state the material offers every facility to the
subsequent manipulation; especially it remains permeable to gases; these properties
it will soon be seen are of high importance.
At the end of the preparation of chloride in grains the action of water upon the
chloride commences to become apparent; there is disengaged in the form of hydro-
chloric gas from 3 to 5 per cent. of the chlorine contained in the material. This gas
is condensed by the means in use in chemical works; then it is neutralized by
magnesia and the chloride is sent back into the solutions to be afterwards treated.
Third phase. The chloride in grains is introduced into a closed vessel furnished
with an outlet pipe, for example, into a retort, such as is employed in making
illuminating gas, set in a furnace so that it can be heated to a red heat. The
application of the heat effects a disengagement of vapour of water and hydrochloric
gas, which I collect in a condensing apparatus connected by pipes to the outlet from
the retort, for example, a series of receivers such as are employed in chemical works.
When the disengagement has ceased and the temperature has been carried to a red
heat the operation is finished. The residue contained in the retort is a mixture of
magnesia and anhydrous of chloride of magnesium containing from 40 to 50 per cent.
of chloride and suitable for immediate treatment with air and heat for the extraction
of chlorine.
To have in the gaseous atmosphere around the chloride the greatest possible tension
of hydrochloric gas to minimise as much as possible the decomposition of the chloride
is the essential condition for obtaining the highest yield of anhydrous chloride.
By further availing myself of this principle I am able to produce a chloride
much richer than that resulting from the operation which I have described and by a
very simple means. The water disengaged from the retort can be evacuated from the
condenser as it is deposited. The hydrochloric gas, which is much more abundant
towards the end of the operation than at the commencement, no longer finds water
with which it can condense and it retains the gaseous state: I send it back into the
retort, which is furnished with this object, with a connection at the front. A passage
connects the condenser with the retort and upon this passage I arrange a gas propeller,
such as a blower of suitable construction, which draws the gas from the condenser and
drives it into the retort. I thus establish a true circulation of hydrochloric gas which
traverses the retort and there increases the hydrochloric tension so effectually
that the product obtained by this process contains from 50 to 80 per cent. of anhydrous
chloride.
:
In place of employing hydrochloric gas disengaged from the chloride, I may borrow
it from any suitable source, whence this gas can be obtained. The effects due to the
augmentation of gas tension in my retort remain the same.
To extract the chlorine from the anhydrous chloride thus obtained it is heated
to a red heat in a suitable apparatus in which a regulated current of air circulates.
: I can carry on this treatment by different means: in retorts, of material suitable to
resist the action of chlorine, heated in furnaces and provided with connections for the
entrance and escape of the gas.' I 'may connect the retorts in series traversed
methodically by the gases. I can employ muffles heated externally and connected in
series so that the solid matter passes from one end to the other whilst the gases travol
in the opposite direction. I may besides have recourse to furnaces in stages or in
compartments furnished with slabs arranged in steps, heated by flues in which furnace.

page_text: gases circulate. Or I may employ any other arrangement which is suitable, having
regard to the three points, the heating the movement of the solid matier; and the
circulation of the gases.
:
The anhydrous chloride obtained by my present process presents in virtue of its
porosity the valuable property of being completely decomposed by air on reaching a
dull red heat and of furnishing a gaseous mixture which contains as it leaves the
apparatus as much as 30 volumes of chlorine in the 100 of gaseous mixture.
Dated this 31st day of August 1887.
CARPMAEL & Co.,
Agents for the Applicant.

page_text: COMPLETE SPECIFICATION.
Extraction of Chlorine from Solutions of Chloride of Magnesium.
I, Professor THEOPHILE SCHLOESING, Chemist, of Paris, Quai d'Orsay, 67, do
hereby declare the nature of this invention and in what manner the same is to he
performed to be particularly described and ascertained in and by the following
statement:-
It is well known that chloride of magnesium raised to a red heat in contact
with air is decomposed by the oxygen into magnesia and free chlorine. This
reaction upon which a process for the manufacture of chlorine may he founded is
not altogether satisfactory unless the chloride of magnesium is anhydrous. If it
contains water this re-acts upon its elements both by its oxygen and its hydrogen
to form magnesia and hydrochloric gas.
It is required then in order to extract the chlorine from chloride of magnesium
to obtain the salt in the first place in an anhydrous condition. Now its principal
sources present it in a state of solution and experience has shewn that the ordinary
methods employed for the extraction of salts from. their solutions are not applicable
to chloride of magnesium in consequence of its disposition to decompose before
becoming dehydrated. It is necessary then to find a new industrial method for
the extraction of anhydrous chloride of magnesium from its solutions. 1 will
presently describe how this problem may be solved.
To entirely expel the water of solution and obtain an anhydrous chloride I have
recourse to heat and I divide the application of it into three phases.
First phase. I simply heat the solution in a boiler analogous for example to those in
salt works, I thus concentrate the solution until it attains the temperature of 165 to
170 degrees centigrade. The foreign salts are deposited during this concentration
and are eliminated. It is unnecessary to say more about this elementary operation
which is well known to all chemists.
Second phase. When the temperature exceeds 170 degrees the solution becomes
pasty and foams a great deal. I could only continue to heat it with extreme slowness
from underneath through the bottom of the boiler. I prefer to continue the evaporation
by heating the matter from above for example by spreading it upon the sole of a
reverberatory furnace analogous to the furnaces used in drying soda salt. Then the
foaming no longer takes place. By stirring the matter frequently it is finally
obtained in the form of porous grains solid and dry in appearance but containing
still about 30 per cent. of water. I then stop the second phase. To simplify the
description I will call the product now obtained chloride in grains.
I attach very great importance to obtaining this chloride in grains. The grains are
porous and solid and the heat to which they are afterwards to be exposed does not
melt them or even soften them. In this state the material offers every facility to the
subsequent manipulation especially it remains permeable to gases, these properties it
will soon be seen are of high importance.
At the end of the preparation of chloride in grains the action of water upon the

page_text: chloride commences to become apparent, there is disengaged in the form of hydrochloric
This gas is
gas from 3 to 5 per cent. of the chlorine contained in the material,
condensed by the means in use in chemical works, then it is neutralized by
magnesia and the chlorile is sent back into the solutions to be afterwards treated.
Third phase. The chloride in grains is introduced into a closed vessel furnished with
an outlet pipe for example into a retort such as is employed in making illuminating
gas, set in a furnace so that it can be heated to a red heat. The application of the heat
effects a disengagement of steam and hydrochloric gas which I collect in a condensing
apparatus connected by pipes to the outlet from the retort, for example a series of
receivers such as are employed in chemical works. When the disengagement has
ceased and the temperature has been carried to a red heat the operation is finished.
The residue contained in the retort is a mixture of magnesia and anhydrous chloride
of magnesium containing from 40 to 50 per cent. of chlorine and suitable for
immediate treatment with air and heat for the extraction of chlorine.
The phenomena observed during this calcination are those which chemists call
phenomena of dissociation. My chloride in grains when in the retort presents a
double example of dissociation insomuch that as hydrated salt it disengages steam,
and as salt decomposable by water it disengages hydrochloric gas.
If it were enclosed in a vessel hermetically sealed, at each increase of temperature
there would be a corresponding increase of tension of steam and of hydrochloric gas;
the tension of steam hindering the continued formation of it as happens in a closed
steam boiler under pressure, and the tension of hydrochloric gas in like manner
hindering the continued decomposition of the chloride by water.
It would be quite different if the same temperatures were applied to the chloride
in grains; but in free contact with air the steam and the gas produced would diffuse
freely in the air and the equilibrium of dissociation realizable in the closed vessel
would be impossible, the disengagement by heat of the steam and gas would continue
until the complete dessication of the product which would then consist principally of
magnesia.
By operating in a closed vessel furnished with an outlet tube 1 place myself in a
position in some sort intermediate between that of the closed vessel which arrests all
dehydration and all decomposition of chloride and that of free air which arrests
nothing. The steam and the gas cannot attain in my retort tensions which arrest the
dehydration and the decomposition of the chloride because the retort allows them to
escape, consequently as the steam and the gas pass away the heat produces more which
escapo in turn. Nevertheless there is always around my material a hydrochloric
tension which retards decomposition of the chloride, the greater this tension the
more the decomposition of the salt will be minimised. When 1 operate in a retort as
above described it is found that the decomposition is reduced to the point of leaving
me still 40 to 50 per cent. of chlorine in my product.
To have then in the gaseous atmosphere around the chloride the greatest possible
tension of hydrochloric gas to minimise as much as possible the decomposition of the
chloride is the essential condition for obtaining the highest yield of anhydrous
chloride.
By further availing myself of this principle I am able to produce a chloride much
richer than that resulting from the operation which I have described and by a very
simple means. The water disengaged from the retort can be evacuated from the
condenser as it is deposited. The hydrochloric gas which is much more abundant
towards the end of the operation than at the commencement no longer finds water
with which it can condense and it retains the gaseous state. I send it back into
the retort which is furnished with this object with a connection at the front.
passage connects the condenser with the retort and upon this passage I arrange a gas
from the
propeller such as a blower of suitable construction which draws the gas
condenser and drives it into the retort. I thus establish a true circulation of
hydrochloric gas which traverses the retort and there increases the hydrochloric
tension so effectually that the product obtained by this process contains as much as
60% of chlorine, namely about 80 per cent. of anhydrous chloride.

page_text: In place of employing hydrochloric gas disengaged from the chloride I may borrow
it from any suitable source. Wherever this gas be obtained, the effects due to the
augmentation of gas tension in my retort remain the same.
It will now be seen why chloride in grains is so valuable. If the matter heated in
the retort were fusible or even softened by the heat there would no longer be porous.
grains nor would there be interstices to allow the whole of the matter to come in
intimate contact with the hydrochloric gas in circulation. This porosity and these
interstices are no less necessary afterwards when putting the oxygen of the air into
intimate contact with the matter in order to extract the chlorine.
If it be convenient for the extraction of chlorine not to operate on too rich a chloride
I can always reduce it by mixing anhydrous magnesia with the chloride in grains
before calcination.
I have mentioned the employment of a retort to convert my chloride in grains into
anhydrous chloride but I can employ any other apparatus which will fulfil the
conditions laid down both as to the application of heat, the manipulation of the solid
mass and the circulation of hydrochloric gas.
To extract the chlorine from the anhydrous chloride thus obtained it is heated to a
red heat in a suitable apparatus in which a regulated current of air circulates.
I can carry on this treatment by different means in retorts, of material suitable to
resist the action of chlorine heated in furnaces and provided with connections for the
entrance and escape of the gas. I may connect the retorts in series traversed
methodically by the gases. I can employ muffles heated externally and connected
in series so that the solid matter passes from one end to the other whilst the gases
travel in the opposite direction. I may besides have recourse to furnaces in stages
or in compartments furnislied with slabs arranged in steps heated by flues in which
furnace gases circulate. Or I may employ any other arrangement which is suitable
having regard to the three points, the heating, the movement of the solid matter,
and the circulation of the gases.
When the magnesium chloride anhydride, prepared as above described, is heated
in a current of air in order to be decomposed by the oxygen and to be freed of
its chlorine, it loses to a great extent its cohesiveness which up to the preat has
facilitated its handling.
If then the apparatus adopted for this operation necessitates the movement of
substance, it may produce rubbish and dust which will impede the circulation of
air. Under these conditions it becomes difficult to employ certain apparatus which
otherwise would be perfectly suitable.
I have succeeded in overcoming this difficulty by employing the magnesium
chloride in the form of briquettes agglomerated with the aid of magnesia anhydride
and sufficient pressure to produce adhesion. 1 place in the same mill both the
chloride of magnesium anhydride and the magnesia anhydride each substance being
in the desired proportion say 70 to 80 of the first to 30 to 20 of the second. The
mixture is then brought to a pressing apparatus which shapes it into briquettes of
cylindrical or other solid form. A great number of machines of this kind exist which
convert very different kinds of powder into a solid material. The briquettes thus
obtained preserve their solidity during and after the decomposition of the chloride
anhydride. I may bere observe that the magnesia introduced exercises no chemical
action during the decomposition, its action being simply mechanical, by the com-
pression it undergoes the magnesia anhydride employed forms a solid network in the
inidst of which the chloride anhydride is disseminated; the latter may lose its
cohesion by chemical decomposition but the magnesia employed does not undergo any
chemical modification and therefore it entirely retains the physical state given to it by
the pressure and continues to form the network or sort of skeleton in which the
residue from the decomposition of the chloride remains.
Thanks to this artifice I can employ for the application of heat to the magnesium
chloride anhydride, apparatus in which substances are more or less heaped up and
in which they are handled and undergo methodical displacements.
I will now particularly describe one of these apparatus: it consists of a kind' of

page_text: draw kiln analogous to those in use for burning lime; the briquettes are introduced
at the top and taken out at the bottom through apertures which should only remain
open during the extraction. The solid substances gradually descend in the kiln whilst
the air traverses it from bottom to the top, and escapes finally by one of several
apertures situated at the top part of the kiln.
The heating is effected as follows. The masonry of the kiln is formed above the
exit doors to the top, of three concentric shells. The interior shell constitutes the
kiln proper, the second surrounds the first leaving between the two a space of from
10 to 15 centimetres which is divided into a certain number of equal compartiments A
by vertical partitions which also serve to connect the two shells; the third shell
surrounds the second also leaving between the two a space divided by vertical
partitions into as many compartments B as there are compartments A and corre-
sponding to them. These compartments B contain bricks arranged as in a Siemens
regenerator, and constitute not regenerators but rather magazines or accumulators of
heat. They receive the flames of a furnace or of a combustible gas forced in with air
which descend through the chambers and yield their heat to the bricks then pass out
of the compartments B by means of flues crossing the third shell and then go to
common chimney.
When the heat accumulated in a compartment B is sufficient the heating is stopped
and air is introduced into B which becomes heated as it rises and then enters the
compartments A down which it descends and then goes into the kiln a little below the
exit doors by openings which form a communication between the compartments A
and the kiln itself. The air then rises amongst the briquettes communicates its heat
to them and maintains it, then after having given off its heat to the freshly introduced
briquettes it escapes. From thence it goes together with the chlorine that it carries
along with it into an apparatus where the latter is cooled washed and collected. The
compartments A and B are of equal and even number so that half of the compart-
ments B receive and accumulate heat whilst the other half give it off communicating
it to the air one compartment B accumulates heat whilst its two right and left
neighbours give it off and conversely. Suitably arranged apertures alternately
opened or closed permit as in ordinary regenerators of the alternate introduction of
flames or air.
The air may be forced into the compartments B or it can be brought there by
exhaustion produced in the kiln by means of a suitable aspirator such as a fan or
pump. The briquettes may be more or less heated before being introduced into the
kiln.
This description will suffice for it to be understood how I maintain my kiln at a
suitable temperature essentially fulfilling two conditions namely heating the air
admitted into the furnace and preventing the internal heat of the kiln from escaping
by the cooling of the envelope.
In the annexed drawing Figure 1 is a vertical section taken through the middle
of the kiln. Figure 2 is an elevation and Figure 3 is a horizontal section taken
partly on the line a, b, in Figure 1 and partly on the line c, d, in the same figure.
A compartments traversed by the heated air.
B heat accumulating compartments.
C circular pipe receiving and distributing gas from a gas generator.
1 circular pipe receiving and distributing compressed air.
E apparatus operating to direct the combustible gaseous mixture alternately into
one or other of two contiguous compartments B between which it is placed.
G pipe receiving the products of combustion from Band conducting them into a
general flue M.
Hpipe receiving air from D and directing it into a compartment B where the
air is heated on its way to the passage A.
O and P peep holes.
Q outlets.
I dampers or valves worked by the iron rods t to change the direction of the
currents.

page_text: The anhydrous chloride obtained by my present process presents in virtue of its
porosity the valuable property of being completely decomposed by air on reaching a
dull red heat and of furnishing a gaseous mixture which contains as it leaves the
apparatus as much as 30 volumes of chlorine in the 100 of gaseous mixture.
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 as my invention in the process above described for the extraction of chlorine
from chloride of magnesium, is :-
1. The treatment of chloride of magnesium with a view to its dehydration con-
sisting of evaporation by ordinary means; then in submitting it to a higher heat
whilst it is stirred or manipulated as above described so as to reduce it to a state of
uniform porous granulation, in which state it is infusible at the temperatures of tho
after operations which transform it into anhydrous chloride and ultimately into
imagnesia by the extraction of the chlorine.
2. The operations described by means of which the chloride of magnesium may
be calcined at a red heat in presence of an atmosphere containing hydrochloric gas
which reduces by its tension, and proportionally to its tension, the decomposition by
water of the chloride of magnesium, this hydrochloric gas being either produced
by the chloride itself or borrowed from any other source.
3. The extraction of the chlorine by the application of a red heat in the presence
of a regulated current of air to the mixture of chloride of magnesium and magnesia
resulting from the preceding operations, the whole substantially as above described
and without confining myself to the details of the process.
4. The extraction of chlorine from solutions of chloride of magnesium, substantially
as described.