Improvements in the Manufacture of Chlorine by Means of Magnesium Chloride.
Year: 1895

page_text: Date of Application, 18th rep., 1899
Complete Specification Left, 16th Dec., 1895-Accepted, 18th Jan., 1896
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Chlorine by Means of
Magnesium Chloride.
I, THOMAS HUGH BELL, of Middlesbrough, in the County of York, Iron
Master, (a communication to me from abroad by Théophile Schloesing, of
67 Quai d'Orsay, Paris, in the Republic of France,) do hereby declare the nature
of this invention to be as follows:-
In a former Patent No. 11821 dated 31st August 1887 Mr. Schloesing indicated
the essential condition which it is necessary to observe when it is proposed to
dehydrate, by means of heat, chloride of magnesium which has been first brought
to the condition of solid grains containing a large quantity of water, and which
I have called hereinafter chloride in grains. This consists in applying the heat to
the material in a close vessel and in the presence of an atmosphere as rich as
possible in hydrochloric acid gas, in order that this gas may prevent by its tension
the dissociation of the chloride into magnesia and hydrochloric acid.
I am now about to describe the apparatus used for the execution of the
dehydration, and the two essential conditions for its use.
The apparatus is a torrefier composed of a fixed horizontal cylinder in cast iron
closed by covers at the two extremities and traversed by a steel shaft which carries
spiral blades of the same metal having a very long pitch, and which is made to
rotate slowly. The cylinder is heated from outside. The chloride in grains is
introduced at one end, either continuously or at intervals, the blades lift it up and
carry it forward, so that it travels the whole length of the cylinder to orifices
placed at the opposite extremity, by which the chloride in grains is delivered into
a suitable receptacle. During this movement the chloride in grains, in consequence
of the action of heat, disengages water and finds itself in contact with the hydro-
chloric acid circulating in the cylinder as hereinafter described.
.
To utilize the heat more completely and to render more methodical the circula-
tion of the solid and gaseous substances, I may superpose two or even three
torrefiers, so that their axes are in the same vertical plane. The chloride in grains
is introduced into the first or upper cylinder, passes into the second, traverses it in
the opposite direction, and passing into the third, traverses it, and finally falls
in the form of dehydrated chloride into a suitable receptacle. On the other hand,
the gaseous hydrochloric acid introduced into the third cylinder, passes into the
second and thence into the first, by the same orifices which have permitted the
passage of the chloride in grains. The hydrochloric acid gas used in this process
may be furnished from any source, but I commonly use the gas produced during
the torrefaction by the partial decomposition of the chloride in grains itself. Gas
produced in this fashion is necessarily mixed with watery vapour expelled from the
chloride in grains. If one has recourse to a cooler to separate this water and to
obtain the hydrochloric acid which is to circulate in the torrefier free from watery
vapour the condensed water begins by saturating itself with the gas, and it is only
after the saturation that an excess of unabsorbed gas is at my disposal to be put
into continuous circulation by means of a propeller, such as a ventilator, for
example, between the cooler and the torrefier. There results a considerable
elimination of chlorine in the state of liquid hydrochloric acid, and the consequent
decomposition of an equivalent quantity of chloride in grains and a proportionate
reduction of the ultimate yield of free chlorine. This hydrochloric acid is not
lost as it is subsequently neutralised with any surplus magnesia resulting from

page_text: preceding operations. It is however possible largely to diminish the quantity thus
eliminated by separating the water from the hydrochloric acid gas by means of
some body which combines with the former, such, for example, as sulphuric acid.
This separation may take place either before or after the condensation of the
water in a cooler. Chemists are well acquainted with such operations in the
laboratory: I now describe how it can be done on an industrial scale.
(1.) Separation of watery vapour not yet condensed. Sulphuric acid at the
temperature and density at which it is drawn from the lead basins used for its
concentration is introduced into a tower filled with materials which are not attacked
by acid. The mixture of watery vapour and hydrochloric acid gas from the
torrefier is introduced into the same tower, the water is absorbed and the gas
passes out.
The quantity of sulphuric acid employed should be such that the cold
acid after it has absorbed the water falls to about 52 degrees B. This acid retains
a small quantity of hydrochloric acid, which it will lose if it is heated and its
temperature maintained between 135 and 145 degrees Cent. This is done in close
vessels, the hydrochloric acid gas is collected, and the sulphuric acid runs into
the concentrating pans in order to be made ready to use again.
(2.) Extraction of hydrochloric acid gas from its solution in water.
If the vapours have already been condensed the hydrochloric acid gas is contained
in the water that is obtained. I have now to extract the hydrochloric acid from
the solution. This is done by replacing the tower by a vessel into which are
introduced the two acids (sulphuric and hydrochloric) in proper proportions. The
gas escapes by a tube from the vessel while the sulphuric acid diluted so as to
stand when cool at 52 degrees B. runs through a series of heated vessels, where it
is maintained for a certain time at a temperature between 135 and 145 degrees C.
to secure the complete elimination of the hydrochloric acid gas which it has
retained. By these means there is no difficulty in maintaining the proper
circulation of hydrochloric acid gas in the torrefier without causing any consider-
able decomposition of the chloride.
But this is not the only condition which we have to fulfil in order to render truly
practical the use of the torrefier in dehydrating the chloride of magnesium.
Practice has shown that to obtain a complete dehydration it is necessary to heat
the material nearly to dull redness, even when the operation is carried on in an
atmosphere composed entirely of hydrochloric acid gas. But such a temperature
causes the hydrochloric acid to attack the interior of the torrefier, and necessitates
frequent repairs. To avoid this it is necessary to operate at a lower temperature,
even though one fails to extract the whole of the water from the chloride. It
retains from 4 to 7 per cent. of water. This water subsequently causes a considerable
quantity of the chlorine given off when the anhydrous chloride is heated in a
current of air to be evolved in the form of hydrochloric acid gas instead of free
chlorine. I dehydrate the chloride practically entirely before submitting it to the
action of the air by adding to the torrefier a vessel heated to dull redness from
without which receives the chloride from the torrefier. The dehydrated chloride
falls on to a grate separated from the bottom of the vessel by a free space and
forms a material through which gases pass quite easily. The hydrochloric acid gas
before entering the torrefier is first introduced under this grate. It passes through
the dehydrated chloride. There is no mechanism to be attacked and the vessel
containing the dehydrated chloride as well as this substance itself can be heated
with impunity to the temperature necessary for complete dehydration. Accordingly
this takes place and after having been completed by the hydrochloric acid gas, the
latter passes into the torrefier.
Moreover, in the processes which have gone before there is a certain loss of
chlorine, and a portion of the chloride of magnesia is converted into magnesia. In
the process I am now describing this magnesia is reconverted into chloride and
I obtain a substance which is practically free from both water and magnesia,
and from which the whole of the chlorine can be expelled in the form of the free
gas by heating in a current of air.

page_text: Thus the operation of dehydration is divided into two phases, the first accomplished
in the torrefier at a temperature insufficient to cause the mechanism to be attacked
but also insufficient for complete dehydration; the second executed in another
vessel where the absence of attackable material permits the use of a sufficient
temperature to complete the dehydration. It is not necessary that the vessel
destined for the second phase should be annexed to the torrefier so as to make an
integral part of it. It may be an independent vessel, say a retort, a muffle of
refractory material or of iron or any similar arrangement. For example, it may
be the vessel in which the extraction of the chlorine by means of air ultimately
takes place. The essential point is to be able to heat to dull redness in an
atmosphere of hydrochloric acid gas the dehydrated chloride as it comes from the
torrefier.
I will now describe the apparatus to be used for extracting the gaseous chlorine
from the anhydrous chlorine of magnesium. It is a muffle furnace of masonry or
brickwork. The hearth formed of fire brick is covered with an arched roof carried
by four walls which form ends and the sides of the muffle. At one side are two
working doors for spreading out the chloride and withdrawing the magnesia
residue. In the end wall, there are two vertical pipes terminating outwardly at
one end and at the other in the muffle; they are used for introducing the anhydrous
chloride into the muffle; they are placed so that each feeds half of the surface
on which the chloride is spread. The roof, ends and floor of the muffle are
enveloped by the flames of a furnace placed at one end. The bed of chloride
lies on a grid made of strong bars of refractory earth placed in juxtaposition on the
floor and across the furnace from side to side, so that the interior of the muffle is
divided by the grid into two spaces which are freely traversed by the gases. The
bottom of the doors is flush with the surface of the grid. Apertures conveniently
placed in the side walls behind or in front permit the grid and the open space
below it to be cleaned should they become choked. The chlorine being heavier
than the oxygen by which it is displaced during the passage of air this should
enter by the upper part of the muffle, while the exit should be from the free space
below the grid. The air should be first dried by passage through a sulphuric acid
tower.
The same form of muffle and grid may be used for the dehydration and
chlorination of the substances coming from the torrefactors. Whatever the shape
of the vessel adopted for this operation, the vessel can always be placed above the
muffle which is used to decompose the chloride and can be heated partially or
entirely by the waste heat from the muffle. Thus the two operations, the one the
completion of the dehydration and the chlorination by hydrochloric acid gas, the
other the decomposition of the anhydrous chloride by air take place simultaneously
in an apparatus arranged in two stages, so that as soon as the decomposition of
the anhydrous chloride is complete and the residual magnesia has been withdrawn,
the anhydrous chloride which has been prepared in the upper apparatus, and is
already at a dull red heat, can be brought down through a passage provided between
the upper and lower stages. The passage is opened and closed at the proper times
and delivers the chloride to the lower stage where it is exposed to the action
of the air. This arrangement economises manual labour and accelerates the
operations.
Or the two operations may be performed in the same muffle. In that case the
dehydrated chloride is introduced into the muffle, heated to dull redness and
exposed to a current of dry hydrochloric acid gas, by which means the magnesia
contained in it is converted into chloride of magnesia, and the remnant of the water
expelled. A current of air is then caused to pass through the heated mass, the
chloride is decomposed, the chlorine is given off and magnesia remains in the
muffle.

page_text: COMPLETE SPECIFICATION.
Improvements in the Manufacture of Chlorine by Means of
Magnesium Chloride.
I, THOMAS HUGH BELL, of Middlesbrough, in the County of York, Iron
Master, do hereby declare the nature of this invention (which has been communicated
to me from abroad by Théophile Schloesing, of 67 Quai d'Orsay, Paris, in the
Republic of France,) and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement:-
In a former Patent No. 11821 dated 31st August 1887 Mr. Schloesing indicated
the essential condition which it is necessary to observe when it is proposed to
dehydrate, by means of heat, chloride of magnesium which has been first brought
to the condition of solid grains containing a large quantity of water, and which I
have called hereinafter chloride in grains. This consists in applying the heat to
the material in a close vessel and in the presence of an atmosphere as rich as
possible in hydrochloric acid gas, in order that this gas may prevent by its tension
the dissociation of the chloride into magnesia and hydrochloric acid.
I am now about to describe the apparatus used for the execution of the
dehydration, and the two essential conditions for its use.
The apparatus is a torrefier--a set of torrefiers is represented by Figures 1 and 2
of the annexed drawings.
Figure 1 is a section and Figure 2 is a front elevation.
The torrefier in its simplest form is composed of a fixed horizontal cylinder a in
cast iron closed by covers at the two extremities and traversed by a steel shaft
which carries spiral blades bb of the same metal having a very long pitch and
which is made to rotate slowly. The cylinder is heated from outside by a gas
furnace as the drawing indicates or by other means. The chloride in grains is
introduced at one end, either continuously or at intervals, the blades lift it up and
carry it forward, so that it travels the whole length of the cylinder to orifices
placed at the opposite extremity, by which the chloride in grains is delivered into
a suitable receptacle. During this movement the chloride in grains, in consequence
of the action of heat, disengages water and finds itself in contact with the
hydrochloric acid circulating in the cylinder as hereinafter described.
To utilize the heat more completely and to render more methodical the circulation
of the solid and gaseous substances, I may as the drawing shews superpose two or
even three torrefiers, so that their axes are in the same vertical plane. The chloride
in grains is introduced into the first or upper cylinder at a passes into the second,
traverses it in the opposite direction, and if a third cylinder be provided, passes
into the third, traverses it, and finally in any case reaches the outlet a² and falls
in the form of dehydrated chloride into a suitable receptacle. On the other hand,
the gaseous hydrochloric acid introduced into the last cylinder of the set, say if
three be provided, into the third cylinder, passes into the second and thence into
the first, by the same orifices which have permitted the passage of the chloride in
grains. The hydrochloric acid gas used in this process may be furnished from any
source but I commonly use the gas produced during the torrefaction by the partial
decomposition of the chloride in grains itself. Gas produced in this fashion is
necessarily mixed with watery vapour expelled from the chloride in grains. One
I may have recourse to a cooler to separate this water and to obtain the hydrochloric
acid which is to circulate in the torrefier free from watery vapour.
In the drawings the cooler is represented by a range of carboys marked c; they
are represented also in plan in Figure 3.
When the cooler is in use the condensed water begins by saturating itself with
the gas, and it is only after the saturation that an excess of unabsorbed gas is at my
disposal to be put into continuous circulation by means of a propeller, such as a

page_text: ventilator at d for example, between the cooler and the torrefier. There results a
considerable elimination of chlorine in the state of liquid hydrochloric acid, and the
consequent decomposition of an equivalent quantity of chloride in grains and a
proportionate reduction of the ultimate yield of free chlorine. This hydrochloric
acid is not lost as it is subsequently neutralised with any surplus magnesia resulting
from preceding operations. It is however possible largely to diminish the quantity
thus eliminated by separating the water from the hydrochloric acid gas by means of
some body which combines with the former, such, for example, as sulphuric acid.
This separation may take place either before or after the condensation of the water
in a cooler. Chemists are well acquainted with such operations in the laboratory.
I now describe how it can be done on an industrial scale.
(1.) Separation of watery vapour not yet condensed, sulphuric acid at the
temperature and density at which it is drawn from the lead basins used for its
concentration is introduced into a tower such as is represented in Figure 4 filled
with materials which are not attacked by acid. The mixture of watery vapour
and hydrochloric acid gas from the torrefier is introduced into the same tower, the
water is absorbed and the gas passes out. The quantity of sulphuric acid employed
should be such that the cold acid after it has absorbed the water falls to about
52 degrees B. This acid retains a small quantity of hydrochloric acid which it will
lose if it is heated and its temperature maintained between 135 and 145 degrees Cent.
This is done in close vessels, the hydrochloric acid gas is collected, and the
sulphuric acid runs into the concentrating pans in order to be made ready to
use again.
(2.) Extraction of hydrochloric acid gas from its solution in water.
If the vapours have already been condensed the hydrochloric acid gas is contained
in the water that is obtained. I have now to extract the hydrochloric acid from
the solution. This is done by replacing or supplementing the tower by a vessel
into which are introduced the two acids (sulphuric and hydrochloric) in proper
proportions. The gas escapes by a tube from the vessel while the sulphuric acid
diluted so as to stand when cool at 52 degrees B. runs through a series of heated
vessels, where it is maintained for a certain time at a temperature between 135 and
145 degrees C. to secure the complete elimination of the hydrochloric acid gas
which it has retained. By these means there is no difficulty in maintaining the
proper circulation of hydrochloric acid gas in the torrefier without causing any
considerable decomposition of the chloride.
But this is not the only condition which we have to fulfil in order to render
truly practical the use of the torrefier in dehydrating the chloride of magnesium.
Practice has shewn that to obtain a complete dehydration it is necessary to heat
the material nearly to dull redness, even when the operation is carried on in an
atmosphere composed entirely of hydrochloric acid gas. But such a temperature
causes the hydrochloric acid to attack the interior of the torrefier, and necessitates
frequent repairs. To avoid this it is necessary to operate at a lower temperature,
even though one fails to extract the whole of the water from the chloride. It
retains from 4 to 7 per cent. of water. This water subsequently causes a considerable
quantity of the chlorine given off when the anhydrous chloride is heated in a current
of air to be evolved in the form of hydrochloric acid gas instead of free chlorine.
I dehydrate the chloride practically entirely before submitting it to the action of
the air by adding to the torrefier a vessel heated to dull redness from without which
receives the chloride from the torrefier. The dehydrated chloride falls on to a
grate separated from the bottom of the vessel by a free space and forms a material
through which gases pass quite easily. The hydrochloric acid gas before entering
the torrefier is first introduced under this grate. It passes through the dehydrated
chloride. There is no mechanism to be attacked and the vessel containing the
dehydrated chloride as well as this substance itself can be heated with impunity to
the temperature necessary for complete dehydration. Accordingly this takes place
and after having been completed by the hydrochloric acid gas, the latter passes
into the torrefier.

page_text: In
Moreover, in the processes which have gone before, there is a certain loss of
chlorine, and a portion of the chloride of magnesia is converted into magnesia.
the process I am now describing this magnesia is reconverted into chloride and
I obtain a substance which is practically free from both water and magnesia, and
from which the whole of the chlorine can be expelled in the form of the free gas,
by heating in a current of air.
Thus the operation of dehydration is divided into two phases, the first
accomplished in the torrefier at a temperature insufficient to cause the mechanism
to be attacked but also insufficient for complete dehydration; the second executed
in another vessel where the absence of attackable material permits the use of a
sufficient temperature to complete the dehydration. It is not necessary that the
vessel destined for the second phase should be annexed to the torrefier so as to
make an integral part of it. It may be an independent vessel, say a retort, a
muffle of refractory material or of iron or any similar arrangement. For example
apparatus such as shown by Figure 4 may be employed. e is a muffle chamber in
which the chloride in grains passes after it leaves the torrefier cylinder at a².
The chamber e is heated by flues e¹ and e² passing under and over it. The material
rests in a layer upon fire brick bars e³ and is heated to a dull red heat. f is a
sulphuric acid tower, it is filled with coke and the acid trickles over the coke, it
being supplied continuously at the top of the tower and drawn off at the bottom to
be reconcentrated.
Hydrochloric acid gas is admitted to the tower at f¹ and passes out in a
perfectly dry state at f, the dry gas enters the muffle chamber, passes through
the layer of chloride in grains and is then passed into the torrifier cylinders.
When the circulation is arranged in this manner the fan d shown in Figure 1 will
not be needed, the expansion of the gas in the muffle chamber being sufficient to
maintain the circulation.
To generate hydrochloric gas I employ apparatus such as is shown by the
Figures 5, 6, 7 and 8.
Figure 5, is an elevation, Figure 6 is a plan, Figures 7 and 8 are sections taken
respectively on the lines 7, 7 and 8, 8 in Figure 6.
gis a leaden box set over a flue, together with a series of pans hhhh, they are
heated by a fire. iii also are a series of evaporating pans with heating flues
beneath. To the box g liquid hydrochloric acid is constantly supplied, and there
the hydrochloric acid meets strong sulphuric acid which flows in from the adjacent
evaporating pan i. The hydrochloric acid enters the box 9 by the pipe g₁ and the
gas passes off by the pipe g2 the liquid runs out from the box g, and in succession
passes through the series of vessels hh and ii. The concentrated sulphuric acid
from the last of the pans i returns to the box g. The pipe 92 may lead the
hydrochloric acid gas to a sulphuric acid tower as shown in Figure 4.
The muffle or vessel in which the chloride in grains is regenerated may be the
vessel in which the extraction of the chlorine by means of air ultimately takes
place. The essential point is to be able to heat to dull redness in an atmosphere
of hydrochloric acid gas the dehydrated chloride as it comes from the torrefier.
I will now describe the apparatus to be used for extracting the gaseous chlorine
from the anhydrous chloride of magnesium. It is shown by the Figures 9. 10. 11. 12
and 13. Figure 9 is an elevation. Figure 10 is a cross section. Figure 11 is a
longitudinal section. Figures 12 and 13 are sections taken on the lines 12. 12
and 13. 13 respectively in Figure 10. It is a muffle furnace of masoury or brick-
work. The hearth formed of fire brick is covered with an arched roof carried
by four walls which form ends and the sides of the muffle. At one side are two
working doors for spreading out the chloride and withdrawing the magnesia residue.
In the end wall, there are two vertical pipes terminating outwardly at one end and
at the other in the muffle, they are used for introducing the anhydrous chloride
into the muffle, they are placed so that each feeds half of the surface on which
the chloride is spread. The roof, ends, and floor of the muffle are enveloped by
the flames of a furnace placed at one end. The bed of chloride lies on a grid

page_text: made of strong bars of refractory earth placed in juxtaposition on the floor, and
across the furnace from side to side, so that the interior of the muffle is divided by
the grid into two spaces, which are freely traversed by the gases. The bottom
of the doors is flush with the surface of the grid. Apertures conveniently placed
in the side walls behind or in front permit the grid and the open space below it to
be cleaned should they become choked. The chlorine being heavier than the
oxygen, by which it is displaced, during the passage of air this should enter by
the upper part of the muffle, while the exit should be from the free space below
the grid. The air should be first dried by passage through a sulphuric acid
tower.
The same form of muffle and grid may be used for the dehydration and
chlorination of the substances coming from the torrefactors. Whatever the shape
of the vessel adopted for this operation, the vessel can always be placed above the
muffle which is used to decompose the chloride and can be heated partially or
entirely by the waste heat from the muffle. Thus the two operations, the one the
completion of the dehydration, and the chlorination by hydrochloric acid gas, the
other the decomposition of the anhydrous chloride by air take place simultaneously
in an apparatus arranged in two stages, so that as soon as the decomposition of the
anhydrous chloride is complete, and the residual magnesia has been withdrawn,
the anhydrous chloride which has been prepared in the upper apparatus, and is
already at a dull red heat, can be brought down through a passage provided
between the upper and lower stages. The passage is opened and closed at the
proper times, and delivers the chloride to the lower stage, where it is exposed to
the action of the air. This arrangement economises manual labour and accelerates
the operations.
Or the two operations may be performed in the same muffle. In that case the
dehydrated chloride is introduced into the muffle, heated to dull redness, and
exposed to a current of dry hydrochloric acid gas, by which means the magnesia
contained in it, is converted into chloride of magnesia, and the remnant of the
water expelled. A current of air is then caused to pass through the heated mass,
the chloride is decomposed the chlorine is given off, and magnesia remains in the
muffle.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what I
claim is:
1. The torrification or partial dehydration of the chloride in grains in a retort
or vessel heated from the exterior and provided with mechanism which keeps the
grains in constant movement, provision being made for the withdrawal of aqueous
vapeur from such retort or vessel and the supply thereto of hydrochloric acid gas,
dried by the means herein described.
2. The regeneration of the portion of the chloride of magnesium decomposed
into hydrochloric acid and magnesia during the operations of granulation and
torrification by means of a gaseous current consisting of this same hydrochloric
acid in a free state and separated from its aqueous solution as herein described or
dry hydrochloric gas from some other suitable source reacting in a closed vessel
at a dull red heat upon the chloride coming out of the torrifier and exposed as
above stated upon an open grid, the spontaneous circulation of the hydrochloric
gas being maintained by its difference of temperature and of density in the two
portions of its travel.
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3. The regeneration of the chloride in grains partially decomposed in the process
of torrification by heating the grains to a dull red heat in a muffle or chamber
divided into two parts by a grid, the grains lying in a layer on this grid and dry
hydrochloric acid gas being caused to pass through from one part of the chamber
to the other.
4. The treatment of chloride in grains in a muffle or chamber divided into two
parts by a grid on which the grains lie in a layer, by first passing through the

page_text: layer hydrochloric acid gas dried by the means herein described to regenerate the
chloride after torrification, and afterwards atmospheric air in order that the oxygen
may displace the chlorine.
5. The treatment of chloride in grains in the manner described in a furnace such
as is described herein and shown by the Figures 9, 10, 11, 12 and 13 of the
drawings.
6. The combination of apparatus for treating chloride in grains consisting of a
muffle furnace in which the chloride is regenerated after torrification and a second
furnace at a lower level into which the charge from the muffle is let down in a
heated state to be decomposed by the passage of atmospheric air amongst it.
Dated this 11th day of December 1895.
T. HUGH BELL.