Method and Apparatus for Treating Solids with Gases, as in Decomposing Certain Chlorides.
Year: 1898

page_text: Method and Apparatus for Treating Solids with Gases, as in
Decomposing Certain Chlorides.
PAUL NAEF, Ph.D., Chemical Engineer, No. 15, 3rd Avenue, New Brighton,
S.T., New York, U.S.A., do hereby declare the nature of this invention to be as
follows:-
:-
This invention refers to a method of producing chlorine from magnesium
chloride or a mixture of the same with magnesium oxide by the action of atmos-
pheric oxygen at elevated temperature MgCl + 0 = MgO + Cl. The method is
also applicable to the manufacture of chlorine from other chlorides, which can
be decomposed with air at elevated temperature such as nickel chloride. The
method and apparatus can further be applied for carrying out other reactions,
in which gases act on solid materials at elevated temperatures.
Objects of the invention are to supply the heat necessary for the chemical
reaction by heating the air or gas, which effects the decomposition of the solid
materials without diluting the resulting gas: to effect as complete a decomposition
of the magnesium chloride as possible without using a large excess of air, so
as to produce a magnesium oxide of sufficient purity for commercial purposes, and
to make the production of chlorine automatic and continuous.
The chemical reaction is carried out in a series of furnaces, preferably one
arranged above the other, which bring the chloride into most intimate contact
with the air.
The mixture of magnesium chloride and oxide is passed through the upper
and afterwards through the lower furnace, which it leaves as magnesium oxide..
The air passes first through the lower and afterwards through the upper fur-
nace, and the concentrated chlorine gas produced by the action of air on the
chloride leaves said upper furnace.
The air is heated in heaters before it enters the lowest furnace. In passing
through the furnace it is brought into intimate contact with material from which
some of the chlorine has already been removed in the upper furnaces. Magnesium
oxide leaves this furnace at the lower end. At the higher end leaves a dilute
chlorine gas; which is again heated in heaters before it enters the upper furnace
in which it is converted into concentrated chlorine gas.
The same operation can be repeated by passing the gas through superheaters
before it enters a third furnace. In this way it is possible to supply sufficient
heat for the reaction with a small volume of gas and as a result a chlorine gas
sufficiently strong for making bleaching powder is obtained.
In the accompanying drawing Figure 1, shows a vertical view of the apparatus
consisting of a system of two furnaces. The revolving furnaces A and B are
held in position by V rollers 2, and are further supported by rollers 1.
Each furnace is rotated by means of a worm 3, which acts on a toothed ring 4
which encircles the furnace. The interior of the cylinder has a fire-proof lining 5*,

page_text: and devices for lifting and showering the solid material so as to bring the same
into most intimate contact with the gas. At the higher end each furnace is
closed by a stationary plate 5 which closes tightly against the end plate 6 which
revolves with the furnace. The plate 5 carries an outlet pipe for the chlorine
gas and an inlet pipe for charging the solid material.
The lower end of the furnace (A and B) is closed by the end plates 7, which
revolves with the furnace. This plate has openings 8 through which the solid
material is discharged. The openings 8 are covered by a tightly fitting stationary
ring 9, into which the material empties at the bottom.
The
The mixture of magnesia and magnesium chloride, which is to be worked up
into chlorine is discharged by any convenient means into hopper 10.
screw 11" charges the mixture from the hopper continuously to the furnace A.
After the material has passed through the furnace A, it empties itself into
hopper 11, and through the pipe into furnace B. Hopper 11, is arranged so as
to be able to stop one of the furnaces when the other one is in operation. In
such cases the damper 13 is closed, which is otherwise left open.
The material which passes from furnace A to B contains a smaller percentage
of chlorine and more magnesium oxide than the original mixture. In the lower
furnace it looses the rest of the chlorine and the magnesium oxide thus produced
is passed from the lower furnace into hopper 14.
The air necessary for the chemical reaction is heated in the hot-air stoves C
and D.
These heaters are alternately used for heating air in a similar way as the hot-
air stoves of blast furnaces, one being heated by combustion of gas while air is
passed through the other heated stove.
If for instance stove D is being heated by gas, and air is passed through stove C,
we have the following at that period.
A mixture of gas and air enters into the heater 1 at 15 and is burned at the
entrance. The hot products of combustion ascend through the fire proof material,
with which the heater is filled, and give off their heat and escape through the
chimney 16. Simultaneously air enters from the blower 17, into the heater C,
through the pipe 18. The air descends and is heated during the passage through
the filling material. The heated air leaves through pipe 19, and enters the lower
furnace B. After stove C is cooled down the conditions are reversed, air being
passed through C while D is heated up again.
In passing through the lower furnace, the hot air acts on the material, which
has already been partly decomposed in the upper furnace A, and effects a more
complete decomposition of the chloride than is obtained by other methods. Dilute
chlorine gas of much lower temperature leaves the lower furnace B, through
pipe 20, and enters alternately one of the heaters E and F. These heaters work
in the same way as C and D and are so constructed, that the dilute chlorine gas
cannot come in contact with any metal parts. The heated gas leaves alternately
heaters E and F at the bottom, and enters the upper furnace A through pipe 21.
In this furnace the heated gas is brought into contact with a material
containing more magnesium chloride and concentrated chlorine gas leaves
the furnace through pipe 22. For the purpose of drawing the gas
through the apparatus and for maintaining a small vacuum in the same, the
exhauster 23 is connected to the pipe leading from the upper furnace A. The
chlorine gas passes through suitable coolers, and washers for removing hydro-
chloric acid, afterwards through an absorbing apparatus to convert the same into
bleaching powder. As these parts can be of any suitable construction they are
not shown in the drawings.
The whole apparatus works automatically and continuously. It furnishes a
continuous stream of chlorine gas of even strength and all the hand labour, which
is necessary consists in changing the valves of the superheaters.
Instead of the superheaters shown, continuous superheaters can be used, in
which the air or gas passes continuously through heated channels. As the gas

page_text: passes through the plant without pres-ure the use of such continuous heaters
has no difficulty.
As it is
The mixture of magnesium oxide, and magnesium chloride, which is charged
into the upper furnace, can be prepared in any convenient manner.
gradually heated in the upper furnace by intimate contact with the hot gases
any moisture which it contains is driven off at low temperature with formation
of a small amount of hydrochloric acid (MgCl2 + H₂O
MgO + HCl.
=
In cases where hydrochloric acid is of value, magnesium chloride can be charged
into the upper furnace. It is then first converted into a mixture of chloride and
oxide in the apparatus itself. At first, until all the moisture is removed a great
deal of hydrochloric acid is driven off, later on chlorine gas is evolved.
The process can be used for producing chlorine and magnesium oxide from
magnesium chloride, from any source, and it can also be used in connection with
my process for the manufacture of chlorine from ammonium chloride, for which
I have applied for Letters Patent 5293/8, date under International Convention
7 Aug. 97.
The same method and apparatus can be applied for carrying out other chemical
operations in which it is necessary to apply heat by means of a limited volume
of air or gas so as not to dilute the gases produced by the reaction. As an example
can be mentioned the roasting of ores containing zinc or copper. Such ores can,
by ordinary methods only be roasted by external heat, and if the sulphurous acid
gas is to be utilized for the manufacture of sulphuric acid, muffle furnaces are
employed. Such furnaces have a small capacity and require much fuel, labour
and expense.
By applying my system of supplying all or part of the heat, by heating first
the air and afterwards the weak sulphurous acid gas once or twice successively
several times, this operation of roasting can be very much cheapened.
If magnesium chloride or a mixture of chloride and oxide is treated as described
hydrochloric acid and the chlorine gas leaves the apparatus mixed.
For the purpose of reducing the amount of hydrochloric acid produced and
obtaining the same in the pure state, it is often better to deprive the chloride or
the mixture of chloride with oxide, of most of the moisture at as a low temperature
as possible and without the presence of oxygen before it is treated for the pro-
duction of chlorine. For this purpose a revolving furnace can be used, which
is preferably arranged above the furnaces described. The material is passed
through this furnace and is brought into intimate contact with the hot gas con-
taining little or no oxygen.
Such gas can be obtained by heating the gases which leave the bleaching
powder apparatus after the absorption of chlorine. The moisture is thus driven off at
low temperature and as no oxygen is present no chlorine is formed and pure
hydrochloric acid can be condensed from the gases leaving this furnace. The
dried material passes into the lower furnaces where it is treated with air and
where mostly chlorine is formed.
For the purpose of preventing waste of heat by discharging the oxide of
magnesium from the lowest furnace in a hot state, the heated air passes through
a pipe, which is shown in the dotted lines in the drawings, into the furnace some
distance from the end plate.
Cold air enters through the pipe 24 in the end plate, and cools the oxide before
it leaves the furnace.
It is obvious that as the case may require the construction of the apparatus
can be varied to effect the best results in the process without departing from the
spirit of my invention.
Dated New York 10th August 1898

page_text: Method and Apparatus for Treating Solids with Gases, as in
Decomposing Certain Chlorides.
I, PAUL NAEF, Ph.D., Chemical Engineer, formerly of No. 15, 3rd Avenue,
New Brighton, S.T., New York, but now of Great Crest Avenue, near 165th
Street, New York City, United States of America, do hereby declare the nature of
this invention and in what manner the same is to be performed, to be particu-
larly described and ascertained in and by the following statement : —
This invention relates to a method of and apparatus for carrying out operations
or reactions in which solid materials are treated with gases at elevated tempera-
tures.
Such operations are usually carried out by supplying the heat through the sides
of a furnace in such apparatus as retorts, muffle-furnaces, etc. These apparatus
have the disadvantage that the material near the sides of the furnace is heated
to a greater degree than that in the interior thereof. The transmission of the
heat is slow and the capacity small, while the first cost is usually high and so
also is that for repairs. If the treatment of solids and gases is carried out by
external heat there is further the danger of leakage of gas through the sides of
the apparatus, which is especially great when the heat in transmitted through fire-
brick.
If instead of supplying external heat through the sides of the apparatus the
gas used in the re-action is heated, the heat so supplied is in most cases not
sufficient to carry on the operation.
The present invention is designed to obviate these disadvantages.
The chief objects of my invention are to supply the heat necessary for effecting
the chemical re-action by heating the gaseous fluid with which the material is to
be treated; to supply sufficient heat without using a large excess of gas and
therefore without dilution of the gaseous products of the reaction to a disadvan-
tageous extent; to enable as complete a decomposition of the material and the
gas as desired to be attained; and to facilitate the carrying out of such operations
on a large scale and in a continuous manner, with economy of heat.
My invention consists in heating the gas, causing the same to act on the
material until its temperature is so reduced that the reaction progresses slowly;
re-heating the dilute gaseous products thus obtained; and again causing the same
to act on the material, whereby a further enrichment of the gaseous products of
the re-action takes place. By repeating the operations of heating the gas and
bringing it into intimate contact with the material it is possible to replace the
gas originally used, or its constituents which enter into the re-action, entirely
by the gaseous product of the re-action or reactions. The number of repetitions
depends on the nature of the reaction, the amount of heat absorbed thereby, and
the degree of completeness of the re-action to which it is desired to attain.
The chemical re-action or re-actions are carried out in a series of furnaces,
preferably one arranged above the other, the material to be treated. and the gas
or re-agent being passed through the said series of furnaces, preferably in opposite
directions, whereby they are brought into intimate contact.
Suitable heaters are provided for heating the gas before it enters the lowest
furnace and for heating the gaseous products on their passage from each furnace
to the next furnace of the series.
As the gas and material are brought into prolonged and most intimate contact
and the heat is directly applied to the material by means of the hot gas, it is
possible to carry out reactions with great ease and perfection on a large scale

page_text: which with ordinary methods and apparatus can hardly be employed commercially.
Moreover when the material and the gas are passed through the apparatus in
opposite directions, the gas, after the final re-heating, will be caused to act upon
fresh material, and the final gaseous product will therefore be delivered at a
comparatively low temperature.
The method is of special advantage in cases where the gaseous product loses its
value if it is obtained mixed with an excess of the gas or vapour used for the
reaction, or if it contains gases of combustion. My method requires the employ-
ment of but a very small excess of gas and it is therefore particularly applicable
to the production of chlorine from magnesium chloride, or from a mixture of
the same with magnesium oxide, by the action of atmospheric oxygen at high
temperatures. Thus MgCl, +0 MgO + Cl₂.
-
=
The decomposition of the chloride is practically complete, the magnesium oxide
produced containing only a small amount of magnesium chloride. The chlorine
gas obtained also, is not diluted with the excess of air which is necessary to supply
the requisite heat, if a nearly complete decomposition of the chloride is desired,
with other methods; and which excess of air renders the gas unsuitable for the
manufacture of bleaching powder of good quality.
My invention is also applicable to the production of chlorine from other
chlorides, such as nickel chloride, which are decomposed under the action of
heated air. The method can also be used in connection with my process for the
manufacture of chlorine from ammonium chloride, for which I have obtained
Letters Patent No. 5293 of 1898, under date of the 7th day of August 1897.
My invention is also applicable to the roasting of ores containing zinc or copper.
Such ores can, by ordinary methods, only be roasted by external heat, and if
the sulphurous gases given off are to be utilized for the manufacture of sulphuric
acid, muffle furnaces are employed. Such furnaces have a small capacity and
require much fuel and labour, and are otherwise expensive. By my improved
method of supplying all or part of the heat by first heating the air and afterwards
heating the weak sulphurous acid gas one or more times successively, this opera-
tion of roasting can be rendered much more economical.
The method is also of great advantage for carrying out reactions which require
a constant temperature such as the oxydation of sulphurous acid to sulphuric
anhydride by catalytic actions. As all the heat is supplied by the hot gas, which
is brought into intimate contact with the material, overheating in parts of the
apparatus is avoided. And as the gas is always heated again to the temperature
most suitable for the re-action, action takes place in the whole apparatus and a
large capacity and high efficiency is thus obtained.
As further applications of the method may be mentioned the destructive dis-
tillation of fuel and the production of water gas by the action of steam on fuel
at high temperatures.
In order that my invention may be clearly understood and readily carried into
effect I will now proceed to describe more fully one application of the same, viz:
the production of chlorine from magnesium chloride, reference being had to the
drawing filed with my Provisional Specification, which is a part sectional elevation
of an apparatus constructed according to my invention consisting of a series of
two furnaces.
A and B are revolving furnaces held in position by V-shaped rollers 2, and
further supported by rollers 1.
Each furnace is adapted to be rotated by means of a worm 3, acting on a toothed
ring 4 which encircles the furnace. The interior of the cylinder has a fire-proof
lining 5, and devices for lifting and showering the solid material so as to bring
the same into intimate contact with the gas. Each furnace is closed at its higher
end by a stationary plate 5 fitting tightly against the end plate 6, which latter
revolves with the furnace. The plate 5 carries an outlet pipe for the gas and
an inlet pipe for charging the solid material. The lower end of each furnace
is closed by an end plate 7, which revolves with the furnace. This plate has

page_text: openings 8 through which the solid material is discharged. These openings 8
are covered by a tightly fitting stationary ring 9, into which the material empties.
The material to be treated, which in this case is a mixture of magnesium oxide
and magnesium chloride for the production of chlorine, is fed by any convenient
means into a hopper 10, and the screw 11" delivers it from the hopper continuously
to the furnace A.
After the material has passed through the furnace A, it falls into the hopper 11,
and thence through a pipe into the furnace B. This hopper 11 has a damper 13
arranged at the bottom thereof and it is provided for the purpose of enabling
one of the furnaces to be put out of action when the other one is in operation,
by closing the said damper.
The material which passes from the furnace A to the furnace B contains a
smaller quantity of magnesium chloride and more magnesium oxide than the
original mixture. In the lower furnace the chloride loses the rest of its chlorine
and the magnesium oxide thus produced is passed from the lower furnace into the
hopper 14.
C and D are hot air stoves in which the air necessary for the chemical reaction
is heated.
These heaters are alternately used for heating air in a manner similar to the
hot-air stoves of blast furnaces, one being heated by combustion of gas such as
producer gas while air is passed through the other, and previously heated, stove.
If, for instance, the stove D is being heated, and air is passed through the stove C,
we have the following condition at that time:
A mixture of combustible gas and air enters the heater D at 15 and is burned
at the entrance. The hot products of combustion ascend through the fireproof
filling material with which the heater is provided, and which absorbs a part of
their heat, and escape through the chimney 16. Simultaneously air enters from
the blower 17 into the heater C through the pipe 18. The air descends through
the filling material and is heated during its passage. The heated air leaves the
stove by way of the pipe 19 and enters the lower furnace B. When the stove C
is cooled down the conditions are reversed, air being passed through D while C is
again heated.
In passing through the lower furnace, the hot air acts on the material, which
has already been partly decomposed in the upper furnace A, and effects a more
complete decomposition of the chloride than is obtained by other commercial
methods. Chlorine gas diluted with air leaves the lower furnace B through the
pipe 20 at a comparatively low temperature and enters one or other of the
heaters E and F. These heaters work in the same way as do those indicated
at C and D, and they are so constructed that the dilute chlorine gas cannot come
in contact with any metal parts. The heated gas and air leaves the one or other
of these heaters at the bottom, and enters the upper furnace A through the pipe 21.
In the furnace A the gas and air are brought into contact with a material
containing a greater proportion of magnesium chloride. Chlorine gas leaves the
furnace through a pipe 22. For the purpose of drawing the gas through the
apparatus and for maintaining therein a pressure preferably less than that of
the atmosphere, an exhauster 23 is connected to the pipe leading from upper
furnace A.
On leaving the apparatus, the chlorine gas is passed through suitable cooling
and washing devices, for removing hydrochloric acid, and afterwards through an
apparatus wherein it is absorbed by slaked lime to convert the same into bleaching
powder. These devices and apparatus however form no part of my invention and
they are not shown in the drawings.
"
The mixture of magnesium oxide and magnesium chloride which is charged
into the upper furnace, can be prepared in any convenient manner. As it is
gradually heated in the upper furnace by intimate contact with the hot gases,
any moisture which it contains is driven off at a low temperature,. forming a
small quantity of hydrochloric acid. Thus - MgCl2 + H2O = MgO + 2HCl.

page_text: In cases where hydrochloric acid is of value, magnesium chloride alone can
be fed into the upper iurnace, in which it will be first converted into a mixture
of chloride and oxide. During the early part of the reaction, or until all the
moisture is removed, a great deal of hydrochloric acid is driven off; later on
chlorine is evolved.
For the purpose of reducing the amount of hydrochloric acid produced, and
obtaining the same in the pure state, it is often better to deprive the chloride, or
the mixture of chloride and oxide, of most of the moisture at as low a temperature
as possible, and without the presence of oxygen, before it is treated for the pro-
duction of chlorine. For this purpose an additional revolving furnace can be used
which is preferably arranged above the furnaces described. The material is
passed through this furnace and is brought into intimate contact with a hot gas
containing little or no oxygen. Such gas can be obtained by heating the gases
which leave the bleaching powder apparatus after the absorption of the chlorine.
The moisture is thus driven off at a low temperature and as no oxygen is present
no chlorine is formed, and pure hydrochloric acid can be condensed from the
gases leaving this furnace. The dried material passes into the lower furnaces
where it is treated with air and where the gases formed are mostly chlorine.
For the purpose of preventing waste of heat by discharging the oxide of
magnesium from the lowest furnace in a hot state, the heated air is caused to pass
through the pipe 19 which protrudes into the furnace B, as shown in dotted lines
in the drawing, and discharges said air some distance from the end of the furnace.
Considerable economy of heat is thus effected. By letting cold air or gas enter
through pipes 24 the material in the lower part of the cylinder B is cooled and
is discharged into the hopper 14 at a low temperature. As described, heat can
be further economized by arranging a third furnace above the furnace A through
which the fresh material is conducted before it enters the furnace A and through
which the gas passes after leaving the said furnace.
The use of a mixture of magnesium chloride and magnesium oxide has the
advantage that the material remains in a state of fine division during the treat-
ment. A more thorough decomposition is therefore possible than if the material
partly melts and forms a sinter.
In applying my improved method to the treatment of ore I may use the appa-
ratus hereinabove described, the ore being continuously fed into the upper fur-
nace A in which it is brought into intimate contact with the gas coming from
the lower furnace B. As this dilute gas is reheated in the heater E or F before.
it enters the upper furnace, the oxygen which it contains acts on the fresh ore
and a concentrated sulphurous acid gas leaves the furnace A. At the same time
the gas gives off some of its heat to the fresh ore and consequently it leaves the
furnace A at a comparatively low temperature. The partially roasted ore on
leaving the furnace A passes through the openings 8 into the hopper 11 and
thence by the pipe 12 into the furnace B. In this furnace the ore is brought
into contact with the hot air entering from the heater C or D through the pipe 19,
and a practically complete elimination of the sulphur is effected. The roasted
ore is discharged into the hopper 14.
My improved apparatus works continuously and, it may be said, automatically
in so far that no attention or manipulation is required after the material to be
treated is put in the hopper 10, beyond the operation of the valves of the heaters.
Furthermore the apparatus has no parts which are liable to require repairs, and
can be built of any size or capacity. A continuous stream of gaseous products
of even strength is given off.
Instead of the form of heaters shown, I may use continuous heaters in which
the air or gas passes continuously through heated channels.
As the gas passes
through the plant without pressure the use of such continuous heaters presents
no difficulty. Other methods of heating may be employed according to the nature
of the gas to be used as the re-agent and to the temperature to which it is to be
raised.

page_text: Additional furnaces may be arranged above the furnace A, to produce an
apparatus in which the process of re-heating the gas or gaseous products and
passing it or them over and in contact with the material to be treated may be
repeated, as herein before described.
For carrying out reactions requiring only a low temperature, the roasting
apparatus described in the Specification of Letters Patent granted to me on the
7th day of February 1895, No. 2736, may with advantage be employed. The
rotary furnace described in the Specification of Letters Patent granted to l'aul
Dunn, for an invention communicated by me, on the 24th day of December 1897,
No. 30496, is suitable for corrosive gases and high temperatures.
It is not however necessary to employ revolving furnaces, and it is moreover
obvious that the construction of the apparatus may be varied in other respects
to effect the best results under certain conditions without departing from the
spirit of my invention.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I wish it to be under-
stood that I do not claim the hereindescribed chemical reactions as such, but
what I do claim is:-
1. The hereindescribed continuous process consisting in bringing a solid
material into intimate contact with a hot gas by passing both simultaneously and
preferably in opposite directions through a suitable apparatus and re-heating the
gaseous products one or more times during the progress of the re-action of con-
ducting them through separate gas heaters.
2. A continuous process of producing chlorine, consisting in bringing a mixture
of magnesium chloride and magnesium oxide into intimate contact with hot air
by passing the mixture successively through a series of furnaces and simul-
taneously conducting air successively through the series in the opposite direction,
and heating said air before it enters the first furnace and also heating the dilute
chlorine gas as it passes from each furnace to the next succeeding furnace.
3. The method of treating solids with gases substantially as described with
reference to the drawing accompanying my Provisional Specification and for the
purposes specified.
4. An apparatus for treating materials with gases comprising a series of fur-
naces through which the material and the gas pass successively, gas heaters
arranged between the source of supply of gas and the first furnace and between
each furnace and the next succeeding one, and means for conducting hot gaseous
fluid successively and continuously through the heaters and furnaces.
5. An apparatus for carrying out the treatment of solid materials with gases
having its parts constructed arranged and combined to operate substantially as
described with reference to the drawing accompanying my Provisional Specifica-
tion and for the purposes set forth.
Dated this 19th day of June 1899
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.