Improvements in the Manufacture of Sulphides of the Alkalies.
Year: 1894

page_text: Date of Application, 22nd Nov., 1894
Complete Specification Left, 11th Feb., 1895-Accepted, 16th Mar., 1895
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Sulphides of the Alkalies.
I, Dr. BERNHARD PEITZSCH, of Höchst on the Main, Germany, Chemist, do
hereby declare the nature of this invention to be as follows:-
As is well known the manufacture of the sulphides of the alkalies, and
particularly those of soda and potash, has been effected by heating to redness
the corresponding sulphate and coal. This process is subject to many
disadvantages and in order to obviate these numerous attempts which have not
been successful have been made during the present century, notably by the
English expert, Walter Weldon, the characteristic feature of whose process
consists mainly in the use of a double furnace. According to his invention the
sulphate to be decomposed is melted in one furnace, and the products of combustion
therefrom are led into the other furnace where they are simultaneously utilized and
in which the conversion into sulphide occurs. The former of the two furnaces is
situated above the latter in order that the molten sulphate may be caused to flow
directly from the upper to the lower one.
In common with the earlier attempts for a like purpose the Weldon process has
however had to be abandoned as impracticable. More recently, Gossage has
endeavoured to manufacture sulphides of the alkalies by causing a mixture of
the corresponding sulphate and coal to flow through a shaft furnace filled with
incandescent coke. The production of the sulphide by this furnace also does
not appear to have met with success, since it was shortly afterwards proposed
by the inventor to neutralize the destructive action of the sulphide upon the
masonry, by the addition of sodium chloride a proposal not tending to simplify
the process.
The foregoing and similar processes fail by reason of the well known fact that
sulphides of the alkalies in a molten condition exert a rapidly destructive action
upon all furnace materials, whether of masonry, or iron, and also owing to the
sulphide being very readily oxidized, and possessing particularly when at high
temperatures a tendency to form polysulphides which are the more quickly
produced if access of air be not entirely prevented; such sulphides also considerably
facilitating the fusibility of the mass." For the above reasons, that is to say, on
account of the greater number of previous investigators having over-heated the
raw material and probably also insufficiently prevented access of air, it has as
previously stated beretofore been impracticable to obtain the sulphides of the
alkalies in an economical and remunerative manner.
66
Now the present invention is based on the fact that the sulphate of an alkali is
reduced completely to sulphide by carbon, at a comparatively low temperature,
without its being necessary to fuse the material which in fact should not be melted
at all. This latter precaution has been recommended by Gossage (see Lunge,
Soda-Industrie" II, 307) though probably without appreciation of its real value,
as he neutralized the effect by constantly stirring of the material undergoing
reduction, by which means ready contact of the material with air was promoted
thereby causing oxidation. According to my invention, satisfactory results are
obtained by conducting the operation at a low temperature in a hermetically
closed furnace, providing the material is spread out uniformly and is not disturbed
until reduction is complete; particular care being also taken that the layer of the

page_text: raw material is not too thick as in this event the reduction will be incomplete eve
if the beating operation be considerably protracted owing to the low heat
conducting nature of the mass. It is found in practice that the best results are
obtained, the reduction of sulphate being complete and relatively speaking in the
minimum period of time, when the depth or thickness of the layer does not exceed
10 centimetres. A further essential is the complete exclusion of air; and this is
easily effected by the employment of retort furnaces, in which the retorts are
either horizontal or vertical. Muffle furnaces may also be used when they permit
of the air being completely excluded. Such furnaces or muffles as well as the
retorts, possess the additional advantage of enabling the gases evolved as a
consequence of the reaction to be wholly recovered and utilized with ease.
The working of these furnaces being intermittent, it follows that the necessity
of opening the same for the purposes of charging and removing the material
cannot well be avoided and that special care should be taken to prevent the
sulphide coming in direct contact with the material of the furnace; it is however
impracticable notwithstanding the exercise of every precaution in the removal of
the material to prevent some portion (however small) of the sulphide remaining
and in consequence of the entrance of air at once melting thereby setting up the
destructive action previously referred to. By the arrangement now to be described
it is possible to avoid contact of the material of the furnace with the sulphide and
thus prevent the apparatus being subjected to more than a normal wear and tear;
such arrangement constitutes one of the specially advantageous features of my
invention of which it forms a very essential part.
When using horizonal retorts or muffles, the raw materials having first been
finely ground and thoroughly mixed are charged into light iron pots or vessels,
which are placed in the furnace and heated for some hours; and on completion of
the reaction, which can be ascertained from the diminished temperature of the
escaping gases, the furnace is opened, and the pots withdrawn as quickly as
possible, the sulphide being placed either in receptacles capable of being
hermetically closed, or preferably at once put into water, in which it dissolves
almost immediately.
The use of pots in combination with suitable furnaces is a characteristic feature
of the present invention as compared with the use of furnaces as heretofore
employed, such as for example reverberatory, muffle, shaft, or revolving furnaces,
all of which have hitherto been found to be impracticable in this connection on
account of the direct contact of the material operated upon with that of the
furnace. Care must be taken to keep the furnace at a strictly determined
temperature which must not exceed the melting point of the sulphide of the alkali,
as already fully explained.
From the foregoing it will be understood that according to my invention I
employ pots, casings or similar vessels or receptacles which after being filled with
raw material, are placed in retort, muffle or other suitable furnaces, in which the
temperature maintained must be below that of the melting point of the sulphide
of the alkali in course of production.
It is found from experiments conducted on a commercial scale that sulphide
produced in the manner described possesses a loose consistency, thus enabling the
pots containing it to be readily emptied without any appreciable residue remaining,
the pots also only being attacked to a slight extent. If the working of the
furnace be properly conducted, the reaction is so perfect as to yield almost
theoretically quantitative results, the sulphide produced being free from
polysulphides and hyposulphides.
It may be observed that in carrying out my invention the simple sulphates of
potassium or sodium need not necessarily be employed as the raw material, the
double salts of potassium and magnesium sulphate, or sodium and magnesium
sulphate, or a mixture of them such as those produced by sulphating the raw
potash salts in the Stassfurt Industry give effective results when employed as the
raw material.

page_text: When operating with vertical retort or similar furnaces I provide in lieu of
pots, casings, of thin sheet metal, which are filled with the raw material and
placed in the furnace the mode of procedure being in other respects similar to
that already described.
It should also be noted that the lye or solution of sulphide of the alkali is
treated in the usual known manner with carbon dioxide for making soda or potash.
Dated this 22nd day of November 1894.
F. WISE HOWORTH,
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicant.
I, Dr. BERNHARD PEITZSCH, of Höchst on the Main, Germany, Chemist, 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 :-
As is well known the manufacture of the sulphides of the alkalies, and particularly
those of soda and potash, has been effected by heating to redness the corresponding
sulphate and coal. This process is subject to many disadvantages and in order to
obviate these numerous but unsuccessful attempts have been made during the
present century, notably by the English expert, Walter Weldon. The charar-
teristic feature of the Weldon process consists mainly in the use of a double
furnace.
The sulphate to be decomposed is melted in one furnace, and the products of
combustion therefrom are led into the other furnace where they are utilized
simultaneously and in which the conversion into sulphide occurs. The former of
the two furnaces is situated above the latter in order that the molten sulphate may
be caused to flow directly from the upper to the lower one. In common with
earlier attempts for a like purpose the Weldon process has however been abandoned
as impracticable. More recently Gossage has endeavoured to manufacture
sulphides of the alkalies by causing a mixture of the corresponding sulphate and
coal to flow through a shaft-furnace filled with incandescent coke. The production
of the sulphide by this furnace also does not appear to have met with success, since
it was shortly afterwards proposed to neutralize the destructive action of the
sulphide upon the masonry, by the addition of sodium chloride; a proposal not
tending to simplify the process.
The foregoing and similar processes fail by reason of the well known fact that
sulphides of the alkalies in a molten condition exert a rapidly destructive action
upon all furnace materials, whether of masonry or iron, and also owing to the
sulphide being very readily oxidized, and possessing particularly when at high
temperatures a tendency to form poly-sulphides which are the more quickly
produced if access of air be not entirely prevented; such sulphides also considerably
facilitating the fusibility of the mass. For the above reasons, that is to say, on
account of the greater number of previous investigators having over heated the
raw material and probably also insufficiently prevented access of air, it has, as
herein previously stated, heretofore been impracticable to obtain the sulphides of
the alkalies, in an economical and remunerative manner.
Now the present invention is based on the fact that the sulphate of an alkali is
reduced completely to sulphide by carbon, at a comparatively low temperature,
without its being necessary to fuse the material and which in fact should not be
melted at all. This latter precaution has been recommended by Gossage (see
Lunge, "Soda-Industrie" II, 307) though probably without appreciation of
its real value, as he neutralized the effect by constant stirring of the material

page_text: undergoing reduction, by which means ready contact of the material with air was
promoted thereby causing oxidation.
It
According to my invention, satisfactory results are obtained by conducting the
operation at a low temperature in a hermetically closed furnace, providing the
material is spread ont uniformly and is not disturbed until the reduction is complete;
particular care being also taken that the layer of the raw material is not too thick
as in this event the reduction will be incomplete, even if the heating operation be
considerably protracted, owing to the low heat conducting nature of the mass.
is found in practice that the best results are obtained, the reduction of sulphate
being complete and relatively speaking being effected in the minimum period of
time, when the depth or thickness of the layer does not exceed 10 centimetres.
further essential is the complete exclusion of air; and this is easily effected by the
employment of retort furnaces, in which the retorts are either horizontal or vertical.
Muffle furnaces may also be used when they permit of the air being completely
excluded. Such furnaces or muffles as well as the retorts, possess the additional
advantage of enabling the gases evolved as a consequence of the reaction to be
wholly recovered and utilized with ease.
A
The working of these furnaces being intermittent, it follows that the necessity of
opening the same, for the purposes of charging and removing the material, cannot
well be avoided and that special care should be taken to prevent the sulphide
coming in direct contact with the material of the furnace. It is however imprac-
ticable notwithstanding the exercise of every precaution in the removal of the
material to prevent some portion (however small) of the sulphide remaining and
in consequence of the entrance of air, at once melting, thereby setting up the
destructive action previously referred to. By the arrangement now to be described
it is possible to avoid contact of the material of the furnace with the sulphide, and
thus to prevent the apparatus being subjected to more than a normal wear and tear;
such arrangement constitutes one of the specially advantageous features of my
invention of which it forms a very essential part.
When using a horizontal retort or muffle, the raw materials having first been
finely ground and thoroughly mixed are charged into light iron pots or vessels,
which are placed in the said retort or muffle and heated for some hours. On
completion of the reaction, which can be ascertained from the diminished tempera-
ture of the escaping gases, the retort or muffle is opened, and the pots withdrawn
as quickly as possible, the sulphide being placed either in receptacles capable of
being hermetically closed, or preferably, at once put into water, in which it dissolves
almost immediately.
The use of pots in combination with suitable furnaces is a characteristic feature
of the present invention as compared with the use of furnaces as heretofore
employed, such as for example reverberatory muffle, shaft, or revolving furnaces all
of which have hitherto been found to be impracticable in this connection on account
of the direct contact of the material operated upon with that of the furnace. Care
must be taken to keep the furnace at a strictly determined temperature which must
not exceed the melting point of the sulphide of the alkali to be produced, as already
fully explained.
From the foregoing it will be understood that according to my invention I
employ pots, casings or similar vessels or receptacles which after being charged
with raw material, are placed in retort, muffle or other suitable furnaces, in which
the temperature must be maintained below that of the melting point of the sulphide
of the alkali in course of production.
It is found from experiments conducted on a commercial scale that sulphide
produced in the manner described, possesses a loose consistency, thus enabling the
pots containing it to be readily emptied without any appreciable residue remaining,
and that the pots are only attacked to a slight extent. If the working of the
furnace be properly conducted, the reaction is so perfect as to yield almost
theoretically quantitative results, the sulphide produced being free from poly-
sulphides and byposulphides.

page_text: It may be observed that in carrying out my invention the simple sulphates of
potassium or sodium need not necessarily be employed as the raw material, the
double salts of potassium and magnesium sulphate, or sodium and magnesium
sulphate, or a mixture of them (such as those produced by sulphating the raw
potash salts in the Stassfurt Industry) give good results when employed as the raw
material.
When operating with a vertical retort, or similar furnaces, I provide in lieu of
pots, casings of thin sheet metal of a diameter of about 10 cm., which are filled
with the raw material and placed in the furnace, the mode of procedure being in
other respects similar to that already described.
The lye or solution of the sulphide of the alkali obtained, is or may be
treated in the usual known manner with carbon-dioxide acid for making soda or
potash.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
The manufacture of an alkaline sulphide or sulphides by heating a mixture of
carbon and sulphate of sodium or of potassium or both, or the double salts of
potassium and magnesium sulphate or sodium and magnesium sulphate, or a mixture
of these double salts (Stassfurt salts), in a pot, casing, vessel or like receptacle
placed in a hermetically closed furnace or chamber to a temperature not exceeding
the melting point of the required sulphide or mixture of sulphides, substantially as
herein described.
Dated this 11th dow of Fahmin 1905
F. WISE HOWORTH,
46, Lincoln's Inn Fields, London, W.C., Agent for the Applicant.