Improvements in the Manufacture of Sulphurous Acid, Sulphuric Acid and Sulphuric Anhydride.
Year: 1898

page_text: PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Sulphurous Acid, Sulphuric
Acid and Sulphuric Anhydride.
I, GEORGE WILLIAM JOHNSON, of 47, Lincoln's Inn Fields, in the County of London,
Patent Agent, do hereby declare the nature of this invention (which has been
communicated to me from abroad by Verein Chemischer Fabriken, of Mannheim,
in the German Empire,) to be as follows:-
Endeavours have long been made to oxidize sulphurous acid arising from the roasting
of pyrites, so as to form sulphuric anhydride or sulphuric acid, use being made of the
heat, generated during the operation of roasting the pyrites, and of an oxidising
agent; but no useful results have so far been obtained.
According to the Specification of Letters Patent 1919 of 1853 granted to William
Hunt the sulphurous acid arising from roasting-fumes or gases of pyrites was proposed
to be partly transformed into sulphuric acid, by passing the sulphurous acid through
a channel, heated to a red heat by the roasting gases, which passage was, if necessary,
to contain pumice stone or stone fragments or other suitable material, resisting the
action of heat and acid.
In his "metallurgical roasting processes" page 339 Plattner describes certain
experiments in Freiberg, Germany, with the view to transforming the roasting gases
into sulphuric acid; broken quartz being used as a medium.
In the year 1852 Wöbler (Ann. Chem. pharm. 81 page 255) states that oxides of
copper, iron, chromium, and precipitated chromium and copper oxide are, when kept
at a moderate red heat, capable of causing the combination of sulphurous acid and
oxygen, so as to form sulphuric anhydride.
It is well known that roasting gases from pyrites contain from 8 to 10 per cent. of
the sulphur in the form of sulphuric acid.
In the "Ber. d. d. chem. Ges." volume 1877 page 1824 and others, Lunge reports on
a comparatively long series of experiments, shewing, that sulphuric acid can be
obtained, amounting to from 16 to 18 per cent. maximum limit, if a mixture of
sulphurous acid and air be passed through a layer of pyrites waste products at a
glowing heat.
It has not so far been possible, to so increase the formation of sulphuric anhydride
from SO, by causing the latter to act upon red hot substances containing oxide of
iron, or to so increase the oxides quoted by Wöhler in the treatise referred to, as
to admit of this reaction being practically utilized in manufacturing sulphuric
anhydride on a large scale.
My foreign correspondents have recently discovered that sulphurous acid can be
transformed into sulphuric anhydride of about 60 per cent. and that this yield
-if the directions and conditions hereinafter stated, be carefully observed―can be
raised to upwards of 90 per cent.
To attain this result it is necessary that moisture should be entirely excluded both
from the air used for the oxidation and from the apparatus used in the process.
These objects may be achieved for example; by drying the air by means of

page_text: concentrated sulphuric acid or the like, and by constructing as air tight an apparatus
as possible, and permanently maintaining it in this condition.
It is further necessary that the oxide yielding bodies such as oxide of iron,
chromium, copper, or the like or mixtures thereof with other porous substances be used
immediately after calcination without having been exposed to any considerable
atmospheric influence or action and this especially applies to the aforesaid pyrites
waste products.
It is further necessary that a temperature such as is possessed by the gases,
discharged from the roasters, preferably a temperature varying between 600 and 700
degrees Centigrade should be employed and that the contact substances be kept at
this temperature during the process. If the above conditions be observed, the result
herein before stated is obtained.
My foreign correspondents have further found that the pyrites waste products
afford an excellent means for extracting in a technically perfect manner the arsenic
from sulphurous gases provided they contain arsenic, so that according to this
invention a large yield, free from arsenic is obtained.
A further result of the experiments of my foreign correspondents is, that in a
similar manner, also sulphurous acid, free from arsenic, may be separately obtained
from initial products, containing arsenic, if the production of comparatively very
large quantities of sulphuric acid be as much as possible avoided. The attainment of
this result is dependent on the operator inore or less strictly adhering to the conditions
herein before referred to.
The substitutes above mentioned may be employed instead of the pyrites waste
products, but under ordinary circumstances the pyrites waste products are
preferred.
Dat
OLL
I
2
1000
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.
Improvements in the Manufacture of Sulphurous Acid, Sulphuric
Acid and Sulphuric Anhydride.
I, GEORGE WILLIAM JOHNSON, of 47, Lincoln's Inn Fields, in the County of
London, Patent Agent, do hereby declare the nature of this invention (which has
been communicated to me from abroad by Verein Chemischer Fabriken, of Mannheim,
in the German Empire,) and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement :--
The principal object of this invention is to produce sulphuric anhydride from the
roaster gases of common iron pyrites, blendes, or analogous products or ores containing
sulphur, employing burnt pyrites-waste, or equivalent substances, containing
peroxide of iron, (ferric oxide), in order to convert the evolved sulphurous acid into
sulphuric anhydride.
Attempts in this direction have already been made, but these attempts have not,
hitherto, resulted in anything practically satisfactory.
Thus as long ago as February 13th 1854 a British Patent 1919 1853, was granted to
William Hunt, under which it was proposed to convert the sulphurous acid from
roaster gases of pyrites into sulphuric acid by conducting it through a channel main-
tained at a red heat, such channel being, when required, filled with a material proof
against the action of heat and acids such as pumice stone, or broken stone.
Plattner, in his work Metallurgische Röst-processe ("Metallurgical Roasting
Processes"), p. 339 described certain experiments which were made at Freiberg, some

page_text: forty years ago, with a view to converting the gases from roasting ores into sulphuric
acid; fragments of quartz being used as a medium.
In 1852, Wöhler (Annal. Chem. Pharm. 81, p. 255) made the observation that the
oxides of copper, iron and chrome, or chrome oxide and copper oxide precipitated
together, were capable of oxydizing a mixture of sulphurous acid and oxygen, at a
gentle red heat, into sulphuric anhydride.
Many years later, Lunge, recognizing the well-known fact that the roaster gases
of iron pyrites contain from 8 to 10 per cent. of roasted sulphur in the form of
sulphurous acid, proceeded to make a somewhat extensive series of experiments (see
Berichte der deutschen Chemischen Gesellschaft 1877 p. 1824 and Chemiker
Zeitung, No. 3, for January 11, 1883, and other publications) in order to ascertain to
what percentage the conversion of sulphurous acid and air into sulphuric acid could
be brought by conducting a mixture of these gases over a layer of red-hot burnt
pyrites waste.
In the Berichte der Deutschen Chemischen Gesellschaft 1877 p. 1824, Lunge.
states that it was owing to the widely contradictory views then prevailing as to the
formation of sulphuric anhydride in the roasting of iron pyrites that he was induced
to investigate anew a subject so important to the practical sulphuric acid
manufacture; also that he was anxious in conducting his tests to select a method
that was not liable to lead him to erroneous conclusions.
It was on these premises, then, that Lunge proceeded with his experiments and
the conclusion he arrived at was that only 16 or 18 per cent. at the outside could be
converted into anhydride.
Later on, as a sequel to his earlier labours, he reported to the Chem. Zeitung, No. 3,
January 11th, 1883, on certain tests he had made to verify the results previously
arrived at, and he found that in both cases the experiments led to the same results,
viz., that the proportion in which sulphurous acid might be transformed into
sulphuric anhydride by roasting, and through the medium of ferric oxide, did not
exceed 15.8 per cent.; and he concluded his report by declaring that that result, so
thoroughly coincided with the result mentioned before that the matter might be
looked upon as settled.
Consequently, it has hitherto been found impracticable to increase the proportion
of sulphuric anhydride from sulphurous acid and air, (by causing them to act upon
red-hot materials containing ferric oxide, or upon any of the oxides named by Wöhler
in the journal cited) in a degree sufficient to warrant the employment of this
reaction in the practical manufacture of sulphuric anhydride, or sulphuric acid on a
large scale.
My foreign correspondents have discovered by searching investigation that the
percentage of conversion of sulphurous acid into sulphuric anhydride can be raised far
beyond the maximum stated by Lunge, indeed very nearly to its theoretical value;
and that therefore the production of sulphuric anhydride, or of sulphuric acid, (as the
case may be) on a manufacturing scale is not only perfectly feasible, but offers, very
material economical advantages.
Hitherto the reaction between sulphurous acid and oxygen, or air, and a contact
substance could only be carried out on a large scale by first producing and purifying,
and then drying, the sulphurous acid; and not until this was done was the acid in
conjunction with oxygen, or air allowed to react upon the substance employed as a
contact medium (viz. platinum) aided by externally applied heat.
The method of operation according to this invention differs very materially from
the foregoing for according to this invention, air is admitted into the roasting
apparatus from the first, and consequently there is at once obtained a mixture of
sulphurous acid and air (oxygen) which is free from water and suitable for the
purposes of the reaction. This mixture without being either purified or cooled, will
act upon the medium containing ferric oxide directly at, and in conjunction with, the
5 temperature developed by the combustion of the pyrites, that is to say, without any
external heating and will, by so doing, produce sulphuric anhydride.

page_text: What Lunge did in his experiment carried out on an extremely small scale was to
roast finely ground iron pyrites in a small porcelain vessel, by conducting dried air
over it. The roaster gases evolved he caused to pass through a glass tube half filled
with burnt pyrites-waste and kept red hot by externally applied heat. It was thus
he arrived at the above mentioned results which, in his opinion, finally settled
adversely the question of utilizing the reaction in the manufacturing trade on a large
scale.
Now the reaction between sulphurous acid and oxygen, or air, which Lunge
performed in a glass tube is, according to this invention, carried out in a pyrites
furnace; and consequently the work is performed with means, and under conditions,
totally different from those which characterized the labours of Lunge.
In order to bring the medium employed as contact substance to a red heat Lunge
was compelled to utilize external heat; and the mere fact of the fusibility of the glass
tube which he used in his experiments must necessarily have made it impossible for
him to maintain the high temperature which is attained in the roasting furnace.
Besides, he could not possibly, in the experimenting apparatus he had chosen,
subject the contact substance to the continued action of the reaction gases. This,
however, is done from the outset in operating according to this invention, and in
pursuing this course my foreign correspondents have come to the conclusion that the
contact substance can only acquire its maximum power, or capacity, as a reagent, in
a gradual manner, and under the continued action of the hot gases arising from the
reaction of sulphurous acid and oxygen; and that to obtain this effect, it is not
sufficient, as Lunge did, to bring the contact substance to a red heat, in a simple
current of air. Lunge, by performing his experiments singly and at intervals, was
precluded from making this discovery; neither had he an opportunity of ascertaining
the fact that the reactive capacity of fresh waste pyrites, just collected from the
roasting furnace is, per se, considerably greater, than that of burnt pyrites which
have been stored for some time and exposed to the influence of air.
When it is further considered that the "yield" obtained according to this
invention is about five times greater than that which Lunge found to be obtainable,
the essential distinction between the process according to this invention which is
applicable for the manufacture on a large scale, and the misleading trials of Lunge,
will be at once apparent.
Thus my foreign correspondents were the first to discover that it was possible to
secure a good commercial production of sulphuric anhydride from roaster gases
containing sulphurous acid, by conducting such gases over materials containing ferric
oxide (i.e. burnt pyrites waste).
In carrying out the process according to this invention in practice for
example in the treatment of iron pyrites the operation may be conducted as
follows:-
The crude iron pyrites is burnt in an ordinary pyrites furnace. The air required
for its combustion is thoroughly dried before being admitted into the furnace and
is also subjected to preliminary heating as it passes the burnt pyrites while yet
hot.
The gas mixture of sulphurous acid and oxygen (or air) evolved by the combustion
of the pyrites, being suitable for the reaction as soon as it is produced, is conducted,
together with the heat developed in the roasting chainber, directly through, or over,
the contact substance containing ferric oxide, which is deposited in an oxidation
chamber; when, by the mutual action of the sulphurous acid and oxygen and of the
contact substance, sulphuric anhydride is produced.
Besides enabling sulphuric anhydride to be obtained economically this improvement
has the advantage of rendering unnecessary the lead chambers, which hitherto have
been required in sulphuric acid manufacture, and also the expensive platinum
apparatus heretofore used in concentrating the acid, so that it completely
revolutionizes, and at the same time simplifies, the manufacture of sulphuric acid,
one of the most important articles of the chemical manufacturing industry.
My foreign correspondents have further found, that the pyrites-waste affords an

page_text: excellent means for extracting, in a technically perfect manner, the arsenic from
sulphurous gases, containing arsenic, so that, according to this invention, a large
yield, free from arsenic, is obtained from the initial materials, containing arsenic, if
in passing the gases over the burnt ore, the production of comparatively large
quantities of sulphuric acid be, as much as possible, avoided. The attainment of this
result, is dependent on the operator more or less strictly adhering to the conditions
hereinbefore referred to.
The substitutes above mentioned may be employed also, in this case, instead of the
pyrites-waste, but, under ordinary conditions, the pyrites-waste is preferred.
Having now particularly described and ascertained the nature of this in-
vention and in what manner the same is to be performed, I declare that what I
claim is :-
1. The manufacture of sulphuric anhydride from sulphurous acid and oxygen (or air)
by conducting the mixture of these gases over red hot pyrites-waste or other contact
substance an essential condition being that the reaction shall take place in immediate
conjunction with the roasting process, and that the roaster gases shall be caused to
flow over the contact substance at the temperature which they have acquired in the
roasting process, and without the application of external heat.
2. In the production of sulphuric anhydride from sulphurous acid in accordance
with the preceding claiming clause, effecting the roasting and oxydation by the use
of previously dried air, the gas mixture thus obtained, consisting of sulphurous acid
and oxygen (or air) being ready for the reaction as soon as evolved and being caused
to act upon the contact substance containing ferric oxide at the temperature developed
in the roasting process.
3. The obtainment of sulphurous acid free from arsenic by passing the said acid
over heated pyrites-waste (burnt ore) or equivalent substances as hereinbefore
described.
Dated this 10th dow of Mov 1800
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.