Improved Means for Recovering Sulphuric Acid and Sulphuric Anhydride from Gases.
Year: 1898

page_text: Date of Application, 29th Nov., 1898-Accepted, 15th Apr., 1899
COMPLETE SPECIFICATION.
Improved Means for Recovering Sulphuric Acid and Sulphuric
Anhydride from Gases.
I, THOMAS RICHARD SHILLITO, of 15, Tooks Court, London, E.C., Engineer, do
hereby declare the nature of this invention, a communication to me from abroad
by the Actien Gesellschaft für Zink-Industrie vormals Wilhelm Grillo, of
Hamborn, Germany, and by Dr. Max Schroeder, of the same place, and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement:―
This invention relates to the recovery of sulphuric acid or sulphuric anhydride
(SO) by the catalytic or contact method wherein, as is well known, platinum has
been found of especial efficacy over all other substances for producing the
desired result.
Inasmuch as platinum even in a finely divided state is of too small a volume to
act effectively throughout in a large current of gases containing sulphurous
anhydride (SO) and oxygen, resort has been had to the expedient of super-
imposing the metal upon an inert or comparatively inert base so as to spread the
metal over a large surface. At first pumice stone was proposed for this purpose
and appeared especially applicable by reason of its porosity. Winkler developed
the subject further and ascertained that almost all loosely porous bodies are
adapted to serve for the contact substance proper, especially asbestos, mineral wool,
infusorial earth, clay, and where in certain contact processes a high femperature
is not required, even organic fibrous materials. In the German Patent Specification
No. 4566, Winkler describes a special process for the chemical application of
platinum upon these bases, which process he likens to the final step in the dyeing
of a fibre in the dye vat. Moreover from later publications it appears that for
the production of these platinised contact bodies there has always been employed
a base either moulded to shape or otherwise in an integral or solid state.
This invention contemplates the subdivision or dilution of the platinum in a
different manner and by other means, whereby, in a very simple way, contact
masses of extraordinary subdivision may be obtained which far exceed in efficiency
those hitherto employed.
Instead of the solid or integral bases above referred to, use is made of the soluble
salts of the alkalies, of the alkaline earths, of the earths, and of the metals, which
salts, for the production of the contact mass, are dissolved in water and then mixed
with a solution of the finely divided platinum salt. For this purpose chloride of
platinum is especially suitable. It can be employed in a solution so diluted that
in 100 parts of the salt serving as a vehicle less than 1 part of the platinum salt
falls out. Even contact bodies of 0.1 per cent. and less of platinum contents are
very efficacious. The mixture of the solutions is then evaporated and the resulting
salt crusts dried and broken up to about a uniform granular size. The powder
which is formed in this reducing or breaking up operation is dissolved afresh
in water and treated as before until all the material has been converted into an
appropriate condition of grains or particles. This material is adapted for filling
direct into the cylinders or other apparatus employed in carrying out the contact

page_text: process. The separation of the metallic platinum in the finest subdivision between
the molecules of the salts serving as vehicles for the platinum, takes place auto-
matically upon heating, that is, upon the starting of the contact process.
It will be apparent that the salts serving as vehicles for the finely divided
platinum will only remain unchanged during the contact process provided that
they are either stable sulphates or that they contain an acid, which, as for instance
phosphoric acid, is stronger at a low red heat than the sulphuric acid which forms
during the process. Other salts, as for instance, chlorides or carbonates, will,
at the beginning of the process be at once converted into sulphates, with develope-
ment of their acids. Inasmuch as this results for the most part, in an alteration
of the structure and injury to the firm cohesion of the individual pieces, it is
advisable to employ stable salts from the beginning.
It will be understood that instead of the single salts, mixtures thereof, or double
salts as for instance alum, can be employed. Further instead of platinum other
metals of the platinum group may be used which however in view of their great
rarity come less into consideration in practice.
The technological advantages of this new contact material consist not only in
the simple manner of producing it but also in its highly superior efficiency. The
platinum finds itself in a condition of extraordinary fine subdivision and appears
to be effective in the interior of the pieces to a degree not less than in the exterior
layers. This may be due to the great porosity produced by the driving off of
the water of crystallisation.
A further advantage consists in the fact that this contact material may be
regenerated with extraordinary ease, which is particularly of value when the
ordinary furnace gases from sulphur ores are employed for the contact process.
Inasmuch as the furnace gases even after purification still contain traces of dust,
the contact bodies in the course of time become covered with thick impenetrable
layers which diminish their efficiency. To lay bare the surface it is only then
necessary to stir the contact body in water and to evaporate the salt solution thus
formed. The dust is thereby dispersed throughout the entire mass and can no
longer diminish the penetrability of the surface.
Finally the dust may be readily separated from the platinum after dissolving
out the salts which serve as the vehicle. For this purpose it is only necessary
to boil with concentrated muriatic acid the slime which has been separated from
the salt solution whereupon the particles of dust pass into solution whilst the
platinum black remains behind in a pure condition.
Having now particularly described and ascertained the nature of said invention
and in what manner the same is to be performed, as communicated to me by my
foreign correspondents, I declare that what I claim is:-
1. The process of recovering sulphuric acid or sulphuric anhydride from gases
containing SO, and O which consists in passing said gases through a mass con-
prising an active agent as platinum and soluble salts, substantially as described.
2. The process of producing a material suitable for the catalytic method, which
consists in forming a mixed solution of a platinum salt with another salt or salts,
evaporating the solution so as to obtain salt crusts therefrom, and finally breaking
up the salt crusts into particles of substantially uniform granular size, for the
purpose specified substantially as described.
3. A contact body for the catalytic process referred to whose base for the
operative substance consists of salts soluble in water.
Dated this 29th day of November 1898.
THOMAS R. SHILLITO,
15, Tooks Court, London, E.C.