Sulphuric Anhydride.
Year: 1887

page_text: Dite of Application, 28th June, 1887.
Specification Accepted, 5th Aug., 1887.
Sulphuric Anhydride.
We EMIL HÄNISCH and Dr. Max SCHRÖDER of Neumühl-Hamborn in the German
Empire, Chemists, do hereby declare the nature of said invention for "AN IMPROVED
"and
PROCESS AND APPARATUS FOR THE PRODUCTION OF SULPHURIC ANHYDRIDE
in what manner the same is to be performed to be particularly described and
ascertained in and by the following statement:-
The combination of sulphuric acid and oxygen to form sulphuric anhydride is
effected in a known manner by conducting the gaseous mixture containing SO² and O
over spongy platinum or other efficacious contact substances at a low red heat.
To obtain a better result the platinum has been transferred to asbestos or other
suitable substance presenting a large surface for the purpose of insuring in the
passage of the combining gases a lengthened duration of contact of the same with the
platinum.
Now the process of this invention has for object the use of a very large
platinum surface and the prolongation of the duration of contact with the same in
the manner that the volume of the SO2 and O gaseous mixture whilst on its passage
over the platinum substance is substantially diminished by subjecting it to a high
pressure. Thus, for example, if such pressure be of three atmospheres the gas will
be compressed to a third part of its original volume and correspondingly it may
remain in the space charged with the platinum substance three times as long as when
its passage takes place under ordinary atmospheric pressure. Further the chemical
process is better performed under the higher pressure as the chemically active
gas molecules come nearer together.
We carry out this process of producing sulphuric anhydride by the aid of the
apparatus shewn in the accompanying drawing. The gaseous mixture to be used
may be held in readiness ready formed; for instance, like the gases which result
from the decomposition of sulphuric acid or sulphates at a high temperature after
displacement of the moisture and which contain S02 and 0 in the proportion most
favourable for the process, but it may be necessary to first prepare the mixture in the
proper proportions, which is effected if sulphurous acid and oxygen are separately
evolved or if instead of pure oxygen atmospheric air is used, and as this latter
method by reason of the difficulties presented in the decomposition of the sulphuric
acid at a high temperature and the high cost of the pure oxygen-appears to offer the
greater commercial advantages the apparatus necessary for the purpose is shewn
as designed for such a method. It is first requisite that the pure sulphurous acid
to be used shall be always mixed with atunospheric air in the proper proportion and
so that no considerable fluctuations occur in the composition of the mixture. For this
method the most favourable proportions are 29.6 vol. 802 to 70.4 vol. atmospheric

page_text: air (with 14.8 vol. 0) but as small fluctuations in the composition of the mixture
cannot in practice be avoided it is preferable to take a slight excess of air in order
that loss in the valuable sulphurous acid may as far as possible he prevented. On
these grounds it is advisable to employ a mixture of about 25 per cent. SO2 and
75 per cent. air. The proper mixing of the sulphurous aeid with the air simul-
taneously with the compression of the gases is effected by a double cylinder compressor
and mixing machine A, the two cylinders a and b being relatively of such dimensions
that the air suction cylinder a has three times the cross sectional area of the
sulphurous acid suction cylinder b with same length of stroke so that when the
compressor is working, three times as much air as sulphurous acid will be supplied.
The compressed gases of both cylinders unite in the pressure tube e through which
they pass to the compressing vessel B provided with a safety valve d and manometer e,
thence the mixed gases under a high pressure pass through a valve and tube to the
combining furnace C. It has, as shewn in the drawing two wrought iron pipes
heated to red heat and charged with the platinised contact substance through which
the gases under pressure simultaneously pass. The pipes are of comparatively
small diameter and very strong so that when at a low red heat they may be capable
of withstanding the pressure of several atmospheres. After passing through the
pipes in which the greater part of the gases are converted into anhydride they again
come together in the tube h and pass to the outlet valve i which is so adjusted that
at the working pressure-generally from two to three atmospheres-they are equably
discharged into the tube k. In order that the formed anhydride may not settle in the
tubes and or in the outlet valve i and so give rise to stoppages, they are encircled
with a lead worm supplied with steam, so that the temperature is maintained above
the volatilising point of the anhydride. Should however from accidental causes these
pipes become stopped, or the outlet valve stick, the pressure would rise in the vessel B
and the safety valve d set in action. This valve is adjusted to discharge at one
atmosphere of pressure above that employed in the normal course of the process.
The gases present after the conversion mainly composed of nitrogen and sulphuric
anhydride are passed through earthenware condensing vessels serving to separate the
anhydride, or for dissolving the same in ordinary sulphuric acid. The small quantity
of sulphurous acid present-after separating the anhydride-in the remaining gases,
is utilised in the usal way as battery cell acid or after eliminating the nitrogen, used
over again in the anhydride process.
Having now particularly described and ascertained the nature of our said invention
and in what manner the same is to be performed we declare that what we claim is :
1. In the manufacture of sulphuric anhydride by contact action the performance
of the contact process under pressure in the manner that the gases containing
sulphurous acid and oxygen are compressed previous to their passage through
the heating pipes and afterwards equably discharged, and in which a higher pressure
is employed than is necessary solely for the unimpeded passage through the contact
substance, substantially as described and shewn.
2. For the purpose of obtaining a suitably composed and compressed gaseous
mixture of sulphurous acid and air the use of a two cylinder combined mixing and
compressing pump the cylinders of which correspond in dimensions to the different
quantities of the gases to be supplied, for the purpose specified substantially as
described and shewn.
EMIL CAPITAINE,
89, Chancery Lane, London, W.C.,
Agent for the Applicants.