Improvements in the Manufacture of Sulphuric Anhydride.
Year: 1898

page_text: Date of Application, 21st July, 1898
Complete Specification Loft 20th Mov 1800 Accented 21st July 1899
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Sulphuric Anhydride.
I, JAMES YATE JOHNSON, of 47, Lincoln's Inn Fields, in the County of London,
Gentleman, do hereby declare the nature of this invention (which has been com-
municated to me from abroad by the Badische Anilin and Soda Fabrik, of Lud-
wigshafen-on-Rhine, in the German Empire,) to be as follows:-
My foreign correspondents have made and communicated to me an important
improvement in the manufacture of sulphuric anhydride by the contact process
which consists in subjecting the gases to be treated to a preliminary purification.
The usual sulphide ores contain various impurities and many of these on roast-
ing the ores are liable to pass, either free or in combination and either as dust,
or as gas into the mixed gases containing the sulphur dioxide. Even if prac-
tically pure sulphur be used as the source of SO 2, some sulphuric anhydride is
formed and since the air used in roasting contains moisture the result is that
the SO2 produced contains sulphuric acid which passes forward as a suspended
mist.
The effect of such impurities of the mixed gases is of various kinds sulphuric
acid for instance from any source is liable in some cases to injure the lead and
iron parts of the apparatus and to cause difficulties in the moving parts of the
machinery. Further and especially my foreign correspondents have found that
the sulphuric acid mist is objectionable as carrying forward other impurities into
the contact apparatus. Any admixture of sulphur vapours which have escaped
combustion act similarly and must therefore be excluded. Other impurities
may clog the contact substance mechanically or combine with it chemically in
either case impairing its efficiency.
The principal impurities of ordinary pyrites are-Iron, manganese, copper,
nickel, arsenic, antimony, phosphorus, mercury, lead, zinc, bismuth, thalliumi and
selenium or compounds thereof.
My foreign correspondents have systematically examined the effect of these
bodies in the contact process and have found that arsenic, phosphorus and mer-
cury and their compounds are especially injurious and small quantities of either
of these impurities may render comparatively large quantities of the contact
substance almost entirely inert and impair the efficiency of the process. They
have ascertained that all the said impurities, such as sulphuric acid, sulphur dust
of any kind, and arsenic, phosphorus and mercury and their compounds must be
removed from the gases in order to allow of the continual use of the contact mass
and a continual and nearly quantitative conversion thereby of sulphurous acid
into sulphuric anhydride.
The perfect purification of the roasting gases is very difficult and is one of the
principle reasons that the direct production of sulphuric anhydride from the said
gases has not hitherto replaced the chamber process.
My foreign correspondents have invented a new process, which allows of the
certain and perfect removal of the said impurities of the roasting gases. This
process discards the idea of immediately passing into the contact mass the rela-

page_text: tively dry and hot roasting gases after having as far as possible freed them from
dust and provides instead a new and particular chemical and mechanical purifi-
cation which preferably consists in a special treatment whilst hot with a jet of
stream or air or other gas for the purpose of thoroughly mixing the gases and
producing when steam is used a sufficient dilution of the condensed sulphuric
acid a subsequent gradual cooling, and then repeated washing with water, or
sulphuric acid, while using special tests, and finally drying the gases by sulphurie
acid all as hereinafter more fully described. The gases before entering the
contact apparatus must satisfy two tests viz.:-an optical test to shew freedom
from dust and mist and a chemical analytical test to shew freedom from arsenic
phosphorous and mercury or their compounds.
To achieve this purity, in the dust flue which the hot gases from the pyrites
burners enter a jet of steam is blown in. Amongst other effects this mixes the
gases thoroughly and brings about a more perfect combustion of any sulphur, or
other combustible matter. This mixture and promoted combustion can also be
effected with a jet of air, or other gas (say with a portion of the purified gases
to be treated) but then the steam must be blown in later. The introduction of
steam has several further most important effects.
My foreign correspondents have found that it is preferable for the purpose of
effecting the easy and complete washing of the roasting, gases especially gases
from pyrites containing much arsenic, to gradually cool the gases in suitable cool-
ing apparatus. All such gases contain concentrated sulphuric acid vapours which
are condensed when cooling, the metal of the cooling apparatus (usually consisting
of iron or lead) being strongly attacked and rapidly deteriorated or destroyed. If
however sufficient steam be blown into the gases to bring down the concentration
of the condensed sulphuric acid to a strength of 10 to 40 degrees Beaumé this
difficulty is overcome.
A further important effect of blowing in steam is that when cooling the gases
without treatment with steam the coolers become incrusted with solid impurities
in combination with sulphuric acid which stop up the pipes and are difficult to
remove.
By blowing steam into the hot gases this incrustation is prevented as the said
impurities form a mud which is easily removed. The addition of steam also
renders it possible to more easily wash the gases subsequently and enables the
desired purity to be attained.
The action of the steam serves also to prevent the formation of volatile hydrogen
compounds of the impurities especially of arsenic and phosphorus or their com-
pounds which otherwise would be formed by the action of the concentrated
sulphuric acid on the metal of the coolers and the impurities and could be removed
only with great difficulty therefore passing into the contact mass and eventually
rendering it inactive.
The gases pass through a flue which may be of iron or brickwork in which they
cool somewhat and thence into a system of lead pipes arranged to act as a cooler.
Here they are cooled down to about 100 degrees Centigrade or lower. They are
then passed into washing towers or other washing apparatus and washed with
water, or dilute, or concentrated sulphuric acid. If not already washed with
concentrated sulphuric acid they finally are thoroughly dried by means of such
concentrated acid, or other drying agent. The extent to which the washing must
be carried will depend on the nature and degree of the impurity to be eliminated
and can be determined by the aforesaid tests.
Dated 01.1 1
T 1
1000
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.

page_text: COMPLETE SPECIFICATION.
Improvements in the Manufacture of Sulphuric Anhydride.
I, JAMES YATE JOHNSON, of 47, Lincoln's Inn Fields, in the County of London,
Gentleman, do hereby declare the nature of this invention (which has been com-
municated to me from abroad by the Badische Anilin and Soda Fabrik, of Lud-
wigshafen-on-Rhine, 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:-
My foreign correspondents have made, and communicated to me, an important
improvement in the manufacture of sulphuric anhydride by the contact-process
which consists in subjecting the gases to be treated to a preliminary purification.
The usual sulphide ores contain various impurities and many of these, ou
roasting the ores, are liable to pass either free, or in combination, and either as
dust, mist, or gas, into the mixed gases containing the sulphur dioxide. Even
if practically pure sulphur be used as the source of SO, some sulphuric anhydride
is formed, and, since the air used in roasting contains moisture, the result is that
the SO, produced contains sulphuric acid which passes forward as a suspended
mist.
The effect of such impurities of the mixed gases is of various kinds, sulphuric
acid, for instance, from any source is, in some cases, liable to injure the lead
and iron parts of the apparatus and to cause difficulties in the moving parts of
the machinery. Further, and especially, my foregn correspondents have found
that the sulphuric acid mist is objectionable as carrying forward other impurities
into the contact-apparatus. Any admixture of sulphur vapours which have
escaped combustion act similarly and must therefore be excluded. Other im-
purities may affect the contact-substance mechanically, or chemically, either as
such, or after combining with the sulphur trioxide formed, or even, in some
cases, they may combine chemically with the contact-substance, and in every
case its efficiency is impaired.
The following bodies come principally into consideration as possible impurities
in the sulphurous gases; viz.:-iron, manganese, copper, nickel, arsenic, anti-
mony, phosphorus, mercury, lead, zinc, bismuth, thallium and selenium, or com-
pounds thereof.
My foreign correspondents have systematically examined the effect of these
bodies in the contact-process and have found that arsenic, phosphorus and mer-
cury, and their compounds are especially injurious, and small quantities of either
of these impurities may render comparatively large quantities of the contact-
substance almost entirely inert, and impair the efficiency of the process. They
have ascertained that all the said impurities, such as sulphuric acid, sulphur,
dust of any kind, and arsenic, phosphorus and mercury, and their compounds,
must be removed from the gases in order to allow of the continual use of the con-
tact-mass, and a continual, and nearly quantitative, conversion thereby of
sulphurous acid into sulphuric anhydride.
The perfect purification of the roaster gases is very difficult and is one of the
principal reasons that the direct production of sulphuric anhydride from the said
gases has not hitherto replaced the chamber-process.
My foreign correspondents have devised a new process which allows of the
certain and perfect removal of the said impurities from the roaster gases. This
process discards the idea of immediately passing into the contact mass the rela-
tively dry and hot roaster gases (from the hearths, or burners, where the sulphide
ore is roasted, or burnt) after freeing them from suspended impurities, as far as
could be done by deposit in a flue, and provides a new and particular purification,
which, preferably, consists in a special treatment whilst hot with a jet of steam.

page_text: or air, or other gas, for the purpose of thoroughly mixing the gases (if steam be
not used to effect the mixing, a sufficient amount of steam must be introduced
to dilute the condensed sulphuric acid) a subsequent gradual cooling and then
repeated washing with water or sulphuric acid whilst using special tests, as herein-
after set forth, and, finally, drying the gases with sulphuric acid, all as hereinafter
more. fully described.. The gases, before entering the contact-apparatus, must
satisfy two tests, viz.:-an optical test to shew freedom from dust and mist, and
a chemical analytical test to shew freedom from, arsenic, phosphorus and mer-
cury, or their compounds.
To achieve this purity, a jet of steam is blown into the dust flue, which the hot
roaster gases enter from the pyrites burner. Amongst other effects the steam
mixes the gases thoroughly, and brings about a most perfect combustion of any
sulphur, or other combustible matter. This mixing and promoted combustion
can also be effected by means of a jet or air; or other gas, (for example, by means
of a portion of the gases to be treated) but then it is recommended that the steam
be blown in later. The introduction of steam has several further most important
effects.
My foreign correspondents have found that it is advantageous for the purpose
of effecting the easy and complete washing of the roaster gases, especially gases
from pyrites burners, containing much arsenic, to gradually cool the gases in
suitable cooling apparatus. All such gases contain concentrated sulphuric acid
vapours which are condensed when cooling, and the metal of the cooling apparatus
(usually consisting of iron, or lead,) is liable to be strongly attacked and rapidly
deteriorated, or destroyed. If, however, sufficient steam be blown into the gases
to bring down the concentration of the condensed sulphuric acid to a strength
of 10 to 40 degrees Beaumé, this difficulty is overcome. Of course where the
cooling apparatus comes into contact with condensed dilute sulphuric acid it
must be made of lead and not of iron.
A further important effect of blowing in steam is that the coolers do not become
incrusted with solid impurities in combination with sulphuric acid, which form
when the gases are cooled and steam is not used, which impurities stop up the
pipes and are difficult to remove.
By blowing steam into the hot gases this incrustation is prevented because the
said impurities form a mud which is easily removed. The addition of steam
also renders it possible to more easily wash the gases subsequently, and enables
the desired purity to be attained.
The action of the steam serves also to prevent the formation of volatile hydrogen
compounds of the impurities, especially of arsenic and phosphorus, or their com-
pounds. These would otherwise be formed by the action of the concentrated
sulphuric acid on the metal of the coolers and the impurities, and could be re-
moved only with great difficulty: and therefore would pass into the contact-
mass and eventually render it inactive.
The gases pass through a flue, which may be of iron, or brickwork, in which
they cool somewhat, and thence into a system of lead pipes arranged to act as a
cooler. Here they are cooled down to about 100 degrees Centigrade, or lower.
They are then passed into washing towers, or other washing apparatus, and washed
with water, or dilute, or concentrated, sulphuric acid. To the wash water there
may be added sodium bisulphite, or similar chemicals, to increase its cleansing
action. This washing is best effected in a system of washing bottles, or other
washing apparatus, set up in series, and pumping machinery is used to move
the gases relatively to the washing liquid. If water be the washing liquid em-
ployed it soon becomes converted into dilute sulphuric acid: the use of con-
centrated sulphuric acid is not recommended in ordinary cases because it requires
considerable expenditure of power to move it in the washing apparatus and
because the said apparatus is liable to become incrusted. The washing appparatus
can be constructed on the principle of the ordinary washing bottles, so that the
gases have to overcome the pressure of the liquids in them, and consequently

page_text: the liquid which is in constant movement becomes intimately mixed with the
gases. Or the gases may be scrubbed by the energetic movement of the washing
liquids through the gases. No material should be used in the washing apparatus
which, in the presence of the acid liquid, might give rise to the production of
noxious gases, for instance, arseniuretted hydrogen. The sulphuric acid, and
any sublimates and flue dust, are all precipitated in the cooler, or in the washing
apparatus and the liquid running from these is collected in lead boxes and allowed
to settle. The sulphuric acid obtained in this way can be poured off from the
sediment and be used as diluted sulphuric acid, or it can be converted into con-
centrated sulphuric acid by the sulphuric anhydride obtained by the contact-pro-
cess. If not already washed with concentrated sulphuric acid, the gases are
finally thoroughly dried by means of such concentrated acid, or other drying
agent.
The extent to which the washing must be carried will depend on the nature and
amount of the impurities to be eliminated and can be determined by tests as
aforesaid.
These tests are effected as follows:-
In the first place the apparatus is so arranged that a layer of the gas, some yards
long, is illuminated by means of a lamp at one end, whilst, from the other end,
the operator can look through the entire layer of gas towards the light. It is
necessary that no dusty, or misty, admixture shall be observable. If this optical
test be permanently successful, it is only necessary to examine the gases for such
impurities as would not be shewn by the optical test. Amongst these impurities
there is, in particular, arseniuretted hydrogen, and possibly also phosphoretted
hydrogen and mercury vapours. In order to detect these, a portion of the stream
of the purified gas is passed for a long period, say 24 hours, through a wash-bottle
containing distilled water, and the water so treated is then examined according
to any chemical analytical method. In this way any considerable traces of the
dangerous impurities can be discovered.
The above description of the process applies most closely to the purification
of the gases derived from the furnaces in which pyrites are burnt, or roasted, but
gases containing sulphur dioxide from other sources can be purified in a similar
way. In practical working it is easy and best to effect both the above-described
tests in the manner described, but, of course, if the chemical test alone constantly
indicated the freedom of the gases from all traces of the noxious impurities, the
optical test could be dispensed with.
Having now particularly described and ascertained the nature of the said in-
vention and in what manner the same is to be performed I declare that what I
claim is
1. The improvement in the manufacture of sulphuric anhydride consisting in
purifying gases containing sulphur dioxide, prior to their use in the contact-
process, by systematically removing the impurities herein before set forth, whilst
preventing the formation of other noxious bodies, until the tests herein before
described are satisfied; all substantially as hereinbefore described.
2. The improvement in the manufacture of sulphuric anhydride consisting in
purifying gases containing sulphur dioxide by introducing steam into the hot
gases, cooling the gases, and then thoroughly washing the gases, whilst preventing
the formation of other noxious bodies, until the tests aforesaid are satisfied; all
substantially as hereinbefore described.
Dated the 20th day of V. 1800
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.