Improvements in the Manufacture of Sulphuric Anhydride.
Year: 1898

page_text: Date of Application, 21st July, 1898
Complete Specification Left, 20th May, 1899-Accepted, 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:-
A process of preparing sulphuric anhydride by the combination of sulphur
dioxide and oxygen from the air, or other source, by passing such a mixture of
gases over platinized asbestos, or other contact substance, at a high temperature,
has long been known and practiced.
My foreign correspondents have invented certain improvements in this process
which are the result of prolonged research and experiment, and their combined
effect involves an entire revolution in the manufacture of sulphuric acid and
sulphuric anhydride and is such as to render the conversion of sulphur dioxide
into sulphuric anhydride practically complete, the production of sulphuric
anhydride being effected so economically that, by the aid of this invention, it is
possible not merely to produce sulphuric anhydride itself, and all the grades of
fuming sulphuric acid advantageously, but even ordinary concentrated sulphuric
acid, or chamber acid, can according to this invention be as cheaply produced as
by the well known chamber process. Acid weaker than, and up to 50° Bé. (that
is containing about 63 per cent. H.SO) can according to this invention be
prepared at least as cheaply as by means of the chamber process, and all stronger
acids are produced in accordance with this invention more cheaply, the advantage
being greater the stronger the acid.
The effects according to this invention have not been achieved by a single
improvement but result from a series of investigations into every part of the
process, and in order to put every manufacturer of sulphuric acid in a position to
treat his sulphur dioxide, from whatever source obtained, successfully with the
best effect by the contact process, the improvements of my foreign correspondents
should be adopted in every part of the process.
The manufacture may be divided into three parts, viz. :-
First The preliminary treatment of the mixed gases to be operated on.
Second The regulation of the conditions, particularly as to temperature, during
the combination.
Third The disposition, or arrangement, of the contact substance to avoid undue
rise of pressure.
I.
The usual sulphide ores, contain various impurities, and many of these on
roasting 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 practically pure sulphur be used as the source of SO₂, some sulphuric anhydride
2
is formal and cines the air used in roasting contains insistum the result is

page_text: that the SO, produced, contains sulphuric acid which passes forward as a sus-
pended 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
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, thallium, 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 mercury
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 ascer-
tained 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 principal 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 relatively 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
purification, which preferably consists in a special treatment whilst hot with a
jet of steam, 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 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 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 cooling
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 concen-
tration of the condensed sulphuric acid to a strength of 10 to 40 degrees Beaumé,
this difficulty is overcome.

page_text: 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
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 sul-
phuric acid in 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° 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 impurity to be eliminated
and can be determined by the aforesaid tests.
Only gases satisfying the above tests of purity, either obtained as above set
forth, or otherwise, can be used in the contact apparatus in the next stage of
the apparatus if this is to retain its efficiency any length of time.
II.
It is well known that when sulphur dioxide is combined with oxygen to form
sulphuric anhydride, a considerable amount of heat is evolved. This is stated
in literature to be in accordance with the equation SO, + 0 = SO, + 32, 2 Cal.
(see Hess Poggendorff's Annalen Vol. 56 p. 471, 1842-Thomsen, (Poggendorff's
Annalen Vol. 150, p. 32, 1873) Ostwald, Allgem Chemie Vol. II. pp. 123 and 124.
The reaction between SO2 and 0 only takes place at an elevated temperature, so
that it is necessary to submit the gases either separately, or in admixture, to a
preliminary heating. During the reaction the heat of chemical union becomes
added to that applied and thus the temperature may rise to an enormous degree,
even to bright red heat, according to the richness of the gas mixture in sulphur
dioxide, or the strength of the current of the gases.
My foreign correspondents have found that this accumulation of heat and rise
of temperature is very injurious when practically manufacturing sulphuric
anhydride. The injurious effects are of various kinds. For instance, the iron parts
of the apparatus are quickly destroyed by oxydation, the action of the contact
substance employed for promoting, or inducing the reaction is weakened, the
efficiency of the apparatus is diminished and the course of the reaction, which
should be approximately quantitative, becomes essentially less perfect.
The overheating is especially injurious if the arrangement of the apparatus
be such that the mixture of gases containing the SO, leaves the contact mass at
the point where it has the highest temperature.
My foreign correspondents have discovered that this deterioration in the course
of the reaction is due to the fact that the reconversion of SO into SO, + 0
takes place at temperatures which are but little higher than those at which the
formation of SO, proceeds most favourably whilst at the same time, the union of SO₂
and takes place very much more rapidly in the first portions of the contact
mass than in those following, so that the whole apparatus, from the beginning
attains too high a temperature.
The reversal of the reaction increases in amount the more the contact apparatus

page_text: becomes overheated by the aforementioned excess of heat, that is accordingly as
more gases or more concentrated gas mixtures, pass through the contact apparatus.
Consequently it is impossible to effect any satisfactory union of sulphur dioxide
and oxygen; or some of the sulphuric anhydride formed is decomposed in the
reverse direction, the gases leaving the apparatus therefore contain unchanged
sulphur dioxide which can only be used in other ways, if at all, such as for the
manufacture of sulphuric acid according to the chamber process, or the manu-
facture of bisulphite or the like.
My foreign correspondents have invented a process which avoid the aforesaid
disadvantages.
The process according to this invention consists in cooling the contact mass
by suitably regulated external cooling whereby the injurious excess of heat is
withdrawn. In this way a condition of temperature in the contact apparatus
is attained which is within wide limits independent of the quantity and con-
centration of the gas treated, and which includes the most favourable temperature
for the formation of SO. By the process according to this invention it is possible
to obtain practically quantitative yield of sulphuric anhydride, to a degree
comparable with the action in the sulphuric acid chambers, further the contact
mass and the apparatus generally are more durable owing to the lower temperature
to which they are subjected and their efficiency is largely increased.
The manner of practising this part of the process according to this invention
can be varied in many respects, in particular, regard must be had to the con-
centration of the gases to be treated. The cooling of the contact chamber so as
to produce the most favourable range of temperature therein is generally effected
by means of a current of gas. Both the rate of flow and the temperature of
this current are kept under control. My foreign correspondents use, for instance,
air in this way, or the actual gases which are to be treated. But the cooling can
be effected in other ways, for instance in liquid baths, especially molten metal
baths, whose temperatures are under control.
When the gases to he treated are themselves used for cooling the contact
apparatus, a part, or the whole, of the current of gases so to be treated is caused
to pass through the space exterior to the chamber containing the contact mass so
as to withdraw from the latter the excess of heat. The gases coming from the
cooling chamber are then brought to the temperature best suited for the most
favorable course of the reaction. For this purpose, in some cases, a further
heating, or a cooling, operation is necessary; this depends largely upon the con-
centration of the gases.
I will now describe apparatus in various forms suitable to the purposes of this
invention.
In a brickwork structure or an iron tube is fixed a second tube consisting of
two parts which have different functions and may differ from one another in
length and diameter and either part or both parts can be replaced by a plurality
of tubes. The one part of the said tube is occupied by the contact-substance,
and this is cooled by cold air entering at the lower end of the outer structure or
tube.
In the other part of the aforesaid inner tube the gases containing the sulphur
dioxide which enter at the upper end thereof are heated to the temperature
necessary for the reaction.
When commencing the operation the whole apparatus is first raised to the
temperature necessary for the reaction by heating by means of gas flames or
otherwise. Then when concentrated gases are used after the reaction has once
commenced further heating is unnecessary, because the air cooling the contact-
mass absorbs heat and transfers sufficient to the portion of the tube containing the
sulphur dioxide gases to prevent a change of position in the reaction zone, or
the entire cessation of the reaction. The stream of air can be regulated by
means of adjustable up draught openings in such a way that the contact-mass
is constantly maintained at the most favourable temperature for the reaction.

page_text: When the gases contain but little sulphur dioxide the air, which is somewhat
heated by its cooling action, is further heated by means such that the gases
flowing in through the part of the tube therefor receive a greater increment of
heat. When the gases are still poorer in SO, it may be necessary to continually
heat to some extent by means of the gas flames or otherwise the current of air
flowing into the outer structure or tube.
The gases containing the sulphuric anhydride issuing from the contact mass
leave the apparatus by a pipe and are worked up in any suitable way.
When the apparatus is made up of a plurality of contact-tubes, they can be
put in connection with one another by means of a tube plate and cover above
and below.
Another form of the apparatus is as follows;-
-
Within brickwork a tube is fixed which contains an inner tube passing
through tube plates above and below which close the space between the outer and
inner tubes. The apparatus is brought to reaction temperature by any source of
heat such for instance as gas flames between the brickwork and the outer tube,
the gases from which flames can pass away through flues in the brickwork.
Then the gases to be treated are passed through entrance passages into the space
between the inner and outer tubes say at bottom or midway or both.
The temperature of this can be further regulated by a heating apparatus through
which the gases pass on their way to the said space. The said gases cool the
contact-mass in the inner tube and pass into the contact mass in the inner tube
and out by the lower end of the said tube. The temperature of the gases can
also be regulated by passing through a temperature regulator on their way to
the inner tube.
This apparatus also can have a plurality of tubes and my foreign correspondents
have found that in large apparatus containing many tubes it is advisable that
the current of gases in the outer tube or chamber be thoroughly subdivided.
This can be effected by gas chambers surrounding the said outer tube or chamber
openings serving to introduce the gases into the said outer tube or chamber around
its entire circumference, and further by the use of tubes passing diametrically
through the said outer tube or chamber and furnished with holes at the sides
varying in size in proportion to the part of the apparatus at which they occur so
that the gases are divided uniformly in the interior of the said tube or chamber.
In order that the cooling gases may retain the direction of their current and
pass as closely as possible in contact with the contact-mass, there are inserted at
intervals, which must not be too great, a number of partitions extending across
the said tube or chamber sufficient space being left for the gases to pass through
close to the walls of the inner tubes.
It is desirable to thoroughly mix the gases before their entrance into the con-
tact mass in order to equalize their temperature. This can be effected by a mixing
apparatus fitted in the cover. The strength of the current and the temperature
of the cooling gases is regulated upon the basis of the readings of the thermometers
in the various parts of the apparatus, and to such an extent that analyses of
the gases entering and leaving the apparatus shew that the most favourable
practical result is being obtained.
In this apparatus also air, or other gas, can be used for cooling, and be passed
in by a ventilator, or fan it of course not being permitted to enter the inner tube
or tubes.
The heat of the air or gas issuing from the apparatus can be utilized in any
way desired for instance by transferring its heat in an interchanger to the cold
gases to be treated.
The following is an arrangement of the apparatus which is particularly suited
for use when treating rich gas mixtures. The entering gas current is lead to
the part surrounding the hottest part of the contact mass in the inner tube so
that the relatively coldest gas acts upon the hottest part of the contact mass and

page_text: energetically cools this. The cooling gas current can leave the cooling chamber
through parts arranged similarly to those herein before described for admittance
in the preceding example and can then be conducted either directly to the inner
tube, or tubes, or through a temperature regulating apparatus. Also a portion
of the gas can be led at the same time directly into the cover and thence into
the inner tubes.
Here also the regulation of the gas currents is based upon gas-analyses and
the readings of thermometers, and here also air, or other gas instead of the gases
to be treated can be used for cooling. This is especially desirable when rich gases
are to be treated for their volume and quantity are comparatively small, and
might not be sufficient to cool efficiently. For this purpose the cooling current
of air or gas is created by a fan, or ventilator, and passed to the part surrounding
the hottest part of the contact mass and streams through the surrounding tube
and cools the contact-mass and then leaves the apparatus. The heat contained
therein can be used in any way desired, for instance for heating up the entering
gases to be treated so that the reaction zone in the inner tube does not change
its position.
Or the apparatus may be arranged as follows:-In a brickwork passage or
tube a tube or several tubes closed at bottom is or are suspended from a plate
which closes it or them above and into this tube or each of these tubes projects
a tube fitted into the said plate. When a plurality of tubes is used the inner
and outer tubes are separated from one another by a box-like chamber the
interior of which serves for the subdivision of the entering gases. The gases
stream through the space between the inner and outer tubes and cool the contact
mass in the inner tube or tubes. They can be heated further by the gas flames
below the lower ends of the outer tubes or otherwise, or be cooled for example by
a regulated stream of air. The treated gases leave the apparatus through a
cover and outlet over the upper end of the inner tube or tubes.
Having described various forms of the apparatus and ways of carrying out the
process, I will now describe what I believe to be the best manner of proceeding in-
order to obtain as favourable a result.as possible.
Taking the case of a mixture of gases, such as frequently occurs, containing
about twelve per cent. by volume, of sulphur dioxide and a similar quantity of
oxygen and an apparatus with a plurality of tubes as described under the preceding
second example of the apparatus.
The apparatus is heated first say by means of gas flames until a thermometer
in the upper cover shews a temperature of about 300° Centigrade. The entire
stream of gases is then passed into the apparatus. The gases entering and leaving
the apparatus are analysed to determine their contents of sulphur dioxide and, in
this way, the practical effect is determined. The temperature in the interior
of the contact apparatus is regulated on the basis of the readings of the ther-
mometers in the upper and lower covers by regulating the intensity of current
of the cooling stream of gases by means of valves, and the-temperature if necessary,
by the aid of the heater, that the most favourable conversion of SO, into SO, is
achieved.
In this example this object is achieved by passing about two-thirds of the
entire gas-current in at the entrance to the chamber surrounding the inner tubes
and one third direct into the top cover, so that the temperature therein (which
becomes uniform owing to the action of the mixing-chamber in the said cover)
is about 380° Centigrade whilst the thermometer in the lower cover indicates
about 234° Centigrade. In this actual case taken from experimental practice on
the factory scale my foreign correspondents effected a conversion of from 96 to 98
per cent. of that theoretically possible, whilst making from 40 to 50 kilograms
of SO, per tube in twenty-four hours. The conversion can be increased to 99 per
cent. if the gas be permitted to remain longer in the presence of the contact-
substance.

page_text: III.
In the chamber-process for the manufacture of sulphuric acid, the gases under
treatment are largely, or entirely, kept in motion in the desired direction by
the very economical means of the draught of a high chimney. If it be desired
to prepare the acid of the strength of ordinary unconcentrated chamber acid by
means of the contact process, a similar regard for economy in details must be
observed and everything avoided causing additional expense.
If, in this process, platinised asbestos, or a similar loose contact mass, be used,
and merely packed into plain tubes, then, on forcing through the mixed gases,
the contact mass is so pressed together as to require considerable pumping pres-
sure to force the gases through the mass. Further it has been held that under
pressure the gases combine more efficiently and patents have been granted for
operating in this way. My foreign correspondents have found that the advantage,
if any, of working under pressure is more than counterbalanced by the cost of
producing the pressure. The process is therefore preferably conducted at about
atmospheric pressure and my foreign correspondents have devised means whereby
the pressure to be overcome in contact tubes, and consequently the cost of pump-
ing, or forcing, the mixed gases through the contact mass is reduced to a minimum.
For this purpose the tubes containing the contact mass are divided into a
number of compartments, by the insertion of a number of perforated plates, or
sieves, and upon each plate or sieve sufficient contact-mass only; is placed to cover
the perforations or reticulations and the periphery of the plates at the wall of
the tube. The principle is that the pressure on one layer of the contact mass,
shall not be transmitted to the next layer so that the layers can be pressed together,
and further the arrangement must be such that the gases cannot pass any plate
except through the contact-mass. Thus an iron-rod may be fixed at the bottom
of the contact tube passing up its central line, over this a narrow tube may be
placed extending up the rod to the height in the interior of the contact-tube, where
the contact-mass begins.
The first perforated or reticulated plate is then passed down the contact-tube,
over the rod, and is held in position by the narrow tube. Upon this sufficient
contact mass is placed to cover the perforation or reticulations and periphery as
aforesaid. Upon this is placed a bead, or short piece of tube, and upon that the
next perforated, or reticulated, plate, and so on. The length of the bead, or piece
of tube, regulates the distance apart of the layers of the contact-mass which can
thus be varied at will. In this way the contact mass presses against the plates,
and this pressure is transferred to the beads and tube, so that the contact mass
as a whole is greatly relieved of pressure and a more satisfactory result achieved.
Of course other means can be adopted, provided that the principles above stated
be observed, for example the plates or sieves can be supported by tripods instead
of by the central rod and tubes, or beads.
Dated this 21st day of July 1900
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-

page_text: 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 follow-
ing statement;
-
A process of preparing sulphuric anhydride by the combination of sulphur
dioxide and oxygen from the air, or other source, by passing such a mixture of
gases over platinized asbestos, or other contact-substance, at a high temperature,
has long been known and practised.
My foreign correspondents have made certain improvements in this process
which are the result of prolonged research and experiment, and their combined
effect involves an entire revolution in the manufacture of sulphuric acid and
sulphuric anhydride, and is such as to render the conversion of sulphur dioxide
into sulphuric anhydride practically complete, the production of sulphuric
anhydride being effected so economically that, by the aid of this invention, it is
possible not merely to produce sulphuric anhydride itself, and all the grades of
fuming sulphuric acid advantageously, but even ordinary concentrated sulphuric
acid, or chamber acid, can, according to this invention, be as cheaply produced as
by the well-known chamber process. Acid weaker than, and up to, 50° Bé. (that
is, containing about 63 per cent. H₂SO) can, according to this invention, be
prepared at least as cheaply as by means of the chamber process, and all stronger
acids are produced in accordance with this invention more cheaply the advantages
being greater the stronger the acid.
The effects, according to this invention, have not been achieved by a single
improvement, but result from a series of investigations into every part of the
process; and, in order to treat sulphur dioxide, from whatever source obtained,
successfully and with the best effect by the contact process, for the production of
sulphuric anhydride, the improvements of my foreign correspondents should be
adopted in every part of the process.
The manufacture may be divided into three parts, viz. :—
First. The preliminary treatment of the mixed gases to be operated on.
Second-The regulation of the conditions, particularly as to temperature,
during the combination.
Third. The disposition, or arrangement, of the contact-substance to avoid undue
rise of pressure.
I.
The usual sulphide ores contain various impurities, and many of these, on
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 sus-
pended 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
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
affect the contact-substance mechanically, or chemically, either as such, or after
chemically combining with the sulphur trioxide, 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, antimony,

page_text: hosphorus, mercury, lead, zinc, bismuth, thallium, 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 mercury
and their compounds are especially injurious and small quantities of any one of
these impurities may render comparatively large quantities of the contact-substance
almost entirely inert and impair the efficiency of the process. They have ascer-
tained 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 roaster 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 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 relatively dry and hot roaster gases, from the hearths, or burners, where the
sulphide ore is roasted, or burnt, after having freed them from dust 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, 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, while using special tests, as
hereinafter set forth, and, finally, drying the gases by 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
mercury, 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 burners. Amongst other effects the steam
mixes the gases thoroughly, and brings about a more perfect combustion of any
sulphur, or other combustible matter. This mixing and promoted combustion
can also be effected by means of a jet of 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 the 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

page_text: 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 removed
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°
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 employed it soon becomes converted into dilute sulphuric acid: the use
of concentrated 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
apparatus 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 conse-
quently 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 wash-
ing 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 pro-
duction of noxious gases, for instance arsenuretted 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 concentrated sulphuric acid by the sulphuric anhydride obtained
by the contact process. 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 the 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 phos-
phoretted 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.

page_text: sulphuric anhydride, a considerable amount of heat is evolved. This is stated
in literature to be in accordance with the equation SO, +0=SO, +32, 2 Cal. (see
Hess Poggendorff's Annalen Vol. 56, page 471, 1842; Thomsen, Ann. ch. ph. (4)
vol. 30, p. 442, 1873; Ostwald, Allgemeine Chemie, Vol. II. pp. 128 & 124). The
reaction between SO, and O only takes place at an elevated temperature, so that
it is necessary to submit the gases, either separately, or in admixture, to a pre-
liminary heating. During the reaction the heat of chemical union becomes added
to that applied, and thus the temperature may rise to an enormous degree, even
to bright red heat, according to the richness of the gas mixture in sulphur dioxide,
or the strength of the current of the gases.
My foreign correspondents have found that this accumulation of heat and rise
of temperature is very injurious when practically manufacturing sulphuric
anhydride. The injurious effects are of various kinds. For instance, the iron parts
of the apparatus are quickly destroyed by oxidation, the action of the contact-
substance employed for promoting, or inducing, the reaction is weakened, the
efficiency of the apparatus is diminished, and the course of the reaction, which
should be approximately quantitative, becomes essentially less perfect.
The overheating is especially injurious if the arrangement of the apparatus be
such that the mixture of gases containing the SO, leaves the contact-mass at the
point where it has the highest temperature.
My foreign correspondents have discovered that this deterioration in the course
of the reaction is due to the fact that the re-conversion of SO, into SO, +0
takes place at temperatures which are but little higher than those at which the
formation of SO, proceeds most favourably, whilst, at the same time, the union
of SO, and O takes place very much more rapidly in the first portions of the con-
tact-mass than in those following, so that the whole apparatus, from the beginning,
attains too high a temperature.
The reversal of the reaction increases in amount the more the contact-apparatus
becomes over-heated by the aforementioned excess of heat, that is, accordingly as
more gases, or more concentrated gas mixtures pass through the contact-apparatus.
Consequently it is impossible to effect any satisfactory union of sulphur dioxide
and oxygen, or some of the sulphuric anhydride formed is decomposed in the
reverse direction. The gases leaving the apparatus therefore contain unchanged
sulphur dioxide which can only be used in other ways, if at all, such as for the
manufacture of sulphuric acid according to the chamber process, or the manu-
facture of bisulphite, or the like.
My foreign correspondents have devised a process, and apparatus in which
the said process can be carried out, by which the aforesaid disadvantages are
avoided. In this process platinised asbestos is the contact-substance recommended
for use.
It can, for instance, be prepared as described in the Specification of
Winckler's German Patent No. 4566. See also Lunge's Sulphuric Acid &
Alkali," 2nd Edit. Vol. 1, p. 863 and Dammer, Chemische Technologie, vol. 1,
p. 189. The process, according to this invention, consists in cooling the contact-
mass by suitably regulated external cooling, whereby the injurious excess of heat
is withdrawn. In this way a condition of temperature in the contact-apparatus
is attained which is, within wide limits, independant of the quantity and concen-
tration of the gas treated, and which includes the most favourable temperature
for the formation of SO. By the process according to this invention it is
possible to obtain a practically quantitative yield of sulphuric anhydride, to a
degree comparable with the action in the sulphuric acid chambers; further, the
contact mass, and the apparatus generally, are more durable, owing to the lower
temperature to which they are subjected, and their efficiency is largely increased.
The manner of practising this part of the process according to this invention
can be varied in many respects, in particular, regard must be had to the con-
centration of the gases to be treated. The cooling of the contact chamber so as
to produce the most favourable range of temperature therein is generally effected
by means of a current of gas. Both the rate of flow and the temperature of

page_text: this current are kept under control. My foreign correspondents use, for instance,
air in this way, or the actual gases which are to be treated. But the cooling can
be effected in other ways, for instance in liquid baths, especially molten metal
baths, whose temperatures are under control.
"
Fr.
When the gases to be treated are themselves used for cooling the contact
apparatus, a part, or the whole, of the current of gases so to be treated is caused
to pass through the space exterior to the chamber containing the contact-mass
so as to withdraw from the latter the excess of heat. The gases coming from
the cooling chamber are then brought to the temperature best suited for the
most favourable course of the reaction. For this purpose, in some cases, a further
heating, or a cooling, operation is necessary; this depends largely upon the con-
centration of the gases.
'
I will now describe with reference to the accompanying drawings, apparatus, in
various forms, suitable to the purposes of this invention. I refer first to Figure I
which is a vertical section.
In a brickwork structure, or an iron tube M, is fixed a tube R, leaving a
space between the outside of the tube R and the inside of the brickwork or
tube M. The two portions a and b of the tube R have different functions, and
may differ from one another in length and diameter, and either part, or both
parts, can be replaced by a plurality of tubes. The one part b, of the said tube R,
is occupied by the contact-substance, (indicated by the crossed lines) and this
is cooled by cold air entering by the inlets n at the lower end of the outer structure,
or tube. In the other part, a, of the aforesaid inner tube, the gases, containing
the sulphur dioxide which enter at the upper end thereof, are heated to the
temperature necessary for the reaction.
When commencing the operation the whole apparatus is first raised to the
temperature necessary for the reaction, by heating by means of gas flames h, or
otherwise. Then, when concentrated gases are used, after the reaction has once
commenced, further heating is unnecessary, because the air cooling the contact-
mass absorbs-heat and transfers sufficient heat to the other portion a of the tube
containing the sulphur dioxide gases to be treated to prevent a change of position
in the reaction zone, or the entire cessation of the reaction. The stream of air
can be regulated by means of adjustable up-draught openings L, in such a way
that the contact-mass in the part is constantly maintained at the temperature
most favourable for the reaction When the gases contain but little sulphur
dioxide, the air, which is somewhat heated by its cooling action, is further heated
by means of the gas flames h¹ h', or in other manner, so that the gases flowing
in through the part a of the tube receive a greater increment of heat. When the
gases are still poorer in SO, it may be necessary to continually heat the current
of air flowing into the outer structure, or tube, to some extent, by means of the
gas flames at h, h, or otherwise.
The gases containing the sulphuric anhydride issuing from the contact-mass
in the part 6 leave the apparatus by a pipe c and can be worked up in any suitable
way.
Figure I shews in vertical section an arrangement wherein the apparatus is
made up of a plurality of contact-tubes R R put in communication with one
another by means of tube plates W, W, and covers D, D¹, above and below.
The parts which correspond with those shewn in Figure 1 are marked with the
same letters of reference.
Another form of the apparatus is illustrated in elevation, partly in section, in
Figure II.
Within the brickwork or tube M a tube S is fixed which contains an inner
tube R, passing through tube plates W and W above and below which close the
spaces between the said tubes.
The apparatus is brought to reaction temperature by any source of heat, such,
for instance, as gas flames at h between the brickwork or tube M and the tube S
the gases from which flames can pass away through flues at L. When the apparatus

page_text: is working the source of heat can usually be removed, and cold air be allowed
to circulate through the space between the brickwork, or tube, M, and the tube S
thus contributing to the cooling of the whole apparatus. Then the gases to be
treated are passed through entrance passages into the space between the tubes S
and R say at bottom E, or midway E, or both. The temperature of these can be
further regulated by a heating apparatus G through which the gases pass on their
way to the said space. The said gases cool the contact-mass in the inner tube R
and afterwards pass through A and F into the said contact-mass and out through
at the lower end of the said tube R. The temperature of the gases can also be
regulated by their passing through a temperature regulator H, on their way
from the space between the tubes S and R to the inner tube R by manipulating the
valves shewn for the purpose.
This apparatus also can have a plurality of tubes R R as illustrated in Figure II*
and my foreign correspondents have found that, in large apparatus containing many
tubes, it is advisable that the current of gases in the outer tube, or chamber, S, be
thoroughly subdivided. This can be effected by means of gas chambers A A¹ sur-
rounding the said outer tube, or chamber, S, the gases passing from the said
chambers A A¹ into the said outer tube, or chamber, S, through openings around
its circumference, or by means of tubes B B¹, passing diametrically through the
said outer tube, or chamber, S, and furnished with holes at the sides varying in
size in proportion to the part of the apparatus at which they occur, so that the
gases are divided and pass uniformly into the interior of the said tube or
chamber S.
In order that the cooling gases may retain the direction of their current and
pass as closely as possible in contact with the walls of the tubes R containing
the contact-mass, there are inserted, at intervals, which must not be too great, a
number of partitions C, C, extending across the said tube, or chamber, S, sufficient
space being left for the gases to pass through close to the walls of the inner
tubes R, R, as indicated by the small arrows.
It is desirable to thoroughly mix the gases before their entrance into the
contact-mass, in order to equalize their temperature. This can be effected by a
mixing apparatus N, fitted in the cover D, the gases passing up the passages 0, F,
and between the plates as shewn. The strength of the current and the temperature
of the cooling gases is regulated upon the basis of the readings of the thermometers
in the various parts of the apparatus and especially within the covers D and D',
and to such an extent that analyses of the gases, entering and leaving the
apparatus, shew that the most favourable practical result is being obtained.
Figure II illustrates a form of apparatus in which the gas distribution
chambers (corresponding to those marked A, A', in Figure II*) are extended to
form a jacket A, to the whole apparatus, thus utilising the radiant heat of the
apparatus to heat the cooling gases. The said jacket is shewn as being provided
with plates for giving a circuitous course to the gases.
In this apparatus also air, or other gas, can be used for cooling, and be passed
in by a fan, the said air, or gas, of course not being permitted to enter the inner
tube, or tubes, R. Thus in the form of apparatus shewn in the Figure II air
could be blown, by means of the fan Vu, in through the heater G, and out
through the interchanger H.
The heat of the air, or gas, issuing from the apparatus can be utilized in any
way for which such a source of heat is suitable, as, for instance, by transferring
its heat, in the said interchanger H, to the cold gases to be treated, and entering
through J.
Figures III and III* illustrate an arrangement of the apparatus which is
particularly suited for use when treating rich gas mixtures:-
The entering gas current is lead through E to the part surrounding the
hottest part of the contact-mass in the inner tube R so that the relatively
coldest gas acts upon the hottest part of the contact-mass and energetically cools
this. The cooling gas current can leave the cooling chamber S through pipes A, A¹, ·

page_text: arranged similarly to those shewn at E E for admittance in the preceding example,
and can then be conducted, either directly by the pipe O to the inner tube, or
tubes, or through a temperature regulating apparatus H by manipulating the
valves shewn. Or the gas can be led partly directly into the inner tube or
tubes R and partly through the regulating apparatus. J is a passage for gas
directly to the inner tubes R.
Here also the regulation of the gas currents is based upon gas analyses and the
readings of thermometers, and here also air, or other gas, instead of the gases to
be treated can be used for cooling. This is especially desirable when rich gases
are to be treated, because their volume and quantity are comparatively small and
might not be sufficient to cool efficiently. For this purpose the cooling current
of air, or gas, is created by a fan Vas shewn in Figure III" and passed through E
to the part surrounding the hottest part 1 of the contact-mass and streams through
the surrounding tube S and cools the contact-mass and then leaves the apparatus.
The heat contained therein can be used in any way desired, for instance, for
heating up the entering gases to be treated so that the reaction zone at P in the
inner tube R does not change its position.
Or the apparatus may be arranged as shewn in Figures IV and IVA.
In a brickwork passage, or tube, M, a tube, or several tubes, S, closed at bottom,
is, or are, suspended from a plate W, which closes it, or them above, as shewn in
Figure IV, and into this tube, or each of these tubes, projects a tube fitted into
the said plate. When a plurality of tubes is used the upper ends of the inner
tubes R extend above the upper ends of the outer tubes S and are surrounded by
a box-like chamber K the interior of which serves for the sub-division of the
entering gases. The gases entering at E stream through the space between the
tubes R and S, and cool the contact-mass in the inner tube, or tubes, R. They
can be further heated by the gas flames h below the lower ends of the tubes S
or otherwise, or be cooled, for example, by a regulated stream of air passing out
at L. The gases pass up through the contact-mass in the tube or tubes R and
the treated gases leave the apparatus through a cover D and outlet c over the upper
end of the said tube or tubes R.
Having described various forms of the apparatus and ways of carrying out the
process I will now describe what I believe to be the best manner of proceeding
in order to obtain as favourable a result as possible, taking the case of a mixture
of gases containing about twelve per cent. by volume, of sulphur dioxide, and a
similar quantity of oxygen, and an apparatus with a plurality of tubes as herein-
before described and illustrated by Figure II^.
The apparatus is heated first (say by means of gas flames or fire heat at h¹) until
a thermometer in the upper cover D indicates a temperature of about 300° Centi-
grade. Then the source of heat is removed, and the whole gas stream passed
into the apparatus at A. The temperature within the cover D first rises. When
it has reached a temperature favourable for the reaction the upper valve V¹ is
opened, so that a part of the gases enter directly through J. The gases entering
and leaving the apparatus are analysed to determine their contents of sulphur
dioxide and, in this way the practical effect is determined. The temperature in
the interior of the contact-apparatus is regulated on the basis of the readings of
the thermometers in the upper and lower covers D D¹ by regulating the intensity of
current of the cooling stream of gases by means of the valves V V1 and V
and the temperature, if necessary, by the aid of the heater G, so that the most
favourable conversion of SO, into SO, is achieved.
In this example this object is achieved by passing about two-thirds of the entire
gas-current in at the entrance A to the chamber S surrounding the inner tubes R
and one third directly into the top cover D, so that the temperature, which becomes
uniform owing to the action of the mixing chamber N, in the said cover, is about
380° Centigrade, whilst the thermometer in the lower cover D¹ indicates about
234° Centigrade. In this actual case, taken from experimental practice on the
factory scale by my foreign correspondents they have effected a conversion of from

page_text: to 95 per cent. Of that theoretically possible, whilst making from 40 to 50
kilograms of SO3 per tube in twenty-four hours. The conversion can be increased
to 99 per cent. if the gas be permitted to remain longer in the presence of the
contact-substance.
In the drawings accompanying this specification, and referring to this part of
the invention, the scale may be taken as being one-twentieth real size but, of
course, the size of the tubes and the relative sizes of the various parts can be
varied.
III.
In the chamber process for the manufacture of sulphuric acid, the gases under
treatment are largely, or entirely, kept in motion in the desired direction by
the very economical means of the draught of a high chimney. If it be desired
to prepare the acid of the strength of ordinary unconcentrated chamber acid by
means of the contact-process a similar regard for economy in details must be
observed and everything avoided causing additional expense.
If, in this process, platinised asbestos be used, and merely packed into plain
tubes, then on forcing the mixed gases through the contact-mass, it is so pressed
together as to require considerable pumping pressure to force the gases through
the mass.
Further it has been held that under pressure the gases combine more
efficiently and patents have been granted for operating in this way. My foreign
correspondents have found that the advantage, if any, of working under pressure,
is more than counter-balanced by the cost of producing the pressure. The process
is therefore preferably conducted at about atmospheric pressure and my foreign
correspondents have devised means whereby the pressure to be overcome in con-
tact tubes, and consequently the cost of pumping, or forcing, the mixed gases
through the contact-mass, is reduced to a minimum.
For this purpose and referring to Figures V and V the tubes R containing
the contact-mass are divided into a number of compartments, by the insertion of a
number of perforated plates, or sieves c, cell (shewn in plan above each figure) and
upon each plate, or sieve, only sufficient contact-mass is placed to cover the per-
forations, or reticulations, and the periphery of the plates at the wall of the tube.
The principle is that the pressure on one layer of the contact-mass shall not be
transmitted to the next layer, so as to press the layers together; and, further, the
arrangement must be such that the gases cannot pass any plate or sieve except
through the contact-mass. Thus an iron rod a may be fixed in the part ]) at
the bottom of the contact-tube R passing up its axis, and over this rod a a
short tube may be placed at the bottom of the rod and extending up it to where
the contact-mass begins in the interior of the contact-tube. The first per-
forated, or reticulated plate,
or sieve, C, is then passed down the
contact-tube, over the rod a, and is held in position by resting on
the tube b. Upon this sufficient contact-mass is placed to cover the per-
forations, or reticulations, and periphery, as aforesaid. Upon this is placed a
bead, or short piece of tube d, and upon this the next perforated, or reticulated
plate, or sieve, c, and so on with the tubes d d and plates cell cll and those
following. The length of the beads or pieces of tube (d) regulates the distance
apart of the layers of the contact-mass which can thus be varied at will. In this
way the contact-mass presses against the plates, or sieves, and this pressure is
transferred to the beads and tube, so that the contact-mass, as a whole, is greatly
relieved of pressure and a more satisfactory result is achieved.
This arrangement of the layers of contact-substance has the further advantage,
that the gas, after passing each layer, has an opportunity of mixing again, so that
the temperature of the gas, passing through the different parts of the layer of
contact-mass, becomes equalized by the mixing and the cooling effect hereinbefore
described and is rendered more effective.
Of course other means can be adopted instead of those given in the above
example, provided that the principle above stated be observed. For example, the

page_text: plates, or sieves, can be supported by tripods (d, di d¹¹) as shewn in Figure VA
instead of by the central rod and tubes as in Figure V.
It is essential that the methods adopted for preventing packing of the contact
substance and consequent increase in the pressure required for forcing the gas
through the apparatus must not be such as to prevent the. regulated..cooling
herein before described which is essential to the success of the process....
Having now particularly described and ascertained the nature of this
invention 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 by the con-
tact-process, consisting in first purifying the gases to be treated, until the tests
described are satisfied, then passing them into the apparatus containing the con-
tact-substance and removing from it, in a regulated way; the excess of heat due
to the reaction.
2. The improved process for the manufacture of sulphuric anhydride which
consists in first purifying the gases to be treated till the tests described are satisfied,
then passing the said gases through the contact-mass, whilst cooling the same in
the regulated manner described, the said contact-mass being arranged in layers
that cannot press upon one another and leave no path to the gases except through
the contact-mass; all substantially as hereinbefore described.
3. The improved process of manufacture of sulphuric anhydride which consists
in obtaining a substantially quantitative yield by the combination of :-
(a). The purification of the gases:
(b). The regulated temperature of the contact-mass.
4. In the process claimed in the third claim the arrangements of the contact-
mass so as to permit working at pressures differing but little from atmospheric
pressure, substantially as hereinbefore described.
Datta this zoth day
ΟΙ
GGOT ABLE
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C.,
Agents.
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C.,
Agents.