Method of Purifying Hydrochloric Acid.
Year: 1899

page_text: Method of Purifying Hydrochloric Acid.
I, SÉBASTIEN JULES BOULOUVARD, of 8, Rue de Falque, Marseilles, in the
French Republic, Engineer, do hereby declare the nature of this invention to
be as follows:-
"
This invention relates to a process for purifying hydrochloric acid gas.
Hydrochloric acid gas which, in its manufacture, is evolved from: the sodà
sulphate pans contains certain impurities such as sulphuric acid, iron chloride,
etc., which are suspended in the gas in the particular state known as vesicular."
The purifying process forming the subject of this invention consists in causing
the gas charged with its impurities to pass across a more or less thick layer or
bed of coarse sand or fine gravel for the purpose of restoring to the liquid state
the vapours of sulphuric acid and other impurities which are carried over in the
vesicular state by the Hydrochloric gas. The liquid thus condensed passes off
or csapes in a regular manner at the base of the filter whilst the hydrochloric
gas accompanied by a certain quantity of air and steam or vapour passes to the
ordinary condensing apparatus and affords a commercial product free from sul-
phuric acid and iron, or, at least, containing only very small traces of these. The
chloride of arsenic is also retained by the filter when the gaseous mixture con-
tains some of this latter. It is proper that the temperature of the gases shoull
be lower than the volatilising temperature of the products it is wished to
eliminate.
The filter should be constructed of materials not liable to be attacked by the
acids, and the sand should be free from dust or powder. It might be very fine
and would then be more efficacious but would also present too great a resistance
to the passage of the gases. The most suitable size is that which results from a
shifting between sieves or nets of 4 and of 10 millimetres mesh.
This apparatus needs no maintenance, and the sand can serve indefinitely to
being quite unable to be attacked. Numerous substances fulfil this requirement..
I may employ quartz, lava, sandstone, or grit, pumice stone etc. Coke is
is also suitable, but it is to be feared that its "life" would be shorter.
When the gases from the sulphate pans are utilised directly for the pro-
duction of chlorine by the Deacon process it is advantageous to free them of the
sulphuric acid which they contain, before sending them to the decomposer.
In this case the filtration is necessary itself and allows gases from the muffles
as well as from the pans to be employed.
A suitable form of apparatus is the following.
The walls are formed of slabs of lava, of stone or other suitable material which
cannot be attacked, fitted together with indiarubber joints as employed in the
construction of chlorine tanks or wells used in the Weldon process. At the
lower portion is a grid or grating composed of transverse bars constructed of
the same stone or other material as the walls, and upon this grating are placed
several rows of silicious flints or large pebbles or of broken coke, the size of

page_text: which gets smaller towards the upper strata, i.e. the heavier or coarse lumps
are towards the bottom. The filter is afterwards filled with the sand previously
mentioned.
The gases arrive by an inlet pipe placed at the upper portion of the filter
above the sand, and pass out by a discharge pipe placed underneath the grid
or grating and above the level of a recessed portion in the base of the apparatus.
As to the condensed liquid it escapes by a small pipe supplied from this lowermost
recessed or shallowing portion.
The quantity of sand should be proportioned to the volume of gas to be puri-
fied and to the degree of purity which it is wished to obtain, but its thickness
is normally not to exceed fifty centimetres (almost nineteen and three-quarter
inches). However when I arrange for or am favoured with a good draught
or when I am able to place a mechanical Blower in some convenient portion of
the apparatus as is in the case in the Deacon process, it is preferable to make
use of a thicker bed of sand.
The construction of the filter is then much less costly. In reality a filter
having a layer of sand two metres thick can do four times as much work as a
filter which is of the same surface area but only fifty centimetres thick.
This invention, as before stated, consists essentially in causing hydrochloric
acid gas, whatever be its source of production and its destination, to pass across
a bed or layer of sand or other suitable divided material, for the purpose of
separating the condensable impurities, such as sulphuric acid, iron chloride etc.,
which have been carried over by this gas.
I, SÉBASTIEN JULES BOULOUVARD, of 8, Rue de Faique, Marseilles, in the
French Republic, Engineer, do hereby declare the nature of this invention 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 a process for purifying hydrochloric acid gas in such
a manner as to free the same from sulphuric acid and iron.
Hydrochloric acid gas which in its manufacture, is evolved from the soda
sulphate pans and more especially from muffle-furnaces, contains certain im-
purities such as sulphuric acid, iron chloride, etc., which are suspended in the
gas in the particular state known as "vesicular."
The purifying process forming the subject of this invention consists in causing
the gas charged with its impurities to pass across a more or less thick layer or
bed of coarse sand or fine gravel for the purpose of restoring to the liquid state
the vapours of sulphuric acid and other impurities which are carried over in the
vesicular state by the hydrochloric gas. The liquid thus condensed passes off
or escapes in a regular manner at the base of the filter whilst the hydrochloric
gas accompanied by a certain quantity of air and steam or vapour passes to the
ordinary condensing apparatus and affords a commercial product free from sul-
phuric acid and iron, or at least containing only very small traces of these. It
is convenient to place the filter as near as possible to the pans in order to avoid

page_text: the cooling of the gas, and, consequently, the condensation of a large proportion
of impure hydrochloric acid before reaching the filter.
The filter should be constructed of materials not liable to be attacked by the
acids, and the sand should be free from dust or powder. It might be very fine
and would then be more efficacious but would in such case present too great a
resistance to the passage of the gases. The most suitable size is that which
results from a sifting between wire gauze, netting or the like of 4 and of 10
millimetres mesh.
This apparatus needs no maintenance, and the sand can serve indefinitely
being quite unable to be attacked. Numerous substances fulfil this requirement.
When the gases from the sulphate pans or furnaces are utilised directly for
the production of chlorine by the Deacon process, it is advantageous to free
them of the sulphuric acid which they contain, before sending them to the
decomposer. In this case filtration is necessary and allows gases from the
muffles as well as from the pans to be employed.
They may also be freed from sulphurous acid which they contain, by mixing
them, "before their entrance into the filter, with a small quantity of the gas
coming from the decomposer. This gas contains chlorine which transforms the
sulphurous acid which may be condensed by the filter at the same time as that
which existed previously. The annexed drawing shows one of the arrangements
which may be adopted. The apparatus is shown in vertical section, Fig. 1,
and in horizontal section Fig. 2.
The walls are formed of slabs of lava (preferably of volvic lava), of stone or
other suitable material which cannot be attacked, fitted together with indiarubber
joints as employed in the construction of chlorine tanks or wells used in the
Weldon process.
At the lower portion is a grid or grating a a composed of
transverse bars constructed of the same stone or other material as the walls,
and upon this grating are placed several rows of silicious flints or lumps of other
suitable substances, the size of which gets smaller towards the upper strata, i.e.
the heavier or coarse lumps are towards the bottom. The filter is afterwards
filled with the sand properly so-called and which has been previously mentioned.
The arrive by an inlet pipe 6 placed at the upper portion of the filter
gases
above the sand, and pass out by a discharge pipe e placed underneath the grid
or grating. With regard to the condensed liquid, it escapes by a small pipe d.
The quantity of sand should be proportioned to the volume of gas to be
purified and to the degree of purity which it is wished to obtain, but its thickness
may be small and depends upon the charge treated.
b
Having now particularly described and ascertained the nature of my said in-
vention, and in what manner the same is to be performed, I declare that what I
claim is:-
A process for purifying hydrochloric acid gas, from any source and for any
purpose, consisting in causing this gas to pass across a filter formed by a bed
or layer of sand or other suitable divided material, for the purpose of separating
from the said gas the sulphuric acid and iron chloride which are mixed therewith.
Dated this 2nd day of December 1899.
For the Appleant,
GEDGE & FEENY,
Chartered Patent Agents, 60, Queen Victoria Street, London, E.C.