Improved Treatment of Hydrochloric Acid Gas for the Production of Chlorine Gas.
Year: 1887

page_text: Date of Application, 3rd Jan., 1887.
Complete Left, 1st Oct., 1887
Complete Accepted, 18th Oct., 1887
PROVISIONAL SPECIFICATION.
Improved Treatment of Hydrochloric Acid Gas for the Production
of Chlorine Gas.
I, WILLIAM DONALD of The Burrows Cottage, Pembrey, Burry Port, Carmarthen-
shire, Analytical and Practical Chemist, do hereby declare the nature of this
invention to be as follows
The object of my invention is to devise an improved process of obtaining chlorine
from hydrochloric acid gas, and the recovery of the bye-products.
To effect this hydrochloric acid gas obtained either direct from the salt cake
furnace, from aqueous hydrochloric acid or other suitable source is dried by passing
it through a suitable tower or receptacle charged with sulphuric acid.
The gas then passes into an apparatus charged with strong nitric acid and sulphuric
acid where the hydrochloric acid gas is decomposed. The evolved gases which
consist of oxides of nitrogen and chlorine pass into a series of Woulff's or other
suitable apparatus charged with strong nitric acid in which the oxides of nitrogen are
taken up.
The chlorine now passes through another tower charged with sulphuric acid and
subsequently through a "Fikentscher" tower the shelves of which are charged with
Ferrous sulphate and sulphuric acid from which the chlorine gas passes in a state
fit for use.
The contents of the Woulft's apparatus, in which the oxides of nitrogen are taken
up, are run into another suitable receptacle where they are heated and a current of
air passed into them by which means conversion into nitric acid takes place.
Dated this 3rd day of January 1887.

page_text: Improved Treatment of Hydrochloric Acid Gas for the Production
of Chlorine Gas.
I, WILLIAM DONALD of The Burrows Cottage, Pembrey, Burry Port, Carmarthon-
shire, Analytical and Practical Chemist, 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 :-
The object of this invention is to obtain chlorine from hydrochloric acid and to
recover the bye products formed during the operation.
To effect this, hydrochloric acid gas obtained either direct from the salt cake
furnace, from aqueous hydrochloric acid or other suitable source is dried by passing
it through a suitable tower or receptacle charged with sulphuric acid. The gas is
then passed into a vessel or apparatus charged with a mixture of strong nitric acid
and sulphuric acid where the hydrochloric acid gas undergoes decomposition. The
relative quantities of the two acids nitric and sulphuric must be proportioned to
the part each has to perform, the nitric acid having to effect the decomposition of the
hydrochloric acid giving rise to oxide of nitrogen and chlorine and the sulphuric
acid having to take up the water formed during the reaction which may be represented
'as follows:

page_text: posing mixture of nitric and sulphuric acids thence in succession through the
pipes c c and absorbers A and A3 and lastly through the pipe ct to the scrubber A*
from which it is drawn off by a second blower C. D, D1 and D2 are a second series
of vessels similar to the vessels A each resting in a tank E. The vessel D is kept
heated by hot water entering by the pipe e or by other means but the other two are
cooled by the overflow of refrigerated water or brine from the tanks B. Each
tank is supplied with two thermometers ab for the purposes of ascertaining the
temperatures of the liquids and the gases.
This second series of vessels D is for the purpose of converting the lower oxides of
nitrogen collected by absorption in the vessels A* A³ into nitric acid. For this
purpose the latter vessels are connected with the vessel D by means of a pipe a so
that the liquid in A2 A3 will flow naturally thereinto when the cocks d' are opened.
Before allowing the liquid to flow into the vessel D water may be added to the
vessels A2 A3 through the pipes which are provided with stop cocks for the
purpose.
When in the vessel D the mixture of acid and oxides is heated and a slow current.
of air passed into the compound through the pipes E' whereby the lower oxides of
nitrogen are oxidised into nitric acid. The air passes from the vessel D through a
tower F carrying with it free oxides of nitrogen and these during their progress
undergo further oxidation the necessary water being supplied through a cock F
The condensed gases flow back into the vessel D and those uncondensed pass into the
vessel D' which is charged with nitric acid in which the uncondensed gases are
absorbed. The air and nitrogen issuing from the vessel D' are scrubbed in the
vessel D which contains sulphuric acid which frees them from all traces of oxides of
nitrogen.
The oxidation of the gases may be assisted by the presence of a quantity of peroxide
of manganese, nitrate of manganese or substance analogous thereto in its property of
liberating oxygen, such for example as compounds of chromium.
If sulphuric acid is used in the vessels A A³ instead of nitric acid the nitro-
sulphuric acid or nitro-compound formed may be run direct into the vessel D which
is then kept cool and water or dilute sulphuric acid injected into it care being taken
that the temperature is not allowed to rise. The decomposition is usually complete
when the acids have acquired a density of about 135° Tw.
The acids are now heated and the oxides of nitrogen converted into nitric-acid by
air blowing. When the oxidation is complete as much sulphuric acid is added as will
take up the water added in the above process plus that formed in the decomposition.
This mixture is now run into the decomposer A' and used to decompose a fresh
charge of gas.
The residue in the vessel A which consists of sulphuric acid and water may now be
used to decompose a fresh charge of common salt and the residue in A' may be used
in A for drying the next charge of gas. The sulphuric acid from the scrubber A¹
is used for the decomposer A' and the scrubber charged with fresh sulphuric acid.
Having now particularly described and ascertained the nature of my said invention,
and in what manner the same is to be performed, I declare that what I claim is :-
1. The improved process of obtaining chlorine gas substantially as described.
2. The separation of oxides of nitrogen from a mixture of oxides of nitrogen and
chlorine in a gaseous state by passing the same through dilute nitric acid at a
temperature not exceeding 30° C.
3. The recovery of the issuing unoxidised nitrogen compounds in the oxidation
process by absorbing them in cold nitric acid and cold sulphuric acid.
WILLIAM DONALD.