Improvements in the Manufacture of Hydrochloric Acid Free from Arsenic.
Year: 1896

page_text: Date of Application, 8th Aug., 1896
Complete Specification Left, 8th May, 1897-Accepted, 19th June, 1897
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Hydrochloric Acid Free from
Arsenic.
We, JOSIAH RIGBY WYLDE, Alkali Manufacturer JOSIAH WYCKLIFFE
KYNASTON Analytical Chemist and JOHN BROCK, Director of The United Alkali
Company Limited all of G 11 Exchange Buildings Liverpool in the County of
Lancaster do hereby declare the nature of this invention to be as follows:-
When liquid hydrochloric acid is manufactured from common salt by acting
thereon with ordinary arsenical sulphuric acid, the liquid hydrochloric acid obtained
is always contaminated with arsenic and is not applicable for use in some of the
arts wherein large quantities of purer hydrochloric acid are required, and in order
to obtain this purer quality of acid it has hitherto been necessary either to use
sulphuric acid free from arsenic, which is much more expensive than the ordinary
arsenical sulphuric acid, or to purify the liquid hydrochloric acid by costly
processes of precipitation.
This invention is based upon the discovery made by the present inventors that
when a suitable mixture of hydrochloric acid gas, chlorine, and vapour of water,
containing arsenic and sulphuric acid is passed over, or through, a porous or
equivalent material, such as coke, under suitable conditions with respect to
temperature, the smaller quantities of the hydrochloric acid gas and steam which
condense during the passage of the gas through the porous material absorb the
whole, or nearly the whole, of the arsenic and hold it in solution, and the larger
quantity of gas after having been passed over or through the coke, or equivalent
material is practically free from arsenic.
According to this invention the arsenical hydrochloric acid gas is passed through
a chamber containing a porous or equivalent substance such as coke, which we
term a "dry tower to distinguish it from the usual coke condensing tower
in which a stream of water or dilute acid meets the ascending gas so as to
condense it.
While passing through the said "dry tower" the gaseous mixture containing
hydrochloric acid gas, arsenic, and a certain amount of steam deposits always a
small amount of liquid acid, and thus moistens the coke or equivalent material.
The arsenic is absorbed and dissolved in this small quantity of liquid acid. If
chlorine be present in the gaseous mixture the arsenic is partially, or wholly,
converted into arsenic acid, which is much more soluble and less volatile. The
gas leaving this "dry tower" is free from arsenic if the conditions be suitable that
is if the temperature within the tower be not too high, if the gases do not contain
too large an admixture of steam, and do contain a sufficient amount of chlorine to
permit the conversion of the arsenic into arsenic acid.
In order to satisfy these conditions there is employed according to this invention
bydrochloric acid gas obtained by the decomposition of ordinary salt with common
arsenical sulphuric acid and we remove from it if necessary any excess of moisture
it, contains (which may be done by partial condensation or by cooling) and we add
a small quantity of chlorine gas. We then pass the gases through the aforesaid
"dry tower" where the arsenic is removed as aforesaid and we convey the gas
freed from arsenic into the usual condensing tower where the hydrochloric acid is
:

page_text: We
condensed by meeting a stream of water, or weak acid, free from arsenic.
thus obtain the greater part of the hydrochloric acid as an aqueous solution free
from arsenic.
We
The gases technically known as "roaster gas" that is the hydrochloric acid
evolved during the calcination process in the manufacture of sulphate of soda, are
specially suitable for treatment by the process according to this invention.
pass these gases through a number of pipes or the like to cool the said gases as far
as possible and we add a small quantity of chlorine, and then we pass the
gases through, the aforesaid "dry tower" before conveying them to the usual
condenser.
The gases obtained in the manufacture of chlorine by the Deacon process just
as they issue from the "decomposer" are also well adapted for treatment by the
process according to this invention. The said gases consist essentially of chlorine,
hydrochloric acid gas, and inert gases contaminated with arsenic. We pass these
gases through the usual cooling pipes or the like and then through the aforesaid
"dry tower" where the arsenic is removed as aforesaid. The gases are then led
to the condensing tower where the hydrochloric acid is absorbed by water and
constitutes a liquid acid free from arsenic.
Dated this 8th day of August 1806
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.
COMPLETE SPECIFICATION.
Improvements in the Manufacture of Hydrochloric Acid Free from
Arsenic.
We, JOSIAH RIGBY WYLDE, Alkali Manufacturer, JOSIAH WYCKLIFFE
KYNASTON, Analytical Chemist, and JOHN BROCK, Director of The United Alkali
Company Limited, all of G 11 Exchange Buildings Liverpool, in the County of
Lancaster 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 :-
When liquid hydrochloric acid is manufactured from common salt by acting
thereon with ordinary arsenical sulphuric acid, the liquid hydrochloric acid
obtained is always contaminated with arsenic and is not applicable for use in some
of the arts wherein large quantities of purer hydrochloric acid are required. In
order to obtain this purer quality of acid, it has hitherto been necessary either to
use sulphuric acid free from arsenic, which is much more expensive than the
ordinary arsenical sulphuric acid, or to purify the liquid bydrochloric acid itself by
processes entailing considerable cost.
The present invention is based upon the discovery made by the present
inventors that, when a suitable mixture of hydrochloric acid gas, chlorine and
vapour of water containing also arsenic and sulphuric acid, with, or without,
admixture of other gases which may be present as diluents, is passed over, or
through, a porous, or equivalent, material; such as coke, or the like, (ordinary
hydrochloric acid condensing towers, packed with the said material are suitable
for the purpose), under suitable conditions with respect to temperature, the
comparatively small quantities of the hydrochloric acid gas and steam, which
condense to liquid acid in the vessel, or tower, containing the coke, or the like,
absorb, and retain in solution, the whole, or nearly the whole, of the arsenic,
whilst the bulk of the hydrochloric acid gas which is uncondensed and leaves the
said vessel, or tower, is practically free from arsenic. We may term the tower. so

page_text: used a "dry tower" to distinguish it from condensing towers in which a stream of
water or other liquid meets the ascending gas. No water, or other liquid, is run
down our dry tower, but the arsenic is, as aforesaid, abstracted from the gases
and retained in solution by the portion of liquid acid always condensed under
the said conditions by reason of the aqueous vapour contained in the gaseous
mixture.
If chlorine be present in the gaseous mixture the arsenic is partially, or
wholly, converted into arsenic acid, which is much more soluble, and less volatile,
than in the forms in which it is usually present. The gas leaving the said vessel,.
or tower, is free from arsenic if the temperature within the tower be not too
high, that is, if the gases have been sufficiently cooled before being passed into
the tower.
We find that a temperature in the tower not exceeding 55° Centigrade gives
good results, but lower temperatures are preferred..
In carrying out our invention we may employ hydrochloric acid gas obtained
by the decomposition of common salt by treatment with the ordinary arsenical
sulphuric acid, and we convey the gas evolved through a length of pipes, sufficient
to cool the said gas considerably, directly to the aforesaid vessel or dry tower.
We insert into the pipe, at, or near, its entrance to the tower, a jet conveying
chlorine gas, and we regulate the supply of chlorine so that it shall be present in
the gases passing from the dry tower in the least possible excess. In passing
through the dry tower, the arsenic is removed from the gases and retained in the
liquid acid produced. The gas issuing from the dry tower, now freed from
arsenic, is conveyed by a pipe, or pipes, from the top of the dry tower to the
bottom of a condensing, or wet, tower, down which a stream of water is passed and
the gas being condensed in this wet tower we obtain the greater part of the
hydrochloric acid, evolved from the decomposed salt, in the form of an aqueous
solution free from arsenic.
The gases technically known as "roaster gas" that is, the hydrochloric acid
evolved during the calcination process in the manufacture of sulphate of soda, are
specially suitable for treatment according to this invention, as hereinbefore
described, for the production of hydrochloric acid free from arsenic.
"
The gases obtained in the manufacture of chlorine by the Deacon process, just
as they issue from the "decomposer are also well adapted for treatment by the
process according to this invention as hereinbefore described. The said gases,
consist of chlorine and hydrochloric acid gas, together with aqueous vapour,
nitrogen, and small quantities of other gases, and they also contain arsenic in a
gaseous condition. We pass these gases through the usual cooling pipes, or other-
wise cool them, and then we pass them through the aforesaid vessel, or "dry
tower," where the arsenic is removed and retained as herein before described.
gases are then led to the condensing, or wet, tower, where the hydrochloric acid is
absorbed by water and constitutes a liquid acid free from arsenic.
The
The hydrochloric acid obtained by the process according to this invention, as
bereinbefore described, when chlorine has been present as an essential constituent
of the gases or has been added thereto in slight excess is not only free from arsenic
but is also free, or nearly free, from sulphuric acid. It may however, contain a
minute quantity of free chlorine in solution, but this can easily be removed by
passing a current of air through the cold acid, which removes the chlorine without
adding to the acid any other element of contamination. But, for many purposes,
the acid may be freed from chlorine, if its presence be objectionable, by the
addition of a deoxydising substance, such as ferrous chloride, or sulphate.
Having now particularly described and ascertained the nature of our inven
tion and in what manner the same is to be performed we declare that what we
claim is :-
1. The manufacture of hydrochloric acid free from arsenic, from the gases
evolved by the treatment of an alkaline chloride with ordinary arsenical sulphuric.

page_text: acid in the manufacture of sulphate of soda, consisting in first cooling the said
gases and adding chlorine thereto and then passing the gases through or in
contact with coke, or equivalent material, in a vessel, or dry tower, in which the
arsenic is retained, and thence to a vessel, or wet tower, in which the hydrochloric
acid is condensed; substantially as hereinbefore described.
2. The manufacture of hydrochloric acid free from arsenic, from the gases
issuing from the decomposer in the Deacon chlorine process, by first cooling the
said gases and then passing them through, or in contact with, coke, or equivalent
material, in a vessel, or dry tower in which the arsenic is retained, and thence to
a vessel, or wet tower, in which the hydrochloric acid is condensed; substantially as
herein before described.
Dated this 8th day of May 1897
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.