Improvements in the Preparation of Chlorine.
Year: 1890

page_text: Date of Application, 28th Apr., 1890
Complete Specification Left, 2nd Feb., 1891-Accepted, 7th Mar., 1891
PROVISIONAL SPECIFICATION.
Improvements in the Preparation of Chlorine.
We, GEORGE EDWARD DAVIS, of 32, Blackfriars Street, Manchester, in the
County of Lancaster, Chemical Engineer, & ALFRED ROLAND DAVIS, also of
32, Blackfriars Street, Manchester, in the County of Lancaster, Chemical Engineer,
do hereby declare the nature of this invention to be as follows:-
It has for a long time been known that hydrochloric acid gas is oxidised by nitric
acid with the production of chlorine, nitrogen oxides and chloronitrous combinations
but the reactions which take place during the action of the one upon the other have
been but imperfectly understood and therefore the various processes that have been
devised from time to time have, till now, all ended in failure. The process patented
by Dunlop (No. 11624, 1847) in which common salt and nitrate of soda were acted
upon by sulphuric acid yielding an oxide of nitrogen and chlorine, is to the best of
our knowledge and belief the only nitric acid process for the manufacture of chlorine
that has been worked continuously on a manufacturing scale and even tliis has been..
abandoned.
The cause of this is not far to seek, seeing that the manufacture of 35 tons per
week, of chlorine would require not less than 2,000 tons of sulphuric acid in which
to absorb the nitrous compounds formed in the reaction.
Our invention relates to a process for the manufacture of chlorine by means of
nitric acid and has for its object the employment of a minimum quantity of sulphuric
acid, sufficient merely to decompose the common salt necessary for the production
of the hydrochloric acid gas and to provide a means for the perpetual regeneration
of the nitric acid used in the process.
In working our invention we separate the operation into three main parts,
First, the production of hydrochloric acid gas by the treatment of common salt
or other suitable chloride, with the sulphuric acid that has played its part in other
portions of the process.
Second, the treatment of the hydrochloric acid gas with nitric acid in such a
manner that the chloronitrous gases and oxides of nitrogen which are formed along
with chlorine interact in the presence of air water and nitric acid with the ultimate
production of chlorine and the reproduction of nitric acid and
Thirdly, the absorption of any remaining oxides of nitrogen in strong sulphuric
acid leaving only chlorine mixed with air and nitrogen to pass on for utilization.
The plant necessary for the carrying out of our invention consists of any ordinary -
and well known arrangement for making salt cake in which the fuel gases are kept
from contact with the hydrochloric acid preferably the mechanical furnace
described in the Specification of our Application of even date a series of two or
more towers packed with suitable material down which nitric acid is made to flow,
and an absorbing tower for arresting the last traces of nitrous compounds which
have escaped the oxidising and other arresting influences at work in the previous
towers.
:
The hydrochloric acid of the first part of the operation as dry as it is possible to
obtain it, is passed up one of the towers aforesaid down which nitri: acid is made

page_text: to flow so that the two acids are decomposed with the formation of various gaseous
products which escape from the top of the tower, whilst the water liberated from
the nitric acid and that formed by the oxidation of the hydrogen of the hydro-
chloric acid together with the residual water of the vitriol used for decomposing
the salt flows gradually down the tower absorbing in its progress a certain amount
of hydrochloric acid and flowing out at the bottom of the tower, as a solution
of muriatic acid. Care must be taken in duly proportioning the quantities of
hydrochloric acid gas passing into the tower and the volume of nitric acid flowing
down the same, otherwise there will flow, out a mixture of nitric and hydrochloric
acids, for which a market could only be found with difficulty.
The action of this tower is very complicated and its construction is capable of
many modifications. One of its main objects is to separate the water formed during
the reactions, the removal of which at some stage or another is necessary for the
success of the process.
The gases leaving this tower pass into a second tower, down which nitric acid is
also caused to flow. In this tower quite a different action takes place, the chloro-
nitrous gases contained in the gaseous mixture are decomposed by the nitric acid
with formation of chlorine and oxides of nitrogen. The former along with the
chlorine present in the gaseous mixture coming from the first tower passes away
unchanged whilst the oxides of nitrogen, in presence of the air contained in the
gaseous mixture and the uncombined water in the nitric acid employed become
reoxidised into nitric acid and flow away from the bottom of the tower.
It is essential that too highly concentrated nitric acid be not employed, as in such
a case there would not be water enough to complete the reaction, but on the other
hand the nitric acid must not be too dilute or the chloronitrous gas will be split up
into nitrogen oxides and hydrochloric acid which would be difficult of subsequent
treatment.
The gases leaving the second nitric acid tower, may if necessary be passed into
a third nitric acid tower, in order to ensure perfect decomposition of the chloro-
nitrous gas and the gases escaping from this tower are passed finally through the
third part of the process, namely, the absorbing tower where the last traces of
nitrogen compounds are absorbed in sulphuric acid. The chlorine gas is then pure
enough for use in the manufacture of bleaching powder, bleaching liquor, chlorate
of potash, or any similar purpose.
We have described the process as it is most easy to work in practice, but it is
not necessary to react upon the hydrochloric acid gas in more than one tower if due
care be taken in proportioning the flow of hydrochloric acid gas to that of nitric
acid. We have discovered that the whole of the hydrochloric acid may be
decomposed in one tower with the exception of that quantity dissolved in the water,
running away from the tower, but we have found the regulation of the acids 'to
require great attention.
When only one nitric acid tower is employed the mixture of nitrogen compounds
air and hydrochloric acid forms three distinct zones of action, a lower one where
chloronitrous gas is being formed, an intermediate zone, where the chloronitrous
gras is converted into chlorine and nitrogen oxides, and an upper: zone where in
presence of the uncombined water of the nitric acid, and the oxygen of the air,
nitric acid is regenerated. In any case provision must be made for the outflow of
the water produced in the reaction, which will so quickly accumulate as to stop the
process if not regularly dealt with.
When only one nitric acid tower is employed the nitrogen compounds must be
kept in circulation in the tower. The nitric acid from the top zone flows downwards
and undergoes decomposition by contact with the hydrochloric acid contained in the
ascending current of gases. The resulting nitrogen compounds, reascend' the tower
and are continually regenerated as beforementioned..
We prefer however to detach these zones from one another and to make each
zone a separate tower or towers, thus rendering it easier to keep the water. formed
during the reaction in its own special tower or towers, or first zone, and to do the

page_text: oxidation of the chloronitrous gas and the regeneration of the nitric acid together
in the next zone, or tower or towers by operating as already described.
The sulphuric acid employed for arresting the last traces of nitrogen compounds
from the chlorine is employed in a subsequent operation for decomposing another
batch of salt or other chloride, for the production of the necessary hydrochloric
acid gas.
In the aforesaid description we have described the passage of the gases as having
an upward direction through the towers, but we have discovered that under certain
conditions it is advantageous to pass them downwards through the same in order to
obtain a more complete reaction.
Dated this 28th day of Auril 1800
GEORGE E. DAVIS.
ALF. R. DAVIS.
COMPLETE SPECIFICATION.
Improvements in the Preparation of Chlorine.
We, GEORGE EDWARD DAVIS and ALFRED ROLAND DAVIS, both of
32, Blackfriars Street, Manchester, in the County of Lancaster, Electrical
Engineers, 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 :-
It has for a long time been known that hydrochloric acid is oxidised by nitric
acid with the production of chlorine, nitrogen oxides and chloronitrous combinations,
but the reactions which take place during the action of the one upon the other
have been but imperfectly understood and therefore the various processes that have
been devised from time to time have not been practically successful.
The process described in the Specification of Dunlop No. 11624 A.D. 1847 has
been worked but finally abandoned. It was probably found to be not economical
seeing that the manufacture of thirty-five tons per week of chlorine would
require not less than two thousand tons of sulphuric acid in which to absorb the
nitrous compounds formed in the reaction proposed by Dunlop.
Our invention the subject of our Patent 6416 A.D. 1890 relates to a process
for the manufacture of chlorine by means of nitric acid and has for its object the
employment of a minimum quantity of sulphuric acid sufficient merely to
decompose the common salt necessary for the production of the hydrochloric acid
gas and to provide a means for the perpetual regeneration of the nitric acid used in
the process. It should, however, be noted that in the Specifications of our subsequent
Patents 6698 of 1890 and 6831 of 1890 we describe further improvements as regards
practical details which, as will be obvious, may be advantageously employed in
carrying out the invention the subject of our Patent 6416.
In working our invention we separate the operation into three main parts:
First, the production of hydrochloric acid gas by the treatment of common salt
or other suitable chloride with sulphuric acid preferably that which has played
its part in other portions of the process in which the following reactions take
place:
TY
Second, the treatment of the hydrochloric acid gas with nitric acid in such a
manner that the chloronitrous gases and oxides of nitrogen which are formed along
with chlorine, interact in the presence of air, water and nitric acid with the ultimate
production of chlorine and the reproduction of nitric acid.
The first action which takes place may be represented by the following chemical
formula which is well known:

page_text: (d) N₂ O₁ + 0 + H₂ O = 2 HNO3.
4
The hydrochloric acid reproduced as shewn in equation (c) undergoes a further
cycle of changes until it is all practically oxidised into chlorine.
The third portion of the operation consists in removing from the mixture of gases
any remaining oxides of nitrogen in strong sulphuric acid leaving only chlorine
mixed with air and nitrogen to pass on for utilization.
In order to ensure a high degree of purity of the chlorine for many purposes in
which it is employed we find it advantageous to pass it through a wash tower,
packed with suitable material down which water is made to flow and this water
charged with impurities, may be employed over and over again until it is taken
away for utilization as subsequently described.
The reactions which take place as already described between the hydrochloric
acid and the nitric acid are not the only ones that take place in the nitric acid
tower. We also have the following reactions taking place:-
but these two last reactions should be suppressed as far as possible by keeping
the nitrogen compounds in the highest state of oxidation by the admixture of
sufficient air.
The plant necessary for the carrying out of our invention consists of any
ordinary and well known arrangements for making salt cake and hydrochloric
acid gas, but we preferably employ the mechanical furnace A described in our
Specification numbered 6433 and dated April 28th 1890 in which the fuel gases
are kept from contact with the hydrochloric acid gases, a series of two or more
towers B B B packed with suitable material down which nitric acid is made to
flow, an absorbing tower C for arresting the traces of nitrous compounds which
have escaped the oxidising and other arresting influences at work in the previous
towers, and a wash tower D down which water is caused to flow as already
described.
The letters aforesaid and those which follow in all cases refer to the drawing
accompanying this Specification.
The hydrochloric acid of the first portion of the operation already described,
as dry as it is possible to obtain it, is caused to pass through the nitric acid
tower B down which nitric acid is made to flow. This may be effected by any well
known means but we prefer to use an ordinary exhauster, such as a Root's blower,
placed where shown at E on the drawing accompanying this Specification so that
the decompositions may take place under a reduced pressure. In this tower the
water formed by the oxidation of the hydrogen of the hydrochloric acid together
with the residual water of the oil of vitriol or sulphuric acid used for decomposing
the salt flows gradually down the tower absorbing in its progress a certain amount
of hydrochloric acid and flowing out of the bottom of the tower B at F as a solu-
tion-of hydrochloric acid which may advantageously be treated as described in our
subsequent Specifications 6698 or 6831 of 1890.
Care should be taken in duly proportioning the quantities of hydrochloric acid
gas passing into the tower B and the volume of nitric acid flowing down the same
otherwise there will flow out at F a mixture of nitric and hydrochloric acid for
which a market could only be found with difficulty. This regulation of the
quantities may casily be performed by the aid of chemical tests well known to
practical chemists.
The actions going on in the tower B are complicated and the construction of the

page_text: tower itself and the material with which it is packed are as will be understood by
persons acquainted with the working of such towers capable of many modifications.
One of its main objects is to separate the water formed during the reactions, the
removal of which at some stage or another is necessary for the success of the
process. Our subsequent Specifications 6698 and 6831 of 1890 deal with this
problem and describe how the water may be separated from the hydrochloric acid
that accompanies it.
The gases leaving the tower B pass into a second tower B down which nitric
acid is also caused to flow. In this tower B quite a different action takes place
from that which takes place in tower B. In tower B the bulk of the water is
eliminated while the chloronitrous gases contained in the gaseous mixture leaving
the said tower B are decomposed by the nitric acid on entering tower B after the
manner set forth in formula (4) aforesaid with the formation of chlorine and oxides
of nitrogen.
The chlorine so produced along with the chlorine from the gaseous mixture
coming from the first tower, passes away unchanged, whilst the oxides of nitrogen
in presence of the air contained in the gaseous mixture and the uncombined water
of the nitric acid employed, become reoxidised into nitric acid and flow away from
the bottom of the tower B' at the point F¹.
It is advisable that too highly concentrated nitric acid should not be employed as
in such a case there would not be water enough present to enable the reaction set
out in formula (d) to proceed, but on the other hand the nitric acid must not be too
dilute, or the chloronitrous gas will be split up into nitrogen acids and oxides and
hydrochloric acid with simultaneous destruction of some of the chlorine already
formed, which products at this point of the process would be difficult of subsequent
treatment.
The gases leaving the second nitric acid tower B' may if necessary be passed into
a third nitric acid tower B in order to ensure perfect decomposition of the
chloronitrous gas, and the gases escaping from this tower are passed through the third
part of the process namely the absorbing tower C where the last traces of nitrogen
compounds are absorbed in sulphuric acid which is caused to flow down the
same. The chlorine is then generally pure enough for use in the manufacture of
bleaching powder, bleaching liquor, chlorate of potash or any similar purpose but
if any impurities be still found in the gaseous current removable by water, the
gaseous current should be passed through a wash tower D down which a flow of
water is maintained. The chlorine, mixed of course with residual air and nitrogen
then passes through the exhauster or blower E to the place where it is to be utilised.
The water running from the wash tower D at the point F can be used over and
over again until it has become super-charged with impurities, when fresh water
must be supplied.
We have already described the necessity of paying strict attention to the strength
of the nitric acid employed to flow down the nitric acid towers.
We have shown that if the acid is too strong there will not be water enough
present to allow the reformation of nitric acid to proceed. In actual practice we
work preferably with nitric acid of 80° Tw., in the towers B and B we find the
strength will increase to 90° Tw.; and to even as high as 97° Tw.; whilst still
higher figures may be obtained in working on an extended scale. We therefore
make provision for collecting the water charged with impurities, such as nitrous
and nitric acid together with hydrochloric acid and this we add to the nitric acid
used to flow down the towers Bi and B". By these means the said nitric acid is
kept to its proper strength and at the same time we utilise the nitrogen acids and
hydrochloric acid that would otherwise be wasted.
We have so far described the process in the way in which it may be advan-
tageously worked on a large scale but it is not necessary to react upon the
hydrochloric acid gas with nitric acid in more than one tower if due care be taken
in proportioning the flow of hydrochloric acid gas to that of nitric acid. We have
found that the whole of the hydrochloric acid may be decomposed in one tower,

page_text: such as B, with the exception of that quantity dissolved in the water running away
from the tower which may be advantageously dealt with according to our subsequent
Specifications 6698 or 6831 of 1890, but we have found that the regulation of the
acids requires great attention and a tower so high that it would be more convenient
to build it in three portions as we have already described as towers B, B¹
and B.
When only one nitric acid tower is employed, as B, the mixture of nitrogen
compounds, air and hydrochloric acid form three distinct zones of action, a lower
one (1) where chlorine and chloronitrous gas is being formed an intermediate
zone (2) where the chloronitrous gas is converted into chlorine and nitrogen oxides
and an upper zone (3) where in the presence of the uncombined water of the nitric
acid and the oxygen of the air nitric acid is regenerated. In any case provision
must be made for the outflow of the water produced in the reaction which will so
quickly accumulate as to stop the process if not regularly dealt with.
When only one nitric acid tower is employed the nitrogen compounds must be
kept in circulation in the tower by accurately following the progress of the reactions
by chemical tests as set forth in the before mentioned chemical formula.
The nitric acid from the top zone (3) flows downwards and undergoes decom-
position by contact with the hydrochloric acid and chloronitrous gases contained in
the ascending current of gases. The resulting nitrogen compounds being gaseous
reascend the tower and are oxidised by contact with the oxygen present. The
result of the oxidation is a liquid which flows down the tower again, and is con-
tinually regenerated as before mentioned the water required for the reaction being
provided from that issuing at F in the tower D from whence it is conveyed to the
tank on the top of tower B. As however this arrangement in which one nitric
tower is employed is not the best form of apparatus (though it is practicable under
well defined conditions) we prefer to detach the zones aforesaid from one another
and to make cach zone a separate tower or towers thus rendering it easy to keep
the water formed during the reaction in its own special tower or towers, or first
zone and to effect the oxidation of the chloronitrous gas and the regeneration of the
nitric acid together in the next zone or zones or tower or towers by operating as
already described, as by this means the strength of the nitric acid is well under
control, and the strength thereof can be increased by withholding the water running
from the wash tower D and decreased by admitting more of it.
The nitric acid running from the tower B is by preference worked over and over
again in the same tower the normal strength being maintained by the introduction
of the water issuing from the wash tower D. As the bulk of the acid increases the
excess is taken for use in tower B where the greatest increase is noticed, and the
excess of stock running from this tower is conveyed to tower B where it is dealt
with as already described.
The sulphuric acid running from tower C and which has been employed for
arresting the last traces of nitrogen compounds from the chlorine is to be employed
in a subsequent operation for decomposing another batch or batches of salt or other
chloride for the production of the necessary hydrochloric acid gas; or it may first
be utilized according to any of the methods described in our subsequent Specifica-
tion 6698 and 6831 of 1890.
In the aforesaid instructions we have described the passage of the gases as having
an upward direction through the towers, but they may be passed downwards through
the same if it is found more convenient to do so.
In describing the methods of working our invention aforesaid we lay no general
claim to the process for the regeneration of the nitric acid from the oxides of
nitrogen mixed with air by passing them through a tower down which nitric acid is
made to flow, or through a series of towers, the last of the series being supplied with
water, the nitric acid so regenerated in that last tower being employed in the
previous towers, as to our own knowledge such operations have been employed on
an industrial scale for many years and have in some cases formed the subject of

page_text: Letters Patent; neither do we claim the process of absorbing the oxides of nitrogen
from a current of mixed gases containing chlorine in cold sulphuric acid as that
process has been known and practised for many years. We also make no claim to
either (i) the method herein described of preparing chlorine from hydrochloric
acid by the aid of nitric acid in the presence of air in which the nitric acid is made
to act as a carrier of oxygen from the air to the hydrogen of the hydrochloric acid
without the necessity of refrigeration or, (2) the use of the apparatus herein described
but what we do claim is :-
The utilization of the water charged with impurities from the wash tower D
for preserving the normal strength of the nitric acid employed in the operation in
the manner herein described.
G. F. REDFERN & Co.,
4, South Street, Finsbury, London, Agents for the Applicants.