IMPROVEMENTS IN THE MANUFACTURE OF HYDROCHLORIC ACID AND CHLORINE
Year: 1881

page_text: LETTERS PATENT to Walter Weldon, of Rede Hall, Burstow, in the County of
Surrey, for an Invention of "IMPROVEMENTS IN THE MANUFACTURE OF
HYDROCHLORIC ACID AND CHLORINE."
PROVISIONAL SPECIFICATION left by the said Walter Weldon at the Office
of the Commissioners of Patents on the 7th March 1881.
"IMPROVE-
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey.
MENTS IN THE MANUFACTURE OF HYDROCHLORIC ACID AND CHLORINE."
This Invention consists in a new method of obtaining either hydrochloric acid
and chlorine, or hydrochloric acid only, from a solution of chloride of magnesium
mixed or not with chloride of sodium or with other salt or salts. One form of the
said method consists in the following operations:-
First. The solution of chloride of magnesium is concentrated by evaporation to
or nearly to the point at which if its evaporation were further continued it would
begin to give off vapour of hydrochloric acid.
Second. The solution so concentrated is mixed with a portion of the product of
the third operation, and the mixture is formed into cakes, balls, briquettes, or other
small lumps, such that when charged into a furnace or other suitable apparatus, air
and other gases can penetrate into and pass through and among the interstices
between them.
Third. The cakes, balls, or briquettes formed in the second operation are strongly
heated in a current of air. Their chlorine is thereby driven off partly in the free
state, but chiefly as vapour of hydrochloric acid, and the solid residual product
consists either simply of magnesia or of magnesia mixed with the other salts, if
any, which were present in the solution of chloride of magnesium commenced with,
or with products of the decomposition of such salts..
The gaseous current from the third operation must pass first to condensing
apparatus, in which its hydrochloric acid shall be condensed out from it, as will be
well understood, and then to apparatus in which its chlorine shall be absorbed.
It may in some cases be necessary to dry the cakes produced in the second
operation before submitting them to the third operation.
מ

page_text: When the third operation is as above set forth, I prefer to effect it by simply
passing through and among the cakes, balls, or briquettes produced in the second
operation, a current of air previously so highly heated as to have been rendered
capable of raising the charge of cakes, balls, or briquettes to the temperature at
which the desired reaction can take place. The said third operation may, however,
be effected also by applying heat externally to the apparatus containing the cakes,
balls, or briquettes, and admitting into that apparatus either cold air or air not
fully heated to the temperature required for the reaction. The said third operation
may be conducted either intermittently or continuously, but I prefer to conduct it
by the system and by means of the apparatus forming the subject of another
Invention, an application for a Patent for which will be filed on the same day as
these presents.
In certain cases I modify in one or other or both of two ways the process as
above described. One modification consists in mixing the chloride of magnesium
with oxide of iron instead of with a portion of the solid residual product of the
third operation, and the other in employing for the third operation, instead of a
current of air, either a current of steam or a current of air, or other gases mingled
with steam, or a current either of products of combustion simply or of products of
combustion to which steam has been added.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Walter Weldon in the Great Seal Patent Office on the 24th August
1881.
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey. "IMPROVE-
MENTS IN THE MANUFACTURE OF HYDROCHLORIC ACID AND CHLORINE."
This Invention consists in a new method of obtaining either both hydrochloric
acid and free chlorine or hydrochloric acid only from a solution of chloride of
magnesium mixed or not with chloride of sodium or other salt or salts. The said
new method consists in the following three operations :-
First. The solution of chloride of magnesium, or of chloride of magnesium and
other salt or salts, is concentrated by evaporation to or nearly to the point at
which if its evaporation were further continued the boiling solution would begin
to give off vapour of hydrochloric acid.
Second. The solution so concentrated by evaporation is mixed with magnesia,
and preferably, after the first operation or the first several operations, with
magnesia resulting from the decomposition in the third operation of previous
charges of chloride of magnesium. The mixture so formed will hereinafter be
called oxychloride of magnesium, this name being convenient whether it expresses
with absolute accuracy the chemical constitution of the mixture or not. This
oxychloride of magnesium is allowed to become solid and is then broken up into
suitable fragments, which are then charged into the apparatus in which the third
operation is to be performed. Or the mixture while it is still plastic is formed
into cakes, cylinders, balls, or other small masses, such that, when they have
become solid and are charged into a suitable apparatus, into which a gas or vapour
is forced, the said gas or vapour can penetrate into and pass through and among
the interstices between the said small masses.
Third. The said fragments or other small masses of oxychloride of magnesium
are heated in a current of air or of products of combustion, mixed or not with
steam, as will hereinafter be explained. Their chlorine is thereby driven off, either
wholly as vapour of hydrochloric acid, or partly as vapour of hydrochloric acid
and partly as free chlorine. The solid residue consists of magnesia mixed with
any chloride of magnesium which may have escaped decomposition, and with any
foreign salts not decomposible by the treatment constituting this third operation
which may have been present in the solution commenced with. These bodies, if
any, may be dissolved out by treatment with water, leaving only magnesia. Thus
to wash the solid residue of the third operation, however, will rarely, if ever, be
essential. A portion of this solid residue is used for a repetition of the second
operation, the remainder of it is not further required for the purposes of the
present Invention,
The first operation above described may be performed by means of any
convenient method of and appliance for evaporating liquids. The precaution
chiefly to be observed is that the evaporation be preferably not pushed to the
point at which it would cause vapour of hydrochloric acid to be disengaged.
Vapour of hydrochloric acid begins to come off, if no salt other than chloride of
magnesium be present in any material quantity, so soon as the proportion of water
to chloride of magnesium begins to fall below six equivalents of the former to one
equivalent of the latter, or below one hundred and eight parts by weight of water
to ninety-five parts by weight of chloride of magnesium. But I have obtained
very good results when the evaporation has not been carried further than to give
a solution containing only about thirty-three parts by weight of chloride of
magnesium per one hundred parts of total weight of solution.

page_text: A solution of chloride of magnesium in six equivalents of water is liquid only
while it is hot, and solidifies on cooling; but a solution containing only thirty-three
per cent. of chloride of magnesium is liquid also when cold. Therefore to mix
magnesia with a solution of chloride of magnesium of the first-mentioned strength
the mixture must be made while the solution is hot; but a solution of the strength
last named may be mixed with magnesia either when the solution is hot or when
it is cold.
One way in which a boiling solution containing only about six equivalents of
water per one equivalent of chloride of magnesium in it may be mixed with
magnesia, is as follows:-A cast-iron or other flat-bottomed mixing vessel is placed
near the evaporating vessel, the dispositions being such that concentrated solution
can be run from the latter into the former at will. Magnesia, preferably in powder,
is first placed in the mixing-vessel, and then boiling concentrated solution is run
from the evaporating vessel into the mixing vessel, a workman rapidly stirring the
contents of the mixing vessel with a suitable rake. A more perfect mixture will
be obtained if heat be applied under the mixing vessel so as to keep its contents
at or about the temperature of the boiling concentrated solution. The magnesia,
water, and chloride of magnesium rapidly combine, and the contents of the mixing-
vessel soon become hard solid lumps of hydrated oxychloride of magnesium.
These on being broken into smaller lumps if need be will be ready to be charged
into the apparatus in which the third operation is to be performed.
The operation of mixing with magnesia a solution of chloride of magnesium, not
too concentrated to remain liquid when cooled to ordinary temperatures, may
either be performed while the solution is hot in the manner just described, or it
may consist simply in adding a suitable quantity of magnesia to the solution when
the latter is cold, intimately mixing the magnesia with the solution by stirring, and
then allowing the mixture to stand, with occasional stirring, if need be, until it has
set into a solid mass of oxychloride. The time necessary to this result will vary
from a few minutes to a day or more, according to the activity of the magnesia
employed. The oxychloride of magnesium thus formed will only need breaking up
into suitably sized small fragments to be ready to be submitted to the third
operation.
The proportion of magnesia, which must be added to the concentrated solution of
chloride of magnesium will vary with the degree of concentration of the solution,
and also with the degree of activity of the magnesia employed. It will be a
sufficient rule to always add enough magnesia to cause the mixture of magnesia
and solution of chloride of magnesium to set into a solid mass, which will not
appreciably soften on being heated. Whatever the degree of activity of the
magnesia employed, from one to two equivalents of it will usually cause the forma-
tion of a solid oxychloride when added to a hot solution containing only about six
equivalents of water per equivalent of chloride of magnesium in it; but as much as
five or six equivalents of magnesia may be necessary to cause a mixture thereof
with a cold solution containing only about thirty-three per cent. of chloride of
magnesium to set into a solid mass. It is true that only one equivalent of magnesia
will do this if the magnesia be extremely finely divided magnesia, which has not
been subjected to a high temperature before being employed, but I have usually
found it necessary to use fully five equivalents of magnesia when employing a cold
thirty-three per cent. solution of chloride of magnesium, and when the magnesia
employed has been the residual product of preceding operations.
In the third operation the oxychloride must be heated in a current of air if it be
desired to obtain as much as possible of the chlorine of the oxychloride in the free
state, and as little as possible of it as vapour of hydrochloric acid; but if it be
desired to obtain hydrochloric acid only, no air should be allowed to enter the
apparatus in which the third operation is performed, beyond such quantities
as must unavoidably enter during charging and discharging.
In such case
the oxychloride should preferably be heated in a current of products of
combustion.

page_text: The manner of performing this third operation may be that of charging the
oxychloride of magnesium, in the state of suitably sized fragments, into apparatus
to which heat is applied externally, and then passing into and through that
apparatus a current of air or of products of combustion, as the case may be, the
heating of the charge to the necessary temperature and its maintenance thereat
being effected solely or partly by heat applied externally to the apparatus employed,
but I prefer to perform it in apparatus to which heat need not necessarily be applied
externally, by forcing into the said apparatus, after it has been charged with
fragments of oxychloride, either just formed and therefore intensely hot products
of combustion, or air which has been so highly heated, by means of a Cowper-
Siemens stove or otherwise, that it can of itself raise the charge to and maintain
the charge at the temperature necessary to the accomplishment of the desired
reaction. The said third operation may be either intermittent or continuous, but I
prefer that it should be performed in a practically continuous manner, and in an
apparatus consisting of a series of distinct compartments, so arranged and disposed
that one or more of the said compartments shall be capable of being isolated at
will to permit of their being discharged and re-charged while the other compart-
ments are at work, and so that the current of gases or of a mixture of gases and
vapour, or vapours passing from one part of the apparatus at a high temperature,
shall be caused to give up a large part of its heat to those portions of the charge
contained in other portions of the apparatus which have not yet attained that
temperature. This manner of proceeding and apparatus for carrying it into effect
are the subject of an Invention for which the Letters Patent numbered 968 of the
current year have been granted to me.
When the oxychloride is treated by products of combustion with a view to drive
off its chlorine wholly as vapour of hydrochloric acid care should be taken that the
products of combustion should not contain any appreciable proportion of free
oxygen. To this end it will be desirable to obtain them by first converting the
fuel employed into what is known as producer gas," and then burning it by
means of a regulated quantity of air, slightly insufficient to burn the whole
of it.
"
When the oxychloride is treated by products of combustion as just said, the
water of hydration of the oxychloride itself, together with that of the products of
combustion, will in many cases be sufficient to react upon all the chloride of
magnesium of the oxychloride and drive off all its chlorine as vapour of hydro-
chloric acid. When this is not the case a little steam should be added to the
products of combustion, but preferably only towards the end of the operation.
When the oxychloride is treated by air only it will still be only a part of the
chlorine of the oxychloride which will come off in the free state. The resulting
mixture of free chlorine, inert gases, vapour of hydrochloric acid, and it may be
vapour of water, must therefore be passed first into apparatus for condensing out
from it its vapour of hydrochloric acid and its vapour of water, if any, and then into
apparatus for the absorption of its free chlorine, as will be well understood.
A part of this Invention consists in mixing concentrated solution of chloride of
magnesium, associated or not with other salts, with oxide of iron or with a mixture
of oxide of iron and magnesia instead of with magnesia only, and heating such
mixture in a current of air. More of the chlorine of the chloride of magnesium is
thereby obtained in the free state than when the chloride of magnesium is mixed
with magnesia, but oxide of iron has to be constantly supplied.
When the oxychloride of magnesium, or a mixture of chloride of magnesium and
oxide of iron, is treated by a current of hot air without having heat applied to it
otherwise, the temperature to which the air has been previously heated should
preferably be such that the heated air shall be capable of raising to or nearly to
dull redness the portions of the charge with which it first comes into contact.
What I regard as constituting the above described Invention consists in obtaining
either vapour of hydrochloric acid only or a mixture of vapour of bydrochloric acid
and free chlorine from chloride of magnesium by mixing solution of the said chloride

page_text: suitably concentrated with either magnesia, preferably from preceding operations,
or with oxide of iron, and heating the resulting mixture in a current either of air
only or of products of combustion only, or of a mixture of one or the other of these
with steam, substantially as is above described.
In witness whereof, I, the said Walter Weldon, have hereto set my hand
and seal, this Twentieth day of August, in the year of our Lord One
thousand eight hundred and eighty-one.
WALTER WELDON. (L.S.)