IMPROVEMENTS IN THE MANUFACTURE OF CHLORINE AND HYDROCHLORIC ACID
Year: 1884

page_text: I, WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey, Fellow
of the Royal Society, do hereby declare the nature of the said Invention for
IMPROVEMENTS IN THE MANUFACTURE OF CHLORINE AND HYDROCHLORIC ACID
to be as follows:-
This invention relates to the manufacture of chlorine and hydrochloric acid from
chloride of magnesium.
The said invention consists in heating solid hydrated chloride of magnesium to
a low temperature, in such wise as to drive off a large part of its water without
driving off more than a small part of its chlorine.
Such solid hydrated chloride of magnesium usually contains six equivalents of
water, but it may contain more than six equivalents of water. By heating it to a
low temperature all but about two equivalents of its water may be driven off
from it. The temperature most suitable to this end is between 150 degrees and
200 degrees Centigrade.
After having thus been partially dehydrated, the solid chloride of magnesium
must be intimately mixed with free magnesia, and the mixture then heated in a
current of air or of oxygen. The chlorine of the chloride of magnesium of the
mixture is thereby driven off, partly as vapour of hydrochloric acid, and partly as
free chlorine.
Instead of partially dehydrating the solid hydrated chloride of magnesium before
adding free magnesia to it, magnesia may be intimately mixed with solid hydrated
chloride of magnesium, without the latter having been first partially dehydrated.
In this case, if it be desired to obtain as much as possible of the chlorine of the
chloride of magnesium in the free state, the mixture should first be partially
dehydrated by heating it to a low temperature, and should be then heated to a
higher temperature in a current of air or of oxygen. In other cases, the mixture
may be at once heated to a high temperature in a current of air or of oxygen.
Prine 21

page_text: The heating to a high temperature in a current of air or of oxygen may be
performed in any one of many kinds of apparatus, but the apparatus believed to
be most suitable for this operation is that for which an application for a patent
was made on the 23rd of June, 1884, which application is numbered 9304.
What is new in this invention thus consists:
Firstly, in obtaining chlorine and vapour of hydrochloric acid by first partially
dehydrating by heating it to a low temperature solid hydrated chloride of
magnesium, then intimately mixing free magnesia with the partially dehydrated
solid chloride of magnesium thus obtained, and then heating the resulting mixture
to a high temperature in a current of air or of oxygen.
Secondly, in mixing magnesia with solid hydrated chloride of magnesium, and
then heating the mixture to a high temperature in a current of air or of oxygen,
having or not first partially dehydrated the mixture by heating it to a low
temperature, accordingly as it is desired to obtain the chlorine of the chloride of
magnesium chiefly as free chlorine or chiefly as vapour of hydrochloric acid.
Dated this sixth day of August 1884.

page_text: I, WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey, Fellow
of the Royal Society, do hereby declare the nature of the said Invention for
"IMPROVEMENTS IN THE MANUFACTURE OF CHLORINE AND HYDROCHLORIC ACID,"
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 the manufacture of chlorine and hydrochloric acid
from solid hydrated magnesium chloride.
It consists essentially in heating to a suitable temperature in a current of
air or of oxygen a mixture of magnesium chloride and magnesia, obtained by
adding free magnesia to solid magnesium chloride, such solid magnesium chloride
being either the ordinary hydrated salt containing six equivalents of water, or
thereabouts, or the product obtained by dehydrating such salt to a greater or less
extent by subjecting it to the action of heat at a much lower temperature than
that necessary to enable oxygen to drive off free chlorine from magnesium chloride,
and the mixture of magnesium chloride and magnesia, when made by adding free
magnesia to solid hydrated magnesium chloride which has not been subjected to
au operation of partial dehydration, being partially dehydrated or not, before
subjecting it to the operation by which free chlorine is to be obtained from it,
according to the case, as will be explained below.
One of the two chief points of novelty of the present invention consists in
subjecting solid hydrated magnesium chloride, before heating it in a current of air
or of oxygen to a temperature at which free oxygen can react upon it, or upon
some of it, to the operation of heating it to a low temperature, in such wise as to
drive off a part of its water without driving off more than a comparatively
inconsiderable proportion of its chlorine.
"
Solid hydrated magnesium chloride, containing six or so equivalents of water,
may have about four equivalents of water driven off from it, by heating it to a
low temperature, under ordinary atmospheric pressure, without losing more than
a very small percentage of its chlorine. The chlorine which it does lose in the
operation of course goes off as vapour of HCl. It is believed that the most
suitable temperature to be employed in this operation is between about 150 degrees
and 200 degrees Centigrade, or, say, between about 300 degrees and about
892 degrees Fahrenheit. That part of the present invention, however, which
relates to the partial dehydration of solid hydrated magnesium chloride, before
proceeding to cause oxygen to react upon it or upon a portion of it, is not confined
to the use of the temperatures indicated, nor to the degree of dehydration just
spoken of. Not only may that degree of dehydration be obtained by exposing
the hydrated chloride to a lower temperature for a longer time; but, if the circum-
stances be such that the evolution during the preliminary partial dehydration of
the chloride of a larger proportion of its chlorine as vapour of HCl than would
otherwise be so evolved be not objectionable, a higher temperature than is above

page_text: indicated may be used, provided only that it be one below that at which hydrated
inagnesium chloride fuses in its water of crystallization.
No particular method of or appliances for performing the operation of
dehydrating to a greater or less degree solid hydrated magnesium chloride
before mixing it with magnesia and then heating the mixture in a current of
air or oxygen to the temperature at which oxygen can drive off free chlorine from
dt, constitute any part of the present invention; and the appliances and methods
of procedure by means of which that operation may be performed are very various,
It may conveniently be performed, however, by spreading the solid magnesium
chloride, in crystals or other small masses, on the floors of flues or chambers the
floors of which are heated from below; or by passing over and through crystals or
other small masses of the said chloride, charged into vessels or flues or chambers
of any convenient kind, air or gases, inert at the temperature employed, which
have first been heated to that temperature..
.1
If the operation of more or less complete preliminary dehydration be performed
in close vessels, to which heat is applied exteriorly, and a minus pressure, be
maintained in the said vessels by means of exhaust pumps, the chloride may be
dehydrated nearly or quite completely without losing any of its chlorine, and
without being heated to a much higher temperature than 200 degrees Fahrenheit..
It is believed that the best method of performing the present invention is to
first dehydrate more or less completely the hydrated solid magnesium chloride
'commenced with, then mix the more or less completely dehydrated magnesium
chloride intimately with free magnesia, and then heat the mixture to a high
temperature in a current of air or of oxygen. The chloride may be mixed with
magnesia, however, before performing the operation of dehydration, and the
operation of preliminary dehydration be then performed, not upon the magnesium
chloride by itself, but upon a mixture of the said chloride with free magnesia.
The method of performing the dehydration may be the same, whether it be
performed upon solid hydrated magnesium chloride only, or upon a mixture of
such solid hydrated chloride with magnesia.
The less the quantity of water which is present in a mixture of magnesium
chloride and magnesia submitted to the action of air or oxygen at a temperature
at which oxygen can drive off free chlorine from inagnesium chloride, the greater
the proportion of the chlorine of the magnesium chloride present in such mixture
which is so driven off in the free state, and the smaller the proportion of it which
is driven off as vapour of HCl. The object of the above described preliminary
dehydration is thus to secure that of the chlorine afterwards driven off from the
magnesium chloride treated a maximum proportion shall be in the free state and
only a minimum proportion in that of vapour of hydrochloric acid. But there
may be cases in which it will not be desired to diminish to the utmost the
proportion of the said chlorine which shall be driven off as H Cl, and to increase to
the utmost the proportion of it which shall be driven off in the free state; and in
such cases the operation of preliminary dehydration need not be performed. In
such cases, the method to be followed will be to mix solid hydrated magnesium
chloride, in crystals or other small masses, with free magnesia, and then at once
charge the mixture into apparatus in which it shall be heated, in a current of
air or of oxygen, to a temperature at which oxygen can drive off. free chlorine
from it.
The higher the temperature to which a mixture of magnesium chloride and
magnesia is heated in contact with a current of air or of oxygen, the more rapidly
will the magnesium chloride thereby be decomposed, and the greater in most cases
will be the proportion of its chlorine which will be evolved in the free state. The
decomposition of magnesium chloride by the method in question can be performed
below dull redness, but a higher temperature is much to be preferred.
-
!.
The operation of heating in a current of air or of oxygen a mixture of
magnesium chloride and magnesia may be performed in various ways and by
means of various appliances, and no particular manner of or appliance for

page_text: performing it constitutes any part of the present invention. It may be performed,
however, by heating the mixture of magnesium chloride and magnesia in a muffle
furnace, into which is admitted a current of air or oxygen; or the apparatus in
which it is performed may be on the principle of that described in the specifications
filed in connection with the application for a patent bearing the number 9304
of 1884.
What passes off from the apparatus in which a mixture of magnesium chlorido
and magnesia is heated in a current of air or oxygen to such temperature that
oxygen can drive off free chlorine from magnesium chloride, is a mixture of gases
and vapours usually containing not only free chlorine but also vapour of HCl. As
will be well understood, this mixture of gases and vapours must be passed first
into apparatus in which its HCl shall be condensed out of it, and from that
apparatus into apparatus in which its free chlorine shall be utilized.
The proportion of magnesia to be mixed with magnesium chloride to be treated
under this invention may vary within wide limits, but should always be sufficient
to prevent the magnesium chloride agglomerating into large masses when heated
to or above its point of fusion. From half an equivalent to an equivalent and
half of magnesia are proportions which have given good results. The magnesia
should be mixed with the magnesium chloride as intimately as possible.
Having now particularly described and ascertained the nature of the said
Invention and in what manner the same is to be performed, I declare that what
I claim is
:
Firstly Obtaining free chlorine and vapour of hydrochloric acid from solid
bydrated magnesium chloride by first dehydrating to a greater or less extent the
said solid hydrated magnesium chloride by heating it to a low temperature, then
intimately mixing the product of this operation of dehydration with free magnesia,
and then heating the resulting mixture in a current of air or of oxygen to a
temperature at which oxygen can drive off free chlorine from it.
Secondly Obtaining chlorine and vapour of hydrochloric acid from solid
hydrated magnesium chloride by mixing such solid hydrated magnesium chloride
with free magnesia and then heating the mixture in a current of air or of oxygen
to a temperature at which oxygen can drive off free chlorine from it, the mixture
of hydrated magnesium chloride and magnesia being or not being heated to a low
temperature, in order to debydrate to a greater or less extent its magnesium
chloride, before being raised to a temperature at which oxygen can drive off free
chlorine from it, according to circumstances, as above explained.