IMPROVEMENTS IN PURIFYING HYDROCHLORIC PROVISIONAL SPECIFICATION
Year: 1881

page_text: LETTERS PATENT to Walter Weldon, of Rede Hall; Burstow, in the County
of Surrey, and William George Strype, of the Murrough, in the County of
Wicklow, for an Invention of "IMPROVEMENTS IN PURIFYING HYDROCHLORIC
PROVISIONAL SPECIFICATION left by the said Walter Weldon and William
George Strype at the Office of the Commissioners of Patents on the 18th
January 1881.
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey, and WILLIAM
GEORGE STRYPE, of the Murrough, in the County of Wicklow. "IMPROVEMENTS IN
PURIFYING HYDROCHLORIC ACID, AND IN MANUFACTURING CHLORINE THEREFROM.'
"
The main object of the present Invention is to economise limestone, acid, and
manganese, in the manufacture of chlorine, but a part of the present Invention is
applicable also to the purification of hydrochloric acid, to whatever purpose the
hydrochloric acid may be afterwards applied.
"
In the manufacture of chlorine, as at present conducted by what is known as
Weldon's process, chlorine is liberated from hydrochloric acid by means of
regenerated peroxide of manganese, in the state of what is known as Weldon
mud." In this state peroxide of manganese is associated with various basic bodies,
and especially with lime and protoxide of manganese. Hydrochloric acid below a
certain degree of strength cannot attack peroxide of manganese, but can be
neutralized by the basic bodies, which are thus associated with it in Weldon mud.
Therefore, but for the fact that all bydrochloric acid used for the manufacture of
chlorine contains sulphuric acid, it would be practicable to completely neutralize
the hydrochloric acid by mud alone. A neutral solution of chloride of manganese
and chloride of calcium would thus be obtained, holding in suspension some
undissolved peroxide of manganese. After this had been allowed to settle the
solution could be decanted from it, the solution then going to the oxidizer, and
the peroxide of manganese to the stills. Hitherto however this mode of working
Price 77

page_text: has not been practicable, owing to the sulphuric acid present in all hydrochloric
acid employed in chlorine factories. This forms sulphate of lime, which must be
got rid of, and with which would have to be thrown away the most valuable
constituent of any mud used in excess of the quantity which the acid can
completely dissolve. Care has therefore to be taken not to use more mud than the
acid employed can dissolve completely. The residual liquor is thus strongly acid,
and has to be neutralized by limestone; it is then left at rest until the sulphate of
lime has deposited as completely as possible; the clear liquor is then drawn off, and
the residue, after being filtered and washed, is thrown away. As it cannot be
washed completely some chloride of manganese is always thrown away with it. The
sulphuric acid present with the hydrochloric acid thus involves the loss of all that
part of the hydrochloric acid which is at present neutralized by limestone, the loss
of the limestone necessary to neutralize that acid, and moreover a certain loss of
chloride of manganese.
By our present Invention we avoid or greatly diminish those losses as
follows:-
Firstly. We treat the hydrochloric acid before sending it into the chlorine stills by
chloride of calcium, whereby its sulphuric acid, or a certain part of it, is converted
into sulphate of lime.
Secondly. We filter the hydrochloric acid which has been so treated, and so
separate a comparatively pure acid, and obtain a precipitate of nearly pure sulphate
of lime, which, after having been washed, can be applied to many purposes in
the arts.
Thirdly. We then employ the acid which has been thus purified or partially
purified in the chlorine stills, either neutralizing it in the stills themselves by an
excess of mud, or running off from the stills an acid residual liquor, as at present,
and neutralizing that liquor, either in the present neutralizing wells, or in special
apparatus, as may be most convenient in each case, instead of by limestone, as at
present, by the bases of a further portion of mud.
Fourthly. We then separate from the neutralized liquor the peroxide of
manganese at first suspended in it, either by deposition and decantation or by any
convenient method of filtration; we then treat the clear liquor for the regeneration
from it of peroxide of manganese for use again, either by what is known as the
Weldon process, or by what is known as Dunlop's process, or by any other con-
venient method. The peroxide of manganese which has been separated from the
neutralized liquor in which it was in suspension we employ in the stills, as will be
well understood.
When the hydrochloric acid is not completely but is only partially freed from
sulphuric acid by the method above described, it will usually be necessary to elimi-
nate from time to time any sulphate of lime which may have accumulated. This
can be done by combining the method of proceeding above described with the
method of proceeding now in use, neutralizing in the greater number of cases by
the bases of an excess of mud, but occasionally neutralizing by limestone and
otherwise proceeding as at present.
A part of our Invention consists in employing for the purification of hydrochloric
acid as aforesaid the solution of chloride of calcium, which is obtained as a waste
product of the Weldon process, and also the solution of chloride of calcium, which is
obtained as a waste product of the Dunlop process, or any solution of chloride of
calcium obtained by decomposing chloride of manganese by lime or carbonate of
lime.
A further part of our Invention consists in employing in the manufacture of
chlorine by the Dunlop process the method of neutralizing that part of the acid
employed which is now neutralized by limestone by the protoxide or protoxides
contained in the product of the Dunlop method of regenerating peroxide of
manganese from a solution of manganese chloride.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Walter Weldon and William George Strype in the Great Seal Patent
Office on the 16th July 1881.
"
WALTER WELDON, of Rede Hall, Burstow, in the County of Surrey, and
WILLIAM GEORGE STRYPE, of the Murrough, in the County of Wicklow.
IMPROVEMENTS IN PURIFYING HYDROCHLORIC ACID, AND IN MANUFACTURING
CHLORINE THEREFROM."
The main object of the present Invention is to economize hydrochloric acid,
limestone, and manganese, in the manufacture of chlorine, but a part of the present
Invention is applicable also to the purification of commercial hydrochloric acid
which is to be applied to other purposes than to the manufacture of chlorine.
Commercial hydrochloric acid nearly always contains sulphuric acid, the presence
of which is very prejudicial to many applications of hydrochloric acid. The first
part of the present Invention consists in treating hydrochloric acid containing
sulphuric acid by solution of chloride of calcium, in order to the separation of
sulphuric acid from it as sulphate of lime.
As sulphate of lime is freely soluble in hot aqueous hydrochloric acid, but is only
very slightly soluble in cold aqueous hydrochloric acid, either the hydrochloric
acid must be cold when the solution of chloride of calcium is added to it, or if the
solution of chloride of calcium be added to hot hydrochloric acid, the mixture must
be allowed to cool before being submitted to the next operation. Hydrated
sulphate of lime will then crystallize out, the mother-liquor being an aqueous
hydrochloric acid containing comparatively little sulphuric acid, from which
mother-liquor the crystals of hydrated sulphate of lime may be easily separated by
filtration.
A filter which has been found to be very suitable for the separation of sulphate of
lime from hydrochloric acid which has been treated by chloride of calcium under
the present Invention is constructed as follows:-Its bottom consists of a thick
Yorkshire flag, and its sides are of timber, their lower edge fitting into a groove
cut in the Yorkshire flag. The sides are firmly bolted down to the bottom, and
the joint between the wood and the stone is further made tight with a mixture of
china clay and tar. Near one end is an aperture in the flag forming the bottom
of the filter, to which aperture is fitted an earthenware pipe by which the filtered
acid is conveyed to the stills or to a reservoir. A little above the bottom of the
filter formed of the Yorkshire flag is a false bottom formed of slates, and on these
slates is a bed of gravel or pebbles of a total depth of about three inches, this bed
being formed of three layers, the lower layer being formed of pebbles of from half
an inch to three-quarters of an inch diameter, the intermediate layer of pebbles of
from half an inch to a quarter of an inch diameter, and the upper layer of pebbles
of from a quarter of an inch to an eighth of an inch diameter. Upon this bed of
gravel are arranged a series of wooden laths, about one and a half inch wide and
three quarters of an inch thick, placed a little distance apart. The object of these
laths is to prevent the gravel filtering bed being disturbed by the wooden spade or
scraper with which a workman from time to time removes the sulphate of lime.
The filter is provided with a wooden cover, in which is an aperture communicating
with a flue for carrying off any vapour of hydrochloric acid. The solution of
chloride of calcium is added to the bydrochloric acid in stone tanks which
communicate with the filtering apparatus by earthen ware pipes, on which are cocks
also of earthenware. The contents of these cisterns are agitated from time to time,
so that sulphate of lime may not fall to the bottom and accumulate in them, but
shall all pass to the filtering apparatus.

page_text: After each operation of filtration, or after a certain number of operations of
filtration, as may be more convenient in each case, the sulphate of lime is removed
from the filter by means of wooden scrapers and spades, all but the small quantity
which fills the spaces between the wooden laths. This should not be removed, on
account of disturbing the filtering bed, until it has become so dense that the
purified acid will not pass through it sufficiently rapidly. From the filter the
sulphate of lime is conveyed to apparatus in which it is washed and otherwise
prepared for any use to which it may be applied.
The quantity of solution of chloride of calcium which must be added to the
hydrochloric acid to be treated by the first part of this Invention will depend
partly upon the proportion of sulphuric acid in the hydrochloric acid employed,
and partly upon the strength of the solution of chloride of calcium used. The
proportion of sulphuric acid in the hydrochloric acid, and the strength of the
solution of chloride of calcium available to be employed, will differ in different
works. In the factory in which our Invention is already applied the hydrochloric
acid contains about one and a quarter per cent. of sulphuric acid, the average
density of the acid, taken cold, being thirty-two degrees Twaddell, and it is found
that ninety per centum of this sulphuric acid can be precipitated as sulphate of
lime by adding to the hydrochloric acid about one-sixth of its volume of the
solution of chloride of calcium drawn off from the Weldon mud produced in the
same factory. This solution of chloride of calcium contains from seventeen to
eighteen per centum of Ca Cl.
'
No
The second part of this Invention consists in combining with the treatment as
above described of the hydrochloric acid which is to be employed in the manu-
facture of chlorine, a method of proceedure which is not possible when employing,
in the manufacture of chlorine, hydrochloric acid which has not been previously
in large part freed from sulphuric acid. Chlorine is now usually obtained by the
reaction upon hydrochloric acid of what is known as Weldon mud. Weldon mud
contains both chloride of calcium and oxide of calcium, and hence sulphate of lime
is one of the products of its reaction upon hydrochloric acid containing sulphuric
acid. The sulphate of lime thus formed has to be continually got rid of, and in
order to get rid of it a mode of working has to be followed which is wasteful of
hydrochloric acid, and wasteful of manganese, and which moreover involves a
consumption of limestone which would otherwise be entirely unnecessary.
more mud is added to the hydrochloric acid employed than will dissolve therein
completely, and hence the residual product of the operation of the generation of
chlorine is run off from the stills in which that operation is performed containing
much free hydrochloric acid. This residual product is run into wells in which it
is agitated with finely divided limestone, by which its free acid is neutralized
and the sulphate of lime which was dissolved in it is sent out of solution. The
neutralized liquor is pumped up into settling vessels and therein left at rest until
its sulphate of lime has deposited, when the clear supernatent liquor is drawn off
and submitted to treatment for the regeneration of peroxide of manganese from it.
The residual mud of sulphate of lime mixed with solution of chloride of manganese
and chloride of calcium is then either filtered and washed, or submitted to washing
only, after which it is thrown away, but notwithstanding. all filtering and washing
an appreciable quantity of chloride of manganese is always thrown away with it.
By combining with the first part of our Invention as above described the method
of proceedure now to be set forth, we are enabled to economize all or nearly all the
hydrochloric acid which in the present mode of working is neutralized by limestone,
and we are at the same time enabled to economize all or nearly all the limestone
which is at present used to neutralize that acid, and also all or nearly all the
chloride of manganese which is at present thrown away with the sulphate
of lime which has settled out of the neutralized still-liquors. By using in
the manufacture of chlorine hydrochloric acid from which most of the sulphuric
acid which it originally contained has been previously separated by that
treatment with chloride of calcium which constitutes the first part of our

page_text: Invention, we are enabled to neutralize the bydrochloric acid completely by
Weldon mud itself. To this end, when the neutralization of the acid in the stills
has proceeded so far that the acid remaining is no longer capable of dissolving
manganese peroxide, instead of ceasing adding mud, as is done at present, and then
neutralizing the acid liquor by limestone we add more mud either in the stills
themselves or in the neutralizing wells, until the acid liquor has been completely
neutralized by the lime and manganese protoxide of such further quantity of mud.
We thus obtain a neutral solution holding in suspension undissolved manganese
peroxide. We pump this into settlers, and separate the manganese peroxide by
deposition and decantation. We then send the clear liquor to the regeneration
operation, and we use the manganese peroxide in the chlorine stills, either by
itself or mixed with ordinary manganese mud, as may be most convenient in each
case.
We have found that a very convenient method of proceedure in order to the
neutralization of the last portions of the hydrochloric acid by the lime and
manganese protoxide of an excess of Weldon mud, consists in running off the
contents of the stills, as is done at present, while the still-liquors still contain much
free acid, and neutralizing them in the wells as at present, but using for their
neutralization Weldon mud instead of limestone. In such case it is desirable that
the mud which is to effect the neutralization should be put into the wells first,
and the still liquors. be then run on to this mud with constant agitation. Less
still-capacity then suffices than is necessary when the acid is completely neutralized
by an excess of mud in the stills themselves.
When, as will usually be the case, the treatment by the first part of the present
Invention of the hydrochloric acid employed in the manufacture of chlorine, while
removing the greater part of the sulphuric acid therefrom, does not remove the
whole, sulphate of lime will slowly accumulate in the Weldon mud and must at
intervals be removed. This can be done by occasionally neutralizing by limestone
as at present, while usually neutralizing by an excess of Weldon mud, as above
described. In the factory in which this Invention is already applied it has been
found that it is not until after several months of continuous neutralization by
excess of mud that sulphate of lime so far accumulates as to require its removal.
When sulphate of lime has so far accumulated the acid still-liquors must be
neutralized by limestone, and the sulphate of lime be allowed to settle out from the
neutralized liquors and be then dealt with as at present. When the accumulated
sulphate of lime has thus been got rid of, neutralization by an excess of Weldon
mud can be recommenced.
Having now described the nature of the said Invention, and the manner in which
the same is to be performed, we claim as. the Invention to be secured to us by the
hereinbefore in part recited Letters Patent,-
Firstly. Removing sulphuric acid from commercial hydrochloric acid by means
of chloride of calcium, substantially as is above set forth; and
Secondly. Combining with the employment in the manufacture of chlorine of
hydrochloric acid, from which sulphuric acid has been so removed, the neutralization
of such hydrochloric acid by an excess of Weldon mud, substantially as is above
described.
In witness whereof, I, the said Walter Weldon, for myself and the said
William George Strype, have hereunto set my hand and seal, this Fifteenth
T... :
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WALTER WELDON. (L.S.)