Improvements in the Production of Caustic Alkali and Chloride of Lead for Conversion into Chlorine and Refined Lead.
Year: 1893

page_text: Date of Application, 13th July, 1893
Complete Specification Left, 11th Apr., 1894-Accepted, 12th May, 1894
PROVISIONAL SPECIFICATION.
Improvements in the Production of Caustic Alkali and Chloride of
Lead for Conversion into Chlorine and Refined Lead.
We FARNHAM MAXWELL LYTE of 60 Finborough Road, London, S:W.
Analytical Chemist, and Dr. George Lunge, Professor of Chemistry at the
Polytechnicum, Zurich, Switzerland do hereby declare the nature of this invention
to be as follows:-
This invention relates to improvements in that part of the process forming the
subject of Patent No. 8692 of 1891 whereby caustic alkali and chloride of lead are
produced (the latter for conversion by electrolytic decomposition into chlorine and
refined lead) from an alkaline chloride and crude lead. In the process as therein
described, nitric acid plays the part of a vehicle for lead, and the intention of the
patentee is that it shall be continuously recovered for use over and over again, but
it has been found in practice that the recovery of the nitric acid is very incomplete
and the consequent loss of nitric acid which ensues is a commercial disadvantage
of the aforesaid process, which it is the object of the present invention to
remedy.
In the process therein described oxide of lead is dissolved in nitric acid to form
nitrate of lead, with which and with an alkaline chloride, say common salt for
example, nitrate of soda and chloride of lead.are formed by double decomposition.
If potassium chloride be employed, caustic potash will be produced, and therefore
wherever in the following description soda is mentioned, potash must be understood
also. On then heating the alkaline nitrate with ferric oxide the former is entirely
decomposed and a compound of ferric oxide and soda is formed which is known as
ferrite of soda, nitrous fumes being evolved.
The quantity of the ferric oxide proposed to be used was only about equal to that
of the nitrate of soda. It has however been found in practice that although
the whole of the nitrate of soda can be decomposed in this way, the recovery of the
nitric acid is very incomplete owing to the fact that by reason of the fluxing of the
mass, such a high temperature is necessary to effect the decomposition of the nitrate
of soda that a certain quantity of the nitrogen oxides is split up too far for recovery
as nitric acid. This objection may however be overcome and this it is the
objection of this invention to accomplish.
The invention consists essentially in maintaining the mass in a porous condition,
and not only heating it externally but also internally, and at same time subjecting
it to the chemical action of a mixed current of air and steam, preferably heated to
the same temperature as that of the mass, the porosity of the mass permitting of its
easy permeation by the heated air and steam whereby the evolution of nitric acid
is rendered possible at a much lower temperature than when the fluxing of the mass
into a mixed solid and liquid portion is permitted. To this end such a quantity of
ferric oxide is used as to form a mass which does not fuse at the temperature of the
reaction but remains solid. and porous throughout the operation of decomposition.
It has been found when employing ferric oxide in the shape of "purple ore that
the best proportion is about two parts thereof by weight to one of nitrate of soda,
but the invention is not limited to that particular quality of ferric oxide, nor to that
particular proportion, as it may be possible, according to the physical state of the
ferric oxide, its degree of division, &c., to use less than the proportion indicated, but
the quantity must always be sufficient not only to prevent any fluxing of the mass,
but also to ensure a sufficiently low temperature of decomposition. It is not
however sufficient to thus prevent the fluxing of the mass and to lower the
"

page_text: temperature of the decomposition; it is also essential that the mass be subjected to
the action of a mixed current of heated air and steam. When therefore the mixed
current of air and steam, heated say to a degree corresponding to an incipient red
heat of the mass, is passed through the porous mass, the latter is converted into a
dirty green mass consisting essentially of ferrite of soda containing no sodium
nitrate or nitrite, with evolution of nitrous fumes, the temperature at which the
decomposition is effected being such that only a very slight proportion of the oxides
of nitrogen becomes destroyed, most of the nitric acid corresponding to the nitrate
of soda used being recoverable by air and water in the ordinary way. Steam alone
is unsuitable, even if superheated, and although hot air alone acts better than
steam, a mixture of air and steam previously heated to the temperature which
prevails in the decomposing retort, gives much the best results. The quantity of
steam is regulated in such manner that the recovered nitric acid is not too weak
and the quantity of air is kept in due excess for reconverting the lower oxides
of nitrogen into nitric acid by means of a "Lunge Tower or other suitable
contrivance.
It is to be observed that the liquor which results after mixing a solution of
equivalent quantities of lead nitrate and alkaline chlorides and filtering from the
chloride of lead separated, still contains a somewhat considerable quantity of lead
chloride dissolved. We concentrate this liquor to such a point that as much as
possible of the lead chloride crystallises out on cooling without any sodium nitrate
crystallising out at the same time. The lead then still remaining in solution is
precipitated by adding an equivalent proportion of an alkali or
earth.
Dated this 10th 1
1000
an alkaline
F. M. LYTE,
GEORGE LUNGE,
By A. M. & Wm. Clark,
53, Chancery Lane, London, Chartered Patent Agents.
COMPLETE SPECIFICATION.
Improvements in the Production of Caustic Alkali and Chloride of
Lead for Conversion into Chlorine and Refined Lead.
We FARNHAM MAXWELL LYTE of 60 Finborough Road, London, S.W.
Analytical Chemist, and Dr. GEORGE LUNGE, Professor of Chemistry at the
Polytechnicum, Zurich, Switzerland 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 :-
'This invention relates to improvements in that part of the process forming the
subject of Patent No. 8692 of 1891, whereby caustic alkali and chloride of lead are
produced (the latter for conversion by electrolytic decomposition into chlorine and
refined lead) from an alkaline chloride and crude lead. In the process as therein
described, nitric acid plays the part of a vehicle for lead and the intention of the
patentee is that it shall be continuously recovered for use over and over again, but
it has been found in practice that the recovery of the nitric acid is very incomplete
and the consequent loss of nitric acid which ensues is a commercial disadvantage
of the aforesaid process, which it is the object of the present invention to
remedy.
In the process above referred to oxide of lead is dissolved in nitric acid to
form nitrate of lead, with which and with an alkaline chloride, say common salt
for example, nitrate of soda and chloride of lead are formed by double decom-
position. If potassium chloride be employed caustic potash will be produced and
therefore wherever in the following description soda is mentioned, potash must be
understood also. On heating the alkaline nitrate in admixture with an equal

page_text: amount (or less) of ferric oxide as in the aforesaid process, the nitrate is entirely
decomposed and a compound of ferric oxide and soda is formed which is known as.
ferrite of soda, nitrous fumes being evolved. But although the whole of the nitrate
of soda can be decomposed in this way, the recovery of the nitric acid is very
incomplete, owing to the fact that the fluxing of the mass renders such a high
temperature necessary to effect the decomposition of the nitrate of soda as to cause
the splitting up of a considerable quantity of the nitrogen oxides too far for
recovery as nitric acid.
This invention has for its object to overcome this objection and it consists in
maintaining the mass in a porous condition throughout the operation so as to render
it easily permeable, heating it not only externally but also internally by subjecting
it to the action of a mixed current of heated air and steam whereby complete
decomposition is effected and the evolution of nitrous fumes wholly or almost.
wholly convertible into nitric acid is rendered possible, at a much lower temperature.
than when the fluxing of the mass into a mixed solid and liquid condition is.
permitted. In carrying out the process such a quantity of ferric oxide is intimately
mixed with the nitrate that the resulting mass will not fuse at the temperature of
the reaction, but will remain solid and porous throughout the operation of decom--
position. The nitrate being in solution the mixing of the ferric oxide with it may
be advantageously effected whilst evaporating the solution to dryness so as to effect:
a uniformly intimate mixture. The mass remaining porous when heated is easily
permeable by the mixed current of heated air and steam which is forced through
it in any convenient way, suitable provision being made for the collection of the
nitrous fumes and their conversion into nitric acid. It has been found when.
employing ferric oxide in the shape of "purple ore " that the best. proportion.
is about two parts thereof by weight to one of nitrate of soda, but the invention.
is not limited to that particular quality of ferric oxide, nor to that particular
proportion, as it may be possible, according to the physical state of the ferric
oxide, its degree of division, etc., to use less than the proportion indicated, but
the quantity must always be sufficient to prevent any fluxing of the mass. It is
not, however, sufficient to thus prevent the fluxing of the mass but it is also
essential to lower the temperature of the decomposition sufficiently to enable the
nitrous fumes evolved to be wholly recoverable or nearly so, as nitric acid, and this
is effected by subjecting the mass to the intimate action of a mixed current of
heated air and steam. The mixed current of air and steam should be heated
preferably to the same temperature as that of the mass, say to a degree corre-
sponding to an incipient red heat that is, between about 450° and 550° C., although.
any temperature between 300° and 700° C. will suffice, and when the heated.
current is passed through the porous mass obtained by mixing nitrate of soda and
ferric oxide as above mentioned, a dirty green mass is formed consisting essentially
of ferrite of soda, with evolution of nitrous fumes, the temperature at which the
decomposition is effected being such that most of the nitric acid corresponding to
the nitrate of soda used is recoverable by air and water in the ordinary way, no.
sodium nitrate or nitrite remaining, and only a very slight proportion of the oxides
of nitrogen being destroyed. Steam alone is unsuitable, even if superheated, and.
although hot air alone acts better than steam, a mixture of air and steam previously
heated to the temperature which prevails in the decomposing retort gives much the
best results. The quantity of steam is regulated in such manner that the recovered
nitric acid is not too weak and the quantity of air is kept in due excess for
reconverting the lower oxides of nitrogen into nitric acid by means of a "Lunge
Tower" or other suitable contrivance. The resulting ferrite is to be decomposed
by heating it with water whereby ferric oxide is precipitated for use over again and
the alkaline base enters into solution from which it is recovered as caustic soda by
evaporation in the ordinary way.
It is to be observed that the liquor which results after mixing a solution of
equivalent quantities of lead nitrate and alkaline chlorides and filtering from the
chloride of lead separated, still contains a somewhat considerable quantity of lead.

page_text: cbloride dissolved. We concentrate this liquor to such a point that as much as
possible of the lead chloride crystallizes out on cooling without any sodium
nitrate crystallizing out at the same time. The lead then still remaining in
solution is precipitated by adding an equivalent proportion of an alkali or an
alkaline earth.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is
1. The herein described process of forming caustic alkali and chloride of lead
from an alkaline chloride and oxide of lead, which process consists in first forming
an alkaline nitrate by the double decomposition of nitrate of lead and an alkaline
chloride, and then decomposing the alkaline nitrate thus formed, while in admixture
with ferric oxide in sufficient proportion to maintain the porosity of the mass by
subjecting the mass to the action of heated air and steam at a temperature sufficient
to convert the whole of the base of the alkaline nitrate into a ferrite of the alkali
with the evolution of nitrous fumes, substantially as specified.
2. The herein described process of forming caustic alkali and chloride of lead
from an alkaline chloride and oxide of lead, and of recovering the nitric acid used
as a vehicle for the lead, which process consists in first forming an alkaline nitrate
by the double decomposition of nitrate of lead and an alkaline chloride, in then
decomposing the alkaline nitrate thus formed while in admixture with ferric oxide,
by subjecting the mass to the action of heated air and steam at a temperature
sufficient to convert the whole of the base of the alkaline nitrate into a ferrite of
the alkali, with the evolution of nitrous fumes, and in then converting the said
nitrous fumes into nitric acid, substantially as specified.
2004
F. MAXWELL LYTĖ,
GEORGE LUNGE,
By A. M. & Wm. Clark,
53, Chancery Lane, London, Chartered Patent Agents.