Improvements in the Production of Nitric Acid, Caustic Alkali, and Ferric Oxide.
Year: 1893

page_text: Date of Application, 13th July, 1893
Complete Specification Left, 11th Apr., 1894-Accepted, 2nd June, 1894
PROVISIONAL SPECIFICATION.
Improvements in the Production of Nitric Acid, Caustic Alkali,
and Ferric Oxide.
We, Dr. GEORGE LUNGE, Professor of Chemistry at The Polytechnicum,"
Zurich, Switzerland, and FARNHAM MAXWELL-LYTE, of 60, Finborough Road,
London, S.W., Analytical Chemist, do hereby declare the nature of this invention
to be as follows :-
This invention relates to improvements in the decomposition of alkaline nitrates
for the production of nitric acid and caustic alkali and incidentally to the production
from purple ore, hæmatite, or other crude ferric oxides, of ferric oxide in a fine
state of division so as to be suitable for use as a pigment or for polishing purposes
(jewellers rouge) or for any other purpose for which Venetian red is employed.
It has heretofore been proposed to effect the decomposition of nitrate of soda as
an incidental step in another process having for its main object the production of
chlorine, the purpose of the decomposition being merely the regeneration of the
nitric acid used in the process and the production of caustic soda as a bye product.
The method by which this decomposition was proposed to be effected, consisted in
heating the nitrate of soda with ferric oxide with a view to form ferrite of soda
and evolve nitrous fumes.
The quantity of 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 object 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 the same time sub-
jecting 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, etc., 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
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

page_text: 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 recon-
verting the lower oxides of nitrogen into nitric acid by means of a "Lunge Tower
. or other suitable contrivance.
"
This process differs essentially from that described in the Specification of
Letters Patent granted to Adolph Vogt dated December 16th 1891 No. 22018,
according to which alkaline nitrate is mixed with a material which will remain
inert and physically and chemically unaltered in presence of the nitrate whilst being
heated in a current of carbonic acid with or without heated air or heated air and
steam. The purpose of mixing refractory or inert material with the alkaline
nitrate is to prevent fusion of the mass and cause it to remain throughout in porous
condition so as to be permeable by gaseous currents, but the use of carbonic acid is
prescribed as an indispensable part of the process and herein lies the essential
difference between Vogt's process and the process of this invention, since. in the
presence of carbonic acid soda does not chemically combine to any considerable
extent with any of the materials specified by Vogt, even oxide of iron remaining
inert and chemically unaltered, the residue after heating in a current of carbonic
acid in the manner described in Vogt's Specification consisting of a mechanical
mixture of carbonate of soda and oxide of iron. In the process of this invention
however in which no carbonic acid is employed, the ferric oxide, so far from
remaining inert is the most essential chemical agent for effecting decomposition of
the nitrate of soda by displacing the nitric acid and combining with the soda to
form a true chemical compound known as ferrite of soda which is only by prolonged
heating decomposable into ferric oxide and caustic soda. The reaction therefore
differs entirely from that specified by Vogt and the process also differs essentially
from Vogt's process by the fact that a much more valuable residual_product is
obtained namely caustic soda in lieu of carbonate of soda produced by Vogt.
The ferric oxide formed by the decomposition of the ferrite of soda is in an
extremely fine state of division and it is possible to separate this recovered oxide
from the excess of purple ore, hæmatite, or other ferric oxide present, by means of
levigation thus obtaining a substance fit for use as paint or for polishing purposes
or for any other object for which Venetian red is employed.
Dated this 13th day of July 1893.
COMPLETE SPECIFICATION.
Improvements in the Production of Nitric Acid, Caustic Alkali,
and Ferric Oxide.
We Dr. GEORGE LUNGE, Professor of Chemistry at The Polytechnicum,
Zurich, Switzerland, and FARNHAM MAXWELL LYTE of 60 Finborough Road,
London, S. W. Analytical Chemist, 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 the decomposition of alkaline nitrates

page_text: for the production of nitric acid and caustic. alkali, and incidentally to the
production from purple ore, hæmatite, or other crude ferric oxides, of ferric oxide
in a fine state of division suitable for use as a pigment or, for polishing purposes
(jewellers rouge) or for any other purpose for which Venetian red is employed.
It has heretofore been proposed to effect the decomposition of alkaline nitrate by
ferric oxide (as an incidental step in a process for producing chlorine) merely for
the purpose of regenerating the nitric acid. used in the process and obtaining
caustic alkali as a bye product. The reaction is similar whether nitrate of soda or
nitrate of potash is decomposed.and therefore, wherever in the following description
a sodium compound is referred to the corresponding potassium. compound is to
be understood. The decomposition was proposed to be effected by applying
external heat to the nitrate in admixture with an equal amount (or less) of ferric
oxide with a view to form. an alkaline ferrite, and evolve, nitrous fumes.. But
although the whole of the nitrate 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 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, and 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 decomposition.
Supposing the alkaline nitrate to be in solution the mixing with it of the ferric
oxide would be preferably effected whilst evaporating the solution to dryness so
as to effect a uniformly intimate mixture. But the mixture of the two materials
may also be effected when in the dry state. The mass remains porous when heated
and 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 effect the decomposition at a temperature sufficiently: low 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 corresponding to an incipient red
heat, which in practice we find. to be between 450° C. and 550° C., although any
temperature between 300° C. and 700° C. will be found effective, 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 corre-
sponding 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

page_text: the oxides of nitrogen becoming 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 and the alkaline base enters into solution and is recovered
as caustic alkali by evaporation in the ordinary way.
This process differs essentially from that described in the Specification of Letters
Patent granted to Adolph Vogt dated December 16th 1891 No. 22018, according
to which alkaline nitrate is mixed with a material which will remain inert and
physically and chemically unaltered in presence of the nitrate whilst being heated
in a current of carbonic acid with or without heated air or heated air and
steam. The purpose of mixing refractory or inert material with the alkaline
nitrate is to prevent fusion of the mass and cause it to remain throughout in
porous condition so as to be permeable by gaseous currents, but the use of
carbonic acid is prescribed as an indispensable part of the process and herein
lies the essential difference between Vogt's process and the process of this
invention since in the presence of carbonic acid the alkaline base of the nitrate
does not chemically combine to any considerable extent with any of the materials
specified by Vogt, even oxide of iron remaining inert and chemically unaltered,
the residue after heating in a current of carbonic acid in the manner described
in Vogt's Specification consisting of a mechanical mixture of carbonate of the
alkali and oxide of iron. In the process of this invention, however, in which
no carbonic acid is employed, the ferric oxide so far from remaining inert is the
most essential chemical agent for effecting decomposition of the alkaline nitrate
by displacing the nitric acid and combining with the alkaline base to form a
true chemical compound known as a ferrite of the alkali which is only by
prolonged heating in water decomposable into ferric oxide and caustic alkali.
The reaction therefore differs entirely from that specified by Vogt, and the
process also differs essentially from Vogt's process by the fact that a much more
valuable residual product is obtained namely caustic alkali in lieu of the alkaline
carbonate produced by Vogt.
The ferric oxide formed by the decomposition of the alkaline ferrite is in an
extremely fine state of division and it is possible to separate this recovered
oxide from the excess of purple ore, hæmatite, or other ferric oxide present, by
means of levigation, thus obtaining a substance fit for use as paint, or for
polishing purposes, or for any other object for which Venetian red is employed.
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 decomposing an alkaline nitrate in admixture
with ferric oxide in sufficient quantity to maintain the porosity of the mass, by
subjecting the heated mass intimately to the action of heated air and steam the
temperature of decomposition being such that the whole of the alkaline base will
be converted into a ferrite cf the alkali, with evolution of nitrous fumes almost
wholly convertible into nitric acid in the ordinary way.
2. The herein described process of producing nitric acid and caustic alkali and
recovering ferric oxide in a finely divided state, which consists in decomposing an
alkaline nitrate in admixture with crude ferric oxide in sufficient quantity to
maintain the porosity of the mass, by subjecting the heated mass intimately to the
action of heated air and steam so as to convert the whole of the alkaline base into
an alkaline ferrite, at a temperature which permits of the evolution of nitrous
fumes almost wholly convertible into nitric acid, and decomposing the alkaline

page_text: ferrite by hot water for recovery of the caustic alkali and ferric oxide, as herein
specified.
3. The herein described process of producing nitric acid and caustic alkali, and
recovering ferric oxide in a finely divided state, which process consists in first
admixing an alkaline nitrate with crude ferric oxide in sufficient quantity to
maintain the porosity of the mass, in then subjecting the heated mass to the action
of heated air and steam at a temperature sufficient to convert the whole of the
alkaline base into an alkaline ferrite, and evolving nitrous fumes, converting the
same into nitric acid, in then decomposing the alkaline ferrite by hot water for
recovery of the caustic alkali and ferric oxide, and then separating the lighter
from the heavier portions of ferric oxide, as and for the purpose specified.
Doted this 11th dor of Anil 1904
GEORGE LUNGE,
••
F. MAXWELL LYTE,
By A. M. & Wm. Clark,
53, Chancery Lane, London, Chartered Patent Agents.