Improvements in the Manufacture of Nitric Acid.
Year: 1891

page_text: Date of Application, 16th Dec., 1891
Complete Specification Left, 7th Sept., 1892-Accepted, 8th Oct., 1892
PROVISIONAL SPECIFICATION.
Improvements in the Manufacture of Nitric Acid.
I, ADOLPH VOGT, of 26, Earls Court Gardens, in the County of London, do
hereby declare the nature of this invention to be as follows:-
This invention relates to the manufacture of nitric acid from alkali nitrates.
It is well known that when an alkali nitrate is heated to a red heat in the
presence of carbonic acid chemically combined with lime, i.e. carbonate of lime,
such nitrate is decomposed, nitric acid gas being given off and carbonate of an
alkali formed.
But this method, to the best of my knowledge, has never been successfully used
on a commercial scale for the reason that the mixture, even with a great excess of
carbonate of lime, fuses at the required heat and rapidly destroys the furnaces in
which the operation is carried on.
The object of my invention is to overcome this difficulty and to this end I force
heated carbonic acid through a slightly heated mixture of nitrate and some
refractory material such as burnt lime, the proportion of the nitrate to the
refractory material being such that the mixture remains porous and open for the
passage of gases at the heat required for the decomposition.
As the carbonic acid is the carrier of the heat required for the decomposition,
the latter takes place only where the carbonic acid comes in contact with particles
of the nitrate whereby nitric acid gas is expelled and carbonate of an alkali is
formed. If the high heat (iz.: bright red,) required for this decomposition was
applied in any other way for instance from outside a part of the nitric acid contained
in the nitrate, even in the presence of carbonic acid, would be split up into oxygen
and nitrogen and would therefore be lost.
The mixture being never fused in my process but on the contrary remaining a
loose and porous mass has no effect whatever on the retorts, and consequently not
only is the alkali carbonate produced pure but the furnaces stand a long time.
In order to transform the nitric acid gases driven off by the carbonic acid into
nitric monohydrate, which may be condensed in the usual way, a sufficient quantity of
steam, superheated or of ordinary pressure is introduced either along with the heated
carbonic acid or after the nitric acid gases are evolved from the mixture.
quantity of steam must be regulated as a larger quantity than required for the
formation of the nitric monohydrate would only produce a weak acid.
The
After the nitric acid has been completely driven off from the mixture in the
aforesaid manner the residue containing carbonate of soda or potash and lime may
be boiled with hot water so as to obtain a caustic alkali solution or it may be
treated with cold water so as to obtain an alkali carbonate solution, which can be
further treated in the usual way.
Instead of burnt lime, slaked lime may be used but in this case weaker nitric acid
is obtained.
Further instead of lime other refractory material may be used such as oxide of
iron, magnesia or baryta.
Dated the 16th day of December 1901

page_text: COMPLETE SPECIFICATION.
Improvements in the Manufacture of Nitric Acid.
I, ADOLPH VOGT, lately of 264, Earls Court Gardens in the County of London,
but now of Carntyne Chemical Works, Parkhead, in the County of Lanark, North
Britain, Chemical Engineer, 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, that is to say :-
My said invention relates to the manufacture of nitric acid from alkali nitrates.
It is well known that when alkali nitrate is heated to a red heat with calcium
carbonate, it is more or less completely decomposed, nitric acid gas being given off
and a carbonate of the alkali formed. But this method, to the best of my
knowledge, has never been successfully used on a commercial scale, because with
the great heat required fusion takes place even with considerable excess of the calcium
carbonate, and causes the rapid destruction of the furnaces in which the operation
was carried on. The method has also proved to be objectionable in practice because
in it there is formed a large amount of lower nitrogen oxides which are not easily
convertible into nitric acid without loss.
The object of iny invention is to overcome or avoid the difficulties referred to; and
to this end I employ carbonic acid in the gaseous state, and force it through a
mixture of the alkali nitrate and some refractory or inert material such as burnt
lime. Steam is mixed with the carbonic acid gas, which is heated to a temperature
between 300 and 400 degrees, centigrade.
As the carbonic acid gas is the carrier of the heat required for the reaction, this
reaction takes place only where the carbonic acid comes in contact with particles of
the nitrate, the nitric acid of which becomes replaced by the carbonic acid, and is
expelled in the gaseous state, a small amount of lower nitrogen oxide or oxides
being also formed.
In my Provisional Specification a bright-red heat was indicated as (possibly) that
to which the carbonic acid would require to be heated; I however find that in
practice a lower heat, or dull-red, that is about 350 degrees centigrade, is quite
sufficient, with which lower heat any fusing of the materials is of course the more
unlikely to occur, whilst at the same time there is with it less formation of lower
nitrogen oxides.
In practically carrying out my invention I obtain satisfactory results with a
mixture consisting of about equal parts, by weight, of the alkali nitrate and burnt
lime. The materials should be well mixed in a coarse granular form, so as to be
porous, or permeable by gaseous currents. I prefer to thoroughly incorporate the
materials with sufficient water to make an adherent mass, which after being
thoroughly dried is broken up into suitable small pieces. The materials are
charged into iron or firebrick retorts which are by preference vertical and of any
convenient size, for example retorts, one foot in diameter, and eight feet in height
may be used, the materials being charged to a depth such that the gases can be
forced through them, upwards, or in any other suitable direction, without requiring
too much power. As in my process the materials remain throughout in a porous or
permeable condition and are never fused, the action and wear and tear on the
retorts are reduced to a minimum and the alkali carbonate produced is free from
metallic impurities.
The retorts are connected to suitable condensing apparatus; and they may be
heated externally in any convenient way, but not so as to raise their contents to a
temperature above 350 degrees centigrade.
In order to oxidise the small quantity of lower nitrogen oxides which may be
formed in the retorts and to transform them into nitric acid before condensation
takes place, I cause a suitable small amount of heated air or heated air and steam
to mix with the gaseous currents issuing from the retorts; or the required air may

page_text: be mixed with the carbonic acid gas and steam on or before entering the retorts.
The quantity of steam introduced is to be regulated according to the strength of
the nitric acid which is wished to be obtained.
Instead of the burnt lime, there may be mixed with the alkali nitrate any other
convenient material which will remain inert and physically and chemically unaltered
in presence of the nitrate at the temperature employed. Thus, for example, I
use as the mixing material any alkaline earth, whether oxide, hydroxide, or
carbonate; or I may use peroxide of manganese or peroxide of iron.
may
After the nitric acid has been driven off from the alkali as completely as possible,
the resi lue in the retort, comprising carbonate of the alkali (soda or potash) is to
be lixiviated and treated by well known means for the separation and recovery of
the alkali as carbonate or caustic, the value of which diminishes the cost of the
nitric acid.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is:
The improved process for obtaining nitric acid from alkali nitrates in which the
nitrate is mixed with inert materials and made into a porous or permeable mass,
through which is forced carbonic acid gas, with steam, and with or without air, the
gas or gases being, prior to acting on the materials, heated to a temperature
between 300 and 400 degrees, centigrade, substantially as hereinbefore described.
Dated this Sixth day of September 1892.
EDMUND HUNT,
Applicant's Agent.