Improvements in Obtaining Oxygen Gas from Atmospheric Air.
Year: 1890

page_text: Date of Application, 29th Apr., 1890-Accepted, 8th Nov., 1890
COMPLETE SPECIFICATION.
Improvements in Obtaining Oxygen Gas from Atmospheric Air.
I, ALFRED LONGSDON of 9 New Broad Street in the City of London, Civil
Engineer do hereby declare the nature of this invention (a communication to me
from abroad by Dr. Fritz Salomon, of Essen in the Empire of Germany) and in what
manner the same is to be performed to be particularly described and ascertained
in and by the following statement :-
The process hitherto usually adopted for obtaining oxygen from air depends upon
the well known property possessed by the spongiform barium oxide, of absorbing
oxygen at a red heat, and of giving it off at a higher temperature, especially when
subjected to a partial vacuum.
This process which has been very successfully carried out of late years by the
Brothers Brin, is nevertheless subject to various defects which hinder its adoption and
prevent it from being carried out on a large scale for industrial purposes. The
difficulty of producing spongiform barium oxide, its relatively high price, the case
with which it is rendered useless by the application of too high a heat or by the
formation of barium carbonate by the leakage of the retorts &c. necessitate for its
useful and successful application an exceedingly complicated apparatus. The general
adoption of this process is therefore scarcely to be expected.
The process which forms the subject matter of the present invention is free from
the above mentioned defects. It depends upon the following chemical re-actions:
When a mixture of lead monoxide (Pb 0) and an alkaline earth is brought into
contact, at a red heat, with air in motion, oxygen is absorbed and lead dioxide
(Pb O2) together with plumbates (R₂ Pb O₁) are formed. This re-action is well
known, and by the researches of Dr. Kassner, has been clearly demonstrated.
If the lead combination be now brought into contact with carbonic acid gas, the
atmospheric oxygen absorbed by it is driven off and a mixture of earthy alkaline
carbonate and lead monoxide is formed; ultimately lead carbonate remains. The
temperatures at which the lead oxide mixture absorbs the atmospheric oxygen and
at which the carbonic acid drives the oxygen out are not much different.
The process comprised in this invention consists in heating a mixture of lead
monoxide and alkaline earth, lime for example, to a good heat in a retort; it thereby
absorbs oxygen from the air. Instead of the monoxide, combinations of this oxide
which change into the monoxide by heating, as for example, the carbonate, may be
employed. The proportions of the constituents in the mixture may be varied, but it
is desirable that for one equivalent of lead monoxide there should be 1 to 2 equivalents
of lime. To bring the mixture to a red heat, it is heated to about 800-1000° C. ;
a stream of atmospheric air is then conducted over it so that the oxygen of the air is
absorbed whilst the nitrogen escapes. If, instead of the monoxide, the corresponding
carbonic acid combination is used, nitrogen and carbonic acid escape simultaneously.
The absorption of the oxygen, at the proper heat is soon accomplished; it is
effected by the lime mixture, for example according to the equation.
2 Ca O + Pb 0 + 0 = Ca₂ Pb O₁.
After the saturation of the mixture with oxygen, when the temperature is fallen on
a certain point, the current of air is turned off and carbonic acid gas is conducted
over the glowing mixture; the oxygen is thereby expelled whilst the carbonic acid
combines with the remaining calcium oxide. The re-action is effected by the lime
mixture according to the equation
2 Ca O+ Pb 0 + 0 = Ca₂ Pb O₁.
After the saturation of the mixture with oxygen, when the temperature is fallen on
a certain point, the current of air is turned off and carbonic acid gas is conducted
over the glowing mixture; the oxygen is thereby expelled whilst the carbonic acid
combines with the remaining calcium oxide. The re-action is effected by the lime
mixture according to the equation

page_text: only at the close of the operation that some carbonic acid is disengaged; this is
easily removed by the introduction of an absorbing agent such as lime or sodium
carbonate.
The mixture of calcium carbonate and lead monoxide remaining in the retort, after
the expulsion of the oxygen is immediately, at a red heat, treated with air; or, to
hasten the expulsion of the carbonic acid with a mixture of air and steam; the
same re-action (the absorption of oxygen by the mixture) is again brought about,
and the process may be repeated at pleasure.
The regeneration of the mixture of earthy alkaline carbonate and lead monoxide
respectively remaining in the retort after the expulsion of the oxygen has the
advantage that it is possible to get back the greatest part of the necessary carbonic
acid and preserve it for future use.
Other metallic oxides than lead monoxide are also applicable for obtaining oxygen
in the manner described above, for example, the lower oxides of manganese, which, at
a red heat form with oxygen the higher oxide of this metal with an earthy alkali,
which is also decomposible by carbonic acid, but the expulsion of the oxygen is not
so easily effected as with the lead combination.
It must be further remarked that both the oxygen of the pure dioxide, for example
Pb 02 (or Mn 02) and of the corresponding metallic peroxide, for example red lead
(Pb, Pb 0) is very easily driven off by the carbonic acid.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
The process herein set forth, and described in detail, for obtaining oxygen gas
from atmospheric air, consisting in heating a mixture of lead monoxide, or other
metallic oxide adapted for the absorption of oxygen, with an alkaline earth-in a
current of air, the oxygen of the air being absorbed and, subsequently, the oxygen
being driven off by the introduction of a stream of gaseous carbonic acid, and finally
collected for use.
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