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Greetings all,

Several years ago I did all the calculations to figure out how many cubic
feet of liquid air would be obtained from a standard 80 tank if it were
filled with liquid gases.  I can recalculate this stuff if there is any
interest.  As well, to change CO2 into C and O2 is not practically
possible.  You would have to change the C (carbon) into some gas rather
than a solid, so the easiest would be CH4 (methane).  This would take a
tremendous amount of energy and of course could form explosive mixtures
(around 6% to 17% or thereabouts if I remember correctly).  As well, you
would have to come up with a source of hydrogen (remember the law of
conservation of matter?).  


If one had a large cylinder (80 ft3 tank) and a pony of oxygen, (both
liquids) you could mix them and form any combination of O2 and N2.  Add to
this another pony of helium (it would be almost impossible to obtain helium in
liquid form as it must be kept at about 4degrees Kelvin (4 degrees above
absolute zero) and you could mix your own gases to suit the situation.

When calculating this stuff, remember that one mole of a substance (for
oxygen a mole is about 32 grams and nitrogen is about 28 grams) forms
22.414 liters of gas at stp (standard pressure and temperature).

I found earlier that the biggest problem of using liquid nitrogen and
oxygen as source breathing materials is that you must convert them from
liquid to gas fast enough to allow breathing at depth.  This means that a
source of heat (energy) is necessary to provide the "heat of
vapourization" of each gas.  You would need some very efficient heat
exchangers to extract the heat from the ambient water, or an outside
source of energy.  Too bad considering that liquid gases are probably
cleaner and purer than the stuff we breathe normally.

Incidentally to distill air into liquid nitrogen, oxygen, argon etc, you
start at about 10,000 psi to 12,000 psi at room temperature.  You must usually
throttle a gas (put it through a small hole under pressure) to further
produce liquids (holds true for liquid nitrogen and liquid oxygen) from
compressed gases.

Good idea with practical limitations though.
hope this helps the discussion.

...Brian Kruschel

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