Science Questions

Recycling Oxygen

Sun, 3rd Feb 2008

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Tom Gallard, London asked:

How is oxygen made and recycled on the International Space Station?


We put this question to Mark Hempsell, Senior Lecturer, University of Bristol:

The International Space StationThe oxygen isnít strictly recycled.  The carbon dioxide that the humans breathe out is filtered out of the air with a molecular sieve then simply dumped overboard.  The oxygen is created from the water that comes from the air and from the washbasins and from the loos.  After that water is cleaned up it is electrolysed.  An electric current is passed through it and it is separated into hydrogen and oxygen.  The hydrogen is dumped overboard; the oxygen is fed into the cabin for the crew to breathe.


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The only way I can think to produce it would be by splitting water into hydrogen & oxygen; but wouldn't it be easier/cheaper to ship pressurised oxygen cylinders from Earth?

As for re-cycling it - a series of biological or chemical filters, maybe? DoctorBeaver, Thu, 31st Jan 2008

If I remember correctly, at least in the past they used compounds like lithium (usually preferred because lighter) or potassium peroxide: it absorbs the CO2 and the H2O produced by the astronauts and in doing this it releases O2:

2Li2O2 + 2CO2 --> 2Li2CO3 + O2

2Li2O2 + 2H2O --> 4LiOH + O2

Edit: In a 15 y.o. chemistry book I have (Malatesta, Inorganic Chemistry, third edition) is stated: "...Potassium superoxyde KO2 is mostly used to "transform" CO2 in O2 in submarines, space veichles, breath masks:
4KO2 + 4CO2 + 2H2O --> 4KHCO3 + 3O2. lightarrow, Fri, 1st Feb 2008
This talks about the problem and makes sense. lyner, Fri, 1st Feb 2008

The NASA article says something very interesting - that emergency oxygen is produced by "perchlorate candles" and that the same system is used to produce the emergency oxygen supply on aeroplanes. Unfortunately they give no details of this reaction - so what is it?

Chris chris, Sun, 3rd Feb 2008

I imagine that with perchlorate it works in the same way. lightarrow, Sun, 3rd Feb 2008

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