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I wonder what's the way to regenerate O2 in air without using consumable chemicals (where one can use electricity through electrolisis or using UV lamps)?

We can dissolve water into O2 & H2, but it won't remove CO2 from air.

Any ideas?

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Ever thought about opening windows? –  Georg Jun 3 '11 at 12:30
In Moscow it makes things even worse :-) Buying gas mask for this Summer :-) –  BarsMonster Jun 3 '11 at 13:29
It is very unlikely that the problem is lack of O2. The problem with the air in big cities is CO and hydrocarbons from cars and the products made from this by sunlight, alltogether called "smog". Moscow is famous for underground peat fires in the vicinity :=( –  Georg Jun 3 '11 at 13:57
Hence the idea - if you can mainain oxygen/CO2 level in isolated environment, you can easily filter out all the dirt & contaminants. Continiously filtering all incoming air from ventilation is going to be very expensive. –  BarsMonster Jun 3 '11 at 15:25
""Continiously filtering all incoming air from ventilation is going to be very expensive. "" How do You know? Without any knowledge of methods and the cost? –  Georg Jun 3 '11 at 16:15
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3 Answers

up vote 1 down vote accepted

Here is a Babelfish translation from German Wiki on Life support systems. (Including NASA!) (English WIKI on the topic is very bad)


In order to make for humans possible a surviving, the supply of breathable gas (thus air) must be guaranteed. But air must be as free of harmful substances as possible and determined parameters keep. Thus on board EAT a total pressure from 97,9 to 102.7 kPa, an oxygen partial pressure from 19,5 to 23.1 kPa, a nitrogen partial pressure of less as 80 kPa and a carbon dioxide partial pressure of less as 1 kPa than acceptable regarded. The air temperature in EAT is appropriate (adjustable) between 18,3 and 26,7 °C. By the air condition technology an air humidity between 25 and 75% and a constant air movement between 0,05 and 1,0 m/s are secured, in order to avoid microbe growth and fungus growth on the one hand and a too dry air (danger of the sparking) on the other hand. Here usually conventional air conditioning systems with refrigerants (e.g. ammonia or Freon) are used. Around air thereby condensing heat exchangers will dehumidify begun. [2] For carbon dioxide connection re-usable zeolites or solid amines, in space suits are used also lithium hydroxide. The production of oxygen takes place usually via the electrolysis from water and partly via recuperation from the carbon dioxide by Sabatier process and the following methane pyrolysis. As Backup or with short term employment oxygen also compressed or chemical reactions is used to the supply of oxygen. Pollutants are constantly supervised by appropriate measuring methods like for example mass spectrometers and gas chromatography and by molecular sieve, activated charcoal or lithium hydroxide filtered. In submarines similar values are valid, and partly also similar processes are used. [3]

  • Think: NASA did/does very different depending on situation! On a spacestation with ample electricity You can do electrolysis, for Apollo they made electricity from oxygen/hydrogen in fuel cells! And cost of upmass includes the cost of energy generators or storage batteries.

But topic here is some (realistic) method for barsmonster to survive the Moscow summer. This is best done by cooling the air intake, demoist it (which would hopefully remove some of the organic "smog" particles) and one could try some PP microfibre filters. The exhaust air would be used to cool down the air taken in. Any separation of carbon dioxide by ad(ab)sorbents would be much more expensive than this air exchange.

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Rather than just splitting water, you want to react it with the CO2 to make O2 and carbohydrates. I think this can be done with an inorganic catalyst (I'd have to Google for the details) but of course the easiest solution is to use photosynthesis.


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There is no inorganic method of which I am aware that is not "messy." They all consume and/or produced something extraneous to the clean reaction you want ---> CO2 + energy = C + O2.

NASA (these are the people who should know) use electrolysis on the ISS to split 2 H2O into 2 H2 + O2. The H2 is vented overboard, the O2 is vented to the cabin. CO2 is captured by a separate system and also vented overboard. With the cost of upmass being on the order of $10K/lb., you can bet that if there was an easy way to rip the O2 out of CO2, that they'd be doing it.

Using photosynthesis sounds like the easiest way to re-use O2 that is bound in CO2. The NET equation is 6 CO2 + 6 H2O + energy (light) ---> C6H12O6 + 6 O2. This uses half the water per liter of O2 produced as electrolysis. If the sugar produced can be consumed, then that upmass is saved also (reduces the weight of food that needs to be shipped to orbit).

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Why the down vote? Got a NASA-hater in the crowd? –  Vintage Jun 3 '11 at 17:57
You can do high temperature electrolysis of $CO_2$, but it's quite energy intensive compared with other methods. –  mmc Jun 4 '11 at 23:19
If you electrolyse the water you can react hydrogen with CO2 using the Sabatier process. The end result will be O2 and methane. –  John Rennie Jun 6 '11 at 7:01
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