How do underwater rebreathers scrub CO2 from air supplies?

I know that alkali metal hydroxides (column I and II metal hydroxides) can be used to absorb carbon dioxide (CO2) in an enclosed atmosphere, like in a space craft or submarine. However, they're corrosive and absorb water vapor. (1) Is there any commonly-available material that is not toxic/dangerous that will absorb CO2? (2) What is used in underwater rebreathers/CO2-scrubbers? Thanks.
Garcia Oliver

Plants absorb CO2, of course, but they take up a lot of room and are slow, inefficient CO2 absorbers.

Most industrial CO2 scrubbers use chemicals that don't meet your criteria. MonoethanolamineMSDS (MEA) is used to scrub carbon dioxide from gas streams, but it's corrosive and toxic in very small amounts. Ascarite IIMSDS is a very efficient CO2 absorbent, but it's basically nonfibrous asbestos covered with sodium hydroxide.

Potassium superoxideMSDS is an interesting possibility for spacecraft and submarine CO2 scrubbing, since it regenerates oxygen as it reacts with carbon dioxide:

4 KO2(s) + 2 CO2(g) = 2 K2CO3(s) + 3 O2(g)
But it isn't common, and it is quite toxic.

Calcium hydroxide (mixed with a small amount of sodium and potassium hydroxides) is used in most underwater rebreathers. The reaction between the hydroxides and CO2 is exothermic, and divers can tell from the warmth of the scrubber canister that the absorption reaction is working. Failure of the canister lid can give the diver a mouthful of hydroxides- called a caustic cocktail in diving circles. It's apparently a memorable experience.

You can learn more about the construction and chemistry of rebreathers here.

The U. S. Department of Energy maintains a site on CO2 removal technologies being considered to reduce global carbon emissions.

Author: Fred Senese

General Chemistry Online! How do underwater rebreathers scrub CO_2_ from air supplies?

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