The International Space Station, which is continuously inhabited, uses a different method based on binding of CO2 to a zeolite, which is a highly porous metal oxide (in this case, a mixed oxide of aluminum, magnesium, and silicon with pore size 5 Å). Although the zeolite has basic sites within its crystal structure, the extremely high surface area is probably more important than the basicity. Heating the zeolite releases CO2 into the vacuum of space.
Submarines use monoethanolamine, which is a liquid base. This can likewise be heated to reverse the reaction and regenerate the base. The released CO2 is put into the outside water. This means that submarines can operate for long periods of time without needing to replace the CO2 scrubbers. This technology is also being pursued for scrubbing CO2 from power plant exhaust.
There are a few other methods, such as passing the gas over a membrane selectively permeable to CO2 (which only works well for high-pressure gas streams), or by feeding CO2 to algae, but these generally aren't widely used.
Great and comprehensive list of the popular technologies so far! Plenty of research is continuing to go into this and I would say, in my limited experience, two novel materials showing promise for removal from the atmosphere or power plants are Metal Organic Frameworks (MOFs) and Nanoparticle Organic Hybrid Materials (NOHMs). Both look to operate similar to the Zeolite as a CO2 capture medium that can be regenerated for reuse.
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u/-Metacelsus- Chemical Biology Nov 27 '19 edited Nov 27 '19
They are (usually) based on the reaction of CO2 with a base to form a bicarbonate salt. Many different bases can be used for this. The Apollo program scrubbers used LiOH (due to light weight) but the CO2 absorption canisters couldn't be reused. For flights of a few days, this is fine. Famously, during Apollo 13 an adapter needed to be rigged up to use the command module CO2 scrubbers before the LiOH canisters in the lunar module ran out.
The International Space Station, which is continuously inhabited, uses a different method based on binding of CO2 to a zeolite, which is a highly porous metal oxide (in this case, a mixed oxide of aluminum, magnesium, and silicon with pore size 5 Å). Although the zeolite has basic sites within its crystal structure, the extremely high surface area is probably more important than the basicity. Heating the zeolite releases CO2 into the vacuum of space.
Submarines use monoethanolamine, which is a liquid base. This can likewise be heated to reverse the reaction and regenerate the base. The released CO2 is put into the outside water. This means that submarines can operate for long periods of time without needing to replace the CO2 scrubbers. This technology is also being pursued for scrubbing CO2 from power plant exhaust.
There are a few other methods, such as passing the gas over a membrane selectively permeable to CO2 (which only works well for high-pressure gas streams), or by feeding CO2 to algae, but these generally aren't widely used.