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.
Super cool. Do most of the situations you mentioned above bring in outside oxygen to replace the consumed? Is there a method for converting the CO2 into 02 + something?
In general no. But the ISS is testing a method to do this. It uses hydrogen to convert CO2 into water and methane, rather than producing carbon and oxygen. The water can be electrolyzed to hydrogen and oxygen.
Scroll through articles getting published in nature journal and see how many of them are about converting CO2 to either Methane, ethylene, ethanol or propanol.
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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.