A carbon dioxide scrubber is a device which absorbs carbon dioxide (CO2). It is used to treat exhaust gases from industrial plants or from exhaled air in life support systems such as rebreathers or in spacecraft, submersible craft or airtight chambers. Carbon dioxide scrubbers are also used in controlled atmosphere (CA) storage.

Various scrubbing processes have been proposed to remove CO2 from the air, or from flue gases. These usually involve using a variant of the Kraft process. Scrubbing processes may be based on sodium hydroxide. The CO2 is absorbed into solution, transferred to lime via a process called causticization and released in a kiln. With some modifications to the existing processes, mainly an oxygen-fired kiln, the end result is a concentrated stream of CO2 ready for storage or use in fuels. An alternative to this thermo-chemical process is an electrical one in which a nominal voltage is applied across the carbonate solution to release the CO2. While simpler, this electrical process consumes more energy as it splits water at the same time. Since it depends on electricity, the electricity needs to be renewable, like PV. Otherwise the CO2 produced during electricity production has to be taken into account. Early incarnations of air capture used electricity as the energy source; hence, were dependent on a carbon-free source. Thermal air capture systems use heat generated on-site, which reduces the inefficiencies associated with off-site electricity production, but of course it still needs a source of (carbon-free) heat. Concentrated solar power is an example of such a source.

The regenerative carbon dioxide removal system (RCRS) on the space shuttle orbiter uses a two-bed system that provides continuous removal of carbon dioxide without expendable products. Regenerable systems allow a shuttle mission a longer stay in space without having to replenish its sorbent canisters. Older lithium hydroxide (LiOH)-based systems, which are non-regenerable, are being replaced by regenerable metal-oxide-based systems. A system based on metal oxide primarily consists of a metal oxide sorbent canister and a regenerator assembly. It works by removing carbon dioxide using a sorbent material and then regenerating the sorbent material. The metal-oxide sorbent is regenerated by pumping air heated to around 400 °F at 7.5 scfm through its canister for 10 hours.

Activated carbon can be used as a carbon dioxide scrubber. Air with high carbon dioxide content, such as air from fruit storage locations, can be blown through beds of activated carbon and the carbon dioxide will absorb onto the activated carbon. Once the bed is saturated it must then be "regenerated" by blowing low carbon dioxide air, such as ambient air, through the bed. This will release the carbon dioxide from the bed, and it can then be used to scrub again, leaving the net amount of carbon dioxide in the air the same as when the process was started.

A catalytic converter is an exhaust emission control device which converts toxic chemicals in the exhaust of an internal combustion engine into less toxic substances. Inside a catalytic converter, a catalyst stimulates a chemical reaction in which toxic byproducts of combustion are converted to less toxic substances by way of catalysed chemical reactions. The specific reactions vary with the type of catalyst installed. Most present-day vehicles that run on gasoline are fitted with a "three way" converter, so named because it converts the three main pollutants in automobile exhaust: an oxidizing reaction converts carbon monoxide (CO) and unburned hydrocarbons (HC), and a reduction reaction converts oxides of nitrogen (NOx) to produce carbon dioxide (CO2), nitrogen (N2), and water (H2O).

For More Information:
Carbon Dioxide Scrubber
Carbon Dioxide Removal
Catalytic Converter

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