Carbon dioxide scrubber
A carbon dioxide scrubber is a piece of equipment that absorbs
Technologies
Amine scrubbing
The primary application for CO2 scrubbing is for removal of CO2 from the exhaust of coal- and gas-fired
- CO2 + 2 HOCH
2CH
2NH
2 ↔ HOCH
2CH
2NH+
3 + HOCH
2CH
2NHCO−
2
As of 2009[update], this technology has only been lightly implemented because of capital costs of installing the facility and the operating costs of utilizing it.[1]
Minerals and zeolites
Several minerals and mineral-like materials reversibly bind CO2.
Various (cyclical) scrubbing processes have been proposed to remove CO2 from the air or from flue gases and release them in a controlled environment, reverting the scrubbing agent. These usually involve using a variant of the
Sodium hydroxide
Zeman and Lackner outlined a specific method of air capture.[10]
First, CO2 is absorbed by an alkaline NaOH solution to produce dissolved sodium carbonate. The absorption reaction is a gas liquid reaction, strongly exothermic, here:
- 2NaOH(aq) + CO2(g) → Na
2CO
3(aq) + H2O(l)
- Na
2CO
3(aq) + Ca(OH)
2(s) → 2NaOH(aq) + CaCO
3(s)
- ΔH° = -114.7 kJ/mol
Causticization is performed ubiquitously in the pulp and paper industry and readily transfers 94% of the carbonate ions from the sodium to the calcium cation.[10] Subsequently, the calcium carbonate precipitate is filtered from solution and thermally decomposed to produce gaseous CO2. The calcination reaction is the only endothermic reaction in the process and is shown here:
- CaCO
3(s) → CaO(s) + CO2(g)
- ΔH° = + 179.2 kJ/mol
The thermal decomposition of calcite is performed in a lime kiln fired with oxygen in order to avoid an additional gas separation step. Hydration of the lime (CaO) completes the cycle. Lime hydration is an exothermic reaction that can be performed with water or steam. Using water, it is a liquid/solid reaction as shown here:
- CaO(s) + H2O(l) → Ca(OH)
2(s)
- ΔH° = -64.5 kJ/mol
Lithium hydroxide
Other strong
The net reaction being:
- 2LiOH(s) + CO2(g) → Li
2CO
3(s) + H2O(g)
Lithium peroxide can also be used as it absorbs more CO2 per unit weight with the added advantage of releasing oxygen.[12]
In recent years lithium orthosilicate has attracted much attention towards CO2capture, as well as energy storage.[8] This material offers considerable performance advantages although it requires high temperatures for the formation of carbonate to take place.
Regenerative carbon dioxide removal system
The regenerative carbon dioxide removal system (RCRS) on the Space Shuttle orbiter used a two-bed system that provided continuous removal of carbon dioxide without expendable products. Regenerable systems allowed 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, were replaced by regenerable metal-oxide-based systems. A system based on metal oxide primarily consisted of a metal oxide sorbent canister and a regenerator assembly. It worked by removing carbon dioxide using a sorbent material and then regenerating the sorbent material. The metal-oxide sorbent canister was regenerated by pumping air at approximately 200 °C (392 °F) through it at a standard flow rate of 3.5 L/s (7.4 cu ft/min) for 10 hours.[13]
Activated carbon
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 adhere to the activated carbon [adsorption]. 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. [citation needed]
Metal-organic frameworks (MOFs)
A MOF could be specifically designed to act like a CO2 removal agent in post-combustion power plants. In this scenario, the flue gas would pass through a bed packed with a MOF material, where CO2 would be stripped. After saturation is reached, CO2 could be desorbed by doing a pressure or temperature swing. Carbon dioxide could then be compressed to supercritical conditions in order to be stored underground or utilized in enhanced oil recovery processes. However, this is not possible in large scale yet due to several difficulties, one of those being the production of MOFs in great quantities.[16]
Another problem is the availability of metals necessary to synthesize MOFs. In a hypothetical scenario where these materials are used to capture all CO2 needed to avoid global warming issues, such as maintaining a global temperature rise less than 2 °C above the pre-industrial average temperature, we would need more metals than are available on Earth. For example, to synthesize all MOFs that utilize vanadium, we would need 1620% of 2010 global reserves. Even if using magnesium-based MOFs, which have demonstrated a great capacity to adsorb CO2, we would need 14% of 2010 global reserves, which is a considerable amount. Also, extensive mining would be necessary, leading to more potential environmental problems.[16]
In a project sponsored by the DOE and operated by
Extend Air Cartridge
An Extend Air Cartridge (EAC) is a make or type of pre-loaded one-use absorbent canister that can be fitted into a recipient cavity in a suitably-designed rebreather.[18]
Other methods
Many other methods and materials have been discussed for scrubbing carbon dioxide.
- Adsorption[19]
- Regenerative carbon dioxide removal system (RCRS)
- Algae filled bioreactors
- Membrane gas separations
- Reversing heat exchangers
See also
- Carbon capture and storage – Collecting carbon dioxide from industrial emissions
- Carbon dioxide removal – Removal of atmospheric carbon dioxide through human activity
- Greenhouse gas – Gas in an atmosphere that absorbs and emits radiation at thermal infrared wavelengths
- Rebreather – Portable apparatus to recycle breathing gas
- Sabatier reaction – Methanation process of carbon dioxide with hydrogen
References
- S2CID 206521374.
- PMID 19731282.
- ^ "Imagine No Restrictions On Fossil-Fuel Usage And No Global Warming". ScienceDaily. April 15, 2002.
- ^ "Natural Mineral Locks Up Carbon Dioxide". ScienceDaily. September 3, 2004. Retrieved 2011-06-01.
- ^ "Sustainability and the TecEco Kiln". Archived from the original on October 25, 2005. Retrieved October 25, 2005.
- ^ Kenneth Chang (February 19, 2008). "Scientists would turn greenhouse gas into gasoline". The New York Times. Retrieved 2009-10-29.
- S2CID 27280943.
- ^ .
- ^ Kunzig, Robert; Broecker, Wallace (January 12, 2009). "Can technology clear the air?". New Scientist. Retrieved 2009-10-29.
- ^ a b Zeman, F.S.; Lackner, K.S. (2004). "Capturing carbon dioxide directly from the atmosphere". World Resour. Rev. 16: 157–172.
- ^ J.R. Jaunsen (1989). "The Behavior and Capabilities of Lithium Hydroxide Carbon Dioxide Scrubbers in a Deep Sea Environment". US Naval Academy Technical Report. USNA-TSPR-157. Archived from the original on 2009-08-24. Retrieved 2008-06-17.
{{cite journal}}
: CS1 maint: unfit URL (link) - S2CID 262306041.
- ^ "Carbon Dioxide Removal". Hamilton Sundstrand. Archived from the original on 2007-10-31. Retrieved 2008-10-27.
The new metal-oxide-based system replaces the existing non-regenerable lithium hydroxide (LiOH) carbon dioxide (CO2) removal system located in the EMU's Primary Life Support System.
- ^ "MOFs for CO2". MOF Technologies. Archived from the original on 2021-02-27. Retrieved 2021-04-07.
- doi:10.1016/j.ccr.2011.02.012. Archived from the original(PDF) on 2016-09-09.
- ^ ISBN 978-1-78326-327-1.
- OSTI 1003992.
- ^ "Extend Air Cartridge". dykarna (in Swedish). Retrieved 2021-12-30.
- CiteSeerX 10.1.1.205.844. DOE/NETL-2001/1144.