Issue Date: July 13, 2009
Browsing through back issues, I encountered Jyllian Kemsley's excellent feature about the possibilities for methanol as a feedstock and fuel (C&EN, Dec. 3, 2007, page 55). I was especially intrigued by the inference in the last paragraph that potential methods for extracting carbon dioxide from the atmosphere have not been developed.
For several years, I have occasionally speculated on the feasibility of concentrating atmospheric CO2 for reaction with hydrogen. I dismissed distillation of liquefied air as energy and capital intensive, in addition to having a very low yield. I did this strictly on the basis of intuition, because my specialty is only remotely related to the necessary disciplines.
Another possibility, so simple that it may not have occurred to those with the resources and expertise to investigate it, has occurred to me. I pass it on for what it may be worth: The unfavorable ratio of the major components of air to CO2 can be almost inverted by the saturation of water with air followed by vacuum extraction.
Solubility data show the contamination of the retrieved gas with nitrogen, oxygen, and argon would total 7%. Water content would depend on the effectiveness of antimist screens, bath additives, and vapor condensers, if used. Additional purification could be done either before or after reaction with hydrogen, depending on whether oxygen or excess water would reduce yield and whether the Haber reaction could be avoided during hydrogenation. Investigators with the appropriate resources and expertise could determine whether either is necessary and feasible.
The process could be made continuous by using multiple chambers and whatever controls apply. The production rate would be increased with the use of efficient spargers, low temperature, and/or high pressure in the dissolution tank. High temperature and vacuum in the extraction tank would have a similar effect.
As always, the economics of the design and operation are likely not as simple as the concept, but large carbon credits or other subsidies seem justified.
G. H. Smith
Sandy Hook, Conn.
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