Q. What are the most efficient ways that carbon can be removed from the atmosphere?
A. In order to remove carbon dioxide and stabilize atmospheric greenhouse gas levels, carbon capture and storage has to be considered with an integrated strategic approach. The processes of capture, stripping and regeneration, transportation and permanent storage need to be achieved both efficiently and economically.
However, carbon dioxide streams invariably contain other gases (methane, carbon monoxide and nitrogen). It is highly desirable to remove carbon dioxide selectively. Many methods, such as amine scrubbing, chemical and physical adsorption, have been proposed to remove atmospheric carbon dioxide.
Amine solvents can be used to remove carbon dioxide, but extensive heating and post-scrubbing treatments are needed before carbon can be stripped and the amines can be reused. Two main adsorption technologies can also be used for this purpose: pressure swing adsorption (PSA) and temperature swing adsorption (TSA).
However, these methods have either low carbon dioxide capacity and poor selectivity or require an extensive amount of energy. Thus, PSA and TSA need more selective and efficient absorbents to be economically feasible for carbon dioxide capture.
Recent reports show that many zeolitic imidazolate frameworks (ZIFs), a new type of microporous crystalline material, can selectively capture carbon dioxide. The selectivity is more than four times higher than that of the state-of-art material, BPL carbon. Due to the large volume ZIFs enclose, they act as carbon dioxide reservoirs capable of holding an exceptional amount (83 liters) of carbon dioxide for each liter of ZIF material under ambient pressure.
Remarkably, carbon dioxide can be easily removed from ZIFs without heating or any complex regeneration. These materials are readily prepared in large quantities. Thus, these ZIFs hold great promise in ameliorating the pressing environmental problem of controlling atmospheric carbon dioxide emissions.
Bo Wang is a graduate student researcher in the UCLA chemistry department.
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