Feasibility Study of Using Brine for Carbon Dioxide Capture
ABSTRACT
A
laboratory-scale reactor was developed to evaluate the capture of carbon
dioxide (CO2) from a gas into a liquid as an approach to control greenhouse
gases emitted from fixed sources. CO2 at 5–50% concentrations was passed through
a gas-exchange membrane and transferred
into liquid media—tap water or simulated brine. When using water, capture
efficiencies exceeded 50% and could be enhanced by adding base (e.g., sodium
hydroxide) or the combination of base and carbonic anhydrase, a catalyst that speeds
the conversion of CO2 to carbonic acid. The transferred CO2 formed ions, such as
bicarbonate or carbonate, depending on the amount of base present. Adding precipitating
cations, like Ca, produced insoluble carbonate salts. Simulated brine proved
nearly as efficient as water in absorbing CO2, with less than a 6% reduction in
CO2 transferred. The CO2 either dissolved into the brine or formed a mixture of
gas and ions. If the chemistry was favorable, carbonate precipitate
spontaneously formed. Energy expenditure of pumping brine up and down from
subterranean depths was modeled. We conclude that using brine in a gas-exchange
membrane system for capturing CO2 from a gas stream to liquid is technically
feasible and can be accomplished at a reasonable expenditure of energy.
* From the Journal of the Air & Waste Management
Association, December 2006, Vol. 56, No. 12
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