Feasibility Study of Using Brine for Carbon Dioxide Capture and Storage from Fixed Sources

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.