An ionic liquid designed specifically to scrub unwanted carbon dioxide from gas streams has an absorption capacity comparable to commercial reagents now used to remove CO₂ from natural gas, according to chemists at the University of South Alabama.

The so-called task-specific ionic liquid, prepared by associate professor of chemistry James H. Davis Jr. and coworkers, chemically fixes CO₂ as a carbamate at room temperature, then releases the gas when heated under vacuum [J. Am. Chem. Soc., 124, 926 (2002)]. The group recycled the recovered ionic liquid for CO₂ uptake five times without any observed loss of efficiency.

"CO₂ contamination lowers the fuel value of natural gas," Davis explains. "Aqueous amines that trap CO₂ by forming ammonium carbamate are used as standard large-scale scrubbing agents, but water and the amines are volatile. Their uptake into the gas stream is frequently problematic."

The new ionic liquid, which has an imidazolium cation to which a primary amine moiety is covalently attached, is nonvolatile and does not appear to require water in order to function, Davis says. It is readily synthesized from commercially available materials.

At the moment, however, the new ionic liquid suffers from a major drawback: its relatively high viscosity at room temperature. The problem may limit its eventual use in large-scale scrubbing applications, Davis and colleagues suggest.

Even so, they say plenty of opportunities exist for designing variants with improved physical and chemical properties for the selective sequestration of CO₂ and other gases.

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