(106b) Reversible Ionic Liquids as Double-Action Solvents for Efficient CO2 Capture

We have developed a new class of smart solvents with the goal of recovering post-combustion CO2 from fossil fuel-fired power plants. Smart solvents are those which undergo large step changes in properties in response to an external stimulus, such as light, heat, or even pH. Because of this abrupt property change, one can build into the solvent its own separation or regeneration methodology.

We have previously reported the development and application of reversible ionic liquids, as from an amadine or guanidine plus and alcohol. With these simply bubbling CO2 at ambient pressure through the mixture gives almost complete conversion to the ionic liquid, and either inert gas sparging or heat achieve reversal. However, the use of these for separation processes is made more complex by the requirement of two starting materials.

Here we report the application of single-component reversible ionic liquids derived from siloxylated amines and carbon dioxide. Many articles have highlighted the selectivity of conventional ionic liquids in separating CO2 from mixed gas streams. Also, ionic liquids are known to have a large capacity for dissolving gases. Our reversible solvents improve upon conventional ionic liquids by enabling a dual capture mechanism. Specifically, they function not only as physical absorbents but also as chemical adsorbents for CO2 offering high selectivity of CO2/N2 in dilute flue gas streams. Two moles of solvent react with one mole of CO2 to form the ionic liquid, which then acts as a solvent to physically absorb additional CO2.

Further, our one-component systems simplify processing requirements when compared to alcohol amine systems due to the large liquid range of our solvents. These novel solvents produce a clean CO2 stream upon reversal. Further, we show that solvent properties, such as regeneration temperature, can be tuned by simple structural modifications. These changes enable us to design our structures to meet desired goals such as high adsorption and absorption capacity, low energy use for CO2 desorption and precursor regeneration, low viscosity, low corrosion and low cost.