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Separating Gases with Ionic Liquids

Lyman Handy Colloquium SeriesPresentsJoan F. BrenneckeUniversity of Notre DameAbstract: Ionic liquids (ILs) are non-volatile organic salts that have low melting points, frequently below room temperature. Typical compounds are comprised of a quaternary ammonium, quaternary phosphonium, imidazolium or pyridinium cation with a wide variety of common anions. Since they cannot evaporate and cause air pollution, they are being vigorously investigated as promising alternatives to volatile organic solvents. Here we report on their use as absorption solvents for gas separations. Many important gas separations are highly energy intensive, especially those involving cryogenic distillation or desorption of chemically-complexed gases. We show that many ILs show good selectivity for CO2 and SO2 over gases such as N2, O2 and H2. We measure pure and mixed gas solubilities using gravimetric microbalances, as well as any of a variety of volumetric systems, with and without gas sampling. We show that some gas separations, especially when the partial pressure of the target gas is relatively high, can be achieved by physical absorption into ionic liquids.Engineering ionic liquids for gas separations involving gases with low partial pressures may be best achieved by including functional groups on the ionic liquid that can chemically react with the target gas. We show results of CO2 uptake as a function of pressure and temperature for a variety of ionic liquids, containing primary and secondary amine functionality on either the cation or the anion. Using FTIR we are able to differentiate between physically dissolved CO2 and CO2 that has reacted with the amine moiety. We show how the capacity and the enthalpy for the reaction can be tailored by the inclusion of additional functionality in the ionic liquid. The physical solubility of N2 and O2 in these same ILs remains low so that the selectivity for CO2 removal is extremely high. Preliminary process design calculations indicate that the functionalized ionic liquids require significantly less energy for CO2 capture from post-combustion flue gas than the commercially available aqueous amine technology.

Location: John Stauffer Science Lecture Hall (SLH) - 100

Audiences: Everyone Is Invited

Contact: Petra Pearce Sapir