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EFFECT OF CATION, WATER AND OTHER ADDITIVES
ON AHA IONIC LIQUIDS FOR CO2 CAPTURE
We have developed a wide variety of Ionic liquids (ILs) containing Aprotic Heterocyclic Anions (AHAs) for CO2 capture applications. While the primary reaction with these ILs occurs between the CO2 and the anion, here we show that the cation does effect the CO2 uptake. The stronger the association between the cation and the anion, the less available the anion is for reaction with CO2. This is borne out in the CO2 uptake isotherms, as well as in deviations from the ideal line on a Walden plot. Since water would be present in post-combustion flue gas, we also show how the presence of water affects the AHA ILs. In particular, we investigate the effect of water on CO2 uptake, as well as any additional chemistry that may be taking place when water and CO2 are in contact with the AHA ILs. Another consideration is the solubility of water in the IL both before and after reaction with CO2. Depending on the nature of the anion, the AHA IL that is complexed with CO2 may have a higher or a lower affinity for water. Finally, we investigate the effect of a variety of organic additives on the uptake of CO2 by one of the AHA ILs – trihexyltetradecylphosphonium cyanopyrrolide. While they may not be useful for industrial CO2 capture applications, these additives make it clear that the CO2 uptake can be adjusted for a given IL by differences in the solvation of the unreacted and CO2 reacted IL in solution.
