Since our first measurements of the phase behavior of CO₂ and 1-butyl-3-methylimidazolium hexafluorophosphate at pressures up to 400 bar, our group has focused on understanding the physical chemistry of CO₂ + ionic liquid systems and designing ionic liquids (ILs) for CO₂ separation applications.  CO₂ capacity based on physical dissolution and selectivity over other gases like N₂ and CH₄ can be tuned by the choice of cation and anion.  Both entropic effects (i.e., free volume) and enthalpic interactions determine the selectivity.  Potential applications for these ILs include natural gas sweetening and pre-combustion CO₂ capture. Moreover, amine functionality can be incorporated into ILs to increase CO₂ capacity at low partial pressures.  These ILs react reversibly with CO₂ to form carbamates and/or carboxylates.  Of particular interest are ILs containing azolides as the anions since they have equimolar CO₂ capacity and very little viscosity increase upon reaction with CO₂.  The enthalpy of reaction can be tuned by the choice of the azolide and electron donating or withdrawing groups.  Thermophysical properties, like viscosity, heat capacity and thermochemical stability can be further tuned by choice of cation and substituents. Potential applications for these azolide ILs include post-combustion CO₂ capture and even direct air capture of CO₂.  Configurations for performing CO₂ separations with ILs include conventional absorber columns, as well as supported ionic liquid membranes.  We will demonstrate advances in each of these areas.

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Prof. Panagiotis Manesiotis

p.manesiotis@qub.ac.uk