High CO2 solubility in ionic liquids and a tetraalkylammonium-based poly(ionic liquid)

Abstract

Carbon dioxide (CO₂) absorption in several imidazolium-based ionic liquids (ILs), pyridinium-based ionic liquids and a tetraalkylammonium-based poly(ionic liquid) (PIL), poly[(p-vinylbenzyl) trimethylammonium hexafluorophosphate] P[[VBTMA][PF₆], was studied. The trend of CO₂ solubility in all of the ILs increases dramatically with decreasing absorption temperature. Based on the same bis(triflamide) [Tf₂N] anion, imidazolium, pyridinium and trihexyltetradecylphosphonium-based ionic liquids all show relatively similar CO₂ solubilities, which were higher than for the [ES] anion. The highest CO₂ absorption was found in a poly(ionic liquid) P[[VBTMA][PF₆]], however, the monomer also showed higher CO₂ capacity than the other ionic liquids. The poly(ionic liquid) is remarkable in that it can adsorb 77% of its body weight of CO₂ with a selectivity over nitrogen of 70 : 1. The absorbed CO₂ gas can be readily desorbed from ionic liquids and poly(ionic liquid) and the selectivity for CO₂ over N₂ was consistent over repeated cycles. The materials can be reused several times for consecutive sorption/desorption cycles, without loss of performance in a large-scale reactor and therefore represent serious candidates for use in commercial adsorbers.