Solubility of Nitrogen in Ionic Liquids at 295-353 K and Pressures to 140 bar

Ionic liquids (ILs) have been evaluated extensively aspost-combustionCO(2) capture solvents, with CO2 solubility dataavailable for a large number of ILs. However, data for the solubilityof the less-soluble gas component, N-2, are sparse. Therefore,the solubility of N-2 was measured gravimetrically at pressuresup to 140 bar in 12 ILs containing imidazolium, ammonium, pyrrolidinium,and phosphonium cations paired with bis(trifluoromethanesulfonyl)imide([TFSI](-)), dicyanamide ([DCA](-)), methanesulfonate ([MeSO3](-)), tetrafluoroborate[BF4](-)), and triflate ([TfO](-)) anions. Increasing the alkyl chain length from ethyl to hexyl todecyl in alkylimidazolium bis(trifluoromethanesulfonyl)imide ILs increasedthe N-2 solubility. The same effect was observed with phosphoniumcations paired with the bis(trifluoromethylsulfonyl)imide anion. Nitrogensolubility in ILs with the 1-ethyl-3-methylimidazolium cation followedthe order [DCA](-) < [MeSO3](-) < [BF4](-) < [TfO](-) < [TFSI](-). Generally, regardless of the ILstructure, the N-2 solubility increased with increasingIL molar volume. For ILs with similar chemical composition and molarvolume (i.e., ILs with tetraalkylammonium and pyrrolidinium cations),N-2 was less soluble in the IL with the cyclic cation. Theabsorption of N-2 in bis(trifluoromethylsulfonyl)imide ILsdid not depend significantly on temperature. However, [emim][BF4] had a significant positive enthalpy of N-2 absorption.These N-2 solubility data, along with the readily availableCO(2) solubilities in ILs, is critical to evaluating ILsfor post-combustion carbon capture processes.