Densities and low pressure solubilities of carbon dioxide in five promising ionic liquids

Abstract

Ionic liquids are presently considered the most energy-efficient and environmentally benign solvents for CO₂ capture. This research aimed at measuring the solubility of CO₂ in five room temperature ionic liquids, triethylsulfoniumbis(trifluoromethylsulfonyl)imide ([S₂₂₂][Tf₂N]), diethylmethyl(2-methoxy ethyl)-ammonium bis(trifluoromethylsulfonyl)imide ([deme][Tf₂N]), 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([pmim][Tf₂N]), 1-allyl-3-methylimidazolium bis-(trifluoromethyl sulfonyl)imide ([amim][Tf₂N]), and 1-butyl-4-methylpyridinium tetrafluoroborate ([4mbp][BF₄]) at (313.15, 323.15 and 333.15 K) and at pressures up to 20 bar using a gravimetric microbalance. The experimental solubility data of CO₂ in these solvents were well correlated using the Peng–Robinson (PR-EoS), Redlich–Kwong–Soave (SRK-EoS), SRK-EoS with quadratic mixing rules, and the Non-Random Two-Liquid (NRTL) with satisfactory average absolute deviations (AADs). Binary interaction parameters for these correlations were also reported. The absorption of CO₂ was prone to diminish in this sequence: [deme][Tf₂N] > [pmim][Tf₂N] > [amim][Tf₂N] > [S₂₂₂][Tf₂N] > [4mbp][BF₄]. The four ionic liquids {[deme][Tf₂N], [pmim][Tf₂N], [amim][Tf₂N], and [S₂₂₂][Tf₂N]} are deemed promising due to comparably high CO₂ absorption (physical) to other prevalent CO₂-absorbing ionic liquids. More interestingly, [deme][Tf₂N] is shown to have the highest CO₂ solubility among all ammonium-based ionic liquids reported in the literature. In addition, Henry's law constants, enthalpies and entropies of absorption for CO₂ in the investigated ionic liquids were also reported.