Solubility 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, triethylsulfonium bis(trifluoromethyIsulfonyI)imide(S₂₂₂][Tf₂N]), diethylmethyl(2-methoxyethyl)-ammonium bis(trifluoromethylsulfony)imide ([deme][Tf₂N]),1-propyl-3-methyl-imidazolium bis(trifluoromethylsulfony)imide ([pmim][Tf₂N]), 1-allyl-3-methyl- imidazolium bis(trifluoromethylsulfonyl)imide ([amim][Tf₂N]), and 1-butyl-4-methylpyridinium tetrafluoroborate ([4mbp][BF₄]) at (313.15, 323.15 and 333.15 K) and at pressure up to 20 bar using a gravimetric microbalance. The experimental solubility data of CO₂ in these solvents were well correlated using the standard Peng-Robinson (PR-EoS), the standard Redlich-Kwong-Soave (SRK-EoS), the 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 obtained. The absorption of CO₂ was prone to diminish in this sequence: [deme][Tf₂N] > [pmim][Tf₂N] > [amim][Tf₂N] > [S₂₂₂][Tf₂N] > [4mbp][BF₄]. Four ionic liquids, [deme][Tf₂N], [pmim][Tf₂N], [amim][Tf₂N], and [S₂₂₂][Tf₂N], are deemed promising due to comparably high CO₂ absorption with physical absorption to other prevalent CO₂-absorbing ionic liquids. More interestingly, [deme][Tf₂N] evidently had the highest CO₂ solubility among all ammonium-based ionic liquids reported in the literature. In addition, Henry's law constants and enthalpies and entropies of absorption for CO₂ in the investigated ionic liquid are also reported.