Solubility of carbon dioxide in promising methylimidazolium-based ionic liquids

Abstract

One of the most pressing environmental concerns facing humanity today is the limitation of carbon dioxide emissions. In the field of natural gas sweetening, carbon capture is equally critical. CO2 solubility in three promising ionic liquids {1-Hexyl-3-methylimidazolium bis(trifluoro-methyl-sulfonyl) imide [HMIM][Tf2N], 1-Butyl-3-methylimidazolium dimethyl-phosphate [BMIM][DMP], and 1-Propyl-3-methylimidazolium (trifluoromethylsulfonyl)imide [PMIM][Tf2N]} was measured at (303.15, 323.15 and 343.15) K and pressures up to 1.4 MPa. The densities of the three ionic liquids were determined at atmospheric pressure (98.5 ± 0.8 kPa) and temperatures ranging from (293.15 to 343.15) K.The lowest Henry's Law constant (highest capacity) for CO2 was that of [HMIM][Tf2N] followed by [PMIM][Tf2N] and [BMIM][DMP]. [HMIM][Tf2N] also had a higher absorption capacity than Selexol/Genesorb 1753 and was second best only to 1-Octyl-3-methylimidazolium bis (trifluoro-methane sulfonyl) imide [OMIM][Tf2N] among all ionic liquids, based on solubility data published in the literature. Note that [BMIM][DMP] was also found to be among the best four ionic liquids according to the Henry's Law data collected from the literature.Three distinct mixing rules were used to correlate the experimental CO2 solubility data with the Peng-Robinson equation of state (PR-EoS) using the van der Waals one (vdW1), van der Waals two (vdW2), and the Wong-Sandler mixing rule along with the Non-Random Two-Liquid model (WS-NRTL). The average absolute deviations for vdW1, vdW2, and WS-NRTL mixing rules, when calculated for the three ionic liquid systems at the three temperatures, were 4.89 %, 0.82 %, and 0.84 %, respectively.