376998 Effect of Anions on CO2 Solubility of Ionic Liquids Using a Magnetic Suspension Balance
Room-temperature ionic liquids (RT-ILs) generally have negligibly small vapor pressure, high thermal and chemical stability, and can have higher solubilities of acidic gases such as CO2, H2S, NOx and SOx than those of normal gases, N2, H2, and O2. These attractive properties could lead the way to clean gas separation technologies that eliminate emissions of the liquid absorbent into the atmosphere. We have proposed an effective CO2 separation process from gas mixtures by physical absorption using ionic liquids. Since the efficiency in the physical absorption process is predominantly determined by the gas solubility in a unit volume/weight of absorbent, it is of primary importance to develop highly CO2 absorbing ILs.
In the present study, we have investigated the effect of anions (i.e., TFSA-; = bis(trifluoromethanesulfonyl)amide, BETA-; = bis(tetrafluoroethanesulfonyl)amide, and NFBS-; = nonafluorobutanesulfonate) for 1-ethyl-3-methylimidazolium cation [Emim] on CO2 absorption using a Magnetic Suspension Balance at 313.2 K and up to 6 MPa.
The CO2 solubility in ionic liquids increased with increasing pressure. [Emim][BETA] showed highest CO2 solubility compared with the other ones, especially, the solubility is increased about 4% in comparison with [TFSA] which have a similar structure. On the other hand, [Emim][NFBS] showed 30% higher CO2 solubility at 3 MPa, compared with [Emim][OTf] (1-ethyl-3-methylimidazolium trifluoromethanesulfonate). The symmetrical structure such as TFSA- and BETA- shows a higher CO2 solubility rather than the asymmetric structure such as NFBS- and OTf-. CO2 solubility was increased with the extension of the perfluoroalkyl chain length of the anion.
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