No abstract

No abstract

No abstract

The phase behavior of the binary system consisting of the supercritical fluid carbon dioxide (CO2) and the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) was studied experimentally. A synthetic method was used to measure its phase behavior. Bubble-point pressures of the system CO2 + [bmim][BF4] are reported for carbon dioxide concentrations ranging from (10.22 to 60.17) mole % and within a temperature range of (278.47 to 368.22) K. The CO2 + [bmim][BF4] binary system has a two-phase liquid−vapor region extending up to very high pressures. Most likely, the type of fluid-phase behavior is type III according to the classification of Scott and Van Konynenburg. The experimental results obtained were compared with the available phase behavior data of the binary system CO2 + 1-hexyl-3-methylimidazolium tetrafluoroborate ([hmim][BF4]) to investigate the effect of the length of the alkyl group on the phase behavior of this type of system. A larger alkyl group leads to lower bubble-point pressures and, therefore, to higher solubilities of carbon dioxide in the imidazolium-based ionic liquid.

In this study, the behaviors of viscosities of nine ionic liquids (ILs) over wide ranges of pressures and temperatures were determined. The investigated ILs belonged to the three imidazolium-based families of tetrafluoroborate, hexafluorophosphate, and bis­[(trifluoromethyl)­sulfonyl]­imide. The two well-known cubic equations of state (EoS’s) of Peng–Robinson (PR) and the Soave–Redlich–Kwong (SRK), as well as the two more-sophisticated EoS’s of cubic plus association (CPA), and perturbed-chain statistical associating fluid theory (PC-SAFT), were each coupled with two well-known theoretical viscosity models, namely the friction theory and the free volume theory. Calculated results showed that the free volume model, coupled with PC-SAFT, has superior results in comparison to the free volume model with the CPA EoS. For the viscosity model of free volume, the studied cubic EoS’s did not give accurate results. When the friction model was used, the PC-SAFT EoS once more showed better accuracy than the CPA EoS; however, the CPA results in this model were quite close to that of the PC-SAFT, while the differences were great with the free volume model. One of the remarkable conclusions for the friction theory model was the unexpectedly reliable results that it gave with the cubic EoS’s. This suggests that when highly accurate results are not crucial, this combination can be the best choice because of the significantly greater simplicity of a cubic EoS over an association EoS.