Surface Tension of 1‑Ethyl-3-methylimidazolium Ethyl Sulfate or 1‑Butyl-3-methylimidazolium Hexafluorophosphate with Argon and Carbon Dioxide

Surface tensions of two ionic liquids (IL): 1-ethyl-3-methylimidazolium ethyl sulfate and 1-butyl-3-methylimidazolium hexafluorophosphate in pressurized atmospheres of argon and carbon dioxide have been measured over the temperature range (303 to 366) K and over the pressure range (0.1 to 15) MPa for the case of argon atmosphere and (0.1 to 5) MPa for the case of carbon dioxide atmosphere by using a pendant drop tensiometer. Based on the experimental measurements, the isothermal surface tension of all IL–gas systems studied decreases as the pressure increases, evidencing a gas adsorption at the IL interface. Isobaric surface tension of an IL–gas does not show a general pattern as the temperature increases. In order to verify the isothermal surface behavior, the relative Gibbs adsorption isotherms have been calculated from the surface tension data by using the theoretical Guggenheim model, corroborating the gas adsorption processes at the IL interface. Comparing the relative Gibbs adsorption isotherms, it is possible to conclude that the ILs studied have the capability to adsorb more carbon dioxide than argon. This fact provides relevant information to use the IL as a capturing agent for carbon dioxide and the use of argon to store pure ILs.