Vapor Pressure Estimation of Imidazolium-Based Ionic Liquids via Non-Isothermal Thermogravimetric Analysis (TGA) and Its Implications for Process Design

Ionic liquids (ILs) are effective entrainers for the separation of hydrofluorocarbon (HFC) mixtures. ILs exhibit an extremely low vapor pressure. However, at temperatures around 373.15 K, typical for reboilers in extractive distillation, property methods and equations of state in ASPEN Plus often overestimate vapor pressure. Such overestimation can result in incorrect predictions of ILs appearing in the vapor phase despite stability in the liquid phase. Inaccurate prediction of vapor pressure influences modeled desorption behavior of dissolved gases, particularly in adiabatic or isothermal flash tank operations. At typical reboiler and flash tank temperatures, minor deviations in predicted vapor pressure can lead to significant differences in the calculated purity of the desorbed stream. However, within the typical operating range (e.g., <450 K), these effects are negligible. In this work, the vapor pressures of [C2C1im][Tf2N], [C2C1im][FSI], and [C2C1im][TCM] were estimated using a thermogravimetric analysis (TGA) instrument. The result for [C2C1im][Tf2N] was validated against the available experimental data.