(299f) Estimating Maximum Operating Temperature and Vapor Pressure of Ionic Liquids Using Isothermal and Non-Isothermal Thermogravimetric Analysis

Ionic liquids (ILs) have been widely utilized in recent years for separation applications over the traditional organic solvents due to their unique properties, such as high thermal stability, negligible vapor pressure, and tunability to perform specific tasks. In refrigerant mixture separation using extractive distillation with ILs entrainers, estimating the maximum operating temperature (T_max) is crucial for process design to optimize the process such that the reboiler temperature is constrained to be kept below T_max, thereby maintaining IL recyclability and preventing thermal decomposition. Isothermal thermogravimetric analysis (TGA) is used to obtain Arrhenius parameters (i.e., activation energy and frequency factor), which are used to estimate T_max. Another important consideration is the estimation of ILs vapor pressures using non-isothermal TGA at different heating rates. Although many ILs exhibit extremely low vapor pressure, determining it provides an indication of whether mass loss at a given temperature is attributable to evaporation or thermal degradation. Moreover, the estimated vapor pressure can be incorporated into an ASPEN Plus model, which can improve the accuracy separation simulations, particularly for flash products where the system pressure is reduced to atmospheric pressure or lower.

In this study, the thermal stability of 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C₂C₁im][Tf₂N], 1-Ethyl-3-methylimidazolium dicyanamide, [C₂C₁im][DCA], 1-Ethyl-3-methylimidazolium tricyanomethanide, [C₂C₁im][TCM], and Trihexyltetradecylphosphonium chloride, [P_6,6,6,14][Cl], was analyzed and the T_max estimated. In addition, vapor pressures over a range of temperatures were evaluated.