Thermodynamic Study of Protic Ionic Liquids

The aim of this thesis was to investigate phase equilibrium and physical properties of a distillable ionic liquid 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]) and a switchable ionic liquid carbon dioxide (CO2) + 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU) + glycerol, and their mixtures with water. In addition, the properties of the precursor amidines (DBU and DBN) and their mixtures with water were investigated. In the physical property study, vapor pressures, densities and several enthalpies (formation, reaction, vaporization, solution) of DBN, DBU and [DBNH][OAc] were determined. The vapor pressure and density measurements were conducted with the distillation column and the oscillating U-tube density meter, respectively. The results were modeled with empirical correlations. [DBNH][OAc] was found to decompose into pure DBN and a stable 5:3 HOAc:DBN complex during the evaporation. Therefore, vapor pressures of the decomposition products were measured from the [DBNH][OAc] samples with the distillation column instead of [DBNH][OAc]. The decomposition of [DBNH][OAc] was observed with several common vapor pressure or vaporization enthalpy measurement methods. The formation and reaction enthalpies of DBN and [DBNH][OAc] were determined with a combination of calorimetric and computational methods. The vaporization enthalpies of DBN and DBU were derived from the vapor pressure correlations. On the other hand, the vaporization enthalpy of [DBNH][OAc] was derived from its gas and liquid phase enthalpies of formation due to its decomposition into DBN and the 5:3 HOAc:DBN complex during the evaporation.The phase equilibrium study consisted of the measurements and modeling vapor-liquid (VLE) and gas-liquid (GLE) equilibrium. The VLE and GLE measurements were conducted by two variations of the static total method. The GLE was studied for CO2 + glycerol, CO2 + DBU and CO2 + DBU + glycerol systems at the 303-353 K temperature range. The results illustrate the effect of DBU:glycerol ratio in CO2 absorption efficiency. CO2 solubility in pure DBU and glycerol was described with the Henry's law constants, which were further modeled with an empirical correlation. The CO2 + DBU + glycerol systems were modeled with a simple Posey type semi-empirical model. In addition, enthalpies of CO2 absorption in DBU + glycerol systems were estimated from the model parameters. The VLE measurements were conducted for the binary mixtures of water with [DBNH][OAc], DBN and DBU at the 303-353 K temperature range. The results of the studied systems indicate negative deviation from the Raoult's law. The measured VLE data were modeled with the Legendre and NRTL activity coefficient models.