Bernd RATHKE1, Maximilian PFEIFFER1, Sabine WAGENFELD1, Marcus STUCKENHOLZ1, Johannes KIEFER1, Wolffram SCHRÖER1
1Univeristät Bremen - Technische Thermodynamik, Bremen, Germany
The present work exhibits the combination of isobaric liquid-liquid (LLE) and vapor-liquid equilibria (VLE) of binary mixtures of 1-ethyl-3-methlimidazolium trifluoromethanesulfonate (C2mimTfO) and 1-butyl-3-methlimidazolium trifluoro-methanesulfonate (C4mimTfO) ionic liquids (ILs). While LLE of the different systems consist of n-alkyl alcohols CnOH with the length of the alkyl chain n ≥ 3, VLE are limited to alcohols with n ≤ 5. In order to adjust the molecular interactions of the different moieties, i.e., a molecular compound and an IL, the chain lengths of one component of the is changed. Thus, the slightly changes of molecular interactions become visible by shifts of the phase behavior. Mixtures with shorter chained alcohols allow for a combined view on the VLE and the LLE, which is discussed here in this unusual combination. The experiments span a range of temperatures which is limited by either the chemical stability of the mixture or the temperature stability of the components. The VLE have been obtained at pressures of p = 500, 700 and 1000 mbar while the LLE have been determined at ambient pressure. The two components IL + CnOH show partial miscibility with an upper critical (liquid-liquid) solution temperature, indicated by a phase split. The LLE have been analyzed in accordance to Ising criticality by fitting procedure. As results the critical temperatures, critical compositions and coefficients describing the shape of the phase diagram are obtained. The results compared with IL mixtures with similar behavior. VLE of mixtures of have been evaluated in terms of the PC-SAFT EoS and the NRTL model. VLE and LLE are both described by a corresponding state.