Solid–liquid phase diagram of the two Ionic Liquids EMIMCl and BMIMCl

Ionic Liquids (ILs) are subject of intensive research for industrial applications due to their versatile properties. Efforts are made to obtain liquids at moderate temperatures by choosing an appropriate combination of cation and anion or by adding solvents to reduce the melting point. An alternative for melting point depression is the addition of another Ionic Liquid while the desired functionalities, like non-volatility or the aprotic character of the IL, are preserved. In the current work the solid–liquid equilibrium (SLE) of the solvent-free model system of the two Ionic Liquids 1-ethyl-3-methylimidazolium chloride (EMIMCl) and 1-butyl-3-methylimidazolium chloride (BMIMCl) are investigated. The solid–liquid phase behavior is found to be of eutectic type with a eutectic composition xEMIMCl,eu = 0.5 and a eutectic temperature Teu = 315 K. Compared to the pure component melting point of EMIMCl a melting point depression ΔT = 46 K is achievable by adding BMIMCl. The SLE data can be described by the Schröder–Van-Laar equation in the simplest form neglecting differences in heat capacity, assuming ideal liquid phase behavior and the crystallization of pure components. This gives evidence that the system of the two Ionic Liquids BMIMCl–EMIMCl exhibits an ideal eutectic solid–liquid phase behavior.