Falling Film Evaporator: Drying of Ionic Liquids with Low Thermal Stress

Abstract

The removal of water from an aqueous ionic liquid (IL) water solution is a new application for falling film evaporators (FFE). As FFE are able to operate at conditions with small thermal gradient and small residence time in the heated zone, the resulting thermal stress to the IL is considerably low compared to other separation methods, e.g. rotary evaporators. The investigations in a steam heated single tube falling film evaporator were conducted concerning two IL water mixtures. One IL was ammonium based and the other imidazolium based. For these two IL experiments were conducted to obtain the equilibrium water content with variation of temperature and pressure. The resulting water contents decreased with elevating the heating temperature and lowering pressure at product side. Minimal water contents of under 0.01 gw/gliquid were achieved at an film exit temperature of 140 °C and an evaporation pressure of 50 mbar abs.