(28a) Separation Science with Ionic Liquids

Ionic liquids (IL) represent a new class of selective solvents. Due to their fascinating properties, they appear as promising substances for the optimization of a number of separation processes such as extractive distillation, extraction and absorption. By choosing task-specific anion-cation combinations, this is by tailoring the properties, remarkable selectivities can be achieved with regard to the separation of many close boiling or azeotropic systems [1, 2]. The lecture aims to elucidate the potential of IL in the field of chemical engineering.

First, our approach for tailoring the chemical structure of IL's by the method COSMO-RS is demonstrated. For the prediction of activity coefficients with this method, the use of different conformations of the components, derived from conformational analyses, leads to varying results. The capacity and selectivity of the unit operation is discussed for mixtures of polar and non-polar compounds. The results can be used for all unit operations described below.

The application of IL is demonstrated for 1.) solvent extraction 2.) absorption 3.) distillation Distillation experience has been created by BASF AG in a test environment. One outcoming is that the IL changed its colour while nevertheless keeping its properties: “we sell performance not color”. A special case occurs if the IL is not fully miscible with the feed mixture.

The properties of the IL used for these applications are: a) the extremely low vapour pressure b) the chemical nature of the cation and anion

Until today, no technical scale commercial application is known but several processes are said to be in progress. But simulations with process simulators show that the use of IL can reduce the investment and the running cost of separation (energy savings). It is necessary that the purchase of IL's is regarded to be an investment. This is due to the present high price. This means that the IL should not be lost or decomposed during the process.

[1] W. Arlt, M. Seiler, C. Jork, T. Schneider (2001), DE Pat. No 10114734 [2] W. Arlt, M. Seiler, C. Jork, T. Schneider (2001), DE Pat. No 10136614