Predicting the Thermodynamic Behaviour of Water + Ionic Liquids Systems Using COSMO‐RS

Abstract

Ionic liquids are a novel class of chemical compounds with interesting properties that are driving much research in several fields. The complete understanding of the phase behavior of ionic liquidswithwater is an important issue, yet there is little data on their phase equilibria. In this work, the predictive capability of COSMO-RS, a predictive model based on unimolecular quantum chemistry calculations, was evaluated on the description of the liquid–liquid equilibria and the vapor–liquid equilibria of water and several imidazolium-based ionic liquid binary mixtures. The performance of the different calculation procedures, the basis set parameterizations, and the effect of the ion conformers on the quality of the predictions were evaluated. COSMO-RS calculations were performed at the following levels: BP/TZVP Q1 , BP/SVP//AM1, and B88-VWN/DNP. It was found that the calculation procedure based on the quantum chemical COSMO calculation at the BP/TZVP level derived from the lower energy ion conformations provides the best prediction capacity of the model. Good agreement between the model predictions and experimental VLE and LLE data was obtained. The COSMO-RS proved to be very helpful for scanning the growing set of already known ionic liquids in order to find suitable candidates for a certain task or to design new ionic liquids for specific applications. Molten Salts and Ionic Liquids: Never the Twain? Edited by Marcelle Gaune-Escard and Kenneth R. Seddon Copyright 2009 John Wiley & Sons, Inc.