Selection of ionic liquids for aromatic/aliphatic separations and determination of LLE data supported by COSMO-RS
Sustainable process-product development & green chemistry
Modelling, Design & Analysis of Processes with Ionic Liquids (T1-1P)
Keywords: ionic liquids, COSMO-RS, extraction
Selection of ionic liquids for aromatic/aliphatic separations and determination of LLE data supported by COSMO-RS
A.R. Hansmeier, M. Minoves Ruiz, G.W. Meindersma, A.B. de Haan*
University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands
*Technical University of Eindhoven, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
E-Mail: a.r.hansmeier@tnw.utwente.nl
Abstract
Ionic liquids can provide higher selectivities () and distribution coefficients (Di) for the separation of aromatic and aliphatic hydrocarbons than common extraction solvents, such as sulfolane, N-methylpyrrolidon (NMP), ethylene glycols, etc. [1]. Ionic liquids (IL) are molten salts, composed of large organic cations and various anions, which are liquid at T < 100 °C. Some of their properties are a negligible vapour pressure, a wide liquid range (~300K) and the ability to dissolve polar, non-polar, organic and inorganic compounds. Since the properties of an ionic liquid are defined by the combination of cation and anion, a great number of combinations (> 1014) is conceivable. To be able to make a selection out of all possible combinations, COSMO-RS was found to be a suitable screening tool. The COSMO-RS approach is based on unimolecular quantum chemical calculations and, therefore, only limited by the availability of the individual component parameters, in which it is different from group contribution methods like UNIFAC [2].
With this simulation tool, suitable ionic liquids have been screened. The screening is based on -profiles which describe the surface charge distribution of a molecule.
It was found that if an ionic liquid has a similar -profile as another substance, thus, similar polarity, this substance is soluble in the ionic liquid and, therefore, the ionic liquid can be used as an extraction solvent. Since the -profiles of the ionic liquid [EMIM]+[AlCl4]- and toluene are resembling, but not for the ionic liquid and n-heptane, this ionic liquid is assumed to be a good solvent for the extraction of toluene from n-heptane.
As we have found, the COSMO-RS prediction is in good agreement with the experimental values we obtained, and, therefore, ILs can be selected by means of this procedure.
Additionally, it is possible to determine NRTL parameters and to calculate the corresponding ternary equilibrium diagrams based on selectivity and distribution coefficient data that have been obtained by LLE experiments. In this work, ternary diagrams for toluene + n-heptane + an ionic liquid have been derived. Aspen 12.1 has been used as a simulation tool for data regression and determining NRTL parameters.
In conclusion, the combination of an initial COMSO-RS screening and verification by experimental results allows a reasonable selection of ionic liquids for specific purposes. With the NRTL parameters determined from LLE experiments, an extraction of toluene from a toluene/n-heptane mixture can be simulated.
References
1. G.W. Meindersma, A. Podt, A.B. de Haan (2005), Selection of ionic liquids for the extraction of aromatic hydrocarbons from aromatic/aliphatic mixtures, Fuel Processing Technology, 87, 59-70
2. A. Klamt, (2005), book, COSMO-RS From Quantum Chemistry to Fluid Phase Thermodynamics and Drug Design, Elsevier
Presented Monday 17, 13:30 to 15:00, in session Modelling, Design & Analysis of Processes with Ionic Liquids (T1-1P).
