Ionic liquids as additives for extractive distillation
Extractive distillation is suitable for the separation of narrow-boiling or azeotropic liquid mixtures that cannot be separated using conventional distillation processes or can only be separated with considerable effort. By adding a high-boiling, non-volatile, miscible substance that does not form an azeotrope with the substances to be separated, the phase equilibrium can be shifted so that separation is possible with reasonable effort.
Ionic liquids are particularly suitable for the extractive distillation of azeotropic or narrow-boiling mixtures, as they often have a low vapor pressure and thermal stability up to 280 °C. Ionic liquids are also usually very stable against acids. With a suitable selection of anions, hydrolytic stability can also be guaranteed. Another important property for suitability as an entrainer for extractive distillation is low corrosiveness and the lowest possible viscosity of the ionic liquid[1].
Figure 1 shows an example of the extractive distillation of a mixture of ethanol and water using an ionic liquid.
Extractive distillation with ionic liquids using the example of a mixture of water and ethanol.
The mixture of ethanol and water to be separated is fed into the center of the main column, while the ionic liquid is added as an auxiliary at the top of the main column. The addition of the ionic liquid at the top of the column ensures that it is present throughout the entire column to entrain the water and therefore anhydrous ethanol can be separated at the top of the main column. Since the ionic liquid is miscible with the water but does not form an azeotropic mixture with the water, the water can be distilled off from the ionic liquid, which has a negligibly low vapor pressure, in an auxiliary column. The recovered ionic liquid can then be fed back into the top of the main column and used to separate water and enthanol again.[2,3,5,6] In addition to the extractive distillation of ethanol/water mixtures, ionic liquids have also been successfully used for the extractive distillation of many other mixtures such as methyl acetate/methanol,[7] 1-hexene/n-hexane,[5] ethylbenzene/styrene,[4] cyclohexane/benzene,[7] benzene/hexane,[7] and methylcyclohexane/toluene[9].
IOLITEC has been one of the world's leading suppliers of ionic liquids for many years. We offer a range of ionic liquids that can be used as auxiliaries for the extractive distillation of narrow-boiling or azeotropic liquid mixtures. Due to our high quality standards and our specially optimized quality control for ionic liquids, our ionic liquids are characterized by a consistently high purity. Our high flexibility enables us to react quickly to our customers' wishes. You can find our product catalog here. If you are interested in ionic liquids that you cannot find in our product catalog, we will be happy to make you an offer for a custom synthesis. We will be happy to answer your questions and support you in the selection of suitable ionic liquids. Please do not hesitate to contact us: info@iolitec.de.
Text: Dr. Maria Ahrens, IOLITEC GmbH, 2015.
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Literature
[1] Y. Beste, M. Eggersmann, H. Schoenmarkers, Chemie Ingenieur Technik 2005, 77, 1800.
[2] http://www.spektrum.de/lexikon/chemie/extraktivdestillation/3192.
[3] G. Ruffert, G. Olf, Chemie Technik 2004, 3, 86.
[4] M. T. G. Jongmans, E. Hermens, M. Raijmakers, J. I. W. Maassen, B. Schuur, A. B. de Haan, Chemical Engineering Research and Design 2012, 90, 2086.
[5] J. P. Gutiérrez, G. W. Meindersma, A. B. de Haan, Ind. Eng. Chem. Res. 2012, 51, 11518.
[6] G. Gonfa, M. A. Bustam, T. Murugesan, et al. in 11TH INTERNATIONAL CONFERENCE ON CHEMICAL AND PROCESS ENGINEERING, PTS 1-4 Book Series: Chemical Engineering Transactions 2013, 32, 1939.
[7] A. B. Pereiro, J. M. M. Araújo, J. M. S. S. Esperanca, I. M. Marrucho, L. P. N. Rebelo, J. Chem. Thermodynamics 2012, 46, 2.