Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

The distillation and volatility of ionic liquids


It is widely believed that a defining characteristic of ionic liquids (or low-temperature molten salts) is that they exert no measurable vapour pressure, and hence cannot be distilled1,2. Here we demonstrate that this is unfounded, and that many ionic liquids can be distilled at low pressure without decomposition. Ionic liquids represent matter solely composed of ions, and so are perceived as non-volatile substances. During the last decade, interest in the field of ionic liquids has burgeoned3, producing a wealth of intellectual and technological challenges and opportunities for the production of new chemical and extractive processes4,5,6, fuel cells and batteries7, and new composite materials8,9. Much of this potential is underpinned by their presumed involatility. This characteristic, however, can severely restrict the attainability of high purity levels for ionic liquids (when they contain poorly volatile components) in recycling schemes, as well as excluding their use in gas-phase processes. We anticipate that our demonstration that some selected families of commonly used aprotic ionic liquids can be distilled at 200–300 °C and low pressure, with concomitant recovery of significant amounts of pure substance, will permit these currently excluded applications to be realized.

This is a preview of subscription content, access via your institution

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Labelled photograph of the Kugelrohr oven and distillation apparatus.
Figure 2: Schematic representation of the differences between protic and aprotic ionic liquids, in both the liquid and the gaseous phases.


  1. Seddon, K. R. Room-temperature ionic liquids—neoteric solvents for clean catalysis. Kinet. Catal. 37, 693–697 (1996)

    CAS  Google Scholar 

  2. Seddon, K. R. in Molten Salt Forum: Proceedings of 5th International Conference on Molten Salt Chemistry and Technology (ed. Wendt, H.) 53–62 (Trans Tech Publications, Zürich, 1998)

    Google Scholar 

  3. ISI Essential Science Indicators Special Topics: Ionic Liquids (ISI, 2004).

  4. Rogers, R. D. & Seddon, K. R. (eds) Ionic Liquids IIIB: Fundamentals, Progress, Challenges, and Opportunities—Transformations and Processes (American Chemical Society, Washington DC, 2005)

  5. Rogers, R. D. & Seddon, K. R. (eds) Ionic Liquids IIIA: Fundamentals, Progress, Challenges, and Opportunities—Properties and Structure (American Chemical Society, Washington DC, 2005)

  6. Atkins, M. P. et al. Ionic Liquids: A Map for Industrial Innovation: Q001 (January 2004) (QUILL, Belfast, 2004)

    Google Scholar 

  7. Ohno, H. (ed.) Electrochemical Aspects of Ionic Liquids (Wiley-Interscience, Hoboken, 2005)

  8. Rogers, R. D. & Seddon, K. R. (eds) Ionic Liquids: Industrial Applications for Green Chemistry (American Chemical Society, Washington DC, 2002)

  9. Rogers, R. D., Seddon, K. R. & Volkov, S. (eds) Green Industrial Applications of Ionic Liquids (Kluwer, Dordrecht, 2002)

  10. Wasserscheid, P. & Welton, T. (eds) Ionic Liquids in Synthesis (Wiley-VCH, Weinheim, 2003)

  11. Dymek, C. J. Jr, Hussey, C. L., Wilkes, J. S. & Øye, H. A. in Joint (Sixth) International Symposium on Molten Salts (eds Mamantov, G. et al.) 93–104 (The Electrochemical Society, Pennington, New Jersey, 1987)

    Google Scholar 

  12. Øye, H. A. & Wahnsiedler, W. E. in The Fourth International Symposium on Molten Salts (eds Blander, M., Newman, D. S., Saboungi, M. L., Mamantov, G. & Johnson, K.) 58–73 (The Electrochemical Society, Pennington, New Jersey, 1984)

    Google Scholar 

  13. Øye, H. A., Jagtoyen, M., Oksefjell, T. & Wilkes, J. S. Vapour pressure and thermodynamics of the system 1-methyl-3-ethylimidazolium chloride-aluminium chloride. Mater. Sci. Forum 73–75, 183–190 (1991)

    Article  Google Scholar 

  14. Jeapes, A. J. et al. Process for recycling ionic liquids. World Patent WO 01/15175 (2001)

  15. Yoshizawa, M., Xu, W. & Angell, C. A. Ionic liquids by proton transfer: Vapor pressure, conductivity, and the relevance of ΔpKa from aqueous solutions. J. Am. Chem. Soc. 125, 15411–15419 (2003)

    Article  CAS  Google Scholar 

  16. Kreher, U. P., Rosamilia, A. E., Raston, C. L., Scott, J. L. & Strauss, C. R. Self-associated, “distillable” ionic media. Molecules 9, 387–393 (2004)

    Article  CAS  Google Scholar 

  17. Abdul-Sada, A. K., Elaiwi, A. E., Greenway, A. M. & Seddon, K. R. Evidence for the clustering of substituted imidazolium salts via hydrogen bonding under the conditions of fast atom bombardment mass spectrometry. Eur. Mass Spectrom. 3, 245–247 (1997)

    Article  CAS  Google Scholar 

  18. Rebelo, L. P. N., Canongia Lopes, J. N., Esperança, J. M. S. S. & Filipe, E. On the critical temperature, normal boiling point, and vapor pressure of ionic liquids. J. Phys. Chem. B 109, 6040–6043 (2005)

    Article  CAS  Google Scholar 

  19. Paulechka, Y. U., Zaitsau, Dz. H., Kabo, G. J. & Strechan, A. A. Vapor pressure and thermal stability of ionic liquid 1-butyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)amide. Thermochim. Acta 439, 158–160 (2005)

    Article  CAS  Google Scholar 

  20. Maase, M. et al. Method for the separation of acids from chemical reaction mixtures by means of ionic fluids. World Patent WO 03/062171 (2003).

  21. Baranyai, K. J., Deacon, G. B., MacFarlane, D. R., Pringle, J. M. & Scott, J. L. Thermal degradation of ionic liquids at elevated temperatures. Aust. J. Chem. 57, 145–147 (2004)

    Article  CAS  Google Scholar 

Download references


This work was supported by a grant from FC&T, Portugal (to J.M.S.S.E. and L.P.N.R.). The Belfast team wishes to thank the industrial members of QUILL for support and Al Robertson (Cytec) for supplying the phosphonium ionic liquids. For J.W.M. and J.A.W. this work represents an official contribution of the National Institute of Standards and Technology and is not subject to copyright in the USA.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Luís P.N. Rebelo.

Ethics declarations

Competing interests

Reprints and permissions information is available at The authors declare no competing financial interests.

Supplementary information

Supplementary Methods

Describes in detail the methodologies of most of the distillations performed as well as those of the NMR Spectra. (DOC 43 kb)

Supplementary Data

Plots of the 1H, 13C and 19F NMR spectra of distilled and undistilled ionic liquids corresponding to the presentation of 30 figures, labelled from Supplementary Figure 1a to Supplementary Figure 12b. (DOC 243 kb)

Supplementary Figures

Supplementary Figure 13: [C6mim][NTf2] in the sublimation apparatus: photographs of atmospheric pressure distillation; and Supplementary Figure 14: < 0.001 mbar distillation compared. (DOC 1143 kb)

Supplementary Video 1

This movie (56 seconds) shows the Kugelrohr distillation process of [C2mim][NTf2] in action – 100 times speeded up. (AVI 4359 kb)

Supplementary Video 2

This movie (50 seconds) shows the Kugelrohr distillation process of [C10mim][NTf2] in action – 150 times speeded up. (AVI 6062 kb)

Supplementary Video Legends

Video 1. Timelapse video of the distillation of [C2mim][NTf2]. Video 2. Timelapse video of the distillation of [C10mim][NTf2]. (DOC 27 kb)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Earle, M., Esperança, J., Gilea, M. et al. The distillation and volatility of ionic liquids. Nature 439, 831–834 (2006).

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing