TECHNOLOGY » APPLICATION » SEPARATION TECHNOLOGIES

Ionic liquids are widely recognized as very suitable materials for separation processes such as extraction, gascleaning and extractive distillations [1]. This is due to their amazing combination of properties such as no measurable vapour pressure, nonflammability and tunability of their solution properties which differentiates them from molecular solvents. This has been impressively demonstrated in homogenous catalysis [2-3] where the transition-metal catalyst dissolved in the ionic liquid can normally be recycled with little decrease in activity.

Extractions and separations in two-phase systems require the knowledge of the miscibilities and immiscibilities of the IL with other solvents. Ionic liquids tend to be immiscible with alkanes and other non-polar organic solvents and hence can be used in two-phase systems. It is also possible to design hydrophobic ILs (like [BMIM][PF₆]) that can be used in aqueous/IL biphasic systems in which the IL is the less polar phase.

Another promising approach is to combine ionic liquids and scCO₂ . Brennecke and Beckman observed that although

scCO₂ is surprisingly soluble in some ionic liquids, the reverse is not the case. On the basis of these results they described a procedure to extract a large variety of different solutes from ionic liquids, without observation of any ionic liquid contamination in the isolated substances [4].

One of the most rapidly emerging areas of research with ionic liquids is their use in biocatalytic reactions. One example for an extraction process in this context is the recovery of n-butanol from a fermentation broth by in situ extraction with [BMIM][PF₆].

In a project which is sponsored by the DBU (German Agency for environmental protection) we investigate the desulfurization of diesel oil together with the University Erlangen-Nürnberg and the University Bayreuth [5].

For further information on separation processes with ionic liquids please contact marc.uerdingen@solvent-innovation.com

[1] W. Arlt, Chemie Ingenieur Technik , 2004 , 76, 735-744.

[2] P. Wasserscheid, W. Keim, Angew. Chem. Int. Ed. Engl. 2000 , 39, 3772.

[3] P. Wasserscheid et al. Green Chemistry , 2002 , 4, 400-404.

[4] J. Brennecke et al., Nature , 1999 , 399 , 28-29.

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