The distillation and volatility of ionic liquids

The QUILL Centre, The Queen's University of Belfast, Stranmillis Road, Belfast BT9 5AG, UK.
Nature (Impact Factor: 41.46). 03/2006; 439(7078):831-4. DOI: 10.1038/nature04451
Source: PubMed


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 distilled. 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 burgeoned, producing a wealth of intellectual and technological challenges and opportunities for the production of new chemical and extractive processes, fuel cells and batteries, and new composite materials. 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 degrees C and low pressure, with concomitant recovery of significant amounts of pure substance, will permit these currently excluded applications to be realized.

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    • "ILs are defined as salts that are in liquid state at below 100 • C. They possess important attributes such as a wide liquid range, non-volatility (except at low pressures and high temperature ), high catalytic activity, excellent chemical and thermal stability, potential recoverability, design possibilities, and ease of separation of the products from reactants [9] [10] [11] [12]. Recent developments have demonstrated that the use of ILs in biodiesel production is a promising alternative for efficient green preparation of biofuels . "
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    • "The pressure, P, can be obtained from Equations (4) and (5). Since ILs have a negligible vapor pressure [25], Equation (4) cancels and after rearranging Equation (5) one obtains the bubble-point pressure of a n-solute (i.e., n is the number of components in the gas phase excluding the IL since it is considered nonvolatile ) system: "

    Fluid Phase Equilibria 09/2015; DOI:10.1016/j.fluid.2015.09.041 · 2.20 Impact Factor
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