Operation Temperature of ILs with Regard to Evaporation

2 Maximum Operation Temperature of ILs with Regard to Evaporation 

Now the question arises, under which circumstances not only thermal decomposition but also evaporation may hmit the operation temperature. For pure ILs, the following cases are instractive (i) storage in an open vessel and (ii) flow of a gas through an IL, which represents the application of ILs for extraction or absorption [27]- Exemplarily, the behavior of [BMIMJfNTf ], which has a relatively high volatihty, is analyzed. The temperature is fixed to regarding decomposi- 

Case 1 [BMIM][NTf2] is stored at 270°C and Ibar in a half-filled open vessel (height h essei)- mass loss takes place by diffusion into the gas phase (assumed to be of infinite size, so saturation is never reached). If the height of the vessel above the IL is taken as boundary layer thickness 8 ( constant for X,l 1%), Eq. (6.5) yields = D/S) [27]  

For a height of the vessel of 0.1 m, which may be regarded as a typical laboratory equipment size, the values for [BMIM][NTf2 in N2 yield a calculated vaporization time of 74 days to reach a mass loss due to evaporation of 1%. For lower temperatures, we get 16years (200°C), 133000years (100°C), and 5.9 bilhonyears ( ) for25°C. 

To summarize the issue of evaporation During storage of ILs, evaporation losses are negligible, and only decomposition limits the temperature. If a relatively volatile IL like [BMIM][NTf2] is in permanent contact with a gas, evaporation may then even limit 

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