Florian Heym

Analysis of evaporation and thermal decomposition of ionic liquids by thermogravimetrical analysis at ambient pressure and high vacuum

Ionic liquids (ILs) are widely discussed as alternative green solvents not only because of their unique chemical properties, but also because of their extremely low vapour pressure and – at least in some cases – relatively high thermal stability. Two complementary methods are analyzed and compared to determine both the rate constant of decomposition and the vapour pressure of four ILs: (1) thermogravimetrical analysis at ambient pressure (TGap) with an overflow of inert gases, and (2) high vacuum (HV) experiments with a magnetic suspension balance (MSB). At ambient pressure, [EMIM][MeSO3] and [EMIM][CF3SO3] decompose without a significant contribution of evaporation, which leads to the rate constant of thermal degradation. For both ILs, the vapour pressure can only be determined at HV by the MSB, because the evaporation rate is then higher than the decomposition rate. For the relatively volatile ILs [EMIM][NTf2] and [BMIM][NTf2] the vapour pressure can be derived both by the MSB at HV as well as by TGap. General strategies to determine the volatility and stability of ILs and criteria for the maximum operation temperature with regard to decomposition and evaporation are presented.

Thermally stable bis(trifluoromethylsulfonyl)imide salts and their mixtures

We show that both tetraphenylphosphonium bis(trifluoromethylsulfonyl)imide ([PPh4][NTf2]) and Cs[NTf2] are low melting salts of exceptionally high and also very similar thermal stability. This similarity indicates that the thermal stability is dominated by the anion. Moreover, eutectic mixtures of [PPh4][NTf2] and Cs[NTf2] with melting points below 100 °C are presented. Surface analysis of the latter in the liquid state reveals a surprising depletion of [PPh4]+ ions from the surface.

Development of Direct and Indirect Methods for the Determination of Vaporization Enthalpies of Extremely Low-Volatile Compounds

Abstract Recent advances in experimental methods for the determination of vapor pressures and vaporization enthalpies of extremely low-volatile compounds related to ionic liquids and biodiesel components have been critically analyzed.