Thermal Stability and Vapor Pressure of Pure ILs

Drawbacks and Opportunities Regarding Stability and Vapor Pressure Measurements of ILs 

Usually, the thermal stability of ILs is characterized by thermogravimetrical analysis (TGA) at ambient pressure in overflow of an inert gas at a constant heating rate, typically 1-20 Kmin [41-43]. The so-called onset temperature (T gg,), at which a certain detectable mass loss of, for example, 1% is reached, is used as a synonym for the decomposition temperature to define the stability of ILs [3, 44]. The application of may be useful as a comparative value, but not as a quantitative measure of the stability due to the following reasons [25, 27]  

Instead of time consuming isothermal experiments (or the use of the vague value of the critical operation temperature should be estimated by extrapolation of kinetic data measured at T if the decomposition kinetics are well known 

To overcome the problems related to simple but also accurate methods to determine the parameters of decomposition and evaporation are needed. As revealed in previous publications [25, 27], thermogravimetrical non-isothermal analysis (TGA) at ambient pressure with different carrier gases such as He and N2 is a suitable method to discriminate between evaporation and decomposition. For decomposition only, the mass loss does not depend on the atmosphere, as 

Experimental Methods to Determine the Stability and Vapor Pressure of ILs 

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For ILs with a low stability regarding thermal decomposition and/or relatively low vapor pressures, HV experiments (<10 Pa) should be conducted, for example, with a magnetic suspension balance (MSB y)- The schematic setup of these two methods used in this work to evaluate the thermal stability and vapor pressure of pure and supported ILs are shown in Figure 6.2. For details see [25-27, 32]. 

For the development and design of supported ionic liquid (IL) processes - but also of those utilizing pure ILs, for example, as solvents-the thermophysical properties such as density, heat capacity, thermal conductivity, viscosity, melting point, solvation properties, mass transport properties in/of ILs, thermal stability, and vapor pressure are important [1-24]. Here, the emphasis is on the three last-mentioned properties. 

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