Radio Frequency‐Based In Situ Determination of the Mass Loss of Supported Ionic Liquids

Abstract

For technical applications of supported ionic liquids (ILs), the stability of the IL layers both with regard to thermal decomposition and to losses by evaporation is of great importance. An innovative radio frequency-based method is presented to determine the pore filling degree of supported ILs in situ and in a contactless way. As an example, the IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, which was supported on the internal surface of porous silica, was selected. The complex permittivity of the porous solid coated with the IL increases linearly with the IL pore filling degree. Therefore, the evaporation rate of the IL in a fixed bed could be measured in situ in the reactor.

Operando Determination of the Thermal Decomposition of Supported Ionic Liquids by a Radio-Frequency-Based Method

“…Further information on the measurement setup can be found in refs. 18,27 With a network analyzer, the transmission parameter S 21 , which is the ratio of the complex amplitudes of transmitted and received waves, 14 is recorded over the excitation frequency. Figure 15 illustrates a transmission spectrum of the empty sample tube (index 0), of a sample tube filled with pure silica (index S) and filled with silica coated with IL (α = 30%, index IL).…”

“…This setup and the fact that all other components in the resonator are made of low-loss quartz allow the complex permittivity of the sample to be determined. Further information on the measurement setup can be found in refs. , …”

“…17 In a previous study, the evaporation rate of supported [EMIM][NTf 2 ] could be determined using the RF-based method. 18,19 In all of these applications, the electrical parameters such as the complex permittivity of the catalyst itself are analyzed. On the basis of the results, conclusions can be drawn about the state of the IL-coated catalyst.…”

“…This method has already been successfully applied to determine the coke loading of heterogeneous catalysts , as well as to measure quantitatively the ammonia sorption of SCR catalysts. , Sulfur poisoning of Ni catalysts has been qualitatively determined as well . In a previous study, the evaporation rate of supported [EMIM]­[NTf 2 ] could be determined using the RF-based method. , In all of these applications, the electrical parameters such as the complex permittivity of the catalyst itself are analyzed. On the basis of the results, conclusions can be drawn about the state of the IL-coated catalyst.…”