A novel method to determine the adsorption of water vapor on porous solids and supported ionic liquids by electrical sensors

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The thermal stability of ionic liquids with regard to evaporation and decomposition is important for the application of pure and supported ionic liquids (ILs). In the course of the soon-finished joint DFG-projects of both PIs, electrical sensors have been successfully developed to detect the pore filling degree of ionic liquids by a radio frequency-based (RF-based) method. By means of this method, the mass loss by evaporation and thermal decomposition can be measured. This was also possible in operando during the selective hydrogenation of butadiene to butene on a Pd-SCILL-catalyst (solid catalyst with ionic liquid layer).Within the applied new research project, which is a continuation of the first project, the promising RF-method shall now be transferred to measure in operando the adsorption of water vapor on porous solids and ionic liquids supported on porous solids. This is in general important for drying of gases by adsorption as well as for the use of supported ionic liquids in catalysis. If possible, the adsorption process should be monitored space-resolved in axial direction in an adsorber (fixed bed).Very preliminary experiments show that the ad- and desorption of water vapor can be measured by the radio frequency-based method both for pure porous solids as well as for porous solids coated with an IL. The ultimate goal of the proposed project is the development of a new electrical method to determine the water load of adsorption agents contact-free, in operando, and space-resolved. Pure porous silica as well as silica coated with an IL will be investigated. In the latter case, the simultaneous determination of the water load and the pore filling degree with the ionic liquid is also a goal of the project. Finally, the results of these investigations should also be applied to determine the influence of water (vapor) on the activity and selectivity of a SCILL-catalyst, namely the IL [DMIM][DMP] supported on silica with palladium as active metal. As a model reaction, the selective hydrogenation of butadiene to butene should again be used.At the end of the project, a model should have been developed that allows to quantitatively explain the radio frequency signals as a function of the input parameters (exposure of water, temperature) and that derives the water load spatially resolved from the RF signals.