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Anke, Marie-Luise ; Hämmerle, Martin ; Moos, Ralf ; Jess, Andreas:
Microwave-based in operando measurements of the thermal stability and the catalytic activity of supported ionic liquid catalysts during the selective hydrogenation of 1,3-butadiene.
2018
Veranstaltung: ProcessNet Jahrestreffen Reaktionstechnik
, 7.-9.5.2018
, Würzburg, Deutschland.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung
,
Poster
)
Abstract
In order to efficiently and economically use ionic liquids (ILs), two methods, the SILP-concept (Supported Ionic Liquid Phase) and the SCILL-concept (Solid Catalyst with Ionic Liquid Layer) support ILs on porous catalysts. In both concepts, the ionic liquid influences the chemical and physical properties of the catalyst and combines the advantages of homogeneous and heterogeneous catalysis. To determine the thermal stability of the ionic liquid layer as well as the actual pore filling degree α, i.e. the ratio of IL volume and pore volume of the uncoated catalyst is of great practical interest. State-of-the-art are thermogravimetric analyses (TG). However, despite very accurate, they are time consuming, ex situ, and destructive. To overcome these disadvantages, a new microwave-based method is presented in this work. The pore filling degree and its potential decrease due to thermal decomposition or evaporation are measured in a contactless manner. This is exemplarily shown in operando during the selective hydrogenation of 1,3-butadiene to butene. A related method was already applied to detect the coke loading on a solid catalyst or the ammonia loading on zeolite-based ammonia SCR-catalysts. In all these studies, the electrical properties of the catalysts themselves are measured. The set-up used in this study comprises a temperature-controlled cylindrical cavity resonator. With a network analyzer (Anritsu VNA Master MS2028B) an electromagnetic field is excited in the aluminum resonator by two loop couplers and the transmission spectrum is recorded. The material under test – here a Pd-catalyst coated with an IL - is placed in the central axis of the resonator. Here, the electric field component of the analyzed resonance mode is almost constant and maximal. Besides the (given) inner diameter and height of the cavity, the electrical material properties of the sample, influenced by the ionic liquid, affect the microwave signal, i.e., the complex permittivity. The latter is a measure for the dielectric and resistive losses. For details on the evaluation procedure. By applying the presented microwave-based method, the evaporation rate of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifuoromethylsulfonyl)imide could be determined. In this study, the ionic liquid 1-butyl-3-methylimidazolium dimethylphosphat, in short [BMIM][DMP], was used for the selective hydrogenation of 1,3-butadien to butene. It was immobilized in variable amounts on silica 150A and coated with palladium as the catalytic component. As shown, the pore filling degree (determined ex situ using TG) and the dielectric and resistive losses, calculated from the transmission signal (measured in operando), correlate linearly. Using this information, the IL mass loss due to thermal decomposition as well as its relation to the catalytic activity could be detected in operando. Further investigations using the presented method to determine the metal loading of the catalyst are in process.