Determination of Transient Reaction Kinetics for Unsteady-State Methanation of CO2 on Ruthenium Catalysts using Periodic Experimentation

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The integration of renewable energies into the chemical value chain requires the design of chemical reactors that can respond flexibly to temporal fluctuations in the availability, quality and composition of the raw materials. On the one hand, a constant product quality should be achieved and, on the other hand, safe operation should be guaranteed even under highly dynamic conditions. Chemical processes that take place on solid catalysts are particularly relevant, as they account for by far the largest share in the chemical industry in terms of value creation. Essential for the design and dimensioning of chemical reactors are the reaction kinetics, which are implemented in suitable mathematical reactor models and represent the catalytic processes at the solid surface. The reactor models are now used to simulate and optimize the reactors with regard to load characteristics, product yield and other aspects. For highly dynamic operation mode, kinetics are required that also adequately represent the transient behavior of the catalysts. However, in most cases, such transient reaction kinetics are not known or only to some extent, since steady-state experiments have usually been performed to obtain kinetic information so far. The proposed project aims to obtain transient kinetic information by means of highly dynamic periodic experiments and model-based evaluation of experimental data. The hydrogenation of CO2 to methane on ruthenium-based catalysts under technically relevant conditions serves as an example reaction with technical relevance. It will be demonstrated that the periodic step response of a chemical reactor contains the corresponding kinetic information and that such information can be determined from the experimental results on the basis of a dynamic reactor model. In particular, the limit cycle that is established during periodic operation will be investigated. The focus is on the development of a methodology for the determination of the transient kinetics from periodic step responses, which includes an adequate experimental procedure and a strategy for model-based evaluation. For this purpose, an application-relevant example reaction from the class of heterogeneously catalyzed gas phase reactions is selected, which offers sufficient complexity with respect to the elementary reactions involved to provide generalizable conclusions.