Speaker
Description
To estimate the kinetic parameters of surface catalytic reactions, ubiquitously ideal reactor models like the CSTR, stagnation point flows, or the plug flows are exploited. This allows the system to be governed by either analytical or a simple ODE based solution. However, modern in-situ atomic scale surface characterization experiments seldom allow such flow geometries, e.g. by the need to install devices like probes and pumps in the vicinity of the catalyst. Also in such scenarios, the coupling of transport and kinetics can be expected to be crucial and computational modelling requires using full scale CFD since the above-mentioned models may lead to misleading information about the surface coverage, activity or reaction conditions over the surface of the catalyst. However, the concomitant huge computational burden prevents conventional CFD from being a practical tool in these cases beyond a few validation runs, particularly when solving optimization problems for kinetic parameter estimation. Therefore, there is a need for surrogate or reduced order CFD models for solving for more general flows and arbitrary reactor geometries.
In this study, we present a kinetic parameter estimation case study employing a Reduced Order CFD Method (ROM) for the non-ideal reactor cases. The ROM relies on the limiting case where experiments are conducted under excess of one species, e.g. a buffer gas or one of the reactants. In this limit, mass density and transport coefficients become independent of the concentration changes caused by the catalytic conversion. This allows the decoupling of transport and kinetics where only the transport needs to be solved in the pre-processing (the offline phase of the ROM), which, while still being a CFD problem, is rather cheap compared to the conventional ROM approaches. The coupling of transport and kinetics then reduces to a small nonlinear algebraic problem with a computational complexity which is comparable to a simple CSTR model, nevertheless, accounting for non-ideal flow behavior which is expected from conventional CFD. Together with the offline phase being completely independent of the kinetic model, this makes the approach particularly suited for extensive testing of kinetic models or parameter estimation for these models based on complex experimental setups, e.g. combinations of surface characterization with non-intrusive concentration imaging.
