Multi-mode reduced order models for real time simulations of monolith reactors with micro-kinetics

We present a novel procedure for computing washcoat diffusional effects in monolith reactors with detailed micro-kinetic models. First, we show that the short time scales associated with the adsorption/desorption steps of micro-kinetic models requires using a significantly larger number of mesh points within the washcoat to obtain a solution that is independent of the mesh size. Next, we present a mull-mode reduced order model that eliminates the degrees of freedom associated with species diffusion in the washcoat using the local property dependent internal mass transfer coefficient matrix. This matrix is shown to be diagonal for most micro-kinetic models of practical interest and can be calculated accurately. We illustrate the new approach with an example of H-2/CO/C3H6 oxidation over a Pt/Al2O3 catalyst with a 20 step micro-kinetic model. Even for this simple single site model, the small time (and length) scales associated with the species adsorption steps make the computation of the mesh size independent solution of the 1+1D model time consuming. However, the reduced order model leads to an accurate solution while speeding-up calculations by about three orders of magnitude.