(291e) Multi-Scale Modelling and Simulation of Catalytic Microreactors

Miniature chemical reactors have received significant attention in chemical engineering community due to many advantages compared to conventional ones, such as intensified mass and heat transfer, uniform flow, inherent safety, smaller plant size, lower cost of production and flexible response to market demand [1].

The aim of this work is to develop a general computational multi-scale framework for continuous microreactors with platinum catalytic walls. The model uses a macroscopic mean field approach for gaseous reactions modelled with a simplified home-made reaction-diffusion formulation and a rigorous computational fluid dynamics (CFD) code COMSOL Multiphysics [2]. Catalytic surface reactions are described with a microscopic kinetic Monte Carlo (kMC) technique to capture effects of adsorption, desorption or surface reactions. They are coupled with the gaseous part of the code through appropriate boundary conditions. Moreover, the heterogeneous reactive platinum surfaces are modelled with sequences of consecutive kMC lattices, efficiently linked [3] in order to model surface diffusion phenomena. Due to slow microscopic surface diffusion processes on the kMC lattices, parallel computing techniques were used to accelerate computational simulations. Overall, the developed multi-scale model is capable to describe coupling between (bio)chemical surface and gaseous reaction mechanisms, if appropriate kinetic parameters are known.

The efficient coupling of time and length scales is investigated through illustrative cases. Comparison with fully macroscopic mean field models, simulated with home-made and CFD codes is presented in order to validate the multi-scale models including interactions between the macroscopic gas-phase and the microscopic reactive surface and lateral interactions between the neighbouring kMC lattices comprising the computational representation of the reactive surface. The relative importance of these interactions is evaluated for a wide range of initial conditions. The methodology is demonstrated for the CO oxidation mechanism [4] and for the NO reduction mechanism with CO oxidation [5].

References:

[1] Ehrfeld W., Hessel V., Lowe H. (2000): Microreactors: New Technology for Modern Chemistry, Wiley-VCH.

[2] COMSOL Multiphysics, User's guide, COMSOL AB (2005).

[3] Gear C.W., Li J., Kevrekidis I.G. (2003) Phys. Lett. A 316, 3-4, 190-195.

[4] Kaul D.J., Sant R., Wolf E.E. (1987): Chem. Eng. Sci. 42, 6, 1399-1411.

[5] Fink Th., Dath J.P., Bassett M.R., Imbihl R., Ertl G. (1991): Surface Science 245, 96-110.