(546f) Multi-Scale Modelling and Design of Catalytic Microreactor Systems

Microreactor systems are receiving increasing attention nowadays due to their enhanced operation characteristics, such as increased mass and heat transfer capabilities, flow uniformity, inherent safety and potential for high throughput through the construction of array configurations. They also ensure a smaller plant size, lower cost of production and more flexible response to market demand [1].

In this work we construct multi-scale models of continuous microreactors with catalytic walls as an alternative to the conventional packed-bed configuration. The bulk (gaseous) phase is treated macroscopically using Computational Fluid Dynamics (CFD), including transport phenomena and gas-phase reactions, while the catalytic activity is modeled at the micro/mesoscopic level using kinetic Monte Carlo (kMC) simulations including effects such as adsorption, desorption surface reactions and surface diffusion. A number of kMC lattices depending on the discretisation of the computational domain are used to effectively represent the reactive surfaces. Massively parallel computations both for the gas-phase using SANDIA's code for reaction transport processes (codename: MPSALSA) [2] and for the surface are used to accelerate the tedious computational tasks.

The efficient coupling of time and length scales is investigated through coarse-graining methodologies and comparisons with fully macroscopic mean field approaches are made in order to assess the window of parameters where the multi-scale approach becomes important. The effect of both vertical interactions (between the macroscopic gas-phase and the microscopic surface) and lateral interactions between neighbouring kMC lattices is studied with the use of efficient numerical techniques. The relative importance of these interactions is evaluated for a wide range of conditions, through sensitivity studies. The methodology is demonstrated through the use of two illustrative reaction systems with well-known kinetics: CO oxidation [3] and the simultaneous NO reduction with CO oxidation [4].

References

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

2. Shadid J, Hutchinson S, Hennigan G, Moffat H, Devine K, Salinger AG, Parallel Computing 23, (1997), 1307-1325.

3. Zhdanov VP and Kasemo B 20 (1994) 111-189.

4. Fink Th, Dath JP, Imbihl R, Ertl G, J. of Chem. Phys. 95 (1991) 2109-2126.