Multiscale Modeling of Reaction and Diffusion in Zeolites: From the Molecular Level to the Reactor

Soft Materials, Volume 10, Issue 1-3, 2012, pages 179-201

Special Issue: Molecular Modeling and Simulation in Process and Materials Engineering

Multiscale Modeling of Reaction and Diffusion in Zeolites: From the Molecular Level to the Reactor

Abstract

Presents a hierarchical multiscale approach to calculate effective rates of reaction for zeolite catalyzed reaction systems.

The first step involves determination of intrinsic rate coefficients for all elementary reactions by means of quantum chemical calculations combined with transition state theory. Step two is the calculation of adsorption isotherms and diffusion coefficients of all species by means of Monte Carlo and molecular dynamics simulations. The third step comprises a continuum description of a zeolite crystal based on the reaction-diffusion equation.

A model is developed for coupling the intrinsic rate coefficients obtained in the first step to the continuum variables. The model calculates the local concentration of reactants at the catalytically active centers from the total concentrations of adsorbed species. The adsorption isotherms and diffusivities are coupled to the continuum variables by analytical theories such as the ideal adsorbed solution theory and the Maxwell-Stefan formulation of multicomponent diffusion. The final step involves fixed-bed reactor simulations based on the continuum description of single zeolite crystals. The alkylation of benzene with ethene over zeolite H-ZSM-5 is used to illustrate the approach.

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