Molecular Simulation of Adsorption in Microporous Materials

The development of industrial software, the decreasing cost of computing time, and the availability of well-tested forcefields make molecular simulation increasingly attractive for chemical engineers. We present here several applications of Monte-Carlo simulation techniques, applied to the adsorption of fluids in microporous solids such as zeolites and model carbons (pores < 2 nm). Adsorption was computed in the Grand Canonical ensemble with the MedeA®-GIBBS software, using energy grids to decrease computing time. MedeA®-GIBBS has been used for simulations in the NVT or NPT ensembles to obtain the density and fugacities of fluid phases. Simulation results are compared with experimental pure component isotherms in zeolites (hydrocarbon gases, water, alkanes, aromatics, ethanethiol, etc.), and mixtures (methane-ethane, n-hexane-benzene), over a large range of temperatures. Hexane/benzene selectivity inversions between silicalite and Na-faujasites are well predicted with published forcefields, providing an insight on the underlying mechanisms. Also, the adsorption isotherms in Na-faujasites for light gases or ethane-thiol are well described. Regarding organic adsorbents, models of mature kerogen or coal were built in agreement with known chemistry of these systems. Obtaining realistic kerogen densities with the simple relaxation approach considered here is encouraging for the investigation of other organic systems. Computing excess sorption curves in qualitative agreement with those recently measured on dry samples of gas shale is also favorable. Although still preliminary, such applications illustrate the strength of molecular modeling in understanding complex systems in conditions where experiments are difficult. L’existence de logiciels industriels, la baisse du coût du calcul et la disponibilité de champs de force éprouvés rendent la simulation moléculaire de plus en plus attrayante pour les applications du domaine du génie chimique. Nous présentons ici plusieurs applications des techniques de simulation de Monte-Carlo, appliquées à l’adsorption de fluides dans des solides microporeux (pores < 2 nm) comme les zéolithes et des structures microporeuses à base de carbone. L’adsorption a été modélisée par simulation dans l’ensemble Grand Canonique grâce au logiciel MedeA®-GIBBS, en utilisant des grilles tridimensionnelles de valeurs pré-calculées de l’énergie pour optimiser le temps calcul. MedeA®-GIBBS a aussi été utilisé pour obtenir les potentiels chimique