Molecular Simulation of Adsorption in Microporous Materials
Résumé
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.
Domaines
Physique [physics]
Origine : Publication financée par une institution
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