Molecular simulations of the adsorption of cycloalkanes in MFI-type silica

Abstract

A new force field for the simulation of the adsorption of cycloalkanes in nanoporous silica affords a significant improvement over any previously employed force field. The simulated isotherms reproduce the most salient features in the experimental isotherms extremely well. The study of cyclo-pentane, -hexane, and -heptane adsorption in MFI-type silica indicates an inflection for cyclopentane but not for cyclohexane at intermediate pressure. If corroborated by experiments, such an inflection point would afford an excellent calibration point for further force field developments. At low pressures, mixture isotherms of cyclohexane and n-hexane show a temperature dependence on the selectivity in accordance with recent results by J. P. Fox and S. P. Bates, J. Phys. Chem., 2004, 108, 17136. This dependence is caused by a difference in temperature dependence of the Henry coefficient for both molecules. At high pressures entropy effects due to packing always favor the sorption of n-hexane. Furthermore, the influence of the flexibility of the zeolite framework on the adsorption of these rather bulky molecules is investigated. It is found that this influence of the flexibility on the adsorption of cyclohexane is as small as with n-alkanes.

Adsorption of Cyclohexane in Pure Silica Zeolites: High‐Throughput Computational Screening Validated by Experimental Data

“…Non‐quantum‐based molecular simulations rely on force fields to describe the atomic interactions. We found that adsorption isotherms/isobars of cyclohexane calculated using force fields available in literature, cannot reproduce accurately the experimental adsorption isobars measured with the QE‐TPDA technique or the isotherms reported by Song et al . (Figure ).…”

“…Among the calculated isotherms, we selected this in better agreement with the experimental data of Song et al . The interactions between the guest molecules were also calculated with Lennard‐Jones potentials, ( σ ij _CH 2 3.93 Å and ϵ ij _CH 2 k B −1 50.37 K) . For all systems, we obtained better agreement with the experimental data using the new parameters, especially at the highest values of temperature in the isobars and at the lowest values of pressure in the isotherms.…”

“…It may indicate that the force field parameters do not reflect the main interactions between the CH 2 alkyl groups and the zeolite framework. Consequently, we refined the set of Lennard‐Jones parameters reported by Schenk et al . (Table ) by calculating adsorption isotherms of cyclohexane in MFI (Figure d) using a number of values for σ and ϵ in a range of 3.5–3.7 Å and 69–75 K, respectively.…”

“…To the best of our knowledge, such studies has not yet been conducted. In addition, we attempted to refine the force field parameters for the guest‐host interactions reported by Schenk et al . aimed at reaching better agreement between the experimental data and simulation results.…”

Adsorption of organic molecules on silica surface

“…A new force field [96] for the simulation of the adsorption of cycloalkanes in nanoporous silica afforded a significant improvement over any previously employed force field. The simulated isotherms reproduced the most salient features in the experimental isotherms extremely well.…”