Adsorption of n-alkanes in faujasite zeolites: molecular simulation study and experimental measurements
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Adsorption of n-alkanes in faujasite zeolites: molecular simulation study and experimental measurements A. Wender · A. Barreau · C. Lefebvre · A. Di Lella · A. Boutin · P. Ungerer · A.H. Fuchs
Received: 30 April 2007 / Revised: 23 July 2007 / Accepted: 24 July 2007 / Published online: 22 September 2007 © Springer Science+Business Media, LLC 2007
Abstract We report an application of a previously developed force field for adsorption of hydrocarbons in silicalite (Pascual, P., et al. in Phys. Chem. Chem. Phys. 5:3684– 3693, 2003), to the case of the linear alkane-sodium faujasite systems. In order to extend this force field from siliceous to cationic zeolites, we propose to take into account the polarization part of the zeolite-molecule interaction energy. A first order polarization term is explicitly considered for this purpose, using standard molecular polarizabilities. Polarization appears to amount to 30–40% of the zeolitealkane interaction energy, as a consequence of the strong electric field created by the sodium cation distribution and negatively charged framework. This approach is compared with experimental adsorption isotherms of ethane, propane, n-octane and n-decane in NaY from the literature and with original measurements of n-butane isotherms in NaY obtained by thermal gravimetry. Henry constants and heats of adsorption at zero coverage of n-alkanes (n = 6–10) are also compared with experimental measurements. Although no specific parameter has been calibrated for extending the force field, the general agreement between simulation results and experiments is satisfactory. Cation redistribution upon alkane adsorption is not observed in these simulations.
A. Wender · A. Barreau · C. Lefebvre · P. Ungerer IFP, 1-4 avenue de Bois Préau, 92852 Rueil-Malmaison Cedex, France A. Di Lella · A. Boutin () Laboratoire de Chimie Physique, Bâtiment 349, UMR 8000 CNRS, Université de Paris-Sud, 91405 Orsay, France e-mail: [email protected] A.H. Fuchs Ecole Nationale Supérieure de Chimie de Paris (ENSCP), 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France
Keywords Adsorption · Alkanes · Zeolites · Faujasites · Grand Canonical Monte Carlo Simulation
Abbreviations ai A B Ei G H0 S0,local fi k KH K N Ni pθ rij T Ubend U¯ ext_new s Uext
Uintra ULJ Upol Utors V Wnew
Torsion parameters Parameter of Henry constant expression, mol/kg/Pa Parameter of Henry constant expression Local electrical field, J/mol Gibbs free energy, kJ/mol Heat of adsorption, kJ/mol Entropy of adsorption at low coverage, kJ/mol/K Fugacity of molecule i, Pa Ideal gas constant, J/mol/K Henry constant, mol/kg/Pa preexponential factor, mol/kg/Pa Number of adsorbed molecules Number of adsorbed molecules i Standard pressure, bar Distance between two centres of force i and j , Å Temperature, K Bond-bending interaction, J/mol Lennard Jones energy obtained with the United Atom model, J/mol Intermolecular interactions in the adsorbed phase, J/mol Intramolecular interaction, J/mol Lennard-Jones potential, J/mol Polarization energy, J/mol Torsi
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