Simulations were performed for ethane, propane and n-butane in siliceous faujasite for various numbers of molecules per unit cell at 300K. Both the adsorbed molecules and the zeolite framework were modelled as flexible entities. A semi-empirical analytical potential function for the systems was constructed. From the mean-square displacement of the molecules, self-diffusion coefficients of 18.7 x 10-5, 13.3 x 10-5 and 4.3 x 10-5cm2/s were calculated for ethane, propane and n-butane, respectively, at a loading of 8 molecules/unit cell. These values compared well with experimental values (10 x 10-5, 9 x 10-5 and 6 x 10-5cm2/s, respectively) arising from pulsed-field gradient nuclear magnetic resonance measurements. As well as depending upon the size of the hydrocarbon, the heats of adsorption and the self-diffusion coefficients also depended strongly upon the loading of adsorbate molecules. The results suggested that the intermolecular force field could adequately describe the adsorption and diffusion behavior of ethane, propane and n-butane in faujasite zeolite.

Adsorption and Diffusion of Light Alkanes on Nanoporous Faujasite Catalysts Investigated by Molecular Dynamics Simulations. Wongthong, P., Rungsirisakun, R., Probst, M., Limtrakul, J.: Journal of the Physical Society of Japan, 2007, 76[4], 044601. See also: Microporous and Mesoporous Materials, 2007, 100[1-3], 160-6