Chain length effects of linear alkanes in zeolite ferrierite. 2. Molecular simulations

Configurational-bias Monte Carlo technique simulations are performed in the grand canonical ensemble to calculate the adsorption isotherms and the isosteric heats of adsorption of propane, n-butane, n-pentane, and n-hexane in ferrierite. The results are generally in good agreement with experiment results. The locations of the molecules in the ferrierite pore structure obtained from the simulations agree well with the locations obtained by earlier C-13 NMR measurements. It is found that only short n-alkane molecules up to n-pentane can access the entire two-dimensional ferrierite pore structure; longer molecules adsorb only in the 10-ring channels and not in the ferrierite 8-ring cage. Adsorption of n-pentane in this cage is possible but only at relatively high pressures due to the high number of repulsive interactions with framework oxygen ions. The results presented are furthermore used to set limits to the size parameter describing the Lennard-Jones interaction between the n-alkane united atoms and the framework oxygen atoms.