Molecular simulations of adsorption and siting of light alkanes in silicalite-1

Configurational-bias Monte Carlo (CBMC) simulations have been used to determine the sorption isotherms of methane, ethane, propane, n- and isobutane in silicalite-1 at 300 K. The equilibrium molecular loadings were determined separately for the straight and zig-zag channels and at the channel intersections. The sorption strengths for each of these locations are different, in general. In particular, isobutane molecules have a strong preference for locating at the channel intersections. The pure component isotherms, obtained from CBMC simulations, could be fitted with a 3-site Langmuir model and are in good agreement with experimental data from the literature. CBMC simulations were also used to determine the sorption isotherms for mixtures of methane-propane, methane-n-butane, n-butane-isobutane and propane-isobutane. The mixture isotherms could be predicted from the pure component isotherms using the ideal adsorbed solution theory (IAST), taking into account the detailed information on the sitings of molecules within the silicalite-1 matrix.