Grand canonical Monte Carlo simulations of nonrigid molecules: Siting and segregation in silicalite zeolite

A method is described for performing grand canonical Monte Carlo simulations of molecules with internal degrees of freedom. The approach is applied to adsorption of methanol and cyclohexane in the zeolite silicalite. Calculated adsorption isotherms and heats of adsorption compare well with experimental data from the literature. In addition, the simulations provide information on preferential siting of molecules in the different pores of silicalite. Binary adsorption results are also predicted for cyclohexane/methane, benzene/methane, and benzene/cyclohexane mixtures. The siting preferences of the single components result in clear segregation effects for these binary systems. Benzene and cyclohexane display preferred siting in the channel intersections, while methane adsorbs preferentially in the channels. In the case of benzene/cyclohexane, the cyclohexane adsorbs in the intersections and the benzene is pushed to the zigzag channels.