MOLECULAR-DYNAMICS STUDIES OF BUTANE AND HEXANE IN SILICALITE

Molecular dynamics simulations are performed for n-butane and n-hexane in the zeolite silicalite over a range of sorbate loadings at 300 K. The simulations show that the molecular conformation of butane is sensitive to its local environment, while hexane is found to remain in a relatively linear conformation at all times. Furthermore, the molecules are found to reside in the two channel segments with 95% or greater probability while avoiding the channel intersection region. The rate of isomerization between conformers is largely independent of position within the zeolite pore structure. Diffusivities of the sorbate molecules are computed to be monotonically decreasing functions of sorbate loading. The computed self-diffusivities are near the largest experimental values, which scatter over many orders of magnitude. The long time constants governing the decay of orientational correlation functions in the hexane system suggest the need for simulations in excess of 1000 ps to properly probe the long time dynamics of the sorbate molecules.