Molecular dynamics simulations were performed for n-butane and n-hexane in silicalite over a range of sorbate loadings at 300K (table 34). The simulations showed that the molecular conformation of butane was sensitive to its local environment, while hexane remained in a relatively linear conformation at all times. The molecules were found to reside in the two channel segments, with 95% or greater probability, while avoiding the channel intersection region. The rate of isomerisation between conformers was largely independent of position within the zeolite pore structure. The diffusivities of the sorbate molecules were calculated to be monotonically decreasing functions of sorbate loading. The computed self-diffusivities were near to the largest experimental values, where the scatter extended over many orders of magnitude. The long-term constants which governed the decay of orientational correlation functions in the hexane system suggested the need for simulations exceeding 1000ps in order to probe properly the long-term dynamics of the sorbate molecules.

Molecular Dynamics Studies of Butane and Hexane in Silicalite. R.L.June, A.T.Bell, D.N.Theodorou: Journal of Physical Chemistry, 1992, 96[3], 1051-60

Table 34

Diffusion of Butane and Hexane in Silicalite at 300K