A hierarchical approach to simulating the diffusion of long n-alkanes in silicalite zeolite was described. The simulation strategy used concepts from Brownian motion theory and transition state theory and could be used to determine diffusivities for chains at least as long as C20 using modest computational resources. The results indicated that self-diffusivities declined steadily with increasing chain length, up to about n-C8, after which the self-diffusivities leveled-out and became nearly constant as a function of chain length. The diffusivity of methane in the z-direction at 300K was estimated to be 5.1 x 10-5cm2/s. The activation energies for diffusion were constant and equal to 5kJ/mol for short chains but increased to roughly 12kJ/mol for chains longer than C8.

Dynamics of Long n-Alkanes in Silicalite:  a Hierarchical Simulation Approach. E.J.Maginn, A.T.Bell, D.N.Theodorou: Journal of Physical Chemistry, 1996, 100[17], 7155-73