DYNAMICS OF LONG N-ALKANES IN SILICALITE - A HIERARCHICAL SIMULATION APPROACH

A hierarchical approach for simulating the diffusion of long n-alkanes in the zeolite silicalite is described. The simulation strategy utili zes concepts from Brownian motion theory and transition state theory a nd can be used to determine diffusivities for chains at least as long as C-20 using modest computational resources. The results indicate tha t self-diffusivities decline steadily with increasing chain length up until about n-C-8, after which the self-diffusivities plateau and beco me nearly constant as a function of chain length. Activation energies for diffusion are constant and equal to 5 kJ/mol for short chains but increase to roughly 12 kJ/mol for chains longer than C-8. A microscopi c explanation for these trends is proposed.