Diffusion of linear and branched alkanes in ZSM-5. A quasi-elastic neutronscattering study

The diffusivities of long n-alkanes in ZSM-5 have been measured by quasi-el astic neutron scattering (QENS). Self-diffusion coefficients and activation energies for chains up to C-14 have been obtained. Reasonable agreement is observed with single-crystal membrane experiments, except for C-6, but lar ge discrepancies are found with the zero-length column (ZLC) method. The di ffusivities predicted by a hierarchical simulation diverge from those measu red by QENS after C-6, although the activation energies for diffusion are c omparable. The discrepancy with MD simulations is larger. QENS results show that diffusion of branched alkanes is much more restricted than the one of linear alkanes in this structure. (C) 2000 Elsevier Science B.V. All right s reserved.