A novel experimental technique which measured the diffusive flux through a single-crystal membrane was developed. Unlike other macroscopic techniques that depended upon a transient response, the single-crystal membrane was used under steady-state conditions, resulting in a wide range of applicability: from 10−2 to 10−11cm2/s. Phenomenological equations for the steady-state data analysis were developed. The variation of driving force over the diffusion path was included in the model. The micropore concentration was given as a function of surface-excess amount adsorbed and gas density. The membrane configuration measured the diffusivity in only one crystallographic direction. The micropore diffusivities of C1 to C10 normal alkanes through a silicalite crystal in the z-direction were measured at 30, 50 and 70C (table 32). The activation energies for micropore diffusion were also reported (table 33). The data agreed closely with those from other studies that measured directional diffusivities. The diffusion and adsorption of hexane and heptane in silicalite exhibited structural heterogeneity induced by the comparable lengths of molecules and silicalite channels rather than molecule-diameter vis-à-vis pore diameter.

Diffusivities of n-Alkanes in Silicalite by Steady-State Single-Crystal Membrane Technique. O.Talu, M.S.Sun, D.B.Shah: AIChE Journal, 1998, 44[3], 681-94