In the one-, two- and three-dimensional micropore system of theta-1, ferrierite, and silicalite-1, respectively, diffusion to the sorption sites was found to control the rate of propane and butane sorption at 373K and 133Pa pressure. The diffusivity of propane (C3) and n-butane (n-C4) was about the same and much faster than that of the i-butane (i-C4). In theta-1 and ferrierite, the i-C4 transport was too slow to be characterized by the frequency–response method. Ten-ring apertures determine the critical pore dimension of each material. In ferrierite, however, the transport diffusivity of the n-alkanes was about 10−15m2/s, several orders of magnitude smaller than that in theta-1 and silicalite-1. The results suggested that normal alkane diffusion occurred in the 3D pore system of silicalite-1 and single-file diffusion prevailed in the micropores of ferrierite and theta-1.

An FR Study of the n- and i-Butane Diffusion in Theta-1, Ferrierite and Silicalite-1. G.Onyestyák, J.Valyon, L.V.C.Rees: Solid State Ionics, 2001, 141–142, 93–7