Single-component data were obtained for methane, ethane, propane, ethene and propene permeation through a silicalite-1 membrane of approximately 40μm thickness at 293K as a function of their partial pressure (table 40). The permeation fluxes generally decreased with increasing molecular size, while the alkenes permeated more rapidly than their corresponding alkanes under identical conditions. In 1:1 mixtures of ethane-ethene and propane-propene (1bar total pressure), the alkanes permeated faster, yielding selectivity factors of 1.9 and 1.3, respectively. The generalized Maxwell-Stefan equations, adapted for surface diffusion, described the permeation data well. The unary systems yielded diffusivity data that were fairly constant or varied at most by a factor of 2 to 3. These diffusivities compared well with published values obtained with other (transient) techniques that yield transport diffusivities. The binary system permeation data could be quantitatively described by the generalized Maxwell-Stefan equations without exchange contributions (so-called single-file diffusion) and required only the diffusivity values of the unary permeation experiments.

Permeation and Separation of Light Hydrocarbons through a Silicalite-1 Membrane: Application of the Generalized Maxwell-Stefan Equations. F.Kapteijn, W.J.W.Bakker, G.Zheng, J.Poppe, J.A.Moulijn: The Chemical Engineering Journal, 1995, 57[2], 145-53