PERMEATION AND SEPARATION OF LIGHT-HYDROCARBONS THROUGH A SILICALITE-1 MEMBRANE - APPLICATION OF THE GENERALIZED MAXWELL-STEFAN EQUATIONS

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