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, propan e, ethene and propene through a silicalite-1 membrane of approximately 40 mu m thickness at 293 K as a function of their partial pressure. T he permeation fluxes generally decrease with increasing molecular size , while the alkenes permeate more rapidly than their corresponding alk anes at identical conditions. In 1:1 mixtures of ethane-ethene and pro pane-propene (1 bar total pressure) the alkanes permeate faster, yield ing selectivity factors of 1.9 and 1.3 respectively. The generalized M axwell-Stefan (GMS) equations, adapted for surface diffusion, could de scribe 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 b inary system permeation data could be quantitatively described by the GMS equations without exchange contributions (''single-file'' diffusio n) and need only the diffusivity values of the unary permeation experi ments.