Prediction of permeation behavior of CO2 and CH4 through silicalite-1 membranes in single-component or binary mixture systems using occupancy-dependent Maxwell–Stefan diffusivities

Permeation behavior of CO2 and/or CH4 through silicalite-1 membranes without support in single-component or binary mixture systems at 298 K was theoretically investigated using occupancy-dependent Maxwell–Stefan (M–S) diffusivities. The M–S surface diffusivity calculated from quasi-chemical theory, which describes occupancy-dependent diffusion more accurately, was compared with those based on weak and strong confinement scenarios in single-component systems. The calculated M–S surface diffusivities of CO2 and CH4 from the quasi-chemical approach were close to those from the strong confinement scenario for CO2 and the weak confinement scenario for CH4, respectively. However, there existed some differences in permeation behavior between the quasi-chemical approach and the scenarios, especially at a high pressure. With the quasi-chemical approach, permeation behavior of each species in CO2/CH4 mixture systems was investigated using three different M–S exchange diffusivities related to correlation effect. The magnitude of M–S exchange diffusivity had a little influence on permeation behavior of the slower and more strongly adsorbed CO2, while it produced a big difference in transient flux and occupancy profile for the faster and most weakly adsorbed CH4.