Prediction of permeation behavior of CO 2 and CH 4 through silicalite-1 membranes in single-component or binary mixture systems using occupancy-dependent Maxwell–Stefan diffusivities

Abstract

Permeation behavior of CO 2 and/or CH 4 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 CO 2 and CH 4 from the quasi-chemical approach were close to those from the strong confinement scenario for CO 2 and the weak confinement scenario for CH 4, 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 CO 2/CH 4 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 CO 2, while it produced a big difference in transient flux and occupancy profile for the faster and most weakly adsorbed CH 4.