Predictive assessment of surface resistances in zeolite membranes using atomically detailed models.

The diffusive transport of molecules through nanoporous membranes is determined by both intracrystalline diffusion and mass transport resistances associated with entering and leaving the membrane material. We compare two methods for assessing the relative importance of these resistances based on atomically detailed descriptions of the membrane material. For extremely thin membranes, net transport can be assessed using dual control volume grand canonical molecular dynamics (DCV-GCMD). We show that previous implementations of this technique may have been influenced by nonisothermal effects in interfacial regions and suggest a simple remedy to this situation. We also introduce an approximate method that uses information only from equilibrium MD simulations, which avoids the significant computational expense associated with DCV-GCMD. This approximate method can be used to rapidly assess the importance of interface-related resistances to mass transport over broad ranges of membrane operating conditions. This method will be useful in allowing a rapid determination of whether these interface resistances are significant in practical experimental situations. These two methods are compared by considering the transport of CH(4) and CF(4) through defect-free silicalite membranes.