Prediction of ideal permeability of hydrocarbons through an MFI-type zeolite membrane by a combined method using molecular simulation techniques and permeation theory

Permeabilities of hydrocarbons (n-alkanes from methane to octane) through an MFI-type silicalite membrane were predicted systematically, using a method based on molecular simulation techniques and permeation theory. This method estimates an ideal permeability that will be observed in perfectly crystallized membranes, in which no grain boundaries or defects in the membrane exist. Comparison of the calculated permeability with experimental results will improve our understanding of the effect of structural defects in membranes on changes in permeability. Calculated permeabilities were independent of the molecular weights of the permeates, and showed a "leveling-off" effect related to the increase of the molecular weight of permeates. The estimated permeabilities were an order of magnitude larger than those previously reported in experimental studies. This inconsistency suggests the existence of a permeation barrier in interfaces of crystalline or grain boundaries, resulting from the discontinuous pore networks of zeolite. In addition, concentration profiles of permeating molecules (CH4, C2H6, C3H8, and n-C4H10) inside the silicalite membranes were also predicted; these monotonically decreased from the feed side to the permeate side.