On the possibility of characterising mesoporous materials by permeability measurements of condensable vapours: theory and experiments

Transport of condensable vapours through a mesoporous medium is used for the first time as a means for the characterization of pore structure. For a condensable vapour, as capillary condensation occurs, the permeability of the vapour goes through a sharp maximum at a pressure below its saturation pressure. In this work, experimental results are presented for water and pentane vapour permeabilities, on a well defined mesoporous alumina membrane. The experimental data are compared to theoretical simulation results obtained from network models. The main processes involved (adsorption, mass transfer, capillary condensation) are simulated over the entire range of relative pressures. It is observed that within a certain relative pressure range, a percolating cluster of capillary condensed pores is formed, resulting in a dramatic increase in the permeability of the vapour. The limits of this pressure range can be related to the percolation threshold and thus to the topology of the medium.