Characterization of meso- and macroporous ceramic membranes in terms of flux measurement: A moment-based analysis

This work addresses the determination of unimodal log-normal pore size distributions (PSDs) in porous symmetric membranes through a convenient selection of a set of statistical moment generating functions. Relevant information concerning such distributions can be obtained by performing three independent permeation experiments: (1) pure Knudsen single-gas diffusion permeance, (2) pure liquid permeability, and (3) non-hindered diffusion permeance of a target solute. In the special case of porous asymmetric UF, NF and MF ceramic membranes, the contribution of the support to the overall mass transfer tends to increase for permeation processes governed by lower moments of the PSD. For such membranes, a mean diameter of the top layer and the thickness-to-porosity ratio of the support can be accurately determined, which constitute two structural parameters relevant for a preliminary membrane selection. The application of moment theory following the guidelines of Mason allows the determination of upper and lower bounds on the cumulative PSD of active layers from measured moments.