CHARACTERIZATION OF THE PORE AREA DISTRIBUTION IN POROUS MEMBRANES USING TRANSPORT MEASUREMENTS

An approach originally proposed by Mason and coworkers has been applie d to model porous membranes to show that transport measurements with s mall and large solutes can be used to distinguish between porous membr anes with the same average pore size but different pore size distribut ions. In addition, it is shown that such measurements can be used to a ccount for membrane heteroporosity when predicting the sieving charact eristics of a membrane. This is done by applying moment theory to resu lts from flux measurements for a small solute at Pe approximate to 1 o r to results from measurements of the reflection coefficient for a lar ge solute at infinite Pe. No a priori assumptions about the nature of the distribution of pore areas are necessary. In this paper, the resul ts from calculations performed with three different model membranes wi th log-normal pore size distributions are reported. These results show that one can begin to distinguish between membranes by measuring the hydraulic and diffusive permeability and performing at least one addit ional flux measurement - with either a small, non-hindered solute at P e approximate to 1 or a large solute at infinite Pe. Results also show that a fairly narrow window can be placed on the sieving curve for a heteroporous membrane without performing any sieving measurements. Thi s is an interesting and encouraging result because it means that many of the problems that arise from measuring and interpreting pore size d istributions using more traditional techniques can be avoided by using small solute flux measurements to predict the separation characterist ics of many porous membranes.