Estimation of the permeability of cellulosic membranes from solute dimensions and diffusivities.

Abstract

AbstractPermeability data were obtained for commercial regenerated cellulose (Cuprophan PT–150) in isotonic saline at 37°C in a dual closed‐loop dialysis cell. Eighteen radioactively labeled monodisperse solutes of widely differing chemical and physical properties, and ranging in molecular weight from 60 (urea) to 1355 (vitamin B12), were evaluated and the permeabilities of these solutes have been successfully correlated with various solute characteristics.Correlations were established between membrane mass transfer resistances (or effective membrane diffusivities) and:(1) characteristic molecular radii determined from both molal volume at normal boiling point (MVNBP) and hydrodynamic theory and (2) molecular diffusivities in saline. Membrane resistance data reported elsewhere for other cellulosic membranes were also found to correlate well with both MVNBP radii and liquid diffusivities.The correlations for Cuprophan have the following form: where Deff = effective membrane diffusivity (cm2/sec), r2 = MVNBP radius (Å), and Ds is saline diffusivity (cm2/sec). Similar correlations were established for other membranes. It should be feasible to use these and similar correlations to predict membrane permeabilities (for a given membrane) from known solute characteristics without resorting to laboratory measurements.Membrane activation energies were also computed for eight solutes by measuring the variation in permeation rate through Cuprophan between 5 to 50°C. Unexpectedly, it was observed that the solute activation energies were not dominated by the activation energy of the membrane but revealed significant differences between solutes.