Determination of Transport Parameters of Synthetic Membranes by Hyperfiltration Experiments Part II: Membrane Transport Parameters Independent of Pressure and/or Pressure Difference

Abstract

AbstractEmploying the transport relationships of the solution‐diffusion model, the Kedem and Spiegler, or the finely‐porous membrane model, and the thermodynamics of irreversible processes, the corresponding transport parameters have been determined from hyperfiltration experiments for homogeneous ion exchange membranes and asymmetric cellulose acetate membranes annealed at 90 °C and 85 °C. The transport relationships reproduce the measured values of salt rejection r and volume flux q equally well except the solution‐diffusion model relationships which yield large deviations between calculated and measured values of r at larger salt concentrations and volume fluxes. The analysis demonstrates that a considerable amount of convective salt flow contributes to the total salt flux also across asymmetric cellulose acetate membranes. In addition to actual transport parameters, partition and diffusion coefficients of NaCl within the membrane are derived from the original transport parameters which agree substantially with corresponding values from the literature. Furthermore, transport parameters have been evaluated for the CA‐90 membrane and a 0.5 M NaCl brine solution using different definitions of the mean salt concentration. Cs. This analysis suggests that the concentration profile in the membrane actually exists at high pressures, as required by the finely‐porous membrane model.