Assessment of the SEDE Model: Determination of Membrane Potential and Salt Rejection of a Nanofiltration Membrane

Abstract

Up to now, the SEDE (Steric Electric and Dielectric Exclusion) model was used to describe solute rejection in nanofiltration or membrane potential measurements. This model uses four fitting parameters: pore size, thickness to membrane porosity ratio, volume charge density (X) and dielectric constant of the solution inside pores (e_p). Because these two latter parameters are extremely difficult to measure, an alternative method for assessing the SEDE model was to study both salt rejections and membrane potentials for a same salt. Experiments were conducted with a NF polyamide membrane in CaCl₂ solutions. In the case of single salt solutions, experimental rejections and membrane potentials can be described by a number of couples (X, e_p) because both electric and dielectric exclusion contribute to reject ions. Only, one of the couples was found to provide a good description of both experimental rejections and membrane potentials. The fact that a unique choice for X and e_p allows accounting simultaneously for both the salt rejection and the membrane potential data is an indicator of the global coherence of the SEDE model.