Electrical characterization of NF membranes. A modified model with charge variation along the pores

Abstract

Nanofiltration rejection measurements have been performed for KCl solutions to characterize a non-commercial NF membrane. Membrane Potential (MP) and Tangential Streaming Potential (TSP) measurements have also been carried out for a wide range of concentrations. The charge of the membrane and the pore dielectric constant has been obtained as functions of the salt concentration from these three ensembles of experiments, showing a fair agreement. For the data treatment, two modifications of the Steric Electric and Dielectric Exclusion (SEDE) model have been proposed to allow the electrical characterization of the NF membrane: (1) the volumetric charge density is considered to change along the pores by means of the inclusion of a charge isotherm (which correlates the membrane charge with the ion concentration) in the transport equations, and (2) the porous support is considered by the inclusion of the adequate transport equations similarly to how the active layer is considered.