Transport Phenomena in Nanofiltration Membranes

A general assessment is presented of Nanofiltration modelling. Transport phenomena across the membrane as well as partitioning mechanisms between the membrane and the external phases are described in detail. Firstly, the more interesting methods are reviewed which had been applied to approach the solution of the membrane characterization problem. Secondly, the Donnan Steric Pore and Dielectric Exclusion model is introduced. It is the evolution of various versions developed in different steps by some authors and it can be recognized as the more simple and complete model developed at the present to simulate the behaviour of Nanofiltration membranes. The Extended Nernst-Planck equation, appropriately modified to account of hindered diffusion and convection inside narrow pores, is used to describe mass transfer across the membrane. Steric hindrance, solution non-ideality, Donnan equilibrium as well as dielectric exclusion are considered as the main partitioning mechanisms existing at the interfaces between the membrane and the external phases. Strength points and critical features of the model are discussed in detail; a general assessment of the membrane characterization procedures is also reported