Effect of solvent properties on permeate flow through nanofiltration membranes: Part II. Transport model

In Part I of this work, permeation flows of a large number of solvents were measured and found to exhibit a wide spread in permeate flux levels. The flux of both pure and mixed solvents was mainly affected by surface tension and viscosity. This paper presents a transport model describing solvent–membrane interactions, governed by viscous and surface forces. The model relates the flux of a solvent mixture with easily measurable solvent and membrane properties (surface tension, viscosity and membrane hydrophobicity). Extensive flux measurements of mixed solvents belonging to several chemical families were well correlated by the model using the following experimentally determined parameters. Membrane properties were characterized by two solvent independent coefficients f1 and f2, while, with minor exceptions, each solvent mixture was characterized by a specific coefficient φ.