Coupled series–parallel resistance model for transport of solvent through inorganic nanofiltration membranes

In this work, permeation of a number of different classes of solvents through commercial TiO2 and ZrO2 ceramic nanofiltration membranes was measured. A wide variety in permeate flux levels were observed. Solvent permeation was found to be a function of solvent characteristics (viscosity, surface tension, effective molecular diameter and dielectric constant) along with membrane characteristics (surface tension, average pore size diameter and dielectric constant).This paper also presents a new mathematical model based on parallel convection–diffusion theory which relates permeation of solvent molecules to three different resistances in the surface and the main body of the membrane.Transport resistances are defined by easily measurable solvent and membrane properties as indicated above. The model was tested on a series of permeability experiments of water, acetonitrile, methanol, methyl ethyl ketone, ethylacetate, ethanol, tetrahydrofuran, 1-propanol, 1-butanol, toluene, cyclohexane and n-hexane, carried out with HITK275 and HITK2750 membranes (Inoceramic, Germany). Compared to the existing models, which are able to make predictions only for a given class of solvents (polar or apolar), the new model can surprisingly fit the results of the permeation study for all solvent classes, and even for water. The maximum deviation from experimental results was calculated as 4.8%.