Temperature effect on transport performance by inorganic nanofiltration membranes

The effect of temperature on nanofiltration performance was examined using three inorganic membranes with a molecular-weight cutoff of approximately 200, 600, and 2, 000, respectively. The inorganic porous membranes were prepared from silica-zirconia colloidal sols and used in nanofiltration experiments for neutral solutes over a temperature range of 20 to 60 degrees C. The rejection of solutes decreased with an increase in temperature for the membranes while the permeate volume flux increased. Three transport coefficients-refection coefficient, solute permeability, and water permeability-were obtained using the Spiegler-Kedem equation, which accounts for the contribution of convection and diffusion to solute flux. As a result, the reflection coefficient corresponding to the fraction of solutes reflected by the membrane in convective flow was almost constant, irrespective of experimental temperature. Solute permeabilities, however, increased with temperature. The dependency was larger for larger solutes and membranes with smaller pore diameters. Therefore, the hindered diffusion of solutes through micropores was indicative of an activated process. Moreover; pure water permeability, after correction for the temperature effect on viscosity, also increased with experimental temperature.