Effect of temperature on the rejection of neutral and charged solutes by Desal 5 DK nanofiltration membrane

This work deals with the temperature effect on rejection of neutral and charged solutes by a nanofiltration membrane (Desal 5 DK of GE Osmonics). The experiments were conducted with a tangential Sepa CF cell with a flow velocity equal to 1.27 m/s. The pressure was varied form 5 to 15 bar and the temperature from 12 to 50°C. A low neutral solute concentration (1 g/L) was used in the experiments in order to render solute–solute interactions negligible. The experiments with charged solutes (NaCl, Na2SO4) were conducted at 10–1M and 10–3M for NaCl and 10–1M and 2×10–1M for Na2SO4. The experimental results: permeate volume flux density and rejection of four neutral solutes (glycerin, arabinose, glucose, and sucrose) were analyzed using the hindered transport model and show that both effective pore radius and effective thickness are temperature dependent otherwise there is no agreement between the experimental data and the numerical results. We have found that the effective pore radius increases from 0.58 to 0.67 nm when the temperature increases from 22 to 50°C. A non-monotonic evolution is obtained for the variation of the effective membrane thickness with temperature. The results obtained with charged solutes show a weak dependence on temperature for low concentration salt solutions. For higher concentrations, the rejection decreases when temperature increases in rough conformity with the extended Nernst–Planck transport model, and this decrease can be partly explained by the hindered transport effects already observed for neutral solutes.