Separation of concentrated organic/inorganic salt mixtures by nanofiltration

This paper considers nanofiltration (NF) of concentrated organic/inorganic mixtures using the FILMTEC(TM) NF-200B membrane. Mixtures of salt (up to 17 % (w/v)) and lactic acid (2% (w/v)) were used as model solutions. The work centres on the effects of salt concentration, pH and temperature on the flu x and rejection of lactate. For all solutions under study, the rejection of salt was low, while the rejection of lactate was maximal at neutral pH, an d decreased with salt concentration and temperature. The flux was found to decrease with salt concentration and increase with temperature, the activat ion energy being higher for low fluxes. The Aux for pure water and 2% (w/v) lactic acid was at a maximum at neutral pH, but for salt-containing soluti ons, it increased with pH in the whole range analysed (pH 3-10). The observ ed flux and rejection patterns suggest that the effects of skin shrinkage i n concentrated salt solutions, and sorption of lac:tate by the membrane, af fect behaviour in addition to the conventional effects of charge, solute si ze and osmotic difference between the retentate and permeate streams. (C) 2 000 Elsevier Science B.V. All rights reserved.