Nanofiltration of solutions containing organic and inorganic salts: Relationship between feed and permeate proportions

Nanofiltration can be considered for the purification of valuable products obtained by fermentation, like organic acids. In this work, nanofiltration experiments are carried out with synthetic solutions of different compositions containing acetate (Ac), propionate (Pr), and butyrate (Bu), as well as inorganic salts (NaCl). Although the retention of charged solutes can be significantly modified according to the composition of the solution, it is observed that there is a filtration flux above which the solutes proportions in the permeate remain constant. These proportions do not depend on the total concentration but only on the solutes proportions in the feed. Finally, individual solute transfer is found to vary linearly with the total solute flux. Similar trends are observed with two NF membranes despite their different properties