Influence of organic solvents on the performance of polymeric nanofiltration membranes

Separations in organic solvents are a new field of application for nanofiltration. Only a few polymeric nanofiltration membranes are commercially available for these separations, the major problem being the limited chemical stability in organic solvents. This article studies the influence of different organic solvents (methylene chloride, acetone, hexane, ethyl acetate, and ethanol), their performance on the four nanofiltration membranes (N30F, NF-PES-10, MPF 44, and MPF 50) specified to be compatible with the solvents used. The pure water flux (distilled water) of these membranes and the rejection of maltose were measured before and after 10 days of exposure to one of the above-mentioned solvents. The results show that not all of the membranes are compatible with the solvents used, and that the membrane performance shifts towards lower rejections for the hydrophilic membranes (N30F, NF-PES-10, and MPF 44) and towards higher pure water fluxes for the hydrophobic membrane (MPF 50). The water flux is not significantly affected for the hydrophilic membranes, and the effect on maltose rejection is small for the hydrophobic membrane. The results are explained by a reorganization of the membrane structure due to the clustering of hydrophobic and hydrophilic zones within the active layer of the membranes. Scanning electron microscopy images for MPF 44 and MPF 50 confirm these findings.