Dynamic formation of a self-rejecting membrane by nanofiltration of a high-formula-weight dye

Nanofiltration of a high-formula-weight dye, Cibacron F3G-A, FW=840, was in vestigated at low- to intermediate-crossflow velocity and pressure using a zirconium hydrous oxide-poly(acrylic acid) membrane. A sharp minimum in the rejection vs, pressure curves obtained at constant crossflow velocities pr ovided a distinct determination of the pressure required to initiate dynami c membrane formation. These minima occurred at a pressure near 2 MPa and on ly at a crossflow velocity less than 0.4 m/s, indicating that a critical pr essure is required for membrane formation while also implying that the conc entration at the membrane surface is involved in the modification.