Retention of pegs in cross-flow ultrafiltration through membranes

This work investigated the difference between membrane cut-offs measured with the CHARMME methods and the values quoted from the manufacturers. Four different membranes were characterised. The two regenerated cellulose membranes that according to the manufacturers had cut-offs of 5 and 10 kD had, in fact, the same cut-off of 2.5 kD. It was also found that the polyethersulfone membrane had a lower cut-off (3 kD) than that stated by the membrane manufacturers (5 kD). A cross-flow velocity of 2 m/s and a flux of 40 l/h/m2 was found to keep the mass transfer coefficient within a tolerable range for all PEGs used.

The cut-off of the C10 F membrane was much smaller than 10 kD and the membrane was not homogeneous. For all membranes investigated, the measured cut-off was either smaller (2.5, 2.5 and 3 for C10F, C005F for P005F, respectively) or larger (6 kD for membrane PES004H) than the value quoted by the manufacturers. The values calculated to be used for flux (40 l/h/m2) and cross-flow velocity (2 m/s) so that concentration polarisation was at a minimum proved to be correct since no concentration polarisation was observed during any of the PEG filtrations.