Separation albumin-PEG: transmission of PEG through ultrafiltration membranes.

Transmission of polyethylene glycol (PEG) through ultrafiltration membranes has been studied under various operating conditions of pressure, crossflow, and concentration, using different membranes cut-offs and two module designs with the aim of understanding the separation of PEG from BSA. The influence of protein adsorption and fouling of the choice of a membrane has also been considered. Retention depends in general on the molecule to average pore size ratio, as expected, but also on concentration polarization. Accordingly, all operating and design parameters favoring concentration polarization lead to higher transmission. At high fluxes, flexible macromolecules can pass through the membrane, even if the random coil is larger than the apparent average pore. From a process selectivity point of view, the best way to separate PEG from BSA would be to use a membrane totally retaining BSA and to enhance concentration polarization of PEG. Unfortunately, such conditions also increase fouling and concentration polarization by BSA, which limits flux and thus PEG concentration polarization and transmission. Consequences of such conditions on separation efficiency are discussed.