Removal of the nonionic surfactant Eumulgin ES from protein solutions by means of adsorption and ultrafiltration

Aqueous micellar two-phase extraction (AMTPE) is a promising technique for large-scale protein purification, however, it is unavoidable that a certain surfactant load will remain in the product stream. Therefore, an industrial application of AMTPE requires efficient and economic ways for the removal of surfactants as a polishing step. In view of this demand, the removal of the nonionic surfactant Eumulgin ES has been investigated by means of fixed bed adsorption and cross-flow ultrafiltration. The critical micelle concentration of an aqueous Eumulgin ES solution is 9.2 mg/L with a hydrodynamic diameter of a micelle of approximately 15 nm at 22 °C. The adsorption of Eumulgin ES to hydrophobic polystyrene beads leads to high loading capacities, but proteins also bind with high affinity to the beads, making the technique of limited use. A better way is to remove the surfactant by means of ultrafiltration through a hydrophobic polyethersulfone membrane. In the course of the filtration process a viscous micelle phase at the membrane forms, by which the flux through the membrane is decreased drastically. While elevated temperatures and salt concentrations decrease the flux and the overall separation performance, the opposite conditions lead to improved surfactant removal efficiencies. Cross-flow ultrafiltration is finally applied for the separation of Eumulgin ES from a proteinaceous solution originating from a technical-scale AMTPE investigation. The filtration results in a total surfactant removal of >98.8% from the target protein solution within 8 exchanged volumes.