Selection of Surfactants for Micellar-Enhanced Ultrafiltration

The selection of a surfactant is an important issue in designing separations processes based on micellar-enhanced ultrafiltration. The binding of hydrophillic solutes to both ionic and nonionic micelles is considered and shown to be a function of the molecular structure of the surfactants, the concentration of the surfactant, and the electrolyte composition of the water. It is also shown that the passage of micelles is only partly restricted by polycarbonate membranes with 100 Å ports but is effectively restricted by some cellulose acetate membranes. Swelling the micelles by cosolubilizing certain nonpolar compounds was found to only marginally improve the separation efficiency. There appears to be an optimum surfactant molecular structure, but it will not be possible even under the best conditions to completely remove a hydrophilic solute such as phenol in a single stage. Thus, the process will necessarily be multistage.