Ultrafiltration of surfactant and aromatic/surfactant solutions using ceramic membranes

Rejection and permeate flux taken together establish the efficiency of an ultrafiltration separation. The controllable factors that may influence the efficiency are systematically studied. These factors include transmembrane pressure, recirculation rate, membrane pore size, and solute and surfactant structure and concentration. Experiments carried out using both cationic and nonionic surfactants show that rejection decreases and permeate flux increases with membranes of increasing pore sizes. However, for the large pore size membrane (200 Angstrom), it is also observed that rejection increases and permeate flux decreases as the filtration proceeds. These unexpected results suggest that micelles penetrate and accumulate into the larger pores, thereby reducing the effective membrane pore size. Depending on the molecular structure and concentration of the surfactant, rejection as high as 99.9% is achieved with a ceramic membrane having 65 Angstrom pores. Permeate fluxes between 30 and 70% of pure water are observed. The addition of a solute tends to improve surfactant rejection and to decrease the permeate flux. Solute rejection increases with surfactant concentration and hydrophobicity. Solubilization isotherms determined here by ultrafiltration are shown to be in agreement with isotherms obtained with head space gas chromatography.