Micellar-enhanced ultrafiltration using a twin-head cationic surfactant

In Micellar-Enhanced Ultrafiltration (MEUF), a surfactant is added to a wastewater stream containing an organic solute. Most of the solute is solubilized in micelles, which are aggregates of surfactant molecules, formed in the feed solution. Separation is achieved through retention of the micelles by an ultrafiltration membrane. Since much of the solute is within the micelles, a membrane with a molecular weight cut off (MWCO) much larger than the molecular weight of the solute is used. Although some unsolubilized solute and surfactant monomers pass through the membrane, the use of a surfactant with a low critical micelle concentration (CMC) ensures little contamination of the permeate by surfactant monomers.Solubilization tests and MEUF experiments were performed with an aqueous feed solution of benzoic acid (molecular weight 122) and Rhodameen T12/90 (molecular weight 798), a twin-head, cationic tertiary amine surfactant. This surfactant has an 18 carbon hydrophobic tail and two hydrophilic polyoxyethylene heads. The equilibrium solubilization of benzoic acid by surfactant solutions was measured by semiquilibrium dialysis. The maximum solubilization was nearly one mole of benzoic acid per mole of Rhodameen.MEUF was carried out in hollow fiber polysulfone membrane units with MWCO of 5,000 and 30,000. The permeate flux and overall rejection of benzoic acid and surfactant were measured for different initial feed compositions and initial surfactant concentrations under varying transmembrane pressures (TMP). The flux increased with TMP and decreased with Rhodameen concentration, but was not affected by the benzoic acid concentration. The highest rejections of benzoic acid (90%) and Rhodameen (95%) were obtained when the molar ratio of surfactant to solute in the feed was 1.2