Surfactant effect on the ultrafiltration of oil-in-water emulsions using ceramic membranes

Abstract Ultrafiltration (UF) of oil-in-water (O/W) emulsions formulated with 1 wt% base oil (an 85/15% (w/w) mixture of a synthetic poly-α-olefin and trimethylol propane trioleate ester, respectively), and a surfactant (anionic, Oleth-10, nonionic, Brij 76, or cationic, CTAB) at several concentrations referred to its critical micelle concentration (CMC) was studied using two different cut-off (50 and 300 kDa) tubular ceramic membranes. Effect of O/W emulsion (surfactant type and its concentration, zeta potential, oil droplet size, pH) and membrane (pore size, surface charge) characteristics on UF process were also investigated. Permeate flux and chemical oxygen demand (COD) in permeate were determined for each emulsion. COD rejections higher than 95% were achieved for both membranes. An UF model of nonionic surfactant-stabilized O/W emulsion was developed based on an osmotic pressure model and a mass transfer model (film theory) by defining two types of rejection for free monomers and micelles of surfactant (Model A). Permeate fluxes were adequately predicted for both membranes, while solute concentration in permeate showed large discrepancies, especially for 50 kDa membrane. Prediction was improved for both membranes when three new parameters were used in a second model (Model B), taking into account diffusion and convection inside membrane pores.