Ultrafiltration of oil-in-water emulsions using ceramic membrane: Roles played by stabilized surfactants

Surfactants widely exist in oil-in-water (O/W) emulsions, and they may exert significant influence on membrane performance during ultrafiltration (UF) of O/W emulsions using ceramic membrane. In this paper, we investigated UF of O/W emulsions stabilized by three surfactants (SDBS, CTAB and Tween-80 as anionic, cationic and nonionic surfactant) at different concentrations (0.25-2 CMC) using silicon carbide (SiC) ceramic membranes. SiC ceramic membrane showed satisfactory separation ability for O/W emulsions with oil rejection higher than 90%. Influence of surfactant on properties of O/W emulsions, oil rejection and permeate flux were studied. The main fouling types for all O/W emulsions were cake filtration and standard pore blocking based on analysis of flux data using Hermia's blocking model, and highest fouling degree occurred in CTAB prepared emulsions which has a opposite charge to ceramic membrane. Generation of fouling is not only related to blocking and adsorption of oil droplets on membrane, but also referred to surfactant adsorption on membrane. Surfactant adsorption on ceramic membrane during UF of O/W emulsions was further investigated based on Zhu and Gu's model. Surfactant was found to deposited in hemimicelle form on membrane surface and in membrane pores which have an important influence on membrane fouling.