Adsorption and filtration behaviour of non-ionic surfactants during reverse micellar-enhanced ultrafiltration

Micellar-enhanced ultrafiltration is an established method for the separation of oil-in-water micelles from aqueous streams, e.g., in wastewater treatment and catalytic reaction processes. However, its counterpart, the ultrafiltration (UF) of reverse micelles, known as water-in-oil-micelles, has been rarely researched until now. Our study shows that UF of non-ionic reverse micelles using the ternary system 1-dodecene/water/Marlophen NP5 is not technically feasible. The effects of hydrophobic and hydrophilic membrane properties as well as the variation of surfactant concentration on the filtration behaviour were investigated. Two regions could be distinguished in terms of filtration behaviour when surfactant concentration was increased: (a) below the critical micelle concentration (cmc) flux declined sharply, and (b) above the cmc it increased. Below the cmc, the adsorption of surfactants onto the membrane surface seems to be irreversible when oil (long-chain olefin) is the continuous phase. Above the cmc, the reverse micelle formation leads to a high flux recovery. However, due to surface diffusion, retention of micelles was negligible in all cases.

► We show the technical infeasibility of UF of non-ionic reverse micelles.
► Micelle retention during w/o-MEUF is negligible.
► Flux behaviour depends on the interaction of surfactant, solvent and membrane surface.
► Below cmc, increasing concentration reduces the flux due to surfactant adsorption.
► Above cmc, increasing concentration improves flux due to reverse micelle formation.