(367c) Separation and Modeling of Oil-in-Water Emulsions Stabilized By Different Types of Surfactants Using Electrospun Fiber Membranes

In this work, we examine the influence of surfactants on the microfiltration of oil-in-water emulsions using electrospun fibrous membranes of poly(trimethyl hexamethylene terephthalamide) (PA6(3)T) with fiber diameters of [121 ± 22 nm]. Four types of surfactants (anionic, cationic, non-ionic and zwitterionic) were used to create monodisperse emulsions of dodecane in water, with average droplet sizes of [475 ± 14 nm]. Both dead-end and cross-flow filtration configurations were employed to study the interaction (i.e. fouling and cleaning) between the emulsion and membrane.

In both dead-end and cross-flow configurations, the emulsions prepared with anionic and non-ionic surfactants exhibited the highest fluxes, around five-fold higher than that for the emulsion stabilized by cationic surfactant. The emulsion with zwitterionic surfactant led to intermediate flux. The oil rejections were generally as high as 90%, with the exception of the emulsion stabilized by non-ionic surfactant, whose rejection was closer to 60%. The observed fluxes using the cross-flow system were about one order of magnitude higher than those observed with the dead-end system, due to a mechanism for foulant removal (cleaning) attributed to hydrodynamic forces. The differences in the fluxes and rejections for emulstions stabilized by different surfactants is traced to electrostatic interactions between the emulsified droplets and the membrane, based on zeta potential measurements and flux recovery after backflushing.

To study the fouling and cleaning mechanism, several models were also applied in this work. Blocking filtration models suggest that the membranes fouled initially in the regime of complete blocking, but then transitioned to cake filtration as the flux continued to decline. Foulant resistivity modeling supported a series resistance model, consistent with cake filtration. The emulsion stabilized by anionic surfactant showed the lowest resistance, while that stabilized by cationic surfactant showed the highest resistance. Using the surface renewal model, the emulsion stabilized by anionic surfactant was found to be most readily removed by hydrodynamic cleaning during cross-flow filtration. Lastly, the decay of flux was well described by the conformally coated fiber model, wherein the fibrous structure of the membrane is considered explicitly, and the flow through the membrane is modified as a foulant layer builds up on the fibers.