Separation of oil-in-water emulsions using electrospun fiber membranes and modeling of the fouling mechanism

• Electrospun fiber membranes are evaluated to separate 250 nm oil-in-water emulsions.
• Performance is examined as a function of pressure, concentration and fiber diameter.
• The fiber membranes exhibit higher flux compared to phase inversion membranes.
• A conformally coated fibers model is shown to describe well the fouling behavior.

Microfiltration of emulsions of oil (dodecane) in water using electrospun membranes of poly(trimethyl hexamethylene terephthalamide) (PA6(3)T) is demonstrated. Rejection of the emulsified dodecane increased from (4.3±0.9)% to (85±5)% when the ratio of droplet diameter to fiber diameter (dp/df) increased from 0.57±0.04 to 2.5±0.4, respectively. The normalized flux (relative to the pure water flux) decreased in proportion to the increase in emulsified oil concentration. The variations observed in flux with time are well-described by models in which the oil fouls the membrane, imparting an additional resistance to transport. The resistivity of the foulant increased with an increase in the concentration of oil in the feed, and grew fastest when dp/df was close to unity. A foulant deposition model is proposed in which the oil droplets form a conformal coating on the fibers. The normalized flux of electrospun membranes was approximately three times higher than that of a commercial phase inversion membrane of comparable bubble point diameter, while exhibiting a similar rejection.