Surface modification of PVDF ultrafiltration membranes by remote argon/methane gas mixture plasma for fouling reduction

•Water-in-oil emulsions (5 vol%) were separated by UF with 30-kDa PVDF membrane.•PVDF membrane was modified by remote Ar and Ar/CH4 atmospheric-pressure plasma.•Flux decline and membrane fouling was analyzed using the resistance-in-series model.•Total filtration resistance reduced by more than 46% compared to virgin membrane.•Resistances due to solute adsorption and cake layer had a key effect on UF flux.

Ultrafiltration (UF) is considered as a potential alternative to gravity settling in liquid surfactant membrane process for fast separation of water-in-oil (W/O) emulsions from the external aqueous phase. Flux behavior was studied in this work during batch UF of W/O/W solutions by poly(vinylidene fluoride) (PVDF) membrane with a molecular weight cut-off of 30 kDa after the membrane was modified by remote cyclonic atmospheric-pressure plasma with argon gas and methane/argon gas mixture. Physicochemical properties of the membrane surfaces including hydrophilicity, functional group concentrations, and pore size distribution before and after plasma modifications were determined by static contact angle measurements, X-ray photoelectron spectroscopy, and capillary flow porometry, respectively. Higher surface concentrations of oxygen functional groups for plasma-functionalized membranes were observed compared to the unmodified membranes. It was shown that UF flux was significantly enhanced with the plasma-modified membranes under the conditions studied (feed, 5 vol% W/O emulsions; stirring, 300 rpm; pressure, 35–138 kPa). Resistance-in-series analysis of the flux data indicated that the proposed remote plasma treatment, particularly with methane/argon gas mixture, could considerably reduce both resistances due to solute adsorption and cake layer formation on the membrane surface, although the above two resistances always contributed more than 71% of the total filtration resistance.