Janus hollow fiber membranes with functionalized outer surfaces for continuous demulsification and separation of oil-in-water emulsions

An incredible amount of oily wastewater is generated each day all over the world from industrial manufacture and daily life. Numerous attempts have been undertaken to separate these oil/water mixtures, especially those surfactant-stabilized oil-in-water emulsions. Janus membranes with asymmetric wettability are widely regarded as a promising oil/water separation technology with the lowest energy consumption. In this work, we demonstrate the fabrication of Janus hollow fiber membranes (JHFM) with functionalized outer surface for the continuous demulsification and separation of oil-in-water emulsions. Polydopamine and polyelectrolyte are co-deposited onto the outer surface of polypropylene hollow fiber microfiltration membrane to construct a thin charged hydrophilic coating with controllable thickness. The prepared JHFMs are assembled into typical modules which can continuously separate surfactant-stabilized oil-in-water emulsions with high efficiency (recovery ratio >99%, purity >99.8%). The JHFM modules show applicability to both light oil and heavy oil collection in the common cross-flow filtration mode. The influences of operating conditions, including feed flow rate, surfactant content, hydrophilization depth and packing density, are demonstrated in detail on the separation performance. This work is of great significance to the practical application of Janus membranes in the separation of oil/water mixtures, especially surfactant-stabilized oil-in-water emulsions which are intractable to be separated effectively by conventional methods.