(3ae) Hygro-Responsive Membranes for Effective Oil-Water Separation

Several recent events, including the Deepwater Horizon oil-spill in the Gulf of Mexico, have highlighted the difficulty of effective oil-water separation. Efficient, cost-effective processes for oil-water separation, especially in the presence of dispersants (or surfactants), are greatly desired. Surfactant-stabilized mixtures of oil and water are classified by the diameter (d) of the dispersed phase as: i) free oil and water, if d > 150 μm, ii) a dispersion, if 20 μm < d < 150 μm, or iii) an emulsion, if d < 20 μm. Conventional gravity separators and skimming techniques are incapable of separating emulsions. Membrane-based technologies are attractive for demulsification, i.e., the conversion of an emulsion to a free oil-water mixture, because they are relatively energy-efficient, cost-effective, and applicable across a wide range of industrial effluents. However, for complete oil-water separation, demulsification is typically followed by either gravity separation or skimming.

In this work, we have developed superhydrophilic and superoleophobic membranes that allow for the separation of a range of different oil-water mixtures including free oil and water, oil-in-water emulsions, water-in-oil emulsions and any combination of these phases in a single unit operation, with greater than 99.9% separation efficiency. Our separation methodology is solely gravity driven and consequently it is expected to be one of the most energy-efficient separation processes for different oil-water mixtures. Further, our dip-coating based membrane fabrication is easily scalable and we demonstrate the separation of several liters of oil-water mixtures using a scaled up apparatus. In addition, we also demonstrate continuous separation of oil-water emulsions for over 100 hours without a decrease in flux. We envision that our separation methodology will be useful for numerous applications including the clean up of oil-spills, wastewater treatment, fuel purification and the separation of numerous commercially relevant emulsions.