Adjusting the morphology of poly(vinylidene fluoride-co-hexafluoropropylene) membranes by the VIPS process for efficient oil-rich emulsion separation

Given its excellent bulk properties and highly hydrophobic nature, poly(vinylidene fluoride-co-hexafluoropropylene), P(VDF-co-HFP), is a candidate material for the gravity-driven separation of water and oil from oil-rich emulsions. For this, highly porous membranes with a controlled large pore size are necessary. An ideal process to design such structures is the vapor-induced phase separation (VIPS) process but it has been underexplored using P(VDF-co-HFP). Here, we address this challenge by presenting and discussing the formulation/ process conditions that permit to obtain the desired P(VDF-co-HFP) porous bi-continuous structure by VIPS process only. Then, the membrane is fully characterized before being applied to the separation of water-in-oil emulsions, from versatile oil-rich phases, with or without the use of surfactants, in both dead-end gravity driven process and cross-flow process. In each situation, high flux and separation efficiencies were obtained, and the membrane outperformed commercial hydrophobic poly(vinylidene fluoride) (PVDF) membranes of similar pore size/porosity in every aspect (flux, separation efficiency, mechanical sustainability). All in all, P(VDF-co-HFP) VIPS membranes appear to be ideal materials for fast and effective gravity-driven separation of oil-rich emulsions.