Demulsification of water/oil/solid emulsions by hollow-fiber membranes

The demulsification techniques investigated use preferential surface wetting to allow separation of oil and water phases in ultrafiltration and microfiltration membranes. A hydrophobic membrane allows the permeation of an oil phase at almost zero pressure and retains the water phase, even though the molecular weight of the water molecule (18) is much smaller than that of the oil molecule (198 for tetradecane, used in this study). Hydrophobic membranes having pore sizes from 0.02 to 0.2 μm were tested for demulsification of water‐in‐oil emulsions and water/oil/solid mixtures. The dispersed (aqueous)‐phase drop sizes ranged from 1 to 5 μm. High separation rates, as well as good permeate quality, were obtained with microfiltration membranes. Water content of permeating oil was 32–830 ppm depending on operating conditions and interfacial properties. For emulsions with high surfactant content, simultaneous operation of a hydrophobic and hydrophilic membrane, or simultaneous membrane separation with electric demulsification was more efficient in obtaining complete phase separation.