The Removal of Particles from Oils by Nonionic Surfactants

The separation of particulate material from a dispersion of particles in an oil can be effected by transport of the particles through the bounding oil interface in a process mediated by surfactant. When the oil phase containing particles is contacted with an aqueous phase, the transport process through the interface is resisted by a capillary force which depends on the interfacial tension and on the contact angle for the three-phase system. It is shown how the addition of a judiciously-chosen nonionic surfactant to a model system of carbon particles in n-alkanes can bring about near-complete transfer of the particles to the aqueous phase. The underlying mechanisms for the transport process are discussed. Some implications for systems of practical importance are discussed.