Extraction of Crude Oil Endogenous Surfactants by an Optimum Three-Phase Microemulsion System: Relation between Interfacial Behavior and a Molecular Fingerprint Obtained by Ultrahigh-Resolution Mass Spectrometry
Résumé
A novel method is described to extract crude oil surface active species. It is based on the formation of balanced three-phase microemulsions (optimum Winsor III systems) with a well-defined temperature-sensitive nonionic surfactant. The crude oil surface-active species are concentrated in the middle-phase microemulsion, which is separated. The interfacial material is then recovered in the surfactant-rich aqueous phase after cooling. This method was applied to five crude oils and the interfacial materials were then analyzed by Fourier transform ion cyclotron resonance mass spectroscopy (FT-ICR MS). This novel extraction method compares well with the established “wet-silica” method, as evidenced by the analysis in the negative electrospray ESI(−) mode of the interfacial materials of the same crude extracted by the two methods. The analytical data have been related to the interfacial activity of the crude oils, namely, their tendency to form stable emulsions with water or viscous phases in surfactant/oil/water systems at equilibrium, and to their equivalent alkane carbon numbers (EACN). The interfacial materials are confirmed to be responsible for the increased stability of water-in-oil emulsions.