Partition coefficients and interfacial activity for polar components in oil/water model systems

Partition coefficients, surface tension, and interfacial tension for some p olar organic components dissolved in oil/water model systems have been inve stigated. The systems consist of isooctane modeling the oil phase and of wa ter solutions of NaCl and CaCl2, modeling the water phase. The organic comp ounds examined were 1-naphtoic acid, 5-indanol, and quinoline, all well-def ined molecules known to be representative of polar components in crude oil. The dependence on pH, salinity, and ionic strength in the water phase was investigated. The surface tension and interfacial tension were also examine d as a function of component concentration. The results show a connection b etween the distribution of the polar components and the interfacial tension . Correspondence between the partition coefficient and the pK(a) value for the components is also reported. For 1-naphtoic acid none of the two ioniza tion forms of the molecule are found to be surface active in aqueous soluti on. For 5-indanol both forms are surface active, and for quinoline only the nonionic form of the molecule is found to be surface active. The results i ndicate that the aqueous phase is the one that governs the interfacial tens ion. Increasing salinity increases the concentration of the component in th e oil phase and decreases the interfacial tension between the oil phase and the aqueous phase. The results are explained due to the "salting-out" effe ct and to changes in the electrostatics for the various systems, (C) 1999 A cademic Press.