Surface Properties of Basic Components Extracted from Petroleum Crude Oil

The properties of the entire separated basic fraction extracted from a crude oil have been investigated, by utilizing a Langmuir trough to determine surface pressure (SP) isotherms and a ring tensiometer for interfacial tension (IFT) measurements. The IFT between oil and water indicated that the interfacial activity is governed by the bases in the lower pH range (pH <= 5) and by the nonbases at higher pH values. However, the results do not imply any interactions between the two separated fractions, but rather that the activity of the crude oil is a combination of the individual components. The SP isotherms did not appear to depend on the pH of the subphase, except at pH I. This was later found to be a result of higher electrolyte concentration rather than a pH effect. An addition of salt to the aqueous subphase increased the surface pressure by screening the electrostatic repulsions in the surfactant monolayer. Salting-in or salting-out effects were not observed in these systems. The SP isotherm for the bases was compared with those for maltenes and asphaltenes, where the similarities with the former support previous statements of bases being a subfraction of maltenes.