Characterization of Crude Oil Interfacial Material Isolated by the Wet Silica Method. Part 2: Dilatational and Shear Interfacial Properties

To better understand the water-in-oil (w/o) emulsion stability problem, the interfacial material (IM) of four different crude oils was isolated using the wet silica method and analyzed by different techniques. In part 1 (10.1021/acs.energyfuels.6b02899), we used gel permeation chromatography to analyze the molecular size distribution of S-, Ni-, and V containing compounds. Here, we report the use of dilatational and shear interfacial rheology to analyze the interfacial properties of the IM films. In the second part of this series of papers, it is shown that the wet silica isolation method is reproducible and concentrates the most surface-active molecules present in crude oils. Shear interfacial rheology results showed perfect correlation to emulsion stability; stronger mechanical properties lead to more stable w/o emulsions. Dilatational rheology revealed that successive IM extracts from a crude oil are composed of molecules that behave increasingly like insoluble surfactants that aggregate at the w/o interface. Lastly, shear rheology experiments with diluted IM and diluted crude oil showed some differences that were ascribed to a different partitioning between the bulk and interface.