The interfacial material (IM) from four different crude oils with different capabilities to form stable water-in-oil (w/o) emulsion was extracted with the wet silica method and analyzed by different techniques. In the first of a series of papers, we report the use of gel permeation chromatography inductively coupled plasma high-resolution mass spectrometry (GPC ICP HR MS) to analyze the size distributions of sulfur-, vanadium-, and nickel-containing compounds present in the IM. The analysis of replicate samples demonstrated the reproducibility of the wet silica extraction method, and successive extractions of the same crude oil concentrated larger and more insoluble IM aggregates containing S, V, and Ni. The analysis of the IM from different crude oils revealed that there is a similar, selective adsorption of high-molecular-weight compounds containing Ni and V at the w/o interface. Conversely, the sulfur profiles for all of these IMs were unique, and given their widely varying ability to stabilize emulsions, it suggests that these species may play a role in the stability of water-in-crude oil emulsions.
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 Vcontaining 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.
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