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

Abstract

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.

Comment on “Mixture Effect on the Dilatation Rheology of Asphaltenes-Laden Interfaces”

“…As expected for all systems that cross the gel point (such as bulk cross-linking polymers or physical gels), G becomes measurable after a while and increases with time with no apparent stabilization. Examples are given in ref . But even in this case (when G ≠ 0), gel-point rheology is observed for dilatational measurements made at low frequencies, , indicating that the interface has evolved to a state not too distant from the gel point, as expected for colloidal aggregation.…”

Characterization of the Interfacial Material in Asphaltenes Responsible for Oil/Water Emulsion Stability

“…The abundance of polar groups in IM promoted hydrogen bonding, acid–base, dipole–dipole, and other van der Waals interactions. ,,, As a result, molecules were able to aggregate once adsorbed at the o/w interface and form a gelled network responsible for emulsion stability . Molecular simulations using archipelago-type model molecules revealed that the association of their sulfoxide groups rather than their aromaticity yields to the formation of the porous networks observed at the interface .…”

“…9,12,13,18 As a result, molecules were able to aggregate once adsorbed at the o/w interface and form a gelled network responsible for emulsion stability. 20 Molecular simulations using archipelago-type model molecules revealed that the association of their sulfoxide groups rather than their aromaticity yields to the formation of the porous networks observed at the interface. 18 On the contrary, continental-type molecules tend to self-assemble into ordered structures through parallel stacking, perpendicular to the water surface.…”

Interfacial Rheology and Heterogeneity of Aging Asphaltene Layers at the Water–Oil Interface

“…Moreover, emulsified water increases the crude oil volume and is strictly regulated, increasing the cost of transportation and refinement. Natural surfactants like asphaltenes, resins, and fine particles in the crude oil adsorb at water–oil interfaces and stabilize emulsions, introducing difficulties for demulsification. Of these, asphaltenes are believed to have the largest effect on emulsion stability. , …”