Demulsification mechanism of asphaltene-stabilized water-in-oil emulsions by a polymeric ethylene oxide-propylene oxide demulsifier

The demulsification mechanism of asphaltene-stabilized water-in-toluene emulsions by an ethylene-oxide-propylene oxide (EO-PO) based polymeric demulsifier was studied. Demulsification efficiency was determined by bottle tests and correlated to the physicochemical properties of asphaltene interfacial films after demulsifier addition. From bottle tests and droplet coalescence experiments, the demulsifier showed an optimal performance at 2.3 ppm (mass basis) in toluene. At high concentrations, the demulsification performance deteriorated due to the intrinsic stabilizing capacity of the demulsifier, which was attributed to steric repulsion between water droplets. Addition of demulsifier was shown to soften the asphaltene film (i.e., reduce the viscoelastic moduli of asphaltene films) under both shear and compressional interfacial deformations. Study of the macrostructures and the chemical composition of asphaltene film at the toluene-water interface after demulsifier addition demonstrated gradual penetration of the demulsifier into the asphaltene film. Demulsifier penetration in the asphaltene film changed the asphaltene interfacial mobility and morphology, as probed with Brewster angle and atomic force microscopy

Asphaltene Subfractions Responsible for Stabilizing Water-in-Crude Oil Emulsions. Part 3. Effect of Solvent Aromaticity

Whole asphaltenes (WA) were fractionated by the E-SARA method according to their adsorption characteristics at oil−water interfaces from either toluene or heptol solutions. Heptol, a mixture of n-heptane and toluene at a 1:1 volume ratio, is a less aromatic solvent than toluene. The effect of solvent aromaticity on the composition of resulting asphaltene subfractions at oil−water interfaces was studied to determine the key functional groups that are critical to the asphaltene-induced stabilization of water-in-oil (W/O) petroleum emulsions. The interfacially active asphaltenes (IAA) were extracted as materials irreversibly adsorbed onto emulsified water droplets, while the asphaltenes remaining in the oil phase were considered as remaining asphaltenes (RA). Although toluene-extracted interfacially active asphaltenes (T-IAA) accounted for only 1.1 ± 0.3 wt % of WA, this subfraction of asphaltenes exhibited a greater interfacial activity and formed more rigid films at the oil−water interface than IAA extracted using heptol, known as HT-IAA which accounted for 4.2 ± 0.3 wt % of WA. The increased potential of T-IAA to stabilize W/O emulsions was attributed to their higher content of oxygen, resulting in a higher content of sulfoxide groups, as verified by elemental analysis, Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Although the toluene-extracted remaining asphaltenes (T-RA) and heptol-extracted remaining asphaltenes (HT-RA) were shown to contain similar H/C ratios and nitrogen contents to those of T-IAA and HT-IAA, the two RA subfractions contained a much less amount of sulfur and oxygen, leading to a much reduced interfacial activity as compared with that of IAA subfractions. In spite of the small proportions in asphaltenes, oxygen-containing functional groups, in particular sulfoxides, were believed to contribute significantly to the increased stability of asphaltene-stabilized W/O petroleum emulsions

Impact of Amphiphilic Nanostructures on Formation and Rheology of Interfacial Layers and on Foam Film Drainage

The aim of the present studies is to clarify how the surfactant adsorption layer properties are related to the course of the drainage parameters of microscopic foam films in the special case of aqueous solutions containing premicellar amphiphilic nanostructures. The scope of the research covers the adsorption dynamics, construction of equilibrium adsorption isotherms, surface rheology of interfacial layers, and foam film drainage kinetics. It is established that, in the premicellar domain, there are concentration intervals, where the considerable irregularities of adsorption layerproperties are observed: several plateau regions in the surface tension isotherms, unusual changes of the surface rheological characteristics, etc. The systematic investigation of the drainage of foam films obtained from these solutions show that the dependences of basic kinetic parameters of the films on the amphiphile concentration run in synchrony with changes in the adsorption layer properties. Thus, the presence of smaller loose aggregates (premicelles) plays a significant role for the kinetic stability of films. The importance of this research is related toproviding a better insight into the initial stages of self-assembling phenomena and into the factors determining thedrainage and the stability of thin liquid films. The results have implications for the understanding and the correct prediction of properties of foam systems.</jats:p