Role of Asphaltenes in Stabilizing Thin Liquid Emulsion Films

Abstract

Drainage kinetics, thickness, and stability of water-in-oil thin liquid emulsion films obtained from asphaltenes, heavy oil (bitumen), and deasphalted heavy oil (maltenes) diluted in toluene are studied. The results show that asphaltenes stabilize thin organic liquid films at much lower concentrations than maltenes and bitumen. The drainage of thin organic liquid films containing asphaltenes is significantly slower than the drainage of the films containing maltenes and bitumen. The films stabilized by asphaltenes are much thicker (40-90 nm) than those stabilized by maltenes (∼10 nm). Such significant variation in the film properties points to different stabilization mechanisms of thin organic liquid films. Apparent aging effects, including gradual increase of film thickness, rigidity of oil/water interface, and formation of submicrometer size aggregates, were observed for thin organic liquid films containing asphaltenes. No aging effects were observed for films containing maltenes and bitumen in toluene. The increasing stability and lower drainage dynamics of asphaltene-containing thin liquid films are attributed to specific ability of asphaltenes to self-assemble and form 3D network in the film. The characteristic length of stable films is well beyond the size of single asphaltene molecules, nanoaggregates, or even clusters of nanoaggregates reported in the literature. Buildup of such 3D structure modifies the rheological properties of the liquid film to be non-Newtonian with yield stress (gel like). Formation of such network structure appears to be responsible for the slower drainage of thin asphaltenes in toluene liquid films. The yield stress of liquid film as small as ∼10(-2) Pa is sufficient to stop the drainage before the film reaches the critical thickness at which film rupture occurs.

Fractionation of Asphaltenes in Understanding Their Role in Petroleum Emulsion Stability and Fouling

“…These thick lenses indicate the formation of aggregates in the IAA film, which was not observed initially before 30 min aging. These films are similar to asphaltene-in-toluene films as reported by Tchoukov et al 58 They proposed that self-association of asphaltenes is not limited to nanoaggregates but also forms an extended macrostructures in the film with gel-like rheological properties. As indicated by molecular dynamics simulations, such formation and extension of asphaltene network upon aging were believed to be related to hydrogen bonding interactions mainly induced by sulfoxide groups present in IAA.…”

Probing Mechanical Properties of Water–Crude Oil Interfaces and Colloidal Interactions of Petroleum Emulsions Using Atomic Force Microscopy

“…However, we acknowledge that the adhesion force magnitude for the asphaltene and corresponding bitumen cases is statistically within the experimental error. Although asphaltenes are expected to be the dominant interfacial component, 6,7 the presence of other indigenous species in bitumen may contribute to the overall adhesion between the two interacting interfaces. 50 The "jump-in" adhesion force at the highest asphaltene concentration may be justified by the increased interpenetration of voluminous asphaltene layers.…”

“…1 Steric stabilization from the interfacial asphaltene layers and non-uniform drainage of the intervening liquid films, as water droplets are pressed together, lead to enhanced emulsion stability. [5][6][7] The strongly elastic interfacial layers act as a mechanical barrier between water droplets and must be deformed beyond the shear yield strength to initiate droplet coalescence. 4,5,7,8 Although other bitumen components such as resins and naphthenic acids cannot stabilize water-in-oil emulsions alone, they interact with asphaltenes to enhance emulsion stability.…”

“…[5][6][7] The strongly elastic interfacial layers act as a mechanical barrier between water droplets and must be deformed beyond the shear yield strength to initiate droplet coalescence. 4,5,7,8 Although other bitumen components such as resins and naphthenic acids cannot stabilize water-in-oil emulsions alone, they interact with asphaltenes to enhance emulsion stability. 9,10 Asphaltenes are also known to change the surface properties of hydrophilic solids (clays), making them bi-wettable and enhancing their potential to partition at the oil-water interface.…”

Molecular Interactions between a Biodegradable Demulsifier and Asphaltenes in an Organic Solvent

“…2,3,4 Asphaltenes and fine bi-wettable solid particles (clays) are known to stabilize such emulsions since they readily partition at the liquid-liquid interface to create mechanical barriers that resist droplet coalescence. [5][6][7][8][9][10][11][12] Recent research has shown that the continual accumulation of asphaltenes at the oil-water interface leads to the formation of elastically-dominated interfacial layers that rupture once a critical yield stress is exceeded. 5,[13][14][15] This yield stress is significantly greater than the typical stress applied during droplet-droplet collision; 16,17 as a result, alternative routes have been explored to reduce the rigidity of these interfacial layers.…”