Interfacial Activity of Bitumen Components

Abstract

The interfacial activity of asphaltenes, naphthenic acids, and naphthenates has been amply studied in the literature, as they are involved in the formation and stabilization of bitumen and heavy crude oil emulsions. While most of the literature evaluates one component at a time, in this work these bitumen components were separated one at a time from Athabasca bitumen, and the surface activity of the resulting fraction was evaluated as a function of pH, solvent aromaticity (heptane/toluene mixtures, known as heptol, at volume ratios 50/50 and 80/20), and temperature for selected systems. The interfacial activity was evaluated in two ways: via dynamic interfacial tension during adsorption on a bitumen drop of constant volume, and via dynamic interfacial tension during drop volume cycling. The adsorption data were interpreted using a model that combined multicomponent adsorption kinetics inspired by Langmuir-Freundlich kinetics with the Fainerman surface equation of state. The volume cycling experiments were interpreted using the compression relaxation model, which segregates adsorption/relaxation effects from elastic phenomena at interfaces. Overall, the adsorption data confirmed that naphthenic acids are the fastest adsorbing species that tend to dominate the interface, but that asphaltenes adsorb, almost irreversibly, at longer time scales and likely forming a sublayer previously proposed in the literature. The dilatational elasticity of the interface seems to be highly influenced by that asphaltene sublayer, which softens at high pH at room temperature, or at 80 C independently of the pH of the system. 642 J Surfact Deterg J Surfact Deterg (2020) 23: 641-659 643 J Surfact Deterg J Surfact Deterg (2020) 23: 641-659 N.C., not calculated; N.O., not observed. Green to red is a desirable to non-desirable scale. 646 J Surfact Deterg J Surfact Deterg (2020) 23: 641-659

Interfacial Tension of the Water-Diluted Bitumen Interface at High Bitumen Concentrations Measured Using a Microfluidic Technique

“…In these experiments, there was no noticeable change in the shape and IFT of the drop even after 30 min, a time scale over which the adsorption of asphaltenes on stagnant oil–water interfaces is known to modify IFT noticeably, ,, as also observed in the CSD-ADSA measurements (see Figure ). These observations appear to suggest that stagnant dilbit-water interfaces could evolve fundamentally differently than sheared ones.…”

“…In these experiments, there was no noticeable change in the shape and IFT of the drop even after 30 min, a time scale over which the adsorption of asphaltenes on stagnant oil−water interfaces is known to modify IFT noticeably, 30,64,57 as also observed in the CSD-ADSA measurements (see Figure 8). 22 These observations appear to suggest that stagnant dilbit-water interfaces could evolve fundamentally differently than sheared ones. The mechanism of the effect of flow on the evolution of the interfacial mechanical properties of the dilbit-water system is not known, but we discuss a mechanism whereby the process of aging and the consequent IFT increase could be explained.…”

“…The time spent by the drop being exposed to the dilbit solution prior to its arrival at the channel center, t R , affects the interfacial concentration of surfactants and therefore the interfacial properties, as seen in the previous dynamic IFT measurements. ,− The time t R can be decomposed into two contributions: (a) the time spent in the main channel, t M , and (b) the time spent in the side channel, t S (see Figure ). where t M is defined as the time taken by a water drop to travel from the inlet to the center of the device.…”

“…The equilibrium IFT results reported in previous studies for the water-bitumen systems ,,, are outlined in Tables and . Only those past studies that employed a dilution less than S/B = 4 are considered in this paper, as the water-bitumen interface is known to have significantly different properties above this dilution, and also because dilutions of S/B < 4 are more relevant to the industrial process.…”

“…Literature has already seen several studies on the measurement of the IFT of the water-dilbit interface using conventional tensiometers. ,− All these past studies show that the equilibrium IFTs of water-bitumen systems at concentrations of interest to the oil sands industry (solvent to bitumen (S/B) weight ratios ranging from 0.5 to 2) have a value of 10 to 20 mN/m at a water pH of 8.3, and a few mN/m at a pH of 9.9. In order to avoid the problem of opacity associated with having dilbit as the suspending medium, almost all past studies have been implemented using oil drops in water.…”