Understanding Stability of Water-in-Diluted Bitumen Emulsions by Colloidal Force Measurements

Removal of emulsified water is a challenge in oil sands and heavy oil processing. The flocculation and coagulation of emulsified water droplets depend on the interactions between the water droplets covered mainly by asphaltenes and oil-contaminated fine solids. To quantitatively evaluate the stability of water-in-diluted bitumen emulsions, this research determined the interactions between asphaltene surfaces in model oils, heptane, toluene or a mixture of the two known as heptol, by colloidal force measurements using atomic force microscopy (AFM) in combination with the Langmuir-Blodgett technique. The effect of aromaticity of the solvents, temperature and water content of the solvents on asphaltenes-asphaltenes interactions was systematically investigated.;Oil-contaminated fine solids not only help stabilize water-in-diluted bitumen emulsions but are detrimental to bitumen upgrading. To control the wettability of these fine solids, a preliminary study was carried out in this work to explore the potential of ethyl cellulose (EC), an effective demulsifier for water-in-diluted bitumen emulsion, as a surface wettability modifier of the oil-contaminated solids. It was found that EC is able to reduce the surface hydrophobicity of the asphaltene- and bitumen-contaminated solids and thus enhances their removal from bitumen froth. The mechanism of increased wettability by EC addition was determined by quartz crystal microbalance with dissipation (QCM-D) and AFM topographical imaging. The results from this study can help establish the criteria for selecting and developing chemical modifiers for applications in wettability control of oil-contaminated solids.;The results showed that the interaction forces between asphaltenes are highly sensitive to the aromaticity of the organic solvents. In solvents of higher aromaticity, a repulsive force existed between asphaltene surfaces; whereas in solvents of lower aromaticity, a weak attraction was detected. The transition from repulsion to attraction indicates that it is possible to control asphaltenes-asphaltenes interactions, and ultimately to control the stability of asphaltene-stabilized water droplets in oil, through tuning the aromaticity of the organic solvents. By fitting the measured force profiles with theoretical models, the nature of the forces was determined, which provides insights into the mechanisms of asphaltene-stabilized water-in-oil emulsions. The concomitant benefit of the results from the direct force measurement is to predict asphaltene precipitation with change of solvent composition.