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Phase behavior of asphaltenes in organic media Open Access


Other title
Solution Calorimetry
colloidal behavior
Phase behavior
Type of item
Degree grantor
University of Alberta
Author or creator
Nikooyeh, Kasra
Supervisor and department
John M. Shaw (Chemical and Materials Engineering)
Examining committee member and department
Dechaine, Greg P. (Chemical and Materials Engineering)
Chalaturnyk, Rick (Civil and environmental Engineering)
Andersen, Simon I. (Schlumberger Canada Ltd.)
Elliott, Janet A. W. (Chemical and Materials Engineering)
de Klerk, Arno (Chemical and Materials Engineering)
Department of Chemical and Materials Engineering
Chemical Engineering
Date accepted
Graduation date
Doctor of Philosophy
Degree level
Unwanted phase separation of asphaltenes poses significant challenges in production and processing of heavy oils and bitumen. The analysis and prediction of asphaltene precipitation behaviors and asphaltene-diluent interactions are typically treated either from a solution thermodynamics or a colloid perspective. However, the polydispersity and multi-phase nature of asphaltenes allows for portions of these materials to exhibit both behaviors concurrently at fixed global composition. Partial specific volume at near infinite dilution and enthalpies of solution are sensitive thermodynamic measures of solute-solvent interactions derived from high precision density and calorimetry measurements for dilute mixtures. Solution calorimetry and density measurements are performed on mixtures of asphaltenes with a variety of diluents ranging from n-alkanes to bicyclic aromatics. The validity of the assumption of solubility of asphaltenes in various diluents is evaluated based on density and calorimetry data. The trends of changes in enthalpies of solution of asphaltenes and their fraction with variations in composition and temperature are used in identifying the interactions of asphaltenes with the diluents and determining the phase state of asphaltenes in organic media. The results indicate co-existence of a soluble and an insoluble fraction of asphaltenes in each organic diluent and at every fixed temperature and concentration. Endothermic phase transitions and exothermic sorption of diluent are detected in n-alkanes as well as 1-methylnaphthalene, tetrahydrofuran, toluene and quinoline. Asphaltenes are shown to have both intermolecular and interfacial interactions with the studied diluents. The results are in agreement with the hypothesis that only a fraction of asphaltenes undergo a solid-liquid phase change upon mixing with diluents and that fraction is a function of diluent properties, global composition and temperature. These results are inconsistent with the application of dissolution as classically defined to asphaltene + diluent mixtures. Quantitation of the asphaltene fractions potentially present as colloidal particles or as dissolved species in a diluent remains a subject for future study.
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Citation for previous publication
Nikooyeh, K.; Shaw, J. M., On the Applicability of the Regular Solution Theory to Asphaltene + Diluent Mixtures. Energy & Fuels 2011, 26, (1), 576-585Nikooyeh, K.; Bagheri, S. R.; Shaw, J. M., Interactions Between Athabasca Pentane Asphaltenes and n-Alkanes at Low Concentrations. Energy & Fuels 2012, 26, (3), 1756-1766.

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