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Characterization of asphaltene molecular structures by cracking under hydrogenation conditions and prediction of the viscosity reduction from visbreaking of heavy oils Open Access


Other title
Type of item
Degree grantor
University of Alberta
Author or creator
Rueda-Velasquez, Rosa I
Supervisor and department
Gray, Murray R. (Chemical and Materials Engineering)
Examining committee member and department
Stryker, Jeffrey (Chemistry)
Abedi, Jalal (Chemical and Petroleum Engineering, University of Calgary)
Semagina, Natalia (Chemical and Materials Engineering)
Dechaine, Greg (Chemical and Materials Engineering)
Department of Chemical and Materials Engineering
Chemical Engineering
Date accepted
Graduation date
Doctor of Philosophy
Degree level
The chemical building blocks that comprise petroleum asphaltenes were determined by cracking samples under conditions that minimized alterations to aromatic and cycloalkyl groups. Hydrogenation conditions that used tetralin as hydrogen-donor solvent, with an iron-based catalyst, allowed asphaltenes from different geological regions to yield 50-60 wt% of distillates (<538°C fraction), with coke yields below 10 wt%. Control experiments with phenanthrene and 5α-cholestane confirmed low hydrogenation catalytic activity, and preservation of the cycloalkyl structures. Quantitative recovery of cracking products and characterization of the distillates, by gas chromatography-field ionization–time of flight high resolution mass spectrometry, displayed remarkable similarity in molecular composition for the different asphaltenes. Paraffins and 1-3 ring aromatics were the most abundant building blocks. The diversity of molecules identified, and the high yield of paraffins were consistent with high heterogeneity and complexity of molecules, built up by smaller fragments attached to each other by bridges. The sum of material remaining as vacuum residue and coke was in the range of 35-45 wt%; this total represents the maximum amount of large clusters in asphaltenes that could not be converted to lighter compounds under the evaluated cracking conditions. These analytical data for Cold Lake asphaltenes were transformed into probability density functions that described the molecular weight distributions of the building blocks. These distributions were input for a Monte Carlo approach that allowed stochastic construction of asphaltenes and simulation of their cracking reactions to examine differences in the distributions of products associated to the molecular topology. The construction algorithm evidenced that a significant amount of asphaltenes would consist of 3-5 building blocks. The results did not show significant differences between linear and dendritic molecular architectures, but suggested that dendritic molecules would experience slower reaction rates as they required more breakages to reach a given yield of distillates. Thermal cracking of asphaltenes in heavy oils and bitumens can dramatically reduce viscosity, enabling pipeline transportation with less solvent addition. The viscosities of the products from visbreaking reactions of two different heavy oils were modeled with lumped kinetics based on boiling point pseudo-components, and with the estimation of their individual fluid properties. The model was tuned with experimental viscosity data, and provided estimations of viscosities at different temperatures with absolute average deviations lower than 31%.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
Rueda-Velásquez, R. I.; Freund, H.; Qian, K.; Olmstead, W. N.; Gray, M. R. Characterization of Asphaltene Building Blocks by Cracking under Favorable Hydrogenation Conditions. Energy & Fuels 2012

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