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The Formation of New Asphaltenes during Visbreaking of Vacuum Residue Deasphalted Oil and the Storage Stability of Product from Visbreaking
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- Author / Creator
- Yan, Yuwei
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Mild thermal cracking by visbreaking emerged as an important partial upgrading technology for reducing the viscosity of Canadian oilsands bitumen to enable pipeline transport. Under typical visbreaking conditions, the conversion of bitumen is described by first-order kinetics, which forms the basis of the equivalent residence time (ERT) concept. The implication of this description is that various reaction temperature and residence time combinations can be selected that result in the same conversion. The objective of this study was to investigate if different process conditions that result in the same conversion, would also lead to the same amount of n-pentane insoluble material (asphaltenes) with the same properties in the final product. This study employed vacuum residue deasphalted oil (VR DAO) that was obtained from an industrial bitumen upgrader as feed material. During thermal conversion in the temperature range 417–438 °C at different residence times, new asphaltenes were formed. The kinetics of vacuum residue conversion was different compared to the kinetic of asphaltenes formation, which implied that visbreaker design based on equivalent residence time did not account for all of the important product characteristics. This was an important contribution, since visbreakers are usually designed using equivalent residence time. Based on the analysis of asphaltenes fraction before and after reaction, there was evidence that asphaltenes were participating in hydrogen transfer reactions. The visbroken product was found to be reactive during storage and after 210 days of storage under nitrogen, the amount of asphaltenes in visbroken product increased by 9 wt%. This observation led to a systematic study to determine how the visbroken product changed over time. A fresh visbroken product was prepared, which was characterized after reaction and then after 2, 4, 8, and 12 weeks storage under nitrogen. The nature of hydrogen transfer during storage was also evaluated. It was found that as the storage time increased, density, viscosity, asphaltenes content, refractive index, H:C of the asphaltenes, and the micro carbon residue all increased.
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- Subjects / Keywords
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- Graduation date
- Spring 2020
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- 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.