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Changes in bitumen due to thermal conversion affecting the description of coke formation
- Author / Creator
- Yanez Jaramillo, Lina Maria
At the heart of heavy oil and bitumen upgrading, thermal conversion technologies are found. One such process is visbreaking where bitumen is thermally converted into lighter materials. However, the conversion by visbreaking is limited by the onset of the formation of solid carbonaceous materials (coke). The formation of coke has been explained by two pathways: (i) The formation of a mesophase (or a second liquid phase) that will eventually lead to coke, and (ii) Asphaltenes as precursors of coke formation due to increasing insolubility.
The objective of this work was to better understand the changes that bitumen and bitumen-related materials undergo in thermal conversion from the perspective of the change in the nature of the species. The results were employed to provide a better understanding of the onset of coke formation in visbreaking, and a different point of view about the process leading to coke formation which results from highlighting potential misconceptions within this field.
Considering the first pathway used to explain the origin of coke, mesophase formation follows from an increase in the aromatic character of the material as the first step. Hydrogen transfer and aromatization reactions are examples of reactions occurring in thermal conversion that could contribute to an increase in the aromatic hydrogen and carbon content. It was found that there was not a fixed relationship between aromatic hydrogen and aromatic carbon content. It was further found that changes in aromatic hydrogen content do not necessarily describe the changes in aromatic carbon content after visbreaking. The formation of aromatic structures as an early step of coke formation would imply an increase in the aromatic content, but the aromatic carbon and coke content of the thermally converted products only had a weak relationship.
The second pathway describes coke formation as a progression of insolubility where asphaltenes are considered precursors. As a result, it was expected to observe a relationship between coke and asphaltenes content in thermally converted samples. Contrary to the expectation, the visbroken products did not show a relationship between coke and asphaltenes content and did not provide evidence of asphaltenes being an intermediate step in coke formation.
The study also made other minor contributions to the field through work on water removal from emulsified bitumen and showing that there might be a relationship of free radical concentration in unconverted petroleum materials that is consistent with the composition continuum proposed by Boduszynski. This study has opened the possibility to further investigations that could address some of the hypotheses in this work and provide valuable inputs into the role of free radical species in coke formation during thermal conversion.
- Graduation date
- Fall 2023
- Type of Item
- Doctor of Philosophy
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