Thermal Treatment of Bitumen Froth at 400 °C: Impact of Water and Minerals on Bitumen Properties and Reaction Chemistry
Creators: Pereira Bassane, Joao Felipe
Publisher: name: University of Alberta Library
Year: 2024

<p>The production of oilsands bitumen from mining operations requires its recovery from the mineral matter through a hot water extraction process, which generates a bitumen froth comprising about 60 wt% bitumen, 30 wt% water, and 10 wt% mineral solids. The challenging separation of water and solids from bitumen is achieved in the froth treatment unit employing a light hydrocarbon solvent. The bitumen product, after solvent recovery, is very viscous and dense, requiring dilution and/or upgrading to be transported through pipelines.The thermal treatment of bitumen froth has potential to integrate froth treatment and partial upgrading of bitumen. With this prospect in mind, the current thesis investigated the impact of water and oilsands minerals on the bitumen properties and the reaction chemistry during the thermal treatment of bitumen froth at 400 °C.The visbreaking of bitumen in the presence of water and solids, with and without solvent addition, was investigated at 400 °C. While visbreaking of froth led to a bitumen product with lower density and viscosity, it was surprising that the treatment in the presence of water and/or solids resulted in a bitumen product with slightly higher viscosity and density as compared to visbreaking of bitumen alone. This finding was contrary to reports in literature that claimed improved quality of the bitumen product when bitumen was thermally treated in the presence of water and solids. Changes in the physicochemical properties of bitumen indicated a decreased aromatic H content when bitumen was treated in the presence of water and/or solids as compared to bitumen alone, a sign that hydrogen transfer reactions were influenced by these components. The study found that it was advantageous to perform bitumen visbreaking in the presence of a lighter hydrocarbon solvent (n-hexane) when compared to a heavier solvent (kerosene) or visbreaking without a solvent.To gain a better fundamental understanding of the influence of water and minerals on bitumen conversion in froth, α-methylstyrene (AMS) was employed as a probe molecule. The presence of water during the treatment resulted in decreased AMS conversion, lowered the formation of addition products, and favored hydrogen transfer reactions. However, it was unclear if water had a direct effect on influencing these changes or if it altered the system properties, which subsequently resulted in the observed changes. There was evidence that the froth minerals favored hydrogen transfer during the treatment, which can potentially be advantageous to bitumen upgrading by suppressing coke formation. The Brønsted-Lowry acidity of clays found in oilsands, such as kaolinite, was expected to enable cationic conversion during the treatment. Nevertheless, due to the complexity of a reaction medium containing bitumen, it was not possible to distinguish between free radical and cationic conversion, which motivated the use of simpler model systems to facilitate interpretation of the results.The specific contributions of water and kaolinite to the reaction rates and pathways during thermal treatment of a model system comprising AMS, tetralin, and n-pentadecane were studied through detailed characterization of the reaction products. The dilution of the reaction medium by water was presented as a potential effect that resulted in decreased conversion rates of AMS. This finding highlighted a possible deleterious effect of water during thermal treatment. Although water affected the conversion rates and promoted the hydration of unsaturated species, there was no evidence that water was a net hydrogen donor during the treatment. The choice of the model systems allowed for differentiating between free radical and cationic conversion. The Brønsted-Lowry acidity of kaolinite had an impact on the reaction pathways by enabling cationic dealkylation to form benzene and cationic dimerization to form the tricyclic AMS dimer 1,1,3-trimethyl-3-phenyl indane. The presence of kaolinite also resulted in increased reaction rates and favored hydrogen transfer reactions. Although kaolinite was catalytically active during the conversion, its catalytic sites were rapidly fouled due to its low surface area.It can be concluded that visbreaking of bitumen froth at 400 °C, particularly in the presence of a light solvent such as n-hexane, has the potential to combine froth treatment and upgrading. Water and mineral matter caused a minor suppression of conversion, but at the same time improved hydrogen transfer, with kaolinite also being responsible for limited cationic conversion.</p>