Hydrothermal Treatment of Bitumen Froth at 250 °C:  Impact on Bitumen Properties and Role of Clay Minerals
Creators: Turuga, Annapurna Sri Sowmya
Publisher: name: University of Alberta Library
Year: 2023

<p>Bitumen froth produced in the hot water extraction process of mined oil sands consists of about 60 wt % bitumen, 30 wt% water and 10 wt% mineral solids. To convert the bitumen in bitumen froth into a marketable product, the water and solids need to be separated. Solvent-based froth treatment processes are currently employed in industry to treat the bitumen froth. These processes are operated in the temperature range 30-85 °C. Depending on the process type (naphthenic vs. paraffinic froth treatment), the resultant bitumen product is either diluted and transported to a high conversion refinery, or fully upgraded to synthetic crude oil that can be processed in a conventional refinery. Partial upgrading of bitumen is a compromise between the two extremes of dilution and full upgrading. In this context, a modified froth treatment process called ‘hydrothermal treatment’, in which the bitumen froth is directly heated without solvent addition to temperatures higher than those used in the current froth treatment processes, is investigated in this thesis. It is anticipated that application of higher temperature can promote reactions in the froth in the presence of water and mineral solids, leading to partial bitumen upgrading, in addition to assisting with froth separation. Previous research on hydrothermal treatment of bitumen froth focused on the separation characteristics of the process. In this thesis, the focus is on investigating the effect of hydrothermal treatment of bitumen froth at moderate conditions (250 °C) on changes in bitumen properties, and the possible role of mineral solids in this process. Reactions performed with industrial bitumen froth indicated that hydrothermal treatment at 250 °C did not lead to partial upgrading of bitumen. Treatment of bitumen at 250 °C was beneficial only when bitumen was treated on its own. Among the properties tested, viscosity and total acid number of bitumen increased significantly after hydrothermal treatment compared to untreated bitumen. An increase in the viscosity of bitumen samples was accompanied by an increase in their free radical content. Minerals, in particular, promoted an increase in the free radical content of bitumen after thermal treatment. Among the various hypotheses that were evaluated against experimental results, generation of additional free radicals by redox reactions and increased radical addition in the presence of minerals seemed to be a plausible explanation for the observed increase in bitumen viscosity. The increase in TAN after hydrothermal treatment was tentatively explained by base-catalyzed hydrolysis of esters and anhydrides, promoted by the bases in bitumen froth. Further, free radical and acid-catalyzed (cationic) addition reaction pathways, which are potential ways by which the clay minerals in bitumen froth may promote heavier material formation were examined using model compounds 𝛼-methyl styrene (AMS) and 1-octene, instead of bitumen froth, at a reaction temperature of 250 °C. Pure thermal conversion of probe molecules was low compared to mineral related conversion. Dimerization of AMS and alkylation of 1-octene and toluene (used as solvent) were identified as major reactions in the presence of minerals, indicating that clay minerals promoted heavier material formation. Additional reactions performed in the presence of minerals and pyridine, used as surrogates for alkaline bitumen froth, and selectivity to different product isomers that enabled differentiation between free radical and cationic pathways, indicated that the mineral related conversion was predominantly cationic in nature. Some conversion of probe molecules to addition products was observed in the presence of minerals and pyridine suggesting that minerals could promote heavier material formation through cationic addition even under alkaline conditions. The possible occurrence of side reactions such as transfer hydrogenation and isomerization in the presence of clay minerals during hydrothermal treatment was also indicated in this work. No evidence was provided in this study to support the claim that clay minerals promote free radical addition reactions.  This thesis sought to test whether the use of a new modified approach for bitumen froth treatment can contribute to partial bitumen upgrading. When that was proved not to be the case, it raised questions about the fundamental chemical mechanisms of organic molecules on clay minerals responsible for heavier material formation. Using model compounds, this study revealed, for the first time, that the clay minerals in bitumen froth can promote cationic addition reactions at a temperature of 250 °C, even under alkaline conditions.</p>