| Canada has the world's largest reserve of oilsands containing over one trillion barrels of bitumen. In the upgrading of the bitumen, however, coke formation causes a considerable loss of the hydrocarbon resource and numerous operational problems. Furthermore, the bitumen produced via surface mining, currently the predominant method of bitumen production, contains high content of fine solids called bitumen solids. The effect of the bitumen solids on coke formation is still not well known.; In this thesis, the mechanism of coke formation at thermal upgrading conditions was studied, and kinetic models were developed. The effects of the bitumen solids and other added fine solids were investigated. The coke produced at coking conditions of low to moderate severity behaved as a viscous liquid at the reaction temperatures, was mainly isotropic under cross-polarized light, and was soluble in quinoline. Upon reheating or at longer reaction times, the coke could be partially transformed to mesophase. Two kinetic models were developed to give improved modeling of the induction phenomenon and the formation of quinoline insoluble from quinoline soluble coke. In model (I), Wiehe's (1993) phase separation model was modified to combine with modeling of quinoline insoluble coke. Model (II) was a lumped kinetic model with a model parameter for the induction time. The mechanism of the coke formation is discussed. The bitumen solids in the Athabasca bitumen reduced coke formation at coking conditions. With increasing concentration of these solids, the coke yield first decreased and then increased after passing a minimum. Bitumen solids were found to have weak catalytic activities towards dehydrogenation and hydrogen shuttling. Added fine solids with oleophilic surfaces, such as carbon black and asphaltene-treated kaolin were also found to reduce coke formation, but only monotonically. Oleophobic solids such as kaolin and ultrafine silica had no significant effect on coking. The mechanism of the effect of bitumen solids on coke formation is discussed and the effect is attributed to the combination of two factors: enhanced mass transfer due to the coating of liquid phase coke on oleophillic surfaces, and the dehydrogenation effect of bitumen solids under coking conditions. |
