Low Temperature Pyrolysis and its Application in Bitumen Processing

Abstract

Observations in literature date back to 1926 to suggest that bitumen should not be treated like a residuum but more like a young crude oil. This is because of its high reactivity at low temperatures. Taking these observations into consideration, lower temperatures (400 °C and lower) were used to improve pyrolysis product quality (particularly liquid viscosity). A major problem in visbreaking is the formation of coke. The effect of specific solvent properties on coke suppression during mild pyrolysis was investigated. It was noticed that coke suppression was based on the overall availability of transferable hydrogen and methyl-groups present in the system, not just donor hydrogen by solvents. In light of these results it was suggested to co-feed light hydrocarbons to help in coke suppression and improve liquid yields. As an extension of the coke suppression studies, the influence of reaction time was investigated. Various regimes were seen when neat bitumen was pyrolysed that affected product quality. A complex relationship was observed between bitumen viscosity and the asphaltene fraction with at least one local maxima and one local minimum being observed. Two orders of magnitude decrease in viscosity was seen when bitumen was heated for 30 minutes at 400 °C. This was not accompanied by a change in the asphaltenes content. Based on this, it was argued that asphaltenes fraction could donate its hydrogen and methyl groups, and, in a solvent deasphalting-visbreaking sequence, the most meaningful difference in the product quality is observed when the reaction time given was equal to the induction period of coke formation of the feed.