Oilsands bitumen has poor fluidity at ambient conditions, which is a challenge. Transport bitumen by pipeline to the refineries is not practical unless the bitumen viscosity is substantially reduced. Achieving this at the lowest reasonable cost is the purpose of partial upgrading of bitumen. The cheapest upgrading process to reduce bitumen viscosity is visbreaking.<br/>Employing visbreaking as partial upgrading technology on its own has two drawbacks. The first is that its conversion performance is limited by the onset of coking. Ideally, delaying the onset of coking could lead to higher conversion to produce a liquid product with lower viscosity. The second is that thermal cracking produces olefins, which undermine storage and thermal stability in a material with measurable persistent free radical content.<br/>This study is based on two main observations. First, hydrogen depletion of heavy products is one of the reasons for phase-separation during thermal conversion. By keeping more of the hydrogen-rich volatile material in the liquid phase, it might be possible to delay the formation of material that is sufficient hydrogen depleted to form a second phase. Second, by keeping more of the volatile olefinic products in the liquid phase, there is an increased probability of these olefinic products participating in free radical addition and hydrogen transfer reactions. Addition reactions of volatile olefins could form less volatile, low viscosity liquid products to increase liquid yield and decrease viscosity.<br/>It uses of vapor-liquid equilibrium to simultaneously suppress the onset of coking and reduce the olefin during the thermal conversion was investigated. Vapor-liquid equilibrium was changed by varying initial pressure (0.5–4 MPa) and relative liquid and vapor volume (1:4–1:5) in batch reactions conducted at constant temperature (400 °C). By doing so, it was possible to study the effect of pressure on the vapor-liquid equilibrium and the impact of the partitioning of material between vapor and liquid phases at the same equilibrium conditions.<br/>Hydrogen transfer was identified as one of the main reactions in these conditions. Results will be presented to show the relevance of pressure as an operating variable for the partial upgrading of bitumen by visbreaking.

Impact of vapor-liquid partitioning and pressure in visbreaking of bitumen

ACS Spring Meeting 2021

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