| Description |
The bitumen extracted from Asphalt Ridge oil sands was hydrotreated over three sulfided NiMo/y-Alumina hydrodenitrogenation catalysts in a fixed bed reactor to study the extent of upgrading as a function of process variables and catalyst. The process variables investigated were temperature (619-685 K), liquid hourly space velocity (0.18-0.95 h-1), and pressure (11.1-15.3 MPa). The hydrogen/oil ratio was fixed at 890 m3/m3 in all experiments. The effects of process variables and catalyst on hydrodenitrogenation, hydrodesulfurization, and hydrodemetallation and on Conradson carbon residue (CCR), asphaltenes, and residuum conversion, viscosity reduction, and yields and product distribution were investigated. Temperature and space velocity exerted a greater influence on heteroatom reduction and conversion than pressure. High surface area was a dominant factor for species conversion in the lower temperature regime, whereas high surface area and wide pore size distribution appeared to exert equivalent effects at temperatures above 684 K. Significant upgrading of the bitumen was achieved after secondary hydrotreating of the liquid product produced at the severest conditions (temperature of 684 K, LHSV of 0.2 h-1, pressure of 13.7 MPa) in primary hydrotreating. The total conversions of sulfur, CCR, nitrogen, asphaltenes, and residuum were 99.5, 95.0, 94.8, 92.2, and 79.8 wt%, respectively. The viscosity, measured at 313 K, was reduced by a factor in excess of four orders of magnitude. The total weight fraction of naphtha plus distillate was 48% and increased fourfold compared with that of the bitumen. It was concluded that the refractory fraction, 20 wt%, of the residuum contained little CCR and asphaltenes and was more difficult to convert than asphaltenes. The conversions of sulfur, nitrogen, CCR, and residuum in bitumen were successfully modeled by nth power rate law kinetics and by a distributed activation energy model using a normal distribution function. Higher-order kinetics was required to represent the conversions of lumped sulfur, nitrogen, CCR and residuum. The asymptotic lumped kinetic model used to describe hydrodesulfurization was supported experimentally. |
