Impacts of Refining Partially Upgraded Bitumen: Vacuum Gas Oil Hydrotreating

Abstract

This study investigates the hydrotreating characteristics of the vacuum gas oil (VGO) fraction of partially upgraded bitumen (PUB), an alternative refinery feedstock from Canadian oil sand bitumen with processability requirements that are yet to be understood. Hydrotreating experiments were conducted in a continuous hydroprocessing pilot plant using VGOs from PUB prepared in-house via thermal cracking and solvent deasphalting, as well as VGOs from unprocessed bitumen and light crude oil as points of comparison. Blends of VGOs from PUB and light crude oil were also tested. The VGOs from PUB were higher in sulfur, nitrogen, aromatics and resins combined, and contained olefins. The hydrotreating experiments were designed to determine the working temperature to desulfurize and denitrogenate a given VGO feed to levels that would be acceptable for further processing in a refining scheme with fluid catalytic cracking and/or hydrocracking units. Hydrotreating the VGOs from PUB proved more difficult than the VGOs from unprocessed bitumen and light crude oil, requiring a 5-15 °C rise in reaction temperature with respect to the reference VGOs to reach the desired sulfur (<300 wppm) and nitrogen (<100 wppm) targets. The hydrotreated VGOs from PUB were in general more aromatic than those from the reference VGOs, despite having similar sulfur and nitrogen levels. More naphtha and light gas oil were generated during the hydrotreating of the VGOs from PUB as a result of using higher temperatures. Hydrotreating the VGOs from PUB consumed up to 43% more hydrogen compared to VGO from bitumen and more than double relative to the VGO from light crude oil. These trends also extended to the VGO blends containing VGO from PUB.