Interplay between the Physical Properties of Athabasca Bitumen + Diluent Mixtures and Coke Deposition on a Commercial Hydroprocessing Catalyst

Bulk and nanoscale physical properties of mixtures comprising Athabasca bitumen, its subfractions, and diluents such as n -dodecane, n -decane, and 1-methylnaphthalene affect coke deposition on a commercial, nanoporous, hydrotreating catalyst (NiMo/γ-Al 2 O 3 ). The interplay among properties at diverse length scales is complex and coking outcomes can appear counterintuitive. For example, in this work we show that dilution of Athabasca bitumen with n -dodecane (a poor physical solvent) reduces coke deposition on catalyst pellets vis-à-vis dilution with 1-methylnaphthalene (a good physical solvent), whereas we show a counter example for Athabasca vacuum residue + n -decane and 1-methylnaphthalene mixtures at the same temperature. Here, we reconcile such findings and link them to mixture properties at the macroscopic scale (the number, nature, and composition of phases present), the nanoscale (asphaltene nanoaggregation within phases) and the molecular scale (hydrogen solubility by phase). We also show that dilution of these feedstocks with n -dodecane and 1-methylnaphthalene enhances vanadium deposition selectivity in a commercial catalyst relative to the feeds. Results such as these underscore the need for the explicit incorporation of physical phenomena in the development of coke deposition models.