Impact of Multiphase Behavior on Coke Deposition in a Commercial Hydrotreating Catalyst under Sedimentation Conditions

Abstract

Diverse coke deposition mechanisms and models, all supported by experimental data, have been proposed for catalytic hydrogenation processes related to heavy oil and bitumen refining. The influence of multiphase behavior on the observed deposition mode is an important but unresolved question in this literature. The model mixture Athabasca vacuum bottoms (ABVB) + decane, which is shown to exhibit L1L2V phase behavior at elevated temperatures and a commercial heavy oil hydrotreating catalyst (NiMo/γ-Al2O3) were employed in this preliminary investigation. Under sedimentation conditions, the impact of phase behavior, per se, on the amount of coke deposited on and within catalyst pellets and the distribution of coke within catalyst pellets was found to be a secondary one despite the differences in the physical properties of the solvent-rich L1 phase and asphaltene-rich L2 phase. In all cases, the exterior surfaces of pellets were coated with a thick nanoporous coke layer. The ratio of pore surface area to pore volume also increased with the extent of reaction in all cases, indicating that larger pores are filled in part or plugged in preference to smaller ones. Observed differences in the properties of coked catalyst exposed to the L1 and L2 phases and to multiphase environments are attributed to differences in the asphaltene aggregate size distribution in the two phases and to multiphase hydrodynamic effects.

Different Mechanisms of Coke Precursor Formation in Thermal Conversion and Deep Hydroprocessing of Vacuum Residue

“…Coking is generally a severe problem in the refining processes. − The formation of coke can reduce the yield of liquid products, cause catalyst deactivation, and shorten the operation period. Many efforts have been devoted to suppress the formation of coke. − A clear elucidation of the mechanism of coke formation would be helpful to promote these endeavors.…”

Non-thermal plasma enhanced heavy oil upgrading

“…The quality of light products from the carbon rejection method is usually poor and low-value coke or asphalt-like material are produced. Hydrogenation can suppress coke formation and improve the quality of light products, but it has to face the problem of catalyst deactivation because of carbon and metal deposition on the catalyst surface [5,6].…”

Diffusion of asphaltene molecules through the pore structure of hydroconversion catalysts

“…Important works have been carried out in the last period to upgrade heavy cuts, like atmospheric or vacuum residues, into valuable distillates using catalysts (Shimada et al, 2009;Elizalde et al, 2009;Rana et al, 2007;Ancheyta et al, 2005;Zhang et al, 2005;Kressmann et al, 1998;Morel et al, 1997;Toulhoat et al, 1990). This conversion requires demetallation (Ni and V), sulfur and nitrogen subtraction.…”