Modeling of hydrotreating catalyst deactivation for heavy oil hydrocarbons

Hydrotreating is one of the most used process for eliminating impurities in heavy oil fractions, in which fixed-bed reactor has been used much more extensively. Nevertheless, the main disadvantage in this type of reactor is the fast catalyst deactivation. The main causes of loss of activity in the catalyst are the deposition of carbonaceous and metallic compounds, and the structural changes of the catalyst components. Some models for hydrotreating catalyst deactivation have been reported in the literature, which are based on coke and metals deposition and exhibit different levels of sophitification. All these models reported in the literature are extensively reviewed, analyzed and discussed in this work. The main model equations, model parameters and results are summarized, as well as the conditions at which they were derived. A general description of the main deactivation mechanisms is also described. The models based on both deactivation mechanisms (coke deposition and metals accumulation) were found to exhibit the best agreement with experimental data. From the analysis of the models reported in the literature, it is recognized the need to develop more robust deactivation models that take into consideration the agents that indeed affect catalyst activity, such as metals content and coke precursors. To do that, various experiments need to be carried out for detailed characterization of spent catalysts obtained at different reaction conditions, time-on-stream, and reactor position. With such an experimental information, deactivation models for heavy oil hydrotreating catalyst can be derived, and further used for reactor design, simulation and optimization.