Unplanned downtime is one of the most critical factors that influence refinery profitability. In terms of hydroprocessing catalyst, minimizing unplanned downtime equates to ensuring the catalyst system is designed to process the most profitable feeds while meeting the target cycle length. An unscheduled pit stop to replace catalyst early either due to rapid activity loss or pressure drop growth, has severe financial consequences. Catalyst deactivation is caused either by contamination from feed poisons or by deposition of coke. Typical poisons include Silicon, Nickel & Vanadium, Iron and Arsenic. The mechanism of interaction with the catalyst and deactivation severity varies from one poison to the next. For example, for the same spent catalyst content, Arsenic (As) is a more severe poison than Silicon (Si), Iron (Fe), Nickel (Ni) & Vanadium (V). However, since these latter poisons often exist at higher feed concentrations than Arsenic, they can still cause severe catalyst deactivation.
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