Sulfidation issue after shutdown screening of refinery diesel hydrofining catalysts

In the refining process, hydrofining catalysts and hydrocracking catalysts are key components used to accelerate reactions and improve product quality. Pre-sulfurization is a very important step prior to the activation of the catalyst; its purpose is to convert the active components in the catalyst, such as cobalt, molybdenum, nickel, etc., into their corresponding sulfide forms, thereby activating the catalyst and enabling it to carry out reactions such as hydrodesulfurization efficiently. When the catalyst needs to be screened (to remove particles that are damaged or clogged) due to shutdowns or other reasons, the sulfurized active metals on the catalyst may be oxidized as a result of exposure to oxygen. Even if not completely deactivated, it usually reduces the catalyst’s activity. Therefore, in this case, after the catalyst is reinstalled in the reactor, it generally needs to undergo pre-sulfidization treatment again to ensure that its activity is fully restored. As for the mixed use of old and new catalysts, if the new catalyst has not been presulfurized, the entire catalyst bed must be presulfurized. During the presulfurization process, the new agent absorbs sulfiding agents (usually hydrogen sulfide H2S or other sulfur-containing compounds), converting the active components in the catalyst into sulfides. If the new catalyst has already undergone sufficient presulfiding, an additional presulfiding step may not be necessary, but this depends on the specific condition of the catalyst and the refinery’s operating procedures. In summary, the pre-sulfurization of catalysts is an important prerequisite for ensuring the efficient operation of hydroprocessing processes in refineries, and it must be carried out strictly in accordance with the refinery’s technical procedures and safety requirements. In practice, it is possible to determine whether re-pre-sulfurization is necessary by analyzing the physicochemical properties of the catalyst (such as the redox state of the active metal), along with the historical operation data of the reactor and the performance requirements of the catalyst. .