Activation of Hydroprocessing Catalysts: an In-Depth Understanding of Dimethyldisulfide (DMDS) Decomposition Chemistry on Hdp Catalysts During Their Activation via Sulfiding

The progress in the improvement of hydroprocessing catalysts has been impressive since the discovery of Type-II acid sites.  Strict regulations on the sulphur and nitrogen levels in finished transportation fuels are being enforced globally, and this has promulgated the need to capture all the available activity of these new catalysts.  The new generations of CoMo and NiMo catalysts have to be carefully activated via sulfiding to accomplish this task.  Dimethyl disulfide (DMDS) has been and continues to be the agent of choice to sulphide “in-situ”, and obtain optimal activity from these catalysts.  The decomposition of DMDS, while verified under laboratory conditions, has not been clearly understood under actual refinery unit conditions. The DMDS decomposition chemistry under a range of commercial unit conditions has been investigated.  Experimental data obtained have been used to build a kinetic model based on the fundamental decomposition mechanism. The data can be used beneficially to fine tune existing sulfiding procedures established by Catalyst Manufacturers and Refining Companies so as to make them optimal for and applicable to different types of units in the refinery. Additionally this information can be used to ascertain essentially complete use of the ‘sulfur’ introduced via DMDS and prevent SO₂ excursions due to inadvertent loss of sulphur intermediates to the flare or flue gas, during the catalyst sulfiding and activation.  Being the leader in DMDS manufacture, Arkema has recently introduced a new formulation, “DMDS Evolution^® E2” that has an improved user-friendly odor.  Details of this formulation and of the “Carelflex^® Service” that Arkema provides will be described.