Q & A > Question Details
why is sulfiding of naphtha hydrotreater (NHT) catalyst necessary after carbon burning (regeneration) before normalization of NHT operation, when the main purpose of the catalyst itself is removal of sulfur from sour naphtha?
02/04/2010 A: Balasubramanian Iyer, Nexen CNOOC Limited, balasubramanian.n@aol.in
Sulphiding of The Hydro Treating Catalysts helps in enhancing the Activity of the Catalyst for the process for Desulphurisation compared to that of the Metal Catalysts in its Oxide State. In this process the metal oxides are converted to Metal Sulphides.
05/03/2010 A: Randy Alexander, EURECAT, randy.alexander@eurecat.com
The metals contained on hydrotreating catalysts are typically Molybdenum with either Nickel or Cobalt as a promoter. As discussed, the metal oxides are not the active form and must be activated by converting them to metal sulfides. During the sulfiding step, moly oxide forms moly sulfide slabs.
During HDS processing, the moly sulfide slabs are exposed to H2 at elevated temperatures. Some of the sulfur molecules along the edge of the slab will react with the H2, forming H2S that will desorb from the moly slab. These leaves a vacancy along the edge of the slab that will attract an an organo-sulfur molecule contained in the sour feed. The sulfur atom contained in the organo-sulfur molecule will stay adsorbed to the moly slab, resulting in a sulfur free organic molecule. The resulting H2S gas is sent to the Sulfur Recovery Unit in order to remove the H2S from the system.
26/02/2010 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
Co- Mo or Ni-Mo catalyst used in NHT are active in Co-MO-S phase or Ni-Mo-S phase. They are inactive in oxide form. So it becomes necessary to sulfide them by providing about 8 to 10 wt % of sulfur as easily decomposable hydrocarbon sulfur.
26/02/2010 A: Syamantak Dhar, Indian Oil corporation Limited, syamantak.dhar@aol.in
The Hydrotreating catalyst are generally present in their stable oxide when shipped or regenerated. To make the catalyst active sulfiding is done where the Co-Mo catalyst are generally converted to their sulphided form from oxide. Sulfiding is done genrally by adding DMDS with the feedstock at temperature starting from 180 to operating temperature.
23/02/2010 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Clarification to the reformer feed comment: Sulfur is a temporary poison to reforming catalyst, thus the reduction of sulfur in the feed to a target of 0.5 wppm. If the sulfur runs less than 0.3 wppm, DMDS is injected to reach that level, for the reasons I mentioned.
23/02/2010 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Corrections to both of my answers: (1) In the old days, we started up at reduced temperature, not reduced feedrate, until the catalyst was sulfided. (2) Reformer feed sulfur level is maintained 0.3-0.5 wppm to prevent coke formation in the furnace tubes and carburization of the furnace tubes. Has nothing to do with catalyst activity.
23/02/2010 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Some sulfur on the catalyst is needed to reach maximum activity. In the old days, we just lived with reduced activity but at reduced feedrate for awhile until the sulfur in the feed sulfided the catalyst.
Interestingly, today's reforming catalyst also requires some sulfur in the feed to that unit to achieve good cat activity.
23/02/2010 A: keith bowers, B and B Consulting, kebowers47@gmail.com
The active form of the metal in the catalyst is the sulfide, not the oxide. If you raise the hydrogen partial pressure and temperature up to 'treating conditions', the oxide will be reduced to metal and will be useless and non-catalytic.