Dimethyl Disulfide (DMDS)

Dimethyl Disulfide (DMDS) is the most commonly used chemical for sulfiding hydrotreating and hydrocracking catalysts.  These hydroprocessing catalysts contain metal oxides that must be converted to the active metal sulfide before they will promote desulfurization and denitrification reactions on hydrocarbon feeds.  The activation process, often called presulfiding, begins with the introduction of DMDS into a reactor pressurized with hydrogen at a temperature of 370F or higher.  Under these conditions and when exposed to a hydrotreating catalyst, DMDS begins to decompose, forming the H2S required to convert the oxides to metal sulfides. Note that if no catalyst is present, thermal decomposition of DMDS to H2S will not occur until the temperature exceeds 1150°F (621°C). (See Sulfiding 101 for more details on the Catalyst Sulfiding Process.)

DMDS is also used to passivate furnace tubes in ethane steam crackers, although Dimethyl Sulfide (DMS) is used more often for this application. Steam crackers require the continual injection of a thiochemical into the dilution steam. This compound will decompose to form H2S that will react to form a layer of iron sulfide on the furnace tubes. The protective FeS layer layer helps minimize coke and CO formation.

DMDS is ideal for catalyst sulfiding because of its high sulfur content (68%) and its decomposition temperature range of 392-482F.  At this temperature level, it is much easier to control the reaction exotherm that occurs as metal oxides are transformed to their corresponding sulfide form.  Note that the temperature for complete decomposition of DMDS over a hydrotreating catalyst is dependent on pressure, residence time, and catalyst type.  For example, CoMo catalysts will decompose DMDS at a lower temperature than NiMo catalysts.

An additional advantage of DMDS is that the by-product of its decomposition, simple methane (CH4), will not cause premature coking of the catalyst bed.  Other spiking agents, such as polysulfides (TBPS), can cause excessive coking during the sulfiding process if the injection rate is too high or if there is insufficient hydrogen available.

In summary, the advantages of sulfiding with DMDS are:

  • High Sulfur Content (68%)
  • Lowest Total Cost
  • By-products will not cause premature coking
  • Low Decomposition Temperature
  • Chosen by Catalyst Manufactures for Activity Testing and Catalyst Development

We are the only producer of DMDS in North America and the sole provider supplying both of the primary sulfiding agents, DMDS and TBPS.

DMDS is registered in Europe as an Intermediate under REACH regulations.

Contact us to discuss the optimum sulfiding agent for your application.