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 form before they will promote desulfurization and denitrification reactions on hydrocarbon feeds.  The activation process, often called presulfiding, begins with the introduction of DMDS into the reactor pressurized with hydrogen at a temperature of 360F or higher.  Under these conditions and when exposed to a hydrotreating catalyst, DMDS rapidly decomposes, forming the H2S that is 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 900F.

DMDS is also used to passivate furnace tubes in ethylene crackers, although Dimethyl Sulfide (DMS) is used more often in this application.

DMDS is ideal for sulfiding because of its high sulfur content (68%) and its decomposition temperature range of 360-420F.  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.

An additional advantage of DMDS is the by-product of its decomposition is simple methane (CH4), which will not cause premature coking of the catalyst bed.  Other sulfiding chemicals, such as polysulfides (TBPS), can cause excess coking during the sulfiding process due to the by-products formed when they decompose to H2S.

In summary, the advantages of sulfiding with DMDS are:

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

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