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 rapidly decomposes, 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 1000°F. (See Sulfiding 101 for more details on the Catalyst Sulfiding Process.)
DMDS is also used to passivate furnace tubes in ethylene crackers, although Dimethyl Sulfide (DMS) is used more often for this application.
DMDS is ideal for sulfiding because of its high sulfur content (68%) and its decomposition temperature range of 360-460F. 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 DMDS decomposition temperature 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 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 due to their decomposition by-products.
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
Our partner, ChevronPhillips Chemical Company, is the only domestic producer of DMDS in the USA. And we are the only provider that supplies both DMDS and TBPS.
Contact us to discuss the optimum sulfiding agent for your application.