Frequently Asked Questions

Dimethyl Disulfide (DMDS) | DMS/DMDS for Steamcrackers

Dimethyl Disulfide (DMDS)

• Why do you recommend dimethyl disulfide (DMDS) for activating hydroprocessing catalysts?
  
• Why should I rather inject DMDS and not use the feedstock alone for hydroprocessing catalyst sulfiding purposes?
  
• What is DMDS Evolution (DMDS E)?
  
• What kind of packaging options are offered for DMDS?
  
• Where are the bulk storages?
  
• Are you providing an injection service for DMDS / DMDS E? Could you describe it?
  
• Where is this service being offered?
  
• What are the steps to be followed if I want to use this service?
  
• How can I obtain more information on DMDS, DMDS Evolution, Carelflex®?
  

  Why do you recommend dimethyl disulfide (DMDS) for activating hydroprocessing catalysts?
  Commercial hydroprocessing catalysts (oxides of CoMo, NiMo or NiW species on alumina and zeolite carriers) have to be sulfided in order to reach their active form. This sulfiding operation is critical as it will have a direct impact on the activity and run length. With DMDS, at intermediate temperature (200 - 250 °C), sulfiding is performed by hydrogen sulfide (H₂S), methyl mercaptan (MeSH) and dimethyl sulfide (DMS). Above 300 °C, the sulfiding species is H₂S. The only hydrocarbon formed is methane (CH₄), which is not a coke precursor. DMDS sulfiding is the safest activation procedure without any risk of sulfur deposits or uncontrollable exotherms. DMDS with a high content of S (68 %) minimizes the quantity of organosulfur to handle.

  Why should I rather inject DMDS and not use the feedstock alone for hydroprocessing catalyst sulfiding purposes?
  In the case of feedstock only sulfiding, organic sulfur donors present in the feed are thiophene, benzothiophene, dibenzothiophene and their substituted homologues. These compounds need higher temperatures and longer times to be converted to active sulfiding species. These conditions will promote coke formation and thus have a negative impact on the activity of the catalyst.

  What is DMDS Evolution (DMDS E)?
  DMDS Evolution is a new and improved DMDS, having a user friendly smell and enabling higher catalyst activity compared to DMDS.

  What kind of packaging options are offered for DMDS?
  DMDS and DMDS Evolution are supplied in road tankers (24t/40,000lb max.), isocontainers (4, 6 or 20 bars, 18 t,
  23 t), isocontainers with baffles (6 bars, 10 to 21 t), semi bulk containers (4 or 20 bars, 1 t, 2.3 t) or drums (200 kg).

  Where are the bulk storages?
  Bulk storages are in Antwerp (Belgium), Lacq (France), Kobe (Japan), Kuala-Lumpur (Malaysia), Houston, TX (USA).

  Are you providing an injection service for DMDS / DMDS E? Could you describe it?
  We do provide an injection service called Carelflex®. This service combines help in defining the method of sulfiding, delivery of the sulfiding agent, on-site injection of the sulfiding agent and submission of a summary report.

  Where is this service being offered?
  Worldwide. Our Carelflex® service teams are based in : France, Netherlands, U.S.A. , Singapore, Japan, Brazil, Venezuela.

  What are the steps to be followed if I want to use this service?
  Send us an e-mail or call us, we will be glad to send you a questionnaire, which is the starting point for the operation. Our technicians will then contact you to elaborate on the details and to plan a pre-visit of your unit, if necessary.

  How can I obtain more information on DMDS, DMDS Evolution, Carelflex®?
  Please visit the webpages of Arkema at:

  • www.arkema.com
  • www.sulfiding.com
  Contact Us or in the U.S. call 800.628.4453

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• Why is dimethyl sulfide (DMS) used in an ethylene furnace?
  
• Why do you also recommend dimethyl disulfide (DMDS) in steamcrackers?
  

  Why is dimethyl sulfide (DMS) used in an ethylene furnace?
  DMS passivates the tubes in an ethylene furnace, thus retarding coke formations.

  Why do you also recommend dimethyl disulfide (DMDS) in steamcrackers?
  Injection of DMDS results in immediate improvements of steamcracking runs, by minimizing the catalytic activity of the furnace tube walls through the creation of a thin layer of metallic sulfides. Organic sulfur is beneficial to the inhibition of coke formation (which causes heat transfer decrease, pressure drop increase, TLE fouling) and to the control of carbon monoxide (CO) production (responsible for poor temperature control in the methanator, poison for downstream units' catalysts). DMDS containing 68 % sulfur, being thermically decomposed at a low temperature and safer than most of the competing sulfur compounds (especially H₂S), is today the best sulfur carrier.

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