DMS Exact-S® carefully controls levels of problematic impurities and is the purest sulfidation agent available.
It is useful to remember that a world-class ethylene facility (1,500,000 MTA capacity) can consume over one million pounds per year of sulfidation agent. Even at low dosage levels, poor quality sulfidation agents can contribute to process contamination problems.
Is the decomposition temperature of sulfidation agents important?
The complete decomposition temperatures of the most popular sulfidation agents – DMS and DMDS – is about 675°C and 575°C, respectively. This is well under standard cracking temperatures, which range from about 825 – 950°C. Both DMS and DMDS are completely decomposed in the furnace.
There is some evidence that DMDS, which is slightly less thermally stable than other sulfidation agents, can actually accelerate coking relative to other sulfidation agents. Presumably this is due to the ability of DMDS to increase rates of noncatalytic coking- a potential disadvantage.
What are the decomposition products from DMS and DMDS?
The decomposition profiles of sulfidation agents under steam cracking conditions has not been studied in a comprehensive way. An early study (2) lists the decomposition products for DMS as methane, methyl mercaptan, and H2S, and the decomposition products for DMDS as methyl mercaptan, H2S, methane, ethylene, ethane, and ‘heavier sulfur compounds’.
There have been reports that DMDS use can affect quench tower acidity in a way that may be attributable to SOx byproduct formation. If this occurs, it suggests that not all sulfur in the DMDS molecule is used productively; any DMDS sulfur converted to SOx introduces operational costs associated with quench water pH regulation. A recent paper has modeled the decomposition pathway for DMDS, which is indeed complex (3).
Dimethyl Sulfide (DMS) is a cost effective and proven sulfidation agent for steamcracking operations. The high purity of DMS Exact-S® helps to minimize the overall burden of feedstock impurities entering the furnace.