Chevron Phillips Sulfide Agents

Sulfiding 101

Sulfur is a naturally occurring substance in petroleum fuels. However, in an effort to reduce harmful SO_x and NO_x emissions, the United States E.P.A (Environmental Protection Agency) began mandating the use of low-sulfur fuel. The main process refineries use to remove sulfur compounds from gasoline, diesel and jet fuel is called hydrotreatment or hydrodesulfurization. 
 

Catalytic hydrotreating is a catalytic refining process widely used to remove sulfur, unsaturated hydrocarbons, and nitrogen from petroleum products such as naphtha, gasoline, diesel fuel*, kerosene, and fuel oil.

It is also referred to as hydroprocessing or hydrodesulfurization, commonly occurs at multiple locations in a refinery.

Hydrodesulfurization processes typically include facilities for the capture and removal of the resulting hydrogen sulfide (H₂S) gas, which is subsequently converted into elemental sulfur or sulfuric acid, as byproducts.

The processes are used to ensure that petroleum products meet performance specifications and involve a number of chemical conversions.

During hydrotreatment, catalysts inside the reactor, typically CoMo (Cobalt Molybdenum) or NiMo (Nickel Molybdenum) convert unwanted sulfur and nitrogen compounds into H₂S (hydrogen sulfide) and NH₃, which is then removed in downstream processing. In order to activate catalytic activity, the hydrotreating catalysts go through a process called "sulfiding" or "presulfiding" where metal oxides are reacted with H₂S in the presence of hydrogen. Sulfiding agents are used to readily decompose sulfur compounds into the H₂S required to complete the sulfiding reactions. Two of the most common sulfiding agents are TBPS 454 and DMS. Below are the advantages of each grade:

TBPS 454

• TBPS 454 is not classified as a flammable material and has a low toxicity rating.
• TBPS 454 has a diesel-like odor, a more friendly and common smell for refineries.
• TBPS 454 starts to convert to H2S at the lowest temperature compared to other sulfiding agents, lowering the risk of reduction of metals and potentially lessening the time of the sulfiding operation.
• The hydrocarbon byproduct during a sulfiding operation for TBPS 454 is isobutane, which does not have the potential to dilute hydrogen in the recycle gas during a sulfiding operation.
   

Dimethyl Sulfide (DMS) 

• DMS directly and completely decomposes to H2S at 1470°F (although some trace CS2 may remain), suitable for furnace operating temperatures.
• DMS usually requires only one injection point in the charge gas as DMS will disperse fairly well throughout the furnace system.

Dimethyl Disulfide (DMDS)

• DMDS can be synthesized through several methods, including the reaction  of methanol with hydrogen sulfide in the presence of a catalyst or the reaction of methanol with sulfur.
• DMDS has a lower ozone- depleting potential and reduced environmental impact, therefore, it contributes to a more sustainable farming practice

Sulfiding Agent Properties

^{*In the presence of H₂ and Catalysts}

TBPS Typical Sulfiding Procedure

The sulfiding process should be carefully monitored and controlled to achieve the optimum sulfur activity. Below is a typical sulfiding procedure for TBPS 454. When decomposed, TBPS 454 can form elemental sulfur that forms solid polymers when reacted with olefins. The solid polymers can form residues on the catalyst bed and in the piping. There is a much higher risk of this happening at temperatures below 500 F. To decrease the likelihood of polymer formation, the injection point should be as near as possible to the catalyst bed.